Author name code: jurcak
ADS astronomy entries on 2022-09-14
author:"Jurcak, Jan" 
------------------------------------------------------------------------  

Title: The European Solar Telescope
Authors: Quintero Noda, C.; Schlichenmaier, R.; Bellot Rubio, L. R.;
   Löfdahl, M. G.; Khomenko, E.; Jurcak, J.; Leenaarts, J.; Kuckein,
   C.; González Manrique, S. J.; Gunar, S.; Nelson, C. J.; de la Cruz
   Rodríguez, J.; Tziotziou, K.; Tsiropoula, G.; Aulanier, G.; Collados,
   M.; the EST team
Bibcode: 2022arXiv220710905Q
Altcode:
  The European Solar Telescope (EST) is a project aimed at studying
  the magnetic connectivity of the solar atmosphere, from the deep
  photosphere to the upper chromosphere. Its design combines the knowledge
  and expertise gathered by the European solar physics community during
  the construction and operation of state-of-the-art solar telescopes
  operating in visible and near-infrared wavelengths: the Swedish 1m Solar
  Telescope (SST), the German Vacuum Tower Telescope (VTT) and GREGOR,
  the French Télescope Héliographique pour l'Étude du Magnétisme
  et des Instabilités Solaires (THÉMIS), and the Dutch Open Telescope
  (DOT). With its 4.2 m primary mirror and an open configuration, EST will
  become the most powerful European ground-based facility to study the Sun
  in the coming decades in the visible and near-infrared bands. EST uses
  the most innovative technological advances: the first adaptive secondary
  mirror ever used in a solar telescope, a complex multi-conjugate
  adaptive optics with deformable mirrors that form part of the optical
  design in a natural way, a polarimetrically compensated telescope design
  that eliminates the complex temporal variation and wavelength dependence
  of the telescope Mueller matrix, and an instrument suite containing
  several (etalon-based) tunable imaging spectropolarimeters and several
  integral field unit spectropolarimeters. This publication summarises
  some fundamental science questions that can be addressed with the
  telescope, together with a complete description of its major subsystems.

Title: Characterization of magneto-convection in sunspots. The
    Gough-Tayler stability criterion in MURaM sunspot simulations
Authors: Schmassmann, M.; Rempel, M.; Bello González, N.;
   Schlichenmaier, R.; Jurčák, J.
Bibcode: 2021A&A...656A..92S
Altcode:
  Context. Observations have shown that in stable sunspots, the umbral
  boundary is outlined by a critical value of the vertical magnetic
  field component. However, the nature of the distinct magnetoconvection
  regimes in the umbra and penumbra is still unclear. <BR /> Aims: We
  analyse a sunspot simulation in an effort to understand the origin
  of the convective instabilities giving rise to the penumbral and
  umbral distinct regimes. <BR /> Methods: We applied the criterion
  from Gough &amp; Tayler (1966, MNRAS, 133, 85), accounting for the
  stabilising effect of the vertical magnetic field, to investigate
  the convective instabilities in a MURaM sunspot simulation. <BR />
  Results: We find: (1) a highly unstable shallow layer right beneath the
  surface extending all over the simulation box in which convection is
  triggered by radiative cooling in the photosphere; (2) a deep umbral
  core (beneath −5 Mm) stabilised against overturning convection
  that underlies a region with stable background values permeated
  by slender instabilities coupled to umbral dots; (3) filamentary
  instabilities below the penumbra nearly parallel to the surface and
  undulating instabilities coupled to the penumbra which originate
  in the deep layers. These deep-rooted instabilities result in the
  vigorous magneto-convection regime characteristic of the penumbra; (4)
  convective downdrafts in the granulation, penumbra, and umbra develop
  at about 2 km s<SUP>−1</SUP>, 1 km s<SUP>−1</SUP>, and 0.1 km
  s<SUP>−1</SUP>, respectively, indicating that the granular regime of
  convection is more vigorous than the penumbra convection regime, which,
  in turn, is more vigorous than the close-to-steady umbra; (5) the GT
  criterion outlines both the sunspot magnetopause and peripatopause,
  highlighting the tripartite nature of the sub-photospheric layers
  of magnetohydrodynamic (MHD) sunspot models; and, finally, (6)
  the Jurčák criterion is the photospheric counterpart of the GT
  criterion in deep layers. <BR /> Conclusions: The GT criterion as a
  diagnostic tool reveals the tripartite nature of sunspot structure
  with distinct regimes of magneto-convection in the umbra, penumbra,
  and granulation operating in realistic MHD simulations. <P
  />Movies associated with Figs. 2 and 3 are available at <A
  href="https://www.aanda.org/10.1051/0004-6361/202141607/olm">https://www.aanda.org</A>

Title: Properties of the inner penumbra boundary and temporal
    evolution of a decaying sunspot (Corrigendum)
Authors: Benko, M.; González Manrique, S. J.; Balthasar, H.; Gömöry,
   P.; Kuckein, C.; Jurčák, J.
Bibcode: 2021A&A...652C...7B
Altcode:
  No abstract at ADS

Title: Magnetic properties on the boundary of an evolving pore
Authors: García-Rivas, M.; Jurčák, J.; Bello González, N.
Bibcode: 2021A&A...649A.129G
Altcode: 2021arXiv210208459G
  Context. Analyses of the magnetic properties on umbrae boundaries
  have led to the Jurčák criterion, which states that umbra-penumbra
  boundaries in stable sunspots are equally defined by a constant value
  of the vertical magnetic field, B<SUB>ver</SUB><SUP>crit</SUP>, and by
  a 50% continuum intensity of the quiet Sun, I<SUB>QS</SUB>. Umbrae with
  vertical magnetic fields stronger than B<SUB>ver</SUB><SUP>crit</SUP>
  are stable, whereas umbrae with vertical magnetic fields weaker than
  B<SUB>ver</SUB><SUP>crit</SUP> are unstable and prone to vanishing. <BR
  /> Aims: We aim to investigate the existence of a critical value of
  the vertical magnetic field on a pore boundary and its role in the
  evolution of the magnetic structure. <BR /> Methods: We analysed
  SDO/HMI vector field maps corrected for scattered light and with a
  temporal cadence of 12 min during a 26.5-hour period. A continuum
  intensity threshold (I<SUB>c</SUB> = 0.55 I<SUB>QS</SUB>) is used to
  define the pore boundary and we study the temporal evolution of the
  magnetic properties there. <BR /> Results: We observe well-defined
  stages in the pore evolution: (1) during the initial formation
  phase, total magnetic field strength (B) and vertical magnetic field
  (B<SUB>ver</SUB>) increase to their maximum values of ∼1920 G and
  ∼1730 G, respectively; (2) then the pore reaches a stable phase;
  (3) in a second formation phase, the pore undergoes a rapid growth
  in terms of size, along with a decrease in B and B<SUB>ver</SUB> on
  its boundary. In the newly formed area of the pore, B<SUB>ver</SUB>
  remains mostly below 1731 G and B remains everywhere below 1921 G;
  (4) ultimately, pore decay starts. We find overall that pore areas with
  B<SUB>ver</SUB> &lt; 1731 G, or equivalently B &lt; 1921 G, disintegrate
  faster than regions that fulfil this criteria. <BR /> Conclusions:
  We find that the most stable regions of the pore, similarly to the
  case of umbral boundaries, are defined by a critical value of the
  vertical component of the magnetic field that is comparable to that
  found in stable sunspots. In addition, in this case study, the same
  pore areas can be similarly well-defined by a critical value of the
  total magnetic field strength.

Title: Evaluating the Reliability of a Simple Method to Map the
    Magnetic Field Azimuth in the Solar Chromosphere
Authors: Jurčák, Jan; Štěpán, Jiří; Trujillo Bueno, Javier
Bibcode: 2021ApJ...911...23J
Altcode: 2021arXiv210202880J
  The Zeeman effect is of limited utility for probing the magnetism
  of the quiet solar chromosphere. The Hanle effect in some spectral
  lines is sensitive to such magnetism, but the interpretation of the
  scattering polarization signals requires taking into account that the
  chromospheric plasma is highly inhomogeneous and dynamic (i.e., that
  the magnetic field is not the only cause of symmetry breaking). Here
  we investigate the reliability of a well-known formula for mapping the
  azimuth of chromospheric magnetic fields directly from the scattering
  polarization observed in the Ca II 8542 Å line, which is typically
  in the saturation regime of the Hanle effect. To this end, we use
  the Stokes profiles of the Ca II 8542 Å line computed with the PORTA
  radiative transfer code in a three-dimensional (3D) model of the solar
  chromosphere, degrading them to mimic spectropolarimetric observations
  for a range of telescope apertures and noise levels. The simulated
  observations are used to obtain the magnetic field azimuth at each
  point of the field of view, which we compare with the actual values
  within the 3D model. We show that, apart from intrinsic ambiguities,
  the method provides solid results. Their accuracy depends more on
  the noise level than on the telescope diameter. Large-aperture solar
  telescopes, like DKIST and EST, are needed to achieve the required
  polarimetric sensitivity using reasonable exposure times.

Title: Solar pores - A magnetic evolution laboratory
Authors: García-Rivas, M.; Jurčák, J.; Bello González, N.
Bibcode: 2020sea..confE.198G
Altcode:
  Analyses of the vector magnetic field on solar magnetic structures led
  to the Jurčák criterion, an empirical law that connects a critical
  value of the vertical component of the magnetic field to the umbral
  magnetoconvective mode in stable sunspots. We study the evolution of the
  vertical component of the magnetic field (B<SUB>ver</SUB>) on evolving
  pores and the existence of an equivalent critical vertical magnetic
  value to provide steadiness. Indeed, we find that areas with weak
  B<SUB>ver</SUB> are unstable and granulation takes over them. However,
  areas with strong B<SUB>ver</SUB> show longer lifetimes.

Title: A distinct magnetic property of the inner penumbral
    boundary. III. Analysis of simulated sunspots
Authors: Jurčák, Jan; Schmassmann, Markus; Rempel, Matthias; Bello
   González, Nazaret; Schlichenmaier, Rolf
Bibcode: 2020A&A...638A..28J
Altcode: 2020arXiv200403940J
  Context. Analyses of sunspot observations revealed a fundamental
  magnetic property of the umbral boundary: the invariance of the
  vertical component of the magnetic field. <BR /> Aims: We analyse
  the magnetic properties of the umbra-penumbra boundary in simulated
  sunspots and thus assess their similarity to observed sunspots. We
  also aim to investigate the role of the plasma β and the ratio of
  kinetic to magnetic energy in simulated sunspots in the convective
  motions because these quantities cannot be reliably determined from
  observations. <BR /> Methods: We used a set of non-gray simulation
  runs of sunspots with the MURaM code. The setups differed in terms
  of subsurface magnetic field structure and magnetic field boundary
  imposed at the top of the simulation domain. These data were used to
  synthesize the Stokes profiles, which were then degraded to the Hinode
  spectropolarimeter-like observations. Then, the data were treated
  like real Hinode observations of a sunspot, and magnetic properties
  at the umbral boundaries were determined. <BR /> Results: Simulations
  with potential field extrapolation produce a realistic magnetic field
  configuration on the umbral boundaries of the sunspots. Two simulations
  with a potential field upper boundary, but different subsurface
  magnetic field structures, differ significantly in the extent of their
  penumbrae. Increasing the penumbra width by forcing more horizontal
  magnetic fields at the upper boundary results in magnetic properties
  that are not consistent with observations. This implies that the size of
  the penumbra is given by the subsurface structure of the magnetic field,
  that is, by the depth and inclination of the magnetopause, which is
  shaped by the expansion of the sunspot flux rope with height. None of
  the sunspot simulations is consistent with the observed properties of
  the magnetic field and the direction of the Evershed flow at the same
  time. Strong outward-directed Evershed flows are only found in setups
  with an artificially enhanced horizontal component of the magnetic
  field at the top boundary that are not consistent with the observed
  magnetic field properties at the umbra-penumbra boundary. We stress
  that the photospheric boundary of simulated sunspots is defined by a
  magnetic field strength of equipartition field value.

Title: Exploiting Solar Visible-Range Observations by Inversion
Techniques: From Flows in the Solar Subsurface to a Flaring Atmosphere
Authors: Švanda, Michal; Jurčák, Jan; Korda, David; Kašparová,
   Jana
Bibcode: 2020rfma.book..349S
Altcode:
  Observations of the Sun in the visible spectral range belong to standard
  measurements obtained by instruments both on the ground and in the
  space. Nowadays, both nearly continuous full-disc observations with
  medium resolution and dedicated campaigns of high spatial, spectral
  and/or temporal resolution constitute a holy grail for studies that
  can capture (both) the long- and short-term changes in the dynamics
  and energetics of the solar atmosphere. Observations of photospheric
  spectral lines allow us to estimate not only the intensity at small
  regions, but also various derived data products, such as the Doppler
  velocity and/or the components of the magnetic field vector. We show
  that these measurements contain not only direct information about the
  dynamics of solar plasmas at the surface of the Sun but also imprints
  of regions below and above it. Here, we discuss two examples: First,
  the local time-distance helioseismology as a tool for plasma dynamic
  diagnostics in the near subsurface and second, the determination of
  the solar atmosphere structure during flares. The methodology in both
  cases involves the technique of inverse modelling.

Title: Chromospheric Heating by Acoustic Waves Compared to Radiative
    Cooling. II. Revised Grid of Models
Authors: Abbasvand, Vahid; Sobotka, Michal; Heinzel, Petr; Švanda,
   Michal; Jurčák, Jan; del Moro, Dario; Berrilli, Francesco
Bibcode: 2020ApJ...890...22A
Altcode: 2020arXiv200103413A
  Acoustic and magnetoacoustic waves are considered to be possible
  agents of chromospheric heating. We present a comparison of deposited
  acoustic energy flux with total integrated radiative losses in the
  middle chromosphere of the quiet Sun and a weak plage. The comparison
  is based on a consistent set of high-resolution observations acquired
  by the Interferometric Bidimensional Spectrometer instrument in the
  Ca II 854.2 nm line. The deposited acoustic-flux energy is derived
  from Doppler velocities observed in the line core and a set of 1737
  non-local thermodynamic equilibrium 1D hydrostatic semi-empirical
  models, which also provide the radiative losses. The models are obtained
  by scaling the temperature and column mass of five initial models by
  Vernazza et al. (1981; VAL) B-F to get the best fit of synthetic to
  observed profiles. We find that the deposited acoustic-flux energy in
  the quiet-Sun chromosphere balances 30%-50% of the energy released by
  radiation. In the plage, it contributes by 50%-60% in locations with
  vertical magnetic field and 70%-90% in regions where the magnetic
  field is inclined more than 50° to the solar surface normal.

Title: Exploiting solar visible-range observations by inversion
techniques: from flows in the solar subsurface to a flaring atmosphere
Authors: Švanda, Michal; Jurčák, Jan; Korda, David; Kašparová,
   Jana
Bibcode: 2020arXiv200103874S
Altcode:
  Observations of the Sun in the visible spectral range belong to standard
  measurements obtained by instruments both on the ground and in the
  space. Nowadays, both nearly continuous full-disc observations with
  medium resolution and dedicated campaigns of high spatial, spectral
  and/or temporal resolution constitute a holy grail for studies that
  can capture (both) the long- and short-term changes in the dynamics
  and energetics of the solar atmosphere. Observations of photospheric
  spectral lines allow us to estimate not only the intensity at small
  regions, but also various derived data products, such as the Doppler
  velocity and/or the components of the magnetic field vector. We show
  that these measurements contain not only direct information about the
  dynamics of solar plasmas at the surface of the Sun but also imprints
  of regions below and above it. Here, we discuss two examples: First,
  the local time-distance helioseismology as a tool for plasma dynamic
  diagnostics in the near subsurface and second, the determination of
  the solar atmosphere structure during flares. The methodology in both
  cases involves the technique of inverse modelling.

Title: Science Requirement Document (SRD) for the European Solar
    Telescope (EST) (2nd edition, December 2019)
Authors: Schlichenmaier, R.; Bellot Rubio, L. R.; Collados, M.;
   Erdelyi, R.; Feller, A.; Fletcher, L.; Jurcak, J.; Khomenko, E.;
   Leenaarts, J.; Matthews, S.; Belluzzi, L.; Carlsson, M.; Dalmasse,
   K.; Danilovic, S.; Gömöry, P.; Kuckein, C.; Manso Sainz, R.;
   Martinez Gonzalez, M.; Mathioudakis, M.; Ortiz, A.; Riethmüller,
   T. L.; Rouppe van der Voort, L.; Simoes, P. J. A.; Trujillo Bueno,
   J.; Utz, D.; Zuccarello, F.
Bibcode: 2019arXiv191208650S
Altcode:
  The European Solar Telescope (EST) is a research infrastructure
  for solar physics. It is planned to be an on-axis solar telescope
  with an aperture of 4 m and equipped with an innovative suite of
  spectro-polarimetric and imaging post-focus instrumentation. The EST
  project was initiated and is driven by EAST, the European Association
  for Solar Telescopes. EAST was founded in 2006 as an association
  of 14 European countries. Today, as of December 2019, EAST consists
  of 26 European research institutes from 18 European countries. The
  Preliminary Design Phase of EST was accomplished between 2008 and
  2011. During this phase, in 2010, the first version of the EST Science
  Requirement Document (SRD) was published. After EST became a project
  on the ESFRI roadmap 2016, the preparatory phase started. The goal
  of the preparatory phase is to accomplish a final design for the
  telescope and the legal governance structure of EST. A major milestone
  on this path is to revisit and update the Science Requirement Document
  (SRD). The EST Science Advisory Group (SAG) has been constituted by
  EAST and the Board of the PRE-EST EU project in November 2017 and has
  been charged with the task of providing with a final statement on the
  science requirements for EST. Based on the conceptual design, the SRD
  update takes into account recent technical and scientific developments,
  to ensure that EST provides significant advancement beyond the current
  state-of-the-art. The present update of the EST SRD has been developed
  and discussed during a series of EST SAG meetings. The SRD develops
  the top-level science objectives of EST into individual science
  cases. Identifying critical science requirements is one of its main
  goals. Those requirements will define the capabilities of EST and the
  post-focus instrument suite. The technical requirements for the final
  design of EST will be derived from the SRD.

Title: The influence of Hinode/SOT NFI instrumental effects on the
    visibility of simulated prominence fine structures in Hα
Authors: Gunár, S.; Jurčák, J.; Ichimoto, K.
Bibcode: 2019A&A...629A.118G
Altcode:
  Context. Models of entire prominences with their numerous fine
  structures distributed within the prominence magnetic field use
  approximate radiative transfer techniques to visualize the simulated
  prominences. However, to accurately compare synthetic images of
  prominences obtained in this way with observations and to precisely
  analyze the visibility of even the faintest prominence features,
  it is important to take into account the influence of instrumental
  properties on the synthetic spectra and images. <BR /> Aims: In the
  present work, we investigate how synthetic Hα images of simulated
  prominences are impacted by the instrumental effects induced by the
  Narrowband Filter Imager (NFI) of the Solar Optical Telescope (SOT)
  onboard the Hinode satellite. <BR /> Methods: To process the synthetic
  Hα images provided by 3D Whole-Prominence Fine Structure (WPFS) models
  into SOT-like synthetic Hα images, we take into account the effects of
  the integration over the theoretical narrow-band transmission profile
  of NFI Lyot filter, the influence of the stray-light and point spread
  function (PSF) of Hinode/SOT, and the observed noise level. This allows
  us to compare the visibility of the prominence fine structures in the
  SOT-like synthetic Hα images with the synthetic Hα line-center images
  used by the 3D models and with a pair of Hinode/SOT NFI observations
  of quiescent prominences. <BR /> Results: The comparison between
  the SOT-like synthetic Hα images and the synthetic Hα line-center
  images shows that all large and small-scale features are very similar
  in both visualizations and that the same very faint prominence fine
  structures can be discerned in both. This demonstrates that the
  computationally efficient Hα line-center visualization technique
  can be reliably used for the purpose of visualization of complex 3D
  prominence models. In addition, the qualitative comparison between the
  SOT-like synthetic images and prominence observations shows that the
  3D WPFS models can reproduce large-scale prominence features rather
  well. However, the distribution of the prominence fine structures
  is significantly more diffuse in the observations than in the models
  and the diffuse intensity areas surrounding the observed prominences
  are also not present in the synthetic images. We also found that the
  maximum intensities reached in the models are about twice as high as
  those present in the observations-an indication that the mass-loading
  assumed in the present 3D WPFS models might be too large.

Title: A Quantitative Comparison of Observed and Theoretical Stokes
    Profiles of the Ca II 8542 Å Line in the Quiet Sun
Authors: Jurčák, J.; Stěpán, J.; Bianda, M.; Trujillo Bueno, J.
Bibcode: 2019ASPC..526..235J
Altcode:
  We present an analysis of the Stokes profiles of the Ca II 8542 Å
  line produced by the joint action of atomic level polarization and the
  Hanle and Zeeman effects. We compare spectropolarimetric observations
  of this line in a quiet region at the solar disk centre, taken with
  the ZIMPOL instrument at IRSOL, with the theoretical Stokes profiles
  computed with the PORTA radiative transfer code using as solar model
  atmosphere a 3D snapshot taken from a radiation MHD simulation of
  an enhanced-network region. Even though the spatial sampling of the
  ZIMPOL observations is only 1.43 arcsec/pixel, we detect Q/I, U/I and
  V/I polarization signals of the order of 0.1%. The synthetic line
  profiles have been obtained by solving the full 3D NLTE radiative
  transfer problem taking into account the symmetry breaking effects
  due to the model's horizontal inhomogeneities and macroscopic velocity
  gradients. After spatial and spectral degradation, in some locations
  we find similar amplitudes between the observed and calculated linear
  polarization profiles. However, in general, the observations show
  stronger polarization signals than the calculated ones, a discrepancy
  that could be used to refine the numerical models of the quiet solar
  chromosphere.

Title: New Insights on Penumbra Magneto-Convection
Authors: Bello González, N.; Jurčák, J.; Schlichenmaier, R.;
   Rezaei, R.
Bibcode: 2019ASPC..526..261B
Altcode:
  Fully-fledged penumbrae are a well characterised phenomenon from
  an observational point of view. Also, MHD simulations reproduce the
  observed characteristics and provide us with insights on the physical
  mechanisms possibly running behind the observed processes. Yet, how this
  penumbral magneto-convection sets in is still an open question. Due to
  the fact that penumbra formation is a relatively fast process (of the
  order of hours), it has eluded its observation with sufficient spatial
  resolution by both space- and ground-based solar observatories. Only
  recently, some researchers have witnessed the onset of both orphan
  and sunspot penumbrae in detail. We are one of those. In July 2009, we
  observed the early stages of the NOAA 11024 AR leading sunspot while
  developing its penumbra. The spectro-polarimetric dataset lead us to
  new observational findings. In this contribution, we put into context
  our and other authors' results to draw the overall picture of sunspot
  formation. Most important, the comparison on the properties of different
  types of penumbrae lead us to the conclusion that the formation of
  penumbrae is not just one mechanism. While the sole cause necessary
  for penumbral magneto-convection is a stably inclined magnetic field,
  observations show that inclined fields can be caused by flux emergence,
  to form orphan penumbrae, or by field lines transported down from
  upper photospheric layers, to form sunspot penumbra. This conclusion,
  together with the recent findings by Jur\čák and collaborators on
  a canonical value of the vertical component of the magnetic field
  blocking the action of penumbral magneto-convection in umbral areas,
  is a crucial step forward towards the understanding of the coupling
  of solar plasmas and magnetic fields in penumbral atmospheres.

Title: Recent advancements in the EST project
Authors: Jurčák, Jan; Collados, Manuel; Leenaarts, Jorrit; van Noort,
   Michiel; Schlichenmaier, Rolf
Bibcode: 2019AdSpR..63.1389J
Altcode: 2018arXiv181100851J
  The European Solar Telescope (EST) is a project of a new-generation
  solar telescope. It has a large aperture of 4 m, which is necessary for
  achieving high spatial and temporal resolution. The high polarimetric
  sensitivity of the EST will allow to measure the magnetic field in the
  solar atmosphere with unprecedented precision. Here, we summarise the
  recent advancements in the realisation of the EST project regarding
  the hardware development and the refinement of the science requirements.

Title: Properties of the inner penumbral boundary and temporal
    evolution of a decaying sunspot
Authors: Benko, M.; González Manrique, S. J.; Balthasar, H.; Gömöry,
   P.; Kuckein, C.; Jurčák, J.
Bibcode: 2018A&A...620A.191B
Altcode: 2018arXiv181013185B
  Context. It has been empirically determined that the umbra-penumbra
  boundaries of stable sunspots are characterized by a constant value of
  the vertical magnetic field. <BR /> Aims: We analyzed the evolution
  of the photospheric magnetic field properties of a decaying sunspot
  belonging to NOAA 11277 between August 28-September 3, 2011. The
  observations were acquired with the spectropolarimeter on-board of
  the Hinode satellite. We aim to prove the validity of the constant
  vertical magnetic-field boundary between the umbra and penumbra in
  decaying sunspots. <BR /> Methods: A spectral-line inversion technique
  was used to infer the magnetic field vector from the full-Stokes
  profiles. In total, eight maps were inverted and the variation of
  the magnetic properties in time were quantified using linear or
  quadratic fits. <BR /> Results: We find a linear decay of the umbral
  vertical magnetic field, magnetic flux, and area. The penumbra showed
  a linear increase of the vertical magnetic field and a sharp decay
  of the magnetic flux. In addition, the penumbral area quadratically
  decayed. The vertical component of the magnetic field is weaker on the
  umbra-penumbra boundary of the studied decaying sunspot compared to
  stable sunspots. Its value seem to be steadily decreasing during the
  decay phase. Moreover, at any time of the sunspot decay shown, the inner
  penumbra boundary does not match with a constant value of the vertical
  magnetic field, contrary to what is seen in stable sunspots. <BR />
  Conclusions: During the decaying phase of the studied sunspot, the
  umbra does not have a sufficiently strong vertical component of the
  magnetic field and is thus unstable and prone to be disintegrated by
  convection or magnetic diffusion. No constant value of the vertical
  magnetic field is found for the inner penumbral boundary.

Title: Heating of the solar photosphere during a white-light flare
Authors: Jurčák, Jan; Kašparová, Jana; Švanda, Michal; Kleint,
   Lucia
Bibcode: 2018A&A...620A.183J
Altcode: 2018arXiv181107794J
  Context. The Fe I lines observed by the Hinode/SOT spectropolarimeter
  were always seen in absorption, apart from the extreme solar limb. Here
  we analyse a unique dataset capturing these lines in emission during
  a solar white-light flare. <BR /> Aims: We analyse the temperature
  stratification in the solar photosphere during a white-light flare and
  compare it with the post-white-light flare state. <BR /> Methods: We
  used two scans of the Hinode/SOT spectropolarimeter to infer, by means
  of the LTE inversion code Stokes Inversion based on Response function
  (SIR), the physical properties in the solar photosphere during and
  after a white-light flare. The resulting model atmospheres are compared
  and the changes are related to the white-light flare. <BR /> Results:
  We show that the analysed white-light flare continuum brightening is
  probably not caused by the temperature increase at the formation height
  of the photospheric continuum. However, the photosphere is heated
  by the flare approximately down to log τ = -0.5 and this results
  in emission profiles of the observed Fe I lines. From the comparison
  with the post-white-light flare state of the atmosphere, we estimate
  that the major contribution to the increase in the continuum intensity
  originates in the heated chromosphere.

Title: Comparison of theoretical and observed Ca II 8542 Stokes
    profiles in quiet regions at the centre of the solar disc
Authors: Jurčák, J.; Štěpán, J.; Trujillo Bueno, J.; Bianda, M.
Bibcode: 2018A&A...619A..60J
Altcode: 2018arXiv180809470J
  Context. Interpreting the Stokes profiles observed in quiet regions
  of the solar chromosphere is a challenging task. The Stokes Q and U
  profiles are dominated by the scattering polarisation and the Hanle
  effect, and these processes can only be correctly quantified if 3D
  radiative transfer effects are taken into account. Forward-modelling
  of the intensity and polarisation of spectral lines using a 3D model
  atmosphere is a suitable approach in order to statistically compare
  the theoretical and observed line profiles. <BR /> Aims: Our aim is to
  present novel observations of the Ca II 8542 Å line profiles in a quiet
  region at the centre of the solar disc and to quantitatively compare
  them with the theoretical Stokes profiles obtained by solving the
  problem of the generation and transfer of polarised radiation in a 3D
  model atmosphere. We aim at estimating the reliability of the 3D model
  atmosphere, excluding its known lack of dynamics and/or insufficient
  density, using not only the line intensity but the full vector of
  Stokes parameters. <BR /> Methods: We used data obtained with the
  ZIMPOL instrument at the Istituto Ricerche Solari Locarno (IRSOL) and
  compared the observations with the theoretical profiles computed with
  the PORTA radiative transfer code, using as solar model atmosphere a
  3D snapshot taken from a radiation-magnetohydrodynamics simulation. The
  synthetic profiles were degraded to match the instrument and observing
  conditions. <BR /> Results: The degraded theoretical profiles of the
  Ca II 8542 line are qualitatively similar to the observed ones. We
  confirm that there is a fundamental difference in the widths of all
  Stokes profiles: the observed lines are wider than the theoretical
  lines. We find that the amplitudes of the observed profiles are larger
  than those of the theoretical ones, which suggests that the symmetry
  breaking effects in the solar chromosphere are stronger than in the
  model atmosphere. This means that the isosurfaces of temperature,
  velocity, and magnetic field strength and orientation are more
  corrugated in the solar chromosphere than in the currently available
  3D radiation-magnetohydrodynamics simulation.

Title: Understanding the HMI Pseudocontinuum in White-light Solar
    Flares
Authors: Švanda, Michal; Jurčák, Jan; Kašparová, Jana; Kleint,
   Lucia
Bibcode: 2018ApJ...860..144S
Altcode: 2018arXiv180503369S
  We analyze observations of the X9.3 solar flare (SOL2017-09-06T11:53)
  observed by SDO/HMI and Hinode/Solar Optical Telescope. Our aim is to
  learn about the nature of the HMI pseudocontinuum I <SUB>c</SUB> used as
  a proxy for the white-light continuum. From model atmospheres retrieved
  by an inversion code applied to the Stokes profiles observed by the
  Hinode satellite, we synthesize profiles of the Fe I 617.3 nm line and
  compare them to HMI observations. Based on a pixel-by-pixel comparison,
  we show that the value of I <SUB>c</SUB> represents the continuum level
  well in quiet-Sun regions only. In magnetized regions, it suffers from
  a simplistic algorithm that is applied to a complex line shape. During
  this flare, both instruments also registered emission profiles in the
  flare ribbons. Such emission profiles are poorly represented by the
  six spectral points of HMI and the MDI-like algorithm does not account
  for emission profiles in general; thus, the derived pseudocontinuum
  intensity does not approximate the continuum value properly.

Title: The magnetic nature of umbra-penumbra boundary in sunspots
Authors: Jurčák, J.; Rezaei, R.; González, N. Bello; Schlichenmaier,
   R.; Vomlel, J.
Bibcode: 2018A&A...611L...4J
Altcode: 2018arXiv180108983J
  Context. Sunspots are the longest-known manifestation of solar
  activity, and their magnetic nature has been known for more than a
  century. Despite this, the boundary between umbrae and penumbrae,
  the two fundamental sunspot regions, has hitherto been solely
  defined by an intensity threshold. Aim. Here, we aim at studying the
  magnetic nature of umbra-penumbra boundaries in sunspots of different
  sizes, morphologies, evolutionary stages, and phases of the solar
  cycle. <BR /> Methods: We used a sample of 88 scans of the Hinode/SOT
  spectropolarimeter to infer the magnetic field properties in at the
  umbral boundaries. We defined these umbra-penumbra boundaries by
  an intensity threshold and performed a statistical analysis of the
  magnetic field properties on these boundaries. <BR /> Results: We
  statistically prove that the umbra-penumbra boundary in stable sunspots
  is characterised by an invariant value of the vertical magnetic field
  component: the vertical component of the magnetic field strength
  does not depend on the umbra size, its morphology, and phase of the
  solar cycle. With the statistical Bayesian inference, we find that the
  strength of the vertical magnetic field component is, with a likelihood
  of 99%, in the range of 1849-1885 G with the most probable value
  of 1867 G. In contrast, the magnetic field strength and inclination
  averaged along individual boundaries are found to be dependent on the
  umbral size: the larger the umbra, the stronger and more horizontal
  the magnetic field at its boundary. <BR /> Conclusions: The umbra and
  penumbra of sunspots are separated by a boundary that has hitherto been
  defined by an intensity threshold. We now unveil the empirical law of
  the magnetic nature of the umbra-penumbra boundary in stable sunspots:
  it is an invariant vertical component of the magnetic field.

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: Granular cells in the presence of magnetic field
Authors: Jurčák, J.; Lemmerer, B.; van Noort, M.
Bibcode: 2017IAUS..327...34J
Altcode:
  We present a statistical study of the dependencies of the shapes
  and sizes of the photospheric convective cells on the magnetic field
  properties. This analysis is based on a 2.5 hour long SST observations
  of active region NOAA 11768. We have blue continuum images taken with a
  cadence of 5.6 sec that are used for segmentation of individual granules
  and 270 maps of spectropolarimetric CRISP data allowing us to determine
  the properties of the magnetic field along with the line-of-sight
  velocities. The sizes and shapes of the granular cells are dependent
  on the the magnetic field strength, where the granules tend to be
  smaller in regions with stronger magnetic field. In the presence of
  highly inclined magnetic fields, the eccentricity of granules is high
  and we do not observe symmetric granules in these regions. The mean
  up-flow velocities in granules as well as the granules intensities
  decrease with increasing magnetic field strength.

Title: A distinct magnetic property of the inner penumbral
    boundary. II. Formation of a penumbra at the expense of a pore
Authors: Jurčák, J.; Bello González, N.; Schlichenmaier, R.;
   Rezaei, R.
Bibcode: 2017A&A...597A..60J
Altcode: 2016arXiv161201745J; 2016A&A...597A..60J
  Context. We recently presented evidence that stable
  umbra-penumbra boundaries are characterised by a distinct
  canonical value of the vertical component of the magnetic
  field, B<SUP>stable</SUP><SUB>ver</SUB>. In order to trigger
  the formation of a penumbra, large inclinations in the magnetic
  field are necessary. In sunspots, the penumbra develops and
  establishes by colonising both umbral areas and granulation, that
  is, penumbral magneto-convection takes over in umbral regions with
  B<SUB>ver</SUB>&lt;B<SUP>stable</SUP><SUB>ver</SUB>, as well as
  in granular convective areas. Eventually, a stable umbra-penumbra
  boundary settles at B<SUP>stable</SUP><SUB>ver</SUB>. <BR /> Aims:
  Here, we aim to study the development of a penumbra initiated at
  the boundary of a pore, where the penumbra colonises the entire pore
  ultimately. <BR /> Methods: We have used Hinode/SOT G-band images to
  study the evolution of the penumbra. Hinode/SOT spectropolarimetric
  data were used to infer the magnetic field properties in the studied
  region. <BR /> Results: The penumbra forms at the boundary of a pore
  located close to the polarity inversion line of NOAA 10960. As the
  penumbral bright grains protrude into the pore, the magnetic flux in
  the forming penumbra increases at the expense of the pore magnetic
  flux. Consequently, the pore disappears completely giving rise to an
  orphan penumbra. At all times, the vertical component of the magnetic
  field in the pore is smaller than B<SUP>stable</SUP><SUB>ver</SUB>
  ≈ 1.8 kG. <BR /> Conclusions: Our findings are in an agreement
  with the need of B<SUP>stable</SUP><SUB>ver</SUB> for establishing
  a stable umbra-penumbra boundary: while B<SUB>ver</SUB> in
  the pore is smaller than B<SUP>stable</SUP><SUB>ver</SUB>, the
  protrusion of penumbral grains into the pore area is not blocked,
  a stable pore-penumbra boundary does not establish, and the pore
  is fully overtaken by the penumbral magneto-convective mode. This
  scenario could also be one of the mechanisms giving rise to orphan
  penumbrae. <P />The movie associated to Fig. 1 is available at <A
  href="http://www.aanda.org/10.1051/0004-6361/201628547/olm">http://www.aanda.org</A>

Title: Canonical Bver value on umbra/penumbra boundaries
Authors: Jurcak, Jan; Bello González, Nazaret; Schlichenmaier, Rolf;
   Rezaei, Reza
Bibcode: 2017psio.confE.112J
Altcode:
  No abstract at ADS

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: Chromospheric Heating by Acoustic Waves Compared to Radiative
    Cooling
Authors: Sobotka, M.; Heinzel, P.; Švanda, M.; Jurčák, J.; del Moro,
   D.; Berrilli, F.
Bibcode: 2016ApJ...826...49S
Altcode: 2016arXiv160504794S
  Acoustic and magnetoacoustic waves are among the possible candidate
  mechanisms that heat the upper layers of the solar atmosphere. A weak
  chromospheric plage near the large solar pore NOAA 11005 was observed
  on 2008 October 15, in the Fe I 617.3 nm and Ca II 853.2 nm lines of
  the Interferometric Bidimemsional Spectrometer attached to the Dunn
  Solar Telescope. In analyzing the Ca II observations (with spatial
  and temporal resolutions of 0.″4 and 52 s) the energy deposited by
  acoustic waves is compared to that released by radiative losses. The
  deposited acoustic flux is estimated from the power spectra of Doppler
  oscillations measured in the Ca II line core. The radiative losses
  are calculated using a grid of seven one-dimensional hydrostatic
  semi-empirical model atmospheres. The comparison shows that the
  spatial correlation of the maps of radiative losses and acoustic flux
  is 72%. In a quiet chromosphere, the contribution of acoustic energy
  flux to radiative losses is small, only about 15%. In active areas
  with a photospheric magnetic-field strength between 300 and 1300 G
  and an inclination of 20°-60°, the contribution increases from 23%
  (chromospheric network) to 54% (a plage). However, these values have
  to be considered as lower limits and it might be possible that the
  acoustic energy flux is the main contributor to the heating of bright
  chromospheric network and plages.

Title: GREGOR observations of a small flare above a sunspot
Authors: Sobotka, M.; Dudík, J.; Denker, C.; Balthasar, H.; Jurčák,
   J.; Liu, W.
Bibcode: 2016IAUS..320...68S
Altcode:
  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 0.1 nm Ca II H interference
  filter. Context observations from SDO/AIA, Hinode/SOT, and IRIS show
  that the ribbon is a part of a larger one that extends through the
  neighboring positive polarities and also participates in several
  other flares within the active region. A 140 second long time series
  of Ca II H images was reconstructed by means of the Multi-Frame
  Blind Deconvolution method, giving the respective 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,
  providing evidence for the presence of slipping reconnection at small
  spatial scales.

Title: Parallelization of the SIR code for the investigation of
    small-scale features in the solar photosphere
Authors: Thonhofer, Stefan; Bellot Rubio, Luis R.; Utz, Dominik;
   Hanslmeier, Arnold; Jurçák, Jan
Bibcode: 2015IAUS..305..251T
Altcode: 2015arXiv150303710T
  Magnetic fields are one of the most important drivers of the highly
  dynamic processes that occur in the lower solar atmosphere. They span a
  broad range of sizes, from large- and intermediate-scale structures such
  as sunspots, pores and magnetic knots, down to the smallest magnetic
  elements observable with current telescopes. On small scales, magnetic
  flux tubes are often visible as Magnetic Bright Points (MBPs). Apart
  from simple V/I magnetograms, the most common method to deduce their
  magnetic properties is the inversion of spectropolarimetric data. Here
  we employ the SIR code for that purpose. SIR is a well-established
  tool that can derive not only the magnetic field vector and other
  atmospheric parameters (e.g., temperature, line-of-sight velocity),
  but also their stratifications with height, effectively producing
  3-dimensional models of the lower solar atmosphere. In order to enhance
  the runtime performance and the usability of SIR we parallelized the
  existing code and standardized the input and output formats. This and
  other improvements make it feasible to invert extensive high-resolution
  data sets within a reasonable amount of computing time. An evaluation
  of the speedup of the parallel SIR code shows a substantial improvement
  in runtime.

Title: A distinct magnetic property of the inner penumbral
    boundary. Formation of a stable umbra-penumbra boundary in a sunspot
Authors: Jurčák, J.; Bello González, N.; Schlichenmaier, R.;
   Rezaei, R.
Bibcode: 2015A&A...580L...1J
Altcode:
  Context. A sunspot emanates from a growing pore or protospot. In order
  to trigger the formation of a penumbra, large inclinations at the
  outskirts of the protospot are necessary. The penumbra develops and
  establishes by colonising both umbral areas and granulation. Evidence
  for a unique stable boundary value for the vertical component of the
  magnetic field strength, B<SUP>stable</SUP><SUB>ver</SUB>, was found
  along the umbra-penumbra boundary of developed sunspots. <BR /> Aims: We
  study the changing value of B<SUB>ver</SUB> as the penumbra forms and as
  it reaches a stable state. We compare this with the corresponding value
  in fully developed penumbrae. <BR /> Methods: We use broadband G-band
  images and spectropolarimetric GFPI/VTT data to study the evolution
  of and the vertical component of the magnetic field on a forming
  umbra-penumbra boundary. For comparison with stable sunspots, we also
  analyse the two maps observed by Hinode/SP on the same spot after the
  penumbra formed. <BR /> Results: The vertical component of the magnetic
  field, B<SUB>ver</SUB>, at the umbra-penumbra boundary increases during
  penumbra formation owing to the incursion of the penumbra into umbral
  areas. After 2.5 h, the penumbra reaches a stable state as shown
  by the GFPI data. At this stable stage, the simultaneous Hinode/SP
  observations show a B<SUB>ver</SUB> value comparable to that of
  umbra-penumbra boundaries of fully fledged sunspots. <BR /> Conclusions:
  We confirm that the umbra-penumbra boundary, traditionally defined by
  an intensity threshold, is also characterised by a distinct canonical
  magnetic property, namely by B<SUB>ver</SUB><SUP>stable</SUP>. During
  the penumbra formation process, the inner penumbra extends
  into regions where the umbra previously prevailed. Hence, in
  areas where B<SUB>ver</SUB>&lt;B<SUP>stable</SUP><SUB>ver</SUB>,
  the magneto-convection mode operating in the umbra turns into a
  penumbral mode. Eventually, the inner penumbra boundary settles at
  B<SUB>ver</SUB><SUP>stable</SUP>, which hints toward the role of
  B<SUB>ver</SUB><SUP>stable</SUP> as inhibitor of the penumbral mode
  of magneto-convection.

Title: GREGOR observations of a small flare above a sunspot
Authors: Sobotka, Michal; Dudik, Jaroslav; Denker, Carsten; Balthasar,
   Horst; Jurcak, Jan; Liu, Wenjuan; GREGOR Team
Bibcode: 2015IAUGA..2246841S
Altcode:
  A small flare ribbon above a sunspot with a light bridge was observed on
  7 November 2014 around 12:00 UT in the blue imaging channel of GREGOR,
  using a 0.1 nm Ca II H interference filter. Context observations from
  SDO/AIA, Hinode/SOT and IRIS show that the ribbon is a part of a larger
  ribbon extending through the neighbouring negative polarities that also
  participates in several other flares within the active region. A 140
  s long time series of Ca II H images was reconstructed by means of the
  Multi Frame Blind Deconvolution method, giving the respective spatial
  and temporal resolutions of 0.1" and 1 s. Light curves and horizontal
  velocities of small-scale brightenings in the flare ribbon located
  above an umbral core were measured. Some of them are stationary but
  three brightenings move in opposite directions along the ribbon with
  speeds of 7 - 11 km/s. Expecting that the brightenings correspond to
  footpoints of flare loops, their motions can be interpreted in terms
  of the slipping reconnection model.

Title: A distinct magnetic property of the inner penumbral boundary
Authors: Jurčák, Jan; Bello Gonzalez, Nazaret; Schlichenmaier,
   Rolf; Rezaei, Reza
Bibcode: 2015arXiv150608574J
Altcode:
  A sunspot emanates from a growing pore or protospot. In order to
  trigger the formation of a penumbra, large inclinations at the
  outskirts of the protospot are necessary. The penumbra develops and
  establishes by colonising both umbral areas and granulation. Evidence
  for a unique stable boundary value for the vertical component of the
  magnetic field strength, $B^{\rm stable}_{\rm ver}$, was found along
  the umbra-penumbra boundary of developed sunspots. We use broadband
  G-band images and spectropolarimetric GFPI/VTT data to study the
  evolution of and the vertical component of the magnetic field on a
  forming umbra-penumbra boundary. For comparison with stable sunspots,
  we also analyse the two maps observed by Hinode/SP on the same spot
  after the penumbra formed. The vertical component of the magnetic
  field, $B_{\rm ver}$, at the umbra-penumbra boundary increases
  during penumbra formation owing to the incursion of the penumbra into
  umbral areas. After 2.5 hours, the penumbra reaches a stable state
  as shown by the GFPI data. At this stable stage, the simultaneous
  Hinode/SP observations show a $B_{\rm ver}$ value comparable to that of
  umbra-penumbra boundaries of fully fledged sunspots. We confirm that
  the umbra-penumbra boundary, traditionally defined by an intensity
  threshold, is also characterised by a distinct canonical magnetic
  property, namely by $B^{\rm stable}_{\rm ver}$. During the penumbra
  formation process, the inner penumbra extends into regions where the
  umbra previously prevailed. Hence, in areas where $B_{\rm ver} &lt;
  B^{\rm stable}_{\rm ver}$, the magneto-convection mode operating in
  the umbra turns into a penumbral mode. Eventually, the inner penumbra
  boundary settles at $B^{\rm stable}_{\rm ver}$, which hints toward the
  role of $B_{\rm ver}^{\rm stable}$ as inhibitor of the penumbral mode
  of magneto-convection.

Title: Magnetic bright point dynamics and evolutions observed by
    Sunrise/IMaX and other instruments
Authors: Utz, D.; del Toro Iniesta, J. C.; Bellot Rubio, L.; Thonhofer,
   S.; Jurčák, J.
Bibcode: 2015hsa8.conf..689U
Altcode:
  In this proceeding we will have a closer look on recent observations
  and results regarding the dynamics and evolution of so-called magnetic
  bright points (MBPs). MBPs are manifestations of kG magnetic field
  strong flux concentrations seen in the solar photosphere. They belong
  to the class of small-scale solar magnetic features with diameters
  starting from low values around the current observational resolution
  limit - about 100 km - up to a few hundred km. They might play an
  important role in several key research questions like the total solar
  irradiance variation (TSI variation) as well as the solar atmospheric
  heating problem. Especially their dynamic behaviour is of interest
  for the heating problem as they might trigger all kinds of MHD waves
  which travel up to the higher solar atmospheric layers, where they can
  get damped leading to a heating of the plasma. Furthermore they might
  engage in magnetic field reconnection processes leading consequently
  also to a heating. Due to these reasons, and also for the sake of a
  better understanding of the physical processes involved on small-scales,
  detailed investigations on the dynamical behaviour and evolution of
  such magnetic field proxies like MBPs is in order. In this conference
  proceeding we wish to give in a first part an overview about the
  obtained knowledge so far. In a second part we highlight recent results
  regarding the dynamical evolution of plasma parameters of MBPs such as
  magnetic field strength, temperature, and line of sight velocity. This
  proceeding is completed by an outlook on what can and should be done
  in the near future with available data from recent telescopes.

Title: Evolution of magnetic field inclination in a forming penumbra
Authors: Jurčák, Jan; Bello González, Nazaret; Schlichenmaier,
   Rolf; Rezaei, Reza
Bibcode: 2014PASJ...66S...3J
Altcode: 2014PASJ..tmp...93J
  As a sunspot penumbra forms, the magnetic field vector at the outer
  boundary of the protospot undergoes a transformation. We study the
  changes of the magnetic field vector at this boundary as a penumbral
  segment forms. We analyze a set of spectropolarimetric maps covering
  2 hr during the formation of a sunspot in NOAA 11024. The data were
  recorded with the GFPI instrument attached to the German VTT. We
  observe a stationary umbra/quiet Sun boundary, where the magnetic
  field becomes more horizontal with time. The magnetic field inclination
  increases by 5°, reaching a maximum value of about 59°. The maximum
  inclination coincides with the onset of filament formation. In time,
  the penumbra filaments become longer and the penumbral bright grains
  protrude into the umbra, where the magnetic field is stronger and
  more vertical. Consequently, we observe a decrease in the magnetic
  field inclination at the boundary as the penumbra grows. In summary,
  in order to initiate the formation of the penumbra, the magnetic
  field at the umbral (protospot) boundary becomes more inclined. As
  the penumbra grows, the umbra/penumbra boundary migrates inwards,
  and at this boundary the magnetic field turns more vertical again,
  while it remains inclined in the outer penumbra.

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 field and radiative transfer modelling of a quiescent
    prominence
Authors: Gunár, S.; Schwartz, P.; Dudík, J.; Schmieder, B.; Heinzel,
   P.; Jurčák, J.
Bibcode: 2014A&A...567A.123G
Altcode:
  <BR /> Aims: The aim of this work is to analyse the multi-instrument
  observations of the June 22, 2010 prominence to study its structure in
  detail, including the prominence-corona transition region and the dark
  bubble located below the prominence body. <BR /> Methods: We combined
  results of the 3D magnetic field modelling with 2D prominence fine
  structure radiative transfer models to fully exploit the available
  observations. <BR /> Results: The 3D linear force-free field model
  with the unsheared bipole reproduces the morphology of the analysed
  prominence reasonably well, thus providing useful information about
  its magnetic field configuration and the location of the magnetic
  dips. The 2D models of the prominence fine structures provide a good
  representation of the local plasma configuration in the region dominated
  by the quasi-vertical threads. However, the low observed Lyman-α
  central intensities and the morphology of the analysed prominence
  suggest that its upper central part is not directly illuminated from the
  solar surface. <BR /> Conclusions: This multi-disciplinary prominence
  study allows us to argue that a large part of the prominence-corona
  transition region plasma can be located inside the magnetic dips in
  small-scale features that surround the cool prominence material located
  in the dip centre. We also argue that the dark prominence bubbles
  can be formed because of perturbations of the prominence magnetic
  field by parasitic bipoles, causing them to be devoid of the magnetic
  dips. Magnetic dips, however, form thin layers that surround these
  bubbles, which might explain the occurrence of the cool prominence
  material in the lines of sight intersecting the prominence bubbles. <P
  />Movie and Appendix A are available in electronic form at <A
  href="http://www.aanda.org/10.1051/0004-6361/201322777/olm">http://www.aanda.org</A>

Title: Orphan penumbrae: Submerging horizontal fields
Authors: Jurčák, J.; Bellot Rubio, L. R.; Sobotka, M.
Bibcode: 2014A&A...564A..91J
Altcode: 2014arXiv1402.6558J
  <BR /> Aims: We investigate the properties of orphan penumbrae,
  which are photospheric filamentary structures observed in active
  regions near polarity inversion lines that resemble the penumbra of
  regular sunspots but are not connected to any umbra. <BR /> Methods:
  We use Hinode data from the Solar Optical Telescope to determine the
  properties of orphan penumbrae. Spectropolarimetric data are employed
  to obtain the vector magnetic field and line-of-sight velocities in
  the photosphere. Magnetograms are used to study the overall evolution
  of these structures, and G-band and Ca ii H filtergrams are to
  investigate their brightness and apparent horizontal motions. <BR />
  Results: Orphan penumbrae form between regions of opposite polarity in
  places with horizontal magnetic fields. Their magnetic configuration
  is that of Ω-shaped flux ropes. In the two cases studied here,
  the opposite-polarity regions approach each other with time and the
  whole structure submerges as the penumbral filaments disappear. Orphan
  penumbrae are very similar to regular penumbrae, including the existence
  of strong gas flows. Therefore, they could have a similar origin. The
  main difference between them is the absence of a "background" magnetic
  field in orphan penumbrae. This could explain most of the observed
  differences. <BR /> Conclusions: The fast flows we detect in orphan
  penumbrae may be caused by the siphon flow mechanism. Based on the
  similarities between orphan and regular penumbrae, we propose that
  the Evershed flow is also a manifestation of siphon flows. <P />A
  movie attached to Fig. 11 is available in electronic form at <A
  href="http://www.aanda.org/10.1051/0004-6361/201322340/olm">http://www.aanda.org</A>

Title: New insights into the evolution of magnetic bright point
    plasma parameters
Authors: Utz, Dominik; Hanslmeier, Arnold; Bellot Rubio, L. R.;
   Del Toro Iniesta, Jose Carlos; Jurcak, Jan
Bibcode: 2014cosp...40E3448U
Altcode:
  The dynamics within the solar atmosphere are governed by the Suńs
  magnetic fields. In the recent years the resolution limits were steadily
  driven up by better and better instruments and telescopes (like Hinode,
  Sunrise, NST, Gregor, ..) leading to higher resolved data. Therefore
  the interest in ever smaller magnetic field structures within the solar
  atmosphere rises. Among the smallest yet identified structures are
  so-called magnetic bright points (MBPs). These features are thought to
  be made up of single flux tubes and they have been studied exhaustively
  in the Fraunhofer G-band since the 70´s of the last century. They are
  important features not only due to their small scale (about 200 km in
  diameter) and hence used as proxies for the smallest solar magnetic
  field physics and processes, but also because they are involved in
  topics like the chromospheric/coronal heating problem or the total
  solar irradiance variation. In the current contribution we want to
  study the evolution of important plasma parameters of MBPs, such
  as temperature, magnetic field strength and line of sight velocity,
  to get a deeper understanding of the involved physics and occuring
  processes. Among the used data will be G-band filtergam data from
  Hinode/SOT and spectro-polarimetric data from the IMaX instrument
  onboard the Sunrise mission.

Title: Dynamics of the solar atmosphere above a pore with a light
    bridge
Authors: Sobotka, M.; Švanda, M.; Jurčák, J.; Heinzel, P.; Del Moro,
   D.; Berrilli, F.
Bibcode: 2013A&A...560A..84S
Altcode: 2013arXiv1309.7790S
  Context. Solar pores are small sunspots lacking a penumbra that have
  a prevailing vertical magnetic-field component. They can include light
  bridges at places with locally reduced magnetic field. Like sunspots,
  they exhibit a wide range of oscillatory phenomena. <BR /> Aims:
  A large isolated pore with a light bridge (NOAA 11005) is studied
  to obtain characteristics of a chromospheric filamentary structure
  around the pore, to analyse oscillations and waves in and around
  the pore, and to understand the structure and brightness of the light
  bridge. <BR /> Methods: Spectral imaging observations in the line Ca II
  854.2 nm and complementary spectropolarimetry in Fe I lines, obtained
  with the DST/IBIS spectrometer and HINODE/SOT spectropolarimeter,
  were used to measure photospheric and chromospheric velocity fields,
  oscillations, waves, the magnetic field in the photosphere, and
  acoustic energy flux and radiative losses in the chromosphere. <BR />
  Results: The chromospheric filamentary structure around the pore has
  all important characteristics of a superpenumbra: it shows an inverse
  Evershed effect and running waves, and has a similar morphology and
  oscillation character. The granular structure of the light bridge in
  the upper photosphere can be explained by radiative heating. Acoustic
  waves leaking up from the photosphere along the inclined magnetic
  field in the light bridge transfer enough energy flux to balance
  the entire radiative losses of the light-bridge chromosphere. <BR />
  Conclusions: A penumbra is not a necessary condition for the formation
  of a superpenumbra. The light bridge is heated by radiation in the
  photosphere and by acoustic waves in the chromosphere.

Title: Atmosphere above a large solar pore
Authors: Sobotka, M.; Švanda, M.; Jurčák, J.; Heinzel, P.; Del
   Moro, D.
Bibcode: 2013JPhCS.440a2049S
Altcode: 2013arXiv1302.4893S
  A large solar pore with a granular light bridge was observed on October
  15, 2008 with the IBIS spectrometer at the Dunn Solar Telescope and a
  69-min long time series of spectral scans in the lines Ca II 854.2 nm
  and Fe I 617.3 nm was obtained. The intensity and Doppler signals in the
  Ca II line were separated. This line samples the middle chromosphere
  in the core and the middle photosphere in the wings. Although no
  indication of a penumbra is seen in the photosphere, an extended
  filamentary structure, both in intensity and Doppler signals, is
  observed in the Ca II line core. An analysis of morphological and
  dynamical properties of the structure shows a close similarity to a
  superpenumbra of a sunspot with developed penumbra. A special attention
  is paid to the light bridge, which is the brightest feature in the
  pore seen in the Ca II line centre and shows an enhanced power of
  chromospheric oscillations at 3-5 mHz. Although the acoustic power
  flux in the light bridge is five times higher than in the "quiet"
  chromosphere, it cannot explain the observed brightness.

Title: Temporal variations in solar magnetic bright points intensity
    and plasma parameters
Authors: Jurčák, J.; Utz, D.; Bellot Rubio, L. R.
Bibcode: 2013JPhCS.440a2032J
Altcode:
  Magnetic bright points are one of the finest magnetic structures
  observed in the solar atmosphere. They possibly represent single
  flux tubes in quiet Sun regions. Their formation is described by the
  convective collapse model, while the decay phase of these structures
  is not well characterized yet. We attempt to follow the evolution of a
  few selected examples of MBPs and to study their changes in brightness
  and also the variations of plasma parameters during their lifetime. We
  use data from the Hinode satellite and the Sunrise mission. The G-band
  observations taken with a cadence of 30 seconds by the Hinode Solar
  Optical Telescope (SOT) show very fast changes of the maximum intensity
  of these structures. The complementary spectropolarimetric data, which
  are used to estimate the plasma parameters, were taken with a cadence
  of approximately two minutes. The variations of plasma parameters
  cannot be matched one to one to the changes in intensity due to the
  different temporal resolution. However, the slow changes of intensity
  with large amplitude are matched with variations of magnetic field
  strength and line-of-sight (LOS) velocity. The Sunrise/IMaX data have
  a temporal resolution of 32 seconds and show fast variations in the
  line wing intensity. These variations are associated with changes in
  the magnetic field strength and LOS velocity.

Title: Variations of Magnetic Bright Point Properties with Longitude
    and Latitude as Observed by Hinode/SOT G-band Data
Authors: Utz, D.; Hanslmeier, A.; Veronig, A.; Kühner, O.; Muller,
   R.; Jurčák, J.; Lemmerer, B.
Bibcode: 2013SoPh..284..363U
Altcode: 2012arXiv1212.1310U
  Small-scale magnetic fields can be observed on the Sun in
  high-resolution G-band filtergrams as magnetic bright points (MBPs). We
  study Hinode/Solar Optical Telescope (SOT) longitude and latitude scans
  of the quiet solar surface taken in the G-band in order to characterise
  the centre-to-limb dependence of MBP properties (size and intensity). We
  find that the MBP's sizes increase and their intensities decrease
  from the solar centre towards the limb. The size distribution can be
  fitted using a log-normal function. The natural logarithm of the mean
  (μ parameter) of this function follows a second-order polynomial
  and the generalised standard deviation (σ parameter) follows a
  fourth-order polynomial or equally well (within statistical errors)
  a sine function. The brightness decrease of the features is smaller
  than one would expect from the normal solar centre-to-limb variation;
  that is to say, the ratio of a MBP's brightness to the mean intensity
  of the image increases towards the limb. The centre-to-limb variations
  of the intensities of the MBPs and the quiet-Sun field can be fitted by
  a second-order polynomial. The detailed physical process that results
  in an increase of a MBP's brightness and size from Sun centre to the
  limb is not yet understood and has to be studied in more detail in
  the future.

Title: Magnetic field strength distribution of magnetic bright points
    inferred from filtergrams and spectro-polarimetric data
Authors: Utz, D.; Jurčák, J.; Hanslmeier, A.; Muller, R.; Veronig,
   A.; Kühner, O.
Bibcode: 2013A&A...554A..65U
Altcode: 2013arXiv1304.5508U
  Context. Small scale magnetic fields can be observed on the Sun in
  G-band filtergrams as magnetic bright points (MBPs) or identified in
  spectro-polarimetric measurements due to enhanced signals of Stokes
  profiles. These magnetic fields and their dynamics play a crucial role
  in understanding the coronal heating problem and also in surface dynamo
  models. MBPs can theoretically be described to evolve out of a patch of
  a solar photospheric magnetic field with values below the equipartition
  field strength by the so-called convective collapse model. After the
  collapse, the magnetic field of MBPs reaches a higher stable magnetic
  field level. <BR /> Aims: The magnetic field strength distribution of
  small scale magnetic fields as seen by MBPs is inferred. Furthermore,
  we want to test the model of convective collapse and the theoretically
  predicted stable value of about 1300 G. <BR /> Methods: We used four
  different data sets of high-resolution Hinode/SOT observations that were
  recorded simultaneously with the broadband filter device (G-band, Ca
  II-H) and the spectro-polarimeter. To derive the magnetic field strength
  distribution of these small scale features, the spectropolarimeter
  (SP) data sets were treated by the Merlin inversion code. The four data
  sets comprise different solar surface types: active regions (a sunspot
  group and a region with pores), as well as quiet Sun. <BR /> Results:
  In all four cases the obtained magnetic field strength distribution of
  MBPs is similar and shows peaks around 1300 G. This agrees well with the
  theoretical prediction of the convective collapse model. The resulting
  magnetic field strength distribution can be fitted in each case by a
  model consisting of log-normal components. The important parameters,
  such as geometrical mean value and multiplicative standard deviation,
  are similar in all data sets, so only the relative weighting of the
  components is different.

Title: Creating 3-dimensional Models of the Photosphere using the
    SIR Code
Authors: Thonhofer, S.; Utz, D.; Jurčák, J.; Pauritsch, J.;
   Hanslmeier, A.; Lemmerer, B.
Bibcode: 2013CEAB...37..471T
Altcode:
  A high-resolution 3-dimensional model of the photospheric magnetic
  field is essential for the investigation of magnetic features such
  as sunspots, pores or smaller elements like single flux tubes seen
  as magnetic bright points. The SIR code is an advanced inversion code
  that retrieves physical quantities, e.g. magnetic field, from Stokes
  profiles. Based on this code, we developed a program for automated
  inversion of Hinode SOT/SP data and for storing these results in
  3-dimensional data cubes in the form of fits files. We obtained models
  of the temperature, magnetic field strength, magnetic field angles
  and LOS-velocity in a region of the quiet sun. We will give a first
  discussion of those parameters in regards of small scale magnetic
  fields and what we can obtain and learn in the future.

Title: A Magnetic Bright Point Case Study
Authors: Utz, D.; Jurčák, J.; Bellot-Rubio, L.; del Toro Iniesta,
   J. C.; Thonhofer, S.; Hanslmeier, A.; Veronig, A.; Muller, R.;
   Lemmerer, B.
Bibcode: 2013CEAB...37..459U
Altcode:
  Due to its magnetic fields our host star - the Sun - becomes the
  interesting object for research as we know it. The magnetic fields
  themselves cover different spatial, lifetime and strength scales and
  reach down from enormous flux concentrations like active sunspot
  groups to single isolated magnetic flux tubes and even weaker,
  predominantly inclined intranetwork structures. Flux tubes can be seen
  in filtergram observations as magnetic bright points (MBPs). They are
  of interest for research not only due to their sheer existence but
  due to their important role in atmospheric heating (wave heating as
  well as reconnection processes), to their role in the understanding
  of creation and annihilation of magnetic fields as well as to their
  influence on the total solar irradiance variation. In this study we
  present a close look onto an evolutionary track of an MBP from its
  formation to its disintegration. Physical quantities of MBPs like
  their magnetic field strength and inclination, their line-of-sight
  velocity, and their temperature at different heights are inferred
  from the inversion of spectropolarimetric data. Original data are
  taken from the Sunrise/IMaX instrument and constitute a time series
  of some 60 min. The presented case resembles the convective collapse
  model and is in agreement with previous studies.

Title: IBIS: High-Resolution Multi-Height Observations and Magnetic
    Field Retrieval
Authors: Del Moro, D. .; Berrilli, F.; Stangalini, M.; Giannattasio,
   F.; Piazzesi, R.; Giovannelli, L.; Viticchiè, B.; Vantaggiato, M.;
   Sobotka, M.; Jurčák, J.; Criscuoli, S.; Giorgi, F.; Zuccarello, F.
Bibcode: 2012ASPC..463...33D
Altcode:
  IBIS (Interferometric BIdimensional Spectrometer) allows us to measure
  the four Stokes parameters in several spectroscopic lines with high
  spatial and spectral resolutions. With this information, we can
  retrieve both the dynamics and the magnetic field at different layers
  of the Photosphere and Chromosphere. The high spectral, spatial and
  temporal resolutions and the polarimetric sensitivity of IBIS allows
  us to study different phenomena taking place in the solar atmosphere
  with new tools. As an example, we highlight some applications of
  IBIS observations and analysis: <BR /> · Radiative and dynamical
  properties of Photospheric Bright Points versus their magnetic field
  concentration. <BR /> · Close up analysis of magnetic, velocity and
  temperature field in a solar pore. <BR /> · MHD wave propagation from
  the photosphere to the chromosphere in complex magnetic configuration.

Title: Magnetic and velocity fields of a solar pore
Authors: Sobotka, M.; Del Moro, D.; Jurčák, J.; Berrilli, F.
Bibcode: 2012A&A...537A..85S
Altcode:
  Context. Solar pores are intermediate-size magnetic flux features
  that emerge at the surface of the Sun. The absence of a filamentary
  penumbra indicates that there is a relatively simple magnetic structure
  with a prevailing vertical magnetic field. <BR /> Aims: Relations
  between the magnetic field components, line-of-sight velocities,
  and horizontal motions in and around a large pore (D<SUB>eff</SUB> =
  8''.5) are analysed to provide observational constraints on theoretical
  models and numerical simulations. <BR /> Methods: Spectropolarimetric
  observations in Fe I 617.3 nm of the pore NOAA 11005 with the IBIS
  spectrometer attached to the Dunn Solar Telescope are inverted into
  series of maps of thermal, magnetic, and velocity parameters using the
  SIR code. Horizontal velocities are obtained from series of white-light
  images by means of local correlation tracking. <BR /> Results: The
  magnetic field B extends from the visible pore border of more than 3''.5
  and has a radial structure in a form of spines that are co-spatial with
  dark intergranular lanes. The horizontal component B<SUB>hor</SUB> is
  more extended than the vertical component B<SUB>z</SUB>. The temperature
  linearly decreases with increasing B<SUB>z</SUB>, by about - 300 K
  kG<SUP>-1</SUP> in the photosphere and - 800 K kG<SUP>-1</SUP> in the
  umbra. The temperature contrast of granulation increases with increasing
  magnetic field strength and is then suppressed for B<SUB>z</SUB> &gt;
  1200 G. Granular upflows dominate in regions with B<SUB>z</SUB> &lt;
  600-700 G. Line-of-sight velocities are lower in stronger fields,
  except for fast isolated downflows at the pore's border. The velocity
  signature of granulation is suppressed completely for B<SUB>hor</SUB>
  &gt; 1000 G. Horizontal motions of granules start to be damped for
  B<SUB>z</SUB> &gt; 500 G and recurrently exploding granules appear
  only in magnetic fields comparable to or weaker than the equipartition
  field strength 400 G.

Title: Azimuthal variations of magnetic field strength and inclination
    on penumbral boundaries
Authors: Jurčák, J.
Bibcode: 2011A&A...531A.118J
Altcode:
  <BR /> Aims: I try to determine the properties of the magnetic field
  on the inner and outer penumbral boundaries and find out if either
  magnetic field strength or inclination are constant there and if
  these plasma parameters depend on the sunspot area. <BR /> Methods:
  The spectropolarimetric data obtained with the Hinode satellite were
  analysed. Active regions located mostly around the disc centre were
  selected to compare sunspots of different sizes. The magnetic field
  strength and inclination were estimated using the inversions of observed
  Stokes profiles. <BR /> Results: Both the magnetic field strength and
  inclination do not vary along individual outer penumbral boundaries,
  and the magnetic field probably becomes weaker and more vertical with
  decreasing sunspot area. The magnetic field strength and inclination
  are changing along the inner penumbral boundaries and also depend on
  the umbral area. Weaker magnetic fields are more vertical on the inner
  penumbral boundaries, which leads to a constant vertical component
  of the magnetic field on these boundaries. The vertical component of
  the magnetic field is possibly independent of the umbral area. <BR />
  Conclusions: The inner penumbral boundaries are defined by the critical
  value of the vertical component of the magnetic field. This implies
  that the penumbral filaments have a convective origin.

Title: Temporal downflows in a penumbra
Authors: Jurčák, J.; Katsukawa, Y.
Bibcode: 2010A&A...524A..21J
Altcode:
  <BR /> Aims: We analyze temporal downflow patches that are located
  in a penumbra and have the same polarity of the magnetic field as
  a sunspot umbra. <BR /> Methods: The repetitive 2'' wide raster
  scans of penumbral regions that are taken with one minute cadence by
  the Hinode spectropolarimeter are used to detect the line-of-sight
  velocities in the penumbra from enhanced signals in the wings of
  Stokes V profiles. The lifetimes and positions within penumbra of the
  identified downflow patches are investigated. The plasma properties
  of the downflow patches are determined using the inversions of the
  observed Stokes profiles. <BR /> Results: The temporal downflows
  have lifetimes of up to fourteen minutes. Some of them are related
  to the disappearance or weakening of nearby upflow regions or to the
  chromospheric brightenings. The downflows take place in regions with
  stronger and more vertical magnetic fields than the upflow regions.

Title: A new type of small-scale downflow patches in sunspot penumbrae
Authors: Katsukawa, Y.; Jurčák, J.
Bibcode: 2010A&A...524A..20K
Altcode: 2010arXiv1007.1702K
  Context. Magnetic and flow structures in a sunspot penumbra are created
  by strong interplay between inclined magnetic fields and photospheric
  convection. They exhibit a complex nature that cannot always be
  explained by the well-known Evershed flow. <BR /> Aims: A sunspot
  penumbra is observationally examined to reveal properties of small-scale
  flow structures and their relationship to the filamentary magnetic
  structures and the Evershed flow. We also study how the photospheric
  dynamics are related to chromospheric activities. <BR /> Methods: This
  study is based on data analysis of spectro-polarimetric observations of
  photospheric Fe I lines with the Solar Optical Telescope aboard Hinode
  in a sunspot penumbra at different heliocentric angles. Vector magnetic
  fields and velocities are derived using the spectro-polarimetric
  data and a Stokes inversion technique. An observation with a Ca II H
  filtergram co-spatial and co-temporal with the spectro-polarimetric
  one is also used to study possible chromospheric responses. <BR />
  Results: We find small patches with downflows in the photospheric
  layers. The downflow patches have a size of 0.5'' or smaller and
  a different geometrical configuration from the Evershed flow. The
  downflow velocity is about 1 km s<SUP>-1</SUP> in the lower photspheric
  layers and is almost zero in the upper layers. Some of the downflow
  patches are associated with brightenings seen in Ca II H images. <BR
  /> Conclusions: The downflows are possible observational signatures
  of downward flows driven by magnetic reconnection in the interlaced
  magnetic field configuration, where upward flows make brightenings in
  the chromosphere. Another possibility is that they are concentrated
  downward flows of overturning magnetoconvection.

Title: Three-Dimensional View of Transient Horizontal Magnetic Fields
    in the Photosphere
Authors: Ishikawa, Ryohko; Tsuneta, Saku; Jurčák, Jan
Bibcode: 2010ApJ...713.1310I
Altcode: 2010arXiv1003.1376I
  We infer the three-dimensional magnetic structure of a transient
  horizontal magnetic field (THMF) during its evolution through
  the photosphere using SIRGAUS inversion code. The SIRGAUS code
  is a modified version of SIR (Stokes Inversion based on Response
  function), and allows for retrieval of information on the magnetic and
  thermodynamic parameters of the flux tube embedded in the atmosphere
  from the observed Stokes profiles. Spectropolarimetric observations of
  the quiet Sun at the disk center were performed with the Solar Optical
  Telescope on board Hinode with Fe I 630.2 nm lines. Using repetitive
  scans with a cadence of 130 s, we first detect the horizontal field
  that appears inside a granule, near its edge. On the second scan,
  vertical fields with positive and negative polarities appear at both
  ends of the horizontal field. Then, the horizontal field disappears
  leaving the bipolar vertical magnetic fields. The results from the
  inversion of the Stokes spectra clearly point to the existence of
  a flux tube with magnetic field strength of ~400 G rising through
  the line-forming layer of the Fe I 630.2 nm lines. The flux tube is
  located at around log τ<SUB>500</SUB> ~ 0 at Δt = 0 s and around log
  τ<SUB>500</SUB> ~ -1.7 at Δt = 130 s. At Δt = 260 s, the horizontal
  part is already above the line-forming region of the analyzed lines. The
  observed Doppler velocity is maximally 3 km s<SUP>-1</SUP>, consistent
  with the upward motion of the structure as retrieved from the SIRGAUS
  code. The vertical size of the tube is smaller than the thickness of
  the line-forming layer. The THMF has a clear Ω-shaped loop structure
  with the apex located near the edge of a granular cell. The magnetic
  flux carried by this THMF is estimated to be 3.1 × 10<SUP>17</SUP> Mx.

Title: Scattering Polarization in the Fe I 630 nm Emission Lines at
    the Extreme Limb of the Sun
Authors: Lites, B. W.; Casini, R.; Manso Sainz, R.; Jurčák, J.;
   Ichimoto, K.; Ishikawa, R.; Okamoto, T. J.; Tsuneta, S.; Bellot
   Rubio, L.
Bibcode: 2010ApJ...713..450L
Altcode:
  Spectro-polarimetric observations with the Solar Optical Telescope
  onboard Hinode reveal the emission spectrum of the Fe I 630 nm lines
  at the solar limb. The emission shell extends for less than 1'' thereby
  making it extremely difficult to detect from ground-based observatories
  viewing the limb through the Earth's atmosphere. The linear polarization
  signal is clearly due to scattering and it is predominantly oriented
  in the radial direction. Using a comprehensive atomic model of
  iron, we are able to interpret qualitatively the observed signals,
  including the radial orientation of the linear polarization. The Hanle
  effect causes the linear polarization of the Fe I 630 nm lines to be
  sensitive to magnetic fields between ~0.1 G and ~40 G, and also to
  be sensitive to the field's topology for stronger fields. The overall
  degree of observed polarization can be reproduced by randomly oriented
  horizontal magnetic fields of strength ≈2 G. The discovery of their
  scattering polarization signals thus opens a new diagnostic opportunity
  for these lines.

Title: Evolution of Umbral Dots and Penumbral Grains
Authors: Sobotka, M.; Jurčák, J.
Bibcode: 2010ASSP...19..507S
Altcode: 2010mcia.conf..507S
  On 27 February 2007, Hinode SOT/SP acquired a time series of full-Stokes
  spectra of a regular, medium-sized sunspot NOAA 10944 located near
  the center of the solar disk. The inversion code SIR (Ruiz Cobo and
  del Toro Iniesta 1992, ApJ 398, 375) was applied to these data and a
  3-h long time series of 34 spatial 3D maps of plasma parameters in the
  umbra and penumbra were computed. The temporal and spatial resolutions
  are 5.5 min and 0 :0032, respectively. A simultaneous series of SOT/BFI
  G-band images was utilized for complementary measurements of horizontal
  motions and sizes of small-scale features.

Title: Downflow Patches in a Penumbra Observed with the Hinode
    Spectro-Polarimeter
Authors: Katsukawa, Y.; Jurčák, J.
Bibcode: 2009ASPC..415..117K
Altcode:
  We here present a new observational signature of dynamics in a sunspot
  penumbra. The dynamics are observed as a small patch of downflows
  distributed sparsely in a center-side penumbra, and not observed in
  a limb-side penumbra. The distribution suggests that the downflow is
  aligned to magnetic field lines relatively vertical to the surface. The
  flow might be related to dissipation of magnetic energies in a penumbra.

Title: Evolution of Physical Characteristics of Umbral Dots and
    Penumbral Grains
Authors: Sobotka, M.; Jurčák, J.
Bibcode: 2009ApJ...694.1080S
Altcode:
  A time series of full-Stokes spectropolarimetric observations of
  the sunspot NOAA 10944, acquired with HINODE/SOT in 2007 February, is
  analyzed. The data were inverted using the code SIR into a series of 34
  maps covering 3 hr of umbra and penumbra evolution. The retrieved maps
  of plasma parameters show the spatial distribution of temperature,
  line-of-sight velocity, magnetic field strength, and inclination
  in two different ranges of optical depths corresponding to the low
  and high photosphere. In these maps, the evolution of central and
  peripheral umbral dots (CUDs and PUDs) and penumbral grains (PGs) was
  traced. While CUDs do not show any excess of line-of-sight velocity
  and magnetic field inclination with respect to the surrounding umbra,
  upflows of 400 m s<SUP>-1</SUP> and a more horizontal magnetic field
  are detected in the low photospheric layers of PUDs. PGs have even
  stronger upflows and magnetic field inclination in the low photosphere
  than PUDs. The absolute values of these parameters decrease when PGs
  evolve into PUDs. It seems that PGs and PUDs are of a similar physical
  nature. Both classes of features appear in regions with a weaker and
  more horizontal magnetic field and their formation height reaches
  the low photosphere. On the other hand, CUDs appear in regions with
  a stronger and more vertical magnetic field and they are formed too
  deep to detect upflows and changes in magnetic field inclination.

Title: The Properties of Penumbral Microjets - Inclinations and
    Possible Potospheric Response
Authors: Jurcak, J.; Katsukawa, Y.
Bibcode: 2008ESPM...12.2.25J
Altcode:
  The dependence of penumbral microjets inclination on the position
  within penumbra is investigated using the Ca II images taken with Hinode
  SOT. The penumbral microjet inclination is increasing towards the outer
  edge of the penumbra; from 35 deg at the umbra-penumbra boundary up
  to 70 deg at the penumbra/quiet sun boundary. The comparison with the
  inclination of photospheric magnetic field suggest that the penumbral
  microjet follows the opening magnetic field lines of a vertical flux
  tube that creates the sunspot. Another data set of Ca II images with
  simultaneous SP measurements is used to study the possible relation
  between the penumbral microjets and the downflows observed in middle
  of the centre-side penumbra. Some of these downflow patches can be
  associated with the Ca II brightenings and might correspond to the
  reconnection outflow. As is retrieved from the Stokes inversion, the
  downflow preferentially take place in the lower photosphere and this
  may provide a constraint on a reconnection site.

Title: The properties of penumbral microjets inclination
Authors: Jurčák, J.; Katsukawa, Y.
Bibcode: 2008A&A...488L..33J
Altcode: 2008arXiv0808.0757J
  Aims: We investigate the dependence of penumbral microjets inclination
  on the position within penumbra. <BR />Methods: The high cadence
  observations taken on 10 November 2006 with the Hinode satellite
  through the Ca II H and G-band filters were analysed to determine the
  inclination of penumbral microjets. The results were then compared with
  the inclination of the magnetic field determined through the inversion
  of the spectropolarimetric observations of the same region. <BR
  />Results: The penumbral microjet inclination is increasing towards
  the outer edge of the penumbra. The results suggest that the penumbral
  microjet follows the opening magnetic field lines of a vertical flux
  tube that creates the sunspot.

Title: Differences between Central and Peripheral Umbral Dots
Authors: Sobotka, M.; Jurcak, J.
Bibcode: 2008ESPM...12.2.23S
Altcode:
  A time series of full-Stokes spectropolarimetric observations of the
  sunspot NOAA 10944, acquired with Hinode SOT/SP in February 2007,
  is analysed. The data were inverted using the code SIR into a series
  of 33 maps covering 3 hours of the umbra and penumbra evolution. Each
  map describes the spatial distribution of temperature, line-of-sight
  velocity, and magnetic field vector in two different ranges of optical
  depths corresponding to lower and upper photosphere. In these maps,
  several long-lived central (CUDs) and moving peripheral (PUDs)
  umbral dots were selected and their evolution was traced. While CUDs
  show only a very weak signature of LOS velocity and magnetic field
  inclination, in the low layers of PUDs were detected upflows of 500
  m/s and an enhanced field inclination with respect to the surrounding
  umbra. These parameters decrease gradually during the evolution of
  PUDs. Hence, concerning the physical characteristics, PUDs resemble
  rather penumbral grains (from which they often originate) than CUDs.

Title: Erratum: The Analysis of Penumbral Fine Structure Using an
    Advanced Inversion Technique
Authors: Jurcák, Jan; Bellot Rubio, Luis; Ichimoto, Kiyoshi;
   Katsukawa, Yukio; Lites, Bruce; Nagata, Shin'ichi; Shimizu, Toshifumi;
   Suematsu, Yoshinori; Tarbell, Theodore D.; Title, Alan M.; Tsuneta,
   Saku
Bibcode: 2008PASJ...60..933J
Altcode:
  In the article [PASJ 59, S601-S606 (2007)], the word ''CSIC'' was
  omitted from the affiliation of Dr. Luis Bellot Rubio. The correct
  affiliation is : <SUP>2</SUP>Instituto de Astrofísica de Andalucía
  (CSIC), Apdo. de Correos 3004, 18080 Granada, Spain

Title: Photospheric Signature of Penumbral Microjets
Authors: Katsukawa, Y.; Jurcak, J.; Ichimoto, K.; Suemtasu, Y.;
   Tsuneta, S.; Shimizu, T.; Berger, T. E.; Shine, R. A.; Tarbell, T. D.;
   Lites, B. W.
Bibcode: 2008AGUSMSP53A..03K
Altcode:
  HINODE Solar Optical Telescope (SOT) discovered ubiquitous occurrence
  of fine-scale jetlike activities in penumbral chromospheres, which
  are referred to as penumbral microjets. The microjets' small width
  of 400 km and short duration of less than 1 min make them difficult
  to identify in existing ground-based observations. The apparent
  rise velocity is faster than 50km/s and is roughly comparable to
  the Alfven speed in the sunspot chromosphere. These properties of
  penumbral microjets suggest that magnetic reconnection in uncombed
  magnetic field configuration is the most possible cause of penumbral
  microjets. In order to understand magnetic configuration associated with
  penumbral microjets and prove the chromospheric magnetic reconnection
  hypothesis, we investigated relationship between penumbral microjets
  seen in CaIIH images and photospheric magnetic fields measured by
  the HINODE spectro-polarimeter. We found the inclination angles of
  penumbral microjets measured in CaII H images are roughly consistent
  with inclination angles of relatively vertical magnetic field
  component in uncombed magnetic field configuration. In addition,
  strong and transient downflows are observed in the photosphere near
  the boundary of a horizontal flux tube associated with a penumbral
  microjet. The size of the downflow region is about 300km, which is
  close to the width of penumbral microjets seen in CaII H images. The
  downflow velocity of several km/s might be a result of an outflow of
  chromospheric magnetic reconnection and suffer deceleration due to
  the higher density in the photosphere.

Title: Penumbral models in the light of Hinode spectropolarimetric
    observations
Authors: Jurčák, J.; Bellot Rubio, L. R.
Bibcode: 2008A&A...481L..17J
Altcode: 2007arXiv0711.1692J
  Aims:The realism of current models of the penumbra is assessed
  by comparing their predictions with the plasma properties
  of penumbral filaments as retrieved from spectropolarimetric
  observations. <BR />Methods: The spectropolarimeter onboard Hinode
  allows us, for the first time, to distinguish the fine structure
  of the penumbra. Therefore, we can use one-component inversions to
  obtain the stratifications of plasma parameters in each pixel. The
  correlations between the plasma parameters and the continuum intensity
  are studied. <BR />Results: We find that, in the outer penumbra,
  the stronger flows and higher values of magnetic field inclination
  tend to be located in dark filaments. This finding does not seem to
  be compatible with the scenario of a field-free gappy penumbra.

Title: The Analysis of Penumbral Fine Structure Using an Advanced
    Inversion Technique
Authors: Jurcák, Jan; Bellot Rubio, Luis; Ichimoto, Kiyoshi;
   Katsukawa, Yukio; Lites, Bruce; Nagata, Shin'ichi; Shimizu, Toshifumi;
   Suematsu, Yoshinori; Tarbell, Theodore D.; Title, Alan M.; Tsuneta,
   Saku
Bibcode: 2007PASJ...59S.601J
Altcode: 2007arXiv0707.1560J
  We present a method to study the penumbral fine structure using data
  obtained by the spectropolarimeter on board Hinode. For the first
  time, the penumbral filaments can be considered as being resolved in
  spectropolarimetric measurements. This enables us to use inversion
  codes with only one-component model atmospheres, and thus to assign
  the obtained stratifications of the plasma parameters directly to the
  penumbral fine structure. This approach was applied to the limb-side
  part of the penumbra in the active region NOAA10923. Preliminary results
  show a clear dependence of the plasma parameters on the continuum
  intensity in the inner penumbra, i.e., a weaker and horizontal magnetic
  field along with an increased line-of-sight velocity are found in the
  low layers of the bright filaments. The results in the mid penumbra
  are ambiguous, and future analyses are necessary to unveil the magnetic
  field structure and other plasma parameters there.

Title: The Use of Spectro-Polarimetric Measurements to determine
    the Plasma Heating
Authors: Jurčák, J.; Martinez Pillet, V.; Sobotka, M.
Bibcode: 2007ASPC..369..171J
Altcode:
  We present the possible use of spectro-polarimetric measurements on
  a set of data recorded with La Palma Stokes Polarimeter attached to
  the Swedish Vacuum Solar Telescope. The stratification over the solar
  atmosphere of different physical parameters is retrieved from these data
  using the Stokes Inversion based on Response functions (SIR). We derive
  the vertical component of electric current density coming out from the
  stratification of the magnetic field strength and orientation of the
  magnetic field vector. We also found spatial and height correlation
  between the temperature enhancement and increase of electric current
  density, this could be caused by the energy dissipation stored in the
  magnetic field configuration.

Title: Observational Evidence for Rising Penumbral Flux Tubes?
Authors: Jurčák, J.; Sobotka, M.
Bibcode: 2007SoPh..241..223J
Altcode:
  On 13 May 2000 parts of a penumbra were observed in an active region
  NOAA 8990 with the La Palma Stokes Polarimeter attached to the Swedish
  Vacuum Solar Telescope. The stratification over the solar atmosphere of
  different physical parameters is retrieved from these data by using the
  Stokes inversion based on response functions. The results confirm the
  previous findings of the penumbral structure. In general, the magnetic
  field becomes weaker and more horizontal with increasing distance from
  the umbra and the line-of-sight velocities are increasing towards the
  outer boundary of the penumbra. The results also suggest the existence
  of the unresolved fine structure of the penumbra. The stratifications
  of the temperature and of the magnetic field strength indicate the
  presence of rising flux tubes, which were predicted theoretically by
  Schlichenmaier, Jahn and Schmidt (1998, Astron. Astrophys.337, 897).

Title: The observational counterpart of the rising flux tube model?
Authors: Jurčák, J.; Sobotka, M.
Bibcode: 2007msfa.conf..225J
Altcode:
  An analysis of Stokes observations of a penumbra in active region NOAA
  8990 is presented. The observations were recorded with the La Palma
  Stokes Polarimeter attached to the 1-m Swedish Solar Telescope. The
  stratification in the solar atmosphere of different physical parameters
  is retrieved from these data using the Stokes Inversion based on
  Response functions (SIR). Our results confirm previous findings,
  that with increasing distance from the umbra the magnetic field
  becomes weaker and more horizontal and the line-of-sight velocities
  increase. The results suggest the existence of unresolved filamentary
  structure in the spatial distributions of temperature, magnetic field
  strength and inclination. The maps of temperature and magnetic field
  strength along the vertical cuts through the penumbra indicate the
  presence of rising flux tubes, predicted theoretically by Schlichenmaier
  et al. (1998).

Title: The magnetic canopy above light bridges
Authors: Jurčák, J.; Martínez Pillet, V.; Sobotka, M.
Bibcode: 2006A&A...453.1079J
Altcode:
  An analysis of high-resolution Stokes observations of two light
  bridges in active region NOAA 8990 is presented. The observations were
  recorded with the La Palma Stokes Polarimeter attached to the Swedish
  Vacuum Solar Telescope. The stratification over the solar atmosphere
  of different physical parameters is retrieved from these data using
  the Stokes inversion based on response functions (SIR). Our results
  confirm previous observations of features such as the decrease in
  magnetic field strength and the increase in inclination in the light
  bridges. We also confirm a temperature increase in these structures
  with respect to the surrounding umbrae. The maps of the magnetic field
  strength and of the orientation of the magnetic field vector indicate
  the presence of a canopy structure above the light bridges. We derive
  the vertical component of electric current density (J_z) from the
  configuration of the magnetic field. The increased temperature found
  in the upper layers is studied in the context of the proposed canopy
  topology and could also explain the recently observed chromospheric
  heating processes found above light bridges.

Title: The Canopy Structure above Light Bridges
Authors: Jurčák, J.; Sobotka, M.; Martínez Pillet, V.
Bibcode: 2006CEAB...30...55J
Altcode:
  An analysis of high-resolution Stokes observations of two light bridges
  in the active region NOAA 8990 is presented. The observations were
  recorded with the La Palma Stokes Polarimeter attached to the Swedish
  Vacuum Solar Telescope. The stratification of different physical
  parameters is retrieved using the Stokes Inversion based on Response
  functions (SIR). Our results confirm the decrease of magnetic field
  strength and the increase of inclination in light bridges. We find a
  complex temperature stratification in these structures Coming out from
  the stratification of the magnetic field strength and the orientation
  of the magnetic field vector, we suggest a canopy structure above the
  light bridge. We derive the vertical component of electric current
  density (J<SUB>z</SUB>). The increase of J<SUB>z</SUB> corresponds to
  temperature enhancements that might be caused by the energy dissipation
  stored in the magnetic field.

Title: The Magnetic Configuration in Light Bridges
Authors: Jurčák, J.; Sobotka, M.; Martínez Pillet, V.
Bibcode: 2005ESASP.600E...8J
Altcode: 2005dysu.confE...8J; 2005ESPM...11....8J
  No abstract at ADS

Title: The structure of a penumbral connection between solar pores
Authors: Hirzberger, J.; Stangl, S.; Gersin, K.; Jurčák, J.;
   Puschmann, K. G.; Sobotka, M.
Bibcode: 2005A&A...442.1079H
Altcode:
  High resolution 2D-spectro-polarimetric observations have been used
  to analyse the magnetic field and flow topologies of a penumbral
  connection between two opposite polarity solar pores. A filamentary
  structured Evershed-like material flow from one pore to the other
  along the magnetic field lines has been detected. The flow channels
  are co-spatial with bright penumbral filaments close to the pore which
  feeds the flow and the clear brightness-velocity relation vanishes close
  to the pore which represents the sink of the flow. The boundary between
  umbra and penumbra of the two pores show significant differences: bright
  comet-like penumbral grains represent endings of penumbral filaments
  at the flow sources whereas no such grains were found at the sinks of
  the flow. Furthermore, a systematic variation of the asymmetries of
  measured Stokes V profiles across the penumbral connection have been
  found. The obtained results are in accordance with the widely-accepted
  uncombed penumbra hypothesis and the moving flux tube model.

Title: Velocity Fields in an Irregular Sunspot
Authors: Jurčák, J.; Sobotka, M.; Martínez-Pillet, V.
Bibcode: 2005ASSL..320..227J
Altcode: 2005smp..conf..227J
  No abstract at ADS

Title: Velocity fields in an irregular sunspot
Authors: Jurčák, J.; Sobotka, M.; Martínez-Pillet, V.
Bibcode: 2003ESASP.535..109J
Altcode: 2003iscs.symp..109J
  Line-of-sight velocity fields in an irregular sunspot (NOAA 8990)
  have been determined from Stokes-I spectra of the line Fe I 630.15
  nm, obtained with the La Palma Stokes Polarimeter at the Swedish
  Vacuum Solar Telescope on May 13, 2000. We show and discuss the
  resulting velocity maps, the dependence of velocities on the
  continuum intensities, and the correlation between velocities and
  line asymmetries.

Title: Burst phenomena in solar flares
Authors: Kotrč, P.; Kupryakov, Yu. A.; Jurčák, J.
Bibcode: 2002ESASP.477..139K
Altcode: 2002scsw.conf..139K
  Solar flares are rapid dissipative processes in which the energy
  accumulated in the magnetic field is released in the forms of plasma
  heating, explosive plasma flows with flare shock generations, particle
  accelerations, and emissions in a very broad range of frequencies
  ranging from radio waves up to gamma-rays. As solar flares and related
  phenomena influence not only the processes in the solar atmosphere, but
  also in the heliosphere, they belong to important components of space
  weather. While some of the flares pass quietly, another ones express
  as very active. Courses of some flares are rather monotone while the
  others are accompanied by bursts during which sudden and usually short
  increase of the radiation outputs can be detected. Analyzing data from
  catalogues and various observations we studied rapid changes occurring
  in solar flare X-ray, radio and optical radiation, especially flare
  optical spectra including their possible polarization as well as other
  indirect evidence of accelerated particle beams occurrence.

