Author name code: solanki
ADS astronomy entries on 2022-09-14
author:"Solanki, Sami K." 
------------------------------------------------------------------------  

Title: What drives decayless kink oscillations in active region
    coronal loops on the Sun?
Authors: Mandal, Sudip; Chitta, Lakshmi P.; Antolin, Patrick; Peter,
   Hardi; Solanki, Sami K.; Auchère, Frédéric; Berghmans, David;
   Zhukov, Andrei N.; Teriaca, Luca; Cuadrado, Regina A.; Schühle,
   Udo; Parenti, Susanna; Buchlin, Éric; Harra, Louise; Verbeeck, Cis;
   Kraaikamp, Emil; Long, David M.; Rodriguez, Luciano; Pelouze, Gabriel;
   Schwanitz, Conrad; Barczynski, Krzysztof; Smith, Phil J.
Bibcode: 2022arXiv220904251M
Altcode:
  We study here the phenomena of decayless kink oscillations in a system
  of active region (AR) coronal loops. Using high resolution observations
  from two different instruments, namely the Extreme Ultraviolet Imager
  (EUI) on board Solar Orbiter and the Atmospheric Imaging Assembly
  (AIA) on board the Solar Dynamics Observatory, we follow these AR
  loops for an hour each on three consecutive days. Our results show
  significantly more resolved decayless waves in the higher-resolution
  EUI data compared with the AIA data. Furthermore, the same system of
  loops exhibits many of these decayless oscillations on Day-2, while on
  Day-3, we detect very few oscillations and on Day-1, we find none at
  all. Analysis of photospheric magnetic field data reveals that at most
  times, these loops were rooted in sunspots, where supergranular flows
  are generally absent. This suggests that supergranular flows, which
  are often invoked as drivers of decayless waves, are not necessarily
  driving such oscillations in our observations. Similarly, our findings
  also cast doubt on other possible drivers of these waves, such as a
  transient driver or mode conversion of longitudinal waves near the loop
  footpoints. In conclusion, through our analysis we find that none of
  the commonly suspected sources proposed to drive decayless oscillations
  in active region loops seems to be operating in this event and hence,
  the search for that elusive wave driver needs to continue.

Title: Erratum: "Faculae Cancel out on the Surfaces of Active Suns"
    (2022, ApJL, 934, L23)
Authors: Nèmec, N. -E.; Shapiro, A. I.; Işık, E.; Sowmya, K.;
   Solanki, S. K.; Krivova, N. A.; Cameron, R. H.; Gizon, L.
Bibcode: 2022ApJ...936L..17N
Altcode:
  No abstract at ADS

Title: Faculae Cancel out on the Surfaces of Active Suns
Authors: Nèmec, N. -E.; Shapiro, A. I.; Işık, E.; Sowmya, K.;
   Solanki, S. K.; Krivova, N. A.; Cameron, R. H.; Gizon, L.
Bibcode: 2022ApJ...934L..23N
Altcode: 2022arXiv220706816N
  Surfaces of the Sun and other cool stars are filled with magnetic
  fields, which are either seen as dark compact spots or more
  diffuse bright structures like faculae. Both hamper detection and
  characterization of exoplanets, affecting stellar brightness and
  spectra, as well as transmission spectra. However, the expected facular
  and spot signals in stellar data are quite different, for instance,
  they have distinct temporal and spectral profiles. Consequently,
  corrections of stellar data for magnetic activity can greatly benefit
  from the insight on whether the stellar signal is dominated by spots or
  faculae. Here, we utilize a surface flux transport model to show that
  more effective cancellation of diffuse magnetic flux associated with
  faculae leads to spot area coverages increasing faster with stellar
  magnetic activity than that by faculae. Our calculations explain the
  observed dependence between solar spot and facular area coverages and
  allow its extension to stars that are more active than the Sun. This
  extension enables anticipating the properties of stellar signal and its
  more reliable mitigation, leading to a more accurate characterization
  of exoplanets and their atmospheres.

Title: Predictions of Astrometric Jitter for Sun-like Stars. III. Fast
    Rotators
Authors: Sowmya, K.; Nèmec, N. -E.; Shapiro, A. I.; Işık, E.;
   Krivova, N. A.; Solanki, S. K.
Bibcode: 2022ApJ...934..146S
Altcode: 2022arXiv220607702S
  A breakthrough in exoplanet detections is foreseen with the
  unprecedented astrometric measurement capabilities offered by
  instrumentation aboard the Gaia space observatory. Besides, astrometric
  discoveries of exoplanets are expected from the planned space mission,
  Small-JASMINE. In this setting, the present series of papers focuses
  on estimating the effect of the magnetic activity of G2V-type host
  stars on the astrometric signal. This effect interferes with the
  astrometric detections of Earth-mass planets. While the first two
  papers considered stars rotating at the solar rotation rate, this paper
  focuses on stars having solar effective temperature and metallicity
  but rotating faster than the Sun, and consequently more active. By
  simulating the distribution of active regions on such stars using the
  Flux Emergence And Transport model, we show that the contribution of
  magnetic activity to the astrometric measurements becomes increasingly
  significant with increasing rotation rates. We further show that the
  jitter for the most variable periodic Kepler stars is high enough to be
  detected by Gaia. Furthermore, due to a decrease in the facula-to-spot
  area ratio for more active stars, the magnetic jitter is found to be
  spot dominated for rapid rotators. Our simulations of the astrometric
  jitter have the potential to aid the interpretation of data from Gaia
  and upcoming space astrometry missions.

Title: A highly dynamic small-scale jet in a polar coronal hole
Authors: Mandal, Sudip; Chitta, Lakshmi Pradeep; Peter, Hardi;
   Solanki, Sami K.; Cuadrado, Regina Aznar; Teriaca, Luca; Schühle,
   Udo; Berghmans, David; Auchère, Frédéric
Bibcode: 2022A&A...664A..28M
Altcode: 2022arXiv220602236M
  We present an observational study of the plasma dynamics at the base
  of a solar coronal jet, using high resolution extreme ultraviolet
  imaging data taken by the Extreme Ultraviolet Imager on board Solar
  Orbiter, and by the Atmospheric Imaging Assembly on board Solar
  Dynamics Observatory. We observed multiple plasma ejection events
  over a period of ∼1 h from a dome-like base that is ca. 4 Mm wide
  and is embedded in a polar coronal hole. Within the dome below the
  jet spire, multiple plasma blobs with sizes around 1−2 Mm propagate
  upwards to the dome apex with speeds of the order of the sound speed
  (ca. 120 km s<SUP>−1</SUP>). Upon reaching the apex, some of these
  blobs initiate flows with similar speeds towards the other footpoint
  of the dome. At the same time, high speed super-sonic outflows
  (∼230 km s<SUP>−1</SUP>) are detected along the jet spire. These
  outflows as well as the intensity near the dome apex appear to be
  repetitive. Furthermore, during its evolution, the jet undergoes
  many complex morphological changes, including transitions between
  the standard and blowout type eruption. These new observational
  results highlight the underlying complexity of the reconnection
  process that powers these jets and they also provide insights into
  the plasma response when subjected to rapid energy injection. <P
  />Movies associated to Figs. 1, 2, and 4 are available at <A
  href="https://www.aanda.org/10.1051/0004-6361/202243765/olm">https://www.aanda.org</A>

Title: Linking Small-scale Solar Wind Properties with Large-scale
    Coronal Source Regions through Joint Parker Solar Probe-Metis/Solar
    Orbiter Observations
Authors: Telloni, Daniele; Zank, Gary P.; Sorriso-Valvo, Luca;
   D'Amicis, Raffaella; Panasenco, Olga; Susino, Roberto; Bruno, Roberto;
   Perrone, Denise; Adhikari, Laxman; Liang, Haoming; Nakanotani, Masaru;
   Zhao, Lingling; Hadid, Lina Z.; Sánchez-Cano, Beatriz; Verscharen,
   Daniel; Velli, Marco; Grimani, Catia; Marino, Raffaele; Carbone,
   Francesco; Mancuso, Salvatore; Biondo, Ruggero; Pagano, Paolo; Reale,
   Fabio; Bale, Stuart D.; Kasper, Justin C.; Case, Anthony W.; de Wit,
   Thierry Dudok; Goetz, Keith; Harvey, Peter R.; Korreck, Kelly E.;
   Larson, Davin; Livi, Roberto; MacDowall, Robert J.; Malaspina, David
   M.; Pulupa, Marc; Stevens, Michael L.; Whittlesey, Phyllis; Romoli,
   Marco; Andretta, Vincenzo; Deppo, Vania Da; Fineschi, Silvano; Heinzel,
   Petr; Moses, John D.; Naletto, Giampiero; Nicolini, Gianalfredo;
   Spadaro, Daniele; Stangalini, Marco; Teriaca, Luca; Capobianco,
   Gerardo; Capuano, Giuseppe E.; Casini, Chiara; Casti, Marta; Chioetto,
   Paolo; Corso, Alain J.; Leo, Yara De; Fabi, Michele; Frassati,
   Federica; Frassetto, Fabio; Giordano, Silvio; Guglielmino, Salvo L.;
   Jerse, Giovanna; Landini, Federico; Liberatore, Alessandro; Magli,
   Enrico; Massone, Giuseppe; Messerotti, Mauro; Pancrazzi, Maurizio;
   Pelizzo, Maria G.; Romano, Paolo; Sasso, Clementina; Schühle, Udo;
   Slemer, Alessandra; Straus, Thomas; Uslenghi, Michela; Volpicelli,
   Cosimo A.; Zangrilli, Luca; Zuppella, Paola; Abbo, Lucia; Auchère,
   Frédéric; Cuadrado, Regina Aznar; Berlicki, Arkadiusz; Ciaravella,
   Angela; Lamy, Philippe; Lanzafame, Alessandro; Malvezzi, Marco;
   Nicolosi, Piergiorgio; Nisticò, Giuseppe; Peter, Hardi; Solanki,
   Sami K.; Strachan, Leonard; Tsinganos, Kanaris; Ventura, Rita; Vial,
   Jean-Claude; Woch, Joachim; Zimbardo, Gaetano
Bibcode: 2022ApJ...935..112T
Altcode:
  The solar wind measured in situ by Parker Solar Probe in the very
  inner heliosphere is studied in combination with the remote-sensing
  observation of the coronal source region provided by the METIS
  coronagraph aboard Solar Orbiter. The coronal outflows observed near
  the ecliptic by Metis on 2021 January 17 at 16:30 UT, between 3.5 and
  6.3 R <SUB>⊙</SUB> above the eastern solar limb, can be associated
  with the streams sampled by PSP at 0.11 and 0.26 au from the Sun,
  in two time intervals almost 5 days apart. The two plasma flows
  come from two distinct source regions, characterized by different
  magnetic field polarity and intensity at the coronal base. It follows
  that both the global and local properties of the two streams are
  different. Specifically, the solar wind emanating from the stronger
  magnetic field region has a lower bulk flux density, as expected,
  and is in a state of well-developed Alfvénic turbulence, with low
  intermittency. This is interpreted in terms of slab turbulence in the
  context of nearly incompressible magnetohydrodynamics. Conversely,
  the highly intermittent and poorly developed turbulent behavior of the
  solar wind from the weaker magnetic field region is presumably due to
  large magnetic deflections most likely attributed to the presence of
  switchbacks of interchange reconnection origin.

Title: Chromospheric extension of the MURaM code
Authors: Przybylski, D.; Cameron, R.; Solanki, S. K.; Rempel, M.;
   Leenaarts, J.; Anusha, L. S.; Witzke, V.; Shapiro, A. I.
Bibcode: 2022A&A...664A..91P
Altcode: 2022arXiv220403126P
  Context. Detailed numerical models of the chromosphere and corona are
  required to understand the heating of the solar atmosphere. An accurate
  treatment of the solar chromosphere is complicated by the effects
  arising from non-local thermodynamic equilibrium (NLTE) radiative
  transfer. A small number of strong, highly scattering lines dominate the
  cooling and heating in the chromosphere. Additionally, the recombination
  times of ionised hydrogen are longer than the dynamical timescales,
  requiring a non-equilibrium (NE) treatment of hydrogen ionisation. <BR
  /> Aims: We describe a set of necessary additions to the MURaM code that
  allow it to handle some of the important NLTE effects. We investigate
  the impact on solar chromosphere models caused by NLTE and NE effects in
  radiation magnetohydrodynamic simulations of the solar atmosphere. <BR
  /> Methods: The MURaM code was extended to include the physical
  process required for an accurate simulation of the solar chromosphere,
  as implemented in the Bifrost code. This includes a time-dependent
  treatment of hydrogen ionisation, a scattering multi-group radiation
  transfer scheme, and approximations for NLTE radiative cooling. <BR />
  Results: The inclusion of NE and NLTE physics has a large impact on the
  structure of the chromosphere; the NE treatment of hydrogen ionisation
  leads to a higher ionisation fraction and enhanced populations in
  the first excited state throughout cold inter-shock regions of the
  chromosphere. Additionally, this prevents hydrogen ionisation from
  buffering energy fluctuations, leading to hotter shocks and cooler
  inter-shock regions. The hydrogen populations in the ground and first
  excited state are enhanced by 10<SUP>2</SUP>-10<SUP>3</SUP> in the
  upper chromosphere and by up to 10<SUP>9</SUP> near the transition
  region. <BR /> Conclusions: Including the necessary NLTE physics
  leads to significant differences in chromospheric structure and
  dynamics. The thermodynamics and hydrogen populations calculated using
  the extended version of the MURaM code are consistent with previous
  non-equilibrium simulations. The electron number and temperature
  calculated using the non-equilibrium treatment of the chromosphere
  are required to accurately synthesise chromospheric spectral
  lines. <P />Movies associated to Fig. 2 are only available at <A
  href="https://www.aanda.org/10.1051/0004-6361/202141230/olm">https://www.aanda.org</A>

Title: Solar cyclic activity over the last millennium
    reconstructedfrom annual <SUP>14</SUP>C data (Corrigendum)
Authors: Usoskin, I. G.; Solanki, S. K.; Krivova, N.; Hofer, B.;
   Kovaltsov, G. A.; Wacker, L.; Brehm, N.; Kromer, B.
Bibcode: 2022A&A...664C...3U
Altcode:
  No abstract at ADS

Title: The on-ground data reduction and calibration pipeline for
    SO/PHI-HRT
Authors: Sinjan, J.; Calchetti, D.; Hirzberger, J.; Orozco Suárez,
   D.; Albert, K.; Albelo Jorge, N.; Appourchaux, T.; Alvarez-Herrero,
   A.; Blanco Rodríguez, J.; Gandorfer, A.; Germerott, D.; Guerrero,
   L.; Gutierrez Marquez, P.; Kahil, F.; Kolleck, M.; Solanki, S. K.; del
   Toro Iniesta, J. C.; Volkmer, R.; Woch, J.; Fiethe, B.; Gómez Cama,
   J. M.; Pérez-Grande, I.; Sanchis Kilders, E.; Balaguer Jiménez,
   M.; Bellot Rubio, L. R.; Carmona, M.; Deutsch, W.; Fernandez-Rico,
   G.; Fernández-Medina, A.; García Parejo, P.; Gasent Blesa, J. L.;
   Gizon, L.; Grauf, B.; Heerlein, K.; Korpi-Lagg, A.; Lange, T.; López
   Jiménez, A.; Maue, T.; Meller, R.; Michalik, H.; Moreno Vacas, A.;
   Müller, R.; Nakai, E.; Schmidt, W.; Schou, J.; Schühle, U.; Staub,
   J.; Strecker, H.; Torralbo, I.; Valori, G.
Bibcode: 2022arXiv220814904S
Altcode:
  The ESA/NASA Solar Orbiter space mission has been successfully launched
  in February 2020. Onboard is the Polarimetric and Helioseismic Imager
  (SO/PHI), which has two telescopes, a High Resolution Telescope
  (HRT) and the Full Disc Telescope (FDT). The instrument is designed
  to infer the photospheric magnetic field and line-of-sight velocity
  through differential imaging of the polarised light emitted by the
  Sun. It calculates the full Stokes vector at 6 wavelength positions
  at the Fe I 617.3 nm absorption line. Due to telemetry constraints,
  the instrument nominally processes these Stokes profiles onboard,
  however when telemetry is available, the raw images are downlinked and
  reduced on ground. Here the architecture of the on-ground pipeline
  for HRT is presented, which also offers additional corrections not
  currently available on board the instrument. The pipeline can reduce
  raw images to the full Stokes vector with a polarimetric sensitivity
  of $10^{-3}\cdot I_{c}$ or better.

Title: Polarimetric calibration of the Sunrise UV Spectropolarimeter
    and Imager
Authors: Iglesias, F. A.; Feller, A.; Gandorfer, A.; Lagg, A.;
   Riethmüller, T. L.; Solanki, S. K.; Katsukawa, Y.; Kubo, M.;
   Zucarelli, G.; Sanchez, M.; Sunrise Team
Bibcode: 2022BAAA...63..305I
Altcode:
  Sunrise is an optical observatory mounted in a stratospheric balloon,
  developed to study magnetic fields in the solar atmosphere with very
  high resolution. In its third flight, Sunrise carry the Sunrise UV
  Spectropolarimeter and Imager (SUSI), that operates in the 313-430 nm
  range, covering thousands of spectral lines not accessible from the
  ground and thus largely unexplored. SUSI does not include a polarimetric
  calibration unit on board. We report about the development status of
  SUSI and the preliminary results of its calibration.

Title: Small-scale dynamo in cool stars. I. Changes in stratification
    and near-surface convection for main-sequence spectral types
Authors: Bhatia, Tanayveer S.; Cameron, Robert H.; Solanki, Sami K.;
   Peter, Hardi; Przybylski, Damien; Witzke, Veronika; Shapiro, Alexander
Bibcode: 2022A&A...663A.166B
Altcode: 2022arXiv220600064B
  Context. Some of the small-scale solar magnetic flux can
  be attributed to a small-scale dynamo (SSD) operating in the
  near-surface convection. The SSD fields have consequences for
  solar granular convection, basal flux, and chromospheric heating. A
  similar SSD mechanism is expected to be active in the near-surface
  convection of other cool main-sequence stars, but this has not been
  investigated thus far. <BR /> Aims: We aim to investigate changes in
  stratification and convection due to inclusion of SSD fields for F3V,
  G2V, K0V, and M0V spectral types in the near-surface convection. <BR
  /> Methods: We studied 3D magnetohydrodynamic (MHD) models of the four
  stellar boxes, covering the subsurface convection zone up to the lower
  photosphere in a small Cartesian box, based on the MURaM radiative-MHD
  simulation code. We compared the SSD runs against reference hydrodynamic
  runs. <BR /> Results: The SSD is found to efficiently produce magnetic
  field with energies ranging between 5% to 80% of the plasma kinetic
  energy at different depths. This ratio tends to be larger for larger
  T<SUB>eff</SUB>. The relative change in density and gas pressure
  stratification for the deeper convective layers due to SSD magnetic
  fields is negligible, except for the F-star. For the F-star, there is
  a substantial reduction in convective velocities due to Lorentz force
  feedback from magnetic fields, which, in turn, reduces the turbulent
  pressure. <BR /> Conclusions: The SSD in near-surface convection for
  cool main-sequence stars introduces small but significant changes
  in thermodynamic stratification (especially for the F-star) due to a
  reduction in the convective velocities.

Title: Historical Ca II K observations for irradiance reconstructions
Authors: Chatzistergos, Theodosios; Krivova, Natalie; Ermolli, Ilaria;
   Leng Yeo, Kok; Solanki, Sami; Mandal, Sudip
Bibcode: 2022cosp...44.1551C
Altcode:
  Solar irradiance has been measured by various instruments
  from space since 1978 and exhibits variations on all accessible
  timescales. Irradiance variations prior to satellite measurements,
  knowledge of which is important for climate studies, can only be
  recovered with models. Models have successfully been used to reconstruct
  solar irradiance variations by attributing the variability on time
  scales longer than about a day to the evolution of the solar surface
  magnetic field. However, to account for the different contributions of
  surface magnetic features, such as sunspots and faculae, models require
  appropriate input data. Unfortunately, due to the scarcity of suitable
  facular data prior to the period of direct irradiance measurements,
  most available irradiance reconstructions rely on sunspot data alone or
  on other, indirect data of solar magnetism. Historical Ca II K archives
  carry direct information on facular regions, but they have not been
  used to their full potential for irradiance reconstructions. The main
  reasons limiting their use were the difficulty to account for the
  non-linear response of the photographic plates along with plentiful
  large-scale artefacts affecting the images. We have extensively studied
  Ca II K data to overcome most issues affecting them thus paving the way
  for them to be used for accurate irradiance reconstructions. We will
  present our latest work on employment of Ca II K data for reconstructing
  past irradiance variations.

Title: The essential role of Earth-Sun L4 in solar particle event
    forecasting for Lunar and Mars exploration
Authors: Posner, Arik; Toit Strauss, Du; Solanki, Sami K.; Effenberger,
   Frederic; Gandorfer, Achim; Hirzberger, Johann; Kühl, Patrick; Heber,
   Bernd; Malandraki, Olga; Folta, David; Jones, Sarah; Arge, Charles;
   Sterken, Veerle; Henney, Carl J.; Staub, Jan; Hatten, Noble; Stcyr,
   O. Chris
Bibcode: 2022cosp...44.1157P
Altcode:
  We learned from the STEREO mission that solar particle events
  originating from behind the west limb of the Sun, i.e., out of view
  from Earth, make up about 30 percent of those significantly affecting
  Earth's vicinity and thus could endanger human exploration of the
  Moon. The Earth-Sun Lagrangian point 4 is a meta-stable location at 1
  au from the Sun, 60° ahead of Earth's orbit. L4 has an uninterrupted
  view of the solar photosphere centered on W60, the Earth's nominal
  magnetic field connection to the Sun. The role of L4 observations
  for improving several existing short-term SEP forecasting techniques,
  including protons, ESPERTA, UMASEP and pps, for Lunar exploration will
  be highlighted. We can show that BFO dose savings from short-term
  solar energetic particle forecasts are critically important in a
  worst-case scenario. Placing a mission at L4 is even a precondition
  for any SEP all-clear forecasting for Lunar exploration. Furthermore,
  we analyzed example trajectories of short-term Mars round trips that
  may be considered for future human exploration of Mars and find that
  L4-based SWx observations would have relevance for protecting Mars
  explorers from radiation exposure.

Title: Reconstruction of Coronal Magnetic Fields Using a
    Poloidal-Toroidal Representation
Authors: Yi, Sibaek; Choe, G. S.; Cho, Kyung-Suk; Solanki, Sami K.;
   Büchner, Jörg
Bibcode: 2022arXiv220607189Y
Altcode:
  A new method for reconstruction of coronal magnetic fields as force-free
  fields (FFFs) is presented. Our method employs poloidal and toroidal
  functions to describe divergence-free magnetic fields. This magnetic
  field representation naturally enables us to implement the boundary
  conditions at the photospheric boundary, i.e., the normal magnetic field
  and the normal current density there, in a straightforward manner. At
  the upper boundary of the corona, a source-surface condition can be
  employed, which accommodates magnetic flux imbalance at the bottom
  boundary. Although our iteration algorithm is inspired by extant
  variational methods, it is non-variational and requires much less
  iteration steps than most of them. The computational code based on our
  new method is tested against the analytical FFF solutions by Titov &amp;
  Démoulin (1999). It is found to excel in reproducing a tightly wound
  flux rope, a bald patch and quasi-separatrix layers with a hyperbolic
  flux tube.

Title: Stellar limb darkening. A new MPS-ATLAS library for Kepler,
    TESS, CHEOPS, and PLATO passbands
Authors: Kostogryz, N. M.; Witzke, V.; Shapiro, A. I.; Solanki, S. K.;
   Maxted, P. F. L.; Kurucz, R. L.; Gizon, L.
Bibcode: 2022arXiv220606641K
Altcode:
  The detection of the first exoplanet paved the way into the era of
  transit photometry space missions with a revolutionary photometric
  precision that aim at discovering new exoplanetary systems around
  different types of stars. With this high precision, it is possible
  to derive very accurately the radii of exoplanets which is crucial
  for constraining their type and composition. However, it requires an
  accurate description of host stars, especially their center-to-limb
  variation of intensities (so called limb darkening) as it affects the
  planet-to-star radius ratio determination. We aim at improving the
  accuracy of limb darkening calculations for stars with a wide range
  of fundamental parameters. We used the recently developed 1D MPS-ATLAS
  code to compute model atmosphere structures and to synthesize stellar
  limb darkening on a very fine grid of stellar parameters. For the
  computations we utilized the most accurate information on chemical
  element abundances and mixing length parameters including convective
  overshoot. The stellar limb darkening was fitted using the two most
  accurate limb darkening laws: the power-2 and 4-parameters non-linear
  laws. We present a new extensive library of stellar model atmospheric
  structures, the synthesized stellar limb darkening curves, and the
  coefficients of parameterized limb-darkening laws on a very fine grid of
  stellar parameters in the Kepler, TESS, CHEOPS, and PLATO passbands. The
  fine grid allows overcoming the sizable errors introduced by the need
  to interpolate. Our computations of solar limb darkening are in a
  good agreement with available solar measurements at different view
  angles and wavelengths. Our computations of stellar limb darkening
  agree well with available measurements of Kepler stars. A new grid of
  stellar model structures, limb darkening and their fitted coefficients
  in different broad filters is provided in CDS.

Title: Making our star sparkle: The Sun's magnetic field, activity
    and variability
Authors: Solanki, Sami
Bibcode: 2022AAS...24040001S
Altcode:
  The magnetic field of the Sun relieves our star from the monotony of an
  unchanging existence, at least unchanging on timescales between days
  and millennia. Instead, it leads the Sun to display a large variety
  of ever-changing features, such as sunspots and faculae at the solar
  surface, a bright network in the chromosphere, and loops and plumes
  in the corona, among many others. It also leads to variations of the
  total brightness of the Sun. From time to time, the incessantly evolving
  magnetic field causes great flashes of radiation in the form of flares,
  or outbursts of particles in the form of coronal mass ejections. In
  other words, the nuclear reactions in the Sun's core may make it shine,
  but it takes the magnetic field to make our star sparkle. <P />How
  the solar magnetic field is structured, how it produces aspects of
  solar activity and variability and how we learn more about it will be
  subjects of this talk.

Title: Magnetized supersonic downflows in the chromosphere. A
    statistical study using the He I 10 830 Å lines
Authors: Sowmya, K.; Lagg, A.; Solanki, S. K.; Castellanos Durán,
   J. S.
Bibcode: 2022A&A...661A.122S
Altcode: 2022arXiv220211679S
  The chromosphere above active regions (ARs) on the Sun hosts
  magnetized supersonic downflows. Studies of these supersonic downflows
  help to decipher the magnetic fine structure and dynamics of the
  chromosphere. We perform a statistical analysis of the magnetized
  supersonic downflows in a number of ARs at different evolutionary stages
  and survey their characteristics. We analyze spectro-polarimetric scans
  of parts of 13 ARs obtained in the infrared He I 10 830 Å triplet
  formed in the upper chromosphere recorded with the GREGOR Infrared
  Spectrograph mounted at the GREGOR solar telescope. We retrieve
  the line-of-sight velocities and the magnetic field vector using
  the HELIX<SUP>+</SUP> inversion code that assumes Milne-Eddington
  atmospheres. We find magnetized supersonic downflows in all the ARs,
  with larger area coverage by such flows in ARs observed during their
  emerging phase. The fact that supersonic downflows were detected
  in all scans, albeit only covering a small fraction, 0.2-6.4%, of
  the observed field-of-view, suggests that they are a comparatively
  common phenomenon in the upper chromospheres of ARs. The supersonic
  downflows are found to be associated with many AR features, such as
  pores, sunspot umbrae, sunspot penumbrae, light bridges, plages, He
  I loops as part of arch filament systems characteristic of emerging
  fields, and filaments. Although several mechanisms are identified to be
  causing the supersonic downflows, by far the most common one appears to
  be the draining of plasma along the legs of rising magnetic loops. The
  loops mainly drain into forming pores. The line-of-sight velocities of
  the supersonic downflows reach values of up to 49 km s<SUP>−1</SUP>,
  and the velocity distribution shows multiple populations. Almost 92% of
  these supersonic downflows coexist with a subsonic flow component. The
  weaker, more horizontal fields associated with the supersonic component
  suggests that it is formed above the subsonic component.

Title: Multiwavelength Mitigation of Stellar Activity in Astrometric
    Planet Detection
Authors: Kaplan-Lipkin, Avi; Macintosh, Bruce; Madurowicz, Alexander;
   Sowmya, Krishnamurthy; Shapiro, Alexander; Krivova, Natalie; Solanki,
   Sami K.
Bibcode: 2022AJ....163..205K
Altcode: 2021arXiv211206383K
  Astrometry has long been a promising technique for exoplanet
  detection. At the theoretical limits, astrometry would allow for
  the detection of smaller planets than previously seen by current
  exoplanet search methods, but stellar activity may make these
  theoretical limits unreachable. Astrometric jitter of a Sun-like
  star due to magnetic activity in its photosphere induces apparent
  variability in the photocenter of order 0.5 mR <SUB>⊙</SUB>. This
  jitter creates a fundamental astrophysical noise floor preventing
  detection of lower-mass planets in a single spectral band. By injecting
  planet orbits into simulated solar data at five different passbands,
  we investigate mitigation of this fundamental astrometric noise using
  correlations across passbands. For a true solar analog and a planet at
  1 au semimajor axis, the 6σ detection limit set by stellar activity for
  an ideal telescope at the best single passband is 0.01 Earth masses. We
  found that pairs of passbands with highly correlated astrometric jitter
  due to stellar activity, but with less motion in the redder band,
  enable higher-precision measurements of the common signal from the
  planet. Using this method improves detectable planet masses at 1 au
  by up to a factor of 10, corresponding to at best 0.005 Earth masses
  for a Sun-like star with a perfect telescope. Given these results,
  we recommend that future astrometry missions consider proceeding with
  two or more passbands to reduce noise due to stellar activity.

Title: The magnetic drivers of campfires seen by the Polarimetric
    and Helioseismic Imager (PHI) on Solar Orbiter
Authors: Kahil, F.; Hirzberger, J.; Solanki, S. K.; Chitta, L. P.;
   Peter, H.; Auchère, F.; Sinjan, J.; Orozco Suárez, D.; Albert,
   K.; Albelo Jorge, N.; Appourchaux, T.; Alvarez-Herrero, A.; Blanco
   Rodríguez, J.; Gandorfer, A.; Germerott, D.; Guerrero, L.; Gutiérrez
   Márquez, P.; Kolleck, M.; del Toro Iniesta, J. C.; Volkmer, R.;
   Woch, J.; Fiethe, B.; Gómez Cama, J. M.; Pérez-Grande, I.; Sanchis
   Kilders, E.; Balaguer Jiménez, M.; Bellot Rubio, L. R.; Calchetti,
   D.; Carmona, M.; Deutsch, W.; Fernández-Rico, G.; Fernández-Medina,
   A.; García Parejo, P.; Gasent-Blesa, J. L.; Gizon, L.; Grauf, B.;
   Heerlein, K.; Lagg, A.; Lange, T.; López Jiménez, A.; Maue, T.;
   Meller, R.; Michalik, H.; Moreno Vacas, A.; Müller, R.; Nakai,
   E.; Schmidt, W.; Schou, J.; Schühle, U.; Staub, J.; Strecker, H.;
   Torralbo, I.; Valori, G.; Aznar Cuadrado, R.; Teriaca, L.; Berghmans,
   D.; Verbeeck, C.; Kraaikamp, E.; Gissot, S.
Bibcode: 2022A&A...660A.143K
Altcode: 2022arXiv220213859K
  Context. The Extreme Ultraviolet Imager (EUI) on board the Solar Orbiter
  (SO) spacecraft observed small extreme ultraviolet (EUV) bursts,
  termed campfires, that have been proposed to be brightenings near the
  apexes of low-lying loops in the quiet-Sun atmosphere. The underlying
  magnetic processes driving these campfires are not understood. <BR
  /> Aims: During the cruise phase of SO and at a distance of 0.523
  AU from the Sun, the Polarimetric and Helioseismic Imager on Solar
  Orbiter (SO/PHI) observed a quiet-Sun region jointly with SO/EUI,
  offering the possibility to investigate the surface magnetic field
  dynamics underlying campfires at a spatial resolution of about 380
  km. <BR /> Methods: We used co-spatial and co-temporal data of the
  quiet-Sun network at disc centre acquired with the High Resolution
  Imager of SO/EUI at 17.4 nm (HRI<SUB>EUV</SUB>, cadence 2 s) and the
  High Resolution Telescope of SO/PHI at 617.3 nm (HRT, cadence 2.5
  min). Campfires that are within the SO/PHI−SO/EUI common field
  of view were isolated and categorised according to the underlying
  magnetic activity. <BR /> Results: In 71% of the 38 isolated events,
  campfires are confined between bipolar magnetic features, which seem to
  exhibit signatures of magnetic flux cancellation. The flux cancellation
  occurs either between the two main footpoints, or between one of the
  footpoints of the loop housing the campfire and a nearby opposite
  polarity patch. In one particularly clear-cut case, we detected the
  emergence of a small-scale magnetic loop in the internetwork followed
  soon afterwards by a campfire brightening adjacent to the location
  of the linear polarisation signal in the photosphere, that is to
  say near where the apex of the emerging loop lays. The rest of the
  events were observed over small scattered magnetic features, which
  could not be identified as magnetic footpoints of the campfire hosting
  loops. <BR /> Conclusions: The majority of campfires could be driven
  by magnetic reconnection triggered at the footpoints, similar to the
  physical processes occurring in the burst-like EUV events discussed
  in the literature. About a quarter of all analysed campfires, however,
  are not associated to such magnetic activity in the photosphere, which
  implies that other heating mechanisms are energising these small-scale
  EUV brightenings.

Title: A solar coronal loop in a box: Energy generation and heating
Authors: Breu, C.; Peter, H.; Cameron, R.; Solanki, S. K.; Przybylski,
   D.; Rempel, M.; Chitta, L. P.
Bibcode: 2022A&A...658A..45B
Altcode: 2021arXiv211211549B
  Context. Coronal loops are the basic building block of the upper solar
  atmosphere as seen in the extreme UV and X-rays. Comprehending how
  these are energized, structured, and evolve is key to understanding
  stellar coronae. <BR /> Aims: Here we investigate how the energy
  to heat the loop is generated by photospheric magneto-convection,
  transported into the upper atmosphere, and how the internal
  structure of a coronal magnetic loop forms. <BR /> Methods: In a 3D
  magnetohydrodynamics model, we study an isolated coronal loop rooted
  with both footpoints in a shallow layer within the convection zone
  using the MURaM code. To resolve its internal structure, we limited
  the computational domain to a rectangular box containing a single
  coronal loop as a straightened magnetic flux tube. Field-aligned heat
  conduction, gray radiative transfer in the photosphere and chromosphere,
  and optically thin radiative losses in the corona were taken into
  account. The footpoints were allowed to interact self-consistently
  with the granulation surrounding them. <BR /> Results: The loop is
  heated by a Poynting flux that is self-consistently generated through
  small-scale motions within individual magnetic concentrations in
  the photosphere. Turbulence develops in the upper layers of the
  atmosphere as a response to the footpoint motions. We see little
  sign of heating by large-scale braiding of magnetic flux tubes
  from different photospheric concentrations at a given footpoint. The
  synthesized emission, as it would be observed by the Atmospheric Imaging
  Assembly or the X-Ray Telescope, reveals transient bright strands that
  form in response to the heating events. Overall, our model roughly
  reproduces the properties and evolution of the plasma as observed
  within (the substructures of) coronal loops. <BR /> Conclusions:
  With this model we can build a coherent picture of how the energy
  flux to heat the upper atmosphere is generated near the solar surface
  and how this process drives and governs the heating and dynamics of
  a coronal loop. <P />Movie associated to Fig. 2 is available at <A
  href="https://www.aanda.org/10.1051/0004-6361/202141451/olm">https://www.aanda.org</A>

Title: Final Report for SAG 21: The Effect of Stellar Contamination
    on Space-based Transmission Spectroscopy
Authors: Rackham, Benjamin V.; Espinoza, Néstor; Berdyugina, Svetlana
   V.; Korhonen, Heidi; MacDonald, Ryan J.; Montet, Benjamin T.; Morris,
   Brett M.; Oshagh, Mahmoudreza; Shapiro, Alexander I.; Unruh, Yvonne C.;
   Quintana, Elisa V.; Zellem, Robert T.; Apai, Dániel; Barclay, Thomas;
   Barstow, Joanna K.; Bruno, Giovanni; Carone, Ludmila; Casewell, Sarah
   L.; Cegla, Heather M.; Criscuoli, Serena; Fischer, Catherine; Fournier,
   Damien; Giampapa, Mark S.; Giles, Helen; Iyer, Aishwarya; Kopp, Greg;
   Kostogryz, Nadiia M.; Krivova, Natalie; Mallonn, Matthias; McGruder,
   Chima; Molaverdikhani, Karan; Newton, Elisabeth R.; Panja, Mayukh;
   Peacock, Sarah; Reardon, Kevin; Roettenbacher, Rachael M.; Scandariato,
   Gaetano; Solanki, Sami; Stassun, Keivan G.; Steiner, Oskar; Stevenson,
   Kevin B.; Tregloan-Reed, Jeremy; Valio, Adriana; Wedemeyer, Sven;
   Welbanks, Luis; Yu, Jie; Alam, Munazza K.; Davenport, James R. A.;
   Deming, Drake; Dong, Chuanfei; Ducrot, Elsa; Fisher, Chloe; Gilbert,
   Emily; Kostov, Veselin; López-Morales, Mercedes; Line, Mike; Močnik,
   Teo; Mullally, Susan; Paudel, Rishi R.; Ribas, Ignasi; Valenti, Jeff A.
Bibcode: 2022arXiv220109905R
Altcode:
  Study Analysis Group 21 (SAG21) of the Exoplanet Exploration Program
  Analysis Group (ExoPAG) was organized to study the effect of stellar
  contamination on space-based transmission spectroscopy, a method for
  studying exoplanetary atmospheres by measuring the wavelength-dependent
  radius of a planet as it transits its star. Transmission spectroscopy
  relies on a precise understanding of the spectrum of the star being
  occulted. However, stars are not homogeneous, constant light sources
  but have temporally evolving photospheres and chromospheres with
  inhomogeneities like spots, faculae, and plages. This SAG has brought
  together an interdisciplinary team of more than 100 scientists, with
  observers and theorists from the heliophysics, stellar astrophysics,
  planetary science, and exoplanetary atmosphere research communities,
  to study the current needs that can be addressed in this context to
  make the most of transit studies from current NASA facilities like
  HST and JWST. The analysis produced 14 findings, which fall into
  three Science Themes encompassing (1) how the Sun is used as our best
  laboratory to calibrate our understanding of stellar heterogeneities
  ("The Sun as the Stellar Benchmark"), (2) how stars other than the Sun
  extend our knowledge of heterogeneities ("Surface Heterogeneities of
  Other Stars") and (3) how to incorporate information gathered for the
  Sun and other stars into transit studies ("Mapping Stellar Knowledge
  to Transit Studies").

Title: Solar Surface Stereoscopy with Solar Orbiter's Polarimetric
    Helioseismic Imager (SO/PHI)
Authors: Romero Avila, Amanda; Inhester, Bernd; Hirzberger, Johann;
   Solanki, Sami
Bibcode: 2021AGUFMSH25B2095R
Altcode:
  A compound method for a stereoscopic analysis of the height variations
  in the solar photosphere is presented. This method allows to estimate
  relevant quantities (i.e. the Wilson depression) and to study structures
  in the solar photosphere and within sunspots. We will demonstrate
  the feasibility of the method using simulated Stokes I continuum
  observations derived from a radiative transfer model using the plasma
  properties of a MHD simulation of the solar surface. The large scale
  variations in our method are estimated by shifting and correlating
  two signals of the same region as observed from two different view
  directions. This result is then introduced as an initial height estimate
  in a least squares optimization algorithm in order to reproduce smaller
  scale structures. This method has been developed to be applied to the
  high resolution images of the PHI instrument on board Solar Orbiter or
  similar instruments on other Sun-observing spacecraft. It will allow
  to perform direct stereoscopic studies of solar surface observations
  in different wavelengths of the solar spectrum. Preliminary results,
  advantages and limitations, applications and particular considerations
  for PHI data will be discussed.

Title: Propagating brightenings in small loop-like structures in
the quiet-Sun corona: Observations from Solar Orbiter/EUI
Authors: Mandal, Sudip; Peter, Hardi; Chitta, Lakshmi Pradeep;
   Solanki, Sami K.; Aznar Cuadrado, Regina; Teriaca, Luca; Schühle,
   Udo; Berghmans, David; Auchère, Frédéric
Bibcode: 2021A&A...656L..16M
Altcode: 2021arXiv211108106M
  Brightenings observed in solar extreme-ultraviolet images are generally
  interpreted as signatures of micro- or nanoflares occurring in the
  transition region or at coronal temperatures. Recent observations
  with the Extreme Ultraviolet Imager (EUI) on board Solar Orbiter have
  revealed the smallest of such brightenings (called campfires) in the
  quiet-Sun corona. Analyzing EUI 174 Å data obtained at a resolution
  of about 400 km on the Sun with a cadence of 5 s on 30 May 2020,
  we report here a number of cases in which these campfires exhibit
  propagating signatures along their apparently small (3-5 Mm) loop-like
  structures. The measured propagation speeds are generally between 25
  km s<SUP>−1</SUP> and 60 km s<SUP>−1</SUP>. If the loop plasma is
  assumed to be at a million Kelvin, these apparent motions would be
  slower than the local sound speed. Furthermore, these brightenings
  exhibit nontrivial propagation characteristics such as bifurcation,
  merging, reflection, and repeated plasma ejections. We suggest that
  these features are manifestations of the internal dynamics of these
  small-scale magnetic structures and could provide important insights
  into the dynamic response (∼40 s) of the loop plasma to the heating
  events and also into the locations of the heating events themselves. <P
  />Movies associated to Figs 2-5, A.1, and B.1 are available at <A
  href="https://www.aanda.org/10.1051/0004-6361/202142041/olm">https://www.aanda.org</A>

Title: The first coronal mass ejection observed in both visible-light
    and UV H I Ly-α channels of the Metis coronagraph on board Solar
    Orbiter
Authors: Andretta, V.; Bemporad, A.; De Leo, Y.; Jerse, G.; Landini,
   F.; Mierla, M.; Naletto, G.; Romoli, M.; Sasso, C.; Slemer, A.;
   Spadaro, D.; Susino, R.; Talpeanu, D. -C.; Telloni, D.; Teriaca, L.;
   Uslenghi, M.; Antonucci, E.; Auchère, F.; Berghmans, D.; Berlicki,
   A.; Capobianco, G.; Capuano, G. E.; Casini, C.; Casti, M.; Chioetto,
   P.; Da Deppo, V.; Fabi, M.; Fineschi, S.; Frassati, F.; Frassetto,
   F.; Giordano, S.; Grimani, C.; Heinzel, P.; Liberatore, A.; Magli, E.;
   Massone, G.; Messerotti, M.; Moses, D.; Nicolini, G.; Pancrazzi, M.;
   Pelizzo, M. -G.; Romano, P.; Schühle, U.; Stangalini, M.; Straus,
   Th.; Volpicelli, C. A.; Zangrilli, L.; Zuppella, P.; Abbo, L.; Aznar
   Cuadrado, R.; Bruno, R.; Ciaravella, A.; D'Amicis, R.; Lamy, P.;
   Lanzafame, A.; Malvezzi, A. M.; Nicolosi, P.; Nisticò, G.; Peter,
   H.; Plainaki, C.; Poletto, L.; Reale, F.; Solanki, S. K.; Strachan,
   L.; Tondello, G.; Tsinganos, K.; Velli, M.; Ventura, R.; Vial, J. -C.;
   Woch, J.; Zimbardo, G.
Bibcode: 2021A&A...656L..14A
Altcode:
  Context. The Metis coronagraph on board Solar Orbiter offers a new
  view of coronal mass ejections (CMEs), observing them for the first
  time with simultaneous images acquired with a broad-band filter in
  the visible-light interval and with a narrow-band filter around the
  H I Ly-α line at 121.567 nm, the so-called Metis UV channel. <BR />
  Aims: We show the first Metis observations of a CME, obtained on 16
  and 17 January 2021. The event was also observed by the EUI/FSI imager
  on board Solar Orbiter, as well as by other space-based coronagraphs,
  such as STEREO-A/COR2 and SOHO/LASCO/C2, whose images are combined here
  with Metis data. <BR /> Methods: Different images are analysed here
  to reconstruct the 3D orientation of the expanding CME flux rope using
  the graduated cylindrical shell model. This also allows us to identify
  the possible location of the source region. Measurements of the CME
  kinematics allow us to quantify the expected Doppler dimming in the
  Ly-α channel. <BR /> Results: Observations show that most CME features
  seen in the visible-light images are also seen in the Ly-α images,
  although some features in the latter channel appear more structured
  than their visible-light counterparts. We estimated the expansion
  velocity of this event to be below 140 km s<SUP>−1</SUP>. Hence,
  these observations can be understood by assuming that Doppler dimming
  effects do not strongly reduce the Ly-α emission from the CME. These
  velocities are comparable with or smaller than the radial velocities
  inferred from the same data in a similar coronal structure on the
  east side of the Sun. <BR /> Conclusions: The first observations by
  Metis of a CME demonstrate the capability of the instrument to provide
  valuable and novel information on the structure and dynamics of these
  coronal events. Considering also its diagnostics capabilities regarding
  the conditions of the ambient corona, Metis promises to significantly
  advance our knowledge of such phenomena. <P />Movies are available at <A
  href="https://www.aanda.org/10.1051/0004-6361/202142407/olm">https://www.aanda.org</A>

Title: Capturing transient plasma flows and jets in the solar corona
Authors: Chitta, L. P.; Solanki, S. K.; Peter, H.; Aznar Cuadrado,
   R.; Teriaca, L.; Schühle, U.; Auchère, F.; Berghmans, D.; Kraaikamp,
   E.; Gissot, S.; Verbeeck, C.
Bibcode: 2021A&A...656L..13C
Altcode: 2021arXiv210915106C
  Intensity bursts in ultraviolet (UV) to X-ray wavelengths and plasma
  jets are typical signatures of magnetic reconnection and the associated
  impulsive heating of the solar atmospheric plasma. To gain new insights
  into the process, high-cadence observations are required to capture
  the rapid response of plasma to magnetic reconnection as well as the
  highly dynamic evolution of jets. Here, we report the first 2 s cadence
  extreme-UV observations recorded by the 174 Å High Resolution Imager of
  the Extreme Ultraviolet Imager on board the Solar Orbiter mission. These
  observations, covering a quiet-Sun coronal region, reveal the onset
  signatures of magnetic reconnection as localized heating events. These
  localized sources then exhibit repeated plasma eruptions or jet
  activity. Our observations show that this spatial morphological change
  from localized sources to jet activity could occur rapidly on timescales
  of about 20 s. The jets themselves are intermittent and are produced
  from the source region on timescales of about 20 s. In the initial
  phases of these events, plasma jets are observed to exhibit speeds,
  as inferred from propagating intensity disturbances, in the range of
  100 km s<SUP>−1</SUP> to 150 km s<SUP>−1</SUP>. These jets then
  propagate to lengths of about 5 Mm. We discuss examples of bidirectional
  and unidirectional jet activity observed to have been initiated from
  the initially localized bursts in the corona. The transient nature
  of coronal bursts and the associated plasma flows or jets along with
  their dynamics could provide a benchmark for magnetic reconnection
  models of coronal bursts and jets. <P />Movies are available at <A
  href="https://www.aanda.org/10.1051/0004-6361/202141683/olm">https://www.aanda.org</A>

Title: Reconstructing solar irradiance from historical Ca II K
    observations. I. Method and its validation
Authors: Chatzistergos, Theodosios; Krivova, Natalie A.; Ermolli,
   Ilaria; Yeo, Kok Leng; Mandal, Sudip; Solanki, Sami K.; Kopp, Greg;
   Malherbe, Jean-Marie
Bibcode: 2021A&A...656A.104C
Altcode: 2021arXiv210905844C
  Context. Knowledge of solar irradiance variability is critical to
  Earth's climate models and understanding the solar influence on Earth's
  climate. Direct solar irradiance measurements have only been available
  since 1978. Reconstructions of past variability typically rely on
  sunspot data. However, sunspot records provide only indirect information
  on the facular and network regions, which are decisive contributors to
  irradiance variability on timescales of the solar cycle and longer. <BR
  /> Aims: Our ultimate goal is to reconstruct past solar irradiance
  variations using historical full-disc Ca II K observations to describe
  the facular contribution independently of sunspot observations. Here,
  we develop the method and test it extensively by using modern CCD-based
  (charge-coupled device) Ca II K observations. We also carry out initial
  tests on two photographic archives. <BR /> Methods: We employ carefully
  reduced and calibrated Ca II K images from 13 datasets, including some
  of the most prominent series, such as those from the Meudon, Mt Wilson,
  and Rome observatories. We convert them to unsigned magnetic field
  maps and then use them as input to the adapted Spectral and Total
  Irradiance Reconstruction (SATIRE) model to reconstruct total solar
  irradiance (TSI) variations over the period 1978-2019, for which
  direct irradiance measurements are available. <BR /> Results: The
  reconstructed irradiance from the analysed Ca II K archives agrees well
  with direct irradiance measurements and existing reconstructions. The
  model also returns good results on data taken with different bandpasses
  and images with low spatial resolution. Historical Ca II K archives
  suffer from numerous inconsistencies, but we show that these archives
  can still be used to reconstruct TSI with reasonable accuracy provided
  the observations are accurately processed and the effects of changes
  in instrumentation and instrumental parameters are identified and
  accounted for. The reconstructions are relatively insensitive to the
  TSI reference record used to fix the single free parameter of the
  model. Furthermore, even employment of a series, itself reconstructed
  from Ca II K data, as a reference for further reconstructions returns
  nearly equally accurate results. This will enable the Ca II K archives
  without an overlap with direct irradiance measurements to be used to
  reconstruct past irradiance. <BR /> Conclusions: By using the unsigned
  magnetic maps of the Sun reconstructed from modern high-quality Ca
  II K observations as input into the SATIRE model, we can reconstruct
  solar irradiance variations nearly as accurately as from directly
  recorded magnetograms. Historical Ca II K observations can also be
  used for past irradiance reconstructions but need additional care,
  for example identifying and accounting for discontinuities and changes
  in the quality of the data with time.

Title: First observations from the SPICE EUV spectrometer on Solar
    Orbiter
Authors: Fludra, A.; Caldwell, M.; Giunta, A.; Grundy, T.; Guest,
   S.; Leeks, S.; Sidher, S.; Auchère, F.; Carlsson, M.; Hassler, D.;
   Peter, H.; Aznar Cuadrado, R.; Buchlin, É.; Caminade, S.; DeForest,
   C.; Fredvik, T.; Haberreiter, M.; Harra, L.; Janvier, M.; Kucera, T.;
   Müller, D.; Parenti, S.; Schmutz, W.; Schühle, U.; Solanki, S. K.;
   Teriaca, L.; Thompson, W. T.; Tustain, S.; Williams, D.; Young, P. R.;
   Chitta, L. P.
Bibcode: 2021A&A...656A..38F
Altcode: 2021arXiv211011252F
  <BR /> Aims: We present first science observations taken during the
  commissioning activities of the Spectral Imaging of the Coronal
  Environment (SPICE) instrument on the ESA/NASA Solar Orbiter
  mission. SPICE is a high-resolution imaging spectrometer operating at
  extreme ultraviolet (EUV) wavelengths. In this paper we illustrate
  the possible types of observations to give prospective users a
  better understanding of the science capabilities of SPICE. <BR />
  Methods: We have reviewed the data obtained by SPICE between April
  and June 2020 and selected representative results obtained with
  different slits and a range of exposure times between 5 s and 180
  s. Standard instrumental corrections have been applied to the raw
  data. <BR /> Results: The paper discusses the first observations
  of the Sun on different targets and presents an example of the full
  spectra from the quiet Sun, identifying over 40 spectral lines from
  neutral hydrogen and ions of carbon, oxygen, nitrogen, neon, sulphur,
  magnesium, and iron. These lines cover the temperature range between
  20 000 K and 1 million K (10 MK in flares), providing slices of the
  Sun's atmosphere in narrow temperature intervals. We provide a list
  of count rates for the 23 brightest spectral lines. We show examples
  of raster images of the quiet Sun in several strong transition region
  lines, where we have found unusually bright, compact structures in the
  quiet Sun network, with extreme intensities up to 25 times greater
  than the average intensity across the image. The lifetimes of these
  structures can exceed 2.5 hours. We identify them as a transition
  region signature of coronal bright points and compare their areas and
  intensity enhancements. We also show the first above-limb measurements
  with SPICE above the polar limb in C III, O VI, and Ne VIII lines, and
  far off limb measurements in the equatorial plane in Mg IX, Ne VIII,
  and O VI lines. We discuss the potential to use abundance diagnostics
  methods to study the variability of the elemental composition that can
  be compared with in situ measurements to help confirm the magnetic
  connection between the spacecraft location and the Sun's surface,
  and locate the sources of the solar wind. <BR /> Conclusions: The
  SPICE instrument successfully performs measurements of EUV spectra
  and raster images that will make vital contributions to the scientific
  success of the Solar Orbiter mission.

Title: First light observations of the solar wind in the outer corona
    with the Metis coronagraph
Authors: Romoli, M.; Antonucci, E.; Andretta, V.; Capuano, G. E.; Da
   Deppo, V.; De Leo, Y.; Downs, C.; Fineschi, S.; Heinzel, P.; Landini,
   F.; Liberatore, A.; Naletto, G.; Nicolini, G.; Pancrazzi, M.; Sasso,
   C.; Spadaro, D.; Susino, R.; Telloni, D.; Teriaca, L.; Uslenghi,
   M.; Wang, Y. -M.; Bemporad, A.; Capobianco, G.; Casti, M.; Fabi, M.;
   Frassati, F.; Frassetto, F.; Giordano, S.; Grimani, C.; Jerse, G.;
   Magli, E.; Massone, G.; Messerotti, M.; Moses, D.; Pelizzo, M. -G.;
   Romano, P.; Schühle, U.; Slemer, A.; Stangalini, M.; Straus, T.;
   Volpicelli, C. A.; Zangrilli, L.; Zuppella, P.; Abbo, L.; Auchère,
   F.; Aznar Cuadrado, R.; Berlicki, A.; Bruno, R.; Ciaravella, A.;
   D'Amicis, R.; Lamy, P.; Lanzafame, A.; Malvezzi, A. M.; Nicolosi,
   P.; Nisticò, G.; Peter, H.; Plainaki, C.; Poletto, L.; Reale, F.;
   Solanki, S. K.; Strachan, L.; Tondello, G.; Tsinganos, K.; Velli,
   M.; Ventura, R.; Vial, J. -C.; Woch, J.; Zimbardo, G.
Bibcode: 2021A&A...656A..32R
Altcode: 2021arXiv210613344R
  In this work, we present an investigation of the wind in the solar
  corona that has been initiated by observations of the resonantly
  scattered ultraviolet emission of the coronal plasma obtained with
  UVCS-SOHO, designed to measure the wind outflow speed by applying
  Doppler dimming diagnostics. Metis on Solar Orbiter complements the
  UVCS spectroscopic observations that were performed during solar
  activity cycle 23 by simultaneously imaging the polarized visible
  light and the H I Lyman-α corona in order to obtain high spatial and
  temporal resolution maps of the outward velocity of the continuously
  expanding solar atmosphere. The Metis observations, taken on May 15,
  2020, provide the first H I Lyman-α images of the extended corona
  and the first instantaneous map of the speed of the coronal plasma
  outflows during the minimum of solar activity and allow us to identify
  the layer where the slow wind flow is observed. The polarized visible
  light (580-640 nm) and the ultraviolet H I Lyα (121.6 nm) coronal
  emissions, obtained with the two Metis channels, were combined in
  order to measure the dimming of the UV emission relative to a static
  corona. This effect is caused by the outward motion of the coronal
  plasma along the direction of incidence of the chromospheric photons
  on the coronal neutral hydrogen. The plasma outflow velocity was then
  derived as a function of the measured Doppler dimming. The static
  corona UV emission was simulated on the basis of the plasma electron
  density inferred from the polarized visible light. This study leads
  to the identification, in the velocity maps of the solar corona, of
  the high-density layer about ±10° wide, centered on the extension
  of a quiet equatorial streamer present at the east limb - the coronal
  origin of the heliospheric current sheet - where the slowest wind
  flows at about 160 ± 18 km s<SUP>−1</SUP> from 4 R<SUB>⊙</SUB>
  to 6 R<SUB>⊙</SUB>. Beyond the boundaries of the high-density layer,
  the wind velocity rapidly increases, marking the transition between
  slow and fast wind in the corona.

Title: Similarities of magnetoconvection in the umbra and in the
    penumbra of sunspots
Authors: Löptien, B.; Lagg, A.; van Noort, M.; Solanki, S. K.
Bibcode: 2021A&A...655A..61L
Altcode: 2021arXiv211001352L
  Context. It is unclear why there is a rather sharp boundary in
  sunspots between the umbra and the penumbra. Both regions exhibit
  magnetoconvection, which manifests in penumbral filaments in the
  penumbra and in umbral dots in the umbra. <BR /> Aims: Here we compare
  the physical properties of umbral dots and penumbral filaments. Our
  goal is to understand how the properties of these convective features
  change across the boundary between the umbra and the penumbra
  and how this is related to the rapid increase in brightness at the
  umbra-penumbra boundary. <BR /> Methods: We derived ensemble averages
  of the physical properties of different types of convective features
  based on observations of two sunspots with Hinode. <BR /> Results:
  There are strong similarities between the convective features in the
  outer parts of the umbra and the ones in the penumbra, with most
  physical parameters being smooth and continuous functions of the
  length of the features. <BR /> Conclusions: Our results indicate
  that the transition in brightness from the umbra to the penumbra
  is solely caused by an increased effectiveness of magnetoconvection
  within individual convective cells. There is no significant difference
  in the number density of convective elements between the outer umbra
  and the inner penumbra. Penumbral filaments exhibit a larger area and
  a higher brightness compared to umbral dots. It is still unclear how
  exactly the underlying magnetic field causes the increase in the size
  and brightness of convective features in the penumbra.

Title: First results of the CAST-RADES haloscope search for axions
    at 34.67 μeV
Authors: Álvarez Melcón, A.; Arguedas Cuendis, S.; Baier, J.; Barth,
   K.; Bräuninger, H.; Calatroni, S.; Cantatore, G.; Caspers, F.; Castel,
   J. F.; Cetin, S. A.; Cogollos, C.; Dafni, T.; Davenport, M.; Dermenev,
   A.; Desch, K.; Díaz-Morcillo, A.; Döbrich, B.; Fischer, H.; Funk,
   W.; Gallego, J. D.; García Barceló, J. M.; Gardikiotis, A.; Garza,
   J. G.; Gimeno, B.; Gninenko, S.; Golm, J.; Hasinoff, M. D.; Hoffmann,
   D. H. H.; Irastorza, I. G.; Jakovčić, K.; Kaminski, J.; Karuza,
   M.; Lakić, B.; Laurent, J. M.; Lozano-Guerrero, A. J.; Luzón,
   G.; Malbrunot, C.; Maroudas, M.; Miralda-Escudé, J.; Mirallas, H.;
   Miceli, L.; Navarro, P.; Ozbey, A.; Özbozduman, K.; Peña Garay, C.;
   Pivovaroff, M. J.; Redondo, J.; Ruz, J.; Ruiz Chóliz, E.; Schmidt, S.;
   Schumann, M.; Semertzidis, Y. K.; Solanki, S. K.; Stewart, L.; Tsagris,
   I.; Vafeiadis, T.; Vogel, J. K.; Widmann, E.; Wuensch, W.; Zioutas, K.
Bibcode: 2021JHEP...10..075A
Altcode: 2021arXiv210413798A
  We present results of the Relic Axion Dark-Matter Exploratory Setup
  (RADES), a detector which is part of the CERN Axion Solar Telescope
  (CAST), searching for axion dark matter in the 34.67 μeV mass range. A
  radio frequency cavity consisting of 5 sub-cavities coupled by inductive
  irises took physics data inside the CAST dipole magnet for the first
  time using this filter-like haloscope geometry. An exclusion limit
  with a 95% credibility level on the axion-photon coupling constant
  of g<SUB>aγ</SUB> ≳ 4 × 10<SUP>−13</SUP> GeV<SUP>−1</SUP>
  over a mass range of 34.6738 μeV &lt; m<SUB>a</SUB>&lt; 34.6771 μeV
  is set. This constitutes a significant improvement over the current
  strongest limit set by CAST at this mass and is at the same time one of
  the most sensitive direct searches for an axion dark matter candidate
  above the mass of 25 μeV. The results also demonstrate the feasibility
  of exploring a wider mass range around the value probed by CAST-RADES
  in this work using similar coherent resonant cavities.

Title: Predictions of Astrometric Jitter for Sun-like
    Stars. II. Dependence on Inclination, Metallicity, and Active-region
    Nesting
Authors: Sowmya, K.; Nèmec, N. -E.; Shapiro, A. I.; Işık, E.;
   Witzke, V.; Mints, A.; Krivova, N. A.; Solanki, S. K.
Bibcode: 2021ApJ...919...94S
Altcode: 2021arXiv210701493S
  Ultra-precise astrometry from the Gaia mission is expected to lead to
  astrometric detections of more than 20,000 exoplanets in our Galaxy. One
  of the factors that could hamper such detections is the astrometric
  jitter caused by the magnetic activity of the planet host stars. In
  our previous study, we modeled astrometric jitter for the Sun observed
  equator-on. In this work, we generalize our model and calculate the
  photocenter jitter as it would be measured by the Gaia and Small-JASMINE
  missions for stars with solar rotation rate and effective temperature,
  but with various values of the inclination angle of the stellar rotation
  axis. In addition, we consider the effect of metallicity and of nesting
  of active regions (i.e., the tendency of active regions to emerge in
  the vicinity of each other). We find that, while the jitter of stars
  observed equator-on does not have any long-term trends and can be
  easily filtered out, the photocenters of stars observed out of their
  equatorial planes experience systematic shifts over the course of
  the activity cycle. Such trends allow the jitter to be detected with
  continuous measurements, in which case it can interfere with planet
  detectability. An increase in the metallicity is found to increase the
  jitter caused by stellar activity. Active-region nesting can further
  enhance the peak-to-peak amplitude of the photocenter jitter to a
  level that could be detected by Gaia.

Title: The relationship between bipolar magnetic regions and their
    sunspots
Authors: Yeo, K. L.; Solanki, S. K.; Krivova, N. A.; Jiang, J.
Bibcode: 2021A&A...654A..28Y
Altcode: 2021arXiv210914313Y
  Context. The relationship between bipolar magnetic regions (BMRs)
  and their sunspots is an important property of the solar magnetic
  field, but it is not well constrained. One consequence is that it is a
  challenge for surface flux transport models (SFTMs) based on sunspot
  observations to determine the details of BMR emergence, which they
  require as input, from such data. <BR /> Aims: We aimed to establish
  the relationship between the amount of magnetic flux in newly emerged
  BMRs and the area of the enclosed sunspots, and examine the results
  of its application to an established SFTM. <BR /> Methods: Earlier
  attempts to constrain BMR magnetic flux were hindered by the fact that
  there is no extensive and reliable record of the magnetic and physical
  properties of newly emerged BMRs currently available. We made use of
  the empirical model of the relationship between the disc-integrated
  facular and network magnetic flux and the total surface coverage by
  sunspots reported in a recent study. The structure of the model is such
  that it enabled us to establish, from these disc-integrated quantities,
  an empirical relationship between the magnetic flux and sunspot area
  of individual newly emerged BMRs, circumventing the lack of any proper
  BMR database. <BR /> Results: Applying the constraint on BMR magnetic
  flux derived here to an established SFTM retained its key features,
  in particular its ability to replicate various independent datasets
  and the correlation between the model output polar field at the end
  of each cycle and the observed strength of the following cycle. The
  SFTM output indicates that facular and network magnetic flux rises
  with increasing sunspot magnetic flux at a slowing rate such that
  it appears to gradually saturate. This is analogous to what earlier
  studies comparing disc-integrated quantities sensitive to the amount
  of faculae and network present to sunspot indices had reported. The
  activity dependence of the ratio of facular and network flux to sunspot
  flux is consistent with the findings of recent studies: although the
  Sun is faculae-dominated (such that its brightness is mostly positively
  correlated with activity), it is only marginally so as facular and
  network brightening and sunspot darkening appear to be closely balanced.

Title: Correction of atmospheric stray light in restored slit spectra
Authors: Saranathan, S.; van Noort, M.; Solanki, S. K.
Bibcode: 2021A&A...653A..17S
Altcode: 2021arXiv211202648S
  Context. A long-standing issue in solar ground-based observations has
  been the contamination of data due to stray light, which is particularly
  relevant in inversions of spectropolarimetric data. <BR /> Aims: We aim
  to build on a statistical method of correcting stray-light contamination
  due to residual high-order aberrations and apply it to ground-based slit
  spectra. <BR /> Methods: The observations were obtained at the Swedish
  Solar Telescope, and restored using the multi-frame blind deconvolution
  restoration procedure. Using the statistical properties of seeing,
  we created artificially degraded synthetic images generated from
  magneto-hydrodynamic simulations. We then compared the synthetic data
  with the observations to derive estimates of the amount of the residual
  stray light in the observations. In the final step, the slit spectra
  were deconvolved with a stray-light point spread function to remove
  the residual stray light from the observations. <BR /> Results: The RMS
  granulation contrasts of the deconvolved spectra were found to increase
  to approximately 12.5%, from 9%. Spectral lines, on average, were found
  to become deeper in the granules and shallower in the inter-granular
  lanes, indicating systematic changes to gradients in temperature. The
  deconvolution was also found to increase the redshifts and blueshifts
  of spectral lines, suggesting that the velocities of granulation in
  the solar photosphere are higher than had previously been observed.

Title: Ti I lines at 2.2 μm as probes of the cooler regions of
    sunspots
Authors: Smitha, H. N.; Castellanos Durán, J. S.; Solanki, S. K.;
   Tiwari, S. K.
Bibcode: 2021A&A...653A..91S
Altcode: 2021arXiv210701247S
  Context. The sunspot umbra harbours the coolest plasma on the solar
  surface due to the presence of strong magnetic fields. The atomic
  lines that are routinely used to observe the photosphere have weak
  signals in the umbra and are often swamped by molecular lines. This
  makes it harder to infer the properties of the umbra, especially in
  the darkest regions. <BR /> Aims: The lines of the Ti I multiplet
  at 2.2 μm are formed mainly at temperatures ≤4500 K and are not
  known to be affected by molecular blends in sunspots. Since the first
  systematic observations in the 1990s, these lines have been seldom
  observed due to the instrumental challenges involved at these longer
  wavelengths. We revisit these lines and investigate their formation
  in different solar features. <BR /> Methods: We synthesized the
  Ti I multiplet using a snapshot from 3D magnetohydrodynamic (MHD)
  simulations of a sunspot and explored the properties of two of its
  lines in comparison with two commonly used iron lines, at 6302.5 Å and
  1.5648 μm. <BR /> Results: We find that the Ti I lines have stronger
  signals than the Fe I lines in both intensity and polarization in the
  sunspot umbra and in penumbral spines. They have little to no signal
  in the penumbral filaments and the quiet Sun, at μ = 1. Their strong
  and well-split profiles in the dark umbra are less affected by stray
  light. Consequently, inside the sunspot, it is easier to invert these
  lines and to infer the atmospheric properties as compared to the iron
  lines. <BR /> Conclusions: The Cryo-NIRSP instrument at the DKIST will
  provide the first-ever high-resolution observations in this wavelength
  range. In this preparatory study, we demonstrate the unique temperature
  and magnetic sensitivities of the Ti multiplet by probing the Sun's
  coolest regions, which are not favourable for the formation of other
  commonly used spectral lines. We thus expect such observations to
  advance our understanding of sunspot properties.

Title: MPS-ATLAS: A fast all-in-one code for synthesising stellar
    spectra
Authors: Witzke, V.; Shapiro, A. I.; Cernetic, M.; Tagirov, R. V.;
   Kostogryz, N. M.; Anusha, L. S.; Unruh, Y. C.; Solanki, S. K.; Kurucz,
   R. L.
Bibcode: 2021A&A...653A..65W
Altcode: 2021arXiv210513611W
  Context. Stellar spectral synthesis is essential for various
  applications, ranging from determining stellar parameters to
  comprehensive stellar variability calculations. New observational
  resources as well as advanced stellar atmosphere modelling, taking three
  dimensional effects from radiative magnetohydrodynamics calculations
  into account, require a more efficient radiative transfer. <BR /> Aims:
  For accurate, fast and flexible calculations of opacity distribution
  functions (ODFs), stellar atmospheres, and stellar spectra, we developed
  an efficient code building on the well-established ATLAS9 code. The new
  code also paves the way for easy and fast access to different elemental
  compositions in stellar calculations. <BR /> Methods: For the generation
  of ODF tables, we further developed the well-established DFSYNTHE code
  by implementing additional functionality and a speed-up by employing
  a parallel computation scheme. In addition, the line lists used can be
  changed from Kurucz's recent lists. In particular, we implemented the
  VALD3 line list. <BR /> Results: A new code, the Merged Parallelised
  Simplified ATLAS, is presented. It combines the efficient generation of
  ODF, atmosphere modelling, and spectral synthesis in local thermodynamic
  equilibrium, therefore being an all-in-one code. This all-in-one code
  provides more numerical functionality and is substantially faster
  compared to other available codes. The fully portable MPS-ATLAS code
  is validated against previous ATLAS9 calculations, the PHOENIX code
  calculations, and high-quality observations.

Title: A Multi-Purpose Heliophysics L4 Mission
Authors: Posner, A.; Arge, C. N.; Staub, J.; StCyr, O. C.; Folta,
   D.; Solanki, S. K.; Strauss, R. D. T.; Effenberger, F.; Gandorfer,
   A.; Heber, B.; Henney, C. J.; Hirzberger, J.; Jones, S. I.; Kühl,
   P.; Malandraki, O.; Sterken, V. J.
Bibcode: 2021SpWea..1902777P
Altcode:
  The Earth-Sun Lagrangian point 4 is a meta-stable location at 1 AU from
  the Sun, 60° ahead of Earth's orbit. It has an uninterrupted view of
  the solar photosphere centered on W60, the Earth's nominal magnetic
  field connection to the Sun. Such a mission on its own would serve
  as a solar remote sensing observatory that would oversee the entire
  solar radiation hemisphere with significant relevance for protecting
  Moon and Mars explorers from radiation exposure. In combination with
  appropriately planned observatories at L1 and L5, the three spacecraft
  would provide 300° longitude coverage of photospheric magnetic field
  structure, and allow continuous viewing of both solar poles, with
  &gt;3.6° elevation. Ideally, the L4 and L5 missions would orbit the Sun
  with a 7.2° inclination out of the heliographic equator, 14.5° out of
  the ecliptic plane. We discuss the impact of extending solar magnetic
  field observations in both longitude and latitude to improve global
  solar wind modeling and, with the development of local helioseismology,
  the potential for long-term solar activity forecasting. Such a mission
  would provide a unique opportunity for interplanetary and interstellar
  dust science. It would significantly add to reliability of operational
  observations on fast coronal mass ejections directed at Earth and
  for human Mars explorers on their round-trip journey. The L4 mission
  concept is technically feasible, and is scientifically compelling.

Title: Magnetic imaging of the outer solar atmosphere (MImOSA)
Authors: Peter, H.; Ballester, E. Alsina; Andretta, V.; Auchère, F.;
   Belluzzi, L.; Bemporad, A.; Berghmans, D.; Buchlin, E.; Calcines, A.;
   Chitta, L. P.; Dalmasse, K.; Alemán, T. del Pino; Feller, A.; Froment,
   C.; Harrison, R.; Janvier, M.; Matthews, S.; Parenti, S.; Przybylski,
   D.; Solanki, S. K.; Štěpán, J.; Teriaca, L.; Bueno, J. Trujillo
Bibcode: 2021ExA...tmp...95P
Altcode:
  The magnetic activity of the Sun directly impacts the Earth and human
  life. Likewise, other stars will have an impact on the habitability of
  planets orbiting these host stars. Although the magnetic field at the
  surface of the Sun is reasonably well characterised by observations,
  the information on the magnetic field in the higher atmospheric layers
  is mainly indirect. This lack of information hampers our progress in
  understanding solar magnetic activity. Overcoming this limitation would
  allow us to address four paramount long-standing questions: (1) How
  does the magnetic field couple the different layers of the atmosphere,
  and how does it transport energy? (2) How does the magnetic field
  structure, drive and interact with the plasma in the chromosphere and
  upper atmosphere? (3) How does the magnetic field destabilise the outer
  solar atmosphere and thus affect the interplanetary environment? (4)
  How do magnetic processes accelerate particles to high energies? New
  ground-breaking observations are needed to address these science
  questions. We suggest a suite of three instruments that far exceed
  current capabilities in terms of spatial resolution, light-gathering
  power, and polarimetric performance: (a) A large-aperture UV-to-IR
  telescope of the 1-3 m class aimed mainly to measure the magnetic
  field in the chromosphere by combining high spatial resolution
  and high sensitivity. (b) An extreme-UV-to-IR coronagraph that is
  designed to measure the large-scale magnetic field in the corona with
  an aperture of about 40 cm. (c) An extreme-UV imaging polarimeter
  based on a 30 cm telescope that combines high throughput in the
  extreme UV with polarimetry to connect the magnetic measurements
  of the other two instruments. Placed in a near-Earth orbit, the data
  downlink would be maximised, while a location at L4 or L5 would provide
  stereoscopic observations of the Sun in combination with Earth-based
  observatories. This mission to measure the magnetic field will finally
  unlock the driver of the dynamics in the outer solar atmosphere and
  thereby will greatly advance our understanding of the Sun and the
  heliosphere.

Title: On the size distribution of spots within sunspot groups
Authors: Mandal, Sudip; Krivova, Natalie A.; Cameron, Robert; Solanki,
   Sami K.
Bibcode: 2021A&A...652A...9M
Altcode: 2021arXiv210403534M
  The size distribution of sunspots provides key information about
  the generation and emergence processes of the solar magnetic
  field. Previous studies of size distribution have primarily focused
  on either the whole group or individual spot areas. In this paper we
  investigate the organisation of spot areas within sunspot groups. In
  particular, we analysed the ratio (R) of the area of the biggest spot
  (A<SUB>big_spot</SUB>) inside a group, to the total area of that group
  (A<SUB>group</SUB>). We used sunspot observations from Kislovodsk,
  Pulkovo, and Debrecen observatories, together covering solar cycles
  17-24. We find that at the time when the group area reaches its maximum,
  the single biggest spot in a group typically occupies about 60% of the
  group area. For half of all groups, R lies in the range between roughly
  50% and 70%. We also find R to change with A<SUB>group</SUB>, such that
  R reaches a maximum of about 0.65 for groups with A<SUB>group</SUB>
  ≈ 200 μHem and then remains at about 0.6 for larger groups. Our
  findings imply a scale-invariant emergence pattern, providing an
  observational constraint on the emergence process. Furthermore,
  extrapolation of our results to larger sunspot groups may have a
  bearing on the giant unresolved starspot features found in Doppler
  images of highly active Sun-like stars. Our results suggest that such
  giant features are composed of multiple spots, with the largest spot
  occupying roughly 55-75% of the total group area (i.e., the area of
  the giant starspots seen in Doppler images).

Title: Slow magneto-acoustic waves in simulations of a solar plage
    region carry enough energy to heat the chromosphere
Authors: Yadav, N.; Cameron, R. H.; Solanki, S. K.
Bibcode: 2021A&A...652A..43Y
Altcode: 2021arXiv210502932Y
  <BR /> Aims: We study the properties of slow magneto-acoustic waves
  that are naturally excited as a result of turbulent convection and we
  investigate their role in the energy balance of a plage region using
  three dimensional radiation magnetohydrodynamic simulations. <BR />
  Methods: To follow slow magneto-acoustic waves traveling along the
  magnetic field lines, we selected 25 seed locations inside a strong
  magnetic element and tracked the associated magnetic field lines both
  in space and time. We calculate the longitudinal component (i.e.,
  parallel to the field) of velocity at each grid point along the field
  line and compute the temporal power spectra at various heights above
  the mean solar surface. Additionally, the horizontally-averaged (over
  the whole domain) frequency power spectra for both longitudinal and
  vertical (i.e., the component perpendicular to the surface) components
  of velocity are calculated using time series at fixed locations. To
  compare our results with the observations, we degrade the simulation
  data with Gaussian kernels having a full width at half maxium of 100
  km and 200 km and calculate the horizontally-averaged power spectra
  for the vertical component of velocity using time series at fixed
  locations. <BR /> Results: The power spectra of the longitudinal
  component of velocity, averaged over 25 field lines in the core of
  a kG magnetic flux concentration reveal that the dominant period
  of oscillations shifts from ∼6.5 min in the photosphere to ∼4
  min in the chromosphere. This behavior is consistent with earlier
  studies that were restricted to vertically propagating waves. At the
  same time, the velocity power spectra, averaged horizontally over
  the whole domain, show that low frequency waves (∼6.5 min period)
  may reach well into the chromosphere. In addition, the power spectra
  at high frequencies follow a power law with an exponent close to
  −5/3, suggestive of turbulent excitation. Moreover, waves with
  frequencies above 5 mHz propagating along different field lines
  are found to be out of phase with each other, even within a single
  magnetic concentration. The horizontally-averaged power spectra of
  the vertical component of velocity at various effective resolutions
  show that the observed acoustic wave energy fluxes are underestimated
  by a factor of three, even if determined from observations carried
  out at a high spatial resolution of 200 km. Since the waves propagate
  along the non-vertical field lines, measuring the velocity component
  along the line-of-sight, rather than along the field, contributes
  significantly to this underestimation. Moreover, this underestimation of
  the energy flux indirectly indicates the importance of high-frequency
  waves that are shown to have a smaller spatial coherence and are thus
  more strongly influenced by the spatial averaging effect compared to
  low-frequency waves. <BR /> Conclusions: Inside a plage region, there
  is on average a significant fraction of low frequency waves leaking
  into the chromosphere due to inclined magnetic field lines. Our results
  show that longitudinal waves carry (just) enough energy to heat the
  chromosphere in the solar plage. However, phase differences between
  waves traveling along different field lines within a single magnetic
  concentration can lead to underestimations of the wave energy flux
  due to averaging effects in degraded simulation data and, similarly,
  in observations with lower spatial resolution. We find that current
  observations (with spatial resolution around 200 km) underestimate the
  energy flux by roughly a factor of three - or more if the observations
  are carried out at a lower spatial resolution. We expect that even
  at a very high resolution, which is expected with the next generation
  of telescopes such as DKIST and the EST, less than half, on average,
  of the energy flux carried by such waves will be detected if only the
  line-of-sight component of the velocity is measured.

Title: How rare are counter Evershed flows?
Authors: Castellanos Durán, J. S.; Lagg, A.; Solanki, S. K.
Bibcode: 2021A&A...651L...1C
Altcode: 2021arXiv210605592S
  One of the main characteristics of sunspot penumbrae is the radially
  outward-directed Evershed flow. Only recently have penumbral regions
  been reported with similar characteristics to normal penumbral
  filaments but with an opposite direction of the flow. Such flows
  directed toward the umbra are known as counter Evershed flows
  (CEFs). We aim to determine the occurrence frequency of CEFs in
  active regions (ARs) and to characterize their lifetime and the
  prevailing conditions in the ARs. We analyzed the continuum images,
  Dopplergrams, and magnetograms recorded by SDO/HMI of 97 ARs that
  appeared from 2011 to 2017. We followed the ARs for 9.6 ± 1.4 days
  on average. We found 384 CEFs in total, with a median value of six
  CEFs per AR. Counter Evershed flows are a rather common feature,
  occurring in 83.5% of all ARs regardless of the magnetic complexity
  of the AR. However, CEFs were only observed, on average, during 5.9%
  of the mean total duration of all the observations analyzed here. The
  lifetime of CEFs follows a log-normal distribution with a median value
  of 10.6<SUB>−6.0</SUB><SUP>+12.4</SUP> h. In addition, we report two
  populations of CEFs, those that are associated with light bridges and
  those that are not. We explain that the rarity of reports of CEFs in
  the literature is a result of highly incomplete coverage of ARs with
  spectropolarimetric data. By using the continuous observations now
  routinely available from space, we are able to overcome this limitation.

Title: Radiative Transfer with Opacity Distribution Functions:
    Application to Narrowband Filters
Authors: Anusha, L. S.; Shapiro, A. I.; Witzke, V.; Cernetic, M.;
   Solanki, S. K.; Gizon, L.
Bibcode: 2021ApJS..255....3A
Altcode: 2021arXiv210413661A
  Modeling of stellar radiative intensities in various spectral passbands
  plays an important role in stellar physics. At the same time, direct
  calculation of the high-resolution spectrum and then integration of it
  over the given spectral passband is computationally demanding due to
  the vast number of atomic and molecular lines. This is particularly so
  when employing three-dimensional (3D) models of stellar atmospheres. To
  accelerate the calculations, one can employ approximate methods, e.g.,
  the use of opacity distribution functions (ODFs). Generally, ODFs
  provide a good approximation of traditional spectral synthesis, i.e.,
  computation of intensities through filters with strictly rectangular
  transmission functions. However, their performance strongly deteriorates
  when the filter transmission noticeably changes within its passband,
  which is the case for almost all filters routinely used in stellar
  physics. In this context, the aims of this paper are (a) to generalize
  the ODFs method for calculating intensities through filters with
  arbitrary transmission functions, and (b) to study the performance of
  the standard and generalized ODFs methods for calculating intensities
  emergent from 3D models of stellar atmospheres. For this purpose we
  use the newly developed MPS-ATLAS radiative transfer code to compute
  intensities emergent from 3D cubes simulated with the radiative
  magnetohydrodynamics code MURaM. The calculations are performed
  in the 1.5D regime, i.e., along many parallel rays passing through
  the simulated cube. We demonstrate that the generalized ODFs method
  allows accurate and fast syntheses of spectral intensities and their
  center-to-limb variations.

Title: Forward modelling of Kepler-band variability due to faculae
    and spots
Authors: Johnson, Luke J.; Norris, Charlotte M.; Unruh, Yvonne C.;
   Solanki, Sami K.; Krivova, Natalie; Witzke, Veronika; Shapiro,
   Alexander I.
Bibcode: 2021MNRAS.504.4751J
Altcode: 2021arXiv210411544J; 2021MNRAS.tmp.1190J
  Variability observed in photometric light curves of late-type stars (on
  time-scales longer than a day) is a dominant noise source in exoplanet
  surveys and results predominantly from surface manifestations of stellar
  magnetic activity, namely faculae and spots. The implementation of
  faculae in light-curve models is an open problem, with scaling typically
  based on spectra equivalent to hot stellar atmospheres or assuming a
  solar-derived facular contrast. We modelled rotational (single period)
  light curves of active G2, K0, M0, and M2 stars, with Sun-like surface
  distributions and realistic limb-dependent contrasts for faculae and
  spots. The sensitivity of light-curve variability to changes in model
  parameters such as stellar inclination, feature area coverage, spot
  temperature, facular region magnetic flux density, and active band
  latitudes is explored. For our light-curve modelling approach we used
  ACTRESS, a geometrically accurate model for stellar variability. ACTRESS
  generates two-sphere maps representing stellar surfaces and populates
  them with user-prescribed spot and facular region distributions. From
  this, light curves can be calculated at any inclination. Quiet star limb
  darkening and limb-dependent facular contrasts were derived from MURaM
  3D magnetoconvection simulations using ATLAS9. 1D stellar atmosphere
  models were used for the spot contrasts. We applied ACTRESS in Monte
  Carlo simulations, calculating light-curve variability amplitudes in
  the Kepler band. We found that, for a given spectral type and stellar
  inclination, spot temperature and spot area coverage have the largest
  effect on variability of all simulation parameters. For a spot coverage
  of $1{{\ \rm per\ cent}}$, the typical variability of a solar-type
  star is around 2 parts per thousand. The presence of faculae clearly
  affects the mean brightness and light-curve shape, but has relatively
  little influence on the variability.

Title: Coronal loops in a box: 3D models of their internal structure,
    dynamics and heating
Authors: Breu, C. A.; Peter, H.; Cameron, R.; Solanki, S.; Przybylski,
   D.; Chitta, L.
Bibcode: 2021AAS...23810606B
Altcode:
  The corona of the Sun, and probably also of other stars, is built
  up by loops defined through the magnetic field. They vividly appear
  in solar observations in the extreme UV and X-rays. High-resolution
  observations show individual strands with diameters down to a few 100
  km, and so far it remains open what defines these strands, in particular
  their width, and where the energy to heat them is generated. <P />The
  aim of our study is to understand how the magnetic field couples the
  different layers of the solar atmosphere, how the energy generated
  by magnetoconvection is transported into the upper atmosphere and
  dissipated, and how this process determines the scales of observed
  bright strands in the loop. <P />To this end, we conduct 3D resistive
  MHD simulations with the MURaM code. We include the effects of heat
  conduction, radiative transfer and optically thin radiative losses.We
  study an isolated coronal loop that is rooted with both footpoints
  in a shallow convection zone layer. To properly resolve the internal
  structure of the loop while limiting the size of the computational box,
  the coronal loop is modelled as a straightened magnetic flux tube. By
  including part of the convection zone, we drive the evolution of
  the corona self-consistently by magnetoconvection. <P />We find that
  the energy injected into the loop is generated by internal coherent
  motions within strong magnetic elements. The resulting Poynting
  flux is channelled into the loop in vortex tubes forming a magnetic
  connection between the photosphere and corona, where it is dissipated
  and heats the upper atmosphere. <P />The coronal emission as it would
  be observed in solar extreme UV or X-ray observations, e.g. with AIA
  or XRT, shows transient bright strands.The widths of these strands are
  consistent with observations. From our model we find that the width
  of the strands is governed by the size of the individual photospheric
  magnetic field concentrations where the field line through these strands
  are rooted. Essentially, each coronal strand is rooted in a single
  magnetic patch in the photosphere, and the energy to heat the strand is
  generated by internal motions within this magnetic concentration. <P
  />With this model we can build a coherent picture of how energy and
  matter are transported into the upper solar atmosphere and how these
  processes structure the interior of coronal loops.

Title: How wrong are the results of inverting Fe I lines when NLTE
    and 3D radiative transfer effects are ignored?
Authors: Narayanamurthy, S.; Holzreuter, R.; van Noort, M.; Solanki, S.
Bibcode: 2021AAS...23811305N
Altcode:
  The Fe I 6301.5 Å and 6302.5 Å lines are widely used to probe the
  solar photosphere. They are known to be affected by the non-local
  thermodynamic equilibrium (NLTE) conditions due to the ultraviolet
  overionisation of iron atoms in the solar atmosphere. This leads
  to deviations in their level populations based on Saha-Boltzmann
  statistics. When inverting their Stokes profiles to determine
  atmospheric parameters, the NLTE effects are often neglected and
  other quantities are tweaked to compensate for deviations from the
  LTE. In this work, we discuss how the routinely employed LTE inversion
  introduces errors in the derived atmospheric quantities. We show that
  when the NLTE effects are neglected, these errors can be as high
  as 13% in temperature, and in line-of-sight velocity and magnetic
  field strength the errors can even exceed 50%. Errors are found
  at the sites of granules, intergranular lanes, magnetic elements,
  and basically in every region with strong vertical gradients in the
  atmosphere. Similarly, strong horizontal gradients in temperature
  introduce 3D effects in these lines. We find that errors due to
  neglecting the 3D effects are more localised and are lower than 5%
  in temperature, and lower than 20% in both velocity and magnetic field
  strength. The NLTE and 3D effects are found to persist when the Stokes
  profiles are spatially and spectrally degraded to the resolution of
  the Swedish Solar Telescope (SST) or Daniel K. Inouye Solar Telescope
  (DKIST). Our findings have wide-ranging consequences since many results
  derived in solar physics are based on inversions of these Fe I lines
  carried out in LTE.

Title: Small-scale Dynamo in Cool Main-Sequence Stars: Effect on
    Stratification, Convection and Bolometric Intensity
Authors: Bhatia, T.; Cameron, R.; Solanki, S.; Peter, H.; Przybylski,
   D.; Witzke, V.; Shapiro, A.
Bibcode: 2021AAS...23830404B
Altcode:
  In cool main-sequence stars, the near-surface convection has an
  impact on the center-to-limb variation of photospheric emission, with
  implications for stellar lightcurves during planetary transits. In
  the Sun, there is strong evidence for a small-scale dynamo (SSD)
  maintaining the small-scale magnetic flux. This field could affect the
  near-surface convection in other cool main-sequence stars. <P />An SSD
  could conceivably generate equipartition magnetic fields, which could
  lead to non-negligible changes not only in convection and intensity
  characteristics, but also in stratification. We aim to investigate these
  changes for F, G, K and M stars. 3D MHD models of the four stellar types
  covering the subsurface region to lower atmosphere in a small cartesian
  box are studied using the MURaM rMHD simulation code. The MHD runs are
  compared against a reference hydrodynamic (HD) run. <P />The deviations
  in stratification for the deeper convective layers is negligible,
  except for the F-star, where reduction in turbulent pressure due to
  magnetic fields is substantial. Convective velocities are reduced
  by a similar percentage for all the cases due to inhibitory effect
  of strong magnetic fields near the bottom boundary. All four cases
  show small-scale brightenings in intergranular lanes, corresponding
  to magnetic field concentrations, but overall effects on the r.m.s
  contrast and spatial powerspectra are varied.

Title: First Results of the Chromospheric MURaM code
Authors: Przybylski, D. F.; Cameron, R.; Solanki, S.; Rempel, M.
Bibcode: 2021AAS...23810605P
Altcode:
  The solar chromosphere, spanning the region between the photosphere
  and the transition to the corona, remains one of the least understood
  parts of the Sun. This is partly because observing the chromosphere
  and interpreting these observations is full of pitfalls. Also, the
  simulation of the chromosphere is complex, as the particle densities
  and collisional rates are too low to maintain local thermodynamic
  equilibrium (LTE). Additionally, the recombination rates of hydrogen are
  larger than the dynamical timescales and the populations must be solved
  in non-equilibrium (NE). Realistic simulations of the chromosphere
  must treat the magneto-hydrodynamics, time-dependant atomic and
  molecular chemistry, and radiation transfer simultaneously. <P />The
  MURaM radiation-MHD code has previously been used for investigation
  of the connection between the solar photosphere and corona, ranging
  from small-scale dynamo generated 'quiet' sun fields to sunspots and
  complex active regions. Until now these simulations have been performed
  in LTE, greatly limiting their realism in the solar chromosphere. We
  have extended MURaM to include NLTE effects following the prescriptions
  used in the Bifrost code. The low viscocity and resistivity of the MURaM
  code leads to turbulent convection in the photosphere with kilo-Gauss
  mixed-polarity magnetic fields. This results in a dynamic chromosphere
  with strong shocks and a finely structured magnetic field. We discuss
  the implications of this new model towards observations of chromospheric
  spectral lines.

Title: Modeling Stellar Ca II H and K Emission Variations. I. Effect
    of Inclination on the S-index
Authors: Sowmya, K.; Shapiro, A. I.; Witzke, V.; Nèmec, N. -E.;
   Chatzistergos, T.; Yeo, K. L.; Krivova, N. A.; Solanki, S. K.
Bibcode: 2021ApJ...914...21S
Altcode: 2021arXiv210313893S
  The emission in the near-ultraviolet Ca II H and K lines is modulated
  by stellar magnetic activity. Although this emission, quantified via
  the S-index, has been serving as a prime proxy of stellar magnetic
  activity for several decades, many aspects of the complex relation
  between stellar magnetism and Ca II H and K emission are still
  unclear. The amount of measured Ca II H and K emission is suspected
  to be affected not only by the stellar intrinsic properties but
  also by the inclination angle of the stellar rotation axis. Until
  now, such an inclination effect on the S-index has remained largely
  unexplored. To fill this gap, we develop a physics-based model to
  calculate S-index, focusing on the Sun. Using the distributions of
  solar magnetic features derived from observations together with Ca II
  H and K spectra synthesized in non-local thermodynamic equilibrium,
  we validate our model by successfully reconstructing the observed
  variations of the solar S-index over four activity cycles. Further,
  using the distribution of magnetic features over the visible solar
  disk obtained from surface flux transport simulations, we obtain
  S-index time series dating back to 1700 and investigate the effect
  of inclination on S-index variability on both the magnetic activity
  cycle and the rotational timescales. We find that when going from
  an equatorial to a pole-on view, the amplitude of S-index variations
  decreases weakly on the activity cycle timescale and strongly on the
  rotational timescale (by about 22% and 81%, respectively, for a cycle
  of intermediate strength). The absolute value of the S-index depends
  only weakly on the inclination. We provide analytical expressions that
  model such dependencies.

Title: Modelling the evolution of the Sun's open and total magnetic
    flux
Authors: Krivova, N. A.; Solanki, S. K.; Hofer, B.; Wu, C. -J.;
   Usoskin, I. G.; Cameron, R.
Bibcode: 2021A&A...650A..70K
Altcode: 2021arXiv210315603K
  Solar activity in all its varied manifestations is driven by the
  magnetic field. Two global quantities are particularly important for
  many purposes, the Sun's total and open magnetic flux, which can be
  computed from sunspot number records using models. Such sunspot-driven
  models, however, do not take into account the presence of magnetic
  flux during grand minima, such as the Maunder minimum. Here we
  present a major update of a widely used simple model, which now takes
  into account the observation that the distribution of all magnetic
  features on the Sun follows a single power law. The exponent of the
  power law changes over the solar cycle. This allows for the emergence
  of small-scale magnetic flux even when no sunspots have been present
  for multiple decades and leads to non-zero total and open magnetic
  flux also in the deepest grand minima, such as the Maunder minimum,
  thus overcoming a major shortcoming of the earlier models. The results
  of the updated model compare well with the available observations and
  reconstructions of the solar total and open magnetic flux. This opens
  up the possibility of improved reconstructions of the sunspot number
  from time series of the cosmogenic isotope production rate.

Title: Solar cyclic activity over the last millennium reconstructed
    from annual <SUP>14</SUP>C data
Authors: Usoskin, I. G.; Solanki, S. K.; Krivova, N. A.; Hofer, B.;
   Kovaltsov, G. A.; Wacker, L.; Brehm, N.; Kromer, B.
Bibcode: 2021A&A...649A.141U
Altcode: 2021arXiv210315112U
  <BR /> Aims: The 11-year solar cycle (Schwabe cycle) is the dominant
  pattern of solar magnetic activity reflecting the oscillatory dynamo
  mechanism in the Sun's convection zone. Solar cycles have been
  directly observed since 1700, while indirect proxy data suggest their
  existence over a much longer period of time, but generally without
  resolving individual cycles and their continuity. Here we reconstruct
  individual solar cycles for the last millennium using recently
  obtained <SUP>14</SUP>C data and state-of-the-art models. <BR />
  Methods: Starting with the <SUP>14</SUP>C production rate determined
  from the so far most precise measurements of radiocarbon content in
  tree rings, solar activity was reconstructed in the following three
  physics-based steps: (1) correction of the <SUP>14</SUP>C production
  rate for the changing geomagnetic field; (2) computation of the
  open solar magnetic flux; and (3) conversion into sunspot numbers
  outside of grand minima. All known uncertainties, including both
  measurement and model uncertainties, were straightforwardly accounted
  for by a Monte-Carlo method. <BR /> Results: Cyclic solar activity is
  reconstructed for the period 971-1900 (85 individual cycles) along with
  its uncertainties. This more than doubles the number of solar cycles
  known from direct solar observations. We found that the lengths and
  strengths of well-defined cycles outside grand minima are consistent
  with those obtained from the direct sunspot observations after 1750. The
  validity of the Waldmeier rule (cycles with fast-rising phase tend to
  be stronger) is confirmed at a highly significant level. Solar activity
  is found to be in a deep grand minimum when the activity is mostly
  below the sunspot formation threshold for about 250 years. Therefore,
  although considerable cyclic variability in <SUP>14</SUP>C is seen even
  during grand minima, individual solar cycles can hardly be reliably
  resolved therein. Three potential solar particle events, ca. 994,
  1052, and 1279 AD, are shown to occur around the maximum phases of
  solar cycles. <BR /> Conclusions: A new approximately 1000-year-long
  solar activity reconstruction, in the form of annual (pseudo) sunspot
  numbers with the full assessment of all known uncertainties, is
  presented based on new high-precision Δ<SUP>14</SUP>C measurements and
  state-of-the-art models, more than doubling the number of individually
  resolved solar cycles. This forms a solid basis for new, more detailed
  studies of solar variability. <P />Tabular data of the reconstructed
  activity are only available at the CDS via anonymous ftp to <A
  href="http://cdsarc.u-strasbg.fr/">cdsarc.u-strasbg.fr</A>
  (ftp://130.79.128.5) or via <A
  href="http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/649/A141">http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/649/A141</A>

Title: Signatures of coronal hole substructure in the solar wind:
    combined Solar Orbiter remote sensing and in situ measurements
Authors: Horbury, T. S.; Laker, R.; Rodriguez, L.; Steinvall, K.;
   Maksimovic, M.; Livi, S.; Berghmans, D.; Auchere, F.; Zhukov, A. N.;
   Khotyaintsev, Yu. V.; Woodham, L.; Matteini, L.; Stawarz, J.; Woolley,
   T.; Bale, S. D.; Rouillard, A.; O'Brien, H.; Evans, V.; Angelini,
   V.; Owen, C.; Solanki, S. K.; Nicula, B.; Muller, D.; Zouganelis, I.
Bibcode: 2021arXiv210414960H
Altcode:
  Context. The Sun's complex corona is the source of the solar wind
  and interplanetary magnetic field. While the large scale morphology
  is well understood, the impact of variations in coronal properties
  on the scale of a few degrees on properties of the interplanetary
  medium is not known. Solar Orbiter, carrying both remote sensing
  and in situ instruments into the inner solar system, is intended
  to make these connections better than ever before. Aims. We combine
  remote sensing and in situ measurements from Solar Orbiter's first
  perihelion at 0.5 AU to study the fine scale structure of the solar
  wind from the equatorward edge of a polar coronal hole with the aim
  of identifying characteristics of the corona which can explain the in
  situ variations. Methods. We use in situ measurements of the magnetic
  field, density and solar wind speed to identify structures on scales
  of hours at the spacecraft. Using Potential Field Source Surface
  mapping we estimate the source locations of the measured solar wind
  as a function of time and use EUI images to characterise these solar
  sources. Results. We identify small scale stream interactions in the
  solar wind with compressed magnetic field and density along with speed
  variations which are associated with corrugations in the edge of the
  coronal hole on scales of several degrees, demonstrating that fine
  scale coronal structure can directly influence solar wind properties
  and drive variations within individual streams. Conclusions. This early
  analysis already demonstrates the power of Solar Orbiter's combined
  remote sensing and in situ payload and shows that with future, closer
  perihelia it will be possible dramatically to improve our knowledge
  of the coronal sources of fine scale solar wind structure, which is
  important both for understanding the phenomena driving the solar wind
  and predicting its impacts at the Earth and elsewhere.

Title: Observing and modelling the young solar analogue EK Draconis:
    starspot distribution, elemental abundances, and evolutionary status
Authors: Şenavcı, H. V.; Kılıçoğlu, T.; Işık, E.; Hussain,
   G. A. J.; Montes, D.; Bahar, E.; Solanki, S. K.
Bibcode: 2021MNRAS.502.3343S
Altcode: 2021MNRAS.tmp..235S; 2021arXiv210107248S
  Observations and modelling of stars with near-solar masses in their
  early phases of evolution are critical for a better understanding
  of how dynamos of solar-type stars evolve. We examine the chemical
  composition and the spot distribution of the pre-main-sequence solar
  analogue EK Dra. Using spectra from the HERMES Spectrograph (La Palma),
  we obtain the abundances of 23 elements with respect to the solar
  ones, which lead to a [Fe/H] = 0.03, with significant overabundance
  of Li and Ba. The s-process elements Sr, Y, and Ce are marginally
  overabundant, while Co, Ni, Cu, Zn are marginally deficient compared
  to solar abundances. The overabundance of Ba is most likely due to the
  assumption of depth-independent microturbulent velocity. Li abundance
  is consistent with the age and the other abundances may indicate
  distinct initial conditions of the pre-stellar nebula. We estimate a
  mass of 1.04 M<SUB>⊙</SUB> and an age of $27^{+11}_{-8}$ Myr using
  various spectroscopic and photometric indicators. We study the surface
  distribution of dark spots, using 17 spectra collected during 15 nights
  using the CAFE Spectrograph (Calar Alto). We also conduct flux emergence
  and transport (FEAT) simulations for EK Dra's parameters and produce
  15-d-averaged synoptic maps of the likely starspot distributions. Using
  Doppler imaging, we reconstruct the surface brightness distributions for
  the observed spectra and FEAT simulations, which show overall agreement
  for polar and mid-latitude spots, while in the simulations there is
  a lack of low-latitude spots compared to the observed image. We find
  indications that cross-equatorial extensions of mid-latitude spots
  can be artefacts of the less visible southern-hemisphere activity.

Title: The influence of NLTE effects in Fe I lines on an inverted
    atmosphere. II. 6301 Å and 6302 Å lines formed in 3D NLTE
Authors: Smitha, H. N.; Holzreuter, R.; van Noort, M.; Solanki, S. K.
Bibcode: 2021A&A...647A..46S
Altcode: 2021arXiv210100506S
  Context. This paper forms the second part of our study of how
  neglecting non-local thermodynamic equilibrium (NLTE) conditions in
  the formation of Fe I 6301.5 Å and the 6302.5 Å lines affects the
  atmosphere that is obtained by inverting the Stokes profiles of these
  lines in LTE. The main cause of NLTE effects in these lines is the line
  opacity deficit that is due to the excess ionisation of Fe I atoms by
  ultraviolet (UV) photons in the Sun. <BR /> Aims: In the first paper,
  these photospheric lines were assumed to have formed in 1D NLTE and the
  effects of horizontal radiation transfer (RT) were neglected. In the
  present paper, the iron lines are computed by solving the RT in 3D. We
  investigate the effect of horizontal RT on the inverted atmosphere and
  how it can enhance or reduce the errors that are due to neglecting 1D
  NLTE effects. <BR /> Methods: The Stokes profiles of the iron lines
  were computed in LTE, 1D NLTE, and 3D NLTE. They were all inverted
  using an LTE inversion code. The atmosphere from the inversion of
  LTE profiles was taken as the reference model. The atmospheres from
  the inversion of 1D NLTE profiles (testmodel-1D) and 3D NLTE profiles
  (testmodel-3D) were compared with it. Differences between reference and
  testmodels were analysed and correspondingly attributed to NLTE and 3D
  effects. <BR /> Results: The effects of horizontal RT are evident in
  regions surrounded by strong horizontal temperature gradients. That is,
  along the granule boundaries, regions surrounding magnetic elements,
  and its boundaries with intergranular lanes. In some regions, the 3D
  effects enhance the 1D NLTE effects, and in some, they weaken these
  effects. In the small region analysed in this paper, the errors due to
  neglecting the 3D effects are lower than 5% in temperature. In most of
  the pixels, the errors are lower than 20% in both velocity and magnetic
  field strength. These errors also persist when the Stokes profiles
  are spatially and spectrally degraded to the resolution of the Swedish
  Solar Telescope (SST) or Daniel K. Inouye Solar Telescope (DKIST). <BR
  /> Conclusions: Neglecting horizontal RT introduces errors not only in
  the derived temperature, but also in other atmospheric parameters. The
  error sizes depend on the strength of the local horizontal temperature
  gradients. Compared to the 1D NLTE effect, the 3D effects are more
  localised in specific regions in the atmosphere and are weaker overall.

Title: VizieR Online Data Catalog: 1000-year sunspot series (Usoskin+,
    2021)
Authors: Usoskin, I. G.; Solanki, S. K.; Krivova, N.; Hofer, B.;
   Kovaltsov, G. A.; Wacker, L.; Brehm, N.; Kromer, B.
Bibcode: 2021yCat..36490141U
Altcode:
  A new quantitative reconstruction of annually resolved solar activity,
  in the form of SNs (at least outside grand minima) with a full
  uncertainty assessment, is presented for the period 971-1900. For the
  first time, individual solar cycles are presented for the whole of the
  last millennium, more than doubling the existing statistics of solar
  cycles. <P />Three tabular files are presented. <P />File 'osf.dat'
  contains annual reconstructions of the opens solar flux (OSF) [Fo]
  along with its 1-sigma uncertainties [sF] and the smoothed (22-yr SSA --
  see text) values [&lt;Fo&gt;]. This table corresponds to Figure 8 in
  the text. <P />File 'osn.dat' contains annual reconstructions of the
  sunspot number (SN) [SN] along with its 1-sigma uncertainties [sSN]
  and the smoothed (22-yr SSA -- see text) values [&lt;SN&gt;]. This
  table corresponds to Figure 11 in the text. <P />File 'table1.dat'
  presents a textual tabular version of Table 1 in the text and contains
  the internal cycle number [n], years of minimum [Ymin] and maximum
  [Ymax] of each cycle, cycle-averaged sunspot number [&lt;SN&gt;], its
  1-sigma uncertainty [sS], cycle length (min-to-min) [T], and quality
  flag [q]. <P />(3 data files).

Title: Amplifying variability of solar-like stars by active longitudes
    and nesting
Authors: Isik, Emre; Shapiro, Alexander I.; Solanki, Sami K.; Krivova,
   Natalie A.
Bibcode: 2021csss.confE.279I
Altcode:
  Many solar-type stars with near-solar rotation
  periods exhibit much stronger variability than the Sun (<A
  href="https://ui.adsabs.harvard.edu/abs/2020Sci...368..518R/abstract">Reinhold
  et al. 2020</A>). Some of these stars even show very regular,
  sine-like light curves. Motivated by solar activity complexes, we
  developed a numerical model to quantify the effect of active-region (AR)
  nesting and active longitudes on stellar brightness variations in the
  rotational time scale. Modelling ARs with facular and spot components,
  we simulated light curves covering four years and using the Kepler
  passband. We found that the combined effect of the degree of nesting
  and the activity level, both being somewhat higher than on the Sun,
  can explain the whole range of observed light-curve amplitudes of
  solar-like stars. While nesting at random longitudes can explain
  variability amplitudes and light-curve morphology in many cases,
  active-longitude-type nesting reproduces sine-like light curves and
  the highest amplitude variability.

Title: Modelling Solar Ca II H&amp;K Emission Variations
Authors: Krishnamurthy, Sowmya; Shapiro, Alexander I.; Witzke,
   Veronika; Nèmec, Nina-E.; Chatzistergos, Theodosis; Yeo, Kok Leng;
   Krivova, Natalie A.; Solanki, Sami K.
Bibcode: 2021csss.confE.154K
Altcode:
  The emission in the near ultraviolet Ca II H&amp;K lines, often
  quantified via the S-index, has been serving as a prime proxy of solar
  and stellar magnetic activity. Despite the broad usage of the S-index,
  the link between the coverage of a stellar disk by magnetic features
  and Ca II H&amp;K emission is not fully understood. In order to fill
  this gap we developed a physics-based model to calculate the solar
  S-index. To this end, we made use of the distributions of the solar
  magnetic features derived from the simulations of magnetic flux
  emergence and surface transport, together with the Ca II H&amp;K
  spectra synthesized using a non-local thermodynamic equilibrium
  (non-LTE) radiative transfer code.We show that the value of the
  solar S-index is influenced by the inclination angle between the
  solar rotation axis and the observer's line-of-sight, i.e. the solar
  S-index values obtained by an out-of-ecliptic observer are different
  from those obtained by an ecliptic-bound observer. This is important
  for comparing the magnetic activity of the Sun to other stars. We
  computed time series of the S-index as they would be observed at
  various inclinations dating back to 1700. We find that depending on
  the inclination and period of observations, the activity cycle in solar
  S-index can appear weaker or stronger than in stars with a solar-like
  level of magnetic activity. We show that there is nothing unusual
  about the solar chromospheric emission variations in the context of
  stars with near-solar magnetic activity.

Title: Small-scale dynamo in an F-star: effects on near-surface
    stratification, convection and intensity
Authors: Bhatia, Tanayveer; Cameron, Robert; Solanki, Sami; Peter,
   Hardi; Przybylski, Damien; Witzke, Veronika; Shapiro, Alexander
Bibcode: 2021csss.confE..75B
Altcode:
  The emission from the photosphere of stars shows a systematic
  center-to-limb variation. In cool main-sequence stars, the near-surface
  convection has an impact on this variation, with implications for
  lightcurves of stars during planetary transits. In the Sun, there
  is strong evidence for a small-scale dynamo (SSD) maintaining the
  small-scale magnetic flux. We aim to investigate what additional
  effects such a field would play for other cool main-sequence
  stars. In our work we first concentrate on F-stars. This is because
  they have sonic velocities near the surface, implying a rough
  equipartition between internal and kinetic energies. In addition,
  an SSD might create a significant magnetic energy density to impact
  the results. We investigate the interplay between internal, kinetic
  and magnetic energies in 3D cartesian box MHD models of a F3V-star in
  the near-surface convection, using the MURaM radiative-MHD simulation
  code. Along with a reference hydrodynamic run, two MHD models with
  self-consistently generated magnetic fields with two different lower
  boundary conditions are considered. We find that the SSD process
  creates a magnetic field with energy within an order of magnitude of the
  internal and the kinetic energy. Compared to the hydrodynamic run, we
  find slight (~1-3%) but significant deviations in density, gas pressure
  and temperature stratification. At the surface, this corresponds to a
  temperature difference of ~130 K. As expected, there is a significant
  reduction in kinetic energy flux once the SSD is operational. The
  changes in intensity are more subtle, both in total intensity and
  granulation pattern. From this we conclude that the presence of an
  SSD will have a significant impact on the atmospheric structure and
  intensity characteristics seen at the surface. This makes it clear
  that it would be important to consider the spatially and temporally
  averaged effects of the SSD also for global stellar models.

Title: Sunspot Simulations: Penumbra Formation and the Fluting
    Instability
Authors: Panja, Mayukh; Cameron, Robert H.; Solanki, Sami K.
Bibcode: 2021ApJ...907..102P
Altcode: 2020arXiv201111447P
  The fluting instability has been suggested as the driver of the
  subsurface structure of sunspot flux tubes. We conducted a series
  of numerical experiments where we used flux tubes with different
  initial curvatures to study the effect of the fluting instability on
  the subsurface structure of spots. We used the MURaM code, which has
  previously been used to simulate complete sunspots, to first compute
  four sunspots in the slab geometry and then two complete circular
  spots of opposite polarities. We find that the curvature of a flux tube
  indeed determines the degree of fluting the flux tube will undergo—the
  more curved a flux tube is, the more fluted it becomes. In addition,
  sunspots with strong curvature have strong horizontal fields at the
  surface and therefore readily form penumbral filaments. The fluted
  sunspots eventually break up from below, with lightbridges appearing
  at the surface several hours after fluting commences.

Title: Predictions of Astrometric Jitter for Sun-like Stars. I. The
    Model and Its Application to the Sun as Seen from the Ecliptic
Authors: Shapiro, Alexander I.; Solanki, Sami K.; Krivova, Natalie A.
Bibcode: 2021ApJ...908..223S
Altcode: 2020arXiv201212312S
  The advent of Gaia, capable of measuring stellar wobbles caused
  by orbiting planets, raised interest in the astrometric detection
  of exoplanets. Another source of such wobbles (often also called
  jitter) is stellar magnetic activity. A quantitative assessment
  of the stellar astrometric jitter is important for a more reliable
  astrometric detection and characterization of exoplanets. We calculate
  the displacement of the solar photocenter due to the magnetic activity
  for an almost 16 yr period (1999 February 2-2014 August 1). We also
  investigate how the displacement depends on the spectral passband chosen
  for observations, including the wavelength range to be covered by the
  upcoming Small-JASMINE mission of JAXA. This is done by extending the
  SATIRE-S model for solar irradiance variability to calculating the
  displacement of the solar photocenter caused by the magnetic features
  on the surface of the Sun. We found that the peak-to-peak amplitude
  of the solar photocenter displacement would reach 0.5 μas if the
  Sun were located 10 pc away from the observer and observed in the
  Gaia G filter. This is by far too small to be detected by the Gaia
  mission. However, the Sun is a relatively inactive star so one can
  expect significantly larger signals for younger, and, consequently,
  more active stars. The model developed in this study can be combined
  with the simulations of emergence and surface transport of magnetic
  flux which have recently become available to model the astrometric
  jitter over the broad range of magnetic activities.

Title: Where Have All the Solar-like Stars Gone? Rotation Period
    Detectability at Various Inclinations and Metallicities
Authors: Reinhold, Timo; Shapiro, Alexander I.; Witzke, Veronika;
   Nèmec, Nina-E.; Işık, Emre; Solanki, Sami K.
Bibcode: 2021ApJ...908L..21R
Altcode: 2021arXiv210111426R
  The plethora of photometric data collected by the Kepler space telescope
  has promoted the detection of tens of thousands of stellar rotation
  periods. However, these periods are not found to an equal extent
  among different spectral types. Interestingly, early G-type stars with
  near-solar rotation periods are strongly underrepresented among those
  stars with known rotation periods. In this study we investigate whether
  the small number of such stars can be explained by difficulties in the
  period determination from photometric time series. For that purpose,
  we generate model light curves of early G-type stars with solar
  rotation periods for different inclination angles, metallicities, and
  (magnitude-dependent) noise levels. We find that the detectability is
  determined by the predominant type of activity (i.e., spot or faculae
  domination) on the surface, which defines the degree of irregularity
  of the light curve, and further depends on the level of photometric
  noise. These two effects significantly complicate the period detection
  and explain the lack of solar-like stars with known near-solar rotation
  periods. We conclude that the rotation periods of the majority of
  solar-like stars with near-solar rotation periods remain undetected
  to date. Finally, we promote the use of new techniques to recover more
  periods of near-solar rotators.

Title: Coronal Heating and Solar Wind Formation in Quiet Sun and
Coronal Holes: A Unified Scenario
Authors: Tripathi, Durgesh; Nived, V. N.; Solanki, Sami K.
Bibcode: 2021ApJ...908...28T
Altcode: 2020arXiv201109803T
  Coronal holes (CHs) are darker than the quiet Sun (QS) when observed
  in coronal channels. This study aims to understand the similarities
  and differences between CHs and QS in the transition region using
  the Si IV 1394 Å line, recorded by the Interface Region Imaging
  Spectrograph, by considering the distribution of magnetic field
  measured by the Helioseismic and Magnetic Imager on board the Solar
  Dynamics Observatory. We find that Si IV intensities obtained in CHs
  are lower than those obtained in QS for regions with identical magnetic
  flux densities. Moreover, the difference in intensities between CHs
  and QS increases with increasing magnetic flux. For the regions with
  equal magnetic flux density, QS line profiles are more redshifted
  than those measured in CHs. Moreover, the blueshifts measured in CHs
  show an increase with increasing magnetic flux density unlike in
  the QS. The non-thermal velocities in QS, as well as in CHs, show
  an increase with increasing magnetic flux. However, no significant
  difference was observed in QS and CHs, albeit a small deviation at
  small flux densities. Using these results, we propose a unified model
  for the heating of the corona in the QS and in CHs and the formation
  of solar wind.

Title: Vortex flow properties in simulations of solar plage region:
    Evidence for their role in chromospheric heating
Authors: Yadav, N.; Cameron, R. H.; Solanki, S. K.
Bibcode: 2021A&A...645A...3Y
Altcode: 2020arXiv201014971Y
  Context. Vortex flows exist across a broad range of spatial and
  temporal scales in the solar atmosphere. Small-scale vortices are
  thought to play an important role in energy transport in the solar
  atmosphere. However, their physical properties remain poorly understood
  due to the limited spatial resolution of the observations. <BR />
  Aims: We explore and analyze the physical properties of small-scale
  vortices inside magnetic flux tubes using numerical simulations, and
  investigate whether they contribute to heating the chromosphere in a
  plage region. <BR /> Methods: Using the three-dimensional radiative
  magnetohydrodynamic simulation code MURaM, we perform numerical
  simulations of a unipolar solar plage region. To detect and isolate
  vortices we use the swirling strength criterion and select the locations
  where the fluid is rotating with an angular velocity greater than
  a certain threshold. We concentrate on small-scale vortices as they
  are the strongest and carry most of the energy. We explore the spatial
  profiles of physical quantities such as density and horizontal velocity
  inside these vortices. Moreover, to learn their general characteristics,
  a statistical investigation is performed. <BR /> Results: Magnetic
  flux tubes have a complex filamentary substructure harboring an
  abundance of small-scale vortices. At the interfaces between vortices
  strong current sheets are formed that may dissipate and heat the solar
  chromosphere. Statistically, vortices have higher densities and higher
  temperatures than the average values at the same geometrical height
  in the chromosphere. <BR /> Conclusions: We conclude that small-scale
  vortices are ubiquitous in solar plage regions; they are denser and
  hotter structures that contribute to chromospheric heating, possibly
  by dissipation of the current sheets formed at their interfaces.

Title: Magnetic Imaging of the Outer Solar Atmosphere (MImOSA):
    Unlocking the driver of the dynamics in the upper solar atmosphere
Authors: Peter, H.; Alsina Ballester, E.; Andretta, V.; Auchere, F.;
   Belluzzi, L.; Bemporad, A.; Berghmans, D.; Buchlin, E.; Calcines, A.;
   Chitta, L. P.; Dalmasse, K.; del Pino Aleman, T.; Feller, A.; Froment,
   C.; Harrison, R.; Janvier, M.; Matthews, S.; Parenti, S.; Przybylski,
   D.; Solanki, S. K.; Stepan, J.; Teriaca, L.; Trujillo Bueno, J.
Bibcode: 2021arXiv210101566P
Altcode:
  The magnetic activity of the Sun directly impacts the Earth and human
  life. Likewise, other stars will have an impact on the habitability
  of planets orbiting these host stars. The lack of information on the
  magnetic field in the higher atmospheric layers hampers our progress in
  understanding solar magnetic activity. Overcoming this limitation would
  allow us to address four paramount long-standing questions: (1) How
  does the magnetic field couple the different layers of the atmosphere,
  and how does it transport energy? (2) How does the magnetic field
  structure, drive and interact with the plasma in the chromosphere and
  upper atmosphere? (3) How does the magnetic field destabilise the outer
  solar atmosphere and thus affect the interplanetary environment? (4)
  How do magnetic processes accelerate particles to high energies? New
  ground-breaking observations are needed to address these science
  questions. We suggest a suite of three instruments that far exceed
  current capabilities in terms of spatial resolution, light-gathering
  power, and polarimetric performance: (a) A large-aperture UV-to-IR
  telescope of the 1-3 m class aimed mainly to measure the magnetic
  field in the chromosphere by combining high spatial resolution and high
  sensitivity. (b) An extreme-UV-to-IR coronagraph that is designed to
  measure the large-scale magnetic field in the corona with an aperture
  of about 40 cm. (c) An extreme-UV imaging polarimeter based on a 30
  cm telescope that combines high throughput in the extreme UV with
  polarimetry to connect the magnetic measurements of the other two
  instruments. This mission to measure the magnetic field will unlock
  the driver of the dynamics in the outer solar atmosphere and thereby
  greatly advance our understanding of the Sun and the heliosphere.

Title: Sunrise Chromospheric Infrared spectroPolarimeter (SCIP)
for SUNRISE III: optical design and performance
Authors: Tsuzuki, Toshihiro; Katsukawa, Yukio; Uraguchi, Fumihiro;
   Hara, Hirohisa; Kubo, Masahito; Nodomi, Yoshifumi; Suematsu, Yoshinori;
   Kawabata, Yusuke; Shimizu, Toshifumi; Gandorfer, Achim; Feller, Alex;
   Grauf, Bianca; Solanki, Sami; Carlos del Toro Iniesta, Jose
Bibcode: 2020SPIE11447E..AJT
Altcode:
  The Sunrise Chromospheric Infrared spectroPolarimeter (SCIP) is a
  near-IR spectro-polarimeter instrument newly designed for Sunrise III,
  which is a balloon-borne solar observatory equipped with a 1 m optical
  telescope. To acquire high-quality 3D magnetic and velocity fields,
  SCIP selects the two wavelength bands centered at 850 nm and 770 nm,
  which contain many spectrum lines that are highly sensitive to magnetic
  fields permeating the photosphere and chromosphere. To achieve high
  spatial and spectral resolution (0.21 arcsec and 2 × 10<SUP>5</SUP>),
  SCIP optics adopt a quasi-Littrow configuration based on an echelle
  grating and two high-order aspheric mirrors. Using different diffraction
  orders of the echelle grating, dichroic beam splitter, and polarizing
  beam-splitters, SCIP can obtain s- and p-polarization signals in the
  two wavelength bands simultaneously within a relatively small space. We
  established the wavefront error budget based on tolerance analysis,
  surface figure errors, alignment errors, and environmental changes. In
  addition, we performed stray light analysis, and designed light traps
  and baffles needed to suppress unwanted reflections and diffraction
  by the grating. In this paper, we present the details of this optical
  system and its performance.

Title: Reconstructing solar irradiance from Ca II K observations
Authors: Chatzistergos, T.; Krivova, N.; Ermolli, I.; Yeo, K. L.;
   Solanki, S. K.; Puiu, C. C.; Giorgi, F.; Mandal, S.
Bibcode: 2020AGUFMA237...10C
Altcode:
  To understand the influence of the Sun on Earth's system, long and
  accurate measurements of solar irradiance are a prerequisite. The
  available direct measurements of solar irradiance since 1978 are
  clearly not sufficient for this purpose. This stimulated development
  of models used to reconstruct past solar irradiance variations from
  alternative observations. The main driver of the irradiance variations
  on time scales of days to millennia is the evolution of the solar
  surface magnetic field in form of dark sunspots and bright faculae
  and network. Therefore, models require input data describing the
  contributions of these various magnetic regions on the Sun at earlier
  times. Unfortunately, records that can be used to describe the facular
  and network contributions are barely longer than the direct irradiance
  measurements. Thus, irradiance reconstructions to earlier periods have
  to rely on sunspot data alone. Data that have hardly been used for solar
  irradiance reconstructions until now are full-disc solar observations in
  the Ca II K line. Such data exist since 1892 from various observatories
  and include all the needed information describing faculae and the
  network. However, they are plagued by a bunch of various problems and
  artefacts, and recovering the non-linear response of the photographic
  material to the radiation is non-trivial since the required information
  is usually missing, too. We have developed a method to process Ca II K
  observations from various sources and demonstrated the higher accuracy
  achieved by our method compared to other techniques presented in the
  literature. Here we use the carefully reduced Ca II K observations
  from multiple archives to reconstruct solar irradiance variations.

Title: Erratum: "Amplification of Brightness Variability by
    Active-region Nesting in Solar-like Stars" (2020, ApJL, 901, L12)
Authors: Işık, Emre; Shapiro, Alexander I.; Solanki, Sami K.;
   Krivova, Natalie A.
Bibcode: 2020ApJ...905L..36I
Altcode:
  No abstract at ADS

Title: The magnetic fine structure of the Sun's polar region as
    revealed by Sunrise
Authors: Prabhu, A.; Lagg, A.; Hirzberger, J.; Solanki, S. K.
Bibcode: 2020A&A...644A..86P
Altcode:
  Context. Polar magnetic fields play a key role in the solar magnetic
  cycle and they are the source of a significant portion of the
  interplanetary magnetic field. However, observations of the poles
  are challenging and hence our understanding of the polar magnetic
  environment is incomplete. <BR /> Aims: We deduce properties of
  small-scale magnetic features in the polar region using high-resolution
  data and specifically aim to determine the flux per patch above which
  one magnetic polarity starts to dominate over the other. <BR /> Methods:
  We study the high spatial resolution, seeing-free observations of the
  north solar polar region, obtained with the IMaX instrument on-board
  the balloon-borne SUNRISE observatory during June 2009, at the solar
  activity minimum. We performed inversions of the full Stokes vector
  recorded by IMaX to retrieve atmospheric parameters of the Sun's
  polar region, mainly the temperature stratification and the magnetic
  field vector. <BR /> Results: We infer kilo-Gauss (kG) magnetic fields
  in patches harbouring polar faculae, without resorting to a magnetic
  filling factor. Within these patches we find the maxima of the magnetic
  field to be near the dark narrow lanes, which are shifted towards the
  disc centre side in comparison to the maxima in continuum intensity. In
  contrast, we did not find any fields parallel to the solar surface
  with kG strengths. In addition to the kG patches, we found the polar
  region to be covered in patches of both polarities, which have a range
  of sizes. We find the field strength of these patches to increase with
  increasing size and flux, with the smaller patches showing a significant
  dispersion in field strength. The dominating polarity of the north
  pole during this phase of the solar cycle is found to be maintained
  by the larger patches with fluxes above 2.3 × 10<SUP>17</SUP> Mx.

Title: Multi-view magnetic synoptic maps with SO/PHI and SDO/HMI
Authors: Löschl, P.; Hirzberger, J.; Schou, J.; Solanki, S. K.
Bibcode: 2020AGUFMSH0360028L
Altcode:
  With the recent launch of Solar Orbiter (SO) and the first data slowly
  becoming available, it will soon be possible to simultaneously observe
  the Sun from additional vantage points off the Earth-Sun line. One
  of its instruments, the Polarimetric and Heliospheric Imager (PHI),
  is the first spectro-polarimeter to operate outside of this line of
  sight. This opens the possibility for joint observational campaigns
  with similar instruments, such as the Heliospheric and Magnetic Imager
  (HMI) on-board the Solar Dynamics Observatory (SDO). We utilise these
  new observational possibilities to produce combined magnetic synoptic
  maps from magnetograms of the PHI and HMI instruments. Building on the
  existing software infrastructure for HMI synoptic maps, we extended
  its current functionality to include PHI data and correct for the
  different and varying relative orbital characteristics of the two
  spacecraft. The result are joint magnetic synoptic maps, that can
  be produced significantly faster than the approximately 27 days of
  one solar rotation and therefore are less likely to suffer from the
  evolution of the magnetic field over the observation period. Once Solar
  Orbiter leaves the ecliptic plane, we will also be able to include
  observations of the polar magnetic field into our synoptic maps,
  which will give an unprecedented insight into the magnetic field of
  the Sun. This work presents our preparatory modelling efforts and
  gives an outlook for the future capabilities of this novel data product.

Title: First results from SO/PHI's on-board data reduction
Authors: Albert, K.; Hirzberger, J.; Kolleck, M.; Albelo Jorge,
   N.; Busse, D.; Blanco Rodriguez, J.; Cobos Carrascosa, J. P.;
   Fiethe, B.; Gandorfer, A.; Germerott, D.; Guan, Y.; Guerrero, L.;
   Gutierrez-Marques, P.; Hernández Expósito, D.; Lange, T.; Michalik,
   H.; Orozco Suárez, D.; Schou, J.; Solanki, S. K.; Woch, J. G.
Bibcode: 2020AGUFMSH038..05A
Altcode:
  The Polarimetric and Helioseismic Imager (PHI), on-board Solar
  Orbiter (SO), is a spectropolarimeter imaging the solar photosphere
  at the wavelengths of the Fe I 617.3 nm Zeeman sensitive absorption
  line. SO/PHI's aim is to provide data about the magnetic structures and
  the line-of-sight (LOS) velocity in the solar atmosphere. For this, it
  takes time series of data sets consisting of 2048 x 2048 pixel images of
  the Sun at 6 wavelengths, each in 4 different polarisation states. With
  the minimum necessary 17 bits pixel depth, one data set amounts to
  approx. 0.2 GB. The guaranteed data telemetry for PHI, in contrast,
  is only 50 GiB/orbit which would also need to contain any calibration
  data obtained on-board, i.e. our flat and dark fields. To cope with
  this discrepancy, SO/PHI is performing full data reduction on-board,
  including the inversion of the radiative transfer equation. The
  downloaded results are science ready data, containing 5 final images: a
  total intensity image from nearby the spectral line, the magnetic field
  strength, azimuth and inclination (describing the magnetic vector) and
  the LOS velocity. This process maximises the science return by reducing
  the number of necessary images in a data set, as well as rendering the
  download of calibration data unessential. In the commissioning phase
  of SO/PHI we used the on-board data reduction system successfully
  for the first time. We have calibrated the instrument to its optimal
  operational parameters (calculation of exposure time, focus, etc.),
  acquired and processed calibration data (dark and flat fields),
  removed the most significant instrumental artefacts from the data
  (dark field, flat field, polarimetric modulation and polarimetric
  cross-talk), and performed the inversion of the radiative transfer
  equation. The data have then been compressed to further maximise the
  use of our telemetry. This contribution presents and discusses the
  final results from this process.

Title: Power spectrum of turbulent convection in the solar photosphere
Authors: Yelles Chaouche, L.; Cameron, R. H.; Solanki, S. K.;
   Riethmüller, T. L.; Anusha, L. S.; Witzke, V.; Shapiro, A. I.;
   Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; van Noort,
   M.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.; Orozco Suárez,
   D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
Bibcode: 2020A&A...644A..44Y
Altcode: 2020arXiv201009037Y
  The solar photosphere provides us with a laboratory for understanding
  turbulence in a layer where the fundamental processes of transport
  vary rapidly and a strongly superadiabatic region lies very closely
  to a subadiabatic layer. Our tools for probing the turbulence are
  high-resolution spectropolarimetric observations such as have recently
  been obtained with the two balloon-borne SUNRISE missions, and numerical
  simulations. Our aim is to study photospheric turbulence with the
  help of Fourier power spectra that we compute from observations
  and simulations. We also attempt to explain some properties of the
  photospheric overshooting flow with the help of its governing equations
  and simulations. We find that quiet-Sun observations and smeared
  simulations are consistent with each other and exhibit a power-law
  behavior in the subgranular range of their Doppler velocity power
  spectra with a power-law index of ≈ - 2. The unsmeared simulations
  exhibit a power law that extends over the full range between the
  integral and Taylor scales with a power-law index of ≈ - 2.25. The
  smearing, reminiscent of observational conditions, considerably reduces
  the extent of the power-law-like portion of the power spectra. This
  suggests that the limited spatial resolution in some observations
  might eventually result in larger uncertainties in the estimation of
  the power-law indices. The simulated vertical velocity power spectra
  as a function of height show a rapid change in the power-law index
  (at the subgranular range) from roughly the optical depth unity layer,
  that is, the solar surface, to 300 km above it. We propose that the
  cause of the steepening of the power-law index is the transition from
  a super- to a subadiabatic region, in which the dominant source of
  motions is overshooting convection. A scale-dependent transport of
  the vertical momentum occurs. At smaller scales, the vertical momentum
  is more efficiently transported sideways than at larger scales. This
  results in less vertical velocity power transported upward at small
  scales than at larger scales and produces a progressively steeper
  vertical velocity power law below 180 km. Above this height, the
  gravity work progressively gains importance at all relevant scales,
  making the atmosphere progressively more hydrostatic and resulting
  in a gradually less steep power law. Radiative heating and cooling of
  the plasma is shown to play a dominant role in the plasma energetics
  in this region, which is important in terms of nonadiabatic damping
  of the convective motions.

Title: The SUNRISE UV Spectropolarimeter and imager for SUNRISE III
Authors: Feller, Alex; Gandorfer, Achim; Iglesias, Francisco A.;
   Lagg, Andreas; Riethmüller, Tino L.; Solanki, Sami K.; Katsukawa,
   Yukio; Kubo, Masahito
Bibcode: 2020SPIE11447E..AKF
Altcode:
  Sunrise is a balloon-borne solar observatory dedicated to the
  investigation of key processes of the magnetic field and the plasma
  flows in the lower solar atmosphere. The observatory operates in
  the stratosphere at an altitude of around 37 km in order to avoid
  image degradation due to turbulence in the Earth's atmosphere and to
  access the UV range. The third science flight of Sunrise will carry new
  instrumentation which samples the solar spectrum over a broad wavelength
  domain from the UV to the near IR and covers an extended height range in
  the solar atmosphere. A key feature of the Sunrise UV Spectropolarimeter
  and Imager (SUSI) operating between 309 nm and 417 nm, is its capability
  to simultaneously record a large number of spectral lines. By combining
  the spectral and polarization information of many individual lines
  with different formation heights and sensitivities, the accuracy and
  the height resolution of the inferred atmospheric parameters can be
  significantly increased. The spectral bands of SUSI are selected one
  at a time by rotating a diffraction grating with respect to a fixed
  polarimetry unit. The spatial and spectral field of view on the 2k x
  2k cameras is 59" and 2.0 - 2.3 nm, respectively. A further innovation
  is the numerical restoration of the spectrograph scans by means of
  synchronized 2D context imaging, a technique that has recently produced
  impressive results at ground-based solar observatories.

Title: The Solar-C (EUVST) mission: the latest status
Authors: Shimizu, Toshifumi; Imada, Shinsuke; Kawate, Tomoko; Suematsu,
   Yoshinori; Hara, Hirohisa; Tsuzuki, Toshihiro; Katsukawa, Yukio; Kubo,
   Masahito; Ishikawa, Ryoko; Watanabe, Tetsuya; Toriumi, Shin; Ichimoto,
   Kiyoshi; Nagata, Shin'ichi; Hasegawa, Takahiro; Yokoyama, Takaaki;
   Watanabe, Kyoko; Tsuno, Katsuhiko; Korendyke, Clarence M.; Warren,
   Harry; De Pontieu, Bart; Boerner, Paul; Solanki, Sami K.; Teriaca,
   Luca; Schuehle, Udo; Matthews, Sarah; Long, David; Thomas, William;
   Hancock, Barry; Reid, Hamish; Fludra, Andrzej; Auchère, Frederic;
   Andretta, Vincenzo; Naletto, Giampiero; Poletto, Luca; Harra, Louise
Bibcode: 2020SPIE11444E..0NS
Altcode:
  Solar-C (EUVST) is the next Japanese solar physics mission to
  be developed with significant contributions from US and European
  countries. The mission carries an EUV imaging spectrometer with
  slit-jaw imaging system called EUVST (EUV High-Throughput Spectroscopic
  Telescope) as the mission payload, to take a fundamental step towards
  answering how the plasma universe is created and evolves and how the
  Sun influences the Earth and other planets in our solar system. In
  April 2020, ISAS (Institute of Space and Astronautical Science) of JAXA
  (Japan Aerospace Exploration Agency) has made the final down-selection
  for this mission as the 4th in the series of competitively chosen
  M-class mission to be launched with an Epsilon launch vehicle in mid
  2020s. NASA (National Aeronautics and Space Administration) has selected
  this mission concept for Phase A concept study in September 2019 and
  is in the process leading to final selection. For European countries,
  the team has (or is in the process of confirming) confirmed endorsement
  for hardware contributions to the EUVST from the national agencies. A
  recent update to the mission instrumentation is to add a UV spectral
  irradiance monitor capability for EUVST calibration and scientific
  purpose. This presentation provides the latest status of the mission
  with an overall description of the mission concept emphasizing on key
  roles of the mission in heliophysics research from mid 2020s.

Title: Sunrise Chromospheric Infrared SpectroPolarimeter (SCIP)
for sunrise III: system design and capability
Authors: Katsukawa, Y.; del Toro Iniesta, J. C.; Solanki, S. K.;
   Kubo, M.; Hara, H.; Shimizu, T.; Oba, T.; Kawabata, Y.; Tsuzuki,
   T.; Uraguchi, F.; Nodomi, Y.; Shinoda, K.; Tamura, T.; Suematsu,
   Y.; Ishikawa, R.; Kano, R.; Matsumoto, T.; Ichimoto, K.; Nagata, S.;
   Quintero Noda, C.; Anan, T.; Orozco Suárez, D.; Balaguer Jiménez,
   M.; López Jiménez, A. C.; Cobos Carrascosa, J. P.; Feller, A.;
   Riethmueller, T.; Gandorfer, A.; Lagg, A.
Bibcode: 2020SPIE11447E..0YK
Altcode:
  The Sunrise balloon-borne solar observatory carries a 1 m aperture
  optical telescope and provides us a unique platform to conduct
  continuous seeing-free observations at UV-visible-IR wavelengths from
  an altitude of higher than 35 km. For the next flight planned for
  2022, the post-focus instrumentation is upgraded with new spectro-
  polarimeters for the near UV (SUSI) and the near-IR (SCIP), whereas
  the imaging spectro-polarimeter Tunable Magnetograph (TuMag) is capable
  of observing multiple spectral lines within the visible wavelength. A
  new spectro-polarimeter called the Sunrise Chromospheric Infrared
  spectroPolarimeter (SCIP) is under development for observing near-IR
  wavelength ranges of around 770 nm and 850 nm. These wavelength ranges
  contain many spectral lines sensitive to solar magnetic fields and
  SCIP will be able to obtain magnetic and velocity structures in the
  solar atmosphere with a sufficient height resolution by combining
  spectro-polarimetric data of these lines. Polarimetric measurements are
  conducted using a rotating waveplate as a modulator and polarizing beam
  splitters in front of the cameras. The spatial and spectral resolutions
  are 0.2" and 2 105, respectively, and a polarimetric sensitivity of
  0.03 % (1σ) is achieved within a 10 s integration time. To detect
  minute polarization signals with good precision, we carefully designed
  the opto-mechanical system, polarization optics and modulation, and
  onboard data processing.

Title: Reconstructing solar irradiance from Ca II K observations
Authors: Chatzistergos, Theodosios; Krivova, Natalie A.; Ermolli,
   Ilaria; Leng Yeo, Kok; Solanki, Sami K.; Puiu, Cosmin C.; Giorgi,
   Fabrizio; Mandal, Sudip
Bibcode: 2020AGUFM.A237..10C
Altcode:
  To understand the influence of the Sun on Earth's system, long and
  accurate measurements of solar irradiance are a prerequisite. The
  available direct measurements of solar irradiance since 1978 are
  clearly not sufficient for this purpose. This stimulated development
  of models used to reconstruct past solar irradiance variations from
  alternative observations. The main driver of the irradiance variations
  on time scales of days to millennia is the evolution of the solar
  surface magnetic field in form of dark sunspots and bright faculae
  and network. Therefore, models require input data describing the
  contributions of these various magnetic regions on the Sun at earlier
  times. Unfortunately, records that can be used to describe the facular
  and network contributions are barely longer than the direct irradiance
  measurements. Thus, irradiance reconstructions to earlier periods have
  to rely on sunspot data alone. Data that have hardly been used for solar
  irradiance reconstructions until now are full-disc solar observations in
  the Ca II K line. Such data exist since 1892 from various observatories
  and include all the needed information describing faculae and the
  network. However, they are plagued by a bunch of various problems and
  artefacts, and recovering the non-linear response of the photographic
  material to the radiation is non-trivial since the required information
  is usually missing, too. We have developed a method to process Ca II K
  observations from various sources and demonstrated the higher accuracy
  achieved by our method compared to other techniques presented in the
  literature. Here we use the carefully reduced Ca II K observations
  from multiple archives to reconstruct solar irradiance variations.

Title: Solar Orbiter: connecting remote sensing and in situ
    measurements
Authors: Horbury, T. S.; Auchere, F.; Antonucci, E.; Berghmans, D.;
   Bruno, R.; Carlsson, M.; del Toro Iniesta, J. C.; Fludra, A.; Harra,
   L.; Hassler, D.; Heinzel, P.; Howard, R. A.; Krucker, S.; Livi, S. A.;
   Long, D.; Louarn, P.; Maksimovic, M.; Mueller, D.; Owen, C. J.; Peter,
   H.; Rochus, P. L.; Rodriguez-Pacheco, J.; Romoli, M.; Schühle, U.;
   Solanki, S. K.; Teriaca, L.; Wimmer-Schweingruber, R. F.; Zouganelis,
   Y.; Laker, R.
Bibcode: 2020AGUFMSH038..10H
Altcode:
  A key science goal of the Solar Orbiter mission is to make connections
  between phenomena on the Sun and their manifestations in interplanetary
  space. To that end, the spacecraft carries a carefully tailored
  payload of six remote sensing instruments and four making in situ
  measurements. During June 2020, while the spacecraft was around 0.5
  AU from the Sun, the remote sensing instruments operated for several
  days. While this was primarily an engineering activity, the resulting
  observations provided outstanding measurements and represent the ideal
  first opportunity to investigate the potential for making connections
  between the remote sensing and in situ payloads on Solar Orbiter. <P
  />We present a preliminary analysis of the available remote sensing and
  in situ observations, showing how connections can be made, and discuss
  the potential for further, more precise mapping to be performed as
  the mission progresses.

Title: Impulsive coronal heating during the interaction of surface
    magnetic fields in the lower solar atmosphere
Authors: Chitta, L. P.; Peter, H.; Priest, E. R.; Solanki, S. K.
Bibcode: 2020A&A...644A.130C
Altcode: 2020arXiv201012560C
  Coronal plasma in the cores of solar active regions is impulsively
  heated to more than 5 MK. The nature and location of the magnetic
  energy source responsible for such impulsive heating is poorly
  understood. Using observations of seven active regions from the Solar
  Dynamics Observatory, we found that a majority of coronal loops hosting
  hot plasma have at least one footpoint rooted in regions of interacting
  mixed magnetic polarity at the solar surface. In cases when co-temporal
  observations from the Interface Region Imaging Spectrograph space
  mission are available, we found spectroscopic evidence for magnetic
  reconnection at the base of the hot coronal loops. Our analysis suggests
  that interactions of magnetic patches of opposite polarity at the
  solar surface and the associated energy release during reconnection
  are key to impulsive coronal heating. <P />Movies are available at <A
  href="https://www.aanda.org/10.1051/0004-6361/202039099/olm">https://www.aanda.org</A>

Title: How faculae and network relate to sunspots, and the
    implications for solar and stellar brightness variations(Corrigendum)
Authors: Yeo, K. L.; Solanki, S. K.; Krivova, N. A.
Bibcode: 2020A&A...642C...2Y
Altcode:
  No abstract at ADS

Title: VizieR Online Data Catalog: Faculae-Spot dominance &amp;
    rotation periods (Amazo-Gomez+, 2020)
Authors: Amazo-Gomez, E. M.; Shapiro, A. I.; Solanki, S. K.; Kopp,
   G.; Oshagh, M.; Reinhold, T.; Reiners, A.
Bibcode: 2020yCat..36420225A
Altcode:
  This table contains an example of the GPS outputs, the compared
  rotation period values from GLS and ACF, and stellar parameters for
  Kepler stars. <P />In column 4 and 5 values of alpha-factor and its
  2-sigma uncertainty are reported respectively. Prot GPS values in
  column 6, as result of applying Eq. 1 using the factor alpha=0.19. 2)
  Column 7 shows the Prot reported by Reinhold &amp; Gizon (2015,
  Cat. J/A+A/583/A65). 3) Prot and variability values reported by
  McQuillan et al. (2014, Cat. J/ApJS/211/24) in column 8. 4) Columns
  10, 11 and 12 show the logg, [Fe/H], and Teff respectively, taken from
  Huber et al. (2014, Cat J/ApJS/211/2). <P />(1 data file).

Title: Coordination within the remote sensing payload on the Solar
    Orbiter mission
Authors: Auchère, F.; Andretta, V.; Antonucci, E.; Bach, N.;
   Battaglia, M.; Bemporad, A.; Berghmans, D.; Buchlin, E.; Caminade,
   S.; Carlsson, M.; Carlyle, J.; Cerullo, J. J.; Chamberlin, P. C.;
   Colaninno, R. C.; Davila, J. M.; De Groof, A.; Etesi, L.; Fahmy,
   S.; Fineschi, S.; Fludra, A.; Gilbert, H. R.; Giunta, A.; Grundy,
   T.; Haberreiter, M.; Harra, L. K.; Hassler, D. M.; Hirzberger, J.;
   Howard, R. A.; Hurford, G.; Kleint, L.; Kolleck, M.; Krucker, S.;
   Lagg, A.; Landini, F.; Long, D. M.; Lefort, J.; Lodiot, S.; Mampaey,
   B.; Maloney, S.; Marliani, F.; Martinez-Pillet, V.; McMullin, D. R.;
   Müller, D.; Nicolini, G.; Orozco Suarez, D.; Pacros, A.; Pancrazzi,
   M.; Parenti, S.; Peter, H.; Philippon, A.; Plunkett, S.; Rich, N.;
   Rochus, P.; Rouillard, A.; Romoli, M.; Sanchez, L.; Schühle, U.;
   Sidher, S.; Solanki, S. K.; Spadaro, D.; St Cyr, O. C.; Straus, T.;
   Tanco, I.; Teriaca, L.; Thompson, W. T.; del Toro Iniesta, J. C.;
   Verbeeck, C.; Vourlidas, A.; Watson, C.; Wiegelmann, T.; Williams,
   D.; Woch, J.; Zhukov, A. N.; Zouganelis, I.
Bibcode: 2020A&A...642A...6A
Altcode:
  Context. To meet the scientific objectives of the mission, the Solar
  Orbiter spacecraft carries a suite of in-situ (IS) and remote sensing
  (RS) instruments designed for joint operations with inter-instrument
  communication capabilities. Indeed, previous missions have shown that
  the Sun (imaged by the RS instruments) and the heliosphere (mainly
  sampled by the IS instruments) should be considered as an integrated
  system rather than separate entities. Many of the advances expected
  from Solar Orbiter rely on this synergistic approach between IS and
  RS measurements. <BR /> Aims: Many aspects of hardware development,
  integration, testing, and operations are common to two or more
  RS instruments. In this paper, we describe the coordination effort
  initiated from the early mission phases by the Remote Sensing Working
  Group. We review the scientific goals and challenges, and give an
  overview of the technical solutions devised to successfully operate
  these instruments together. <BR /> Methods: A major constraint for the
  RS instruments is the limited telemetry (TM) bandwidth of the Solar
  Orbiter deep-space mission compared to missions in Earth orbit. Hence,
  many of the strategies developed to maximise the scientific return from
  these instruments revolve around the optimisation of TM usage, relying
  for example on onboard autonomy for data processing, compression,
  and selection for downlink. The planning process itself has been
  optimised to alleviate the dynamic nature of the targets, and an
  inter-instrument communication scheme has been implemented which can
  be used to autonomously alter the observing modes. We also outline the
  plans for in-flight cross-calibration, which will be essential to the
  joint data reduction and analysis. <BR /> Results: The RS instrument
  package on Solar Orbiter will carry out comprehensive measurements
  from the solar interior to the inner heliosphere. Thanks to the close
  coordination between the instrument teams and the European Space
  Agency, several challenges specific to the RS suite were identified
  and addressed in a timely manner.

Title: Models and data analysis tools for the Solar Orbiter mission
Authors: Rouillard, A. P.; Pinto, R. F.; Vourlidas, A.; De Groof, A.;
   Thompson, W. T.; Bemporad, A.; Dolei, S.; Indurain, M.; Buchlin, E.;
   Sasso, C.; Spadaro, D.; Dalmasse, K.; Hirzberger, J.; Zouganelis, I.;
   Strugarek, A.; Brun, A. S.; Alexandre, M.; Berghmans, D.; Raouafi,
   N. E.; Wiegelmann, T.; Pagano, P.; Arge, C. N.; Nieves-Chinchilla,
   T.; Lavarra, M.; Poirier, N.; Amari, T.; Aran, A.; Andretta, V.;
   Antonucci, E.; Anastasiadis, A.; Auchère, F.; Bellot Rubio, L.;
   Nicula, B.; Bonnin, X.; Bouchemit, M.; Budnik, E.; Caminade, S.;
   Cecconi, B.; Carlyle, J.; Cernuda, I.; Davila, J. M.; Etesi, L.;
   Espinosa Lara, F.; Fedorov, A.; Fineschi, S.; Fludra, A.; Génot,
   V.; Georgoulis, M. K.; Gilbert, H. R.; Giunta, A.; Gomez-Herrero, R.;
   Guest, S.; Haberreiter, M.; Hassler, D.; Henney, C. J.; Howard, R. A.;
   Horbury, T. S.; Janvier, M.; Jones, S. I.; Kozarev, K.; Kraaikamp,
   E.; Kouloumvakos, A.; Krucker, S.; Lagg, A.; Linker, J.; Lavraud,
   B.; Louarn, P.; Maksimovic, M.; Maloney, S.; Mann, G.; Masson, A.;
   Müller, D.; Önel, H.; Osuna, P.; Orozco Suarez, D.; Owen, C. J.;
   Papaioannou, A.; Pérez-Suárez, D.; Rodriguez-Pacheco, J.; Parenti,
   S.; Pariat, E.; Peter, H.; Plunkett, S.; Pomoell, J.; Raines, J. M.;
   Riethmüller, T. L.; Rich, N.; Rodriguez, L.; Romoli, M.; Sanchez,
   L.; Solanki, S. K.; St Cyr, O. C.; Straus, T.; Susino, R.; Teriaca,
   L.; del Toro Iniesta, J. C.; Ventura, R.; Verbeeck, C.; Vilmer, N.;
   Warmuth, A.; Walsh, A. P.; Watson, C.; Williams, D.; Wu, Y.; Zhukov,
   A. N.
Bibcode: 2020A&A...642A...2R
Altcode:
  Context. The Solar Orbiter spacecraft will be equipped with a wide
  range of remote-sensing (RS) and in situ (IS) instruments to record
  novel and unprecedented measurements of the solar atmosphere and
  the inner heliosphere. To take full advantage of these new datasets,
  tools and techniques must be developed to ease multi-instrument and
  multi-spacecraft studies. In particular the currently inaccessible
  low solar corona below two solar radii can only be observed
  remotely. Furthermore techniques must be used to retrieve coronal
  plasma properties in time and in three dimensional (3D) space. Solar
  Orbiter will run complex observation campaigns that provide interesting
  opportunities to maximise the likelihood of linking IS data to their
  source region near the Sun. Several RS instruments can be directed
  to specific targets situated on the solar disk just days before
  data acquisition. To compare IS and RS, data we must improve our
  understanding of how heliospheric probes magnetically connect to the
  solar disk. <BR /> Aims: The aim of the present paper is to briefly
  review how the current modelling of the Sun and its atmosphere
  can support Solar Orbiter science. We describe the results of a
  community-led effort by European Space Agency's Modelling and Data
  Analysis Working Group (MADAWG) to develop different models, tools,
  and techniques deemed necessary to test different theories for the
  physical processes that may occur in the solar plasma. The focus here
  is on the large scales and little is described with regards to kinetic
  processes. To exploit future IS and RS data fully, many techniques have
  been adapted to model the evolving 3D solar magneto-plasma from the
  solar interior to the solar wind. A particular focus in the paper is
  placed on techniques that can estimate how Solar Orbiter will connect
  magnetically through the complex coronal magnetic fields to various
  photospheric and coronal features in support of spacecraft operations
  and future scientific studies. <BR /> Methods: Recent missions such as
  STEREO, provided great opportunities for RS, IS, and multi-spacecraft
  studies. We summarise the achievements and highlight the challenges
  faced during these investigations, many of which motivated the Solar
  Orbiter mission. We present the new tools and techniques developed
  by the MADAWG to support the science operations and the analysis of
  the data from the many instruments on Solar Orbiter. <BR /> Results:
  This article reviews current modelling and tool developments that ease
  the comparison of model results with RS and IS data made available
  by current and upcoming missions. It also describes the modelling
  strategy to support the science operations and subsequent exploitation
  of Solar Orbiter data in order to maximise the scientific output
  of the mission. <BR /> Conclusions: The on-going community effort
  presented in this paper has provided new models and tools necessary
  to support mission operations as well as the science exploitation of
  the Solar Orbiter data. The tools and techniques will no doubt evolve
  significantly as we refine our procedure and methodology during the
  first year of operations of this highly promising mission.

Title: The Dimmest State of the Sun
Authors: Yeo, K. L.; Solanki, S. K.; Krivova, N. A.; Rempel, M.;
   Anusha, L. S.; Shapiro, A. I.; Tagirov, R. V.; Witzke, V.
Bibcode: 2020GeoRL..4790243Y
Altcode: 2021arXiv210209487Y
  How the solar electromagnetic energy entering the Earth's atmosphere
  varied since preindustrial times is an important consideration in
  the climate change debate. Detrimental to this debate, estimates
  of the change in total solar irradiance (TSI) since the Maunder
  minimum, an extended period of weak solar activity preceding the
  industrial revolution, differ markedly, ranging from a drop of 0.75
  W m<SUP>-2</SUP> to a rise of 6.3 W m<SUP>-2</SUP>. Consequently, the
  exact contribution by solar forcing to the rise in global temperatures
  over the past centuries remains inconclusive. Adopting a novel approach
  based on state-of-the-art solar imagery and numerical simulations, we
  establish the TSI level of the Sun when it is in its least-active state
  to be 2.0 ± 0.7 W m<SUP>-2</SUP> below the 2019 level. This means TSI
  could not have risen since the Maunder minimum by more than this amount,
  thus restricting the possible role of solar forcing in global warming.

Title: The Solar Orbiter Science Activity Plan. Translating solar
    and heliospheric physics questions into action
Authors: Zouganelis, I.; De Groof, A.; Walsh, A. P.; Williams, D. R.;
   Müller, D.; St Cyr, O. C.; Auchère, F.; Berghmans, D.; Fludra,
   A.; Horbury, T. S.; Howard, R. A.; Krucker, S.; Maksimovic, M.;
   Owen, C. J.; Rodríguez-Pacheco, J.; Romoli, M.; Solanki, S. K.;
   Watson, C.; Sanchez, L.; Lefort, J.; Osuna, P.; Gilbert, H. R.;
   Nieves-Chinchilla, T.; Abbo, L.; Alexandrova, O.; Anastasiadis, A.;
   Andretta, V.; Antonucci, E.; Appourchaux, T.; Aran, A.; Arge, C. N.;
   Aulanier, G.; Baker, D.; Bale, S. D.; Battaglia, M.; Bellot Rubio,
   L.; Bemporad, A.; Berthomier, M.; Bocchialini, K.; Bonnin, X.; Brun,
   A. S.; Bruno, R.; Buchlin, E.; Büchner, J.; Bucik, R.; Carcaboso,
   F.; Carr, R.; Carrasco-Blázquez, I.; Cecconi, B.; Cernuda Cangas, I.;
   Chen, C. H. K.; Chitta, L. P.; Chust, T.; Dalmasse, K.; D'Amicis, R.;
   Da Deppo, V.; De Marco, R.; Dolei, S.; Dolla, L.; Dudok de Wit, T.;
   van Driel-Gesztelyi, L.; Eastwood, J. P.; Espinosa Lara, F.; Etesi,
   L.; Fedorov, A.; Félix-Redondo, F.; Fineschi, S.; Fleck, B.; Fontaine,
   D.; Fox, N. J.; Gandorfer, A.; Génot, V.; Georgoulis, M. K.; Gissot,
   S.; Giunta, A.; Gizon, L.; Gómez-Herrero, R.; Gontikakis, C.; Graham,
   G.; Green, L.; Grundy, T.; Haberreiter, M.; Harra, L. K.; Hassler,
   D. M.; Hirzberger, J.; Ho, G. C.; Hurford, G.; Innes, D.; Issautier,
   K.; James, A. W.; Janitzek, N.; Janvier, M.; Jeffrey, N.; Jenkins,
   J.; Khotyaintsev, Y.; Klein, K. -L.; Kontar, E. P.; Kontogiannis,
   I.; Krafft, C.; Krasnoselskikh, V.; Kretzschmar, M.; Labrosse, N.;
   Lagg, A.; Landini, F.; Lavraud, B.; Leon, I.; Lepri, S. T.; Lewis,
   G. R.; Liewer, P.; Linker, J.; Livi, S.; Long, D. M.; Louarn, P.;
   Malandraki, O.; Maloney, S.; Martinez-Pillet, V.; Martinovic, M.;
   Masson, A.; Matthews, S.; Matteini, L.; Meyer-Vernet, N.; Moraitis,
   K.; Morton, R. J.; Musset, S.; Nicolaou, G.; Nindos, A.; O'Brien,
   H.; Orozco Suarez, D.; Owens, M.; Pancrazzi, M.; Papaioannou, A.;
   Parenti, S.; Pariat, E.; Patsourakos, S.; Perrone, D.; Peter, H.;
   Pinto, R. F.; Plainaki, C.; Plettemeier, D.; Plunkett, S. P.; Raines,
   J. M.; Raouafi, N.; Reid, H.; Retino, A.; Rezeau, L.; Rochus, P.;
   Rodriguez, L.; Rodriguez-Garcia, L.; Roth, M.; Rouillard, A. P.;
   Sahraoui, F.; Sasso, C.; Schou, J.; Schühle, U.; Sorriso-Valvo, L.;
   Soucek, J.; Spadaro, D.; Stangalini, M.; Stansby, D.; Steller, M.;
   Strugarek, A.; Štverák, Š.; Susino, R.; Telloni, D.; Terasa, C.;
   Teriaca, L.; Toledo-Redondo, S.; del Toro Iniesta, J. C.; Tsiropoula,
   G.; Tsounis, A.; Tziotziou, K.; Valentini, F.; Vaivads, A.; Vecchio,
   A.; Velli, M.; Verbeeck, C.; Verdini, A.; Verscharen, D.; Vilmer, N.;
   Vourlidas, A.; Wicks, R.; Wimmer-Schweingruber, R. F.; Wiegelmann,
   T.; Young, P. R.; Zhukov, A. N.
Bibcode: 2020A&A...642A...3Z
Altcode: 2020arXiv200910772Z
  Solar Orbiter is the first space mission observing the solar plasma
  both in situ and remotely, from a close distance, in and out of the
  ecliptic. The ultimate goal is to understand how the Sun produces
  and controls the heliosphere, filling the Solar System and driving
  the planetary environments. With six remote-sensing and four in-situ
  instrument suites, the coordination and planning of the operations are
  essential to address the following four top-level science questions:
  (1) What drives the solar wind and where does the coronal magnetic field
  originate?; (2) How do solar transients drive heliospheric variability?;
  (3) How do solar eruptions produce energetic particle radiation that
  fills the heliosphere?; (4) How does the solar dynamo work and drive
  connections between the Sun and the heliosphere? Maximising the
  mission's science return requires considering the characteristics
  of each orbit, including the relative position of the spacecraft
  to Earth (affecting downlink rates), trajectory events (such
  as gravitational assist manoeuvres), and the phase of the solar
  activity cycle. Furthermore, since each orbit's science telemetry
  will be downloaded over the course of the following orbit, science
  operations must be planned at mission level, rather than at the level
  of individual orbits. It is important to explore the way in which those
  science questions are translated into an actual plan of observations
  that fits into the mission, thus ensuring that no opportunities are
  missed. First, the overarching goals are broken down into specific,
  answerable questions along with the required observations and the
  so-called Science Activity Plan (SAP) is developed to achieve this. The
  SAP groups objectives that require similar observations into Solar
  Orbiter Observing Plans, resulting in a strategic, top-level view of
  the optimal opportunities for science observations during the mission
  lifetime. This allows for all four mission goals to be addressed. In
  this paper, we introduce Solar Orbiter's SAP through a series of
  examples and the strategy being followed.

Title: Inflection point in the power spectrum of stellar brightness
    variations. III. Facular versus spot dominance on stars with known
    rotation periods
Authors: Amazo-Gómez, E. M.; Shapiro, A. I.; Solanki, S. K.; Kopp,
   G.; Oshagh, M.; Reinhold, T.; Reiners, A.
Bibcode: 2020A&A...642A.225A
Altcode: 2020arXiv200811492A
  Context. Stellar rotation periods can be determined by observing
  brightness variations caused by active magnetic regions transiting
  visible stellar disk as the star rotates. Successful stellar photometric
  surveys stemming from the Kepler and TESS observations have led to
  the determination of rotation periods in tens of thousands of young
  and active stars. However, there is still a lack of information on
  the rotation periods of older and less active stars like the Sun. The
  irregular temporal profiles of light curves caused by the decay times of
  active regions, which are comparable to, or even shorter than, stellar
  rotation periods, in combination with the random emergence of active
  regions make period determination for such stars very difficult. <BR />
  Aims: We tested the performance of a new method for the determination
  of stellar rotation periods against stars with previously determined
  rotation periods. The method is based on calculating the gradient of the
  power spectrum (GPS) and identifying the position of the inflection
  point (i.e. point with the highest gradient). The GPS method is
  specifically aimed at determining rotation periods of low-activity
  stars like the Sun. <BR /> Methods: We applied the GPS method to 1047
  Sun-like stars observed by the Kepler telescope. We considered two
  stellar samples individually: one with near-solar rotation periods
  (24-27.4 d) and a broad range of effective temperatures (5000-6000 K)
  and the other with near-solar effective temperatures (5700-5900 K)
  and a broad range of rotation periods (15-40 d). <BR /> Results: We
  show that the GPS method returns precise values for stellar rotation
  periods. Furthermore, it allows us to constrain the ratio between
  facular and spot areas of active regions at the moment of their
  emergence. We also show that the relative facular area decreases with
  the stellar rotation rate. <BR /> Conclusions: Our results suggest
  that the GPS method can be successfully applied to retrieve the
  periods of stars with both regular and non-regular light curves. <P
  />Full Table 2 is only available at the CDS via anonymous ftp to <A
  href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
  (ftp://130.79.128.5) or via <A
  href="http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/642/A225">http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/642/A225</A>

Title: Autonomous on-board data processing and instrument calibration
    software for the Polarimetric and Helioseismic Imager on-board the
    Solar Orbiter mission
Authors: Albert, Kinga; Hirzberger, Johann; Kolleck, Martin; Jorge,
   Nestor Albelo; Busse, Dennis; Rodríguez, Julian Blanco; Carrascosa,
   Juan Pedro Cobos; Fiethe, Björn; Gandorfer, Achim; Germerott, Dietmar;
   Guan, Yejun; Guerrero, Lucas; Gutierrez-Marques, Pablo; Expósito,
   David Hernández; Lange, Tobias; Michalik, Harald; Suárez, David
   Orozco; Schou, Jesper; Solanki, Sami K.; del Toro Iniesta, José
   Carlos; Woch, Joachim
Bibcode: 2020JATIS...6d8004A
Altcode:
  A frequent problem arising for deep space missions is the discrepancy
  between the amount of data desired to be transmitted to the ground
  and the available telemetry bandwidth. A part of these data consists
  of scientific observations, being complemented by calibration data
  to help remove instrumental effects. We present our solution for this
  discrepancy, implemented for the Polarimetric and Helioseismic Imager
  on-board the Solar Orbiter mission, the first solar spectropolarimeter
  in deep space. We implemented an on-board data reduction system that
  processes calibration data, applies them to the raw science observables,
  and derives science-ready physical parameters. This process reduces
  the raw data for a single measurement from 24 images to five, thus
  reducing the amount of downlinked data, and in addition, renders the
  transmission of the calibration data unnecessary. Both these on-board
  actions are completed autonomously.

Title: The Polarimetric and Helioseismic Imager on Solar Orbiter
Authors: Solanki, S. K.; del Toro Iniesta, J. C.; Woch, J.; Gandorfer,
   A.; Hirzberger, J.; Alvarez-Herrero, A.; Appourchaux, T.; Martínez
   Pillet, V.; Pérez-Grande, I.; Sanchis Kilders, E.; Schmidt, W.;
   Gómez Cama, J. M.; Michalik, H.; Deutsch, W.; Fernandez-Rico, G.;
   Grauf, B.; Gizon, L.; Heerlein, K.; Kolleck, M.; Lagg, A.; Meller, R.;
   Müller, R.; Schühle, U.; Staub, J.; Albert, K.; Alvarez Copano, M.;
   Beckmann, U.; Bischoff, J.; Busse, D.; Enge, R.; Frahm, S.; Germerott,
   D.; Guerrero, L.; Löptien, B.; Meierdierks, T.; Oberdorfer, D.;
   Papagiannaki, I.; Ramanath, S.; Schou, J.; Werner, S.; Yang, D.;
   Zerr, A.; Bergmann, M.; Bochmann, J.; Heinrichs, J.; Meyer, S.;
   Monecke, M.; Müller, M. -F.; Sperling, M.; Álvarez García, D.;
   Aparicio, B.; Balaguer Jiménez, M.; Bellot Rubio, L. R.; Cobos
   Carracosa, J. P.; Girela, F.; Hernández Expósito, D.; Herranz, M.;
   Labrousse, P.; López Jiménez, A.; Orozco Suárez, D.; Ramos, J. L.;
   Barandiarán, J.; Bastide, L.; Campuzano, C.; Cebollero, M.; Dávila,
   B.; Fernández-Medina, A.; García Parejo, P.; Garranzo-García, D.;
   Laguna, H.; Martín, J. A.; Navarro, R.; Núñez Peral, A.; Royo, M.;
   Sánchez, A.; Silva-López, M.; Vera, I.; Villanueva, J.; Fourmond,
   J. -J.; de Galarreta, C. Ruiz; Bouzit, M.; Hervier, V.; Le Clec'h,
   J. C.; Szwec, N.; Chaigneau, M.; Buttice, V.; Dominguez-Tagle, C.;
   Philippon, A.; Boumier, P.; Le Cocguen, R.; Baranjuk, G.; Bell,
   A.; Berkefeld, Th.; Baumgartner, J.; Heidecke, F.; Maue, T.; Nakai,
   E.; Scheiffelen, T.; Sigwarth, M.; Soltau, D.; Volkmer, R.; Blanco
   Rodríguez, J.; Domingo, V.; Ferreres Sabater, A.; Gasent Blesa,
   J. L.; Rodríguez Martínez, P.; Osorno Caudel, D.; Bosch, J.; Casas,
   A.; Carmona, M.; Herms, A.; Roma, D.; Alonso, G.; Gómez-Sanjuan, A.;
   Piqueras, J.; Torralbo, I.; Fiethe, B.; Guan, Y.; Lange, T.; Michel,
   H.; Bonet, J. A.; Fahmy, S.; Müller, D.; Zouganelis, I.
Bibcode: 2020A&A...642A..11S
Altcode: 2019arXiv190311061S
  <BR /> Aims: This paper describes the Polarimetric and Helioseismic
  Imager on the Solar Orbiter mission (SO/PHI), the first magnetograph and
  helioseismology instrument to observe the Sun from outside the Sun-Earth
  line. It is the key instrument meant to address the top-level science
  question: How does the solar dynamo work and drive connections between
  the Sun and the heliosphere? SO/PHI will also play an important role
  in answering the other top-level science questions of Solar Orbiter,
  while hosting the potential of a rich return in further science. <BR
  /> Methods: SO/PHI measures the Zeeman effect and the Doppler shift
  in the Fe I 617.3 nm spectral line. To this end, the instrument
  carries out narrow-band imaging spectro-polarimetry using a tunable
  LiNbO<SUB>3</SUB> Fabry-Perot etalon, while the polarisation modulation
  is done with liquid crystal variable retarders. The line and the nearby
  continuum are sampled at six wavelength points and the data are recorded
  by a 2k × 2k CMOS detector. To save valuable telemetry, the raw data
  are reduced on board, including being inverted under the assumption of
  a Milne-Eddington atmosphere, although simpler reduction methods are
  also available on board. SO/PHI is composed of two telescopes; one,
  the Full Disc Telescope, covers the full solar disc at all phases of
  the orbit, while the other, the High Resolution Telescope, can resolve
  structures as small as 200 km on the Sun at closest perihelion. The high
  heat load generated through proximity to the Sun is greatly reduced by
  the multilayer-coated entrance windows to the two telescopes that allow
  less than 4% of the total sunlight to enter the instrument, most of
  it in a narrow wavelength band around the chosen spectral line. <BR />
  Results: SO/PHI was designed and built by a consortium having partners
  in Germany, Spain, and France. The flight model was delivered to
  Airbus Defence and Space, Stevenage, and successfully integrated into
  the Solar Orbiter spacecraft. A number of innovations were introduced
  compared with earlier space-based spectropolarimeters, thus allowing
  SO/PHI to fit into the tight mass, volume, power and telemetry budgets
  provided by the Solar Orbiter spacecraft and to meet the (e.g. thermal)
  challenges posed by the mission's highly elliptical orbit.

Title: The Solar Orbiter SPICE instrument. An extreme UV imaging
    spectrometer
Authors: SPICE Consortium; Anderson, M.; Appourchaux, T.; Auchère, F.;
   Aznar Cuadrado, R.; Barbay, J.; Baudin, F.; Beardsley, S.; Bocchialini,
   K.; Borgo, B.; Bruzzi, D.; Buchlin, E.; Burton, G.; Büchel, V.;
   Caldwell, M.; Caminade, S.; Carlsson, M.; Curdt, W.; Davenne, J.;
   Davila, J.; Deforest, C. E.; Del Zanna, G.; Drummond, D.; Dubau,
   J.; Dumesnil, C.; Dunn, G.; Eccleston, P.; Fludra, A.; Fredvik, T.;
   Gabriel, A.; Giunta, A.; Gottwald, A.; Griffin, D.; Grundy, T.; Guest,
   S.; Gyo, M.; Haberreiter, M.; Hansteen, V.; Harrison, R.; Hassler,
   D. M.; Haugan, S. V. H.; Howe, C.; Janvier, M.; Klein, R.; Koller,
   S.; Kucera, T. A.; Kouliche, D.; Marsch, E.; Marshall, A.; Marshall,
   G.; Matthews, S. A.; McQuirk, C.; Meining, S.; Mercier, C.; Morris,
   N.; Morse, T.; Munro, G.; Parenti, S.; Pastor-Santos, C.; Peter, H.;
   Pfiffner, D.; Phelan, P.; Philippon, A.; Richards, A.; Rogers, K.;
   Sawyer, C.; Schlatter, P.; Schmutz, W.; Schühle, U.; Shaughnessy,
   B.; Sidher, S.; Solanki, S. K.; Speight, R.; Spescha, M.; Szwec, N.;
   Tamiatto, C.; Teriaca, L.; Thompson, W.; Tosh, I.; Tustain, S.; Vial,
   J. -C.; Walls, B.; Waltham, N.; Wimmer-Schweingruber, R.; Woodward,
   S.; Young, P.; de Groof, A.; Pacros, A.; Williams, D.; Müller, D.
Bibcode: 2020A&A...642A..14S
Altcode: 2019arXiv190901183A; 2019arXiv190901183S
  <BR /> Aims: The Spectral Imaging of the Coronal Environment (SPICE)
  instrument is a high-resolution imaging spectrometer operating at
  extreme ultraviolet wavelengths. In this paper, we present the concept,
  design, and pre-launch performance of this facility instrument on the
  ESA/NASA Solar Orbiter mission. <BR /> Methods: The goal of this paper
  is to give prospective users a better understanding of the possible
  types of observations, the data acquisition, and the sources that
  contribute to the instrument's signal. <BR /> Results: The paper
  discusses the science objectives, with a focus on the SPICE-specific
  aspects, before presenting the instrument's design, including optical,
  mechanical, thermal, and electronics aspects. This is followed by a
  characterisation and calibration of the instrument's performance. The
  paper concludes with descriptions of the operations concept and data
  processing. <BR /> Conclusions: The performance measurements of the
  various instrument parameters meet the requirements derived from the
  mission's science objectives. The SPICE instrument is ready to perform
  measurements that will provide vital contributions to the scientific
  success of the Solar Orbiter mission.

Title: Understanding the origins of the heliosphere: integrating
    observations and measurements from Parker Solar Probe, Solar Orbiter,
    and other space- and ground-based observatories
Authors: Velli, M.; Harra, L. K.; Vourlidas, A.; Schwadron,
   N.; Panasenco, O.; Liewer, P. C.; Müller, D.; Zouganelis, I.;
   St Cyr, O. C.; Gilbert, H.; Nieves-Chinchilla, T.; Auchère, F.;
   Berghmans, D.; Fludra, A.; Horbury, T. S.; Howard, R. A.; Krucker,
   S.; Maksimovic, M.; Owen, C. J.; Rodríguez-Pacheco, J.; Romoli,
   M.; Solanki, S. K.; Wimmer-Schweingruber, R. F.; Bale, S.; Kasper,
   J.; McComas, D. J.; Raouafi, N.; Martinez-Pillet, V.; Walsh, A. P.;
   De Groof, A.; Williams, D.
Bibcode: 2020A&A...642A...4V
Altcode:
  Context. The launch of Parker Solar Probe (PSP) in 2018, followed
  by Solar Orbiter (SO) in February 2020, has opened a new window in
  the exploration of solar magnetic activity and the origin of the
  heliosphere. These missions, together with other space observatories
  dedicated to solar observations, such as the Solar Dynamics Observatory,
  Hinode, IRIS, STEREO, and SOHO, with complementary in situ observations
  from WIND and ACE, and ground based multi-wavelength observations
  including the DKIST observatory that has just seen first light,
  promise to revolutionize our understanding of the solar atmosphere
  and of solar activity, from the generation and emergence of the Sun's
  magnetic field to the creation of the solar wind and the acceleration of
  solar energetic particles. <BR /> Aims: Here we describe the scientific
  objectives of the PSP and SO missions, and highlight the potential for
  discovery arising from synergistic observations. Here we put particular
  emphasis on how the combined remote sensing and in situ observations of
  SO, that bracket the outer coronal and inner heliospheric observations
  by PSP, may provide a reconstruction of the solar wind and magnetic
  field expansion from the Sun out to beyond the orbit of Mercury in the
  first phases of the mission. In the later, out-of-ecliptic portions of
  the SO mission, the solar surface magnetic field measurements from SO
  and the multi-point white-light observations from both PSP and SO will
  shed light on the dynamic, intermittent solar wind escaping from helmet
  streamers, pseudo-streamers, and the confined coronal plasma, and on
  solar energetic particle transport. <BR /> Methods: Joint measurements
  during PSP-SO alignments, and magnetic connections along the same
  flux tube complemented by alignments with Earth, dual PSP-Earth,
  and SO-Earth, as well as with STEREO-A, SOHO, and BepiColumbo will
  allow a better understanding of the in situ evolution of solar-wind
  plasma flows and the full three-dimensional distribution of the
  solar wind from a purely observational point of view. Spectroscopic
  observations of the corona, and optical and radio observations,
  combined with direct in situ observations of the accelerating solar
  wind will provide a new foundation for understanding the fundamental
  physical processes leading to the energy transformations from solar
  photospheric flows and magnetic fields into the hot coronal plasma
  and magnetic fields and finally into the bulk kinetic energy of the
  solar wind and solar energetic particles. <BR /> Results: We discuss
  the initial PSP observations, which already provide a compelling
  rationale for new measurement campaigns by SO, along with ground-
  and space-based assets within the synergistic context described above.

Title: The Solar Orbiter mission. Science overview
Authors: Müller, D.; St. Cyr, O. C.; Zouganelis, I.; Gilbert, H. R.;
   Marsden, R.; Nieves-Chinchilla, T.; Antonucci, E.; Auchère, F.;
   Berghmans, D.; Horbury, T. S.; Howard, R. A.; Krucker, S.; Maksimovic,
   M.; Owen, C. J.; Rochus, P.; Rodriguez-Pacheco, J.; Romoli, M.;
   Solanki, S. K.; Bruno, R.; Carlsson, M.; Fludra, A.; Harra, L.;
   Hassler, D. M.; Livi, S.; Louarn, P.; Peter, H.; Schühle, U.;
   Teriaca, L.; del Toro Iniesta, J. C.; Wimmer-Schweingruber, R. F.;
   Marsch, E.; Velli, M.; De Groof, A.; Walsh, A.; Williams, D.
Bibcode: 2020A&A...642A...1M
Altcode: 2020arXiv200900861M
  <BR /> Aims: Solar Orbiter, the first mission of ESA's Cosmic Vision
  2015-2025 programme and a mission of international collaboration between
  ESA and NASA, will explore the Sun and heliosphere from close up and
  out of the ecliptic plane. It was launched on 10 February 2020 04:03
  UTC from Cape Canaveral and aims to address key questions of solar and
  heliospheric physics pertaining to how the Sun creates and controls
  the Heliosphere, and why solar activity changes with time. To answer
  these, the mission carries six remote-sensing instruments to observe
  the Sun and the solar corona, and four in-situ instruments to measure
  the solar wind, energetic particles, and electromagnetic fields. In
  this paper, we describe the science objectives of the mission, and how
  these will be addressed by the joint observations of the instruments
  onboard. <BR /> Methods: The paper first summarises the mission-level
  science objectives, followed by an overview of the spacecraft and
  payload. We report the observables and performance figures of each
  instrument, as well as the trajectory design. This is followed by a
  summary of the science operations concept. The paper concludes with a
  more detailed description of the science objectives. <BR /> Results:
  Solar Orbiter will combine in-situ measurements in the heliosphere
  with high-resolution remote-sensing observations of the Sun to address
  fundamental questions of solar and heliospheric physics. The performance
  of the Solar Orbiter payload meets the requirements derived from the
  mission's science objectives. Its science return will be augmented
  further by coordinated observations with other space missions and
  ground-based observatories. <P />ARRAY(0x207ce98)

Title: The Solar Orbiter EUI instrument: The Extreme Ultraviolet
    Imager
Authors: Rochus, P.; Auchère, F.; Berghmans, D.; Harra, L.; Schmutz,
   W.; Schühle, U.; Addison, P.; Appourchaux, T.; Aznar Cuadrado,
   R.; Baker, D.; Barbay, J.; Bates, D.; BenMoussa, A.; Bergmann, M.;
   Beurthe, C.; Borgo, B.; Bonte, K.; Bouzit, M.; Bradley, L.; Büchel,
   V.; Buchlin, E.; Büchner, J.; Cabé, F.; Cadiergues, L.; Chaigneau,
   M.; Chares, B.; Choque Cortez, C.; Coker, P.; Condamin, M.; Coumar,
   S.; Curdt, W.; Cutler, J.; Davies, D.; Davison, G.; Defise, J. -M.;
   Del Zanna, G.; Delmotte, F.; Delouille, V.; Dolla, L.; Dumesnil, C.;
   Dürig, F.; Enge, R.; François, S.; Fourmond, J. -J.; Gillis, J. -M.;
   Giordanengo, B.; Gissot, S.; Green, L. M.; Guerreiro, N.; Guilbaud,
   A.; Gyo, M.; Haberreiter, M.; Hafiz, A.; Hailey, M.; Halain, J. -P.;
   Hansotte, J.; Hecquet, C.; Heerlein, K.; Hellin, M. -L.; Hemsley, S.;
   Hermans, A.; Hervier, V.; Hochedez, J. -F.; Houbrechts, Y.; Ihsan,
   K.; Jacques, L.; Jérôme, A.; Jones, J.; Kahle, M.; Kennedy, T.;
   Klaproth, M.; Kolleck, M.; Koller, S.; Kotsialos, E.; Kraaikamp, E.;
   Langer, P.; Lawrenson, A.; Le Clech', J. -C.; Lenaerts, C.; Liebecq,
   S.; Linder, D.; Long, D. M.; Mampaey, B.; Markiewicz-Innes, D.;
   Marquet, B.; Marsch, E.; Matthews, S.; Mazy, E.; Mazzoli, A.; Meining,
   S.; Meltchakov, E.; Mercier, R.; Meyer, S.; Monecke, M.; Monfort,
   F.; Morinaud, G.; Moron, F.; Mountney, L.; Müller, R.; Nicula, B.;
   Parenti, S.; Peter, H.; Pfiffner, D.; Philippon, A.; Phillips, I.;
   Plesseria, J. -Y.; Pylyser, E.; Rabecki, F.; Ravet-Krill, M. -F.;
   Rebellato, J.; Renotte, E.; Rodriguez, L.; Roose, S.; Rosin, J.;
   Rossi, L.; Roth, P.; Rouesnel, F.; Roulliay, M.; Rousseau, A.; Ruane,
   K.; Scanlan, J.; Schlatter, P.; Seaton, D. B.; Silliman, K.; Smit,
   S.; Smith, P. J.; Solanki, S. K.; Spescha, M.; Spencer, A.; Stegen,
   K.; Stockman, Y.; Szwec, N.; Tamiatto, C.; Tandy, J.; Teriaca, L.;
   Theobald, C.; Tychon, I.; van Driel-Gesztelyi, L.; Verbeeck, C.;
   Vial, J. -C.; Werner, S.; West, M. J.; Westwood, D.; Wiegelmann, T.;
   Willis, G.; Winter, B.; Zerr, A.; Zhang, X.; Zhukov, A. N.
Bibcode: 2020A&A...642A...8R
Altcode:
  Context. The Extreme Ultraviolet Imager (EUI) is part of the remote
  sensing instrument package of the ESA/NASA Solar Orbiter mission
  that will explore the inner heliosphere and observe the Sun from
  vantage points close to the Sun and out of the ecliptic. Solar Orbiter
  will advance the "connection science" between solar activity and the
  heliosphere. <BR /> Aims: With EUI we aim to improve our understanding
  of the structure and dynamics of the solar atmosphere, globally as well
  as at high resolution, and from high solar latitude perspectives. <BR />
  Methods: The EUI consists of three telescopes, the Full Sun Imager and
  two High Resolution Imagers, which are optimised to image in Lyman-α
  and EUV (17.4 nm, 30.4 nm) to provide a coverage from chromosphere
  up to corona. The EUI is designed to cope with the strong constraints
  imposed by the Solar Orbiter mission characteristics. Limited telemetry
  availability is compensated by state-of-the-art image compression,
  onboard image processing, and event selection. The imposed power
  limitations and potentially harsh radiation environment necessitate
  the use of novel CMOS sensors. As the unobstructed field of view of
  the telescopes needs to protrude through the spacecraft's heat shield,
  the apertures have been kept as small as possible, without compromising
  optical performance. This led to a systematic effort to optimise the
  throughput of every optical element and the reduction of noise levels
  in the sensor. <BR /> Results: In this paper we review the design
  of the two elements of the EUI instrument: the Optical Bench System
  and the Common Electronic Box. Particular attention is also given to
  the onboard software, the intended operations, the ground software,
  and the foreseen data products. <BR /> Conclusions: The EUI will
  bring unique science opportunities thanks to its specific design,
  its viewpoint, and to the planned synergies with the other Solar
  Orbiter instruments. In particular, we highlight science opportunities
  brought by the out-of-ecliptic vantage point of the solar poles,
  the high-resolution imaging of the high chromosphere and corona,
  and the connection to the outer corona as observed by coronagraphs.

Title: PMI: The Photospheric Magnetic Field Imager
Authors: Staub, Jan; Fernandez-Rico, German; Gandorfer, Achim; Gizon,
   Laurent; Hirzberger, Johann; Kraft, Stefan; Lagg, Andreas; Schou,
   Jesper; Solanki, Sami K.; del Toro Iniesta, Jose Carlos; Wiegelmann,
   Thomas; Woch, Joachim
Bibcode: 2020JSWSC..10...54S
Altcode:
  We describe the design and the capabilities of the Photospheric Magnetic
  field Imager (PMI), a compact and lightweight vector magnetograph,
  which is being developed for ESA's Lagrange mission to the Lagrange
  L5 point. After listing the design requirements and give a scientific
  justification for them, we describe the technical implementation and
  the design solution capable of fulfilling these requirements. This is
  followed by a description of the hardware architecture as well as the
  operations principle. An outlook on the expected performance concludes
  the paper.

Title: Metis: the Solar Orbiter visible light and ultraviolet
    coronal imager
Authors: Antonucci, Ester; Romoli, Marco; Andretta, Vincenzo; Fineschi,
   Silvano; Heinzel, Petr; Moses, J. Daniel; Naletto, Giampiero; Nicolini,
   Gianalfredo; Spadaro, Daniele; Teriaca, Luca; Berlicki, Arkadiusz;
   Capobianco, Gerardo; Crescenzio, Giuseppe; Da Deppo, Vania; Focardi,
   Mauro; Frassetto, Fabio; Heerlein, Klaus; Landini, Federico; Magli,
   Enrico; Marco Malvezzi, Andrea; Massone, Giuseppe; Melich, Radek;
   Nicolosi, Piergiorgio; Noci, Giancarlo; Pancrazzi, Maurizio; Pelizzo,
   Maria G.; Poletto, Luca; Sasso, Clementina; Schühle, Udo; Solanki,
   Sami K.; Strachan, Leonard; Susino, Roberto; Tondello, Giuseppe;
   Uslenghi, Michela; Woch, Joachim; Abbo, Lucia; Bemporad, Alessandro;
   Casti, Marta; Dolei, Sergio; Grimani, Catia; Messerotti, Mauro;
   Ricci, Marco; Straus, Thomas; Telloni, Daniele; Zuppella, Paola;
   Auchère, Frederic; Bruno, Roberto; Ciaravella, Angela; Corso,
   Alain J.; Alvarez Copano, Miguel; Aznar Cuadrado, Regina; D'Amicis,
   Raffaella; Enge, Reiner; Gravina, Alessio; Jejčič, Sonja; Lamy,
   Philippe; Lanzafame, Alessandro; Meierdierks, Thimo; Papagiannaki,
   Ioanna; Peter, Hardi; Fernandez Rico, German; Giday Sertsu, Mewael;
   Staub, Jan; Tsinganos, Kanaris; Velli, Marco; Ventura, Rita; Verroi,
   Enrico; Vial, Jean-Claude; Vives, Sebastien; Volpicelli, Antonio;
   Werner, Stephan; Zerr, Andreas; Negri, Barbara; Castronuovo, Marco;
   Gabrielli, Alessandro; Bertacin, Roberto; Carpentiero, Rita; Natalucci,
   Silvia; Marliani, Filippo; Cesa, Marco; Laget, Philippe; Morea, Danilo;
   Pieraccini, Stefano; Radaelli, Paolo; Sandri, Paolo; Sarra, Paolo;
   Cesare, Stefano; Del Forno, Felice; Massa, Ernesto; Montabone, Mauro;
   Mottini, Sergio; Quattropani, Daniele; Schillaci, Tiziano; Boccardo,
   Roberto; Brando, Rosario; Pandi, Arianna; Baietto, Cristian; Bertone,
   Riccardo; Alvarez-Herrero, Alberto; García Parejo, Pilar; Cebollero,
   María; Amoruso, Mauro; Centonze, Vito
Bibcode: 2020A&A...642A..10A
Altcode: 2019arXiv191108462A
  <BR /> Aims: Metis is the first solar coronagraph designed for a
  space mission and is capable of performing simultaneous imaging of the
  off-limb solar corona in both visible and UV light. The observations
  obtained with Metis aboard the Solar Orbiter ESA-NASA observatory
  will enable us to diagnose, with unprecedented temporal coverage and
  spatial resolution, the structures and dynamics of the full corona
  in a square field of view (FoV) of ±2.9° in width, with an inner
  circular FoV at 1.6°, thus spanning the solar atmosphere from 1.7
  R<SUB>⊙</SUB> to about 9 R<SUB>⊙</SUB>, owing to the eccentricity
  of the spacecraft orbit. Due to the uniqueness of the Solar Orbiter
  mission profile, Metis will be able to observe the solar corona
  from a close (0.28 AU, at the closest perihelion) vantage point,
  achieving increasing out-of-ecliptic views with the increase of the
  orbit inclination over time. Moreover, observations near perihelion,
  during the phase of lower rotational velocity of the solar surface
  relative to the spacecraft, allow longer-term studies of the off-limb
  coronal features, thus finally disentangling their intrinsic evolution
  from effects due to solar rotation. <BR /> Methods: Thanks to a novel
  occultation design and a combination of a UV interference coating of
  the mirrors and a spectral bandpass filter, Metis images the solar
  corona simultaneously in the visible light band, between 580 and 640
  nm, and in the UV H I Lyman-α line at 121.6 nm. The visible light
  channel also includes a broadband polarimeter able to observe the
  linearly polarised component of the K corona. The coronal images in
  both the UV H I Lyman-α and polarised visible light are obtained at
  high spatial resolution with a spatial scale down to about 2000 km
  and 15 000 km at perihelion, in the cases of the visible and UV light,
  respectively. A temporal resolution down to 1 s can be achieved when
  observing coronal fluctuations in visible light. <BR /> Results: The
  Metis measurements, obtained from different latitudes, will allow for
  complete characterisation of the main physical parameters and dynamics
  of the electron and neutral hydrogen/proton plasma components of the
  corona in the region where the solar wind undergoes the acceleration
  process and where the onset and initial propagation of coronal mass
  ejections (CMEs) take place. The near-Sun multi-wavelength coronal
  imaging performed with Metis, combined with the unique opportunities
  offered by the Solar Orbiter mission, can effectively address crucial
  issues of solar physics such as: the origin and heating/acceleration
  of the fast and slow solar wind streams; the origin, acceleration,
  and transport of the solar energetic particles; and the transient
  ejection of coronal mass and its evolution in the inner heliosphere,
  thus significantly improving our understanding of the region connecting
  the Sun to the heliosphere and of the processes generating and driving
  the solar wind and coronal mass ejections. <BR /> Conclusions: This
  paper presents the scientific objectives and requirements, the overall
  optical design of the Metis instrument, the thermo-mechanical design,
  and the processing and power unit; reports on the results of the
  campaigns dedicated to integration, alignment, and tests, and to
  the characterisation of the instrument performance; describes the
  operation concept, data handling, and software tools; and, finally,
  the diagnostic techniques to be applied to the data, as well as a brief
  description of the expected scientific products. The performance of the
  instrument measured during calibrations ensures that the scientific
  objectives of Metis can be pursued with success. <P />Metis website:
  <A href="http://metis.oato.inaf.it">http://metis.oato.inaf.it</A>

Title: Simulating Variability due to Faculae and Spots on GKM Stars
Authors: Johnson, Luke; Unruh, Yvonne; Norris, Charlotte; Solanki,
   Sami; Krivova, Natalie; Witzke, Veronika; Shapiro, Alexander
Bibcode: 2020EPSC...14..844J
Altcode:
  Stellar variability is a dominant noise source in exoplanet surveys
  and results largely from the presence of photospheric faculae and
  spots. The implementation of faculae in lightcurve models is an open
  problem, with scaling based on spectra equivalent to hot stellar
  atmospheres or assuming a solar-derived facular contrast. We model the
  lightcurves of active late-type stars as they rotate, using emergent
  intensity spectra calculated from 3D magnetoconvection simulations
  of G, K and M-type stellar atmosphere regions at different viewing
  angles to reproduce centre-to-limb brightness variations. We present
  mean expected variability levels for several cases and compare with
  solar and stellar observations. We also investigate the wavelength
  dependence of variability. Fig. 1: Example of our geometrically
  accurate lightcurve modelling approach. Top: normalised intensity
  maps of a limb darkened, solar-type star viewed in the \textit{Kepler}
  band at rotational phase 0.5 with stellar inclinations 90 deg (left)
  and 30 deg (right). At 90 deg, the star is viewed equator-on. Middle:
  Corresponding lightcurves calculated at inclinations 90 deg (black line)
  and 30 deg (red line). Bottom: HealPix map representing the active
  stellar surface, cosine-scaled in latitude and flattened in longitude
  to resemble a solar synoptic map. The quiet photosphere is displayed
  in orange, facular regions are bright yellow and spot regions are dark
  blue. The crosses represent the centres of the stellar discs in the
  top panel. Fig. 2: Example showing simulated lightcurves calculated
  at different wavelengths. Rotational lightcurves are on the left,
  transit lightcurves on the right. In the centre, one hemisphere of the
  simulated stellar surface is shown, with a quarter of the disc shown
  in each wavelength band. 'Giant' spots and facular regions are used
  in this example. The transit path is highlighted in grey.

Title: Amplification of Brightness Variability by Active-region
    Nesting in Solar-like Stars
Authors: Işık, Emre; Shapiro, Alexander I.; Solanki, Sami K.;
   Krivova, Natalie A.
Bibcode: 2020ApJ...901L..12I
Altcode: 2020arXiv200900692I
  Kepler observations revealed that hundreds of stars with near-solar
  fundamental parameters and rotation periods have much stronger and
  more regular brightness variations than the Sun. Here we identify one
  possible reason for the peculiar behavior of these stars. Inspired by
  solar nests of activity, we assume that the degree of inhomogeneity
  of active-region (AR) emergence on such stars is higher than on the
  Sun. To test our hypothesis, we model stellar light curves by injecting
  ARs consisting of spots and faculae on stellar surfaces at various
  rates and nesting patterns, using solar AR properties and differential
  rotation. We show that a moderate increase of the emergence frequency
  from the solar value combined with the increase of the degree of nesting
  can explain the full range of observed amplitudes of variability of
  Sun-like stars with nearly the solar rotation period. Furthermore,
  nesting in the form of active longitudes, in which ARs tend to emerge
  in the vicinity of two longitudes separated by 180°, leads to highly
  regular, almost sine-like variability patterns, rather similar to
  those observed in a number of solar-like stars.

Title: Simulations Show that Vortex Flows Could Heat the Chromosphere
    in Solar Plage
Authors: Yadav, N.; Cameron, R.; Solanki, S.
Bibcode: 2020SPD....5120107Y
Altcode:
  Recent advances in both, observational techniques and numerical
  simulations have enabled us to detect small-scale vortices in the solar
  atmosphere. Vortices are ubiquitous throughout the solar surface and
  at all layers of the solar atmosphere existing over a wide range of
  spatial and temporal scales. Small-scale vortices are suggested to play
  an important role in the energy transport of the solar atmosphere,
  however, their physical properties remain poorly understood due
  to limited resolution. We explored the relationship between vortex
  flows at different spatial scales, analyze their physical properties,
  and investigate their contribution to Poynting flux transport. Using
  three-dimensional (3D) radiative magnetohydrodynamic (MHD)simulation
  code 'MURaM', we perform numerical simulations of a unipolar solar
  plage region. For detecting and isolating vortices, we use the
  'Swirling Strength' criterion. We explore the spatial profiles of
  physical quantities viz. density, horizontal velocity, etc. inside
  these vortices. Moreover, to apprehend their general characteristics,
  a statistical investigation is performed. We found that magnetic flux
  tubes have a complex filamentary substructure abundant of small-scale
  vortices. On their interfaces strong current sheets are formed that
  may dissipate and heat the solar chromosphere. Statistically, vortices
  have higher densities and higher temperatures than the average values
  at the same geometrical height. We also degrade our simulation data to
  get an effective spatial resolution of 50 km, 100 km, 250 km, and 500
  km, respectively. Analyzing simulation data at different effective
  resolutions, we found vortex flows existing over various spatial
  scales. In high-resolution simulation data, we detect a large number
  of small-scale vortices. Whereas, in the degraded data with relatively
  poor resolutions, smaller vortices are averaged-out and larger vortices
  are detected. The Poynting flux over vortex locations is more than
  adequate to compensate for the radiative losses in the chromosphere
  indicating their possible role in the chromospheric heating.

Title: A Coronal Loop in a Box: Energy Generation, Heating and
    Dynamics
Authors: Breu, C.; Peter, H.; Cameron, R.; Solanki, S.; Chitta, P.;
   Przybylski, D.
Bibcode: 2020SPD....5121008B
Altcode:
  In our study we aim at an understanding how the energy to heat the
  upper atmosphere is generated by the photospheric magneto-convection,
  transported into the upper atmosphere, and how its dissipation governs
  the formation of the internal structure of a coronal magnetic loop. In
  a 3D MHD model we study a coronal loop that is rooted with both
  footpoints in a shallow convection zone layer. Therefore the driving
  at the coronal base arises self-consistently from magneto-convection
  in plage-type areas. To fit into a cartesian box, we straighten the
  coronal loop. This allows a high spatial resolution within the loop
  that cannot be achieved in a model of a whole active region. To
  conduct the numerical experiments we employ the MURaM code that
  includes heat conduction, radiative transfer and optically thin
  radiative losses. We find that the Poynting flux into the loop is
  generated by small-scale photospheric motions within strong magnetic
  flux concentrations. Turbulent behaviour develops in the upper layers
  of the atmosphere as a response to the footpoint motions. Vortex flows
  are found at various heights within the loop. These are organised in
  swirls that form coherent structures with a magnetic connection from
  the intergranular lanes in the photosphere through the chromosphere
  up to several megameters into the corona. In the coronal part of
  the loop plasma motions perpendicular to the magnetic axis of the
  swirl are associated with an increased heating rate and thus enhanced
  temperatures. At any given time, only part of the loop is filled with
  swirls which leads to a substructure of the loop in terms of temperature
  and density. Consequently the emission as it would be observed by AIA
  or XRT reveals transient bright strands that form in response to the
  heating events related to the swirls. With this model we can build a
  coherent picture of how the energy flux to heat the upper atmosphere
  is generated near the solar surface and how this process drives and
  governs the heating and dynamics of a coronal loop

Title: Effects of inclusion of small-scale dynamo in near-surface
    structure of F-stars
Authors: Bhatia, T. S.; Cameron, R.; Solanki, S.; Peter, H.; Przbylski,
   D.; Witzke, V.
Bibcode: 2020SPD....5120704B
Altcode:
  The presence of (unresolved) small-scale mixed polarity regions in
  the quiet Sun photosphere plays an important role in determining
  the basal magnetic flux. Observationally, the magnitude of the
  vertical component of this field is estimated to be ~50-100 G on the
  Sun. This field is important for determining the energy balance in
  the chromosphere and may also subtly affect the radiative properties
  of the photosphere. These fields are believed to be the result of a
  small-scale dynamo (SSD) operating near the surface. While significant
  progress has been made in investigating the role of the SSD in the Sun,
  it is unclear what effects SSDs have on other stars. In particular,
  for F-stars, the photosheric kinetic and internal energies seem to be
  of the same order of magnitude. Since there is a rough equipartition
  in energies for a saturated SSD, deviations from a pure hydrodynamic
  (HD) stratification are expected. We aim to characterize these
  deviations. Box simulations of the upper convection zone and the
  photosphere are carried out using the radiative MHD code MURaM. To
  obtain SSD simulations, we use initial HD simulations and seed a
  magnetic field of negligible strength and zero net flux, which we
  then run till the magnetic field reaches saturation. We consider two
  different lower boundary conditions (BCs) for the magnetic field to
  characterize BC-effects: a) only vertical magnetic field is allowed, b)
  both vertical and horizontal magnetic field is allowed. Both boundary
  conditions exhibit SSD action. We observe slight increase (fraction
  of a percent) in the horizontally-averaged temperature profile for
  both the cases. Other thermodynamic quantities exhibit deviations (~
  a percent) depending on the boundary condition considered. In addition,
  the spatial power spectra of the bolometric intensity shows deviations
  from the corresponding HD (without magnetic field) run, implying
  larger power at smaller spatial scales for SSD case. The presence of
  a SSD results in a significant amount of "quiet"-star magnetic flux
  with associated changes in the stratification of the atmosphere and
  spatial distribution of the bolometric intensity.

Title: Magnetohydrostatic modeling of AR11768 based on a SUNRISE/IMaX
    vector magnetogram
Authors: Zhu, X.; Wiegelmann, T.; Solanki, S. K.
Bibcode: 2020A&A...640A.103Z
Altcode: 2020arXiv200514332Z
  Context. High-resolution magnetic field measurements are routinely
  only done in the solar photosphere. Higher layers, such as the
  chromosphere and corona, can be modeled by extrapolating these
  photospheric magnetic field vectors upward. In the solar corona,
  plasma forces can be neglected and the Lorentz force vanishes. This
  is not the case in the upper photosphere and chromosphere where
  magnetic and nonmagnetic forces are equally important. One way to
  deal with this problem is to compute the plasma and magnetic field
  self-consistently, in lowest order with a magnetohydrostatic (MHS)
  model. The non-force-free layer is rather thin and MHS models require
  high-resolution photospheric magnetic field measurements as the lower
  boundary condition. <BR /> Aims: We aim to derive the magnetic field,
  plasma pressure, and density of AR11768 by applying the newly developed
  extrapolation technique to the SUNRISE/IMaX data embedded in SDO/HMI
  magnetogram. <BR /> Methods: We used an optimization method for the MHS
  modeling. The initial conditions consist of a nonlinear force-free field
  (NLFFF) and a gravity-stratified atmosphere. During the optimization
  procedure, the magnetic field, plasma pressure, and density are computed
  self-consistently. <BR /> Results: In the non-force-free layer, which
  is spatially resolved by the new code, Lorentz forces are effectively
  balanced by the gas pressure gradient force and gravity force. The
  pressure and density are depleted in strong field regions, which is
  consistent with observations. Denser plasma, however, is also observed
  at some parts of the active region edges. In the chromosphere, the
  fibril-like plasma structures trace the magnetic field nicely. Bright
  points in SUNRISE/SuFI 3000 Å images are often accompanied by the
  plasma pressure and electric current concentrations. In addition, the
  average of angle between MHS field lines and the selected chromospheric
  fibrils is 11.8°, which is smaller than those computed from the NLFFF
  model (15.7°) and linear MHS model (20.9°). This indicates that the
  MHS solution provides a better representation of the magnetic field
  in the chromosphere.

Title: Sunspot area catalog revisited: Daily cross-calibrated areas
    since 1874
Authors: Mandal, Sudip; Krivova, Natalie A.; Solanki, Sami K.; Sinha,
   Nimesh; Banerjee, Dipankar
Bibcode: 2020A&A...640A..78M
Altcode: 2020arXiv200414618M
  Context. Long and consistent sunspot area records are important for
  understanding long-term solar activity and variability. Multiple
  observatories around the globe have regularly recorded sunspot
  areas, but such individual records only cover restricted periods of
  time. Furthermore, there are systematic differences between these
  records and require cross-calibration before they can reliably be used
  for further studies. <BR /> Aims: We produce a cross-calibrated and
  homogeneous record of total daily sunspot areas, both projected and
  corrected, covering the period between 1874 and 2019. In addition,
  we generated a catalog of calibrated individual group areas for
  the same period. <BR /> Methods: We compared the data from nine
  archives: Royal Greenwich Observatory (RGO), Kislovodsk, Pulkovo,
  Debrecen, Kodaikanal, Solar Optical Observing Network (SOON), Rome,
  Catania, and Yunnan Observatories, covering the period between
  1874 and 2019. Cross-comparisons of the individual records were
  done to produce homogeneous and inter-calibrated records of daily
  projected and corrected areas. As in earlier studies, the basis
  of the composite is formed by the data from RGO. After 1976, the
  only datasets used are those from Kislovodsk, Pulkovo, and Debrecen
  observatories. This choice was made based on the temporal coverage
  and the quality of the data. While there are still 776 days missing
  in the final composite, these remaining gaps could not be filled
  with data from the other archives as the missing days lie either
  before 1922 or after 2016 and none of the additional archives cover
  these periods. <BR /> Results: In contrast to the SOON data used in
  previous area composites for the post-RGO period, the properties of
  the data from Kislovodsk and Pulkovo are very similar to those from
  the RGO series. They also directly overlap the RGO data in time, which
  makes their cross-calibration with RGO much more reliable. Indeed,
  comparing our area catalog with previous such composites, we find
  improvements both in data quality and coverage. We also computed the
  daily Photometric Sunspot Index, which is widely used, for example,
  in empirical reconstructions of solar irradiance. <P />Generated
  composites are available at the CDS via anonymous ftp to <A
  href="http://cdsarc.u-strasbg.fr/">http://cdsarc.u-strasbg.fr</A>
  (ftp://130.79.128.5) or via <A
  href="http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/640/A78">http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/640/A78</A>
  and at <A
  href="http://www2.mps.mpg.de/projects/sun-climate/data.html">http://www2.mps.mpg.de/projects/sun-climate/data.html</A>

Title: Radiative MHD Simulations of Starspots
Authors: Panja, M.; Cameron, R.; Solanki, S.
Bibcode: 2020SPD....5121117P
Altcode:
  We have performed the first-ever, realistic 3D simulations of the
  photospheric structure of complete starspots, including their penumbrae,
  for a range of cool main-sequence stars, namely the spectral types M0V,
  K0V, and G2V. We used the MHD code MURaM which includes radiative energy
  transfer and the effects of partial ionization. We explore several
  fundamental properties like umbral intensity contrast, temperature, and
  magnetic field strength as functions of spectral type. Our simulations
  show that there is an increase in spot contrast with the increase in
  stellar surface temperature, which is consistent with observations. The
  umbral field strength is determined by the depth at which the optical
  surface forms and the surface pressures of the host stars. We will
  present our results and discuss the physics behind them.

Title: Analysis of full-disc Ca II K spectroheliograms. III. Plage
    area composite series covering 1892-2019
Authors: Chatzistergos, Theodosios; Ermolli, Ilaria; Krivova,
   Natalie A.; Solanki, Sami K.; Banerjee, Dipankar; Barata, Teresa;
   Belik, Marcel; Gafeira, Ricardo; Garcia, Adriana; Hanaoka, Yoichiro;
   Hegde, Manjunath; Klimeš, Jan; Korokhin, Viktor V.; Lourenço, Ana;
   Malherbe, Jean-Marie; Marchenko, Gennady P.; Peixinho, Nuno; Sakurai,
   Takashi; Tlatov, Andrey G.
Bibcode: 2020A&A...639A..88C
Altcode: 2020arXiv200501435C
  Context. Studies of long-term solar activity and variability require
  knowledge of the past evolution of the solar surface magnetism. The
  archives of full-disc Ca II K observations that have been performed
  more or less regularly at various sites since 1892 can serve as an
  important source of such information. <BR /> Aims: We derive the plage
  area evolution over the last 12 solar cycles by employing data from all
  Ca II K archives that are publicly available in digital form, including
  several as-yet-unexplored Ca II K archives. <BR /> Methods: We analysed
  more than 290 000 full-disc Ca II K observations from 43 datasets
  spanning the period between 1892-2019. All images were consistently
  processed with an automatic procedure that performs the photometric
  calibration (if needed) and the limb-darkening compensation. The
  processing also accounts for artefacts affecting many of the images,
  including some very specific artefacts, such as bright arcs found
  in Kyoto and Yerkes data. Our employed methods have previously been
  tested and evaluated on synthetic data and found to be more accurate
  than other methods used in the literature to treat a subset of the data
  analysed here. <BR /> Results: We produced a plage area time-series
  from each analysed dataset. We found that the differences between the
  plage areas derived from individual archives are mainly due to the
  differences in the central wavelength and the bandpass used to acquire
  the data at the various sites. We empirically cross-calibrated and
  combined the results obtained from each dataset to produce a composite
  series of plage areas. The 'backbone' approach was used to bridge
  the series together. We have also shown that the selection of the
  backbone series has little effect on the final composite of the plage
  area. We quantified the uncertainty of determining the plage areas
  with our processing due to shifts in the central wavelength and found
  it to be less than 0.01 in fraction of the solar disc for the average
  conditions found on historical data. We also found the variable seeing
  conditions during the observations to slightly increase the plage
  areas during the activity maxima. <BR /> Conclusions: We provide the
  most complete so far time series of plage areas based on corrected
  and calibrated historical and modern Ca II K images. Consistent
  plage areas are now available on 88% of all days from 1892 onwards
  and on 98% from 1907 onwards. <P />The whole series described in
  the paper are only available at the CDS via anonymous ftp to <A
  href="http://cdsarc.u-strasbg.fr/">http://cdsarc.u-strasbg.fr</A>
  (ftp://130.79.128.5) or via <A
  href="http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/639/A88">http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/639/A88</A>

Title: No universal connection between the vertical magnetic field
    and the umbra-penumbra boundary in sunspots
Authors: Löptien, B.; Lagg, A.; van Noort, M.; Solanki, S. K.
Bibcode: 2020A&A...639A.106L
Altcode: 2020arXiv200602346L
  Context. It has been reported that the boundary between the umbra and
  the penumbra of sunspots occurs at a canonical value of the strength
  of the vertical magnetic field, independently of the size of the
  spot. This critical field strength is interpreted to be the threshold
  for the onset of magnetoconvection. <BR /> Aims: Here we investigate
  the reasons why this criterion, also called the Jurčák criterion
  in the literature, does not always identify the boundary between the
  umbra and the penumbra. <BR /> Methods: We performed a statistical
  analysis of 23 sunspots observed with Hinode/SOT. We compared the
  properties of the continuum intensity and the vertical magnetic
  field between filaments and spines and how they vary between spots of
  different sizes. <BR /> Results: We find that the inner boundary of the
  penumbra is not related to a universal value of the vertical magnetic
  field. The properties of spines and filaments vary between spots of
  different sizes. Both components are darker in larger spots and the
  spines exhibit a stronger vertical magnetic field. These variations of
  the properties of filaments and spines with the spot size are also the
  reason for the reported invariance in the averaged vertical magnetic
  field at 50% of the mean continuum intensity. <BR /> Conclusions:
  The formation of filaments and the onset of magnetoconvection are not
  related to a canonical value of the strength of the vertical magnetic
  field. The seemingly unique magnetic field strength is rather an effect
  of the filling factor of spines and penumbral filaments.

Title: How faculae and network relate to sunspots, and the
    implications for solar and stellar brightness variations
Authors: Yeo, K. L.; Solanki, S. K.; Krivova, N. A.
Bibcode: 2020A&A...639A.139Y
Altcode: 2020arXiv200614274Y
  Context. How global faculae and network coverage relates to that
  of sunspots is relevant to the brightness variations of the Sun and
  Sun-like stars. <BR /> Aims: We aim to extend and improve on earlier
  studies that established that the facular-to-sunspot-area ratio
  diminishes with total sunspot coverage. <BR /> Methods: Chromospheric
  indices and the total magnetic flux enclosed in network and faculae,
  referred to here as "facular indices", are modulated by the amount
  of facular and network present. We probed the relationship between
  various facular and sunspot indices through an empirical model, taking
  into account how active regions evolve and the possible non-linear
  relationship between plage emission, facular magnetic flux, and sunspot
  area. This model was incorporated into a model of total solar irradiance
  (TSI) to elucidate the implications for solar and stellar brightness
  variations. <BR /> Results: The reconstruction of the facular indices
  from the sunspot indices with the model presented here replicates
  most of the observed variability, and is better at doing so than
  earlier models. Contrary to recent studies, we found the relationship
  between the facular and sunspot indices to be stable over the past four
  decades. The model indicates that, like the facular-to-sunspot-area
  ratio, the ratio of the variation in chromospheric emission and
  total network and facular magnetic flux to sunspot area decreases
  with the latter. The TSI model indicates the ratio of the TSI excess
  from faculae and network to the deficit from sunspots also declines
  with sunspot area, with the consequence being that TSI rises with
  sunspot area more slowly than if the two quantities were linearly
  proportional to one another. This explains why even though solar cycle
  23 is significantly weaker than cycle 22, TSI rose to comparable levels
  over both cycles. The extrapolation of the TSI model to higher activity
  levels indicates that in the activity range where Sun-like stars are
  observed to switch from growing brighter with increasing activity to
  becoming dimmer instead, the activity-dependence of TSI exhibits a
  similar transition. This happens as sunspot darkening starts to rise
  more rapidly with activity than facular and network brightening. This
  bolsters the interpretation of this behaviour of Sun-like stars as
  the transition from a faculae-dominated to a spot-dominated regime.

Title: Reply to the comment of T. Metcalfe and J. van Saders on the
    Science report "The Sun is less active than other solar-like stars"
Authors: Reinhold, T.; Shapiro, A. I.; Solanki, S. K.; Montet, B. T.;
   Krivova, N. A.; Cameron, R. H.; Amazo-Gómez, E. M.
Bibcode: 2020arXiv200704817R
Altcode:
  This is our reply to the comment of T. Metcalfe and J. van Saders
  on the Science report "The Sun is less active than other solar-like
  stars" by T. Reinhold, A. I. Shapiro, S. K. Solanki, B. T. Montet,
  N. A. Krivova, R. H. Cameron, E. M. Amazo-Gomez. We hope that both
  the comment and our reply lead to fruitful discussions which of the
  two presented scenarios is more likely.

Title: Connecting measurements of solar and stellar brightness
    variations
Authors: Nèmec, N. -E.; Işık, E.; Shapiro, A. I.; Solanki, S. K.;
   Krivova, N. A.; Unruh, Y.
Bibcode: 2020A&A...638A..56N
Altcode: 2020arXiv200406974N
  Context. A comparison of solar and stellar brightness variations is
  hampered by the difference in spectral passbands that are used in
  observations, and also by the possible difference in the inclination
  of the solar and stellar rotation axes from the line of sight. <BR />
  Aims: We calculate the rotational variability of the Sun as it would
  be measured in passbands used for stellar observations. In particular,
  we consider the filter systems used by the CoRoT, Kepler, TESS, and
  Gaia space missions. We also quantify the effect of the inclination
  of the rotation axis on the solar rotational variability. <BR />
  Methods: We employed the spectral and total irradiance reconstruction
  (SATIRE) model to calculate solar brightness variations in different
  filter systems as observed from the ecliptic plane. We then combined
  the simulations of the surface distribution of the magnetic features
  at different inclinations using a surface flux transport model with
  the SATIRE calculations to compute the dependence of the variability
  on the inclination. <BR /> Results: For an ecliptic-bound observer,
  the amplitude of the solar rotational variability, as observed in
  the total solar irradiance (TSI), is 0.68 mmag (averaged over solar
  cycles 21-24). We obtained corresponding amplitudes in the Kepler
  (0.74 mmag), CoRoT (0.73 mmag), TESS (0.62 mmag), Gaia G (0.74 mmag),
  Gaia G<SUB>RP</SUB> (0.62 mmag), and Gaia G<SUB>BP</SUB> (0.86 mmag)
  passbands. Decreasing the inclination of the rotation axis decreases
  the rotational variability. For a sample of randomly inclined stars,
  the variability is on average 15% lower in all filter systems we
  considered. This almost compensates for the difference in amplitudes
  of the variability in TSI and Kepler passbands, making the amplitudes
  derived from the TSI records an ideal representation of the solar
  rotational variability for comparison to Kepler stars with unknown
  inclinations. <BR /> Conclusions: The TSI appears to be a relatively
  good measure of solar variability for comparisons with stellar
  measurements in the CoRoT, Kepler, TESS Gaia G, and Gaia G<SUB>RP</SUB>
  filters. Whereas the correction factors can be used to convert the
  variability amplitude from solar measurements into the values expected
  for stellar missions, the inclination affects the shapes of the light
  curves so that a much more sophisticated correction than simple scaling
  is needed to obtain light curves out of the ecliptic for the Sun.

Title: On the Magnetic Nature of an Exploding Granule as Revealed
    by Sunrise/IMaX
Authors: Guglielmino, Salvo L.; Martínez Pillet, Valentín; Ruiz
   Cobo, Basilio; Bellot Rubio, Luis R.; del Toro Iniesta, José Carlos;
   Solanki, Sami K.; Riethmüller, Tino L.; Zuccarello, Francesca
Bibcode: 2020ApJ...896...62G
Altcode: 2020arXiv200503371G
  We study the photospheric evolution of an exploding granule
  observed in the quiet Sun at high spatial (∼0"3) and temporal
  (31.5 s) resolution by the imaging magnetograph Sunrise/IMaX in 2009
  June. These observations show that the exploding granule is cospatial
  to a magnetic flux emergence event occurring at mesogranular scale
  (up to ∼12 Mm<SUP>2</SUP> area). Using a modified version of the
  SIR code for inverting the IMaX spectropolarimetric measurements, we
  obtain information about the magnetic configuration of this photospheric
  feature. In particular, we find evidence of highly inclined emerging
  fields in the structure, carrying a magnetic flux content up to ∼4
  × 10<SUP>18</SUP> Mx. The balance between gas and magnetic pressure
  in the region of flux emergence, compared with a very quiet region of
  the Sun, indicates that the additional pressure carried by the emerging
  flux increases the total pressure by about 5% and appears to allow the
  granulation to be modified, as predicted by numerical simulations. The
  overall characteristics suggest that a multipolar structure emerges
  into the photosphere, resembling an almost horizontal flux sheet. This
  seems to be associated with exploding granules. Finally, we discuss
  the origin of such flux emergence events.

Title: Detection of the Strongest Magnetic Field in a Sunspot
    Light Bridge
Authors: Castellanos Durán, J. S.; Lagg, Andreas; Solanki, Sami K.;
   van Noort, Michiel
Bibcode: 2020ApJ...895..129C
Altcode: 2020arXiv200312078C; 2020ApJ...895..129D
  Traditionally, the strongest magnetic fields on the Sun have been
  measured in sunspot umbrae. More recently, however, much stronger
  fields have been measured at the ends of penumbral filaments carrying
  the Evershed and counter-Evershed flows. Superstrong fields have
  also been reported within a light bridge separating two umbrae of
  opposite polarities. We aim to accurately determine the strengths of the
  strongest fields in a light bridge using an advanced inversion technique
  and to investigate their detailed structure. We analyze observations
  from the spectropolarimeter on board the Hinode spacecraft of the
  active region AR 11967. The thermodynamic and magnetic configurations
  are obtained by inverting the Stokes profiles using an inversion scheme
  that allows multiple height nodes. Both the traditional 1D inversion
  technique and the so-called 2D coupled inversions, which take into
  account the point-spread function of the Hinode telescope, are used. We
  find a compact structure with an area of 32.7 arcsec<SUP>2</SUP> within
  a bipolar light bridge with field strengths exceeding 5 kG, confirming
  the strong fields in this light bridge reported in the literature. Two
  regions associated with downflows of ∼5 km s<SUP>-1</SUP> harbor
  field strengths larger than 6.5 kG, covering a total area of 2.97
  arcsec<SUP>2</SUP>. The maximum field strength found is 8.2 kG, which
  is the largest ever observed field in a bipolar light bridge up to now.

Title: Simulations Show that Vortex Flows Could Heat the Chromosphere
    in Solar Plage
Authors: Yadav, Nitin; Cameron, R. H.; Solanki, S. K.
Bibcode: 2020ApJ...894L..17Y
Altcode: 2020arXiv200413996Y
  The relationship between vortex flows at different spatial scales
  and their contribution to the energy balance in the chromosphere
  is not yet fully understood. We perform three-dimensional (3D)
  radiation-magnetohydrodynamic simulations of a unipolar solar plage
  region at a spatial resolution of 10 km using the MURaM code. We
  use the swirling-strength criterion that mainly detects the smallest
  vortices present in the simulation data. We additionally degrade our
  simulation data to smooth out the smaller vortices, so that also the
  vortices at larger spatial scales can be detected. Vortex flows at
  various spatial scales are found in our simulation data for different
  effective spatial resolutions. We conclude that the observed large
  vortices are likely clusters of much smaller ones that are not yet
  resolved by observations. We show that the vertical Poynting flux
  decreases rapidly with reduced effective spatial resolutions and
  is predominantly carried by the horizontal plasma motions rather
  than vertical flows. Since the small-scale horizontal motions or the
  smaller vortices carry most of the energy, the energy transported by
  vortices deduced from low-resolution data is grossly underestimated. In
  full-resolution simulation data, the Poynting flux contribution due to
  vortices is more than adequate to compensate for the radiative losses
  in plage, indicating their importance for chromospheric heating.

Title: Optical design of the multi-wavelength imaging coronagraph
    Metis for the solar orbiter mission
Authors: Fineschi, S.; Naletto, G.; Romoli, M.; Da Deppo, V.;
   Antonucci, E.; Moses, D.; Malvezzi, A. M.; Nicolini, G.; Spadaro,
   D.; Teriaca, L.; Andretta, V.; Capobianco, G.; Crescenzio, G.;
   Focardi, M.; Frassetto, F.; Landini, F.; Massone, G.; Melich, R.;
   Nicolosi, P.; Pancrazzi, M.; Pelizzo, M. G.; Poletto, L.; Schühle,
   U.; Uslenghi, M.; Vives, S.; Solanki, S. K.; Heinzel, P.; Berlicki,
   A.; Cesare, S.; Morea, D.; Mottini, S.; Sandri, P.; Alvarez-Herrero,
   A.; Castronuovo, M.
Bibcode: 2020ExA....49..239F
Altcode: 2020ExA...tmp...14F
  This paper describes the innovative optical design of the Metis
  coronagraph for the Solar Orbiter ESA-NASA mission. Metis is a
  multi-wavelength, externally occulted telescope for the imaging
  of the solar corona in both the visible and ultraviolet wavelength
  ranges. Metis adopts a novel occultation scheme for the solar disk,
  that we named "inverse external occulter", for reducing the extremely
  high thermal load on the instrument at the spacecraft perihelion. The
  core of the Metis optical design is an aplanatic Gregorian telescope
  common to both the visible and ultraviolet channels. A suitable
  dichroic beam-splitter, optimized for transmitting a narrow-band in
  the ultraviolet (121.6 nm, HI Lyman-α) and reflecting a broadband
  in the visible (580-640 nm) spectral range, is used to separate the
  two optical paths. Along the visible light optical path, a liquid
  crystal electro-optical modulator, used for the first time in space,
  allows making polarimetric measurements.

Title: Historical solar Ca II K observations at the Kyoto and
    Sacramento Peak observatories
Authors: Chatzistergos, T.; Ermolli, I.; Krivova, N. A.; Solanki, S. K.
Bibcode: 2020JPhCS1548a2007C
Altcode:
  Archives of full-disc solar Ca II K observations covering even short
  periods of time can offer important data to fill observation gaps
  and to allow a better transition from historical to modern data. Two
  examples of such archives are those from the Kyoto and Sacramento
  Peak observatories. As most other historical Ca II K data, they suffer
  from artefacts that need to be accounted for to derive accurate plage
  areas. Here we present the results of our analysis of these archives
  of solar Ca II K images.

Title: The SO/PHI instrument on Solar Orbiter and its data products
Authors: Solanki, Sami K.; Hirzberger, Johann; Wiegelmann, Thomas;
   Gandorfer, Achim; Woch, Joachim; del Toro Iniesta, José Carlos
Bibcode: 2020EGUGA..2217904S
Altcode:
  A central instrument of Solar Orbiter is the Polarimetric and
  Helioseismic Imager, SO/PHI. It is a vector magnetograph that also
  provides data for helioseismology. SO/PHI is composed of two telescopes,
  a full-disk telescope (FDT) and a high-resolution telescope (HRT). The
  HRT will observe at a resolution as high as 200 km on the solar
  surface, while the FDT will obtain the magnetic field and velocity of
  the full solar disc whenever it observes. SO/PHI will be the first
  solar spectro-polarimeter to leave the Sun-Earth line, opening up
  some unique perspectives, such as the first detailed view of the solar
  poles. This will allow not just a more precise and exact mapping of the
  polar magnetic field than possible so far, but will also enable us to
  follow the dynamics of individual magnetic features at high latitudes
  and to determine solar surface and sub-surface flows right up to the
  poles. In addition to its standard data products (vector magnetograms,
  continuum images and maps of the line-of-sight velocity), SO/PHI will
  also provide higher-level data products. These will include synoptic
  charts, local magnetic field extrapolations starting from HRT data and
  global magnetic field extrapolations (from FDT data) with potential
  field source-surface (PFSS) models and possibly also non-potential
  models such as NLFFF (non-linear force-free fields), magnetostatics
  and MHD. The SO/PHI data products will usefully complement the data
  taken by other instruments on Solar Orbiter and on Solar Probe, as
  well as instruments on the ground or in Earth orbit. Combining with
  observations by Earth-based and near-Earth telescopes will enable
  new types of investigations, such as stereoscopic polarimetry and
  stereoscopic helioseismology.

Title: VizieR Online Data Catalog: Rotation periods of 97 solar-like
    stars (Witzke+, 2020)
Authors: Witzke, V.; Reinhold, T.; Shapiro, A. I.; Krivova, N. A.;
   Solanki, S. K.
Bibcode: 2020yCat..36349009W
Altcode:
  The Kepler field of view was selected in order to contain a large
  fraction of solar-like stars. Focusing on stars in the effective
  temperature range of 5600K-5900K, it is challenging to determine their
  rotational periods. <P />Stellar fundamental parameters and rotation
  periods of the 97 periodic stars are presented. <P />(1 data file).

Title: The Sun is less active than other solar-like stars
Authors: Reinhold, Timo; Shapiro, Alexander I.; Solanki, Sami K.;
   Montet, Benjamin T.; Krivova, Natalie A.; Cameron, Robert H.;
   Amazo-Gómez, Eliana M.
Bibcode: 2020Sci...368..518R
Altcode: 2020arXiv200501401R
  The magnetic activity of the Sun and other stars causes their brightness
  to vary. We investigated how typical the Sun’s variability is
  compared with other solar-like stars, i.e., those with near-solar
  effective temperatures and rotation periods. By combining 4 years
  of photometric observations from the Kepler space telescope with
  astrometric data from the Gaia spacecraft, we were able to measure
  photometric variabilities of 369 solar-like stars. Most of those with
  well-determined rotation periods showed higher variability than the Sun
  and are therefore considerably more active. These stars appear nearly
  identical to the Sun except for their higher variability. Therefore,
  we speculate that the Sun could potentially also go through epochs of
  such high variability.

Title: VizieR Online Data Catalog: Plage area composite series
    (Chatzistergos+, 2020)
Authors: Chatzistergos, T.; Ermolli, I.; Krivova, N. A.; Solanki,
   S. K.; Banerjee, D.; Barata, T.; Belik, M.; Gafeira, R.; Garcia,
   A.; Hanaoka, Y.; Hegde, M.; Klimes, J.; Korokhin, V. V.; Lourenco,
   A.; Malherbe, J. -M.; Marchenko, G. P.; Peixinho, N.; Sakurai, T.;
   Tlatov, A. G.
Bibcode: 2020yCat..36390088C
Altcode:
  Annual, monthly, and daily values of the plage area composite series. <P
  />The archives included are those from the Arcetri (Ar), Baikal (Ba),
  Brussels (Br), Calern (CL), Catania (CT), Coimbra (Co), Kanzelhoehe
  (Ka), Kenwood (Ke), Kharkiv (Kh), Kislovodsk (Ki), Kodaikanal taken with
  the spectroheliograph (Ko), Kodaikanal taken with the Twin telescope
  (KT), Kodaikanal taken with the White-Light Active Region Monitor (WARM)
  telescope (KW), Kyoto (Ky), Manila (Ma), Mauna Loa (ML) taken with the
  Precision Solar Photometric Telescope (PSPT), McMath-Hulbert (MM), Mees
  (MS), Meudon taken with the spectroheliograph (MD1), Meudon taken with
  an interference filter (MD2), Mitaka taken with the spectroheliograph
  (Mi1), Mitaka taken with the Solar Flare Telescope with an interference
  filter (Mi2), Mt Wilson (MW), Pic du Midi (PM), SOlar Diameter Imager
  and Surface Mapper (SODISM) telescope on board the PICARD spacecraft
  (PS), Rome taken with the equatorial bar at Monte Mario (Ro), Rome taken
  with the PSPT (RP1), Rome taken with the PSPT with narrow bandwidth
  (RP2), Sacramento Peak (SP), San Fernando taken with the Cartesian
  Full-Disk Telescope (CFDT) 1 (SF1), San Fernando taken with the CFDT2
  (SF2), Schauinsland (Sc), Teide (Te) taken with the Chromospheric
  Telescope (ChroTel), Upice (UP), Valasske Mezirici (VM), Wendelstein
  (WS), and Yerkes (YR) sites <P />(3 data files).

Title: Solar Disk Center Shows Scattering Polarization in the Sr I
    4607 Å Line
Authors: Zeuner, Franziska; Manso Sainz, Rafael; Feller, Alex; van
   Noort, Michiel; Solanki, Sami K.; Iglesias, Francisco A.; Reardon,
   Kevin; Martínez Pillet, Valentín
Bibcode: 2020ApJ...893L..44Z
Altcode: 2020arXiv200403679Z
  Magnetic fields in turbulent, convective high-β plasma naturally
  develop highly tangled and complex topologies - the solar photosphere
  being the paradigmatic example. These fields are mostly undetectable by
  standard diagnostic techniques with finite spatio-temporal resolution
  due to cancellations of Zeeman polarization signals. Observations of
  resonance scattering polarization have been considered to overcome
  these problems. But up to now, observations of scattering polarization
  lack the necessary combination of high sensitivity and high spatial
  resolution in order to directly infer the turbulent magnetic structure
  at the resolution limit of solar telescopes. Here, we report the
  detection of clear spatial structuring of scattering polarization
  in a magnetically quiet solar region at disk center in the Sr I
  4607 Å spectral line on granular scales, confirming theoretical
  expectations. We find that the linear polarization presents a
  strong spatial correlation with the local quadrupole of the radiation
  field. The result indicates that polarization survives the dynamic and
  turbulent magnetic environment of the middle photosphere and is thereby
  usable for spatially resolved Hanle observations. This is an important
  step toward the long-sought goal of directly observing turbulent
  solar magnetic fields at the resolution limit and investigating their
  spatial structure.

Title: 3D Radiative MHD Simulations of Starspots
Authors: Panja, Mayukh; Cameron, Robert; Solanki, Sami K.
Bibcode: 2020ApJ...893..113P
Altcode: 2020arXiv200309656P
  There are no direct spatially resolved observations of spots on stars
  other than the Sun, and starspot properties are inferred indirectly
  through lightcurves and spectropolarimetric data. We present the first
  self-consistent 3D radiative MHD computations of starspots on G2V, K0V,
  and M0V stars, which will help us to better understand observations of
  activity, variability, and magnetic fields in late-type main-sequence
  stars. We used the MURaM code, which has been extensively used to
  compute "realistic" sunspots, for our simulations. We aim to study
  how fundamental starspot properties such as intensity contrast,
  temperature, and magnetic field strength vary with spectral type. We
  first simulated in 2D multiple spots of each spectral type to find
  out appropriate initial conditions for our 3D runs. We find that
  with increasing stellar effective temperature, there is an increase
  in the temperature difference between the umbra of the spot and its
  surrounding photosphere, from 350 K on the M0V star to 1400 K on the
  G2V star. This trend in our simulated starspots is consistent with
  observations. The magnetic field strengths of all the starspot umbrae
  are in the 3-4.5 kG range. The G2V and K0V umbrae have comparable
  magnetic field strengths around 3.5 kG, while the M0V umbra has a
  relatively higher field strength around 4 kG. We discuss the physical
  reasons behind both these trends. All of the three starspots develop
  penumbral filament-like structures with Evershed flows. The average
  Evershed flow speed drops from 1.32 km s<SUP>-1</SUP> in the G2V
  penumbra to 0.6 km s<SUP>-1</SUP> in the M0V penumbra.

Title: Power spectra of solar brightness variations at various
    inclinations
Authors: Nèmec, N. -E.; Shapiro, A. I.; Krivova, N. A.; Solanki,
   S. K.; Tagirov, R. V.; Cameron, R. H.; Dreizler, S.
Bibcode: 2020A&A...636A..43N
Altcode: 2020arXiv200210895N
  Context. Magnetic features on the surfaces of cool stars lead to
  variations in their brightness. Such variations on the surface of
  the Sun have been studied extensively. Recent planet-hunting space
  telescopes have made it possible to measure brightness variations
  in hundred thousands of other stars. The new data may undermine
  the validity of setting the sun as a typical example of a variable
  star. Putting solar variability into the stellar context suffers,
  however, from a bias resulting from solar observations being carried
  out from its near-equatorial plane, whereas stars are generally
  observed at all possible inclinations. <BR /> Aims: We model solar
  brightness variations at timescales from days to years as they would
  be observed at different inclinations. In particular, we consider the
  effect of the inclination on the power spectrum of solar brightness
  variations. The variations are calculated in several passbands that are
  routinely used for stellar measurements. <BR /> Methods: We employ the
  surface flux transport model to simulate the time-dependent spatial
  distribution of magnetic features on both the near and far sides of
  the Sun. This distribution is then used to calculate solar brightness
  variations following the Spectral And Total Irradiance REconstruction
  approach. <BR /> Results: We have quantified the effect of the
  inclination on solar brightness variability at timescales down to a
  single day. Thus, our results allow for solar brightness records to
  be made directly comparable to those obtained by planet-hunting space
  telescopes. Furthermore, we decompose solar brightness variations into
  components originating from the solar rotation and from the evolution
  of magnetic features.

Title: Inflection point in the power spectrum of stellar brightness
    variations. II. The Sun
Authors: Amazo-Gómez, E. M.; Shapiro, A. I.; Solanki, S. K.; Krivova,
   N. A.; Kopp, G.; Reinhold, T.; Oshagh, M.; Reiners, A.
Bibcode: 2020A&A...636A..69A
Altcode: 2020arXiv200203455A
  Context. Young and active stars generally have regular, almost
  sinusoidal, patterns of variability attributed to their rotation,
  while the majority of older and less active stars, including the Sun,
  have more complex and non-regular light curves, which do not have clear
  rotational-modulation signals. Consequently, the rotation periods have
  been successfully determined only for a small fraction of the Sun-like
  stars (mainly the active ones) observed by transit-based planet-hunting
  missions, such as CoRoT, Kepler, and TESS. This suggests that only
  a small fraction of such systems have been properly identified as
  solar-like analogues. <BR /> Aims: We aim to apply a new method of
  determining rotation periods of low-activity stars, such as the Sun. The
  method is based on calculating the gradient of the power spectrum
  (GPS) of stellar brightness variations and identifying a tell-tale
  inflection point in the spectrum. The rotation frequency is then
  proportional to the frequency of that inflection point. In this paper,
  we compare this GPS method to already-available photometric records of
  the Sun. <BR /> Methods: We applied GPS, auto-correlation functions,
  Lomb-Scargle periodograms, and wavelet analyses to the total solar
  irradiance (TSI) time series obtained from the Total Irradiance Monitor
  on the Solar Radiation and Climate Experiment and the Variability of
  solar IRradiance and Gravity Oscillations experiment on the SOlar
  and Heliospheric Observatory missions. We analysed the performance
  of all methods at various levels of solar activity. <BR /> Results:
  We show that the GPS method returns accurate values of solar rotation
  independently of the level of solar activity. In particular, it performs
  well during periods of high solar activity, when TSI variability
  displays an irregular pattern, and other methods fail. Furthermore,
  we show that the GPS and light curve skewness can give constraints
  on facular and spot contributions to brightness variability. <BR />
  Conclusions: Our results suggest that the GPS method can successfully
  determine the rotational periods of stars with both regular and
  non-regular light curves. <P />The two movies are available at <A
  href="https://www.aanda.org/10.1051/0004-6361/201936925/olm">https://www.aanda.org</A>

Title: Solar-cycle irradiance variations over the last four billion
    years
Authors: Shapiro, Anna V.; Shapiro, Alexander I.; Gizon, Laurent;
   Krivova, Natalie A.; Solanki, Sami K.
Bibcode: 2020A&A...636A..83S
Altcode: 2020arXiv200208806S
  Context. The variability of the spectral solar irradiance (SSI) over the
  course of the 11-year solar cycle is one of the manifestations of solar
  magnetic activity. There is strong evidence that the SSI variability
  has an effect on the Earth's atmosphere. The faster rotation of the
  Sun in the past lead to a more vigorous action of solar dynamo and
  thus potentially to larger amplitude of the SSI variability on the
  timescale of the solar activity cycle. This could lead to a stronger
  response of the Earth's atmosphere as well as other solar system
  planets' atmospheres to the solar activity cycle. <BR /> Aims: We
  calculate the amplitude of the SSI and total solar irradiance (TSI)
  variability over the course of the solar activity cycle as a function
  of solar age. <BR /> Methods: We employed the relationship between the
  stellar magnetic activity and the age based on observations of solar
  twins. Using this relation, we reconstructed solar magnetic activity
  and the corresponding solar disk area coverages by magnetic features
  (i.e., spots and faculae) over the last four billion years. These disk
  coverages were then used to calculate the amplitude of the solar-cycle
  SSI variability as a function of wavelength and solar age. <BR />
  Results: Our calculations show that the young Sun was significantly
  more variable than the present Sun. The amplitude of the solar-cycle TSI
  variability of the 600 Myr old Sun was about ten times larger than that
  of the present Sun. Furthermore, the variability of the young Sun was
  spot-dominated (the Sun being brighter at the activity minimum than
  in the maximum), that is, the Sun was overall brighter at activity
  minima than at maxima. The amplitude of the TSI variability decreased
  with solar age until it reached a minimum value at 2.8 Gyr. After this
  point, the TSI variability is faculae-dominated (the Sun is brighter
  at the activity maximum) and its amplitude increases with age.

Title: Solar Photosphere
Authors: Chitta, L. P.; Smitha, H. N.; Solanki, S. K.
Bibcode: 2020orep.bookE...1C
Altcode:
  No abstract at ADS

Title: VizieR Online Data Catalog: Sunspot area catalogue revisited
    (1874-2019) (Mandal+, 2020)
Authors: Mandal, S.; Krivova, N.; Solanki, S. K.; Sinha, N.;
   Banerjee, D.
Bibcode: 2020yCat..36400078M
Altcode:
  A number of observatories around the globe have carried
  out measurements of sunspot areas and positions over the last
  century. RGO, the longest sunspot area database to date, started its
  campaign in 1874 and after continuing for a century, stopped it in
  1976. Several other observatories from different parts of the world
  (e.g., Kodaikanal, Kislovodsk, Debrecen, Rome etc.) also carried out
  such observing programs throughout the 20th century. Sunspot area
  datasets are invaluable historical records of solar magnetic fields
  and are key to understanding the solar variability and its historical
  reconstructions. <P />In this work, we analyze and compare sunspot group
  areas from a total of nine observatories (RGO, Kislovodsk, Pulkovo,
  Debrecen, Kodaikanal, SOON, Rome, Catania, Yunnan). It turns out that
  data from only four observatories (RGO, Kislovodsk, Pulkovo, Debrecen)
  are sufficient to produce cross-calibrated, up-to-date (1874-2019)
  catalogs of daily total and individual group areas. The remaining
  gaps (776 days in total) could not be filled with data from the other
  archives as the missing days lie either before 1922 or after 2016 and
  none of the other archives cover these periods. <P />(2 data files).

Title: Connecting the Wilson depression to the magnetic field
    of sunspots
Authors: Löptien, B.; Lagg, A.; van Noort, M.; Solanki, S. K.
Bibcode: 2020A&A...635A.202L
Altcode: 2020arXiv200207484L
  Context. In sunspots, the geometric height of continuum optical depth
  unity is depressed compared to the quiet Sun. This so-called Wilson
  depression is caused by the Lorentz force of the strong magnetic
  field inside the spots. However, it is not understood in detail yet
  how the Wilson depression is related to the strength and geometry
  of the magnetic field or to other properties of the sunspot. <BR />
  Aims: We aim to study the dependence of the Wilson depression on the
  properties of the magnetic field of the sunspots and how exactly the
  magnetic field contributes to balancing the Wilson depression with
  respect to the gas pressure of the surroundings of the spots. <BR
  /> Methods: Our study is based on 24 spectropolarimetric scans of
  12 individual sunspots performed with Hinode. We derived the Wilson
  depression for each spot using both a recently developed method that
  is based on minimizing the divergence of the magnetic field and an
  approach that was developed earlier, which enforces an equilibrium
  between the gas pressure and the magnetic pressure inside the spot and
  the gas pressure in the quiet Sun, thus neglecting the influence of the
  curvature force. We then performed a statistical analysis by comparing
  the Wilson depression resulting from the two techniques with each other
  and by relating them to various parameters of the sunspots, such as
  their size or the strength of the magnetic field. <BR /> Results: We
  find that the Wilson depression becomes larger for spots with a stronger
  magnetic field, but not as much as one would expect from the increased
  magnetic pressure. This suggests that the curvature integral provides
  an important contribution to the Wilson depression, particularly
  for spots with a weak magnetic field. Our results indicate that the
  geometry of the magnetic field in the penumbra is different between
  spots with different strengths of the average umbral magnetic field.

Title: Effect of metallicity on the detectability of rotational
    periods in solar-like stars
Authors: Witzke, V.; Reinhold, T.; Shapiro, A. I.; Krivova, N. A.;
   Solanki, S. K.
Bibcode: 2020A&A...634L...9W
Altcode: 2020arXiv200101934W
  The accurate determination of stellar rotation periods is important
  for estimating stellar ages and for understanding stellar activity
  and evolution. While rotation periods can be determined for about
  thirty thousand stars in the Kepler field, there are over one
  hundred thousand stars, especially with low photometric variability
  and irregular pattern of variations, for which rotational periods
  are unknown. Here we investigate the effect of metallicity on the
  detectability of rotation periods. This is done by synthesising light
  curves of hypothetical stars that are identical to our Sun with the
  exception of the metallicity. These light curves are then used as an
  input to the period determination algorithms. We find that the success
  rate for recovering the rotation signal has a minimum close to the solar
  metallicity value. This can be explained by the compensation effect
  of facular and spot contributions. In addition, selecting solar-like
  stars with near-solar effective temperature and photometric variability,
  and with metallicity between M/H = -0.35 and M/H = 0.35 from the Kepler
  sample, we analyse the fraction of stars for which rotational periods
  have been detected as a function of metallicity. In agreement with
  our theoretical estimate we find a local minimum for the detection
  fraction close to the solar metallicity. We further report rotation
  periods of 87 solar-like Kepler stars for the first time.

Title: The influence of NLTE effects in Fe I lines on an inverted
    atmosphere. I. 6301 Å and 6302 Å lines formed in 1D NLTE
Authors: Smitha, H. N.; Holzreuter, R.; van Noort, M.; Solanki, S. K.
Bibcode: 2020A&A...633A.157S
Altcode: 2019arXiv191207007S
  Context. Ultraviolet overionisation of iron atoms in the solar
  atmosphere leads to deviations in their level populations based on
  Saha-Boltzmann statistics. This causes their line profiles to form in
  non-local thermodynamic equilibrium (NLTE) conditions. When inverting
  such profiles to determine atmospheric parameters, the NLTE effects
  are often neglected and other quantities are tweaked to compensate for
  deviations from the LTE. <BR /> Aims: We investigate how the routinely
  employed LTE inversion of iron lines formed in NLTE underestimates
  or overestimates atmospheric quantities, such as temperature (T),
  line-of-sight velocity (v<SUB>LOS</SUB>), magnetic field strength (B),
  and inclination (γ) while the earlier papers have focused mainly
  on T. Our findings has wide-ranging consequences since many results
  derived in solar physics are based on inversions of Fe I lines carried
  out in LTE. <BR /> Methods: We synthesized the Stokes profiles of Fe I
  6301.5 Å and 6302.5 Å lines in both LTE and NLTE using a snapshot of
  a 3D magnetohydrodynamic simulation. The profiles were then inverted
  in LTE. We considered the atmosphere inferred from the inversion of
  LTE profiles as the fiducial model and compared it to the atmosphere
  resulting from the inversion of NLTE profiles. The observed differences
  have been attributed to NLTE effects. <BR /> Results: Neglecting the
  NLTE effects introduces errors in the inverted atmosphere. While the
  errors in T can go up to 13%, in v<SUB>LOS</SUB> and B, the errors can
  go as high as 50% or above. We find these errors to be present at all
  three inversion nodes. Importantly, they survive degradation from the
  spatial averaging of the profiles. <BR /> Conclusions: We provide an
  overview of how neglecting NLTE effects influences the values of T,
  v<SUB>LOS</SUB>, B, and γ that are determined by inverting the Fe I
  6300 Å line pair, as observed, for example, by Hinode/SOT/SP. Errors
  are found at the sites of granules, intergranular lanes, magnetic
  elements, and basically in every region susceptible to NLTE effects. For
  an accurate determination of the atmospheric quantities and their
  stratification, it is, therefore, important to take the NLTE effects
  into account.

Title: Inflection point in the power spectrum of stellar brightness
    variations. I. The model
Authors: Shapiro, A. I.; Amazo-Gómez, E. M.; Krivova, N. A.; Solanki,
   S. K.
Bibcode: 2020A&A...633A..32S
Altcode: 2019arXiv191008351S
  Context. Considerable effort has gone into using light curves observed
  by such space telescopes as CoRoT, Kepler, and TESS for determining
  stellar rotation periods. While rotation periods of active stars
  can be reliably determined, the light curves of many older and less
  active stars, such as stars that are similar to the Sun, are quite
  irregular. This hampers the determination of their rotation periods. <BR
  /> Aims: We aim to examine the factors causing these irregularities in
  stellar brightness variations and to develop a method for determining
  rotation periods for low-activity stars with irregular light curves. <BR
  /> Methods: We extended the Spectral And Total Irradiance Reconstruction
  approach for modeling solar brightness variations to Sun-like stars. We
  calculated the power spectra of stellar brightness variations for
  various combinations of parameters that define the surface configuration
  and evolution of stellar magnetic features. <BR /> Results: The short
  lifetime of spots in comparison to the stellar rotation period, as well
  as the interplay between spot and facular contributions to brightness
  variations of stars with near solar activity, cause irregularities in
  their light curves. The power spectra of such stars often lack a peak
  associated with the rotation period. Nevertheless, the rotation period
  can still be determined by measuring the period where the concavity
  of the power spectrum plotted in the log-log scale changes its sign,
  that is, by identifying the position of the inflection point. <BR />
  Conclusions: The inflection point of the (log-log) power spectrum is
  found to be a new diagnostic for stellar rotation periods which is
  shown to work even in cases where the power spectrum shows no peak at
  the rotation rate.

Title: Fast downflows in a chromospheric filament
Authors: Sowmya, K.; Lagg, A.; Solanki, S. K.; Castellanos Durán,
   J. S.
Bibcode: 2020IAUS..354..454S
Altcode: 2019arXiv191206586S
  An active region filament in the upper chromosphere is studied using
  spectropolarimetric data in He i 10830 Å from the GREGOR telescope. A
  Milne-Eddingon based inversion of the Unno-Rachkovsky equations is
  used to retrieve the velocity and the magnetic field vector of the
  region. The plasma velocity reaches supersonic values closer to the feet
  of the filament barbs and coexist with a slow velocity component. Such
  supersonic velocities result from the acceleration of the plasma as it
  drains from the filament spine through the barbs. The line-of-sight
  magnetic fields have strengths below 200 G in the filament spine and
  in the filament barbs where fast downflows are located, their strengths
  range between 100 - 700 G.

Title: First results on the search for chameleons with the KWISP
    detector at CAST
Authors: Arguedas Cuendis, S.; Baier, J.; Barth, K.; Baum, S.; Bayirli,
   A.; Belov, A.; Bräuninger, H.; Cantatore, G.; Carmona, J. M.; Castel,
   J. F.; Cetin, S. A.; Dafni, T.; Davenport, M.; Dermenev, A.; Desch,
   K.; Döbrich, B.; Fischer, H.; Funk, W.; García, J. A.; Gardikiotis,
   A.; Garza, J. G.; Gninenko, S.; Hasinoff, M. D.; Hoffmann, D. H. H.;
   Iguaz, F. J.; Irastorza, I. G.; Jakovčić, K.; Kaminski, J.; Karuza,
   M.; Krieger, C.; Lakić, B.; Laurent, J. M.; Luzón, G.; Maroudas, M.;
   Miceli, L.; Neff, S.; Ortega, I.; Ozbey, A.; Pivovaroff, M. J.; Rosu,
   M.; Ruz, J.; Chóliz, E. Ruiz; Schmidt, S.; Schumann, M.; Semertzidis,
   Y. K.; Solanki, S. K.; Stewart, L.; Tsagris, I.; Vafeiadis, T.; Vogel,
   J. K.; Vretenar, M.; Yildiz, S. C.; Zioutas, K.
Bibcode: 2019PDU....2600367A
Altcode: 2019arXiv190601084A
  We report on a first measurement with a sensitive opto-mechanical force
  sensor designed for the direct detection of coupling of real chameleons
  to matter. These dark energy candidates could be produced in the Sun
  and stream unimpeded to Earth. The KWISP detector installed on the
  CAST axion search experiment at CERN looks for tiny displacements of a
  thin membrane caused by the mechanical effect of solar chameleons. The
  displacements are detected by a Michelson interferometer with a homodyne
  readout scheme. The sensor benefits from the focusing action of the
  ABRIXAS X-ray telescope installed at CAST, which increases the chameleon
  flux on the membrane. A mechanical chopper placed between the telescope
  output and the detector modulates the incoming chameleon stream. We
  present the results of the solar chameleon measurements taken at CAST in
  July 2017, setting an upper bound on the force acting on the membrane
  of 80 pN at 95% confidence level. The detector is sensitive for direct
  coupling to matter 10<SUP>4</SUP> ≤β<SUB>m</SUB> ≤ 10<SUP>8</SUP>
  , where the coupling to photons is locally bound to β<SUB>γ</SUB>
  ≤ 10<SUP>11</SUP> .

Title: The Polarimetric and Helioseismic Imager on Solar Orbiter
Authors: Mueller, D.; Solanki, S. K.; del Toro Iniesta, J. C.
Bibcode: 2019AGUFMSH21D3292M
Altcode:
  The Polarimetric and Helioseismic Imager on the Solar Orbiter mission
  (SO/PHI) is the first magnetograph and helioseismology instrument
  to observe the Sun from outside the Sun-Earth line. It is the key
  instrument meant to address the top-level science question: How does
  the solar dynamo work and drive connections between the Sun and the
  heliosphere? SO/PHI will also play an important role in answering the
  other top-level science questions of Solar Orbiter. It will provide
  valuable supporting observations for Parker Solar Probe. <P />The
  instrument carries out narrow-band imaging spectro-polarimetry using a
  tunable LiNbO3 Fabry-Perot etalon, while the polarisation modulation is
  done with liquid crystal variable retarders (LCVRs). The line and the
  nearby continuum are sampled at six wavelength points and the data are
  recorded by a 2k x 2k CMOS detector. To save valuable telemetry, the
  raw data are reduced already on board, including being inverted under
  the assumption of a Milne-Eddington atmosphere. SO/PHI is composed of
  two telescopes, the Full Disc Telescope (FDT), covers the full solar
  disc at all phases of the orbit, while the High Resolution Telescope
  (HRT), can resolve structures as small as 200 km on the Sun at closest
  perihelion. <P />The standard data products of SO/PHI are maps of the
  photospheric magnetic field vector, line-of-sight velocity and continuum
  intensity with a highest cadence of one minute. The operational modes
  of SO/PHI are kept highly flexible allowing to adjust to the actual
  science goal chosen for a Solar Orbiter operation window.

Title: Readdressing the UV solar variability with SATIRE-S: non-LTE
    effects
Authors: Tagirov, R. V.; Shapiro, A. I.; Krivova, N. A.; Unruh, Y. C.;
   Yeo, K. L.; Solanki, S. K.
Bibcode: 2019A&A...631A.178T
Altcode: 2019arXiv190911736T
  Context. Solar spectral irradiance (SSI) variability is one of the key
  inputs to models of the Earth's climate. Understanding solar irradiance
  fluctuations also helps to place the Sun among other stars in terms of
  their brightness variability patterns and to set detectability limits
  for terrestrial exoplanets. <BR /> Aims: One of the most successful
  and widely used models of solar irradiance variability is Spectral
  And Total Irradiance REconstruction model (SATIRE-S). It uses spectra
  of the magnetic features and surrounding quiet Sun that are computed
  with the ATLAS9 spectral synthesis code under the assumption of local
  thermodynamic equilibrium (LTE). SATIRE-S has been at the forefront
  of solar variability modelling, but due to the limitations of the LTE
  approximation its output SSI has to be empirically corrected below
  300 nm, which reduces the physical consistency of its results. This
  shortcoming is addressed in the present paper. <BR /> Methods: We
  replaced the ATLAS9 spectra of all atmospheric components in SATIRE-S
  with spectra that were calculated using the Non-LTE Spectral SYnthesis
  (NESSY) code. To compute the spectrum of the quiet Sun and faculae,
  we used the temperature and density stratification models of the FAL
  set. <BR /> Results: We computed non-LTE contrasts of spots and faculae
  and combined them with the corresponding fractional disc coverages,
  or filling factors, to calculate the total and spectral irradiance
  variability during solar cycle 24. The filling factors have been derived
  from solar full-disc magnetograms and continuum images recorded by
  the Helioseismic and Magnetic Imager on Solar Dynamics Observatory
  (SDO/HMI). <BR /> Conclusions: The non-LTE contrasts yield total and
  spectral solar irradiance variations that are in good agreement with
  empirically corrected LTE irradiance calculations. This shows that
  the empirical correction applied to the SATIRE-S total and spectral
  solar irradiance is consistent with results from non-LTE computations.

Title: Superstrong photospheric magnetic fields in sunspot penumbrae
Authors: Siu-Tapia, A.; Lagg, A.; van Noort, M.; Rempel, M.; Solanki,
   S. K.
Bibcode: 2019A&A...631A..99S
Altcode: 2019arXiv190913619S
  Context. Recently, there have been some reports of unusually strong
  photospheric magnetic fields (which can reach values of over 7 kG)
  inferred from Hinode SOT/SP sunspot observations within penumbral
  regions. These superstrong penumbral fields are even larger than the
  strongest umbral fields on record and appear to be associated with
  supersonic downflows. The finding of such fields has been controversial
  since they seem to show up only when spatially coupled inversions
  are performed. <BR /> Aims: Here, we investigate and discuss the
  reliability of those findings by studying in detail observed spectra
  associated with particularly strong magnetic fields at the inner edge
  of the penumbra of active region 10930. <BR /> Methods: We applied
  classical diagnostic methods and various inversions with different
  model atmospheres to the observed Stokes profiles in two selected
  pixels with superstrong magnetic fields, and compared the results
  with a magnetohydrodynamic simulation of a sunspot whose penumbra
  contains localized regions with strong fields (nearly 5 kG at τ = 1)
  associated with supersonic downflows. <BR /> Results: The different
  inversions provide different results: while the SPINOR 2D inversions
  consider a height-dependent single-component model and return B &gt;
  7 kG and supersonic positive v<SUB>LOS</SUB> (corresponding to a
  counter-Evershed flow), height-dependent two-component inversions
  suggest the presence of an umbral component (almost at rest)
  with field strengths ∼4 - 4.2 kG and a penumbral component with
  v<SUB>LOS</SUB> ∼ 16 - 18 km s<SUP>-1</SUP> and field strengths up
  to ∼5.8 kG. Likewise, height-independent two-component inversions
  find a solution for an umbral component and a strongly redshifted
  (v<SUB>LOS</SUB> ∼ 15 - 17 km s<SUP>-1</SUP>) penumbral component
  with B ∼ 4 kG. According to a Bayesian information criterion,
  the inversions providing a better balance between the quality of
  the fits and the number of free parameters considered by the models
  are the height-independent two-component inversions, but they lie
  only slightly above the SPINOR 2D inversions. Since it is expected
  that the physical parameters all display considerable gradients with
  height, as supported by magnetohydrodynamic (MHD) sunspot simulations,
  the SPINOR 2D inversions are the preferred ones. <BR /> Conclusions:
  According to the MHD sunspot simulation analyzed here, the presence
  of counter-Evershed flows in the photospheric penumbra can lead to
  the necessary conditions for the observation of ∼5 kG fields at the
  inner penumbra. Although a definite conclusion about the potential
  existence of fields in excess of 7 kG cannot be given, their nature
  could be explained (based on the simulation results) as the consequence
  of the extreme dynamical effects introduced by highly supersonic
  counter-Evershed flows (v<SUB>LOS</SUB> &gt; 10 km s<SUP>-1</SUP>
  and up to ∼30 km s<SUP>-1</SUP> according to SPINOR 2D). The latter
  are much faster and more compressive downflows than those found in
  the MHD simulations and therefore could lead to field intensification
  up to considerably stronger fields. Also, a lower gas density would
  lead to a deeper depression of the τ = 1 surface, making possible
  the observation of deeper-lying stronger fields. The superstrong
  magnetic fields are expected to be nearly force-free, meaning that
  they can attain much larger strengths than expected when considering
  only balance between magnetic pressure and the local gas pressure.

Title: Delving into the Historical Ca II K Archive from the Kodaikanal
Observatory: The Potential of the Most Recent Digitized Series
Authors: Chatzistergos, Theodosios; Ermolli, Ilaria; Solanki, Sami K.;
   Krivova, Natalie A.; Banerjee, Dipankar; Jha, Bibhuti K.; Chatterjee,
   Subhamoy
Bibcode: 2019SoPh..294..145C
Altcode: 2019arXiv190805493C
  Full-disc Ca II K photographic observations of the Sun carry direct
  information as regards the evolution of solar-plage regions for more
  than a century and are therefore a unique dataset for solar-activity
  studies. For a long time Ca II K observations were barely explored, but
  recent digitizations of multiple archives have allowed their extensive
  analysis. However, various studies have reported diverse results partly
  due to the insufficient quality of the digitized data. Furthermore,
  inhomogeneities have been identified within the individual archives,
  which, at least partly, could be due to the digitization. As a result,
  some of the archives, e.g. that from the Kodaikanal observatory, were
  re-digitized. The results obtained by different authors who analyzed the
  data from the new digitization of the Kodaikanal archive differ from
  each other and from those derived from the old digitization. Since
  the data were processed and analyzed using different techniques,
  it is not clear, however, whether the differences are due to the
  digitization or the processing of the data. To understand the reasons
  for such discrepancies, we analyze here the data from the two most
  recent digitizations of this archive. We use the same techniques
  to consistently process the images from both archives and to derive
  the plage areas from them. Some issues have been identified in both
  digitizations, implying that they are intrinsic characteristics of
  the data. Moreover, errors in timing of the observations plague both
  digitizations. Overall, the most recent 16-bit digitization offers an
  improvement over the earlier 8-bit one. It also includes considerably
  more data and should be preferred.

Title: A comparison between solar plage and network properties
Authors: Buehler, D.; Lagg, A.; van Noort, M.; Solanki, S. K.
Bibcode: 2019A&A...630A..86B
Altcode: 2019arXiv190807464B
  <BR /> Aims: We compare the properties of kG magnetic structures
  in the solar network and in active region plage at high spatial
  resolution. <BR /> Methods: Our analysis used six SP scans of the solar
  disc centre aboard Hinode SOT and inverted the obtained spectra of the
  photospheric 6302 Å line pair using the 2D SPINOR code. <BR /> Results:
  Photospheric magnetic field concentrations in network and plage areas
  are on average 1.5 kG strong with inclinations of 10° -20°, and have
  &lt; 400 m s<SUP>-1</SUP> internal and 2-3 km s<SUP>-1</SUP> external
  downflows. At the disc centre, the continuum intensity of magnetic
  field concentrations in the network are on average 10% brighter than the
  mean quiet Sun, whilst their plage counterparts are 3% darker. A more
  detailed analysis revealed that all sizes of individual kG patches in
  the network have 150 G higher field strengths on average, 5% higher
  continuum contrasts, and 800 m s<SUP>-1</SUP> faster surrounding
  downflows than similarly sized patches in the plage. The speed of
  the surrounding downflows also correlates with the patch area, and
  patches containing pores can produce supersonic flows exceeding 11 km
  s<SUP>-1</SUP> in individual pixels. Furthermore, the magnetic canopies
  of kG patches are on average 9° more horizontal in the plage compared
  to the network. <BR /> Conclusions: Most of the differences between the
  network and plage are due to their different patch size distributions,
  but the intrinsic differences between similarly sized patches likely
  results from the modification of the convection photospheric convection
  with increasing amounts of magnetic flux.

Title: Performance Analysis of the SO/PHI Software Framework for
    On-board Data Reduction
Authors: Albert, K.; Hirzberger, J.; Busse, D.; Rodríguez, J. Blanco;
   Castellanos Duran, J. S.; Cobos Carrascosa, J. P.; Fiethe, B.;
   Gandorfer, A.; Guan, Y.; Kolleck, M.; Lagg, A.; Lange, T.; Michalik,
   H.; Solanki, S. K.; del Toro Iniesta, J. C.
Bibcode: 2019ASPC..523..151A
Altcode: 2019arXiv190508690A
  The Polarimetric and Helioseismic Imager (PHI) is the first deep-space
  solar spectropolarimeter, on-board the Solar Orbiter (SO) space
  mission. It faces: stringent requirements on science data accuracy, a
  dynamic environment, and severe limitations on telemetry volume. SO/PHI
  overcomes these restrictions through on-board instrument calibration
  and science data reduction, using dedicated firmware in FPGAs. This
  contribution analyses the accuracy of a data processing pipeline by
  comparing the results obtained with SO/PHI hardware to a reference
  from a ground computer. The results show that for the analyzed pipeline
  the error introduced by the firmware implementation is well below the
  requirements of SO/PHI.

Title: Achievements of Hinode in the first eleven years
Authors: Hinode Review Team; Al-Janabi, Khalid; Antolin, Patrick;
   Baker, Deborah; Bellot Rubio, Luis R.; Bradley, Louisa; Brooks,
   David H.; Centeno, Rebecca; Culhane, J. Leonard; Del Zanna, Giulio;
   Doschek, George A.; Fletcher, Lyndsay; Hara, Hirohisa; Harra,
   Louise K.; Hillier, Andrew S.; Imada, Shinsuke; Klimchuk, James A.;
   Mariska, John T.; Pereira, Tiago M. D.; Reeves, Katharine K.; Sakao,
   Taro; Sakurai, Takashi; Shimizu, Toshifumi; Shimojo, Masumi; Shiota,
   Daikou; Solanki, Sami K.; Sterling, Alphonse C.; Su, Yingna; Suematsu,
   Yoshinori; Tarbell, Theodore D.; Tiwari, Sanjiv K.; Toriumi, Shin;
   Ugarte-Urra, Ignacio; Warren, Harry P.; Watanabe, Tetsuya; Young,
   Peter R.
Bibcode: 2019PASJ...71R...1H
Altcode:
  Hinode is Japan's third solar mission following Hinotori (1981-1982)
  and Yohkoh (1991-2001): it was launched on 2006 September 22 and is in
  operation currently. Hinode carries three instruments: the Solar Optical
  Telescope, the X-Ray Telescope, and the EUV Imaging Spectrometer. These
  instruments were built under international collaboration with the
  National Aeronautics and Space Administration and the UK Science and
  Technology Facilities Council, and its operation has been contributed
  to by the European Space Agency and the Norwegian Space Center. After
  describing the satellite operations and giving a performance evaluation
  of the three instruments, reviews are presented on major scientific
  discoveries by Hinode in the first eleven years (one solar cycle long)
  of its operation. This review article concludes with future prospects
  for solar physics research based on the achievements of Hinode.

Title: Solar irradiance variability over last four billion years
Authors: Shapiro, Anna V.; Shapiro, Alexander I.; Gizon, Laurent;
   Krivova, Natalie A.; Solanki, Sami K.
Bibcode: 2019EPSC...13.2071S
Altcode:
  The action of dynamo generates magnetic field in the solar
  interior. This field then travels through the convective zone and
  emerges on the solar surface, leading to a various manifestations
  of solar magnetic activity. One of the most appealing among them
  is the variations of Spectral Solar Irradiance (SSI). There is an
  evidence that these variations have substantial effect on the Earth's
  climate system. The faster rotation of the Sun in the past led to
  a more vigorous dynamo and consequently larger amplitude of solar
  spectral irradiance variability. This could led to a stronger effect
  of the SSI variability on the Earth. The main goal of our study is to
  calculate the amplitude of the SSI variability over the course of the
  solar activity cycle (which presently lasts 11 years but could have
  different duration in the past) as a function of solar age. We utilise
  recently published relation between the stellar chromospheric activity
  and stellar age to reconstruct solar chromospheric activity back in
  time. It is used to calculate solar disk coverages by magnetic features,
  i.e. solar spots and faculae. Corresponding brightness variations are
  then computed using the SATIRE (which stands for Spectral and Total
  Irradiance Reconstruction) approach. Our study shows that the facular
  component of the irradiance variability over the solar activity cycle
  decreases slower with the solar age than the spot component. This
  makes the dependence of the amplitude of the solar variability on the
  age non-monotonic. The am- plitude decreases for the young Sun till
  it reaches minimum value and then gradually increases again. The
  variability of the Total Solar Irradiance (TSI, i.e. irradiance
  integrated over the entire spectral domain) changes from being spot- to
  facular-dominated at the solar age of about 2.8 Gyr. Our calculations
  show that the amplitude of the TSI variability of 600-Myr Sun was one
  order of magnitude larger than the present-day value. We have found that
  the age of the transition between spot- and facular-dominated regimes
  of the variability depends on the wavelength. For example, it is about
  1.3 Gyr for the 210-400 nm spectral domain and becomes approximately
  3.7 Gyr for the 400-700 nm spectral range. Our calculations of the past
  solar irradiance variability on the activity cycle timescale might be
  of interest for paleoclimate researchers as well as for modelling of
  atmospheres of exoplanets.

Title: The Solar-C_EUVST mission
Authors: Shimizu, Toshifumi; Imada, Shinsuke; Kawate, Tomoko;
   Ichimoto, Kiyoshi; Suematsu, Yoshinori; Hara, Hirohisa; Katsukawa,
   Yukio; Kubo, Masahito; Toriumi, Shin; Watanabe, Tetsuya; Yokoyama,
   Takaaki; Korendyke, Clarence M.; Warren, Harry P.; Tarbell, Ted; De
   Pontieu, Bart; Teriaca, Luca; Schühle, Udo H.; Solanki, Sami; Harra,
   Louise K.; Matthews, Sarah; Fludra, A.; Auchère, F.; Andretta, V.;
   Naletto, G.; Zhukov, A.
Bibcode: 2019SPIE11118E..07S
Altcode:
  Solar-C EUVST (EUV High-Throughput Spectroscopic Telescope) is a
  solar physics mission concept that was selected as a candidate for
  JAXA competitive M-class missions in July 2018. The onboard science
  instrument, EUVST, is an EUV spectrometer with slit-jaw imaging
  system that will simultaneously observe the solar atmosphere from the
  photosphere/chromosphere up to the corona with seamless temperature
  coverage, high spatial resolution, and high throughput for the first
  time. The mission is designed to provide a conclusive answer to the
  most fundamental questions in solar physics: how fundamental processes
  lead to the formation of the solar atmosphere and the solar wind, and
  how the solar atmosphere becomes unstable, releasing the energy that
  drives solar flares and eruptions. The entire instrument structure
  and the primary mirror assembly with scanning and tip-tilt fine
  pointing capability for the EUVST are being developed in Japan, with
  spectrograph and slit-jaw imaging hardware and science contributions
  from US and European countries. The mission will be launched and
  installed in a sun-synchronous polar orbit by a JAXA Epsilon vehicle in
  2025. ISAS/JAXA coordinates the conceptual study activities during the
  current mission definition phase in collaboration with NAOJ and other
  universities. The team is currently working towards the JAXA final
  down-selection expected at the end of 2019, with strong support from
  US and European colleagues. The paper provides an overall description
  of the mission concept, key technologies, and the latest status.

Title: Stellar Physics with High-Resolution UV Spectropolarimetry
Authors: Morin, Julien; Bouret, Jean-Claude; Neiner, Coralie; Aerts,
   Conny; Bagnulo, Stefano; Catala, Claude; Charbonnel, Corinne;
   Evans, Chris; Fossati, Luca; Garcia, Miriam; Gómez de Castro,
   Ana I; Herrero, Artemio; Hussain, Gaitee; Kaper, Lex; Kochukhov,
   Oleg; Konstantinova-Antova, Renada; de Koter, Alex; Kraus, Michaela;
   Jiří\K{r}tička; Lèbre, Agnes; Lueftinger, Theresa; Meynet, Georges;
   Petit, Pascal; Shore, Steve; Solanki, Sami; Stelzer, Beate; Strugarek,
   Antoine; Vidotto, Aline; Vink, Jorick S
Bibcode: 2019arXiv190801545M
Altcode:
  Current burning issues in stellar physics, for both hot and cool
  stars, concern their magnetism. In hot stars, stable magnetic fields
  of fossil origin impact their stellar structure and circumstellar
  environment, with a likely major role in stellar evolution. However,
  this role is complex and thus poorly understood as of today. It
  needs to be quantified with high-resolution UV spectropolarimetric
  measurements. In cool stars, UV spectropolarimetry would provide
  access to the structure and magnetic field of the very dynamic upper
  stellar atmosphere, providing key data for new progress to be made
  on the role of magnetic fields in heating the upper atmospheres,
  launching stellar winds, and more generally in the interaction of
  cool stars with their environment (circumstellar disk, planets) along
  their whole evolution. UV spectropolarimetry is proposed on missions
  of various sizes and scopes, from POLLUX on the 15-m telescope LUVOIR
  to the Arago M-size mission dedicated to UV spectropolarimetry.

Title: Cosmic-ray variability on the multi-millennial time scale:
    A new multi-proxy reconstruction
Authors: Usoskin, I.; Wu, C. J.; Krivova, N.; Solanki, S. K.;
   Kovaltsov, G.; Baroni, M.; Bard, E.
Bibcode: 2019ICRC...36.1164U
Altcode: 2019PoS...358.1164U
  No abstract at ADS

Title: Opacity distribution functions for stellar spectra synthesis
Authors: Cernetic, M.; Shapiro, A. I.; Witzke, V.; Krivova, N. A.;
   Solanki, S. K.; Tagirov, R. V.
Bibcode: 2019A&A...627A.157C
Altcode: 2019arXiv190603112C
  Context. Stellar spectra synthesis is essential for the characterization
  of potential planetary hosts. In addition, comprehensive stellar
  variability calculations with fast radiative transfer are needed
  to disentangle planetary transits from stellar magnetically driven
  variability. The planet-hunting space telescopes, such as CoRoT, Kepler,
  and TESS, bring vast quantities of data, rekindling the interest in
  fast calculations of the radiative transfer. <BR /> Aims: We revisit
  the opacity distribution functions (ODF) approach routinely applied to
  speed up stellar spectral synthesis. To achieve a considerable speedup
  relative to the state of the art, we further optimize the approach and
  search for the best ODF configuration. Furthermore, we generalize the
  ODF approach for fast calculations of flux in various filters often
  used in stellar observations. <BR /> Methods: In a parameter-sweep
  fashion, we generated ODF in the spectral range from UV to IR with
  different setups. The most accurate ODF configuration for each spectral
  interval was determined. We adapted the wavelength grid based on the
  transmission curve for calculations of the radiative fluxes through
  filters before performing the normal ODF procedure. <BR /> Results:
  Our optimum ODF configuration allows for a three-fold speedup, compared
  to the previously used ODF configurations. The ODF generalization to
  calculate fluxes through filters results in a speedup of more than
  two orders of magnitude.

Title: ALMA detection of dark chromospheric holes
Authors: White, Stephen M.; Loukitcheva, Maria A.; Solanki, Sami K.
Bibcode: 2019AAS...23421704W
Altcode:
  Atacama Large Millimeter/submillimeter Array (ALMA) observations of a
  quiet-Sun region at a wavelength of 3 mm are compared with available
  chromospheric observations in the UV and visible as well as with
  photospheric magnetograms. The ALMA images clearly reveal the presence
  of distinctive cold areas in the millimeter maps having temperatures of
  around 60% of the normal quiet Sun at 3 mm, which are not seen in the
  other data. We speculate that ALMA is sensing cool chromospheric gas,
  whose presence had earlier been inferred from infrared CO spectra.

Title: ALMA Detection of Dark Chromospheric Holes in the Quiet Sun
Authors: Loukitcheva, Maria A.; White, Stephen M.; Solanki, Sami K.
Bibcode: 2019ApJ...877L..26L
Altcode: 2019arXiv190506763L
  We present Atacama Large Millimeter/submillimeter Array (ALMA)
  observations of a quiet-Sun region at a wavelength of 3 mm, obtained
  during the first solar ALMA cycle on 2017 April 27, and compare them
  with available chromospheric observations in the UV and visible as
  well as with photospheric magnetograms. ALMA images clearly reveal the
  presence of distinct particularly dark/cool areas in the millimeter
  maps with temperatures as low as 60% of the normal quiet Sun at 3 mm,
  which are not seen in the other data. We speculate that ALMA is sensing
  cool chromospheric gas, whose presence had earlier been inferred from
  infrared CO spectra.

Title: Recovering the unsigned photospheric magnetic field from Ca
    II K observations
Authors: Chatzistergos, Theodosios; Ermolli, Ilaria; Solanki, Sami K.;
   Krivova, Natalie A.; Giorgi, Fabrizio; Yeo, Kok Leng
Bibcode: 2019A&A...626A.114C
Altcode: 2019arXiv190503453C
  Context. A number of studies have aimed at defining the exact form
  of the relation between magnetic field strength and Ca II H and K
  core brightness. All previous studies have however been restricted
  to isolated regions on the solar disc or to a limited set of
  observations. <BR /> Aims: We reassess the relationship between the
  photospheric magnetic field strength and the Ca II K intensity for
  a variety of surface features as a function of the position on the
  disc and the solar activity level. This relationship can be used to
  recover the unsigned photospheric magnetic field from images recorded
  in the core of Ca II K line. <BR /> Methods: We have analysed 131
  pairs of high-quality, full-disc, near-co-temporal observations from
  the Helioseismic and Magnetic Imager (SDO/HMI) and Precision Solar
  Photometric Telescope (Rome/PSPT) spanning half a solar cycle. To
  analytically describe the observationally determined relation, we
  considered three different functions: a power law with an offset,
  a logarithmic function, and a power-law function of the logarithm
  of the magnetic flux density. We used the obtained relations to
  reconstruct maps of the line-of-sight component of the unsigned
  magnetic field (unsigned magnetograms) from Ca II K observations,
  which were then compared to the original magnetograms. <BR /> Results:
  We find that both power-law functions represent the data well, while
  the logarithmic function is good only for quiet periods. We see
  no significant variation over the solar cycle or over the disc in
  the derived fit parameters, independently of the function used. We
  find that errors in the independent variable, which are usually
  not accounted for, introduce attenuation bias. To address this, we
  binned the data with respect to the magnetic field strength and Ca II
  K contrast separately and derived the relation for the bisector of
  the two binned curves. The reconstructed unsigned magnetograms show
  good agreement with the original ones. Root mean square differences
  are less than 90 G. The results were unaffected by the stray-light
  correction of the SDO/HMI and Rome/PSPT data. <BR /> Conclusions:
  Our results imply that accurately processed and calibrated Ca II K
  observations can be used to reconstruct unsigned magnetograms by using
  the relations derived in our study.

Title: Moving Magnetic Features around a Pore
Authors: Kaithakkal, A.; Riethmueller, T.; Solanki, S. K.; Lagg, A.
Bibcode: 2019ASPC..526..307K
Altcode:
  Moving magnetic features (MMFs) are small-scale magnetic elements
  observed to move radially outward from sunspots. Some studies have
  reported the presence of MMFs around pores as well. We analyzed data
  from SunriseII/IMaX observations obtained on 2013 June 12 between
  23:39:10 and 23:55:37 UT. IMaX scanned the Fe I 5250.225 Å spectral
  line at eight wavelength positions and recorded the full Stokes vector
  at each of these positions. The field of view covered a large pore
  (μ = 0.93) with pixel scale of 0″.055. MMFs of opposite (positive)
  and same (negative) polarity as the pore were observed to stream
  from the pore boundary. We carried out a statistical analysis of the
  physical properties of MMFs and the main results are: 1) the number
  of opposite polarity MMFs within 1.5 Mm from the pore border, when
  they were first identified, is twice that of the same polarity MMFs. 2)
  Only 11% of the chosen MMFs appear to be monopolar and they all have the
  same polarity as the pore. 3) Majority of MMFs of both polarities move
  away from the pore border with an average speed of 1.5 km/s. However,
  they do not always follow a smooth radial track and some of them even
  move in tangential direction to the pore. 4) MMFs of opposite polarity
  show a preferential up-flow whereas those of the same polarity do not
  show any preference. 5) MMFs of both polarities are characterized by
  inclined fields. <P />This work, presented in an oral contribution
  at this Workshop, has been published on The Astrophysical Journal
  Supplement Series (Kaithakkal et al. 2017).

Title: Fast Solar Polarimeter (Prototype): Preliminary Results of
    Stokes Measurements in the Sr I 4607 Å Line at VTT/TESOS
Authors: Zeuner, F.; Feller, A.; Iglesias, F. A.; Solanki, S. K.
Bibcode: 2019ASPC..526..295Z
Altcode:
  Scattering polarization measurements at spatial scales in the
  0.1″-1″ regime are a very promising complementary diagnostic for the
  Sun's atmosphere and magnetism at small spatial scales (e.g., Trujillo
  Bueno et al. 2004). So far, for the Sr I line at 4607.3 Å, which
  exhibits a large scattering polarization signal (Stenflo et al. 1997;
  Gandorfer 2002), only theoretical predictions for the strength and
  spatial distribution of linear polarization signals at sub-arcsecond
  scales close to disk center are made available by Trujillo Bueno &amp;
  Shchukina (2007), whereas observational feedback is still very rare. <BR
  /> Here, we present preliminary results of two observational campaigns
  with the prototype of the Fast Solar Polarimeter (FSP, Iglesias et
  al. 2016) attached to the TESOS filtergraph, which is located at the
  German Vacuum Tower Telescope (VTT) in Tenerife, Spain. <BR /> We
  measured the center-to-limb variation of spatially averaged Stokes
  Q/I profiles in the Sr I line at 11 wavelength positions to check
  for systematic errors and to compare with previous results by other
  instruments. We find that our results are in agreement with previous
  findings reported in the literature (i.e., Stenflo et al. 1997). <BR
  /> In May 2015, we observed the Sr I line in the quiet Sun at
  μ=0.6 from the north solar limb with a spatial sampling of 0.08″
  pixel<SUP>-1</SUP> and noise levels significantly below 1% per pixel
  for linear polarized signals with 1.25 s integration time. To obtain
  lower noise levels (&lt; 0.1%), while conserving sufficient spatial
  resolution to resolve solar granulation, we carefully used spatial,
  spectral, and temporal averaging, as well as a MOMFBD restoration
  (see van Noort et al. 2005). We compare our findings in the Sr I line
  with the neighboring, but not scattering sensitive Fe I line at 4607.6
  Å. <BR /> Our statistical analysis of Stokes Q/I signals in the line
  core of Sr I reveals that the polarization amplitude is correlating
  with the intensity of the continuum image. We find stronger linear
  polarimetric signals corresponding to intergranular lanes of the Stokes
  I image, which is in contrast to the findings of Malherbe et al. (2007)
  at μ=0.3. <BR /> The results have been published as an article entitled
  "Detection of spatially structured scattering polarization of Sr I
  4607.3 Å with the Fast Solar Polarimeter" (Zeuner et al. 2018).

Title: On the Magnetic Nature of Solar Exploding Granules
Authors: Guglielmino, S. L.; Martínez Pillet, V.; Ruiz Cobo,
   B.; Bellot Rubio, L. R.; del Toro Iniesta, J. C.; Solanki, S. K.;
   Zuccarello, F.
Bibcode: 2019ASPC..526..299G
Altcode:
  We report on spectropolarimetric observations acquired by the imaging
  magnetograph SUNRISE/IMaX at high spatial 0.''3 and temporal (31.5 s)
  resolution during the first science flight of this balloon-borne solar
  observatory. We describe the photospheric evolution of an exploding
  granule observed in the quiet Sun. This granule is cospatial with
  a magnetic flux emergence event occurring at mesogranular scales
  (up to ∼12 Mm<SUP>2</SUP> area). Using a modified version of the
  SIR code, we show that we can estimate the longitudinal field also
  in the presence of a residual cross-talk in these IMaX longitudinal
  measurements. We determine the magnetic flux content of the structure
  (∼3 ×10<SUP>18</SUP> Mx), which appears to have a multipolar
  configuration, and discuss the origin of such flux emergence events.

Title: GPS, decrypting brightness variations of the Sun and Sun-like
Authors: Amazo-Gómez, Eliana Maritza; Shapiro, Alexander I.; Solanki,
   Sami K.; Kopp, Greg; Oshagh, Mahmoudreza; Reinhold, Timo; Krivova,
   Natalie A.; Reiners, Ansgar
Bibcode: 2019shin.confE.109A
Altcode:
  The rotation period is in general detectable in the light curves of
  young and active stars. Even after successful stellar surveys stemmed
  from Kepler mission, there is still a lack of information in photometric
  records of rotation periods in Sun-like stars. Non-periodic light-curve
  profiles, low variability contrast -therefore low modulation amplitude-
  short lifetime evolution and random emergence of magnetic features
  (in comparison to the rotation time-scale) are the main reasons of
  unreliable determination of rotation periodicity in the Sun and its
  closer analogs. This indicates that only a small fraction of solar-like
  systems have been properly analyzed. We show that the rotation periods
  of those stars can be reliably determined from the profile of the
  gradient of the power spectra, GPS. By analysing periodic patterns
  in high-accuracy measurements of the total solar irradiance, TSI,
  by SORCE/TIM and SoHO/VIRGO missions, here we test and validate
  GPS, linking the variability by transits of magnetic features over
  the stellar surface with a clear and enhanced signal of the solar
  rotation. GPS method retrieves accurate and stable values of rotation
  period during different regimes of solar activity cycle and could
  be applied to stars of comparable and higher activity - where other
  methods underperform. Furthermore, GPS gives us constraints on the
  faculae to spot driver ratio and consequently help us to interpret
  the stellar surface.

Title: Spectropolarimetric Observations of an Arch Filament System
    with GREGOR
Authors: Balthasar, H.; Gömöry, P.; González Manrique, S. J.;
   Kuckein, C.; Kučera, A.; Schwartz, P.; Berkefeld, T.; Collados, M.;
   Denker, C.; Feller, A.; Hofmann, A.; Schlichenmaier, R.; Schmidt,
   D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau,
   D.; Staude, J.; Strassmeier, K. G.; von der Lühe, O.
Bibcode: 2019ASPC..526..217B
Altcode: 2018arXiv180401789B
  We observed an arch filament system (AFS) in a sunspot group with the
  GREGOR Infrared Spectrograph attached to the GREGOR solar telescope. The
  AFS was located between the leading sunspot of negative polarity and
  several pores of positive polarity forming the following part of the
  sunspot group. We recorded five spectro-polarimetric scans of this
  region. The spectral range included the spectral lines Si I 1082.7
  nm, He I 1083.0 nm, and Ca I 1083.9 nm. In this work we concentrate
  on the silicon line which is formed in the upper photosphere. The
  line profiles are inverted with the code 'Stokes Inversion based
  on Response functions' to obtain the magnetic field vector. The
  line-of-sight velocities are determined independently with a Fourier
  phase method. Maximum velocities are found close to the ends of AFS
  fibrils. These maximum values amount to 2.4 km s<SUP>-1</SUP> next
  to the pores and to 4 km s<SUP>-1</SUP> at the sunspot side. Between
  the following pores, we encounter an area of negative polarity that
  is decreasing during the five scans. We interpret this by new emerging
  positive flux in this area canceling out the negative flux. In summary,
  our findings confirm the scenario that rising magnetic flux tubes
  cause the AFS.

Title: Photospheric Magnetic Fields of the Trailing Sunspots in
    Active Region NOAA 12396
Authors: Verma, M.; Balthasar, H.; Denker, C.; Böhm, F.; Fischer,
   C. E.; Kuckein, C.; González Manrique, S. J.; Sobotka, M.; Bello
   González, N.; Diercke, A.; Berkefeld, T.; Collados, M.; Feller, A.;
   Hofmann, A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pastor Yabar,
   A.; Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth,
   M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K.; Volkmer,
   R.; von der Lühe, O.; Waldmann, T.
Bibcode: 2019ASPC..526..291V
Altcode: 2018arXiv180507752V
  The solar magnetic field is responsible for all aspects of solar
  activity. Sunspots are the main manifestation of the ensuing solar
  activity. Combining high-resolution and synoptic observations has
  the ambition to provide a comprehensive description of the sunspot
  growth and decay processes. Active region NOAA 12396 emerged on 2015
  August 3 and was observed three days later with the 1.5-meter GREGOR
  solar telescope on 2015 August 6. High-resolution spectropolarimetric
  data from the GREGOR Infrared Spectrograph (GRIS) are obtained in the
  photospheric lines Si I λ1082.7 nm and Ca I λ1083.9 nm, together
  with the chromospheric He I λ1083.0 nm triplet. These near-infrared
  spectropolarimetric observations were complemented by synoptic
  line-of-sight magnetograms and continuum images of the Helioseismic
  and Magnetic Imager (HMI) and EUV images of the Atmospheric Imaging
  Assembly (AIA) on board the Solar Dynamics Observatory (SDO).

Title: Formation of the Penumbra and Start of the Evershed Flow
Authors: Murabito, M.; Romano, P.; Guglielmino, S. L.; Zuccarello,
   F.; Solanki, S. K.
Bibcode: 2019ASPC..526..243M
Altcode:
  We analyze high-resolution observations of Active Region NOAA 11490,
  acquired on 2012 May 28 and 29. Spectropolarimetric measurements of
  the photospheric lines of Fe I at 617.3 nm and 630.25 nm were taken
  with the Interferometric BIdimensional Spectrometer (IBIS), mounted on
  NSO/DST, during about 30 minutes for each day. To study the evolution
  of continuum intensity, LOS velocity, inclination and strength of the
  magnetic field during the entire time interval, we also used data taken
  by SDO/HMI. We used the SIR code to invert the Stokes profiles observed
  with IBIS, using different initial models to take into account the
  physical conditions of the plasma in the region of umbra, penumbra,
  and quiet Sun. From the analysis of the SIR results, we found that,
  before the formation of the penumbra, the annular zone is characterized
  by downflows in the inner part. Furthermore, we observed that the onset
  of the classical Evershed flow occurs on a short time scale, 1-3 hours,
  while the penumbra is forming. In order to investigate the conditions
  that lead to the establishment of the classical Evershed flow, we
  analyzed the evolution of the continuum intensity, LOS velocity,
  inclination and strength of the magnetic field in a segment in the
  north-western part of the leading spot. In about 1 hour, we noted a
  clear evolution from redshift to blueshift in the penumbral filaments
  along the selected segment. We propose a scenario in which the penumbra
  is formed by magnetic flux dragged down from the canopy surrounding
  the initial pore: the Evershed flow starts when the sinking magnetic
  field dips below the solar surface and magnetoconvection sets in.

Title: Analysis of full disc Ca II K spectroheliograms. II. Towards
    an accurate assessment of long-term variations in plage areas
Authors: Chatzistergos, Theodosios; Ermolli, Ilaria; Krivova, Natalie
   A.; Solanki, Sami K.
Bibcode: 2019A&A...625A..69C
Altcode: 2019arXiv190207122C
  Context. Reconstructions of past irradiance variations require suitable
  data on solar activity. The longest direct proxy is the sunspot number,
  and it has been most widely employed for this purpose. These data,
  however, only provide information on the surface magnetic field
  emerging in sunspots, while a suitable proxy of the evolution of the
  bright magnetic features, specifically faculae/plage and network,
  is missing. This information can potentially be extracted from the
  historical full-disc observations in the Ca II K line. <BR /> Aims: We
  use several historical archives of full-disc Ca II K observations to
  derive plage areas over more than a century. Employment of different
  datasets allows the identification of systematic effects in the
  images, such as changes in instruments and procedures, as well as
  an assessment of the uncertainties in the results. <BR /> Methods:
  We have analysed over 100 000 historical images from eight digitised
  photographic archives of the Arcetri, Kodaikanal, McMath-Hulbert,
  Meudon, Mitaka, Mt Wilson, Schauinsland, and Wendelstein observatories,
  and one archive of modern observations from the Rome/PSPT. The analysed
  data cover the period 1893-2018. We first performed careful photometric
  calibration and compensation for the centre-to-limb variation, and
  then segmented the images to identify plage regions. This has been
  consistently applied to both historical and modern observations. <BR
  /> Results: The plage series derived from different archives are
  generally in good agreement with each other. However, there are also
  clear deviations that most likely hint at intrinsic differences in the
  data and their digitisation. We showed that accurate image processing
  significantly reduces errors in the plage area estimates. Accurate
  photometric calibration also allows precise plage identification on
  images from different archives without the need to arbitrarily adjust
  the segmentation parameters. Finally, by comparing the plage area
  series from the various records, we found the conversion laws between
  them. This allowed us to produce a preliminary composite of the plage
  areas obtained from all the datasets studied here. This is a first
  step towards an accurate assessment of the long-term variation of plage
  regions. <P />The data are only available at the CDS via anonymous ftp
  to <A href="http://cdsarc.u-strasbg.fr/">http://cdsarc.u-strasbg.fr</A>
  (ftp://130.79.128.5) or via <A
  href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/625/A69">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/625/A69</A>

Title: VizieR Online Data Catalog: Plage area composite series
    (Chatzistergos+, 2019)
Authors: Chatzistergos, T.; Ermolli, I.; Krivova, N. A.; Solanki, S. K.
Bibcode: 2019yCat..36250069C
Altcode:
  Annual, monthly, and daily values of the plage area composite series
  produced in the paper. <P />(3 data files).

Title: The potential of many-line inversions of photospheric
    spectropolarimetric data in the visible and near UV
Authors: Riethmüller, T. L.; Solanki, S. K.
Bibcode: 2019A&A...622A..36R
Altcode: 2018arXiv181203757R
  Our knowledge of the lower solar atmosphere is mainly obtained from
  spectropolarimetric observations, which are often carried out in the red
  or infrared spectral range and almost always cover only a single or a
  few spectral lines. Here we compare the quality of Stokes inversions of
  only a few spectral lines with many-line inversions. In connection with
  this, we have also investigated the feasibility of spectropolarimetry
  in the short-wavelength range, 3000 Å-4300 Å, where the line density
  but also the photon noise are considerably higher than in the red,
  so that many-line inversions could be particularly attractive in
  that wavelength range. This is also timely because this wavelength
  range will be the focus of a new spectropolarimeter in the third
  science flight of the balloon-borne solar observatory SUNRISE. For
  an ensemble of state-of-the-art magneto-hydrodynamical atmospheres we
  synthesize exemplarily spectral regions around 3140 Å (containing 371
  identified spectral lines), around 4080 Å (328 lines), and around
  6302 Å (110 lines). The spectral coverage is chosen such that at a
  spectral resolving power of 150 000 the spectra can be recorded by a
  2K × 2K detector. The synthetic Stokes profiles are degraded with a
  typical photon noise and afterward inverted. The atmospheric parameters
  of the inversion of noisy profiles are compared with the inversion
  of noise-free spectra. We find that significantly more information
  can be obtained from many-line inversions than from a traditionally
  used inversion of only a few spectral lines. We further find that
  information on the upper photosphere can be significantly more reliably
  obtained at short wavelengths. In the mid and lower photosphere, the
  many-line approach at 4080 Å provides equally good results as the
  many-line approach at 6302 Å for the magnetic field strength and the
  line-of-sight (LOS) velocity, while the temperature determination is
  even more precise by a factor of three. We conclude from our results
  that many-line spectropolarimetry should be the preferred option in
  the future, and in particular at short wavelengths it offers a high
  potential in solar physics.

Title: Cancelation of small-scale magnetic features
Authors: Kaithakkal, A. J.; Solanki, S. K.
Bibcode: 2019A&A...622A.200K
Altcode: 2018arXiv181211496K
  <BR /> Aims: We investigate small-scale flux cancelations in a young
  active region observed with the high-resolution imaging magnetograph
  IMaX on the SUNRISE balloon-borne solar observatory. <BR /> Methods: The
  observed Stokes profiles of the photospheric Fe I 5250.2 Å line were
  inverted using the SPINOR code to obtain the atmospheric parameters,
  including magnetic field vector and the line-of-sight velocity. We then
  identified 11 opposite-polarity canceling pairs using an automatic
  detection code, studied their evolution in detail, and derived
  their statistical properties. We classified the cancelations into two
  groups. Class I events are those for which cancelation happens between
  a pre-existing large magnetic feature of one polarity and a smaller
  feature of the other polarity that emerged or appeared nearby. For
  Class II events cancelations occur between two pre-existing, previously
  unconnected features that converge. <BR /> Results: All studied events
  have an apparent cancelation time of less than ten minutes and display
  a significant transient linear polarization signal along the polarity
  inversion line. The cancelation events are characterized by a flux decay
  rate of about 10<SUP>15</SUP> Mx s<SUP>-1</SUP>. For Class I events,
  the Doppler velocity of the disappearing patch gradually switches
  from blueshift during the initial phase of cancelation to redshift
  toward the end of the cancelation. For class II events, the Doppler
  velocity is consistently redshifted. Horizontal convergence speeds
  of Class II pairs fall between 0.3 and 1.22 km s<SUP>-1</SUP>. The
  elements often do not converge directly toward each other, so that
  the proper motion speeds of the individual elements is higher,
  in the range of 1-2.7 km s<SUP>-1</SUP>. <BR /> Conclusions: We
  propose that these cancelation events result from either field-line
  submergence (Class I), or reconnection followed by submergence
  (Class II and/or Class I). Ohmic dissipation of magnetic energy
  could also play a role for both classes. The dynamics and evolution
  of these events are influenced by neighboring granular motions. We
  also propose that, at least for the Class II events, the granular
  motions could possibly be driving magnetic reconnection, rather than
  the supergranular motions proposed for the larger cancelation events
  studied earlier. Specific flux cancelation rates of the Class II events
  seem to indicate that they belong to somewhat different category
  of cancelations when compared with those studied in SOT/Hinode and
  MDI/SOHO data. <P />A movie associated to Fig. 5 is available at <A
  href="https://www.aanda.org/10.1051/0004-6361/201833770/olm">https://www.aanda.org</A>

Title: Chapter 3 - The Sun's Atmospher
Authors: Shapiro, Alexander I.; Peter, Hardi; Solanki, Sami K.
Bibcode: 2019sgsp.book...59S
Altcode:
  The solar atmosphere covers a broad range of temperatures and densities
  from the solar surface, via the chromosphere and transition region, and
  to the corona. Although one-dimensional (1D) models of the atmospheric
  structure have reached a high level of maturity, high-spatial
  resolution observations have cast some doubt on their validity. Thus,
  such observations have revealed a richness of highly variable spatial
  structure, often reaching down to the current resolution limit
  of 0.1 arcsec, or roughly 70 km on the Sun, in the photosphere and
  chromosphere. These observational advances have led to a new generation
  of models that describe the solar atmosphere self-consistently using 3D
  magnetohydrodynamic approximation simulations, including 3D radiative
  energy transport for those that cover the lower atmosphere, while
  simplistically taking into account the complex magnetic structure and
  energy dissipation processes in the upper atmosphere. These models have
  achieved considerable success in explaining the best observations,
  although there are still a number of open questions. Nonetheless,
  thanks to modern advances, the solar atmosphere now provides an
  excellent setting to test models of stellar atmospheres critically.

Title: Intensity contrast of solar plage as a function of magnetic
    flux at high spatial resolution
Authors: Kahil, F.; Riethmüller, T. L.; Solanki, S. K.
Bibcode: 2019A&A...621A..78K
Altcode: 2018arXiv181105759K
  Magnetic elements have an intensity contrast that depends on the type
  of region they are located in (for example quiet Sun, or active region
  plage). Observed values also depend on the spatial resolution of the
  data. Here we investigate the contrast-magnetic field dependence in
  active region plage observed near disk center with SUNRISE during
  its second flight in 2013. The wavelengths under study range from
  the visible at 525 nm to the near ultraviolet (NUV) at 300 nm and
  397 nm. We use quasi-simultaneous spectropolarimetric and photometric
  data from the Imaging Magnetograph eXperiment (IMaX) and the Sunrise
  Filter Imager (SuFI), respectively. We find that in all wavelength
  bands, the contrast exhibits a qualitatively similar dependence on
  the line-of-sight magnetic field, B<SUB>LOS</SUB>, as found in the
  quiet Sun, with the exception of the continuum at 525 nm. There, the
  contrast of plage magnetic elements peaks for intermediate values of
  B<SUB>LOS</SUB> and decreases at higher field strengths. By comparison,
  the contrast of magnetic elements in the quiet Sun saturates at its
  maximum value at large B<SUB>LOS</SUB>. We find that the explanation
  of the turnover in contrast in terms of the effect of finite spatial
  resolution of the data is incorrect with the evidence provided by the
  high-spatial resolution SUNRISE data, as the plage magnetic elements are
  larger than the quiet Sun magnetic elements and are well-resolved. The
  turnover comes from the fact that the core pixels of these larger
  magnetic elements are darker than the quiet Sun. We find that plages
  reach lower contrast than the quiet Sun at disk center at wavelength
  bands formed deep in the photosphere, such as the visible continuum
  and the 300 nm band. This difference decreases with formation height
  and disappears in the Ca II H core, in agreement with empirical models
  of magnetic element atmospheres.

Title: Historical solar Ca II K observations at the Rome and Catania
    observatories
Authors: Chatzistergos, T.; Ermolli, I.; Falco, M.; Giorgi, F.;
   Guglielmino, S. L.; Krivova, N. A.; Romano, P.; Solanki, S. K.
Bibcode: 2019NCimC..42....5C
Altcode: 2019arXiv190207483C
  Here we present the little explored Ca II K archives from the Rome
  and the Catania observatories and analyse the digitised images from
  these archives to derive plage areas.

Title: Improved search for solar chameleons with a GridPix detector
    at CAST
Authors: Anastassopoulos, V.; Aune, S.; Barth, K.; Belov, A.;
   Bräuninger, H.; Cantatore, G.; Carmona, J. M.; Castel, J. F.; Cetin,
   S. A.; Christensen, F.; Dafni, T.; Davenport, M.; Dermenev, A.; Desch,
   K.; Döbrich, B.; Eleftheriadis, C.; Fanourakis, G.; Ferrer-Ribas,
   E.; Fischer, H.; Funk, W.; Garcimatha, J. A.; Gardikiotis, A.; Garza,
   J. G.; Gazis, E. N.; Geralis, T.; Giomataris, I.; Gninenko, S.; Hailey,
   C. J.; Hasinoff, M. D.; Hoffmann, D. H. H.; Iguaz, F. J.; Irastorza,
   I. G.; Jakobsen, A.; Jacoby, J.; Jakovčić, K.; Kaminski, J.; Karuza,
   M.; Kostoglou, S.; Kralj, N.; Krčmar, M.; Krieger, C.; Lakić, B.;
   Laurent, J. M.; Liolios, A.; Ljubičić, A.; Luzón, G.; Maroudas,
   M.; Miceli, L.; Neff, S.; Ortega, I.; Papaevangelou, T.; Paraschou,
   K.; Pivovaroff, M. J.; Raffelt, G.; Rosu, M.; Ruz, J.; Ruiz Chóliz,
   E.; Savvidis, I.; Schmidt, S.; Semertzidis, Y. K.; Solanki, S. K.;
   Stewart, L.; Vafeiadis, T.; Vogel, J. K.; Vretenar, M.; Wuensch, W.;
   Yildiz, S. C.; Zioutas, K.; Brax, P.
Bibcode: 2019JCAP...01..032A
Altcode: 2018arXiv180800066A
  We report on a new search for solar chameleons with the CERN
  Axion Solar Telescope (CAST). A GridPix detector was used to
  search for soft X-ray photons in the energy range from 200 eV
  to 10 keV from converted solar chameleons. No significant excess
  over the expected background has been observed in the data taken
  in 2014 and 2015. We set an improved limit on the chameleon
  photon coupling, β<SUB>γ</SUB>lesssim#5.7×10<SUP>10</SUP> for
  1&lt;β<SUB>m</SUB>&lt;10<SUP>6</SUP> at 95% C.L. improving our previous
  results by a factor two and for the first time reaching sensitivity
  below the solar luminosity bound for tachocline magnetic fields up to
  12.5 T.

Title: Solar total and spectral irradiance reconstruction over the
    last 9000 years
Authors: Wu, C. -J.; Krivova, N. A.; Solanki, S. K.; Usoskin, I. G.
Bibcode: 2018A&A...620A.120W
Altcode: 2018arXiv181103464W
  Context. Changes in solar irradiance and in its spectral distribution
  are among the main natural drivers of the climate on Earth. However,
  irradiance measurements are only available for less than four decades,
  while assessment of solar influence on Earth requires much longer
  records. <BR /> Aims: The aim of this work is to provide the most
  up-to-date physics-based reconstruction of the solar total and spectral
  irradiance (TSI/SSI) over the last nine millennia. <BR /> Methods:
  The concentrations of the cosmogenic isotopes <SUP>14</SUP>C and
  <SUP>10</SUP>Be in natural archives have been converted to decadally
  averaged sunspot numbers through a chain of physics-based models. TSI
  and SSI are reconstructed with an updated SATIRE model. Reconstructions
  are carried out for each isotope record separately, as well as
  for their composite. <BR /> Results: We present the first ever
  SSI reconstruction over the last 9000 years from the individual
  <SUP>14</SUP>C and <SUP>10</SUP>Be records as well as from their
  newest composite. The reconstruction employs physics-based models to
  describe the involved processes at each step of the procedure. <BR
  /> Conclusions: Irradiance reconstructions based on two different
  cosmogenic isotope records, those of <SUP>14</SUP>C and <SUP>10</SUP>Be,
  agree well with each other in their long-term trends despite their
  different geochemical paths in the atmosphere of Earth. Over the last
  9000 years, the reconstructed secular variability in TSI is of the
  order of 0.11%, or 1.5 W m<SUP>-2</SUP>. After the Maunder minimum,
  the reconstruction from the cosmogenic isotopes is consistent with
  that from the direct sunspot number observation. Furthermore, over
  the nineteenth century, the agreement of irradiance reconstructions
  using isotope records with the reconstruction from the sunspot number
  by Chatzistergos et al. (2017, A&amp;A, 602, A69) is better than that
  with the reconstruction from the WDC-SILSO series (Clette et al. 2014,
  Space Sci. Rev., 186, 35), with a lower χ<SUP>2</SUP>-value.

Title: Activity variation driven by flux emergence and transport on
    Sun-like stars
Authors: Işık, Emre; Solanki, Sami K.; Krivova, Natalie A.; Shapiro,
   Alexander I.
Bibcode: 2018arXiv181208976I
Altcode:
  In G dwarfs, the surface distribution, coverage and lifetimes
  of starspots deviate from solar-like patterns as the rotation
  rate increases. We set up a numerical platform which includes the
  large-scale rotational and surface flow effects, aiming to simulate
  evolving surface patterns over an activity cycle for up to 8 times the
  solar rotation and flux emergence rates. At the base of the convection
  zone, we assume a solar projected butterfly diagram. We then follow
  the rotationally distorted trajectories of rising thin flux tubes to
  obtain latitudes and tilt angles. Using them as source distributions,
  we run a surface flux transport model with solar parameters. Our model
  predicts surface distributions of the signed radial fields and the
  starspots that qualitatively agree with observations.

Title: Forward modelling of brightness variations in Sun-like
    stars. I. Emergence and surface transport of magnetic flux
Authors: Işık, E.; Solanki, S. K.; Krivova, N. A.; Shapiro, A. I.
Bibcode: 2018A&A...620A.177I
Altcode: 2018arXiv181006728I
  Context. The latitudinal distribution of starspots deviates
  from the solar pattern with increasing rotation rate. Numerical
  simulations of magnetic flux emergence and transport can help model
  the observed stellar activity patterns and the associated brightness
  variations. <BR /> Aims: We set up a composite model for the processes
  of flux emergence and transport on Sun-like stars to simulate stellar
  brightness variations for various levels of magnetic activity and
  rotation rates. <BR /> Methods: Assuming that the distribution of
  magnetic flux at the base of the convection zone follows solar scaling
  relations, we calculate the emergence latitudes and tilt angles of
  bipolar regions at the surface for various rotation rates, using
  thin-flux-tube simulations. Taking these two quantities as input to a
  surface flux transport (SFT) model, we simulate the diffusive-advective
  evolution of the radial field at the stellar surface, including
  effects of active region nesting. <BR /> Results: As the rotation
  rate increases, (1) magnetic flux emerges at higher latitudes and an
  inactive gap opens around the equator, reaching a half-width of 20° for
  8 Ω<SUB>⊙</SUB>; and (2) the tilt angles of freshly emerged bipolar
  regions show stronger variations with latitude. Polar spots can form
  at 8 Ω<SUB>⊙</SUB> by accumulation of follower-polarity flux from
  decaying bipolar regions. From 4 Ω<SUB>⊙</SUB> to 8 Ω<SUB>⊙</SUB>,
  the maximum spot coverage changes from 3 to 20%, respectively, compared
  to 0.4% in the solar model. Nesting of activity can lead to strongly
  non-axisymmetric spot distributions. <BR /> Conclusions: On Sun-like
  stars rotating at 8 Ω<SUB>⊙</SUB> (P<SUB>rot</SUB> ≃ 3 days),
  polar spots can form, owing to higher levels of flux emergence rate and
  tilt angles. Defining spots by a threshold field strength yields global
  spot coverages that are roughly consistent with stellar observations.

Title: Detection of spatially structured scattering polarization of
    Sr I 4607.3 Å with the Fast Solar Polarimeter
Authors: Zeuner, F.; Feller, A.; Iglesias, F. A.; Solanki, S. K.
Bibcode: 2018A&A...619A.179Z
Altcode: 2018arXiv180806539Z
  Context. Scattering polarization in the Sr I 4607.3 Å line observed
  with high resolution is an important diagnostic of the Sun's atmosphere
  and magnetism at small spatial scales. Investigating the scattering
  polarization altered by the Hanle effect is key to constraining the
  role of small-scale magnetic activity in solar atmospheric activity
  and energy balance. At present, spatially resolved observations of
  this diagnostic are rare and have not been reported as close to the
  disk center as for μ = 0.6. <BR /> Aims: Our aim is to measure the
  scattering polarization in the Sr I line at μ = 0.6 and to identify the
  spatial fluctuations with a statistical approach. <BR /> Methods: Using
  the Fast Solar Polarimeter (FSP) mounted on the TESOS filtergraph at the
  German Vacuum Tower Telescope (VTT) in Tenerife, Spain, we measured both
  the spatially resolved full Stokes parameters of the Sr I line at μ =
  0.6 and the center-to-limb variation of the spatially averaged Stokes
  parameters. <BR /> Results: We find that the center-to-limb variation
  of the scattering polarization in the Sr I line measured with FSP
  is consistent with previous measurements. A statistical analysis of
  Stokes Q/I (i.e., the linear polarization component parallel to the
  solar limb), sampled with 0.16″ pixel<SUP>-1</SUP> in the line core
  of Sr I reveals that the signal strength is inversely correlated with
  the intensity in the continuum. We find stronger linear polarimetric
  signals corresponding to dark areas in the Stokes I continuum image
  (intergranular lanes). In contrast, independent measurements at μ =
  0.3 show a positive correlation of Q/I with respect to the continuum
  intensity. We estimate that the subregion diameter responsible for the
  excess Q/I signal is on the order of 0.5″-1″. <BR /> Conclusions:
  The presented observations and the statistical analysis of Q/I signals
  at μ = 0.6 complement reported scattering polarization observations
  as well as simulations. The FSP has proven to be a suitable instrument
  to measure spatially resolved scattering polarization signals. In
  the future, a systematic center-to-limb series of observations with
  subgranular spatial resolution and increased polarimetric sensitivity
  (&lt;10<SUP>-3</SUP>) compared to that in the present study is needed
  in order to investigate the change in trend with μ that the comparison
  of our results with the literature suggests.

Title: From solar to stellar brightness variations. The effect
    of metallicity
Authors: Witzke, V.; Shapiro, A. I.; Solanki, S. K.; Krivova, N. A.;
   Schmutz, W.
Bibcode: 2018A&A...619A.146W
Altcode: 2018arXiv180904360W
  Context. Comparison studies of Sun-like stars with the Sun suggest an
  anomalously low photometric variability of the Sun compared to Sun-like
  stars with similar magnetic activity. Comprehensive understanding
  of stellar variability is needed to find a physical reason for this
  observation. <BR /> Aims: We investigate the effect of metallicity
  and effective temperature on the photometric brightness change
  of Sun-like stars seen at different inclinations. The considered
  range of fundamental stellar parameters is sufficiently small so
  the stars investigated here still count as Sun-like or even as solar
  twins. <BR /> Methods: To model the brightness change of stars with
  solar magnetic activity, we extended a well-established model of
  solar brightness variations based on solar spectra, Spectral And
  Total Irradiance REconstruction (SATIRE), to stars with different
  fundamental parameters. For this we calculated stellar spectra for
  different metallicities and effective temperature using the radiative
  transfer code ATLAS9. <BR /> Results: We show that even a small change
  (e.g. within the observational error range) of metallicity or effective
  temperature significantly affects the photometric brightness change
  compared to the Sun. We find that for Sun-like stars, the amplitude
  of the brightness variations obtained for Strömgren (b + y)/2 reaches
  a local minimum for fundamental stellar parameters close to the solar
  metallicity and effective temperature. Moreover, our results show that
  the effect of inclination decreases for metallicity values greater than
  the solar metallicity. Overall, we find that an exact determination of
  fundamental stellar parameters is crucially important for understanding
  stellar brightness changes.

Title: Measuring the Wilson depression of sunspots using the
    divergence-free condition of the magnetic field vector
Authors: Löptien, B.; Lagg, A.; van Noort, M.; Solanki, S. K.
Bibcode: 2018A&A...619A..42L
Altcode: 2018arXiv180806867L
  Context. The Wilson depression is the difference in geometric height of
  unit continuum optical depth between the sunspot umbra and the quiet
  Sun. Measuring the Wilson depression is important for understanding
  the geometry of sunspots. Current methods suffer from systematic
  effects or need to make assumptions on the geometry of the magnetic
  field. This leads to large systematic uncertainties of the derived
  Wilson depressions. <BR /> Aims: We aim to develop a robust method
  for deriving the Wilson depression that only requires the information
  about the magnetic field that is accessible from spectropolarimetry,
  and that does not rely on assumptions on the geometry of sunspots
  or on their magnetic field. <BR /> Methods: Our method is based on
  minimizing the divergence of the magnetic field vector derived from
  spectropolarimetric observations. We have focused on large spatial
  scales only in order to reduce the number of free parameters. <BR />
  Results: We tested the performance of our method using synthetic Hinode
  data derived from two sunspot simulations. We find that the maximum and
  the umbral averaged Wilson depression for both spots determined with
  our method typically lies within 100 km of the true value obtained
  from the simulations. In addition, we applied the method to Hinode
  observations of a sunspot. The derived Wilson depression (∼600 km) is
  consistent with results typically obtained from the Wilson effect. We
  also find that the Wilson depression obtained from using horizontal
  force balance gives 110-180 km smaller Wilson depressions than both,
  what we find and what we deduce directly from the simulations. This
  suggests that the magnetic pressure and the magnetic curvature force
  contribute to the Wilson depression by a similar amount.

Title: Observations of solar chromospheric heating at sub-arcsec
    spatial resolution
Authors: Smitha, H. N.; Chitta, L. P.; Wiegelmann, T.; Solanki, S. K.
Bibcode: 2018A&A...617A.128S
Altcode: 2018arXiv180701078S
  A wide variety of phenomena such as gentle but persistent
  brightening, dynamic slender features (∼100 km), and compact
  (∼1″) ultraviolet (UV) bursts are associated with the heating of
  the solar chromosphere. High spatio-temporal resolution is required to
  capture the finer details of the likely magnetic reconnection-driven,
  rapidly evolving bursts. Such observations are also needed to reveal
  their similarities to large-scale flares, which are also thought to be
  reconnection driven, and more generally their role in chromospheric
  heating. Here we report observations of chromospheric heating in
  the form of a UV burst obtained with the balloon-borne observatory
  SUNRISE. The observed burst displayed a spatial morphology similar
  to that of a large-scale solar flare with a circular ribbon. While
  the co-temporal UV observations at 1.5″ spatial resolution and
  24 s cadence from the Solar Dynamics Observatory showed a compact
  brightening, the SUNRISE observations at diffraction-limited spatial
  resolution of 0.1″ at 7 s cadence revealed a dynamic substructure
  of the burst that it is composed of an extended ribbon-like feature
  and a rapidly evolving arcade of thin (∼0.1″) magnetic loop-like
  features, similar to post-flare loops. Such a dynamic substructure
  reveals the small-scale nature of chromospheric heating in these
  bursts. Furthermore, based on magnetic field extrapolations, this
  heating event is associated with a complex fan-spine magnetic
  topology. Our observations strongly hint at a unified picture of
  magnetic heating in the solar atmosphere from some large-scale
  flares to small-scale bursts, all associated with such a magnetic
  topology. <P />The movie associated to Fig. 2 is available at <A
  href="https://www.aanda.org/10.1051/0004-6361/201833276/olm">https://www.aanda.org/</A>

Title: Emission of solar chromospheric and transition region features
    related to the underlying magnetic field
Authors: Barczynski, K.; Peter, H.; Chitta, L. P.; Solanki, S. K.
Bibcode: 2018A&A...619A...5B
Altcode: 2018arXiv180702372B
  Context. The emission of the upper atmosphere of the Sun is closely
  related to magnetic field concentrations at the solar surface. <BR />
  Aims: It is well established that this relation between chromospheric
  emission and magnetic field is nonlinear. Here we investigate
  systematically how this relation, characterised by the exponent
  of a power-law fit, changes through the atmosphere, from the upper
  photosphere through the temperature minimum region and chromosphere
  to the transition region. <BR /> Methods: We used spectral maps from
  the Interface Region Imaging Spectrograph (IRIS) covering Mg II and
  its wings, C II, and Si IV together with magnetograms and UV continuum
  images from the Solar Dynamics Observatory. After a careful alignment
  of the data we performed a power-law fit for the relation between each
  pair of observables and determine the power-law index (or exponent) for
  these. This was done for different spatial resolutions and different
  features on the Sun. <BR /> Results: While the correlation between
  emission and magnetic field drops monotonically with temperature,
  the power-law index shows a hockey-stick-type variation: from the
  upper photosphere to the temperature-minimum it drops sharply and then
  increases through the chromosphere into the transition region. This
  is even seen through the features of the Mg II line, this is,
  from k1 to k2 and k3. It is irrespective of spatial resolution or
  whether we investigate active regions, plage areas, quiet Sun, or
  coronal holes. <BR /> Conclusions: In accordance with the general
  picture of flux-flux relations from the chromosphere to the corona,
  above the temperature minimum the sensitivity of the emission to the
  plasma heating increases with temperature. Below the temperature
  minimum a different mechanism has to govern the opposite trend of
  the power-law index with temperature. We suggest four possibilities,
  in other words, a geometric effect of expanding flux tubes filling the
  available chromospheric volume, the height of formation of the emitted
  radiation, the dependence on wavelength of the intensity-temperature
  relationship, and the dependence of the heating of flux tubes on the
  magnetic flux density.

Title: Quiet-Sun and Coronal Hole in Mg II k Line as Observed by IRIS
Authors: Kayshap, Pradeep; Tripathi, Durgesh; Solanki, Sami K.;
   Peter, Hardi
Bibcode: 2018ApJ...864...21K
Altcode: 2018arXiv180703494K
  Coronal hole (CH) regions are dark in comparison to the quiet Sun (QS)
  at coronal temperatures. However, at chromospheric and transition
  region temperatures, the QS and CHs are hardly distinguishable. In
  this study, we have used the Mg II 2796.35 Å spectral line recorded
  by the Interface Region Imaging Spectrometer (IRIS) to understand
  the similarities and differences in the QS and CH at chromospheric
  levels. Our analysis reveals that the emission from Mg II k3 and k2v
  that originates in the chromosphere is significantly lower in CH than
  in QS for the regions with similar magnetic field strength. The wing
  emissions of Mg II k that originates from the photospheric layer,
  however, do not show any difference between QS and CH. The difference
  in Mg II k3 intensities between QS and CH increases with increasing
  magnetic field strength. We further studied the effects of spectral
  resolution on these differences and found that the difference in
  the intensities decreases with decreasing spectral resolution. For
  a resolution of 11 Å, the difference completely disappears. These
  findings are not only important for mass and energy supply from the
  chromosphere to the corona but also provides essential ingredients for
  the modeling of the solar spectral irradiance for the understanding
  of the Sun-climate relationships.

Title: Dark Structures in Sunspot Light Bridges
Authors: Zhang, Jingwen; Tian, Hui; Solanki, Sami K.; Wang, Haimin;
   Peter, Hardi; Ahn, Kwangsu; Xu, Yan; Zhu, Yingjie; Cao, Wenda; He,
   Jiansen; Wang, Linghua
Bibcode: 2018ApJ...865...29Z
Altcode: 2018arXiv180900146Z
  We present unprecedented high-resolution TiO images and Fe I 1565
  nm spectropolarimetric data of two light bridges taken by the 1.6
  m Goode Solar Telescope at Big Bear Solar Observatory. In the first
  light bridge (LB1), we find striking knot-like dark structures within
  the central dark lane. Many dark knots show migration away from the
  penumbra along the light bridge. The sizes, intensity depressions,
  and apparent speeds of their proper motion along the light bridges of
  33 dark knots identified from the TiO images are mainly in the ranges
  of 80 ∼ 200 km, 30% ∼ 50%, and 0.3 ∼ 1.2 km s<SUP>-1</SUP>,
  respectively. In the second light bridge (LB2), a faint central dark
  lane and striking transverse intergranular lanes were observed. These
  intergranular lanes have sizes and intensity depressions comparable
  to those of the dark knots in LB1 and also migrate away from the
  penumbra at similar speeds. Our observations reveal that LB2 is made
  up of a chain of evolving convection cells, as indicated by patches of
  blueshift surrounded by narrow lanes of redshift. The central dark lane
  generally corresponds to blueshifts, supporting the previous suggestion
  of central dark lanes being the top parts of convection upflows. In
  contrast, the intergranular lanes are associated with redshifts and
  located at two sides of each convection cell. The magnetic fields are
  stronger in intergranular lanes than in the central dark lane. These
  results suggest that these intergranular lanes are manifestations of
  convergent convective downflows in the light bridge. We also provide
  evidence that the dark knots observed in LB1 may have a similar origin.

Title: Temporal evolution of arch filaments as seen in He I 10 830 Å
Authors: González Manrique, S. J.; Kuckein, C.; Collados, M.; Denker,
   C.; Solanki, S. K.; Gömöry, P.; Verma, M.; Balthasar, H.; Lagg,
   A.; Diercke, A.
Bibcode: 2018A&A...617A..55G
Altcode: 2018arXiv180700728G
  <BR /> Aims: We study the evolution of an arch filament system (AFS)
  and of its individual arch filaments to learn about the processes
  occurring in them. <BR /> Methods: We observed the AFS at the
  GREGOR solar telescope on Tenerife at high cadence with the very
  fast spectroscopic mode of the GREGOR Infrared Spectrograph (GRIS)
  in the He I 10 830 Å spectral range. The He I triplet profiles
  were fitted with analytic functions to infer line-of-sight (LOS)
  velocities to follow plasma motions within the AFS. <BR /> Results:
  We tracked the temporal evolution of an individual arch filament
  over its entire lifetime, as seen in the He I 10 830 Å triplet. The
  arch filament expanded in height and extended in length from 13″ to
  21″. The lifetime of this arch filament is about 30 min. About 11
  min after the arch filament is seen in He I, the loop top starts to
  rise with an average Doppler velocity of 6 km s<SUP>-1</SUP>. Only two
  minutes later, plasma drains down with supersonic velocities towards
  the footpoints reaching a peak velocity of up to 40 km s<SUP>-1</SUP>
  in the chromosphere. The temporal evolution of He I 10 830 Å profiles
  near the leading pore showed almost ubiquitous dual red components of
  the He I triplet, indicating strong downflows, along with material
  nearly at rest within the same resolution element during the whole
  observing time. <BR /> Conclusions: We followed the arch filament as it
  carried plasma during its rise from the photosphere to the corona. The
  material then drained toward the photosphere, reaching supersonic
  velocities, along the legs of the arch filament. Our observational
  results support theoretical AFS models and aids in improving future
  models. <P />The movie associated to Fig. 3 is available at <A
  href="https://www.aanda.org/10.1051/0004-6361/201832684/olm">https://www.aanda.org/</A>

Title: Sunrise Chromospheric Infrared spectroPolarimeter (SCIP)
    for the SUNRISE balloon-borne solar observatory
Authors: Suematsu, Yoshinori; Katsukawa, Yukio; Hara, Hirohisa;
   Ichimoto, Kiyoshi; Shimizu, Toshifumi; Kubo, Masahito; Barthol,
   Peter; Riethmueller, Tino; Gandorfer, Achim; Feller, Alex; Orozco
   Suárez, David; Del Toro Iniesta, Jose Carlos; Kano, Ryouhei; Ishikawa,
   Shin-nosuke; Ishikawa, Ryohko; Tsuzuki, Toshihiro; Uraguchi, Fumihiro;
   Quintero Noda, Carlos; Tamura, Tomonori; Oba, Takayoshi; Kawabata,
   Yusuke; Nagata, Shinichi; Anan, Tetsu; Cobos Carrascosa, Juan Pedro;
   Lopez Jimenez, Antonio Carlos; Balaguer Jimenez, Maria; Solanki, Sami
Bibcode: 2018cosp...42E3285S
Altcode:
  The SUNRISE balloon-borne solar observatory carries a 1 m aperture
  optical telescope, and allows us to perform seeing-free continuous
  observations at visible-IR wavelengths from an altitude higher than
  35 km. In the past two flights, in 2009 and 2013, observations mainly
  focused on fine structures of photospheric magnetic fields. For the
  third flight planned for 2021, we are developing a new instrument
  for conducting spectro-polarimetry of spectral lines formed over a
  larger height range in the solar atmosphere from the photosphere to
  the chromosphere. Targets of the spectro-polarimetric observation
  are (1) to determine 3D magnetic structure from the photosphere to
  the chromosphere, (2) to trace MHD waves from the photosphere to the
  chromosphere, and (3) to reveal the mechanism driving chromospheric
  jets, by measuring height- and time-dependent velocities and magnetic
  fields. To achieve these goals, a spectro-polarimeter called SCIP
  (Sunrise Chromospheric Infrared spectroPolarimeter) is designed to
  observe near-infrared spectrum lines sensitive to solar magnetic
  fields. The spatial and spectral resolutions are 0.2 arcsec and
  200,000, respectively, while 0.03% polarimetric sensitivity is
  achieved within a 10 sec integration time. The optical system employs
  an Echelle grating and off-axis aspheric mirrors to observe the two
  wavelength ranges centered at 850 nm and 770 nm simultaneously by
  two cameras. Polarimetric measurements are performed using a rotating
  waveplate and polarization beam-splitters in front of the cameras. For
  detecting minute polarization signals with good precision, we carefully
  assess the temperature dependence of polarization optics, and make
  the opto-structural design that minimizes the thermal deformation
  of the spectrograph optics. Another key technique is to attain good
  (better than 30 msec) synchronization among the rotating phase of
  the waveplate, read-out timing of cameras, and step timing of a
  slit-scanning mirror. On-board accumulation and data processing are
  also critical because we cannot store all the raw data read-out from the
  cameras. We demonstrate that we can reduce the data down to almost 10%
  with loss-less image compression and without sacrificing polarimetric
  information in the data. The SCIP instrument is developed by internal
  collaboration among Japanese institutes including Japan Aerospace
  Exploration Agency (JAXA), the Spanish Sunrise consortium, and the
  German Max Planck Institute for Solar System Research (MPS) with a
  leadership of the National Astronomical Observatory of Japan (NAOJ).

Title: ACTReSS: ACTive Rotating Star Simulator
Authors: Johnson, Luke Jonathan; Norris, Charlotte; Unruh, Yvonne;
   Solanki, Sami; Krivova, Natalie
Bibcode: 2018csss.confE..58J
Altcode:
  Variability of late-type stars on timescales of days or longer is
  largely due to magnetic surface features (starspots and faculae). We
  present ACTReSS, a software tool to calculate rotational lightcurves
  of stars. The model uses limb-dependent intensities derived from
  MURaM 3-D magneto-convection simulations (Beeck et al. 2014) for
  quiet stellar photospheres and bright active regions. This allows us
  to investigate the dependence of the flux variation on spectral type,
  inclination and wavelength.

Title: Solar irradiance variability on time scales of decades to
    millennia
Authors: Krivova, Natalie; Solanki, Sami K.; Leng Yeo, Kok; Wu, Chi-Ju
Bibcode: 2018cosp...42E1847K
Altcode:
  Reconstructions of past solar irradiance changes over as long periodsof
  time as possible are crucial to our understanding of solarinfluence on
  climate. They are only possible with the help of suitablemodels, based
  on detailed understanding of the mechanisms of thevariability. With
  the advance of such models, also the pastreconstructions are becoming
  more reliable. Nevertheless, theremaining uncertainties spread out when
  extrapolating back over longperiods of time. They are further amplified
  by the increasingly pooreramount and quality of the available data that
  bear information on pastsolar activity. We will discuss the progress
  and the uncertainties ofirradiance reconstructions on time scales of
  decades to millennia.

Title: Solar Activity and Irradiance Reconstruction over the Holocene
Authors: Wu, Chi-Ju; Usoskin, Ilya; Krivova, Natalie; Solanki, Sami
   K.; Kovaltsov, Gennady A.; Baroni, Melanie; Bard, Edouard
Bibcode: 2018cosp...42E3695W
Altcode:
  Direct measurements of the solar irradiance are only available since
  1978. To understand the solar influence on Earth's climate, longer
  records and thus reconstructions of the solar variability in the past
  are needed. The directly observed sunspot number allows going back
  to 1610 A.D, although with progressively increasing uncertainty. To
  assess solar variability at earlier times, one has to rely on indirect
  proxies of solar activity, such as concentrations of cosmogenic isotopes
  10Be and 14C in terrestrial archives. They are produced mostly in
  the upper atmosphere by impinging galactic cosmic rays (GCRs). The
  flux of GCRs is modulated by both the heliospheric magnetic field and
  the geomagnetic field. Therefore, the isotope signals retrieved from
  various sites around the globe show a very high degree of similarity,
  reflecting changes in the solar activity. Still, short-and mid-term
  deviations can be observed due to various systematic effects, such as
  different geochemical production, atmospheric distribution processes
  and local climatic conditions. To account for these differences, we
  have constructed a state-of-the-art consistent multi-isotope composite
  from one global 14C and six regional 10Be data sets. This composite is
  then used to reconstruct decadal values of the total and spectral solar
  irradiance over the Holocene with the semi-empirical SATIRE-M model,
  while the quasi-11 year solar cycle has been simulated statistically.

Title: Image compression on reconfigurable FPGA for the SO/PHI
    space instrument
Authors: Hernández Expósito, D.; Cobos Carrascosa, J. P.; Ramos
   Mas, J. L.; Rodríguez Valido, M.; Orozco Suárez, D.; Hirzberger,
   J.; Woch, J.; Solanki, S.; del Toro Iniesta, J. C.
Bibcode: 2018SPIE10707E..2FH
Altcode:
  In this paper we present a novel FPGA implementation of the Consultative
  Committee for Space Data Systems Image Data Compression (CCSDS-IDC
  122.0-B-1) for performing image compression aboard the Polarimetric
  Helioseismic Imager instrument of the ESA's Solar Orbiter mission. This
  is a System-On-Chip solution based on a light multicore architecture
  combined with an efficient ad-hoc Bit Plane Encoder core. This hardware
  architecture performs an acceleration of 30 times with respect to a
  software implementation running into space-qualified processors, like
  LEON3. The system stands out over other FPGA implementations because
  of the low resource usage, which does not use any external memory,
  and of its configurability.

Title: Solar activity over nine millennia: A consistent multi-proxy
    reconstruction
Authors: Wu, C. J.; Usoskin, I. G.; Krivova, N.; Kovaltsov, G. A.;
   Baroni, M.; Bard, E.; Solanki, S. K.
Bibcode: 2018A&A...615A..93W
Altcode: 2018arXiv180401302W
  <BR /> Aims: The solar activity in the past millennia can only
  be reconstructed from cosmogenic radionuclide proxy records in
  terrestrial archives. However, because of the diversity of the proxy
  archives, it is difficult to build a homogeneous reconstruction. All
  previous studies were based on individual, sometimes statistically
  averaged, proxy datasets. Here we aim to provide a new consistent
  multi-proxy reconstruction of the solar activity over the last 9000
  yr, using all available long-span datasets of <SUP>10</SUP>Be and
  <SUP>14</SUP>C in terrestrial archives. <BR /> Methods: A new method,
  based on a Bayesian approach, was applied for the first time to solar
  activity reconstruction. A Monte Carlo search (using the χ<SUP>2</SUP>
  statistic) for the most probable value of the modulation potential was
  performed to match data from different datasets for a given time. This
  provides a straightforward estimate of the related uncertainties. We
  used six <SUP>10</SUP>Be series of different lengths (from 500-10
  000 yr) from Greenland and Antarctica, and the global <SUP>14</SUP>C
  production series. The <SUP>10</SUP>Be series were resampled to match
  wiggles related to the grand minima in the <SUP>14</SUP>C reference
  dataset. The stability of the long data series was tested. <BR />
  Results: The Greenland Ice-core Project (GRIP) and the Antarctic EDML
  (EPICA Dronning Maud Land) <SUP>10</SUP>Be series diverge from each
  other during the second half of the Holocene, while the <SUP>14</SUP>C
  series lies in between them. A likely reason for the discrepancy is the
  insufficiently precise beryllium transport and deposition model for
  Greenland, which leads to an undercorrection of the GRIP series for
  the geomagnetic shielding effect. A slow 6-7 millennia variability
  with lows at ca. 5500 BC and 1500 AD in the long-term evolution
  of solar activity is found. Two components of solar activity can
  be statistically distinguished: the main component, corresponding
  to the "normal" moderate level, and a component corresponding to
  grand minima. A possible existence of a component representing
  grand maxima is indicated, but it cannot be separated from the main
  component in a statistically significant manner. <BR /> Conclusions:
  A new consistent reconstruction of solar activity over the last nine
  millennia is presented with the most probable values of decadal sunspot
  numbers and their realistic uncertainties. Independent components
  of solar activity corresponding to the main moderate activity
  and the grand-minimum state are identified; they may be related
  to different operation modes of the dynamo. <P />A table with the
  reconstructed SN series is available at the CDS via anonymous ftp to <A
  href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>(ftp://130.79.128.5)
  or via <A
  href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/615/A93">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/615/A93</A>

Title: Getting Ready for the Third Science Flight of SUNRISE
Authors: Barthol, Peter; Katsukawa, Yukio; Lagg, Andreas; Solanki,
   Sami K.; Kubo, Masahito; Riethmueller, Tino; Martínez Pillet,
   Valentin; Gandorfer, Achim; Feller, Alex; Berkefeld, . Thomas; Orozco
   Suárez, David; Del Toro Iniesta, Jose Carlos; Bernasconi, Pietro;
   Álvarez-Herrero, Alberto; Quintero Noda, Carlos
Bibcode: 2018cosp...42E.215B
Altcode:
  SUNRISE is a balloon-borne, stratospheric solar observatory dedicated
  to the investigation of the structure and dynamics of the Sun's
  magnetic field and its interaction with convective plasma flows and
  waves. The previous science flights of SUNRISE in 2009 and 2013 have
  led to many new scientific results, so far described in around 90
  refereed publications. This success has shown the huge potential of the
  SUNRISE concept and the recovery of the largely intact payload offers
  the opportunity for a third flight.The scientific instrumentation of
  SUNRISE 3 will have extended capabilities in particular to measure
  magnetic fields, plasma velocities and temperatures with increased
  sensitivity and over a larger height range in the solar atmosphere, from
  the convectively dominated photosphere up to the still poorly understood
  chromosphere. The latter is the key interaction region between magnetic
  field, waves and radiation and plays a central role in transporting
  energy to the outer layers of the solar atmosphere including the
  corona.SUNRISE 3 will carry 2 new grating-based spectro-polarimeters
  with slit-scanning and context imaging with slitjaw cameras. The
  SUNRISE UV Spectro-polarimeter and Imager (SUSI) will explore the rich
  near-UV range between 300 nm and 430 nm which is poorly accessible
  from the ground. The SUNRISE Chromospheric Infrared spectro-Polarimeter
  (SCIP) will sample 2 spectral windows in the near-infrared, containing
  many spectral lines highly sensitive to magnetic fields at different
  formation heights. In addition to the two new instruments the Imaging
  Magnetograph eXperiment (IMaX), an etalon-based tunable filtergraph and
  spectro-polarimeter flown on both previous missions, will be upgraded
  to IMaX+, enhancing its cadence and giving access to 2 spectral lines
  in the visible spectral range. All three instruments will allow
  investigating both the photosphere and the chromosphere and will
  ideally complement each other in terms of sensitivity, height coverage
  and resolution.A new gondola with a sophisticated attitude control
  system including roll damping will provide improved pointing/tracking
  performance. Upgraded image stabilization with higher bandwidth will
  further reduce residual jitter, maximizing the quality of the science
  data.SUNRISE 3 is a joint project of the German Max-Planck-Institut für
  Sonnensystemforschung together with the Spanish SUNRISE consortium, the
  Johns Hopkins University Applied Physics Laboratory, USA, the German
  Kiepenheuer Institut für Sonnenphysik, the National Astronomical
  Observatory of Japan and the Japan Aerospace eXploraion Agency (JAXA).

Title: Nature of the energy source powering solar coronal loops
    driven by nanoflares
Authors: Chitta, L. P.; Peter, H.; Solanki, S. K.
Bibcode: 2018A&A...615L...9C
Altcode: 2018arXiv180611045C
  Context. Magnetic energy is required to heat the corona, the outer
  atmosphere of the Sun, to millions of degrees. <BR /> Aims: We study the
  nature of the magnetic energy source that is probably responsible for
  the brightening of coronal loops driven by nanoflares in the cores of
  solar active regions. <BR /> Methods: We consider observations of two
  active regions (ARs), 11890 and 12234, in which nanoflares have been
  detected. To this end, we use ultraviolet (UV) and extreme ultraviolet
  (EUV) images from the Atmospheric Imaging Assembly (AIA) onboard the
  Solar Dynamics Observatory (SDO) for coronal loop diagnostics. These
  images are combined with the co-temporal line-of-sight magnetic
  field maps from the Helioseismic and Magnetic Imager (HMI) onboard
  SDO to investigate the connection between coronal loops and their
  magnetic roots in the photosphere. <BR /> Results: The core of
  these ARs exhibit loop brightening in multiple EUV channels of AIA,
  particularly in its 9.4 nm filter. The HMI magnetic field maps reveal
  the presence of a complex mixed polarity magnetic field distribution
  at the base of these loops. We detect the cancellation of photospheric
  magnetic flux at these locations at a rate of about 10<SUP>15</SUP>
  Mx s<SUP>-1</SUP>. The associated compact coronal brightenings directly
  above the cancelling magnetic features are indicative of plasma heating
  due to chromospheric magnetic reconnection. <BR /> Conclusions:
  We suggest that the complex magnetic topology and the evolution of
  magnetic field, such as flux cancellation in the photosphere and
  the resulting chromospheric reconnection, can play an important role
  in energizing active region coronal loops driven by nanoflares. Our
  estimate of magnetic energy release during flux cancellation in the
  quiet Sun suggests that chromospheric reconnection can also power the
  quiet corona. <P />The movie associated to Fig. 1 is available at <A
  href="https://www.aanda.org/10.1051/0004-6361/201833404/olm">https://www.aanda.org</A>

Title: Autonomous on-board data processing and instrument calibration
    software for the SO/PHI
Authors: Albert, K.; Hirzberger, J.; Busse, D.; Lange, T.; Kolleck, M.;
   Fiethe, B.; Orozco Suárez, D.; Woch, J.; Schou, J.; Blanco Rodriguez,
   J.; Gandorfer, A.; Guan, Y.; Cobos Carrascosa, J. P.; Hernández
   Expósito, D.; del Toro Iniesta, J. C.; Solanki, S. K.; Michalik, H.
Bibcode: 2018SPIE10707E..0OA
Altcode: 2018arXiv181003493A
  The extension of on-board data processing capabilities is an
  attractive option to reduce telemetry for scientific instruments
  on deep space missions. The challenges that this presents, however,
  require a comprehensive software system, which operates on the limited
  resources a data processing unit in space allows. We implemented such
  a system for the Polarimetric and Helioseismic Imager (PHI) on-board
  the Solar Orbiter (SO) spacecraft. It ensures autonomous operation
  to handle long command-response times, easy changing of the processes
  after new lessons have been learned and meticulous book-keeping of all
  operations to ensure scientific accuracy. This contribution presents
  the requirements and main aspects of the software implementation,
  followed by an example of a task implemented in the software frame,
  and results from running it on SO/PHI. The presented example shows
  that the different parts of the software framework work well together,
  and that the system processes data as we expect. The flexibility of
  the framework makes it possible to use it as a baseline for future
  applications with similar needs and limitations as SO/PHI.

Title: The High Resolution Telescope (HRT) of the Polarimetric and
    Helioseismic Imager (PHI) onboard Solar Orbiter
Authors: Gandorfer, A.; Grauf, B.; Staub, J.; Bischoff, J.; Woch, J.;
   Hirzberger, J.; Solanki, S. K.; Álvarez-Herrero, A.; García Parejo,
   P.; Schmidt, W.; Volkmer, R.; Appourchaux, T.; del Toro Iniesta, J. C.
Bibcode: 2018SPIE10698E..4NG
Altcode:
  Solar Orbiter is a joint mission of ESA and NASA scheduled for
  launch in 2020. Solar Orbiter is a complete and unique heliophysics
  mission, combining remote sensing and in-situ analysis; its special
  elliptical orbit allows viewing the Sun from a distance of only 0.28
  AU, and - leaving the ecliptic plane - to observe the solar poles from
  a hitherto unexplored vantage point. One of the key instruments for
  Solar Orbiter's science is the "Polarimetric and Helioseismic Imager"
  (PHI), which will provide maps of the solar surface magnetic fields and
  the gas flows on the visible solar surface. Two telescopes, a full disc
  imager, and a high resolution channel feed a common Fabry-Perot based
  tunable filter and thus allow sampling a single Fraunhofer line at 617.3
  nm with high spectral resolution; a polarization modulation system
  makes the system sensitive to the full state of polarization. From
  the analysis of the Doppler shift and the magnetically induced Zeeman
  polarization in this line, the magnetic field and the line-of-sight
  gas motions can be detected for each point in the image. In this
  paper we describe the opto-mechanical system design of the high
  resolution telescope. It is based on a decentred Ritchey-Chrétien
  two-mirror telescope. The telescope includes a Barlow type magnifier
  lens group, which is used as in-orbit focus compensator, and a beam
  splitter, which sends a small fraction of the collected light onto
  a fast camera, which provides the error signals for the actively
  controlled secondary mirror compensating for spacecraft jitter and other
  disturbances. The elliptical orbit of the spacecraft poses high demands
  on the thermo-mechanical stability. The varying size of the solar disk
  image requires a special false-light suppression architecture, which is
  briefly described. In combination with a heat-rejecting entrance window,
  the optical energy impinging on the polarimetric and spectral analysis
  system is efficiently reduced. We show how the design can preserve the
  diffraction-limited imaging performance over the design temperature
  range of -20°C to +60°C. The decentred hyperbolical mirrors require
  special measures for the inter-alignment and their alignment with
  respect to the mechanical structure. A system of alignment flats and
  mechanical references is used for this purpose. We will describe the
  steps of the alignment procedure, and the dedicated optical ground
  support equipment, which are needed to reach the diffraction limited
  performance of the telescope. We will also report on the verification
  of the telescope performance, both - in ambient condition - and in
  vacuum at different temperatures.

Title: Effect of Transport Coefficients on Excitation of Flare-induced
    Standing Slow-mode Waves in Coronal Loops
Authors: Wang, Tongjiang; Ofman, Leon; Sun, Xudong; Solanki, Sami K.;
   Davila, Joseph M.
Bibcode: 2018ApJ...860..107W
Altcode: 2018arXiv180503282W
  Standing slow-mode waves have been recently observed in flaring loops by
  the Atmospheric Imaging Assembly of the Solar Dynamics Observatory. By
  means of the coronal seismology technique, transport coefficients in
  hot (∼10 MK) plasma were determined by Wang et al., revealing that
  thermal conductivity is nearly suppressed and compressive viscosity is
  enhanced by more than an order of magnitude. In this study, we use 1D
  nonlinear MHD simulations to validate the predicted results from the
  linear theory and investigate the standing slow-mode wave excitation
  mechanism. We first explore the wave trigger based on the magnetic
  field extrapolation and flare emission features. Using a flow pulse
  driven at one footpoint, we simulate the wave excitation in two types
  of loop models: Model 1 with the classical transport coefficients and
  Model 2 with the seismology-determined transport coefficients. We
  find that Model 2 can form the standing wave pattern (within about
  one period) from initial propagating disturbances much faster than
  Model 1, in better agreement with the observations. Simulations of
  the harmonic waves and the Fourier decomposition analysis show that
  the scaling law between damping time (τ) and wave period (P) follows
  τ ∝ P <SUP>2</SUP> in Model 2, while τ ∝ P in Model 1. This
  indicates that the largely enhanced viscosity efficiently increases
  the dissipation of higher harmonic components, favoring the quick
  formation of the fundamental standing mode. Our study suggests that
  observational constraints on the transport coefficients are important
  in understanding both the wave excitation and damping mechanisms.

Title: Initial features of an X-class flare observed with SUMER
    and TRACE
Authors: Wang, T. J.; Solanki, S. K.; Innes, D. E.; Curdt, W.
Bibcode: 2018arXiv180510418W
Altcode:
  A class X1.5 flare started on the solar limb at 00:43 UT on 21 April
  2002, which was associated with a CME observed at 01:27 UT by LASCO
  C2. The coordinated analyses of this flare include TRACE 195 Å images
  and SUMER spectra in lines of Fe XXI, Fe XII, and C II. We find that:
  1) The flare began with a jet seen by TRACE, which was detected by
  SUMER in the C II line as a strong brightening with blue shifts up
  to 170 km s$^{-1}$. At that time only weak emission was detected
  in Fe XII and Fe XXI. 2) Subsequently, a weak looplike brightening
  started south of the jet, moving outwards with an average speed of
  about 150 km s$^{-1}$. The SUMER spectra responded this moving loop
  as separatingly brightenings, visible only in the Fe XXI line. The
  southwards moving component contains red- and blue-shifted emission
  features and has an apparent speed of $\sim$120 km s$^{-1}$. The absence
  of signatures in Fe XII and C II lines indicates that the moving weak
  loop seen by TRACE corresponds to the emission from very hot plasma,
  in a blend line in the 195 Å bandpass due to Fe XXIV formed at T &gt;
  10 MK. 3) The trigger mechanism of the flare and associated CME can
  be interpreted in the same way as that proposed by Wang et al. (2002)
  for an event with similar initial features.

Title: Excitation and Damping of Standing Slow-Mode Waves in Flaring
    Coronal Loops
Authors: Wang, Tongjiang; Ofman, Leon; Sun, Xudong; Solanki, Sami K.;
   Davila, Joseph M.
Bibcode: 2018tess.conf22204W
Altcode:
  We analyze and model a flare-induced longitudinal oscillation event
  detected by SDO/AIA. The magnetic field extrapolation and flare emission
  features suggest that the wave event is generated by slipping and
  null-point-type reconnections in a closed fan-spine magnetic topology,
  and the large spine loop appears to be heated impulsively to the flare
  temperature before the wave disturbances travel along it. By means of
  the seismology technique, we determined the transport coefficients
  in hot (about 10 MK) plasma, and found that thermal conductivity is
  nearly suppressed and compressive viscosity is enhanced by more than
  an order of magnitude from the observed wave properties. Using a flow
  pulse injected at the loop's footpoint constrained by the observation,
  we simulate the excitation of slow-mode waves in two types of 1D loop
  models. We find that the models with the seismology-determined transport
  coefficients can excite the standing waves quickly as observed, while
  the models with the classical transport coefficients excites basically
  the reflecting propagating waves. Simulations of harmonic waves and
  the Fourier decomposition analysis reveal a scaling between damping
  time and wave period as T<SUB>d</SUB> ~ P in the former type of models,
  while T<SUB>d</SUB> ~ P<SUP>2</SUP> in the latter type. This suggests
  that anomalously large viscosity can efficiently enhance the dissipation
  of higher harmonic components, favoring quick setup of the fundamental
  standing mode. Our study indicates that observational constraints on
  the transport coefficients are crucial in understanding both the wave
  excitation and damping mechanisms.

Title: Reconstructing Total Solar Irradiance with the help of MHD
    simulations
Authors: Leng Yeo, Kok; Solanki, Sami; Noris, Charlotte; Unruh,
   Yvonne; Krivova, Natalie; Beeck, Benjamin
Bibcode: 2018EGUGA..20.8166L
Altcode:
  The variation in the solar irradiance is an important input into the
  climate system. Whereas it is commonly thought that solar irradiance
  variability is driven by the evolving surface magnetism, verifying this
  assumption has been more difficult. Making use of 3D MHD simulations
  of the solar atmosphere layers and state-of-the-art solar magnetograms
  from the Solar Dynamics Observatory, we present a model of total solar
  irradiance (TSI) that does not require any calibration of the modeled
  TSI by the measured TSI. I.e., the modeled irradiance variability
  is entirely independent of the observational record, except for the
  absolute level. The model replicates 95% of the observed variability
  between April 2010 and July 2016, leaving little scope for alternative
  drivers of solar irradiance variability, at least over the time scales
  examined (days to years).

Title: Physical Processes on The Sun's Surface
Authors: Solanki, Sami
Bibcode: 2018iss..confE..35S
Altcode:
  The Sun, as our nearest star, allows us to probe the surface of a
  main sequence G star in great detail and to determine the features and
  processes acting there with the help of high-resolution observations and
  MHD simulations. These features (possibly in somewhat different guises)
  and processes are thought to be present/acting also on other cool stars,
  whose spectra they influence and whose variability and activity they
  are responsible for. In this presentation a brief introduction will be
  given to the main physical processes acting in the solar photosphere
  and the structures and dynamics that they produce. An attempt will also
  be made to work out what influence these processes and structures have
  on the Sun seen as an unresolved star.

Title: VizieR Online Data Catalog: Reconstructed decadal sunspot
    numbers (Wu+, 2018)
Authors: Wu, C. J.; Usoskin, I. G.; Krivova, N.; Kovaltsov, G. A.;
   Baroni, M.; Bard, E.; Solanki, S. K.
Bibcode: 2018yCat..36150093W
Altcode:
  The file contains the decadal numbers of sunspot groups including
  the decade central year [Y], the low [S<SUB>l], the mean [S</SUB>M]
  and the upper [S_u] 1-sigma (68% bounds). <P />(1 data file).

Title: Solar polarimetry in the K I D<SUB>2</SUB> line : A novel
    possibility for a stratospheric balloon
Authors: Quintero Noda, C.; Villanueva, G. L.; Katsukawa, Y.; Solanki,
   S. K.; Orozco Suárez, D.; Ruiz Cobo, B.; Shimizu, T.; Oba, T.; Kubo,
   M.; Anan, T.; Ichimoto, K.; Suematsu, Y.
Bibcode: 2018A&A...610A..79Q
Altcode: 2018arXiv180101655Q
  Of the two solar lines, K I D<SUB>1</SUB> and D<SUB>2</SUB>, almost
  all attention so far has been devoted to the D<SUB>1</SUB> line, as
  D<SUB>2</SUB> is severely affected by an O<SUB>2</SUB> atmospheric
  band. This, however, makes the latter appealing for balloon and space
  observations from above (most of) the Earth's atmosphere. We estimate
  the residual effect of the O<SUB>2</SUB> band on the K I D<SUB>2</SUB>
  line at altitudes typical for stratospheric balloons. Our aim is to
  study the feasibility of observing the 770 nm window. Specifically,
  this paper serves as a preparation for the third flight of the Sunrise
  balloon-borne observatory. The results indicate that the absorption
  by O<SUB>2</SUB> is still present, albeit much weaker, at the expected
  balloon altitude. We applied the obtained O<SUB>2</SUB> transmittance
  to K I D<SUB>2</SUB> synthetic polarimetric spectra and found that in
  the absence of line-of-sight motions, the residual O<SUB>2</SUB> has
  a negligible effect on the K I D<SUB>2</SUB> line. On the other hand,
  for Doppler-shifted K I D<SUB>2</SUB> data, the residual O<SUB>2</SUB>
  might alter the shape of the Stokes profiles. However, the residual
  O<SUB>2</SUB> absorption is sufficiently weak at stratospheric levels
  that it can be divided out if appropriate measurements are made,
  something that is impossible at ground level. Therefore, for the
  first time with Sunrise III, we will be able to perform polarimetric
  observations of the K I D<SUB>2</SUB> line and, consequently, we will
  have improved access to the thermodynamics and magnetic properties of
  the upper photosphere from observations of the K I lines.

Title: Long-term Datasets for the Understanding of Solar and Stellar
    Magnetic Cycles
Authors: Banerjee, D.; Jiang, J.; Kusano, K.; Solanki, S.
Bibcode: 2018IAUS..340.....B
Altcode:
  No abstract at ADS

Title: Ca II K spectroheliograms for studies of long-term changes
    in solar irradiance
Authors: Chatzistergos, Theodosios; Ermolli, Ilaria; Krivova, Natalie
   A.; Solanki, Sami K.
Bibcode: 2018IAUS..340..125C
Altcode: 2018arXiv180503928C
  We address the importance of historical full-disc Ca II K
  spectroheliograms for solar activity and irradiance reconstruction
  studies. We review our work on processing such data to enable them to
  be used in irradiance reconstructions. We also present our preliminary
  estimates of the plage areas from five of the longest available
  historical Ca II K archives.

Title: The potential of Ca II K observations for solar activity and
    variability studies
Authors: Ermolli, Ilaria; Chatzistergos, Theodosios; Krivova, Natalie
   A.; Solanki, Sami K.
Bibcode: 2018IAUS..340..115E
Altcode: 2018arXiv180504483E
  Several observatories around the globe started regular full-disc imaging
  of the solar atmosphere in the Ca II K line in the early decades of
  the 20<SUP>th</SUP> century. These observations are continued today
  at a few sites with either old spectroheliographs or modern telescopes
  equipped with narrow-band filters. The Ca II K time series are unique
  in representing long-term variations of the Sun's chromospheric magnetic
  field. However, meaningful results from their analysis require accurate
  processing of the available data and robust merging of the information
  stored in different archives. This paper provides an overview of the
  historical and modern full-disc Ca II K observations, with focus on
  their quality and the main results obtained from their analysis over
  the last decade.

Title: Frequently Occurring Reconnection Jets from Sunspot Light
    Bridges
Authors: Tian, Hui; Yurchyshyn, Vasyl; Peter, Hardi; Solanki, Sami
   K.; Young, Peter R.; Ni, Lei; Cao, Wenda; Ji, Kaifan; Zhu, Yingjie;
   Zhang, Jingwen; Samanta, Tanmoy; Song, Yongliang; He, Jiansen; Wang,
   Linghua; Chen, Yajie
Bibcode: 2018ApJ...854...92T
Altcode: 2018arXiv180106802T
  Solid evidence of magnetic reconnection is rarely reported within
  sunspots, the darkest regions with the strongest magnetic fields
  and lowest temperatures in the solar atmosphere. Using the world’s
  largest solar telescope, the 1.6 m Goode Solar Telescope, we detect
  prevalent reconnection through frequently occurring fine-scale jets
  in the Hα line wings at light bridges, the bright lanes that may
  divide the dark sunspot core into multiple parts. Many jets have an
  inverted Y-shape, shown by models to be typical of reconnection in a
  unipolar field environment. Simultaneous spectral imaging data from
  the Interface Region Imaging Spectrograph show that the reconnection
  drives bidirectional flows up to 200 km s<SUP>-1</SUP>, and that the
  weakly ionized plasma is heated by at least an order of magnitude up
  to ∼80,000 K. Such highly dynamic reconnection jets and efficient
  heating should be properly accounted for in future modeling efforts
  of sunspots. Our observations also reveal that the surge-like activity
  previously reported above light bridges in some chromospheric passbands
  such as the Hα core has two components: the ever-present short surges
  likely to be related to the upward leakage of magnetoacoustic waves
  from the photosphere, and the occasionally occurring long and fast
  surges that are obviously caused by the intermittent reconnection jets.

Title: Solar Magnetic Fields
Authors: Balogh, André; Cliver, Edward; Petrie, Gordon; Solanki,
   Sami; Thompson, Michael; von Steiger, Rudolf
Bibcode: 2018smf..book.....B
Altcode:
  No abstract at ADS

Title: Solar Magnetoconvection and Small-Scale Dynamo
Authors: Borrero, J. M.; Jafarzadeh, S.; Schüssler, M.; Solanki, S. K.
Bibcode: 2018smf..book..275B
Altcode:
  No abstract at ADS

Title: The Influence of Metallicity on Stellar Differential Rotation
    and Magnetic Activity
Authors: Karoff, Christoffer; Metcalfe, Travis S.; Santos, Ângela
   R. G.; Montet, Benjamin T.; Isaacson, Howard; Witzke, Veronika;
   Shapiro, Alexander I.; Mathur, Savita; Davies, Guy R.; Lund, Mikkel N.;
   Garcia, Rafael A.; Brun, Allan S.; Salabert, David; Avelino, Pedro P.;
   van Saders, Jennifer; Egeland, Ricky; Cunha, Margarida S.; Campante,
   Tiago L.; Chaplin, William J.; Krivova, Natalie; Solanki, Sami K.;
   Stritzinger, Maximilian; Knudsen, Mads F.
Bibcode: 2018ApJ...852...46K
Altcode: 2017arXiv171107716K
  Observations of Sun-like stars over the past half-century have improved
  our understanding of how magnetic dynamos, like that responsible for the
  11 yr solar cycle, change with rotation, mass, and age. Here we show
  for the first time how metallicity can affect a stellar dynamo. Using
  the most complete set of observations of a stellar cycle ever obtained
  for a Sun-like star, we show how the solar analog HD 173701 exhibits
  solar-like differential rotation and a 7.4 yr activity cycle. While
  the duration of the cycle is comparable to that generated by the solar
  dynamo, the amplitude of the brightness variability is substantially
  stronger. The only significant difference between HD 173701 and the
  Sun is its metallicity, which is twice the solar value. Therefore,
  this provides a unique opportunity to study the effect of the
  higher metallicity on the dynamo acting in this star and to obtain a
  comprehensive understanding of the physical mechanisms responsible
  for the observed photometric variability. The observations can be
  explained by the higher metallicity of the star, which is predicted to
  foster a deeper outer convection zone and a higher facular contrast,
  resulting in stronger variability.

Title: Analysis of full disc Ca II K spectroheliograms. I. Photometric
    calibration and centre-to-limb variation compensation
Authors: Chatzistergos, Theodosios; Ermolli, Ilaria; Solanki, Sami K.;
   Krivova, Natalie A.
Bibcode: 2018A&A...609A..92C
Altcode: 2017arXiv171004949C
  Context. Historical Ca II K spectroheliograms (SHG) are unique in
  representing long-term variations of the solar chromospheric magnetic
  field. They usually suffer from numerous problems and lack photometric
  calibration. Thus accurate processing of these data is required to get
  meaningful results from their analysis. <BR /> Aims: In this paper we
  aim at developing an automatic processing and photometric calibration
  method that provides precise and consistent results when applied
  to historical SHG. <BR /> Methods: The proposed method is based on
  the assumption that the centre-to-limb variation of the intensity in
  quiet Sun regions does not vary with time. We tested the accuracy of
  the proposed method on various sets of synthetic images that mimic
  problems encountered in historical observations. We also tested our
  approach on a large sample of images randomly extracted from seven
  different SHG archives. <BR /> Results: The tests carried out on the
  synthetic data show that the maximum relative errors of the method are
  generally &lt;6.5%, while the average error is &lt;1%, even if rather
  poor quality observations are considered. In the absence of strong
  artefacts the method returns images that differ from the ideal ones by
  &lt;2% in any pixel. The method gives consistent values for both plage
  and network areas. We also show that our method returns consistent
  results for images from different SHG archives. <BR /> Conclusions:
  Our tests show that the proposed method is more accurate than other
  methods presented in the literature. Our method can also be applied
  to process images from photographic archives of solar observations at
  other wavelengths than Ca II K.

Title: Evershed and Counter-Evershed Flows in Sunspot MHD Simulations
Authors: Siu-Tapia, A. L.; Rempel, M.; Lagg, A.; Solanki, S. K.
Bibcode: 2018ApJ...852...66S
Altcode: 2017arXiv171201202S
  There have been a few reports in the literature of counter-Evershed
  flows observed in well-developed sunspot penumbrae, i.e., flows
  directed toward the umbra along penumbral filaments. Here, we
  investigate the driving forces of such counter-Evershed flows in a
  radiative magnetohydrodynamic simulation of a sunspot, and compare
  them to the forces acting on the normal Evershed flow. The simulation
  covers a timespan of 100 solar hours and generates an Evershed outflow
  exceeding 8 km s<SUP>-1</SUP> in the penumbra along radially aligned
  filaments where the magnetic field is almost horizontal. Additionally,
  the simulation produces a fast counter-Evershed flow (i.e., an inflow
  near τ =1) in some regions within the penumbra, reaching peak flow
  speeds of ∼12 km s<SUP>-1</SUP>. The counter-Evershed flows are
  transient and typically last a few hours before they turn into outflows
  again. By using the kinetic energy equation and evaluating its various
  terms in the simulation box, we found that the Evershed flow occurs
  due to overturning convection in a strongly inclined magnetic field,
  while the counter-Evershed flows can be well-described as siphon flows.

Title: Solar Spectral Irradiance Reconstruction over 9 Millennia
    from a Composite 14C and 10Be Series
Authors: Wu, C. J.; Usoskin, I. G.; Krivova, N.; Kovaltsov, G.;
   Solanki, S. K.
Bibcode: 2017AGUFMSH42A..03W
Altcode:
  The Sun is the main external energy source to the Earth and thus the
  knowledge of solar variability on different time scales is important
  for understanding the solar influence on the terrestrial atmosphere
  and climate. The overall energy input and its spectral distribution
  are described by the total (TSI) and spectral (SSI) solar irradiance,
  respectively. Direct measurements of the solar irradiance provide
  information on solar variability on the decadal and shorter time
  scales, while the sunspot number record covers four centuries. On
  yet longer time scales only indirect proxies can be used, such
  as the concentrations of the cosmogenic isotopes 10Be and 14C in
  terrestrial archives. These isotopes are produced in the terrestrial
  atmosphere by impinging cosmic rays, whose flux is modulated by solar
  activity. Therefore the isotope data retrieved from various natural
  archives around the globe show a very high degree of similarity
  reflecting changes in the solar activity. Nevertheless, significant
  short-term deviations can be observed due to the different geochemical
  production processes and local climatic conditions. We will present
  the newest TSI/SSI reconstruction over the last 9000 years based
  on a new consistent composite multi-isotope proxy series. The solar
  irradiance reconstruction reveals the global and robust pattern of
  solar variability in the past.

Title: Probing photospheric magnetic fields with new spectral
    line pairs
Authors: Smitha, H. N.; Solanki, S. K.
Bibcode: 2017A&A...608A.111S
Altcode: 2017arXiv170908926S
  Context. The magnetic line ratio (MLR) method has been extensively
  used in the measurement of photospheric magnetic field strength. It
  was devised for the neutral iron line pair at 5247.1 Å and 5250.2 Å
  (5250 Å pair). Other line pairs as well-suited as this pair have not
  been reported in the literature. <BR /> Aims: The aim of the present
  work is to identify new line pairs useful for the MLR technique and to
  test their reliability. <BR /> Methods: We used a three-dimensional
  magnetohydrodynamic 3D MHD simulation representing the quiet Sun
  atmosphere to synthesize the Stokes profiles. Then, we applied the MLR
  technique to the Stokes V profiles to recover the fields in the MHD
  cube both at original resolution and after degrading with a point spread
  function. In both these cases, we aim to empirically represent the field
  strengths returned by the MLR method in terms of the field strengths
  in the MHD cube. <BR /> Results: We have identified two new line pairs
  that are very well adapted to be used for MLR measurements. The first
  pair is in the visible, Fe I 6820-6842 Å, whose intensity profiles
  have previously been used to measure stellar magnetic fields, and
  the other pair is in the infrared (IR), Fe I 15 534-15 542 Å. The
  lines in these pairs reproduce the magnetic fields in the MHD cube
  rather well and, in fact, somewhat better than the original 5250 Å
  pair. <BR /> Conclusions: The newly identified line pairs complement
  the old pairs. The lines in the new IR pair, because of their higher
  Zeeman sensitivity, are ideal for the measurement of weak fields. The
  new visible pair works best above 300 G. The new IR pair, due to its
  large Stokes V signal samples more fields in the MHD cube than the old
  IR pair at 1.56 μm, even in the presence of noise, and hence likely
  also on the real Sun. Owing to their low formation heights (100-200 km
  above τ<SUB>5000</SUB> = 1), both the new line pairs are well suited
  for probing magnetic fields in the lower photosphere.

Title: ALMA Discovery of Solar Umbral Brightness Enhancement at λ =
    3 mm
Authors: Iwai, K.; Loukitcheva, M.; Shimojo, M.; Solanki, S. K.;
   White, S. M.
Bibcode: 2017AGUFMSH43A2806I
Altcode:
  We report the discovery of a brightness enhancement in the center of
  a large sunspot umbra at a wavelength of 3 mm using the Atacama Large
  Millimeter/sub-millimeter Array (ALMA). Sunspots are among the most
  prominent features on the solar surface, but many of their aspects are
  surprisingly poorly understood. We analyzed a λ = 3 mm (100 GHz) mosaic
  image obtained by ALMA that includes a large sunspot within the active
  region AR12470, on 2015 December 16. The 3 mm map has a 300''×300''
  field of view and 4.9''×2.2'' spatial resolution, which is the highest
  spatial resolution map of an entire sunspot in this frequency range. We
  find a gradient of 3 mm brightness from a high value in the outer
  penumbra to a low value in the inner penumbra/outer umbra. Within the
  inner umbra, there is a marked increase in 3 mm brightness temperature,
  which we call an umbral brightness enhancement. This enhanced emission
  corresponds to a temperature excess of 800 K relative to the surrounding
  inner penumbral region and coincides with excess brightness in the
  1330 and 1400 Å slit-jaw images of the Interface Region Imaging
  Spectrograph (IRIS), adjacent to a partial lightbridge. This λ = 3 mm
  brightness enhancement may be an intrinsic feature of the sunspot umbra
  at chromospheric heights, such as a manifestation of umbral flashes, or
  it could be related to a coronal plume, since the brightness enhancement
  was coincident with the footpoint of a coronal loop observed at 171 Å.

Title: METIS, the Multi Element Telescope for Imaging and
Spectroscopy: an instrument proposed for the solar orbiter mission
Authors: Antonucci, E.; Andretta, V.; Cesare, S.; Ciaravella, A.;
   Doschek, G.; Fineschi, S.; Giordano, S.; Lamy, P.; Moses, D.; Naletto,
   G.; Newmark, J.; Poletto, L.; Romoli, M.; Solanki, S.; Spadaro, D.;
   Teriaca, L.; Zangrilli, L.
Bibcode: 2017SPIE10566E..0LA
Altcode:
  METIS, the Multi Element Telescope for Imaging and Spectroscopy,
  is an instrument proposed to the European Space Agency to be part of
  the payload of the Solar Orbiter mission. The instrument design has
  been conceived for performing extreme ultraviolet (EUV) spectroscopy
  both on the solar disk and off-limb, and near-Sun coronagraphy
  and spectroscopy. The proposed instrument suite consists of three
  different interconnected elements, COR, EUS and SOCS, sharing the
  same optical bench, electronics, and S/C heat shield aperture. COR is
  a visible-EUV multiband coronagraph based on a classical externally
  occulted design. EUS is the component of the METIS EUV disk spectrometer
  which includes the telescope and all the related mechanisms. Finally,
  SOCS is the METIS spectroscopic component including the dispersive
  system and the detectors. The capability of inserting a small telescope
  collecting coronal light has been added to perform also EUV coronal
  spectroscopy. METIS can simultaneously image the visible and ultraviolet
  emission of the solar corona and diagnose, with unprecedented temporal
  coverage and space resolution the structure and dynamics of the full
  corona in the range from 1.2 to 3.0 (1.6 to 4.1) solar radii (R⊙,
  measured from Sun centre) at minimum (maximum) perihelion during the
  nominal mission. It can also perform spectroscopic observations of the
  solar disk and out to 1.4 R⊙ within the 50-150 nm spectral region,
  and of the geo-effective coronal region 1.7-2.7 R⊙ within the 30-125
  nm spectral band.

Title: Normal and counter Evershed flows in the photospheric penumbra
    of a sunspot. SPINOR 2D inversions of Hinode-SOT/SP observations
Authors: Siu-Tapia, A.; Lagg, A.; Solanki, S. K.; van Noort, M.;
   Jurčák, J.
Bibcode: 2017A&A...607A..36S
Altcode: 2017arXiv170907386S
  Context. The Evershed effect, a nearly horizontal outflow of material
  seen in the penumbrae of sunspots in the photospheric layers, is a
  common characteristic of well-developed penumbrae, but is still not well
  understood. Even less is known about photospheric horizontal inflows in
  the penumbra, also known as counter Evershed flows. <BR /> Aims: Here we
  present a rare feature observed in the penumbra of the main sunspot of
  AR NOAA 10930. This spot displays the normal Evershed outflow in most
  of the penumbra, but harbors a fast photospheric inflow of material
  over a large sector of the disk-center penumbra. We investigate the
  driving forces of both, the normal and the counter Evershed flows. <BR
  /> Methods: We invert the spectropolarimetric data from Hinode SOT/SP
  using the spatially coupled version of the SPINOR inversion code,
  which allows us to derive height-dependent maps of the relevant
  physical parameters in the sunspot. These maps show considerable fine
  structure. Similarities and differences between the normal Evershed
  outflow and the counter Evershed flow are investigated. <BR /> Results:
  In both the normal and the counter Evershed flows, the material flows
  from regions with field strengths of the order of 1.5-2 kG to regions
  with stronger fields. The sources and sinks of both penumbral flows
  display opposite field polarities, with the sinks (tails of filaments)
  harboring local enhancements in temperature, which are nonetheless
  colder than their sources (heads of filaments). <BR /> Conclusions:
  The anti-correlation of the gradients in the temperature and magnetic
  pressure between the endpoints of the filaments from the two distinct
  penumbral regions is compatible with both the convective driver and
  the siphon flow scenarios. A geometrical scale of the parameters is
  necessary to determine which is the dominant force driving the flows.

Title: Solar ALMA Observations: Constraining the Chromosphere above
    Sunspots
Authors: Loukitcheva, Maria A.; Iwai, Kazumasa; Solanki, Sami K.;
   White, Stephen M.; Shimojo, Masumi
Bibcode: 2017ApJ...850...35L
Altcode: 2017arXiv171003812L
  We present the first high-resolution Atacama Large
  Millimeter/Submillimeter Array (ALMA) observations of a sunspot at
  wavelengths of 1.3 and 3 mm, obtained during the solar ALMA Science
  Verification campaign in 2015, and compare them with the predictions
  of semi-empirical sunspot umbral/penumbral atmosphere models. For
  the first time, millimeter observations of sunspots have resolved
  umbral/penumbral brightness structure at the chromospheric heights,
  where the emission at these wavelengths is formed. We find that the
  sunspot umbra exhibits a radically different appearance at 1.3 and 3
  mm, whereas the penumbral brightness structure is similar at the two
  wavelengths. The inner part of the umbra is ∼600 K brighter than the
  surrounding quiet Sun (QS) at 3 mm and is ∼700 K cooler than the QS
  at 1.3 mm, being the coolest part of sunspot at this wavelength. On
  average, the brightness of the penumbra at 3 mm is comparable to
  the QS brightness, while at 1.3 mm it is ∼1000 K brighter than
  the QS. Penumbral brightness increases toward the outer boundary in
  both ALMA bands. Among the tested umbral models, that of Severino et
  al. provides the best fit to the observational data, including both
  the ALMA data analyzed in this study and data from earlier works. No
  penumbral model among those considered here gives a satisfactory fit
  to the currently available measurements. ALMA observations at multiple
  millimeter wavelengths can be used for testing existing sunspot models,
  and serve as an important input to constrain new empirical models.

Title: The Small-scale Structure of Photospheric Convection Retrieved
    by a Deconvolution Technique Applied to Hinode/SP Data
Authors: Oba, T.; Riethmüller, T. L.; Solanki, S. K.; Iida, Y.;
   Quintero Noda, C.; Shimizu, T.
Bibcode: 2017ApJ...849....7O
Altcode: 2017arXiv170906933O
  Solar granules are bright patterns surrounded by dark channels, called
  intergranular lanes, in the solar photosphere and are a manifestation of
  overshooting convection. Observational studies generally find stronger
  upflows in granules and weaker downflows in intergranular lanes. This
  trend is, however, inconsistent with the results of numerical
  simulations in which downflows are stronger than upflows through the
  joint action of gravitational acceleration/deceleration and pressure
  gradients. One cause of this discrepancy is the image degradation caused
  by optical distortion and light diffraction and scattering that takes
  place in an imaging instrument. We apply a deconvolution technique to
  Hinode/SP data in an attempt to recover the original solar scene. Our
  results show a significant enhancement in both the convective upflows
  and downflows but particularly for the latter. After deconvolution,
  the up- and downflows reach maximum amplitudes of -3.0 km s<SUP>-1</SUP>
  and +3.0 km s<SUP>-1</SUP> at an average geometrical height of roughly
  50 km, respectively. We found that the velocity distributions after
  deconvolution match those derived from numerical simulations. After
  deconvolution, the net LOS velocity averaged over the whole field of
  view lies close to zero as expected in a rough sense from mass balance.

Title: The Maximum Entropy Limit of Small-scale Magnetic Field
    Fluctuations in the Quiet Sun
Authors: Gorobets, A. Y.; Berdyugina, S. V.; Riethmüller, T. L.;
   Blanco Rodríguez, J.; Solanki, S. K.; Barthol, P.; Gandorfer, A.;
   Gizon, L.; Hirzberger, J.; van Noort, M.; Del Toro Iniesta, J. C.;
   Orozco Suárez, D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
Bibcode: 2017ApJS..233....5G
Altcode: 2017arXiv171008361G
  The observed magnetic field on the solar surface is characterized by a
  very complex spatial and temporal behavior. Although feature-tracking
  algorithms have allowed us to deepen our understanding of this behavior,
  subjectivity plays an important role in the identification and tracking
  of such features. In this paper, we continue studies of the temporal
  stochasticity of the magnetic field on the solar surface without relying
  either on the concept of magnetic features or on subjective assumptions
  about their identification and interaction. We propose a data analysis
  method to quantify fluctuations of the line-of-sight magnetic field by
  means of reducing the temporal field’s evolution to the regular Markov
  process. We build a representative model of fluctuations converging to
  the unique stationary (equilibrium) distribution in the long time limit
  with maximum entropy. We obtained different rates of convergence to the
  equilibrium at fixed noise cutoff for two sets of data. This indicates
  a strong influence of the data spatial resolution and mixing-polarity
  fluctuations on the relaxation process. The analysis is applied to
  observations of magnetic fields of the relatively quiet areas around an
  active region carried out during the second flight of the Sunrise/IMaX
  and quiet Sun areas at the disk center from the Helioseismic and
  Magnetic Imager on board the Solar Dynamics Observatory satellite.

Title: Flows along arch filaments observed in the GRIS `very fast
    spectroscopic mode'
Authors: González Manrique, S. J.; Denker, C.; Kuckein, C.; Pastor
   Yabar, A.; Collados, M.; Verma, M.; Balthasar, H.; Diercke, A.;
   Fischer, C. E.; Gömöry, P.; Bello González, N.; Schlichenmaier,
   R.; Cubas Armas, M.; Berkefeld, T.; Feller, A.; Hoch, S.; Hofmann,
   A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Schmidt, D.; Schmidt,
   W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude,
   J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
Bibcode: 2017IAUS..327...28G
Altcode: 2017arXiv170102206G
  A new generation of solar instruments provides improved spectral,
  spatial, and temporal resolution, thus facilitating a better
  understanding of dynamic processes on the Sun. High-resolution
  observations often reveal multiple-component spectral line profiles,
  e.g., in the near-infrared He i 10830 Å triplet, which provides
  information about the chromospheric velocity and magnetic fine
  structure. We observed an emerging flux region, including two small
  pores and an arch filament system, on 2015 April 17 with the `very
  fast spectroscopic mode' of the GREGOR Infrared Spectrograph (GRIS)
  situated at the 1.5-meter GREGOR solar telescope at Observatorio del
  Teide, Tenerife, Spain. We discuss this method of obtaining fast (one
  per minute) spectral scans of the solar surface and its potential to
  follow dynamic processes on the Sun. We demonstrate the performance
  of the `very fast spectroscopic mode' by tracking chromospheric
  high-velocity features in the arch filament system.

Title: Spectral variability of photospheric radiation due to
    faculae. I. The Sun and Sun-like stars
Authors: Norris, Charlotte M.; Beeck, Benjamin; Unruh, Yvonne C.;
   Solanki, Sami K.; Krivova, Natalie A.; Yeo, Kok Leng
Bibcode: 2017A&A...605A..45N
Altcode: 2017arXiv170504455N
  Context. Stellar spectral variability on timescales of a day and
  longer, arising from magnetic surface features such as dark spots
  and bright faculae, is an important noise source when characterising
  extra-solar planets. Current 1D models of faculae do not capture the
  geometric properties and fail to reproduce observed solar facular
  contrasts. Magnetoconvection simulations provide facular contrasts
  accounting for geometry. <BR /> Aims: We calculate facular contrast
  spectra from magnetoconvection models of the solar photosphere with
  a view to improve (a) future parameter determinations for planets
  with early G type host stars and (b) reconstructions of solar spectral
  variability. <BR /> Methods: Regions of a solar twin (G2, log g = 4.44)
  atmosphere with a range of initial average vertical magnetic fields
  (100 to 500 G) were simulated using a 3D radiation-magnetohydrodynamics
  code, MURaM, and synthetic intensity spectra were calculated from
  the ultraviolet (149.5 nm) to the far infrared (160 000 nm) with the
  ATLAS9 radiative transfer code. Nine viewing angles were investigated
  to account for facular positions across most of the stellar disc. <BR
  /> Results: Contrasts of the radiation from simulation boxes with
  different levels of magnetic flux relative to an atmosphere with no
  magnetic field are a complicated function of position, wavelength
  and magnetic field strength that is not reproduced by 1D facular
  models. Generally, contrasts increase towards the limb, but at UV
  wavelengths a saturation and decrease are observed close to the
  limb. Contrasts also increase strongly from the visible to the UV;
  there is a rich spectral dependence, with marked peaks in molecular
  bands and strong spectral lines. At disc centre, a complex relationship
  with magnetic field was found and areas of strong magnetic field
  can appear either dark or bright, depending on wavelength. Spectra
  calculated for a wide variety of magnetic fluxes will also serve to
  improve total and spectral solar irradiance reconstructions.

Title: Solar Irradiance Variability is Caused by the Magnetic Activity
    on the Solar Surface
Authors: Yeo, K. L.; Solanki, S. K.; Norris, C. M.; Beeck, B.; Unruh,
   Y. C.; Krivova, N. A.
Bibcode: 2017PhRvL.119i1102Y
Altcode: 2017arXiv170900920Y
  The variation in the radiative output of the Sun, described in terms
  of solar irradiance, is important to climatology. A common assumption
  is that solar irradiance variability is driven by its surface
  magnetism. Verifying this assumption has, however, been hampered by
  the fact that models of solar irradiance variability based on solar
  surface magnetism have to be calibrated to observed variability. Making
  use of realistic three-dimensional magnetohydrodynamic simulations
  of the solar atmosphere and state-of-the-art solar magnetograms from
  the Solar Dynamics Observatory, we present a model of total solar
  irradiance (TSI) that does not require any such calibration. In doing
  so, the modeled irradiance variability is entirely independent of the
  observational record. (The absolute level is calibrated to the TSI
  record from the Total Irradiance Monitor.) The model replicates 95%
  of the observed variability between April 2010 and July 2016, leaving
  little scope for alternative drivers of solar irradiance variability
  at least over the time scales examined (days to years).

Title: Solar Magnetoconvection and Small-Scale Dynamo. Recent
    Developments in Observation and Simulation
Authors: Borrero, J. M.; Jafarzadeh, S.; Schüssler, M.; Solanki, S. K.
Bibcode: 2017SSRv..210..275B
Altcode: 2015SSRv..tmp..113B; 2015arXiv151104214B
  A number of observational and theoretical aspects of solar
  magnetoconvection are considered in this review. We discuss recent
  developments in our understanding of the small-scale structure of
  the magnetic field on the solar surface and its interaction with
  convective flows, which is at the centre of current research. Topics
  range from plage areas in active regions over the magnetic network
  shaped by supergranulation to the ubiquituous `turbulent' internetwork
  fields. On the theoretical side, we focus upon magnetic field generation
  by small-scale dynamo action.

Title: Three-dimensional magnetic structure of a sunspot: Comparison
    of the photosphere and upper chromosphere
Authors: Joshi, Jayant; Lagg, Andreas; Hirzberger, Johann; Solanki,
   Sami K.
Bibcode: 2017A&A...604A..98J
Altcode: 2017arXiv170508404J
  <BR /> Aims: We investigate the magnetic field of a sunspot in the
  upper chromosphere and compare it to the photospheric properties
  of the field. <BR /> Methods: We observed the main leading sunspot
  of the active region NOAA 11124 during two days with the Tenerife
  Infrared Polarimeter-2 (TIP-2) mounted at the German Vacuum Tower
  Telescope (VTT). Through inversion of Stokes spectra of the He I
  triplet at 10 830 Å, we obtained the magnetic field vector of the
  upper chromosphere. For comparison with the photosphere, we applied
  height-dependent inversions of the Si I 10 827.1 Å and Ca I 10 833.4 Å
  lines. <BR /> Results: We found that the umbral magnetic field strength
  in the upper chromosphere is lower by a factor of 1.30-1.65 compared
  to the photosphere. The magnetic field strength of the umbra decreases
  from the photosphere toward the upper chromosphere by an average rate of
  0.5-0.9 G km<SUP>-1</SUP>. The difference in the magnetic field strength
  between both atmospheric layers steadily decreases from the sunspot
  center to the outer boundary of the sunspot; the field, in particular
  its horizontal component, is stronger in the chromopshere outside the
  spot and this is suggestive of a magnetic canopy. The sunspot displays
  a twist that on average is similar in the two layers. However, the
  differential twist between the photosphere and chromosphere increases
  rapidly toward the outer penumbral boundary. The magnetic field
  vector is more horizontal with respect to the solar surface by roughly
  5-20° in the photosphere compared to the upper chromosphere. Above
  a lightbridge, the chromospheric magnetic field is equally strong as
  that in the umbra, whereas the field of the lightbridge is weaker than
  its surroundings in the photosphere by roughly 1 kG. This suggests a
  cusp-like magnetic field structure above the lightbridge.

Title: The Solar Ultraviolet Imaging Telescope on-board Aditya-L1
Authors: Tripathi, Durgesh; Ramaprakash, A. N.; Khan, Aafaque;
   Ghosh, Avyarthana; Chatterjee, Subhamoy; Banerjee, Dipankar; Chordia,
   Pravin; Gandorfer, Achim; Krivova, Natalie; Nandy, Dibyendu; Rajarshi,
   Chaitanya; Solanki, Sami K.
Bibcode: 2017CSci..113..616T
Altcode: 2022arXiv220407732T
  The Solar Ultraviolet Imaging Telescope (SUIT) is an instrument
  onboard the Aditya-L1 mission of ISRO that will measure and monitor
  the solar radiation emitted in the near-ultraviolet wavelength range
  (200-400 nm). SUIT will simultaneously map the photosphere and the
  chromosphere of the Sun using 11 filters sensitive to different
  wavelengths and covering different heights in the solar atmosphere
  and help us understand the processes involved in the transfer of
  mass and energy from one layer to the other. SUIT will also allow us
  to measure and monitor spatially resolved solar spectral irradiance
  that governs the chemistry of oxygen and ozone in the stratosphere of
  Earth's atmosphere. This is central to our understanding of the Sun
  climate relationship.

Title: The nature of solar brightness variations
Authors: Shapiro, A. I.; Solanki, S. K.; Krivova, N. A.; Cameron,
   R. H.; Yeo, K. L.; Schmutz, W. K.
Bibcode: 2017NatAs...1..612S
Altcode: 2017arXiv171104156S
  Determining the sources of solar brightness variations<SUP>1,2</SUP>,
  often referred to as solar noise<SUP>3</SUP>, is important because
  solar noise limits the detection of solar oscillations<SUP>3</SUP>,
  is one of the drivers of the Earth's climate system<SUP>4,5</SUP> and
  is a prototype of stellar variability<SUP>6,7</SUP>—an important
  limiting factor for the detection of extrasolar planets. Here,
  we model the magnetic contribution to solar brightness variability
  using high-cadence<SUP>8,9</SUP> observations from the Solar Dynamics
  Observatory (SDO) and the Spectral And Total Irradiance REconstruction
  (SATIRE)<SUP>10,11</SUP> model. The brightness variations caused by
  the constantly evolving cellular granulation pattern on the solar
  surface were computed with the Max Planck Institute for Solar System
  Research (MPS)/University of Chicago Radiative Magnetohydrodynamics
  (MURaM)<SUP>12</SUP> code. We found that the surface magnetic field
  and granulation can together precisely explain solar noise (that
  is, solar variability excluding oscillations) on timescales from
  minutes to decades, accounting for all timescales that have so far
  been resolved or covered by irradiance measurements. We demonstrate
  that no other sources of variability are required to explain the
  data. Recent measurements of Sun-like stars by the COnvection ROtation
  and planetary Transits (CoRoT)<SUP>13</SUP> and Kepler<SUP>14</SUP>
  missions uncovered brightness variations similar to that of the Sun,
  but with a much wider variety of patterns<SUP>15</SUP>. Our finding
  that solar brightness variations can be replicated in detail with
  just two well-known sources will greatly simplify future modelling of
  existing CoRoT and Kepler as well as anticipated Transiting Exoplanet
  Survey Satellite<SUP>16</SUP> and PLAnetary Transits and Oscillations
  of stars (PLATO)<SUP>17</SUP> data.

Title: The variability of magnetic activity in solar-type stars
Authors: Fabbian, D.; Simoniello, R.; Collet, R.; Criscuoli, S.;
   Korhonen, H.; Krivova, N. A.; Oláh, K.; Jouve, L.; Solanki, S. K.;
   Alvarado-Gómez, J. D.; Booth, R.; García, R. A.; Lehtinen, J.;
   See, V.
Bibcode: 2017AN....338..753F
Altcode:
  No abstract at ADS

Title: Association of solar coronal loops to photospheric magnetic
    field
Authors: Pradeep Chitta, Lakshmi; Peter, Hardi; Solanki, Sami
Bibcode: 2017SPD....4810630P
Altcode:
  Magnetic connectivity and its evolution from the solar photosphere
  to the corona will play a crucial role in the energetics of the
  solar atmosphere. To explore this connectivity, we use high spatial
  resolution magnetic field observations of an active region from the
  balloon-borne SUNRISE telescope, in combination with the observations
  of coronal loops imaged in extreme ultraviolet by SDO/AIA. We show
  that photospheric magnetic field at the base of coronal loops is
  rapidly evolving through small-scale flux emergence and cancellation
  events with rates on the order of 10^15 Mx/s. When observed at high
  spatial resolution better than 0.5 arcsec, we find that basically
  all coronal loops considered so far are rooted in the photosphere
  above small-scale opposite polarity magnetic field patches. In the
  photosphere, the magnetic field threading coronal loops is interacting
  with opposite polarity parasitic magnetic concentrations leading to
  dynamic signatures in the upper atmosphere. Chromospheric small-scale
  jets aligned to coronal loops are observed at these locations. We
  will present preliminary results from 3D MHD simulations of coronal
  loops driven by realistic magneto-convection and discuss what role
  the magnetic interactions at coronal loop footpoints could play in
  the evolution of coronal loops and their heating.

Title: The Sunrise balloon-borne observatory: Results from the second
    flight and outlook on the third flight
Authors: Solanki, Sami K.
Bibcode: 2017SPD....4810507S
Altcode:
  The balloon-borne solar observatory Sunrise flew for a second time in
  June 2013 and provided seeing-free UV images and spectropolarimetric
  data at close to the diffraction limit of the 1m telescope. The data
  analysis has so far concentrated on a time series of the heart of
  an active region recorded in the Stokes vector of the Fe I 525.02 nm
  line and a time series of UV images of the same region. First results
  were published in a special issue of the ApJ Supplement, vol. 229,
  in April 2017. The data suggest the presence of very strong fields
  in pores, a low-lying canopy of slender fibrils and different types
  of waves propagating along these fibrils. Furthermore, properties of
  the complex emergence of magnetic flux, of moving magnetic features
  around a pore and of a siphon flow along a low-lying slender magnetic
  loop are determined. A novel technique for inversions of Stokes
  profiles including constraints to make the results more physically
  consistent has also been developed and for the first time applied
  to Sunrise II data. In addition, the presence of small-scale mixed
  polarities and chromospheric jets was detected at the footpoints of
  particularly bright coronal loops. These and more results will be
  briefly presented. Preparations for the next flight of Sunrise have
  started. Many new features are being designed for this flight, which
  will allow it to reach considerably extended science goals. Thus it
  will feature two new spectropolarimeters, one exploring the near
  UV (from MPS), the other concentrating on chromospheric fields
  and their connection to the photosphere (led by NAOJ). The IMaX
  vector-magnetograph (provided by a Spanish consortium) will also
  be updated to be able to sample multiple spectral lines. Finally,
  Sunrise will have a new gondola (coming from APL) and an improved
  image stabilization system (from KIS).

Title: ALMA Discovery of Solar Umbral Brightness Enhancement at λ =
    3 mm
Authors: Iwai, Kazumasa; Loukitcheva, Maria; Shimojo, Masumi; Solanki,
   Sami K.; White, Stephen M.
Bibcode: 2017ApJ...841L..20I
Altcode: 2017arXiv170503147I
  We report the discovery of a brightness enhancement in the center
  of a large sunspot umbra at a wavelength of 3 mm using the Atacama
  Large Millimeter/sub-millimeter Array (ALMA). Sunspots are among
  the most prominent features on the solar surface, but many of their
  aspects are surprisingly poorly understood. We analyzed a λ = 3 mm
  (100 GHz) mosaic image obtained by ALMA that includes a large sunspot
  within the active region AR12470, on 2015 December 16. The 3 mm map
  has a 300″ × 300″ field of view and 4.″9 × 2.″2 spatial
  resolution, which is the highest spatial resolution map of an entire
  sunspot in this frequency range. We find a gradient of 3 mm brightness
  from a high value in the outer penumbra to a low value in the inner
  penumbra/outer umbra. Within the inner umbra, there is a marked increase
  in 3 mm brightness temperature, which we call an umbral brightness
  enhancement. This enhanced emission corresponds to a temperature
  excess of 800 K relative to the surrounding inner penumbral region
  and coincides with excess brightness in the 1330 and 1400 Å slit-jaw
  images of the Interface Region Imaging Spectrograph (IRIS), adjacent
  to a partial lightbridge. This λ = 3 mm brightness enhancement may be
  an intrinsic feature of the sunspot umbra at chromospheric heights,
  such as a manifestation of umbral flashes, or it could be related to
  a coronal plume, since the brightness enhancement was coincident with
  the footpoint of a coronal loop observed at 171 Å.

Title: New reconstruction of the sunspot group numbers since 1739
    using direct calibration and "backbone" methods
Authors: Chatzistergos, Theodosios; Usoskin, Ilya G.; Kovaltsov,
   Gennady A.; Krivova, Natalie A.; Solanki, Sami K.
Bibcode: 2017A&A...602A..69C
Altcode: 2017arXiv170206183C
  Context. The group sunspot number (GSN) series constitute the longest
  instrumental astronomical database providing information on solar
  activity. This database is a compilation of observations by many
  individual observers, and their inter-calibration has usually been
  performed using linear rescaling. There are multiple published series
  that show different long-term trends for solar activity. <BR /> Aims:
  We aim at producing a GSN series, with a non-linear non-parametric
  calibration. The only underlying assumptions are that the differences
  between the various series are due to different acuity thresholds
  of the observers, and that the threshold of each observer remains
  constant throughout the observing period. <BR /> Methods: We used a
  daisy chain process with backbone (BB) observers and calibrated all
  overlapping observers to them. We performed the calibration of each
  individual observer with a probability distribution function (PDF)
  matrix constructed considering all daily values for the overlapping
  period with the BB. The calibration of the BBs was carried out in a
  similar manner. The final series was constructed by merging different
  BB series. We modelled the propagation of errors straightforwardly
  with Monte Carlo simulations. A potential bias due to the selection
  of BBs was investigated and the effect was shown to lie within the 1σ
  interval of the produced series. The exact selection of the reference
  period was shown to have a rather small effect on our calibration
  as well. <BR /> Results: The final series extends back to 1739 and
  includes data from 314 observers. This series suggests moderate
  activity during the 18th and 19th century, which is significantly
  lower than the high level of solar activity predicted by other recent
  reconstructions applying linear regressions. <BR /> Conclusions:
  The new series provides a robust reconstruction, based on modern and
  non-parametric methods, of sunspot group numbers since 1739, and it
  confirms the existence of the modern grand maximum of solar activity in
  the second half of the 20th century. <P />Values of the group sunspot
  number series are only available at the CDS via anonymous ftp to <A
  href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
  (<A href="http://130.79.128.5">http://130.79.128.5</A>) or via <A
  href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/602/A69">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/602/A69</A>

Title: Millimeter radiation from a 3D model of the solar
    atmosphere. II. Chromospheric magnetic field
Authors: Loukitcheva, M.; White, S. M.; Solanki, S. K.; Fleishman,
   G. D.; Carlsson, M.
Bibcode: 2017A&A...601A..43L
Altcode: 2017arXiv170206018L
  <BR /> Aims: We use state-of-the-art, three-dimensional non-local
  thermodynamic equilibrium (non-LTE) radiative magnetohydrodynamic
  simulations of the quiet solar atmosphere to carry out detailed tests
  of chromospheric magnetic field diagnostics from free-free radiation at
  millimeter and submillimeter wavelengths (mm/submm). <BR /> Methods:
  The vertical component of the magnetic field was deduced from the
  mm/submm brightness spectra and the degree of circular polarization
  synthesized at millimeter frequencies. We used the frequency bands
  observed by the Atacama Large Millimeter/Submillimeter Array (ALMA)
  as a convenient reference. The magnetic field maps obtained describe
  the longitudinal magnetic field at the effective formation heights of
  the relevant wavelengths in the solar chromosphere. <BR /> Results:
  The comparison of the deduced and model chromospheric magnetic fields
  at the spatial resolution of both the model and current observations
  demonstrates a good correlation, but has a tendency to underestimate
  the model field. The systematic discrepancy of about 10% is probably
  due to averaging of the restored field over the heights contributing
  to the radiation, weighted by the strength of the contribution. On
  the whole, the method of probing the longitudinal component of the
  magnetic field with free-free emission at mm/submm wavelengths
  is found to be applicable to measurements of the weak quiet-Sun
  magnetic fields. However, successful exploitation of this technique
  requires very accurate measurements of the polarization properties
  (primary beam and receiver polarization response) of the antennas,
  which will be the principal factor that determines the level to which
  chromospheric magnetic fields can be measured. <BR /> Conclusions:
  Consequently, high-resolution and high-precision observations of
  circularly polarized radiation at millimeter wavelengths can be a
  powerful tool for producing chromospheric longitudinal magnetograms.

Title: Erratum: Morphological Properties of
    Slender CaII H Fibrils Observed by sunrise II (<A
href="http://doi.org/10.3847/1538-4365/229/1/6">ApJS 229, 1, 6</A>)
Authors: Gafeira, R.; Lagg, A.; Solanki, S. K.; Jafarzadeh, S.;
   van Noort, M.; Barthol, P.; Blanco Rodríguez, J.; del Toro Iniesta,
   J. C.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Knölker, M.; Orozco
   Suárez, D.; Riethmüller, T. L.; Schmidt, W.
Bibcode: 2017ApJS..230...11G
Altcode:
  No abstract at ADS

Title: High-frequency Oscillations in Small Magnetic Elements Observed
    with Sunrise/SuFI
Authors: Jafarzadeh, S.; Solanki, S. K.; Stangalini, M.; Steiner,
   O.; Cameron, R. H.; Danilovic, S.
Bibcode: 2017ApJS..229...10J
Altcode: 2016arXiv161109302J
  We characterize waves in small magnetic elements and investigate
  their propagation in the lower solar atmosphere from observations at
  high spatial and temporal resolution. We use the wavelet transform to
  analyze oscillations of both horizontal displacement and intensity
  in magnetic bright points found in the 300 nm and the Ca II H 396.8
  nm passbands of the filter imager on board the Sunrise balloon-borne
  solar observatory. Phase differences between the oscillations at the
  two atmospheric layers corresponding to the two passbands reveal
  upward propagating waves at high frequencies (up to 30 mHz). Weak
  signatures of standing as well as downward propagating waves are also
  obtained. Both compressible and incompressible (kink) waves are found
  in the small-scale magnetic features. The two types of waves have
  different, though overlapping, period distributions. Two independent
  estimates give a height difference of approximately 450 ± 100 km
  between the two atmospheric layers sampled by the employed spectral
  bands. This value, together with the determined short travel times of
  the transverse and longitudinal waves provide us with phase speeds of 29
  ± 2 km s<SUP>-1</SUP> and 31 ± 2 km s<SUP>-1</SUP>, respectively. We
  speculate that these phase speeds may not reflect the true propagation
  speeds of the waves. Thus, effects such as the refraction of fast
  longitudinal waves may contribute to an overestimate of the phase speed.

Title: Slender Ca II H Fibrils Mapping Magnetic Fields in the Low
    Solar Chromosphere
Authors: Jafarzadeh, S.; Rutten, R. J.; Solanki, S. K.; Wiegelmann, T.;
   Riethmüller, T. L.; van Noort, M.; Szydlarski, M.; Blanco Rodríguez,
   J.; Barthol, P.; del Toro Iniesta, J. C.; Gandorfer, A.; Gizon, L.;
   Hirzberger, J.; Knölker, M.; Martínez Pillet, V.; Orozco Suárez,
   D.; Schmidt, W.
Bibcode: 2017ApJS..229...11J
Altcode: 2016arXiv161003104J
  A dense forest of slender bright fibrils near a small solar active
  region is seen in high-quality narrowband Ca II H images from the SuFI
  instrument onboard the Sunrise balloon-borne solar observatory. The
  orientation of these slender Ca II H fibrils (SCF) overlaps with the
  magnetic field configuration in the low solar chromosphere derived
  by magnetostatic extrapolation of the photospheric field observed
  with Sunrise/IMaX and SDO/HMI. In addition, many observed SCFs are
  qualitatively aligned with small-scale loops computed from a novel
  inversion approach based on best-fit numerical MHD simulation. Such
  loops are organized in canopy-like arches over quiet areas that differ
  in height depending on the field strength near their roots.

Title: EMPIRE: A robust empirical reconstruction of solar irradiance
    variability
Authors: Yeo, K. L.; Krivova, N. A.; Solanki, S. K.
Bibcode: 2017JGRA..122.3888Y
Altcode: 2017arXiv170407652Y
  We present a new empirical model of total and spectral solar irradiance
  (TSI and SSI) variability entitled EMPirical Irradiance REconstruction
  (EMPIRE). As with existing empirical models, TSI and SSI variability
  is given by the linear combination of solar activity indices. In
  empirical models, UV SSI variability is usually determined by
  fitting the rotational variability in activity indices to that in
  measurements. Such models have to date relied on ordinary least
  squares regression, which ignores the uncertainty in the activity
  indices. In an advance from earlier efforts, the uncertainty in the
  activity indices is accounted for in EMPIRE by the application of
  an error-in-variables regression scheme, making the resultant UV SSI
  variability more robust. The result is consistent with observations and
  unprecedentedly, with that from other modeling approaches, resolving
  the long-standing controversy between existing empirical models and
  other types of models. We demonstrate that earlier empirical models,
  by neglecting the uncertainty in activity indices, underestimate UV
  SSI variability. The reconstruction of TSI and visible and IR SSI from
  EMPIRE is also shown to be consistent with observations. The EMPIRE
  reconstruction is of utility to climate studies as a more robust
  alternative to earlier empirical reconstructions.

Title: Magneto-static Modeling from Sunrise/IMaX: Application to an
    Active Region Observed with Sunrise II
Authors: Wiegelmann, T.; Neukirch, T.; Nickeler, D. H.; Solanki, S. K.;
   Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Riethmüller,
   T. L.; van Noort, M.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.;
   Orozco Suárez, D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
Bibcode: 2017ApJS..229...18W
Altcode: 2017arXiv170101458N; 2017arXiv170101458W
  Magneto-static models may overcome some of the issues facing force-free
  magnetic field extrapolations. So far they have seen limited use
  and have faced problems when applied to quiet-Sun data. Here we
  present a first application to an active region. We use solar vector
  magnetic field measurements gathered by the IMaX polarimeter during
  the flight of the Sunrise balloon-borne solar observatory in 2013
  June as boundary conditions for a magneto-static model of the higher
  solar atmosphere above an active region. The IMaX data are embedded
  in active region vector magnetograms observed with SDO/HMI. This work
  continues our magneto-static extrapolation approach, which was applied
  earlier to a quiet-Sun region observed with Sunrise I. In an active
  region the signal-to-noise-ratio in the measured Stokes parameters
  is considerably higher than in the quiet-Sun and consequently the
  IMaX measurements of the horizontal photospheric magnetic field allow
  us to specify the free parameters of the model in a special class of
  linear magneto-static equilibria. The high spatial resolution of IMaX
  (110-130 km, pixel size 40 km) enables us to model the non-force-free
  layer between the photosphere and the mid-chromosphere vertically
  by about 50 grid points. In our approach we can incorporate some
  aspects of the mixed beta layer of photosphere and chromosphere, e.g.,
  taking a finite Lorentz force into account, which was not possible with
  lower-resolution photospheric measurements in the past. The linear model
  does not, however, permit us to model intrinsic nonlinear structures
  like strongly localized electric currents.

Title: The Second Flight of the Sunrise Balloon-borne Solar
Observatory: Overview of Instrument Updates, the Flight, the Data,
    and First Results
Authors: Solanki, S. K.; Riethmüller, T. L.; Barthol, P.; Danilovic,
   S.; Deutsch, W.; Doerr, H. -P.; Feller, A.; Gandorfer, A.; Germerott,
   D.; Gizon, L.; Grauf, B.; Heerlein, K.; Hirzberger, J.; Kolleck, M.;
   Lagg, A.; Meller, R.; Tomasch, G.; van Noort, M.; Blanco Rodríguez,
   J.; Gasent Blesa, J. L.; Balaguer Jiménez, M.; Del Toro Iniesta,
   J. C.; López Jiménez, A. C.; Orozco Suarez, D.; Berkefeld, T.;
   Halbgewachs, C.; Schmidt, W.; Álvarez-Herrero, A.; Sabau-Graziati,
   L.; Pérez Grande, I.; Martínez Pillet, V.; Card, G.; Centeno, R.;
   Knölker, M.; Lecinski, A.
Bibcode: 2017ApJS..229....2S
Altcode: 2017arXiv170101555S
  The Sunrise balloon-borne solar observatory, consisting of a 1 m
  aperture telescope that provides a stabilized image to a UV filter
  imager and an imaging vector polarimeter, carried out its second science
  flight in 2013 June. It provided observations of parts of active regions
  at high spatial resolution, including the first high-resolution images
  in the Mg II k line. The obtained data are of very high quality, with
  the best UV images reaching the diffraction limit of the telescope
  at 3000 Å after Multi-Frame Blind Deconvolution reconstruction
  accounting for phase-diversity information. Here a brief update is
  given of the instruments and the data reduction techniques, which
  includes an inversion of the polarimetric data. Mainly those aspects
  that evolved compared with the first flight are described. A tabular
  overview of the observations is given. In addition, an example time
  series of a part of the emerging active region NOAA AR 11768 observed
  relatively close to disk center is described and discussed in some
  detail. The observations cover the pores in the trailing polarity of
  the active region, as well as the polarity inversion line where flux
  emergence was ongoing and a small flare-like brightening occurred in
  the course of the time series. The pores are found to contain magnetic
  field strengths ranging up to 2500 G, and while large pores are clearly
  darker and cooler than the quiet Sun in all layers of the photosphere,
  the temperature and brightness of small pores approach or even exceed
  those of the quiet Sun in the upper photosphere.

Title: Estimation of the Magnetic Flux Emergence Rate in the Quiet
    Sun from Sunrise Data
Authors: Smitha, H. N.; Anusha, L. S.; Solanki, S. K.; Riethmüller,
   T. L.
Bibcode: 2017ApJS..229...17S
Altcode: 2016arXiv161106432S
  Small-scale internetwork (IN) features are thought to be the major
  source of fresh magnetic flux in the quiet Sun. During its first science
  flight in 2009, the balloon-borne observatory Sunrise captured images of
  the magnetic fields in the quiet Sun at a high spatial resolution. Using
  these data we measure the rate at which the IN features bring magnetic
  flux to the solar surface. In a previous paper it was found that the
  lowest magnetic flux in small-scale features detected using the Sunrise
  observations is 9 × 10<SUP>14</SUP> Mx. This is nearly an order of
  magnitude smaller than the smallest fluxes of features detected in
  observations from the Hinode satellite. In this paper, we compute the
  flux emergence rate (FER) by accounting for such small fluxes, which
  was not possible before Sunrise. By tracking the features with fluxes
  in the range {10}<SUP>15</SUP>{--}{10}<SUP>18</SUP> Mx, we measure an
  FER of 1100 {Mx} {{cm}}<SUP>-2</SUP> {{day}}<SUP>-1</SUP>. The smaller
  features with fluxes ≤slant {10}<SUP>16</SUP> Mx are found to be the
  dominant contributors to the solar magnetic flux. The FER found here
  is an order of magnitude higher than the rate from Hinode, obtained
  with a similar feature tracking technique. A wider comparison with the
  literature shows, however, that the exact technique of determining the
  rate of the appearance of new flux can lead to results that differ by
  up to two orders of magnitude, even when applied to similar data. The
  causes of this discrepancy are discussed and first qualitative
  explanations proposed.

Title: Vertical magnetic field gradient in the photospheric layers
    of sunspots
Authors: Joshi, Jayant; Lagg, Andreas; Hirzberger, Johann; Solanki,
   Sami K.; Tiwari, Sanjiv K.
Bibcode: 2017A&A...599A..35J
Altcode: 2016arXiv161000500J
  <BR /> Aims: We investigate the vertical gradient of the magnetic
  field of sunspots in the photospheric layer. <BR /> Methods:
  Independent observations were obtained with the Solar Optical
  Telescope/Spectropolarimeter (SOT/SP) on board the Hinode spacecraft and
  with the Tenrife Infrared Polarimeter-2 (TIP-2) mounted at the German
  Vacuum Tower Telescope (VTT). We apply state-of-the-art inversion
  techniques to both data sets to retrieve the magnetic field and the
  corresponding vertical gradient along with other atmospheric parameters
  in the solar photosphere. <BR /> Results: In the sunspot penumbrae we
  detected patches of negative vertical gradients of the magnetic field
  strength, I.e., the magnetic field strength decreases with optical depth
  in the photosphere. The negative gradient patches are located in the
  inner and partly in the middle penumbrae in both data sets. From the
  SOT/SP observations we found that the negative gradient patches are
  restricted mainly to the deep photospheric layers and are concentrated
  near the edges of the penumbral filaments. Magnetohydrodynamic (MHD)
  simulations also show negative gradients in the inner penumbrae, also
  at the locations of filaments. In the observations and the simulation
  negative gradients of the magnetic field vs. optical depth dominate
  at some radial distances in the penumbra. The negative gradient with
  respect to optical depth in the inner penumbrae persists even after
  averaging in the azimuthal direction in the observations and, to a
  lesser extent, in the MHD simulations. If the gradients in the MHD
  simulations are determined with respect to geometrical height, then
  the azimuthal averages are always positive within the sunspot (above
  log τ = 0), corresponding to magnetic field increasing with depth,
  as generally expected. <BR /> Conclusions: We interpret the observed
  localized presence of negative vertical gradient of the magnetic
  field strength in the observations as a consequence of stronger field
  from spines expanding with height and closing above the weaker field
  inter-spines. The presence of the negative gradients with respect
  to optical depth after azimuthal averaging can be explained by two
  different mechanisms: the high corrugation of equal optical depth
  surfaces and the cancellation of polarized signal due to the presence
  of unresolved opposite polarity patches in the deeper layers of the
  penumbra.

Title: A Tale of Two Emergences: Sunrise II Observations of Emergence
    Sites in a Solar Active Region
Authors: Centeno, R.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.;
   Solanki, S. K.; Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger,
   J.; Riethmüller, T. L.; van Noort, M.; Orozco Suárez, D.; Berkefeld,
   T.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
Bibcode: 2017ApJS..229....3C
Altcode: 2016arXiv161003531C
  In 2013 June, the two scientific instruments on board the second Sunrise
  mission witnessed, in detail, a small-scale magnetic flux emergence
  event as part of the birth of an active region. The Imaging Magnetograph
  Experiment (IMaX) recorded two small (∼ 5<SUP>\prime\prime</SUP> )
  emerging flux patches in the polarized filtergrams of a photospheric Fe
  I spectral line. Meanwhile, the Sunrise Filter Imager (SuFI) captured
  the highly dynamic chromospheric response to the magnetic fields pushing
  their way through the lower solar atmosphere. The serendipitous capture
  of this event offers a closer look at the inner workings of active
  region emergence sites. In particular, it reveals in meticulous detail
  how the rising magnetic fields interact with the granulation as they
  push through the Sun’s surface, dragging photospheric plasma in
  their upward travel. The plasma that is burdening the rising field
  slides along the field lines, creating fast downflowing channels at
  the footpoints. The weight of this material anchors this field to the
  surface at semi-regular spatial intervals, shaping it in an undulatory
  fashion. Finally, magnetic reconnection enables the field to release
  itself from its photospheric anchors, allowing it to continue its
  voyage up to higher layers. This process releases energy that lights
  up the arch-filament systems and heats the surrounding chromosphere.

Title: Photospheric Response to an Ellerman Bomb-like Event—An
    Analogy of Sunrise/IMaX Observations and MHD Simulations
Authors: Danilovic, S.; Solanki, S. K.; Barthol, P.; Gandorfer,
   A.; Gizon, L.; Hirzberger, J.; Riethmüller, T. L.; van Noort, M.;
   Blanco Rodríguez, J.; Del Toro Iniesta, J. C.; Orozco Suárez, D.;
   Schmidt, W.; Martínez Pillet, V.; Knölker, M.
Bibcode: 2017ApJS..229....5D
Altcode: 2016arXiv160903817D
  Ellerman Bombs are signatures of magnetic reconnection, which is an
  important physical process in the solar atmosphere. How and where they
  occur is a subject of debate. In this paper, we analyze Sunrise/IMaX
  data, along with 3D MHD simulations that aim to reproduce the exact
  scenario proposed for the formation of these features. Although
  the observed event seems to be more dynamic and violent than the
  simulated one, simulations clearly confirm the basic scenario for the
  production of EBs. The simulations also reveal the full complexity of
  the underlying process. The simulated observations show that the Fe I
  525.02 nm line gives no information on the height where reconnection
  takes place. It can only give clues about the heating in the aftermath
  of the reconnection. However, the information on the magnetic field
  vector and velocity at this spatial resolution is extremely valuable
  because it shows what numerical models miss and how they can be
  improved.

Title: Transverse Oscillations in Slender Ca II H Fibrils Observed
    with Sunrise/SuFI
Authors: Jafarzadeh, S.; Solanki, S. K.; Gafeira, R.; van Noort, M.;
   Barthol, P.; Blanco Rodríguez, J.; del Toro Iniesta, J. C.; Gandorfer,
   A.; Gizon, L.; Hirzberger, J.; Knölker, M.; Orozco Suárez, D.;
   Riethmüller, T. L.; Schmidt, W.
Bibcode: 2017ApJS..229....9J
Altcode: 2016arXiv161007449J
  We present observations of transverse oscillations in slender Ca II
  H fibrils (SCFs) in the lower solar chromosphere. We use a 1 hr long
  time series of high- (spatial and temporal-) resolution seeing-free
  observations in a 1.1 Å wide passband covering the line core of Ca
  II H 3969 Å from the second flight of the Sunrise balloon-borne solar
  observatory. The entire field of view, spanning the polarity inversion
  line of an active region close to the solar disk center, is covered with
  bright, thin, and very dynamic fine structures. Our analysis reveals
  the prevalence of transverse waves in SCFs with median amplitudes and
  periods on the order of 2.4 ± 0.8 km s<SUP>-1</SUP> and 83 ± 29 s,
  respectively (with standard deviations given as uncertainties). We
  find that the transverse waves often propagate along (parts of) the
  SCFs with median phase speeds of 9 ± 14 km s<SUP>-1</SUP>. While the
  propagation is only in one direction along the axis in some of the
  SCFs, propagating waves in both directions, as well as standing waves
  are also observed. The transverse oscillations are likely Alfvénic
  and are thought to be representative of magnetohydrodynamic kink
  waves. The wave propagation suggests that the rapid high-frequency
  transverse waves, often produced in the lower photosphere, can
  penetrate into the chromosphere with an estimated energy flux of ≈15
  kW m<SUP>-2</SUP>. Characteristics of these waves differ from those
  reported for other fibrillar structures, which, however, were observed
  mainly in the upper solar chromosphere.

Title: Kinematics of Magnetic Bright Features in the Solar Photosphere
Authors: Jafarzadeh, S.; Solanki, S. K.; Cameron, R. H.; Barthol, P.;
   Blanco Rodríguez, J.; del Toro Iniesta, J. C.; Gandorfer, A.; Gizon,
   L.; Hirzberger, J.; Knölker, M.; Martínez Pillet, V.; Orozco Suárez,
   D.; Riethmüller, T. L.; Schmidt, W.; van Noort, M.
Bibcode: 2017ApJS..229....8J
Altcode: 2016arXiv161007634J
  Convective flows are known as the prime means of transporting magnetic
  fields on the solar surface. Thus, small magnetic structures are good
  tracers of turbulent flows. We study the migration and dispersal
  of magnetic bright features (MBFs) in intergranular areas observed
  at high spatial resolution with Sunrise/IMaX. We describe the flux
  dispersal of individual MBFs as a diffusion process whose parameters are
  computed for various areas in the quiet-Sun and the vicinity of active
  regions from seeing-free data. We find that magnetic concentrations
  are best described as random walkers close to network areas (diffusion
  index, γ =1.0), travelers with constant speeds over a supergranule
  (γ =1.9{--}2.0), and decelerating movers in the vicinity of flux
  emergence and/or within active regions (γ =1.4{--}1.5). The three
  types of regions host MBFs with mean diffusion coefficients of 130
  km<SUP>2</SUP> s<SUP>-1</SUP>, 80-90 km<SUP>2</SUP> s<SUP>-1</SUP>,
  and 25-70 km<SUP>2</SUP> s<SUP>-1</SUP>, respectively. The MBFs in
  these three types of regions are found to display a distinct kinematic
  behavior at a confidence level in excess of 95%.

Title: Spectropolarimetric Evidence for a Siphon Flow along an
    Emerging Magnetic Flux Tube
Authors: Requerey, Iker S.; Ruiz Cobo, B.; Del Toro Iniesta, J. C.;
   Orozco Suárez, D.; Blanco Rodríguez, J.; Solanki, S. K.; Barthol,
   P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Riethmüller, T. L.;
   van Noort, M.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
Bibcode: 2017ApJS..229...15R
Altcode: 2016arXiv161106732R
  We study the dynamics and topology of an emerging magnetic flux
  concentration using high spatial resolution spectropolarimetric data
  acquired with the Imaging Magnetograph eXperiment on board the sunrise
  balloon-borne solar observatory. We obtain the full vector magnetic
  field and the line of sight (LOS) velocity through inversions of
  the Fe I line at 525.02 nm with the SPINOR code. The derived vector
  magnetic field is used to trace magnetic field lines. Two magnetic flux
  concentrations with different polarities and LOS velocities are found
  to be connected by a group of arch-shaped magnetic field lines. The
  positive polarity footpoint is weaker (1100 G) and displays an upflow,
  while the negative polarity footpoint is stronger (2200 G) and shows
  a downflow. This configuration is naturally interpreted as a siphon
  flow along an arched magnetic flux tube.

Title: Morphological Properties of Slender Ca II H Fibrils Observed
    by SUNRISE II
Authors: Gafeira, R.; Lagg, A.; Solanki, S. K.; Jafarzadeh, S.;
   van Noort, M.; Barthol, P.; Blanco Rodríguez, J.; del Toro Iniesta,
   J. C.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Knölker, M.; Orozco
   Suárez, D.; Riethmüller, T. L.; Schmidt, W.
Bibcode: 2017ApJS..229....6G
Altcode: 2016arXiv161200319G
  We use seeing-free high spatial resolution Ca II H data obtained by
  the SUNRISE observatory to determine properties of slender fibrils
  in the lower solar chromosphere. In this work we use intensity images
  taken with the SuFI instrument in the Ca II H line during the second
  scientific flight of the SUNRISE observatory to identify and track
  elongated bright structures. After identification, we analyze theses
  structures to extract their morphological properties. We identify
  598 slender Ca II H fibrils (SCFs) with an average width of around
  180 km, length between 500 and 4000 km, average lifetime of ≈400
  s, and average curvature of 0.002 arcsec<SUP>-1</SUP>. The maximum
  lifetime of the SCFs within our time series of 57 minutes is ≈2000
  s. We discuss similarities and differences of the SCFs with other
  small-scale, chromospheric structures such as spicules of type I and
  II, or Ca II K fibrils.

Title: A New MHD-assisted Stokes Inversion Technique
Authors: Riethmüller, T. L.; Solanki, S. K.; Barthol, P.; Gandorfer,
   A.; Gizon, L.; Hirzberger, J.; van Noort, M.; Blanco Rodríguez, J.;
   Del Toro Iniesta, J. C.; Orozco Suárez, D.; Schmidt, W.; Martínez
   Pillet, V.; Knölker, M.
Bibcode: 2017ApJS..229...16R
Altcode: 2016arXiv161105175R
  We present a new method of Stokes inversion of spectropolarimetric
  data and evaluate it by taking the example of a Sunrise/IMaX
  observation. An archive of synthetic Stokes profiles is obtained
  by the spectral synthesis of state-of-the-art magnetohydrodynamics
  (MHD) simulations and a realistic degradation to the level of the
  observed data. The definition of a merit function allows the archive
  to be searched for the synthetic Stokes profiles that best match the
  observed profiles. In contrast to traditional Stokes inversion codes,
  which solve the Unno-Rachkovsky equations for the polarized radiative
  transfer numerically and fit the Stokes profiles iteratively, the new
  technique provides the full set of atmospheric parameters. This gives
  us the ability to start an MHD simulation that takes the inversion
  result as an initial condition. After a relaxation process of half an
  hour solar time we obtain physically consistent MHD data sets with
  a target similar to the observation. The new MHD simulation is used
  to repeat the method in a second iteration, which further improves
  the match between observation and simulation, resulting in a factor
  of 2.2 lower mean {χ }<SUP>2</SUP> value. One advantage of the new
  technique is that it provides the physical parameters on a geometrical
  height scale. It constitutes a first step toward inversions that give
  results consistent with the MHD equations.

Title: Oscillations on Width and Intensity of Slender Ca II H Fibrils
    from Sunrise/SuFI
Authors: Gafeira, R.; Jafarzadeh, S.; Solanki, S. K.; Lagg, A.;
   van Noort, M.; Barthol, P.; Blanco Rodríguez, J.; del Toro Iniesta,
   J. C.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Knölker, M.; Orozco
   Suárez, D.; Riethmüller, T. L.; Schmidt, W.
Bibcode: 2017ApJS..229....7G
Altcode: 2017arXiv170102801G
  We report the detection of oscillations in slender Ca II H fibrils
  (SCFs) from high-resolution observations acquired with the Sunrise
  balloon-borne solar observatory. The SCFs show obvious oscillations in
  their intensity, but also their width. The oscillatory behaviors are
  investigated at several positions along the axes of the SCFs. A large
  majority of fibrils show signs of oscillations in intensity. Their
  periods and phase speeds are analyzed using a wavelet analysis. The
  width and intensity perturbations have overlapping distributions
  of the wave period. The obtained distributions have median values
  of the period of 32 ± 17 s and 36 ± 25 s, respectively. We
  find that the fluctuations of both parameters propagate in
  the SCFs with speeds of {11}<SUB>-11</SUB><SUP>+49</SUP> km
  s<SUP>-1</SUP> and {15}<SUB>-15</SUB><SUP>+34</SUP> km s<SUP>-1</SUP>,
  respectively. Furthermore, the width and intensity oscillations have a
  strong tendency to be either in anti-phase or, to a smaller extent, in
  phase. This suggests that the oscillations of both parameters are caused
  by the same wave mode and that the waves are likely propagating. Taking
  all the evidence together, the most likely wave mode to explain all
  measurements and criteria is the fast sausage mode.

Title: Solar Coronal Loops Associated with Small-scale Mixed Polarity
    Surface Magnetic Fields
Authors: Chitta, L. P.; Peter, H.; Solanki, S. K.; Barthol, P.;
   Gandorfer, A.; Gizon, L.; Hirzberger, J.; Riethmüller, T. L.; van
   Noort, M.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.; Orozco
   Suárez, D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
Bibcode: 2017ApJS..229....4C
Altcode: 2016arXiv161007484C
  How and where are coronal loops rooted in the solar lower
  atmosphere? The details of the magnetic environment and its evolution
  at the footpoints of coronal loops are crucial to understanding the
  processes of mass and energy supply to the solar corona. To address
  the above question, we use high-resolution line-of-sight magnetic
  field data from the Imaging Magnetograph eXperiment instrument on the
  Sunrise balloon-borne observatory and coronal observations from the
  Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory
  of an emerging active region. We find that the coronal loops are
  often rooted at the locations with minor small-scale but persistent
  opposite-polarity magnetic elements very close to the larger dominant
  polarity. These opposite-polarity small-scale elements continually
  interact with the dominant polarity underlying the coronal loop through
  flux cancellation. At these locations we detect small inverse Y-shaped
  jets in chromospheric Ca II H images obtained from the Sunrise Filter
  Imager during the flux cancellation. Our results indicate that magnetic
  flux cancellation and reconnection at the base of coronal loops due
  to mixed polarity fields might be a crucial feature for the supply of
  mass and energy into the corona.

Title: Moving Magnetic Features around a Pore
Authors: Kaithakkal, A. J.; Riethmüller, T. L.; Solanki, S. K.; Lagg,
   A.; Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; vanNoort,
   M.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.; Orozco Suárez,
   D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
Bibcode: 2017ApJS..229...13K
Altcode: 2016arXiv160905664K
  Spectropolarimetric observations from Sunrise/IMaX, obtained in 2013
  June, are used for a statistical analysis to determine the physical
  properties of moving magnetic features (MMFs) observed near a pore. MMFs
  of the same and opposite polarity, with respect to the pore, are found
  to stream from its border at an average speed of 1.3 km s<SUP>-1</SUP>
  and 1.2 km s<SUP>-1</SUP>, respectively, with mainly same-polarity MMFs
  found further away from the pore. MMFs of both polarities are found to
  harbor rather weak, inclined magnetic fields. Opposite-polarity MMFs
  are blueshifted, whereas same-polarity MMFs do not show any preference
  for up- or downflows. Most of the MMFs are found to be of sub-arcsecond
  size and carry a mean flux of ∼1.2 × 10<SUP>17</SUP> Mx.

Title: Brightness of Solar Magnetic Elements As a Function of Magnetic
    Flux at High Spatial Resolution
Authors: Kahil, F.; Riethmüller, T. L.; Solanki, S. K.
Bibcode: 2017ApJS..229...12K
Altcode: 2017arXiv170100759K
  We investigate the relationship between the photospheric magnetic
  field of small-scale magnetic elements in the quiet-Sun (QS) at disk
  center and the brightness at 214, 300, 313, 388, 397, and 525.02
  nm. To this end, we analyzed spectropolarimetric and imaging time
  series acquired simultaneously by the Imaging Magnetograph eXperiment
  magnetograph and the SuFI filter imager on board the balloon-borne
  observatory {{S}}{{UNRISE}} during its first science flight in 2009,
  with high spatial and temporal resolution. We find a clear dependence
  of the contrast in the near ultraviolet and the visible on the
  line-of-sight component of the magnetic field, B <SUB>LOS</SUB>, which
  is best described by a logarithmic model. This function effectively
  represents the relationship between the Ca II H-line emission and
  B <SUB>LOS</SUB> and works better than the power-law fit adopted
  by previous studies. This, along with the high contrast reached
  at these wavelengths, will help with determining the contribution
  of small-scale elements in the QS to the irradiance changes for
  wavelengths below 388 nm. At all wavelengths, including the continuum
  at 525.40 nm, the intensity contrast does not decrease with increasing
  B <SUB>LOS</SUB>. This result also strongly supports the fact that
  {{S}}{{UNRISE}} has resolved small strong magnetic field elements in the
  internetwork, resulting in constant contrasts for large magnetic fields
  in our continuum contrast at 525.40 nm versus the B <SUB>LOS</SUB>
  scatterplot, unlike the turnover obtained in previous observational
  studies. This turnover is due to the intermixing of the bright magnetic
  features with the dark intergranular lanes surrounding them.

Title: Convectively Driven Sinks and Magnetic Fields in the Quiet-Sun
Authors: Requerey, Iker S.; Del Toro Iniesta, Jose Carlos; Bellot
   Rubio, Luis R.; Martínez Pillet, Valentín; Solanki, Sami K.;
   Schmidt, Wolfgang
Bibcode: 2017ApJS..229...14R
Altcode: 2016arXiv161007622R
  We study the relation between mesogranular flows, convectively
  driven sinks and magnetic fields using high spatial resolution
  spectropolarimetric data acquired with the Imaging Magnetograph
  eXperiment on board Sunrise. We obtain the horizontal velocity
  flow fields of two quiet-Sun regions (31.2 × 31.2 Mm<SUP>2</SUP>)
  via local correlation tracking. Mesogranular lanes and the central
  position of sinks are identified using Lagrange tracers. We find
  6.7× {10}<SUP>-2</SUP> sinks per Mm<SUP>2</SUP> in the two observed
  regions. The sinks are located at the mesogranular vertices and turn
  out to be associated with (1) horizontal velocity flows converging to a
  central point and (2) long-lived downdrafts. The spatial distribution
  of magnetic fields in the quiet-Sun is also examined. The strongest
  magnetic fields are preferentially located at sinks. We find that 40% of
  the pixels with longitudinal components of the magnetic field stronger
  than 500 G are located in the close neighborhood of sinks. In contrast,
  the small-scale magnetic loops detected by Martínez González et al. in
  the same two observed areas do not show any preferential distribution
  at mesogranular scales. The study of individual examples reveals
  that sinks can play an important role in the evolution of quiet-Sun
  magnetic features.

Title: Overview of the Special Issue on the First Science Results
    from the Second Flight of Sunrise
Authors: Solanki, Sami K.
Bibcode: 2017ApJS..229....1S
Altcode:
  No abstract at ADS

Title: Statistical evolution of quiet-Sun small-scale magnetic
    features using Sunrise observations
Authors: Anusha, L. S.; Solanki, S. K.; Hirzberger, J.; Feller, A.
Bibcode: 2017A&A...598A..47A
Altcode: 2016arXiv160808499A
  The evolution of small magnetic features in quiet regions of the Sun
  provides a unique window for probing solar magneto-convection. Here
  we analyze small-scale magnetic features in the quiet Sun, using the
  high resolution, seeing-free observations from the Sunrise balloon
  borne solar observatory. Our aim is to understand the contribution of
  different physical processes, such as splitting, merging, emergence
  and cancellation of magnetic fields to the rearrangement, addition
  and removal of magnetic flux in the photosphere. We have employed a
  statistical approach for the analysis and the evolution studies are
  carried out using a feature-tracking technique. In this paper we provide
  a detailed description of the feature-tracking algorithm that we have
  newly developed and we present the results of a statistical study
  of several physical quantities. The results on the fractions of the
  flux in the emergence, appearance, splitting, merging, disappearance
  and cancellation qualitatively agrees with other recent studies. To
  summarize, the total flux gained in unipolar appearance is an order of
  magnitude larger than the total flux gained in emergence. On the other
  hand, the bipolar cancellation contributes nearly an equal amount to
  the loss of magnetic flux as unipolar disappearance. The total flux
  lost in cancellation is nearly six to eight times larger than the
  total flux gained in emergence. One big difference between our study
  and previous similar studies is that, thanks to the higher spatial
  resolution of Sunrise, we can track features with fluxes as low as
  9 × 10<SUP>14</SUP> Mx. This flux is nearly an order of magnitude
  lower than the smallest fluxes of the features tracked in the highest
  resolution previous studies based on Hinode data. The area and flux
  of the magnetic features follow power-law type distribution, while
  the lifetimes show either power-law or exponential type distribution
  depending on the exact definitions used to define various birth and
  death events. We have also statistically determined the evolution
  of the flux within the features in the course of their lifetime,
  finding that this evolution depends very strongly on the birth and
  death process that the features undergo.

Title: VizieR Online Data Catalog: Group sunspot number series since
    1739 (Chatzistergos+, 2017)
Authors: Chatzistergos, T.; Usoskin, I. G.; Kovaltsov, G. A.; Krivova,
   N. A.; Solanki, S. K.
Bibcode: 2017yCat..36020069C
Altcode:
  Annual, monthly, and daily values of the Group sunspot number series
  produced in the paper. <P />(3 data files).

Title: Fan Loops Observed by IRIS, EIS, and AIA
Authors: Ghosh, Avyarthana; Tripathi, Durgesh; Gupta, G. R.; Polito,
   Vanessa; Mason, Helen E.; Solanki, Sami K.
Bibcode: 2017ApJ...835..244G
Altcode: 2017arXiv170101617G
  A comprehensive study of the physical parameters of active region fan
  loops is presented using the observations recorded with the Interface
  Region Imaging Spectrometer (IRIS), the EUV Imaging Spectrometer (EIS)
  on board Hinode, and the Atmospheric Imaging Assembly (AIA) and the
  Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics
  Observatory (SDO). The fan loops emerging from non-flaring AR 11899
  (near the disk center) on 2013 November 19 are clearly discernible in
  AIA 171 Å images and in those obtained in Fe viii and Si vii images
  using EIS. Our measurements of electron densities reveal that the
  footpoints of these loops are at an approximately constant pressure
  with electron densities of {log} {N}<SUB>e</SUB>=10.1 cm<SUP>-3</SUP> at
  {log} [T/K]=5.15 (O IV), and {log} {N}<SUB>e</SUB>=8.9 cm<SUP>-3</SUP>
  at {log} [T/K]=6.15 (Si x). The electron temperature diagnosed
  across the fan loops by means of EM-Loci suggest that two temperature
  components exist at {log} [T/K]=4.95 and 5.95 at the footpoints. These
  components are picked up by IRIS lines and EIS lines, respectively. At
  higher heights, the loops are nearly isothermal at {log} [T/K]=5.95,
  which remained constant along the loop. The measurement of the Doppler
  shift using IRIS lines suggests that the plasma at the footpoints of
  these loops is predominantly redshifted by 2-3 km s<SUP>-1</SUP> in C
  II, 10-15 km s<SUP>-1</SUP> in Si IV, and 15-20 km s<SUP>-1</SUP> in O
  IV, reflecting the increase in the speed of downflows with increasing
  temperature from {log} [T/K]=4.40 to 5.15. These observations can
  be explained by low-frequency nanoflares or impulsive heating, and
  provide further important constraints on the modeling of the dynamics
  of fan loops.

Title: The dark side of solar photospheric G-band bright points
Authors: Riethmüller, T. L.; Solanki, S. K.
Bibcode: 2017A&A...598A.123R
Altcode: 2016arXiv161207887R
  Bright, small-scale magnetic elements found mainly in intergranular
  lanes at the solar surface are named bright points (BPs). They show
  high contrasts in Fraunhofer G-band observations and are described
  by nearly vertical slender flux tubes or sheets. A recent comparison
  between BP observations in the ultraviolet (UV) and visible spectral
  range recorded with the balloon-borne observatory Sunrise and
  state-of-the-art magnetohydrodynamical (MHD) simulations revealed
  a kilogauss magnetic field for 98% of the synthetic BPs. Here we
  address the opposite question, namely which fraction of pixels hosting
  kilogauss fields coincides with an enhanced G-band brightness. We
  carried out 3D radiation MHD simulations for three magnetic activity
  levels (corresponding to the quiet Sun, weak and strong plage)
  and performed a full spectral line synthesis in the G-band. Only 7%
  of the kilogauss pixels in our quiet-Sun simulation coincide with a
  brightness lower than the mean quiet-Sun intensity, while 23% of the
  pixels in the weak-plage simulation and even 49% in the strong-plage
  simulation are associated with a local darkening. Dark strong-field
  regions are preferentially found in the cores of larger flux patches
  that are rare in the quiet Sun, but more common in plage regions,
  often in the vertices of granulation cells. The significant brightness
  shortfall in the core of larger flux patches coincides with a slight
  magnetic field weakening. Kilogauss elements in the quiet Sun are,
  on average, brighter than similar features in plage regions. Almost
  all strong-field pixels display a more or less vertical magnetic field
  orientation. Hence, in the quiet Sun, G-band BPs correspond almost
  one-to-one with kilogauss elements. In weak plage, the correspondence
  is still very good, but not perfect.

Title: Flux emergence rate in the quiet Sun from Sunrise data
Authors: Smitha, H. N.; Anusha, L. S.; Solanki, S. K.; Riethmüller,
   T. L.
Bibcode: 2017psio.confE.106S
Altcode:
  No abstract at ADS

Title: Lambda-shaped jets from a penumbral intrusion into a sunspot
umbra: a possibility for magnetic reconnection
Authors: Bharti, L.; Solanki, S. K.; Hirzberger, J.
Bibcode: 2017A&A...597A.127B
Altcode:
  We present the results of high resolution co-temporal and co-spatial
  photospheric and chromospheric observations of sunspot penumbral
  intrusions. The data were taken with the Swedish Solar Telescope
  (SST) on the Canary Islands. Time series of Ca II H images show
  a series of transient jets extending roughly 3000 km above a
  penumbral intrusion into the umbra. For most of the time series,
  jets were seen along the whole length of the intruding bright
  filament. Some of these jets develop a clear λ-shaped structure,
  with a small loop appearing at their footpoint and lasting for around
  a minute. In the framework of earlier studies, the observed transient
  λ shape of these jets suggests that they could be caused by magnetic
  reconnection between a curved arcade-like or flux rope-like field in
  the lower part of the penumbral intrusion and the more vertical umbral
  magnetic field forming a cusp-shaped structure above the penumbral
  intrusion. <P />Movies associated to Figs. 1 and 2 are available at
  <A href="http://www.aanda.org">http://www.aanda.org</A>

Title: Helioseismology with Solar Orbiter
Authors: Löptien, Björn; Birch, Aaron C.; Gizon, Laurent; Schou,
   Jesper; Appourchaux, Thierry; Blanco Rodríguez, Julián; Cally,
   Paul S.; Dominguez-Tagle, Carlos; Gandorfer, Achim; Hill, Frank;
   Hirzberger, Johann; Scherrer, Philip H.; Solanki, Sami K.
Bibcode: 2017hdsi.book..257L
Altcode:
  No abstract at ADS

Title: Handling Historical Ca II K Spectroheliogram Observation
Authors: Solanki, S. K.; Chatzistergos, T.; Ermolli, I.; Krivova, N.
Bibcode: 2016AGUFMSA51B2429S
Altcode:
  The total solar irradiance has been continuously monitored since 1978,
  but climate studies require time-series extending further back in
  time. Models assuming that the irradiance variations are due to the
  evolution of the solar surface magnetic field manifesting itself
  as bright faculae and dark sunspots have been quite successful in
  reproducing the measured changes. Unfortunately full-disk observations
  of the magnetic field exist only for the last four decades. Sunspot
  observations (areas or numbers) have been employed to reconstruct past
  irradiance changes, however they provide information about the plage
  regions only indirectly. Information about the evolution of the plage
  regions can potentially be obtained from Ca II K spectroheliograms that
  are available for the last century. Such observational programs have
  been carried out at several observatories and some of these photographic
  archives have been digitised. However, analysis of such data is plagued
  by numerous problems affecting the images and the lack of photometric
  calibration. Here we present a new method to process historical Ca II K
  spectroheliograms in order to perform the photometric calibration and
  compensate for the centre-to-limb variations and artefacts affecting
  the data. The method is tested on synthetic images with known artefacts
  and a sample of images from various historical archives.

Title: Solar Total and Spectral Irradiance Reconstruction over Last
    9000 Years
Authors: Wu, C. J.; Krivova, N.; Solanki, S. K.; Usoskin, I. G.
Bibcode: 2016AGUFMSA51B2430W
Altcode:
  Although the mechanisms of solar influence on Earth climate system
  are not yet fully understood, solar total and spectral irradiance are
  considered to be among the main determinants. Solar total irradiance
  is the total flux of solar radiative energy entering Earth's climate
  system, whereas the spectral irradiance describes this energy is
  distributed over the spectrum. Solar irradiance in the UV band is of
  special importance since it governs chemical processes in the middle and
  upper atmosphere. On timescales of the 11-year solar cycle and shorter,
  solar irradiance is measured by space-based instruments while models
  are needed to reconstruct solar irradiance on longer timescale. The
  SATIRE-M model (Spectral And Total Irradiance Reconstruction over
  millennia) is employed in this study to reconstruct solar irradiance
  from decadal radionuclide isotope data such as 14C and 10Be stored in
  tree rings and ice cores, respectively. A reconstruction over the last
  9000 years will be presented.

Title: Non-linear re-calibration of group sunspot number series back
    to 1819
Authors: Chatzistergos, T.; Usoskin, I. G.; Kovaltsov, G.; Solanki,
   S. K.; Krivova, N.
Bibcode: 2016AGUFMSH31B2547C
Altcode:
  Sunspot numbers form the longest series of direct observations
  that give information about the activity of the Sun. It consists in
  numerous records from different observers with different instruments
  and techniques, and unavoidably requires a calibration of individual
  observers to a standard reference condition. Such calibrations pose a
  challenge and are still a subject of debate. Most of the calibration
  methods are based on a simple linear scaling of data from one observer
  to the other, proposed in the mid-19th century by Rudolf Wolf. This
  method is still used in many recent reconstructions. However, this
  linear method is shown, on both real and synthetic data, to be
  very rough and incorrect because of the essentially non-linearity
  of the relation.Here we present a new reconstruction of the
  group sunspot number series back to 1819 attempting to take into
  account the non-linearity of the relation between data of different
  observers. We use an approach incorporating several overlapping backbone
  observers (similar to Svalgaard and Schatten, 2016) and perform the
  straightforward non-linear calibration of each observer to the backbone
  (and the backbones with each other) based on the actual statistics of
  the common daily values.

Title: Lower solar atmosphere and magnetism at ultra-high spatial
    resolution
Authors: Collet, Remo; Criscuoli, Serena; Ermolli, Ilaria; Fabbian,
   Damian; Guerreiro, Nuno; Haberreiter, Margit; Peck, Courtney; Pereira,
   Tiago M. D.; Rempel, Matthias; Solanki, Sami K.; Wedemeyer-Boehm, Sven
Bibcode: 2016arXiv161202348C
Altcode:
  We present the scientific case for a future space-based telescope
  aimed at very high spatial and temporal resolution imaging of the
  solar photosphere and chromosphere. Previous missions (e.g., HINODE,
  SUNRISE) have demonstrated the power of observing the solar photosphere
  and chromosphere at high spatial resolution without contamination from
  Earth's atmosphere. We argue here that increased spatial resolution
  (from currently 70 km to 25 km in the future) and high temporal cadence
  of the observations will vastly improve our understanding of the
  physical processes controlling solar magnetism and its characteristic
  scales. This is particularly important as the Sun's magnetic field
  drives solar activity and can significantly influence the Sun-Earth
  system. At the same time a better knowledge of solar magnetism can
  greatly improve our understanding of other astrophysical objects.

Title: Far side Helioseismology with Solar Orbiter
Authors: Appourchaux, T.; Birch, A.; Gizon, L. C.; Löptien, B.;
   Schou, J.; Solanki, S. K.; del Toro Iniesta, J. C.; Gandorfer, A.;
   Hirzberger, J.; Alvarez-Herrero, A.; Woch, J. G.; Schmidt, W.
Bibcode: 2016AGUFMSH43A2554A
Altcode:
  The Solar Orbiter mission, to be launched in October 2018, will
  carry a suite of remote sensing and in-situ instruments, including
  the Polarimetric and Helioseismic Imager (PHI). PHI will deliver
  high-cadence images of the Sun in intensity and Doppler velocity
  suitable for carrying out novel helioseismic studies. The orbit
  of the Solar Orbiter spacecraft will reach a solar latitude up to
  34 degrees by the end of the extended mission and thus will enable
  the first local helioseismology studies of the polar regions. The
  full range of Earth-Sun-spacecraft angles provided by the orbit will
  enable helioseismology from two vantage points by combining PHI with
  another instrument: stereoscopic helioseismology will allow the study
  of the deep solar interior and a better understanding of the physics
  of solar oscillations in both quiet Sun and sunspots. In this paper
  we will review the helioseismic objectives achievable with PHI, and
  will also give a short status report of the development of the Flight
  Model of PHI.

Title: Relationship between supergranulation flows, magnetic
    cancellation and network flares
Authors: Attie, R.; Innes, D. E.; Solanki, S. K.; Glassmeier, K. H.
Bibcode: 2016A&A...596A..15A
Altcode: 2017arXiv170510389A
  Context. Photospheric flows create a network of often mixed-polarity
  magnetic field in the quiet Sun, where small-scale eruptions and network
  flares are commonly seen. <BR /> Aims: The aim of this paper is (1)
  to describe the characteristics of the flows that lead to these energy
  releases, (2) to quantify the energy build up due to photospheric flows
  acting on the magnetic field, and (3) to assess its contribution to the
  energy of small-scale, short-lived X-ray flares in the quiet Sun. <BR />
  Methods: We used photospheric and X-ray data from the SoHO and Hinode
  spacecraft combined with tracking algorithms to analyse the evolution
  of five network flares. The energy of the X-ray emitting thermal plasma
  is compared with an estimate of the energy built up due to converging
  and sheared flux. <BR /> Results: Quiet-Sun network flares occur above
  sites of converging opposite-polarity magnetic flux that are often found
  on the outskirts of network cell junctions, sometimes with observable
  vortex-like motion. In all studied flares the thermal energy was more
  than an order of magnitude higher than the magnetic free energy of the
  converging flux model. The energy in the sheared field was always higher
  than in the converging flux but still lower than the thermal energy. <BR
  /> Conclusions: X-ray network flares occur at sites of magnetic energy
  dissipation. The energy is probably built up by supergranular flows
  causing systematic shearing of the magnetic field. This process appears
  more efficient near the junction of the network lanes. Since this work
  relies on 11 case studies, our results call for a follow-up statistical
  analysis to test our hypothesis throughout the quiet Sun.

Title: Slipping reconnection in a solar flare observed in high
    resolution with the GREGOR solar telescope
Authors: Sobotka, M.; Dudík, J.; Denker, C.; Balthasar, H.; Jurčák,
   J.; Liu, W.; Berkefeld, T.; Collados Vera, M.; Feller, A.; Hofmann,
   A.; Kneer, F.; Kuckein, C.; Lagg, A.; Louis, R. E.; von der Lühe, O.;
   Nicklas, H.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth,
   M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.;
   Volkmer, R.; Waldmann, T.
Bibcode: 2016A&A...596A...1S
Altcode: 2016arXiv160500464S
  A small flare ribbon above a sunspot umbra in active region 12205 was
  observed on November 7, 2014, at 12:00 UT in the blue imaging channel
  of the 1.5 m GREGOR telescope, using a 1 Å Ca II H interference
  filter. Context observations from the Atmospheric Imaging Assembly
  (AIA) onboard the Solar Dynamics Observatory (SDO), the Solar Optical
  Telescope (SOT) onboard Hinode, and the Interface Region Imaging
  Spectrograph (IRIS) show that this ribbon is part of a larger one
  that extends through the neighboring positive polarities and also
  participates in several other flares within the active region. We
  reconstructed a time series of 140 s of Ca II H images by means of the
  multiframe blind deconvolution method, which resulted in spatial and
  temporal resolutions of 0.1″ and 1 s. Light curves and horizontal
  velocities of small-scale bright knots in the observed flare ribbon
  were measured. Some knots are stationary, but three move along the
  ribbon with speeds of 7-11 km s<SUP>-1</SUP>. Two of them move in the
  opposite direction and exhibit highly correlated intensity changes,
  which provides evidence of a slipping reconnection at small spatial
  scales. <P />Movies associated to Figs. 1 and 2 are available at <A
  href="http://www.aanda.org/10.1051/0004-6361/201527966/olm">http://www.aanda.org</A>

Title: Deep probing of the photospheric sunspot penumbra: no evidence
    of field-free gaps
Authors: Borrero, J. M.; Asensio Ramos, A.; Collados, M.;
   Schlichenmaier, R.; Balthasar, H.; Franz, M.; Rezaei, R.; Kiess, C.;
   Orozco Suárez, D.; Pastor Yabar, A.; Berkefeld, T.; von der Lühe,
   O.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Soltau, D.; Volkmer, R.;
   Waldmann, T.; Denker, C.; Hofmann, A.; Staude, J.; Strassmeier, K. G.;
   Feller, A.; Lagg, A.; Solanki, S. K.; Sobotka, M.; Nicklas, H.
Bibcode: 2016A&A...596A...2B
Altcode: 2016arXiv160708165B
  Context. Some models for the topology of the magnetic field in
  sunspot penumbrae predict regions free of magnetic fields or with
  only dynamically weak fields in the deep photosphere. <BR /> Aims:
  We aim to confirm or refute the existence of weak-field regions in
  the deepest photospheric layers of the penumbra. <BR /> Methods:
  We investigated the magnetic field at log τ<SUB>5</SUB> = 0 is
  by inverting spectropolarimetric data of two different sunspots
  located very close to disk center with a spatial resolution of
  approximately 0.4-0.45''. The data have been recorded using the GRIS
  instrument attached to the 1.5-m solar telescope GREGOR at the El
  Teide observatory. The data include three Fe I lines around 1565 nm,
  whose sensitivity to the magnetic field peaks half a pressure scale
  height deeper than the sensitivity of the widely used Fe I spectral
  line pair at 630 nm. Before the inversion, the data were corrected
  for the effects of scattered light using a deconvolution method with
  several point spread functions. <BR /> Results: At log τ<SUB>5</SUB>
  = 0 we find no evidence of regions with dynamically weak (B&lt;
  500 Gauss) magnetic fields in sunspot penumbrae. This result is much
  more reliable than previous investigations made on Fe I lines at 630
  nm. Moreover, the result is independent of the number of nodes employed
  in the inversion, is independent of the point spread function used to
  deconvolve the data, and does not depend on the amount of stray light
  (I.e., wide-angle scattered light) considered.

Title: Spectropolarimetric observations of an arch filament system
    with the GREGOR solar telescope
Authors: Balthasar, H.; Gömöry, P.; González Manrique, S. J.;
   Kuckein, C.; Kavka, J.; Kučera, A.; Schwartz, P.; Vašková, R.;
   Berkefeld, T.; Collados Vera, M.; Denker, C.; Feller, A.; Hofmann,
   A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pastor Yabar, A.;
   Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth,
   M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
   K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
Bibcode: 2016AN....337.1050B
Altcode: 2016arXiv160901514B
  Arch filament systems occur in active sunspot groups, where a fibril
  structure connects areas of opposite magnetic polarity, in contrast to
  active region filaments that follow the polarity inversion line. We
  used the GREGOR Infrared Spectrograph (GRIS) to obtain the full
  Stokes vector in the spectral lines Si I λ1082.7 nm, He I λ1083.0
  nm, and Ca I λ1083.9 nm. We focus on the near-infrared calcium line
  to investigate the photospheric magnetic field and velocities, and
  use the line core intensities and velocities of the helium line to
  study the chromospheric plasma. The individual fibrils of the arch
  filament system connect the sunspot with patches of magnetic polarity
  opposite to that of the spot. These patches do not necessarily coincide
  with pores, where the magnetic field is strongest. Instead, areas are
  preferred not far from the polarity inversion line. These areas exhibit
  photospheric downflows of moderate velocity, but significantly higher
  downflows of up to 30 km s<SUP>-1</SUP> in the chromospheric helium
  line. Our findings can be explained with new emerging flux where the
  matter flows downward along the field lines of rising flux tubes,
  in agreement with earlier results.

Title: Magnetic fields of opposite polarity in sunspot penumbrae
Authors: Franz, M.; Collados, M.; Bethge, C.; Schlichenmaier, R.;
   Borrero, J. M.; Schmidt, W.; Lagg, A.; Solanki, S. K.; Berkefeld,
   T.; Kiess, C.; Rezaei, R.; Schmidt, D.; Sigwarth, M.; Soltau, D.;
   Volkmer, R.; von der Luhe, O.; Waldmann, T.; Orozco, D.; Pastor Yabar,
   A.; Denker, C.; Balthasar, H.; Staude, J.; Hofmann, A.; Strassmeier,
   K.; Feller, A.; Nicklas, H.; Kneer, F.; Sobotka, M.
Bibcode: 2016A&A...596A...4F
Altcode: 2016arXiv160800513F
  Context. A significant part of the penumbral magnetic field returns
  below the surface in the very deep photosphere. For lines in the
  visible, a large portion of this return field can only be detected
  indirectly by studying its imprints on strongly asymmetric and
  three-lobed Stokes V profiles. Infrared lines probe a narrow layer
  in the very deep photosphere, providing the possibility of directly
  measuring the orientation of magnetic fields close to the solar
  surface. <BR /> Aims: We study the topology of the penumbral magnetic
  field in the lower photosphere, focusing on regions where it returns
  below the surface. <BR /> Methods: We analyzed 71 spectropolarimetric
  datasets from Hinode and from the GREGOR infrared spectrograph. We
  inferred the quality and polarimetric accuracy of the infrared data
  after applying several reduction steps. Techniques of spectral
  inversion and forward synthesis were used to test the detection
  algorithm. We compared the morphology and the fractional penumbral
  area covered by reversed-polarity and three-lobed Stokes V profiles for
  sunspots at disk center. We determined the amount of reversed-polarity
  and three-lobed Stokes V profiles in visible and infrared data of
  sunspots at various heliocentric angles. From the results, we computed
  center-to-limb variation curves, which were interpreted in the context
  of existing penumbral models. <BR /> Results: Observations in visible
  and near-infrared spectral lines yield a significant difference in the
  penumbral area covered by magnetic fields of opposite polarity. In
  the infrared, the number of reversed-polarity Stokes V profiles is
  smaller by a factor of two than in the visible. For three-lobed Stokes
  V profiles the numbers differ by up to an order of magnitude.

Title: Horizontal flow fields in and around a small active region. The
    transition period between flux emergence and decay
Authors: Verma, M.; Denker, C.; Balthasar, H.; Kuckein, C.; González
   Manrique, S. J.; Sobotka, M.; Bello González, N.; Hoch, S.; Diercke,
   A.; Kummerow, P.; Berkefeld, T.; Collados, M.; Feller, A.; Hofmann,
   A.; Kneer, F.; Lagg, A.; Löhner-Böttcher, J.; Nicklas, H.; Pastor
   Yabar, A.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Schubert,
   M.; Sigwarth, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
   K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
Bibcode: 2016A&A...596A...3V
Altcode: 2016arXiv160507462V
  Context. The solar magnetic field is responsible for all aspects
  of solar activity. Thus, emergence of magnetic flux at the surface
  is the first manifestation of the ensuing solar activity. <BR />
  Aims: Combining high-resolution and synoptic observations aims to
  provide a comprehensive description of flux emergence at photospheric
  level and of the growth process that eventually leads to a mature
  active region. <BR /> Methods: The small active region NOAA 12118
  emerged on 2014 July 17 and was observed one day later with the 1.5-m
  GREGOR solar telescope on 2014 July 18. High-resolution time-series
  of blue continuum and G-band images acquired in the blue imaging
  channel (BIC) of the GREGOR Fabry-Pérot Interferometer (GFPI) were
  complemented by synoptic line-of-sight magnetograms and continuum
  images obtained with the Helioseismic and Magnetic Imager (HMI) onboard
  the Solar Dynamics Observatory (SDO). Horizontal proper motions and
  horizontal plasma velocities were computed with local correlation
  tracking (LCT) and the differential affine velocity estimator (DAVE),
  respectively. Morphological image processing was employed to measure
  the photometric and magnetic area, magnetic flux, and the separation
  profile of the emerging flux region during its evolution. <BR />
  Results: The computed growth rates for photometric area, magnetic
  area, and magnetic flux are about twice as high as the respective
  decay rates. The space-time diagram using HMI magnetograms of five days
  provides a comprehensive view of growth and decay. It traces a leaf-like
  structure, which is determined by the initial separation of the two
  polarities, a rapid expansion phase, a time when the spread stalls,
  and a period when the region slowly shrinks again. The separation
  rate of 0.26 km s<SUP>-1</SUP> is highest in the initial stage, and
  it decreases when the separation comes to a halt. Horizontal plasma
  velocities computed at four evolutionary stages indicate a changing
  pattern of inflows. In LCT maps we find persistent flow patterns such
  as outward motions in the outer part of the two major pores, a diverging
  feature near the trailing pore marking the site of upwelling plasma and
  flux emergence, and low velocities in the interior of dark pores. We
  detected many elongated rapidly expanding granules between the two
  major polarities, with dimensions twice as large as the normal granules.

Title: A New Calibrated Sunspot Group Series Since 1749: Statistics
    of Active Day Fractions
Authors: Usoskin, I. G.; Kovaltsov, G. A.; Lockwood, M.; Mursula,
   K.; Owens, M.; Solanki, S. K.
Bibcode: 2016SoPh..291.2685U
Altcode: 2016SoPh..tmp....6U; 2015arXiv151206421U
  Although sunspot-number series have existed since the mid-nineteenth
  century, they are still the subject of intense debate, with the largest
  uncertainty being related to the "calibration" of the visual acuity
  of individual observers in the past. A daisy-chain regression method
  is usually applied to inter-calibrate the observers, which may lead
  to significant bias and error accumulation. Here we present a novel
  method for calibrating the visual acuity of the key observers to the
  reference data set of Royal Greenwich Observatory sunspot groups for the
  period 1900 - 1976, using the statistics of the active-day fraction. For
  each observer we independently evaluate their observational thresholds
  [S<SUB>S</SUB>] defined such that the observer is assumed to miss all
  of the groups with an area smaller than S<SUB>S</SUB> and report all
  the groups larger than S<SUB>S</SUB>. Next, using a Monte-Carlo method,
  we construct a correction matrix for each observer from the reference
  data set. The correction matrices are significantly non-linear and
  cannot be approximated by a linear regression or proportionality. We
  emphasize that corrections based on a linear proportionality between
  annually averaged data lead to serious biases and distortions of the
  data. The correction matrices are applied to the original sunspot-group
  records reported by the observers for each day, and finally the
  composite corrected series is produced for the period since 1748. The
  corrected series is provided as supplementary material in electronic
  form and displays secular minima around 1800 (Dalton Minimum) and 1900
  (Gleissberg Minimum), as well as the Modern Grand Maximum of activity in
  the second half of the twentieth century. The uniqueness of the grand
  maximum is confirmed for the last 250 years. We show that the adoption
  of a linear relationship between the data of Wolf and Wolfer results
  in grossly inflated group numbers in the eighteenth and nineteenth
  centuries in some reconstructions.

Title: Upper chromospheric magnetic field of a sunspot penumbra:
    observations of fine structure
Authors: Joshi, J.; Lagg, A.; Solanki, S. K.; Feller, A.; Collados,
   M.; Orozco Suárez, D.; Schlichenmaier, R.; Franz, M.; Balthasar,
   H.; Denker, C.; Berkefeld, T.; Hofmann, A.; Kiess, C.; Nicklas, H.;
   Pastor Yabar, A.; Rezaei, R.; Schmidt, D.; Schmidt, W.; Sobotka, M.;
   Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe,
   O.; Waldmann, T.
Bibcode: 2016A&A...596A...8J
Altcode: 2016arXiv160801988J
  <BR /> Aims: The fine-structure of the magnetic field in a sunspot
  penumbra in the upper chromosphere is to be explored and compared
  to that in the photosphere. <BR /> Methods: Spectropolarimetric
  observations with high spatial resolution were recorded with the 1.5-m
  GREGOR telescope using the GREGOR Infrared Spectrograph (GRIS). The
  observed spectral domain includes the upper chromospheric Hei triplet
  at 10 830 Å and the photospheric Sii 10 827.1 Å and Cai 10 833.4 Å
  spectral lines. The upper chromospheric magnetic field is obtained
  by inverting the Hei triplet assuming a Milne-Eddington-type model
  atmosphere. A height-dependent inversion was applied to the Sii 10
  827.1 Å and Cai 10 833.4 Å lines to obtain the photospheric magnetic
  field. <BR /> Results: We find that the inclination of the magnetic
  field varies in the azimuthal direction in the photosphere and in the
  upper chromosphere. The chromospheric variations coincide remarkably
  well with the variations in the inclination of the photospheric field
  and resemble the well-known spine and interspine structure in the
  photospheric layers of penumbrae. The typical peak-to-peak variations
  in the inclination of the magnetic field in the upper chromosphere
  are found to be 10°-15°, which is roughly half the variation in
  the photosphere. In contrast, the magnetic field strength of the
  observed penumbra does not vary on small spatial scales in the upper
  chromosphere. <BR /> Conclusions: Thanks to the high spatial resolution
  of the observations that is possible with the GREGOR telescope at 1.08
  microns, we find that the prominent small-scale fluctuations in the
  magnetic field inclination, which are a salient part of the property
  of sunspot penumbral photospheres, also persist in the chromosphere,
  although at somewhat reduced amplitudes. Such a complex magnetic
  configuration may facilitate penumbral chromospheric dynamic phenomena,
  such as penumbral micro-jets or transient bright dots.

Title: Active region fine structure observed at 0.08 arcsec resolution
Authors: Schlichenmaier, R.; von der Lühe, O.; Hoch, S.; Soltau, D.;
   Berkefeld, T.; Schmidt, D.; Schmidt, W.; Denker, C.; Balthasar, H.;
   Hofmann, A.; Strassmeier, K. G.; Staude, J.; Feller, A.; Lagg, A.;
   Solanki, S. K.; Collados, M.; Sigwarth, M.; Volkmer, R.; Waldmann,
   T.; Kneer, F.; Nicklas, H.; Sobotka, M.
Bibcode: 2016A&A...596A...7S
Altcode: 2016arXiv160707094S
  Context. The various mechanisms of magneto-convective energy transport
  determine the structure of sunspots and active regions. <BR />
  Aims: We characterise the appearance of light bridges and other
  fine-structure details and elaborate on their magneto-convective
  nature. <BR /> Methods: We present speckle-reconstructed images taken
  with the broad-band imager (BBI) at the 1.5 m GREGOR telescope in the
  486 nm and 589 nm bands. We estimate the spatial resolution from the
  noise characteristics of the image bursts and obtain 0.08″ at 589
  nm. We describe structure details in individual best images as well
  as the temporal evolution of selected features. <BR /> Results: We
  find branched dark lanes extending along thin (≈1″) light bridges
  in sunspots at various heliocentric angles. In thick (≳ 2″) light
  bridges the branches are disconnected from the central lane and have a Y
  shape with a bright grain toward the umbra. The images reveal that light
  bridges exist on varying intensity levels and that their small-scale
  features evolve on timescales of minutes. Faint light bridges show
  dark lanes outlined by the surrounding bright features. Dark lanes are
  very common and are also found in the boundary of pores. They have a
  characteristic width of 0.1″ or smaller. Intergranular dark lanes of
  that width are seen in active region granulation. <BR /> Conclusions: We
  interpret our images in the context of magneto-convective simulations
  and findings: while central dark lanes in thin light bridges are
  elevated and associated with a density increase above upflows, the dark
  lane branches correspond to locations of downflows and are depressed
  relative to the adjacent bright plasma. Thick light bridges with central
  dark lanes show no projection effect. They have a flat elevated plateau
  that falls off steeply at the umbral boundary. There, Y-shaped filaments
  form as they do in the inner penumbra. This indicates the presence of
  inclined magnetic fields, meaning that the umbral magnetic field is
  wrapped around the convective light bridge.

Title: Probing deep photospheric layers of the quiet Sun with high
    magnetic sensitivity
Authors: Lagg, A.; Solanki, S. K.; Doerr, H. -P.; Martínez González,
   M. J.; Riethmüller, T.; Collados Vera, M.; Schlichenmaier, R.;
   Orozco Suárez, D.; Franz, M.; Feller, A.; Kuckein, C.; Schmidt, W.;
   Asensio Ramos, A.; Pastor Yabar, A.; von der Lühe, O.; Denker, C.;
   Balthasar, H.; Volkmer, R.; Staude, J.; Hofmann, A.; Strassmeier,
   K.; Kneer, F.; Waldmann, T.; Borrero, J. M.; Sobotka, M.; Verma, M.;
   Louis, R. E.; Rezaei, R.; Soltau, D.; Berkefeld, T.; Sigwarth, M.;
   Schmidt, D.; Kiess, C.; Nicklas, H.
Bibcode: 2016A&A...596A...6L
Altcode: 2016arXiv160506324L
  Context. Investigations of the magnetism of the quiet Sun are hindered
  by extremely weak polarization signals in Fraunhofer spectral
  lines. Photon noise, straylight, and the systematically different
  sensitivity of the Zeeman effect to longitudinal and transversal
  magnetic fields result in controversial results in terms of the strength
  and angular distribution of the magnetic field vector. <BR /> Aims:
  The information content of Stokes measurements close to the diffraction
  limit of the 1.5 m GREGOR telescope is analyzed. We took the effects of
  spatial straylight and photon noise into account. <BR /> Methods: Highly
  sensitive full Stokes measurements of a quiet-Sun region at disk center
  in the deep photospheric Fe I lines in the 1.56 μm region were obtained
  with the infrared spectropolarimeter GRIS at the GREGOR telescope. Noise
  statistics and Stokes V asymmetries were analyzed and compared to a
  similar data set of the Hinode spectropolarimeter (SOT/SP). Simple
  diagnostics based directly on the shape and strength of the profiles
  were applied to the GRIS data. We made use of the magnetic line ratio
  technique, which was tested against realistic magneto-hydrodynamic
  simulations (MURaM). <BR /> Results: About 80% of the GRIS spectra
  of a very quiet solar region show polarimetric signals above a 3σ
  level. Area and amplitude asymmetries agree well with small-scale
  surface dynamo-magneto hydrodynamic simulations. The magnetic line ratio
  analysis reveals ubiquitous magnetic regions in the ten to hundred Gauss
  range with some concentrations of kilo-Gauss fields. <BR /> Conclusions:
  The GRIS spectropolarimetric data at a spatial resolution of ≈0.̋4
  are so far unique in the combination of high spatial resolution scans
  and high magnetic field sensitivity. Nevertheless, the unavoidable
  effect of spatial straylight and the resulting dilution of the weak
  Stokes profiles means that inversion techniques still bear a high risk
  of misinterpretating the data.

Title: Flow and magnetic field properties in the trailing sunspots
    of active region NOAA 12396
Authors: Verma, M.; Denker, C.; Böhm, F.; Balthasar, H.; Fischer,
   C. E.; Kuckein, C.; Bello González, N.; Berkefeld, T.; Collados,
   M.; Diercke, A.; Feller, A.; González Manrique, S. J.; Hofmann, A.;
   Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pator Yabar, A.; Rezaei,
   R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.;
   Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
   K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
Bibcode: 2016AN....337.1090V
Altcode:
  Improved measurements of the photospheric and chromospheric
  three-dimensional magnetic and flow fields are crucial for a precise
  determination of the origin and evolution of active regions. We present
  an illustrative sample of multi-instrument data acquired during a
  two-week coordinated observing campaign in August 2015 involving,
  among others, the GREGOR solar telescope (imaging and near-infrared
  spectroscopy) and the space missions Solar Dynamics Observatory (SDO)
  and Interface Region Imaging Spectrograph (IRIS). The observations
  focused on the trailing part of active region NOAA 12396 with complex
  polarity inversion lines and strong intrusions of opposite polarity
  flux. The GREGOR Infrared Spectrograph (GRIS) provided Stokes IQUV
  spectral profiles in the photospheric Si I λ1082.7 nm line, the
  chromospheric He I λ1083.0 nm triplet, and the photospheric Ca I
  λ1083.9 nm line. Carefully calibrated GRIS scans of the active region
  provided maps of Doppler velocity and magnetic field at different
  atmospheric heights. We compare quick-look maps with those obtained
  with the ``Stokes Inversions based on Response functions'' (SIR)
  code, which furnishes deeper insight into the magnetic properties
  of the region. We find supporting evidence that newly emerging flux
  and intruding opposite polarity flux are hampering the formation
  of penumbrae, i.e., a penumbra fully surrounding a sunspot is only
  expected after cessation of flux emergence in proximity to the sunspots.

Title: Three-dimensional structure of a sunspot light bridge
Authors: Felipe, T.; Collados, M.; Khomenko, E.; Kuckein, C.; Asensio
   Ramos, A.; Balthasar, H.; Berkefeld, T.; Denker, C.; Feller, A.;
   Franz, M.; Hofmann, A.; Joshi, J.; Kiess, C.; Lagg, A.; Nicklas, H.;
   Orozco Suárez, D.; Pastor Yabar, A.; Rezaei, R.; Schlichenmaier,
   R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki,
   S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.;
   von der Lühe, O.; Waldmann, T.
Bibcode: 2016A&A...596A..59F
Altcode: 2016arXiv161104803F
  Context. Active regions are the most prominent manifestations of solar
  magnetic fields; their generation and dissipation are fundamental
  problems in solar physics. Light bridges are commonly present during
  sunspot decay, but a comprehensive picture of their role in the
  removal of the photospheric magnetic field is still lacking. <BR />
  Aims: We study the three-dimensional configuration of a sunspot,
  and in particular, its light bridge, during one of the last stages of
  its decay. <BR /> Methods: We present the magnetic and thermodynamical
  stratification inferred from full Stokes inversions of the photospheric
  Si I 10 827 Å and Ca I 10 839 Å lines obtained with the GREGOR
  Infrared Spectrograph of the GREGOR telescope at the Observatorio del
  Teide, Tenerife, Spain. The analysis is complemented by a study of
  continuum images covering the disk passage of the active region, which
  are provided by the Helioseismic and Magnetic Imager on board the Solar
  Dynamics Observatory. <BR /> Results: The sunspot shows a light bridge
  with penumbral continuum intensity that separates the central umbra from
  a smaller umbra. We find that in this region the magnetic field lines
  form a canopy with lower magnetic field strength in the inner part. The
  photospheric light bridge is dominated by gas pressure (high-β),
  as opposed to the surrounding umbra, where the magnetic pressure
  is higher. A convective flow is observed in the light bridge. This
  flow is able to bend the magnetic field lines and to produce field
  reversals. The field lines merge above the light bridge and become
  as vertical and strong as in the surrounding umbra. We conclude that
  this occurs because two highly magnetized regions approach each other
  during the sunspot evolution. <P />Movies associated to Figs. 2 and 13
  are available at <A href="http://www.aanda.org">http://www.aanda.org</A>

Title: Inference of magnetic fields in the very quiet Sun
Authors: Martínez González, M. J.; Pastor Yabar, A.; Lagg, A.;
   Asensio Ramos, A.; Collados, M.; Solanki, S. K.; Balthasar, H.;
   Berkefeld, T.; Denker, C.; Doerr, H. P.; Feller, A.; Franz, M.;
   González Manrique, S. J.; Hofmann, A.; Kneer, F.; Kuckein, C.;
   Louis, R.; von der Lühe, O.; Nicklas, H.; Orozco, D.; Rezaei, R.;
   Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka,
   M.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Verma, M.; Waldman,
   T.; Volkmer, R.
Bibcode: 2016A&A...596A...5M
Altcode: 2018arXiv180410089M
  Context. Over the past 20 yr, the quietest areas of the solar surface
  have revealed a weak but extremely dynamic magnetism occurring
  at small scales (&lt;500 km), which may provide an important
  contribution to the dynamics and energetics of the outer layers of
  the atmosphere. Understanding this magnetism requires the inference
  of physical quantities from high-sensitivity spectro-polarimetric
  data with high spatio-temporal resolution. <BR /> Aims: We present
  high-precision spectro-polarimetric data with high spatial resolution
  (0.4'') of the very quiet Sun at 1.56 μm obtained with the GREGOR
  telescope to shed some light on this complex magnetism. <BR /> Methods:
  We used inversion techniques in two main approaches. First, we assumed
  that the observed profiles can be reproduced with a constant magnetic
  field atmosphere embedded in a field-free medium. Second, we assumed
  that the resolution element has a substructure with either two constant
  magnetic atmospheres or a single magnetic atmosphere with gradients of
  the physical quantities along the optical depth, both coexisting with
  a global stray-light component. <BR /> Results: Half of our observed
  quiet-Sun region is better explained by magnetic substructure within
  the resolution element. However, we cannot distinguish whether this
  substructure comes from gradients of the physical parameters along the
  line of sight or from horizontal gradients (across the surface). In
  these pixels, a model with two magnetic components is preferred, and
  we find two distinct magnetic field populations. The population with
  the larger filling factor has very weak ( 150 G) horizontal fields
  similar to those obtained in previous works. We demonstrate that the
  field vector of this population is not constrained by the observations,
  given the spatial resolution and polarimetric accuracy of our data. The
  topology of the other component with the smaller filling factor is
  constrained by the observations for field strengths above 250 G:
  we infer hG fields with inclinations and azimuth values compatible
  with an isotropic distribution. The filling factors are typically
  below 30%. We also find that the flux of the two polarities is not
  balanced. From the other half of the observed quiet-Sun area 50% are
  two-lobed Stokes V profiles, meaning that 23% of the field of view
  can be adequately explained with a single constant magnetic field
  embedded in a non-magnetic atmosphere. The magnetic field vector and
  filling factor are reliable inferred in only 50% based on the regular
  profiles. Therefore, 12% of the field of view harbour hG fields with
  filling factors typically below 30%. At our present spatial resolution,
  70% of the pixels apparently are non-magnetised.

Title: Fitting peculiar spectral profiles in He I 10830Å absorption
    features
Authors: González Manrique, S. J.; Kuckein, C.; Pastor Yabar, A.;
   Collados, M.; Denker, C.; Fischer, C. E.; Gömöry, P.; Diercke, A.;
   Bello González, N.; Schlichenmaier, R.; Balthasar, H.; Berkefeld, T.;
   Feller, A.; Hoch, S.; Hofmann, A.; Kneer, F.; Lagg, A.; Nicklas, H.;
   Orozco Suárez, D.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka,
   M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Verma,
   M.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
Bibcode: 2016AN....337.1057G
Altcode: 2016arXiv160300679G
  The new generation of solar instruments provides better
  spectral, spatial, and temporal resolution for a better
  understanding of the physical processes that take place on the
  Sun. Multiple-component profiles are more commonly observed with these
  instruments. Particularly, the He I 10830 Å triplet presents such
  peculiar spectral profiles, which give information on the velocity
  and magnetic fine structure of the upper chromosphere. The purpose
  of this investigation is to describe a technique to efficiently fit
  the two blended components of the He I 10830 Å triplet, which are
  commonly observed when two atmospheric components are located within
  the same resolution element. The observations used in this study were
  taken on 2015 April 17 with the very fast spectroscopic mode of the
  GREGOR Infrared Spectrograph (GRIS) attached to the 1.5-m GREGOR solar
  telescope, located at the Observatorio del Teide, Tenerife, Spain. We
  apply a double-Lorentzian fitting technique using Levenberg-Marquardt
  least-squares minimization. This technique is very simple and much
  faster than inversion codes. Line-of-sight Doppler velocities can
  be inferred for a whole map of pixels within just a few minutes. Our
  results show sub- and supersonic downflow velocities of up to 32 km
  s<SUP>-1</SUP> for the fast component in the vicinity of footpoints of
  filamentary structures. The slow component presents velocities close
  to rest.

Title: Variability Of The Sun And Sun-Like Stars On Different
    Timescales
Authors: Solanki, Sami K.
Bibcode: 2016csss.confE..16S
Altcode:
  Although many features can be seen moving across it at various
  wavelengths, the Sun is an almost constant star with regard to its
  radiative output. Its radiative variability has generally only been
  discovered after the beginning of the space age. For Sun-like stars
  it is easier to measure their small levels of variability from the
  ground, leading to some unexpected discoveries that seemed to suggest
  a behaviour rather different than that displayed by the Sun. However,
  revisions of the measurements as well as advances in modelling have
  in recent years shown that some of the main differences between the
  Sun and stars can be reconciled. A much richer data set of short and
  medium-term variability has been provided by the COROT and Kepler
  missions. Although a number of exciting results have already been
  obtained from these data, many more are expected in the coming years as
  the data are more thoroughly analysed and models of solar variability
  are extended to describe stars which, while similar to the Sun, are
  not exact solar analogs.

Title: The statistical study of global properties of sunspots observed
    by SoHO/MDI continuum images over solar cycle 23
Authors: Goel, Suruchi; Krivova, Natalie; Solanki, Sami K.; Mathew,
   Shibu K.
Bibcode: 2016cosp...41E.687G
Altcode:
  A better understanding of inter-dependency of various sunspot parameters
  such as magnetic field, intensity, temperature, size etc., and also
  their variation with strength of solar activity cycle is important to
  understand the magneto-convection process involved in sunspot formation
  and evolution and hence to develop a consistent sunspot model. We have
  investigated global sunspot properties using parameters of sunspots
  identified from stray-light-corrected continuum images from SoHO/MDI
  spanning from years 1996 to 2011. We find that the non-linear relation
  between umbral core (minimum) intensity and sunspot area is best
  represented by an exponential function, which reaches an asymptotic
  value at 600 MSH. For the first time we have also observed that the
  core intensity depends on shape of umbrae, i.e., circular umbrae
  are statistically darker compared to the elongated ones. The core
  intensity increases slightly towards the limb (by value of ~0.1 from
  disk center to the limb). From sunspots sampled over the complete solar
  cycle 23 and during the rising phase of cycle 24, we did not find any
  solar-cycle variation in umbral core intensity. The penumbra to umbra
  area ratio is found to be not a constant parameter, instead it shows a
  quadratic decrease with sunspot area. Leading and following sunspots
  usually have different morphological features, however in this study
  we did not observe significant differences in their core intensity
  and penumbra-umbra area ratio relation with the sunspot area.

Title: Formation of the Penumbra and Start of the Evershed Flow
Authors: Murabito, M.; Romano, P.; Guglielmino, S. L.; Zuccarello,
   F.; Solanki, S. K.
Bibcode: 2016ApJ...825...75M
Altcode: 2016arXiv160405610M
  We studied the variations of line of sight photospheric plasma flows
  during the formation phase of the penumbra around a pore in active
  region NOAA 11490. We used a high spatial, spectral, and temporal
  resolution data set acquired by the Interferometric BIdimensional
  Spectrometer operating at the NSO/Dunn Solar Telescope as well as
  data taken by the Helioseismic and Magnetic Imager on board the
  Solar Dynamics Observatory satellite (SDO/HMI). Before the penumbra
  formed we observed a redshift of the spectral line in the inner part
  of the annular zone surrounding the pore as well as a blueshift of
  material associated with opposite magnetic polarity farther away from
  the pore. We found that the onset of the classical Evershed flow
  occurs on a very short timescale (1 to 3 hr) while the penumbra is
  forming. During the same time interval we found changes in the magnetic
  field inclination in the penumbra, with the vertical field actually
  changing sign near the penumbral edge, while the total magnetic field
  showed a significant increase, about 400 G. To explain these and other
  observations related to the formation of the penumbra and the onset
  of the Evershed flow we propose a scenario in which the penumbra is
  formed by magnetic flux dragged down from the canopy surrounding the
  initial pore. The Evershed flow starts when the sinking magnetic field
  dips below the solar surface and magnetoconvection sets in.

Title: Solar total and spectral irradiance reconstruction over last
    9000 years
Authors: Wu, Chi-Ju; Usoskin, Ilya; Krivova, Natalie; Solanki, Sami K.
Bibcode: 2016cosp...41E2072W
Altcode:
  Although the mechanisms of solar influence on Earth climate system
  are not yet fully understood, solar total and spectral irradiance are
  considered to be among the main determinants. Solar total irradiance
  is the total flux of solar radiative energy entering Earth's climate
  system, whereas the spectral irradiance describes this energy is
  distributed over the spectrum. Solar irradiance in the UV band is of
  special importance since it governs chemical processes in the middle and
  upper atmosphere. On timescales of the 11-year solar cycle and shorter,
  solar irradiance is measured by space-based instruments while models
  are needed to reconstruct solar irradiance on longer timescale. The
  SATIRE-M model (Spectral And Total Irradiance Reconstruction over
  millennia) is employed in this study to reconstruct solar irradiance
  from decadal radionuclide isotope data such as 14C and 10Be stored in
  tree rings and ice cores, respectively. A reconstruction over the last
  9000 years will be presented.

Title: The Solar Ultraviolet Imaging Telescope onboard Aditya-L1
Authors: Ghosh, Avyarthana; Chatterjee, Subhamoy; Khan, Aafaque R.;
   Tripathi, Durgesh; Ramaprakash, A. N.; Banerjee, Dipankar; Chordia,
   Pravin; Gandorfer, Achim M.; Krivova, Natalie; Nandy, Dibyendu;
   Rajarshi, Chaitanya; Solanki, Sami K.; Sriram, S.
Bibcode: 2016SPIE.9905E..03G
Altcode:
  The Solar Ultraviolet Imaging Telescope (SUIT) is an instrument onboard
  the Aditya-L1 spacecraft, the first dedicated solar mission of the
  Indian Space Research Organization (ISRO), which will be put in a
  halo orbit at the Sun-Earth Langrage point (L1). SUIT has an off-axis
  Ritchey-Chrétien configuration with a combination of 11 narrow and
  broad bandpass filters which will be used for full-disk solar imaging
  in the Ultravoilet (UV) wavelength range 200-400 nm. It will provide
  near simultaneous observations of lower and middle layers of the solar
  atmosphere, namely the Photosphere and Chromosphere. These observations
  will help to improve our understanding of coupling and dynamics of
  various layers of the solar atmosphere, mechanisms responsible for
  stability, dynamics and eruption of solar prominences and Coronal Mass
  ejections, and possible causes of solar irradiance variability in the
  Near and Middle UV regions, which is of central interest for assessing
  the Sun's influence on climate.

Title: Long-term solar irradiance variability: knowns and unknowns
Authors: Krivova, Natalie; Solanki, Sami K.; Dasi Espuig, Maria;
   Leng Yeo, Kok; Wu, Chi-Ju
Bibcode: 2016cosp...41E1066K
Altcode:
  Long-term reconstructions of solar irradiance variability are crucial
  to our understanding of solar influence on climate. They are only
  possible with the help of suitable models, which in turn require a
  thorough understanding of the mechanisms of this variability. With the
  advance of such models, also the past reconstructions are becoming
  more reliable. Nevertheless, the remaining uncertainties spread out
  when extrapolating back over long periods of time, amplified by the
  increasingly poorer quality and reliability of the available data that
  bear information on past solar activity. We will discuss the progress
  and the reliability of irradiance reconstructions on time scales of
  decades to millennia.

Title: EMPIRE reconstruction of TSI and SSI since 1947
Authors: Leng Yeo, Kok; Krivova, Natalie; Solanki, Sami K.
Bibcode: 2016cosp...41E2107L
Altcode:
  TSI and SSI, at least in the UV, have been monitored from space
  since 1978. This is accompanied by the development of models aimed
  at reproducing TSI and SSI by relating the variability to solar
  magnetism. We present a reconstruction of TSI and SSI, spanning 1947
  to 2016, based on the EMPirical Irradiance REconstruction (EMPIRE)
  model. EMPIRE is what is termed a proxy model, based on the regression
  of solar activity indices to measured solar irradiance. One of the main
  open questions in our understanding of solar irradiance variability,
  and consequently its influence on the Earth's climate, is the
  variation in UV SSI over the solar cycle. Solar cycle variability
  in UV SSI in preceding proxy models, such as NRLSSI, NRLSSI2 and
  MGNM, is significantly weaker than that indicated by other types
  of models longwards of around 240 nm. We demonstrate here that this
  discrepancy arises from previous proxy models neglecting the influence
  of measurement uncertainty on regression analyses. EMPIRE is based
  on the same activity indices as NRLSSI(2) but by taking measurement
  uncertainty into account, reproduces variability consistent with other
  modelling approaches and measurements. As such, EMPIRE supersedes
  earlier proxy models, including NRLSSI(2) and MGNM.

Title: Solar electromagnetic emission and climate
Authors: Solanki, Sami K.
Bibcode: 2016cosp...41E1831S
Altcode:
  Ever since the first solar radiometer flew in space it has been known
  that the level of emission of electromagnetic radiation from the Sun
  (the Sun's total irradiance) varies with time. This record now covers
  roughly 3.5 solar cycles. With time the quality of the observations has
  improved and the set of quantities that are observed have increased
  (now including the spectral solar irradiance over a wide range of
  wavelengths). At the same time, our understanding of the processes
  leading to variations in the Sun's radiative output and our ability to
  model such variations quantitatively have steadily improved, so that
  we are at a stage where we can reconstruct solar total and spectral
  irradiance over most of the Holocene, with increasing accuracy the
  closer we come to recent decades. The variable solar radiative output
  drives changes in the Earth's atmosphere, with such changes being
  well-documented in the upper and middle atmosphere of the Earth and
  becoming increasingly more subtle with depth in the atmosphere. In
  particular, uncovering the influence of the variable Sun on the
  troposphere, where the Earth's climate change mainly plays out, is
  a challenging task. In this talk an overview will be given of the
  chain from the Sun to the Earth, with the emphasis lying more on the
  solar part.

Title: The origin of Total Solar Irradiance variability on timescales
    less than a day
Authors: Shapiro, Alexander; Krivova, Natalie; Schmutz, Werner;
   Solanki, Sami K.; Leng Yeo, Kok; Cameron, Robert; Beeck, Benjamin
Bibcode: 2016cosp...41E1774S
Altcode:
  Total Solar Irradiance (TSI) varies on timescales from minutes to
  decades. It is generally accepted that variability on timescales of
  a day and longer is dominated by solar surface magnetic fields. For
  shorter time scales, several additional sources of variability have
  been proposed, including convection and oscillation. However, available
  simplified and highly parameterised models could not accurately explain
  the observed variability in high-cadence TSI records. We employed the
  high-cadence solar imagery from the Helioseismic and Magnetic Imager
  onboard the Solar Dynamics Observatory and the SATIRE (Spectral And
  Total Irradiance Reconstruction) model of solar irradiance variability
  to recreate the magnetic component of TSI variability. The recent 3D
  simulations of solar near-surface convection with MURAM code have been
  used to calculate the TSI variability caused by convection. This allowed
  us to determine the threshold timescale between TSI variability caused
  by the magnetic field and convection. Our model successfully replicates
  the TSI measurements by the PICARD/PREMOS radiometer which span the
  period of July 2010 to February 2014 at 2-minute cadence. Hence,
  we demonstrate that solar magnetism and convection can account for
  TSI variability at all timescale it has ever been measured (sans the
  5-minute component from p-modes).

Title: Modelling the Spectral Contrasts of Stellar Faculae.
Authors: Norris, Charlotte M.; Beeck, Benjamin; Unruh, Yvonne; Solanki,
   Sami; Yeo, Kok Leng; Krivova, Natalie
Bibcode: 2016csss.confE..63N
Altcode:
  Facular contrasts are an important parameter in modelling stellar
  variability and exoplanet transits. The ultimate goal of this work
  will be to model the contrasts of faculae for different spectral types
  and thus improve the modelling of solar and stellar photospheric
  variability. This is done by using a radiative transfer algorithm
  (ATLAS9) on magneto-convection simulations. Starting with solar twins,
  we derive facular contrasts as a function of limb angle and discuss
  their wavelength dependence.

Title: Diagnostics of Coronal Magnetic Fields Through the Hanle
    Effect in UV and IR Lines
Authors: Raouafi, Nour E.; Riley, Pete; Gibson, Sarah; Fineschi,
   Silvano; Solanki, Sami K.
Bibcode: 2016FrASS...3...20R
Altcode: 2016arXiv160608493R
  The plasma thermodynamics in the solar upper atmosphere, particularly in
  the corona, are dominated by the magnetic field, which controls the flow
  and dissipation of energy. The relative lack of knowledge of the coronal
  vector magnetic field is a major handicap for progress in coronal
  physics. This makes the development of measurement methods of coronal
  magnetic fields a high priority in solar physics. The Hanle effect in
  the UV and IR spectral lines is a largely unexplored diagnostic. We
  use magnetohydrodynamic (MHD) simulations to study the magnitude of the
  signal to be expected for typical coronal magnetic fields for selected
  spectral lines in the UV and IR wavelength ranges, namely the HI Ly-α
  and the He I 10830 Å lines. We show that the selected lines are useful
  for reliable diagnosis of coronal magnetic fields. The results show
  that the combination of polarization measurements of spectral lines
  with different sensitivities to the Hanle effect may be most appropriate
  for deducing coronal magnetic properties from future observations.

Title: Formation of a solar Hα filament from orphan penumbrae
Authors: Buehler, D.; Lagg, A.; van Noort, M.; Solanki, S. K.
Bibcode: 2016A&A...589A..31B
Altcode: 2016arXiv160305899B
  <BR /> Aims: The formation and evolution of an Hα filament in active
  region (AR) 10953 is described. <BR /> Methods: Observations from the
  Solar Optical Telescope (SOT) aboard the Hinode satellite starting
  from UT 18:09 on 27th April 2007 until UT 06:08 on 1st May 2007 were
  analysed. 20 scans of the 6302 Å Fe I line pair recorded by SOT/SP were
  inverted using the spatially coupled version of the SPINOR code. The
  inversions were analysed together with co-spatial SOT/BFI G-band and
  Ca II H and SOT/NFI Hα observations. <BR /> Results: Following the
  disappearance of an initial Hα filament aligned along the polarity
  inversion line (PIL) of the AR, a new Hα filament formed in its place
  some 20 h later, which remained stable for, at least, another 1.5
  days. The creation of the new Hα filament was driven by the ascent of
  horizontal magnetic fields from the photosphere into the chromosphere
  at three separate locations along the PIL. The magnetic fields at
  two of these locations were situated directly underneath the initial
  Hα filament and formed orphan penumbrae already aligned along the Hα
  filament channel. The 700 G orphan penumbrae were stable and trapped in
  the photosphere until the disappearance of the overlying initial Hα
  filament, after which they started to ascend into the chromosphere at
  10 ± 5 m/s. Each ascent was associated with a simultaneous magnetic
  flux reduction of up to 50% in the photosphere. The ascended orphan
  penumbrae formed dark seed structures in Hα in parallel with the PIL,
  which elongated and merged to form an Hα filament. The filament channel
  featured horizontal magnetic fields of on average 260 G at log (τ) =
  -2 suspended above the nearly field-free lower photosphere. The fields
  took on an overall inverse configuration at log (τ) = -2 suggesting
  a flux rope topology for the new Hα filament. The destruction of the
  initial Hα filament was likely caused by the flux emergence at the
  third location along the PIL. <BR /> Conclusions: We present a new
  interpretation of the Hα filament formation in AR 10953 whereby the
  mainly horizontal fields of orphan penumbrae, aligned along the Hα
  filament channel, ascend into the chromosphere, forming seed fragments
  for a new, second Hα filament. The orphan penumbral fields ascend
  into the chromosphere ~9-24 h before the Hα filament is fully formed.

Title: Reconstruction of spectral solar irradiance since 1700 from
    simulated magnetograms
Authors: Dasi-Espuig, M.; Jiang, J.; Krivova, N. A.; Solanki, S. K.;
   Unruh, Y. C.; Yeo, K. L.
Bibcode: 2016A&A...590A..63D
Altcode: 2016arXiv160502039D
  <BR /> Aims: We present a reconstruction of the spectral solar
  irradiance since 1700 using the SATIRE-T2 (Spectral And Total Irradiance
  REconstructions for the Telescope era version 2) model. This model
  uses as input magnetograms simulated with a surface flux transport
  model fed with semi-synthetic records of emerging sunspot groups. <BR
  /> Methods: The record of sunspot group areas and positions from the
  Royal Greenwich Observatory (RGO) is only available since 1874. We
  used statistical relationships between the properties of sunspot
  group emergence, such as the latitude, area, and tilt angle, and the
  sunspot cycle strength and phase to produce semi-synthetic sunspot
  group records starting in the year 1700. The semi-synthetic records
  are fed into a surface flux transport model to obtain daily simulated
  magnetograms that map the distribution of the magnetic flux in active
  regions (sunspots and faculae) and their decay products on the solar
  surface. The magnetic flux emerging in ephemeral regions is accounted
  for separately based on the concept of extended cycles whose length
  and amplitude are linked to those of the sunspot cycles through the
  sunspot number. The magnetic flux in each surface component (sunspots,
  faculae and network, and ephemeral regions) was used to compute the
  spectral and total solar irradiance (TSI) between the years 1700
  and 2009. This reconstruction is aimed at timescales of months or
  longer although the model returns daily values. <BR /> Results: We
  found that SATIRE-T2, besides reproducing other relevant observations
  such as the total magnetic flux, reconstructs the TSI on timescales
  of months or longer in good agreement with the PMOD composite of
  observations, as well as with the reconstruction starting in 1878
  based on the RGO-SOON data. The model predicts an increase in the TSI
  of 1.2<SUP>+0.2</SUP><SUB>-0.3</SUB> Wm<SUP>-2</SUP> between 1700
  and the present. The spectral irradiance reconstruction is in good
  agreement with the UARS/SUSIM measurements as well as the Lyman-α
  composite. <P />The complete total and spectral (115 nm-160 μm)
  irradiance reconstructions since 1700 will be available from <A
  href="http://www2.mps.mpg.de/projects/sun-climate/data.html">http://www2.mps.mpg.de/projects/sun-climate/data.html</A>

Title: High-resolution, high-sensitivity, ground-based solar
    spectropolarimetry with a new fast imaging polarimeter. I. Prototype
    characterization
Authors: Iglesias, F. A.; Feller, A.; Nagaraju, K.; Solanki, S. K.
Bibcode: 2016A&A...590A..89I
Altcode: 2016arXiv160401521I
  Context. Remote sensing of weak and small-scale solar magnetic fields is
  of utmost relevance when attempting to respond to a number of important
  open questions in solar physics. This requires the acquisition of
  spectropolarimetric data with high spatial resolution (~10<SUP>-1</SUP>
  arcsec) and low noise (10<SUP>-3</SUP> to 10<SUP>-5</SUP> of the
  continuum intensity). The main limitations to obtain these measurements
  from the ground, are the degradation of the image resolution produced
  by atmospheric seeing and the seeing-induced crosstalk (SIC). <BR
  /> Aims: We introduce the prototype of the Fast Solar Polarimeter
  (FSP), a new ground-based, high-cadence polarimeter that tackles the
  above-mentioned limitations by producing data that are optimally suited
  for the application of post-facto image restoration, and by operating
  at a modulation frequency of 100 Hz to reduce SIC. <BR /> Methods:
  We describe the instrument in depth, including the fast pnCCD camera
  employed, the achromatic modulator package, the main calibration steps,
  the effects of the modulation frequency on the levels of seeing-induced
  spurious signals, and the effect of the camera properties on the image
  restoration quality. <BR /> Results: The pnCCD camera reaches 400
  fps while keeping a high duty cycle (98.6%) and very low noise (4.94
  e<SUP>-</SUP> rms). The modulator is optimized to have high (&gt;80%)
  total polarimetric efficiency in the visible spectral range. This allows
  FSP to acquire 100 photon-noise-limited, full-Stokes measurements per
  second. We found that the seeing induced signals that are present in
  narrow-band, non-modulated, quiet-sun measurements are (a) lower than
  the noise (7 × 10<SUP>-5</SUP>) after integrating 7.66 min, (b) lower
  than the noise (2.3 × 10<SUP>-4</SUP>) after integrating 1.16 min and
  (c) slightly above the noise (4 × 10<SUP>-3</SUP>) after restoring
  case (b) by means of a multi-object multi-frame blind deconvolution. In
  addition, we demonstrate that by using only narrow-band images (with
  low S/N of 13.9) of an active region, we can obtain one complete set
  of high-quality restored measurements about every 2 s.

Title: Are solar brightness variations faculae- or spot-dominated?
Authors: Shapiro, A. I.; Solanki, S. K.; Krivova, N. A.; Yeo, K. L.;
   Schmutz, W. K.
Bibcode: 2016A&A...589A..46S
Altcode: 2016arXiv160204447S
  Context. Regular spaceborne measurements have revealed that
  solar brightness varies on multiple timescales, variations on
  timescales greater than a day being attributed to a surface magnetic
  field. Independently, ground-based and spaceborne measurements suggest
  that Sun-like stars show a similar, but significantly broader pattern
  of photometric variability. <BR /> Aims: To understand whether the
  broader pattern of stellar variations is consistent with the solar
  paradigm, we assess relative contributions of faculae and spots to
  solar magnetically-driven brightness variability. We investigate
  how the solar brightness variability and its facular and spot
  contributions depend on the wavelength, timescale of variability,
  and position of the observer relative to the ecliptic plane. <BR />
  Methods: We performed calculations with the SATIRE model, which
  returns solar brightness with daily cadence from solar disc area
  coverages of various magnetic features. We took coverages as seen by
  an Earth-based observer from full-disc SoHO/MDI and SDO/HMI data and
  projected them to mimic out-of-ecliptic viewing by an appropriate
  transformation. <BR /> Results: Moving the observer away from the
  ecliptic plane increases the amplitude of 11-year variability as it
  would be seen in Strömgren (b + y)/2 photometry, but decreases the
  amplitude of the rotational brightness variations as it would appear
  in Kepler and CoRoT passbands. The spot and facular contributions to
  the 11-year solar variability in the Strömgren (b + y)/2 photometry
  almost fully compensate each other so that the Sun appears anomalously
  quiet with respect to its stellar cohort. Such a compensation does not
  occur on the rotational timescale. <BR /> Conclusions: The rotational
  solar brightness variability as it would appear in the Kepler and
  CoRoT passbands from the ecliptic plane is spot-dominated, but the
  relative contribution of faculae increases for out-of-ecliptic viewing
  so that the apparent brightness variations are faculae-dominated for
  inclinations less than about I = 45°. Over the course of the 11-year
  activity cycle, the solar brightness variability is faculae-dominated
  shortwards of 1.2 μm independently of the inclination.

Title: An update on the Axion Helioscopes front: current activities
    at CAST and the IAXO project
Authors: Dafni, T.; Arik, M.; Armengaud, E.; Aune, S.; Avignone, F. T.;
   Barth, K.; Belov, A.; Betz, M.; Bräuninger, H.; Brax, P.; Breijnholt,
   N.; Brun, P.; Cantatore, G.; Carmona, J. M.; Carosi, G. P.; Caspers,
   F.; Caspi, S.; Cetin, S. A.; Chelouche, D.; Christensen, F. E.;
   Collar, J. I.; Dael, A.; Davenport, M.; Derbin, A. V.; Desch, K.;
   Diago, A.; Döbrich, B.; Dratchnev, I.; Dudarev, A.; Eleftheriadis, C.;
   Fanourakis, G.; Ferrer-Ribas, E.; Friedrich, P.; Galán, J.; García,
   J. A.; Gardikiotis, A.; Garza, J. G.; Gazis, E. N.; Georgiopoulou,
   E.; Geralis, T.; Gimeno, B.; Giomataris, I.; Gninenko, S.; Gómez,
   H.; González-Díaz, D.; Gruber, E.; Guendelman, E.; Guthörl, T.;
   Hailey, C. J.; Hartmann, R.; Hauf, S.; Haug, F.; Hasinoff, M. D.;
   Hiramatsu, T.; Hoffmann, D. H. H.; Horns, D.; Iguaz, F. J.; Irastorza,
   I. G.; Isern, J.; Imai, K.; Jacoby, J.; Jaeckel, J.; Jakobsen, A. C.;
   Jakovčić, K.; Kaminski, J.; Kawasaki, M.; Karuza, M.; Königsmann,
   K.; Kotthaus, R.; Krčmar, M.; Kousouris, K.; Krieger, C.; Kuster, M.;
   Lakić, B.; Laurent, J. M.; Limousin, O.; Lindner, A.; Liolios, A.;
   Ljubičić, A.; Luzón, G.; Matsuki, S.; Muratova, V. N.; Neff, S.;
   Niinikoski, T.; Nones, C.; Ortega, I.; Papaevangelou, T.; Pivovaroff,
   M. J.; Raffelt, G.; Redondo, J.; Riege, H.; Ringwald, A.; Rodríguez,
   A.; Rosu, M.; Russenschuck, S.; Ruz, J.; Saikawa, K.; Savvidis, I.;
   Sekiguchi, T.; Semertzidis, Y. K.; Shilon, I.; Sikivie, P.; Silva,
   H.; Solanki, S. K.; Stewart, L.; ten Kate, H. H. J.; Tomas, A.;
   Troitsky, S.; Vafeiadis, T.; van Bibber, K.; Vedrine, P.; Villar,
   J. A.; Vogel, J. K.; Walckiers, L.; Weltman, A.; Wester, W.; Yildiz,
   S. C.; Zioutas, K.
Bibcode: 2016NPPP..273..244D
Altcode:
  Although they have not yet been detected, axions and axion-like
  particles (ALPs) continue to maintain the interest (even increasingly
  so) of the rare-event searches community as viable candidates for the
  Dark Matter of the Universe but also as a solution for several other
  puzzles of astrophysics. Their property of coupling to photons has
  inspired different experimental methods for their detection, one of
  which is the helioscope technique. The CERN Axion Solar Telescope
  (CAST) is the most sensitive helioscope built up to date and has
  recently published part of the latest data taken with the magnet
  bores gradually filled with <SUP>3</SUP>He, probing the mass range
  up to 1.17 eV. The International AXion Observatory (IAXO) is being
  proposed as a facility where different axion studies can be performed,
  with the primary goal to study axions coming from the Sun. Designed to
  maximize sensitivity, it will improve the levels reached by CAST by
  almost 5 orders of magnitude in signal detection, that is more than
  one order of magnitude in terms of g<SUB>a</SUB><SUB>γ</SUB>. Here
  we will summarize the most important aspects of the helioscopes,
  and focus mainly on IAXO, based on the recent papers [1, 2].

Title: Modelling Solar and Stellar Brightness Variabilities
Authors: Yeo, K. L.; Shapiro, A. I.; Krivova, N. A.; Solanki, S. K.
Bibcode: 2016ASPC..504..273Y
Altcode:
  Total and spectral solar irradiance, TSI and SSI, have been measured
  from space since 1978. This is accompanied by the development of
  models aimed at replicating the observed variability by relating
  it to solar surface magnetism. Despite significant progress,
  there remains persisting controversy over the secular change and the
  wavelength-dependence of the variation with impact on our understanding
  of the Sun's influence on the Earth's climate. We highlight the recent
  progress in TSI and SSI modelling with SATIRE. Brightness variations
  have also been observed for Sun-like stars. Their analysis can profit
  from knowledge of the solar case and provide additional constraints
  for solar modelling. We discuss the recent effort to extend SATIRE to
  Sun-like stars.

Title: Flows in and around Active Region NOAA12118 Observed with
    the GREGOR Solar Telescope and SDO/HMI
Authors: Verma, M.; Denker, C.; Balthasar, H.; Kuckein, C.; González
   Manrique, S. J.; Sobotka, M.; Bello González, N.; Hoch, S.; Diercke,
   A.; Kummerow, P.; Berkefeld, T.; Collados, M.; Feller, A.; Hofmann,
   A.; Kneer, F.; Lagg, A.; Löhner-Böttcher, J.; Nicklas, H.; Pastor
   Yabar, A.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Schubert,
   M.; Sigwarth, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
   K.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
Bibcode: 2016ASPC..504...29V
Altcode: 2016arXiv160301109V
  Accurate measurements of magnetic and velocity fields in and around
  solar active regions are key to unlocking the mysteries of the
  formation and the decay of sunspots. High spatial resolution images
  and spectral sequences with a high cadence obtained with the GREGOR
  solar telescope give us an opportunity to scrutinize 3-D flow fields
  with local correlation tracking and imaging spectroscopy. We present
  GREGOR early science data acquired in 2014 July - August with the GREGOR
  Fabry-Pérot Interferometer and the Blue Imaging Channel. Time-series
  of blue continuum (λ 450.6 nm) images of the small active region
  NOAA 12118 were restored with the speckle masking technique to derive
  horizontal proper motions and to track the evolution of morphological
  changes. In addition, high-resolution observations are discussed in
  the context of synoptic data from the Solar Dynamics Observatory.

Title: Solar Science with the Atacama Large Millimeter/Submillimeter
    Array—A New View of Our Sun
Authors: Wedemeyer, S.; Bastian, T.; Brajša, R.; Hudson, H.;
   Fleishman, G.; Loukitcheva, M.; Fleck, B.; Kontar, E. P.; De Pontieu,
   B.; Yagoubov, P.; Tiwari, S. K.; Soler, R.; Black, J. H.; Antolin,
   P.; Scullion, E.; Gunár, S.; Labrosse, N.; Ludwig, H. -G.; Benz,
   A. O.; White, S. M.; Hauschildt, P.; Doyle, J. G.; Nakariakov, V. M.;
   Ayres, T.; Heinzel, P.; Karlicky, M.; Van Doorsselaere, T.; Gary,
   D.; Alissandrakis, C. E.; Nindos, A.; Solanki, S. K.; Rouppe van
   der Voort, L.; Shimojo, M.; Kato, Y.; Zaqarashvili, T.; Perez, E.;
   Selhorst, C. L.; Barta, M.
Bibcode: 2016SSRv..200....1W
Altcode: 2015SSRv..tmp..118W; 2015arXiv150406887W
  The Atacama Large Millimeter/submillimeter Array (ALMA) is a new
  powerful tool for observing the Sun at high spatial, temporal, and
  spectral resolution. These capabilities can address a broad range
  of fundamental scientific questions in solar physics. The radiation
  observed by ALMA originates mostly from the chromosphere—a complex
  and dynamic region between the photosphere and corona, which plays a
  crucial role in the transport of energy and matter and, ultimately,
  the heating of the outer layers of the solar atmosphere. Based on
  first solar test observations, strategies for regular solar campaigns
  are currently being developed. State-of-the-art numerical simulations
  of the solar atmosphere and modeling of instrumental effects can help
  constrain and optimize future observing modes for ALMA. Here we present
  a short technical description of ALMA and an overview of past efforts
  and future possibilities for solar observations at submillimeter and
  millimeter wavelengths. In addition, selected numerical simulations
  and observations at other wavelengths demonstrate ALMA's scientific
  potential for studying the Sun for a large range of science cases.

Title: Exploiting Four Historical Ca II K Spectroheliogram Archives
Authors: Chatzistergos, T.; Ermolli, I.; Solanki, S. K.; Krivova, N. A.
Bibcode: 2016ASPC..504..227C
Altcode:
  Here we briefly review the status of the project aimed to analyse
  the potential of historical Ca II K archives for studies of long-term
  (decades to a century) solar variability.

Title: Fast Solar Polarimeter: Prototype Characterization and
    First Results
Authors: Iglesias, F. A.; Feller, A.; Krishnappa, N.; Solanki, S. K.
Bibcode: 2016ASPC..504..325I
Altcode:
  Due to the differential and non-simultaneous nature of polarization
  measurements, seeing induced crosstalk (SIC) and seeing limited spatial
  resolution can easily counterbalance the benefits of solar imaging
  polarimetry from the ground. The development of instrumental techniques
  to treat these issues is necessary to fully exploit the next generation
  of large-aperture solar facilities, and maintain ground-based data at
  a competitive level with respect to its space-based counterpart. In
  particular, considering that many open questions in modern solar
  physics demand data with challenging specifications of resolution
  and polarimetric sensitivity that can only be achieved with large
  telescope apertures (Stenflo 1999). Even if state-of-the-art adaptive
  optics systems greatly improve image quality, their limited correction
  —due to finite bandwidth, mode number and seeing anisoplanat-
  ism— produces large residual values of SIC (Krishnappa &amp; Feller
  2012). Dual beam polarimeters are commonly used to reduce SIC between
  the intensity and polarization signals, however, they cannot compensate
  for the SIC introduced between circular and linear polarization,
  which can be relevant for high-precision polarimetry. It is known
  that fast modulation effectively reduces SIC, but the demodulation of
  the corresponding intensity signals imposes hard requirements on the
  frame rate of the associated cameras. One way to avoid a fast sensor,
  is to decouple the camera readout from the intensity demodulation
  step. This concept is the cornerstone of the very successful Zurich
  Imaging Polarimeter (ZIMPOL). Even though the ZIMPOL solution allows
  the detection of very faint signals (∼10<SUP>-5</SUP>), its design is
  not suitable for high-spatial-resolution applications. We are developing
  a polarimeter that focuses on both spatial resolution (&lt;0.5 arcsec)
  and polarimetric sensitivity (10<SUP>-4</SUP>). The prototype of this
  Fast Solar Polarimeter (FSP, see Feller et al. 2014), employs a high
  frame-rate (400 fps), low-noise (&lt;4 e- RMS), pnCCD camera (Hartmann
  et al. 2006) that is read in synchronization with a polarization
  modulator based on ferroelectric liquid crystals. The modulator package
  is similar to the SOLIS (Keller et al. 2003) design and optimized to
  have an achromatic total polarimetric efficiency above 80 % in the
  400-700 nm wavelength range. The fast modulation frequency of FSP,
  yielding up to 100 full-Stokes measurements per second, and high duty
  cycle (&gt;95%), have the double benefit of reducing seeing induced
  artifacts and improving the final spatial resolution by providing an
  optimal regime for the application of post-facto image reconstruction
  techniques. In this poster we describe the FSP prototype, including
  the characterization results, a technique to correct image smearing
  due to the sensor frame transfer (Iglesias et al. 2015) and some of
  the first measurements obtained with the 68-cm Vacuum Tower Telescope
  located at the Observatorio del Teide, Spain.

Title: Variation of the Mn I 539.4 nm line with the solar cycle
Authors: Danilovic, S.; Solanki, S. K.; Livingston, W.; Krivova, N.;
   Vince, I.
Bibcode: 2016A&A...587A..33D
Altcode: 2015arXiv151101286D
  Context. As a part of the long-term program at Kitt Peak National
  Observatory (KPNO), the Mn I 539.4 nm line has been observed for
  nearly three solar cycles using the McMath telescope and the 13.5 m
  spectrograph in double-pass mode. These full-disk spectrophotometric
  observations revealed an unusually strong change of this line's
  parameters over the solar cycle. <BR /> Aims: Optical pumping by the Mg
  II k line was originally proposed to explain these variations. More
  recent studies have proposed that this is not required and that
  the magnetic variability (I.e., the changes in solar atmospheric
  structure due to faculae) might explain these changes. Magnetic
  variability is also the mechanism that drives the changes in total
  solar irradiance variations (TSI). With this work we investigate this
  proposition quantitatively by using the same model that was earlier
  successfully employed to reconstruct the irradiance. <BR /> Methods:
  We reconstructed the changes in the line parameters using the model
  SATIRE-S, which takes only variations of the daily surface distribution
  of the magnetic field into account. We applied exactly the same model
  atmospheres and value of the free parameter as were used in previous
  solar irradiance reconstructions to now model the variation in the Mn
  I 539.4 nm line profile and in neighboring Fe I lines. We compared
  the results of the theoretical model with KPNO observations. <BR />
  Results: The changes in the Mn I 539.4 nm line and a neighbouring Fe
  I 539.52 nm line over approximately three solar cycles are reproduced
  well by the model without additionally tweaking the model parameters,
  if changes made to the instrument setup are taken into account. The
  model slightly overestimates the change for the strong Fe I 539.32 nm
  line. <BR /> Conclusions: Our result confirms that optical pumping
  of the Mn II 539.4 nm line by Mg II k is not the main cause of its
  solar cycle change. It also provides independent confirmation of solar
  irradiance models which are based on the assumption that irradiance
  variations are caused by the evolution of the solar surface magnetic
  flux. The result obtained here also supports the spectral irradiance
  variations computed by these models.

Title: Probing the Sun with ALMA: Observations and Simulations
Authors: Loukitcheva, M.; Solanki, S. K.; White, S. M.; Carlsson, M.
Bibcode: 2015ASPC..499..349L
Altcode: 2015arXiv150805686L
  ALMA will open a new chapter in the study of the Sun by providing a leap
  in spatial resolution and sensitivity compared to currently available
  mm wavelength observations. In preparation of ALMA, we have carried out
  a large number of observational tests and state-of-the-art radiation
  MHD simulations. Here we review the best available observations of
  the Sun at millimeter wavelengths.Using state of the art radiation
  MHD simulations of the solar atmosphere we demonstrate the huge
  potential of ALMA observations for uncovering the nature of the solar
  chromosphere. We show that ALMA will not only provide a reliable probe
  of the thermal structure and dynamics of the chromosphere, it will also
  open up a powerful new diagnostic of magnetic field at chromospheric
  heights, a fundamentally important, but so far poorly known parameter.

Title: Sunspot areas and tilt angles for solar cycles 7-10
Authors: Senthamizh Pavai, V.; Arlt, R.; Dasi-Espuig, M.; Krivova,
   N. A.; Solanki, S. K.
Bibcode: 2015A&A...584A..73S
Altcode: 2015arXiv150807849S
  <BR /> Aims: Extending the knowledge about the properties of solar
  cycles into the past is essential for understanding the solar
  dynamo. This paper aims to estimate areas of sunspots observed by
  Schwabe in 1825-1867 and to calculate the tilt angles of sunspot
  groups. <BR /> Methods: The sunspot sizes in Schwabe's drawings are
  not to scale and need to be converted into physical sunspot areas. We
  employed a statistical approach assuming that the area distribution
  of sunspots was the same in the 19th century as it was in the 20th
  century. <BR /> Results: Umbral areas for about 130 000 sunspots
  observed by Schwabe were obtained, as well as the tilt angles of
  sunspot groups assuming them to be bipolar. There is, of course,
  no polarity information in the observations. The annually averaged
  sunspot areas correlate reasonably with sunspot number. We derived
  an average tilt angle by attempting to exclude unipolar groups with
  a minimum separation of the two alleged polarities and an outlier
  rejection method which follows the evolution of each group and detects
  the moment it turns unipolar at its decay. As a result, the tilt angles,
  although displaying considerable scatter, average to 5̊.85 ± 0, with
  the leading polarity located closer to the equator, in good agreement
  with tilt angles obtained from 20th century data sets. Sources of
  uncertainties in the tilt angle determination are discussed and need to
  be addressed whenever different data sets are combined. The sunspot area
  and tilt angle data are provided at the CDS. <P />The sunspot area and
  tilt angle data are only available at the CDS via anonymous ftp to <A
  href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
  (ftp://130.79.128.5) or via <A
  href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/584/A73">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/584/A73</A>

Title: Helioseismology with Solar Orbiter
Authors: Löptien, Björn; Birch, Aaron C.; Gizon, Laurent; Schou,
   Jesper; Appourchaux, Thierry; Blanco Rodríguez, Julián; Cally,
   Paul S.; Dominguez-Tagle, Carlos; Gandorfer, Achim; Hill, Frank;
   Hirzberger, Johann; Scherrer, Philip H.; Solanki, Sami K.
Bibcode: 2015SSRv..196..251L
Altcode: 2014arXiv1406.5435L; 2014SSRv..tmp...31L
  The Solar Orbiter mission, to be launched in July 2017, will
  carry a suite of remote sensing and in-situ instruments, including
  the Polarimetric and Helioseismic Imager (PHI). PHI will deliver
  high-cadence images of the Sun in intensity and Doppler velocity
  suitable for carrying out novel helioseismic studies. The orbit of
  the Solar Orbiter spacecraft will reach a solar latitude of up to
  21<SUP>∘</SUP> (up to 34<SUP>∘</SUP> by the end of the extended
  mission) and thus will enable the first local helioseismology studies of
  the polar regions. Here we consider an array of science objectives to be
  addressed by helioseismology within the baseline telemetry allocation
  (51 Gbit per orbit, current baseline) and within the science observing
  windows (baseline 3×10 days per orbit). A particularly important
  objective is the measurement of large-scale flows at high latitudes
  (rotation and meridional flow), which are largely unknown but play an
  important role in flux transport dynamos. For both helioseismology
  and feature tracking methods convection is a source of noise in
  the measurement of longitudinally averaged large-scale flows, which
  decreases as T <SUP>-1/2</SUP> where T is the total duration of the
  observations. Therefore, the detection of small amplitude signals (e.g.,
  meridional circulation, flows in the deep solar interior) requires long
  observation times. As an example, one hundred days of observations at
  lower spatial resolution would provide a noise level of about three m/s
  on the meridional flow at 80<SUP>∘</SUP> latitude. Longer time-series
  are also needed to study temporal variations with the solar cycle. The
  full range of Earth-Sun-spacecraft angles provided by the orbit will
  enable helioseismology from two vantage points by combining PHI with
  another instrument: stereoscopic helioseismology will allow the study
  of the deep solar interior and a better understanding of the physics
  of solar oscillations in both quiet Sun and sunspots. We have used a
  model of the PHI instrument to study its performance for helioseismology
  applications. As input we used a 6 hr time-series of realistic solar
  magneto-convection simulation (Stagger code) and the SPINOR radiative
  transfer code to synthesize the observables. The simulated power
  spectra of solar oscillations show that the instrument is suitable for
  helioseismology. In particular, the specified point spread function,
  image jitter, and photon noise are no obstacle to a successful mission.

Title: Magneto-static Modeling of the Mixed Plasma Beta Solar
    Atmosphere Based on Sunrise/IMaX Data
Authors: Wiegelmann, T.; Neukirch, T.; Nickeler, D. H.; Solanki,
   S. K.; Martínez Pillet, V.; Borrero, J. M.
Bibcode: 2015ApJ...815...10W
Altcode: 2015arXiv151105568W
  Our aim is to model the three-dimensional magnetic field structure
  of the upper solar atmosphere, including regions of non-negligible
  plasma beta. We use high-resolution photospheric magnetic field
  measurements from SUNRISE/IMaX as the boundary condition for a
  magneto-static magnetic field model. The high resolution of IMaX
  allows us to resolve the interface region between the photosphere
  and corona, but modeling this region is challenging for the following
  reasons. While the coronal magnetic field is thought to be force-free
  (the Lorentz force vanishes), this is not the case in the mixed plasma
  β environment in the photosphere and lower chromosphere. In our model,
  pressure gradients and gravity forces are self-consistently taken into
  account and compensate for the non-vanishing Lorentz force. Above a
  certain height (about 2 Mm) the non-magnetic forces become very weak
  and consequently the magnetic field becomes almost force-free. Here,
  we apply a linear approach where the electric current density consists
  of a superposition of a field-line parallel current and a current
  perpendicular to the Sun's gravity field. We illustrate the prospects
  and limitations of this approach and give an outlook for an extension
  toward a nonlinear model.

Title: Sunrise Mission Highlights
Authors: Riethmüller, Tino L.; Solanki, Sami K.
Bibcode: 2015arXiv151103487R
Altcode:
  Solar activity is controlled by the magnetic field, which also causes
  the variability of the solar irradiance that in turn is thought to
  influence the climate on Earth. The magnetic field manifests itself
  in the form of structures of different sizes, starting with sunspots
  (10-50 Mm) down to the smallest known magnetic features that often
  have spatial extents of 100 km or less. The study of the fine scale
  structure of the Sun's magnetic field has been hampered by the limited
  spatial resolution of the available observations. This has recently
  changed thanks to new space and ground-based telescopes. A significant
  step forward has been taken by the Sunrise observatory, built around
  the largest solar telescope to leave the ground, and containing two
  science instruments. Sunrise had two successful long-duration science
  flights on a stratospheric balloon in June 2009 (solar activity minimum)
  and in June 2013 (at a high activity level) and a number of scientific
  results have been obtained that have greatly advanced our understanding
  of solar magnetism, with data analysis still ongoing. After a brief
  introduction to the Sunrise mission, an overview of a selection of
  these results will be given.

Title: Depth-dependent global properties of a sunspot observed by
    Hinode using the Solar Optical Telescope/Spectropolarimeter
Authors: Tiwari, Sanjiv K.; van Noort, Michiel; Solanki, Sami K.;
   Lagg, Andreas
Bibcode: 2015A&A...583A.119T
Altcode: 2015arXiv150804830T
  Context. For the past two decades, the three-dimensional structure
  of sunspots has been studied extensively. A recent improvement in the
  Stokes inversion technique prompts us to revisit the depth-dependent
  properties of sunspots. <BR /> Aims: In the present work, we aim to
  investigate the global depth-dependent thermal, velocity, and magnetic
  properties of a sunspot, as well as the interconnection between
  various local properties. <BR /> Methods: We analysed high-quality
  Stokes profiles of the disk-centred, regular, leading sunspot of NOAA
  AR 10933, acquired by the Solar Optical Telescope/Spectropolarimeter
  (SOT/SP) on board the Hinode spacecraft. To obtain depth-dependent
  stratification of the physical parameters, we used the recently
  developed, spatially coupled version of the SPINOR inversion code. <BR
  /> Results: First, we study the azimuthally averaged physical parameters
  of the sunspot. We find that the vertical temperature gradient in the
  lower- to mid-photosphere is at its weakest in the umbra, while it is
  considerably stronger in the penumbra, and stronger still in the spot's
  surroundings. The azimuthally averaged field becomes more horizontal
  with radial distance from the centre of the spot, but more vertical
  with height. At continuum optical depth unity, the line-of-sight
  velocity shows an average upflow of ~300 ms<SUP>-1</SUP> in the inner
  penumbra and an average downflow of ~1300 ms<SUP>-1</SUP> in the
  outer penumbra. The downflow continues outside the visible penumbral
  boundary. The sunspot shows, at most, a moderate negative twist of
  &lt;5° at log (τ) = 0, which increases with height. The sunspot umbra
  and the spines of the penumbra show considerable similarity with regard
  to their physical properties, albeit with some quantitative differences
  (weaker, somewhat more horizontal fields in spines, commensurate
  with their location being further away from the sunspot's core). The
  temperature shows a general anti-correlation with the field strength,
  with the exception of the heads of penumbral filaments, where a weak
  positive correlation is found. The dependence of the physical parameters
  on each other over the full sunspot shows a qualitative similarity to
  that of a standard penumbral filament and its surrounding spines. <BR />
  Conclusions: The large-scale variation in the physical parameters of
  a sunspot at various optical depths is presented. Our results suggest
  that the spines in the penumbra are basically the outward extension
  of the umbra. The spines and the penumbral filaments, together, are
  the basic elements that form a sunspot penumbra.

Title: VizieR Online Data Catalog: Sunspot areas and tilt angles
    (Senthamizh Pavai+, 2015)
Authors: Senthamizh Pavai, V.; Arlt, R.; Dasi-Espuig, M.; Krivova,
   N.; Solanki, S.
Bibcode: 2015yCat..35840073S
Altcode:
  We present sunspot positions and areas from historical observations
  of sunspots by Samuel Heinrich Schwabe from Dessau, Germany. He has
  recorded his observations of sunspots from 1825-1867 as drawings in
  small circles of about 5cm diameter (representing the solar disk). Even
  though he has used quite a number of telescopes for his observations,
  the majority of the full-disk drawings were made with a 3-1/2-foot
  telescope from Fraunhofer. His observing log books are stored in the
  library of the Royal Astronomical Society in London. Those drawings
  were digitized photographically with a resolution of 2912x4378 pixels
  per page. The sizes and positions of the sunspots were measured using
  a dozen of circular mouse cursor shapes with different diameters. The
  sunspot sizes in Schwabe's drawings are not to scale and need to
  be converted into physical sunspot areas. We employed a statistical
  approach assuming that the area distribution of sunspots was the same
  in the 19th century as it was in the 20th century. Umbral areas for
  about 130,000 sunspots observed by Schwabe were obtained, as well as
  the tilt angles of sunspot groups assuming them to be bipolar (two
  or more spots). There is, of course, no polarity information in the
  observations. <P />Both an updated sunspot database and a tilt angle
  database are available at http://www.aip.de/Members/rarlt/ sunspots
  for further study. <P />(2 data files).

Title: Flarelike brightenings of active region loops observed
    with SUMER
Authors: Wang, T. J.; Innes, D. E.; Solanki, S. K.; Curdt, W.
Bibcode: 2015arXiv151000337W
Altcode:
  Coronal loops on the east limb of the Sun were observed by SUMER on
  SOHO for several days. Small flare-like brightenings are detected very
  frequently in the hot flare line Fe~{\small XIX}. We find that the
  relatively intense events are in good coincidence with the transient
  brightenings seen by Yohkoh/SXT. A statistical analysis shows that these
  brightenings have durations of 5-84 min and extensions along the slit
  of 2-67 Mm. The integrated energy observed in Fe~{\small XIX} for each
  event is in the range of $3\times10^{18}-5\times10^{23}$ ergs, and the
  estimated thermal energy ranges from $10^{26}-10^{29}$ ergs. Application
  of the statistical method proposed by Parnell \&amp; Jupp (2000) yields
  a value of 1.5 to 1.8 for the index of a power law relation between
  the frequency of the events and the radiated energy in Fe~{\small XIX},
  and a value of 1.7 to 1.8 for the index of the frequency distribution of
  the thermal energy in the energy range $&gt;10^{27}$ ergs. We examine
  the possibility that these small brightenings give a big contribution
  to heating of the active region corona.

Title: Three-dimensional non-LTE radiative transfer effects in Fe
    i lines. III. Line formation in magneto-hydrodynamic atmospheres
Authors: Holzreuter, R.; Solanki, S. K.
Bibcode: 2015A&A...582A.101H
Altcode: 2015arXiv150704224H
  Non-local thermodynamic equilibrium (NLTE) effects in diagnostically
  important solar Fe i lines are important because of the strong
  sensitivity of Fe i to ionizing UV radiation, which may lead to
  a considerable underpopulation of the Fe i levels in the solar
  atmosphere and, therefore, to a sizeable weakening of Fe i lines. These
  NLTE effects may be intensified or weakened by horizontal radiative
  transfer (RT) in a three-dimensionally (3D) structured atmosphere. We
  analyze the influence of horizontal RT on commonly used Fe i lines in
  a snapshot of a 3D radiation magneto-hydrodynamic (MHD) simulation of
  a plage region. NLTE and horizontal RT effects occur with considerable
  strength (up to 50% in line depth or equivalent width) in the analyzed
  snapshot. Because they may have either sign, and both signs occur with
  approximately the same frequency and strength, the net effects are small
  when considering spatially averaged quantities. The situation in the
  plage atmosphere turns out to be rather complex. Horizontal transfer
  leads to line weakening relative to 1D NLTE transfer near the boundaries
  of kG magnetic elements. Around the centers of these elements, however,
  we find line strengthening, which is often significant. This behavior
  contrasts with what is expected from previous 3D RT computations in
  idealized flux-tube models, which only display line weakening. The
  origin of this unexpected behavior lies in the fact that magnetic
  elements are surrounded by dense and relatively cool downflowing gas,
  which forms the walls of the magnetic elements. The continuum in these
  dense walls is often formed in colder gas than in the central part of
  the magnetic elements. Consequently, the central parts of the magnetic
  element experience a subaverage UV-irradiation leading to the observed
  3D NLTE line strengthening.

Title: ADAHELI: exploring the fast, dynamic Sun in the x-ray, optical,
    and near-infrared
Authors: Berrilli, Francesco; Soffitta, Paolo; Velli, Marco; Sabatini,
   Paolo; Bigazzi, Alberto; Bellazzini, Ronaldo; Bellot Rubio, Luis
   Ramon; Brez, Alessandro; Carbone, Vincenzo; Cauzzi, Gianna; Cavallini,
   Fabio; Consolini, Giuseppe; Curti, Fabio; Del Moro, Dario; Di Giorgio,
   Anna Maria; Ermolli, Ilaria; Fabiani, Sergio; Faurobert, Marianne;
   Feller, Alex; Galsgaard, Klaus; Gburek, Szymon; Giannattasio, Fabio;
   Giovannelli, Luca; Hirzberger, Johann; Jefferies, Stuart M.; Madjarska,
   Maria S.; Manni, Fabio; Mazzoni, Alessandro; Muleri, Fabio; Penza,
   Valentina; Peres, Giovanni; Piazzesi, Roberto; Pieralli, Francesca;
   Pietropaolo, Ermanno; Martinez Pillet, Valentin; Pinchera, Michele;
   Reale, Fabio; Romano, Paolo; Romoli, Andrea; Romoli, Marco; Rubini,
   Alda; Rudawy, Pawel; Sandri, Paolo; Scardigli, Stefano; Spandre,
   Gloria; Solanki, Sami K.; Stangalini, Marco; Vecchio, Antonio;
   Zuccarello, Francesca
Bibcode: 2015JATIS...1d4006B
Altcode:
  Advanced Astronomy for Heliophysics Plus (ADAHELI) is a project concept
  for a small solar and space weather mission with a budget compatible
  with an European Space Agency (ESA) S-class mission, including launch,
  and a fast development cycle. ADAHELI was submitted to the European
  Space Agency by a European-wide consortium of solar physics research
  institutes in response to the "Call for a small mission opportunity
  for a launch in 2017," of March 9, 2012. The ADAHELI project builds
  on the heritage of the former ADAHELI mission, which had successfully
  completed its phase-A study under the Italian Space Agency 2007 Small
  Mission Programme, thus proving the soundness and feasibility of
  its innovative low-budget design. ADAHELI is a solar space mission
  with two main instruments: ISODY: an imager, based on Fabry-Pérot
  interferometers, whose design is optimized to the acquisition of
  highest cadence, long-duration, multiline spectropolarimetric images
  in the visible/near-infrared region of the solar spectrum. XSPO: an
  x-ray polarimeter for solar flares in x-rays with energies in the 15
  to 35 keV range. ADAHELI is capable of performing observations that
  cannot be addressed by other currently planned solar space missions,
  due to their limited telemetry, or by ground-based facilities, due to
  the problematic effect of the terrestrial atmosphere.

Title: The Polarimetric and Helioseismic Imager for Solar Orbiter:
    SO/PHI
Authors: Solanki, Sami K.; del Toro Iniesta, Jose Carlos; Woch,
   Joachim; Gandorfer, Achim; Hirzberger, Johann; Schmidt, Wolfgang;
   Appourchaux, Thierry; Alvarez-Herrero, Alberto
Bibcode: 2015IAUS..305..108S
Altcode: 2015arXiv150203368S
  The Solar Orbiter is the next solar physics mission of the European
  Space Agency, ESA, in collaboration with NASA, with a launch planned in
  2018. The spacecraft is designed to approach the Sun to within 0.28 AU
  at perihelion of a highly eccentric orbit. The proximity with the Sun
  will also allow its observation at uniformly high resolution at EUV and
  visible wavelengths. Such observations are central for learning more
  about the magnetic coupling of the solar atmosphere. At a later phase
  in the mission the spacecraft will leave the ecliptic and study the
  enigmatic poles of the Sun from a heliographic latitude of up to 33°.

Title: Search for chameleons with CAST
Authors: Anastassopoulos, V.; Arik, M.; Aune, S.; Barth, K.; Belov,
   A.; Bräuninger, H.; Cantatore, G.; Carmona, J. M.; Cetin, S. A.;
   Christensen, F.; Collar, J. I.; Dafni, T.; Davenport, M.; Desch, K.;
   Dermenev, A.; Eleftheriadis, C.; Fanourakis, G.; Ferrer-Ribas, E.;
   Friedrich, P.; Galán, J.; García, J. A.; Gardikiotis, A.; Garza,
   J. G.; Gazis, E. N.; Geralis, T.; Giomataris, I.; Hailey, C.; Haug,
   F.; Hasinoff, M. D.; Hoffmann, D. H. H.; Iguaz, F. J.; Irastorza,
   I. G.; Jacoby, J.; Jakobsen, A.; Jakovčić, K.; Kaminski, J.; Karuza,
   M.; Kavuk, M.; Krčmar, M.; Krieger, C.; Krüger, A.; Lakić, B.;
   Laurent, J. M.; Liolios, A.; Ljubičić, A.; Luzón, G.; Neff, S.;
   Ortega, I.; Papaevangelou, T.; Pivovaroff, M. J.; Raffelt, G.; Riege,
   H.; Rosu, M.; Ruz, J.; Savvidis, I.; Solanki, S. K.; Vafeiadis, T.;
   Villar, J. A.; Vogel, J. K.; Yildiz, S. C.; Zioutas, K.; Brax, P.;
   Lavrentyev, I.; Upadhye, A.
Bibcode: 2015PhLB..749..172A
Altcode: 2015arXiv150304561A
  In this work we present a search for (solar) chameleons with the CERN
  Axion Solar Telescope (CAST). This novel experimental technique,
  in the field of dark energy research, exploits both the chameleon
  coupling to matter (β<SUB>m</SUB>) and to photons (β<SUB>γ</SUB>)
  via the Primakoff effect. By reducing the X-ray detection energy
  threshold used for axions from 1 keV to 400 eV CAST became sensitive
  to the converted solar chameleon spectrum which peaks around 600
  eV. Even though we have not observed any excess above background, we
  can provide a 95% C.L. limit for the coupling strength of chameleons to
  photons of β<SUB>γ</SUB> ≲10<SUP>11</SUP> for 1 &lt;β<SUB>m</SUB>
  &lt;10<SUP>6</SUP>.

Title: The Maunder minimum (1645-1715) was indeed a grand minimum:
    A reassessment of multiple datasets
Authors: Usoskin, Ilya G.; Arlt, Rainer; Asvestari, Eleanna; Hawkins,
   Ed; Käpylä, Maarit; Kovaltsov, Gennady A.; Krivova, Natalie;
   Lockwood, Michael; Mursula, Kalevi; O'Reilly, Jezebel; Owens, Matthew;
   Scott, Chris J.; Sokoloff, Dmitry D.; Solanki, Sami K.; Soon, Willie;
   Vaquero, José M.
Bibcode: 2015A&A...581A..95U
Altcode: 2015arXiv150705191U
  <BR /> Aims: Although the time of the Maunder minimum (1645-1715) is
  widely known as a period of extremely low solar activity, it is still
  being debated whether solar activity during that period might have
  been moderate or even higher than the current solar cycle #24. We have
  revisited all existing evidence and datasets, both direct and indirect,
  to assess the level of solar activity during the Maunder minimum. <BR />
  Methods: We discuss the East Asian naked-eye sunspot observations, the
  telescopic solar observations, the fraction of sunspot active days,
  the latitudinal extent of sunspot positions, auroral sightings at
  high latitudes, cosmogenic radionuclide data as well as solar eclipse
  observations for that period. We also consider peculiar features of
  the Sun (very strong hemispheric asymmetry of the sunspot location,
  unusual differential rotation and the lack of the K-corona) that imply
  a special mode of solar activity during the Maunder minimum. <BR />
  Results: The level of solar activity during the Maunder minimum is
  reassessed on the basis of all available datasets. <BR /> Conclusions:
  We conclude that solar activity was indeed at an exceptionally low
  level during the Maunder minimum. Although the exact level is still
  unclear, it was definitely lower than during the Dalton minimum of
  around 1800 and significantly below that of the current solar cycle
  #24. Claims of a moderate-to-high level of solar activity during the
  Maunder minimum are rejected with a high confidence level.

Title: The role of the Fraunhofer lines in solar brightness
    variability
Authors: Shapiro, A. I.; Solanki, S. K.; Krivova, N. A.; Tagirov,
   R. V.; Schmutz, W. K.
Bibcode: 2015A&A...581A.116S
Altcode: 2015arXiv150705437S
  Context. The solar brightness varies on timescales from minutes to
  decades. A clear identification of the physical processes behind such
  variations is needed for developing and improving physics-based models
  of solar brightness variability and reconstructing solar brightness
  in the past. This is, in turn, important for better understanding
  the solar-terrestrial and solar-stellar connections. <BR /> Aims:
  We estimate the relative contributions of the continuum, molecular,
  and atomic lines to the solar brightness variations on different
  timescales. <BR /> Methods: Our approach is based on the assumption that
  variability of the solar brightness on timescales greater than a day
  is driven by the evolution of the solar surface magnetic field. We
  calculated the solar brightness variations employing the solar
  disc area coverage of magnetic features deduced from the MDI/SOHO
  observations. The brightness contrasts of magnetic features relative
  to the quiet Sun were calculated with a non-LTE radiative transfer
  code as functions of disc position and wavelength. By consecutive
  elimination of molecular and atomic lines from the radiative transfer
  calculations, we assessed the role of these lines in producing solar
  brightness variability. <BR /> Results: We show that the variations
  in Fraunhofer lines define the amplitude of the solar brightness
  variability on timescales greater than a day and even the phase of
  the total solar irradiance variability over the 11-year cycle. We also
  demonstrate that molecular lines make substantial contribution to solar
  brightness variability on the 11-year activity cycle and centennial
  timescales. In particular, our model indicates that roughly a quarter
  of the total solar irradiance variability over the 11-year cycle
  originates in molecular lines. The maximum of the absolute spectral
  brightness variability on timescales greater than a day is associated
  with the CN violet system between 380 and 390 nm.

Title: Magnetic reconnection as a source of jets from a penumbral
    intrusion into a sunspot umbra
Authors: Bharti, L.; Solanki, S. K.; Hirzberger, J.
Bibcode: 2015arXiv150902123B
Altcode:
  We present the results of high resolution co-temporal and co-spatial
  photospheric and chromospheric observations of sunspot penumbral
  intrusions. The data was taken with the Swedish Solar Telescope (SST)
  on the Canary Islands. Time series of Ca\,II H images show a series of
  transient jets extending roughly 3000 km above a penumbral intrusion
  into the umbra. For most of the time series jets were seen along
  the whole length of the intruding bright filament. Some of these jets
  develop a clear $\lambda$-shaped structure, with a small loop appearing
  at their footpoint and lasting for around a minute. In the framework
  of earlier studies, the observed transient $\lambda$ shape of these
  jets strongly suggests that they are caused by magnetic reconnection
  between a curved arcade-like or flux-rope like field in the lower part
  of the penumbral intrusion and the more vertical umbral magnetic field
  forming a cusp-shaped structure above the penumbral intrusion.

Title: Dynamics of Multi-cored Magnetic Structures in the Quiet Sun
Authors: Requerey, Iker S.; Del Toro Iniesta, Jose Carlos; Bellot
   Rubio, Luis R.; Martínez Pillet, Valentín; Solanki, Sami K.;
   Schmidt, Wolfgang
Bibcode: 2015ApJ...810...79R
Altcode: 2015arXiv150806998R
  We report on the dynamical interaction of quiet-Sun magnetic fields and
  granular convection in the solar photosphere as seen by Sunrise. We
  use high spatial resolution (0.″15-0.″18) and temporal cadence
  (33 s) spectropolarimetric Imaging Magnetograph eXperiment data,
  together with simultaneous CN and Ca ii H filtergrams from Sunrise
  Filter Imager. We apply the SIR inversion code to the polarimetric
  data in order to infer the line of sight velocity and vector magnetic
  field in the photosphere. The analysis reveals bundles of individual
  flux tubes evolving as a single entity during the entire 23 minute data
  set. The group shares a common canopy in the upper photospheric layers,
  while the individual tubes continually intensify, fragment and merge in
  the same way that chains of bright points in photometric observations
  have been reported to do. The evolution of the tube cores are driven
  by the local granular convection flows. They intensify when they
  are “compressed” by surrounding granules and split when they are
  “squeezed” between two moving granules. The resulting fragments
  are usually later regrouped in intergranular lanes by the granular
  flows. The continual intensification, fragmentation and coalescence of
  flux results in magnetic field oscillations of the global entity. From
  the observations we conclude that the magnetic field oscillations first
  reported by Martínez González et al. correspond to the forcing by
  granular motions and not to characteristic oscillatory modes of thin
  flux tubes.

Title: Solar extreme ultraviolet variability of the quiet Sun
Authors: Shakeri, F.; Teriaca, L.; Solanki, S. K.
Bibcode: 2015A&A...581A..51S
Altcode: 2015arXiv150705786S
  The last solar minimum has been unusually quiet compared to the previous
  minima (since space-based radiometric measurements are available). The
  Sun's magnetic flux was substantially lower during this minimum. Some
  studies also show that the total solar irradiance during the minimum
  after cycle 23 may have dropped below the values known from the two
  minima prior to that. For chromospheric and coronal radiation, the
  situation is less clear-cut. The Sun's 10.7 cm flux shows a decrease of
  ~4% during the solar minimum in 2008 compared to the previous minimum,
  but Ca ii K does not. Here we consider additional wavelengths in
  the extreme ultraviolet (EUV), specifically transitions of He i at
  584.3 Å and O v at 629.7 Å, of which the CDS spectrometer aboard
  SOHO has been taking regular scans along the solar central meridian
  since 1996. We analysed this unique dataset to verify if and how the
  radiance distribution undergoes measurable variations between cycle
  minima. To achieve this aim we determined the radiance distribution
  of quiet areas around the Sun centre. Concentrating on the last two
  solar minima, we found out that there is very little variation in the
  radiance distribution of the chromospheric spectral line He i between
  these minima. The same analysis shows a modest, although significant,
  4% variation in the radiance distribution of the TR spectral line O
  v. These results are comparable to those obtained by earlier studies
  employing other spectral features, and they confirm that chromospheric
  indices display a small variation, whereas in the transition region
  a more significant reduction of the brighter features is visible.

Title: Modelling stellar brightness variations
Authors: Shapiro, Alexander; Solanki, Sami K.; Krivova, Natalie
Bibcode: 2015IAUGA..2256741S
Altcode:
  We develop a model that attributes the variability of the stellar
  brightness to the imbalance between starspot darkening and facular
  brightening. Our approach is based on the assumption that the
  photometric variability of the Sun and Sun-like stars have the same
  fundamental causes so that we can describe stellar variability by
  extrapolating the solar model. Our results suggest that the solar
  paradigm is remarkably successful in explaining the stellar variability
  on the activity cycle time-scale. In particular, the model reproduces
  the observed reversal of the in-phase activity-brightness relationship
  for low-activity stars to an anti-phase one for more active stars.We
  simulate the solar variability as it would be measured out-of-ecliptic
  by Kepler and CoRoT and discuss the relative contributions of spots
  and faculae to the photometric stellar variability.

Title: Statistical analysis of supersonic downflows in sunspot
    penumbrae.
Authors: Kim, Hyunnam; Lagg, Andreas; Solanki, Sami K.; Narayan,
   Gautam; van Noort, Michiel; Kim, Kap-Sung
Bibcode: 2015IAUGA..2254868K
Altcode:
  Supersonic downflow patches was found in the outer edge of sunspot
  penumbra. These patches are believed to be the return channels of the
  Evershed flow. There was previous study to investigate their structure
  in detail using Hinode SOT/SP observations (M. van Noort et al. 2013)
  but their data sample was only two sunspots. To make general description
  it needs to check more sunspot data sample.We selected 242 downflow
  patches of 16 sunspots using Hinode SOT/SP observations from 2006 to
  2012. Height-dependent maps of atmospheric parameters of these downflows
  was produced by using HeLix which was height dependent LTE inversion
  code of Stokes profiles.Statistical analysis of magnetic field strength,
  inclination angle of field line, temperature and line-of-sight velocity
  are presented. The recovered atmospheric data tell us that downflow
  patches have different physical signatures comparing normal penumbra
  properties. Furthermore, our results of three height-dependent layer
  support that heating process should occur on the downflow patches in
  the middle of layer.

Title: UV solar irradiance in observations and the NRLSSI and
    SATIRE-S models
Authors: Yeo, K. L.; Ball, W. T.; Krivova, N. A.; Solanki, S. K.;
   Unruh, Y. C.; Morrill, J.
Bibcode: 2015JGRA..120.6055Y
Altcode: 2015arXiv150701224Y
  Total solar irradiance and UV spectral solar irradiance has been
  monitored since 1978 through a succession of space missions. This is
  accompanied by the development of models aimed at replicating solar
  irradiance by relating the variability to solar magnetic activity. The
  Naval Research Laboratory Solar Spectral Irradiance (NRLSSI) and
  Spectral And Total Irradiance REconstruction for the Satellite era
  (SATIRE-S) models provide the most comprehensive reconstructions of
  total and spectral solar irradiance over the period of satellite
  observation currently available. There is persistent controversy
  between the various measurements and models in terms of the wavelength
  dependence of the variation over the solar cycle, with repercussions on
  our understanding of the influence of UV solar irradiance variability
  on the stratosphere. We review the measurement and modeling of UV solar
  irradiance variability over the period of satellite observation. The
  SATIRE-S reconstruction is consistent with spectral solar irradiance
  observations where they are reliable. It is also supported by an
  independent, empirical reconstruction of UV spectral solar irradiance
  based on Upper Atmosphere Research Satellite/Solar Ultraviolet Spectral
  Irradiance Monitor measurements from an earlier study. The weaker
  solar cycle variability produced by NRLSSI between 300 and 400 nm is
  not evident in any available record. We show that although the method
  employed to construct NRLSSI is principally sound, reconstructed solar
  cycle variability is detrimentally affected by the uncertainty in the
  SSI observations it draws upon in the derivation. Based on our findings,
  we recommend, when choosing between the two models, the use of SATIRE-S
  for climate studies.

Title: Models of Solar Irradiance Variability
Authors: Solanki, Sami K.
Bibcode: 2015IAUGA..2250049S
Altcode:
  Models of solar irradiance variability have an important role to
  play due to the relatively short (although steadily increasing)
  length of measured irradiance time series. Advanced models also allow
  identifying the source of solar irradiance variations and give insight
  into the variation of irradiance as a function of wavelength. The
  first generation of models of solar irradiance were proxy-based,
  i.e. purely empirical. These were followed by models that combine
  spectra computed from semi-empirical model atmospheres, with a
  measure of solar activity variations. In future, models will build
  increasingly on 3D MHD simulations instead of 1D model atmospheres
  to compute the spectra. On longer timescales models are generally
  simpler, although there too considerable progress has been made,
  with irradiance reconstructions now available for multiple millennia,
  albeit with lower resolution and accuracy than at shorter timescales.

Title: The Maunder minimum: A reassessment from multiple dataset
Authors: Usoskin, Ilya; Arlt, Rainer; Asvestari, Eleanna; Kovaltsov,
   Gennady; Krivova, Natalie; Lockwood, Michael; Käpylä, Maarit; Owens,
   Matthew; Sokoloff, Dmitry D.; Solanki, Sami; Soon, Willie; Vaquero,
   Jose; Scott, Chris
Bibcode: 2015IAUGA..2253036U
Altcode:
  The Maunder minimum (MM) in 1645-1715 was a period of the lowest ever
  known solar activity recorded via sunspot numbers since 1610. Since
  it is the only Grand minimum of solar activity directly observed,
  it forms a benchmark for the solar variability studies. Therefore,
  it is crucially important to assess the level and other features
  of temporal and spatial solar magnetic variability during that
  time. However, because of uncertainties related mostly to ambiguity
  of some historical sunspot observation records, the exact level of
  solar activity during the MM is somewhat unclear, leaving room for
  continuous discussions and speculations. Many of these issues have been
  addressed by Jack Eddy in his cornerstone papers of 1976 and 1983,
  but since then numerous new pieces of evidence and datasets have
  appeared, making it possible to verify the paradigm of the Maunder
  minimum with far greater certainty than before.Here we provide a full
  reassessment of the Maunder minimum using all the available datasets:
  augmented sunspot counts and drawings; revisited historical archives;
  both well-known and newly revealed records of auroral observations;
  cosmic ray variability via cosmogenic isotope records of <SUP>14</SUP>C
  in tree trunks, <SUP>10</SUP>Be in ice cores and<SUP> 44</SUP>Ti in
  fallen meteorites. We show that, while the exact level of the activity
  is not easy to determine, the Sun indeed exhibited exceptionally low
  magnetic activity during the MM, in comparison to other periods of
  moderate or decreased activity, such as the Dalton minimum (ca. 1800),
  the Gleissberg minimum (ca. 1900) and the present weak solar cycle #
  24. We show that a scenario of moderate or strong activity during the
  MM contradicts all the available datasets.Thus, we confirm, using
  all the presently available datasets of different nature, that the
  period of the Maunder minimum in 1645-1715 was indeed a Grand minimum,
  with very low solar surface magnetic activity, low intensity of the
  interplanetary magnetic field, as well as lower frequency and higher
  geographical latitude of auroral occurrence. Meanwhile some indications
  of the continuation, but at a very low level, of the 11-year solar
  cycle can be found in the data.

Title: Solar cycle variation in UV solar spectral irradiance
Authors: Leng Yeo, Kok; Krivova, Natalie; Solanki, Sami K.
Bibcode: 2015IAUGA..2253798L
Altcode:
  Solar spectral irradiance, SSI, in the UV has been measured from space,
  almost without interruption, since 1978. This is accompanied by the
  development of models aimed at reconstructing SSI by relating its
  variability to solar magnetic activity. The various satellite records
  and model reconstructions differ significantly in terms of the variation
  over the solar cycle, with the consequence that their application to
  climate models yield qualitatively different results. Here, we highlight
  the key discrepancies between available records and reconstructions,
  and discuss the possible underlying causes.

Title: New solar axion search using the CERN Axion Solar Telescope
    with <SUP>4</SUP>He filling
Authors: Arik, M.; Aune, S.; Barth, K.; Belov, A.; Bräuninger,
   H.; Bremer, J.; Burwitz, V.; Cantatore, G.; Carmona, J. M.; Cetin,
   S. A.; Collar, J. I.; Da Riva, E.; Dafni, T.; Davenport, M.; Dermenev,
   A.; Eleftheriadis, C.; Elias, N.; Fanourakis, G.; Ferrer-Ribas, E.;
   Galán, J.; García, J. A.; Gardikiotis, A.; Garza, J. G.; Gazis,
   E. N.; Geralis, T.; Georgiopoulou, E.; Giomataris, I.; Gninenko, S.;
   Gómez Marzoa, M.; Hasinoff, M. D.; Hoffmann, D. H. H.; Iguaz, F. J.;
   Irastorza, I. G.; Jacoby, J.; Jakovčić, K.; Karuza, M.; Kavuk,
   M.; Krčmar, M.; Kuster, M.; Lakić, B.; Laurent, J. M.; Liolios,
   A.; Ljubičić, A.; Luzón, G.; Neff, S.; Niinikoski, T.; Nordt,
   A.; Ortega, I.; Papaevangelou, T.; Pivovaroff, M. J.; Raffelt, G.;
   Rodríguez, A.; Rosu, M.; Ruz, J.; Savvidis, I.; Shilon, I.; Solanki,
   S. K.; Stewart, L.; Tomás, A.; Vafeiadis, T.; Villar, J.; Vogel,
   J. K.; Yildiz, S. C.; Zioutas, K.; CAST Collaboration
Bibcode: 2015PhRvD..92b1101A
Altcode: 2015arXiv150300610A
  The CERN Axion Solar Telescope (CAST) searches for a →γ conversion
  in the 9 T magnetic field of a refurbished LHC test magnet that can
  be directed toward the Sun. Two parallel magnet bores can be filled
  with helium of adjustable pressure to match the x-ray refractive mass
  m<SUB>γ</SUB> to the axion search mass m<SUB>a</SUB>. After the vacuum
  phase (2003-2004), which is optimal for m<SUB>a</SUB>≲0.02 eV , we
  used <SUP>4</SUP>He in 2005-2007 to cover the mass range of 0.02-0.39
  eV and <SUP>3</SUP>He in 2009-2011 to scan from 0.39 to 1.17 eV. After
  improving the detectors and shielding, we returned to <SUP>4</SUP>He
  in 2012 to investigate a narrow m<SUB>a</SUB> range around 0.2 eV
  ("candidate setting" of our earlier search) and 0.39-0.42 eV, the
  upper axion mass range reachable with <SUP>4</SUP>He, to "cross the
  axion line" for the KSVZ model. We have improved the limit on the
  axion-photon coupling to g<SUB>a γ</SUB>&lt;1.47 ×10<SUP>-10</SUP>
  GeV<SUP>-1</SUP> (95% C.L.), depending on the pressure settings. Since
  2013, we have returned to the vacuum and aim for a significant increase
  in sensitivity.

Title: Properties of solar plage from a spatially coupled inversion
    of Hinode SP data
Authors: Buehler, D.; Lagg, A.; Solanki, S. K.; van Noort, M.
Bibcode: 2015A&A...576A..27B
Altcode: 2015arXiv150101151B
  <BR /> Aims: The properties of magnetic fields forming an extended
  plage region in AR 10953 were investigated. <BR /> Methods:
  Stokes spectra of the Fe I line pair at 6302 Å recorded by the
  spectropolarimeter aboard the Hinode satellite were inverted using
  the SPINOR code. The code performed a 2D spatially coupled inversion
  on the Stokes spectra, allowing the retrieval of gradients in optical
  depth within the atmosphere of each pixel, whilst accounting for the
  effects of the instrument's PSF. Consequently, no magnetic filling
  factor was needed. <BR /> Results: The inversion results reveal that
  plage is composed of magnetic flux concentrations (MFCs) with typical
  field strengths of 1520 G at log (τ) = -0.9 and inclinations of
  10°-15°. The MFCs expand by forming magnetic canopies composed of
  weaker and more inclined magnetic fields. The expansion and average
  temperature stratification of isolated MFCs can be approximated well
  with an empirical plage thin flux tube model. The highest temperatures
  of MFCs are located at their edges in all log (τ) layers. Whilst
  the plasma inside MFCs is nearly at rest, each is surrounded by a
  ring of downflows of on average 2.4 km s<SUP>-1</SUP> at log (τ)
  = 0 and peak velocities of up to 10 km s<SUP>-1</SUP>, which are
  supersonic. The downflow ring of an MFC weakens and shifts outwards
  with height, tracing the MFC's expansion. Such downflow rings often
  harbour magnetic patches of opposite polarity to that of the main MFC
  with typical field strengths below 300 G at log (τ) = 0. These opposite
  polarity patches are situated beneath the canopy of their main MFC. We
  found evidence of a strong broadening of the Stokes profiles in MFCs
  and particularly in the downflow rings surrounding MFCs (expressed
  by a microturbulence in the inversion). This indicates the presence
  of strong unresolved velocities. Larger magnetic structures such as
  sunspots cause the field of nearby MFCs to be more inclined.

Title: Millimeter radiation from a 3D model of the solar
    atmosphere. I. Diagnosing chromospheric thermal structure
Authors: Loukitcheva, M.; Solanki, S. K.; Carlsson, M.; White, S. M.
Bibcode: 2015A&A...575A..15L
Altcode: 2015arXiv150102898L
  <BR /> Aims: We use advanced 3D non-local thermodynamic equilibrium
  radiative magnetohydrodynamic simulations of the solar atmosphere to
  carry out detailed tests of chromospheric diagnostics at millimeter and
  submillimeter wavelengths. <BR /> Methods: We focused on the diagnostics
  of the thermal structure of the chromosphere in the wavelength bands
  from 0.4 mm up to 9.6 mm that can be accessed with the Atacama Large
  Millimeter/Submillimeter Array (ALMA) and investigated how these
  diagnostics are affected by the instrumental resolution. <BR /> Results:
  We find that the formation height range of the millimeter radiation
  depends on the location in the simulation domain and is related to the
  underlying magnetic structure. Nonetheless, the brightness temperature
  is a reasonable measure of the gas temperature at the effective
  formation height at a given location on the solar surface. There is
  considerable scatter in this relationship, but this is significantly
  reduced when very weak magnetic fields are avoided. Our results
  indicate that although instrumental smearing reduces the correlation
  between brightness and temperature, millimeter brightness can still
  be used to reliably diagnose electron temperature up to a resolution
  of 1''. If the resolution is more degraded, then the value of the
  diagnostic diminishes rapidly. <BR /> Conclusions: We conclude that
  millimeter brightness can image the chromospheric thermal structure
  at the height at which the radiation is formed. Thus multiwavelength
  observations with ALMA with a narrow step in wavelength should provide
  sufficient information for a tomographic imaging of the chromosphere.

Title: Simulated magnetic flows in the solar photosphere
Authors: Danilovic, S.; Cameron, R. H.; Solanki, S. K.
Bibcode: 2015A&A...574A..28D
Altcode: 2014arXiv1408.6159D
  Context. Recent Sunrise/IMaX observations have revealed supersonic
  magnetic flows. <BR /> Aims: Our aim is to determine the origin of
  these flows by using realistic magnetohydrodynamics simulations. <BR
  /> Methods: We simulated cancellation and emergence of magnetic
  flux through the solar photosphere. Our first numerical experiment
  started with a magnetic field of both polarities. To simulate
  emergence into a region with pre-existing field, we introduced a
  large-scale horizontally uniform sheet of a horizontal field. We
  followed the subsequent evolution and created synthetic polarimetric
  observations, including known instrumental effects of the Sunrise/IMaX
  and Hinode/SP instruments. We compared the simulated and observed
  spectropolarimetric signals. <BR /> Results: Strongly blue- and
  redshifted Stokes V signals are produced in locations where strong
  line-of-sight velocities coincide with the strong line-of-sight
  component of the magnetic field. The size and strength of simulated
  events is smaller than observed, and they are mostly associated with
  downflows, contrary to observations. In a few cases where they appear
  above a granule, single blue-lobed Stokes V are produced by strong
  gradients in magnetic field and velocity. No change of magnetic field
  sign is detected along the line of sight in these instances. More
  high-speed magnetised flows occurred when an emergence was simulated
  than when no horizontal field was added. <BR /> Conclusions: The
  simulations indicate that the observed events result from magnetic flux
  emergences in which reconnection may take place, but does not seem to
  be necessary. <P />The movies are available in electronic form at <A
  href="http://www.aanda.org/10.1051/0004-6361/201423779/olm">http://www.aanda.org</A>

Title: Centre-to-limb properties of small, photospheric quiet-Sun jets
Authors: Rubio da Costa, F.; Solanki, S. K.; Danilovic, S.; Hizberger,
   J.; Martínez-Pillet, V.
Bibcode: 2015A&A...574A..95R
Altcode: 2014arXiv1412.1620R
  Context. Strongly Doppler-shifted Stokes V profiles have been detected
  in the quiet Sun with the IMaX instrument on-board the SUNRISE
  stratospheric balloon-borne telescope. High velocities are required
  to produce such signals, hence these events have been interpreted as
  jets, although other sources are also possible. <BR /> Aims: We aim
  to characterize the variation of the main properties of these events
  (occurrence rate, lifetime, size, and velocities) with their position on
  the solar disk between disk centre and the solar limb. <BR /> Methods:
  These events were identified in SUNRISE/IMaX data according to the same
  objective criteria at all available positions on the solar disk. Their
  properties were determined using standard techniques. <BR /> Results:
  Our study yielded a number of new insights into this phenomenon. Most
  importantly, the number density of these events is independent of
  the heliocentric angle, meaning that the investigated supersonic
  flows are nearly isotropically distributed. Size and lifetime are
  also nearly independent of the heliocentric angle, while their
  intensity contrast increases towards the solar limb. The Stokes V
  jets are associated with upflow velocities deduced from Stokes I,
  which are stronger towards the limb. Their intensity decreases with
  time, while their line-of-sight velocity does not display a clear
  temporal evolution. Their association with linear polarization signals
  decreases towards the limb. <BR /> Conclusions: The density of events
  appears to be independent of heliocentric angle, establishing that they
  are directed nearly randomly. If these events are jets triggered by
  magnetic reconnection between emerging magnetic flux and the ambient
  field, then our results suggest that there is no preferred geometry
  for the reconnection process.

Title: Magnetic Flux Transport at the Solar Surface
Authors: Jiang, J.; Hathaway, D. H.; Cameron, R. H.; Solanki, S. K.;
   Gizon, L.; Upton, L.
Bibcode: 2015sac..book..491J
Altcode:
  No abstract at ADS

Title: Solar Cycle Variation in Solar Irradiance
Authors: Yeo, K. L.; Krivova, N. A.; Solanki, S. K.
Bibcode: 2015sac..book..137Y
Altcode:
  No abstract at ADS

Title: The Formation and Disintegration of Magnetic Bright Points
    Observed by Sunrise/IMaX
Authors: Utz, D.; del Toro Iniesta, J. C.; Bellot Rubio, L. R.;
   Jurčák, J.; Martínez Pillet, V.; Solanki, S. K.; Schmidt, W.
Bibcode: 2014ApJ...796...79U
Altcode: 2014arXiv1411.3240U
  The evolution of the physical parameters of magnetic bright points
  (MBPs) located in the quiet Sun (mainly in the interwork) during
  their lifetime is studied. First, we concentrate on the detailed
  description of the magnetic field evolution of three MBPs. This
  reveals that individual features follow different, generally complex,
  and rather dynamic scenarios of evolution. Next, we apply statistical
  methods on roughly 200 observed MBP evolutionary tracks. MBPs are found
  to be formed by the strengthening of an equipartition field patch,
  which initially exhibits a moderate downflow. During the evolution,
  strong downdrafts with an average velocity of 2.4 km s<SUP>-1</SUP>
  set in. These flows, taken together with the concurrent strengthening of
  the field, suggest that we are witnessing the occurrence of convective
  collapses in these features, although only 30% of them reach kG field
  strengths. This fraction might turn out to be larger when the new 4
  m class solar telescopes are operational as observations of MBPs with
  current state of the art instrumentation could still be suffering from
  resolution limitations. Finally, when the bright point disappears
  (although the magnetic field often continues to exist) the magnetic
  field strength has dropped to the equipartition level and is generally
  somewhat weaker than at the beginning of the MBP's evolution. Also,
  only relatively weak downflows are found on average at this stage of
  the evolution. Only 16% of the features display upflows at the time
  that the field weakens, or the MBP disappears. This speaks either for
  a very fast evolving dynamic process at the end of the lifetime, which
  could not be temporally resolved, or against strong upflows as the cause
  of the weakening of the field of these magnetic elements, as has been
  proposed based on simulation results. It is noteworthy that in about 10%
  of the cases, we observe in the vicinity of the downflows small-scale
  strong (exceeding 2 km s<SUP>-1</SUP>) intergranular upflows related
  spatially and temporally to these downflows. The paper is complemented
  by a detailed discussion of aspects regarding the applied methods,
  the complementary literature, and in depth analysis of parameters
  like magnetic field strength and velocity distributions. An important
  difference to magnetic elements and associated bright structures in
  active region plage is that most of the quiet Sun bright points display
  significant downflows over a large fraction of their lifetime (i.e.,
  in more than 46% of time instances/measurements they show downflows
  exceeding 1 km s<SUP>-1</SUP>).

Title: Magnetic Flux Transport at the Solar Surface
Authors: Jiang, J.; Hathaway, D. H.; Cameron, R. H.; Solanki, S. K.;
   Gizon, L.; Upton, L.
Bibcode: 2014SSRv..186..491J
Altcode: 2014SSRv..tmp...43J; 2014arXiv1408.3186J
  After emerging to the solar surface, the Sun's magnetic field displays a
  complex and intricate evolution. The evolution of the surface field is
  important for several reasons. One is that the surface field, and its
  dynamics, sets the boundary condition for the coronal and heliospheric
  magnetic fields. Another is that the surface evolution gives us insight
  into the dynamo process. In particular, it plays an essential role
  in the Babcock-Leighton model of the solar dynamo. Describing this
  evolution is the aim of the surface flux transport model. The model
  starts from the emergence of magnetic bipoles. Thereafter, the model is
  based on the induction equation and the fact that after emergence the
  magnetic field is observed to evolve as if it were purely radial. The
  induction equation then describes how the surface flows—differential
  rotation, meridional circulation, granular, supergranular flows,
  and active region inflows—determine the evolution of the field (now
  taken to be purely radial). In this paper, we review the modeling of
  the various processes that determine the evolution of the surface
  field. We restrict our attention to their role in the surface flux
  transport model. We also discuss the success of the model and some of
  the results that have been obtained using this model.

Title: Solar Cycle Variation in Solar Irradiance
Authors: Yeo, K. L.; Krivova, N. A.; Solanki, S. K.
Bibcode: 2014SSRv..186..137Y
Altcode: 2014arXiv1407.4249Y; 2014SSRv..tmp...25Y
  The correlation between solar irradiance and the 11-year solar activity
  cycle is evident in the body of measurements made from space, which
  extend over the past four decades. Models relating variation in solar
  irradiance to photospheric magnetism have made significant progress
  in explaining most of the apparent trends in these observations. There
  are, however, persistent discrepancies between different measurements
  and models in terms of the absolute radiometry, secular variation and
  the spectral dependence of the solar cycle variability. We present an
  overview of solar irradiance measurements and models, and discuss the
  key challenges in reconciling the divergence between the two.

Title: The magnetic field in the solar atmosphere
Authors: Wiegelmann, Thomas; Thalmann, Julia K.; Solanki, Sami K.
Bibcode: 2014A&ARv..22...78W
Altcode: 2014arXiv1410.4214W
  This publication provides an overview of magnetic fields in the solar
  atmosphere with the focus lying on the corona. The solar magnetic field
  couples the solar interior with the visible surface of the Sun and with
  its atmosphere. It is also responsible for all solar activity in its
  numerous manifestations. Thus, dynamic phenomena such as coronal mass
  ejections and flares are magnetically driven. In addition, the field
  also plays a crucial role in heating the solar chromosphere and corona
  as well as in accelerating the solar wind. Our main emphasis is the
  magnetic field in the upper solar atmosphere so that photospheric and
  chromospheric magnetic structures are mainly discussed where relevant
  for higher solar layers. Also, the discussion of the solar atmosphere
  and activity is limited to those topics of direct relevance to the
  magnetic field. After giving a brief overview about the solar magnetic
  field in general and its global structure, we discuss in more detail
  the magnetic field in active regions, the quiet Sun and coronal holes.

Title: A New SATIRE-S Spectral Solar Irradiance Reconstruction for
    Solar Cycles 21-23 and Its Implications for Stratospheric Ozone*
Authors: Ball, William T.; Krivova, Natalie A.; Unruh, Yvonne C.;
   Haigh, Joanna D.; Solanki, Sami K.
Bibcode: 2014JAtS...71.4086B
Altcode: 2014arXiv1408.0365B
  We present a revised and extended total and spectral solar irradiance
  (SSI) reconstruction, which includes a wavelength-dependent uncertainty
  estimate, spanning the last three solar cycles using the SATIRE-S
  model. The SSI reconstruction covers wavelengths between 115 and
  160,000 nm and all dates between August 1974 and October 2009. This
  represents the first full-wavelength SATIRE-S reconstruction to
  cover the last three solar cycles without data gaps and with an
  uncertainty estimate. SATIRE-S is compared with the NRLSSI model and
  SORCE/SOLSTICE ultraviolet (UV) observations. SATIRE-S displays similar
  cycle behaviour to NRLSSI for wavelengths below 242 nm and almost twice
  the variability between 242 and 310 nm. During the decline of last
  solar cycle, between 2003 and 2008, SSI from SORCE/SOLSTICE version
  12 and 10 typically displays more than three times the variability of
  SATIRE-S between 200 and 300 nm. All three datasets are used to model
  changes in stratospheric ozone within a 2D atmospheric model for a
  decline from high solar activity to solar minimum. The different flux
  changes result in different modelled ozone trends. Using NRLSSI leads
  to a decline in mesospheric ozone, while SATIRE-S and SORCE/SOLSTICE
  result in an increase. Recent publications have highlighted increases
  in mesospheric ozone when considering version 10 SORCE/SOLSTICE
  irradiances. The recalibrated SORCE/SOLSTICE version 12 irradiances
  result in a much smaller mesospheric ozone response than when using
  version 10 and now similar in magnitude to SATIRE-S. This shows that
  current knowledge of variations in spectral irradiance is not sufficient
  to warrant robust conclusions concerning the impact of solar variability
  on the atmosphere and climate.

Title: Evolution of Small Scale Magnetic Structures from Sunrise Data
Authors: Anusha, L. S.; Feller, A.; Hirzberger, J.; Solanki, S. K.
Bibcode: 2014ASPC..489...83A
Altcode:
  We present the results of an analysis of small scale magnetic features
  in the quiet Sun, observed with the Sunrise balloon borne telescope. Our
  aim is to understand the contribution of different physical processes
  that drive the evolution of magnetic features in quiet regions of
  the photosphere. To this end, we study the rearrangement, addition,
  and removal of magnetic flux through splitting, merging, cancellation,
  and emergence of magnetic fields.

Title: Discriminant analysis of solar bright points and faculae
    II. Contrast and morphology analysis
Authors: Kobel, P.; Hirzberger, J.; Solanki, S. K.
Bibcode: 2014arXiv1410.5354K
Altcode:
  Taken at a high spatial resolution of 0.1 arcsec, Bright Points (BPs)
  are found to coexist with faculae in images and the latter are often
  resolved as adjacent striations. Understanding the properties of these
  different features is fundamental to carrying out proxy magnetometry. To
  shed light on the relationship between BPs and faculae, we studied
  them separately after the application of a classification method,
  developed and described in a previous paper) on active region images
  at various heliocentric angles. In this Paper, we explore different
  aspects of the photometric properties of BPs and faculae, namely
  their G-band contrast profiles, their peak contrast in G-band and
  continuum, as well as morphological parameters. We find that: (1)
  the width of the contrast profiles of the classified BPs and faculae
  are consistent with studies of disk center BPs at and limb faculae,
  which indirectly confirms the validity of our classification, (2) the
  profiles of limb faculae are limbward skewed on average, while near
  disk center they exhibit both centerward and limbward skewnesses due
  to the distribution of orientations of the faculae, (3) the relation
  between the peak contrasts of BPs and faculae and their apparent area
  discloses a trend reminiscent of magnetogram studies. The skewness
  of facular profiles provides a novel constraint for 3D MHD models of
  faculae. As suggested by the asymmetry and orientation of their contrast
  profiles, faculae near disk center could be induced by inclined fields,
  while apparent BPs near the limb seem to be in fact small faculae
  misidentified. The apparent area of BPs and faculae could be possibly
  exploited for proxy magnetometry.

Title: Modelling total solar irradiance since 1878 from simulated
    magnetograms
Authors: Dasi-Espuig, M.; Jiang, J.; Krivova, N. A.; Solanki, S. K.
Bibcode: 2014A&A...570A..23D
Altcode: 2014arXiv1409.1941D
  <BR /> Aims: We present a new model of total solar irradiance (TSI)
  based on magnetograms simulated with a surface flux transport model
  (SFTM) and the Spectral And Total Irradiance REconstructions (SATIRE)
  model. Our model provides daily maps of the distribution of the
  photospheric field and the TSI starting from 1878. <BR /> Methods:
  The modelling is done in two main steps. We first calculate the
  magnetic flux on the solar surface emerging in active and ephemeral
  regions. The evolution of the magnetic flux in active regions (sunspots
  and faculae) is computed using a surface flux transport model fed
  with the observed record of sunspot group areas and positions. The
  magnetic flux in ephemeral regions is treated separately using the
  concept of overlapping cycles. We then use a version of the SATIRE
  model to compute the TSI. The area coverage and the distribution of
  different magnetic features as a function of time, which are required by
  SATIRE, are extracted from the simulated magnetograms and the modelled
  ephemeral region magnetic flux. Previously computed intensity spectra
  of the various types of magnetic features are employed. <BR /> Results:
  Our model reproduces the PMOD composite of TSI measurements starting
  from 1978 at daily and rotational timescales more accurately than the
  previous version of the SATIRE model computing TSI over this period of
  time. The simulated magnetograms provide a more realistic representation
  of the evolution of the magnetic field on the photosphere and also
  allow us to make use of information on the spatial distribution
  of the magnetic fields before the times when observed magnetograms
  were available. We find that the secular increase in TSI since 1878
  is fairly stable to modifications of the treatment of the ephemeral
  region magnetic flux.

Title: Reconstruction of total and spectral solar irradiance from
    1974 to 2013 based on KPVT, SoHO/MDI, and SDO/HMI observations
Authors: Yeo, K. L.; Krivova, N. A.; Solanki, S. K.; Glassmeier, K. H.
Bibcode: 2014A&A...570A..85Y
Altcode: 2014arXiv1408.1229Y
  Context. Total and spectral solar irradiance are key parameters in the
  assessment of solar influence on changes in the Earth's climate. <BR />
  Aims: We present a reconstruction of daily solar irradiance obtained
  using the SATIRE-S model spanning 1974 to 2013 based on full-disc
  observations from the KPVT, SoHO/MDI, and SDO/HMI. <BR /> Methods:
  SATIRE-S ascribes variation in solar irradiance on timescales
  greater than a day to photospheric magnetism. The solar spectrum
  is reconstructed from the apparent surface coverage of bright
  magnetic features and sunspots in the daily data using the modelled
  intensity spectra of these magnetic structures. We cross-calibrated
  the various data sets, harmonizing the model input so as to yield a
  single consistent time series as the output. <BR /> Results: The model
  replicates 92% (R<SUP>2</SUP> = 0.916) of the variability in the PMOD
  TSI composite including the secular decline between the 1996 and 2008
  solar cycle minima. The model also reproduces most of the variability
  in observed Lyman-α irradiance and the Mg II index. The ultraviolet
  solar irradiance measurements from the UARS and SORCE missions are
  mutually consistent up to about 180 nm before they start to exhibit
  discrepant rotational and cyclical variability, indicative of unresolved
  instrumental effects. As a result, the agreement between model and
  measurement, while relatively good below 180 nm, starts to deteriorate
  above this wavelength. As with earlier similar investigations,
  the reconstruction cannot reproduce the overall trends in SORCE/SIM
  SSI. We argue, from the lack of clear solar cycle modulation in the
  SIM record and the inconsistency between the total flux recorded
  by the instrument and TSI, that unaccounted instrumental trends are
  present. <BR /> Conclusions: The daily solar irradiance time series
  is consistent with observations from multiple sources, demonstrating
  its validity and utility for climate models. It also provides further
  evidence that photospheric magnetism is the prime driver of variation
  in solar irradiance on timescales greater than a day.

Title: Nonlinear Force-free Field Modeling of the Solar Magnetic
    Carpet and Comparison with SDO/HMI and Sunrise/IMaX Observations
Authors: Chitta, L. P.; Kariyappa, R.; van Ballegooijen, A. A.;
   DeLuca, E. E.; Solanki, S. K.
Bibcode: 2014ApJ...793..112C
Altcode: 2014arXiv1408.0497C
  In the quiet solar photosphere, the mixed polarity fields form a
  magnetic carpet that continuously evolves due to dynamical interaction
  between the convective motions and magnetic field. This interplay is a
  viable source to heat the solar atmosphere. In this work, we used the
  line-of-sight (LOS) magnetograms obtained from the Helioseismic and
  Magnetic Imager on the Solar Dynamics Observatory, and the Imaging
  Magnetograph eXperiment instrument on the Sunrise balloon-borne
  observatory, as time-dependent lower boundary conditions, to study the
  evolution of the coronal magnetic field. We use a magneto-frictional
  relaxation method, including hyperdiffusion, to produce a time series
  of three-dimensional nonlinear force-free fields from a sequence
  of photospheric LOS magnetograms. Vertical flows are added up to a
  height of 0.7 Mm in the modeling to simulate the non-force-freeness
  at the photosphere-chromosphere layers. Among the derived quantities,
  we study the spatial and temporal variations of the energy dissipation
  rate and energy flux. Our results show that the energy deposited in
  the solar atmosphere is concentrated within 2 Mm of the photosphere and
  there is not sufficient energy flux at the base of the corona to cover
  radiative and conductive losses. Possible reasons and implications are
  discussed. Better observational constraints of the magnetic field in
  the chromosphere are crucial to understand the role of the magnetic
  carpet in coronal heating.

Title: Fast Solar Polarimeter: Description and First Results
Authors: Feller, A.; Iglesias, F. A.; Nagaraju, K.; Solanki, S. K.;
   Ihle, S.
Bibcode: 2014ASPC..489..271F
Altcode:
  We are developing a novel fast solar imaging polarimeter with an
  emphasis on significantly increased polarimetric accuracy and high
  spatial resolution. The instrument is based on a fast pnCCD sensor
  and shall work at frame rates of up to 400 fps, which suppresses
  spurious polarization signals induced by external disturbances such
  as atmospheric turbulence or jitter. The much higher polarimetric
  accuracy that can be achieved with the new instrument is in particular
  expected to extend studies of the enigmatic small-scale magnetic field
  in the quiet Sun, and of chromospheric magnetic fields. Here we will
  report on some key concepts of the polarimeter, and on first results
  obtained with an evaluation model at the spectrograph of the Vacuum
  Tower Telescope on Tenerife.

Title: Inclinations of small quiet-Sun magnetic features based on
    a new geometric approach
Authors: Jafarzadeh, S.; Solanki, S. K.; Lagg, A.; Bellot Rubio,
   L. R.; van Noort, M.; Feller, A.; Danilovic, S.
Bibcode: 2014A&A...569A.105J
Altcode: 2014arXiv1408.2443J
  Context. High levels of horizontal magnetic flux have been reported
  in the quiet-Sun internetwork, often based on Stokes profile
  inversions. <BR /> Aims: Here we introduce a new method for deducing
  the inclination of magnetic elements and use it to test magnetic field
  inclinations from inversions. <BR /> Methods: We determine accurate
  positions of a set of small, bright magnetic elements in high spatial
  resolution images sampling different photospheric heights obtained by
  the Sunrise balloon-borne solar observatory. Together with estimates
  of the formation heights of the employed spectral bands, these provide
  us with the inclinations of the magnetic features. We also compute
  the magnetic inclination angle of the same magnetic features from the
  inversion of simultaneously recorded Stokes parameters. <BR /> Results:
  Our new, geometric method returns nearly vertical fields (average
  inclination of around 14° with a relatively narrow distribution
  having a standard deviation of 6°). In strong contrast to this, the
  traditionally used inversions give almost horizontal fields (average
  inclination of 75 ± 8°) for the same small magnetic features,
  whose linearly polarised Stokes profiles are adversely affected by
  noise. We show that for such magnetic features inversions overestimate
  the flux in horizontal magnetic fields by an order of magnitude. <BR />
  Conclusions: The almost vertical field of bright magnetic features from
  our geometric method is clearly incompatible with the nearly horizontal
  magnetic fields obtained from the inversions. This indicates that the
  amount of magnetic flux in horizontal fields deduced from inversions is
  overestimated in the presence of weak Stokes signals, in particular if
  Stokes Q and U are close to or under the noise level. Inversions should
  be used with great caution when applied to data with no clear Stokes Q
  and no U signal. By combining the proposed method with inversions we are
  not just improving the inclination, but also the field strength. This
  technique allows us to analyse features that are not reliably treated
  by inversions, thus greatly extending our capability to study the
  complete magnetic field of the quiet Sun.

Title: Variability of Sun-like stars: reproducing observed photometric
    trends
Authors: Shapiro, A. I.; Solanki, S. K.; Krivova, N. A.; Schmutz,
   W. K.; Ball, W. T.; Knaack, R.; Rozanov, E. V.; Unruh, Y. C.
Bibcode: 2014A&A...569A..38S
Altcode: 2014arXiv1406.2383S
  Context. The Sun and stars with low magnetic activity levels become
  photometrically brighter when their activity increases. Magnetically
  more active stars display the opposite behavior and become fainter
  when their activity increases. <BR /> Aims: We reproduce the observed
  photometric trends in stellar variations with a model thattreats stars
  as hypothetical suns with coverage by magnetic features different from
  that of the Sun. <BR /> Methods: The model attributes the variability
  of stellar spectra to the imbalance between the contributions from
  different components of the solar atmosphere, such as dark starspots
  and bright faculae. A stellar spectrum is calculated from spectra
  of the individual components by weighting them with corresponding
  disk-area coverages. The latter are obtained by extrapolating
  the solar dependences of spot and facular disk-area coverages
  on chromospheric activity to stars with different levels of mean
  chromospheric activity. <BR /> Results: We find that the contribution
  by starspots to the variability increases faster with chromospheric
  activity than the facular contribution. This causes the transition from
  faculae-dominated variability and direct activity-brightness correlation
  to spot-dominated variability and inverse activity-brightness
  correlation with increasing chromospheric activity level. We show that
  the regime of the variability also depends on the angle between the
  stellar rotation axis and the line-of-sight and on the latitudinal
  distribution of active regions on the stellar surface. Our model
  can be used as a tool for extrapolating the observed photometric
  variability of the Sun to Sun-like stars at different activity levels,
  which makes a direct comparison between solar and stellar irradiance
  data possible. <P />Appendices are available in electronic form at <A
  href="http://www.aanda.org/10.1051/0004-6361/201323086/olm">http://www.aanda.org</A>

Title: Comparison of solar photospheric bright points between Sunrise
    observations and MHD simulations
Authors: Riethmüller, T. L.; Solanki, S. K.; Berdyugina, S. V.;
   Schüssler, M.; Martínez Pillet, V.; Feller, A.; Gandorfer, A.;
   Hirzberger, J.
Bibcode: 2014A&A...568A..13R
Altcode: 2014arXiv1406.1387R
  Bright points (BPs) in the solar photosphere are thought to be the
  radiative signatures (small-scale brightness enhancements) of magnetic
  elements described by slender flux tubes or sheets located in the darker
  intergranular lanes in the solar photosphere. They contribute to the
  ultraviolet (UV) flux variations over the solar cycle and hence may
  play a role in influencing the Earth's climate. Here we aim to obtain
  a better insight into their properties by combining high-resolution
  UV and spectro-polarimetric observations of BPs by the Sunrise
  Observatory with 3D compressible radiation magnetohydrodynamical
  (MHD) simulations. To this end, full spectral line syntheses are
  performed with the MHD data and a careful degradation is applied
  to take into account all relevant instrumental effects of the
  observations. In a first step it is demonstrated that the selected
  MHD simulations reproduce the measured distributions of intensity at
  multiple wavelengths, line-of-sight velocity, spectral line width,
  and polarization degree rather well. The simulated line width also
  displays the correct mean, but a scatter that is too small. In
  the second step, the properties of observed BPs are compared with
  synthetic ones. Again, these are found to match relatively well,
  except that the observations display a tail of large BPs with strong
  polarization signals (most likely network elements) not found in the
  simulations, possibly due to the small size of the simulation box. The
  higher spatial resolution of the simulations has a significant effect,
  leading to smaller and more numerous BPs. The observation that most BPs
  are weakly polarized is explained mainly by the spatial degradation,
  the stray light contamination, and the temperature sensitivity of the Fe
  i line at 5250.2 Å. Finally, given that the MHD simulations are highly
  consistent with the observations, we used the simulations to explore
  the properties of BPs further. The Stokes V asymmetries increase with
  the distance to the center of the mean BP in both observations and
  simulations, consistent with the classical picture of a production
  of the asymmetry in the canopy. This is the first time that this has
  been found also in the internetwork. More or less vertical kilogauss
  magnetic fields are found for 98% of the synthetic BPs underlining
  that basically every BP is associated with kilogauss fields. At the
  continuum formation height, the simulated BPs are on average 190 K
  hotter than the mean quiet Sun, the mean BP field strength is found to
  be 1750 G, and the mean inclination is 17°, supporting the physical
  flux-tube paradigm to describe BPs. On average, the synthetic BPs
  harbor downflows increasing with depth. The origin of these downflows
  is not yet understood very well and needs further investigation.

Title: Vigorous convection in a sunspot granular light bridge
Authors: Lagg, Andreas; Solanki, Sami K.; van Noort, Michiel;
   Danilovic, Sanja
Bibcode: 2014A&A...568A..60L
Altcode: 2014arXiv1407.1202L
  Context. Light bridges are the most prominent manifestation of
  convection in sunspots. The brightest representatives are granular
  light bridges composed of features that appear to be similar to
  granules. <BR /> Aims: An in-depth study of the convective motions,
  temperature stratification, and magnetic field vector in and around
  light bridge granules is presented with the aim of identifying
  similarities and differences to typical quiet-Sun granules. <BR />
  Methods: Spectropolarimetric data from the Hinode Solar Optical
  Telescope were analyzed using a spatially coupled inversion technique
  to retrieve the stratified atmospheric parameters of light bridge and
  quiet-Sun granules. <BR /> Results: Central hot upflows surrounded by
  cooler fast downflows reaching 10 km s<SUP>-1</SUP> clearly establish
  the convective nature of the light bridge granules. The inner part
  of these granules in the near surface layers is field free and is
  covered by a cusp-like magnetic field configuration. We observe
  hints of field reversals at the location of the fast downflows. The
  quiet-Sun granules in the vicinity of the sunspot are covered by a
  low-lying canopy field extending radially outward from the spot. <BR
  /> Conclusions: The similarities between quiet-Sun and light bridge
  granules point to the deep anchoring of granular light bridges in
  the underlying convection zone. The fast, supersonic downflows are
  most likely a result of a combination of invigorated convection
  in the light bridge granule due to radiative cooling into the
  neighboring umbra and the fact that we sample deeper layers, since the
  downflows are immediately adjacent to the slanted walls of the Wilson
  depression. <P />The two movies are available in electronic form at <A
  href="http://www.aanda.org/10.1051/0004-6361/201424071/olm">http://www.aanda.org</A>

Title: Scattered Lyman-α radiation of comet 2012/S1 (ISON) observed
    by SUMER/SOHO
Authors: Curdt, W.; Boehnhardt, H.; Vincent, J. -B.; Solanki, S. K.;
   Schühle, U.; Teriaca, L.
Bibcode: 2014A&A...567L...1C
Altcode: 2014arXiv1406.4343C
  During its sungrazing perihelion passage, comet ISON appeared in
  the field of view of the SUMER spectrometer and allowed unique
  observations at far-ultraviolet wavelengths with high spatial and
  temporal resolution. We report results of these observations completed
  on November 28, 2013, when the comet was only 2.82 R<SUB>ʘ</SUB>
  away from the Sun. Our data show the arrow-shaped dust tail in Ly-α
  emission trailing behind the predicted position of the nucleus, but
  offset from the trajectory. We interpret the emission as sunlight
  that is scattered at μm-sized dust particles. We modeled the dust
  emission and dynamics to reproduce the appearance of the tail. We
  were unable to detect any signature of cometary gas or plasma around
  the expected position of the nucleus and conclude that the outgassing
  processes must have stopped before the observation started. Moreover,
  the model we used to reproduce the observed dust tail needs a sharp
  fall-off of the dust production hours before perihelion transit. We
  compare the radiances of the disk and the dust tail for an estimate
  of the dust column density and tail mass.

Title: The History of a Quiet-Sun Magnetic Element Revealed by
    IMaX/SUNRISE
Authors: Requerey, Iker S.; Del Toro Iniesta, Jose Carlos; Bellot
   Rubio, Luis R.; Bonet, José A.; Martínez Pillet, Valentín; Solanki,
   Sami K.; Schmidt, Wolfgang
Bibcode: 2014ApJ...789....6R
Altcode: 2014arXiv1405.2837R
  Isolated flux tubes are considered to be fundamental magnetic building
  blocks of the solar photosphere. Their formation is usually attributed
  to the concentration of magnetic field to kG strengths by the convective
  collapse mechanism. However, the small size of the magnetic elements in
  quiet-Sun areas has prevented this scenario from being studied in fully
  resolved structures. Here, we report on the formation and subsequent
  evolution of one such photospheric magnetic flux tube, observed in
  the quiet Sun with unprecedented spatial resolution (0.''15-0.''18)
  and high temporal cadence (33 s). The observations were acquired by
  the Imaging Magnetograph eXperiment on board the SUNRISE balloon-borne
  solar observatory. The equipartition field strength magnetic element
  is the result of the merging of several same polarity magnetic flux
  patches, including a footpoint of a previously emerged loop. The
  magnetic structure is then further intensified to kG field strengths
  by convective collapse. The fine structure found within the flux
  concentration reveals that the scenario is more complex than can be
  described by a thin flux tube model with bright points and downflow
  plumes being established near the edges of the kG magnetic feature. We
  also observe a daisy-like alignment of surrounding granules and a
  long-lived inflow toward the magnetic feature. After a subsequent
  weakening process, the field is again intensified to kG strengths. The
  area of the magnetic feature is seen to change in anti-phase with the
  field strength, while the brightness of the bright points and the speed
  of the downflows varies in phase. We also find a relation between the
  brightness of the bright point and the presence of upflows within it.

Title: Scattered Lyman-alpha radiation of comet 2012/S1 (ISON)
    observed by SUMER/SOHO
Authors: Curdt, W.; Boehnhardt, H.; Germerott, D.; Schuehle, U.;
   Solanki, S.; Teriaca, L.; Vincent, J.
Bibcode: 2014acm..conf..119C
Altcode:
  During its recent perihelion passage, comet ISON came so close to
  the Sun that it appeared in the field of view (FOV) of the SUMER
  spectrometer on SOHO and allowed unique observations at far-UV
  wavelengths with high spatial and temporal resolution. We report results
  of these observations completed during the comet's encounter with the
  Sun on November 28.75, 2013. Our data show the dust tail trailing behind
  the predicted position of the nucleus seen in Lyman-alpha emission
  as light from the solar disk that is scattered by micron-sized dust
  particles. The arrow-shaped tail is offset from the trajectory and not
  aligned with it. We model the dust emission and dynamics to reproduce
  the appearance of the tail. We could not detect any signature of
  cometary gas or plasma around the expected position of the nucleus
  and conclude that the out-gassing processes must have stopped before
  the comet entered our FOV. Also the model we used to reproduce the
  observed dust tail needs a sharp fall-off of the dust production hours
  before perihelion. We compare the radiance of the dust tail to the
  Lyman-alpha emission of the disk for an estimate of the dust column
  density. After observing 18 years mostly solar targets, this was the
  first time that SUMER completed spectroscopic observations of a comet.

Title: Search for Solar Axions by the CERN Axion Solar Telescope
with He3 Buffer Gas: Closing the Hot Dark Matter Gap
Authors: Arik, M.; Aune, S.; Barth, K.; Belov, A.; Borghi, S.;
   Bräuninger, H.; Cantatore, G.; Carmona, J. M.; Cetin, S. A.; Collar,
   J. I.; Da Riva, E.; Dafni, T.; Davenport, M.; Eleftheriadis, C.;
   Elias, N.; Fanourakis, G.; Ferrer-Ribas, E.; Friedrich, P.; Galán,
   J.; García, J. A.; Gardikiotis, A.; Garza, J. G.; Gazis, E. N.;
   Geralis, T.; Georgiopoulou, E.; Giomataris, I.; Gninenko, S.; Gómez,
   H.; Gómez Marzoa, M.; Gruber, E.; Guthörl, T.; Hartmann, R.; Hauf,
   S.; Haug, F.; Hasinoff, M. D.; Hoffmann, D. H. H.; Iguaz, F. J.;
   Irastorza, I. G.; Jacoby, J.; Jakovčić, K.; Karuza, M.; Königsmann,
   K.; Kotthaus, R.; Krčmar, M.; Kuster, M.; Lakić, B.; Lang, P. M.;
   Laurent, J. M.; Liolios, A.; Ljubičić, A.; Luzón, G.; Neff, S.;
   Niinikoski, T.; Nordt, A.; Papaevangelou, T.; Pivovaroff, M. J.;
   Raffelt, G.; Riege, H.; Rodríguez, A.; Rosu, M.; Ruz, J.; Savvidis,
   I.; Shilon, I.; Silva, P. S.; Solanki, S. K.; Stewart, L.; Tomás,
   A.; Tsagri, M.; van Bibber, K.; Vafeiadis, T.; Villar, J.; Vogel,
   J. K.; Yildiz, S. C.; Zioutas, K.; CAST Collaboration
Bibcode: 2014PhRvL.112i1302A
Altcode: 2013arXiv1307.1985A
  The CERN Axion Solar Telescope has finished its search for
  solar axions with He3 buffer gas, covering the search range
  0.64 eV≲m<SUB>a</SUB>≲1.17 eV. This closes the gap to the
  cosmological hot dark matter limit and actually overlaps with
  it. From the absence of excess x rays when the magnet was pointing
  to the Sun we set a typical upper limit on the axion-photon coupling
  of g<SUB>aγ</SUB>≲3.3×<SUP>10-10</SUP> GeV-<SUP>1</SUP> at 95%
  C.L., with the exact value depending on the pressure setting. Future
  direct solar axion searches will focus on increasing the sensitivity
  to smaller values of g<SUB>aγ</SUB>, for example by the currently
  discussed next generation helioscope International AXion Observatory.

Title: Comparison between Mg II k and Ca II H Images Recorded by
    SUNRISE/SuFI
Authors: Danilovic, S.; Hirzberger, J.; Riethmüller, T. L.; Solanki,
   S. K.; Barthol, P.; Berkefeld, T.; Gandorfer, A.; Gizon, L.; Knölker,
   M.; Schmidt, W.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.
Bibcode: 2014ApJ...784...20D
Altcode:
  We present a comparison of high-resolution images of the solar surface
  taken in the Mg II k and Ca II H channels of the Filter Imager on the
  balloon-borne solar observatory SUNRISE. The Mg and Ca lines are sampled
  with 0.48 nm and 0.11 nm wide filters, respectively. The two channels
  show remarkable qualitative and quantitative similarities in the quiet
  Sun, in an active region plage and during a small flare. However, the Mg
  filtergrams display 1.4-1.7 times higher intensity contrast and appear
  more smeared and smoothed in the quiet Sun. In addition, the fibrils
  in a plage are wider. Although the exposure time is 100 times longer
  for Mg images, the evidence suggests that these differences cannot be
  explained only with instrumental effects or the evolution of the solar
  scene. The differences at least partially arise because of different
  line-formation heights, the stronger response of Mg k emission peaks
  to the higher temperatures, and the larger height range sampled by
  the broad Mg filter used here. This is evidently manifested during
  the flare when a surge in Mg evolves differently than in Ca.

Title: Migration of Ca II H bright points in the internetwork
Authors: Jafarzadeh, S.; Cameron, R. H.; Solanki, S. K.; Pietarila,
   A.; Feller, A.; Lagg, A.; Gandorfer, A.
Bibcode: 2014A&A...563A.101J
Altcode: 2014arXiv1401.7522J
  Context. The migration of magnetic bright point-like features (MBP)
  in the lower solar atmosphere reflects the dispersal of magnetic
  flux as well as the horizontal flows of the atmospheric layer they
  are embedded in. <BR /> Aims: We analyse trajectories of the proper
  motion of intrinsically magnetic, isolated internetwork Ca ii H MBPs
  (mean lifetime 461 ± 9 s) to obtain their diffusivity behaviour. <BR
  /> Methods: We use seeing-free high spatial and temporal resolution
  image sequences of quiet-Sun, disc-centre observations obtained in
  the Ca ii H 3968 Å passband of the Sunrise Filter Imager (SuFI)
  onboard the Sunrise balloon-borne solar observatory. Small MBPs in
  the internetwork are automatically tracked. The trajectory of each
  MBP is then calculated and described by a diffusion index (γ) and
  a diffusion coefficient (D). We also explore the distribution of the
  diffusion indices with the help of a Monte Carlo simulation. <BR />
  Results: We find γ = 1.69 ± 0.08 and D = 257 ± 32 km<SUP>2</SUP>
  s<SUP>-1</SUP> averaged over all MBPs. Trajectories of most MBPs are
  classified as super-diffusive, i.e. γ &gt; 1, with the determined γ
  being the largest obtained so far to our knowledge. A direct correlation
  between D and timescale (τ) determined from trajectories of all MBPs is
  also obtained. We discuss a simple scenario to explain the diffusivity
  of the observed, relatively short-lived MBPs while they migrate within
  a small area in a supergranule (i.e. an internetwork area). We show
  that the scatter in the γ values obtained for individual MBPs is due
  to their limited lifetimes. <BR /> Conclusions: The super-diffusive
  MBPs can be described as random walkers (due to granular evolution and
  intergranular turbulence) superposed on a large systematic (background)
  velocity, caused by granular, mesogranular, and supergranular flows.

Title: Magnetic structure of an activated filament in a flaring
    active region
Authors: Sasso, C.; Lagg, A.; Solanki, S. K.
Bibcode: 2014A&A...561A..98S
Altcode: 2013arXiv1312.2781S
  <BR /> Aims: While the magnetic field in quiescent prominences has
  been widely investigated, less is known about the field in activated
  prominences. We report observational results on the magnetic field
  structure of an activated filament in a flaring active region. In
  particular, we studied its magnetic structure and line-of-sight flows
  during its early activated phase, shortly before it displayed signs
  of rotation. <BR /> Methods: We inverted the Stokes profiles of the
  chromospheric He i 10 830 Å triplet and the photospheric Si i 10 827
  Å line observed in this filament by the Vacuum Tower Telescope on
  Tenerife. Using these inversion results, we present and interpret the
  first maps of the velocity and magnetic field obtained in an activated
  filament, both in the photosphere and the chromosphere. <BR /> Results:
  Up to five different magnetic components are found in the chromospheric
  layers of the filament, while outside the filament a single component is
  sufficient to reproduce the observations. Magnetic components displaying
  an upflow are preferentially located towards the centre of the filament,
  while the downflows are concentrated along its periphery. Moreover,
  the upflowing gas is associated with an opposite-polarity magnetic
  configuration with respect to the photosphere, while the downflowing gas
  is associated with a same-polarity configuration. <BR /> Conclusions:
  The activated filament has a very complex structure. Nonetheless,
  it is compatible with a flux rope, albeit a distorted one, in
  the normal configuration. The observations are best explained
  by a rising flux rope in which part of the filament material is
  still stably stored (upflowing material, rising with the field),
  while the rest is no longer stably stored and flows down along the
  field lines. <P />The movie is available in electronic form at <A
  href="http://www.aanda.org/10.1051/0004-6361/201322481/olm">http://www.aanda.org</A>

Title: The chromosphere above sunspots at millimeter wavelengths
Authors: Loukitcheva, M.; Solanki, S. K.; White, S. M.
Bibcode: 2014A&A...561A.133L
Altcode: 2014arXiv1403.3436L
  <BR /> Aims: The aim of this paper is to demonstrate that millimeter
  wave data can be used to distinguish between various atmospheric models
  of sunspots, whose temperature structure in the upper photosphere
  and chromosphere has been the source of some controversy. <BR />
  Methods: We use observations of the temperature contrast (relative
  to the quiet Sun) above a sunspot umbra at 3.5 mm obtained with
  the Berkeley-Illinois-Maryland Array (BIMA), complemented by submm
  observations from Lindsey &amp; Kopp (1995) and 2 cm observations
  with the Very Large Array. These are compared with the umbral contrast
  calculated from various atmospheric models of sunspots. <BR /> Results:
  Current mm and submm observational data suggest that the brightness
  observed at these wavelengths is low compared to the most widely used
  sunspot models. These data impose strong constraints on the temperature
  and density stratifications of the sunspot umbral atmosphere, in
  particular on the location and depth of the temperature minimum and the
  location of the transition region. <BR /> Conclusions: A successful
  model that is in agreement with millimeter umbral brightness should
  have an extended and deep temperature minimum (below 3000 K). Better
  spatial resolution as well as better wavelength coverage are needed
  for a more complete determination of the chromospheric temperature
  stratification above sunspot umbrae.

Title: Time evolution of a single, quiet-Sun magnetic structure
Authors: Requerey, Iker S.; Bonet, José Antonio; Solanki, Sami K.;
   Bellot Rubio, L. R.; Del Toro Iniesta, Jose Carlos
Bibcode: 2014cosp...40E2828R
Altcode:
  Isolated flux tubes are considered to be fundamental magnetic building
  blocks of the solar photosphere. Their formation is usually attributed
  to the concentration of magnetic field to kG strengths by the convective
  instability mechanism. However, the small size of the magnetic elements
  in quiet-Sun areas has prevented this scenario from being studied
  in fully resolved structures. Here we report on the formation and
  subsequent evolution of a photospheric magnetic flux tube, observed
  in the quiet Sun with unprecedented spatial resolution (0. ('') 15 -
  0. ('') 18) and high temporal cadence (33 s). The observations were
  acquired by the Imaging Magnetograph Experiment (IMaX) aboard the
  textsc{Sunrise} balloon-borne solar observatory. The equipartition
  field strength magnetic element is reached from the merging of
  several magnetic flux patches in a mesogranule-sized sink. The
  magnetic structure is then further intensified to kG field strengths by
  convective collapse and granular compression. The fine structure found
  within the flux concentration reveal that the scenario is more complex
  than a canonical flux tube model. After a subsequent weakening process,
  the field is further intensified to kG strengths. Seen as a whole, the
  evolution of the magnetic structure is compatible with oscillations in
  all basic physical quantities. A discussion on whether this evolution
  fits to the current theoretical descriptions is also presented.

Title: Point spread function of SDO/HMI and the effects of stray
    light correction on the apparent properties of solar surface phenomena
Authors: Yeo, K. L.; Feller, A.; Solanki, S. K.; Couvidat, S.;
   Danilovic, S.; Krivova, N. A.
Bibcode: 2014A&A...561A..22Y
Altcode: 2013arXiv1310.4972Y
  <BR /> Aims: We present a point spread function (PSF) for the
  Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics
  Observatory (SDO) and discuss the effects of its removal on the
  apparent properties of solar surface phenomena in HMI data. <BR />
  Methods: The PSF was retrieved from observations of Venus in transit
  by matching it to the convolution of a model of the Venusian disc and
  solar background with a guess PSF. We described the PSF as the sum of
  five Gaussian functions, the amplitudes of which vary sinusoidally with
  azimuth. This relatively complex functional form was required by the
  data. Observations recorded near in time to the transit of Venus were
  corrected for instrumental scattered light by the deconvolution with the
  PSF. We also examined the variation in the shape of the solar aureole in
  daily data, as an indication of PSF changes over time. <BR /> Results:
  Granulation contrast in restored HMI data is greatly enhanced relative
  to the original data and exhibit reasonable agreement with numerical
  simulations. Image restoration enhanced the apparent intensity and
  pixel averaged magnetic field strength of photospheric magnetic features
  significantly. For small-scale magnetic features, restoration enhanced
  intensity contrast in the continuum and core of the Fe I 6173 Å line
  by a factor of 1.3, and the magnetogram signal by a factor of 1.7. For
  sunspots and pores, the enhancement varied strongly within and between
  features, being more acute for smaller features. Magnetic features are
  also rendered smaller, as signal smeared onto the surrounding quiet
  Sun is recovered. Image restoration increased the apparent amount of
  magnetic flux above the noise floor by a factor of about 1.2, most
  of the gain coming from the quiet Sun. Line-of-sight velocity due to
  granulation and supergranulation is enhanced by a factor of 1.4 to 2.1,
  depending on position on the solar disc. The shape of the solar aureole
  varied, with time and between the two CCDs. There are also indications
  that the PSF varies across the FOV. However, all these variations were
  found to be relatively small, such that a single PSF can be applied to
  HMI data from both CCDs, over the period examined without introducing
  significant error. <BR /> Conclusions: Restoring HMI observations
  with the PSF presented here returns a reasonable estimate of the stray
  light-free intensity contrast. Image restoration affects the measured
  radiant, magnetic and dynamic properties of solar surface phenomena
  sufficiently to significantly impact interpretation.

Title: Reconstructions of solar irradiance on centennial time scales
Authors: Krivova, Natalie; Solanki, Sami K.; Dasi Espuig, Maria;
   Kok Leng, Yeo
Bibcode: 2014cosp...40E1664K
Altcode:
  Solar irradiance is the main external source of energy to Earth's
  climate system. The record of direct measurements covering less than 40
  years is too short to study solar influence on Earth's climate, which
  calls for reconstructions of solar irradiance into the past with the
  help of appropriate models. An obvious requirement to a competitive
  model is its ability to reproduce observed irradiance changes, and a
  successful example of such a model is presented by the SATIRE family of
  models. As most state-of-the-art models, SATIRE assumes that irradiance
  changes on time scales longer than approximately a day are caused by
  the evolving distribution of dark and bright magnetic features on the
  solar surface. The surface coverage by such features as a function of
  time is derived from solar observations. The choice of these depends
  on the time scale in question. Most accurate is the version of the
  model that employs full-disc spatially-resolved solar magnetograms and
  reproduces over 90% of the measured irradiance variation, including
  the overall decreasing trend in the total solar irradiance over
  the last four cycles. Since such magnetograms are only available
  for about four decades, reconstructions on time scales of centuries
  have to rely on disc-integrated proxies of solar magnetic activity,
  such as sunspot areas and numbers. Employing a surface flux transport
  model and sunspot observations as input, we have being able to produce
  synthetic magnetograms since 1700. This improves the temporal resolution
  of the irradiance reconstructions on centennial time scales. The most
  critical aspect of such reconstructions remains the uncertainty in
  the magnitude of the secular change.

Title: Analysis of magnetic fields in a plage region using a spatially
    coupled 2D inversion technique
Authors: Buehler, David; Lagg, Andreas; Solanki, Sami K.; Van Noort,
   Michiel
Bibcode: 2014cosp...40E.427B
Altcode:
  The properties of magnetic features (MFCs) within a plage region
  in the vicinity of a sunspot were investigated at high spatial
  resolution. Stokes spectra of the 630nm line pair recorded by the
  spectropolarimeter aboard Hinode were inverted using an extended
  version of the SPINOR code. The code preformed a spatially coupled
  inversion of the Stokes spectra using three log(tau) nodes in optical
  depth. No magnetic filling factors was employed. The analysis of the
  inversion results reveals that the MFCs have typical field strengths
  of 1500G at log(tau)=-0.9 and inclinations between 10-15 degrees in
  all three log(tau) nodes. The MFCs expand by forming magnetic canopies
  composed of weaker and more inclined magnetic fields. The expansion of
  the magnetic field and temperature stratification of MFCs with optical
  depth is in good agreement with a thin flux tube model. Whilst the gas
  inside magnetic flux concentrations is typically at rest, the majority
  of MFCs were surrounded by a ring of downflows with an average value
  of 2.5km/s at log(tau)=0. The ring gradually shifts outwards following
  the expansion of the MFC. Within the downflow rings of MFCs small
  magnetic patches of opposite polarity to that of the main MFC were
  identified, which are predominantly situated beneath the canopy of
  its main MFC. We found evidence for a strong broadening of the Stokes
  profiles within MFCs and their surrounding downflow rings (expressed
  by a microturbulence in the inversion). This indicates the presence
  of strong unresolved velocities.

Title: Total solar irradiance reconstruction since 1700 using a flux
    transport model
Authors: Dasi Espuig, Maria; Krivova, Natalie; Solanki, Sami K.;
   Jiang, Jie
Bibcode: 2014cosp...40E.634D
Altcode:
  Reconstructions of solar irradiance into the past are crucial for
  studies of solar influence on climate. Models based on the assumption
  that irradiance changes are caused by the evolution of the photospheric
  magnetic fields have been most successful in reproducing the measured
  irradiance variations. Daily magnetograms, such as those from MDI and
  HMI, provide the most detailed information on the changing distribution
  of the photospheric magnetic fields. Since such magnetograms are
  only available from 1974, we used a surface flux transport model to
  describe the evolution of the magnetic fields on the solar surface
  due to the effects of differential rotation, meridional circulation,
  and turbulent diffusivity, before 1974. In this model, the sources of
  magnetic flux are the active regions, which are introduced based on
  sunspot group areas, positions, and tilt angles. The RGO record is,
  however, only available since 1874. Here we present a model of solar
  irradiance since 1700, which is based on a semi-synthetic sunspot
  record. The semi-synthetic record was obtained using statistical
  relationships between sunspot group properties (areas, positions,
  tilt angles) derived from the RGO record on one hand, and the cycle
  strength and phase derived from the sunspot group number (Rg) on the
  other. These relationships were employed to produce daily records
  of sunspot group positions, areas, and tilt angles before 1874. The
  semi-synthetic records were fed into the surface flux transport model
  to simulate daily magnetograms since 1700. By combining the simulated
  magnetograms with a SATIRE-type model, we then reconstructed total
  solar irradiance since 1700.

Title: Sunrise Mission Highlights
Authors: Riethmüller, T.; Solanki, S. K.; Sunrise Team
Bibcode: 2014frap.confE..34R
Altcode: 2014PoS...237E..34R
  No abstract at ADS

Title: Fast Solar Polarimeter: First Light Results
Authors: Krishnappa, N.; Feller, A.; Iglesia, F. A.; Solanki, S.
Bibcode: 2013AGUFMSM53A2213K
Altcode:
  Accurate measurements of magnetic fields on the Sun are crucial
  to understand various physical processes that take place in the
  solar atmosphere such as solar eruptions, coronal heating, solar
  wind acceleration, etc. The Fast Solar Polarimeter (FSP) is a new
  instrument that is being developed to probe magnetic fields on the
  Sun. One of the main goals of this polarimeter is to carry out high
  precision spectropolarimetric observations with spatial resolution
  close to the telescope diffraction limit. The polarimeter is based
  on pnCCD technology with split frame transfer and simultaneous
  multi-channel readout, resulting in frame rate upto 1 kHz. The FSP
  prototype instrument uses a small format pnCCD of 264x264 pixels
  which has been developed by PNSensor and by the semiconductor lab of
  the Max Planck Society. The polarization modulator is based on two
  ferro-electric liquid crystals (FLCs) interlaced between two static
  retarders. The first solar observations have been carried out with this
  prototype during May-June, 2013 at German Vacuum Tower Telescope (VTT)
  on Tenerife, Canary Islands, Spain. Here we present the instrument
  performance assessments and the first results on the magnetic field
  measurements. Further, we briefly discuss about the next phase of FSP
  which will be a dual beam system with 1k x 1k CCDs.

Title: Three-dimensional non-LTE radiative transfer effects in Fe
    i lines. II. Line formation in 3D radiation hydrodynamic simulations
Authors: Holzreuter, R.; Solanki, S. K.
Bibcode: 2013A&A...558A..20H
Altcode: 2013arXiv1308.2490H
  Here we investigate the effects of horizontal radiative transfer
  (RT) in combination with non-local thermodynamic equilibrum (NLTE)
  on important diagnostic iron lines in a realistic atmosphere. Using
  a snapshot of a 3D radiation-hydrodynamic (HD) simulation and a
  multilevel iron atom, we computed widely used Fe i line profiles at
  three different levels of approximation of the RT (3D NLTE, 1D NLTE,
  LTE). By comparing the resulting line profiles and the circumstances of
  their formation, we gain new insight into the importance of horizontal
  RT. We find that the influence of horizontal RT is of the same order
  of magnitude as that of NLTE, although spatially more localized. Also,
  depending on the temperature of the surroundings, horizontal RT is
  found to either weaken or strengthen spectral lines. Line depths
  and equivalent width may differ by up to 20% from the corresponding
  LTE value if 3D RT is applied. Residual intensity contrasts in LTE
  are found to be larger than those in 3D NLTE by up to a factor of
  two. When compared to 1D NLTE, we find that horizontal RT weakens the
  contrast by up to 30% almost independently of the angle of line of
  sight. While the center-to-limb variation (CLV) of the 1D and 3D NLTE
  contrasts have a similar form, the LTE contrast CLV shows a different
  run. Determination of temperatures by 1D NLTE inversions of spatially
  resolved observations may produce errors of up to 200 K if one neglects
  3D RT. We find a linear correlation between the intensity difference
  of 1D and 3D NLTE and a simple estimate of the temperature in the
  horizontal environment of the line formation region. This correlation
  could be used to coarsely correct inversions done in 1D NLTE for some
  of the effects of horizontal RT. Horizontal RT is less important if
  one considers spatially averaged line profiles because local line
  strengthening and weakening occur with similar frequency in our HD
  atmosphere. Thus, the iron abundance is underestimated by 0.012 dex if
  calculated using 1D NLTE RT. Since effects of horizontal RT are greatest
  for spatially resolved quantities, the use of 3D RT is particularly
  important for interpreting high spatial resolution observations.

Title: Temporal relation between quiet-Sun transverse fields and
    the strong flows detected by IMaX/SUNRISE
Authors: Quintero Noda, C.; Martínez Pillet, V.; Borrero, J. M.;
   Solanki, S. K.
Bibcode: 2013A&A...558A..30Q
Altcode: 2013arXiv1309.0627Q
  Context. Localized strongly Doppler-shifted Stokes V signals were
  detected by IMaX/SUNRISE. These signals are related to newly emerged
  magnetic loops that are observed as linear polarization features. <BR
  /> Aims: We aim to set constraints on the physical nature and causes
  of these highly Doppler-shifted signals. In particular, the temporal
  relation between the appearance of transverse fields and the strong
  Doppler shifts is analyzed in some detail. <BR /> Methods: We calculated
  the time difference between the appearance of the strong flows and the
  linear polarization. We also obtained the distances from the center
  of various features to the nearest neutral lines and whether they
  overlap or not. These distances were compared with those obtained from
  randomly distributed points on observed magnetograms. Various cases of
  strong flows are described in some detail. <BR /> Results: The linear
  polarization signals precede the appearance of the strong flows by on
  average 84 ± 11 s. The strongly Doppler-shifted signals are closer
  (0.″19) to magnetic neutral lines than randomly distributed points
  (0.″5). Eighty percent of the strongly Doppler-shifted signals are
  close to a neutral line that is located between the emerging field and
  pre-existing fields. That the remaining 20% do not show a close-by
  pre-existing field could be explained by a lack of sensitivity or
  an unfavorable geometry of the pre-existing field, for instance, a
  canopy-like structure. <BR /> Conclusions: Transverse fields occurred
  before the observation of the strong Doppler shifts. The process is
  most naturally explained as the emergence of a granular-scale loop
  that first gives rise to the linear polarization signals, interacts
  with pre-existing fields (generating new neutral line configurations),
  and produces the observed strong flows. This explanation is indicative
  of frequent small-scale reconnection events in the quiet Sun.

Title: First High-resolution Images of the Sun in the 2796 Å Mg II
    k Line
Authors: Riethmüller, T. L.; Solanki, S. K.; Hirzberger, J.;
   Danilovic, S.; Barthol, P.; Berkefeld, T.; Gandorfer, A.; Gizon, L.;
   Knölker, M.; Schmidt, W.; Del Toro Iniesta, J. C.
Bibcode: 2013ApJ...776L..13R
Altcode: 2013arXiv1309.5213R
  We present the first high-resolution solar images in the Mg II k 2796
  Å line. The images, taken through a 4.8 Å broad interference filter,
  were obtained during the second science flight of Sunrise in 2013 June
  by the Sunrise Filter Imager (SuFI) instrument. The Mg II k images
  display structures that look qualitatively very similar to images taken
  in the core of Ca II H. The Mg II images exhibit reversed granulation
  (or shock waves) in the internetwork regions of the quiet Sun, at
  intensity contrasts that are similar to those found in Ca II H. Very
  prominent in Mg II are bright points, both in the quiet Sun and in plage
  regions, particularly near the disk center. These are much brighter than
  at other wavelengths sampled at similar resolution. Furthermore, Mg II k
  images also show fibril structures associated with plage regions. Again,
  the fibrils are similar to those seen in Ca II H images, but tend to
  be more pronounced, particularly in weak plage.

Title: Peripheral downflows in sunspot penumbrae
Authors: van Noort, M.; Lagg, A.; Tiwari, S. K.; Solanki, S. K.
Bibcode: 2013A&A...557A..24V
Altcode: 2013arXiv1308.0466V
  Context. Sunspot penumbrae show high-velocity patches along
  the periphery. <BR /> Aims: The high-velocity downflow patches
  are believed to be the return channels of the Evershed flow. We
  aim to investigate their structure in detail using Hinode SOT/SP
  observations. <BR /> Methods: We employ Fourier interpolation in
  combination with spatially coupled height dependent LTE inversions
  of Stokes profiles to produce high-resolution, height-dependent maps
  of atmospheric parameters of these downflows and investigate their
  properties. <BR /> Results: High-speed downflows are observed over
  a wide range of viewing angles. They have supersonic line-of-sight
  velocities, some in excess of 20 km s<SUP>-1</SUP>, and very high
  magnetic field strengths, reaching values of over 7 kG. A relation
  between the downflow velocities and the magnetic field strength is
  found, in good agreement with MHD simulations. <BR /> Conclusions:
  The coupled inversion at high resolution allows for the accurate
  determination of small-scale structures. The recovered atmospheric
  structure indicates that regions with very high downflow velocities
  contain some of the strongest magnetic fields that have ever been
  measured on the Sun. <P />Two movies are available in electronic form
  at <A href="http://www.aanda.org">http://www.aanda.org</A>

Title: Structure of sunspot penumbral filaments: a remarkable
    uniformity of properties
Authors: Tiwari, Sanjiv Kumar; van Noort, Michiel; Lagg, Andreas;
   Solanki, Sami K.
Bibcode: 2013A&A...557A..25T
Altcode: 2013arXiv1307.3668T
  Context. The sunspot penumbra comprises numerous thin, radially
  elongated filaments that are central for heat transport within
  the penumbra, but whose structure is still not clear. <BR /> Aims:
  We aim to investigate the fine-scale structure of these penumbral
  filaments. <BR /> Methods: We perform a depth-dependent inversion of
  spectropolarimetric data of a sunspot very close to solar disk center
  obtained by Solar Optical Telescope/Spectropolarimeter onboard the
  Hinode spacecraft. We have used a recently developed, spatially coupled
  2D inversion scheme, which allows us to analyze the fine structure
  of individual penumbral filaments up to the diffraction limit of
  the telescope. <BR /> Results: Filaments of different sizes in all
  parts of the penumbra display very similar magnetic field strengths,
  inclinations, and velocity patterns. The temperature structure is also
  similar, although the filaments in the inner penumbra have cooler
  tails than those in the outer penumbra. The similarities allowed
  us to average all these filaments and to subsequently extract the
  physical properties common to all of them. This average filament
  shows upflows associated with an upward-pointing field at its inner,
  umbral end (head) and along its axis, as well as downflows along the
  lateral edge and strong downflows in the outer end (tail) associated
  with a nearly vertical, strong, and downward-pointing field. The
  upflowing plasma is significantly, i.e., up to 800 K, hotter than the
  downflowing plasma. The hot, tear-shaped head of the averaged filament
  can be associated with a penumbral grain. The central part of the
  filament shows nearly horizontal fields with strengths in the range
  of 1 kG. The field above the filament converges, whereas a diverging
  trend is seen in the deepest layers near the head of the filament. The
  fluctuations in the physical parameters along and across the filament
  increase rapidly with depth. <BR /> Conclusions: We put forward a
  unified observational picture of a sunspot penumbral filament. It
  is consistent with such a filament being a magneto-convective cell,
  in line with recent magnetohydrodynamic simulations. The uniformity
  of its properties over the penumbra sets constraints on penumbral
  models and simulations. The complex and inhomogeneous structure of the
  filament provides a natural explanation for a number of long-running
  controversies in the literature.

Title: Solar Irradiance Variability and Climate
Authors: Solanki, Sami K.; Krivova, Natalie A.; Haigh, Joanna D.
Bibcode: 2013ARA&A..51..311S
Altcode: 2013arXiv1306.2770S
  The brightness of the Sun varies on all timescales on which it has been
  observed, and there is increasing evidence that this has an influence
  on climate. The amplitudes of such variations depend on the wavelength
  and possibly the timescale. Although many aspects of this variability
  are well established, the exact magnitude of secular variations (going
  beyond a solar cycle) and the spectral dependence of variations are
  under discussion. The main drivers of solar variability are thought
  to be magnetic features at the solar surface. The climate response
  can be, on a global scale, largely accounted for by simple energetic
  considerations, but understanding the regional climate effects is more
  difficult. Promising mechanisms for such a driving have been identified,
  including through the influence of UV irradiance on the stratosphere and
  dynamical coupling to the surface. Here, we provide an overview of the
  current state of our knowledge, as well as of the main open questions.

Title: Sunspot group tilt angles and the strength of the solar cycle
    (Corrigendum)
Authors: Dasi-Espuig, M.; Solanki, S. K.; Krivova, N. A.; Cameron,
   R.; Peñuela, T.
Bibcode: 2013A&A...556C...3D
Altcode:
  No abstract at ADS

Title: Quiet Sun magnetic fields observed by Hinode: Support for a
    local dynamo
Authors: Buehler, D.; Lagg, A.; Solanki, S. K.
Bibcode: 2013A&A...555A..33B
Altcode: 2013arXiv1307.0789B
  Context. The Hinode mission has revealed copious amounts of horizontal
  flux covering the quiet Sun. Local dynamo action has been proposed
  to explain the presence of this flux. <BR /> Aims: We sought to
  test whether the quiet Sun flux detected by Hinode is due to a
  local or the global dynamo by studying long-term variations in the
  polarisation signals detectable at the disc centre of the quiet Sun
  between November 2006 and May 2012, with particular emphasis on weak
  signals in the internetwork. <BR /> Methods: The investigation focusses
  on line-integrated circular polarisation V<SUB>tot</SUB> and linear
  polarisation LP<SUB>tot</SUB> profiles obtained from the Fe I 6302.5
  Å absorption line in Hinode SOT/SP. <BR /> Results: Both circular and
  linear polarisation signals show no overall variation in the fraction
  of selected pixels from 2006 until 2012. There is also no variation
  in the magnetic flux in this interval of time. The probability density
  functions (PDF) of the line-of-sight magnetic flux can be fitted with
  a power law from 1.17 × 10<SUP>17</SUP> Mx to 8.53 × 10<SUP>18</SUP>
  Mx with index α = -1.82 ± 0.02 in 2007. The variation of α's across
  all years does not exceed a significance of 1σ. Linearly polarised
  features are also fitted with a power law, with index α = -2.60 ±
  0.06 in 2007. Indices derived from linear polarisation PDFs of other
  years also show no significant variation. <BR /> Conclusions: Our
  results show that the ubiquitous horizontal polarisation on the edges
  of bright granules seen by Hinode are invariant during the minimum of
  cycle 23. This supports the notion that the weak circular and linear
  polarisation is primarily caused by an independent local dynamo.

Title: Chromospheric magnetic field of an active region filament
    using the He I triplet and the primary observation of filaments
    (prominences) using New Vacuum Solar Tower of China
Authors: Xu, Zhi; Lagg, A.; Solanki, S.; Liu, Z.; New Vacuum Solar
   Telescope Observers
Bibcode: 2013SPD....4410504X
Altcode:
  There are two parts in my presentation. In the first part I present the
  magnetic field measurement of an active region filament using the full
  Stokes profiles of He I 10830 and Si I 10827 band when the filament in
  its stable phase. This observation was fulfilled using German Vacuum
  Tower Telescope (VTT). The vector magnetic field and Doppler velocity
  map both in the photosphere and chromosphere were observed and analyzed
  co-temporally and co-spatially. The observation findings reveal that we
  were observing the emergence of a flux rope with a subsequent formation
  of a filament. In the second part, I would like to exhibit another
  ground-based observation facility, 1m New Vacuum Solar Telescope
  (NVST) located in Fu-Xian Lake Solar Observatory of China. After
  the basic introduction including the location and instrumentations,
  I give some high lights including granulation, faculae, micro-flares,
  jets, and filaments or prominence since the first running in 2010,
  showing our potential ability to do high-resolution solar observation
  from the ground. Observation proposals from the international solar
  community are well appreciated in future.

Title: Vertical flows and mass flux balance of sunspot umbral dots
Authors: Riethmüller, T. L.; Solanki, S. K.; van Noort, M.; Tiwari,
   S. K.
Bibcode: 2013A&A...554A..53R
Altcode: 2013arXiv1305.1164R
  A new Stokes inversion technique that greatly reduces the effect of the
  spatial point spread function of the telescope is used to constrain
  the physical properties of umbral dots (UDs). The depth-dependent
  inversion of the Stokes parameters from a sunspot umbra recorded
  with Hinode SOT/SP revealed significant temperature enhancements and
  magnetic field weakenings in the core of the UDs in deep photospheric
  layers. Additionally, we found upflows of around 960 m/s in peripheral
  UDs (i.e., UDs close to the penumbra) and ≈600 m/s in central UDs. For
  the first time, we also detected systematic downflows for distances
  larger than 200 km from the UD center that balance the upflowing mass
  flux. In the upper photosphere, we found almost no difference between
  the UDs and their diffuse umbral background.

Title: First evidence of interaction between longitudinal and
    transverse waves in solar magnetic elements
Authors: Stangalini, M.; Solanki, S. K.; Cameron, R.; Martínez
   Pillet, V.
Bibcode: 2013A&A...554A.115S
Altcode: 2013arXiv1304.7088S
  Small-scale magnetic fields are thought to play an important role in
  the heating of the outer solar atmosphere. By taking advantage of
  the unprecedented high-spatial and temporal cadence of the Imaging
  Magnetograph eXperiment (IMaX), the filter vector polarimeter on board
  the Sunrise balloon-borne observatory, we study the transversal and
  longitudinal velocity oscillations in small magnetic elements. The
  results of this analysis are then compared to magnetohydrodynamic (MHD)
  simulations, showing excellent agreement. We found buffeting-induced
  transverse oscillations with velocity amplitudes of the order of 1-2
  km s<SUP>-1</SUP> to be common along with longitudinal oscillations
  with amplitudes ~0.4 km s<SUP>-1</SUP>. Moreover, we also found an
  interaction between transverse oscillations and longitudinal velocity
  oscillations, showing a ± 90° phase lag at the frequency at which
  they exhibit the maximum coherence in the power spectrum. Our results
  are consistent with the theoretical picture in which MHD longitudinal
  waves are excited inside small magnetic elements as a response of the
  flux tube to the forcing action of the granular flows.

Title: Evolution of the Fine Structure of Magnetic Fields in the
Quiet Sun: Observations from Sunrise/IMaX and Extrapolations
Authors: Wiegelmann, Thomas; Solanki, Sami; Borrero, Juan; Peter,
   Hardi; Sunrise Team
Bibcode: 2013EGUGA..15.5251W
Altcode:
  Observations with the balloon-borne Sunrise/ Imaging Magnetograph
  eXperiment (IMaX) provide high spatial resolution (roughly 100 km at
  disk center) measurements of the magnetic field in the photosphere of
  the quiet Sun. To investigate the magnetic structure of the chromosphere
  and corona, we extrapolate these photospheric measurements into
  the upper solar atmosphere and analyse a 22-minute long time series
  with a cadence of 33 seconds. Using the extrapolated magnetic-field
  lines as tracer, we investigate temporal evolution of the magnetic
  connectivity in the quiet Sun's atmosphere. The majority of magnetic
  loops are asymmetric in the sense that the photospheric field strength
  at the loop footpoints is very different. We find that the magnetic
  connectivity of the loops changes rapidly with a typical connection
  recycling time of about 3 ± 1 minutes in the upper solar atmosphere and
  12 ± 4 minutes in the photosphere. This is considerably shorter than
  previously found. Nonetheless, our estimate of the energy released by
  the associated magnetic-reconnection processes is not likely to be the
  sole source for heating the chromosphere and corona in the quiet Sun.

Title: A Collaborative FP7 Effort towards the First European
    Comprehensive SOLar Irradiance Data Exploitation (SOLID)
Authors: Haberreiter, Margit; Dasi, Maria; Delouille, Veronique; Del
   Zanna, Giulio; Dudok de Wit, Thierry; Ermolli, Ilaria; Kretzschmar,
   Matthieu; Krivova, Natalie; Mason, Helen; Qahwaji, Rami; Schmutz,
   Werner; Solanki, Sami; Thuillier, Gerard; Tourpali, Kleareti; Unruh,
   Yvonne; Verbeeck, Cis; Weber, Mark; Woods, Tom
Bibcode: 2013EGUGA..1513079H
Altcode:
  Variations of solar irradiance are the most important natural factor
  in the terrestrial climate and as such, the time dependent spectral
  solar irradiance is a crucial input to any climate modelling. There
  have been previous efforts to compile solar irradiance but it is
  still uncertain by how much the spectral and total solar irradiance
  changed on yearly, decadal and longer time scales. Observations of
  irradiance data exist in numerous disperse data sets. Therefore, it
  is important to bring together the European expertise in the field
  to analyse and merge the complete set of European irradiance data,
  complemented by archive data that include data from non-European
  missions. We report on the initiation of a collaborative effort to unify
  representatives from all European solar space experiments and European
  teams specialized in multi-wavelength solar image processing. It is
  intended to include the European groups involved in irradiance modelling
  and reconstruction. They will work with two different state of the art
  approaches to produce reconstructed spectral and total solar irradiance
  data as a function of time. These results will be used to bridge
  gaps in time and wavelength coverage of the observational data. This
  will allow the proposing SOLID team to reduce the uncertainties in
  the irradiance time series - an important requirement by the climate
  community - and to provide uniform data sets of modelled and observed
  solar irradiance data from the beginning of the space era to the
  present including proper error and uncertainty estimates. Climate
  research needs these data sets and therefore, the primary benefit
  is for the climate community, but the stellar community, planetary,
  lunar, and ionospheric researchers are also interested in having at
  their disposition incident radiation of the Sun. The proposing team
  plans to realize a wide international synergy in solar physics from
  7 European countries, and collaborators from the US, complemented by
  representatives from the climate community, who will accompany their
  research work with wide dissemination activities.

Title: The AD775 cosmic event revisited: the Sun is to blame
Authors: Usoskin, I. G.; Kromer, B.; Ludlow, F.; Beer, J.; Friedrich,
   M.; Kovaltsov, G. A.; Solanki, S. K.; Wacker, L.
Bibcode: 2013A&A...552L...3U
Altcode: 2013arXiv1302.6897U
  <BR /> Aims: Miyake et al. (2012, Nature, 486, 240, henceforth M12)
  recently reported, based on <SUP>14</SUP>C data, an extreme cosmic
  event in about AD775. Using a simple model, M12 claimed that the event
  was too strong to be caused by a solar flare within the standard
  theory. This implied a new paradigm of either an impossibly strong
  solar flare or a very strong cosmic ray event of unknown origin that
  occurred around AD775. However, as we show, the strength of the event
  was significantly overestimated by M12. Several subsequent works have
  attempted to find a possible exotic source for such an event, including
  a giant cometary impact upon the Sun or a gamma-ray burst, but they are
  all based on incorrect estimates by M12. We revisit this event with
  analysis of new datasets and consistent theoretical modelling. <BR
  /> Methods: We verified the experimental result for the AD775 cosmic
  ray event using independent datasets including <SUP>10</SUP>Be series
  and newly measured <SUP>14</SUP>C annual data. We surveyed available
  historical chronicles for astronomical observations for the period
  around the AD770s to identify potential sightings of aurorae borealis
  and supernovae. We interpreted the <SUP>14</SUP>C measurements using
  an appropriate carbon cycle model. <BR /> Results: We show that:
  (1) The reality of the AD775 event is confirmed by new measurements
  of <SUP>14</SUP>C in German oak; (2) by using an inappropriate
  carbon cycle model, M12 strongly overestimated the event's strength;
  (3) the revised magnitude of the event (the global <SUP>14</SUP>C
  production Q = (1.1 - 1.5) × 10<SUP>8</SUP> atoms/cm<SUP>2</SUP>)
  is consistent with different independent datasets (<SUP>14</SUP>C,
  <SUP>10</SUP>Be, <SUP>36</SUP>Cl) and can be associated with a
  strong, but not inexplicably strong, solar energetic particle event
  (or a sequence of events), and provides the first definite evidence
  for an event of this magnitude (the fluence &gt;30 MeV was about
  4.5 × 10<SUP>10</SUP> cm<SUP>-2</SUP>) in multiple datasets; (4)
  this interpretation is in agreement with increased auroral activity
  identified in historical chronicles. <BR /> Conclusions: The results
  point to the likely solar origin of the event, which is now identified
  as the greatest solar event on a multi-millennial time scale, placing
  a strong observational constraint on the theory of explosive energy
  releases on the Sun and cool stars.

Title: Modeling the variability of Sun-like stars
Authors: Shapiro, Alexander; Knaack, Reto; Krivova, Natalie; Schmutz,
   Werner; Solanki, Sami; Unruh, Yvonne
Bibcode: 2013EGUGA..15.9981S
Altcode:
  We present a model which attributes the variability of the stellar
  radiative energy flux to the imbalance between the contributions from
  dark starspots and bright faculae. The stellar radiative energy flux
  variations are modeled from the individual component's spectra, by
  weighting them with corresponding filling factors. The filling factors
  are deduced by extrapolating the sunspot and facular filling factors
  dependencies on solar CaII S-index to stars with different levels
  of the chromospheric activity. Our approach allows us to model the
  stellar photometric variability vs. activity dependency and reproduce
  the transition from spot-dominated to facula-dominated regimes of
  variability. We show how the effect of inclination (arising due to the
  random position of the Earth-bound observer relative to the directions
  of stellar rotational axis) can affect these dependencies and present
  the modeling of the individual stellar photometric light curves.

Title: What can we learn about the Sun with PREMOS/PICARD?
Authors: Cessateur, Gaël; Shapiro, Alexander; Schmutz, Werner;
   Krivova, Natalie; Solanki, Sami K.; Yeo, Kok Leng; Thuillier, Gérard
Bibcode: 2013EGUGA..1511720C
Altcode:
  Total and Spectral Solar Irradiance are key input parameters to
  atmospheric/oceanic and space weather models. We present here
  spectral solar irradiance data from the radiometer PREMOS onboard
  the PICARD satellite. This instrument convers the solar spectrum from
  the Ultraviolet to near-infrared, and provides valuable information
  and nourishes theoretical models. Based on redundancy strategies,
  instrumental degradation has been mostly corrected, revealing
  surprising behavior from the visible and near-infrared filters. We
  compare these data with those from the VIRGO/SOHO and SOLSTIC/SORCE
  experiments. Finally we use COSI to model the variability of the
  irradiance, assuming that the latter is determined by the evolution
  of the solar surface magnetic field as seen with SDO/HMI data. A
  direct comparison shows a very good correlation for most of channels
  from PREMOS.

Title: Analysis of Ca II K images aiming to determine long-term
    trends in solar irradiance variability
Authors: Kar, Anuradha; Ermolli, Ilaria; Krivova, Natalie; Solanki,
   Sami
Bibcode: 2013EGUGA..15..330K
Altcode:
  The change in radiative output of the Sun on time scales longer than
  a day is attributed to the variability in solar surface magnetic
  fields. Direct irradiance measurements are only available for less
  than four decades. To reconstruct long term trends in solar total and
  spectral irradiance, proxies of solar surface magnetism like sunspot,
  facular and network areas are needed. Currently, sunspot records
  alone are used for this purpose, from which the deduction of facular
  and network areas is rather indirect. Historical records of full disk
  images of the Sun taken in the Ca II K spectral line (393.3 nm) have the
  potential to provide far more direct information about the distribution
  and evolution of faculae and network elements. The latter appear as
  bright regions in the Ca II K spectroheliograms and their intensity
  is correlated with the magnetic field strength of the features on the
  solar surface. Solar full disk images in the Ca II K line have been
  recorded since the beginning of the 20th century at a number of solar
  observatories such as at Arcetri (Italy), Mount Wilson(California,
  US) and Kodaikanal (India). The images are available in digitized
  archives that contain the data processed for standard instrumental
  calibrations. To utilize these records for irradiance studies, the next
  step is to identify the bright magnetic features from the images using
  feature recognition techniques. We test different feature identification
  methods which are first applied to a set of recent images from the PSPT
  instrument at the Osservatorio Astronomico di Roma, taken during three
  periods characterized by high, medium and low levels of activity. Then
  the performance of these methods to historical images from Arcetri,
  Mt. Wilson and Kodaikanal archives is tested. The results will be
  presented and discussed here.

Title: Evolution of the Fine Structure of Magnetic Fields in the
Quiet Sun: Observations from Sunrise/IMaX and Extrapolations
Authors: Wiegelmann, T.; Solanki, S. K.; Borrero, J. M.; Peter,
   H.; Barthol, P.; Gandorfer, A.; Martínez Pillet, V.; Schmidt, W.;
   Knölker, M.
Bibcode: 2013SoPh..283..253W
Altcode:
  Observations with the balloon-borne Sunrise/Imaging Magnetograph
  eXperiment (IMaX) provide high spatial resolution (roughly 100 km at
  disk center) measurements of the magnetic field in the photosphere of
  the quiet Sun. To investigate the magnetic structure of the chromosphere
  and corona, we extrapolate these photospheric measurements into
  the upper solar atmosphere and analyze a 22-minute long time series
  with a cadence of 33 seconds. Using the extrapolated magnetic-field
  lines as tracer, we investigate temporal evolution of the magnetic
  connectivity in the quiet Sun's atmosphere. The majority of magnetic
  loops are asymmetric in the sense that the photospheric field strength
  at the loop foot points is very different. We find that the magnetic
  connectivity of the loops changes rapidly with a typical connection
  recycling time of about 3±1 minutes in the upper solar atmosphere and
  12±4 minutes in the photosphere. This is considerably shorter than
  previously found. Nonetheless, our estimate of the energy released by
  the associated magnetic-reconnection processes is not likely to be the
  sole source for heating the chromosphere and corona in the quiet Sun.

Title: Fine structures in the atmosphere above a sunspot umbra
Authors: Bharti, L.; Hirzberger, J.; Solanki, S. K.
Bibcode: 2013A&A...552L...1B
Altcode: 2013arXiv1302.2772B
  We present simultaneous photospheric and chromospheric observations
  of the trailing sunspot in NOAA 10904, obtained with the Swedish
  Solar Telescope (SST) La Palma, Canary Islands. Time series of high
  resolution Ca ii H images show transient jet-like structures in sunspot
  umbrae are elongated, which we call umbral microjets. These jets are
  directed roughly parallel to nearby penumbral microjets, suggesting
  that they are aligned with the background magnetic field. In general,
  first a bright dot-like structure appears, from which a jet later
  emerges, although some jets appear without an associated chromospheric
  dot. Bright photospheric umbral dots are associated with umbral
  microjets arising in the outer umbra. Nevertheless, a one-to-one
  correspondence between jet-like events and underlying umbral dots
  is not seen. They are typically less than 1'' long and less than 0.3
  arcsec wide. The typical lifetime of umbral microjets is around one
  minute. The brightness of these structures increases from the center of
  the umbra toward the umbra-penumbra boundary along with the brightness
  of the local background.

Title: Recent variability of the solar spectral irradiance and its
    impact on climate modelling
Authors: Ermolli, I.; Matthes, K.; Dudok de Wit, T.; Krivova,
   N. A.; Tourpali, K.; Weber, M.; Unruh, Y. C.; Gray, L.; Langematz,
   U.; Pilewskie, P.; Rozanov, E.; Schmutz, W.; Shapiro, A.; Solanki,
   S. K.; Woods, T. N.
Bibcode: 2013ACP....13.3945E
Altcode: 2012ACPD...1224557E; 2013arXiv1303.5577E
  The lack of long and reliable time series of solar spectral irradiance
  (SSI) measurements makes an accurate quantification of solar
  contributions to recent climate change difficult. Whereas earlier SSI
  observations and models provided a qualitatively consistent picture of
  the SSI variability, recent measurements by the SORCE (SOlar Radiation
  and Climate Experiment) satellite suggest a significantly stronger
  variability in the ultraviolet (UV) spectral range and changes in the
  visible and near-infrared (NIR) bands in anti-phase with the solar
  cycle. A number of recent chemistry-climate model (CCM) simulations
  have shown that this might have significant implications on the
  Earth's atmosphere. Motivated by these results, we summarize here
  our current knowledge of SSI variability and its impact on Earth's
  climate. <BR /><BR /> We present a detailed overview of existing SSI
  measurements and provide thorough comparison of models available to
  date. SSI changes influence the Earth's atmosphere, both directly,
  through changes in shortwave (SW) heating and therefore, temperature
  and ozone distributions in the stratosphere, and indirectly, through
  dynamical feedbacks. We investigate these direct and indirect effects
  using several state-of-the art CCM simulations forced with measured
  and modelled SSI changes. A unique asset of this study is the use
  of a common comprehensive approach for an issue that is usually
  addressed separately by different communities. <BR /><BR /> We show
  that the SORCE measurements are difficult to reconcile with earlier
  observations and with SSI models. Of the five SSI models discussed
  here, specifically NRLSSI (Naval Research Laboratory Solar Spectral
  Irradiance), SATIRE-S (Spectral And Total Irradiance REconstructions
  for the Satellite era), COSI (COde for Solar Irradiance), SRPM (Solar
  Radiation Physical Modelling), and OAR (Osservatorio Astronomico di
  Roma), only one shows a behaviour of the UV and visible irradiance
  qualitatively resembling that of the recent SORCE measurements. However,
  the integral of the SSI computed with this model over the entire
  spectral range does not reproduce the measured cyclical changes of the
  total solar irradiance, which is an essential requisite for realistic
  evaluations of solar effects on the Earth's climate in CCMs. <BR /><BR
  /> We show that within the range provided by the recent SSI observations
  and semi-empirical models discussed here, the NRLSSI model and SORCE
  observations represent the lower and upper limits in the magnitude
  of the SSI solar cycle variation. <BR /><BR /> The results of the
  CCM simulations, forced with the SSI solar cycle variations estimated
  from the NRLSSI model and from SORCE measurements, show that the direct
  solar response in the stratosphere is larger for the SORCE than for the
  NRLSSI data. Correspondingly, larger UV forcing also leads to a larger
  surface response. <BR /><BR /> Finally, we discuss the reliability
  of the available data and we propose additional coordinated work,
  first to build composite SSI data sets out of scattered observations
  and to refine current SSI models, and second, to run coordinated
  CCM experiments.

Title: Intensity contrast of solar network and faculae
Authors: Yeo, K. L.; Solanki, S. K.; Krivova, N. A.
Bibcode: 2013A&A...550A..95Y
Altcode: 2013arXiv1302.1442Y
  <BR /> Aims: This study aims at setting observational constraints
  on the continuum and line core intensity contrast of network and
  faculae, specifically, their relationship with magnetic field and
  disc position. <BR /> Methods: Full-disc magnetograms and intensity
  images by the Helioseismic and Magnetic Imager (HMI) onboard the Solar
  Dynamics Observatory (SDO) were employed. Bright magnetic features,
  representing network and faculae, were identified and the relationship
  between their intensity contrast at continuum and line core with
  magnetogram signal and heliocentric angle examined. Care was taken
  to minimize the inclusion of the magnetic canopy and straylight from
  sunspots and pores as network and faculae. <BR /> Results: In line
  with earlier studies, network features, on a per unit magnetic flux
  basis, appeared brighter than facular features. Intensity contrasts
  in the continuum and line core differ considerably, most notably, they
  exhibit opposite centre-to-limb variations. We found this difference in
  behaviour to likely be due to the different mechanisms of the formation
  of the two spectral components. From a simple model based on bivariate
  polynomial fits to the measured contrasts we confirmed spectral line
  changes to be a significant driver of facular contribution to variation
  in solar irradiance. The discrepancy between the continuum contrast
  reported here and in the literature was shown to arise mainly from
  differences in spatial resolution and treatment of magnetic signals
  adjacent to sunspots and pores. <BR /> Conclusions: HMI is a source of
  accurate contrasts and low-noise magnetograms covering the full solar
  disc. For irradiance studies it is important to consider not just the
  contribution from the continuum but also from the spectral lines. In
  order not to underestimate long-term variations in solar irradiance,
  irradiance models should take the greater contrast per unit magnetic
  flux associated with magnetic features with low magnetic flux into
  account.

Title: Solar irradiance variability
Authors: Solanki, S. K.; Unruh, Y. C.
Bibcode: 2013AN....334..145S
Altcode: 2013csss...17..145S; 2012arXiv1210.5911S
  The Sun has long been considered a constant star, to the extent
  that its total irradiance was termed the solar constant. It required
  radiometers in space to detect the small variations in solar irradiance
  on timescales of the solar rotation and the solar cycle. A part of
  the difficulty is that there are no other constant natural daytime
  sources to which the Sun's brightness can be compared. The discovery
  of solar irradiance variability rekindled a long-running discussion on
  how strongly the Sun affects our climate. A non-negligible influence is
  suggested by correlation studies between solar variability and climate
  indicators. The mechanism for solar irradiance variations that fits
  the observations best is that magnetic features at the solar surface,
  i.e. sunspots, faculae and the magnetic network, are responsible for
  almost all variations (although on short timescales convection and
  p-mode oscillations also contribute). In spite of significant progress
  important questions are still open. Thus there is a debate on how
  strongly irradiance varies on timescales of centuries (i.e. how much
  darker the Sun was during the Maunder minimum than it is today). It is
  also not clear how the solar spectrum changes over the solar cycle. Both
  these questions are of fundamental importance for working out just how
  strongly the Sun influences our climate. Another interesting question
  is how solar irradiance variability compares with that of other cool
  dwarfs, particularly now that observations from space are available
  also for stars.

Title: European Solar Physics: moving from SOHO to Solar Orbiter
    and beyond
Authors: Solanki, S. K.; Teriaca, L.; Barthol, P.; Curdt, W.;
   Inhester, B.
Bibcode: 2013MmSAI..84..286S
Altcode:
  When ESA and NASA launched the Solar and Heliospheric Observatory (SOHO)
  to the Sun-Earth L1 point, they also launched European solar physics
  into a steep upward trajectory. Thanks to the battery of instruments
  on SOHO our picture of the Sun changed dramatically from that of a
  sedate, nearly static star into that of a highly structured, dynamic
  one. Subsequent solar missions have probed higher energy radiation,
  gazed at the Sun from new vantage points in the ecliptic, analysed
  the Sun at higher spatial resolution and imaged the whole Sun in many
  wavelengths at high cadence. Nonetheless, SOHO is still going strong and
  still delivering unique data. In the meantime European solar physicists
  are working hard on the next major mission, Solar Orbiter, now being
  implemented as the M1 mission of ESA's Cosmic Vision program. Solar
  Orbiter will leave the Earth's orbit and move ever closer to the Sun,
  reaching a perihelion inside the orbit of Mercury. This will allow it
  to sample the Sun's dynamic inner heliosphere in situ, while probing
  the source regions of the ambient solar wind with its remote sensing
  instruments, a unique combination. Solar Orbiter will also leave the
  ecliptic and, for the first time, image the Sun's poles. This will
  bring us closer to finding the missing pieces of the puzzle on how
  the solar dynamo works. Beyond Solar Orbiter are further exciting
  prospects, such as the Solar-C mission, or the large European Solar
  Telescope. Here an overview of solar missions and telescopes and the
  associated science is given from a European perspective.

Title: Structure and dynamics of isolated internetwork Ca II H bright
    points observed by SUNRISE
Authors: Jafarzadeh, S.; Solanki, S. K.; Feller, A.; Lagg, A.;
   Pietarila, A.; Danilovic, S.; Riethmüller, T. L.; Martínez Pillet, V.
Bibcode: 2013A&A...549A.116J
Altcode: 2012arXiv1211.4836J
  <BR /> Aims: We aim to improve our picture of the low chromosphere in
  the quiet-Sun internetwork by investigating the intensity, horizontal
  velocity, size and lifetime variations of small bright points (BPs;
  diameter smaller than 0.3 arcsec) observed in the Ca II H 3968 Å
  passband along with their magnetic field parameters, derived from
  photospheric magnetograms. <BR /> Methods: Several high-quality
  time series of disc-centre, quiet-Sun observations from the Sunrise
  balloon-borne solar telescope, with spatial resolution of around 100
  km on the solar surface, have been analysed to study the dynamics
  of BPs observed in the Ca II H passband and their dependence on the
  photospheric vector magnetogram signal. <BR /> Results: Parameters such
  as horizontal velocity, diameter, intensity and lifetime histograms of
  the isolated internetwork and magnetic Ca II H BPs were determined. Mean
  values were found to be 2.2 km s<SUP>-1</SUP>, 0.2 arcsec (≈150 km),
  1.48 ⟨ I<SUB>Ca</SUB> ⟩ and 673 s, respectively. Interestingly, the
  brightness and the horizontal velocity of BPs are anti-correlated. Large
  excursions (pulses) in horizontal velocity, up to 15 km s<SUP>-1</SUP>,
  are present in the trajectories of most BPs. These could excite kink
  waves travelling into the chromosphere and possibly the corona, which we
  estimate to carry an energy flux of 310 W m<SUP>-2</SUP>, sufficient to
  heat the upper layers, although only marginally. <BR /> Conclusions:
  The stable observing conditions of Sunrise and our technique for
  identifying and tracking BPs have allowed us to determine reliable
  parameters of these features in the internetwork. Thus we find, e.g.,
  that they are considerably longer lived than previously thought. The
  large velocities are also reliable, and may excite kink waves. Although
  these wave are (marginally) energetic enough to heat the quiet corona,
  we expect a large additional contribution from larger magnetic elements
  populating the network and partly also the internetwork.

Title: Pathway to the Square Kilometre Array - The German White
    Paper -
Authors: Aharonian, F.; Arshakian, T. G.; Allen, B.; Banerjee, R.;
   Beck, R.; Becker, W.; Bomans, D. J.; Breitschwerdt, D.; Brüggen,
   M.; Brunthaler, A.; Catinella, B.; Champion, D.; Ciardi, B.; Crocker,
   R.; de Avillez, M. A.; Dettmar, R. J.; Engels, D.; Enßlin, T.; Enke,
   H.; Fieseler, T.; Gizon, L.; Hackmann, E.; Hartmann, B.; Henkel, C.;
   Hoeft, M.; Iapichino, L.; Innes, D.; James, C.; Jasche, J.; Jones,
   D.; Kagramanova, V.; Kauffmann, G.; Keane, E.; Kerp, J.; Klöckner,
   H. -R.; Kokkotas, K.; Kramer, M.; Krause, M.; Krause, M.; Krupp, N.;
   Kunz, J.; Lämmerzahl, C.; Lee, K. J.; List, M.; Liu, K.; Lobanov,
   A.; Mann, G.; Merloni, A.; Middelberg, E.; Niemeyer, J.; Noutsos,
   A.; Perlick, V.; Reich, W.; Richter, P.; Roy, A.; Saintonge, A.;
   Schäfer, G.; Schaffner-Bielich, J.; Schinnerer, E.; Schleicher, D.;
   Schneider, P.; Schwarz, D. J.; Sedrakian, A.; Sesana, A.; Smolčić,
   V.; Solanki, S.; Tuffs, R.; Vetter, M.; Weber, E.; Weller, J.; Wex,
   N.; Wucknitz, O.; Zwaan, M.
Bibcode: 2013arXiv1301.4124A
Altcode:
  The Square Kilometre Array (SKA) is the most ambitious radio telescope
  ever planned. With a collecting area of about a square kilometre,
  the SKA will be far superior in sensitivity and observing speed to
  all current radio facilities. The scientific capability promised by
  the SKA and its technological challenges provide an ideal base for
  interdisciplinary research, technology transfer, and collaboration
  between universities, research centres and industry. The SKA in
  the radio regime and the European Extreme Large Telescope (E-ELT)
  in the optical band are on the roadmap of the European Strategy Forum
  for Research Infrastructures (ESFRI) and have been recognised as the
  essential facilities for European research in astronomy. This "White
  Paper" outlines the German science and R&amp;D interests in the SKA
  project and will provide the basis for future funding applications to
  secure German involvement in the Square Kilometre Array.

Title: Inversions of L12-2 IMaX data of an emerging flux mantle
Authors: Guglielmino, S. L.; Martínez Pillet, V.; Ruiz Cobo,
   B.; del Toro Iniesta, J. C.; Bellot Rubio, L. R.; Solanki, S. K.;
   Sunrise/IMaX Team
Bibcode: 2013MmSAI..84..355G
Altcode:
  We present the analysis of a flux emergence event observed with
  the IMaX magnetograph flown aboard the SUNRISE balloon. IMaX took a
  15' sequence with cadence of 31 s along the Fe I line at 525.0 nm,
  acquiring only Stokes I and V at 12 line positions (L12-2 mode). This
  sequence shows the emergence of a flux mantle at mesogranular scale,
  cospatial with a large exploding granule. An undesired cross-talk
  between Stokes U and V was found in such L12-2 data. We show that the
  use of a modified version of the SIR inversion code is able to remove
  such effect in inferring the physical quantities of interest.

Title: MHD waves in small magnetic elements: comparing IMaX
    observations to simulations.
Authors: Stangalini, M.; Solanki, S. K.; Cameron, R.
Bibcode: 2013MmSAI..84..444S
Altcode:
  Small-scale magnetic fields are thought to play an important role in the
  heating of the outer solar atmosphere. By exploiting the high-spatial
  and temporal resolution of IMaX, the bidimensional spectropolarimeter on
  board the Sunrise balloon-borne observatory, we study the excitation of
  MHD waves in small magnetic elements, providing clues on the interaction
  of the magnetic structures with the photospheric forcing and the ambient
  acoustic field. The large fraction of magnetic features observed by
  IMaX made it possible to study the interaction between the photospheric
  granulation and the flux tubes from a statistical point-of-view. In
  particular we find a 90 degree phase lag with an high confidence level
  between the horizontal displacements of the flux tubes and the velocity
  perturbations measured inside them. We also find that the observational
  results are in excellent agreement with MHD simulations. This result
  suggests that the horizontal displacement of small-scale magnetic
  features by the surrounding granulation excites longitudinal waves
  within the magnetic elements.

Title: The GREGOR Solar Telescope on Tenerife
Authors: Schmidt, W.; von der Lühe, O.; Volkmer, R.; Denker, C.;
   Solanki, S. K.; Balthasar, H.; Bello González, N.; Berkefeld, T.;
   Collados Vera, M.; Hofmann, A.; Kneer, F.; Lagg, A.; Puschmann, K. G.;
   Schmidt, D.; Sobotka, M.; Soltau, D.; Strassmeier, K. G.
Bibcode: 2012ASPC..463..365S
Altcode: 2012arXiv1202.4289S
  2011 was a successful year for the GREGOR project. The telescope was
  finally completed in May with the installation of the 1.5-meter primary
  mirror. The installation of the first-light focal plane instruments was
  completed by the end of the year. At the same time, the preparations
  for the installation of the high-order adaptive optics were finished,
  its integration to the telescope is scheduled for early 2012. This
  paper describes the telescope and its instrumentation in their present
  first-light configuration, and provides a brief overview of the science
  goals of GREGOR.

Title: The GREGOR Solar Telescope
Authors: Denker, C.; Lagg, A.; Puschmann, K. G.; Schmidt, D.; Schmidt,
   W.; Sobotka, M.; Soltau, D.; Strassmeier, K. G.; Volkmer, R.; von
   der Luehe, O.; Solanki, S. K.; Balthasar, H.; Bello Gonzalez, N.;
   Berkefeld, T.; Collados Vera, M.; Hofmann, A.; Kneer, F.
Bibcode: 2012IAUSS...6E.203D
Altcode:
  The 1.5-meter GREGOR solar telescope is a new facility for
  high-resolution observations of the Sun. The telescope is located at the
  Spanish Observatorio del Teide on Tenerife. The telescope incorporates
  advanced designs for a foldable-tent dome, an open steel-truss telescope
  structure, and active and passive means to minimize telescope and mirror
  seeing. Solar fine structure can be observed with a dedicated suite
  of instruments: a broad-band imaging system, the "GREGOR Fabry-Perot
  Interferometer", and the "Grating Infrared Spectrograph". All post-focus
  instruments benefit from a high-order (multi-conjugate) adaptive optics
  system, which enables observations close to the diffraction limit of
  the telescope. The inclusion of a spectrograph for stellar activity
  studies and the search for solar twins expands the scientific usage
  of the GREGOR to the nighttime domain. We report on the successful
  commissioning of the telescope until the end of 2011 and the first
  steps towards science verification in 2012.

Title: Doppler shift of hot coronal lines in a moss area of an
    active region
Authors: Dadashi, N.; Teriaca, L.; Tripathi, D.; Solanki, S. K.;
   Wiegelmann, T.
Bibcode: 2012A&A...548A.115D
Altcode: 2012arXiv1211.5473D
  The moss is the area at the footpoint of the hot (3 to 5 MK) loops
  forming the core of the active region where emission is believed to
  result from the heat flux conducted down to the transition region from
  the hot loops. Studying the variation of Doppler shift as a function
  of line formation temperatures over the moss area can give clues
  on the heating mechanism in the hot loops in the core of the active
  regions. We investigate the absolute Doppler shift of lines formed
  at temperatures between 1 MK and 2 MK in a moss area within active
  region NOAA 11243 using a novel technique that allows determining the
  absolute Doppler shift of EUV lines by combining observations from
  the SUMER and EIS spectrometers. The inner (brighter and denser) part
  of the moss area shows roughly constant blue shift (upward motions)
  of 5 km s<SUP>-1</SUP> in the temperature range of 1 MK to 1.6 MK. For
  hotter lines the blue shift decreases and reaches 1 km s<SUP>-1</SUP>
  for Fe xv 284 Å (~2 MK). The measurements are discussed in relation
  to models of the heating of hot loops. The results for the hot coronal
  lines seem to support the quasi-steady heating models for nonsymmetric
  hot loops in the core of active regions.

Title: A retrospective of the GREGOR solar telescope in scientific
    literature
Authors: Denker, C.; von der Lühe, O.; Feller, A.; Arlt, K.;
   Balthasar, H.; Bauer, S. -M.; Bello González, N.; Berkefeld, Th.;
   Caligari, P.; Collados, M.; Fischer, A.; Granzer, T.; Hahn, T.;
   Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Kentischer, T.; Klva{ňa,
   M.; Kneer, F.; Lagg, A.; Nicklas, H.; Popow, E.; Puschmann, K. G.;
   Rendtel, J.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Solanki, S. K.;
   Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; Waldmann,
   T.; Wiehr, E.; Wittmann, A. D.; Woche, M.
Bibcode: 2012AN....333..810D
Altcode: 2012arXiv1210.3167D
  In this review, we look back upon the literature, which had the
  GREGOR solar telescope project as its subject including science cases,
  telescope subsystems, and post-focus instruments. The articles date
  back to the year 2000, when the initial concepts for a new solar
  telescope on Tenerife were first presented at scientific meetings. This
  comprehensive bibliography contains literature until the year 2012,
  i.e., the final stages of commissioning and science verification. Taking
  stock of the various publications in peer-reviewed journals and
  conference proceedings also provides the ``historical'' context
  for the reference articles in this special issue of Astronomische
  Nachrichten/Astronomical Notes.

Title: Three-dimensional non-LTE radiative transfer effects in Fe
    I lines. I. Flux sheet and flux tube geometries
Authors: Holzreuter, R.; Solanki, S. K.
Bibcode: 2012A&A...547A..46H
Altcode: 2012arXiv1209.0559H
  In network and active region plages, the magnetic field is concentrated
  into structures often described as flux tubes (FTs) and sheets
  (FSs). Three-dimensional (3D) radiative transfer is important for
  energy transport in these concentrations. It is also expected to be
  important for diagnostic purposes but has rarely been applied for
  that purpose. Using true 3D, non-local thermodynamic-equilibrium
  (non-LTE or NLTE) radiative transfer (RT) in FT and FS models, we
  compute iron line profiles commonly used to diagnose the Sun's magnetic
  field by using and comparing the results with those obtained from LTE
  or one-dimensional (1D) NLTE calculations. Employing a multilevel
  iron atom, we study the influence of several basic parameters such
  as either FS or FT Wilson depression, wall thickness, radius/width,
  thermal stratification or magnetic field strength on Stokes I and the
  polarized Stokes parameters in the thin-tube approximation. The use
  of different levels of approximations of RT (3D NLTE, 1D NLTE, LTE)
  may lead to considerable differences in profile shapes, intensity
  contrasts, equivalent widths, and the determination of magnetic field
  strengths. In particular, LTE, which often provides a good approach in
  planar 1D atmospheres, is a poor approximation in our flux sheet model
  for some of the most important diagnostic Fe i lines (524.7 nm, 525.0
  nm, 630.1 nm, and 630.2 nm). The observed effects depend on parameters
  such as the height of line formation, field strength, and internal
  temperature stratification. Differences between the profile shapes may
  lead to errors in the determination of magnetic fields on the order of
  10% to 20%, while errors in the determined temperature can reach 300-400
  K. The empirical FT models NET and PLA turn out to minimize the effects
  of 3D RT, so that results obtained with these models by applying LTE may
  also remain valid for 3D NLTE calculations. Finally, horizontal RT is
  found to only insignificantly smear out structures such as the optically
  thick walls of flux tubes and sheets, allowing features as narrow as
  10 km to remain visible. <P />Appendices are available in electronic
  form at <A href="http://www.aanda.org">http://www.aanda.org</A>

Title: The 1.5 meter solar telescope GREGOR
Authors: Schmidt, W.; von der Lühe, O.; Volkmer, R.; Denker, C.;
   Solanki, S. K.; Balthasar, H.; Bello Gonzalez, N.; Berkefeld, Th.;
   Collados, M.; Fischer, A.; Halbgewachs, C.; Heidecke, F.; Hofmann,
   A.; Kneer, F.; Lagg, A.; Nicklas, H.; Popow, E.; Puschmann, K. G.;
   Schmidt, D.; Sigwarth, M.; Sobotka, M.; Soltau, D.; Staude, J.;
   Strassmeier, K. G.; Waldmann , T. A.
Bibcode: 2012AN....333..796S
Altcode:
  The 1.5 m telescope GREGOR opens a new window to the understanding
  of solar small-scale magnetism. The first light instrumentation
  includes the Gregor Fabry Pérot Interferometer (GFPI), a filter
  spectro-polarimeter for the visible wavelength range, the GRating
  Infrared Spectro-polarimeter (GRIS) and the Broad-Band Imager (BBI). The
  excellent performance of the first two instruments has already been
  demonstrated at the Vacuum Tower Telescope. GREGOR is Europe's largest
  solar telescope and number 3 in the world. Its all-reflective Gregory
  design provides a large wavelength coverage from the near UV up to at
  least 5 microns. The field of view has a diameter of 150 arcsec. GREGOR
  is equipped with a high-order adaptive optics system, with a subaperture
  size of 10 cm, and a deformable mirror with 256 actuators. The science
  goals are focused on, but not limited to, solar magnetism. GREGOR
  allows us to measure the emergence and disappearance of magnetic flux
  at the solar surface at spatial scales well below 100 km. Thanks to its
  spectro-polarimetric capabilities, GREGOR will measure the interaction
  between the plasma flows, different kinds of waves, and the magnetic
  field. This will foster our understanding of the processes that heat the
  chromosphere and the outer layers of the solar atmosphere. Observations
  of the surface magnetic field at very small spatial scales will shed
  light on the variability of the solar brightness.

Title: GRIS: The GREGOR Infrared Spectrograph
Authors: Collados, M.; López, R.; Páez, E.; Hernández, E.; Reyes,
   M.; Calcines, A.; Ballesteros, E.; Díaz, J. J.; Denker, C.; Lagg,
   A.; Schlichenmaier, R.; Schmidt, W.; Solanki, S. K.; Strassmeier,
   K. G.; von der Lühe, O.; Volkmer, R.
Bibcode: 2012AN....333..872C
Altcode:
  This paper describes the main characteristics of GRIS (GREGOR Infrared
  Spectrograph), the grating spectrograph installed in the recently
  inaugurated (May 2012) 1.5-meter GREGOR telescope located at the
  Observatorio del Teide in Tenerife. The spectrograph has a standard
  Czerny-Turner configuration with parabolic collimator and camera mirrors
  that belong to the same conic surface. Although nothing prevents its
  use at visible wavelengths, the spectrograph will be initially used
  in combination with the infrared detector of the Tenerife Infrared
  Polarimeter (TIP-II) in standard spectroscopic mode as well as for
  spectropolarimetric measurements.

Title: LEMUR: Large European module for solar Ultraviolet
    Research. European contribution to JAXA's Solar-C mission
Authors: Teriaca, Luca; Andretta, Vincenzo; Auchère, Frédéric;
   Brown, Charles M.; Buchlin, Eric; Cauzzi, Gianna; Culhane, J. Len;
   Curdt, Werner; Davila, Joseph M.; Del Zanna, Giulio; Doschek, George
   A.; Fineschi, Silvano; Fludra, Andrzej; Gallagher, Peter T.; Green,
   Lucie; Harra, Louise K.; Imada, Shinsuke; Innes, Davina; Kliem,
   Bernhard; Korendyke, Clarence; Mariska, John T.; Martínez-Pillet,
   Valentin; Parenti, Susanna; Patsourakos, Spiros; Peter, Hardi; Poletto,
   Luca; Rutten, Robert J.; Schühle, Udo; Siemer, Martin; Shimizu,
   Toshifumi; Socas-Navarro, Hector; Solanki, Sami K.; Spadaro, Daniele;
   Trujillo-Bueno, Javier; Tsuneta, Saku; Dominguez, Santiago Vargas;
   Vial, Jean-Claude; Walsh, Robert; Warren, Harry P.; Wiegelmann,
   Thomas; Winter, Berend; Young, Peter
Bibcode: 2012ExA....34..273T
Altcode: 2011ExA...tmp..135T; 2011arXiv1109.4301T
  The solar outer atmosphere is an extremely dynamic environment
  characterized by the continuous interplay between the plasma and the
  magnetic field that generates and permeates it. Such interactions play a
  fundamental role in hugely diverse astrophysical systems, but occur at
  scales that cannot be studied outside the solar system. Understanding
  this complex system requires concerted, simultaneous solar observations
  from the visible to the vacuum ultraviolet (VUV) and soft X-rays, at
  high spatial resolution (between 0.1'' and 0.3''), at high temporal
  resolution (on the order of 10 s, i.e., the time scale of chromospheric
  dynamics), with a wide temperature coverage (0.01 MK to 20 MK,
  from the chromosphere to the flaring corona), and the capability of
  measuring magnetic fields through spectropolarimetry at visible and
  near-infrared wavelengths. Simultaneous spectroscopic measurements
  sampling the entire temperature range are particularly important. These
  requirements are fulfilled by the Japanese Solar-C mission (Plan B),
  composed of a spacecraft in a geosynchronous orbit with a payload
  providing a significant improvement of imaging and spectropolarimetric
  capabilities in the UV, visible, and near-infrared with respect to
  what is available today and foreseen in the near future. The Large
  European Module for solar Ultraviolet Research (LEMUR), described
  in this paper, is a large VUV telescope feeding a scientific payload
  of high-resolution imaging spectrographs and cameras. LEMUR consists
  of two major components: a VUV solar telescope with a 30 cm diameter
  mirror and a focal length of 3.6 m, and a focal-plane package composed
  of VUV spectrometers covering six carefully chosen wavelength ranges
  between 170 Å and 1270 Å. The LEMUR slit covers 280'' on the Sun with
  0.14'' per pixel sampling. In addition, LEMUR is capable of measuring
  mass flows velocities (line shifts) down to 2 km s<SUP> - 1</SUP> or
  better. LEMUR has been proposed to ESA as the European contribution
  to the Solar C mission.

Title: Spectroscopic observations of propagating disturbances in a
polar coronal hole: evidence of slow magneto-acoustic waves
Authors: Gupta, G. R.; Teriaca, L.; Marsch, E.; Solanki, S. K.;
   Banerjee, D.
Bibcode: 2012A&A...546A..93G
Altcode: 2012arXiv1209.3524G
  <BR /> Aims: We focus on detecting and studying quasi-periodic
  propagating features that have been interpreted in terms of both slow
  magneto-acoustic waves and of high-speed upflows. <BR /> Methods:
  We analyzed long-duration spectroscopic observations of the on-disk
  part of the south polar coronal hole taken on 1997 February 25 by
  the SUMER spectrometer onboard SOHO. We calibrated the velocity
  with respect to the off-limb region and obtained time-distance maps
  in intensity, Doppler velocity, and line width. We also performed a
  cross-correlation analysis on different time series curves at different
  latitudes. We studied average spectral line profiles at the roots
  of propagating disturbances and along the propagating ridges, and
  performed a red-blue asymmetry analysis. <BR /> Results: We clearly
  find propagating disturbances in intensity and Doppler velocity with
  a projected propagation speed of about 60 ± 4.8 km s<SUP>-1</SUP>
  and a periodicity of ≈14.5 min. To our knowledge, this is the first
  simultaneous detection of propagating disturbances in intensity as
  well as in Doppler velocity in a coronal hole. During the propagation,
  an intensity enhancement is associated with a blueshifted Doppler
  velocity. These disturbances are clearly seen in intensity also
  at higher latitudes (i.e., closer to the limb), while disturbances
  in Doppler velocity become faint there. The spectral line profiles
  averaged along the propagating ridges are found to be symmetric, to
  be well fitted by a single Gaussian, and have no noticeable red-blue
  asymmetry. <BR /> Conclusions: Based on our analysis, we interpret
  these disturbances in terms of propagating slow magneto-acoustic waves.

Title: Resolving the Internal Magnetic Structure of the Solar Network
Authors: Martínez González, M. J.; Bellot Rubio, L. R.; Solanki,
   S. K.; Martínez Pillet, V.; Del Toro Iniesta, J. C.; Barthol, P.;
   Schmidt, W.
Bibcode: 2012ApJ...758L..40M
Altcode: 2012arXiv1209.2584M
  We analyze the spectral asymmetry of Stokes V (circularly polarized)
  profiles of an individual network patch in the quiet Sun observed
  by Sunrise/IMaX. At a spatial resolution of 0farcs15-0farcs18, the
  network elements contain substructure which is revealed by the spatial
  distribution of Stokes V asymmetries. The area asymmetry between the
  red and blue lobes of Stokes V increases from nearly zero at the core
  of the structure to values close to unity at its edges (single-lobed
  profiles). Such a distribution of the area asymmetry is consistent
  with magnetic fields expanding with height, i.e., an expanding
  magnetic canopy (which is required to fulfill pressure balance and
  flux conservation in the solar atmosphere). Inversion of the Stokes
  I and V profiles of the patch confirms this picture, revealing a
  decreasing field strength and increasing height of the canopy base
  from the core to the periphery of the network patch. However, the
  non-roundish shape of the structure and the presence of negative area
  and amplitude asymmetries reveal that the scenario is more complex than
  a canonical flux tube expanding with height surrounded by downflows.

Title: Nitrate in Polar Ice: A New Tracer of Solar Variability
Authors: Traversi, R.; Usoskin, I. G.; Solanki, S. K.; Becagli, S.;
   Frezzotti, M.; Severi, M.; Stenni, B.; Udisti, R.
Bibcode: 2012SoPh..280..237T
Altcode: 2012SoPh..tmp..169T
  Knowledge of the long-term variability of solar activity is of
  both astrophysical and geoscientific interest. Reconstructions of
  solar activity over multiple millennia are traditionally based on
  cosmogenic isotopes <SUP>14</SUP>C or <SUP>10</SUP>Be measured in
  natural terrestrial archives, but the two isotopes exhibit significant
  differences on millennial time scales, so that our knowledge of solar
  activity at this time scale remains somewhat uncertain. Here we present
  a new potential proxy of solar activity on the centennial-millennial
  time scale, based on a chemical tracer, viz. nitrate content in an ice
  core drilled at Talos Dome (Antarctica). We argue that this location
  is optimal for preserving the solar signal in the nitrate content
  during the Holocene. By using the firn core from the same location
  we show that the 11-year and Gleissberg cycles are present with the
  variability of 10 - 25 % in nitrate content in the pre-industrial
  epoch. This is consistent with the results of independent efforts of
  modeling HNO<SUB>3</SUB> and NO<SUB>y</SUB> in Antarctic near surface
  air. However, meteorological noise on the interannual scale makes
  it impossible to resolve individual solar cycles. Based on different
  processes of formation and transport compared to cosmogenic isotopes,
  it provides new, independent insight into long-term solar activity
  and helps resolve the uncertainties related to cosmogenic isotopes as
  diagnostics of solar activity.

Title: Results and perspectives of the solar axion search with the
    CAST experiment
Authors: Ferrer-Ribas, E.; Arik, M.; Aune, S.; Barth, K.; Belov,
   A.; Borghi, S.; Bräuninger, H.; Cantatore, G.; Carmona, J. M.;
   Cetin, S. A.; Collar, J. I.; Dafni, T.; Davenport, M.; Eleftheriadis,
   C.; Elias, N.; Ezer, C.; Fanourakis, G.; Friedrich, P.; Galán, J.;
   García, J. A.; Gardikiotis, A.; Garza, J. G.; Gazis, E. N.; Geralis,
   T.; Giomataris, I.; Gninenko, S.; Gómez, H.; Gruber, E.; Guthörl,
   T.; Hartmann, R.; Haug, F.; Hasinoff, M. D.; Hoffmann, D. H. H.;
   Iguaz, F. J.; Irastorza, I. G.; Jacoby, J.; Jakovčić, K.; Karuza,
   M.; Königsmann, K.; Kotthaus, R.; Krčmar, M.; Kuster, M.; Lakić,
   B.; Laurent, J. M.; Liolios, A.; Ljubičić, A.; Lozza, V.; Lutz, G.;
   Luzón, G.; Morales, J.; Niinikoski, T.; Nordt, A.; Papaevangelou, T.;
   Pivovaroff, M. J.; Raffelt, G.; Rashba, T.; Riege, H.; Rodríguez,
   A.; Rosu, M.; Ruz, J.; Savvidis, I.; Silva, P. S.; Solanki, S. K.;
   Stewart, L.; Tomás, A.; Tsagri, M.; van Bibber, K.; Vafeiadis, T.;
   Villar, J.; Vogel, J. K.; Yildiz, S. C.; Zioutas, K.
Bibcode: 2012arXiv1209.6347F
Altcode:
  The status of the solar axion search with the CERN Axion Solar Telescope
  (CAST) will be presented. Recent results obtained by the use of $^3$He
  as a buffer gas has allowed us to extend our sensitivity to higher axion
  masses than our previous measurements with $^4$He. With about 1 h of
  data taking at each of 252 different pressure settings we have scanned
  the axion mass range 0.39 eV$ \le m_{a} \le $ 0.64 eV. From the absence
  of an excess of x rays when the magnet was pointing to the Sun we set
  a typical upper limit on the axion-photon coupling of g$_{a\gamma} \le
  2.3\times 10^{-10}$ GeV$^{-1}$ at 95% C.L., the exact value depending
  on the pressure setting. CAST published results represent the best
  experimental limit on the photon couplings to axions and other similar
  exotic particles dubbed WISPs (Weakly Interacting Slim Particles)
  in the considered mass range and for the first time the limit enters
  the region favored by QCD axion models. Preliminary sensitivities for
  axion masses up to 1.16 eV will also be shown reaching mean upper limits
  on the axion-photon coupling of g$_{a\gamma} \le 3.5\times 10^{-10}$
  GeV$^{-1}$ at 95% C.L. Expected sensibilities for the extension of the
  CAST program up to 2014 will be presented. Moreover long term options
  for a new helioscope experiment will be evoked.

Title: Multi Element Telescope for Imaging and Spectroscopy (METIS)
    coronagraph for the Solar Orbiter mission
Authors: Antonucci, Ester; Fineschi, Silvano; Naletto, Giampiero;
   Romoli, Marco; Spadaro, Daniele; Nicolini, Gianalfredo; Nicolosi,
   Piergiorgio; Abbo, Lucia; Andretta, Vincenzo; Bemporad, Alessandro;
   Auchère, Frédéric; Berlicki, Arkadiusz; Bruno, Roberto; Capobianco,
   Gerardo; Ciaravella, Angela; Crescenzio, Giuseppe; Da Deppo, Vania;
   D'Amicis, Raffaella; Focardi, Mauro; Frassetto, Fabio; Heinzel,
   Peter; Lamy, Philippe L.; Landini, Federico; Massone, Giuseppe;
   Malvezzi, Marco A.; Moses, J. Dan; Pancrazzi, Maurizio; Pelizzo,
   Maria-Guglielmina; Poletto, Luca; Schühle, Udo H.; Solanki, Sami K.;
   Telloni, Daniele; Teriaca, Luca; Uslenghi, Michela
Bibcode: 2012SPIE.8443E..09A
Altcode:
  METIS, the “Multi Element Telescope for Imaging and Spectroscopy”,
  is a coronagraph selected by the European Space Agency to be part of
  the payload of the Solar Orbiter mission to be launched in 2017. The
  unique profile of this mission will allow 1) a close approach to the
  Sun (up to 0.28 A.U.) thus leading to a significant improvement in
  spatial resolution; 2) quasi co-rotation with the Sun, resulting in
  observations that nearly freeze for several days the large-scale outer
  corona in the plane of the sky and 3) unprecedented out-of-ecliptic
  view of the solar corona. This paper describes the experiment concept
  and the observational tools required to achieve the science drivers
  of METIS. METIS will be capable of obtaining for the first time: •
  simultaneous imaging of the full corona in polarized visible-light
  (590-650 nm) and narrow-band ultraviolet HI Lyman α (121.6 nm); •
  monochromatic imaging of the full corona in the extreme ultraviolet
  He II Lyman α (30.4 nm); • spectrographic observations of the HI
  and He II Ly α in corona. These measurements will allow a complete
  characterization of the three most important plasma components of
  the corona and the solar wind, that is, electrons, hydrogen, and
  helium. This presentation gives an overview of the METIS imaging and
  spectroscopic observational capabilities to carry out such measurements.

Title: METIS: a novel coronagraph design for the Solar Orbiter mission
Authors: Fineschi, Silvano; Antonucci, Ester; Naletto, Giampiero;
   Romoli, Marco; Spadaro, Daniele; Nicolini, Gianalfredo; Abbo, Lucia;
   Andretta, Vincenzo; Bemporad, Alessandro; Berlicki, Arkadiusz;
   Capobianco, Gerardo; Crescenzio, Giuseppe; Da Deppo, Vania; Focardi,
   Mauro; Landini, Federico; Massone, Giuseppe; Malvezzi, Marco A.;
   Moses, J. Dan; Nicolosi, Piergiorgio; Pancrazzi, Maurizio; Pelizzo,
   Maria-Guglielmina; Poletto, Luca; Schühle, Udo H.; Solanki, Sami K.;
   Telloni, Daniele; Teriaca, Luca; Uslenghi, Michela
Bibcode: 2012SPIE.8443E..3HF
Altcode:
  METIS (Multi Element Telescope for Imaging and Spectroscopy) METIS,
  the “Multi Element Telescope for Imaging and Spectroscopy”,
  is a coronagraph selected by the European Space Agency to be part
  of the payload of the Solar Orbiter mission to be launched in
  2017. The mission profile will bring the Solar Orbiter spacecraft
  as close to the Sun as 0.3 A.U., and up to 35° out-of-ecliptic
  providing a unique platform for helio-synchronous observations of
  the Sun and its polar regions. METIS coronagraph is designed for
  multi-wavelength imaging and spectroscopy of the solar corona. This
  presentation gives an overview of the innovative design elements of
  the METIS coronagraph. These elements include: i) multi-wavelength,
  reflecting Gregorian-telescope; ii) multilayer coating optimized for
  the extreme UV (30.4 nm, HeII Lyman-α) with a reflecting cap-layer
  for the UV (121.6 nm, HI Lyman-α) and visible-light (590-650); iii)
  inverse external-occulter scheme for reduced thermal load at spacecraft
  peri-helion; iv) EUV/UV spectrograph using the telescope primary mirror
  to feed a 1<SUP>st</SUP> and 4<SUP>th</SUP>-order spherical varied
  line-spaced (SVLS) grating placed on a section of the secondary mirror;
  v) liquid crystals electro-optic polarimeter for observations of the
  visible-light K-corona. The expected performances are also presented.

Title: Grand minima of solar activity during the last millennia
Authors: Usoskin, Ilya G.; Solanki, Sami K.; Kovaltsov, Gennady A.
Bibcode: 2012IAUS..286..372U
Altcode:
  In this review we discuss the occurrence and statistical properties of
  Grand minima based on the available data covering the last millennia. In
  particular, we consider the historical record of sunspot numbers
  covering the last 400 years as well as records of cosmogenic isotopes
  in natural terrestrial archives, used to reconstruct solar activity
  for up to the last 11.5 millennia, i.e. throughout the Holocene. Using
  a reconstruction of solar activity from cosmogenic isotope data, we
  analyze statistics of the occurrence of Grand minima. We find that: the
  Sun spends about most of the time at moderate activity, 1/6 in a Grand
  minimum and some time also in a Grand maximum state; Occurrence of Grand
  minima is not a result of long-term cyclic variations but is defined
  by stochastic/chaotic processes; There is a tendency for Grand minima
  to cluster with the recurrence rate of roughly 2000-3000 years, with
  a weak ~210-yr periodicity existing within the clusters. Grand minima
  occur of two different types: shorter than 100 years (Maunder-type)
  and long ~150 years (Spörer-type). It is also discussed that solar
  cycles (most possibly not sunspots cycle) could exist during the
  Grand minima, perhaps with stretched length and asymmetric sunspot
  latitudinal distribution. <P />These results set new observational
  constraints on long-term solar and stellar dynamo models.

Title: A reconstruction of solar irradiance using a flux transport
    model
Authors: Dasi Espuig, Maria; Krivova, Natalie; Solanki, Sami K.;
   Jiang, Jie
Bibcode: 2012cosp...39..418D
Altcode: 2012cosp.meet..418D
  Solar irradiance is one of the important drivers of the Earth's
  global climate, but it has only been measured for the past 33
  years. Its reconstructions are therefore crucial to study longer
  term variations relevant to climate timescales. Most successful in
  reproducing the measured irradiance variations have being the models
  that are based on the assumption that irradiance changes are caused by
  the evolution of the photospheric magnetic field. Our SATIRE-S model
  is one of these, which uses solar full-disc magnetograms as an input,
  and these are available for less than four decades. To reconstruct the
  irradiance back to times when no observed magnetograms are available,
  we combine the SATIRE-S model with synthetic magnetograms, produced
  using a surface flux transport model. The model is fed with daily,
  observed or modelled statistically, records of sunspot positions,
  areas, and tilt angles. The concept of overlapping ephemeral region
  cycles is used to describe the secular change in the irradiance.

Title: Solar Spectral Irradiance as observed by LYRA/PROBA2 and
    PREMOS/PICARD
Authors: Cessateur, Gaël.; Kretzschmar, Matthieu; Krivova, Natalie;
   Schmutz, Werner; Solanki, Sami K.; Thuillier, Gerard; Shapiro,
   Alexander; Schoell, Micha; Shapiro, Anna; Dominique, Marie; Tagirov,
   Rinat; Wehrli, Christoph; Yeo, Kok Leng
Bibcode: 2012cosp...39..287C
Altcode: 2012cosp.meet..287C
  No abstract at ADS

Title: Spectroscopic Observations of Propagating Disturbances in
    Polar Coronal Hole
Authors: Gupta, Girjesh R.; Marsch, Eckart; Solanki, Sami K.; Banerjee,
   Dipankar; Teriaca, Luca
Bibcode: 2012cosp...39..689G
Altcode: 2012cosp.meet..689G
  We focus on long duration spectroscopic observations of the south
  polar coronal hole taken on 1997 February 25 by the Solar Ultraviolet
  Measurements of Emitted Radiation (SUMER) spectrometer aboard SOHO. We
  analyze the data in the on-disk part of the coronal hole to find any
  signature of propagating waves or high speed up-flows. We find the
  clear presence of propagating disturbances in intensity and Doppler
  velocity with a projected propagation speed of about 60~km~s^{-1} and
  a periodicity of ≈14.5~min. During the propagation, the intensity
  enhancement is associated with a blue-shifted Doppler velocity. These
  disturbances are clearly seen in intensity at higher latitudes
  (i.e. closer to the limb), whereas disturbances in Doppler velocity
  becomes faint there. We study average spectral line profiles at the
  roots of these disturbances and along the propagating ridge. Based on
  our analysis, we interpret these disturbances in terms of propagating
  slow magneto-acoustic waves.

Title: Long-term reconstructions of total solar irradiance
Authors: Krivova, Natalie; Solanki, Sami K.; Dasi Espuig, Maria
Bibcode: 2012cosp...39..985K
Altcode: 2012cosp.meet..985K
  Solar irradiance is the main external driver of the Earth's climate,
  although its relative contribution compared to other internal and
  anthropogenic factors is not yet well determined. Variations of total
  solar irradiance have being measured for over three decades and are
  relatively well understood. Reconstructions of the irradiance into the
  past remain, however, rather uncertain. In particular, the magnitude of
  the secular change is highly debated. The reason is the lack of direct
  and well-sampled proxies of solar magnetic activity on time scales
  longer than a few decades. Reconstructions on time scales of centuries
  rely on sunspot observations available since 1610. Reconstructions on
  millennial time scales use concentrations of the cosmogenic isotopes
  in terrestrial archives. We will review long-term reconstructions of
  the solar irradiance using the SATIRE set of models, compare them with
  other recent models and discuss the remaining uncertainties.

Title: Nitrate in polar ice as a new index of solar variability
Authors: Traversi, Rita; Usoskin, Ilya; Solanki, Sami K.; Becagli,
   Silvia; Frezzotti, Massimo; Severi, Mirko; Stenni, Barbara; Udisti,
   Roberto
Bibcode: 2012cosp...39.2001T
Altcode: 2012cosp.meet.2001T
  The Sun affects Earth's climate and environment in multiple ways and
  on different time scales but understanding if and how the variations
  in solar radiative output might drive global climatic change has
  revealed to be a complex and controversial issue. In order to address
  the question about the Sun's role on the climate in the past, present
  and, eventually, in the future, a reliable reconstruction of solar
  activity is mandatory. Over millennia time scales, a quantitative
  information about past solar activity can only be obtained through
  proxies recorded in natural stratified archives (e.g., tree rings or
  ice cores), such as the cosmogenic isotopes 14C and 10Be. Nonetheless,
  the two isotopes exhibit significant differences on millennial time
  scales, making our knowledge of solar activity at this time scale less
  certain. Here we present a new potential proxy of solar activity on the
  centennial-millennial time scale, namely nitrate content in the TALDICE
  ice core (Talos Dome, placeEast Antarctica). Talos Dome site was shown
  to be favourably located to minimize possible local climate effects,
  which may be dominant in other coastal sites and, due to a sufficiently
  high snow accumulation rate throughout the Holocene, such a reversibly
  deposited species as nitrate is preserved here (in contrast to inland
  Antarctic sites) making it a potential paleomarker. Comparing the
  TALDICE nitrate record with the two traditionally used cosmogenic
  proxies of solar activity, we observed that a highly significant
  agreement on the millennial and multi-millennial time scales over the
  Holocene. The relation at centennial time scales is less significant,
  likely due to ice core dating uncertainties. No statistical relationship
  was found between the nitrate data series and other chemical markers
  of local climate/transport. Consequently, the coherence between
  nitrate and cosmogenic isotopes univocally suggests a common origin
  of their long-term variability. As concerning the more recent times,
  we show that the 11-year and Gleissberg cycles are present at a level
  of 10-25% in nitrate content in the pre-industrial epoch after the
  Maunder minimum, which is in agreement with model results. However, the
  ``meteorological noise'' on the interannual scale makes it impossible
  to resolve individual solar cycles. Since nitrate is characterised by
  different processes of formation and transport, compared to cosmogenic
  isotopes, we conclude that nitrate in this Antarctic ice core forms
  a novel proxy of solar activity on the centennial and longer time
  scales and could help in reconciling the discrepancies between the
  two cosmogenic isotopes as diagnostics of solar activity.

Title: Status and perspectives of the CAST experiment
Authors: Lakić, B.; Arik, M.; Aune, S.; Barth, K.; Belov, A.;
   Borghi, S.; Bräuninger, H.; Cantatore, G.; Carmona, J. M.; Cetin,
   S. A.; Collar, J. I.; Dafni, T.; Davenport, M.; Eleftheriadis, C.;
   Elias, N.; Ezer, C.; Fanourakis, G.; Ferrer-Ribas, E.; Friedrich, P.;
   Galán, J.; García, J. A.; Gardikiotis, A.; Gazis, E. N.; Geralis,
   T.; Giomataris, I.; Gninenko, S.; Gómez, H.; Gruber, E.; Guthörl,
   T.; Hartmann, R.; Haug, F.; Hasinoff, M. D.; Hoffmann, D. H. H.;
   Iguaz, F. J.; Irastorza, I. G.; Jacoby, J.; Jakovčić, K.; Karuza,
   M.; Königsmann, K.; Kotthaus, R.; Krčmar, M.; Kuster, M.; Laurent,
   J. M.; Liolios, A.; Ljubičić, A.; Lozza, V.; Lutz, G.; Luzón, G.;
   Morales, J.; Niinikoski, T.; Nordt, A.; Papaevangelou, T.; Pivovaroff,
   M. J.; Raffelt, G.; Rashba, T.; Riege, H.; Rodríguez, A.; Rosu, M.;
   Ruz, J.; Savvidis, I.; Silva, P. S.; Solanki, S. K.; Stewart, L.;
   Tomás, A.; Tsagri, M.; van Bibber, K.; Vafeiadis, T.; Villar, J.;
   Vogel, J. K.; Yildiz, S. C.; Zioutas, K.; Cast Collaboration
Bibcode: 2012JPhCS.375b2001L
Altcode:
  The CERN Axion Solar Telescope (CAST) is currently the most sensitive
  axion helioscope designed to search for axions produced by the Primakoff
  process in the solar core. CAST is using a Large Hadron Collider (LHC)
  test magnet where axions could be converted into X-rays with energies
  up to 10 keV. During the phase I, the experiment operated with vacuum
  inside the magnet bores and covered axion masses up to 0.02 eV. In
  the phase II, the magnet bores were filled with a buffer gas (first
  <SUP>4</SUP>He and later <SUP>3</SUP>He) at various densities in order
  to extend the sensitivity to higher axion masses (up to f .18 eV). The
  phase II data taking was completed in 2011. So far, no evidence of axion
  signal has been found and CAST set the most restrictive experimental
  limit on the axion-photon coupling constant over a broad range of axion
  masses. The latest CAST results with <SUP>3</SUP>He data in the mass
  range 0.39 eV &lt; m<SUB>a</SUB> &lt; 0.64 eV will be presented.

Title: Waves as the Source of Apparent Twisting Motions in Sunspot
    Penumbrae
Authors: Bharti, L.; Cameron, R. H.; Rempel, M.; Hirzberger, J.;
   Solanki, S. K.
Bibcode: 2012ApJ...752..128B
Altcode: 2012arXiv1204.2221B
  The motion of dark striations across bright filaments in a sunspot
  penumbra has become an important new diagnostic of convective gas
  flows in penumbral filaments. The nature of these striations has,
  however, remained unclear. Here, we present an analysis of small-scale
  motions in penumbral filaments in both simulations and observations. The
  simulations, when viewed from above, show fine structure with dark lanes
  running outward from the dark core of the penumbral filaments. The
  dark lanes either occur preferentially on one side or alternate
  between both sides of the filament. We identify this fine structure
  with transverse (kink) oscillations of the filament, corresponding to
  a sideways swaying of the filament. These oscillations have periods in
  the range of 5-7 minutes and propagate outward and downward along the
  filament. Similar features are found in observed G-band intensity time
  series of penumbral filaments in a sunspot located near disk center
  obtained by the Broadband Filter Imager on board the Hinode. We also
  find that some filaments show dark striations moving to both sides
  of the filaments. Based on the agreement between simulations and
  observations we conclude that the motions of these striations are
  caused by transverse oscillations of the underlying bright filaments.

Title: Chromospheric magnetic fields of an active region filament
Authors: Xu, Z.; Solanki, S.; Lagg, A.
Bibcode: 2012EAS....55..163X
Altcode:
  Vector magnetic fields of an active region filament are co-spatially
  and co-temporally mapped in photosphere and upper chromosphere, by
  using spectro-polarimetric observations made by Tenerife Infrared
  Polarimeter (TIP II) at the German Vacuum Tower Telescope (VTT). A
  Zeeman-based ME inversion is performed on the full Stokes vectors
  of both the photospheric Si I 1082.7 nm and the chromospheric He
  I 1083.0 nm lines. We found that the strong magnetic fields, with
  the field strength of 600 - 800 G in the He I line formation height,
  are not uncommon among AR filaments. But such strong magnetic field
  is not always found in AR filaments.

Title: The continuum intensity as a function of magnetic
    field. II. Local magnetic flux and convective flows
Authors: Kobel, P.; Solanki, S. K.; Borrero, J. M.
Bibcode: 2012A&A...542A..96K
Altcode: 2014arXiv1402.3474K
  Context. To deepen our understanding of the role of small-scale magnetic
  fields in active regions (ARs) and in the quiet Sun (QS) on the solar
  irradiance, it is fundamental to investigate the physical processes
  underlying their continuum brightness. Previous results showed that
  magnetic elements in the QS reach larger continuum intensities than
  in ARs at disk center, but left this difference unexplained. <BR />
  Aims: We use Hinode/SP disk center data to study the influence of
  the local amount of magnetic flux on the vigour of the convective
  flows and the continuum intensity contrasts. <BR /> Methods: The
  apparent (i.e. averaged over a pixel) longitudinal field strength
  and line-of-sight (LOS) plasma velocity were retrieved by means
  of Milne-Eddington inversions (VFISV code). We analyzed a series
  of boxes taken over AR plages and the QS, to determine how the
  continuum intensity contrast of magnetic elements, the amplitude of
  the vertical flows and the box-averaged contrast were affected by the
  mean longitudinal field strength in the box (which scales with the total
  unsigned flux in the box). <BR /> Results: Both the continuum brightness
  of the magnetic elements and the dispersion of the LOS velocities
  anti-correlate with the mean longitudinal field strength. This can
  be attributed to the "magnetic patches" (here defined as areas where
  the longitudinal field strength is above 100 G) carrying most of the
  flux in the boxes. There the velocity amplitude and the spatial scale
  of convection are reduced. Due to this hampered convective transport,
  these patches appear darker than their surroundings. Consequently, the
  average brightness of a box decreases as the the patches occupy a larger
  fraction of it and the amount of embedded flux thereby increases. <BR />
  Conclusions: Our results suggest that as the magnetic flux increases
  locally (e.g. from weak network to strong plage), the heating of the
  magnetic elements is reduced by the intermediate of a more suppressed
  convective energy transport within the larger and stronger magnetic
  patches. This, together with the known presence of larger magnetic
  features, could explain the previously found lower contrasts of the
  brightest magnetic elements in ARs compared to the QS. The inhibition
  of convection also affects the average continuum brightness of a
  photospheric region, so that at disk center, an area of photosphere in
  strong network or plage appears darker than a purely quiet one. This
  is qualitatively consistent with the predictions of 3D MHD simulations.

Title: First Results from the SUNRISE Mission
Authors: Solanki, S. K.; Barthol, P.; Danilovic, S.; Feller, A.;
   Gandorfer, A.; Hirzberger, J.; Jafarzadeh, S.; Lagg, A.; Riethmüller,
   T. L.; Schüssler, M.; Wiegelmann, T.; Bonet, J. A.; González,
   M. J. M.; Pillet, V. M.; Khomenko, E.; Yelles Chaouche, L.; Iniesta,
   J. C. d. T.; Domingo, V.; Palacios, J.; Knölker, M.; González,
   N. B.; Borrero, J. M.; Berkefeld, T.; Franz, M.; Roth, M.; Schmidt,
   W.; Steiner, O.; Title, A. M.
Bibcode: 2012ASPC..455..143S
Altcode:
  The SUNRISE balloon-borne solar observatory consists of a 1m aperture
  Gregory telescope, a UV filter imager, an imaging vector polarimeter,
  an image stabilization system, and further infrastructure. The first
  science flight of SUNRISE yielded high-quality data that reveal the
  structure, dynamics, and evolution of solar convection, oscillations,
  and magnetic fields at a resolution of around 100 km in the quiet
  Sun. Here we describe very briefly the mission and the first results
  obtained from the SUNRISE data, which include a number of discoveries.

Title: Detection of Vortex Tubes in Solar Granulation from
    Observations SUNRISE
Authors: Steiner, O.; Franz, M.; González, N. B.; Nutto, C.; Rezaei,
   R.; Pillet, V. M.; Bonet, J. A.; Iniesta, J. C. d. T.; Domingo, V.;
   Solanki, S. K.; Knölker, M.; Schmidt, W.; Barthol, P.; Gandorfer, A.
Bibcode: 2012ASPC..455...35S
Altcode:
  We investigated a time series of continuum intensity maps and
  Dopplergrams of granulation in a very quiet solar region at the disk
  center, recorded with the Imaging Magnetograph eXperiment (IMaX)
  on board the balloon-borne solar observatory SUNRISE. We find that
  granules frequently show substructure in the form of lanes composed of
  a leading bright rim and a trailing dark edge, which move together
  from the boundary of a granule into the granule itself. We find
  strikingly similar events in synthesized intensity maps from an ab
  initio numerical simulation of solar surface convection. We conclude
  that these granular lanes are the visible signature of (horizontally
  oriented) vortex tubes. The characteristic optical appearance of vortex
  tubes at the solar surface is explained. This paper is a summary and
  update of the results previously presented in Steiner et al. (2010).

Title: Supersonic Magnetic Flows in the Quiet Sun Observed with
    SUNRISE/IMaX
Authors: Borrero, J. M.; Pillet, V. M.; Schlichenmaier, R.; Schmidt,
   W.; Berkefeld, T.; Solanki, S. K.; Bonet, J. A.; Iniesta, J. C. d. T.;
   Domingo, V.; Barthol, P.; Gandorfer, A.
Bibcode: 2012ASPC..455..155B
Altcode: 2012arXiv1202.4354B
  In this contribution we describe some recent observations of high-speed
  magnetized flows in the quiet Sun granulation. These observations
  were carried out with the Imaging Magnetograph eXperiment (IMaX)
  onboard the stratospheric balloon SUNRISE, and possess an unprecedented
  spatial resolution and temporal cadence. These flows were identified as
  highly shifted circular polarization (Stokes V) signals. We estimate
  the LOS velocity responsible for these shifts to be larger than 6 km
  s<SUP>-1</SUP>, and therefore we refer to them as supersonic magnetic
  flows. The average lifetime of the detected events is 81.3 s and
  they occupy an average area of about 23 000 km<SUP>2</SUP>. Most of
  the events occur within granular cells and correspond therefore to
  upflows. However some others occur in intergranular lanes or bear no
  clear relation to the convective velocity pattern. We analyze a number
  of representative examples and discuss them in terms of magnetic loops,
  reconnection events, and convective collapse.

Title: Reconstruction of total solar irradiance 1974-2009
Authors: Ball, W. T.; Unruh, Y. C.; Krivova, N. A.; Solanki, S.;
   Wenzler, T.; Mortlock, D. J.; Jaffe, A. H.
Bibcode: 2012A&A...541A..27B
Altcode: 2012arXiv1202.3554B
  Context. The study of variations in total solar irradiance (TSI)
  is important for understanding how the Sun affects the Earth's
  climate. <BR /> Aims: Full-disk continuum images and magnetograms are
  now available for three full solar cycles. We investigate how modelled
  TSI compares with direct observations by building a consistent modelled
  TSI dataset. The model, based only on changes in the photospheric
  magnetic flux can then be tested on rotational, cyclical and secular
  timescales. <BR /> Methods: We use Kitt Peak and SoHO/MDI continuum
  images and magnetograms in the SATIRE-S model to reconstruct TSI over
  cycles 21-23. To maximise independence from TSI composites, SORCE/TIM
  TSI data are used to fix the one free parameter of the model. We compare
  and combine the separate data sources for the model to estimate an
  uncertainty on the reconstruction and prevent any additional free
  parameters entering the model. <BR /> Results: The reconstruction
  supports the PMOD composite as being the best historical record of
  TSI observations, although on timescales of the solar rotation the
  IRMB composite provides somewhat better agreement. Further to this,
  the model is able to account for 92% of TSI variations from 1978
  to 2009 in the PMOD composite and over 96% during cycle 23. The
  reconstruction also displays an inter-cycle, secular decline of
  0.20<SUP>+0.12</SUP><SUB>-0.09</SUB> W m<SUP>-2</SUP> between cycle
  23 minima, in agreement with the PMOD composite. <BR /> Conclusions:
  SATIRE-S is able to recreate TSI observations on all timescales of a
  day and longer over 31 years from 1978. This is strong evidence that
  changes in photospheric magnetic flux alone are responsible for almost
  all solar irradiance variations over the last three solar cycles.

Title: Solar Spectral Irradiance as observed by LYRA/PROBA2 and
    PREMOS/PICARD
Authors: Cessateur, G.; Shapiro, A. I.; Dominique, M.; Kretzschmar,
   M.; Krivova, N.; Shapiro, A. V.; Schmutz, W.; Schoell, M.; Solanki,
   S.; Tagirov, R.; Thuillier, G.; Wehrli, C.; Yeo, K. L.
Bibcode: 2012EGUGA..14.8254C
Altcode:
  Total and Spectral Solar Irradiance are key input parameters to
  atmospheric/oceanic and space weather models. Both vary on time-scales
  ranging from days to millennia, although a complete picture of the
  solar irradiance variability is still missing. The recent launch of
  two European missions PROBA-2 with LYRA radiometer onboard and PICARD
  with PREMOS package onboard provides therefore valuable information and
  nourishes theoretical models. Both instruments covers the solar spectrum
  from the EUV to near-infrared. Here we present spectral solar irradiance
  data from these two recent missions. After a proper correction of the
  degradation and non-solar signatures, we compare these data with those
  from the VIRGO/SOHO and SOLSTICE+SIM/SORCE experiments. Both LYRA and
  PREMOS have also observed several solar eclipses, which allows us to
  accurately retrieve the center-to-limb variations (CLVs) of the quiet
  Sun's brightness at the wavelengths of the corresponding channels. CLVs
  play indeed an important role in modelling of the solar irradiance
  variability. We show that calculations with the published COde for
  Solar Irradiance (COSI) yield CLVs that are in good agreement with
  measurements. Finally we use COSI to model the variability of the
  irradiance, assuming that the latter is determined by the evolution
  of the solar surface magnetic field as seen with SDO/HMI data. These
  theoretical results are compared to PREMOS and LYRA measurements.

Title: Break up of returning plasma after the 7 June 2011 filament
    eruption by Rayleigh-Taylor instabilities
Authors: Innes, D. E.; Cameron, R. H.; Fletcher, L.; Inhester, B.;
   Solanki, S. K.
Bibcode: 2012A&A...540L..10I
Altcode: 2012arXiv1202.4981I
  Context. A prominence eruption on 7 June 2011 produced spectacular
  curtains of plasma falling through the lower corona. At the solar
  surface they created an incredible display of extreme ultraviolet
  brightenings. <BR /> Aims: To identify and analyze some of the local
  instabilities which produce structure in the falling plasma. <BR />
  Methods: The structures were investigated using SDO/AIA 171 Å and
  193 Å images in which the falling plasma appeared dark against
  the bright coronal emission. <BR /> Results: Several instances of
  the Rayleigh-Taylor instability were investigated. In two cases the
  Alfvén velocity associated with the dense plasma could be estimated
  from the separation of the Rayleigh-Taylor fingers. A second type of
  feature, which has the appearance of self-similar branching horns was
  discussed. <P />Appendix A and two movies are available in electronic
  form at <A href="http://www.aanda.org">http://www.aanda.org</A>

Title: Long-term magnetic field monitoring of the Sun-like star ξ
    Bootis A
Authors: Morgenthaler, A.; Petit, P.; Saar, S.; Solanki, S. K.; Morin,
   J.; Marsden, S. C.; Aurière, M.; Dintrans, B.; Fares, R.; Gastine,
   T.; Lanoux, J.; Lignières, F.; Paletou, F.; Ramírez Vélez, J. C.;
   Théado, S.; Van Grootel, V.
Bibcode: 2012A&A...540A.138M
Altcode: 2011arXiv1109.5066M
  <BR /> Aims: We aim to investigate the long-term temporal evolution
  of the magnetic field of the solar-type star ξ Bootis A, both from
  direct magnetic field measurements and from the simultaneous estimate
  of indirect activity indicators. <BR /> Methods: We obtained seven
  epochs of high-resolution, circularly-polarized spectra from the
  NARVAL spectropolarimeter between 2007 and 2011, for a total of 76
  spectra. Using approximately 6100 photospheric spectral lines covering
  the visible domain, we employed a cross-correlation procedure to compute
  a mean polarized line profile from each spectrum. The large-scale
  photospheric magnetic field of the star was then modelled by means
  of Zeeman-Doppler Imaging, allowing us to follow the year-to-year
  evolution of the reconstructed magnetic topology. Simultaneously, we
  monitored the width of several magnetically sensitive spectral lines,
  the radial velocity, the line asymmetry of intensity line profiles,
  and the chromospheric emission in the cores of the Ca II H and Hα
  lines. <BR /> Results: During the highest observed activity states,
  in 2007 and 2011, the large-scale field of ξ Bootis A is almost
  completely axisymmetric and is dominated by its toroidal component. The
  toroidal component persists with a constant polarity, containing
  a significant fraction of the magnetic energy of the large-scale
  surface field through all observing epochs. The magnetic topologies
  reconstructed for these activity maxima are very similar, suggesting
  a form of short cyclicity in the large-scale field distribution. The
  mean unsigned large-scale magnetic flux derived from the magnetic
  maps varies by a factor of about 2 between the lowest and highest
  observed magnetic states. The chromospheric flux is less affected and
  varies by a factor of 1.2. Correlated temporal evolution, due to both
  rotational modulation and seasonal variability, is observed between
  the Ca II emission, the Hα emission and the width of magnetically
  sensitive lines. The rotational dependence of polarimetric magnetic
  measurements displays a weak correlation with other activity proxies,
  presumably due to the different spatial scales and centre-to-limb
  darkening associated with polarimetric signatures, as compared to
  non-polarized activity indicators. Better agreement is observed on the
  longer term. When measurable, the differential rotation reveals a strong
  latitudinal shear in excess of 0.2 rad d<SUP>-1</SUP>. <P />Based on
  observations obtained at the Bernard Lyot Telescope (TBL, Pic du Midi,
  France) of the Midi-Pyrénées Observatory, which is operated by the
  Institut National des Sciences de l'Univers of the Centre National de la
  Recherche Scientifique of France.Tables 3-6 are available in electronic
  form at <A href="http://www.aanda.org">http://www.aanda.org</A>

Title: Solar magnetism eXplorer (SolmeX). Exploring the magnetic
    field in the upper atmosphere of our closest star
Authors: Peter, Hardi; Abbo, L.; Andretta, V.; Auchère, F.; Bemporad,
   A.; Berrilli, F.; Bommier, V.; Braukhane, A.; Casini, R.; Curdt,
   W.; Davila, J.; Dittus, H.; Fineschi, S.; Fludra, A.; Gandorfer, A.;
   Griffin, D.; Inhester, B.; Lagg, A.; Landi Degl'Innocenti, E.; Maiwald,
   V.; Sainz, R. Manso; Martínez Pillet, V; Matthews, S.; Moses, D.;
   Parenti, S.; Pietarila, A.; Quantius, D.; Raouafi, N. -E.; Raymond, J.;
   Rochus, P.; Romberg, O.; Schlotterer, M.; Schühle, U.; Solanki, S.;
   Spadaro, D.; Teriaca, L.; Tomczyk, S.; Trujillo Bueno, J.; Vial, J. -C.
Bibcode: 2012ExA....33..271P
Altcode: 2011arXiv1108.5304P; 2011ExA...tmp..134P
  The magnetic field plays a pivotal role in many fields of
  Astrophysics. This is especially true for the physics of the solar
  atmosphere. Measuring the magnetic field in the upper solar atmosphere
  is crucial to understand the nature of the underlying physical
  processes that drive the violent dynamics of the solar corona—that
  can also affect life on Earth. SolmeX, a fully equipped solar space
  observatory for remote-sensing observations, will provide the first
  comprehensive measurements of the strength and direction of the
  magnetic field in the upper solar atmosphere. The mission consists
  of two spacecraft, one carrying the instruments, and another one in
  formation flight at a distance of about 200 m carrying the occulter to
  provide an artificial total solar eclipse. This will ensure high-quality
  coronagraphic observations above the solar limb. SolmeX integrates two
  spectro-polarimetric coronagraphs for off-limb observations, one in
  the EUV and one in the IR, and three instruments for observations on
  the disk. The latter comprises one imaging polarimeter in the EUV for
  coronal studies, a spectro-polarimeter in the EUV to investigate the low
  corona, and an imaging spectro-polarimeter in the UV for chromospheric
  studies. SOHO and other existing missions have investigated the emission
  of the upper atmosphere in detail (not considering polarization),
  and as this will be the case also for missions planned for the near
  future. Therefore it is timely that SolmeX provides the final piece of
  the observational quest by measuring the magnetic field in the upper
  atmosphere through polarimetric observations.

Title: Magnetic Fields of an Active Region Filament from Full Stokes
    Analysis of Si I 1082.7 nm and He I 1083.0 nm
Authors: Xu, Z.; Lagg, A.; Solanki, S.; Liu, Y.
Bibcode: 2012ApJ...749..138X
Altcode: 2012arXiv1202.4562X
  Vector magnetic fields of an active region filament in the photosphere
  and upper chromosphere are obtained from spectro-polarimetric
  observations recorded with the Tenerife Infrared Polarimeter (TIP II) at
  the German Vacuum Tower Telescope. We apply Milne-Eddington inversions
  on full Stokes vectors of the photospheric Si I 1082.7 nm and the upper
  chromospheric He I triplet at 1083.0 nm to obtain the magnetic field
  vector and velocity maps in two atmosphere layers. We find that (1) a
  complete filament was already present in Hα at the beginning of the TIP
  II data acquisition. Only a partially formed one, composed of multiple
  small threads, was present in He I. (2) The AR filament comprises two
  sections. One shows strong magnetic field intensities, about 600-800
  G in the upper chromosphere and 800-1000 G in the photosphere. The
  other exhibits only comparatively weak magnetic field strengths in both
  layers. (3) The Stokes V signal is indicative of a dip in the magnetic
  field strength close to the chromospheric PIL. (4) In the chromosphere,
  consistent upflows are found along the PIL flanked by downflows. (5)
  The transversal magnetic field is nearly parallel to the PIL in the
  photosphere and inclined by 20°-30° in the chromosphere. (6) The
  chromospheric magnetic field around the filament is found to be in
  normal configuration, while the photospheric field presents a concave
  magnetic topology. The observations are consistent with the emergence
  of a flux rope with a subsequent formation of a filament.

Title: Diffusivity of Isolated Internetwork Ca II H Bright Points
    Observed by SuFI/SUNRISE
Authors: Jafarzadeh, S.; Solanki, S. K.; Cameron, R. H.; Feller, A.;
   Pietarila, A.; Lagg, A.; Barthol, P.; Berkefeld, T.; Gandorfer, A.;
   Knoelker, M.; Martinez Pillet, V.; Schmidt, W.; Title, A.
Bibcode: 2012decs.confE..99J
Altcode:
  We analyze trajectories of the proper motion of intrinsically magnetic,
  isolated internetwork Ca II H BPs (with mean lifetime of 461 sec) to
  obtain their diffusivity behaviors. We use high spatial and temporal
  resolution image sequences of quiet-Sun, disc-centre observations
  obtained in the Ca II H 397 nm passband of the Sunrise Filter Imager
  (SuFI) on board the SUNRISE balloon-borne solar observatory. In
  order to avoid misidentification, the BPs are semi-manually selected
  and then automatically tracked. The trajectory of each BP is then
  calculated and its diffusion index is described by a power law
  exponent, using which we classify the BPs' trajectories into sub-,
  normal and super- diffusive. In addition, the corresponding diffusion
  coefficients (D) based on the observed displacements are consequently
  computed. We find a strong super-diffusivity at a height sampled by the
  SuFI/SUNRISE Ca II H passband (i.e. a height corresponding roughly to
  the temperature minimum). We find that 74% of the identified tiny BPs
  are super-diffusive, 18% move randomly (i.e. their motion corresponds
  to normal diffusion) and only 8% belong to the sub-diffusion regime. In
  addition, we find that 53% of the super-diffusion regime (i.e. 39% of
  all BPs) have the diffusivity index of 2 which are termed as "Ballistic
  BPs". Finally, we explore the distribution of diffusion index with the
  help of a simple simulation. The results suggest that the BPs are random
  walkers superposed by a systematic (background) velocity in which the
  magnitude of each component (and hence their ratio) depends on the time
  and spatial scales. We further discuss a simple sketch to explain the
  diffusivity of observed BPs while they migrate within a supergranule
  (i.e. internetwork areas) or close to the network regions.

Title: The Frontier between Small-scale Bipoles and Ephemeral Regions
in the Solar Photosphere: Emergence and Decay of an Intermediate-scale
    Bipole Observed with SUNRISE/IMaX
Authors: Guglielmino, S. L.; Martínez Pillet, V.; Bonet, J. A.;
   del Toro Iniesta, J. Carlos; Bellot Rubio, L. R.; Solanki, S. K.;
   Schmidt, W.; Gandorfer, A.; Barthol, P.; Knölker, M.
Bibcode: 2012ApJ...745..160G
Altcode: 2011arXiv1110.1405G
  We report on the photospheric evolution of an intermediate-scale (≈4
  Mm footpoint separation) magnetic bipole, from emergence to decay,
  observed in the quiet Sun at high spatial (0farcs3) and temporal (33 s)
  resolution. The observations were acquired by the Imaging Magnetograph
  Experiment imaging magnetograph during the first science flight of the
  SUNRISE balloon-borne solar observatory. The bipole flux content is 6 ×
  10<SUP>17</SUP> Mx, representing a structure bridging the gap between
  granular scale bipoles and the smaller ephemeral regions. Footpoints
  separate at a speed of 3.5 km s<SUP>-1</SUP> and reach a maximum
  distance of 4.5 Mm before the field dissolves. The evolution of the
  bipole is revealed to be very dynamic: we found a proper motion of
  the bipole axis and detected a change of the azimuth angle of 90° in
  300 s, which may indicate the presence of some writhe in the emerging
  structure. The overall morphology and behavior are in agreement with
  previous analyses of bipolar structures emerging at the granular scale,
  but we also found several similarities with emerging flux structures
  at larger scales. The flux growth rate is 2.6 × 10<SUP>15</SUP> Mx
  s<SUP>-1</SUP>, while the mean decay rate is one order of magnitude
  smaller. We describe in some detail the decay phase of the bipole
  footpoints that includes break up into smaller structures, and
  interaction with preexisting fields leading to cancellation, but it
  appears to be dominated by an as-yet unidentified diffusive process
  that removes most of the flux with an exponential flux decay curve. The
  diffusion constant (8 × 10<SUP>2</SUP> km<SUP>2</SUP> s<SUP>-1</SUP>)
  associated with this decay is similar to the values used to describe
  the large-scale diffusion in flux transport models.

Title: The influence of spectral solar irradiance data on
    stratospheric heating rates during the 11 year solar cycle
Authors: Oberländer, S.; Langematz, U.; Matthes, K.; Kunze, M.; Kubin,
   A.; Harder, J.; Krivova, N. A.; Solanki, S. K.; Pagaran, J.; Weber, M.
Bibcode: 2012GeoRL..39.1801O
Altcode: 2012GeoRL..3901801O
  Heating rate calculations with the FUBRad shortwave (SW) radiation
  parameterization have been performed to examine the effect of
  prescribed spectral solar fluxes from the NRLSSI, MPS and IUP
  data sets on SW heating rates over the 11 year solar cycle 22. The
  corresponding temperature response is derived from perpetual January
  General Circulation Model (GCM) simulations with prescribed ozone
  concentrations. The different solar flux input data sets induce clear
  differences in SW heating rates at solar minimum, with the established
  NRLSSI data set showing the smallest solar heating rates. The stronger
  SW heating in the middle and upper stratosphere in the MPS data
  warms the summer upper stratosphere by 2 K. Over the solar cycle,
  SW heating rate differences vary up to 40% between the irradiance
  data sets, but do not result in a significant change of the solar
  temperature signal. Lower solar fluxes in the newer SIM data lead
  to a significantly cooler stratosphere and mesosphere when compared
  to NRLSSI data for 2007. Changes in SW heating from 2004 to 2007 are
  however up to six times stronger than for the NRLSSI data.

Title: Magnetic field emergence in mesogranular-sized exploding
    granules observed with sunrise/IMaX data
Authors: Palacios, J.; Blanco Rodríguez, J.; Vargas Domínguez, S.;
   Domingo, V.; Martínez Pillet, V.; Bonet, J. A.; Bellot Rubio, L. R.;
   Del Toro Iniesta, J. C.; Solanki, S. K.; Barthol, P.; Gandorfer, A.;
   Berkefeld, T.; Schmidt, W.; Knölker, M.
Bibcode: 2012A&A...537A..21P
Altcode: 2011arXiv1110.4555P
  We report on magnetic field emergences covering significant
  areas of exploding granules. The balloon-borne mission Sunrise
  provided high spatial and temporal resolution images of the solar
  photosphere. Continuum images, longitudinal and transverse magnetic
  field maps and Dopplergrams obtained by IMaX onboard Sunrise are
  analyzed by local correlation traking (LCT), divergence calculation
  and time slices, Stokes inversions and numerical simulations are also
  employed. We characterize two mesogranular-scale exploding granules
  where ~10<SUP>18</SUP> Mx of magnetic flux emerges. The emergence
  of weak unipolar longitudinal fields (~100 G) start with a single
  visible magnetic polarity, occupying their respective granules' top
  and following the granular splitting. After a while, mixed polarities
  start appearing, concentrated in downflow lanes. The events last around
  20 min. LCT analyses confirm mesogranular scale expansion, displaying
  a similar pattern for all the physical properties, and divergence
  centers match between all of them. We found a similar behaviour
  with the emergence events in a numerical MHD simulation. Granule
  expansion velocities are around 1 kms<SUP>-1</SUP> while magnetic
  patches expand at 0.65 kms<SUP>-1</SUP>. One of the analyzed events
  evidences the emergence of a loop-like structure. Advection of
  the emerging magnetic flux features is dominated by convective
  motion resulting from the exploding granule due to the magnetic
  field frozen in the granular plasma. Intensification of the
  magnetic field occurs in the intergranular lanes, probably
  because of being directed by the downflowing plasma. <P />Movies
  associated to Figs. 2-4 are available in electronic form at <A
  href="http://www.aanda.org">http://www.aanda.org</A>

Title: Search for Sub-eV Mass Solar Axions by the CERN Axion Solar
    Telescope with He3 Buffer Gas
Authors: Arik, M.; Aune, S.; Barth, K.; Belov, A.; Borghi, S.;
   Bräuninger, H.; Cantatore, G.; Carmona, J. M.; Cetin, S. A.;
   Collar, J. I.; Dafni, T.; Davenport, M.; Eleftheriadis, C.; Elias,
   N.; Ezer, C.; Fanourakis, G.; Ferrer-Ribas, E.; Friedrich, P.;
   Galán, J.; García, J. A.; Gardikiotis, A.; Gazis, E. N.; Geralis,
   T.; Giomataris, I.; Gninenko, S.; Gómez, H.; Gruber, E.; Guthörl,
   T.; Hartmann, R.; Haug, F.; Hasinoff, M. D.; Hoffmann, D. H. H.;
   Iguaz, F. J.; Irastorza, I. G.; Jacoby, J.; Jakovčić, K.; Karuza,
   M.; Königsmann, K.; Kotthaus, R.; Krčmar, M.; Kuster, M.; Lakić,
   B.; Laurent, J. M.; Liolios, A.; Ljubičić, A.; Lozza, V.; Lutz, G.;
   Luzón, G.; Morales, J.; Niinikoski, T.; Nordt, A.; Papaevangelou, T.;
   Pivovaroff, M. J.; Raffelt, G.; Rashba, T.; Riege, H.; Rodríguez,
   A.; Rosu, M.; Ruz, J.; Savvidis, I.; Silva, P. S.; Solanki, S. K.;
   Stewart, L.; Tomás, A.; Tsagri, M.; van Bibber, K.; Vafeiadis, T.;
   Villar, J. A.; Vogel, J. K.; Yildiz, S. C.; Zioutas, K.
Bibcode: 2011PhRvL.107z1302A
Altcode: 2011arXiv1106.3919A
  The CERN Axion Solar Telescope (CAST) has extended its search for
  solar axions by using He3 as a buffer gas. At T=1.8K this allows
  for larger pressure settings and hence sensitivity to higher axion
  masses than our previous measurements with He4. With about 1 h
  of data taking at each of 252 different pressure settings we have
  scanned the axion mass range 0.39eV≲m<SUB>a</SUB>≲0.64eV. From
  the absence of excess x rays when the magnet was pointing to the
  Sun we set a typical upper limit on the axion-photon coupling
  of g<SUB>aγ</SUB>≲2.3×10<SUP>-10</SUP>GeV<SUP>-1</SUP>
  at 95% C.L., the exact value depending on the pressure
  setting. Kim-Shifman-Vainshtein-Zakharov axions are excluded
  at the upper end of our mass range, the first time ever for any
  solar axion search. In the future we will extend our search to
  m<SUB>a</SUB>≲1.15eV, comfortably overlapping with cosmological hot
  dark matter bounds.

Title: Fast Up-flows Observed on Granules with Sunrise
Authors: Macdonald, G. A.; Hirzberger, J.; Solanki, S.; Choudhary,
   D. P.
Bibcode: 2011AGUFMSH13B1985M
Altcode:
  We present results from a rigorous study of fast granular up flows
  observed with the Imaging Magnetograph eXperiment (IMaX) aboard
  the SUNRISE balloon-borne observatory. A time series ∼ 23 minutes
  long made June 9, 2009 with a cadence of ∼ 33sec and resolution
  of 0.15--0.18<SUP>''</SUP> was used. Our study concentrates on up
  flows with a LOS speeds in excess of 2km/s. These flows occur most
  frequently on the bright areas of the smallest granules, and less
  so on the bright edges of larger granules. The maximum up flow speed
  tends to scale with its area which scales with the size of the host
  granule. The longest-lived up flows are located on larger granules,
  while shorter-lived ones tend to be located on smaller granules. Results
  from simulations carried out in other studies suggest that the fastest
  granular up flows occur chiefly during two scenarios: 1) on the edges
  of granules when their centers cool, before the granules subsequently
  split and 2) when a granule is forced under the surface by powerful
  down flows from adjacent granules. Our observations provide evidence
  for these results.

Title: Evolution of the fine structure of magnetic fields in the
quiet Sun: Combining Sunrise observations and modelling
Authors: Wiegelmann, T.; Solanki, S.; Borrero, J.; Martinez Pillet,
   V.; Sunrise Team
Bibcode: 2011AGUFMSH41B..06W
Altcode:
  Observations with the balloon borne SUNRISE/IMAX instrument provide
  us with unprecedented high spatial resolution (pixel size 40 km)
  measurements of the magnetic field in the photosphere of the quiet
  Sun. To investigate the magnetic structure of the chromosphere and
  corona we extrapolate these photospheric measurements into the upper
  solar atmosphere and analyse a timeseries with a cadence of 33s. We find
  that the majority of closed loops which reach into the chromosphere
  or corona have one foot point in strong photospheric magnetic field
  regions (B&gt;300 G). Most loops are asymmetric and the weaker foot
  point is often located in the internetwork. We find that the magnetic
  connectivity of the loops changes rapidly with a typical recycling
  time of about 2 min in the upper solar atmosphere and 14 min in the
  photosphere. We discuss, to which extend the observed topological
  changes can be interpreted as evidence for magnetic reconnection and
  the relevance of these processes for coronal heating.

Title: Chromospheric Observations of a Kink Wave in an On-disk Active
    Region Fibril
Authors: Pietarila, A. M.; Aznar Cuadrado, R.; Hirzberger, J.;
   Solanki, S.
Bibcode: 2011AGUFMSH13B1951P
Altcode:
  Most observations of kink and Alfven waves in the chromosphere are
  made in off-limb spicules. Here we present observations of a kink wave
  in high spatial and temporal resolution Ca II 8542 data of an active
  region fibril on the solar disk. The properties of the observed wave
  are similar to kink waves in spicules. From the inferred wave phase
  and period we estimate the lower limit for the field strength in the
  chromospheric fibril to be a few hundred Gauss. The observations
  indicate that the event may have been triggered by a small-scale
  reconnection event higher up in the atmosphere.

Title: Zeeman Broadening in Optical Stokes I of Solar-like Stars
Authors: Anderson, R. I.; Reiners, A.; Solanki, S. K.
Bibcode: 2011ASPC..448.1061A
Altcode: 2010arXiv1012.2968A; 2011csss...16.1061A
  We present our analysis aimed at inferring average magnetic fields in
  slowly-rotating solar-like stars. Using the spectral line inversion code
  SPINOR, we perform high-accuracy line profile fitting and investigate
  whether Zeeman broadening can be reliably detected in optical data
  of unprecedented quality. We argue that our usage of both high-
  and low-g<SUB>eff</SUB> lines does provide a certain sensitivity to
  magnetic fields that may, indeed, be detected. However, the measurement
  is subject to a model dependence and prone to ambiguities, e.g. due to
  spectral blends. Hence, while a field may be successfully recovered,
  the quantification of this field is subject to large uncertainties,
  even for the highest-quality optical data.

Title: Long-term Magnetic Field Monitoring of the Sun-like Star ζ
    Bootis A
Authors: Morgenthaler, A.; Petit, P.; Aurière, M.; Dintrans, B.;
   Fares, R.; Gastine, T.; Lanoux, J.; Lignières, F.; Morin, J.; Ramirez,
   J.; Saar, S.; Solanki, S. K.; Théado, S.; Van Grootel V., V.
Bibcode: 2011ASPC..448.1203M
Altcode: 2011csss...16.1203M
  Phase-resolved observations of the solar-type star ζ Bootis A were
  obtained using the NARVAL spectropolarimeter at the Telescope Bernard
  Lyot (Pic du Midi, France) during years 2007, 2008, 2009 and 2010. The
  data sets enable us to study both the rotational modulation and the
  long-term evolution of various magnetic and activity tracers. Here,
  we focus on the large-scale photospheric magnetic field (reconstructed
  by Zeeman-Doppler Imaging), the Zeeman broadening of the FeI 846.84
  nm magnetic line, and the chromospheric CaII H and Hα emission.

Title: Analyzing Solar Cycles
Authors: Solanki, Sami K.; Krivova, Natalie A.
Bibcode: 2011Sci...334..916S
Altcode:
  No abstract at ADS

Title: The quiet Sun average Doppler shift of coronal lines up to 2 MK
Authors: Dadashi, N.; Teriaca, L.; Solanki, S. K.
Bibcode: 2011A&A...534A..90D
Altcode: 2011arXiv1109.4493D
  Context. The average Doppler shift shown by spectral lines formed
  from the chromosphere to the corona reveals important information
  on the mass and energy balance of the solar atmosphere, providing
  an important observational constraint to any models of the solar
  corona. Previous spectroscopic observations of vacuum ultra-violet
  (VUV) lines have revealed a persistent average wavelength shift of
  lines formed at temperatures up to 1 MK. At higher temperatures,
  the behaviour is still essentially unknown. <BR /> Aims: Here we
  analyse combined SUMER (Solar Ultraviolet Measurements of Emitted
  Radiation)/SoHO (Solar and Heliospheric Observatory) and EIS (EUV
  Imaging Spectrometer)/Hinode observations of the quiet Sun around
  disk centre to determine, for the first time, the average Doppler
  shift of several spectral lines formed between 1 and 2 MK, where the
  largest part of the quiet coronal emission is formed. <BR /> Methods:
  The measurements are based on a novel technique applied to EIS spectra
  to measure the difference in Doppler shift between lines formed at
  different temperatures. Simultaneous wavelength-calibrated SUMER spectra
  allow establishing the absolute value at the reference temperature of
  T ≈ 1 MK. <BR /> Results: The average line shifts at 1 MK &lt; T &lt;
  1.8 MK are modestly, but clearly bluer than those observed at 1 MK. By
  accepting an average blue shift of about (-1.8 ± 0.6) km s<SUP>-1</SUP>
  at 1 MK (as provided by SUMER measurements), this translates into a
  maximum Doppler shift of (-4.4 ± 2.2) km s<SUP>-1</SUP> around 1.8
  MK. The measured value appears to decrease to about (-1.3 ± 2.6) km
  s<SUP>-1</SUP> at the Fe xv formation temperature of 2.1 MK. <BR />
  Conclusions: The measured average Doppler shift between 0.01 and 2.1
  MK, for which we provide a parametrisation, appears to be qualitatively
  and roughly quantitatively consistent with what foreseen by 3D coronal
  models where heating is produced by dissipation of currents induced
  by photospheric motions and by reconnection with emerging magnetic flux.

Title: Erratum:"Convective Nature of Sunspot Penumbral
Filaments: Discovery of Downflows in the Deep Photosphere" <A
    href="/abs/2011ApJ...734L..18J">(2011, ApJ, 734, L18)</A>
Authors: Joshi, Jayant; Pietarila, A.; Hirzberger, J.; Solanki, S. K.;
   Aznar Cuadrado, R.; Merenda, L.
Bibcode: 2011ApJ...740L..55J
Altcode:
  No abstract at ADS

Title: Kink Waves in an Active Region Dynamic Fibril
Authors: Pietarila, A.; Aznar Cuadrado, R.; Hirzberger, J.; Solanki,
   S. K.
Bibcode: 2011ApJ...739...92P
Altcode: 2011arXiv1107.3113P
  We present high spatial and temporal resolution Ca II 8542 Å
  observations of a kink wave in an on-disk chromospheric active region
  fibril. The properties of the wave are similar to those observed in
  off-limb spicules. From the observed phase and period of the wave we
  determine a lower limit for the field strength in the chromospheric
  active region fibril located at the edge of a sunspot to be a few
  hundred gauss. We find indications that the event was triggered by a
  small-scale reconnection event higher up in the atmosphere.

Title: Variation of quiet Sun magnetic elements between 2006 and
    2011 using Hinode SOT/SP
Authors: Buehler, D.; Lagg, A.; Solanki, S. K.
Bibcode: 2011sdmi.confE..76B
Altcode:
  The Hinode satellite has revealed copious amounts of horizontal flux
  covering the quiet Sun, nurturing the notion of local dynamo action
  operating close to the solar surface. We sought to investigate the
  variation in the occurrence as well as the strength of circular and
  linear polarisation on the quiet Sun during the minimum of cycle
  23, covering a period from November 2006 until August 2011. This
  investigation used Hinode SOT/SP images of the disk centre and a large
  FOV and focussed on line-integrated linear and circular polarisation
  signals obtained from the Fe I 6302.5 Å absorption line. The circular
  polarisation showed an overall linear decline in occurrence from
  November 2006 until August 2011. By comparing PDFs we found that
  this decline is associated in particular with network elements. The
  internetwork on the other hand showed a 10% decrease in occurrence
  from November 2010 until June 2009, followed by an equal increase
  until August 2011. The investigation also revealed a reduction of 30%
  in the occurrence of linear polarisation signals between November 2006
  and December 2009. From August 2010 until August 2011 the occurrence of
  linear polarisation was increasing again. Hence, our results show that
  the occurrence of the ubiquitous linear polarisation of the internetwork
  as seen by Hinode is measurably influenced by the solar cycle. This
  implies that an independent local dynamo process is unlikely to be
  the sole cause responsible for the generation of this magnetic flux.

Title: Chromosphere above sunspots as seen at millimeter wavelengths
Authors: Loukitcheva, Maria A.; Solanki, Sami K.; White, Stephen M.
Bibcode: 2011IAUS..273..408L
Altcode:
  Millimeter emission is known to be a sensitive diagnostic of temperature
  and density in the solar chromosphere. In this work we use millimeter
  wave data to distinguish between various atmospheric models of sunspots,
  whose temperature structure in the upper photosphere and chromosphere
  has been the source of some controversy. From mm brightness simulations
  we expect a radio umbra to change its appearance from dark to bright
  (compared to the Quiet Sun) at a given wavelength in the millimeter
  spectrum (depending on the exact temperature in the model used). Thereby
  the millimeter brightness observed above an umbra at several wavelengths
  imposes strong constraints on temperature and density stratification of
  the sunspot atmosphere, in particular on the location and depth of the
  temperature minimum and the location of the transition region. Current
  mm/submm observational data suggest that brightness observed at
  short wavelengths is unexpectedly low compared to the most widely
  used sunspot models such as of Maltby et al. (1986). A successful
  model that is in agreement with millimeter umbral brightness should
  have an extended and deep temperature minimum (below 3000 K), such as
  in the models of Severino et al. (1994). However, we are not able to
  resolve the umbra cleanly with the presently available observations
  and better resolution as well as better wavelength coverage are
  needed for accurate diagnostics of umbral brightness at millimeter
  wavelengths. This adds one more scientific objective for the Atacama
  Large Millimeter/Submillimeter Array (ALMA).

Title: The Sun at high resolution: first results from the Sunrise
    mission
Authors: Solanki, S. K.; Barthol, P.; Danilovic, S.; Feller,
   A.; Gandorfer, A.; Hirzberger, J.; Lagg, A.; Riethmüller, T. L.;
   Schüssler, M.; Wiegelmann, T.; Bonet, J. A.; Pillet, V. Martínez;
   Khomenko, E.; del Toro Iniesta, J. C.; Domingo, V.; Palacios, J.;
   Knölker, M.; González, N. Bello; Borrero, J. M.; Berkefeld, T.;
   Franz, M.; Roth, M.; Schmidt, W.; Steiner, O.; Title, A. M.
Bibcode: 2011IAUS..273..226S
Altcode:
  The Sunrise balloon-borne solar observatory consists of a 1m aperture
  Gregory telescope, a UV filter imager, an imaging vector polarimeter,
  an image stabilization system and further infrastructure. The first
  science flight of Sunrise yielded high-quality data that reveal the
  structure, dynamics and evolution of solar convection, oscillations
  and magnetic fields at a resolution of around 100 km in the quiet
  Sun. Here we describe very briefly the mission and the first results
  obtained from the Sunrise data, which include a number of discoveries.

Title: The height of chromospheric loops in an emerging flux region
Authors: Merenda, L.; Lagg, A.; Solanki, S. K.
Bibcode: 2011A&A...532A..63M
Altcode: 2012arXiv1202.1113M
  Context. The chromospheric layer observable with the He i 10 830 Å
  triplet is strongly warped. The analysis of the magnetic morphology of
  this layer therefore requires a reliable technique to determine the
  height at which the He i absorption takes place. <BR /> Aims: The He
  i absorption signature connecting two pores of opposite polarity in an
  emerging flux region is investigated. This signature is suggestive of a
  loop system connecting the two pores. We aim to show that limits can be
  set on the height of this chromospheric loop system. <BR /> Methods: The
  increasing anisotropy in the illumination of a thin, magnetic structure
  intensifies the linear polarization signal observed in the He i triplet
  with height. This signal is altered by the Hanle effect. We apply an
  inversion technique incorporating the joint action of the Hanle and
  Zeeman effects, with the absorption layer height being one of the
  free parameters. <BR /> Results: The observed linear polarization
  signal can be explained only if the loop apex is higher than ≈ 5
  Mm. Best agreement with the observations is achieved for a height of
  6.3 Mm. <BR /> Conclusions: The strength of the linear polarization
  signal in the loop apex is inconsistent with the assumption of a He
  i absorption layer at a constant height level. The determined height
  supports the earlier conclusion that dark He 10 830 Å filaments in
  emerging flux regions trace emerging loops.

Title: Latest results and prospects of the CERN Axion Solar Telescope
Authors: Irastorza, I. G.; Aune, S.; Barth, K.; Belov, A.; Borghi,
   S.; Bräuninger, H.; Cantatore, G.; Carmona, J. M.; Cetin, S. A.;
   Collar, J. I.; Dafni, T.; Davenport, M.; Eleftheriadis, C.; Elias,
   N.; Ezer, C.; Fanourakis, G.; Ferrer-Ribas, E.; Friedrich, P.;
   Galán, J.; Gardikiotis, A.; Gazis, E. N.; Geralis, T.; Giomataris,
   I.; Gninenko, S.; Gómez, H.; Gruber, E.; Guthörl, T.; Hartmann,
   R.; Haug, F.; Hasinoff, M. D.; Hoffmann, D. H. H.; Iguaz, F. J.;
   Jacoby, J.; Jakovčić, K.; Karuza, M.; Königsmann, K.; Kotthaus,
   R.; Krčmar, M.; Kuster, M.; Lakić, B.; Laurent, J. M.; Liolios,
   A.; Ljubičić, A.; Lozza, V.; Lutz, G.; Luzón, G.; Morales, J.;
   Niinikoski, T.; Nordt, A.; Papaevangelou, T.; Pivovaroff, M. J.;
   Raffelt, G.; Rashba, T.; Riege, H.; Rodríguez, A.; Rosu, M.; Ruz,
   J.; Savvidis, I.; Silva, P. S.; Solanki, S. K.; Soufli, R.; Stewart,
   L.; Tomás, A.; Tsagri, M.; van Bibber, K.; Vafeiadis, T.; Villar,
   J.; Vogel, J. K.; Yildiz, S. C.; Zioutas, K.
Bibcode: 2011JPhCS.309a2001I
Altcode:
  The CERN Axion Solar Telescope (CAST) experiment searches for axions
  from the Sun converted into few keV photons via the inverse Primakoff
  effect in the high magnetic field of a superconducting Large Hadron
  Collider (LHC) decommissioned test magnet. After results obtained
  with vacuum in the magnet pipes (phase I of the experiment) as well
  as with <SUP>4</SUP>He the collaboration is now immersed in the data
  taking with <SUP>3</SUP>He, to be finished in 2011. The status of
  the experiment will be presented, including a preliminary exclusion
  plot of the first <SUP>3</SUP>He data. CAST is currently sensitive to
  realistic QCD axion models at the sub-eV scale, and with axion-photon
  couplings down to the ~ 2 × 10<SUP>-10</SUP> GeV<SUP>-1</SUP>,
  compatible with solar life limits. Future plans include revisiting
  vaccuum and <SUP>4</SUP>He configurations with improved sensitivity,
  as well as possible additional search for non-standard signals from
  chamaleons, paraphotons or other WISPs. For the longer term, we
  study the feasibility of an altogether improved version of the axion
  helioscope concept, with a jump in sensitivity of about one order of
  magnitude in g<SUB>aγ</SUB> beyond CAST.

Title: Exploring the magnetic topologies of cool stars
Authors: Morin, J.; Donati, J. -F.; Petit, P.; Albert, L.; Auriére,
   M.; Cabanac, R.; Catala, C.; Delfosse, X.; Dintrans, B.; Fares,
   R.; Forveille, T.; Gastine, T.; Jardine, M.; Konstantinova-Antova,
   R.; Lanoux, J.; Lignires, F.; Morgenthaler, A.; Paletou, F.; Velez,
   J. C. Ramirez; Solanki, S. K.; Thado, S.; Van Grootel, V.
Bibcode: 2011IAUS..273..181M
Altcode: 2010arXiv1009.2589M
  Magnetic fields of cool stars can be directly investigated through
  the study of the Zeeman effect on photospheric spectral lines using
  several approaches. With spectroscopic measurement in unpolarised
  light, the total magnetic flux averaged over the stellar disc can
  be derived but very little information on the field geometry is
  available. Spectropolarimetry provides a complementary information
  on the large-scale magnetic topology. With Zeeman-Doppler Imaging
  (ZDI), this information can be retrieved to produce a map of the vector
  magnetic field at the surface of the star, and in particular to assess
  the relative importance of the poloidal and toroidal components as
  well as the degree of axisymmetry of the field distribution. <P />The
  development of high-performance spectropolarimeters associated with
  multi-lines techniques and ZDI allows us to explore magnetic topologies
  throughout the Hertzsprung-Russel diagram, on stars spanning a wide
  range of mass, age and rotation period. These observations bring novel
  constraints on magnetic field generation by dynamo effect in cool
  stars. In particular, the study of solar twins brings new insight on
  the impact of rotation on the solar dynamo, whereas the detection of
  strong and stable dipolar magnetic fields on fully convective stars
  questions the precise role of the tachocline in this process.

Title: Modelling solar irradiance variability on time scales from
    minutes to months
Authors: Seleznyov, A. D.; Solanki, S. K.; Krivova, N. A.
Bibcode: 2011A&A...532A.108S
Altcode: 2013arXiv1303.1961S
  We analyze and model total solar irradiance variability on time scales
  from minutes to months, excluding variations due to p-mode oscillations,
  using a combination of convective and magnetic components. These include
  granulation, the magnetic network, faculae and sunspots. Analysis of
  VIRGO data shows that on periods of a day or longer solar variability
  depends on magnetic activity, but is nearly independent at shorter
  periods. We assume that only granulation affects the solar irradiance
  variability on time scales from minutes to hours. Granulation is
  described as a large sample of bright cells and dark lanes that
  evolve according to rules deduced from observations and radiation
  hydrodynamic simulations. Comparison of this model combined with a high
  time resolution magnetic-field based irradiance reconstruction, with
  solar data reveals a good correspondence except at periods of 10 to 30
  h. This suggests that the model is missing some power at these periods,
  which may be due to the absence of supergranulation or insufficient
  sensitivity of MDI magnetograms used for the reconstruction of the
  magnetic field-based irradiance reconstructions. Our model also shows
  that even for spatially unresolved data (such as those available for
  stars) the Fourier or wavelet transform of time series sampled at high
  cadence may allow properties of stellar granulation, in particular
  granule lifetimes to be determined.

Title: Continuous upflows and sporadic downflows observed in active
    regions
Authors: Kamio, S.; Peter, H.; Curdt, W.; Solanki, S. K.
Bibcode: 2011A&A...532A..96K
Altcode: 2011arXiv1107.1993K
  <BR /> Aims: We present a study of the temporal evolution of coronal
  loops in active regions and its implications for the dynamics in coronal
  loops. <BR /> Methods: We analyzed images of the Atmospheric Imaging
  Assembly (AIA) on the Solar Dynamics Observatory (SDO) at multiple
  temperatures to detect apparent motions in the coronal loops. <BR />
  Results: Quasi-periodic brightness fluctuations propagate upwards from
  the loop footpoint in hot emission at 1 MK, while sporadic downflows
  are seen in cool emission below 1 MK. The upward motion in hot
  emission increases just after the cool downflows. <BR /> Conclusions:
  The apparent propagating pattern suggests a hot upflow from the
  loop footpoints, and is considered to supply hot plasma into the
  coronal loop, but a wavelike phenomenon cannot be ruled out. Coronal
  condensation occasionally happens in the coronal loop, and the cool
  material flows down to the footpoint. Emission from cool plasma could
  have a significant contribution to hot AIA channels in the event of
  coronal condensation.

Title: Evolution of the solar irradiance during the Holocene
Authors: Vieira, L. E. A.; Solanki, S. K.; Krivova, N. A.; Usoskin, I.
Bibcode: 2011A&A...531A...6V
Altcode: 2011arXiv1103.4958V
  Context. Long-term records of solar radiative output are vital for
  understanding solar variability and past climate change. Measurements
  of solar irradiance are available for only the last three decades,
  which calls for reconstructions of this quantity over longer time
  scales using suitable models. <BR /> Aims: We present a physically
  consistent reconstruction of the total solar irradiance for the
  Holocene. <BR /> Methods: We extend the SATIRE (Spectral And Total
  Irradiance REconstruction) models to estimate the evolution of the
  total (and partly spectral) solar irradiance over the Holocene. The
  basic assumption is that the variations of the solar irradiance are
  due to the evolution of the dark and bright magnetic features on the
  solar surface. The evolution of the decadally averaged magnetic flux
  is computed from decadal values of cosmogenic isotope concentrations
  recorded in natural archives employing a series of physics-based
  models connecting the processes from the modulation of the cosmic
  ray flux in the heliosphere to their record in natural archives. We
  then compute the total solar irradiance (TSI) as a linear combination
  of the jth and jth + 1 decadal values of the open magnetic flux. In
  order to evaluate the uncertainties due to the evolution of the Earth's
  magnetic dipole moment, we employ four reconstructions of the open flux
  which are based on conceptually different paleomagnetic models. <BR />
  Results: Reconstructions of the TSI over the Holocene, each valid for
  a different paleomagnetic time series, are presented. Our analysis
  suggests that major sources of uncertainty in the TSI in this model
  are the heritage of the uncertainty of the TSI since 1610 reconstructed
  from sunspot data and the uncertainty of the evolution of the Earth's
  magnetic dipole moment. The analysis of the distribution functions
  of the reconstructed irradiance for the last 3000 years, which is the
  period that the reconstructions overlap, indicates that the estimates
  based on the virtual axial dipole moment are significantly lower at
  earlier times than the reconstructions based on the virtual dipole
  moment. We also present a combined reconstruction, which represents
  our best estimate of total solar irradiance for any given time during
  the Holocene. <BR /> Conclusions: We present the first physics-based
  reconstruction of the total solar irradiance over the Holocene, which
  will be of interest for studies of climate change over the last 11 500
  years. The reconstruction indicates that the decadally averaged total
  solar irradiance ranges over approximately 1.5 W/m<SUP>2</SUP> from
  grand maxima to grand minima. <P />Appendix A is available in electronic
  form at <A href="http://www.aanda.org">http://www.aanda.org</A>The
  TSI data is only available at the CDS via anonymous
  ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via <A
  href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/531/A6">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/531/A6</A>

Title: The continuum intensity as a function of magnetic
    field. I. Active region and quiet Sun magnetic elements
Authors: Kobel, P.; Solanki, S. K.; Borrero, J. M.
Bibcode: 2011A&A...531A.112K
Altcode: 2011arXiv1105.1958K
  Context. Small-scale magnetic fields are major contributors to
  the solar irradiance variations. Hence, the continuum intensity
  contrast of magnetic elements in the quiet Sun (QS) network and in
  active region (AR) plage is an essential quantity that needs to be
  measured reliably. <BR /> Aims: By using Hinode/SP disk center data
  at a constant, high spatial resolution, we aim at updating results of
  earlier ground-based studies of contrast vs. magnetogram signal, and to
  look for systematic differences between AR plages and QS network. <BR
  /> Methods: The field strength, filling factor and inclination of the
  field was retrieved by means of a Milne-Eddington inversion (VFISV
  code). As in earlier studies, we then performed a pixel-by-pixel study
  of 630.2 nm continuum contrast vs. apparent (i.e. averaged over a pixel)
  longitudinal magnetic field over large fields of view in ARs and in the
  QS. <BR /> Results: The continuum contrast of magnetic elements reaches
  larger values in the QS (on average 3.7%) than in ARs (on average
  1.3%). This could not be attributed to any systematic difference in
  the chosen contrast references, so that it mainly reflects an intrinsic
  brightness difference. The larger contrasts in the QS are in agreement
  with earlier, lower resolution results, although our values are larger
  due to our better spatial resolution. At Hinode's spatial resolution,
  moreover, the relationship between contrast and apparent longitudinal
  field strength exhibits a peak at around 700 G in both the QS and ARs,
  whereas earlier lower resolution studies only found a peak in the QS and
  a monotonic decrease in ARs. We attribute this discrepancy both to our
  careful removal of the pores and their close surroundings affected by
  the telescope diffraction, as well as to the enhanced spatial resolution
  and very low scattered light of the Hinode Solar Optical Telescope. We
  verified that the magnetic elements producing the peak in the contrast
  curve are rather vertical in the AR and in the QS, so that the larger
  contrasts in the QS cannot be explained by larger inclinations, as had
  been proposed earlier. The opposite polarities in ARs do not exhibit
  any noticeable difference in inclination either, although they reach
  different contrasts when the amount of flux is significantly unbalanced
  between the polarities. <BR /> Conclusions: According to our inversions,
  the magnetic elements producing the peak of the contrast curves have
  similar properties (field strength, inclination, filling factor) in ARs
  and in the QS, so that the larger brightness of magnetic elements in the
  QS remains unexplained. Indirect evidence suggests that the contrast
  difference is not primarily due to any difference in average size of
  the magnetic elements. A possible explanation lies in the different
  efficiencies of convective energy transport in the QS and in ARs,
  which will be the topic of a second paper.

Title: EUV jets, type III radio bursts and sunspot waves investigated
    using SDO/AIA observations
Authors: Innes, D. E.; Cameron, R. H.; Solanki, S. K.
Bibcode: 2011A&A...531L..13I
Altcode: 2011arXiv1106.3417I
  Context. Quasi-periodic plasma jets are often ejected from the Sun
  into interplanetary space. The commonly observed signatures are
  day-long sequences of type III radio bursts. <BR /> Aims: The aim is
  to identify the source of quasi-periodic jets observed on 3 Aug. 2010
  in the Sun's corona and in interplanetary space. <BR /> Methods:
  Images from the Solar Dynamics Observatory (SDO) at 211 Å are used
  to identify the solar source of the type III radio bursts seen in
  WIND/WAVES dynamic spectra. We analyse a 2.5 h period during which six
  strong bursts are seen. The radio signals are cross-correlated with
  emission from extreme ultraviolet (EUV) jets coming from the western
  side of a sunspot in AR 11092. The jets are further cross-correlated
  with brightening at a small site on the edge of the sunspot umbra,
  and the brightening with 3-min sunspot intensity oscillations. <BR />
  Results: The radio bursts correlate very well with the EUV jets. The
  EUV jet emission also correlates well with brightening at what looks
  like their footpoint at the edge of the umbra. The jet emission lags
  the radio signals and the footpoint brightening by about 30 s because
  the EUV jets take time to develop. For 10-15 min after strong EUV jets
  are ejected, the footpoint brightens at roughly 3 min intervals. In
  both the EUV images and the extracted light curves, it looks as though
  the brightening is related to the 3-min sunspot oscillations, although
  the correlation coefficient is rather low. The only open field near
  the jets is rooted in the sunspot. <BR /> Conclusions: Active region
  EUV/X-ray jets and interplanetary electron streams originate on the
  edge of the sunspot umbra. They form along a current sheet between
  the sunspot open field and closed field connecting to underlying
  satellite flux. Sunspot running penumbral waves cause roughly 3-min
  jet footpoint brightening. The relationship between the waves and
  jets is less clear. <P />Movie is available in electronic form at <A
  href="http://www.aanda.org">http://www.aanda.org</A>

Title: Convective Nature of Sunspot Penumbral Filaments: Discovery
    of Downflows in the Deep Photosphere
Authors: Joshi, Jayant; Pietarila, A.; Hirzberger, J.; Solanki, S. K.;
   Aznar Cuadrado, R.; Merenda, L.
Bibcode: 2011ApJ...734L..18J
Altcode: 2011arXiv1105.1877J
  We study the velocity structure of penumbral filaments in the deep
  photosphere to obtain direct evidence for the convective nature of
  sunspot penumbrae. A sunspot was observed at high spatial resolution
  with the 1 m Swedish Solar Telescope in the deep photospheric C I 5380
  Å absorption line. The Multi-Object Multi-Frame Blind Deconvolution
  method is used for image restoration and straylight is filtered out. We
  report here the discovery of clear redshifts in the C I 5380 Å line
  at multiple locations in sunspot penumbral filaments. For example,
  bright head of filaments show larger concentrated blueshift and are
  surrounded by darker, redshifted regions, suggestive of overturning
  convection. Elongated downflow lanes are also located beside bright
  penumbral fibrils. Our results provide the strongest evidence yet
  for the presence of overturning convection in penumbral filaments and
  highlight the need to observe the deepest layers of the penumbra in
  order to uncover the energy transport processes taking place there.

Title: Solar irradiance variability: a six-year comparison between
    SORCE observations and the SATIRE model
Authors: Ball, W. T.; Unruh, Y. C.; Krivova, N. A.; Solanki, S.;
   Harder, J. W.
Bibcode: 2011A&A...530A..71B
Altcode: 2011arXiv1104.0885B
  <BR /> Aims: We investigate how well modeled solar irradiances agree
  with measurements from the SORCE satellite, both for total solar
  irradiance and broken down into spectral regions on timescales of
  several years. <BR /> Methods: We use the SATIRE model and compare
  modeled total solar irradiance (TSI) with TSI measurements over the
  period 25 February 2003 to 1 November 2009. Spectral solar irradiance
  over 200-1630 nm is compared with the SIM instrument on SORCE over
  the period 21 April 2004 to 1 November 2009. We discuss the overall
  change in flux and the rotational and long-term trends during this
  period of decline from moderate activity to the recent solar minimum
  in ~10 nm bands and for three spectral regions of significant interest:
  the UV integrated over 200-300 nm, the visible over 400-691 nm and the
  IR between 972-1630 nm. <BR /> Results: The model captures 97% of the
  observed TSI variation. This is on the order at which TSI detectors
  agree with each other during the period considered. In the spectral
  comparison, rotational variability is well reproduced, especially
  between 400 and 1200 nm. The magnitude of change in the long-term
  trends is many times larger in SIM at almost all wavelengths while
  trends in SIM oppose SATIRE in the visible between 500 and 700 nm and
  again between 1000 and 1200 nm. We discuss the remaining issues with
  both SIM data and the identified limits of the model, particularly
  with the way facular contributions are dealt with, the limit of flux
  identification in MDI magnetograms during solar minimum and the model
  atmospheres in the IR employed by SATIRE. However, it is unlikely that
  improvements in these areas will significantly enhance the agreement
  in the long-term trends. This disagreement implies that some mechanism
  other than surface magnetism is causing SSI variations, in particular
  between 2004 and 2006, if the SIM data are correct. Since SATIRE
  was able to reproduce UV irradiance between 1991 and 2002 from UARS,
  either the solar mechanism for SSI variation fundamentally changed
  around the peak of cycle 23, or there is an inconsistency between UARS
  and SORCE UV measurements. We favour the second explanation.

Title: Small-scale flux emergence events observed by Sunrise/IMaX
Authors: Guglielmino, S. L.; Pillet, V. Martínez; del Toro Iniesta,
   J. C.; Rubio, L. R. Bellot; Zuccarello, F.; Solanki, S. K.; Solanki
Bibcode: 2011IAUS..274..140G
Altcode:
  Thanks to the unprecedented combination of high spatial resolution
  (0''.2) and high temporal cadence (33 s) spectropolarimetric
  measurements, the IMaX magnetograph aboard the Sunrise balloon-borne
  telescope is revealing new insights about the plasma dynamics
  of the all-pervasive small-scale flux concentrations in the quiet
  Sun. We present the result of a case study concerning the appearance
  of a bipole, with a size of about 4'' and a flux content of 5 ×
  10<SUP>17</SUP> Mx, with strong signal of horizontal fields during
  the emergence. We analyze the data set using the SIR inversion code
  and obtain indications about the three-dimensional shape of the bipole
  and its evolution with time.

Title: Solar total irradiance in cycle 23
Authors: Krivova, N. A.; Solanki, S. K.; Schmutz, W.
Bibcode: 2011A&A...529A..81K
Altcode: 2011arXiv1102.3077K
  Context. The most recent minimum of solar activity was deeper and
  longer than the previous two minima as indicated by different proxies
  of solar activity. This is also true for the total solar irradiance
  (TSI) according to the PMOD composite. <BR /> Aims: The apparently
  unusual behaviour of the TSI has been interpreted as evidence against
  solar surface magnetism as the main driver of the secular change
  in the TSI. We test claims that the evolution of the solar surface
  magnetic field does not reproduce the observed TSI in cycle 23. <BR
  /> Methods: We use sensitive, 60-min averaged MDI magnetograms and
  quasi-simultaneous continuum images as an input to our SATIRE-S model
  and calculate the TSI variation over cycle 23, sampled roughly every
  two weeks. The computed TSI is then compared with the PMOD composite of
  TSI measurements and with the data from two individual instruments,
  SORCE/TIM and UARS/ACRIM II, that monitored the TSI during the
  declining phase of cycle 23 and over the previous minimum in 1996,
  respectively. <BR /> Results: Excellent agreement is found between the
  trends shown by the model and almost all sets of measurements. The
  only exception is the early, i.e. 1996 to 1998, PMOD data. Whereas
  the agreement between the model and the PMOD composite over the
  period 1999-2009 is almost perfect, the modelled TSI shows a steeper
  increase between 1996 and 1999 than implied by the PMOD composite. On
  the other hand, the steeper trend in the model agrees remarkably well
  with the ACRIM II data. A closer look at the VIRGO data, which are the
  basis of the PMOD composite after 1996, reveals that only one of the
  two VIRGO instruments, the PMO6V, shows the shallower trend present
  in the composite, whereas the DIARAD measurements indicate a steeper
  trend. <BR /> Conclusions: Based on these results, we conclude that (1)
  the sensitivity changes of the PMO6V radiometers within VIRGO during
  the first two years have very likely not been correctly evaluated;
  and that (2) the TSI variations over cycle 23 and the change in the
  TSI levels between the minima in 1996 and 2008 are consistent with
  the solar surface magnetism mechanism.

Title: VizieR Online Data Catalog: Evolution of solar irradiance
    during Holocene (Vieira+, 2011)
Authors: Vieira, L. E. A.; Solanki, S. K.; Krivova, N. A.; Usoskin, I.
Bibcode: 2011yCat..35310006V
Altcode: 2011yCat..35319006V
  This is a composite total solar irradiance (TSI) time series for 9495BC
  to 2007AD constructed as described in Sect. 3.3 of the paper. Since
  the TSI is the main external heat input into the Earth's climate
  system, a consistent record covering as long period as possible
  is needed for climate models. This was our main motivation for
  constructing this composite TSI time series. <P />In order to
  produce a representative time series, we divided the Holocene into
  four periods according to the available data for each period. Table
  4 (see below) summarizes the periods considered and the models
  available for each period. After the end of the Maunder Minimum we
  compute daily values, while prior to the end of the Maunder Minimum
  we compute 10-year averages. For the period for which both solar disk
  magnetograms and continuum images are available (period 1) we employ
  the SATIRE-S reconstruction (Krivova et al. 2003A&amp;A...399L...1K;
  Wenzler et al. 2006A&amp;A...460..583W). SATIRE-T (Krivova et
  al. 2010JGRA..11512112K) reconstruction is used from the beginning of
  the Maunder Minimum (approximately 1640AD) to 1977AD. Prior to 1640AD
  reconstructions are based on cosmogenic isotopes (this paper). Different
  models of the Earth's geomagnetic field are available before and after
  approximately 5000BC. Therefore we treat periods 3 and 4 (before and
  after 5000BC) separately. Further details can be found in the paper. We
  emphasize that the reconstructions based on different proxies have
  different time resolutions. <P />(1 data file).

Title: Performance validation of phase diversity image reconstruction
    techniques
Authors: Hirzberger, J.; Feller, A.; Riethmüller, T. L.; Gandorfer,
   A.; Solanki, S. K.
Bibcode: 2011A&A...529A.132H
Altcode:
  We present a performance study of a phase diversity (PD) image
  reconstruction algorithm based on artificial solar images obtained
  from MHD simulations and on seeing-free data obtained with the SuFI
  instrument on the Sunrise balloon borne observatory. The artificial
  data were altered by applying different levels of degradation with
  synthesised wavefront errors and noise. The PD algorithm was modified
  by changing the number of fitted polynomials, the shape of the pupil and
  the applied noise filter. The obtained reconstructions are evaluated by
  means of the resulting rms intensity contrast and by the conspicuousness
  of appearing artifacts. The results show that PD is a robust method
  which consistently recovers the initial unaffected image contents. The
  efficiency of the reconstruction is, however, strongly dependent on the
  number of used fitting polynomials and the noise level of the images. If
  the maximum number of fitted polynomials is higher than 21, artifacts
  have to be accepted and for noise levels higher than 10<SUP>-3</SUP>
  the commonly used noise filtering techniques are not able to avoid
  amplification of spurious structures.

Title: The Continuum Contrast of Magnetic Elements as a Function of
Magnetic Field (Disk Center): Early Studies and Hinode/SP Results
Authors: Kobel, P.; Solanki, S. K.; Borrero, J. M.
Bibcode: 2011ASPC..437..297K
Altcode:
  To deepen our understanding of the role of small-scale magnetic
  fields on the solar irradiance, it is essential to quantify the
  continuum contrast of magnetic elements in the quiet Sun (QS)
  network and in active region (AR) plage. By using Hinode/SP disk
  center data at constant spatial resolution, we aimed at updating
  results of earlier ground-based studies of contrast vs. magnetogram
  signal, and to look for systematic differences between AR plages
  and QS network. We performed a pixel-per-pixel study of continuum
  contrast vs. longitudinal flux density over large fields of view in
  AR and in QS (as in earlier studies). Even at Hinode's resolution,
  the contrast of magnetic elements reaches larger values in the QS than
  in ARs. We show that this difference cannot be explained by different
  inclinations of magnetic elements in ARs and QS. We compared our
  contrast vs. magnetic flux density with earlier studies and attributed
  the differences both to our proper removal of the pores and their
  surrounding diffraction-spread radiation, as well as to our enhanced
  spatial resolution and quasi-absence of scattered light. At Hinode's
  resolution, the contrast of magnetic elements peaks on average at
  similar magnetic flux densities in ARs and in the QS, which indicates
  that the brightest flux tubes have similar sizes in ARs and QS.

Title: Unnoticed Magnetic Field Oscillations in the Very Quiet Sun
    Revealed by SUNRISE/IMaX
Authors: Martínez González, M. J.; Asensio Ramos, A.; Manso Sainz,
   R.; Khomenko, E.; Martínez Pillet, V.; Solanki, S. K.; López Ariste,
   A.; Schmidt, W.; Barthol, P.; Gandorfer, A.
Bibcode: 2011ApJ...730L..37M
Altcode: 2011arXiv1103.0145M
  We present observational evidence for oscillations of magnetic flux
  density in the quiet areas of the Sun. The majority of magnetic
  fields on the solar surface have strengths of the order of or lower
  than the equipartition field (300-500 G). This results in a myriad of
  magnetic fields whose evolution is largely determined by the turbulent
  plasma motions. When granules evolve they squash the magnetic field
  lines together or pull them apart. Here, we report on the periodic
  deformation of the shapes of features in circular polarization observed
  at high resolution with SUNRISE. In particular, we note that the
  area of patches with a constant magnetic flux oscillates with time,
  which implies that the apparent magnetic field intensity oscillates
  in antiphase. The periods associated with this oscillatory pattern
  are compatible with the granular lifetime and change abruptly, which
  suggests that these oscillations might not correspond to characteristic
  oscillatory modes of magnetic structures, but to the forcing by granular
  motions. In one particular case, we find three patches around the same
  granule oscillating in phase, which means that the spatial coherence
  of these oscillations can reach 1600 km. Interestingly, the same kind
  of oscillatory phenomenon is also found in the upper photosphere.

Title: Transport of Magnetic Flux from the Canopy to the Internetwork
Authors: Pietarila, A.; Cameron, R. H.; Danilovic, S.; Solanki, S. K.
Bibcode: 2011ApJ...729..136P
Altcode: 2011arXiv1102.1397P
  Recent observations have revealed that 8% of linear polarization
  patches in the internetwork (INW) quiet Sun are fully embedded in
  downflows. These are not easily explained with the typical scenarios for
  the source of INW fields which rely on flux emergence from below. Using
  radiative MHD simulations, we explore a scenario where magnetic flux
  is transported from the magnetic canopy overlying the INW into the
  photosphere by means of downward plumes associated with convective
  overshoot. We find that if a canopy-like magnetic field is present in
  the simulation, the transport of flux from the canopy is an important
  process for seeding the photospheric layers of the INW with magnetic
  field. We propose that this mechanism is relevant for the Sun as well,
  and it could naturally explain the observed INW linear polarization
  patches entirely embedded in downflows.

Title: Intensity contrast from MHD simulations and HINODE observations
Authors: Afram, N.; Unruh, Y. C.; Solanki, S. K.; Schüssler, M.;
   Lagg, A.; Vögler, A.
Bibcode: 2011A&A...526A.120A
Altcode: 2010arXiv1011.6102A
  Context. Changes in the solar surface area, which is covered by
  small-scale magnetic elements, are thought to cause long-term changes
  in the solar spectral irradiance, which are important for determining
  the impact on Earth's climate. <BR /> Aims: To study the effect of
  small-scale magnetic elements on the total and spectral irradiance,
  we derive their contrasts from 3-D MHD simulations of the solar
  atmosphere. These calculations are necessary because measurements of
  small-scale flux tube contrasts are confined to a few wavelengths and
  affected by scattered light and instrument defocus, even for space
  observations. <BR /> Methods: To test the contrast calculations,
  we compare rms contrasts from simulations with those obtained with
  the broad-band filter imager mounted on the Solar Optical Telescope
  (SOT) onboard the Hinode satellite and also analyse centre-to-limb
  variations (CLV). The 3-D MHD simulations include the interaction
  between convection and magnetic flux tubes. They are performed by
  assuming non-grey radiative transfer and using the MURaM code. The
  simulations have an average vertical magnetic field of 0 G, 50 G, and
  200 G. Emergent intensities are calculated with the spectral synthesis
  code ATLAS9 and are convolved with a theoretical point-spread function
  to account for the properties of the observations' optical system. <BR
  /> Results: We find reasonable agreement between simulated and observed
  intensity distributions in the visible continuum bands. Agreement is
  poorer for the CN and G-bands. The analysis of the simulations uncovers
  a potentially more realistic centre-to-limb behaviour than calculations
  based on 1-D model atmospheres. <BR /> Conclusions: We conclude that
  starting from 3-D MHD simulations represents a powerful approach
  to obtaining intensity contrasts for a wide wavelength coverage and
  different positions across on the solar disk. This also paves the way
  for future calculations of facular and network contrast as a function
  of magnetic fluxes.

Title: The Role of Active Region Loop Geometry. II. Symmetry Breaking
in Three-dimensional Active Region: Why are Vertical Kink Oscillations
    Observed so Rarely?
Authors: Selwa, M.; Solanki, S. K.; Ofman, L.
Bibcode: 2011ApJ...728...87S
Altcode:
  We present numerical results of simulations of kink oscillations of
  coronal loops in an idealized active region (AR) that is initialized
  as a potential dipole magnetic configuration with gravitationally
  stratified density. We consider loops, with density higher than
  the surrounding plasma, embedded into the dipolar AR. We study the
  excitation of kink oscillations of such loops by velocity pulses at
  different positions, of a given duration and amplitude. The position of
  the pulse varies in the parametric studies. For a central (symmetric)
  loop within the AR, we find that the amplitude of vertical kink
  oscillations is significantly amplified in comparison to horizontal
  kink oscillations for exciters located centrally (symmetrically) below
  the loop. For pulses initiated further from such a symmetric loop a
  combination of vertical and horizontal oscillations is excited. The
  scenario changes significantly when we study an inclined loop
  (non-symmetric within a dipole field). In this case, we do not
  see vertical kink oscillations of any significant amplitude being
  excited, while horizontal ones can be easily detected. These results
  indicate that the reason why vertical kink oscillations are observed so
  rarely is that their excitation requires a set of conditions to occur
  simultaneously: the exciting pulse must be located roughly below the
  loop apex and the loop itself must be located symmetrically within
  the group of loops. The new findings of the present study show the
  importance of not only the position of the pulse, but mainly of the
  location of the loop within the set of field lines having the same
  magnetic connectivity. We find that the slow propagating wave is excited
  in all the studied loops and its excitation does not depend either on
  the geometry of the loop or the pulse. We discuss TRACE observations
  of coronal loop oscillations in view of our findings and find that
  our results can be used for identifying the polarization of the kink
  mode based on the location of the loop within the set of field lines
  of the same connectivity and the position of the flare.

Title: Towards a long-term record of solar total and spectral
    irradiance
Authors: Krivova, N. A.; Solanki, S. K.; Unruh, Y. C.
Bibcode: 2011JASTP..73..223K
Altcode: 2009arXiv0911.4002K
  The variation of total solar irradiance (TSI) has been measured since
  1978 and that of the spectral irradiance for an even shorter amount of
  time. Semi-empirical models are now available that reproduce over 80%
  of the measured irradiance variations. An extension of these models into
  the more distant past is needed in order to serve as input to climate
  simulations. Here we review our most recent efforts to model solar
  total and spectral irradiance on time scales from days to centuries and
  even longer. Solar spectral irradiance has been reconstructed since
  1947. Reconstruction of solar total irradiance goes back to 1610 and
  suggests a value of about 1-1.5W/m<SUP>2</SUP> for the increase in
  the cycle-averaged TSI since the end of the Maunder minimum, which
  is significantly lower than previously assumed but agrees with other
  modern models. First steps have also been made towards reconstructions
  of solar total and spectral irradiance on time scales of millennia.

Title: Multicomponent He I 10 830 Å profiles in an active filament
Authors: Sasso, C.; Lagg, A.; Solanki, S. K.
Bibcode: 2011A&A...526A..42S
Altcode: 2011arXiv1101.5563S
  <BR /> Aims: We present new spectropolarimetric observations of the
  chromospheric He i 10 830 Å multiplet observed in a filament during
  its phase of activity. <BR /> Methods: The data were recorded with the
  new Tenerife Infrared Polarimeter (TIP-II) at the German Vacuum Tower
  Telescope (VTT) on 2005 May 18. We inverted the He Stokes profiles
  using multiple atmospheric components. <BR /> Results: The observed
  He Stokes profiles display a remarkably wide variety of shapes. Most
  of the profiles show very broad Stokes I absorptions and complex and
  spatially variable Stokes V signatures. The inversion of the profiles
  shows evidence of different atmospheric blue- and redshifted components
  of the He i lines within the resolution element (~1 arcsec), with
  supersonic velocities of up to ~100 km s<SUP>-1</SUP>. Up to five
  different atmospheric components are found in the same profile. We
  show that even these complex profiles can be reliably inverted.

Title: Mesogranulation and the Solar Surface Magnetic Field
    Distribution
Authors: Yelles Chaouche, L.; Moreno-Insertis, F.; Martínez Pillet,
   V.; Wiegelmann, T.; Bonet, J. A.; Knölker, M.; Bellot Rubio, L. R.;
   del Toro Iniesta, J. C.; Barthol, P.; Gandorfer, A.; Schmidt, W.;
   Solanki, S. K.
Bibcode: 2011ApJ...727L..30Y
Altcode: 2010arXiv1012.4481Y
  The relation of the solar surface magnetic field with mesogranular
  cells is studied using high spatial (≈100 km) and temporal (≈30
  s) resolution data obtained with the IMaX instrument on board
  SUNRISE. First, mesogranular cells are identified using Lagrange
  tracers (corks) based on horizontal velocity fields obtained through
  local correlation tracking. After ≈20 minutes of integration, the
  tracers delineate a sharp mesogranular network with lanes of width
  below about 280 km. The preferential location of magnetic elements in
  mesogranular cells is tested quantitatively. Roughly 85% of pixels with
  magnetic field higher than 100 G are located in the near neighborhood
  of mesogranular lanes. Magnetic flux is therefore concentrated in
  mesogranular lanes rather than intergranular ones. Second, magnetic
  field extrapolations are performed to obtain field lines anchored in
  the observed flux elements. This analysis, therefore, is independent
  of the horizontal flows determined in the first part. A probability
  density function (PDF) is calculated for the distribution of distances
  between the footpoints of individual magnetic field lines. The PDF has
  an exponential shape at scales between 1 and 10 Mm, with a constant
  characteristic decay distance, indicating the absence of preferred
  convection scales in the mesogranular range. Our results support
  the view that mesogranulation is not an intrinsic convective scale
  (in the sense that it is not a primary energy-injection scale of solar
  convection), but also give quantitative confirmation that, nevertheless,
  the magnetic elements are preferentially found along mesogranular lanes.

Title: The Solar Orbiter Mission and its Polarimetric and Helioseismic
    Imager (SO/PHI)
Authors: Gandorfer, Achim; Solanki, Sami K.; Woch, Joachim; Martínez
   Pillet, Valentin; Álvarez Herrero, Alberto; Appourchaux, Thierry
Bibcode: 2011JPhCS.271a2086G
Altcode:
  We briefly outline the scientific and instrumental aspects of ESA's
  Solar Orbiter mission. Special emphasis is given to the Polarimetric
  and Helioseismic Imager, the instrument with the highest relevance for
  helioseismology applications, which will observe gas motions and the
  vector magnetic field in the photosphere at high spatial and temporal
  resolution.

Title: The Imaging Magnetograph eXperiment (IMaX) for the Sunrise
    Balloon-Borne Solar Observatory
Authors: Martínez Pillet, V.; del Toro Iniesta, J. C.;
   Álvarez-Herrero, A.; Domingo, V.; Bonet, J. A.; González Fernández,
   L.; López Jiménez, A.; Pastor, C.; Gasent Blesa, J. L.; Mellado, P.;
   Piqueras, J.; Aparicio, B.; Balaguer, M.; Ballesteros, E.; Belenguer,
   T.; Bellot Rubio, L. R.; Berkefeld, T.; Collados, M.; Deutsch, W.;
   Feller, A.; Girela, F.; Grauf, B.; Heredero, R. L.; Herranz, M.;
   Jerónimo, J. M.; Laguna, H.; Meller, R.; Menéndez, M.; Morales, R.;
   Orozco Suárez, D.; Ramos, G.; Reina, M.; Ramos, J. L.; Rodríguez,
   P.; Sánchez, A.; Uribe-Patarroyo, N.; Barthol, P.; Gandorfer, A.;
   Knoelker, M.; Schmidt, W.; Solanki, S. K.; Vargas Domínguez, S.
Bibcode: 2011SoPh..268...57M
Altcode: 2010SoPh..tmp..181M; 2010arXiv1009.1095M
  The Imaging Magnetograph eXperiment (IMaX) is a spectropolarimeter
  built by four institutions in Spain that flew on board the Sunrise
  balloon-borne solar observatory in June 2009 for almost six days over
  the Arctic Circle. As a polarimeter, IMaX uses fast polarization
  modulation (based on the use of two liquid crystal retarders),
  real-time image accumulation, and dual-beam polarimetry to reach
  polarization sensitivities of 0.1%. As a spectrograph, the instrument
  uses a LiNbO<SUB>3</SUB> etalon in double pass and a narrow band
  pre-filter to achieve a spectral resolution of 85 mÅ. IMaX uses the
  high-Zeeman-sensitive line of Fe I at 5250.2 Å and observes all four
  Stokes parameters at various points inside the spectral line. This
  allows vector magnetograms, Dopplergrams, and intensity frames to be
  produced that, after reconstruction, reach spatial resolutions in the
  0.15 - 0.18 arcsec range over a 50×50 arcsec field of view. Time
  cadences vary between 10 and 33 s, although the shortest one only
  includes longitudinal polarimetry. The spectral line is sampled in
  various ways depending on the applied observing mode, from just two
  points inside the line to 11 of them. All observing modes include
  one extra wavelength point in the nearby continuum. Gauss equivalent
  sensitivities are 4 G for longitudinal fields and 80 G for transverse
  fields per wavelength sample. The line-of-sight velocities are estimated
  with statistical errors of the order of 5 - 40 m s<SUP>−1</SUP>. The
  design, calibration, and integration phases of the instrument,
  together with the implemented data reduction scheme, are described in
  some detail.

Title: The Wave-Front Correction System for the Sunrise Balloon-Borne
    Solar Observatory
Authors: Berkefeld, T.; Schmidt, W.; Soltau, D.; Bell, A.;
   Doerr, H. P.; Feger, B.; Friedlein, R.; Gerber, K.; Heidecke, F.;
   Kentischer, T.; v. d. Lühe, O.; Sigwarth, M.; Wälde, E.; Barthol,
   P.; Deutsch, W.; Gandorfer, A.; Germerott, D.; Grauf, B.; Meller, R.;
   Álvarez-Herrero, A.; Knölker, M.; Martínez Pillet, V.; Solanki,
   S. K.; Title, A. M.
Bibcode: 2011SoPh..268..103B
Altcode: 2010SoPh..tmp..236B; 2010arXiv1009.3196B
  This paper describes the wave-front correction system developed for
  the Sunrise balloon telescope, and it provides information about its
  in-flight performance. For the correction of low-order aberrations,
  a Correlating Wave-Front Sensor (CWS) was used. It consisted of a
  six-element Shack - Hartmann wave-front sensor (WFS), a fast tip-tilt
  mirror for the compensation of image motion, and an active telescope
  secondary mirror for focus correction. The CWS delivered a stabilized
  image with a precision of 0.04 arcsec (rms), whenever the coarse
  pointing was better than ± 45 arcsec peak-to-peak. The automatic
  focus adjustment maintained a focus stability of 0.01 waves in the
  focal plane of the CWS. During the 5.5 day flight, good image quality
  and stability were achieved during 33 hours, containing 45 sequences,
  which lasted between 10 and 45 min.

Title: The Sunrise Mission
Authors: Barthol, P.; Gandorfer, A.; Solanki, S. K.; Schüssler,
   M.; Chares, B.; Curdt, W.; Deutsch, W.; Feller, A.; Germerott, D.;
   Grauf, B.; Heerlein, K.; Hirzberger, J.; Kolleck, M.; Meller, R.;
   Müller, R.; Riethmüller, T. L.; Tomasch, G.; Knölker, M.; Lites,
   B. W.; Card, G.; Elmore, D.; Fox, J.; Lecinski, A.; Nelson, P.;
   Summers, R.; Watt, A.; Martínez Pillet, V.; Bonet, J. A.; Schmidt,
   W.; Berkefeld, T.; Title, A. M.; Domingo, V.; Gasent Blesa, J. L.;
   del Toro Iniesta, J. C.; López Jiménez, A.; Álvarez-Herrero, A.;
   Sabau-Graziati, L.; Widani, C.; Haberler, P.; Härtel, K.; Kampf,
   D.; Levin, T.; Pérez Grande, I.; Sanz-Andrés, A.; Schmidt, E.
Bibcode: 2011SoPh..268....1B
Altcode: 2010arXiv1009.2689B; 2010SoPh..tmp..224B
  The first science flight of the balloon-borne Sunrise telescope took
  place in June 2009 from ESRANGE (near Kiruna/Sweden) to Somerset
  Island in northern Canada. We describe the scientific aims and
  mission concept of the project and give an overview and a description
  of the various hardware components: the 1-m main telescope with its
  postfocus science instruments (the UV filter imager SuFI and the imaging
  vector magnetograph IMaX) and support instruments (image stabilizing
  and light distribution system ISLiD and correlating wavefront sensor
  CWS), the optomechanical support structure and the instrument mounting
  concept, the gondola structure and the power, pointing, and telemetry
  systems, and the general electronics architecture. We also explain
  the optimization of the structural and thermal design of the complete
  payload. The preparations for the science flight are described,
  including AIV and ground calibration of the instruments. The course
  of events during the science flight is outlined, up to the recovery
  activities. Finally, the in-flight performance of the instrumentation
  is discussed.

Title: The Filter Imager SuFI and the Image Stabilization and Light
Distribution System ISLiD of the Sunrise Balloon-Borne Observatory:
    Instrument Description
Authors: Gandorfer, A.; Grauf, B.; Barthol, P.; Riethmüller, T. L.;
   Solanki, S. K.; Chares, B.; Deutsch, W.; Ebert, S.; Feller, A.;
   Germerott, D.; Heerlein, K.; Heinrichs, J.; Hirche, D.; Hirzberger,
   J.; Kolleck, M.; Meller, R.; Müller, R.; Schäfer, R.; Tomasch,
   G.; Knölker, M.; Martínez Pillet, V.; Bonet, J. A.; Schmidt, W.;
   Berkefeld, T.; Feger, B.; Heidecke, F.; Soltau, D.; Tischenberg, A.;
   Fischer, A.; Title, A.; Anwand, H.; Schmidt, E.
Bibcode: 2011SoPh..268...35G
Altcode: 2010SoPh..tmp..176G; 2010arXiv1009.1037G
  We describe the design of the Sunrise Filter Imager (SuFI) and the
  Image Stabilization and Light Distribution (ISLiD) unit onboard the
  Sunrise balloon borne solar observatory. This contribution provides the
  necessary information which is relevant to understand the instruments'
  working principles, the relevant technical data, and the necessary
  information about calibration issues directly related to the science
  data.

Title: The Role of Active Region Loop Geometry. I. How Can it Affect
    Coronal Seismology?
Authors: Selwa, M.; Ofman, L.; Solanki, S. K.
Bibcode: 2011ApJ...726...42S
Altcode:
  We present numerical results of coronal loop oscillation excitation
  using a three-dimensional (3D) MHD model of an idealized active region
  (AR) field. The AR is initialized as a potential dipole magnetic
  configuration with gravitationally stratified density and contains a
  loop with a higher density than its surroundings. We study different
  ways of excitation of vertical kink oscillations of this loop by
  velocity: as an initial condition, and as an impulsive excitation
  with a pulse of a given position, duration, and amplitude. We vary the
  geometry of the loop in the 3D MHD model and find that it affects both
  the period of oscillations and the synthetic observations (difference
  images) that we get from oscillations. Due to the overestimated
  effective length of the loop in the case of loops which have maximum
  separation between their legs above the footpoints (&gt;50% of observed
  loops), the magnetic field obtained from coronal seismology can also
  be overestimated. The 3D MHD model shows how the accuracy of magnetic
  field strength determined from coronal seismology can be improved. We
  study the damping mechanism of the oscillations and find that vertical
  kink waves in 3D stratified geometry are damped mainly due to wave
  leakage in the horizontal direction.

Title: Reconstruction of solar spectral irradiance since the Maunder
    minimum
Authors: Krivova, N. A.; Vieira, L. E. A.; Solanki, S. K.
Bibcode: 2010JGRA..11512112K
Altcode:
  Solar irradiance is the main external driver of the Earth's
  climate. Whereas the total solar irradiance is the main source of
  energy input into the climate system, solar UV irradiance exerts
  control over chemical and physical processes in the Earth's upper
  atmosphere. The time series of accurate irradiance measurements are,
  however, relatively short and limit the assessment of the solar
  contribution to the climate change. Here we reconstruct solar total
  and spectral irradiance in the range 115-160,000 nm since 1610. The
  evolution of the solar photospheric magnetic flux, which is a central
  input to the model, is appraised from the historical record of the
  sunspot number using a simple but consistent physical model. The model
  predicts an increase of 1.25 W/m<SUP>2</SUP>, or about 0.09%, in the
  11-year averaged solar total irradiance since the Maunder minimum. Also,
  irradiance in individual spectral intervals has generally increased
  during the past four centuries, the magnitude of the trend being higher
  toward shorter wavelengths. In particular, the 11-year averaged Ly-α
  irradiance has increased by almost 50%. An exception is the spectral
  interval between about 1500 and 2500 nm, where irradiance has slightly
  decreased (by about 0.02%).

Title: SUNRISE: Instrument, Mission, Data, and First Results
Authors: Solanki, S. K.; Barthol, P.; Danilovic, S.; Feller, A.;
   Gandorfer, A.; Hirzberger, J.; Riethmüller, T. L.; Schüssler, M.;
   Bonet, J. A.; Martínez Pillet, V.; del Toro Iniesta, J. C.; Domingo,
   V.; Palacios, J.; Knölker, M.; Bello González, N.; Berkefeld, T.;
   Franz, M.; Schmidt, W.; Title, A. M.
Bibcode: 2010ApJ...723L.127S
Altcode: 2010arXiv1008.3460S
  The SUNRISE balloon-borne solar observatory consists of a 1 m aperture
  Gregory telescope, a UV filter imager, an imaging vector polarimeter,
  an image stabilization system, and further infrastructure. The first
  science flight of SUNRISE yielded high-quality data that revealed the
  structure, dynamics, and evolution of solar convection, oscillations,
  and magnetic fields at a resolution of around 100 km in the quiet
  Sun. After a brief description of instruments and data, the first
  qualitative results are presented. In contrast to earlier observations,
  we clearly see granulation at 214 nm. Images in Ca II H display narrow,
  short-lived dark intergranular lanes between the bright edges of
  granules. The very small-scale, mixed-polarity internetwork fields
  are found to be highly dynamic. A significant increase in detectable
  magnetic flux is found after phase-diversity-related reconstruction
  of polarization maps, indicating that the polarities are mixed right
  down to the spatial resolution limit and probably beyond.

Title: Supersonic Magnetic Upflows in Granular Cells Observed with
    SUNRISE/IMAX
Authors: Borrero, J. M.; Martínez-Pillet, V.; Schlichenmaier, R.;
   Solanki, S. K.; Bonet, J. A.; del Toro Iniesta, J. C.; Schmidt, W.;
   Barthol, P.; Gandorfer, A.; Domingo, V.; Knölker, M.
Bibcode: 2010ApJ...723L.144B
Altcode: 2010arXiv1009.1227B
  Using the IMaX instrument on board the SUNRISE stratospheric balloon
  telescope, we have detected extremely shifted polarization signals
  around the Fe I 5250.217 Å spectral line within granules in the solar
  photosphere. We interpret the velocities associated with these events
  as corresponding to supersonic and magnetic upflows. In addition, they
  are also related to the appearance of opposite polarities and highly
  inclined magnetic fields. This suggests that they are produced by the
  reconnection of emerging magnetic loops through granular upflows. The
  events occupy an average area of 0.046 arcsec<SUP>2</SUP> and last for
  about 80 s, with larger events having longer lifetimes. These supersonic
  events occur at a rate of 1.3 × 10<SUP>-5</SUP> occurrences per second
  per arcsec<SUP>2</SUP>.

Title: Detection of Vortex Tubes in Solar Granulation from
    Observations with SUNRISE
Authors: Steiner, O.; Franz, M.; Bello González, N.; Nutto, Ch.;
   Rezaei, R.; Martínez Pillet, V.; Bonet Navarro, J. A.; del Toro
   Iniesta, J. C.; Domingo, V.; Solanki, S. K.; Knölker, M.; Schmidt,
   W.; Barthol, P.; Gandorfer, A.
Bibcode: 2010ApJ...723L.180S
Altcode: 2010arXiv1009.4723S
  We have investigated a time series of continuum intensity maps and
  corresponding Dopplergrams of granulation in a very quiet solar region
  at the disk center, recorded with the Imaging Magnetograph eXperiment
  (IMaX) on board the balloon-borne solar observatory SUNRISE. We
  find that granules frequently show substructure in the form of lanes
  composed of a leading bright rim and a trailing dark edge, which move
  together from the boundary of a granule into the granule itself. We
  find strikingly similar events in synthesized intensity maps from an
  ab initio numerical simulation of solar surface convection. From cross
  sections through the computational domain of the simulation, we conclude
  that these granular lanes are the visible signature of (horizontally
  oriented) vortex tubes. The characteristic optical appearance of vortex
  tubes at the solar surface is explained. We propose that the observed
  vortex tubes may represent only the large-scale end of a hierarchy of
  vortex tubes existing near the solar surface.

Title: On detectability of Zeeman broadening in optical spectra of F-
    and G-dwarfs
Authors: Anderson, R. I.; Reiners, A.; Solanki, S. K.
Bibcode: 2010A&A...522A..81A
Altcode: 2010arXiv1008.2213A
  We investigate the detectability of Zeeman broadening in optical Stokes
  I spectra of slowly rotating sun-like stars. To this end, we apply the
  LTE spectral line inversion package SPINOR to very-high quality CES
  data and explore how fit quality depends on the average magnetic field,
  Bf. One-component (OC) and two-component (TC) models are adopted. In
  OC models, the entire surface is assumed to be magnetic. Under this
  assumption, we determine formal 3σ upper limits on the average magnetic
  field of 200 G for the Sun, and 150 G for 61 Vir (G6V). Evidence
  for an average magnetic field of ~500 G is found for 59 Vir (G0V),
  and of ~ 1000 G for HD 68456 (F6V). A distinction between magnetic
  and non-magnetic regions is made in TC models, while assuming a
  homogeneous distribution of both components. In our TC inversions
  of 59 Vir, we investigate three cases: both components have equal
  temperatures; warm magnetic regions; cool magnetic regions. Our TC
  model with equal temperatures does not yield significant improvement
  over OC inversions for 59 Vir. The resulting Bf values are consistent
  for both. Fit quality is significantly improved, however, by using two
  components of different temperatures. The inversions for 59 Vir that
  assume different temperatures for the two components yield results
  consistent with 0-450 G at the formal 3σ confidence level. We thus
  find a model dependence of our analysis and demonstrate that the
  influence of an additional temperature component can dominate over
  the Zeeman broadening signature, at least in optical data. Previous
  comparable analyses that neglected effects due to multiple temperature
  components may be prone to the same ambiguities. <P />Based on
  observations collected at the European Southern Observatory,
  La Silla.Appendix A is only available in electronic form at <A
  href="http://www.aanda.org">http://www.aanda.org</A>

Title: Where the Granular Flows Bend
Authors: Khomenko, E.; Martínez Pillet, V.; Solanki, S. K.; del Toro
   Iniesta, J. C.; Gandorfer, A.; Bonet, J. A.; Domingo, V.; Schmidt,
   W.; Barthol, P.; Knölker, M.
Bibcode: 2010ApJ...723L.159K
Altcode: 2010arXiv1008.0517K
  Based on IMaX/SUNRISE data, we report on a previously undetected
  phenomenon in solar granulation. We show that in a very narrow region
  separating granules and intergranular lanes, the spectral line width
  of the Fe I 5250.2 Å line becomes extremely small. We offer an
  explanation of this observation with the help of magneto-convection
  simulations. These regions with extremely small line widths correspond
  to the places where the granular flows bend from upflow in granules
  to downflow in intergranular lanes. We show that the resolution and
  image stability achieved by IMaX/SUNRISE are important requisites to
  detect this interesting phenomenon.

Title: Bright Points in the Quiet Sun as Observed in the Visible
    and Near-UV by the Balloon-borne Observatory SUNRISE
Authors: Riethmüller, T. L.; Solanki, S. K.; Martínez Pillet, V.;
   Hirzberger, J.; Feller, A.; Bonet, J. A.; Bello González, N.; Franz,
   M.; Schüssler, M.; Barthol, P.; Berkefeld, T.; del Toro Iniesta,
   J. C.; Domingo, V.; Gandorfer, A.; Knölker, M.; Schmidt, W.
Bibcode: 2010ApJ...723L.169R
Altcode: 2010arXiv1009.1693R
  Bright points (BPs) are manifestations of small magnetic elements
  in the solar photosphere. Their brightness contrast not only gives
  insight into the thermal state of the photosphere (and chromosphere) in
  magnetic elements, but also plays an important role in modulating the
  solar total and spectral irradiance. Here, we report on simultaneous
  high-resolution imaging and spectropolarimetric observations of
  BPs using SUNRISE balloon-borne observatory data of the quiet Sun
  at the disk center. BP contrasts have been measured between 214 nm
  and 525 nm, including the first measurements at wavelengths below
  388 nm. The histograms of the BP peak brightness show a clear trend
  toward broader contrast distributions and higher mean contrasts at
  shorter wavelengths. At 214 nm, we observe a peak brightness of up to
  five times the mean quiet-Sun value, the highest BP contrast so far
  observed. All BPs are associated with a magnetic signal, although in
  a number of cases it is surprisingly weak. Most of the BPs show only
  weak downflows, the mean value being 240 m s<SUP>-1</SUP>, but some
  display strong down- or upflows reaching a few km s<SUP>-1</SUP>.

Title: Transverse Component of the Magnetic Field in the Solar
    Photosphere Observed by SUNRISE
Authors: Danilovic, S.; Beeck, B.; Pietarila, A.; Schüssler, M.;
   Solanki, S. K.; Martínez Pillet, V.; Bonet, J. A.; del Toro Iniesta,
   J. C.; Domingo, V.; Barthol, P.; Berkefeld, T.; Gandorfer, A.;
   Knölker, M.; Schmidt, W.; Title, A. M.
Bibcode: 2010ApJ...723L.149D
Altcode: 2010arXiv1008.1535D
  We present the first observations of the transverse component of
  a photospheric magnetic field acquired by the imaging magnetograph
  SUNRISE/IMaX. Using an automated detection method, we obtain statistical
  properties of 4536 features with significant linear polarization
  signal. We obtain a rate of occurrence of 7 × 10<SUP>-4</SUP>
  s<SUP>-1</SUP> arcsec<SUP>-2</SUP>, which is 1-2 orders of magnitude
  larger than the values reported by previous studies. We show that
  these features have no characteristic size or lifetime. They appear
  preferentially at granule boundaries with most of them being caught
  in downflow lanes at some point. Only a small percentage are entirely
  and constantly embedded in upflows (16%) or downflows (8%).

Title: Detection of Large Acoustic Energy Flux in the Solar Atmosphere
Authors: Bello González, N.; Franz, M.; Martínez Pillet, V.; Bonet,
   J. A.; Solanki, S. K.; del Toro Iniesta, J. C.; Schmidt, W.; Gandorfer,
   A.; Domingo, V.; Barthol, P.; Berkefeld, T.; Knölker, M.
Bibcode: 2010ApJ...723L.134B
Altcode: 2010arXiv1009.4795B
  We study the energy flux carried by acoustic waves excited by convective
  motions at sub-photospheric levels. The analysis of high-resolution
  spectropolarimetric data taken with IMaX/SUNRISE provides a total
  energy flux of ~6400-7700 W m<SUP>-2</SUP> at a height of ~250 km
  in the 5.2-10 mHz range, i.e., at least twice the largest energy
  flux found in previous works. Our estimate lies within a factor of
  two of the energy flux needed to balance radiative losses from the
  chromosphere according to the estimates of Anderson &amp; Athay and
  revives interest in acoustic waves for transporting energy to the
  chromosphere. The acoustic flux is mainly found in the intergranular
  lanes but also in small rapidly evolving granules and at the bright
  borders, forming dark dots and lanes of splitting granules.

Title: Magnetic Loops in the Quiet Sun
Authors: Wiegelmann, T.; Solanki, S. K.; Borrero, J. M.; Martínez
   Pillet, V.; del Toro Iniesta, J. C.; Domingo, V.; Bonet, J. A.;
   Barthol, P.; Gandorfer, A.; Knölker, M.; Schmidt, W.; Title, A. M.
Bibcode: 2010ApJ...723L.185W
Altcode: 2010arXiv1009.4715W
  We investigate the fine structure of magnetic fields in the atmosphere
  of the quiet Sun. We use photospheric magnetic field measurements from
  SUNRISE/IMaX with unprecedented spatial resolution to extrapolate
  the photospheric magnetic field into higher layers of the solar
  atmosphere with the help of potential and force-free extrapolation
  techniques. We find that most magnetic loops that reach into the
  chromosphere or higher have one footpoint in relatively strong magnetic
  field regions in the photosphere. Ninety-one percent of the magnetic
  energy in the mid-chromosphere (at a height of 1 Mm) is in field
  lines, whose stronger footpoint has a strength of more than 300 G,
  i.e., above the equipartition field strength with convection. The
  loops reaching into the chromosphere and corona are also found to be
  asymmetric in the sense that the weaker footpoint has a strength B &lt;
  300 G and is located in the internetwork (IN). Such loops are expected
  to be strongly dynamic and have short lifetimes, as dictated by the
  properties of the IN fields.

Title: SUNRISE/IMaX Observations of Convectively Driven Vortex Flows
    in the Sun
Authors: Bonet, J. A.; Márquez, I.; Sánchez Almeida, J.; Palacios,
   J.; Martínez Pillet, V.; Solanki, S. K.; del Toro Iniesta, J. C.;
   Domingo, V.; Berkefeld, T.; Schmidt, W.; Gandorfer, A.; Barthol, P.;
   Knölker, M.
Bibcode: 2010ApJ...723L.139B
Altcode: 2010arXiv1009.1992B
  We characterize the observational properties of the convectively driven
  vortex flows recently discovered on the quiet Sun, using magnetograms,
  Dopplergrams, and images obtained with the 1 m balloon-borne SUNRISE
  telescope. By visual inspection of time series, we find some 3.1
  × 10<SUP>-3</SUP> vortices Mm<SUP>-2</SUP> minute<SUP>-1</SUP>,
  which is a factor of ~1.7 larger than previous estimates. The mean
  duration of the individual events turns out to be 7.9 minutes, with
  a standard deviation of 3.2 minutes. In addition, we find several
  events appearing at the same locations along the duration of the time
  series (31.6 minutes). Such recurrent vortices show up in the proper
  motion flow field map averaged over the time series. The typical
  vertical vorticities are lsim6 × 10<SUP>-3</SUP> s<SUP>-1</SUP>,
  which corresponds to a period of rotation of some 35 minutes. The
  vortices show a preferred counterclockwise sense of rotation, which
  we conjecture may have to do with the preferred vorticity impinged by
  the solar differential rotation.

Title: Radiative emission of solar features in the Ca II K line:
    comparison of measurements and models
Authors: Ermolli, I.; Criscuoli, S.; Uitenbroek, H.; Giorgi, F.;
   Rast, M. P.; Solanki, S. K.
Bibcode: 2010A&A...523A..55E
Altcode: 2010arXiv1009.0227E
  Context. The intensity of the Ca II K resonance line observed with
  spectrographs and Lyot-type filters has long served as a diagnostic of
  the solar chromosphere. However, the literature contains a relative
  lack of photometric measurements of solar features observed at this
  spectral range. <BR /> Aims: We study the radiative emission of various
  types of solar features, such as quiet Sun, enhanced network, plage,
  and bright plage regions, identified on filtergrams taken in the Ca II
  K line. <BR /> Methods: We analysed full-disk images obtained with the
  PSPT, by using three interference filters that sample the Ca II K line
  with different bandpasses. We studied the dependence of the radiative
  emission of disk features on the filter bandpass. We also performed a
  non-local thermal equilibrium (NLTE) spectral synthesis of the Ca II
  K line integrated over the bandpass of PSPT filters. The synthesis
  was carried out by utilizing the partial frequency redistribution
  (PRD) with the most recent set of semi-empirical atmosphere models
  in the literature and some earlier atmosphere models. As the studied
  models were computed by assuming the complete redistribution formalism
  (CRD), we also performed simulations with this approximation for
  comparison. <BR /> Results: We measured the center-to-limb variation
  of intensity values for various solar features identified on PSPT
  images and compared the results obtained with those derived from the
  synthesis. We find that CRD calculations derived using the most recent
  quiet Sun model, on average, reproduce the measured values of the
  quiet Sun regions slightly more accurately than PRD computations with
  the same model. This may reflect that the utilized atmospheric model
  was computed assuming CRD. Calculations with PRD on earlier quiet Sun
  model atmospheres reproduce measured quantities with a similar accuracy
  as to that achieved here by applying CRD to the recent model. We
  also find that the median contrast values measured for most of the
  identified bright features, disk positions, and filter bandpasses
  are, on average, a factor ≈1.9 lower than those derived from PRD
  simulations performed using the recent bright feature models. The
  discrepancy between measured and modeled values decreases by ≈12%
  after taking into account straylight effects on PSPT images. When
  moving towards the limb, PRD computations display closer agreement with
  the data than performed in CRD. Moreover, PRD computations on either
  the most recent or the earlier atmosphere models of bright features
  reproduce measurements from plage and bright plage regions with a
  similar accuracy. <P />Appendix A is only available in electronic form
  at <A href="http://www.aanda.org">http://www.aanda.org</A>

Title: Surface Waves in Solar Granulation Observed with SUNRISE
Authors: Roth, M.; Franz, M.; Bello González, N.; Martínez Pillet,
   V.; Bonet, J. A.; Gandorfer, A.; Barthol, P.; Solanki, S. K.;
   Berkefeld, T.; Schmidt, W.; del Toro Iniesta, J. C.; Domingo, V.;
   Knölker, M.
Bibcode: 2010ApJ...723L.175R
Altcode: 2010arXiv1009.4790R
  Solar oscillations are expected to be excited by turbulent flows in
  the intergranular lanes near the solar surface. Time series recorded
  by the IMaX instrument on board the SUNRISE observatory reveal solar
  oscillations at high spatial resolution, which allow the study of
  the properties of oscillations with short wavelengths. We analyze
  two time series with synchronous recordings of Doppler velocity and
  continuum intensity images with durations of 32 minutes and 23 minutes,
  respectively, recorded close to the disk center of the Sun to study
  the propagation and excitation of solar acoustic oscillations. In
  the Doppler velocity data, both the standing acoustic waves and the
  short-lived, high-degree running waves are visible. The standing
  waves are visible as temporary enhancements of the amplitudes of the
  large-scale velocity field due to the stochastic superposition of
  the acoustic waves. We focus on the high-degree small-scale waves by
  suitable filtering in the Fourier domain. Investigating the propagation
  and excitation of f- and p <SUB>1</SUB>-modes with wavenumbers k&gt;1.4
  Mm<SUP>-1</SUP>, we also find that exploding granules contribute to
  the excitation of solar p-modes in addition to the contribution of
  intergranular lanes.

Title: Fully Resolved Quiet-Sun Magnetic flux Tube Observed with
    the SUNRISE/IMAX Instrument
Authors: Lagg, A.; Solanki, S. K.; Riethmüller, T. L.; Martínez
   Pillet, V.; Schüssler, M.; Hirzberger, J.; Feller, A.; Borrero,
   J. M.; Schmidt, W.; del Toro Iniesta, J. C.; Bonet, J. A.; Barthol, P.;
   Berkefeld, T.; Domingo, V.; Gandorfer, A.; Knölker, M.; Title, A. M.
Bibcode: 2010ApJ...723L.164L
Altcode: 2010arXiv1009.0996L
  Until today, the small size of magnetic elements in quiet-Sun areas has
  required the application of indirect methods, such as the line-ratio
  technique or multi-component inversions, to infer their physical
  properties. A consistent match to the observed Stokes profiles could
  only be obtained by introducing a magnetic filling factor that specifies
  the fraction of the observed pixel filled with magnetic field. Here,
  we investigate the properties of a small magnetic patch in the quiet
  Sun observed with the IMaX magnetograph on board the balloon-borne
  telescope SUNRISE with unprecedented spatial resolution and low
  instrumental stray light. We apply an inversion technique based on
  the numerical solution of the radiative transfer equation to retrieve
  the temperature stratification and the field strength in the magnetic
  patch. The observations can be well reproduced with a one-component,
  fully magnetized atmosphere with a field strength exceeding 1 kG and
  a significantly enhanced temperature in the mid to upper photosphere
  with respect to its surroundings, consistent with semi-empirical flux
  tube models for plage regions. We therefore conclude that, within the
  framework of a simple atmospheric model, the IMaX measurements resolve
  the observed quiet-Sun flux tube.

Title: Quiet-sun Intensity Contrasts in the Near-ultraviolet as
    Measured from SUNRISE
Authors: Hirzberger, J.; Feller, A.; Riethmüller, T. L.; Schüssler,
   M.; Borrero, J. M.; Afram, N.; Unruh, Y. C.; Berdyugina, S. V.;
   Gandorfer, A.; Solanki, S. K.; Barthol, P.; Bonet, J. A.; Martínez
   Pillet, V.; Berkefeld, T.; Knölker, M.; Schmidt, W.; Title, A. M.
Bibcode: 2010ApJ...723L.154H
Altcode:
  We present high-resolution images of the Sun in the near-ultraviolet
  spectral range between 214 nm and 397 nm as obtained from the first
  science flight of the 1 m SUNRISE balloon-borne solar telescope. The
  quiet-Sun rms intensity contrasts found in this wavelength range are
  among the highest values ever obtained for quiet-Sun solar surface
  structures—up to 32.8% at a wavelength of 214 nm. We compare the
  rms contrasts obtained from the observational data with theoretical
  intensity contrasts obtained from numerical magnetohydrodynamic
  simulations. For 388 nm and 312 nm the observations agree well with
  the numerical simulations whereas at shorter wavelengths discrepancies
  between observed and simulated contrasts remain.

Title: Evidence for Convection in Sunspot Penumbrae
Authors: Bharti, L.; Solanki, S. K.; Hirzberger, J.
Bibcode: 2010ApJ...722L.194B
Altcode: 2010arXiv1009.2919B
  We present an analysis of twisting motions in penumbral filaments in
  sunspots located at heliocentric angles from 30° to 48° using three
  time series of blue continuum images obtained by the Broadband Filter
  Imager (BFI) on board Hinode. The relations of the twisting motions to
  the filament brightness and the position within the filament and within
  the penumbra, respectively, are investigated. Only certain portions
  of the filaments show twisting motions. In a statistical sense, the
  part of the twisting portion of a filament located closest to the
  umbra is brightest and possesses the fastest twisting motion, with a
  mean twisting velocity of 2.1 km s<SUP>-1</SUP>. The middle and outer
  sections of the twisting portion of the filament (lying increasingly
  further from the umbra), which are less bright, have mean velocities
  of 1.7 km s<SUP>-1</SUP> and 1.35 km s<SUP>-1</SUP>, respectively. The
  observed reduction of brightness and twisting velocity toward the
  outer section of the filaments may be due to reducing upflow along the
  filament's long axis. No significant variation of twisting velocity as
  a function of viewing angles was found. The obtained correlation of
  brightness and velocity suggests that overturning convection causes
  the twisting motions observed in penumbral filament and may be the
  source of the energy needed to maintain the brightness of the filaments.

Title: Reply to comment by P. Foukal on “A homogeneous database
    of sunspot areas covering more than 130 years”
Authors: Balmaceda, L. A.; Solanki, S. K.; Krivova, N. A.; Foster, S.
Bibcode: 2010JGRA..115.9103B
Altcode: 2010JGRA..11509103B
  <A href="/journals/ja/ja1009/2010JA015375/">Abstract Available</A>
  from <A href="http://www.agu.org">http://www.agu.org</A>

Title: Magnetic structures of an emerging flux region in the solar
    photosphere and chromosphere
Authors: Xu, Z.; Lagg, A.; Solanki, S. K.
Bibcode: 2010A&A...520A..77X
Altcode:
  <BR /> Aims: We investigate the vector magnetic field and Doppler
  velocity in the photosphere and upper chromosphere of a young
  emerging flux region of the sun close to disk center. <BR /> Methods:
  Spectropolarimetric scans of a young active region made using the
  second generation Tenerife Infrared Polarimeter (TIP II) on the German
  Vacuum Tower Telescope (VTT) are analyzed. The scanned area contained
  multiple sunspots and an emerging flux region. An inversion based on
  the Milne-Eddington approximation was performed on the full Stokes
  vector of the chromospheric He I 10 830 Å and the photospheric Si I
  10 827.1 Å lines. This provided the magnetic vector and line-of-sight
  velocity at each spatial point in both atmospheric layers. <BR />
  Results: A clear difference is seen between the complex magnetic
  structure of the emerging flux region (EFR) in the photosphere and
  the much simpler structure in the upper chromosphere. The upper
  chromospheric structure is consistent with a set of emerging loops
  following elongated dark structures seen in the He I 10 830 Å triplet,
  similar to arch filament systems (AFS), while in the photosphere we
  infer the presence of U-loops within the emergence zone. Nonetheless, in
  general the upper chromospheric field has a similar linear relationship
  between inclination angle and field strength as the photospheric field:
  the field is weak (≈300 G) and horizontal in the emergence zone,
  but strong (up to 850 G) and more vertical near its edges. The field
  strength decreases from the photosphere to the upper chromosphere
  by approximately 0.1-0.2 G km<SUP>-1</SUP> (or even less) within the
  emergence zone and by 0.3-0.6 G km<SUP>-1</SUP> in sunspots located
  at its edge. We reconstructed the magnetic field in 3D based on the
  chromospheric vector field under the assumption that the He I 10 830 Å
  triplet forms along the magnetic field loops. The reconstructed loops
  are quite flat with supersonic downflows at both footpoints. Arguments
  and evidence for an enhanced formation height of He I 10 830 Å in
  arch-filaments seen in this line are provided, which support the
  validity of the reconstructed loops. <BR /> Conclusions: The main
  chromospheric properties of EFRs previously deduced for a single region
  NOAA 9451 are shown to be valid for another region as well, suggesting
  that the main original results may have a wider application. The main
  exception is that only the first region displayed a current sheet in
  the chromosphere. We propose a scenario in which the relatively complex
  photospheric structure evolves into the simpler chromospheric one.

Title: Quiet-Sun intensity contrasts in the near ultraviolet
Authors: Hirzberger, Johann; Feller, Alex; Riethmüller, Tino L.;
   Schüssler, Manfred; Borrero, Juan M.; Afram, Nadine; Unruh, Yvonne C.;
   Berdyugina, Svetlana V.; Gandorfer, Achim; Solanki, Sami K.; Barthol,
   Peter; Bonet, Jose A.; Martínez Pillet, Valentin; Berkefeld, Thomas;
   Knölker, Michael; Schmidt, Wolfgang; Title, Alan M.
Bibcode: 2010arXiv1009.1050H
Altcode:
  We present high-resolution images of the Sun in the near ultraviolet
  spectral range between 214 nm and 397 nm as obtained from the first
  science flight of the 1-m Sunrise balloon-borne solar telescope. The
  quiet-Sun rms intensity contrasts found in this wavelength range
  are among the highest values ever obtained for quiet-Sun solar
  surface structures - up to 32.8% at a wavelength of 214 nm. We
  compare with theoretical intensity contrasts obtained from numerical
  magneto-hydrodynamic simulations. For 388 nm and 312 nm the observations
  agree well with the numerical simulations whereas at shorter wavelengths
  discrepancies between observed and simulated contrasts remain.

Title: Sunspot group tilt angles and the strength of the solar cycle
Authors: Dasi-Espuig, M.; Solanki, S. K.; Krivova, N. A.; Cameron,
   R.; Peñuela, T.
Bibcode: 2010A&A...518A...7D
Altcode: 2010arXiv1005.1774D
  Context. It is well known that the tilt angles of active regions
  increase with their latitude (Joy's law). It has never been checked
  before, however, whether the average tilt angles change from one cycle
  to the next. Flux transport models show the importance of tilt angles
  for the reversal and build up of magnetic flux at the poles, which is in
  turn correlated to the strength of the next cycle. <BR /> Aims: Here we
  analyse time series of tilt angle measurements and look for a possible
  relationship of the tilt angles with other solar cycle parameters,
  in order to glean information on the solar dynamo and to estimate
  their potential for predicting solar activity. <BR /> Methods: We
  employed tilt angle data from Mount Wilson and Kodaikanal observatories
  covering solar cycles 15 to 21. We analyse the latitudinal distribution
  of the tilt angles (Joy's law), their variation from cycle to cycle,
  and their relationship to other solar cycle parameters, such as the
  strength (or total area covered by sunspots in a cycle), amplitude,
  and length. <BR /> Results: The two main results of our analysis
  follow. 1. We find an anti-correlation between the mean normalised
  tilt angle of a given cycle and the strength (or amplitude) of that
  cycle, with a correlation coefficient of r<SUB>c</SUB> = -0.95 (99.9%
  confidence level) and r<SUB>c</SUB> = -0.93 (99.76% confidence level)
  for Mount Wilson and Kodaikanal data, respectively. 2. The product
  of the cycle's averaged tilt angle and the strength of the same cycle
  displays a significant correlation with the strength of the next cycle
  (r<SUB>c</SUB> = 0.65 at 89% confidence level and r<SUB>c</SUB> =
  0.70 at 92% confidence level for Mount Wilson and Kodaikanal data,
  respectively). An even better correlation is obtained between the
  source term of the poloidal flux in Babcock-Leighton-type dynamos (which
  contains the tilt angle) and the amplitude of the next cycle. Further we
  confirm the linear relationship (Joy's law) between the tilt angle and
  latitude with slopes of 0.26 and 0.28 for Mount Wilson and Kodaikanal
  data, respectively. In addition, we obtain good positive correlations
  between the normalised-area-weighted tilt angle and the length of the
  following cycle, whereas the strength or the amplitude of the next cycle
  does not appear to be correlated to the tilt angles of the current cycle
  alone. <BR /> Conclusions: The results of this study indicate that,
  in combination with the cycle strength, the active region tilt angles
  play an important role in building up the polar fields at cycle minimum.

Title: GREGOR telescope: start of commissioning
Authors: Volkmer, R.; von der Lühe, O.; Denker, C.; Solanki, S.;
   Balthasar, H.; Berkefeld, T.; Caligari, P.; Collados, M.; Halbgewachs,
   C.; Heidecke, F.; Hofmann, A.; Klvana, M.; Kneer, F.; Lagg, A.; Popow,
   E.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Soltau, D.; Strassmeier, K.
Bibcode: 2010SPIE.7733E..0KV
Altcode: 2010SPIE.7733E..18V
  With the integration of a 1-meter Cesic primary mirror the GREGOR
  telescope pre-commissioning started. This is the first time, that
  the entire light path has seen sunlight. The pre-commissioning period
  includes testing of the main optics, adaptive optics, cooling system,
  and pointing system. This time was also used to install a near-infrared
  grating spectro-polarimeter and a 2D-spectropolarimeter for the visible
  range as first-light science instruments. As soon as the final 1.5
  meter primary mirror is installed, commissioning will be completed,
  and an extended phase of science verification will follow. In the near
  future, GREGOR will be equipped with a multi-conjugate adaptive optics
  system that is presently under development at KIS.

Title: Accelerating Waves in Polar Coronal Holes as Seen by EIS
    and SUMER
Authors: Gupta, G. R.; Banerjee, D.; Teriaca, L.; Imada, S.;
   Solanki, S.
Bibcode: 2010ApJ...718...11G
Altcode: 2010arXiv1005.3453G
  We present EIS/Hinode and SUMER/SOHO observations of propagating
  disturbances detected in coronal lines in inter-plume and plume
  regions of a polar coronal hole. The observation was carried out on
  2007 November 13 as part of the JOP196/HOP045 program. The SUMER
  spectroscopic observation gives information about fluctuations in
  radiance and on both resolved (Doppler shift) and unresolved (Doppler
  width) line-of-sight velocities, whereas EIS 40'' wide slot images
  detect fluctuations only in radiance but maximize the probability
  of overlapping field of view between the two instruments. From
  distance-time radiance maps, we detect the presence of propagating
  waves in a polar inter-plume region with a period of 15-20 minutes
  and a propagation speed increasing from 130 ± 14 km s<SUP>-1</SUP>
  just above the limb to 330 ± 140 km s<SUP>-1</SUP> around 160'' above
  the limb. These waves can be traced to originate from a bright region
  of the on-disk part of the coronal hole where the propagation speed
  is in the range of 25 ± 1.3 to 38 ± 4.5 km s<SUP>-1</SUP>, with the
  same periodicity. These on-disk bright regions can be visualized as the
  base of the coronal funnels. The adjacent plume region also shows the
  presence of propagating disturbances with the same range of periodicity
  but with propagation speeds in the range of 135 ± 18 to 165 ± 43 km
  s<SUP>-1</SUP> only. A comparison between the distance-time radiance
  map of the two regions indicates that the waves within the plumes are
  not observable (may be getting dissipated) far off-limb, whereas this
  is not the case in the inter-plume region. A correlation analysis was
  also performed to find out the time delay between the oscillations at
  several heights in the off-limb region, finding results consistent with
  those from the analysis of the distance-time maps. To our knowledge,
  this result provides first spectroscopic evidence of the acceleration of
  propagating disturbances in the polar region close to the Sun (within
  1.2 R/R <SUB>sun</SUB>), which provides clues to the understanding of
  the origin of these waves. We suggest that the waves are likely either
  Alfvénic or fast magnetoacoustic in the inter-plume region and slow
  magnetoacoustic in the plume region. This may lead to the conclusion
  that inter-plumes are a preferred channel for the acceleration of the
  fast solar wind.

Title: Expansion of magnetic flux concentrations: a comparison of
    Hinode SOT data and models
Authors: Pietarila, A.; Cameron, R.; Solanki, S. K.
Bibcode: 2010A&A...518A..50P
Altcode: 2010arXiv1005.3405P
  Context. The expansion of network magnetic fields with height is a
  fundamental property of flux tube models. A rapid expansion is required
  to form a magnetic canopy. <BR /> Aims: We characterize the observed
  expansion properties of magnetic network elements and compare them
  with the thin flux tube and sheet approximations, as well as with
  magnetoconvection simulations. <BR /> Methods: We used data from
  the Hinode SOT NFI NaD<SUB>1</SUB> channel and spectropolarimeter to
  study the appearance of magnetic flux concentrations seen in circular
  polarization as a function of position on the solar disk. We compared
  the observations with synthetic observables from models based on the
  thin flux tube approximation and magnetoconvection simulations with two
  different upper boundary conditions for the magnetic field (potential
  and vertical). <BR /> Results: The observed circular polarization signal
  of magnetic flux concentrations changes from unipolar at disk center to
  bipolar near the limb, which implies an expanding magnetic field. The
  observed expansion agrees with expansion properties derived from the
  thin flux sheet and tube approximations. Magnetoconvection simulations
  with a potential field as the upper boundary condition for the magnetic
  field also produce bipolar features near the limb while a simulation
  with a vertical field boundary condition does not. <BR /> Conclusions:
  The near-limb apparent bipolar magnetic features seen in high-resolution
  Hinode observations can be interpreted using a simple flux sheet
  or tube model. This lends further support to the idea that magnetic
  features with vastly varying sizes have similar relative expansion
  rates. The numerical simulations presented here are less useful in
  interpreting the expansion since the diagnostics we are interested in
  are strongly influenced by the choice of the upper boundary condition
  for the magnetic field in the purely photospheric simulations.

Title: Flight control software for the wave-front sensor of SUNRISE
    1m balloon telescope
Authors: Bell, Alexander; Barthol, Peter; Berkefeld, Thomas; Feger,
   Bernhard; Gandorfer, Achim M.; Heidecke, Frank; Knoelker, Michael;
   Martinez Pillet, Valentin; Schmidt, Wolfgang; Sigwarth, Michael;
   Solanki, Sami K.; Soltau, Dirk; Title, Alan M.
Bibcode: 2010SPIE.7740E..03B
Altcode: 2010SPIE.7740E...2B
  This paper describes the flight control software of the wave-front
  correction system that flew on the 2009 science flight of the Sunrise
  balloon telescope. The software discussed here allowed fully automated
  operations of the wave-front sensor, communications with the adaptive
  optics sub-system, the pointing system, the instrument control unit
  and the main telescope controller. The software was developed using
  modern object oriented analysis and design techniques, and consists
  of roughly 13.000 lines of C++ code not counting code written for the
  on-board communication layer. The software operated error free during
  the 5.5 day flight.

Title: SUNRISE Impressions from a successful science flight
Authors: Schmidt, W.; Solanki, S. K.; Barthol, P.; Berkefeld, T.;
   Gandorfer, A.; Knölker, M.; Martínez Pillet, V.; Schüssler, M.;
   Title, A.
Bibcode: 2010AN....331..601S
Altcode:
  SUNRISE is a balloon-borne telescope with an aperture of one meter. It
  is equipped with a filter imager for the UV wavelength range between
  214 nm and 400 nm (SUFI), and with a spectro-polarimeter that measures
  the magnetic field of the photosphere using the Fe I line at 525.02
  nm that has a Landé factor of 3. SUNRISE performed its first science
  flight from 8 to 14 June 2009. It was launched at the Swedish ESRANGE
  Space Center and cruised at an altitude of about 36 km and geographic
  latitudes between 70 and 74 degrees to Somerset Island in northern
  Canada. There, all data, the telescope and the gondola were successfully
  recovered. During its flight, Sunrise achieved high pointing stability
  during 33 hours, and recorded about 1.8 TB of science data. Already at
  this early stage of data processing it is clear that SUNRISE recorded
  UV images of the solar photosphere, and spectropolarimetric measurements
  of the quiet Sun's magnetic field of unprecedented quality.

Title: Spectropolarimetric analysis of 3D MHD sunspot simulations
Authors: Borrero, J. M.; Rempel, M.; Solanki, S. K.
Bibcode: 2010AN....331..567B
Altcode:
  We have employed 3D non-grey MHD simulations of sunspots to compute
  theoretical Stokes profiles and compare the levels of circular and
  linear polarization in the simulations with those observed in a real
  sunspot. We find that the spatial distribution and average values
  of these quantities agree very well with the observations, although
  the polarization levels in the simulations are slightly larger. This
  can be explained by a slightly larger magnetic field strength or a
  larger temperature gradient in the simulated penumbra as compared to
  the observations.

Title: Sideways displacement of penumbral fibrils by the solar flare
    on 2006 December 13
Authors: Zhang, Jun; Li, Leping; Solanki, S. K.
Bibcode: 2010arXiv1007.0056Z
Altcode:
  Flares are known to restructure the magnetic field in the corona and
  to accelerate the gas between the field lines, but their effect on
  the photosphere is less well studied. New data of the Solar Optical
  Telescope (SOT) onboard Hinode provide unprecedented opportunity to
  uncover the photospheric effect of a solar flare, which associates
  with an active region NOAA AR 10930 on 2006 December 13. We find a
  clear lateral displacement of sunspot penumbral regions scanned by two
  flare ribbons. In the impulsive phase of the flare, the flare ribbons
  scan the sunspot at a speed of around 18 km/s, derived from Ca II and
  G-band images. We find instantaneous horizontal shear of penumbral
  fibrils, with initial velocities of about 1.6 km/s, produced when
  a flare ribbon passes over them. This velocity decreases rapidly at
  first, then gradually decays, so that about one hour later, the fibrils
  return to a new equilibrium. During the one hour interval, the total
  displacement of these fibrils is around 2.0 Mm, with an average shear
  velocity of 0.55 km/s. This lateral motion of the penumbral fibrils
  indicates that the magnetic footpoints of these field lines being
  rearranged in the corona also move.

Title: GREGOR solar telescope: Design and status
Authors: Volkmer, R.; von der Lühe, O.; Denker, C.; Solanki, S. K.;
   Balthasar, H.; Berkefeld, T.; Caligari, P.; Collados, M.; Fischer, A.;
   Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Klvaňa, M.; Kneer, F.;
   Lagg, A.; Popow, E.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Soltau,
   D.; Strassmeier, K. G.
Bibcode: 2010AN....331..624V
Altcode:
  The integration and verification phase of the GREGOR telescope
  reached an important milestone with the installation of the
  interim 1 m SolarLite primary mirror. This was the first time
  that the entire light path had seen sunlight. Since then extensive
  testing of the telescope and its subsystems has been carried out. The
  integration and verification phase will culminate with the delivery and
  installation of the final 1.5 m Zerodur primary mirror in the summer of
  2010. Observatory level tests and science verification will commence in
  the second half of 2010 and in 2011. This phase includes testing of the
  main optics, adaptive optics, cooling and pointing systems. In addition,
  assuming the viewpoint of a typical user, various observational modes
  of the GREGOR Fabry-Pérot Interferometer (GFPI), the Grating Infrared
  Spectrograph (GRIS), and high-speed camera systems will be tested to
  evaluate if they match the expectations and science requirements. This
  ensures that GREGOR will provide high-quality observations with its
  combination of (multi-conjugate) adaptive optics and advanced post-focus
  instruments. Routine observations are expected for 2012.

Title: Are cold winters in Europe associated with low solar activity?
Authors: Lockwood, M.; Harrison, R. G.; Woollings, T.; Solanki, S. K.
Bibcode: 2010ERL.....5b4001L
Altcode:
  Solar activity during the current sunspot minimum has fallen to levels
  unknown since the start of the 20th century. The Maunder minimum
  (about 1650-1700) was a prolonged episode of low solar activity
  which coincided with more severe winters in the United Kingdom and
  continental Europe. Motivated by recent relatively cold winters in
  the UK, we investigate the possible connection with solar activity. We
  identify regionally anomalous cold winters by detrending the Central
  England temperature (CET) record using reconstructions of the northern
  hemisphere mean temperature. We show that cold winter excursions from
  the hemispheric trend occur more commonly in the UK during low solar
  activity, consistent with the solar influence on the occurrence of
  persistent blocking events in the eastern Atlantic. We stress that
  this is a regional and seasonal effect relating to European winters
  and not a global effect. Average solar activity has declined rapidly
  since 1985 and cosmogenic isotopes suggest an 8% chance of a return
  to Maunder minimum conditions within the next 50 years (Lockwood 2010
  Proc. R. Soc. A 466 303-29): the results presented here indicate that,
  despite hemispheric warming, the UK and Europe could experience more
  cold winters than during recent decades.

Title: Probing quiet Sun magnetism using MURaM simulations and
Hinode/SP results: support for a local dynamo
Authors: Danilovic, S.; Schüssler, M.; Solanki, S. K.
Bibcode: 2010A&A...513A...1D
Altcode: 2010arXiv1001.2183D
  Context. Owing to the limited spatial resolution and the weak
  polarization signal coming from the quietest regions on the Sun, the
  organization of the magnetic field on the smallest scales is largely
  unknown. <BR /> Aims: We obtain information about the magnetic flux
  present in the quiet Sun by comparing radiative MHD simulations with
  observations, with particular emphasis on the role of surface dynamo
  action. <BR /> Methods: We synthesized Stokes profiles on the basis of
  the MHD simulation results. The profiles are degraded by taking the
  properties of the spectropolarimeter (SP) into account onboard the
  Hinode satellite. We used simulation runs with different magnetic
  Reynolds numbers (R<SUB>m</SUB>) and observations at different
  heliocentric angles with different levels of noise. <BR /> Results:
  Simulations with an imposed mixed-polarity field and R<SUB>m</SUB>
  below the threshold for dynamo action reproduce the observed vertical
  flux density, but do not display a high enough horizontal flux
  density. Surface dynamo simulations at the highest R<SUB>m</SUB>
  feasible at the moment yield a ratio of the horizontal and vertical
  flux density consistent with observational results, but the overall
  amplitudes are too low. Based on the properties of the local dynamo
  simulations, a tentative scaling of the magnetic field strength
  by a factor 2-3 reproduces the signal observed in the internetwork
  regions. <BR /> Conclusions: We find agreement with observations at
  different heliocentric angles. The mean field strength in internetwork
  implied by our analysis is roughly 170 G at the optical depth unity. Our
  study shows that surface dynamo could be responsible for most of the
  magnetic flux in the quiet Sun outside the network, given that the
  extrapolation to higher R<SUB>m</SUB> is valid.

Title: Excitation of vertical kink waves in a solar coronal arcade
    loop by a periodic driver
Authors: Selwa, M.; Murawski, K.; Solanki, S. K.; Ofman, L.
Bibcode: 2010A&A...512A..76S
Altcode:
  <BR /> Aims: We study an oscillatory driver as a possible excitation
  mechanism of vertical kink loop oscillations in the ideal MHD
  regime. <BR /> Methods: We consider a solar coronal magnetic arcade
  with a dense photospheric layer. The two-dimensional numerical model
  that we implement includes the effects of nonlinearity and line
  curvature on the excitation and attenuation of fast magnetosonic kink
  waves. We investigate the effects of a driven sinusoidal pressure
  pulse and compare it with the impulsive excitation by a pressure
  pulse that impacts the overlying loop. <BR /> Results: Our numerical
  simulations reveal wave signatures that are reminiscent of vertical
  loop oscillations seen in TRACE observational data. <BR /> Conclusions:
  We conclude that attenuation of vertical kink oscillations can be
  reduced to the value observed by adopting an oscillatory instead of an
  impulsive excitation. An oscillatory driver also naturally explains why
  only a small subset of all loops is excited to oscillate transversally
  in an active region.

Title: A comparison of measured and simulated solar network contrast
Authors: Afram, N.; Unruh, Y. C.; Solanki, S. K.; Schüssler, M.;
   Mathew, S. K.
Bibcode: 2010IAUS..264...63A
Altcode: 2009arXiv0910.0976A
  Long-term trends in the solar spectral irradiance are important to
  determine the impact on Earth's climate. These long-term changes are
  thought to be caused mainly by changes in the surface area covered by
  small-scale magnetic elements. The direct measurement of the contrast
  to determine the impact of these small-scale magnetic elements
  is, however, limited to a few wavelengths, and is, even for space
  instruments, affected by scattered light and instrument defocus. In
  this work we calculate emergent intensities from 3-D simulations of
  solar magneto-convection and validate the outcome by comparing with
  observations from Hinode/SOT. In this manner we aim to construct the
  contrast at wavelengths ranging from the NUV to the FIR.

Title: Observations of a rotating macrospicule associated with an
    X-ray jet
Authors: Kamio, S.; Curdt, W.; Teriaca, L.; Inhester, B.; Solanki,
   S. K.
Bibcode: 2010A&A...510L...1K
Altcode: 2010arXiv1001.1924K
  <BR /> Aims: We attempt to understand the driving mechanism of a
  macrospicule and its relationship with a coronal jet. <BR /> Methods:
  We study the dynamics of a macrospicule and an associated coronal jet
  captured by multi-spacecraft observations. Doppler velocities in both
  the macrospicule and the coronal jet are determined by EIS and SUMER
  spectra. Their temporal evolution is studied using X-ray and He II λ304
  images. <BR /> Results: A blueshift of -120 ± 15 km s<SUP>-1</SUP>
  is detected on one side of the macrospicule, while a redshift of 50
  ± 6 km s<SUP>-1</SUP> is found at the base of the other side. The
  inclination angle of the macrospicule inferred from a stereoscopic
  analysis with STEREO suggests that the measured Doppler velocities can
  be attributed to a rotating motion of the macrospicule rather than
  a radial flow or an expansion. <BR /> Conclusions: The macrospicule
  is driven by the unfolding motion of a twisted magnetic flux rope,
  while the associated X-ray jet is a radial outflow.

Title: Nonlinear force-free modelling: influence of inaccuracies in
    the measured magnetic vector
Authors: Wiegelmann, T.; Yelles Chaouche, L.; Solanki, S. K.; Lagg, A.
Bibcode: 2010A&A...511A...4W
Altcode: 2009arXiv0912.3002W
  Context. Solar magnetic fields are regularly extrapolated into the
  corona starting from photospheric magnetic measurements that can
  be affected by significant uncertainty. <BR /> Aims: We study how
  inaccuracies introduced into the maps of the photospheric magnetic
  vector by the inversion of ideal and noisy Stokes parameters influence
  the extrapolation of nonlinear force-free magnetic fields. <BR />
  Methods: We compute nonlinear force-free magnetic fields based on
  simulated vector magnetograms, by the inversion of Stokes profiles
  that were computed by a 3-D radiation MHD simulation snapshot. These
  extrapolations are compared with extrapolations that originate directly
  in the field in the MHD simulations, which is our reference. We
  investigate how line formation and instrumental effects such as noise,
  limited spatial resolution, and the effect of employing a filter
  instrument influence the resulting magnetic field structure. The
  comparison is performed qualitatively by visually inspecting the
  magnetic field distribution and quantitatively by different metrics. <BR
  /> Results: The reconstructed field is most accurate if ideal Stokes
  data are inverted and becomes less accurate if instrumental effects
  and noise are included. The results demonstrate that the nonlinear
  force-free field extrapolation method tested here is relatively
  insensitive to the effects of noise in measured polarization spectra
  at levels consistent with present-day instruments. <BR /> Conclusions:
  Our results show that we can reconstruct the coronal magnetic field as
  a nonlinear force-free field from realistic photospheric measurements
  with an accuracy of a few percent, at least in the absence of sunspots.

Title: Convective Motions and Net Circular Polarization in Sunspot
    Penumbrae
Authors: Borrero, J. M.; Solanki, S. K.
Bibcode: 2010ApJ...709..349B
Altcode: 2009arXiv0911.2570B
  We have employed a penumbral model, which includes the Evershed flow
  and convective motions inside penumbral filaments, to reproduce the
  azimuthal variation of the net circular polarization (NCP) in sunspot
  penumbrae at different heliocentric angles for two different spectral
  lines. The theoretical NCP fits the observations as satisfactorily
  as penumbral models based on flux tubes. The reason for this is that
  the effect of convective motions on the NCP is very small compared
  to the effect of the Evershed flow. In addition, the NCP generated by
  convective upflows cancels out the NCP generated by the downflows. We
  have also found that, in order to fit the observed NCP, the strength
  of the magnetic field inside penumbral filaments must be very close
  to 1000 G. In particular, field-free or weak-field filaments fail to
  reproduce both the correct sign of the NCP and its dependence on the
  azimuthal and heliocentric angles.

Title: Evolution of the solar magnetic flux on time scales of years
    to millenia
Authors: Vieira, L. E. A.; Solanki, S. K.
Bibcode: 2010A&A...509A.100V
Altcode: 2009arXiv0911.4396V
  <BR /> Aims: We improve the description of the evolution of the Sun's
  open and total magnetic flux on time scales of years to millenia. <BR />
  Methods: In the model employed here the evolution of the solar total
  and open magnetic flux is computed from the flux emerging at the solar
  surface in the form of bipolar magnetic features, which is related to
  the sunspot number cycle parameters and can be estimated from historical
  records. Compared to earlier versions of the model in addition to the
  long-lived open flux, now also a more rapidly decaying component of
  the open flux is considered. The model parameters are constrained by
  comparing its output with observations of the total surface magnetic
  flux and with a reconstruction of the open magnetic flux based on the
  geomagnetic indexes. A method to compute the Sun's total magnetic flux
  and the sunspot number during the Holocene, starting from the open flux
  obtained from cosmogenic isotopes records, is also presented. <BR />
  Results: By considering separately a rapidly evolving and a slowly
  evolving component of the open flux the model reproduces the Sun's
  open flux, as reconstructed based on the aa-index, much better and
  a reasonable description of the radial component of interplanetary
  magnetic field data is obtained. The greatest improvement is in the
  reproduction of the cyclic variation of the open flux, including
  the amplitudes of individual cycles. Furthermore, we found that
  approximately 25% of the modeled open flux values since the end of
  the Maunder minimum are lower than the averaged value over 2008,
  i.e. during the current low minimum. The same proportion is observed
  in reconstructions of the open flux during the Holocene based on
  cosmogenic isotopes, which suggests that the present solar minimum
  conditions are below average, but not exceptional in terms of the
  heliospheric magnetic flux.

Title: Evolution of the solar radiative forcing on climate during
    the Holocene
Authors: Vieira, Luis Eduardo; Solanki, Sami K.; Krivova, Natalie
Bibcode: 2010cosp...38.1785V
Altcode: 2010cosp.meet.1785V
  The main external heating source of the Earth's coupled atmosphere-ocean
  system is the solar radiative energy input. The variability of
  this energy source produces corresponding changes on the coupled
  system. However, there is still significant uncertainty on the level of
  changes. One way to distinguish the influence of the Sun on the climate
  from other sources is to search for its influence in the pre-industrial
  period, when the influence of human activities on the atmosphere
  composition and Earth's surface properties can be neglected. Such
  studies require long time series of solar and geophysical parameters,
  ideally covering the whole Holocene. Here, we compute the total and
  spectral irradiance for the Holocene employing the reconstructions of
  the open flux and sunspot number obtained from the cosmogenic isotope
  14C. The model employed in this study is identical to the spectral
  and total irradiance reconstruction (SATIRE) models employed to study
  these parameters on time scales from days to centuries, but adapted
  to work with decadal averaged data. The model is tested by comparing
  to the total and spectral solar irradiance reconstructions from the
  sunspot number for the last 4 centuries. We also discuss limits and
  uncertainties of the model.

Title: Is the current solar activity minimum special?
Authors: Solanki, Sami K.; Krivova, Natalie; Antunes Vieira, Luis
   Eduardo
Bibcode: 2010cosp...38.1693S
Altcode: 2010cosp.meet.1693S
  Is the current solar activity minimum special? Sami K. Solanki(1,2),
  Natalie Krivova(1), Luis E. Vieira(1,3) (1) Max Planck Institute
  for Solar System Research, Katlenburg-Lindau, Germany (2) Kyung-Hee
  University, Yongin, Gyeonggi, Korea (3) Laboratory for Physics and
  Chemistry of the Terrestrial Environment/CNRS, Or-leans, France In many
  respects the current minimum of solar activity is rather different
  from other minima during the last half century, which has seen the
  Sun in a state of unusually high activity. This uncommon minimum
  has fascinated solar physicists. Of particular importance for our
  understanding is the behaviour of the magnetic field, which is the
  source of all activity observed in the solar atmosphere, including the
  heliosphere. Furthermore, the evolution of dark and bright magnetic
  features on the solar surface modulates the solar irradiance, which
  could directly influence the Earth's climate. In this presentation
  observations and models of the evolution of the Sun's magnetic field,
  sunspots and irradiance are reviewed. After discussing the variation
  of these quantities over the solar cycle and from cycle to cycle,
  the current minimum is considered in greater detail. It is compared
  to earlier minima going back to the Maunder minimum and, in a more
  averaged sense, to solar activity and irradiance during the whole
  Holocene. Questions that will be onsidered are: Are we leaving the
  period of high solar activity (a grand maximum) to enter into a phase
  of more moderate activity, or even into a grand minimum? How could
  such a change in the level of the magnetic field and irradiance aid
  us in gaining further insight into the nature of the Sun's influence
  on the Earth's climate?

Title: Temperatures of small scale magnetic structures in deep solar
    photospheric layers
Authors: Oklay, Nilda; Gandorfer, Achim; Lagg, Andreas; Solanki,
   Sami K.; Bianda, Michele; Ramelli, Renzo
Bibcode: 2010cosp...38.2857O
Altcode: 2010cosp.meet.2857O
  With current solar instrumentation, small scale magnetic
  structures still remain unresolved. Nevertheless, it is possible
  to retrieve information about these unresolved magnetic structures
  via spectropolarimetry. For this reason, IRSOL (Istituto Ricerche
  Solari Locarno) facility is used to obtain simultaneously recorded
  spectra of Stokes I and Stokes V/I of CI (5380.3 A), FeI (5379.6 A,
  5383.4 A) and TiII (5381.0 A) lines on an active region using the
  ZIMPOL II (Zurich Imaging Polarimeter II) instrument. We used Stokes V
  amplitude ratios technique to investigate temperatures of unresolved
  magnetic features down to deep photospheric layers. Atmospheric
  parameters are obtained from the inversions done with the SPINOR code
  (Stokes-Profile-INversion-O-Routines). Then the results are compared
  with the results from the realistic MHD simulations obtained from
  MURaM code (MPS/University of Chicago radiative MHD). Comparisons of
  the results from observations, inversions and numerical simulations
  show a good agreement, which confirms the usage of this technique as
  a temperature diagnostic tool.

Title: Observations of the solar chromosphere at millimeter
    wavelengths
Authors: Loukitcheva, M.; Solanki, S. K.; White, S. M.
Bibcode: 2010MmSAI..81..592L
Altcode:
  Millimeter wavelengths provide a powerful tool to study the thermal
  structure of the solar chromosphere and its response to dynamic
  processes. We present initial studies of chromospheric fine structure
  and its dynamics obtained from observations of the quiet Sun with
  BIMA at 3.5 mm with a resolution of 12 arcsec. The two-dimensional
  millimeter maps of the solar chromosphere reveal brightness features
  corresponding to supergranular network boundaries and bright points
  within cells. Significant intensity oscillations with frequencies of
  1.5 - 8.0 mHz with a tendency toward shorter-period oscillations in
  the internetwork and longer periods in network regions are found in
  the data. However, higher spatial resolution is required for a more
  detailed study. We discuss the requirements imposed on observations in
  the millimeter domain that might provide an insight into the fundamental
  questions of solar physics. We also review the capabilities of the
  current and future millimeter-wave interferometers, including the
  CARMA and ALMA arrays.

Title: Solar Spectral Irradiance variations: the long-term view
Authors: Solanki, Sami K.
Bibcode: 2010cosp...38...19S
Altcode: 2010cosp.meet...19S
  Solar Spectral Irradiance variations: the long-term view S.K. Solanki
  Max Planck Institute for Solar System Research, Katlenburg-Lindau,
  Germany The total and spectral irradiance of the Sun are prime
  candidates for external forcing of the Earth's climate system. Whereas
  variations of total solar irradiance have been observed and modelled
  with great success, our corresponding knowledge of the variation of
  spectral irradi-ance is, by comparison, still in its infancy. Although,
  on short time-scales multiple measured time series and models are
  now available, on longer time-scales models are the only source of
  information. Until recently even the models were rather restricted,
  being either based purely on proxies, or limited in spectral range. A
  new generation of models is now available, which goes beyond the
  limitations of the earlier approaches. An overview of the models and
  their results is given, with the emphasis being placed on the most
  recent ones.

Title: How do inaccuracies and unresolved structures in the measured
    solar photospheric magnetic vector influence the accuracy of coronal
    magnetic field models?
Authors: Wiegelmann, Thomas; Yelles, Lotfi; Solanki, Sami; Lagg,
   Andreas
Bibcode: 2010cosp...38.2827W
Altcode: 2010cosp.meet.2827W
  Solar magnetic fields are usually extrapolated into the corona
  starting from photospheric mag-netic measurements that can suffer from
  significant uncertainties caused by the presence of unresolved fine
  structures due to a limited spatial resolution and by the limited
  polarimet-ric accuracy and spectral resolution. We investigate
  how these inaccuracies in the measured photospheric magnetic field
  vector influence the accuracy of the extrapolated coronal mag-netic
  field. We compare non-linear force-free coronal magnetic field
  extrapolations from a 3-D radiation MHD simulation snapshot with
  corresponding extrapolations from synthetic vector magnetograms. The
  synthetic magnetograms contain instrumental effects such as noise,
  limited spatial and spectral resolution and the effect of employing a
  filter instrument. The parameters are chosen in particular to mimic the
  effects of the Hinode/SOT and the future Solar Orbiter PHI instruments,
  respectively. We discuss, how photospheric structures, which are
  inherent in the MHD snapshot, but not resolved in the photospheric
  magnetic field measurements, influence the quality of the computed
  coronal magnetic field model.

Title: Accelerating disturbances in polar plume and inter-plume
Authors: Gupta, Girjesh R.; Banerjee, Dipankar; Teriaca, Luca; Imada,
   Shinsuke; Solanki, Sami
Bibcode: 2010cosp...38.2937G
Altcode: 2010cosp.meet.2937G
  We present EIS/Hinode &amp; SUMER/SoHO joint observations allowing the
  first spectroscopic detection of accelerating disturbances as recorded
  with coronal lines in inter-plume and plume regions of a polar coronal
  hole. From time-distance radiance maps, we detect the presence of
  propagating disturbances in a polar inter-plume region with a period
  of 15 to 20 min and a propagation speed increasing from 130±14 km/s
  just above the limb, to 330±140 km/s around 160" above the limb. These
  disturbances can also be traced to originate from a bright region of
  the on-disk part of the coronal hole where the propagation speed was
  found to be in the range of 25±1.3 to 38±4.5 km/s, with the same
  periodicity. These on-disk bright regions can be vi-sualized as the
  base of the coronal funnels. The adjacent plume region also shows the
  presence of propagating disturbance with the same range of period but
  with propagation speeds in the range of 135±18 to 165±43 km/s only. A
  comparison between the time-distance radiance map of both regions,
  indicate that the disturbances within the plumes are not observable (may
  be getting dissipated) far off-limb whereas this is not the case in the
  inter-plume region. Conclu-sions drawn from these observations in terms
  of accelerating waves or high speed jets/upflows will be discussed.

Title: High resolution imaging and polarimetry with SUNRISE, a
    balloon-borne stratospheric solar observatory
Authors: Barthol, Peter; Chares, Bernd; Deutsch, Werner; Feller, Alex;
   Gandorfer, Achim; Grauf, Bianca; Hirzberger, Johann; Meller, Reinhard;
   Riethmueller, Tino; Schuessler, Manfred; Solanki, Sami K.; Knoelker,
   Michael; Martinez Pillet, Valentin; Schmidt, Wolfgang; Title, Alan
Bibcode: 2010cosp...38.4063B
Altcode: 2010cosp.meet.4063B
  SUNRISE is an international collaboration for the development
  and operation of a meter-class balloon-borne stratospheric solar
  observatory. Prime science goal is the study of structure and dynamics
  of the magnetic field in the solar atmosphere and the interaction of
  the magnetic field with convective plasma flows. These processes are
  studied by high resolution imaging in the UV and polarimetry at visible
  wavelengths. The instrument has been successfully launched on June 8,
  2009 from ESRANGE, Kiruna, Northern Sweden. During the more than 5
  days flight about 1.5 TByte of scientific data were collected. The
  paper gives an overview of the instrument and mission, examples of
  the scientific output will also be presented. SUNRISE is a joint
  project of the Max-Planck-Institut fuer Sonnensystemforschung (MPS),
  Katlenburg-Lindau, with the Kiepenheuer-Institut fuer Sonnenphysik
  (KIS), Freiburg, the High-Altitude Observatory (HAO), Boulder, the
  Lockheed-Martin Solar and Astrophysics Lab. (LMSAL), Palo Alto, and
  the Spanish IMaX consortium.

Title: The Ultraviolet Filter Imager (SuFI) onboard the Sunrise
balloon-borne solar observatory: Instrument description and first
    results
Authors: Gandorfer, Achim; Barthol, Peter; Feller, Alex; Grauf,
   Bianca; Hirzberger, Johann; Riethmueller, Tino; Solanki, Sami K.;
   Berkefeld, Thomas; Knoelker, Michael; Martinez Pillet, Valentin;
   Schmidt, Wolfgang; Title, Alan
Bibcode: 2010cosp...38.4064G
Altcode: 2010cosp.meet.4064G
  We describe the design of the near UV filter imager SuFi onboard
  Sunrise, which was successfully flown in the stratosphere in June
  2009. During its five days flight SuFI captured the highest contrast
  images of solar granulation ever. SuFI is a diffraction limited filter
  imager with an effective focal length of 121m, working in 5 distinct
  wavelength bands between 210nm and 397nm. It is based on a two mirror
  modified Schwarzschild microscope, which is integral part of the central
  Image stabilization and light Distribution unit (ISLiD) of Sunrise,
  which acts as the reimaging optics between the 1m telescope and the
  science instruments. The key technical features of the instrument are
  presented under the view of the specific demands of balloon-borne
  optical systems. First results obtained with the instrument are
  presented to demonstrate the capabilities of the instrument.

Title: UV intensity distributions of the quiet Sun observed with
    Sunrise
Authors: Hirzberger, Johann; Feller, A.; Riethmueller, T.; Borrero,
   J. M.; Schüssler, M.; Barthol, P.; Berkefeld, T.; Gandorfer, A.;
   Knoelker, M.; Martínez Pillet, V.; Schmidt, W.; Solanki, S.; Title, A.
Bibcode: 2010cosp...38.1735H
Altcode: 2010cosp.meet.1735H
  High resolution solar images in the near UV have been obtained with
  the Solar UV Filtergraph (SUFI) onboard the Sunrise balloon borne
  observatory, amongst others in wavelength regions not accessible
  from the ground. We present intensity distributions of the quiet
  Sun at different heliocentric angles, from disk center to the solar
  limb. These results, obtained in spectral windows at 214 nm, 313 nm
  (OH band), 388 nm (CN band) and 396.7 nm (CaIIH), represent an important
  validation of numerical models of the solar photosphere and are, thus,
  fundamental ingredients for our understanding of the thermal processes
  in the solar surface region.

Title: Magnetic field intensification: comparison of 3D MHD
    simulations with Hinode/SP results
Authors: Danilovic, S.; Schüssler, M.; Solanki, S. K.
Bibcode: 2010A&A...509A..76D
Altcode: 2009arXiv0910.1211D
  Context. Recent spectro-polarimetric observations have provided detailed
  measurements of magnetic field, velocity and intensity during events of
  magnetic field intensification in the solar photosphere. <BR /> Aims:
  By comparing with synthetic observations derived from MHD simulations,
  we investigate the physical processes underlying the observations,
  as well as verify the simulations and the interpretation of the
  observations. <BR /> Methods: We consider the temporal evolution of
  the relevant physical quantities for three cases of magnetic field
  intensification in a numerical simulation. In order to compare with
  observations, we calculate Stokes profiles and take into account the
  spectral and spatial resolution of the spectropolarimeter (SP) on
  board Hinode. We determine the evolution of the intensity, magnetic
  flux density and zero-crossing velocity derived from the synthetic
  Stokes parameters, using the same methods as applied to the Hinode/SP
  observations to derive magnetic field and velocity information from
  the spectro-polarimetric data. <BR /> Results: The three events
  considered show a similar evolution: advection of magnetic flux to a
  granular vertex, development of a strong downflow, evacuation of the
  magnetic feature, increase of the field strength and the appearance
  of the bright point. The magnetic features formed have diameters of
  0.1-0.2´´. The downflow velocities reach maximum values of 5-10
  km s<SUP>-1</SUP> at τ = 1. In the largest feature, the downflow
  reaches supersonic speed in the lower photosphere. In the same case,
  a supersonic upflow develops approximately 200 s after the formation of
  the flux concentration. We find that synthetic and real observations
  are qualitatively consistent and, for one of the cases considered,
  also agree very well quantitatively. The effect of finite resolution
  (spatial smearing) is most pronounced in the case of small features,
  for which the synthetic Hinode/SP observations miss the bright point
  formation and also the high-velocity downflows during the formation
  of the smaller magnetic features. <BR /> Conclusions: The observed
  events are consistent with the process of field intensification by
  flux advection, radiative cooling, and evacuation by strong downflow
  found in MHD simulations. The quantitative agreement of synthetic and
  real observations indicates the validity of both the simulations and
  the interpretations of the spectro-polarimetric observations.

Title: Radiative emission of solar features in Ca II K
Authors: Criscuoli, S.; Ermolli, I.; Fontenla, J.; Giorgi, F.; Rast,
   M.; Solanki, S. K.; Uitenbroek, H.
Bibcode: 2010MmSAI..81..773C
Altcode: 2010arXiv1002.0244C
  We investigated the radiative emission of different types of solar
  features in the spectral range of the Ca II K line. We analyzed
  full-disk 2k × 2k observations from the Precision Solar Photometric
  Telescope (PSPT). The data were obtained by using three narrow-band
  interference filters that sample the Ca II K line with different pass
  bands. Two filters are centered in the line core, the other in the red
  wing of the line. We measured the intensity and contrast of various
  solar features, specifically quiet Sun (inter-network), network,
  enhanced network, plage, and bright plage (facula) regions. Moreover,
  we compared the results obtained with those derived from the numerical
  synthesis performed for the three PSPT filters with a widely used
  radiative code on a set of reference semi-empirical atmosphere models.

Title: Analysis of Ca II K spectroheliogram time-series for solar
    irradiance studies
Authors: Ermolli, Ilaria; Krivova, Natalie; Solanki, Sami K.
Bibcode: 2010cosp...38..133E
Altcode: 2010cosp.meet..133E
  Historic Ca II K observations constitute an extremely valuable
  resource for many research topics, including investigations of solar
  activity and irradiance variations on century timescales. In fact,
  the intensities measured on these observations can serve as proxies for
  magnetic activity, due to the strong correlation found between the Ca
  II K emission and the line-of-sight magnetic flux density. We analyzed
  three time-series of historic Ca II K observations, specifically those
  obtained by the digitization of the Arcetri, Kodaikanal, and Mt Wilson
  spectroheliohram archives. We examined the quality of these data,
  in order to estimate their value for irradiance studies focusing
  on time-scales longer than the solar cycle. We employ different
  processing techniques in order to investigate whether uniform results
  on the evolution of the solar magnetic field, both in quiet and active
  regions, can be obtained for the three analyzed series. ——-Session
  A1.1 Atmosphere Chemistry and Physics (i) Solar Spectral Irradiance
  Variations and Their Influence on the Earth's Atmosphere

Title: Relation between the Sunrise photospheric magnetic field and
    the Ca II H bright features
Authors: Jafarzadeh, Shahin; Hirzberger, J.; Feller, A.; Lagg, A.;
   Solanki, S. K.; Pietarila, A.; Danilovic, S.; Riethmueller, T.;
   Barthol, P.; Berkefeld, T.; Gandorfer, A.; Knülker, M.; Martínez
   Pillet, V.; Schmidt, W.; Schüssler, M.; Title, A.
Bibcode: 2010cosp...38.2856J
Altcode: 2010cosp.meet.2856J
  Recent observations from the Sunrise balloon-borne solar telescope
  have enabled us to reach an unprecedented high spatial resolution
  on the solar surface with the near-ultraviolet photo-spheric and
  chromospheric images as well as the magnetograms. We use these high
  resolution observations to investigate the structure of the solar
  upper photosphere and lower chromosphere as well as their temporal
  evolutions. We study the relation between the inter-granular Ca II
  397 nm bright structures in images obtained by the Sunrise Filter
  Imager (SuFI) and their corresponding photospheric vector magnetic
  field computed from the Imaging Magnetogram eXperiment (IMaX)
  observations. The targets under study are in a quiet Sun region and
  close to disc-centre.

Title: Total and spectral irradiance comparisons between SIM and
    the SATIRE model in the declining phase of cycle 23
Authors: Ball, Will; Unruh, Yvonne; Krivova, Natalie; Solanki, Sami
   K.; Harder, Jerald
Bibcode: 2010cosp...38..136B
Altcode: 2010cosp.meet..136B
  Climate models rely on accurate total and spectral solar irradiance
  inputs, but until 2003 con-tinuous spectral irradiance information
  across a large portion of the solar spectrum was lacking. Since the
  launch of the Solar Radiation and Climate Experiment (SORCE), with the
  Spectral Irradiance Monitor (SIM) observing the UV, visible and IR,
  data have been accumulating and now cover a significant portion of
  a cycle. For the first time this allows spectral models to be tested
  over periods greater than a solar rotation. We present six years of
  total and spectral irradiance reconstructions using the SATIRE model
  that incorporates SOHO/MDI continuum and magnetogram images for the
  period April 2004 to November 2009 in the declining phase of cycle 23
  and through the recent unusual minimum. We compare these results with
  the SIM instrument and so cover the spectral region 200 -1600 nm. While
  detrended, short-term, variation is recreated well by the model, there
  are discrepancies in longer-term trends between observations and the
  model. This may become important when considering the radiative forcing
  from the Sun used in climate research and so understanding why there is
  such a significant disagreement is an important area of investigation.

Title: Center-to-Limb Variation of the continuum contrast of quiet
    Sun magnetic features from Hinode/SP
Authors: Kobel, Philippe; Borrero Santiago, Juan Manuel; Solanki,
   Sami K.
Bibcode: 2010cosp...38.1788K
Altcode: 2010cosp.meet.1788K
  The center-to-limb variation (CLV) of the continuum contrast of
  magnetic features represents an important constraint for flux tube
  models, as well as a useful input to reproduce the total solar
  irradiance. However, precise measurements are difficult because
  the contrast depends on the atmospheric and magnetic parameters of
  those features, and is severely affected by the observing conditions
  (seeing). Here we present the first assessment of the dependence of
  the continuum contrast of magnetic features on both the heliocentric
  angle and on their magnetic properties, inferred from high spatial
  resolution spectro-polarimetric maps (Hinode/SP). At the same time,
  it allowed us to improve the results of previous lower resolution
  studies of contrast as a function of magnetogram signal. The magnetic
  parameters (field strength, filling factor and inclination) were
  inferred by Milne-Eddington inversions (VFISV) of spectro-polarimetric
  maps covering a continuous range of mu between 1 and 0.2 in the
  quiet Sun. Our contrasts reach positive values at disk center,
  and the peak of the contrast as a function of magnetogram signal
  at different are larger than in previous studies. The contrast was
  found to behave differently in two distinct regimes of "apparent flux
  density", characterizing fields that are tied to granulation and strong
  network-like magnetic features, respectively. The weak fields seem to be
  "wrapped" around granules and the contrasts reflects their location:
  pixels with horizontal fields are on average located within granules
  and are brighter, while pixels with more vertical fields are preferably
  located in the intergranular lanes and are thus darker. For the stronger
  fields, the contrast CLV was found to depend essentially on the apparent
  flux density, with a rather symmetric dependence on the field strength
  and on the filling factor, while the fields are quasi-vertical.

Title: Long term variability of solar magnetic activity: the
    solar-stellar connection
Authors: Solanki, Sami K.
Bibcode: 2010cosp...38.2890S
Altcode: 2010cosp.meet.2890S
  Long term variability of solar magnetic activity: the solar-stellar
  connection S.K. Solanki Max Planck Institute for Solar System
  Research, Katlenburg-Lindau, Germany The dominant time-scales of
  solar variability are the solar rotation period and in particular
  the length of the solar cycle, but variations of solar activity on
  longer time scales are also present. Variations of stellar activity
  are also well documented on time scales up to stellar activity
  cycles, although secular variations on longer time scales are
  somewhat less well established, due to the limited length of the
  available observational time series. Multi-wavelength observations
  of solar variability is mainly limited to the space age, while
  direct observations of sunspots are available back to the year 1610,
  i.e. over the whole era of telescopic astronomy. In the last decades
  considerable progress has been made in extending our knowledge of solar
  activity to pre-telescopic times, using records of the concentration of
  cosmogenic isotopes in terrestrial archives.Such studies have shown,
  e.g., that in addition to grand minima, the Sun has also enjoyed
  times of significantly anhanced activity, so called grand maxima. The
  recent decades formed a particularly prominent such grand maximum. The
  current peculiar minimum has shown strong indications that we are in
  the process of leaving this last grand maximum. There is also strong
  evidence that there are significant secular changes of the magnetic
  flux and other active phenomena. Although the period over which we
  have data on stellar activity is far shorter than for the Sun, these
  data allow stars of different types to be sampled (i.e. stars with
  different activity levels, of different spectral types, at different
  evolutionary stages, etc.) that display the full variety of active
  phenomena, including cycles, but also chaotic variability. After an
  overview of our knowledge and understanding of the longer-term evolution
  of solar activity, comparisons with observations of stellar activity
  time series are presented and some implications for our understanding
  of stellar activity variations are deduced.

Title: Expansion of Magnetic Flux Concentrations with Height:
    A Comparison of Hinode SOT Data and MHD Simulations
Authors: Pietarila, A.; Cameron, R.; Solanki, S.
Bibcode: 2009ASPC..415...91P
Altcode:
  The Hinode SOT (Tsuneta et al. 2008) NFI Na I D<SUB>1</SUB> and SP Fe I
  data sampled at different positions on the solar disk provide a unique
  diagnostic for studying the expansion of magnetic flux concentrations
  with height. We make a comparative study of SOT observations and
  2-dimensional (2D) radiative MHD-simulations to see how well the
  simulations capture the expansion properties. The expansion of flux
  concentrations is clearly seen in the SOT Na I D<SUB>1</SUB> data,
  where most of the magnetic features appear unipolar at disk center while
  close to the limb bipolar appearance strongly dominates. This trend,
  albeit not as strong, is seen in the SP data as well. Some aspects of
  the observations are qualitatively reproduced by simulations with a
  potential (as opposed to vertical) upper boundary condition for the
  magnetic field.

Title: Simulation of a flux emergence event and comparison with
    observations by Hinode
Authors: Yelles Chaouche, L.; Cheung, M. C. M.; Solanki, S. K.;
   Schüssler, M.; Lagg, A.
Bibcode: 2009A&A...507L..53Y
Altcode: 2009arXiv0910.5737Y
  Aims: We study the observational signature of flux emergence in
  the photosphere using synthetic data from a 3D MHD simulation of the
  emergence of a twisted flux tube. <BR />Methods: Several stages in the
  emergence process are considered. At every stage we compute synthetic
  Stokes spectra of the two iron lines Fe I 6301.5 Å and Fe I 6302.5
  Å and degrade the data to the spatial and spectral resolution of
  Hinode's SOT/SP. Then, following observational practice, we apply
  Milne-Eddington-type inversions to the synthetic spectra in order
  to retrieve various atmospheric parameters and compare the results
  with recent Hinode observations. <BR />Results: During the emergence
  sequence, the spectral lines sample different parts of the rising
  flux tube, revealing its twisted structure. The horizontal component
  of the magnetic field retrieved from the simulations is close to the
  observed values. The flattening of the flux tube in the photosphere is
  caused by radiative cooling, which slows down the ascent of the tube
  to the upper solar atmosphere. Consistent with the observations, the
  rising magnetized plasma produces a blue shift of the spectral lines
  during a large part of the emergence sequence. <P />Figure 3 is only
  available in electronic form at http://www.aanda.org

Title: Internetwork Horizontal Magnetic Fields in the Quiet Sun
Chromosphere: Results from a Joint Hinode/VTT Study
Authors: Lagg, A.; Ishikawa, R.; Merenda, L.; Wiegelmann, T.; Tsuneta,
   S.; Solanki, S. K.
Bibcode: 2009ASPC..415..327L
Altcode:
  We present results from a joint Hinode/VTT campaign (May
  2008). Spectropolarimetric data of a quiet Sun super-granular network
  cell at a heliocentric angle of 28° in the He I 10830 Å line were
  analyzed using an inversion code incorporating Hanle and Zeeman effects
  (HeLIx^+) to retrieve magnetic field strength and direction in the upper
  chromosphere. Simultaneously recorded Hinode SOT/SP data reveal the
  photospheric magnetic field morphology, clearly showing magnetic flux
  concentrations in the internetwork. The photospheric magnetic field
  maps are used to feed potential field extrapolations similar to the
  work by Schrijver &amp; Title (2003). The extrapolated magnetic field
  structure is compared with the magnetic field configuration resulting
  from the He 10830 inversions. These inversions also reveal horizontal
  magnetic structures extending over a length of up to 20 Mm above the
  internetwork, indicative of the presence of a magnetic canopy. The
  photospheric magnetic flux concentrations in the internetwork are
  obviously not sufficiently strong to prevent the formation of a canopy
  at chromospheric heights.

Title: Solar magnetic field and irradiance: how unusual is the
    current minimum? (Invited)
Authors: Solanki, S. K.; Krivova, N.; Vieira, L. A.
Bibcode: 2009AGUFM.U34A..01S
Altcode:
  In many respects the current minimum of solar activity is rather
  different from other minima during the last half century, which has
  seen the Sun in a state of unusually high activity. This uncommon
  minimum has fascinated solar physicists. Of particular importance for
  our understanding is the behaviour of the magnetic field, which is the
  source of all activity observed in the solar atmosphere, including the
  heliosphere. Furthermore, the evolution of dark and bright magnetic
  features on the solar surface modulates the solar irradiance, which
  could directly influence the Earth's climate. In this presentation
  observations and models of the evolution of the Sun's magnetic field
  and irradiance are reviewed. After discussing the variation of these
  quantities over the solar cycle and from cycle to cycle, the current
  minimum is considered in greater detail. It is compared to earlier
  minima going back to the Maunder minimum and, in a more averaged sense,
  to solar activity and irradiance during the whole Holocene. Questions
  that will be considered are: Are we leaving the period of high solar
  activity (a grand maximum) to enter into a phase of more moderate
  activity, or even into a grand minimum? How could such a change in the
  level of the magnetic field and irradiance aid us in gaining further
  insight into the nature of the Sun's influence on the Earth's climate?

Title: The Local Dust Foregrounds in the Microwave Sky. I. Thermal
    Emission Spectra
Authors: Dikarev, Valeri; Preuß, Oliver; Solanki, Sami; Krüger,
   Harald; Krivov, Alexander
Bibcode: 2009ApJ...705..670D
Altcode: 2009arXiv0910.1317D
  Analyses of the cosmic microwave background (CMB) radiation maps made by
  the Wilkinson Microwave Anisotropy Probe (WMAP) have revealed anomalies
  not predicted by the standard inflationary cosmology. In particular, the
  power of the quadrupole moment of the CMB fluctuations is remarkably
  low, and the quadrupole and octopole moments are aligned mutually
  and with the geometry of the solar system. It has been suggested in
  the literature that microwave sky pollution by an unidentified dust
  cloud in the vicinity of the solar system may be the cause for these
  anomalies. In this paper, we simulate the thermal emission by clouds
  of spherical homogeneous particles of several materials. Spectral
  constraints from the WMAP multi-wavelength data and earlier infrared
  observations on the hypothetical dust cloud are used to determine the
  dust cloud's physical characteristics. In order for its emissivity
  to demonstrate a flat, CMB-like wavelength dependence over the WMAP
  wavelengths (3 through 14 mm), and to be invisible in the infrared
  light, its particles must be macroscopic. Silicate spheres of several
  millimeters in size and carbonaceous particles an order of magnitude
  smaller will suffice. According to our estimates of the abundance of
  such particles in the zodiacal cloud and trans-Neptunian belt, yielding
  the optical depths of the order of 10<SUP>-7</SUP> for each cloud,
  the solar system dust can well contribute 10 μK (within an order of
  magnitude) in the microwaves. This is not only intriguingly close to
  the magnitude of the anomalies (about 30 μK), but also alarmingly
  above the presently believed magnitude of systematic biases of the
  WMAP results (below 5 μK) and, to an even greater degree, of the
  future missions with higher sensitivities, e.g., Planck.

Title: ACRIM-gap and total solar irradiance revisited: Is there a
    secular trend between 1986 and 1996?
Authors: Krivova, N. A.; Solanki, S. K.; Wenzler, T.
Bibcode: 2009GeoRL..3620101K
Altcode: 2009arXiv0911.3817K
  A gap in the total solar irradiance (TSI) measurements between
  ACRIM-1 and ACRIM-2 led to the ongoing debate on the presence or not
  of a secular trend between the minima preceding cycles 22 (in 1986)
  and 23 (1996). It was recently proposed to use the SATIRE model of
  solar irradiance variations to bridge this gap. When doing this, it is
  important to use the appropriate SATIRE-based reconstruction, which we
  do here, employing a reconstruction based on magnetograms. The accuracy
  of this model on months to years timescales is significantly higher
  than that of a model developed for long-term reconstructions used by
  the ACRIM team for such an analysis. The constructed ‘mixed’ ACRIM
  — SATIRE composite shows no increase in the TSI from 1986 to 1996,
  in contrast to the ACRIM TSI composite.

Title: High-resolution spectro-polarimetry of a flaring sunspot
    penumbra
Authors: Hirzberger, J.; Riethmüller, T.; Lagg, A.; Solanki, S. K.;
   Kobel, P.
Bibcode: 2009A&A...505..771H
Altcode: 2009arXiv0908.3803H
  We present simultaneous photospheric and chromospheric observations
  of the trailing sunspot in NOAA 10904 during a weak flare eruption
  (GOES magnitude B7.8), obtained with the Swedish Solar Telescope
  (SST) in La Palma, Canary Islands. High-resolution Ca II H images
  show a typical two-ribbon structure that has been hitherto only
  known for larger flares, and the flare appears in a confined region
  that is discernible by a bright border. The underlying photosphere
  shows a disturbed penumbral structure with intersecting branches of
  penumbral filaments. High-resolution Doppler- and vector-magnetograms
  exhibit oppositely directed Evershed flows and magnetic field vectors
  in the individual penumbral branches, resulting in several regions
  of magnetic azimuth discontinuity and several islands where the
  vertical magnetic field is reversed. The discontinuity regions are
  co-spatial with the locations of the onset of the flare ribbons. From
  the results, we conclude that the confined flare region is detached
  from the global magnetic field structure by a separatrix marked by the
  bright border visible in C II H. We further conclude that the islands
  of reversed vertical field appear because of flux emergence and that
  the strong magnetic shear appearing in the regions of magnetic azimuth
  discontinuity triggers the flare. <P />Movies are only available in
  electronic form at http://www.aanda.org

Title: Comparison of the thin flux tube approximation with 3D MHD
    simulations
Authors: Yelles Chaouche, L.; Solanki, S. K.; Schüssler, M.
Bibcode: 2009A&A...504..595Y
Altcode: 2009arXiv0910.1796Y
  Context: The structure and dynamics of small vertical photospheric
  magnetic flux concentrations has been often treated in the framework
  of an approximation based upon a low-order truncation of the Taylor
  expansions of all quantities in the horizontal direction, together
  with the assumption of instantaneous total pressure balance at
  the boundary to the non-magnetic external medium. Formally, such
  an approximation is justified if the diameter of the structure (a
  flux tube or a flux sheet) is small compared to all other relevant
  length scales (scale height, radius of curvature, wavelength,
  etc.). The advent of realistic 3D radiative MHD simulations opens
  the possibility of checking the consistency of the approximation with
  the properties of the flux concentrations that form in the course of
  a simulation. <BR />Aims: We carry out a comparative analysis between
  the thin flux tube/sheet models and flux concentrations formed in a 3D
  radiation-MHD simulation. <BR />Methods: We compare the distribution
  of the vertical and horizontal components of the magnetic field in a 3D
  MHD simulation with the field distribution in the case of the thin flux
  tube/sheet approximation. We also consider the total (gas plus magnetic)
  pressure in the MHD simulation box. <BR />Results: Flux concentrations
  with super-equipartition fields are reasonably well reproduced by
  the second-order thin flux tube/sheet approximation. The differences
  between approximation and simulation are due to the asymmetry and the
  dynamics of the simulated structures.

Title: Reconstruction of solar UV irradiance since 1974
Authors: Krivova, N. A.; Solanki, S. K.; Wenzler, T.; Podlipnik, B.
Bibcode: 2009JGRD..114.0I04K
Altcode: 2009arXiv0907.1500K; 2009JGRD..11400I04K
  Variations of the solar UV irradiance are an important driver of
  chemical and physical processes in the Earth's upper atmosphere and may
  also influence global climate. Here we reconstruct solar UV irradiance
  in the range 115-400 nm over the period 1974-2007 by making use of
  the recently developed empirical extension of the Spectral And Total
  Irradiance Reconstruction (SATIRE) models employing Solar Ultraviolet
  Spectral Irradiance Monitor (SUSIM) data. The evolution of the solar
  photospheric magnetic flux, which is a central input to the model,
  is described by the magnetograms and continuum images recorded at
  the Kitt Peak National Solar Observatory between 1974 and 2003 and
  by the Michelson Doppler Imager instrument on SOHO since 1996. The
  reconstruction extends the available observational record by 1.5
  solar cycles. The reconstructed Ly-α irradiance agrees well with
  the composite time series by Woods et al. (2000). The amplitude of
  the irradiance variations grows with decreasing wavelength and in
  the wavelength regions of special interest for studies of the Earth's
  climate (Ly-α and oxygen absorption continuum and bands between 130
  and 350 nm) is 1-2 orders of magnitude stronger than in the visible
  or if integrated over all wavelengths (total solar irradiance).

Title: Bright fibrils in Ca II K
Authors: Pietarila, A.; Hirzberger, J.; Zakharov, V.; Solanki, S. K.
Bibcode: 2009A&A...502..647P
Altcode: 2009arXiv0905.3124P
  Context: Except for the Ca II resonance lines, fibrils are ubiquitously
  present in most high-resolution observations of chromospheric lines. <BR
  />Aims: We show that fibrils are also a prevailing feature in Ca II K,
  provided the spatial-resolution is sufficiently high. <BR />Methods:
  We present high spatial resolution observations of an active region in
  the Ca II K line from the Swedish Solar Telescope. Through a comparison
  between photospheric intensity and magnetic field data, we study the
  connection between bright chromospheric fibrils and photospheric
  structures. Additionally, using Fourier analysis we study how the
  fibrils are linked to the observed dynamics. <BR />Results: We find
  that very narrow, bright fibrils are a prevailing feature over large
  portions of the observed field. We also find a clear connection between
  the fibril footpoints and photospheric magnetic features. We show that
  the fibrils play two distinct roles in the observed dynamics: depending
  on their location they can act as a canopy suppressing oscillations or
  they can channel low-frequency oscillations into the chromosphere. <BR
  />Conclusions: The Ca II K fibrils share many characteristics with
  fibrils observed in other chromospheric lines, but some features,
  such as the very small widths, are unique to these observations.

Title: Solar Surface Magnetism and Irradiance on Time Scales from
    Days to the 11-Year Cycle
Authors: Domingo, V.; Ermolli, I.; Fox, P.; Fröhlich, C.; Haberreiter,
   M.; Krivova, N.; Kopp, G.; Schmutz, W.; Solanki, S. K.; Spruit, H. C.;
   Unruh, Y.; Vögler, A.
Bibcode: 2009SSRv..145..337D
Altcode:
  The uninterrupted measurement of the total solar irradiance during the
  last three solar cycles and an increasing amount of solar spectral
  irradiance measurements as well as solar imaging observations
  (magnetograms and photometric data) have stimulated the development
  of models attributing irradiance variations to solar surface
  magnetism. Here we review the current status of solar irradiance
  measurements and modelling efforts based on solar photospheric
  magnetic fields. Thereby we restrict ourselves to the study of solar
  variations from days to the solar cycle. Phenomenological models
  of the solar atmosphere in combination with imaging observations of
  solar electromagnetic radiation and measurements of the photospheric
  magnetic field have reached high enough quality to show that a large
  fraction (at least, about 80%) of the solar irradiance variability
  can be explained by the radiative effects of the magnetic activity
  present in the photosphere. Also, significant progress has been made
  with magnetohydrodynamic simulations of convection that allow us to
  relate the radiance of the photospheric magnetic structures to the
  observations.

Title: Stray light correction and contrast analysis of Hinode
    broad-band images
Authors: Mathew, S. K.; Zakharov, V.; Solanki, S. K.
Bibcode: 2009A&A...501L..19M
Altcode: 2009arXiv0906.2451M
  The contrasts of features in the quiet Sun are studied using filtergrams
  recorded by the broad-band filter imager mounted on the Hinode/Solar
  Optical Telescope. In a first step, the scattered light originating
  in the instrument is modeled using Mercury transit data. Combinations
  of four two-dimensional Gaussians with different widths and weights
  were employed to retrieve the point-spread functions (PSF) of the
  instrument at different wavelengths, which also describe instrumental
  scattered light. The parameters of the PSFs at different wavelengths
  are tabulated. The observed images were then deconvolved using the
  PSFs. The corrected images were used to determine the contrasts of
  features such as bright points and granulation in different wavelength
  bands. After correction, rms contrasts of the granulation of between
  0.11 (at 668 nm) and 0.22 (at 388 nm) were obtained. Similarly, bright
  point contrasts ranging from 0.07 (at 668 nm) to 0.78 (at 388 nm) are
  found, which are a factor of 1.8 to 2.8 higher than those obtained
  before PSF deconvolution. The mean contrast of the bright points is
  found to be somewhat higher in the CN-band than in the G-band, which
  confirms theoretical predictions. <P />Appendices are only available
  in electronic form at http://www.aanda.org

Title: A homogeneous database of sunspot areas covering more than
    130 years
Authors: Balmaceda, L. A.; Solanki, S. K.; Krivova, N. A.; Foster, S.
Bibcode: 2009JGRA..114.7104B
Altcode: 2009JGRA..11407104B; 2009arXiv0906.0942B
  The historical record of sunspot areas is a valuable and widely used
  proxy of solar activity and variability. The Royal Greenwich Observatory
  regularly measured this and other parameters between 1874 and
  1976. After that time records from a number of different observatories
  are available. These, however, show systematic differences and often
  have significant gaps. Our goal is to obtain a uniform and complete
  sunspot area time series by combining different data sets. A homogeneous
  composite of sunspot areas is essential for different applications
  in solar physics, among others for irradiance reconstructions. Data
  recorded simultaneously at different observatories are statistically
  compared in order to determine the intercalibration factors. Using
  these data we compile a complete and cross-calibrated time series. The
  Greenwich data set is used as a basis until 1976, the Russian data
  (a compilation of observations made at stations in the former USSR)
  are used between 1977 and 1985, and data compiled by the USAF network
  are used since 1986. Other data sets (Rome, Yunnan, and Catania)
  are used to fill up the remaining gaps. Using the final sunspot areas
  record the Photometric Sunspot Index is calculated. We also show that
  the use of uncalibrated sunspot areas data sets can seriously affect
  the estimate of irradiance variations. Our analysis implies that there
  is no basis for the claim that UV irradiance variations have a much
  smaller influence on climate than total solar irradiance variations.

Title: Stereoscopic Polar Plume Reconstructions from STEREO/SECCHI
    Images
Authors: Feng, L.; Inhester, B.; Solanki, S. K.; Wilhelm, K.;
   Wiegelmann, T.; Podlipnik, B.; Howard, R. A.; Plunkett, S. P.; Wuelser,
   J. P.; Gan, W. Q.
Bibcode: 2009ApJ...700..292F
Altcode: 2009arXiv0908.2365F
  We present stereoscopic reconstructions of the location and
  inclination of polar plumes of two data sets based on the two
  simultaneously recorded images taken by the EUVI telescopes in the
  SECCHI instrument package onboard the Solar TErrestrial RElations
  Observatory spacecraft. The 10 plumes investigated show a superradial
  expansion in the coronal hole in three dimensions (3D) which is
  consistent with the two-dimensional results. Their deviations from the
  local meridian planes are rather small with an average of 6fdg47. By
  comparing the reconstructed plumes with a dipole field with its axis
  along the solar rotation axis, it is found that plumes are inclined
  more horizontally than the dipole field. The lower the latitude is, the
  larger is the deviation from the dipole field. The relationship between
  plumes and bright points has been investigated and they are not always
  associated. For the first data set, based on the 3D height of plumes
  and the electron density derived from SUMER/SOHO Si VIII line pair,
  we found that electron densities along the plumes decrease with height
  above the solar surface. The temperature obtained from the density
  scale height is 1.6-1.8 times larger than the temperature obtained
  from Mg IX line ratios. We attribute this discrepancy to a deviation
  of the electron and the ion temperatures. Finally, we have found that
  the outflow speeds studied in the O VI line in the plumes corrected
  by the angle between the line of sight and the plume orientation are
  quite small with a maximum of 10 km s<SUP>-1</SUP>. It is unlikely
  that plumes are a dominant contributor to the fast solar wind.

Title: Discriminant analysis of solar bright points and
    faculae. I. Classification method and center-to-limb distribution
Authors: Kobel, P.; Hirzberger, J.; Solanki, S. K.; Gandorfer, A.;
   Zakharov, V.
Bibcode: 2009A&A...502..303K
Altcode: 2010arXiv1001.5143K
  Context: While photospheric magnetic elements appear mainly as
  Bright Points (BPs) at the disk center and as faculae near the limb,
  high-resolution images reveal the coexistence of BPs and faculae over a
  range of heliocentric angles. This is not explained by a “hot wall”
  effect through vertical flux tubes, and suggests that the transition
  from BPs to faculae needs to be quantitatively investigated. <BR />Aims:
  To achieve this, we made the first recorded attempt to discriminate
  BPs and faculae, using a statistical classification approach based
  on Linear Discriminant Analysis (LDA). This paper gives a detailed
  description of our method, and shows its application on high-resolution
  images of active regions to retrieve a center-to-limb distribution of
  BPs and faculae. <BR />Methods: Bright “magnetic” features were
  detected at various disk positions by a segmentation algorithm using
  simultaneous G-band and continuum information. By using a selected
  sample of those features to represent BPs and faculae, suitable
  photometric parameters were identified for their discrimination. We
  then carried out LDA to find a unique discriminant variable, defined
  as the linear combination of the parameters that best separates the
  BPs and faculae samples. By choosing an adequate threshold on that
  variable, the segmented features were finally classified as BPs and
  faculae at all the disk positions. <BR />Results: We thus obtained
  a Center-to-Limb Variation (CLV) of the relative number of BPs and
  faculae, revealing the predominance of faculae at all disk positions
  except close to disk center (μ ≥ 0.9). <BR />Conclusions: Although
  the present dataset suffers from limited statistics, our results are
  consistent with other observations of BPs and faculae at various disk
  positions. The retrieved CLV indicates that at high resolution, faculae
  are an essential constituent of active regions all across the solar
  disk. We speculate that the faculae near disk center as well as the BPs
  away from disk center are associated with inclined fields. <P />Figures
  11-14 are only available in electronic form at http://www.aanda.org

Title: Center to Limb Distribution of Bright Points and Faculae:
    First Results of an Automated Detection Algorithm
Authors: Kobel, P.; Hirzberger, J.; Zakharov, V.; Gandorfer, A.;
   Solanki, S. K.
Bibcode: 2009ASPC..405..211K
Altcode:
  Center to limb variations (CLV) of photospheric Bright Points (BPs)
  and faculae are important to understand the fundamental relationship
  between these magnetic features. In this context, we present a
  statistical study of the center to limb distribution of BPs and faculae
  in active regions. Magnetic brightenings were detected at various disk
  positions by an automated segmentation algorithm based on joint G-band
  and continuum information. They were then classified as BPs or faculae
  according to a linear discriminant analysis, which allowed to determine
  the relative fraction of the two classes at each disk position.

Title: Spectropolarimetric Investigations of the Deep Photospheric
    Layers of Solar Magnetic Structures
Authors: Oklay, N.; Gandorfer, A.; Solanki, S. K.; Bianda, M.;
   Ramelli, R.
Bibcode: 2009ASPC..405..233O
Altcode:
  Solar surface magnetism manifests itself in a variety of structures
  with sizes often comparable or even below our spatial resolution
  capabilities. Nevertheless, sub-resolution information about
  the intrinsic atmospheric structure can be obtained via indirect
  techniques. We use state-of-the-art spectropolarimetric observations
  in carefully selected photospheric lines which include C~I~(5380.3~Å)
  as well as strong lines of Fe~I, Ti~I covering also the deep layers of
  the photosphere and obtain ratios of their Stokes V amplitudes. From
  there we deduce that the temperature within magnetic features is higher
  at locations of smaller magnetic flux.

Title: Reconstructed and measured total solar irradiance: Is there
    a secular trend between 1978 and 2003?
Authors: Wenzler, T.; Solanki, S. K.; Krivova, N. A.
Bibcode: 2009GeoRL..3611102W
Altcode: 2009arXiv0909.2975W
  Total solar irradiance reconstructed between 1978 and 2003 using solar
  surface magnetic field distributions is compared with three composites
  of total solar irradiance measurements. A good correspondence is found
  with the total solar irradiance composite from PMOD/WRC, with no bias
  between the three cycles. The agreement with the other composites
  (the ACRIM composite, mainly based on the Active Cavity Radiometer
  Irradiance Monitors I, II, and III, and the IRMB composite from the
  Institut Royal Meteorologique Belgique) is significantly poorer. In
  particular, a secular increase in the irradiance exhibited by these
  composites is not present in the reconstructions. Hence any secular
  trend in total solar irradiance between 1978 and 2003 is not due to
  magnetic fields at the solar surface.

Title: Photospheric Magnetic Field: Quiet Sun
Authors: Solanki, S. K.
Bibcode: 2009ASPC..405..135S
Altcode:
  The solar photosphere is the layer in which the magnetic field has been
  most reliably and most often measured. Zeeman- and Hanle-effect based
  probes have revealed many details of a rich variety of structures and
  dynamic processes, but the number of open and debated questions has
  remained large. The magnetic field in the quiet Sun has maintained
  a particularly large number of secrets and has been a topic of a
  particularly lively debate as new observations and analysis techniques
  have revealed new and often unexpected aspects of its organization,
  physical structure and origin.

Title: Spectropolarimetric Diagnostics at the Solar Photosphere near
    the Limb
Authors: Yelles Chaouche, L.; Solanki, S. K.; Rouppe van der Voort,
   L.; van Noort, M.
Bibcode: 2009ASPC..405..189Y
Altcode: 2009arXiv0910.2885Y
  In the present work, we investigate the formation of Stokes profiles
  and spectro-polarimetric diagnostics in an active region plage near
  the limb. We use 3-D radiation-MHD simulations with unipolar fields
  of an average strength of 400 G, which is largely concentrated in
  flux tubes in which the field reaches typical kilo-Gauss values. We
  generate synthetic Stokes spectra by radiative transfer calculations,
  then we degrade the simulated Stokes signal to account for observational
  conditions. The synthetic data treated in this manner are compared with
  and found to roughly reproduce spectro-polarimetric high-resolution
  observations at μ=0.39 obtained by the SOUP instrument with the
  Swedish 1-m Solar Telescope at the beginning of 2006.

Title: Full Magnetic Field Vector of an Emerging Flux Region
Authors: Xu, Z.; Lagg, A.; Solanki, S. K.
Bibcode: 2009ASPC..405..223X
Altcode:
  We present maps of the full magnetic field vector of an emerging flux
  region in both the photosphere and chromosphere. The magnetic and
  velocity structure of freshly emerged loops is determined.

Title: Comparison Among Ca II K Spectroheliogram Time Series with
    an Application to Solar Activity Studies
Authors: Ermolli, I.; Solanki, S. K.; Tlatov, A. G.; Krivova, N. A.;
   Ulrich, R. K.; Singh, J.
Bibcode: 2009ApJ...698.1000E
Altcode:
  Various observatories around the globe started regular full-disk imaging
  of the solar atmosphere in the Ca II K line in the early decades of
  the 20th century. The archives made by these observations have the
  potential of providing far more detailed information on solar magnetism
  than just the sunspot number and area records to which most studies
  of solar activity and irradiance changes are restricted. We evaluate
  the image quality and contents of three Ca II K spectroheliogram time
  series, specifically those obtained by the digitization of the Arcetri,
  Kodaikanal, and Mt Wilson photographic archives, in order to estimate
  their value for studies focusing on timescales longer than the solar
  cycle. We analyze the quality of these data and compare the results
  obtained with those achieved for similar present-day observations
  taken with the Meudon spectroheliograph and with the Rome-PSPT. We
  also investigate whether image-segmentation techniques, such as
  those developed for identification of plage regions on present-day Ca
  II K observations, can be used to process historic series. We show
  that historic data suffer from stronger geometrical distortions and
  photometric uncertainties than similar present-day observations. The
  latter uncertainties mostly originate from the photographic calibration
  of the original data and from stray-light effects. We also show that
  the image contents of the three analyzed series vary in time. These
  variations are probably due to instrument changes and aging of the
  spectrographs used, as well as changes of the observing programs. The
  segmentation technique tested in this study gives reasonably consistent
  results for the three analyzed series after application of a simple
  photographic calibration. Although the plage areas measured from the
  three analyzed series differ somewhat, the difference to previously
  published results is larger.

Title: Multi-Channel Observations of a Solar Flare
Authors: Hirzberger, J.; Riethmüller, T.; Solanki, S. K.; Kobel, P.
Bibcode: 2009ASPC..405..125H
Altcode:
  On August 13, 2006 we performed simultaneous observations in Ca IIH,
  G-band and Fe I 6303 Å of a complex sunspot in NOAA~10904 with
  the Swedish Solar Telescope (SST) on La Palma, Canary Islands. From
  spectro-polarimetric scans through the Fe I line with the tunable
  SOUP filter we computed the full Stokes vectors at each pixel of the
  field of view. At 8:47 UT a weak flare eruption (GOES class B7.8) was
  registered in the line core of Ca IIH. We present the changing magnetic
  field and flow topologies in the underneath penumbral photosphere
  during the flaring phase. The unmatched spatial resolution of SST
  observations allows detailed simultaneous mapping of chromospheric
  and photospheric events.

Title: Hanle Effect Diagnostics of the Coronal Magnetic Field:
    A Test Using Realistic Magnetic Field Configurations
Authors: Raouafi, N. -E.; Solanki, S. K.; Wiegelmann, T.
Bibcode: 2009ASPC..405..429R
Altcode: 2008arXiv0801.2202R
  Our understanding of coronal phenomena, such as coronal plasma
  thermodynamics, faces a major handicap caused by missing coronal
  magnetic field measurements. Several lines in the UV wavelength range
  present suitable sensitivity to determine the coronal magnetic field
  via the Hanle effect. The latter is a largely unexplored diagnostic
  of coronal magnetic fields with a very high potential. Here we study
  the magnitude of the Hanle-effect signal to be expected outside the
  solar limb due to the Hanle effect in polarized radiation from the
  H I Lyα and β lines, which are among the brightest lines in the
  off-limb coronal FUV spectrum. For this purpose we use a magnetic field
  structure obtained by extrapolating the magnetic field starting from
  photospheric magnetograms. The diagnostic potential of these lines for
  determining the coronal magnetic field, as well as their limitations
  are studied. We show that these lines, in particular H I Lyβ, are
  useful for such measurements.

Title: Propagating waves in polar coronal holes as seen by SUMER
    &amp; EIS
Authors: Banerjee, D.; Teriaca, L.; Gupta, G. R.; Imada, S.; Stenborg,
   G.; Solanki, S. K.
Bibcode: 2009A&A...499L..29B
Altcode: 2009arXiv0905.1013B
  Context: To study the dynamics of coronal holes and the role of waves in
  the acceleration of the solar wind, spectral observations were performed
  over polar coronal hole regions with the SUMER spectrometer on SoHO and
  the EIS spectrometer on Hinode. <BR />Aims: Using these observations,
  we aim to detect the presence of propagating waves in the corona and
  to study their properties. <BR />Methods: The observations analysed
  here consist of SUMER spectra of the Ne viii 770 Å line (T = 0.6 MK)
  and EIS slot images in the Fe xii 195 Å line (T = 1.3 MK). Using the
  wavelet technique, we study line radiance oscillations at different
  heights from the limb in the polar coronal hole regions. <BR />Results:
  We detect the presence of long period oscillations with periods of 10
  to 30 min in polar coronal holes. The oscillations have an amplitude
  of a few percent in radiance and are not detectable in line-of-sight
  velocity. From the time distance maps we find evidence for propagating
  velocities from 75 km s<SUP>-1</SUP> (Ne viii) to 125 km s<SUP>-1</SUP>
  (Fe xii). These velocities are subsonic and roughly in the same ratio
  as the respective sound speeds. <BR />Conclusions: We interpret the
  observed propagating oscillations in terms of slow magneto-acoustic
  waves. These waves can be important for the acceleration of the fast
  solar wind.

Title: Constraints on O5+ Ions Kinetic Temperature Anisotropies in
    the Polar Coronal Holes
Authors: Raouafi, Noureddine; Solanki, S.
Bibcode: 2009SPD....40.1404R
Altcode:
  We present new constraints on the kinetic temperature anisotropies of
  the O5+ ions in the polar coronal holes. Our analysis is based on the
  observations of the Ultraviolet Coronagraph Spectrometer (UVCS) on the
  Solar and Heliospheric Observatory (SOHO) spacecraft. We find that the
  observations are consistently reproduced when considering anisotropies
  less than 5 between heliocentric distances 2.0 R<SUB>sun</SUB> and 2.7
  R<SUB>sun</SUB>. Below 2.0 R<SUB>sun</SUB> and above 2.7 R<SUB>sun</SUB>
  no anisotropies or T<SUB>perpendicular</SUB>/T<SUB>parallel</SUB>
  significantly smaller than 5 are sufficient to obtain the observed
  spectral line profiles. Our analysis provides also height dependencies
  of T<SUB>perpendicular</SUB> and T<SUB>parallel</SUB>. We also discuss
  the possible existence of other mechanisms that may reduce kinetic
  temperature anisotropies in the polar coronal holes.

Title: On the relation between photospheric magnetic field and
    chromospheric emission in the quiet Sun
Authors: Loukitcheva, Maria A.; Solanki, Sami K.; White, Stephen M.
Bibcode: 2009IAUS..259..185L
Altcode:
  In this contribution we present an observational study of the
  interaction of the photosphere with different chromospheric layers. We
  study the correlations between emissions at varying temperature from the
  temperature minimum region (UV continuum at 1600 Å from TRACE) through
  the low chromosphere (CaII K-line from BBSO) to the middle chromosphere
  (continuum at 3.5 mm from BIMA) and photospheric magnetic field from
  MDI/SOHO. For the first time millimeter observational data are included
  in such analysis. <P />We report a high degree of correlation between
  considered emissions formed at different heights in the chromosphere. A
  power law is found to be a good representation for the relationship
  between photospheric magnetic field and chromospheric emissions at
  all considered wavelengths. Our analysis shows that the dependence
  of chromospheric intensities on magnetic field is different for the
  network and internetwork regions. In the network a power law provides
  the best fit with the exponent being close to 0.5-0.6, while almost
  no dependence of chromospheric intensity on magnetic flux is found for
  the cell interiors. The obtained results support the idea of different
  heating mechanisms acting in the network (magnetic) and cell interiors
  (acoustic).

Title: The relationship between chromospheric emissions and magnetic
    field strength
Authors: Loukitcheva, M.; Solanki, S. K.; White, S. M.
Bibcode: 2009A&A...497..273L
Altcode: 2009arXiv0910.1985L
  Aims: We analyze observational data from 4 instruments to study the
  correlations between chromospheric emission, spanning the heights
  from the temperature minimum region to the middle chromosphere,
  and photospheric magnetic field. <BR />Methods: The data consist of
  radio images at 3.5 mm from the Berkeley-Illinois-Maryland Array
  (BIMA), UV images at 1600 Å from TRACE, Ca II K-line filtergrams
  from BBSO, and MDI/SOHO longitudinal photospheric magnetograms. For
  the first time interferometric millimeter data with the highest
  currently available resolution are included in such an analysis. We
  determine various parameters of the intensity maps and correlate the
  intensities with each other and with the magnetic field. <BR />Results:
  The chromospheric diagnostics studied here show a pronounced similarity
  in their brightness structures and map out the underlying photospheric
  magnetic field relatively well. We find a power law to be a good
  representation of the relationship between photospheric magnetic field
  and emission from chromospheric diagnostics at all wavelengths. The
  dependence of chromospheric brightness on magnetic field is found to
  be different for network and internetwork regions.

Title: Small-Scale Solar Magnetic Fields
Authors: de Wijn, A. G.; Stenflo, J. O.; Solanki, S. K.; Tsuneta, S.
Bibcode: 2009SSRv..144..275D
Altcode: 2008SSRv..tmp..190D; 2008SSRv..tmp..191D; 2008arXiv0812.4465D
  As we resolve ever smaller structures in the solar atmosphere,
  it has become clear that magnetism is an important component of
  those small structures. Small-scale magnetism holds the key to many
  poorly understood facets of solar magnetism on all scales, such as the
  existence of a local dynamo, chromospheric heating, and flux emergence,
  to name a few. Here, we review our knowledge of small-scale photospheric
  fields, with particular emphasis on quiet-sun field, and discuss the
  implications of several results obtained recently using new instruments,
  as well as future prospects in this field of research.

Title: Magnetic geometries of Sun-like stars: exploring the
    mass-rotation plane
Authors: Petit, Pascal; Dintrans, B.; Aurière, M.; Catala, C.; Donati,
   J. -F.; Fares, R.; Gastine, T.; Lignières, F.; Morgenthaler, A.;
   Morin, J.; Paletou, F.; Ramirez Velez, J.; Solanki, S. K.; Théado, S.
Bibcode: 2009IAUS..259..441P
Altcode:
  Sun-like stars are able to continuously generate a large-scale
  magnetic field through the action of a dynamo. Various physical
  parameters of the star are able to affect the dynamo output, in
  particular the rotation and mass. Using the NARVAL spectropolarimeter
  (Observatoire du Pic du Midi, France), it is now possible to measure
  the large-scale magnetic field of solar analogues (i.e. stars very
  close to the Sun in the mass-rotation plane, including strict solar
  twins). From spectropolarimetric time-series, tomographic inversion
  enables one to reconstruct the field geometry and its progressive
  distortion under the effect of surface differential rotation. We
  show the first results obtained on a sample of main-sequence dwarfs,
  probing masses between 0.7 and 1.4 solar mass and rotation rates
  between 1 and 3 solar rotation rate.

Title: On the common solar signal in different cosmogenic isotope
    data sets
Authors: Usoskin, Ilya G.; Horiuchi, Kazuho; Solanki, Sami; Kovaltsov,
   Gennady A.; Bard, Edouard
Bibcode: 2009JGRA..114.3112U
Altcode: 2009JGRA..11403112U
  In this article, we aim to determine frequency ranges and intervals
  of time in which the solar signal dominates in different cosmogenic
  isotope data. From a <SUP>14</SUP>C-based reconstruction of cosmic ray
  intensity over the last millennia, we computed expected <SUP>10</SUP>Be
  variations in two Antarctic sites (Dom Fuji and South Pole) and two
  Greenland sites (Dye-3 and GISP-2) and compared them with the actually
  measured <SUP>10</SUP>Be abundance at the sites. By applying different
  methods of analysis, such as bivariate correlation, conventional
  FFT coherence, and wavelet coherence, we found the following: (1)
  The modeled series, on the basis of <SUP>14</SUP>C data, are in good
  agreement with the measured <SUP>10</SUP>Be data sets, on different
  timescales and at different locations, confirming the existence of a
  common solar signal in both isotope data. (2) The <SUP>10</SUP>Be data
  are driven by the solar signal on timescales from about 100 years up
  to 1000 years or even to multimillennial scales (at the longer scales,
  paleomagnetism plays an increasingly important role). (3) The local
  climate dominates the <SUP>10</SUP>Be data mostly on short (&lt;100
  years) timescales, but the solar signal becomes important even at short
  scales during periods of Grand minima of solar activity. (4) There is an
  indication of a possible systematic uncertainty in the early Holocene,
  likely due to a not-perfectly-stable thermohaline circulation, which
  requires additional studies. We have shown that both <SUP>14</SUP>C- and
  <SUP>10</SUP>Be-based records are consistent with each other over a wide
  range of timescales and time intervals. They form a robust basis for
  quantitative reconstructions of solar activity variations in the past.

Title: Multiple-spacecraft study of an extended magnetic structure
    in the solar wind
Authors: Ruan, P.; Korth, A.; Marsch, E.; Inhester, B.; Solanki, S.;
   Wiegelmann, T.; Zong, Q. -G.; Bucik, R.; Fornacon, K. -H.
Bibcode: 2009JGRA..114.2108R
Altcode: 2009JGRA..11402108R
  An extended magnetic structure was observed consecutively by five
  spacecraft (ACE, WIND, STEREO A and B, and CLUSTER) in the solar wind on
  15 January 2007. The similar bipolar magnetic field variations from five
  spacecraft suggest that the magnetic structure is two-dimensional. The
  abrupt disappearance of the beam electrons in the core of the structure
  suggests that the core of the structure is magnetically isolated from
  the surrounding environment. Our analysis shows that this magnetic
  structure is a magnetic flux rope, which extends over at least 180 R
  <SUB>E</SUB> in space. The length and orientation of the flux rope were
  determined by a local minimum variance analysis (MVA) from individual
  spacecraft observations of the magnetic field and a timing analysis
  based on the joint observations by all five spacecraft. The results
  show that the orientation of the flux rope stays constant in space
  and time. The flux rope is embedded in a corotating interaction region
  (CIR), which followed a magnetic cloud.

Title: Zeeman Broadening in Cool Stars
Authors: Anderson, Richard I.; Reiners, Ansgar; Solanki, Sami K.;
   Lagg, Andreas
Bibcode: 2009AIPC.1094..708A
Altcode: 2009csss...15..708A
  We investigate detectability of magnetic fields by Zeeman broadening
  of well-isolated spectral lines in F, G and K type stars. Data of
  unprecedented quality were taken with CES<SUP>1</SUP> mounted on the 3.6
  m ESO telescope at La Silla, Chile, in three campaigns in the optical
  range between 5770 Å and 6280 Å, each with a wavelength coverage
  of roughly 40 Å. We use the SPINOR/STOPRO (cf. Frutiger et al. [1])
  package developed by ETH<SUP>2</SUP> and MPS<SUP>3</SUP> to perform
  spectral line inversion via χ<SUP>2</SUP> minimization. Starting from
  constraints given by previous measurements of stellar parameters,
  we fit a number of extracted spectral lines. Eventually, our goal
  is to determine the product of the magnetic field strength B and the
  surface filling factor, B×f. <P />Our work is in progress and thus
  no final measurements can be presented at this stage.

Title: Slow magnetoacoustic standing waves in a curved solar
    coronal slab
Authors: Ogrodowczyk, R.; Murawski, K.; Solanki, S. K.
Bibcode: 2009A&A...495..313O
Altcode:
  Aims: We consider a model of a two-dimensional solar coronal arcade to
  explore the effects of a curved magnetic field topology on excitation
  and attenuation of slow magnetoacoustic standing waves. <BR />Methods:
  The time-dependent ideal magnetohydrodynamic equations are solved
  numerically to find the spatial and temporal signatures of these
  waves. <BR />Results: A pulse in gas pressure initially launched at
  a loop footpoint excites the fundamental mode of slow magnetoacoustic
  standing waves. The typical excitation time of such a wave mode is 2.5
  wave periods, with a similar attenuation timescale. These values are
  remarkably similar to those recovered from observations by SOHO/SUMER in
  an Fe XIX line. <BR />Conclusions: Slow magnetoacoustic standing waves
  are excited and attenuated more efficiently in curved magnetic field
  lines than in a straight magnetic slab topology. The waves supported
  by the magnetic arcade are in far closer agreement with observations.

Title: Towards Long-Term Solar Irradiance Modelling: Network Contrasts
    from Magneto-Convection Simulations
Authors: Unruh, Y. C.; Solanki, S. K.; Schüssler, M.; Vögler, A.;
   Garcia-Alvarez, D.
Bibcode: 2009AIPC.1094..768U
Altcode: 2009csss...15..768U
  Solar irradiance changes on a wide range of time scales and is a key
  driver of the Earth's climate where secular variability in particular is
  relevant. This is, however, not well understood and our knowledge relies
  on reconstructions based on sunspot numbers and similar proxies. <P
  />The prime candidate to produce secular variability is a change
  in the surface coverage of small-scale magnetic elements. Direct
  observational determination of the flux emitted by these magnetic
  elements is difficult, especially as information covering a large
  spectral range is needed. Here we present a theoretical approach
  to this problem using intensity calculations from 3-D simulations
  of solar magneto-convection and compare these with the intensity
  calculations used in the successful semi-empirical S ATIRE models at
  disk centre. Eventually, such a comparison should lead to the removal
  of the last free parameter from S ATIRE-based irradiance reconstruction.

Title: Faculae and Plague
Authors: Solanki, Sami; Krivova, Natalie
Bibcode: 2009LanB...4B..153S
Altcode: 2009LanB...4B.4124S
  No abstract at ADS

Title: Sunspots
Authors: Solanki, Sami; Krivova, Natalie
Bibcode: 2009LanB...4B..141S
Altcode: 2009LanB...4B.4123S
  No abstract at ADS

Title: The Origin and Dynamics of Solar Magnetism
Authors: Thompson, M. J.; Balogh, A.; Culhane, J. L.; Nordlund, Å.;
   Solanki, S. K.; Zahn, J. -P.
Bibcode: 2009odsm.book.....T
Altcode:
  No abstract at ADS

Title: Solar Space Missions: present and future
Authors: Solanki, Sami K.; Marsch, Eckart
Bibcode: 2009RvMA...21..229S
Altcode:
  No abstract at ADS

Title: The Solar Chromosphere: Old Challenges, New Frontiers
Authors: Ayres, T.; Uitenbroek, H.; Cauzzi, G.; Reardon, K.; Berger,
   T.; Schrijver, C.; de Pontieu, B.; Judge, P.; McIntosh, S.; White,
   S.; Solanki, S.
Bibcode: 2009astro2010S...9A
Altcode:
  No abstract at ADS

Title: Solar Activity Cycle
Authors: Solanki, Sami; Krivova, Natalie
Bibcode: 2009LanB...4B..124S
Altcode: 2009LanB...4B.4122S
  No abstract at ADS

Title: Dynamos and magnetic fields of the Sun and other cool stars,
    and their role in the formation and evolution of stars and in the
    habitability of planets
Authors: Schrijver, Karel; Carpenter, Ken; Karovska, Margarita; Ayres,
   Tom; Basri, Gibor; Brown, Benjamin; Christensen-Dalsgaard, Joergen;
   Dupree, Andrea; Guinan, Ed; Jardine, Moira; Miesch, Mark; Pevtsov,
   Alexei; Rempel, Matthias; Scherrer, Phil; Solanki, Sami; Strassmeier,
   Klaus; Walter, Fred
Bibcode: 2009astro2010S.262S
Altcode:
  No abstract at ADS

Title: Small-Scale Solar Magnetic Fields
Authors: de Wijn, A. G.; Stenflo, J. O.; Solanki, S. K.; Tsuneta, S.
Bibcode: 2009odsm.book..275D
Altcode:
  As we resolve ever smaller structures in the solar atmosphere,
  it has become clear that magnetism is an important component of
  those small structures. Small-scale magnetism holds the key to many
  poorly understood facets of solar magnetism on all scales, such as the
  existence of a local dynamo, chromospheric heating, and flux emergence,
  to name a few. Here, we review our knowledge of small-scale photospheric
  fields, with particular emphasis on quiet-sun field, and discuss the
  implications of several results obtained recently using new instruments,
  as well as future prospects in this field of research.

Title: German Data Center for the Solar Dynamics Observatory:
    A model for the PLATO mission?
Authors: Burston, R.; Gizon, L.; Saidi, Y.; Solanki, S. K.
Bibcode: 2008CoAst.157..293B
Altcode:
  The German Data Center for the Solar Dynamics Observatory
  (GDC-SDO), hosted by the Max Planck Institute for Solar System
  Research in Germany, will provide access to SDO data for the
  German solar physics community. The GDC-SDO will make available
  all the relevant Helioseismic and Magnetic Imager (HMI) data
  for helioseismology and smaller se- lected Atmospheric Imaging
  Assembly (AIA) data sets. This project commenced in August 2007
  and is funded by the German Aerospace Center (Deutsches zentrum
  fuer Luft- und Raumfahrt or DLR) until December 2012. An important
  component of the GDC-SDO is the Data Record Management System (DRMS),
  developed in collaboration with the Stan- ford/Lockheed Joint Science
  Operations Center (JSOC). The PEGASUS workflow manage- ment system
  will be used to implement GDC-SDO data analysis pipelines. This
  makes use of the CONDOR High Throughput Computing Project for
  optimal job scheduling and also the GLOBUS Toolkit to enable grid
  technologies. Additional information about the GDC-SDO can be found at
  http://www.mps.mpg.de/projects/seismo/GDC1/index.html. Here, we sug-
  gest a similar structure and philosophy should be ideal for the PLATO
  mission, which looks for planetary transits and stellar oscillations
  and is being studied by ESA for an M-Mission slot in Cosmic Vision.

Title: A nanoflare model for active region radiance: application of
    artificial neural networks
Authors: Bazarghan, M.; Safari, H.; Innes, D. E.; Karami, E.; Solanki,
   S. K.
Bibcode: 2008A&A...492L..13B
Altcode: 2008arXiv0808.3925B
  Context: Nanoflares are small impulsive bursts of energy that blend with
  and possibly make up much of the solar background emission. Determining
  their frequency and energy input is central to understanding the
  heating of the solar corona. One method is to extrapolate the energy
  frequency distribution of larger individually observed flares to
  lower energies. Only if the power law exponent is greater than 2 is
  it considered possible that nanoflares contribute significantly to
  the energy input. <BR />Aims: Time sequences of ultraviolet line
  radiances observed in the corona of an active region are modelled
  with the aim of determining the power law exponent of the nanoflare
  energy distribution. <BR />Methods: A simple nanoflare model based
  on three key parameters (the flare rate, the flare duration, and
  the power law exponent of the flare energy frequency distribution)
  is used to simulate emission line radiances from the ions Fe XIX,
  Ca XIII, and Si III, observed by SUMER in the corona of an active
  region as it rotates around the east limb of the Sun. Light curve
  pattern recognition by an Artificial Neural Network (ANN) scheme is
  used to determine the values. <BR />Results: The power law exponents,
  α≈2.8, 2.8, and 2.6 are obtained for Fe XIX, Ca XIII, and Si III
  respectively. <BR />Conclusions: The light curve simulations imply
  a power law exponent greater than the critical value of 2 for all
  ion species. This implies that if the energy of flare-like events is
  extrapolated to low energies, nanoflares could provide a significant
  contribution to the heating of active region coronae.

Title: Brightness, distribution, and evolution of sunspot umbral dots
Authors: Riethmüller, T. L.; Solanki, S. K.; Zakharov, V.;
   Gandorfer, A.
Bibcode: 2008A&A...492..233R
Altcode: 2008arXiv0812.0477R
  Context: Umbral Dots (UDs) are thought to be manifestations
  of magnetoconvection in sunspot umbrae. Recent advances in their
  theoretical description point to the need for a thorough study of their
  properties and evolution based on data with the highest currently
  achievable resolution. <BR />Aims: Our UD analysis aims to provide
  parameters such as lifetimes, diameters, horizontal velocities, and
  peak intensities, as well as the evolution of selected parameters. <BR
  />Methods: We present a 106-min TiO (705.7 nm) time series of high
  spatial and temporal resolution that contains thousands of UDs in
  the umbra of a mature sunspot in the active region NOAA 10667 at μ =
  0.95. The data were acquired with the 1-m Swedish Solar Telescope (SST)
  on La Palma. With the help of a multilevel tracking (MLT) algorithm the
  sizes, brightnesses, and trajectories of 12 836 umbral dots were found
  and extensively analyzed. The MLT allows UDs with very low contrast to
  be reliably identified. <BR />Results: Inside the umbra we determine a
  UD filling factor of 11%. The histogram of UD lifetimes is monotonic,
  i.e. a UD does not have a typical lifetime. Three quarters of the UDs
  lived for less than 150 s and showed no or little motion. The histogram
  of the UD diameters exhibits a maximum at 225 km, i.e. most of the
  UDs are spatially resolved. UDs display a typical horizontal velocity
  of 420 m s<SUP>-1</SUP> and a typical peak intensity of 51% of the
  mean intensity of the quiet photosphere, making them on average 20%
  brighter than the local umbral background. Almost all mobile UDs (large
  birth-death distance) were born close to the umbra-penumbra boundary,
  move towards the umbral center, and are brighter than average. Notably
  bright and mobile UDs were also observed along a prominent UD chain,
  both ends of which are located at the umbra-penumbra boundary. Their
  motion started primarily at either of the ends of the chain, continued
  along the chain, and ended near the chain's center. We observed the
  splitting and merging of UDs and the temporal succession of both. For
  the first time the evolution of brightness, size, and horizontal speed
  of a typical UD could be determined in a statistically significant
  way. Considerable differences between the evolution of central and
  peripheral UDs are found, which point to a difference in origin.

Title: Future high-latitude observations anticipated from the Solar
    Orbiter mission
Authors: Woch, J.; Solanki, S. K.; Marsch, E.
Bibcode: 2008AGUFMSH44A..08W
Altcode:
  As one of the cornerstones of the HELEX programme, the Solar Orbiter
  mission is currently scheduled for launch in 2015. After an initial
  cruise phase, Solar Orbiter will reach its science orbit in 2018. This
  orbit comprises initially a nearly Sun-synchronous phase at a distance
  of only 0.22 AU from Sun center. In a later stage, the orbital
  inclination will be raised, thus allowing Solar Orbiter to reach
  solar latitudes of about 35 degrees, and making it the first mission
  after Ulysses to study the Sun from a high-latitude vantage point. In
  contrast to Ulysses, however, Solar Orbiter will carry a complementary
  suite of both, in-situ and remote- sensing instruments, which will
  allow the study of the solar atmosphere to be extended to the largely
  unexplored polar regions of the Sun. The polar magnetic fields are
  responsible for the polar coronal holes driving the fast solar wind,
  but are poorly known. From its vantage point outside the ecliptic,
  Solar Orbiter will uncover the surface and sub-surface flows at the
  poles, the polar magnetic field structure and its evolution. It will
  provide new insights into the formation of the polar coronal holes,
  the nature of their boundaries and the acceleration of the fast
  solar wind emanating from the holes. The potential of Solar Orbiter
  for investigating the acceleration mechanism of the fast wind, the
  plumes and X-ray jets at the poles, and the high-latitude meridional
  circulation will be discussed.

Title: Magnetic geometries of Sun-like stars : impact of rotation
Authors: Petit, P.; Dintrans, B.; Aurière, M.; Catala, C.; Donati,
   J. -F.; Fares, R.; Gastine, T.; Lignières, F.; Morin, J.; Paletou,
   F.; Ramirez, J.; Solanki, S. K.; Théado, S.
Bibcode: 2008sf2a.conf..523P
Altcode:
  Sun-like stars are able to continuously generate a large-scale magnetic
  field through the action of a dynamo. Various physical parameters
  of the star are able to affect the dynamo output, in particular the
  rotation and mass. Using new generation stellar spectropolarimeters
  (ESPaDOnS@CFHT, NARVAL@TBL), it is now possible to measure the
  large-scale magnetic field of solar analogues (i.e. stars very close
  to the Sun in the stellar-parameter plane, including strict solar
  twins). From spectropolarimetric time-series, tomographic inversion
  of polarized Zeeman signatures allows us to reconstruct the field
  geometry and its progressive distortion under the effect of surface
  differential rotation. We detail the first results obtained on a sample
  of four main-sequence dwarfs, with masses close to 1 solar mass and
  rotation rates between 1 and 3 solar rotation rate.

Title: Are There Field-Free Gaps near τ = 1 in Sunspot Penumbrae?
Authors: Borrero, J. M.; Solanki, S. K.
Bibcode: 2008ApJ...687..668B
Altcode: 2008arXiv0806.4454B
  The vertical stratification of the magnetic field strength in sunspot
  penumbrae is investigated by means of spectropolarimetric observations
  at high spatial resolution from the Hinode spacecraft. Assuming that
  the magnetic field changes linearly with optical depth we find that, in
  those regions where the magnetic field is more inclined and the Evershed
  flow is strongest (penumbral intraspines), the magnetic field can either
  increase or decrease with depth. Allowing more degrees of freedom to the
  magnetic field stratification reveals that the magnetic field initially
  decreases from log τ<SUB>5</SUB> = - 3 until log τ<SUB>5</SUB>simeq -
  1.0, but increases again below that. The presence of strong magnetic
  fields near the continuum is at odds with the existence of regions
  void of magnetic fields at, or right below, the τ<SUB>5</SUB> = 1
  level in the penumbra. However, they are compatible with the presence
  of a horizontal flux-tube-like field embedded in a magnetic atmosphere.

Title: SUMER observations of the inverse Evershed effect in the
    transition region above a sunspot
Authors: Teriaca, L.; Curdt, W.; Solanki, S. K.
Bibcode: 2008A&A...491L...5T
Altcode: 2009arXiv0901.3317T
  Aims: We analyse SUMER spectral scans of a large sunspot within active
  region NOAA 10923, obtained on 14-15 November 2006, to determine
  the morphology and dynamics of the sunspot atmosphere at different
  heights/temperatures. <BR />Methods: The data analysed here consist
  of spectroheliograms in the continuum around 142.0 nm and in the Si
  iv 140.2 nm, O iii 70.3 nm, N iv 76.5 nm, and O iv 79.0 nm spectral
  lines. Gaussian-fitting of the observed profiles provides line-of-sight
  velocity and Doppler-width maps. <BR />Results: The data show an
  asymmetric downflow pattern compatible with the presence of the inverse
  Evershed flow in a region within roughly twice the penumbral radius
  at transition-region temperatures up to 0.18 MK. The motions, highly
  inhomogeneous on small scales, seem to occur in a collar of radially
  directed filamentary structures, with an average width less than the 1
  Mm spatial resolution of SUMER and characterised by different plasma
  speeds. Assuming that the flows are directed along the field lines,
  we deduce that such field lines are inclined by 10° to 25° with
  respect to the solar surface.

Title: Identification of different types of kink modes in coronal
loops: principles and application to TRACE results
Authors: Wang, T. J.; Solanki, S. K.; Selwa, M.
Bibcode: 2008A&A...489.1307W
Altcode: 2008arXiv0808.0685W
  We explore the possible observational signatures of different types of
  kink modes (horizontal and vertical oscillations in their fundamental
  mode and second harmonic) that may arise in coronal loops, with the
  aim of determining how well the individual modes can be uniquely
  identified from time series of images. A simple, purely geometrical
  model is constructed to describe the different types of kink-mode
  oscillations. These are then “observed” from a given direction. In
  particular, we employ the 3D geometrical parameters of 14 TRACE loops
  of transverse oscillations to try to identify the correct observed wave
  mode. We find that for many combinations of viewing and loop geometry
  it is not straightforward to distinguish between at least two types of
  kink modes just using time series of images. We also considered Doppler
  signatures and find that these can help obtain unique identifications of
  the oscillation modes when employed in combination with imaging. We then
  compare the modeled spatial signatures with the observations of 14 TRACE
  loops. We find that out of three oscillations previously identified
  as fundamental horizontal mode oscillations, two cases appear to be
  fundamental vertical mode oscillations (but possibly combined with the
  fundamental horizontal mode), and one case appears to be a combination
  of the fundamental vertical and horizontal modes, while in three cases
  it is not possible to clearly distinguish between the fundamental mode
  and the second-harmonic of the horizontal oscillation. In five other
  cases it is not possible to clearly distinguish between a fundamental
  horizontal mode and the second-harmonic of a vertical mode.

Title: Loop Morphology and Flows and their Relation to the Magnetic
    Field
Authors: Teriaca, L.; Wiegelmann, T.; Lagg, A.; Solanki, S. K.; Curdt,
   W.; Sekii, T.
Bibcode: 2008ASPC..397..196T
Altcode:
  In November 2006 we obtained several rasters of a large sunspot
  and its trailing region using the SUMER spectrometer on SOHO. The
  observations consist of spectroheliograms in the continuum around
  142 nm and in several spectral lines formed between 80000 K and
  0.6 MK, covering the temperature range from the chromosphere to
  the lower corona. The observed profiles provide LOS velocity and
  Doppler width maps. TRACE images in the EUV passbands and in the 160
  nm continuum provide a clear picture of the coronal loops and the
  chromosphere near their footpoints. The same target was also observed
  by all the instruments aboard Hinode and, in particular, by the SOT
  spectro-polarimeter measuring the photospheric magnetic vector. We
  combined SOT and MDI data (covering a larger FOV) to infer the coronal
  magnetic field of the active region by a nonlinear force-free field
  extrapolation. The observed radiance and velocity patterns at the
  various heights/temperatures throughout the solar atmosphere are
  compared with the field topology.

Title: Fibrils in Ca II K
Authors: Pietarila, A.; Solanki, S.; Hirzberger, J.; Zakharov, V.
Bibcode: 2008ESPM...12.2.51P
Altcode:
  High spatial resolution observations have revealed that fibril-like
  structures are a ubiquitous feature of the solar chromosphere. They are
  observed in most chromospheric lines, e.g., H-? and Ca II IRT. Until
  recently, there have been no reports of these structures in the Ca
  II H and K lines. Instead, these lines have revealed a hazy, uniform
  chromosphere and only in the highest resolution images have there been
  any indications of fibril structures. <P />We present high spatial
  resolution Ca II K observations from the Swedish Solar Telescope
  which show that fibrils are a prevailing feature in regions where
  the bulk of the signal is chromospheric. Based on the cotemporal
  continuum and nearly cotemporal magnetic field observations it is
  clear that the fibril foot points originate from photospheric magnetic
  concentrations. The fibrils share many characteristics, e.g. lifetime
  and dynamics, with fibrils observed in other spectral lines. They are
  also found to play an important role in the dynamics: in the plage
  they channel low frequency waves into the chromosphere while in the
  more quiet regions the highly inclined fibrils form a multi-layer
  canopy that suppresses oscillations from below.

Title: The Magnetic Vector Structure of an Active Region Plage Field
Authors: Meling, M. H. M.; Lagg, A.; Solanki, S. K.
Bibcode: 2008ESPM...12.2.58M
Altcode:
  We present scans of the active region plage associated with NOAA 10953,
  recorded with the Tenerife Infrared Polarimeter 2 (TIP-2) mounted
  behind the German Vacuum Tower Telescope (VTT) on Tenerife and the
  SOT-SP instrument on-board the HINODE spacecraft. TIP-2 recorded the
  full Stokes vector close to the diffraction limit of the telescope over
  a 20 angstroem wavelength range containing six magnetically sensitive
  FeI lines in the infrared including the g=3 line FeI 15648.5. With
  these lines we use the advantage that the Zeeman splitting dominates
  over the Doppler broadening for kG fields. The iron lines used by
  HINODE are FeI 6301.501and FeI 6302.494. <P />We analyzed the data by
  applying a Milne-Eddington type inversion to it. In the context of a
  two-component model we found a bimodal distribution of field strengths,
  strong fields whose field strength distribution peaks at 1400 [G]
  and a weak field distribution, which may be associated with quiet sun
  regions bordering on the plage.

Title: Spectropolarimetric Investigations of the Deep Photospheric
    Layers of Magnetic Elements
Authors: Oklay, N.; Gandorfer, A.; Solanki, S. K.
Bibcode: 2008ESPM...12.2.49O
Altcode:
  We observed simultaneously Stokes I and Stokes V/I profiles of Fe I
  (5379.574Å), C I(5380.332Å), Ti II(5381.021Å) and Fe I(5383.369Å)
  using the ZIMPOL II spectropolarimeter at the IRSOL (Istituto Ricerche
  Solari Locarno) facility. This set of spectral lines covers not only
  the mid-photosphere but also the deep photospheric layers, where
  the temperature sensitive C I line is formed. We analyzed ratios
  and asymmetries of their Stokes V amplitudes and areas. Further,
  the spectral profiles were analyzed using the SPINOR inversion code
  (Frutiger et al. 2000) to constrain the temperature structure of
  the magnetic elements down to deep photospheric layers. In this way,
  our understanding of the lowest photospheric layers of solar magnetic
  elements can be tested.

Title: Structure and Evolution of Supergranulation from Local
    Helioseismology
Authors: Hirzberger, Johann; Gizon, Laurent; Solanki, Sami K.; Duvall,
   Thomas L.
Bibcode: 2008SoPh..251..417H
Altcode: 2008SoPh..tmp..106H
  Supergranulation is visible at the solar surface as a cellular
  pattern of horizontal outflows. Although it does not show a distinct
  intensity pattern, it manifests itself indirectly in, for example,
  the chromospheric network. Previous studies have reported significant
  differences in the inferred basic parameters of the supergranulation
  phenomenon. Here we study the structure and temporal evolution of a
  large sample of supergranules, measured by using local helioseismology
  and SOHO/MDI data from the year 2000 at solar activity minimum. Local
  helioseismology with f modes provides maps of the horizontal divergence
  of the flow velocity at a depth of about 1 Mm. From these divergence
  maps supergranular cells were identified by using Fourier segmentation
  procedures in two dimensions and in three dimensions (two spatial
  dimensions plus time). The maps that we analyzed contain more than
  10<SUP>5</SUP> supergranular cells and more than 10<SUP>3</SUP>
  lifetime histories, which makes possible a detailed analysis with high
  statistical significance. We find that the supergranular cells have
  a mean diameter of 27.1 Mm. The mean lifetime is estimated to be 1.6
  days from the measured distribution of lifetimes (three-dimensional
  segmentation), with a clear tendency for larger cells to live longer
  than smaller ones. The pair and mark correlation functions do not
  show pronounced features on scales larger than the typical cell size,
  which suggests purely random cell positions. The temporal histories of
  supergranular cells indicate a smooth evolution from their emergence
  and growth in the first half of their lives to their decay in the
  second half of their lives (unlike exploding granules, which reach
  their maximum size just before they fragment).

Title: Evidence of convective rolls in a sunspot penumbra
Authors: Zakharov, V.; Hirzberger, J.; Riethmüller, T. L.; Solanki,
   S. K.; Kobel, P.
Bibcode: 2008A&A...488L..17Z
Altcode: 2008arXiv0808.2317Z
  Aims: We study the recently discovered twisting motion of bright
  penumbral filaments with the aim of constraining their geometry and
  the associated magnetic field. <BR />Methods: A large sunspot located
  40° from disk center was observed at high resolution with the 1-m
  Swedish Solar Telescope. Inversions of multi-wavelength polarimetric
  data and speckle reconstructed time series of continuum images were
  used to determine proper motions, as well as the velocity and magnetic
  structure in penumbral filaments. <BR />Results: The continuum movie
  reveals apparent lateral motions of bright and dark structures inside
  bright filaments oriented parallel to the limb, confirming recent
  Hinode results. In these filaments we measure upflows of ≈1.1
  km s<SUP>-1</SUP> on their limbward side and weak downflows on
  their centerward side. The magnetic field in them is significantly
  weaker and more horizontal than in the adjacent dark filaments. <BR
  />Conclusions: The data indicate the presence of vigorous convective
  rolls in filaments with a nearly horizontal magnetic field. These
  are separated by filaments harbouring stronger, more vertical
  fields. Because of reduced gas pressure, we see deeper into the
  latter. When observed near the limb, the disk-centerward side of the
  horizontal-field filaments appear bright due to the hot wall effect
  known from faculae. We estimate that the convective rolls transport
  most of the energy needed to explain the penumbral radiative flux.

Title: Discriminant Analysis of Bright Points and Faculae:
    Center-to-Limb Distribution, Contrast and Morphology
Authors: Kobel, P.; Hirzberger, J.; Gandorfer, A.; Solanki, S. K.;
   Zakharov, V.
Bibcode: 2008ESPM...12.2.60K
Altcode:
  High-resolution images of the solar photosphere reveal an intriguing
  mixture of Brights Points (BPs) and faculae at several disk positions,
  which is not explained by the conventional "hot wall'' model. Together
  with quantitative discrepancies between observations and simulations
  of faculae, it stresses that the fundamental relationship between BPs
  and faculae is not yet clear: How are BPs and faculae distributed on
  the solar disk? How do the photometric properties of BPs and faculae
  differ and vary with disk position? <P />To tackle these issues, a
  necessary step is to sort the BPs and faculae at various disk positions,
  in order to treat them separately. We present here the first attempt
  to discriminate BPs and faculae, using a statistical classification
  approach based on Linear Discriminant Analysis (LDA). This has never
  been done so far, presumably due to the lack of known automated methods
  to distinguish such features, and to the difficulty to obtain a coherent
  dataset of high-resolution images recorded in the same conditions. We
  applied our method to high-resolution G-band and continuum images
  of active regions recorded at the Swedish Solar Telescope, covering
  several disk positions where the transition from BPs to faculae
  is expected. <P />This allowed us to retrieve a first estimate of
  the center-to-limb variation of the relative distribution of both
  species. The center-to-limb distribution of BPs and faculae reveals
  the predominance of faculae at all disk positions except close to disk
  center. We argue that these ubiquitous faculae could be the transient
  signatures of swaying flux tubes with a wide range of inclination
  angles. Moreover, we statistically compared the G-band and continuum
  contrast of BPs and faculae, and characterized their morphology. Both
  the G-band and continuum contrast of BPs and faculae are found to
  similarly increase from center to limb. But when comparing G-band
  to continuum, BPs and faculae exhibit slightly different behaviours,
  which are related to radiative transfer processes. By orienting the
  features in local coordinate frames corresponding to the principal axes
  of their contrast moment of inertia, we could retrieve characteristic
  G-band contrast profiles exhibiting the typical predicted asymmetry
  for faculae. Finally, our BPs and faculae were found to have very
  similar morphological properties. <P />Although our study is essentially
  descriptive and based on purely photometric information, we hope that it
  will provide novel useful constraints for future BPs/faculae MHD models.

Title: The Solar Chromosphere at Millimeter Wavelengths
Authors: Loukitcheva, M.; Solanki, S. K.; White, S.
Bibcode: 2008ESPM...12.2.18L
Altcode:
  The solar chromosphere remains the least understood layer of the
  solar atmosphere. There is yet no answer to the question concerning
  its structure. Is it better described by the classical picture of a
  steady temperature rise as a function of height, with superposed weak
  oscillations, or does the temperature keep dropping outwards, with hot
  shocks producing strong localized heating? Observations in the UV and
  the IR give contrasting results, since they only sample either the
  hot or the cool parts of the chromosphere. Computations carried out
  with sophisticated dynamic models of the solar chromosphere demonstrate
  that millimeter emission is extremely sensitive to dynamic processes in
  the chromosphere and the appropriate wavelengths to look for dynamic
  signatures are in the range 0.8-5.0 mm. The models also suggest
  that high resolution observations at mm wavelengths have the unique
  property of reacting to both the hot and the cool gas, and thus have the
  potential of distinguishing between models. <P />In this contribution
  we use high-resolution millimeter-interferometer observations, obtained
  with the Berkeley-Illinois-Maryland Array at 3.5 mm (resolution of
  12 arcsec), as a diagnostic tool to study the thermal structure of
  the solar chromosphere and its response to dynamic processes. <P
  />Our initial results obtained from the observations of the quiet
  Sun reveal brightness features corresponding to supergranular network
  boundaries and bright points within the cells. We found significant
  intensity oscillations with frequencies of 1.5-8 mHz with a tendency
  toward short-period oscillations in internetwork and longer periods in
  network regions. However higher spatial resolution is required for a
  clean separation between the brightness features and for an adequate
  comparison with the output of the comprehensive dynamic simulations.

Title: Magnetic Structure of a Filament during its Phase of Activity
Authors: Sasso, C.; Lagg, A.; Solanki, S. K.
Bibcode: 2008ESPM...12.2.19S
Altcode:
  We analyze and interpret spectropolarimetric observations of an active
  region filament located close to the solar disc center, during its
  phase of activity. The observations are obtained in the chromospheric
  He I lines at 1083.0 nm. We provide novel observational results on the
  magnetic field measurements in solar filaments to give constraints
  to the theoretical models of their support in the solar corona. Our
  main goal is to interpret the behavior of the atmospheric parameters
  retrieved from the spectropolarimetric data to give a picture of
  the magnetic structure of the observed filament. The analysis of the
  observed polarization of the He I 1083.0 nm multiplet in the filament,
  carried out by inverting the Stokes profiles, reveals the presence of
  different unresolved atmospheric components of the He lines, coexisting
  within the resolution element (1.2 arcsec). The different components,
  belonging to different magnetic field lines, show supersonic up-
  and downflows, sometimes within the same resolution element. The He
  blueshifted components belong to mostly transversal field lines in
  the body of the filament. These field lines are found to be curving
  upwards on both sides. This picture suggests the presence of dipped
  field lines that are moving upward, carrying with them the filament
  material. During this movement, we also observe filament material
  flowing down along field lines having the same polarity as the
  photospheric field (i.e. they have the opposite inclination with
  respect to the dipped field lines). These downflows are faster at the
  filament end points and can reach values close to 10 times the speed of
  sound. The field lines are found to be almost parallel to the filament
  axis in the plane perpendicular to the line of sight. We use the two
  main theoretical models of prominence support (dip or flux rope models)
  to interpret the results obtained.

Title: Comparison of Magnetoconvection Simulations with the
    Approximation of Thin Flux Tubes
Authors: Yelles Chaouche, L.; Solanki, S.; Schuessler, M.
Bibcode: 2008ESPM...12..3.8Y
Altcode:
  The structure and dynamics of small vertical photospheric magnetic
  flux concentrations has been often treated in the framework of
  an approximation based upon a low-order truncation of the Taylor
  expansions of all quantities in the horizontal direction, together with
  the assumption of instantaneous total pressure balance at the boundary
  to the non-magnetic external medium. Formally, such an approximation
  is justified if the diameter of the structure (a flux tube or a
  flux sheet) is small compared to all other relevant length scales
  (scale height, radius of curvature, wavelength, etc.). The advent of
  realistic 3D radiative MHD simulations opens the possibility to check
  the consistency of the approximation with the properties of the flux
  concentrations that form in the course of the simulation. We make
  a comparative analysis between the thin flux tube/sheet model and
  flux concentrations existing in a 3D radiation-MHD simulation. We
  have found that for flux concentration well above the equipartition
  distribution, the MHD magnetic structures are reasonably well reproduced
  by the second-order thin flux tube/sheet approximation. The differences
  between approximation and simulation are due to the asymmetry and the
  dynamics of the simulated structures.

Title: Evidence for Polar Jets as Precursors of Polar Plume Formation
Authors: Raouafi, N. -E.; Petrie, G. J. D.; Norton, A. A.; Henney,
   C. J.; Solanki, S. K.
Bibcode: 2008ApJ...682L.137R
Altcode: 2008arXiv0806.3045R
  Observations from the Hinode/XRT telescope and STEREO/SECCHI/EUVI
  are utilized to study polar coronal jets and plumes. The study
  focuses on the temporal evolution of both structures and their
  relationship. The data sample, spanning 2007 April 7-8, shows that
  over 90% of the 28 observed jet events are associated with polar
  plumes. EUV images (STEREO/SECCHI) show plume haze rising from the
  location of approximately 70% of the polar X-ray (Hinode/XRT) and EUV
  jets, with the plume haze appearing minutes to hours after the jet was
  observed. The remaining jets occurred in areas where plume material
  previously existed, causing a brightness enhancement of the latter after
  the jet event. Short-lived, jetlike events and small transient bright
  points are seen (one at a time) at different locations within the base
  of preexisting long-lived plumes. X-ray images also show instances
  (at least two events) of collimated thin jets rapidly evolving into
  significantly wider plumelike structures that are followed by the
  delayed appearance of plume haze in the EUV. These observations provide
  evidence that X-ray jets are precursors of polar plumes and in some
  cases cause brightenings of plumes. Possible mechanisms to explain
  the observed jet and plume relationship are discussed.

Title: SUNRISE: High resolution UV/VIS observations of the sun from
    the stratosphere
Authors: Sunrise Team; Barthol, P.; Gandorfer, A. M.; Solanki,
   S. K.; Knölker, M.; Martinez Pillet, V.; Schmidt, W.; Title, A. M.;
   SUNRISE Team
Bibcode: 2008AdSpR..42...70S
Altcode:
  SUNRISE is an international project for the development, construction
  and operation of a balloon-borne solar telescope with an aperture
  of 1 m, working in the UV/VIS spectral domain. The main scientific
  goal of SUNRISE is to understand the structure and dynamics of the
  magnetic field in the atmosphere of the Sun. SUNRISE will provide
  near diffraction-limited images of the photosphere and chromosphere
  with an unprecedented resolution down to 35 km on the solar surface
  at wavelengths around 220 nm. Active in-flight alignment and image
  stabilization techniques are used. The focal-plane instrumentation
  consists of a polarization sensitive spectrograph, a Fabry Perot
  filter magnetograph and a phase-diverse filter imager working in
  the near UV. The first stratospheric long-duration balloon flight
  of SUNRISE is planned in summer 2009 from the Swedish ESRANGE
  station. SUNRISE is a joint project of the German Max-Planck-Institut
  für Sonnensystemforschung (MPS), Katlenburg-Lindau, with the
  Kiepenheuer-Institut für Sonnenphysik (KIS), Freiburg, Germany, the
  High-Altitude Observatory (HAO), Boulder, USA, the Lockheed-Martin
  Solar and Astrophysics Laboratory (LMSAL), Palo Alto, USA, and the
  Spanish IMaX consortium. This paper will give an overview about the
  mission and a description of its scientific and technological aspects.

Title: Toroidal versus poloidal magnetic fields in Sun-like stars:
    a rotation threshold
Authors: Petit, P.; Dintrans, B.; Solanki, S. K.; Donati, J. -F.;
   Aurière, M.; Lignières, F.; Morin, J.; Paletou, F.; Ramirez Velez,
   J.; Catala, C.; Fares, R.
Bibcode: 2008MNRAS.388...80P
Altcode: 2008MNRAS.tmp..715P; 2008arXiv0804.1290P
  From a set of stellar spectropolarimetric observations, we report
  the detection of surface magnetic fields in a sample of four
  solar-type stars, namely HD 73350, HD 76151, HD 146233 (18 Sco) and HD
  190771. Assuming that the observed variability of polarimetric signal
  is controlled by stellar rotation, we establish the rotation periods of
  our targets, with values ranging from 8.8 d (for HD 190771) to 22.7 d
  (for HD 146233). Apart from rotation, fundamental parameters of the
  selected objects are very close to the Sun's, making this sample
  a practical basis to investigate the specific impact of rotation
  on magnetic properties of Sun-like stars. <P />We reconstruct the
  large-scale magnetic geometry of the targets as a low-order (l &lt; 10)
  spherical harmonic expansion of the surface magnetic field. From the set
  of magnetic maps, we draw two main conclusions. (i) The magnetic energy
  of the large-scale field increases with rotation rate. The increase
  in chromospheric emission with the mean magnetic field is flatter than
  observed in the Sun. Since the chromospheric flux is also sensitive to
  magnetic elements smaller than those contributing to the polarimetric
  signal, this observation suggests that a larger fraction of the surface
  magnetic energy is stored in large scales as rotation increases. (ii)
  Whereas the magnetic field is mostly poloidal for low rotation rates,
  more rapid rotators host a large-scale toroidal component in their
  surface field. From our observations, we infer that a rotation period
  lower than ~12 d is necessary for the toroidal magnetic energy to
  dominate over the poloidal component.

Title: Spectral irradiance variations: comparison between observations
    and the SATIRE model on solar rotation time scales
Authors: Unruh, Y. C.; Krivova, N. A.; Solanki, S. K.; Harder, J. W.;
   Kopp, G.
Bibcode: 2008A&A...486..311U
Altcode: 2008arXiv0802.4178U
  Aims: We test the reliability of the observed and calculated spectral
  irradiance variations between 200 and 1600 nm over a time span of
  three solar rotations in 2004. <BR />Methods: We compare our model
  calculations to spectral irradiance observations taken with SORCE/SIM,
  SoHO/VIRGO, and UARS/SUSIM. The calculations assume LTE and are based
  on the SATIRE (Spectral And Total Irradiance REconstruction) model. We
  analyse the variability as a function of wavelength and present time
  series in a number of selected wavelength regions covering the UV to
  the NIR. We also show the facular and spot contributions to the total
  calculated variability. <BR />Results: In most wavelength regions,
  the variability agrees well between all sets of observations and the
  model calculations. The model does particularly well between 400 and
  1300 nm, but fails below 220 nm, as well as for some of the strong NUV
  lines. Our calculations clearly show the shift from faculae-dominated
  variability in the NUV to spot-dominated variability above approximately
  400 nm. We also discuss some of the remaining problems, such as the low
  sensitivity of SUSIM and SORCE for wavelengths between approximately
  310 and 350 nm, where currently the model calculations still provide
  the best estimates of solar variability.

Title: SOHO/SUMER observations of prominence oscillation before
    eruption
Authors: Chen, P. F.; Innes, D. E.; Solanki, S. K.
Bibcode: 2008A&A...484..487C
Altcode: 2008arXiv0802.1961C
  Context: Coronal mass ejections (CMEs), as a large-scale eruptive
  phenomenon, often reveal some precursors in the initiation phase, e.g.,
  X-ray brightening, filament darkening, etc., which are useful for CME
  modelling and space weather forecasting. <BR />Aims: With the Solar
  Ultraviolet Measurements of Emitted Radiation (SUMER) spectroscopic
  observations of the 2000 September 26 CME, we propose another
  precursor for CMEs, namely, long-time prominence oscillations. <BR
  />Methods: We observed the prominence oscillation-and-eruption event by
  ground-based Hα telescopes and space-borne white-light, EUV imaging,
  and spectroscopic instruments. In particular, the SUMER slit was
  observing the prominence in a sit-and-stare mode. <BR />Results:
  The observations indicate that a siphon flow was moving from the
  proximity of the prominence to a site at a projected distance of 270'',
  which was followed by repetitive Hα surges and continual prominence
  oscillations. The oscillation lasted 4 hours before the prominence
  erupted as a blob-like CME. The analysis of the multiwavelength
  data indicates that the whole series of processes fits well into the
  emerging flux trigger mechanism for CMEs. In this mechanism, emerging
  magnetic flux drives a siphon flow due to increased gas pressure
  where the background polarity emerges. It also drives Hα surges
  through magnetic reconnection where the opposite polarity emerges. The
  magnetic reconnection triggers the prominence oscillations, as well
  as its loss of equilibrium, which finally leads to the eruption of the
  prominence. It is also found that the reconnection between the emerging
  flux and the pre-existing magnetic loop proceeds in an intermittent,
  probably quasi-periodic, way.

Title: Understanding the WMAP Results: Low-Order Multipoles and Dust
    in the Vicinity of the Solar System
Authors: Dikarev, Valeri; Preuß, Oliver; Solanki, Sami; Krüger,
   Harald; Krivov, Alexander
Bibcode: 2008EM&P..102..555D
Altcode: 2007EM&P..tmp...47D
  Analyses of the cosmic microwave background (CMB) radiation maps
  produced by the Wilkinson Microwave Anisotropy Probe (WMAP) have
  revealed anomalies not predicted by the standard cosmological
  theory. It has been suggested that a dust cloud in the vicinity of
  the Solar system may be the cause for these anomalies. In this paper,
  the thermal emission by particles from two known interplanetary
  meteoroid complexes is tested against the CMB maps. Conclusions are
  drawn based on the geometry of cloud projections onto the WMAP sky
  whether these clouds are likely to explain the observed anomaly. The
  smooth background Zodiacal cloud and one of the Taurid meteor complex
  branches do not explain the WMAP anomaly.

Title: Models of solar irradiance variations: Current status
Authors: Krivova, Natalie A.; Solanki, Sami K.
Bibcode: 2008JApA...29..151K
Altcode:
  Regular monitoring of solar irradiance has been carried out since 1978
  to show that solar total and spectral irradiance varies at different
  time scales. Whereas variations on time scales of minutes to hours
  are due to solar oscillations and granulation, variations on longer
  time scales are driven by the evolution of the solar surface magnetic
  field. Here the most recent advances in modelling of solar irradiance
  variations on time scales longer than a day are briefly reviewed.

Title: The intensity contrast of solar granulation: comparing Hinode
    SP results with MHD simulations
Authors: Danilovic, S.; Gandorfer, A.; Lagg, A.; Schüssler, M.;
   Solanki, S. K.; Vögler, A.; Katsukawa, Y.; Tsuneta, S.
Bibcode: 2008A&A...484L..17D
Altcode: 2008arXiv0804.4230D
  Context: The contrast of granulation is an important quantity
  characterizing solar surface convection. <BR />Aims: We compare the
  intensity contrast at 630 nm, observed using the Spectro-Polarimeter
  (SP) aboard the Hinode satellite, with the 3D radiative MHD simulations
  of Vögler &amp; Schüssler (2007, A&amp;A, 465, L43). <BR />Methods:
  A synthetic image from the simulation is degraded using a theoretical
  point-spread function of the optical system, and by considering other
  important effects. <BR />Results: The telescope aperture and the
  obscuration by the secondary mirror and its attachment spider, reduce
  the simulated contrast from 14.4% to 8.5%. A slight effective defocus
  of the instrument brings the simulated contrast down to 7.5%, close to
  the observed value of 7.0%. <BR />Conclusions: A proper consideration
  of the effects of the optical system and a slight defocus, lead to
  sufficient degradation of the synthetic image from the MHD simulation,
  such that the contrast reaches almost the observed value. The remaining
  small discrepancy can be ascribed to straylight and slight imperfections
  of the instrument, which are difficult to model. Hence, Hinode SP data
  are consistent with a granulation contrast which is predicted by 3D
  radiation MHD simulations.

Title: Moments of the latitudinal dependence of the sunspot cycle:
    a new diagnostic of dynamo models
Authors: Solanki, S. K.; Wenzler, T.; Schmitt, D.
Bibcode: 2008A&A...483..623S
Altcode:
  Aims: The latitude-distribution of solar activity as represented by
  sunspots is studied. <BR />Methods: We first determined the latitudinal
  distribution of a sunspot cycle by integrating the butterfly diagram
  at each latitude over the length of each cycle. We then formed the five
  lowest moments of the latitudinal distribution of all complete sunspot
  cycles since 1874 and compared these moments with each other. <BR
  />Results: The three lowest moments correlate remarkably well with
  each other. For example, the mean latitude of the sunspots during a
  cycle and the latitude range are correlated at the 0.96 level. A clear
  asymmetry is seen between the two hemispheres, with the southern solar
  hemisphere showing consistently stronger and more positive correlations
  than the northern hemisphere. When applied to different simple dynamo
  models, the same analysis reveals significant differences between the
  models and demonstrates that such moments are a useful diagnostic in
  distinguishing between dynamo models. Remarkably, dynamos without a
  meridional flow provide results closer to those of the Sun's northern
  hemisphere, while a dynamo with a meridional flow produces fields more
  like those in the Sun's southern hemisphere. This may provide a clue
  to the cause of the well-known north-south asymmetry of solar activity.

Title: Multiheight Analysis of Asymmetric Stokes Profiles in a Solar
    Active Region
Authors: Deng, N.; Choudhary, D.; Solanki, S. K.; Lagg, A.
Bibcode: 2008AGUSMSP51D..06D
Altcode:
  Parameters characterizing Stokes asymmetries are derived from full
  Stokes I,Q,U,V spectra of FeI λλ 630.15, 630.25~nm line pair
  (formed at two different heights in the photosphere) and MgI b
  517.27~nm line (formed at lower chromosphere) in a solar active
  region near disc center. The spectropolarimetric observations were
  taken with the National Solar Observatory/High Altitude Observatory
  Advanced Stokes Polarimeter. The observed active region consists
  of a α sunspot, a δ sunspot, several pores and granulation. The
  line center shifts and bi-sectors derived from Stokes-I profiles
  describe the line-of-sight Doppler velocity and Stokes-I asymmetry,
  respectively. Stokes-V amplitude and area asymmetries are defined by
  the normalized difference of respective quantities between blue and
  red lobes of circular polarization profiles. The same can be derived
  from linear polarization profiles ([Q2+U2]1/2). The Stokes asymmetries
  are compared for different regions and at multiple heights. Neutral
  line regions of the δ spot and outer penumbral regions show distinct
  large Stokes asymmetries. Both Stokes-V amplitude and area asymmetries
  become larger from lower to higher atmosphere in neutral line regions
  that have strong transverse field and mixed polarities. The Stokes-V
  area asymmetry of outer edge of penumbrae changes from positive in
  the photosphere to negative in lower chromosphere. Detailed results
  and interpretation will be presented.

Title: The nature of running penumbral waves revealed
Authors: Bloomfield, D. S.; Lagg, A.; Solanki, S. K.
Bibcode: 2008IAUS..247...55B
Altcode: 2007IAUS..247...55B
  We seek to clarify the nature of running penumbral (RP) waves:
  are they chromospheric trans-sunspot waves or a visual pattern of
  upward-propagating waves? Full Stokes spectropolarimetric time series
  of the photospheric Sii10827 Å line and the chromospheric Hei10830 Å
  multiplet were inverted using a Milne-Eddington code. Spatial pixels
  were paired between the outer umbral/inner penumbral photosphere
  and the penumbral chromosphere using inclinations retrieved by the
  inversion and the dual-height pairings of line-of-sight velocity time
  series were studied for signatures of wave propagation using a Fourier
  phase difference analysis. The dispersion relation for radiatively
  cooling acoustic waves, modified to incorporate an inclined propagation
  direction, fits well the observed phase differences between the pairs
  of photospheric and chromospheric pixels. We have thus demonstrated
  that RP waves are in effect low-β slow-mode waves propagating along
  the magnetic field.

Title: Identification of types of kink modes in coronal loops:
    principles and application to TRACE results
Authors: Wang, T.; Solanki, S.; Selwa, M.; Ofman, L.
Bibcode: 2008AGUSMSP31C..08W
Altcode:
  We explore the possible signatures of different types of kink modes
  (horizontal and vertical oscillations in their fundamental mode and
  second harmonic) which may arise in coronal loops. Based on the 3D
  geometrical parameters of 14 TRACE loops of transverse oscillations,
  we simulate qualitatively the loop displacements due to these types
  of kink mode oscillations. We find that for many combinations of
  viewing and loop geometry it is not straightforward to distinguish
  between the two types of kink modes. We have also considered Doppler
  signatures and found that these can in principle help to obtain
  unique identifications of the oscillation modes. We then compared
  the simulated spatial signatures with the observations for 14
  TRACE loops. We find that two cases of loop oscillations previously
  identified as a fundamental horizontal mode appear to be a fundamental
  vertical mode, while in two other cases it is not possible to clearly
  distinguish between a horizontal oscillation of the fundamental
  mode and the second-harmonic, and in six cases it is not possible
  to clearly distinguish between a fundamental horizontal mode and a
  second-harmonic vertical mode. In addition, for the particular case
  that the oscillating loop has a S-shape, we find that the fundamental
  vertical oscillation can take on the appearance of the horizontal second
  harmonic due to projection effects. We also present numerical results
  of three dimensional MHD model of an idealized active region field with
  S-shaped field-lines. The active region is initialized as a force-free
  dipole magnetic configuration with uniform density and contains a loop
  with a higher density than its surroundings. We introduce a velocity
  pulse which models the impact of a flare on surrounding fields. Both
  the qualitative study and the MHD simulation support the conclusion
  of the presence of fundamental mode of vertical kink oscillations in
  an S-shaped loop. Our interpretation can naturally solve the puzzle of
  the absence of the fundamental mode and the apparent presence of second
  harmonic oscillations observed in a TRACE loop by De Moortel and Brady
  (2007).

Title: Stratification of Sunspot Umbral Dots from Inversion of Stokes
    Profiles Recorded by Hinode
Authors: Riethmüller, T. L.; Solanki, S. K.; Lagg, A.
Bibcode: 2008ApJ...678L.157R
Altcode: 2008arXiv0805.4324R
  This work aims to constrain the physical nature of umbral dots (UDs)
  using high-resolution spectropolarimetry. Full Stokes spectra recorded
  by the spectropolarimeter on Hinode of 51 UDs in a sunspot close to the
  disk center are analyzed. The height dependence of the temperature,
  magnetic field vector, and line-of-sight velocity across each UD
  is obtained from an inversion of the Stokes vectors of the two Fe I
  lines at 630 nm. No difference is found at higher altitudes [-3 &lt;=
  log (τ<SUB>500</SUB>) &lt;= - 2] between the UDs and the diffuse
  umbral background. Below that level the difference rapidly increases,
  so that at the continuum formation level [log (τ<SUB>500</SUB>) = 0]
  we find on average a temperature enhancement of 570 K, a magnetic field
  weakening of 510 G, and upflows of 800 m s<SUP>-1</SUP> for peripheral
  UDs, whereas central UDs display an excess temperature of on average
  550 K, a field weakening of 480 G, and no significant upflows. The
  results for, in particular, the peripheral UDs, including cuts of
  magnetic vector and velocity through them, look remarkably similar to
  the output of recent radiation MHD simulations. They strongly suggest
  that UDs are produced by convective upwellings.

Title: First stereoscopic polar plume reconstructions from
    STEREO/SECCHI images
Authors: Feng, L.; Inhester, B.; Solanki, S. K.; Wiegelmann, T.;
   Podlipnik, B.; Howard, R.; Plunkett, S.; Wuelser, J.; Gan, W.
Bibcode: 2008AGUSMSH23A..01F
Altcode:
  We present the first stereoscopic reconstruction of the
  three-dimensional structures of polar plumes based on the two
  simultaneously recorded images taken by the EUVI telescopes in
  the SECCHI instrument package onboard the recently launched STEREO
  mission. The reconstructed polar plumes were observed on April 7th,
  2007 when the two spacecraft were well below the solar equatorial
  plane, an appropriate time for the observation of the plumes in the
  south polar coronal hole. The heliocentric separation of the two
  spacecraft was 3.6 degrees at that time. We determine locations of
  the footpoints of five EUV polar plumes on the solar surface as well
  as their inclinations relative to the line-of-sight and to their
  local radial directions. The five plumes are all within 21 degrees
  of the south pole and their inclinations to the line-of-sight of
  STEREO A(head) and radial directions are on average 107 degrees and
  28 degrees, respectively. A simple dipole model for the south pole's
  magnetic field does not provide a good correspondence with the obtained
  inclinations. Of the three plumes in front of the limb only one is
  associated with an EUV bright point.

Title: The FeH F<SUP>4</SUP>Δ-X<SUP>4</SUP>Δ system. Creating a
    valuable diagnostic tool to explore solar and stellar magnetic fields
Authors: Afram, N.; Berdyugina, S. V.; Fluri, D. M.; Solanki, S. K.;
   Lagg, A.
Bibcode: 2008A&A...482..387A
Altcode:
  Context: Lines of diatomic molecules are ideal tools for studying
  cool stellar atmospheres and the internal structure of sunspots
  and starspots, given their temperature and pressure sensitivities,
  which are typically higher than in atomic lines. The Wing-Ford FeH
  F<SUP>4</SUP>Δ-X<SUP>4</SUP>Δ system represents such a diatomic
  molecule that is, in addition, highly sensitive to magnetic fields. The
  current theoretical description of those transitions that include the
  involved molecular constants, however, are only based on intensity
  measurements because polarimetric observations have not been available
  until now, which limits their diagnostic value. Furthermore, the theory
  has so far been optimized to reproduce energy levels and line strengths
  without taking magnetic sensitivities into account. <BR />Aims: The
  FeH F<SUP>4</SUP>Δ-X<SUP>4</SUP>Δ system is produced by transitions
  between two electronic states with the coupling of the angular momenta
  that is intermediate between limiting Hund's cases (a) and (b). Our goal
  is to investigate the diagnostic capabilities of the current theoretical
  description of the molecule FeH. <BR />Methods: Using the most precise
  available Hamiltonian, we carried out the perturbation calculation
  of the molecular Zeeman effect for this transition and computed the
  Landé factors of the energy levels and of transitions. We extracted
  Landé factors from a comparison of observed and calculated Stokes
  I and V profiles. Certain spectral lines, most frequently with high
  magnetic sensitivity, exhibited discrepancies between the theory and
  observations. We extended the theoretical model with a semi-empirical
  approach to obtain a diagnostic tool that is able to reproduce many
  of the interesting spectral lines. <BR />Results: We find that the
  current theory successfully reproduces the magnetic properties of
  a large number of lines in the FeH F<SUP>4</SUP>Δ-X<SUP>4</SUP>Δ
  system and that the modified Hamiltonian allows us to synthesize
  and successfully reproduce the most sensitive lines. Thus, our
  observations have provided valuable constraints for determining
  empirical molecular constants and Landé factors. <BR />Conclusions:
  The FeH F<SUP>4</SUP>Δ-X<SUP>4</SUP>Δ system is found to be a very
  sensitive magnetic diagnostic tool. Polarimetric data of these lines,
  in contrast to intensity measurements, provide us with more direct
  and detailed information to study the coolest parts of sunspot and
  starspot umbrae, as well as cool active dwarfs.

Title: A first step in reconstructing the solar corona
    self-consistently with a magnetohydrostatic model during solar
    activity minimum
Authors: Ruan, P.; Wiegelmann, T.; Inhester, B.; Neukirch, T.; Solanki,
   S. K.; Feng, L.
Bibcode: 2008A&A...481..827R
Altcode:
  Aims: We compute the distribution of the magnetic field and the plasma
  in the global corona with a self-consistent magnetohydrostatic (MHS)
  model. <BR />Methods: Because direct measurements of the solar coronal
  magnetic field and plasma are extremely difficult and inaccurate, we
  use a modeling approach based on observational quantities, e.g. the
  measured photospheric magnetic field, to reconstruct the structure
  of the global solar corona. We take an analytic magnetohydrostatic
  model to extrapolate the magnetic field in the corona from photospheric
  magnetic field measurement. In the model, the electric current density
  can be decomposed into two components: one component is aligned with the
  magnetic field lines, whereas the other component flows in spherical
  shells. The second component of the current produces finite Lorentz
  forces that are balanced by the pressure gradient and the gravity
  force. We derive the 3D distribution of the magnetic field and plasma
  self-consistently in one model. The boundary conditions are given by
  a synoptic magnetogram on the inner boundary and by a source surface
  model at the outer boundary. <BR />Results: The density in the model is
  higher in the equatorial plane than in the polar region. We compare the
  magnetic field distribution of our model with potential and force-free
  field models for the same boundary conditions and find that our model
  differs noticeably from both. We discuss how to apply the model and
  how to improve it.

Title: Evidence of magnetic field wrapping around penumbral filaments
Authors: Borrero, J. M.; Lites, B. W.; Solanki, S. K.
Bibcode: 2008A&A...481L..13B
Altcode: 2007arXiv0712.2548B
  We employ high-spatial resolution spectropolarimetric observations
  from the Solar Optical Telescope on-board the Hinode spacecraft to
  investigate the fine structure of the penumbral magnetic fields. The
  Stokes vector of two neutral iron lines at 630 nm is inverted at every
  spatial pixel to retrieve the depth-dependence of the magnetic field
  vector, line-of-sight velocity and thermodynamic parameters. We show
  that the azimuthal angle of the magnetic field vector has opposite sign
  on both sides above the penumbral filaments. This is consistent with
  the wrapping of an inclined field around the horizontal filaments. The
  wrapping effect is stronger for filaments with larger horizontal
  extensions. In addition, we find that the external magnetic field can
  penetrate into the intraspines, leading to non-radial magnetic fields
  inside them. These findings shed some light on the controversial
  small-scale structure of the sunspot penumbra.

Title: Theoretical modeling for the stereo mission
Authors: Aschwanden, Markus J.; Burlaga, L. F.; Kaiser, M. L.; Ng,
   C. K.; Reames, D. V.; Reiner, M. J.; Gombosi, T. I.; Lugaz, N.;
   Manchester, W.; Roussev, I. I.; Zurbuchen, T. H.; Farrugia, C. J.;
   Galvin, A. B.; Lee, M. A.; Linker, J. A.; Mikić, Z.; Riley, P.;
   Alexander, D.; Sandman, A. W.; Cook, J. W.; Howard, R. A.; Odstrčil,
   D.; Pizzo, V. J.; Kóta, J.; Liewer, P. C.; Luhmann, J. G.; Inhester,
   B.; Schwenn, R. W.; Solanki, S. K.; Vasyliunas, V. M.; Wiegelmann, T.;
   Blush, L.; Bochsler, P.; Cairns, I. H.; Robinson, P. A.; Bothmer,
   V.; Kecskemety, K.; Llebaria, A.; Maksimovic, M.; Scholer, M.;
   Wimmer-Schweingruber, R. F.
Bibcode: 2008SSRv..136..565A
Altcode: 2006SSRv..tmp...75A
  We summarize the theory and modeling efforts for the STEREO mission,
  which will be used to interpret the data of both the remote-sensing
  (SECCHI, SWAVES) and in-situ instruments (IMPACT, PLASTIC). The
  modeling includes the coronal plasma, in both open and closed magnetic
  structures, and the solar wind and its expansion outwards from the Sun,
  which defines the heliosphere. Particular emphasis is given to modeling
  of dynamic phenomena associated with the initiation and propagation
  of coronal mass ejections (CMEs). The modeling of the CME initiation
  includes magnetic shearing, kink instability, filament eruption, and
  magnetic reconnection in the flaring lower corona. The modeling of CME
  propagation entails interplanetary shocks, interplanetary particle
  beams, solar energetic particles (SEPs), geoeffective connections,
  and space weather. This review describes mostly existing models of
  groups that have committed their work to the STEREO mission, but is by
  no means exhaustive or comprehensive regarding alternative theoretical
  approaches.

Title: On the potential value of Ca II K spectroheliogram time-series
    for solar activity and irradiance studies
Authors: Ermolli, I.; Solanki, S. K.; Tlatov, A. G.; Krivova, N. A.;
   Ulrich, R. K.; Singh, J.
Bibcode: 2008arXiv0802.3806E
Altcode:
  Various observatories around the globe started regular full-disk imaging
  of the solar atmosphere in the Ca II K line since the early decades
  of the 20th century. The archives made by these observations have the
  potential of providing far more detailed information on solar magnetism
  than just the sunspot number and area records to which most studies
  of solar activity and irradiance changes are restricted. We evaluate
  the image contents of three Ca II K spectroheliogram time-series,
  specifically those obtained by the digitization of the Arcetri,
  Kodaikanal, and Mt Wilson photographic archives. We describe the
  main problems afflicting these data and analyze their quality by
  expressing the image contents through several quantities. We compare
  the results obtained with those for similar present-day observations
  taken with the Meudon spectroheliograph and with the Rome-PSPT. We show
  that historic data suffer from stronger geometrical distortions and
  photometric uncertainties than similar present-day observations. The
  latter uncertainties mostly originate from the photographic calibration
  of the original data and from stray-light effects. We also show that
  the image contents of the three analyzed series vary in time. These
  variations are probably due to instrument changes and aging of the
  spectrographs used, as well as changes of the observing programs. Our
  results imply that the main challenge for the analysis of historic data
  is their accurate photometric calibration. This problem must be solved
  before they can provide reliable information about solar magnetism and
  activity over the last century. Moreover, inter-calibration of results
  obtained from independent time-series is required to reliably trace
  changes of solar properties with time from the analysis of such data.

Title: SOHO/SUMER observations of prominence oscillation before
    eruption
Authors: Chen, P. F.; Innes, D. E.; Solanki, Sami
Bibcode: 2008cosp...37..502C
Altcode: 2008cosp.meet..502C
  Coronal mass ejections (CMEs) often reveal some precursors in the
  initiation phase, such as X- ray brightening and filament darkening,
  which are useful for CME modeling and space weather forecast. With the
  SOHO/SUMER spectroscopic observations of the 2000 September 26 event,
  we propose another precursor for CME eruptions, namely, long-time
  prominence oscillations. The observations indicate that a siphon
  flow was moving from the proximity of the prominence to a far site,
  which was followed by repetitive Hα surges and continual prominence
  oscillations. The oscillation lasted 4 hours before the prominence
  erupted as a blob-like CME. The analysis of the multiwavelength
  data indicates that the whole series of processes fits well into the
  emerging flux trigger mechanism for CMEs. In this mechanism, emerging
  magnetic flux drives a siphon flow due to increased gas pressure
  where the background polarity emerges. It also drives Hα surges
  through magnetic reconnection where the opposite polarity emerges. The
  magnetic reconnection triggers the prominence oscillations, as well
  as its loss of equilibrium, which finally leads to the eruption of the
  prominence. It is also found that the reconnection between the emerging
  flux and the pre-existing magnetic loop proceeds in an intermittent,
  probably quasiperiodic, way.

Title: 3D MHD model of kink waves in a loop anchored in a realistic
    active region
Authors: Selwa, Malgorzata; Ofman, Leon; Wang, Tongjiang; Solanki, Sami
Bibcode: 2008cosp...37.2804S
Altcode: 2008cosp.meet.2804S
  We present numerical results of three dimensional MHD model of the
  active region field. The active region is initialized using MDI data
  of 15 May 2001, 02:57 UT and potential extrapolation of the magnetic
  field with gravitationally stratified density and contains a loop
  with a higher density than its surroundings. The potential model
  imitates the original TRACE AR quite well, however, the choice of
  particular loop within AR is inaccurate due to limitation of the
  plane-of-the-sky view. This study represents an extension to the
  model of Ofman (2007). We introduce a velocity pulse based on TRACE
  observations to model the impact of a flare on surrounding fields, and
  study the resulting loop oscillations. The flare is initialized as a
  semispherical velocity pulse at the bottom of AR and corresponds to the
  event between loop's footpoints captured by TRACE. We investigate the
  influence of a realistic dense loop on the excitation and damping of
  the oscillations and compare our results with TRACE observations. By
  the means of 3D computer simulation we confirm that considering
  combination of viewing and loop geometry and Doppler signatures it
  is straightforward to distinguish between at least two types of kink
  modes: horizontal and vertical in the real loop observed by Aschwanden
  et al. (2002). We find that oscillation previously identified as a
  fundamental horizontal mode (Aschwanden et al. 2002) appears to be a
  fundamental vertical mode. As such vertical kink oscillations are not
  as rare compared to horizontal ones as previously thought.

Title: Grand minima and maxima of solar activity on multi-millennial
    scale
Authors: Usoskin, Ilya; Solanki, Sami; Kovaltsov, Gennady
Bibcode: 2008cosp...37.3264U
Altcode: 2008cosp.meet.3264U
  Using a reconstruction of sunspot numbers stretching over multiple
  millennia, we analyze the statistics of the occurrence of grand minima
  and maxima and set new observational constraints on long-term solar
  and stellar dynamo models. We present an updated reconstruction of
  sunspot number over multiple millennia, from 14C data by means of
  a physics-based model, using an updated model of the evolution of
  the solar open magnetic flux. A list of grand minima and maxima of
  solar activity is presented for the Holocene (since 9500 BC) and
  the statistics of both the length of individual events as well as
  the waiting time between them are analyzed. It is discussed that the
  occurrence of grand minima/maxima is driven not by long-term cyclic
  variability, but by a stochastic/chaotic process. The waiting time
  distribution of the occurrence of grand minima/maxima deviates from an
  exponential distribution, implying that these events tend to cluster
  together with long event-free periods between the clusters. Two
  different types of grand minima are observed: short (30-90 years)
  minima of Maunder type and long (&gt;110 years) minima of Sp¨rer type,
  implying that a deterministic behaviour of the dynamo during o a grand
  minimum defines its length. The duration of grand maxima follows an
  exponential distribution, suggesting that the duration of a grand
  maximum is determined by a random process.

Title: Variability of solar irradiance from the UV to the NIR from
    GOME and SCIAMACHY for use in atmospheric models
Authors: Ambrose Pagaran, Joseph; Weber, Mark; Ambrose Pagaran, Joseph;
   Burrows, John P.; Krivova, Natalie; Solanki, Sami; Floyd, Linton
Bibcode: 2008cosp...37.2329A
Altcode: 2008cosp.meet.2329A
  The Sun is the primary energy source that drives the Earth's
  climate system. Its radiative output is known to vary in time,
  for instance, with the 11-year solar cycle and 27-day solar
  rotation period. Variations in the solar spectral irradiance (SSI)
  affect the thermal structure and chemical composition of the Earth's
  atmosphere. Although the largest solar variations are observed in the UV
  spectral region, a large fraction of the total solar irradiance (TSI,
  solar constant) variation over a solar cycle comes from the visible
  and near IR spectral range. In order to understand how SSI variations
  cause a detectable change in climate, we need to quantify UV, visible,
  and near IR variation in the solar spectral irradiance to a high level
  of certainty both over the short term solar rotation 27-day period and
  11-year solar cycle. Using daily solar irradiance observations from
  SUSIM (1992-2005), GOME (1995-present), and SCIAMACHY (2002-present),
  we study solar variations over 27-day solar rotations from 120 nm to
  1600 nm. The variability is modelled by parameterizing SSI in terms
  of faculae brightening (using the Mg II core-to-wing ratio proxy)
  and sunspot darkening (using the photospheric sunspot index). Since
  the variations in the visible and NIR are well below 1

Title: ALMA as the ideal probe of the solar chromosphere
Authors: Loukitcheva, Maria A.; Solanki, Sami K.; White, Stephen
Bibcode: 2008Ap&SS.313..197L
Altcode: 2007arXiv0704.0023L; 2007Ap&SS.tmp..371L
  The very nature of the solar chromosphere, its structuring and
  dynamics, remains far from being properly understood, in spite of
  intensive research. Here we point out the potential of chromospheric
  observations at millimeter wavelengths to resolve this long-standing
  problem. Computations carried out with a sophisticated dynamic model
  of the solar chromosphere due to Carlsson and Stein demonstrate that
  millimeter emission is extremely sensitive to dynamic processes in
  the chromosphere and the appropriate wavelengths to look for dynamic
  signatures are in the range 0.8 5.0 mm. The model also suggests that
  high resolution observations at mm wavelengths, as will be provided
  by ALMA, will have the unique property of reacting to both the hot
  and the cool gas, and thus will have the potential of distinguishing
  between rival models of the solar atmosphere. Thus, initial results
  obtained from the observations of the quiet Sun at 3.5 mm with the
  BIMA array (resolution of 12″) reveal significant oscillations with
  amplitudes of 50 150 K and frequencies of 1.5 8 mHz with a tendency
  toward short-period oscillations in internetwork and longer periods
  in network regions. However higher spatial resolution, such as that
  provided by ALMA, is required for a clean separation between the
  features within the solar atmosphere and for an adequate comparison
  with the output of the comprehensive dynamic simulations.

Title: The Nature of Running Penumbral Waves Revealed
Authors: Bloomfield, D. Shaun; Lagg, Andreas; Solanki, Sami K.
Bibcode: 2007ApJ...671.1005B
Altcode: 2007arXiv0709.3731B
  We seek to clarify the nature of running penumbral (RP) waves:
  are they chromospheric trans-sunspot waves or a visual pattern of
  upward-propagating waves? Full Stokes spectropolarimetric time series of
  the photospheric Si I λ10827 line and the chromospheric He I λ10830
  multiplet were inverted using a Milne-Eddington atmosphere. Spatial
  pixels were paired between the outer umbral/inner penumbral photosphere
  and the penumbral chromosphere using inclinations retrieved by the
  inversion and the dual-height pairings of line-of-sight velocity time
  series were studied for signatures of wave propagation using a Fourier
  phase difference analysis. The dispersion relation for radiatively
  cooling acoustic waves, modified to incorporate an inclined propagation
  direction, fits well the observed phase differences between the pairs
  of photospheric and chromospheric pixels. We have thus demonstrated
  that RP waves are in effect low-β slow-mode waves propagating along
  the magnetic field.

Title: First Stereoscopic Coronal Loop Reconstructions from STEREO
    SECCHI Images
Authors: Feng, L.; Inhester, B.; Solanki, S. K.; Wiegelmann, T.;
   Podlipnik, B.; Howard, R. A.; Wuelser, J. -P.
Bibcode: 2007ApJ...671L.205F
Altcode: 2008arXiv0802.0773F
  We present the first reconstruction of the three-dimensional shape of
  magnetic loops in an active region from two different vantage points
  based on simultaneously recorded images. The images were taken by the
  two EUVI telescopes of the SECCHI instrument on board the recently
  launched STEREO spacecraft when the heliocentric separation of the
  two space probes was 12°. We demonstrate that these data allow us to
  obtain a reliable three-dimensional reconstruction of sufficiently
  bright loops. The result is compared with field lines derived from
  a coronal magnetic field model extrapolated from a photospheric
  magnetogram recorded nearly simultaneously by SOHO MDI. We attribute
  discrepancies between reconstructed loops and extrapolated field lines
  to the inadequacy of the linear force-free field model used for the
  extrapolation.

Title: First Stereoscopic Coronal Loop Reconstructions From
    STEREO/SECCHI Images
Authors: Feng, L.; Inhester, B.; Solanki, S. K.; Wiegelmann, T.;
   Podlipnik, B.; Howard, R. A.
Bibcode: 2007AGUFMSH41B..06F
Altcode:
  We for the first time use simultaneously observed EUV images to
  reconstruct the 3D shape of magnetic loops which emerge from an active
  region. The images were taken by the two EUVI cameras of the SECCHI
  telescopes onboard the STEREO spacecraft. At the time the data was
  taken, the heliocentric separation of the two STEREO probes was 12
  degrees. We show that under these conditions it is possible to obtain
  a reliable three- dimensional reconstruction of sufficiently bright
  loops as they usually emerge from an active region. The result is
  compared with field lines derived from a coronal magnetic field model
  extrapolated from a surface magnetogram. The magnetogram was abserved
  by SOHO/MDI only 9 seconds before the the EUV images were taken.

Title: Discovery of inward moving magnetic enhancements in sunspot
    penumbrae
Authors: Zhang, J.; Solanki, S. K.; Woch, J.
Bibcode: 2007A&A...475..695Z
Altcode: 2007arXiv0705.0604Z
  Context: Sunspot penumbrae show a fine structure in continuum intensity
  which displays considerable dynamics. The magnetic field, in contrast,
  although also highly structured, has been shown to be relatively static
  in earlier studies. <BR />Aims: We report on the discovery of inward
  moving magnetic enhancements in the penumbrae of two regular sunspots,
  and characterize their fundamental properties. <BR />Methods: Using
  continuum images, longitudinal magnetograms and Dopplergrams, recorded
  in high resolution mode by the Michelson Doppler Imager (MDI) instrument
  on the Solar and Heliospheric Observatory (SOHO), we have probed the
  evolution of magnetic features in the inner penumbra. The relationship
  between magnetic features, corresponding brightness in continuum images
  and Dopplergrams is also considered. <BR />Results: Local enhancements
  of the line-of-sight (LOS) component of the magnetic field in the inner
  part of the penumbral region move inward towards the umbra-penumbra
  boundary with a radial speed of about 0.3 km s<SUP>-1</SUP>. These local
  inward-moving enhancements of the LOS component of the magnetic fields
  appear to be relatively common. They are associated with dark structures
  and tend to display downflows relative to the penumbral background. We
  also confirm the presence of outward moving magnetic enhancments in
  the outer half of the penumbra. Possible explanations are discussed.

Title: The Fraction of DA White Dwarfs with Kilo--Gauss Magnetic
    Fields
Authors: Jordan, S.; Aznar Cuadrado, R.; Napiwotzki, R.; Schmid,
   H. M.; Solanki, S. K.
Bibcode: 2007ASPC..372..169J
Altcode: 2006astro.ph.10881J
  Current estimates for white dwarfs with fields in excess of 1 MG are
  about 10%; according to our first high-precision circular-polarimetric
  study of 12 bright white dwarfs with the VLT tep{p26_Aznar-etal:04}
  this number increases up to about 25%\ in the kG regime. With our
  new sample of ten white dwarf observations (plus one sdO star) we
  wanted to improve the sample statistics to determine the incident
  of kG magnetic fields in white dwarfs. In one of our objects (LTT
  7987) we detected a statistically significant (97% confidence level)
  longitudinal magnetic field varying between (-1± 0.5) kG and (+1±
  0.5) kG. This would be the weakest magnetic field ever found in a
  white dwarf, but at this level of accuracy, systematic errors cannot
  completely be ruled out. Together with previous investigations, the
  fraction of kG magnetic fields in white dwarfs amounts to about 11-15%
  , which is close to current estimates for highly magnetic white dwarfs
  (&gt;1 MG).

Title: A bright coronal downflow seen in multi-wavelength
observations: evidence of a bifurcating flux-rope?
Authors: Tripathi, D.; Solanki, S. K.; Mason, H. E.; Webb, D. F.
Bibcode: 2007A&A...472..633T
Altcode: 2008arXiv0802.3616T
  Aims:We study the origin and characteristics of a bright coronal
  downflow seen after a coronal mass ejection associated with
  erupting prominences on 5 March 2000. <BR />Methods: This study
  extends that of Tripathi et al. (2006b, A&amp;A, 449, 369) based
  on the Extreme-ultraviolet Imaging Telescope (EIT), the Soft X-ray
  Telescope (SXT) and the Large Angle Spectrometric Coronagraph (LASCO)
  observations. We combined those results with an analysis of the
  observations taken by the Hα and the Mk4 coronagraphs at the Mauna Loa
  Solar Observatory (MLSO). The combined data-set spans a broad range of
  temperature as well as continuous observations from the solar surface
  out to 30 R<SUB>⊙</SUB>. <BR />Results: The downflow started at
  around 1.6 R<SUB>⊙</SUB> and contained both hot and cold gas. The
  downflow was observed in the Hα and the Mk4 coronagraphs as well as
  the EIT and the SXT and was approximately co-spatial and co-temporal
  providing evidence of multi-thermal plasma. The Hα and Mk4 images
  show cusp-shaped structures close to the location where the downflow
  started. Mk4 observations reveal that the speed of the downflow in
  the early phase was substantially higher than the free-fall speed,
  implying a strong downward acceleration near the height at which
  the downflow started. <BR />Conclusions: The origin of the downflow
  was likely to have been magnetic reconnection taking place inside
  the erupting flux rope that led to its bifurcation. <P />Movies are
  available in electronic form at http://www.aanda.org

Title: The velocity structure of moving magnetic feature pairs around
sunspots: support for the U-loop model
Authors: Zhang, J.; Solanki, S. K.; Woch, J.; Wang, J.
Bibcode: 2007A&A...471.1035Z
Altcode: 2007arXiv0705.2507Z
  Context: Moving magnetic feature (MMF) pairs are among the most
  significant fine-scale structures around sunspots. Several models have
  been proposed to interpret the origin and evolution of MMF pairs. These
  models provide important clues to understanding MMF pairs. <BR />Aims:
  We present an analysis of the velocity structure of MMF pairs in
  order to put further constrains on the MMF models. <BR />Methods:
  Using continuum images, longitudinal magnetograms and Dopplergrams,
  recorded by the Michelson Doppler Imager (MDI) instrument on the
  Solar and Heliospheric Observatory (SOHO), we have traced 123 pairs
  of opposite magnetic polarity moving magnetic features (MMFs) in three
  active regions NOAA ARs 8375, 0330 and 9575. At the time of observation,
  AR 8375 was young, AR 0330 mature, and AR 9575 decaying. <BR />Results:
  The vertical velocity, measured from MDI Dopplergrams for the three
  active regions, indicates that the elements of MMF pairs with polarity
  opposite to that of the sunspot support a downflow (Doppler redshift)
  of around 50-100 m s<SUP>-1</SUP>. The average Doppler shift difference
  between negative and positive elements of an MMF pair is about 150 m
  s<SUP>-1</SUP> in AR 8375, 100 m s<SUP>-1</SUP> in AR 0330, and 20 m
  s<SUP>-1</SUP> in AR 9575. These observational results are in agreement
  with the model where MMF pairs are part of a U-loop emanating from the
  sunspot's magnetic canopy. According to this model, the downflow is
  caused by the Evershed flow returning below the solar surface. For AR
  8375, the horizontal velocity of MMFs ranges from 0.1 km s<SUP>-1</SUP>
  to 0.7 km s<SUP>-1</SUP>, and on average, the velocity of an MMF
  pair decreases significantly (from 0.6 km s<SUP>-1</SUP> to 0.35 km
  s<SUP>-1</SUP>) with increasing distance from the MMF's birth place. In
  contrast, the decrease of the average velocity is far less obvious
  from 0.5 km s<SUP>-1</SUP> to 0.4 km s<SUP>-1</SUP> with increasing
  distance from the sunspot. This result suggests that the change in
  MMF flow speed does not reflect the radial structure of the moat flow,
  but rather is intrinsic to the evolution of the MMF pairs. This result
  is also in agreement with the U-loop model of MMF pairs. We also find
  that properties of MMF pairs, most strikingly the lifetime, depend on
  the evolution stages of the parent sunspot. The mean lifetimes of MMF
  pairs in ARs 9575 and 0330 are 0.7 h and 1.6 h, respectively, which is
  considerably shorter than the 4 h lifetime previously found for AR 8375.

Title: Grand minima and maxima of solar activity: new observational
    constraints
Authors: Usoskin, I. G.; Solanki, S. K.; Kovaltsov, G. A.
Bibcode: 2007A&A...471..301U
Altcode: 2007arXiv0706.0385U
  Aims:Using a reconstruction of sunspot numbers stretching over
  multiple millennia, we analyze the statistics of the occurrence of
  grand minima and maxima and set new observational constraints on
  long-term solar and stellar dynamo models. <BR />Methods: We present
  an updated reconstruction of sunspot number over multiple millennia,
  from <SUP>14</SUP>C data by means of a physics-based model, using an
  updated model of the evolution of the solar open magnetic flux. A
  list of grand minima and maxima of solar activity is presented for
  the Holocene (since 9500 BC) and the statistics of both the length
  of individual events as well as the waiting time between them are
  analyzed. <BR />Results: The occurrence of grand minima/maxima is
  driven not by long-term cyclic variability, but by a stochastic/chaotic
  process. The waiting time distribution of the occurrence of grand
  minima/maxima deviates from an exponential distribution, implying that
  these events tend to cluster together with long event-free periods
  between the clusters. Two different types of grand minima are observed:
  short (30-90 years) minima of Maunder type and long (&gt;110 years)
  minima of Spörer type, implying that a deterministic behaviour of
  the dynamo during a grand minimum defines its length. The duration of
  grand maxima follows an exponential distribution, suggesting that the
  duration of a grand maximum is determined by a random process. <BR
  />Conclusions: These results set new observational constraints upon
  the long-term behaviour of the solar dynamo.

Title: Solar irradiance variability
Authors: Solanki, Sami K.
Bibcode: 2007HiA....14..279S
Altcode:
  We study solar irradiance variability. The current generation of models
  show that the irradiance since then has increased by between 0.9 and
  1.5 W m<SUP>-2</SUP>.

Title: Attenuation of Alfvén waves in straight and curved coronal
    slabs
Authors: Gruszecki, M.; Murawski, K.; Solanki, S. K.; Ofman, L.
Bibcode: 2007A&A...469.1117G
Altcode:
  Aims:We consider impulsively generated Alfvén waves in coronal loops
  to investigate the role of energy leakage on wave attenuation, which
  includes lateral leakage, leakage into dense photospheric regions and
  nonlinear driving of magnetosonic waves. <BR />Methods: A coronal loop
  is modelled either as a straight magnetic slab or as a curved slab
  of smooth mass density profiles. We perform numerical simulations of
  2.5D ideal magnetohydrodynamic equations to determine the signatures of
  Alfvén waves. <BR />Results: The numerical results show that lateral
  leakage of Alfvén waves is significant in comparison to leakage into
  the photospheric regions for realistic corona to photospheric density
  ratios. Energy leakage is enhanced by curvature of magnetic field lines
  and for large amplitude Alfvén waves for which nonlinear driving of
  magnetosonic waves is more significant than in the linear regime.

Title: Low-lying magnetic loops in the solar internetwork
Authors: Martínez González, M. J.; Collados, M.; Ruiz Cobo, B.;
   Solanki, S. K.
Bibcode: 2007A&A...469L..39M
Altcode: 2007arXiv0705.1319M
  Aims:We study the structure of the magnetic field vector in the
  internetwork and search for the presence of small-scale loops. <BR
  />Methods: We invert 1.56 μm spectropolarimetric observations of
  internetwork regions at disc centre by applying the SIR code. This
  allows us to recover the atmospheric parameters that play a role in
  the formation of these spectral lines. We are mainly interested in the
  structure of the magnetic field vector. <BR />Results: We find that
  many opposite polarity elements of the internetwork are connected by
  short (2-6´´), low-lying (photospheric) loops. These loops connect
  at least the 10-20% of the internetwork flux visible in our data. Also
  we have some evidence that points towards a dynamic scenario that can
  be produced by the emergence of internetwork magnetic flux.

Title: Modified p-modes in penumbral filaments?
Authors: Bloomfield, D. S.; Solanki, S. K.; Lagg, A.; Borrero, J. M.;
   Cally, P. S.
Bibcode: 2007A&A...469.1155B
Altcode: 2007arXiv0705.0481B
  Aims:The primary objective of this study is to search for and identify
  wave modes within a sunspot penumbra. <BR />Methods: Infrared
  spectropolarimetric time series data are inverted using a model
  comprising two atmospheric components in each spatial pixel. Fourier
  phase difference analysis is performed on the line-of-sight velocities
  retrieved from both components to determine time delays between the
  velocity signals. In addition, the vertical separation between the
  signals in the two components is calculated from the Stokes velocity
  response functions. <BR />Results: The inversion yields two atmospheric
  components, one permeated by a nearly horizontal magnetic field, the
  other with a less-inclined magnetic field. Time delays between the
  oscillations in the two components in the frequency range 2.5-4.5 mHz
  are combined with speeds of atmospheric wave modes to determine wave
  travel distances. These are compared to expected path lengths obtained
  from response functions of the observed spectral lines in the different
  atmospheric components. Fast-mode (i.e., modified p-mode) waves exhibit
  the best agreement with the observations when propagating toward the
  sunspot at an angle ~50° to the vertical.

Title: Stokes diagnostics of simulated solar magneto-convection
Authors: Shelyag, S.; Schüssler, M.; Solanki, S. K.; Vögler, A.
Bibcode: 2007A&A...469..731S
Altcode: 2007astro.ph..3490S
  We present results of synthetic spectro-polarimetric diagnostics of
  radiative MHD simulations of solar surface convection with magnetic
  fields. Stokes profiles of Zeeman-sensitive lines of neutral iron in
  the visible and infrared spectral ranges emerging from the simulated
  atmosphere have been calculated in order to study their relation to the
  relevant physical quantities and compare with observational results. We
  have analyzed the dependence of the Stokes-I line strength and width as
  well as of the Stokes-V signal and asymmetries on the magnetic field
  strength. Furthermore, we have evaluated the correspondence between
  the actual velocities in the simulation with values determined from
  the Stokes-I (Doppler shift of the centre of gravity) and Stokes-V
  profiles (zero-crossing shift). We confirm that the line weakening in
  strong magnetic fields results from a higher temperature (at equal
  optical depth) in the magnetic flux concentrations. We also confirm
  that considerable Stokes-V asymmetries originate in the peripheral
  parts of strong magnetic flux concentrations, where the line of sight
  cuts through the magnetopause of the expanding flux concentration into
  the surrounding convective donwflow.

Title: News and Views: Does the Sun affect the Earth's climate?
Authors: Priest, Eric; Lockwood, Mike; Solanki, Sami; Wolfendale,
   Arnold; Coustenis, A.
Bibcode: 2007A&G....48c...7P
Altcode: 2007A&G....48c...7C
  Svensmark's article in the February issue (A&amp;G 2007 48 1.18)
  presented a possible mechanism for the way the Sun could influence
  the Earth's climate. He suggested that water droplets condense in the
  ionization trail left by cosmic rays, whose flux varies inversely with
  solar activity: when the magnetic field of the solar wind is stronger,
  it shields the Earth from galactic cosmic rays and so decreases their
  flux on the Earth; according to Svensmark's ideas, this produces fewer
  clouds and thereby heats the Earth.

Title: Observations of Running Waves in a Sunspot Chromosphere
Authors: Bloomfield, D. S.; Lagg, A.; Solanki, S. K.
Bibcode: 2007ASPC..368..239B
Altcode: 2007astro.ph..2056B
  Spectropolarimetric time series data of the primary spot of active
  region NOAA 9448 were obtained in the Si I 10827 Å line and the He I
  10830 Å multiplet with the Tenerife Infrared Polarimeter. Throughout
  the time series the spectrograph slit was fixed over a region covering
  umbra, a light bridge, penumbra, and quiet sun. We present speeds
  of running penumbral waves in the chromosphere, their relation to
  both photospheric and chromospheric umbral oscillations, and their
  dependence on the magnetic field topology.

Title: Solar Cycle Variation of Chromospheric Radiation
Authors: Solanki, S. K.
Bibcode: 2007ASPC..368..481S
Altcode:
  Radiation emitted by the Sun's chromospheric gas displays a significant
  cyclic variation. The magnitude of this variability and the shape of
  the light curve differs from that exhibited by photospheric radiation,
  or total solar irradiance. The amplitude of the cyclic variation of
  chromospheric radiation is larger and less affected by the contribution
  of sunspots. Consequently, the influence of small-scale magnetic
  features forming plage and the network dominates. Here a brief
  introduction is given to the solar cycle variation of chromospheric
  radiation, its connection with the magnetic field, its quantitative
  modeling and related questions, such as the solar cycle variability
  of the quiet Sun chromosphere and its cause. Finally, some thoughts
  on the possible secular change of chromospheric (and total) irradiance
  are presented.

Title: Solar Activity and Irradiance Studies with Ca II
Spectroheliograms: Potential and Problems
Authors: Ermolli, I.; Tlatov, A.; Solanki, S. K.; Krivova, N. A.;
   Singh, J.
Bibcode: 2007ASPC..368..533E
Altcode:
  Various observatories around the globe carried out synoptic full-disk
  observations of the Sun since the beginning of the 20th century. The
  archives created by these observations, especially those including
  Ca II spectroheliograms, have the potential of providing far more
  detailed information on solar activity than the indices usually used to
  study activity variations, solar cycle and irradiance changes. However,
  these data suffer significantly from various problems including numerous
  defects in the photographic plates, missing or inaccurate calibration of
  the blackening curve, changes in the positioning of the exit slit with
  respect to the spectral line and variable seeing. Here we discuss the
  quality of images obtained by the digitization of three historic Ca II
  K time series, specifically those stored by the Arcetri, Kodaikanal
  and Mt Wilson Observatories. The aim of this work is to evaluate
  the potential value of these data for studies of solar activity and
  variability. It also shows the importance of the detailed and accurate
  image processing technique, in order to obtain uniform and trustable
  results from images coming from different historic archives.

Title: Tenerife Infrared Polarimeter II
Authors: Collados, M.; Lagg, A.; Díaz Garcí A, J. J.; Hernández
   Suárez, E.; López López, R.; Páez Mañá, E.; Solanki, S. K.
Bibcode: 2007ASPC..368..611C
Altcode:
  Since May 2005 the Tenerife Infrared Polarimeter II (TIP-II) has been
  operational at the Vacuum Tower Telescope on Tenerife. The core of the
  polarimeter is a 1024×1020 pixel infrared camera allowing for high
  precision measurements of the full Stokes vector with a pixel size of
  0.18 arcsec, corresponding to the diffraction limit of the telescope at
  1 μm. The polarimeter is able to reach a polarimetric accuracy of a few
  times 10<SUP>-4</SUP>, covering a wavelength range of 1 to 1.8 μm. With
  an upgrade in July 2006, the slit size has been increased to 77 arcsec
  allowing most active regions to be covered with a single scan. Here
  we present the technical details of the polarimeter and the camera. We
  also show some data illustrating the power of this new instrumentation.

Title: 2d Simulations Of Excitation And Damping Of Vertical Kink Waves
Authors: Selwa, Malgorzata; Murawski, K.; Solanki, S. K.; Ofman, L.
Bibcode: 2007AAS...210.9115S
Altcode: 2007BAAS...39S.206S
  We consider different kinds of excitation of fast vertical kink
  standing waves in a solar coronal loop that is embedded in a potential
  arcade. The two dimensional numerical model we implement includes the
  effects of field line curvature and nonlinearity on the excitation
  and damping of standing fast magnetosonic waves. We investigate the
  effects of a driven sinusodial pressure pulse and compare it with an
  impulsive excitation by a pressure pulse that impacts the overlaying
  loop. The results of the numerical simulations reveal wave signatures
  which are characteristic of vertical loop oscillations seen in recent
  TRACE observational data.

Title: Reconstruction of the Long-Term Irradiance Variations
Authors: Balmaceda, L.; Krivova, N.; Solanki, S.
Bibcode: 2007AGUSMGP54A..05B
Altcode:
  Solar irradiance variations have been recorded only since 1978. Clearly,
  there is a need to extend these records into the past in order to
  evaluate their possible influence on the Earth's climate. Here, a
  reconstruction of solar irradiance back to the Maunder minimum from
  the surface magnetic flux is presented. The reconstruction is based on
  a simple physical model that builds on the sunspot number records and
  sunspot areas where available. Since the sunspot area records generally
  consist of a compilation of data from multiple observatories, a proper
  cross-calibration is essential. The use of data of different sources
  directly combined can lead to errors in estimating the increase of
  solar irradiance during the past centuries. Thus, a brief description
  of the cross-calibration of sunspot areas is also presented.

Title: Reconstruction of solar total irradiance since 1700 from the
    surface magnetic flux
Authors: Krivova, N. A.; Balmaceda, L.; Solanki, S. K.
Bibcode: 2007A&A...467..335K
Altcode:
  Context: Total solar irradiance changes by about 0.1% between solar
  activity maximum and minimum. Accurate measurements of this quantity are
  only available since 1978 and do not provide information on longer-term
  secular trends. <BR />Aims: In order to reliably evaluate the Sun's
  role in recent global climate change, longer time series are, however,
  needed. They can only be assessed with the help of suitable models. <BR
  />Methods: The total solar irradiance is reconstructed from the end of
  the Maunder minimum to the present based on variations of the surface
  distribution of the solar magnetic field. The latter is calculated
  from the historical record of the sunspot number using a simple but
  consistent physical model. <BR />Results: Our model successfully
  reproduces three independent data sets: total solar irradiance
  measurements available since 1978, total photospheric magnetic
  flux since 1974 and the open magnetic flux since 1868 empirically
  reconstructed using the geomagnetic aa-index. The model predicts an
  increase in the solar total irradiance since the Maunder minimum of
  1.3^+0.2_-0.4 Wm<SUP>-2</SUP>.

Title: Full-Stokes Observations and Analysis of He I 10830 Å in a
    Flaring Region
Authors: Sasso, C.; Lagg, A.; Solanki, S. K.; Aznar Cuadrado, R.;
   Collados, M.
Bibcode: 2007ASPC..368..467S
Altcode:
  We present observations of the full Stokes vector in a flaring
  region, taken in the chromospheric He I 10830 Å multiplet. The data
  were recorded with the new Tenerife Infrared Polarimeter (TIP 2)
  at the German Vacuum Tower Telescope (VTT) during May 2005. The He
  profiles during the flare are extraordinary, showing extremely broad
  Stokes I absorption and very complex and spatially variable Stokes V
  signatures. We give first results on the line-of-sight velocities and
  the magnetic field vector values in the chromosphere for one observed
  Stokes profile by applying an inversion code to the He I lines.

Title: Magnetic Stereoscopy of Coronal Loops in NOAA 8891
Authors: Feng, L.; Wiegelmann, T.; Inhester, B.; Solanki, S.; Gan,
   W. Q.; Ruan, P.
Bibcode: 2007SoPh..241..235F
Altcode:
  The Solar TErrestrial RElations Observatory (STEREO) requires powerful
  tools for the three-dimensional (3D) reconstruction of the solar
  corona. Here we test such a program with data from SOHO and TRACE. By
  taking advantage of solar rotation, a newly developed stereoscopy tool
  for the reconstruction of coronal loops is applied to the solar active
  region NOAA 8891 observed from 1 March to 2 March 2000. The stereoscopic
  reconstruction is composed of three steps. First, we identify loop
  structures in two TRACE images observed from two vantage viewpoints
  approximately 17 degrees apart, which corresponds to observations
  made about 30 hours apart. In the second step, we extrapolate the
  magnetic field in the corona with the linear force-free field model
  from the photospheric line-of-sight SOHO/MDI data. Finally, combining
  the extrapolated field lines and one-dimensional loop curves from two
  different viewpoints, we obtain the 3D loop structures with the magnetic
  stereoscopy tool. We demonstrate that by including the magnetic modeling
  this tool is more powerful than pure geometrical stereoscopy, especially
  in resolving the ambiguities generated by classical stereoscopy. This
  work will be applied to the STEREO mission in the near future.

Title: Properties of sunspots in cycle 23. I. Dependence of brightness
    on sunspot size and cycle phase
Authors: Mathew, S. K.; Martínez Pillet, V.; Solanki, S. K.; Krivova,
   N. A.
Bibcode: 2007A&A...465..291M
Altcode: 2007astro.ph..1401M
  Aims:In this paper we investigate the dependence of umbral core
  brightness, as well as the mean umbral and penumbral brightness on the
  phase of the solar cycle and on the size of the sunspot. <BR />Methods:
  Albregtsen &amp; Maltby (1978, Nature, 274, 41) reported an increase
  in umbral core brightness from the early to the late phase of solar
  cycle from the analysis of 13 sunspots which cover solar cycles 20
  and 21. Here we revisit this topic by analysing continuum images
  of more than 160 sunspots observed by the MDI instrument on board
  the SOHO spacecraft for the period between 1998 March to 2004 March,
  i.e. a sizable part of solar cycle 23. The advantage of this data set
  is its homogeneity, with no seeing fluctuations. A careful stray light
  correction, which is validated using the Mercury transit of 7th May,
  2003, is carried out before the umbral and penumbral intensities are
  determined. The influence of the Zeeman splitting of the nearby Ni I
  spectral line on the measured "continuum" intensity is also taken into
  account. <BR />Results: We did not observe any significant variation
  in umbral core, mean umbral and mean penumbral intensities with solar
  cycle, which is in contrast to earlier findings for the umbral core
  intensity. We do find a strong and clear dependence of the umbral
  brightness on sunspot size, however. The penumbral brightness also
  displays a weak dependence. The brightness-radius relationship has
  numerous implications, some of which, such as those for the energy
  transport in umbrae, are pointed out.

Title: Properties of Solar Polar Coronal Plumes Constrained by
    Ultraviolet Coronagraph Spectrometer Data
Authors: Raouafi, N. -E.; Harvey, J. W.; Solanki, S. K.
Bibcode: 2007ApJ...658..643R
Altcode: 2007astro.ph..3745R
  We investigate the plasma dynamics (outflow speed and turbulence)
  inside polar plumes. We compare line profiles (mainly of O VI) observed
  by the Ultraviolet Coronagraph Spectrometer (UVCS) instrument on
  SOHO at the minimum of solar cycle 22-23 with model calculations. We
  consider Maxwellian velocity distributions with different widths in
  plume and interplume regions. Electron densities are assumed to be
  enhanced in plumes and to approach interplume values with increasing
  height. Different combinations of the outflow and turbulence velocity
  in the plume regions are considered. We compute line profiles and total
  intensities of the H I Lyα and the O VI doublets. The observed profile
  shapes and intensities are reproduced best by a small solar wind speed
  at low altitudes in plumes that increases with height to reach ambient
  interplume values above roughly 3-4 R<SUB>solar</SUB>, combined with
  a similar variation of the width of the velocity distribution of the
  scattering atoms/ions. We also find that plumes very close to the
  pole give narrow profiles at heights above 2.5 R<SUB>solar</SUB>,
  which are not observed. This suggests a tendency for plumes to be
  located away from the pole. We find that the inclusion of plumes in
  the model computations provides an improved correspondence with the
  observations and confirms previous results showing that published UVCS
  observations in polar coronal holes can be roughly reproduced without
  the need for large temperature anisotropy. The latitude distributions
  of plumes and magnetic flux distributions are studied by analyzing
  data from different instruments on SOHO and with SOLIS.

Title: Magnetic flux transport on active cool stars and starspot
    lifetimes
Authors: Işik, E.; Schüssler, M.; Solanki, S. K.
Bibcode: 2007A&A...464.1049I
Altcode: 2006astro.ph.12399I
  Context: Many rapidly rotating cool stars show signatures of large
  magnetic regions at all latitudes. Mid-latitude starspots and magnetic
  regions have characteristic lifetimes of 1 month or less, as indicated
  by observations using (Zeeman-) Doppler imaging techniques. <BR
  />Aims: We aim to estimate the lifetimes of bipolar magnetic regions
  and starspots on the surfaces of cool stars. We consider different
  possible configurations for starspots and compare their flux variations
  and lifetimes based on a magnetic flux transport model. <BR />Methods:
  We carry out numerical simulations of the surface evolution of bipolar
  magnetic regions (BMRs) and magnetic spots on stars, which have radii
  and surface rotational shears of <ASTROBJ>AB Doradus</ASTROBJ>, the Sun,
  and the <ASTROBJ>HR 1099</ASTROBJ> primary. The surface flux transport
  model is based on the magnetic induction equation for radial fields
  under the effects of surface differential rotation, meridional flow,
  and turbulent diffusion due to convective flow patterns. We calculate
  the flux evolution and the lifetimes of BMRs and unipolar starspots,
  varying the emergence latitude, surface shear rate, and tilt angle. <BR
  />Results: For BMRs comparable to the largest observed on the Sun, we
  find that varying the surface flows and the tilt angle modifies the
  lifetimes over a range of one month. For very large BMRs (area ~10%
  of the stellar surface) the assumption of a tilt angle increasing with
  latitude leads to a significant increase of lifetime, as compared to
  the case without tilt. Such regions can evolve to polar spots that live
  more than a year. Adopting the observed weak latitudinal shear and the
  radius of the active subgiant component of HR 1099, we find longer
  BMR lifetimes as compared to the more strongly sheared <ASTROBJ>AB
  Dor</ASTROBJ> case. Random emergence of six additional tilted bipoles
  in an activity belt at 60° latitude enhanced the lifetimes of polar
  caps up to 7 years. We have also compared the evolution and lifetime
  of monolithic starspots with those of conglomerates of smaller spots
  of similar total area. We find similar decay patterns and lifetimes
  for both configurations.

Title: Energy leakage as an attenuation mechanism for vertical kink
    oscillations in solar coronal wave guides
Authors: Selwa, M.; Murawski, K.; Solanki, S. K.; Wang, T. J.
Bibcode: 2007A&A...462.1127S
Altcode:
  Aims:We study wave leakage as a possible attenuation mechanism of
  coronal loop oscillations in the ideal MHD regime. <BR />Methods:
  We consider impulsively generated oscillations in solar coronal
  magnetic wave guides such as a straight slab and a curved arcade
  loop. The two-dimensional numerical model we implement includes the
  effects of nonlinearity and line curvature on attenuation of fast
  magnetosonic kink waves. <BR />Results: We show that these waves
  are more strongly attenuated in the arcade loop than in the slab and
  provide evidence that the curvature of magnetic field lines results in
  excess energy leakage. For parameters appropriate for a coronal loop
  the kink oscillation is too efficiently attenuated by energy leakage,
  suggesting that in the solar atmosphere wave leakage must be reduced
  compared to our simulations. We conclude that energy leakage is an
  efficient source of attenuation of coronal loop oscillations.

Title: The fraction of DA white dwarfs with kilo-Gauss magnetic fields
Authors: Jordan, S.; Aznar Cuadrado, R.; Napiwotzki, R.; Schmid,
   H. M.; Solanki, S. K.
Bibcode: 2007A&A...462.1097J
Altcode: 2006astro.ph.10875J
  Context: Weak magnetic fields have been searched for on only a small
  number of white dwarfs. Current estimates find that about 10% of all
  white dwarfs have fields in excess of 1 MG; according to previous
  studies this number increases up to about 25% in the kG regime. <BR
  />Aims: Our aim is to improve on these statistics by a new sample
  of ten white dwarfs in order to determine the ratio of magnetic to
  field-free white dwarfs. <BR />Methods: Mean longitudinal magnetic
  fields strengths were determined by means of high-precision circular
  polarimetry of Hβ and Hγ with the FORS1 spectrograph of the VLT
  "Kueyen" 8 m telescope. <BR />Results: In one of our objects (LTT
  7987), we detected a statistically significant (97% confidence level)
  longitudinal magnetic field varying between (-1± 0.5) kG and (+1±
  0.5) kG. This would be the weakest magnetic field ever found in a
  white dwarf, but systematic errors cannot completely be ruled out at
  this level of accuracy. We also observed the sdO star EC 11481-2303 but
  could not detect a magnetic field. <BR />Conclusions: . VLT observations
  with uncertainties typically of 1000 G or less suggest that 15-20% of
  WDs have kG fields. Together with previous investigations, the fraction
  of kG magnetic fields in white dwarfs amounts to about 11-15%, which is
  close to the current estimations for highly magnetic white dwarfs (&gt;1
  MG). <P />Based on observations made with ESO Telescopes at the La Silla
  or Paranal Observatories under programme ID 073.D-0356. Figures A.1
  and A.2 are only available in electronic form at http://www.aanda.org

Title: Supersonic downflows in the vicinity of a growing
    pore. Evidence of unresolved magnetic fine structure at chromospheric
    heights
Authors: Lagg, A.; Woch, J.; Solanki, S. K.; Krupp, N.
Bibcode: 2007A&A...462.1147L
Altcode:
  Aims:The velocity and magnetic fine structure of the chromosphere at
  the leg of an emerging magnetic loop is investigated at a location
  of supersonic downflows. <BR />Methods: We analyze a time series of
  spectropolarimetric data in the He i 1083 nm triplet covering a time
  interval of ≈70 min. The temporal evolution as well as the topology
  of the magnetic field in the downflow region are investigated. We
  apply an inversion technique based on a genetic algorithm using the
  Milne-Eddington approach. The technique is very reliable and robust in
  retrieving maps of the velocity and the magnetic field vector for both
  atmospheric components separately. <BR />Results: We observe redshifts
  corresponding to a downflow speed of up to 40 km s<SUP>-1</SUP> in the
  vicinity of a growing pore. These supersonic downflows always coexist
  with a second atmospheric component almost at rest (slow component)
  within the same resolution element. The redshifted component is more
  inclined to the solar normal than the slow component and has a different
  field strength. <BR />Conclusions: .We interpret this downflow as a
  consequence of the draining of the rising loops. The different magnetic
  field orientation of the redshifted and the slow component give rise to
  two possible interpretations: an uncombed structure of the chromosphere,
  similar to the differently inclined flux-tubes in the penumbra of
  a sunspot, or a cloud-like structure containing gas at different
  velocities in two separate height layers of the solar atmosphere.

Title: T he Lower Transition Region As Seen In The H I Lyman-α Line
Authors: Teriaca, L.; Schühle, U.; Solanki, S. K.; Curdt, W.;
   Marsch, E.
Bibcode: 2007ESASP.641E..84T
Altcode:
  The SUMER spectrometer aboard SOHO has been used to acquire several
  raster images and temporal series of quiet-Sun targets at both disk
  centre and the limb. Spectra have been recorded simultaneously in the
  H I Lyman α and the Si III 120.6 nm line. Both spatial and temporal
  maps of the integrated radiances appear very similar in the two lines,
  despite the huge difference in optical thickness, a result showing the
  H I Lyman α to be a good diagnostic of the dynamics and morphology of
  the lower transition region. Oscillations can be detected and studied
  at all observed locations. At disk centre, the 3 minute oscillations are
  sporadically observed in the inter-network but also at locations at the
  edges of network lanes, while 5 minute oscillations clearly dominate
  the network. At the limb, evidence of 3 to 5 minute oscillations is
  found at the base of spicules. Moreover, H I Lyman α spectra shows a
  high degree of variability, revealing also the signature of explosive
  events. The combination of high spectral purity images and slit spectra
  in the H I Lyman α line would therefore be an exceptional new tool
  to investigate the nature of the solar transition region. This line
  is therefore of interest for both, a high resolution channel in the
  EUI instrument and for the EUS spectrometer.

Title: T he Lower Transitio n Region As Seen In The H I Lyman-α Line.
Authors: Teriaca, L.; Schühle, U.; Solanki, S. K.; Curdt, W.;
   Marsch, E.
Bibcode: 2007ESASP.641E..36T
Altcode:
  The SUMER spectrometer aboard SOHO has been used to acquire several
  raster images and temporal series of quiet-Sun targets at both disk
  centre and the limb. Spectra have been recorded simultaneously in the
  H I Lyman α and the Si III 120.6 nm line. Both spatial and temporal
  maps of the integrated radiances appear very similar in the two lines,
  despite the huge difference in optical thickness, a result showing the
  H I Lyman α to be a good diagnostic of the dynamics and morphology of
  the lower transition region. Oscillations can be detected and studied
  at all observed locations. At disk centre, the 3 minute oscillations are
  sporadically observed in the inter-network but also at locations at the
  edges of network lanes, while 5 minute oscillations clearly dominate
  the network. At the limb, evidence of 3 to 5 minute oscillations is
  found at the base of spicules. Moreover, H I Lyman α spectra shows a
  high degree of variability, revealing also the signature of explosive
  events. The combination of high spectral purity images and slit spectra
  in the H I Lyman α line would therefore be an exceptional new tool
  to investigate the nature of the solar transition region. This line
  is therefore of interest for both, a high resolution channel in the
  EUI instrument and for the EUS spectrometer.

Title: SUNRISE: High resolution UV/VIS observations of the Sun from
    the stratosphere
Authors: Gandorfer, A. M.; Solanki, S. K.; Barthol, P.; Martínez
   Pillet, V.; Schmidt, W.; Title, A. M.; Knölker, M.
Bibcode: 2007msfa.conf...69G
Altcode:
  SUNRISE is an international project for the development, construction,
  and operation of a balloon-borne solar telescope with an aperture
  of 1 m, working in the UV/VIS spectral domain. The main scientific
  goal of SUNRISE is to understand the structure and dynamics of the
  magnetic field in the atmosphere of the Sun. SUNRISE will provide
  near diffraction-limited images of the photosphere and chromosphere
  with an unpredecented resolution down to 35 km on the solar surface at
  wavelengths around 220 nm. The focal-plane instrumentation consists of a
  polarization sensitive spectrograph, a Fabry-Perot filter magnetograph,
  and a phase-diverse filter imager working in the near UV. The first
  stratospheric long-duration balloon flight of SUNRISE is planned in
  summer 2009 from the Swedish ESRANGE station. SUNRISE is a joint project
  of the German Max-Planck-Institut für Sonnensystemforschung (MPS),
  Katlenburg-Lindau, with the Kiepenheuer-Institut für Sonnenphysik
  (KIS), Freiburg, Germany, the High-Altitude Observatory (HAO), Boulder,
  USA, the Lockheed-Martin Solar and Astrophysics Lab. (LMSAL), Palo
  Alto, USA, and the Spanish IMaX consortium. In this paper we will
  present a brief description of the scientific and technological aspects
  of SUNRISE.

Title: Magnetic source of the solar cycle variation of the Mn I
    539.4 nm line
Authors: Danilović, S.; Solanki, S. K.; Livingston, W.; Krivova,
   N.; Vince, I.
Bibcode: 2007msfa.conf..189D
Altcode:
  As a part of the long term program at KPNO, the Mn I 539.4 nm line has
  been observed for nearly three solar cycles using the McMath telescope
  and the 13.5 m spectrograph in double pass mode. These full-disk
  spectrophotometric observations revealed an unusually large amplitude
  change of its parameters over the solar cycle and its correlation with
  Ca II K intensity. One of the proposed explanations for this phenomenon
  is the optical pumping by the Mg II k line. With this work we would like
  to show that this may not be the main mechanism behind the change. We
  reconstructed the changes of the line parameters using a model that
  takes into account only changes of the daily surface distributions of
  magnetic field. This model has already been used to successfully model
  total solar irradiance. We now apply it for modelling the Mn I line,
  as well as its neighboring Fe I line using exactly the same value
  of the free parameter as used for the reconstruction of total solar
  irradiance. We reproduce well the Mn I and Fe I line changes over the
  cycle purely with LTE modelling. This indicates that optical pumping
  of the Mn I line by Mg II k is not the main cause of its solar cycle
  change and sets an independent constraint on solar irradiance models.

Title: Structure and evolution of supergranulation from local
    helioseismology
Authors: Hirzberger, J.; Gizon, L.; Solanki, S. K.; Duvall, T. L.
Bibcode: 2007msfa.conf..103H
Altcode:
  Maps of the horizontal divergence of the near-surface velocity field
  have been calculated using local helioseismology and SOHO/MDI full-disk
  Dopplergrams. These maps provide a continuous coverage for two to
  three months each year with a cadence of 12 hours. Geometrical and
  evolutional properties of individual supergranular cells have been
  studied. Supergranular cells have sizes in a range around 650Mm2
  (circular diameter of 28.77 Mm) with lifetimes of up to 4.5 days. We
  also observe a clear trend for larger cells to have stronger divergence
  values and larger lifetimes than smaller ones.

Title: EUI, The Ultraviolet Imaging Telescopes Of Solar Orbiter
Authors: Hochedez, J. -F.; Appourchaux, T.; Defise, J. -M.; Harra,
   L. K.; Schühle, U.; Auchère, F.; Curdt, W.; Hancock, B.; Kretzschmar,
   M.; Lawrence, G.; Leclec'h, J. -C.; Marsch, E.; Mercier, R.; Parenti,
   S.; Podladchikova, E.; Ravet, M. -F.; Rochus, P.; Rodriguez, L.;
   Rouesnel, F.; Solanki, S.; Teriaca, L.; Van Driel, L.; Vial, J. -C.;
   Winter, B.; Zhukov, A.
Bibcode: 2007ESASP.641E..33H
Altcode:
  The scientific objectives of Solar Orbiter rely ubiquitously on EUI,
  its suite of solar atmosphere imaging telescopes. In the configuration
  discussed here, EUI includes three co-aligned High Resolution Imagers
  (HRI) and one Full Sun Imager (FSI). FSI and two HRIs observe in extreme
  ultraviolet passbands, dominated by coronal emission. Another HRI is
  designed for the hydrogen Lyman α radiation in the far UV, imaging the
  Chromosphere and the lower Transition Region. The current EUI design
  and some of its development challenges are highlighted. EUI profits from
  co-rotation phases, solar proximity and departure from the ecliptic. In
  synergy with the other S.O. payload, EUI probes the dynamics of the
  solar atmosphere, provides context data for all investigations and helps
  to link in-situ and remote-sensing observations. In short, it serves all
  four top-level goals of the mission. For these reasons, the EUI suite
  is keenly anticipated in the European scientific community and beyond.

Title: Nanoflare model of emission line radiance distributions in
    active region coronae
Authors: Safari, H.; Innes, D. E.; Solanki, S. K.; Pauluhn, A.
Bibcode: 2007msfa.conf..359S
Altcode:
  Nanoflares are small impulsive bursts of energy that blend with and
  possibly make up much of the solar background emission. Determining
  their overall contribution is central to understanding the heating of
  the solar corona. Here, a simple nanoflare model based on three key
  parameters: the flare rate, the flare damping time, and the power-law
  slope of the flare energy frequency distribution has been used to
  simulate emission line radiances observed by SUMER in the corona
  above an active region. The three lines analysed, Fe XIX, Ca XIII,
  and Si III have very different formation temperatures, damping times
  and flare rates but all suggest a power-law slope greater than 2. Thus
  it is possible that nanoflares provide a significant fraction of the
  flare energy input to active region coronae.

Title: A nanoflare model of quiet Sun EUV emission
Authors: Pauluhn, A.; Solanki, S. K.
Bibcode: 2007A&A...462..311P
Altcode: 2006astro.ph.12585P
  Nanoflares have been proposed as the main source of heating of the
  solar corona. However, detecting them directly has so far proved
  elusive, and extrapolating to them from the properties of larger
  brightenings gives unreliable estimates of the power-law exponent
  α characterising their distribution. Here we take the approach of
  statistically modelling light curves representative of the quiet Sun
  as seen in EUV radiation. The basic assumption is that all quiet-Sun
  EUV emission is due to micro- and nanoflares, whose radiative energies
  display a power-law distribution. Radiance values in the quiet Sun
  follow a lognormal distribution. This is irrespective of whether the
  distribution is made over a spatial scan or over a time series. We show
  that these distributions can be reproduced by our simple model. By
  simultaneously fitting the radiance distribution function and the
  power spectrum obtained from the light curves emitted by transition
  region and coronal lines the power-law distribution of micro- and
  nanoflare brightenings is constrained. A good statistical match to the
  measurements is obtained for a steep power-law distribution of nanoflare
  energies, with power-law exponent α&gt; 2. This is consistent with
  the dominant heat input to the corona being provided by nanoflares,
  i.e., by events with energies around 10<SUP>23</SUP> erg. In order to
  reproduce the observed SUMER time series approximately 10<SUP>3</SUP>
  to 10<SUP>4</SUP> nanoflares are needed per second throughout the
  atmosphere of the quiet Sun (assuming the nanoflares to cover an
  average area of 10<SUP>13</SUP> m<SUP>2</SUP>).

Title: Reconstruction of solar irradiance using the Group sunspot
    number
Authors: Balmaceda, L.; Krivova, N. A.; Solanki, S. K.
Bibcode: 2007AdSpR..40..986B
Altcode: 2007astro.ph..3147B
  We present a reconstruction of total solar irradiance since 1610 to
  the present based on variations of the surface distribution of the
  solar magnetic field. The latter is calculated from the historical
  record of the Group sunspot number using a simple but consistent
  physical model. Our model successfully reproduces three independent
  data sets: total solar irradiance measurements available since 1978,
  total photospheric magnetic flux from 1974 and the open magnetic
  flux since 1868 (as empirically reconstructed from the geomagnetic
  aa-index). The model predicts an increase in the total solar irradiance
  since the Maunder Minimum of about 1.3 Wm <SUP>-2</SUP>.

Title: T he Performance Of The SOLO-VIM Instrument: Effects Of
    Instrumental Noise And Lossy Data Compression
Authors: Lagg, A.; Yelles, L.; Hirzberger, J.; Woch, J.; Solanki, S. K.
Bibcode: 2007ESASP.641E..69L
Altcode:
  Spectropolarimetric observations in photospheric lines reveal a
  wealth of information on physical parameters of the solar atmosphere
  like magnetic field strength and di rection or the line-of sight
  velocity. These observations require the measurement of the four Stokes
  parameters at a sample of N wavelength positions around the core of the
  spectral line, resulting in 4N images for one observation. The Visible
  light Imager and Magnetograph (VIM) instrument on board Solar Orbiter
  is capable of performing these measurements. However, the data rate
  required to transfer all 4N images with the required cadence is well
  beyond the telemetry limit. Here we use realistic, three-dimensional
  MHD simulations in order to simulate science data provided by VIM which
  are then used to test various compression techniques. We conclude that
  lossy data compression and instrumental noise have similar effects on
  the output data.

Title: S imulations Of Science Data Of The Solo-VIM Instrument
Authors: Yelles, L.; Hirzberger, J.; Lagg, A.; Woch, J.; Solanki,
   S. K.; Vögler, A.
Bibcode: 2007ESASP.641E..34Y
Altcode:
  The SolO-VIM instrument will be a two-dimensional full-Stokes
  spectro-polarimeter which will provide diffraction-limited
  vector-magnetograms, Dopplergrams, and continuum images of the solar
  photosphere. The instrument's performance depends on various parameters
  such as aperture diameter, filter characteristics, spectral- line
  sampling, and orbital position. Here we compute Stokes profiles in
  realistic 3D MHD simulations. These synthetic data are then degraded to
  match the output ex- pected from the VIM instrument, and subsequently
  inverted using a Milne-Eddington atmosphere. We present parameter
  studies in order to set up minimum require- ments on limitations of
  VIM's capabilities.

Title: Velocity distribution of chromospheric downflows
Authors: Aznar Cuadrado, R.; Solanki, S. K.; Lagg, A.
Bibcode: 2007msfa.conf..173A
Altcode:
  Infrared spectropolarimetric observations were obtained with the
  Tenerife Infrared Polarimeter (TIP) at the German Vacuum Tower
  Telescope (VTT) of the Spanish observatory of Izana, Tenerife. We
  present the velocity distributions of a large dataset composed of
  maps of the Stokes I, Q, U, and V profiles of active and quiet sun
  regions obtained in the chromospheric He I 1083.0 nm triplet. The
  line-of-sight velocities were determined by applying a multi-Gaussian
  fit to the intensity profiles. Single and double component fits were
  carried out for all datasets. We find that 18.7% of all observed
  pixels show strong downflows as evidenced by a second line profile
  component, generally shifted by more than 8 km s-1 relative to the rest
  wavelegth. The distribution of these strong down-flows displays two
  distinct populations. The slower one (near sonic and weakly supersonic
  flows) has line-of-sight velocities up to 17 km s-1 and is associated
  with moderate to strong magnetic signal (up to √(Q2 + U2 + V2)/Ic =
  0.08). Strongly supersonic downflows (reaching up to 60 km s-1) are
  found at places with weak to moderate magnetic signal, with √(Q2 +
  U2 + V2)/Ic values mainly between 0.01 and 0.03.

Title: Spectropolarimetry in the chromospheric He I 1083.0 nm
    multiplet
Authors: Sasso, C.; Lagg, A.; Solanki, S. K.
Bibcode: 2007waas.work...43S
Altcode:
  Spectropolarimetry in the He I 1083.0 nm multiplet has a great
  potential to obtain information on the magnetic field in the solar
  upper chromosphere. We apply an inversion technique to infrared
  spectropolarimetric observations, to retrieve the full magnetic vector
  and the line-of sight velocity. The observations, obtained with the
  Tenerife Infrared Polarimeter (TIP) II at the German Vacuum Tower
  Telescope (VTT), provide maps in the Stokes parameters I, Q, U and V.

Title: A comparative study of the contrast of solar magnetic elements
    in CN and CH
Authors: Zakharov, V.; Gandorfer, A.; Solanki, S. K.; Löfdahl, M.
Bibcode: 2007A&A...461..695Z
Altcode:
  No abstract at ADS

Title: Magnetic flux transport and the lifetimes of spots on active
    cool stars
Authors: Işik, E.; Schüssler, M.; Solanki, S. K.
Bibcode: 2007msfa.conf..367I
Altcode:
  We present results of numerical simulations of magnetic flux transport
  on the surfaces of cool stars with radii of 1 Rm and 3.3 Rm. The
  effects of differential rotation and the tilt angle on the lifetimes
  of stellar bipolar magnetic regions are discussed. The existence of
  long-lasting polar spots can be explained by high-latitude persistent
  emergence of bipolar regions.

Title: High-resolution CN spectroscopy of small-scale solar magnetic
    features
Authors: Zakharov, V. V.; Gandorfer, A.; Solanki, S. K.
Bibcode: 2007msfa.conf..161Z
Altcode:
  High-resolution spectroscopic observations of small-scale magnetic
  elements in the solar photosphere were carried out in the spectral
  region 387.5388.4 nm with the 1-m Swedish Solar Telescope (SST). This
  part of the spectrum covers not only the violet CN band-head, but also
  contains some lines of the CH molecule. The analysis of the line-core
  intensity contrasts of the CN and CH lines in bright points (BPs)
  yielded that on average the BPs appear brighter, thus providing a higher
  rms contrast, in the CN than in the CH lines in the same spectral band.

Title: Wavelet-based method for coronal loop oscillations analysis
Authors: Tothova, D.; Innes, D. E.; Solanki, S. K.
Bibcode: 2007msfa.conf..265T
Altcode:
  We study the properties of Doppler shift oscillations observed
  in hot coronal loops by SoHO/SUMER. These oscillations have been
  identified as magnetoacoustic slow mode standing waves and may be an
  important magnetic field diagnostic for the oscillating loops. Visual
  inspection of the SUMER data suggests that one in three microflares
  trigger oscillation. So for an average active region we can expect
  several oscillation events per hour. To study the statistics of
  the oscillations, automatic identification and classification of
  the events is required. We have performed a Wavelet analysis on a 12
  hour time series of SUMER Fe XIX data and find that almost all of the
  oscillation events in the data set are identified by this technique,
  with very few false positives. The method is expected to be useful
  for the analysis of future Ca XVII and Fe XXIV spectra of microflares
  observed with HINODE/EIS.

Title: Modified p-modes in penumbral filaments
Authors: Bloomfield, D. S.; Lagg, A.; Solanki, S. K.; Borrero, J. M.
Bibcode: 2007msfa.conf..241B
Altcode:
  A time series analysis was performed on velocity signals in a sunspot
  penumbra to search for possible wave modes. The spectropolarimetric
  photospheric data obtained by the Tenerife Infrared Polarimeter were
  inverted using the SPINOR code. An atmospheric model comprising two
  magnetic components and one stray-light component gave an optimal fit
  to the data. Fourier phase difference analysis between line-of-sight
  velocities of both magnetic components provided time delays between
  the two atmospheres. These delays were combined with the speeds of
  atmospheric wave modes and compared to height separations derived from
  velocity response functions to determine the wave mode.

Title: Nonlinear Force-Free Magnetic Field Modelling For VIM On SO
Authors: Wiegelmann, T.; Solanki, S. K.; Yelles, L.; Lagg, A.
Bibcode: 2007ESASP.641E..19W
Altcode:
  The aim of this work is to investigate how photon noise and errors
  in the retrieval of solar magnetic parameters from measured Stokes
  profiles influences the extrapolartion of nonlinear force-free
  coronal magnetic fields from photospheric vector magnetograms. To
  do so we use a nonlinear force-free extrapolation code based on an
  optimization principle. The extrapolation methods has been extensively
  tested and applied to data from various telescopes. Here we apply the
  code artificial vector magnetograms obtained from 3-D radiation-MHD
  simulations. As a reference case we compute the coronal magnetic field
  from an ideal magnetogram and compare the result with more realistic
  magnetograms based on simulated Solar Orbiter/VIM-measurements. We
  investigate the effect of noise, ambiguities, spatial resolution,
  inversion mechanism, of Stokes profiles etc. We rate the quality of
  the reconstructed coronal magnetic field qualitatively by magnetic
  field line plots and quantitatively by a number of comparison metrices,
  e.g., the vector correlation with the exact solution and how accurate
  the free magnetic energy is computed. Not surprisingly, the instrument
  effects and noise influence the quality of the nonlinear force-free
  coronal magnetic field model. The extrapolations from realistic vector
  magnetograms show a reasonable agreement with the ideal reconstruction,
  however, and are in particular significantly better than extrapolations
  based on line-of-sight magnetograms only. High quality VIM data
  will thus allow reasonably accurate extrapolations that can serve
  as the basis for magnetic coupling science through a comparison with
  observations from EUS and EUI.

Title: S pace Qualification Of A Thin Wafer Lithium Niobate Etalon
    For The Visible Light Imager And Magnetograph (Vim)
Authors: Schühle, U.; Mathew, S. K.; Wedemeier, M.; Hartwig, H.;
   Ballesteros, E.; Martinez Pillet, V.; Solanki, S. K.
Bibcode: 2007ESASP.641E..82S
Altcode:
  For the Visible Light Imager and Magnetograph (VIM) a high-resolution
  filtergraph is under design. The system takes advantage of a lithium
  niobate (LiNbO3) crystal which can be used as a scanning filter using
  high voltage for tuning. We have undertaken first studies to qualify
  a lithium niobate wafer of 70 mm aperture size for deployment and use
  in space. We show the results of the mechanical mounting and vibration
  and thermal cycling tests as well as stability tests under fast voltage
  tuning in vacuum. Although these tests have all been very successful,
  further environmental testing is necessary to fully space-qualify the
  filter for the Solar Orbiter mission.

Title: Spectro-Polarimetry of a Sunspot in Atomic and Molecular
    Lines with THEMIS
Authors: Arnaud, J.; Berdyugina, S. V.; Fluri, D. M.; Afram, N.;
   Solanki, S. K.; Raouafi, N. -E.
Bibcode: 2006ASPC..358..319A
Altcode:
  We present spectro-polarimetric observations of a sunspot, which were
  recorded simultaneously with THEMIS in various atomic and molecular
  lines. These observations include the first full Stokes measurements
  of the band-head of TiO around 7055 Å.

Title: Molecular Diagnostics of the Internal Structure of Starspots
    and Sunspots
Authors: Afram, N.; Berdyugina, S. V.; Fluri, D. M.; Solanki, S. K.;
   Lagg, A.; Petit, P.; Arnaud, J.
Bibcode: 2006ASPC..358..375A
Altcode:
  We have analyzed the usefulness of molecules as a diagnostic tool for
  studying solar and stellar magnetism with the molecular Zeeman and
  Paschen-Back effects. In the first part we concentrate on molecules
  that are observed in sunspots such as MgH and TiO. We present calculated
  molecular line profiles obtained by assuming magnetic fields of 2-3 kG
  and compare these synthetic Stokes profiles with spectro-polarimetric
  observations in sunspots. The good agreement between the theory and
  observations allows us to turn our attention in the second part to
  starspots to gain insight into their internal structure. We investigate
  the temperature range in which the selected molecules can serve as
  indicators for magnetic fields on highly active cool stars and compare
  synthetic Stokes profiles with our recent observations.

Title: The Molecular Paschen-Back Effect
Authors: Berdyugina, S. V.; Fluri, D. M.; Solanki, S. K.
Bibcode: 2006ASPC..358..329B
Altcode:
  The molecular Paschen-Back effect (PBE) lacks a detailed description
  since the problem was first addressed by Hill in 1929. However,
  many diatomic molecules exhibit the PBE at field strengths typical of
  sunspots and active cool stars. Recently we have presented a complete
  theoretical description of the molecular PBE in Hund's cases (a), (b),
  and all intermediate cases. This description allows us to compute the
  splitting of levels of any multiplicity and the transitions between
  them. We find that in the partial PBE regime strongly asymmetric
  Stokes profiles are produced, whose strengths and asymmetries depend
  sensitively on the magnetic field. Also, the strength of the forbidden
  and satellite transitions increases rapidly with field strength,
  while the strength of the main branch transitions decreases. These
  signatures hold promise to form the basis of new diagnostics of solar
  and stellar magnetic fields.

Title: Measuring the Magnetic Vector with the He I 10830 Å Line:
    A Rich New World
Authors: Solanki, S. K.; Lagg, A.; Aznar Cuadrado, R.; Orozco Suárez,
   D.; Collados, M.; Wiegelmann, T.; Woch, J.; Sasso, C.; Krupp, N.
Bibcode: 2006ASPC..358..431S
Altcode:
  The triplet of the He I transitions around 10830 Å not only shows a
  rich variety of Stokes profiles, but also allows the full magnetic
  vector in the upper chromosphere to be probed, thus revealing
  the magnetic structure of loops, current sheets, finely structured
  supersonic downflows, the chromospheric layers of sunspots (supporting
  the presence of uncombed fields in the penumbra), flares, and the
  quiet Sun. A very brief overview of some of the observations and
  results obtained so far is given.

Title: Reconstruction of solar irradiance variations in cycles 21-23
    based on surface magnetic fields
Authors: Wenzler, T.; Solanki, S. K.; Krivova, N. A.; Fröhlich, C.
Bibcode: 2006A&A...460..583W
Altcode:
  Aims.We present a reconstruction of total solar irradiance (TSI) back
  to 1974, i.e. from the minimum of cycle 21 to the declining phase of
  cycle 23. We also present a cross-calibration between the magnetograms
  obtained by the 512 channel magnetograph and the spectromagnetograph
  at Kitt Peak.<BR /> Methods: .The TSI reconstruction is carried out
  using data from the 512-channel Diode Array Magnetograph and the newer
  spectromagnetograph on Kitt Peak. The model is based on the assumption
  that all irradiance changes on time-scales of a day and longer are
  entirely due to the variations of the surface distribution of the
  solar magnetic field. The reconstructed irradiance is compared with
  the composite of total solar irradiance measurements from PMOD/WRC
  (version 41).<BR /> Results: .A good correspondence is found with the
  PMOD TSI composite, with no bias between the three cycles on time-scales
  longer than the solar rotation period, although the accuracy of the
  TSI reconstruction is somewhat lower when 512 channel magnetograph
  data are used. This suggests that the same driver of the irradiance
  variations, namely the evolution of the magnetic flux at the solar
  surface, is acting in cycles 21-23. Different methods of comparing
  the magnetograms obtained by the two Kitt Peak magnetographs give
  somewhat different results, with factors by which 512 channel data
  must be divided in the range 1.38-1.63 being found. This is due to the
  non-linearity of the relationship between the magnetic field measured
  by the two instruments.<BR />

Title: The Uncombed Penumbra
Authors: Borrero, J. M.; Rempel, M.; Solanki, S. K.
Bibcode: 2006ASPC..358...19B
Altcode: 2006astro.ph..2130B
  The uncombed penumbral model explains the structure of the sunspot
  penumbra in terms of thick magnetic fibrils embedded in a surrounding,
  magnetic atmosphere. This model has been successfully applied to explain
  the polarization signals emerging from the sunspot penumbra. Thick
  penumbral fibrils face some physical problems, however. In this
  contribution we will offer possible solutions to these shortcomings.

Title: Supersonic Downflows in the Vicinity of a Solar Pore
Authors: Lagg, A.; Woch, J.; Solanki, S. K.; Gandorfer, A.
Bibcode: 2006ASPC..358..437L
Altcode:
  At the footpoints of magnetic arcades spanning over a site of flux
  emergence we observe strong redshifts in the He I triplet at 1083
  nm. These redshifts are associated with downflow speeds of up to
  40 km s<SUP>-1</SUP>. Within the spatial resolution of our data (1
  arcsec-2 arcsec) obtained with the Tenerife Infrared Polarimeter at
  the VTT we find an almost unshifted atmospheric component coexisting
  with the redshifted component. We were able to retrieve the magnetic
  field configuration in both the unshifted and the redshifted component
  simultaneously and infer an uncombed, fibril-like structure of the
  upper chromosphere. The supersonic downflow speeds are interpreted as
  a consequence of a significantly reduced pressure scale height above
  the pore, where the magnetic arcades are rooted. A temporal series of
  the fast downflow region reveals that the supersonic flow is maintained
  for more than one hour. Making use of the increased spatial resolution
  of the new TIP2 instrument we are working on reducing the upper limit
  on the size of the fibril-like flux channels in the upper chromosphere.

Title: Secular variations of solar activity and irradiance
Authors: Solanki, S.
Bibcode: 2006AGUFMSH41A..01S
Altcode:
  Regular direct measurements of solar activity started around 1611
  when sunspots detected by telescopic means began to be counted. Solar
  irradiance variations have been recorded for a much shorter time, only
  since 1978. Clearly, there is a need to extend both of these records
  into the past. In this talk reconstructions of solar irradiance back
  to the Maunder minimum and of sunspot number over multiple millenia
  are introduced. A comparison with climate reconstructions over the
  last millenium is shown and the next necessary steps in this line of
  research are considered.

Title: Long-term solar activity reconstructions: direct test by
    cosmogenic <SUP>44</SUP>Ti in meteorites
Authors: Usoskin, I. G.; Solanki, S. K.; Taricco, C.; Bhandari, N.;
   Kovaltsov, G. A.
Bibcode: 2006A&A...457L..25U
Altcode:
  Aims.Long-term solar activity in the past is usually estimated from
  cosmogenic isotopes, <SUP>10</SUP>Be or <SUP>14</SUP>C, deposited in
  terrestrial archives such as ice cores and tree rings. A number of such
  reconstruction models have been proposed which differ from each other
  significantly. This approach suffers, however, from uncertainties due
  to the sensitivity of the data to several terrestrial processes. Here
  we propose a method to constrain these solar activity reconstructions
  using cosmogenic <SUP>44</SUP>Ti activity in meteorites which is
  not affected by terrestrial processes. <BR /> Methods: .We test the
  veracity of recent solar activity reconstructions using the data on
  the activity of cosmogenic isotope <SUP>44</SUP>Ti in meteorites which
  fell during the past 235 years, and provide an independent and direct
  measure of the cosmic ray flux near the Earth and allow decoupling of
  solar activity variations from terrestrial influences.<BR /> Results:
  .We demonstrate that the <SUP>44</SUP>Ti data can distinguish between
  various reconstructions of past solar activity based on cosmogenic
  isotope data in terrestrial archives, allowing unrealistic models to
  be ruled out. We also show that a model based on the sunspot number
  record is consistent with the data on <SUP>44</SUP>Ti activity in
  meteorites, thus confirming the validity of the method. In particular
  the <SUP>44</SUP>Ti data confirm significant secular variations of
  the solar magnetic flux during the last century.<BR />

Title: High-resolution millimeter-interferometer observations of
    the solar chromosphere
Authors: White, S. M.; Loukitcheva, M.; Solanki, S. K.
Bibcode: 2006A&A...456..697W
Altcode:
  The use of millimeter-interferometer data for the study of chromospheric
  structure and dynamics is tested using 85 GHz observations with the
  10-element Berkeley-Illinois-Maryland Array (BIMA). Interferometer
  data have the advantage over single-dish data that they allow both high
  spatial resolution and dense temporal sampling simultaneously. However,
  snapshot imaging of the quiet solar atmosphere with a small number of
  dishes is challenging. We demonstrate that techniques are available to
  carry out this task successfully using maximum entropy deconvolution
  from a default image constructed from the entire observation: one of
  our results is that the solar chromosphere at millimeter wavelengths
  exhibits features that are long-lasting and the map of the entire
  observation is significant provided that atmospheric phase errors do
  not prevent deconvolution. We compare observations of quiet Sun, active
  region and coronal hole targets. The interferometer is not sensitive
  to the disk emission and the positivity constraint of the maximum
  entropy algorithm used forces the zero level in the images to be at
  the temperature of the coolest feature in each field. The brightest
  features in the images are typically 1000-1500 K above the zero level,
  with a snapshot noise level of order 100 K. We use extensive tests to
  determine whether oscillation power can be recovered from sequences of
  snapshot images and show that individual sources can be down to quite
  weak levels at locations in the image where significant flux is present;
  oscillation power located in cool regions of the image is not well
  recovered due to the deconvolution method used and may be redistributed
  to brighter regions of the millimeter image. We then investigate
  whether the data do show oscillation power using uninterrupted 30-min
  scans of the target regions. Intensity oscillations with significant
  power in the frequency range 1.5-8.0 mHz are found in the quiet-Sun
  and active region targets. For the quiet-Sun region we compare the
  oscillation properties of network boundaries and cell interiors
  (internetwork) in the spatially-resolved time series. In agreement
  with investigations at other wavelengths, in the millimeter data the
  power in the network tends to be at periods of 5 min and longer while
  power in the internetwork is present also at shorter (3-min) periods.

Title: The dynamics of the solar chromosphere: comparison of model
    predictions with millimeter-interferometer observations
Authors: Loukitcheva, M.; Solanki, S. K.; White, S.
Bibcode: 2006A&A...456..713L
Altcode:
  We analyze the millimeter intensity spectrum expected from the dynamic
  model of Carlsson &amp; Stein together with the interferometric
  observations of the quiet Sun obtained at a wavelength of 3.5 mm with
  the Berkeley-Illinois-Maryland Array. The observational data products
  (Fourier and wavelet spectra, brightness histograms) are compared
  with the corresponding products obtained for the Carlsson &amp;
  Stein (CS) models. We estimate how the limited spatial resolution
  of the observations influences the comparison with the predictions
  of chromospheric dynamic models and discuss the limitations of a
  one-dimensional non-magnetic modeling approach. In addition, we test the
  effect of the integration time of the BIMA observations on the dynamic
  signatures. The dependence of the observed brightness variations on
  spatial resolution is studied by employing artificial image degradation
  and approximating the obtained dependence by power laws. We are able
  to establish a correspondence between the CS model predictions and
  the observational data under assumptions on the horizontal coherence
  length of the oscillations. The reconstructed brightness rms values
  indicate that, assuming the coherence length of oscillating elements
  to be of order of 1'', the oscillation power in the observations
  recorded with 10'' resolution agrees within a factor of 2 with the
  power predicted by the CS model. We argue that millimeter continuum
  observations promise to be an important diagnostic of chromospheric
  structure and dynamics. Based on the analysis carried out in this work,
  the appropriate wavelengths to look for dynamic signatures are in the
  range 0.8-5.0 mm. Further millimeter interferometric observations with
  longer sequences and higher spatial resolution are highly desirable
  along with the development of realistic three-dimensional radiation
  magnetohydrodynamic simulations.

Title: Fe XIX observations of active region brightenings in the corona
Authors: Wang, T. J.; Innes, D. E.; Solanki, S. K.
Bibcode: 2006A&A...455.1105W
Altcode:
  Small flarelike brightenings seen in the hot flare line, Fe XIX,
  by the spectrometer SUMER on SOHO are analysed. We observe active
  region coronae about 30 Mm off the limb of the Sun for a period of
  several days. Brightenings are observed with a frequency 3-14 per hour
  and their lifetimes range from 5-150 min, with an average of about
  25 min. The measured size of the events along the spectrometer slit
  range from 2-67 Mm, but most are around 7 Mm. Like soft X-ray active
  region transient brightenings, they range in estimated thermal energy
  from 10<SUP>26</SUP> to 10<SUP>29</SUP> erg with a power law index of
  1.7 to 1.8, beyond 10<SUP>27</SUP> erg. We conclude that they are the
  coronal parts of loops heated to &gt; 6 MK by soft X-ray microflares.

Title: Milne-Eddington inversions of the He &lt;sf&gt;I&lt;/sf&gt;
10 830 Å Stokes profiles: influence of the Paschen-Back effect
Authors: Sasso, C.; Lagg, A.; Solanki, S. K.
Bibcode: 2006A&A...456..367S
Altcode: 2011arXiv1102.0898S
  Context: .The Paschen-Back effect influences the Zeeman sublevels
  of the He I multiplet at 10 830 Å, leading to changes in strength
  and in position of the Zeeman components of these lines.<BR /> Aims:
  .We illustrate the relevance of this effect using synthetic Stokes
  profiles of the He I 10 830 Å multiplet lines and investigate its
  influence on the inversion of polarimetric data.<BR /> Methods: .We
  invert data obtained with the Tenerife Infrared Polarimeter (TIP)
  at the German Vacuum Tower Telescope (VTT). We compare the results of
  inversions based on synthetic profiles calculated with and without the
  Paschen-Back effect being included.<BR /> Results: .We find that when
  taking into account the incomplete Paschen-Back effect, on average 16%
  higher field strength values are obtained. We also show that this effect
  is not the main cause for the area asymmetry exhibited by many He I
  10 830 Stokes V-profiles. This points to the importance of velocity
  and magnetic field gradients over the formation height range of these
  lines.<BR />

Title: Vector tomography for the coronal magnetic
    field. I. Longitudinal Zeeman effect measurements
Authors: Kramar, M.; Inhester, B.; Solanki, S. K.
Bibcode: 2006A&A...456..665K
Altcode:
  Aims.We study the possibility of applying tomographic techniques in
  order to reconstruct the 3D magnetic field configuration in the solar
  corona. Our simulations are based on data which can be obtained from
  longitudinal Zeeman-effect (or from Faraday rotation) measurements
  obtained during a solar rotation.<BR /> Methods: .The Zeeman effect
  provides essentially the integrated line-of-sight component of the
  magnetic field. The reconstruction problem relates to a family of
  similar problems termed vector tomography. For inversion of this type
  problems it is known that the curl-free part of a vector field cannot
  be reconstructed from the integrated along line-of-sight data. To
  remove the resulting ambiguity of the reconstruction we include the
  additional constraint, ∇\cdotB=0, into the inversion similar to
  smoothing constraints in Tikhonov regularization problems.<BR />
  Results: .It is shown that Zeeman data obtained from vantage points
  in the ecliptic plane alone is sensitive only to certain magnetic
  field structures. For a full reconstruction it is necessary either to
  have also observations from viewing directions at higher heliographic
  latitudes, or to combine the longitudinal Zeeman-effect data with
  observations that provide the transverse component of the field,
  e.g. from the Hanle effect.<BR />

Title: Solar Variability of Possible Relevance for Planetary Climates
Authors: Solanki, S. K.; Krivova, N. A.
Bibcode: 2006SSRv..125...25S
Altcode: 2006SSRv..tmp...97S
  The global variability of the Sun of relevance for planetary climates
  has been directly measured for the past few decades. For longer
  stretches of time models are required. Semi-empirical models can now
  accurately reproduce the measured records of solar total and spectral
  irradiance, as well as of the magnetic flux. They can also provide
  reconstructions of these quantities on longer time scales. Here a
  summary is given of some of the modelling efforts and of the results
  achieved so far.

Title: Multi-component analysis of a flaring region in the
    chromospheric He I 1083.0 nm triplet
Authors: Sasso, C.; Lagg, A.; Solanki, S. K.
Bibcode: 2006IAUJD...3E..31S
Altcode:
  We present infrared spectropolarimetric observations of the solar active
  region NOAA 0763 obtained with the new Tenerife Infrared Polarimeter
  (TIP 2) at the German Vacuum Tower Telescope (VTT) during May 2005,
  taken in the chromospheric He I 1083.0 nm multiplet. The region was
  in the initial phase of a C2.0 flare. We observe up to 4 atmospheric
  components within the spatial resolution of our observations. The
  components are clearly separated in wavelength, the largest separation
  corresponding to downflow velocities of up to 64 km/s. We give
  preliminary results on the magnetic vector and the line-of sight
  velocity obtained by inverting the Stokes I, Q, U and V profiles of
  the He 1083.0 nm triplet.

Title: High-Resolution CN Spectroscopy of Small-Scale Solar Magnetic
    Features
Authors: Zakharov, V. V.; Gandorfer, A.; Solanki, S. K.
Bibcode: 2006IAUJD...3E..87Z
Altcode:
  High-resolution spectroscopic observations of the Sun have been
  carried out with the TRIPPEL spectrograph installed at the new 1-m
  Swedish Solar Telescope (SST) using realtime AO correction. A detailed
  spectroscopic analysis of individual photospheric bright points (BP)
  and faculae-like structures simultaneously in two spectral domains,
  i.e 387.588&lt;λ&lt;388.473 nm (violet CN band) and in a blue spectral
  band at 436.1&lt;λ&lt;436.9 nm, containing absorption lines of CH,
  obtained at the disc center and near the limb is presented. The
  estimated spatial resolution of the obtained spectra is around
  0.25 arcsec while the spectral resolving power is around 130.000
  in the first domain, and 76.000 in the second spectral region,
  respectivlely. The first spectral band covers absorption lines of
  both, CH and CN molecules, as well as many atomic lines. This enabled
  us to make a quantitative comparison of their absorption and Doppler
  shifts in the different photospheric features. The absorption lines
  of the CN molecule and many atoms are depressed in a BP's interior
  with respect to those in the quiet Sun. Our quantitative comparison
  of the relative line depression of CH lines with respect to CN lines
  showed that the latter have weaker absorption by a factor of 1.28 at
  the disc centre and 1.32 near the limb. The CN line-core intensity,
  at the disc centre, has higher BP contrast than the contrast in the
  CH line-core by a factor of 1.9, and the ratio of these contrasts
  is decreasing with increasing continuum intensity of the BPs. This
  trend is similar to that obtained from previous simultaneous G-band
  and violet CN-band imaging observations. Measurements of contrasts and
  rms contrasts of line-core, integrated and local continuum intensities
  are provided. Analysis of Doppler shifts and line broadening of an
  Fe I line at 387.777 nm revealed an increase of the FWHM in the BP's
  interior and in dark intergranular lanes and a decrease with increasing
  intensity of the granules. The first results of a direct comparison
  of observed CN spectra with those simulated in MHD models in different
  photospheric features is presented.

Title: Flux Emergence In The Solar Photosphere - Diagnostics Based
    On 3-D Rradiation-MHD Simulations
Authors: Yelles Chaouche, L.; Cheung, M.; Lagg, A.; Solanki, S.
Bibcode: 2006IAUJD...3E..75Y
Altcode:
  We investigate flux tube emergence in the solar photosphere using a
  diagnostic procedure based on analyzing Stokes signals from different
  spectral lines calculated in 3-D radiation-MHD simulations. The
  simulations include the effects of radiative transport and partial
  ionization and cover layers both above and below the solar surface. The
  simulations consider the emergence of a twisted magnetic flux tube
  through the solar surface. We consider different stages in the emergence
  process, starting from the early appearance of the flux tube at the
  solar surface, and following the emergence process until the emerged
  flux looks similar to a normal bipolar region. At every stage we compute
  line profiles by numerically solving the Unno-Rachkovsky equations at
  every horizontal grid point. Then, following observational practice,
  we apply Milne-Eddington-type inversions to the synthetic spectra in
  order to retrieve different atmospheric parameters. We include the
  influence of spatial smearing on the deduced atmospheric parameters
  to identify signatures of different stages of flux emergence in the
  solar photosphere.

Title: Variations of solar irradiance
Authors: Solanki, S. K.
Bibcode: 2006IAUJD...8E..43S
Altcode:
  Since 1978 satellite based radiometers have been measuring changes
  in solar irradiance, so that the available record now covers almost 3
  solar cycles. In addition, spectral irradiance has been measured with
  increasing precision time has passed. These data have uncoverd a rich
  structure of the variable solar irradiance. In addition, the physical
  understanding of irradiance variations and the detailed reconstruction
  of this quantity (both for the time in which observations are available
  and for earlier times) have made great strides over the last years. It
  is now possible to reproduce both the total and spectral irradiance
  variations with very high precision. In this talk an overview of
  the measurements and the modelling of total and spectral irradiance
  variations is given, highlighting in particular the progress of the
  last few years.

Title: Magnetic Flux Transport on Active Cool Stars and Starspot
    Lifetimes
Authors: Isik, E.; Schüssler, M.; Solanki, S. K.
Bibcode: 2006IAUJD...8E..21I
Altcode:
  Rapidly rotating cool stars are known to have large magnetic regions
  at mid- to high-latitudes. Mid-latitude starspots and magnetic regions
  have characteristic lifetimes on the order of one month as observed
  using (Zeeman-) Doppler imaging techniques. The structure and detailed
  morphology of starspots are not observable at present. In this study,
  we present numerical simulations of the surface transport of bipolar
  magnetic regions (BMRs) and magnetic spots on stars which have radii
  and surface rotational shears of AB Doradus, the Sun, and the HR 1099
  primary. The surface flux transport model is based on the magnetic
  induction equation for radial fields under the effects of surface
  differential rotation, meridional flow, and turbulent diffusion due to
  supergranulation. We calculate flux evolution and lifetimes of BMRs with
  different emergence latitudes, surface shear rates, and tilt angles. For
  BMRs comparable to the largest ones on the Sun, we find that varying
  the surface flows and tilt angle modifies the lifetimes over a range
  of a month. For very large BMRs (area fraction ~ 0.1) the assumption
  of Joy's law for the tilt angle - as compared to the case with zero
  tilt - leads to a significant increase of lifetime. Such regions can
  evolve to form circumpolar spots that live more than a year. Taking the
  observed weak latitudinal shear and the radius of the active subgiant
  component of HR 1099, we find longer BMR lifetimes as compared to
  the more strongly sheared AB Dor case. We have also considered the
  effect on decay and lifetimes of starspots if they are monolithic or
  a conglomerate of smaller spots of similar total size. We find these
  different configurations differ neither in their decay patterns,
  nor in their lifetimes. We also give an analytical explanation for
  the linear decay of magnetic flux in the monolithic-spot simulation.

Title: Quiet Sun magnetic fields
Authors: Solanki, S. K.
Bibcode: 2006IAUJD...3E..69S
Altcode:
  The amount of magnetic flux in the quiet Sun, its distribution on the
  solar surface, its origin and evolution are topics that have been
  strongly debated in recent years. Here a critical overview will be
  given of some of the results obtained from high-sensitivity polarimetric
  data and from numerical 3-D radiation-MHD simulations.

Title: Numerical simulations of impulsively generated vertical
    oscillations in a solar coronal arcade loop
Authors: Selwa, M.; Solanki, S. K.; Murawski, K.; Wang, T. J.;
   Shumlak, U.
Bibcode: 2006A&A...454..653S
Altcode:
  Aims.The main aims of the paper are to carry out numerical simulations
  of the vertical oscillations in a coronal loop in order to determine
  their dependence on various parameters and to compare them with recent
  TRACE observations. <BR /> Methods: .We consider impulsively generated
  oscillations in a solar coronal arcade loop. The two-dimensional
  numerical model we implement in the ideal MHD regime includes the
  effects of nonlinearity and line curvature. We perform parametric
  studies by varying both the position and the width/strength of
  the pulse. <BR /> Results: .A pulse launched below a loop is in
  general found to excite multiple wave modes, in particular a vertical
  oscillation with many properties of a kink mode, fast mode oscillations
  and a slow mode pulse (or two slow mode pulses, depending on the
  location of the original pulse). From our parametric studies we deduce
  that wave periods and attenuation times of the excited waves depend
  on the position below the loop summit, as well as on the width of the
  pulse. Wider pulses launched closer to a foot-point and to the loop's
  apex trigger wave packets of longer period waves which are more strongly
  attenuated. A perturbed loop does not return to its initial state but
  is instead stretched, with its apex shifted upwards. As a result the
  perturbations propagate along the stretched loop and consequently
  stronger and wider pulses which stretch a loop more lead to longer
  period oscillations. A pulse located near one of the foot-points is
  found to excite a distortion mode leading to asymmetric oscillations
  which are distinct from the vertical or horizontal kink modes that
  have been identified in TRACE data. <BR />

Title: Microflares and Loop Oscillations
Authors: Innes, D. E.; Wang, T. J.; Solanki, S. K.; Tothova, D.
Bibcode: 2006ESASP.617E.132I
Altcode: 2006soho...17E.132I
  No abstract at ADS

Title: Properties of Plasma Dynamics In The Polar Coronal Plumes
Authors: Raouafi, N. -E.; Harvey, J. W.; Solanki, S. K.
Bibcode: 2006ESASP.617E..16R
Altcode: 2006soho...17E..16R
  No abstract at ADS

Title: Large Temperature Anisotropies in Polar Coronal Holes: How
    Reliable are they?
Authors: Raouafi, N. -E.; Solanki, S. K.
Bibcode: 2006ESASP.617E.105R
Altcode: 2006soho...17E.105R
  No abstract at ADS

Title: Solar Coronal Magnetic Field Mapper
Authors: Solanki, S. K.; Raouafi, N. -E.; Gandorfer, A.; Schühle,
   U.; Lagg, A.
Bibcode: 2006ESASP.617E.160S
Altcode: 2006soho...17E.160S
  No abstract at ADS

Title: Solar Microscopy: Unveiling the Sun's Basic Physical Processes
    at their Intrinsic Scales
Authors: Solanki, S. K.; Marsch, E.
Bibcode: 2006ESASP.617E..34S
Altcode: 2006soho...17E..34S
  No abstract at ADS

Title: The Dynamic Nature of the Lower Transition Region as Revealed
    by Spectroscopy of the Hydrogen Lyman-α Line
Authors: Teriaca, L.; Schühle, U.; Solanki, S. K.; Curdt, W.;
   Marsch, E.
Bibcode: 2006ESASP.617E..77T
Altcode: 2006soho...17E..77T
  No abstract at ADS

Title: SUNRISE: high resolution UV/VIS observations of the Sun from
    the stratosphere
Authors: Gandorfer, A. M.; Solanki, S. K.; Barthol, P.; Lites, B. W.;
   Martínez Pillet, V.; Schmidt, W.; Soltau, D.; Title, A. M.
Bibcode: 2006SPIE.6267E..0SG
Altcode: 2006SPIE.6267E..25G
  SUNRISE is an international project for the development, construction,
  and operation of a balloon-borne solar telescope with an aperture
  of 1 m, working in the UV/VIS spectral domain. The main scientific
  goal of SUNRISE is to understand the structure and dynamics of the
  magnetic field in the atmosphere of the Sun. SUNRISE will provide
  near diffraction-limited images of the photosphere and chromosphere
  with an unpredecented resolution down to 35 km on the solar surface at
  wavelengths around 220 nm. The focal-plane instrumentation consists of a
  polarization sensitive spectrograph, a Fabry-Perot filter magnetograph,
  and a phase-diverse filter imager working in the near UV. The first
  stratospheric long-duration balloon flight of SUNRISE is planned
  in Summer 2009 from the swedish ESRANGE station. SUNRISE is a joint
  project of the german Max-Planck-Institut fur Sonnensystemforschung
  (MPS), Katlenburg-Lindau, with the Kiepenheuer-Institut fur Sonnenphysik
  (KIS), Freiburg, Germany, the High-Altitude Observatory (HAO), Boulder,
  USA, the Lockheed-Martin Solar and Astrophysics Lab. (LMSAL), Palo Alto,
  USA, and the spanish IMaX consortium. In this paper we will present
  an actual update on the mission and give a brief description of its
  scientific and technological aspects.

Title: Reconstruction of solar UV irradiance in cycle 23
Authors: Krivova, N. A.; Solanki, S. K.; Floyd, L.
Bibcode: 2006A&A...452..631K
Altcode:
  Solar irradiance variations show a strong wavelength dependence. Whereas
  the total solar irradiance varies by about 0.1% during the course
  of the solar cycle, variations at the wavelengths around the Ly-α
  emission line near 121.6 nm range up to 50-100%. These variations may
  have a significant impact on the Earth's climate system. Being almost
  completely absorbed in the upper atmosphere, solar UV radiation below
  300 nm affects stratospheric chemistry and controls production and
  destruction of ozone. Models of the solar UV irradiance remain far from
  perfect, even though considerable progress has been made in modelling
  the irradiance variations longwards of about 200-300 nm. We show that
  after correcting for the exposure dependent degradation of the SUSIM
  channels sampling irradiance at λ &gt;240 nm (making use of the Mg
  II core-to-wing ratio) the agreement between model and measurement is
  significantly improved. At shorter wavelengths the LTE approximation
  usually made in such models fails, which makes a reconstruction of the
  solar UV irradiance a rather intricate problem. We choose an alternative
  approach and use the observed SUSIM UV spectra to extrapolate available
  models to shorter wavelengths. The model reproduces observed solar
  cycle variations of the irradiance at wavelengths down to 115 nm and
  indicates an important role of UV irradiance variability: up to 60%
  of the total irradiance variations over the solar cycle might be
  produced at wavelengths below 400 nm.

Title: Observation of a bright coronal downflow by SOHO/EIT
Authors: Tripathi, D.; Solanki, S. K.; Schwenn, R.; Bothmer, V.;
   Mierla, M.; Stenborg, G.
Bibcode: 2006A&A...449..369T
Altcode:
  A distinct coronal downflow has been discovered in the course of a
  prominence eruption associated coronal mass ejection (CME) imaged by
  EIT (Extreme ultraviolet Imaging Telescope) and LASCO (Large Angle
  Spectrometric Coronagraph) on board SOHO (Solar and Heliospheric
  Observatory) on 5-Mar.-2000. Evolution of the prominences seen by EIT
  was tracked into the LASCO/C2 and C3 field-of-view where they developed
  as the core of a typical three-part CME. In contrast to the inflow
  structures reported earlier in the literatures, which were dark and
  were interpreted as plasma voids moving down, the downflow reported
  here was bright. The downflow, which was only seen in EIT FOV had an
  onset time that coincided with the deceleration phase of the core
  of the CME. The downflow showed a rapid acceleration followed by a
  strong deceleration. The downflow followed a curved path which may be
  explained by material following the apex of a contracting magnetic loop
  sliding down along other field lines, although other explanations are
  also possible. Irrespective of the detailed geometry, this observation
  provides support for the pinching off of the field lines drawn-out by
  the erupting prominences and the contraction of the arcade formed by
  the reconnection.

Title: On the fine structure of sunspot penumbrae. III. The vertical
    extension of penumbral filaments
Authors: Borrero, J. M.; Solanki, S. K.; Lagg, A.; Socas-Navarro,
   H.; Lites, B.
Bibcode: 2006A&A...450..383B
Altcode: 2005astro.ph.10586B
  In this paper we study the fine structure of the penumbra as inferred
  from the uncombed model (flux tube embedded in a magnetic surrounding)
  when applied to penumbral spectropolarimetric data from the neutral
  iron lines at 6300 Å. The inversion infers very similar radial
  dependences in the physical quantities (LOS velocity, magnetic field
  strength etc.) as those obtained from the inversion of the Fe I 1.56
  μm lines. In addition, the large Stokes V area asymmetry exhibited
  by the visible lines helps to constrain the size of the penumbral
  flux tubes. As we demonstrate here, the uncombed model is able to
  reproduce the area asymmetry with striking accuracy, returning flux
  tubes as thick as 100-300 kilometers in the vertical direction, in
  good agreement with previous investigations.

Title: Solar proton events in cosmogenic isotope data
Authors: Usoskin, Ilya G.; Solanki, Sami K.; Kovaltsov, Gennady A.;
   Beer, Jürg; Kromer, Bernd
Bibcode: 2006GeoRL..33.8107U
Altcode:
  A possible contribution of solar energetic particle events to the
  production of cosmogenic <SUP>10</SUP>Be and <SUP>14</SUP>C in the
  atmosphere is studied. The solar particle effect is negligible in
  the <SUP>14</SUP>C data, but extreme events may be detectable in
  high-resolution <SUP>14</SUP>C data. Although the overall effect
  is small in the <SUP>10</SUP>Be data, strong events may contribute
  notably on the inter-annual time scale. In combination with the
  11-year solar modulation of galactic cosmic rays, it may lead to an
  intermittent 5.5-year periodicity, which is seen in high resolution
  <SUP>10</SUP>Be data. We have identified ten episodes during 1750-1950
  when <SUP>10</SUP>Be may hold signatures of strong solar proton
  events. This opens a new possibility to study extreme solar particle
  events in the past using high resolution cosmogenic isotope data.

Title: Solar activity reconstructed over the last 7000 years: The
    influence of geomagnetic field changes
Authors: Usoskin, I. G.; Solanki, S. K.; Korte, M.
Bibcode: 2006GeoRL..33.8103U
Altcode:
  The long-term solar activity, as manifested by sunspot number,
  has been recently reconstructed on multi-millennium time scales
  by S. K. Solanki et al. (2004) from the measured concentration of
  <SUP>14</SUP>C in tree rings. The exact level of the reconstructed
  solar activity depends, however, on independently evaluated data of
  the geomagnetic dipole strength variations. Recently, a new series
  of the palaeomagnetic dipole moment reconstruction for the last 7000
  years has been presented by M. Korte and C. G. Constable (2005a) on the
  basis of a thorough analysis of global samples. The new palaeomagnetic
  series yields a systematically lower dipole moment in the past,
  compared to the earlier geomagnetic reconstructions. We have revised
  the earlier sunspot activity reconstruction since 5000 BC, using the
  new geomagnetic data series, and found that it is roughly consistent
  with the previous results during most of the period, although the
  revised sunspot number values are in general higher. Nonetheless, it
  is confirmed with the new palaeomagnetic series that the Sun spends
  only 2-3% of the time in a state of high activity, similar to the
  modern episode. This strengthens the conclusion that the modern high
  activity level is very unusual during the last 7000 years.

Title: The solar magnetic field
Authors: Solanki, Sami K.; Inhester, Bernd; Schüssler, Manfred
Bibcode: 2006RPPh...69..563S
Altcode: 2010arXiv1008.0771S
  The magnetic field of the Sun is the underlying cause of the many
  diverse phenomena combined under the heading of solar activity. Here
  we describe the magnetic field as it threads its way from the bottom
  of the convection zone, where it is built up by the solar dynamo, to
  the solar surface, where it manifests itself in the form of sunspots
  and faculae, and beyond into the outer solar atmosphere and, finally,
  into the heliosphere. On the way it transports energy from the surface
  and the subsurface layers into the solar corona, where it heats the
  gas and accelerates the solar wind.

Title: The uncombed penumbra
Authors: Borrero, J. M.; Rempel, M.; Solanki, S. K.
Bibcode: 2006astro.ph..2129B
Altcode:
  The uncombed penumbral model explains the structure of the sunspot
  penumbra in terms of thick magnetic fibrils embedded in a magnetic
  surrounding atmosphere. This model has been successfully applied
  to explain the polarization signals emerging from the sunspot
  penumbra. Thick penumbral fibrils face some physical problems,
  however. In this contribution we will offer possible solutions to
  these shortcomings.

Title: Plasma dynamics in the polar coronal plumes
Authors: Raouafi, N. -E.; Harvey, J. W.; Solanki, S. K.
Bibcode: 2006IAUS..233..193R
Altcode:
  We use the spectral shapes of the EUV line profiles to study the plasma
  dynamics, acceleration and heating, in polar plumes (PP). We find
  that the observed profiles are reproduced fairly well when considering
  low plume wind speeds and velocity turbulence (α_S) at low altitudes
  followed by a rapid acceleration and heating of the plasma to reach
  the properties of inter-plumes (IP) by ≈3-4~R_⊙. We also find that
  plumes very close to the pole give narrow profiles at all heights
  that are not observed above ≈2.5~R_⊙. This suggests a tendency
  for plume footpoints to lie more than 10° away from the pole. High
  resolution magnetograms of SOLIS and EUV images support this hypothesis.

Title: Acoustic shock waves in the solar chromosphere from millimeter
    observations
Authors: Loukitcheva, Maria A.; Solanki, Sami K.; White, Stephen
Bibcode: 2006IAUS..233..104L
Altcode:
  We argue that millimeter continuum observations promise to be an
  important diagnostic of chromospheric dynamics and the appropriate
  wavelengths to look for dynamic signatures are in the range 0.8-5.0
  mm. We have analyzed the millimeter intensity spectrum expected from
  the dynamic model of the solar non-magnetic atmosphere of Carlsson
  &amp; Stein (1992, 1995, 1997, 2002, hereafter CS) together with the
  interferometric observations of the quiet Sun obtained at a wavelength
  of 3.5 mm with the Berkeley-Illinois-Maryland Array. Model radio
  emission at millimeter wavelengths is found to be extremely sensitive
  to dynamic processes in the chromosphere, if these are spatially and
  temporally resolved. The estimated millimeter brightness temperatures
  are time-dependent, following changes in the atmospheric parameters,
  and result in clear signatures of waves with a period of 180 s seen
  in the radio intensity as a function of time. At the same time,
  the interferometric observations of the internetwork regions reveal
  significant oscillations with amplitudes of 50-150 K in the frequency
  range 1.5-8 mHz. We give an estimate of the influence of the limited
  available spatial resolution of observations on the comparison with the
  predictions of dynamic models. We are able to establish a correspondence
  between the CS model predictions and the observational data if we
  assume that the horizontal coherence length of the oscillations is on
  the order of 1 arcsec.

Title: Multi-millennium changes of the geomagnetic field and solar
    activity
Authors: Usoskin, I. G.; Solanki, S.; Korte, M.
Bibcode: 2006cosp...36.2281U
Altcode: 2006cosp.meet.2281U
  The long-term solar activity has been recently reconstructed on
  the multi-millennium time scale Solanki et al Nature 431 384 2004
  from the measured concentration of radiocarbon 14 C in tree rings
  The exact level of the reconstructed solar activity depends however
  on independently evaluated data of the geomagnetic dipole strength
  variations Recently a new series of the palaeomagnetic dipole moment
  reconstruction for the last 7000 years has been presented by Korte and
  Constable Earth Plan Sci Lett 236 348 2005 on the basis of a thorough
  complex analysis of global samples The new palaeomagnetic series yields
  systematically lower dipole moment in the past compared to the earlier
  geomagnetic reconstructions We have revised the earlier sunspot activity
  reconstruction since 5000 BC using the new geomagnetic data and found
  that it is consistent with the previous results during most of the
  period although it yields a slightly higher level of the reconstructed
  sunspot activity The earlier finding on the very unusual level of the
  contemporary solar activity over the last millennia is confirmed with
  the new palaeomagnetic series The Sun spent only 2-3 of the time in
  a high activity state similar to the modern episode implying that the
  modern high activity level is very unusual during the last 7000 years On
  the other hand grand minima occupy about 12 of the time in the recent
  history of the Sun The new reconstruction allows for a comparative
  study of solar-terrestrial relations in the multi-millennium time scale

Title: Influence of the Paschen-Back effect on the results of
    polarimetric inversions of the He I 10830 Å triplet
Authors: Sasso, C.; Lagg, A.; Solanki, S. K.; Socas-Navarro, H.
Bibcode: 2006MSAIS...9..126S
Altcode:
  The He I triplet at 10830 Å has a great potential for determining the
  magnetic field vector in the upper chromosphere. The triplet is Zeeman
  sensitive (Landé factors 2.0, 1.75 and 1.25) and shows the signature of
  the Hanle effect under appropriate conditions. Additionally, the Zeeman
  sublevels are influenced by the Paschen-Back effect leading to changes
  in strength and in position of the Zeeman components of the transitions
  forming the triplet. In this work we calculate the influence of the
  Paschen-Back effect on the Stokes profiles and investigate its relevance
  to inversions on spectro-polarimetric data obtained with the Tenerife
  Infrared Polarimeter (TIP) at the German Vacuum Tower Telescope (VTT).

Title: SUNRISE: high-resolution UV/VIS observations of the Sun from
    the stratosphere
Authors: Solanki, S. K.; Barthol, P.; Gandorfer, A.; Schüssler, M.;
   Lites, B. W.; Martinez Pillet, V.; Schmidt, W.; Title, A. M.
Bibcode: 2006cosp...36.2416S
Altcode: 2006cosp.meet.2416S
  SUNRISE is a balloon-borne solar telescope with an aperture of 1m
  working in the UV VIS optical domain The main scientific goal of
  SUNRISE is to study the structure and dynamics of the magnetic field
  in the atmosphere of the Sun at high spatial resolution SUNRISE will
  provide diffraction-limited images of the photosphere and chromosphere
  with an unprecedented resolution down to 35km at wavelengths around
  220nm Focal-plane instruments are a UV filter imager a Fabry-Perot
  filter magnetograph and a spectrograph polarimeter Stratospheric
  long-duration balloon flights of SUNRISE over the North Atlantic
  and or Antarctica are planned SUNRISE is a joint project of the
  Max-Planck-Institut fuer Sonnensystemforschung MPS Katlenburg-Lindau
  with the Kiepenheuer-Institut fuer Sonnenphysik KIS Freiburg the
  High-Altitude Observatory HAO Boulder the Lockheed-Martin Solar and
  Astrophysics Lab LMSAL Palo Alto and the spanish IMaX consortium The
  presentation will give an overview about the mission and a description
  of the instrumentation now at the beginning of the hardware construction
  phase

Title: Sensitivity of solar off-limb line profiles to electron
    density stratification and the velocity distribution anisotropy
Authors: Raouafi, N. -E.; Solanki, S. K.
Bibcode: 2006A&A...445..735R
Altcode: 2007arXiv0704.1127R
  The effect of the electron density stratification on the intensity
  profiles of the H I Ly-α line and the O VI and Mg X doublets formed
  in solar coronal holes is investigated. We employ an analytical 2-D
  model of the large scale coronal magnetic field that provides a good
  representation of the corona at the minimum of solar activity. We use
  the mass-flux conservation equation to determine the outflow speed of
  the solar wind at any location in the solar corona and take into account
  the integration along the line of sight (LOS). The main assumption we
  make is that no anisotropy in the kinetic temperature of the coronal
  species is considered. We find that at distances greater than 1
  R<SUB>sun</SUB> from the solar surface the widths of the emitted lines
  of O VI and Mg X are sensitive to the details of the adopted electron
  density stratification. However, Ly-α, which is a pure radiative line,
  is hardly affected. The calculated total intensities of Ly-α and the O
  VI doublet depend to a lesser degree on the density stratification and
  are comparable to the observed ones for most of the considered density
  models. The widths of the observed profiles of Ly-α and Mg X are well
  reproduced by most of the considered electron density stratifications,
  while for the O VI doublet only few stratifications give satisfying
  results. The densities deduced from SOHO data result in O VI profiles
  whose widths and intensity ratio are relatively close to the values
  observed by UVCS although only isotropic velocity distributions are
  employed. These density profiles also reproduce the other considered
  observables with good accuracy. Thus the need for a strong anisotropy
  of the velocity distribution (i.e. a temperature anisotropy) is not so
  clear cut as previous investigations of UVCS data suggested. However,
  these results do not rule completely out the existence of some degree
  of anisotropy in the corona. The results of the present computations
  also suggest that the data can also be reproduced if protons, heavy
  ions and electrons have a common temperature, if the hydrogen and
  heavy-ion spectral lines are also non-thermally broadened by a roughly
  equal amount.

Title: Magnetic field measurements at different levels in the solar
    atmosphere and magnetic coupling
Authors: Solanki, S. K.; Lagg, A.
Bibcode: 2006cosp...36..916S
Altcode: 2006cosp.meet..916S
  The magnetic field couples the different layers of the solar atmosphere
  with each other To unravel this coupling we need to be able to
  measure the field at all the relevant levels Most measurements of
  the magnetic field refer to the photosphere where magnetographs
  and spectropolarimetry using the Zeeman effect have allowed the
  magnetic structure and its evolution to be studied Observations of
  the field at higher layers in the atmosphere are more rare although
  a number of techniques are available These include Zeeman-effect and
  Hanle effect based measurements in the chromosphere and the corona
  as well as radio observations of coronal magnetic field These direct
  measurements are complemented by magnetic field extrapolations starting
  from the photosphere A brief overview of results obtained by various
  techniques of magnetic field measurements is given and a more detailed
  discussion of the main results of recent measurements of the field in
  the photosphere and the upper chromosphere are presented

Title: How reliable are the large temperature anisotropies in polar
    coronal holes?
Authors: Raouafi, N. -E.; Solanki, S. K.
Bibcode: 2006IAUS..233..185R
Altcode:
  We examine the influence of different electron density stratifications
  on the coronal LOS-integrated profiles of H I Ly-α and O VI
  lines at 103nm. We find that the widths of the emitted lines are
  significantly affected by the details of the adopted electron density
  profiles. Densities deduced from SOHO data result in O VI profiles
  whose widths and intensity ratio are relatively close to the values
  observed by UVCS although only isotropic kinetic temperatures are
  employed. Hence we expect the magnitude of the anisotropy to depend
  strongly on the density stratification adopted when analyzing the data.

Title: Chromospheric Dynamics: Model Predictions and Comparison
    With Observations
Authors: Loukitcheva, M.; Solanki, S. K.; White, S.
Bibcode: 2006apri.meet...38L
Altcode:
  No abstract at ADS

Title: Fundamental parameters and granulation properties of Alpha
    Centauri A and B obtained from inversions of their spectra
Authors: Frutiger, C.; Solanki, S. K.; Mathys, G.
Bibcode: 2005A&A...444..549F
Altcode:
  Properties of stellar granulation are obtained by inverting spectra
  of the late-type stars α Centauri A and B. Our inversions are based
  on a multi-component model of the stellar photosphere and take into
  account the center-to-limb variation and rotational broadening. The
  different atmospheric components describe the areas harboring up-,
  down- and horizontal flows. The inversions are constrained by
  fitting not only the flux profiles, but also their line bisectors,
  and by using a simple mass conservation scheme. The inversions return
  the properties of convection at the stellar surface, including the
  stratification of the thermodynamic parameters, as well as fundamental
  parameters such as the gravitational acceleration, v sin i and the
  element abundances. For α Cen A (G2V) the derived stratifications of
  the temperature and convective velocity are very similar to the Sun,
  while for α Cen B (K1V) we find similar up- and downflow velocities,
  but lower horizontal speeds and a reduced overshoot. The latter is
  consistent with the smaller scale height of the atmosphere, while mass
  conservation arguments taken with the lower horizontal speed imply
  that the granules on α Cen B are smaller than on the Sun. Both these
  properties are in good agreement with the hydrodynamic simulation of
  Nordlund &amp; Dravins (1990, A&amp;A, 228, 155). The inversions also
  return the fundamental parameters (T_eff, log g, abundances, v sin i,
  etc.) of the two stars. These values are on the whole in good agreement
  with literature values. Also, most of them do not strongly depend on the
  details of the inversion. However, importantly, the element abundances
  are 0.1 to 0.15 dex lower when a 2- or 3-component inversion is carried
  out than with a 1-component inversion. <P />Based on observations
  collected at the European Southern Observatories, La Silla, Chile.

Title: Flarelike Brightenings of Active Region Loops Observed
    with SUMER
Authors: Wang, T. J.; Innes, D. E.; Solanki, S. K.; Curdt, W.
Bibcode: 2005ESASP.600E.105W
Altcode: 2005ESPM...11..105W; 2005dysu.confE.105W
  No abstract at ADS

Title: On the size distribution of sunspot groups in the Greenwich
    sunspot record 1874-1976
Authors: Baumann, I.; Solanki, S. K.
Bibcode: 2005A&A...443.1061B
Altcode: 2005astro.ph.10516B
  We investigate the size distribution of the maximum areas and the
  instantaneous distribution of areas of sunspot groups using the
  Greenwich sunspot group record spanning the interval 1874-1976. Both
  distributions are found to be well described by log-normal
  functions. Using a simple model we can transform the maximum area
  distribution into the instantaneous area distribution if the sunspot
  area decay rates are also distributed log-normally. For single-valued
  decay rates the resulting snapshot distribution is incompatible with the
  observations. The current analysis therefore supports the results of
  Howard (1992, Sol. Phys., 137, 51) and Martínez Pillet et al. (1993,
  A&amp;A, 274, 521). It is not possible to distinguish between a linear
  and a quadratic decay law, however, with the employed data set.

Title: The Dynamics of the Lower Transition Region as Inferred from
    Spectroscopy of the Hydrogen LYMAN-α Line
Authors: Teriaca, L.; Schühle, U.; Solanki, S. K.; Curdt, W.;
   Marsch, E.
Bibcode: 2005ESASP.600E.100T
Altcode: 2005ESPM...11..100T; 2005dysu.confE.100T
  No abstract at ADS

Title: The molecular Zeeman effect and diagnostics of solar and
    stellar magnetic fields. III. Theoretical spectral patterns in the
    Paschen-Back regime
Authors: Berdyugina, S. V.; Braun, P. A.; Fluri, D. M.; Solanki, S. K.
Bibcode: 2005A&A...444..947B
Altcode:
  Many diatomic molecules present in the atmospheres of the Sun and cool
  stars exhibit the Paschen-Back effect at field strengths typical of
  sunspots and active cool stars. Here we present a complete theoretical
  description of the molecular Paschen-Back efect in Hund's cases (a),
  (b) and all cases intermediate to them. This description allows
  us to compute the splitting of levels of any multiplicity and the
  transitions between them. We also introduce a generalized description
  of the effective magnetic Landé factor applicable not just in the
  Zeeman regime, but also in the Paschen-Back regime. We find that in
  the regime of the partial Paschen-Back effect strongly asymmetric
  Stokes profiles are produced, whose strengths and asymmetries depend
  sensitively on the magnetic field. In the regime of the complete
  Paschen-Back effect the profiles become symmetric again (although
  they may be strongly shifted). The strength of the forbidden and
  satellite transitions increases rapidly with field strength in the
  partial Paschen-Back regime, while the strength of the main branch
  transitions decreases. These signatures hold promise to form the basis
  of new diagnostics of solar and stellar magnetic fields.

Title: Diagnostics of a Simulated Flux Tube Emergence
Authors: Yelles Chaouche, L.; Cheung, M.; Lagg, A.; Solanki, S.
Bibcode: 2005ESASP.600E..74Y
Altcode: 2005ESASP.600E..74C; 2005ESPM...11...74C; 2005dysu.confE..74C
  No abstract at ADS

Title: Impulsive Generation of Vertical Oscillations of a Solar
    Coronal Arcade Loop
Authors: Selwa, M.; Murawski, K.; Solanki, S. K.; Wang, T. J.;
   Shumlak, U.
Bibcode: 2005ESASP.596E..43S
Altcode: 2005ccmf.confE..43S
  No abstract at ADS

Title: Influence of the Paschen-Back Effect on the Stokes Profiles
    of the he 10830 Å Triplet
Authors: Sasso, C.; Lagg, A.; Solanki, S. K.
Bibcode: 2005ESASP.596E..64S
Altcode: 2005ccmf.confE..64S
  No abstract at ADS

Title: Stokes diagnostics of simulations of magnetoconvection of
    mixed-polarity quiet-Sun regions
Authors: Khomenko, E. V.; Shelyag, S.; Solanki, S. K.; Vögler, A.
Bibcode: 2005A&A...442.1059K
Altcode:
  Realistic solar magneto-convection simulations including the
  photospheric layers are used to study the polarization of the Fe i
  Zeeman-sensitive spectral lines at 6301.5, 6302.5, 15 648 and 15 652
  Å. The Stokes spectra are synthesized in a series of snapshots with
  a mixed-polarity magnetic field whose average unsigned strength varies
  from &lt; B &gt; = 10 to 140 G. The effects of spatial resolution and
  of the amount of magnetic flux in the simulation box on the profiles
  shapes, amplitudes and shifts are discussed. The synthetic spectra show
  many properties in common with those observed in quiet solar regions. In
  particular, the simulations reproduce the width and depth of spatially
  averaged Stokes I profiles, the basic classes of the Stokes V profiles
  and their amplitude and area asymmetries, as well as the abundance of
  the irregular-shaped Stokes V profiles. It is demonstrated that the
  amplitudes of the 1.56 μm lines observed in the inter-network are
  consistent with a "true" average unsigned magnetic field strength of
  20 G. We show that observations using these and visible lines, carried
  out under different seeing conditions (e.g., simultaneous observations
  at different telescopes), may result in different asymmetries and
  even opposite polarities of the profiles in the two spectral regions
  observed at the same spatial point.

Title: Photospheric and Chromospheric Magnetic Structure of a Sunspot
Authors: Orozco Suarez, D.; Lagg, A.; Solanki, S. K.
Bibcode: 2005ESASP.596E..59O
Altcode: 2005ccmf.confE..59O
  No abstract at ADS

Title: Magnetic Loops: a Comparison of Extrapolations from the
    Photosphere with Chromospheric Measurements
Authors: Wiegelmann, T.; Lagg, A.; Solanki, S.; Inhester, B.; Woch, J.
Bibcode: 2005ESASP.596E...7W
Altcode: 2005ccmf.confE...7W
  No abstract at ADS

Title: The Structure of the Lower Transition Region as Inferred from
    the Hydrogen LYMAN-α Line Radiance
Authors: Teriaca, L.; Schühle, U.; Solanki, S. K.; Curdt, W.;
   Marsch, E.
Bibcode: 2005ESASP.596E..66T
Altcode: 2005ccmf.confE..66T
  No abstract at ADS

Title: Supersonic Downflows in the Solar Chromosphere are Very Common
Authors: Aznar Cuadrado, R.; Solanki, S. K.; Lagg, A.
Bibcode: 2005ESASP.596E..49A
Altcode: 2005ccmf.confE..49A
  No abstract at ADS

Title: Polar Coronal Holes During Solar Cycles 22 and 23
Authors: Zhang, Jun; Woch, J.; Solanki, S.
Bibcode: 2005ChJAA...5..531Z
Altcode:
  Data from the Solar Wind Ion Composition Spectrometer (SWICS) on
  Ulysses and synoptic maps from Kitt Peak are used to analyze the
  polar coronal holes of solar activity cycles 22 and 23 (from 1990
  to end of 2003). In the beginning of the declining phase of solar
  cycles 22 and 23, the north polar coronal holes (PCHs) appear about
  one year earlier than the ones in the south polar region. The solar
  wind velocity and the solar wind ionic charge composition exhibit a
  characteristic dependence on the solar wind source position within
  a PCH. From the center toward the boundary of a young PCH, the solar
  wind velocity decreases, coinciding with a shift of the ionic charge
  composition toward higher charge states. However, for an old PCH, the
  ionic charge composition does not show any obvious change, although the
  latitude evolution of the velocity is similar to that of a young PCH.

Title: Solar activity, cosmic rays, and Earth's temperature: A
    millennium-scale comparison
Authors: Usoskin, I. G.; Schüssler, M.; Solanki, S. K.; Mursula, K.
Bibcode: 2005JGRA..11010102U
Altcode:
  Previous studies of a solar influence on climate variations have often
  suffered from the relatively short length of continuous direct solar
  observations of less than 400 years. We use two recently reconstructed
  series of the sunspot number and the cosmic ray flux to study this
  question over time intervals of up to nearly 1800 years. Comparison of
  the Sun-related data sets with various reconstructions of terrestrial
  Northern Hemisphere mean surface temperatures reveals consistently
  positive correlation coefficients for the sunspot numbers and
  consistently negative correlation coefficients for the cosmic rays. The
  significance levels reach up to 99% but vary strongly for the different
  data sets. The major part of the correlation is due to the similarity
  of the long-term trends in the data sets. The trend of the cosmic ray
  flux correlates somewhat better with the terrestrial temperature than
  the sunspot numbers derived from the same cosmogenic isotope data.

Title: Numerical simulations of vertical oscillations of a solar
    coronal loop
Authors: Selwa, M.; Murawski, K.; Solanki, S. K.; Wang, T. J.;
   Tóth, G.
Bibcode: 2005A&A...440..385S
Altcode:
  We consider the impulsive excitation of fast vertical kink standing
  waves in a solar coronal loop that is embedded in a potential
  arcade. The two-dimensional numerical model we implement includes the
  effects of field line curvature and nonlinearity on the excitation
  and damping of standing fast magnetosonic waves. The results of the
  numerical simulations reveal wave signatures which are characteristic
  of vertical loop oscillations seen in recent TRACE observational data.

Title: Detection of planetary transits using wavelet analysis and
    genetic algorithms.
Authors: Husser, T. -O.; Dreizler, S.; Solanki, S.; Thomas, R.
Bibcode: 2005AN....326R.628H
Altcode:
  No abstract at ADS

Title: Gravity-induced birefringence within the framework of Poincaré
    gauge theory
Authors: Preuss, Oliver; Solanki, Sami K.; Haugan, Mark P.; Jordan,
   Stefan
Bibcode: 2005PhRvD..72d2001P
Altcode: 2005gr.qc.....7071P
  Gauge theories of gravity provide an elegant and promising extension
  of general relativity. In this paper we show that the Poincaré gauge
  theory exhibits gravity-induced birefringence under the assumption
  of a specific gauge invariant nonminimal coupling between torsion
  and Maxwell’s field. Furthermore we give for the first time an
  explicit expression for the induced phase shift between two orthogonal
  polarization modes within the Poincaré framework. Since such a phase
  shift can lead to a depolarization of light emitted from an extended
  source this effect is, in principle, observable. We use white dwarf
  polarimetric data to constrain the essential coupling constant
  responsible for this effect.

Title: Kilo-Gauss Magnetic Fields in Three DA White Dwarfs
Authors: Aznar Cuadrado, R.; Jordan, S.; Napiwotzki, R.; Schmid,
   H. M.; Solanki, S. K.; Mathys, G.
Bibcode: 2005ASPC..334..159A
Altcode: 2005astro.ph..1191A; 2005astro.ph..1191C
  We have detected longitudinal magnetic fields between 2 and 4 kG in
  three normal DA white dwarfs (WD 0446-790, WD 1105-048, WD 2359-434)
  out of a sample of 12 by using optical spectropolarimetry done with
  the VLT Antu 8 m telescope equipped with FORS1. With the exception of
  40 Eri B (4 kG) these are the first positive detections of magnetic
  fields in white dwarfs below 30 kG. A detection rate of 25 % (3/12)
  may indicate now for the first time that a substantial fraction of
  white dwarfs have weak magnetic fields. This result, if confirmed by
  future observations, would form a cornerstone for our understanding
  of the evolution of stellar magnetic fields.

Title: A comparative study of the contrast of solar magnetic elements
    in CN and CH
Authors: Zakharov, V.; Gandorfer, A.; Solanki, S. K.; Löfdahl, M.
Bibcode: 2005A&A...437L..43Z
Altcode:
  Photospheric bright points were investigated in three different
  wavelength bands using interference filters centered at 436.5 nm
  (continuum), 430.5 nm (Fraunhofer's G-band dominated by absorption due
  to CH), and 388.7 nm (absorption band of CN). Such bright points serve
  as proxies of small-scale solar magnetic elements. Near diffraction
  limited imaging was achieved by real-time frame selection and
  subsequent joint phase diverse speckle reconstruction. Comparison of
  the filtergrams of NOAA0670 taken in CH and CN shows that the contrast
  of bright points is on average 1.4 times <P />higher in CN than in
  G-band, which is in good quantitative agreement with the predictions
  of Berdyugina et al. (2003, A&amp;A, 412, 513) and Rutten et al. (2001,
  ASP Conf. Ser., 236, 445).

Title: Constraining Gravitational Theories by Observing Magnetic
    White Dwarfs
Authors: Preuss, O.; Jordan, S.; Haugan, M. P.; Solanki, S. K.
Bibcode: 2005ASPC..334..265P
Altcode: 2004astro.ph.11688P
  Under the assumption of a specific nonminimal coupling of torsion
  to electromagnetism, spacetime is birefringent in the presence of a
  gravitational field leading to depolarization of light emitted from
  extended astrophysical sources. We use polarimetric data of the magnetic
  white dwarf RE J0317-853 to set for the very first time constraints on
  the essential coupling constant for this effect, giving k<SUP>2</SUP>
  ∼ (22 m)<SUP>2</SUP>.

Title: Climate:  How unusual is today's solar activity? (reply)
Authors: Solanki, S. K.; Usoskin, I. G.; Kromer, B.; Schüssler, M.;
   Beer, J.
Bibcode: 2005Natur.436E...4S
Altcode:
  Muscheler et al. claim that the solar activity affecting cosmic rays
  was much higher in the past than we deduced from <SUP>14</SUP>C
  measurements. However, this claim is based on a problematic
  normalization and is in conflict with independent results, such as
  the <SUP>44</SUP>Ti activity in meteorites and the <SUP>10</SUP>Be
  concentration in ice cores.

Title: Magnetic flux in the internetwork quiet Sun
Authors: Khomenko, E. V.; Martínez González, M. J.; Collados, M.;
   Vögler, A.; Solanki, S. K.; Ruiz Cobo, B.; Beck, C.
Bibcode: 2005A&A...436L..27K
Altcode:
  We report a direct comparison of the amplitudes of Stokes spectra of the
  Fe i 630 nm and 1.56 μm lines produced by realistic MHD simulations
  with simultaneous observations in the same spectral regions. The
  Stokes spectra were synthesized in snapshots with a mixed polarity
  magnetic field having a spatially averaged strength, &lt; B &gt;,
  between 10 and 30 G. The distribution of Stokes V amplitudes depends
  sensitively on &lt; B &gt;. A quiet inter-network region was observed
  at the German VTT simultaneously with TIP (1.56 μm) and POLIS (630
  nm). We find that the Stokes V amplitudes of both infrared and visible
  observations are best reproduced by the simulation snapshot with &lt;
  B &gt; = 20 G. In observations with 1 resolution, up to 2/3 of the
  magnetic flux can remain undetected.

Title: Excitation and damping of slow magnetosonic standing waves
    in a solar coronal loop
Authors: Selwa, M.; Murawski, K.; Solanki, S. K.
Bibcode: 2005A&A...436..701S
Altcode:
  We consider slow magnetosonic standing waves that are impulsively
  excited in a solar coronal loop. The one-dimensional numerical model
  we implement includes the effects of nonlinearity, optionally thermal
  conduction, heating, and cooling of the solar plasma. We numerically
  evaluate excitation and damping times of a standing wave in hot coronal
  loops on the basis of a parametric study. Results of the numerical
  simulations reveal that initially launched impulses mainly trigger
  the fundamental mode and its first harmonic, depending on the location
  of these pulses in space. Parametric study shows that these standing
  waves are excited in a dozen or so wave periods corresponding roughly
  to 13 min and that they are strongly damped over a similar time-scale.

Title: On the fine structure of sunspot penumbrae. II. The nature
    of the Evershed flow
Authors: Borrero, J. M.; Lagg, A.; Solanki, S. K.; Collados, M.
Bibcode: 2005A&A...436..333B
Altcode: 2005astro.ph..3677B
  We investigate the fine structure of the sunspot penumbra by means of
  a model that allows for a flux tube in horizontal pressure balance
  with the magnetic background atmosphere in which it is embedded. We
  apply this model to spectropolarimetric observations of two neutral
  iron lines at 1.56 μm and invert several radial cuts in the penumbra
  of the same sunspot at two different heliocentric angles. In the inner
  part of the penumbra we find hot flux tubes that are somewhat inclined
  to the horizontal. They become gradually more horizontal and cooler
  with increasing radial distance. This is accompanied by an increase
  in the velocity of the plasma and a decrease of the gas pressure
  difference between flux tube and the background component. At large
  radial distances the flow speed exceeds the critical speed and evidence
  is found for the formation of a shock front. These results are in good
  agreement with simulations of the penumbral fine structure and provide
  strong support for the siphon flow as the physical mechanism driving
  the Evershed flow.

Title: Millimeter-Interferometer Observations of Oscillations in
    the Solar Chromosphere
Authors: White, S. M.; Loukitcheva, M.; Solanki, S. K.
Bibcode: 2005AGUSMSH12A..03W
Altcode:
  The use of millimeter-interferometer data for the study of chromospheric
  structure and dynamics is tested using 85 GHz observations with the
  10-element Berkeley-Illinois-Maryland Array (BIMA). Interferometer
  data have the advantage over single-dish data that they allow both high
  spatial resolution and dense temporal sampling simultaneously. However,
  snapshot imaging of the quiet solar atmosphere with a small number of
  dishes is challenging. We demonstrate that techniques are available to
  carry out this task successfully. We compare observations of quiet Sun,
  active region and coronal hole targets using images with 10 arcsec
  resolution at 15 second cadence. The brightest features in the images
  are typically 1500 K above the background level, with a snapshot noise
  level of order 100 K. We use extensive tests to determine whether
  oscillation power can be recovered from sequences of snapshot images
  and show that they can down to quite weak levels. Intensity oscillations
  with significant power in the frequency range 1.5-8.0 mHz are found in
  the quiet-Sun and active region targets. For the quiet-Sun region we
  use the spatially-resolved time series to investigate the properties
  of network boundaries and cell interiors (internetwork) separately. In
  agreement with investigations at other wavelengths, the millimeter
  data show that power in the network tends to be at periods of 5 minutes
  and longer while power in the internetwork is present also at shorter
  (3-minute) periods.

Title: Initiation of hot coronal loop oscillations: Spectral features
Authors: Wang, T. J.; Solanki, S. K.; Innes, D. E.; Curdt, W.
Bibcode: 2005A&A...435..753W
Altcode:
  We explore the excitation of hot loop oscillations observed with the
  SUMER spectrograph on SOHO by analysing Fe XIX and Fe XXI spectral
  line profiles in the initial phase of the events. We investigate all
  54 Doppler shift oscillations in 27 flare-like events, whose physical
  parameters have been measured so far. In nearly 50% of the cases, the
  spectral evolution reveals the presence of two spectral components,
  one of them almost undisturbed, the other highly shifted. We find that
  the shifted component reaches maximum Doppler shift (on the order of
  100-300 km s<SUP>-1</SUP>) and peak intensity almost simultaneously. The
  velocity amplitude of the shifted component has no correlation with
  the oscillation amplitudes. These features imply that in these events
  the initial shifts are not caused by the locally oscillating plasma
  (or waves), but most likely by a pulse of hot plasma travelling
  along the loop through the slit position. This interpretation is also
  supported by several examples showing that standing slow mode waves
  are set up immediately after the initial line shift pulse (standing
  slow mode waves are inferred from the 1/4-period phase relationship
  between the velocity and intensity oscillations). We re-measure the
  physical parameters of the 54 Doppler oscillations by fitting the time
  profiles excluding the first peak, and find that the periods are almost
  unchanged, damping times are shorter by 5%, and amplitudes are smaller
  by 37% than measured when the first peak is included. We also measure
  the velocity of the net (background) flow during the oscillations,
  which is found to be nearly zero. Our result of initial hot flows
  supports the model of single footpoint (asymmetric) excitation, but
  contradicts chromospheric evaporation as the trigger.

Title: How To Use Magnetic Field Information For Coronal Loop
    Identification
Authors: Wiegelmann, T.; Inhester, B.; Lagg, A.; Solanki, S. K.
Bibcode: 2005SoPh..228...67W
Altcode: 2008arXiv0801.4573W
  The structure of the solar corona is dominated by the magnetic field
  because the magnetic pressure is about four orders of magnitude
  higher than the plasma pressure. Due to the high conductivity the
  emitting coronal plasma (visible, e.g., in SOHO/EIT) outlines the
  magnetic field lines. The gradient of the emitting plasma structures
  is significantly lower parallel to the magnetic field lines than
  in the perpendicular direction. Consequently information regarding
  the coronal magnetic field can be used for the interpretation of
  coronal plasma structures. We extrapolate the coronal magnetic field
  from photospheric magnetic field measurements into the corona. The
  extrapolation method depends on assumptions regarding coronal currents,
  e.g., potential fields (current-free) or force-free fields (current
  parallel to magnetic field). As a next step we project the reconstructed
  3D magnetic field lines on an EIT-image and compare with the emitting
  plasma structures. Coronal loops are identified as closed magnetic
  field lines with a high emissivity in EIT and a small gradient of the
  emissivity along the magnetic field.

Title: Comparing magnetic field extrapolations with measurements of
    magnetic loops
Authors: Wiegelmann, T.; Lagg, A.; Solanki, S. K.; Inhester, B.;
   Woch, J.
Bibcode: 2005A&A...433..701W
Altcode: 2008arXiv0801.4519W
  We compare magnetic field extrapolations from a photospheric magnetogram
  with the observationally inferred structure of magnetic loops in
  a newly developed active region. This is the first time that the
  reconstructed 3D-topology of the magnetic field is available to test
  the extrapolations. We compare the observations with potential fields,
  linear force-free fields and non-linear force-free fields. This
  comparison reveals that a potential field extrapolation is not
  suitable for a reconstruction of the magnetic field in this young,
  developing active region. The inclusion of field-line-parallel
  electric currents, the so called force-free approach, gives much better
  results. Furthermore, a non-linear force-free computation reproduces
  the observations better than the linear force-free approximation,
  although no free parameters are available in the former case.

Title: Can surface magnetic fields reproduce solar irradiance
    variations in cycles 22 and 23?
Authors: Wenzler, T.; Solanki, S. K.; Krivova, N. A.
Bibcode: 2005A&A...432.1057W
Altcode:
  Total solar irradiance is reconstructed using data from the
  spectromagnetograph on Kitt Peak for 1992 2003 (covering parts of cycles
  22 and 23) and compared with observational data. The model assumes
  that solar irradiance variations are caused by surface magnetism and
  its single free parameter is kept at the same value for both cycles. A
  good correspondence is found for the whole period of time, with no bias
  between the two cycles on time-scales longer than the solar rotation
  period. This is in agreement with the recent results of [CITE], but it
  is in contrast to the earlier analysis of [CITE], and suggests that the
  source of the irradiance variations is the same for cycles 22 and 23,
  namely the evolution of the magnetic flux at the solar surface.

Title: Solar activity over the last 1150 years: does it correlate
    with climate?
Authors: Usoskin, I. G.; Schüssler, M.; Solanki, S. K.; Mursula, K.
Bibcode: 2005ESASP.560...19U
Altcode: 2005csss...13...19U
  No abstract at ADS

Title: SoHO/EIT Observation of a Coronal Inflow
Authors: Tripathi, D.; Bothmer, V.; Solanki, S. K.; Schwenn, R.;
   Mierla, M.; Stenborg, G.
Bibcode: 2005IAUS..226..133T
Altcode:
  A distinct coronal inflow has been discovered after ∼90 min
  of prominence eruption associated coronal mass ejection (CME) on
  05-Mar-2000 by EIT (Extreme ultraviolet Imaging Telescope) aboard SoHO
  (Solar and Heliospheric Observatory). Evolution of the prominence seen
  by EIT was tracked into the LASCO/C2 and C3 field-of-view (FOV; 4-10
  R<SUB>⊙</SUB>) where it developed as the core of a typical three-part
  CME. The speed of the inflow, which was only seen in EIT FOV, was 70-80
  km/s at a height between 1.5-1.2 R<SUB>⊙</SUB> coinciding with the
  deceleration phase of the core of the CME in LASCO/C2. In contrast to
  dark inflow structures observed earlier and interpreted as plasma void
  moving down, the inflow reported here was bright. The inflow showed a
  constant deceleration and followed a curved path suggesting the apex
  of a contracting magnetic loop sliding down along other field lines.

Title: Modelling of irradiance variations through atmosphere models .
Authors: Krivova, N. A.; Solanki, S. K.
Bibcode: 2005MmSAI..76..834K
Altcode:
  Regular space-based measurements of solar total and spectral irradiance
  reveal its variations on time scales from minutes to decades. About
  90% of these variations are reproduced by recent models assuming
  that the evolution of the solar surface magnetic fields is their
  main cause. Circumstantial evidence suggests that variations on yet
  longer time scales, which are of special interest for climate studies,
  are also possible. Once good understanding of the directly observed
  variations has been gained, we can then attempt to extend the models
  back in time. Here a brief overview of our recent efforts to reconstruct
  solar total and spectral irradiance on time scales of days to centuries
  is given.

Title: A cross-calibrated sunspot areas time series since 1874
Authors: Balmaceda, L.; Solanki, S. K.; Krivova, N.
Bibcode: 2005MmSAI..76..929B
Altcode:
  A complete and homogeneous historical record of sunspot areas is
  a valuable proxy of solar variability, and is widely used, e.g.,
  to understand the behaviour of total and spectral solar irradiance
  at earlier times. Since 1874, the Royal Greenwich Observatory (RGO)
  regularly carried out these and other measurements until December
  1976. After that time the records from a number of different
  observatories are available. These, however, show some systematic
  differences and often have a lot of gaps. In order to compile a
  complete and cross-calibrated time series we compare the data from
  different observatories when they overlap and find the corresponding
  correction factors. The Greenwich data set is used as a basis until
  1976, the Russian data (stations from the former USSR) between 1977
  and 1985 and the Mt. Wilson data since 1986. Other data sets (Rome,
  Yunnan, Catania) are used to fill in the remaining gaps.

Title: Reconstruction of solar UV irradiance
Authors: Krivova, N. A.; Solanki, S. K.
Bibcode: 2005AdSpR..35..361K
Altcode:
  Understanding solar influence on the Earth’s climate requires
  a reconstruction of solar irradiance for the pre-satellite
  period. Considerable advances have been made in modelling the irradiance
  variations at wavelengths longer than 200 nm. At shorter wavelengths,
  however, the LTE approximation usually taken in such models fails, which
  makes a reconstruction of the solar UV irradiance a rather intricate
  problem. We choose an alternative approach and use the observed SUSIM
  UV spectra to extrapolate available models to shorter wavelengths.

Title: Irradiance models
Authors: Solanki, S. K.; Krivova, N. A.; Wenzler, T.
Bibcode: 2005AdSpR..35..376S
Altcode:
  Measurements of solar irradiance have revealed variations at all the
  sampled time scales (ranging from minutes to the length of the solar
  cycle). One important task of models is to identify the causes of the
  observed (total and spectral) irradiance variations. Another major
  aim is to reconstruct irradiance over time scales longer than sampled
  by direct measurements in order to consider if and to what extent
  solar irradiance variations may be responsible for global climate
  change. Here, we describe recent efforts to model solar irradiance
  over the current and the previous two solar cycles. These irradiance
  models are remarkably successful in reproducing the observed total and
  spectral irradiance, although further improvements are still possible.

Title: Shock Wave Driven by an Expanding System of Loops
Authors: Raouafi, N. -E.; Mancuso, S.; Solanki, S. K.; Inhester, B.;
   Mierla, M.; Stenborg, G.; Delaboudinière, J. P.; Benna, C.
Bibcode: 2005IAUS..226..127R
Altcode:
  We report on a Coronal Mass Ejection (CME) observed on June 27
  1999 by the UltraViolet Coronagraph Spectrometer (UVCS) telescope
  operating on board the SOHO spacecraft. The CME was also observed
  by LASCO (SOHO). Emission of hot material has been recorded by UVCS
  propagating in front of an opening system of loops generated by the
  CME. The evolution of the UVCS structure is highly correlated to the
  evolution of the opening loop. The data reveal excess broadening of
  the O VI doublet lines and an enhancement in the intensity of the Si
  XII λ 520.66 and λ499.37 lines due to the motion of the expanding hot
  gas. The hot gas emission seems to be due to a shock wave propagating in
  front of a very fast gas bubble traveling along the opening loop system.

Title: Mechanisms of secular magnetic field variations.
Authors: Solanki, S. K.; Schüssler, M.
Bibcode: 2005MmSAI..76..781S
Altcode:
  The variability of the solar magnetic field on time scales of decades
  and longer lies at the root of the various mechanisms by which the
  changing Sun could affect Earth's climate. We discuss the origin of
  the secular variability of both the open heliospheric flux and the
  total unsigned solar surface flux and review models that have been put
  forward to describe these variations. We propose that a combination of
  the effects of overlapping activity cycles and the long decay time of
  large-scale magnetic patterns is responsible for the secular variability
  of the solar magnetic field.

Title: Excitation and Damping of Slow Magnetosonic Standing Waves
    in a Solar Coronal Loop
Authors: Selwa, M.; Murawski, K.; Solanki, S. K.
Bibcode: 2004ESASP.575...91S
Altcode: 2004soho...15...91S
  No abstract at ADS

Title: Signature of Current Sheets as Seen by Tip at VTT in the HeI
    Multiplet at 1083.0 nm
Authors: Aznar Cuadrado, R.; Solanki, S. K.; Lagg, A.; Thomas, R. M.
Bibcode: 2004ESASP.575..593A
Altcode: 2004soho...15..593A
  No abstract at ADS

Title: Small-Scale Flares as the Cause of Quiet Sun EUV Emission
Authors: Pauluhn, A.; Solanki, S. K.
Bibcode: 2004ESASP.575..501P
Altcode: 2004soho...15..501P
  No abstract at ADS

Title: Sensitivity of Solar Off-Limb Line Profiles to Electron
    Density Stratification and the Velocity Distribution Anisotropy
Authors: Raouafi, N. -E.; Solanki, S. K.
Bibcode: 2004ESASP.575..170R
Altcode: 2004soho...15..170R
  No abstract at ADS

Title: Why are Coronal Holes Indistinguishable from the Quiet Sun
    in Transition Region Radiation?
Authors: Wiegelmann, T.; Solanki, S. K.
Bibcode: 2004ESASP.575...35W
Altcode: 2004soho...15...35W
  No abstract at ADS

Title: Similarities and Differences between Coronal Holes and the
Quiet Sun: Are Loop Statistics the Key?
Authors: Wiegelmann, T.; Solanki, S. K.
Bibcode: 2004SoPh..225..227W
Altcode: 2008arXiv0802.0120W
  Coronal holes (CH) emit significantly less at coronal temperatures
  than quiet-Sun regions (QS), but can hardly be distinguished in most
  chromospheric and lower transition region lines. A key quantity for the
  understanding of this phenomenon is the magnetic field. We use data from
  SOHO/MDI to reconstruct the magnetic field in coronal holes and the
  quiet Sun with the help of a potential magnetic model. Starting from
  a regular grid on the solar surface we then trace field lines, which
  provide the overall geometry of the 3D magnetic field structure. We
  distinguish between open and closed field lines, with the closed field
  lines being assumed to represent magnetic loops. We then try to compute
  some properties of coronal loops. The loops in the coronal holes (CH)
  are found to be on average flatter than in the QS. High and long closed
  loops are extremely rare, whereas short and low-lying loops are almost
  as abundant in coronal holes as in the quiet Sun. When interpreted in
  the light of loop scaling laws this result suggests an explanation for
  the relatively strong chromospheric and transition region emission
  (many low-lying, short loops), but the weak coronal emission (few
  high and long loops) in coronal holes. In spite of this contrast
  our calculations also suggest that a significant fraction of the cool
  emission in CHs comes from the open flux regions. Despite these insights
  provided by the magnetic field line statistics further work is needed
  to obtain a definite answer to the question if loop statistics explain
  the differences between coronal holes and the quiet Sun.

Title: Comparison between KPVT/SPM and SoHO/MDI magnetograms with
    an application to solar irradiance reconstructions
Authors: Wenzler, T.; Solanki, S. K.; Krivova, N. A.; Fluri, D. M.
Bibcode: 2004A&A...427.1031W
Altcode:
  To be able to use both space- and ground-based solar magnetograms and
  construct long time series of derived parameters it is important to
  cross-calibrate them so that we can estimate their reliability and
  combine them. Using two different techniques, we compare magnetograms
  as well as continuum images recorded by the Spectropolarimeter (SPM)
  on Kitt Peak and the Michelson Doppler Interferometer (MDI) on board
  SoHO. We find that the result obtained depends on the method used. The
  method we favour gives almost identical umbral and penumbral areas and
  very similar total magnetic fluxes in faculae. The magnetic fluxes in
  umbrae and penumbrae returned by the two instruments, however, differ
  considerably. We also demonstrate that SPM data can be employed to
  reconstruct total solar irradiance variations with almost the same
  accuracy as recently shown for MDI data.

Title: Small-Scale Solar Magnetic Elements: Simulations and
    Observations
Authors: Solanki, S. K.; Schüssler, M.
Bibcode: 2004ASPC..325..105S
Altcode:
  Both the small-scale and large-scale properties of solar features,
  such as sunspots and the solar corona, are influenced strongly by
  the small-scale structure of the underlying magnetic field. Even
  some global properties of the Sun, such as variations of the Sun's
  irradiance, depend on the local properties of small-scale magnetic
  features. We briefly describe these dependences, as well as recent
  results concerning the small-scale magnetic elements deduced from
  radiation MHD simulations and spectropolarimetric observations. The
  simulations reproduce a number of sensitive observational tests and
  explain, e.g. why G-band images allow only a part of the magnetic flux
  to be identified.

Title: The Magnetic Field from the Solar Interior to the Heliosphere
Authors: Solanki, Sami K.
Bibcode: 2004ASSL..317..373S
Altcode: 2004shis.conf..373S
  No abstract at ADS

Title: G-band spectral synthesis and diagnostics of simulated solar
    magneto-convection
Authors: Shelyag, S.; Schüssler, M.; Solanki, S. K.; Berdyugina,
   S. V.; Vögler, A.
Bibcode: 2004A&A...427..335S
Altcode:
  Realistic simulations of radiative magneto-convection in the solar
  (sub)photosphere are used for a spectral synthesis of Fraunhofer's G
  band, which is dominated by spectral lines from the CH molecule. It
  is found that the spatial pattern of integrated G-band brightness
  closely matches the spatial structure of magnetic flux concentrations
  in the convective downflow regions. The brightness contrast is mainly
  caused by the weakening of CH lines due to the reduced CH abundance
  and the resulting shift of the optical depth scale in the hot and
  tenuous magnetic flux concentrations. Various properties of the
  synthetic brightness images agree well with G-band observations. These
  results lends credit to the observational usage of G-band bright
  features as proxies for magnetic flux concentrations in the solar
  photosphere. However, the converse is only correct in a limited sense:
  only a fraction of the magnetic flux concentrations turn out to be
  bright in the G band.

Title: Apparent solar radius variations. The influence of magnetic
    network and plage
Authors: Bruls, J. H. M. J.; Solanki, S. K.
Bibcode: 2004A&A...427..735B
Altcode:
  Solar radius measurements, a by-product of the magnetograms recorded
  several times daily at Mt. Wilson Observatory over a period of a few
  decades, have revealed apparent variations of about 0.4 arcsec that are
  correlated with the solar cycle. We note that the radius definition
  used for the analysis of those magnetograms automatically converts
  intensity variations near the limb into apparent radius variations. A
  change in the average temperature structure of the quiet Sun can be
  ruled out as the source of these variations, since such a change would
  need to be very significant and would lead to other easily measurable
  consequences that are not observed. We show that plage emission near
  the solar limb associated with the magnetic activity variation during a
  solar cycle produces apparent radius changes of the correct sign. The
  use of plane-parallel or spherically-symmetric models to describe
  the faculae gives apparent radius variations that are a factor of
  4-10 too small in magnitude. If the Mt. Wilson results are correct,
  then this implies that the small-scale structure of faculae produces
  limb extensions that are considerably larger than those returned by
  a plane-parallel or spherically-symmetric model.

Title: Effect of the electron density stratification on off-limb O
VI line profiles: How large is the velocity distribution anisotropy
    in the solar corona?
Authors: Raouafi, N. -E.; Solanki, S. K.
Bibcode: 2004A&A...427..725R
Altcode:
  Coronagraphic spectral observations carried out with UVCS on SoHO
  have shown that the velocity distribution in the solar corona is
  highly anisotropic. Here we examine the influence of the density
  stratification on the interpretation of such observations. In
  particular, we investigate the profiles of O VI lines emitted in
  the corona by employing an analytical 2-D model of the large scale
  coronal magnetic field and solar wind. We concentrate on the polar
  coronal holes and take into account the integration along the line of
  sight. We find that at distances greater than 1 R<SUB>⊙</SUB> from
  the solar surface the widths of the emitted lines are significantly
  affected by the details of the adopted electron density profiles. In
  particular, the densities deduced by Doyle et al. (\cite{Doyle1999a},b)
  from SoHO data result in O VI profiles whose widths and intensity ratio
  are relatively close to the values observed by UVCS/SoHO although only
  isotropic velocity distributions are employed. Hence we expect that
  the magnitude of anisotropy of the velocity distribution deduced from
  UVCS data depends strongly on the adopted density profile.

Title: Evolution of the large-scale magnetic field on the solar
surface: A parameter study
Authors: Baumann, I.; Schmitt, D.; Schüssler, M.; Solanki, S. K.
Bibcode: 2004A&A...426.1075B
Altcode:
  Magnetic flux emerging on the Sun's surface in the form of bipolar
  magnetic regions is redistributed by supergranular diffusion, a poleward
  meridional flow and differential rotation. We perform a systematic and
  extensive parameter study of the influence of various parameters on the
  large-scale field, in particular the total unsigned surface flux and the
  flux in the polar caps, using a flux transport model. We investigate
  both, model parameters and source term properties. We identify the
  average tilt angle of the emerging bipolar regions, the diffusion
  coefficient (below a critical value), the total emergent flux and,
  for the polar field, the meridional flow velocity and the cycle length
  as parameters with a particularly large effect. Of special interest is
  the influence of the overlap between successive cycles. With increasing
  overlap, an increasing background field (minimum flux at cycle minimum)
  is built up, which is of potential relevance for secular trends of
  solar activity and total irradiance.

Title: SUNRISE: high-resolution UV/VIS observations of the Sun from
    the stratosphere
Authors: Gandorfer, Achim M.; Solanki, Sami K.; Schüssler, Manfred;
   Curdt, Werner; Lites, Bruce W.; Martínez Pillet, Valentin; Schmidt,
   Wolfgang; Title, Alan M.
Bibcode: 2004SPIE.5489..732G
Altcode:
  SUNRISE is a balloon-borne solar telescope with an aperture of 1m,
  working in the UV/VIS optical domain. The main scientific goal
  of SUNRISE is to understand the structure and dynamics of the
  magnetic field in the atmosphere of the Sun. SUNRISE will provide
  diffraction-limited images of the photosphere and chromosphere with
  an unpredecented resolution down to 35km at wavelengths around
  220nm. Focal-plane instruments are a spectrograph/polarimeter,
  a Fabry-Perot filter magnetograph, and a filter imager. The first
  stratospheric long-duration balloon flight of SUNRISE over Antarctica
  is planned in winter 2006/2007. SUNRISE is a joint project of the
  Max-Planck-Institut fur Sonnensystemforschung (MPS), Katlenburg-Lindau,
  with the Kiepenheuer-Institut für Sonnenphysik (KIS), Freiburg, the
  High-Altitude Observatory (HAO), Boulder, the Lockheed-Martin Solar and
  Astrophysics Lab. (LMSAL), Palo Alto, and the Instituto de Astrofisica
  de Canarias, La Laguna, Tenerife. In this paper we will present an
  overview on the mission and give a description of the instrumentation,
  now, at the beginning of the hardware construction phase.

Title: Solar Irradiance Variations: From Current Measurements to
    Long-Term Estimates
Authors: Solanki, Sami K.; Krivova, Natalie A.
Bibcode: 2004SoPh..224..197S
Altcode: 2005SoPh..224..197S
  Variations of solar total and spectral irradiance are prime
  solar quantities purported to have an influence on the Earth's
  climate. Quantitative estimates of irradiance over as long a time
  as possible are needed to judge their effectiveness in forcing the
  climate. In order to do this reliably, first the measured record must
  be reproduced and a feeling for the physics underlying the irradiance
  variations must be developed. With the help of this knowledge combined
  with the available proxy data, reconstructions of irradiance in the
  past, generally since the Maunder minimum, are attempted. Here a brief
  introduction to some of the irradiance reconstruction work aiming at
  irradiance on time scales of days to the solar cycle is given, followed
  by a brief and incomplete overview of the longer-term reconstructions.

Title: Unusual activity of the Sun during recent decades compared
    to the previous 11,000 years
Authors: Solanki, S. K.; Usoskin, I. G.; Kromer, B.; Schüssler, M.;
   Beer, J.
Bibcode: 2004Natur.431.1084S
Altcode:
  Direct observations of sunspot numbers are available for the past
  four centuries, but longer time series are required, for example,
  for the identification of a possible solar influence on climate
  and for testing models of the solar dynamo. Here we report a
  reconstruction of the sunspot number covering the past 11,400 years,
  based on dendrochronologically dated radiocarbon concentrations. We
  combine physics-based models for each of the processes connecting
  the radiocarbon concentration with sunspot number. According to our
  reconstruction, the level of solar activity during the past 70 years is
  exceptional, and the previous period of equally high activity occurred
  more than 8,000 years ago. We find that during the past 11,400 years
  the Sun spent only of the order of 10% of the time at a similarly high
  level of magnetic activity and almost all of the earlier high-activity
  periods were shorter than the present episode. Although the rarity
  of the current episode of high average sunspot numbers may indicate
  that the Sun has contributed to the unusual climate change during the
  twentieth century, we point out that solar variability is unlikely
  to have been the dominant cause of the strong warming during the past
  three decades.

Title: Shock wave driven by an expanding system of loops
Authors: Raouafi, N. -E.; Mancuso, S.; Solanki, S. K.; Inhester, B.;
   Mierla, M.; Stenborg, G.; Delaboudinière, J. P.; Benna, C.
Bibcode: 2004A&A...424.1039R
Altcode:
  We report on a Coronal Mass Ejection (CME) observed on June 27, 1999 by
  the UltraViolet Coronagraph Spectrometer (UVCS) telescope operating on
  board the SOHO spacecraft. The CME was also observed by the Large Angle
  Spectroscopic Coronagraph (LASCO). Emission of hot material has been
  recorded by UVCS propagating in front of an opening system of loops
  generated by the CME. The evolution of the UVCS structure is highly
  correlated with the evolution of the opening loop. The data reveal
  excess broadening of the O VI doublet lines and an enhancement in the
  intensity of the Si XII λ520.66 and λ499.37 lines due to the motion
  of the expanding hot gas. The hot gas emission seems to be due to a
  shock wave propagating in front of a very fast gas bubble traveling
  along the opening loop system.

Title: Discovery of kilogauss magnetic fields in three DA white dwarfs
Authors: Aznar Cuadrado, R.; Jordan, S.; Napiwotzki, R.; Schmid,
   H. M.; Solanki, S. K.; Mathys, G.
Bibcode: 2004A&A...423.1081A
Altcode: 2004astro.ph..5308C; 2004astro.ph..5308A
  We have detected longitudinal magnetic fields between 2 and 4 kG in
  three (WD 0446-790, WD 1105-048, WD 2359-434) out of a sample of 12
  normal DA white dwarfs by using optical spectropolarimetry done with the
  VLT Antu 8 m telescope equipped with FORS1. With the exception of 40 Eri
  B (4 kG) these are the first positive detections of magnetic fields in
  white dwarfs below 30 kG. Although suspected, it was not clear whether
  a significant fraction of white dwarfs contain magnetic fields at this
  level. These fields may be explained as relics from magnetic fields in
  the main-sequence progenitors considerably enhanced by magnetic flux
  conservation during the shrinkage of the core. A detection rate of 25%
  (3/12) may indicate now for the first time that a substantial fraction
  of white dwarfs have a weak magnetic field. This result, if confirmed
  by future observations, would form a cornerstone for our understanding
  of the evolution of stellar magnetic fields. <P />Based on observations
  collected at the European Southern Observatory, Paranal, Chile, under
  programme ID 70.D-0259.

Title: An astronomical search for evidence of new physics: Limits
    on gravity-induced birefringence from the magnetic white dwarf
    REJ0317-853
Authors: Preuss, Oliver; Haugan, Mark P.; Solanki, Sami K.; Jordan,
   Stefan
Bibcode: 2004PhRvD..70f7101P
Altcode: 2004gr.qc.....5068P
  The coupling of the electromagnetic field directly with gravitational
  gauge fields leads to new physical effects that can be tested using
  astronomical data. Here we consider a particular case for closer
  scrutiny, a specific nonminimal coupling of torsion to electromagnetism,
  which enters into a metric-affine geometry of space-time. We show
  that under the assumption of this nonminimal coupling, space-time is
  birefringent in the presence of such a gravitational field. This leads
  to the depolarization of light emitted from extended astrophysical
  sources. We use polarimetric data of the magnetic white dwarf
  REJ0317-853 to set, for the very first time, constraints on the
  essential coupling constant for this effect, giving k<SUP>2</SUP>≲(19
  m)<SUP>2</SUP>.

Title: Thermal-magnetic relation in a sunspot and a map  of its
    Wilson depression
Authors: Mathew, S. K.; Solanki, S. K.; Lagg, A.; Collados, M.;
   Borrero, J. M.; Berdyugina, S.
Bibcode: 2004A&A...422..693M
Altcode:
  We present relations between thermal and magnetic quantities in a
  simple, isolated sunspot, as deduced from the inversion of 1.56 μm
  spectropolarimetric data. We used a combination of two infrared Fe I
  lines at 15 648.5 Å and 15 652.8 Å/ in the inversions. Due to the
  high Zeeman sensitivity of these lines, we can study this relationship
  in the entire sunspot. The relevant parameters were derived both as a
  function of location within the sunspot and of height in the atmosphere
  using an inversion technique based on response functions. In this paper
  we relate the magnetic vector with temperature. We find a non-linear
  relationship between the various components of the magnetic vector and
  temperature, which confirm the results from earlier investigations. We
  also computed the Wilson depression and the plasma β for the observed
  sunspot and compare our results with earlier findings.

Title: On the fine structure of sunspot penumbrae. I. A quantitative
    comparison of two semiempirical models with implications for the
    Evershed effect
Authors: Borrero, J. M.; Solanki, S. K.; Bellot Rubio, L. R.; Lagg,
   A.; Mathew, S. K.
Bibcode: 2004A&A...422.1093B
Altcode:
  Sunspot penumbrae exhibit prominent fine structure. Different
  interpretations of spectropolarimetric observations suggest different,
  sometimes contradictory, properties of this fine structure. In this
  paper we show that the results of inversions of penumbral infrared
  profiles based on one-component models with gradients of the atmospheric
  parameters and two-component models without gradients are compatible
  with each other. Our analysis reconciles the results of previous
  investigations and provides further support for the picture that sunspot
  penumbrae are composed of penumbral flux tubes embedded in a magnetic
  background. The magnetic field in the tubes is more horizontal and
  weaker than that of the background atmosphere. While the tubes carry
  most of the Evershed flow, the background is essentially at rest. We
  notice also that the magnetic field strength in the flux tubes drops
  much more slowly with radial distance than the background field. This
  finding is discussed as a possible driver for the Evershed flow.

Title: Vertical oscillations of a coronal loop observed by TRACE
Authors: Wang, T. J.; Solanki, S. K.
Bibcode: 2004A&A...421L..33W
Altcode:
  We report on a loop oscillation event observed by TRACE in the
  195 Åbandpass at the solar limb. The difference images reveal the
  first evidence for vertical kink oscillations of the loop, i.e.,
  alternately expanding and shrinking motions, in contrast to horizontal
  transverse loop oscillations reported before, which exhibit swaying
  motions. Based on the 3D geometry of the oscillating loop derived from
  the observation by fitting with a circular or elliptical loop model,
  we simulate these two kinds of global kink modes and find that only
  the vertical oscillations produce a signature in the difference images
  in agreement with the observations. We also find that the oscillating
  loop is associated with intensity variations. Based on the measured
  displacement amplitude, the simulation predicts an intensity variation
  of about 13% due to density changes produced by the change of the
  loop length. The observed intensity changes have the same sign but
  are considerably larger than the predictions although the error bars
  are also large. This suggests that these oscillations are compressible.

Title: Line profile characteristics of solar explosive event bursts
Authors: Ning, Z.; Innes, D. E.; Solanki, S. K.
Bibcode: 2004A&A...419.1141N
Altcode:
  The spatial structure and temporal evolution of explosive events
  are explored using spectral observations of the Si IV 1393 Å line
  obtained with the Solar Ultraviolet Measurements of Emitted Radiation
  spectrograph (SUMER). Three areas of quiet Sun near disk center,
  8 arcsec×120 arcsec each, were rastered with a cadence of less than
  1 min for a period of over half an hour. Events were identified by a
  non-Gaussian excess in the blue and/or red wings of the line. We found
  21 sites where events re-occur. The sites are clustered near regions of
  evolving network fields seen in low resolution Michelson Doppler Imager
  (MDI) magnetic field images. Events tend to expand and shrink across the
  surface with a speed ∼ 25 km s<SUP>-1</SUP>. Individual events were
  also seen to move at this speed across the solar surface. Consecutive
  events often have different line profile characteristics and sizes,
  suggesting changes in the structure of the accelerated plasma from event
  to event. In the majority of events, blue and red wing brightenings do
  not produce a simultaneous line intensity increase. Also, the red and
  blue wing emission is mostly co-spatial implying either non-directed
  flow or jets orientated along the line-of-sight (i.e. out from and
  towards the solar surface). The explosive events within a burst are
  in some cases separated by 3-5 min, suggesting that oscillations,
  which are known to have such periods, may play a role in triggering
  the individual events of a burst.

Title: Millimeter observations and chromospheric dynamics
Authors: Loukitcheva, M.; Solanki, S. K.; Carlsson, M.; Stein, R. F.
Bibcode: 2004A&A...419..747L
Altcode:
  The intensities of submillimeter and millimeter continua, which are
  formed in LTE and depend linearly on temperature, may be able to provide
  a test of models of the Solar chromosphere. We have taken a collection
  of submillimeter and millimeter wave observed brightness temperatures
  T<SUB>b</SUB> of the quiet Sun from the literature and compared it
  with brightness temperatures computed from the standard static models
  of Fontenla, Avrett and Loeser (FAL) and the dynamic simulations of
  Carlsson &amp; Stein (CS). The analysis of the dynamic simulations
  of Carlsson &amp; Stein reveals that radio emission at millimeter
  wavelengths is extremely sensitive to dynamic processes in the
  chromosphere, if these are spatially and temporally resolved. The most
  striking result is that the dynamic picture of the solar internetwork
  chromosphere is consistent with currently available millimeter and
  submillimeter brightness observations. The spectrum obtained by
  averaging over the spectra from all time-steps of CS simulations
  provides a good fit to observed temporally and spatially averaged
  millimeter data in spite of the absence of a permanent temperature
  rise at low chromospheric heights in the simulations. This does not by
  itself rule out the presence of a chromospheric temperature rise as
  present in the FAL models, since a combination of such models also
  reproduces the (low resolution) data relatively well. Millimeter
  observations indicate that using radio techniques it is possible
  to extend observations of the solar oscillatory component to the
  heights above those previously observed in the photospheric and low
  chromospheric spectral lines and submillimeter continuum. For more
  precise diagnostics of chromospheric dynamics, high temporal and spatial
  resolution interferometric observations in the millimeter-wavelength
  region would be particularly useful. <P />Table \ref{tab:table} is
  only available in electronic form at http://www.edpsciences.org

Title: Usoskin et al. Reply:
Authors: Usoskin, Ilya G.; Solanki, Sami K.; Schüssler, Manfred;
   Mursula, Kalevi
Bibcode: 2004PhRvL..92s9002U
Altcode:
  A Reply to the Comment by G. M. Raisbeck and F. Yiou.

Title: Measuring Stellar Differential rotation with asteroseismology
Authors: Gizon, Laurent; Solanki, Sami K.
Bibcode: 2004SoPh..220..169G
Altcode:
  The variation of rotation with latitude is poorly known on stars
  other than the Sun. Several indirect techniques, photometric and
  spectroscopic, have been used to search for departure from rigid
  rotation for sufficiently fast rotators. Here we investigate the
  possibility of measuring stellar differential rotation for solar-type
  stars through asteroseismology. Rotationally split frequencies of
  global oscillation provide information about rotation at different
  latitudes depending on the azimuthal order, m, of the mode of
  pulsation. We present a method to estimate differential rotation
  based on the realization that the m = ±1 and m = ±2 components
  of quadrupole oscillations can be observed simultaneously in
  asteroseismology. Rotational frequency splittings can be inverted
  to provide an estimate of the difference in stellar angular velocity
  between the equator and 45° latitude. The precision of the method,
  assessed through Monte Carlo simulations, depends on the value of the
  mean rotation and on the inclination angle between the rotation axis
  and the line of sight.

Title: Effect of spatial resolution on estimating the Sun's magnetic
    flux
Authors: Krivova, N. A.; Solanki, S. K.
Bibcode: 2004A&A...417.1125K
Altcode:
  A critical question related to a possible secular trend in the Sun's
  total magnetic flux and consequently in solar irradiance is the total
  amount of magnetic flux present on the Sun and how it is distributed
  between active regions and the quiet Sun. NSO/Kitt Peak synoptic
  charts have in the past been used to estimate the total flux and the
  fraction of the flux in active regions and in the quiet Sun. Since a
  single pixel of these synoptic charts is much bigger than individual
  small-scale magnetic elements and opposite polarities may be present
  within the same pixel, some magnetic flux escaped notice. Here we
  estimate the fraction of the magnetic flux escaping detection in Kitt
  Peak synoptic charts. By artificially reducing the spatial resolution of
  MDI full-disc and high-resolution magnetograms we study the influence
  of the resolution on the measured total magnetic flux. Noise in the
  data poses the main difficulty to this approach and is carefully
  studied. It is concluded that at least half of the magnetic flux in
  the quiet Sun remains undetected in Kitt Peak synoptic charts and that
  the total flux present on the solar surface at maxima of activity is
  around twice the flux present at activity minima.

Title: Distribution of magnetically confined circumstellar matter
    in oblique rotators
Authors: Preuss, O.; Schüssler, M.; Holzwarth, V.; Solanki, S. K.
Bibcode: 2004A&A...417..987P
Altcode: 2004astro.ph..1599P
  We consider the mechanical equilibrium and stability of matter trapped
  in the magnetosphere of a rapidly rotating star. Assuming a dipolar
  magnetic field and arbitrary inclination of the magnetic axis with
  respect to the axis of rotation we find stable equilibrium positions a)
  in a (warped) disk roughly aligned with the magnetic equatorial plane
  and b) at two locations above and below the disk, whose distance from
  the star increases with decreasing inclination angle between dipole and
  rotation axis. The distribution of matter is not strongly affected by
  allowing for a spatial offset of the magnetic dipole. These results
  provide a possible explanation for some observations of corotating
  localized mass concentrations in hot magnetic stars.

Title: Towards understanding the β Pictoris dust stream
Authors: Krivov, A. V.; Krivova, N. A.; Solanki, S. K.; Titov, V. B.
Bibcode: 2004A&A...417..341K
Altcode:
  The recent radar detection by \citet{baggaley-2000} of a collimated
  stream of interstellar meteoroids postulated to be sourced at β
  Pictoris, a nearby star with a prominent dust disk, presents a challenge
  to theoreticians. Two mechanisms of possible dust ejection from β
  Pic have been proposed: ejection of dust by radiation pressure from
  comets in eccentric orbits and by gravity of a hypothetical planet
  in the disk. Here we re-examine observational data and reconsider
  theoretical scenarios, substantiating them with detailed modeling
  to test whether they can explain quantitatively and simultaneously
  the masses, speeds, and fluxes. Our analysis of the stream geometry
  and kinematics confirms that β Pic is the most likely source of the
  stream and suggests that an intensive dust ejection phase took place
  ∼0.7 Myr ago. Our dynamical simulations show that high ejection
  speeds retrieved from the observations can be explained by both
  planetary ejection and radiation pressure mechanisms, providing,
  however, several important constraints. In the planetary ejection
  scenario, only a ``hot Jupiter''-type planet with a semimajor axis
  of less than 1 AU can be responsible for the stream, and only if the
  disk was dynamically ``heated'' by a more distant massive planet. The
  radiation pressure scenario also requires the presence of a relatively
  massive planet at several AU or more, that had heated the cometesimal
  disk before the ejection occurred. Finally, the dust flux measured at
  Earth can be brought into reasonable agreement with both scenarios,
  provided that β Pic's protoplanetary disk recently passed through an
  intensive short-lasting (∼0.1 Myr) clearance stage by nascent giant
  planets, similar to what took place in the early solar system.

Title: Solar constraints on new couplings between electromagnetism
    and gravity
Authors: Solanki, S. K.; Preuss, O.; Haugan, M. P.; Gandorfer, A.;
   Povel, H. P.; Steiner, P.; Stucki, K.; Bernasconi, P. N.; Soltau, D.
Bibcode: 2004PhRvD..69f2001S
Altcode: 2004gr.qc.....2055S
  The unification of quantum field theory and general relativity is a
  fundamental goal of modern physics. In many cases, theoretical efforts
  to achieve this goal introduce auxiliary gravitational fields, ones
  in addition to the familiar symmetric second-rank tensor potential
  of general relativity, and lead to nonmetric theories because of
  direct couplings between these auxiliary fields and matter. Here,
  we consider an example of a metric-affine gauge theory of gravity in
  which torsion couples nonminimally to the electromagnetic field. This
  coupling causes a phase difference to accumulate between different
  polarization states of light as they propagate through the metric-affine
  gravitational field. Solar spectropolarimetric observations are reported
  and used to set strong constraints on the relevant coupling constant k:
  k<SUP>2</SUP>&lt;(2.5 km)<SUP>2</SUP>.

Title: Spot sizes on Sun-like stars
Authors: Solanki, S. K.; Unruh, Y. C.
Bibcode: 2004MNRAS.348..307S
Altcode: 2003astro.ph.11310S
  The total area coverage by starspots is of interest for a variety
  of reasons, but direct techniques only provide estimates of this
  important quantity. Sunspot areas exhibit a lognormal size distribution
  irrespective of the phase of the activity cycle, implying that most
  sunspots are small. Here we explore the consequences if starspot areas
  were similarly distributed. The solar data allow for an increase in
  the fraction of larger sunspots with increasing activity. Taking
  this difference between the size distribution at sunspot maximum
  and minimum, we extrapolate to higher activity levels, assuming
  different dependences of the parameters of the lognormal distribution
  on total spot coverage. We find that, even for very heavily spotted
  (hypothetical) stars, a large fraction of the spots are smaller than
  the current resolution limit of Doppler images and hence might be
  missed on traditional Doppler maps.

Title: Retrieval of the full magnetic vector with the He I multiplet
    at 1083 nm. Maps of an emerging flux region
Authors: Lagg, A.; Woch, J.; Krupp, N.; Solanki, S. K.
Bibcode: 2004A&A...414.1109L
Altcode:
  A technique is presented to invert Stokes profiles of the He I 1083
  nm multiplet lines in order to obtain the full magnetic vector and the
  line-of-sight velocity. The technique makes use of spectropolarimetry
  connected with the Zeeman effect supplemented by a simple Hanle effect
  based diagnostic when appropriate. It takes into account effects
  like line saturation, magnetooptieffects, etc. and is coupled with a
  genetic algorithm, which ensures that the global minimum in a goodness
  of fit hypersurface is found. Tests using both artificial and real
  data demonstrated the robustness of the method. As an illustration
  maps of deduced parameters of an emerging flux region are shown and
  briefly discussed.

Title: Dynamic Behaviors of the Quiet Sun Seen by SUMER
Authors: Ning, Z.; Innes, D. E.; Solanki, S. K.
Bibcode: 2004ESASP.547..297N
Altcode: 2004soho...13..297N
  No abstract at ADS

Title: Radiance Emission by Flaring Activity
Authors: Pauluhn, A.; Solanki, S. K.
Bibcode: 2004ESASP.547..323P
Altcode: 2004soho...13..323P
  Radiance values in the quiet Sun follow a lognormal distribution, with
  shape and scaling parameters varying significantly over the temperature
  range from chromosphere to corona. We show that these distributions
  can be reproduced by a simple model, which assumes that the radiance
  is produced by a stochastic (micro-, nano-) flaring process. This
  allows the diagnostic capabilities of the radiance distribution to
  be judged, performing, e.g., estimates of the true damping times of
  the flares. Several energy distributions are tested for the flaring
  process, like a Gaussian and a power law. The resulting time series
  are compared with SUMER time series of equivalent sampling, after
  adjustment of the parameters of the simulation. A good statistical match
  of the measurements is obtained for a steep power law distribution of
  nanoflare energies.

Title: Magnetic Coupling and Topological Change
Authors: Solanki, S. K.
Bibcode: 2004ESASP.547..155S
Altcode: 2004soho...13..155S
  Magnetic field lines thread the convective layers of the Sun's interior
  and its atmosphere. They couple these parts of the Sun in the sense
  that energy is transported from the Sun's interior and surface into
  its atmosphere, where it is deposited, leading to a heating of the
  gas present there. One way of energy release is through magnetic
  reconnection, which leads to a change of the magnetic topology. Both
  these topics are briefly discussed and some recent results are reviewed,
  including, new measurements of the magnetic vector near the base of
  the corona which reveal the magnetic structure of loops and have led to
  the first detection of a magnetic current sheet in the solar atmosphere.

Title: Reconstruction of solar UV irradiance
Authors: Krivova, N. A.; Solanki, S. K.
Bibcode: 2004cosp...35..504K
Altcode: 2004cosp.meet..504K
  Understanding solar influence on the Earth's climate requires
  a reconstruction of solar irradiance for the pre-satellite
  period. Considerable advances have been made in modelling the irradiance
  variations at wavelengths longer than 300 nm. At shorter wavelengths,
  however, the LTE approximation usually taken in such models fails, which
  makes a reconstruction of the solar UV irradiance a rather intricate
  problem. We choose an alternative approach and use the observed SUSIM
  UV spectra to extrapolate available models to shorter wavelengths.

Title: Effect of the electron density stratification on the off-limb
    O VI line profiles
Authors: Raouafi, N. -E.; Solanki, S. K.
Bibcode: 2004IAUS..223..481R
Altcode: 2005IAUS..223..481R
  Coronagraphic spectral observations carried out with UVCS on SoHO
  above polar coronal holes have shown that the velocity distribution
  is highly anisotropic. Here we examine the influence of the density
  stratification on the interpretation of such observations. In
  particular, we investigate the profiles of O VI spectral lines emitted
  in polar coronal holes. We find that at distances greater than 1
  R_{odot} from the solar surface the widths of the emitted lines are
  significantly affected by the details of the adopted electron density
  profiles. In particular, the densities deduced by Doyle et al. (1999)
  from SoHO data result in O VI profiles whose widths and intensity
  ratio are relatively close to the values observed by UVCS although
  only isotropic velocity distributions are employed. Hence we expect
  that the magnitude of the anisotropy of the velocity distribution
  deduced from UVCS data depends strongly on the adopted density profile.

Title: Stokes diagnostics of magneto-convection. Profile shapes
    and asymmetries
Authors: Khomenko, E. V.; Shelyag, S.; Solanki, S. K.; Vögler, A.;
   Schüssler, M.
Bibcode: 2004IAUS..223..635K
Altcode: 2005IAUS..223..635K
  We discuss the polarization signals produced in recent realistic 3D
  simulations of solar magnetoconvection. The Stokes profiles of the
  Fe I 6301.5, 6302.5, 15648 and 15652 mathrm{Å} Zeeman-sensitive
  spectral lines are synthesised and smeared to simulate the image
  degradation caused by the Earth's atmosphere and finite telescope
  resolution. A Principal Component Analysis approach is applied to
  classify the profiles. We find that the classes of Stokes V profiles
  as well as their amplitude and area asymmetries are very close to the
  observations in the network and inter-network regions.

Title: Structure of the solar chromosphere
Authors: Solanki, Sami K.
Bibcode: 2004IAUS..223..195S
Altcode: 2005IAUS..223..195S
  The chromosphere is an intriguing part of the Sun that has stubbornly
  resisted all attempts at a comprehensive description. Thus, observations
  carried out in different wavelength bands reveal very different,
  seemingly incompatible properties. Not surprisingly, a debate is raging
  between supporters of the classical picture of the chromosphere as
  a nearly plane parallel layer exhibiting a gentle temperature rise
  from the photosphere to the transition region and proponents of a
  highly dynamical atmosphere that includes extremely cool gas. New
  data are required in order settle this issue. Here a brief overview
  of the structure and dynamics of the solar chromosphere is given,
  with particular emphasis on the chromospheric structure of the quiet
  Sun. The structure of the magnetic field is also briefly discussed,
  although filaments and prominences are not considered. Besides the
  observations, contrasting models are also critically discussed.

Title: Temporal evolution of chromospheric downflows
Authors: Lagg, Andreas; Woch, J.; Krupp, N.; Gandorfer, A.; Solanki,
   S. K.
Bibcode: 2004IAUS..223..279L
Altcode: 2005IAUS..223..279L
  At the footpoints of loops spanning a site of flux emergence, earlier
  investigated in the papers by Solanki et al. (2003) and Lagg et
  al. (2004), we find large redshifts in the He 1083 nm line coexisting
  with an almost unshifted component. The speed associated with these
  redshifts reaches values as high as 40 km/s. We interpret these
  downflows in the context of several models: the free-fall downflow of
  matter along vertical field lines (Schmidt et al. 2000), the redshift
  by downward propagating acoustic waves (Hansteen 1993) and the motion
  of condensation regions to either side of loop footpoints (Müller et
  al. 2003). We present the temporal evolution of these redshifts and
  reconstruct the magnetic field vector in these regions for both the
  redshifted and the unshifted atmospheric component.

Title: Overview of Slow Mode Oscillations in Hot Coronal Loops
    Observed by SUMER
Authors: Wang, T. J.; Solanki, S. K.; Curdt, W.; Innes, D. E.
Bibcode: 2004IAUS..219..712W
Altcode: 2003IAUS..219E..70W
  No abstract at ADS

Title: Understanding Solar Variability as a Groundwork for Planet
    Transit Detection
Authors: Seleznyov, A. D.; Krivova, N. A.; Solanki, S. K.
Bibcode: 2004IAUS..219..815S
Altcode: 2003IAUS..219E...7K
  Detection of planetary transits holds the greatest promise for
  the search of terrestrial planets. However intrinsic stellar
  variability can mask real transits or lead to 'false' planet transit
  detections. Understanding the origin of stellar variability can
  help to estimate the minimum sizes of planets detectable with this
  technique around different types of stars and to identify the best
  wavelength range for such measurements. The only star for which data
  with sufficient photometric accuracy and temporal sampling exist is
  the Sun. We analyze and model solar variability on timescales relevant
  for planetary transits (hours to several days) using a variety of
  components such as granulation network (supergranulation) faculae
  and sunspots. This study extends our successful work to model solar
  irradiance variations on days to years timescales (Fligge et al. 2000;
  Krivova et al. 2003).

Title: Plasma dynamics of a prominence associated coronal mass
    ejection
Authors: Tripathi, D.; Bothmer, V.; Solanki, S. K.; Schwenn, R.;
   Mierla, M.; Stenborg, G.
Bibcode: 2004IAUS..223..401T
Altcode: 2005IAUS..223..401T
  An erupting prominence seen by SOHO/EIT was tracked into the field of
  view of the LASCO C2 and C3 coronagraphs where it developed into the
  core of a structured CME. The erupting prominence was deflected by an
  angle of sim 20^{circ} towards the north pole whereas the consequent
  core of the CME and it's leading edge propagated in the outer corona at
  constant position angle. The prominence material underwent a constant
  acceleration phase until a height of sim1.5 solar radii before it
  started to decelerate up to a distance of 5.0 solar radii. An inflow
  of plasma with a speed of about 70-80 km/s was discovered in the EIT
  observations at a height of 1.5-1.2 solar radii in the course of the
  prominence eruption, matching in time the prominence deceleration
  phase. The downflowing material followed a curved path, suggestive
  of the apex of a contracting magnetic loop sliding down along other
  field lines.

Title: The solar chromosphere as seen in high-resolution millimeter
    observations
Authors: Loukitcheva, M. A.; Solanki, S. K.; White, S.
Bibcode: 2004IAUS..223..643L
Altcode: 2005IAUS..223..643L
  We report on chromospheric oscillations studied with 15 sec
  cadence observations obtained at a wavelength of 3.5 mm with the
  Berkeley-Illinois-Maryland Array (BIMA). Different solar structures,
  including active and quiet-Sun regions, are analyzed. We compare the
  high-resolution millimeter 2-D images with Ca II K line images from Big
  Bear Solar Observatory. Using Fourier and wavelet time series analysis
  techniques we find signatures of intensity oscillations with periods
  in the range of 2-7 minutes. We discuss the results in the context of
  the dynamical model of the solar atmosphere by Carlsson &amp; Stein
  (1995, 1997).

Title: Stokes Diagnostics of Magnetoconvection. Profile shapes
    and asymmetries.
Authors: Khomenko, E. V.; Shelyag, S.; Solanki, S. K.; Vogler, A.;
   Schussler, M.
Bibcode: 2004cosp...35.2131K
Altcode: 2004cosp.meet.2131K
  Stokes profiles observed in the quiet Sun have a broad range of
  asymmetries and show a variety of shapes. These asymmetries are the
  result of the velocity and magnetic field gradients both in horizontal
  and vertical directions. We use the most recent realistic 3D simulations
  of magnetoconvection at the solar surface to synthesize Stokes profiles
  of some photospheric lines and to compare them with observations. Such
  comparison provides an important constrains on the MHD models allowing
  to conclude about their realism and, thus, to understand the nature of
  solar magnetoconvection. The following Zeeman-sensitive spectral lines
  are considered: Fe I 6301.5, 6302.5, 15648 and 15652 Å. These lines are
  extensively used in observations. The computed Stokes profiles of these
  lines were spatially smeared to simulate the effects of a telescope and
  atmospheric seeing. A Principal Component Analysis approach is applied
  to classify the profiles. The effects of spatial resolution and the
  amount of the magnetic flux in the MHD model on the profile shapes are
  discussed. The profiles of different classes are clustered together and
  form patches on the surface. The size of these patches decreases with
  increasing spatial resolution. The distributions of the amplitude and
  area asymmetries of Stokes V profiles are very close to the observations
  in network and inter-network regions. Some 15% of the profiles smeared
  with a 0.''5 seeing have irregular shape with 3 or more lobes. Finally,
  we show that simultaneous observations of the same area of the solar
  disc using infrared Fe I 15648, 15652 Å and the visible Fe I 6301.5,
  6302.5 Å lines done under different seeing conditions (for example
  in the case of simultaneous observations at different telescopes)
  may result in different asymmetries and even different polarities
  of the profiles in two spectral regions observed at the same spatial
  point. This work was partially supported by INTAS grant 00-00084.

Title: Reconstruction of solar activity for the last millennium
    using <SUP>10</SUP>Be data
Authors: Usoskin, I. G.; Mursula, K.; Solanki, S.; Schüssler, M.;
   Alanko, K.
Bibcode: 2004A&A...413..745U
Altcode: 2003astro.ph..9556U
  In a recent paper (Usoskin et al. 2002a), we have reconstructed
  the concentration of the cosmogenic <SUP>10</SUP>Be isotope in ice
  cores from the measured sunspot numbers by using physical models
  for <SUP>10</SUP>Be production in the Earth's atmosphere, cosmic ray
  transport in the heliosphere, and evolution of the Sun's open magnetic
  flux. Here we take the opposite route: starting from the <SUP>10</SUP>Be
  concentration measured in ice cores from Antarctica and Greenland, we
  invert the models in order to reconstruct the 11-year averaged sunspot
  numbers since 850 AD. The inversion method is validated by comparing
  the reconstructed sunspot numbers with the directly observed sunspot
  record since 1610. The reconstructed sunspot record exhibits a prominent
  period of about 600 years, in agreement with earlier observations
  based on cosmogenic isotopes. Also, there is evidence for the century
  scale Gleissberg cycle and a number of shorter quasi-periodicities
  whose periods seem to fluctuate in the millennium time scale. This
  invalidates the earlier extrapolation of multi-harmonic representation
  of sunspot activity over extended time intervals.

Title: Solar variability and global warming: a statistical comparison
    since 1850
Authors: Krivova, N. A.; Solanki, S. K.
Bibcode: 2004AdSpR..34..361K
Altcode:
  The magnitude of the Sun's influence on climate has been a subject
  of intense debate. Estimates of this magnitude are generally based on
  assumptions regarding the forcing due to solar irradiance variations
  entering climate modelling. Given the complexity of the climate system,
  however, such modelling is perforce based on simplifying assumptions,
  which leaves it open to criticism. We take a complementary approach. We
  assume that the Sun has been responsible for climate change prior to
  1970 and that their interrelation remained unchanged afterwards. Then,
  employing reconstructions and measured records of relevant solar
  quantities as well as of the cosmic-ray flux, we estimate statistically
  which fraction of the dramatic temperature rise after that date could
  be due to the influence of the Sun. We show that at least in the most
  recent past (since about 1970) the solar influence on climate cannot
  have been significant.

Title: Irradiance models
Authors: Solanki, S. K.
Bibcode: 2004cosp...35..318S
Altcode: 2004cosp.meet..318S
  Measurements of solar irradiance have revealed variations at all the
  sampled time scales (ranging from minutes to the length of the solar
  cycle). One important task of models is to identify the causes of the
  observed (total and spectral) irradiance variations. Another major
  aim is to reconstruct irradiance over time scales longer than sampled
  by direct measurements in order to consider if and to what extent
  solar irradiance variations may be responsible for global climate
  change. Here I describe recent efforts to model solar irradiance
  both on the short-term and at longer time scales. On time scales up
  to the solar cycle the irradiance models are remarkably successful
  in reproducing the observed total and spectral irradiance, although
  further improvements are still possible. On longer time scales,
  in spite of considerable advances, some uncertainties still remain,
  although there is hope of reducing these in the near future.

Title: Solar activity and climate during the last millennium
Authors: Solanki, S. K.; Usoskin, I.; Schüssler, M.
Bibcode: 2004cosp...35.2535S
Altcode: 2004cosp.meet.2535S
  The sunspot number is the longest running direct index of solar
  activity, with direct measurements starting in 1610. For many purposes,
  e.g., for comparisons with climate indices, it is still too short. We
  present a reconstruction of the cycle-averaged sunspot number over the
  last millennium based on <SUP>10</SUP>Be concentrations in Greenland
  and Antarctic ice cores. As intermediate steps of the method, we also
  reconstruct the cosmic ray flux at Earth and the Sun's open magnetic
  flux. The reconstructions are validated by comparison with direct
  measurements or independent reconstructions. We also compare with
  records of global climate, in particular with the global temperature
  ("hockey stick") curve of Mann et al (1998). A reasonable agreement
  is found for the entire millennium, excluding only the last decades,
  when the two curves start diverging from each other.

Title: Effect of the Line-of-Sight Integration on the Profiles of
    Coronal Lines
Authors: Raouafi, N. -E.; Solanki, S. K.
Bibcode: 2004ESASP.547..401R
Altcode: 2004soho...13..401R
  We reexamine the interpretation of coronal observations aiming at
  the determination of the coronal magnetic field and/or the solar
  wind velocity vectors. In particular we investigate the effect of the
  integration along the line-of-sight on the profiles of O vi spectral
  lines emitted in the corona employing a simple model of the large scale
  coronal magnetic field and solar wind. Here we present preliminary
  results. We concentrate on the polar coronal holes and find that
  although the line-of-sight integration is not important at small
  heights, the width of the emitted line is increasingly affected when
  moving outwards from the solar disk. At distances of 2.5 R and greater
  the width of the profile integrated along the LOS is more than 2 times
  as larger as the line profile obtained from an elementary emitting
  volume on the polar axis.

Title: Interpretation of the Coronal EUV Signature of the CME Event
    on June 27 1999
Authors: Raouafi, N. -E.; Mancuso, S.; Solanki, S. K.; Inhester, B.;
   Benna, C.; Delaboudinière, J. P.; Stenborg, G.; Mierla, M.
Bibcode: 2004ESASP.547..317R
Altcode: 2004soho...13..317R
  We report the observation of a Coronal Mass Ejection (CME) detected
  on June 27 1999 by the UltraViolet Coronagraph Spectrometer (UVCS)
  telescope operating on board the SOHO spacecraft. The CME, whose
  leading edge was expanding at a projected speed of about 1200 km s,
  was observed in white light by the Large Angle Spectroscopic Coronagraph
  (LASCO). The UVCS spectra reveal excess broadening of the O VI doublet
  lines and enhancement in the intensity of the Si XII lines due to the
  motion of expanding hot material. The evolution of the UVCS structure
  is highly correlated to the evolution of the CME observed by LASCO
  in white light, so that the hot gas emission could be attributable to
  the passage of a shock wave propagating just in front of the fast CME.

Title: Effect of anisotropic velocity distribution on the linear
    polarization of coronal lines.  Does the ion cyclotron exist in the
    inner corona?
Authors: Raouafi, N. -E.; Solanki, S. K.
Bibcode: 2003A&A...412..271R
Altcode:
  The effect of an anisotropic velocity field distribution of scattering
  ions on the polarization parameters of a spectral line emitted by
  resonance scattering is considered. The anisotropy of the velocity field
  distribution can be interpreted in terms of the ion-cyclotron effect
  that is believed to influence some heavy ions in the solar corona. We
  present a theoretical study of the Stokes parameters of a spectral
  line emitted by atoms or ions in the presence of a bi-Maxwellian
  velocity field distribution. It is found from test calculations that
  such a distribution measurably changes the polarization properties
  of the \ion {O}{vi} D_2 coronal line. Consequently, measurements of
  the linear polarization of this line may serve as a new diagnostic
  of a possible bi-Maxwellian velocity distribution. As a preliminary
  application, the obtained theoretical results are used to interpret
  the polarization parameters of the O Vi D_2 coronal line (lambda1031
  .92) measured using SUMER/SoHO observations. The obtained results
  are compatible with SUMER's observations for more reasonable solar
  wind parameters than for an isotropic velocity field distribution
  of the scattering ions. Thus, the outflow velocity field vector of
  the emitting ions is less inclined with respect to the polar axis of
  the Sun (the minimal value of the polar angle eta is 8<SUP>deg</SUP>
  for an anisotropic velocity distribution versus 17<SUP>deg</SUP> for
  an isotropic velocity field distribution). These results are obtained
  assuming that the re-emitted photons come from a small area in the
  center of the coronal polar hole, with zero magnetic field. Since
  SUMER/SoHO observations integrate over the line of sight, the results of
  the current analysis must be considered preliminary pending computations
  including an integration along the line of sight.

Title: Models of Solar Irradiance on Time Scales of Minutes to
    Centuries
Authors: Solanki, S. K.
Bibcode: 2003AGUFMSH31C..01S
Altcode:
  Solar irradiance varies on all time scales accessible to observations
  from minutes to the solar cycle. For the Earth's climate even longer
  time scales are of relevance, from centuries to millennia. A series of
  models have been or are being constructed to account for the irradiance
  variations at these different time scales, which are dominated by
  different physical processes. The results of the modelling are described
  and, where possible, are compared with the data and are discussed.

Title: The molecular Zeeman effect and diagnostics of solar and
    stellar magnetic fields. II. Synthetic Stokes profiles in the
    Zeeman regime
Authors: Berdyugina, S. V.; Solanki, S. K.; Frutiger, C.
Bibcode: 2003A&A...412..513B
Altcode:
  Recent advances in the computation of the Zeeman splitting of
  molecular lines have paved the way for their use as diagnostics
  of solar and stellar magnetic fields. A systematic study of their
  diagnostic capabilities had not been carried out so far, however. Here
  we investigate how molecular lines can be used to deduce the magnetic
  and thermal structure of sunspots, starspots and cool stars. First, we
  briefly describe the Stokes radiative transfer of Zeeman-split molecular
  lines. Then, we compute Stokes spectra of TiO, OH, CH and FeH lines and
  investigate their diagnostic capabilities. We also compare the synthetic
  profiles with observations. Spectra of TiO, OH and FeH are found to be
  interesting diagnostics of sunspot magnetic fields. This is also true
  for cool stars, where, however, the OH Stokes V profiles may require
  very high S/N data to be reliably employed. Finally we investigate
  the potential of various molecular bands for high-contrast imaging
  of the solar surface. The violet CN and CH bands turn out to be most
  promising for imaging the photosphere, the TiO bands are excellent for
  imaging sunspot umbrae, while the UV OH band can be used for imaging
  both the photosphere and sunspots.

Title: Successful Measurement of the Full Magnetic Vector Near the
    Base of the Solar Corona
Authors: Solanki, S. K.; Lagg, A.; Woch, J.; Krupp, N.; Landi
   Degl'Innocenti, E.; Collados, M.
Bibcode: 2003AGUFMSH41D..05S
Altcode:
  The measurement of coronal fields has in the past generally been
  restricted to the field strength or to only some of the components of
  the magnetic vector. We present here a technique for measuring the full
  magnetic vector near the base of the solar corona. As an application
  we report on observations of a developing active region with ongoing
  magnetic flux emergence. The data allow the first measurement of the 3-D
  structure of magnetic loops. They also provide the first detection of an
  electric current sheet located near the base of the solar corona. Such
  current sheets or tangential discontinuities of the coronal magnetic
  field have long been thought to be a major source of coronal heating.

Title: Why Solar Magnetic Flux Concentrations Are Bright in Molecular
    Bands
Authors: Schüssler, M.; Shelyag, S.; Berdyugina, S.; Vögler, A.;
   Solanki, S. K.
Bibcode: 2003ApJ...597L.173S
Altcode:
  Using realistic ab initio simulations of radiative magnetoconvection,
  we show that the bright structures in images taken in the ``G band,''
  a spectral band dominated by lines of the CH molecule, precisely
  outline small-scale concentrations of strong magnetic fields on the
  visible solar surface. The brightening is caused by a depletion of CH
  molecules in the hot and tenuous magnetic structures, thus confirming
  the model of radiatively heated magnetic flux concentrations. These
  results provide a firm basis for observational studies of the evolution
  and dynamics of the small-scale solar magnetic field derived through
  ``proxy magnetometry'' with G-band images.

Title: Millennium-Scale Sunspot Number Reconstruction: Evidence for
    an Unusually Active Sun since the 1940s
Authors: Usoskin, Ilya G.; Solanki, Sami K.; Schüssler, Manfred;
   Mursula, Kalevi; Alanko, Katja
Bibcode: 2003PhRvL..91u1101U
Altcode: 2003astro.ph.10823U
  The extension of the sunspot number series backward in time is of
  considerable interest for dynamo theory, solar, stellar, and climate
  research. We have used records of the <SUP>10</SUP>Be concentration in
  polar ice to reconstruct the average sunspot activity level for the
  period between the year 850 to the present. Our method uses physical
  models for processes connecting the <SUP>10</SUP>Be concentration with
  the sunspot number. The reconstruction shows reliably that the period
  of high solar activity during the last 60years is unique throughout
  the past 1150years. This nearly triples the time interval for which
  such a statement could be made previously.

Title: Spatial and temporal fluctuations in sunspots derived from
    MDI data
Authors: Solanki, S. K.; Rüedi, I.
Bibcode: 2003A&A...411..249S
Altcode:
  The penumbra radiates an energy flux that is 0.75-0.8 times the
  photospheric value. One mechanism proposed to bring this flux to the
  surface is interchange convection according to which hot flux tubes
  rise to the surface, lie horizontally there while they cool and finally
  sink down again. We search for possible signatures of such a process
  using time series of magnetograms and continuum images recorded by the
  Michelson Doppler Imager (MDI) in its high resolution mode (0.6\arcsec
  pixels). The data reveal that at the spatial scales accessible to MDI,
  magnetic structures are on average smaller in the azimuthal direction
  than brightness features. The small-scale magnetic pattern resolvable
  by MDI lives for well over two hours, i.e. longer than the brightness
  pattern. As shown in a parallel paper (Schlichenmaier &amp; Solanki
  \cite{Sch03}) this result, taken together with theoretical predictions,
  suggests that interchange convection is unable to account for the
  observed penumbral radiative flux. The need for higher resolution data
  obtained under stable conditions is pointed out.

Title: On the heat transport in a sunspot penumbra
Authors: Schlichenmaier, R.; Solanki, S. K.
Bibcode: 2003A&A...411..257S
Altcode:
  The penumbra radiates an energy flux that is roughly 75% of the
  quiet-sun value. One mechanism proposed to bring this flux to the
  surface is interchange convection of magnetic flux tubes according
  to which hot flux tubes rise to the surface, cool off their heat
  by radiation and sink down again. Another way to deposit heat in
  the penumbral photosphere is by steady upflows along magnetic flux
  tubes. We discuss these two mechanisms and elaborate on consequences
  that can be compared with and constrained by observations. We estimate
  the time scales for variations of the intensity and the magnetic field
  pattern. By comparing them with the corresponding observed time scales,
  we find that pure interchange convection is unable to account for the
  observed penumbral heat flux. Heating the penumbra by steady upflows
  along magnetic flux tubes, however, turns out to be sufficient to
  explain the penumbral brightness, under the condition that significant
  magnetic return flux is present within the penumbra. Associated with
  the magnetic return flux, downflows within the penumbra should be
  present, in accordance with recent observational findings of such
  downflows. Exploring other possible heating mechanisms, we find that
  dissipation of magnetic energy is negligible, while dissipation of the
  kinetic energy of the Evershed flow could contribute significantly to
  the brightness of the penumbra.

Title: Three dimensional structure of a regular sunspot from the
    inversion of IR Stokes profiles
Authors: Mathew, S. K.; Lagg, A.; Solanki, S. K.; Collados, M.;
   Borrero, J. M.; Berdyugina, S.; Krupp, N.; Woch, J.; Frutiger, C.
Bibcode: 2003A&A...410..695M
Altcode:
  The magnetic, thermal and velocity structure of a regular sunspot,
  observed close to solar disk center is presented. Spectropolarimetric
  data obtained with the Tenerife Infrared Polarimeter (TIP) in two
  infrared FeI lines at 15 648.5 Å and 15 652.8 Å are inverted
  employing a technique based on response functions to retrieve the
  atmospheric stratification at every point in the sunspot. In order
  to improve the results for the umbra, profiles of Zeeman split OH
  lines blending the FeI 15 652.8 Å are also consistently fit. Thus
  we obtain maps of temperature, line-of-sight velocity, magnetic
  field strength, inclination, and azimuth, as a function of both
  location within the sunspot and height in the atmosphere. We present
  these maps for an optical depth range between log tau<SUB>5</SUB> =
  0 and log tau<SUB>5</SUB> = -1.5, where these lines provide accurate
  results. We find decreasing magnetic field strength with increasing
  height all over the sunspot, with a particularly large vertical field
  gradient of ~ -4 G km<SUP>-1</SUP> in the umbra. We also observe the
  so called ``spine'' structures in the penumbra, i.e. extended radial
  features with a stronger and more vertical magnetic field than the
  surroundings. Also we found that the magnetic field zenith angle
  increases with height. From the velocity map it is clear that the
  Evershed flow avoids the spines and mostly concentrates in the more
  inclined intervening field. The field inclination at a few locations
  in the outer penumbra in lower layers goes beyond 90<SUP>o</SUP>. These
  locations coincide with the strongest flows in the velocity map.

Title: Three-dimensional magnetic field topology in a region of
    solar coronal heating
Authors: Solanki, S. K.; Lagg, A.; Woch, J.; Krupp, N.; Collados, M.
Bibcode: 2003Natur.425..692S
Altcode:
  Flares and X-ray jets on the Sun arise in active regions where magnetic
  flux emerges from the solar interior amd interacts with the ambient
  magnetic field. The interactions are believed to occur in electric
  current sheets separating regions of opposite magnetic polarity. The
  current sheets located in the corona or upper chromosphere have long
  been thought to act as an important source of coronal heating, requiring
  their location in the corona or upper chromosphere. The dynamics and
  energetics of these sheets are governed by a complex magnetic field
  structure that, until now, has been difficult to measure. Here we report
  the determination of the full magnetic vector in an interaction region
  near the base of the solar corona. The observations reveal two magnetic
  features that characterize young active regions on the Sun: a set of
  rising magnetic loops and a tangential discontinuity of the magnetic
  field direction, the latter being the observational signature of an
  electric current sheet. This provides strong support for coronal heating
  models based on the dissipation of magnetic energy at current sheets.

Title: On the origin of solar variability, with an application to
    the search for extrasolar planets
Authors: Seleznyov, A. D.; Solanki, S. K.; Krivova, N. A.
Bibcode: 2003ESASP.539..589S
Altcode: 2003toed.conf..589S
  Detection of planetary transits holds great promise for the search of
  terrestrial planets. However, most stars are variable at the level of
  the signal produced by the transit of an Earth-like planet. Hence,
  intrinsic stellar variability can lead to "false" planet transit
  detections. An understanding of the origin of the stellar variability
  is needed to ensure reliable transit detections. We consider the
  Sun as the closest and best studied star and analyze its variability
  on timescales relevant to the transit effect, namely from an hour to
  several days. Total and spectral solar irradiance measurements obtained
  by the VIRGO instrument on board the SOHO spacecraft have been analyzed
  by applying Fourier and wavelet techniques. Preliminary results suggest
  that at the time scales of interest solar variability is driven partly
  by solar magnetic activity, which dominates at longer time scales,
  and convection, in particular solar granulation, which dominates at
  shorter time scales. As part of a more quantitative analysis a simple
  numerical model of the irradiance variations due to granulation has
  been constructed. Irradiance variability of stars with different surface
  gravity was calculated in the frequency band of relevance to transits.

Title: Molecular Lines as Diagnostics of Solar and Stellar Magnetic
    Fields
Authors: Berdyugina, S. V.; Solanki, S. K.; Lagg, A.
Bibcode: 2003csss...12..210B
Altcode:
  Thanks to recent advances in theory we can now calculate molecular
  line profiles in the presence of magnetic fields with high accuracy,
  both in the Zeeman and Paschen-Back regimes (Berdyugina et al. 2000;
  Berdyugina &amp; Solanki 2001a). The synthetic Stokes profiles of
  various molecular species (e.g. TiO, OH, MgH, CN, FeH) have been
  compared with profiles observed in sunspots. The agreement between
  the theory and observations is remarkable. For example, the mutually
  opposite polarities of different OH lines are reproduced without
  invoking any free parameters, except the magnetic field strength and
  sunspot temperature. Introducing molecular lines into the inversion
  of sunspot spectra leads to significant improvements in the deduced
  magnetic field vector. Here we investigate how molecular lines can be
  used to deduce magnetic parameters of cool stars. We find that such
  lines are of great interest for measuring magnetic fields on cooler
  stars and in starspots.

Title: Solar total and spectral irradiance: modelling and a possible
    impact on climate
Authors: Krivova, N. A.; Solanki, S. K.
Bibcode: 2003ESASP.535..275K
Altcode: 2003iscs.symp..275K
  There is growing evidence that solar variability influences the
  Earth's climate, although the underlying mechanism is not yet
  understood. Variations in the solar total and spectral irradiance
  often play a central role within various processes that have been
  suggested. Whereas changes in the total irradiance can affect the
  overall energy balance of the Earth's atmosphere, variations in its
  spectral distribution, in particular in the UV, have a pronounced effect
  on the chemistry of the Earth's upper atmosphere. Measurements of the
  solar total irradiance are only available since 1978 and the spectral
  irradiance record is even shorter. This calls for a reconstruction of
  irradiance variations at earlier times with the help of models. We first
  outline our current understanding of the main mechanism responsible
  for irradiance variations and describe the efforts to reconstruct
  them. The reconstructed total and UV irradiance is then employed to
  estimate the solar contribution to global warming, with particular
  emphasis to the period since 1970.

Title: Solar irradiance fluctuations on short timescales
Authors: Solanki, S. K.; Seleznyov, A. D.; Krivova, N. A.
Bibcode: 2003ESASP.535..285S
Altcode: 2003iscs.symp..285S
  Although solar irradiance variability at time-scales of days to the
  solar cycle has been well studied, comparatively little is known about
  the causes of such variations on shorter time-scales. We present an
  analysis that aims to distinguish between magnetic and convective
  causes. It suggests that on time-scales longer than 1-2 days magnetic
  structures are the dominant source while for time-scales shorter than
  a few hours convection appears to dominate. We also present a simple
  granulation model that includes the various paths of granule birth
  and death and compare its output with VIRGO data.

Title: Quiet-Sun inter-network magnetic fields  observed in the
    infrared
Authors: Khomenko, E. V.; Collados, M.; Solanki, S. K.; Lagg, A.;
   Trujillo Bueno, J.
Bibcode: 2003A&A...408.1115K
Altcode:
  This paper presents the results of an investigation of the quiet Sun's
  magnetic field based on high-resolution infrared spectropolarimetric
  observations obtained with the Tenerife Infrared Polarimeter (TIP)
  at the German VTT of the Observatorio del Teide. We observed two very
  quiet regions at disc centre. The seeing was exceptionally good during
  both observing runs, being excellent during one of them. In both cases
  the network was intentionally avoided to the extent possible, to focus
  the analysis on the characteristics of the weak polarization signals
  of the inter-network regions. We find that the Stokes V profile of
  Fe I 15648 Å line in almost 50% of the pixels and Stokes Q and/or
  U in 20% of the pixels have a signal above 10<SUP>-3</SUP> (in units
  of continuum intensity I<SUB>c</SUB>), which is significantly above
  the noise level of 2-3 x 10<SUP>-4</SUP>. This implies that we detect
  fluxes as low as 2 x 10<SUP>15</SUP> Mx/px. We find evidence that we
  have detected most of the net flux that is in principle detectable at
  1<SUP>''</SUP> resolution with the Zeeman effect. The observed linear
  polarization resulting from the transverse Zeeman effect indicates that
  the magnetic fields have a broad range of inclinations, although most
  of the pixels show polarization signatures which imply an inclination
  of about 20<SUP>o</SUP>. Nearly 30% of the selected V-profiles have
  irregular shapes with 3 or more lobes, suggesting mixed polarities with
  different LOS velocity within the resolution element. The profiles are
  classified using a single value decomposition approach. The spatial
  distribution of the magnetic signal shows that profiles of different
  classes (having different velocities, splitting, asymmetries) are
  clustered together and form patches, close to the spatial resolution
  in size. Most of the field is found to be located in intergranular
  lanes. The statistical properties of the mainly inter-network field
  sampled by these observations are presented, showing that most of
  the observed fields are weak with relatively few kG features. The
  field strength distribution peaks at 350 G and has a FWHM of 300
  G. Other parameters, such as profile asymmetries, filling factors and
  line-of-sight velocities are also determined and discussed. <P />Based
  on observations with the German Vacuum Tower Telescope (VTT) operated by
  the Kiepenheuer-Institut für Sonnenphysik at the Spanish Observatorio
  del Teide of the Instituto de Astrofísica de Canarias (IAC).

Title: Dependence of UV radiance of the quiet Sun on the solar cycle:
    Surface magnetic fields as the cause
Authors: Pauluhn, A.; Solanki, S. K.
Bibcode: 2003A&A...407..359P
Altcode:
  The quiet-Sun UV radiance depends on the solar cycle, as shown by
  data collected by the SUMER spectrograph on the Solar and Heliospheric
  Observatory (SOHO). The cause of this dependence is still unclear. Here
  the hypothesis is tested for the He I 584 Å line that these variations
  are due to changes in the magnetic network. The quiet-Sun variability
  is investigated with the two EUV instruments CDS (Coronal Diagnostic
  Spectrometer) and SUMER (Solar Ultraviolet Measurements of Emitted
  Radiation) and the MDI (Michelson Doppler Imager) magnetograph
  on SOHO. Using a monthly data set of co-spatial and co-temporal
  observations of quiet Sun areas near disk centre we follow the
  evolution of the quiet Sun over four years from solar cycle minimum
  to maximum conditions and find that the magnetic flux of the quiet
  network increases during this period. Furthermore, its variation is
  well correlated with the radiance change in the He I 584 Å line. Also,
  we find that the largest fractional change is in the flux of the strong
  network elements (largest average field strengths), while the weaker
  elements do not exhibit a significant change.

Title: Hot coronal loop oscillations observed with SUMER: Examples
    and statistics
Authors: Wang, T. J.; Solanki, S. K.; Curdt, W.; Innes, D. E.;
   Dammasch, I. E.; Kliem, B.
Bibcode: 2003A&A...406.1105W
Altcode:
  We give an extensive overview of Doppler shift oscillations in
  hot active region loops obtained with SUMER. The oscillations have
  been detected in loops sampled 50-100 arcsec off the limb of the
  Sun in ultraviolet lines, mainly Fe Xix and Fe Xxi, with formation
  temperature greater than 6 MK. The spectra were recorded along a
  300 arcsec slit placed at a fixed position in the corona above the
  active regions. Oscillations are usually seen along an extended
  section of the slit and often appear to be from several different
  portions of the loops (or from different loops). Different portions
  are sometimes in phase, sometimes out of phase and sometimes show
  phase shifts along the slit. We measure physical parameters of 54
  Doppler shift oscillations in 27 flare-like events and give geometric
  parameters of the associated hot loops when soft X-ray (SXR) images
  are available. The oscillations have periods in the range 7-31 min,
  with decay times 5.7-36.8 min, and show an initial large Doppler
  shift pulse with peak velocities up to 200 km s<SUP>-1</SUP>. The
  oscillation periods are on average a factor of three longer than the
  TRACE transverse loop oscillations. The damping times and velocity
  amplitude are roughly the same, but the derived displacement amplitude
  is four or five times larger than the transverse oscillation amplitude
  measured in TRACE images. Unlike TRACE oscillations, only a small
  fraction of them are triggered by large flares, and they often recur
  2-3 times within a couple of hours. All recurring events show initial
  shifts of the same sign. These data provide the following evidence to
  support the conclusion that these oscillations are slow magnetoacoustic
  standing waves in hot loops: (1) the phase speeds derived from observed
  periods and loop lengths roughly agree with the sound speed; (2)
  the intensity fluctuation lags the Doppler shifts by 1/4 period; (3)
  The scaling of the dissipation time of slow waves with period agrees
  with the observed scaling for 49 cases. They seem to be triggered
  by micro- or subflares near a footpoint, as revealed in one example
  with SXR image observations. However other mechanisms cannot as yet
  be ruled out. Some oscillations showed phase propagation along the
  slit in one or both directions with apparent speeds in the range of
  8-102 km s<SUP>-1</SUP>, together with distinctly different intensity
  and line width distributions along the slit. These features can be
  explained by the excitation of the oscillation at a footpoint of an
  inhomogeneous coronal loop, e.g. a loop with fine structure. <P />Table
  \ref{osctab} and Appendices A and B are only available in electronic
  form at http://www.edpsciences.org

Title: Long-Term Cosmic Ray Intensities: Physical Reconstruction
Authors: Usoskin, I. G.; Mursula, K.; Solanki, S. K.; Schuessler,
   M.; Kovaltsov, G. A.
Bibcode: 2003ICRC....7.4041U
Altcode: 2003ICRC...28.4041U
  Solanki et al. (2000) have recently calculated the open solar magnetic
  flux for the last 400 years from sunspot data. Using this reconstructed
  magnetic flux as an input to a simple spherically symmetric quasi-steady
  state model of the heliosphere, we calculate the expected differential
  spectra and integral intensity of galactic cosmic rays at the Earth's
  orbit since 1610. The calculated cosmic ray integral intensity is in
  good agreement with the neutron monitor measurements during the last
  50 years. Moreover, using the specific yield function of cosmogenic
  10 Be radionuclide production in the atmosphere, we also calculate
  the expected 10 Be production rate which exhibits an excellent
  agreement with the actual 10 Be abundance in polar ice over the
  last 400 years. Here we present a physical model for the long-term
  reconstruction of cosmic ray intensity at 1 AU. The reconstruction
  is based on a combination of the solar magnetic flux model and a
  heliospheric model. This model allows us to calculate the expected
  intensity of galactic cosmic rays (GCR) at the Earth's orbit for the
  last 400 years. Details can be found in [25]. Using the numerical recip
  e of Solanki et al. [21] and the group sunspot number series (Fig. 1.a)
  [11] we have calculated the open solar magnetic flux Fo since 1610 as
  shown in Fig. 1.b. In order to calculate galactic cosmic ray (GCR)
  spectra we use a spherically symmetric quasi-steady sto chastic
  simulation model described in detail elsewhere [24], which reliably
  describes the long-term GCR modulation during the last 50 years. In this
  model, the most important parameter of the heliospheric modulation of
  GCR is the modulation strength [10]: Φ = (D - rE )V /(3κo), where D
  = 100 AU is the heliospheric boundary and rE = 1 AU, V = 400 km/s is
  the constant solar wind velocity and κo is the rigidity indep endent
  part of the diffusion coefficient. Thus, all changes in the modulation
  strength Φ in our model are related to the changing diffusion

Title: Overview of Recent Results on Coronal Loop Oscillations
Authors: Wang, T. J.; Solanki, S. K.; Curdt, W.; Innes, D. E.
Bibcode: 2003ANS...324...19W
Altcode: 2003ANS...324..B18W
  No abstract at ADS

Title: Infrared Polarimetry at the MPAe: The Solar Atmosphere from
    the Photosphere to the Upper Chromosphere
Authors: Lagg, Andreas; Woch, Joachim; Solanki, Sami K.; Mathew,
   Shibu; Borrero, Juan M.; Krupp, N.; Raouafi, N. E.
Bibcode: 2003ANS...324...29L
Altcode: 2003ANS...324..D04L
  No abstract at ADS

Title: SUNRISE: Balloon-borne High-Resolution Observation of the Sun
Authors: Solanki, S. K.; Curdt, W.; Gandorfer, A.; Schüssler,
   M.; Lites, B. W.; Martinez Pillet, V.; Schmidt, W.; Title, A. M.;
   Sunrise Team
Bibcode: 2003ANS...324..113S
Altcode: 2003ANS...324..P20S
  No abstract at ADS

Title: Determining the Inclination of the Rotation Axis of a
    Sun-like Star
Authors: Gizon, L.; Solanki, S. K.
Bibcode: 2003ApJ...589.1009G
Altcode:
  Asteroseismology provides us with the possibility of determining the
  angle, i, between the direction of the rotation axis of a pulsating
  Sun-like star and the line of sight. A knowledge of i is important
  not just for obtaining improved stellar parameters, but also in order
  to determine the true masses of extrasolar planets detected from the
  radial velocity shifts of their central stars. By means of Monte Carlo
  simulations, we estimate the precision of the measurement of i and
  other stellar parameters. We find that the inclination angle can be
  retrieved accurately when i&gt;~30<SUP>deg</SUP> for stars that rotate
  at least twice as fast as the Sun.

Title: Slow-mode standing waves observed by SUMER  in hot coronal
    loops
Authors: Wang, T. J.; Solanki, S. K.; Innes, D. E.; Curdt, W.;
   Marsch, E.
Bibcode: 2003A&A...402L..17W
Altcode:
  We report the first detection of postflare loop oscillations seen in
  both Doppler shift and intensity. The observations were recorded in
  an Fe Xix line by the SUMER spectrometer on SOHO in the corona about
  70 min after an M-class flare on the solar limb. The oscillation has a
  period of about 17 min in both the Doppler velocity and the intensity,
  but their decay times are different (i.e., 37 min for the velocity and
  21 min for the intensity). The fact that the velocity and the intensity
  oscillations have exactly a 1/4-period phase difference points to the
  existence of slow-mode standing waves in the oscillating loop. This
  interpretation is also supported by two other pieces of evidence:
  (1) the wave period and (2) the amplitude relationship between the
  intensity and velocity are as expected for a slow-mode standing wave.

Title: Variability of EUV-spectra from the quiet upper solar
atmosphere: Intensity and Doppler shift
Authors: Brković, A.; Peter, H.; Solanki, S. K.
Bibcode: 2003A&A...403..725B
Altcode:
  We have studied SUMER and CDS time series of spectra and images of
  quiet-Sun regions at the solar disc centre. The data contain ultraviolet
  emission lines sampling temperatures of the chromosphere, transition
  region and corona. We find a high correlation between average net
  Doppler shifts and relative brightness variabilities of the studied
  lines (correlation coefficient of 0.92), suggesting a connection between
  the two quantities. The anti-correlation between differential emission
  measures and relative brightness variabilities is weaker (correlation
  coefficient of -0.78). We discuss the observed relationships on the
  basis of differential emission measures and linear wave calculations.

Title: Can solar variability explain global warming since 1970?
Authors: Solanki, S. K.; Krivova, N. A.
Bibcode: 2003JGRA..108.1200S
Altcode:
  The magnitude of the Sun's influence on climate has been a subject
  of intense debate. Estimates of this magnitude are generally based on
  assumptions regarding the forcing due to solar irradiance variations
  and climate modeling. This approach suffers from uncertainties that
  are difficult to estimate. Such uncertainties are introduced because
  the employed models may not include important but complex processes
  or mechanisms or may treat these in too simplified a manner. Here
  we take a more empirical approach. We employ time series of the most
  relevant solar quantities, the total and UV irradiance between 1856
  and 1999 and the cosmic rays flux between 1868 and 1999. The time
  series are constructed using direct measurements wherever possible and
  reconstructions based on models and proxies at earlier times. These
  time series are compared with the climate record for the period 1856 to
  1970. The solar records are scaled such that statistically the solar
  contribution to climate is as large as possible in this period. Under
  this assumption we repeat the comparison but now including the period
  1970-1999. This comparison shows without requiring any recourse to
  modeling that since roughly 1970 the solar influence on climate (through
  the channels considered here) cannot have been dominant. In particular,
  the Sun cannot have contributed more than 30% to the steep temperature
  increase that has taken place since then, irrespective of which of the
  three considered channels is the dominant one determining Sun-climate
  interactions: tropospheric heating caused by changes in total solar
  irradiance, stratospheric chemistry influenced by changes in the solar
  UV spectrum, or cloud coverage affected by the cosmic ray flux.

Title: A stream of particles from the begin {equation}ta Pictoris
disc: A possible ejection mechanism
Authors: Krivova, N. A.; Solanki, S. K.
Bibcode: 2003A&A...402L...5K
Altcode:
  Recently, a stream of particles originating from the direction of begin
  {equation}ta Pictoris, a young main sequence star surrounded by a dust
  disc, has been reported (Baggaley \cite{baggaley-2000}). Standard
  mechanisms of particle ejection from a disc fail to reproduce
  the properties of this stream. We find that scattering by a giant
  proto-planet with properties taken from the literature is consistent
  with the observations. The fact that a straightforward ejection
  mechanism reproduces the data supports the identification of the
  particle stream's source with beta Pic. Our work also indicates that
  protoplanetary dust discs form a potentially rich source of large
  interstellar grains, as widely detected in the Solar System.

Title: Interplanetary and solar surface properties of coronal holes
    observed during solar maximum
Authors: Zhang, J.; Woch, J.; Solanki, S. K.; von Steiger, R.;
   Forsyth, R.
Bibcode: 2003JGRA..108.1144Z
Altcode:
  Data from the Solar Wind Ion Composition Spectrometer (SWICS) on board
  the Ulysses spacecraft and synoptic maps from Kitt Peak are used to
  analyze the relatively short-lived coronal holes which exist during
  the maximum phase of the solar activity cycle 23. They are compared
  with the persistent polar coronal holes which prevail around solar
  minimum. A solar wind velocity increase coinciding with a shift of
  the ionic charge composition toward lower charge states serves as a
  robust criterion for identifying solar wind streams emanating from
  solar maximum holes. This allows an unambiguous association of every
  stream identified in interplanetary space with a coronal hole on the
  solar surface with consistent magnetic polarity. Solar wind streams
  emanating from the solar maximum holes generally show lower velocities
  of 400 to 600 km/s compared to the polar hole stream velocities of
  700 to 800 km/s. However, the SWICS O<SUP>7+</SUP>/O<SUP>6+</SUP>
  charge-state ratios, which are a proxy for coronal temperatures, do not
  reveal a consistent difference. Though a number of solar maximum holes
  have a significantly, up to three times, higher temperature compared
  to the polar coronal holes, the majority of the investigated holes and
  specifically those with new cycle polarity have a coronal temperature
  within the range of polar hole temperatures. Likewise, the magnetic flux
  density in the solar maximum holes and in the polar coronal holes, as
  derived from the synoptic maps, is not strikingly different. Therefore
  any intrinsic difference between solar maximum holes and polar coronal
  holes is small. The striking discrepancy in their kinetic properties,
  namely the slower velocity of the solar wind streams emanating from
  solar maximum holes, may partly be attributed to deceleration of the
  solar wind during propagation to the spacecraft. The discrepancy may
  also be influenced by active regions in close proximity to the coronal
  holes, which presumably is more likely for smaller holes. There may,
  however, be a tendency for the faster wind streams to emanate from
  cooler holes.

Title: Ejection of Dust from Planetary Systems into Interstellar Space
Authors: Krivov, A.; Krivova, N.; Solanki, S.; Titov, V.
Bibcode: 2003EAEJA.....4264K
Altcode:
  Extensive observational and theoretical research of the last two decades
  have made it clear that young exoplanetary systems comprise not only
  planets themselves, but also disks of small bodies and of dust-sized
  material these bodies replenish. In much the same way as in the young
  Solar System, interaction of the solids in a circumstellar disk with
  planets at late stages of planet formation should hang the material on
  the outskirts of the system, creating exosolar Kuiper belts and Oort
  clouds. A portion of the material is ejected by the exoplanets from the
  disks into interstellar space, which may represent an important source
  of large interstellar dust grains in the Galaxy. Here we study how
  the efficiency of the ejection mechanism and the involved timescales
  depend on the mass and orbital parameters of the planet, as well
  as on the `unperturbed' spatial distribution of disk particles. We
  also derive the distribution of the final velocities of the ejected
  material. The study is done semianalytically with the aid of the
  Oepik-Weidenschilling statistical theory of planetary encounters and
  numerically with direct Monte-Carlo orbital simulations. The results
  may have particular implications to the beta Pictoris system: they
  lend further support to the idea (Krivova and Solanki 2002) that a
  collimated stream of interstellar radiometeors detected by Baggaley
  (2000) originates at beta Pic and consists of grains ejected by a
  presumed jovian planet orbiting this star.

Title: Cycles and cyclicities of the Sun
Authors: Solanki, S. K.; Krivova, N. A.
Bibcode: 2003ASPC..292..423S
Altcode: 2003ipc..conf..423S
  The solar activity cycle is discussed in the broader context of solar
  variability. It is pointed out that the Sun exhibits periodic, cyclic,
  chaotic and stochastic phenomena. The origins of solar variability
  are mentioned and the importance of secular variations of the solar
  cycle for a putative influence of the Sun on the Earth's climate is
  briefly discussed.

Title: SUNRISE: a balloon-borne telescope for high resolution solar
    observations in the visible and UV
Authors: Solanki, Sami K.; Gandorfer, Achim M.; Schuessler, Manfred;
   Curdt, W.; Lites, Bruce W.; Martinez-Pillet, Valentin; Schmidt,
   Wolfgang; Title, Alan M.
Bibcode: 2003SPIE.4853..129S
Altcode:
  Sunrise is a light-weight solar telescope with a 1 m aperture for
  spectro-polarimetric observations of the solar atmosphere. The telescope
  is planned to be operated during a series of long-duration balloon
  flights in order to obtain time series of spectra and images at the
  diffraction-limit and to study the UV spectral region down to ~200 nm,
  which is not accessible from the ground. The central aim of Sunrise
  is to understand the structure and dynamics of the magnetic field in
  the solar atmosphere. Through its interaction with the convective flow
  field, the magnetic field in the solar photosphere develops intense
  field concentrations on scales below 100 km, which are crucial for the
  dynamics and energetics of the whole solar atmosphere. In addition,
  Sunrise aims to provide information on the structure and dynamics
  of the solar chromosphere and on the physics of solar irradiance
  changes. Sunrise is a joint project of the Max-Planck-Institut fuer
  Aeronomie (MPAe), Katlenburg-Lindau, with the Kiepenheuer-Institut fuer
  Sonnenphysik (KIS), Freiburg, the High-Altitude Observatory (HAO),
  Boulder, the Lockheed-Martin Solar and Astrophysics Lab. (LMSAL),
  Palo Alto, and the Instituto de Astrofi sica de Canarias, La Laguna,
  Tenerife. In addition, there are close contacts with associated
  scientists from a variety of institutes.

Title: On the nature of moving magnetic feature pairs around sunspots
Authors: Zhang, Jun; Solanki, S. K.; Wang, Jingxiu
Bibcode: 2003A&A...399..755Z
Altcode:
  Employing data recorded by the Michelson Doppler Imager (MDI) instrument
  on the Solar and Heliospheric Observatory (SOHO), we have identified
  144 pairs of opposite magnetic polarity moving magnetic features
  (MMFs) in two active regions (NOAA ARs 8375 and 9236). The following
  results are obtained: (1) The majority of MMF pairs first appears at
  a distance of 1000 to 5000 km from the outer boundary of the sunspot,
  although MMF pairs appearing closer to the sunspot may be missed. (2)
  MMF bipoles are not randomly oriented. The member of an MMF pair further
  from the sunspot has the polarity of the parent sunspot in 85% of the
  cases. Furthermore, the orientations of MMF pairs are associated with
  the twist of the sunspot superpenumbra deduced from Hα images. (3) The
  mean lifetime of the studied MMFs is around 4 hours. (4) The separation
  between the two polarities of the MMFs falls in the range of 1100-1700
  km. This separation remains almost unchanged, even decreases slightly
  as the MMF pairs move outwards. (5) MMFs are observed to cluster at
  particular azimuths around the parent sunspot, in particular in AR
  8375. (6) MMF pairs move approximately radially outward from sunspots
  at an average speed of around 0.5 km s<SUP>-1</SUP>. Their motion is
  deflected towards large concentrations of magnetic flux of opposite
  polarity to that of the parent sunspot. A qualitative model based on
  these and other observations is presented. MMF pairs are proposed to be
  part of a U-loop emanating from the sunspot's magnetic canopy. Possible
  mechanisms leading to the formation of such a loop are discussed.

Title: Reconstruction of solar irradiance variations in cycle 23:
    Is solar surface magnetism the cause?
Authors: Krivova, N. A.; Solanki, S. K.; Fligge, M.; Unruh, Y. C.
Bibcode: 2003A&A...399L...1K
Altcode:
  A model of solar irradiance variations is presented which is based
  on the assumption that solar surface magnetism is responsible for all
  total irradiance changes on time scales of days to years. A time series
  of daily magnetograms and empirical models of the thermal structure
  of magnetic features (sunspots, faculae) are combined to reconstruct
  total (and spectral) irradiance from 1996 to 2002. Comparisons with
  observational data reveal an excellent correspondence, although the
  model only contains a single free parameter. This provides strong
  support for the hypothesis that solar irradiance variations are caused
  by changes in the amount and distribution of magnetic flux at the
  solar surface.

Title: Intercalibration of SUMER and CDS on SOHO. III. SUMER and
    CDS-GIS
Authors: Pauluhn, Anuschka; Lang, Jim; Breeveld, Eddie R.; Solanki,
   Sami K.; Schühle, Udo
Bibcode: 2003ApOpt..42..657P
Altcode:
  Simultaneous observation of the same solar sources with different
  instruments is one way to test prelaunch radiometric calibrations and
  to detect changes in responsivity with time of extreme-ultraviolet
  instruments in space. Here we present the results of intercalibration
  of the SUMER (Solar Ultraviolet Measurements of Emitted Radiation)
  spectrometer (detectors A and B) and the GIS (Grazing Incidence
  Spectrometer), one of two spectrometers that compose the CDS (Coronal
  Diagnostic Spectrometer) on the Solar and Heliospheric Observatory
  (SOHO). The two instruments observed simultaneously radiances of
  emission lines at or near the center of the solar disk. The emission
  line chosen for intercomparison was Ne viii at 770 Å. However,
  such an intercomparison of the SUMER and CDS-GIS measurements means
  comparing two data sets with large differences in resolution and field
  of view. The latter difference, especially, introduces differences
  in the measured intensities caused by the solar variability that is
  relatively strong in the 770- Å line. Using a statistical approach to
  overcome this problem, we found that the ratio of the GIS to the SUMER
  average radiances amounted to 2.6 +/- 0.9 before the SOHO ’s loss of
  attitude and to 2.1 +/- 0.7 afterward. These findings confirm earlier
  estimates of the GIS ’s responsivity being too low, and an update
  of the GIS calibration is recommended. Despite the large differences
  in resolution and field of view of the two instruments, the shapes of
  their normalized and rescaled histograms of the radiances agree well
  and therefore represent characteristic features of the Ne viii line.

Title: The Magnetic Field from the Sun to the Interstellar Medium
Authors: Solanki, Sami K.
Bibcode: 2003IAUJD...7E..11S
Altcode:
  The magnetic field of the Sun is responsible for a vast variety of
  phenomena on the Sun and in the heliosphere. The field extends from
  the bottom of the convection zone into the interstellar medium and
  is the main agent that couples the various layers of the atmosphere
  together. The strength structure spatial scales complexity and evolution
  of the magnetic field changes very significantly with distance from
  the solar surface. In particular the energy density of the field
  compared to that of the gas (thermal kinetic) is a strong function of
  location. Furthermore although the global magnetic structure becomes
  simpler with increasing height complex fine-scale features are seen
  at all heights.

Title: New Molecular Indicators of Sunspot Magnetic Fields: Infrared
    OH Lines
Authors: Berdyugina, S. V.; Solanki, S. K.; Lagg, A.
Bibcode: 2003ASPC..286..299B
Altcode: 2003ctmf.conf..299B
  No abstract at ADS

Title: Molecular lines observations with THEMIS
Authors: Arnaud, J.; Faurobert, M.; Raouafi, N. -E.; Solanki, S. K.
Bibcode: 2003sf2a.conf..111A
Altcode: 2003sf2a.confE..39A
  Lines of molecules like MgH, C2, TiO, ... represent powerful tools
  for the study of the solar atmosphere. Their observations on the
  Sun can also help to constrain the polarizability and Lande factors
  calculations which are much more complex than for atomic lines. We will
  present THEMIS polarimetric observations of these lines to illustrate
  some aspects of their use for solar physics.

Title: Structure of a simple sunspot from the inversion of IR
    spectral data
Authors: Mathew, S. K.; Solanki, S. K.; Lagg, A.; Collados, M.;
   Berdyugina, S. V.; Frutiger, C.; Krupp, N.; Woch, J.
Bibcode: 2003AN....324..388M
Altcode:
  Analysis of spectral data of two neighboring infrared lines, Fe i
  15648.5 Å (g = 3) and Fe i 15652.9 Å (g_eff = 1.53) are carried out
  for a simple sunspot when it was near the solar disk center (mu = 0.92),
  to understand the basic structure of sunspot magnetic field. Inversions
  of Stokes profiles are carried out to derive different atmospheric
  parameters both as a function of location within the sunspot and height
  in the atmosphere. As a result of the inversion we have obtained maps
  of magnetic field strength, temperature, line-of-sight velocity, field
  inclination and azimuth for different optical depth layers between log
  (tau_ {5}) = 0 and log (tau_ {5}) = -2.0 . In this paper we present
  few results from our inversion for a layer averaged between log (tau_
  {5}) from 0.0 to -0.5.

Title: Doppler Oscillations of Active Region Loops: Steps towards
    Coronal Seismology
Authors: Curdt, W.; Wang, T. J.; Dammasch, I. E.; Solanki, S. K.
Bibcode: 2003HvaOB..27...83C
Altcode:
  Oscillations of coronal loops -- subject of theoretical work for a long
  time -- can help to determine coronal plasma parameters not otherwise
  accessible. Therefore, the Doppler oscillations recently observed by
  the SUMER spectrometer on SOHO are of extreme interest and constitute a
  significant contribution to the old, but rejuvenated field of coronal
  seismology. High-velocity oscillation events in hot EUV flare lines
  are seen almost every time these lines brighten. Such events seem to
  be a common feature of active region loops. The oscillations always
  have an impulsive trigger and are strongly damped while they cool
  down. Lines formed at normal coronal temperatures do not show any
  signature of these oscillations.

Title: Commission 12: Solar radiation and structure (Rayonnement et
    structure solaires)
Authors: Solanki, Sami K.
Bibcode: 2003IAUTA..25...90S
Altcode: 2003IAUTr..25A..90S
  No abstract at ADS

Title: Sunspots: An overview
Authors: Solanki, Sami K.
Bibcode: 2003A&ARv..11..153S
Altcode:
  Sunspots are the most readily visible manifestations of solar
  magnetic field concentrations and of their interaction with the Sun's
  plasma. Although sunspots have been extensively studied for almost
  400 years and their magnetic nature has been known since 1908,
  our understanding of a number of their basic properties is still
  evolving, with the last decades producing considerable advances. In the
  present review I outline our current empirical knowledge and physical
  understanding of these fascinating structures. I concentrate on the
  internal structure of sunspots, in particular their magnetic and
  thermal properties and on some of their dynamical aspects.

Title: Hot loop oscillations seen by SUMER
Authors: Wang, T. J.; Solanki, S. K.; Curdt, W.; Innes, D. E.;
   Dammasch, I. E.
Bibcode: 2003AN....324..340W
Altcode:
  No abstract at ADS

Title: Magnetic Elements Near the Solar Limb: Inversions Based on
    a Flux-tube Model
Authors: Frutiger, C.; Solanki, S. K.; Gandorfer, A.
Bibcode: 2003ASPC..307..344F
Altcode:
  No abstract at ADS

Title: Molecules as Diagnostics of Solar and Stellar Magnetic Fields
Authors: Berdyugina, S. V.; Solanki, S. K.; Stenflo, J. O.
Bibcode: 2003ASPC..307..181B
Altcode:
  No abstract at ADS

Title: Modeling the Fine Structure of a Sunspot Penumbra through
    the Inversion of Stokes Profiles
Authors: Borrero, J. M.; Lagg, A.; Solanki, S. K.; Frutiger, C.;
   Collados, M.; Bellot Rubio, L. R.
Bibcode: 2003ASPC..286..235B
Altcode: 2003ctmf.conf..235B
  No abstract at ADS

Title: Asteroseismic Determination of a Star
Authors: Gizon, Laurent; Solanki, Sami K.
Bibcode: 2003IAUJD..12E..19G
Altcode:
  Asteroseismology provides us with the possibility of determining the
  angle i between the direction of the rotation axis of a pulsating
  Sun-like star and the line of sight. A knowledge of i is important
  not just for obtaining improved stellar parameters but also in order
  to determine the true masses of extra-solar planets detected from the
  radial velocity shifts of their central stars. By means of Monte-Carlo
  simulations we estimate the precision of the measurement of i and
  other stellar parameters. We find that the inclination angle can be
  retrieved accurately for sufficiently large i for stars that rotate
  at least twice faster than the Sun.

Title: Doppler oscillations in hot coronal loops
Authors: Curdt, W.; Wang, T. J.; Innes, D. E.; Solanki, S. K.;
   Dammasch, I. E.; Kliem, B.; Ofman, L.
Bibcode: 2002ESASP.506..581C
Altcode: 2002ESPM...10..581C; 2002svco.conf..581C
  Recently, a new kind of damped oscillations of hot coronal loops was
  revealed by the Solar Ultraviolet Measurements of Emitted Radiation
  (SUMER) spectrometer on SOHO. Such events seem to be a common feature
  observed in active region loops, seen very often when these lines
  brighten. The oscillations always have an impulsive trigger and
  are strongly damped while they cool down. However, in lines formed
  at coronal temperatures of ≍2 MK never any signature of these
  oscillations has been observed. In this study, we present the main
  properties of Doppler oscillations derived from a statistical study
  of 17 flare-like events, and a comparison with TRACE transverse loop
  oscillations. We also discuss the oscillation modes and their damping
  mechanism.

Title: Was one sunspot cycle in the 18th century really lost?
Authors: Krivova, N. A.; Solanki, S. K.; Beer, J.
Bibcode: 2002A&A...396..235K
Altcode:
  The unusually long 4th solar cycle has recently been proposed by
  Usoskin et al. (2001) to be composed of two cycles. They argue that
  a weak and short cycle might have been lost in sparse sunspot data at
  the end of the 18th century. Here we check this hypothesis in different
  ways. First, we consider the sunspot number record in greater detail
  and compare in a statistical sense the sunspot observations of the
  period in question with those at other times. In a statistical sense the
  sunspot numbers recorded at the time of the proposed new cycle minimum
  are extremely untypical for other minima in the solar cycle record,
  but quite usual for the declining phase of the solar cycle. We also
  analyse other available proxies of solar activity, such as variations
  of the cosmogenic nuclides <SUP>10</SUP>Be and <SUP>14</SUP>C as well
  as auroral activity. These historical records are sufficiently long
  and provide an independent testimony of the cyclic behaviour of solar
  activity at the end of the 18th century. We found no evidence for a lost
  cycle in any of these data sets. Finally, we compare the proposed new
  cycle with the other cycles in the sunspot record. This reveals that
  the proposed ``missing'' cycle has very unusual properties, much more
  so than the original, standard cycle 4. Taken together, the evidence
  from these various tests strongly suggests that no cycle was missed and
  that the official sunspot cycle numbering and parameters are correct.

Title: Search for a relationship between solar cycle amplitude
    and length
Authors: Solanki, S. K.; Krivova, N. A.; Schüssler, M.; Fligge, M.
Bibcode: 2002A&A...396.1029S
Altcode:
  The cross-correlation between time series of solar cycle length
  and amplitude suggests that the length precedes the amplitude. The
  relationship between the two is found to be more complex than a simple
  lag or phase shift, however. A simple empirical model is constructed
  which allows the amplitude of a given cycle to be predicted with
  relatively high accuracy from the lengths of earlier cycles. This
  result not only adds to the means at our disposal for predicting the
  amplitudes of future cycles, but also implies that the solar dynamo
  carries a memory of the length of one cycle over into the next. It may
  also have a bearing on why solar cycle length correlates better with
  the Earth's temperature record than cycle amplitude (Friis-Christensen
  &amp; Lassen \cite{Friis-Christensen:Lassen:1991}). Thoughts on possible
  physical causes are presented.

Title: A physical reconstruction of cosmic ray intensity since 1610
Authors: Usoskin, Ilya G.; Mursula, Kalevi; Solanki, Sami K.;
   Schüssler, Manfred; Kovaltsov, Gennady A.
Bibcode: 2002JGRA..107.1374U
Altcode:
  The open solar magnetic flux has been recently reconstructed by [2000,
  2002] for the last 400 years from sunspot data. Using this reconstructed
  magnetic flux as an input to a spherically symmetric quasi-steady
  state model of the heliosphere, we calculate the expected intensity
  of galactic cosmic rays at the Earth's orbit since 1610. This new,
  physical reconstruction of the long-term cosmic ray intensity is
  in good agreement with the neutron monitor measurements during the
  last 50 years. Moreover, it resolves the problems related to previous
  reconstruction for the last 140 years based on linear correlations. We
  also calculate the flux of 2 GeV galactic protons and compare it to
  the cosmogenic <SUP>10</SUP>Be level in polar ice in Greenland and
  Antarctica. An excellent agreement between the calculated and measured
  levels is found over the last 400 years.

Title: The 1.3-year and 156-day periodicities in sunspot data:
    Wavelet analysis suggests a common origin
Authors: Krivova, N. A.; Solanki, S. K.
Bibcode: 2002A&A...394..701K
Altcode:
  Helioseismic data have revealed a 1.3-year periodicity in the solar
  rotation rate near the bottom of the solar convection zone. In order
  to test whether these rotation rate variations have a significant
  impact on the solar dynamo, we search for such a periodicity in
  tracers of relatively freshly emerged flux at the solar surface,
  namely sunspots. Sunspot areas and sunspot number time series are
  studied with the help of the wavelet transform. Significant power
  at this period (1.28 years) is indeed found and is observed to vary
  strongly with time. This provides independent support for the presence
  of a 1.3 year periodicity in solar data. The power at the 154-158-day
  Rieger period of solar flares is seen to vary approximately in phase
  with the 1.28-year period. Based on this we propose that the Rieger
  period is the third harmonic (3x 156 days= 1.28 years) of the 1.3-year
  period. If the rotation rate of the Sun does vary with 1.3 years then
  the enhanced flaring with the Rieger period may finally be driven by
  the 1.3 year periodicity. However, the power in both periods is also
  found to approximately follow the total number of sunspots. Therefore
  we cannot rule out that the 1.3-year and 156-day periods are harmonics
  of the solar activity cycle. Finally, our analysis of a calibrated
  sunspot area record reveals that the 156-day period continues into
  the most recent cycles, in contrast to earlier results.

Title: Sunrise: a 1-m balloon borne solar telescope
Authors: Solanki, S. K.; Schüssler, M.; Curdt, W.; Lites, B. W.;
   Martinez Pillet, V.; Schmidt, W.; Title, A. M.; Sunrise Team
Bibcode: 2002ESASP.505...27S
Altcode: 2002solm.conf...27S; 2002IAUCo.188...27S
  Sunrise is a light-weight solar telescope with a 1 m aperture
  for spectro-polarimetric observations of the solar atmosphere. The
  telescope is planned to be operated during a series of long-duration
  balloon flights in order to obtain time series of spectra and images
  at the diffraction-limit and to study the UV spectral region down to
  ≅200 nm, which is not accessible from the ground. The central aim of
  Sunrise is to understand the structure and dynamics of the magnetic
  field in the solar atmosphere. Interacting with the convective flow
  field, the magnetic field in the solar photosphere develops intense
  field concentrations on scales below 100 km, which are crucial for the
  dynamics and energetics of the whole solar atmosphere. In addition,
  Sunrise aims to provide information on the structure and dynamics of
  the solar chromosphere and on the physics of solar irradiance changes.

Title: Thermal-magnetic relation of a sunspot as inferred from the
    inversion of 1.5 μm spectral data
Authors: Mathew, S. K.; Solanki, S. K.; Lagg, A.; Krupp, N.; Woch,
   J.; Collados, M.; Berdyugina, S.; Frutiger, C.
Bibcode: 2002ESASP.505..501M
Altcode: 2002IAUCo.188..501M; 2002solm.conf..501M
  We present the thermal-magnetic relation in a simple, isolated sunspot
  deduced from the inversion of 1.56 μm spectropolarimetric data. Due to
  the high Zeeman sensitivity of the g = 3, Fe I 1.5648 μm line, we can
  study this relationship in the entire sunspot. An inversion technique
  based on response functions is used to derive various parameters,
  both as a function of location within the sunspot and of height in the
  atmosphere. In this paper we attempt to relate field strength, vertical
  and radial field components and the field inclination with temperature.

Title: Initial features of an X-class flare observed with SUMER
    and TRACE
Authors: Wang, T. J.; Solanki, S. K.; Innes, D. E.; Curdt, W.
Bibcode: 2002ESASP.505..607W
Altcode: 2002IAUCo.188..607W; 2002solm.conf..607W
  A class X1.5 flare started on the solar limb at 00:43 UT on 21 April
  2002, which was associated with a CME observed at 01:27 UT by LASCO
  C2. The coordinated analyses of this flare include TRACE 195 Å images
  and SUMER spectra in lines of Fe XXI, Fe XII, and C II. We find that:
  1) The flare began with a jet seen by TRACE, which was detected by
  SUMER in the C II line as a strong brightening with blue shifts up to
  170 km s<SUP>-1</SUP>. At that time only weak emission was detected
  in Fe XII and Fe XXI. 2) Subsequently, a weak looplike brightening
  started south of the jet, moving outwards with an average speed of
  about 150 km s<SUP>-1</SUP>. The SUMER spectra responded this moving
  loop as separatingly brightenings, visible only in the Fe XXI line. The
  southwards moving component contains red- and blue-shifted emission
  features and has an apparent speed of ~120 km s<SUP>-1</SUP>. The
  absence of signatures in Fe XII and C II lines indicates that the
  moving weak loop seen by TRACE corresponds to the emission from very
  hot plasma, in a blend line in the 195 Å bandpass due to Fe XXIV
  formed at T &gt; 10 MK. 3) The trigger mechanism of the flare and
  associated CME can be interpreted in the same way as that proposed by
  Wang et al. (2002) for an event with similar initial features.

Title: Harold Jeffreys Lecture: Solar variability and climate change:
    is there a link?
Authors: Solanki, Sami K.
Bibcode: 2002A&G....43e...9S
Altcode:
  Radiation from the Sun makes Earth a habitable planet. Fluctuations in
  the solar output are therefore likely to affect the climate on Earth,
  but establishing both how the output of he Sun varies and how such
  variations influence Earth's climate have proved tricky. But increased
  amounts of data from the Sun and about the climate on Earth over
  recent years mean that rapid progress is being made. In this paper,
  I review the current debate on the influence of the Sun and summarize
  the state of play in this area of solar physics.

Title: Statistical properties of magnetic fields in intranetwork
Authors: Khomenko, E. V.; Collados, M.; Lagg, A.; Solanki, S. K.;
   Trujillo Bueno, J.
Bibcode: 2002ESASP.505..445K
Altcode: 2002IAUCo.188..445K; 2002solm.conf..445K
  We report a study of the quiet sun's magnetic field based
  on high-resolution infrared spectropolarimetric observations
  (TIP/VTT). We find that in almost 50% of the pixels Stokes V and in 15%
  the Stokes Q and/or U profiles have a signal above 10<SUP>-3</SUP>. The
  statistical properties of the mainly intranetwork field sampled by these
  observations are presented, showing that most of the observed fields
  are weak (the field strength distribution peaks at 350 G and has a FWHM
  of 300 G) with very few kG features. The magnetized regions occupy a
  very small fill fractions (about 2%). The field changes properties on
  granular spatial scales and the size of the patches formed by similar
  profiles is close to 1". Most of the parameters of the observed
  polarization profiles show correlations with granulation parameters.

Title: How large is the Sun's total magnetic flux?
Authors: Krivova, N. A.; Solanki, S. K.; Fligge, M.
Bibcode: 2002ESASP.505..461K
Altcode: 2002solm.conf..461K; 2002IAUCo.188..461K
  Variations in the radiative output of the Sun are directly allied
  to changes in the amount and distribution of solar surface magnetic
  field. The variability of irradiance on time-scales significantly
  shorter than a solar cycle can be produced by the spatial and temporal
  evolution of active regions, whereas its secular variations ensue
  from changes of the quiet-Sun magnetic flux on longer time-scales. The
  relative amounts of the magnetic flux in active regions and in the quiet
  Sun as well as their cyclic evolution have been studied by Harvey (1994)
  on the basis of the NSO/Kitt Peak synoptic maps. Since a single pixel of
  such a map is much bigger than individual small-scale magnetic elements
  and opposite polarities may be present within the same pixel, some
  magnetic flux went uncounted, so that the flux obtained by Harvey (1994)
  represents a lower limit to the true amount of magnetic flux present
  on the Sun. We use MDI full-disc and high-resolution magnetograms to
  estimate the total magnetic flux of the Sun.

Title: Surface magnetic fields and UV radiance of the quiet Sun
Authors: Pauluhn, A.; Solanki, S. K.
Bibcode: 2002ESASP.505..521P
Altcode: 2002solm.conf..521P; 2002IAUCo.188..521P
  In order to investigate the correspondence between the quiet-Sun UV
  radiance and changes in the magnetic network during the solar cycle,
  we study the quiet-Sun variability with the two EUV instruments
  CDS (Coronal Diagnostic Spectrometer) and SUMER (Solar Ultraviolet
  Measurements of Emitted Radiation) and the MDI (Michelson Doppler
  Imager) magnetograph on SOHO. Using a monthly data set of co-spatial and
  co-temporal observations of quiet-Sun areas near disk centre we follow
  the evolution of the quiet Sun over four years from solar minimum to
  solar maximum conditions. Although the magnetic flux of the quiet
  network increases by a rather low percentage over the solar cycle,
  its variation is well correlated with the radiance change in the He
  I 584 Å line. We test our data set of quiet-Sun measurements for a
  pixelwise relation between magnetic flux density and radiance.

Title: Hot loop oscillations seen by SUMER: examples and statistics
Authors: Wang, T. J.; Solanki, S. K.; Curdt, W.; Innes, D. E.;
   Dammasch, I. E.
Bibcode: 2002ESASP.505..199W
Altcode: 2002solm.conf..199W; 2002IAUCo.188..199W
  We measure physical parameters of Doppler-shift oscillations in
  17 flare-like events. These events have been recorded by the Solar
  Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer
  on SOHO, along a slit fixed above limb active regions. The selected
  spectral windows contain emission lines with formation temperatures
  from ~10<SUP>4</SUP> to 10<SUP>7</SUP>K. The events were only
  detected in hot flare lines, without any signature in lines formed
  around 2×10<SUP>6</SUP>K. Similarly, the Doppler shift oscillations
  occur in regions coincident with hot soft X-ray loops, but not with
  EUV loops. The oscillations have periods of 11 - 31 min, with an
  exponential decay time of 5.5 - 29 min, and show an initial large
  shift pulse with peak velocities up to 200 km s<SUP>-1</SUP>. Several
  indications suggest that the Doppler oscillations are incompressible
  coronal loop oscillations, that are usually excited impulsively by
  weak flare (or microflare) events that also produced a strong emission
  increase at 5 - 8×10<SUP>6</SUP>K.

Title: Doppler Shift Oscillations of Hot Solar Coronal Plasma Seen
by SUMER: A Signature of Loop Oscillations?
Authors: Wang, Tongjiang; Solanki, S. K.; Curdt, W.; Innes, D. E.;
   Dammasch, I. E.
Bibcode: 2002ApJ...574L.101W
Altcode:
  We report observations of strongly damped Doppler shift oscillations
  detected in a flare line, Fe XIX, with the Solar Ultraviolet
  Measurement of Emitted Radiation spectrometer. Spectra were recorded
  above an active region at the western limb of the Sun, from lines
  with formation temperatures ranging from 0.01 to 10 MK. However, the
  oscillations were seen only in the hot plasma (&gt;6 MK) lines. The
  Doppler oscillations have periods of 14-18 minutes, with an exponential
  decay time of 12-19 minutes, and show an initial large blueshift pulse
  with peak velocities up to 77 km s<SUP>-1</SUP>. Several indications
  suggest that the Doppler oscillations are incompressible coronal loop
  oscillations that are excited impulsively by a flarelike event that
  also produced a strong increase in Fe XIX emission.

Title: The magnetic structure of sunspots and starspots
Authors: Solanki, S. K.
Bibcode: 2002AN....323..165S
Altcode:
  The single most important quantity determining the properties of
  sunspots and presumably starspots is their magnetic field. First
  an overview of the magnetic structure of sunspots is given, some
  of the progress made in recent years is described and some of the
  unsolved questions are pointed out. Both observational and theoretical
  aspects are dealt with. Finally, the magnetic structure of starspots
  is discussed. After presenting the evidence for (and against) their
  magnetic nature the signature of starspots in Zeeman Doppler images
  is described. It is pointed out that if the properties of sunspots
  are extrapolated to giant spots on rapidly rotating stars then the
  observed signature can be at least qualitatively explained.

Title: Modelling solar irradiance variations: separate models for
    the network and active region faculae
Authors: Wenzler, T.; Solanki, S. K.; Fluri, D. M.; Frutiger, C.;
   Fligge, M.; Ortiz, A.
Bibcode: 2002ESASP.508..231W
Altcode: 2002soho...11..231W
  In order to determine to what extent solar surface magnetism
  affects solar irradiance we need to reconstruct the irradiance from
  magnetograms. This process requires the use of model atmospheres. Here
  we present two model atmospheres describing faculae in active regions
  and the network. The models have been constructed such that they
  reproduce various data sets simultaneously.

Title: Intercalibration of CDS and SUMER
Authors: Pauluhn, A.; Lang, J.; Schühle, U.; Solanki, S. K.; Wilhelm,
   K.; Pike, C. D.; Thompson, W. T.; Rüedi, I.; Hollandt, J.; Huber,
   M. C. E.
Bibcode: 2002ESASP.508..223P
Altcode: 2002soho...11..223P
  The outcome of the Joint Observing Programme (JOP) Intercal-01, which
  is the intercalibration of the SUMER (Solar Ultraviolet Measurements
  of Emitted Radiation) instrument (detectors A and B) and the two CDS
  (Coronal Diagnostic Spectrometer) instruments, the Normal Incidence
  Spectrometer (NIS) and the Grazing Incidence Spectrometer (GIS),
  is presented. Recent calibration updates of both instruments have
  been employed, and the results indicate a very good correlation and
  agreement of the measured radiances within the individual uncertainties.

Title: Relative brightness variability vs. averaged Doppler shift
    in the quiet Sun
Authors: Brković, A.; Peter, H.; Solanki, S. K.
Bibcode: 2002ESASP.508..281B
Altcode: 2002soho...11..281B
  We studied SUMER and CDS time series of spectra and images of quiet-Sun
  regions at disc centre. Ultraviolet emission lines sampling temperatures
  of the chromosphere, transition region and corona were recorded. We
  found a high correlation between average net Doppler shifts and
  relative brightness variabilities of the studied lines. We point to
  some basic ideas which could eventually model the variability-Doppler
  shift relationship.

Title: How does the magnetic cycle change radiance and irradiance
    of the Sun?
Authors: Solanki, Sami K.
Bibcode: 2002ESASP.508..173S
Altcode: 2002soho...11..173S
  The Sun's magnetic field, which is concentrated into flux tubes in the
  photosphere, affects the radiance. Depending on the size of a flux
  tube it radiates more (for slender tubes) or less (for broad tubes)
  strongly than the quiet Sun. The Sum of all magnetic features on the
  whole solar disc affects the Sun's irradiance. As the number and the
  size distribution of the flux tubes changes over the solar cycle it
  produces a variation of total irradiance, which is very similar to the
  observed variation. There is also evidence that the Sun's magnetic
  field exhibits a secular variation, which is expected to produce a
  slow irradiance change, whose amplitude is expected to be larger than
  the cyclic variation. In this review some of the relevant processes
  taking place in flux tubes are pointed out and models describing the
  irradiance variations over the solar cycle based on the Sun's magnetic
  field are discussed. Finally, the results of the modelling of the
  secular variation of the Sun's magnetic field are presented.

Title: Total solar magnetic flux: dependence on spatial resolution
    of magnetograms
Authors: Krivova, N. A.; Solanki, S. K.; Fligge, M.
Bibcode: 2002ESASP.508..155K
Altcode: 2002soho...11..155K
  The variability of the solar radiative output is tied to the evolution
  of the surface magnetic field. Irradiance changes on time-scales of the
  solar rotation are governed by the varying distribution of the magnetic
  features and the evolution of sunspots and individual active regions,
  whereas the total amount of magnetic flux in particular small-scale
  magnetic elements seems to dominate the irradiance variations on the
  time scale of the solar cycle. Possibly of even greater relevance for
  climate on Earth are secular variations of solar irradiance, which
  are at least partly caused by changes in the quiet-Sun magnetic flux
  on long time scales. Using NSO/Kitt Peak synoptic charts Harvey (1994)
  found that the total magnetic flux in active regions at activity maximum
  is about 3 times higher than the flux at activity minimum. The size of
  small-scale magnetic elements is, however, far below the resolution of
  currently obtainable magnetograms. At the same time, their distribution
  on the solar surface is highly non-uniform, with magnetic elements of
  opposite polarities often being grouped close together. This leads to
  an apparent cancellation of the flux within a relatively large pixel
  of a Kitt Peak synoptic chart and underestimates the total magnetic
  flux, mainly in the quiet Sun. Using MDI full-disc and high-resolution
  magnetograms and artificially reducing their spatial resolution by
  binning several pixels together we study the influence of the resolution
  on the measured total magnetic flux.

Title: On the intensity contrast of solar photospheric faculae and
    network elements
Authors: Ortiz, A.; Solanki, S. K.; Domingo, V.; Fligge, M.;
   Sanahuja, B.
Bibcode: 2002A&A...388.1036O
Altcode: 2002astro.ph..7008O
  Sunspots, faculae and the magnetic network contribute to solar
  irradiance variations. The contribution due to faculae and the network
  is of basic importance, but suffers from considerable uncertainty. We
  determine the contrasts of active region faculae and the network,
  both as a function of heliocentric angle and magnetogram signal. To
  achieve this, we analyze near-simultaneous full disk images of
  photospheric continuum intensity and line-of-sight magnetic field
  provided by the Michelson Doppler Interferometer (MDI) on board
  the SOHO spacecraft. Starting from the surface distribution of
  the solar magnetic field we first construct a mask, which is then
  used to determine the brightness of magnetic features, and the
  relatively field-free part of the photosphere separately. By sorting
  the magnetogram signal into different bins we are able to distinguish
  between the contrasts of different concentrations of magnetic field. We
  find that the center-to-limb variation (CLV) of the contrast changes
  strongly with magnetogram signal. Thus, the contrasts of active region
  faculae (large magnetogram signal) and the network (small signal)
  exhibit a very different CLV, showing that the populations of magnetic
  flux tubes that underly the two kinds of features are different. The
  results are compatible with, on average, larger flux tubes in faculae
  than in the network. This implies that these elements need to be treated
  separately when reconstructing variations of the total solar irradiance
  with high precision. We have obtained an analytical expression for
  the contrast of photospheric magnetic features as a function of both
  position on the disk and spatially averaged magnetic field strength,
  by performing a 2-dimensional fit to the observations. We also provide
  a linear relationship between magnetogram signal and the mu =cos (theta
  ), where theta is the heliocentric angle, at which the contrast is
  maximal. Finally, we show that the maximum contrast per unit magnetic
  flux decreases rapidly with increasing magnetogram signal, supporting
  earlier evidence that the intrinsic contrast of magnetic flux tubes
  in the network is higher.

Title: Oscillating hot loops observed by SUMER
Authors: Wang, T. J.; Solanki, S. K.; Curdt, W.; Innes, D. E.;
   Dammasch, I. E.
Bibcode: 2002ESASP.508..465W
Altcode: 2002soho...11..465W
  We report observations of Doppler shift oscillations in hot flare lines
  emitted from active region loops. The Solar Ultraviolet Measurements
  of Emitted Radiation (SUMER) spectrometer on SOHO recorded spectra
  of limb active regions loops in several emission lines with formation
  temperatures from ~10<SUP>4</SUP> to 10<SUP>7</SUP>K. The events were
  only detected in the hot flare lines, without any signature in lines
  formed around 2×10<SUP>6</SUP>K. There is a large shift pulse of up
  to 190 km s<SUP>-1</SUP> during the rising phase of the flux which
  is followed by two or three periods of strongly damped alternating
  red and blue shift oscillations with periods in the range 12-31
  min. Slow mode standing waves match the observed period. However,
  the initial large Doppler shift pulse suggests that the waves are
  impulsively generated. Unlike the oscillating loops seen in the TRACE
  images, these Doppler shift oscillations are sometimes seen without
  an associated flare.

Title: Variation of the facular and network contrast during the
    rising phase of cycle 23
Authors: Ortiz, A.; Domingo, V.; Sanahuja, B.; Solanki, S. K.
Bibcode: 2002ESASP.508..185O
Altcode: 2002soho...11..185O
  Magnetic activity contributes to solar irradiance variations, both on
  short and long time-scales. While sunspots and active region faculae
  are the dominant contributors to irradiance changes on time-scales of
  days to weeks, the origin of the long-term increase of the irradiance
  between activity minimum and maximum (~0.1%) is still debated. It
  has been proposed that the small-scale magnetic elements composing the
  enhanced and quiet network contribute substantially to this increase. To
  contribute to this debate, we attempt to see if there is a change in
  the radiative properties of these elements along the solar cycle,
  and to evaluate such a change. We use near-simultaneous full disk
  magnetograms and images of the photospheric continuum intensity provided
  by MDI/SOHO. We have studied the center-to-limb variations (CLV) of the
  contrast as a function of magnetic strength and we are now analyzing how
  the noise level of the images changes throughout time, as a preliminary
  step towards an analysis of the temporal irradiance variations.

Title: Dependence of UV radiance of the quiet Sun on the solar cycle
Authors: Pauluhn, A.; Solanki, S. K.
Bibcode: 2002ESASP.508..227P
Altcode: 2002soho...11..227P
  Recent SOHO measurements of UV radiance of the quiet Sun show
  a dependence of the radiance on the solar cycle. We study the
  hypothesis that changes in the magnetic network are causing these
  variations. The quiet-Sun variability is investigated with the two
  EUV instruments CDS and SUMER and the MDI magnetograph on SOHO. We
  find that although the magnetic flux of the quiet network increases
  by a rather low percentage over the rising part of the solar cycle,
  its variation is well correlated with the radiance change in the He I
  584 Å line. The main change occurs in the flux of the strong network
  elements while the weaker elements do not exhibit a significant change.

Title: The Sun at solar minimum: North - south asymmetry of the
    polar coronal holes
Authors: Zhang, J.; Woch, J.; Solanki, S. K.; von Steiger, R.
Bibcode: 2002GeoRL..29.1236Z
Altcode: 2002GeoRL..29h..77Z
  Data from the Solar Wind Ion Composition Spectrometer (SWICS) on
  Ulysses and synoptic charts derived from Kitt Peak magnetograms are
  used to compare the south and north polar coronal holes which existed
  during the declining/minimum phase of the solar activity cycle from
  1992 to 1997. The kinetic properties of the solar wind emanating from
  the two polar coronal holes, as represented by solar wind speed, do
  not differ significantly. However, the electron temperature in the
  two coronal holes inferred from ionic charge composition data, namely
  the O<SUP>7+</SUP>/O<SUP>6+</SUP> ratio, show consistent differences,
  with the south polar hole being 10 to 15% hotter. The ground-based
  magnetograms show that the north polar coronal hole covers a larger
  part of the solar surface than the southern one. The total magnetic
  flux and, specifically, the flux density of the north polar coronal
  hole is considerably lower for the whole interval of time between 1992
  and 1997. This strongly indicates that the difference in coronal hole
  temperature between the southern and northern coronal hole is intrinsic
  and is not due to the fact that the Ulysses observations in the south
  and north coronal hole streams were made at different phases of the
  solar cycle. Thus the differences found represent a real north-south
  asymmetry during this time period.

Title: Quiet-Sun variability observed with SUMER and CDS
Authors: Brković, A.; Solanki, S. K.; Rüedi, I.
Bibcode: 2002A&A...385..257B
Altcode:
  Brightness variations of solar features are investigated using time
  series of images and spectra of quiet-Sun regions at disc centre
  obtained with the Coronal Diagnostic Spectrometer (CDS) and the Solar
  Ultraviolet Measurements of Emitted Radiation (SUMER) instrument onboard
  the SOHO spacecraft. Ultraviolet emission lines sampling temperatures
  of the chromosphere, transition region and corona were recorded, with
  the \hei 584.3 Å and \oxv 629.7 Å lines being recorded simultaneously
  by both instruments. A comparison shows that both instruments give
  similar results except that SUMER reveals a factor of three higher
  absolute and relative variability than CDS. Simple tests suggest
  that the higher spatial resolution of SUMER compared to CDS, and the
  broad slit used for the CDS observations, are responsible for this
  difference. This points to the need for higher spatial resolution for
  future variability studies. The SUMER results confirm and extend to
  lower temperatures the trends deduced in an earlier paper from CDS data.

Title: The molecular Zeeman effect and diagnostics of solar and
    stellar magnetic fields. I. Theoretical spectral patterns in the
    Zeeman regime
Authors: Berdyugina, S. V.; Solanki, S. K.
Bibcode: 2002A&A...385..701B
Altcode:
  An overview of the theory of the Zeeman effect in diatomic molecules
  for the limiting Hund's cases (a) and (b) is given and a numerical
  approach for the intermediate coupling case (a-b) is developed. In
  contrast to earlier derivations, which were limited to doublets, this
  approach is valid for terms of any multiplicity. General properties
  of the Zeeman effect for the various cases are deduced. Finally,
  calculated Landé factors for prominent molecular bands in sunspot
  and cool-star spectra are employed to predict the general behaviour of
  these bands in the presence of a magnetic field below the Paschen-Back
  limit. The limiting field strength is calculated and listed.

Title: Solar irradiance variations and climate
Authors: Solanki, S. K.; Fligge, M.
Bibcode: 2002JASTP..64..677S
Altcode: 2002JATP...64..677S
  The irradiance of the Sun is observed to vary in phase with the solar
  cycle at an amplitude of /~0.1% and a period of roughly 11 years. There
  is indirect evidence that the irradiance also exhibits a larger secular
  variation. Direct measurements only cover the last 21/2 solar cycles
  and a longer record is needed to study the possible coupling with
  climate. Therefore, it is necessary to develop successful models
  of solar irradiance variations and to reconstruct it back into the
  past. In the present paper, the current observational knowledge and
  the state-of-the-art of the modelling are introduced and reviewed.

Title: Models for solar magnetic loops. II. Comparison with SOHO-CDS
    observations on the solar disk
Authors: Brković, A.; Landi, E.; Landini, M.; Rüedi, I.; Solanki,
   S. K.
Bibcode: 2002A&A...383..661B
Altcode:
  The present work describes a detailed comparison between SOHO-CDS
  observations of active region loops with a static, isobaric loop
  model developed assuming a temperature-independent heating function
  in the energy balance equation and a variable loop cross-section. The
  loop model is described in Landini &amp; Landi (2002). Observations
  of an active region recorded by CDS have been analyzed. Additional
  data from the EIT and MDI instruments on board the SOHO satellite,
  and broad band soft X-rays images from the Yohkoh satellite, have
  been used to complement the CDS dataset. CDS monochromatic images
  from lines at different temperatures have been co-aligned with EIT,
  MDI and Yohkoh images and a loop structure has been identified. Two
  other loop structures are visible but their footpoints are not clearly
  identified, and have not been analyzed. Electron density, temperature
  and pressure along the selected loop structure have been measured by
  means of line ratio techniques. These quantities have been used to test
  the assumption of constant pressure adopted in the theoretical model,
  and to compare their values with its predictions. The loop filling
  factor has also been estimated from the CDS data after assumptions on
  the loop geometry have been made. Comparison with CDS data has shown
  that a classical model is not able to reproduce the observations;
  despite the large uncertainties, mainly given by the limited CDS
  spatial resolution, indications suggest that agreement occurs only if an
  ``ad hoc'' isothermal region is added on top of the loop and a large
  conductive flux at the base is assumed. Suggestions for improvements
  of theoretical loop models and further studies with the EIS instrument
  on Solar-B, due for launch in 2005, are given.

Title: Secular variation of the Sun's magnetic flux
Authors: Solanki, S. K.; Schüssler, M.; Fligge, M.
Bibcode: 2002A&A...383..706S
Altcode:
  We present an extension of the model of \citet{Solanki:etal:2000}
  that allows us to reconstruct the time evolution of both the total
  and the open magnetic flux at the solar surface since 1700. The flux
  emerging in large active regions is determined using the sunspot number
  as a proxy, while the flux emergence in small ephemeral regions is
  described by an extended cycle whose amplitude and length are related
  to the corresponding sunspot cycle. Both types of regions contribute
  to the open flux, which is the source of the heliospheric field. The
  overlap of the activity cycles of ephemeral regions leads to a secular
  variation of the total cycle-related magnetic flux (active region
  flux + ephemeral region flux + open flux). The model results indicate
  that the total surface flux has doubled in the first half of the last
  century. The evolution of the open flux is in good agreement with the
  reconstruction by \citet{Lockwood:etal:1999}.

Title: Solar variability and global warming
Authors: Krivova, N.; Solanki, S.
Bibcode: 2002cosp...34E.274K
Altcode: 2002cosp.meetE.274K
  The magnitude of the Sun's influence on climate has been a subject
  of intense debate. Estimates of this magnitude are generally based on
  assumptions regarding the forcing due to solar irradiance variations
  entering climate modelling. Given the complexity of the climate system,
  however, such modelling is perforce based on simplifying assumptions,
  which leaves it open to criticism. We take a complementary approach. We
  assume that the Sun has been responsible for climate change prior to
  1970. Then, using reconstructions and measured records of relevant
  solar quantities as well as of the cosmic-ray flux, we estimate which
  fraction of the dramatic temperature rise after that date could be
  due to the influence of the Sun. We show that at least in the most
  recent past (since 1970) the solar influence on climate cannot have
  been significant.

Title: The solar atmosphere
Authors: Solanki, S. K.; Hammer, R.
Bibcode: 2002css1.book.1065S
Altcode:
  No abstract at ADS

Title: Irradiance Medels based on Magnetic Activity
Authors: Solanki, S.; Krivova, N.; Unruh, Y.
Bibcode: 2002cosp...34E1357S
Altcode: 2002cosp.meetE1357S
  An introduction is given to the modelling of irradiance variations
  based on solar surface magnetism. We describe how a time series of daily
  magnetograms and empirical models of the thermal structure of magnetic
  features (sunspots, magnetic elements) are combined to reconstruct total
  and spectral irradiance on a time scale of weeks to years. Comparisons
  with observational data reveal an excellent correspondence. On a
  longer time scale of decades to centuries we first need to know how
  the Sun's magnetic field evolved. Hence reconstructions of the Sun's
  total magnetic flux are briefly introduced, before we present longer
  term reconstructions of the total and spectral irradiance since the
  Maunder minimum.

Title: Physical reconstruction of the long-term heliospheric
    modulation of cosmic rays
Authors: Usoskin, I.; Mursula, K.; Solanki, S.; Shuessler, M.;
   Kovaltsov, G.
Bibcode: 2002cosp...34E.902U
Altcode: 2002cosp.meetE.902U
  Open solar magnetic flux has been recently reconstructed by Solanki
  et al. (2000, 2002) for the last 400 years from sunspot data. Using
  this reconstructed magnetic flux as an input to a spherically symmetric
  quasi-steady state model of the heliosphere, we calculate the expected
  intensity of galactic cosmic rays at the Earth's orbit since 1610. This
  calculated cosmic ray intensity is in good agreement with the neutron
  monitor measurements during the last 50 years. Moreover, we calculate
  the flux of 2 GeV galactic protons and compare it to the cosmogenic
  10 B e level in polar ice in Greenland and Antarctica. An excellent
  agreement between the calculated and actual levels is found over the
  last 400 years.

Title: Solar Variability
Authors: Solanki, S. K.
Bibcode: 2002ISSIR...2....1S
Altcode: 2002rcs..conf....1S; 2002ESASR...2....1S
  With increasing sensitivity, wavelength coverage and photometric
  accuracy (including reliability in calibrations) it is becoming
  ever more clear that the Sun is a variable star at practically all
  wavelengths and timescales. A short and incomplete overview is given
  of the forms which this variability can take. Some of the underlying
  physics is also very briefly touched upon.

Title: The Sun At Solar Minimum: North - South Asymmetry of The
    Polar Coronal Holes
Authors: Woch, J.; Zhang, J.; Solanki, S. K.; von Steiger, R.
Bibcode: 2002EGSGA..27.4007W
Altcode:
  Data from the Solar Wind Ion Composition Spectrometer (SWICS) on Ulysses
  and synoptic charts derived from Kitt Peak magnetograms are used to
  compare the south and north polar coronal holes which existed during
  the declining/minimum phase of the solar activity cycle from 1992 to
  1997. The kinetic properties of the solar wind emanating from the two
  polar coronal holes, as represented by solar wind speed, do not differ
  significantly. However, the electron temperature in the two coronal
  holes inferred from ionic charge composition data, namely the O7+/O6+
  ratio, show consis- tent differences, with the south polar hole being
  10 to 15% hotter. The ground-based magnetograms show that the north
  polar coronal hole covers a larger part of the so- lar surface than
  the southern one. The total magnetic flux and, specifically, the flux
  density of the north polar coronal hole is considerably lower for the
  whole interval of time between 1992 and 1997. This strongly indicates
  that the difference in coronal hole temperature between the southern
  and northern coronal hole is intrinsic and is not due to the fact that
  the Ulysses observations in the south and north coronal hole streams
  were made at different phases of the solar cycle Thus the differences
  found represents a real north-south asymmetry.

Title: Interplanetary and solar surface properties of coronal holes
Authors: Woch, J.; Zhang, J.; Solanki, S.; von Steiger, R.
Bibcode: 2002cosp...34E.967W
Altcode: 2002cosp.meetE.967W
  Data from the Solar Wind Ion Composition Spectrometer (SWICS) on
  Ulysses and synoptic maps from Kitt Peak are used to analyse coronal
  holes throughout the solar activity cycle. The large polar coronal
  holes existing during the declining/minimum phase of solar cycle 22
  show a persistent north-south asymmetry. The coronal temperature,
  inferred from ionic charge-state distributions, and the magnetic flux
  density are significantly lower in the north polar coronal hole. The
  temperature of the emerging north polar hole of solar cycle 23 is
  remarkably similar to that of solar cycle 22, confirming that the
  coronal temperatures of the polar coronal holes do not evolve in the
  course of the activity cycle. Solar wind streams emanating from the
  small-scale coronal holes observed around solar maximum generally show
  lower velocities compared to the polar coronal hole streams. However,
  the coronal temperatures do not reveal a consistent difference. Though
  a large number of solar maximum holes have a significantly higher
  temperature compared to the polar coronal holes the majority has a
  coronal temperature within the range of polar hole temperatures. Above
  all, the latter holds for solar maximum coronal holes having a magnetic
  polarity consistent with the polarity of the new solar cycle. Likewise,
  the magnetic flux density in the solar maximum holes and in the polar
  coronal holes, as derived from the synoptic maps, is not strikingly
  different. Therefore, it can be concluded that there is no indication
  for an intrinsic difference of solar maximum and polar coronal holes.

Title: How much of the solar irradiance variations is caused by the
    magnetic field at the solar surface?
Authors: Solanki, S. K.; Fligge, M.
Bibcode: 2002AdSpR..29.1933S
Altcode:
  The contribution to total solar irradiance variations by the magnetic
  field at the solar surface is estimated. Detailed models of the
  irradiance changes on the basis of magnetograms show that magnetic
  features at the solar surface account for over 90% of the irradiance
  variations on a solar rotation time scale and at least 70% on a solar
  cycle time scale. If the correction to the VIRGO record proposed by
  Fröhlich &amp; Finsterle (2001) is accepted, then magnetic features
  at the solar surface are responsible for over 90% of the solar cycle
  irradiance variations as well.

Title: Intercalibration of CDS and SUMER
Authors: Pauluhn, A.; Lang, J.; Schuhle, U.; Solanki, S. K.; Wilhelm,
   K.; Thompson, W. T.; Pike, C. D.; Ruedi, I.; Hollandt, J.; Huber,
   M. C. E.
Bibcode: 2002ISSIR...2..235P
Altcode: 2002rcs..conf..235P; 2002ESASR...2..235P
  Simultaneous observations of the same solar features with different
  instruments provide a way to compare radiometric calibrations and
  detect changes in responsivity with time of EUV instruments in space
  within the combined uncertainties of the individual instruments. Here
  we present the intercalibration of the SUMER (Solar Ultraviolet
  Measurements of Emitted Radiation) instrument (detectors A and B) and
  the two CDS (Coronal Diagnostic Spectrometer) instruments, the Normal
  Incidence Spectrometer (NIS) and the Grazing Incidence Spectrometer
  (GIS) on the Solar and Heliospheric Observatory (SOHO). This work
  describes the results of the Joint Observing Programme Intercal 01
  and presents quiet-Sun comparisons from March 1996 up to February
  2001, which represents the complete set of all available Intercal
  01 measurements. Recent calibration updates of both instruments are
  employed, and the results indicate a very good correlation and agreement
  of the measured radiances within the combined uncertainties.

Title: Properties of ultraviolet lines observed with the Coronal
    Diagnostic Spectrometer (CDS/SOHO) in coronal holes and the quiet Sun
Authors: Stucki, K.; Solanki, S. K.; Pike, C. D.; Schühle, U.;
   Rüedi, I.; Pauluhn, A.; Brković, A.
Bibcode: 2002A&A...381..653S
Altcode:
  We present an analysis of 14 ultraviolet emission lines belonging to
  different atoms and ions observed inside polar coronal holes and in
  the normal quiet Sun. The observations were made with the Coronal
  Diagnostic Spectrometer (CDS) onboard the Solar and Heliospheric
  Observatory (SOHO). This study extends previous investigations made
  with the Solar Ultraviolet Measurements of Emitted Radiation (SUMER)
  spectrometer to higher temperatures. We compare line intensities,
  shifts and widths in coronal holes with the corresponding values
  obtained in the quiet Sun. While all lines formed at temperatures above
  7 x 10<SUP>5</SUP> K show clearly the presence of the hole in their
  intensities, differences in line width are more subtle, with cooler
  lines being broader in coronal holes, while hotter lines tend to be
  narrower. According to the present data all lines are blueshifted inside
  the coronal hole compared to the normal quiet Sun. Almost all the lines
  formed between 80 000 K and 600 000 K (i.e. transition-region lines)
  show a correlation between blueshifts and brightness within coronal
  holes. This is in agreement with the conclusion reached by Hassler et
  al. (\cite{Hassler1999}) that the fast solar wind emanates from the
  network and supports our previous study (Stucki et al. 2000b). For
  coronal lines, this trend seems to be reversed.

Title: Reconstruction of Cosmic Ray Intensity Since 1610
Authors: Usoskin, I. G.; Mursula, K.; Solanki, S. K.; Schüssler,
   M.; Kovaltsov, G. A.
Bibcode: 2002EGSGA..27.5173U
Altcode:
  Open solar magnetic flux has been recently reconstructed by Solanki
  et al. (2000, 2002) for the last 400 years from sunspot data. Using
  this reconstructed magnetic flux as an input to a spherically symmetric
  quasi-steady state model of the heliosphere, we calculate the expected
  intensity of galactic cosmic rays at the Earth's orbit since 1610. This
  calculated cosmic ray intensity is in good agreement with the neutron
  monitor measurements during the last 50 years. Moreover, we calculate
  the flux of 2 GeV galactic protons and compare it to the cosmogenic
  10Be level in polar ice in Greenland and Antarctica. An excellent
  agreement between the calculated and actual levels is found over the
  last 400 years.

Title: Physical reconstruction of long-term solar activity
Authors: Usoskin, I.; Solanki, S.; Schuessler, M.; Mursula, K.;
   Kovaltsov, G.
Bibcode: 2002cosp...34E.901U
Altcode: 2002cosp.meetE.901U
  For many applications in dynamo theory and solar-terrestrial research
  it is important to know the evolution of solar activity on long time
  scales (centuries to millennia). Previous reconstructions were based
  upon either multi-harmonic backward extrapolation of the known sunspot
  records or on the assumption of a linear relation between terrestrial
  proxies (e.g., cosmogenic isotope abundance) and solar activity. Here
  we present, for the first time, a physical reconstruction of sunspot
  activity on long time scales from the cosmogenic 10 Be records. We
  use a numerical inversion of a combined physical solar-heliospheric
  model (Usoskin et al., 2002), which is essentially non-linear. Using
  physical rather than empirical relations on all steps, we present a
  reconstruction of sunspot activity since the 15th century. Uncertainties
  of the reconstruction are discussed in details. It is important that
  the current high level of sunspot activity is unique on the millennium
  time scale.

Title: Coronal Holes During Solar Maximum: Swics/ulysses and Kitt
    Peak Observations
Authors: Zhang, J.; Woch, J.; Solanki, S. K.; von Steiger, R.
Bibcode: 2002EGSGA..27.4034Z
Altcode:
  Synoptic maps of the solar coronal magnetic field from Kitt Peak show
  the existence of small-scale coronal holes at low and mid latitudes
  during the maximum phase of the present solar cycle. The solar
  wind originating from the most prominent holes can be unambiguously
  identified in interplanetary space at distances of 2 to 4 AU with
  the Solar Wind Ion Composition Spectrometer (SWICS) on Ulysses. The
  coronal hole plasma is characterized by an enhanced velocity and a
  decreased O7+/O6+ ratio com- pared to the ambient solar wind. The
  decreased ratio is indicative for a lower coronal temperature in the
  source region on the Sun. Though clearly distinguishable from the
  ambient solar wind plasma, the solar wind originating from small
  scale coronal holes has a lower velocity and less reduced O7+/O6+
  ratio than the solar wind emanating from the large-scale polar coronal
  holes during solar minimum. This difference is re- flected in synoptic
  coronal hole maps and magnetograms. The magnetic flux density of the
  small scale coronal holes is considerably lower compared to the flux
  density of the polar coronal holes. We suggest that the two types of
  coronal holes are intrinsically different.

Title: Noise reduction in helioseismic power spectra\ by
    non-orthogonal wavelets
Authors: Solanki, S. K.; Régulo, C.; Fligge, M.; Kosovichev, A. G.
Bibcode: 2001A&A...379.1039S
Altcode:
  We present a method to reduce noise in helioseismic power spectra
  using a non-orthogonal wavelet transform based on quadratic spline
  functions. The quality of our method is tested by applying it to
  artificially generated time-series approximating solar p-modes. The
  mode frequencies and line widths obtained from least-squares fits to
  the smoothed spectra are compared with the corresponding parameters
  deduced from maximum likelihood fits to the original spectra. The
  results from both approaches are very similar and suggest that there
  is no major bias in either of these rather independent approaches. As a
  practical example we denoise parts of the power spectrum obtained from
  the two first years of operation of the GOLF instrument onboard SOHO.

Title: Zeeman-split opposite-polarity OH lines in sunspot spectra:
    Resolution of a puzzle
Authors: Berdyugina, S. V.; Solanki, S. K.
Bibcode: 2001A&A...380L...5B
Altcode:
  We present the first synthetic Zeeman-split Stokes I and V profiles
  of OH lines. They explain the puzzling observations reported by Harvey
  (\cite{har85}) of two pairs of lines from the infrared (2, 0) band with
  Stokes V profiles exhibiting opposite polarities. Our new perturbation
  calculations of the Zeeman effect in diatomic molecules, which allow
  states of any multiplicity to be treated, resolve the puzzle. They
  reveal that the unusual behaviour of these lines stems from the fact
  that the two pairs have effective Landé factors of similar magnitude,
  but of opposite signs.

Title: Intercalibration of SUMER and CDS on SOHO. II. SUMER detectors
    A and B and CDS NIS
Authors: Pauluhn, Anuschka; Rüedi, Isabelle; Solanki, Sami K.;
   Schühle, Udo; Wilhelm, Klaus; Lang, Jim; Thompson, William T.;
   Hollandt, Jörg
Bibcode: 2001ApOpt..40.6292P
Altcode:
  Results of an intercalibration between the extreme-ultraviolet
  spectrometers Coronal Diagnostic Spectrometer (CDS) and Solar
  Ultraviolet Measurements of Emitted Radiation (SUMER) on board the Solar
  and Heliospheric Observatory (SOHO) are reported. The results of the
  joint observing program Intercal_01 are described, and intercalibration
  results up to July 2000 of both SUMER detectors A and B and of the
  CDS Normal Incidence Spectrometer (NIS) are presented. The instruments
  simultaneously observed radiance of emission lines at the center of the
  Sun, and three lines have been chosen for intercomparison: He I 584 Å,
  Mg X 609 Å, and Mg X 624 Å. Initially the same area was observed by
  both instruments, but, after restrictions were imposed by the scanning
  mechanism of SUMER in November 1996, the instruments viewed areas of
  different sizes. Nevertheless, the temporal correlation between the
  two instruments remained good through June 1998, when contact with
  the SOHO spacecraft was lost. Until then the CDS instrument measured
  (33+/-5)% and (38+/-7)% (+/-1σ) higher intensity than SUMER in the
  Hz I 584-Å line on average for detectors A and B, respectively. Data
  from SUMER detector B agreed well for Mg X 609 Å and Mg X 624 Å
  with the CDS intensities, showing offsets of (2+/-10)% and (9+/-15)%,
  much less than the data of detector A with offsets of (7+/-8)% and
  (16+/-7)% for the two lines, respectively, relative to CDS. Finally,
  the intercalibration measurements after the loss and recovery of the
  SOHO spacecraft are analyzed. The data for observations from November
  1998 to July 2000 are compared, and it is shown that, although the
  responses of the instruments have changed, the CDS and the SUMER still
  perform well, and their temporal correlation is good.

Title: High-resolution solar polarimetry with Sunrise
Authors: Schmidt, W.; Solanki, S. K.; Lites, B. W.; Title, A. M.;
   Martínez Pillet, V.
Bibcode: 2001AN....322..363S
Altcode:
  Sunrise is a solar telescope with an aperture of 1 m, and is dedicated
  for spectropolarimetric measurements in the visible and the near
  UV. The total wavelength range is 200 to 1000 nm for narrowband imaging
  and diagnostic spectroscopy. Sunrise is planned as a stratospheric
  long-duration balloon mission with a first flight in 2006

Title: A formation mechanism of magnetic elements in regions of
    mixed polarity
Authors: Gadun, A. S.; Solanki, S. K.; Sheminova, V. A.; Ploner,
   S. R. O.
Bibcode: 2001SoPh..203....1G
Altcode:
  We present 2-D, fully compressible radiation-MHD simulations of
  the solar photospheric and subphotospheric layers that run for
  2 hours of solar time starting from a magnetic configuration
  with mixed polarities. In the atmospheric layers the simulation
  reveals a correlation between field strength and inclination, with a
  nearly vertical strong-field magnetic component and a more horizontal
  weak-field component, in agreement with the observations. Our simulation
  also shows that magnetic flux is converted from one of these states to
  the other. In particular, magnetic flux sheets can also be formed when
  a new downflow lane starts due to granule fragmentation. The dynamics
  of the granulation and field-line reconnection are found to play a
  role in the initial stages of a magnetic element's formation. The
  simulation predicts that during or shortly after their formation
  magnetic elements could be associated with oppositely polarized flux
  at a small spatial scale.

Title: The sun's variable spectrum and its terrestrial effects
Authors: Fligge, M.; Solanki, S. K.
Bibcode: 2001A&AT...20..467F
Altcode:
  The solar radiation exhibits strong temporal variations not only in
  intensity but also in its spectrum which are linked to the evolution of
  the Sun through its magnetic activity cycle. The irradiance variability
  increases from longer to shorter wavelengths, with variations in the
  UV being orders of magnitude larger than those in the visible. While
  99% of the total solar radiative output occurs at wavelengths longer
  than 300 nm, solar UV radiation accounts for up to 30% of the total
  variation. The continuous rise of the Earth's surface temperature over
  the last decades urgently raises a question about the physical origin
  of so-called global warming. A reliable estimate of the influence
  of human activity on the Earth's climate requires detailed knowledge
  about the natural sources of variability. One of the unknown boundary
  conditions for models of the evolution of the Earth's climate is the
  variation of the solar irradiance.

Title: The influence of an inclined rotation axis on solar irradiance
    variations
Authors: Knaack, R.; Fligge, M.; Solanki, S. K.; Unruh, Y. C.
Bibcode: 2001A&A...376.1080K
Altcode:
  Compared with Sun-like stars, the irradiance variations of the
  Sun over the solar cycle appear to be relatively small for its
  average activity level (Lockwood et al. \cite{Lockwood:etal:1992};
  Radick et al. \cite{Radick:etal:1998}). It has been proposed that
  the special position of Earth-based observers in the ecliptic plane
  may give the impression of a subdued solar photometric variability
  (Schatten \cite{Schatten:1993}). The aim of the present paper is to
  examine the influence on irradiance variations of a solar rotation
  axis inclined towards the observer. A three-component model is
  used to calculate relative flux variations of a given active-region
  distribution on the surface of the Sun as a function of inclination
  and wavelength. Wavelength-dependent intensity spectra are used to
  describe the contributions of the undisturbed photosphere, sunspots and
  faculae. The spectra result from models that have successfully been
  used to reproduce a host of solar data and thus represent realistic
  estimates of the radiative output from these solar features. We find
  that an inclined rotation axis increases the total solar irradiance
  variations maximally by 40%. The most probable value is approximately
  6%. This is much less than that suggested by former studies, which
  were based on simple contrast functions. In the averaged Strömgren
  filters we estimate a most probable increase of the solar variability
  of 30%. In addition, we estimate the dependence of the flux in the
  chromospheric Ca II H&amp;K lines on inclination. We find that the
  average chromospheric activity level depends only slightly on the
  inclination angle. The chromospheric variability of Sun-like stars,
  however, is significantly affected. Nonetheless, our results indicate
  that a different average inclination of stellar rotation axes relative
  to the observer cannot explain the discrepancy between the brightness
  variations of the Sun and Sun-like stars.

Title: Variations of solar spectral irradiance from near UV to the
    infrared-measurements and results
Authors: Fligge, M.; Solanki, S. K.; Pap, J. M.; Fröhlich, C.;
   Wehrli, C.
Bibcode: 2001JASTP..63.1479F
Altcode: 2001JATP...63.1479F
  Solar spectral irradiance variations are known to exhibit a strong
  wavelength dependence with the amount of variability increasing towards
  shorter wavelengths. The bulk of solar radiation is emitted at visible
  and infrared wavelengths. Thus, the spectral radiation length of 300nm
  accounts for 99% of the total solar radiative output. Deposited in the
  Earth's troposphere and biosphere, this part of the solar irradiance
  spectrum determines direct solar radiative forcing and is therefore
  of particular interest for climate studies. First, measurements of
  solar irradiance and irradiance variability from near UV to the IR are
  reviewed with particular emphasis on the results obtained from the
  Variability of Irradiance and Gravity Oscillations (VIRGO) on SOHO
  and Solar Spectrum Measurement (SOLSPEC) instruments. In the second
  part a model is presented which describes solar spectral irradiance
  variations in terms of the changing distribution of solar surface
  magnetic features.

Title: The lower polar atmosphere and the solar dynamo: perspectives
    for the Solar Orbiter
Authors: Solanki, Sami K.
Bibcode: 2001ESASP.493...35S
Altcode: 2001sefs.work...35S
  The Solar Orbiter will, by flying out of the ecliptic, allow its battery
  of remote-sensing instruments to focus on the Sun's polar regions,
  providing solar physicists with a unique opportunity to study this
  enigmatic part of the Sun for the first time. Some of the scientific
  questions which may be addressed by the Solar Orbiter in its out of
  the ecliptic phase are presented here, with emphasis being placed on
  those related to the lower solar atmosphere and the solar interior.

Title: Analysis of blinkers and EUV brightenings in the quiet Sun
    observed with CDS
Authors: Brković, A.; Solanki, S. K.; Rüedi, I.
Bibcode: 2001A&A...373.1056B
Altcode:
  Movies of quiet Sun regions at disc centre obtained with the
  Coronal Diagnostic Spectrometer (CDS) onboard the SOHO spacecraft
  are used to study the properties of transient brightenings seen in
  the extreme ultraviolet (EUV), so-called blinkers, at three different
  temperatures sampled simultaneously in the chromospheric He I 584.3
  Å (2 x 10<SUP>4</SUP> K), the transition region O V 629.7 Å (2.5
  x 10<SUP>5</SUP> K) and coronal Mg IX 368.1 Å (10<SUP>6</SUP> K)
  lines. Blinkers, here defined somewhat differently than in previous
  studies, were clearly detected in the O V and He I lines. Brightenings
  of the Mg IX line were also seen. A thorough analysis of blinker
  properties is carried out and their detailed properties are
  determined. Blinkers are found to be present in both bright (network)
  and dark (intranetwork) regions, but their number density is larger
  in the brighter areas (in O V) although the rest of their properties
  appear to be unaffected. The average sizes of brightenings range
  from 2.8 Mm<SUP>2</SUP> in Mg IX, 12.4 Mm<SUP>2</SUP> in He I to 23.5
  Mm<SUP>2</SUP> in O V. The durations of blinkers are in the range 3-110
  min, with the average durations being 23 min in He I, about 16 min in
  O V and 12 min in Mg IX. The frequency distributions of ratio of peak
  to background intensity, excess energy and size follow power laws with
  exponents &lt;-5 for the intensity ratio, and between -1 and -3 for
  the other two parameters. The correlation coefficients between pairs of
  ratio, energy and size are at least 0.5, while other pairs of parameters
  describing the blinkers appear to be uncorrelated. The best correlation
  is between size and energy. The blinker durations exhibit a distribution
  whose form is compatible with a log-normal function. Finally, blinkers
  in the 3 lines (i.e. 3 temperature regimes) are poorly correlated; with
  the correlation coefficient being always less than 0.4. This suggests
  that to a large extent the transition region reacts independently of the
  corona and chromosphere to energy deposition, so that these parts of the
  atmosphere are at least partly decoupled from each other. This agrees
  with the expectations from models having separate transition-region
  loops, but contradicts the classical picture of the transition region,
  as being heated dominantly by energy conduction from the corona.

Title: Small-Scale Magnetic Elements in 2-D Nonstationary
    Magnetogranulation
Authors: Gadun, A. S.; Solanki, S. K.
Bibcode: 2001ASSL..259..295G
Altcode: 2001dysu.conf..295G
  2-D simulations of magnetogranulation provide evidence of a close
  connection between the magnetic field and nonstationary thermal
  convection. Fragmentation of large granules can lead to the formation
  of compact nearly vertical magnetic tubes from a weaker horizontal
  field. Conversely, the dissolution of granules can lead to a merging
  of magnetic elements and either to field cancellation (leading to the
  transformation of strong vertical field to its weaker horizontal state)
  or to the formation of broader and stronger magnetic structures.

Title: Diagnostics from Spectral Irradiance Measurements
Authors: Unruh, Y. C.; Solanki, S. K.
Bibcode: 2001AGUSM..SP32B01U
Altcode:
  Solar irradiance varies in tune with solar activity. The irradiance
  changes show a strong wavelength dependence, being an order of magnitude
  larger in the UV than in the visible. The spectral dependence of the
  irradiance variations can be used to differentiate between mechanisms
  that may be responsible for the irradiance changes. I review some of
  the mechanisms that have been invoked in the past to explain the solar
  irradiance variations and compare their predicted spectral irradiance
  changes with solar irradiance measurements. The comparisons imply
  that surface magnetic features alone are sufficient to explain solar
  irradiance data.

Title: Comparison of quiet-Sun radiances measured by CDS and SUMER
    on SOHO
Authors: Pauluhn, A.; Solanki, S. K.; Schühle, U.; Wilhelm, K.;
   Lang, J.; Thompson, W. T.; Rüedi, I.; Hollandt, J.; Huber, M. C. E.
Bibcode: 2001SSRv...97...63P
Altcode:
  Since the beginning of the SOHO (Solar and Heliospheric Observatory)
  mission an intercalibration programme was carried out which included
  simultaneous observations of the EUV instruments CDS (Coronal Diagnostic
  Spectrometer) and SUMER (Solar Ultraviolet Measurements of Emitted
  Radiation) of common targets on the quiet Sun. The observations in the
  chromospheric line of He i (584 Å) and the two coronal lines of Mg x
  (609 Å and 624 Å) thus cover the long period of 4 years and provide a
  data set highly suitable not only for instrumental comparison but also
  for studies of the quiet Sun's long term variability. Up to the SOHO
  accident, both instruments show a very good temporal correlation and
  stability. Even after the loss and recovery of the spacecraft, when
  the instruments had been exposed to extreme temperature conditions,
  the performance of the CDS and SUMER instruments is still good, as is
  the temporal correlation. However, the ratio between the efficiencies
  of the two instruments, which remained constant with time until the
  SOHO accident seems to have changed afterwards. In the coronal lines
  both instruments show an increase of average radiances towards the
  solar maximum.

Title: Empirical models of solar magnetic flux-tubes and their
    non-magnetic surroundings
Authors: Frutiger, C.; Solanki, S. K.
Bibcode: 2001A&A...369..646F
Altcode:
  A powerful method for the analysis of the structure of small
  scale magnetic elements in the solar photosphere is the
  inversion of Stokes spectra. In previous papers based on such
  inversions \cite{BellotRubio:etal:1997, BellotRubio:etal:1999}
  and \cite{Frutiger:etal:1999} have argued in favor of models with
  rather different dynamic properties. In this paper we return to
  this debate and compare results returned by inversions based on
  new multi-component models applied to several Fe i, Fe ii and C i
  spectral line profiles obtained in active region plage with a Fourier
  Transform Spectrometer. These inversions differ from earlier ones by
  the fact that mass conservation is strictly imposed both inside the
  magnetic elements and on the surrounding external flow field. These
  flux-tube models are not only able to reproduce the characteristic
  Stokes V asymmetries and line-shifts observed in active regions
  plages or network elements, but also the Stokes I line profiles,
  including line bisectors. It is confirmed that from the quality of the
  fits alone it is not possible to distinguish between the steady flow
  proposed by \cite{BellotRubio:etal:1997} and the oscillatory model of
  \cite{Frutiger:Solanki:1998}. If, however, physical constraints are
  imposed (e.g. mass conservation or that the flow retains the same
  direction over height in the flux tube) then the oscillatory model
  is found to be superior. In addition, the current investigation also
  provides the first inversion-based model of abnormal granulation.

Title: Large Doppler Shifts in X-Ray Plasma: An Explosive Start to
    Coronal Mass Ejection
Authors: Innes, D. E.; Curdt, W.; Schwenn, R.; Solanki, S.; Stenborg,
   G.; McKenzie, D. E.
Bibcode: 2001ApJ...549L.249I
Altcode:
  We report observations, taken with the Solar Ultraviolet Measurements
  of Emitted Radiation spectrometer, of spatially resolved high red and
  blue Doppler shifts (up to 650 km s<SUP>-1</SUP>) from X-ray-emitting
  plasma in the corona above a flare. The high Doppler shifts are seen
  minutes after a fast, faint optical front is seen racing through the
  same part of the corona in images taken with the Mirror Coronagraph
  for Argentina. The association of the large-scale fast optical emission
  front with soft X-ray emission and high Doppler shifts suggests plasma
  heating and acceleration in the wake of a shock.

Title: Division II: Sun and Heliosphere
Authors: Benz, Arnold O.; Bogdan, T.; Foukal, P. V.; Melrose, D. B.;
   Solanki, S.; Vandas, M.; Webb, D. F.
Bibcode: 2001IAUTB..24..110B
Altcode:
  No abstract at ADS

Title: The Formation of One-Lobed Stokes V Profiles in an
    Inhomogeneous Atmosphere
Authors: Ploner, S. R. O.; Schussler, M.; Solanki, S. K.; Sheminova,
   V. A.; Gadun, A. S.; Frutiger, C.
Bibcode: 2001ASPC..236..371P
Altcode: 2001aspt.conf..371P
  We assess the diagnostic potential of the observed pathological Stokes V
  profiles that differ strongly from the customary, nearly antisymmetric
  two-lobed shape. In particular, we consider the formation of one-lobed
  Stokes V profiles using the results of an MHD simulation. We find
  that the majority of one-lobed profiles is produced in regions of
  weak horizontal field with significant cancellation caused by mixed
  polarity along the line of sight. A minority of one-lobed profiles
  originates close to strong magnetic field concentrations with strong
  gradients of velocity and magnetic field strength.

Title: Stellar Irradiance Variations Caused by Magnetic Activity:
    The Influence of an Inclined Rotation Axis
Authors: Knaack, R.; Fligge, M.; Solanki, S. K.; Unruh, Y. C.
Bibcode: 2001ASPC..248..227K
Altcode: 2001mfah.conf..227K
  No abstract at ADS

Title: A Model for the Decline of Coronal X-ray Emission of Cool
    Giant Stars
Authors: Holzwarth, V.; Schüssler, M.; Solanki, S. K.
Bibcode: 2001ASPC..248..259H
Altcode: 2001mfah.conf..259H
  No abstract at ADS

Title: Are the Sun's Brightness Variations Really Tamer than Those of
Other Comparable Solar-type Stars? (CD-ROM Directory: contribs/unruh1)
Authors: Unruh, Y. C.; Knaack, R.; Fligge, M.; Solanki, S. K.
Bibcode: 2001ASPC..223..748U
Altcode: 2001csss...11..748U
  No abstract at ADS

Title: Consistent Empirical Models of Solar Magnetic Flux Tubes and
the Surrounding Convection (CD-ROM Directory: contribs/frutige2)
Authors: Frutiger, C.; Solanki, S. K.
Bibcode: 2001ASPC..223..632F
Altcode: 2001csss...11..632F
  No abstract at ADS

Title: The Quiet-Sun Variability as seen by CDS and by SUMER
Authors: Brkovic, A.; Solanki, S. K.; Rüedi, I.
Bibcode: 2001IAUS..203..381B
Altcode:
  Blinkers are transient brightenings seen in the extreme
  ultraviolet. These brightenings are candidates for microflare
  activity. Here we determine their properties, using co-aligned
  observations with SUMER and CDS, in the latter case with an open
  slit. We use CDS to find evidence for blinkers in the quiet Sun, and
  SUMER to measure the velocities, and line width changes associated
  with them.

Title: Magnetic Splitting of Molecular Lines in Sunspot
Authors: Berdyugina, S. V.; Frutiger, C.; Solanki, S. K.
Bibcode: 2001IAUS..203..254B
Altcode:
  A study of molecular lines in sunspots is of particular interest
  because of their high temperature and pressure sensitivity. Many of
  them are also magnetically sensitive, but this was not yet widely
  investigated. With high-resolution, high signal-to-noise Fourier
  spectroscopy in four Stokes parameters now available, the use of
  molecular lines for studying the structure of sunspots brings real
  gains. One is the extension of spot models, including magnetic field,
  up to layers, where atomic lines suffer from NLTE effects but molecules
  can still be treated in the LTE approximation. Equally important is the
  fact that since molecular lines are extremely temperature sensitive
  they can be used to probe the thermal and magnetic structure of the
  coolest parts of sunspots. We present calculations of splitting and
  the Stokes parameters for a number of molecular lines in the visible
  and near-infrared regions. Our first selections are the green system of
  MgH A<SUP>2</SUP>Π-X<SUP>2</SUP>σ and the TiO triplet α, γ' and γ
  systems as the most studied band systems in the sunspot spectrum. The
  calculations involve different regimes of the molecular Zeeman effect,
  up to the complete Paschen-Back effect for individual lines. We look
  for molecular lines which can be used along with atomic lines to derive
  magnetic, thermal and dynamic properties of the umbra.

Title: An Example of Reconnection and Magnetic Flux Recycling near
    the Solar Surface
Authors: Ploner, S. R. O.; Schüssler, M.; Solanki, S. K.; Gadun, A. S.
Bibcode: 2001ASPC..236..363P
Altcode: 2001aspt.conf..363P
  No abstract at ADS

Title: Statistical Features of the Quiet Sun in EUV
Authors: Pauluhn, A.; Solanki, S. K.; Rüedi, I.; Landi, E.;
   Schühle, U.
Bibcode: 2001IAUS..203..416P
Altcode:
  The frequency distribution of the extreme ultraviolet (EUV) intensities
  in the quiet Sun has in the past usually been modelled using two
  Gaussians. Here we test this and other distribution functions against
  observed distributions with exceptional statistics. The data were
  obtained in a number of spectral lines observed with two extreme
  ultraviolet spectrometers, CDS (Coronal Diagnostic Spectrometer)
  and SUMER (Solar Ultraviolet Measurements of Emitted Radiation) on
  board the Solar and Heliospheric Observatory (SOHO). We show that the
  frequency distribution of the radiance is best modelled by a lognormal
  distribution or by a sum of a lognormal and a Gaussian. The fact that
  the radiance distribution of the quiet Sun including the network and
  the intranetwork is better reproduced by a single lognormal distribution
  function than by two Gaussians suggests that the same heating processes
  are acting in both types of features. The shape of the distribution
  function shows a clear temperature dependence.

Title: Small-scale Photospheric Structure of the Solar Magnetic
    Fields outside Sunspots
Authors: Solanki, S. K.
Bibcode: 2001ASPC..248...45S
Altcode: 2001mfah.conf...45S
  No abstract at ADS

Title: The Molecular Zeeman Effect and Solar Magnetic Fields
Authors: Berdyugina, S. V.; Frutiger, C.; Solanki, S. K.; Livingston,
   W.
Bibcode: 2001ASPC..236..551B
Altcode: 2001aspt.conf..551B
  No abstract at ADS

Title: Solar and Stellar Magnetic Fields: the Molecular Zeeman Effect
    as a Probe
Authors: Berdyugina, S. V.; Solanki, S. K.; Frutiger, C.
Bibcode: 2001ASPC..248...99B
Altcode: 2001mfah.conf...99B
  No abstract at ADS

Title: Magnetic Fields in Cool Stars (CD-ROM Directory:
    contribs/moreno)
Authors: Moreno Insertis, F.; Saar, S. H.; Solanki, S. K.
Bibcode: 2001ASPC..223..435M
Altcode: 2001csss...11..435M
  No abstract at ADS

Title: Empirical Models of Stellar Convection (CD-ROM Directory:
    contribs/frutige1)
Authors: Frutiger, C.; Solanki, S. K.
Bibcode: 2001ASPC..223..626F
Altcode: 2001csss...11..626F
  No abstract at ADS

Title: Buried Flux Tubes in the Coronal Graveyard (CD-ROM Directory:
    contribs/schussle)
Authors: Schüssler, M.; Holzwarth, V.; Solanki, S. K.; Charbonnel, C.
Bibcode: 2001ASPC..223.1114S
Altcode: 2001csss...11.1114S
  No abstract at ADS

Title: Magnetic Fields Across the Hertzsprung-Russell Diagram
Authors: Mathys, G.; Solanki, S. K.; Wickramasinghe, D. T.
Bibcode: 2001ASPC..248.....M
Altcode: 2001mfah.conf.....M
  No abstract at ADS

Title: Variations of the Solar Spectral Irradiance
Authors: Solanki, S. K.; Fligge, M.; Unruh, Y. C.
Bibcode: 2001IAUS..203...66S
Altcode:
  Not just the total solar irradiance is known to vary, but also the
  solar spectrum. Observations and models of solar spectral irradiance
  variations are presented.

Title: Radiance of Solar Spectral Lines observed with CDS and SUMER
on SOHO (CD-ROM Directory: contribs/pauluhn)
Authors: Pauluhn, A.; Schühle, U.; Solanki, S. K.; Rüedi, I.; Lang,
   J.; Pike, C. D.; Thompson, W. T.; Huber, M. C. E.
Bibcode: 2001ASPC..223..721P
Altcode: 2001csss...11..721P
  No abstract at ADS

Title: Noise Reduction in GOLF Spectra Using Wavelets (CD-ROM
Directory: contribs/regulo)
Authors: Régulo, C.; Roca Cortés, T.; Solanki, S. K.; Fligge, M.;
   GOLF Team
Bibcode: 2001ASPC..223..734R
Altcode: 2001csss...11..734R
  No abstract at ADS

Title: High-resolution Solar Polarimetry with Sunrise
Authors: Schmidt, W.; Solanki, S. K.; Schüssler, M.; Curdt, W.;
   Lites, B. W.; Title, A. M.; Martinez Pillet, V.
Bibcode: 2001AGM....18S1001S
Altcode:
  Sunrise is a 1m balloon-borne solar telescope. It is equipped with
  a spectrograph polarimeter which combines vector-polarimetry in the
  visible with diagnostic spectroscopy in the visible and the UV, down
  to 200 nm. The instrumentation includes a filter-magnetograph and a
  medium-band filtergraph. The wavelength bands of the latter include
  the CH-band (430.6 nm) and a UV continuum at 205 nm. Diffraction
  limited resolution in the UV will be achieved by employing a phase
  diversity technique. The main telescope is based on a lightweight
  silicon-carbide mirror, developed within the Solar Lite program. During
  the long-duration flight at Antarctica, foreseen for late 2005, Sunrise
  will continuously observe the sun for a period of about ten days,
  with constant image quality across the full field of view. In-flight
  alignment of the telescope optics will be controlled by a wavefront
  sensor. The main goal of Sunrise is to understand the structure and
  dynamics of the magnetic field in the atmosphere of the sun. To this
  end, Sunrise will observe small magnetic flux concentrations with
  dimensions of less than 70 km with high polarimetric accuracy. At the
  same time, Sunrise will provide diffraction-limited filtergrams of
  the photosphere and chromosphere with a resolution down to 35 km at
  a wavelength of 200 nm.

Title: Successful spectral synthesis of Zeeman-split molecular bands
    in sunspot spectra
Authors: Berdyugina, S. V.; Frutiger, C.; Solanki, S. K.; Livingstone,
   W.
Bibcode: 2000A&A...364L.101B
Altcode:
  We present the first spectral synthesis of Zeeman-split Stokes profiles
  of the MgH A<SUP>2</SUP>Pi -X<SUP>2</SUP>BLAigma green system and
  TiO gamma -system. The calculations involve different regimes of the
  molecular Zeeman effect, up to the complete Paschen-Back effect for
  individual lines. The synthetic spectra are compared with observations
  of Stokes I and V in sunspot umbrae. We find that although the Stokes
  I spectra are reasonably reproduced, some lines are obviously still
  missing from the employed line lists. The Stokes V spectra turn
  out to be much cleaner since the missing lines do not appear to
  be Zeeman-split. We thus provide the first good fit to Zeeman-split
  molecular lines, including profiles with unconventional Stokes V shapes,
  determined by the Paschen-Back effect. Based on observations from
  the Canada-France-Hawaii Telescope operated by the National Research
  Council of Canada, the Centre National de la Recherche Scientifique
  de France and the University of Hawaii

Title: Comparison of far-ultraviolet emission lines formed in coronal
    holes and the quiet Sun
Authors: Stucki, K.; Solanki, S. K.; Schühle, U.; Rüedi, I.; Wilhelm,
   K.; Stenflo, J. O.; Brković, A.; Huber, M. C. E.
Bibcode: 2000A&A...363.1145S
Altcode:
  We present an analysis of 26 far-ultraviolet emission lines belonging
  to 19 atoms and ions observed on both sides of the boundary of polar
  coronal holes as well as other quiet Sun areas along the limb. The
  observations were made with the SUMER instrument (Solar Ultraviolet
  Measurements of Emitted Radiation) onboard the Solar and Heliospheric
  Observatory (SOHO). We compare line intensities, shifts and widths
  in coronal holes with the corresponding values obtained in the quiet
  Sun. We find that with increasing formation temperature, spectral
  lines show on average an increasingly stronger blueshift in coronal
  holes relative to the quiet Sun at equal heliospheric angle, with the
  coolest lines in our sample (formation temperature ~ 10<SUP>4</SUP>
  K) indicating a small relative redshift. With respect to the rest
  wavelength, however, only lines formed above 5 * 10<SUP>5</SUP> K
  show blueshifts in coronal holes, which is not very different from
  the quiet Sun. The width of the lines is generally larger (by a few
  kilometers per second) inside the coronal hole. Intensity measurements
  clearly show the presence of the coronal hole in Ne VIII lines as well
  as in Fe XII, and provide evidence for a slightly enhanced emission
  in polar coronal holes for lines formed below 10<SUP>5</SUP> K. This
  last result is, however, less certain than the rest due to relatively
  poor statistics. Intensity histograms also exhibit distinct differences
  between coronal hole and quiet-Sun data. For cooler chromospheric lines,
  such as Ni II, the coronal holes display a greater spread in intensities
  than the quiet Sun. Transition-region lines, e.g. O IV, do not reveal
  such differences, while Ne VIII shows characteristics of a coronal line
  with lower average intensity and lower intensity spread inside holes.

Title: Sunspot Magnetic Fields
Authors: Solanki, S.
Bibcode: 2000eaa..bookE2298S
Altcode:
  The magnetic field is the central quantity determining the property of
  a SUNSPOT. It permeates every part of sunspots and by greatly reducing
  the convective transport of heat from below is also responsible for
  sunspot darkness. Conversely, sunspots were the first astronomical
  objects recognized (by G E Hale in 1908) to harbor a magnetic field....

Title: Evolution of the Sun's large-scale magnetic field since the
    Maunder minimum
Authors: Solanki, S. K.; Schüssler, M.; Fligge, M.
Bibcode: 2000Natur.408..445S
Altcode:
  The most striking feature of the Sun's magnetic field is its cyclic
  behaviour. The number of sunspots, which are dark regions of strong
  magnetic field on the Sun's surface, varies with a period of about
  11 years. Superposed on this cycle are secular changes that occur on
  timescales of centuries and events like the Maunder minimum in the
  second half of the seventeenth century, when there were very few
  sunspots. A part of the Sun's magnetic field reaches out from the
  surface into interplanetary space, and it was recently discovered
  that the average strength of this interplanetary field has doubled
  in the past 100 years. There has hitherto been no clear explanation
  for this doubling. Here we present a model describing the long-term
  evolution of the Sun's large-scale magnetic field, which reproduces
  the doubling of the interplanetary field. The model indicates that
  there is a direct connection between the length of the sunspot cycle
  and the secular variations.

Title: Modelling solar irradiance variations: Comparison with
    observations, including line-ratio variations
Authors: Unruh, Y. C.; Solanki, S. K.; Fligge, M.
Bibcode: 2000SSRv...94..145U
Altcode:
  Solar irradiance variations show a strong temporal and spectral
  dependence. The progression of the Sun through its activity cycle as
  well as solar rotation are mirrored in the irradiance variations. The
  spectral dependence is such that the variations are several magnitudes
  larger in the EUV than in the visible or infrared. We present a simple
  3-component model that is based on the assumption that changes in
  the solar flux are exclusively due to changes in spot and facular
  coverage. We compare our model to observations of the spectral solar
  irradiance variations. Despite its simplicity, we find that the
  agreement between our model and the observations is surprisingly
  good. We also explore the reliability and the limitations of our
  approach by comparing observations of the solar facular contrast and
  of the changes in spectral line depths with our calculations.

Title: Modelling Short-Term Spectral Irradiance Variations
Authors: Fligge, M.; Solanki, S. K.; Unruh, Y. C.
Bibcode: 2000SSRv...94..139F
Altcode:
  On time-scales of the solar rotation most of the solar irradiance
  variations are caused by the changing distribution of solar surface
  magnetic features. We model these short-term irradiance variations
  using calculations of sunspot and facular contrasts as a function of
  wavelength and limb angle on the Sun. The position of active regions on
  the solar disc is derived from the MDI magnetograms. The reconstructed
  irradiance variations are compared with total and spectral irradiance
  measurements obtained by the VIRGO experiment on SOHO.

Title: Sunspot Models
Authors: Solanki, S.
Bibcode: 2000eaa..bookE2300S
Altcode:
  Models of SUNSPOTS aim either to reproduce observed properties
  of sunspots, or to understand the physical processes occurring in
  them. Sunspot models are of very diverse types, ranging from empirically
  derived models of their thermal stratification to MHD models of their
  magnetic configuration and evolution. The final aim of all modelling
  is to obtain a consistent and detailed description and und...

Title: Reconstruction of Past Solar Irradiance
Authors: Solanki, S. K.; Fligge, M.
Bibcode: 2000SSRv...94..127S
Altcode:
  Accurate measurements of solar irradiance started in 1978, but a much
  longer time series is needed in order to uncover a possible influence
  on the Earth's climate. In order to reconstruct the irradiance prior to
  1978 we require both an understanding of the underlying causes of solar
  irradiance variability as well as data describing the state of the Sun
  (in particular its magnetic field) at the relevant epochs. Evidence
  is accumulating that on the time-scale of the solar cycle or less,
  variations in solar irradiance are produced mainly by changes in the
  amount and distribution of magnetic flux on the solar surface. The main
  solar features contributing to a darkening of the Sun are sunspots,
  while active-region faculae and the network lead to a brightening. There
  is also increasing evidence for secular changes of the solar magnetic
  field and the associated of solar brightness variability. In part
  the behavior of sun-like stars is used as a guide of such secular
  changes. Under the assumption that solar irradiance variations are due
  to solar surface magnetism on all relevant time scales it is possible to
  reconstruct the irradiance with some reliability from today to around
  1874, and with lower accuracy back to the Maunder minimum. One major
  problem is the decreasing amount and accuracy of the relevant data with
  age. In this review the various reconstructions of past solar irradiance
  are presented and the assumptions underlying them are scrutinized.

Title: Solar Photospheric Magnetic Flux Tubes: Observations
Authors: Solanki, S.
Bibcode: 2000eaa..bookE2013S
Altcode:
  The magnetic field on the solar surface (SOLAR MAGNETIC FIELD)
  is highly filamentary, with a considerable fraction being in the
  form of flux tubes (roughly speaking bundles of concentrated field
  lines). Small-scale flux tubes have diameters below approximately 400
  km. They appear bright and are the basic magnetic features underlying
  the magnetic network and active region plages (SOLAR CHROMOSPHER...

Title: Statistics of quiet Sun extreme ultraviolet intensities
Authors: Pauluhn, A.; Solanki, S. K.; Rüedi, I.; Landi, E.;
   Schühle, U.
Bibcode: 2000A&A...362..737P
Altcode:
  The frequency distribution of the extreme ultraviolet (EUV) emission
  line intensities in the quiet Sun has in the past often been modelled
  using two Gaussians. This gives adequate fits to observed distributions
  of average statistical significance. In this paper we test this
  and other distribution functions against observed distributions with
  exceptional statistical significance. The data were obtained in a number
  of spectral lines observed with two extreme ultraviolet spectrometers
  on board the Solar and Heliospheric Observatory (SOHO). In this way,
  the influence of spatial resolution and other instrument-specific
  parameters can be identified. The observations span a period of
  more than two years and provide a very large data set of radiance
  measurements of the quiet Sun at or near solar disk centre. We show
  that the frequency distribution of the radiance is best modelled by
  a lognormal distribution. The fact that the radiance distribution of
  the quiet Sun including the network and the intranetwork is better
  reproduced by a single lognormal distribution function than by two
  Gaussians suggests that the same heating processes are acting in both
  types of features. The parameters of the lognormal fit show a clear
  temperature dependence, with the transition region lines exhibiting the
  largest skewness of the distribution and the chromospheric intensity
  distributions being the most symmetric.

Title: On the relationship between shift and intensity of ultraviolet
    lines in coronal holes and the quiet Sun
Authors: Stucki, K.; Solanki, S. K.; Schühle, U.; Rüedi, I.
Bibcode: 2000A&A...362L..49S
Altcode:
  We study the relationship between wavelength shifts and intensities
  of chromospheric, transition-region and coronal ultraviolet emission
  lines in polar coronal holes and in the normal quiet Sun using SUMER
  data. Within coronal holes almost all the lines showing the network
  and formed above 30 000 K show a correlation between blueshifts
  and brightness. This extends and supports the conclusion reached
  by Hassler et al. (1999) that the fast solar wind emanates from the
  network. In the normal quiet Sun, however, we find that only lines
  formed above 2-3 * 10<SUP>5</SUP> K show such a trend, the cooler
  lines being more redshifted in the network. This suggests that either
  there is a fundamental difference in the initial acceleration of
  the solar wind in coronal holes and the normal quiet Sun, or that
  the wavelength-shift versus brightness relationship in the quiet Sun
  stems from other processes or structures (loops) than in coronal holes
  (open field lines).

Title: Size-dependent properties of simulated 2-D solar granulation
Authors: Gadun, A. S.; Hanslmeier, A.; Pikalov, K. N.; Ploner,
   S. R. O.; Puschmann, K. G.; Solanki, S. K.
Bibcode: 2000A&AS..146..267G
Altcode:
  Two time-dependent sets of two-dimensional hydrodynamic models of solar
  granulation have been analyzed to obtain dependence of simulated thermal
  convection on the horizontal size of the convection cells. The two
  sets of models treat thermal convection either as fully non-stationary,
  multiscale convection (granular convection is a surface phenomenon) or
  as quasi-steady-state convection cells (they treat granular convection
  as a collection of deep-formed cells). The following results were
  obtained: 1) quasi-steady convection cells can be divided into 3
  groups according to their properties and evolution, namely small-scale
  (up to L ~ 900 km), intermediate-scale (1000-1500 km) and large-scale
  (larger 1500 km) convection cells. For the first group thermal damping
  due to radiative exchange of energy, mostly in the horizontal direction,
  is very important. Large-scale cells build up a pressure excess, which
  can lead to their total fragmentation. Similar processes also acts on
  the fully non-stationary convection. 2) The largest horizontal size
  of convection cells for which steady-state solutions can be obtained
  is about 1500 km. This corresponds to granules, i.e. the bright
  parts of the convection cells, with a diameter of about 1000 km. 3)
  In addition to the zone of high convective instability associated
  with the partial ionization of hydrogen, we identify another layer
  harboring important dynamic processes in steady-state models. Just
  below the hydrogen-ionization layer pressure fluctuations and the
  acoustic flux are reduced. Steady-state models with reflecting lateral
  boundaries even exhibit an inversion of pressure fluctuations there. 4)
  From observational point of view the surface convection differs from
  steady-state deep treatment of thermal convection in the dependence
  of vertical granular velocities on their sizes for small-scale
  inhomogeneous. However, they cannot be distinguished by the dependence
  of temperature or emergent intensity of brightness structures. 5) Both
  kinds of models demonstrate the inversion of density in subphotospheric
  layers. It is more pronounced in small-scale cells and inside hot
  upflows. 6) The brightness of simulated granules linearly increases
  with their size for small granules and is approximately constant or
  even decreases slightly for larger granules. For intergranular lanes
  the simulations predict a decrease of their brightness with increasing
  size. It falls very rapidly for narrow lanes and remains unchanged
  for broader lanes. 7) A quantitative comparison of the brightness
  properties of simulated granulation with real observations shows
  that the strong size-dependence of the properties of the smallest
  simulated granules is not accessible to current observations due to
  their limited spatial resolution. The observed size dependences result
  rather from spatial smoothing and the granule-finding algorithm. We
  do not exclude, however, an influence of the limitations of the 2-D
  treatment of thermal convection on the present results.

Title: The solar spectral irradiance since 1700
Authors: Fligge, M.; Solanki, S. K.
Bibcode: 2000GeoRL..27.2157F
Altcode:
  The change in the irradiance spectrum of the Sun from 1700 to the
  last solar minimum is determined and compared to the change in the
  spectrum between activity minimum and maximum. For this purpose we have
  used detailed model flux spectra of solar magnetic features. Also,
  time-series of the solar spectral irradiance since 1700 in different
  wavelength bands are reconstructed. We expect that these reconstructions
  are more accurate than previously published ones, although they suffer
  (like all reconstructions of solar irradiance on such time-scales)
  from uncertainties in our knowledge of the evolution of the solar
  network with time.

Title: Spin and orbital angular momentum exchange in binary star
systems. II. Ascending the giant branch: a new path to FK Comae stars
Authors: Keppens, R.; Solanki, S. K.; Charbonnel, C.
Bibcode: 2000A&A...359..552K
Altcode:
  Using the model by Keppens (1997), we investigate the angular momentum
  (AM) evolution in asymmetric binary star systems from Zero-Age Main
  Sequence times until at least one component has ascended the giant
  branch. We concentrate on stars ranging in mass from 0.9 M<SUB>sun</SUB>
  - 1.7 M<SUB>sun</SUB>, in almost synchronous, short period systems
  (P_orb&lt;9 days). We address synchronization and circularization
  by tidal interaction, allowing for structural evolution and
  stellar winds. A Weber-Davis prescription is used to quantify the
  wind influence, thereby accounting for changes in its acceleration
  mechanism from the interplay of the evolving thermal-magneto-centrifugal
  effects. We identify a scenario for fast in-spiraling components with d
  ln P_orb/dt =~ -{cal O}(10<SUP>-8</SUP>) which is primarily driven by
  fast structural evolution as the heaviest component ascends the giant
  branch. This leads to the formation of contact systems, which ultimately
  coalesce and form FK Comae-like objects on relatively short timescales
  due to the continuing expansion of the primary. The obtained mass loss
  rates and orbital period variations d ln P_orb/dt are confronted with
  their observed ranges. The predicted mass loss rates agree with the
  solar value on the main sequence and with the Reimers relation in the
  giant phase. Observations of period evolution in close, active binaries
  suggest, however, that other influences than those considered here must
  play an important role. Finally, we point out how the mass asymmetry of
  the binary system can be a crucial ingredient in the angular momentum
  evolution: while the primary dictates the spin-orbital AM exchange
  in the system, the slowly evolving lighter component can develop an
  efficient magneto-centrifugally driven wind and thereby drain the AM
  from the system.

Title: Cyclic Evolution of Sunspots: Gleaning New Results from
    Old Data
Authors: Solanki, S. K.; Fligge, M.; Pulkkinen, P.; Hoyng, P.
Bibcode: 2000JApA...21..163S
Altcode:
  No abstract at ADS

Title: Properties of the solar granulation obtained from the inversion
    of low spatial resolution spectra
Authors: Frutiger, C.; Solanki, S. K.; Fligge, M.; Bruls, J. H. M. J.
Bibcode: 2000A&A...358.1109F
Altcode:
  The spectra of cool stars are rich in information on elemental
  abundances, convection and non-thermal heating. Extracting this
  information is by no means straightforward, however. Here we demonstrate
  that an inversion technique may not only provide the stratification of
  the classical parameters describing a model atmosphere, but can also
  determine the properties of convection at the stellar surface. The
  inversion technique is applied to spectra of photospheric lines, one
  recorded at the quiet solar disk center, the other integrated over the
  whole disk. We find that a model based on a single plane-parallel
  atmosphere gives unsatisfactory fits to the spectral lines and
  suffers from considerable uncertainties in the derived temperature
  stratification. Also, the elemental abundances returned by the inversion
  are not particularly reliable. These problems are greatly reduced if
  two atmospheric components, corresponding to granular up- and downflows
  are allowed for. The best results are obtained if the line profiles
  and bisectors of a neutral and ionized species are fit and the results
  are constrained using a simple mass conservation scheme. We find that
  inversions based on two- and three-component models of disk-integrated
  spectra give similar results to inversions of disk-center observations,
  although with somewhat lower accuracy. This similarity is promising
  for future applications of line profile inversions to the study of
  late-type stars and in particular their convection.

Title: Properties of Flux Tubes and the Relation with Solar Irradiance
    Variability
Authors: Fligge, M.; Solanki, S. K.
Bibcode: 2000JApA...21..275F
Altcode:
  No abstract at ADS

Title: Is solar mesogranulation a surface phenomenon?
Authors: Ploner, S. R. O.; Solanki, S. K.; Gadun, A. S.
Bibcode: 2000A&A...356.1050P
Altcode:
  Convection is the main form of energy transport in the subsurface
  layers of the sun and other cool stars. The imprint of cellular
  convection can be directly observed on the solar surface, with
  a hierarchy of four size scales. The smallest observed convection
  cells, called granules, have typical horizontal sizes of 1,000-2,000
  km and have been successfully reproduced by numerical simulations
  \citep{spruit:97,stein:nordlund:98}. Cells at three larger scales are
  also detected \citep{leighton:etal:62,november:etal:81,beck:etal:98},
  but these have so far not been amenable to numerical modelling,
  so that their formation scenarios remain untested. Here we present
  a numerical simulation which resolves both the granular and the next
  larger, mesogranular, scale. The mesogranules have horizontal extents
  of 5,000-10,000 km. Our 2D simulation reproduces key properties of both
  granules and mesogranules. In addition, our simulation demonstrates
  that the observed mesogranulation is driven close to the solar surface
  and therefore rules out the text-book explanation of mesogranulation
  as cellular convection driven by superadiabaticity in the deeper
  layer where neutral helium ionizes. By proxy, this result also casts
  doubt on the traditional explanation of supergranulation, even larger
  convection cells with diameters of 20,000-30,000 km, as being driven
  by the yet deeper second ionization of helium.

Title: Distribution of magnetic flux on the solar surface and
    low-degree p-modes
Authors: Moreno-Insertis, F.; Solanki, S. K.
Bibcode: 2000MNRAS.313..411M
Altcode:
  The frequencies of solar p-modes are known to change over the solar
  cycle. There is also recent evidence that the relation between frequency
  shift of low-degree modes and magnetic flux or other activity indicators
  differs between the rising and falling phases of the solar cycle,
  leading to a hysteresis in such diagrams. We consider the influence
  of the changing large-scale surface distribution of the magnetic
  flux on low-degree (l&lt;=3) p-mode frequencies. To that end, we use
  time-dependent models of the magnetic flux distribution and study the
  ensuing frequency shifts of modes with different order and degree as a
  function of time. The resulting curves are periodic functions (in simple
  cases just sine curves) shifted in time by different amounts for the
  different modes. We show how this may easily lead to hysteresis cycles
  comparable to those observed. Our models suggest that high-latitude
  fields are necessary to produce a significant difference in hysteresis
  between odd- and even-degree modes. Only magnetic field distributions
  within a small parameter range are consistent with the observations
  by Jiménez-Reyes et al. Observations of p-mode frequency shifts
  are therefore capable of providing an additional diagnostic of the
  magnetic field near the solar poles. The magnetic distribution that
  is consistent with the p-mode observations also appears reasonable
  compared with direct measurements of the magnetic field.

Title: Reconstruction of Past Solar Irradiance
Authors: Solanki, S. K.; Fligge, M.
Bibcode: 2000svc..book..127S
Altcode:
  No abstract at ADS

Title: Long-Term Changes in Solar Irradiance
Authors: Solanki, S.; Fligge, M.
Bibcode: 2000ESASP.463...51S
Altcode: 2000sctc.proc...51S
  No abstract at ADS

Title: Modelling irradiance variations from the surface distribution
    of the solar magnetic field
Authors: Fligge, M.; Solanki, S. K.; Unruh, Y. C.
Bibcode: 2000A&A...353..380F
Altcode:
  An important question in solar physics is to what extent solar surface
  magnetism affects the solar irradiance. Previous attempts to answer this
  question have employed proxies of the magnetic field to reconstruct the
  irradiance and compare it with observations. Here we present the first
  model calculations of solar irradiance variations based on variations
  of the surface distribution of the solar magnetic field. The irradiance
  reconstruction makes use of sunspot and facular contrasts calculated
  as a function of wavelength and limb angle on the Sun. The position
  and size of magnetic features on the solar disk are extracted from
  full-disk magnetograms obtained by the Michelson Doppler Interferometer
  (MDI) onboard the SOHO spacecraft. The reconstructed spectral irradiance
  variations are compared with total and spectral contrast measurements
  obtained by the VIRGO instrument onboard SOHO. Our reconstructions are
  able to reproduce variations on the time-scale of the solar rotation
  with much greater accuracy than previous models based on disk-integrated
  magnetic proxies.

Title: The influence of an inclined rotation axis on solar irradiance
    variations
Authors: Knaack, R.; Fligge, M.; Solanki, S. K.; Unruh, Y. C.
Bibcode: 2000ssls.work...45K
Altcode:
  The irradiance variations of the Sun over the solar cycle are relatively
  small compared with sun-like stars (Radick et al., 1998). It has been
  proposed that a random distribution of stellar rotation axes relative to
  the ecliptic plane could explain their larger variability (Schatten,
  1993). We examine the influence on total irradiance variations of
  the inclination of the solar rotation axis relative to an observer. A
  three-component model is used to calculate the relative flux variations
  of a given distribution of active regions on the surface of the Sun as
  a function of the inclination. One component is the quiet Sun, another
  is a sunspot component and the third describes the faculae. We find
  that the inclination effect increases the total irradiance variations
  of the Sun maximally by 40%. The most probable value is approximately
  5%. This is much less than former studies (Schatten, 1993, Radick et
  al., 1998) suggested.

Title: Commission 12: Solar Radiation and Structure (Radiation et
    Structure Solaires)
Authors: Foukal, Peter; Solanki, Sami; Mariska, J.; Baliunas, S.;
   Dravins, D.; Duvall, T.; Fang, C.; Gaizauskas, V.; Heinzel, P.;
   Kononovich, E.; Koutchmy, S.; Melrose, D.; Stix, M.; Suematsu, Y.;
   Deubner, F.
Bibcode: 2000IAUTA..24...73F
Altcode:
  No abstract at ADS

Title: Solar Surface Magnetism and the Increase of Solar Irradiance
    between Activity Minimum and Maximum
Authors: Fligge, M.; Solanki, Sami K.; Meunier, Nadege; Unruh,
   Yvonne C.
Bibcode: 2000ESASP.463..117F
Altcode: 2000sctc.proc..117F
  No abstract at ADS

Title: On the Contrast of Faculae and Small Magnetic Features
Authors: Ortiz, A.; Solanki, S. K.; Fligge, M.; Domingo, V.;
   Sanahuja, B.
Bibcode: 2000ESASP.463..399O
Altcode: 2000sctc.proc..399O
  Sunspots, faculae and the magnetic network contribute to solar
  irradiance variations. The contribution due to faculae and the network
  is important for understanding solar irradiance variations, but suffers
  from considerable uncertainty. We focus our study on the faculae and
  the network which produce an increase in the irradiance. Data from
  the Michelson Doppler Interferometer (MDI) are employed. Starting from
  the surface distribution of the solar magnetic field we build a mask
  to detect bright features and study their contrast dependence on limb
  angle and magnetic field. By sorting the magnetic field strength into
  different bins we can distinguish between different associated bright
  features. We find that the contrast of active region faculae and the
  network exhibits different centre to limb variations, implying that
  they need to be treated separately when reconstructing variations of
  the total solar irradiance.

Title: Modelling Solar Irradiance Variations: Comparison with
    Observations, Including Line-Ratio Variations
Authors: Unruh, Y. C.; Solanki, S. K.; Fligge, M.
Bibcode: 2000svc..book..145U
Altcode:
  No abstract at ADS

Title: Modelling Short-Term Spectral Irradiance Variations
Authors: Fligge, M.; Solanki, S. K.; Unruh, Y. C.
Bibcode: 2000svc..book..139F
Altcode:
  No abstract at ADS

Title: EUV brightness variations in the quiet Sun
Authors: Brković, A.; Rüedi, I.; Solanki, S. K.; Fludra, A.;
   Harrison, R. A.; Huber, M. C. E.; Stenflo, J. O.; Stucki, K.
Bibcode: 2000A&A...353.1083B
Altcode:
  The Coronal Diagnostic Spectrometer (CDS) onboard the SOHO satellite has
  been used to obtain movies of quiet Sun regions at disc centre. These
  movies were used to study brightness variations of solar features at
  three different temperatures sampled simultaneously in the chromospheric
  He I 584.3 Ä (2 * 10<SUP>4</SUP> K), the transition region O V 629.7
  Ä (2.5 * 10<SUP>5</SUP> K) and coronal Mg IX 368.1 Ä (10<SUP>6</SUP>
  K) lines. In all parts of the quiet Sun, from darkest intranetwork to
  brightest network, we find significant variability in the He I and O
  V line, while the variability in the Mg IX line is more marginal. The
  relative variability, defined by rms of intensity normalised to the
  local intensity, is independent of brightness and strongest in the
  transition region line. Thus the relative variability is the same
  in the network and the intranetwork. More than half of the points
  on the solar surface show a relative variability, determined over a
  period of 4 hours, greater than 15.5% for the O V line, but only 5%
  of the points exhibit a variability above 25%. Most of the variability
  appears to take place on time-scales between 5 and 80 minutes for the
  He I and O V lines. Clear signs of ``high variability'' events are
  found. For these events the variability as a function of time seen
  in the different lines shows a good correlation. The correlation is
  higher for more variable events. These events coincide with the (time
  averaged) brightest points on the solar surface, i.e. they occur in
  the network. The spatial positions of the most variable points are
  identical in all the lines.

Title: Division II: The Sun and Heliosphere: (Le Soleil et
    Heliosphere)
Authors: Foukal, Peter; Ai, Guoxiang; Benz, Arnold; Engvold, Oddbjorn;
   Solanki, Sami; Vandas, Marek; Verheest, Frank
Bibcode: 2000IAUTA..24...65F
Altcode:
  No abstract at ADS

Title: The evolution of solar granules deduced from 2-D simulations
Authors: Ploner, S. R. O.; Solanki, S. K.; Gadun, A. S.
Bibcode: 1999A&A...352..679P
Altcode:
  The evolution of solar granules is investigated on the basis of two
  dimensional numerical solutions of the hydrodynamic equations describing
  a compressible, radiatively coupled and gravitationally stratified
  medium representative of the solar surface layers. The simulation covers
  17 Mm on the solar surface and was run for over 5 h of solar time,
  hence allowing the evolution of over 400 granules to be followed. A
  statistical investigation of the temporal evolution of granules
  therefore becomes feasible. Two types of granules can be distinguished
  by their means of death: fragmenting and dissolving granules. Properties
  and average evolutionary histories of these two types of granules
  are considered. It is found that fragmenting granules are in general
  large at birth and expand further with time. It is confirmed that
  fragmentation into two (or more) parts is produced by buoyancy braking,
  which in turn is initiated by the stronger horizontal flows in larger
  granules. This last property, finally, is due to mass conservation. The
  expansion, however, is due to a pressure excess relative to neighbouring
  granules. The pressure excess is particularly marked if the neighbours
  are dissolving granules. In contrast, dissolving granules are born
  small and shrink before finally disappearing. The shrinkage is caused
  by their neighbours which generally posses excess gas pressure and
  larger horizontal flows. In summary, according our findings the fate
  of a granule is decided by its properties at birth and the company
  it keeps. Evidence is presented suggesting that the evolution of both
  types of granules is driven by events near the solar surface.

Title: Is the FIP effect present inside solar photospheric magnetic
    flux tubes?
Authors: Sheminova, V. A.; Solanki, S. K.
Bibcode: 1999A&A...351..701S
Altcode:
  The first determination of the elemental composition in the photospheric
  layers of solar magnetic flux tubes is described. Stokes I and V
  profiles of 13 elements observed in solar active region plage and in
  the network are analysed. The abundances are obtained for elements
  with high (C, O) and low (Al, Ca, Cr, Na, Ni, Sc, Si, Ti, Y, Zn) first
  ionization potential (FIP) in order to investigate to what extent the
  abundance anomalies observed in the upper solar atmosphere (FIP-effect)
  are already present in the photospheric layers of flux tubes, which
  are the source of much of the gas in the upper atmosphere. Various
  sources of error are considered and the uncertainties introduced by
  them are estimated. There are hints of a weak FIP-effect in the flux
  tubes, corresponding to an overabundance of a factor of 1.1-1.2 of
  the low-FIP elements relative to high-FIP elements, as compared to
  the quiet photosphere. However, our data set a firm upper limit of
  1.3-1.6 on this factor, which is well below the enhancement seen in
  many parts of the upper solar atmosphere.

Title: Relationship between Line Shift and Intensity Inside Coronal
    Holes
Authors: Stucki, K.; Solanki, S. K.; Rüedi, I.; Schüehle, U.
Bibcode: 1999ESASP.446..633S
Altcode: 1999soho....8..633S
  We analyse SUMER spectra of a group of lines belonging to chromospheric,
  transition region and coronal ions obtained on both sides of the
  boundary of polar coronal holes as well as at other locations along the
  limb. We study the relationship between line shifts and intensities in
  coronal holes and compare to values obtained in the quiet Sun. We find
  that within coronal holes, a trend can be detected in some transition
  region lines, like O V and N V, in the sense that the lines are more
  strongly blueshifted in brighter regions. This is in agreement with
  the conclusion reached by Hassler et al. (1999, Science 283, 810-813)
  that the fast solar wind emanates from the network. Furthermore,
  a correlation of line shifts of ions formed at higher temperatures
  (Ne VIII, Fe XII) with intensities of lines showing network structures
  (Si I, N III) is presented.

Title: Hanle effect observations with the CA BT I 4227 Å line
Authors: Bianda, M.; Stenflo, J. O.; Solanki, S. K.
Bibcode: 1999A&A...350.1060B
Altcode:
  The Hanle effect in the Ca i 4227 Ä line has been explored through
  the analysis of a large number of Stokes profile recordings obtained
  on the quiet Sun with the beam-splitter polarimeter system at IRSOL
  (Istituto Ricerche Solari Locarno). In contrast to previous Hanle
  observations with this line, which were limited to the Stokes I and
  Q parameters, we are now in a position to study the combined effects
  of Hanle depolarization (via Stokes Q) and rotation of the plane
  of linear polarization (via Stokes U) with the same methods that
  we recently applied to the Sr ii 4078 Ä line. The Hanle histograms
  for the distributions of the depolarization and rotation parameters
  are very similar for the two lines and show that there must be mixed
  contributions to the Hanle signals from spatially unresolved magnetic
  fields with random orientations (which do not contribute to Stokes U)
  and partially resolved magnetic fields with a net orientation of the
  field vectors. Field strengths in the range 5-10 G are preferred. We
  also determine the ``Hanle efficiency profile'', which shows how the
  Hanle effect is confined to the Doppler core but vanishes in the line
  wings. It is wider than the corresponding profile for the Sr line,
  as expected from the difference in atomic weight and wavelength
  between the two lines. The Q/I profiles of the Ca i 4227 Ä line
  have minima around the Doppler core which turn negative (polarization
  perpendicular to the limb) for limb distances mu =cos theta &gt;~ 0.2,
  a likely signature of partial redistribution effects.

Title: Loop Models from SOHO Observations
Authors: Landini, M.; Brkovic, A.; Landi, E.; Rüedi, I.; Solanki, S.
Bibcode: 1999ESASP.446..423L
Altcode: 1999soho....8..423L
  SOHO CDS, GIS and NIS, observations are used to evaluate the
  electron temperature, density and pressure of active region loops. The
  measurements are used to constrain empirical models of loops, which are
  compared with an improved version of theoretical models from Landini
  and Monsignori Fossi 1975. Energy balance is investigated to evaluate
  temperature, pressure and heating release along the loop.

Title: Magnetic Field Structuring
Authors: Solanki, S. K.
Bibcode: 1999ESASP.446...25S
Altcode: 1999soho....8...25S
  No abstract at ADS

Title: Two-dimensional simulation of solar granulation: description
    of technique and comparison with observations
Authors: Gadun, A. S.; Solanki, S. K.; Johannesson, A.
Bibcode: 1999A&A...350.1018G
Altcode:
  The physical properties of the solar granulation are analyzed on the
  basis of 2-D fully compressible, radiation-hydrodynamic simulations and
  the synthetic spectra they produce. The basic physical and numerical
  treatment of the problem as well as tests of this treatment are
  described. The simulations are compared with spatially averaged spectral
  observations made near disk centre and high resolution spectra recorded
  near the solar limb. The present simulations reproduce a significant
  number of observed features, both at the centre of the solar disc and
  near the solar limb. Reproduced observables include the magnitude of
  continuum and line-core intensity fluctuations, line bisectors and
  correlations between different line parameters. Spatially averaged
  line shifts near disc centre, however, are not so well reproduced,
  as are individual correlations between line parameters near the solar
  limb. Possible causes of these discrepancies are discussed. The present
  models predict the existence of two photospheric layers at which the
  temperature fluctuations change sign. We point out a diagnostic of
  the hitherto undetected upper sign reversal based on high spatial
  resolution spectral observations of a sample of lines formed over a
  wide range of heights in the photosphere.

Title: Characteristics Of Blinkers Observed With CDS
Authors: Brkovic, A.; Ruedi, I.; Solanki, S. K.
Bibcode: 1999ESASP.446..191B
Altcode: 1999soho....8..191B
  Blinkers are transient brightenings seen in the extreme
  ultraviolet. They probably can not heat the corona, but are candidates
  for microflare activity. Here we determine their properties on the
  basis of a larger sample than previously studied. We used the Normal
  Incidence Spectrometer of the Coronal Diagnostic Spectrometer (CDS)
  onboard the SOHO satellite in its movie mode, i.e. 90"x240" slit,
  to find evidence for blinkers in the quiet Sun. The He I 584.3 A
  (20'000 K), the O V 629.7 (250'000 K) and the Mg IX 368.1 (1'000'000
  K) lines are recorded simultaneously at a cadence of 31 seconds
  for a duration of 4 hours each on December 3 1996. Harrison (1997)
  defined the blinker as a phenomenon showing an enhancement of a factor
  2-3 in the flux of transition region lines at network junctions. The
  criterion we used was similar to his. We applied the threshold to the
  O V line, and identified 74 distinct blinkers. The average properties
  of these blinkers and the scatter around these mean values were then
  determined. These properties include the duration of the blinker, the
  energy content of the event, ratio of maximum to minimum brightness and
  the sizes of these brightenings. We find that the overall brightening
  is often composed of a number of shorter events. Finally, we checked
  if these blinkers were also present in the images obtained in the two
  other lines, of He I and Mg IX. In the He I line we found 65 events and
  in the Mg IX line 16 events. On average the brightening was smaller
  in these lines than in O V. The work is still in progress. We plan
  to investigate how the locations of these events are related to the
  distribution of the magnetic field and if they are also related to other
  phenomena. References: Harrison, R.A.: 1997, Solar Physics 162, 467.

Title: Oscillations of Sunspot Magnetic Fields: MDI Observations of
    a Symmetrical Sunspot
Authors: Rüedi, I.; Solanki, S. K.
Bibcode: 1999ASPC..184..131R
Altcode:
  We report on sunspot magnetic field oscillations observed using the
  MDI instrument on the SOHO spacecraft. Clear oscillations are seen in
  both the 3- and 5-min bands, but appear to be intermittent.

Title: A reconstruction of total solar irradiance since 1700
Authors: Solanki, S. K.; Fligge, M.
Bibcode: 1999GeoRL..26.2465S
Altcode:
  The irradiance of the Sun is reconstructed from 1700 to the present,
  whereby the contributions of active regions and the quiet Sun are
  modelled separately. A method is proposed which allows the contribution
  of active-region faculae and sunspots to irradiance changes to be
  isolated even when only a single proxy of solar activity, such as
  sunspot relative number, R<SUB>z</SUB>, is available. The resulting
  reconstruction explicitly takes the non-linear relationship between
  R<SUB>z</SUB> and irradiance variations into account. Nevertheless,
  due to the decreasing accuracy of the solar proxy data the accuracy of
  the reconstruction decreases at earlier epochs. The main uncertainty,
  however, lies in the reconstruction of the quiet-sun irradiance
  variations.

Title: Infrared lines as probes of solar magnetic
    features. XV. Evershed flow in cool, weak penumbral fields
Authors: Rüedi, I.; Solanki, S. K.; Keller, C. U.
Bibcode: 1999A&A...348L..37R
Altcode:
  Observations of Ti I lines at 2.2 mu m show that the Evershed flow takes
  place in cool, almost horizontal channels with a low magnetic field
  strength (~ 500-900 G) that does not appear to change significantly
  across the penumbra. This property might allow an outward directed
  siphon flow to exist along such cool flux tubes.

Title: Expansion of solar magnetic flux tubes large and small
Authors: Solanki, S. K.; Finsterle, W.; Rüedi, I.; Livingston, W.
Bibcode: 1999A&A...347L..27S
Altcode:
  In the solar photosphere the magnetic field of magnetic elements and
  sunspots is known to expand with height. In the case of sunspots this
  expansion is known to be very rapid, with the field forming an almost
  horizontal canopy. In this contribution we present new results on
  the superpenumbral canopy of sunspots based on fits to Stokes I and
  V profiles of infrared spectral lines. The new models take pressure
  balance across the boundary of the canopy field into account, which
  leads to significantly lower canopy base heights than previously
  determined from similar data. Due to the lower canopy base height,
  the density above the canopy base is larger, so that estimates of
  the mass transported by the Evershed effect in the canopy need to be
  revised upwards: approximately 15-50% of the mass flowing through the
  penumbra travels beyond the sunspot boundary above the canopy base. A
  comparison with small flux tubes leads to the surprising result that
  although the two types of features have magnetic fluxes that differ by
  5-6 orders of magnitude, their relative rate of expansion with height
  is very similar, suggesting that at least in this respect sunspots
  can be described by the thin-tube approximation. The remaining small
  differences between the relative expansion of the two types of flux
  tubes is qualitatively compatible with the presence of magnetic flux
  that returns into the solar interior at the spot boundary, as has been
  proposed by Westendorp Plaza et al. (1997).

Title: Determination of solar cycle length variations using the
    continuous wavelet transform
Authors: Fligge, M.; Solanki, S. K.; Beer, J.
Bibcode: 1999A&A...346..313F
Altcode:
  The length of the sunspot cycle determined by Friis-Christensen
  &amp; Lassen (1991) correlates well with indicators of terrestrial
  climate, but has been criticized as being subjective. In the
  present paper we present a more objective and general cycle-length
  determination. Objectivity is achieved by using the continuous
  wavelet transform based on Morlet wavelets and carrying out a careful
  error analysis. Greater generality comes from the application of this
  technique to different records of solar activity, e.g. sunspot number,
  sunspot area, plage area or (10) Be records. The use of different
  indicators allows us to track cycle length variations back to the 15th
  century. All activity indicators give cycle length records which agree
  with each other within the error bars, whereby the signal due to the
  solar cycle is weaker within (10) Be than in the other indicators. In
  addition, all records exhibit cycle length variations which are, within
  the error bars, in accordance with the record originally proposed by
  Friis-Christensen &amp; Lassen (1991). In the 16th century, however,
  the (10) Be record suggests a much longer cycle than the auroral
  record used by Friis-Christensen &amp; Lassen. Also, the presence
  of a distinct 11-year cycle in the (10) Be record during the Maunder
  Minimum is confirmed. By combining the results from all the indicators
  a composite of the solar cycle length is constructed, which we expect
  to be more reliable than the length derived from individual records.

Title: The spectral dependence of facular contrast and solar
    irradiance variations
Authors: Unruh, Y. C.; Solanki, S. K.; Fligge, M.
Bibcode: 1999A&A...345..635U
Altcode:
  We present model calculations of facular and sunspot contrasts as a
  function of wavelength and limb angle on the Sun. These are the first
  such calculations; they assume LTE and are based on opacity distribution
  functions (ODFs). The calculated facular contrasts as a function of
  limb angle fit into the general picture of contrast measurements,
  and the behaviour of the contrast with wavelength at a given limb
  angle is in excellent agreement with the measurements. The calculated
  intensity spectra are used to construct the solar flux spectrum for
  different levels of solar activity. It is assumed that the irradiance
  or flux variations are due to changes in the sunspot and facular
  filling factors. The model atmosphere used to calculate the facular
  intensities has been tuned so that the calculated irradiance variations
  match the observed total and spectral irradiance variations during
  the last solar cycles. The model calculations have also been used
  to estimate the relative importance of continuum and spectral-line
  variations in producing irradiance variations. The results suggest
  that the continuum variations only contribute negligibly to the total
  irradiance variations on solar-cycle time scales.

Title: Influence of torsional waves in solar magnetic flux tubes on
    spectral lines
Authors: Ploner, S. R. O.; Solanki, S. K.
Bibcode: 1999A&A...345..986P
Altcode:
  The influence of torsional waves propagating along a thin, vertical,
  photospheric flux tube on Zeeman-split polarized line profiles (Stokes
  profiles) is investigated using a simple MHD model. In the presence of
  such a wave spatially resolved Stokes profiles are found to oscillate
  strongly in wavelength, amplitude and blue-red asymmetry. Qualitatively,
  torsional waves induce similar changes into the line profiles as kink
  waves (Ploner &amp; Solanki 1997). The magnitude of the line parameter
  variation depends strongly on the observed location with respect to
  the flux-tube axis. The spatially averaged Stokes V and Q profiles
  are found to follow the torsional wave with double the wave frequency,
  some parameters of Stokes U fluctuate directly at the wave frequency,
  however. The other main feature of the spatially averaged profiles is
  their comparatively small reaction to the wave. The reason for the
  latter is that most polarized light is produced near the centre of
  the flux tube where, however, the torsional wave produces only weak
  perturbations. Temporally and spatially averaged Stokes profiles are
  found to be only negligibly shifted, but strongly broadened. The sign
  of the small remaining asymmetry is opposite in Stokes Q to that in
  V and U. The amplitude of the wave and the location of the flux tube
  on the solar disk have a strong influence on the magnitude of the
  perturbation of the Stokes profiles.

Title: Formation of small-scale magnetic elements: surface mechanism
Authors: Gadun, A. S.; Sheminova, V. A.; Solanki, S. K.
Bibcode: 1999KFNT...15..387G
Altcode: 2012arXiv1210.3499G; 1999KFNT...15e.387G
  The first results of a two-dimensional MHD simulation of solar
  magnetogranulation are given. The medium was treated as compressible,
  gravitationally stratified, radiatively coupled, partially ionized,
  and turbulent. The evolution of magnetogranulation was simulated in
  course of 2 hours of hydrodynamic (solar) time. A surface (magnetic
  plume-like) mechanism which forms thin magnetic elements was found to
  exist. This sort of field formation occurs due to fragmentation of
  large-scale granules. Active role of such mechanism shows that the
  magnetogranulation not only concentrates and intensifies the global
  magnetic flux at the boundaries of convective cells but also forms
  nearly vertical compact magnetic tubes by involving the weak horizontal
  field of the photosphere, which in general may be of local nature.

Title: Limits on gravity-induced depolarization of light from the
    white dwarf Grw +70°8247
Authors: Solanki, Sami K.; Haugan, Mark P.; Mann, R. B.
Bibcode: 1999PhRvD..59d7101S
Altcode:
  We use measurements of the polarization of light from a magnetic white
  dwarf to impose sharp constraints on the gravity-induced birefringence
  of space predicted by a broad class of nonmetric gravitation
  theories. Since gravity-induced birefringence violates the Einstein
  equivalence principle, our measurements test this foundation of general
  relativity and other metric gravitation theories in a new setting.

Title: Can Chromospheric Activity mimic a Polar Spot?
Authors: Bruls, J. H. M. J.; Schüssler, M.; Solanki, S. K.
Bibcode: 1999ASPC..158..182B
Altcode: 1999ssa..conf..182B
  No abstract at ADS

Title: Solar Line Bisectors in the Infrared
Authors: Puschmann, K.; Hanslmeier, A.; Solanki, S. K.
Bibcode: 1999ASSL..239..227P
Altcode: 1999msa..proc..227P
  In the present work we made some analysis with respect to shifts
  and asymmetries of infrared solar spectral lines to get information
  about vertical velocity fields in the deep layers of the Solar
  Photosphere. For the analysis of shifts and asymmetries of bisectors
  were used. We averaged bisectors belonging to a group of similar line
  parameter. Therefore it was possible, to analyse correlations between
  asymmetries and line shifts and corresponding vertical velocities with
  line parameters and to discuss the results with other literature.

Title: Inversion of Stokes profiles
Authors: Frutiger, C.; Solanki, S. K.; Fligge, M.; Bruls, J. H. M. J.
Bibcode: 1999ASSL..243..281F
Altcode: 1999sopo.conf..281F
  No abstract at ADS

Title: Observations of the Hanle effect in the Ca I 4227 and Sr II
    4078 Å lines
Authors: Bianda, M.; Stenflo, J. O.; Solanki, S. K.
Bibcode: 1999ASSL..243...31B
Altcode: 1999sopo.conf...31B
  No abstract at ADS

Title: Formation of small-scale magnetic elements: surface mechanism.
Authors: Gadun, A. S.; Sheminova, V. A.; Solanki, S. K.
Bibcode: 1999KPCB...15..291G
Altcode:
  The authors present results of a two-dimensional MHD simulation of the
  solar magnetogranulation. The medium was assumed to be compressible,
  gravitationally stratified, radiatively coupled, partially ionized,
  and turbulent. The simulated magnetogranulation evolved over the
  course of two hours of hydrodynamic (solar) time. A surface (magnetic
  plume-like) mechanism which forms thin magnetic elements was found to
  operate during the process of granule fragmentation. The activity of
  such a mechanism suggests that the magnetogranulation can concentrate
  and intensify the global magnetic flux at the boundaries of convective
  cells and can also form nearly vertical compact magnetic flux tubes
  by involving the weak horizontal photospheric field, which may be,
  in general, of local (turbulent) nature.

Title: Coronal Hole Properties Observed with SUMER
Authors: Stucki, K.; Solanki, S. K.; Rüedi, I.; Stenflo, J. O.;
   Brković , A.; Schühle, U.; Wilhelm, K.; Huber, M. C. E.
Bibcode: 1999SSRv...87..315S
Altcode:
  We analyze SUMER spectra of 14 lines belonging to 12 ions, obtained
  on both sides of the boundary of polar coronal holes as well as at
  other locations along the limb. We compare line intensities, shifts
  and widths in coronal holes with values obtained in the quiet Sun. We
  find that with increasing formation temperature, spectral lines show
  an increasingly stronger blueshift in coronal holes relative to the
  quiet Sun at an equal heliospheric angle. The width of the lines is
  generally larger (by a few km/s) inside the coronal hole. Intensity
  measurements show the presence of the coronal hole in Ne VIII lines
  as well as in Fe XII, with evidence for a slightly enhanced emission
  in polar coronal holes for lines formed below 10<SUP>5</SUP> K.

Title: Coronal Holes Versus Normal Quiet Sun Observed with SUMER
Authors: Stucki, K.; Solanki, S. K.; Rüedi, I.; Stenflo, J. O.;
   Brković, A.; Schühle, U.; Wilhelm, K.; Huber, M. C. E.
Bibcode: 1999Ap&SS.264...53S
Altcode: 1998Ap&SS.264...53S
  We present a preliminary analysis of spectral lines obtained with the
  SUMER instrument (Solar Ultraviolet Measurements of Emitted Radiation)
  onboard the Solar and Heliospheric Observatory (SOHO), as observed
  during three observing campaigns. From the 70 observed spectral lines,
  we selected 12, representing 9 ions or atoms, in order to analyse line
  intensities, shifts and widths in polar coronal holes as well as in the
  normal quiet Sun. We find that coronal lines show a distinct blueshift
  in coronal holes relative to the quiet Sun at equal heliospheric
  angle, while there is no evidence for such a shift for lines formed at
  temperatures below 10^5 K. The widths of lines formed at temperatures
  above 3 - 10^4 K are slightly increased inside the coronal hole,
  but unaffected for lower temperatures. Intensity measurements clearly
  show the center-to-limb variation, as well as an intensity diminution
  inside the coronal hole for lines formed above approximately 10^5 K.

Title: Spots and Plages: the Solar Perspective
Authors: Solanki, S. K.
Bibcode: 1999ASPC..158..109S
Altcode: 1999ssa..conf..109S
  No abstract at ADS

Title: Loop Models from SOHO Observations
Authors: Landini, M.; Brković , A.; Landi, E.; Rüedi, I.; Solanki, S.
Bibcode: 1999SSRv...87..245L
Altcode:
  The Coronal Diagnostic Spectrometer (CDS) on SOHO is a grazing/normal
  incidence spectrograph, aimed to produce stigmatic spectra of selected
  regions of the solar surface in six spectral windows of the extreme
  ultraviolet from 150 Å to 785 Å (Harrison et al. 1995). In the
  present work, CDS, EIT, MDI and Yohkoh observations of active region
  lops have been analyzed. These observations are part of JOP 54. CDS
  monochromatic images from lines at different temperatures have been
  co-aligned with EIT and MDI images, and loop structures have been
  clearly identified using Fe XVI emission lines. Density sensitive
  lines and lines from adjacent stages of ionization of Fe ions have
  been used to measure electron density and temperature along the loop
  length; these measurements have been used to determine the electron
  pressure along the loop and test the constant pressure assumption
  commonly used in loop modeling. The observations have been compared
  with a static, isobaric loop model (Landini and Monsignori Fossi 1975)
  assuming a temperature-constant heating function in the energy balance
  equation. Good agreement is found for the temperature distribution
  along the loop at the coronal level. The model pressure is somewhat
  higher than obtained from density sensitive line ratios.

Title: Granulation Near the Solar Limb: Observations and 2-D Modeling
Authors: Gadun, A. S.; Solanki, S. K.; Johannesson, A.
Bibcode: 1999ASSL..239..201G
Altcode: 1999msa..proc..201G
  Based on high spatial resolution spectra and using 2-D fully
  compressible, HD simulations of granules we analyze the correlations
  between spectral line parameters: their CLV, height-dependence and
  sensitivity to spatial resolution. We also point out some discrepancies
  between the model results and observations.

Title: Signatures of Coronal Hole Spectra Between 660 Å and 1460
    Å Measured with SUMER on SOHO
Authors: Schühle, U.; Curdt, W.; Wilhelm, K.; Solanki, S. K.;
   Stucki, K.
Bibcode: 1999SSRv...87..299S
Altcode:
  Spectra of the northern polar coronal hole measured with the SUMER
  spectrometer on SOHO on 25 October 1996 are analyzed. We present spectra
  taken at locations on the solar disk where part of the spectrometer
  slit intersects a polar coronal hole region and an area of brighter
  emission from outside of the coronal hole area. By comparing the line
  intensities between the parts of the spectrum taken inside the "dark"
  area of the coronal holes and the brighter regions, we work out the
  signatures of the specific coronal hole in the chromosphere, transition
  region and lower corona. We find that emissions of neutral atom lines,
  of which there are many in the spectrum of SUMER, show no difference
  between the coronal hole and the bright boundary areas, whereas all
  ionized species show strong intensity enhancements, including the
  continuum emissions of carbon and hydrogen. These enhancements are
  larger than in normal quiet Sun areas.

Title: On the expansion of large and small flux tubes with height
Authors: Solanki, S. K.; Rüedi, I.; Finsterle, W.; Livingston, W.
Bibcode: 1999ASSL..243..397S
Altcode: 1999sopo.conf..397S
  No abstract at ADS

Title: Sunspot magnetic oscillations: Comparison between observations
    and models
Authors: Rüedi, I.; Solanki, S. K.; Bogdan, T.; Cally, P.
Bibcode: 1999ASSL..243..337R
Altcode: 1999sopo.conf..337R
  No abstract at ADS

Title: Brightness Variations in the Solar Atmosphere as Seen by SOHO
Authors: Brkovic, A.; Rüedi, I.; Solanki, S. K.; Huber, M. C. E.;
   Stenflo, J. O.; Stucki, K.; Harrison, R.; Fludra, A.
Bibcode: 1999ASSL..239..231B
Altcode: 1999msa..proc..231B
  We present preliminary results of a statistical analysis of the
  brightness variations of solar features at different levels in
  the solar atmosphere. We observed quiet Sun regions at disc centre
  using the Coronal Diagnostic Spectrometer (CDS) onboard the Solar and
  Heliospheric Observatory (SOHO). We find significant variability at all
  time scales in all parts of the quiet Sun, from darkest intranetwork
  to brightest network. Such variations are observed simultaneously in
  the chromospheric He I 584.33 Angstroms (2 \cdot 10^4 K) line, the
  transition region O V 629.74 Angstroms (2.5 \cdot 10^5 K) and coronal
  Mg IX 368.06 Angstroms (10^6 K) line. The relative variability is
  independent of brightness and most of the variability appears to take
  place on time scales longer than 5 minutes for all 3 spectral lines. No
  significant differences are observed between the different data sets.

Title: Infrared lines as probes of solar magnetic features. XIV. TI
    i and the cool components of sunspots
Authors: Rueedi, I.; Solanki, S. K.; Keller, C. U.; Frutiger, C.
Bibcode: 1998A&A...338.1089R
Altcode:
  The first systematic observations of sunspot umbrae using the lines
  of the Ti Ii multiplet at 2.2 mu m are presented. Their diagnostic
  capabilities are investigated, developed and used to investigate the
  magnetic and velocity structure of a sunspot. These lines are most
  sensitive to cool plasma. In addition, they are extremely Zeeman
  sensitive. We find that a sunspot is composed of two distinct cool
  magnetic components. One of them is fairly vertical, has a large
  magnetic field strength and is associated with the central (umbral)
  part of the sunspot. The other component is strongest near the outer
  boundary of the spot (penumbra), is much more inclined, has a very
  low magnetic field strength and shows the signature of the Evershed
  effect. In contrast to the smooth transition of field strength from
  the darkest part of the umbra to the outer penumbral boundary usually
  visible in observations carried out in other spectral lines, the Ti
  Ii lines exhibit a sharp transition between the two magnetic components.

Title: Hanle diagnostics of solar magnetic fields: the SR II 4078
    Angstrom line
Authors: Bianda, M.; Stenflo, J. O.; Solanki, S. K.
Bibcode: 1998A&A...337..565B
Altcode:
  The Hanle depolarization and rotation effects in the Sr ii
  4078\tsAngstroms line have been explored with the instrumentation at
  IRSOL (Istituto Ricerche Solari Locarno) by recording the Stokes I,
  Q, and U line profiles with high spectral resolution and polarimetric
  accuracy in a large number of regions across the solar disk. &gt;From
  the extracted line parameters we have constructed ``Hanle histograms''
  showing the statistical distributions of the Hanle rotation and
  depolarization effects. Comparison with theoretical calculations allow
  these histograms to be understood in terms of magnetic fields with a
  strength of about 5-10\ts G, which is similar to the field strengths
  previously found through analysis of Q/I Hanle depolarization in the
  Ca i 4227\tsAngstroms line. While small-scale magnetic fields with
  spatially unresolved angular distributions contribute to the observed
  Hanle depolarization effects, the observed Hanle rotation effects in
  Stokes U are due to spatially resolved fields with net large-scale
  orientations (e.g. global or canopy-type fields). We have also for the
  first time determined empirical ``Hanle efficiency profiles'', derived
  independently for the Hanle rotation and depolarization effects. They
  show how the Hanle efficiency has its maximum in the Doppler core of
  the line and then rapidly decreases to become zero in the line wings.

Title: Doppler imaging: the polar SPOT controversy
Authors: Bruls, J. H. M. J.; Solanki, S. K.; Schuessler, M.
Bibcode: 1998A&A...336..231B
Altcode:
  Doppler imaging studies have revealed that most rapidly rotating cool
  stars have high-latitude spots, which in many cases cover the stellar
  poles. The spectroscopic signature of polar spots is a filling in
  of the cores of spectral lines, which become flat-bottomed and may
  show bumps. Although the existence of polar spots is corroborated by
  spectroscopic and photometric measurements, and although theoretical
  models predict polar spots, they remain controversial. Most notably, it
  has been proposed that the line core filling in might also be caused by
  chromospheric activity. We present a NLTE radiative transfer analysis
  of 14 of the most-used Doppler-imaging lines which demonstrates that
  chromospheric activity can produce filling in of the observed line
  profiles only in a few of these lines. Moreover, such filling in is in
  general not of the type observed in the spectra of active stars. We
  are able to produce a flat-bottomed line core by concentrating the
  chromospheric activity near the poles, but only for two of the strongest
  lines, Fe i 5497 Angstroms and Fe i 6430 Angstroms. In the observations,
  however, also the weaker lines have flat-bottomed cores. Therefore, it
  is unlikely that polar spots are an artifact due to misinterpretation
  of the spectral signature of chromospheric activity. Nevertheless, we
  cannot exclude that chromospheric activity provides part of the filling
  in of the cores of some stronger lines; we present a diagnostic that may
  help to separate the contributions of chromospheric activity and spots.

Title: Do solar magnetic elements harbor downflows?
Authors: Frutiger, C.; Solanki, S. K.
Bibcode: 1998A&A...336L..65F
Altcode:
  In a recent paper Bellot Rubio et al. (1997) inverted Zeeman split
  Stokes profiles to infer the stratification of the temperature,
  velocity and magnetic field in the photospheric layers of solar
  magnetic elements (modeled as thin flux tubes). One controversial
  result of their inversions is the presence of a strong downflow
  within the flux tubes. In the model underlying their inversion such
  a downflow is necessary to reproduce the asymmetric shape of the
  observed V profiles. We present inversions based on two different
  flux-tube models, both of which reproduce the Stokes I and V profiles
  obtained in plages and the network with high accuracy, including the
  V profile asymmetry. One model is almost identical to that employed
  by Bellot Rubio et al. (1997), and results in a significant downflow
  within the flux tube. The other, although similar in most respects,
  has mass conservation enforced inside the flux tubes, i.e. they contain
  both an upflow and a downflow which could arise from oscillations or
  siphon flows. Hence, current data may not be sufficiently sensitive
  to distinguish between the two velocity structures, so that there is
  no compelling evidence for a net downflow of matter inside magnetic
  elements. From a physical point of view the model incorporating mass
  conservation is to be preferred.

Title: Oscillations of sunspot magnetic fields
Authors: Rueedi, I.; Solanki, S. K.; Stenflo, J. O.; Tarbell, T.;
   Scherrer, P. H.
Bibcode: 1998A&A...335L..97R
Altcode:
  We report on velocity and magnetic field oscillations observed
  in sunspots using the MDI instrument onboard SOHO. In addition to
  the well-known velocity oscillations, the data clearly show highly
  localised oscillations of the magnetogram signal in different parts
  of the sunspots. We show that only oscillations of the magnetic field
  vector can produce the observed magnetogram oscillations, and that the
  observed phase relations suggest an origin in terms of magnetoacoustic
  gravity waves.

Title: A model of solar total and spectral irradiance variations
Authors: Fligge, M.; Solanki, S. K.; Unruh, Y. C.; Froehlich, C.;
   Wehrli, Ch.
Bibcode: 1998A&A...335..709F
Altcode:
  We model solar spectral irradiance variations under the assumption
  that they are produced by sunspots and faculae alone. The model is
  based on three components, i.e. quiet Sun, assumed to be temporally
  invariant, sunspots and faculae whose temporal variations are mimicked
  using time series of sunspot areas and Mg II core-to-wing ratios. The
  detailed flux spectrum for each component is employed. The results
  are compared to spectral irradiance measurements at 402 nm, 500 nm
  and 862 nm obtained between February 22 and December 31, 1996 by
  the three-channel sunphotometers (SPM) which are part of the VIRGO
  package onboard SOHO. Our model shows a good correlation with the
  measured variations of the three colour channels and of the total
  irradiance. Since it also successfully reproduces changes in the UV
  spectral irradiance, irradiance variations and observed variations
  of the faculae-to-spots filling factor ratio since 1978, our model
  supports earlier suggestions that a large part of the solar irradiance
  variations is caused by magnetic fields at the solar surface. Finally,
  we use the model to test whether the difference between the magnitude
  of solar and stellar brightness variations reported by Lockwood et
  al. (1992) is due to the particular filters they use for their stellar
  observations. Our results suggest that this effect can explain only
  a small part of the discrepancy.

Title: On the reliability of Stokes diagnostics of magnetic elements
    away from solar disc centre
Authors: Solanki, S. K.; Steiner, O.; Buente, M.; Murphy, G.; Ploner,
   S. R. O.
Bibcode: 1998A&A...333..721S
Altcode:
  {The spectropolarimetric signature of models of small-scale magnetic
  features is well understood at the centre of the solar disc, but
  has been little studied near the solar limb, mainly because the
  detailed geometry of the flux tubes must then be taken into account
  in a realistic analysis. We present multi-ray calculations of Stokes
  profiles through arrays of 2-D magnetohydrostatic models of small flux
  tubes. We compare the Stokes profile shapes and Stokes based diagnostics
  (Q to V ratio, V amplitude, magnetic line ratio, centre of gravity
  wavelengths, etc.) resulting from plane-parallel and 2-D flux-tube
  models at different limb distances for two lines in the visible and
  an infrared H-band line. For the visible lines around 5250 Angstroms
  all the diagnostics we have studied, with the exception of the Q and U
  to V ratio, are significantly affected by the finite size of the flux
  tubes and the passage of the rays through non-magnetic material near
  the limb. We show that magnetic filling factors and the global magnetic
  flux may be underestimated using the usual calibration techniques. In
  addition, near the solar limb the magnetic line ratio can move into
  a regime that is forbidden according to simpler models. The spatially
  averaged longitudinal field derived from the centre-of-gravity method
  also becomes strongly model dependent. The thermal structure of the
  non-magnetic atmosphere appears to play a particularly important role
  in determining the values of these diagnostic parameters. The infrared
  line at 1.5648 mu m, on the one hand, reacts little to the external
  atmosphere and provides superior diagnostics of both the magnetic field
  strength and filling factor. On the other hand, for a flux tube with
  a sharp boundary this line shows little dependence on the flux-tube
  diameter, in contrast to the earlier findings of Zayer et al. (1989). }

Title: Temporal Evolution of Artificial Solar Granules
Authors: Ploner, S. R. O.; Solanki, S. K.; Gadun, A. S.; Hanslmeier, A.
Bibcode: 1998SSRv...85..261P
Altcode:
  We study the evolution of artificial granulation on the basis of 2-D
  hydrodynamical simulations. These clearly show that granules die in
  two different ways. One route to death is the well known bifurcation
  or fragmentation of a large granule into 2 smaller ones (exploding
  granules). The other pathway to death is characterized by merging
  intergranular lanes and the accompanying dissolution of the granule
  located between them. It is found that the lifetime and maximum
  brightness is independent of the way in which granules evolve and
  die. They clearly differ in size, however, with exploding granules
  being in general significantly larger.

Title: Structure of the Solar Photosphere
Authors: Solanki, Sami K.
Bibcode: 1998SSRv...85..175S
Altcode:
  The majority of measured solar abundances refer to the solar
  photosphere. In general, when determining photospheric abundances a
  plane-parallel atmosphere and LTE are assumed. However, the photosphere
  is structured by granulation, magnetic fields and p-modes. They change
  line profiles by the thermal inhomogeneities and wavelength shifts they
  introduce. A brief description of the first two of these phenomena
  is given and some of the ways in which they influence abundances are
  pointed out. Departures from LTE also occur. The magnitude of the errors
  introduced into elemental abundances by neglecting such departures is
  also briefly discussed.

Title: Foreword
Authors: Fröhlich, C.; Huber, M. C. E.; Solanki, S. K.; von Steiger,
   R.
Bibcode: 1998SSRv...85...11F
Altcode:
  No abstract at ADS

Title: Long-term behavior of emission from solar faculae: steps
    towards a robust index
Authors: Fligge, M.; Solanki, S. K.
Bibcode: 1998A&A...332.1082F
Altcode:
  Facular emission is one of the major contributors to long-term solar
  irradiance variations. Reconstructions of past facular variations,
  however, are strongly hampered by the lack of reliable proxies,
  particularly on time-scales longer than a solar cycle. We consider
  the five potential facular proxies with records covering more than
  40 years. By suitably weighting and combining them we create a new
  proxy. In comparison with sunspot relative number the combined proxy
  exhibits enhanced values during solar cycles 16 and 17. This suggests
  that the Sun may have been brighter during those cycles than earlier
  models, which used sunspot numbers as the facular proxy, indicate.

Title: Hanle depolarisation in the solar chromosphere
Authors: Bianda, M.; Solanki, S. K.; Stenflo, J. O.
Bibcode: 1998A&A...331..760B
Altcode:
  A new polarimeter and an extension of the polarimetric technique of
  Donati et al. (1990) to higher polarisation values are presented. With
  this system, which allows low-noise polarimetric observations in the
  blue and near-UV part of the solar spectrum, we have recorded more than
  200 Q/I profiles of Ca I 4227 Angstroms with an accuracy of 2-3x 10(-4)
  . We find that while the Q/I line shape outside the line core is very
  stable from one part of the solar surface to the next, the line core
  exhibits large variations relative to the rest of the profile. These
  variations are best interpreted in terms of partial depolarisation
  produced by the Hanle effect in the presence of weak fields. We obtain
  a quantitative and model-independent estimate of the depolarisation,
  from which we deduce field strengths of 5-15 G at the level of line-core
  formation, i.e. in the low to mid chromosphere. We also find evidence
  that the field strength is distributed around these average values
  with a FWHM that is approximately the same as the average value.

Title: Infrared lines as probes of solar magnetic features. XIII. The
    relative flux in weak and strong quiet-sun magnetic fields
Authors: Meunier, N.; Solanki, S. K.; Livingston, W. C.
Bibcode: 1998A&A...331..771M
Altcode:
  An estimate of the fraction of magnetic flux in intrinsically weak-field
  form, i.e. fields with less than 1 kG intrinsic strength, in the
  quiet Sun is presented. We find that on average approximately 2/3 of
  the flux is in weak-field form, although our data allow a range of
  values between 25%\ and 85%. These estimates have been derived with
  the help of radiative transfer model calculations from low-noise
  scans through the quiet Sun at fixed wavelengths within a Zeeman
  sensitive spectral line at 1.56 mu m. They represent the first rapidly
  modulated polarimetric observations of solar 1.56 mu m radiation. These
  scans show that the polarimetric signature near the core of the line
  exhibits a very different spatial structure than in the outer line
  wings. Since the outer part of the line profile is only sensitive to
  intrinsically strong magnetic fields, while the central part reacts
  also to intrinsically weak fields, this implies that intrinsically weak
  fields are distributed differently on the surface than strong fields
  are (weak-field features lie closer together). The spatial distribution
  suggests that the strong fields we are observing are network elements,
  whereas the weak fields are intranetwork features. Further results,
  such as the average distance between weak and strong field features,
  flux distribution, spatial power spectra and the Stokes asymmetry
  of intrinsically weak fields are also presented. In particular, we
  find that the flux per magnetic feature is distributed lognormally,
  in agreement with a similar finding for sunspot umbral areas by Bogdan
  et al. (1988).

Title: Solar irradiance since 1874 revisited
Authors: Solanki, S. K.; Fligge, M.
Bibcode: 1998GeoRL..25..341S
Altcode:
  We reconstruct the solar irradiance since 1874 employing an evolved
  version of previously published models and improved sunspot and
  facular data. A good correlation between reconstructed irradiance
  and Earth's global air temperature on time scales longer than the
  solar cycle is obtained and, in contrast to many earlier models, solar
  irradiance does not on average lag behind global temperature prior to
  1975, although the exact time lag between the two quantities depends
  somewhat on details of the reconstruction. Since that epoch, however,
  air temperatures have increased by 0.2 K, whereas solar irradiance
  has risen a disproportionately smaller amount. Therefore, unless the
  influence of solar variability on Earth is very strongly non-linear,
  at least this most recent temperature increase reflects the influence of
  man-made greenhouse gases or non-solar sources of natural variability.

Title: Velocity fields below the magnetic canopy of solar flux tubes:
    evidence for high-speed downflows?
Authors: Briand, C.; Solanki, S. K.
Bibcode: 1998A&A...330.1160B
Altcode:
  It is well-established that velocities in the immediate surroundings of
  solar magnetic elements produce an asymmetry in the Stokes V profiles
  emerging from the magnetic feature. Conversely, the observed Stokes V
  asymmetry can be used to infer the velocity field. Taking as constraints
  the area asymmetries of the Stokes V profiles of two lines of neutral
  magnesium (lambda 457nm and lambda 517nm) observed near the center of
  the solar disk, the (vertical) component of the velocity field below
  the magnetic canopy of flux tubes is investigated. We find that the
  strong Mg I b_2 line at 517nm qualitatively extends the diagnostic
  capabilities of Stokes V asymmetry, mainly due to the fact that it is
  sensitive to velocities over a large range of heights and hence also at
  relatively large distances from the flux tube axis. In order to retrieve
  the observed area asymmetry of both lines, up- as well as downflows
  have to be introduced in the models. If the temperature differences
  between the two flows are neglected then a downflow of 1.5 - 2km s(-1)
  close to the edge of the flux tube and an almost equally strong upflow
  at greater distances (corresponding to the central part of a granule)
  reproduces the observed area asymmetries. If we take into account
  that the temperature in the downflow is lower than in the upflow,
  we can only reproduce the observations if the downflow is fast (&gt;=
  5 km s(-1) ) and concentrated into narrow lanes.

Title: The photospheric sources of jets
Authors: Solanki, S. K.
Bibcode: 1998ESASP.421..115S
Altcode: 1998sjcp.conf..115S
  No abstract at ADS

Title: Complex magnetic fields in an active region
Authors: Bernasconi, P. N.; Keller, C. U.; Solanki, S. K.; Stenflo,
   J. O.
Bibcode: 1998A&A...329..704B
Altcode:
  High-resolution observations of the full Stokes vector in Fe\sc i
  spectral lines around 5250 Angstroms obtained at the Swedish Vacuum
  Solar Telescope on La Palma with the ZIMPOL I Stokes polarimeter in a
  complex active region reveal the presence of anomalously shaped Stokes
  profiles indicating the coexistence of at least two magnetic components
  within the same spatial resolution element. These Stokes profiles have
  been analyzed with an inversion code based on a 3-component atmospheric
  model with two magnetic and one field-free component. The fits to
  the observations in a magnetic region that resembles a small penumbra
  reveal the presence of a horizontal magnetic field component with an
  average field strength of /line{B}=840 G, a mean filling factor of
  /lineα=0.12, and an average temperature /line{T}=5400 K at log {tau_
  {5000}}=-1.5 embedded in the main ``penumbral'' magnetic field that
  has /line{B}=1500 G, /lineα=0.56, and /line{T}=4900 K. The horizontal
  component exhibits a mean outflow of 2.7 km s(-1) which is mainly due
  to the Evershed flow. In a region where there are strong downflows up
  to 7 km s(-1) , we infer the possible presence of a shock front whose
  height changes along the slit. The height variation can be explained by
  a change of the gas pressure at the base of the photosphere below the
  shock front as proposed by Thomas &amp; Montesinos (1991). Small plages
  with field strengths below 900 G have been observed in the vicinity
  of some pores. Finally, we present a puzzling field structure at the
  boundary between two adjacent pores. Ambiguous results suggest that
  although the inversion code is able to successfully invert even very
  complex Stokes profiles, we are far from a complete description of the
  field structure in complex magnetic regions. We warn that magnetograms
  and fits to data involving only a single magnetic component may hide
  the true complexity of the magnetic structure in at least some parts
  of active regions.

Title: Solar Composition and Its Evolution -- From Core to Corona
Authors: Fröhlich, C.; Huber, M. C. E.; Solanki, S. K.; von Steiger,
   R.
Bibcode: 1998sce..conf.....F
Altcode:
  No abstract at ADS

Title: Search for a Robust Index of Long-Term Facular Variations
Authors: Fligge, M.; Solanki, S. K.
Bibcode: 1998ASPC..140..317F
Altcode: 1998ssp..conf..317F
  No abstract at ADS

Title: Kink Waves in Solar Flux Tubes and Polarized Line Profiles
Authors: Ploner, S. R. O.; Solanki, S. K.
Bibcode: 1998ASPC..154..679P
Altcode: 1998csss...10..679P
  Waves are thought to play a fundamental role in the heating processes
  of the chromosphere and corona of the Sun and other cool stars. Of
  particular interest are periodic motions in so called flux tubes,
  elements of concentrated magnetic field. We investigate the influence
  of kink waves in flux tubes on polarized line profiles and demonstrate
  that they have a large effect. This should help us to set limits on
  the energy flux in such waves.

Title: Temporal Evolution of Artificial Solar Granules
Authors: Ploner, S. R. O.; Solanki, S. K.; Gadun, A. S.; Hanslmeier, A.
Bibcode: 1998sce..conf..261P
Altcode:
  No abstract at ADS

Title: A Non-LTE Analysis of Doppler Imaging Lines
Authors: Bruls, J. H. M. J.; Solanki, S. K.; Schussler, M.
Bibcode: 1998ASPC..154.1959B
Altcode: 1998csss...10.1959B
  Doppler imaging studies have revealed that most stars with high activity
  levels have polar spots. Although their existence is corroborated by
  spectroscopic and photometric measurements, and although theoretical
  models have been produced that include polar spots, their existence
  remains controversial. Based on a NLTE radiative transfer analysis
  of the most-used Doppler-imaging lines we reject the claim that
  chromospheric activity might be responsible for the features in the
  spectral lines that are commonly interpreted as polar spots.

Title: Torsional waves in solar flux tubes and polarized line
    profiles.
Authors: Ploner, S. R. O.; Solanki, S. K.
Bibcode: 1998joso.proc..113P
Altcode:
  Waves are thought to play a fundamental role in the heating of the
  chromosphere and corona of the Sun and other cool stars. Of particular
  interest are periodic motions in so called flux tubes, elements of
  concentrated magnetic field. The authors investigate the influence of
  torsional waves from different locations in flux tubes on polarized
  line profiles. They find that the magnitude of the influence of those
  waves strongly depends on the location within the flux tube.

Title: A model of the wavelength dependence of solar irradiance
    variations
Authors: Solanki, S. K.; Unruh, Y. C.
Bibcode: 1998A&A...329..747S
Altcode:
  The variation of the solar irradiance over the solar cycle has a strong
  wavelength dependence, being larger at shorter wavelengths. Here
  we present simple models of the spectral dependence of irradiance
  variations between solar activity maximum and minimum. We find that the
  observations (which concentrate on the UV) cannot be reproduced by a
  change in effective temperature of the Sun (or of parts of its surface)
  alone. We can, however, reproduce the data with either a 2-component or
  a 3-component model, of which one component is the quiet Sun, another
  is a facular component, and the third (in the case of the 3-component
  model) represents the temperature stratification of sunspots. The
  facular component is found to be very close to the facular models F
  or P of Fontenla et al. (1993). The success of these models supports
  the assumption underlying many studies of total solar irradiance
  variations that these are caused mainly by magnetic fields at the solar
  surface. Our investigation also allows an improved estimate of the
  relative contribution of the various layers in the solar photosphere and
  of the different wavelength regions to the total irradiance variations.

Title: The Wavelength Dependence of Solar Irradiance Variations
Authors: Unruh, Yvonne C.; Solanki, Sami K.
Bibcode: 1998ASPC..154..700U
Altcode: 1998csss...10..700U
  The observed irradiance variations over a solar cycle show a strong
  wavelength dependence; the variations are strongest in the UV and
  very weak in the visible. Here we present a simple model of the
  spectral dependence of the solar irradiance. We can exclude models that
  postulate a change in the effective temperature of the Sun or of parts
  of the Sun. However, we find that the observed irradiance variations
  can be matched with a model that includes the different temperature
  stratification of the quiet photosphere, the faculae and the sunspots.

Title: Structure of the Solar Photosphere
Authors: Solanki, S. K.
Bibcode: 1998sce..conf..175S
Altcode:
  No abstract at ADS

Title: Manifestations of Solar Magnetic Fields
Authors: Solanki, S. K.
Bibcode: 1998HiA....11..857S
Altcode:
  The magnetism of the Sun manifests itself in innumerable ways, many
  of which constitute what is referred to as solar magnetic activity,
  while others are counted among the phenomena of the quiet Sun. After
  a brief overview of the structure of the solar magnetic field, a few
  examples of its manifestations are pointed out.

Title: Modelling Spectral Irradiance Variations obtained by VIRGO
Authors: Fligge, M.; Solanki, S. K.; Unruh, Y.; Frohlich, C.;
   Wehrli, Ch.
Bibcode: 1998ASPC..140..311F
Altcode: 1998ssp..conf..311F
  No abstract at ADS

Title: The flare of November 29, 1996 observed by SOHO/CDS
Authors: Czaykowska, A.; Rank, G.; Ruedi, I.; Solanki, S. K.; de
   Pontieu, B.
Bibcode: 1998cee..workE..32C
Altcode:
  We present flare and post-flare observations obtained with the Coronal
  Diagnostic Spectrometer (CDS) onboard the Solar and Heliospheric
  Observatory (SOHO) on November 29, 1996. On this day at around 20:40
  UT, an M 1.0/1F flare occurred in the solar active region NOAA 7999 and
  was accidentally observed by the Normal Incidence Spectrometer (NIS),
  one of the two spectrometers of CDS (Harrison et al., 1995). The
  data consist of two rasters lasting for 135 minutes each and both
  cover an area of 4 times 4 arcminutes. The first raster is pointed at
  the northern part of the active region during the flare whereas the
  second one covers the southern part of the active region after the main
  phase of the flare. The observations were part of the Joint Observing
  Program (JOP) 54 which is aimed at the investigation of scaling laws in
  coronal loops. Consequently the details of observations such as line
  list and exposure time weren't convenient for flare observations. In
  addition a flare can lead to over-exposures, i.e., saturation of the
  CCD detector pixels, and a burn-in degeneration of the detector in
  bright lines. Therefore observations of flares with CDS are avoided
  and the flare from November 29, 1996, is so far the only noteworthy
  flare observed by CDS. In our case we have remarkable saturation in
  the chromospheric He I line at 584 AA and the coronal Fe XVI lines
  at 335 AA and 361 AA, which are formed at an equilibrium temperature
  of about 2.5 cdot 10^6 K. Another effect of illumination on the CCD
  detector being too high is that the electron well of each pixel may
  fill and hence bleed to adjacent pixels. This effect is clearly seen
  in our data. As the flare occurred, the 2 times 240 arcseconds slit
  was being rastered across the active region from west to east. We thus
  have a convolution of spatial and temporal effects which are not easy
  to separate. However, we have spectral information of each pixel in all
  lines and exposures which are not saturated. Hence, line parameters such
  as intensity and relative Doppler shifts can be calculated. Moreover,
  the line list contains two density sensitive line pairs, Fe XII 338
  AA/364 AA and Fe XIII 348 AA / 360 AA (see, e.g., Mason et al., 1997)
  which can be used to determine the electron density. Using this data we
  intend to study the temporal evolution of characteristics and geometry
  of the loop during the flare.

Title: Solar Magnetic Fields: an Introduction
Authors: Solanki, Sami K.
Bibcode: 1998LNP...507...41S
Altcode: 1998sspt.conf...41S
  The magnetic field of the Sun is thought to be produced by a dynamo
  in the solar interior and exhibits its greatest influence on the
  solar plasma in the tenuous outer layers of the solar atmosphere,
  where it lies at the heart of almost every major phenomenon. Most
  direct observations of the magnetic field are restricted to the solar
  surface, however. Both observational and theoretical methods have
  been employed heavily to obtain information on and an understanding
  of solar magnetism. It is the aim of these lecture notes to impart
  some of this knowledge to the reader: knowledge both of the magnetic
  field and of some of the methods used to investigate it.

Title: Sunspot Oscillations Observed with MDI
Authors: Rüedi, I.; Solanki, S. K.; Stenflo, J. O.; Scherrer, P. H.
Bibcode: 1998ESASP.417..281R
Altcode: 1998cesh.conf..281R
  No abstract at ADS

Title: Solar composition and its evolution - from core to
    corona. Proceedings. ISSI (International Space Science Institute)
    Workshop, Bern (Switzerland), 26 - 30 Jan 1998.
Authors: Fröhlich, C.; Huber, M. C. E.; Solanki, S. K.; von Steiger,
   R.
Bibcode: 1998SSRv...85.....F
Altcode:
  The following topics were dealt with: solar composition, solar
  evolution, the solar interior, helioseismology, photosphere,
  chromosphere, solar corona, solar wind, the Sun as a Sun-like star.

Title: Evolved Stars: What Happens to Activity Off the Main Sequence
Authors: Strassmeier, K. G.; Fekel, F. C.; Gray, D. F.; Hatzes, A. P.;
   Schmitt, J. H. M. M.; Solanki, S. K.
Bibcode: 1998ASPC..154..257S
Altcode: 1998csss...10..257S
  Magnetic activity on the main sequence has been well studied, in
  contrast to researches on sub-giants, giants, and supergiant stars. In
  this discussion we will address three main topics associated with
  activity in evolved stars: (1) rotation regimes for evolved stars;
  (2) rotation-activity relations in the H-R diagram; (3) polar spots.

Title: Noise Reduction in Astronomical Spectra: A New Wavelet-Based
    Method
Authors: Fligge, M.; Solanki, S. K.
Bibcode: 1998ASPC..154..833F
Altcode: 1998csss...10..833F
  We present a wavelet technique to de-noise astronomical spectra based on
  non-orthogonal wavelet packets and compare it to Fourier-smoothing and
  other wavelet-based de-noising algorithms. It is found to give better
  results than any other tested de-noising algorithm and is particularly
  successful in recovering weak signals that are practically drowned by
  the noise.

Title: Solar Oscillations in CO at 4.6 Microns
Authors: Livingston, W.; Solanki, S.; Muglach, K.; Wallace, L.
Bibcode: 1998ASPC..135..186L
Altcode: 1998hcsp.conf..186L
  The fundamental band lines of CO originate in the solar temperature
  minimum and lower cool parts of the chromosphere. We have observed
  velocity and intensity oscillations in the quiet sun disk center
  and extreme limb, sunspots, and plage. We have also looked for CO
  oscillations in the Sun-as-a-star (but detect nothing). We compare the
  power spectra of these various features, noting well separated 3 min and
  5 min peaks. We interpret our observations in terms of the models of
  Carlsson and Stein (1995), and Solanki, et al., (1994). Active Region
  Seismology: Results from TON Project Bala Balachandran (Dept. Physics,
  National Tsing Hua University, Hsinchu, Taiwan 30043, R.O.C.) Taiwan
  Oscillation Network (TON) is a ground based observation facility
  for the study of solar oscillations. The data consists of full-disc
  K-line images taken at every minute. Using the 512 images time series,
  we have tried to infer the location of the magnetic field below the
  photosphere using the property of the active regions to absorb the
  p-mode power. Two consecutive days, one just when the magnetic flux
  appears on the surface and the other the day before the emergence, were
  analysed. For this, an annular region of 15 deg. around the region of
  emerging flux was chosen for the analysis. The modes were decomposed
  into incoming and outgoing waves and the absorption coefficient was
  calculated as the fractional difference of the two types. We found
  that the absorption is stronger after the emergence of the flux and
  the flux was at a depth of about 4000 km below the surface just before
  its appearance on the surface; that is about 15 hrs before. It was also
  reported earlier by other groups that the quiet sun exhibits acoustic
  emission. It is believed to be an observational effect and the cause is
  yet to find out. We have carried out a systematic analysis of the quiet
  sun emission using 512 images. The analysis is similar to the active
  region study, but the region of interest is the solar disc centre. We
  found that there exists negative absoption or emission for most modes
  and the negative absorption increases with the angular distance from
  the centre of the sun.

Title: Wavelength Dependence of Solar Irradiance Variability from
    VIRGO Onboard SOHO
Authors: Wehrli, C.; Fröhlich, C.; Anklin, M.; Fligge, M.; SOlanki,
   S. K.; Unruh, Y.
Bibcode: 1997ESASP.415..497W
Altcode: 1997cpsh.conf..497W
  No abstract at ADS

Title: Polar spots and stellar spindown: is dynamo saturation needed?
Authors: Solanki, S. K.; Motamen, S.; Keppens, R.
Bibcode: 1997A&A...325.1039S
Altcode:
  Dynamo saturation is often invoked when calculating the rotational
  evolution of cool stars. At rapid rotation rates a saturated
  dynamo reduces the angular momentum carried away by the stellar
  wind. This, in turn, may explain the high rotation rates present in
  the distribution of rotation periods in young clusters. Here we point
  out that concentration of magnetic flux near the poles of rapidly
  rotating cool stars provides an alternative to dynamo saturation. A
  high-latitude concentration of field on rapid rotators saturates
  the angular momentum loss induced by the stellar wind, due to the
  reduced torque arm. We show that the inclusion of this effect in
  model calculations is able to reproduce the observed high rotation
  rates without the need for dynamo saturation. Taken together with the
  results of O'Dell et al. (1995A&amp;A...294..715O) this argues against
  dynamo saturation at low rotation rates.

Title: Noise reduction in astronomical spectra using wavelet packets
Authors: Fligge, M.; Solanki, S. K.
Bibcode: 1997A&AS..124..579F
Altcode:
  The wavelet representation of a signal offers greater flexibility in
  de-noising astronomical spectra than classical Fourier smoothing due
  to the additional wavelength resolution of the decomposed signal. We
  present here a new wavelet-based approach to noise reduction. It is
  similar to an application of the splitting algorithm of a wavelet
  packets analysis using non-orthogonal wavelets. It clearly separates
  the signal from the noise, in particular also at the noise-dominated
  highest frequencies. This allows a better suppression of the noise,
  so that the spectrum de-noised in this manner provides a closer
  approximation of the uncorrupted signal than in the case of a single
  wavelet transformation or a Fourier transform. We test this method on
  intensity and circularly polarized spectra of the sun and compare with
  Fourier and other wavelet-based de-noising algorithms. Our technique
  is found to give better results than any other tested de-noising
  algorithm. It is shown to be particularly successful in recovering
  weak signals that are practically drowned by the noise.

Title: Influence of kink waves in solar magnetic flux tubes on
    spectral lines.
Authors: Ploner, S. R. O.; Solanki, S. K.
Bibcode: 1997A&A...325.1199P
Altcode:
  The kink-mode waves in solar magnetic flux tubes have been proposed
  as the carriers of significant amounts of energy into the upper
  atmosphere. Their observational signature, i.e. their influence
  on polarized spectral lines, is investigated theoretically using a
  simple MHD model and radiative transfer calculations. The results of
  a large model grid are presented. The wave is found to periodically
  shift, broaden, strengthen and change the asymmetry of circularly
  and linearly polarized profiles (Stokes V and Q, respectively). For
  most, but not all line parameters it exhibits its largest influence
  close to the limb. The time fluctuations of all quantities are in
  phase for Stokes Q and V, except for their amplitudes, which are in
  antiphase. The signal of the wave in time-averaged profiles depends
  on the wave frequency. Stokes Q and V exhibit opposite senses of the
  blue-red asymmetry and wavelength shift. This behaviour is found to be
  a result of the dependence on frequency of the phase relation between
  velocity and flux tube inclination. As the wave frequency approaches
  the cutoff frequency the phase relation changes and the time-averaged
  line asymmetry and shift decrease rapidly. High frequency kink waves are
  found to be an extremely efficient source of Stokes Q and V asymmetry,
  while maintaining a small line shift.

Title: Simulations of Zeeman-split CA II K-line Stokes profiles with
    angle-dependent partial redistribution.
Authors: Bruls, J. H. M. J.; Solanki, S. K.
Bibcode: 1997A&A...325.1179B
Altcode:
  The formulation of the polarized radiative transfer equations
  for Zeeman-split spectral lines is still incomplete for cases
  with frequency-dependent line source function, e.g. when partial
  frequency distribution (PRD) of line photons occurs (strong resonance
  lines). Under the well-founded assumption that the field-free
  approximation works equally well for lines with partial redistribution
  as for lines with complete redistribution (CRD), we decouple the
  computation of the level populations (accounting for PRD effects) from
  the formal Stokes vector solution. The level populations are obtained
  with the Hubeny &amp; Lites (1995ApJ...455..376H) version of Carlsson's
  (1986UppOR..33....1C) MULTI code, and the formal solution follows
  by means of a modified version of the Murphy &amp; Rees (1990, NCAR
  Technical Note NCAR/TN-348+IA) SPSR code. Due to lack of the appropriate
  equations concerning the combination of partial redistribution and
  Zeeman splitting of spectral lines, an ad hoc partial redistribution
  approach (basically allowing for wavelength dependence of the line
  source function) is implemented in the SPSR code. This combination
  of codes is used to study the relevance of partial redistribution
  to the Caii K-line diagnostics of solar plage regions using grids of
  flux-tube models. In addition to magnetic fields, velocity fields play
  an important role in the formation of the K-line profiles, but these
  invalidate the commonly-used angle-averaged PRD formalism. We therefore
  extended the Hubeny &amp; Lites (1995ApJ...455..376H) angle-averaged
  PRD version of MULTI code to the angle-dependent case, which allows
  line profiles to be computed under PRD conditions for arbitrary (but
  not too large) velocity fields. This code is subsequently used to
  perform the non-magnetic non-LTE statistical equilibrium computations
  for a few schematic velocity structures in plage flux tubes and in the
  surrounding non-magnetic atmosphere. The SPSR code is again used to
  obtain the K-line Stokes profiles. We investigate in particular the
  asymmetry of the K line intensity and circularly polarized profiles
  produced by the velocity fields.

Title: Polar spots and stellar spindown: is dynamo saturation needed?
Authors: Solanki, S. K.; Motamen, S.; Keppens, R.
Bibcode: 1997A&A...324..943S
Altcode:
  Dynamo saturation is often invoked when calculating the rotational
  evolution of cool stars. At rapid rotation rates a saturated
  dynamo reduces the angular momentum carried away by the stellar
  wind. This, in turn, may explain the high rotation rates present in
  the distribution of rotation periods in young clusters. Here we point
  out that concentration of magnetic flux near the poles of rapidly
  rotating cool stars provides an alternative to dynamo saturation. A
  high-latitude concentration of field on rapid rotators saturates
  the angular momentum loss induced by the stellar wind, due to the
  reduced torque arm. We show that the inclusion of this effect in
  model calculations is able to reproduce the observed high rotation
  rates without the need for dynamo saturation. Taken together with the
  results of O'Dell et al. (1995A&amp;A...294..715O) this argues against
  dynamo saturation at low rotation rates.

Title: Inter-Cycle Variations of Solar Irradiance: Sunspot Areas as
    a Pointer
Authors: Fligge, M.; Solanki, S. K.
Bibcode: 1997SoPh..173..427F
Altcode:
  Most of the present models and reconstructions of solar irradiance
  use the concept of Photometric Sunspot Index (PSI) to account for
  the influence of sunspots on solar brightness. Since PSI is based on
  measured sunspot areas a firm database of such areas is essential. We
  show, however, that a significant disagreement exists between the
  data provided by the Royal Greenwich Observatory (from 1874 to 1976)
  and newer measurements provided by the observatories of Rome, Yunnan,
  Catania, and the US Air Force. The overlap of the time intervals over
  which sunspot areas were measured at Greenwich and Rome allows us to
  quantify the difference between the Greenwich and other data sets. We
  find that the various data sets differ, at least in a statistical sense,
  mainly by a correction factor of between 1.15 and 1.25.

Title: Center-to-limb variation of the second solar spectrum.
Authors: Stenflo, J. O.; Bianda, M.; Keller, C. U.; Solanki, S. K.
Bibcode: 1997A&A...322..985S
Altcode:
  The linear polarization that is caused by scattering processes in the
  solar atmosphere has been refered to as the "second solar spectrum",
  since it is structurally as rich as the ordinary intensity spectrum
  but quite different in appearance and information contents. One
  of the most used and theoretically best understood lines in the
  second solar spectrum is the SrI 4607Å line, which has served as a
  diagnostic tool for determinations of spatially unresolved, turbulent
  magnetic fields via the Hanle effect. Here we present the detailed
  center-to-limb variation of the scattering polarization in this line
  for a number of new data sets obtained both with an electrooptical
  modulation system (ZIMPOL) and a non-modulating beam splitter system
  (at IRSOL, Locarno), to provide improved observational constraints for
  theoretical modelling. The amplitude and width of the polarization
  profile, the amount of continuum polarization, as well as the depth
  and width of the intensity profile have been evaluated and carefully
  corrected for spectral broadening and stray light. While there is
  generally good agreement between the five data sets, some systematic
  differences are shown to be of solar rather than instrumental origin,
  most likely due to spatially varying Hanle depolarization across the
  solar disk. A number of other spectral lines have been observed with
  the ZIMPOL system at two different limb distances (μ=0.1 and 0.2) to
  allow us to compare the steepness of the center-to-limb variation of
  their polarization amplitudes. The steepest variation is exhibited by
  the continuum polarization, which declines by approximately a factor of
  6 when going the 15 arcsec distance from μ=0.1 to μ=0.2. The spectral
  lines with the steepest center-to-limb variation are molecular lines,
  the CaII infrared triplet, and Hα. In contrast the SrI 4607 and BaII
  4554Å lines have only moderately steeper center-to-limb variations
  than that of an ideal, purely dipole-scattering atmosphere, for
  which the polarization ratio between μ=0.1 and μ=0.2 is 1.38. These
  center-to-limb variations may be used to constrain temperature-density
  models of the upper photosphere and chromosphere.

Title: Translimb Spectroscopy with SOHO/SUMER
Authors: Ayres, T. R.; Lemaire, P.; Schuhle, U.; Wilhelm, K.; Ruedi,
   I.; Solanki, S.
Bibcode: 1997SPD....28.0104A
Altcode: 1997BAAS...29..879A
  We have used SUMER to obtain deep exposures of the 1300--1400 Angstroms
  spectrum, at the extreme limb and off-limb. Previous ``translimb''
  studies in the thermal infrared had revealed remarkable extensions
  of cold material (T ~ 3000 K)---traced by carbon monoxide emission
  lines---into the heart of the hot chromosphere. A main objective of
  our program was to search for corresponding far-UV signatures of the
  ``thermally-bifurcated'' low chromosphere; for example, radiatively
  fluoresced emissions of the CO A--X 4th-positive system (collisional
  excitation would be negligible in cold gas). We conducted two separate
  observing programs with SUMER. Both made use of the 1('') -diameter
  circular aperture, translated across the limb in the minimum motor
  step increments of 0.('') 375, along the central meridian in the
  Northern polar coronal hole. The first program executed for nine hours
  beginning 19UT 25 Oct 1996. The full wavelength range was 1340--1400
  Angstroms. It was recorded in two overlapping segments, placing key
  regions of the spectrum alternately on the KBr and bare parts of
  the detector, to help isolate 2nd-order features. Each segment was
  integrated for 500 s, and 32 pairs were obtained to span a 12('')
  swath centered on the optical limb. The second program was conducted
  00--09UT 01 Dec 1996. It consisted of a single wavelength setting
  (1300--1340 Angstroms) with exposure time 500 s, but twice the spatial
  coverage of the earlier series: 64 steps, for a total displacement
  of 24('') . The strong chromospheric resonance lines of atomic oxygen
  (1302--1305 Angstroms) and ionized carbon (1334--1335 Angstroms) were
  observed on the bare part of the MCP camera. We report our progress
  in cataloging the rich, diverse translimb emission spectrum; and our
  efforts to deduce fundamental properties of the thermally heterogeneous
  chromosphere. [-3mm] SOHO is a project of international cooperation;
  the participation of TRA was supported by NASA grant NAG5-3226.

Title: Magnetic field measurements on moderately active cool dwarfs.
Authors: Rueedi, I.; Solanki, S. K.; Mathys, G.; Saar, S. H.
Bibcode: 1997A&A...318..429R
Altcode:
  We present a careful analysis of 13 high-quality optical spectra
  of low to moderately active late-type dwarfs (G1-K5) aimed at
  determining their magnetic parameters. Among our sample only one
  star, ɛ Eri (spatially averaged field strength=~165+/-30G), exhibits
  the unambiguous signature of a magnetic field, a few are candidates
  and the remaining show no sign of a magnetic field in the observed
  spectra. Our analysis is based on an inversion of the spectra using
  detailed numerical solutions of the Unno-Rachkovsky equations, for
  multiple spectral lines at different positions on the stellar disk,
  and including magneto-optical effects. It gives results for ɛ Eri
  which are in good agreement with the detailed analysis of infrared
  spectra by Valenti et al. (1995ApJ...439..939V). However, the low
  value of the spatially averaged field strength of these recent analyses
  imply that most values of the magnetic flux determined previously for
  moderately active stars are probably too large, often by considerable
  amounts. We find that the magnetic flux can be reliably determined if
  considerable care is taken in the analysis, but the magnetic field
  strength and filling factor cannot be determined separately for
  moderately active stars with optical spectra of spectral resolution
  &lt;=10^5^ and S/N&lt;=250. In the case of ɛ Eri we are able to
  constrain the temperature of the detected magnetic features, which we
  find to be similar to or hotter than the non-magnetic surroundings,
  providing the first direct evidence that the detected field is in the
  form of plages. We also find that if an inversion approach is used,
  which determines various line broadening parameters simultaneously
  in a self-consistent manner, the presence of a magnetic field is not
  as obvious as some previous analyses have suggested. In addition,
  we determine fundamental parameters of the stellar sample.

Title: Properties of Brightenings Seen in CDS Movies
Authors: Rüedi, I.; Brkovic, A.; Solanki, S. K.; Harrison, R.;
   Fludra, A.; Huber, M. C. E.; Stenflo, J. O.; Stucki, K.
Bibcode: 1997ESASP.404..641R
Altcode: 1997cswn.conf..641R
  No abstract at ADS

Title: Dynamics of Flux Tubes in the Solar Atmosphere: Observations
Authors: Solanki, S. K.
Bibcode: 1997LNP...489...49S
Altcode: 1997shpp.conf...49S
  Ground-based observations of the dynamics of solar magnetic flux tubes
  are reviewed. First a brief overview of the range of dynamic phenomena
  observed in both the largest and smallest flux tubes, i.e. in sunspots
  and magnetic elements, is given. Then three such phenomena — the
  Evershed effect, steady flows in small-scale magnetic features and
  oscillations in such features — are selected and discussed in detail.

Title: Empirical Modelling and Thermal Structure of Sunspots
Authors: Solanki, Sami K.
Bibcode: 1997ASPC..118..178S
Altcode: 1997fasp.conf..178S
  An overview of empirical models of sunspot thermal structure is
  presented. First a few remarks are made on empirical modelling in
  general. After that the literature on the various types of models,
  1- and 2-component models of the umbra and penumbra, is reviewed. The
  evidence for or against the dependence of umbral temperature on various
  parameters like sunspot size, magnetic field strength and phase of
  the solar cycle is critically reviewed.

Title: Umbral Polarimetric Measurements Using the TI I Multiplet at
    2.2 MU M %The temperature gradient of a sunspot umbra
Authors: Ruedi, I.; Solanki, S. K.; Livingston, W.
Bibcode: 1997ASPC..118..237R
Altcode: 1997fasp.conf..237R
  We present the first measurements of sunspot magnetic fields using the
  lines of the Ti I multiplet at 2.2 mu m. These lines are most sensitive
  to the plasma in the umbra. The observed line profiles suggest that
  the temperature gradient in mid-photospheric layers of a sunspot
  umbra is steeper than that of the standard sunspot models of Maltby
  et al. (1986).

Title: Velocity fields around magnetic flux tubes.
Authors: Briand, C.; Solanki, S. K.
Bibcode: 1997joso.proc...55B
Altcode:
  No abstract at ADS

Title: The beat of the solar chromosphere's cold heart.
Authors: Solanki, S. K.; Livingston, W.; Muglach, K.; Wallace, L.
Bibcode: 1996A&A...315..303S
Altcode:
  The cold heart of the solar chromosphere is best investigated using
  fundamental band lines of carbon monoxide, CO, at 4.7μm. We have
  obtained time series of CO spectra in the quiet sun and in active-region
  plage at the solar limb and at disk centre. In addition, we have
  recorded time series in sunspot umbrae located near disk centre. The
  power spectra and RMS amplitudes of the quiet-sun oscillations at
  disk centre and at the limb are not compatible with a generally
  hot chromosphere which is periodically cooled, but support recent
  suggestions that the low chromosphere is pervasively cool, interspersed
  with hot, possibly shocked material. In the plage the CO oscillations
  provide indirect evidence for the expansion of hot material (probably
  inside magnetic elements) with height. In umbrae the CO lines exhibit
  well-separated 3min and 5min peaks. We also present spectra of the phase
  shift between velocity and intensity oscillations of CO lines. At disk
  centre in the quiet sun the phase shift is on the whole similar to that
  seen in atomic lines formed near the classical temperature minimum,
  although with some properties peculiar to CO. In plages the quality
  of the phase shift is marginal, but suggests either large radiative
  damping or propagating waves in the 4 mHz frequency range. Finally,
  in sunspots the phase shift resembles that of atomic chromospheric
  lines in some umbrae.

Title: Distribution of starspots on cool stars. I. Young and main
    sequence stars of 1M<SUB>sun</SUB>_.
Authors: Schuessler, M.; Caligari, P.; Ferriz-Mas, A.; Solanki, S. K.;
   Stix, M.
Bibcode: 1996A&A...314..503S
Altcode:
  Sunspots are restricted to a latitude band within 30degof the solar
  equator. In contrast, the latitudes of spots on the surfaces of
  rapidly rotating cool stars can range from their polar regions, for
  RS CVn systems and for T Tauri stars leaving the Hayashi track, to
  mid latitudes for stars close to or on the main sequence. In order to
  find an explanation for these observed spot latitudes we have applied
  the criteria for the undulatory instability (Parker instability) of
  a toroidal magnetic flux tube embedded in the convective overshoot
  layer below the outer convection zone and calculated the non-linear
  evolution of the rising magnetic loops formed by this instability. We
  describe the results for a star of one solar mass in different phases
  of its evolution before and on the main sequence. We find that there
  usually is a range of latitudes at which magnetic flux can emerge on
  the stellar surface. The mean latitude of emergence shifts towards
  the poles for increasingly rapid rotation. The internal structure
  of the star, however, plays an almost equally important role in
  determining the latitude of magnetic emergence. For stars of solar
  mass only the youngest objects, with extremely deep convection zones,
  should show spots emerging at the stellar poles. Pre-main sequence
  stars at an age of 10^7^ y (convection zone reaching down half-way to
  the centre) exhibit high latitude, but not truly polar spots, while
  a main sequence star of one solar mass, even at high rotation rates,
  only shows intermediate latitude spots. These results are found to be
  in good agreement with Doppler images of young rapid rotators.

Title: Infrared lines as probes of solar magnetic
features. XII. Magnetic flux tubes: evidence of convective collapse?
Authors: Solanki, S. K.; Zufferey, D.; Lin, H.; Rueedi, I.; Kuhn, J. R.
Bibcode: 1996A&A...310L..33S
Altcode:
  The magnetic field in the solar photosphere is mainly composed of
  magnetic flux tubes. Their formation is not well understood, largely due
  to an absence of observational tests of theoretical predictions. Here we
  use infrared polarimetric data to test and confirm the prediction that
  whereas the field strength of large flux tubes is almost independent
  of their magnetic flux, small flux tubes show a strong dependence. Our
  work thus strengthens the case for convective collapse as the source of
  concentrated solar magnetic fields. We also present the first direct
  measurement of the intrinsic field strength of typical intranetwork
  elements. A significant fraction of them is in equipartition with the
  kinetic energy of convection. Nevertheless, our results suggest that
  as far as their internal structure is concerned intranetwork magnetic
  features are better described by flux tubes than by turbulent fields.

Title: Book Review: The Sun as a variable star ; solar and stellar
    irradiance variations (IAU colloquium 143) / Cambridge U Press, 1994
Authors: Pap, J. M.; Fröhlich, C.; Hudson, H. D.; Solanki, S. K.
Bibcode: 1996SSRv...76..354P
Altcode:
  No abstract at ADS

Title: On the detection of shocks in the solar granulation.
Authors: Solanki, S. K.; Rueedi, I.; Bianda, M.; Steffen, M.
Bibcode: 1996A&A...308..623S
Altcode:
  We investigate the spectral signature of a hydrodynamic simulation of
  solar granulation and compare it with high resolution observations. The
  model gives the correct qualitative trend of increasing line width
  with decreasing continuum intensity seen by Nesis et al. (1992)
  and interpreted by them as a sign of post-shock turbulence. We find,
  however, that the profiles in the dark downflow lanes are broader even
  when there is no horizontal transonic flow or shock in the vicinity. We
  conclude that the observations of Nesis et al. do not provide any firm
  evidence for the presence of granular transonic flows. Nevertheless,
  the simulation predicts a promising diagnostic of shocked horizontal
  flows. We find that at the locations of the shocks the line profiles
  are particularly broad, especially near the solar limb. We present
  observations of quiet solar regions that show this specific signature
  of shocks and thus support the theoretical prediction of transonic
  granular flows.

Title: Measurement of the full Stokes vector of He I 10830 Å
Authors: Rüedi, I.; Keller, C. U.; Solanki, S. K.
Bibcode: 1996SoPh..164..265R
Altcode:
  First observations of the full Stokes vector in the upper chromosphere
  are presented. The He I 10830 Å line, which has been shown to give
  reliable measurements of the line-of-sight component of the magnetic
  field vector, has been used for this purpose. It is shown that the
  difference between the appearance of chromospheric and photospheric
  magnetic structures observed close to the solar limb is largely
  due to the difference in height to which they refer and projection
  effects. The observations do suggest, however, that the magnetic field
  above sunspot penumbrae is somewhat more vertical in the chromosphere
  than in the photosphere.

Title: The Influence of Sunspot Canopies on Magnetic Inclination
    Measurements in Solar Plages
Authors: Solanki, Sami K.; Finsterle, Wolfgang; Rüedi, Isabelle
Bibcode: 1996SoPh..164..253S
Altcode:
  Sunspots are known to have large, low-lying magnetic canopies,
  i.e. horizontal magnetic fields overlying a field-free medium,
  that cover substantial fractions of active region plage. In this
  paper we consider the influence of such canopies on the inclination
  of plage magnetic fields. We find that for observations in spectral
  lines like 5250.2Å the neglect of a sunspot canopy when determining
  magnetic inclination angles of plage fields can introduce errors
  exceeding 5-10°. This is particularly true if the observations
  do not have high spatial resolution. Thus this effect may explain
  some of the measurements of substantially inclined fields in solar
  plages. Furthermore we find that the Fe I 15648 Å line is far superior
  in giving correct flux-tube inclinations in the presence of a sunspot
  magnetic canopy. Finally, the inversion of full Stokes profiles is shown
  to produce more reliable results than results obtained by considering
  only ratios of individual Stokes profile parameters.

Title: Inversion of Stokes Vector Profiles in Terms of a 3-Component
    Model
Authors: Bernasconi, P. N.; Solanki, S. K.
Bibcode: 1996SoPh..164..277B
Altcode:
  Various spectropolarimetric observations show peculiar Stokes profiles
  that reveal the coexistence of at least two magnetic components in
  the same resolution element. An example is given by observations of
  the full Stokes vector in a complex active region performed with the
  ZIMPOL I Stokes polarimeter. In order to deduce the physical parameters
  of the observed regions from such measured profiles, we have extended
  an existing inversion code, so that it can now fit the data with models
  composed of up to three different atmospheric components. Two of these
  components are magnetic and may possess different field strengths,
  field geometries, temperature stratifications, and velocity fields. The
  third component describes the field free atmosphere surrounding the
  magnetic features.

Title: Flux Tube Dynamics in Active Stars
Authors: Caligari, P.; Schüssler, M.; Solanki, S. K.; Schaerer, D.;
   Stix, M.
Bibcode: 1996ApL&C..34...17C
Altcode:
  No abstract at ADS

Title: New constraints on gravity-induced birefringence
Authors: Solanki, Sami K.; Haugan, Mark P.
Bibcode: 1996PhRvD..53..997S
Altcode:
  A wide class of gravitation theories predicts gravity-induced
  birefringence. For Moffat's NGT, the prototypical theory of this type,
  Gabriel, Haugan, Mann, and Palmer used the predicted gravitational
  birefringence and observations of solar polarization to constrain
  the Sun's nonsymmetric charge l<SUB>solar</SUB>. We improve on this
  constraint by making use of improved knowledge of the solar source
  of polarization and of a refined analysis procedure. We obtain
  l<SUP>2</SUP><SUB>solar</SUB>&lt; (305 km)<SUP>2</SUP>.

Title: PRD vs. CRD CaII K Stokes profiles from solar plage
Authors: Bruls, J. H. M. J.; Solanki, S. K.; Uitenbroek, H.
Bibcode: 1996ASPC..109..113B
Altcode: 1996csss....9..113B
  No abstract at ADS

Title: Solar and stellar magnetic flux tubes (review)
Authors: Solanki, S. K.
Bibcode: 1996IAUS..176..201S
Altcode:
  No abstract at ADS

Title: Observing stellar surface structure with the ESO-VLT
    interferometer
Authors: von der Luhe, O.; Solanki, S.; Reinheimer, Th.
Bibcode: 1996IAUS..176..147V
Altcode:
  No abstract at ADS

Title: Interesting lines in the infrared solar spectrum. III. A
    polarimetric survey between 1.05 and 2.50 μm.
Authors: Rueedi, I.; Solanki, S. K.; Livingston, W.; Harvey, J.
Bibcode: 1995A&AS..113...91R
Altcode:
  We present a survey of Stokes I, V and Q in the near infrared
  spectral range between 1.05 and 2.50μm, based on Fourier transform
  spectrometer data obtained in a sunspot umbra and in an active region
  plage. We discuss the diagnostic potential of a number of lines for
  studying solar magnetic features. These include the Ti I multiplet near
  22000A, the Fe I g=3 line at 15648.5A, He I 10830A, high excitation C I
  lines, as well as CO and CN lines. As an example, we provide the first
  estimate of the field strength gradient averaged over the height range
  covered by the photosphere and chromosphere. We also identify lines
  that show large Stokes V or Q amplitudes and analyze their profile
  asymmetries. In our J-band plage spectrum the Stokes V and Q profiles
  show an extremely large blue-red asymmetry, whose origin is not yet
  clear. As an incidental result we obtain the first measured value of the
  vertical gradient of the magnetic field strength in a plage. Averaged
  over approximately 1500-2000km it corresponds to roughly 0.6G/km.

Title: Infrared lines as probes of solar magnetic
    features. XI. Structure of a sunspot umbra with a light bridge.
Authors: Rueedi, I.; Solanki, S. K.; Livingston, W.
Bibcode: 1995A&A...302..543R
Altcode:
  We investigate the magnetic structure of an umbra and the light bridge
  it contains using spectra at 1.56μm. The magnetic field strength in
  the umbra reaches over 3500G on the first day of observation and 3200G
  on the second and third days, while the field strength in the light
  bridge is reduced by 1000-1400G relative to the nearby umbra. The
  magnetic vector is also found to be much more horizontal in the light
  bridge. There is evidence that the boundary between the strong and
  weak magnetic field is less than 1" wide, implying the presence of
  large currents there. At some locations a downflow of up to 1.5km/s is
  seen in the light bridge relative to the umbral material. Finally, we
  discuss the blending of the 1.5648μm line in sunspots and develop the
  depth of the OH 15650.7A line as a diagnostic of umbral temperatures.

Title: Interesting lines in the infrared solar spectrum. II. Unblended
    lines between λ1.0 and λ1.8 μm.
Authors: Ramsauer, J.; Solanki, S. K.; Biemont, E.
Bibcode: 1995A&AS..113...71R
Altcode:
  We list 603 spectral lines between 1.0 and 1.8μm that are judged
  to be relatively unblended from a visual inspection of spectra of
  the quiet sun. Much of the atomic data of relevance to studies of
  solar and stellar magnetism, convection and atmospheric structure are
  also provided. Particular attention is paid to blending by telluric
  lines. We determine the level of blending both in the presence and
  the absence of telluric lines. We also describe how telluric blends
  may be removed from spectra with high spectral resolution.

Title: Book Review: Planetary systems : formation, evolution and
    detection / Kluwer, 1994
Authors: Solanki, S. K.; Švestka, Zdeněk; Svestka, Z.
Bibcode: 1995SoPh..159..403S
Altcode: 1995SoPh..159..403B
  No abstract at ADS

Title: Empirical models of solar magnetic elements: constraints
    imposed by MgI Stokes profiles.
Authors: Briand, C.; Solanki, S. K.
Bibcode: 1995A&A...299..596B
Altcode:
  Although the temperature structure of small-scale magnetic features
  in the lower and middle photosphere has been constrained quite well,
  there are still considerable uncertainties in the upper photospheric
  and lower chromospheric thermal structure. As a step towards an
  improvement of this situation we investigate, using a non-LTE analysis,
  the diagnostic capabilities of the Stokes I and V profiles of the Mg
  I b_2_ 517.3nm and the Mg I 457.1nm lines. We find that the V profile
  of the former line can constrain the magnetic element thermal and
  velocity structure near the temperature minimum, which goes beyond
  the capabilities of the commonly used Fe I and II lines. The λ457.1nm
  line, on the other hand, does not provide any additional information
  on its own. A comparison of synthetic profiles with plage and network
  Stokes I and V spectra confirms the findings of Bruls &amp; Solanki
  (???) that the chromospheric temperature rise starts at a substantially
  lower height in magnetic elements than in the quiet Sun. Some of the
  ambiguities in previous empirical models of magnetic elements are also
  removed. We confirm that small-scale magnetic features are associated
  with larger line broadening velocities than the quiet Sun, particularly
  in the higher layers. Finally, the Mg I b_2_ line is revealed to be
  a direct diagnostic of the merging height of magnetic elements.

Title: VizieR Online Data Catalog: Lines in the infrared solar
    spectrum (Ramsauer+, 1995)
Authors: Ramsauer, J.; Solanki, S. K.; Biemont, E.
Bibcode: 1995yCat..41130071R
Altcode:
  We list 603 spectral lines between 1.0, 1.8um that are judged to
  be relatively unblended from a visual inspection of spectra of the
  quiet sun. Much of the atomic data of relevance to studies of solar
  and stellar magnetism, convection and atmospheric structure are also
  provided. Particular attention is paid to blending by telluric lines. We
  determine the level of blending both in the presence and the absence
  of telluric lines. We also describe how telluric blends may be removed
  from spectra with high spectral resolution. (4 data files).

Title: The Evershed effect: rise and fall of the wave model.
Authors: Buente, M.; Solanki, S. K.
Bibcode: 1995A&A...297..861B
Altcode:
  Adiabatic surface and trapped body waves have recently been proposed
  as the source of the Evershed effect. We show that such waves fail to
  simultaneously reproduce the main features of the Evershed effect in a
  set of spectral lines with different temperature sensitivities. This
  result sets constraints on all models that attempt to explain the
  Evershed effect on the basis of a wave-like correlation between
  temperature and velocity. In the photospheric layers in which
  the waves are expected to propagate, dissipative effects due to
  radiative diffusion are likely to damp the wave-induced temperature
  perturbations. We show, however, that in the line forming penumbral
  layers radiatively damped ("isothermal") waves shift spectral lines of
  neutral and ionized species in opposite directions. We conclude that,
  in spite of a number of highly attractive features, linear wave models
  have great difficulty in explaining the Evershed effect.

Title: Infrared lines as probes of solar magnetic features. IX. MgI
    12μm diagnostics of solar plage.
Authors: Bruls, J. H. M. J.; Solanki, S. K.
Bibcode: 1995A&A...293..240B
Altcode:
  The MgI 12.32μm line is a prime diagnostic for studying upper
  photospheric magnetic fields on the Sun. We study for the first time
  its behavior using flux-tube models with magnetic field strengths and
  filling factors characteristic of solar plage in order to establish
  the line's capabilities for measuring plage magnetic fields. We
  show that this line is only moderately sensitive to the range of
  temperatures expected for solar plages, including the chromospheric
  temperature rise. This low sensitivity considerably enhances this line
  as a magnetic field diagnostic for the upper photosphere of plages. We
  find that besides being highly sensitive to the field strength in flux
  tubes, the shape and Zeeman splitting of this line are almost equally
  sensitive to the magnetic filling factor at the flux-tube base. This
  combined sensitivity leads to the large range of profile shapes observed
  in plages. Not only can the 12μm emission lines be used to determine
  the sub-spatial-resolution distribution of flux-tube field strengths,
  but also the sub-spatial-resolution distribution of filling factors
  (i.e. they can provide an estimate of the "clumpiness" of the flux-tube
  distribution on a small scale). We also provide evidence that simple
  two-component modeling of magnetic flux tubes, without taking into
  account the height-dependence of the flux-tube size, may lead to
  erroneous conclusions in the case of the MgI 12μm lines, and that at
  least 1.5-D computations are required to adequately model these lines
  in magnetic flux tubes. Computations also show that standard flux-tube
  models simultaneously reproduce the observed splitting of the g=3 FeI
  lines at 1.5648μm (formed in the low photosphere) and at 525.02nm
  (middle photosphere), as well as of the 12.32μm emission line (upper
  photosphere). Our computations thus support the currently standard
  view that solar plages are composed of flux tubes with kGauss fields
  in the lower and mid photosphere, and that the thin-tube approximation
  is an adequate representation of the magnetic stratification in these
  flux tubes.

Title: FTS Polarimetric Survey of the Infrared Solar Spectrum Between
    1.0 and 2.5 MU M
Authors: Ruedi, I.; Solanki, S. K.; Livingston, W.; Harvey, J.
Bibcode: 1995ASPC...81..107R
Altcode: 1995lahr.conf..107R
  No abstract at ADS

Title: Oscillations in Active Plage Regions as Observed in 1.56
    Micron Lines
Authors: Muglach, K.; Solanki, S. K.; Livingston, W. C.
Bibcode: 1995itsa.conf..387M
Altcode:
  No abstract at ADS

Title: Infrared lines as probes of solar magnetic features. VIII. MgI
    12μm diagnostics of sunspots.
Authors: Bruls, J. H. M. J.; Solanki, S. K.; Rutten, R. J.; Carlsson,
   M.
Bibcode: 1995A&A...293..225B
Altcode:
  Due to their large Zeeman sensitivity, the MgI lines at 12μm are
  important diagnostics of solar magnetism. The formation of their
  central emission features is now understood, enabling quantitative
  modeling and diagnostic application of these lines. We supply the
  first systematic analysis of solar MgI 12μm Stokes profiles employing
  detailed line-profile synthesis. We compute Stokes profiles of MgI
  12.32μm for the quiet Sun, for sunspot penumbrae and for the extended
  ("superpenumbral") magnetic canopies surrounding sunspots. We use these
  computations to analyze recent MgI 12μm observations by Hewagama
  et al. (1993). Our results are the following: (1) -Saha-Boltzmann
  temperature sensitivity explains that the emission peaks are stronger in
  penumbrae than in the quiet Sun, and that they disappear in umbrae. (2)
  -The formation heights of the emission features are approximately the
  same in penumbrae and in the quiet Sun, namely τ_500_=~10^-3^. (3)
  -The simple Seares formula allows relatively accurate determinations
  of field strength and magnetic inclination. (4) -The observed excess
  broadening of the σ-component peaks compared with the π component
  in penumbrae is well explained by primarily horizontal, smooth radial
  variation of the magnetic field strength. Additional small-scale
  variations are less than {DELTA}B =~200G. (5) -The vertical field
  gradients dB/dz in penumbrae range from 0.7G/km to 3G/km; the larger
  gradients occur near the umbra, the smaller ones near the outer edge of
  the penumbra. (6) -The MgI 12μm lines are well-suited to measure the
  base heights of superpenumbral magnetic canopies. These heights range
  between 300km and 500km above τ_500_=1 out to twice the sunspot radius,
  in excellent agreement with determinations from other infrared lines.

Title: Solar line bisectors in the infrared
Authors: Puschmann, K.; Hanslmeier, A.; Solanki, S. K.
Bibcode: 1995IAUS..176P.117P
Altcode:
  No abstract at ADS

Title: Observation of Surface Activity on Cool Giants with the VLT
    Interferometer
Authors: von der Lühe, O.; Schüssler, M.; Solanki, S. K.; Caligari,
   P.
Bibcode: 1995svlt.conf...94V
Altcode:
  No abstract at ADS

Title: Magnetic Field Measurements in the Infrared
Authors: Solanki, S. K.
Bibcode: 1995itsa.conf..341S
Altcode:
  No abstract at ADS

Title: Infrared lines as probes of solar magnetic features. X. HeI
    10830A as a diagnostic of chromospheric magnetic fields.
Authors: Rueedi, I.; Solanki, S. K.; Livingston, W. C.
Bibcode: 1995A&A...293..252R
Altcode:
  The need for a simple but quantitative diagnostic of upper chromospheric
  magnetic fields is keenly felt. We develop the HeI 10830A line as such a
  diagnostic. An application to observations of an active region allows us
  to compare the magnetic field in the upper chromosphere with the field
  in the underlying photosphere. In general, the magnetic field in the
  chromosphere is found to be significantly more homogeneous. We find that
  dB/dz in the umbra of a large sunspot (0.4-0.6G/km) is similar to other
  determinations of this quantity over an equivalent height range. Also,
  dB/dz decreases outwards in the spot. Thus, in the outer penumbra it
  has dropped to 0.1-0.3 G/km. A comparison of these values with the
  results of dB/dz measurements in the photosphere suggests that dB/dz
  decreases with height. We also find evidence for magnetic canopies near
  sunspots and for the conservation of magnetic flux with height in solar
  plages when averaged horizontally over a few arc s. Observations of
  complex Stokes V profiles at the neutral line in a sunspot penumbra
  (crossover effect) suggest that the upper chromospheric penumbral
  magnetic field is not fluted to the same extent as the photospheric
  field. The large line broadening of He I (up to 10km/s) is found to
  be due to motions which are largely field aligned.

Title: Magnetic flux observed over entire solar disk
Authors: Livingston, Willam; Solanki, Sami
Bibcode: 1994AAS...18512306L
Altcode: 1994BAAS...26.1523L
  A single channel Babock-type magnetograph, using the favorable Fe
  1.5648 microns (g=3) line, reveals fields everywhere from equator to
  the polar limb. Good seeing is essential. Experimental setup includes
  a 2.5 arcsec image slicer as the input, the NIM modulator driven at
  20Hz, and an exit slit of 0.20 Angstroms. Noise is 5 (10(-3) ) percent
  polarization with a time constant of 3 sec and is negligible. Presumably
  we mainly sense the intranetwork fields in agreement with S. Martin
  (1988). New results are that the fields (flux) may strengthen near the
  limb and that the best signal is obtained at line center. The latter
  could indicate unresolved doppler shifts or the transverse Zeeman
  effect. (Both circular and linear polarized light is detected by the
  modulator). Field strength will be deduced by a statistical analysis
  of signal vs. position on the line profile.

Title: New contribution functions for Zeeman split spectral lines
Authors: Solanki, S. K.; Bruls, J. H. M. J.
Bibcode: 1994A&A...286..269S
Altcode:
  The recently introduced emergent line radiation contribution function
  (Achmad + de Jager + Nieuwenhuijzen 1991; Gurtovenko + Sheminova +
  Sarychev 1991) is extended to the Stokes vector of Zeeman split spectral
  lines. This contribution function is compared to the line depresssion
  contribution function on the basis of an analytical relation and of
  numerical NLTE computations of a set of spectral lines. In general the
  two contribution functions give very similar results, although in some
  cases the one or the other of them is more suitable.

Title: The deep layers of solar magnetic elements
Authors: Grossmann-Doerth, U.; Knoelker, M.; Schuessler, M.; Solanki,
   S. K.
Bibcode: 1994A&A...285..648G
Altcode:
  We compare self-consistent theoretical models of solar magnetic
  flux sheets with spectropolarimetric observations of a solar plage
  and a network region. Our observational diagnostics mainly provide
  information on temperature and magnetic field of the deep photospheric
  layers. They are used to constrain the two free parameters of the
  models, viz. width and initial evacuation of the flux sheets. We find
  that the width of flux sheets in the network is approximately 200 km,
  while it is 300-350 km in an active plage. The flux sheets turn out
  to be less evacuated than previously thought, so they have continuum
  intensities close to unity. Since these are average values, however,
  our results do not exclude the presence of either smaller and brighter
  or larger and darker magnetic structures.

Title: Infrared lines as probes of solar magnetic features. 7:
    On the nature of the Evershed effect in sunspots
Authors: Solanki, S. K.; Montavon, C. A. P.; Livingston, W.
Bibcode: 1994A&A...283..221S
Altcode:
  Stokes I and V profiles of 1.56 micron lines are observed in sunspots
  and their surroundings near the solar limb. An analysis of these
  observations confirms that the magnetic field of the sunspots continues
  beyond their visible boundaries in the form of an extensive, low-lying
  (supernumbral) canopy. We also find that the V profiles, which are
  only formed above the canopy base, exhibit the Evershed effect with
  line shifts of 0.5-2 km/s, while the non-magnetic material below the
  canopy is at rest. The deduced geometry of the flow outside the sunspot
  suggests a resolution of the long standing dispute about the existence
  or not of an Evershed flow outside the visible sunspot. In addition,
  the low density of the gas above the canopy base implies that the mass
  flux in the magnetic canopy is much smaller (approximately equals 10%)
  than the mass flux in the penumbra, where the 1.5 micron lines exhibit
  wavelength shifts of approximately 4 km/s. The present observations
  cast doubt on the standard interpretation of the photospheric Evershed
  effect in terms of a steady flow, in particular if it is driven by
  the siphon-flow mechanism.

Title: 1.5 MU M Observations the Depth of Sunspot Penumbrae
Authors: Solanki, S. K.; Ruedi, I.; Livingston, W.; Schmidt, H. U.
Bibcode: 1994IAUS..154..471S
Altcode:
  No abstract at ADS

Title: Magnetic Field Strength and Filling Factor Sensitivity of
    the MgI 12 MU M Infrared Lines in Solar Plage
Authors: Bruls, J. H. M. J.; Solanki, S. K.
Bibcode: 1994ASPC...68..294B
Altcode: 1994sare.conf..294B
  No abstract at ADS

Title: Flux Tube Shredding Its Infrared Signature
Authors: Bunte, M.; Steiner, O.; Solanki, S. K.; Pizzo, V. J.
Bibcode: 1994IAUS..154..459B
Altcode:
  No abstract at ADS

Title: Are Magnetic Features on epsilon ERI Cold or Hot?
Authors: Rueedi, I.; Solanki, S. K.; Mathys, G.; Saar, S. H.
Bibcode: 1994ASPC...64..465R
Altcode: 1994csss....8..465R
  We analyse high-quality spectra of epsilon Eri with the aim of
  determining its magnetic and thermal parameters. From a careful analysis
  we conclude that it is not possible to separate the field strength
  and filling factor of this star based on data obtained in the visible
  spectral range. The data do suggest, however, that the magnetic field
  of the star is concentrated in cool, starspot-like structures.

Title: How Accurate Are Stellar Magnetic Field
    Measurements? II. Analysis of Disk-Integrated Flux Tube Models
Authors: Saar, S. H.; Buente, M.; Solanki, S. K.
Bibcode: 1994ASPC...64..474S
Altcode: 1994csss....8..474S
  We analyze disk-integrated line profiles generated in atmospheres
  embedded with fluxtubes to test the accuracy of simple radiative
  transfer (RT) analyses in determining stellar magnetic parameters.

Title: Distribution of Magnetic Flux on the Surface of Rapidly
    Rotating Stars
Authors: Caligari, P.; Schussler, M.; Stix, M.; Solanki, S. K.
Bibcode: 1994ASPC...64..387C
Altcode: 1994csss....8..387C
  No abstract at ADS

Title: A Search for Sunspot Canopies Using a Vector Magnetograph
Authors: Adams, M.; Solanki, S. K.; Hagyard, M. J.; Moore, R. L.
Bibcode: 1994ASPC...64..342A
Altcode: 1994csss....8..342A
  No abstract at ADS

Title: New Light on the Heart of Darkness of the Solar Chromosphere
Authors: Solanki, S. K.; Livingston, W.; Ayres, T.
Bibcode: 1994Sci...263...64S
Altcode:
  Solar carbon monoxide spectra indicate the existence of a cool (less
  than 4000 kelvin) component to the solar chromosphere coexisting with
  the hot, bright gas at 6000 to 7000 kelvin. However, both the existence
  and the location of the cool component have been controversial. New
  high-resolution spectra show that carbon monoxide goes into emission
  just beyond the limb, allowing it to be probed without photospheric
  contamination. The cool component has temperatures as low as 3000 to
  3500 kelvin and appears to cover 50 to 85 percent of the quiet solar
  surface. There is a steep temperature rise to normal chromospheric
  temperatures at a height of 900 to 1100 kilometers. Large horizontal
  velocities are seen, suggesting that the cool component is maintained
  by the supersonic adiabatic expansion of upwelling gas in overshooting
  granules.

Title: Some consequences of an uncombed and inhomogeneous penumbra
Authors: Solanki, S. K.; Montavon, C. A. P.
Bibcode: 1994ASIC..433..239S
Altcode:
  No abstract at ADS

Title: Preliminary properties of pores derived from 1.56 micron lines
Authors: Muglach, K.; Solanki, S. K.; Livingston, W. C.
Bibcode: 1994ASIC..433..127M
Altcode:
  No abstract at ADS

Title: Poster Proceedings from IAU Colloquium 143: The Sun as a
Variable Star: Solar and Stellar Irradiance Variations
Authors: Pap, J. M.; Frohlich, C.; Hudson, H. S.; Solanki, S. K.
Bibcode: 1994svsp.coll.....P
Altcode: 1994IAUCo.143P....P
  No abstract at ADS

Title: The upper photosphere and lower chromosphere of small-scale
    magnetic features
Authors: Solanki, S. K.; Bruls, J. H. M. J.; Steiner, O.; Ayres, T.;
   Livingston, W.; Uitenbroek, H.
Bibcode: 1994ASIC..433...91S
Altcode:
  No abstract at ADS

Title: Properties of Magnetic Features from the Analysis of
    Near-Infrared Spectral Lines
Authors: Solanki, S. K.
Bibcode: 1994IAUS..154..393S
Altcode:
  No abstract at ADS

Title: Must the Magnetic Field Saturate on Rapidly Rotating Stars?
Authors: Solanki, S. K.
Bibcode: 1994ASPC...64..477S
Altcode: 1994csss....8..477S
  No abstract at ADS

Title: Solar Magnetic Elements: Models Compared with Observations
Authors: Grossmann-Doerth, U.; Knolker, M.; Schussler, M.; Solanki,
   S. K.
Bibcode: 1994ASPC...68...96G
Altcode: 1994sare.conf...96G
  No abstract at ADS

Title: Solar line bisectors in the infrared.
Authors: Puschmann, K.; Anslmeier, A.; Solanki, S.
Bibcode: 1994AGAb...10..117P
Altcode:
  No abstract at ADS

Title: On the nature of the Evershed effect
Authors: Solanki, S. K.; Montavon, C. A. P.; Livingston, W.
Bibcode: 1994smf..conf..173S
Altcode:
  No abstract at ADS

Title: Magnetic fields in the upper chromosphere: He I 10830 Å as
    an almost ideal diagnostic
Authors: Rüedi, I.; Solanki, S. K.; Livingston, W. C.
Bibcode: 1994smf..conf..363R
Altcode:
  No abstract at ADS

Title: Flux tube dynamics in pre-main-sequence and giant stars.
Authors: Caligari, P.; Schaerer, D.; Schüssler, M.; Solanki, S.
Bibcode: 1994AGAb...10...92C
Altcode:
  No abstract at ADS

Title: MgI 12 μm diagnostics of sunspot penumbrae
Authors: Bruls, J. H. M. J.; Solanki, S. K.; Rutten, R. J.; Carlsson,
   M.
Bibcode: 1994smf..conf..191B
Altcode:
  No abstract at ADS

Title: Irradiance Effects of Small-Scale Magnetic Fields on the Sun
Authors: Solanki, S. K.
Bibcode: 1994svsp.coll..226S
Altcode: 1994IAUCo.143P.226S
  No abstract at ADS

Title: Surface waves: Origin of the Evershed phenomenon?
Authors: Bünte, M.; Solanki, S. K.
Bibcode: 1994smf..conf..179B
Altcode:
  No abstract at ADS

Title: A Search for Sunspot Canopies Using a Vector Magnetograph
Authors: Adams, M.; Solanki, S. K.; Hagyard, M.; Moore, R. L.
Bibcode: 1993SoPh..148..201A
Altcode:
  Using a magnetograph, we examine four sunspots for evidence of a
  magnetic canopy at the penumbra/photosphere boundary. The penumbral
  edge is determined from the photometric intensity and is defined
  to correspond to the value of the average intensity minus twice the
  standard deviation from the average. From a comparison of the location
  of this boundary with the location of contours of the vertical and
  horizontal components of the magnetic field, we conclude that the
  data are best represented by canopy-type fields close to all four
  sunspots. There is some evidence that the magnetic inclination in the
  canopies is 5°-15° with respect to the horizontal and that the canopy
  base height lies in the middle/upper photosphere. The observations
  further suggest that the magnetic canopy of a sunspot begins at its
  outer penumbral boundary.

Title: Evidence for siphon flows with shocks in solar magnetic
    flux tubes
Authors: Degenhardt, D.; Solanki, S. K.; Montesinos, B.; Thomas, J. H.
Bibcode: 1993A&A...279L..29D
Altcode:
  We synthesize profiles of the infrared line Fe I 15648.5 A (g = 3) for a
  recently developed theoretical model of siphon flows along photospheric
  magnetic loops. The synthesized line profiles are compared with the
  observations from which Rueedi et al. (1992) deduced the presence of
  such flows across the neutral line of an active region plage. This
  comparison supports the interpretation of Rueedi et al. (1992). It
  also suggests that the average footpoint separation of the observed
  loops carrying the siphon flow is 8-15 sec and that the siphon flow
  experiences a standing tube shock in the downstream leg near the top
  of the arch.

Title: Infrared lines as probes of solar magnetic features. VI. The
    thermal-magnetic relation and Wilson depression of a simple sunspot
Authors: Solanki, S. K.; Walther, U.; Livingston, W.
Bibcode: 1993A&A...277..639S
Altcode:
  We analyse the relationship between the temperature and the magnetic
  vector, as derived from 1.56 μm spectra, in a simple sunspot. Due to
  the high Zeeman sensitivity of the = 3, 1.56 μm line, we can study this
  relationship throughout the sunspot. We confirm the field-strength, B,
  vs. temperature, T, relationship found by Kopp &amp; Rabin (1992). In
  addition, we also find a linear relation between the magnetic
  inclination angle, γ‧, and T. An analysis based on the assumption
  of magnetohydrostatic force balance gives an estimate of the Wilson
  depression, Z<SUB>W</SUB>, throughout the sunspot. Our analysis supports
  a jump in Z<SUB>W</SUB> of 200-500 km at the umbral boundary and agrees
  with a relatively constant Z<SUB>W</SUB> in the penumbra. In addition,
  we constrain various gradients of magnetic parameters and judge the
  strength of magnetic curvature forces. For example, we set tight limits
  on the vertical gradient of γ‧, the magnetic inclination angle to
  the vertical, in the penumbra. Finally, we discuss the consequences
  for, e.g., the model proposed by Sanchez Almeida &amp; Lites (1992)
  to explain the broad-band circular polarization measured in sunspots.

Title: Uncombed fields as the source of the broad-band circular
    polarization of sunspots.
Authors: Solanki, S. K.; Montavon, C. A. P.
Bibcode: 1993A&A...275..283S
Altcode:
  We investigate the production of broad-band circular polarization (BBC)
  of sunspots using a model inspired by the discovery of small-scale
  variations of magnetic inclination in sunspot penumbrae. The proposed
  model is a simple representation of a horizontal magnetic flux tube
  embedded in an inclined magnetic field, with a flow in either one
  or both components (Evershed flow). This model is shown to produce a
  sizable BBC without requiring substantial net vertical gradients of the
  magnetic vector. It reproduces the BBC observations in a qualitatively
  correct and quantitatively acceptable manner for reasonable values of
  its free parameters. In addition, our model also explains the crossover
  effect observed in sunspot penumbrae. The fits to the observations
  support the presence of a larger velocity in the horizontal magnetic
  filaments than in the inclined field. We point out that the BBC is
  complementary to high resolution images in that it diagnoses the
  height variation of the small-scale structure of sunspot magnetic
  fields. By combining the results from both techniques we outline the
  3-D fine-scale structure of the magnetic field in the photospheric
  layers of sunspot penumbrae. The most important result is that the
  two differently inclined components of the field do not simply form
  vertical sheets, but rather must have a horizontal interface near the
  level of line formation.

Title: Surface waves as the origin of the Evershed phenomenon
Authors: Bunte, M.; Darconza, G.; Solanki, S. K.
Bibcode: 1993A&A...274..478B
Altcode:
  We investigate the spectral signature of magnetoacoustic-gravity surface
  waves (MAGS-waves), which we expect to exist at the interface between
  the lower boundary of the magnetic field of the sunspot penumbra and
  the non-magnetic gas below. MAGS-waves have a number of properties
  that make them attractive candidates for explaining the photo spheric
  Evershed effect: 1. Since they transport only energy but no mass,
  they resolve the problem of mass conservation at the outer penumbral
  boundary. 2. Since they are restricted to magnetic interfaces, they
  are only (or dominantly) present in the penumbra and absent in the
  umbra. 3. The phase relation between the temperature, the horizontal,
  and vertical velocity perturbations leads to line shifts and asymmetries
  in observations at the limb, but none at disc centre. 4. The amplitude
  of the velocity perturbation drops approximately exponentially with
  height, in good agreement with observations. 5. Waves travelling in
  opposite directions with respect to the observer produce oppositely
  directed line shifts and asymmetries, making it straightforward to
  explain the opposite shifts and asymmetries observed in the limb-side
  and centre-side penumbra.

Title: The chromospheric temperature rise in solar magnetic flux tubes
Authors: Bruls, J. H. M. J.; Solanki, S. K.
Bibcode: 1993A&A...273..293B
Altcode:
  We set constraints on the location and steepness of the chromospheric
  temperature rise in solar magnetic flux tubes by synthesizing Stokes
  V profiles in non-local thermodynamic equilibrium (NLTE) of a set of
  "clean" Fe I and Fe II lines of different strengths. We compute profiles
  for several flux-tube models of the magnetic features within solar
  network and plage. Comparison with observed V profiles indicates that
  both in network and plage the chromospheric temperature rise starts
  at larger optical depth within the flux tubes than in the surrounding
  non-magnetic atmosphere. The exact onset cannot be determined with the
  present set of lines because they cannot easily distinguish between
  the location and initial steepness of the temperature rise. Assuming
  a similar T(τ) gradient as in quiet-Sun models, the chromosphere
  sets in 200 - 300 km deeper in flux tubes than in the quiet Sun. The
  similarity between the plage and network results suggests that in the
  low chromosphere the heating per flux tube is almost independent of
  magnetic filling factor.

Title: Smallscale Solar Magnetic Fields - an Overview
Authors: Solanki, Sami K.
Bibcode: 1993SSRv...63....1S
Altcode:
  An overview is given of the observational and the theoretical
  methods used to investigate solar magnetic fields. It includes an
  introduction to the Stokes parameters, their radiative transfer in the
  presence of a magnetic field, and empirical techniques used to measure
  various properties of solar magnetic features, such as the strength
  and direction of the magnetic field, magnetic flux, temperature,
  velocity, size and lifetime. The MHD equations are introduced and
  some of the most common simplifications used to describe solar
  magnetic features are outlined. The application of these techniques
  to small-scale magnetic features is surveyed. The results of empirical
  and theoretical investigations of small-scale solar magnetic features
  are reviewed. Current views on their magnetic structure, thermal
  stratification, velocity field, size, distribution and evolution are
  presented. Finally, some open questions concerning small-scale solar
  magnetic fields are listed.

Title: Centre-to-limb variation of the Stokes V asymmetry in solar
    magnetic flux tubes
Authors: Buente, M.; Solanki, S. K.; Steiner, O.
Bibcode: 1993A&A...268..736B
Altcode:
  The center-to-limb variation (CLV) of synthetic Stokes V line
  profiles of the spectral lines Fe 15250.22 A and Fe I 5083.35 A is
  computed and compared with observations. The basic elements of the
  hydromagnetic model used to calculate the Stokes V profiles consist
  of a vertical cylindrical flux tube surrounded by a field-free plasma
  in stationary motion with a downflow along the tube boundary and
  an upflow further away from it. It is shown that an array of such
  magnetic flux tubes reproduces the peculiar observed CLV of the Stokes
  V asymmetry, in particular the sign reversal of the asymmetry near the
  limb. We determine a minimum number of model components needed for the
  reproduction of the Stokes V area asymmetry and study the influence of
  various free model parameters on it. Satisfactory agreement between
  synthetic and observed Stokes V profiles can only be achieved by
  including a considerable amount of realism into the model such as
  a granular temperature-velocity correlation. This suggests that the
  basic picture of magnetic structures in the quiet solar network and
  active region plages is correct.

Title: Field Strength vs. Temperature Relation and the Structure
    of Sunspots
Authors: Solanki, S. K.; Walther, U.; Livingston, W.
Bibcode: 1993ASPC...46...48S
Altcode: 1993IAUCo.141...48S; 1993mvfs.conf...48S
  No abstract at ADS

Title: Siphon Flow Across the Magnetic Neutral-Line of an Active
    Region
Authors: Solanki, S. K.; Ruedi, I.; Rabin, D.
Bibcode: 1993ASPC...46..534S
Altcode: 1993IAUCo.141..534S; 1993mvfs.conf..534S
  No abstract at ADS

Title: Are sunspot penumbrae deep or shallow?
Authors: Solanki, S. K.; Schmidt, H. U.
Bibcode: 1993A&A...267..287S
Altcode:
  From the strength and inclination of the magnetic field measured
  across large symmetric sunspots, we estimate the fraction of the
  total magnetic flux of the sunspot passing through the solar surface
  in the penumbra. It is found that on average approximately 1/2-2/3 of
  the total magnetic flux of the spot emerges in its penumbra. Sunspot
  penumbrae are therefore deep, i.e. the tau = 1 level does not correspond
  to the lower magnetic boundary of the spot in its penumbra (except
  perhaps near its outer edge). Furthermore, the analyzed data do not
  support the passage of any significant amount of magnetic flux through
  the solar surface (in either direction) at or beyond the edge of the
  sunspot. The observations support models of the sunspot magnetic field
  which are bounded by a relatively sharp current sheet. Evidence for a
  substantial deviation from a potential field in the penumbra is found
  in the analyzed symmetric sunspots. Finally, at the height of line
  formation the field strength averaged over the whole umbra of all the
  analyzed sunspots is approximately 2250 G, while the field strength
  averaged over the whole sunspot is roughly 1350 G. The latter value is
  similar to the field strength measured in small-scale magnetic features.

Title: Evershed Effect in Sunspots and Their Canopies
Authors: Solanki, S. K.; Montavon, C.; Livingston, W.
Bibcode: 1993ASPC...46...52S
Altcode: 1993IAUCo.141...52S; 1993mvfs.conf...52S
  No abstract at ADS

Title: Why rapid rotators have polar spots.
Authors: Schuessler, M.; Solanki, S. K.
Bibcode: 1992A&A...264L..13S
Altcode:
  Starspots on magnetically active, cool stars preferentially appear near
  the poles. We suggest that this preference of high latitudes is due
  to the rapid rotation to these stars which leads to a dominance of the
  Coriolis force over the buoyancy force in the dynamics of magnetic flux
  tubes. As a consequence, flux tubes erupting from the deep parts of the
  stellar convection zone follow a path nearly parallel to the axis of
  rotation and thus necessarily surface at high latitudes, unless their
  initial field strength exceeds a critical value for which buoyancy
  becomes dominant again. It is shown that for stars with rotation
  periods below about 10 days flux tubes with such large field strength
  (of the order of 10 exp 6 G) cannot be formed and stored since they are
  unstable with respect to non-axisymmetric disturbances. Consequently,
  magnetically active stars with rapid rotation exhibit magnetic flux
  eruption at high latitudes and polar starspots.

Title: Infrared lines as probes of solar magnetic features. V -
    The magnetic structure of a simple sunspot and its canopy
Authors: Solanki, S. K.; Rueedi, I.; Livingston, W.
Bibcode: 1992A&A...263..339S
Altcode:
  The Zeeman Lande g = 3 Fe I line at 15648 A is used here to determine
  the strength and inclination of the magnetic field of a simple,
  relatively symmetric sunspot. The largest field strength observed in
  the sunspot is approximately 3100 G. The field strength at different
  points along the outer penumbral edge varies beween 800 and 1000 G. The
  angle of inclination at the outer penumbral boundary is close to 80
  deg. A low-lying, almost horizontal superpenumbral magnetic canopy best
  reproduces the observations. The magnetic field strength in the canopy
  is consistent with a magnetic monopole. Evidence of small magnetic
  elements underlying the superpenumbral canopy is presented.

Title: Infrared lines as probes of solar magnetic features. I -
    A many-line analysis of a network region
Authors: Muglach, K.; Solanki, S. K.
Bibcode: 1992A&A...263..301M
Altcode:
  The results are presented of an analysis of a Fourier transform
  spectrometer Stokes I and V spectrum in the H band of a solar network
  region. From a many-line statistical analysis of the measured Stokes F
  profiles, it is concluded that there is no evidence for s systematic
  up or downflow greater than 200-300 m/s within the magnetic element
  of the observed region. The Stokes V profiles in the H band show
  a blue-red asymmetry having the same sign as in the visible, but
  a smaller magnitude. The lines with g(eff) greater than about 1.5
  are more or less completely Zeeman split in the observed region, and
  only lines with g(eff) values well below unity can be considered to
  be in the weak-field regime. An analysis based on radiative transfer
  calculations of 16 selected spectral lines in a flux tube model shows
  that a thin tube with a field strength of 2050 G at tau (1.6) = 1 ,
  corresponding to 1500 G at z = 0, fits the profiles best.

Title: Infrared lines as probes of solar magnetic features. II -
    Diagnostic capabilities of Fe I 15648.5 A and 15652.9 A
Authors: Solanki, S. K.; Rueedi, I. K.; Livingston, W.
Bibcode: 1992A&A...263..312S
Altcode:
  The properties of two Fe I lines at 15648.5 A and 15652.9 A in the
  infrared H-band are investigated using numerical radiative transfer
  calculations. It is shown that using this combination of a Lande g = 3
  and a g(eff) = 1.53 line it is possible to measure the field strength in
  solar magnetic features simply and with great accuracy. The g = 3 line
  alone allows field strengths as low as 300-600 G to be measured. By
  forming the line ratio between the V profiles of these lines it is,
  in principle, possible to measure field strengths as low as 100 G,
  thus achieving a sensitivity otherwise only possible with the emission
  lines near 12 microns. Other diagnostic capabilities of these lines
  are also analyzed.

Title: Infrared lines as probes of solar magnetic features. III -
    Strong and weak magnetic fields in plages
Authors: Rueedi, I.; Solanki, S. K.; Livingston, W.; Stenflo, J. O.
Bibcode: 1992A&A...263..323R
Altcode:
  The diagnostics developed by Zayer et al. 1989 are applied to 27
  Stokes V spectra of solar plates. The 1.5 micron lines at 15648 A and
  15652 A are used to measure magnetic field strengths between 400 G
  and 1700 G at z = 0 in active region plages with an accuracy of up
  to 2-3 percent. The results confirm the accuracy of the line-ratio
  technique of Stenflo (1973). It is estimated that the fraction of net
  magnetic flux in strong-field form is close to 90 percent, supporting
  the view that the small-scale magnetic fields are concentrated very
  efficiently. The data clearly contradict the claims of Zirin and Popp
  (1989) based on 12 micron lines that there is at most indirect evidence
  for kG fields in solar plages. They also contradict the large fraction
  of weak-field flux reported by Del Toro et al. (1990).

Title: Continuum brightness of solar magnetic elements
Authors: Solanki, S. K.; Brigljevic, V.
Bibcode: 1992A&A...262L..29S
Altcode:
  Ratios between the Stokes V profiles of C I lines and Fe II lines are
  used to determine the temperature of the continuum-forming layers of
  solar magnetic features. From the derived temperature stratification
  the continuum intensity of the spatially unresolved magnetic features
  is obtained independently of spatial resolution. First results suggest
  that whereas magnetic features have, on average, a brighter continuum
  than the quiet sun in a region of small magnetic filling, they are
  darker in a region with large filling factor. Consequences for flux-tube
  sizes and the interpretation of the global solar luminosity variation
  are discussed.

Title: Infrared lines as probes of solar magnetic features. IV -
    Discovery of a siphon flow
Authors: Rueedi, I.; Solanki, S. K.; Rabin, D.
Bibcode: 1992A&A...261L..21R
Altcode:
  Spectra of two neighboring IR lines, Fe I 15648.5 A and Fe I 15652.9 A,
  are analyzed. The spectra were obtained with an IR array detector in
  active region plages with the entrance slit of the spectrograph placed
  across the polarity-inversion (neutral) line. Near the neutral line the
  positive polarity field is weaker (about 1200 G) and shows an upflow
  of up to 2 km/s, while the negative polarity field is stronger (about
  1500 G) and exhibits a downflow of up to 1 km/s. This configuration
  corresponds to the expected signature of a siphon flow along a loop
  connecting flux tubes across the neutral line.

Title: Waves in solar magnetic flux tubes - The observational
    signature of undamped longitudinal tube waves
Authors: Solanki, S. K.; Roberts, B.
Bibcode: 1992MNRAS.256...13S
Altcode:
  Linear calculations of undamped magnetoacoustic waves utilizing
  the thin-tube approximation are presented and their influence on the
  Stokes I and V line parameters of a set of photospheric spectral lines
  is analyzed. To improve the observational diagnostics of flux tube
  waves, the dependence of various line parameters, such as the Stokes V
  zero-crossing wavelength, Stokes V amplitude, width area and asymmetry,
  on wave parameters is studied. It is determined that it is possible
  to set a lower limit on the energy flux transported by longitudinal
  tube waves by measuring time series of the Stokes V zero-crossing
  wavelength of a selected group of lines.

Title: Polarimetry with an imaging FTS.
Authors: Stenflo, J. O.; Solanki, S. K.
Bibcode: 1992ESASP.344..197S
Altcode: 1992spai.rept..197S
  The concept of an imaging FTS polarimeter based on piezoelastic
  modulation and direct demodulation in partially masked CCDs is
  outlined. To illustrate its principle the currently operational FTS
  polarimeter at the McMath telescope as well as the detection scheme
  of the ETH polarimeter, based on partially masked CCD cameras, are
  briefly described.

Title: Small-scale physics of convection and magnetic fields.
Authors: Solanki, S. K.
Bibcode: 1992ESASP.344...27S
Altcode: 1992spai.rept...27S
  An overview is given of the current knowledge of the properties and
  the physics of small-scale magnetic features, magnetoconvection and
  convection. This review concentrates on the theoretical aspects. Some
  examples are given of features or processes which require very high
  spatial resolution to be observed.

Title: CA II K Line Diagnostics of Two Dimensional Models of the
    Solar Chromosphere
Authors: Solanki, S. K.; Buente, M.; Steiner, O.; Uitenbroek, H.
Bibcode: 1992ASPC...26..294S
Altcode: 1992csss....7..294S
  No abstract at ADS

Title: Magnetic Fields in Stellar Photospheres (Invited Review)
Authors: Solanki, S.
Bibcode: 1992ASPC...26..211S
Altcode: 1992csss....7..211S
  No abstract at ADS

Title: How Accurate are Stellar Magnetic Field Measurements?
Authors: Saar, S. H.; Solanki, S. K. .
Bibcode: 1992ASPC...26..259S
Altcode: 1992csss....7..259S
  We study the accuracy of two magnetic analysis methods by applying
  them to a large grid of lines computed using detailed 1.5-D radiative
  transfer (RT) calculations in a variety of stellar atmospheres
  imbedded with fluxtubes. We find errors of &lt; +/- 20% when using
  the more realistic analysis method if the fluxtube and external quiet
  atmospheres are similar; errors can increase substantially if this
  condition is relaxed.

Title: The Chromospheric Temperature Rise in Fluxtubes
Authors: Bruls, J. H. M. J.; Solanki, S. K.
Bibcode: 1992ASPC...26..512B
Altcode: 1992csss....7..512B
  No abstract at ADS

Title: Strong; Weak Solar Magnetic Fields
Authors: Solanki, S. K.; Ruedi, I.; Livingston, W. C.; Stenflo, J. O.
Bibcode: 1992ASPC...26..262S
Altcode: 1992csss....7..262S
  No abstract at ADS

Title: Two-dimensional models of the solar chromosphere. I - The CA
II K line as a diagnostic: 1.5-D radiative transfer
Authors: Solanki, S. K.; Steiner, O.; Uitenbroeck, H.
Bibcode: 1991A&A...250..220S
Altcode:
  Ca II K line calculations for a 5-level atom and partial frequency
  redistribution along multiple rays passing through 2D MHD models of
  magnetic flux tubes in the solar atmosphere are presented. Temperature
  stratifications corresponding to various empirical chromospheric
  models are incorporated into the models. The influence of a number
  of model parameters on individual and spatially averaged line
  profiles is considered in detail. The profiles are also compared
  with observations. It is found that the present models can, at
  least qualitatively, reproduce a wide variety of observations if the
  temperature within the magnetic component lies between that of model
  F of Vernazza et al. (1981) and of model VALP of Ayres et al. (1986)
  and if the temperature in the nonmagnetic part of the atmosphere
  corresponds to that of the COOLC model of Ayres et al. Observations
  that are consistent with this model are presented.

Title: The effect of non-linear oscillations in magnetic flux tubes
    on Stokes V asymmetry
Authors: Grossmann-Doerth, U.; Schuessler, M.; Solanki, S. K.
Bibcode: 1991A&A...249..239G
Altcode:
  The present knowledge on, and interpretation of, the asymmetry of
  Stokes V of spectral lines thought to be formed in and around magnetic
  flux tubes is reviewed. Crude models of nonlinear oscillations in the
  flux tube were investigated in order to explain the observed values
  of Stokes V amplitude and area asymmetry. It was found that flux tube
  models with quasi-oscillatory motions, consisting of a slow upflow
  and a rapid downflow in the magnetic region, as well as a downflow
  in the nonmagnetic surroundings, may reproduce the observations,
  both asymmetries and zero-crossing shift of Stokes V.

Title: Flux tube diagnostics based on the Stokes V profiles of
    infrared H-band lines.
Authors: Muglach, K.; Solanki, S. K.
Bibcode: 1991sopo.work..489M
Altcode:
  Stokes V profiles of the unblended Fe I lines in the wavelength range
  1.5 - 1.8 μ (H-band) observed in the solar network are analysed. The
  data are consistent with an absence of stationary flows larger than
  0.3 km s<SUP>-1</SUP>. The infrared Stokes V profiles are asymmetric
  in the same sense as lines in the visible, but tend to be of smaller
  magnitude, in particular the area asymmetry. The widths of the Stokes
  V profiles are consistent with kG field strengths. Finally, model
  calculations allow an upper limit of 2 to be set on the continuum
  intensity of small magnetic features relative to the quiet Sun.

Title: Stokes profile formation heights in solar magnetic flux tubes.
Authors: Larson, B.; Solanki, S. K.; Grossmann-Doerth, U.
Bibcode: 1991sopo.work..479L
Altcode:
  The formation heights of magnetically split lines in small solar
  magnetic flux tubes are investigated. In particular, the authors
  are interested in how the heights of formation depend on different
  flux tube parameters, like magnetic field strength, temperature and
  temperature gradient, as well as on line parameters, such as line
  strength, excitation potential and ionization stage.

Title: Filigree and flux tube physics.
Authors: Spruit, H. C.; Schuessler, M.; Solanki, S. K.
Bibcode: 1991sia..book..890S
Altcode:
  This review covers the properties of the small-scale (outside
  sunspots) magnetic field from observational and theoretical points
  of view. Special emphasis is put on the physics of small isolated
  magnetic concentrations (flux tubes). Topics discussed include the
  basic observational properties, the origin and disappearance of the
  small-scale field, the properties of individual magnetic elements,
  their influence on the solar irradiance and their interaction with
  solar oscillations.

Title: Inversion of Stokes V profiles: The structure of solar magnetic
    fluxtubes and its dependence on the filling factor.
Authors: Keller, C. U.; Solanki, S. K.; Stenflo, J. O.; Zayer, I.
Bibcode: 1991sopo.work..387K
Altcode:
  The authors present results from an inversion procedure that derive the
  temperature stratification, the turbulent velocity, and the magnetic
  field strength of the photospheric layers of magnetic fluxtubes from
  observed Stokes V spectra near disk center. In a first step the
  inversion has been applied to 10 Fe I and Fe II Stokes V profiles
  of a plage and a network region to obtain reliable models of the
  fluxtubes. In a second step the dependence of the fluxtube structure
  on the filling factor has been studied with spectra of 3 Fe I lines
  from 23 different regions based on the models derived in the first step.

Title: Center-to-limb variation of the Stokes V asymmetry in solar
    magnetic flux tubes.
Authors: Bünte, M.; Steiner, O.; Solanki, S. K.
Bibcode: 1991sopo.work..468B
Altcode:
  The center-to-limb-variation of synthetic Stokes V line profiles
  of the spectral line Fe I 5250.22 Å is presented and compared with
  observations. These synthetic profiles are calculated using models
  that contain the main features of the current basic pictures of small
  scale magnetic fields on the Sun.

Title: Magnetic Field Measurements on Cool Stars.
Authors: Solanki, S. K.
Bibcode: 1991RvMA....4..208S
Altcode:
  No abstract at ADS

Title: Dependence of the properties of solar magnetic flux tubes on
    filling factor. II - Results of an inversion approach
Authors: Zayer, I.; Stenflo, J. O.; Keller, C. U.; Solanki, S. K.
Bibcode: 1990A&A...239..356Z
Altcode:
  The dependence of the properties of solar magnetic elements on the
  magnetic filling factor is studied using Stokes V spectra of three
  lines observed near the center of the solar disk. The inversion
  technique developed by Keller et al. (1990) is applied to three
  neighboring spectral lines, and the average temperature difference,
  the magnetic field strength, and the nonstationary velocity in the
  relevant line-forming layers are quantitatively determined. Quantitative
  evidence is provided for the dependence of the temperature within
  flux tubes on the amount of magnetic flux. The flux tubes are found
  to become cooler and their field strengths, at a given optical depth,
  to become larger as the filling factor increases. The presence of
  kilogauss field strengths within flux tubes is reconfirmed.

Title: The influence of vertical magnetic field gradients on the
    measured field strength and filling factor in late-type stars.
Authors: Grossmann-Doerth, U.; Solanki, S. K.
Bibcode: 1990A&A...238..279G
Altcode:
  The influence of a vertical gradient of the magnetic field in late type
  stars on the measurement of magnetic field strengths and filling factors
  is studied. Line profiles and contribution functions of spectral lines
  with large Lande factors are calculated in model stellar atmospheres in
  the presence of a magnetic field with a vertical gradient. It is found
  that the four lines, which have often been used to measure solar and
  stellar magnetic fields in the past, are formed at heights sufficiently
  different to account for differences in apparent field strength of up
  to 1000 G if the fields are assumed to be similarly structured as in
  the sun. Thus it is concluded that the vertical gradient of the field
  may contribute to a good part of the discrepancy between different
  published measurements of field strength and filling factor in the K2
  dwarf Epsilon-Eri.

Title: Solar magnetic field strength determinations from high spatial
    resolution filtergrams
Authors: Keller, C. U.; Stenflo, J. O.; Solanki, S. K.; Tarbell,
   T. D.; Title, A. M.
Bibcode: 1990A&A...236..250K
Altcode:
  Circularly polarized images with high spatial resolution (better than 1
  arcsec) of a solar active region, obtained with a tunable filter in the
  wings of Fe I 5247.1 A and Fe I 5250.2 A, have been analyzed in terms of
  the magnetic line ratio technique introduced by Stenflo (1973). Whenever
  a measurable amount of polarization is present, the distribution of
  the observed magnetic-line ratio is compatible with a unique value,
  which is randomly blurred by noise due to the photon statistics,
  the CCD camera, and atmospheric distortions. There is no need for a
  distribution of field strengths to explain the observed distribution of
  the magnetic line ratio. Consequently, the observations are compatible
  with a unique magnetic field strength in solar small-scale magnetic
  elements of about 1000 G at the level of line formation. For a thin
  flux tube, this corresponds to a field strength of approximately 2000
  G at the level of continuum formation, which is in excellent agreement
  with previous field strength determinations from low spatial resolution
  spectra (4-10 arcsec).

Title: How magnetic is the solar chromosphere?
Authors: Solanki, S. K.; Steiner, O.
Bibcode: 1990A&A...234..519S
Altcode:
  The lower solar chromosphere is thought to have a very inhomogeneous
  temperature structure, with hot magnetic flux tubes surrounded by cool
  (T less than 4000 K) nonmagnetic gas (Ayres et al., 1986). The effect
  of such a thermally bifurcated atmosphere on the structure of the
  magnetic field in the chromosphere is considered. It is shown that
  magnetic flux tubes expand much more rapidly if the atmosphere is
  thermally bifurcated than if it is homogeneous. They merge and form a
  magnetic canopy with an almost horizontal base which does not exceed
  approximately 800-1000 km above tau = 1, irrespective of the magnetic
  filling factor. Hence the middle and upper chromosphere is filled with
  a magnetic field almost everywhere on the sun. The consequences of this
  result both for the sun and for other late type stars are discussed.

Title: Structure of solar magnetic fluxtubes from the inversion of
    Stokes spectra at disk center
Authors: Keller, C. U.; Steiner, O.; Stenflo, J. O.; Solanki, S. K.
Bibcode: 1990A&A...233..583K
Altcode:
  The paper presents an inversion procedure that derives the temperature
  stratification, the turbulent velocity, and the magnetic field strength
  of the photospheric layers of small-scale magnetic fields from observed
  Stokes V spectra and the continuum intensity. The inversion is based
  on the determination of a small number of model flux parameters by a
  nonlinear least squares fitting algorithm. The minimization of the sum
  of the squared differences between observed and synthetic observables
  makes it possible to determine the temperature stratification and the
  magnetic field strength.

Title: Solar line asymmetries and the magnetic filling factor
Authors: Brandt, P. N.; Solanki, S. K.
Bibcode: 1990A&A...231..221B
Altcode:
  Results are presented of an analysis of high-quality Fourier transform
  spectrometer spectra obtained in facular regions near solar disk center
  having different amounts of magnetic flux or, equivalently, different
  filling factors, alpha. The line parameters (width, equivalent width,
  depth, bisector shape, and wavelength) of 32 spectral lines and their
  variation with alpha are studied. Line depth is seen to decrease with
  increasing filling factor for all the observed lines, while the line
  width increases, even after compensation has been made for the Zeeman
  broadening. For strong or temperature-insensitive lines the equivalent
  width stays practically unchanged, but decreases for weak lines. The
  findings are qualitatively explained by a decrease in the contrast
  between the upflow and downflow components of the nonmagnetic part
  of the atmosphere in active regions (abnormal granulation) coupled to
  either a decrease in the average temperature of the nonmagnetic part
  or a significant increase in small-scale velocity.

Title: Interesting lines in the infrared solar spectrum between 1.49
    and 1.8 microns
Authors: Solanki, S. K.; Biemont, E.; Muerset, U.
Bibcode: 1990A&AS...83..307S
Altcode:
  Lists are presented of two groups of spectral lines interesting for the
  study of solar and stellar magnetic fields, convection and atmospheric
  structure and appearing in the IR solar spectrum between 1.49 and
  1.8 microns. The first group contains 130 spectral lines judged to be
  relatively unblended from a visual inspection of the spectra, while the
  second is composed of 30 lines exhibiting large Stokes V amplitudes
  in a quiet network, region. Some interesting aspects of these lines
  are discussed. In particular, it is pointed out that blending due
  to magnetically unsplit spectral lines, such as telluric lines, can
  seriously affect all four Stokes parameters.

Title: Flux tube diagnostics based on infrared H-band lines.
Authors: Muglach, K.; Solanki, S. K.
Bibcode: 1990AGAb....5...45M
Altcode:
  No abstract at ADS

Title: Empirical Models of Photospheric Flux Tubes
Authors: Solanki, S. K.
Bibcode: 1990IAUS..138..103S
Altcode:
  No abstract at ADS

Title: The Observational Signature of Flux Tube Waves and an Upper
    Limit on the Energy Flux Transported by Them
Authors: Solanki, S. K.; Roberts, B.
Bibcode: 1990IAUS..138..259S
Altcode:
  No abstract at ADS

Title: Waves in solar photospheric flux tubes and their influence
    on the observable spectrum
Authors: Solanki, S. K.; Roberts, B.
Bibcode: 1990GMS....58..181S
Altcode:
  Linear calculations of undamped magnetoacoustic waves in thin solar
  magnetic flux tubes are presented and their influence on the Stokes
  V profiles of various iron lines is studied. This is a necessary
  first step for the diagnostics of the properties of flux tube waves,
  in particular the amount of energy transported by them into the upper
  atmosphere. It is shown that, with sufficiently high spatial resolution,
  observations can distinguish between standing and propagating waves
  on the basis of line parameters of photospheric spectral lines
  alone. Particular attention is given to exploring quantitative
  diagnostics for the wave amplitude, since it is currently the most
  important unknown parameter determining the energy flux carried by
  the waves. It is found that although this parameter can be derived
  relatively simply if the thermal fluctuations produced by the wave
  are ignored (i.e., for an isothermal wave), the task becomes much
  more complex for the more realistic case of a coupled variation of
  temperature and velocity.

Title: Quantitative explanation of Stokes V asymmetry in solar
    magnetic flux tubes
Authors: Solanki, S. K.
Bibcode: 1990GMS....58..185S
Altcode:
  A 2D flux-tube model of a solar magnetic element is presently used
  to calculate Stokes profiles of four spectral lines with various
  properties. This model, which uses empirically-derived temperature and
  magnetic field strength values, is able to reproduce the asymmetry
  between the blue and red Stokes V wings in addition to other line
  parameters observed near the disk center in solar active-region
  plages. The Stokes V symmetry is a straightforward consequence of
  the current view of magnetic elements that are embedded in cool,
  downflowing intergranular lanes, in the presence of large-amplitude
  nonstationary mass motions within magnetic elements.

Title: At what heights are spectral lines formed in solar magnetic
    flux tubes?
Authors: Larsson, B.; Solanki, S.; Grossmann-Doerth, U.
Bibcode: 1990nba..meet..169L
Altcode: 1990taco.conf..169L
  Illustrative examples, taken from a study of the formation of
  magnetically split lines in solar magnetic flux tubes, are presented. A
  particular interest is: in how the heights of formation depend on
  different flux tube parameters, like the magnetic field strength, the
  temperature and temperature gradient, as well as on line parameters,
  such as line strength, excitation potential and ionization stage. The
  result should help to improve the construction of empirical models
  of magnetic features and provide a new understanding of the spectral
  diagnostics used in the study of the solar magnetic field.

Title: The origin and the diagnostic capabilities of the Stokes V
    asymmetry observed in solar faculae and the network
Authors: Solanki, S. K.
Bibcode: 1989A&A...224..225S
Altcode:
  The origin of the Stokes V asymmetry observed near disk center
  in solar active regions and in the quiet network is studied with
  the help of a two-dimensional flux tube model of solar magnetic
  elements. It is shown that the observed relative area and amplitude
  asymmetry, the zero-crossing wavelengths, and the width of four Fe
  I and II Stokes V profiles belonging to lines with widely different
  properties can be reproduced relatively well within the framework
  of the model incorporating certain features. The sensitivity of the
  Stokes V asymmetry to the thermal and velocity structure in and around
  solar magnetic elements is also demonstrated. It is the Stokes V line
  parameter most sensitive to the atmosphere in the vicinity of magnetic
  elements, and can also become a powerful diagnostic of the mass motions
  inside the magnetic elements. Values of the temperature and velocity
  in the immediate surroundings of these elements at the height of line
  formation are derived for the first time.

Title: Stokes V asymmetry and shift of spectral lines
Authors: Grossmann-Doerth, U.; Schuessler, M.; Solanki, S. K.
Bibcode: 1989A&A...221..338G
Altcode:
  Further evidence is given for the interpretation of the observed
  unshifted and asymmetric Stokes V profiles in the solar atmosphere
  in terms of a magnetic flux concentration expanding with height and
  surrounded by a downflow. A general proof is given that a V profile
  originating in an atmosphere in which magnetic field and flow are
  spatially separated along the line of sight has a zero-crossing
  wavelength which is unshifted with respect to the rest wavelength of
  the line center. Heuristic considerations for the dependence of the
  asymmetry of Stokes V on Zeeman shift, Doppler shift, line width,
  and strength are described and confirmed by exploratory calculations.

Title: The internal magnetic field structure of solar magnetic
    elements
Authors: Solanki, S.; Zayer, I.; Stenflo, J. O.
Bibcode: 1989hsrs.conf..409S
Altcode:
  No abstract at ADS

Title: The internal magnetic distribution and the diameters of solar
    magnetic elements.
Authors: Zayer, I.; Solanki, S. K.; Stenflo, J. O.
Bibcode: 1989A&A...211..463Z
Altcode:
  A diagnostic is proposed for the horizontal distribution and vertical
  gradient of the magnetic field with spatially unresolved solar magnetic
  elements. Radiative transfer calculations are conducted to model the
  magnetic field structure, which is fitted to observational data from a
  Fourier transform spectrometer. It is found that a vertical gradient
  of the magnetic field strength must be present in solar magnetic
  fluxtubes and that, in the lower photosphere, the field strength inside
  the fluxtube must be horizontally nearly constant. The magnetic field
  strengths and gradients derived at the disk center satisfy observations
  near 0.6 microns, if the appropriate model fluxtube size is chosen.

Title: On the Analysis of Stokes J and V Profiles in the Infrared
Authors: Solanki, S. K.
Bibcode: 1989AGAb....3...20S
Altcode:
  No abstract at ADS

Title: Magnetic fields in late-type dwarfs : preliminary results
    from a multiline approach.
Authors: Mathys, G.; Solanki, S. K.
Bibcode: 1989A&A...208..189M
Altcode:
  Preliminary results of a multiline approach to the diagnosis of magnetic
  fields in late-type dwarfs are presented. The spectra of fours stars
  observed with the Coude Echelle Spectrometer of the European Southern
  Observatory are analyzed using the Stenflo-Lindegren technique, which
  permits empirical relations to be obtained between various parameters
  characterizing a statistical sample of observed line profiles and the
  atomic quantities pertaining to the corresponding transitions. These
  empirical relations are first tested on solar and stellar data and then
  interpreted with the help of a simple model of the line formation,
  and constraints on the magnetic field properties (mean strength,
  filling factor, thermodynamic properties of the magnetic regions
  compared to the nonmagnetic parts of the stellar surface) are derived.

Title: Magnetic fields in late-type dwarfs: Preliminary results from
    a multiline approach
Authors: Mathys, G.; Solanki, S. K.
Bibcode: 1988STIN...9019928M
Altcode:
  Results of a multiline approach to the diagnosis of magnetic fields in
  late-type dwarfs are presented. The spectra of four stars observed with
  the Coude echelle spectrometer of the European Southern Observatory are
  analyzed using the Stenflo-Lindegren technique, which permits empirical
  relations to be obtained between various parameters characterizing a
  statistical sample of observed line profiles and the atomic quantities
  pertaining to the corresponding transitions. These empirical relations
  are tested on solar and stellar data and interpreted with a simple model
  of the line formation. Constraints on the magnetic field properties
  (mean strength, filling factor, thermodynamic properties of the magnetic
  regions compared to the nonmagnetic parts of the stellar surface) are
  derived. In spite of the crudeness of approximations, the results are
  compatible with those obtained with other methods. The advantages of
  the Stenflo-Lindegren technique over other approaches are sketched.

Title: Unshifted, asymmetric Stokes V-profiles - Possible solution
    of a riddle
Authors: Grossmann-Doerth, U.; Schuessler, M.; Solanki, S. K.
Bibcode: 1988A&A...206L..37G
Altcode:
  We show that Stokes V-profiles originating in an atmosphere
  in which a magnetic field and a systematic velocity field are
  spatially separated along the line of sight are asymmetric with
  unshifted zero-crossings. Such a configuration is probably realized
  in the peripheral parts of magnetic flux concentrations in the solar
  photosphere: Since the magnetic field flares out with height, the line
  of sight traverses both a static magnetic region and a downdraft in
  the non-magnetic surroundings. V-profiles formed in these parts of the
  flux concentation will be strongly asymmetric but unshifted while the
  V-profiles from the central parts are symmetric and unshifted. The
  resulting mean V-profiles show the characteristics of the observed
  profiles, i.e. they are unshifted and asymmetric.

Title: Interpretation of broad band circular polarization measurements
    using Stokes V spectra
Authors: Muerset, U.; Stenflo, J. O.; Solanki, S. K.
Bibcode: 1988A&A...204..279M
Altcode:
  The wavelength dependence and the center to limb variation of the broad
  band circular polarization of solar active regions are determined by
  integrating over spectra with a large wavelength range obtained with a
  Fourier transform spectrometer (FTS). It is shown that the broad band
  circular polarization (BBC) is due mainly to the asymmetry of the Stokes
  V profiles. The approximate contributions of lines of different depths
  to the total broad band signal are analyzed. The diagnostic contents
  of BBC observations with low spatial resolution, such as those of
  Kemp et al. (1987), are discussed. These observations are reproduced
  with the help of simulated broad band polarization data obtained by
  integrating FTS spectra. It is shown that the spatial distribution
  of the net field on the solar surface (within a single large spatial
  resolution element) can affect the measured BBC signal considerably,
  and may even change its sign.

Title: Contribution and response functions for Stokes line profiles
    formed in a magnetic field
Authors: Grossmann-Doerth, U.; Larsson, B.; Solanki, S. K.
Bibcode: 1988A&A...204..266G
Altcode:
  Expressions defining the contribution functions of the 'line depression'
  Stokes profiles formed in a general magnetic field are derived. Such
  contribution functions are better suited to determining the heights at
  which the bound-bound transitions responsible for spectral lines are
  important than the contribution functions to the 'intensity' Stokes
  parameters defined by Van Ballegooijen (1985). Expressions defining
  response functions for both 'intensity' and 'line depression' Stokes
  parameters are also derived for an arbitrary atmosphere and magnetic
  field. A code for calculating the various Stokes contribution functions
  is described and some example calculations are presented. These clearly
  demonstrate the superior diagnostic value of the contribution functions
  to the 'line depression' Stokes profiles.

Title: Can stationary velocity fields explain the Stokes V asymmetry
    observed in solar magnetic elements?
Authors: Solanki, S. K.; Pahlke, K. D.
Bibcode: 1988A&A...201..143S
Altcode:
  A mechanism for producing the observed asymmetry between the amplitudes
  and areas of the blue and red wings of Stokes V profiles, which
  is based on velocity gradients, is explored. It is found that the
  velocity gradients do not produce a Stokes V area asymmetry in very
  weak lines. A stationary velocity gradient is neither able to reproduce
  the observed asymmetry of lines of different strengths and excitation
  potentials nor simultaneously reproduce the widths and asymmetries
  of strong lines. If the asymmetries of Fe I 5250.2 A, Fe I 6301.5 A,
  and Fe I 6302.5 A are reproduced, it is shown that their zero crossing
  wavelengths are too strongly redshifted as compared to observations.

Title: Magnetic field strength in solar flux tubes - A model
    atmosphere independent determination
Authors: Sanchez Almeida, J.; Collados, M.; del Toro Iniesta, J. C.;
   Solanki, S. K.
Bibcode: 1988A&A...196..266S
Altcode:
  The "line ratio method" (Stenflo, 1973) has been extensively used in
  the past to carry out measurements of the magnetic field strength in
  spatially unresolved magnetic flux concentrations. The authors present
  here a new variant of this technique, which is particularly simple as
  it does not depend on any radiative transfer calculations and thus the
  assumption of a model atmosphere is not required. General properties
  of the transfer equation lead to a relationship between the circular
  polarization generated by two lines which are identical except for
  their Landé factors. This can be used to directly determine the field
  strength from the measured line profiles. In order to test the method
  the authors have applied it to experimental data. A comparison with
  the traditional line ratio method is shown.

Title: Continuum intensity of magnetic flux concentrations - Are
    magnetic elements bright points?
Authors: Schuessler, M.; Solanki, S. K.
Bibcode: 1988A&A...192..338S
Altcode:
  The authors use the weakening of temperature sensitive spectral
  lines (Fe I λ5250.2 and λ5247.1) in a strong plage region to
  derive a lower limit (≈1.4 of the quiet photospheric value) for the
  continuum intensity in magnetic flux concentrations. This suggests an
  identification of magnetic elements with the observed photospheric
  bright points. The authors discuss the implications of this result
  for the quantitative determination of magnetic flux and propose a
  procedure for obtaining information on the physical structure of the
  non-magnetic surroundings of flux concentrations.

Title: Magnetic Field of Late-Type Stars : a New Approach
Authors: Mathys, G.; Solanki, S. K.
Bibcode: 1988IAUS..132..325M
Altcode:
  Magnetic field diagnosis in three late-type stars is performed using
  the multiline technique originally developed by Stenflo and Lindegren
  (1977) to study spatially unresolved magnetic features on the sun.

Title: A new technique for the measurement of stellar magnetic fields:
    First Results
Authors: Solanki, S. K.; Mathys, G.
Bibcode: 1988ASSL..143...39S
Altcode: 1988acse.conf...39S
  A technique for determining strengths and filling factors of stellar
  magnetic fields is presented. It is based on a statistical analysis
  of a large number of unblended Fe I lines and was first introduced
  by Stenflo and Lindegren (1977). It has been tested in solar active
  regions and is now applied to late type stars. First results of an
  analysis of high S/N spectra of three stars are presented and compared
  to previous measurements.

Title: Velocity and temperature in solar magnetic fluxtubes from a
    statistical centre-to-limb analysis
Authors: Pantellini, F. G. E.; Solanki, S. K.; Stenflo, J. O.
Bibcode: 1988A&A...189..263P
Altcode:
  Stokes I and V profiles of a large number of unblended Fe I
  lines observed at different positions on the solar disk have
  been analyzed. Asymmetries in the Stokes V profile are noted. The
  center-to-limb variation of the zero-crossing wavelength of the weak
  and medium strong lines is found to be consistent with the absence of
  stationary flows in fluxtubes. The stronger lines are shown to be more
  blueshifted than the weak ones at all limb distances. The fluxtube
  temperature structure is confirmed to be a function of the filling
  factor. The rms velocity amplitude is found to increase somewhat when
  approaching the limb, in contrast to what would be expected if the
  mass motions were mostly vertical.

Title: NLTE effects in solar magnetic fluxtubes
Authors: Solanki, S. K.; Steenbock, W.
Bibcode: 1988A&A...189..243S
Altcode:
  NLTE calculations of approximately 200 Fe I and Fe II spectral lines
  with a comprehensive model atom are presented for a quiet sun model
  and a grid of fluxtube models. These calculations are compared with
  LTE results and the departures from LTE in fluxtubes are estimated. For
  all the fluxtube models tested, the departures from LTE ionization for
  the Fe I lines are found to be larger than for the quiet sun. Fe II
  lines show almost no difference between LTE and NLTE. The influence
  of temperature gradients on the departures is also studied and
  discussed. The profiles of five Fe I and one Fe II lines are analyzed
  in detail and the errors in empirically determined velocities and
  temperatures in fluxtubes, introduced by the assumption of LTE, are
  estimated. It is found that assuming LTE has practically no effect on
  the determined velocities, but that it may lead to an overestimation
  of the temperature in fluxtubes at the heights at which the lines
  are formed.

Title: Properties of solar magnetic fluxtubes from only two spectral
    lines
Authors: Solanki, S. K.; Keller, C.; Stenflo, J. O.
Bibcode: 1987A&A...188..183S
Altcode:
  A method for the determination of the magnetic field strength,
  velocity, and temperatures inside solar flux tubes, in addition to
  their inclinations and filling factors, is presented which requires
  only the Stokes V and Q profiles of the Fe I 5250.2 A and Fe I 5247.1
  A spectral lines. Application of the procedure to spectra of the two
  lines obtained at various distances from the solar limb shows that
  considerable velocity broadening is required at all positions on the
  disk in order to reproduce the polarimeter data. The center to limb
  variation of the 5250/5247 Stokes V and Q line ratios is found to
  contain little information on the height variation of the magnetic
  field in the context of one-dimensional models.

Title: The Photospheric Layers of Solar Magnetic Flux Tubes
Authors: Solanki, S. K.
Bibcode: 1987PhDT.......251S
Altcode:
  This thesis is concerned with the structure and properties of magnetic
  fluxtubes in the solar photosphere. After a brief introduction outlining
  the importance of magnetic fields for the Sun and the stars, with
  particular emphasis on the role of fluxtubes, a brief description
  of polarised light, its properties, production, radiative transfer
  and measurement is given. There follows an overview of spectroscopy
  and polarimetry with a Fourier transform spectrometer (FTS). The data
  forming the basis of the thesis, FTS spectra of Stokes I, V, and partly
  also Q in the visible and the infrared (1.5-1.7μm), are described. The
  analysis procedure is partly based on the weak-field approximation,
  which is used to determine an approximation of the magnetically
  unsplit Stokes I inside the fluxtubes. The lines to be analysed (a
  set of 450 unblended Fe lines) are listed and their effective Landé
  factors are determined from laboratory measurements. The line profiles
  are parameterised and a statistical analysis of these parameters is
  carried out. Line of sight bulk and turbulent velocities, temperatures
  and the magnetic field in magnetic fluxtubes are determined, partly
  directly from the measured profiles, but partly on the basis of
  radiative transfer calculations in model fluxtubes. It is shown that
  fluxtubes do not harbour significant net flows and that fluxtubes in
  the network are on average hotter than those in plage regions. Finally,
  MHD models of cylindrically symmetric fluxtubes are presented. The
  effects of magnetic tension are included. A self-consistent formalism
  is developed to take the influence of neighbouring fluxtubes into
  account. The dependence of the merging height on various parameters
  of the fluxtubes is discussed. It is shown that the thin fluxtube
  approximation is quite reliable for fluxtubes with radii less than
  approximately 100 km near the solar surface.

Title: Diagnostics of solar magnetic fluxtubes with the infrared
    line Fe I lambda 15648.54 A
Authors: Stenflo, J. O.; Solanki, S. K.; Harvey, J. W.
Bibcode: 1987A&A...173..167S
Altcode:
  Fourier Transform Spectrometer recordings of May 1984 have been used to
  explore the center-to-limb variation of the Stokes I, V, and Q profiles
  of the solar infrared Fe I line at 15,648.54 A. The aim is to examine
  the new possibilities offerred for the diagnostics of the spatially
  unresolved magnetic flux tubes on the sun when lines with complete
  Zeeman splitting are used. Comparison is made with the line-ratio
  method, which must be used at visible wavelengths, where the splitting
  is incomplete. The Stokes V asymmetries observed in the infrared line
  are small or even of opposite sign as compared with the corresponding
  asymmetries observed at visible wavelengths. This suggests that the
  time-averaged height gradient of the Doppler velocities inside the
  fluxtubes becomes small and may change its sign when moving down to
  the bottom of the fluxtube photosphere.

Title: The photospheric layers of solar magnetic fluxtubes
Authors: Solanki, Sami Khan
Bibcode: 1987PhDT.......295S
Altcode:
  No abstract at ADS

Title: Center-to-limb variation of Stokes profiles and the diagnostics
    of solar magnetic fluxtubes
Authors: Stenflo, J. O.; Solanki, S. K.; Harvey, J. W.
Bibcode: 1987A&A...171..305S
Altcode:
  Simultaneous recordings of the Stokes I, Q, and V spectra have been
  performed with a Fourier transform spectrometer in 10 solar regions
  distributed over various center-to-limb distances, from disk center
  to the extreme limb. The observational material and the recording
  technique used are presented. The authors then evaluate the Stokes
  profile parameters for a small selected set of spectral lines to explore
  the potential of this qualitatively new data set for the diagnostics
  of spatially unresolved magnetic fluxtubes.

Title: Magnetic fields: observations and theory.
Authors: Solanki, S. K.
Bibcode: 1987PAICz..66...95S
Altcode: 1987eram....1...95S
  Theoretical model calculations of magnetic elements in the photospheric
  layers of solar active regions are compared with the results of
  observations.

Title: Structure of Magnetic Flux tubes as derived from Observations
    with Moderate Spatial Resolution
Authors: Solanki, S. K.
Bibcode: 1987rfsm.conf...67S
Altcode:
  Motions with large amplitudes and probably a vertical velocity gradient
  are present in the fluxtubes or their immediate surroundings. The exact
  nature of such motions is unknown. Candidates are: stationary up-
  and downflows in different fluxtubes, so that on the average little
  vertical mass transfer takes place. Oscillations or waves in fluxtubes
  are another possibility, whereby these motions are not in phase in
  different fluxtubes. Finally, due to the geometry of the fluxtubes
  (expansion with height), it is possible that motions in their immediate
  surroundings may also affect Stokes V.

Title: Intensity profiles in fluxtubes.
Authors: Sanches Almeida, J.; Collados, M.; del Toro Iniesta, J. C.;
   Solanki, S. K.
Bibcode: 1987PAICz..66..261S
Altcode: 1987eram....1..261S
  Spectroscopic analysis of the light coming from an atmosphere is a
  powerful tool for revealing its properties. The problem when using
  conventional spectroscopy for solar fluxtubes is their unresolved
  character: magnetic and non-magnetic regions of a plage have to be
  observed as a whole. With the aim of obtaining the true intensity
  spectrum of an unresolved tube, the authors have developed a simple
  method which can reconstruct the intensity generated in the magnetic
  component. Only observed parameters are used: intensity and circular
  polarization in the plage and intensity in the quiet photosphere.

Title: FTS Measurements of Solar Line Asymmetries in Quiet and
    Active Regions
Authors: Brandt, P. N.; Solanki, S. K.
Bibcode: 1987rfsm.conf...82B
Altcode:
  Spatially averaged Fourier transform spectra (FTS) with their well known
  high spectral resolution, their highly symmetric apparatus profile,
  low scattered light and high S/N ratio can be used as a complementing
  tool for the diagnosis of atmospheric parameters. The possibility to use
  many lines measured strictly simultaneously and covering a wide range
  of excitation potentials, heights of formation etc. represents another
  advantage of the FTS and at the same time reduces possible errors due
  to line blending. The main motivation for the present investigation of
  plage versus quiet sun line profiles came from the exciting results
  by Livingston &amp; Holweger (1982) and by Livingston (1983) on the
  possible cycle dependence of line equivalent widths and asymmetries,
  as measured in integrated sunlight. Preliminary results are given.

Title: Some effects of finite spectral resolution on the Stokes
    V profile
Authors: Solanki, S. K.; Stenflo, J. O.
Bibcode: 1986A&A...170..120S
Altcode:
  The authors consider some general effects of spectral smearing on the
  Stokes V profile of the Fe I 5250.2 Å line, as observed on the sun with
  a Fourier transform spectrometer at a very high spectral resolution. The
  effects of low spectral resolution are numerically simulated by
  convoluting the observed line profiles with model instrumental
  profiles. The authors also try to find some Stokes V parameters which
  are insensitive to the spectral resolution. Finally, they show that
  the large Stokes V zero-crossing wavelength shifts observed by Wiehr
  (1985) and by Scholier and Wiehr (1985) from complete profiles, and
  by Giovanelli and Slaughter (1978) with the line-centre-magnetogram
  technique of Giovanelli and Ramsey (1971) are compatible with the
  results of Stenflo and Harvey (1985) and Solanki (1985, 1986).

Title: Velocities in solar magnetic fluxtubes.
Authors: Solanki, S. K.
Bibcode: 1986A&A...168..311S
Altcode:
  Stokes V zero-crossing wavelengths and I(V) profiles of a large number
  of unblended Fe I and II lines are used to study the velocities in
  solar magnetic flux tubes. No net flows are seen in the photospheric
  layers of flux tubes at disk center in both active region plages
  and the quiet network. Stokes V zero-crossing wavelength shifts
  relative to the wavelengths of the Stokes I profiles do not support
  the presence of downflows inside flux tubes. One dimensional LTE model
  calculations are used to show that the observed line profiles formed
  inside a flux tube can only be reproduced if the model profiles are
  broadened by velocity. The dependence of the total turbulent velocity
  on line strength in the flux tube is found to differ strongly from
  its dependence in the quiet photosphere.

Title: Lines in the wavelength range λλ 4300 6700 Å with large
    stokes V amplitudes outside sunspots
Authors: Solanki, S. K.; Pantellini, F. G. E.; Stenflo, J. O.
Bibcode: 1986SoPh..107...57S
Altcode: 1987SoPh..107...57S
  A list of solar spectral lines in the wavelength λλ 4300-6700 å
  exhibiting large Stokes V amplitudes in observed spectra of active
  region plages and the quiet network is presented.

Title: Can velocity gradients explain the observed Stokes V asymmetry
    in the absence of large zero-crossing shifts?
Authors: Pahlke, K. D.; Solanki, S. K.
Bibcode: 1986MitAG..65..162P
Altcode:
  No abstract at ADS

Title: Structure and merging of solar magnetic fluxtubes
Authors: Pneuman, G. W.; Solanki, S. K.; Stenflo, J. O.
Bibcode: 1986A&A...154..231P
Altcode:
  In the present, expansion technique-based model of the solar
  atmosphere's magnetic flux tubes, account is taken of the effects of
  field line curvature, internal structural variations, and the merging
  of the tube with its contiguous neighbors as it expands (through the
  use of a small 'seed' magnetic field between the tubes that has no
  influence on the solution in the limit of vanishing strength). For the
  solutions obtained, the internal magnetic structure of the tube evolves
  in height in a nonself-similar manner, although the gas pressure can
  vary self-similarly for the special case in which internal temperature
  is both uniform and equal to the external temperature. In the vicinity
  of the merging height, the field approaches uniformity consistent with
  a vertical tube with constant cross section.

Title: High Spectral Resolution and Properties of Small Magnetic
    Flux Tubes
Authors: Solanki, S. K.
Bibcode: 1985tphr.conf..172S
Altcode:
  No abstract at ADS

Title: Models of solar magnetic fluxtubes - Constraints imposed by
    Fe I and II lines
Authors: Solanki, S. K.; Stenflo, J. O.
Bibcode: 1985A&A...148..123S
Altcode:
  The diagnostic contents of the Stokes I and V profiles of about 50
  unblended Fe II lines have been explored and used to set new constraints
  on the temperature structure of magnetic fluxtubes. The simultaneous use
  of Fe I and II lines makes it possible to determine the temperature in
  both the upper and lower fluxtube photosphere. The Fe II lines further
  make it possible to obtain model-insensitive values of the magnetic
  filling factors. Empirically determined effective Lande factors of most
  of the unblended iron lines in the visible part of the solar spectrum
  are presented and compared with the corresponding LS coupling values.

Title: High spectral resolution and properties of small magnetic
    fluxtubes.
Authors: Solanki, S. K.
Bibcode: 1985MPARp.212..172S
Altcode:
  Some empirical results pertaining to properties of small magnetic
  fluxtubes are described. Using data obtained with a Fourier transform
  spectrometer it has been possible to set constraints on the temperature
  structure of fluxtubes, on the types of mass motions and velocities
  inside them, and on the magnetic field strength near their τ = 1
  level. The Stokes V asymmetries observed in fluxtube spectra are also
  discussed and evidence is presented favouring the hypothesis that they
  are produced by velocities.

Title: Can Velocity Gradients Explain the Observed Stokes V Asymmetry
    in the Absence of Large Zero-Crossing Shifts?
Authors: Pahlke, K. D.; Solanki, S. K.
Bibcode: 1985MitAG..65..162P
Altcode:
  No abstract at ADS

Title: The photospheric temperature structure of magnetic fluxtubes.
Authors: Solanki, S. K.
Bibcode: 1984ESASP.220...63S
Altcode: 1984ESPM....4...63S
  The temperature stratifications of plage and network fluxtubes are
  determined by comparing a large number of observed Fe I and Fe II lines
  with LTE model calculations. The data are also compared with profiles
  published in the literature. It is shown that in order to reproduce the
  data correctly, a sharp dip in the fluxtube temperature must occur in
  the photosphere, where the temperature of fluxtube and surroundings
  become similar (at equal optical depth). The effects of different
  pressure stratifications on the depths of the iron lines are briefly
  discussed and it is shown that the pressure stratification giving the
  best agreement with the data corresponds to a rapid expansion of the
  fluxtube near the height at which the temperature dip occurs.

Title: Properties of solar magnetic fluxtubes as revealed by Fe
    I lines
Authors: Solanki, S. K.; Stenflo, J. O.
Bibcode: 1984A&A...140..185S
Altcode:
  The information contents in the solar spectrum for modelling of magnetic
  fluxtubes is explored by analysing the statistical properties of the
  Stokes I and V line profiles of 400 unblended Fe I lines. Methods of
  determining the temperature structure, photospheric magnetic field
  strength, magnetic filling factor, and microturbulence velocity are
  presented and used to provide estimates of these quantities in enhanced
  network and plage regions. Analysis of the magnetic line broadening
  shows that the magnetic field strength is approximately equal in network
  and plage regions, consistent with previous results. On the other hand,
  the temperature structures of the plage fluxtubes and the network
  elements are observed to be substantially different. The variation
  of the Stokes V line asymmetries with line strength are found to be
  similar in the different solar regions, indicating similar velocity
  structures in plages and network elements.

Title: Diagnostics of solar magnetic fluxtubes using a Fourier
    transform spectrometer
Authors: Stenflo, J. O.; Solanki, S.; Harvey, J. W.; Brault, J. W.
Bibcode: 1984A&A...131..333S
Altcode:
  An overview is presented of the diagnostic contents for fluxtube
  modelling of Fourier transform spectrometer recordings of the
  longitudinal Zeeman effect near the solar disk center made in
  April 1979. The observations and data reductions are summarized
  and the application of the weak-field model to the Stokes profiles
  is examined. The significance of telluric lines and blends and the
  validity of LS coupling are considered. The magnetic fluxes, intrinsic
  field strengths, and area factors are discussed and the thermodynamic
  properties of fluxtubes are addressed. Mass motions inside the fluxtubes
  and the height variation of fluxtube parameters are considered.

