Author name code: derosa
ADS astronomy entries on 2022-09-14
author:"DeRosa, M." 
------------------------------------------------------------------------  

Title: Suppression of Torus Instability on Cool Stars
Authors: Sun, Xudong; Derosa, Marc; Torok, Tibor
Bibcode: 2022cosp...44.1389S
Altcode:
  Despite the frequent detection of stellar super flares, reports on
  stellar coronal mass ejections (CMEs) are rare. This is in contrast with
  our Sun, where almost all large flares are accompanied by a CME. Here,
  we use an analytical coronal magnetic field model to demonstrate that
  the torus instability, a leading mechanism for solar CMEs, tends to
  be suppressed in stellar magnetic environment. Contributing factors
  include larger starspots, stronger global dipole field, and more
  closed magnetic geometry compared to the Sun. Suppression of the torus
  instability may contribute to the low apparent CME rate on cool stars.

Title: Coronal Dimming as a Proxy for Solar and Stellar Coronal
    Mass Ejections
Authors: Jin, Meng; Nitta, Nariaki; Derosa, Marc; Cheung, Mark; Osten,
   Rachel; France, Kevin; Mason, James; Kowalski, Adam; Schrijver, Carolus
Bibcode: 2022cosp...44.1404J
Altcode:
  Solar coronal dimmings have been observed extensively in the past two
  decades. Due to their close association with coronal mass ejections
  (CMEs), there is a critical need to improve our understanding of the
  physical processes that cause dimmings as well as their relationship
  with CMEs. Recent study (e.g., Veronig et al. 2021) also shows promising
  dimming signals from distant stars, which suggest the possibility of
  using coronal dimming as a proxy to diagnose stellar CMEs. In this
  study, we first conduct a comparative study of solar coronal dimming
  using MHD simulations and SDO observations. A detailed analysis of
  the simulation and observation data reveals how transient dimming
  / brightening are related to plasma heating processes, while the
  long-lasting core and remote dimmings are caused by mass loss process
  induced by the CME. Using metrics such as dimming depth and dimming
  slope, we uncover a relationship between dimmings and CME properties
  (e.g., CME mass, CME speed) in the simulation. We further extend the
  model for simulating the stellar CMEs and dimmings and compare with
  solar cases. Our result suggests that coronal dimmings encode important
  information about the associated CMEs, which provides a physical basis
  for detecting stellar CMEs from distant solar-like stars.

Title: The Impact of Nonlinear Interactions Between Solar Photospheric
    Magnetic Fields and Flows on the Evolution of the Polar Fields During
    Recent Sunspot Cycles
Authors: Derosa, Marc; Hoeksema, J. Todd; Mahajan, Sushant; Upton,
   Lisa A.
Bibcode: 2022cosp...44.3224D
Altcode:
  The observed polar fields during solar activity minimum intervals
  are believed to be a useful predictor of future sunspot cycle
  amplitudes. Such polar fields result from the poleward transport
  of magnetic flux from the many active regions that emerge onto the
  photosphere at lower latitudes. Recent studies suggest that a subset of
  emergent active regions have an outsized influence on the buildup and
  eventual maximal amplitude of polar fields. Additionally, the nonlinear
  interactions between these fields with the observed surface flows may
  also affect the evolution of polar fields. In the work presented here,
  we use surface-flux transport modeling, in combination with a curated
  list of emergent active regions during sunspot cycles 24 and 25, to
  investigate the effects of both active-region emergence properties
  and inflows surrounding active regions on the buildup of polar fields,
  with an eye toward the ability to constrain the polar field amplitude
  following sunspot cycle 25.

Title: Coronal Mass Ejections and Dimmings: A Comparative Study
    Using MHD Simulations and SDO Observations
Authors: Jin, Meng; Cheung, Mark C. M.; DeRosa, Marc L.; Nitta,
   Nariaki V.; Schrijver, Carolus J.
Bibcode: 2022ApJ...928..154J
Altcode: 2022arXiv220213034J
  Solar coronal dimmings have been observed extensively in recent
  years. Due to their close association with coronal mass ejections
  (CMEs), there is a critical need to improve our understanding of the
  physical processes that cause dimmings as well as their relationship
  with CMEs. In this study, we investigate coronal dimmings by combining
  simulation and observational efforts. By utilizing a data-constrained
  global magnetohydrodynamics model (Alfvén-wave solar model), we
  simulate coronal dimmings resulting from different CME energetics and
  flux rope configurations. We synthesize the emissions of different EUV
  spectral bands/lines and compare with SDO/AIA and EVE observations. A
  detailed analysis of the simulation and observation data suggests
  that the transient dimming/brightening are related to plasma heating
  processes, while the long-lasting core and remote dimmings are caused
  by mass-loss process induced by the CME. Moreover, the interaction
  between the erupting flux rope with different orientations and the
  global solar corona could significantly influence the coronal dimming
  patterns. Using metrics such as dimming depth and dimming slope,
  we investigate the relationship between dimmings and CME properties
  (e.g., CME mass, CME speed) in the simulation. Our result suggests
  that coronal dimmings encode important information about the associated
  CMEs, which provides a physical basis for detecting stellar CMEs from
  distant solar-like stars.

Title: Probing the Physics of the Solar Atmosphere with the Multi-slit
    Solar Explorer (MUSE). II. Flares and Eruptions
Authors: Cheung, Mark C. M.; Martínez-Sykora, Juan; Testa, Paola;
   De Pontieu, Bart; Chintzoglou, Georgios; Rempel, Matthias; Polito,
   Vanessa; Kerr, Graham S.; Reeves, Katharine K.; Fletcher, Lyndsay; Jin,
   Meng; Nóbrega-Siverio, Daniel; Danilovic, Sanja; Antolin, Patrick;
   Allred, Joel; Hansteen, Viggo; Ugarte-Urra, Ignacio; DeLuca, Edward;
   Longcope, Dana; Takasao, Shinsuke; DeRosa, Marc L.; Boerner, Paul;
   Jaeggli, Sarah; Nitta, Nariaki V.; Daw, Adrian; Carlsson, Mats; Golub,
   Leon; The
Bibcode: 2022ApJ...926...53C
Altcode: 2021arXiv210615591C
  Current state-of-the-art spectrographs cannot resolve the fundamental
  spatial (subarcseconds) and temporal (less than a few tens of
  seconds) scales of the coronal dynamics of solar flares and eruptive
  phenomena. The highest-resolution coronal data to date are based on
  imaging, which is blind to many of the processes that drive coronal
  energetics and dynamics. As shown by the Interface Region Imaging
  Spectrograph for the low solar atmosphere, we need high-resolution
  spectroscopic measurements with simultaneous imaging to understand the
  dominant processes. In this paper: (1) we introduce the Multi-slit Solar
  Explorer (MUSE), a spaceborne observatory to fill this observational
  gap by providing high-cadence (&lt;20 s), subarcsecond-resolution
  spectroscopic rasters over an active region size of the solar transition
  region and corona; (2) using advanced numerical models, we demonstrate
  the unique diagnostic capabilities of MUSE for exploring solar coronal
  dynamics and for constraining and discriminating models of solar flares
  and eruptions; (3) we discuss the key contributions MUSE would make
  in addressing the science objectives of the Next Generation Solar
  Physics Mission (NGSPM), and how MUSE, the high-throughput Extreme
  Ultraviolet Solar Telescope, and the Daniel K Inouye Solar Telescope
  (and other ground-based observatories) can operate as a distributed
  implementation of the NGSPM. This is a companion paper to De Pontieu
  et al., which focuses on investigating coronal heating with MUSE.

Title: Torus-stable zone above starspots
Authors: Sun, Xudong; Török, Tibor; DeRosa, Marc L.
Bibcode: 2022MNRAS.509.5075S
Altcode: 2021arXiv211103665S; 2021MNRAS.tmp.2934S
  Whilst intense solar flares are almost always accompanied by a coronal
  mass ejection (CME), reports on stellar CMEs are rare, despite the
  frequent detection of stellar 'super flares'. The torus instability of
  magnetic flux ropes is believed to be one of the main driving mechanisms
  of solar CMEs. Suppression of the torus instability, due to a confining
  background coronal magnetic field that decreases sufficiently slowly
  with height, may contribute to the lack of stellar CME detection. Here,
  we use the solar magnetic field as a template to estimate the vertical
  extent of this 'torus-stable zone' (TSZ) above a stellar active
  region. For an idealized potential field model comprising the fields
  of a local bipole (mimicking a pair of starspots) and a global dipole,
  we show that the upper bound of the TSZ increases with the bipole
  size, the dipole strength, and the source surface radius where the
  coronal field becomes radial. The boundaries of the TSZ depend on the
  interplay between the spots' and the dipole's magnetic fields, which
  provide the local- and global-scale confinement, respectively. They
  range from about half the bipole size to a significant fraction of the
  stellar radius. For smaller spots and an intermediate dipole field,
  a secondary TSZ arises at a higher altitude, which may increase the
  likelihood of 'failed eruptions'. Our results suggest that the low
  apparent CME occurrence rate on cool stars is, at least partially,
  due to the presence of extended TSZs.

Title: Probing the Physics of the Solar Atmosphere with the Multi-slit
Solar Explorer (MUSE): II. Flares and Eruptions
Authors: Cheung, Chun Ming Mark; Martinez-Sykora, Juan; Testa, Paola;
   De Pontieu, Bart; Chintzoglou, Georgios; Rempel, Matthias; Polito,
   Vanessa; Kerr, Graham; Reeves, Katharine; Fletcher, Lyndsay; Jin,
   Meng; Nobrega, Daniel; Danilovic, Sanja; Antolin, Patrick; Allred,
   Joel; Hansteen, Viggo; Ugarte-Urra, Ignacio; DeLuca, Edward; Longcope,
   Dana; Takasao, Shinsuke; DeRosa, Marc; Boerner, Paul; Jaeggli, Sarah;
   Nitta, Nariaki; Daw, Adrian; Carlsson, Mats; Golub, Leon
Bibcode: 2021AGUFMSH51A..08C
Altcode:
  Current state-of-the-art spectrographs cannot resolve the fundamental
  spatial (sub-arcseconds) and temporal scales (less than a few tens
  of seconds) of the coronal dynamics of solar flares and eruptive
  phenomena. The highest resolution coronal data to date are based on
  imaging, which is blind to many of the processes that drive coronal
  energetics and dynamics. As shown by IRIS for the low solar atmosphere,
  we need high-resolution spectroscopic measurements with simultaneous
  imaging to understand the dominant processes. In this paper: (1)
  we introduce the Multi-slit Solar Explorer (MUSE), a spaceborne
  observatory to fill this observational gap by providing high-cadence
  (&lt;20 s), sub-arcsecond resolution spectroscopic rasters over an
  active region size of the solar transition region and corona; (2)
  using advanced numerical models, we demonstrate the unique diagnostic
  capabilities of MUSE for exploring solar coronal dynamics, and for
  constraining and discriminating models of solar flares and eruptions;
  (3) we discuss the key contributions MUSE would make in addressing the
  science objectives of the Next Generation Solar Physics Mission (NGSPM),
  and how MUSE, the high-throughput EUV Solar Telescope (EUVST) and the
  Daniel K Inouye Solar Telescope (and other ground-based observatories)
  can operate as a distributed implementation of the NGSPM. This is a
  companion paper to De Pontieu et al. (2021, also submitted to SH-17),
  which focuses on investigating coronal heating with MUSE.

Title: Assessing the Impact of Cross-Equatorial Surface Flows on
    the Buildup of Polar Fields Using Surface Flux Transport Models
Authors: DeRosa, Marc; Mahajan, Sushant
Bibcode: 2021AGUFMSH54A..02D
Altcode:
  Observed polar magnetic flux on the Sun is a useful indicator and
  predictor of the sunspot cycle amplitudes. The buildup of such polar
  flux is dependent on a number of factors, most prominently the tilt
  angle of emergent active-region flux (Joy's Law) and the speed of
  the near-surface meridional flow, as well as other factors such as
  the inflows surrounding active regions. Surface-flux transport models
  use such observations to model the evolution of solar polar fields,
  transporting flux based on empirical prescriptions for differential
  rotation, meridional flows, and convective dispersal. In the study
  presented here, we illustrate the effects on the polar fields of
  incorporating meridional flow profiles derived from observations into
  a surface-flux transport model, and compare these effects to other
  processes that are known to affect the buildup of polar fields. We
  find that the cross-equatorial flows that are typically found from
  observed meridional flow profiles typically enhance the resulting
  polar fields. Such flows may also enhance hemispheric asymmetries.

Title: Sun-as-a-star Spectral Irradiance Observations of Transiting
Active Regions: a Milestone for Characterization of Stellar Active
    Regions
Authors: Toriumi, Shin; Airapetian, Vladimir; Hudson, Hugh; Schrijver,
   Karel; Cheung, Chun Ming Mark; DeRosa, Marc
Bibcode: 2021AGUFM.U43B..05T
Altcode:
  Recent observations have revealed that solar-type stars can produce
  massive "superflares". The strongest flares on the Sun are almost
  always associated with large, complex, rapidly-evolving active regions
  (ARs) including sunspots. Therefore, to understand why and how stellar
  flares and coronal eruptions occur, which may directly determine
  the circumstances of exoplanets, it is critically important to gain
  information on stellar ARs. One possible way to do so is to monitor the
  star in multiple wavelengths. In this study, we perform multi-wavelength
  irradiance monitoring of transiting solar ARs by using full-disk
  observational (i.e. Sun-as-a-star) data from four satellites. We find
  that the near UV light curves show strong correlations with photospheric
  total magnetic flux and that there are time lags between the coronal
  and photospheric light curves when ARs are close to the limb. Such time
  lags result from high-arching, bright coronal loops above stellar ARs
  being visible even when the AR is behind the limb. It is also found
  that the EUV light curves sensitive to transition-region temperatures
  are sometimes dimmed because of a reduction in the emission measure of
  0.60.8 MK due to the plasma being heated to higher temperatures over a
  wide area around the AR. These results indicate that, by measuring the
  stellar light curves in multiple wavelengths, we may obtain information
  on the structures and evolution of stellar ARs.

Title: The Multiview Observatory for Solar Terrestrial Science (MOST)
Authors: Gopalswamy, Nat; Kucera, Therese; Leake, James; MacDowall,
   Robert; Wilson, Lynn; Kanekal, Shrikanth; Shih, Albert; Christe,
   Steven; Gong, Qian; Viall, Nicholeen; Tadikonda, Sivakumar; Fung,
   Shing; Yashiro, Seiji; Makela, Pertti; Golub, Leon; DeLuca, Edward;
   Reeves, Katharine; Seaton, Daniel; Savage, Sabrina; Winebarger, Amy;
   DeForest, Craig; Desai, Mihir; Bastian, Tim; Lazio, Joseph; Jensen,
   P. E., C. S. P., Elizabeth; Manchester, Ward; Wood, Brian; Kooi,
   Jason; Wexler, David; Bale, Stuart; Krucker, Sam; Hurlburt, Neal;
   DeRosa, Marc; Pevtsov, Alexei; Tripathy, Sushanta; Jain, Kiran;
   Gosain, Sanjay; Petrie, Gordon; Kholikov, Shukirjon; Zhao, Junwei;
   Scherrer, Philip; Woods, Thomas; Chamberlin, Philip; Kenny, Megan
Bibcode: 2021AGUFMSH12A..07G
Altcode:
  The Multiview Observatory for Solar Terrestrial Science (MOST) is a
  comprehensive mission concept targeting the magnetic coupling between
  the solar interior and the heliosphere. The wide-ranging imagery and
  time series data from MOST will help understand the solar drivers and
  the heliospheric responses as a system, discerning and tracking 3D
  magnetic field structures, both transient and quiescent in the inner
  heliosphere. MOST will have seven remote-sensing and three in-situ
  instruments: (1) Magnetic and Doppler Imager (MaDI) to investigate
  surface and subsurface magnetism by exploiting the combination of
  helioseismic and magnetic-field measurements in the photosphere; (2)
  Inner Coronal Imager in EUV (ICIE) to study large-scale structures
  such as active regions, coronal holes and eruptive structures by
  capturing the magnetic connection between the photosphere and the
  corona to about 3 solar radii; (3) Hard X-ray Imager (HXI) to image
  the non-thermal flare structure; (4) White-light Coronagraph (WCOR) to
  seamlessly study transient and quiescent large-scale coronal structures
  extending from the ICIE field of view (FOV); (5) Faraday Effect
  Tracker of Coronal and Heliospheric structures (FETCH), a novel radio
  package to determine the magnetic field structure and plasma column
  density, and their evolution within 0.5 au; (6) Heliospheric Imager
  with Polarization (HIP) to track solar features beyond the WCOR FOV,
  study their impact on Earth, and provide important context for FETCH;
  (7) Radio and Plasma Wave instrument (M/WAVES) to study electron beams
  and shocks propagating into the heliosphere via passive radio emission;
  (8) Solar High-energy Ion Velocity Analyzer (SHIVA) to determine spectra
  of electrons, and ions from H to Fe at multiple spatial locations
  and use energetic particles as tracers of magnetic connectivity; (9)
  Solar Wind Magnetometer (MAG) to characterize magnetic structures at
  1 au; (10) Solar Wind Plasma Instrument (SWPI) to characterize plasma
  structures at 1 au. MOST will have two large spacecraft with identical
  payloads deployed at L4 and L5 and two smaller spacecraft ahead of L4
  and behind L5 to carry additional FETCH elements. MOST will build upon
  SOHO and STEREO achievements to expand the multiview observational
  approach into the first half of the 21st Century.

Title: Torus-Stable Zone Above Starspots
Authors: Sun, Xudong; Torok, Tibor; DeRosa, Marc
Bibcode: 2021AGUFMSH32A..02S
Altcode:
  The torus instability (TI) of magnetic flux ropes is one of the main
  driving mechanisms of solar coronal mass ejections (CMEs). If the
  stabilizing background magnetic field decreases sufficiently slowly
  with height, the TI will be suppressed. Here we estimate the vertical
  extent of this "torus-stable zone" (TSZ) above starspots using the
  solar magnetic field as a template. For a potential field comprising
  a bipole as a pair of starspots and a global dipole, we show that the
  upper bound of the TSZ increases with the bipole size, the dipole
  strength, and the source surface radius where the coronal field
  becomes radial. The values depend on the interplay between the spot
  and dipole magnetic fields, which provide the local and global-scale
  confinement, respectively. They range from about half the bipole size
  to a significant fraction of the stellar radius. A secondary TSZ
  sometimes arises at a higher altitude which may facilitate "failed
  eruptions". The suppression of the TI may contribute to the lack of
  CME detection on cool stars, as larger starspots, stronger dipole,
  and more closed magnetic topology significantly expand the TSZ.

Title: Coronal and Heliospheric Modeling with WSA: Recent Updates
    and Applications
Authors: Jones, Shaela; Arge, Charles; Barnes, Graham; Casti, Marta;
   Cheung, Chun Ming Mark; da Silva, Daniel; DeRosa, Marc; Henney, Carl;
   Kirk, Michael; Simpson, David; Upton, Lisa; Wallace, Samantha
Bibcode: 2021AGUFMSH15G2088J
Altcode:
  The Wang-Sheeley-Arge (WSA) model is a combined empirical and
  physics-based model for the solar corona and inner heliosphere, widely
  used in the heliophysics community for over two decades. In recent
  years the model has been updated to allow solar wind forecasting for
  satellites in non-Earth-like orbits, such as Parker Solar Probe (PSP)
  and Solar Orbiter (SolO). Here we will describe subsequent improvements
  to the model with the release of WSA version 5.3, including the
  incorporation of additional photospheric map sources. We will also
  present comparisons between coronal magnetic field models and solar
  wind forecasts based on a number of different photospheric map sources
  and discuss the variability of these results due to the uncertainty
  in the photospheric flux. Finally, we will discuss the application of
  the WSA model to forecasting for PSP and SolO.

Title: A Comparative Study of Measurements of the Suns Axisymmetric
Flows: A COFFIES Effort
Authors: Upton, Lisa; Jain, Kiran; Komm, Rudolf; Mahajan, Sushant;
   Pevtsov, Alexei; Roudier, Thierry; Tripathy, Sushanta; Ulrich, Roger;
   Zhao, Junwei; Basu, Sarbani; Chen, Ruizhu; DeRosa, Marc; Hess Webber,
   Shea; Hoeksema, J.
Bibcode: 2021AGUFMSH55D1871U
Altcode:
  Consequence Of Fields and Flows in the Interior and Exterior of
  the Sun (COFFIES) is a Phase-1 NASA DRIVE Science Center (DSC),
  with the primary objective of developing a data driven model of
  solar activity. One of COFFIES five primary science questions is
  What drives varying large-scale motions in the Sun? To address this
  question, we are developing a comprehensive catalog of the variable
  differential rotation and meridional circulation flow patterns. This
  catalog includes measurements of these flows as obtained by several
  measurement techniques: Doppler imaging, granule tracking, magnetic
  pattern tracking, magnetic feature tracking, as well as both time
  distance and ring diagram helioseismology. We show a comparison of
  these flows across these varied techniques, with a particular focus
  on the MDI/HMI/GONG/Mount Wilson overlap period (May-July 2010). We
  investigate the uncertainties and attempt to reconcile any discrepancies
  (e.g., due to flow depth or systematics associated with the different
  measurement techniques). This analysis will pave the way toward
  accurately determining the global patterns of axisymmetric flows and
  their regular and irregular variations during the cycle.

Title: Are Potential Field Source Surface models from different
    magnetic maps sufficiently robust to track the evolution of the
    coronal magnetic topology?
Authors: Barnes, G.; DeRosa, M.; Jones, S.; Cheung, M.; Arge, C.;
   Henney, C.
Bibcode: 2021AAS...23821308B
Altcode:
  The geometry, connectivity, and topology of the large-scale coronal
  magnetic field play a key role in determining whether a solar
  reconnection event will result in an eruption, either by influencing
  the location where magnetic reconnection releases energy for an event,
  or by determining the pathways and access to open field that allow an
  eruption to proceed. Knowing how reliably the coronal magnetic field
  can be inferred is critical to understanding its role in energetic
  events. Potential Field Source Surface (PFSS) models are a commonly
  used tool for both modeling the coronal field itself, and as input
  to other models. Multiple methods exist for generating the boundary
  condition needed for a PFSS model. We present here results of examining
  how robust the PFSS model topology is to different boundary maps, as
  measured by the presence of coronal magnetic null points and solar wind
  predictions from the Wang-Sheely-Arge (WSA) model, and characterize the
  evolution of these null points within a given model. <P />This material
  is based upon work supported by NASA under award No. 80NSSC19K0087. Any
  opinions, findings, and conclusions or recommendations expressed in
  this material are those of the authors and do not necessarily reflect
  the views of the National Aeronautics and Space Administration.

Title: Enhancements to Hinode/SOT-SP Vector Magnetic Field Data
    Products
Authors: DeRosa, M. L.; Leka, K. D.; Barnes, G.; Wagner, E.; Centeno,
   R.; De Wijn, A.; Bethge, C.
Bibcode: 2021AAS...23821305D
Altcode:
  The Solar Optical Telescope Spectro-Polarimeter (SOT-SP), on board the
  Hinode spacecraft (launched in 2006), is a scanning-slit spectrograph
  that continues to provide polarization spectra useful for inferring the
  vector (three-component) magnetic field at the solar photosphere. SOT-SP
  achieves this goal by obtaining line profiles of two magnetically
  sensitive lines, namely the Fe I 6302 Angstrom doublet, using a
  0.16"×164" slit as it scans a region of interest. Once the data are
  merged, a Milne-Eddington based spectropolarimetric inversion scheme is
  used to infer multiple physical parameters in the solar photosphere,
  including the vector magnetic field, from the calibrated polarization
  spectra. All of these data are publicly available once the processing
  has occurred. <P />As of this year, the Hinode/SOT team is also making
  available the disambiguated vector magnetic field and the re-projected
  heliographic components of the field. In making the disambiguated vector
  field data product, the 180° ambiguity in the plane-of-sky component
  of the vector magnetic field inherent in the spectropolarimetric
  inversion process has been resolved. This ambiguity is resolved
  using the Minimum-Energy algorithm, which is the same algorithm used
  within the pipeline producing the vector-magnetogram data product
  for the Helioseismic and Magnetic Imager aboard the Solar Dynamics
  Observatory. The heliographic field components (B<SUB>phi</SUB>,
  B<SUB>theta</SUB>, B<SUB>r</SUB>) on the same grid as the inverted data
  are also now provided. This poster provides more details about these
  data product enhancements, and some examples on how the scientific
  community may readily obtain these data.

Title: Sun-as-a-star Spectral Irradiance Observations: Milestone
    For Characterizing The Stellar Active Regions
Authors: Toriumi, S.; Airapetian, V.; Hudson, H.; Schrijver, C.;
   Cheung, M.; DeRosa, M.
Bibcode: 2021AAS...23820503T
Altcode:
  For understanding the physical mechanism behind the solar flares, it
  is crucial to measure the magnetic fields of active regions (ARs) from
  the photosphere to the corona and investigate their scale, complexity,
  and evolution. This is true for the stellar flares. However, it is
  still difficult to spatially resolve the starspots, and one possible
  way to probe their evolution and structure is to monitor the star in
  multiple wavelengths. To test this possibility with the solar data,
  we perform multi-wavelength irradiance monitoring of transiting solar
  ARs by using full-disk observation data from SDO, Hinode, GOES, and
  SORCE. As a result, we find, for instance, that the near UV light
  curves show strong correlations with photospheric total magnetic flux
  and that there are time lags between the coronal and photospheric light
  curves when ARs are close to the limb, which together may enable one
  to discern how high bright coronal loops extend above stellar ARs. It
  is also revealed that the sub-MK (i.e. transition-region temperature)
  EUV light curves are sometimes dimmed because the emission measure
  is reduced owing to the heating over a wide area around the AR. These
  results indicate that, by measuring the stellar light curves in multiple
  wavelengths, we may obtain information on the structure and evolution
  of stellar ARs.

Title: Torus-Stable Zone Above Starspots
Authors: Sun, X.; Torok, T.; DeRosa, M.
Bibcode: 2021AAS...23820801S
Altcode:
  The torus instability (TI) of current-carrying magnetic flux tubes
  is thought to drive many solar coronal mass ejections (CMEs). The
  background magnetic field provides the stabilizing force: if it
  decreases with height at a rate (decay index) slower than a critical
  value, the TI may be suppressed. Here we estimate the vertical extent
  of a "torus-stable zone" above starspots using a scaled model for the
  Sun. For a potential-field model comprising a bipole (as a pair of
  starspots) in alignment with a global dipole, we show that the upper
  bound of this zone h<SUB>c</SUB> increases with the bipole size a,
  the dipole field with harmonic coefficient g<SUB>10</SUB>, and the
  source surface radius R<SUB>s</SUB> where the magnetic field becomes
  radial. The value of h<SUB>c</SUB>, ranging from about 0.5a to a
  significant fraction of the stellar radius, depends on the interplay
  between the spot and dipole magnetic fields; its upper limit is set
  by R<SUB>s</SUB>. Suppression of the TI may contribute to the lack of
  CME detection from active cool stars, as larger starspots, stronger
  dipole, and more closed magnetic topology significantly expand the
  torus-stable zone.

Title: Torus-Stable Zone Above Starspots
Authors: Sun, Xudong; Török, Tibor; DeRosa, Marc
Bibcode: 2021csss.confE..15S
Altcode:
  The torus instability (TI) of current-carrying magnetic flux tubes
  is thought to drive many solar coronal mass ejections (CMEs). The
  background magnetic field provides the stabilizing force: if it
  decreases with height at a rate slower than a critical value, the
  TI may be suppressed. Here we estimate the vertical extent of a
  "torus-stable zone" above starspots using a scaled model for the
  Sun. For a potential-field model comprising a bipole (as a pair of
  starspots) in alignment with a global dipole, we show that the upper
  bound of this zone h<SUB>c</SUB> increases with the bipole size a,
  the dipole field with harmonic coefficient g<SUB>10</SUB>, and the
  source surface radius R<SUB>s</SUB> where the magnetic field becomes
  radial. The value of h<SUB>c</SUB>, ranging from about 0.5a to a
  significant fraction of the stellar radius, depends on the interplay
  between the spot and dipole magnetic fields; its upper limit is set
  by R<SUB>s</SUB>. Suppression of the TI may contribute to the lack of
  CME detection from active cool stars, as larger starspots, stronger
  dipole, and more closed magnetic topology significantly expand the
  torus-stable zone.

Title: Sun-as-a-star Multi-wavelength Observations: A Milestone for
    Characterization of Stellar Active Regions
Authors: Toriumi, Shin; Airapetian, Vladimir S.; Hudson, Hugh S.;
   Schrijver, Carolus J.; Cheung, Mark C. M.; DeRosa, Marc L.
Bibcode: 2021csss.confE..46T
Altcode:
  It has been revealed that "superflares" can occur on solar-type
  stars. The magnetic energy of the flares is likely to be stored in
  active-region atmospheres. Therefore, to explain the energy storage and
  occurrence of the flares, it is important to monitor the evolutions of
  the active regions, not only in visible light but also in ultraviolet
  (UV) and X-rays. To demonstrate this, we perform multi-wavelength
  irradiance monitoring of transiting solar active regions by using
  full-disk observation data. As a result of this sun-as-a-star spectral
  irradiance analysis, we confirm that the visible continuum that
  corresponds to the photosphere becomes darkened when the spot is at the
  central meridian, whereas most of the UV, EUV and X-rays, which are
  sensitive to chromospheric to coronal temperatures, are brightened,
  reflecting the bright magnetic features above the starspots. The
  time lags between the coronal and photospheric light curves have
  the potential to probe the extent of coronal magnetic fields above
  the starspots. These results indicate that, by measuring the stellar
  light curves in multiple wavelengths, we may obtain information on
  the structures and evolution of stellar active regions.

Title: The Coronal Global Evolutionary Model: Using HMI Vector
    Magnetogram and Doppler Data to Determine Coronal Magnetic Field
    Evolution
Authors: Kazachenko, Maria; Abbett, Bill; Liu, Yang; Fisher, George;
   Welsch, Brian; Bercik, Dave; DeRosa, Marc; Cheung, Mark; Sun, Xudong;
   Hoeksema, J. Todd; Erkka Lumme, .; Hayashi, Keiji; Lynch, Benjamin
Bibcode: 2021cosp...43E1785K
Altcode:
  The Coronal Global Evolutionary Model (CGEM) provides data-driven
  simulations of the magnetic field in the solar corona to better
  understand the build-up of magnetic energy that leads to eruptive
  events. The CGEM project has developed six capabilities. CGEM modules
  (1) prepare time series of full-disk vector magnetic field observations
  to (2) derive the changing electric field in the solar photosphere over
  active-region scales. This local electric field is (3) incorporated
  into a surface flux transport model that reconstructs a global
  electric field that evolves magnetic flux in a consistent way. These
  electric fields drive a (4) 3D spherical magnetofrictional (SMF) model,
  either at high resolution over a restricted range of solid angles or
  at lower resolution over a global domain to determine the magnetic
  field and current density in the low corona. An SMF-generated initial
  field above an active region and the evolving electric field at the
  photosphere are used to drive (5) detailed magnetohydrodynamic (MHD)
  simulations of active regions in the low corona. SMF or MHD solutions
  are then used to compute emissivity proxies that can be compared
  with coronal observations. Finally, a lower-resolution SMF magnetic
  field is used to initialize (6) a global MHD model that is driven by
  an SMF electric field time series to simulate the outer corona and
  heliosphere, ultimately connecting Sun to Earth. As a demonstration,
  this report features results of CGEM applied to observations of the
  evolution of NOAA Active Region 11158 in 2011 February.

Title: Using New Acoustically-Derived Solar Far-Side Magnetic-Flux
    Maps for Data Assimilation in Flux Transport Models
Authors: Hess Webber, S. A.; Chen, R.; DeRosa, M. L.; Upton, L.;
   Zhao, J.
Bibcode: 2020AGUFMSH0020005H
Altcode:
  The Sun's far-side magnetic field is important to space weather
  forecasting and solar wind modeling, but currently it is not directly
  observed. The far-side magnetic field can be approximated using
  (a) flux transport models, which are incapable of predicting growth
  or new emergence of active regions; (b) conversion from STEREO EUV
  observations, which are only available for a limited time period; or
  (c) helioseismic far-side acoustic images, which provide general active
  region sizes and locations, but not magnetic flux. Recently, Zhao
  et al. [2019] and Chen et al. [ in prep ] developed an approach that
  calculates far-side acoustic images and calibrates them into far-side
  magnetic-flux maps in near-real-time, using machine-learning and STEREO
  EUV observations as a bridge. These far-side acoustically-derived
  magnetic-flux maps are starting to be tested as assimilated data in
  multiple flux transport models. In this work, we show examples of the
  results from two different models, and discuss the implications of
  the fully-assimilated global models of synchronic magnetic flux as
  operational input for coronal or solar wind models.

Title: Understanding Solar Cycle Magnetic Evolution with Properties
    of Solar Active Regions
Authors: Liu, Y.; Hoeksema, T.; Zhao, J.; DeRosa, M. L.; Sun, X.
Bibcode: 2020AGUFMSH0020015L
Altcode:
  Understanding the solar cycle is a fundamental and important objective
  in solar physics. Recent studies have revealed correlations between
  variations of the poleward transport of photospheric magnetic fields
  with properties of both magnetic field in solar active regions as well
  as their decay products. Features such as poleward surges often play
  an outsized role in advecting flux away from the activity belts into
  polar regions, and therefore affect solar cycle activity. This report
  describes our plans and reviews preliminary results investigating the
  effects of active region-modified zonal and meridional flows on flux
  evolution and the solar cycle.

Title: Search Tool for Retrieving Level 2 Data from Hinode's
    Spectro-Polarimeter (SP)
Authors: Kam, C.; Arbolante, Q.; Frank, Z.; DeRosa, M. L.
Bibcode: 2020AGUFMED0260056K
Altcode:
  A joint project between JAXA and NASA, the Hinode Solar Optical
  Telescope (SOT) has observed our Sun since its launch in October
  2006. Mission data has been used extensively to study solar flares,
  polar magnetic fields, prominence structures, and changes over the
  solar cycle. Archived databases of the SOT filtergraph (FG) images
  and spectropolarimeter (SP) maps are maintained in the US, Japan,
  and Norway. Many tools for accessing SOT data were developed early
  in the mission timeline and are based on Harris Geospatial Solutions
  Inc. Interactive Data Language (IDL). We demonstrate a new open source
  Python-based search and cross referencing tool for the Hinode SOT
  SP. This tool maps their associated Level 2 inversion data products
  from the Heliophysics Events Knowlegebase (HEK) and enables greater
  accessibility to this ongoing international mission.

Title: Flux-Transport Simulations of Solar Polar Magnetic Fields
    Based on Various Meridional Surface Flow Profiles
Authors: DeRosa, M. L.; Zhao, J.; Liu, Y.
Bibcode: 2020AGUFMSH0020016D
Altcode:
  Magnetic fields located in the polar regions of the Sun during
  solar minima appear to be a useful predictor of the amplitude of the
  subsequent sunspot cycles. These polar fields are the result of flows
  that move magnetic flux, on a net basis, poleward from active-region
  latitudes. This process is captured well by two-dimensional global
  flux-transport schemes, which use empirical prescriptions for
  differential rotation, meridional flows, and convective dispersal to
  kinematically advect flux. As a result, these models are useful for
  investigating the evolution of solar surface flux and their effects
  on the formation of the polar fields. In the study presented here,
  we use a surface-flux transport model to gain intuition toward an
  understanding of the importance of different meridional flow profiles
  on the formation and evolution of the polar fields. The meridional flow
  profiles used for this study are based on helioseismic determinations
  of near-surface flows during recently activity cycles.

Title: Sun-as-a-star Spectral Irradiance Observations of Transiting
    Active Regions
Authors: Toriumi, Shin; Airapetian, Vladimir S.; Hudson, Hugh S.;
   Schrijver, Carolus J.; Cheung, Mark C. M.; DeRosa, Marc L.
Bibcode: 2020ApJ...902...36T
Altcode: 2020arXiv200804319T
  Major solar flares are prone to occur in active-region (AR) atmospheres
  associated with large, complex, dynamically evolving sunspots. This
  points to the importance of monitoring the evolution of starspots,
  not only in visible but also in ultraviolet (UV) and X-rays, in
  understanding the origin and occurrence of stellar flares. To this end,
  we perform spectral irradiance analysis on different types of transiting
  solar ARs by using a variety of full-disk synoptic observations. The
  target events are an isolated sunspot, spotless plage, and emerging flux
  in prolonged quiet-Sun conditions selected from the past decade. We find
  that the visible continuum and total solar irradiance become darkened
  when the spot is at the central meridian, whereas it is bright near
  the solar limb; UV bands sensitive to the chromosphere correlate well
  with the variation of total unsigned magnetic flux in the photosphere;
  amplitudes of extreme ultraviolet (EUV) and soft X-ray increase with
  the characteristic temperature, whose light curves are flat-topped
  due to their sensitivity to the optically thin corona; the transiting
  spotless plage does not show the darkening in the visible irradiance,
  while the emerging flux produces an asymmetry in all light curves about
  the central meridian. The multiwavelength Sun-as-a-star study described
  here indicates that the time lags between the coronal and photospheric
  light curves have the potential to probe the extent of coronal magnetic
  fields above the starspots. In addition, EUV wavelengths that are
  sensitive to temperatures just below 1 MK sometimes show antiphased
  variations, which may be used for diagnosing plasmas around starspots.

Title: The Coronal Global Evolutionary Model: Using HMI Vector
    Magnetogram and Doppler Data to Determine Coronal Magnetic Field
    Evolution
Authors: Hoeksema, J. Todd; Abbett, William P.; Bercik, David J.;
   Cheung, Mark C. M.; DeRosa, Marc L.; Fisher, George H.; Hayashi, Keiji;
   Kazachenko, Maria D.; Liu, Yang; Lumme, Erkka; Lynch, Benjamin J.;
   Sun, Xudong; Welsch, Brian T.
Bibcode: 2020ApJS..250...28H
Altcode: 2020arXiv200614579H
  The Coronal Global Evolutionary Model (CGEM) provides data-driven
  simulations of the magnetic field in the solar corona to better
  understand the build-up of magnetic energy that leads to eruptive
  events. The CGEM project has developed six capabilities. CGEM modules
  (1) prepare time series of full-disk vector magnetic field observations
  to (2) derive the changing electric field in the solar photosphere over
  active-region scales. This local electric field is (3) incorporated
  into a surface flux transport model that reconstructs a global
  electric field that evolves magnetic flux in a consistent way. These
  electric fields drive a (4) 3D spherical magnetofrictional (SMF) model,
  either at high resolution over a restricted range of solid angles or
  at lower resolution over a global domain to determine the magnetic
  field and current density in the low corona. An SMF-generated initial
  field above an active region and the evolving electric field at the
  photosphere are used to drive (5) detailed magnetohydrodynamic (MHD)
  simulations of active regions in the low corona. SMF or MHD solutions
  are then used to compute emissivity proxies that can be compared
  with coronal observations. Finally, a lower-resolution SMF magnetic
  field is used to initialize (6) a global MHD model that is driven by
  an SMF electric field time series to simulate the outer corona and
  heliosphere, ultimately connecting Sun to Earth. As a demonstration,
  this report features results of CGEM applied to observations of the
  evolution of NOAA Active Region 11158 in 2011 February.

Title: On Measuring Divergence for Magnetic Field Modeling
Authors: Gilchrist, S. A.; Leka, K. D.; Barnes, G.; Wheatland, M. S.;
   DeRosa, M. L.
Bibcode: 2020ApJ...900..136G
Altcode: 2020arXiv200808863G
  A physical magnetic field has a divergence of zero. Numerical error
  in constructing a model field and computing the divergence, however,
  introduces a finite divergence into these calculations. A popular metric
  for measuring divergence is the average fractional flux $\left\langle
  | {f}_{i}| \right\rangle $ . We show that $\left\langle | {f}_{i}|
  \right\rangle $ scales with the size of the computational mesh, and
  may be a poor measure of divergence because it becomes arbitrarily
  small for increasing mesh resolution, without the divergence actually
  decreasing. We define a modified version of this metric that does
  not scale with mesh size. We apply the new metric to the results of
  DeRosa et al., who measured $\left\langle | {f}_{i}| \right\rangle
  $ for a series of nonlinear force-free field models of the coronal
  magnetic field based on solar boundary data binned at different spatial
  resolutions. We compute a number of divergence metrics for the DeRosa et
  al. data and analyze the effect of spatial resolution on these metrics
  using a nonparametric method. We find that some of the trends reported
  by DeRosa et al. are due to the intrinsic scaling of $\left\langle |
  {f}_{i}| \right\rangle $ . We also find that different metrics give
  different results for the same data set and therefore there is value
  in measuring divergence via several metrics.

Title: The PDFI_SS Electric Field Inversion Software
Authors: Fisher, George H.; Kazachenko, Maria D.; Welsch, Brian T.;
   Sun, Xudong; Lumme, Erkka; Bercik, David J.; DeRosa, Marc L.; Cheung,
   Mark C. M.
Bibcode: 2020ApJS..248....2F
Altcode: 2019arXiv191208301F
  We describe the PDFI_SS software library, which is designed to
  find the electric field at the Sun's photosphere from a sequence of
  vector magnetogram and Doppler velocity measurements and estimates of
  horizontal velocities obtained from local correlation tracking using the
  recently upgraded Fourier Local Correlation Tracking code. The library,
  a collection of FORTRAN subroutines, uses the "PDFI" technique described
  by Kazachenko et al., but modified for use in spherical, Plate Carrée
  geometry on a staggered grid. The domain over which solutions are found
  is a subset of the global spherical surface, defined by user-specified
  limits of colatitude and longitude. Our staggered grid approach, based
  on that of Yee, is more conservative and self-consistent compared to
  the centered, Cartesian grid used by Kazachenko et al. The library can
  be used to compute an end-to-end solution for electric fields from data
  taken by the HMI instrument aboard NASA's SDO mission. This capability
  has been incorporated into the HMI pipeline processing system operating
  at SDO's Joint Science Operations Center. The library is written in a
  general and modular way so that the calculations can be customized to
  modify or delete electric field contributions, or used with other data
  sets. Other applications include "nudging" numerical models of the solar
  atmosphere to facilitate assimilative simulations. The library includes
  an ability to compute "global" (whole-Sun) electric field solutions. The
  library also includes an ability to compute potential magnetic field
  solutions in spherical coordinates. This distribution includes a number
  of test programs that allow the user to test the software.

Title: Coronal dimming as a proxy for stellar coronal mass ejections
Authors: Jin, M.; Cheung, M. C. M.; DeRosa, M. L.; Nitta, N. V.;
   Schrijver, C. J.; France, K.; Kowalski, A.; Mason, J. P.; Osten, R.
Bibcode: 2020IAUS..354..426J
Altcode: 2020arXiv200206249J
  Solar coronal dimmings have been observed extensively in the past
  two decades and are believed to have close association with coronal
  mass ejections (CMEs). Recent study found that coronal dimming
  is the only signature that could differentiate powerful flares
  that have CMEs from those that do not. Therefore, dimming might be
  one of the best candidates to observe the stellar CMEs on distant
  Sun-like stars. In this study, we investigate the possibility of using
  coronal dimming as a proxy to diagnose stellar CMEs. By simulating a
  realistic solar CME event and corresponding coronal dimming using a
  global magnetohydrodynamics model (AWSoM: Alfvén-wave Solar Model),
  we first demonstrate the capability of the model to reproduce solar
  observations. We then extend the model for simulating stellar CMEs
  by modifying the input magnetic flux density as well as the initial
  magnetic energy of the CME flux rope. Our result suggests that with
  improved instrument sensitivity, it is possible to detect the coronal
  dimming signals induced by the stellar CMEs.

Title: Global Magnetohydrodynamics Simulation of EUV Waves and Shocks
    from the X8.2 Eruptive Flare on 2017 September 10
Authors: Jin, M.; Liu, W.; Cheung, C. M. M.; Nitta, N.; DeRosa,
   M. L.; Manchester, W.; Ofman, L.; Downs, C.; Petrosian, V.; Omodei,
   N.; Moschou, S. P.; Sokolov, I.
Bibcode: 2019AGUFMSH32A..01J
Altcode:
  As one of the largest flare-CME eruptions during solar cycle 24, the
  2017 September 10 X8.2 flare event is associated with spectacular
  global EUV waves that transverse almost the entire visible solar
  disk, a CME with speed &gt; 3000 km/s, which is one of the fastest
  CMEs ever recorded, and &gt;100 MeV Gamma-ray emission lasting for
  more than 12 hours. All these unique observational features pose new
  challenge on current numerical models to reproduce the multi-wavelength
  observations. To take this challenge, we simulate the September 10
  event using a global MHD model (AWSoM: Alfven Wave Solar Model) within
  the Space Weather Modeling Framework and initiate CMEs by Gibson-Low
  flux rope. We assess several important observed and physical inputs
  (e.g., flux rope properties, polar magnetic field) in the model to
  better reproduce the multi-wavelength observations. We find that the
  simulated EUV wave morphology and kinematics are sensitive to the
  orientation of the initial flux rope introduced to the source active
  region. An orientation with the flux-rope axis in the north-south
  direction produces the best match to the observations, which suggests
  that EUV waves may potentially be used to constrain the flux-rope
  geometry for such limb or behind-the-limb eruptions that lack good
  magnetic field observations. By further combining with the white
  light and radio observations, we demonstrate the flux rope-corona
  interaction can greatly impact the early phase shock evolution (e.g.,
  geometry and shock parameters) therefore plays a significant role
  for particle acceleration near the Sun in this event. By propagating
  the CMEs into the heliosphere and beyond the Earth and Mars orbits, we
  compare the model results with the in-situ measurements and demonstrate
  the importance of input polar magnetic field on the realistic CME
  modeling therefore space weather forecasting.

Title: Inferring the Sun's Far-Side Magnetic Flux for Operations
    Using Time-Distance Helioseismic Imaging
Authors: Hess Webber, S. A.; Zhao, J.; Chen, R.; Hoeksema, J. T.;
   Liu, Y.; Bobra, M.; DeRosa, M. L.
Bibcode: 2019AGUFMSH33C3353H
Altcode:
  Solar wind models are highly dependent on global magnetic fields
  at the solar surface as their inner boundary condition, and the
  lack of global field data is a significant problem plaguing solar
  wind modeling. Currently, only direct observations of the near-side
  magnetic field exist and far-side approximations are incapable of
  predicting growth of existing active regions or new magnetic flux
  emergence. To fill this data gap, we develop a method that calibrates
  far-side helioseismic images, which are calculated using near-side
  Doppler observations, to far-side magnetic flux maps. The calibration
  employs multiple machine-learning methods that use EUV 304 Å data as a
  bridge. These algorithms determine a relation 1) between the near-side
  AIA 304 Å data and HMI magnetic field data, and 2) between STEREO
  304 Å data and far-side helioseismic images obtained from a newly
  developed time-distance helioseismic far-side imaging method. The
  resulting magnetic flux maps have been further calibrated using maps
  produced by a flux transport model. The various data products from
  this work — far-side acoustic maps, far-side STEREO EUV-derived
  magnetic flux maps, and near-real-time acoustically-driven far-side
  magnetic flux maps, along with maps of the associated uncertainties
  — are being made available to enable a synchronic global magnetic
  flux input into coronal and solar wind models.

Title: Characterizing the Magnetic Environment of Exoplanet Stellar
    Systems
Authors: Farrish, Alison O.; Alexander, David; Maruo, Mei; DeRosa,
   Marc; Toffoletto, Frank; Sciola, Anthony M.
Bibcode: 2019ApJ...885...51F
Altcode:
  We employ a flux transport model incorporating observed stellar
  activity relations to characterize stellar interplanetary fields
  on cycle timescales for a range of stellar activity defined by the
  Rossby number. This framework allows us to examine the asterospheric
  environments of exoplanetary systems and yields references against
  which exoplanetary observations can be compared. We examine several
  quantitative measures of star-exoplanet interaction: the ratio of open
  to total stellar magnetic flux, the location of the stellar Alfvén
  surface, and the strength of interplanetary magnetic field polarity
  inversions, all of which influence planetary magnetic environments. For
  simulations in the range of Rossby numbers considered (0.1-5
  Ro<SUB>Sun</SUB>), we find that (1) the fraction of open magnetic flux
  available to interplanetary space increases with Rossby number, with a
  maximum of around 40% at stellar minimum for low-activity stars, while
  the open flux for very active stars (Ro ∼ 0.1-0.25 Ro<SUB>Sun</SUB>)
  is ∼1-5% (2) the mean Alfvén surface radius, R <SUB>A</SUB>,
  varies between 0.7 and 1.3 R <SUB>A,Sun</SUB> and is larger for
  lower stellar activity; and (3) at high activity, the asterospheric
  current sheet becomes more complex with stronger inversions, possibly
  resulting in more frequent reconnection events (e.g., magnetic storms)
  at the planetary magnetosphere. The simulations presented here serve to
  bound a range of asterospheric magnetic environments within which we
  can characterize the conditions impacting any exoplanets present. We
  relate these results to several known exoplanets and discuss how they
  might be affected by changes in asterospheric magnetic field topologies.

Title: A comprehensive three-dimensional radiative magnetohydrodynamic
    simulation of a solar flare
Authors: Cheung, M. C. M.; Rempel, M.; Chintzoglou, G.; Chen, F.;
   Testa, P.; Martínez-Sykora, J.; Sainz Dalda, A.; DeRosa, M. L.;
   Malanushenko, A.; Hansteen, V.; De Pontieu, B.; Carlsson, M.; Gudiksen,
   B.; McIntosh, S. W.
Bibcode: 2019NatAs...3..160C
Altcode: 2018NatAs...3..160C
  Solar and stellar flares are the most intense emitters of X-rays and
  extreme ultraviolet radiation in planetary systems<SUP>1,2</SUP>. On
  the Sun, strong flares are usually found in newly emerging sunspot
  regions<SUP>3</SUP>. The emergence of these magnetic sunspot groups
  leads to the accumulation of magnetic energy in the corona. When
  the magnetic field undergoes abrupt relaxation, the energy released
  powers coronal mass ejections as well as heating plasma to temperatures
  beyond tens of millions of kelvins. While recent work has shed light
  on how magnetic energy and twist accumulate in the corona<SUP>4</SUP>
  and on how three-dimensional magnetic reconnection allows for rapid
  energy release<SUP>5,6</SUP>, a self-consistent model capturing how
  such magnetic changes translate into observable diagnostics has remained
  elusive. Here, we present a comprehensive radiative magnetohydrodynamics
  simulation of a solar flare capturing the process from emergence to
  eruption. The simulation has sufficient realism for the synthesis of
  remote sensing measurements to compare with observations at visible,
  ultraviolet and X-ray wavelengths. This unifying model allows us to
  explain a number of well-known features of solar flares<SUP>7</SUP>,
  including the time profile of the X-ray flux during flares, origin
  and temporal evolution of chromospheric evaporation and condensation,
  and sweeping of flare ribbons in the lower atmosphere. Furthermore,
  the model reproduces the apparent non-thermal shape of coronal X-ray
  spectra, which is the result of the superposition of multi-component
  super-hot plasmas<SUP>8</SUP> up to and beyond 100 million K.

Title: Coronal Magnetic Field Topologies of Solar Active Regions
Authors: DeRosa, Marc L.; Barnes, Graham
Bibcode: 2019AAS...23430504D
Altcode:
  The magnetic field overlying the coronae of solar active regions
  displays many complex configurations. In this work, we show renderings
  of the important topological surfaces corresponding to potential
  fields above solar active regions. Common geometries are identified,
  such as nested domains of connectivity, and the presence of narrow
  channels of open flux having high expansion factors. Additionally, a
  sequence of magnetic field topologies is used to demonstrate null-point
  creation and annihilation. Due to the presence of electric currents,
  the real coronal magnetic field topology is expected to be even more
  complex than that found in these potential fields.

Title: Radiative MHD Simulation of a Solar Flare
Authors: Cheung, Mark; Rempel, Matthias D.; Chintzoglou, Georgios;
   Chen, Feng; Testa, Paola; Martinez-Sykora, Juan; Sainz Dalda, Alberto;
   DeRosa, Marc L.; Malanushenko, Anna; Hansteen, Viggo; Carlsson, Mats;
   De Pontieu, Bart; Gudiksen, Boris; McIntosh, Scott W.
Bibcode: 2019AAS...23431005C
Altcode:
  We present a radiative MHD simulation of a solar flare. The
  computational domain captures the near-surface layers of the convection
  zone and overlying atmosphere. Inspired by the observed evolution of
  NOAA Active Region (AR) 12017, a parasitic bipolar region is imposed
  to emerge in the vicinity of a pre-existing sunspot. The emergence of
  twisted magnetic flux generates shear flows that create a pre-existing
  flux rope underneath the canopy field of the sunspot. Following erosion
  of the overlying bootstrapping field, the flux rope erupts. Rapid
  release of magnetic energy results in multi-wavelength synthetic
  observables (including X-ray spectra, narrowband EUV images, Doppler
  shifts of EUV lines) that are consistent with flare observations. This
  works suggests the super-position of multi-thermal, superhot (up
  to 100 MK) plasma may be partially responsible for the apparent
  non-thermal shape of coronal X-ray sources in flares. Implications
  for remote sensing observations of other astrophysical objects is also
  discussed. This work is an important stepping stone toward high-fidelity
  data-driven MHD models.

Title: Reliably Inferring the Sun's Far-Side Magnetic Flux for
    Operations Using Time-Distance Helioseismic Imaging - Updates
Authors: Hess Webber, Shea A.; Zhao, Junwei; Chen, Ruizhu; Hoeksema,
   Jon Todd; Liu, Yang; Bobra, Monica; DeRosa, Marc L.
Bibcode: 2019AAS...23411805H
Altcode:
  Solar wind models are highly dependent on global magnetic fields at
  the solar surface as their inner boundary condition, and the lack
  of global field data is a significant problem plaguing solar wind
  modeling. Currently, only near-side magnetic field observations exist
  and far-side approximations are incapable of predicting growth of
  existing active regions or new magnetic flux emergence. We therefore
  plan to develop a method that calibrates far-side helioseismic
  images, calculated using near-side Doppler observations, to far-side
  magnetic flux maps to fill this data gap. The calibration will employ
  machine-learning methods that use EUV 304 Å data as a bridge: a
  relation will be sought 1) between the near-side AIA 304 Å data and
  HMI magnetic field data, and 2) between STEREO 304 Å data and far-side
  helioseismic images obtained from a newly developed time-distance
  helioseismic far-side imaging method. As an update, progress has been
  made in establishing the relation between the near-side 304 Å data
  and magnetic flux data, and some previously-unknown systematics were
  identified and corrected in the helioseismic far-side images. These
  systematic-effect-corrected far-side images will then be used to
  establish a relation with the far-side EUV data.

Title: Simulating the Inner Asterospheric Magnetic Fields of Exoplanet
    Host Stars
Authors: Farrish, Alison; Alexander, David; Maruo, Mei; Sciola,
   Anthony; Toffoletto, Frank; DeRosa, Marc L.
Bibcode: 2019AAS...23430305F
Altcode:
  We study magnetic and energetic activity across a range of stellar
  behavior via the application of an observationally-based heliophysics
  modeling framework. We simulate the inner asterospheric magnetic fields
  of host stars with the aim of better understanding and constraining the
  space weather environments of exoplanets, and improving our knowledge of
  the solar-stellar connection. As astronomy instrumentation has improved,
  Earth-like exoplanets are increasingly being found orbiting in the
  habitable zones of a variety of stars, ranging from the smallest
  and coolest M dwarfs to larger and more solar-like stars. We are
  therefore interested in characterizing a broad range of stellar magnetic
  activity and the resulting impacts on asterospheric environments. We
  will present our work simulating stellar magnetic activity on cycle
  timescales via the integration of modeled magnetic flux emergence,
  coronal field structure and related plasma emission, and stellar
  winds. We use this self-consistent framework of heliophysics-based
  models to simulate stellar and asterospheric evolution, in order
  to better understand the dynamic connections between host stars and
  potential impacts on planetary space weather and habitability. We also
  remark on the comparative heliophysics approach which we plan to extend
  to star-planet interactions via coupling to models of magnetospheric
  activity and dynamo-driven stellar flux emergence.

Title: The Global EUV Wave Associated with the SOL2017-09-10 X8.2
Flare: SDO/AIA Observations and Data-constrained MHD Simulations
Authors: Liu, Wei; Jin, Meng; Ofman, Leon; DeRosa, Marc L.
Bibcode: 2019AAS...23430701L
Altcode:
  While large-scale extreme ultraviolet (EUV) waves associated with
  coronal mass ejections (CMEs) and solar flares are common, the EUV
  wave triggered by the X8 flare-CME eruption on 2017 September 10
  was an extreme. This was, to the best of our knowledge, the first
  detection of an EUV wave traversing the full-Sun corona over the entire
  visible disk and off-limb circumference, manifesting a truly global
  nature. In addition to commonly observed reflections, it had strong
  transmissions in and out of both polar coronal holes, at elevated
  wave speeds of &gt;2000 km/s within them. With an exceptionally large
  wave amplitude, it produced significant compressional heating to local
  coronal plasma. We present detailed analysis of SDO/AIA observations,
  global magnetic field extrapolations with the potential-field source
  surface (PFSS) model, and data-constrained MHD simulations of this
  event using the University of Michigan Alfven Wave Solar Model
  (AWSoM). By comparing the observations and simulations, we benchmark
  diagnostics of the magnetic field strengths and thermal properties of
  the solar corona on global scales. We discuss the future prospects of
  using such extreme EUV waves as probes for global coronal seismology,
  an area yet to be fully exploited.

Title: Magnetic Properties of Asterospheres of Exoplanet Systems
Authors: Farrish, Alison; Alexander, David; Maruo, Mei; Sciola,
   Anthony; Toffoletto, Frank; DeRosa, Marc
Bibcode: 2019shin.confE.152F
Altcode:
  We study magnetic and energetic activity across a range of stellar
  behavior via the application of an observationally-based heliophysics
  modeling framework. We simulate the inner asterospheric magnetic fields
  of host stars with the aim of better understanding and constraining the
  space weather environments of exoplanets, and improving our knowledge of
  the solar-stellar connection. As astronomy instrumentation has improved,
  Earth-like exoplanets are increasingly being found orbiting in the
  habitable zones of a variety of stars, ranging from the smallest
  and coolest M dwarfs to larger and more solar-like stars. We are
  therefore interested in characterizing a broad range of stellar magnetic
  activity and the resulting impacts on asterospheric environments. We
  will present our work simulating stellar magnetic activity on cycle
  timescales via the integration of modeled magnetic flux emergence,
  coronal field structure and related plasma emission, and stellar
  winds. We use this self-consistent framework of heliophysics-based
  models to simulate stellar and asterospheric evolution, in order
  to better understand the dynamic connections between host stars and
  potential impacts on planetary space weather and habitability. We also
  remark on the comparative heliophysics approach which we plan to extend
  to star-planet interactions via coupling to models of magnetospheric
  activity and dynamo-driven stellar flux emergence.

Title: Reliably Inferring the Sun's Far-Side Magnetic Flux for
    Operations Using Time-Distance Helioseismic Imaging
Authors: Hess Webber, Shea A.; Zhao, Junwei; Chen, Ruizhu; Hoeksema,
   J. Todd; Liu, Yang; Bobra, Monica; DeRosa, Marc
Bibcode: 2019spwe.confE...1H
Altcode:
  Solar wind models are highly dependent on global magnetic fields at
  the solar surface as their inner boundary condition, and the lack
  of global field data is a significant problem plaguing solar wind
  modeling. Currently, only near-side magnetic field observations exist
  and far-side approximations are incapable of predicting growth of
  existing active regions or new magnetic flux emergence. We therefore
  plan to develop a method that calibrates far-side helioseismic
  images, calculated using near-side Doppler observations, to far-side
  magnetic flux maps to fill this data gap. The calibration will
  employ machine-learning methods that use EUV 304 Angstrom data as a
  bridge: a relation will be sought 1) between the near-side AIA 304
  Angstrom data and HMI magnetic field data, and 2) between STEREO 304
  Angstrom data and far-side helioseismic images obtained from a newly
  developed time-distance helioseismic far-side imaging method. As an
  update, progress has been made in establishing the relation between
  the near-side 304 Angstrom data and magnetic flux data, and some
  previously-unknown systematics were identified and corrected in
  the helioseismic far-side images. These systematic-effect-corrected
  far-side images will then be used to establish a relation with the
  far-side EUV data.

Title: To what degree do regions of open flux located near active
    regions affect their eruptivity?
Authors: DeRosa, Marc; Barnes, Graham
Bibcode: 2019EGUGA..21.4673D
Altcode:
  Most, but not all, X-class flares are associated with CMEs. The
  conventional wisdom likely ascribes this association to the large
  amount of energy released during the flare reconnection process that
  then becomes available for accelerating matter upward. For those
  X-class flares that are non-eruptive, what properties set these
  apart such that there is no discernible eruption? In this study, we
  investigate whether active regions that produce non-eruptive X-class
  flares are correlated with the lack of a nearby channel of open flux
  in the overlying global coronal magnetic field configuration. We
  analyze PFSS models of the coronal magnetic field associated with 56
  X-class flares (in 37 flaring active regions) occurring during Cycles
  23 and 24, and evaluate whether properties the field configuration
  are associated with the properties of the associated flares. We find
  a positive correlation between whether a region is non-eruptive and
  the absence of nearby open magnetic field lines in the PFSS models,
  however the confidence we assign to this result is limited by the
  small number of non-eruptive X-class flares in the sample.

Title: Roadmap for Reliable Ensemble Forecasting of the Sun-Earth
    System
Authors: Nita, Gelu; Angryk, Rafal; Aydin, Berkay; Banda, Juan;
   Bastian, Tim; Berger, Tom; Bindi, Veronica; Boucheron, Laura; Cao,
   Wenda; Christian, Eric; de Nolfo, Georgia; DeLuca, Edward; DeRosa,
   Marc; Downs, Cooper; Fleishman, Gregory; Fuentes, Olac; Gary, Dale;
   Hill, Frank; Hoeksema, Todd; Hu, Qiang; Ilie, Raluca; Ireland,
   Jack; Kamalabadi, Farzad; Korreck, Kelly; Kosovichev, Alexander;
   Lin, Jessica; Lugaz, Noe; Mannucci, Anthony; Mansour, Nagi; Martens,
   Petrus; Mays, Leila; McAteer, James; McIntosh, Scott W.; Oria, Vincent;
   Pan, David; Panesi, Marco; Pesnell, W. Dean; Pevtsov, Alexei; Pillet,
   Valentin; Rachmeler, Laurel; Ridley, Aaron; Scherliess, Ludger; Toth,
   Gabor; Velli, Marco; White, Stephen; Zhang, Jie; Zou, Shasha
Bibcode: 2018arXiv181008728N
Altcode:
  The authors of this report met on 28-30 March 2018 at the New Jersey
  Institute of Technology, Newark, New Jersey, for a 3-day workshop
  that brought together a group of data providers, expert modelers, and
  computer and data scientists, in the solar discipline. Their objective
  was to identify challenges in the path towards building an effective
  framework to achieve transformative advances in the understanding
  and forecasting of the Sun-Earth system from the upper convection
  zone of the Sun to the Earth's magnetosphere. The workshop aimed to
  develop a research roadmap that targets the scientific challenge
  of coupling observations and modeling with emerging data-science
  research to extract knowledge from the large volumes of data (observed
  and simulated) while stimulating computer science with new research
  applications. The desire among the attendees was to promote future
  trans-disciplinary collaborations and identify areas of convergence
  across disciplines. The workshop combined a set of plenary sessions
  featuring invited introductory talks and workshop progress reports,
  interleaved with a set of breakout sessions focused on specific topics
  of interest. Each breakout group generated short documents, listing
  the challenges identified during their discussions in addition to
  possible ways of attacking them collectively. These documents were
  combined into this report-wherein a list of prioritized activities
  have been collated, shared and endorsed.

Title: Simulation of Exoplanet Host Star Magnetic Activity on Stellar
    Cycle Timescales
Authors: Farrish, A. O.; Maruo, M.; Barnes, W. T.; Alexander, D.;
   Bradshaw, S.; DeRosa, M.
Bibcode: 2018LPICo2065.2043F
Altcode:
  We apply solar physics modeling tools to the study of star-exoplanet
  interaction, with a focus on how variations in stellar magnetic
  field and energetic emission on cycle timescales may impact planetary
  habitability.

Title: Using Sun's Far-Side Images Inferred by the Time-Distance
Helioseismic Imaging to Improve Synoptic Maps of Magnetic Field:
    Importance and Methodology
Authors: Liu, Yang; Zhao, Junwei; Hoeksema, J. T.; Chen, Ruizhu;
   Bobra, Monica; Hess Webber, Shea; DeRosa, M.; Sun, X.
Bibcode: 2018shin.confE.147L
Altcode:
  Synoptic map of magnetic field is an important piece of data used
  for many space weather models. Currently solar observation can only
  provide magnetic field measurement on the earth-side surface. To
  generate magnetic field synoptic maps, the magnetic field measured
  about 13 days ago is used for the far-side surface when it was at
  the earth-side. This kind of synoptic maps was improved later on by
  evolving the measured magnetic field to the day of interest using a flux
  transfer model. It takes into account of evolution of magnetic field,
  but fails to include newly emerging magnetic flux, especially emerging
  active regions, that start to emerge at the far-side surface. <P
  />In this presentation, we first demonstrate that the newly emerging
  fluxes in the far-side change the coronal magnetic field structure,
  and this change can be global, far reaching to the earth-side. Because
  coronal magnetic field is related to the solar wind property and CMEs'
  speed, this change has potential to impact space weather forecast. We
  then present examples that convert far-side images into magnetic flux
  distribution using deep learning. The far-side images are inferred by
  the time-distance helioseismic method. Finally we propose to improve
  the synoptic maps of magnetic field by combining the far-size images
  and the machine learning technique.

Title: Simulation of Exoplanet Host Star Magnetic Activity on Stellar
    Cycle Timescales
Authors: Farrish, Alison; Maruo, M.; Barnes, W.; Alexander, D.;
   Bradshaw, S.; DeRosa, M.
Bibcode: 2018shin.confE...4F
Altcode:
  We apply an empirical photospheric magnetic flux transport
  model, derived from solar behavior, and a magnetically-driven
  stellar atmosphere model to explore the range of stellar effects on
  habitability of Earth-size exoplanets around M dwarf stars. We create
  detailed, dynamic simulations of stellar activity and its variability
  over stellar cycle timescales. In particular, we examine how the
  asterospheric magnetic field and related extreme ultraviolet (EUV)
  and X-ray emission vary in time and consider the potential impact on
  exoplanet habitability.

Title: Do Topological Features of the Solar Corona Affect EUV
    Wave Events?
Authors: DeRosa, Marc; Barnes, Graham; Sun, Xudong
Bibcode: 2018shin.confE.142D
Altcode:
  We present visualizations of the topology of the coronal magnetic
  field associated with an EUV wave event. This case study will be used
  to evaluate whether topological features of interest, such as null
  points, separatrix surfaces, domains of high Q (squashing factor),
  play any role in determining the morphology of the EUV wave propagation.

Title: Does Nearby Open Flux Affect the Eruptivity of Solar Active
    Regions?
Authors: DeRosa, Marc L.; Barnes, Graham
Bibcode: 2018ApJ...861..131D
Altcode: 2018arXiv180201199D
  The most energetic solar flares are typically associated with the
  ejection of a cloud of coronal material into the heliosphere in the
  form of a coronal mass ejection (CME). However, large flares exist that
  are not accompanied by a CME. The existence of these noneruptive flares
  raises the question of whether such flares suffer from a lack of access
  to nearby open fields in the vicinity above the flare (reconnection)
  site. In this study, we use a sample of 56 flares from sunspot Cycles
  23 and 24 to test whether active regions that produce eruptive X-class
  flares are preferentially located near coronal magnetic field domains
  that are open to the heliosphere, as inferred from a potential field
  source-surface model. The study shows that X-class flares with access
  to open fields are eruptive at a higher rate than those for which
  access is lacking. The significance of this result should be moderated
  due to the small number of noneruptive X-class flares in the sample,
  based on the associated Bayes factor.

Title: Modeling the Global Coronal Field with Simulated Synoptic
    Magnetograms from Earth and the Lagrange Points L<SUB>3</SUB>,
    L<SUB>4</SUB>, and L<SUB>5</SUB>
Authors: Petrie, Gordon; Pevtsov, Alexei; Schwarz, Andrew; DeRosa, Marc
Bibcode: 2018SoPh..293...88P
Altcode:
  The solar photospheric magnetic flux distribution is key to structuring
  the global solar corona and heliosphere. Regular full-disk photospheric
  magnetogram data are therefore essential to our ability to model
  and forecast heliospheric phenomena such as space weather. However,
  our spatio-temporal coverage of the photospheric field is currently
  limited by our single vantage point at/near Earth. In particular,
  the polar fields play a leading role in structuring the large-scale
  corona and heliosphere, but each pole is unobservable for &gt;6 months
  per year. Here we model the possible effect of full-disk magnetogram
  data from the Lagrange points L<SUB>4</SUB> and L<SUB>5</SUB>, each
  extending longitude coverage by 60<SUP>∘</SUP>. Adding data also from
  the more distant point L<SUB>3</SUB> extends the longitudinal coverage
  much further. The additional vantage points also improve the visibility
  of the globally influential polar fields. Using a flux-transport model
  for the solar photospheric field, we model full-disk observations from
  Earth/L<SUB>1</SUB>, L<SUB>3</SUB>, L<SUB>4</SUB>, and L<SUB>5</SUB>
  over a solar cycle, construct synoptic maps using a novel weighting
  scheme adapted for merging magnetogram data from multiple viewpoints,
  and compute potential-field models for the global coronal field. Each
  additional viewpoint brings the maps and models into closer agreement
  with the reference field from the flux-transport simulation, with
  particular improvement at polar latitudes, the main source of the fast
  solar wind.

Title: What Happens to Coronal Field Models when Fake East-Limb
    Active Regions are Inserted into Real Synoptic Charts?
Authors: DeRosa, Marc L.
Bibcode: 2018tess.conf41603D
Altcode:
  Global coronal magnetic field models and solar wind models make use of
  synoptic maps of the photospheric magnetic field as a lower boundary
  condition. These maps have historically been constructed using observed
  magnetograms, such that a full-sun map is assembled over the course
  of a full solar rotation. As a result of this process, a single maps
  contains observations made at different times over the course of a
  month, with east-limb longitudes being the most out-of-date. However,
  there are many instances where significant missing flux located on
  the east limb of the sun has been shown to affect the configuration
  of coronal magnetic fields on the Earth-facing side, and in many cases
  significant downstream effects occur when predicting solar wind speeds
  and other quantities related to space weather. Here, the same fictitious
  east-limb active region is inserted into a series of synoptic charts
  spanning sunspot cycles 23 and 24 as a way to approximate magnetic flux
  located at east-limb longitudes that would be missing from a synoptic
  chart. The resulting ensemble of photospheric magnetic maps allows
  us to evaluate how often and much of an effect such "hidden flux"
  affects potential-field models of the global coronal field.

Title: Simulated Coronal EUV Emission from Exoplanet Host Stars
Authors: Farrish, Alison; Barnes, Will; Alexander, David; Bradshaw,
   Stephen J.; DeRosa, Mark L.
Bibcode: 2018tess.conf40649F
Altcode:
  We apply a modified solar flux transport (SFT) model, developed
  by Schrijver and colleagues, to emulate the magnetic activity of
  the host stars of recently discovered habitable-zone planets. The
  magnetic flux distributions produced by the SFT simulations serve
  as a first-order proxy for the expected magnetic behavior of an
  exoplanet host star. We couple the simulated magnetic structure
  to a coronal heating model and simulate the expected EUV and X-ray
  emission of the target star. The EUV emission is a key energetic input
  to the exoplanetary atmosphere, governing ionospheric conductance and
  therefore influencing the magnetospheric response to stellar activity -
  a key factor in determining the overall atmospheric loss and ultimately
  the potential of the planet for habitation. In addition, the simulated
  stellar coronal emission may provide signatures for comparison with
  astronomical observations. We consider the simulated activity over a
  number of stellar cycles to explore the long-term impact of the star
  on the exo-planetary environment.

Title: Modeling the Global Coronal Field with Simulated Synoptic
    Magnetograms from Earth and the Lagrange points L3, L4 and L5
Authors: Petrie, Gordon J. D.; Pevtsov, Alexei A.; Schwarz, Andrew
   Michael; DeRosa, Marc
Bibcode: 2018tess.conf40132P
Altcode:
  The solar photospheric magnetic flux distribution determines the
  global structure of the solar corona and heliosphere. Regular
  full-disk photospheric magnetogram data are therefore essential to
  our ability to model and forecast heliospheric phenomena such as space
  weather. However, our spatio-temporal coverage of the photospheric field
  is currently limited by our single vantage point at/near Earth. In
  particular, the polar fields define the large-scale structure of the
  corona and heliosphere but each pole is unobservable for &gt; 6 months
  per year. Here we model the possible effect of full-disk magnetogram
  data from the Lagrange points L4 and L5, each extending longitude
  coverage by 60 degrees. Adding data also from the more distant point
  L3 extends longitudinal coverage much further. The additional vantage
  points also improve the visibility of the globally influential polar
  fields. Using a flux-transport model for the solar photospheric field
  we model full-disk observations from Earth/L1, L3, L4 and L5 over a
  solar cycle, construct synoptic maps using a novel weighting scheme
  adapted for merging magnetogram data from multiple viewpoints, and
  compute potential-field models for the global coronal field. Each
  additional viewpoint significantly improves the performance of the
  maps and models with particular improvement at polar latitudes, the
  main source of the fast solar wind.

Title: The Application of Solar Flux Transport Modeling to Exoplanet
    Systems
Authors: Alexander, David; Farrish, Alison; Maruo, Mei; De Rosa,
   Marc L.
Bibcode: 2018tess.conf40648A
Altcode:
  Earth-size exoplanets are preferentially detected close-in around small
  stars; Proxima Centauri b, Ross 128 b, and the TRAPPIST-1 planets are
  newly discovered exoplanets in this class. The effects of magnetic
  interactions between the host star and such close-in exoplanets are
  still not well-constrained. We utilize an empirical solar magnetic flux
  transport model, first developed by Schrijver and colleagues, to explore
  the possible relationships between stellar properties (e.g. rotation
  period, radius, flux emergence rate, and meridional and differential
  flow rates) and the expected surface magnetic flux distributions,
  along with their evolution over the stellar cycle. The surface field
  then provides key information about the interplanetary magnetic fields,
  stellar winds, dynamic activity, and coronal emission, all of which
  influence the star-planet interactions. We present simulated magnetic
  flux patterns representing a range of possible exoplanet host stars,
  including potential observables such as starspots, active regions,
  and stellar cycle variations. The magnetic and energetic environment at
  an exoplanet and its impact on the magnetospheric-atmospheric coupling
  are important components of a planet's habitability that we expect to
  constrain further with this application of simulated stellar magnetic
  activity.

Title: Coronal Mass Ejections and Dimmings: A Comparative Study
    using MHD Simulations and SDO Observations
Authors: Jin, M.; Cheung, C. M. M.; DeRosa, M. L.; Nitta, N.;
   Schrijver, K.
Bibcode: 2017AGUFMSH41A2758J
Altcode:
  Solar coronal dimmings have been observed extensively in the past two
  decades. Due to their close association with coronal mass ejections
  (CMEs), there is a critical need to improve our understanding of the
  physical processes that cause dimmings and determine their relationship
  with CMEs. In this study, we investigate coronal dimmings by combining
  simulation and observational efforts. By utilizing a data-driven global
  magnetohydrodynamics model (AWSoM: Alfven-wave Solar Model), we simulate
  coronal dimmings resulting from different CME energetics and flux rope
  configurations. We synthesize the emissions of different EUV spectral
  bands/lines and compare with SDO/AIA and EVE observations. A detailed
  analysis of simulation and observation data suggests that although
  the transient dimming / brightening patterns could relate to plasma
  heating processes (either by adiabatic compression or reconnection),
  the long-lasting "core" and "remote" (also known as "secondary")
  dimmings both originate from regions with open/quasi-open fields and
  are caused by mass loss process. The mass loss in the remote dimming
  region is induced by CME-driven shock. Using metrics such as dimming
  depth, dimming slope, and recovery time, we investigate the relationship
  between dimmings and CME properties (e.g., CME mass, CME speed) in the
  simulation. Our result suggests that coronal dimmings encode important
  information about CME energetics, CME-driven shock properties, and
  magnetic configuration of erupting flux ropes. We also discuss how our
  knowledge about solar coronal dimmings could be extended to the study
  of stellar CMEs, which may prove important for exoplanet atmospheres
  and habitability but which are currently not observable.

Title: The Open Flux Problem
Authors: Linker, J. A.; Caplan, R. M.; Downs, C.; Riley, P.; Mikic,
   Z.; Lionello, R.; Henney, C. J.; Arge, C. N.; Liu, Y.; Derosa, M. L.;
   Yeates, A.; Owens, M. J.
Bibcode: 2017ApJ...848...70L
Altcode: 2017arXiv170802342L
  The heliospheric magnetic field is of pivotal importance in solar
  and space physics. The field is rooted in the Sun’s photosphere,
  where it has been observed for many years. Global maps of the solar
  magnetic field based on full-disk magnetograms are commonly used as
  boundary conditions for coronal and solar wind models. Two primary
  observational constraints on the models are (1) the open field regions
  in the model should approximately correspond to coronal holes (CHs)
  observed in emission and (2) the magnitude of the open magnetic
  flux in the model should match that inferred from in situ spacecraft
  measurements. In this study, we calculate both magnetohydrodynamic and
  potential field source surface solutions using 14 different magnetic
  maps produced from five different types of observatory magnetograms,
  for the time period surrounding 2010 July. We have found that for
  all of the model/map combinations, models that have CH areas close
  to observations underestimate the interplanetary magnetic flux, or,
  conversely, for models to match the interplanetary flux, the modeled
  open field regions are larger than CHs observed in EUV emission. In
  an alternative approach, we estimate the open magnetic flux entirely
  from solar observations by combining automatically detected CHs for
  Carrington rotation 2098 with observatory synoptic magnetic maps. This
  approach also underestimates the interplanetary magnetic flux. Our
  results imply that either typical observatory maps underestimate the
  Sun’s magnetic flux, or a significant portion of the open magnetic
  flux is not rooted in regions that are obviously dark in EUV and
  X-ray emission.

Title: Realistic radiative MHD simulation of a solar flare
Authors: Rempel, Matthias D.; Cheung, Mark; Chintzoglou, Georgios;
   Chen, Feng; Testa, Paola; Martinez-Sykora, Juan; Sainz Dalda, Alberto;
   DeRosa, Marc L.; Viktorovna Malanushenko, Anna; Hansteen, Viggo H.;
   De Pontieu, Bart; Carlsson, Mats; Gudiksen, Boris; McIntosh, Scott W.
Bibcode: 2017SPD....4840001R
Altcode:
  We present a recently developed version of the MURaM radiative
  MHD code that includes coronal physics in terms of optically thin
  radiative loss and field aligned heat conduction. The code employs
  the "Boris correction" (semi-relativistic MHD with a reduced speed
  of light) and a hyperbolic treatment of heat conduction, which allow
  for efficient simulations of the photosphere/corona system by avoiding
  the severe time-step constraints arising from Alfven wave propagation
  and heat conduction. We demonstrate that this approach can be used
  even in dynamic phases such as a flare. We consider a setup in which
  a flare is triggered by flux emergence into a pre-existing bipolar
  active region. After the coronal energy release, efficient transport
  of energy along field lines leads to the formation of flare ribbons
  within seconds. In the flare ribbons we find downflows for temperatures
  lower than ~5 MK and upflows at higher temperatures. The resulting
  soft X-ray emission shows a fast rise and slow decay, reaching a peak
  corresponding to a mid C-class flare. The post reconnection energy
  release in the corona leads to average particle energies reaching 50
  keV (500 MK under the assumption of a thermal plasma). We show that
  hard X-ray emission from the corona computed under the assumption of
  thermal bremsstrahlung can produce a power-law spectrum due to the
  multi-thermal nature of the plasma. The electron energy flux into the
  flare ribbons (classic heat conduction with free streaming limit) is
  highly inhomogeneous and reaches peak values of about 3x10<SUP>11</SUP>
  erg/cm<SUP>2</SUP>/s in a small fraction of the ribbons, indicating
  regions that could potentially produce hard X-ray footpoint sources. We
  demonstrate that these findings are robust by comparing simulations
  computed with different values of the saturation heat flux as well as
  the "reduced speed of light".

Title: Global Evolving Models of Photospheric Flux as Driven by
    Electric Fields
Authors: DeRosa, Marc L.; Cheung, Mark; Kazachenko, Maria D.; Fisher,
   George H.
Bibcode: 2017SPD....4811105D
Altcode:
  We present a novel method for modeling the global radial magnetic field
  that is based on the incorporation of time series of photospheric
  electric fields. The determination of the electric fields is the
  result of a recently developed method that uses as input various data
  products from SDO/HMI, namely vector magnetic fields and line-of-sight
  Doppler images. For locations on the sphere where electric field data
  are unavailable, we instead use electric fields that are consistent
  with measurements of the mean differential rotation, meridional flow,
  and flux dispersal profiles. By combining these electric fields,
  a full-Sun model of the photospheric radial magnetic field can be
  advanced forward in time via Faraday's Law.

Title: Coronal Mass Ejections and Dimmings: A Comparative Study
    using MHD Simulations and SDO Observations
Authors: Jin, Meng; Cheung, Mark; DeRosa, Marc L.; Nitta, Nariaki;
   Schrijver, Karel
Bibcode: 2017SPD....4820602J
Altcode:
  Solar coronal dimmings have been observed extensively in the past two
  decades. Due to their close association with coronal mass ejections
  (CMEs), there is a critical need to improve our understanding of the
  physical processes that cause dimmings and determine their relationship
  with CMEs. In this study, we investigate coronal dimmings by combining
  simulation and observational efforts. By utilizing a data-driven
  global magnetohydrodynamics model (AWSoM: Alfven-wave Solar Model), we
  simulate coronal dimmings resulting from different CME energetics and
  flux rope configurations. We synthesize the emissions of different EUV
  spectral bands/lines and compare with SDO/AIA and EVE observations. A
  detailed analysis of simulation and observation data suggests that the
  “core” dimming is mainly caused by the mass loss from the CME, while
  the “remote” dimming could have a different origin (e.g., plasma
  heating). Moreover, the interaction between the erupting flux rope with
  different orientations and the global solar corona could significantly
  influence the coronal dimming patterns. Using metrics such as dimming
  depth, dimming slope, and recovery time, we investigate the relationship
  between dimmings and CME properties (e.g., CME mass, CME speed) in the
  simulation. Our result suggests that coronal dimmings encode important
  information about CMEs. We also discuss how our knowledge about solar
  coronal dimmings could be extended to the study of stellar CMEs.

Title: Does erupting material in flaring active regions always have
    access to open flux?
Authors: DeRosa, Marc; Barnes, Graham
Bibcode: 2017shin.confE..46D
Altcode:
  Most, but not all, X-class flares are associated with CMEs. The
  conventional wisdom likely ascribes this association to the large
  amount of energy released during the flare reconnection process that
  then becomes available for accelerating matter upward. Of the class of
  X flares that are non-eruptive, what properties set these apart such
  that there is no discernible eruption? In this study, we investigate
  whether active regions that produce non-eruptive X-class flares
  are correlated with the lack of a nearby channel of open flux in the
  overlying global coronal magnetic field configuration. We analyze PFSS
  models of the coronal magnetic field associated with 36 flaring active
  regions spanning Cycles 23 and 24, and evaluate whether properties
  the field configuration are correlated with the properties of the
  associated flares. We find only a weak correlation between whether a
  region is eruptive and the presence of overlying open magnetic fields,
  suggesting the involvement of other factors in determining whether
  X-class flaring regions produce CMEs.

Title: A study of the long term evolution in active region upflows
Authors: Harra, Louise K.; Ugarte-Urra, Ignacio; De Rosa, Marc;
   Mandrini, Cristina; van Driel-Gesztelyi, Lidia; Baker, Deborah;
   Culhane, J. Leonard; Démoulin, Pascal
Bibcode: 2017PASJ...69...47H
Altcode:
  Since their discovery, upflows at the edges of active regions have
  attracted a lot of interest, primarily as they could potentially
  contribute to the slow solar wind. One aspect that has not been studied
  yet is how the long term evolution of active regions impacts the
  upflows. In this work, we analyze one active region that survives three
  solar rotations. We track how the flows change with time. We use local
  and global modeling of the decaying active region to determine how the
  age of the active region will impact the extent of the open magnetic
  fields, and then how some of the upflows could become outflows. We
  finish with a discussion of how these results, set in a broader context,
  can be further developed with the Solar Orbiter mission.

Title: Magnetic Nulls and Super-radial Expansion in the Solar Corona
Authors: Gibson, Sarah E.; Dalmasse, Kevin; Rachmeler, Laurel A.;
   De Rosa, Marc L.; Tomczyk, Steven; de Toma, Giuliana; Burkepile,
   Joan; Galloy, Michael
Bibcode: 2017ApJ...840L..13G
Altcode: 2017arXiv170407470G
  Magnetic fields in the Sun’s outer atmosphere—the corona—control
  both solar-wind acceleration and the dynamics of solar eruptions. We
  present the first clear observational evidence of coronal magnetic
  nulls in off-limb linearly polarized observations of pseudostreamers,
  taken by the Coronal Multichannel Polarimeter (CoMP) telescope. These
  nulls represent regions where magnetic reconnection is likely to act
  as a catalyst for solar activity. CoMP linear-polarization observations
  also provide an independent, coronal proxy for magnetic expansion into
  the solar wind, a quantity often used to parameterize and predict the
  solar wind speed at Earth. We introduce a new method for explicitly
  calculating expansion factors from CoMP coronal linear-polarization
  observations, which does not require photospheric extrapolations. We
  conclude that linearly polarized light is a powerful new diagnostic
  of critical coronal magnetic topologies and the expanding magnetic
  flux tubes that channel the solar wind.

Title: Deriving the Properties of Coronal Pressure Fronts in 3D:
    Application to the 2012 May 17 Ground Level Enhancement
Authors: Rouillard, A. P.; Plotnikov, I.; Pinto, R. F.; Tirole, M.;
   Lavarra, M.; Zucca, P.; Vainio, R.; Tylka, A. J.; Vourlidas, A.;
   De Rosa, M. L.; Linker, J.; Warmuth, A.; Mann, G.; Cohen, C. M. S.;
   Mewaldt, R. A.
Bibcode: 2016ApJ...833...45R
Altcode: 2016arXiv160505208R
  We study the link between an expanding coronal shock and the energetic
  particles measured near Earth during the ground level enhancement of
  2012 May 17. We developed a new technique based on multipoint imaging to
  triangulate the three-dimensional (3D) expansion of the shock forming
  in the corona. It uses images from three vantage points by mapping
  the outermost extent of the coronal region perturbed by the pressure
  front. We derive for the first time the 3D velocity vector and the
  distribution of Mach numbers, M <SUB>FM</SUB>, of the entire front as
  a function of time. Our approach uses magnetic field reconstructions
  of the coronal field, full magnetohydrodynamic simulations and imaging
  inversion techniques. We find that the highest M <SUB>FM</SUB> values
  appear near the coronal neutral line within a few minutes of the
  coronal mass ejection onset; this neutral line is usually associated
  with the source of the heliospheric current and plasma sheet. We
  illustrate the variability of the shock speed, shock geometry, and
  Mach number along different modeled magnetic field lines. Despite the
  level of uncertainty in deriving the shock Mach numbers, all employed
  reconstruction techniques show that the release time of GeV particles
  occurs when the coronal shock becomes super-critical (M <SUB>FM</SUB>
  &gt; 3). Combining in situ measurements with heliospheric imagery,
  we also demonstrate that magnetic connectivity between the accelerator
  (the coronal shock of 2012 May 17) and the near-Earth environment is
  established via a magnetic cloud that erupted from the same active
  region roughly five days earlier.

Title: Flare Clustering
Authors: Title, Alan; DeRosa, Marc
Bibcode: 2016usc..confE..50T
Altcode:
  The continuous full disk observations provided by the Atmospheric
  Imaging Assembly (AIA ) can give an observer the impression that
  many flare eruptions are causally related to one another. However,
  both detailed analyses of a number of events as well as several
  statistical studies have provided only rare examples or weak evidence
  of causal behavior. Since the mechanisms of flare triggering are not
  well understood, the lack of hard evidence is not surprising. For
  this study we looked instead for groups of flares (flare clusters)
  in which successive flares occur within a fixed time - the selection
  time. The data set used for the investigation is the flare waiting
  times provided by the X-ray flare detectors on the Geostationary
  Operational Environmental Satellites (GOES). We limited the study
  to flares of magnitude C5 and greater obtained during cycles 21,
  22, 23, and 24. The GOES field of view includes the entire visible
  surface. While many flares in a cluster may come from the same active
  region, the larger clusters often have origins in multiple regions. The
  longest C5 cluster found with a linking window of 36 hours in cycles
  21, 22, 23,and 24 was 54, 82, 42, and 18 days, respectively. X flares
  also cluster. A superposed epoch analyses demonstrates that there is
  a pronounced enhancement of number of C5 and and above flares that are
  centered on the X flare clusters. We suggest that this behavior implies
  that a component of the observed coordinated behavior originates from
  the MHD processes driven by the solar dynamo that in turn creates
  unstable states in the solar atmosphere. The relationship between
  flare clusters and magnetic centers of activity was explored as was
  the correlation between high flare rates and significant changes in
  the total solar magnetic flux,

Title: a Numerical Study of Long-Range Magnetic Impacts during
    Coronal Mass Ejections
Authors: Jin, Meng; Schrijver, Karel; Cheung, Mark; DeRosa, Marc;
   Nitta, Nariaki; Title, Alan
Bibcode: 2016shin.confE..38J
Altcode:
  With the global view and high-cadence observations from SDO/AIA and
  STEREO, many spatially separated solar eruptive events appear to be
  coupled. However, the mechanisms for 'sympathetic' events are still
  largely unknown. In this study, we investigate the impact of an erupting
  flux rope on surrounding solar structures through large-scale magnetic
  coupling. We build a realistic environment of the solar corona on
  2011 February 15 using a global magnetohydrodynamics (MHD) model and
  initiate coronal mass ejections (CMEs) in active region (AR) 11158
  by inserting Gibson-Low analytical flux ropes. We show that a CME's
  impact on the surrounding structures depends not only on the magnetic
  strength of these structures and their distance to the source region,
  but also on the interaction between the CME with the large-scale
  magnetic field. Within the CME expansion domain where the flux rope
  field directly interacts with the solar structures, expansion-induced
  reconnection often modifies the overlying field, thereby increasing
  the decay index. This effect may provide a primary coupling mechanism
  underlying the sympathetic eruptions. The magnitude of the impact
  is found to depend on the orientation of the erupting flux rope,
  with the largest impacts occurring when the flux rope is favorably
  oriented for reconnecting with the surrounding regions. Outside the
  CME expansion domain, the influence of the CME is mainly through field
  line compression or post-eruption relaxation. Based on our numerical
  experiments, we discuss a way to quantify the eruption impact, which
  could be useful for forecasting purposes.

Title: Do large-scale topological features correlate with flare
    properties?
Authors: DeRosa, Marc; Barnes, Graham
Bibcode: 2016shin.confE.129D
Altcode:
  In this study, we aim to identify whether the presence or absence of
  particular topological features in the large-scale coronal magnetic
  field are correlated with whether a flare is confined or eruptive. To
  this end, we first determine the locations of null points, spine lines,
  and separatrix surfaces within the potential fields associated with
  the locations of several strong flares from the current and previous
  sunspot cycles. We then validate the topological skeletons against
  large-scale features in observations, such as the locations of streamers
  and pseudostreamers in coronagraph images. Finally, we characterize the
  topological environment in the vicinity of the flaring active regions
  and identify the trends involving their large-scale topologies and
  the properties of the associated flares.

Title: The Topology of Coronal Magnetic Fields, Shine Characterizing
    the Properties of Coronal Magnetic Null Points
Authors: Barnes, Graham; DeRosa, Marc; Wagner, Eric
Bibcode: 2016shin.confE.133B
Altcode:
  The topology of the coronal magnetic field plays a role in a wide range
  of phenomena, from Coronal Mass Ejections (CMEs) through heating of
  the corona. One fundamental topological feature is the null point,
  where the magnetic field vanishes. These points are natural sites of
  magnetic reconnection, and hence the release of energy stored in the
  magnetic field. We present preliminary results of a study using data
  from the Helioseismic and Magnetic Imager aboard NASA's Solar Dynamics
  Observatory to characterize the properties and evolution of null points
  in a Potential Field Source Surface model of the coronal field. The
  main properties considered are the lifetime of the null points, their
  distribution with height, and how they form and subsequently vanish. <P
  />This work is supported by NSF/SHINE grant 1357018 and by NASA/LWS
  Grant NNX14AD45G.

Title: Do Large-Scale Topological Features Correlate with Flare
    Properties?
Authors: DeRosa, Marc L.; Barnes, Graham
Bibcode: 2016SPD....47.1005D
Altcode:
  In this study, we aim to identify whether the presence or absence of
  particular topological features in the large-scale coronal magnetic
  field are correlated with whether a flare is confined or eruptive. To
  this end, we first determine the locations of null points, spine lines,
  and separatrix surfaces within the potential fields associated with
  the locations of several strong flares from the current and previous
  sunspot cycles. We then validate the topological skeletons against
  large-scale features in observations, such as the locations of streamers
  and pseudostreamers in coronagraph images. Finally, we characterize the
  topological environment in the vicinity of the flaring active regions
  and identify the trends involving their large-scale topologies and
  the properties of the associated flares.

Title: Physics &amp; Diagnostics of the Drivers of Solar Eruptions
Authors: Cheung, Mark; Rempel, Matthias D.; Martinez-Sykora, Juan;
   Testa, Paola; Hansteen, Viggo H.; Viktorovna Malanushenko, Anna;
   Sainz Dalda, Alberto; DeRosa, Marc L.; De Pontieu, Bart; Carlsson,
   Mats; Chen, Feng; McIntosh, Scott W.; Gudiksen, Boris
Bibcode: 2016SPD....47.0607C
Altcode:
  We provide an update on our NASA Heliophysics Grand Challenges Research
  (HGCR) project on the ‘Physics &amp; Diagnostics of the Drivers of
  Solar Eruptions’. This presentation will focus on results from a
  data-inspired, 3D radiative MHD model of a solar flare. The model
  flare results from the interaction of newly emerging flux with a
  pre-existing active region. Synthetic observables from the model
  reproduce observational features compatible with actual flares. These
  include signatures of coronal magnetic reconnection, chromospheric
  evaporation, EUV flare arcades, sweeping motion of flare ribbons
  and sunquakes.

Title: A Numerical Study of Long-range Magnetic Impacts during
    Coronal Mass Ejections
Authors: Jin, M.; Schrijver, C. J.; Cheung, M. C. M.; DeRosa, M. L.;
   Nitta, N. V.; Title, A. M.
Bibcode: 2016ApJ...820...16J
Altcode: 2016arXiv160304900J
  With the global view and high-cadence observations from Solar Dynamics
  Observatory/Atmospheric Imaging Assembly and Solar TErrestrial RElations
  Observatory, many spatially separated solar eruptive events appear
  to be coupled. However, the mechanisms for “sympathetic” events
  are still largely unknown. In this study, we investigate the impact
  of an erupting flux rope on surrounding solar structures through
  large-scale magnetic coupling. We build a realistic environment of the
  solar corona on 2011 February 15 using a global magnetohydrodynamics
  model and initiate coronal mass ejections (CMEs) in active region
  11158 by inserting Gibson-Low analytical flux ropes. We show that a
  CME’s impact on the surrounding structures depends not only on the
  magnetic strength of these structures and their distance to the source
  region, but also on the interaction between the CME and the large-scale
  magnetic field. Within the CME expansion domain where the flux rope
  field directly interacts with the solar structures, expansion-induced
  reconnection often modifies the overlying field, thereby increasing
  the decay index. This effect may provide a primary coupling mechanism
  underlying the sympathetic eruptions. The magnitude of the impact
  is found to depend on the orientation of the erupting flux rope,
  with the largest impacts occurring when the flux rope is favorably
  oriented for reconnecting with the surrounding regions. Outside the
  CME expansion domain, the influence of the CME is mainly through field
  line compression or post-eruption relaxation. Based on our numerical
  experiments, we discuss a way to quantify the eruption impact, which
  could be useful for forecasting purposes.

Title: The Role of Large-scale Magnetic Coupling for Solar Corona
    Sympathy
Authors: Jin, M.; Schrijver, K.; Cheung, C. M. M.; DeRosa, M. L.;
   Nitta, N.; Title, A. M.
Bibcode: 2015AGUFMSH23A2425J
Altcode:
  With the comprehensive view and high cadence observations from
  SDO/AIA and STEREO in solar cycle 24, a large number of spatially
  separated solar eruptive events are found to be coupled. However,
  compared with the established initiation mechanisms for "isolated"
  events, the mechanisms for "sympathetic" events are still largely
  unknown, and nascent theories are untested. In this study, we build
  a realistic environment of solar corona on 2011 February 15 using
  a global MHD model and investigate how an eruption can impact the
  surrounding solar structures. Our result shows that the solar eruption's
  impact on the different structures can be quite different. Within
  the CME expansion domain, it is possible to trigger an eruption by
  overlaying field removal through expansion induced reconnection. The
  magnitude of impact is found to be dependent on the orientation
  of the erupting flux rope. Outside the CME expansion domain, the
  post-eruption reconfiguration could play an important role for solar
  sympathy. Based on the modeling results, we discuss the possibility of
  using observable/estimable parameters to quantify the eruption impact
  therefore providing an useful parameter for forecasting sympathy.

Title: The Influence of Spatial resolution on Nonlinear Force-free
    Modeling
Authors: DeRosa, M. L.; Wheatland, M. S.; Leka, K. D.; Barnes, G.;
   Amari, T.; Canou, A.; Gilchrist, S. A.; Thalmann, J. K.; Valori,
   G.; Wiegelmann, T.; Schrijver, C. J.; Malanushenko, A.; Sun, X.;
   Régnier, S.
Bibcode: 2015ApJ...811..107D
Altcode: 2015arXiv150805455D
  The nonlinear force-free field (NLFFF) model is often used to
  describe the solar coronal magnetic field, however a series of
  earlier studies revealed difficulties in the numerical solution of the
  model in application to photospheric boundary data. We investigate
  the sensitivity of the modeling to the spatial resolution of the
  boundary data, by applying multiple codes that numerically solve the
  NLFFF model to a sequence of vector magnetogram data at different
  resolutions, prepared from a single Hinode/Solar Optical Telescope
  Spectro-Polarimeter scan of NOAA Active Region 10978 on 2007 December
  13. We analyze the resulting energies and relative magnetic helicities,
  employ a Helmholtz decomposition to characterize divergence errors, and
  quantify changes made by the codes to the vector magnetogram boundary
  data in order to be compatible with the force-free model. This study
  shows that NLFFF modeling results depend quantitatively on the spatial
  resolution of the input boundary data, and that using more highly
  resolved boundary data yields more self-consistent results. The
  free energies of the resulting solutions generally trend higher
  with increasing resolution, while relative magnetic helicity values
  vary significantly between resolutions for all methods. All methods
  require changing the horizontal components, and for some methods also
  the vertical components, of the vector magnetogram boundary field in
  excess of nominal uncertainties in the data. The solutions produced
  by the various methods are significantly different at each resolution
  level. We continue to recommend verifying agreement between the modeled
  field lines and corresponding coronal loop images before any NLFFF
  model is used in a scientific setting.

Title: Evolving Models of Surface and Coronal Activity of Sun-Like
    Stars
Authors: DeRosa, Marc; Cheung, Mark
Bibcode: 2015IAUGA..2257506D
Altcode:
  Surface flux transport models have proven useful for modeling the
  evolution of magnetic patterns on the solar photospheric surface on
  timescales ranging from as short as a few days to as long as multiple
  magnetic cycles. In the work presented here, we use surface flux
  transport models to study variations in the magnetic activity of
  Sun-like stars, and to explore the dependence of flux evolution on
  the properties of flux emergence, large-scale flows, and dispersal
  by convective turbulence. These time sequences of surface magnetic
  evolution are then used to drive magnetofrictional models of stellar
  coronal fields to study how coronal fields evolve. From such models,
  we can begin to assess how the evolution of various stellar features,
  such as interacting starspot groups, might affect the overlying
  stellar coronae.

Title: Characterizing the Properties of Coronal Magnetic Null Points
Authors: Barnes, Graham; DeRosa, Marc; Wagner, Eric
Bibcode: 2015IAUGA..2258194B
Altcode:
  The topology of the coronal magnetic field plays a role in a wide range
  of phenomena, from Coronal Mass Ejections (CMEs) through heating of
  the corona. One fundamental topological feature is the null point,
  where the magnetic field vanishes. These points are natural sites of
  magnetic reconnection, and hence the release of energy stored in the
  magnetic field. We present preliminary results of a study using data
  from the Helioseismic and Magnetic Imager aboard NASA's Solar Dynamics
  Observatory to characterize the properties and evolution of null points
  in a Potential Field Source Surface model of the coronal field. The
  main properties considered are the lifetime of the null points,
  their distribution with height, and how they form and subsequently
  vanish.This work is supported by NASA/LWS Grant NNX14AD45G, and by
  NSF/SHINE grant 1357018.

Title: Characterizing the Properties of Coronal Magnetic Null Points
Authors: Barnes, Graham; DeRosa, Marc; Wagner, Eric
Bibcode: 2015shin.confE..79B
Altcode:
  The topology of the coronal magnetic field plays a role in a wide range
  of phenomena, from Coronal Mass Ejections (CMEs) through heating of
  the corona. One fundamental topological feature is the null point,
  where the magnetic field vanishes. These points are natural sites of
  magnetic reconnection, and hence the release of energy stored in the
  magnetic field. We present preliminary results of a study using data
  from the SOHO/Michelson Doppler Imager and SDO/Helioseismic and Magnetic
  Imager to characterize the properties and evolution of null points
  in a Potential Field Source Surface model of the coronal field. The
  main properties considered are the lifetime of the null points, their
  distribution with height, and how they form and subsequently vanish. In
  addition, we look at how the distribution of null points varies with
  solar cycle.

Title: The Coronal Global Evolutionary Model: Using HMI Vector
    Magnetogram and Doppler Data to Model the Buildup of Free Magnetic
    Energy in the Solar Corona
Authors: Fisher, G. H.; Abbett, W. P.; Bercik, D. J.; Kazachenko,
   M. D.; Lynch, B. J.; Welsch, B. T.; Hoeksema, J. T.; Hayashi, K.;
   Liu, Y.; Norton, A. A.; Dalda, A. Sainz; Sun, X.; DeRosa, M. L.;
   Cheung, M. C. M.
Bibcode: 2015SpWea..13..369F
Altcode: 2015arXiv150506018F
  The most violent space weather events (eruptive solar flares and
  coronal mass ejections) are driven by the release of free magnetic
  energy stored in the solar corona. Energy can build up on timescales
  of hours to days, and then may be suddenly released in the form of a
  magnetic eruption, which then propagates through interplanetary space,
  possibly impacting the Earth's space environment. Can we use the
  observed evolution of the magnetic and velocity fields in the solar
  photosphere to model the evolution of the overlying solar coronal
  field, including the storage and release of magnetic energy in such
  eruptions? The objective of CGEM, the Coronal Global Evolutionary Model,
  funded by the NASA/NSF Space Weather Modeling program, is to develop
  and evaluate such a model for the evolution of the coronal magnetic
  field. The evolving coronal magnetic field can then be used as a
  starting point for magnetohydrodynamic (MHD) models of the corona,
  which can then be used to drive models of heliospheric evolution and
  predictions of magnetic field and plasma density conditions at 1AU.

Title: What Do EUV Dimmings Tell Us About CME Topology
Authors: Thompson, Barbara J.; DeRosa, Marc L.; Fisher, Richard R.;
   Krista, Larisza D.; Kwon, Ryun Young; Mason, James P.; Mays, Mona L.;
   Nitta, Nariaki V.; Webb, David F.; West, Matthew J.
Bibcode: 2015TESS....121201T
Altcode:
  Large-scale coronal EUV dimmings develop on timescales of hours in
  association with a flare or filament eruption, and are known to be
  well correlated with coronal mass ejections (CMEs). However, it is not
  clear why some CMEs have dimmings and some do not, nor is it clear how
  these dimmings relate to CME topology. The inner coronal coverage of
  SDO AIA and STEREO EUVI, combined with the extended field of view of
  PROBA2's SWAP imager, allow us the opportunity to map the topology of
  a dimming region in three dimensions into an erupting CME. Although
  the location and extent of a dimming region appears to be the best
  indicator of the inner "footprint" of a CME, the correlation is far
  from perfect. However, dimmings can provide vital clues about the
  development and 3D kinematics of CMEs. This is particularly important
  as we are currently in an extended period where the STEREO coronagraph
  images are not always available and are increasingly "mirroring" LASCO
  images, and therefore the 3D properties of a CME will be difficult
  to deduce. Thus, understanding the inner coronal manifestations of
  a CME can provide clues to its structure and dynamics, even without
  multi-viewpoint coronagraph observations. We present the results of
  this combined analysis effort, along with a discussion of how dimmings
  can be used to forecast CME trajectories.

Title: Inferring the Structure of the Solar Corona and Inner
    Heliosphere During the Maunder Minimum Using Global Thermodynamic
    Magnetohydrodynamic Simulations
Authors: Riley, Pete; Lionello, Roberto; Linker, Jon A.; Cliver,
   Ed; Balogh, Andre; Beer, Jürg; Charbonneau, Paul; Crooker, Nancy;
   DeRosa, Marc; Lockwood, Mike; Owens, Matt; McCracken, Ken; Usoskin,
   Ilya; Koutchmy, S.
Bibcode: 2015ApJ...802..105R
Altcode:
  Observations of the Sun’s corona during the space era have led to
  a picture of relatively constant, but cyclically varying solar output
  and structure. Longer-term, more indirect measurements, such as from
  <SUP>10</SUP>Be, coupled by other albeit less reliable contemporaneous
  reports, however, suggest periods of significant departure from this
  standard. The Maunder Minimum was one such epoch where: (1) sunspots
  effectively disappeared for long intervals during a 70 yr period; (2)
  eclipse observations suggested the distinct lack of a visible K-corona
  but possible appearance of the F-corona; (3) reports of aurora were
  notably reduced; and (4) cosmic ray intensities at Earth were inferred
  to be substantially higher. Using a global thermodynamic MHD model,
  we have constructed a range of possible coronal configurations for the
  Maunder Minimum period and compared their predictions with these limited
  observational constraints. We conclude that the most likely state of the
  corona during—at least—the later portion of the Maunder Minimum was
  not merely that of the 2008/2009 solar minimum, as has been suggested
  recently, but rather a state devoid of any large-scale structure,
  driven by a photospheric field composed of only ephemeral regions,
  and likely substantially reduced in strength. Moreover, we suggest
  that the Sun evolved from a 2008/2009-like configuration at the start
  of the Maunder Minimum toward an ephemeral-only configuration by the
  end of it, supporting a prediction that we may be on the cusp of a
  new grand solar minimum.

Title: Low-temperature Spectroscopy of the
    <SUP>12</SUP>C<SUB>2</SUB>H<SUB>2</SUB> (υ<SUB>1</SUB> +
    υ<SUB>3</SUB>) Band in a Helium Buffer Gas
Authors: Santamaria, L.; Di Sarno, V.; Ricciardi, I.; De Rosa, M.;
   Mosca, S.; Santambrogio, G.; Maddaloni, P.; De Natale, P.
Bibcode: 2015ApJ...801...50S
Altcode: 2014arXiv1410.5310S
  Buffer gas cooling with a <SUP>4</SUP>He gas is
  used to perform laser-absorption spectroscopy of the
  <SUP>12</SUP>C<SUB>2</SUB>H<SUB>2</SUB> (υ<SUB>1</SUB> +
  υ<SUB>3</SUB>) band at cryogenic temperatures. Doppler thermometry
  is first carried out to extract translational temperatures from
  the recorded spectra. Then, rotational temperatures down to 20 K
  are retrieved by fitting the Boltzmann distribution to the relative
  intensities of several ro-vibrational lines. The potential of our
  setup to tune the thermal equilibrium between translational and
  rotational degrees of freedom is also demonstrated. This can be used
  to reproduce in a controlled way the regime of non-local thermal
  equilibrium typically encountered in the interstellar medium. The
  underlying helium-acetylene collisional physics, relevant for modeling
  planetary atmospheres, is also addressed. In particular, the diffusion
  time of <SUP>12</SUP>C<SUB>2</SUB>H<SUB>2</SUB> in the buffer cell is
  measured against the <SUP>4</SUP>He flux at two separate translational
  temperatures; the observed behavior is then compared with that
  predicted by a Monte Carlo simulation, thus providing an estimate for
  the respective total elastic cross sections: σ<SUB>el</SUB>(100 K) =
  (4 ± 1) × 10<SUP>-20</SUP> m<SUP>2</SUP> and σ<SUB>el</SUB>(25 K) =
  (7 ± 2) × 10<SUP>-20</SUP> m<SUP>2</SUP>.

Title: What Do EUV Dimmings Tell Us About CME Topology?
Authors: Thompson, B. J.; DeRosa, M. L.; Fisher, R. R.; Krista, L. D.;
   Kwon, R. Y.; Mason, J. P.; Mays, M. L.; Nitta, N.; Savani, N.; West,
   M. J.
Bibcode: 2014AGUFMSH43B4202T
Altcode:
  Large-scale coronal EUV dimmings, developing on timescales of minutes
  to hours in association with a flare or filament eruption, are known to
  exhibit a high correlation with coronal mass ejections. However, it is
  not clear why some CMEs have dimmings and some do not, nor is it clear
  how these dimmings relate to CME topology. The inner coronal coverage
  of SDO AIA and STEREO EUVI, combined with the extended field of view
  of PROBA2's SWAP imager, allow us the opportunity to map the topology
  of a dimming region in three dimensions into an erupting CME. Although
  the location and extent of a dimming region appears to be the best
  indicator of the inner "footprint" of a CME, the correlation is far
  from perfect. However, dimmings can provide vital clues about the
  development and 3D kinematics of a CME. This is particularly important
  as we are entering an extended period of time where STEREO coronagraph
  images will not always be available, and therefore the 3D properties of
  a CME will be difficult to deduce. Therefore, understanding the inner
  coronal manifestations of a CME can provide clues to its structure and
  dynamics, even without multi-viewpoint coronagraph observations. We
  present the results of this combined analysis effort, along with a
  discussion of how dimmings can be used in forecasting CME directions.

Title: Tracking Solar Active Region Outflow Plasma from Its Source
    to the Near-Earth Environment
Authors: Culhane, J. L.; Brooks, D. H.; van Driel-Gesztelyi, L.;
   Démoulin, P.; Baker, D.; DeRosa, M. L.; Mandrini, C. H.; Zhao, L.;
   Zurbuchen, T. H.
Bibcode: 2014SoPh..289.3799C
Altcode: 2014SoPh..tmp...90C; 2014arXiv1405.2949C
  Seeking to establish whether active-region upflow material contributes
  to the slow solar wind, we examine in detail the plasma upflows from
  Active Region (AR) 10978, which crossed the Sun's disc in the interval 8
  to 16 December 2007 during Carrington rotation (CR) 2064. In previous
  work, using data from the Hinode/EUV Imaging Spectrometer, upflow
  velocity evolution was extensively studied as the region crossed the
  disc, while a linear force-free-field magnetic extrapolation was used
  to confirm aspects of the velocity evolution and to establish the
  presence of quasi-separatrix layers at the upflow source areas. The
  plasma properties, temperature, density, and first ionisation potential
  bias [FIP-bias] were measured with the spectrometer during the disc
  passage of the active region. Global potential-field source-surface
  (PFSS) models showed that AR 10978 was completely covered by the
  closed field of a helmet streamer that is part of the streamer
  belt. Therefore it is not clear how any of the upflowing AR-associated
  plasma could reach the source surface at 2.5 R<SUB>⊙</SUB> and
  contribute to the slow solar wind. However, a detailed examination of
  solar-wind in-situ data obtained by the Advanced Composition Explorer
  (ACE) spacecraft at the L<SUB>1</SUB> point shows that increases in
  O<SUP>7+</SUP>/O<SUP>6+</SUP>, C<SUP>6+</SUP>/C<SUP>5+</SUP>, and Fe/O -
  a FIP-bias proxy - are present before the heliospheric current-sheet
  crossing. These increases, along with an accompanying reduction in
  proton velocity and an increase in density are characteristic of
  both AR and slow-solar-wind plasma. Finally, we describe a two-step
  reconnection process by which some of the upflowing plasma from the
  AR might reach the heliosphere.

Title: Characterizing the Properties of Coronal Magnetic Null Points
Authors: Barnes, Graham; Wagner, Eric; DeRosa, Marc
Bibcode: 2014shin.confE..74B
Altcode:
  The topology of the coronal magnetic field plays a role in a wide range
  of phenomena, from Coronal Mass Ejections to heating of the corona. One
  fundamental topological feature is the null point, where the magnetic
  field vanishes. These points are natural sites of magnetic reconnection,
  and hence the release of energy stored in the magnetic field. We present
  preliminary results of a study using data from the Helioseismic and
  Magnetic Imager aboard NASA's Solar Dynamics Observatory to characterize
  the properties and evolution of null points in a Potential Field Source
  Surface model of the coronal field. The main properties considered
  are the lifetime of the null points, their distribution with height,
  and how they form and subsequently vanish.

Title: Active Region Magnetic Field Modeling Guided by Coronal Loops
    and Surface Fields
Authors: DeRosa, Marc L.; Malanushenko, Anna; Schrijver, Carolus J.;
   Wheatland, Michael S
Bibcode: 2014AAS...22432319D
Altcode:
  Dynamic events such as solar flares, filament eruptions, and mass
  ejections are powered by the evolving coronal magnetic field. However,
  the ways in which energy is stored in, and released from, the coronal
  magnetic field are poorly understood, in large part because the field
  configuration cannot be determined directly from observations and has
  eluded the successful application of routine modeling based on surface
  magnetograms. Recently, we have demonstrated that the Quasi-Grad-Rubin
  (QGR) method for modeling the current-carrying field associated with
  active regions shows promise. In Malanushenko et al. (2014, ApJ 783:102)
  we have used the QGR method to construct the magnetic field at several
  times during the evolution of AR11158 during February 2011. The QGR
  method does not require vector magnetograms, and instead uses the
  trajectories of observed coronal loops to constrain the locations
  of electric currents within the modeling domain. In this study,
  we continue to assess the utility of QGR by applying this method to
  additional active regions from the current activity cycle, making use
  of SDO/HMI line-of-sight magnetograms and imagery from the extreme
  ultraviolet channels of SDO/AIA.

Title: Using Coronal Loops to Reconstruct the Magnetic Field of an
    Active Region before and after a Major Flare
Authors: Malanushenko, A.; Schrijver, C. J.; DeRosa, M. L.; Wheatland,
   M. S.
Bibcode: 2014ApJ...783..102M
Altcode: 2013arXiv1312.5389M
  The shapes of solar coronal loops are sensitive to the presence
  of electrical currents that are the carriers of the non-potential
  energy available for impulsive activity. We use this information in
  a new method for modeling the coronal magnetic field of active region
  (AR) 11158 as a nonlinear force-free field (NLFFF). The observations
  used are coronal images around the time of major flare activity on
  2011 February 15, together with the surface line-of-sight magnetic
  field measurements. The data are from the Helioseismic and Magnetic
  Imager and Atmospheric Imaging Assembly on board the Solar Dynamics
  Observatory. The model fields are constrained to approximate the coronal
  loop configurations as closely as possible, while also being subject
  to the force-free constraints. The method does not use transverse
  photospheric magnetic field components as input and is thereby
  distinct from methods for modeling NLFFFs based on photospheric vector
  magnetograms. We validate the method using observations of AR 11158
  at a time well before major flaring and subsequently review the field
  evolution just prior to and following an X2.2 flare and associated
  eruption. The models indicate that the energy released during the
  instability is about 1 × 10<SUP>32</SUP> erg, consistent with what
  is needed to power such a large eruptive flare. Immediately prior to
  the eruption, the model field contains a compact sigmoid bundle of
  twisted flux that is not present in the post-eruption models, which
  is consistent with the observations. The core of that model structure
  is twisted by ≈0.9 full turns about its axis.

Title: Solar Cycle Variations of the Radio Brightness of the Solar
    Polar Regions as Observed by the Nobeyama Radioheliograph
Authors: Nitta, Nariaki V.; Sun, Xudong; Hoeksema, J. Todd; DeRosa,
   Marc L.
Bibcode: 2014ApJ...780L..23N
Altcode:
  We have analyzed daily microwave images of the Sun at 17 GHz obtained
  with the Nobeyama Radioheliograph (NoRH) in order to study the solar
  cycle variations of the enhanced brightness in the polar regions. Unlike
  in previous works, the averaged brightness of the polar regions is
  obtained from individual images rather than from synoptic maps. We
  confirm that the brightness is anti-correlated with the solar cycle and
  that it has generally declined since solar cycle 22. Including images
  up to 2013 October, we find that the 17 GHz brightness temperature
  of the south polar region has decreased noticeably since 2012. This
  coincides with a significant decrease in the average magnetic field
  strength around the south pole, signaling the arrival of solar maximum
  conditions in the southern hemisphere more than a year after the
  northern hemisphere. We do not attribute the enhanced brightness
  of the polar regions at 17 GHz to the bright compact sources that
  occasionally appear in synthesized NoRH images. This is because they
  have no correspondence with small-scale bright regions in images
  from the Atmospheric Imaging Assembly on board the Solar Dynamics
  Observatory with a broad temperature coverage. Higher-quality radio
  images are needed to understand the relationship between microwave
  brightness and magnetic field strength in the polar regions.

Title: Using coronal loops to model the coronal magnetic field before
    and after major eruptive events
Authors: Malanushenko, Anna; Schrijver, Carolus; Wheatland, M. S.;
   DeRosa, Marc
Bibcode: 2014cosp...40E1960M
Altcode:
  Solar flares are believed to be a manifestation of major release of
  magnetic energy stored in active region field. Modeling the coronal
  magnetic field may enable us to evaluate the energy available for
  release, as well as possible sites of the reconnection and other
  relevant properties of the field. We use a new method to aid this
  problem by including the observed structure of the field (manifested
  in coronal loops) as additional constraints. We verify that the method
  (previously shown to work on synthetic data in Malanushenko et. al.,
  ApJ, 756, 153, 2012) is generally acceptable for the solar data, as
  it gives self-consistent, slowly changing results for slowly evolving
  structures. We further develop the potential of this method to access
  changes in the coronal magnetic field triggered by major eruptive
  events, and compare the results with observations.

Title: Properties of Solar Flare Clustering
Authors: Title, Alan; DeRosa, Marc
Bibcode: 2014cosp...40E3345T
Altcode:
  The continuous full disk observations provided by the Atmospheric
  Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO) give
  an observer the impression that flare and filament eruptions are
  related. However, both detailed analysis of a number of events as well
  as a number of statistical studies have provided only rare examples of
  clear causal behavior. But the mechanisms of flare triggering are not
  well understood, so the lack of hard evidence is not surprising. Here
  we have examined the waiting-time statistics of GOES X-ray flares of
  magnitude C5 or greater during the last sunspot cycle with the aim of
  assessing the degree to which flares are clustered in time. Clusters are
  groups of flares in which all successive flares occur within a fixed
  separation time - the linking window. While many of the flares in a
  cluster may come from the same active region, the clusters that last
  more than a disk passage must result from flares in multiple active
  regions. The longest cluster of the last cycle lasted more than 42
  days. None of the flares were separated by more than 36 hours. Since
  that cluster lasted more than three disk passages, it could not have
  been caused by a single region. We find that during the last maximum,
  eight clusters contributed 44% of all flares. All of these clusters
  spanned multiple disk passages, but occupied only 16.5% of the cycle
  duration. Two of the clusters provided 34% of the flares. We suggest
  that this behavior implies that a component of the observed coordinated
  behavior has its origin in the solar dynamo.

Title: The Perihelion Passage of Comet ISON as seen by SDO
Authors: Pesnell, W. D.; Schrijver, C. J.; Boerner, P.; DeRosa, M. L.;
   Liu, W.; Thompson, B. J.
Bibcode: 2013AGUFM.P24A..10P
Altcode:
  Comet ISON will fly through perihelion on November 28, 2013. It is one
  of the largest sungrazing comets to be seen in the Space Age. The Solar
  Dynamics Observatory (SDO) has seen two previous sungrazing comets in
  the extreme ultraviolet channels of the Atmospheric Imaging Assembly
  (AIA). Comet ISON will fly farther from the Sun (perihelion distance
  of 2.7 Rsun compared to 1.15 for Comet Lovejoy), meaning it probes
  a different part of the solar corona, but its larger size should
  provide enough mass to illuminate the path of the nucleus. Based on
  the latest ephemeris, SDO will be able to track Comet ISON through
  the entire perihelion passage by a series of off-point maneuvers. We
  will present the AIA data obtained from the Comet ISON perihelion,
  discussing the differences between Comets ISON and Lovejoy. We will
  then summarize what we have learned from the observations and offer
  some thoughts on what sungrazing comets may reveal about comets,
  the Sun, and their interaction.

Title: Pathways of Large-scale Magnetic Couplings between Solar
    Coronal Events
Authors: Schrijver, Carolus J.; Title, Alan M.; Yeates, Anthony R.;
   DeRosa, Marc L.
Bibcode: 2013ApJ...773...93S
Altcode: 2013arXiv1305.0801S
  The high-cadence, comprehensive view of the solar corona by SDO/AIA
  shows many events that are widely separated in space while occurring
  close together in time. In some cases, sets of coronal events are
  evidently causally related, while in many other instances indirect
  evidence can be found. We present case studies to highlight a variety
  of coupling processes involved in coronal events. We find that physical
  linkages between events do occur, but concur with earlier studies that
  these couplings appear to be crucial to understanding the initiation
  of major eruptive or explosive phenomena relatively infrequently. We
  note that the post-eruption reconfiguration timescale of the large-scale
  corona, estimated from the extreme-ultraviolet afterglow, is on average
  longer than the mean time between coronal mass ejections (CMEs), so
  that many CMEs originate from a corona that is still adjusting from a
  previous event. We argue that the coronal field is intrinsically global:
  current systems build up over days to months, the relaxation after
  eruptions continues over many hours, and evolving connections easily
  span much of a hemisphere. This needs to be reflected in our modeling
  of the connections from the solar surface into the heliosphere to
  properly model the solar wind, its perturbations, and the generation and
  propagation of solar energetic particles. However, the large-scale field
  cannot be constructed reliably by currently available observational
  resources. We assess the potential of high-quality observations from
  beyond Earth's perspective and advanced global modeling to understand
  the couplings between coronal events in the context of CMEs and solar
  energetic particle events. <P />.

Title: On the role of asymmetries in the reversal of the solar
    magnetic field
Authors: Brun, A. S.; Derosa, M. L.; Hoeksema, J. T.
Bibcode: 2013IAUS..294...75B
Altcode:
  We study how the solar magnetic field evolves from antisymmetric
  (dipolar) to symmetric (quadrupolar) state during the course of
  its 11-yr cycle. We show that based on equatorial symmetries of the
  induction equation, flux transport solar mean field dynamo models excite
  mostly the antisymmetric (dipolar) family whereas a decomposition of the
  solar magnetic field data reveals that both families should be excited
  to similar amplitude levels. We propose an alternative solar dynamo
  solution based on North-South asymmetry of the meridional circulation
  to better reconcile models and observations.

Title: The Coronal Global Evolutionary Model (CGEM)
Authors: Fisher, George H.; DeRosa, M. L.; Hoeksema, J. T.
Bibcode: 2013SPD....4410102F
Altcode:
  The Coronal Global Evolutionary Model, or CGEM, is a collaborative
  effort from the UC Berkeley Space Sciences Laboratory (SSL), Stanford
  University, and Lockheed-Martin. In work that led up to the selection of
  this project, the team demonstrated its capability to use sequences of
  vector magnetograms and Dopplergrams from the Helioseismic and Magnetic
  Imager (HMI) instrument aboard the SDO to drive a magnetofrictional
  (MF) model of the coronal magnetic field in AR 11158, which produced an
  X2.2 flare. We will implement this MF model in spherical coordinates
  to enable real-time, long-term modeling of the non-potential coronal
  magnetic field, both globally and for individual active region
  (ARs). The model's Earth-facing hemisphere will be driven using
  electric fields derived from the observed evolution of photospheric
  line-of-sight magnetic fields and electric currents. Far-side data
  inputs will be from an existing flux transport code, combined with
  HMI far-side observations of new active regions, with empirical
  parametrizations of orientation and flux. Because this model includes
  large-scale coronal electric currents, it is a substantial improvement
  over existing real-time global coronal models, which assume potential
  fields. Data products available from the model will include: 1) the
  evolving photospheric electric field, Poynting flux, and helicity
  flux; 2) estimates of coronal free energy and non-potential geometry
  and topology; 3) initial and time-dependent boundary conditions
  for MHD modeling of active regions; and 4) time-dependent boundary
  conditions and flux tube expansion factors for MHD and empirical
  solar wind models. Unstable configurations found from MF models will
  be dynamically evolved with local and global MHD codes. Modules used
  to derive surface electric fields from magnetic evolution will be
  incorporated into the SDO/HMI data pipeline, and data products will
  be distributed through the Joint Science Operations Center (JSOC) and
  directly to space weather forecasters and users. The electric field
  and MF codes will be delivered to the Community Coordinated Modeling
  Center (CCMC) for science analysis and use with other models. This
  project is being jointly funded by NASA and NSF.

Title: Some Difficulties in Determining Causality of Sympathetic
    Solar Events
Authors: DeRosa, M. L.; Schrijver, C. J.; Title, A. M.; Yeates, A. R.
Bibcode: 2013enss.confE..91D
Altcode:
  Much has been made regarding the occurrence of synchronous eruptive
  events occurring in the solar corona. Determining the frequencies at
  which they occur and understanding the causal linkages that may connect
  such events (making them sympathetic in addition to synchronous) are an
  area of active research. Causal linkages are observed to take the form
  of (1) disturbances in magnetic fields that connect active regions,
  (2) disturbances in the magnetic field configuration overlying active
  regions, and/or (3) triggering by disturbances propagating from one
  region to another. Here we display two types of synchronous events:
  those where, using a combination of image sequences from SDO and STEREO
  as well as coronal-field modeling, evidence for sympathy seems solid,
  and those where evidence of sympathy is more ambiguous. We use these two
  types of cases to illustrate some difficulties in establishing whether
  synchronous events are in fact sympathetic. This has implications
  for determining the frequency and importance of sympathetic events,
  and thus for understanding of coronal field evolution and the origins
  of space weather.

Title: Collective Solar Behavior
Authors: Title, Alan; Schrijver, Karel; Derosa, MArc
Bibcode: 2013enss.confE.120T
Altcode:
  The Atmospheric Imaging Assembly (AIA) on the Solar Dynamic Observatory
  (SDO) together with the Helioseismic and Magnetic Imager (HMI) and the
  Extreme Ultraviolet Variability Experiment (EVE) allow observations of
  the entire Sun from 6000 K to 20,000,000 K with arcsecond resolution
  and a 12 second cadence (AIA), obtain doppler and continuum images at
  a 45 second cadence and Line of Sight and vector magnetograms (HMI)
  every few minutes, and integrated solar spectra from 1 to 100 nm on a 2
  second cadence (EVE) 24/7. Because of the enhanced thermal and temporal
  coverage and the high dynamic range available with AIA, it has been
  able to discovery associated behavior associated with extreme solar
  events that are apparently driven by the rapid expansion of magnetic
  structures. The extent of the events are recognized by using co-temporal
  STEREO data. The rapidly expanding magnetic structures, speeds between
  500 and 2000 km/s, can apparently trigger filament eruptions, CME's,
  and other flares. These "triggered" events are sometimes larger that
  the initial disturbance. The remote triggering makes flare prediction
  based upon ONLY local energy build up models less valuable, but suggests
  that with proper coverage prediction of solar events with potential
  for Earth impact may be made more reliable. Movies of sample events
  discovered in AIA together with STEREO data will be shown.

Title: Photospheric Drivers of Coronal Evolution
Authors: Welsch, B. T.; Kazachenko, M.; Fisher, G. H.; Cheung,
   M. C. M.; DeRosa, M. L.; CGEM Team
Bibcode: 2013enss.confE.108W
Altcode:
  Flares and coronal mass ejections (CMEs) are driven by the release
  of free magnetic energy stored in the coronal magnetic field. While
  this energy is stored in the corona, photospheric driving must play
  a central role in its injection, storage, and release, since magnetic
  fields present in the corona originated within the solar interior, and
  are anchored at the photosphere. Also, the corona's low diffusivity
  and high Alfven speed (compared to that at the photosphere) imply
  that the large-scale coronal field essentially maintains equilibrium
  (outside of episodic flares and CMEs!), and therefore only evolves
  due to forcing from photospheric evolution. But fundamental questions
  about each stage of this "storage and release" paradigm remain open:
  How does free magnetic energy build up in the corona? How is this energy
  stored? And what triggers its release? The unprecedented combination of
  high cadence, resolution, and duty cycle of the HMI vector magnetograph
  enables modeling coronal magnetic evolution in response to photospheric
  driving, a powerful approach to addressing these questions. I will
  discuss our efforts to use HMI vector magneotgrams of AR 11158 to derive
  time-dependent boundary conditions for a data-driven coronal magnetic
  field model. These efforts will play a key role in the planned Coronal
  Global Evolutionary Model (CGEM), a data-driven, time-dependent model of
  the global coronal field. This work is supported by NASA's Living With
  a Star program and NSF's Division of Atmospheric and Geospace Sciences.

Title: Initiation of Coronal Mass Ejections: A Comparison of AR11158
    with a Simulation of Flux Cancellation
Authors: Manchester, W. B.; Fang, F.; Burns, C.; Kosovichev, A. G.;
   Sun, X.; DeRosa, M. L.; Cheung, C.
Bibcode: 2012AGUFMSH53B..06M
Altcode:
  We present a detailed comparison of an MHD simulation of magnetic
  flux emergence with observations of a large-scale active region. The
  simulation (Fang et al. 2012) addresses the buoyant rise of a flux
  rope through the convection zone into the corona, which spontaneously
  reproduces several features found in AR11158. We focus our study on
  the central part of AR11158 from which an energetic CME was observed
  on 2011 February 15. We examine AIA loops, HMI vector magnetograms,
  photospheric flow patterns, and convection zone flow patterns to fully
  characterize the active region and relate its dynamics to basic features
  found in the MHD simulation. Salient features are the convergence of
  flux concentrations of opposite polarity and strong shear flows along
  the polarity inversion line observed prior to and during the CME. We
  will show that such shear flows are readily explained as a response to
  the Lorentz force, and the convergence are associated with convective
  downdrafts that form over the polarity inversion line. We also compare
  the brightening of coronal loops observed with AIA to tether-cutting
  reconnection observed in or simulation. Together, these mechanisms
  explain the buildup, concentration and release of energy necessary
  for eruptive events.

Title: Tracking Solar Active Region Outflow Plasma from its Source
    to the near-Earth Environment
Authors: Culhane, J. L.; Brooks, D.; Zurbuchen, T.; van
   Driel-Gesztelyi, L.; Fazakerley, A. N.; DeRosa, M. L.
Bibcode: 2012AGUFMSH53A2255C
Altcode:
  In a recent study of persistent active region outflow from AR 10978 in
  the period 10 - 15, December, 2007, Brooks and Warren (2011), using the
  Hinode EUV Imaging Spectrometer (EIS) instrument showed the presence
  of a strong low-FIP element enhancement in the outflowing plasma that
  was replicated three days later in the in-situ solar wind measurements
  made by the ACE/SWICS instrument. In the present work, we examine the
  outflowing plasma properties (Te, Ne, v, abundances) as a function
  of time in greater detail as AR 10978 passes the Earth-Sun line. The
  structure of the magnetic field above the two outflow regions - E and
  W of the AR, is also examined. Following an assessment of the relevant
  magnetic structures between Sun and Earth, the properties of the solar
  wind plasma arriving at ACE approximately three days later are measured
  and compared with those of the outflowing AR plasma. The relationship
  of these measurements to the in-situ magnetic field observed by the
  ACE magnetometer is also studied. Finally the role of persistent AR
  outflows in contributing to the slow solar wind is assessed.

Title: Evolution of the solar luminosity during solar cycle 23
Authors: Vieira, L. A.; Schrijver, C.; DeRosa, M. L.; Norton, A.;
   Dudok de Wit, T.; Da Silva, L.; Vuets, A.
Bibcode: 2012AGUFMSH12A..04V
Altcode:
  The effect of the solar activity on the solar luminosity, which is
  the total electromagnetic solar output, is one of the fundamental
  questions in solar physics. Changes of the solar luminosity can arise
  from changes of the energy flux in the convection zone that can also
  affects other solar parameters such as the surface temperature, the
  apparent radius and shape, and the symmetry of the radiative field
  itself. Additionally, understanding the latitudinal distribution of the
  flux density is needed to compare the solar variability and its stellar
  analogues. Nevertheless, our observations of the solar flux density
  are limited to a region near the ecliptic plane, which have provided
  just a raw estimate of the variability of the solar luminosity. Here
  we present a reconstruction of the solar flux density and solar
  luminosity for the solar cycle 23 and ascending phase of cycle 24. The
  reconstruction is based on a combination of a state-of-art solar surface
  magnetic flux transport model and a semi-empirical total and spectral
  irradiance model. The flux transport model is based on assimilation
  of MDI/SOHO and HMI/SDO magnetograms. The irradiance model's free
  parameters are estimated by minimizing the difference between
  the model's output and the PMOD Composite of TSI measurements. We
  have obtained a good agreement between the model's output and the
  measurements. The distribution of active regions leads to a clear
  low latitude brightening during the solar maximum. This brightening
  results from the balance of the contributions from bright (faculae and
  network) and dark features (sunspots) located in the solar surface,
  which peaks near the solar equator. As the effects of dark features
  are limited to a narrower region, the variability of the flux density
  at the poles is dominated by the evolution of faculae and network. The
  preliminary results indicate that the heat flux blocked by sunspots
  is lower than the flux leaked by bright features. Consequently, an
  increase of the luminosity through the cycle is observed as previously
  estimated based on near ecliptic measurements. This work also enables
  an assessment of the properties of solar variability when viewed from
  out of the ecliptic, i.e., such as we might be viewing other stars of
  solar activity level. Finally, the limitations of the model and future
  strategies to extend the reconstruction of the flux density and solar
  luminosity will be presented.

Title: Magnetic Topology of Active Regions and Coronal Holes:
    Implications for Coronal Outflows and the Solar Wind
Authors: van Driel-Gesztelyi, L.; Culhane, J. L.; Baker, D.; Démoulin,
   P.; Mandrini, C. H.; DeRosa, M. L.; Rouillard, A. P.; Opitz, A.;
   Stenborg, G.; Vourlidas, A.; Brooks, D. H.
Bibcode: 2012SoPh..281..237V
Altcode: 2012SoPh..tmp..228V
  During 2 - 18 January 2008 a pair of low-latitude opposite-polarity
  coronal holes (CHs) were observed on the Sun with two active regions
  (ARs) and the heliospheric plasma sheet located between them. We use
  the Hinode/EUV Imaging Spectrometer (EIS) to locate AR-related outflows
  and measure their velocities. Solar-Terrestrial Relations Observatory
  (STEREO) imaging is also employed, as are the Advanced Composition
  Explorer (ACE) in-situ observations, to assess the resulting impacts on
  the solar wind (SW) properties. Magnetic-field extrapolations of the two
  ARs confirm that AR plasma outflows observed with EIS are co-spatial
  with quasi-separatrix layer locations, including the separatrix of a
  null point. Global potential-field source-surface modeling indicates
  that field lines in the vicinity of the null point extend up to the
  source surface, enabling a part of the EIS plasma upflows access
  to the SW. We find that similar upflow properties are also observed
  within closed-field regions that do not reach the source surface. We
  conclude that some of plasma upflows observed with EIS remain confined
  along closed coronal loops, but that a fraction of the plasma may be
  released into the slow SW. This suggests that ARs bordering coronal
  holes can contribute to the slow SW. Analyzing the in-situ data, we
  propose that the type of slow SW present depends on whether the AR is
  fully or partially enclosed by an overlying streamer.

Title: Modeling Magnetic Field Structure of a Solar Active Region
    Corona Using Nonlinear Force-free Fields in Spherical Geometry
Authors: Guo, Y.; Ding, M. D.; Liu, Y.; Sun, X. D.; DeRosa, M. L.;
   Wiegelmann, T.
Bibcode: 2012ApJ...760...47G
Altcode: 2012arXiv1210.0998G
  We test a nonlinear force-free field (NLFFF) optimization code
  in spherical geometry using an analytical solution from Low and
  Lou. Several tests are run, ranging from idealized cases where exact
  vector field data are provided on all boundaries, to cases where noisy
  vector data are provided on only the lower boundary (approximating
  the solar problem). Analytical tests also show that the NLFFF code
  in the spherical geometry performs better than that in the Cartesian
  one when the field of view of the bottom boundary is large, say, 20°
  × 20°. Additionally, we apply the NLFFF model to an active region
  observed by the Helioseismic and Magnetic Imager on board the Solar
  Dynamics Observatory (SDO) both before and after an M8.7 flare. For
  each observation time, we initialize the models using potential field
  source surface (PFSS) extrapolations based on either a synoptic chart
  or a flux-dispersal model, and compare the resulting NLFFF models. The
  results show that NLFFF extrapolations using the flux-dispersal model
  as the boundary condition have slightly lower, therefore better,
  force-free, and divergence-free metrics, and contain larger free
  magnetic energy. By comparing the extrapolated magnetic field lines with
  the extreme ultraviolet (EUV) observations by the Atmospheric Imaging
  Assembly on board SDO, we find that the NLFFF performs better than
  the PFSS not only for the core field of the flare productive region,
  but also for large EUV loops higher than 50 Mm.

Title: What Are Special About Ground-Level Events?. Flares, CMEs,
    Active Regions and Magnetic Field Connection
Authors: Nitta, N. V.; Liu, Y.; DeRosa, M. L.; Nightingale, R. W.
Bibcode: 2012SSRv..171...61N
Altcode: 2012arXiv1203.5777N; 2012SSRv..tmp...21N
  Ground level events (GLEs) occupy the high-energy end of gradual solar
  energetic particle (SEP) events. They are associated with coronal
  mass ejections (CMEs) and solar flares, but we still do not clearly
  understand the special conditions that produce these rare events. During
  Solar Cycle 23, a total of 16 GLEs were registered, by ground-based
  neutron monitors. We first ask if these GLEs are clearly distinguishable
  from other SEP events observed from space. Setting aside possible
  difficulties in identifying all GLEs consistently, we then try to find
  observables which may unmistakably isolate these GLEs by studying the
  basic properties of the associated eruptions and the active regions
  (ARs) that produced them. It is found that neither the magnitudes of
  the CMEs and flares nor the complexities of the ARs give sufficient
  conditions for GLEs. It is possible to find CMEs, flares or ARs that
  are not associated with GLEs but that have more extreme properties than
  those associated with GLEs. We also try to evaluate the importance of
  magnetic field connection of the AR with Earth on the detection of GLEs
  and their onset times. Using the potential field source surface (PFSS)
  model, a half of the GLEs are found to be well-connected. However,
  the GLE onset time with respect to the onset of the associated flare
  and CME does not strongly depend on how well-connected the AR is. The
  GLE onset behavior may be largely determined by when and where the
  CME-driven shock develops. We could not relate the shocks responsible
  for the onsets of past GLEs with features in solar images, but the
  combined data from the Solar TErrestrial RElations Observatory (STEREO)
  and the Solar Dynamics Observatory (SDO) have the potential to change
  this for GLEs that may occur in the rising phase of Solar Cycle 24.

Title: A Method for Data-driven Simulations of Evolving Solar
    Active Regions
Authors: Cheung, Mark C. M.; DeRosa, Marc L.
Bibcode: 2012ApJ...757..147C
Altcode: 2012arXiv1208.2954C
  We present a method for performing data-driven simulations of
  solar active region formation and evolution. The approach is based
  on magnetofriction, which evolves the induction equation assuming
  that the plasma velocity is proportional to the Lorentz force. The
  simulations of active region (AR) coronal field are driven by temporal
  sequences of photospheric magnetograms from the Helioseismic Magnetic
  Imager instrument on board the Solar Dynamics Observatory (SDO). Under
  certain conditions, the data-driven simulations produce flux ropes that
  are ejected from the modeled AR due to loss of equilibrium. Following
  the ejection of flux ropes, we find an enhancement of the photospheric
  horizontal field near the polarity inversion line. We also present
  a method for the synthesis of mock coronal images based on a proxy
  emissivity calculated from the current density distribution in the
  model. This method yields mock coronal images that are somewhat
  reminiscent of images of ARs taken by instruments such as SDO's
  Atmospheric Imaging Assembly at extreme ultraviolet wavelengths.

Title: First Three-dimensional Reconstructions of Coronal Loops
    with the STEREO A+B Spacecraft. IV. Magnetic Modeling with Twisted
    Force-free Fields
Authors: Aschwanden, Markus J.; Wuelser, Jean-Pierre; Nitta, Nariaki
   V.; Lemen, James R.; DeRosa, Marc L.; Malanushenko, Anna
Bibcode: 2012ApJ...756..124A
Altcode: 2012arXiv1207.2790A
  The three-dimensional coordinates of stereoscopically triangulated
  loops provide strong constraints for magnetic field models of active
  regions in the solar corona. Here, we use STEREO/A and B data from some
  500 stereoscopically triangulated loops observed in four active regions
  (2007 April 30, May 9, May 19, and December 11), together with SOHO/MDI
  line-of-sight magnetograms. We measure the average misalignment angle
  between the stereoscopic loops and theoretical magnetic field models,
  finding a mismatch of μ = 19°-46° for a potential field model,
  which is reduced to μ = 14°-19° for a non-potential field model
  parameterized by twist parameters. The residual error is commensurable
  with stereoscopic measurement errors (μ<SUB>SE</SUB> ≈ 8°-12°). We
  developed a potential field code that deconvolves a line-of-sight
  magnetogram into three magnetic field components (B<SUB>x</SUB> ,
  B<SUB>y</SUB> , B<SUB>z</SUB> ), as well as a non-potential field
  forward-fitting code that determines the full length of twisted loops
  (L ≈ 50-300 Mm), the number of twist turns (median N <SUB>twist</SUB>
  = 0.06), the nonlinear force-free α-parameter (median α ≈ 4 ×
  10<SUP>-11</SUP> cm<SUP>-1</SUP>), and the current density (median
  j<SUB>z</SUB> ≈ 1500 Mx cm<SUP>-2</SUP> s<SUP>-1</SUP>). All twisted
  loops are found to be far below the critical value for kink instability,
  and Joule dissipation of their currents is found to be far below the
  coronal heating requirement. The algorithm developed here, based on an
  analytical solution of nonlinear force-free fields that is accurate to
  second order (in the force-free parameter α), represents the first
  code that enables fast forward fitting to photospheric magnetograms
  and stereoscopically triangulated loops in the solar corona.

Title: Guiding Nonlinear Force-free Modeling Using Coronal
Observations: First Results Using a Quasi-Grad-Rubin Scheme
Authors: Malanushenko, A.; Schrijver, C. J.; DeRosa, M. L.; Wheatland,
   M. S.; Gilchrist, S. A.
Bibcode: 2012ApJ...756..153M
Altcode: 2012arXiv1202.5420M
  At present, many models of the coronal magnetic field rely on
  photospheric vector magnetograms, but these data have been shown
  to be problematic as the sole boundary information for nonlinear
  force-free field extrapolations. Magnetic fields in the corona
  manifest themselves in high-energy images (X-rays and EUV) in the
  shapes of coronal loops, providing an additional constraint that
  is not at present used as constraints in the computational domain,
  directly influencing the evolution of the model. This is in part due
  to the mathematical complications of incorporating such input into
  numerical models. Projection effects, confusion due to overlapping
  loops (the coronal plasma is optically thin), and the limited number
  of usable loops further complicate the use of information from
  coronal images. We develop and test a new algorithm to use images of
  coronal loops in the modeling of the solar coronal magnetic field. We
  first fit projected field lines with those of constant-α force-free
  fields to approximate the three-dimensional distribution of currents
  in the corona along a sparse set of trajectories. We then apply a
  Grad-Rubin-like iterative technique, which uses these trajectories as
  volume constraints on the values of α, to obtain a volume-filling
  nonlinear force-free model of the magnetic field, modifying a code
  and method presented by Wheatland. We thoroughly test the technique
  on known analytical and solar-like model magnetic fields previously
  used for comparing different extrapolation techniques and compare the
  results with those obtained by currently available methods relying
  only on the photospheric data. We conclude that we have developed a
  functioning method of modeling the coronal magnetic field by combining
  the line-of-sight component of the photospheric magnetic field with
  information from coronal images. Whereas we focus on the use of coronal
  loop information in combination with line-of-sight magnetograms, the
  method is readily extended to incorporate vector-magnetic data over
  any part of the photospheric boundary.

Title: Solar Magnetic Field Reversals and the Role of Dynamo Families
Authors: DeRosa, M. L.; Brun, A. S.; Hoeksema, J. T.
Bibcode: 2012ApJ...757...96D
Altcode: 2012arXiv1208.1768D
  The variable magnetic field of the solar photosphere exhibits periodic
  reversals as a result of dynamo activity occurring within the solar
  interior. We decompose the surface field as observed by both the Wilcox
  Solar Observatory and the Michelson Doppler Imager into its harmonic
  constituents, and present the time evolution of the mode coefficients
  for the past three sunspot cycles. The interplay between the various
  modes is then interpreted from the perspective of general dynamo
  theory, where the coupling between the primary and secondary families
  of modes is found to correlate with large-scale polarity reversals
  for many examples of cyclic dynamos. Mean-field dynamos based on the
  solar parameter regime are then used to explore how such couplings may
  result in the various long-term trends in the surface magnetic field
  observed to occur in the solar case.

Title: Effects of Granulation upon Larger-Scale Convection
Authors: Hurlburt, N. E.; DeRosa, M. L.; Augustson, K. C.; Toomre, J.
Bibcode: 2012ASPC..454...13H
Altcode: 2012arXiv1201.4809H
  We examine the role of small-scale granulation in helping to drive
  supergranulation and even larger scales of convection. The granulation
  is modeled as localized cooling events introduced at the upper boundary
  of a 3-D simulation of compressible convection in a rotating spherical
  shell segment. With a sufficient number of stochastic cooling events
  compared to uniform cooling, we find that supergranular scales are
  realized, along with a differential rotation that becomes increasingly
  solar-like.

Title: Magnetic topology, coronal outflows, and the solar wind
Authors: Mandrini, Cristina H.; Culhane, J. Leonard; Vourlidas,
   Angelos; Demoulin, Pascal; Stenborg, Guillermo; Opitz, Andrea;
   Rouillard, Alexis; Van Driel-Gesztelyi, Lidia; Baker, Deborah; DeRosa,
   Marc; Brooks, David
Bibcode: 2012cosp...39.1173M
Altcode: 2012cosp.meet.1173M
  During 2-18 January 2008 a pair of low-latitude opposite polarity
  coronal holes were observed on the Sun flanked by two ARs with
  the heliospheric plasma sheet between them. Hinode/EUV Imaging
  Telescope (EIS) is used to locate AR-related outflows and measure their
  velocities. The Advanced Composition Explorer (ACE) in-situ observations
  are employed to assess the resulting impacts on the interplanetary solar
  wind (SW). Magnetic field extrapolations of the two ARs confirm that AR
  plasma outflows observed with EIS are co-spatial with quasi-separatrix
  layer locations, including the separatrix of a null point. Global
  potential field source-surface modeling indicates that field lines
  in the vicinity of the null point extend up to the source-surface,
  enabling a part of the EIS plasma upflows access to the SW. Similar
  upflow magnitude is also observed within closed field regions. Though
  part of the plasma upflows observed with EIS remain confined along
  closed coronal loops, a subset of them are indeed able to make their
  imprint in the slow SW, making ARs bordering coronal holes a slow
  SW contributor.

Title: Using Electric Fields to drive simulations of the solar
    coronal magnetic field
Authors: Fisher, George H.; Cheung, Mark; DeRosa, Marc; Kazachenko,
   Maria; Welsch, Brian; Hoeksema, Todd; Sun, Xudong
Bibcode: 2012shin.confE..47F
Altcode:
  The availability of high-cadence vector magnetograms and Doppler flow
  information measured from the HMI instrument on SDO make it possible to
  determine the electric field at the solar photosphere. This electric
  field, in turn, can be used to drive time-dependent simulations of
  the magnetic field in the solar corona, employing the MHD equations,
  or simpler time-dependent models such as the magneto-frictional (MF)
  model. Here, we demonstrate these concepts by using electric fields
  determined from HMI data to drive a time-dependent MF model of the
  solar corona in the volume overlying the photosphere near NOAA AR 11158.

Title: Topology of Coronal Fields from Evolving Magnetofrictional
    Models
Authors: DeRosa, Marc L.; Cheung, M.
Bibcode: 2012AAS...22041104D
Altcode:
  The evolving magnetofrictional (MF) scheme enables the construction
  of time-dependent models of the active region coronal magnetic field
  in response to photospheric driving. When advancing such models, only
  the magnetic induction is solved, during which the velocity at each
  point is assumed to be oriented parallel to the Lorentz force. This
  leads to the field to evolve toward a force-free state. We present
  results from an evolving MF model of NOAA AR11158 using driving
  from time sequences of SDO/HMI data. Utilizing this simulation, we
  <P />investigate changes in magnetic configurations and topology,
  including the number of null points, evolution of quasi-separatrix
  layers, and the time-history of total and free magnetic energies as
  well as relative helicity. This work seeks to elucidate the relation(s)
  between topological and energetic properties of the AR.

Title: Estimate of Energy Release In a Major Flare Using Coronal
    Loops Data
Authors: Malanushenko, Anna; Schrijver, C. J.; DeRosa, M. L.
Bibcode: 2012AAS...22052115M
Altcode:
  Coronal loops provide with valuable source of information about coronal
  magnetic field. In particular, they allow one to observe reconfiguration
  of the coronal magnetic field during eruptive episodes. The changes
  in the coronal field, as observed in X-rays and extreme ultraviolet,
  are often dramatic in even minor eruptions. Therefore, models of
  magnetic field which take coronal loops into account might provide
  for new insight at changes of the field during eruptions. We use
  coronal loops data (gathered from SDO/AIA images) along with the
  line-of-sight magnetograms (by SDO/HMI) to model magnetic field in
  AR 11158 before and after the so-called Valentine's Flare, an X-class
  flare in Feb 15, 2011. This is done using the recently developed Quasi
  Grad-Rubin algorithm (QGR), which allows a reconstruction of non-linear
  force-free field based on information about electric currents along
  a set of arbitrary tracks in the computational domain. Tests of QGR
  on solar-like fields demonstrate its ability to recover over 50% of
  the free energy, as well as the large-scale structure of currents and
  overall shape of field lines. We analyze model magnetic fields of AR
  11158 before and after the flare, demonstrate their resemblance with
  the observed structure of coronal loops and analyze the changes in
  the structure of currents caused by the flare, and compare our results
  with existing studies of the same event.

Title: Force-Free Magneto-Stereoscopy of Coronal Loops
Authors: Aschwanden, Markus J.; Malanushenko, A.; Wuelser, J.; Nitta,
   N.; Lemen, J. R.; DeRosa, M.
Bibcode: 2012AAS...22041103A
Altcode:
  We derive an analytical approximation of nonlinear force-free
  magnetic field solutions (NLFFF) that can efficiently be used for
  fast forward-fitting to solar magnetic data, constrained either by
  observed line-of-sight magnetograms and stereoscopically triangulated
  coronal loops, or by 3D vector-magnetograph data. We test the code by
  forward-fitting to simulated data, to force-free solutions derived by
  Low and Lou (1990), and to active regions observed with STEREO/EUVI and
  SOHO/MDI. The forward-fitting tests demonstrate: (i) a satisfactory
  convergence behavior (with typical misalignment angles of 1-10 deg),
  (ii) a high fidelity of retrieved force-free alpha-parameters, and
  (iii) relatively fast computation times (from seconds to minutes). The
  novel feature of this NLFFF code is the derivation of a quasi-forcefree
  field based on coronal constraints, which bypasses the non-forcefree
  photosphere of standard magnetograms. Applications range from magnetic
  modeling of loops to the determnination of electric currents, twist,
  helicity, and free (non-potential) energy in active regions.

Title: A First Look at Magnetic Field Data Products from SDO/HMI
Authors: Liu, Y.; Scherrer, P. H.; Hoeksema, J. T.; Schou, J.; Bai,
   T.; Beck, J. G.; Bobra, M.; Bogart, R. S.; Bush, R. I.; Couvidat,
   S.; Hayashi, K.; Kosovichev, A. G.; Larson, T. P.; Rabello-Soares,
   C.; Sun, X.; Wachter, R.; Zhao, J.; Zhao, X. P.; Duvall, T. L., Jr.;
   DeRosa, M. L.; Schrijver, C. J.; Title, A. M.; Centeno, R.; Tomczyk,
   S.; Borrero, J. M.; Norton, A. A.; Barnes, G.; Crouch, A. D.; Leka,
   K. D.; Abbett, W. P.; Fisher, G. H.; Welsch, B. T.; Muglach, K.;
   Schuck, P. W.; Wiegelmann, T.; Turmon, M.; Linker, J. A.; Mikić,
   Z.; Riley, P.; Wu, S. T.
Bibcode: 2012ASPC..455..337L
Altcode:
  The Helioseismic and Magnetic Imager (HMI; Scherrer &amp; Schou 2011)
  is one of the three instruments aboard the Solar Dynamics Observatory
  (SDO) that was launched on February 11, 2010 from Cape Canaveral,
  Florida. The instrument began to acquire science data on March 24. The
  regular operations started on May 1. HMI measures the Doppler velocity
  and line-of-sight magnetic field in the photosphere at a cadence of
  45 seconds, and the vector magnetic field at a 135-second cadence,
  with a 4096× 4096 pixels full disk coverage. The vector magnetic
  field data is usually averaged over 720 seconds to suppress the p-modes
  and increase the signal-to-noise ratio. The spatial sampling is about
  0".5 per pixel. HMI observes the Fe i 6173 Å absorption line, which
  has a Landé factor of 2.5. These data are further used to produce
  higher level data products through the pipeline at the HMI-AIA Joint
  Science Operations Center (JSOC) - Science Data Processing (Scherrer et
  al. 2011) at Stanford University. In this paper, we briefly describe the
  data products, and demonstrate the performance of the HMI instrument. We
  conclude that the HMI is working extremely well.

Title: Data-Driven Modeling of the Evolution of Active Regions and
    Coronal Holes
Authors: Cheung, M. C. M.; DeRosa, M. L.
Bibcode: 2012decs.confE..83C
Altcode:
  We present results from numerical simulations of the evolution of
  solar Active Regions (ARs) and Coronal Holes (CHs). The simulations
  use the magnetofrictional method, which solves the induction equation
  to drive magnetic configurations toward force-free states in response
  to photospheric changes. The method is applied to modeling energy
  build-up in ARs and morphological changes in CHs. Comparisons with
  AIA data will be presented.

Title: Non-Linear Force-Free Modeling of Solar Corona With The Aid
    of Coronal Loops
Authors: Malanushenko, A.; DeRosa, M.; Schrijver, C.; Wheatland,
   M. S.; Gilchrist, S.
Bibcode: 2012decs.confE.113M
Altcode:
  Accurate models of the coronal magnetic field are vital for
  understanding and predicting solar activity and are therefore of the
  greatest interest for solar physics. As no reliable measurements of the
  coronal magnetic field exists at present, the problem of constructing
  field models is typically viewed as a boundary value problem. The
  construction of realistic field models requires knowledge of the full
  vector of magnetic field at the boundaries of the model domain; vector
  magnetograms are, however, measured in the non force-free photosphere
  and their horizontal components are subject to large uncertainties. Even
  if an uncertainty-free vector magnetogram at the top layer of the
  chromosphere was known, the problem remains an extremely challenging
  non-linear problem. There are various methods for pre-processing
  vector magnetograms and using them to construct models of the coronal
  field. The success of these models is often judged based on how close
  its field lines correspond to the observed coronal loops, which are
  believed to follow lines of the coronal magnetic field. At present,
  the correspondence between coronal loops and magnetic field lines
  of many models based on the vector magnetograms is far from perfect
  (DeRosa et. al., 2009). The estimates of free energy in the field as
  well as distribution of the magnetic currents through the volume could
  be dramatically different for different models used (Schrijver et. al.,
  2008). This testifies to the need of a completely new approach to this
  problem. We present such an approach and demonstrate its results based
  on AIA and HMI data. We have developed a way to use coronal loops as a
  constraint for magnetic modelling; the field is therefore constructed to
  match coronal loops. We found that when tested on known magnetic fields
  the new method is able to reproduce overall shape of the field lines,
  large-scale spatial distribution of the electric currents and measure
  up to 60% of the free energy stored in the field. This was achieved
  with as little as line-of-sight magnetogram and less than hundred of
  synthetic "loops", that is, lines of magnetic fields projected onto
  a plane of the sky. We found that line-of-sight HMI magnetograms and
  spatial resolution of the AIA instrument combined with the amount of
  filters available are more than sufficient for obtaining such data. We
  briefly describe this new method and demonstrate reconstructions of the
  coronal magnetic field obtained using AIA and HMI data. We evaluate how
  well it reproduces coronal features and how much energy and helicity
  estimates fluctuate with time for a stable non-flaring active region,
  thus establishing the reliability of the new method.

Title: The impact of the chromosphere on magnetic fields: field
    extrapolations
Authors: DeRosa, Marc L.
Bibcode: 2012decs.confE..88D
Altcode:
  Because knowledge of the coronal magnetic field is the key to gaining an
  understanding of the dynamics of the coronal plasma, efforts to measure
  or infer coronal magnetic fields have received much attention. In
  particular, many techniques for extrapolating the coronal magnetic
  field from photospheric boundary data have been developed, especially
  as magnetic field data at increasingly higher resolution in space and
  time as well as vector magnetogram inversions have become more readily
  available. However, it has become apparent that some extrapolation
  methods encounter difficulties, as the resulting extrapolations often
  do not provide reliable estimates of important coronal properties
  such as free energy and relative helicity. In this talk, we review
  some of the various difficulties associated with magnetic field
  extrapolations based on photospheric magnetograms, and discuss likely
  causes and solutions. We will particularly elucidate the impact of the
  chromospheric layer on such extrapolations, which is likely impacting
  the reliability of the extrapolation process as it lies between the
  region sampled by the boundary data [the photosphere] and the region
  of interest [the corona].

Title: Data-driven Simulations of Evolving Active Regions
Authors: Cheung, M.; DeRosa, M. L.
Bibcode: 2011AGUFMSH33C..04C
Altcode:
  We present results from numerical simulations of coronal field evolution
  in response to photospheric driving. In the simulations, the coronal
  field evolves according to magnetofriction, which ensures that the
  model field evolves toward a non-linear force-free state. Unlike
  static field extrapolation methods, this approach takes into account
  the history of the photospheric field evolution. This allows for the
  formation of flux ropes as well as current sheets between magnetic
  domains of connectivity. Using time sequences of HMI magnetograms
  as the bottom boundary condition, we apply this method to model the
  emergence and evolution of various active regions. Comparisons of the
  models with AIA observations and with HMI vector magnetogram inversions
  will be discussed.

Title: Spectropolarimetric Comparison Between SDO/HMI and
    Hinode-SOT/SP Through THEMIS/MTR
Authors: Sainz Dalda, A.; Lopez Ariste, A.; Gelly, B.; Tarbell, T. D.;
   Centeno, R.; DeRosa, M. L.; Hoeksema, J. T.
Bibcode: 2011AGUFMSH31A1986S
Altcode:
  In the golden age of solar spacecraft observatories, the use of similar
  instruments observing same targets offers us the possibility to get
  more accurate information of the physical processes taking place on
  them. We present a comparison between the vector magnetic field and
  thermodynamic quantities obtained by three different spectropolarimetric
  instruments. We have used the simultaneous multi-wavelength capabilities
  of THEMIS/MTR as bridge between the observations at Fe I 6173 Å
  provided by SDO/HMI and at Fe I 6301 &amp; 6302 Å by Hinode-SOT/SP
  observations. The official inversion codes for these instruments (PCA
  based-on, VFISV and MERLIN respectively) have been used with the data
  properly arranged for them. Therefore, we compare the final products
  usually offered to the community, i.e. after the inversion, using
  different codes and these different wavelengths. The cross-calibration
  of these products shall allow us to go forward from one instrument
  result to other one in an easy, convenient way.

Title: Non-Linear Force-Free Modeling With The Aid of Coronal
    Observations
Authors: Malanushenko, A. V.; DeRosa, M. L.; Schrijver, C. J.;
   Gilchrist, S. A.; Wheatland, M. S.
Bibcode: 2011AGUFMSH43B1956M
Altcode:
  Currently many models of coronal magnetic field rely on vector
  magnetograms and other kinds of information drawn from the
  photosphere. Magnetic fields in the corona, however, manifest themselves
  in the shapes of coronal loops, providing a constraint that at the
  present stage receives little use due to mathematical complications of
  incorporating such input into the numeric models. Projection effects
  and the limited number of usable loops further complicate their
  use. We present a possible way to account for coronal loops in the
  models of magnetic field. We first fit the observed loops with lines
  of constant-alpha fields and thus approximate three-dimensional
  distribution of currents in the corona along a sparse set of
  trajectories. We then apply a Grad-Rubin-like averaging technique
  to obtain a volume-filling non-linear force-free model of magnetic
  field, modified from the method presented in Wheatland &amp; Regnier
  (2009). We present thorough tests of this technique on several known
  magnetic fields that were previously used for comparing different
  extrapolation techniques (Schrijver et. al., 2006; Metcalf et. al.,
  2008; Schrijver et. al., 2008; DeRosa et. al., 2009), as well as on
  solar data and compare the results with those obtained by the currently
  developed methods that rely completely on the photospheric data.

Title: Magnetic Field Modeling with Stereoscopy and Magnetograms
Authors: Aschwanden, Wuelser; Nitta, Schrijver; DeRosa, Malanushenko
Bibcode: 2011sdmi.confE..81A
Altcode:
  We developed a new code to reconstruct the 3D magnetic field of solar
  active regions using stereoscopically triangulated loops with STEREO/A+B
  and magnetogram data from MDI or HMI. We are using potential field
  models as well as non-potential field models (nonlinear quasi-force-free
  fields) that can be quickly forward-fitted to observations using
  parameterizations of analytical approximations of uniformly twisted
  flux tubes. This method improves the misalignment angles between
  theoretical models and observed magnetic fields down to 5 degrees.

Title: Dipolar and Quadrupolar Magnetic Field Evolution over Solar
    Cycles 21, 22, and 23
Authors: DeRosa, M. L.; Brun, A. S.; Hoeksema, J. T.
Bibcode: 2011IAUS..271...94D
Altcode:
  Time series of photospheric magnetic field maps from two observatories,
  along with data from an evolving surface-flux transport model,
  are decomposed into their constituent spherical harmonic modes. The
  evolution of these spherical harmonic spectra reflect the modulation
  of bipole emergence rates through the solar activity cycle, and the
  subsequent dispersal, shear, and advection of magnetic flux patterns
  across the solar photosphere. In this article, we discuss the evolution
  of the dipolar and quadrupolar modes throughout the past three solar
  cycles (Cycles 21-23), as well as their relation to the reversal of
  the polar dipole during each solar maximum, and by extension to aspects
  of the operation of the global solar dynamo.

Title: Topology of Coronal Fields from Potential Field Models
Authors: DeRosa, Marc L.; Schrijver, C. J.; Barnes, G.
Bibcode: 2011SPD....42.1810D
Altcode: 2011BAAS..43S.1810D
  The topology of the solar coronal magnetic field has been the subject of
  much recent interest, due to its apparent importance in determining (for
  example) the sources of the solar wind, the evolution of coronal hole
  boundaries, and whether the configurations of coronae overlying active
  regions are unstable and thus possibly eruption-prone. We identify
  the topological skeleton (null points, spline lines, separators, and
  separatrix surfaces) for a selection of dates of interest from the
  database of potential-field source-surface models available through
  the ``PFSS'' SolarSoft package. Several features of interest have been
  identified by recent studies (e.g., Antiochos et al. 2007, Parnell et
  al. 2010, Titov et al. 2011), including exceedingly narrow channels of
  open field or separators associated with inferred reconnection sites. We
  find that these features of interest occur frequently in the topologies
  of even potential-field models of the magnetic corona. The actual solar
  corona is of course likely to involve even more complex topologies,
  especially as its dynamics and evolution are taken into account.

Title: Simulating Coronal Emission in Six AIA Channels Using
    Quasi-Static Atmosphere Models and Non-Linear Magnetic Field Models
Authors: Malanushenko, Anna; Schrijver, C.; DeRosa, M.; Aschwanden,
   M.; Wheatland, M. S.; van Ballegooijen, A. A.
Bibcode: 2011SPD....42.2116M
Altcode: 2011BAAS..43S.2116M
  We present the results of simulations of the EUV coronal emission in
  AIA channels. We use a non-linear force-free model of magnetic field
  constructed in such a way that its field lines resemble the observed
  coronal loops in EUV. We then solve one-dimensional quasi-steady
  atmosphere model along the magnetic field lines (Schrijver &amp;
  Ballegooijen, 2005). Using coronal abundances from CHIANTI and AIA
  response functions we then simulate the emission that would be observed
  in AIA EUV channels. The resulting intensities are compared against the
  real observations in a manner similar to that in Aschwanden et. al.,
  2011. The study is similar to those by Lindquist et. al., 2008, with a
  few important differences. We use a model of the coronal magnetic field
  that resembles the topology observed in EUV, we study EUV emission of
  cool loops (rather than SXR) and we make use of high resolution and
  cadence AIA and HMI data.

Title: Data-Driven Simulations of Coronal Magnetic Fields: A First
    Attempt with SDO Data
Authors: Cheung, C.; Derosa, M. L.
Bibcode: 2010AGUFMSH14A..04C
Altcode:
  We present results from numerical simulations of coronal field evolution
  in response to photospheric driving. In the simulations, the coronal
  field evolves according to magnetofriction, which ensures that the model
  field evolves toward a non-linear force-free state. Unlike static field
  extrapolation methods, this approach takes into account the history
  of the photospheric field evolution. This allows for the formation
  of flux ropes as well as current sheets between magnetic domains of
  connectivity. Using time sequences of HMI magnetograms as the bottom
  boundary condition, we apply this method to model the emergence and
  evolution of recent active regions. For the case of AR 11066, flux
  cancellation between opposite polarities within the AR leads to the
  formation of a flux rope, which subsequently lifts off. Comparisons
  of the models with AIA observations will be presented.

Title: Uncovering Mechanisms of Coronal Magnetism via Advanced 3D
    Modeling of Flares and Active Regions
Authors: Fleishman, Gregory; Gary, Dale; Nita, Gelu; Alexander,
   David; Aschwanden, Markus; Bastian, Tim; Hudson, Hugh; Hurford,
   Gordon; Kontar, Eduard; Longcope, Dana; Mikic, Zoran; DeRosa, Marc;
   Ryan, James; White, Stephen
Bibcode: 2010arXiv1011.2800F
Altcode:
  The coming decade will see the routine use of solar data of
  unprecedented spatial and spectral resolution, time cadence, and
  completeness. To capitalize on the new (or soon to be available)
  facilities such as SDO, ATST and FASR, and the challenges they present
  in the visualization and synthesis of multi-wavelength datasets,
  we propose that realistic, sophisticated, 3D active region and flare
  modeling is timely and critical, and will be a forefront of coronal
  studies over the coming decade. To make such modeling a reality, a
  broad, concerted effort is needed to capture the wealth of information
  resulting from the data, develop a synergistic modeling effort, and
  generate the necessary visualization, interpretation and model-data
  comparison tools to accurately extract the key physics.

Title: Magnetic Field Topology and the Thermal Structure of the
    Corona over Solar Active Regions
Authors: Schrijver, Carolus J.; DeRosa, Marc L.; Title, Alan M.
Bibcode: 2010ApJ...719.1083S
Altcode:
  Solar extreme ultraviolet (EUV) images of quiescent active-region
  coronae are characterized by ensembles of bright 1-2 MK loops that fan
  out from select locations. We investigate the conditions associated
  with the formation of these persistent, relatively cool, loop fans
  within and surrounding the otherwise 3-5 MK coronal environment by
  combining EUV observations of active regions made with TRACE with
  global source-surface potential-field models based on the full-sphere
  photospheric field from the assimilation of magnetograms that are
  obtained by the Michelson Doppler Imager (MDI) on SOHO. We find that in
  the selected active regions with largely potential-field configurations
  these fans are associated with (quasi-)separatrix layers (QSLs) within
  the strong-field regions of magnetic plage. Based on the empirical
  evidence, we argue that persistent active-region cool-loop fans are
  primarily related to the pronounced change in connectivity across a QSL
  to widely separated clusters of magnetic flux, and confirm earlier work
  that suggested that neither a change in loop length nor in base field
  strengths across such topological features are of prime importance to
  the formation of the cool-loop fans. We discuss the hypothesis that
  a change in the distribution of coronal heating with height may be
  involved in the phenomenon of relatively cool coronal loop fans in
  quiescent active regions.

Title: A Spherical Harmonic Analysis of the Evolution of the
    Photospheric Magnetic Field, and Consequences for the Solar Dynamo
Authors: DeRosa, Marc L.; Hoeksema, J. T.; Brun, A. S.
Bibcode: 2010AAS...21631701D
Altcode: 2010BAAS...41..898D
  Time series of synoptic maps from several observatories, along with data
  from an evolving surface-flux transport model, are analyzed in terms
  of their spherical harmonic decomposition. The characteristics of these
  spherical harmonic spectra, such as the relative amplitudes of various
  harmonic modes, at different phases of the solar cycle are shown. We
  illustrate how the rise and decline of the flux emergence rates, and
  the associated reversal of the polar dipole, throughout a sunspot
  cycle are reflected in the evolution of the various harmonic mode
  coefficients. We further discuss the interplay between the low-degree
  modes, in particular the dipole and quadrupole, and how such dynamics
  may trigger the reversal of the polar dipole during solar maximum.

Title: Erratum: "The Dependence of Ephemeral Region Emergence on
    Local Flux Imbalance" <A href="/abs/2008ApJ...678..541H">(2008, ApJ,
    678, 541)</A>
Authors: Hagenaar, Hermance J.; DeRosa, Marc L.; Schrijver, Carolus J.
Bibcode: 2010ApJ...715..696H
Altcode:
  We have discovered an error in the labeling of Figure 5. The importance
  of the figure is to indicate the dependence of flux emergence on local
  flux (im-) balance. However, the scales of the figures were incorrect,
  causing a discrepancy between Table 2 and Figure 5(a). The corrected
  Figure 5 appears below. The change does not affect the conclusion.

Title: Magnetic Field Topology and the Thermal Structure of the
    Corona over Solar Active Regions
Authors: Schrijver, Carolus J.; DeRosa, M. L.; Title, A. M.
Bibcode: 2010AAS...21631201S
Altcode:
  Solar extreme-ultraviolet images of active-region coronae are
  characterized by ensembles of bright 1-2 MK loops that fan out from
  select locations. We investigate the conditions associated with the
  formation of these relatively cool loop fans within the otherwise
  3-5 MK coronal environment by combining EUV observations of active
  regions made with the Transition Region and Coronal Explorer (TRACE)
  with global source-surface potential-field models based on the
  full-sphere photospheric field from the assimilation of magnetograms
  that are obtained by MDI on SOHO. We find that in the selected active
  regions with largely potential field configurations these fans are
  associated with (quasi-)separatrices within the strong-field regions
  of magnetic plage and vice versa. We argue that the divergence of the
  field lines across a (quasi-)separatrix may cause heating to happen
  relatively low in the corona, resulting in a lower loop temperature
  and flatter thermal profile of relatively dense (and thus EUV-bright)
  loops that are surrounded by warmer, thermally more stratified loops
  in field that does not straddle such topological divides.

Title: Modeling the Near-Surface Shear Layer Through Coupled
    Simulations of Surface and Deep Convection
Authors: Augustson, Kyle; Hurlburt, N.; DeRosa, M.; Toomre, J.
Bibcode: 2010AAS...21640008A
Altcode: 2010BAAS...41..855A
  We examine the role of small-scale granulation in helping to drive
  supergranulation and even larger scales of convection. The granulation
  is modeled as localized plumes with statistics taken from surface
  convection simulations introduced at the upper boundary of a 3-D
  simulation of compressible convection in a rotating spherical shell
  segment. With a sufficient number of stochastic plume events compared
  to a uniform cooling, we find that supergranular scales are realized,
  along with a differential rotation that becomes increasingly solar-like.

Title: Direct Imaging of an Emerging Flux Rope and a Resulting
    Chromospheric Jet Observed by Hinode
Authors: Liu, Wei; Berger, T.; Title, A. M.; Tarbell, T. D.; DeRosa, M.
Bibcode: 2010AAS...21640307L
Altcode: 2010BAAS...41R.878L
  Magnetic flux emergence has been traditionally observed on the disk by
  identifying changes in magnetograms. Observations near the limb offer
  an alternative perspective and allow direct imaging of emerging flux
  ropes. We present Hinode/SOT Ca II H observations of such an event in
  an equatorial coronal hole on 2007 February 9. The precursor of the
  event was a bundle of fine material threads that extended at an oblique
  angle above the chromosphere and appeared to rotate about a common
  axis. This bundle first slowly and then rapidly swung up, accompanied
  by a loop that appeared at the base of the bundle and expanded at
  comparable rates. During the first (slow rise) stage, the apex of the
  loop ascended at 16 km/s, a velocity similar to that of H-alpha arch
  filaments (e.g., Chou &amp; Zirin) and of emerging flux ropes expanding
  into the corona as found in MHD simulations (e.g., Fan &amp; Gibson;
  Martinez-Sykora). The second stage started at the onset of a GOES A5
  flare and the loop expansion accelerated, reaching a velocity of 130
  km/s when the loop appeared to rupture near the peak of the flare. The
  material bundle then swung back in a whiplike manner and developed into
  a collimated jet, exhibiting oscillatory transverse motions across its
  axis, as expected from unwinding twists. Some jet material fell back
  along smooth streamlines, which bypass an unseen dome and presumably
  a null point in the low corona, depicting an inverted-Y shape. Some
  of these observations resemble the model (e.g., Uchida &amp; Shibata)
  of the emergence of a twisted flux rope into an open field region that
  leads to reconnection and formation of a jet. Some observations are,
  however, not predicted in previous models and we will discuss their
  implications.

Title: Seismic Constraints on Interior Solar Convection
Authors: Hanasoge, Shravan M.; Duvall, Thomas L., Jr.; DeRosa, Marc L.
Bibcode: 2010ApJ...712L..98H
Altcode: 2010arXiv1001.4508H
  We constrain the velocity spectral distribution of global-scale solar
  convective cells at depth using techniques of local helioseismology. We
  calibrate the sensitivity of helioseismic waves to large-scale
  convective cells in the interior by analyzing simulations of waves
  propagating through a velocity snapshot of global solar convection
  via methods of time-distance helioseismology. Applying identical
  analysis techniques to observations of the Sun, we are able to bound
  from above the magnitudes of solar convective cells as a function of
  spatial convective scale. We find that convection at a depth of r/R
  <SUB>sun</SUB> = 0.95 with spatial extent ell &lt; 20, where ell is the
  spherical harmonic degree, comprises weak flow systems, on the order
  of 15 m s<SUP>-1</SUP> or less. Convective features deeper than r/R
  <SUB>sun</SUB> = 0.95 are more difficult to image due to the rapidly
  decreasing sensitivity of helioseismic waves.

Title: Non-force-free extrapolation of solar coronal magnetic field
    using vector magnetograms
Authors: Hu, Qiang; Dasgupta, B.; Derosa, M. L.; Büchner, J.; Gary,
   G. A.
Bibcode: 2010JASTP..72..219H
Altcode:
  We report our recent improvement in non-force-free extrapolation
  of coronal magnetic field, using vector magnetograms. Based on the
  principle of minimum (energy) dissipation rate (MDR), a generally
  non-force-free magnetic field solution is expressed as the superposition
  of one potential field and two (constant-[alpha]) linear force-free
  fields, with distinct [alpha] parameters. With a known potential field,
  the system is reduced to a second-order one that can be solved using
  one single-layer vector magnetogram. We devise an iteration procedure
  to determine the potential field, by achieving satisfactory agreement
  between the MDR-model computed and measured transverse magnetic
  field vectors on the bottom boundary. We illustrate this approach by
  applying it to real magnetograph measurement of solar active region
  AR 10953. We show that the results are satisfactory as judged from
  the quantitative magnetic field measurement, and the behavior of the
  derived Lorentz force.

Title: Comparison of STEREO/EUVI Loops with Potential Magnetic
    Field Models
Authors: Sandman, A. W.; Aschwanden, M. J.; DeRosa, M. L.; Wülser,
   J. P.; Alexander, D.
Bibcode: 2009SoPh..259....1S
Altcode:
  The Solar Terrestrial Relations Observatory (STEREO) provides the
  first opportunity to triangulate the three-dimensional coordinates of
  active region loops simultaneously from two different vantage points in
  space. Three-dimensional coordinates of the coronal magnetic field have
  been calculated with theoretical magnetic field models for decades,
  but it is only with the recent availability of STEREO data that a
  rigorous, quantitative comparison between observed loop geometries and
  theoretical magnetic field models can be performed. Such a comparison
  provides a valuable opportunity to assess the validity of theoretical
  magnetic field models. Here we measure the misalignment angles between
  model magnetic fields and observed coronal loops in three active
  regions, as observed with the Extreme Ultraviolet Imager (EUVI) on
  STEREO on 30 April, 9 May, and 19 May 2007. We perform stereoscopic
  triangulation of some 100 - 200 EUVI loops in each active region and
  compute extrapolated magnetic field lines using magnetogram information
  from the Michelson Doppler Imager (MDI) on the Solar and Heliospheric
  Observatory (SOHO). We examine two different magnetic extrapolation
  methods: (1) a potential field and (2) a radially stretched potential
  field that conserves the magnetic divergence. We find considerable
  disagreement between each theoretical model and the observed loop
  geometries, with an average misalignment angle on the order of 20°
  - 40°. We conclude that there is a need for either more suitable
  (coronal rather than photospheric) magnetic field measurements or more
  realistic field extrapolation models.

Title: Coronal Radiation Belts
Authors: Hudson, H. S.; MacKinnon, A. L.; De Rosa, M. L.; Frewen,
   S. F. N.
Bibcode: 2009ApJ...698L..86H
Altcode: 2009arXiv0905.3824H
  The magnetic field of the solar corona has a large-scale dipole
  character, which maps into the bipolar field in the solar wind. Using
  standard representations of the coronal field, we show that high-energy
  ions can be trapped stably in these large-scale closed fields. The
  drift shells that describe the conservation of the third adiabatic
  invariant may have complicated geometries. Particles trapped in these
  zones would resemble the Van Allen belts and could have detectable
  consequences. We discuss potential sources of trapped particles.

Title: Nonlinear Force-Free Magnetic Field Modeling of AR 10953:
    A Critical Assessment
Authors: De Rosa, Marc L.; Schrijver, C. J.; Barnes, G.; Leka, K. D.;
   Lites, B. W.; Aschwanden, M. J.; Amari, T.; Canou, A.; McTiernan,
   J. M.; Régnier, S.; Thalmann, J. K.; Valori, G.; Wheatland, M. S.;
   Wiegelmann, T.; Cheung, M. C. M.; Conlon, P. A.; Fuhrmann, M.;
   Inhester, B.; Tadesse, T.
Bibcode: 2009SPD....40.3102D
Altcode:
  Nonlinear force-free field (NLFFF) modeling seeks to provide accurate
  representations of the structure of the magnetic field above solar
  active regions, from which estimates of physical quantities of interest
  (e.g., free energy and helicity) can be made. However, the suite of
  NLFFF algorithms have failed to arrive at consistent solutions when
  applied to (thus far, two) cases using the highest-available-resolution
  vector magnetogram data from Hinode/SOT-SP (in the region of the
  modeling area of interest) and line-of-sight magnetograms from
  SOHO/MDI (where vector data were not available). One issue is that
  NLFFF models require consistent, force-free vector magnetic boundary
  data, and vector magnetogram data sampling the photosphere do not
  satisfy this requirement. Consequently, several problems have arisen
  that are believed to affect such modeling efforts. We use AR 10953
  to illustrate these problems, namely: (1) some of the far-reaching,
  current-carrying connections are exterior to the observational field
  of view, (2) the solution algorithms do not (yet) incorporate the
  measurement uncertainties in the vector magnetogram data, and/or (3)
  a better way is needed to account for the Lorentz forces within the
  layer between the photosphere and coronal base. In light of these
  issues, we conclude that it remains difficult to derive useful and
  significant estimates of physical quantities from NLFFF models.

Title: A Critical Assessment of Nonlinear Force-Free Field Modeling
    of the Solar Corona for Active Region 10953
Authors: De Rosa, Marc L.; Schrijver, Carolus J.; Barnes, Graham;
   Leka, K. D.; Lites, Bruce W.; Aschwanden, Markus J.; Amari, Tahar;
   Canou, Aurélien; McTiernan, James M.; Régnier, Stéphane; Thalmann,
   Julia K.; Valori, Gherardo; Wheatland, Michael S.; Wiegelmann, Thomas;
   Cheung, Mark C. M.; Conlon, Paul A.; Fuhrmann, Marcel; Inhester,
   Bernd; Tadesse, Tilaye
Bibcode: 2009ApJ...696.1780D
Altcode: 2009arXiv0902.1007D
  Nonlinear force-free field (NLFFF) models are thought to be viable
  tools for investigating the structure, dynamics, and evolution of
  the coronae of solar active regions. In a series of NLFFF modeling
  studies, we have found that NLFFF models are successful in application
  to analytic test cases, and relatively successful when applied
  to numerically constructed Sun-like test cases, but they are less
  successful in application to real solar data. Different NLFFF models
  have been found to have markedly different field line configurations
  and to provide widely varying estimates of the magnetic free energy in
  the coronal volume, when applied to solar data. NLFFF models require
  consistent, force-free vector magnetic boundary data. However,
  vector magnetogram observations sampling the photosphere, which is
  dynamic and contains significant Lorentz and buoyancy forces, do not
  satisfy this requirement, thus creating several major problems for
  force-free coronal modeling efforts. In this paper, we discuss NLFFF
  modeling of NOAA Active Region 10953 using Hinode/SOT-SP, Hinode/XRT,
  STEREO/SECCHI-EUVI, and SOHO/MDI observations, and in the process
  illustrate three such issues we judge to be critical to the success of
  NLFFF modeling: (1) vector magnetic field data covering larger areas
  are needed so that more electric currents associated with the full
  active regions of interest are measured, (2) the modeling algorithms
  need a way to accommodate the various uncertainties in the boundary
  data, and (3) a more realistic physical model is needed to approximate
  the photosphere-to-corona interface in order to better transform the
  forced photospheric magnetograms into adequate approximations of nearly
  force-free fields at the base of the corona. We make recommendations
  for future modeling efforts to overcome these as yet unsolved problems.

Title: Stochastic Effects of Granulation and Supergranulation Upon
    Deep Convection
Authors: Augustson, Kyle; De Rosa, M. L.; Hurlburt, N. E.; Toomre, J.
Bibcode: 2009SPD....40.0805A
Altcode:
  Vigorous fluid motions associated with the observed patterns of
  supergranulation, mesogranulation, and granulation play a large
  role in the turbulent transport of heat to the solar surface. The
  downflows associated with these convective motions plunge from the
  surface into the near-surface layers of the Sun bringing cooler,
  low entropy material with them. These flow structures may provide
  some stochastic effects upon the dynamics of the giant cells of deep
  convection that extend into the near-surface regions. To investigate
  such dynamics, we have carried out several 3-D numerical simulations of
  fully compressible fluids within curved, spherical segments that, at
  this stage, approximate conditions near the top of the rotating solar
  convection zone. The upper boundary of the segment is stochastically
  driven with cool plumes that approximate the spatial and temporal
  scales of supergranular cell downflows, in essence creating a network
  of supergranular cells. The segment spans 30° in latitude and 30°
  in longitude, and has a radial extent of 15% of the solar radius. We
  explore the formation and evolution of the boundary layer resulting
  from such stochastic driving, and discuss these dynamics in the context
  of the near-surface shear layer of the solar convection zone.

Title: Interaction Between Emerging Magnetic Flux And The Ambient
    Solar Coronal Field
Authors: Cheung, Mark; De Rosa, M.
Bibcode: 2009SPD....40.3103C
Altcode:
  We study the interaction between emerging magnetic flux and
  pre-existing coronal field by means of numerical simulations using
  the magneto-frictional method. By advancing the induction equation,
  the magneto-frictional method models the coronal magnetic field as a
  quasi-static sequence of non-linear force-free field configurations
  evolving in response to photospheric driving. A general feature of the
  simulations is the spontaneous formation of current sheets. At these
  interfaces, the field line torsional coefficient changes abruptly
  across separate domains of connectivity. Since the code evolves the
  vector potential, it allows us to calculate how much relative magnetic
  helicity and free energy is stored in the system. By using temporal
  sequences of observed vector magnetograms as the boundary condition,
  this model is potentially suitable for modeling the evolution of solar
  coronal fields.

Title: Nonlinear Force-Free Magnetic Field Modeling of the Solar
Corona: A Critical Assessment
Authors: De Rosa, M. L.; Schrijver, C. J.; Barnes, G.; Leka, K. D.;
   Lites, B. W.; Aschwanden, M. J.; McTiernan, J. M.; Régnier, S.;
   Thalmann, J.; Valori, G.; Wheatland, M. S.; Wiegelmann, T.; Cheung,
   M.; Conlon, P. A.; Fuhrmann, M.; Inhester, B.; Tadesse, T.
Bibcode: 2008AGUFMSH41A1604D
Altcode:
  Nonlinear force-free field (NLFFF) modeling promises to provide accurate
  representations of the structure of the magnetic field above solar
  active regions, from which estimates of physical quantities of interest
  (e.g., free energy and helicity) can be made. However, the suite of
  NLFFF algorithms have so far failed to arrive at consistent solutions
  when applied to cases using the highest-available-resolution vector
  magnetogram data from Hinode/SOT-SP (in the region of the modeling
  area of interest) and line-of-sight magnetograms from SOHO/MDI (where
  vector data were not been available). It is our view that the lack of
  robust results indicates an endemic problem with the NLFFF modeling
  process, and that this process will likely continue to fail until (1)
  more of the far-reaching, current-carrying connections are within the
  observational field of view, (2) the solution algorithms incorporate
  the measurement uncertainties in the vector magnetogram data, and/or
  (3) a better way is found to account for the Lorentz forces within
  the layer between the photosphere and coronal base. In light of these
  issues, we conclude that it remains difficult to derive useful and
  significant estimates of physical quantities from NLFFF models.

Title: Using STEREO/EUVI to Study Active Region Magnetic Fields
Authors: Sandman, A.; Aschwanden, M.; Wuelser, J.; De Rosa, M.;
   Alexander, D.
Bibcode: 2008AGUFMSH13B1523S
Altcode:
  We examine the effect of linear transformations on the misalignment
  between model magnetic fields and coronal loops in active regions,
  as observed with STEREO/EUVI on three separate occasions between
  April 30 and May 19, 2007. We perform stereoscopic triangulation of
  some 100 EUVI loops in each active region, and identify the tangent
  vectors along every loop. Using magnetogram information from SOHO/MDI
  we compute a 3D potential field and interpolate the magnetic field
  vector at every position along the EUVI loops. The angle between the
  loop tangent vector and the magnetic field vector provides a measure
  of the misalignment angle between the observed field configuration
  and the model. We then transform the field in a way that preserves
  the divergence-free condition while injecting electric currents into
  the system. With this modified field we repeat our calculation of the
  misalignment angles between the magnetic field vectors and the EUV
  loop tangent vectors, quantifying the improvement of the transformed
  magnetic field model. Results of this type of magnetic modeling are
  presented for three active regions.

Title: The Buildup of Large-Scale Polar Magnetic Fields on the Sun:
    Small Things Can Make a Difference
Authors: De Rosa, M. L.
Bibcode: 2008AGUFMSH44A..01D
Altcode:
  Large-scale magnetic field patterns visible at high latitudes on the
  solar photosphere are thought to form primarily from the poleward
  transport of flux that has emerged at lower latitudes. It is only a
  small percentage of this lower-latitude (i.e., active region) flux,
  however, that makes it to the poles, as much active-region flux
  cancels during its emergence and subsequent dispersal. This dispersal
  is characterized by the shearing and advection caused by the surface
  differential rotation and meridional flows, as well as by constant
  buffeting by near-surface convection and interactions with nearby flux
  concentrations. Consequently, these processes can play an important role
  in the transport of flux to the poles and the buildup of the polar caps,
  and their nonlinear nature implies that interactions between patterns
  with differing spatial (and temporal) scales can affect the timing of
  the formation of the polar cap as well as its overall amplitude. Such
  possibilities are investigated using a surface flux-transport model,
  and implications regarding the heliosphere are discussed.

Title: Non-force Free Coronal Extrapolation Based on the Principle
    of Minimum Dissipation Rate
Authors: Hu, Q.; Dasgupta, B.; Buechner, J.; De Rosa, M.
Bibcode: 2008AGUFMSH13A1514H
Altcode:
  The Principle of Minimum (energy) Dissipation Rate (MDR) originates from
  irreversible thermodynamics. In analogy to the Principle of Minimum
  Energy, it also follows a variational approach, but is more suitable
  for a complex and externally driven system like the solar corona. And
  in contrast, while the former yields a force- free magnetic field, the
  MDR gives a more general non-force free magnetic field with flow. The
  solution to the equation describing non-force free magnetic field
  resulted from MDR can be expressed as a superposition of two linear
  force-free fields with distinct α parameters, and one potential
  field (α≡0). Subsequently, the plasma states can also be derived,
  following standard MHD theory, given necessary boundary conditions. We
  present recent progress on applying the MDR theory to non-force free
  extrapolation of solar active region from vector magnetograms as bottom
  boundary data. We illustrate the approach of complete characterization
  of 3D magnetic field and plasma states by using numerical simulation
  data, and discuss its advantages and limitations.

Title: Modeling of Solar Radiation Belts
Authors: Frewen, S. S.; De Rosa, M.; Hudson, H.; MacKinnon, A.
Bibcode: 2008AGUFMSH13B1526F
Altcode:
  Stable particle trapping in the complicated magnetic field of the solar
  corona -- "solar radiation belts" -- at first seems unlikely in the face
  of the Sun's complex, variable magnetic field. By integrating particle
  orbit equations in the guiding-center approximation, we investigate
  the fates of energetic ions in model coronal magnetic fields. We use
  both PFSS (Potential Field Source Surface) and simple analytic field
  models. Contrary to naive expectation, we find that significant numbers
  of particles remain trapped more than long enough to circumnavigate
  the Sun, neither precipitating to the surface nor attaining open field
  lines. The drift "shells" corresponding to conservation of the third
  adiabatic invariant may be complicated in form. A close look at the
  dependence of the cross-field drift speed on magnetic field strength
  and topology accounts for this finding.

Title: On the Solar Origins of Open Magnetic Fields in the Heliosphere
Authors: Rust, David M.; Haggerty, Dennis K.; Georgoulis, Manolis K.;
   Sheeley, Neil R.; Wang, Yi-Ming; DeRosa, Marc L.; Schrijver, Carolus J.
Bibcode: 2008ApJ...687..635R
Altcode:
  A combination of heliospheric and solar data was used to identify open
  magnetic fields stretching from the lower corona to Earth orbit. 35
  near-relativistic electron beams detected at the ACE spacecraft
  "labeled" the heliospheric segments of the open fields. An X-ray
  flare occurred &lt;20 minutes before injection of the electrons
  in 25 events. These flares labeled the solar segment of the open
  fields. The flares occurred in western-hemisphere active regions (ARs)
  with coronal holes whose polarity agreed with the polarity of the
  beam-carrying interplanetary fields in 23 of the 25 events. We conclude
  that electron beams reach 1 AU from open AR fields adjacent to flare
  sites. The Wang &amp; Sheeley implementation of the potential-field
  source-surface model successfully identified the open fields in
  36% of cases. Success meant that the open fields reached the source
  surface within 3 heliographic deg of the interplanetary magnetic field
  connected to ACE at 1 AU. Inclusion of five near misses improves
  the success rate to 56%. The success rate for the Schrijver &amp;
  DeRosa PFSS implementation was 50%. Our results suggest that, even
  if the input magnetic data are updated frequently, the PFSS models
  succeed in only ~50% of cases to identify the coronal segment of open
  fields. Development of other techniques is in its infancy.

Title: On the Stability of Active Regions and Sunspots
Authors: Hurlburt, Neal; DeRosa, Marc
Bibcode: 2008ApJ...684L.123H
Altcode:
  Recent helioseismic measurements of large-scale subsurface flows
  indicate that systematic horizontal inflows near the photosphere
  surround many active regions. Such active-region inflows are likely
  to impede the dispersal of magnetic flux into the surrounding network
  and thus can influence larger-scale and longer-term patterns and
  evolution of the surface magnetic field throughout the course of a
  solar activity cycle. We present results of numerical simulations
  of compressible magnetoconvection in which an initial unipolar
  magnetic field undergoes evolution resulting from convectively driven
  motions. Inflows surrounding regions of concentrated magnetic flux
  are driven by reducing the surface temperature as a function of
  local magnetic flux. We find flow patterns that are consistent with
  observations of those observed around active regions and sunspots.

Title: Preprocessing of Hinode/SOT Vector Magnetograms for Nonlinear
    Force-Free Coronal Magnetic Field Modeling
Authors: Wiegelmann, T.; Thalmann, J. K.; Schrijver, C. J.; De Rosa,
   M. L.; Metcalf, T. R.
Bibcode: 2008ASPC..397..198W
Altcode: 2008arXiv0801.2884W
  The solar magnetic field is key to understanding the physical processes
  in the solar atmosphere. Nonlinear force-free codes have been shown
  to be useful in extrapolating the coronal field from underlying vector
  boundary data (for an overview see Schrijver et al. (2006)). However,
  we can only measure the magnetic field vector routinely with high
  accuracy in the photosphere with, e.g., Hinode/SOT, and unfortunately
  these data do not fulfill the force-free consistency condition as
  defined by Aly (1989). We must therefore apply some transformations
  to these data before nonlinear force-free extrapolation codes can be
  legitimately applied. To this end, we have developed a minimization
  procedure that uses the measured photospheric field vectors as input
  to approximate a more chromospheric like field (The method was dubbed
  preprocessing. See Wiegelmann et al. (2006) for details). The procedure
  includes force-free consistency integrals and spatial smoothing. The
  method has been intensively tested with model active regions (see
  Metcalf et al. 2008) and been applied to several ground based vector
  magnetogram data before. Here we apply the preprocessing program to
  photospheric magnetic field measurements with the Hinode/SOT instrument.

Title: Erratum: "Tests and Comparisons of Velocity-Inversion
    Techniques" (ApJ, 670, 1434 [2007])
Authors: Welsch, B. T.; Abbett, W. P.; DeRosa, M. L.; Fisher, G. H.;
   Georgoulis, M. K.; Kusano, K.; Longcope, D. W.; Ravindra, B.; Schuck,
   P. W.
Bibcode: 2008ApJ...680..827W
Altcode:
  No abstract at ADS

Title: The Dependence of Ephemeral Region Emergence on Local Flux
    Imbalance
Authors: Hagenaar, Hermance J.; DeRosa, Marc L.; Schrijver, Carolus J.
Bibcode: 2008ApJ...678..541H
Altcode:
  We investigate the distribution and evolution of existing and emerging
  magnetic network elements in the quiet-Sun photosphere. The ephemeral
  region emergence rate is found to depend primarily on the imbalance of
  magnetic flux in the area surrounding its emergence location, such that
  the rate of flux emergence is lower within strongly unipolar regions by
  at least a factor of 3 relative to flux-balanced quiet Sun. As coronal
  holes occur over unipolar regions, this also means that ephemeral
  regions occur less frequently there, but we show that this is an
  indirect effect—independent of whether the region is located within
  an open-field coronal hole or a closed-field quiet region. We discuss
  the implications of this finding for near-photospheric dynamo action and
  for the coupling between closed coronal and open heliospheric fields.

Title: A joint search for gravitational wave bursts with AURIGA
    and LIGO
Authors: Baggio, L.; Bignotto, M.; Bonaldi, M.; Cerdonio, M.; De Rosa,
   M.; Falferi, P.; Fattori, S.; Fortini, P.; Giusfredi, G.; Inguscio, M.;
   Liguori, N.; Longo, S.; Marin, F.; Mezzena, R.; Mion, A.; Ortolan, A.;
   Poggi, S.; Prodi, G. A.; Re, V.; Salemi, F.; Soranzo, G.; Taffarello,
   L.; Vedovato, G.; Vinante, A.; Vitale, S.; Zendri, J. P.; Abbott, B.;
   Abbott, R.; Adhikari, R.; Agresti, J.; Ajith, P.; Allen, B.; Amin, R.;
   Anderson, S. B.; Anderson, W. G.; Arain, M.; Araya, M.; Armandula, H.;
   Ashley, M.; Aston, S.; Aufmuth, P.; Aulbert, C.; Babak, S.; Ballmer,
   S.; Bantilan, H.; Barish, B. C.; Barker, C.; Barker, D.; Barr, B.;
   Barriga, P.; Barton, M. A.; Bayer, K.; Belczynski, K.; Betzwieser,
   J.; Beyersdorf, P. T.; Bhawal, B.; Bilenko, I. A.; Billingsley, G.;
   Biswas, R.; Black, E.; Blackburn, K.; Blackburn, L.; Blair, D.; Bland,
   B.; Bogenstahl, J.; Bogue, L.; Bork, R.; Boschi, V.; Bose, S.; Brady,
   P. R.; Braginsky, V. B.; Brau, J. E.; Brinkmann, M.; Brooks, A.; Brown,
   D. A.; Bullington, A.; Bunkowski, A.; Buonanno, A.; Burmeister, O.;
   Busby, D.; Butler, W. E.; Byer, R. L.; Cadonati, L.; Cagnoli, G.; Camp,
   J. B.; Cannizzo, J.; Cannon, K.; Cantley, C. A.; Cao, J.; Cardenas,
   L.; Carter, K.; Casey, M. M.; Castaldi, G.; Cepeda, C.; Chalkley, E.;
   Charlton, P.; Chatterji, S.; Chelkowski, S.; Chen, Y.; Chiadini, F.;
   Chin, D.; Chin, E.; Chow, J.; Christensen, N.; Clark, J.; Cochrane,
   P.; Cokelaer, T.; Colacino, C. N.; Coldwell, R.; Conte, R.; Cook, D.;
   Corbitt, T.; Coward, D.; Coyne, D.; Creighton, J. D. E.; Creighton,
   T. D.; Croce, R. P.; Crooks, D. R. M.; Cruise, A. M.; Cumming, A.;
   Dalrymple, J.; D'Ambrosio, E.; Danzmann, K.; Davies, G.; DeBra, D.;
   Degallaix, J.; Degree, M.; Demma, T.; Dergachev, V.; Desai, S.;
   DeSalvo, R.; Dhurandhar, S.; Díaz, M.; Dickson, J.; Di Credico,
   A.; Diederichs, G.; Dietz, A.; Doomes, E. E.; Drever, R. W. P.;
   Dumas, J. -C.; Dupuis, R. J.; Dwyer, J. G.; Ehrens, P.; Espinoza,
   E.; Etzel, T.; Evans, M.; Evans, T.; Fairhurst, S.; Fan, Y.; Fazi,
   D.; Fejer, M. M.; Finn, L. S.; Fiumara, V.; Fotopoulos, N.; Franzen,
   A.; Franzen, K. Y.; Freise, A.; Frey, R.; Fricke, T.; Fritschel, P.;
   Frolov, V. V.; Fyffe, M.; Galdi, V.; Ganezer, K. S.; Garofoli, J.;
   Gholami, I.; Giaime, J. A.; Giampanis, S.; Giardina, K. D.; Goda, K.;
   Goetz, E.; Goggin, L. M.; González, G.; Gossler, S.; Grant, A.; Gras,
   S.; Gray, C.; Gray, M.; Greenhalgh, J.; Gretarsson, A. M.; Grosso,
   R.; Grote, H.; Grunewald, S.; Guenther, M.; Gustafson, R.; Hage, B.;
   Hammer, D.; Hanna, C.; Hanson, J.; Harms, J.; Harry, G.; Harstad,
   E.; Hayler, T.; Heefner, J.; Heng, I. S.; Heptonstall, A.; Heurs, M.;
   Hewitson, M.; Hild, S.; Hirose, E.; Hoak, D.; Hosken, D.; Hough, J.;
   Howell, E.; Hoyland, D.; Huttner, S. H.; Ingram, D.; Innerhofer, E.;
   Ito, M.; Itoh, Y.; Ivanov, A.; Jackrel, D.; Johnson, B.; Johnson,
   W. W.; Jones, D. I.; Jones, G.; Jones, R.; Ju, L.; Kalmus, P.;
   Kalogera, V.; Kasprzyk, D.; Katsavounidis, E.; Kawabe, K.; Kawamura,
   S.; Kawazoe, F.; Kells, W.; Keppel, D. G.; Khalili, F. Ya; Kim, C.;
   King, P.; Kissel, J. S.; Klimenko, S.; Kokeyama, K.; Kondrashov,
   V.; Kopparapu, R. K.; Kozak, D.; Krishnan, B.; Kwee, P.; Lam, P. K.;
   Landry, M.; Lantz, B.; Lazzarini, A.; Lee, B.; Lei, M.; Leiner, J.;
   Leonhardt, V.; Leonor, I.; Libbrecht, K.; Lindquist, P.; Lockerbie,
   N. A.; Longo, M.; Lormand, M.; Lubiński, M.; Lück, H.; Machenschalk,
   B.; MacInnis, M.; Mageswaran, M.; Mailand, K.; Malec, M.; Mandic, V.;
   Marano, S.; Márka, S.; Markowitz, J.; Maros, E.; Martin, I.; Marx,
   J. N.; Mason, K.; Matone, L.; Matta, V.; Mavalvala, N.; McCarthy, R.;
   McClelland, D. E.; McGuire, S. C.; McHugh, M.; McKenzie, K.; McNabb,
   J. W. C.; McWilliams, S.; Meier, T.; Melissinos, A.; Mendell, G.;
   Mercer, R. A.; Meshkov, S.; Messenger, C. J.; Meyers, D.; Mikhailov,
   E.; Mitra, S.; Mitrofanov, V. P.; Mitselmakher, G.; Mittleman, R.;
   Miyakawa, O.; Mohanty, S.; Moreno, G.; Mossavi, K.; Lowry, C. Mow;
   Moylan, A.; Mudge, D.; Mueller, G.; Mukherjee, S.; Müller-Ebhardt,
   H.; Munch, J.; Murray, P.; Myers, E.; Myers, J.; Nash, T.; Newton, G.;
   Nishizawa, A.; Nocera, F.; Numata, K.; O'Reilly, B.; O'Shaughnessy,
   R.; Ottaway, D. J.; Overmier, H.; Owen, B. J.; Pan, Y.; Papa, M. A.;
   Parameshwaraiah, V.; Parameswariah, C.; Patel, P.; Pedraza, M.;
   Penn, S.; Pierro, V.; Pinto, I. M.; Pitkin, M.; Pletsch, H.; Plissi,
   M. V.; Postiglione, F.; Prix, R.; Quetschke, V.; Raab, F.; Rabeling,
   D.; Radkins, H.; Rahkola, R.; Rainer, N.; Rakhmanov, M.; Ramsunder,
   M.; Rawlins, K.; Ray-Majumder, S.; Regimbau, T.; Rehbein, H.; Reid,
   S.; Reitze, D. H.; Ribichini, L.; Riesen, R.; Riles, K.; Rivera, B.;
   Robertson, N. A.; Robinson, C.; Robinson, E. L.; Roddy, S.; Rodriguez,
   A.; Rogan, A. M.; Rollins, J.; Romano, J. D.; Romie, J.; Route, R.;
   Rowan, S.; Rüdiger, A.; Ruet, L.; Russell, P.; Ryan, K.; Sakata, S.;
   Samidi, M.; Sancho de la Jordana, L.; Sandberg, V.; Sanders, G. H.;
   Sannibale, V.; Saraf, S.; Sarin, P.; Sathyaprakash, B. S.; Sato, S.;
   Saulson, P. R.; Savage, R.; Savov, P.; Sazonov, A.; Schediwy, S.;
   Schilling, R.; Schnabel, R.; Schofield, R.; Schutz, B. F.; Schwinberg,
   P.; Scott, S. M.; Searle, A. C.; Sears, B.; Seifert, F.; Sellers, D.;
   Sengupta, A. S.; Shawhan, P.; Shoemaker, D. H.; Sibley, A.; Siemens,
   X.; Sigg, D.; Sinha, S.; Sintes, A. M.; Slagmolen, B. J. J.; Slutsky,
   J.; Smith, J. R.; Smith, M. R.; Somiya, K.; Strain, K. A.; Strom,
   D. M.; Stuver, A.; Summerscales, T. Z.; Sun, K. -X.; Sung, M.; Sutton,
   P. J.; Takahashi, H.; Tanner, D. B.; Tarallo, M.; Taylor, R.; Taylor,
   R.; Thacker, J.; Thorne, K. A.; Thorne, K. S.; Thüring, A.; Tinto,
   M.; Tokmakov, K. V.; Torres, C.; Torrie, C.; Traylor, G.; Trias, M.;
   Tyler, W.; Ugolini, D.; Ungarelli, C.; Urbanek, K.; Vahlbruch, H.;
   Vallisneri, M.; Van Den Broeck, C.; van Putten, M.; Varvella, M.;
   Vass, S.; Vecchio, A.; Veitch, J.; Veitch, P.; Villar, A.; Vorvick,
   C.; Vyachanin, S. P.; Waldman, S. J.; Wallace, L.; Ward, H.; Ward,
   R.; Watts, K.; Webber, D.; Weidner, A.; Weinert, M.; Weinstein, A.;
   Weiss, R.; Wen, S.; Wette, K.; Whelan, J. T.; Whitbeck, D. M.;
   Whitcomb, S. E.; Whiting, B. F.; Wiley, S.; Wilkinson, C.; Willems,
   P. A.; Williams, L.; Willke, B.; Wilmut, I.; Winkler, W.; Wipf, C. C.;
   Wise, S.; Wiseman, A. G.; Woan, G.; Woods, D.; Wooley, R.; Worden,
   J.; Wu, W.; Yakushin, I.; Yamamoto, H.; Yan, Z.; Yoshida, S.; Yunes,
   N.; Zanolin, M.; Zhang, J.; Zhang, L.; Zhao, C.; Zotov, N.; Zucker,
   M.; zur Mühlen, H.; Zweizig, J.
Bibcode: 2008CQGra..25i5004B
Altcode: 2007arXiv0710.0497A
  The first simultaneous operation of the AURIGA detector<A
  href="http://www.auriga.lnl.infn.it">http://www.auriga.lnl.infn.it</A>
  and the LIGO observatory<A
  href="http://www.ligo.org">http://www.ligo.org</A> was an opportunity
  to explore real data, joint analysis methods between two very
  different types of gravitational wave detectors: resonant bars and
  interferometers. This paper describes a coincident gravitational
  wave burst search, where data from the LIGO interferometers are
  cross-correlated at the time of AURIGA candidate events to identify
  coincident transients. The analysis pipeline is tuned with two
  thresholds, on the signal-to-noise ratio of AURIGA candidate events and
  on the significance of the cross-correlation test in LIGO. The false
  alarm rate is estimated by introducing time shifts between data sets
  and the network detection efficiency is measured by adding simulated
  gravitational wave signals to the detector output. The simulated
  waveforms have a significant fraction of power in the narrower AURIGA
  band. In the absence of a detection, we discuss how to set an upper
  limit on the rate of gravitational waves and to interpret it according
  to different source models. Due to the short amount of analyzed data
  and to the high rate of non-Gaussian transients in the detectors' noise
  at the time, the relevance of this study is methodological: this was
  the first joint search for gravitational wave bursts among detectors
  with such different spectral sensitivity and the first opportunity
  for the resonant and interferometric communities to unify languages
  and techniques in the pursuit of their common goal.

Title: Non-Linear Force-Free Field Modeling of a Solar Active Region
    Around the Time of a Major Flare and Coronal Mass Ejection
Authors: De Rosa, M. L.; Schrijver, C. J.; Metcalf, T. R.; Barnes,
   G.; Lites, B.; Tarbell, T.; McTiernan, J.; Valori, G.; Wiegelmann,
   T.; Wheatland, M.; Amari, T.; Aulanier, G.; Démoulin, P.; Fuhrmann,
   M.; Kusano, K.; Régnier, S.; Thalmann, J.
Bibcode: 2008AGUSMSP31A..06D
Altcode:
  Solar flares and coronal mass ejections are associated with rapid
  changes in coronal magnetic field connectivity and are powered by
  the partial dissipation of electrical currents that run through
  the solar corona. A critical unanswered question is whether the
  currents involved are induced by the advection along the photosphere
  of pre-existing atmospheric magnetic flux, or whether these currents
  are associated with newly emergent flux. We address this problem by
  applying nonlinear force-free field (NLFFF) modeling to the highest
  resolution and quality vector-magnetographic data observed by the
  recently launched Hinode satellite on NOAA Active Region 10930 around
  the time of a powerful X3.4 flare in December 2006. We compute 14
  NLFFF models using 4 different codes having a variety of boundary
  conditions. We find that the model fields differ markedly in geometry,
  energy content, and force-freeness. We do find agreement of the best-fit
  model field with the observed coronal configuration, and argue (1)
  that strong electrical currents emerge together with magnetic flux
  preceding the flare, (2) that these currents are carried in an ensemble
  of thin strands, (3) that the global pattern of these currents and
  of field lines are compatible with a large-scale twisted flux rope
  topology, and (4) that the ~1032~erg change in energy associated with
  the coronal electrical currents suffices to power the flare and its
  associated coronal mass ejection. We discuss the relative merits of
  these models in a general critique of our present abilities to model
  the coronal magnetic field based on surface vector field measurements.

Title: Exploring large-scale coronal magnetic field over extended
    longitudes by STEREO/EUVI and its effect on solar wind prediction
Authors: Nitta, N. V.; De Rosa, M. L.; Zarro, D. M.; Wuelser, J.;
   Aschwanden, M. J.; Lemen, J. R.
Bibcode: 2008AGUSMSH23A..06N
Altcode:
  The potential field source surface (PFSS) model forms the basis of
  a wide range of heliospheric science and applications, including
  prediction of the solar wind speed near Earth. Experience shows that
  the model sometimes works quite well, but not always. Possible reasons
  for failure include deviation of the interplanetary magnetic field from
  the nominal Parker spiral, violation of the assumptions used in the
  model such as the discontinuity at the source surface, and the lack of
  simultaneous full-surface magnetograms. Here we study the impact of the
  lack of simultaneous full-surface magnetograms, using observations of
  the corona over an extended longitude range made possible by the EUVI
  on board the STEREO mission. In spite of the lack of magnetographs on
  STEREO, EUVI data with a growing separation angle between spacecraft
  A and B at least allow us to locate major active regions and coronal
  holes in the area not seen from Earth. The PFSS extrapolations and their
  input synoptic maps are compared with EUVI data to measure how well the
  model fits the observations. These comparisons are discussed in terms of
  the solar wind speed predicted by the model and observed at L1 by ACE.

Title: Tracing the 3-D coronal structure during CMEs with
    STEREO/SECCHI EUVI observations
Authors: Wuelser, J.; Aschwanden, M.; De Rosa, M.; Lee, C.; Lemen,
   J.; Nitta, N.; Sandman, A.
Bibcode: 2008AGUSMSH31A..05W
Altcode:
  STEREO/SECCHI EUVI observations of solar coronal loops, filaments,
  and dimming regions provide unique information on the 3-D topology
  of the coronal magnetic field above active regions and its evolution
  during coronal mass ejections (CMEs). Active Region #10956 produced
  several CMEs during its passage across the solar disk in May 2007,
  some of them showing filament eruptions and dimming. The SECCHI/EUVI
  instrument on STEREO obtained high cadence observations in multiple
  lines simultaneously from both STEREO spacecraft. 3-D reconstructions
  of coronal features over the course of a CME show significant changes
  of the field topology. Comparisons with the potential field topology
  from magnetic field extrapolations show the degree of non-potentiality
  of the real field and changes in the vicinity of the CME onset. We
  present initial results of this study.

Title: Searching for Large-scale flows around Active Regions with
    Hinode
Authors: Hurlburt, N.; Derosa, M.; Hagenaar, M.
Bibcode: 2008AGUSMSP43C..08H
Altcode:
  Heliosiemic studies have suggested that active regions are surrounded
  by large-scale inflows (Haber et al. 2004), and it has recently been
  hypothesized by Hurlburt and DeRosa (2008,HD) that these are due to
  the enhanced surface cooling resulting from plage and faculae. We seek
  confirmation of these results using Hinode observations of Active
  Regions using a variety of methods to infer inflow velocities from
  of continuum images and Dopplergrams. These flow patterns are then
  compared to the HD hypothesis. This work has been supported by NASA
  through contracts NNM07AA01C and NNG06GD45G. References: Haber, D.,
  Hindman, B., Toomre, J. and Thompson, M. 2004, ÐOrganized Subsurface
  Flows near Active Regions,î Sol. Phys. 220,371. Hurlburt &amp; DeRosa,
  2008 ÐOn the longevity of Active Regions,î Ap.J. Lett., submitted

Title: Nonlinear Force-free Field Modeling of a Solar Active Region
    around the Time of a Major Flare and Coronal Mass Ejection
Authors: Schrijver, C. J.; DeRosa, M. L.; Metcalf, T.; Barnes, G.;
   Lites, B.; Tarbell, T.; McTiernan, J.; Valori, G.; Wiegelmann, T.;
   Wheatland, M. S.; Amari, T.; Aulanier, G.; Démoulin, P.; Fuhrmann,
   M.; Kusano, K.; Régnier, S.; Thalmann, J. K.
Bibcode: 2008ApJ...675.1637S
Altcode: 2007arXiv0712.0023S
  Solar flares and coronal mass ejections are associated with rapid
  changes in field connectivity and are powered by the partial dissipation
  of electrical currents in the solar atmosphere. A critical unanswered
  question is whether the currents involved are induced by the motion of
  preexisting atmospheric magnetic flux subject to surface plasma flows or
  whether these currents are associated with the emergence of flux from
  within the solar convective zone. We address this problem by applying
  state-of-the-art nonlinear force-free field (NLFFF) modeling to the
  highest resolution and quality vector-magnetographic data observed
  by the recently launched Hinode satellite on NOAA AR 10930 around
  the time of a powerful X3.4 flare. We compute 14 NLFFF models with
  four different codes and a variety of boundary conditions. We find
  that the model fields differ markedly in geometry, energy content,
  and force-freeness. We discuss the relative merits of these models in
  a general critique of present abilities to model the coronal magnetic
  field based on surface vector field measurements. For our application
  in particular, we find a fair agreement of the best-fit model field
  with the observed coronal configuration, and argue (1) that strong
  electrical currents emerge together with magnetic flux preceding the
  flare, (2) that these currents are carried in an ensemble of thin
  strands, (3) that the global pattern of these currents and of field
  lines are compatible with a large-scale twisted flux rope topology,
  and (4) that the ~10<SUP>32</SUP> erg change in energy associated with
  the coronal electrical currents suffices to power the flare and its
  associated coronal mass ejection.

Title: A Comparison of Solar Open Field Regions Found by Type III
    Radio Bursts and the Potential Field Source Surface Model
Authors: Nitta, Nariaki V.; DeRosa, Marc L.
Bibcode: 2008ApJ...673L.207N
Altcode:
  For heliophysics research and applications, the potential field
  source surface (PFSS) model is often employed to extrapolate the
  photospheric magnetic field to the corona. In an attempt to evaluate
  the performance of the PFSS model, we compare the computed footpoints
  of the heliospheric magnetic field with the locations of flares
  associated with type III radio bursts, which are a good indicator
  of open field lines that extend to interplanetary space. Consistent
  with past experiences, the agreement is not satisfactory. We discuss
  possible reasons for the discrepancy, including the model's inadequacy
  to reproduce the coronal magnetic field above evolving active regions
  and the lack of a simultaneous full-surface magnetic map. It is argued
  that the performance of the PFSS model needs to be quantified further
  against solar observations, including type III bursts, before it is
  applied to heliospheric models.

Title: Can We Improve the Preprocessing of Photospheric Vector
    Magnetograms by the Inclusion of Chromospheric Observations?
Authors: Wiegelmann, T.; Thalmann, J. K.; Schrijver, C. J.; De Rosa,
   M. L.; Metcalf, T. R.
Bibcode: 2008SoPh..247..249W
Altcode: 2008arXiv0801.2707W; 2008SoPh..tmp...27W
  The solar magnetic field is key to understanding the physical processes
  in the solar atmosphere. Nonlinear force-free codes have been shown to
  be useful in extrapolating the coronal field upward from underlying
  vector boundary data. However, we can only measure the magnetic
  field vector routinely with high accuracy in the photosphere, and
  unfortunately these data do not fulfill the force-free condition. We
  must therefore apply some transformations to these data before nonlinear
  force-free extrapolation codes can be self-consistently applied. To
  this end, we have developed a minimization procedure that yields a more
  chromosphere-like field, using the measured photospheric field vectors
  as input. The procedure includes force-free consistency integrals,
  spatial smoothing, and - newly included in the version presented here
  - an improved match to the field direction as inferred from fibrils
  as can be observed in, for example, chromospheric Hα images. We test
  the procedure using a model active-region field that included buoyancy
  forces at the photospheric level. The proposed preprocessing method
  allows us to approximate the chromospheric vector field to within a few
  degrees and the free energy in the coronal field to within one percent.

Title: Nonlinear Force-Free Modeling of Coronal Magnetic
    Fields. II. Modeling a Filament Arcade and Simulated Chromospheric
    and Photospheric Vector Fields
Authors: Metcalf, Thomas R.; De Rosa, Marc L.; Schrijver, Carolus J.;
   Barnes, Graham; van Ballegooijen, Adriaan A.; Wiegelmann, Thomas;
   Wheatland, Michael S.; Valori, Gherardo; McTtiernan, James M.
Bibcode: 2008SoPh..247..269M
Altcode: 2008SoPh..tmp...17M
  We compare a variety of nonlinear force-free field (NLFFF) extrapolation
  algorithms, including optimization, magneto-frictional, and Grad -
  Rubin-like codes, applied to a solar-like reference model. The model
  used to test the algorithms includes realistic photospheric Lorentz
  forces and a complex field including a weakly twisted, right helical
  flux bundle. The codes were applied to both forced "photospheric" and
  more force-free "chromospheric" vector magnetic field boundary data
  derived from the model. When applied to the chromospheric boundary data,
  the codes are able to recover the presence of the flux bundle and the
  field's free energy, though some details of the field connectivity are
  lost. When the codes are applied to the forced photospheric boundary
  data, the reference model field is not well recovered, indicating
  that the combination of Lorentz forces and small spatial scale
  structure at the photosphere severely impact the extrapolation of the
  field. Preprocessing of the forced photospheric boundary does improve
  the extrapolations considerably for the layers above the chromosphere,
  but the extrapolations are sensitive to the details of the numerical
  codes and neither the field connectivity nor the free magnetic energy in
  the full volume are well recovered. The magnetic virial theorem gives
  a rapid measure of the total magnetic energy without extrapolation
  though, like the NLFFF codes, it is sensitive to the Lorentz forces in
  the coronal volume. Both the magnetic virial theorem and the Wiegelmann
  extrapolation, when applied to the preprocessed photospheric boundary,
  give a magnetic energy which is nearly equivalent to the value derived
  from the chromospheric boundary, but both underestimate the free
  energy above the photosphere by at least a factor of two. We discuss
  the interpretation of the preprocessed field in this context. When
  applying the NLFFF codes to solar data, the problems associated with
  Lorentz forces present in the low solar atmosphere must be recognized:
  the various codes will not necessarily converge to the correct, or
  even the same, solution.

Title: Ephemeral Bipolar Regions in Coronal Holes
Authors: Hagenaar, H.; Schrijver, C.; De Rosa, M.
Bibcode: 2008ASPC..383..343H
Altcode:
  We investigate the distribution and evolution of magnetic network
  elements in quiet Sun with or without coronal holes. Ephemeral region
  emergence rates are found to depend on the degree of imbalance of
  magnetic flux, but independent of whether there is a coronal hole or
  not. We discuss the implications of this finding for near-photospheric
  dynamo action and for the coupling between closed coronal and open
  heliospheric fields.

Title: Structure and Evolution of Giant Cells in Global Models of
    Solar Convection
Authors: Miesch, Mark S.; Brun, Allan Sacha; DeRosa, Marc L.;
   Toomre, Juri
Bibcode: 2008ApJ...673..557M
Altcode: 2007arXiv0707.1460M
  The global scales of solar convection are studied through
  three-dimensional simulations of compressible convection carried out
  in spherical shells of rotating fluid that extend from the base of
  the convection zone to within 15 Mm of the photosphere. Such modeling
  at the highest spatial resolution to date allows study of distinctly
  turbulent convection, revealing that coherent downflow structures
  associated with giant cells continue to play a significant role in
  maintaining the differential rotation that is achieved. These giant
  cells at lower latitudes exhibit prograde propagation relative to
  the mean zonal flow, or differential rotation, that they establish,
  and retrograde propagation of more isotropic structures with vortical
  character at mid and high latitudes. The interstices of the downflow
  networks often possess strong and compact cyclonic flows. The
  evolving giant-cell downflow systems can be partly masked by the
  intense smaller scales of convection driven closer to the surface,
  yet they are likely to be detectable with the helioseismic probing that
  is now becoming available. Indeed, the meandering streams and varying
  cellular subsurface flows revealed by helioseismology must be sampling
  contributions from the giant cells, yet it is difficult to separate
  out these signals from those attributed to the faster horizontal flows
  of supergranulation. To aid in such detection, we use our simulations
  to describe how the properties of giant cells may be expected to vary
  with depth and how their patterns evolve in time.

Title: Tests and Comparisons of Velocity-Inversion Techniques
Authors: Welsch, B. T.; Abbett, W. P.; De Rosa, M. L.; Fisher, G. H.;
   Georgoulis, M. K.; Kusano, K.; Longcope, D. W.; Ravindra, B.; Schuck,
   P. W.
Bibcode: 2007ApJ...670.1434W
Altcode:
  Recently, several methods that measure the velocity of magnetized
  plasma from time series of photospheric vector magnetograms have been
  developed. Velocity fields derived using such techniques can be used
  both to determine the fluxes of magnetic energy and helicity into the
  corona, which have important consequences for understanding solar
  flares, coronal mass ejections, and the solar dynamo, and to drive
  time-dependent numerical models of coronal magnetic fields. To date,
  these methods have not been rigorously tested against realistic,
  simulated data sets, in which the magnetic field evolution and
  velocities are known. Here we present the results of such tests
  using several velocity-inversion techniques applied to synthetic
  magnetogram data sets, generated from anelastic MHD simulations of
  the upper convection zone with the ANMHD code, in which the velocity
  field is fully known. Broadly speaking, the MEF, DAVE, FLCT, IM, and
  ILCT algorithms performed comparably in many categories. While DAVE
  estimated the magnitude and direction of velocities slightly more
  accurately than the other methods, MEF's estimates of the fluxes of
  magnetic energy and helicity were far more accurate than any other
  method's. Overall, therefore, the MEF algorithm performed best in
  tests using the ANMHD data set. We note that ANMHD data simulate
  fully relaxed convection in a high-β plasma, and therefore do not
  realistically model photospheric evolution.

Title: Can we Improve the Preprocessing of Photospheric
    Vectormagnetograms by the Inclusion of Chromospheric Observations?
Authors: Wiegelmann, T.; Thalmann, J. K.; Schrijver, C. J.; De Rosa,
   M. L.; Metcalf, T. R.
Bibcode: 2007AGUFMSH51C..02W
Altcode:
  The solar magnetic field is key to understanding the physical
  processes in the solar atmosphere. Unfortunately, we can measure
  the magnetic field vector routinely with high accuracy only in the
  photosphere with, e.g., Hinode/SOT and in future with SDO/HMI. These
  measurements are extrapolated into the corona under the assumption
  that the field is force-free. That condition is not fulfilled in the
  photosphere, but is in the chromosphere and corona. In order to make
  the observed boundary data consistent with the force-free assumption,
  we therefore have to apply some transformations before nonlinear
  force-free extrapolation codes can be legitimately applied. We develop
  a minimization procedure that uses the measured photospheric field
  vectors as input to approximate a more chromospheric-like field. The
  procedure includes force-free consistency integrals, spatial smoothing,
  and - newly included in the version presented here - an improved match
  to the field direction as inferred from fibrils as can be observed in,
  e.g., chromospheric H-alpha images. We test the procedure using a model
  active-region field that included buoyancy forces at the photospheric
  level. We apply the combined preprocessing and nonlinear force-free
  extrapolation method to compute the coronal magnetic field in an active
  region measured with the Hinode/SOT instrument.

Title: Results of the IGEC-2 search for gravitational wave bursts
    during 2005
Authors: Astone, P.; Babusci, D.; Baggio, L.; Bassan, M.; Bignotto,
   M.; Bonaldi, M.; Camarda, M.; Carelli, P.; Cavallari, G.; Cerdonio,
   M.; Chincarini, A.; Coccia, E.; Conti, L.; D'Antonio, S.; de Rosa,
   M.; di Paolo Emilio, M.; Drago, M.; Dubath, F.; Fafone, V.; Falferi,
   P.; Foffa, S.; Fortini, P.; Frasca, S.; Gemme, G.; Giordano, G.;
   Giusfredi, G.; Hamilton, W. O.; Hanson, J.; Inguscio, M.; Johnson,
   W. W.; Liguori, N.; Longo, S.; Maggiore, M.; Marin, F.; Marini,
   A.; McHugh, M. P.; Mezzena, R.; Miller, P.; Minenkov, Y.; Mion, A.;
   Modestino, G.; Moleti, A.; Nettles, D.; Ortolan, A.; Pallottino, G. V.;
   Parodi, R.; Piano Mortari, G.; Poggi, S.; Prodi, G. A.; Quintieri, L.;
   Re, V.; Rocchi, A.; Ronga, F.; Salemi, F.; Soranzo, G.; Sturani, R.;
   Taffarello, L.; Terenzi, R.; Torrioli, G.; Vaccarone, R.; Vandoni,
   G.; Vedovato, G.; Vinante, A.; Visco, M.; Vitale, S.; Weaver, J.;
   Zendri, J. P.; Zhang, P.
Bibcode: 2007PhRvD..76j2001A
Altcode: 2007arXiv0705.0688I
  The network of resonant bar detectors of gravitational waves resumed
  coordinated observations within the International Gravitational
  Event Collaboration (IGEC-2). Four detectors are taking part in this
  Collaboration: ALLEGRO, AURIGA, EXPLORER and NAUTILUS. We present here
  the results of the search for gravitational wave bursts over 6 months
  during 2005, when IGEC-2 was the only gravitational wave observatory
  in operation. The implemented network data analysis is based on a time
  coincidence search among AURIGA, EXPLORER and NAUTILUS; ALLEGRO data
  was reserved for follow-up studies. The network amplitude sensitivity to
  bursts improved by a factor ≈3 over the 1997-2000 IGEC observations;
  the wider sensitive band also allowed the analysis to be tuned over
  a larger class of waveforms. Given the higher single-detector duty
  factors, the analysis was based on threefold coincidence, to ensure
  the identification of any single candidate of gravitational waves with
  high statistical confidence. The false detection rate was as low as
  1 per century. No candidates were found.

Title: Can we detect convection in the Sun?
Authors: Hanasoge, Shravan M.; Duvall, T. L.; De Rosa, M. L.; Miesch,
   M. S.
Bibcode: 2007IAUS..239..364H
Altcode:
  No abstract at ADS

Title: Simulations of Large-Scale Solar Surface Inflows Surrounding
    Magnetic Fields
Authors: De Rosa, Marc L.; Hurlburt, N. E.
Bibcode: 2007AAS...210.2211D
Altcode: 2007BAAS...39..126D
  Recent helioseismic measurements of large-scale subsurface flows have
  indicated that systematic horizontal inflows near the photosphere
  surround many active regions. Such active-region inflows are likely
  to impede the dispersal into the surrounding network, and thus can
  influence larger-scale and longer-term patterns of magnetic field
  throughout the course of a solar activity cycle. We present preliminary
  results of numerical simulations of compressible magnetoconvection,
  in which an initial unipolar magnetic field undergoes evolution
  resulting from convectively driven motions. Inflows surrounding regions
  of concentrated magnetic flux are driven by reducing the surface
  temperature in regions where the magnetic flux is strong. The effects
  of these resulting inflows on the dynamics are then studied.

Title: Structure and Evolution of Giant Cells in Global Models of
    Solar Convection
Authors: Miesch, Mark S.; Brun, A. S.; De Rosa, M. L.; Toomre, J.
Bibcode: 2007AAS...210.2217M
Altcode: 2007BAAS...39..127M
  We present the highest-resolution simulations of global-scale solar
  convection so far achieved, dealing with turbulent compressible
  flows interacting with rotation in a full spherical shell. The
  three-dimensional simulation domain extends from 0.71R-0.98R, close
  enough to the photosphere to overlap with solar subsurface weather
  (SSW) maps inferred from local helioseismology. The convective patterns
  achieved are complex and continually evolving on a time scale of several
  days. However, embedded within the intricate downflow network near
  the surface are coherent downflow lanes associated with giant cells
  which persist for weeks to months and which extend through much of the
  convection zone. These coherent downflow lanes are generally confined
  to low latitudes and are oriented in a north-south direction. The low
  dissipation in these simulations permits a more realistic balance of
  forces which yields differential rotation and meridional circulation
  profiles in good agreement with those inferred from helioseismology.

Title: Non-linear Force-free Modeling Of Coronal Magnetic Fields
Authors: Metcalf, Thomas R.; De Rosa, M. L.; Schrijver, C. J.; Barnes,
   G.; van Ballegooijen, A.; Wiegelmann, T.; Wheatland, M. S.; Valori,
   G.; McTiernan, J. M.
Bibcode: 2007AAS...210.9102M
Altcode: 2007BAAS...39..204M
  We compare a variety of nonlinear force-free field (NLFFF)
  extrapolation algorithms, including optimization, magneto-frictional,
  and Grad-Rubin-like codes, applied to a solar-like reference
  model. The model used to test the algorithms includes realistic
  photospheric Lorentz forces and a complex field including a weakly
  twisted, right helical flux bundle. The codes were applied to both
  forced "photospheric'' and more force-free "chromospheric'' vector
  magnetic field boundary data derived from the model. When applied to
  the <P />chromospheric boundary data, the codes are able to recover
  the presence of the flux bundle and the field's free energy, though
  some details of the field connectivity are lost. When the codes are
  applied to the forced photospheric boundary data, the reference
  model field is not well recovered, indicating that the Lorentz
  forces on the photosphere severely impact the extrapolation of the
  field. Preprocessing of the photospheric boundary does improve the
  extrapolations considerably, although the results depend sensitively
  on the details of the numerical codes. When applying the NLFFF codes
  to solar data, the problems associated with Lorentz forces present in
  the low solar atmosphere must be recognized: the various codes will
  not necessarily converge to the correct, or even the same, solution.

Title: SEP Properties and Magnetic Field Connection of the Source
    Region
Authors: Nitta, N. V.; De Rosa, M. L.
Bibcode: 2006AGUFMSH41B..06N
Altcode:
  There seems to be no clear explanation as to why some CME/flare events
  produce major SEP events whereas others do not. Furthermore, we still
  cannot reliably predict the peak flux and rise time of an SEP event
  using remote sensing data. Even though CME shocks are the primary
  accelerator for gradual SEP events and they are likely to have wide
  angular extensions, we suggest that the magnetic field connection of the
  source region to the observer may be an important factor for determining
  their occurrence and basic properties. In order to address this issue,
  we need to go beyond the common assumption that the longitudes around
  W60 have the strongest connection to the Earth. For a number of
  SEP-productive active regions, we compare the properties of intense
  flares and energetic CMEs that originated from them over their disk
  passage with the peak fluxes and rise times of the associated &gt;10 MeV
  and &gt;50 MeV protons. We perform magnetic field extrapolation with the
  potential field source surface (PFSS) model to locate well-connected
  field lines with respect to the source region. Once evaluated against
  multiple criteria, the PFSS extrapolation would be a useful tool to
  characterize the magnetic field topology in and around the active
  region responsible for the intense flares and energetic CMEs. This
  study is expected to partially answer the question of whether flare-
  accelerated particles contribute to gradual SEP events.

Title: Coronal particle trapping revisited
Authors: Hudson, H. S.; MacKinnon, A.; De Rosa, M.
Bibcode: 2006AGUFMSH54A..07H
Altcode:
  We re-examine the idea of long-term particle storage in the solar
  corona in the context of modern PFSS (potential-field source surface)
  magnetic models. As pointed out by H. Elliot in 1964 and others since
  then, such particles could be energetically important, at the level
  of some large fraction of the magnetic energy density B2/8π. We
  estimate the distribution and time scales of particle trapping by
  using representative PFSS coronal models from the Schrijver-De Rosa
  SolarSoft code. As the coronal field simplifies during solar minimum, it
  approaches axisymmetry and thus contains volumes inaccessible to charged
  particles under the guiding-center approximation. We conclude that time
  scales can be sufficiently long, so long in fact that the azimuthal
  drift time scale (third adiabatic invariant of guiding-center motion),
  for the large-scale dipolar configuration characteristic of solar
  minimum, can exceed one solar cycle. We discuss the possible sources
  of trapped particles, starting with the basic CRAND (cosmic-ray albedo
  neutron decay) mechanism, and relate their X-ray and γ-ray signatures
  to future observational capabilities including the Sentinels spacecraft.

Title: Consequences of large-scale flows around active regions on
    the dispersal of magnetic field across the solar surface
Authors: De Rosa, M. L.; Schrijver, C. J.
Bibcode: 2006ESASP.624E..12D
Altcode: 2006soho...18E..12D
  No abstract at ADS

Title: Solar Sources of Impulsive Solar Energetic Particle Events
    and Their Magnetic Field Connection to the Earth
Authors: Nitta, Nariaki V.; Reames, Donald V.; De Rosa, Marc L.; Liu,
   Yang; Yashiro, Seiji; Gopalswamy, Natchimuthuk
Bibcode: 2006ApJ...650..438N
Altcode:
  This paper investigates the solar origin of impulsive solar energetic
  particle (SEP) events, often referred to as <SUP>3</SUP>He-rich flares,
  by attempting to locate the source regions of 117 events as observed
  at ~2-3 MeV amu<SUP>-1</SUP>. Given large uncertainties as to when
  ions at these energies were injected, we use type III radio bursts
  that occur within a 5 hr time window preceding the observed ion onset,
  and search in EUV and X-ray full-disk images for brightenings around
  the times of the type III bursts. In this way we find the solar sources
  in 69 events. High cadence EUV images often reveal a jet in the source
  region shortly after the type III burst. We also study magnetic field
  connections between the Earth and the solar sources of impulsive SEP
  events as identified above, combining the potential field source
  surface (PFSS) model for the coronal field and the Parker spiral
  for the interplanetary magnetic field. We find open field lines in
  and around ~80% of the source regions. But only in ~40% of the cases,
  can we find field lines that are both close to the source region at the
  photosphere and to the Parker spiral coordinates at the source surface,
  suggesting challenges in understanding the Sun-Earth magnetic field
  with observations available at present and in near future.

Title: Computational Acoustics in Spherical Geometry: Steps toward
    Validating Helioseismology
Authors: Hanasoge, S. M.; Larsen, R. M.; Duvall, T. L., Jr.; De Rosa,
   M. L.; Hurlburt, N. E.; Schou, J.; Roth, M.; Christensen-Dalsgaard,
   J.; Lele, S. K.
Bibcode: 2006ApJ...648.1268H
Altcode:
  Throughout the past decade, detailed helioseismic analyses of
  observations of solar surface oscillations have led to advances in our
  knowledge of the structure and dynamics of the solar interior. Such
  analyses involve the decomposition of time series of the observed
  surface oscillation pattern into its constituent wave modes, followed
  by inversion procedures that yield inferences of properties of the
  solar interior. While this inverse problem has been a major focus in
  recent years, the corresponding forward problem has received much less
  attention. We aim to rectify this situation by taking the first steps
  toward validating and determining the efficacy of the helioseismic
  measurement procedure. The goal of this effort is to design a means
  to perform differential studies of various effects such as flows and
  thermal perturbations on helioseismic observables such as resonant
  frequencies, travel-time shifts, etc. Here we describe our first
  efforts to simulate wave propagation within a spherical shell,
  which extends from 0.2 to about 1.0004 R<SUB>solar</SUB> (where
  R<SUB>solar</SUB> is the radius of the Sun) and which possesses a
  solar-like stratification. We consider a model containing no flows
  that will serve as a reference model for later studies. We discuss the
  computational procedure, some difficulties encountered in a simulation
  of this kind, and the means to overcome them. We also present techniques
  used to validate the simulation.

Title: Non-linear Force-free Modeling: Applications To Solar Data
Authors: De Rosa, Marc L.; Schrijver, C. J.; Metcalf, T. R.; NLFFF Team
Bibcode: 2006SPD....37.1805D
Altcode: 2006BAAS...38..247D
  Understanding the conditions under which solar magnetic fields can
  destabilizeto cause flares and other eruptive events requires a
  quantitativeunderstanding of the coronal magnetic field and of the
  currents that itcarries. Because no direct measurements of magnetic
  fields and current withincoronal volumes exist, the coronal field is
  typically modeled usinginformation contained in photospheric vector
  magnetograms, to be compared toH-alpha images of the chromosphere
  and EUV and X-ray imagery of the corona.We report on recent results
  of a team effort to further understand theintricacies of non-linear
  force-free extrapolations of the coronal magneticfield, presenting
  results from several solar and solar-like test cases. Wealso consider
  the use of such coronal field modeling in the upcoming Solar-Band
  SDO missions.

Title: The Consequences Of Active-region Inflows On The Large-scale
    Dispersal Of Magnetic Field Across The Solar Surface.
Authors: Schrijver, Carolus J.; De Rosa, M. L.; Hurlburt, N. E.
Bibcode: 2006SPD....37.0716S
Altcode: 2006BAAS...38..230S
  Helioseismic analysis of near-surface modes recently revealed horizontal
  flows near the solar surface towards regions with enhanced magnetic
  activity. The magnitude of these flows appears to increase with the
  magnetic flux contained within them. Such flows help to confine magnetic
  flux to the activity belt and perhaps even to theactive regions within
  which the field emerges, and will likely slow the random-walk dispersal
  of the field. We report on experiments witha surface flux dispersal
  model to study the consequences of such inflows towards strong-flux
  regions. We constrain the flow magnitudeby comparing results of a flux
  assimilation model to solar observations over six-month intervals
  throughout the last solar cycle. The best-fit model is then used to
  quantify the effects of these flows on the Sun's global dipole and
  quadrupole fields on time scales of multiple centuries.

Title: The PFSS Model in the Context of Impulsive SEP Events
Authors: Nitta, Nariaki; De Rosa, M.
Bibcode: 2006SPD....37.2406N
Altcode: 2006BAAS...38..251N
  We have located the solar sources of 67 impulsive solar energetic
  particle (SEP) events, using type III bursts to narrow down the times
  of particle injection in the solar corona. This information serves
  as a direct means to test the model of the Sun-Earth magnetic field
  connection because the particles simply trace the field lines. We
  consider the standard technique to model the Sun-Earth magnetic field,
  known as the potential field source surface (PFSS) model for the coronal
  part and the Parker spiral for the interplanetary part. In each of
  selected SEP events, we calculate the distance of the footpoint of
  the well-connected field line from the observed source location. It is
  found that the technique does not work as well as when it is used to
  predict the solar wind speed and the polarity of the interplanetary
  magnetic field. We suggest what we need to do to better understand
  the Sun-Earth magnetic field connection, or, more broadly speaking,
  the interplanetary magnetic field, which is an important element in
  NASA's Exploration Initiative.

Title: Nonlinear Force-Free Modeling of Coronal Magnetic Fields Part
I: A Quantitative Comparison of Methods
Authors: Schrijver, Carolus J.; De Rosa, Marc L.; Metcalf, Thomas R.;
   Liu, Yang; McTiernan, Jim; Régnier, Stéphane; Valori, Gherardo;
   Wheatland, Michael S.; Wiegelmann, Thomas
Bibcode: 2006SoPh..235..161S
Altcode:
  We compare six algorithms for the computation of nonlinear force-free
  (NLFF) magnetic fields (including optimization, magnetofrictional,
  Grad-Rubin based, and Green's function-based methods) by evaluating
  their performance in blind tests on analytical force-free-field models
  for which boundary conditions are specified either for the entire
  surface area of a cubic volume or for an extended lower boundary
  only. Figures of merit are used to compare the input vector field to
  the resulting model fields. Based on these merit functions, we argue
  that all algorithms yield NLFF fields that agree best with the input
  field in the lower central region of the volume, where the field and
  electrical currents are strongest and the effects of boundary conditions
  weakest. The NLFF vector fields in the outer domains of the volume
  depend sensitively on the details of the specified boundary conditions;
  best agreement is found if the field outside of the model volume is
  incorporated as part of the model boundary, either as potential field
  boundaries on the side and top surfaces, or as a potential field in
  a skirt around the main volume of interest. For input field (B) and
  modeled field (b), the best method included in our study yields an
  average relative vector error E<SUB>n</SUB> = « |B−b|»/« |B|» of
  only 0.02 when all sides are specified and 0.14 for the case where only
  the lower boundary is specified, while the total energy in the magnetic
  field is approximated to within 2%. The models converge towards the
  central, strong input field at speeds that differ by a factor of one
  million per iteration step. The fastest-converging, best-performing
  model for these analytical test cases is the Wheatland, Sturrock, and
  Roumeliotis (2000) optimization algorithm as implemented by Wiegelmann
  (2004).

Title: Experimental investigation of dynamic photo-thermal effect
Authors: De Rosa, M.; Marin, F.; Marino, F.; Arcizet, O.; Heidmann,
   A.; Pinard, M.
Bibcode: 2006CQGra..23S.259D
Altcode:
  In an optical interferometer, a part of the laser power is absorbed
  by the mirrors and gives rise to surface displacements through thermal
  expansion. The position measurement sensitivity is, therefore, limited
  by the shot noise of the absorbed radiation. This phenomenon is called
  the photo-thermal effect and its typical frequency dependence and size
  can span over several orders of magnitude, depending on the mirror
  material and temperature, hence it is crucial to have an accurate model
  extending over such a large range. We present an extensive experimental
  investigation of dynamic photo-thermal effects, covering more than
  seven decades in frequency and including finite mirror size effects
  (low frequency) and coating effects (high frequency) and showing the
  dependence on the beam waist. A specific extension of the basic model
  is being developed that can well explain the results.

Title: Canard orbits in Fabry-Perot cavities induced by radiation
    pressure and photothermal effects
Authors: Marino, F.; de Rosa, M.; Marin, F.
Bibcode: 2006PhRvE..73b6217M
Altcode:
  A theoretical study of a high-finesse Fabry-Perot cavity considering
  radiation pressure and photothermal displacement is reported. We show
  that the competition between these two effects induces a different
  kind of dynamic behavior in such a system, consisting of canard orbits
  and excitability. The transition between the excitable regime and the
  canard oscillations, occurring through a supercritical Hopf bifurcation,
  appears in an order compatible with the van der Pol FitzHugh-Nagumo
  equations. Besides its interest as a study of general nonlinear
  dynamics, the characterization of the effects described is critical
  for high sensitivity interferometric displacement measurements as
  those employed for gravitational waves detection.

Title: Small-Scale Surface Flows and their Implications for Solar
    Activity
Authors: De Rosa, Marc L.
Bibcode: 2006IAUS..233...25D
Altcode:
  The broad range of dynamics exhibited by plasma motions within the
  solar interior affects many aspects of the generation and transport
  of magnetic fields during the solar magnetic activity cycle. On the
  photosphere, such dynamics include the differential rotation, meridional
  flows, and a hierarchy of convection cells, and these fluid motions are
  observed to readily advect any small-scale magnetic fields embedded
  within them. While the effects of large-scale flows on the global
  activity cycle are well known, it is becoming increasingly apparent
  that small-scale dynamics can also affect global magnetic activity
  throughout the solar cycle. Such effects include variations in the
  strength of the magnetic dipole moment with time, and the timing of
  the reversals of the polar-cap flux. In this article, several aspects
  of this coupling between small and large scales will be illustrated,
  and the implications of such coupling on the solar activity cycle will
  be discussed.

Title: The status of the VIRGO experiment
Authors: Acernese, F.; Amico, P.; Arnaud, N.; Babusci, D.; Ballardin,
   G.; Barille, R.; Barone, F.; Barsuglia, M.; Beauville, F.; Bellachia,
   F.; Bizouard, M. A.; Boccara, C.; Boget, D.; Bondu, F.; Bourgoin,
   C.; Bozzi, A.; Bracci, L.; Braccini, S.; Bradaschia, C.; Brillet,
   A.; Brisson, V.; Brocco, L.; Buskulic, D.; Cachenaut, J.; Calamai,
   G.; Calloni, E.; Campagna, E.; Casciano, C.; Cattuto, C.; Cavalier,
   F.; Cavaliere, S.; Cavalieri, R.; Cella, G.; Chassande-Mottin, E.;
   Chollet, F.; Cleva, F.; Cokelaer, T.; Conforto, G.; Cortese, S.;
   Coulon, J. P.; Cuoco, E.; Dattilo, V.; Davier, P. Y.; de Rosa, M.;
   de Rosa, R.; di Fiore, L.; di Virgilio, A.; Dujardin, B.; Dominici,
   P.; Eleuteri, A.; Enard, D.; Evangelista, G.; Fabbroni, L.; Ferrante,
   I.; Fidecaro, F.; Fiori, I.; Flaminio, R.; Forest, D.; Fournier,
   J. D.; Fournier, L.; Frasca, S.; Frasconi, F.; Gammaitoni, L.; Ganau,
   P.; Gennai, A.; Gennaro, G.; Giacobone, L.; Giazotto, A.; Giordano,
   G.; Girard, C.; Gougoulat, G.; Guigi, G.; Heitmann, H.; Hello, P.;
   Hermel, R.; Heusse, P.; Holloway, L.; Honglie, F.; Iannarelli, M.;
   Journet, L.; Krecklbergh, S.; Lagrange, B.; La Penna, P.; Leliboux,
   M.; Leiunard, B.; Lomtadze, T.; Loriette, V.; Losurda, G.; Loupias,
   M.; Mackowski, J. M.; Majorana, E.; Man, C. N.; Marchesoni, F.; Marion,
   F.; Martelli, F.; Masserot, A.; Massonnet, L.; Mataguez, S.; Menzinger,
   F.; Mazzoni, M.; Michel, C.; Milano, L.; Montorio, J. L.; Moreau, F.;
   Moreau, J.; Morgado, M.; Mornet, F.; Mours, B.; Mugnier, P.; Nenci,
   F.; Pacheco, J.; Pai, A.; Palomba, C.; Paoletti, F.; Paoli, A.; Paoli,
   L.; Pasqualetti, A.; Passaquieti, R.; Passuello, D.; Perciballi, M.;
   Peruzzi, S.; Perniola, B.; Pinard, L.; Poggiani, R.; Pololizio, P.;
   Porter, E.; Puccinelli, S.; Punturo, M.; Puppo, P.; Qipiani, K.;
   Ramonet, J.; Rapagnani, P.; Reita, V.; Remillieux, A.; Ricci, F.;
   Richard, F.; Roger, J. P.; Ruggi, P.; Russo, G.; Solimeno, S.; Stanga,
   R.; Taddei, R.; Teuler, J. M.; Tournfier, E.; Travasso, F.; Trinquet,
   H.; Turri, E.; Varvella, M.; Verkind, D.; Vetran, F.; Veziant, O.;
   Viceré, A.; Vilalte, S.; Vinet, J. Y.; Vocca, H.; Yvert, M.; Zhang, Z.
Bibcode: 2006rdgp.conf..427A
Altcode:
  No abstract at ADS

Title: Influence of Small-scale Dynamics on Large-scale Solar Activity
Authors: De Rosa, M. L.
Bibcode: 2005ASPC..346..337D
Altcode:
  The range of dynamical scales of motion within the solar convection zone
  is estimated to span at least six orders of magnitude in both space
  and time. Despite such breadth of scales, fluid motions occurring
  on the smallest spatial and temporal scales are expected to play an
  important role in the establishment and maintenance of the large-scale
  differential rotation and meridional flows within the turbulent
  convection zone. In turn, flows on all scales affect the transport
  of magnetic fields within the solar interior, causing field to be
  continually regenerated and redistributed. The surface manifestation
  of these magnetic fields exhibits a surprising degree of regularity,
  despite such fields being embedded in an extremely turbulent medium. The
  largest magnetic fields observed at the surface follow episodic patterns
  of emergence and evolution that collectively form each activity cycle,
  but there is also evidence that smaller-scale magnetic fields also
  possess an imprint of such cyclic behavior. This article focuses on
  two specific aspects of the coupling between small and large scales
  on the sun. First, the maintenance of the interior differential
  rotation by small-scale Reynolds stresses is addressed, followed by
  an investigation into the effects of small-scale surface magnetism on
  the strength of the surface dipole and the timing of its reversals.

Title: Erratum: Upper Limits on Gravitational-Wave Emission
    in Association with the 27 Dec 2004 Giant Flare of SGR1806-20
    [Phys. Rev. Lett. 95, 081103 (2005)]
Authors: Baggio, L.; Bignotto, M.; Bonaldi, M.; Cerdonio, M.; Conti,
   L.; de Rosa, M.; Falferi, P.; Fortini, P.; Inguscio, M.; Liguori, N.;
   Marin, F.; Mezzena, R.; Mion, A.; Ortolan, A.; Prodi, G. A.; Poggi,
   S.; Salemi, F.; Soranzo, G.; Taffarello, L.; Vedovato, G.; Vinante,
   A.; Vitale, S.; Zendri, J. P.
Bibcode: 2005PhRvL..95m9903B
Altcode:
  No abstract at ADS

Title: Upper Limits on Gravitational-Wave Emission in Association
    with the 27 Dec 2004 Giant Flare of SGR1806-20
Authors: Baggio, L.; Bignotto, M.; Bonaldi, M.; Cerdonio, M.; Conti,
   L.; de Rosa, M.; Falferi, P.; Fortini, P.; Inguscio, M.; Liguori, N.;
   Marin, F.; Mezzena, R.; Mion, A.; Ortolan, A.; Prodi, G. A.; Poggi,
   S.; Salemi, F.; Soranzo, G.; Taffarello, L.; Vedovato, G.; Vinante,
   A.; Vitale, S.; Zendri, J. P.
Bibcode: 2005PhRvL..95h1103B
Altcode: 2005astro.ph..6142B
  At the time when the giant flare of SGR1806-20 occurred, the AURIGA
  “bar” gravitational-wave (GW) detector was on the air with a noise
  performance close to stationary Gaussian. This allows us to set relevant
  upper limits, at a number of frequencies in the vicinities of 900 Hz,
  on the amplitude of the damped GW wave trains, which, according to
  current models, could have been emitted, due to the excitation of
  normal modes of the star associated with the peak in x-ray luminosity.

Title: The Nonpotentiality of Active-Region Coronae and the Dynamics
    of the Photospheric Magnetic Field
Authors: Schrijver, Carolus J.; De Rosa, Marc L.; Title, Alan M.;
   Metcalf, Thomas R.
Bibcode: 2005ApJ...628..501S
Altcode:
  The magnetic field in the solar photosphere frequently carries strong
  electric currents, even though the global coronal configuration often
  resembles a potential field ringed by the heliospheric current sheet. To
  understand this, we compare TRACE EUV images of active-region coronae
  and potential-field source-surface extrapolations based on SOHO MDI
  magnetograms for 95 active regions. We conclude that significant
  nonpotentiality of the overall active-region coronal field occurs
  (1) when new flux has emerged within or very near a region within
  the last ~30 hr, resulting in complex polarity separation lines, or
  (2) when rapidly evolving, opposite-polarity concentrations are in
  contact at 4" resolution. If these criteria are met by more than 15%
  of the region's flux, they correctly identify the (non) potentiality of
  active-region coronae in 88% of the cases. Flares are found to occur
  2.4 times more frequently in active regions with nonpotential coronae
  than in near-potential regions, while their average X-ray peak flare
  brightness is 3.3 times higher. We suggest that the currents associated
  with coronal nonpotentiality have a characteristic growth and decay
  timescale of ~10-30 hr. We find that shear flows drive enhanced flaring
  or coronal nonpotentiality only if associated with complex and dynamic
  flux emergence within the above timescale. We discuss the implications
  of this finding for the modeling of the coronal-heliospheric coupling.

Title: Non-linear force-free field modeling: model techniques,
    boundary conditions, hares, and hounds
Authors: Schrijver, C. J.; De Rosa, M. L.; Metcalf, T.
Bibcode: 2005AGUSMSH31A..05S
Altcode:
  Understanding the conditions under which solar magnetic fields can
  destabilize to erupt in flares and coronal mass ejections requires
  a quantitative understanding of the coronal magnetic field and of
  the currents that it carries. The increased availability of vector
  magnetograms, together with EUV and X-ray coronal images, should
  provide adequate constraints to model the coronal field, and thus to
  visualize its 3D geometry and to measure the available free energy
  and helicity. Non-linear force-free fields (NLFFF) are likely a useful
  model to use when extrapolating the solar surface field upward into the
  coronal volume. It may even be possible to use the observed trajectories
  of coronal loops, evident in EUV images of the corona, as a further
  constraint. We present initial results of a team effort to understand
  the intricacies of NLFFF modeling: we discuss and evaluate comparisons
  of NLFFF models computed with different models and applications of
  boundary conditions, and look ahead to full coronal field modeling
  for the upcoming Solar-B and SDO missions.

Title: Simulations Of Acoustic-Flow Interaction In Spherical Geometry:
    Steps Toward Validating Helioseismology
Authors: Hanasoge, S. M.; Duvall, T. L.; De Rosa, M. L.; Hurlburt,
   N. E.
Bibcode: 2005AGUSMSP11B..11H
Altcode:
  We simulate acoustic wave interaction with flows in spherical geometry
  with the specific intent of using them as artificial data for validation
  of helioseismology. The numerical procedure is pseudo-spectral; we
  employ a spherical harmonic representation of the spherical surface,
  compact finite differences in the radial direction and a fourth order
  Runge-Kutta time stepping scheme. We also excite surface gravity modes,
  modeling all waves as linear perturbations to the background state so as
  to gain further insight into wave-flow interaction. Towards validation,
  we apply techniques of helioseismology to the artificial data to
  determine the efficacy of the helioseismic inversion procedure. In
  other words, we are attempting the forward problem.

Title: Comparison of Heliospheric Magnetic Field Lines from PFSS
    Models with SEP Observations
Authors: Nitta, N. V.; Liu, Y.; De Rosa, M. L.
Bibcode: 2005AGUSMSH13A..12N
Altcode:
  Impulsive Solar Energetic Particle (SEP) events are thought to come
  locally from solar flares, in contrast with large gradual SEP events
  that are attributed to extended shocks driven by fast CMEs. For several
  impulsive SEP events, we identified the possible solar sources, using
  the timings of type III bursts. The solar sources thus indentified
  tend to be minor brightenings, sometimes not even detectable by the
  GOES X-ray Spectrometer. We found whether the source active region is
  open to the heliosphere, using potential field source surface (PFSS)
  models. We also traced field lines from the spacecraft observing SEPs
  to the source surface assuming constant solar wind speed, and then
  mapped them to the photosphere using PFSS models. In a number of cases,
  these traced field lines go close to the flare site. In other cases,
  their foot-points are far from the flare, or the source active region
  shows no open field lines. We interpret these various results in terms
  of different magnetograms for PFSS modeling, and assumptions used in
  the models.

Title: Numerical Simulations of Bipolar Magnetic Field Decay in
    Turbulent Convection
Authors: De Rosa, M. L.; Hurlburt, N. E.
Bibcode: 2005AGUSMSP11C..02D
Altcode:
  We present numerical simulations of compressible magnetoconvection
  in spherical segments, seeking to examine the decay of active region
  magnetic fields on the sun. It is surprising that after their emergence,
  active regions are observed to persist in relative stasis for long
  periods of time (weeks to months) before suddenly disintegrating. We
  perform a series of calculations to investigate this process, in which
  we drive turbulent convection (Rayleigh numbers of order 107) within
  two- and three-dimensional spherical segments, and measure the decay
  rates of the embedded bipolar magnetic fields.

Title: Interferometric readout for acoustic gravitational wave
    detectors
Authors: Conti, L.; de Rosa, M.; Marin, F.; Taffarello, L.; Cerdonio,
   M.
Bibcode: 2005AIPC..751...75C
Altcode:
  A review is given of the optical readout for acoustic gravitational
  wave detectors, ranging from the working principle, to the experimental
  data and to the future developments. A summary is also given of the
  scientific results obtained while developing the optical readout for a
  bar detector, of interest also for the broader interferometer community.

Title: Coronal heating and the appearance of solar and stellar coronae
Authors: Schrijver, C. J.; Sandman, A. W.; Aschwanden, M. J.; De Rosa,
   M. L.
Bibcode: 2005ESASP.560...65S
Altcode: 2005csss...13...65S
  No abstract at ADS

Title: Evolution of Solar Supergranulation
Authors: De Rosa, Marc L.; Toomre, Juri
Bibcode: 2004ApJ...616.1242D
Altcode:
  The structure and evolution of solar supergranulation is studied using
  horizontal velocity fields, deduced from applying local correlation
  tracking (LCT) techniques to full-disk, line-of-sight Doppler velocity
  data observed by the Michelson Doppler Imager on board the Solar
  and Heliospheric Observatory spacecraft. Two 45° square regions
  of photospheric plasma, one of the quiet Sun and one with increased
  magnetic activity, are tracked for as long as they remain visible on
  the disk of the Sun (about 6 days), enabling a determination of the
  complete life histories of over 3000 supergranules in each region. With
  this method, the horizontal outflows associated with the pattern of
  supergranulation are revealed with clarity, even for locations near
  disk center where little of the horizontal velocity field is projected
  into the line of sight. The LCT flow mappings are of sufficient temporal
  extent that they can be used to study the complex evolution of a broad
  spectrum of supergranules, revealing that merging and fragmentation
  events figure prominently in the life histories of more than half of the
  supergranules in each data set. Such dynamics lead to many short-lived
  supergranules (about 75% of the total population) having lifetimes of
  less than 24 hr, coexisting among numerous long-lived supergranules,
  many of which exist for several days. Average supergranular lifetimes
  lie in the 16-23 hr range, although about 7% of all are recognizable
  for time periods of 48 hr or more. The average supergranular cell
  diameter lies in the 12-20 Mm range, with smaller cells more prevalent
  in areas of greater magnetism. There exists a tendency for larger cells
  to preferentially have longer lifetimes when embedded in a region of
  increased magnetic flux.

Title: The Coronal Heating Mechanism as Identified by Full-Sun
    Visualizations
Authors: Schrijver, Carolus J.; Sandman, Anne W.; Aschwanden, Markus
   J.; De Rosa, Marc L.
Bibcode: 2004ApJ...615..512S
Altcode:
  We constrain the properties of the mechanism(s) responsible for the
  bulk of the heating of the corona of the Sun by simulating, for the
  first time, the appearance of the entire solar corona. Starting from
  full-sphere magnetic field maps for 2000 December 1 and 8, when
  the Sun was moderately active, we populate nearly 50,000 coronal
  field lines with quasi-static loop atmospheres. These atmospheres
  are based on heating flux densities F<SUB>H</SUB> that depend in
  different ways on the loop half-length L, the field strength B at
  the chromospheric base, the loop expansion with height, and the
  heating scale height. The best match to X-ray and EUV observations
  of the corona over active regions and their environs is found for
  F<SUB>H</SUB>~4×10<SUP>14</SUP>B<SUP>1.0+/-0.3</SUP>/L<SUP>1.0+/-0.5</SUP>
  (in ergs cm<SUP>-2</SUP> s<SUP>-1</SUP> for B in Mx cm<SUP>-2</SUP> and
  L in cm), while allowing for substantial loop expansion with increasing
  height, and for a heating scale height that is at least a sizeable
  fraction of the loop length. This scaling for coronal heating points
  to DC reconnection at tangential discontinuities as the most likely
  coronal heating mechanism, provided that the reconnection progresses
  proportional to the Alfvén velocity. The best-fit coronal filling
  factor equals unity, suggesting that most of the corona is heated most
  of the time. We find evidence that loops with half-lengths exceeding
  ~100,000 km are heated significantly more than suggested by the above
  scaling, possibly commensurate with the power deposited in the open
  field of coronal holes.

Title: Supergranular and Larger-Scale Surface Flows Within Magnetic
    Environments
Authors: De Rosa, M. L.
Bibcode: 2004ESASP.559..404D
Altcode: 2004soho...14..404D
  No abstract at ADS

Title: Tomographic 3D-Modeling of the Solar Corona with FASR
Authors: Aschwanden, Markus J.; Alexander, David; de Rosa, Marc L.
Bibcode: 2004ASSL..314..243A
Altcode: 2003astro.ph..9501A
  The Frequency-Agile Solar Radiotelescope (FASR) literally opens up
  a new dimension, in addition to the 3D Euclidian geometry—the
  frequency dimension. The 3D geometry is degenerated to 2D in all
  images from astronomical telescopes, but the additional frequency
  dimension allows us to retrieve the missing third dimension by means of
  physical modeling. We call this type of 3D reconstruction Frequency
  Tomography. In this study we simulate a realistic 3D model of an
  active region, composed of 500 coronal loops with the 3D geometry
  [x(s), y(s), z(s)] constrained by magnetic field extrapolations and
  the physical parameters of the density n<SUB>e</SUB>(s) and temperature
  T<SUB>e</SUB>(s) given by hydrostatic solutions. We simulate a series
  of 20 radio images in a frequency range of ν=0.1-10 GHz, anticipating
  the capabilities of FASR, and investigate what physical information
  can be retrieved from such a dataset. We discuss also forward-modeling
  of the chromospheric and Quiet Sun density and temperature structure,
  another primary goal of future FASR science.

Title: Numerical Models of solar Magnetoconvection: Toward a Coupling
    to the Corona
Authors: De Rosa, M. L.; Hurlburt, N. E.
Bibcode: 2004AAS...204.3908D
Altcode: 2004BAAS...36..715D
  We present numerical simulations of a stratified magnetized fluid,
  confined to a spherical shell, that approximates the transition from
  a high- to low-beta regime, similar to the conditions present at the
  solar photosphere. In these simulations, a model corona atmosphere is
  situated above a convectively unstable, high-beta fluid layer. As a
  result, the dynamics associated with evolving magnetic features in the
  solar atmosphere can be modeled in a manner that is self-consistent
  with the convective motions that provide the driving. Our simulations
  exhibit arcade-like structures that undergo reconnection as a result
  of the supergranular-scale fluid motions in the convective layer below,
  and discuss possible observational consequences.

Title: Solar Coronal Heating Inferred from Full-disk Models of
    Coronal Emission
Authors: Schrijver, C. J.; Sandman, A. W.; De Rosa, M. L.; Aschwanden,
   M. J.
Bibcode: 2004AAS...204.9501S
Altcode: 2004BAAS...36Q.826S
  The appearance of the corona as viewed by different instruments, as
  well as its global spectral irradiance, sensitively depends on how
  coronal heating scales with the properties of the coronal magnetic
  field. We explore a variety of scaling dependences by simulating the
  appearance of the full-disk solar corona as viewed by SOHO/EIT and by
  YOHKOH/SXT, based on observed photospheric magnetic fields combined with
  a potential-field source-surface model. This leads us to conclude that
  the best match to X-ray and EUV observations of the corona over active
  regions and their environments is found for a heating flux density going
  into the corona that scales linearly with the field strength at the
  coronal base and roughly inversely with loop length. This scaling points
  to DC reconnection at tangential discontinuities as the most likely
  coronal heating mechanism, provided that the reconnection progresses
  at a rate proportional to the Alfven velocity. We also find that the
  best-fit coronal filling factor equals unity, suggesting that most of
  the corona is heated most of the time. We find evidence that loops with
  half lengths exceeding approximately 100,000 km are heated significantly
  more than suggested by the above scaling, possibly commensurate with
  the power deposited in the open field of coronal holes.

Title: Molecular and Compound-Specific Isotopic Study of
    Monocarboxylic Acids in Murchison and Antarctic Meteorites
Authors: Huang, Y.; Wang, Y.; de'Rosa, M.; Fuller, M.; Pizzarello, S.
Bibcode: 2004LPI....35.1888H
Altcode:
  We studied molecular distributions and C and H isotopic ratios of
  individual monocarboxylic acids in Murchison and EET96029,20 using a
  new and improved sample indtroduction method (SPME), and reveal new
  monoacids and isotopic characteristics.

Title: An optical readout scheme for advanced acoustic GW detectors
Authors: Marin, F.; Conti, L.; De Rosa, M.
Bibcode: 2004CQGra..21S1237M
Altcode: 2004CQGra..21.1237M
  We have recently proposed a large reading area, optical readout scheme
  for advanced acoustic gravitational wave (GW) detectors. In this
  work we focus the analysis on a dual-cylinder detector. A specific
  configuration is designed and the expected performance is calculated.

Title: Solar-like convective and coronal layers in a single numerical
    model
Authors: Hurlburt, N.; De Rosa, M.
Bibcode: 2004cosp...35.3551H
Altcode: 2004cosp.meet.3551H
  We investigate the coupling between turbulent magnetoconvection
  and an atmospheric layer on the sun using numerical simulations of
  compressible fluids. The model consists of a stratified MHD fluid
  spanning multiple scale heights, encompassing the transition of the
  plasma beta from high to low values. Although a heat flux is imposed at
  the lower boundary, only the lower portion of the domain where the beta
  is high is convectively unstable. The upper portions are stabilized by
  a parameterized heating function and the presence of a strong magnetic
  field and, similar to the solar chromosphere and corona. As a result,
  the dynamics associated with evolving magnetic features in the solar
  atmosphere can be modeled in a manner that is self-consistent with the
  convective motions that provide the driving. We present simulations
  of arcade-like reconnection in the presence of supergranular-scale
  flows and discuss possible observational consequences.

Title: Modeling solar magnetoconvection and coronal structures
Authors: Hurlburt, Neal E.; De Rosa, Marc L.
Bibcode: 2004IAUS..223..253H
Altcode: 2005IAUS..223..253H
  We present results of an investigation into the coupling
  between solar-like magnetoconvection and coronal structures using
  self-consistent numerical simulations of compressible fluids. The
  model consists of a stratified MHD fluid spanning multiple scale
  heights, encompassing the transition of the plasma beta from high to
  low values. The lower portion of the domain, where the beta is high,
  is convectively unstable while the upper portion is stabilized by the
  presence of a strong magnetic field and energy losses. As a result,
  the dynamics associated with evolving magnetic features in the solar
  atmosphere can be modelled in a manner that is self-consistent with the
  convective motions that provide the driving. We present simulations of
  arcade-like reconnection in the presence of supergranular-scale flows.

Title: TRACE and SOHO/MDI Observations of 3 Rotating Sunspots in
    AR9002 and AR9004, Along With Modeled Coronal Magnetic Fields
Authors: Nightingale, R. W.; Schrijver, C. J.; De Rosa, M. L.
Bibcode: 2003AGUFMSH42B0511N
Altcode:
  The TRACE data set provides a view of the solar atmosphere from the
  photosphere in white light, through the transition region in ultraviolet
  wavelengths, and into the corona in extreme ultraviolet wavelengths
  (EUV). From May 16-23, 2000 TRACE and MDI/SOHO observed at least 3
  rotating sunspots in AR9002 and AR9004 at several wavelengths. Over this
  time period several small flares, along with a CME on May 23, occurred
  in these regions. In addition we have potential-field renderings of the
  coronal magnetic fields for the TRACE pointings, extrapolated based on
  the Virtual Starlab forecaster data, which in turn has been generated
  from the MDI/SOHO observations. An analysis of the rotating sunspots,
  together with images and movies, will be provided for these active
  regions, accompanied by images of the extrapolated coronal magnetic
  fields for comparison with images of the TRACE 1-1.5 MK EUV loops. This
  work was supported by NASA, in part under the TRACE contract NAS5-38099
  and in part under the MDI/SOHO contract NAG5-13261.

Title: Coronal heating and the appearance of the solar corona
Authors: Schrijver, C. J.; Sandman, A.; De Rosa, M. L.; Aschwanden,
   M. J.
Bibcode: 2003AGUFMSH32A1104S
Altcode:
  The details of the dependence of coronal heating on the conditions
  within the corona determine the appearance of the corona as viewed
  by different instruments. For example, strong fields at the base of
  short loops cause relatively hot, X-ray bright loops, whereas the
  much weaker fields over the quiet Sun result in cooler, EUV bright
  loops. Any dependence of the volume heating rates on local conditions
  (such as height or field strength) has a signature in the thermal
  profiles along the loops, translating into an appearance that depends
  on the instrumental pass band. In this preliminary study, we explore
  how such dependences of coronal heating on coronal conditions affect
  the appearance of the solar corona, and investigate the consequences
  for the global EUV and X-ray spectral irradiance. These results will
  eventually be used to compute the solar spectral irradiance in the
  EUV and X-rays for quiescent conditions throughout the solar cycle.

Title: Data analysis methods for non-Gaussian, nonstationary and
    nonlinear features and their application to VIRGO
Authors: Virgo Collaboration; Acernese, F.; Amico, P.; Arnaud, N.;
   Babusci, D.; Ballardin, G.; Barillé, R.; Barone, F.; Barsuglia,
   M.; Beauville, F.; Bellachia, F.; Bizouard, M. A.; Boccara,
   C.; Boget, D.; Bondu, F.; Bourgoin, C.; Bozzi, A.; Braccini, S.;
   Bradaschia, C.; Brillet, A.; Brisson, V.; Brocco, L.; Buskulic, D.;
   Cachenaut, J.; Calamai, G.; Calloni, E.; Campagna, E.; Casciano,
   C.; Cattuto, C.; Cavalier, F.; Cavaliere, S.; Cavalieri, R.; Cella,
   G.; Chassande-Mottin, E.; Chollet, F.; Cleva, F.; Cokelaer, T.;
   Conforto, G.; Cortese, S.; Coulon, J. P.; Cuoco, E.; Dattilo, V.;
   Y Davíd, P.; Davier, M.; De Rosa, M.; De Rosa, R.; Di Fiore, L.;
   Di Virgilio, A.; Dujardin, B.; Dominici, P.; Eleuteri, A.; Enard,
   D.; Evangelista, G.; Ferrante, I.; Fidecaro, F.; Fiori, I.; Flaminio,
   R.; Forest, D.; Fournier, J. D.; Fournier, L.; Frasca, S.; Frasconi,
   F.; Gammaitoni, L.; Ganau, P.; Gennai, A.; Gennaro, G.; Giacobone,
   L.; Giazotto, A.; Giordano, G.; Girard, C.; Gougoulat, G.; Guidi,
   G. M.; Heitmann, H.; Hello, P.; Hermel, R.; Heusse, P.; Holloway,
   L.; Honglie, F.; Iannarelli, M.; Journet, L.; Krecklbergh, S.;
   Lagrange, B.; La Penna, P.; Leliboux, M.; Lieunard, B.; Lomtadze, T.;
   Loriette, V.; Losurdo, G.; Loupias, M.; Mackowski, J. M.; Majorana,
   E.; Man, C. N.; Marchesoni, F.; Marion, F.; Martelli, F.; Masserot,
   A.; Massonnet, L.; Mataguez, S.; Menzinger, F.; Mazzoni, M.; Michel,
   C.; Milano, L.; Montorio, J. L.; Moreau, F.; Moreau, J.; Morgado,
   N.; Mornet, F.; Mours, B.; Mugnier, P.; Nenci, F.; Pacheco, J.; Pai,
   A.; Palomba, C.; Paoletti, F.; Paoli, A.; Paoli, L.; Pasqualetti,
   A.; Passaquieti, R.; Passuello, D.; Perciballi, M.; Peruzzi, S.;
   Perniola, B.; Pinard, L.; Poggiani, R.; Popolizio, P.; Porter, E.;
   Puccinelli, S.; Punturo, M.; Puppo, P.; Qipiani, K.; Ramonet, J.;
   Rapagnani, P.; Reita, V.; Remillieux, A.; Ricci, F.; Richard, F.;
   Roger, J. P.; Ruggi, P.; Russo, G.; Solimeno, S.; Stanga, R.; Taddei,
   R.; Teuler, J. M.; Tournefier, E.; Travasso, F.; Trinquet, H.; Turri,
   E.; Varvella, M.; Verkindt, D.; Vetrano, F.; Veziant, O.; Viceré,
   A.; Vilalte, S.; Y Vinet, J.; Vocca, H.; Yvert, M.; Zhang, Z.
Bibcode: 2003CQGra..20S.915V
Altcode:
  The commissioning of the VIRGO central interferometer occasioned the
  implementation and tests of various algorithms for the characterization
  of the non-Gaussianity, non-stationarity and non-linearity of the
  dark fringe data. This library of prototypes will serve as groundwork
  for the near commissioning of VIRGO (full scale). We make a summary
  of the activities on that subject including the description of the
  selected algorithms and some results obtained with the data of the
  engineering runs.

Title: Status of VIRGO
Authors: Virgo Collaboration; Acernese, F.; Amico, P.; Arnaud, N.;
   Babusci, D.; Ballardin, G.; Barillé, R.; Barone, F.; Barsuglia,
   M.; Beauville, F.; Bellachia, F.; Bizouard, M. A.; Boccara,
   C.; Boget, D.; Bondu, F.; Bourgoin, C.; Bozzi, A.; Braccini, S.;
   Bradaschia, C.; Brillet, A.; Brisson, V.; Brocco, L.; Buskulic, D.;
   Cachenaut, J.; Calamai, G.; Calloni, E.; Campagna, E.; Casciano,
   C.; Cattuto, C.; Cavalier, F.; Cavaliere, S.; Cavalieri, R.; Cella,
   G.; Chassande-Mottin, E.; Chollet, F.; Cleva, F.; Cokelaer, T.;
   Conforto, G.; Cortese, S.; Coulon, J. P.; Cuoco, E.; Dattilo, V.;
   Y Davíd, P.; Davier, M.; De Rosa, M.; De Rosa, R.; Di Fiore, L.;
   Di Virgilio, A.; Dujardin, B.; Dominici, P.; Eleuteri, A.; Enard,
   D.; Evangelista, G.; Ferrante, I.; Fidecaro, F.; Fiori, I.; Flaminio,
   R.; Forest, D.; Fournier, J. D.; Fournier, L.; Frasca, S.; Frasconi,
   F.; Gammaitoni, L.; Ganau, P.; Gennai, A.; Gennaro, G.; Giacobone,
   L.; Giazotto, A.; Giordano, G.; Girard, C.; Gougoulat, G.; Guidi,
   G. M.; Heitmann, H.; Hello, P.; Hermel, R.; Heusse, P.; Holloway,
   L.; Honglie, F.; Iannarelli, M.; Journet, L.; Krecklbergh, S.;
   Lagrange, B.; La Penna, P.; Leliboux, M.; Lieunard, B.; Lomtadze, T.;
   Loriette, V.; Losurdo, G.; Loupias, M.; Mackowski, J. M.; Majorana,
   E.; Man, C. N.; Marchesoni, F.; Marion, F.; Martelli, F.; Masserot,
   A.; Massonnet, L.; Mataguez, S.; Menzinger, F.; Mazzoni, M.; Michel,
   C.; Milano, L.; Montorio, J. L.; Moreau, F.; Moreau, J.; Morgado,
   N.; Mornet, F.; Mours, B.; Mugnier, P.; Nenci, F.; Pacheco, J.; Pai,
   A.; Palomba, C.; Paoletti, F.; Paoli, A.; Paoli, L.; Pasqualetti,
   A.; Passaquieti, R.; Passuello, D.; Perciballi, M.; Peruzzi, S.;
   Perniola, B.; Pinard, L.; Poggiani, R.; Popolizio, P.; Porter, E.;
   Puccinelli, S.; Punturo, M.; Puppo, P.; Qipiani, K.; Ramonet, J.;
   Rapagnani, P.; Reita, V.; Remillieux, A.; Ricci, F.; Richard, F.;
   Roger, J. P.; Ruggi, P.; Russo, G.; Solimeno, S.; Stanga, R.; Taddei,
   R.; Teuler, J. M.; Tournefier, E.; Travasso, F.; Trinquet, H.; Turri,
   E.; Varvella, M.; Verkindt, D.; Vetrano, F.; Veziant, O.; Viceré,
   A.; Vilalte, S.; Y Vinet, J.; Vocca, H.; Yvert, M.; Zhang, Z.
Bibcode: 2003CQGra..20S.609V
Altcode:
  We report on the status of the VIRGO detector as of the beginning
  of 2003. In particular, we summarize the results obtained during the
  commissioning of the central portion of the detector, consisting of a
  power-recycled Michelson interferometer, and we outline the steps which
  will lead during 2003 and 2004 to the commissioning and operation of
  the full scale, 3 km long VIRGO detector.

Title: Asterospheric Magnetic Fields and Winds of Cool Stars
Authors: Schrijver, Carolus J.; De Rosa, Marc L.; Title, Alan M.
Bibcode: 2003ApJ...590..493S
Altcode:
  This study addresses the winds and magnetic fields in the inner
  asterospheres of Sun-like magnetically active stars by combining
  empirical relationships between rotation rate and mass loss,
  angular-momentum loss, and radiative losses with models of the magnetic
  fields at the surfaces of cool stars and in their inner asterospheres
  based on the solar example. Our models, for mean magnetic flux densities
  up to 10 times solar, suggest that the asterospheric fields of such
  stars are dominated by the large-scale dipole component of the surface
  field, as is the case for the Sun. Hence, most of the time a single
  current sheet is expected to separate domains of opposite magnetic
  polarity; the current sheets of more active stars generally have smaller
  latitudinal ripples. Magnetic braking requires that the total unsigned
  asterospheric magnetic flux increase linearly with the stellar angular
  velocity, which is a very much weaker increase than seen for the flux at
  the stellar surface. We show that this can be achieved by an increase
  in the radial distance at which the coronal field is forced open as
  surface activity increases. Combined with measured mass-loss rates
  and the assumption that the wind velocity is largely independent of
  activity, this requires the wind's Alfvén radius to be nearly constant,
  decreasing with surface activity with a power of only -0.16+/-0.13. We
  point out that the surface flux density of energy needed to drive a
  cool-star wind scales linearly with the unsigned surface magnetic flux
  density, as does that needed to heat the corona.

Title: The nature of impulsive solar energetic particle events
Authors: Nitta, N. V.; Hudson, H. S.; De Rosa, M. L.
Bibcode: 2003SPD....34.1606N
Altcode: 2003BAAS...35..833N
  Impulsive solar energetic particle (SEP) events, as opposed to
  gradual SEP events, are usually thought to originate from flares in
  the well-connected regions. In order to test this idea, we compute
  the solar locations of the field lines that cross the spacecraft
  encountering particles from SEP events, and compare them with
  the flare locations. We combine two frequently used techniques,
  i.e., the ballistic approximation for the interplanetary magnetic
  field and the potential-field source-surface model for the coronal
  field. Such comparisons are made for selected impulsive SEP events
  during 1995-2001. We check the validity of the techniques using
  Yohkoh SXT and SOHO EIT images, which often show coronal holes on
  the disk. Furthermore, we study the properties of the flares that are
  identified with impulsive SEP events, and compare them with those of
  other flares in the well-connected areas but without impulsive SEP
  events. This will give us a clue as to the importance of the flare
  processes relative to the magnetic field connectivity on the detection
  of impulsive SEP events.

Title: MHD Simulations Spanning the Convection Zone, Chromosphere,
    and Corona
Authors: De Rosa, M. L.; Hurlburt, N. E.
Bibcode: 2003SPD....34.0407D
Altcode: 2003BAAS...35..811D
  The dynamics associated with evolving magnetic structures in the solar
  atmosphere are ultimately driven by vigorous convective motions below
  the photosphere. There, nonlinear interactions between the flows
  and fields lead to the transport of energy up into the atmosphere,
  which is later converted to heat in the chromosphere and corona and
  radiated into space. To investigate such dynamics, we have constructed
  a self-consistent model of the sun encompassing the upper layers of the
  convection zone, chromosphere, transition region, and lower corona. The
  fully compressible magnetized fluid comprising the convective layer is
  dynamically coupled to the atmosphere through the magnetic field. These
  models allow us to investigate the dynamics associated with waves,
  magnetic fields, and fluid motions within the solar atmosphere.

Title: Room temperature gravitational wave bar detector with
    optomechanical readout
Authors: Conti, L.; De Rosa, M.; Marin, F.; Taffarello, L.; Cerdonio,
   M.
Bibcode: 2003JAP....93.3589C
Altcode: 2002gr.qc.....5115C
  We present the full implementation of a room-temperature gravitational
  wave bar detector equipped with an optomechanical readout. The bar
  mechanical vibrations are read by a Fabry-Pérot interferometer whose
  length changes are compared with a stable reference optical cavity by
  means of a resonant laser. The detector performance is completely
  characterized in terms of spectral sensitivity and statistical
  properties of the fluctuations in the system output signal. This kind
  of readout technique allows for wide-band detection sensitivity and we
  can accurately test the model of the coupled oscillators for thermal
  noise. Our results are very promising for cryogenic operation and
  represent an important step towards significant improvements in the
  performance of massive gravitational wave detectors.

Title: Simulations of Near-Surface Solar Magnetoconvection Within
    Localized Spherical Segments
Authors: De Rosa, M. L.; Hurlburt, N. E.
Bibcode: 2003ASPC..293..229D
Altcode: 2003tdse.conf..229D
  Turbulent fluid motions near the surface of the sun, such as those
  associated with the observed pattern of supergranulation, are thought
  to play a role in the decay of the magnetic field within plage and
  active regions on the sun. To investigate such dynamics, we have
  constructed two related numerical simulations of fully compressible
  magnetoconvecting fluids, each contained within a curved, spherical
  segment that approximates the conditions within the upper part of the
  solar convection zone. The spherical segment domains span 30 degrees in
  latitude and 60 degrees in longitude, and have a radial extent of 4%
  of the solar radius. We find that bipolar field configurations decay
  on diffusive (Ohmic) time scales, rather than on turbulent decay time
  scales, despite the network of convection cells around and within the
  magnetized regions.

Title: Photospheric and heliospheric magnetic fields
Authors: Schrijver, Carolus J.; De Rosa, Marc L.
Bibcode: 2003SoPh..212..165S
Altcode:
  The magnetic field in the heliosphere evolves in response to the
  photospheric field at its base. This evolution, together with the
  rotation of the Sun, drives space weather through the continually
  changing conditions of the solar wind and the magnetic field embedded
  within it. We combine observations and simulations to investigate the
  sources of the heliospheric field from 1996 to 2001. Our algorithms
  assimilate SOHO/MDI magnetograms into a flux-dispersal model,
  showing the evolving field on the full sphere with an unprecedented
  duration of 5.5 yr and temporal resolution of 6 hr. We demonstrate
  that acoustic far-side imaging can be successfully used to estimate
  the location and magnitude of large active regions well before they
  become visible on the solar disk. The results from our assimilation
  model, complemented with a potential-field source-surface model for the
  coronal and inner-heliospheric magnetic fields, match Yohkoh/SXT and
  KPNO/He 10830 Å coronal hole boundaries quite well. Even subject to the
  simplification of a uniform, steady solar wind from the source surface
  outward, our model matches the polarity of the interplanetary magnetic
  field (IMF) at Earth ∼3% of the time during the period 1997-2001
  (independent of whether far-side acoustic data are incorporated into
  the simulation). We find that around cycle maximum, the IMF originates
  typically in a dozen disjoint regions. Whereas active regions are
  often ignored as a source for the IMF, the fraction of the IMF that
  connects to magnetic plage with absolute flux densities exceeding 50 Mx
  cm<SUP>−2</SUP> increases from ≲10% at cycle minimum up to 30-50%
  at cycle maximum, with even direct connections between sunspots and the
  heliosphere. For the overall heliospheric field, these fractions are
  ≲1% to 20-30%, respectively. Two case studies based on high-resolution
  TRACE observations support the direct connection of the IMF to magnetic
  plage, and even to sunspots. Parallel to the data assimilation,
  we run a pure simulation in which active regions are injected based
  on random selection from parent distribution functions derived from
  solar data. The global properties inferred for the photospheric and
  heliospheric fields for these two models are in remarkable agreement,
  confirming earlier studies that no subtle flux-emergence patterns or
  field-dispersal properties are required of the solar dynamo beyond those
  that are included in the model in order to understand the large-scale
  solar and heliospheric fields.

Title: Active regions as sources of the heliospheric field
Authors: Schrijver, C. J.; De Rosa, M. L.; Title, A. M.
Bibcode: 2002AGUFMSH52A0436S
Altcode:
  The magnetic field in the heliosphere originates from a variety
  of sources on the surface of the Sun, including mature, decaying,
  and decayed active regions, as well as sunspots. The emergence of new
  active regions together with the dispersal of flux from older active
  regions causes the coronal magnetic field topology to continually
  evolve, allowing previously closed-field regions to open into the
  heliosphere and previously open-field regions to close. Such evolution
  of the coronal field, together with the rotation of the Sun, drive
  space weather through the continually changing conditions of the solar
  wind and the magnetic field embedded within it. We combine observations
  and numerical simulations by assimilating SOHO/MDI magnetograms into a
  surface flux transport model, in order to investigate the origins of
  the heliospheric field on the solar surface through the rising phase
  of the current activity cycle. We find that around cycle maximum,
  the interplanetary magnetic field (IMF) is typically rooted in a
  dozen disjoint regions on the solar surface. Whereas active regions
  are sometimes ignored as a source for the IMF, the fraction of the
  IMF that connects directly to magnetic plage is found to reach up to
  30-50%\ at cycle maximum, with even direct connections between sunspots
  and the heliosphere. We further compare this data assimilation model
  with a pure simulation model, in which the properties of the emergent
  active regions were chosen at random from parent distribution functions
  measured for the sun. The two models show remarkable agreement in the
  temporal behavior of the sector structure of the IMF, in the magnitude
  and time-behavior of the heliospheric field, and even in such global
  properties as the tilt angle of the Sun's large scale dipole. We thus
  conclude that no additional flux-emergence patterns or field-dispersal
  properties are required of the solar dynamo beyond those that are
  included in the model in order to understand the large-scale solar
  and heliospheric fields.

Title: Numerical Simulations of Solar Active Region Magnetoconvection
Authors: De Rosa, M. L.; Hurlburt, N. E.
Bibcode: 2002AGUFMSH52A0495D
Altcode:
  Vigorous fluid motions associated with the observed patterns of
  supergranulation, mesogranulation, and granulation on the sun are
  likely to play a large role in the continual emergence, evolution,
  and redistribution of magnetic field within solar active regions. To
  investigate such non-linear dynamics, we have constructed numerical
  simulations of fully compressible magnetized fluids, each contained
  within curved, spherical segments nominally located near the top of
  the solar convection zone. Overturning motions having length scales
  comparable to that of solar supergranulation are driven by imposing
  a solar-like heat flux through the bottom of the domain. We present
  recent results of several idealized active region simulations within
  thin spherical segments, each spanning 60°x 30° in longitude and
  latitude and extending up to 0.04~R<SUB>sun</SUB> in radius. We are able
  to investigate the analogs of both plage and active regions by varying
  the amount of magnetic flux that permeates the layer. Simplified
  field-line extrapolations into the volume above the spherical
  segments are then used to assess how the corona might respond to the
  structure and evolution of magnetic field emerging through the solar
  photosphere. This work was supported by NASA through grant NAG 5-3077
  to Stanford University and by Lockheed Martin Independent Research
  and Development funds.

Title: Solar Multiscale Convection and Rotation Gradients Studied
    in Shallow Spherical Shells
Authors: De Rosa, Marc L.; Gilman, Peter A.; Toomre, Juri
Bibcode: 2002ApJ...581.1356D
Altcode: 2002astro.ph..9054D
  The differential rotation of the Sun, as deduced from helioseismology,
  exhibits a prominent radial shear layer near the top of the convection
  zone wherein negative radial gradients of angular velocity are
  evident in the low- and midlatitude regions spanning the outer 5%
  of the solar radius. Supergranulation and related scales of turbulent
  convection are likely to play a significant role in the maintenance
  of such radial gradients and may influence dynamics on a global scale
  in ways that are not yet understood. To investigate such dynamics, we
  have constructed a series of three-dimensional numerical simulations
  of turbulent compressible convection within spherical shells, dealing
  with shallow domains to make such modeling computationally tractable. In
  all but one case, the lower boundary is forced to rotate differentially
  in order to approximate the influence that the differential rotation
  established within the bulk of the convection zone might have upon a
  near-surface shearing layer. These simulations are the first models
  of solar convection in a spherical geometry that can explicitly
  resolve both the largest dynamical scales of the system (of order the
  solar radius) as well as smaller scale convective overturning motions
  comparable in size to solar supergranulation (20-40 Mm). We find that
  convection within these simulations spans a large range of horizontal
  scales, especially near the top of each domain, where convection
  on supergranular scales is apparent. The smaller cells are advected
  laterally by the larger scales of convection within the simulations,
  which take the form of a connected network of narrow downflow lanes that
  horizontally divide the domain into regions measuring approximately
  100-200 Mm across. We also find that the radial angular velocity
  gradient in these models is typically negative, especially in the low-
  and midlatitude regions. Analyses of the angular momentum transport
  indicate that such gradients are maintained by Reynolds stresses
  associated with the convection, transporting angular momentum inward
  to balance the outward transport achieved by viscous diffusion and
  large-scale flows in the meridional plane, a mechanism first proposed
  by Foukal &amp; Jokipii and tested by Gilman &amp; Foukal. We suggest
  that similar mechanisms associated with smaller scale convection in
  the Sun may contribute to the maintenance of the observed radial shear
  layer located immediately below the solar photosphere.

Title: Experimental Measurement of the Dynamic Photothermal Effect
    in Fabry-Perot Cavities for Gravitational Wave Detectors
Authors: de Rosa, M.; Conti, L.; Cerdonio, M.; Pinard, M.; Marin, F.
Bibcode: 2002PhRvL..89w7402D
Altcode: 2002gr.qc.....1038D
  We report the experimental observation of the frequency dependence of
  the photothermal effect. The measurements are performed by modulating
  the laser power absorbed by the mirrors of two high-finesse
  Fabry-Perot cavities. The results are very well described by
  a recently proposed theoretical model [M. Cerdonio, L. Conti,
  A. Heidmann, and M. Pinard, &lt;journal&gt;Phys. Rev. D&lt;/journal&gt;
  &lt;volume&gt;63&lt;/volume&gt;, &lt;pages&gt;082003&lt;/pages&gt;
  (&lt;date&gt;2001&lt;/date&gt;)&lt;/citeinfo&gt;], confirming the
  correctness of such calculations. Our observations and quantitative
  characterization of the dynamic photothermal effect demonstrate its
  critical importance for interferometric displacement measurements
  towards the quantum limit, as those necessary for gravitational wave
  detection.

Title: Simulations of near-photospheric magnetoconvection within
    localized spherical segments
Authors: De Rosa, M. L.; Hurlburt, N. E.; Alexander, D.
Bibcode: 2002ESASP.505..385D
Altcode: 2002IAUCo.188..385D; 2002solm.conf..385D
  Vigorous fluid motions associated with the observed patterns of
  supergranulation, mesogranulation, and granulation are likely to play a
  large role during the evolution of magnetic field within solar active
  regions. To investigate such dynamics, we have constructed numerical
  simulations of fully compressible, magnetized fluids, each contained
  within curved, spherical segments that approximate conditions near
  the top of the solar convection zone. We present recent results of
  one three-dimensional simulation of an idealized bipolar active region
  contained within a thin spherical segment. The segment nominally spans
  30° in latitude and 60° in longitude, and has a radial extent of 4%
  of the solar radius. Upon initialization, the domain is threaded by a
  bipolar radial magnetic field, which subsequently cancels as the ensuing
  convection advects field horizontally across the segment. We find that
  the time scale at which the field decays is slower than the expected
  turbulent decay time scale, and is much closer to the diffusive (Ohmic)
  decay time scale, despite the network of convection cells surrounding
  the magnetized regions. We suggest that this convection serves to
  confine field of like polarity and thus suppresses the turbulent decay
  of magnetic field.

Title: The long-term variations of the solar and heliospheric fields
Authors: Schrijver, Carolus J.; De Rosa, Marc L.; Title, Alan M.
Bibcode: 2002ESASP.505..253S
Altcode: 2002IAUCo.188..253S; 2002solm.conf..253S
  The heliospheric field is determined by the largest-scale patterns of
  magnetism at the solar surface, dominated by the lower-latitude active
  regions during cycle maximum, and by the circumpolar fields during
  cycle minimum. To study these patterns, we simulate the evolution of
  the magnetic field at the solar surface and in the heliosphere during
  the last 340 years. We conclude that, contrary to current thinking,
  the observed magnetic flux in the polar regions of the Sun cannot be
  understood as merely a long-term accumulation of active-region decay
  products from a dynamo that modulates only the rate at which flux
  emerges from cycle to cycle. We suggest that simulation and observation
  may be reconciled if the high-latitude solar field decays on a time
  scale comparable to that of the sunspot cycle.

Title: What Is Missing from Our Understanding of Long-Term Solar
    and Heliospheric Activity?
Authors: Schrijver, Carolus J.; De Rosa, Marc L.; Title, Alan M.
Bibcode: 2002ApJ...577.1006S
Altcode:
  The heliospheric magnetic field is associated with changes in space
  weather, cosmic-ray flux, and likely climate. This field is determined
  by the largest scale patterns of magnetism at the solar surface,
  dominated by the lower latitude active regions during cycle maximum and
  by the circumpolar fields during cycle minimum. Whereas the magnetic
  field in the activity belt is readily studied, the high-latitude
  field is much less accessible, and its study requires a combination of
  modeling and observation. Current models hold that the high-latitude
  magnetic field on the Sun is determined solely by the accumulation of
  field transported poleward from lower latitude active regions. We test
  this hypothesis by simulating the evolution of the magnetic field at
  the solar surface and in the heliosphere during the last 340 yr using a
  state-of-the-art model that incorporates all processes that are known to
  contribute significantly to the evolution of the large-scale patterns
  in the solar field. We find that if only the emergence frequency of
  magnetic bipoles is varied in accordance with observed sunspot records,
  the polar-cap field reservoir does not match measurements during past
  years. Based on comparisons of our simulations with observed polar
  fluxes over the last few decades and with the proxy for the heliospheric
  flux formed by 340 yr of <SUP>10</SUP>Be ice-core data, we suggest that
  the high-latitude field may be subject to decay on a timescale of 5-10
  yr. We discuss the consequences of this finding for our understanding
  of the Sun-Earth connection and explore inferences for the coupling
  of the Sun's internal magnetic field to the heliospheric field.

Title: A neural network-based approach to noise identification of
interferometric GW antennas: the case of the 40 m Caltech laser
    interferometer
Authors: Acernese, F.; Barone, F.; de Rosa, M.; De Rosa, R.; Eleuteri,
   A.; Milano, L.; Tagliaferri, R.
Bibcode: 2002CQGra..19.3293A
Altcode:
  In this paper, a neural network-based approach is presented for the real
  time noise identification of a GW laser interferometric antenna. The
  40 m Caltech laser interferometer output data provide a realistic
  test bed for noise identification algorithms because of the presence
  of many relevant effects: violin resonances in the suspensions,
  main power harmonics, ring-down noise from servo control systems,
  electronic noises, glitches and so on. These effects can be assumed to
  be present in all the first interferometric long baseline GW antennas
  such as VIRGO, LIGO, GEO and TAMA. For noise identification, we used
  the Caltech-40 m laser interferometer data. The results we obtained are
  pretty good notwithstanding the high initial computational cost. The
  algorithm we propose is general and robust, taking into account that
  it does not require a priori information on the data, nor a precise
  model, and it constitutes a powerful tool for time series data analysis.

Title: Numerical Simulations of Supergranular Magnetoconvection
Authors: De Rosa, M. L.; Hurlburt, N. E.; Alexander, D.; Rucklidge,
   A. M.
Bibcode: 2002AAS...200.0418D
Altcode: 2002BAAS...34..646D
  The complex interactions between the turbulent fluid motions within
  the solar convection zone and the related processes of emergence,
  evolution, and cancellation of magnetic field at the photosphere have
  received much recent attention. It is likely that such interactions
  depend on the relative magnitudes of the field and of the flows,
  but the details of this coupling are not well understood. To further
  investigate the magnetohydrodynamics within such turbulent convection,
  we have constructed several idealized simulations of fully compressible
  MHD fluids, each contained within a curved, spherical segment that
  approximates a localized volume of subphotospheric convection on the
  sun. In some cases, the horizontal extent of the computational volume
  spans 30 heliographic degrees in both latitude and longitude, thereby
  enabling the dynamics within a large field containing approximately
  100 supergranular-sized cells to be studied. By varying the amount of
  total (unsigned) flux permeating the domain, we are able to investigate
  analogs to patches of subsurface convection that generally resemble
  either quiet-sun or active regions when viewed from above. In addition,
  simplified potential-field extrapolations into the volume above the
  computational domain are used to illustrate how the coronal field
  topology might behave in response to the continually evolving magnetic
  field within the convecting layers. This work was supported by NASA
  through grant NAG 5-3077 to Stanford University and by Lockheed Martin
  Independent Research and Development funds.

Title: Status report and near future prospects for the gravitational
    wave detector AURIGA
Authors: Zendri, J. -P.; Baggio, L.; Bignotto, M.; Bonaldi, M.;
   Cerdonio, M.; Conti, L.; De Rosa, M.; Falferi, P.; Fortini, P. L.;
   Inguscio, M.; Marin, A.; Marin, F.; Mezzena, R.; Ortolan, A.; Prodi,
   G. A.; Rocco, E.; Salemi, F.; Soranzo, G.; Taffarello, L.; Vedovato,
   G.; Vinante, A.; Vitale, S.
Bibcode: 2002CQGra..19.1925Z
Altcode:
  We describe the experimental efforts to set up the second AURIGA
  run. Thanks to the upgraded capacitive readout, fully characterized
  and optimized in a dedicated facility, we predict an improvement
  in the detector sensitivity and bandwidth by at least one order of
  magnitude. In the second run, AURIGA will also benefit from newly
  designed cryogenic mechanical suspensions and the upgraded data
  acquisition and data analysis.

Title: First room temperature operation of the AURIGA optical readout
Authors: De Rosa, M.; Baggio, L.; Cerdonio, M.; Conti, L.; Galet,
   G.; Marin, F.; Ortolan, A.; Prodi, G. A.; Taffarello, L.; Vedovato,
   G.; Vitale, S.; Zendri, J. -P.
Bibcode: 2002CQGra..19.1919D
Altcode:
  In the frame of the AURIGA collaboration, a readout scheme based on
  an optical resonant cavity has been implemented on a room temperature
  resonant bar detector of gravitational waves. The bar equipped with
  the optical readout has been operating for a few weeks and we report
  here the first results.

Title: The present status of the VIRGO Central Interferometer*The
    present status of the VIRGO Central Interferometer
Authors: Acernese, F.; Amico, P.; Arnaud, N.; Arnault, C.; Babusci,
   D.; Ballardin, G.; Barone, F.; Barsuglia, M.; Bellachia, F.; Beney,
   J. L.; Bilhaut, R.; Bizouard, M. A.; Boccara, C.; Boget, D.; Bondu,
   F.; Bourgoin, C.; Bozzi, A.; Bracci, L.; Braccini, S.; Bradaschia,
   C.; Brillet, A.; Brisson, V.; Buskulic, D.; Cachenaut, J.; Calamai,
   G.; Calloni, E.; Canitrot, P.; Caron, B.; Casciano, C.; Cattuto,
   C.; Cavalier, F.; Cavaliere, S.; Cavalieri, R.; Cecchi, R.; Cella,
   G.; Chiche, R.; Chollet, F.; Cleva, F.; Cokelaer, T.; Cortese, S.;
   Coulon, J. P.; Cuoco, E.; Cuzon, S.; Dattilo, V.; David, P. Y.;
   Davier, M.; De Rosa, M.; De Rosa, R.; Dehamme, M.; Di Fiore, L.;
   Di Virgilio, A.; Dominici, P.; Dufournaud, D.; Eder, C.; Eleuteri,
   A.; Enard, D.; Errico, A.; Evangelista, G.; Fabbroni, L.; Fang, H.;
   Ferrante, I.; Fidecaro, F.; Flaminio, R.; Fournier, J. D.; Fournier,
   L.; Frasca, S.; Frasconi, F.; Gammaitoni, L.; Ganau, P.; Garufi, F.;
   Gaspard, M.; Gennaro, G.; Giacobone, L.; Giazotto, A.; Giordano, G.;
   Girard, C.; Guidi, G.; Heitmann, H.; Hello, P.; Hermel, R.; Heusse, P.;
   Holloway, L.; Iannarelli, M.; Innocent, J. M.; Jules, E.; La Penna, P.;
   Lacotte, J. C.; Lagrange, B.; Leliboux, M.; Lieunard, B.; Lodygenski,
   O.; Lomtadze, T.; Loriette, V.; Losurdo, G.; Loupias, M.; Mackowski,
   J. M.; Majorana, E.; Man, C. N.; Mansoux, B.; Marchesoni, F.; Marin,
   P.; Marion, F.; Marrucho, J. C.; Martelli, F.; Masserot, A.; Massonnet,
   L.; Mataguez, S.; Mazzoni, M.; Mencik, M.; Michel, C.; Milano, L.;
   Montorio, J. L.; Morgado, N.; Mours, B.; Mugnier, P.; Nicolosi, L.;
   Pacheco, J.; Palomba, C.; Paoletti, F.; Paoli, A.; Pasqualetti, A.;
   Passaquieti, R.; Passuello, D.; Perciballi, M.; Pinard, L.; Poggiani,
   R.; Popolizio, P.; Pradier, T.; Punturo, M.; Puppo, P.; Qipiani,
   K.; Ramonet, J.; Rapagnani, P.; Reboux, A.; Regimbau, T.; Reita, V.;
   Remillieux, A.; Ricci, F.; Richard, F.; Ripepe, M.; Rivoirard, P.;
   Roger, J. P.; Scheidecker, J. P.; Solimeno, S.; Sottile, R.; Stanga,
   R.; Taddei, R.; Taurigna, M.; Teuler, J. M.; Tourrenc, P.; Trinquet,
   H.; Turri, E.; Varvella, M.; Verkindt, D.; Vetrano, F.; Veziant, O.;
   Viceré, A.; Vinet, J. Y.; Vocca, H.; Yvert, M.; Zhang, Z.
Bibcode: 2002CQGra..19.1421A
Altcode:
  The VIRGO Central Interferometer (CITF) is a short suspended
  interferometer operated with the central area elements of the
  VIRGO detector. The main motivation behind the CITF is to allow
  the integration and debugging of a large part of the subsystems of
  VIRGO while the construction of the long arms of the antenna is being
  completed. This will permit a faster commissioning of the full-size
  antenna. In fact, almost all the main components of the CITF, with
  the exception of the large mirrors and a few other details, are the
  same as those to be used for the full-size detector. In this paper
  the present status of the VIRGO CITF is reported.

Title: Advanced readout configurations for the gravitational wave
    detector AURIGA
Authors: Zendri, J. -P.; Bignotto, M.; Bonaldi, M.; Cerdonio, M.;
   Conti, L.; Crivelli Visconti, V.; de Rosa, M.; Falferi, P.; Marin,
   A.; Marin, F.; Mezzena, R.; Prodi, G. A.; Salviato, M.; Soranzo, G.;
   Taffarello, L.; Vinante, A.; Vitale, S.
Bibcode: 2002rdgr.conf..317Z
Altcode:
  We report the status of the experimental effort devoted at improving
  the sensitivity and widening the band of the gravitational wave
  detector AURIGA. The focus is on an optimized setup of the capacitive
  resonant transducer, read by an improved dc-SQUID amplifier and on
  the implementation of an opto-mechanical resonant transducer. Both
  techniques, which are complementary, should lead to an improvement of
  the detector performances of at least two orders of magnitude in both
  energy sensitivity and bandwidth.

Title: Coupled modeling of photospheric and coronal dynamics
Authors: Alexander, D.; Hurlburt, N. E.; Rucklidge, A. M.; De Rosa, M.
Bibcode: 2001AGUFMSH11C0718A
Altcode:
  The coupling of the motions within and below te photosphere to the
  chromosphere and corona is one of the fundamental issues in solar
  physics. We have developed a model coupling the simulated dynamics of
  sunspots to the simulated heating of coronal loops. In this paper we
  present an extension of our earlier work to the inclusion of (a) fully
  three dimensional magnetoconvection, (b) new analytical representations
  of hydrostatic loops with spatially-dependent heating rates and (c)
  fully time-dependent hydrodynamic coronal modeling. The dynamic loop
  model uses the same numerical scheme as the magnetoconvective model
  used to simulate the photospheric behavior in this sunspot system,
  making it possible to more fully integrate the two regimes. We present
  the first results of a hybrid model utilizing a time-dependent coronal
  model and a fully three-dimensional magnetoconvective model.

Title: Numerical simulations of supergranular scales of convection
    in shallow spherical shells
Authors: De Rosa, Marc L.; Toomre, Juri
Bibcode: 2001ESASP.464..595D
Altcode: 2001soho...10..595D
  The differential rotation of the sun, as deduced from helioseismology,
  exhibits a prominent radial shear layer near the top of the convection
  zone. Supergranulation and related scales of turbulent convection
  are likely to play a significant role in the maintenance of strong
  radial gradients in angular velocity which vary with latitude near
  the surface. We present results from 3-D numerical simulations of such
  turbulent convection in shallow spherical shells, using the anelastic
  spherical harmonic (ASH) code running on massively parallel computers
  to study the effects of rotation and compressibility on the resulting
  highly nonlinear convection. Convection of supergranular nature is
  driven by imposing the solar heat flux at the bottom of a shallow
  spherical shell located near the top of the convection zone which is
  rotating at the mean solar rate. The angular momentum balance in the
  shell is studied for cases where a solar-like differential rotation
  profile is imposed at the lower boundary. Convection spanning a large
  range of horizontal scales is driven within the shell, especially near
  the top of the domain. The resulting radial angular velocity gradient
  is negative for all latitudes, suggesting that fluid parcels partially
  conserve their angular momentum while moving radially.

Title: Turbulent Convection and Subtleties of Differential Rotation
    Within the Sun
Authors: Toomre, J.; Brun, A. Sacha; De Rosa, M.; Elliott, J. R.;
   Miesch, M. S.
Bibcode: 2001IAUS..203..131T
Altcode:
  Differential rotation and cycles of magnetic activity are
  intimately linked dynamical processes within the deep shell of
  highly turbulent convection occupying the outer 200 Mm below the
  solar surface. Helioseismology has shown that the angular velocity
  Ω within the solar convection zone involves strong shear layers
  both near the surface and especially at its base near the interface
  with the radiative interior. The tachocline of radial shear there
  that varies with latitude is thought to be the site of the global
  magnetic dynamo. Most recent continuous helioseismic probing with
  MDI on SOHO and from GONG have revealed systematic temporal changes
  in Ω with the advancing solar cycle. These include propagating bands
  of zonal flow speedup extending from the surface to a depth of about
  70 Mm, distinctive out-of-phase vacillations in Ω above and below the
  tachocline with a period of about 1.3 years near the equator, a changing
  pattern of meridional circulation cells with broken symmetries in the
  two hemispheres, and complex speedups and slowdowns in the bulk of
  the convection zone. We review these helioseismic findings and their
  implications. We also describe current 3-D numerical simulations of
  anelastic rotating convection in full spherical shells used to study
  the differential rotation that can be established by such turbulence
  exhibiting coherent structures. These simulations enabled by massively
  parallel computers are making promising contact with aspects of the
  Ω profiles deduced from helioseismology, but challenges remain.

Title: Dynamics in the upper solar convection zone
Authors: DeRosa, Marc Lyle
Bibcode: 2001PhDT.........8D
Altcode:
  The differential rotation of the sun, as deduced from helioseismology,
  exhibits a prominent layer of radial shear near the top of the
  convection zone. This shearing boundary layer just below the solar
  surface is composed of convection possessing a broad range of
  length and time scales, including granulation, mesogranulation, and
  supergranulation. Such turbulent convection is likely to influence
  the dynamics of the deep convection zone in ways that are not yet
  fully understood. We seek to assess the effects of this near-surface
  shear layer through two complementary studies, one observational and
  the other theoretical in nature. Both deal with turbulent convection
  occurring on supergranular scales within the upper solar convection
  zone. We characterize the horizontal outflow patterns associated with
  solar supergranulation by individually identifying several thousand
  supergranules from a 45°-square field of quiet sun. This region is
  tracked for a duration of six days as it rotates across the disk of the
  sun, using full-disk (2<SUP> '</SUP> pixels) SOI-MDI images from the
  SOHO space-craft of line- of-sight Doppler velocity imaging the solar
  photosphere at a cadence of one minute. This time series represents the
  first study of solar supergranulation at such high combined temporal
  and spatial resolution over an extended period of time. The outflow
  cells in this region are observed to have a distribution of sizes,
  ranging from 14-20 Mm across, while continuously evolving on time
  scales of several days. Such evolution manifests itself in the form of
  cell merging, fragmentation, and advection, as the supergranules and
  their associated network of convergence lanes respond to the turbulent
  convection occurring a short distance below the photosphere. We have
  also conducted three-dimensional numerical simulations of turbulent
  compressible convection within thin spherical shells located near the
  top of the convection zone. Vigorous fluid motions possessing several
  length and time scales are driven by imposing the solar heat flux and
  differential rotation at the bottom of the domain. The convection
  patterns form a connected network of downflow lanes in the surface
  layers that break up into more plume-like structures with depth. The
  regions delineated by this downflow network enclose broad upflows
  that fragment into smaller structures near the surface. We find that a
  negative radial gradient of angular velocity Ω is maintained against
  diffusion in these simulations by the tendency for the convective
  motions to partially conserve their angular momentum in radial
  motion. This behavior suggests that similar dynamics may be responsible
  for the decrease of Ω with radius as deduced from helioseismology
  within the upper shear layer of the solar convection zone.

Title: New Approach to Study Extended Evolution of Supergranular
    Flows and Their Advection of Magnetic Elements
Authors: Lisle, Jason; De Rosa, Marc; Toomre, Juri
Bibcode: 2000SoPh..197...21L
Altcode:
  Using velocity and magnetogram data extracted from the full-disk field
  of view of MDI during the 1999 Dynamics Program, we have studied the
  dynamics of small-scale magnetic elements (3-7 Mm in size) over time
  periods as long as six days while they are readily visible on the
  solar disk. By exploiting concurrent time series of magnetograms and
  Doppler images, we have compared the motion of magnetic flux elements
  with the supergranular velocity field inferred from the correlation
  tracking of mesogranular motions. Using this new method (which combines
  the results from correlation tracking of mesogranules with detailed
  analysis of simultaneous magnetograms), it is now possible to correlate
  the motions of the velocity field and magnetic flux for long periods of
  time and at high temporal resolution. This technique can be utilized
  to examine the long-term evolution of supergranulation and associated
  magnetic fields, for it can be applied to data that span far longer
  time durations than has been possible previously. As tests of its
  efficacy, we are able to use this method to verify many results of
  earlier investigations. We confirm that magnetic elements travel at
  approximately 350 m s <SUP>−1</SUP> throughout the duration of their
  lifetime as they are transported by supergranular outflows. We also
  find that the positions of the magnetic flux elements coincide with
  the supergranular network boundaries and adjust as the supergranular
  network itself evolves over the six days of this data set. Thus
  we conclude that this new method permits us to study the extended
  evolution of the supergranular flow field and its advection of magnetic
  elements. Since small-scale magnetic elements are strongly advected
  by turbulent convection, their dynamics can give important insight
  into the properties of the subsurface convection.

Title: An optical transduction chain for the AURIGA detector
Authors: Conti, L.; Marin, F.; de Rosa, M.; Prodi, G. A.; Taffarello,
   L.; Zendri, J. P.; Cerdonio, M.; Vitale, S.
Bibcode: 2000AIPC..523..261C
Altcode: 2000grwa.conf..261C
  We describe the principle of operation of an opto-mechanical readout
  for resonant mass gravitational wave detectors; with such a device
  the AURIGA detector is expected to reach a sensitivity at the level
  of S<SUB>hh</SUB>=10<SUP>-22</SUP>/Hz over a bandwidth of about
  40Hz. Recent developments in the implementation of this transduction
  chain are also reported. In particular we achieve quantum limited laser
  power noise in the frequency range of 200Hz around the bar fundamental
  frequency (about 1kHz) by means of active stabilization. We also
  set up a reference cavity of finesse 40000 with optically contacted
  mirrors on a 0.2m long Zerodur spacer. The cavity can be heated from
  room temperature to about 100 °C and temperature stabilized with
  fluctuations within 1mK over a period of several days. The cavity is
  under vacuum and isolated from mechanical disturbancies by means of
  a double stage cantilever system. .

Title: Evolving Dynamics of the Supergranular Flow Field
Authors: De Rosa, M. L.; Lisle, J. P.; Toomre, J.
Bibcode: 2000SPD....31.0106D
Altcode: 2000BAAS...32..802D
  We study several large (45-degree square) fields of supergranules
  for as long as they remain visible on the solar disk (about 6 days)
  to characterize the dynamics of the supergranular flow field and its
  interaction with surrounding photospheric magnetic field elements. These
  flow fields are determined by applying correlation tracking methods
  to time series of mesogranules seen in full-disk SOI-MDI velocity
  images. We have shown previously that mesogranules observed in this
  way are systematically advected by the larger scale supergranular
  flow field in which they are embedded. Applying correlation tracking
  methods to such time series yields the positions of the supergranular
  outflows quite well, even for locations close to disk center. These
  long-duration datasets contain several instances where individual
  supergranules are recognizable for time scales as long as 50 hours,
  though most cells persist for about 25 hours that is often quoted as a
  supergranular lifetime. Many supergranule merging and splitting events
  are observed, as well as other evolving flow patterns such as lanes
  of converging and diverging fluid. By comparing the flow fields with
  the corresponding images of magnetic fields, we confirm the result
  that small-scale photospheric magnetic field elements are quickly
  advected to the intercellular lanes to form a network between the
  supergranular outflows. In addition, we characterize the influence
  of larger-scale regions of magnetic flux, such as active regions,
  on the flow fields. Furthermore, we have measured even larger-scale
  flows by following the motions of the supergranules, but these flow
  fields contain a high noise component and are somewhat difficult to
  interpret. This research was supported by NASA through grants NAG
  5-8133 and NAG 5-7996, and by NSF through grant ATM-9731676.

Title: Near-Surface Flow Fields Deduced Using Correlation Tracking
    and Time-Distance Analyses
Authors: De Rosa, Marc; Duvall, T. L., Jr.; Toomre, Juri
Bibcode: 2000SoPh..192..351D
Altcode:
  Near-photospheric flow fields on the Sun are deduced using two
  independent methods applied to the same time series of velocity images
  observed by SOI-MDI on SOHO. Differences in travel times between f
  modes entering and leaving each pixel measured using time-distance
  helioseismology are used to determine sites of supergranular
  outflows. Alternatively, correlation tracking analysis of mesogranular
  scales of motion applied to the same time series is used to deduce
  the near-surface flow field. These two approaches provide the means to
  assess the patterns and evolution of horizontal flows on supergranular
  scales even near disk center, which is not feasible with direct
  line-of-sight Doppler measurements. We find that the locations of the
  supergranular outflows seen in flow fields generated from correlation
  tracking coincide well with the locations of the outflows determined
  from the time-distance analysis, with a mean correlation coefficient
  after smoothing of <SUB>s</SUB>=0.890. Near-surface velocity field
  measurements can be used to study the evolution of the supergranular
  network, as merging and splitting events are observed to occur in these
  images. The data consist of one 2048-min time series of high-resolution
  (0.6'' pixels) line-of-sight velocity images taken by MDI on 1997
  January 16 -18 at a cadence of one minute.

Title: An Optical Transducer for Bar Detectors
Authors: Marin, F.; de Rosa, M.; Conti, L.; Prodi, G.; Vitale, S.;
   Cerdonio, M.; Taffarello, L.; Zendri, J. P.
Bibcode: 2000epgw.conf..306M
Altcode:
  We present a new kind of transducer for gravitational waves
  bar detectors. The bar vibrations are measured by means of a
  mechanically coupled optical cavity whose length is compared with
  that of a reference cavity by means of a laser system. We describe in
  details the transduction chain, we analyze the noise sources and the
  achievable sensitivity and present some experimental steps for the
  system implementation.

Title: Comparison Between Near-Surface Flow Fields Deduced from
    Correlation Tracking and Time-Distance Helioseismology Methods
Authors: De Rosa, M. L.; Toomre, J.; Duvall, T. L., Jr.
Bibcode: 1999AAS...194.5608D
Altcode: 1999BAAS...31..913D
  Near-photospheric flow fields deduced using two independent methods
  applied to the same SOI-MDI time series of images from SOHO are
  compared. Differences in travel times between incoming and outgoing
  f modes measured using time-distance helioseismology are used to
  determine the sites of supergranule outflows. Alternatively, correlation
  tracking analysis is applied to granular and mesogranular structures
  seen in time series of Doppler and intensity images. We find that the
  locations of the supergranular outflows seen in flow fields generated
  from correlation tracking coincide well with the locations of the
  outflows determined from the time-distance analysis. The near-surface
  flow fields provide us with insight in understanding the dyanmics
  of the turbulent convection occurring below the photosphere. The data
  consist of four 512-minute time series of high-resolution (0.6'' pixels)
  Doppler images and continuum intensity images taken by MDI on 17--18
  January 1997 at a cadence of one minute.

Title: Collisional broadening and shift of lines in the
    2ν<SUB>1</SUB>+2ν<SUB>2</SUB>+ν<SUB>3</SUB> band of CO<SUB>2</SUB>.
Authors: de Rosa, M.; Corsi, C.; Gabrysch, M.; D'Amato, F.
Bibcode: 1999JQSRT..61...97D
Altcode:
  Using a distributed feedback diode laser, pressure induced
  self-broadening and shift have been measured for several transitions
  in the 2ν<SUB>1</SUB>+2ν<SUB>2</SUB>+ν<SUB>3</SUB> band of
  CO<SUB>2</SUB>, centered at 1.573 μm. Foreign broadening and shift,
  with N<SUB>2</SUB> and O<SUB>2</SUB> as perturbing gas, have been
  measured for the most intense lines. The results for broadening have
  been compared with the data given by HITRAN molecular database and
  some discrepancies have been found, especially for air broadening
  derived from N<SUB>2</SUB> and O<SUB>2</SUB> broadening.

Title: Comparison Between Near-Surface Flow Fields Deduced from
    Correlation Tracking and Time-Distance Helioseismology Methods
Authors: de Rosa, Marc; Toomre, Juri; Duvall, T. L., Jr.
Bibcode: 1999soho....9E..51D
Altcode:
  Near-photospheric flow fields deduced using two independent methods
  applied to the same SOI-MDI time series of images from SOHO are
  compared. Differences in travel times between incoming and outgoing f
  modes measured using time-distance helioseismology are used to determine
  the sites of supergranule outflows. Alternatively, correlation tracking
  analysis is applied to granular and mesogranular structures seen in time
  series of Doppler and intensity images. We find that the locations
  of the supergranular outflows seen in flow fields generated from
  correlation tracking coincide well with the locations of the outflows
  determined from the time-distance analysis. The near-surface flow fields
  provide us with insight in understanding the dynamics of the turbulent
  convection occurring below the photosphere. The data consist of four
  512-minute time series of high-resolution (0.6 arc-second pixels)
  Doppler images and continuum intensity images taken by MDI on 17-18
  January 1997 at a cadence of one minute.

Title: Long-Term Dynamics of Small-Scale Magnetic Flux Elements
    Embedded in the Near-Surface Velocity Field
Authors: Lisle, Jason; de Rosa, Marc; Toomre, Juri
Bibcode: 1999soho....9E..72L
Altcode:
  Using velocity and magnetogram data generated by SOI-MDI during the
  1999 Dynamics Program, we have studied the dynamics of small-scale
  magnetic elements over time periods of several days. By exploiting
  concurrent time series of MDI magnetograms and velocity images, we
  have correlated the motions of the magnetic flux elements with the
  supergranular velocity field inferred from tracking of mesogranular
  motions. We confirm that these magnetic elements travel at approximately
  200 m/s throughout the duration of their lifetime (10-20 hours) as they
  are transported by supergranular outflows. We also find that boundaries
  of supergranules traced by magnetic flux elements coincide with the
  boundaries determined from the tracking of mesogranules. In addition,
  we have studied the association between magnetic flux emergence and
  destruction events and the evolution of the supergranular network. The
  data consist of several tracked regions of corresponding magnetogram and
  photospheric velocity images extracted from full-disk SOI-MDI images
  taken during the 1999 Dynamics Program when the MDI instrument was at
  best focus. Time series were created by following these individual
  patches as they rotated across the solar disk. Individual magnetic
  elements were identified by thresholding the magnetograms, while the
  supergranular flow fields were determined by applying a correlation
  tracking algorithm to time series of mesogranules. The mesogranules
  were isolated by removing the signal due to solar rotation, p-mode
  oscillations, and supergranulation from the velocity data.

Title: Correlation Tracking of Mesogranules from SOI-MDI Doppler
    Images to Reveal Supergranular Flow Fields
Authors: De Rosa, Marc L.; Toomre, Juri
Bibcode: 1998ESASP.418..753D
Altcode: 1998soho....6..753D
  We present evidence that mesogranules on the sun are advected
  horizontally by the underlying supergranular flow field. Correlation
  tracking of mesogranules, as observed in full-disk SOI-MDI Doppler
  images, reveal that the flow field experienced by the mesogranules is
  composed of several long-lived regions of divergent fluid. These outflow
  regions correlate well with the locations of supergranules present on
  related Doppler images. The flow fields also contain regions where the
  fluid is converging or is moving slowly, both corresponding to areas of
  the related Doppler images where no organized supergranular outflows
  exist. Typical velocities are of order 200 m s<SUP>-1</SUP>. The data
  used in this study consist of 30-circ-square patches of the photospheric
  velocity field extracted from full-disk SOI-MDI Dopplergrams. Time
  series were created by tracking each patch in a frame corotating
  with the surface plasma. Images of mesogranulation superimposed on
  supergranulation were created by removing the velocity signals due
  to rotation and acoustic oscillations. The supergranular signal is
  isolated by spatially smoothing each image, while the mesogranular
  signal is isolated by taking the residual of the smoothed and unsmoothed
  images. The correlation tracking calculation was performed on the time
  series of mesogranulation, from which the surface flow-fields analyzed
  in this study were deduced.

Title: The Nature of Supergranulation from SOI-MDI Dopplergrams
Authors: De Rosa, Marc L.; Toomre, Juri
Bibcode: 1997SPD....28.0257D
Altcode: 1997BAAS...29..903D
  We discuss the distribution of supergranule cell areas and
  evolutionary characteristics as determined from a series of SOI-MDI
  dopplergrams. Patches of the photospheric velocity field 30(deg)
  x30(deg) (heliographic) in size were tracked as they rotated across the
  disk of the sun. Supergranule boundaries were identified on each tracked
  image by a pattern recognition algorithm, from which supergranule area
  distributions and evolutionary trends are found.

Title: Temperature dependence of self-shift of ammonia transitions
    in the ν<SUB>2</SUB> band.
Authors: Baldacchini, G.; D'Amato, F.; de Rosa, M.; Buffa, G.;
   Tarrini, O.
Bibcode: 1996JQSRT..55..745B
Altcode:
  Pressure-induced lineshift has been measured as a function of
  temperature, in the range 200-400 K, for five transitions of the
  ν<SUB>2</SUB> band of ammonia lines near 937 cm<SUP>-1</SUP>. Results
  are compared with semiclassical calculations that rely on the impact
  approximation. In general the theory does not agree very well with
  the experimental values of the shift, but the sign and the order of
  magnitude are confirmed. The present work shows that extensive and
  detailed measurement of the lineshifts is feasible and reliable, even
  when their absolute values in ammonia as a function of temperature
  are very small.

Title: Differential Rotation and Dynamics of the Solar Interior
Authors: Thompson, M. J.; Toomre, J.; Anderson, E. R.; Antia, H. M.;
   Berthomieu, G.; Burtonclay, D.; Chitre, S. M.; Christensen-Dalsgaard,
   J.; Corbard, T.; De Rosa, M.; Genovese, C. R.; Gough, D. O.; Haber,
   D. A.; Harvey, J. W.; Hill, F.; Howe, R.; Korzennik, S. G.; Kosovichev,
   A. G.; Leibacher, J. W.; Pijpers, F. P.; Provost, J.; Rhodes, E. J.,
   Jr.; Schou, J.; Sekii, T.; Stark, P. B.; Wilson, P. R.
Bibcode: 1996Sci...272.1300T
Altcode:
  Splitting of the sun's global oscillation frequencies by large-scale
  flows can be used to investigate how rotation varies with radius
  and latitude within the solar interior. The nearly uninterrupted
  observations by the Global Oscillation Network Group (GONG) yield
  oscillation power spectra with high duty cycles and high signal-to-noise
  ratios. Frequency splittings derived from GONG observations confirm
  that the variation of rotation rate with latitude seen at the surface
  carries through much of the convection zone, at the base of which is
  an adjustment layer leading to latitudinally independent rotation at
  greater depths. A distinctive shear layer just below the surface is
  discernible at low to mid-latitudes.

Title: Propagation of electromagnetic waves in inhomogeneous plasmas
Authors: Busatti, E.; Ciucci, A.; De Rosa, M.; Palleschi, V.; Rastelli,
   S.; Lontano, M.; Lunin, N.
Bibcode: 1994JPlPh..52..443B
Altcode:
  The reflection and transmission coefficients for an electromagnetic
  beam propagating in an inhomogeneous plasma are calculated analytically
  using the Magnus approximation in different physical configurations. The
  theoretical predictions for such coefficients are expressed in simple
  analytical form, and are compared with the exact results obtained by
  numerical solution of the wave propagation equations, using the Berreman
  4 × 4 matrix method. It is shown that the theoretical approach is
  able to reproduce the correct results for reflection and transmission
  coefficients over a wide range of physical parameters. The accuracy
  of the theoretical analysis, at different orders of approximation,
  is also discussed.

