explanation      blue bibcodes open ADS page with paths to full text
Author name code: kosovichev
ADS astronomy entries on 2022-09-14
author:"Kosovichev, Alexander G." 

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Title: Implicit large eddy simulations of global solar convection:
    effects of numerical resolution in non-rotating and rotating cases
Authors: Guerrero, G.; Stejko, A. M.; Kosovichev, A. G.; Smolarkiewicz,
   P. K; Strugarek, A.
2022arXiv220805738G    Altcode:
  Simulating deep solar convection and its coupled mean-field motions is
  a formidable challenge where few observational results constrain models
  that suffer from the non-physical influence of the grid resolution. We
  present hydrodynamic global Implicit Large-Eddy simulations (ILES) of
  deep solar convection performed with the EULAG-MHD code, and explore
  the effects of grid resolution on the properties of rotating and
  non-rotating convection. The results, based on low-order moments
  and turbulent spectra reveal that convergence could be achieved
  in non-rotating simulations provided sufficient resolution in the
  radial direction. The flow is highly anisotropic, with the energy
  contained in horizontal divergent motions exceeding by more than
  three orders of magnitude their radial counterpart. By contrast, in
  rotating simulations the largest energy is in the toroidal part of the
  horizontal motions. As the grid resolution increases, the turbulent
  correlations change in such a way that a solar-like differential
  rotation, obtained in the simulation with the coarser grid, transitions
  to the anti-solar differential rotation. The reason for this change
  is the contribution of the effective viscosity to the balance of the
  forces driving large-scale flows. As the effective viscosity decreases,
  the angular momentum balance improves, yet the force balance in the
  meridional direction lessens, favoring a strong meridional flow that
  advects angular momentum towards the poles. The results suggest that
  obtaining the correct distribution of angular momentum may not be a
  mere issue of numerical resolution. Accounting for additional physics,
  such as magnetism or the near-surface shear layer, may be necessary
  in simulating the solar interior.

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Title: Spatial Scales and Time Variation of Solar Subsurface
    Convection
Authors: Getling, Alexander V.; Kosovichev, Alexander G.
2022arXiv220804642G    Altcode:
  Spectral analysis of the spatial structure of solar subphotospheric
  convection is carried out for subsurface flow maps constructed
  using the time--distance helioseismological technique. The source
  data are obtained from the Helioseismic and Magnetic Imager
  (HMI) onboard Solar Dynamics Observatory (SDO) from 2010 May to
  2020 September. A spherical-harmonic transform is applied to the
  horizontal-velocity-divergence field at depths from 0 to 19~Mm. The
  range of flow scales is fairly broad in shallow layers and narrows
  as the depth increases. The horizontal flow scales rapidly increase
  with depth, from supergranulation to giant-cell values, and indicate
  the existence of large-scale convective motions in the near-surface
  shear layer. The results can naturally be interpreted in terms of
  a superposition of differently scaled flows localized in different
  depth intervals. There is some tendency toward the emergence of
  meridionally elongated (banana-shaped) convection structures in the
  deep layers. The total power of convective flows is anticorrelated
  with the sunspot-number variation over the solar activity cycle in
  shallow subsurface layers and positively correlated at larger depths,
  which is suggestive of the depth redistribution of the convective-flow
  energy due to the action of magnetic fields.

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Title: Constraining Global Solar Models through Helioseismic Analysis
Authors: Stejko, Andrey M.; Kosovichev, Alexander G.; Featherstone,
   Nicholas A.; Guerrero, Gustavo; Hindman, Bradley W.; Matilsky, Loren
   I.; Warnecke, Jörn
2022ApJ...934..161S    Altcode: 2022arXiv220405207S
  Global hydrodynamic simulations of internal solar dynamics have focused
  on replicating the conditions for solar-like (equator rotating faster
  than the poles) differential rotation and meridional circulation using
  the results of helioseismic inversions as a constraint. Inferences
  of meridional circulation, however, have provided controversial
  results showing the possibility of one, two, or multiple cells along
  the radius. To help address this controversy and develop a more
  robust understanding of global flow regimes in the solar interior,
  we apply a "forward-modeling" approach to the analysis of helioseismic
  signatures of meridional circulation profiles obtained from numerical
  simulations. We employ the global acoustic modeling code GALE to
  simulate the propagation of acoustic waves through regimes of mean
  mass-flows generated by global hydrodynamic and magnetohydrodynamic
  models: EULAG, the Pencil code, and the Rayleigh code. These models are
  used to create synthetic Dopplergram data products, used as inputs for
  local time-distance helioseismology techniques. Helioseismic travel-time
  signals from solutions obtained through global numerical simulations
  are compared directly with inferences from solar observations, in
  order to set additional constraints on global model parameters in a
  direct way. We show that even though these models are able to replicate
  solar-like differential rotation, the resulting rotationally constrained
  convection develops a multicell global meridional circulation profile
  that is measurably inconsistent with local time-distance inferences
  of solar observations. However, we find that the development of
  rotationally unconstrained convection close to the model surface is able
  to maintain solar-like differential rotation, while having a significant
  impact on the helioseismic travel-time signal, replicating solar
  observations within one standard deviation of the error due to noise.

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Title: Physics-based Modeling of Multiscale Solar Dynamics for
    Understanding Origins of Space Weather Disturbances
Authors: Kitiashvili, Irina; Sadykov, Viacheslav; Wray, Alan;
   Kosovichev, Alexander
2022cosp...44.3232K    Altcode:
  Forecasting space weather on different temporal scales is a problem that
  requires the development of advanced physics-based models, algorithms,
  and data analysis approaches for a variety of observations and their
  inferences. We take advantage of currently available computational
  capabilities to model solar dynamics from the deep interior to
  the corona and investigate mechanisms that may drive space weather
  conditions. Comparison of the synthetic observables obtained from
  numerical simulations and actual observations allows us to uncover
  physical processes associated with observed phenomena. To facilitate a
  transition from modeling short-term physical phenomena to developing a
  reliable forecast-oriented model, we suggest using the data assimilation
  approach. It allows us to cross-analyze dynamo model solutions and
  observations and to consider possible uncertainties and errors. Our
  results demonstrate promising potential for modeling upcoming solar
  activity combined with observations. In this presentation, we briefly
  summarize current multi-scale modeling capabilities and results
  and discuss ongoing developments to build a reliable physics-based
  forecast-oriented model of solar activity.

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Title: Helioseismic Monitoring of Solar Subsurface Dynamics and
    Activity
Authors: Kosovichev, Alexander; Pipin, Valery; Getling, Alexander;
   Stejko, Andrey; Stefan, John; Guerrero, Gustavo
2022cosp...44.3215K    Altcode:
  Uninterrupted helioseismic data from Michelson Doppler Imager (MDI)
  onboard Solar and Heliospheric Observatory (SoHO) and from Helioseismic
  and Magnetic Imager (HMI) onboard Solar Dynamics Observatory (SDO)
  have provided unique information about flows and structures evolving
  on various temporal and spatial scales inside the Sun. The data
  cover the past two solar cycles and the rising phase of the current
  solar cycle. In particular, our analysis of variations of the internal
  differential rotation reveals "extended" cyclic variations of migrating
  zonal flows ("torsional oscillations") through the whole convection
  zone. The observed patterns of subsurface flow acceleration provide
  evidence of hydromagnetic dynamo waves, which control the strength
  of sunspot cycles, and potentially carry information about the future
  solar cycles. Similarly, "extended" cyclic variations of the subsurface
  meridional circulation, detected by local helioseismic techniques,
  reflect the evolution of subsurface magnetic fields and emerging
  magnetic flux. Furthermore, to monitor emerging active regions, we
  develop a "deep-focus" helioseismic diagnostics, which allows us to
  detect large emerging active regions before they become visible on
  the surface. We present recent advances in helioseismic monitoring
  of solar activity and discuss helioseismic constraints on models of
  global solar variability and space weather forecasting.

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Title: Characterization of Stellar Jitter Using 3D Realistic Modeling
    of Solar-Type Stars
Authors: Kitiashvili, Irina; Granovsky, Samuel; Wray, Alan; Kosovichev,
   Alexander
2022AAS...24041702K    Altcode:
  Recent progress in the ab-initio modeling of solar magnetoconvection
  makes it possible to simulate the surface dynamics of solar-type
  stars with a high degree of realism. These simulations can be used
  to characterize stellar photospheric disturbances which contaminate
  the radial velocity signal and limit our capabilities to detect
  Earth-mass exoplanets. We use the 3D radiative MHD "StellarBox" code
  to obtain realistic stellar (magneto)convection models and characterize
  photospheric noise. The initial conditions for the numerical simulations
  are generated using the MESA stellar evolution code. The computational
  domain covers the upper layers of the convection zone and the lower
  atmosphere. We present numerical models of solar-type planet-host stars,
  disk-integrated synthetic observations, and observables such as line
  profiles, Doppler shift, etc. Synthesis of observations performed for
  a list of FeI lines using the radiative transfer "Spinor" code. We
  present the stellar jitter modeling results for selected target stars,
  discuss the origin of the noise and compare with high-resolution
  HARPS observations.

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Title: Simulating Solar Near-surface Rossby Waves by Inverse Cascade
    from Supergranule Energy
Authors: Dikpati, Mausumi; Gilman, Peter A.; Guerrero, Gustavo
   A.; Kosovichev, Alexander G.; McIntosh, Scott W.; Sreenivasan,
   Katepalli. R.; Warnecke, Jörn; Zaqarashvili, Teimuraz V.
2022ApJ...931..117D    Altcode:
  Rossby waves are found at several levels in the Sun, most recently in
  its supergranule layer. We show that Rossby waves in the supergranule
  layer can be excited by an inverse cascade of kinetic energy from the
  nearly horizontal motions in supergranules. We illustrate how this
  excitation occurs using a hydrodynamic shallow-water model for a 3D
  thin rotating spherical shell. We find that initial kinetic energy
  at small spatial scales inverse cascades quickly to global scales,
  exciting Rossby waves whose phase velocities are similar to linear
  Rossby waves on the sphere originally derived by Haurwitz. Modest
  departures from the Haurwitz formula originate from nonlinear finite
  amplitude effects and/or the presence of differential rotation. Like
  supergranules, the initial small-scale motions in our model contain
  very little vorticity compared to their horizontal divergence, but the
  resulting Rossby waves are almost all vortical motions. Supergranule
  kinetic energy could have mainly gone into gravity waves, but we find
  that most energy inverse cascades to global Rossby waves. Since kinetic
  energy in supergranules is three or four orders of magnitude larger
  than that of the observed Rossby waves in the supergranule layer,
  there is plenty of energy available to drive the inverse-cascade
  mechanism. Tachocline Rossby waves have previously been shown to
  play crucial roles in causing seasons of space weather through their
  nonlinear interactions with global flows and magnetic fields. We briefly
  discuss how various Rossby waves in the tachocline, convection zone,
  supergranule layer, and corona can be reconciled in a unified framework.

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Title: Detection of Phase Travel Time Anisotropy from Subsurface
    Horizontal Magnetic Fields in the Sun
Authors: Stefan, John; Kosovichev, Alexander
2022AAS...24035014S    Altcode:
  We derive a helioseismic measurement technique which isolates phase
  travel time deviations caused by horizontal magnetic fields from
  other contributions such as sound speed perturbations and flows. The
  technique also allows for the azimuth of the subsurface magnetic field
  to be determined in addition to a direct proxy for the horizontal
  field's magnitude. We validate this technique using two independent
  MHD simulations. The first model simulates propagation of acoustic
  waves from a point source in a uniform, inclined magnetic field, and
  we recover the correct azimuth and the expected travel time anisotropy
  from ray theory. The second model simulates a realistic sunspot with
  non-uniform magnetic field, where we find the anisotropy and azimuth
  of the subsurface magnetic field. Finally, we apply the technique to
  several active regions observed by HMI (Helioseismic and Magnetic
  Imager) and examine characteristics of the subsurface horizontal
  magnetic field at depths z=-5 to -7 Mm, -7 to -10 Mm, and -10 to -13 Mm.

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Title: Detection of Travel Time Anisotropy from Subsurface Horizontal
    Magnetic Fields
Authors: Stefan, John T.; Kosovichev, Alexander G.
2022ApJ...930...10S    Altcode: 2022arXiv220303495S
  A time-distance measurement technique is derived to isolate phase
  travel time anisotropy caused by subsurface horizontal magnetic
  fields; a method that uses the measured anisotropy to estimate the
  field's orientation is also derived. A simulation of acoustic waves
  propagating in a uniform, inclined magnetic field with solar background
  structure is used to verify the derived technique. Then the procedure is
  applied to a numerical simulation of a sunspot for which the subsurface
  state is known to provide context for the results obtained from the
  study of several sunspots observed by the Helioseismic and Magnetic
  Imager. Significant anisotropies are detected, on the order of 1 minute,
  and the subsurface field's azimuth is estimated and compared with the
  azimuth of the surface magnetic field. In all cases, the subsurface
  azimuth is found to be well aligned with that of the surface, and the
  results from the numerical simulation are used to interpret features
  in the detected travel time anisotropy.

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Title: Numerical Convergence of 2D Solar Convection in Implicit
    Large-eddy Simulations
Authors: Nogueira, H. D.; Guerrero, G.; Smolarkiewicz, P. K.;
   Kosovichev, A. G.
2022ApJ...928..148N    Altcode: 2022arXiv220202767N
  Large-eddy simulations (LES) and implicit LES (ILES) are wise
  and affordable alternatives to the unfeasible direct numerical
  simulations of turbulent flows at high Reynolds (Re) numbers. However,
  for systems with few observational constraints, it is a formidable
  challenge to determine if these strategies adequately capture the
  physics of the system. Here, we address this problem by analyzing
  numerical convergence of ILES of turbulent convection in 2D, with
  resolutions between 64<SUP>2</SUP> and 2048<SUP>2</SUP> grid points,
  along with the estimation of their effective viscosities, resulting
  in effective Reynolds numbers between 1 and ~10<SUP>4</SUP>. The
  thermodynamic structure of our model resembles the solar interior,
  including a fraction of the radiative zone and the convection zone. In
  the convective layer, the ILES solutions converge for the simulations
  with ≥512<SUP>2</SUP> grid points, as evidenced by the integral
  properties of the flow and its power spectra. Most importantly,
  we found that even a resolution of 128<SUP>2</SUP> grid points,
  $\mathrm{Re}\,\sim \,10$ , is sufficient to capture the dynamics
  of the large scales accurately. This is a consequence of the ILES
  method allowing the energy contained in these scales to be the same in
  simulations with low and high resolution. Special attention is needed
  in regions with a small density scale height driving the formation of
  fine structures unresolved by the numerical grid. In the stable layer,
  we found the excitation of internal gravity waves, yet high resolution
  is needed to capture their development and interaction.

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Title: Advances and Challenges in Observations and Modeling of the
    Global-Sun Dynamics and Dynamo
Authors: Kosovichev, A. G.; Guerrero, G.; Stejko, A. M.; Pipin, V. V.;
   Getling, A. V.
2022arXiv220310721K    Altcode:
  Computational heliophysics has shed light on the fundamental physical
  processes inside the Sun, such as the differential rotation, meridional
  circulation, and dynamo-generation of magnetic fields. However,
  despite the substantial advances, the current results of 3D MHD
  simulations are still far from reproducing helioseismic inferences
  and surface observations. The reason is the multi-scale nature of
  the solar dynamics, covering a vast range of scales, which cannot be
  solved with the current computational resources. In such a situation,
  significant progress has been achieved by the mean-field approach,
  based on the separation of small-scale turbulence and large-scale
  dynamics. The mean-field simulations can reproduce solar observations,
  qualitatively and quantitatively, and uncover new phenomena. However,
  they do not reveal the complex physics of large-scale convection,
  solar magnetic cycles, and the magnetic self-organization that causes
  sunspots and solar eruptions. Thus, developing a synergy of these
  approaches seems to be a necessary but very challenging task.

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Title: Leptocline as a Shallow Substructure of Near-Surface Shear
    Layer in 3D Radiative Hydrodynamic Simulations
Authors: Kitiashvili, Irina N.; Kosovichev, Alexander G.; Wray,
   Alan A.; Sadykov, Viacheslav M.; Guerrero, Gustavo
2022arXiv220301484K    Altcode:
  Understanding effects driven by rotation in the solar convection zone
  is essential for many problems related to solar activity, such as
  the formation of differential rotation, meridional circulation, and
  others. We analyze realistic 3D radiative hydrodynamics simulations
  of solar subsurface dynamics in the presence of rotation in a local
  domain 80 Mm wide and 25 Mm deep, located at 30 degrees latitude. The
  simulation results reveal the development of a shallow 10-Mm deep
  substructure of the Near-Surface Shear Layer (NSSL), characterized
  by a strong radial rotational gradient and self-organized meridional
  flows. This shallow layer ("leptocline") is located in the hydrogen
  ionization zone associated with enhanced anisotropic overshooting-type
  flows into a less unstable layer between the H and HeII ionization
  zones. We discuss current observational evidence of the presence of
  the leptocline and show that the radial variations of the differential
  rotation and meridional flow profiles obtained from the simulations
  in this layer qualitatively agree with helioseismic observations.

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Title: Revisiting the Solar Research Cyberinfrastructure Needs:
    A White Paper of Findings and Recommendations
Authors: Nita, Gelu; Ahmadzadeh, Azim; Criscuoli, Serena;
   Davey, Alisdair; Gary, Dale; Georgoulis, Manolis; Hurlburt, Neal;
   Kitiashvili, Irina; Kempton, Dustin; Kosovichev, Alexander; Martens,
   Piet; McGranaghan, Ryan; Oria, Vincent; Reardon, Kevin; Sadykov,
   Viacheslav; Timmons, Ryan; Wang, Haimin; Wang, Jason T. L.
2022arXiv220309544N    Altcode:
  Solar and Heliosphere physics are areas of remarkable data-driven
  discoveries. Recent advances in high-cadence, high-resolution
  multiwavelength observations, growing amounts of data from realistic
  modeling, and operational needs for uninterrupted science-quality data
  coverage generate the demand for a solar metadata standardization and
  overall healthy data infrastructure. This white paper is prepared as
  an effort of the working group "Uniform Semantics and Syntax of Solar
  Observations and Events" created within the "Towards Integration of
  Heliophysics Data, Modeling, and Analysis Tools" EarthCube Research
  Coordination Network (@HDMIEC RCN), with primary objectives to discuss
  current advances and identify future needs for the solar research
  cyberinfrastructure. The white paper summarizes presentations and
  discussions held during the special working group session at the
  EarthCube Annual Meeting on June 19th, 2020, as well as community
  contribution gathered during a series of preceding workshops and
  subsequent RCN working group sessions. The authors provide examples
  of the current standing of the solar research cyberinfrastructure, and
  describe the problems related to current data handling approaches. The
  list of the top-level recommendations agreed by the authors of the
  current white paper is presented at the beginning of the paper.

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Title: Spatial Spectrum of Solar Convection from Helioseismic Data:
    Flow Scales and Time Variations
Authors: Getling, Alexander V.; Kosovichev, Alexander G.
2022arXiv220100638G    Altcode:
  We analyze spectral properties of solar convection in the range of
  depths from 0 to 19~Mm using subsurface flow maps obtained by the
  time-distance heiioseismology analysis of solar-oscillation data from
  the Helioseismic and Magnetic Imager (HMI) onboard Solar Dynamics
  Observatory (SDO) from May 2010 to September 2020. The results reveal
  a rapid increase of the horizontal flow scales with the depth, from
  supergranulation to giant-cell scales, and support the evidence of
  large-scale convection, previously detected by tracking the motion of
  supergranular cells on the surface. The total power of convective flows
  correlates with the solar activity cycle. During the solar maximum,
  the total power decreases in shallow subsurface layers and increases
  in the deeper layers.

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Title: Large-Scale Dynamics of Solar Subsurface Shear Layer:
    Theoretical Predictions and Helioseismic Inferences
Authors: Kosovichev, Alexander; Getling, Alexander; Guerrero, Gustavo;
   Pipin, Valery; Stejko, Andrey
2021AGUFMSH53C..03K    Altcode:
  Helioseismic observations show that the solar rotation rate sharply
  increases with depth in the outer 30 Mm-deep layers of the solar
  convection zone. This subsurface shear layer (SSL) plays a critical role
  in the formation of migrating activity belts (the butterfly diagram)
  and the emergence of active regions. Measurements of the rotation
  rate indicate that the magnetic field of sunspots and active regions
  is anchored in the subsurface shear layer. The magnetic structure of
  the SSL has not been directly measured by helioseismology, but it can
  be inferred by comparing variations of subsurface flows and sound-speed
  variations predicted by dynamo models with helioseismic measurements. To
  establish the connections between the flows and fields, we construct
  and analyze synoptic maps of subsurface flows in the SSL, obtained
  from time-distance helioseismic inversion during the whole Solar Cycle
  24 and the rising phase of Cycle 25. The results reveal the extended
  solar-cycle pattern of variations of the meridional circulation,
  predicted by the dynamo models and previously known from surface and
  subsurface observations of zonal flows. We discuss the origin of the
  observed variations and their links to the magnetism and dynamics of
  the subsurface shear layer.

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Title: Origin of Rossby waves observed near the solar surface
Authors: Gilman, Peter; Dikpati, Mausumi; Guerrero, Gustavo;
   Kosovichev, Alexander; McIntosh, Scott; Sreenivasan, Katepalli;
   Warnecke, Joern; Zaqarashvili, Teimuraz
2021AGUFMSH53C..04G    Altcode:
  Differential rotation and toroidal magnetic bands in the tachocline
  are unstable to MHD Rossby waves and may be responsible for patterns
  of solar activity seen in the photosphere. Helioseismic and surface
  velocity measurements reveal energetically neutral Rossby waves in the
  supergranulation layer. To explore plausible sources of energy for
  these Rossby waves, we study nonlinear dynamics of horizontal flows
  in the supergranular layer in thepresence of rotation and differential
  rotation. With a shallow-water model we show that kinetic energy, put
  into smallest resolved spatial scales, very quickly 'reverse cascades'
  to largest scales, exciting energetically neutral Rossby-Haurwitz type
  waves, as well as energetically active ones with low longitudinal
  spectral modes, depending on differential rotation. Horizontal
  velocities in supergranules are known to be much larger than their
  vertical motions; our shallow-water system includes a similar ratio. If
  supergranules are responsible for Rossby waves seen in photosphere, it
  paradoxically follows that (i) stable stratification of a thin rotating
  spherical shell may be a sufficient but not a necessary condition for
  Rossby waves, and (ii) small-scale convection producing global Rossby
  waves in a thin differentially rotating fluid may be the first ever
  example found in a celestial body.

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Title: Physical Properties of the Solar Atmosphere Derived from
    Comparison of Spectro-Polarimetric SDO/HMI Observables with 3D
    Radiative MHD Simulations
Authors: Sadykov, Viacheslav; Kitiashvili, Irina; Kosovichev,
   Alexander; Wray, Alan
2021AGUFMSH44A..06S    Altcode:
  In this study, we compare the SDO/HMI line-of-sight observables
  (magnetic field, velocity, continuum intensity, and line depth) with
  the related physical properties for dynamo simulations performed using
  the StellarBox 3D Radiative MHD code. The modeling of the Fe I 6173 A
  Stokes profiles is performed using the SPINOR radiative transfer code in
  the LTE approximation. The reproduced SDO/HMI line-of-sight pipeline is
  applied to the modeled spectra, and the observables are synthesized with
  high (numerical) and SDO/HMI (instrumental) resolutions. Correlations
  between the observables and the physical properties at various
  heights in the atmosphere are studied for a set of view angles (0,
  30, 45, 60, 70, and 80 degrees away from the solar disk center). It
  is found that SDO/HMI velocity and magnetic field (less prominently)
  observables are correlated with physical parameters at certain heights
  of the solar atmosphere. These heights increase from about 100-150 km
  above the photosphere for the disk center case to 300-600 km above the
  photosphere for the 80-degree case, however, are almost the same for
  the 0-60 degree projection angles. The integrated unsigned magnetic
  flux calculated from the observables underestimates the actual magnetic
  flux at strongest correlation heights for about 40% on average. The
  integrated continuum intensity as calculated from the observables
  is about 4-8% larger with respect to its actual values. In addition,
  we discuss a problem of contribution of unresolved magnetic elements
  to solar brightness based on the modeling data. The results improve
  physics-based interpretations of the SDO/HMI observables and provide a
  better understanding of the physical properties of the solar atmosphere.

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Title: 3D Radiative MHD Modeling of the Solar Atmospheric Dynamics
    and Structure
Authors: Kitiashvili, Irina; Sadykov, Viacheslav; Wray, Alan;
   Kosovichev, Alexander
2021AGUFMSH45B2370K    Altcode:
  Dramatic dynamical phenomena accompanied by strong thermodynamic
  and magnetic structuring are the primary drivers of great interest
  in studying the solar atmosphere with high spatial and temporal
  resolutions. Using current computational capabilities, it became
  possible to model the magnetized solar plasma in different regimes
  with a high degree of realism. To study the fine structuring of the
  solar atmosphere and dynamics, we use 3D MHD radiative models covering
  all layers from the upper convection zone to the corona. Realistic 3D
  radiative MHD modeling of the solar magnetoconvection and atmosphere
  allows us to generate synthetic observables that directly link the
  physical properties of the solar plasma to spectroscopic observables. We
  calculate series of synthetic spectropolarimetric imaging data that
  model observations from different space instruments: HMI and AIA (SDO),
  SOT (Hinode), and IRIS, as well as for the upcoming DKIST ground
  observations, and investigate how the observational data are linked
  to physical processes in the solar atmosphere. In the presentation,
  we discuss qualitative and quantitative changes of the atmospheric
  structure and dynamics at different layers of the solar atmosphere,
  properties of acoustic and surface gravity waves, sources of the local
  heating in the chromosphere-corona transition region, formation of
  shocks, and high-frequency oscillations in the corona, as well as
  manifestation of these phenomena in the modeled observables.

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Title: Dynamical Coupling of the Solar Subsurface Shear Layer and
    the Atmosphere
Authors: Kitiashvili, Irina; Sadykov, Viacheslav; Kosovichev,
   Alexander; Wray, Alan
2021AGUFMSH53C..01K    Altcode:
  The dynamical coupling of subsurface and surface layers of the Sun is
  crucial for understanding how phenomena observed in the solar atmosphere
  reflect the evolution of subsurface plasma flows in the present
  global-scale rotation. In this work, we use long time-series (over
  100-hours) of high-resolution 3D radiative hydrodynamic simulations
  obtained for an 80-Mm wide and 25-Mm deep computational domain, using
  the SolarBox code, to investigate the formation and dynamics of the
  Subsurface Shear Layer (SSL) and observational manifestations. The
  solar rotation is modeled in the f-plane approximation at 30 degrees
  latitude. The simulation results reveal the formation of the SSL, and
  meridional circulation. To compare the simulation results with the
  SDO/HMI observations, we generate synthetic time series of the Fe I
  (6173A) line profile for different locations on the solar disk, using
  the SPINOR radiative transfer code. The line-profile data are converted
  into the SDO/HMI observables using an HMI pipeline emulator and analyzed
  for both the modeled and instrumental resolutions. The analysis results
  reproduce the photospheric structure and dynamics as well as various
  helioseismic properties such as rotational frequency splitting, ring-
  and time-distance diagrams, and the center-to-limb effect. This work
  provides a basis for a deeper understanding of the solar subsurface
  dynamics and physical interpretation of observational data.

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Title: Simulating Exoplanet Host Star -Horologii from the Surface
    to the Bottom of the Convection Zone
Authors: Guerrero, Gustavo; Kitiashvili, Irina; Bonanno, Alfio;
   Kosovichev, Alexander
2021AGUFM.U44B..02G    Altcode:
  The G0 type, planet-hosting, star -Horologii has been observed for
  several years through different techniques. While there is still some
  debate about its rotational period (4-8 days), it seems conclusive that
  it exhibits a magnetic cycle of ~1.6 years. This short period allowed
  for constructing the first butterfly diagram for a star different from
  the Sun. The detailed study of this object provides unique opportunities
  to understand the dynamo operating in solar-like stars. In this work,
  we present realistic 3D radiative hydrodynamics simulations (RHD) of
  surface and subsurface convection of this star. The depth reached by
  these models connects with anelastic global MHD simulations (AMHD) of
  the -Horologiis dynamo. The RHD models provide an understanding of the
  structure and signal of surface convection and its spectra, allowing for
  direct comparison with high-resolution spectroscopic observations. The
  AMHD simulations enlighten the magnetic contribution to this signal. In
  addition, we provide predictions of the star differential rotation,
  meridional circulation and the alpha-Omega dynamo sustaining its
  magnetic field.

---------------------------------------------------------
Title: Multiscale Organization of Turbulent Convection in Global-Sun
    Simulations
Authors: Guerrero, Gustavo; Stejko, Andrey; Kosovichev, Alexander;
   Getling, Alexander; Smolarkiewicz, Piotr
2021AGUFMSH55D1885G    Altcode:
  Solar convection is at the core of fundamental phenomena such as
  differential rotation and meridional circulation and, ultimately, the
  solar dynamo. The governing mechanisms, amplitude, and dominant scales
  of convection in the solar interior remain under debate. Furthermore,
  the large Reynolds and Rayleigh numbers involved make it implausible
  to resolve all relevant scales using direct numerical simulation. In
  this work, we study solar convection through global, non-rotating, and
  non-magnetic implicit large-eddy simulations (ILES), using the 3D global
  hydrodynamic code EULAG. Our simulations exhibit a pattern of multiscale
  convection, clearly visible on the domain surface (~0.96 R), generated
  by a solar-like density and entropy stratification. Scale-splitting
  is evident at various depths throughout the model, with the upper
  boundary of convective cells penetrating surface layers, resembling
  solar-like convection. A continuous and coherent multiscale structure
  of convective cells is observed throughout the convective interior. The
  power peak of convective scales continuously shrinks with height to a
  maximum spherical harmonic degree of l = 40-50 on the model surface,
  compatible with reports of giant cell observations. Simulations are
  performed from low to high resolution to explore whether integral
  properties of convection, such as the RMS velocity, temperature
  profiles, and turbulent spectra, become independent of the mesh
  size. Results are compared with current observations of surface and
  sub-surface solar convection.

---------------------------------------------------------
Title: The Observational Uncertainty of Coronal Hole Boundaries in
    Automated Detection Schemes
Authors: Reiss, Martin; Muglach, Karin; Moestl, Christian; Arge,
   Charles; Bailey, Rachel; Delouille, Veronique; Garton, Tadhg; Hamada,
   Amr; Hofmeister, Stefan; Illarionov, Egor; Jarolim, Robert; Kirk,
   Michael; Kosovichev, Alexander; Krista, Larisza; Lee, Sangwoo; Lowder,
   Chris; MacNeice, Peter; Veronig, Astrid
2021AGUFMSH15G2083R    Altcode:
  Solar coronal holes are the observational manifestation of the solar
  magnetic field open to the heliosphere and are of pivotal importance
  for understanding the origin and acceleration of the solar wind. Space
  missions such as the Solar Dynamics Observatory now allow us to observe
  coronal holes in unprecedented detail. Instrumental effects and other
  factors, however, pose a challenge to automated detection of coronal
  holes in solar imagery. The science community addresses these challenges
  with a variety of detection schemes. Until now, scant attention has
  been paid to assessing the disagreement between these schemes. Here
  we present the first comprehensive comparison of widely-applied
  automated detection schemes in solar and space science. By tying
  together scientific expertise worldwide, we study a coronal hole
  observed by the Atmospheric Imaging Assembly instrument on 2018 May
  30. We find that the choice of detection scheme significantly affects
  the location of the coronal hole boundary. Depending on the detection
  scheme, the physical properties of the coronal hole including the area,
  mean intensity, and mean magnetic field strength vary by a factor of
  up to 4.5 between the maximum and minimum values. This presentation
  discusses the implications of these findings for coronal hole research
  from the past decade. We also outline future strategies on how to use
  our results to diagnose and improve coronal magnetic field models.

---------------------------------------------------------
Title: 3D Helioseismic Forward-Modeling and Analysis of Meridional
    Circulation
Authors: Stejko, Andrey; Kosovichev, Alexander; Pipin, Valery;
   Guerrero, Gustavo; Getling, Alexander; Smolarkiewicz, Piotr
2021AGUFMSH55D1870S    Altcode:
  The 3D Global Acoustic Linearized Euler (GALE) code is used to explore
  the variance in helioseismic signatures that result from various
  profiles of meridional circulation. The structure of meridional
  circulation regulates the redistribution of angular momentum and
  magnetic flux that governs the solar cycle. Forward-modeling is a useful
  tool in exploring the structure of meridional circulation and its impact
  on global parameters and can help resolve the current controversy
  between single and double-cell circulation profiles. Profiles of
  meridional circulation are generated using mean-field dynamo models,
  which induce a reverse flow near the base of the convection zone,
  characteristic of double-cell meridional circulation, with the inclusion
  of turbulent pumping (-effect) resulting from a strong rotational
  gradient in the region. These models provide physics-based mechanisms
  for the low-end in potential differences between single- and double-cell
  meridional circulation profiles. The resulting flows are used as
  background velocities in the linearized acoustic GALE codesimulating the
  stochastic excitation of acoustic perturbations. Techniques in local
  helioseismology are then applied to measure flow signatures, showing
  that within the observational time-period of the HMI instrument onboard
  Solar Dynamics Observatory, it may not be possible to definitively
  distinguish between single-cell and double-cell meridional circulation
  structure. This analysis is extended to models of meridional circulation
  generated in convectively-driven non-linear 3D global-Sun simulations
  to explore the helioseismic differences generated by these models and
  compare them with observations.

---------------------------------------------------------
Title: Examining Correlations Between Helioseismic Signatures of
    Active Regions and their Emergence
Authors: Stefan, John; Kosovichev, Alexander
2021AGUFMSH55D1866S    Altcode:
  Active regions, areas on the Sun characterized by their enhanced
  magnetic field, are known for their high flare productivity. Therefore,
  a comprehensive understanding of active regions and their evolution is
  key to developing effective space weather forecasting tools. In order
  to improve this understanding, a time-distance helioseismic method
  is applied to a collection of 70 active regions observed by the HMI
  instrument aboard SDO. The active regions in this analysis are chosen
  based on their eventual maximum size and longitude of emergence; those
  which reach a maximum size of at least 150 millionths of a hemisphere
  and emerge within 45 degrees of the disk center are selected. The
  corresponding Dopplergrams and Magnetograms are tracked and remapped
  for two days prior to emergence and one day after emergence. The
  time-distance method, building on the work of Ilonidis et al, reduces
  noise in helioseismic measurements by averaging many cross-correlations
  across depth - after shifting relative to reference travel times - and
  across the orientation and size of correlation axes. The time-distance
  method is used to obtain mean travel time perturbations and travel
  time differences between depths of 40 and 70 Mm. Correlations in the
  time delay between the magnitude of these travel time measurements
  and the unsigned magnetic flux on the surface are examined, and the
  relationship between an active regions size and magnitude of its
  magnitude field with travel time measurements is estimated.

---------------------------------------------------------
Title: Solar Gravitational Moments: What Are They and What Do They
    Do? A Short Comprehensive Review
Authors: Rozelot, J. P.; Kosovichev, A. G.
2021simi.conf...92R    Altcode:
  Among all the fundamental solar parameters, mass, diameter, surface
  gravity, temperature, luminosity..., all well inventoried since several
  years in reference books, multi-gravitational moments are not yet well
  documented. Several theoretical estimates have been proposed through
  different approaches, mainly theory of Figure, helioseismology. We
  will show their own merits. Exact values of multipolar gravitational
  moments are important as they are at the crossroads of solar physics,
  solar astrometry, celestial mechanics, and General Relativity. Their
  temporal variations are still often neglected; they are yet an essential
  aspect for constraining solar-cycle modeling or solar-evolution
  theories. They induced planet-planet inclinations in multi-transiting
  systems gravitating in the neighboring of a star. This paper emphasizes
  some key issues to understand the role of these parameters.

---------------------------------------------------------
Title: Probing Stellar Cores by Asteroseismic Inversions
Authors: Kosovichev, Alexander; Kitiashvili, Irina
2021tsc2.confE.130K    Altcode:
  Precision asteroseismology data from Kepler and TESS provide a unique
  opportunity to investigate the interior structure of stars at various
  stages of stellar evolution. Detection of mixed acoustic-gravity
  oscillation modes has opened perspectives for probing the properties
  of energy-generating cores. Most of the previous analysis was focused
  on fitting standard evolutionary stellar models using mode frequency
  splitting and scaling laws for oscillation properties. We present
  direct asteroseismic inversions using the method of optimally localized
  averages, which effectively eliminates the surface effects and attempts
  to resolve the stellar core structure.

---------------------------------------------------------
Title: Prediction of Solar Proton Events with Machine Learning:
    Comparison with Operational Forecasts and "All-Clear" Perspectives
Authors: Sadykov, Viacheslav; Kosovichev, Alexander; Kitiashvili,
   Irina; Oria, Vincent; Nita, Gelu M; Illarionov, Egor; O'Keefe, Patrick;
   Jiang, Yucheng; Fereira, Sheldon; Ali, Aatiya
2021arXiv210703911S    Altcode:
  Solar Energetic Particle events (SEPs) are among the most dangerous
  transient phenomena of solar activity. As hazardous radiation, SEPs may
  affect the health of astronauts in outer space and adversely impact
  current and future space exploration. In this paper, we consider the
  problem of daily prediction of Solar Proton Events (SPEs) based on
  the characteristics of the magnetic fields in solar Active Regions
  (ARs), preceding soft X-ray and proton fluxes, and statistics of solar
  radio bursts. The machine learning (ML) algorithm uses an artificial
  neural network of custom architecture designed for whole-Sun input. The
  predictions of the ML model are compared with the SWPC NOAA operational
  forecasts of SPEs. Our preliminary results indicate that 1) for the
  AR-based predictions, it is necessary to take into account ARs at
  the western limb and on the far side of the Sun; 2) characteristics
  of the preceding proton flux represent the most valuable input for
  prediction; 3) daily median characteristics of ARs and the counts of
  type II, III, and IV radio bursts may be excluded from the forecast
  without performance loss; and 4) ML-based forecasts outperform SWPC
  NOAA forecasts in situations in which missing SPE events is very
  undesirable. The introduced approach indicates the possibility of
  developing robust "all-clear" SPE forecasts by employing machine
  learning methods.

---------------------------------------------------------
Title: Travel Time Anisotropy Due to Subsurface Magnetic Fields
Authors: Stefan, J.; Kosovichev, A.
2021AAS...23811317S    Altcode:
  While there has been near-continuous observation of the Sun's surface
  magnetic field over the past few decades, there remains little insight
  concerning the configuration of the subsurface field. This work
  presents a simple helioseismic technique to estimate the orientation
  of the subsurface horizontal magnetic field as well as a proxy for
  the horizontal field's magnitude. The technique is applied to several
  HMI Dopplergram series of active regions and quiet-sun regions, with
  notable differences between the two. Some discussion on the challenges
  and limitations of the technique is provided.

---------------------------------------------------------
Title: The Origin Of The Extended Solar Cycle
Authors: Kosovichev, A.; Pipin, V.; Getling, A.
2021AAS...23830405K    Altcode:
  The extended 22-year solar cycle phenomenon, discovered in observations
  of the solar corona and variations of the solar differential rotation
  (torsional oscillations), represents a fundamental heliophysics problem
  linked to dynamo processes inside the Sun. As observed on the surface,
  the extended solar cycle starts during a sunspot maximum at high
  latitudes and consists of a relatively short polar branch (described
  as "rush to the poles") and a long equatorward branch that continues
  through the solar minimum and the next sunspot cycle. Helioseismic
  observations of the internal dynamics of the Sun during the last two
  solar activity cycles allow us to identify the dynamical processes
  associated with the extended solar cycle throughout the depth of the
  convective zone and to link them with dynamo models. Observational
  data obtained from the SoHO (1996-2010) and SDO (2010-2020) spacecraft
  represent measurements of the internal differential rotation, meridional
  circulation, and thermodynamic parameters. The data indicate that the
  development of a new extended solar cycle begins at about 60 degrees
  latitude at the base of the convective zone during the maximum of
  the previous cycle. Then, the process of magnetic field migration to
  the Sun's surface is divided into two branches: fast (in 1-2 years)
  migration to the poles in the high-latitude zone and slow migration to
  the equator at middle and low latitudes for ~ 10 years. The subsurface
  rotational shear layer (leptocline) plays a key role in the formation
  of the magnetic butterfly diagram. Both the zonal flows (torsional
  oscillations) and the meridional circulation reveal the 22-year
  pattern of the extended solar cycle. A self-consistent MHD model
  of the solar dynamo developed in the mean-field theory framework is
  in good qualitative and quantitative agreement with the helioseismic
  observations. The model shows that the extended solar-cycle phenomenon
  is caused by magnetic field quenching of the convective heat flux
  and modulation of the meridional circulation induced by the heat
  flux variations. The model explains why the solar minimum polar field
  predicts the next sunspot maximum and points to new possibilities for
  predicting solar cycles from helioseismological data.

---------------------------------------------------------
Title: Physical Properties of the Solar Atmosphere Derived from
    Comparison of Spectro-Polarimetric SDO/HMI Observables with 3D
    Radiative MHD Simulations
Authors: Sadykov, V.; Kitiashvili, I.; Kosovichev, A.; Wray, A.
2021AAS...23832804S    Altcode:
  In this study, we compare the SDO/HMI line-of-sight observables
  (magnetic field, velocity, continuum intensity, and line depth) with the
  related physical properties for several dynamo simulation runs performed
  using the "StellarBox" 3D Radiative MHD code. The modeling of the Fe I
  6173 Å Stokes profiles is performed using the SPINOR radiative transfer
  code in the LTE approximation. The reproduced SDO/HMI line-of-sight
  pipeline is applied to the modeled spectra, and the observables
  are synthesized with high (numerical) and SDO/HMI (instrumental)
  resolutions. Correlations between the observables and the physical
  properties at various heights in the atmosphere are studied for a set
  of view angles (0, 30, 45, 60, 70, and 80 degrees away from the solar
  disk center). It is found that the SDO/HMI magnetic field and velocity
  measurements are unambiguously correlated with physical parameters
  at certain heights of the solar atmosphere. These heights increase
  from about 100 km above the photosphere for the disk center case to
  300-600 km above the photosphere for the 80-degree case. The heights
  are found to be slightly lower in regions where stronger magnetic
  fields are found. The comparison of the photospheric magnetic flux and
  integrated continuum intensity derived from the SDO/HMI observables and
  high-resolution observations and spectra is discussed. The results
  of our study improve physics-based interpretations of the SDO/HMI
  observables and provide a better understanding of the physical
  properties of the solar atmosphere.

---------------------------------------------------------
Title: Analysis of Time-Distance Helioseismology for Detection of
    Emerging Active Regions
Authors: Stefan, John T.; Kosovichev, Alexander G.; Stejko, Andrey M.
2021ApJ...913...87S    Altcode: 2020arXiv201201367S
  A time-distance helioseismic technique, similar to the one used by
  Ilonidis et al., is applied to two independent numerical models of
  subsurface sound-speed perturbations to determine the spatial resolution
  and accuracy of phase travel time shift measurements. The technique is
  also used to examine pre-emergence signatures of several active regions
  observed by the Michelson Doppler Imager and the Helioseismic Magnetic
  Imager. In the context of similar measurements of quiet-Sun regions,
  three of the five studied active regions show strong phase travel
  time shifts several hours prior to emergence. These results form the
  basis of a discussion of noise in the derived phase travel time maps
  and possible criteria to distinguish between true and false-positive
  detection of emerging flux.

---------------------------------------------------------
Title: Understanding the Consequences Of Fields and Flows in the
    Interior and Exterior of the Sun (COFFIES)
Authors: Hoeksema, J. T.; Brummell, N.; Bush, R.; Hess Webber, S.;
   Kitiashvili, I.; Komm, R.; Kosovichev, A.; Mendez, B.; Scherrer, P.;
   Upton, L.; Wray, A.; Zevin, D.; The Coffies Team
2021AAS...23811322H    Altcode:
  The solar activity cycle is the Consequence Of Fields and Flows in the
  Interior and Exterior of the Sun (COFFIES). As a Phase-1 NASA DRIVE
  Science Center (DSC), COFFIES ultimately aims to develop a data-driven
  model of solar activity. To attain this goal COFFIES members are
  learning to work together effectively to perform the investigations
  needed to answer five primary science questions: <P />1) What drives
  varying large-scale motions in the Sun? <P />2) How do flows interact
  with the magnetic field to cause varying activity cycles? <P />3) Why
  do active regions emerge when and where they do? <P />4) What do the
  manifestations of activity and convection reveal about the internal
  processes? <P />5) How does our understanding of the Sun as a star
  inform us more generally about activity dynamics and structure? <P />The
  virtual COFFIES center brings together a broad spectrum of observers,
  data analysts, theorists, computational scientists, and educators
  who collaborate through interacting working groups of four principal
  science teams. The principal objectives of the four primary science
  teams are to 1) understand the generation of quasi-periodic stellar
  magnetic cycles, 2) further develop 3D physical models of interior
  dynamics and convection, 3) establish clear physical links between solar
  flow fields and near-surface observations, and 4) develop more robust
  helioseismic techniques to resolve solar interior flows. Additional
  cross-team activities are facilitated by teams for numerical modeling,
  center effectiveness, outreach and eduction, and diversity, equity,
  inclusion and access (DEIA).

---------------------------------------------------------
Title: The Observational Uncertainty of Coronal Hole Boundaries in
    Automated Detection Schemes
Authors: Reiss, Martin A.; Muglach, Karin; Möstl, Christian; Arge,
   Charles N.; Bailey, Rachel; Delouille, Véronique; Garton, Tadhg M.;
   Hamada, Amr; Hofmeister, Stefan; Illarionov, Egor; Jarolim, Robert;
   Kirk, Michael S. F.; Kosovichev, Alexander; Krista, Larisza; Lee,
   Sangwoo; Lowder, Chris; MacNeice, Peter J.; Veronig, Astrid; Cospar
   Iswat Coronal Hole Boundary Working Team
2021ApJ...913...28R    Altcode: 2021arXiv210314403R
  Coronal holes are the observational manifestation of the solar
  magnetic field open to the heliosphere and are of pivotal importance
  for our understanding of the origin and acceleration of the solar
  wind. Observations from space missions such as the Solar Dynamics
  Observatory now allow us to study coronal holes in unprecedented
  detail. Instrumental effects and other factors, however, pose a
  challenge to automatically detect coronal holes in solar imagery. The
  science community addresses these challenges with different detection
  schemes. Until now, little attention has been paid to assessing the
  disagreement between these schemes. In this COSPAR ISWAT initiative,
  we present a comparison of nine automated detection schemes widely
  applied in solar and space science. We study, specifically, a prevailing
  coronal hole observed by the Atmospheric Imaging Assembly instrument
  on 2018 May 30. Our results indicate that the choice of detection
  scheme has a significant effect on the location of the coronal hole
  boundary. Physical properties in coronal holes such as the area, mean
  intensity, and mean magnetic field strength vary by a factor of up
  to 4.5 between the maximum and minimum values. We conclude that our
  findings are relevant for coronal hole research from the past decade,
  and are therefore of interest to the solar and space research community.

---------------------------------------------------------
Title: Forward Modeling Helioseismic Signatures of One- and Two-cell
    Meridional Circulation
Authors: Stejko, Andrey M.; Kosovichev, Alexander G.; Pipin, Valery V.
2021ApJ...911...90S    Altcode: 2021arXiv210101220S
  Using a 3D global solver of the linearized Euler equations, we
  model acoustic oscillations over background velocity flow fields of
  single-cell meridional circulation with deep and shallow return flows
  as well as double-cell meridional circulation with strong and weak
  reversals. The velocities are generated using a mean-field hydrodynamic
  and dynamo model—moving through the regimes with minimal parameter
  changes, counterrotation near the base of the tachocline is induced
  by sign inversion of the nondiffusive action of turbulent Reynolds
  stresses (Λ-effect) due to the radial inhomogeneity of the Coriolis
  number. By mimicking the stochastic excitation of resonant modes in
  the convective interior, we simulate realization noise present in solar
  observations. Using deep-focusing to analyze differences in travel-time
  signatures between the four regimes, as well as comparing to solar
  observations, we show that current helioseismology techniques may offer
  important insights about the location and strength of the return flow;
  however, it may not currently be possible to definitively distinguish
  between profiles of single-cell or double-cell meridional circulation.

---------------------------------------------------------
Title: Characteristics of Sunquake Events Observed in Solar Cycle 24
Authors: Kosovichev, Alexander; Sharykin, Ivan
2021EGUGA..23.1461K    Altcode:
  Helioseismic response to solar flares ("sunquakes") occurs due to
  localized force or/and momentum impacts observed during the flare
  impulsive phase in the lower atmosphere. Such impacts may be caused by
  precipitation of high-energy particles, downward shocks, or magnetic
  Lorentz force. Understanding the mechanism of sunquakes is a key problem
  of the flare energy release and transport. Our statistical analysis
  of M-X class flares observed by the Solar Dynamics Observatory during
  Solar Cycle 24 has shown that contrary to expectations, many relatively
  weak M-class flares produced strong sunquakes, while for some powerful
  X-class flares, helioseismic waves were not observed or were weak. The
  analysis also revealed that there were active regions characterized by
  the most efficient generation of sunquakes during the solar cycle. We
  found that the sunquake power correlates with maximal values of the
  X-ray flux derivative better than with the X-ray class. The sunquake
  data challenge the current theories of solar flares.

---------------------------------------------------------
Title: Helioseismic Modeling of Background Flows
Authors: Stejko, Andrey M.; Kosovichev, Alexander G.; Mansour, Nagi N.
2021ApJS..253....9S    Altcode: 2020arXiv201103131S
  We present a three-dimensional (3D) numerical solver of the linearized
  compressible Euler equations (Global Acoustic Linearized Euler),
  used to model acoustic oscillations throughout the solar interior. The
  governing equations are solved in conservation form on a fully global
  spherical mesh (0 ≤ ϕ ≤ 2π, 0 ≤ θ ≤ π, 0 ≤ r ≤ R
  <SUB>⊙</SUB>) over a background state generated by the standard solar
  model S. We implement an efficient pseudospectral computational method
  to calculate the contribution of the compressible material derivative
  dyad to internal velocity perturbations, computing oscillations over
  arbitrary 3D background velocity fields. This model offers a foundation
  for a “forward-modeling” approach, using helioseismology techniques
  to explore various regimes of internal mass flows. We demonstrate the
  efficacy of the numerical method presented in this paper by reproducing
  observed solar power spectra, showing rotational splitting due to
  differential rotation, and applying local helioseismology techniques
  to measure travel times created by a simple model of single-cell
  meridional circulation.

---------------------------------------------------------
Title: Helioseismic Observations and Modeling of Solar Dynamo
Authors: Kosovichev, Alexander G.; Getling, Alexander V.; Pipin,
   Valery V.
2021csss.confE.115K    Altcode:
  Helioseismological observations of the internal dynamics of the
  Sun during the last two solar activity cycles make it possible
  to trace the development of solar dynamo processes throughout the
  depth of the convective zone and to link them with models of solar
  cycles. Observational data obtained from the SoHO (1996-2010) and
  SDO (2010-2020) spacecraft represent measurements of the internal
  differential rotation, meridional circulation, and thermodynamic
  parameters. The structure and dynamics of zonal and meridional
  plasma flows reveal the processes of generation and transfer of
  magnetic fields inside the Sun. The data analysis shows that active
  latitudes and regions of a strong polar field on the Sun's surface
  coincide with regions of deceleration of zonal currents ("torsional
  oscillations"). The observed structure of zonal flows and their
  latitudinal and radial migration in deep layers of the convective
  zone correspond to dynamo waves predicted by dynamo theories and
  numerical MHD models. The data indicate that the development of a new
  solar cycle begins at about 60 degrees latitude at the base of the
  convective zone during the maximum of the previous cycle. Then, the
  process of magnetic field migration to the Sun's surface is divided
  into two branches: fast (in 1-2 years) migration in the high-latitude
  zone and slow migration at middle and low latitudes for ~ 10 years. The
  subsurface rotational shear layer ("leptocline") plays a key role in
  the formation of the magnetic "butterfly diagram". Both the zonal
  flows ("torsional oscillations") and the meridional circulation
  reveal the 22-year pattern of the "extended" solar cycle, initially
  discovered from observations of Doppler velocities and the structure
  of the solar corona.A self-consistent MHD model of the solar dynamo
  developed in the mean-field theory framework is in good qualitative
  and quantitative agreement with the helioseismic observations. The
  model shows that the observed variations of the solar dynamics are
  associated with a magnetic field effect on convective heat transfer
  and the corresponding modulation of the meridional circulation. The
  model explains why the solar minimum polar field predicts the next
  sunspot maximum and points to new possibilities for predicting solar
  cycles from helioseismological data.

---------------------------------------------------------
Title: Compression of Solar Spectroscopic Observations: a Case Study
    of Mg II k Spectral Line Profiles Observed by NASA's IRIS Satellite
Authors: Sadykov, Viacheslav M; Kitiashvili, Irina N; Sainz Dalda,
   Alberto; Oria, Vincent; Kosovichev, Alexander G; Illarionov, Egor
2021arXiv210307373S    Altcode:
  In this study we extract the deep features and investigate the
  compression of the Mg II k spectral line profiles observed in quiet
  Sun regions by NASA's IRIS satellite. The data set of line profiles
  used for the analysis was obtained on April 20th, 2020, at the
  center of the solar disc, and contains almost 300,000 individual
  Mg II k line profiles after data cleaning. The data are separated
  into train and test subsets. The train subset was used to train the
  autoencoder of the varying embedding layer size. The early stopping
  criterion was implemented on the test subset to prevent the model from
  overfitting. Our results indicate that it is possible to compress the
  spectral line profiles more than 27 times (which corresponds to the
  reduction of the data dimensionality from 110 to 4) while having a 4 DN
  average reconstruction error, which is comparable to the variations in
  the line continuum. The mean squared error and the reconstruction error
  of even statistical moments sharply decrease when the dimensionality of
  the embedding layer increases from 1 to 4 and almost stop decreasing
  for higher numbers. The observed occasional improvements in training
  for values higher than 4 indicate that a better compact embedding may
  potentially be obtained if other training strategies and longer training
  times are used. The features learned for the critical four-dimensional
  case can be interpreted. In particular, three of these four features
  mainly control the line width, line asymmetry, and line dip formation
  respectively. The presented results are the first attempt to obtain
  a compact embedding for spectroscopic line profiles and confirm the
  value of this approach, in particular for feature extraction, data
  compression, and denoising.

---------------------------------------------------------
Title: Modeling Helioseismic Signatures of Meridional Circulation
Authors: Stejko, Andrey; Kosovichev, Alexander; Pipin, Valery
2021csss.confE.114S    Altcode:
  We present the application of a new 3D global linearized acoustic
  algorithm (GALE). With the wide variance of inferred profiles of
  meridional circulation currently being made from similar observational
  data, we choose a "forward-modeling" approach to test the helioseismic
  signatures generated by several physics-based mean-field models of
  meridional velocities. We simulate the effect of realization noise
  in measurements in order to place a low-end baseline for whether it
  is possible to see the difference between single- and double-cell
  meridional circulation. With minimal parameter changes between the
  two regimes we show that it may not be possible two distinguish these
  profiles within the operational time-frame of HMI. We also test several
  other profiles in an attempt to use mean-field theory to help constrain
  inferences made through helioseismology inversions.

---------------------------------------------------------
Title: Connecting Atmospheric Properties and Synthetic Emission of
    Shock Waves Using 3D RMHD Simulations of the Quiet Sun
Authors: Sadykov, Viacheslav M.; Kitiashvili, Irina N.; Kosovichev,
   Alexander G.; Wray, Alan A.
2021ApJ...909...35S    Altcode: 2020arXiv200805995S
  We analyze the evolution of shock waves in high-resolution 3D radiative
  MHD simulations of the quiet Sun and their synthetic emission
  characteristics. The simulations model the dynamics of a 12.8 ×
  12.8 × 15.2 Mm quiet-Sun region (including a 5.2 Mm layer of the
  upper convection zone and a 10 Mm atmosphere from the photosphere
  to corona) with an initially uniform vertical magnetic field of
  10 G, naturally driven by convective flows. We synthesize the Mg
  II and C II spectral lines observed by the Interface Region Imaging
  Spectrograph (IRIS) satellite and extreme ultraviolet emission observed
  by the Solar Dynamics Observatory (SDO)/AIA telescope. Synthetic
  observations are obtained using the RH1.5D radiative transfer code and
  temperature response functions at both the numerical and instrumental
  resolutions. We found that the Doppler velocity jumps of the C II 1334.5
  Å IRIS line and a relative enhancement of the emission in the 335 Å
  SDO/AIA channel are the best proxies for the enthalpy deposited by shock
  waves into the corona (with Kendall's τ correlation coefficients of
  0.59 and 0.38, respectively). The synthetic emission of the lines and
  the extreme ultraviolet passbands are correlated with each other during
  the shock-wave propagation. All studied shocks are mostly hydrodynamic
  (i.e., the magnetic energy carried by horizontal fields is ≤2.6%
  of the enthalpy for all events) and have Mach numbers &gt;1.0-1.2 in
  the low corona. The study reveals the possibility of diagnosing energy
  transport by shock waves into the solar corona, as well as their other
  properties, by using IRIS and SDO/AIA sensing observations.

---------------------------------------------------------
Title: Evolution of Subsurface Zonal and Meridional Flows in Solar
    Cycle 24 from Helioseismological Data
Authors: Getling, Alexander V.; Kosovichev, Alexander G.; Zhao, Junwei
2021ApJ...908L..50G    Altcode: 2020arXiv201215555G
  The results of determinations of the azimuthal and meridional
  velocities by time-distance helioseismology from Helioseismic and
  Magnetic Imager on board Solar Dynamics Observatory from 2010 May to
  2020 September at latitudes and Stonyhurst longitudes from - 60° to
  + 60° and depths to about 19 Mm below the photosphere are used to
  analyze spatiotemporal variations of the solar differential rotation
  and meridional circulation. The pattern of torsional oscillations,
  or latitudinal belts of alternating "fast" and "slow" zonal flows
  migrating from high latitudes toward the equator, is found to extend in
  the time-latitude diagrams over the whole time interval. The oscillation
  period is comparable with a doubled solar-activity-cycle and can be
  described as an extended solar cycle. The zonal-velocity variations
  are related to the solar-activity level, the local-velocity increases
  corresponding to the sunspot-number increases and being localized at
  latitudes where the strongest magnetic fields are recorded. The dramatic
  growth of the zonal velocities in 2018 appears to be a precursor of
  the beginning of Solar Cycle 25. The strong symmetrization of the
  zonal-velocity field by 2020 can be considered another precursor. The
  general pattern of poleward meridional flows is modulated by latitudinal
  variations similar to the extended-solar-cycle behavior of the zonal
  flows. During the activity maximum, these variations are superposed
  with a higher harmonic corresponding to meridional flows converging to
  the spot-formation latitudes. Our results indicate that variations of
  both the zonal and meridional flows exhibit the extended-solar-cycle
  behavior, which is an intrinsic feature of the solar dynamo.

---------------------------------------------------------
Title: 3D Realistic Modeling of Main-Sequence Stars with Shallow
    Outer Convection Zone
Authors: Kitiashvili, I. N.; Wray, A. A.; Kosovichev, A. G.
2021AAS...23741505K    Altcode:
  Our current state-of-the-art computer simulations allow us to build
  3D dynamical and radiation models of F-type stars from physical first
  principles. Using the stellar interior's structure from the MESA
  stellar evolution code as initial conditions, we generate models of
  main-sequence stars with the mass from 1.4 Msun to 2 Msun for various
  metallicity composition, in the range of [Fe/H] from -0.3 to 0.2. The
  radiative 3D dynamical stellar models obtained with the StellarBox
  code take into account the effects of turbulence, stellar abundances,
  and radiation. We investigate the turbulent dynamics from the radiative
  zone to the outer convection zone and the lower atmosphere for these
  stars and compare their turbulent properties. <P />Also, we investigate
  the effects of stellar rotation for a 1.47Msun star for rotational
  periods of 1 and 14 days. The simulations are performed for the
  different latitudinal location of the computation domain. The models
  reproduce the subsurface shear layer, structural changes of convection,
  and the tachocline, which is the interface between the inner radiative
  zone and the outer convection zone and plays a crucial role in stellar
  variability. In particular, the model results reveal the formation of
  differential rotation of an anti-solar type. The simulation results shed
  light on differential rotation properties, the excitation of oscillation
  modes, the tachocline's dynamics and structure, and support analysis
  and interpretation of observational data from Kepler and TESS missions.

---------------------------------------------------------
Title: COFFIES - Developing a Reliable Physical Model of the Solar
    Activity Cycle
Authors: Hoeksema, J. T.; Brummell, N.; Bush, R. I.; Komm, R.;
   Kosovichev, A. G.; Mendez, B.; Scherrer, P. H.; Upton, L.; Wray,
   A. A.; Zevin, D.
2020AGUFMSH0020007H    Altcode:
  The solar activity cycle is the Consequence Of Fields and Flows in
  the Interior and Exterior of the Sun (COFFIES). The COFFIES Drive
  Science Center ultimately aims to develop a data driven model of solar
  activity. The challenging goals are 1) to understand the generation
  of the quasi-periodic stellar magnetic cycles, 2) further develop 3D
  physical models of interior dynamics and convection, 3) establish the
  physical links between solar flow fields and near-surface observations,
  and 4) develop more robust helioseismic techniques to resolve solar
  interior flows. To reach these goals the COFFIES team is focusing on
  what is needed to answer five primary science questions: 1) What drives
  varying large-scale motions in the Sun? 2) How do flows interact with
  the magnetic field to cause varying activity cycles? 3) Why do active
  regions emerge when and where they do? 4) What do the manifestations
  of activity and convection reveal about the internal processes? And
  5) How does our understanding of the Sun as a star inform us more
  generally about activity dynamics and structure? The virtual COFFIES
  center is bringing together a broad spectrum of observers, analysts,
  theorists, computational scientists, and educators who collaborate
  through interacting teams focused on helioseismology, dynamos, solar
  convection, surface links, numerical modeling, center effectiveness,
  outreach, education, diversity and inclusion.

---------------------------------------------------------
Title: Helioseismic Constraints on the Solar Interior Dynamics
    and Dynamo
Authors: Kosovichev, A. G.; Brummell, N.; Dikpati, M.; Guerrero,
   G.; Kitiashvili, I.; Komm, R.; Korzennik, S.; Pipin, V.; Reiter, J.;
   Stejko, A.; Ulrich, R. K.; Warnecke, J.
2020AGUFMSH007..04K    Altcode:
  Uninterrupted helioseismic observations from the SoHO/MDI, SDO/HMI and
  GONG instruments for more than two decades provide unique observational
  data for studying the solar-cycle variations of the differential
  rotation, large-scale and meridional flows. The data also allows
  us to investigate changes in the thermodynamic structure associated
  with dynamo-generated magnetic fields. The wealth of global and local
  helioseismic data provides theoretical constraints on the solar dynamics
  and dynamo models. The synergy of helioseismic inferences with advanced
  MHD modeling sheds light on the origin of the solar activity cycles. It
  helps to understand better the physical processes that control the
  strength and duration of the cyclic magnetic activity and leads to
  new physics-based approaches for prediction of the solar cycles. We
  briefly overview the current status, discuss the solar dynamical
  structure and evolution revealed by helioseismic inversions and the
  forward-modeling method, and focus on the most critical points of the
  problem. In particular, we discuss recent advances in measurements and
  modeling of the solar-cycle variations of the meridional circulation
  and migrating zonal flows (torsional oscillations) on the solar surface
  and in the subsurface layers, the deep convection zone, and the solar
  tachocline. The relationships between the internal dynamics and the
  evolution of global magnetic fields lead to new ideas of how magnetic
  fields are generated and affect the solar flows and structure.

---------------------------------------------------------
Title: Multi-Wavelength Modeling and Analysis of the Center-to-Limb
    Effects of Solar Spectroscopy and Helioseismology
Authors: Kitiashvili, I.; Zhao, J.; Sadykov, V. M.; Criscuoli, S.;
   Kosovichev, A. G.; Wray, A. A.
2020AGUFMSH0020003K    Altcode:
  An accurate interpretation of observed solar dynamics with different
  instruments requires modeling solar magnetoconvection in different
  regimes, as well as taking into account center-to-limb effects,
  magnetic fields, and turbulence. Realistic 3D radiative MHD modeling
  of the solar magnetoconvection and atmosphere allows us to generate
  synthetic observables that directly link the physical properties of
  the solar plasma to spectroscopic and helioseismic observables. In
  this work, we investigate the influence of the center-to-limb effects
  for a wide range of wavelengths, which correspond to the operational
  lines of HMI/SDO, Hinode, DKIST, and other instruments. In particular,
  we discuss the wavelength-dependency of the center-to-limb helioseismic
  observations of acoustic travel times that are used for diagnostics of
  the deep meridional circulation, as well as 'concave' Sun effect. The
  presented study will support interpretation of helioseismic inversion
  results by taking into account realistic coupling of subsurface and
  atmosphere, and geometry-related effects. In particular, it allows us
  to improve accuracy of solar subsurface measurements from the SoHO and
  SDO missions, and resolve the long-standing problem of the meridional
  circulation and evolution with the solar cycle.

---------------------------------------------------------
Title: Early Detection of Emerging Magnetic Flux using Time-Distance
    Helioseismology
Authors: Stefan, J. T.; Kosovichev, A. G.
2020AGUFMSH0020011S    Altcode:
  We employ a time-distance measurement procedure, similar to the one
  used by Ilonidis et al in their 2013 work, to detect solar subsurface
  structures associated with emerging magnetic flux. We compute the
  spatially-averaged cross-covariance of Dopplergram signals, and fit to
  a Gabor wavelet so that the phase travel time of acoustic waves can be
  extracted. Deviations from the mean phase travel time are interpreted
  as fluctuations in density and gas pressure. We independently confirm
  the analysis of AR10488 from Stathis et al (2013), a result that was
  hotly debated after publishing. We also calibrate this time-distance
  method using numerical models provided by Hartlep et al (2011) and
  Stejko et al (under review). Based on this calibration, we propose an
  estimate for the magnitude of local sound-speed perturbations necessary
  to produce the observed signal.

---------------------------------------------------------
Title: Challenges and Advances in Modeling of the Solar Atmosphere:
    A White Paper of Findings and Recommendations
Authors: Criscuoli, Serena; Kazachenko, Maria; Kitashvili, Irina;
   Kosovichev, Alexander; Martínez Pillet, Valentín; Nita, Gelu;
   Sadykov, Viacheslav; Wray, Alan
2021arXiv210100011C    Altcode:
  The next decade will be an exciting period for solar astrophysics, as
  new ground- and space-based instrumentation will provide unprecedented
  observations of the solar atmosphere and heliosphere. The synergy
  between modeling effort and comprehensive analysis of observations
  is crucial for the understanding of the physical processes behind
  the observed phenomena. However, the unprecedented wealth of data on
  one hand, and the complexity of the physical phenomena on the other,
  require the development of new approaches in both data analysis and
  numerical modeling. In this white paper, we summarize recent numerical
  achievements to reproduce structure, dynamics, and observed phenomena
  from the photosphere to the low corona and outline challenges we expect
  to face for the interpretation of future observations.

---------------------------------------------------------
Title: Machine-learning Approach to Identification of Coronal Holes
    in Solar Disk Images and Synoptic Maps
Authors: Illarionov, Egor; Kosovichev, Alexander; Tlatov, Andrey
2020ApJ...903..115I    Altcode: 2020arXiv200608529I
  Identification of solar coronal holes (CHs) provides information both
  for operational space weather forecasting and long-term investigation
  of solar activity. Source data for the first problem are typically
  from the most recent solar disk observations, while for the second
  problem it is convenient to consider solar synoptic maps. Motivated
  by the idea that the concept of CHs should be similar for both cases
  we investigate universal models that can learn CH segmentation in
  disk images and reproduce the same segmentation in synoptic maps. We
  demonstrate that convolutional neural networks trained on daily disk
  images provide an accurate CH segmentation in synoptic maps and their
  pole-centric projections. Using this approach we construct a catalog of
  synoptic maps for the period of 2010-20 based on SDO/AIA observations
  in the 193 Å wavelength. The obtained CH synoptic maps are compared
  with magnetic synoptic maps in the time-latitude and time-longitude
  diagrams. The initial results demonstrate that while in some cases the
  CHs are associated with magnetic flux-transport events there are other
  mechanisms contributing to the CH formation and evolution. To stimulate
  further investigations the catalog of synoptic maps is published in
  open access.

---------------------------------------------------------
Title: Solar Multipolar Moments: an up-to-date Pedagogical
Approach. Implications for Stellar Properties. Part I: an Analytical
    Overview (TUTORIAL)
Authors: Rozelot, J. P.; Kosovichev, A. G.; Kilcik, A.; Sahin, S.;
   Xu, Y.; Javaraiah, J.; Georgieva, K.; Özgüҫ, A.
2020simi.conf....1R    Altcode:
  Solar gravitational multipolar moments have not been yet extensively
  analyzed. However, they are at the crossroads of solar physics,
  solar astrometry, celestial mechanics and General Relativity. Their
  values reflect the physics of solar models: non-rigid rotation, solar
  latitudinal rotation, solar- core properties, solar-cycle variations
  and structure evolution. Their temporal variations are still often
  neglected; they are yet an essential aspect for constraining
  solar-cycle modeling or solar-evolution theories. They induced
  planet-planet inclinations in multitransiting systems gravitating in
  the neighboring of a star, leading to key issues future studies. This
  paper is devoted to an analytical analysis; a second part will address
  an helioseismology analysis.

---------------------------------------------------------
Title: Torsional Oscillations in Dynamo Models with Fluctuations
    and Potential for Helioseismic Predictions of the Solar Cycles
Authors: Pipin, Valery V.; Kosovichev, Alexander G.
2020ApJ...900...26P    Altcode: 2020arXiv200408537P
  Using a nonlinear mean-field solar dynamo model, we study relationships
  between the amplitude of the "extended" mode of migrating zonal flows
  ("torsional oscillations") and magnetic cycles, and investigate whether
  properties the torsional oscillations in subsurface layers and in the
  deep convection zone can provide information about the future solar
  cycles. We consider two types of dynamo models: models with regular
  variations of the α-effect, and models with stochastic fluctuations,
  simulating "long-memory" and "short-memory" types of magnetic activity
  variations. It is found that torsional oscillation parameters, such the
  zonal acceleration, show a considerable correlation with the magnitude
  of the subsequent cycles with a time lag of 11-20 yr. The sign of the
  correlation and the time-lag parameters can depend on the depth and
  latitude of the torsional oscillations as well as on the properties of
  long-term ("centennial") variations of the dynamo cycles. The strongest
  correlations are found for the zonal acceleration at high latitudes
  at the base of the convection zone. The model results demonstrate that
  helioseismic observations of the torsional oscillations can be useful
  for advanced prediction of the solar cycles, 1-2 sunspot cycles ahead.

---------------------------------------------------------
Title: Early Detection of Emerging Magnetic Flux
Authors: Stefan, J.; Kosovichev, A.
2020SPD....5120401S    Altcode:
  We employ a time-distance measurement procedure, similar to the one
  used by Ilonidis et al in their 2013 work, to detect solar subsurface
  structures associated with emerging magnetic flux. We compute the
  spatially-averaged cross-covariance of Dopplergram signals, and fit to
  a Gabor wavelet so that the phase travel time of acoustic waves can be
  extracted. Deviations from the mean phase travel time are interpreted as
  fluctuations in density and gas pressure. We independently confirm the
  analysis of AR10488 from Stathis et al (2013), a result that was hotly
  debated after publishing. We also calibrate this time-distance method
  using numerical models provided by Hartlep et al (2011) and Stejko
  et al (2020, this meeting). Based on this calibration, we propose an
  estimate for the magnitude of local sound-speed perturbations necessary
  to produce the observed signal.

---------------------------------------------------------
Title: Machine Learning in Heliophysics and Space Weather Forecasting:
    A White Paper of Findings and Recommendations
Authors: Nita, Gelu; Georgoulis, Manolis; Kitiashvili, Irina; Sadykov,
   Viacheslav; Camporeale, Enrico; Kosovichev, Alexander; Wang, Haimin;
   Oria, Vincent; Wang, Jason; Angryk, Rafal; Aydin, Berkay; Ahmadzadeh,
   Azim; Bai, Xiaoli; Bastian, Timothy; Filali Boubrahimi, Soukaina; Chen,
   Bin; Davey, Alisdair; Fereira, Sheldon; Fleishman, Gregory; Gary, Dale;
   Gerrard, Andrew; Hellbourg, Gregory; Herbert, Katherine; Ireland,
   Jack; Illarionov, Egor; Kuroda, Natsuha; Li, Qin; Liu, Chang; Liu,
   Yuexin; Kim, Hyomin; Kempton, Dustin; Ma, Ruizhe; Martens, Petrus;
   McGranaghan, Ryan; Semones, Edward; Stefan, John; Stejko, Andrey;
   Collado-Vega, Yaireska; Wang, Meiqi; Xu, Yan; Yu, Sijie
2020arXiv200612224N    Altcode:
  The authors of this white paper met on 16-17 January 2020 at the New
  Jersey Institute of Technology, Newark, NJ, for a 2-day workshop that
  brought together a group of heliophysicists, data providers, expert
  modelers, and computer/data scientists. Their objective was to discuss
  critical developments and prospects of the application of machine and/or
  deep learning techniques for data analysis, modeling and forecasting
  in Heliophysics, and to shape a strategy for further developments in
  the field. The workshop combined a set of plenary sessions featuring
  invited introductory talks interleaved with a set of open discussion
  sessions. The outcome of the discussion is encapsulated in this white
  paper that also features a top-level list of recommendations agreed
  by participants.

---------------------------------------------------------
Title: A Method for the Estimation of f- and p-mode Parameters and
    Rotational Splitting Coefficients from Un-averaged Solar Oscillation
    Power Spectra
Authors: Reiter, J.; Rhodes, E. J., Jr.; Kosovichev, A. G.; Scherrer,
   P. H.; Larson, T. P.; , S. F. Pinkerton, II
2020ApJ...894...80R    Altcode:
  We present a new methodology for the fitting of the peaks in
  solar oscillation power spectra that is equally well-suited for the
  estimation of low-, medium, and high-degree f- and p-mode parameters and
  frequency-splitting coefficients. The method can provide accurate input
  data over a wide portion of the dispersion plane for both structural and
  rotational inversions. This method, which we call the Multiple-Peak,
  Tesseral-Spectrum (MPTS) method, operates directly upon of all of the
  modes in a multiplet (n, l) of radial order n and degree l, and employs
  a fitting profile that consists of the sum of numerous individual
  overlapping profiles whose relative amplitudes are determined by the
  leakage matrix appropriate to the targeted mode. Hence, 2l + 1 sets
  of modal parameters are obtained simultaneously for each multiplet
  (n, l). By fitting an appropriate polynomial to the run of the
  fitted frequencies versus the azimuthal order, frequency-splitting
  coefficients are also obtained for the same multiplet. Using power
  spectra obtained from the 66 day long 2010 MDI Dynamics Run, we
  present sample structural and rotational inversions that employed
  frequencies and frequency-splitting coefficients from modes in the
  degree range of 0-1000 and the frequency range of 965-4600 μHz. The
  structural inversion confirms evidence for a pronounced departure of
  the sound speed in the outer solar convection zone from the radial
  sound-speed profile contained in Model S of Christensen-Dalsgaard
  and his collaborators that we obtained previously using a different
  fitting method.

---------------------------------------------------------
Title: Sunquakes of Solar Cycle 24
Authors: Sharykin, Ivan N.; Kosovichev, Alexander G.
2020ApJ...895...76S    Altcode: 2019arXiv191104197S
  The paper presents results of a search for helioseismic events
  (sunquakes) produced by M-X class solar flares during Solar Cycle
  24. The search is performed by analyzing photospheric Dopplergrams
  from the Helioseismic Magnetic Imager. Among the total number of 500
  M-X class flares, 94 helioseismic events were detected. Our analysis
  has shown that many strong sunquakes were produced by solar flares of
  low M class (M1-M5), while in some powerful X-class flares helioseismic
  waves were not observed or were weak. Our study has also revealed that
  only several active regions were characterized by the most efficient
  generation of helioseismic waves during flares. We found that the
  sunquake power correlates with the maximum value of the soft X-ray flux
  time derivative better than with the X-ray class, indicating that the
  sunquake mechanism is associated with high-energy particles. We also
  show that the seismically active flares are more impulsive than the
  flares without helioseismic perturbations. We present a new catalog of
  helioseismic solar flares, which opens opportunities for performing
  statistical studies to better understand the physics of sunquakes as
  well as the flare-energy release and transport.

---------------------------------------------------------
Title: Estimation of Key Sunquake Parameters through Hydrodynamic
    Modeling and Cross-correlation Analysis
Authors: Stefan, John T.; Kosovichev, Alexander G.
2020ApJ...895...65S    Altcode: 2019arXiv191106839S
  Sunquakes are one of the more distinct secondary phenomena related to
  solar flares, where energy deposition in the lower layers of the Sun's
  atmosphere excites acoustic waves easily visible in photospheric
  dopplergrams. We explore two possible excitation mechanisms
  of sunquakes in the context of the electron beam hypothesis: an
  instantaneous transfer of momentum and a gradual applied force due
  to flare eruption. We model the sunquake excitation and compare with
  five observed sunquake events using a cross-correlation analysis. We
  find that at least half the events studied are consistent with the
  electron beam hypothesis and estimate the energy required to excite
  the sunquakes to be within the range determined by previous studies.

---------------------------------------------------------
Title: Determination of the solar rotation parameters via orthogonal
    polynomials
Authors: Mdzinarishvili, T. G.; Shergelashvili, B. M.; Japaridze,
   D. R.; Chargeishvili, B. B.; Kosovichev, A. G.; Poedts, S.
2020AdSpR..65.1843M    Altcode:
  Accurate measurements of the solar differential rotation parameters
  are necessary for understanding the solar dynamo mechanism. We use the
  orthogonalization process to estimate these parameters. The advantage
  of the orthogonalization of the data in the tracer motion statistical
  analysis is outlined. The differential rotation is represented in
  terms of various types of polynomials. We compare the quality of a
  set of models of the solar differential rotation using the Akaike
  information criterion and choose the best one. Applying the proposed
  method, we studied the solar differential rotation and its North-South
  asymmetry using observations of coronal holes. A statistical analysis
  of observations from the Atmospheric Imaging Assembly (AIA) on Solar
  Dynamics Observatory (SDO) reveals the differential rotation pattern
  of coronal holes and its North-South asymmetry.

---------------------------------------------------------
Title: Response of SDO/HMI Observables to Heating of the Solar
    Atmosphere by Precipitating High-energy Electrons
Authors: Sadykov, Viacheslav M.; Kosovichev, Alexander G.; Kitiashvili,
   Irina N.; Kerr, Graham S.
2020ApJ...893...24S    Altcode: 2019arXiv190610788S
  We perform an analysis of the line-of-sight (LOS) observables of the
  Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics
  Observatory (SDO) for models of the solar atmosphere heated by
  precipitating high-energy electrons during solar flares. The radiative
  hydrodynamic (RADYN) flare models are obtained from the F-CHROMA
  database. The Stokes profiles for the Fe 6173 Å line observed by
  SDO/HMI are calculated using the radiative transfer code RH1.5D,
  assuming statistical equilibrium for atomic level populations,
  and imposing uniform background vertical magnetic fields of various
  strengths. The SDO/HMI observing sequence and LOS data processing
  pipeline algorithm are applied to derive the observables (continuum
  intensity, line depth, Doppler velocity, LOS magnetic field). Our
  results reveal that the strongest deviations of the observables from
  the actual spectroscopic line parameters are found for the model with
  a total energy deposited of E<SUB>total</SUB> = 1.0 × 10<SUP>12</SUP>
  erg cm<SUP>-2</SUP>, injected with a power-law spectral index of δ =
  3 above a low-energy cutoff of E<SUB>c</SUB> = 25 keV. The magnitudes
  of the velocity and magnetic field deviations depend on the imposed
  magnetic field, and can reach 0.35 km s<SUP>-1</SUP> for LOS velocities,
  90 G for LOS magnetic field, and 3% for continuum enhancement for the
  1000 G imposed LOS magnetic field setup. For E<SUB>total</SUB> ≥
  3.0 × 10<SUP>11</SUP> erg cm<SUP>-2</SUP> models, the velocity and
  magnetic field deviations are most strongly correlated with the energy
  flux carried by ∼50 keV electrons, and the continuum enhancement
  is correlated with the synthesized ∼55-60 keV hard X-ray photon
  flux. The relatively low magnitudes of perturbations of the observables
  and absence of magnetic field sign reversals suggest that the considered
  RADYN beam heating models augmented with the uniform vertical magnetic
  field setups cannot explain the strong transient changes found in the
  SDO/HMI observations.

---------------------------------------------------------
Title: Resolving Power of Asteroseismic Inversion of the Kepler
    Legacy Sample
Authors: Kosovichev, Alexander G.; Kitiashvili, Irina N.
2020IAUS..354..107K    Altcode: 2020arXiv200209839K
  The Kepler Asteroseismic Legacy Project provided frequencies, separation
  ratios, error estimates, and covariance matrices for 66 Kepler main
  sequence targets. Most of the previous analysis of these data was
  focused on fitting standard stellar models. We present results of
  direct asteroseismic inversions using the method of optimally localized
  averages (OLA), which effectively eliminates the surface effects and
  attempts to resolve the stellar core structure. The inversions are
  presented for various structure properties, including the density
  stratification and sound speed. The results show that the mixed modes
  observed in post-main sequence F-type stars allow us to resolve the
  stellar core structure and reveal significant deviations from the
  evolutionary models obtained by the grid-fitting procedure to match
  the observed oscillation frequencies.

---------------------------------------------------------
Title: Realistic 3D MHD modeling of self-organized magnetic
    structuring of the solar corona
Authors: Kitiashvili, Irina N.; Wray, Alan A.; Sadykov, Viacheslav;
   Kosovichev, Alexander G.; Mansour, Nagi N.
2020IAUS..354..346K    Altcode:
  The dynamics of solar magnetoconvection spans a wide range of spatial
  and temporal scales and extends from the interior to the corona. Using
  3D radiative MHD simulations, we investigate the complex interactions
  that drive various phenomena observed on the solar surface, in the
  low atmosphere, and in the corona. We present results of our recent
  simulations of coronal dynamics driven by underlying magnetoconvection
  and atmospheric processes, using the 3D radiative MHD code StellarBox
  (Wray et al. 2018). In particular, we focus on the evolution of
  thermodynamic properties and energy exchange across the different
  layers from the solar interior to the corona.

---------------------------------------------------------
Title: Solar oblateness &amp; asphericities temporal variations:
    Outstanding some unsolved issues
Authors: Rozelot, Jean P.; Kosovichev, Alexander G.; Kilcik, Ali
2020IAUS..354..232R    Altcode:
  Solar oblateness has been the subject of several studies dating back
  to the nineteenth century. Despite difficulties, both theoretical
  and observational, tangible results have been achieved. However,
  variability of the solar oblateness with time is still poorly
  known. How the solar shape evolves with the solar cycle has been a
  challenging problem. Analysis of the helioseismic data, which are the
  most accurate measure of the solar structure up to now, leads to the
  determination of asphericity coefficients which have been found to
  change with time. We show here that by inverting even coefficients
  of f-mode oscillation frequency splitting to obtain the oblateness
  magnitude and its temporal dependence can be inferred. It is found
  that the oblateness variations lag the solar activity cycles by about
  3 years. A major change occurred between solar cycles 23 and 24 is that
  the oblateness was greater in cycle 24 despite the lower solar activity
  level. Such results may help to better understand the near-subsurface
  layers as they strongly impacts the internal dynamics of the Sun and
  may induce instabilities driving the transport of angular momentum.

---------------------------------------------------------
Title: 3D MHD Modeling of the Impact of Subsurface Stratification
    on the Solar Dynamo
Authors: Stejko, Andrey M.; Guerrero, Gustavo; Kosovichev, Alexander
   G.; Smolarkiewicz, Piotr K.
2020ApJ...888...16S    Altcode:
  Various models of solar subsurface stratification are tested in the
  global EULAG-MHD solver to simulate diverse regimes of near-surface
  convective transport. Sub- and superadiabacity are altered at the
  surface of the model (r &gt; 0.95R <SUB>⊙</SUB>) to either suppress or
  enhance convective flow speeds in an effort to investigate the impact
  of the near-surface layer on global dynamics. A major consequence
  of increasing surface convection rates appears to be a significant
  alteration of the distribution of angular momentum, especially below
  the tachocline where the rotational frequency predominantly increases
  at higher latitudes. These hydrodynamic changes correspond to large
  shifts in the development of the current helicity in this stable layer
  (r &lt; 0.72R <SUB>⊙</SUB>), significantly altering its impact on
  the generation of poloidal and toroidal fields at the tachocline and
  below, acting as a major contributor toward transitions in the dynamo
  cycle. The enhanced near-surface flow speed manifests in a global shift
  of the toroidal field (B <SUB> ϕ </SUB>) in the butterfly diagram, from
  a north-south symmetric pattern to a staggered antisymmetric emergence.

---------------------------------------------------------
Title: Solar and Stellar Magnetic Fields: Origins and Manifestations
Authors: Kosovichev, A.; Strassmeier, S.; Jardine, M.
2020IAUS..354.....K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: A Generalized Spectral Kurtosis Solar Image Variability
    Descriptor
Authors: Nita, G. M.; Sadykov, V. M.; Kosovichev, A. G.; Oria, V.
2019AGUFMSH31E3340N    Altcode:
  The growing need for accurate Space Weather forecasts motivates
  researchers to implement comprehensive prediction algorithms for solar
  transient events that rely on large amounts of observational data, which
  often require sophisticated processing in order to extract relevant
  information that is used to guide or constrain the forecasts. From
  the perspective of such ongoing efforts, continuing to search for
  alternative physical or mathematical descriptors and investigating their
  ability to encode the dynamics of solar variability may provide means
  for improved forecast performance. <P />Here we introduce a novel solar
  image variability descriptor built from time series of SDO/AIA images,
  which can automatically identify and discriminate quite-Sun areas,
  active regions, and developing eruptive events. Our approach is based
  on the empirical observation that the statistical distribution of the
  squared pixel intensities corresponding to quiet-Sun areas imaged by
  SDO/AIA in certain observing channels may be well approximated by Gamma
  distributions, while active and eruptive solar disk areas obey different
  statistics, also distinguishable from each other. This finding justifies
  the direct use of the well-developed Generalized Spectral Kurtosis
  Estimator theory, which offers reliable means to discriminate non-quiet
  image areas in terms of analytically defined detection thresholds having
  known probabilities of false alarm. <P />We present the results of our
  analysis in the case of several active regions, which were obtained
  using an automated data processing pipeline that we have developed under
  the framework provided by two ongoing projects, namely "EarthCube Data
  Infrastructure: Intelligent Databases and Analysis Tools for Geospace
  Data and Models," and "EarthCube Research Coordination Network:
  Towards Integration of Heliophysics Data, Modeling, and Analysis Tools."

---------------------------------------------------------
Title: Cluster Analysis of Spectroscopic Line Profiles in IRIS
    Observations and RMHD Simulations of the Solar Atmosphere
Authors: Sadykov, V. M.; Kitiashvili, I.; Kosovichev, A. G.
2019AGUFMSH31E3345S    Altcode:
  Spatially-resolved spectroscopic observations from IRIS satellite,
  especially when coupled with realistic 3D RMHD simulations, are a
  powerful tool for analysis of processes in the solar chromosphere
  and transition region. However, the complexity of spectroscopic data
  makes comparison of observations and modeling results difficult. In
  this work, we apply unsupervised clustering algorithms for analysis
  of observational and synthetic line profiles to find a compact
  representation of spectroscopic data and classification in terms
  of physical characteristics of the radiating solar plasma. In
  particular, we utilize the quiet-Sun observations from IRIS, and
  for their interpretation compute synthetic line profiles of the
  chromospheric Mg II h&amp;k 2796 Å &amp; 2803 Å and transition
  region C II 1334 Å &amp; 1335 Å lines using the realistic 3D RMHD
  simulations of the quiescent solar atmosphere (using StellarBox and
  RH1.5 codes). K-Means clustering algorithm is applied separately
  to the observed or synthetic spectroscopic line profiles, as well
  as to their statistical moments (intensity maxima, Doppler shifts,
  line widths etc). The average silhouette width maximization technique
  for the K-Means algorithm is utilized to obtain optimal numbers of
  clusters. We discuss applications of the line profile clustering method
  to 1) visualizations of computational and observational spectroscopic
  imaging data; 2) understanding of evolutionary trends and behavior
  patterns; 3) recognition of heating events and shock waves.

---------------------------------------------------------
Title: Solar activity modeling: from subgranular scales to the
    solar cycles
Authors: Kitiashvili, I.; Wray, A. A.; Sadykov, V. M.; Kosovichev,
   A. G.; Mansour, N. N.
2019AGUFMSH31E3350K    Altcode:
  Dynamical effects of solar magnetoconvection span a wide range
  spatial and temporal scales that extends from the interior to the
  corona and from fast turbulent motions to the global-Sun magnetic
  activity. To study the solar activity on short temporal scales (from
  minutes to hours), we use 3D radiative MHD simulations that allow
  us to investigate complex turbulent interactions that drive various
  phenomena, such as plasma eruptions, spontaneous formation of magnetic
  structures, funnel-like structures and magnetic loops in the corona,
  and others. In particular, we focus on multi-scale processes of energy
  exchange across the different layers, which contribute to the corona
  heating and eruptive dynamics, as well as interlinks between different
  layers of the solar interior and atmosphere. <P />For modeling the
  global-scale activity we use the data assimilation approach that has
  demonstrated great potential for building reliable long-term forecasts
  of solar activity. In particular, it has been shown that the Ensemble
  Kalman Filter (EnKF) method applied to the Parker-Kleeorin-Ruzmakin
  dynamo model is capable of predicting solar activity up to one
  sunspot cycle ahead in time, as well as estimating the properties of
  the next cycle a few years before it begins. In this presentation,
  using the available magnetogram data, we discuss development of
  the methodology and forecast quality criteria (including forecast
  uncertainties and sources of errors). We demonstrate the influence
  of observational limitation on the prediction accuracy. We present
  the EnKF predictions of the upcoming Solar Cycle 25 based on both
  the sunspot number series and observed magnetic fields, and discuss
  the uncertainties and potential of the data assimilation approach for
  modeling and forecasting the solar activity.

---------------------------------------------------------
Title: On the Origin of Solar Torsional Oscillations and Extended
    Solar Cycle
Authors: Pipin, V. V.; Kosovichev, A. G.
2019ApJ...887..215P    Altcode: 2019arXiv190804525P
  We present a nonlinear mean-field model of the solar interior dynamics
  and dynamo, which reproduces the observed cyclic variations of the
  global magnetic field of the Sun, as well as the differential rotation
  and meridional circulation. Using this model, we explain, for the first
  time, the extended 22 yr pattern of the solar torsional oscillations,
  observed as propagation of zonal variations of the angular velocity
  from high latitudes to the equator during the time equal to the full
  dynamo cycle. In the literature, this effect is usually attributed to
  the so-called “extended solar cycle.” In agreement with the commonly
  accepted idea, our model shows that the torsional oscillations can be
  driven by a combination of magnetic field effects acting on turbulent
  angular momentum transport and the large-scale Lorentz force. We find
  that the 22 yr pattern of the torsional oscillations can result from a
  combined effect of an overlap of subsequent magnetic cycles and magnetic
  quenching of the convective heat transport. The latter effect results in
  cyclic variations of the meridional circulation in the sunspot formation
  zone, in agreement with helioseismology results. The variations of the
  meridional circulation, together with other drivers of the torsional
  oscillations, maintain their migration to the equator during the 22
  yr magnetic cycle, resulting in the observed extended pattern of the
  torsional oscillations.

---------------------------------------------------------
Title: Characterization of Subsurface Flow Dynamics for Forecasting
    of Solar Activity
Authors: Kosovichev, A. G.; Sadykov, V. M.
2019AGUFMSH31E3347K    Altcode:
  Evolution of large-scale magnetic field structures in the solar
  photosphere and corona is controlled by motions beneath the visible
  surface of the Sun. Subsurface plasma flows play a critical role
  in formation and evolution of active regions and their activity. We
  analyze subsurface flow maps provided by the local helioseismology
  pipeline from the Helioseismic and Magnetic Imager (HMI) data on
  board the Solar Dynamics Observatory, and investigate links between
  flow characteristics and magnetic activity. The primary goal is
  to determine flow descriptors, which can improve solar activity
  forecasts. In particular, by employing machine learning classifiers,
  we test how the flow helicity and velocity shear descriptors can
  improve the prediction of initiation of flares and CME eruptions.

---------------------------------------------------------
Title: 3D MHD Modeling of the Impact of Subsurface Stratification
    on the Solar Dynamo
Authors: Stejko, Andrey M.; Guerrero, Gustavo; Kosovichev, Alexander
   G.; Smolarkiewicz, Piotr K.
2019arXiv191109658S    Altcode:
  Various models of solar subsurface stratification are tested in the
  global EULAG-MHD solver to simulate diverse regimes of near-surface
  convective transport. Sub- and superadiabacity are altered at the
  surface of the model ($ r &gt; 0.95~R_{\odot}$) to either suppress or
  enhance convective flow speeds in an effort to investigate the impact
  of the near-surface layer on global dynamics. A major consequence
  of increasing surface convection rates appears to be a significant
  alteration of the distribution of angular momentum, especially below
  the tachocline where the rotational frequency predominantly increases
  at higher latitudes. These hydrodynamic changes correspond to large
  shifts in the development of the current helicity in this stable
  layer ($r&lt;0.72R_{\odot}$), significantly altering its impact on
  the generation of poloidal and toroidal fields at the tachocline and
  below, acting as a major contributor towards transitions in the dynamo
  cycle. The enhanced near-surface flow speed manifests in a global shift
  of the toroidal field ($B_{\phi}$) in the butterfly diagram - from a
  North-South symmetric pattern to a staggered anti-symmetric emergence.

---------------------------------------------------------
Title: What Sets the Magnetic Field Strength and Cycle Period in
    Solar-type Stars?
Authors: Guerrero, G.; Zaire, B.; Smolarkiewicz, P. K.; de Gouveia
   Dal Pino, E. M.; Kosovichev, A. G.; Mansour, N. N.
2019ApJ...880....6G    Altcode: 2018arXiv181007978G
  Two fundamental properties of stellar magnetic fields have been
  determined by observations for solar-like stars with different Rossby
  numbers ({{Ro}}), namely, the magnetic field strength and the magnetic
  cycle period. The field strength exhibits two regimes: (1) for fast
  rotation, it is independent of {{Ro}}, and (2) for slow rotation,
  it decays with {{Ro}} following a power law. For the magnetic cycle
  period, two regimes of activity, the active and inactive branches,
  have also been identified. For both of them, the longer the rotation
  period, the longer the activity cycle. Using global dynamo simulations
  of solar-like stars with Rossby numbers between ∼0.4 and ∼2, this
  paper explores the relevance of rotational shear layers in determining
  these observational properties. Our results, consistent with nonlinear
  {α }<SUP>2</SUP>{{Ω }} dynamos, show that the total magnetic field
  strength is independent of the rotation period. Yet at surface levels,
  the origin of the magnetic field is determined by {{Ro}}. While for
  {{Ro}}≲ 1, it is generated in the convection zone, for {{Ro}}≳ 1,
  strong toroidal fields are generated at the tachocline and rapidly
  emerge toward the surface. In agreement with the observations, the
  magnetic cycle period increases with the rotational period. However,
  a bifurcation is observed for {{Ro}}∼ 1, separating a regime where
  oscillatory dynamos operate mainly in the convection zone from the
  regime where the tachocline has a predominant role. In the latter,
  the cycles are believed to result from the periodic energy exchange
  between the dynamo and the magneto-shear instabilities developing in
  the tachocline and the radiative interior.

---------------------------------------------------------
Title: Modeling of Subsurface Shear with EULAG-MHD
Authors: Stejko, Andrey Maksimovich; Guerrero, Gustavo; Kosovichev,
   Alexander G.
2019AAS...23430208S    Altcode:
  The 3D Global solar convection algorithm EULAG-MHD has recently been
  used to recreate solar hydrodynamic profiles of differential rotation
  and meridional circulation along with simulation of long-term evolution
  of the global magnetic field. In previous studies we saw some of the
  large effects that are created by including strong shear layers in the
  tachocline and on the surface; changing the period of the solar cycle
  from an order of years to that of decades. We attempt to explore the
  global consequences of these regions by simulating various levels of
  sub/super-adiabaticity in the background potential temperature profiles
  - modeled by a polytropic ideal gas with manually controlled polytropic
  indeces, simulating the creation or suppression of a near-surface shear
  layer (NSSL). We also attempt to understand how the MPDATA algorithm
  that is implemented in the model will function under various resolutions
  (512 φ, 256 θ, 256 R; 256 φ, 128 θ, 128 R) where an implicit viscous
  dissipation is implemented using the implicit Large-Eddy simulation
  (ILES) approach for turbulent advective motions - a method that can be
  unpredictable as large changes in resolution begin to change scales of
  dissipation in low viscosity environments. The simulation of our NSSL
  is done at a lower resolution (128 φ, 64 θ, 64 R) that has repeatedly
  been shown to adequately simulate solar-like hydrodynamic effects such
  as differential rotation, as well as generate well defined cyclical
  magnetic dynamo patterns. These models show the NSSL as playing an
  important role in the proper distribution of angular momentum and
  resulting in more realistic solar-like magnetic and hydrodynamic
  patterns.

---------------------------------------------------------
Title: Long-Term Prediction of Solar Activity Using Magnetogram Data
    and Ensemble Kalman Filter
Authors: Kitiashvili, Irina; Kosovichev, Alexander G.
2019AAS...23440101K    Altcode:
  Solar activity predictions using the data assimilation approach have
  demonstrated great potential to build reliable long-term forecasts of
  solar activity. In particular, it has been shown that the Ensemble
  Kalman Filter (EnKF) method applied to a non-linear dynamo model is
  capable of predicting solar activity up to one sunspot cycle ahead
  in time, as well as estimating the properties of the next cycle a
  few years before it begins. These developments assume an empirical
  relationship between the mean toroidal magnetic field flux and the
  sunspot number. Estimated from the sunspot number series, variations
  of the toroidal field have been used to assimilate the data into the
  Parker-Kleeorin-Ruzmakin (PKR) dynamo model by applying the EnKF
  method. The dynamo model describes the evolution of the toroidal
  and poloidal components of the magnetic field and the magnetic
  helicity. Full-disk magnetograms provide more accurate and complete
  input data by constraining both the toroidal and poloidal global
  field components, but these data are available only for the last four
  solar cycles. In this presentation, using the available magnetogram
  data, we discuss development of the methodology and forecast quality
  criteria (including forecast uncertainties and sources of errors). We
  demonstrate the influence of limited time series observations on the
  accuracy of solar activity predictions. We present EnKF predictions of
  the upcoming Solar Cycle 25 based on both the sunspot number series and
  observed magnetic fields and discuss the uncertainties and potential
  of the data assimilation approach. The research is funded by the NSF
  SHINE program AGS-1622341.

---------------------------------------------------------
Title: Evolution of Magnetic Helicity in Solar Cycle 24
Authors: Pipin, Valery V.; Pevtsov, Alexei A.; Liu, Yang; Kosovichev,
   Alexander G.
2019ApJ...877L..36P    Altcode: 2019arXiv190500772P
  We propose a novel approach to reconstruct the surface magnetic
  helicity density on the Sun or Sun-like stars. The magnetic vector
  potential is determined via decomposition of vector magnetic-field
  measurements into toroidal and poloidal components. The method is
  verified using data from a non-axisymmetric dynamo model. We apply the
  method to vector field synoptic maps from the Helioseismic and Magnetic
  Imager on board the Solar Dynamics Observatory to study the evolution
  of the magnetic helicity density during solar cycle 24. It is found
  that the mean helicity density of the non-axisymmetric magnetic field
  of the Sun evolves in a way similar to that reported for the current
  helicity density of the solar active regions. It predominantly has a
  negative sign in the northern hemisphere, while it is mainly positive
  in the southern hemisphere. Also, the hemispheric helicity rule for
  the non-axisymmetric magnetic field showed the sign inversion at the
  end of cycle 24. The evolution of the magnetic helicity density of
  a large-scale axisymmetric magnetic field is different from what is
  predicted by dynamo theory. On one hand, the mean large- and small-scale
  components of magnetic helicity density display the hemispheric helicity
  rule of opposite signs at the beginning of cycle 24. However, later
  in the cycle, the two helicities exhibit the same sign, in contrast
  with theoretical expectations.

---------------------------------------------------------
Title: 3D Realistic Modeling of Chromospheric and Coronal Heating
    and Self-Organization
Authors: Kitiashvili, Irina; Wray, Alan A.; Kosovichev, Alexander G.;
   Sadykov, Viacheslav M.; Mansour, Nagi N.
2019AAS...23410615K    Altcode:
  Turbulent magnetoconvection is a primary driver of the dynamics and
  structure of the solar atmosphere and corona. Realistic high-resolution
  radiative MHD simulations reveal a complex multiscale structuring
  and dynamics above the photosphere. We present a detailed study of
  dynamical links between small-scale magnetic fields generated by
  local dynamo action and properties of the chromosphere and corona,
  as well as effects of coherent self-organized magnetic structures. In
  particular, we discuss formation of coherent structures, eruptive
  dynamics, and contributions of multi-scale structuring and highly
  non-linear dynamics to heating of the chromosphere and corona.

---------------------------------------------------------
Title: Detection of Dynamo Waves in the Solar Convection Zone by
    Helioseismology
Authors: Kosovichev, Alexander G.; Pipin, Valery
2019AAS...23430703K    Altcode:
  Analysis of helioseismology data obtained in 1996-2019 for two solar
  cycles from two space missions, Solar and Heliospheric Observatory
  (SoHo) and Solar Dynamics Observatory (SDO), reveals that latitudinal
  variations of solar rotation ('torsional oscillations') are associated
  with hydromagnetic dynamo waves initiated in the solar tachocline
  and travelling in radius and latitude towards the surface during the
  solar cycles. On the surface, the waves form two branches of zonal
  deceleration migrating towards the poles and equator, and coinciding
  with the large-scale magnetic field patterns observed in synoptic
  magnetograms. The results explain the phenomenon of 'extended solar
  cycle', and provide first observational evidence for magnetic dynamo
  waves predicted by the Parker's theory of solar activity cycles. We
  compare the observational results with dynamic models of the solar
  dynamo, and discuss driving mechanisms of the torsional oscillations.

---------------------------------------------------------
Title: Time-Dependent Hydrodynamic Modeling of Solar Acoustic Waves
Authors: Stefan, John; Kosovichev, Alexander G.
2019AAS...23430209S    Altcode:
  We consider linear perturbations to appropriate hydrodynamic equations,
  such as mass continuity and the adiabatic condition. Using the Solar
  Model S (Christensen-Dalsgaard 1996- 2014) as mesh, we discretize
  the governing equations as well as decompose the various modes
  using spherical harmonics. We take advantage of parallel computing
  resources by running simulations up to very high modes of order
  l=3000. This allows us to model so-called "sunquakes" with fairly high
  precision; since the governing equations allow for different types
  of perturbations, we aim to determine the location and mechanism of
  these impulsive events.

---------------------------------------------------------
Title: Cluster analysis of spectroscopic line profiles in RMHD
    simulations and observations of the solar atmosphere
Authors: Sadykov, Viacheslav M.; Kitiashvili, Irina N.; Kosovichev,
   Alexander G.
2019shin.confE..11S    Altcode:
  Spatially-resolved spectroscopic observations from the IRIS space
  mission and ground-based telescopes, coupled with realistic 3D RMHD
  simulations, are a powerful tool for analysis of processes in the
  solar atmosphere. To better understand the dynamical and thermodynamic
  properties in the simulation data and their connection to observations,
  it is essential to determine similarities in the behaviors of the
  synthesized and observed spectral line profiles. In this work, we
  utilize realistic 3D RMHD simulations of the solar atmosphere (using
  the StellarBox and Bifrost codes) and compute synthetic line profiles of
  photospheric (Fe I 6173A), chromospheric (H-alpha 6563A, Ca II h&amp;k
  3969A&amp;3934A, Mg II h&amp;k 2796A&amp;2803A), and transition region
  (C II 1334A&amp;1335A) lines. Several clustering algorithms (k-Means
  clustering, Density-based spatial clustering of applications with
  noise) are applied separately to the profiles of each calculated
  spectroscopic line, as well as to the multi-line synthetic data. We
  discuss application of line profile clustering to visualizations of
  the computational volume, understanding its evolutionary trends and
  behavior patterns, and inversion (reconstruction) of physical properties
  of the solar atmosphere from multi-line spectroscopic data.

---------------------------------------------------------
Title: Helioseismic Effects of Solar Flares in Cycle 24
Authors: Kosovichev, Alexander; Sharykin, Ivan
2019shin.confE.204K    Altcode:
  Helioseismic flare waves (""sunquakes"") occur due to localized force
  or/and momentum impacts observed during the flare impulsive phase in
  the lower atmosphere. Such impacts may be caused by precipitation of
  high-energy particles, downward traveling shock wave, or by magnetic
  Lorentz force associated with plasma eruption. Understanding the
  mechanism of sunquakes is a key problem of the flare energy release and
  transport. We present results of a statistical study of the helioseismic
  response of M-X class solar flares observed during Solar Cycle 24. For
  detection of sunquakes, we apply the helioseismic holography technique
  to analysis of Dopplergram data from Helioseismic Magnetic Imager
  (HMI). Among the total number ( 500) of the M - X class flares, we
  found 82 helioseismic events. This result is quite unexpected because
  it was previously thought that sunquakes are rare and observed mainly
  during strong flares. However, our analysis has shown that there
  are many M-class flares, which produced strong sunquakes, while in
  some powerful X flares helioseismic waves were not observed or were
  weak. The analysis also revealed that during the solar cycle, there
  were active regions that are characterized by most efficient generation
  of sunquakes. We found that the sunquake power correlates with maximal
  values of the GOES X-ray lightcurve time derivative better than with
  the GOES X-ray class. The new catalog of helioseismic solar flares
  allows us to make new steps for deeper understanding of the mechanism
  of sunquakes and the flare physics, in general.

---------------------------------------------------------
Title: Hydrodynamic Modeling of Impulsive Helioseismic Events
Authors: Stefan, John T.; Kosovichev, Alexander G.
2019shin.confE..14S    Altcode:
  We consider impulsive helioseismic events (sunquakes) as a hydrodynamic
  phenomenon, modeling them through linear perturbations to a modified
  form of Euler's equations. Realistic wave damping is simulated from
  measurements of characteristic decay times, and the resulting waveforms
  are compared with observational data to constrain possible excitation
  mechanisms.

---------------------------------------------------------
Title: Statistical Properties of Soft X-Ray Emission of Solar Flares
Authors: Sadykov, Viacheslav M.; Kosovichev, Alexander G.; Kitiashvili,
   Irina N.; Frolov, Alexander
2019ApJ...874...19S    Altcode: 2018arXiv181005610S
  We present a statistical analysis of properties of Soft X-Ray (SXR)
  emission, plasma temperature (T), and emission measure (EM), derived
  from Geostationary Operational Environmental Satellite observations
  of flares in 2002-2017. The temperature and EMs are obtained using
  the Temperature and EM-based Background Subtraction algorithm, which
  delivers reliable results together with uncertainties even for weak
  B-class flare events. More than 96% of flares demonstrate a sequential
  appearance of T, SXR, and EM maxima, in agreement with the expected
  behavior of the chromospheric evaporation process. The relative number
  of such flares increases with increasing the SXR flux maximum. The
  SXR maximum is closer in time to the T maximum for B-class flares than
  for ≥C-class flares, while it is very close to the EM maximum for M-
  and X-class flares. We define flares as “T-controlled” if the time
  interval between the SXR and T maxima is at least two times shorter than
  the interval between the EM and SXR maxima, and as “EM-controlled”
  if the time interval between the EM and SXR maxima is at least two
  times shorter than the interval between the SXR and T maxima. For
  any considered flare class range, the T-controlled events compared
  to EM-controlled events have: (a) higher EM but lower T; (b) longer
  durations and shorter relative growth times; and (c) longer FWHM and
  characteristic decay times. Interpretation of these statistical results
  based on analysis of a single loop dynamics suggests that for flares
  of the same class range, the T-controlled events can be developed in
  longer loops than the EM-controlled events.

---------------------------------------------------------
Title: The Origin of Deep Acoustic Sources Associated with Solar
    Magnetic Structures
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Mansour, N. N.; Wray,
   A. A.; Sandstrom, T. A.
2019ApJ...872...34K    Altcode: 2018arXiv181006133K
  It is generally accepted that solar acoustic (p) modes are excited
  by near-surface turbulent motions, in particular by downdrafts and
  interacting vortices in intergranular lanes. Recent analysis of Solar
  Dynamics Observatory data by Zhao et al. (2015) revealed fast-moving
  waves around sunspots, which are consistent with magnetoacoustic waves
  excited approximately 5 Mm beneath the sunspot. We analyzed 3D radiative
  MHD simulations of solar magnetoconvection with a self-organized
  pore-like magnetic structure, and identified more than 600 individual
  acoustic events both inside and outside this structure. By performing
  a case-by-case study, we found that acoustic sources surrounding
  the magnetic structure are associated with downdrafts. Their depth
  correlates with downdraft speed and magnetic field strength. The
  sources often can be transported into deeper layers by downdrafts. The
  wave front shape, in the case of a strong or inclined downdraft,
  can be stretched along the downdraft. Inside the magnetic structure,
  excitation of acoustic waves is driven by converging flows. Frequently,
  strong converging plasma streams hit the structure boundaries, causing
  compressions in its interior that excite acoustic waves. Analysis
  of the depth distribution of acoustic events shows the strongest
  concentration at 0.2-1 Mm beneath the surface for the outside sources
  and mostly below 1 Mm inside the magnetic region, that is, deeper than
  their counterparts outside the magnetic region.

---------------------------------------------------------
Title: Dynamo Wave Patterns inside of the Sun Revealed by Torsional
    Oscillations
Authors: Kosovichev, Alexander G.; Pipin, Valery V.
2019ApJ...871L..20K    Altcode:
  Torsional oscillations represent bands of fast and slow zonal flows
  around the Sun, which extend deep into the convection zone and
  migrate during solar cycles toward the equator following the sunspot
  “butterfly” diagram. Analysis of helioseismology data obtained in
  1996-2018 for almost two solar cycles reveals zones of deceleration of
  the torsional oscillations inside of the Sun due to dynamo-generated
  magnetic field. The zonal deceleration originates near the bottom of
  the convection zone at high latitudes, and migrates to the surface
  revealing patterns of magnetic dynamo waves predicted by Parker’s
  dynamo theory. The analysis reveals that the primary seat of the
  solar dynamo is located in a high-latitude zone of the tachocline. It
  suggests a dynamo scenario that can explain “extended solar cycles”
  previously observed in the evolving shape of the solar corona. The
  results show a substantial decrease of the zonal acceleration in the
  current solar cycle and indicate a further decline of activity in
  the next solar cycle. Although the relationship between the magnitude
  of zonal deceleration and the amount of emerged toroidal field that
  leads to formation of sunspots is not yet established, the results
  reveal a new perspective for solar cycle modeling and prediction using
  helioseismology data.

---------------------------------------------------------
Title: Statistical Study of Chromospheric Evaporation in Impulsive
    Phase of Solar Flares
Authors: Sadykov, Viacheslav M.; Kosovichev, Alexander G.; Sharykin,
   Ivan N.; Kerr, Graham S.
2019ApJ...871....2S    Altcode: 2018arXiv180510729S
  We present a statistical study of chromospheric evaporation in solar
  flares using simultaneous observations by the RHESSI X-ray telescope
  and the Interface Region Imaging Spectrograph UV spectrograph. The
  results are compared with radiation hydrodynamic flare models from
  the F-CHROMA RADYN database. For each event, we study spatially
  resolved Doppler shifts of spectral lines formed in the transition
  region (C II 1334.5 Å) and hot coronal plasma (Fe XXI 1354.1 Å)
  to investigate the dynamics of the solar atmosphere during the
  flare impulsive phase. We estimate the energy fluxes deposited by
  high-energy electrons using X-ray imaging spectroscopy and assuming
  the standard thick-target model. Using the RADYN flare models, the RH
  1.5D radiative transfer code, and the Chianti atomic line database,
  we calculate C II and Fe XXI line profiles and compare with the
  observations. While the RADYN models predict a correlation between
  the Doppler shifts and deposited energy flux for both lines, this was
  only observed in the C II data. Several quantitative discrepancies are
  found between the observations and models: the Fe XXI Doppler shifts
  are substantially stronger in the models than in the data, and the
  C II mean blueshifts are absent in the observations but predicted
  by the models. The transition energies between “gentle” and
  “explosive” evaporation regimes estimated from the observations
  ((2{--}8)× {10}<SUP>9</SUP> erg cm<SUP>-2</SUP> s<SUP>-1</SUP>)
  and derived from the models ((2.2{--}10.1)× {10}<SUP>9</SUP> erg
  cm<SUP>-2</SUP> s<SUP>-1</SUP>) are comparable with each other. The
  results illustrate relationships among the processes of chromospheric
  evaporation, the response of the colder layers, and the flare energy
  flux deposited by high-energy electrons, although demonstrating
  discrepancy between analyzed observations and RADYN models.

---------------------------------------------------------
Title: Does Nonaxisymmetric Dynamo Operate in the Sun?
Authors: Pipin, V. V.; Kosovichev, A. G.
2018ApJ...867..145P    Altcode: 2018arXiv180805332P
  We explore effects of random nonaxisymmetric perturbations of kinetic
  helicity (the α effect) and diffusive decay of bipolar magnetic
  regions on generation and evolution of large-scale nonaxisymmetric
  magnetic fields on the Sun. Using a reduced 2D nonlinear mean-field
  dynamo model and assuming that bipolar regions emerge due to magnetic
  buoyancy in situ of the large-scale dynamo action, we show that
  fluctuations of the α effect can maintain the nonaxisymmetric magnetic
  fields through a solar-type α <SUP>2</SUP>Ω dynamo process. It is
  found that diffusive decay of bipolar active regions is likely to be
  the primary source of nonaxisymmetric magnetic fields observed on the
  Sun. Our results show that nonaxisymmetric dynamo models with stochastic
  perturbations of the α effect can explain periods of extremely high
  activity (“super-cycle” events) as well as periods of deep decline
  of magnetic activity. We compare the models with synoptic observations
  of solar magnetic fields for the last four activity cycles and discuss
  implications of our results for interpretation of observations of
  stellar magnetic activity.

---------------------------------------------------------
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
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: Dynamo Wave Patterns Inside the Sun Revealed by Torsional
    Oscillations
Authors: Kosovichev, Alexander G.; Pipin, Valery V.
2018arXiv180910776K    Altcode:
  Torsional oscillations represent bands of fast and slow zonal flows
  around the Sun, which extend deep into the convection zone and migrate
  during solar cycles towards the equator following the sunspot butterfly
  diagram. Analysis of helioseismology data obtained in 1996-2018 for
  almost two solar cycles reveals zones of deceleration of the torsional
  oscillations inside the Sun due to dynamo-generated magnetic field. The
  zonal deceleration originates near the bottom of the convection zone
  at high latitudes, and migrates to the surface revealing patterns
  of magnetic dynamo waves predicted by the Parker's dynamo theory. The
  analysis reveals that the primary seat of the solar dynamo is located in
  a high-latitude zone of the tachocline. It suggests a dynamo scenario
  that can explain 'extended solar cycles' previously observed in the
  evolving shape of the solar corona. The results show a substantial
  decrease of the zonal acceleration in the current solar cycle and
  indicate further decline of activity in the next solar cycle. Although
  the relationship between the magnitude of zonal deceleration and the
  amount of emerged toroidal field that leads to formation of sunspots
  is not yet established, the results open a new perspective for solar
  cycle modeling and prediction using helioseismology data.

---------------------------------------------------------
Title: Onset of Photospheric Impacts and Helioseismic Waves in X9.3
    Solar Flare of 2017 September 6
Authors: Sharykin, Ivan N.; Kosovichev, Alexander G.
2018ApJ...864...86S    Altcode: 2018arXiv180406565S
  The X9.3 flare of 2017 September 6, was the most powerful flare of
  Solar Cycle 24. It generated strong white-light emission and multiple
  helioseismic waves (sunquakes). By using data from the Helioseismic and
  Magnetic Imager (HMI) on board the Solar Dynamics Observatory as well
  as hard X-ray (HXR) data from the KONUS instrument on board the WIND
  spacecraft, and Anti-Coincidence System on board the INTERGRAL space
  observatory, we investigate spatio-temporal dynamics of photospheric
  emission sources, identify sources of helioseismic waves, and compare
  the flare photospheric dynamics with the HXR temporal profiles. The
  results show that the photospheric flare impacts started to develop in
  compact regions in close vicinity of the magnetic polarity inversion
  line (PIL) in the preimpulsive phase before detection of the HXR
  emission. The initial photospheric disturbances were localized in the
  region of strong horizontal magnetic field of the PIL, and, thus,
  are likely associated with a compact sheared magnetic structure
  elongated along the PIL. The acoustic egression power maps revealed
  two primary sources of generation of sunquakes, which were associated
  with places of the strongest photospheric impacts in the preimpulsive
  phase and the early impulsive phase. This can explain the two types of
  helioseismic waves observed in this flare. Analysis of the high-cadence
  HMI filtergrams suggests that the flare energy release developed in
  the form of sequential involvement of compact low-lying magnetic loops
  that were sheared along the PIL.

---------------------------------------------------------
Title: Solar cycle variations of rotation and asphericity in the
    near-surface shear layer
Authors: Kosovichev, A. G.; Rozelot, J. P.
2018JASTP.176...21K    Altcode: 2018arXiv180405081K
  The precise shape of the Sun is sensitive to the influence of gravity,
  differential rotation, local turbulence and magnetic fields. So its
  precise measurement is a long-standing astrometric objective. It
  has been previously shown by different methods that the solar shape
  exhibits asphericity that evolves with the solar cycle. Thanks to the
  Michelson Doppler Imager (MDI) on Solar and Heliospheric Observatory
  (SoHO) and the Helioseismic and Magnetic Imager (HMI) aboard NASA's
  Solar Dynamics Observatory (SDO), and their capability to observe with
  an unprecedented accuracy the surface gravity oscillation (f) modes,
  it is possible to extract information concerning the coefficients
  of rotational frequency splitting, a<SUB>1</SUB> , a<SUB>3</SUB> and
  a<SUB>5</SUB> , that measure the latitudinal differential rotation,
  together with the a<SUB>2</SUB> , a<SUB>4</SUB> and a<SUB>6</SUB>
  asphericity coefficients. Analysis of these helioseismology data with
  time for almost two solar cycles, from 1996 to 2017, reveals a close
  correlation of the a<SUB>1</SUB> and a<SUB>5</SUB> coefficients with
  the solar activity, whilst a<SUB>3</SUB> exhibits a long-term trend
  and a weak correlation with the solar activity in the current solar
  cycle indicating a substantial change of the global solar rotation,
  potentially associated with a long-term evolution of the solar
  cycles. Looking in more details, the asphericity coefficients,
  a<SUB>2</SUB> , a<SUB>4</SUB> and a<SUB>6</SUB> are more strongly
  associated with the solar cycle when applying a time lag of respectively
  0.1, 1.6 and -1.6 years. The magnitude of a<SUB>6</SUB> -coefficient
  varies in phase with the sunspot number (SN), but its amplitude is
  ahead of the SN variation. The latest measurements made in mid 2017
  indicate that the magnitude of the a<SUB>6</SUB> -coefficient has
  probably reached its minimum; therefore, the next solar minimum can be
  expected by the end of 2018 or in the beginning of 2019. The so-called
  "seismic radius" in the range of f-mode angular degree: ℓ = 137 - 299
  exhibits a temporal variability in anti-phase with the solar activity;
  its relative value decreased by ∼ 2.3 ×10<SUP>-5</SUP> in Solar
  Cycle 23 and ∼ 1.7 ×10<SUP>-5</SUP> in Cycle 24. Such results will
  be useful for better understanding the physical mechanisms which act
  inside the Sun, and so, better constrain dynamo models for forecasting
  the solar cycles.

---------------------------------------------------------
Title: Modeling Impulsive Helioseismic Events
Authors: Stefan, John Thomas; Kosovichev, Alexander
2018shin.confE.246S    Altcode:
  We consider linear perturbations to appropriate hydrodynamic equations,
  such as mass continuity and the adiabatic condition. Using the Solar
  Model S (Christensen-Dalsgaard 1996-2014) as mesh, we discretize
  the governing equations as well as decompose the various modes using
  spherical harmonics. We take advantage of parallel computing resources
  by running simulations up to very high modes of order 10E3 . This allows
  us to model so-called "sunquakes" with fairly high precision; since
  the governing equations allow for different types of perturbations, we
  aim to determine the location and mechanism of these impulsive events.

---------------------------------------------------------
Title: Using Machine-Learning Methods and Expert Prediction
    Probabilities to Forecast Solar Flares
Authors: Sadykov, Viacheslav M.; Kosovichev, Alexander G.
2018shin.confE.144S    Altcode:
  It has long been known that studying connection between solar
  flares and properties of magnetic field in active regions is very
  important for understanding the flare physics and developing space
  weather forecasts. The Helioseismic and Magnetic Imager onboard the
  Solar Dynamics Observatory (SDO/HMI) obtains tremendous amounts of
  the magnetic field data products. However, the operational NOAA
  Space Weather Prediction Center (SWPC) forecasts of solar flares
  still represent prediction probabilities issued by the experts. In
  this research we investigate the possibilities to enhance the daily
  operational flare forecasts performed at the SWPC/NOAA by developing
  a synergy of the expert predictions and physics-based criteria,
  and by employing machine-learning methods. Among the physics-based
  criteria, we consider the descriptors of the Polarity Inversion Line
  (PIL, previously tested by Sadykov and Kosovichev 2017, ApJ, 849, 148)
  and Space weather HMI Active Region Patches (SHARP, Bobra et al. 2014,
  SoPh, 289, 3549) and derive from them the daily-cadence characteristics
  the entire Sun. We also consider the daily descriptors of the GOES
  Soft X-ray 1-8Å flux such as previous day flare history and averaged
  X-ray flux. We estimate the effectiveness in separation of flaring and
  non-flaring cases for each characteristic, as well as for the expert
  prediction probabilities, and find that some PIL and SHARP descriptors
  are as effective as the expert prediction probabilities and should be
  considered to issue the flare forecast. Finally, we train and test three
  Machine-Learning classification algorithms (Support Vector Classifier,
  k-Nearest Neighbor Classifier, and Random Forest Classifier) using the
  most effective descriptors and expert prediction probabilities, and
  compare the received predictions with the current SWPC/NOAA forecasts.

---------------------------------------------------------
Title: Cyclic Changes of the Sun’s Seismic Radius
Authors: Kosovichev, Alexander; Rozelot, Jean-Pierre
2018ApJ...861...90K    Altcode: 2018arXiv180509385K
  The questions asking whether the Sun shrinks with the solar activity
  and what causes this have been a subject of debate. Helioseismology
  provides a means to measure with high precision the radial displacement
  of subsurface layers, the so-called “seismic radius,” through the
  analysis of oscillation frequencies of surface gravity (f) modes. Here,
  we present results of a new analysis of 21 years of helioseismology
  data from two space missions, the Solar and Heliospheric Observatory
  and the Solar Dynamics Observatory, which allow us to resolve previous
  uncertainties and compare variations of the seismic radius in two solar
  cycles. After removing the f-mode frequency changes associated with
  the surface activity, we find that the mean seismic radius is reduced
  by 1-2 km during the solar maxima and that most significant variations
  of the solar radius occur beneath the visible surface of the Sun at a
  depth of about 5 ± 2 Mm, where the radius is reduced by 5-8 km. These
  variations can be interpreted as changes in the solar subsurface
  structure caused by the predominately vertical ∼10 kG magnetic field.

---------------------------------------------------------
Title: Helioseismic Observations of Torsional Oscillations Inside
    the Sun and Their Potential for Predicting Solar Cycles
Authors: Kosovichev, Alexander G.
2018shin.confE.152K    Altcode:
  The helioseismic analysis of torsional oscillations of the Sun from
  the SOHO and SDO, obtained in 1996-2018, reveals the spatio-temporal
  dynamics of the solar convection zone, associated with the dynamo
  process. The data reveal new relationships between the migrating
  magnetic field patterns observed in synoptic magnetograms and
  the dynamics of torsional oscillations near the surface and in
  the interior. In particular, it is found that the evolution of
  torsional oscillations in the deep convection zone is ahead of
  the surface magnetic evolution by several years, and that it is
  related to the extended solar cycle phenomenon previously observed
  in the solar corona. The data show substantial differences in the
  torsional oscillation properties between Cycles 23 and 24 indicating
  on fundamental changes in the dynamo regime. The helioseismology
  observations of the torsional oscillations open new perspectives for
  understanding the global dynamo processes inside the Sun, and for
  predicting the next solar cycle.

---------------------------------------------------------
Title: Dynamics of Self-Formed Funnel Structure in 3D Realistic
    Simulations of a Quiet-Sun Region
Authors: Kitiashvili, Irina; Wray, Alan A.; Kosovichev, Alexander G.;
   Mansour, Nagi Nicolas
2018tess.conf10629K    Altcode:
  Dynamical interaction of the solar convection zone dynamics,
  chromosphere and corona is challenging in both observational and
  modeling aspects. Because of complex multi-scale interactions of
  turbulent MHD flows and structures realistic 3D radiative MHD numerical
  simulations are needed to shed light on self-organization processes
  of the turbulent magnetic fields, and investigate physical properties
  of the solar plasma and dynamical coupling across the layers from the
  subphotosphere to the corona. We present 3D MHD realistic simulations
  of the quiet-Sun dynamics, which covers upper layers of the convection
  zone to 10Mm above the photosphere. The simulations reveal a spontaneous
  formation of a self-organized funnel-like structure that extends through
  the chromosphere and corona. We will present thermodynamical properties
  of the structure, its influence on the dynamics of surrounding areas
  of the chromosphere and corona, discuss the formation mechanism, and
  compare the simulation results with IRIS, Hinode and SDO observations.

---------------------------------------------------------
Title: Subsurface Flow Dynamics and Flaring Activity of AR 12673
Authors: Kosovichev, Alexander G.; Sadykov, Viacheslav M.; Sharykin,
   Ivan; Zhao, Junwei
2018tess.conf30605K    Altcode:
  The flare-rich AR 12673 is characterized by rapid magnetic flux
  emergence, strong shearing and twisting flows, and complex magnetic
  topology. We use time-distance helioseismology data from SDO/HMI to
  investigate relationships among the subsurface dynamics, emergence,
  evolution and flaring activity of this active region. The subsurface
  flow maps are obtained with 1-hour cadence in the depth range of
  0-20 Mm during August 29 - September 9, 2017, covering the whole AR
  passage on the disk, from its emergence to the period of high flaring
  activity. Using the maps, we calculate the flow characteristics:
  divergence, vorticity, shear rate and helicity, and their correlations
  with the GOES X-ray flux, as well as with global and local magnetic
  field properties, including the vector magnetogram descriptors from
  the SHARP database, characteristics of the Polarity Inversion Line
  (PIL) and reconstructed topological properties (flux of high-twist
  magnetic field lines and free-energy excess). Among the subsurface
  flow characteristics, the highest correlation with the X-ray flux (with
  correlation coefficient 0.82) is found for the total unsigned kinetic
  helicity in the depth range 1.2-7.5 Mm beneath the PIL region. We
  discuss relationship of the flow and magnetic field characteristics to
  the onset of major flares of AR 12673, and compare the subsurface flow
  patterns with those observed for AR 10486 that produced the largest
  flares in the declining phase of the previous solar cycle.

---------------------------------------------------------
Title: Effects of Distributed Magnetic Fields and Compact Magnetic
    Structures on Properties of Acoustic Waves Excitation on the Sun
Authors: Kitiashvili, Irina; Kosovichev, Alexander G.; Wray, Alan A.;
   Mansour, Nagi Nicolas
2018tess.conf11504K    Altcode:
  Recent helioseismology interferences have shown possibility of acoustic
  waves excitation in the subsurface layers much deeper than 200 km. Using
  3D radiative MHD numerical simulations, we investigate acoustic wave
  excitation in the case of distributed magnetic field and spontaneously
  formed highly magnetized pore-like structures, and show that in the
  presence of strong magnetic field structures acoustic waves can be
  excited much deeper than in the quiet-Sun regions. The distribution
  of acoustic events with depth depends on the magnetic field scale. In
  particular, in the case of small-scale magnetic patches the acoustic
  events are located in a relative shallow, 1.5 Mm deep layer, while
  the acoustic sources located inside of a self-organized pore-like
  magnetic structure can be found up to 3-4Mm below the surface. We
  discuss the excitation mechanism, and present an explanation of recent
  helioseismology observations of deep acoustic sources in sunspots.

---------------------------------------------------------
Title: Intelligent Database of Solar Events and Active Regions
    (IDSEAR)
Authors: Sadykov, Viacheslav M.; Kosovichev, Alexander G.; Nita,
   Gelu M.; Oria, Vincent; Wang, Wei
2018tess.conf30713S    Altcode:
  The growing needs for the accurate Space Weather Forecasts motivate
  the researchers to implement comprehensive prediction algorithms
  for solar transient events (flares, coronal mass ejections,
  filament eruptions). However, each prediction attempt will face
  the data preparation and processing phase, which usually takes
  a significant part of the research time. Besides some attempts
  (e.g. SDO SHARP archive), currently there are no databases
  containing processed descriptors of the Active Regions (AR) and
  related observations of flares and eruptive events. We develop an
  Intelligent Database of Solar Events and Active Regions (IDSEAR)
  which is the continuation of the Interactive Multi-Instrument Database
  of Solar Flares (IMIDSF, &lt;a href="https://solarflare.njit.edu/"
  https://solarflare.njit.edu/&lt;/a&gt;) previously developed by
  our team. The IDSEAR will have full IMIDSF functionality (search of
  solar flares based on their physical descriptors) extended to the
  integration of Solar Events, ARs and related observations, which will
  allow users to make queries using descriptors of ARs and solar events
  linked to the ARs. In addition to the commonly-used AR descriptors,
  we plan to add new physical data products (NLFFF extrapolations and
  local helioseismology subsurface flow maps) and their descriptors, as
  well as operational data from SWPC NOAA (to include expert estimates in
  machine-learning procedures). The structure of the IDSEAR is scalable
  and allows addition of any descriptors and data products via the user
  contribution system (UCS). We envision that the developed database
  will allow the researchers to significantly speed up data processing
  and preparation for statistical analysis and physics-based prediction
  of solar events, as well as get access to and share high-quality
  scientific data products.

---------------------------------------------------------
Title: Testing the Standard Model of Solar Flares through a
    Statistical Study of Soft X-ray Emission Properties from GOES
    observations
Authors: Sadykov, Viacheslav M.; Kosovichev, Alexander G.
2018tess.conf40804S    Altcode:
  We present a statistical analysis of properties of Soft X-Ray
  (SXR) emission, plasma Temperatures (T) and Emission Measures (EM),
  derived from GOES observations of flares for 2002-2017 time period,
  and compare with qualitative predictions of the standard thick-target
  flare model. Temperatures and emission measures are obtained using the
  TEBBS algorithm (Ryan et al. 2012), which delivers reliable results
  even for weak B-class flare events. For each event, we compute
  the maxima of SXR, SXR derivative, T and EM, as well as their time
  delays with respect to each other. Our study of distributions of
  these parameters for the flares of different GOES classes leads to
  the following findings. First, more than 96% of flares demonstrate
  the sequential appearance of T, SXR, and EM maxima, which agrees with
  expected behavior of the chromospheric evaporation process predicted
  by radiative hydrodynamics simulations. The relative number of such
  flares increases with the increase of the GOES class. Second, the
  SXR maxima occur closer to the T maxima for the B-class flares, but
  closer to the EM maxima for the M-class flares, demonstrating that the
  different physical parameters (T and EM correspondingly) contribute
  differently to the SXR emission of strong and weak flares. Third,
  we selected two subgroups of C-class flares (one with dominating T
  contribution to SXR, the other with dominating EM contribution) and
  found no difference in distribution of their GOES classes, T and EM
  maxima. However, the events with dominating EM contribution are 30%
  longer and grow 72% slower in average. We discuss such statistical
  relationships in terms of the standard flare model, and, in particular,
  in terms of the influence of electron beam heating parameters on the
  chromospheric evaporation rates.

---------------------------------------------------------
Title: Machine-Learning Approach for Solar Flare Forecasts Based
    on Automatic Identification and Characterization of Magnetic Field
    Polarity Inversion Line
Authors: Sadykov, Viacheslav M.; Kosovichev, Alexander G.
2018tess.conf32202S    Altcode:
  It has long been known that major flares and eruptions are associated
  with polarity inversion line (PIL) in regions of strong magnetic field
  (such as in delta-type sunspots). However, what physical characteristics
  of PIL are the primary factors, which define the flare triggering
  mechanism and energetics, is still an open question. We analyze the
  relationship between the flare X-ray peak flux, and characteristics
  of the PIL and active regions (ARs), derived from line-of-sight (LOS)
  magnetograms. The automatic PIL detection procedure is based on a
  magnetogram segmentation algorithm using a variational principle. The
  procedure is applied to SDO/HMI magnetograms to calculate a set of the
  PIL physical characteristics for each AR with 1 hr cadence. The PIL
  characteristics are associated with the AR flare history and divided
  into flaring and nonflaring cases. Effectiveness of the derived
  characteristics for flare forecasting is determined by the number of
  nonflaring cases separated from flaring cases by a certain threshold,
  and by their Fisher ranking score. The Support Vector Machine (SVM)
  classifier trained only on the PIL characteristics is used for the
  flare prediction. We have obtained the following results: (1) the PIL
  characteristics are more effective than global characteristics of ARs,
  (2) the highest True Skill Statistics (TSS) values of 0.76 ± 0.03
  for ≥M1.0 flares and 0.84 ± 0.07 for ≥X1.0 flares are obtained
  using the "Sigmoid" SVM kernel, (3) the TSS scores obtained using only
  the LOS magnetograms are slightly lower than the scores obtained using
  vector magnetograms, but significantly better than current expert-based
  predictions, (4) for prediction of ≥M1.0 class flares 74.4% of all
  cases, and 91.2% for ≥X1.0 class, can be pre-classified as negative
  with no significant effect on the results, (5) the inclusion of global
  AR characteristics does not improve the forecast. The study confirms the
  unique role of the PIL region characteristics in the flare initiation
  process and demonstrates possibilities for operational flare forecasting
  using only the LOS magnetograms. We also discuss the extension of the
  proposed algorithm for prediction of the flare onset times and GOES
  classes (and other physical parameters).

---------------------------------------------------------
Title: How big is the Sun: Solar diameter changes over time
Authors: Rozelot, J. P.; Kosovichev, A. G.; Kilcik, A.
2018SunGe..13...63R    Altcode: 2018arXiv180406930R
  The measurement of the Sun's diameter has been first tackled by the
  Greek astronomers from a geometric point of view. Their estimation of
  ? 1800?, although incorrect, was not truly called into question for
  several centuries. The first pioneer works for measuring the Sun's
  diameter with an astrometric precision were made around the year 1660
  by Gabriel Mouton, then by Picard and La Hire. A canonical value of
  the solar radius of 959?.63 was adopted by Auwers in 1891. In spite
  of considerable efforts during the second half of the XXth century,
  involving dedicated space instruments, no consensus was reached on
  this issue. However, with the advent of high sensitivity instruments
  on board satellites, such as the Michelson Doppler Imager (MDI) on
  Solar and Heliospheric Observatory (SoHO) and the Helioseismic and
  Magnetic Imager (HMI) aboard NASA's Solar Dynamics Observatory (SDO),
  it was possible to extract with an unprecedented accuracy the surface
  gravity oscillation ? modes, over nearly two solar cycles, from 1996 to
  2017. Their analysis in the range of angular degree l = 140 - 300 shows
  that the so-called "seismic radius" exhibits a temporal variability in
  anti-phase with the solar activity. Even if the link between the two
  radii (photospheric and seismic) can be made only through modeling,
  such measurements provide an interesting alternative which led to a
  revision of the standard solar radius by the International Astronomical
  Union in 2015. This new look on such modern measurements of the Sun's
  global changes from 1996 to 2017 gives a new way for peering into
  the solar interior, mainly to better understand the subsurface fields
  which play an important role in the implementation of the solar cycles.

---------------------------------------------------------
Title: A brief history of the solar diameter measurements: a critical
    quality assessment of the existing data
Authors: Rozelot, Jean Pierre; Kosovichev, Alexander G.; Kilcik, Ali
2018vsss.book...89R    Altcode: 2016arXiv160902710R
  The size of the diameter of the Sun has been debated for a very
  long time. First tackled by the Greek astronomers from a geometric
  point of view, an estimate, although incorrect, has been determined,
  not truly called into question for several centuries. The French
  school of astronomy, under the impetus of Mouton and Picard in the
  XVIIth century can be considered as a pioneer in this issue. It was
  followed by the German school at the end of the XIXth century whose
  works led to a canonical value established at 959".63 (second of
  arc). A number of ground-based observations has been made in the
  second half of the XIXth century leading to controversial results
  mainly due to the difficulty to disentangle between the solar and
  atmospheric effects. Dedicated space measurements yield to a very
  faint dependence of the solar diameter with time. New studies over
  the entire radiation spectrum lead to a clear relationship between
  the solar diameter and the wavelength, reflecting the height at which
  the lines are formed. Thus the absolute value of the solar diameter,
  which is a reference for many astrophysical applications, must be
  stated according to the wavelength. Furthermore, notable features
  of the Near Sub-Surface Layer (NSSL), called the leptocline, can be
  established in relation to the solar limb variations, mainly through
  the shape asphericities coefficients. The exact relationship has not
  been established yet, but recent studies encourage further in-depth
  investigations of the solar subsurface dynamics, both observationally
  and by numerical MHD simulations.

---------------------------------------------------------
Title: Realistic Simulations of Stellar Radiative MHD
Authors: Wary, Alan A.; Bensassiy, Khalil; Kitiashvili, Irina N.;
   Mansour, Nagi N.; Kosovichev, Alexander G.
2018vsss.book...39W    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Local Helioseismology of Emerging Active Regions: A Case Study
Authors: Kosovichev, Alexander G.; Zhao, Junwei; Ilonidis, Stathis
2018vsss.book...15K    Altcode: 2016arXiv160704987K
  Local helioseismology provides a unique opportunity to investigate the
  subsurface structure and dynamics of active regions and their effect
  on the large-scale flows and global circulation of the Sun. We use
  measurements of plasma flows in the upper convection zone, provided
  by the Time-Distance Helioseismology Pipeline developed for analysis
  of solar oscillation data obtained by Helioseismic and Magnetic
  Imager (HMI) on Solar Dynamics Observatory (SDO), to investigate the
  subsurface dynamics of emerging active region NOAA 11726. The active
  region emergence was detected in deep layers of the convection zone
  about 12 hours before the first bipolar magnetic structure appeared on
  the surface, and 2 days before the emergence of most of the magnetic
  flux. The speed of emergence determined by tracking the flow divergence
  with depth is about 1.4 km/s, very close to the emergence speed in
  the deep layers. As the emerging magnetic flux becomes concentrated
  in sunspots local converging flows are observed beneath the forming
  sunspots. These flows are most prominent in the depth range 1-3 Mm,
  and remain converging after the formation process is completed. On the
  larger scale converging flows around active region appear as a diversion
  of the zonal shearing flows towards the active region, accompanied
  by formation of a large-scale vortex structure. This process occurs
  when a substantial amount of the magnetic flux emerged on the surface,
  and the converging flow pattern remains stable during the following
  evolution of the active region. The Carrington synoptic flow maps
  show that the large-scale subsurface inflows are typical for active
  regions. In the deeper layers (10-13 Mm) the flows become diverging,
  and surprisingly strong beneath some active regions. In addition,
  the synoptic maps reveal a complex evolving pattern of large-scale
  flows on the scale much larger than supergranulation

---------------------------------------------------------
Title: Influence of stellar radiation pressure on flow structure in
    the envelope of hot-Jupiter HD 209458b
Authors: Cherenkov, A. A.; Bisikalo, D. V.; Kosovichev, A. G.
2018MNRAS.475..605C    Altcode:
  Close-in exoplanets are subjected to extreme radiation of their
  host stars. Photometric observations of the hot-Jupiter HD 209458b
  transit by HST/STIS detected strong absorption in the Ly α line, thus
  indicating the existence of a hydrogen envelope extending beyond the
  Roche lobe. The gasdynamic modelling (Bisikalo et al.) showed that the
  stable structure of this envelope is maintained by the balance between
  the Roche lobe overfilling and stellar wind pressure. Obviously, the
  dynamics and stability of the envelope can be affected by stellar
  radiation pressure. Using 3D gasdynamic simulations, we study the
  impact of radiation pressure in the Ly α line on the envelope of
  hot-Jupiter HD 209458b, and show that the effect is not strong enough
  to significantly affect the gasdynamics in the system. For a detectable
  radiation pressure effect the intensity of the Ly α line has to be
  by two orders of magnitude greater.

---------------------------------------------------------
Title: On the Origin of the Double-cell Meridional Circulation in
    the Solar Convection Zone
Authors: Pipin, V. V.; Kosovichev, A. G.
2018ApJ...854...67P    Altcode: 2017arXiv170803073P
  Recent advances in helioseismology, numerical simulations and
  mean-field theory of solar differential rotation have shown that the
  meridional circulation pattern may consist of two or more cells in
  each hemisphere of the convection zone. According to the mean-field
  theory the double-cell circulation pattern can result from the sign
  inversion of a nondiffusive part of the radial angular momentum
  transport (the so-called Λ-effect) in the lower part of the solar
  convection zone. Here, we show that this phenomenon can result from
  the radial inhomogeneity of the Coriolis number, which depends on
  the convective turnover time. We demonstrate that if this effect is
  taken into account then the solar-like differential rotation and
  the double-cell meridional circulation are both reproduced by the
  mean-field model. The model is consistent with the distribution of
  turbulent velocity correlations determined from observations by tracing
  motions of sunspots and large-scale magnetic fields, indicating that
  these tracers are rooted just below the shear layer.

---------------------------------------------------------
Title: 3D Realistic Radiative Hydrodynamic Modeling of a Moderate-Mass
Star: Effects of Rotation
Authors: Kitiashvili, Irina; Kosovichev, Alexander G.; Mansour,
   Nagi N.; Wray, Alan A.
2018AAS...23133404K    Altcode:
  Recent progress in stellar observations opens new perspectives in
  understanding stellar evolution and structure. However, complex
  interactions in the turbulent radiating plasma together with effects
  of magnetic fields and rotation make inferences of stellar properties
  uncertain. The standard 1D mixing-length-based evolutionary models
  are not able to capture many physical processes of stellar interior
  dynamics, but they provide an initial approximation of the stellar
  structure that can be used to initialize 3D time-dependent radiative
  hydrodynamics simulations, based on first physical principles, that
  take into account the effects of turbulence, radiation, and others. In
  this presentation we will show simulation results from a 3D realistic
  modeling of an F-type main-sequence star with mass 1.47 Msun, in which
  the computational domain includes the upper layers of the radiation
  zone, the entire convection zone, and the photosphere. The simulation
  results provide new insight into the formation and properties of the
  convective overshoot region, the dynamics of the near-surface, highly
  turbulent layer, the structure and dynamics of granulation, and the
  excitation of acoustic and gravity oscillations. We will discuss the
  thermodynamic structure, oscillations, and effects of rotation on the
  dynamics of the star across these layers.

---------------------------------------------------------
Title: Helioseismic Observations of Two Solar Cycles and Constraints
    on Dynamo Theory
Authors: Kosovichev, Alexander
2018AAS...23131505K    Altcode:
  Helioseismology data from the SOHO and SDO, obtained in 1996-2017 for
  almost two solar cycles, provide a unique opportunity to investigate
  variations of the solar interior structure and dynamics, and link these
  variations to the current dynamo models and simulations. The solar
  oscillation frequencies and frequency splitting of medium-degree p- and
  f-modes, as well as helioseismic inversions have been used to analyze
  variations of the differential rotation (“torsional oscillations”)
  and the global asphericity. By comparing the helioseismology results
  with the synoptic surface magnetic fields we identify characteristic
  changes associated the initiation and evolution of the solar cycles,
  23 and 24. The observational results are compared with the current
  mean-field dynamo models and 3D MHD dynamo simulations. It is shown
  that the helioseismology inferences provide important constraints on
  the dynamics of the tachocline and near-surface shear layer, and also
  may explain the fundamental difference between the two solar cycles
  and detect the onset of the next cycle.

---------------------------------------------------------
Title: Helioseismology Observations of Solar Cycles and Dynamo
    Modeling
Authors: Kosovichev, A. G.; Guerrero, G.; Pipin, V.
2017AGUFMSH12A..04K    Altcode:
  Helioseismology observations from the SOHO and SDO, obtained in
  1996-2017, provide unique insight into the dynamics of the Sun's
  deep interior for two solar cycles. The data allow us to investigate
  variations of the solar interior structure and dynamics, and compare
  these variations with dynamo models and simulations. We use results
  of the local and global helioseismology data processing pipelines
  at the SDO Joint Science Operations Center (Stanford University) to
  study solar-cycle variations of the differential rotation, meridional
  circulation, large-scale flows and global asphericity. By comparing
  the helioseismology results with the evolution of surface magnetic
  fields we identify characteristic changes associated the initiation and
  development of Solar Cycles 23 and 24. For the physical interpretation
  of observed variations, the results are compared with the current
  mean-field dynamo models and 3D MHD dynamo simulations. It is shown
  that the helioseismology inferences provide important constraints on
  the solar dynamo mechanism, may explain the fundamental difference
  between the two solar cycles, and also give information about the next
  solar cycle.

---------------------------------------------------------
Title: Solar activity across the scales: from small-scale quiet-Sun
    dynamics to magnetic activity cycles
Authors: Kitiashvili, I.; Collins, N.; Kosovichev, A. G.; Mansour,
   N. N.; Wray, A. A.
2017AGUFMSH13A2466K    Altcode:
  Observations as well as numerical and theoretical models show that
  solar dynamics is characterized by complicated interactions and
  energy exchanges among different temporal and spatial scales. It
  reveals magnetic self-organization processes from the smallest scale
  magnetized vortex tubes to the global activity variation known as
  the solar cycle. To understand these multiscale processes and their
  relationships, we use a two-fold approach: 1) realistic 3D radiative MHD
  simulations of local dynamics together with high-resolution observations
  by IRIS, Hinode, and SDO; and 2) modeling of solar activity cycles by
  using simplified MHD dynamo models and mathematical data assimilation
  techniques. We present recent results of this approach, including
  the interpretation of observational results from NASA heliophysics
  missions and predictive capabilities. In particular, we discuss the
  links between small-scale dynamo processes in the convection zone and
  atmospheric dynamics, as well as an early prediction of Solar Cycle 25.

---------------------------------------------------------
Title: Relationship between Hard X-Ray Footpoint Sources and
Photospheric Electric Currents in Solar Flares: a Statistical Study
Authors: Zimovets, I. V.; Sharykin, I. N.; Wang, R.; Liu, Y. D.;
   Kosovichev, A. G.
2017AGUFMSH41A2751Z    Altcode:
  It is believed that solar flares are a result of release of free
  magnetic energy contained in electric currents (ECs) flowing in active
  regions (ARs). However, there are still debates whether the primary
  energy release and acceleration of electrons take place in coronal
  current sheets or in chromospheric footpoints of current-carrying
  magnetic flux tubes (loops). We present results of an observational
  statistical study of spatial relationship between hard X-ray (HXR;
  EHXR≥50keV) footpoint sources detected by RHESSI and vertical
  photospheric ECs calculated using vector magnetograms obtained from the
  SDO/HMI data. We found that for a sample of 47 flares (from C3.0 to X3.1
  class) observed on the solar disk by both instruments in 2010-2016,
  at least one HXR source was in a region of strong (within 20% of the
  maximum EC density in the corresponding ARs) vertical ECs having the
  form of a ribbon (79%) or an island (21%). The total vertical ECs in
  such HXR sources are in the range of 1010-1013 A. The EC density is in
  the range of 0.01-1.0 A/m2. We found no correlation between intensity
  of the HXR sources and the EC density. By comparing pre-flare and
  post-flare EC maps we did not find evidences of significant dissipation
  of vertical ECs in the regions corresponding to the HXR sources. In
  some cases, we found amplification of ECs during flares. We discuss
  effects of sensitivity and angular resolution of RHESSI and SDO/HMI. In
  general, the results indicate that there is a link between the flare HXR
  footpoint sources and enhanced vertical ECs in the photosphere. However,
  the results do not support a concept of electron acceleration by the
  electric field excited in footpoints of current-carrying loops due
  to some (e.g. Rayleigh-Taylor) instabilities (Zaitsev et al., 2016),
  since strong correlation between the HXR intensity and the EC density
  is expected in such concept.

---------------------------------------------------------
Title: Reduction of mass loss by the hot Jupiter WASP-12b due to
    its magnetic field
Authors: Arakcheev, A. S.; Zhilkin, A. G.; Kaigorodov, P. V.; Bisikalo,
   D. V.; Kosovichev, A. G.
2017ARep...61..932A    Altcode:
  The influence of the dipolar magnetic field of a "hot Jupiter" with
  the parameters of the object WASP-12b on the mass-loss rate from
  its atmosphere is investigated. The results of three-dimensional
  gas-dynamical and magnetohydrodynamical computations show that the
  presence of a magnetic moment with a strength of 0.1 the magnetic
  moment of Jupiter leads to appreciable variations of the matter
  flow structure. For example, in the case of the exoplanet WASP-12b
  with its specified set of atmospheric parameters, the stream from
  the vicinity of the Lagrange point L<SUB>1</SUB> is not stopped
  by the dynamical pressure of the stellar wind, and the envelope
  remains open. Including the effect of the magnetic field leads to
  a variation in this picture—the atmosphere becomes quasi-closed,
  with a characteristic size of order 14 planetary radii, which, in turn,
  substantially decreases the mass-loss rate by the exoplanet atmosphere
  (by 70%). This reduction of the mass-loss rate due to the influence of
  the magnetic fieldmakes it possible for exoplanets to form closed and
  quasi-closed envelopes in the presence of more strongly overflowing
  Roche lobes than is possible without a magnetic field.

---------------------------------------------------------
Title: Relationships between Characteristics of the Line-of-sight
    Magnetic Field and Solar Flare Forecasts
Authors: Sadykov, Viacheslav M.; Kosovichev, Alexander G.
2017ApJ...849..148S    Altcode: 2017arXiv170403423S
  We analyze the relationship between the flare X-ray peak flux,
  and characteristics of the polarity inversion line (PIL) and active
  regions (ARs), derived from line-of-sight (LOS) magnetograms. The PIL
  detection algorithm based on a magnetogram segmentation procedure is
  applied for each AR with 1 hr cadence. The PIL and AR characteristics
  are associated with the AR flare history and divided into flaring
  and nonflaring cases. Effectiveness of the derived characteristics
  for flare forecasting is determined by the number of nonflaring cases
  separated from flaring cases by a certain threshold, and by their Fisher
  ranking score. The Support Vector Machine (SVM) classifier trained only
  on the PIL characteristics is used for the flare prediction. We have
  obtained the following results: (1) the PIL characteristics are more
  effective than global characteristics of ARs, (2) the highest True
  Skill Statistics (TSS) values of 0.76 ± 0.03 for ≥M1.0 flares and
  0.84 ± 0.07 for ≥X1.0 flares are obtained using the “Sigmoid”
  SVM kernel, (3) the TSS scores obtained using only the LOS magnetograms
  are slightly lower than the scores obtained using vector magnetograms,
  but significantly better than current expert-based predictions, (4)
  for prediction of ≥M1.0 class flares 74.4% of all cases, and 91.2%
  for ≥X1.0 class, can be pre-classified as negative with no significant
  effect on the results, (5) the inclusion of global AR characteristics
  does not improve the forecast. The study confirms the unique role
  of the PIL region characteristics in the flare initiation process,
  and demonstrates possibilities of flare forecasting using only the
  LOS magnetograms.

---------------------------------------------------------
Title: Are tachoclines important for solar and stellar dynamos? What
    can we learn from global simulations
Authors: Guerrero, G.; Smolarkiewicz, P. K.; de Gouveia Dal Pino,
   E. M.; Kosovichev, A. G.; Zaire, B.; Mansour, N. N.
2017IAUS..328...61G    Altcode:
  The role of tachoclines, the thin shear layers that separate solid
  body from differential rotation in the interior of late-type stars, in
  stellar dynamos is still controversial. In this work we discuss their
  relevance in view of recent results from global dynamo simulations
  performed with the EULAG-MHD code. The models have solar-like
  stratification and different rotation rates (i.e., different Rossby
  number). Three arguments supporting the key role of tachoclines are
  presented: the solar dynamo cycle period, the origin of torsional
  oscillations and the scaling law of stellar magnetic fields as function
  of the Rossby number. This scaling shows a regime where the field
  strength increases with the rotation and a saturated regime for fast
  rotating stars. These properties are better reproduced by models that
  consider the convection zone and a fraction of the radiative core,
  naturally developing a tachocline, than by those that consider only
  the convection zone.

---------------------------------------------------------
Title: Fine Structure and Dynamics of the Solar Atmosphere
Authors: Vargas Domínguez, S.; Kosovichev, A. G.; Antolin, P.;
   Harra, L.
2017IAUS..327.....V    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Magnetic field generation in PMS stars with and without
    radiative core
Authors: Zaire, B.; Guerrero, G.; Kosovichev, A. G.; Smolarkiewicz,
   P. K.; Landin, N. R.
2017IAUS..328...30Z    Altcode: 2017arXiv171102057Z
  Recent observations of the magnetic field in pre-main sequence stars
  suggest that the magnetic field topology changes as a function of
  age. The presence of a tachocline could be an important factor in the
  development of magnetic field with higher multipolar modes. In this
  work we performed MHD simulations using the EULAG-MHD code to study the
  magnetic field generation and evolution in models that mimic stars at
  two evolutionary stages. The stratification for both stellar phases was
  computed by fitting stellar structure profiles obtained with the ATON
  stellar evolution code. The first stage is at 1.1Myr, when the star
  is completely convective. The second stage is at 14Myrs, when the star
  is partly convective, with a radiative core developed up to 30% of the
  stellar radius. In this proceedings we present a preliminary analysis
  of the resulting mean-flows and magnetic field. The mean-flow analysis
  shown that the star rotate almost rigidly on the fully convective
  phase, whereas at the partially convective phase there is differential
  rotation with conical contours of iso-rotation. As for the mean magnetic
  field both simulations show similarities with respect to the field
  evolution. However, the topology of the magnetic field is different.

---------------------------------------------------------
Title: Exploring shallow sunspot formation by using Implicit
    Large-eddy simulations
Authors: Camacho, F. J.; Guerrero, G.; Smolarkiewicz, P. K.;
   Kosovichev, A. G.; Mansour, N. N.
2017IAUS..328..117C    Altcode:
  The mechanism by which sunspots are generated at the surface of
  the sun remains unclear. In the current literature two types of
  explanations can be found. The first one is related to the buoyant
  emergence of toroidal magnetic fields generated at the tachocline. The
  second one states that active regions are formed, from initially
  diffused magnetic flux, by MHD instabilities that develop in the
  near-surface layers of the Sun. Using the anelastic MHD code EULAG
  we address the problem of sunspot formation by performing implicit
  large-eddy simulations of stratified magneto-convection in a domain
  that resembles the near-surface layers of the Sun. The development
  of magnetic structures is explored as well as their effect on the
  convection dynamics. By applying a homogeneous magnetic field over an
  initially stationary hydrodynamic convective state, we investigate
  the formation of self-organized magnetic structures in the range of
  the initial magnetic field strength, 0.01 &lt; B <SUB>0</SUB>/B <SUB>
  eq </SUB> &lt; 0.5, where B <SUB> eq </SUB> is the characteristic
  equipartition field strength.

---------------------------------------------------------
Title: Initiation and chromospheric effects of a M1.0 class solar
    flare from high-resolution multi-wavelength observations
Authors: Sadykov, V. M.; Kosovichev, A. G.; Sharykin, I. N.; Zimovets,
   I. V.; Vargas Dominguez, S.
2017IAUS..327..103S    Altcode:
  Initiation and development of a M 1.0 class flare of June 12, 2014, was
  observed by space and ground-based telescopes, including EUV and X-ray
  imaging spectroscopy by IRIS and RHESSI, and high-resolution optical
  imaging by 1.6 m New Solar Telescope (NST). Analyzing the NST data,
  we found small-scale loop-like structures in the region of the magnetic
  field Polarity Inversion Line (PIL), the emergence and interaction of
  which caused photospheric brightenings temporarily coinciding with hard
  X-ray impulses. Detailed studies of the PIL region reveal signatures of
  photospheric plasma downflows and dissipation of electric currents. The
  reconstructed magnetic field topology shows a bundle of lines connecting
  the PIL region with the flare ribbons which were places of chromospheric
  evaporation observed by IRIS. The observations suggest a scenario with
  the primary energy release processes located in the low atmospheric
  layers of the PIL, energizing the overlying large-scale magnetic
  structure and causing “gentle” chromospheric evaporation.

---------------------------------------------------------
Title: A Look on the Solar Diameter Data Analysis over the Centuries
Authors: Rozelot, J. P.; Kosovichev, A. G.; Kilcik, A.
2017simi.conf...70R    Altcode:
  The measurement of the Sun's diameter has been first tackled by the
  Greek astronomers from a geometric point of view. Their estimation of
  ≈ 1800″, although incorrect, was not truly called into question
  for several centuries. The first pioneer works for measuring the Sun's
  diameter with an astrometric precision were made around the year 1660
  by Gabriel Mouton, then by Picard and La Hire. A canonical value of
  the solar radius of 959″.63 was adopted by Auwers in 1891. In spite
  of considerable efforts during the second half of the XXth century,
  involving dedicated space instruments, no consensus was reached on
  this issue. However, with the advent of high sensitivity instruments
  on board satellites, such as the Michelson Doppler Imager (MDI)
  on Solar and Heliospheric Observatory (SoHO) and the Helioseismic
  and Magnetic Imager (HMI) aboard NASA's Solar Dynamics Observatory
  (SDO), it was possible to extract with an unprecedented accuracy the
  surface gravity oscillation f modes, over nearly two solar cycles,
  from 1996 to 2017. Their analysis in the range of angular degree =
  140 300 shows that the so-called "seismic radius" exhibits a temporal
  variability in antiphase with the solar activity; This new look on
  such modern measurements of the Sun's global changes from 1996 to 2017
  gives a new way for peering into the solar interior.

---------------------------------------------------------
Title: Characteristics of the Polarity Inversion Line and Solar
    Flare Forecasts
Authors: Sadykov, Viacheslav M.; Kosovichev, Alexander G.
2017SPD....4811601S    Altcode:
  Studying connection between solar flares and properties of magnetic
  field in active regions is very important for understanding the flare
  physics and developing space weather forecasts. In this work, we analyze
  relationship between the flare X-ray peak flux from the GOES satellite,
  and characteristics of the line-of-sight (LOS) magnetograms obtained
  by the SDO/HMI instrument during the period of April, 2010 - June,
  2016. We try to answer two questions: 1) What characteristics of
  the LOS magnetic field are most important for the flare initiation
  and magnitude? 2) Is it possible to construct a reliable forecast
  of ≥ M1.0 and ≥ X1.0 class flares based only on the LOS magnetic
  field characteristics? To answer these questions, we apply a Polarity
  Inversion Line (PIL) detection algorithm, and derive various properties
  of the PIL and the corresponding Active Regions (AR). The importance
  of these properties for flare forecasting is determined by their
  ability to separate flaring cases from non-flaring, and their Fisher
  ranking score. It is found that the PIL characteristics are of special
  importance for the forecasts of both ≥ M1.0 and ≥ X1.0 flares,
  while the global AR characteristics become comparably discriminative
  only for ≥ X1.0 flares. We use the Support Vector Machine (SVM)
  classifier and train it on the six characteristics of the most
  importance for each case. The obtained True Skill Statistics (TSS)
  values of 0.70 for ≥ M1.0 flares and 0.64 for ≥ X1.0 flares are
  better than the currently-known expert-based predictions. Therefore,
  the results confirm the importance of the LOS magnetic field data and,
  in particular, the PIL region characteristics for flare forecasts.

---------------------------------------------------------
Title: Analysis of Chromospheric Evaporation in Solar Flares
Authors: Sadykov, Viacheslav M.; Kosovichev, Alexander G.
2017SPD....4810817S    Altcode:
  Chromospheric evaporation is one of the key processes of solar
  flares. Properties of chromospheric evaporation are thought to be
  closely connected to the energy release rates and energy transport
  mechanisms. Previous investigations revealed that in addition to
  electron-beam heating the chromospheric evaporation can be driven
  by heat fluxes and, probably, by other mechanisms. In this work,
  we present a study of flare events simultaneously observed by IRIS,
  SDO and RHESSI, focusing on spatio-temporal characteristics of the
  flare dynamics and its relation to the magnetic field topology. Event
  selection is performed using the Interactive Multi-Instrument
  Database of Solar Flares (IMIDSF) recently developed by the Center
  for Computational Heliophysics (CCH) at NJIT. The selection of
  IRIS observations was restricted to the fast-scanning regimes
  (coarse-raster or sparse-raster modes with ≥ 4 slit positions, ≥
  6“ spatial coverage, and ≤ 60 sec loop time). We have chosen 14
  events, and estimated the spatially-resolved intensities and Doppler
  shifts of the chromospheric (Mg II), transition region (C II) and hot
  coronal (Fe XXI) lines reflecting the dynamics of the chromospheric
  evaporation. The correlations among the derived line profile properties,
  flare morphology, magnetic topology and hard X-ray characteristics
  will be presented, and compared with the RADYN flare models and other
  scenarios of chromospheric evaporations.

---------------------------------------------------------
Title: Interactive Multi-Instrument Database of Solar Flares (IMIDSF)
Authors: Sadykov, Viacheslav M.; Nita, Gelu M.; Oria, Vincent;
   Kosovichev, Alexander G.
2017SPD....48.0101S    Altcode:
  Solar flares represent a complicated physical phenomenon observed
  in a broad range of the electromagnetic spectrum, from radiowaves to
  gamma-rays. For a complete understanding of the flares it is necessary
  to perform a combined multi-wavelength analysis using observations
  from many satellites and ground-based observatories. For efficient
  data search, integration of different flare lists and representation of
  observational data, we have developed the Interactive Multi-Instrument
  Database of Solar Flares (https://solarflare.njit.edu/). The
  web database is fully functional and allows the user to search
  for uniquely-identified flare events based on their physical
  descriptors and availability of observations of a particular set of
  instruments. Currently, data from three primary flare lists (GOES,
  RHESSI and HEK) and a variety of other event catalogs (Hinode,
  Fermi GBM, Konus-Wind, OVSA flare catalogs, CACTus CME catalog,
  Filament eruption catalog) and observing logs (IRIS and Nobeyama
  coverage), are integrated. An additional set of physical descriptors
  (temperature and emission measure) along with observing summary, data
  links and multi-wavelength light curves is provided for each flare
  event since January 2002. Results of an initial statistical analysis
  will be presented.

---------------------------------------------------------
Title: Realistic Modeling of Interaction of Quiet-Sun Magnetic Fields
    with the Chromosphere
Authors: Kitiashvili, Irina; Kosovichev, Alexander G.; Mansour,
   Nagi N.; Wray, Alan A.
2017SPD....4810502K    Altcode:
  High-resolution observations and 3D MHD simulations reveal intense
  interaction between the convection zone dynamics and the solar
  atmosphere on subarcsecond scales. To investigate processes of
  the dynamical coupling and energy exchange between the subsurface
  layers and the chromosphere we perform 3D radiative MHD modeling
  for a computational domain that includes the upper convection zone
  and the chromosphere, and investigate the structure and dynamics for
  different intensity of the photospheric magnetic flux. For comparison
  with observations, the simulation models have been used to calculate
  synthetic Stokes profiles of various spectral lines. The results show
  intense energy exchange through small-scale magnetized vortex tubes
  rooted below the photosphere, which provide extra heating of the
  chromosphere, initiate shock waves, and small-scale eruptions.

---------------------------------------------------------
Title: Solar-Cycle Variations Observed by Helioseismology and
    Constraints on Solar Dynamo
Authors: Kosovichev, Alexander G.; Larson, Timothy P.; Guerrero,
   Gustavo; Pipin, Valery
2017SPD....4840303K    Altcode:
  Helioseismology data from the SOHO and SDO, obtained in 1996-2017 for
  almost two solar cycles, provide a unique opportunity to investigate
  variations of the solar interior structure and dynamics, and link
  these variations to the current dynamo models and simulations. The
  solar oscillation frequencies and frequency splitting of medium-degree
  p- and f-modes, as well as helioseismic inversions have been used to
  analyze the differential rotation and global asphericity. By comparing
  the helioseismology results with the synoptic surface magnetic fields
  we identify characteristic changes associated the initiation and
  evolution of the solar cycles, 23 and 24. The observational results are
  compared with the current mean-field dynamo models and 3D MHD dynamo
  simulations. It is shown that the helioseismology inferences provide
  important constraints on the dynamics of the tachocline and near-surface
  shear layer, and also may explain the fundamental difference between
  the two solar cycles and detect the onset of the next cycle.

---------------------------------------------------------
Title: Relationship Between High-Energy X-ray Sources and Helioseismic
    Impact of X-Class Flare
Authors: Kosovichev, Alexander G.; Sharykin, Ivan N.; Sadykov,
   Viacheslav M.; Zimovets, Ivan V.; Myshyakov, Ivan I.
2017SPD....48.0203K    Altcode:
  The X-class solar flare of October 23, 2012, generated the strongest
  sunquake event of the current solar cycle. We study properties of
  the energy release with high temporal and spatial resolutions, using
  photospheric data from the Helioseismic Magnetic Imager (HMI) onboard
  Solar Dynamics Observatory (SDO), and hard X-ray observations made
  by the Ramaty High-Energy Solar Spectroscopic Imager (RHESSI). To
  investigate the photospheric impact with high temporal resolution
  we developed a special procedure for analysis of level-1 HMI data
  (filtergrams), obtained by scanning the Fe I line (6731 A) with
  the time cadence of 3.6 s and spatial resolution of 0.5 arcsec per
  pixel. The helioseismic holography technique was used to reconstruct
  the helioseismic impact. It is found that the photospheric disturbances
  caused by the flare spatially coincide with the region of hard X-ray
  emission, but are delayed by 4 seconds. This delay is consistent
  with predictions of the flare hydrodynamics RADYN models. However,
  the models fail to explain the magnitude of variations observed by the
  HMI. The data indicate that the photospheric impact and helioseismic
  wave might be caused by the electron energy flux substantially higher
  than that in the current flare radiative hydrodynamic models.

---------------------------------------------------------
Title: An Interactive Multi-instrument Database of Solar Flares
Authors: Sadykov, Viacheslav M.; Kosovichev, Alexander G.; Oria,
   Vincent; Nita, Gelu M.
2017ApJS..231....6S    Altcode: 2017arXiv170202991S
  Solar flares are complicated physical phenomena that are observable
  in a broad range of the electromagnetic spectrum, from radio waves
  to γ-rays. For a more comprehensive understanding of flares, it
  is necessary to perform a combined multi-wavelength analysis using
  observations from many satellites and ground-based observatories. For
  an efficient data search, integration of different flare lists,
  and representation of observational data, we have developed the
  Interactive Multi-Instrument Database of Solar Flares (IMIDSF, <A
  href="https://solarflare.njit.edu/">https://solarflare.njit.edu/</A>).
  The web-accessible database is fully functional and allows the user to
  search for uniquely identified flare events based on their physical
  descriptors and the availability of observations by a particular set
  of instruments. Currently, the data from three primary flare lists
  (Geostationary Operational Environmental Satellites, RHESSI, and HEK)
  and a variety of other event catalogs (Hinode, Fermi GBM, Konus-WIND,
  the OVSA flare catalogs, the CACTus CME catalog, the Filament eruption
  catalog) and observing logs (IRIS and Nobeyama coverage) are integrated,
  and an additional set of physical descriptors (temperature and emission
  measure) is provided along with an observing summary, data links,
  and multi-wavelength light curves for each flare event since 2002
  January. We envision that this new tool will allow researchers to
  significantly speed up the search of events of interest for statistical
  and case studies.

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Title: Investigation of Relationship between High-energy X-Ray
    Sources and Photospheric and Helioseismic Impacts of X1.8 Solar
    Flare of 2012 October 23
Authors: Sharykin, I. N.; Kosovichev, A. G.; Sadykov, V. M.; Zimovets,
   I. V.; Myshyakov, I. I.
2017ApJ...843...67S    Altcode: 2017arXiv170303767S
  The X-class solar flare of 2012 October 23 generated continuum
  photospheric emission and a strong helioseismic wave (“sunquake”)
  that points to an intensive energy release in the dense part of the
  solar atmosphere. We study properties of the energy release with high
  temporal and spatial resolutions, using photospheric data from the
  Helioseismic Magnetic Imager (HMI) on board Solar Dynamics Observatory,
  and hard X-ray observations made by RHESSI. For this analysis we use
  level-1 HMI data (filtergrams), obtained by scanning the Fe I line
  (6731 Å) with the time cadence of ∼3.6 s and spatial resolution of
  ∼0.″5 per pixel. It is found that the photospheric disturbances
  caused by the flare spatially coincide with the region of hard X-ray
  emission but are delayed by ≲4 s. This delay is consistent with
  predictions of the flare hydrodynamics RADYN models. However, the models
  fail to explain the magnitude of variations observed by the HMI. The
  data indicate that the photospheric impact and helioseismic wave might
  be caused by the electron energy flux, which is substantially higher
  than that in the current flare radiative hydrodynamic models.

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Title: Statistical properties of coronal hole rotation rates: Are
    they linked to the solar interior?
Authors: Bagashvili, S. R.; Shergelashvili, B. M.; Japaridze,
   D. R.; Chargeishvili, B. B.; Kosovichev, A. G.; Kukhianidze, V.;
   Ramishvili, G.; Zaqarashvili, T. V.; Poedts, S.; Khodachenko, M. L.;
   De Causmaecker, P.
2017A&A...603A.134B    Altcode: 2017arXiv170604464B
  Context. The present paper discusses results of a statistical study
  of the characteristics of coronal hole (CH) rotation in order to
  find connections to the internal rotation of the Sun. <BR /> Aims:
  The goal is to measure CH rotation rates and study their distribution
  over latitude and their area sizes. In addition, the CH rotation rates
  are compared with the solar photospheric and inner layer rotational
  profiles. <BR /> Methods: We study CHs observed within ± 60° latitude
  and longitude from the solar disc centre during the time span from
  the 1 January 2013 to 20 April 2015, which includes the extended peak
  of solar cycle 24. We used data created by the spatial possibilistic
  clustering algorithm (SPoCA), which provides the exact location and
  characterisation of solar coronal holes using SDO/AIA193 Å channel
  images. The CH rotation rates are measured with four-hour cadence
  data to track variable positions of the CH geometric centre. <BR />
  Results: North-south asymmetry was found in the distribution of coronal
  holes: about 60 percent were observed in the northern hemisphere and
  40 percent were observed in the southern hemisphere. The smallest and
  largest CHs were present only at high latitudes. The average sidereal
  rotation rate for 540 examined CHs is 13.86( ± 0.05)°/d. <BR />
  Conclusions: The latitudinal characteristics of CH rotation do
  not match any known photospheric rotation profile. The CH angular
  velocities exceed the photospheric angular velocities at latitudes
  higher than 35-40 degrees. According to our results, the CH rotation
  profile perfectly coincides with tachocline and the lower layers of
  convection zone at around 0.71 R<SUB>⊙</SUB>; this indicates that
  CHs may be linked to the solar global magnetic field, which originates
  in the tachocline region.

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Title: Helioseismic Observations and Constraints on Solar and Stellar
    Dynamo Models
Authors: Kosovichev, Alexander G.; Guerrero, Gustavo; Pipin, Valery V.
2017shin.confE..56K    Altcode:
  Helioseismology data from the SOHO and SDO, obtained in 1996-2017 for
  almost two solar cycles, provide a unique opportunity to investigate
  variations of the solar interior structure and dynamics, and link
  these variations to the current dynamo models and simulations. The
  solar oscillation frequencies and frequency splitting of medium-degree
  p- and f-modes, as well as helioseismic inversions have been used to
  analyze the differential rotation and global asphericity. By comparing
  the helioseismology results with the synoptic surface magnetic fields
  we identify characteristic changes associated the initiation and
  evolution of the solar cycles, 23 and 24. The observational results are
  compared with the current mean-field dynamo models and 3D MHD dynamo
  simulations. It is shown that the helioseismology inferences provide
  important constraints on the dynamics of the tachocline and near-surface
  shear layer, and also may explain the fundamental difference between
  the two solar cycles and detect the onset of the next cycle.

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Title: Realistic 3D radiative modeling of turbulent structure of
    moderate-mass stars and Sun
Authors: Kitiashvili, Irina N.; Kosovichev, Alexander G.; Wray,
   Alan A.; Mansour, Nagi N.
2017shin.confE..60K    Altcode:
  Understanding the turbulent dynamics of the Sun and stars is a
  critical element for interpreting observed processes and phenomena on
  different scales and for predicting extreme events such as flares and
  superflares. High-resolution observations of the Sun and high-fidelity
  radiative MHD numerical simulations have substantially advanced our
  understanding of solar and stellar local dynamics and magnetism from
  the upper convection zone to the atmosphere and corona. However,
  global modeling of the Sun with such a high degree of realism is
  currently not affordable due to the extremely high computational cost
  of resolving the scales in the convection zone. The physics of the
  deep solar dynamics can be effectively addressed through modeling
  more massive solar-type stars where the convection zone is shallower
  and the convective overturning time is much shorter than those on the
  Sun. We present recent 3D realistic simulation results of moderate-mass
  stars and discuss links between solar and stellar dynamics, such
  as the multiscale structure of granulation, convective overshoot,
  and others. In particular, these simulations have provided better
  understanding of the dynamics of the tachocline (the overshoot layer
  at the bottom of the convection zone) and have explained long-standing
  results from helioseismology.

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Title: Flare Energy Release in the Lower Solar Atmosphere near the
    Magnetic Field Polarity Inversion Line
Authors: Sharykin, I. N.; Sadykov, V. M.; Kosovichev, A. G.; Vargas
   Dominguez, S.; Zimovets, I. V.
2017ApJ...840...84S    Altcode: 2018arXiv180104921S
  We study flare processes in the solar atmosphere using observational
  data for an M1-class flare of 2014 June 12, obtained by the New Solar
  Telescope (NST/BBSO) and Helioseismic Magnetic Imager (HMI/SDO). The
  main goal is to understand triggers and manifestations of the flare
  energy release in the photosphere and chromosphere using high-resolution
  optical observations and magnetic field measurements. We analyze
  optical images, HMI Dopplergrams, and vector magnetograms, and use
  nonlinear force-free field (NLFFF) extrapolations for reconstruction
  of the magnetic topology and electric currents. The NLFFF modeling
  reveals the interaction of two magnetic flux ropes with oppositely
  directed magnetic fields in the polarity inversion line (PIL). These
  flux ropes are observed as a compact sheared arcade along the PIL in the
  high-resolution broadband continuum images from NST. In the vicinity of
  the PIL, the NST {{H}}α observations reveal the formation of a thin
  three-ribbon structure corresponding to a small-scale photospheric
  magnetic arcade. The observational results are evidence in favor of
  the primary energy release site located in the chromospheric plasma
  with strong electric currents concentrated near the PIL. In this case,
  magnetic reconnection is triggered by the interacting magnetic flux
  ropes forming a current sheet elongated along the PIL.

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Title: Magnetoacoustic Waves Excitation in Self-Organized Solar
    Magnetic Structures
Authors: Kitiashvili, I.; Kosovichev, A. G.; Mansour, N. N.; Sandstrom,
   T. A.; Wray, A. A.
2016AGUFMSH21E2570K    Altcode:
  Interaction of the turbulent plasma and magnetic fields is of great
  interest as a key to understanding self-organization processes and
  dynamics of the solar magnetism. We develop 3D time-dependent radiative
  MHD simulations that are based on first principles and provide an
  important tool for uncovering the basic physical mechanisms. Our
  simulations are able to reproduce many observed phenomena, and, in
  particular, allow us to investigate spontaneous formation of coherent
  highly magnetized flux-robe structures that are observed as "pores"
  in the photosphere. The dynamical evolution of these structures is
  accompanied by numerous magnetoacoustic waves that are excited in
  subphotospheric layers and propagate into the solar atmosphere. We
  present analysis of the pore dynamics, and properties and excitation
  mechanism of the magnetoacoustic waves, as well as a comparison with
  observations.

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Title: Three-Fluid collisional and reactive magnetic reconnection
    with radiative effects in chromospheric conditions
Authors: Alvarez Laguna, A.; Ozak, N. O.; Maneva, Y. G.; Lani, A.;
   Kosovichev, A. G.; Mansour, N. N.; Poedts, S.
2016AGUFMSH21E2566A    Altcode:
  The partially ionized chomosphere hosts the interplay of complex
  physical phenomena, i.e., collisional processes, non-chemical
  equilibrium conditions and non-LTE radiation effects, etc. We study the
  magnetic reconnection in different ionization levels under chromospheric
  conditions for a multi-fluid, compressible, collisional and reactive
  model. We will extend previous work that considers two-fluid models
  (plasma + neutrals), to a three-fluid model accounting for electron
  dynamics. The model includes chemical reactions of ionization,
  recombination and charge exchange collisions. The transport fluxes
  consider the anisotropy introduced by the magnetic field in the charged
  species. The radiative losses, that are known to play an important role
  in the chromosphere, are modeled with an effectively thin radiation
  loss function, fitting a three-level Hydrogen atom. In a set of 2-D
  computational simulations, we study different ionization levels from
  0.5% to 50%, with fixed Lundquist number, analyzing the radiation
  effects on the tearing mode instability.

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Title: Triggers and Manifestations of Flare Energy Release in the
    Low Atmosphere
Authors: Kosovichev, A. G.; Sharykin, I. N.; Sadykov, V. M.; Vargas,
   S.; Zimovets, I. V.
2016AGUFMSH14B..05K    Altcode:
  The main goal is to understand triggers and manifestations of the
  flare energy release in the lower layers of the solar atmosphere (the
  photosphere and chromosphere) using high-resolution optical observations
  and magnetic field measurements. As a case study we present results
  for an M-class flare. We analyze optical images, HMI Dopplergrams
  and vector magnetograms, and use Non-Linear Force-Free Field (NLFFF)
  extrapolation for reconstruction of the magnetic topology. The NLFFF
  modelling reveals interaction of oppositely directed magnetic flux-tubes
  in the Polarity Inversion Line (PIL). These two interacting magnetic
  flux tubes are observed as a compact sheared arcade along the PIL in the
  high-resolution broad-band continuum images from New Solar Telescope
  (NST). In the vicinity of the PIL, the NST H-alpha observations
  reveal formation of a thin three-ribbon structure corresponding to
  the small-scale photospheric magnetic arcade. Magnetic reconnection is
  triggered by two interacting magnetic flux tubes with forming current
  sheet extended along the PIL. Presented observational results evidence
  in favor of location of the primary energy release site in the dense
  chromosphere where plasma is partially ionized in the region of strong
  electric currents concentrated near the polarity inversion line.

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Title: Angular momentum fluxes caused by Λ -effect and meridional
    circulation structure of the Sun
Authors: Pipin, Valery V.; Kosovichev, Alexander G.
2016AdSpR..58.1490P    Altcode: 2016arXiv160105178P
  Using mean-field hydrodynamic models of the solar angular momentum
  balance we show that the non-monotonic latitudinal dependence of
  the radial angular momentum fluxes caused by Λ -effect can affect
  the number of the meridional circulation cells stacking in the radial
  direction in the solar convection zone. In particular, our results show
  the possibility of a complicated triple-cell meridional circulation
  structure. This pattern consists of two large counterclockwise
  circulation cells (the N-hemisphere) and a smaller clockwise cell
  located at low latitudes at the bottom of the convection zone. Similar
  triple-cell circulation patterns were previously earlier found in a
  number of 3D global simulations models. The effect is demonstrated for
  the first time using the mean-field parametrization of the Λ -effect.

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Title: Understanding Solar Torsional Oscillations from Global
    Dynamo Models
Authors: Guerrero, G.; Smolarkiewicz, P. K.; de Gouveia Dal Pino,
   E. M.; Kosovichev, A. G.; Mansour, N. N.
2016ApJ...828L...3G    Altcode: 2016arXiv160802278G
  The phenomenon of solar “torsional oscillations” (TO) represents
  migratory zonal flows associated with the solar cycle. These flows
  are observed on the solar surface and, according to helioseismology,
  extend through the convection zone. We study the origin of the TO
  using results from a global MHD simulation of the solar interior that
  reproduces several of the observed characteristics of the mean-flows and
  magnetic fields. Our results indicate that the magnetic tension (MT)
  in the tachocline region is a key factor for the periodic changes in
  the angular momentum transport that causes the TO. The torque induced
  by the MT at the base of the convection zone is positive at the poles
  and negative at the equator. A rising MT torque at higher latitudes
  causes the poles to speed up, whereas a declining negative MT torque
  at the lower latitudes causes the equator to slow-down. These changes
  in the zonal flows propagate through the convection zone up to the
  surface. Additionally, our results suggest that it is the magnetic
  field at the tachocline that modulates the amplitude of the surface
  meridional flow rather than the opposite as assumed by flux-transport
  dynamo models of the solar cycle.

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Title: Relationship Between Chromospheric Evaporation and Magnetic
    Field Topology in an M-Class Solar Flare
Authors: Sadykov, Viacheslav M.; Kosovichev, Alexander G.; Sharykin,
   Ivan N.; Zimovets, Ivan V.; Vargas Dominguez, Santiago
2016ApJ...828....4S    Altcode: 2016arXiv160405346S
  Chromospheric evaporation is observed as Doppler blueshift during
  solar flares. It plays a key role in the dynamics and energetics of
  solar flares; however, its mechanism is still unknown. In this paper,
  we present a detailed analysis of spatially resolved multi-wavelength
  observations of chromospheric evaporation during an M 1.0-class
  solar flare (SOL2014-06-12T21:12) using data from NASA’s Interface
  Region Imaging Spectrograph and HMI/SDO (the Helioseismic and Magnetic
  Imager on board the Solar Dynamics Observatory), and high-resolution
  observations from VIS/NST (the Visible Imaging Spectrometer at the New
  Solar Telescope). The results show that the averaged over the flare
  region Fe xxi blueshift of the hot (10<SUP>7</SUP> K) evaporating
  plasma is delayed relative to the C II redshift of the relatively
  cold (10<SUP>4</SUP> K) chromospheric plasma by about one minute. The
  spatial distribution of the delays is not uniform across the region
  and can be as long as two minutes in several zones. Using vector
  magnetograms from HMI, we reconstruct the magnetic field topology and
  the quasi-separatrix layer, and find that the blueshift delay regions
  as well as the Hα flare ribbons are connected to the region of the
  magnetic polarity inversion line (PIL) and an expanding flux rope
  via a system of low-lying loop arcades with a height of ≲4.5 Mm. As
  a result, the chromospheric evaporation may be driven by the energy
  release in the vicinity of PIL, and has the observed properties due
  to a local magnetic field topology.

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Title: 3D Realistic MHD Modeling of Solar Activity in Quiet-Sun
    Regions
Authors: Kitiashvili, Irina N.; Kosovichev, Alexander G.; Mansour,
   Nagi N.; Wray, Alan A.
2016shin.confE.149K    Altcode:
  Despite on the absence of strong highly-energetic events in quiet-Sun
  regions the amount of energy flux into the chromosphere and corona,
  generated by small-scale events, makes these areas of great interest
  to address problems of coronal heating as well as solar wind
  acceleration. The quiet-Sun regions represent an evolving background
  state in which the turbulent MHD environment affects properties of
  sunspots formed from magnetic fluxes emerging from the deep convection,
  formation of filaments, coronal loops etc. We present recent 3D
  radiative MHD numerical studies of magnetic self-organization processes
  driven by the turbulent magnetoconvection in quiet-Sun regions,
  such as small-scale dynamo and plasma eruptions, and discuss their
  physical nature, links to high-resolution observations by modeling
  synthetic spectro-polarimetric data, and also potential impacts on
  the energetics and dynamics of the corona and inner heliosphere.

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Title: Links Between Global Solar Magnetic Fields and Subsurface Flows
Authors: Kosovichev, Alexander; Zhao, Junwei
2016shin.confE.145K    Altcode:
  The distribution of magnetic fields on the solar surface and magnetic
  flux transport are controlled by surface and subsurface plasma
  flows. Thus, understanding the links between the flow dynamics and
  global magnetic fields is potentially important for predicting the
  flux evolution and estimating the structure of the corona. We use local
  helioseismology and magnetic field measurements from the HMI instrument
  on SDO to investigate detailed dynamics of the upper convection zone
  and its relation to the magnetic field evolution during the first five
  years of the current solar cycle. The helioseismology data represent 3D
  flow maps in the depth range of 0-20 Mm, obtained uninterruptedly every
  8 hours for almost the whole solar disk with the spatial sampling of
  two arcsec. We calculate the flow characteristics (such as divergence,
  vorticity and kinetic helicity) on different spatio-temporal scales
  from supergranulation to global-scale zonal and meridional flows. The
  subsurface flow maps reveal a complex multi-scale organization linked
  to the solar magnetic activity. This study is focused on comparison
  of the flow maps with the corresponding HMI magnetic field and AIA
  coronal maps. In particular, we look for a relationship between the
  near-surface flows, coronal holes and other large-scale structures. We
  present the flow maps for the SHINE initial challenge event of July
  8, 2010, and analyze the synoptic evolution of the Solar Subsurface
  Weather associated with this event.

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Title: Initiation and Energy Release Mechanisms of Non-eruptive
Flares: Two Case Studies
Authors: Kosovichev, Alexander G.; Sharykin, Ivan N.; Sadykov,
   Viacheslav M.; Zimovets, Ivan V.
2016shin.confE.160K    Altcode:
  We present a detailed analysis of two non-eruptive solar flares. The
  solar flare on July 30, 2011 was of a modest X-ray class (M9.3),
  but it made a strong photospheric impact and produced a sunquake,
  observed with the Helioseismic and Magnetic Imager (HMI) on Solar
  Dynamics Observatory (SDO). In addition to the helioseismic waves
  (also observed with the SDO/AIA instrument), the flare caused a
  large expanding area of white-light emission and was accompanied by
  substantial restructuring of magnetic fields, leading to the rapid
  formation of a sunspot structure in the flare region. The flare produced
  no significant hard X-ray emission and no coronal mass ejection. This
  indicates that the flare energy release was mostly confined to the lower
  atmosphere. Another non-eruptive M1-class flare of June 12, 2014, is
  studied by using high-resolution images obtained by New Solar Telescope
  (NST/BBSO) and HMI vector magnetograms. The NLFFF modelling reveals
  interaction of oppositely directed magnetic flux-tubes in the polarity
  inversion line (PIL). These two interacting magnetic flux tubes are
  observed as a compact sheared arcade along the PIL. In the vicinity
  of the PIL, the NST H-alpha observations reveal formation of a thin
  three-ribbon structure corresponding to the small-scale photospheric
  magnetic arcade. The observational results evidence in favor of location
  of the primary energy release site in the dense chromosphere where
  plasma is partially ionized in the region of strong electric currents
  and shearing plasma flows concentrated near the polarity inversion
  line. Magnetic reconnection may be triggered by interacting magnetic
  flux tubes with forming a current sheet elongated along the PIL.

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Title: Dependence of Stellar Magnetic Activity Cycles on Rotational
    Period in a Nonlinear Solar-type Dynamo
Authors: Pipin, V. V.; Kosovichev, A. G.
2016ApJ...823..133P    Altcode: 2016arXiv160207815P
  We study the turbulent generation of large-scale magnetic fields using
  nonlinear dynamo models for solar-type stars in the range of rotational
  periods from 14 to 30 days. Our models take into account nonlinear
  effects of dynamical quenching of magnetic helicity, and escape of
  magnetic field from the dynamo region due to magnetic buoyancy. The
  results show that the observed correlation between the period of
  rotation and the duration of activity cycles can be explained in the
  framework of a distributed dynamo model with a dynamical magnetic
  feedback acting on the turbulent generation from either magnetic
  buoyancy or magnetic helicity. We discuss implications of our findings
  for the understanding of dynamo processes operating in solar-like stars.

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Title: Solar-Cycle Evolution of Subsurface Flows and Magnetic Field
Authors: Kosovichev, Alexander G.; Zhao, Junwei
2016SPD....47.0709K    Altcode:
  Local helioseismology and magnetic field measurements from the HMI
  instrument on SDO provide unique high-resolution data that allow us
  to investigate detailed dynamics of the upper convection zone and its
  relation to the magnetic field evolution during the first five years
  of the current solar cycle. This study is focused on the understanding
  the role of the near-surface shear layer (NSSL) in the dynamo process,
  generation, emergence and transport of the solar magnetic flux. The
  helioseismology data represent 3D flow maps in the depth range of 0-20
  Mm, obtained uninterruptedly every 8 hours for almost the whole solar
  disk with the spatial sampling of two arcsec. We calculate the flow
  characteristics (such as divergence, vorticity and kinetic helicity) on
  different spatio-temporal scales from supergranulation to global-scale
  zonal and meridional flows. We investigate the multi-scale organization
  of the subsurface flows, including the inflows into active regions,
  the hemispheric `flip-flop’ asymmetry of variations of the meridional
  flows, the structure and dynamics of torsional oscillations, and compare
  the flow behavior with the evolution of the observed magnetic activity
  of the current cycle.

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Title: Reconstruction of Solar Subsurfaces by Local Helioseismology
Authors: Kosovichev, Alexander G.; Zhao, Junwei
2016LNP...914...25K    Altcode: 2016arXiv160705681K
  Local helioseismology has opened new frontiers in our quest for
  understanding of the internal dynamics and dynamo on the Sun. Local
  helioseismology reconstructs subsurface structures and flows by
  extracting coherent signals of acoustic waves traveling through the
  interior and carrying information about subsurface perturbations
  and flows, from stochastic oscillations observed on the surface. The
  initial analysis of the subsurface flow maps reconstructed from the
  5 years of SDO/HMI data by time-distance helioseismology reveals
  the great potential for studying and understanding of the dynamics
  of the quiet Sun and active regions, and the evolution with the solar
  cycle. In particular, our results show that the emergence and evolution
  of active regions are accompanied by multi-scale flow patterns, and
  that the meridional flows display the North-South asymmetry closely
  correlating with the magnetic activity. The latitudinal variations
  of the meridional circulation speed, which are probably related to
  the large-scale converging flows, are mostly confined in shallow
  subsurface layers. Therefore, these variations do not necessarily
  affect the magnetic flux transport. The North-South asymmetry is also
  pronounced in the variations of the differential rotation (`torsional
  oscillations'). The calculations of a proxy of the subsurface kinetic
  helicity density show that the helicity does not vary during the
  solar cycle, and that supergranulation is a likely source of the
  near-surface helicity.

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Title: Observational Investigation of Energy Release in the Lower
    Solar Atmosphere of a Solar Flare
Authors: Sharykin, I. N.; Sadykov, V. M.; Kosovichev, A. G.; Vargas
   Dominguez, S.; Zimovets, I. V.
2016arXiv160405380S    Altcode:
  We study flare processes in the lower solar atmosphere using
  observational data for a M1-class flare of June 12, 2014, obtained
  by New Solar Telescope (NST/BBSO) and Helioseismic Magnetic Imager
  (HMI/SDO). The main goal is to understand triggers and manifestations of
  the flare energy release in the lower layers of the solar atmosphere
  (the photosphere and chromosphere) using high-resolution optical
  observations and magnetic field measurements. We analyze optical
  images, HMI Dopplergrams and vector magnetograms, and use Non-Linear
  Force-Free Field (NLFFF) extrapolations for reconstruction of the
  magnetic topology. The NLFFF modelling reveals interaction of oppositely
  directed magnetic flux-tubes in the PIL. These two interacting magnetic
  flux tubes are observed as a compact sheared arcade along the PIL in the
  high-resolution broad-band continuum images from NST. In the vicinity
  of the PIL, the NST H alpha observations reveal formation of a thin
  three-ribbon structure corresponding to the small-scale photospheric
  magnetic arcade. Presented observational results evidence in favor of
  location of the primary energy release site in the dense chromosphere
  where plasma is partially ionized in the region of strong electric
  currents concentrated near the polarity inversion line. Magnetic
  reconnection may be triggered by two interacting magnetic flux tubes
  with forming current sheet elongated along the PIL.

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Title: Dynamics of Turbulent Convection and Convective Overshoot in
    a Moderate-mass Star
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Mansour, N. N.; Wray,
   A. A.
2016ApJ...821L..17K    Altcode: 2015arXiv151207298K
  We present results of realistic three-dimensional (3D) radiative
  hydrodynamic simulations of the outer layers of a moderate-mass
  star (1.47 M <SUB>⊙</SUB>), including the full convection zone,
  the overshoot region, and the top layers of the radiative zone. The
  simulation results show that the surface granulation has a broad range
  of scales, from 2 to 12 Mm, and that large granules are organized in
  well-defined clusters, consisting of several granules. Comparison of
  the mean structure profiles from 3D simulations with the corresponding
  one-dimensional (1D) standard stellar model shows an increase of the
  stellar radius by ∼800 km, as well as significant changes in the
  thermodynamic structure and turbulent properties of the ionization
  zones. Convective downdrafts in the intergranular lanes between
  granulation clusters reach speeds of more than 20 km s<SUP>-1</SUP>,
  penetrate through the whole convection zone, hit the radiative zone,
  and form an 8 Mm thick overshoot layer. Contrary to semi-empirical
  overshooting models, our results show that the 3D dynamic overshoot
  region consists of two layers: a nearly adiabatic extension of
  the convection zone and a deeper layer of enhanced subadiabatic
  stratification. This layer is formed because of heating caused by
  the braking of the overshooting convective plumes. This effect has to
  be taken into account in stellar modeling and the interpretation of
  asteroseismology data. In particular, we demonstrate that the deviations
  of the mean structure of the 3D model from the 1D standard model of the
  same mass and composition are qualitatively similar to the deviations
  for the Sun found by helioseismology.

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Title: Commission 12: Solar Radiation and Structure
Authors: Cauzzi, Gianna; Shchukina, Nataliya; Kosovichev, Alexander;
   Bianda, Michele; Brandenburg, Axel; Chou, Dean-Yi; Dasso, Sergio; Ding,
   Ming-De; Jefferies, Stuart; Krivova, Natalie; Kuznetsov, Vladimir D.;
   Moreno-Insertis, Fernando
2016IAUTA..29..278C    Altcode:
  Commission 12 of the International Astronomical Union encompasses
  investigations of the internal structure and dynamics of the Sun,
  the quiet solar atmosphere, solar radiation and its variability, and
  the nature of relatively stable magnetic structures like sunspots,
  faculae and the magnetic network. The Commission sees participation
  of over 300 scientists worldwide.

---------------------------------------------------------
Title: On the Role of Tachoclines in Solar and Stellar Dynamos
Authors: Guerrero, G.; Smolarkiewicz, P. K.; de Gouveia Dal Pino,
   E. M.; Kosovichev, A. G.; Mansour, N. N.
2016ApJ...819..104G    Altcode: 2015arXiv150704434G
  Rotational shear layers at the boundary between radiative and convective
  zones, tachoclines, play a key role in the process of magnetic
  field generation in solar-like stars. We present two sets of global
  simulations of rotating turbulent convection and dynamo. The first set
  considers a stellar convective envelope only; the second one, aiming
  at the formation of a tachocline, also considers the upper part of the
  radiative zone. Our results indicate that the resulting properties of
  the mean flows and dynamo, such as the growth rate, saturation energy,
  and mode, depend on the Rossby number (Ro). For the first set of models
  either oscillatory (with ∼2 yr period) or steady dynamo solutions are
  obtained. The models in the second set naturally develop a tachocline,
  which in turn leads to the generation of a strong mean magnetic
  field. Since the field is also deposited in the stable deeper layer,
  its evolutionary timescale is much longer than in the models without
  a tachocline. Surprisingly, the magnetic field in the upper turbulent
  convection zone evolves on the same timescale as the deep field. These
  models result in either an oscillatory dynamo with a ∼30 yr period
  or a steady dynamo depending on Ro. In terms of the mean-field dynamo
  coefficients computed using the first-order smoothing approximation,
  the field evolution in the oscillatory models without a tachocline
  seems to be consistent with dynamo waves propagating according to
  the Parker-Yoshimura sign rule. In the models with tachoclines the
  dynamics is more complex and involves other transport mechanisms as
  well as tachocline instabilities.

---------------------------------------------------------
Title: Spectroscopic UV observations of M1.0 class solar flare from
    IRIS satellite
Authors: Sadykov, Viacheslav M.; Kosovichev, Alexander G.; Sharykin,
   Ivan N.; Vargas Dominguez, Santiago
2016IAUS..320...64S    Altcode:
  This work presents an analysis of UV spectroscopic observations from the
  IRIS satellite of an M1.0 class flare occurred on 12 June 2014 in active
  region NOAA 12087. Our analysis of the IRIS spectra and Slit-Jaw images
  revealed presence of a strongly redshifted chromospheric jet before
  the flare. We also found strong emission of the chromospheric lines,
  and studied the C II 1334.5 Å line emission distribution in details. A
  blueshift of the Fe XXI line across the flaring region corresponds to
  evaporation flows of the hot chromospheric plasma with a speed of 50
  km/s. Although the enhancement of the C II line integrated redshift
  correlates with the flare X-ray emission, we classify the evaporation
  as of a “gentle” type because of its long time scale and subsonic
  velocities. Analysis of X-ray data from the RHESSI satellite showed that
  both, an injection of accelerated particles and a heat flux from the
  energy release site can explain the energetics of the observed event.

---------------------------------------------------------
Title: 2-D and 3-D models of convective turbulence and oscillations
    in intermediate-mass main-sequence stars
Authors: Guzik, Joyce A.; Morgan, T. H.; Nelson, N. J.; Lovekin, C.;
   Kosak, K.; Kitiashvili, I. N.; Mansour, N. N.; Kosovichev, A.
2016IAUFM..29B.540G    Altcode: 2016arXiv160504455G
  We present multidimensional modeling of convection and oscillations in
  main-sequence stars somewhat more massive than the Sun, using three
  separate approaches: 1) Using the 3-D planar StellarBox radiation
  hydrodynamics code to model the envelope convection zone and part
  of the radiative zone. Our goals are to examine the interaction
  of stellar pulsations with turbulent convection in the envelope,
  excitation of acoustic modes, and the role of convective overshooting;
  2) Applying the spherical 3-D MHD ASH (Anelastic Spherical Harmonics)
  code to simulate the core convection and radiative zone. Our goal is
  to determine whether core convection can excite low-frequency gravity
  modes, and thereby explain the presence of low frequencies for some
  hybrid γ Dor/δ Sct variables for which the envelope convection zone
  is too shallow for the convective blocking mechanism to drive gravity
  modes; 3) Applying the ROTORC 2-D stellar evolution and dynamics
  code to calculate evolution with a variety of initial rotation rates
  and extents of core convective overshooting. The nonradial adiabatic
  pulsation frequencies of these nonspherical models are calculated using
  the 2-D pulsation code NRO. We present new insights into pulsations
  of 1-2 M<SUB>⊙</SUB> stars gained by multidimensional modeling.

---------------------------------------------------------
Title: Solar radius variations: new look on the wavelength dependence
Authors: Rozelot, Jean-Pierre; Kosovichev, Alexander; Kilcik, Ali
2016IAUS..320..342R    Altcode:
  The possibility that the Sun's radius is changing, even at a faint
  level, has been discussed over a long time. As the solar radius is
  certainly one of the most important basic pieces of astrophysical
  information, it is crucial to determine the physical mechanisms
  that may cause shrinking or expansion of the solar envelope. The
  wavelength dependence has been poorly inspected up to now. Here we
  examine recent solar radius determinations from space observations,
  mainly from Mercury and Venus transits, made by different teams
  in 2006, 2012 and 2014. Seemingly, the results are not consistent:
  authors interpreted the discrepancies because of the different methods
  of analysis used in their work. However, looking at the wavelength
  dependence, adding other available observations, from X-EUV up to
  radio, a typical relationship between the radius and the wavelength
  can be found, reflecting the different heights at which the lines
  are formed. Possible explanations are discussed. Such results can be
  interesting for studying solar-stellar connections.

---------------------------------------------------------
Title: Solar and Stellar Flares and their Effects on Planets
Authors: Kosovichev, A. G.; Hawley, S. L.; Heinzel, P.
2016IAUS..320.....K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Solar Dynamo on Small and Global Scales
Authors: Kitiashvili, I.; Kosovichev, A. G.; Mansour, N. N.; Wray,
   A. A.
2015AGUFMSH23A2432K    Altcode:
  Phenomenon of the solar variability is primarily driven by the evolution
  of magnetic fields on both small and global scales. Because connection
  between the dynamo processes on different scales remains unclear,
  we consider them separately. In particular, we analyze 1) a global
  dynamo model, which is reduced to a dynamical system in the context
  of the solar cycle variations, and 2) realistic-type 3D numerical
  simulations of the small-scale dynamo, and discuss possible interlinks
  between these dynamo processes.

---------------------------------------------------------
Title: Relationship Between Subsurface Flows and Magnetic Field
    Evolution in Solar Cycle 24
Authors: Kosovichev, A. G.; Zhao, J.
2015AGUFMSH33D..05K    Altcode:
  Local time-distance helioseismology and magnetic field measurements from
  the HMI instrument on SDO provide unique high-resolution data that allow
  us to investigate detailed dynamics of the upper convection zone and
  its relation to the magnetic field evolution during the first five years
  of the current solar cycle. This study is focused on the understanding
  the role of the near-surface shear layer (NSSL) in the dynamo process,
  generation, emergence and transport of the solar magnetic flux. The
  helioseismology data represent 3D flow maps in the depth range of 0-20
  Mm, obtained uninterruptedly every 8 hours for almost the whole solar
  disk with the spatial sampling of two arcsec. We calculate the flow
  characteristics (such as divergence, vorticity and kinetic helicity) on
  different spatio-temporal scales from supergranulation to global-scale
  zonal and meridional flows. We investigate the multi-scale organization
  of the subsurface flows, including the inflows into active regions,
  the hemispheric `flip-flop' asymmetry of variations of the meridional
  flows, the structure and dynamics of torsional oscillations, and compare
  the flow behavior with the evolution of the observed magnetic activity.

---------------------------------------------------------
Title: Partially Ionized Plasma Three-Fluid Modeling of Magnetic
    Reconnection in the Sun Chromosphere
Authors: Alvarez Laguna, A.; Lani, A.; Mansour, N. N.; Kosovichev,
   A. G.; Poedts, D. S.
2015AGUFMSH43A2424A    Altcode:
  Magnetic reconnection is present in most of the unsteady and eruptive
  phenomena in the Sun atmosphere, including Coronal Mass Ejections (CMEs)
  and solar flares. Also, it occurs in the chromosphere, bringing about
  chromospheric jets and spicules and being considered a likely mechanism
  to play an important role in heating up the corona. In this work,
  we present a computational model that simulates magnetic reconnection
  in the Sun chromosphere using a three-fluid model (electrons + ions +
  neutrals). The model treats separately ions, electrons and neutrals,
  considering mass, momentum and energy conservation for each fluid. The
  fluids interact among each other by means of collisions and chemical
  reactions. The charged particles heat fluxes are anisotropic with
  the magnetic field, following Braginskii's description. This model
  also considers non-equilibrium partial ionization effects including
  electron impact ionization, radiative recombination reactions and charge
  exchange. The electromagnetic field evolution is represented by the full
  Maxwell's equations, allowing for high frequency waves disregarded by
  the MHD approximation. Previous two-fluid simulations showed that the
  dynamics of ions and neutrals are decoupled during the reconnection
  process when the width of the current sheet becomes comparable to the
  ion scales. Also, the effect of the chemical non-equilibrium in the
  reconnection region plays a crucial role, yielding faster reconnection
  rates. We extended these simulations with a three-fluid model that
  considers separately the dynamics of electrons. This new model provides
  a better description of the complex dynamics taking place during the
  reconnection, both in Sweet-Parker reconnections and during the tearing
  instability. The results are compared with the two-fluid simulations.

---------------------------------------------------------
Title: Effects of Large-scale Non-axisymmetric Perturbations in the
    Mean-field Solar Dynamo.
Authors: Pipin, V. V.; Kosovichev, A. G.
2015ApJ...813..134P    Altcode: 2015arXiv150500219P
  We explore the response of a nonlinear non-axisymmetric mean-field
  solar dynamo model to shallow non-axisymmetric perturbations. After a
  relaxation period, the amplitude of the non-axisymmetric field depends
  on the initial condition, helicity conservation, and the depth of
  perturbation. It is found that a perturbation that is anchored at 0.9 R
  <SUB>⊙</SUB> has a profound effect on the dynamo process, producing
  a transient magnetic cycle of the axisymmetric magnetic field, if it
  is initiated at the growing phase of the cycle. The non-symmetric,
  with respect to the equator, perturbation results in a hemispheric
  asymmetry of the magnetic activity. The evolution of the axisymmetric
  and non-axisymmetric fields depends on the turbulent magnetic
  Reynolds number R <SUB> m </SUB>. In the range of R <SUB> m </SUB> =
  10<SUP>4</SUP>-10<SUP>6</SUP> the evolution returns to the normal course
  in the next cycle, in which the non-axisymmetric field is generated
  due to a nonlinear α-effect and magnetic buoyancy. In the stationary
  state, the large-scale magnetic field demonstrates a phenomenon of
  “active longitudes” with cyclic 180° “flip-flop” changes of
  the large-scale magnetic field orientation. The flip-flop effect is
  known from observations of solar and stellar magnetic cycles. However,
  this effect disappears in the model, which includes the meridional
  circulation pattern determined by helioseismology. The rotation rate
  of the non-axisymmetric field components varies during the relaxation
  period and carries important information about the dynamo process.

---------------------------------------------------------
Title: Solar Radius Variations: An Inquisitive Wavelength Dependence
Authors: Rozelot, Jean Pierre; Kosovichev, Alexander; Kilcik, Ali
2015ApJ...812...91R    Altcode:
  Recent solar radius determinations from space observations of Mercury
  and Venus transits have been made by different teams in 2003, 2006,
  2012, and 2014. Seemingly the results are not consistent: the authors
  interpreted the discrepancies as caused by the different methods of
  analysis. However, looking at the wavelength dependence and adding other
  available observations from X-EUV up to radio, a typical wavelength
  dependence can be found, reflecting the different heights at which
  the lines are formed. Measurements obtained during different periods
  of time would, in principle, allow us to detect a signature of radius
  temporal dependence. However, the available data are not sufficiently
  numerous to detect a significant dependence, at least at the level
  of the uncertainty at which the observations were made. Lastly, no
  unique theoretical model is available today to reproduce the strong
  wavelength dependence of the solar radius, which shows an unexpected
  minimum at around (6.6 ± 1.9) μm, after a parabolic fit.

---------------------------------------------------------
Title: Dynamo Effects Near the Transition from Solar to Anti-Solar
    Differential Rotation
Authors: Simitev, Radostin D.; Kosovichev, Alexander G.; Busse,
   Friedrich H.
2015ApJ...810...80S    Altcode: 2015arXiv150407835S
  Numerical MHD simulations play an increasingly important role
  for understanding the mechanisms of stellar magnetism. We present
  simulations of convection and dynamos in density-stratified rotating
  spherical fluid shells. We employ a new 3D simulation code for obtaining
  the solution of a physically consistent anelastic model of the process
  with a minimum number of parameters. The reported dynamo simulations
  extend into a “buoyancy-dominated” regime where the buoyancy
  forcing is dominant while the Coriolis force is no longer balanced
  by pressure gradients, and strong anti-solar differential rotation
  develops as a result. We find that the self-generated magnetic fields,
  despite being relatively weak, are able to reverse the direction of
  differential rotation from anti-solar to solar-like. We also find
  that convection flows in this regime are significantly stronger in the
  polar regions than in the equatorial region, leading to non-oscillatory
  dipole-dominated dynamo solutions, and to a concentration of magnetic
  field in the polar regions. We observe that convection has a different
  morphology in the inner and the outer part of the convection zone
  simultaneously such that organized geostrophic convection columns
  are hidden below a near-surface layer of well-mixed highly chaotic
  convection. While we focus our attention on the buoyancy-dominated
  regime, we also demonstrate that conical differential rotation profiles
  and persistent regular dynamo oscillations can be obtained in the
  parameter space of the rotation-dominated regime even within this
  minimal model.

---------------------------------------------------------
Title: Effects of Tachocline in Solar-Stellar Dynamo Simulations
Authors: Kosovichev, Alexander; Guerrero, Gustavo; Smolarkiewicz,
   Petr; de Gouveia Dal Pino, Elisabete; Mansour, Nagi N.
2015IAUGA..2258507K    Altcode:
  Using 3D implicit large-eddy simulations and comparing these with
  observational constrains we investigate variations of the solar rotation
  and dynamo-generated magnetic fields. Two sets of simulations models are
  explored, the first one considers the solar convective envelope only;
  the second one, aiming at the formation of a tachocline, considers also
  a fraction of the radiative core. In both kind of models the rotation
  profile and the dynamo solution depend on the Rossby number, however,
  the flux of angular momentum is also affected by the Lorentz force. The
  slow rotating models without tachocline reproduce remarkably well the
  solar differential rotation in the convection zone (CZ) including
  the tilted iso-rotation contours and the near-surface shear layer
  (NSSL). Two of these models exhibit periodic reversals of the magnetic
  field with a cycle of ∼ 2 yr. With this short dynamic timescale, the
  NSSL apparently does not affect the migration of the surface magnetic
  field which results to be poleward. The radial shear at the tachocline
  gives rise to a strong toroidal magnetic field at this location. Since
  it is also deposited in the stable layer below, it diffuses in longer
  timescales than the field at the CZ. These models result either in
  an oscillatory dynamo with a ∼ 30 yr cycle period or in steady
  fields. In all the models with magnetic cycles the evolution of the
  fields seems to be consistent with dynamo waves propagating according
  to the Parker-Yoshimura sign rule. We compare the modeling results
  with recent helioseismology inferences, and observations of solar and
  stellar differential rotation and cycles, including intermittency of
  the Maunder-minimum type.

---------------------------------------------------------
Title: Detection of Fast-moving Waves Propagating Outward along
    Sunspots’ Radial Direction in the Photosphere
Authors: Zhao, Junwei; Chen, Ruizhu; Hartlep, Thomas; Kosovichev,
   Alexander G.
2015ApJ...809L..15Z    Altcode: 2015arXiv150704795Z
  Helioseismic and magnetohydrodynamic waves are abundant in and
  above sunspots. Through cross-correlating oscillation signals in the
  photosphere observed by the Solar Dynamics Observatory/Helioseismic
  and Magnetic Imager, we reconstruct how waves propagate away from
  virtual wave sources located inside a sunspot. In addition to the
  usual helioseismic wave, a fast-moving wave is detected traveling along
  the sunspot’s radial direction from the umbra to about 15 Mm beyond
  the sunspot boundary. The wave has a frequency range of 2.5-4.0 mHz
  with a phase velocity of 45.3 km s<SUP>-1</SUP>, substantially faster
  than the typical speeds of Alfvén and magnetoacoustic waves in the
  photosphere. The observed phenomenon is consistent with a scenario of
  that a magnetoacoustic wave is excited at approximately 5 Mm beneath the
  sunspot. Its wavefront travels to and sweeps across the photosphere with
  a speed higher than the local magnetoacoustic speed. The fast-moving
  wave, if truly excited beneath the sunspot’s surface, will help open a
  new window for studying the internal structure and dynamics of sunspots.

---------------------------------------------------------
Title: Sunquakes and Two Types of Solar Flares
Authors: Kosovichev, Alexander
2015IAUGA..2258219K    Altcode:
  Uninterrupted observations from Solar Dynamics Observatory provide
  unique opportunity for investigation of "sunquakes", helioseismic
  waves caused by strong localized impacts in the low atmosphere during
  impulsive phase of solar flares. The SDO observations show that these
  events are more frequent than previously thought. They are observed in
  solar flares from C- to X-classes. However, not all X-class flares
  produce sunquakes, and it is puzzling why some relatively weak
  flares produce sunquakes, while significantly more powerful flares
  do not. Using data from the Helioseismic and Magnetic Imager (HMI)
  and Atmospheric Imaging Assembly (AIA) I investigate properties of
  sunquakes by detecting and analyzing the seismic wave fronts and the
  sources of the flare impact, and discuss physical mechanisms of the
  impact. By comparing energetic and morphological characteristics of
  the flares with and without sunquakes, I present arguments that this
  phenomenon reflects a division between two classes of solar flares:
  confined and eruptive, which may be fundamentally different in terms
  of the energy release mechanism.

---------------------------------------------------------
Title: Solar Radius Variations: a New Look on the Wavelength
    Dependence
Authors: Rozelot, Jean-Pierre; Kosovichev, Alexander; Kilcik, Ali
2015IAUGA..2297672R    Altcode:
  The possibility that the the Sun's radius is changing, even at a faint
  level, has been talk over a long time. As solar radius is certainly one
  of the most important basic pieces of astrophysical information, it is
  crucial to determine the physical mechanisms that may cause shrinking
  or expansion of the solar envelope. The wavelength dependence has been
  poorly examine up to now. In this talk, we examine recent solar radius
  determinations from space observation of Mercury and Venus transits that
  have been made by different teams, in 2006, 2012 and 2014. Seemingly
  results are not consistent: authors interpreted the discrepancies by the
  different methods of analysis used. However, looking at the wavelength
  dependence, adding other available observations, from X-EUV up to radio,
  a typical wavelength dependence can be found, reflecting the different
  heights at which the lines are formed. A possible explanation is
  proposed. Such results can be interesting for solar-stellar connections.

---------------------------------------------------------
Title: Division II: Commission 12: Solar Radiation and Structure
Authors: Kosovichev, Alexander; Cauzzi, Gianna; Martinez Pillet,
   Valentin; Asplund, Martin; Brandenburg, Axel; Chou, Dean-Yi;
   Christensen-Dalsgaard, Jorgen; Gan, Weiqun; Kuznetsov, Vladimir D.;
   Rovira, Marta G.; Shchukina, Nataliya; Venkatakrishnan, P.
2015IAUTB..28..109K    Altcode:
  The President of C12, Alexander Kosovichev, presented the status of
  the Commission and its working Group(s). Primary activities included
  organization of international meetings (IAU Symposia, Special Sessions
  and Joint Discussion); review and support of proposals for IAU sponsored
  meetings; organization of working groups on the Commission topics
  to promote the international cooperation; preparation of triennial
  report on the organizational and science activities of Commission
  members. Commission 12 broadly encompasses topics of solar research
  which include studies of the Sun's internal structure, composition,
  dynamics and magnetism (through helioseismology and other techniques),
  studies of the quiet photosphere, chromosphere and corona, and also
  research of the mechanisms of solar radiation, and its variability on
  various time scales. Some overlap with topics covered by Commission
  10 Solar Activity is unavoidable, and many activities are sponsored
  jointly by these two commissions. The Commission website can be found
  at http://sun.stanford.edu/IAU-Com12/, with information about related
  IAU Symposiums and activities, and links to appropriate web sites.

---------------------------------------------------------
Title: Dynamics of Electric Currents, Magnetic Field Topology and
    Helioseismic Response of a Solar Flare
Authors: Sharykin, Ivan; Kosovichev, Alexander
2015IAUGA..2286139S    Altcode:
  The solar flare on July 30, 2011 was of a modest X-ray class (M9.3),
  but it made a strong photospheric impact and produced a "sunquake,'"
  observed with the Helioseismic and Magnetic Imager (HMI) on NASA's
  Solar Dynamics Observatory (SDO). In addition to the helioseismic
  waves (also observed with the SDO/AIA instrument), the flare caused a
  large expanding area of white-light emission and was accompanied by
  the rapid formation of a sunspot structure in the flare region. The
  flare produced hard X-ray emission less than 300 keV and no coronal
  mass ejection. The absence of significant coronal mass ejection rules
  out magnetic rope eruption as a mechanism of helioseismic waves. We
  discuss the connectivity of the flare energy release with the electric
  currents dynamics and show the potential importance of high-speed plasma
  flows in the lower solar atmosphere during the flare energy release.

---------------------------------------------------------
Title: 2D and 3D Models of Convective Turbulence and Oscillations
    in Intermediate-Mass Main-Sequence Stars
Authors: Guzik, Joyce Ann; Morgan, Taylor H.; Nelson, Nicholas
   J.; Lovekin, Catherine; Kitiashvili, Irina N.; Mansour, Nagi N.;
   Kosovichev, Alexander
2015IAUGA..2255601G    Altcode:
  We present multidimensional modeling of convection and oscillations
  in main-sequence stars somewhat more massive than the sun, using
  three separate approaches: 1) Applying the spherical 3D MHD ASH
  (Anelastic Spherical Harmonics) code to simulate the core convection
  and radiative zone. Our goal is to determine whether core convection
  can excite low-frequency gravity modes, and thereby explain the
  presence of low frequencies for some hybrid gamma Dor/delta Sct
  variables for which the envelope convection zone is too shallow for
  the convective blocking mechanism to drive g modes; 2) Using the 3D
  planar ‘StellarBox’ radiation hydrodynamics code to model the
  envelope convection zone and part of the radiative zone. Our goals
  are to examine the interaction of stellar pulsations with turbulent
  convection in the envelope, excitation of acoustic modes, and the
  role of convective overshooting; 3) Applying the ROTORC 2D stellar
  evolution and dynamics code to calculate evolution with a variety of
  initial rotation rates and extents of core convective overshooting. The
  nonradial adiabatic pulsation frequencies of these nonspherical models
  will be calculated using the 2D pulsation code NRO of Clement. We will
  present new insights into gamma Dor and delta Sct pulsations gained
  by multidimensional modeling compared to 1D model expectations.

---------------------------------------------------------
Title: Waldmeier's Rules in the Solar and Stellar Dynamos
Authors: Pipin, Valery; Kosovichev, Alexander
2015IAUGA..2255933P    Altcode:
  The Waldmeier's rules [1] establish important empirical relations
  between the general parameters of magnetic cycles (such as the
  amplitude, period, growth rate and time profile) on the Sun and
  solar-type stars [2]. Variations of the magnetic cycle parameters
  depend on properties of the global dynamo processes operating in the
  stellar convection zones. We employ nonlinear mean-field axisymmetric
  dynamo models [3] and calculate of the magnetic cycle parameters,
  such as the dynamo cycle period, total magnetic and Poynting fluxes
  for the Sun and solar-type stars with rotational periods from 15 to
  30 days. We consider two types of the dynamo models: 1) distributed
  (D-type) models employing the standard α - effect distributed in
  the whole convection zone, and 2) Babcock-Leighton (BL-type) models
  with a non-local α - effect. The dynamo models take into account the
  principal mechanisms of the nonlinear dynamo generation and saturation,
  including the magnetic helicity conservation, magnetic buoyancy effects,
  and the feedback on the angular momentum balance inside the convection
  zones. Both types of models show that the dynamo generated magnetic flux
  increases with the increase of the rotation rate. This corresponds to
  stronger brightness variations. The distributed dynamo model reproduces
  the observed dependence of the cycle period on the rotation rate for
  the Sun analogs better than the BL-type model. For the solar-type
  stars rotating more rapidly than the Sun we find dynamo regimes with
  multiple periods. Such stars with multiple cycles form a separate
  branch in the variability-rotation diagram.1. Waldmeier, M., Prognose
  für das nächste Sonnenfleckenmaximum, 1936, Astron. Nachrichten,
  259,262. Soon,W.H., Baliunas,S.L., Zhang,Q.,An interpretation
  of cycle periods of stellar chromospheric activity, 1993, ApJ,
  414,333. Pipin,V.V., Dependence of magnetic cycle parameters on period
  of rotation in nonlinear solar-type dynamos, 2015, astro-ph: 14125284

---------------------------------------------------------
Title: Properties of Turbulent Dynamics and Oscillations of
    Main-Sequence Stars Deduced From Numerical Simulations
Authors: Kitiashvili, Irina N.; Mansour, Nagi N.; Kosovichev,
   Alexander; Wray, Alan A.
2015IAUGA..2258520K    Altcode:
  Unique observational data from the Kepler mission open new perspectives
  for detail investigation of dynamical and internal properties of
  numerous stars. However, the new observational results require
  better understand links between the stellar turbulent convection
  and oscillations. We perform 3D numerical radiative hydrodynamics
  simulations of convective and oscillation properties of main-sequence
  stars from the solar-type stars to more massive F- and A-type stars. As
  the stellar mass increases the convection zone shrinks making it
  possible to include the whole convection zone in the computational
  domain. Also in more massive stars the scale and intensity of the
  turbulent motions dramatically increases, providing more energy for
  excitation of acoustic and gravity modes. In this talk I will discuss
  properties of the turbulent dynamics of the stars, interaction between
  the radiative and convection zones, and excitation of acoustic and
  gravity modes.

---------------------------------------------------------
Title: Generation and Properties of Large-Scale Non-axisymmetric
    Magnetic Fields by Solar Dynamo
Authors: Pipin, Valery; Kosovichev, Alexander
2015IAUGA..2258424P    Altcode:
  Large-scale non-axisymmetric magnetic fields generated by the solar
  dynamo, and presumably responsible for the phenomenon of "active
  longitudes", play an important role in the distribution of solar
  activity and flares. By calculating 3D mean-field dynamo models, we
  show that nonlinear coupling between axisymmetric and non-axisymmetric
  modes, e.g. due to the magnetic feedback on the alpha-effect (see,
  e.g., [1]), can maintain a large-scale non-axisymmetric dynamo
  process. Non-axisymmetric random fluctuations of dynamo parameters
  can be another source for the non-axisymmetric magnetic fields on the
  Sun. Such fluctuations can provide a mechanism of the magnetic energy
  transfer from the global field to the non-axisymmetric modes. It
  is shown that the rotational periods of the non-axisymmetric field
  correspond to the dynamo process operating in the subsurface shear
  layer which is located in the range of depths 0.85-0.95R. We find
  that the magnetic helicity conservation quenches generation of the
  non-axisymmetric dynamo modes as well as it does for the axisymmetric
  dynamo. It is concluded that the 3D mean-field non-axisymmetric dynamo
  models can potentially explain the observed distribution of the solar
  magnetic activity.1. Moss, D.,Non-axisymmetric solar magnetic fields,
  1999, MNRAS, 306, 300On 3/18/2015 2:29 PM, Valery Pipin wrote:

---------------------------------------------------------
Title: NST and IRIS multi-wavelength observations of an M1.0 class
    solar flare
Authors: Vargas Domínguez, Santiago; Sadykov, Viacheslav; Kosovichev,
   Alexander; Sharykin, Ivan; Struminsky, Alexei; Zimovets, Ivan
2015IAUGA..2257574V    Altcode:
  Although solar flares are the most energetic events in the Solar System
  and have direct impact in the interplanetary space and ultimately
  in our planet, there are still many unresolved issues concerning
  their generation, the underlying processes of particle acceleration
  involved, the effect at different layer in the solar atmosphere,
  among others. This work presents new coordinated observations from the
  New Solar Telescope (NST) and the space telescope IRIS that acquired
  simultaneous observations of an M1.0 class flare occurred on 12 June,
  2014 in active region NOAA 12087. NST filtergrams using the TiO filter,
  together with chromospheric data from the Halpha line allow us to study
  the evolution of the event from the first signs of the intensification
  of the intensity in the region. We focused on a small portion where
  the intensity enhancement in Halpha (blue and red wings) seems to be
  triggered, and discovered a rapid expansion of a flux-rope structure
  near the magnetic neutral line, in the sequence of high-resolution
  photospheric images. IRIS observations evidenced strong emission of the
  chromospheric and transition region lines during the flare. Jet-like
  structures are detected before the initiation of the flare in
  chromospheric lines and strong non-thermal emission in the transition
  region at the beginning of the impulsive phase. Evaporation flows with
  velocities up to 50 km/s occurred in the hot chromospheric plasma. We
  interpreted the result in terms of the “gentle” evaporation that
  occurs after accelerated particles heat the chromosphere.

---------------------------------------------------------
Title: Dynamics of electric currents, magnetic field topology and
    helioseismic response of a solar flare
Authors: Sharykin, Ivan; Kosovichev, Alexander
2015IAUGA..2256452S    Altcode:
  The solar flare on July 30, 2011 was of a modest X-ray class (M9.3),
  but it made a strong photospheric impact and produced a "sunquake,"
  observed with the Helioseismic and Magnetic Imager (HMI) on NASA's
  Solar Dynamics Observatory (SDO). In addition to the helioseismic
  waves (also observed with the SDO/AIA instrument), the flare caused
  a large expanding area of white-light emission and was accompanied
  by substantial restructuring of magnetic fields, leading to the rapid
  formation of a sunspot structure in the flare region. The flare produced
  no significant hard X-ray emission and no coronal mass ejection. This
  indicates that the flare energy release was mostly confined to the lower
  atmosphere. The absence of significant coronal mass ejection rules out
  magnetic rope eruption as a mechanism of helioseismic waves. We discuss
  the connectivity of the flare energy release with the electric currents
  dynamics and show the potential importance of high-speed plasma flows
  in the lower solar atmosphere during the flare energy release.

---------------------------------------------------------
Title: Realistic Modeling of Local Dynamo Processes on the Sun
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Mansour, N. N.; Wray,
   A. A.
2015ApJ...809...84K    Altcode: 2015arXiv150608924K
  Magnetic fields are usually observed in the quiet Sun as small-scale
  elements that cover the entire solar surface (the “salt-and-pepper”
  patterns in line-of-sight magnetograms). By using 3D radiative MHD
  numerical simulations, we find that these fields result from a local
  dynamo action in the top layers of the convection zone, where extremely
  weak “seed” magnetic fields (e.g., from a 10<SUP>-6</SUP> G) can
  locally grow above the mean equipartition field to a stronger than 2000
  G field localized in magnetic structures. Our results reveal that the
  magnetic flux is predominantly generated in regions of small-scale
  helical downflows. We find that the local dynamo action takes place
  mostly in a shallow, about 500 km deep, subsurface layer, from which
  the generated field is transported into the deeper layers by convective
  downdrafts. We demonstrate that the observed dominance of vertical
  magnetic fields at the photosphere and horizontal fields above the
  photosphere can be explained by small-scale magnetic loops produced
  by the dynamo. Such small-scale loops play an important role in the
  structure and dynamics of the solar atmosphere and their detection in
  observations is critical for understanding the local dynamo action on
  the Sun.

---------------------------------------------------------
Title: Dynamics of Electric Currents, Magnetic Field Topology,
    and Helioseismic Response of a Solar Flare
Authors: Sharykin, I. N.; Kosovichev, A. G.
2015ApJ...808...72S    Altcode: 2015arXiv150205190S
  The solar flare on 2011 July 30 was of a modest X-ray class (M9.3),
  but it made a strong photospheric impact and produced a “sunquake,”
  which was observed with the Helioseismic and Magnetic Imager on board
  NASA's Solar Dynamics Observatory. In addition to the helioseismic
  waves, the flare caused a large expanding area of white-light emission
  and was accompanied by the rapid formation of a sunspot structure in the
  flare region. The flare produced hard X-ray (HXR) emission less then
  300 keV and no coronal mass ejection (CME). The absence of CME rules
  out magnetic rope eruption as a mechanism of helioseismic waves. The
  sunquake impact does not coincide with the strongest HXR source,
  which contradicts the standard beam-driven mechanism of sunquake
  generation. We discuss the connectivity of the flare energy release
  with the electric currents dynamics and show the potential importance
  of high-speed plasma flows in the lower solar atmosphere during the
  flare energy release.

---------------------------------------------------------
Title: Sunquakes: Helioseismic response to solar flares
Authors: Kosovichev, A. G.
2015exse.book..306K    Altcode: 2014arXiv1402.1249K
  Sunquakes observed in the form of expanding wave ripples on the surface
  of the Sun during solar flares represent packets of acoustic waves
  excited by flare impacts and traveling through the solar interior. The
  excitation impacts strongly correlate with the impulsive flare phase,
  and are caused by the energy and momentum transported from the
  energy release sites. The flare energy is released in the form of
  energetic particles, waves, mass motions, and radiation. However,
  the exact mechanism of the localized hydrodynamic impacts that
  generate sunquakes is unknown. Solving the problem of the sunquake
  mechanism will substantially improve our understanding of the flare
  physics. In addition, sunquakes offer a unique opportunity for
  studying the interaction of acoustic waves with magnetic fields and
  flows in flaring active regions, and for developing new approaches to
  helioseismic acoustic tomography.

---------------------------------------------------------
Title: Energy Release and Initiation of a Sunquake in a C-class Flare
Authors: Sharykin, I. N.; Kosovichev, A. G.; Zimovets, I. V.
2015ApJ...807..102S    Altcode: 2014arXiv1405.5912S
  We present an analysis of the C7.0 solar flare from 2013 February
  17, revealing a strong helioseismic response (sunquake) caused by a
  compact impact observed with the Helioseismic and Magnetic Imager on
  board the Solar Dynamics Observatory (SDO) in the low atmosphere. This
  is the weakest known C-class flare generating a sunquake event. To
  investigate the possible mechanisms of this event and understand
  the role of accelerated charged particles and photospheric electric
  currents, we use data from three space observatories: RHESSI, SDO,
  and Geostationary Operational Environmental Satellite. We find that the
  photospheric flare impact does not spatially correspond to the strongest
  hard X-ray emission source, but both of these events are parts of the
  same energy release. Our analysis reveals a close association of the
  flare energy release with a rapid increase in the electric currents
  and suggests that the sunquake initiation is unlikely to be caused
  by the impact of high-energy electrons, but may be associated with
  rapid current dissipation or a localized impulsive Lorentz force in
  the lower layers of the solar atmosphere.

---------------------------------------------------------
Title: Simulations of Stellar Magnetoconvection using the Radiative
    MHD Code `StellarBox'
Authors: Wray, Alan A.; Bensassi, Khalil; Kitiashvili, Irina N.;
   Mansour, Nagi N.; Kosovichev, Alexander G.
2015arXiv150707999W    Altcode:
  Realistic numerical simulations, i.e., those that make minimal use
  of ad hoc modeling, are essential for understanding the complex
  turbulent dynamics of the interiors and atmospheres of the Sun and
  other stars and the basic mechanisms of their magnetic activity and
  variability. The goal of this paper is to present a detailed description
  and test results of a compressible radiative MHD code, `StellarBox',
  specifically developed for simulating the convection zones, surface,
  and atmospheres of the Sun and moderate-mass stars. The code solves the
  three-dimensional, fully coupled compressible MHD equations using a
  fourth-order Padé spatial differentiation scheme and a fourth-order
  Runge-Kutta scheme for time integration. The radiative transfer
  equation is solved using the Feautrier method for bi-directional
  ray tracing and an opacity-binning technique. A specific feature
  of the code is the implementation of subgrid-scale MHD turbulence
  models. The data structures are automatically configured, depending
  on the computational grid and the number of available processors, to
  achieve good load balancing. We present test results and illustrate
  the code's capabilities for simulating the granular convection on the
  Sun and a set of main-sequence stars. The results reveal substantial
  changes in the near-surface turbulent convection in these stars, which
  in turn affect properties of the surface magnetic fields. For example,
  in the solar case initially uniform vertical magnetic fields tend to
  self-organize into compact (pore-like) magnetic structures, while in
  more massive stars such structures are not formed and the magnetic
  field is distributed more-or-less uniformly in the intergranular lanes.

---------------------------------------------------------
Title: Oscillations in stellar superflares
Authors: Balona, L. A.; Broomhall, A. -M.; Kosovichev, A.; Nakariakov,
   V. M.; Pugh, C. E.; Van Doorsselaere, T.
2015MNRAS.450..956B    Altcode: 2015arXiv150401491B
  Two different mechanisms may act to induce quasi-periodic pulsations
  (QPP) in whole-disc observations of stellar flares. One mechanism may be
  magnetohydromagnetic forces and other processes acting on flare loops
  as seen in the Sun. The other mechanism may be forced local acoustic
  oscillations due to the high-energy particle impulse generated by the
  flare (known as `sunquakes' in the Sun). We analyse short-cadence Kepler
  data of 257 flares in 75 stars to search for QPP in the flare decay
  branch or post-flare oscillations which may be attributed to either
  of these two mechanisms. About 18 per cent of stellar flares show a
  distinct bump in the flare decay branch of unknown origin. The bump
  does not seem to be a highly damped global oscillation because the
  periods of the bumps derived from wavelet analysis do not correlate
  with any stellar parameter. We detected damped oscillations covering
  several cycles (QPP), in seven flares on five stars. The periods of
  these oscillations also do not correlate with any stellar parameter,
  suggesting that these may be a due to flare loop oscillations. We
  searched for forced global oscillations which might result after
  a strong flare. To this end, we investigated the behaviour of the
  amplitudes of solar-like oscillations in eight stars before and after
  a flare. However, no clear amplitude change could be detected. We
  also analysed the amplitudes of the self-excited pulsations in two δ
  Scuti stars and one γ Doradus star before and after a flare. Again,
  no clear amplitude changes were found. Our conclusions are that a new
  process needs to be found to explain the high incidence of bumps in
  stellar flare light curves, that flare loop oscillations may have been
  detected in a few stars and that no conclusive evidence exists as yet
  for flare induced global acoustic oscillations (starquakes).

---------------------------------------------------------
Title: Properties of Chromospheric Evaporation and Plasma Dynamics
    of a Solar Flare from Iris
Authors: Sadykov, Viacheslav M.; Vargas Dominguez, Santiago;
   Kosovichev, Alexander G.; Sharykin, Ivan N.; Struminsky, Alexei B.;
   Zimovets, Ivan
2015ApJ...805..167S    Altcode: 2014arXiv1412.0172S
  The dynamics of hot chromospheric plasma of solar flares is a
  key to understanding the mechanisms of flare energy release and
  particle acceleration. A moderate M1.0 class flare of 2014 June 12,
  (SOL2014-06-12T21:12) was simultaneously observed by NASA's Interface
  Region Imaging Spectrograph (IRIS) and other spacecraft, and also by
  the New Solar Telescope at the BBSO. This paper presents the first
  part of our investigation focused on analysis of the IRIS data. Our
  analysis of the IRIS data in different spectral lines reveals a strong
  redshifted jet-like flow with a speed of ∼100 km s<SUP>-1</SUP> of the
  chromospheric material before the flare. Strong nonthermal emission
  of the C ii k 1334.5 Å line, formed in the chromosphere-corona
  transition region, is observed at the beginning of the impulsive
  phase in several small (with a size of ∼1″) points. It is also
  found that the C ii k line is redshifted across the flaring region
  before, during, and after the impulsive phase. A peak of integrated
  emission of the hot (1.1 · 10<SUP>7</SUP> K) plasma in the Fe xxi
  1354.1 Å line is detected approximately five minutes after the
  integrated emission peak of the lower temperature C ii k. A strong
  blueshift of the Fe xxi line across the flaring region corresponds to
  evaporation flows of the hot chromospheric plasma with a speed of 50
  km s<SUP>-1</SUP>. Additional analysis of the RHESSI data supports
  the idea that the upper chromospheric dynamics observed by IRIS has
  features of “gentle” evaporation driven by heating of the solar
  chromosphere by accelerated electrons and by a heat flux from the
  flare energy release site.

---------------------------------------------------------
Title: A Method for the Estimation of p-Mode Parameters from Averaged
    Solar Oscillation Power Spectra
Authors: Reiter, J.; Rhodes, E. J., Jr.; Kosovichev, A. G.; Schou,
   J.; Scherrer, P. H.; Larson, T. P.
2015ApJ...803...92R    Altcode: 2015arXiv150407493R
  A new fitting methodology is presented that is equally well suited for
  the estimation of low-, medium-, and high-degree mode parameters from
  m-averaged solar oscillation power spectra of widely differing spectral
  resolution. This method, which we call the “Windowed, MuLTiple-Peak,
  averaged-spectrum” or WMLTP Method, constructs a theoretical profile
  by convolving the weighted sum of the profiles of the modes appearing
  in the fitting box with the power spectrum of the window function of
  the observing run, using weights from a leakage matrix that takes into
  account observational and physical effects, such as the distortion of
  modes by solar latitudinal differential rotation. We demonstrate that
  the WMLTP Method makes substantial improvements in the inferences of
  the properties of the solar oscillations in comparison with a previous
  method, which employed a single profile to represent each spectral
  peak. We also present an inversion for the internal solar structure,
  which is based upon 6366 modes that we computed using the WMLTP method
  on the 66 day 2010 Solar and Heliospheric Observatory/MDI Dynamics
  Run. To improve both the numerical stability and reliability of the
  inversion, we developed a new procedure for the identification and
  correction of outliers in a frequency dataset. We present evidence
  for a pronounced departure of the sound speed in the outer half of the
  solar convection zone and in the subsurface shear layer from the radial
  sound speed profile contained in Model S of Christensen-Dalsgaard and
  his collaborators that existed in the rising phase of Solar Cycle 24
  during mid-2010.

---------------------------------------------------------
Title: Detection of Fast-Moving Waves Propagating Outward from
    Sunspots in the Photosphere
Authors: Zhao, Junwei; Chen, Ruizhu; Hartlep, Thomas; Kosovichev,
   Alexander
2015TESS....110504Z    Altcode:
  Helioseismic and magnetohydrodynamic waves are abundant in and above
  sunspots. Through cross-correlating oscillation signals at various
  locations, we are able to reconstruct how waves propagate away from
  a wave source inside a sunspot in the photospheric level. Before
  helioseismic waves are visible propagating away from the source,
  a surprisingly fast-moving wave is detected traveling along the
  sunspot's radial directionfrom inside of the sunspot to the outside,
  extending about 15 Mm beyond the sunspot boundary. The wave has a
  frequency range of 2.5 - 4.0 mHz, and appears dispersionless with a
  phase velocity of 45.3 km/s, a few times faster than typical speeds of
  sound and magnetohydrodynamic waves in the photosphere. The observed
  wave is consistent with a magnetoacoustic wave, excited at approximately
  5 Mm beneath the sunspot surface, sweeping across the photosphere,
  although it is not clear how this wave is excited at that depth. If the
  fast-moving wave is truly excited in the sunspot's subsurface area,
  this will help open a new window to study the internal structure and
  dynamics of sunspots.

---------------------------------------------------------
Title: Preface: Cosmic magnetic fields
Authors: Kosovichev, Alexander
2015AdSpR..55..779K    Altcode:
  Recent advances in observations and modeling have opened new
  perspectives for the understanding of fundamental dynamical processes
  of cosmic magnetism, and associated magnetic activity on the Sun,
  stars and galaxies. The goal of the Special Issue is to discuss
  the progress in solar physics and astrophysics, similarities and
  differences in phenomenology and physics of magnetic phenomena on the
  Sun and other stars. Space observatories, ground-based telescopes,
  and new observational methods have provided tremendous amount of
  data that need to be analyzed and understood. The solar observations
  discovered multi-scale organization of solar activity, dramatically
  changing current paradigms of solar variability. On the other side,
  stellar observations discovered new regimes of dynamics and magnetism
  that are different from the corresponding solar phenomena, but described
  by the same physics. Stars represent an astrophysical laboratory for
  studying the dynamical, magnetic and radiation processes across a broad
  range of stellar masses and ages. These studies allow us to look at
  the origin and evolution of our Sun, whereas detailed investigations
  of the solar magnetism give us a fundamental basis for interpretation
  and understanding of unresolved stellar data.

---------------------------------------------------------
Title: Flare Energy Release in the Low Solar Atmosphere: Fine
    Structuring, Electric Currents and Sunquakes.
Authors: Sharykin, I.; Kosovichev, A. G.
2014AGUFMSH41C4163S    Altcode:
  Observations of C2.1 flare of August 15, 2011, obtained at NST/BBSO,
  reveal fine structuring of H-alpha flare ribbons (with a characteristic
  width ~100 km). Using SDO/HMI vector magnetic field measurements we
  calculate vertical electric currents and discuss their role in the
  flare energy release. We argue that the observed fine structuring of the
  flare ribbons can be associated with dissipation of electric currents
  in the partially ionized chromospheric plasma. We also discuss the
  role of electric currents in two flares with sunquakes: C7.0 flare
  of Febrary 17, 2013, and M9.2 flare of July 30, 2011. We find that
  the observed sunquake impacts do not spatially correlate with the
  strongest HXR emission sources but coincide with the intensive electric
  currents. These observations suggest that the primary energy release
  can be connected with rapid dissipation of electric currents in the low
  atmosphere. We also conclude that the fine structuring of the electric
  currents may play a very important role, as it leads to enhanced and
  fast magnetic energy release, especially in the case of turbulent and
  ambipolar resistivity which can take place in the low solar atmosphere.

---------------------------------------------------------
Title: Large-scale flows and magnetic fields in solar-like stars
    from global simulation with and without tachocline
Authors: Guerrero, G.; Kosovichev, A. G.; Smolarkiewicz, P. K.;
   de Gouveia Dal Pino, E. M.
2014AGUFMSH41B4150G    Altcode:
  The large-scale flows patterns like differential rotation and
  meridional circulation as well as the mean-field dynamo action in the
  Sun and solar-like stars are thought to have their origin in helical
  turbulent motions in the stellar convection zones. In this work we will
  present recent results of HD and MHD global simulations of stars whose
  stratification resemble that of the solar interior. The simulations are
  performed with the EULAG code (Smolarkiewicz et al. 2001). They include
  implicit modeling of the large-eddy contribution from the turbulent
  scales to the resolved scales, thus, allowing higher turbulent levels
  (e.g., Guerrero et al. 2013). In the HD regime, the value of the Rossby
  (Ro) number defines large-scale flow patterns. Large values of Ro result
  in an anti-solar differential rotation and a meridional circulation
  consistent with a single circulation cell per hemisphere. Lower values
  of Ro result in a solar-type differential rotation and a meridional
  flow with multiple cells in radius and latitude. Due to the low
  dissipation of the numerical scheme, the models are also able to
  reproduce the tachocline and sustain it over a longer time scale. In
  the MHD regime, both solutions are still allowed, however, the shift
  from anti-solar to the solar-like rotation happens at a larger value
  or Ro. A wide range of dynamo solutions is obtained for the magnetic
  field, including steady and oscillating modes (see e.g., Fig. 1). We
  also compare models with and without a stable stratified layer at
  the bottom of the convection zone. We notice that the presence of a
  naturally developed tachocline plays an important role in the dynamo
  solution, modifying the morphology of the magnetic field, the cycles
  period and influencing the large-scale flows.References:Smolarkiewicz,
  P. K., Margolin, L. G., &amp; Wyszogrodzki, A. A. 2001, JAtS, 58,
  349; Guerrero, G., Smolarkiewicz, P. K., Kosovichev, A.K., Mansour,
  N.N. 2013, ApJ, 779, 176.

---------------------------------------------------------
Title: Three-Dimensional Magnetic Reconnection Under Low Chromospheric
    Conditions Using a Two-Fluid Weakly Ionized Reactive Plasma Model
Authors: Alvarez Laguna, A.; Lani, A.; Poedts, S.; Mansour, N. N.;
   Kosovichev, A. G.
2014AGUFMSH23A4151A    Altcode:
  Magnetic reconnection is a physical process enabling for the conversion
  of so-called free (non-potential) magnetic energy into kinetic and
  thermal energy by breaking the flux conservation law that exists for
  ideal (i.e. perfectly conducting) plasmas. This ubiquitous phenomenon in
  magnetized plasma plays an important role in the Sun's chromosphere as
  likely being responsible for transient plasma phenomena such as solar
  flares, spicules and chromospheric jets. In this work, we present
  a computational model that simulates magnetic reconnection under
  low chromospheric conditions using a two-fluid (plasma + neutrals)
  approach introduced by Leake et al. (2012). This model considers
  non-equilibrium partial ionization effects including ionization,
  recombination reactions and scattering collisions while simulating
  the interplay between the charged particles with the electromagnetic
  field. Previous 2D simulations showed that the dynamics of ions
  and neutrals are decoupled during the reconnection process. Also,
  the effect of the chemical non-equilibrium in the reconnection region
  plays a crucial role, yielding faster reconnection rates. We extended
  these simulations to study different 3D configurations in order to
  analyze the impact of non-equilibrium partial ionization effects on
  the neutral sheet configuration(s) and the reconnection rate of more
  realistic geometries. The results are compared with the two-dimensional
  simulations.

---------------------------------------------------------
Title: Swirling motions, fast plasma flows and small-scale
    chromospheric eruptions in a sunspot light-bridge
Authors: Vargas Domínguez, S.; Kosovichev, A. G.
2014AGUFMSH41C4159V    Altcode:
  Multi-wavelength observations with the 1.6m New Solar Telescope (NST)
  at Big Bear Solar Observatory (BBSO) have evidenced a complex dynamics
  of sunspots. We present photospheric and chromospheric observations
  of a sunspot light-bridge in AR 11850 taken on 29 September 2013. The
  NST/BFI data in the TiO reveal strong shearing and high-speed swirling
  flows in the light-bridge. Scanning of the H-alpha spectral line shows
  strong chromospheric downflows in the red wing near the outermost
  part of the light-bridge. Chromospheric structuring around the spot
  appears to be more complex due to the presence of the light-bridge. We
  detect small-scale explosive events that are likely to be boosted by
  the interactions of magnetic field lines at the chromospheric level
  and therefore triggered by the evolution of the light bridge in the
  photosphere beneath. In particular a very localized explosive event
  reaching the transition region and coronal temperatures is observed
  from simultaneous IRIS and SDO data.

---------------------------------------------------------
Title: Realistic Modeling of Multi-Scale MHD Dynamics of the Solar
    Atmosphere
Authors: Kitiashvili, I.; Mansour, N. N.; Wray, A. A.; Yoon, S.;
   Kosovichev, A. G.
2014AGUFMSH41B4134K    Altcode:
  Realistic 3D radiative MHD simulations open new perspectives for
  understanding the turbulent dynamics of the solar surface, its
  coupling to the atmosphere, and the physical mechanisms of generation
  and transport of non-thermal energy. Traditionally, plasma eruptions
  and wave phenomena in the solar atmosphere are modeled by prescribing
  artificial driving mechanisms using magnetic or gas pressure forces
  that might arise from magnetic field emergence or reconnection
  instabilities. In contrast, our 'ab initio' simulations provide a
  realistic description of solar dynamics naturally driven by solar
  energy flow. By simulating the upper convection zone and the solar
  atmosphere, we can investigate in detail the physical processes of
  turbulent magnetoconvection, generation and amplification of magnetic
  fields, excitation of MHD waves, and plasma eruptions. We present recent
  simulation results of the multi-scale dynamics of quiet-Sun regions, and
  energetic effects in the atmosphere and compare with observations. For
  the comparisons we calculate synthetic spectro-polarimetric data to
  model observational data of SDO, Hinode, and New Solar Telescope.

---------------------------------------------------------
Title: Analysis of High-Resolution Observations of Sunspot
    Oscillations and Waves
Authors: Kosovichev, A. G.
2014AGUFMSH41C4164K    Altcode:
  Oscillations of sunspots with a characteristic period of 3 minutes are
  prominent features of the sunspot dynamics. In the sunspot chromosphere,
  the oscillations are observed in the form of "running penumbral waves"
  representing shocks with narrow compression fronts, traveling along the
  expanding magnetic field lines. The origin of the sunspot oscillations
  and waves is not understood, and is a subject of hot debates. It had
  been suggested that the sunspot oscillations may be due to leakage of
  high-frequency acoustic (p) modes excited in subphotospheric layers. An
  alternative point of view is that the sources of sunspot oscillations
  and waves are in the chromosphere. Using long series of high-resolution
  sunspot images obtained with a narrow-band H-alpha filter at the
  1.6m New Solar Telescope at Big Bear Solar Observatory, I identify
  individual wave excitation events, investigate their properties and
  discuss potential physical mechanisms.

---------------------------------------------------------
Title: Using MHD simulations to model H-alpha and UV spectral lines
    for interpretation of IRIS and NST data
Authors: Sadykov, Viacheslav M.; Kosovichev, Alexander G.
2014arXiv1412.0288S    Altcode:
  We present results of non-LTE modeling of H-alpha 6563 A and Mg
  II k&amp;h 2796 A and 2803 A lines. This modeling is important for
  interpretation of coordinated observations from the recently launched
  NASA's IRIS mission and from the New Solar Telescope at Big Bear
  Solar Observatory. Among available codes for the non-LTE modeling,
  the RH code is chosen as the most appropriate for modeling of the line
  profiles. The most suitable Hydrogen and Magnesium atomic models are
  selected by performing several tests of the code. The influence of the
  ionization degree on the line profiles is also studied. Radiative-MHD
  simulations of the solar atmosphere, obtained with the Bifrost code,
  are used as input data for calculation of synthetic spectra of the
  H-alpha and Mg II h&amp;k lines for particular locations evolving with
  time. The spectral line variations reveal the presence of MHD waves in
  the simulation results. We construct oscillation power spectra of the
  line intensity for different wavelength, and compare these with the
  corresponding height-dependent power spectra of atmospheric parameters
  from the simulations. We find correlations between the power spectra
  of intensities of the line profiles at certain wavelengths and the
  power spectra of the atmospheric parameters at the tau-unity heights
  for these wavelengths. These results provide a new diagnostic method
  of chromospheric oscillations; however, larger amounts of data are
  needed to confirm these correlations.

---------------------------------------------------------
Title: Multi-wavelength High-resolution Observations of a Small-scale
    Emerging Magnetic Flux Event and the Chromospheric and Coronal
    Response
Authors: Vargas Domínguez, Santiago; Kosovichev, Alexander;
   Yurchyshyn, Vasyl
2014ApJ...794..140V    Altcode: 2014arXiv1405.3550V
  State-of-the-art solar instrumentation is now revealing magnetic
  activity of the Sun with unprecedented temporal and spatial
  resolutions. Observations with the 1.6 m aperture New Solar Telescope
  (NST) of the Big Bear Solar Observatory are making next steps in our
  understanding of the solar surface structure. Granular-scale magnetic
  flux emergence and the response of the solar atmosphere are among the
  key research topics of high-resolution solar physics. As part of a joint
  observing program with NASA's Interface Region Imaging Spectrograph
  (IRIS) mission on 2013 August 7, the NST observed active region
  NOAA 11,810 in the photospheric TiO 7057 Å band with a resolution
  of pixel size of 0.”034 and chromospheric He I 10830 Å and Hα
  6563 Å wavelengths. Complementary data are provided by the Solar
  Dynamics Observatory (SDO) and Hinode space-based telescopes. The
  region displayed a group of solar pores, in the vicinity of which we
  detect a small-scale buoyant horizontal magnetic flux tube causing
  granular alignments and interacting with the preexisting ambient field
  in the upper atmospheric layers. Following the expansion of distorted
  granules at the emergence site, we observed a sudden appearance of an
  extended surge in the He I 10830 Å data (bandpass of 0.05 Å). The
  IRIS transition region imaging caught ejection of a hot plasma jet
  associated with the He I surge. The SDO/HMI data used to study the
  evolution of the magnetic and Doppler velocity fields reveal emerging
  magnetic loop-like structures. Hinode/Ca II H and IRIS filtergrams
  detail the connectivities of the newly emerged magnetic field in the
  lower solar chromosphere. From these data, we find that the orientation
  of the emerging magnetic field lines from a twisted flux tube formed
  an angle of ~45° with the overlying ambient field. Nevertheless,
  the interaction of emerging magnetic field lines with the pre-existing
  overlying field generates high-temperature emission regions and boosts
  the surge/jet production. The localized heating is detected before
  and after the first signs of the surge/jet ejection. We compare the
  results with previous observations and theoretical models and propose a
  scenario for the activation of plasma jet/surges and confined heating
  triggered by buoyant magnetic flux tubes rising up into a magnetized
  upper environment. Such process may play a significant role in the
  mass and energy flow from the interior to the corona.

---------------------------------------------------------
Title: Control and operation of the 1.6 m New Solar Telescope in
    Big Bear
Authors: Varsik, J.; Plymate, C.; Goode, P.; Kosovichev, A.; Cao,
   W.; Coulter, R.; Ahn, K.; Gorceix, N.; Shumko, S.
2014SPIE.9147E..5DV    Altcode:
  The 1.6m New Solar Telescope (NST) has developed a modern and
  comprehensive suite of instruments which allow high resolution
  observations of the Sun. The current instrument package comprises
  diffraction limited imaging, spectroscopic and polarimetric instruments
  covering the wavelength range from 0.4 to 5.0 microns. The instruments
  include broadband imaging, visible and near-infrared scanning
  Fabry-Perot interferometers, an imaging spectropolarimeter,
  a fast visible-light imaging spectrograph, and a unique new
  scanning cryogenic infrared spectrometer/spectropolarimeter
  that is nearing completion. Most instruments are operated with
  a 308 subaperture adaptive optics system, while the thermal-IR
  spectrometer has a correlation tracker. This paper reports on the
  current observational programs and operational performance of the
  telescope and instrumentation. The current control, data processing,
  and archiving systems are also briefly discussed.

---------------------------------------------------------
Title: Solar Meridional Flow in the Shallow Interior during the
    Rising Phase of Cycle 24
Authors: Zhao, Junwei; Kosovichev, A. G.; Bogart, R. S.
2014ApJ...789L...7Z    Altcode: 2014arXiv1406.2735Z
  Solar subsurface zonal- and meridional-flow profiles during the
  rising phase of solar cycle 24 are studied using the time-distance
  helioseismology technique. The faster zonal bands in the
  torsional-oscillation pattern show strong hemispheric asymmetries and
  temporal variations in both width and speed. The faster band in the
  northern hemisphere is located closer to the equator than the band
  in the southern hemisphere and migrates past the equator when the
  magnetic activity in the southern hemisphere is reaching maximum. The
  meridional-flow speed decreases substantially with the increase of
  magnetic activity, and the flow profile shows two zonal structures in
  each hemisphere. The residual meridional flow, after subtracting a mean
  meridional-flow profile, converges toward the activity belts and shows
  faster and slower bands like the torsional-oscillation pattern. More
  interestingly, the meridional-flow speed above latitude 30° shows
  an anti-correlation with the poleward-transporting magnetic flux,
  slower when the following-polarity flux is transported and faster when
  the leading-polarity flux is transported. It is expected that this
  phenomenon slows the process of magnetic cancellation and polarity
  reversal in high-latitude areas.

---------------------------------------------------------
Title: Studying Shallow Meridional Flow by Time-Distance
    Helioseismology during the Rising Phase of Cycle 24
Authors: Zhao, Junwei; Kosovichev, Alexander G.; Bogart, Richard S.
2014AAS...22421805Z    Altcode:
  Using continuous SDO/HMI Doppler observations, we have studied the
  solar subsurface torsional oscillation and meridional flow during the
  rising phase of solar cycle 24. The faster bands of the torsional
  oscillation pattern show clear temporal variations in both width
  and strength, and the band in the northern hemisphere extends past
  the equator into the southern hemisphere. The meridional-flow speed
  drops substantially with the rise of magnetic activity, and at some
  depths and for some briefperiods, the flow even reverses directions in
  mid-latitudes. The residual meridional flow shows faster and slower
  bands like the torsional oscillation patterns, but its faster bands
  approach the equator earlier than the torsional oscillation bands. More
  interestingly, the meridional flow speed in latitudes above 35 degree
  slows down (speeds up) when the following-polarity (leading-polarity)
  magnetic flux is transported poleward, essentially delaying the magnetic
  polarity reversal and the onset of the next solar cycle.

---------------------------------------------------------
Title: Transient Small-Scale Magnetic Flux Emergence and Atmospheric
    Response Observed with New Solar Telescope and SDO
Authors: Vargas Domínguez, Santiago; Kosovichev, Alexander G.
2014AAS...22412345V    Altcode:
  State-of-the art solar instrumentation is now revealing the activity of
  the Sun at the highest temporal and spatial resolution. Granular-scale
  magnetic flux emergence and the response of the solar atmosphere is
  one of the key topics. Observations with the 1.6m aperture New Solar
  Telescope (NST) at Big Bear Solar Observatory (BBSO) are making next
  steps in our understanding of the solar surface structure. On August 7,
  2013, NST observed active region NOAA 11810 in different photospheric
  and chromospheric wavelengths. The region displays a group of solar
  pores, in the vicinity of which we detected a site of emerging magnetic
  flux accompanied by intense and very confined abnormal granulation
  dynamics, observed in the photospheric TiO 7057 A with a resolution
  of 0.034 “/pix. Following the expansion of exploding granules in
  this site, we observed a sudden appearance of an extended surge in the
  HeI 10830A data (bandpass of 0.05 A). The SDO/HMI data used to study
  the evolution of the magnetic field and Doppler velocities reveal a
  short-lived emerging loop-like structure with strong upflows. We used
  the SDO/AIA data to investigate the response of the transition region
  and corona to the transient emerging flux phenomenon. We compare the
  results with previous observations, and propose a scenario for the
  production of plasma surges by the transient magnetic flux emergence
  events.

---------------------------------------------------------
Title: Fine Structure of Flare Ribbons and Evolution of Electric
    Currents
Authors: Sharykin, I. N.; Kosovichev, A. G.
2014ApJ...788L..18S    Altcode: 2014arXiv1404.5104S
  Emission of solar flares across the electromagnetic spectrum is often
  observed in the form of two expanding ribbons. The standard flare model
  explains flare ribbons as footpoints of magnetic arcades, emitting
  due to interaction of energetic particles with the chromospheric
  plasma. However, the physics of this interaction and properties of
  the accelerated particles are still unknown. We present results of
  multiwavelength observations of the C2.1 flare of 2013 August 15,
  observed with the New Solar Telescope of the Big Bear Solar Observatory,
  and the Solar Dynamics Observatory, GOES, and Fermi spacecraft. The
  observations reveal previously unresolved sub-arcsecond structure of
  flare ribbons in regions of strong magnetic field consisting from
  numerous small-scale bright knots. We observe a red-blue asymmetry
  of H<SUB>α</SUB> flare ribbons with a width as small as ~100 km. We
  discuss the relationship between the ribbons and vertical electric
  currents estimated from vector magnetograms, and show that Joule
  heating can be responsible for energization of H<SUB>α</SUB> knots
  in the ribbons.

---------------------------------------------------------
Title: Multiscale Properties of the Local Dynamo on the Sun
Authors: Kitiashvili, Irina; Kosovichev, Alexander G.; Mansour,
   Nagi N; Wray, Alan A
2014AAS...22410304K    Altcode:
  Dynamics of the quiet Sun represents a background ('salt-and-pepper')
  state for powerful manifestations of solar activity. Current numerical
  simulations have shown that small-scale turbulent dynamics can
  strongly couple with processes on larger scales, such as formation
  of pores and sunspots. We perform 3D MHD radiative simulations of
  top layers of the convection zone and the low atmosphere, taking
  into account effects of turbulence, magnetic fields, ionization and
  excitation of all abundant elements. To model the dynamo process we
  carry a series of the simulations with various initial weak levels
  of magnetic field perturbations. The results show that an initial,
  randomly distributed ('seed') magnetic field of 1 micro-gauss, greatly
  amplifies by subsurface turbulent dynamics. The self generated magnetic
  field (dynamo) reaches 2 kG magnetic levels in the photosphere. The
  local dynamo process primary operates 1 Mm below the surface
  where the magnetic fields are amplified by helical flows. These
  dynamo-generated magnetic fields are transported by downflows into
  deeper layers. The process of the magnetic field amplification has
  a substantially multiscale character, during which self-organized
  turbulent helical flows work coherently on scales much larger then the
  turbulent scales. We discuss the apparent contradiction of our results
  with current paradigm that local dynamo can generate magnetic fields
  only on the small turbulent scales. We compare our results with other
  simulations and observations.

---------------------------------------------------------
Title: Sub-arcsecond Structure and Dynamics of Flare Ribbons Observed
    with New Solar Telescope
Authors: Sharykin, Ivan; Kosovichev, Alexander G.
2014AAS...22412310S    Altcode:
  Emission of solar flares across the electromagnetic spectrum is often
  observed in the form of two expanding ribbons. The standard flare
  model explains the flare ribbons as footpoints of magnetic arcades,
  emitting due to the interaction of energetic particles with the
  chromospheric plasma. However, the physics of this interaction and
  properties of the accelerated particles are still unknown. We present
  results of multiwavelength observations of C2.1 flare of August 15,
  2011, observed with the 1.6-meter New Solar Telescope of Big Bear
  Solar Observatory. These unique data are characterized by the great
  spatial resolution reaching the telescope diffraction limit with good
  spectral scanning of H-alpha line, and photospheric imaging. The
  observations reveal previously unresolved sub-arcsecond structure
  of the flare ribbons in regions of strong magnetic field. We discuss
  the fine structure of the flare ribbons, their dynamics, and possible
  mechanisms of the energy release and transport, using also data from
  SDO, GOES and FERMI spacecraft.

---------------------------------------------------------
Title: High Resolution Observations of Chromospheric Jets in
    Sunspot Umbra
Authors: Yurchyshyn, Vasyl B.; Abramenko, Valentyna; Kosovichev,
   Alexander G.; Goode, Philip R.
2014AAS...22432301Y    Altcode:
  Recent observations of sunspot's umbra suggested that it may be finely
  structured at a sub-arcsecond scale representing a mix of hot and cool
  plasma elements. In this study we report the first detailed observations
  of the umbral spikes, which are cool jet-like structures seen in the
  chromosphere of an umbra. The spikes are cone-shaped features with
  a typical height of 0.5-1. Mm and a width of about 0. Mm. Their life
  time ranges from 2 to 3 ~min and they tend to re-appear at the same
  location. The preliminary analysis indicates that the spikes are not
  associated with photospheric umbral dots and they rather tend to
  occur above darkest parts of the umbra, where magnetic fields are
  strongest. The spikes exhibit up and down oscillatory motions and
  their spectral evolution suggests that they might be driven by upward
  propagating shocks generated by photospheric oscillations. It is worth
  noting that triggering of the running penumbral waves seems to occur
  during the interval when the spikes reach their maximum height.

---------------------------------------------------------
Title: Unusual Sunquake Events Challenge the Standard Model of
    Solar Flares
Authors: Kosovichev, Alexander G.; Sharykin, Ivan; Zimovets, Ivan
2014AAS...22410403K    Altcode:
  "Sunquakes" represent helioseismic waves excited by solar
  flares. According to the standard flare model, sunquakes are associated
  with the hydrodynamic response of the low atmosphere to beams of
  flare-accelerated particles. Observations with the HMI instrument
  on Solar Dynamics Observatory have shown that sunquakes are a much
  more common phenomenon than this was found from the previous SOHO/MDI
  observations. The HMI observations reveal that sunquakes may occur not
  only during strong X-class flare but also in relatively weak flares
  of low M-class (as low as M1). It is particularly surprising that,
  in some cases, the sunquake initiating impacts are observed in the
  early impulsive or even pre-heating phase, prior to the main hard X-ray
  impulse and even without a significant hard X-ray signal. We examine
  properties of such sunquake events, present a detailed analysis of
  M2.8 flare of February 17, 2013, using HMI, AIA, GOES and RHESSI data,
  and discuss implications for the standard flare model.

---------------------------------------------------------
Title: Photospheric and Chromospheric Dynamics of Sunspots Observed
    with New Solar Telescope
Authors: Kosovichev, Alexander G.; Yurchyshyn, Vasyl B.
2014AAS...22421811K    Altcode:
  The 1.6m New Solar Telescope (NST) of Big Bear Solar Observatory
  allows us to investigate the structure and dynamics of sunspots with
  unprecedented spatial and temporal resolutions. We present results
  of simultaneous observations of a sunspot in the photosphere with a
  broad-band TiO-line filter and in the chromospheric H-alpha line with
  Visible Imaging Spectrometer, and compare the observational results with
  MHD models of sunspots. The observations reveal previously unresolved
  features of the sunspot umbra and penumbra. In particular, the TiO data
  clearly demonstrate highly twisted dynamics of penumbral filaments and
  umbral dots and reveal strong shearing plasma flows in sunspot bridges,
  not explained by the MHD simulations. The high-resolution H-alpha
  spectroscopic data provide new views of the sunspot chromospheric
  dynamics, including the fine structure of oscillations and waves,
  penumbral jets, ubiquitous small-scale eruptions, and accretion
  flows in a form of dense plasma sheets. The diffraction-limited NST
  observations show that the sunspot dynamics is more complicated and
  much richer than it is described by the current sunspot models.

---------------------------------------------------------
Title: High Resolution Observations of Chromospheric Jets in
    Sunspot Umbra
Authors: Yurchyshyn, V.; Abramenko, V.; Kosovichev, A.; Goode, P.
2014ApJ...787...58Y    Altcode: 2014arXiv1404.7444Y
  Recent observations of a sunspot's umbra have suggested that it may
  be finely structured on a subarcsecond scale representing a mix of hot
  and cool plasma elements. In this study, we report the first detailed
  observations of umbral spikes, which are cool jet-like structures seen
  in the chromosphere of an umbra. The spikes are cone-shaped features
  with a typical height of 0.5-1.0 Mm and a width of about 0.1 Mm. Their
  lifetime ranges from 2 to 3 minutes and they tend to re-appear at
  the same location. The spikes are not associated with photospheric
  umbral dots and they instead tend to occur above the darkest parts of
  the umbra where magnetic fields are strongest. The spikes exhibit up
  and down oscillatory motions and their spectral evolution suggests
  that they might be driven by upward propagating shocks generated by
  photospheric oscillations. It is worth noting that triggering of the
  running penumbral waves seems to occur during the interval when the
  spikes reach their maximum height.

---------------------------------------------------------
Title: Verification of the Helioseismology Travel-time Measurement
    Technique and the Inversion Procedure for Sound Speed Using
    Artificial Data
Authors: Parchevsky, K. V.; Zhao, J.; Hartlep, T.; Kosovichev, A. G.
2014ApJ...785...40P    Altcode:
  We performed three-dimensional numerical simulations of the solar
  surface acoustic wave field for the quiet Sun and for three models with
  different localized sound-speed perturbations in the interior with
  deep, shallow, and two-layer structures. We used the simulated data
  generated by two solar acoustics codes that employ the same standard
  solar model as a background model, but utilize different integration
  techniques and different models of stochastic wave excitation. Acoustic
  travel times were measured using a time-distance helioseismology
  technique, and compared with predictions from ray theory frequently
  used for helioseismic travel-time inversions. It is found that the
  measured travel-time shifts agree well with the helioseismic theory
  for sound-speed perturbations, and for the measurement procedure with
  and without phase-speed filtering of the oscillation signals. This
  testing verifies the whole measuring-filtering-inversion procedure
  for static sound-speed anomalies with small amplitude inside the
  Sun outside regions of strong magnetic field. It is shown that the
  phase-speed filtering, frequently used to extract specific wave packets
  and improve the signal-to-noise ratio, does not introduce significant
  systematic errors. Results of the sound-speed inversion procedure show
  good agreement with the perturbation models in all cases. Due to its
  smoothing nature, the inversion procedure may overestimate sound-speed
  variations in regions with sharp gradients of the sound-speed profile.

---------------------------------------------------------
Title: Effects of Anisotropies in Turbulent Magnetic Diffusion in
    Mean-field Solar Dynamo Models
Authors: Pipin, V. V.; Kosovichev, A. G.
2014ApJ...785...49P    Altcode: 2013arXiv1307.6651P
  We study how anisotropies of turbulent diffusion affect the
  evolution of large-scale magnetic fields and the dynamo process
  on the Sun. The effect of anisotropy is calculated in a mean-field
  magnetohydrodynamics framework assuming that triple correlations provide
  relaxation to the turbulent electromotive force (so-called the "minimal
  τ-approximation"). We examine two types of mean-field dynamo models:
  the well-known benchmark flux-transport model and a distributed-dynamo
  model with a subsurface rotational shear layer. For both models,
  we investigate effects of the double- and triple-cell meridional
  circulation, recently suggested by helioseismology and numerical
  simulations. To characterize the anisotropy effects, we introduce
  a parameter of anisotropy as a ratio of the radial and horizontal
  intensities of turbulent mixing. It is found that the anisotropy
  affects the distribution of magnetic fields inside the convection
  zone. The concentration of the magnetic flux near the bottom and top
  boundaries of the convection zone is greater when the anisotropy is
  stronger. It is shown that the critical dynamo number and the dynamo
  period approach to constant values for large values of the anisotropy
  parameter. The anisotropy reduces the overlap of toroidal magnetic
  fields generated in subsequent dynamo cycles, in the time-latitude
  "butterfly" diagram. If we assume that sunspots are formed in the
  vicinity of the subsurface shear layer, then the distributed dynamo
  model with the anisotropic diffusivity satisfies the observational
  constraints from helioseismology and is consistent with the value of
  effective turbulent diffusion estimated from the dynamics of surface
  magnetic fields.

---------------------------------------------------------
Title: Sunquakes and starquakes
Authors: Kosovichev, Alexander G.
2014IAUS..301..349K    Altcode: 2014arXiv1401.8036K
  In addition to well-known mechanisms of excitation of solar and
  stellar oscillations by turbulent convection and instabilities, the
  oscillations can be excited by an impulsive localized force caused
  by the energy release in solar and stellar flares. Such oscillations
  have been observed on the Sun (`sunquakes'), and created a lot of
  interesting discussions about physical mechanisms of the impulsive
  excitation and their relationship to the flare physics. The observation
  and theory have shown that most of a sunquake's energy is released
  in high-degree, high-frequency p modes. In addition, there have been
  reports on helioseismic observations of low-degree modes excited by
  strong solar flares. Much more powerful flares observed on other stars
  can cause `starquakes' of substantially higher amplitude. Observations
  of such oscillations can provide new asteroseismic information and
  also constraints on mechanisms of stellar flares. I discuss the basic
  properties of sunquakes, and initial attempts to detect flare-excited
  oscillations in Kepler short-cadence data.

---------------------------------------------------------
Title: Emergence of a small-scale magnetic flux tube and the response
    of the solar atmosphere
Authors: Vargas Dominguez, S.; Kosovichev, A. G.; Yurchyshyn, V.
2014CEAB...38...25V    Altcode:
  Cutting-edge observations with the 1.6-meter telescope at Big Bear
  Solar Observatory (BBSO) in California have taken research into the
  activity of the Sun to new levels of understanding of the structure
  and evolution of the solar atmosphere at high-resolution spatial and
  temporal scales. On August 7, 2013 the NST observed active region NOAA
  11810 in photospheric and chromospheric wavelengths. The observations
  were performed as part of a program conducted jointly with NASA's
  Interface Region Imaging Spectrograph (IRIS) mission, Solar Dynamics
  Observatory (SDO) and Hinode satellite. These observations provided a
  unique view on the emergence of a buoyant small-scale magnetic-flux
  rope in the solar photosphere. The event is accompanied by response
  of the solar atmosphere once the newly emerged field interacts with
  the pre-existing overlying one. The reconnection process that takes
  place in the region produces jet emission and high-temperature points
  in the chromosphere and corona.

---------------------------------------------------------
Title: Mechanism of local dynamo action on the Sun
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Mansour, N. N.; Wray,
   A. A.
2013arXiv1312.0982K    Altcode:
  In the quiet Sun, magnetic fields are usually observed as small-scale
  magnetic elements, `salt and pepper', covering the entire solar
  surface. By using 3D radiative MHD numerical simulations we demonstrate
  that these fields are a result of local dynamo action in the top layers
  of the convection zone, where extremely weak `seed' magnetic fields can
  locally grow above the mean equipartition field (e.g., from a $10^{-6}$
  G `seed' field to more than 1000 G magnetic structures). We find that
  the local dynamo action takes place only in a shallow, about 500 km
  deep, subsurface layer, from which the generated field is transported
  into deeper layers by convection downdrafts. We demonstrate that the
  observed dominance of vertical magnetic fields at the photosphere
  and the horizontal fields above the photosphere can be explained by
  multi-scale magnetic loops produced by the dynamo.

---------------------------------------------------------
Title: Turbulent Hydrodynamics and Oscillations of Moderate-Mass Stars
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Lele, S. K.; Mansour,
   N. N.; Wray, A. A.
2013ASPC..479..377K    Altcode:
  The solar-type pulsators are characterized by acoustic oscillation
  modes excited by turbulent convection in the upper convective boundary
  layer. As the stellar mass increases the convection zone shrinks, the
  scale and intensity of the turbulent motions increases, providing more
  energy for excitation of acoustic modes. When the stellar mass reaches
  about 1.6 solar masses the upper convection zone consists of two very
  thin layers corresponding to H and He ionization, and in addition to
  the acoustic modes the stars show strong internal gravity modes. The
  thin convection zone is often considered insignificant for the stellar
  dynamics and variability. We use three-dimensional (3D) numerical
  radiative hydrodynamics simulations to study convective and oscillation
  properties of Main Sequence stars from the solar-type stars to more
  massive stars. We present simulation results for some of the target
  stars selected for the Kepler Guest Observer project “Transition
  in Variable Stars: From Solar-Type Stars to Gamma-Doradus Stars.”
  For the moderate-mass (A-type) stars the simulations reveal supersonic
  granular-type convection of a scale significantly larger than the solar
  granulation scale, and strong overshooting plumes penetrating into the
  stable radiative zone, that can affect the oscillation properties of
  these stars.

---------------------------------------------------------
Title: Differential Rotation in Solar-like Stars from Global
    Simulations
Authors: Guerrero, G.; Smolarkiewicz, P. K.; Kosovichev, A. G.;
   Mansour, N. N.
2013ApJ...779..176G    Altcode: 2013arXiv1310.8178G
  To explore the physics of large-scale flows in solar-like stars, we
  perform three-dimensional anelastic simulations of rotating convection
  for global models with stratification resembling the solar interior. The
  numerical method is based on an implicit large-eddy simulation approach
  designed to capture effects from non-resolved small scales. We obtain
  two regimes of differential rotation, with equatorial zonal flows
  accelerated either in the direction of rotation (solar-like) or in the
  opposite direction (anti-solar). While the models with the solar-like
  differential rotation tend to produce multiple cells of meridional
  circulation, the models with anti-solar differential rotation result
  in only one or two meridional cells. Our simulations indicate that the
  rotation and large-scale flow patterns critically depend on the ratio
  between buoyancy and Coriolis forces. By including a sub-adiabatic layer
  at the bottom of the domain, corresponding to the stratification of a
  radiative zone, we reproduce a layer of strong radial shear similar
  to the solar tachocline. Similarly, enhanced super-adiabaticity at
  the top results in a near-surface shear layer located mainly at lower
  latitudes. The models reveal a latitudinal entropy gradient localized
  at the base of the convection zone and in the stable region, which,
  however, does not propagate across the convection zone. In consequence,
  baroclinicity effects remain small, and the rotation isocontours
  align in cylinders along the rotation axis. Our results confirm the
  alignment of large convective cells along the rotation axis in the
  deep convection zone and suggest that such "banana-cell" pattern can
  be hidden beneath the supergranulation layer.

---------------------------------------------------------
Title: Astrophysical processes on the Sun
Authors: Kosovichev, Alexander
2013GApFD.107..717K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Helioseismic Constraints and a Paradigm Shift in the Solar
    Dynamo
Authors: Kosovichev, Alexander G.; Pipin, Valery V.; Zhao, J.
2013ASPC..479..395K    Altcode: 2014arXiv1402.1901K
  Helioseismology provides important constraints for the solar dynamo
  problem. However, the basic properties and even the depth of the dynamo
  process, which operates also in other stars, are unknown. Most of the
  dynamo models suggest that the toroidal magnetic field that emerges
  on the surface and forms sunspots is generated near the bottom of the
  convection zone, in the tachocline. However, there are a number of
  theoretical and observational problems with justifying the deep-seated
  dynamo models. This leads to the idea that the subsurface angular
  velocity shear may play an important role in the solar dynamo. Using
  helioseismology measurements of the internal rotation and meridional
  circulation, we investigate a mean-field magneto-hydrodynamic model
  of a dynamo distributed in the bulk of the convection zone but shaped
  in a near-surface layer. We show that if the boundary conditions at
  the top of the dynamo region allow the large-scale toroidal magnetic
  fields to penetrate into the surface, then the dynamo wave propagates
  along the isosurface of angular velocity in the subsurface shear layer,
  forming the butterfly diagram in agreement with the Parker-Yoshimura
  rule and solar-cycle observations. Unlike the flux-transport dynamo
  models, this model does not depend on the transport of magnetic field
  by meridional circulation at the bottom of the convection zone, and
  works well when the meridional circulation forms two cells in radius,
  as recently indicated by the deep-focus time-distance helioseismology
  analysis of the SDO/HMI and SOHO/MDI data. We compare the new dynamo
  model with various characteristics of the solar magnetic cycles,
  including the cycle asymmetry (Waldmeier's relations) and magnetic
  ‘butterfly’ diagrams.

---------------------------------------------------------
Title: The Mean-field Solar Dynamo with a Double Cell Meridional
    Circulation Pattern
Authors: Pipin, V. V.; Kosovichev, A. G.
2013ApJ...776...36P    Altcode: 2013arXiv1302.0943P
  Recent helioseismology findings, as well as advances in direct
  numerical simulations of global dynamics of the Sun, have indicated
  that in each solar hemisphere meridional circulation may form more
  than one cell along the radius in the convection zone. In particular,
  recent helioseismology results revealed a double-cell structure of
  the meridional circulation. We investigate properties of a mean-field
  solar dynamo with such double-cell meridional circulation. The dynamo
  model also includes the realistic profile of solar differential
  rotation (including the tachocline and subsurface shear layer)
  and takes into account effects of turbulent pumping, anisotropic
  turbulent diffusivity, and conservation of magnetic helicity. Contrary
  to previous flux-transport dynamo models, we find that the dynamo model
  can robustly reproduce the basic properties of the solar magnetic cycles
  for a wide range of model parameters and circulation speeds. The best
  agreement with observations is achieved when the surface meridional
  circulation speed is about 12 m s<SUP>-1</SUP>. For this circulation
  speed, the simulated sunspot activity shows good synchronization with
  the polar magnetic fields. Such synchronization was indeed observed
  during previous sunspot Cycles 21 and 22. We compare theoretical and
  observed phase diagrams of the sunspot number and the polar field
  strength and discuss the peculiar properties of Cycle 23.

---------------------------------------------------------
Title: Variability of Solar Five-Minute Oscillations in the Corona
    as Observed by the Extreme Ultraviolet Spectrophotometer (ESP) on the
    Solar Dynamics Observatory/Extreme Ultraviolet Variability Experiment
    (SDO/EVE)
Authors: Didkovsky, L.; Kosovichev, A.; Judge, D.; Wieman, S.;
   Woods, T.
2013SoPh..287..171D    Altcode: 2012arXiv1211.0711D; 2012SoPh..tmp..307D
  Solar five-minute oscillations have been detected in the power spectra
  of two six-day time intervals from soft X-ray measurements of the Sun
  observed as a star using the Extreme Ultraviolet Spectrophotometer
  (ESP) onboard the Solar Dynamics Observatory (SDO)/Extreme Ultraviolet
  Variability Experiment (EVE). The frequencies of the largest amplitude
  peaks were found to match the known low-degree (ℓ=0 - 3) modes of
  global acoustic oscillations within 3.7 μHz and can be explained
  by a leakage of the global modes into the corona. Due to the strong
  variability of the solar atmosphere between the photosphere and the
  corona, the frequencies and amplitudes of the coronal oscillations
  are likely to vary with time. We investigated the variations in the
  power spectra for individual days and their association with changes
  of solar activity, e.g. with the mean level of the EUV irradiance,
  and its short-term variations caused by evolving active regions. Our
  analysis of samples of one-day oscillation power spectra for a 49-day
  period of low and intermediate solar activity showed little correlation
  with the mean EUV irradiance and the short-term variability of the
  irradiance. We suggest that some other changes in the solar atmosphere,
  e.g., magnetic fields and/or inter-network configuration may affect
  the mode leakage to the corona.

---------------------------------------------------------
Title: Preface
Authors: Mansour, Nagi N.; Kosovichev, Alexander G.; Komm, Rudolf;
   Longcope, Dana; Leibacher, John W.
2013SoPh..287....1M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Detection of Equatorward Meridional Flow and Evidence of
    Double-cell Meridional Circulation inside the Sun
Authors: Zhao, Junwei; Bogart, R. S.; Kosovichev, A. G.; Duvall,
   T. L., Jr.; Hartlep, Thomas
2013ApJ...774L..29Z    Altcode: 2013arXiv1307.8422Z
  Meridional flow in the solar interior plays an important role in
  redistributing angular momentum and transporting magnetic flux inside
  the Sun. Although it has long been recognized that the meridional
  flow is predominantly poleward at the Sun's surface and in its
  shallow interior, the location of the equatorward return flow and the
  meridional flow profile in the deeper interior remain unclear. Using
  the first 2 yr of continuous helioseismology observations from the
  Solar Dynamics Observatory/Helioseismic Magnetic Imager, we analyze
  travel times of acoustic waves that propagate through different
  depths of the solar interior carrying information about the solar
  interior dynamics. After removing a systematic center-to-limb effect
  in the helioseismic measurements and performing inversions for flow
  speed, we find that the poleward meridional flow of a speed of 15 m
  s<SUP>-1</SUP> extends in depth from the photosphere to about 0.91 R
  <SUB>⊙</SUB>. An equatorward flow of a speed of 10 m s<SUP>-1</SUP>
  is found between 0.82 and 0.91 R <SUB>⊙</SUB> in the middle of the
  convection zone. Our analysis also shows evidence of that the meridional
  flow turns poleward again below 0.82 R <SUB>⊙</SUB>, indicating an
  existence of a second meridional circulation cell below the shallower
  one. This double-cell meridional circulation profile with an equatorward
  flow shallower than previously thought suggests a rethinking of how
  magnetic field is generated and redistributed inside the Sun.

---------------------------------------------------------
Title: Solar differential rotation: hints to reproduce a near-surface
    shear layer in global simulations
Authors: Guerrero, G.; Smolarkiewicz, P. K.; Kosovichev, A.;
   Mansour, N.
2013IAUS..294..417G    Altcode: 2013arXiv1301.1330G
  Convective turbulent motions in the solar interior, as well as the
  mean flows resulting from them, determine the evolution of the solar
  magnetic field. With the aim to get a better understanding of these
  flows we study anelastic rotating convection in a spherical shell whose
  stratification resembles that of the solar interior. This study is
  done through numerical simulations performed with the EULAG code. Due
  to the numerical formulation, these simulations are known as implicit
  large eddy simulations (ILES), since they intrinsically capture the
  contribution of, non-resolved, small scales at the same time maximizing
  the effective Reynolds number. We reproduce some previous results and
  find a transition between buoyancy and rotation dominated regimes which
  results in anti-solar or solar like rotation patterns. Even thought the
  rotation profiles are dominated by Taylor-Proudman columnar rotation,
  we are able to reproduce the tachocline and a low latitude near-surface
  shear layer. We find that simulations results depend on the grid
  resolution as a consequence of a different sub-grid scale contribution.

---------------------------------------------------------
Title: Effects of Double-Cell Meridional Circulation on the Solar
    Dynamo and Activity Cycles
Authors: Pipin, Valery; Kosovichev, A. G.
2013SPD....4440303P    Altcode:
  It was long assumed that the meridional circulation on the Sun is
  represented by a single cell occupying the whole convection zone,
  with poleward flow at the top and with the return equator-ward flow
  at the bottom. However, recent helioseismology observations and
  numerical simulations provided clear evidence that the meridional
  circulation has a double-cell structure with a return equator-ward
  flow in the middle of the convection zone. This discovery requires
  to re-examine the solar dynamo models. We discuss the properties of
  a new mean-field solar dynamo that is coupled with the double-cell
  meridional circulation pattern. It is found that such dynamo model
  (which also includes the subsurface rotational shear layer, turbulent
  pumping and other turbulence effects) can robustly reproduce the basic
  properties of the solar magnetic activity within the wide range of
  the dynamo parameters and amplitudes of the circulation speed. The
  properties of the simulated sunspot activity migration are discussed
  and compared with observations. It is found that the best agreement with
  observation is achieved when the surface speed of circulation is about
  12 m/s. Interesting that for this amplitude of the circulation speed the
  simulated sunspot activity show the pretty good synchronization with
  the polar magnetic field activity. Such synchronization was indeed
  observed during the past Cycles 21 and 22. We compare our findings
  with these observations.

---------------------------------------------------------
Title: Solar Interior Meridional Flow from SDO/HMI
Authors: Zhao, Junwei; Bogart, R. S.; Kosovichev, A. G.; Duvall,
   T. L.; Hartlep, T.
2013SPD....4420402Z    Altcode:
  Since the launch of Solar Dynamics Observatory, the Helioseismic
  and Magnetic Imager has accumulated 3 years of continuous
  observations. Using time-distance helioseismology, we have obtained
  new results on both global and local scales. By analyzing the first two
  years' observations, we were able to detect the equatorward meridional
  flow at a depth of around 65 Mm, and detect the existence of a second
  meridional circulation cell below about 120 Mm. This new profile of
  interior meridional flow will pose challenges to the solar dynamo
  models. At the shallower depths, we studied the temporal evolution of
  the zonal and meridional flows. We found that both quantities showed
  strong hemispherical asymmetries. Using global wavefield simulations
  that have pre-set meridional flow profiles, we also assess the
  capability of our analysis technique in recovering week flows in the
  deep interior.

---------------------------------------------------------
Title: Solar and Astrophysical Dynamos and Magnetic Activity
Authors: Kosovichev, Alexander G.; de Gouveia Dal Pino, Elisabete;
   Yan, Yihua
2013IAUS..294.....K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Ubiquitous Solar Eruptions Driven by Magnetized Vortex Tubes
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Lele, S. K.; Mansour,
   N. N.; Wray, A. A.
2013ApJ...770...37K    Altcode: 2013arXiv1301.0018K
  The solar surface is covered by high-speed jets transporting mass
  and energy into the solar corona and feeding the solar wind. The
  most prominent of these jets have been known as spicules. However,
  the mechanism initiating these eruption events is still unknown. Using
  realistic numerical simulations we find that small-scale eruptions are
  produced by ubiquitous magnetized vortex tubes generated by the Sun's
  turbulent convection in subsurface layers. The swirling vortex tubes
  (resembling tornadoes) penetrate into the solar atmosphere, capture and
  stretch background magnetic field, and push the surrounding material up,
  generating shocks. Our simulations reveal complicated high-speed flow
  patterns and thermodynamic and magnetic structure in the erupting vortex
  tubes. The main new results are: (1) the eruptions are initiated in
  the subsurface layers and are driven by high-pressure gradients in the
  subphotosphere and photosphere and by the Lorentz force in the higher
  atmosphere layers; (2) the fluctuations in the vortex tubes penetrating
  into the chromosphere are quasi-periodic with a characteristic period
  of 2-5 minutes; and (3) the eruptions are highly non-uniform: the flows
  are predominantly downward in the vortex tube cores and upward in their
  surroundings; the plasma density and temperature vary significantly
  across the eruptions.

---------------------------------------------------------
Title: Recent Local Helioseismology Results from SDO/HMI
Authors: Zhao, Junwei; Bogart, R. S.; Kosovichev, A. G.; Duvall,
   T. L., Jr.; Hartlep, Thomas
2013enss.confE.118Z    Altcode:
  Since the launch of Solar Dynamics Observatory, the Helioseismic
  and Magnetic Imager has accumulated 2.5 years of continuous
  observations. Using time-distance helioseismology, we have obtained
  new results on both global and local scales. By analyzing the first
  two years' observations, we were able to detect the equator-ward
  meridional flow at a depth of around 70 Mm, and detect the existence
  of a second meridional circulation below about 120 Mm. This new profile
  of interior meridional flow will pose challenges to the current dynamo
  models. At the shallower depth, we studied the temporal evolution of
  zonal flows, as well as the residual meridional flow, which was obtained
  by subtracting an averaged meridional flow profile. We found that both
  quantities showed strong hemispherical asymmetries. On local scales,
  we studied subsurface flows inside active regions and supergranules,
  as well as the potential links between solar flares and these subsurface
  dynamics.

---------------------------------------------------------
Title: Approach to Integrate Global-Sun Models of Magnetic Flux
    Emergence and Transport for Space Weather Studies
Authors: Mansour, Nagi Nicolas; Wray, A.; Mehrotra, P.; Henney, C.;
   arge, N.; Manchester, C.; Godinez, H.; Koller, J.; Kosovichev, A.;
   Scherrer, P.; Zhao, J.; Stein, R.; Duvall, T.; Fan, Y.
2013enss.confE.125M    Altcode:
  The Sun lies at the center of space weather and is the source of its
  variability. The primary input to coronal and solar wind models is
  the activity of the magnetic field in the solar photosphere. Recent
  advancements in solar observations and numerical simulations provide
  a basis for developing physics-based models for the dynamics of
  the magnetic field from the deep convection zone of the Sun to the
  corona with the goal of providing robust near real-time boundary
  conditions at the base of space weather forecast models. The goal is
  to develop new strategic capabilities that enable characterization
  and prediction of the magnetic field structure and flow dynamics of
  the Sun by assimilating data from helioseismology and magnetic field
  observations into physics-based realistic magnetohydrodynamics (MHD)
  simulations. The integration of first-principle modeling of solar
  magnetism and flow dynamics with real-time observational data via
  advanced data assimilation methods is a new, transformative step in
  space weather research and prediction. This approach will substantially
  enhance an existing model of magnetic flux distribution and transport
  developed by the Air Force Research Lab. The development plan is to use
  the Space Weather Modeling Framework (SWMF) to develop Coupled Models
  for Emerging flux Simulations (CMES) that couples three existing models:
  (1) an MHD formulation with the anelastic approximation to simulate
  the deep convection zone (FSAM code), (2) an MHD formulation with
  full compressible Navier-Stokes equations and a detailed description
  of radiative transfer and thermodynamics to simulate near-surface
  convection and the photosphere (Stagger code), and (3) an MHD
  formulation with full, compressible Navier-Stokes equations and an
  approximate description of radiative transfer and heating to simulate
  the corona (Module in BATS-R-US). CMES will enable simulations of the
  emergence of magnetic structures from the deep convection zone to the
  corona. Finally, a plan will be summarized on the development of a
  Flux Emergence Prediction Tool (FEPT) in which helioseismology-derived
  data and vector magnetic maps are assimilated into CMES that couples
  the dynamics of magnetic flux from the deep interior to the corona.

---------------------------------------------------------
Title: Sunquake Observations from HMI: Time-Distance and Holography
    Analyses
Authors: Kosovichev, Alexander; Zhao, Junwei
2013enss.confE.124K    Altcode:
  HMI observations of solar flares revealed new sunquake events. We
  analyze and compare the results obtained using two different approaches:
  time-distance analysis and holography. The time-distance analysis
  provides detailed information about physical properties of the
  flare-excited helioseismic waves, including their interaction with
  strong magnetic field regions. On the other hand, the holography
  approach, which measures the integrated signal, allows us to detect
  weak events and investigate their relative power and its frequency
  dependence. A remarkable features of the observed events are their
  strong anisotropy, associated with the rapid motion of the flare
  impacts in the low atmosphere, which are the source of the energy and
  momentum of sunquakes. We identify the sunquake source spatial-temporal
  characteristics and show that source locations determined from the
  holographic method systematically differ from the HMI observed Doppler
  impact locations. We discuss the potential mechanisms of sunquakes, and
  their relationship to the energy release and transport in solar flares.

---------------------------------------------------------
Title: Using realistic MHD simulations for modeling HMI observables
Authors: Kitiashvili, I.; Couvidat, S.; Mansour, N.; Wray, A.;
   Kosovichev, A.
2013enss.confE.127K    Altcode:
  The solar atmosphere is extremely dynamic, and many important
  phenomena which develop on small scales are unresolved in the
  SDO/HMI observations. For correct calibration and interpretation of
  HMI observations it is very important to investigate the effects of
  small-scale structures and dynamics on the HMI observables. We use
  radiative MHD simulations of the upper turbulent convective layer and
  atmosphere of the Sun and spectro-polarimetric radiative transfer
  codes to study Stokes profiles of the FeI 6173 line for different
  conditions in the solar atmosphere, including quiet-Sun regions with
  various background magnetic field strengths and sunspot umbrae and
  penumbrae, and discuss effects on HMI observables and interpretation
  of the HMI data.

---------------------------------------------------------
Title: An analysis of apparent r-mode oscillations in solar activity,
    the solar diameter, the solar neutrino flux, and nuclear decay
    rates, with implications concerning the Sun's internal structure
    and rotation, and neutrino processes
Authors: Sturrock, P. A.; Bertello, L.; Fischbach, E.; Javorsek, D.;
   Jenkins, J. H.; Kosovichev, A.; Parkhomov, A. G.
2013APh....42...62S    Altcode: 2012arXiv1211.6352S
  This article presents a comparative analysis of solar activity data, Mt
  Wilson diameter data, Super-Kamiokande solar neutrino data, and nuclear
  decay data acquired at the Lomonosov Moscow State University (LMSU). We
  propose that salient periodicities in all of these datasets may be
  attributed to r-mode oscillations. Periodicities in the solar activity
  data and in Super-Kamiokande solar neutrino data may be attributed to
  r-mode oscillations in the known tachocline, with normalized radius
  in the range 0.66-0.74, where the sidereal rotation rate is in the
  range 13.7-14.6 year<SUP>-1</SUP>. We propose that periodicities
  in the Mt Wilson and LMSU data may be attributed to similar r-mode
  oscillations where the sidereal rotation rate is approximately
  12.0 year<SUP>-1</SUP>, which we attribute to a hypothetical "inner"
  tachocline separating a slowly rotating core from the radiative zone. We
  also discuss the possible role of the Resonant Spin Flavor Precession
  (RSFP) process, which leads to estimates of the neutrino magnetic
  moment and of the magnetic field strength in or near the solar core.

---------------------------------------------------------
Title: Solar Wave-field Simulation for Testing Prospects of
    Helioseismic Measurements of Deep Meridional Flows
Authors: Hartlep, T.; Zhao, J.; Kosovichev, A. G.; Mansour, N. N.
2013ApJ...762..132H    Altcode: 2012arXiv1209.4602H
  The meridional flow in the Sun is an axisymmetric flow that is
  generally directed poleward at the surface, and is presumed to be of
  fundamental importance in the generation and transport of magnetic
  fields. Its true shape and strength, however, are debated. We present
  a numerical simulation of helioseismic wave propagation in the whole
  solar interior in the presence of a prescribed, stationary, single-cell,
  deep meridional circulation serving as synthetic data for helioseismic
  measurement techniques. A deep-focusing time-distance helioseismology
  technique is applied to the synthetic data, showing that it can in
  fact be used to measure the effects of the meridional flow very deep
  in the solar convection zone. It is shown that the ray approximation
  that is commonly used for interpretation of helioseismology measurements
  remains a reasonable approximation even for very long distances between
  12° and 42° corresponding to depths between 52 and 195 Mm. From the
  measurement noise, we extrapolate that time-resolved observations on
  the order of a full solar cycle may be needed to probe the flow all
  the way to the base of the convection zone.

---------------------------------------------------------
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.
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: Investigation of Small-Scale Turbulent MHD Phenomena Using
    Numerical Simulations and NST Observations
Authors: Kitiashvili, I.; Abramenko, V.; Goode, P. R.; Kosovichev,
   A.; Mansour, N.; Wray, A.; Yurchyshyn, V.
2012IAUSS...6E.104K    Altcode:
  Recent progress in observational capabilities and numerical modeling
  have provided unique high-resolution information demonstrating
  complicated dynamics and structures of turbulent flows and magnetic
  field on the Sun. The realistic approach to numerical simulations is
  based on physical first principles and takes into account compressible
  fluid flow in a highly stratified magnetized medium, 3D multi-bin
  radiative energy transfer between fluid elements, a real-gas equation
  of state, ionization, and excitation of all abundant species, magnetic
  effects and sub-grid turbulence. We present new results of 3D radiative
  MHD simulations of the upper solar convection zone and chromosphere
  that reveal a fundamental role of small-scale vortex dynamics, and
  compare the numerical results and predictions with observational
  results from the 1.6 m clear aperture New Solar Telescope (NST) at
  Big Bear Observatory. In particular, we investigate formation and
  dynamics of ubiquitous small-scale vortex tubes mostly concentrated
  in the intergranular lanes and their role in magnetic structuring
  and acoustic emission of the Sun. These whirlpool-like flows are
  characterized by very strong horizontal shear velocities (7 - 11 km/s)
  and downflows (~7 km/s), and are accompanied by sharp decreases in
  temperature, density and pressure at the surface. High-speed whirlpool
  flows can attract and capture other vortices, penetrate into the low
  chromosphere, and form stable magnetic flux tubes. The simulations also
  reveal a strong connection between acoustic wave excitation events and
  the dynamics of vortex tubes. In this talk, we will discuss different
  aspects of small-scale turbulent dynamics of the low atmosphere from the
  high-resolution simulations in comparison with recent NST observations,
  and the strategy for future synergies of numerical simulations and
  observations with large aperture solar telescopes.

---------------------------------------------------------
Title: Numerical Simulation of Thermal and Magnetic Effects of MHD
    Wave Propagation in Sunspot Models
Authors: Parchevsky, K.; Kosovichev, A. G.
2012AGUFMSH13A2247P    Altcode:
  Understanding of MHD wave propagation and transformation in sunspots
  is very important for understanding helioseismic measurements and
  improving helioseismic inversion procedures. Numerical simulations
  help to reveal details of wave interaction with the non-uniform
  background magnetic field and flows. Such simulations also provide
  artificial data for testing and calibration techniques used for
  analysis of data from space missions SOHO/MDI, SDO/HMI, HINODE, and
  GONG network. There are three competing processes, which affect the
  wave speed in sunspots: (i) thermal effects, (ii) magnetic field and
  (iii) mass flows. Comparison of numerical simulations of the MHD wave
  propagation in different models of sunspot helps to disentangle these
  effects. We present simulation results of 3D MHD wave propagation
  in sunspot models with separated and combined thermal and magnetic
  effects. Simulations of MHD wave propagation from a single source in
  the self-consistent magnetostatic sunspot model show flattening of
  the wave front when the wave entrs the sunspot due to the reduced
  background sound speed near the photosphere. At later moments of
  time, the wave front is formed by waves propagating through deeper
  layers. In these layers contribution of the magnetic field dominates
  and the wave front restores its symmetric shape. The asymmetry of the
  wave front decreases when the distance from the source to the axis
  of the sunspot model increases. Separation of p- and f- modes shows
  that mostly f-modes contribute to the wave front asymmetry while the
  wave front of p-modes stays almost unperturbed. In the model with the
  potential magnetic field configuration and quiet Sun background model,
  the wave front accelerates from the moment when the wave enters the
  magnetized region, forming a bulge toward the sunspot axis. For both
  types of models simulations also show weak fast-to-slow conversion
  of MHD waves near the surface where the plasma parameter beta equals
  one. Mode conversion is stronger in the self-consistent magnetostatic
  model than in the potential sunspot model, indicating that thermal
  effects implicitly contribute to the mode conversion. We also present
  simulations in realistic sunspot model calculated by M. Rempel.

---------------------------------------------------------
Title: Detection of Equator-ward Meridional Flows in the Deep Solar
    Interior
Authors: Zhao, J.; Bogart, R. S.; Kosovichev, A. G.; Duvall, T. L.
2012AGUFMSH13C2266Z    Altcode:
  The meridional flow observed on the solar surface is a slow plasma
  motion from the equator to the poles. Flux-transport dynamo models
  of the solar cycle assume that this flow transports magnetic field of
  decaying active regions and causes polar field reversals. At what depth
  the meridional flow turns to equator-ward and how fast is the return
  flow are important questions for a better understanding of the dynamo
  process, and are also long-time puzzles of helioseismology. A recent
  finding of a systematic center-to-limb variation in the time-distance
  helioseismology measurements allows us to develop an empirical
  correction procedure for acoustic travel times, and improve the accuracy
  of helioseismic inferences. Using the helioseismic data of two entire
  years of SDO/HMI continuous observations and removing the systematic
  effect, we have detected the equator-ward meridional flows. Inversion
  of the travel times shows that the near-surface pole-ward meridional
  flow starts turning equator-ward at approximately 0.92 R_sun at low
  latitudes, and that the depth of the flow turning point increases
  with latitude. The equator-ward flow has a speed of 10 m/s or so, and
  extends from the surface to about 0.82 R_sun. Our analysis also shows
  evidences for a second meridional circulation cell starting at about
  0.82 R_sun and extending deep to near the tachocline area (0.7 R_sun).

---------------------------------------------------------
Title: Sunquakes and Two Types of Flares
Authors: Kosovichev, A. G.
2012AGUFMSH43B2167K    Altcode:
  Uninterrupted observations from Solar Dynamics Observatory provide
  unique opportunity for investigation of "sunquakes", helioseismic
  waves caused by strong localized impacts in the low atmosphere during
  impulsive phase of solar flares. The SDO observations show that these
  events are more frequent than previously thought. They are observed
  in solar flares from moderate M- to X-class. However, not all X-class
  flares produce sunquakes, and it is puzzling why some moderate class
  flares produce sunquakes, while significantly more powerful flares
  do not. Using data from the HMI and AIA instruments I investigate
  properties of sunquakes by detecting and analyzing the seismic wave
  fronts and the sources of the flare impact, and discuss physical
  mechanisms of the impact. By comparing energetic and morphological
  characteristics of the flares with and without sunquakes, I present
  arguments that this phenomenon reflects a division between two classes
  of solar flares: confined and eruptive, which may be fundamentally
  different in terms of the energy release mechanism.

---------------------------------------------------------
Title: 3D MHD Simulations of Spontaneous Flow Ejections by Turbulent
    Convection into the Chromosphere
Authors: Kitiashvili, I.; Kosovichev, A. G.; Mansour, N.; Wray, A.
2012AGUFMSH51A2192K    Altcode:
  Dynamical interaction of the highly turbulent subsurface and the low
  atmosphere layers is a source of many observed phenomena on various
  scales in the solar chromosphere. We investigate the energetic and
  dynamical links between the turbulent convection and the chromosphere
  by using 3D radiative MHD simulations. Our simulations of quiet-Sun
  regions reveal ubiquitous formation of small-scale vortex tubes which
  can drive flow ejections into the chromosphere. The vortex tubes are
  formed through two basic mechanisms: convective instability inside
  the granules and the Kelvin-Helmholtz instability in the intergranular
  lanes. During their formation the vortex tubes become mostly vertical
  and usually can be detected in the intergranular lanes. Dispute their
  small scale the vortex tubes represent highly dynamical structures,
  which can capture surrounding magnetic field and easily penetrate
  into the atmosphere layers, producing quasi-periodic flow ejections,
  shocks and Alfven waves, and contribute to the chromosphere heating.

---------------------------------------------------------
Title: Helioseismic measurements of large-scale flows and meridional
    circulation models using artificial data from numerical simulations
Authors: Hartlep, T.; Kosovichev, A. G.; Zhao, J.
2012AGUFMSH13C2265H    Altcode:
  The detection and measurement of flows in the solar interior is
  of great importance for studying the dynamics of solar convection
  zone. Over the years, helioseismology has been able to detect flows
  in increasingly deeper layer of the Sun. Numerical simulations can
  provide means for testing and calibrating such measurement techniques,
  and can help increase our confidence in the inferences obtained
  from observations. Here, we present numerical simulations of the 3D
  helioseismic wave field in the presence of various flow models, and
  time-distance helioseismology measurement using the artificial data from
  the simulations. The simulations solve the linearized propagation of
  helioseismic wave in the whole solar interior through stationary flow
  fields. Recently, there has been evidence for a multi-cell meridional
  flow. We have therefore simulated different models of meridional flows
  -- single-cell, shallow and deep meridional flows and a multi-cell
  meridional flow -- to evaluate if helioseismology measurements can
  differentiate the models. Also, we have performed a simulation with
  flows from a full-resolution snapshot of a solar convection simulation
  in anelastic approximation using the "ASH" code, provided to us by
  Mark Miesch. Time-distance helioseismology measurements and inversions
  are performed.

---------------------------------------------------------
Title: Dark Matter and Its Effects on Helioseismology
Authors: Hamerly, R.; Kosovichev, A. G.
2012ASPC..462..537H    Altcode: 2011arXiv1110.1169H
  Helioseismology can be used to place new constraints on the properties
  of dark matter, allowing solar observations to complement more
  conventional dark matter searches currently in operation. During the
  course of its lifetime, the Sun accretes a sizeable amount of dark
  matter. This accreted matter affects the heat transport of the stellar
  core in ways that helioseismology can detect, or at least constrain. We
  modify the CESAM stellar evolution code to take account of dark matter
  and determine the effect of WIMP models on the stellar structure and
  normal-mode oscillation frequencies.

---------------------------------------------------------
Title: Self-organization of the Solar Turbulent Convection in
    Magnetic Field
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Mansour, N. N.; Wray,
   A. A.
2012ASPC..462..382K    Altcode:
  Observations of the solar surface show a highly turbulent behavior
  of convection, and reveal coherent structures in distributed magnetic
  fields. We present results of realistic radiation magneto-hydrodynamics
  (MHD) simulations in three dimensions (3D) of the solar subsurface
  layers, and investigate properties of magneto-convection for various
  magnetic field topologies and strengths. In particular, we discuss the
  filamentary structure and dynamics of sunspot penumbra, spontaneous
  formation of pore-like and small-scale magnetic structures, and compare
  the simulation results with observations.

---------------------------------------------------------
Title: Radiation Hydrodynamics Simulations of Turbulent Convection
    for Kepler Target Stars
Authors: Kitiashvili, I. N.; Guzik, J. A.; Kosovichev, A. G.; Mansour,
   N. N.; Saio, H.; Shibahashi, H.; Wray, A. A.
2012ASPC..462..378K    Altcode:
  The solar-type pulsators are characterized by acoustic oscillation
  modes excited by turbulent granular convection in the upper convective
  boundary layer. As the stellar mass increases the convection zone
  shrinks, the scale and intensity of the turbulent motions increases,
  providing more energy for excitation of acoustic modes. When the stellar
  mass reaches about 1.6 solar masses the upper convection zone consists
  of two very thin layers corresponding to H and He ionization, and in
  addition to the acoustic modes the stars show strong internal gravity
  modes The thin convection zone is often considered insignificant for
  the stellar dynamics and variability. We use numerical radiation
  transfer simulations in three dimensions (3D) to study convective
  and oscillation properties of main-sequence stars from the solar-type
  stars to more massive stars. In the simulations we used models of the
  stellar interior, calculated for individual Kepler mission targets. The
  3D radiation hydrodynamics simulations reveal supersonic granular-type
  convection on a scale significantly larger than the solar granulation,
  and strong overshooting plumes penetrating into the stable radiative
  zone, which can affect oscillation properties of a star.

---------------------------------------------------------
Title: Verification of the Travel Time Measurement Technique and the
    Helioseismic Inversion Procedure for Sound Speed Using Artificial Data
Authors: Parchevsky, Konstantin V.; Zhao, Junwei; Hartlep, Thomas;
   Kosovichev, Alexander G.
2012arXiv1209.4877P    Altcode:
  We performed 3D numerical simulations of the solar surface wave
  field for the quiet Sun and for three models with different localized
  sound-speed variations in the interior with: (i) deep, (ii) shallow,
  and (iii) two-layer structures. We used simulated data generated
  by two different codes which use the same standard solar model as a
  background model, but utilize two different integration techniques
  and use different models of stochastic wave excitation. Acoustic
  travel times were measured from all data sets using the time-distance
  helioseismology technique and compared with the ray theory predictions,
  frequently used for helioseismic travel-time inversions. It is
  found that the measured travel-time shifts agree well with the ray
  theory in both cases with and without phase-speed filtering for
  the shallow and deep perturbations. This testing verifies the whole
  measuring-filtering-inversion procedure for sound-speed anomalies inside
  the Sun. It is shown, that the phase-speed filtering, frequently used
  to improve the signal-to-noise ratio does not introduce significant
  systematic errors. Results of the sound-speed inversion procedure
  show good agreement with the background sound-speed profiles in
  all cases. Due to its smoothing nature, the inversion procedure
  overestimates sound speed variations in areas with sharp gradients of
  the sound-speed profile.

---------------------------------------------------------
Title: Interaction of Helioseismic Waves with Sunspots: Observations
    and Numerical MHD Simulations
Authors: Zhao, J.; Parchevsky, K. V.; Kosovichev, A. G.
2012ASPC..462..277Z    Altcode:
  We investigate how helioseismic waves that originate from effective
  point sources interact with sunspots. For observations, the waves
  from point sources are reconstructed by cross-correlating observed
  photospheric Doppler signals. For numerical simulations, the waves are
  generated by simulating perturbation propagation from a pulse near the
  surface and propagate through magnetostatic and magnetohydrodynamic
  (MHD) sunspot models. For both cases, we study f-mode and p-mode waves
  separately. We also study different cases when the point source is
  located outside the sunspot, and when the source is located inside the
  sunspot. Our results nicely visualize how the waves, including both wave
  amplitudes and phases, interact with the magnetic field, thermodynamic
  and flow structure of sunspots, and how the waveform evolves before,
  during, and after the propagation through sunspots. Our analysis of
  wave-magnetic-field interactions also extends below the sunspot's
  surface. This brings us new rich information of how the waves respond
  to the magnetic field below the surface, but also poses new challenges
  for local helioseismology to infer the sunspot's interior properties
  from waveform observations.

---------------------------------------------------------
Title: Helioseismic Detection of Emerging Magnetic Flux
Authors: Ilonidis, S.; Zhao, J.; Kosovichev, A. G.
2012ASPC..462..283I    Altcode: 2012arXiv1203.2546I
  Investigating the properties of magnetic flux emergence is one of the
  most important problems of solar physics. In this study we present a
  newly developed deep-focus time-distance measurement scheme which is
  able to detect strong emerging flux events in the deep solar interior,
  before the flux becomes visible on the surface. We discuss in detail the
  differences between our method and previous methods, and demonstrate
  step-by-step how the signal-to-noise (S/N) ratio is increased. The
  method is based on detection of perturbations in acoustic phase travel
  times determined from cross-covariances of solar oscillations observed
  on the surface. We detect strong acoustic travel-time reductions of
  an order of 12 - 16 seconds at a depth of 42 - 75 Mm. These acoustic
  anomalies are detected 1 - 2 days before high peaks in the photospheric
  magnetic flux rate implying that the average emerging speed is 0.3 -
  0.6 km s<SUP>-1</SUP>. The results of this work contribute to our
  understanding of solar magnetism and benefit space weather forecasting.

---------------------------------------------------------
Title: Detection of Small-scale Granular Structures in the Quiet
    Sun with the New Solar Telescope
Authors: Abramenko, V. I.; Yurchyshyn, V. B.; Goode, P. R.;
   Kitiashvili, I. N.; Kosovichev, A. G.
2012ApJ...756L..27A    Altcode: 2012arXiv1208.4337A
  Results of a statistical analysis of solar granulation are presented. A
  data set of 36 images of a quiet-Sun area on the solar disk center was
  used. The data were obtained with the 1.6 m clear aperture New Solar
  Telescope at Big Bear Solar Observatory and with a broadband filter
  centered at the TiO (705.7 nm) spectral line. The very high spatial
  resolution of the data (diffraction limit of 77 km and pixel scale of
  0farcs0375) augmented by the very high image contrast (15.5% ± 0.6%)
  allowed us to detect for the first time a distinct subpopulation of
  mini-granular structures. These structures are dominant on spatial
  scales below 600 km. Their size is distributed as a power law with an
  index of -1.8 (which is close to the Kolmogorov's -5/3 law) and no
  predominant scale. The regular granules display a Gaussian (normal)
  size distribution with a mean diameter of 1050 km. Mini-granular
  structures contribute significantly to the total granular area. They are
  predominantly confined to the wide dark lanes between regular granules
  and often form chains and clusters, but different from magnetic bright
  points. A multi-fractality test reveals that the structures smaller
  than 600 km represent a multi-fractal, whereas on larger scales the
  granulation pattern shows no multi-fractality and can be considered
  as a Gaussian random field. The origin, properties, and role of the
  population of mini-granular structures in the solar magnetoconvection
  are yet to be explored.

---------------------------------------------------------
Title: Local-Helioseismology Study of Supergranulation in the
    Polar Region
Authors: Nagashima, K.; Zhao, J.; Kosovichev, A. G.; Sekii, T.
2012ASPC..454...19N    Altcode:
  Hinode/SOT data have been used to study supergranulation in the polar
  region. Although foreshortening generally makes it difficult to observe
  the polar region in detail, to partially overcome the difficulty we
  use the high-resolution Hinode/SOT observations of the polar regions
  during the period of the highest inclination of the solar axis to the
  ecliptic. By time-distance helioseismology we have found 'alignment'
  of the supergranular cells peculiar in the polar region. <P />This
  might be an indication of the giant-cell structure in the polar region.

---------------------------------------------------------
Title: Fine-scale Magnetic Structures and Flows in Sunspot Simulations
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Wray, A. A.; Mansour,
   N. N.
2012ASPC..454..253K    Altcode:
  One of most intriguing processes on the Sun is the formation and
  dynamics of sunspots and active regions, where magneto-convective
  conditions are very different from quiet Sun regions. High-resolution
  observations from Hinode and numerical simulations shed light into these
  processes. In our 3D radiative MHD simulations we take into account
  real-gas equation of state, ionization and excitation of all abundant
  spices, turbulent and magnetic effects. We present recent results of
  numerical simulations of a top layer of the convective zone and the
  photosphere in the presence of magnetic field of various strength and
  inclination. The simulation results explain the filamentary organization
  of penumbra, reveal the mechanisms of the Evershed effect and the
  sea-serpent behavior of magnetic field lines, and show the subsurface
  dynamics of umbral dots as a natural consequence of magnetoconvection
  processes.

---------------------------------------------------------
Title: Local Helioseismology of Sunspots: Current Status and
    Perspectives
Authors: Kosovichev, Alexander G.
2012SoPh..279..323K    Altcode: 2010arXiv1010.4927K
  Mechanisms of the formation and stability of sunspots are among
  the longest-standing and intriguing puzzles of solar physics and
  astrophysics. Sunspots are controlled by subsurface dynamics, hidden
  from direct observations. Recently, substantial progress in our
  understanding of the physics of the turbulent magnetized plasma in
  strong-field regions has been made by using numerical simulations
  and local helioseismology. Both the simulations and helioseismic
  measurements are extremely challenging, but it is becoming clear that
  the key to understanding the enigma of sunspots is a synergy between
  models and observations. Recent observations and radiative MHD numerical
  models have provided a convincing explanation for the Evershed flows in
  sunspot penumbrae. Also, they lead to the understanding of sunspots as
  self-organized magnetic structures in the turbulent plasma of the upper
  convection zone, which are maintained by a large-scale dynamics. Local
  helioseismic diagnostics of sunspots still have many uncertainties,
  some of which are discussed in this review. However, there have
  been significant achievements in resolving these uncertainties,
  verifying the basic results by new high-resolution observations,
  testing the helioseismic techniques by numerical simulations, and
  comparing results obtained by different methods. For instance, a recent
  analysis of helioseismology data from the Hinode space mission has
  successfully resolved several uncertainties and concerns (such as the
  inclined-field and phase-speed filtering effects) that might affect
  the inferences of the subsurface wave-speed structure of sunspots
  and the flow pattern. It is becoming clear that for the understanding
  of the phenomenon of sunspots it is important to further improve the
  helioseismology methods and investigate the whole life cycle of active
  regions, from magnetic flux emergence to dissipation. The Solar Dynamics
  Observatory mission has started to provide data for such investigations.

---------------------------------------------------------
Title: Vortex tubes of turbulent solar convection
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Mansour, N. N.; Lele,
   S. K.; Wray, A. A.
2012PhyS...86a8403K    Altcode: 2011arXiv1112.5925K
  The investigation of the turbulent properties of solar convection is
  important for understanding the multi-scale dynamics observed on the
  solar surface. In particular, recent high-resolution observations have
  revealed ubiquitous vortical structures, and numerical simulations have
  demonstrated links between vortex tube dynamics and the magnetic field
  organization. Simulations have shown the importance of vortex tube
  interactions in mechanisms of acoustic wave excitation on the Sun. In
  this paper, we investigate the mechanisms of formation of vortex tubes
  in highly turbulent convective flows near the solar surface by using
  realistic radiative hydrodynamic large-eddy simulations. Analysis of
  data from the simulations indicates two basic processes of vortex tube
  formation: (i) the development of small-scale convective instability
  inside convective granules and (ii) a Kelvin-Helmholtz-type instability
  of shearing flows in intergranular lanes. Our analysis shows that
  vortex stretching during these processes is a primary source of the
  generation of small-scale vorticity on the Sun.

---------------------------------------------------------
Title: Special issue on current research in astrophysical magnetism
Authors: Kosovichev, Alexander; Lundstedt, Henrik; Brandenburg, Axel
2012PhyS...86a0201K    Altcode:
  Much of what Hannes Alfvén envisaged some 70 years ago has now
  penetrated virtually all branches of astrophysical research. Indeed,
  magnetic fields can display similar properties over a large range
  of scales. We have therefore been able to take advantage of the
  transparency of galaxies and the interstellar medium to obtain
  measurements inside them. On the other hand, the Sun is much closer,
  allowing us to obtain a detailed picture of the interaction of flows
  and magnetic fields at the surface, and more recently in the interior
  by helioseismology. Moreover, the solar timescales are generally
  much shorter, making studies of dynamical processes more direct. <P
  />This special issue on current research in astrophysical magnetism
  is based on work discussed during a one month Nordita program Dynamo,
  Dynamical Systems and Topology and comprises papers that fall into four
  different categories (A)-(D). <P />(A) Papers on small-scale magnetic
  fields and flows in astrophysics 1. E M de Gouveia Dal Pino, M R M
  Leão, R Santos-Lima, G Guerrero, G Kowal and A Lazarian Magnetic flux
  transport by turbulent reconnection in astrophysical flows 2. Philip
  R Goode, Valentyna Abramenko and Vasyl Yurchyshyn New solar telescope
  in Big Bear: evidence for super-diffusivity and small-scale solar
  dynamos? 3. I N Kitiashvili, A G Kosovichev, N N Mansour, S K Lele
  and A A Wray Vortex tubes of turbulent solar convection <P />The above
  collection of papers begins with a review of astrophysical reconnection
  and introduces the concept of dynamos necessary to explain the existence
  of contemporary magnetic fields both on galactic and solar scales
  (paper 1). This is complemented by observations with the new Big
  Bear Solar Observatory telescope, allowing us to see magnetic field
  amplification on small scales (paper 2). This in turn is complemented
  by realistic simulations of subsurface and surface flow patterns
  (paper 3). <P />(B) Papers on theoretical approaches to turbulent
  fluctuations 4. Nathan Kleeorin and Igor Rogachevskii Growth rate
  of small-scale dynamo at low magnetic Prandtl numbers 5. Erico L
  Rempel, Abraham C-L Chian and Axel Brandenburg Lagrangian chaos in
  an ABC-forced nonlinear dynamo 6. J E Snellman, M Rheinhardt, P J
  Käpylä, M J Mantere and A Brandenburg Mean-field closure parameters
  for passive scalar turbulence <P />Research in dynamo theory has been
  actively pursued for over half a century. It started by trying to
  understand the large-scale magnetic fields of the Sun and the Earth,
  and subsequently also in galaxies. Such large-scale fields can nowadays
  be understood in terms of mean-field dynamo theory that explains the
  possibility of large-scale field generation under anisotropic conditions
  lacking mirror symmetry. However, even when none of this is the case,
  dynamos can still work, and they are called small-scale dynamos that
  were referred to in paper 2. This was studied originally under the
  assumption that the flow is smooth compared with the magnetic field,
  but in the Sun the opposite is the case. This is because viscosity
  is much smaller than magnetic diffusivity, i.e., their ratio, which
  is the magnetic Prandtl number, is small. In that case the physics
  of small-scale dynamos changes, but dynamos still exist even then
  (paper 4). Tracing the flow lines in nonlinear small-scale dynamos is
  important for understanding their mixing properties (paper 5). Turbulent
  mixing is a generic concept that applies not only to magnetic field,
  but also to passive scalars which are often used as a prototype for
  studying this. Turbulence simulations have helped tremendously in
  quantifying the ability of turbulent flows to mix, but the more we
  know, the more complicated it becomes. It turns out that spatial and
  temporal coupling is an important consideration for allowing accurate
  comparison between numerical simulations and mean-field theory (paper
  6). <P />(C) The large-scale solar cycle 7. V V Pipin and D D Sokoloff
  The fluctuating α-effect and Waldmeier relations in the nonlinear
  dynamo models<SUP>1</SUP> 8. Radostin D Simitev and Friedrich H Busse
  Solar cycle properties described by simple convection-driven dynamos
  <P />The mean-field concept has helped us constructing detailed models
  of the solar cycle and to make comparison with observed features of
  the solar 11-year cycle. One such feature is the Waldmeier relation
  between growth time and amplitude of the cycle, and there is another
  relation for the declining part of the cycle. These relations
  reflect nonlinear aspects of the model and therefore constitute an
  important test of the model (paper 7). While mean-field theory is
  a useful concept for modeling solar activity, it must eventually be
  tested against fully three-dimensional simulations. At present, such
  simulations are often quite idealized, because only the large scales
  of the turbulent convection of stars can be resolved. Nevertheless,
  numerical simulations begin to show many properties that are also seen
  in the Sun (paper 8). <P />(D) Flow and dynamo properties in spherical
  shells 9. Maxim Reshetnyak and Pavel Hejda Kinetic energy cascades
  in quasi-geostrophic convection in a spherical shell 10. Radostin
  D Simitev and Friedrich H Busse Bistable attractors in a model of
  convection-driven spherical dynamos <P />As the rotation speed is
  increased, the flow becomes more strongly constrained by the Coriolis
  force. In a spherical shell, such a flow is additionally constrained
  by gravity, or at least by the geometry of the domain. Such flows
  are called geostrophic. Only now are we beginning to learn about the
  subtle properties of the kinetic energy cascade in such flows (paper
  9). Turbulent systems are highly nonlinear and it is in principle
  possible to find multiple solutions of the equations even for the same
  boundary and initial conditions. For turbulent systems, we can only ask
  about the statistical properties of the solutions, and the question
  of multiple solutions is then less obvious. However, in turbulent
  dynamos in convective shells, a nice example has been found where
  this is possible. A detailed account of this is given in paper 10. <P
  />Most of the participants of the Nordita program were able to stay for
  the full month of the program, allowing them to think about new ideas
  that will be reflected not only in papers on the short term, but also
  in new projects and collaborations on a larger scale in the years to
  come. We therefore thank Nordita for providing a stimulating atmosphere
  and acknowledge the generous support. <P /><SUP>1</SUP>This paper
  has been published as V V Pipin and D D Sokoloff 2011 Phys. Scr. <A
  href="http://iopscience.iop.org/1402-4896/84/6/065903"> 84 065903</A>.

---------------------------------------------------------
Title: Diagnostics of Magnetic Flux Emergence and Evolution by
    Local Helioseismology
Authors: Kosovichev, Alexander; Ilonidis, Stathis; Zhao, Junwei;
   Kholikov, Shukur
2012shin.confE..48K    Altcode:
  We investigate the capability of local (time-distance)helioseismology
  for forecasting the emergence and developmentof major active regions
  and eruptive events, flares and CMEs,as well as for data driven MHD
  modeling of CME events. Therecent successful detection of several
  large solar activeregions in acoustic travel-time signals before
  the emergence ofactive regions has opened a new opportunity for
  predictingmajor magnetic flux emergence events that are a primary
  sourceof solar flares and CMEs, from several hours to two days
  inadvance. In addition, time-distance helioseismology has becomea
  useful tool to map solar subsurface flow fields up to morethan
  20 Mm below the photosphere, and discovered strongshearing flows
  associated with flaring and CME activity. Wediscuss the current
  status of these measurements, theirsensitivity and uncertainties,
  implementation for the SDO/HMIpipeline processing, and the data
  products available for thedata-driven MHD modeling. This work can make
  a substantialcontribution to the primary goals of the SHINE program
  toinvestigate the connections between eruptive events andmagnetic
  phenomena on the Sun, their ultimate origins andprecursors.

---------------------------------------------------------
Title: Energy Release in Solar Flares: Catastrophic Magnetic Field
    Changes, Sunquakes and Coronal Eruptions
Authors: Kosovichev, Alexander
2012shin.confE.101K    Altcode:
  Understanding the mechanisms of energy release in solar flaresis
  critical for quantitative data-driven modeling of coronaleruptions
  and CMEs. Uninterrupted observations of the Sun fromSDO and other
  space missions provide unique opportunities fordiagnostics of solar
  flares from the low atmosphere to thecorona. These multi-wavelength
  observations indicate that thetwo basic classes of solar flares:
  confined and eruptive, areprobably related to two different
  mechanisms of the energyrelease. In confined (compact) flares, the
  energy is mostlyreleased in the low atmosphere. Typically, such flares
  areaccompanied by catastrophic changes of photospheric magneticfields,
  produce helioseismic waves ('sunquakes') and coronalshocks, but no
  substantial CMEs. Contrary, in eruptive flareswith large CME events,
  the energy is released in the highcorona, making little impact in the
  lower atmosphere. Usingdata from the HMI and AIA SDO instruments,
  Hinode, RHESSI andGOES, I focus on analysis of energy release in
  confined flares,which represent particular challenge for flare theories
  andacceleration physics. The results show that contrary to thestandard
  flare model the initial energy release, which triggersthe whole chain
  of flare events, probably occurs in the loweratmosphere during the
  flare pre-heating phase.

---------------------------------------------------------
Title: Turbulent Kinetic Energy Spectra of Solar Convection from
    NST Observations and Realistic MHD Simulations
Authors: Kitiashvili, I. N.; Abramenko, V. I.; Goode, P. R.;
   Kosovichev, A. G.; Lele, S. K.; Mansour, N. N.; Wray, A. A.;
   Yurchyshyn, V. B.
2012arXiv1206.5300K    Altcode:
  Turbulent properties of the quiet Sun represent the basic state of
  surface conditions, and a background for various processes of solar
  activity. Therefore understanding of properties and dynamics of this
  `basic' state is important for investigation of more complex phenomena,
  formation and development of observed phenomena in the photosphere and
  atmosphere. For characterization of the turbulent properties we compare
  kinetic energy spectra on granular and sub-granular scales obtained
  from infrared TiO observations with the New Solar Telescope (Big Bear
  Solar Observatory) and from 3D radiative MHD numerical simulations
  ('SolarBox' code). We find that the numerical simulations require a high
  spatial resolution with 10 - 25 km grid-step in order to reproduce the
  inertial (Kolmogorov) turbulence range. The observational data require
  an averaging procedure to remove noise and potential instrumental
  artifacts. The resulting kinetic energy spectra show a good agreement
  between the simulations and observations, opening new perspectives for
  detailed joint analysis of more complex turbulent phenomena on the Sun,
  and possibly on other stars. In addition, using the simulations and
  observations we investigate effects of background magnetic field,
  which is concentrated in self-organized complicated structures in
  intergranular lanes, and find an increase of the small-scale turbulence
  energy and its decrease at larger scales due to magnetic field effects.

---------------------------------------------------------
Title: Helioseismic Measurements of Emerging Magnetic Flux in the
    Solar Convection Zone
Authors: Ilonidis, Stathis; Zhao, J.; Kosovichev, A.; Hartlep, T.
2012AAS...22010902I    Altcode:
  Solar magnetic fields are probably generated deep inside the
  convection zone and then emerge to the surface and form active
  regions. Helioseismology is capable of probing acoustic perturbations in
  the solar interior by cross-correlating oscillation signals observed at
  the surface. In this study, we employ the time-distance helioseismology
  technique, and for several active regions observed with SOHO/MDI,
  SDO/HMI and GONG instruments investigate variations of the acoustic
  cross-correlation signals and phase travel-time shifts caused by
  emerging magnetic structures as deep as 65,000 km and 1-2 days before
  these structures appear at the surface. We discuss optimization of
  the time-distance method for the detection of emerging flux, present
  characteristics of the helioseismic signatures, and make comparisons
  with numerical simulations. We also investigate the relationship between
  the helioseismic signals and properties of the emerged active regions,
  and discuss perspectives for utilizing this method to improve space
  weather forecast.

---------------------------------------------------------
Title: Searching For Equator-ward Meridional Flows In The Solar
    Interior
Authors: Zhao, Junwei; Bogart, R. S.; Kosovichev, A. G.; Duvall,
   T. L., Jr.
2012AAS...22010905Z    Altcode:
  At what depth the equator-ward meridional flow exists and what is
  its speed are important questions for a better understanding of
  solar dynamo and a better prediction of how active a solar cycle
  is. However, the depth and the speed of the equator-ward flow are
  still not determined from helioseismology after studies of more than
  one decade. The new high-resolution observations from HMI has offered
  us a new chance to tackle these problems. Moreover, the systematic
  center-to-limb variation that was recently found in time-distance
  helioseismology analysis probably implies that the equator-ward flows
  exist in areas much shallower than the tachocline. Utilizing two years'
  HMI observations, we examine how well we can determine the depth and
  speed of the returning meridional flow.

---------------------------------------------------------
Title: Dynamics of Magnetized Vortex Tubes in the Solar Chromosphere
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Mansour, N. N.; Wray,
   A. A.
2012ApJ...751L..21K    Altcode: 2012arXiv1201.5442K
  We use three-dimensional radiative MHD simulations to investigate the
  formation and dynamics of small-scale (less than 0.5 Mm in diameter)
  vortex tubes spontaneously generated by turbulent convection in
  quiet-Sun regions with an initially weak (10 G) mean magnetic
  field. The results show that the vortex tubes penetrate into the
  chromosphere and substantially affect the structure and dynamics
  of the solar atmosphere. The vortex tubes are mostly concentrated
  in intergranular lanes and are characterized by strong (near sonic)
  downflows and swirling motions that capture and twist magnetic field
  lines, forming magnetic flux tubes that expand with height and attain
  magnetic field strengths ranging from 200 G in the chromosphere to more
  than 1 kG in the photosphere. We investigate in detail the physical
  properties of these vortex tubes, including thermodynamic properties,
  flow dynamics, and kinetic and current helicities, and conclude that
  magnetized vortex tubes provide an important path for energy and
  momentum transfer from the convection zone into the chromosphere.

---------------------------------------------------------
Title: Convection-Chromosphere Coupling due to Vortex Tube Dynamic
Authors: Kitiashvili, Irina; Kosovichev, A.; Mansour, N.; Wray, A.
2012AAS...22012405K    Altcode:
  Ubiquitous distribution of small-scale vortex tubes on the solar surface
  was found both in observations and simulations. Complicated dynamics
  of the turbulent vortex tubes is a source of various observed effects
  such as acoustic waves excitation and processes of self-organization
  in magnetized solar plasma. We use realistic-type radiative 3D MHD
  simulations to investigate in detail different mechanisms of the
  vortex tube formation by granular flows in the upper convection zone,
  appearance of vortex tubes on the surface and their interaction with
  the atmosphere. The simulation results reveal new interesting effects of
  penetration of the vortex tubes from the turbulent subphotosphere into
  the chromosphere, interaction between these layers, and influence of
  the helical motions on thermodynamic properties of the chromosphere. In
  the presence of background magnetic field, the vortex tubes lead to
  formation of compact magnetic flux tubes, playing important role in
  the mass and energy flux into the chromosphere. We discuss implication
  of the simulation results for future high-resolution observations.

---------------------------------------------------------
Title: Physics of Sunquakes Events Observed with SDO
Authors: Kosovichev, Alexander G.
2012AAS...22010903K    Altcode:
  Sunquake events representing helioseismic response to solar flares
  are caused by strong localized impacts in the low atmosphere during
  the flare impulsive phase. Several mechanisms of the impact have
  been debated, but there is no clear understanding of how energy
  and momentum are transported from the magnetic energy release site
  (presumably located in the higher atmosphere) to the solar surface. It
  is also puzzling why some moderate class flares produce sunquakes,
  while significantly more powerful flares do not. Observations with SDO
  have substantially improved our ability to investigate details of the
  helioseismic response and the impact source properties and dynamics,
  providing data with high spatial and temporal resolutions, as well as
  spectro-polarimetric properties. I will present new results on several
  sunquake events observed with the HMI and AIA instruments and discuss
  the basic properties of the helioseismic waves, their interaction with
  active regions, the source dynamics and its relation to the amplitude
  and direction of the waves. The observations also reveal interesting
  relationships between the sunquake impacts, X-ray and white-light
  emissions and magnetic field changes in solar flares. I will compare
  the observational results with the physical models of sunquakes
  (thick-target model, McClymont jerk, backwarming, mass eruption),
  and discuss model constraints from the new observations.

---------------------------------------------------------
Title: Magnetic and Thermal Effects of MHD Wave Propagation in
    Different Models of Sunspots
Authors: Parchevsky, Konstantin; Kosovichev, A. G.
2012AAS...22020619P    Altcode:
  Understanding of MHD wave propagation and transformation in sunspots
  is very important for understanding helioseismic measurements and
  improving helioseismic inversion procedures. Numerical simulations help
  to reveal details of wave interaction with the non-uniform background
  magnetic field and flows. Such simulations also provide artificial
  data for testing and calibration techniques used for analysis of data
  from space missions SOHO/MDI, SDO/HMI, HINODE, and GONG network. <P
  />There are three competing processes, which affect the wave speed
  in sunspots: (i) thermal effects, (ii) magnetic field and (iii) mass
  flows. Comparison of numerical simulations of the MHD wave propagation
  in different models of sunspot helps to disentangle these effects. We
  present simulation results of 3D MHD wave propagation in sunspot models
  with separated and combined thermal and magnetic effects. When an MHD
  wave enters a self-consistent magnetostatic model of the sunspot, the
  wave front flattens due to the reduced background sound speed near the
  photosphere. Later, when the wave propagates further, the wave front
  restores it's original shape, because waves propagate through deeper
  regions where contribution of the magnetic field dominates. In the
  model with the potential magnetic field configuration and quiet Sun
  background model, the wave front accelerates from the moment when the
  wave enters the magnetized region, forming a bulge toward the sunspot
  axis. Simulations also show weak fast-to-slow conversion of MHD waves
  near the surface where the plasma parameter beta equals one. We also
  present simulations in realistic sunspot model calculated by M. Rempel.

---------------------------------------------------------
Title: Effects of Spectral Line Formation Height in Time-Distance
    Helioseismology
Authors: Nagashima, K.; Parchevsky, K. V.; Zhao, J.; Duvall, T. L.,
   Jr.; Kosovichev, A. G.; Sekii, T.
2012ASPC..456...57N    Altcode:
  To understand the effect of the formation-height difference in
  time-distance helioseismology analyses, we consider the wave behavior
  above the surface. We show that by using the numerically-simulated
  wavefields at two different heights this difference may cause
  travel-time shifts due to the non-stationary character of waves excited
  by near-surface acoustic sources. This needs to be taken into account
  in multi-wavelength helioseismology and measurements close to the
  solar limb.

---------------------------------------------------------
Title: Testing Helioseismic Measurements Of Subsurface Meridional
    And Large-scale Flows Using Artificial Data From Numerical Simulations
Authors: Hartlep, Thomas; Zhao, J.; Kosovichev, A. G.; Mansour, N. N.
2012AAS...22010904H    Altcode:
  Numerical simulations of the solar acoustic wave-field have become an
  important tool for validating helioseismic measurement and inversion
  techniques. Here, we present results from simulating linearized
  wave propagation in the full 3D solar interior through stationary
  flow fields, and measurements applied to this artificial data. The
  background flow include different meridional flow models with deep
  and shallow return flows, as well as a full-resolution snapshot from a
  solar convection simulation in anelastic approximation using the "ASH"
  code, provided to us by Mark Miesch. Time-distance helioseismology
  measurements and inversions are carried using this artificial data
  and the results are compared to the models. We determine and discuss
  the accuracy and resolution of the subsurface flow patterns.

---------------------------------------------------------
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.
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: Response to Comment on “Detection of Emerging Sunspot
    Regions in the Solar Interior”
Authors: Ilonidis, Stathis; Zhao, Junwei; Kosovichev, Alexander
2012Sci...336..296I    Altcode:
  Braun claims that his analysis using helioseismic holography does
  not confirm the detection of emerging sunspot regions. We examine
  his measurement procedure and explain why his method has different
  sensitivity than our method. We also discuss possible physical processes
  that may cause the detected phase travel-time shifts.

---------------------------------------------------------
Title: Systematic Center-to-limb Variation in Measured Helioseismic
    Travel Times and its Effect on Inferences of Solar Interior Meridional
    Flows
Authors: Zhao, Junwei; Nagashima, Kaori; Bogart, R. S.; Kosovichev,
   A. G.; Duvall, T. L., Jr.
2012ApJ...749L...5Z    Altcode: 2012arXiv1203.1904Z
  We report on a systematic center-to-limb variation in measured
  helioseismic travel times, which must be taken into account for
  an accurate determination of solar interior meridional flows. The
  systematic variation, found in time-distance helioseismology analysis
  using SDO/HMI and SDO/AIA observations, is different in both travel-time
  magnitude and variation trend for different observables. It is not clear
  what causes this systematic effect. Subtracting the longitude-dependent
  east-west travel times, obtained along the equatorial area, from
  the latitude-dependent north-south travel times, obtained along the
  central meridian area, gives remarkably similar results for different
  observables. We suggest this as an effective procedure for removing
  the systematic center-to-limb variation. The subsurface meridional
  flows obtained from inversion of the corrected travel times are
  approximately 10 m s<SUP>-1</SUP> slower than those obtained without
  removing the systematic effect. The detected center-to-limb variation
  may have important implications in the derivation of meridional flows
  in the deep interior and needs to be better understood.

---------------------------------------------------------
Title: Commission 12: Solar Radiation and Structure
Authors: Kosovichev, Alexander; Cauzzi, Gianna; Pillet, Valentin
   Martinez; Asplund, Martin; Brandenburg, Axel; Chou, Dean-Yi;
   Christensen-Dalsgaard, Jorgen; Gan, Weiqun; Kuznetsov, Vladimir D.;
   Rovira, Marta G.; Shchukina, Nataliya; Venkatakrishnan, P.
2012IAUTA..28...81K    Altcode: 2012IAUTB..28...81K
  Commission 12 of the International Astronomical Union encompasses
  investigations of the internal structure and dynamics of the Sun, mostly
  accessible through the techniques of local and global helioseismology,
  the quiet solar atmosphere, solar radiation and its variability, and
  the nature of relatively stable magnetic structures like sunspots,
  faculae and the magnetic network. The Commission sees participation
  of over 350 scientists worldwide.

---------------------------------------------------------
Title: Division II: Sun and Heliosphere
Authors: Martínez Pillet, Valentín; Klimchuk, James A.; Melrose,
   Donald B.; Cauzzi, Gianna; van Driel-Gesztelyi, Lidia; Gopalswamy,
   Natchimuthuk; Kosovichev, Alexander; Mann, Ingrid; Schrijver,
   Carolus J.
2012IAUTA..28...61M    Altcode: 2012IAUTA..28...61P
  The solar activity cycle entered a prolonged quiet phase that started
  in 2008 and ended in 2010. This minimum lasted for a year longer
  than expected and all activity proxies, as measured from Earth and
  from Space, reached minimum values never observed before (de Toma,
  2012). The number of spotless days from 2006 to 2009 totals 800, the
  largest ever recorded in modern times. Solar irradiance was at historic
  minimums. The interplanetary magnetic field was measured at values as
  low as 2.9 nT and the cosmic rays were observed at records-high. While
  rumors spread that the Sun could be entering a grand minimum quiet
  phase (such as the Maunder minimum of the XVII century), activity
  took over in 2010 and we are now well into Solar Cycle 24 (albeit,
  probably, a low intensity cycle), approaching towards a maximum due
  by mid 2013. In addition to bringing us the possibility to observe
  a quiet state of the Sun and of the Heliosphere that was previously
  not recorded with modern instruments, the Sun has also shown us how
  little we know about the dynamo mechanism that drives its activity as
  all solar cycle predictions failed to see this extended minimum coming.

---------------------------------------------------------
Title: Effects of vortex tube dynamics in the chromosphere
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Lele, S. K.; Mansour,
   N. N.; Wray, A. A.
2012decs.confE..96K    Altcode:
  Investigation of the solar atmosphere dynamics cannot be complete
  without understanding coupling, and mass and energy exchange between
  the strongly-turbulent subphotosphere and the chromosphere. Modern
  computational capabilities allow us to construct realistic dynamical
  models, which take into account dynamical, chemical and radiative
  properties of the solar plasma. Such simulations based on first physical
  principles and accurate modeling of effects of magnetic field and
  small-scale turbulence, coupled with spectro-polarimetric line formation
  calculations, provide synthetic multi-wavelength observables, and are
  very important for interpretation of observational data. The simulations
  allow us to study physical processes and phenomena that have not been
  resolved in observations. In this talk we will present our recent
  results of high-resolution 3D radiative MHD numerical simulations of
  top layers of the convective zone and the chromosphere. The simulations
  reveal ubiquitous distribution of small-scale swirling motions in
  quiet-Sun and magnetic regions, forming vortex tubes extending from
  the subphosphere into the chromosphere. Our results show that these
  small-scale vortex tubes that originally formed in subsurface layer
  and penetrate into the chromosphere provide an efficient coupling
  of the turbulent convective layers with the atmosphere. They play
  important role in various processes, such as shearing instabilities,
  wave excitation, formation of magnetic flux tubes and transport
  of energy, mass, momentum and also turbulent properties from the
  convection zone into the chromosphere. In the presentation, we will
  focus on the physical aspects of the vortex tube formation, penetration
  into the atmosphere, interaction with magnetic fields, their role in
  the energy exchange, and on observational diagnostics and comparison
  with observational data.

---------------------------------------------------------
Title: Links between photospheric and chromospheric oscillations
Authors: Kosovichev, A. G.; Kitiashvili, I. N.; Mitra-Kraev, U.;
   Sekii, T.
2012decs.confE..97K    Altcode:
  Oscillations excited by turbulent convection play important in the
  dynamics and energetics of the solar atmosphere. Oscillations below the
  acoustic cut-off frequency form photospheric resonant modes trapped
  in the interior but also penetrating into the chromosphere. Above
  the frequency cut-off, the oscillations represent traveling waves
  in the chromosphere that form pseudo-modes due to interference with
  waves coming from the interior. The physics of the chromospheric
  oscillations, their coupling to the photospheric oscillations, and
  their role in the chromospheric dynamics and energetics are not fully
  understood. The observed oscillation properties strongly depend on
  the excitation mechanism, interaction with turbulence and radiation,
  and local structure and dynamics of the chromosphere. Significant
  advances can be made through multi-wavelength observations of
  atmospheric oscillations and realistic numerical radiative hydrodynamics
  simulations. Using Hinode/SOT data we investigate the basic properties
  of solar oscillations observed at two levels in the solar atmosphere,
  in the G-band (formed in the photosphere) and in the CaII H line
  (chromospheric emission). We analyzed the data by calculating the
  individual power spectra as well as the cross-spectral properties,
  i.e., coherence and phase shift. The observational properties are
  compared with theoretical models and numerical simulations. The
  results reveal significant frequency shifts between the CaII H and
  G-band spectra, in particular above the acoustic cutoff frequency for
  pseudo-modes. The cross-spectrum phase shows peaks associated with
  the acoustic oscillation (p-mode) lines, and begins to increase with
  frequency around the acoustic cut-off. However, we find no phase shift
  for the (surface gravity wave) f-mode. The observed properties for
  the p-modes are qualitatively reproduced in a model that includes a
  correlated background due to radiative effects. Our results show that
  multi-wavelength observations of solar oscillations, in combination
  with radiative hydrodynamics modeling, help to understand the coupling
  between photospheric and chromospheric oscillations.

---------------------------------------------------------
Title: Bipolar Magnetic Regions on the Sun: Global Analysis of the
    SOHO/MDI Data Set
Authors: Stenflo, J. O.; Kosovichev, A. G.
2012ApJ...745..129S    Altcode: 2011arXiv1112.5226S
  The magnetic flux that is generated by dynamo processes inside the
  Sun emerges in the form of bipolar magnetic regions. The properties
  of these directly observable signatures of the dynamo can be extracted
  from full-disk solar magnetograms. The most homogeneous, high-quality
  synoptic data set of solar magnetograms has been obtained with the
  Michelson Doppler Imager (MDI) instrument on the Solar and Heliospheric
  Observatory spacecraft during 1995-2011. We have developed an IDL
  program that has, when applied to the 73,838 magnetograms of the MDI
  data set, automatically identified 160,079 bipolar magnetic regions that
  span a range of scale sizes across nearly four orders of magnitude. The
  properties of each region have been extracted and statistically
  analyzed, in particular with respect to the polarity orientations of
  the bipolar regions, including their tilt-angle distributions and
  their violations of Hale's polarity law. The latitude variation of
  the average tilt angles (with respect to the E-W direction), which is
  known as Joy's law, is found to closely follow the relation 32fdg1 ×
  sin (latitude). There is no indication of a dependence on region size
  that one may expect if the tilts were produced by the Coriolis force
  during the buoyant rise of flux loops from the tachocline region. A few
  percent of all regions have orientations that violate Hale's polarity
  law. We show explicit examples, from different phases of the solar
  cycle, where well-defined medium-size bipolar regions with opposite
  polarity orientations occur side by side in the same latitude zone in
  the same magnetogram. Such oppositely oriented large bipolar regions
  cannot be part of the same toroidal flux system, but different flux
  systems must coexist at any given time in the same latitude zones. These
  examples are incompatible with the paradigm of coherent, subsurface
  toroidal flux ropes as the source of sunspots, and instead show that
  fluctuations must play a major role at all scales for the turbulent
  dynamo. To confirm the profound role of fluctuations at large scales,
  we show explicit examples in which large bipolar regions differ from the
  average Joy's law orientation by an amount between 90° and 100°. We
  see no observational support for a separation of scales or a division
  between a global and a local dynamo, since also the smallest scales in
  our sample retain a non-random component that significantly contributes
  to the accumulated emergence of a north-south dipole moment that will
  lead to the replacement of the old global poloidal field with a new
  one that has the opposite orientation.

---------------------------------------------------------
Title: Implementation and Comparison of Acoustic Travel-Time
    Measurement Procedures for the Solar Dynamics Observatory/Helioseismic
    and Magnetic Imager Time - Distance Helioseismology Pipeline
Authors: Couvidat, S.; Zhao, J.; Birch, A. C.; Kosovichev, A. G.;
   Duvall, T. L.; Parchevsky, K.; Scherrer, P. H.
2012SoPh..275..357C    Altcode:
  The Helioseismic and Magnetic Imager (HMI) instrument onboard the
  Solar Dynamics Observatory (SDO) satellite is designed to produce
  high-resolution Doppler-velocity maps of oscillations at the solar
  surface with high temporal cadence. To take advantage of these
  high-quality oscillation data, a time - distance helioseismology
  pipeline (Zhao et al., Solar Phys. submitted, 2010) has been
  implemented at the Joint Science Operations Center (JSOC) at Stanford
  University. The aim of this pipeline is to generate maps of acoustic
  travel times from oscillations on the solar surface, and to infer
  subsurface 3D flow velocities and sound-speed perturbations. The wave
  travel times are measured from cross-covariances of the observed
  solar oscillation signals. For implementation into the pipeline we
  have investigated three different travel-time definitions developed in
  time - distance helioseismology: a Gabor-wavelet fitting (Kosovichev
  and Duvall, SCORE'96: Solar Convection and Oscillations and Their
  Relationship, ASSL, Dordrecht, 241, 1997), a minimization relative to a
  reference cross-covariance function (Gizon and Birch, Astrophys. J.571,
  966, 2002), and a linearized version of the minimization method (Gizon
  and Birch, Astrophys. J.614, 472, 2004). Using Doppler-velocity data
  from the Michelson Doppler Imager (MDI) instrument onboard SOHO,
  we tested and compared these definitions for the mean and difference
  travel-time perturbations measured from reciprocal signals. Although
  all three procedures return similar travel times in a quiet-Sun region,
  the method of Gizon and Birch (Astrophys. J.614, 472, 2004) gives travel
  times that are significantly different from the others in a magnetic
  (active) region. Thus, for the pipeline implementation we chose the
  procedures of Kosovichev and Duvall (SCORE'96: Solar Convection and
  Oscillations and Their Relationship, ASSL, Dordrecht, 241, 1997)
  and Gizon and Birch (Astrophys. J.571, 966, 2002). We investigated
  the relationships among these three travel-time definitions, their
  sensitivities to fitting parameters, and estimated the random errors
  that they produce.

---------------------------------------------------------
Title: Time-Distance Helioseismology Data-Analysis Pipeline for
    Helioseismic and Magnetic Imager Onboard Solar Dynamics Observatory
    (SDO/HMI) and Its Initial Results
Authors: Zhao, J.; Couvidat, S.; Bogart, R. S.; Parchevsky, K. V.;
   Birch, A. C.; Duvall, T. L.; Beck, J. G.; Kosovichev, A. G.; Scherrer,
   P. H.
2012SoPh..275..375Z    Altcode: 2011SoPh..tmp...86Z; 2011SoPh..tmp..163Z; 2011arXiv1103.4646Z;
   2011SoPh..tmp..232Z
  The Helioseismic and Magnetic Imager onboard the Solar Dynamics
  Observatory (SDO/HMI) provides continuous full-disk observations
  of solar oscillations. We develop a data-analysis pipeline based
  on the time-distance helioseismology method to measure acoustic
  travel times using HMI Doppler-shift observations, and infer solar
  interior properties by inverting these measurements. The pipeline
  is used for routine production of near-real-time full-disk maps of
  subsurface wave-speed perturbations and horizontal flow velocities
  for depths ranging from 0 to 20 Mm, every eight hours. In addition,
  Carrington synoptic maps for the subsurface properties are made from
  these full-disk maps. The pipeline can also be used for selected target
  areas and time periods. We explain details of the pipeline organization
  and procedures, including processing of the HMI Doppler observations,
  measurements of the travel times, inversions, and constructions of the
  full-disk and synoptic maps. Some initial results from the pipeline,
  including full-disk flow maps, sunspot subsurface flow fields, and
  the interior rotation and meridional flow speeds, are presented.

---------------------------------------------------------
Title: Magnetohydrodynamic simulations of flows around rotating and
    non-rotating axisymmetric magnetic flux concentrations
Authors: Hartlep, T.; Busse, F. H.; Hurlburt, N. E.; Kosovichev, A. G.
2012MNRAS.419.2325H    Altcode: 2011MNRAS.tmp.1880H
  We present results on modelling magnetic flux tubes in an unstably
  stratified medium and the flows around them using 2D axisymmetric
  magnetohydrodynamic (MHD) simulations. The study is motivated by the
  formation of magnetic field concentrations at the solar surface in
  sunspots and magnetic pores and the large-scale flow patterns associated
  with them. The simulations provide consistent, self-maintained models of
  concentrated magnetic field in a convective environment, although they
  are not fully realistic or directly applicable to the solar case. In
  this paper, we explore under which conditions the associated flows near
  the surface are converging (towards the spot centre) or diverging (away
  from the axis) in nature. It is found that, depending on the parameters
  of the problem, the results can depend on the initial conditions, in
  particular for zero or low rotation rates and Prandtl numbers smaller
  than unity. The solutions with a converging flow generally produce
  more strongly confined magnetic flux tubes.

---------------------------------------------------------
Title: The Helioseismic and Magnetic Imager (HMI) Investigation for
    the Solar Dynamics Observatory (SDO)
Authors: Scherrer, P. H.; Schou, J.; Bush, R. I.; Kosovichev, A. G.;
   Bogart, R. S.; Hoeksema, J. T.; Liu, Y.; Duvall, T. L.; Zhao, J.;
   Title, A. M.; Schrijver, C. J.; Tarbell, T. D.; Tomczyk, S.
2012SoPh..275..207S    Altcode:
  The Helioseismic and Magnetic Imager (HMI) instrument and investigation
  as a part of the NASA Solar Dynamics Observatory (SDO) is designed
  to study convection-zone dynamics and the solar dynamo, the origin
  and evolution of sunspots, active regions, and complexes of activity,
  the sources and drivers of solar magnetic activity and disturbances,
  links between the internal processes and dynamics of the corona and
  heliosphere, and precursors of solar disturbances for space-weather
  forecasts. A brief overview of the instrument, investigation objectives,
  and standard data products is presented.

---------------------------------------------------------
Title: Turbulent Cross-helicity in the Mean-field Solar Dynamo Problem
Authors: Pipin, V. V.; Kuzanyan, K. M.; Zhang, H.; Kosovichev, A. G.
2011ApJ...743..160P    Altcode: 2011arXiv1105.4285P
  We study the dynamical and statistical properties of turbulent
  cross-helicity (correlation of the aligned fluctuating velocity
  and magnetic field components). We derive an equation governing
  generation and evolution of the turbulent cross-helicity and
  discuss its meaning for the dynamo. Using the symmetry properties
  of the problem we suggest a general expression for the turbulent
  cross-helicity. Effects of the density stratification, large-scale
  magnetic fields, differential rotation, and turbulent convection
  are taken into account. We investigate the relative contribution
  of these effects to the cross-helicity evolution for two kinds of
  dynamo models of the solar cycle: a distributed mean-field model and
  a flux-transport dynamo model. We show that the contribution from the
  density stratification follows the evolution of the radial magnetic
  field, while large-scale electric currents produce a more complicated
  pattern of the cross-helicity of comparable magnitude. The pattern
  of the cross-helicity evolution strongly depends on details of the
  dynamo mechanism. Thus, we anticipate that direct observations of the
  cross-helicity on the Sun may serve for the diagnostic purpose of the
  solar dynamo process.

---------------------------------------------------------
Title: Testing Helioseismic Measurements of the Solar Meridional
    Flow with Numerical Simulations
Authors: Hartlep, T.; Zhao, J.; Kosovichev, A. G.; Mansour, N. N.;
   Rempel, M.; Pipin, V.
2011AGUFMSH52B..03H    Altcode:
  The meridional flow is of fundamental importance for understanding
  magnetic flux transport in the solar interior. Reliable measurements of
  the flow could provide important constraints for dynamo theories. The
  actual shape and strength of the meridional flow, particularly in the
  deep interior, remains unknown. Detecting such weak flows with a speed
  of 10-20 m/s in the deep solar interior is a challenging problem for
  helioseismology. Numerical simulations of helioseismic wave propagation
  provide means for testing and calibrating measurement techniques,
  and can help increase our confidence in the inferences obtained from
  helioseismic inversions. We have developed a 3D numerical spectral code
  to simulate the propagation of acoustic waves in the whole-Sun. With
  this code, we simulate the propagation of stochastic wave fields given
  mean meridional flows of different strength and circulation patterns
  (including flow models with deep and shallow stagnation points). Our
  helioseismic measurement techniques are based on estimating acoustic
  travel times from wave-field cross-correlations (time-distance
  helioseismology method). We investigate various cross-correlation
  schemes, and study the sensitivity of acoustic travel times to the
  depth and speed of the meridional flow. Using the numerical simulation
  results we discuss the prospects of measuring the Sun's meridional
  flow from Solar Dynamics Observatory (SDO/HMI) data.

---------------------------------------------------------
Title: Vortex tubes of solar convection: formation, properties
    and dynamics
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Lele, S. K.; Mansour,
   N. N.; Wray, A. A.
2011AGUFMSH43A1927K    Altcode:
  Turbulent convection of the Sun demonstrates very complicated dynamics,
  which is often associated with different scales of self-organization. In
  particular, vortex tube structures have been identified initially in
  numerical simulations and then in high-resolution observations. We
  present new results of 3D radiative MHD simulations of a top layer of
  the convective zone that reveal the important role of turbulent vortex
  tubes in various solar processes: acoustic waves excitation, convective
  downdrafts, spontaneous formation of stable magnetic structures and
  others. We consider various aspects of the vortex tubes dynamics,
  including their formation, identification, physical characteristics, and
  links to phenomena observed in the quiet Sun and magnetic regions. We
  compare the simulation results with observational data from SDO/HMI,
  Hinode and large ground-based telescope.

---------------------------------------------------------
Title: Detection of Emerging Sunspot Regions in the Solar Interior
    by Helioseismology
Authors: Ilonidis, S.; Zhao, J.; Kosovichev, A. G.
2011AGUFMSH54A..01I    Altcode:
  Predicting solar magnetic activity is one of the most important
  problems of solar and space physics. Helioseismology allows us to
  probe conditions inside the Sun by observing acoustic oscillations
  on the solar surface. In this study, we analyze Doppler observations
  from the MDI and HMI instruments on SOHO and SDO spacecraft using a
  time-distance helioseismology technique specifically developed for
  measuring acoustic travel time anomalies caused by perturbations in
  the deep interior. We have detected strong perturbations associated
  with emerging active regions at a depth of about 60Mm, about 1-2 days
  before these regions are formed in the photosphere. We compare our
  results with numerical simulation models of magnetic flux emergence,
  discuss implications for solar magnetism studies, and suggest potential
  applications for space weather forecast.

---------------------------------------------------------
Title: The Waldmeier relations as due to nonlinear surface-shear
    shaped dynamo
Authors: Pipin, V.; Kosovichev, A. G.
2011AGUFMSH43A1922P    Altcode:
  We present a study of a solar dynamo model operating in the bulk of
  the convection zone with the toroidal magnetic field flux concentrated
  in the subsurface rotational shear layer. We explore how this type of
  dynamo may depend on spatial variations of turbulent parameters and on
  the differential rotation near the surface. The mean-field dynamo model
  takes into account the evolution of magnetic helicity and describes its
  nonlinear feedback on the generation of large-scale magnetic field by
  the α -effect. We compare the magnetic cycle characteristics predicted
  by the model, including the cycle asymmetry (associated with the growth
  and decay times) and the duration - amplitude relation (Waldmeier's
  effects), with the observed sunspot cycle properties. We show that the
  model qualitatively reproduces the basic properties of the solar cycles.

---------------------------------------------------------
Title: Amazing M9-Flare: Sunquakes, White Light Emission and Magnetic
    Restructuring
Authors: Kosovichev, A.; Desai, P.; Hayashi, K.
2011AGUFMSH33A2042K    Altcode:
  The solar flare of July 30, 2011 (start time 2:04UT), in active
  region NOAA 11261, observed with the Helioseismic and Magnetic Imager
  (HMI) on Solar Dynamics Observatory, had a modest X-ray class (M9),
  but it made a very strong photospheric impact. The flare generated
  helioseismic waves, "sunquakes" (also observed with the SDO/AIA
  instrument), caused a large expanding area of white-light emission,
  and was accompanied by substantial restructuring of magnetic field
  around the magnetic neutral line in the flare region. Surprisingly,
  there was no significant hard X-ray emission and coronal mass ejection,
  associated with this flare. This provides an indication that the
  flare energy release was probably confined in the lower atmosphere. We
  present results of initial analysis of the SDO data, and discuss new
  challenges from these observations for the standard flare model.

---------------------------------------------------------
Title: Measuring Acoustic Travel Times in Higher-Latitude Regions
    of the Sun using Hinode and SDO Data
Authors: Nagashima, K.; Duvall, T.; Zhao, J.; Kosovichev, A. G.;
   Parchevsky, K.; Sekii, T.
2011AGUFMSH51B2016N    Altcode:
  The interior structure and dynamics of the Sun can be probed by
  measuring and inverting travel times of acoustic waves, widely
  known as time-distance helioseismology. Recent high-resolution
  observations of solar oscillations with Hinode/SOT and SDO/HMI
  provide us with an opportunity to investigate the flow dynamics in
  higher-latitude regions of the Sun. Of particular interest is the
  meridional circulation flow, which is crucial for understanding the
  solar dynamo mechanism and predicting the solar activity cycles. We
  investigate systematic uncertainties of the travel times due to
  the center-to-limb variations, which may significantly affect the
  helioseismic inferences of the meridional flows. We present the results
  of analysis of the cross-correlations in the Doppler velocity, line
  core and intensity observations, and the corresponding travel-time fits
  for various positions on the solar disk. We discuss the origin of the
  center-to-limb variations, including the foreshortening effect, the
  difference in the line formation height, and other effects. For better
  understanding of the relative role of these effects we use 3D numerical
  simulations of solar oscillations in a realistic model of the Sun.

---------------------------------------------------------
Title: The Asymmetry of Sunspot Cycles and Waldmeier Relations as
    a Result of Nonlinear Surface-shear Shaped Dynamo
Authors: Pipin, V. V.; Kosovichev, A. G.
2011ApJ...741....1P    Altcode: 2011arXiv1105.1828P
  The paper presents a study of a solar dynamo model operating in the
  bulk of the convection zone with the toroidal magnetic field flux
  concentrated in the subsurface rotational shear layer. We explore how
  this type of dynamo may depend on spatial variations of turbulent
  parameters and on the differential rotation near the surface. The
  mean-field dynamo model takes into account the evolution of magnetic
  helicity and describes its nonlinear feedback on the generation
  of large-scale magnetic field by the α-effect. We compare the
  magnetic cycle characteristics predicted by the model, including
  the cycle asymmetry (associated with the growth and decay times)
  and the duration-amplitude relation (Waldmeier's effects), with the
  observed sunspot cycle properties. We show that the model qualitatively
  reproduces the basic properties of the solar cycles.

---------------------------------------------------------
Title: Excitation of Solar Acoustic Waves and Vortex Tube Dynamics
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Lele, S. K.; Mansour,
   N. N.; Wray, A. A.
2011sdmi.confE..26K    Altcode:
  Oscillatory behavior is one of the basic properties of the solar
  surface. Therefore understanding the mechanism of acoustic waves
  excitation in the turbulent near-surface layer is very important for
  the interpretation of helioseismology data and development of new
  methods of helioseismic diagnostics of the solar interior, as well
  as for understanding of the role of the acoustic flux in the energy
  transport. Observations of individual impulsive events generating
  acoustic waves have been mostly detected in the intergranular lanes
  and are associated with local strong cooling of fluid elements. Also,
  the modern high-resolution observations revealed a process of dragging
  of small-scale magnetic concentrations toward the center of a convective
  vortex motion in the photosphere. A substantial progress is being made
  from the analysis of high-resolution observational data, particularly
  from Hinode, Sunrise, NST, and SDO/HMI, and also from high-resolution
  realistic numerical simulations. The simulations take into account
  all essential turbulent and other physical properties of the solar
  plasma, and allow us to look at the scales that cannot be resolved
  in observations, and also compare the data and models. We present new
  results of 3D radiative MHD simulations of the upper convection zone and
  atmosphere, and show that one of the possible mechanisms of the acoustic
  waves generation is a result of interaction two and more vortex tubes
  in the intergranular lanes. The process of a vortex annihilation,
  which produces acoustic waves, the properties of these waves and
  vortices, magnetic influence on the efficiency of acoustic emission,
  and comparison with the available observational data will be discussed.

---------------------------------------------------------
Title: Multi-wavelength time-distance helioseismology analyses
Authors: Nagashima, Kaori; Zhao, Junwei; Duvall, Thomas, Jr.;
   Kosovichev, Alexander G.; Parchevsky, Konstantin; Sekii, Takashi
2011sdmi.confE..37N    Altcode:
  Travel times of the acoustic waves in the Sun tell us the structure
  and the dynamics of the Sun. This information have been used to probe
  the solar interior. If we exploit multi-layer observation datasets,
  however, it will provide us with means to study the wave propagation
  between the layers as well (Nagashima et al. 2009). In this study, using
  multi-wavelength datasets obtained by Hinode/SOT, SDO/HMI, and SDO/AIA
  we calculate the cross-correlation function of the wavefield and carry
  out time-distance helioseismology analyses. Our preliminary results show
  that when we cross-correlate the wavefields of two different layers
  the cross-correlation functions between these layers are different
  from the cross-correlation functions of both single layers, and this
  provides us with an insight of wave propagation properties. We also
  use numerical simulations of solar oscillations to help interpret our
  observational results.

---------------------------------------------------------
Title: Strong photospheric impact of M-class flare: helioseismic
    response, white light emission and magnetic restructuring
Authors: Kosovichev, Alexander; Desai, Priya; Hayashi, Keiji
2011sdmi.confE.101K    Altcode:
  Solar flare of July 30, 2011, had a modest X-ray class (M9), but
  made a very strong photospheric impact, observed by the Helioseismic
  and Magnetic Imager (HMI) on Solar Dynamics Observatory. The flare
  generated helioseismic waves, (also observed with the SDO/AIA
  instrument), caused a large expanding area of white-light emission,
  and was accompanied by substantial restructuring of magnetic fields in
  the flare region. There was no significant hard X-ray emission and no
  coronal mass ejection. This indicates that the flare energy release
  was probably confined in the lower atmosphere. We present results of
  initial analysis of the SDO data.

---------------------------------------------------------
Title: Helioseismic Frechet Traveltime Kernels in Spherical
    Coordinates
Authors: Schlottmann, R. B.; Kosovichev, A. G.
2011sdmi.confE..29S    Altcode: 2011arXiv1105.4619S
  Seismic traveltime measurements are a crucial tool in the investigation
  of the solar interior, particularly in the examination of fine-scale
  structure. Traditional analysis of traveltimes relies on a geometrical
  ray picture of acoustic wave propagation, which assumes high
  frequencies. However, it is well-known that traveltimes obtained
  from finite-frequency waves are sensitive to variations of medium
  parameters in a wide Fresnel zone around the ray path. To address this
  problem, Frechet traveltime sensitivity kernels have previously been
  developed. These kernels use a more realistic approximation of the wave
  propagation to obtain a linear relationship between traveltimes and
  variations in medium parameters. Frechet kernels take into account the
  actual frequency content of the measured waves and, thus, reproduce the
  Fresnel zone. Kernel theory has been well-developed in previous work on
  plane-parallel models of the Sun for use in local helioseismology. Our
  primary purpose is to apply kernel theory to much larger scales and in
  a spherical geometry. We also present kernel theory in a different way,
  using basic functional analytic methods, in the hope that this approach
  provides an even clearer understanding of the theory, as well as a
  set of tools for calculating kernels. Our results are very general
  and can be used to develop kernels for sensitivity to sound speed,
  density, magnetic fields, fluid flows, and any other medium parameter
  which can affect wave propagation.

---------------------------------------------------------
Title: Variability of five-minute solar oscillations in the corona
    as observed by the Extreme Ultraviolet Spectrophotometer (ESP) on the
    Solar Dynamics Observatory Extreme Ultraviolet Variability Experiment
    (SDO/EVE)
Authors: Didkovsky, Leonid; Judge, Darrell; Kosovichev, Alexander;
   Wieman, Seth; Woods, Tom
2011sdmi.confE..98D    Altcode:
  Solar oscillations in the corona were detected in the frequency
  range corresponding to five-minute acoustic modes of the Sun. The
  oscillations have been observed using soft Xray measurements from the
  Extreme Ultraviolet Spectrophotometer (ESP) of the Extreme Ultraviolet
  Variability Experiment (EVE) onboard the Solar Dynamics Observatory
  (SDO). The ESP zeroth-order channel observes the Sun as a star without
  spatial resolution in the wavelength range of 0.1 to 7.0 nm (the energy
  range is 0.18 to 12.4 keV). The amplitude spectrum of the oscillations,
  calculated from six-day time series, showed a significant increase in
  the frequency range of 2 to 4 mHz. This increase was interpreted as a
  response of the corona to solar acoustic (p) modes, and some p-mode
  frequencies among the strongest peaks were identified. In this work
  we show how these increases in the 2 to 4 mHz frequency range vary on
  a daily basis and compare this variability for quiet and intermediate
  levels of solar activity. We found that the increases do not correlate
  with the changes of daily mean irradiance or with the standard deviation
  of the irradiance.

---------------------------------------------------------
Title: Propagation and transformation of MHD waves in sunspots
Authors: Parchevsky, K. V.; Kosovichev, A. G.
2011sdmi.confE..46P    Altcode:
  It has long been suggested that the fast MHD waves (which are analog of
  the acoustic waves in non-magnetized regions) can convert into other
  types of MHD waves (slow MHD and/or Alfven waves) inside sunspots due
  to the interaction with the magnetic field. Transformed waves propagate
  in the deeper layers of the sunspot along the magnetic field lines,
  removing the energy from the observed wave field. Such mode conversion
  (if exists) will contribute to the suppression of the acoustic power
  inside the sunspots. Results of numerical simulations of interaction
  of MHD waves with magnetized areas show that the mode conversion
  occurs near the sunspot axis in regions where the wavefront of the
  fast MHD wave crosses the level where the plasma parameter beta is of
  order of unity. The transformed wave is primarily transverse. Detailed
  simulations show, that the transformed wave exists even in case where
  the source is located completely outside of the magnetic region, so
  the wave, which enters the model of the sunspot, is pure acoustic. To
  compare simulations of MHD waves in sunspots and observations we
  need to know at what geometrical depth this comparison has to be
  done. We propose a method of the wave amplitude and travel-time
  shortening corrections. Our method is based on the combination of
  three-dimensional numerical simulations of propagation of MHD waves
  with 1D LTE radiation transfer simulations of the Stokes profiles of
  the HMI line. For measuring the Doppler shift we use the same set
  of 6 narrow-band filters which is used by the HMI instrument. Such
  simulations will provide the artificial HMI level 1 data (if necessary,
  non-simultaneity of frames for different polarization channels can be
  simulated) which can test the whole Time-Distance Pipeline.

---------------------------------------------------------
Title: A Method for the Calculation of Acoustic Green's Functions
    for Use in Computing Frechet Traveltime Sensitivity Kernels
Authors: Schlottmann, R. B.; Kosovichev, A. G.
2011sdmi.confE..27S    Altcode:
  We have modified a semi-analytical approach, originally intended
  for the calculation of stellar acoustic normal modes, for use in
  the efficient calculation of Green's functions. The primary purpose
  of this code is to provide necessary acoustic responses in the
  calculation of Frechet traveltime sensitivity kernels. Assuming
  a spherically symmetric star in hydrostatic equilibrium and the
  Cowling approximation, we perform the usual spherical harmonic
  decomposition on the linearized acoustic wave equation, resulting in
  two coupled first-order ODEs in the radial displacement and Eulerian
  pressure. Following Gabriel &amp; Noels (1976), we break the radial
  domain into a finite number of non-uniformly spaced intervals within
  which we assume that the coefficients of the equations are constant. For
  each interval, we obtain a sum of two analytical solutions with unknown
  coefficients. Continuity of the fields yields a system of equations
  for the coefficients. However, instead of using this system to obtain
  eigenfunctions and eigenfrequencies, we instead solve it assuming a
  point source, yielding Green's functions for each frequency and degree,
  eliminating the usual need to sum a truncated series over mode order. We
  have made a couple of other modifications to the method to improve
  efficiency. First, the original system of equations is pentadiagonal,
  but these can be reduced analytically to a tridiagonal system, which
  is solved approximately 10 times faster. Next, using a technique from
  complex analysis, we are able to calculate, in the frequency domain,
  Green's functions that are windowed in time. This naturally spreads
  out the linewidths of the mode resonance peaks present in the Green's
  functions, allowing us to fully capture modes with very small linewidths
  without resorting to excessively fine sampling in frequency.

---------------------------------------------------------
Title: Effects of Turbulence Models on Self-Organization Processes
    in Solar Convection
Authors: Wray, A. A.; Mansour, N. N.; Rogachevskii, I.; Kleeorin,
   N.; Kitiashvili, I. N.; Kosovichev, A. G.
2011sdmi.confE...5W    Altcode:
  Realistic MHD numerical simulations of subsurface flows and magnetic
  structures have become achievable because of the development of fast
  supercomputer systems and efficient parallel computer codes. The
  dynamics of the subsurface layer is particularly critical for
  understanding the self-organization processes of magnetoconvection
  on different scales. Realistic simulations of solar convection
  in the presence of magnetic fields reveal very interesting
  dynamics and reproduce several phenomena observed in solar active
  regions. “SolarBox”, a 3-D real-gas radiative MHD code developed at
  NASA Ames, was used for our simulations. Because both the Reynolds and
  magnetic Reynolds numbers are extremely high, research into subgrid
  modeling of MHD in the solar context is essential, and an important
  feature of this code is the implementation of various subgrid-scale
  LES turbulence models. We present a comparison of two such models:
  a Smagorinskii-type subgrid resistivity model and the Turbulent
  Effective Lorentz Force model (TELF) and discuss the role of LES
  models for studying the process of magnetic flux tube formation and
  the turbulent properties of magnetoconvection.

---------------------------------------------------------
Title: Subphotospheric flows and evolution of active regions
Authors: Kosovichev, A. G.; Zhao, J.
2011sdmi.confE.102K    Altcode:
  The HMI instrument on SDO has provided unprecedented opportunities
  for studying the subsurface dynamics of active regions during
  their emergence and various stages of the evolution. We analyzed
  maps of subsurface flows, obtained by using the HMI time-distance
  helioseismology pipeline, in order to investigate links between the
  subsurface properties and surface magnetic structures, and also their
  relationships to flaring and CME activity for several interesting
  regions. The results reveal strong shearing and twisting flows during
  high-activity periods. We discuss how properties of the subphotospheric
  flows, such as divergence, vorticity and helicity, can characterize
  the evolution and activity of magnetic regions.

---------------------------------------------------------
Title: Mean-field Solar Dynamo Models with a Strong Meridional Flow
    at the Bottom of the Convection Zone
Authors: Pipin, V. V.; Kosovichev, A. G.
2011ApJ...738..104P    Altcode: 2011arXiv1104.1433P
  This paper presents a study of kinematic axisymmetric mean-field dynamo
  models for the case of meridional circulation with a deep-seated
  stagnation point and a strong return flow at the bottom of the
  convection zone. This kind of circulation follows from mean-field models
  of the angular momentum balance in the solar convection zone. The
  dynamo models include turbulent sources of the large-scale poloidal
  magnetic field production due to kinetic helicity and a combined effect
  due to the Coriolis force and large-scale electric current. In these
  models the toroidal magnetic field, which is responsible for sunspot
  production, is concentrated at the bottom of the convection zone and is
  transported to low-latitude regions by a meridional flow. The meridional
  component of the poloidal field is also concentrated at the bottom
  of the convection zone, while the radial component is concentrated
  in near-polar regions. We show that it is possible for this type
  of meridional circulation to construct kinematic dynamo models that
  resemble in some aspects the sunspot magnetic activity cycle. However,
  in the near-equatorial regions the phase relation between the toroidal
  and poloidal components disagrees with observations. We also show
  that the period of the magnetic cycle may not always monotonically
  decrease with the increase of the meridional flow speed. Thus, for
  further progress it is important to determine the structure of the
  meridional circulation, which is one of the critical properties,
  from helioseismology observations.

---------------------------------------------------------
Title: Observations of Five-minute Solar Oscillations in the Corona
    Using the Extreme Ultraviolet Spectrophotometer (ESP) On Board the
    Solar Dynamics Observatory Extreme Ultraviolet Variability Experiment
    (SDO/EVE)
Authors: Didkovsky, L.; Judge, D.; Kosovichev, A. G.; Wieman, S.;
   Woods, T.
2011ApJ...738L...7D    Altcode:
  We report on the detection of oscillations in the corona in the
  frequency range corresponding to five-minute acoustic modes of
  the Sun. The oscillations have been observed using soft X-ray
  measurements from the Extreme Ultraviolet Spectrophotometer (ESP)
  of the Extreme Ultraviolet Variability Experiment on board the Solar
  Dynamics Observatory. The ESP zeroth-order channel observes the
  Sun as a star without spatial resolution in the wavelength range
  of 0.1-7.0 nm (the energy range is 0.18-12.4 keV). The amplitude
  spectrum of the oscillations calculated from six-day time series
  shows a significant increase in the frequency range of 2-4 mHz. We
  interpret this increase as a response of the corona to solar acoustic
  (p) modes and attempt to identify p-mode frequencies among the strongest
  peaks. Due to strong variability of the amplitudes and frequencies of
  the five-minute oscillations in the corona, we study how the spectrum
  from two adjacent six-day time series combined together affects the
  number of peaks associated with the p-mode frequencies and their
  amplitudes. This study shows that five-minute oscillations of the
  Sun can be observed in the corona in variations of the soft X-ray
  emission. Further investigations of these oscillations may improve
  our understanding of the interaction of the oscillation modes with
  the solar atmosphere, and the interior-corona coupling, in general.

---------------------------------------------------------
Title: Comparison of numerical simulations and observations of
    helioseismic MHD waves in sunspots
Authors: Parchevsky, K. V.; Zhao, J.; Kosovichev, A. G.; Rempel, M.
2011IAUS..273..422P    Altcode:
  Numerical 3D simulations of MHD waves in magnetized regions
  with background flows are very important for the understanding of
  propagation and transformation of waves in sunspots. Such simulations
  provide artificial data for testing and calibration of helioseismic
  techniques used for analysis of data from space missions SOHO/MDI,
  SDO/HMI, and HINODE. We compare with helioseismic observations
  results of numerical simulations of MHD waves in different models
  of sunspots. The simulations of waves excited by a localized source
  provide a detailed picture of the interaction of the MHD waves with
  the magnetic field and background flows (deformation of the waveform,
  wave transformation, amplitude variations and anisotropy). The observed
  cross-covariance function represents an effective Green's function of
  helioseismic waves. As an initial step, we compare it with simulations
  of waves generated by a localized source. More thorough analysis
  implies using multiple sources and comparison of the observed and
  simulated cross-covariance functions. We plan to do such calculations
  in the nearest future. Both, the simulations and observations show
  that the wavefront inside the sunspot travels ahead of a reference
  “quiet Sun” wavefront, when the wave enters the sunspot. However,
  when the wave passes the sunspot, the time lag between the wavefronts
  becomes unnoticeable.

---------------------------------------------------------
Title: Numerical simulations of magnetic structures
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Wray, A. A.; Mansour,
   N. N.
2011IAUS..273..315K    Altcode:
  We use 3D radiative MHD simulations of the upper turbulent convection
  layer for investigation of physical mechanisms of formation of
  magnetic structures on the Sun. The simulations include all essential
  physical processes, and are based of the LES (Large-Eddy Simulations)
  approach for describing the sub-grid scale turbulence. The simulation
  domain covers the top layer of the convection zone and the lower
  atmosphere. The results reveal a process of spontaneous formation of
  stable magnetic structures from an initially weak vertical magnetic
  field, uniformly distributed in the simulation domain. The process
  starts concentration of magnetic patches at the boundaries of granular
  cells, which are subsequently merged together into a stable large-scale
  structure by converging downdrafts below the surface. The resulting
  structure represents a compact concentration of strong magnetic
  field, reaching 6 kG in the interior. It has a cluster-like internal
  structurization, and is maintained by strong downdrafts extending into
  the deep layers.

---------------------------------------------------------
Title: "Hare and Hounds" Tests of Helioseismic Holography
Authors: Birch, A. C.; Parchevsky, K. V.; Braun, D. C.; Kosovichev,
   A. G.
2011SoPh..272...11B    Altcode: 2011SoPh..tmp..315B; 2011SoPh..tmp..290B; 2011SoPh..tmp..257B;
   2011SoPh..tmp..188B
  We use the output of numerical wave-propagation simulations as synthetic
  data for "hare and hounds" tests of helioseismic holography. In
  the simple non-magnetic models examined here, we show that when the
  inversion method includes a consistent treatment of the filtering
  applied during the data analysis the inversions for the subsurface
  sound speed are qualitatively correct.

---------------------------------------------------------
Title: Detection of Emerging Sunspot Regions in the Solar Interior
Authors: Ilonidis, Stathis; Zhao, Junwei; Kosovichev, Alexander
2011Sci...333..993I    Altcode:
  Sunspots are regions where strong magnetic fields emerge from the solar
  interior and where major eruptive events occur. These energetic events
  can cause power outages, interrupt telecommunication and navigation
  services, and pose hazards to astronauts. We detected subsurface
  signatures of emerging sunspot regions before they appeared on the
  solar disc. Strong acoustic travel-time anomalies of an order of 12 to
  16 seconds were detected as deep as 65,000 kilometers. These anomalies
  were associated with magnetic structures that emerged with an average
  speed of 0.3 to 0.6 kilometer per second and caused high peaks in the
  photospheric magnetic flux rate 1 to 2 days after the detection of the
  anomalies. Thus, synoptic imaging of subsurface magnetic activity may
  allow anticipation of large sunspot regions before they become visible,
  improving space weather forecast.

---------------------------------------------------------
Title: Advances in Plasma Astrophysics (IAU S274)
Authors: Bonanno, Alfio; de Gouveia Dal Pino, Elisabete; Kosovichev,
   Alexander G.
2011IAUS..274.....B    Altcode:
  Preface; 1. Plasma astrophysics in the laboratory; 2. Interstellar,
  space and planetary plasmas; 3. Solar and stellar plasma; 4. Plasma
  around compact objects; 5. Observational and modelling programs for
  plasma astrophysics; 6. Plasmas in galaxies and galaxy clusters;
  7. Plasma astrophysics in numerical simulations; Author index;
  Object index.

---------------------------------------------------------
Title: Investigation of a sunspot complex by time-distance
    helioseismology
Authors: Kosovichev, A. G.; Duvall, T. L.
2011IAUS..273..320K    Altcode: 2011arXiv1102.3961K
  Sunspot regions often form complexes of activity that may live for
  several solar rotations, and represent a major component of the Sun's
  magnetic activity. It had been suggested that the close appearance of
  active regions in space and time might be related to common subsurface
  roots, or “nests” of activity. EUV images show that the active regions
  are magnetically connected in the corona, but subsurface connections
  have not been established. We investigate the subsurface structure and
  dynamics of a large complex of activity, NOAA 10987-10989, observed
  during the SOHO/MDI Dynamics run in March-April 2008, which was a
  part of the Whole Heliospheric Interval (WHI) campaign. The active
  regions in this complex appeared in a narrow latitudinal range,
  probably representing a subsurface toroidal flux tube. We use the
  MDI full-disk Dopplergrams to measure perturbations of travel times
  of acoustic waves traveling to various depths by using time-distance
  helioseismology, and obtain sound-speed and flow maps by inversion of
  the travel times. The subsurface flow maps show an interesting dynamics
  of decaying active regions with persistent shearing flows, which may be
  important for driving the flaring and CME activity, observed during the
  WHI campaign. Our analyses, including the seismic sound-speed inversion
  results and the distribution of deep-focus travel-time anomalies, gave
  indications of diverging roots of the magnetic structures, as could be
  expected from Ω-loop structures. However, no clear connection in the
  depth range of 0-48 Mm among the three active regions in this complex
  of activity was detected.

---------------------------------------------------------
Title: Helioseismic Response to the X2.2 Solar Flare of 2011
    February 15
Authors: Kosovichev, A. G.
2011ApJ...734L..15K    Altcode: 2011arXiv1105.0953K
  The X2.2-class solar flare of 2011 February 15 produced a powerful
  "sunquake" event, representing a helioseismic response to the
  flare impact in the solar photosphere, which was observed with the
  Helioseismic and Magnetic Imager (HMI) instrument on board the Solar
  Dynamics Observatory (SDO). The impulsively excited acoustic waves
  formed a compact wave packet traveling through the solar interior and
  appearing on the surface as expanding wave ripples. The initial flare
  impacts were observed in the form of compact and rapid variations
  of the Doppler velocity, line-of-sight magnetic field, and continuum
  intensity. These variations formed a typical two-ribbon flare structure,
  and are believed to be associated with thermal and hydrodynamic effects
  of high-energy particles heating the lower atmosphere. The analysis of
  the SDO/HMI and X-ray data from RHESSI shows that the helioseismic waves
  were initiated by the photospheric impact in the early impulsive phase,
  observed prior to the hard X-ray (50-100 keV) impulse, and were probably
  associated with atmospheric heating by relatively low-energy electrons
  (~6-50 keV) and heat flux transport. The impact caused a short motion
  in the sunspot penumbra prior to the appearance of the helioseismic
  wave. It is found that the helioseismic wave front traveling through a
  sunspot had a lower amplitude and was significantly delayed relative
  to the front traveling outside the spot. These observations open new
  perspectives for studying the flare photospheric impacts and for using
  the flare-excited waves for sunspot seismology.

---------------------------------------------------------
Title: Investigations of solar plasma in the interior and corona
    from Solar Dynamics Observatory
Authors: Kosovichev, A. G.
2011IAUS..274..287K    Altcode:
  The Sun is a plasma laboratory for astrophysics, which allows us to
  investigate many important phenomena in turbulent magnetized plasma
  in detail. Solar Dynamics Observatory (SDO) launched in February 2010
  provides unique information about plasma processes from the interior
  to the corona. The primary processes of magnetic field generation
  and formation of magnetic structures are hidden beneath the visible
  surface. Helioseismic diagnostics, based on observations and analysis
  of solar oscillations and waves, give insights into the physical
  processes in the solar interior and mechanisms of solar magnetic
  activity. In addition, simultaneous high-resolution multi-wavelength
  observations of the solar corona provide opportunity to investigate in
  unprecedented detail the coronal dynamics and links to the interior
  processes. These capabilities are illustrated by initial results on
  the large-scale dynamics of the Sun, the subsurface structure and
  dynamics of a sunspot and observations of a X-class solar flare.

---------------------------------------------------------
Title: Realistic MHD simulations of magnetic self-organization in
    solar plasma
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Wray, A. A.; Mansour,
   N. N.
2011IAUS..274..120K    Altcode:
  Filamentary structure is a fundamental property of the magnetized solar
  plasma. Recent high-resolution observations and numerical simulations
  have revealed close links between the filamentary structures and
  plasma dynamics in large-scale solar phenomena, such as sunspots and
  magnetic network. A new emerging paradigm is that the mechanisms
  of the filamentary structuring and large-scale organization are
  natural consequences of turbulent magnetoconvection on the Sun. We
  present results of 3D radiative MHD large-eddy simulations (LES) of
  magnetic structures in the turbulent convective boundary layer of the
  Sun. The results show how the initial relatively weak and uniformly
  distributed magnetic field forms the filamentary structures, which
  under certain conditions gets organized on larger scales, creating
  stable long-living magnetic structures. We discuss the physics of
  magnetic self-organization in the turbulent solar plasma, and compare
  the simulation results with observations.

---------------------------------------------------------
Title: High-resolution 3D Radiative MHD Simulations Of Turbulent
    Convection And Spectro-polarimetric Properties
Authors: Kitiashvili, Irina; Kosovichev, A. G.; Mansour, N. N.;
   Stenflo, J. O.; Wray, A. A.
2011SPD....42.1708K    Altcode: 2011BAAS..43S.1708K
  Realistic numerical simulations of solar magnetoconvection play a
  key role for our understanding of the basic physical phenomena in
  the subsurface convective boundary layer and the atmosphere. For the
  accurate modeling of the turbulent processes on the Sun it is important
  to perform the simulations with the highest possible resolution. Our
  results have revealed significant changes in properties of the
  turbulent motions when the resolution is increased. It is particularly
  interesting that small-scale vortex motions in the intergranular
  lanes become ubiquitous and strong, and play a critical role in the
  large-scale organization of the solar dynamics. For the comparison
  with observational data it is necessary to investigate relationships
  between the physical and spectro-polarimetric properties in various
  conditions of the quiet-Sun and magnetic regions, and model the observed
  parameters. By using the radiative line formation code, SPINOR/STOPRO,
  we have calculated the Stokes profiles and other characteristics
  for the spectral line of the Hinode/SOT and SDO/HMI instruments,
  and compared the simulation results with the observational data.

---------------------------------------------------------
Title: Helioseismic Measurements Of Meridional Flows In Artificial
    Data From 3d Numerical Simulations Of Wave Propagation In The
    Whole Sun
Authors: Hartlep, Thomas; Roth, M.; Doerr, H.; Zhao, J.; Kosovichev,
   A. G.
2011SPD....42.1611H    Altcode: 2011BAAS..43S.1611H
  Measuring the structure of the deep solar interior is of considerable
  interest for understanding how the solar dynamo functions. In
  particular, the structure of the meridional flow and the depth of
  its return flow are of significant interest. Detecting such small
  flows in the deep interior is a challenging problem. Numerical
  simulations can provide means for testing and calibrating measurement
  techniques and help increase our confidence in the inferences obtained
  from observations. We present results from analyzing artificial
  helioseismology data obtained from numerical simulations of helioseismic
  wave propagation in the whole 3D solar interior with models of the
  meridional circulation present in the background state. Two methods
  - a time-distance helioseismology technique and a Fourier-Legendre
  decomposition technique - are used in this paper to try to detect and
  measure this flow from the oscillations at the solar surface.

---------------------------------------------------------
Title: The Waldmeier Effect and Asymmetry of Solar Magnetic Cycles
    in a Surface-Shear Dynamo Model
Authors: Pipin, Valery; Kosovichev, A.
2011SPD....42.0202P    Altcode: 2011BAAS..43S.0202P
  We present a study of solar dynamo model distributed in the bulk of
  the convection zone with toroidal magnetic-field flux concentrated in
  a near-surface layer. We explore how this effect may depend on spatial
  variations of the turbulent parameters and the differential rotation
  near the surface. The model includes the magnetic helicity non-linear
  feedback on the dynamo alpha-effect. We compute the magnetic cycle
  characteristics predicted by the model, including the cycle skewness
  (associated with duration of the growth and decay phases) and the
  duration-strength dependence (Waldmeier's effects). We confront the
  theoretical expectations with the solar sunspot cycle properties.

---------------------------------------------------------
Title: A Mechanism of the Solar Acoustic Emission
Authors: Kitiashvili, Irina; Kosovichev, A. G.; Lele, S. K.; Mansour,
   N. N.; Wray, A. A.
2011SPD....42.1701K    Altcode: 2011BAAS..43S.1701K
  Understanding the mechanism of acoustic waves excitation in the
  turbulent surface layer is very important for the interpretation of
  helioseismology data and development of new methods of helioseismic
  diagnostics of the solar interior, as well as for understanding of
  the role of the acoustic flux in the energy transport. A substantial
  progress is being made from the analysis of high-resolution
  observational data, particularly from Hinode, Sunrise, and SDO/HMI,
  and also from high-resolution realistic numerical simulations. The
  simulations take into account all essential turbulent and other
  physical properties of the solar plasma, and allow us to look at the
  scales that cannot be resolved in observations, and also compare the
  data and models. We present new results of 3D radiative hydrodynamics
  simulations of the upper convection zone and atmosphere, and show that
  one of the possible mechanisms of the acoustic waves generation is a
  result of interaction two and more vortex tubes. The process of a vortex
  annihilation, which produces acoustic waves, the properties of these
  waves and vortices, and comparison with the available observational
  data will be discussed.

---------------------------------------------------------
Title: Subsurface Structure and Dynamics of Active Regions Observed
    with SDO/HMI
Authors: Kosovichev, Alexander G.; Zhao, J.
2011SPD....42.2110K    Altcode: 2011BAAS..43S.2110K
  The HMI instrument on SDO has provided unprecedented opportunities
  to investigate the subsurface evolution of active regions. We use
  maps of subsurface flows and wave-speed perturbations, obtained
  using the HMI time-distance helioseismology pipeline, to study links
  between the subsurface properties and surface magnetic structures,
  and their relationships to the flaring and CME activity for several
  interesting active regions. A particular attention is paid to AR1158,
  which produced X2.2 flare.

---------------------------------------------------------
Title: Flare-excited Waves in the Solar Interior and Atmosphere
Authors: Kosovichev, Alexander G.
2011SPD....42.2107K    Altcode: 2011BAAS..43S.2107K
  The X2.2 flare of February 15, 2011, produced powerful waves traveling
  in the solar interior and atmosphere, which were observed with the HMI
  and AIA instruments on SDO. These data provide a unique opportunity
  for high-resolution spatial and spectral analyses of the helioseismic
  and atmospheric responses and their relationship to the flare energy
  release. In particular, the analysis of the SDO/HMI and X-ray data
  from RHESSI shows that the helioseismic waves were initiated by the
  photospheric impact in the early impulsive phase, observed prior to
  the hard X-ray (50-100 keV) impulse, and were probably associated with
  atmospheric heating by relatively low-energy electrons (6-50 keV) and
  heat flux transport. The impact caused a short wave-like motion in the
  sunspot penumbra prior to the appearance of the helioseismic wave. The
  AIA observations revealed for the first time the propagation of this
  wave in the upper atmosphere, and the accompanying shock wave. The
  multi-instrument observations of the flare-excited waves open new
  perspectives for studying the energy release and transport in solar
  flares, and also for the magnetic field seismology in active regions.

---------------------------------------------------------
Title: MHD Wave Transformation and Radiation Transfer Simulations
    in Sunspots
Authors: Parchevsky, Konstantin; Kosovichev, A.
2011SPD....42.1707P    Altcode: 2011BAAS..43S.1707P
  We present results of resonant wave transformation in MHD models of
  sunspot. Numerical 3D MHD simulations of waves excited by subsurface
  point sources and traveling through the sunspot models reveal details
  of the MHD mode conversion, which happens in the regions where the
  wavefront crosses the level where the plasma parameter β is of the
  order of unity. In particular, the wave transformation produces
  slow MHD waves traveling predominantly along the magnetic lines
  in the central part of sunspot. This process is clearly seen when
  plotted as a projection of velocity (and magnetic field) variations
  along and perpendicular to the local direction of the magnetic field
  lines. Detailed simulations show that the transformed wave appears
  even in the case where the source is located completely outside the
  magnetic region, so that when the initial wave is pure acoustic. To
  investigate the wave amplitude and travel-time corrections due to
  the variations of thermodynamic properties and magnetic effects in
  sunspots we apply the 1D LTE radiation transfer code SPINOR/STOPRO to
  the wave simulation results. This permits us to simulate the profile
  of the HMI Fe6173A spectral line, and model the HMI observations of
  the line-of-sight velocity and magnetic field, and also the Stokes
  profiles. For calculation of the observables we use the same set of 6
  narrow-band filters as used in the HMI instrument. Such simulations
  provide artificial HMI level-1 data for testing helioseismology
  measurements in sunspots and magnetic active regions.

---------------------------------------------------------
Title: Solar Subsurface Dynamics from the First Year of SDO/HMI
    Time-Distance Helioseismology Analysis
Authors: Zhao, Junwei; Bogart, R. S.; Kosovichev, A. G.; Nagashima, K.
2011SPD....42.2131Z    Altcode: 2011BAAS..43S.2131Z
  It has been about one year since SDO/HMI started to take continuous
  observations of the Sun. Time-distance pipeline designed for a routine
  processing of HMI observations has generated plenty of results. We
  will present the solar interior rotational rate and meridional flow
  speed and their evolution during the entire year. For local areas,
  we study the subsurface flows of supergranules and some selected
  active regions. We also apply the time-distance analysis in higher
  latitude areas, and study the rotational and meridional speed above
  the latitude of 65 degree.

---------------------------------------------------------
Title: Analysis of SOHO/MDI and TRACE Observations of Sunspot
    Torsional Oscillation in AR10421
Authors: Gopasyuk, O. S.; Kosovichev, A. G.
2011ApJ...729...95G    Altcode: 2011arXiv1102.3953G
  Rotation of the leading sunspot of active region NOAA 10421 was
  investigated using magnetograms and Dopplergrams from the MDI instrument
  of the Solar and Heliospheric Observatory, and white-light images
  from the Transition Region and Coronal Explorer (TRACE). The vertical,
  radial, and azimuthal axisymmetrical components of both magnetic and
  velocity field vectors were reconstructed for the sunspot umbra and
  penumbra. All three components of both vectors in the umbra and penumbra
  show torsional oscillations with the same rotational period of about
  3.8 days. The TRACE white-light data also show that the sunspot umbra
  and penumbra are torsionally rotating with the same period. Possible
  mechanisms of sunspot torsional motions are discussed.

---------------------------------------------------------
Title: Signatures of Emerging Subsurface Structures in Acoustic
    Power Maps of the Sun
Authors: Hartlep, T.; Kosovichev, A. G.; Zhao, J.; Mansour, N. N.
2011SoPh..268..321H    Altcode: 2010arXiv1003.4305H
  We show that under certain conditions, subsurface structures in
  the solar interior can alter the average acoustic power observed at
  the photosphere above them. By using numerical simulations of wave
  propagation, we show that this effect is large enough for it to be
  potentially used for detecting emerging active regions before they
  appear on the surface. In our simulations, simplified subsurface
  structures are modeled as regions with enhanced or reduced acoustic
  wave speed. We investigate the dependence of the acoustic power
  above a subsurface region on the sign, depth, and strength of the
  wave-speed perturbation. Observations from the Solar and Heliospheric
  Observatory/Michelson Doppler Imager (SOHO/MDI) prior and during the
  emergence of NOAA active region 10488 are used to test the use of
  acoustic power as a potential precursor of the emergence of magnetic
  flux.

---------------------------------------------------------
Title: A brief history of the solar oblateness. A review
Authors: Damiani, C.; Rozelot, J. P.; Lefebvre, S.; Kilcik, A.;
   Kosovichev, A. G.
2011JASTP..73..241D    Altcode:
  We hereby present a review on solar oblateness measurements. By
  emphasizing historical data, we illustrate how the discordance between
  experimental results can lead to substantial improvements in the
  building of new technical apparatus as well as to the emergence of new
  ideas to develop new theories. We stress out the need to get accurate
  data from space to enhance our knowledge of the solar core in order
  to develop more precise ephemerids and ultimately build possible new
  gravitational theories.

---------------------------------------------------------
Title: Numerical MHD Simulations of Solar Magnetoconvection and
    Oscillations in Inclined Magnetic Field Regions
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Mansour, N. N.; Wray,
   A. A.
2011SoPh..268..283K    Altcode: 2010SoPh..tmp..239K; 2010arXiv1011.5527K
  The sunspot penumbra is a transition zone between the strong vertical
  magnetic field area (sunspot umbra) and the quiet Sun. The penumbra
  has a fine filamentary structure that is characterized by magnetic
  field lines inclined toward the surface. Numerical simulations of
  solar convection in inclined magnetic field regions have provided an
  explanation of the filamentary structure and the Evershed outflow in
  the penumbra. In this article, we use radiative MHD simulations to
  investigate the influence of the magnetic field inclination on the
  power spectrum of vertical velocity oscillations. The results reveal a
  strong shift of the resonance mode peaks to higher frequencies in the
  case of a highly inclined magnetic field. The frequency shift for the
  inclined field is significantly greater than that in vertical-field
  regions of similar strength. This is consistent with the behavior of
  fast MHD waves.

---------------------------------------------------------
Title: Toward Waveform Heliotomography: Observing Interactions of
    Helioseismic Waves with a Sunspot
Authors: Zhao, Junwei; Kosovichev, Alexander G.; Ilonidis, Stathis
2011SoPh..268..429Z    Altcode: 2010arXiv1011.3837Z; 2010SoPh..tmp..240Z
  We investigate how helioseismic waves that originate from effective
  point sources interact with a sunspot. These waves are reconstructed
  from observed stochastic wavefields on the Sun by cross-correlating
  photospheric Doppler-velocity signals. We select the wave sources at
  different locations relative to the sunspot, and investigate the p-
  and f-mode waves separately. The results reveal a complicated picture
  of waveform perturbations caused by the wave interaction with the
  sunspot. In particular, it is found that for waves originating from
  outside of the sunspot, p-mode waves travel across the sunspot with a
  small amplitude reduction and slightly higher speed, and wave amplitude
  and phase get mostly restored to the quiet-Sun values after passing the
  sunspot. The f-mode wave experiences some amplitude reduction passing
  through the sunspot, and the reduced amplitude is not recovered after
  that. The wave-propagation speed does not change before encountering
  the sunspot and inside the sunspot, but the wavefront becomes faster
  than the reference wave after passing through the sunspot. For
  waves originating from inside the sunspot umbra, both f- and p-mode
  waves show significant amplitude reductions and faster speed for all
  propagation paths. A comparison of positive and negative time lags
  of cross-correlation functions shows an apparent asymmetry in the
  waveform changes for both the f- and p-mode waves. We suggest that the
  waveform variations of the helioseismic waves interacting with a sunspot
  found in this article can be used for developing a method of waveform
  heliotomography, similar to the waveform tomography of the Earth.

---------------------------------------------------------
Title: LES of turbulent convection in solar-type stars and formation
    of large-scale magnetic structures
Authors: Rogachevskii, I.; Kleeorin, N.; Kitiashvili, I. N.;
   Kosovichev, A. G.; Wray, A. A.; Mansour, N. N.
2011arXiv1102.1206R    Altcode:
  In this study we investigate the effects of turbulent convection on
  formation of large-scale inhomogeneous magnetic structures by means of
  Large-Eddy Simulation (LES) for convection in solar-type stars. The
  main idea of this study is the implementation of a new subgrid-scale
  model for the effective Lorentz force in a three-dimensional nonlinear
  radiative magnetohydrodynamics (MHD) code developed for simulating
  the upper solar convection zone and lower atmosphere. To this end we
  derived the energy budget equations, which include the effects of the
  subgrid-scale turbulence on the Lorentz-force, and implemented the
  new subgrid-scale turbulence model (TELF-Model) in a three-dimensional
  nonlinear MHD LES code. Using imposed initial vertical and horizontal
  uniform magnetic fields in LES with the TELF-Model, we have shown that
  the magnetic flux tubes formation is started when the initial mean
  magnetic field is larger than a threshold value (about 100 G). This is
  in agreement with the theoretical studies by Rogachevskii and Kleeorin
  (2007). We have determined the vertical profiles of the velocity and
  magnetic fluctuations, total MHD energy and anisotropy of turbulent
  magneto-convection, kinetic and current and cross helicities.

---------------------------------------------------------
Title: Excitation of Acoustic Waves by Vortices in the Quiet Sun
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Mansour, N. N.; Wray,
   A. A.
2011ApJ...727L..50K    Altcode: 2010arXiv1011.3775K
  The five-minute oscillations are one of the basic properties of solar
  convection. Observations show a mixture of a large number of acoustic
  wave fronts propagating from their sources. We investigate the process
  of acoustic waves excitation from the point of view of individual
  events, by using a realistic three-dimensional radiative hydrodynamic
  simulation of the quiet Sun. The results show that the excitation events
  are related to the dynamics of vortex tubes (or swirls) in intergranular
  lanes of solar convection. These whirlpool-like flows are characterized
  by very strong horizontal velocities (7-11 km s<SUP>-1</SUP>) and
  downflows (≈7 km s<SUP>-1</SUP>), and are accompanied by strong
  decreases of temperature, density, and pressure at the surface and
  0.5-1 Mm below the surface. High-speed whirlpool flows can attract
  and capture other vortices. According to our simulation results the
  processes of vortex interaction, such as vortex annihilation, can
  cause excitation of acoustic waves on the Sun.

---------------------------------------------------------
Title: The Subsurface-shear-shaped Solar αΩ Dynamo
Authors: Pipin, V. V.; Kosovichev, A. G.
2011ApJ...727L..45P    Altcode: 2010arXiv1011.4276P
  We propose a solar dynamo model distributed in the bulk of the
  convection zone with toroidal magnetic-field flux concentrated in a
  near-surface layer. We show that if the boundary conditions at the top
  of the dynamo region allow the large-scale toroidal magnetic fields to
  penetrate close to the surface, then the modeled butterfly diagram for
  the toroidal magnetic field in the upper convection zone is formed by
  the subsurface rotational shear layer. The model is in agreement with
  observed properties of the magnetic solar cycle.

---------------------------------------------------------
Title: First Sunquake of Solar Cycle 24 Observed by Solar Dynamics
    Observatory
Authors: Kosovichev, A. G.
2011arXiv1102.3954K    Altcode:
  The X2.2-class solar flare of February 15, 2011, produced a powerful
  `sunquake' event, representing a seismic response to the flare
  impact. The impulsively excited seismic waves formed a compact
  wavepacket traveling through the solar interior and appeared on the
  surface as expanding wave ripples. The Helioseismic and Magnetic Imager
  (HMI), instrument on SDO, observes variations of intensity, magnetic
  field and plasma velocity (Dopplergrams) on the surface of Sun almost
  uninterruptedly with high resolution (0.5 arcsec/pixel) and high cadence
  (45 sec). The flare impact on the solar surface was observed in the
  form of compact and rapid variations of the HMI observables (Doppler
  velocity, line-of-sight magnetic field and continuum intensity). These
  variations, caused by the impact of high-energy particles in the
  photosphere, formed a typical two-ribbon flare structure. The sunquake
  can be easily seen in the raw Dopplergram differences without any
  special data processing. The source of this quake was located near the
  outer boundary of a very complicated complicated sunspot region, NOAA
  1158, in a sunspot penumbra and at the penumbra boundary. This caused
  an interesting plasma dynamics in the impact region. I present some
  preliminary results of analysis of the near-real-time data from HMI,
  and discuss properties of the sunquake and the flare impact sources.

---------------------------------------------------------
Title: HMI time-distance pipeline: An overview and data products
Authors: Zhao, J.; Couvidat, S.; Bogart, R. S.; Duvall, T. L., Jr.;
   Kosovichev, A. G.; Beck, J. G.; Birch, A. C.
2011JPhCS.271a2063Z    Altcode:
  The Helioseismic and Magnetic Imager onboard Solar Dynamics
  Observatory provides uninterrupted high-resolution observations of solar
  oscillations over the entire disk. This gives a unique opportunity for
  mapping subsurface flows and wave-speed structures and investigating
  their role in the Sun's dynamics and magnetic activity on various
  scales by methods of local helioseismology. A data analysis pipeline
  for the time-distance helioseismology analysis has been developed
  and implemented at the SDO Joint Science Operation Center (JSOC) at
  Stanford. It provides near-real time processing of the helioseismology
  data. We provide an overview of this pipeline, including the data flow
  procedures, measurement and inversion codes, and our data products.

---------------------------------------------------------
Title: Modeling and Prediction of Solar Cycles Using Data Assimilation
    Methods
Authors: Kitiashvili, Irina N.; Kosovichev, Alexander G.
2011LNP...832..121K    Altcode:
  Variations of solar activity are a result of a complicate dynamo process
  in the convection zone. We consider this phenomenon in the context
  of sunspot number variations, which have detailed observational data
  during the past 23 solar cycles. However, despite the known general
  properties of the solar cycles a reliable forecast of the 11-year
  sunspot number is still a problem. The main reasons are imperfect
  dynamo models and deficiency of the necessary observational data. To
  solve this problem we propose to use data assimilation methods. These
  methods combine observational data and models for best possible,
  efficient and accurate estimates of physical properties that cannot be
  observed directly. The methods are capable of providing a forecast of
  the system future state. It is demonstrated that the Ensemble Kalman
  Filter (EnKF) method can be used to assimilate the sunspot number data
  into a non-linear α{-}Upomega mean-field dynamo model, which takes
  into account dynamics of turbulent magnetic helicity. We apply this
  method for characterization of the solar dynamo properties and for
  prediction of the sunspot number.

---------------------------------------------------------
Title: Advances in Global and Local Helioseismology: An Introductory
    Review
Authors: Kosovichev, Alexander G.
2011LNP...832....3K    Altcode: 2011arXiv1103.1707K
  Helioseismology studies the structure and dynamics of the Sun's interior
  by observing oscillations on the surface. These studies provide
  information about the physical processes that control the evolution
  and magnetic activity of the Sun. In recent years, helioseismology has
  made substantial progress towards the understanding of the physics of
  solar oscillations and the physical processes inside the Sun, thanks to
  observational, theoretical and modeling efforts. In addition to global
  seismology of the Sun based on measurements of global oscillation modes,
  a new field of local helioseismology, which studies oscillation travel
  times and local frequency shifts, has been developed. It is capable
  of providing 3D images of subsurface structures and flows. The basic
  principles, recent advances and perspectives of global and local
  helioseismology are reviewed in this article.

---------------------------------------------------------
Title: Detection of Supergranulation Alignment in Polar Regions of
    the Sun by Helioseismology
Authors: Nagashima, Kaori; Zhao, Junwei; Kosovichev, Alexander G.;
   Sekii, Takashi
2011ApJ...726L..17N    Altcode: 2010arXiv1011.1025N
  We report on a new phenomenon of "alignment" of supergranulation cells
  in the polar regions of the Sun. Recent high-resolution data sets
  obtained by the Solar Optical Telescope on board the Hinode satellite
  enabled us to investigate supergranular structures in high-latitude
  regions of the Sun. We have carried out a local helioseismology
  time-distance analysis of the data and detected acoustic travel-time
  variations due to the supergranular flows. The supergranulation cells
  in both the north and south polar regions show systematic alignment
  patterns in the north-south direction. The south-pole data sets obtained
  in a month-long Hinode campaign indicate that the supergranulation
  alignment property may be quite common in the polar regions. We also
  discuss the latitudinal dependence of the supergranulation cell sizes;
  the data show that the east-west cell size decreases toward higher
  latitudes.

---------------------------------------------------------
Title: Local helioseismology of sunspot regions: Comparison of
    ring-diagram and time-distance results
Authors: Kosovichev, A. G.; Basu, S.; Bogart, R.; Duvall, T. L., Jr.;
   Gonzalez-Hernandez, I.; Haber, D.; Hartlep, T.; Howe, R.; Komm, R.;
   Kholikov, S.; Parchevsky, K. V.; Tripathy, S.; Zhao, J.
2011JPhCS.271a2005K    Altcode: 2010arXiv1011.0799K
  Local helioseismology provides unique information about the subsurface
  structure and dynamics of sunspots and active regions. However,
  because of complexity of sunspot regions local helioseismology
  diagnostics require careful analysis of systematic uncertainties
  and physical interpretation of the inversion results. We present new
  results of comparison of the ring-diagram analysis and time-distance
  helioseismology for active region NOAA 9787, for which a previous
  comparison showed significant differences in the subsurface sound-speed
  structure, and discuss systematic uncertainties of the measurements
  and inversions. Our results show that both the ring-diagram and
  time-distance techniques give qualitatively similar results, revealing
  a characteristic two-layer seismic sound-speed structure consistent
  with the results for other active regions. However, a quantitative
  comparison of the inversion results is not straightforward. It must
  take into account differences in the sensitivity, spatial resolution
  and the averaging kernels. In particular, because of the acoustic
  power suppression, the contribution of the sunspot seismic structure
  to the ring-diagram signal can be substantially reduced. We show that
  taking into account this effect reduces the difference in the depth
  of transition between the negative and positive sound-speed variations
  inferred by these methods. Further detailed analysis of the sensitivity,
  resolution and averaging properties of the local helioseismology methods
  is necessary for consolidation of the inversion results. It seems to
  be important that both methods indicate that the seismic structure of
  sunspots is rather deep and extends to at least 20 Mm below the surface,
  putting constraints on theoretical models of sunspots.

---------------------------------------------------------
Title: Subsurface structure of the Evershed flows in sunspots
Authors: Kitiashvili, Irina N.; Kosovichev, Alexander G.; Mansour,
   Nagi N.; Wray, Alan A.
2011JPhCS.271a2076K    Altcode:
  The radial outflows in sunspot penumbrae, known as the Evershed
  effect, are of significant interest for understanding the dynamics
  of sunspots. Local helioseismology has not been able to determine
  the depth of these flows nor their relationship to mass circulation
  in sunspots. Recent radiative MHD simulations have provided a
  convincing explanation of the Evershed flow as a natural consequence
  of magnetoconvection in the strongly inclined magnetic field region of
  the penumbra. The simulations reproduce many observational features of
  penumbra dynamics, including the filamentary structure, the high-speed
  non-stationary "Evershed clouds", and the "sea-serpent" behavior
  of magnetic field lines. We present the subsurface structure of the
  Evershed effect, obtained from numerical simulations, and determine the
  depth of the radial outflows for various magnetic field strengths and
  inclinations. The simulations predict that Evershed flows are rather
  shallow and concentrated in the top 0.5 - 1 Mm layer of the convection
  zone. This prediction can be tested by local helioseismology methods.

---------------------------------------------------------
Title: Helioseismology Study of Subsurface Dynamics in the Polar
    Regions of the Sun
Authors: Nagashima, K.; Zhao, J.; Kosovichev, A. G.; Sekii, T.
2010AGUFM.S32A..03N    Altcode:
  We report on our time-distance helioseismology study of the
  subsurface dynamics in the polar regions of the Sun. It is generally
  difficult to observe the polar regions in details because of severe
  foreshortening. The high-resolution data obtained by Solar Optical
  Telescope (SOT) onboard the Hinode satellite, however, enabled
  us to investigate dynamics in the regions with up to 80 degrees
  in latitude. The measurements are obtained by calculating the
  cross-covariance function of the random solar oscillations observed
  as fluctuations of intensity of the Ca II H line, and by fitting a
  Gabor-wavelet function for estimating the phase and group travel times
  of solar acoustic waves. We obtain the maps of subsurface velocity field
  by inverting the differences of the phase travel times, calculated for
  the cross-correlations with positive and negative lag times, using a
  ray-path approximation. Among the subsurface dynamical processes in the
  polar region, we focus on supergranulation in this study. Supergranules
  are thought to be one of convective cells in the convective envelope
  of the Sun. Typical temporal and spatial scales of supergranular cells
  are 1 day and 30 Mm, respectively. The supergranulation is considered
  to play important roles in the magnetic flux transport and formation
  of the magnetic network. However, we still do not have sufficient
  knowledge of their origin and properties. In our study, we have observed
  a curious alignment of the supergranular cells in the polar regions
  approximately in the North-South direction. The alignment was seen
  in both northern and southern polar regions. We discuss properties
  and temporal evolution of the supergranular structures in the region,
  as well as the possibilities of measuring the differential rotation
  and meridional flows in the polar regions, which are critical for the
  solar dynamo theories.

---------------------------------------------------------
Title: Initial Analysis of the Solar Dynamics Observatory Radiation
    Environment
Authors: Vafai, A. D.; Close, S.; Kosovichev, A. G.; Stern, R. A.
2010AGUFMSH23C1875V    Altcode:
  The purpose of this poster is to explain the method used to extract data
  from images sent by the Solar Dynamics Observatory (SDO) to investigate
  patterns of cosmic rays and electron fluxes in space. For this study we
  analyze cosmic ray and X-ray hits in the corners of the AIA images. The
  X-rays are produced by high-energy electrons in the outer radiation
  belts interacting with the shielding/instrument/spacecraft. In the past
  twenty years, several spacecraft in geosynchronous and geostationary
  orbits have suffered mechanical and systems damage that are believed
  to be caused by energetic protons and electrons. Using Dark Image data
  from the GOES-13 spacecraft, the number of X-ray hits per day show a
  variation correlated with the GOES-12 high energy electron fluxes. We
  demonstrate how the SDO/AIA images are used to study this behavior. We
  also provide an overview on methods used to distinguish cosmic rays
  hits from X-ray detections within an image.

---------------------------------------------------------
Title: Validating Helioseismic Imaging Techniques using 3D Global-Sun
    Simulations of Helioseismic Wave Propagation
Authors: Hartlep, T.; Zhao, J.; Kosovichev, A. G.; Mansour, N. N.
2010AGUFM.S32A..05H    Altcode:
  Significant advancements in our understanding of the interior
  structure and dynamics of the Sun have been made by studying solar
  oscillation. Waves, randomly excited by the vigorous convective flows
  near the solar surface, propagate through the interior where they
  are affected by inhomogeneities such as flows and local temperature
  variations. Local helioseismology tries to infer the properties of
  these inhomogeneities by analyzing the observed waves field near
  the solar photosphere. In general, such inferences are based on
  more or less simplified models of wave propagation in the Sun. For
  correct interpretation of helioseismic measurements and for testing
  and validating inversion techniques, numerical simulation of wave
  propagation play a crucial role. We present result from testing
  various local helioseismology techniques using numerical simulation
  of wave propagation in global-Sun models. Our simulation code solves
  the time-dependent linearized wave propagation problem in a full
  spherical model and takes into account mass flows as well as sound
  speed variations. We present results from testing time-distance
  helioseismology far-side imaging and imaging of the solar tachocline,
  results from with active regions and subsurface regions, differential
  rotation, and meridional flows. Datasets are available for download
  at the included URL.

---------------------------------------------------------
Title: Interaction of MHD Waves with Sunspots
Authors: Parchevsky, K.; Zhao, J.; Kosovichev, A. G.; Rempel, M.
2010AGUFM.S32A..07P    Altcode:
  Understanding of MHD wave propagation, transformation and scattering
  by sunspots and their interaction with the non-uniform background
  magnetic field and flows is very important for improving helioseismic
  inversion procedures. Such simulations also provide artificial data
  for testitng and calibration techniques used for analysis of data from
  space missions SOHO/MDI, SDO/HMI, and HINODE. We developed 3D linear MHD
  code for numerical simulation of excitation and propagation of MHD waves
  in non-uniform medium in presence of the background magnetic field and
  flows. We present simulations of MHD wave propagation in magnetostatic
  and dynamic models of sunspots. We consider separately two cases when
  the waves are excited by point sources, located at different distances
  from the spot, and by stochastic noise source. The results are compared
  with the waveforms of the cross-correlation function extracted from
  the observational data. We discuss the differences between the models
  and observations in terms of the amplitude variations and travel-time
  shifts. Comparison of the simulations with helioseismic observations
  allows us to test the sunspot and helioseismic models, and suggest
  improvements. The numerically simulated helioseismic data are publicly
  accessible for the helioseismic community for testing and verification
  of various ambient noise imaging techniques of helioseismology
  (time-distance, holography, and ring diagrams).

---------------------------------------------------------
Title: Initial Results from SDO/HMI Time-Distance Helioseismology
    Data Analysis Pipeline
Authors: Zhao, J.; Bogart, R. S.; Couvidat, S. P.; Duvall, T. L.;
   Birch, A. C.; Parchevsky, K.; Kosovichev, A. G.; Beck, J. G.
2010AGUFMSH14A..08Z    Altcode:
  The Helioseismic and Magnetic Imager on Solar Dynamics Observatory
  provides uninterrupted high-resolution observations of solar
  oscillations over the entire disk. Time-distance helioseismology
  data analysis pipeline was developed to perform a near real-time
  analysis of these observations, and provide full-disk subsurface flow
  fields and wave-speed perturbation maps every 8 hours. These routine
  productions give us substantial information of the solar interior,
  and are very useful to study the solar interior dynamics, connections
  between subsurface dynamics and photospheric activities, and solar
  large-scale and global-scale flows and structures. We present our
  initial results in these respects.

---------------------------------------------------------
Title: Investigation of Formation and Subsurface Dynamics of Active
    Regions by Local Helioseismology from SDO
Authors: Kosovichev, A. G.; Duvall, T. L.; Zhao, J.
2010AGUFMSH11A1604K    Altcode:
  Despite a long history of observations of sunspots and active
  regions the mechanisms of their formation and stability are still a
  puzzle. These mechanisms are controlled by a complex interaction of
  magnetic fields and turbulent convection below the solar surface. The
  helioseismology observations on SOHO/MDI have provided snapshots of the
  subsurface dynamics during formation and evolution of several active
  regions and sunspots. They showed substantial changes in the structure
  and flow patterns at various stages of the evolution and flaring
  activity. However, the MDI data were too fragmented for systematic
  studies. The Helioseismic and Magnetic Imager (HMI) on SDO gives us a
  unique opportunity for detailed high-resolution investigations of the
  subsurface structures and mass flows associated with the formation and
  life cycle of active regions. We present the results of the initial
  analysis of magnetic active regions by time-distance helioseismology
  of the HMI Doppler-shift data. These include some interesting events,
  previously not investigated by helioseismology, such as splitting of a
  sunspot into two separate spot and formation of penumbra. We discuss
  also the capabilities of SDO for time-distance helioseismology,
  current uncertainties, and potentials based on the initial experience.

---------------------------------------------------------
Title: Realistic MHD Simulations of Formation of Sunspot-like
    Structures and Comparison with Observations
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Mansour, N. N.; Wray,
   A. A.
2010AGUFMSH31A1782K    Altcode:
  The process of formation of magnetic structures such as sunspot and
  pores in the turbulent convection zone is still enigma. However,
  the recent progress in numerical radiative MHD simulations provides
  clues about the possible mechanism of magnetic field accumulation in
  spontaneously formed stable structures. Implementation of sub-grid
  turbulent models in our "SolarBox" code, gives us the possibility
  to model more accurately turbulent properties, and reproduce the
  dynamics of the magnetized plasma. The code takes into account
  non-ideal (tabular) EOS, effects of ionization, chemical composition,
  radiation, turbulence and magnetic field. Our simulation results show
  an important role of vortices, which create local cavity of pressure
  and are associated with strong converging flows under the surface,
  during the initial stage of the spontaneous structure formation. The
  resulting structure represents a compact self-organized concentration
  of strong magnetic field, reaching ~6 kG in the interior, and ~1.5 kG
  on the surface. It has a cluster-like internal structurization, and
  is maintained by strong downdrafts extending into the deep layers. We
  discuss the role of turbulent MHD dynamics in this mechanism, and
  compare the simulation results with observations of the sunspot
  formation process during a magnetic flux emergence, from the Solar
  Dynamics Observatory and Hinode.

---------------------------------------------------------
Title: Cross-helicity turbulence model: Application to MHD phenomena
    from solar convection zone to heliosphere
Authors: Yokoi, N.; Kitiashvili, I. N.; Kosovichev, A. G.
2010AGUFMSH31A1793Y    Altcode:
  Cross helicity (velocity-magnetic field correlation) is expected
  to play a key role in several geo/astrophysical processes including
  dynamo action, suppression of turbulent transport, etc. We discuss the
  relevance of the cross-helicity effects with the aid of the turbulence
  model. A turbulence model with the cross-helicity effects incorporated
  may be called the “cross-helicity turbulence model”. This model is
  applied to several MHD phenomena ranging from the formations of magnetic
  fields and plasma motions in the solar convection zone to the solar-wind
  evolution in the heliosphere. Generation of turbulence quantities
  depends on the inhomogeneity of large-scale fields, and turbulence
  in turn determines the configuration of the mean fields through the
  turbulent transport. Such nonlinear interactions between the mean- and
  fluctuation-fields are explored with the aid of numerical simulations
  with cross-helicity turbulence model. Through the comparisons to the
  observation, validity of the turbulence model is examined. Examinations
  include (i) A large-eddy simulation of the sunspot flow reveals how and
  how much cross helicity is generated there; (ii) A eddy-viscosity-type
  turbulence model shows how the turbulence quantities evolves under
  the influence of the large-scale velocity and magnetic-field shears.

---------------------------------------------------------
Title: The future of helioseismology
Authors: Kosovichev, Alexander G.
2010HiA....15..352K    Altcode:
  Helioseismology has provided us with the unique knowledge of the
  interior structure and dynamics of the Sun, and the variations with the
  solar cycle. However, the basic mechanisms of solar magnetic activity,
  formation of sunspots and active regions are still unknown. Determining
  the physical properties of the solar dynamo, detecting emerging active
  regions and observing the subsurface dynamics of sunspots are among
  the most important and challenging problems. The current status and
  perspectives of helioseismology are briefly discussed.

---------------------------------------------------------
Title: Numerical simulation of propagation of the MHD waves in
    sunspots
Authors: Parchevsky, K.; Kosovichev, A.; Khomenko, E.; Olshevsky,
   V.; Collados, M.
2010HiA....15..354P    Altcode:
  We present results of numerical 3D simulation of propagation of MHD
  waves in sunspots. We used two self consistent magnetohydrostatic
  background models of sunspots. There are two main differences
  between these models: (i) the topology of the magnetic field and
  (ii) dependence of the horizontal profile of the sound speed on
  depth. The model with convex shape of the magnetic field lines near
  the photosphere has non-zero horizorntal perturbations of the sound
  speed up to the depth of 7.5 Mm (deep model). In the model with concave
  shape of the magnetic field lines near the photosphere Δ c/c is close
  to zero everywhere below 2 Mm (shallow model). Strong Alfven wave is
  generated at the wave source location in the deep model. This wave is
  almost unnoticeable in the shallow model. Using filtering technique
  we separated magnetoacoustic and magnetogravity waves. It is shown,
  that inside the sunspot magnetoacoustic and magnetogravity waves
  are not spatially separated unlike the case of the horizontally
  uniform background model. The sunspot causes anisotropy of the
  amplitude distribution along the wavefront and changes the shape
  of the wavefront. The amplitude of the waves is reduced inside the
  sunspot. This effect is stronger for the magnetogravity waves than for
  magnetoacoustic waves. The shape of the wavefront of the magnetogravity
  waves is distorted stronger as well. The deep model causes bigger
  anisotropy for both mgnetoacoustic and magneto gravity waves than the
  shallow model.

---------------------------------------------------------
Title: A Precise Asteroseismic Age and Radius for the Evolved Sun-like
    Star KIC 11026764
Authors: Metcalfe, T. S.; Monteiro, M. J. P. F. G.; Thompson, M. J.;
   Molenda-Żakowicz, J.; Appourchaux, T.; Chaplin, W. J.; Doǧan, G.;
   Eggenberger, P.; Bedding, T. R.; Bruntt, H.; Creevey, O. L.; Quirion,
   P. -O.; Stello, D.; Bonanno, A.; Silva Aguirre, V.; Basu, S.; Esch,
   L.; Gai, N.; Di Mauro, M. P.; Kosovichev, A. G.; Kitiashvili, I. N.;
   Suárez, J. C.; Moya, A.; Piau, L.; García, R. A.; Marques, J. P.;
   Frasca, A.; Biazzo, K.; Sousa, S. G.; Dreizler, S.; Bazot, M.; Karoff,
   C.; Frandsen, S.; Wilson, P. A.; Brown, T. M.; Christensen-Dalsgaard,
   J.; Gilliland, R. L.; Kjeldsen, H.; Campante, T. L.; Fletcher, S. T.;
   Handberg, R.; Régulo, C.; Salabert, D.; Schou, J.; Verner, G. A.;
   Ballot, J.; Broomhall, A. -M.; Elsworth, Y.; Hekker, S.; Huber, D.;
   Mathur, S.; New, R.; Roxburgh, I. W.; Sato, K. H.; White, T. R.;
   Borucki, W. J.; Koch, D. G.; Jenkins, J. M.
2010ApJ...723.1583M    Altcode: 2010arXiv1010.4329M
  The primary science goal of the Kepler Mission is to provide
  a census of exoplanets in the solar neighborhood, including the
  identification and characterization of habitable Earth-like planets. The
  asteroseismic capabilities of the mission are being used to determine
  precise radii and ages for the target stars from their solar-like
  oscillations. Chaplin et al. published observations of three bright
  G-type stars, which were monitored during the first 33.5 days of science
  operations. One of these stars, the subgiant KIC 11026764, exhibits a
  characteristic pattern of oscillation frequencies suggesting that it
  has evolved significantly. We have derived asteroseismic estimates of
  the properties of KIC 11026764 from Kepler photometry combined with
  ground-based spectroscopic data. We present the results of detailed
  modeling for this star, employing a variety of independent codes and
  analyses that attempt to match the asteroseismic and spectroscopic
  constraints simultaneously. We determine both the radius and the age
  of KIC 11026764 with a precision near 1%, and an accuracy near 2%
  for the radius and 15% for the age. Continued observations of this
  star promise to reveal additional oscillation frequencies that will
  further improve the determination of its fundamental properties.

---------------------------------------------------------
Title: Realistic MHD numerical simulations of solar convection and
    oscillations in inclined magnetic field regions
Authors: Kitiashvili, Irina N.; Kosovichev, Alexander G.; Wray,
   Alan A.; Mansour, Nagi N.
2010HiA....15..348K    Altcode:
  It is known that physical properties of solar turbulent convection and
  oscillations strongly depend on magnetic field. In particular, recent
  observations from SOHO/MDI revealed significant changes of the wave
  properties in inclined magnetic field regions of sunspots, which affect
  helioseismic inferences. We use realistic 3D radiative MHD numerical
  simulations to investigate solar convection and oscillations and their
  relationship in the presence of inclined magnetic field. In the case of
  highly inclined and strong 1-1.5 kG field the solar convection develops
  filamentary structure and high-speed flows (Fig. 1a), which provide an
  explanation to the Evershed effect in sunspot penumbra (Kitiashvili,
  et al. 2009).

---------------------------------------------------------
Title: Modeling of the subgrid-scale term of the filtered magnetic
    field transport equation
Authors: Balarac, G.; Kosovichev, A. G.; Brugière, O.; Wray, A. A.;
   Mansour, N. N.
2010arXiv1010.5759B    Altcode:
  Accurate subgrid-scale turbulence models are needed to perform realistic
  numerical magnetohydrodynamic (MHD) simulations of the subsurface flows
  of the Sun. To perform large-eddy simulations (LES) of turbulent MHD
  flows, three unknown terms have to be modeled. As a first step, this
  work proposes to use a priori tests to measure the accuracy of various
  models proposed to predict the SGS term appearing in the transport
  equation of the filtered magnetic field. It is proposed to evaluate the
  SGS model accuracy in term of "structural" and "functional" performance,
  i.e. the model capacity to locally approximate the unknown term and
  to reproduce its energetic action, respectively. From our tests, it
  appears that a mixed model based on the scale-similarity model has
  better performance.

---------------------------------------------------------
Title: Mechanism of Spontaneous Formation of Stable Magnetic
    Structures on the Sun
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Wray, A. A.; Mansour,
   N. N.
2010ApJ...719..307K    Altcode: 2010arXiv1004.2288K
  One of the puzzling features of solar magnetism is formation of
  long-living compact magnetic structures, such as sunspots and
  pores, in the highly turbulent upper layer of the solar convective
  zone. We use realistic radiative three-dimensional MHD simulations
  to investigate the interaction between magnetic field and turbulent
  convection. In the simulations, a weak vertical uniform magnetic
  field is imposed in a region of fully developed granular convection,
  and the total magnetic flux through the top and bottom boundaries is
  kept constant. The simulation results reveal a process of spontaneous
  formation of stable magnetic structures, which may be a key to
  understanding the magnetic self-organization on the Sun and formation
  of pores and sunspots. This process consists of two basic steps: (1)
  formation of small-scale filamentary magnetic structures associated with
  concentrations of vorticity and whirlpool-type motions, and (2) merging
  of these structures due to the vortex attraction, caused by converging
  downdrafts around magnetic concentration below the surface. In the
  resulting large-scale structure maintained by the converging plasma
  motions, the magnetic field strength reaches ~1.5 kG at the surface
  and ~6 kG in the interior, and the surface structure resembles solar
  pores. The magnetic structure remains stable for the whole simulation
  run of several hours with no sign of decay.

---------------------------------------------------------
Title: Explanation of the Sea-serpent Magnetic Structure of Sunspot
    Penumbrae
Authors: Kitiashvili, I. N.; Bellot Rubio, L. R.; Kosovichev, A. G.;
   Mansour, N. N.; Sainz Dalda, A.; Wray, A. A.
2010ApJ...716L.181K    Altcode: 2010arXiv1003.0049K
  Recent spectro-polarimetric observations of a sunspot showed the
  formation of bipolar magnetic patches in the mid-penumbra and their
  propagation toward the outer penumbral boundary. The observations
  were interpreted as being caused by sea-serpent magnetic fields near
  the solar surface. In this Letter, we develop a three-dimensional
  radiative MHD numerical model to explain the sea-serpent structure
  and the wave-like behavior of the penumbral magnetic field lines. The
  simulations reproduce the observed behavior, suggesting that the
  sea-serpent phenomenon is a consequence of magnetoconvection in
  a strongly inclined magnetic field. It involves several physical
  processes: filamentary structurization, high-speed overturning
  convective motions in strong, almost horizontal magnetic fields with
  partially frozen field lines, and traveling convective waves. The
  results demonstrate a correlation of the bipolar magnetic patches with
  high-speed Evershed downflows in the penumbra. This is the first time
  that a three-dimensional numerical model of the penumbra results in
  downward-directed magnetic fields, an essential ingredient of sunspot
  penumbrae that has eluded explanation until now.

---------------------------------------------------------
Title: Diverging and Converging Flows around Sunspot Structures in
    Rotating and Non-Rotating Axisymmetric MHD Simulations
Authors: Hartlep, T.; Busse, F. H.; Hulburt, N. E.; Kosovichev, A. G.
2010arXiv1006.4156H    Altcode:
  We present results on modeling solar pores and sunspots using 2D
  axisymmetric magneto-hydrodynamic (MHD) simulations. These models are
  helpful for understanding the mechanisms of magnetic field concentration
  in sunspots, and the large-scale flow patterns associated with
  them. The simulations provide consistent, self-maintained, although
  not fully realistic, models of concentrated magnetic field near the
  solar surface. In this paper, we explore under which conditions the
  associated flows are converging or diverging near the surface. We
  find that in most cases in which a stable, pore-like concentration of
  magnetic field forms, a configuration with converging over diverging
  flow is established.

---------------------------------------------------------
Title: Sea-Serpent Magnetic Structure of Sunspot Penumbrae:
    Observations and MHD Simulations
Authors: Kitiashvili, Irina; Bellot Rubio, L. R.; Kosovichev, A. G.;
   Mansour, N. N.; Sainz Dalda, A.; Wray, A. A.
2010AAS...21631706K    Altcode: 2010BAAS...41..899K
  Recent high-resolution spectro-polarimetric observations of a sunspot
  detected formation of bipolar magnetic patches in the mid penumbra and
  propagation of these patches toward the outer penumbral boundary. The
  observations have been interpreted as an evidence of sea-serpent field
  lines near the solar surface. Using a radiative 3D MHD code, we model
  the behavior of solar magnetoconvection in strongly inclined magnetic
  field of penumbra. The numerical simulation results reproduce the
  moving bipolar magnetic elements observed in high-resolution SOHO/MDI
  and Hinode/SOT data and also their physical properties, supporting the
  sea-serpent model. The simulations explain the sea-serpent structure
  and dynamics of the penumbral field as a consequence of turbulent
  magnetoconvection in a highly inclined, strong magnetic field,
  which forms filamentary structures and has properties of traveling
  convective wave. The model also shows that the appearance of the
  sea-serpent magnetic field lines is closely related to high-speed
  patches ("Evershed clouds") of the penumbra radial outflow.

---------------------------------------------------------
Title: Observations of Emerging Active Regions and Sunspot Formation
    from SDO/HMI
Authors: Kitiashvili, Irina; Kosovichev, A. G.; Mansour, N. N.; Wray,
   A. A.
2010AAS...21640233K    Altcode:
  Continuous high-resolution data of magnetic fields, Doppler velocity
  and intensity from the Helioseismic and Magnetic Imager (HMI) on
  SDO provide an excellent opportunity to investigate the process of
  formation of sunspots and active regions and compare with theoretical
  models. We analyze the HMI observations of an emerging active
  region and formation of sunspots. The results show that the sunspot
  formation involves accumulation of small-scale magnetic elements
  into a large-scale magnetic structure and substantial changes of the
  properties of convection in the region of flux emergence. We discuss
  the HMI capabilities for studying these processes, and compare the
  observations with results of numerical MHD simulations.

---------------------------------------------------------
Title: Initial Time-Distance Helioseismology Results from SDO/HMI. I.
Authors: Zhao, Junwei; Couvidat, S.; Bogart, R.; Parchevsky, K. V.;
   Duvall, T. L., Jr.; Kosovichev, A. G.; Beck, J. G.; Birch, A. C.
2010AAS...21640234Z    Altcode:
  The Helioseismic and Magnetic Imager on Solar Dynamics Observatory
  provides uninterrupted high-resolution observations of solar
  oscillations over the entire disk. This gives a unique opportunity for
  mapping subsurface flows and wave-speed structures and investigating
  their role in the Sun's dynamics and magnetic activity on various
  scales by methods of local helioseismology. A data analysis pipeline
  for the time-distance helioseismology analysis has been developed
  and implemented at the SDO Joint Science Operation Center (JSOC) at
  Stanford. It provides near-real time processing of the helioseismology
  data. We present the basic characteristics and capabilities of the
  pipeline, initial time-distance measurement results, and compare these
  with the simultaneous SOHO/MDI measurements.

---------------------------------------------------------
Title: Initial Time-distance Helioseismology Results from SDO/HMI. II.
Authors: Zhao, Junwei; Couvidat, S.; Bogart, R.; Parchevsky, K. V.;
   Duvall, T. L., Jr.; Kosovichev, A. G.; Beck, J. G.; Birch, A. C.
2010AAS...21640235Z    Altcode:
  Investigations of the interaction between large-scale subsurface
  flows and magnetic fields are very important for understanding and
  predicting the processes of solar dynamo and evolution of active
  regions. The time-distance helioseismology data analysis pipeline
  (presented in our poster I) is designed to provide global-Sun maps
  of subsurface flows from the SDO/HMI observations every 8 hours. We
  present an initial subsurface flow map, and compare this with the
  magnetic field distribution also obtained from the HMI instrument.

---------------------------------------------------------
Title: Supergranulation in the Polar Regions Observed by Hinode/SOT
Authors: Nagashima, Kaori; Zhao, J.; Kosovichev, A.; Sekii, T.
2010AAS...21640002N    Altcode: 2010BAAS...41..855N
  We report on our investigation of the supergranular structure in the
  polar regions of the Sun by local helioseismology. Supergranules
  represent large-scale convective cells: the horizontal spatial
  scale is about 30 Mm and the lifetime is about 1 day. They play
  important role in the magnetic flux transport and formation of the
  magnetic network. Recent helioseismological studies have found
  that the depth of the cells is much smaller than the horizontal
  scale, and that the supergranulation pattern exhibits a wave-like
  behavior. However, we still do not have sufficient knowledge of
  the origin and properties of the supergranulation. In this work, we
  have carried out a new time-distance helioseismology analysis using
  high-resolution datasets of the polar regions of the Sun obtained
  by the Solar Optical Telescope (SOT) onboard the Hinode satellite
  during the periods of the high inclination of the solar axis to the
  ecliptic. Because of the foreshortening such measurements are not
  currently possible with any other helioseismology instrument. We have
  measured the travel-time shifts of acoustic waves traveling to various
  depth below the photosphere, and obtain the subphotospheric horizontal
  flow maps by inversion. We have detected the supergranular cells in
  the polar regions and studied their properties. For comparison we did a
  similar analysis for low-latitude regions at the East limb of the Sun,
  and at the disk center. Comparing with the cells in the lower-latitude
  regions, we have observed a curious alignment of the cells in the polar
  regions, approximately in the North-South direction. This `alignment'
  has been found in both the North and the South polar regions. In
  the presentation, we discuss the alignment phenomenon as well as the
  physical properties of the supergranular cells in the polar regions.

---------------------------------------------------------
Title: Division II: Sun and Heliosphere
Authors: Melrose, Donald B.; Martinez Pillet, Valentin; Webb, David
   F.; Bougeret, Jean-Louis; Klimchuk, James A.; Kosovichev, Alexander;
   van Driel-Gesztelyi, Lidia; von Steiger, Rudolf
2010IAUTB..27..146M    Altcode:
  This report is on activities of the Division at the General Assembly
  in Rio de Janeiro. Summaries of scientific activities over the past
  triennium have been published in Transactions A, see Melrose et
  al. (2008), Klimchuk et al. (2008), Martinez Pillet et al. (2008) and
  Bougeret et al. (2008). The business meeting of the three Commissions
  were incorporated into the business meeting of the Division. This
  report is based in part on minutes of the business meeting, provided
  by the Secretary of the Division, Lidia van Driel-Gesztelyi, and it
  also includes reports provided by the Presidents of the Commissions
  (C10, C12, C49) and of the Working Groups (WGs) in the Division.

---------------------------------------------------------
Title: Diverging And Converging Flows Around Sunspot Structures In
    Axisymmetric Mhd Simulations
Authors: Hartlep, Thomas; Busse, F. H.; Kosovichev, A. G.; Hurlburt,
   N. E.
2010AAS...21640005H    Altcode: 2010BAAS...41..855H
  We present results on modeling solar pores and sunspots using 2D
  axisymmetric magneto-hydrodynamic (MHD) simulations. These models
  are helpful for understanding the mechanisms of magnetic field
  concentration in sunspots, and the large-scale flow patterns associated
  with them. The simulations provide consistent, self-maintained, even
  if not fully realistic, models of concentrated magnetic field near
  the solar surface. We explore under which conditions the associated
  flows are converging or diverging in nature near the surface.

---------------------------------------------------------
Title: Radiative Hydrodynamic Simulations of Turbulent Convection
    and Oscillations from Solar-Type to A-Type Stars
Authors: Kitiashvili, Irina; Kosovichev, A. G.; Saio, H.; Shibahashi,
   H.; Wray, A. A.; Mansour, N. N.
2010AAS...21640012K    Altcode: 2010BAAS...41..856K
  We use 3D numerical radiative hydrodynamic simulations to study
  convective and oscillation properties of main sequence stars from
  the solar-type stars to more massive stars. The solar-type pulsators
  are characterized by acoustic oscillation modes excited by turbulent
  granular convection in the upper convective boundary layer. As the
  stellar mass increases the convection zone shrinks, the scale and
  intensity of the turbulent motions increases, providing more energy for
  excitation of acoustic modes. When the stellar mass reaches about 1.6
  solar masses the upper convection zone consists of two very thin layers
  corresponding to H and He ionization, and in addition to the acoustic
  modes the stars show strong internal gravity modes The thin convection
  zone is often considered insignificant for the stellar dynamics and
  variability. However, the 3D radiative hydrodynamics simulations reveal
  supersonic granular-type convection of the scale significantly larger
  than the solar granulation, and strong overshooting plumes penetrating
  into the stable radiative zone. These plumes may contribute to the
  excitation of oscillation in A-type stars.

---------------------------------------------------------
Title: Time-Distance Helioseismology Analysis of a Numerically
    Simulated Sunspot
Authors: Ilonidis, Efstathios; Zhao, J.; Kosovichev, A.
2010AAS...21640007I    Altcode: 2010BAAS...41..855I
  In this work a numerically simulated sunspot embedded in a realistic
  model of solar magnetoconvection is analyzed using time-distance
  technique of local helioseismology. The purpose of this study
  is to improve our understanding of travel-time shifts measured in
  sunspots. We use the oscillation data obtained from the simulations for
  measurements of p-modes travel-time shifts by applying the time-distance
  helioseismology technique. The measurements are carried out for several
  distances permitted by the depth of the simulation box, with and
  without use of phase-speed filters. The phase-speed filtering procedure
  improves the signal-to-noise ratio of the travel-time measurements for
  short distances, but it may also introduce a bias in the travel-time
  shifts. We discuss the interior properties of the sunspot inferred
  from our measurements. The data for this work is kindly provided by
  Matthias Rempel (HAO/NCAR).

---------------------------------------------------------
Title: Investigation of Subsurface Connections in Complexes of
    Activity by Local Helioseismology
Authors: Kosovichev, Alexander G.; Duvall, T. L., Jr.
2010AAS...21631903K    Altcode: 2010BAAS...41..909K
  Solar active regions often emerge close to each other forming complexes
  of activity. The complexes may live for several solar rotations,
  and represent a major component of the Sun's magnetic activity. It
  had been suggested that the close appearance of active regions in
  space and time might be related to common subsurface roots, "nests" of
  activity. The EUV images show that the active regions are magnetically
  connected in the corona, but subsurface connections have not been
  established. We investigate the subsurface structure and dynamics of
  two large complexes of activity, observed during the SOHO/MDI Dynamics
  campaigns: AR 10484-10488 in October-November 2003, and AR 10987-10989
  in March-April 2008 (this complex is a part of the Whole Heliospheric
  Interval campaign). The former was organized across the equator in a
  range of longitudes, while the later appeared in a narrow latitudinal
  range, probably representing a subsurface toroidal flux tube. We use
  the MDI full-disk Dopplergrams to measure perturbations of travel times
  of acoustic waves traveling to various depths by applying the surface-
  and deep-focusing time-distance helioseismology techniques, and obtain
  the sound-speed and flow maps by inversion. We compare the evolution
  of the large-scale subsurface sound-speed structures and dynamics of
  these complexes, and discuss the evidence of subsurface connections.

---------------------------------------------------------
Title: Tests of Helioseismic Holography Sound-Speed Inversions Using
    Synthetic Data
Authors: Birch, Aaron; Braun, D.; Crouch, A.; Parchevsky, K.;
   Kosovichev, A.
2010AAS...21640006B    Altcode: 2010BAAS...41..855B
  Helioseismic holography is an important method for measuring physical
  conditions in the solar interior. Synthetic data is a powerful tool
  for validating the methods of local helioseismology. Here we show
  some example inversions of surface-focusing holography measurements of
  synthetic data sets. We show that Born-approximation based inversions
  of phase-speed and ridge-filtered measurements yield models that
  are consistent with the true sound-speed structure in some simple
  test cases. This work is supported by NASA contracts NNH09CE41C and
  NNG07EI51C.

---------------------------------------------------------
Title: Limits on Energy, Momentum and Excitation Mechanism of
    Sunquakes
Authors: Kosovichev, Alexander G.
2010AAS...21640004K    Altcode: 2010BAAS...41..855K
  Investigations of the helioseismic response to solar flares
  ("sunquakes") are of significant interest for understanding the
  mechanisms of the flare energy release and the dynamics of the solar
  atmosphere and interior. The seismic response is observed in the form
  of expanding ripples on the surface in Doppler-shift data, and in
  images of an acoustic signal integrated over local ares. Recently,
  it was suggested that solar flares can also excite global low-degree
  acoustic modes of the Sun. I present results of a general theory of
  the seismic response to the energy release in solar flares putting
  strong limits on the energy and momentum, which can be deposited in the
  solar oscillation modes. These limits show that it is unlikely that the
  signals observed in the SOHO/VIRGO and GOLF data during solar flares
  are caused by sunquakes. However, the energy and momentum released in
  flaring stars may be sufficient for generating detectable signals.

---------------------------------------------------------
Title: Overview of First-Result SDO Posters
Authors: Kosovichev, Alexander G.; SDO Team
2010AAS...21630806K    Altcode:
  Solar Dynamics Observatory launched on February 11, 2010, is designed to
  study the internal dynamics, magnetism, coronal structures and spectral
  irradiance of the Sun with high spatial and temporal resolutions
  uninterruptedly during the rising phase of the activity cycle and the
  solar maximum. This talk presents an overview of the late-breaking
  poster presentations of the initial SDO results.

---------------------------------------------------------
Title: Ray-Path and Born Kernels for SDO Time-Distance Helioseismology
    Pipeline
Authors: Parchevsky, Konstantin; Birch, A.; Kosovichev, A.; Couvidat,
   S.; Duvall, T., Jr.; Zhao, J.
2010AAS...21640009P    Altcode: 2010BAAS...41..856P
  We present a detailed procedure for calculating 3D sound speed and
  flow kernels in the ray-path and Born approximations for inversion
  procedures in the SDO/HMI Time-Distance Helioseismology pipeline. The
  total integral from the kernel is a convenient parameter which can
  be used for comparison of contribution of different factors (ray-path
  and wave approximation, spherical and Cartesian geometry). Comparison
  of the total integral from sound speed kernels in ray-path and Born
  approximation with full disk MDI observations show good agreement. For
  distances shorter than 25 Mm the total integrals from Born kernels
  are systematically lower than integrals from ray-path kernels that
  can be explained by contribution of wave effects. Taking into account
  sphericity in ray-path kernels causes a reducing the total integral
  of 2%.

---------------------------------------------------------
Title: Numerical Simulation of Propagation and Transformation of
    the MHD Waves in Sunspots
Authors: Parchevsky, Konstantin; Zhao, J.; Kosovichev, A.
2010AAS...21621106P    Altcode:
  Direct numerical simulation of propagation of MHD waves in stratified
  medium in regions with non-uniform magnetic field is very important
  for understanding of scattering and transformation of waves by
  sunspots. We present numerical simulations of wave propagation
  through the sunspot in 3D. We compare results propagation in two
  different magnitostatic models of sunspots refferred to as "deep" and
  "shallow" models. The "deep" model has convex shape of magnetic field
  lines near the photosphere and non-zero horizorntal perturbations of
  the sound speed up to the bottom of the model. The "shallow" model
  has concave shape of the magnetic field lines near the photosphere
  and horizontally uniform sound speed below 2 Mm. Waves reduce their
  amplitude when they reach the center of the sunspot and estore the
  amplitude when pass the center. For the "deep" model this effect is
  bigger than for the "shallow" model. The wave amplitude depends on
  the distance of the source from the sunspot center. For the "shallow"
  model and source distance of 9 Mm from the sunspot center the wave
  amplitude at some moment (when the wavefront passes the sunspot center)
  becomes bigger inside the sunspot than outside. For the source distance
  of 12 Mm the wave amplitude remains smaller inside the sunspot than
  outside for all moments of time. <P />Using filtering technique we
  separated magnetoacoustic and magnetogravity waves. Simulations show
  that the sunspot changes the shape of the wave front and amplitude
  of the f-modes significantly stronger than the p-modes. It is shown,
  that inside the sunspot magnetoacoustic and magnetogravity waves are
  not spatially separated unlike the case of the horizontally uniform
  background model. We compared simulation results with the wave signals
  (Green's functions) extracted from the SOHO/MDI data for AR9787.

---------------------------------------------------------
Title: Validating Time-Distance Subsurface Sound-Speed Structure
    Inversions
Authors: Zhao, Junwei; Parchevsky, K. V.; Hartlep, T.; Kosovichev,
   A. G.
2010AAS...21631905Z    Altcode: 2010BAAS...41..910Z
  Inversions for subsurface sound-speed perturbations in the Sun using
  time-distance helioseismology are important for studying the interior
  structures of sunspots and supergranules. However, it is essential
  to assess how well these inversion techniques perform. By analyzing
  numerical simulations of acoustic wave fields, which are obtained on
  both local and global scales employing various subsurface sunspot
  models, we invert for the subsurface sound-speed structures. These
  inverted structures are then compared with the models prescribed in
  the simulations. We find that our inversions generally agree well with
  the models.

---------------------------------------------------------
Title: The Asteroseismic Potential of Kepler: First Results for
    Solar-Type Stars
Authors: Chaplin, W. J.; Appourchaux, T.; Elsworth, Y.; García,
   R. A.; Houdek, G.; Karoff, C.; Metcalfe, T. S.; Molenda-Żakowicz,
   J.; Monteiro, M. J. P. F. G.; Thompson, M. J.; Brown, T. M.;
   Christensen-Dalsgaard, J.; Gilliland, R. L.; Kjeldsen, H.; Borucki,
   W. J.; Koch, D.; Jenkins, J. M.; Ballot, J.; Basu, S.; Bazot, M.;
   Bedding, T. R.; Benomar, O.; Bonanno, A.; Brandão, I. M.; Bruntt,
   H.; Campante, T. L.; Creevey, O. L.; Di Mauro, M. P.; Doǧan,
   G.; Dreizler, S.; Eggenberger, P.; Esch, L.; Fletcher, S. T.;
   Frandsen, S.; Gai, N.; Gaulme, P.; Handberg, R.; Hekker, S.; Howe,
   R.; Huber, D.; Korzennik, S. G.; Lebrun, J. C.; Leccia, S.; Martic,
   M.; Mathur, S.; Mosser, B.; New, R.; Quirion, P. -O.; Régulo, C.;
   Roxburgh, I. W.; Salabert, D.; Schou, J.; Sousa, S. G.; Stello, D.;
   Verner, G. A.; Arentoft, T.; Barban, C.; Belkacem, K.; Benatti, S.;
   Biazzo, K.; Boumier, P.; Bradley, P. A.; Broomhall, A. -M.; Buzasi,
   D. L.; Claudi, R. U.; Cunha, M. S.; D'Antona, F.; Deheuvels, S.;
   Derekas, A.; García Hernández, A.; Giampapa, M. S.; Goupil, M. J.;
   Gruberbauer, M.; Guzik, J. A.; Hale, S. J.; Ireland, M. J.; Kiss,
   L. L.; Kitiashvili, I. N.; Kolenberg, K.; Korhonen, H.; Kosovichev,
   A. G.; Kupka, F.; Lebreton, Y.; Leroy, B.; Ludwig, H. -G.; Mathis, S.;
   Michel, E.; Miglio, A.; Montalbán, J.; Moya, A.; Noels, A.; Noyes,
   R. W.; Pallé, P. L.; Piau, L.; Preston, H. L.; Roca Cortés, T.;
   Roth, M.; Sato, K. H.; Schmitt, J.; Serenelli, A. M.; Silva Aguirre,
   V.; Stevens, I. R.; Suárez, J. C.; Suran, M. D.; Trampedach, R.;
   Turck-Chièze, S.; Uytterhoeven, K.; Ventura, R.; Wilson, P. A.
2010ApJ...713L.169C    Altcode: 2010arXiv1001.0506C
  We present preliminary asteroseismic results from Kepler on three G-type
  stars. The observations, made at one-minute cadence during the first
  33.5 days of science operations, reveal high signal-to-noise solar-like
  oscillation spectra in all three stars: about 20 modes of oscillation
  may be clearly distinguished in each star. We discuss the appearance of
  the oscillation spectra, use the frequencies and frequency separations
  to provide first results on the radii, masses, and ages of the stars,
  and comment in the light of these results on prospects for inference
  on other solar-type stars that Kepler will observe.

---------------------------------------------------------
Title: Solar and Stellar Variability: Impact on Earth and Planets
Authors: Kosovichev, Alexander G.; Andrei, Alexandre H.; Rozelot,
   Jean-Pierre
2010IAUS..264.....K    Altcode:
  Preface; Organizing committee; Conference participants; 1. Introduction:
  the Sun and stars as the primary energy input in planetary atmospheres;
  2. Observations of solar and stellar variability; 3. Solar and stellar
  cycles and variability on century timescale; 4. Magnetic activity
  and dynamo mechanisms; 5. Physical mechanisms of solar and stellar
  variability; 6. Effects on space weather and climate; 7. Effects of
  magnetic activity on planet formation and evolution; 8. Impact of
  solar and stellar variability on planetary atmospheres and climate;
  9. Current and future space missions and ground-based observing
  programs; 10. Summary and conclusions; Author index; Subject index.

---------------------------------------------------------
Title: The quest for the solar g modes
Authors: Appourchaux, T.; Belkacem, K.; Broomhall, A. -M.; Chaplin,
   W. J.; Gough, D. O.; Houdek, G.; Provost, J.; Baudin, F.; Boumier,
   P.; Elsworth, Y.; García, R. A.; Andersen, B. N.; Finsterle, W.;
   Fröhlich, C.; Gabriel, A.; Grec, G.; Jiménez, A.; Kosovichev, A.;
   Sekii, T.; Toutain, T.; Turck-Chièze, S.
2010A&ARv..18..197A    Altcode: 2010A&ARv.tmp....1A; 2009arXiv0910.0848A
  Solar gravity modes (or g modes)—oscillations of the solar interior
  on which buoyancy acts as the restoring force—have the potential
  to provide unprecedented inference on the structure and dynamics of
  the solar core, inference that is not possible with the well-observed
  acoustic modes (or p modes). The relative high amplitude of the g-mode
  eigenfunctions in the core and the evanesence of the modes in the
  convection zone make the modes particularly sensitive to the physical
  and dynamical conditions in the core. Owing to the existence of the
  convection zone, the g modes have very low amplitudes at photospheric
  levels, which makes the modes extremely hard to detect. In this article,
  we review the current state of play regarding attempts to detect g
  modes. We review the theory of g modes, including theoretical estimation
  of the g-mode frequencies, amplitudes and damping rates. Then we go
  on to discuss the techniques that have been used to try to detect g
  modes. We review results in the literature, and finish by looking to
  the future, and the potential advances that can be made—from both
  data and data-analysis perspectives—to give unambiguous detections
  of individual g modes. The review ends by concluding that, at the time
  of writing, there is indeed a consensus amongst the authors that there
  is currently no undisputed detection of solar g modes.

---------------------------------------------------------
Title: Numerical Simulation of Excitation and Propagation of
    Helioseismic MHD Waves in Magnetostatic Models of Sunspots
Authors: Parchevsky, K.; Kosovichev, A.; Khomenko, E.; Olshevsky,
   V.; Collados, M.
2010arXiv1002.1117P    Altcode:
  We present comparison of numerical simulations of propagation of
  MHD waves,excited by subphotospheric perturbations, in two different
  ("deep" and "shallow") magnetostatic models of the sunspots. The "deep"
  sunspot model distorts both the shape of the wavefront and its amplitude
  stronger than the "shallow" model. For both sunspot models, the surface
  gravity waves (f-mode) are affected by the sunspots stronger than
  the acoustic p-modes. The wave amplitude inside the sunspot depends
  on the photospheric strength of the magnetic field and the distance
  of the source from the sunspot axis. For the source located at 9 Mm
  from the center of the sunspot, the wave amplitude increases when
  the wavefront passes through the central part of the sunspot. For
  the source distance of 12 Mm, the wave amplitude inside the sunspot
  is always smaller than outside. For the same source distance from
  the sunspot center but for the models with different strength of the
  magnetic field, the wave amplitude inside the sunspot increases with
  the strength of the magnetic field. The simulations show that unlike
  the case of the uniform inclined background magnetic field, the p-
  and f-mode waves are not spatially separated inside the sunspot where
  the magnetic field is strongly non-uniform. These properties have to
  be taken into account for interpretation of observations of MHD waves
  traveling through sunspot regions.

---------------------------------------------------------
Title: Prediction of solar activity cycles by assimilating sunspot
    data into a dynamo model
Authors: Kitiashvili, Irina N.; Kosovichev, Alexander G.
2010IAUS..264..202K    Altcode:
  Solar activity is a determining factor for space climate of the
  Solar system. Thus, predicting the magnetic activity of the Sun is
  very important. However, our incomplete knowledge about the dynamo
  processes of generation and transport of magnetic fields inside
  Sun does not allow us to make an accurate forecast. For predicting
  the solar cycle properties use the Ensemble Kalman Filter (EnKF)
  to assimilate the sunspot data into a simple dynamo model. This
  method takes into account uncertainties of both the dynamo model and
  the observed sunspot number series. The method has been tested by
  calculating predictions of the past cycles using the observed annual
  sunspot numbers only until the start of these cycles, and showed a
  reasonable agreement between the predicted and actual data. After this,
  we have calculated a prediction for the upcoming solar cycle 24, and
  found that it will be approximately 30% weaker than the previous one,
  confirming some previous expectations. In addition, we have investigated
  the properties of the dynamo model during the solar minima, and their
  relationship to the strength of the following solar cycles. The results
  show that prior the weak cycles, 20 and 23, and the upcoming cycle,
  24, the vector-potential of the poloidal component of magnetic field
  and the magnetic helicity substantial decrease. The decrease of the
  poloidal field corresponds to the well-known correlation between the
  polar magnetic field strength at the minimum and the sunspot number at
  the maximum. However, the correlation between the magnetic helicity and
  the future cycle strength is new, and should be further investigated.

---------------------------------------------------------
Title: Note on Travel Time Shifts Due to Amplitude Modulation in
    Time-Distance Helioseismology Measurements
Authors: Nigam, R.; Kosovichev, A. G.
2010ApJ...708.1475N    Altcode: 2009arXiv0911.4295N
  Correct interpretation of acoustic travel times measured by
  time-distance helioseismology is essential to get an accurate
  understanding of the solar properties that are inferred from them. It
  has long been observed that sunspots suppress p-mode amplitude, but its
  implications on travel times have not been fully investigated so far. It
  has been found in test measurements using a "masking" procedure, in
  which the solar Doppler signal in a localized quiet region of the Sun
  is artificially suppressed by a spatial function, and using numerical
  simulations that the amplitude modulations in combination with the
  phase-speed filtering may cause systematic shifts of acoustic travel
  times. To understand the properties of this procedure, we derive
  an analytical expression for the cross-covariance of a signal that
  has been modulated locally by a spatial function that has azimuthal
  symmetry and then filtered by a phase-speed filter typically used
  in time-distance helioseismology. Comparing this expression to the
  Gabor wavelet fitting formula without this effect, we find that there
  is a shift in the travel times that is introduced by the amplitude
  modulation. The analytical model presented in this paper can be useful
  also for interpretation of travel time measurements for the non-uniform
  distribution of oscillation amplitude due to observational effects.

---------------------------------------------------------
Title: High-Resolution Helioseismic Imaging of Subsurface Structures
    and Flows of a Solar Active Region Observed by Hinode
Authors: Zhao, Junwei; Kosovichev, Alexander G.; Sekii, Takashi
2010ApJ...708..304Z    Altcode: 2009arXiv0911.1161Z
  We analyze a solar active region observed by the Hinode Ca II H line
  using the time-distance helioseismology technique, and infer wave-speed
  perturbation structures and flow fields beneath the active region
  with a high spatial resolution. The general subsurface wave-speed
  structure is similar to the previous results obtained from Solar and
  Heliospheric Observatory/Michelson Doppler Imager observations. The
  general subsurface flow structure is also similar, and the downward
  flows beneath the sunspot and the mass circulations around the sunspot
  are clearly resolved. Below the sunspot, some organized divergent flow
  cells are observed, and these structures may indicate the existence of
  mesoscale convective motions. Near the light bridge inside the sunspot,
  hotter plasma is found beneath, and flows divergent from this area
  are observed. The Hinode data also allow us to investigate potential
  uncertainties caused by the use of phase-speed filter for short travel
  distances. Comparing the measurements with and without the phase-speed
  filtering, we find out that inside the sunspot, mean acoustic travel
  times are in basic agreement, but the values are underestimated by a
  factor of 20%-40% inside the sunspot umbra for measurements with the
  filtering. The initial acoustic tomography results from Hinode show
  a great potential of using high-resolution observations for probing
  the internal structure and dynamics of sunspots.

---------------------------------------------------------
Title: Recent Progress and Future Directions for Helioseismology
Authors: Kosovichev, A.; Zhao, J.; Sekii, T.; Nagashima, K.;
   Mitra-Kraev, U.
2009ASPC..415..399K    Altcode:
  Hinode/SOT observations provide unique data for high-resolution
  helioseismology. These data have allowed us for the first
  time to resolve the subsurface convective boundary layer, obtain
  high-resolution images of structures and mass flows beneath a sunspot,
  detect flare-generated MHD waves in the sunspot umbra, carry out
  multi-wavelength studies of solar oscillations, and obtain unique
  helioseismic data for probing the subsurface dynamics in near-polar
  regions. Future directions in helioseismology will be focused on
  understanding the mechanism of solar dynamo, diagnostics of emerging
  magnetic flux, formation and evolution of sunspot regions and their
  flaring activity. Of particular interest are investigations of solar
  convection dynamics, differential rotation and meridional flows
  in the near polar regions. These tasks require development of new
  helioseismology methods for probing conditions in strong magnetic
  field regions and improving temporal and spatial resolutions. The new
  developments in helioseismology will be supported by realistic MHD
  simulations and based on massive data analysis from Hinode and Solar
  Dynamics Observatory.

---------------------------------------------------------
Title: Travel-Time Analyses of an Emerging-Flux Region
Authors: Nagashima, K.; Sekii, T.; Kosovichev, A. G.; Zhao, J.;
   Tarbell, T. D.
2009ASPC..415..417N    Altcode:
  Travel-time analyses of a newly-formed plage region are presented. The
  dataset has been obtained from the 12-hr Hinode observation of an
  emerging-flux region (to be NOAA AR 10975) close to the disc center
  on 23 November 2007. The SOT provides data in Ca II H line and in
  Fe I 557.6nm line; we use both chromospheric intensity oscillation
  data and photospheric Dopplergrams for travel-time measurement by
  a cross-correlation method. In the plage region, we have detected
  a travel-time anomaly in the chromospheric data, but not in the
  photospheric data. This can be interpreted as a signature of downflows
  in the chromosphere. This result illustrates how time-distance
  techniques can be used to study chromospheric flows.

---------------------------------------------------------
Title: Signatures of Emerging Subsurface Structures in Acoustic
    Power Maps
Authors: Hartlep, T.; Kosovichev, A. G.; Zhao, J.; Mansour, N. N.
2009ASPC..416..147H    Altcode:
  We show that under suitable conditions subsurface structures can
  alter the average acoustic power observed at the photosphere. By using
  numerical simulations of wave propagation, we investigate whether this
  effect can be used to detect emerging active regions before they appear
  on the surface. In the simulations, subsurface structures are modeled
  as regions with enhanced or reduced acoustic wave speed. We show how
  the acoustic power above a subsurface region depends on the sign, depth
  and strength of the wave speed perturbation. For comparison, we analyze
  observations from SoHO/MDI of the emergence of active region NOAA~10488.

---------------------------------------------------------
Title: Transport of Supergranules and their Vertical Coherence
Authors: Švanda, M.; Kosovichev, A. G.; Klvaňa, M.; Sobotka, M.;
   Duvall, T. L., Jr.
2009ASPC..416..547S    Altcode:
  In recent papers, we have introduced a method for measuring the
  photospheric flow field that is based on the tracking of supergranular
  structures. Here, in combination with helioseismic data, we are
  able to estimate the depth in the solar convection envelope to
  which the detected large-scale flow field is coherent. We show that
  the upper 10 Mm in the convection zone depicts similar features in
  horizontal velocity. Our interpretation of this observation is that
  the supergranulation is a coherent structure 10 Mm deep and is subject
  to large-scale transport by the underlying velocity field.

---------------------------------------------------------
Title: Time-Distance Helioseismic Imaging of a Numerically Simulated
    Solar Tachocline
Authors: Zhao, J.; Hartlep, T.; Kosovichev, A. G.; Mansour, N. N.
2009ASPC..416...25Z    Altcode:
  The solar tachocline, located near the bottom of the convection zone,
  is a very important region for solar dynamics and the solar dynamo. We
  develop a time-distance helioseismology technique, including both
  surface- and deep-focusing measurements, together with inversions,
  to derive the interior image of the sound speed perturbation at the
  tachocline with a latitudinal dependence. We test the technique on
  numerically simulated global wavefields and find that the technique is
  able to recover the major features that are preset in the numerical
  model, though a bit more widespread into the deeper interior. This
  measurement and inversion technique will be applied to MDI observations
  to derive the structures of solar tachocline.

---------------------------------------------------------
Title: Excitation, Propagation and Conversion of Helioseismic MHD
    Waves in Strong Field Regions
Authors: Parchevsky, K. V.; Kosovichev, A. G.
2009ASPC..416...61P    Altcode:
  We present the results of 3D numerical simulations of MHD wave
  excitation, propagation, and conversion in various configurations of the
  background magnetic field, including realistic models of sunspots. The
  background field causes anisotropy of the wave amplitude along the
  wave front and distortion of the wave front itself. This effect is
  stronger for f- than for p-modes. Comparison of calculated travel time
  variations caused by the magnetic field with observations obtained from
  MDI Doppler velocity data shows that only about 25% of the observed
  mean travel time variation around sunspots can be explained by the
  direct interaction of MHD waves with the inclined magnetic field
  (even for strong fields of 1400-1900 G). We show that for a height of
  300 km and such strong fields the phase of the simulated travel time
  variations coincides with the observed phase.

---------------------------------------------------------
Title: New Results of High-Resolution Helioseismology from Hinode
Authors: Kosovichev, A.; Zhao, J.; Sekii, T.; Nagashima, K.;
   Mitra-Kraev, U.
2009ASPC..416...41K    Altcode:
  The Solar Optical Telescope of Hinode provides unique multi-wavelength
  high-resolution data for local helioseismic diagnostics of the
  sub-surface structure and dynamics of the Sun. The helioseismology data
  from Hinode have allowed us for the first time to observe oscillations
  of very high angular degree and high frequencies, and substantially
  improve the spatial resolution of time-distance helioseismology in
  near-surface layers of the Sun, compared to the previous SOHO/MDI
  data. The Hinode data have also provided important insight on the
  nature of sunspot oscillations, and the correlated component of
  stochastic excitation. Initial attempts have been made to investigate
  the dynamics of the polar regions, critical for dynamo modeling, but
  previously unaccessible for helioseismology. In addition, a new type
  of flare-excited MHD oscillations was detected from Hinode observations
  of the solar flare of December 13, 2006.

---------------------------------------------------------
Title: Subsurface Structures and Flow Fields of an Active Region
    Observed by Hinode
Authors: Zhao, J.; Kosovichev, A. G.; Sekii, T.
2009ASPC..415..411Z    Altcode:
  We analyze a solar active region observed by Hinode Ca II H line using
  the time-distance helioseismology technique, and derive the subsurface
  structure and flow fields of this active region. The basic subsurface
  wave speed structure is essentially the same as the previous results
  obtained from MDI observations. The subsurface flow structure is
  also similar to the previous results, but the downward flows are more
  resolved. Additionally, vertical mass circulations outside the sunspot
  are more clearly detected, although no mass conservation constraints
  are imposed in the inversion procedure. Near a light bridge area,
  hotter plasma is found beneath, and flows divergent from this area
  are observed. Inside the sunspot umbra and penumbra, some organized
  divergent flow cells of an intermediate size between granulation and
  supergranulation are also observed. These initial results demonstrate
  the potential and importance of high-resolution helioseismology of
  sunspots.

---------------------------------------------------------
Title: Realistic MHD Simulations of Solar Convection and Oscillations
in Magnetic Regions: Mode Excitation and Effects of Acoustic Halos
Authors: Jacoutot, L.; Kosovichev, A.; Wray, A.; Mansour, N.
2009ASPC..416...67J    Altcode:
  We have used a 3D, compressible, non-linear radiative
  magnetohydrodynamics code developed at the NASA Ames Research Center
  to model solar convection and oscillations in magnetic regions. This
  code takes into account several physical phenomena: compressible fluid
  flow in a highly stratified medium, sub-grid scale turbulence models,
  radiative energy transfer, and a real-gas equation of state. We have
  studied the influence of the magnetic field of various strength
  on the convective cells and on the excitation mechanisms of the
  acoustic oscillations by calculating spectral properties of the
  convective motions and oscillations. The results reveal substantial
  changes of the granulation structure with increased magnetic field,
  and a frequency-dependent reduction in the oscillation power in a
  good agreement with solar observations. The simulations provide a
  solution to the long-standing problem of enhanced high-frequency
  acoustic emission at the boundaries of active region ("acoustic
  halos"), suggesting that this phenomenon is caused by the changes of
  the spatial-temporal spectrum of the turbulent convection in magnetic
  field, resulting in turbulent motions of smaller scales and higher
  frequencies than in quiet Sun regions. These simulation results may
  have also important implications for understanding high-frequency
  oscillations of magnetic stars.

---------------------------------------------------------
Title: Modeling of sunspot structures using simulations of
    axisymmetric MHD convection
Authors: Hartlep, T.; Hurlburt, N. E.; Busse, F. H.; Kosovichev, A. G.
2009AGUFMSH23B1538H    Altcode:
  We present our efforts on modeling solar pores and sunspots in 2D
  and 2.5D axisymmetric magneto-hydrodynamic (MHD) simulations of
  the upper layers of the Sun's convection zone. One goals of this
  work is to produce consistent, self-maintained, even if not fully
  realistic, models of concentrated, strong magnetic field in subsurface
  layers of the Sun. These models are important for understanding the
  mechanisms of magnetic field concentration in sunspots, and associated
  large-scale flow patterns. Also, these can be used as background
  models in acoustic wave propagation simulations for testing local
  helioseismology techniques and their performance and problems in
  magnetic regions. This study explores the parameters under which
  magnetic field can spontaneously concentrate, and the kind of flow
  patterns that form in these cases (for instance if there are inflows
  or outflow at the surface).

---------------------------------------------------------
Title: A Functional Analytic Approach to Fréchet Traveltime Kernels
Authors: Schlottmann, R.; Kosovichev, A. G.
2009AGUFMSH13A1509S    Altcode:
  Fréchet kernels, an emerging tool in helioseismic data analysis,
  describe the first-order (linear) relationship between medium
  properties affecting helioseismic wave propagation and measured wave
  traveltimes. Although many treatments of these kernels exist in the
  literature, we believe a need exists to provide a consistent, systematic
  method of deriving them. We present an approach using some basic tools
  and concepts of functional analysis, such as functional derivatives
  and functional Taylor series. Although no fundamentally new results are
  obtained from this approach, it clarifies the approximations used and
  provides a nice organizing principle for the theory. In addition to the
  theoretical apparatus, we also provide general formulas for any desired
  medium property that can affect helioseismic wave propagation. We also
  supply specific formulas for some properties, such as wave speed and
  density, and calculate some sample kernels.

---------------------------------------------------------
Title: Implementation of Data Assimilation Methods for Dynamo Models
    to Predict Solar Activity
Authors: Kitiashvili, I.; Kosovichev, A.
2009ASPC..416..511K    Altcode:
  Cyclic variations of solar activity are a result of a complicated
  dynamo process in the convection zone. Despite the regular cyclic
  variations of solar activity, the chaotic variations of sunspot number
  from cycle to cycle are difficult to predict. The main reasons are the
  imperfect dynamo models and deficiency of the necessary observational
  data. Data assimilation methods iterate observational data and models
  for possible efficient and accurate estimations of physical properties,
  which cannot be observed directly. We apply the Ensemble Kalman Filter
  method for assimilation of the sunspot data into a non-linear mean-field
  dynamo model, which takes into variations of magnetic helicity and
  parameters of the solar convection zone from helioseismology. We
  present the results of application of this data assimilation method
  for representation of the solar cycles and prediction of variations
  of the sunspot number, and discuss potentials of data assimilation
  methods for solar dynamo modeling.

---------------------------------------------------------
Title: NUMERICAL SIMULATION OF PROPAGATION AND SCATTERING OF THE
    MHD WAVES IN SUNSPOTS
Authors: Parchevsky, K.; Kosovichev, A. G.; Khomenko, E.; Collados, M.
2009AGUFMSH23B1535P    Altcode:
  We present comparison of numerical simulation results of MHD wave
  propagation in two different magnitostatic models of sunspots
  refferred to as "deep" and "shallow" models. The "deep" model has
  convex shape of magnetic field lines near the photosphere and non-zero
  horizorntal perturbations of the sound speed up to the bottom of the
  model (7.5 Mm). The "shallow" model has concave shape of the magnetic
  field lines near the photosphere and horizontally uniform sound speed
  below 2 Mm. Common feature of MHD waves behaviour in these two models
  is that for weak magnetic field (less than 1kG at the photosphere)
  waves reduce their amplitude when they reach the center of the sunspot
  and restore the amplitude when pass the center. For the "deep" model
  this effect is bigger than for the "shallow" model. The wave amplitude
  inside sunspots depends on the strength of the magnetic field. For the
  "shallow" model with photospheric magnetic field of 2.2 kG the wave
  amplitude inside the sunspot becomes bigger than outside (opposite to
  the weak magnetic field). The wave amplitude depends on the distance
  of the source from the sunspot center. For the "shallow" model and
  source distance of 9 Mm from the sunspot center the wave amplitude at
  some moment (when the wavefront passes the sunspot center) becomes
  bigger inside the sunspot than outside. For the source distance
  of 12 Mm the wave amplitude remains smaller inside the sunspot
  than outside for all moments of time. Using filtering technique we
  separated magnetoacoustic and magnetogravity waves. Simulations show
  that the sunspot changes the shape of the wave front and amplitude
  of the f-modes significantly stronger than the p-modes. It is shown,
  that inside the sunspot magnetoacoustic and magnetogravity waves are
  not spatially separated unlike the case of the horizontally uniform
  background model. Strong Alfven wave is generated at the wave source
  location in the "deep" model. This wave exists in the "shallow" model
  as well, but with much smaller amplitude.

---------------------------------------------------------
Title: Time-Distance Helioseismology Data Analysis Pipeline for
    SDO/HMI
Authors: Zhao, J.; Couvidat, S. P.; Parchevsky, K.; Duvall, T. L.;
   Beck, J. G.; Birch, A. C.; Kosovichev, A. G.
2009AGUFMSH13A1507Z    Altcode:
  Solar Dynamics Observatory (SDO) will be launched shortly, and
  high-resolution helioseismic data from Heliosesimic and Magnetic
  Imager (HMI) will soon be available. We have developed a data
  analysis procedure based on the time-distance helioseismology method,
  to automatically process 2 TB/day of solar oscillation data from the
  HMI instrument. The pipeline will provide the following data to the
  solar physics community: nearly whole disk maps of acoustic travel
  times, subsurface flow fields and sound-speed perturbation maps
  every eight hours. The data products include also real-time updated
  synoptic maps for subsurface flows and sound-speed perturbations. For
  the helioseismology community, the pipeline will provide intermediate
  data products such as cross-covariances of solar oscillations. This
  poster explains how we process the observational data, how we perform
  the travel-time measurements, how we derive the sensitivity kernels
  for inversions, and how we perform and test the inversion results.

---------------------------------------------------------
Title: The Origin of High-Speed Evershed Flows in Sunspots
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Wray, A. A.; Mansour,
   N. N.
2009AGUFMSH23B1534K    Altcode:
  Radial outflow of magnetized plasma in sunspot penumbrae, the
  Evershed effect, has a long history of observations and modeling,
  since its discovery in 1909. There are several different approaches
  for explaining this phenomenon, but these models cannot describe
  various observational facts. We have carried out 3D radiative MHD
  simulations of solar convection in the presence of magnetic field
  of different strength and inclination. The simulation results show
  that when the magnetic field is strong (1-2 kG) and highly inclined
  towards the surface (by 80-85 degrees) the granular convective cells
  transform into filamentary, flux-tube like structures with strong
  horizontal velocities. In addition, the convective process takes the
  form of traveling waves with convective cells moving in the direction
  of the field inclination. The combination of these two effects, the
  filamentary structure and the traveling convective waves, result in
  high-speed, 4-6 km/s, plasma streams, identified in observations as
  "Evershed clouds". In the case of a very strong magnetic field the
  streams form coherent structures across the field. The simulation
  results reproduce many observed features of the Evershed effect,
  and allow us to establish links with the previous models.

---------------------------------------------------------
Title: Realistic Numerical Modeling of Solar Magnetoconvection
    and Oscillations
Authors: Kitiashvili, I.; Jacoutot, L.; Kosovichev, A.
2009ASPC..415...83K    Altcode: 2009arXiv0901.4369K
  We have developed 3D, compressible, non-linear radiative MHD simulations
  to study the influence of magnetic fields of various strengths and
  geometries on the turbulent convective cells and on the excitation
  mechanisms of the acoustic oscillations. The results reveal substantial
  changes of the granulation structure with increased magnetic field,
  and a frequency-dependent reduction in the oscillation power. These
  simulation results reproduce the enhanced high-frequency acoustic
  emission observed at the boundaries of active region (“acoustic halo”
  phenomenon). In the presence of inclined magnetic field the solar
  convection develops filamentary structure with flows concentrated
  along magnetic filaments, and also exhibits behavior of running
  magnetoconvective waves, resembling recent observations of the sunspot
  penumbra dynamics from Hinode/SOT.

---------------------------------------------------------
Title: Comparing the Hinode and SOHO/MDI Data to the Simulated Large
    Scale Solar Convection
Authors: Georgobiani, D.; Zhao, J.; Kosovichev, A.; Benson, D.; Stein,
   R. F.; Nordlund, Å.
2009ASPC..415..421G    Altcode:
  Large-scale simulations of solar turbulent convection produce realistic
  data and provide a unique opportunity to study solar oscillations
  and test various techniques commonly used for the analysis of solar
  observations. We applied helioseismic methods to the sets of simulated
  as well as observed data and find remarkable similarities. Power
  spectra, k-ν diagrams, time-distance diagrams exhibit similar details,
  although sometimes subtle differences are present.

---------------------------------------------------------
Title: Solar Oscillations
Authors: Kosovichev, A. G.
2009AIPC.1170..547K    Altcode: 2010arXiv1001.5283K
  In recent years solar oscillations have been studied in great detail,
  both observationally and theoretically; so, perhaps, the Sun currently
  is the best understood pulsating star. The observational studies include
  long, almost uninterrupted series of oscillation data from the SOHO
  spacecraft and ground-based networks, GONG and BiSON, and more recently,
  extremely high-resolution observations from the Hinode mission. These
  observational data cover the whole oscillation spectrum, and have been
  extensively used for helioseismology studies, providing frequencies
  and travel times for diagnostics of the internal stratification,
  differential rotation, zonal and meridional flows, subsurface convection
  and sunspots. Together with realistic numerical simulations, they lead
  to better understanding of the excitation mechanism and interactions
  of the oscillations with turbulence and magnetic fields. However,
  many problems remain unsolved. In particular, the precision of the
  helioseismology measurements is still insufficient for detecting
  the dynamo zone and deep routes of sunspots. Our knowledge of the
  oscillation physics in strong magnetic field regions is inadequate for
  interpretation of MHD waves in sunspots and for sunspot seismology. A
  new significant progress in studying the solar oscillations is expected
  from the Solar Dynamics Observatory scheduled for launch in 2009.

---------------------------------------------------------
Title: Imaging the Solar Tachocline by Time-Distance Helioseismology
Authors: Zhao, Junwei; Hartlep, Thomas; Kosovichev, A. G.; Mansour,
   N. N.
2009ApJ...702.1150Z    Altcode: 2009arXiv0907.2118Z
  The solar tachocline at the bottom of the convection zone is an
  important region for the dynamics of the Sun and the solar dynamo. In
  this region, the sound speed inferred by global helioseismology
  exhibits a bump of approximately 0.4% relative to the standard solar
  model. Global helioseismology does not provide any information on
  possible latitudinal variations or asymmetries between the northern and
  southern hemisphere. Here, we develop a time-distance helioseismology
  technique, including surface- and deep-focusing measurement schemes and
  a combination of both, for two-dimensional tomographic imaging of the
  solar tachocline that infers radial and latitudinal variations in the
  sound speed. We test the technique using artificial solar oscillation
  data obtained from numerical simulations. The technique successfully
  recovers major features of the simplified tachocline models. The
  technique is then applied to SOHO/MDI medium-ell data and provides
  for the first time a full two-dimensional sound-speed perturbation
  image of the solar tachocline. The one-dimensional radial profile
  obtained by latitudinal averaging of the image is in good agreement
  with the previous global helioseismology result. It is found that the
  amplitude of the sound-speed perturbation at the tachocline varies
  with latitude, but it is not clear whether this is in part or fully an
  effect of instrumental distortion. Our initial results demonstrate that
  time-distance helioseismology can be used to probe the deep interior
  structure of the Sun, including the solar tachocline.

---------------------------------------------------------
Title: Numerical Modeling of Solar Convection and Oscillations in
    Magnetic Regions
Authors: Kitiashvili, I. N.; Jacoutot, L.; Kosovichev, A. G.; Wray,
   A. A.; Mansour, N. N.
2009AIPC.1170..569K    Altcode:
  Solar observations show that the spectra of turbulent convection
  and oscillations significantly change in magnetic regions, resulting
  in interesting phenomena, such as high-frequency “acoustic halos”
  around active regions. In addition, recent observations from SOHO/MDI
  revealed significant changes of the wave properties in inclined magnetic
  field regions of sunspots, which affect helioseismic inferences. We
  use realistic 3D radiative MHD numerical simulations to investigate
  properties of solar convection and excitation and propagation of
  oscillations in magnetic regions. A new feature of these simulations is
  implementation of a dynamic sub-grid turbulence model, which allows more
  accurate description of turbulent dissipation and wave excitation. We
  present the simulation results for a wide range of the field strength
  and inclination in the top 6 Mm layer of the convection zone. The
  results show interesting and unexpected effects in the dynamics and
  large-scale organization of the magnetoconvection (including traveling
  waves and shearing flows), and also changes in the excitation properties
  and spectrum of oscillations, suggesting an explanation of the acoustic
  “halos” observed above the acoustic cut-off frequency.

---------------------------------------------------------
Title: Traveling Waves of Magnetoconvection and the Origin of the
    Evershed Effect in Sunspots
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Wray, A. A.; Mansour,
   N. N.
2009ApJ...700L.178K    Altcode: 2009arXiv0904.3599K
  Discovered in 1909, the Evershed effect represents strong mass outflows
  in sunspot penumbra, where the magnetic field of sunspots is filamentary
  and almost horizontal. These flows play an important role in sunspots
  and have been studied in detail using large ground-based and space
  telescopes, but the basic understanding of its mechanism is still
  missing. We present results of realistic numerical simulations of
  the Sun's subsurface dynamics, and argue that the key mechanism of
  this effect is in nonlinear magnetoconvection that has properties
  of traveling waves in the presence of a strong, highly inclined
  magnetic field. The simulations reproduce many observed features of
  the Evershed effect, including the high-speed "Evershed clouds," the
  filamentary structure of the flows, and the nonstationary quasiperiodic
  behavior. The results provide a synergy of previous theoretical models
  and lead to an interesting prediction of a large-scale organization
  of the outflows.

---------------------------------------------------------
Title: Cosmic Magnetic Fields (IAU S259)
Authors: Strassmeier, Klaus G.; Kosovichev, Alexander G.; Beckman,
   John E.
2009IAUS..259.....S    Altcode:
  Preface K. G. Strassmeier, A. G. Kosovichev and J. E. Beckman;
  Organising committee; Conference photograph; Conference participants;
  Session 1. Interstellar magnetic fields, star-forming regions and
  the Death Valley Takahiro Kudoh and Elisabeta de Gouveia Dal Pino;
  Session 2. Multi-scale magnetic fields of the Sun; their generation
  in the interior, and magnetic energy release Nigel O. Weiss;
  Session 3. Planetary magnetic fields and the formation and evolution
  of planetary systems and planets; exoplanets Karl-Heinz Glassmeier;
  Session 4. Stellar magnetic fields: cool and hot stars Swetlana Hubrig;
  Session 5. From stars to galaxies and the intergalactic space Dimitry
  Sokoloff and Bryan Gaensler; Session 6. Advances in methods and
  instrumentation for measuring magnetic fields across all wavelengths
  and targets Tom Landecker and Klaus G. Strassmeier; Author index;
  Object index; Subject index.

---------------------------------------------------------
Title: Cosmic Magnetic Fields (IAU S259)
Authors: Strassmeier, Klaus G.; Kosovichev, Alexander G.; Beckman,
   John E.
2009cmf..book.....S    Altcode:
  Preface K. G. Strassmeier, A. G. Kosovichev and J. E. Beckman;
  Organising committee; Conference photograph; Conference participants;
  Session 1. Interstellar magnetic fields, star-forming regions and
  the Death Valley Takahiro Kudoh and Elisabeta de Gouveia Dal Pino;
  Session 2. Multi-scale magnetic fields of the Sun; their generation
  in the interior, and magnetic energy release Nigel O. Weiss;
  Session 3. Planetary magnetic fields and the formation and evolution
  of planetary systems and planets; exoplanets Karl-Heinz Glassmeier;
  Session 4. Stellar magnetic fields: cool and hot stars Swetlana Hubrig;
  Session 5. From stars to galaxies and the intergalactic space Dimitry
  Sokoloff and Bryan Gaensler; Session 6. Advances in methods and
  instrumentation for measuring magnetic fields across all wavelengths
  and targets Tom Landecker and Klaus G. Strassmeier; Author index;
  Object index; Subject index.

---------------------------------------------------------
Title: Testing the Sunspot Subsurface ("Coffee-Cup") Structure
Authors: Kosovichev, Alexander G.; Zhao, J.; Parchevsky, K. V.;
   Hartlep, T.
2009SPD....40.0703K    Altcode:
  Helioseismic inferences of the subsurface structure of sunspots
  have been in the focus of local helioseismology investigations and
  discussions during the past decade. Initially obtained from the SOHO/MDI
  high-resolution data using a simple ray-path perturbation theory for
  inversions of acoustic travel times the results draw significant
  criticism and concerns, but, in general, have been confirmed by
  subsequent measurements and inversions. Nevertheless, because of the
  complexity of the wave excitation and propagation in the subsurface
  layers there are still potential systematic uncertainties that must
  be resolved. Recently developed 3D simulations of MHD waves provide an
  important tool for the verification and testing of local helioseismology
  results. However, the use of the simulations is not as straightforward
  as originally thought. In particular, we present results of testing of
  the time-distance helioseismology measurement and inversion procedures
  for sound-speed perturbations modeling the sunspot subsurface structure,
  and discuss the limitations and uncertainties of the simulations and
  helioseismic inferences.

---------------------------------------------------------
Title: Simulated Large Scale Solar Convection Versus Observations:
    A Multiwavelength Approach
Authors: Georgobiani, Dali; Zhao, J.; Kosovichev, A. G.; Benson, D.;
   Stein, R. F.; Nordlund, A.
2009SPD....40.0301G    Altcode:
  The realistic 3D radiative-hydrodynamic simulations of the upper layers
  of solar convection provide a perfect opportunity to validate various
  techniques, widely used in solar physics and helioseismology. Our
  aim is to perform multiwavelength analysis of large scale flows. We
  analyze the simulated intensity and velocities at certain heights
  in the solar atmosphere, and compare our results with the outcome
  of the similar analysis of the SOHO/MDI and Hinode observations. To
  fine tune the comparison, we use the instrumental response functions
  to weigh the simulated parameters at different heights to emulate
  the observational lines. We find the remarkable similarity between
  the simulated and observed power spectra, their spatial parts, and
  time-distance diagrams. This demonstrates one more time that the
  simulations can be efficiently used to perform and validate local
  helioseismology techniques, and to study solar flows and structures
  beneath the surface, inaccessible for direct observations.

---------------------------------------------------------
Title: Observing Interactions of Helioseismic Waves with Sunspots
Authors: Zhao, Junwei; Kosovichev, A. G.
2009SPD....40.0302Z    Altcode:
  Recently, the interactions between solar magnetic field and acoustic
  waves have been widely investigated using both numerical simulations
  and theoretical analysis,including effects of MHD wave transformations
  and absorption. However, a picture of how solar waves interact
  with a sunspot at the photospherical level has not been obtained
  observationally. In this presentation, we apply a time-distance
  correlation analysis to high-resolution MDI observations to investigate
  how the solar acoustic and surface gravity waves interact with
  sunspots. The analysis is carried out separately for the p- and f-mode
  waves. It is found that when acoustic sources are located outside
  the sunspot, the p-mode waves propagate through the sunspot with a
  faster speed and a reduced amplitude. The speed and amplitude become
  similar to the quiet Sun values after the waves pass through the active
  region. If the acoustic source is located inside the sunspot, the waves
  propagate with a reduced amplitude, and initially have a reduced speed
  but then accelerate. The f-mode waves often go through the sunspot with
  a reduced amplitude and a faster speed, but their amplitude and speed
  do not recover after passing the sunspot area. The results are nicely
  illustrated in movies showing the waves interacting with a sunspot.

---------------------------------------------------------
Title: Acoustic Power and Travel Time Signatures of Emerging
    Subsurface Structures
Authors: Kosovichev, A. G.; Hartlep, Thomas; Zhao, J.; Mansour, N. N.
2009SPD....40.0709K    Altcode:
  It is generally believed that larger magnetic structures rising from
  below the surface by self induction and convection can lead to the
  formation of active regions and sunspots on the solar surface. For
  space weather forecasting, one would like to detect such subsurface
  structures before they become visible on the surface. In this work
  we investigate signatures of such emerging subsurface structures. <P
  />Numerical simulations of solar acoustic wave propagation performed
  by us show that under suitable conditions subsurface structures that
  modify the propagation speed of the waves can result, depending on
  the sign of the perturbation, in a reduction or enhancement of the
  acoustic power observed at the photosphere above them. Results from our
  simulations and observational evidence is presented. <P />In principle,
  measurements of travel times may also be able to detect signatures of
  such emerging subsurface structures. The limiting factor is here the
  short measurement time required, since active region usually emerge
  rather quickly, and the associated noise level. We will present results
  from analyzing artificial data obtained from our simulations as well
  as MDI observations.

---------------------------------------------------------
Title: Large-scale horizontal flows in the solar photosphere IV. On
    the vertical structure of large-scale horizontal flows
Authors: Švanda, M.; Klvaňa, M.; Sobotka, M.; Kosovichev, A. G.;
   Duvall, T. L.
2009NewA...14..429S    Altcode: 2008arXiv0812.1971S
  In the recent papers, we introduced a method utilised to measure
  the flow field. The method is based on the tracking of supergranular
  structures. We did not precisely know, whether its results represent
  the flow field in the photosphere or in some subphotospheric
  layers. In this paper, in combination with helioseismic data, we
  are able to estimate the depths in the solar convection envelope,
  where the detected large-scale flow field is well represented by
  the surface measurements. We got a clear answer to question what
  kind of structures we track in full-disc Dopplergrams. It seems that
  in the quiet Sun regions the supergranular structures are tracked,
  while in the regions with the magnetic field the structures of the
  magnetic field are dominant. This observation seems obvious, because
  the nature of Doppler structures is different in the magnetic regions
  and in the quiet Sun. We show that the large-scale flow detected by
  our method represents the motion of plasma in layers down to ∼10
  Mm. The supergranules may therefore be treated as the objects carried
  by the underlying large-scale velocity field.

---------------------------------------------------------
Title: Realistic 3D MHD Simulations of the Evershed Effect
Authors: Kitiashvili, Irina; Kosovichev, A. G.; Wray, A. A.; Mansour,
   N. N.
2009SPD....40.0906K    Altcode:
  Effect of the horizontal radial outflow in a sunspot penumbra (called
  "Evershed effect") has a 100-year history of investigations, but its
  physical nature is not clear yet. The Evershed flows begin at bright
  penumbral grains and propagate outward along penumbra filaments
  with the mean velocity of 1 - 2 km/s. High-resolution observations
  reveal that the Evershed flows are non-stationary, and that the
  strongest, 4 - 5 km/s, flows appear in quasi-periodic patches,
  "Evershed clouds". To study the nature of the Evershed effect we
  simulate behavior of convective motions in the presence strong
  inclined magnetic field. We use a 3D radiative non-linear MHD code,
  which describes realistic physical properties: compressible fluid
  flow in a highly stratified and magnetized plasma, 3D multi-group
  radiative energy transfer, a real-gas equation of state, and sub-grid
  scale turbulence models. We present a set of numerical experiments,
  which include the upper solar convection zone and lower atmosphere for
  different magnetic field strength (600 - 2000 Gauss) and inclination
  (0 - 90 degrees). The results show the development of filamentary
  magnetic structures and systematic flows in the direction of field
  inclination, strongly resembling the Evershed effect in penumbra. In
  particular, the simulations reproduce the high-speed "Evershed clouds",
  relationships between the flow velocity and the field strength and
  inclination, and other observational characteristics. We discuss the
  simulation results in the context of previously models, such as the
  embedded flux tube model, the magnetic gap model and the overturning
  magnetoconvection model, and argue that the physical mechanism of
  the Evershed effect is in a non-linear interaction between the narrow
  overturning convective motions and traveling magnetoconvection waves,
  formed in highly inclined strong magnetic field regions.

---------------------------------------------------------
Title: Subsurface Flows in Solar Active Regions and Polar Areas from
    Hinode Observations
Authors: Zhao, Junwei; Kosovichev, A. G.; Sekii, T.
2009SPD....40.0706Z    Altcode:
  High-resolution observations of Ca II H line intensity made by Hinode
  have provided us an opportunity to study subsurface flow fields of
  solar active regions with an unprecedented high spatial resolution,
  and a possibility to study subsurface meridional flows in the solar
  polar areas. For a large active region, we have found a strong
  downdraft below the sunspot, a mass circulation around the spot, and
  an evidence of magnetoconvection beneath the strong field area. For
  the polar regions, we have been able to derive a poleward meridional
  flow of an order of 5 m/s for the first time using the time-distance
  helioseismology technique.

---------------------------------------------------------
Title: Scattering of MHD Waves by Sunspots
Authors: Parchevsky, Konstantin; Kosovichev, A. G.
2009SPD....40.0704P    Altcode:
  Investigation of the interaction of MHD waves with sunspots is very
  important for correct interpretation of local helioseismology data and
  sunspot seismology. We compare results of 3D numerical simulations of
  propagation of the MHD waves in subphotospheric and photospheric layers
  of sunspots. Two self-consistent magnetohydrostatic background models
  of sunspots based on a solution of Pizzo and a self-similar solution of
  Low were chosen as the background models. We consider the models with
  different magnetic field and sound-speed depth structures, extended into
  the deep interior and shallow. The MHD waves form two distinct classes:
  magnetoacoustic and magnetogravity modes. There are similarities and
  differences in wave behavior in the sunspot models. It is shown, that
  inside the sunspot magnetoacoustic and magnetogravity waves are not
  spatially separated unlike the case of the horizontally uniform magnetic
  field. The sunspot causes anisotropy of the amplitude distribution along
  the wavefront and changes the shape of the wavefront. The amplitude of
  the waves is reduced inside the sunspot. This effect is stronger for
  the magnetogravity waves than for the magnetoacoustic waves. The shape
  of the wavefront of the magnetogravity waves is distorted stronger
  as well. For the deep sunspot model the anisotropy is stronger for
  both magnetoacoustic and magnetogravity waves than for the shallow
  model. These effects cause changes in wave travel times. A strong
  Alfven wave is generated at the wave source location in the deep
  sunspot model. This wave is almost unnoticeable in the shallow model.

---------------------------------------------------------
Title: Prediction of solar magnetic cycles by a data assimilation
    method
Authors: Kitiashvili, Irina N.; Kosovichev, Alexander G.
2009IAUS..259..235K    Altcode:
  We consider solar magnetic activity in the context of sunspot number
  variations, as a result of a non-linear oscillatory dynamo process. The
  apparent chaotic behavior of the 11-year sunspot cycles and undefined
  errors of observations create uncertainties for predicting the
  strength and duration of the cycles. Uncertainties in dynamo model
  parameters create additional difficulties for the forecasting. Modern
  data assimilation methods allow us to assimilate the observational
  data into the models for possible efficient and accurate estimations
  of the physical properties, which cannot be observed directly, such as
  the internal magnetic fields and helicity. We apply the Ensemble Kalman
  Filter method to a low-order non-linear dynamo model, which takes into
  account variations of the turbulent magnetic helicity and reproduces
  basic characteristics of the solar cycles. We investigate the predictive
  capabilities of this approach, and present test results for prediction
  of the previous cycles and a forecast of the next solar cycle 24.

---------------------------------------------------------
Title: Magnetic fields and dynamics of the Sun's interior
Authors: Kosovichev, Alexander G.
2009IAUS..259..147K    Altcode:
  Advances in helioseismology provide new knowledge about the origin of
  solar magnetic activity. The key questions addressed by helioseismology
  are: what is the physical mechanism of the solar dynamo, how deep inside
  the Sun are the magnetic fields generated, how are they transported to
  the surface and form sunspots? Direct helioseismic signatures of the
  internal magnetic fields are weak and difficult to detect. Therefore,
  most of the information comes from observations of dynamical effects
  caused by the magnetic fields. I review results of recent helioseismic
  observations of the magnetohydrodynamics of the solar interior on
  various scales, including global dynamics associated with the dynamo
  processes, and formation of sunspots and active regions.

---------------------------------------------------------
Title: Photospheric and Subphotospheric Dynamics of Emerging
    Magnetic Flux
Authors: Kosovichev, A. G.
2009SSRv..144..175K    Altcode: 2009arXiv0901.0035K
  Magnetic fields emerging from the Sun’s interior carry information
  about physical processes of magnetic field generation and transport
  in the convection zone. Soon after appearance on the solar surface the
  magnetic flux gets concentrated in sunspot regions and causes numerous
  active phenomena on the Sun. This paper discusses some properties
  of the emerging magnetic flux observed on the solar surface and
  in the interior. A statistical analysis of variations of the tilt
  angle of bipolar magnetic regions during the emergence shows that
  the systematic tilt with respect to the equator (the Joy’s law) is
  most likely established below the surface. However, no evidence of the
  dependence of the tilt angle on the amount of emerging magnetic flux,
  predicted by the rising magnetic flux rope theories, is found. Analysis
  of surface plasma flows in a large emerging active region reveals strong
  localized upflows and downflows at the initial phase of emergence but
  finds no evidence for large-scale flows indicating future appearance
  a large-scale magnetic structure. Local helioseismology provides
  important tools for mapping perturbations of the wave speed and mass
  flows below the surface. Initial results from SOHO/MDI and GONG reveal
  strong diverging flows during the flux emergence, and also localized
  converging flows around stable sunspots. The wave speed images obtained
  during the process of formation of a large active region, NOAA 10488,
  indicate that the magnetic flux gets concentrated in strong field
  structures just below the surface. Further studies of magnetic flux
  emergence require systematic helioseismic observations from the ground
  and space, and realistic MHD simulations of the subsurface dynamics.

---------------------------------------------------------
Title: Solution to the discrepancy between the seismic and
    photospheric solar radius
Authors: Haberreiter, M.; Kosovichev, A. G.; Schmutz, W.
2009EGUGA..11.3961H    Altcode:
  Two methods are usually used to observationally determine the solar
  radius: One is the observation of the intensity profile at the limb,
  the other one uses f-mode frequencies to derive a 'seismic' solar
  radius which is then corrected to optical depth unity. The two methods
  are inconsistent and lead to a difference in the solar radius of
  approx. 0.3 Mm. Based on radiative transfer calculations we show that
  this discrepancy can be explained by the difference between the height
  at disk center where tau500=1 and the inflection point of the intensity
  profile on the limb. We calculate the intensity profile of the limb
  for the MDI continuum and the continuum at 5000 A for two atmosphere
  structures and compare the position of the inflection points with the
  radius at optical depth unity. The calculated difference between the
  'seismic' radius and the inflection point is 0.347 Mm with respect to
  optical depth unity and 0.333 Mm with respect to the Rossland mean
  opacity. We conclude that the standard solar radius in evolutionary
  models has to be lowered by 0.333 Mm and is 695.66 Mm. This correction
  reconciles inflection point measurements and the seismic radius within
  the uncertainty. This finding is very important for the analysis of
  the solar diameter measurements with the SODISM instrument on PICARD.

---------------------------------------------------------
Title: Helioseismic Signature of Chromospheric Downflows in Acoustic
    Travel-Time Measurements From Hinode
Authors: Nagashima, Kaori; Sekii, Takashi; Kosovichev, Alexander G.;
   Zhao, Junwei; Tarbell, Theodore D.
2009ApJ...694L.115N    Altcode: 2009arXiv0903.1323N
  We report on a signature of chromospheric downflows in two emerging
  flux regions detected by time-distance helioseismology analysis. We
  use both chromospheric intensity oscillation data in the Ca II H line
  and photospheric Dopplergrams in the Fe I 557.6 nm line obtained
  by Hinode/SOT for our analyses. By cross-correlating the Ca II
  oscillation signals, we have detected a travel-time anomaly in the
  plage regions; outward travel times are shorter than inward travel
  times by 0.5-1 minute. However, such an anomaly is absent in the Fe
  I data. These results can be interpreted as evidence of downflows in
  the lower chromosphere. The downflow speed is estimated to be below
  10 km s<SUP>-1</SUP>. This result demonstrates a new possibility of
  studying chromospheric flows by time-distance analysis.

---------------------------------------------------------
Title: Numerical Simulation of Excitation and Propagation of
Helioseismic MHD Waves: Effects of Inclined Magnetic Field
Authors: Parchevsky, K. V.; Kosovichev, A. G.
2009ApJ...694..573P    Altcode: 2008arXiv0806.2897P
  Investigation of propagation, conversion, and scattering of MHD
  waves in the Sun is very important for understanding the mechanisms of
  observed oscillations and waves in sunspots and active regions. We have
  developed a three-dimensional linear MHD numerical model to investigate
  the influence of the magnetic field on excitation and properties of
  the MHD waves. The results show that surface gravity waves (f-modes)
  are affected by the background magnetic field more than acoustic-type
  waves (p-modes). Comparison of our simulations with the time-distance
  helioseismology results from Solar and Heliospheric Observatory/MDI
  shows that the amplitude of travel time variations with azimuth around
  sunspots caused by the inclined magnetic field does not exceed 25%
  of the observed amplitude even for strong fields of 1400-1900 G. This
  can be an indication that other effects (e.g., background flows and
  nonuniform distribution of the magnetic field) can contribute to the
  observed azimuthal travel time variations. The azimuthal travel time
  variations caused by the wave interaction with the magnetic field are
  similar for simulated and observed travel times for strong fields of
  1400-1900 G if Doppler velocities are taken at the height of 300 km
  above the photosphere where the plasma parameter β Lt 1. For the
  photospheric level the travel times are systematically smaller by
  approximately 0.12 minutes than for the height of 300 km above the
  photosphere for all studied ranges of the magnetic field strength and
  inclination angles. Numerical MHD wave modeling and new data from the
  HMI instrument of the Solar Dynamics Observatory will substantially
  advance our knowledge of the wave interaction with strong magnetic
  fields on the Sun and improve the local helioseismology diagnostics.

---------------------------------------------------------
Title: POLAR investigation of the Sun—POLARIS
Authors: Appourchaux, T.; Liewer, P.; Watt, M.; Alexander, D.;
   Andretta, V.; Auchère, F.; D'Arrigo, P.; Ayon, J.; Corbard, T.;
   Fineschi, S.; Finsterle, W.; Floyd, L.; Garbe, G.; Gizon, L.; Hassler,
   D.; Harra, L.; Kosovichev, A.; Leibacher, J.; Leipold, M.; Murphy,
   N.; Maksimovic, M.; Martinez-Pillet, V.; Matthews, B. S. A.; Mewaldt,
   R.; Moses, D.; Newmark, J.; Régnier, S.; Schmutz, W.; Socker, D.;
   Spadaro, D.; Stuttard, M.; Trosseille, C.; Ulrich, R.; Velli, M.;
   Vourlidas, A.; Wimmer-Schweingruber, C. R.; Zurbuchen, T.
2009ExA....23.1079A    Altcode: 2008ExA...tmp...40A; 2008arXiv0805.4389A
  The POLAR Investigation of the Sun (POLARIS) mission uses a combination
  of a gravity assist and solar sail propulsion to place a spacecraft
  in a 0.48 AU circular orbit around the Sun with an inclination of 75°
  with respect to solar equator. This challenging orbit is made possible
  by the challenging development of solar sail propulsion. This first
  extended view of the high-latitude regions of the Sun will enable
  crucial observations not possible from the ecliptic viewpoint or from
  Solar Orbiter. While Solar Orbiter would give the first glimpse of
  the high latitude magnetic field and flows to probe the solar dynamo,
  it does not have sufficient viewing of the polar regions to achieve
  POLARIS’s primary objective: determining the relation between the
  magnetism and dynamics of the Sun’s polar regions and the solar cycle.

---------------------------------------------------------
Title: Theoretical Modeling of Propagation of Magnetoacoustic Waves
    in Magnetic Regions Below Sunspots
Authors: Khomenko, E.; Kosovichev, A.; Collados, M.; Parchevsky, K.;
   Olshevsky, V.
2009ApJ...694..411K    Altcode: 2008arXiv0809.0278K
  We use two-dimensional numerical simulations and eikonal approximation
  to study properties of magnetohydrodynamic (MHD) waves traveling below
  the solar surface through the magnetic structure of sunspots. We
  consider a series of magnetostatic models of sunspots of different
  magnetic field strengths, from 10 Mm below the photosphere to the
  low chromosphere. The purpose of these studies is to quantify the
  effect of the magnetic field on local helioseismology measurements
  by modeling waves excited by subphotospheric sources. Time-distance
  propagation diagrams and wave travel times are calculated for models
  of various field strengths and compared to the nonmagnetic case. The
  results clearly indicate that the observed time-distance helioseismology
  signals in sunspot regions correspond to fast MHD waves. The slow MHD
  waves form a distinctly different pattern in the time-distance diagram,
  which has not been detected in observations. The numerical results are
  in good agreement with the solution in the short-wavelength (eikonal)
  approximation, providing its validation. The frequency dependence of
  the travel times is in good qualitative agreement with observations.

---------------------------------------------------------
Title: Nonlinear dynamical modeling of solar cycles using dynamo
    formulation with turbulent magnetic helicity
Authors: Kitiashvili, I. N.; Kosovichev, A. G.
2009GApFD.103...53K    Altcode: 2008arXiv0807.3192K
  Variations of the sunspot number are important indicators of the
  solar activity cycles. The sunspot formation is a result of a dynamo
  process inside the Sun, which is far from being understood. We use
  simple dynamical models of the dynamo process to simulate the magnetic
  field evolution and investigate general properties of the sunspot
  number variations during the solar cycles. We have found that the
  classical Parker's model with a standard kinetic helicity quenching
  cannot represent the typical profiles of the solar-cycle variations
  of the sunspot number, and also does not give chaotic solutions. For
  modeling of the solar cycle properties we use a nonlinear dynamo model
  of Kleeorin and Ruzmaikin (1982), which takes into account dynamics of
  the turbulent magnetic helicity. We have obtained a series of periodic
  and chaotic solutions for different layers of the convective zone. The
  solutions qualitatively reproduce some basic observational features of
  the solar cycle properties, in particular, the relationship between
  the growth time and the cycle amplitude. Also, on the longer time
  scale the dynamo model with the magnetic helicity has intermittent
  solutions, which may be important for modeling long-term variations
  of the solar cycles.

---------------------------------------------------------
Title: Division II: Sun and Heliosphere
Authors: Melrose, Donald B.; Martínez Pillet, Valentin; Webb, David
   F.; van Driel-Gesztelyi, Lidia; Bougeret, Jean-Louis; Klimchuk,
   James A.; Kosovichev, Alexander; von Steiger, Rudolf
2009IAUTA..27...73M    Altcode:
  Division II of the IAU provides a forum for astronomers and
  astrophysicists studying a wide range of phenomena related to the
  structure, radiation and activity of the Sun, and its interaction with
  the Earth and the rest of the solar system. Division II encompasses
  three Commissions, 10, 12 and 49, and four Working Groups.

---------------------------------------------------------
Title: Photospheric and Subphotospheric Dynamics of Emerging
    Magnetic Flux
Authors: Kosovichev, A. G.
2009odsm.book..175K    Altcode:
  Magnetic fields emerging from the Sun's interior carry information
  about physical processes of magnetic field generation and transport
  in the convection zone. Soon after appearance on the solar surface the
  magnetic flux gets concentrated in sunspot regions and causes numerous
  active phenomena on the Sun. This paper discusses some properties of
  the emerging magnetic flux observed on the solar surface and in the
  interior. A statistical analysis of variations of the tilt angle
  of bipolar magnetic regions during the emergence shows that the
  systematic tilt with respect to the equator (the Joy's law) is most
  likely established below the surface. However, no evidence of the
  dependence of the tilt angle on the amount of emerging magnetic flux,
  predicted by the rising magnetic flux rope theories, is found. Analysis
  of surface plasma flows in a large emerging active region reveals strong
  localized upflows and downflows at the initial phase of emergence but
  finds no evidence for large-scale flows indicating future appearance
  a large-scale magnetic structure. Local helioseismology provides
  important tools for mapping perturbations of the wave speed and mass
  flows below the surface. Initial results from SOHO/MDI and GONG reveal
  strong diverging flows during the flux emergence, and also localized
  converging flows around stable sunspots. The wave speed images obtained
  during the process of formation of a large active region, NOAA 10488,
  indicate that the magnetic flux gets concentrated in strong field
  structures just below the surface. Further studies of magnetic flux
  emergence require systematic helioseismic observations from the ground
  and space, and realistic MHD simulations of the subsurface dynamics.

---------------------------------------------------------
Title: Solar Dynamo and Magnetic Self-Organization
Authors: Kosovichev, A. G.; Arlt, R.; Bonanno, A.; Brandenburg,
   A.; Brun, A. S.; Busse, F.; Dikpati, M.; Hill, F.; Gilman, P. A.;
   Nordlund, A.; Ruediger, G.; Stein, R. F.; Sekii, T.; Stenflo, J. O.;
   Ulrich, R. K.; Zhao, J.
2009astro2010S.160K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Signatures of emerging subsurface structures in the sun
Authors: Hartlep, T.; Kosovichev, A. G.; Zhao, J.; Mansour, N. N.
2009arXiv0901.4585H    Altcode:
  The complex dynamics that lead to the emergence of active regions on the
  sun are poorly understood. One possibility is that magnetic structures
  (flux tubes, etc.) rise from below the surface by self induction and
  convection that lead to the formation of active regions and sunspots
  on the solar surface. For space weather forecasting, one would like
  to detect the subsurface structures before they reach the surface. The
  goal of this study is to investigate whether sound speed perturbations
  associated with subsurface structures could affect the acoustic power
  observed at the solar surface above them. Possible mechanisms for
  this effect are wave reflection, scattering or diffraction. By using
  numerical simulations of wave propagation in the solar interior, we
  investigate whether observations of the acoustic power can be used to
  detect emerging active regions before they appear on the surface. In
  the simulations, subsurface structures are modeled as regions with
  enhanced or reduced acoustic wavespeed. We show how the acoustic power
  above a subsurface region depends on the sign, depth and strength of
  the wavespeed perturbation. For comparison, we analyze observations
  from SOHO/MDI of the emergence of solar active region NOAA 10488.

---------------------------------------------------------
Title: Commission 12: Solar Radiation and Structure
Authors: Martínez Pillet, Valentin; Kosovichev, Alexander;
   Mariska, John T.; Bogdan, Thomas J.; Asplund, Martin; Cauzzi, Gianna;
   Christensen-Dalsgaard, Jørgen; Cram, Lawrence E.; Gan, Weiqun; Gizon,
   Laurent; Heinzl, Petr; Rovira, Marta G.; Venkatakrishnan, P.
2009IAUTA..27..104M    Altcode:
  Commission 12 encompasses investigations on the internal structure
  and dynamics of the Sun, mostly accessible through the techniques of
  local and global helioseismology, the quiet solar atmosphere, solar
  radiation and its variability, and the nature of relatively stable
  magnetic structures like sunspots, faculae and the magnetic network. A
  revision of the progress made in these fields is presented. For some
  specific topics, the review has counted with the help of experts
  outside the Commission Organizing Committee that are leading and/or
  have recently presented relevant works in the respective fields. In
  this cases the contributor's name is given in parenthesis.

---------------------------------------------------------
Title: Validating Time-Distance Far-Side Imaging of Solar Active
    Regions through Numerical Simulations
Authors: Hartlep, Thomas; Zhao, Junwei; Mansour, Nagi N.; Kosovichev,
   Alexander G.
2008ApJ...689.1373H    Altcode: 2008arXiv0805.0472H
  Far-side imaging using time-distance helioseismology methods is
  assessed using numerically generated artificial data. The data are
  generated using direct numerical simulations of acoustic oscillations
  in a spherical solar model. Localized variations of the sound speed in
  the surface and subsurface layers are used to model the perturbations
  associated with sunspots and active regions. The accuracy of acoustic
  travel-time far-side maps is shown to depend on the size and location of
  active regions. Potential artifacts in the far-side imaging procedure,
  such as those caused by the presence of active regions on the solar
  near side, are also investigated.

---------------------------------------------------------
Title: Tilt of Emerging Bipolar Magnetic Regions on the Sun
Authors: Kosovichev, A. G.; Stenflo, J. O.
2008ApJ...688L.115K    Altcode:
  Magnetic fields emerging from the Sun's interior carry information about
  the physical processes of magnetic field generation and transport in the
  convection zone. A statistical analysis of variations of the tilt angle
  of bipolar magnetic regions during the emergence, observed from SOHO
  MDI, shows that the systematic tilt with respect to the equator (Joy's
  law) is established by the middle of the emergence period. This suggests
  that the tilt is most likely generated below the surface. However,
  the data do not show evidence of a dependence of the tilt angle on
  the amount of flux or a relaxation of the bipolar orientation toward
  the east-west direction, in contrast to the predictions of the rising
  magnetic flux rope theories.

---------------------------------------------------------
Title: Using Data Assimilation Methods for Modeling and Predicting
    Solar Activity Cycles
Authors: Kitiashvili, I. N.; Kosovichev, A. G.
2008AGUFMSH13A1506K    Altcode:
  Modern data assimilation methods allow us to adapt a model to
  observations by estimating the true state of a system and taking into
  account uncertainties in the data and the model. The Ensemble Kalman
  Filter (EnKF) method provides an effective data assimilation for
  models of nonlinear dynamics. It is based on analysis of an ensemble
  of model solutions. We implement the EnKF method for modeling the
  11-year sunspot number variations. Using this approach we propose a
  new physics-based method for predicting for the strength of the solar
  sunspot cycles. For the initial modeling of the sunspot number we use
  a dynamo model of Kleeorin and Ruzmaikin dynamo model in a low-mode
  approximation. The model includes the Parker's dynamo equations
  and an equation for conservation of the magnetic helicity. Also, we
  accept Bracewell's suggestion to relate the toroidal magnetic field,
  B, to the sunspot number, W,in the form of a three-halfs law: W ~
  B3/2. We investigate non-linear solutions of the dynamo model and find
  periodic and chaotic solutions for the convection zone parameters, which
  represent basic properties of the solar cycles, such as the mean profile
  of solar cycle and the relationship between the cycle amplitude and the
  growth and decay times. By applying the EnKF method to the non-linear
  periodic solutions we reproduce the annual variations of the sunspot
  number and investigate the predictive capabilities. For testing we
  calculate forecasts for the 10 previous cycles and find a reasonable
  agreement with the observations. The calculations of the forecast of the
  upcoming solar cycle 24 indicate that this cycle will be weaker than
  the previous one, with the maximum sunspot number of about 80. This
  investigation shows that data assimilation methods may be useful for
  evaluating solar dynamo models and for forecasting solar activity.

---------------------------------------------------------
Title: High-Resolution Helioseismology from Hinode
Authors: Kosovichev, A. G.; Zhao, J.; Sekii, T.; Nagashima, K.;
   Mitra-Kraev, U.
2008AGUFMSH41B1627K    Altcode:
  The Solar Optical Telescope (SOT) on the Hinode space mission provides
  unique multi-wavelength high-resolution data for local helioseismic
  diagnostics of the sub-photospheric structure and dynamics of the
  Sun. The helioseismology data from Hinode have allowed us for the
  first time to observe oscillations of very high angular degree and
  high frequencies. The Hinde data provide a potential for substantial
  improvement of the spatial resolution of time-distance helioseismology
  in near-surface layers of the Sun, compared to the previous SOHO/MDI
  data. The Hinode data have also provided important insight in the nature
  of sunspot oscillations. Simultaneous observations of solar oscillations
  in two different spectral interval have allowed us to investigate the
  mode physics and the correlated component of stochastic excitation. In
  addition, a new type of flare-excited MHD oscillations was detected
  from Hinode observations of the solar flare of December 13, 2006.

---------------------------------------------------------
Title: Helioseismic Measurement of Subsurface Flows at Solar High
    Latitude
Authors: Zhao, J.; Kosovichev, A. G.; Sekii, T.
2008AGUFMSH44A..03Z    Altcode:
  The solar polar magnetic field is of great interest as it is where
  solar magnetic field reversal starts. Surface and subsurface plasma
  flows are very important in understanding the field reversal because
  magnetic field flux is transported to solar high latitude from lower
  latitude according to flux transport theory. Local helioseismology
  has been able to derive subsurface flow fields, rotation rates,
  and meridional flows up to 30 Mm in depth. The results obtained by
  time-distance helioseismology during Solar Cycle 23 from SOHO/MDI have
  also revealed significant changes of the speed and the longitudinal
  structure of the flows. We used these measurements to compare with the
  magnetic flux transport determined from the magnetic field synoptic
  data. Furthermore, by use of MDI dynamic campaign observations and
  a recent high resolution observation of solar South Pole by Hinode,
  we explore the possibility to detect subsurface flow fields in solar
  high latitude.

---------------------------------------------------------
Title: Application of Data Assimilation Method for Predicting
    Solar Cycles
Authors: Kitiashvili, I.; Kosovichev, A. G.
2008ApJ...688L..49K    Altcode: 2008arXiv0807.3284K
  Despite the known general properties of the solar cycles, a reliable
  forecast of the 11 yr sunspot number variations is still a problem. The
  difficulties are caused by the apparent chaotic behavior of the
  sunspot numbers from cycle to cycle and by the influence of various
  turbulent dynamo processes, which we are far from understanding. For
  predicting the solar cycle properties we make an initial attempt to use
  the Ensemble Kalman Filter (EnKF), a data assimilation method, which
  takes into account uncertainties of a dynamo model and measurements, and
  allows us to estimate future observational data. We present the results
  of forecasting of the solar cycles obtained by the EnKF method in
  application to a low-mode nonlinear dynamical system modeling the solar
  α Ω -dynamo process with variable magnetic helicity. Calculations
  of the predictions for the previous sunspot cycles show a reasonable
  agreement with the actual data. This forecast model predicts that the
  next sunspot cycle will be significantly weaker (by ~30%) than the
  previous cycle, continuing the trend of low solar activity.

---------------------------------------------------------
Title: Realistic Numerical Simulations of Solar Convection and
    Oscillations in Magnetic Regions
Authors: Jacoutot, L.; Kosovichev, A. G.; Wray, A.; Mansour, N. N.
2008ApJ...684L..51J    Altcode:
  We have used 3D, compressible, nonlinear radiative magnetohydrodynamics
  simulation to study the influence of magnetic fields of various
  strengths on convective cells and on the excitation mechanisms of
  acoustic oscillations by calculating the spectral properties of the
  convective motions and oscillations. The results reveal substantial
  changes of the granulation structure with increased magnetic field and
  a frequency-dependent reduction in the oscillation power in a good
  agreement with solar observations. These simulations suggest that
  the enhanced high-frequency acoustic emission at the boundaries of
  active regions ("acoustic halo" phenomenon) is caused by changes of
  the spatial-temporal spectrum of turbulent convection in a magnetic
  field, resulting in turbulent motions of smaller scales and higher
  frequencies than in quiet-Sun regions.

---------------------------------------------------------
Title: Numerical Simulation of Excitation of Solar Oscillation Modes
    for Different Turbulent Models
Authors: Jacoutot, L.; Kosovichev, A. G.; Wray, A. A.; Mansour, N. N.
2008ApJ...682.1386J    Altcode: 2007arXiv0710.2317J
  The goal of this research is to investigate how well various turbulence
  models can describe the physical properties of the upper convective
  boundary layer of the Sun. Accurate modeling of these turbulent
  motions is necessary for understanding the excitation mechanisms of
  solar oscillation modes. We have carried out realistic numerical
  simulations using a hyperviscosity approach and various physical
  Large-Eddy Simulation (LES) models (Smagorinsky and dynamic models)
  to investigate how the differences in turbulence modeling affect
  the damping and excitation of the oscillations and their spectral
  properties and to compare with observations. We have first calculated
  the oscillation power spectra of radial and nonradial modes supported
  by the computational box with the different turbulence models, followed
  by calculation of the work integral input to the modes to estimate
  the influence of the turbulence model on the depth and strength of
  the oscillation sources. We have compared these results with previous
  studies and with the observed properties of solar oscillations. We
  find that the dynamic turbulence model provides the best agreement
  with the helioseismic observations.

---------------------------------------------------------
Title: A solar mean field dynamo benchmark
Authors: Jouve, L.; Brun, A. S.; Arlt, R.; Brandenburg, A.; Dikpati,
   M.; Bonanno, A.; Käpylä, P. J.; Moss, D.; Rempel, M.; Gilman, P.;
   Korpi, M. J.; Kosovichev, A. G.
2008A&A...483..949J    Altcode:
  Context: The solar magnetic activity and cycle are linked to an
  internal dynamo. Numerical simulations are an efficient and accurate
  tool to investigate such intricate dynamical processes. <BR />Aims:
  We present the results of an international numerical benchmark
  study based on two-dimensional axisymmetric mean field solar dynamo
  models in spherical geometry. The purpose of this work is to provide
  reference cases that can be analyzed in detail and that can help in
  further development and validation of numerical codes that solve such
  kinematic problems. <BR />Methods: The results of eight numerical
  codes solving the induction equation in the framework of mean field
  theory are compared for three increasingly computationally intensive
  models of the solar dynamo: an αΩ dynamo with constant magnetic
  diffusivity, an αΩ dynamo with magnetic diffusivity sharply varying
  with depth and an example of a flux-transport Babcock-Leighton dynamo
  which includes a non-local source term and one large single cell of
  meridional circulation per hemisphere. All cases include a realistic
  profile of differential rotation and thus a sharp tachocline. <BR
  />Results: The most important finding of this study is that all codes
  agree quantitatively to within less than a percent for the αΩ dynamo
  cases and within a few percent for the flux-transport case. Both
  the critical dynamo numbers for the onset of dynamo action and the
  corresponding cycle periods are reasonably well recovered by all
  codes. Detailed comparisons of butterfly diagrams and specific cuts of
  both toroidal and poloidal fields at given latitude and radius confirm
  the good quantitative agreement. <BR />Conclusions: We believe that
  such a benchmark study will be a very useful tool since it provides
  detailed standard cases for comparison and reference.

---------------------------------------------------------
Title: Effects of Solar Active Regions on Meridional Flows
Authors: Švanda, Michal; Kosovichev, Alexander G.; Zhao, Junwei
2008ApJ...680L.161S    Altcode: 2008arXiv0805.1789S
  The aim of this Letter is to extend our previous study of the
  solar-cycle variations of meridional flows and to investigate their
  latitudinal and longitudinal structure in the subphotospheric layer,
  especially their variations in magnetic regions. Helioseismology
  observations indicate that mass flows around active regions are
  dominated by inflows into those regions. On average, those local
  flows are more important around the leading magnetic polarities of
  active regions than around the following polarities and depend on
  the evolutionary stage of particular active regions. We present a
  statistical study based on MDI/SOHO observations of 1996-2002 and show
  that this effect explains a significant part of the cyclic change
  of meridional flows in near-equatorial regions, but not at higher
  latitudes. A different mechanism driving solar-cycle variations of
  the meridional flow probably operates.

---------------------------------------------------------
Title: Influence of Nonuniform Distribution of Acoustic Wavefield
    Strength on Time-Distance Helioseismology Measurements
Authors: Parchevsky, Konstantin V.; Zhao, Junwei; Kosovichev,
   Alexander G.
2008ApJ...678.1498P    Altcode: 2008arXiv0802.3866P
  By analyzing numerically simulated solar oscillation data we study
  the influence of nonuniform distribution of acoustic wave amplitude,
  acoustic source strength, and perturbations of the sound speed on
  the shifts of acoustic travel times measured by the time-distance
  helioseismology method. It is found that for short distances, the
  contribution to the mean travel-time shift caused by nonuniform
  distribution of acoustic sources in sunspots may be comparable to
  (but smaller than) the contribution from the sound-speed perturbation
  in sunspots, and that it has the opposite sign to the sound-speed
  effect. This effect may cause some underestimation of the negative
  sound-speed perturbations in sunspots just below the surface, which
  was found in previous time-distance helioseismology inferences. This
  effect cannot be corrected by artificially increasing the amplitude of
  oscillations in sunspots. For large time-distance annuli, the nonuniform
  distribution of wavefields does not have significant effects on the mean
  travel times, and thus the sound-speed inversion results. The measured
  travel-time differences, which are used to determine the mass flows
  beneath sunspots, can also be systematically shifted by this effect,
  but only by an insignificant magnitude.

---------------------------------------------------------
Title: Study of the magnetoconvection and oscillations in the upper
    convection zone by means of realistic numerical simulations
Authors: Jacoutot, L.; Kosovichev, A.; Mansour, N.; Wray, A.
2008AGUSMSP21A..06J    Altcode:
  Recent high-resolution data from the Hinode space mission have
  shown that magnetic fields on the Sun are concentrated in small
  high-intensity magnetic flux tubes in the intergranular lanes. Our
  objective is to investigate how magnetic field affects the dynamics
  of granular convection and excitation of solar oscillations by means
  of realistic numerical simulations. We have used a 3D, compressible,
  non-linear radiative magnetohydrodynamics code developed at the NASA
  Ames Research Center. This code takes into account several physical
  phenomena: compressible fluid flow in a highly stratified medium,
  sub-grid scale turbulence models, radiative energy transfer between the
  fluid elements, and a real-gas equation of state. We have studied the
  influence of the magnetic field of various strength on the convective
  cells and on the excitation mechanisms of the acoustic oscillations
  by calculating spectral properties of the convective motions and
  oscillations. The results reveal substantial changes of the granulation
  structure with increased magnetic field, and a frequency-dependent
  reduction in the oscillation power. The simulation results are compared
  with Hinode observations.

---------------------------------------------------------
Title: Solar convection and oscillations in magnetic regions
Authors: Jacoutot, L.; Kosovichev, A. G.; Wray, A.; Mansour, N. N.
2008arXiv0805.3741J    Altcode:
  The goal of this research is to investigate how magnetic field
  affects the dynamics of granular convection and excitation of solar
  oscillations by means of realistic numerical simulations. We have
  used a 3D, compressible, non-linear radiative magnetohydrodynamics
  code developed at the NASA Ames Research Center. This code takes
  into account several physical phenomena: compressible fluid flow in a
  highly stratified medium, sub-grid scale turbulence models, radiative
  energy transfer between the fluid elements, and a real-gas equation of
  state. We have studied the influence of the magnetic field of various
  strength on the convective cells and on the excitation mechanisms of
  the acoustic oscillations by calculating spectral properties of the
  convective motions and oscillations. The results reveal substantial
  changes of the granulation structure with increased magnetic field,
  and a frequency-dependent reduction in the oscillation power in a good
  agreement with solar observations. These simulations suggest that the
  enhanced high-frequency acoustic emission at the boundaries of active
  region ("acoustic halo" phenomenon) is caused by the changes of the
  spatial-temporal spectrum of the turbulent convection in magnetic field,
  resulting in turbulent motions of smaller scales and higher frequencies
  than in quiet Sun regions.

---------------------------------------------------------
Title: Initial Helioseismology Results from Hinode
Authors: Kosovichev, A.; Zhao, J.; Sekii, T.; Nagashima, K.
2008AGUSMSP21A..01K    Altcode:
  Solar Optical Telescope of Hinode provides unique multi-wavelength
  high-resolution data for local helioseismic diagnostics of the
  sub-surface structure and dynamics of the Sun. The helioseismology data
  from Hinode have allowed us for the first time to observe oscillations
  of very high angular degree and high frequencies, and substantially
  improve the spatial resolution of time-distance helioseismology in
  near-surface layers of the Sun, compared to the previous SOHO/MDI
  data. The Hinode data have also provided important insight in the
  nature of sunspot oscillations. Initial attempts have been made to
  investigate the dynamics of the polar regions, previously unaccessible
  for helioseismology. We present the first results and discuss the
  potential and perspective of the Hinode helioseismology program.

---------------------------------------------------------
Title: Development of Time-Distance Helioseismology Data Analysis
    Pipeline for SDO/HMI
Authors: Duvall, T. L.; Zhao, J.; Couvidat, S.; Parchevsky, K. V.;
   Beck, J.; Kosovichev, A. G.; Scherrer, P. H.
2008AGUSMSP51B..15D    Altcode:
  The Helioseismic and Magnetic Imager of SDO will provide uninterrupted
  4kx4k-pixel Doppler-shift images of the Sun with ~45 sec cadence. These
  data will have a unique potential for advancing local helioseismic
  diagnostics of the Sun's interior structure and dynamics. They
  will help to understanding the basics mechanisms of solar activity
  and developing predictive capabilities for the NASA's Living with
  a Star Program. Because of the tremendous amount of data the HMI
  team is developing a data analysis pipeline, which will provide maps
  of subsurface flows and sound-speed distributions inferred from the
  Doppler data by the time-distance technique. We discuss the development
  plan, methods and algorithms, and present the status of the pipeline,
  testing results and examples of the data products.

---------------------------------------------------------
Title: First Detection of MHD Oscillations Excited by Solar Flare
    in Sunspot Umbra
Authors: Kosovichev, A.; Sekii, T.
2008AGUSMSP21B..07K    Altcode:
  We report on detection of a new type of flare-excited oscillations
  from Hinode observations of the solar flare of December 13, 2006. The
  oscillations observed in Ca II H images appeared in the sunspot
  umbra immediately after the impulsive phase of the flare. They had
  the amplitude 2-4 times larger than the pre-flare oscillations in
  the umbra. Also, their frequency seemed to be higher. There is an
  evidence that during the first 30-40 min the oscillations represent
  waves traveling through the umbra in the direction away from the flare
  ribbon with a speed of 50-100 km/s. Then, the oscillation become more
  irregular with some occasional wave packets. The lifetime of these
  oscillations is probable about 8 hours. The estimated speed indicates
  that the waves are of an MHD type, and if their speed is of the order
  of magnitude of the Alfven speed then they should propagate rather low
  in the sunspot chromosphere. Sunspot oscillations have been studied
  intensively for many years but the Hinode observations are the first
  that show enhanced oscillations in the umbra, associated with a solar
  flare. Further investigations of these oscillations are of great
  interest for understanding the processes in solar flares and sunspots.

---------------------------------------------------------
Title: Modeling of Helioseismic MHD Waves in Presence of Inclined
    Magnetic Field.
Authors: Parchevsky, K. V.; Kosovichev, A. G.
2008AGUSMSH54A..02P    Altcode:
  Studying of propagation, conversion, and scattering of MHD waves in
  the Sun is very important for developing robust local helioseismology
  techniques and diagnostics of subsurface magnetic fields. We use
  3D numerical simulations to study propagation of MHD waves from
  wave sources of different types (vertical force and pressure) in
  presence of uniform and non-uniform inclined magnetic field, and for
  an equilibrium sunspot model. Numerical simulations show that presence
  of the background magnetic field significantly alters properties of
  the surface gravity f-modes, but has substantially smaller effect on
  p-modes. When the wave source is located in a strong field region it
  generates Alfven waves. The Alfven waves do not appear if the wave
  source is located in the region without magnetic field, and waves
  propagate from that region into the region with magnetic field without
  significant transformation. The wave travel times obtained from cross
  covariance of the p-mode line-of-sight velocities at the observation
  point and the source point show variation of about 1 min along the wave
  front. Due to asymmetry, average of travel times along the wave front
  is not zero and show variations of about a few seconds. Comparison of
  the simulations with the time-distance helioseismology results from
  SOHO/MDI shows that the observed variations of acoustic travel times
  obtained from the Doppler velocity measurements are not caused by the
  inclined magnetic field effects contrary to previous suggestions.

---------------------------------------------------------
Title: Application of Data Assimilation Methods to Non-Linear Dynamo
    Models of Solar Cycle
Authors: Kitiashvili, I.; Kosovichev, A.
2008AGUSMSP23A..02K    Altcode:
  Solar dynamo is a very complicated non-linear oscillatory MHD process,
  which is far from understanding. It produces 11-year sunspot cycles,
  which show chaotic behavior and are hard to predict. It has been
  suggested that the basic oscillatory behavior of the solar dynamo can
  be described in terms of simple non-linear dynamical systems. The data
  assimilation approach developed in meteorology and Earth science makes
  possible efficient and accurate estimations of physical properties,
  which cannot be observed directly. The applications of data assimilation
  to non-linear dynamo models for modeling and predicting the solar
  cycle are discussed in this presentation.

---------------------------------------------------------
Title: Time-Distance Helioseismic Image of Solar Tachocline Area
Authors: Zhao, J.; Hartlep, T.; Kosovichev, A. G.; Mansour, N. N.
2008AGUSMSP21A..02Z    Altcode:
  Solar tachocline is an area located at the bottom of solar convection
  zone. It is also a location where sound speed exhibits a bump
  relative to the standard solar model, and where solar rotation has a
  large shear. Tachocline is generally believed as the location where
  solar dynamo operates, therefore, it is important and interesting
  to image its structure, as well as its structure evolution with
  solar cycle. Using both surface- and deep-focusing time-distance
  helioseismology techniques, we have designed measurement schemes and
  developed inversion codes to derive sound speed perturbations at the
  tachocline area. Those codes are tested on numerically simulated data,
  which simulates the global acoustic wavefields with an artificial
  tachocline model. After getting some satisfactory results from
  simulation data, we apply the technique on SOHO/MDI medium-l data,
  and study the acoustic structure of solar interior, as well as its
  evolution with the solar cycle.

---------------------------------------------------------
Title: Properties of high-degree oscillation modes of the Sun observed
    with Hinode/SOT
Authors: Mitra-Kraev, U.; Kosovichev, A. G.; Sekii, T.
2008A&A...481L...1M    Altcode: 2007arXiv0711.2210M
  Aims:With the Solar Optical Telescope on Hinode, we investigate
  the basic properties of high-degree solar oscillations observed at
  two levels in the solar atmosphere, in the G-band (formed in the
  photosphere) and in the Ca II H line (chromospheric emission). <BR
  />Methods: We analyzed the data by calculating the individual power
  spectra as well as the cross-spectral properties, i.e., coherence and
  phase shift. The observational properties are compared with a simple
  theoretical model, which includes the effects of correlated noise. <BR
  />Results: The results reveal significant frequency shifts between the
  Ca II H and G-band spectra, in particular above the acoustic cut-off
  frequency for pseudo-modes. The cross-spectrum phase shows peaks
  associated with the acoustic oscillation (p-mode) lines, and begins to
  increase with frequency around the acoustic cut-off. However, we find
  no phase shift for the (surface gravity wave) f-mode. The observed
  properties for the p-modes are qualitatively reproduced in a simple
  model with a correlated background if the correlated noise level in
  the Ca II H data is higher than in the G-band data. These results
  suggest that multi-wavelength observations of solar oscillations,
  in combination with the traditional intensity-velocity observations,
  may help to determine the level of the correlated background noise
  and to determine the type of wave excitation sources on the Sun.

---------------------------------------------------------
Title: Solving the Discrepancy between the Seismic and Photospheric
    Solar Radius
Authors: Haberreiter, M.; Schmutz, W.; Kosovichev, A. G.
2008ApJ...675L..53H    Altcode:
  Two methods are used to observationally determine the solar radius:
  One is the observation of the intensity profile at the limb; the other
  one uses f-mode frequencies to derive a "seismic" solar radius which is
  then corrected to optical depth unity. The two methods are inconsistent
  and lead to a difference in the solar radius of ~0.3 Mm. Because of the
  geometrical extension of the solar photosphere and the increased path
  lengths of tangential rays the Sun appears to be larger to an observer
  who measures the extent of the solar disk. Based on radiative transfer
  calculations we show that this discrepancy can be explained by the
  difference between the height at disk center where τ<SUB>5000</SUB> =
  1 (τ<SUB>Ross</SUB> = 2/3) and the inflection point of the intensity
  profile on the limb. We calculate the intensity profile of the limb
  for the MDI continuum and the continuum at 5000 Å for two atmosphere
  structures and compare the position of the inflection points with
  the radius at τ<SUB>5000</SUB> = 1 (τ<SUB>Ross</SUB> = 2/3). The
  calculated difference between the seismic radius and the inflection
  point is 0.347 +/- 0.006 Mm with respect to τ<SUB>5000</SUB> = 1,
  and 0.333 +/- 0.008 Mm with respect to τ<SUB>Ross</SUB> = 2/3. We
  conclude that the standard solar radius in evolutionary models has to
  be lowered by 0.333 +/- 0.008 Mm and is 695.66 Mm. Furthermore, this
  correction reconciles inflection point measurements and the seismic
  radii within the uncertainties.

---------------------------------------------------------
Title: Modeling Non-Uniform Distribution of Acoustic Sources and
    Wave Leakage in Sunspots
Authors: Parchevsky, K. V.; Kosovichev, A. G.
2008ASPC..383..289P    Altcode:
  Observations show suppression of the amplitude of 5-min oscillations
  in sunspots. We developed a 3D numerical simulation code to model
  wave excitation and propagation in the upper convection zone and the
  atmosphere of the Sun. We model how suppression of acoustic sources
  affects the oscillation amplitude in sunspot regions. The calculations
  show that this suppression (due to strong magnetic field) significantly
  reduces the oscillation amplitude to a level comparable with the
  observed amplitude deficit. The precise value of the amplitude ratio
  outside and inside sunspots depends on the rate of wave leakage and
  damping in the lower atmosphere. We present the results of detailed
  investigation of this effect, including modeling of wave damping at
  various heights in the atmosphere and the frequency dependence of the
  amplitude ratio. These results show the importance of the wave energy
  leakage through the atmospheric layers of sunspots.

---------------------------------------------------------
Title: Probing solar and stellar interior dynamics and dynamo
Authors: Kosovichev, Alexander G.
2008AdSpR..41..830K    Altcode:
  Solar and stellar activity is a result of complex interaction between
  magnetic field, turbulent convection and differential rotation in
  a star’s interior. Magnetic field is believed to be generated by
  a dynamo process in the convection zone. It emerges on the surface
  forming sunspots and starspots. Localization of the magnetic spots and
  their evolution with the activity cycle is determined by large-scale
  interior flows. Thus, the internal dynamics of the Sun and other
  stars hold the key to understanding the dynamo mechanism and activity
  cycles. Recently, significant progress has been made for modeling
  magnetohydrodynamics of the stellar interiors and probing the internal
  rotation and large-scale dynamics of the Sun by helioseismology. Also,
  asteroseismology is beginning to probe interiors of distant stars. I
  review key achievements and challenges in our quest to understand the
  basic mechanisms of solar and stellar activity.

---------------------------------------------------------
Title: Local Helioseismology and Magnetic Flux Emergence
Authors: Kosovichev, A. G.; Duvall, T. L., Jr.
2008ASPC..383...59K    Altcode:
  Investigations of emerging magnetic flux are important for understanding
  the basic properties of solar magnetism (such as the depth of the solar
  dynamo processes and “nests” of solar activity, formation of sunspots
  and active regions, organization of solar activity on various spatial
  and temporal scales), and also for forecasting solar activity and space
  weather. Local helioseismology is capable of detecting emerging magnetic
  flux in the solar interior, and determining variations of the sound
  speed and large-scale flows caused by the emerging flux. The initial
  results obtained by time-distance helioseismology for large emerging
  active regions reveal unexpected properties of the flux emergence and
  challenge the current theories and models. In this paper, we present
  results for AR 10488, which was observed from SOHO/MDI in October
  2003. In particular, it is found that the magnetic flux propagates
  very rapidly in the upper convective zone. The active regions are a
  result of multiple flux emergence events, occurring in the region of
  the Sun during a period at least several days long. The emergence
  is accompanied by strong localized shearing outflows. However, no
  large-scale diverging flow pattern or significant upflows are detected
  prior to the emergence. The initial analysis shows that it is necessary
  to develop special local helioseismology methodology and theoretical
  models for studying fast dynamical processes associated with magnetic
  flux emergence.

---------------------------------------------------------
Title: Solar Polar Imager: Observing Solar Activity from a New
    Perspective
Authors: Liewer, P. C.; Ayon, J.; Alexander, D.; Kosovichev, A.;
   Mewaldt, R. A.; Socker, D. G.; Vourlidas, A.
2008nssv.book....1L    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Realistic Numerical Simulations of Solar Magneto-Convection
    and Oscillations
Authors: Jacoutot, L.; Kosovichev, A. G.; Mansour, N. N.; Wray, A.
2007AGUFMSH23A1167J    Altcode:
  The objective of this research is to study how magnetic field affects
  the structure and dynamics of solar convection and the sources that
  drive the waves in the Sun. We use a 3D, compressible, non-linear
  radiative magnetohydrodynamics code developed by Dr. A. Wray for
  simulating the upper solar photosphere and lower atmosphere. This
  code takes into account several physical phenomena: compressible
  fluid flow in a highly stratified medium, radiative energy transfer
  between the fluid elements, magnetic phenomena, and a real-gas equation
  of state. Magnetic fields play a crucial role in the structure and
  heating of the outer atmosphere. Our objectives are to understand the
  processes related to magnetic fields in this zone. We investigate the
  interaction between convection, magnetic fields, and oscillations.

---------------------------------------------------------
Title: Imaging Solar Farside and Tachocline Using SOHO/MDI Data and
    Numerical Simulations
Authors: Zhao, J.; Hartlep, T.; Kosovichev, A. G.; Mansour, N. N.
2007AGUFMSH32A0791Z    Altcode:
  To be able to see large solar active regions when they are located
  on the farside of the Sun before rotating into the earth side is of
  great importance for space weather forecast. By analyzing acoustic wave
  signals that are reflected back to the near-side from the farside after
  four and five skips, we are able to map the real-time farside active
  regions with good signal to noise ratio by use of SOHO/MDI medium-l
  observations. This technique is validated by employing numerical data
  that simulate the solar global acoustic wavefields. Solar tachocline
  is generally believed as the location where solar dynamo operates. We
  have developed a time-distance helioseismology code to measure and
  invert sound speed perturbations at the tachocline area, and also
  tested the code by use of numerical simulation data. The technique is
  then used on SOHO/MDI medium-l observations to map the evolution of
  the tachocline from 1996 through 2007.

---------------------------------------------------------
Title: Validation of Far-side Imaging of Solar Active Regions through
    Numerical Simulations
Authors: Hartlep, T.; Zhao, J.; Mansour, N. N.; Kosovichev, A. G.
2007AGUFMSH32A0790H    Altcode:
  Helioseismology provides important tools for understanding the solar
  interior as well as for space weather forecast. Using observation
  data from instruments such as MDI (Michelson Doppler Imager) aboard
  the SOHO (Solar and Heliospheric Observatory) spacecraft, helioseismic
  inferences have tremendously advanced our knowledge and understanding
  of the interior structure and dynamics of the Sun. In general, the
  methods used for analyzing observations are based on simplified models
  of wave propagation such as ray or Born approximation, but have not been
  validated by more sophisticated models or numerical simulations. Here,
  we evaluate one technique, far-side imaging of solar active region by
  time-distance helioseismology, by using artificial oscillation data
  derived from numerical simulations of wave propagation in the Sun. The
  simulations are performed for the full spherical Sun. Active regions
  are modeled by locally modifying the speed of sound. We evaluate the
  performance of the far-side imaging technique by varying the size and
  location of the artificial active region, and analyse the appearance of
  ghost images and artifacts. This research is supported by NASA's Living
  with a Star program. The support ot the NASA Postdoctoral Program
  administered by Oak Ridge Associated Universities is gratefully
  acknowledged. Simulations have been performed on the Columbia
  Supercomputer at NASA Ames Research Center.

---------------------------------------------------------
Title: Numerical Simulations of MHD Waves in the Sun
Authors: Parchevsky, K. V.; Kosovichev, A. G.
2007AGUFMSH31A0220P    Altcode:
  Investigation of propagation, conversion, and scattering of MHD
  waves in the Sun is very important for understanding the mechanisms
  of transformation of the acoustic waves into different types of MHD
  waves. Such studying is also an essential part of developing robust
  local helioseismology techniques and diagnostics of subsurface magnetic
  fields. In this studying we investigate excitation, propagation, and
  conversion of different kinds of MHD waves in presence of the background
  inclined magnetic field. Waves are generated by the localized force
  and pressure sources with different frequencies placed at different
  depths. We have developed a complete linear 3D MHD numerical model
  to investigate influence of the magnetic field on wave properties and
  helioseismology measurements in realistic solar conditions. The results
  show that the magnetic field effects can substantially change the
  properties of the surface gravity waves (f-mode), but their influence
  on the acoustic-type waves (p-modes) is rather moderate. We find that
  magnetic field can lead to a collimation of the wave front. We also
  observe formation of Alfven waves in our simulations. The numerical
  modeling and new data from the HMI instrument on SDO will substantially
  advance our knowledge of the wave interaction with magnetic fields on
  the Sun and improve the local helioseismology diagnostics.

---------------------------------------------------------
Title: Initial Observations of Sunspot Oscillations Excited by
    Solar Flare
Authors: Kosovichev, A. G.; Sekii, T.
2007ApJ...670L.147K    Altcode: 2007arXiv0710.1808K
  Observations of a large solar flare on 2006 December 13 using Solar
  Optical Telescope (SOT) on board the Hinode spacecraft revealed
  high-frequency oscillations excited by the flare in the sunspot
  chromosphere. These oscillations are observed in the region of strong
  magnetic field of the sunspot umbra and may provide a new diagnostic
  tool for probing the structure of sunspots and understanding physical
  processes in solar flares.

---------------------------------------------------------
Title: Helioseismic Observations of Active Regions Below the Solar
    Surface from SOHO/MDI
Authors: Kosovichev, A. G.; Duvall, T. L.
2007AGUFMSH23A1168K    Altcode:
  We apply the time-distance helioseismology technique to obtain 3D
  tomographic images of sound-speed variations and mass flow velocity maps
  below the visible surface of the Sun, for emerging and evolving magnetic
  active regions. In particular, using uninterrupted helioseismology
  observations from the MDI instrument on the SOHO spacecraft we
  investigate the development of the large complex of activity NOAA
  10484-10488, which produced a series of giant proton flares in October,
  2003. The flow maps reveal new interesting properties, such as strong
  divergent and shearing flows associated with the magnetic flux emergence
  and flaring activity. Using the sound-speed image we attempt to find
  the common roots and links of these remarkable active regions.

---------------------------------------------------------
Title: Initial Helioseismic Observations by Hinode/SOT
Authors: Sekii, Takashi; Kosovichev, Alexander G.; Zhao, Junwei;
   Tsuneta, Saku; Shibahashi, Hiromoto; Berger, Thomas E.; Ichimoto,
   Kiyoshi; Katsukawa, Yukio; Lites, Bruce; Nagata, Shin'ichi; Shimizu,
   Toshifumi; Shine, Richard A.; Suematsu, Yoshinori; Tarbell, Theodore
   D.; Title, Alan M.
2007PASJ...59S.637S    Altcode: 2007arXiv0709.1806S
  Results from initial helioseismic observations by the Solar Optical
  Telescope on-board Hinode are reported. It has been demonstrated
  that intensity oscillation data from the Broadband Filter Imager
  can be used for various helioseismic analyses. The k - ω power
  spectra, as well as the corresponding time-distance cross-correlation
  function, which promise high-resolution time-distance analysis below
  the 6-Mm travelling distance, were obtained for G-band and CaII-H
  data. Subsurface supergranular patterns were observed from our first
  time-distance analysis. The results show that the solar oscillation
  spectrum is extended to much higher frequencies and wavenumbers, and
  the time-distance diagram is extended to much shorter travel distances
  and times than were observed before, thus revealing great potential
  for high-resolution helioseismic observations from Hinode.

---------------------------------------------------------
Title: Observations of Sunspot Oscillations in G Band and CaII H
    Line with Solar Optical Telescope on Hinode
Authors: Nagashima, Kaori; Sekii, Takashi; Kosovichev, Alexander G.;
   Shibahashi, Hiromoto; Tsuneta, Saku; Ichimoto, Kiyoshi; Katsukawa,
   Yukio; Lites, Bruce; Nagata, Shin'ichi; Shimizu, Toshifumi; Shine,
   Richard A.; Suematsu, Yoshinori; Tarbell, Theodore D.; Title, Alan M.
2007PASJ...59S.631N    Altcode: 2007arXiv0709.0569N
  Exploiting high-resolution observations made by the Solar Optical
  Telescope on board Hinode, we investigate the spatial distribution
  of the power spectral density of the oscillatory signal in and around
  the active region NOAA 10935. The G-band data show that in the umbra
  the oscillatory power is suppressed in all frequency ranges. On
  the other hand, in CaII H intensity maps oscillations in the umbra,
  so-called umbral flashes, are clearly seen with the power peaking around
  5.5mHz. The CaII H power distribution shows the enhanced elements with
  the spatial scale of the umbral flashes over most of the umbra, but
  there is a region with suppressed power at the center of the umbra. The
  origin and property of this node-like feature remain unexplained.

---------------------------------------------------------
Title: The Cause of Photospheric and Helioseismic Responses to Solar
Flares: High-Energy Electrons or Protons?
Authors: Kosovichev, A. G.
2007ApJ...670L..65K    Altcode: 2007arXiv0710.0757K
  Analysis of the hydrodynamic and helioseismic effects in the photosphere
  during the solar flare of 2002 July 23, observed by MDI/SOHO, and
  high-energy images from RHESSI show that these effects are closely
  associated with sources of the hard X-ray emission but that no such
  effects existed in the centroid region of the flare's gamma-ray
  emission. These results demonstrate that, contrary to expectations,
  these hydrodynamic and helioseismic responses (“sunquakes”) are
  more likely to be caused by accelerated electrons than by high-energy
  protons. A series of multiple impulses of high-energy electrons form
  a hydrodynamic source that is moving in the photosphere at supersonic
  speed. This moving source plays a critical role in the formation of
  the anisotropic wave front of sunquakes.

---------------------------------------------------------
Title: Speed of Meridional Flows and Magnetic Flux Transport on
    the Sun
Authors: Švanda, Michal; Kosovichev, Alexander G.; Zhao, Junwei
2007ApJ...670L..69S    Altcode: 2007arXiv0710.0590S
  We use the magnetic butterfly diagram to determine the speed of the
  magnetic flux transport on the solar surface toward the poles. The
  manifestation of the flux transport is clearly visible as elongated
  structures extended from the sunspot belt to the polar regions. The
  slopes of these structures are measured and interpreted as meridional
  magnetic flux transport speed. Comparison with the time-distance
  helioseismology measurements of the mean speed of the meridional flows
  at a depth of 3.5-12 Mm shows a generally good agreement, but the
  speeds of the flux transport and the meridional flow are significantly
  different in areas occupied by the magnetic field. The local circulation
  flows around active regions, especially the strong equatorward flows
  on the equatorial side of active regions, affect the mean velocity
  profile derived by helioseismology but do not influence the magnetic
  flux transport. The results show that the mean longitudinally averaged
  meridional flow measurements by helioseismology may not be used directly
  in solar dynamo models for describing the magnetic flux transport, and
  that it is necessary to take into account the longitudinal structure
  of these flows.

---------------------------------------------------------
Title: Observations of Helioseismic Response to Flare energy-release
    Events
Authors: Kosovichev, A. G.
2007ASPC..369..325K    Altcode:
  The energy release in solar flares may cause not only plasma eruptions
  in the corona and heliosphere, but also may lead to excitation of
  acoustic wave packets propagating inside the Sun. These waves are
  observed on the solar surface as ripples propagating from the places
  where high-energy particles hit the lower chromosphere. Observations of
  such seismic event (called "sunquakes") provide important information
  about properties of the high-energy particles accelerated during the
  energy release events, their interaction with the plasma of the low
  atmosphere, hydrodynamic and MHD processes in solar flares, and also
  open perspectives for developing new helioseismic diagnostics. In
  this paper, I review some recent observational results and discuss an
  observing program for Solar-B to study such events.

---------------------------------------------------------
Title: Effect of Suppressed Excitation on the Amplitude Distribution
    of 5 Minute Oscillations in Sunspots
Authors: Parchevsky, K. V.; Kosovichev, A. G.
2007ApJ...666L..53P    Altcode: 2007arXiv0707.2586P
  Five minute oscillations on the Sun (acoustic and surface gravity waves)
  are excited by subsurface turbulent convection. However, in sunspots
  the excitation is suppressed because a strong magnetic field inhibits
  convection. We use three-dimensional simulations to investigate how
  the suppression of excitation sources affects the distribution of
  the oscillation power in sunspot regions. The amplitude of random
  acoustic sources was reduced in circular-shaped regions to simulate
  the suppression in sunspots. The simulation results show that the
  amplitude of the oscillations can be approximately 2-4 times lower in
  the sunspot regions in comparison to the quiet Sun, just because of
  the suppressed sources. Using SOHO MDI data we measured the amplitude
  ratio for the same frequency bands outside and inside sunspots and
  found that this ratio is approximately 3-4. Hence, the absence of
  excitation sources inside sunspots makes a significant contribution
  (about 50% or higher) to the observed amplitude ratio and must be
  taken into account in sunspot seismology.

---------------------------------------------------------
Title: Three-dimensional Numerical Simulations of the Acoustic Wave
    Field in the Upper Convection Zone of the Sun
Authors: Parchevsky, K. V.; Kosovichev, A. G.
2007ApJ...666..547P    Altcode: 2006astro.ph.12364P
  Results of numerical three-dimensional (3D) simulations of propagation
  of acoustic waves inside the Sun are presented. A linear 3D code
  which utilizes the realistic OPAL equation of state was developed. A
  modified convectively stable standard solar model with a smoothly joined
  chromosphere was used as a background model. A high-order dispersion
  relation-preserving numerical scheme was used. The top nonreflecting
  boundary condition established in the chromosphere absorbs waves with
  frequencies greater than the acoustic cutoff frequency which pass
  through the chromosphere, simulating a realistic situation. We simulate
  acousto-gravity wave fields on the Sun, generated by localized randomly
  distributed sources in a subphotospheric layer. Three applications for
  solar wave physics are presented: changes in oscillation properties due
  to the mechanism of wave damping, effects of nonuniform distribution
  of sources, and effects of nonuniform localized perturbations on
  wave properties. In particular, we studied two models of wave damping
  with leakage and with an explicit friction-type damping term in the
  photospheric layers and chromosphere. In both cases we were able to
  reproduce observed characteristics of the acoustic spectrum (line
  widths and amplitude distribution). We found that the suppression of
  acoustic sources, e.g., in sunspots, may significantly contribute to
  the observed power deficit. The lower sound speed in sunspot areas
  may cause an increase of the wave amplitude, but this effect is less
  important for the acoustic power distribution than the suppression of
  the acoustic sources.

---------------------------------------------------------
Title: Magnetic Effect on Wavelike Properties of Solar
    Supergranulation
Authors: Green, C. A.; Kosovichev, A. G.
2007ApJ...665L..75G    Altcode:
  Supergranular convective cells on the Sun rotate faster than surface
  plasma or any other feature. Recent time-distance helioseismology
  results suggest that supergranulation has properties of traveling
  waves. We have suggested that these properties may be due to the steep
  gradient of the subsurface shear layer. We used a linear model to
  calculate the phase speeds of the unstable convective modes. These
  phase speeds are greater than the speed of the surface plasma;
  however, they are significantly lower than the observed speed of the
  supergranular pattern. This suggests to us that the subsurface shear
  layer is a plausible explanation for the wavelike behavior. We now
  investigate the contribution of the magnetic field to the wavelike
  behavior produced by the shear gradient, and we show that a horizontal
  (toroidal) magnetic field in the subsurface layer will result in an
  increase in the phase speed of the traveling convective modes. This
  prediction can be checked by an analysis of the observational data.

---------------------------------------------------------
Title: Joint Discussion 8 Solar and stellar activity cycles
Authors: Kosovichev, Alexander G.; Strassmeier, Klaus G.
2007HiA....14..271K    Altcode:
  The solar magnetic field and its associated atmospheric activity
  exhibits periodic variations on a number of time scales. The 11-year
  sunspot cycle and its underlying 22-year magnetic cycle are, besides
  the 5-minute oscillation, the most widely known. Amplitudes and
  periods range from a few parts per million (ppm) and 2 3 minutes for
  p-modes in sunspots, a few 10 ppm and 10 minutes for the granulation
  turn around, a few 100 ppm and weeks for the lifetime of plages and
  faculae, 1000 ppm and 27 days for the rotational signal from spots, to
  the long-term cycles of 90 yr (Gleissberg cycle), 200 - 300 yr (Wolf,
  Spörer, Maunder minima), 2,400 yr from <SUP>14</SUP>C tree-ring data,
  and possibly in excess of 100,000 yr.

---------------------------------------------------------
Title: Effects of Magnetism and Turbulent Viscosity on the Wave-like
    Behaviour of Supergranulation
Authors: Green, Cristina; Kosovichev, A. G.
2007AAS...210.4605G    Altcode: 2007BAAS...39..161G
  Supergranular convective cells on the Sun rotate faster than surface
  plasma or any other feature. Recent time-distance helioseismology
  results suggest that supergranulation also has properties of travelling
  waves. We had suggested that these properties may be due to the steep
  gradient of the subsurface shear layer, and had calculated the phase
  speeds of the unstable convective modes, using a linear model. These
  phase speeds were greater than the speed of the surface plasma;
  however, they were significantly lower than the observed speed of the
  supergranular pattern. We now consider the contributions of viscosity
  and magnetic field. Adding either of these to the previous linear
  model can produce phase speeds matching the observations. We consider
  different viscosity and magnetic field profiles, and investigate if
  the observed phase speeds can be reproduced with realistic viscosity
  or magnetic fields.

---------------------------------------------------------
Title: Investigation of Emerging Active Regions by Time-Distance
    Helioseismology
Authors: Kosovichev, Alexander G.; Duvall, T. L., Jr.
2007AAS...210.4602K    Altcode: 2007BAAS...39R.160K
  Prediction of emerging active regions and their evolution is one of the
  central problems of local helioseismology. Previous investigations
  showed that magnetic flux emerges very rapidly, so that it very
  difficult to obtain tomographic images of the associated sound-speed
  perturbations and flows in the interior before the first magnetic
  field elements appear on the surface. We continue investigating this
  problems by reducing the time intervals between the sound-speed
  images and flow maps to 2 hours. The helioseismology results are
  compared with the photospheric magnetograms and white-light images. In
  particular, we present results of the investigation of the emergence
  and development of large active region NOAA 10488 observed during the
  SOHO/MDI Dynamics campaign in October 2003, compare the results with
  helioseismic observations of other emerging active regions, and discuss
  the potential of local helioseismology for forecasting emergence and
  evolution of active regions.

---------------------------------------------------------
Title: Validating Time-Distance Helioseismology by Use of Realistic
    Simulations of Solar Convection
Authors: Zhao, Junwei; Georgobiani, D.; Kosovichev, A. G.; Benson,
   D.; Stein, R. F.; Nordlund, A.
2007AAS...210.2203Z    Altcode: 2007BAAS...39..124Z
  Recent progress in realistic simulations of solar convection have
  enabled us to evaluate the robustness of solar interior structures
  and dynamics obtained by methods of local helioseismology. We
  present results of testing the time-distance method using realistic
  simulations. By computing acoustic wave propagation time and distance
  relations for different depths of the simulated data, we confirm that
  acoustic waves propagate into the interior and then turn back to the
  photosphere. For the surface gravity waves (f-mode), we calculate
  perturbations of their travel times, caused by localized downdrafts,
  and demonstrate that the spatial pattern of these perturbations
  (representing so-called sensitivity kernels) is similar to the
  patterns obtained from the real Sun, displaying characteristic
  hyperbolic structures. We then test the time-distance measurements
  and inversions by calculating acoustic travel times from a sequence
  of vertical velocities at the photosphere of the simulated data, and
  inferring a mean 3D flow fields by performing inversion based on the
  ray approximation. The inverted horizontal flow fields agree very well
  with the simulated data in subsurface areas up to 3 Mm deep, but differ
  in deeper areas. These initial tests provide important validation of
  time-distance helioseismology measurements of supergranular-scale
  convection, illustrate limitations of this technique, and provide
  guidance for future improvements.

---------------------------------------------------------
Title: Numerical Simulations of Solar Acoustic Waves in the Whole Sun
Authors: Hartlep, Thomas; Mansour, N. N.; Kosovichev, A. G.
2007AAS...210.2204H    Altcode: 2007BAAS...39..125H
  Helioseismology provides important tools for studying solar internal
  structure and dynamics, and for space weather forecast. For testing
  and correct interpretation of inversion results, as well as advancing
  our general understanding of wave propagation in stars, numerical
  simulations of wave propagation promise to be immensly valuable. We
  present a new numerical method and code for studying the 3D propagation
  of acoustic and MHD waves in the Sun as a full sphere. The waves are
  excited randomly, and are propagated through a statitionary solar model
  which includes localized structures such as models of sunspots. <P
  />Here, we show results from simulations for structures with localized
  variations of the sound speed compared with the averaged, quiet Sun. For
  instance, we show how the oscillation power varies from the quiet Sun
  model, and compare with observations. The simulation results also
  provide artificial data for testing time-distance helioseismology
  inferences including far-side imaging and probing the tachocline
  structure. <P />This research was supported by an appointment to the
  NASA Postdoctoral Program at Ames Research Center, administered by
  Oak Ridge Associated Universities through a contract with NASA.

---------------------------------------------------------
Title: Study Of Excitation Mechanism Of Solar Oscillation Modes
    Using Realistic Numerical Simulations
Authors: Jacoutot, Laetitia; Kosovichev, A. G.; Mansour, N. N.;
   Wray, A.
2007AAS...210.4603J    Altcode: 2007BAAS...39..161J
  Investigation of the excitation mechanisms of solar oscillations is
  important for understanding the interaction between turbulence and
  waves in the Sun and for developing helioseismology diagnostics. <P
  />The objective of this research is to study the sources which drive the
  waves in the Sun by means of realistic numerical simulations. We used
  a 3D, compressible, non-linear radiative-hydrodynamics code developed
  by Wray et al. (2005) for simulating the upper solar photosphere
  and lower atmosphere. This code takes into account several physical
  phenomena: compressible fluid flow in a highly stratified medium,
  radiative energy transfer between the fluid elements, and a real-gas
  equation of state. Strong fluctuations in the outer convective layers
  of the sun generate dominant acoustic sources in this region. Therefore
  we simulate the upper layers of the convection zone using 64^3 grid
  cells. The region extends 6x6 Mm horizontally and from 4.5 Mm below
  the visible surface to 1 Mm above the surface. We calculate the
  oscillation power spectra of radial and non-radial modes, extract
  the eigenfunctions, and calculate the work integral to estimate the
  depth of the oscillation sources; we then compare with the previous
  studies of Stein and Nordlund (2001) and Georgobiani et al. (2006)
  and with the observed properties of solar oscillations.

---------------------------------------------------------
Title: Modeling of solar wave damping
Authors: Parchevsky, Konstantin; Kosovichev, A. G.
2007AAS...210.4604P    Altcode: 2007BAAS...39..161P
  The damping mechanism of solar modes below the acoustic cut-off
  frequency is not yet completely understood. Both the scattering on
  turbulence in subsurface layers and partial escaping waves into the
  chromosphere may play significant role. Using 3D numerical simulations
  of wave propagation in the solar atmosphere with the realistic top
  boundary condition we studied both mechanisms. The wave sources were
  modeled by stochastic randomly distributed perturbations of vertical
  component of force. In both cases we were able to reproduce the observed
  characteristics of the acoustic spectrum (line-widths and relative
  amplitude distribution). We masked the sources in the central circle
  to simulate the absence of sources in sunspots, and we found that the
  oscillation amplitude in regions of suppressed excitation only weakly
  depends on the wave damping mechanism in the upper convection zone
  and chromosphere.

---------------------------------------------------------
Title: Investigation of Magnetic Properties of Emerging Active Regions
Authors: Kosovichev, Alexander G.; Stenflo, J. O.
2007AAS...210.9214K    Altcode: 2007BAAS...39..210K
  Magnetic flux emerging from the Sun's interior carries information
  about the physical processes of magnetic field generation and transport
  in the convection zone. The current paradigm is that solar magnetic
  fields are generated in the tachocline region and emerge in the form
  of toroidal flux tubes forming bipolar active regions, and that because
  of the Coriolis force the flux tubes emerge with a particular tilt with
  respect to the equator, observationally known as Joy's law. In order to
  test this and other properties of emerging magnetic flux we have carried
  out a systematic study of all, more than 500, emerging active regions
  observed by SOHO/MDI during 1996-2006, using 96-min cadence full-disk
  MDI magnetograms. The results reveal new interesting properties of
  emerging magnetic flux. <P />In particular, they indicate that the
  initial tilt may be quite different from Joy's law, but that after
  emergence the polarities quickly rearrange themselves to better conform
  to this law, something that presents a challenge to current theoretical
  models. We investigate statistics of the emerging flux properties,
  their changes during the solar cycle and discuss implications for
  dynamo theories and models of magnetic flux emergence and formation
  of active regions.

---------------------------------------------------------
Title: Helioseismic inferences on subsurface solar convection
Authors: Kosovichev, Alexander G.
2007IAUS..239..113K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Imaging Far-Side Solar Active Regions by Use of Time-Distance
    Helioseismology and Its Validation
Authors: Zhao, Junwei; Hartlep, T.; Kosovichev, A. G.; Mansour, N. N.
2007AAS...210.4606Z    Altcode: 2007BAAS...39..161Z
  Helioseismic holography has succeeded in imaging the solar far-side
  active regions, providing a useful tool for space weather forecast by
  monitoring large active regions in the back of the Sun. In order to
  check the robustness of the holography results, as well as to provide
  another far-side imaging technique, we developed the code to image
  the far-side of the Sun by use of time-distance helioseismology. In
  addition to the four-skip acoustic signals that were used by holography
  analysis, five-skip acoustic signals were also taken into computation
  in this new time-distance technique. The combination of both far-side
  images, computed from four-skip and five-skip signals, greatly enhances
  the picture of active regions, and reduces spurious signals. <P />To
  validate our technique of far-side imaging, we performed medium-l
  numerical simulation of the Sun as a whole sphere, and tested the
  time-distance far-side imaging technique on this simulated data set. It
  was found that this technique could successfully identify the location
  and size of the far-side active regions which typically have a faster
  interior sound-speed.

---------------------------------------------------------
Title: The Cause Of Sunquakes: Electrons Or Protons?
Authors: Kosovichev, Alexander G.
2007AAS...210.9326K    Altcode: 2007BAAS...39..215K
  Sunquakes, the helioseismic response to solar flares, are caused
  by strong localized hydrodynamic impacts in the photosphere, which
  are observed directly in SOHO/MDI Dopplergrams during the impulsive
  phase. These impacts correlate very well both temporary and spatially
  with hard X-ray sources, and in some cases are close to gamma-ray
  sources imaged by RHESSI. A common paradigm is <P />the sunquake events
  are caused by accelerated protons because protons carry more momentum
  and penetrate much deeper into the solar atmosphere than electrons
  which loose most of their energy in the upper chromosphere. I present
  the results of analysis of the hydrodynamic <P />response for the
  sunquake events when both hard X-rays and gamma-rays were observed
  by RHESSI. In one event, X5.6 flare of July 23, 2002, the hard X-ray
  and gamma-ray sources were significantly separated from each other,
  approximately by 20" (with 5-sigma confidence). Analysis of MDI
  Dopplergrams reveals hydrodynamic and seismic responses associated the
  hard X-ray source and shows no significant signal in the gamma-source
  area. These observations effectively rule out high-energy protons as
  a source of sunquakes. Furthermore, detailed analysis of the dynamics
  of sunquake sources reveals their close association with expanding
  flare ribbons, and thus with the magnetic reconnection process. The
  fast motion of these sources results in strong anisotropy of the
  seismic waves, clearly observed in the MDI data. The general picture
  that comes from the analysis of MDI and RHESSI is consistent with
  the previously developed hydrodynamic thick-target model, in which
  electrons heat the upper chromosphere to high temperatures generating
  a high-pressure region, expansion of which causes a high compression
  shock, which reaches the photosphere and excites the seismic waves. I
  discuss how the observations and modeling of sunquakes and their sources
  help to understand processes of the energy release and transport in
  solar flares.

---------------------------------------------------------
Title: Modeling Of Magnetic Effects In Local Helioseismology
Authors: Parchevsky, Konstantin; Kosovichev, A. G.
2007AAS...210.2209P    Altcode: 2007BAAS...39..125P
  Investigation of magnetic field effects in wave propagation on the
  Sun is very important for developing robust local helioseismology
  techniques and diagnostics of subsurface magnetic fields. We have
  developed a complete 3D MHD numerical model to investigate how magnetic
  fields affect wave properties and helioseismology measurements in
  realistic solar conditions. We investigate the variations of wave
  amplitudes, wavelengths, phase shifts and travel times in various
  models of magnetic field structures in the solar convection zone and
  atmosphere. A particular attention is paid to the so-called "inclined
  field effect", which is of significant interest for time-distance and
  holography techniques. The simulation results are compared with the
  observational data.

---------------------------------------------------------
Title: Analytical Models for Cross-Correlation Signal in Time-Distance
    Helioseismology
Authors: Nigam, R.; Kosovichev, A. G.; Scherrer, P. H.
2007ApJ...659.1736N    Altcode: 2007astro.ph..2499N
  In time-distance helioseismology, the time signals (Doppler shifts) at
  two points on the solar surface separated by a fixed angular distance
  are cross-correlated, and this leads to a wave packet signal. Accurately
  measuring the travel times of these wave packets is crucial for
  inferring the subsurface properties in the Sun. The observed signal
  is quite noisy, and to improve the signal-to-noise ratio and make
  the cross-correlation more robust, the temporal oscillation signal is
  phase-speed filtered at the two points in order to select waves that
  travel a fixed horizontal distance. Hence a new formula to estimate the
  travel times is derived in the presence of a phase-speed filter, and it
  includes both the radial and horizontal component of the oscillation
  displacement signal. It generalizes the previously used Gabor wavelet
  that was derived without a phase-speed filter and included only the
  radial component of the displacement. This is important since it will be
  consistent with the observed cross-correlation that is computed using
  a phase-speed filter, and it also accounts for both the components of
  the displacement. The new formula depends on the location of the two
  points on the solar surface that are being cross-correlated and accounts
  for the travel time shifts at different locations on the solar surface.

---------------------------------------------------------
Title: Validation of Time-Distance Helioseismology by Use of Realistic
    Simulations of Solar Convection
Authors: Zhao, Junwei; Georgobiani, Dali; Kosovichev, Alexander G.;
   Benson, David; Stein, Robert F.; Nordlund, Åke
2007ApJ...659..848Z    Altcode: 2006astro.ph.12551Z
  Recent progress in realistic simulations of solar convection have
  given us an unprecedented opportunity to evaluate the robustness of
  solar interior structures and dynamics obtained by methods of local
  helioseismology. We present results of testing the time-distance
  method using realistic simulations. By computing acoustic wave
  propagation time and distance relations for different depths of the
  simulated data, we confirm that acoustic waves propagate into the
  interior and then turn back to the photosphere. This demonstrates
  that in numerical simulations properties of acoustic waves (p-modes)
  are similar to the solar conditions, and that these properties can be
  analyzed by the time-distance technique. For surface gravity waves
  (f-modes), we calculate perturbations of their travel times caused
  by localized downdrafts and demonstrate that the spatial pattern of
  these perturbations (representing so-called sensitivity kernels)
  is similar to the patterns obtained from the real Sun, displaying
  characteristic hyperbolic structures. We then test time-distance
  measurements and inversions by calculating acoustic travel times from
  a sequence of vertical velocities at the photosphere of the simulated
  data and inferring mean three-dimensional flow fields by performing
  inversion based on the ray approximation. The inverted horizontal
  flow fields agree very well with the simulated data in subsurface
  areas up to 3 Mm deep, but differ in deeper areas. Due to the cross
  talk effects between the horizontal divergence and downward flows,
  the inverted vertical velocities are significantly different from the
  mean convection velocities of the simulation data set. These initial
  tests provide important validation of time-distance helioseismology
  measurements of supergranular-scale convection, illustrate limitations
  of this technique, and provide guidance for future improvements.

---------------------------------------------------------
Title: Helioseismic Test of Nonhomologous Solar Radius Changes with
    the 11 Year Activity Cycle
Authors: Lefebvre, S.; Kosovichev, A. G.; Rozelot, J. P.
2007ApJ...658L.135L    Altcode: 2007astro.ph..2497L
  Recent models of variations of the Sun's structure with the 11 year
  activity cycle by Sofia et al. predict strong nonhomologous changes
  of the radius of subsurface layers, due to subsurface magnetic fields
  and field-modulated turbulence. According to their best model, the
  changes of the surface radius may be 1000 times larger than those at
  the depth of 5 Mm. We use f-mode oscillation frequency data from the
  SOHO MDI and measurements of the solar surface radius variations from
  SOHO and ground-based observatories during solar cycle 23 (1996-2005)
  to put constraints on the radius changes. The results show that the
  above model overestimates the change of the radius at the surface
  relative to the change at 5 Mm.

---------------------------------------------------------
Title: Comparison of Large-Scale Flows on the Sun Measured by
    Time-Distance Helioseismology and Local Correlation Tracking
Authors: Švanda, Michal; Zhao, Junwei; Kosovichev, Alexander G.
2007SoPh..241...27S    Altcode: 2007astro.ph..1717S
  We present a direct comparison between two different techniques:
  time-distance helioseismology and a local correlation tracking
  method for measuring mass flows in the solar photosphere and in
  a near-surface layer. We applied both methods to the same dataset
  (MDI high-cadence Dopplergrams covering almost the entire Carrington
  rotation 1974) and compared the results. We found that, after necessary
  corrections, the vector flow fields obtained by these techniques are
  very similar. The median difference between directions of corresponding
  vectors is 24°, and the correlation coefficients of the results for
  mean zonal and meridional flows are 0.98 and 0.88, respectively. The
  largest discrepancies are found in areas of small velocities where the
  inaccuracies of the computed vectors play a significant role. The good
  agreement of these two methods increases confidence in the reliability
  of large-scale synoptic maps obtained by them.

---------------------------------------------------------
Title: Commission 12: Solar Radiation &amp; Structure
Authors: Bogdan, Thomas. J.; Martínez Pillet, Valentin; Asplund,
   M.; Christensen-Dalsgaard, J.; Cauzzi, G.; Cram, L. E.; Dravins, D.;
   Gan, W.; Henzl, P.; Kosovichev, A.; Mariska, J. T.; Rovira, M. G.;
   Venkatakrishnan, P.
2007IAUTA..26...89B    Altcode:
  Commission 12 covers research on the internal structure and dynamics
  of the Sun, the "quiet" solar atmosphere, solar radiation and its
  variability, and the nature of relatively stable magnetic structures
  like sunspots, faculae and the magnetic network. There is considerable
  productive overlap with the other Commissions of Division II as
  investigations move progressively toward the fertile intellectual
  boundaries between traditional research disciplines. In large part,
  the solar magnetic field provides the linkage that connects these
  diverse themes. The same magnetic field that produces the more subtle
  variations of solar structure and radiative output over the 11 yr
  activity cycle is also implicated in rapid and often violent phenomena
  such as flares, coronal mass ejections, prominence eruptions, and
  episodes of sporadic magnetic reconnection.The last three years have
  again brought significant progress in nearly all the research endeavors
  touched upon by the interests of Commission 12. The underlying causes
  for this success remain the same: sustained advances in computing
  capabilities coupled with diverse observations with increasing levels
  of spatial, temporal and spectral resolution. It is all but impossible
  to deal with these many advances here in anything except a cursory and
  selective fashion. Thankfully, the Living Reviews in Solar Physics; has
  published several extensive reviews over the last two years that deal
  explicitly with issues relevant to the purview of Commission 12. The
  reader who is eager for a deeper and more complete understanding of
  some of these advances is directed to http://www.livingreviews.org
  for access to these articles.

---------------------------------------------------------
Title: Helioseismology program for Solar Dynamics Observatory
Authors: Kosovichev, A. G.; HMI Science Team
2007AN....328..339K    Altcode:
  An overview of the science investigation program for the Helioseismic
  and Magnetic Imager (HMI) of the Solar Dynamics Observatory (SDO)
  space mission scheduled for launch in 2008 is presented. The HMI
  investigation encompasses three primary objectives of the Living With a
  Star Program: first, to determine how and why the Sun varies; second,
  to improve our understanding of how the Sun drives global change and
  space weather; and third, to determine to what extent predictions of
  space weather and global change can be made and to prototype predictive
  techniques. Helioseismology provides unique tools to study the basic
  mechanisms of the Sun's magnetic activity and variability. It plays a
  crucial role in all HMI investigations, which include convection-zone
  dynamics and the solar dynamo; origin and evolution of sunspots,
  active regions and complexes of activity; sources and drivers
  of solar activity and disturbances; links between the internal
  processes and dynamics of the corona and heliosphere; and precursors
  of solar disturbances for space-weather forecasts. We describe new
  unique opportunities for helioseismology studies with HMI data, in
  combination with data from the other SDO instruments, Atmospheric
  Imaging Assembly (AIA) and Extreme-ultraviolet Variability Experiment
  (EVE), and also from various space and ground-based observatories. The
  complete HMI science investigation and data analysis plan is available
  at http://hmi.stanford.edu.

---------------------------------------------------------
Title: Local Helioseismology and Correlation Tracking Analysis of
    Surface Structures in Realistic Simulations of Solar Convection
Authors: Georgobiani, Dali; Zhao, Junwei; Kosovichev, Alexander G.;
   Benson, David; Stein, Robert F.; Nordlund, Åke
2007ApJ...657.1157G    Altcode: 2006astro.ph..8204G
  We apply time-distance helioseismology, local correlation tracking, and
  Fourier spatial-temporal filtering methods to realistic supergranule
  scale simulations of solar convection and compare the results with
  high-resolution observations from the Solar and Heliospheric Observatory
  (SOHO) Michelson Doppler Imager (MDI). Our objective is to investigate
  the surface and subsurface convective structures and test helioseismic
  measurements. The size and grid of the computational domain are
  sufficient to resolve various convective scales from granulation to
  supergranulation. The spatial velocity spectrum is approximately a
  power law for scales larger than granules, with a continuous decrease
  in velocity amplitude with increasing size. Aside from granulation
  no special scales exist, although a small enhancement in power at
  supergranulation scales can be seen. We calculate the time-distance
  diagram for f- and p-modes and show that it is consistent with the SOHO
  MDI observations. From the simulation data we calculate travel-time
  maps for surface gravity waves (f-mode). We also apply correlation
  tracking to the simulated vertical velocity in the photosphere to
  calculate the corresponding horizontal flows. We compare both of these
  to the actual large-scale (filtered) simulation velocities. All three
  methods reveal similar large-scale convective patterns and provide an
  initial test of time-distance methods.

---------------------------------------------------------
Title: Active Region Dynamics
Authors: Kosovichev, A. G.; Duvall, T. L., Jr.
2007sdeh.book....1K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The change of solar shape in time and depth. Some consequences
    for space climate
Authors: Lefebvre, S.; Rozelot, J. P.; Kosovichev, A. G.
2007AdSpR..40.1000L    Altcode:
  During the last five years, studies of the Sun and Sun-Earth
  relationships have dramatically changed our view on solar terrestrial
  physics. We will here focus on new views on the solar interior. The
  internal non-homogeneous mass distribution and non-uniform angular
  velocity (function of the radial distance to the center and of the
  latitude) yield a complex outer shape. Beyond a "spherical" Sun is a
  new approach of solar-physics taking into account the gravitational
  energy which triggers the various layers. Such energy has been
  skipped in many ways up to now in theoretical models describing
  the solar output variability. In spite of many works on solar
  variations, there is not yet a consensus on the global experimental
  phenomenology. For instance, it is not yet known if this gravitational
  energy may explain faint observed irradiance variations, and the way
  the asphericity-luminosity parameter W acts on our stratosphere. Such
  issues must be solved to understand how the solar output variability
  may influence the Earth's environment (helioclimatology). We will
  emphasize the key role of the subsurface layers (the leptocline,
  recently put in evidence by helioseismology) for a better prediction
  of the solar cycles. Regarding the solar core dynamics, the subject
  is of high priority for new investigations. We will conclude by giving
  some imprints on space-dedicated missions: GOLF-NG/DynaMICS in a joint
  effort with SDO (Solar Dynamics Observatory).

---------------------------------------------------------
Title: Direct Observations of Acoustic Waves Excited by Solar Flares
    and their Propagation in Sunspot Regions
Authors: Kosovichev, A. G.
2006ASPC..354..154K    Altcode:
  I present new results from SOHO-MDI of direct observations and analysis
  of “sunquakes”, seismic acoustic waves excited by solar flares and
  propagating below the surface through surrounding sunspot regions. The
  main results are the following: the sources of the seismic waves
  are associated with hydrodynamic response of the solar atmosphere to
  high-energy electrons (`thick-target' model); the seismic sources are
  identified in MDI Dopplergrams as compact regions of strong Doppler
  shift during the flare impulsive phase; the seismic sources are close
  to the sources of hard X-ray emission and located in flare ribbons;
  the expanding waves are often anisotropic and non-circular reflecting
  the properties of the hydrodynamic impact controlled by magnetic
  field topology in the energy-release regions and subphotospheric
  condition; the waves have periods of three -- five minutes and are
  best observed about 20 minutes after the impulsive phase; the fronts
  of the sunquake waves propagating through surrounding sunspots do not
  show significant distortion and decay, thus giving no evidence for
  mode conversion in magnetic fields; time-distance diagrams of the
  seismic waves show only small deviations caused by sunspots in the
  travel times from the quiet Sun data, which are consistent with the
  standard travel time measurements from cross-covariance functions. The
  direct observations of acoustic waves excited by flares open new
  perspectives for high-resolution helioseismic diagnostics of sunspots
  and understanding the hydrodynamic processes in solar flares.

---------------------------------------------------------
Title: Anisotropy of Helioseismic Waves Excited by Solar Flares
Authors: Kosovichev, A.
2006AGUFMSH23A0335K    Altcode:
  Recent observations of helioseismic response to solar flares
  ("sunquakes") revealed strong anisotropy in the seismic wave
  amplitude. It appears that the acoustic waves excited by solar flares
  and propagating through the solar interior have the strongest amplitude
  in the direction of the expansion of the flare ribbons. Our analysis
  of the flare data from SOHO/MDI and RHESSI, and modeling of sunquakes
  show that this anisotropy is likely to be caused by moving seismic
  sources. These sources correspond to the places where high-energy
  particles penetrate into the lower atmosphere of the Sun, and their
  motion is related to the dynamics of the magnetic reconnection process
  in the corona.

---------------------------------------------------------
Title: Suppression of amplitude of 5-min oscillations in sunspots
    due to the lack of acoustic sources
Authors: Parchevsky, K.; Kosovichev, A.
2006ESASP.624E..39P    Altcode: 2006soho...18E..39P
  No abstract at ADS

---------------------------------------------------------
Title: The DynaMICS perspective
Authors: Turck-Chièze, S.; Schmutz, W.; Thuillier, G.; Jefferies,
   S.; Pallé; Dewitt, S.; Ballot, J.; Berthomieu, G.; Bonanno, A.;
   Brun, A. S.; Christensen-Dalsgaard, J.; Corbard, T.; Couvidat, S.;
   Darwich, A. M.; Dintrans, B.; Domingo, V.; Finsterle, W.; Fossat,
   E.; Garcia, R. A.; Gelly, B.; Gough, D.; Guzik, J.; Jiménez, A. J.;
   Jiménez-Reyes, S.; Kosovichev, A.; Lambert, P.; Lefebvre, S.; Lopes,
   I.; Martic, M.; Mathis, S.; Mathur, S.; Nghiem, P. A. P.; Piau, L.;
   Provost, J.; Rieutord, M.; Robillot, J. M.; Rogers, T.; Roudier, T.;
   Roxburgh, I.; Rozelot, J. P.; Straka, C.; Talon, S.; Théado, S.;
   Thompson, M.; Vauclair, S.; Zahn, J. P.
2006ESASP.624E..24T    Altcode: 2006soho...18E..24T
  No abstract at ADS

---------------------------------------------------------
Title: Sunquake sources and wave propagation
Authors: Kosovichev, A. G.
2006ESASP.624E.134K    Altcode: 2006soho...18E.134K
  No abstract at ADS

---------------------------------------------------------
Title: Effect of the subsurface shear layer on solar supergranulation
Authors: Green, C. A.; Kosovichev, A. G.; Miesch, M. S.
2006ESASP.624E..13G    Altcode: 2006soho...18E..13G
  No abstract at ADS

---------------------------------------------------------
Title: Properties of Flares-Generated Seismic Waves on the Sun
Authors: Kosovichev, A. G.
2006SoPh..238....1K    Altcode: 2006astro.ph..1006K; 2006SoPh..tmp...33K
  The helioseismic waves excited by solar flares ("sunquakes") are
  observed as circular, expanding waves on the Sun's surface. The first
  sunquake was observed for a flare on July 9, 1996, by the Solar and
  Heliospheric Observatory (SOHO) space mission. This paper presents
  results of new observations and a detailed qualitative analysis of
  the basic properties of the helioseismic waves generated by four solar
  flares in 2003 - 2005. For two of these flares, the X17 flare of October
  28, 2003, and the X1.2 flare of January 15, 2005, the helioseismology
  observations are compared with simultaneous observations of flare
  X-ray fluxes measured from the RHESSI satellite. These observations
  show a close association between the flare seismic waves and the
  hard X-ray source, indicating that high-energy electrons accelerated
  during the flare impulsive phase produced strong compression waves in
  the photosphere, causing the sunquake. The results also reveal new
  physical properties such as strong anisotropy of the seismic waves,
  the amplitude of which varies significantly with the direction of
  propagation. The waves travel through surrounding sunspot regions to
  large distances, up to 120 Mm, without significant distortion. These
  observations open new perspectives for helioseismic diagnostics of
  flaring active regions on the Sun and for understanding the mechanisms
  of the energy release and transport in solar flares.

---------------------------------------------------------
Title: Cyclic variability of the seismic solar radius from SOHO/MDI
    and related physics
Authors: Lefebvre, S.; Kosovichev, A. G.; Nghiem, P.; Turck-Chièze,
   S.; Rozelot, J. P.
2006ESASP.624E...9L    Altcode: 2006soho...18E...9L
  No abstract at ADS

---------------------------------------------------------
Title: The internal structure of the Sun inferred from g modes and
    low-frequency p modes
Authors: Elsworth, Y. P.; Baudin, F.; Chaplin, W; Andersen, B;
   Appourchaux, T.; Boumier, P.; Broomhall, A. -M.; Corbard, T.;
   Finsterle, W.; Fröhlich, C.; Gabriel, A.; García, R. A.; Gough,
   D. O.; Grec, G.; Jiménez, A.; Kosovichev, A.; Provost, J.; Sekii,
   T.; Toutain, T.; Turck-Chièze, S.
2006ESASP.624E..22E    Altcode: 2006soho...18E..22E
  The Phoebus group is an international collaboration of
  helioseismologists, its aim being to detect low-frequency solar g
  modes. Here, we report on recent work, including the development and
  application of new techniques based on the detection of coincidences
  in contemporaneous datasets and the asymptotic properties of the g-mode
  frequencies. The length of the time series available to the community is
  now more than ten years, and this has reduced significantly the upper
  detection limits on the g-mode amplitudes. Furthermore, low-degree p
  modes can now be detected clearly at frequencies below 1000 μHz.

---------------------------------------------------------
Title: Solar dynamics, asphericities and gravitational moments:
    present state of the art
Authors: Rozelot, J. -P.; Lefebvre, S.; Kosovichev, A.; Pireaux, S.
2006IAUJD..17E..10R    Altcode:
  Solar gravitational moments J[n] reflect the internal non-homogeneous
  mass distribution and non-uniform angular velocity (function
  of the radial distance to the center and of the latitude). The
  result is the complex outer shape of the Sun, described by shape
  coefficients c[n] , also referred to as asphericities. The study of
  solar gravitational moments is not only crucial for solar physics, but
  also for astrometry (when computing light deflection in the vicinity
  of the Sun), celestial mechanics: relativistic precession of planets,
  planetary orbit inclination and spin-orbit couplings) and for future
  tests of alternative theories of gravitation (correlation of J[2]
  with Post-Newtonian parameters). A variability of c[n] and J[n]
  might be due to the temporal variation of the internal structure
  and the angular velocity which is known at the surface down to the
  tachocline. Applying helioseismic inversions just below the surface,
  new results have been obtained showing temporal variations with solar
  activity inside the surface layers. Regarding the solar core dynamics,
  the subject is of high priority for new investigations. Space-dedicated
  missions, such as Golf-NG/Dynamics in a joint effort with SDO (Solar
  Dynamics Observatory), should provide a new insight on the question.

---------------------------------------------------------
Title: Local helioseismology techniques and results
Authors: Kosovichev, A. G.
2006IAUJD..17E..12K    Altcode:
  Local helioseismology techniques (time-distance helioseismology,
  acoustic imaging and holography, and ring-diagram analysis) use
  measurements of variations of acoustic travel times, phase shifts
  and local oscillation frequencies to infer the internal properties
  of the Sun. These techniques provide 3D maps of subsurface wave speed
  variations and flow velocities. The anisotropy of wave propagation in
  magnetic field is used to estimate properties of subsurface magnetic
  fields. The techniques are verified by using realistic numerical
  simulations of solar dynamics and wave propagation. The results reveal
  complicated dynamical structure of the solar interior. They provide
  new insight into large-scale convection and global circulation of the
  Sun, emergence and evolution of active regions, structure and dynamics
  sunspots and twisting and sheering flows in flaring regions.

---------------------------------------------------------
Title: Scientific Objectives of the Novel Formation Flying Mission
    Aspiics
Authors: Turck-Chièze, S.; Schmutz, W.; Thuillier, G.; Jefferies,
   S.; Pallé; Dewitt, S.; Ballot, J.; Berthomieu, G.; Bonanno, A.;
   Brun, A. S.; Christensen-Dalsgaard, J.; Corbard, T.; Couvidat, S.;
   Darwich, A. M.; Dintrans, B.; Domingo, V.; Finsterle, W.; Fossat,
   E.; Garcia, R. A.; Gelly, B.; Gough, D.; Guzik, J.; Jiménez, A. J.;
   Jiménez-Reyes, S.; Kosovichev, A.; Lambert, P.; Lefebvre, S.; Lopes,
   I.; Martic, M.; Mathis, S.; Mathur, S.; Nghiem, P. A. P.; Piau, L.;
   Provost, J.; Rieutord, M.; Robillot, J. M.; Rogers, T.; Roudier, T.;
   Roxburgh, I.; Rozelot, J. P.; Straka, C.; Talon, S.; Théado, S.;
   Thompson, M.; Vauclair, S.; Zahn, J. P.
2006ESASP.617E.164L    Altcode: 2006soho...17E.164L
  No abstract at ADS

---------------------------------------------------------
Title: Helioseismic Measurements of Solar Radius Changes from SOHO/MDI
Authors: Lefebvre, S.; Kosovichev, A. G.; Rozelot, J. P.
2006ESASP.617E..43L    Altcode: 2006soho...17E..43L
  No abstract at ADS

---------------------------------------------------------
Title: The EUV Variability Experiment (EVE) on the Solar Dynamics
Observatory (SDO): Science Plan and Instrument Overview
Authors: Turck-Chièze, S.; Schmutz, W.; Thuillier, G.; Jefferies,
   S.; Pallé; Dewitt, S.; Ballot, J.; Berthomieu, G.; Bonanno, A.;
   Brun, A. S.; Christensen-Dalsgaard, J.; Corbard, T.; Couvidat, S.;
   Darwich, A. M.; Dintrans, B.; Domingo, V.; Finsterle, W.; Fossat,
   E.; Garcia, R. A.; Gelly, B.; Gough, D.; Guzik, J.; Jiménez, A. J.;
   Jiménez-Reyes, S.; Kosovichev, A.; Lambert, P.; Lefebvre, S.; Lopes,
   I.; Martic, M.; Mathis, S.; Mathur, S.; Nghiem, P. A. P.; Piau, L.;
   Provost, J.; Rieutord, M.; Robillot, J. M.; Rogers, T.; Roudier, T.;
   Roxburgh, I.; Rozelot, J. P.; Straka, C.; Talon, S.; Théado, S.;
   Thompson, M.; Vauclair, S.; Zahn, J. P.
2006ESASP.617E.165W    Altcode: 2006soho...17E.165W
  No abstract at ADS

---------------------------------------------------------
Title: Analysis of a Relation between Subphotospheric Plasma Flows
    and Photospheric Current Kernels
Authors: Kulinová, A.; Dzifčáková, E.; Kosovichev, A. G.; Duvall,
   T. L.
2006ESASP.617E..69K    Altcode: 2006soho...17E..69K
  No abstract at ADS

---------------------------------------------------------
Title: Recent Progresses on g-Mode Search
Authors: Appourchaux, T.; Andersen, B.; Baudin, F.; Boumier, P.;
   Broomhall, A. -M.; Chaplin, W.; Corbard, T.; Elsworth, Y.; Finsterle,
   W.; Fröhlich, C.; Gabriel, A.; Garcia, R.; Gough, D. O.; Grec, G.;
   Jiménez, A.; Kosovichev, A.; Provost, J.; Sekii, T.; Toutain, T.;
   Turck-Chièze, S.
2006ESASP.617E...2A    Altcode: 2006soho...17E...2A
  No abstract at ADS

---------------------------------------------------------
Title: The Dynamics Project
Authors: Turck-Chièze, S.; Schmutz, W.; Thuillier, G.; Jefferies,
   S.; Pallé; Dewitt, S.; Ballot, J.; Berthomieu, G.; Bonanno, A.;
   Brun, A. S.; Christensen-Dalsgaard, J.; Corbard, T.; Couvidat, S.;
   Darwich, A. M.; Dintrans, B.; Domingo, V.; Finsterle, W.; Fossat,
   E.; Garcia, R. A.; Gelly, B.; Gough, D.; Guzik, J.; Jiménez, A. J.;
   Jiménez-Reyes, S.; Kosovichev, A.; Lambert, P.; Lefebvre, S.; Lopes,
   I.; Martic, M.; Mathis, S.; Mathur, S.; Nghiem, P. A. P.; Piau, L.;
   Provost, J.; Rieutord, M.; Robillot, J. M.; Rogers, T.; Roudier, T.;
   Roxburgh, I.; Rozelot, J. P.; Straka, C.; Talon, S.; Théado, S.;
   Thompson, M.; Vauclair, S.; Zahn, J. P.
2006ESASP.617E.162T    Altcode: 2006soho...17E.162T
  No abstract at ADS

---------------------------------------------------------
Title: Helioseismic measurements of solar radius changes from SOHO/MDI
Authors: Lefebvre, S.; Kosovichev, A. G.; Rozelot, J. P.
2006sf2a.conf..551L    Altcode:
  The sub-surface of the Sun is much more complex than it does
  appear up to now. Analysing the SOHO/MDI (SOlar and Heliospheric
  Observatory/Michelson Doppler Imager) f-mode frequencies and their
  temporal variation for the last 9 years, we computed the variation of
  the radius in the subsurface layers of the Sun by applying helioseismic
  inversions. We have found a variability of the “helioseismic”
  radius in antiphase with the solar activity, with the strongest
  variations of the stratification being just below the surface around
  0.995R<SUB>⊙</SUB>. In addition, the radius of the deeper layers
  of the Sun, between 0.975R<SUB>⊙</SUB> and 0.99R<SUB>⊙</SUB>
  changes in phase with the 11-year cycle. These results imply a
  non-homogeneous variation of the radius with depth and time and may
  explain discrepancies in ground-based observations.

---------------------------------------------------------
Title: Active Region Dynamics
Authors: Kosovichev, A. G.; Duvall, T. L.
2006SSRv..124....1K    Altcode: 2007SSRv..tmp...56K
  New methods of local helioseismology and uninterrupted time series
  of solar oscillation data from the Solar and Heliospheric Observatory
  (SOHO) have led to a major advance in our understanding of the structure
  and dynamics of active regions in the subsurface layers. The initial
  results show that large active regions are formed by repeated magnetic
  flux emergence from the deep interior, and that their roots are at least
  50 Mm deep. The active regions change the temperature structure and
  flow dynamics of the upper convection zone, forming large circulation
  cells of converging flows. The helioseismic observations also indicate
  that the processes of magnetic energy release, flares and coronal mass
  ejections, might be associated with strong (1 2 km/s) shearing flows,
  4 6 Mm below the surface.

---------------------------------------------------------
Title: Modeling of Suppression of Acoustic Oscillation Power in
    Sunspots
Authors: Parchevsky, Konstantin V.; Kosovichev, A. G.
2006SPD....37.3204P    Altcode: 2006BAAS...38..258P
  In this paper we make an attempt to explain the suppression of
  amplitude of 5-min. acoustic oscillations inside sunspot. A program for
  numerical simulation of propagation of acoustic waves in 3D has been
  developed. Realistic top boundary condition is a characteristic feature
  of this program. Nonreflecting boundary condition based on PML layer is
  established above the temperature minimum, and absorbs all waves not
  reflected by photosphere. Acoustic sources with random amplitudes and
  phases were distributed below the photosphere. Sources were masked in
  a central circle, simulating the absence of acoustic sources inside
  sunspots. Large scale simulations in rectangular box of size 120Mm
  x 120Mm x 50Mm showed that acoustic amplitude is approximately 4
  times lower in the region without sources in comparison with the
  quiet Sun. This is in a good agreement with observations. Hence, the
  observed suppression of oscillations in sunspots can be explained by
  the lack of acoustic sources in sunspot areas where strong magnetic
  field inhibits convection.

---------------------------------------------------------
Title: Investigating Mechanisms of Wave-Like Behaviour of
    Supergranulation
Authors: Green, Cristina A.; Kosovichev, A. G.; Miesch, M. S.
2006SPD....37.0503G    Altcode: 2006BAAS...38R.223G
  Recent time-distance helioseismology results suggest that
  supergranulation has properties of travelling waves. The supergranular
  pattern rotates faster than the surface plasma or any other features
  on the Sun. We investigate possible mechanisms of the wave-like
  behaviour of supergranulation. In particular, we suggest that this may
  be caused by the steep gradient of the subsurface shear layer. Using
  a linear model, we calculated the phase speed of unstable modes of
  convection. The speeds were found to depend on the stratification
  of the convective layer. The phase speeds of the linear convective
  modes were greater than the surface plasma speed, though lower than
  observations. An alternate suggested explanation is a non-linear
  effect of the Coriolis force. We analyzed the results of non-linear
  3D simulations of the convection zone including solar rotation, and
  found no evidence of wave-like behaviour. These results suggest that
  the subsurface shear layer is a plausible explanation for the wave-like
  behaviour, but the non-linear effects need to be studied.

---------------------------------------------------------
Title: Time-Distance and Correlation Tracking Analysesof Convective
    Structures using Realistic Large-ScaleSimulations of Solar Convection
Authors: Georgobiani, Dali; Zhao, J.; Kosovichev, A. G.; Benson, D.;
   Stein, R. F.; Nordlund, A.
2006SPD....37.0509G    Altcode: 2006BAAS...38..224G
  Recent large-scale simulations of solar turbulentconvection and
  oscillations produce a wealth of realisticdata and provide a great
  opportunity to study solaroscillations and test various techniques,
  such aslocal helioseismology or local correlation trackingmethods,
  widely used for the analysis of the realobserved solar data.The
  application of the time-distance analysis to theartificial data produced
  with a realistic 3D radiativehydrodynamic code successfully reproduces
  thetime-distance diagram and travel time maps. Resultingtravel times are
  similar to the travel times obtainedfrom the SOHO/MDI observations. To
  further validatethe model, the inversion will be performed in
  orderto infer the interior velocities at various depthsand compare
  them with the simulated data.f-mode time-distanceanalysis as well as
  local correlation tracking can be usedto study the morphology of the
  simulated convection. Bothmethods reveal the large-scale convective
  structures, whichare also directly visible in the time-averaged
  simulatedflow fields.

---------------------------------------------------------
Title: Surface Magnetism Effects in Time-Distance Helioseismology
Authors: Zhao, Junwei; Kosovichev, Alexander G.
2006ApJ...643.1317Z    Altcode: 2006astro.ph..2260Z
  Recent observations of helioseismic holography revealed that magnetic
  fields that are inclined relative to the line-of-sight direction
  could cause systematic variations in measured acoustic phase shifts
  (hereafter, inclined magnetic field effect) and that the presence of
  surface magnetic field may shift the phases and impair the coherence of
  acoustic waves (known as the showerglass effect), thus complicating
  the interpretation of acoustic wave propagation time through the
  solar interior. In this paper we examine how these two observational
  effects affect time-distance helioseismology measurements in magnetic
  regions. It is confirmed that the inclined magnetic field could
  cause variations in time-distance measured acoustic travel times
  inside sunspot penumbra as well; however, inversions of the measured
  times for the wave propagation show that this effect only slightly
  shifts the location of negative sound-speed variations near the solar
  surface but basically does not change the inverted deeper interior
  structures. Further measurements using continuum intensitygrams and
  line-depth data from the MDI on board SOHO illustrate that the inclined
  magnetic field does not cause any obvious systematic travel-time
  variations in these observations. Regarding to the showerglass effect,
  we find that outgoing and ingoing travel-time perturbations through
  sunspots from our typical time-distance measurements are significantly
  smaller than those reported from helioseismic holography and also
  strongly depend on the propagation depth indicating deep changes. In
  addition, our second-skip cross-correlation experiments demonstrate
  that inside sunspots, the half of the double-skip travel times are
  very similar to the mean single-skip travel times, indicating that
  acoustic signals observed inside sunspots do not introduce detectable
  phase shifts after applying proper phase-speed filtering.

---------------------------------------------------------
Title: Measuring Surface Magnetism Effects in Time-Distance
    Helioseismology
Authors: Zhao, Junwei; Kosovichev, A. G.
2006SPD....37.0507Z    Altcode: 2006BAAS...38..224Z
  It was found recently by helioseismic holography analysis that
  magneticfields that are inclined relative to the line-of-sight
  direction couldcause systematic variations in measured acoustic
  phase shifts, andthe presence of surface magnetic field may shift
  the phases and impairthe coherence of acoustic waves, known as
  "showerglass effect". Weexamine how these two observational effects
  affect time-distancemeasurements in magnetic regions. It is confirmed
  that the inclinedmagnetic field could cause variations in measured
  travel times insidesunspot penumbra, however, inversions of the
  measured times showthat this effect only slightly shift the location of
  negativesound-speed variations near the solar surface, but basically
  does notchange the inverted deeper interior structures. Measurements
  by useof continuum intensitygrams and line-depth data illustrate
  that theinclined magnetic field does not cause any obvious systematic
  traveltime variations. For the showerglass effect, we find that the
  outgoingand ingoing travel time perturbations through sunspots from our
  typicaltime-distance measurements are significantly smaller than those
  reportedfrom holography, and also strongly depend on the propagation
  depths.Additionally, our second-skip travel time measurements
  demonstrate thatthe signals inside sunspots do not introduce detectable
  phase shiftsafter applying phase-speed filtering. We finally conclude
  that thesesurface magnetism effects do not cause considerable systematic
  errorsin time-distance helioseismology of active regions.

---------------------------------------------------------
Title: Helioseismic and Photospheric Effects of Solar Flares
Authors: Kosovichev, Alexander G.
2006SPD....37.0825K    Altcode: 2006BAAS...38..235K
  I present a detailed analysis of new observations ofhelioseismic waves
  ('sunquakes') generated by solarflares, using SOHO/MDI and RHESSI
  data. Theseobservations show a close association between theflare
  seismic waves and the hard X-ray source,indicating that high-energy
  electrons acceleratedduring the flare impulsive phase produced
  strongcompression waves in the photosphere, causing thesunquake. The
  results also reveal new physicalproperties such as strong anisotropy
  of the seismicwaves, the amplitude of which varies significantlywith
  the direction of propagation. The waves travelthrough surrounding
  sunspot regions to largedistances, up to 120 Mm, without significant
  decay.They provide new diagnostics of sunspot regions. Inaddition,
  I discuss whether high-energy electrons orprotons are the prime cause
  of these effects.

---------------------------------------------------------
Title: Traveling Convective Modes in the Sun's Subsurface Shear Layer
Authors: Green, C. A.; Kosovichev, A. G.
2006ApJ...641L..77G    Altcode:
  Observations reveal that supergranular convective cells on the Sun
  rotate faster than the plasma on the solar surface. Recent time-distance
  helioseismology results from the Solar and Heliospheric Observatory
  Michelson Doppler Imager suggest that supergranulation has properties
  of traveling waves. We consider the idea that these properties are
  related to the steep increase of the angular rotation rate with
  depth, obtained by helioseismic inversions. The subsurface shear
  layer causes the convective modes to travel faster than the surface
  plasma. We calculate the phase speed of unstable modes of convection
  in the linear approximation for a standard solar model as a function
  of the velocity gradient in the shear layer. We find that for the
  helioseismically determined gradient, the calculated phase speed is
  significantly smaller than the observed speed of the supergranular
  pattern relative to the surface plasma. This suggests that, while
  the subsurface shear layer provides a plausible explanation for the
  wavelike behavior, it is necessary to study nonlinear effects in the
  dynamics of supergranulation.

---------------------------------------------------------
Title: Three-dimensional Inversion of Sound Speed below a Sunspot
    in the Born Approximation
Authors: Couvidat, S.; Birch, A. C.; Kosovichev, A. G.
2006ApJ...640..516C    Altcode:
  We revise the inversion of acoustic travel times for the
  three-dimensional sound-speed structure below the solar NOAA
  Active Region 8243 of 1998 June. We benefit from recent progress in
  time-distance helioseismology that provides us with more reliable
  tools to infer subsurface solar properties. Among the improvements
  we implement here are the use of Born approximation-based travel-time
  sensitivity kernels that take into account finite-wavelength effects
  and thus are more accurate than the previously employed ray-path
  kernels, the inclusion of solar noise statistical properties in the
  inversion procedure through the noise covariance matrix, and the use
  of the actual variance of the noise in the temporal cross-covariances
  in the travel-time fitting procedure. Of these three improvements,
  the most significant is the application of the Born approximation to
  time-distance helioseismology. This puts the results of this discipline
  at the same level of confidence as those of global helioseismology based
  on inversion of normal-mode frequencies. Also, we compare inversion
  results based on ray-path and Born approximation kernels. We show
  that both approximations return a similar two-region structure for
  sunspots. However, the depth of inverted structures may be offset by 1
  or 2 Mm, and the spatial resolution of the results is more accurately
  estimated with the more realistic Born sensitivity kernels. Finally,
  using artificial realizations of Doppler velocities of the quiet Sun,
  we are now able to estimate the statistical uncertainties of these
  inversion results.

---------------------------------------------------------
Title: Comparison of subsurface sound-speed structures of three
    active regions
Authors: Couvidat, S.; Birch, A. C.; Rajaguru, S. P.; Kosovichev, A. G.
2006IAUS..233...75C    Altcode:
  We analyze three solar active regions observed with the MDI instrument
  onboard SoHO (Scherrer et al. 1995). We apply the time-distance
  helioseismology formalism to derive the travel times of acoustic
  waves propagating through these active regions. The inversion of
  these acoustic travel times gives us access to the 3D sound-speed
  structure below the sunspots. We compare the main characteristics of
  these inversion results as a function of the active region size and
  magnetic field strength.

---------------------------------------------------------
Title: Subsurface characteristics of sunspots
Authors: Kosovichev, Alexander G.
2006AdSpR..38..876K    Altcode:
  Time distance helioseismology provides 3-D subphotospheric maps of
  sunspots, emerging magnetic structures and associated convective
  flows. This gives us new insights into the basic physical processes
  inside the Sun, formation of magnetic structures in the solar plasma and
  mechanisms of solar activity. Recent results from the MDI instrument
  on SOHO reveal complicated stratification and flow patterns of solar
  plasma beneath sunspots, with a characteristic temperature increase
  in deeper layers and multiple vortex systems, providing evidence for
  a cluster model of sunspots. The helioseismic observations provide
  important clues for understanding the mechanisms of the formation
  of sunspots and active regions, and the subphotospheric dynamics of
  convective flows shearing and twisting magnetic fields in the corona.

---------------------------------------------------------
Title: Subsurface flows of solar active regions
Authors: Kosovichev, A. G.
2006cosp...36.1489K    Altcode: 2006cosp.meet.1489K
  Mass flows below the solar surface are likely to play significant
  role in evolution of solar active regions their magnetic topology and
  dynamics Recently new methods of local helioseismology have provided
  three-dimensional maps of subsurface flows in active regions These maps
  have revealed a great variety of complicated flow patterns of various
  scales In particular local helioseismology discovered around active
  regions large-scale circulation flows converging in the upper convective
  layer and diverging at greater depths These persistent flows affect the
  global meridional circulation on the Sun and magnetic flux transport
  during the solar cycle These flows may also influence the convective
  energy transport and large-scale zonal flows - torsional oscillations
  Another class of subsurface flows associated with horizontal vortices
  is probably important for twisting magnetic field of active regions
  and generating magnetic helicity In addition local helioseismology has
  found initial evidence for strong shearing flows below flaring active
  regions which may be significant for initiation of solar flares and CMEs

---------------------------------------------------------
Title: Probing solar and stellar interior dynamics and dynamo
Authors: Kosovichev, A. G.
2006cosp...36.3458K    Altcode: 2006cosp.meet.3458K
  Solar and stellar activity is a result of complex interaction between
  magnetic field turbulent convection and differential rotation in
  a star s interior Magnetic field is believed to be generated by
  a dynamo process in the convection zone It emerges on the surface
  forming sunspots and starspots Localization of the magnetic spots and
  their evolution with the activity cycle is determined by large-scale
  interior flows Thus the internal dynamics of the Sun and other stars
  hold the key to understanding the dynamo mechanism and activity
  cycles Recently significant progress has been made for modeling
  magnetohydrodynamics of the stellar interiors and probing the internal
  rotation and large-scale dynamics of the Sun by helioseismology Also
  asteroseismology is beginning to probe interiors of distant stars I
  review key achievements and challenges in our quest to understand the
  basic mechanisms of solar and stellar activity

---------------------------------------------------------
Title: Probing plasma properties and dynamics inside the Sun
Authors: Kosovichev, Alexander G.
2006AdSpR..37.1455K    Altcode:
  Helioseismology experiment MDI on board the SOHO spacecraft has provided
  tremendous amount of new information about the thermodynamic properties
  and dynamics of plasma in the Sun’s interior, uncovering remarkable
  new perspectives for studying complex interactions between turbulent
  convection, rotation and magnetism below the solar surface, and their
  relationship to solar irradiance variations and coronal activity. In
  particular, the new results have revealed the deep structure of
  sunspots and associated complicated patterns of plasma flows, the
  dynamics of the emerging magnetic flux and formation of active regions,
  the supergranular structure and dynamics of the upper convection zone,
  as well as the global structures and circulation patterns in the deep
  interior, evolving with the activity cycle. In addition, first attempts
  are made to find the links between the internal dynamics and processes
  of magnetic energy release in the solar corona. Understanding these
  results, often puzzling and counter-intuitive, is a major challenge
  for MHD theories of astrophysical plasma.

---------------------------------------------------------
Title: Helioseismic observations of magnetic flux emergence and
    flare effects
Authors: Kosovichev, A. G.; Duvall, T. L.
2006IAUS..233..365K    Altcode:
  Time-distance helioseismology and data from SOHO/MDI are used for
  obtaining 3D images of subsurface sound-speed perturbations and maps
  of plasma flows, associated with emerging magnetic flux and flaring
  activity of large active regions in October 2003. The results reveal
  extremely complicated dynamical processes in the upper convection
  zone and indicate that subsurface shear flows may play an important
  role in magnetic energy release in solar flares. Strong X-class flares
  generated impulsive seismic waves (“sunquakes”), traveling through
  surrounding sunspots, thus providing new insight into the interaction
  of seismic waves with magnetic fields.

---------------------------------------------------------
Title: New Observations of Flare-Generated Sunquakes
Authors: Kosovichev, A.
2005AGUFMSH11A0244K    Altcode:
  Solar flares may produce "sunquakes", strong localized compressions
  in the photosphere, which generate acoustic waves propagating through
  the Sun's interior. These seismic waves are observed on the solar
  surface as expanding wave rings. Several strong sunquake events were
  observed by the Solar and Heliospheric Observatory (SOHO) in 2003-2005,
  long after the first sunquake detected in 1996. Detailed analysis of
  these events SOHO and RHESSI space missions reveals new interesting
  properties of the seismic response to solar flares, such as close
  association between the hard X-ray flare emission and the hydrodynamic
  impacts on the solar surface, strong anizotropy of the seismic waves,
  and their interaction with sunspots. These results are of significant
  interest for understanding the physics of energy release and transport
  in solar flares, and for helioseismic diagnostics of flaring active
  regions. An intriguing question is why the sunquakes have been observed
  only during the declining phases of the solar activity cycle.

---------------------------------------------------------
Title: Variability of the solar interior and irradiance
Authors: Kosovichev, A.
2005AGUFMSH33C..03K    Altcode:
  Solar variability is controlled by dynamo processes in the Sun's
  interior. The interior properties are measured by helioseismology. These
  measurements are based on observations of solar oscillations and waves
  which are excited by turbulent convection near the surface and propagate
  through the interior. Oscillation frequencies and travel times provide
  information about variations of the structure and large-scale dynamics
  inside the Sun. Recently developed methods of acoustic tomography
  provide 3D images of the solar interior. Variations of the global
  internal properties of the Sun have been measured for two solar cycles,
  and for the last 10 years the space mission SOHO and ground-based
  networks (GONG, BiSON, TON) provided continuous monitoring of the
  global properties including total irradiance. I review recent results
  of the helioseismic measurements of the structure and dynamics of the
  Sun, and discuss their relation for understanding mechanisms of solar
  variability and activity.

---------------------------------------------------------
Title: Numerical Simulations of Solar Acoustic Field
Authors: Parchevsky, K. V.; Kosovichev, A. G.
2005AGUFMSH41A1118P    Altcode:
  We present numerical simulations of propagation of acoustic waves in
  the upper convection zone using a standard solar model and realistic
  equation of state (OPAL model). The main goals are to study properties
  of solar waves for various excitation sources and interaction of these
  waves with spatial inhomogeneities, and also to generate artificial wave
  fields for testing local helioseismic diagnostics of the solar interior,
  currently used for SOHO/MDI and GONG data. In our numerical model,
  non-reflecting boundary conditions based on absorbing 3D perfectly
  matched layer (PML) are imposed at all boundaries of the computational
  domain in Cartesian geometry. This prevents spurious reflection of
  acoustic waves from boundaries back to the computational domain. The
  top non-reflecting boundary is set in the solar atmosphere above the
  temperature minimum. This allowed us to realistically model the wave
  reflection from the solar atmosphere. We have developed a special
  PLM model, numerically stable in the case of a stratified medium
  with gravity, and investigated and tested various numerical schemes
  (including high-order dispersion-relation-preserving scheme). Numerical
  simulations have been carried out on parallel computers for different
  kinds of acoustic sources(force and energy sources). Single point
  sources are used to calculate realistic Green functions required for
  holographic seismic imaging. Simulated acoustic field from multiple
  sources randomly distributed below the photosphere is used as artificial
  data for testing helioseismic inversions, accuracy of Born and ray
  approximations.

---------------------------------------------------------
Title: Time-distance analysis of realistic simulations of solar
    convection
Authors: Georgobiani, D.; Zhao, J.; Benson, D.; Stein, R. F.;
   Kosovichev, A. G.; Nordlund, A.
2005AGUFMSH41A1117G    Altcode:
  The results of the new realistic large-scale simulations of solar
  turbulent convection provide an unprecedented opportunity to study
  solar oscillations and perform similar local helioseismology techniques
  as for the real solar data. The results offer an unique opportunity
  to compare the simulated flow fields with the flows and sounds speed
  variations inferred from the time-distance analysis. Applying some
  of the existing local helioseismology methods to the simulated solar
  convection and comparing to the observed results, one can validate
  the accuracy of these methods. We apply the time-distance analysis
  to the simulated data and successfully obtain the time-distance
  curve and travel time maps. Our travel times are consistent with the
  SOHO/MDI observations. The next step is to perform inversion to infer
  the interior flow fields at various depths and compare them with the
  simulated data in order to validate the model. This work is currently
  in progress.

---------------------------------------------------------
Title: Changes in the Subsurface Stratification of the Sun with the
    11-Year Activity Cycle
Authors: Lefebvre, S.; Kosovichev, A. G.
2005ApJ...633L.149L    Altcode: 2005astro.ph.10111L
  We report on changes in the Sun's subsurface stratification inferred
  from helioseismology data. Using data from the Solar and Heliospheric
  Observatory (SOHO) Michelson Doppler Imager (MDI) for the last 9 years
  and, more precisely, the temporal variation of f-mode frequencies, we
  have computed the variation in the radius of subsurface layers of the
  Sun by applying helioseismic inversions. We have found a variability
  of the “helioseismic” radius in antiphase with the solar activity,
  with the strongest variations of the stratification being just below
  the surface, around 0.995 R<SUB>solar</SUB>. In addition, the radius of
  the deeper layers of the Sun, between 0.975 and 0.99 R<SUB>solar</SUB>,
  changes in phase with the 11-year cycle.

---------------------------------------------------------
Title: Solar Polar Imager: Observing Solar Activity from a New
    Perspective
Authors: Alexander, D.; Sandman, A.; Liewer, P.; Ayon, J.; Goldstein,
   B.; Murphy, N.; Velli, M.; Floyd, L.; Moses, D.; Socker, D.; Vourlidas,
   A.; Garbe, G.; Suess, S.; Hassler, D.; Kosovichev, A.; Mewaldt, R.;
   Neugebauer, M.; Ulrich, R.; Zurbuchen, T.
2005ESASP.592..663A    Altcode: 2005soho...16E.131A; 2005ESASP.592E.131A
  No abstract at ADS

---------------------------------------------------------
Title: Properties of the Solar Acoustic Source Inferred from
    Nonadiabatic Oscillation Spectra
Authors: Wachter, R.; Kosovichev, A. G.
2005ApJ...627..550W    Altcode:
  Severino et al. suggested in 2001 that observed power and cross spectra
  of medium-degree p-modes in velocity and intensity can be described
  by splitting the solar background noise into correlated, coherent,
  and uncoherent components. We account for the nonadiabatic nature of
  solar oscillations by including the perturbations of the radiative
  energy flux in our model for the oscillations. Our calculations show
  the potential to explain the observations without the ad hoc phase
  differences between velocity and intensity oscillations introduced in
  the model of Severino et al. The phases and amplitudes of the correlated
  noise components are obtained by fitting our nonadiabatic model to the
  SOHO MDI power and cross spectra. These parameters provide information
  about the p-mode excitation process. We show that the type and location
  of the source can not be uniquely determined by the properties of
  the resonant p-modes in power and cross spectra of velocity and
  intensity oscillations. However, we obtain estimates for the phases
  and amplitudes of the correlated noise, which we interpret in terms of
  isolated rapid downdrafts in intergranular lanes. This idea is supported
  by three-dimensional simulations of the upper solar convection zone.

---------------------------------------------------------
Title: Time-Distance Helioseismology: Inversion of Noisy Correlated
    Data
Authors: Couvidat, S.; Gizon, L.; Birch, A. C.; Larsen, R. M.;
   Kosovichev, A. G.
2005ApJS..158..217C    Altcode:
  In time-distance helioseismology most inversion procedures ignore the
  correlations in the data errors. Here we simulate the travel-time
  perturbations of wavepackets that result from known distributions
  of sound speed inhomogeneities. The forward and inverse problems are
  carried out using recently developed Born approximation sensitivity
  kernels. A realistic solar noise component, with the correct
  statistics, is added to the data. We then apply a three-dimensional
  inversion procedure based on an improved multichannel deconvolution
  algorithm that includes the full covariance matrix of the simulated
  data and constrains the solution both in the vertical and horizontal
  directions. The validation of the inversion is achieved through
  comparison of the inferred sound speed distributions with the exact
  solutions. We show that including the covariance matrix matters for
  sound speed inhomogeneities varying on a length scale smaller than
  the correlation length. We also find that the inversion procedure is
  improved by adding horizontal regularization.

---------------------------------------------------------
Title: Multi-Wavelength Investigations of Solar Activity (IAU S223)
Authors: Stepanov, Alexander V.; Benevolenskaya, Elena E.; Kosovichev,
   Alexander G.
2005misa.book.....S    Altcode:
  Section I: Solar Cycle in the Interior, Atmosphere and Heliosphere;
  Section II-III: Structure and Evolution of Active Regions from the
  Sub-Photospheric Layers to the Corona, Filaments and Prominences;
  Section IV: Multi-Scale Coronal Structures and Links to Photospheric
  Magnetic Field; Section V: Energy Transport, Storage and Release in
  the Solar Atmosphere and Corona; Section VI: Heliospheric Effects and
  Space Weather Research; Section VII: Multi-Wavelength Observations of
  the Sun from Ground and Space.

---------------------------------------------------------
Title: Large-Scale Solar Photosphere Simulations
Authors: Wray, A.; Mansour, N. N.; Kosovichev, A.
2005AGUSMSP11C..01W    Altcode:
  We have developed a 3D, compressible radiative-hydrodynamics code
  for simulating the upper solar photosphere and lower atmosphere,
  from depths of a few 10's of megameters below to an altitude of a few
  hundred kilometers above the visible surface. Real gas opacities and
  equation of state are used, and the radiation is captured through full
  3D solution of the radiative transfer equation in opacity bands. The
  code is fully parallelized using the Message-Passing Interface (MPI)
  standard, allowing execution on both distributed and shared-memory
  architectures. We have benchmarked the code on the NASA Columbia
  system at Ames (an SGI Altix computer), obtaining near-ideal, linear
  scaling for a 500× 500× 500 node spatial mesh using from 1 to
  500 processors. This scaling behavior gives us confidence that the
  code can be used to run large meshes effectively on large numbers of
  processors. We will show preliminary results from a simulation of a
  box 20 Mm × 20 Mm × 18 Mm at a resolution (Δ x) of approximately
  40km, with a 5123 grid. Granular and intergranular lane structure and
  dynamics, turbulent statistics, thermal, and radiative properties will
  be described and compared to observations. Testing of subgrid-scale
  turbulence models will be discussed.

---------------------------------------------------------
Title: Effect of phase speed filters on time-distance correlations
    of acoustic waves on the Sun.
Authors: Nigam, R.; Rajaguru, P.; Kosovichev, A. G.
2005AGUSMSP11B..02N    Altcode:
  Use of phase-speed filters in time-distance helioseismic measurements
  is crucial to obtain spatially resolved information about localised
  sub-surface structures. These filters have to be chosen such that
  the travel times of the waves that are filtered in are themselves
  not affected by the filtering process. Here we derive analytically the
  cross-correlation signal that results from phase-speed filtered signals,
  assuming plane wave conditions. The resulting wavelet explicitly depends
  on the parameters of the filters, such as the phase-speed and its
  dispersion, in contrast to the currently used Gabor wavelet, and hence
  accounts for any filter induced changes in travel times. Alternatively,
  this new wavelet allows the determination of optimum parameters for
  the filters.

---------------------------------------------------------
Title: The Effects of Inclined Magnetic Field over Time-Distance
    Measurements
Authors: Zhao, J.; Kosovichev, A. G.
2005AGUSMSP13A..02Z    Altcode:
  Recent observation by phase-sensitive acoustic holography has shown
  that the inclined magnetic field has significant effects over the
  local helioseismology measurements, and it was thus suggested that the
  acoustic wave phase shift is substantially caused by the photospheric
  magnetic field. We make the similar measurements by use of time-distance
  helioseismology technique over a sunspot when it rotated from the
  solar east limb to the west. We find that the wave travel time is often
  longer in the part of sunspot penumbra that is closer to the solar disk
  center, similar to what was found by acoustic holography analysis. We
  investigate the other possible reasons that may cause this effect,
  e.g., projection effect, Doppler velocity masking effect, and find
  these effects do not account for all the travel time variations. We
  perform time-distance inversions to investigate how these measurements
  affect interior structures inferred from inversions.

---------------------------------------------------------
Title: Systematic errors in Dopplergrams of active regions
Authors: Wachter, R.; Schou, J.; Kosovichev, A. G.; Rajaguru, P.
2005AGUSMSP13A..07W    Altcode:
  Dopplergrams of magnetic regions are used in time-distance
  helioseismology and for the investigation of oscillations in
  sunspots. MDI Dopplergrams are produced onboard SOHO by measuring four
  filtergrams which are sensitive to intensity fluctuations in the wings
  of the Ni i absorption line at 6768 Å. The line of sight velocity
  is inferred from a lookup table which is based on the shape of the
  line in the quiet sun. In magnetic regions, however, the line shape
  changes drastically and molecular absorption lines appear close to the
  line's wavelength. This problem is equally relevant for the upcoming
  Helioseismic and Magnetic Imager (HMI) which measures velocities based
  on the same principles as MDI, using however a different absorption
  line (Fe i at 6173 Å). Based on high spectral resolution images of
  magnetic regions obtained by the ASP (Advanced Stokes Polarimeter)
  instrument we show that the MDI Doppler velocities are systematically
  underestimated in magnetic regions. We discuss possibilities to correct
  the velocity measurements in magnetic regions using intensity and
  magnetic field data.

---------------------------------------------------------
Title: A Search for the Relationship Between Subphotospheric Dynamics
    of Active Regions and Flaring Activity
Authors: Kosovichev, A. G.; Duvall, T. L.
2005AGUSMSP51C..04K    Altcode:
  MHD models of solar flares and CMEs suggest the magnetic energy for
  these events can be accumulated and released in magnetic structures
  sheared and twisted by plasma motions. We use time-distance
  helioseismology for investigating subphotospheric structures and
  dynamics of active regions that might be related to their flaring
  activity. In particular, we present a detailed study of active region
  NOAA 10486, which produced a series of X-class flares, during its
  passage on the solar disk for 8 days, Oct.25-Nov.1, 2003. The maps
  of subsurface flows and sound-speed perturbations are obtained from
  the SOHO/MDI data every 2-hours during this period, with 8-hour
  resolution and for the depth range of 0-12 Mm, and compared with the
  MDI magnetograms and X-ray data from RHESSI and GOES. The results
  reveal interesting dynamics at the depth of 4-6 Mm, which is compared
  with the restructuring, emergence and cancellation the magnetic field
  in this region.

---------------------------------------------------------
Title: Solar Supergranulation as Propagating Waves
Authors: Green, C.; Kosovichev, A. G.
2005AGUSMSP11C..03G    Altcode:
  It has been observed that the supergranulation pattern on the surface
  of the Sun appears to rotate faster than the photospheric plasma
  and magnetic features. It is postulated that this could be due to
  instabilities in the subsurface convective shear layer. This behaviour
  is modelled, starting with a linearized system of differential equations
  describing a convectively unstable region containing a horizontal
  shear flow. The system is solved numerically, using parameters drawn
  from the solar model and helioseismic inversions and assuming linear
  and non-linear shear flow profiles, for a range of wavenumbers. The
  phase speeds of the resulting wave solutions are found to be greater
  than the surface speed, possibly explaining the observed behaviour.

---------------------------------------------------------
Title: Study of the Solar Cycle Dependence of Low-Degree p-Modes
    with Michelson Doppler Imager and VIRGO
Authors: Toutain, T.; Kosovichev, A. G.
2005ApJ...622.1314T    Altcode:
  Studying variations of observational properties of low-degree solar
  acoustic p-modes (radial, dipole, and quadrupole) with the activity
  cycle is important for understanding potential effects of the cycle
  in the deep interior, obtaining more accurate inversions for the sound
  speed and rotation, and also for estimating prospective investigation
  of stellar activity by asteroseismology. We have analyzed changes
  of low-degree p-mode parameters during the current solar cycle
  (number 23) by using velocity and intensity oscillation data from two
  instruments on the Solar and Heliospheric Observatory (SOHO): the
  Michelson Doppler Imager (MDI) and Variability of Solar Irradiance
  and Gravity Oscillations (VIRGO). We show a clear dependence of
  mode frequency, line width, frequency splitting, and line asymmetry
  on the solar cycle. Moreover, we demonstrate that these properties
  change differently for modes of different frequency, angular degree,
  and order. The greatest changes are observed for sectorial modes of
  frequencies higher than 3 mHz, corresponding to the fact that the most
  significant variations of the solar structure occur in low-latitude
  regions close to the solar surface.

---------------------------------------------------------
Title: Sun's global property measurements: helioseismic probing of
    solar variability
Authors: Kosovichev, A. G.
2005MmSAI..76..743K    Altcode:
  Solar variability is controlled by dynamo processes in the Sun's
  interior. Global and local interior properties are measured by
  helioseismology. These measurements are based on observations of solar
  oscillations and waves which are excited by turbulent convection near
  the surface and propagate through the interior. Oscillation frequencies
  and travel times provide information about variations of the structure
  and large-scale dynamics inside the Sun. Recently developed methods of
  acoustic tomography provide 3D images of the solar interior. Variations
  of the global internal properties of the Sun have been measured for
  two solar cycles, and for the last 10 years the space mission SOHO
  and ground-based networks (GONG, BiSON, TON) provided continuous
  monitoring of the global properties. Recent helioseismic measurements
  of the structure and dynamics of the Sun provide new information about
  variations of the solar radius, asphericity, internal structure of
  sunspots and active regions, important for understanding mechanisms
  of the solar irradiance variations. The results provide support for a
  picture of a smaller and cooler, on average, Sun during the activity
  maxima, the higher irradiance of which is explained by a corrugated
  surface due to magnetic fields.

---------------------------------------------------------
Title: The Solar Energetic Particle Event of 16 August 2001: ~
    400 MeV Protons Following an Eruption at ~ W180
Authors: Cliver, E. W.; Thompson, B. J.; Lawrence, G. R.; Zhukov,
   A. N.; Tylka, A. J.; Dietrich, W. F.; Reames, D. V.; Reiner, M. J.;
   MacDowall, R . J.; Kosovichev, A. G.; Ling, A. G.
2005ICRC....1..121C    Altcode: 2005ICRC...29a.121C
  No abstract at ADS

---------------------------------------------------------
Title: Helioseismology for SolarB and Joint Investigations with
    SDO/HMI Project
Authors: Kosovichev, A.
2004ASPC..325...75K    Altcode:
  New methods of local helioseismology provide information about
  subsurface convective and shear flows, thermal and magnetic
  structures, which is critical for accomplishing the SolarB scientific
  objectives. I review the current status of acoustic tomography,
  observational requirements and limitations, and discuss observations
  of sub-photospheric vortex and shear motions, subsurface transport and
  flux emergence, and links between subphotospheric dynamics, magnetic
  topology, and coronal activity.

---------------------------------------------------------
Title: Large-Scale Flow Fields Beneath Major Solar Active Regions
Authors: Zhao, J.; Kosovichev, A. G.
2004AGUFMSH13A1143Z    Altcode:
  By use of MDI dynamic campaign data and by employing time-distance
  helioseismology, we have continued our efforts to map synoptic flow
  charts in the solar interior to deeper depths, especially under some
  major active regions, such as AR9393 and AR10486. Two dimensional
  horizontal flow fields, as well as vorticity and kinetic helicity
  distributions, are presented for a few Carrington rotations. Flow
  fields, vorticity and kinetic helicity distributions are studied in
  more details under major solar active regions, in particular, before
  and after major solar flares. We try to identify connections between
  solar flares with these subsurface dynamical properties.

---------------------------------------------------------
Title: Diagnostics of Subphotospheric Sources of Solar Variability
Authors: Kosovichev, A. G.; Duvall, T. L.; Zhao, J.
2004AGUFMSH13A1144K    Altcode:
  Local helioseismology provides new tools for studying subphotospheric
  processes that are related to solar variability of various spatial
  and temporal scales. Large-scale flow patterns beneath active
  regions and sunspots affect the solar energy transport in the upper
  convection zone. Smaller-scale shearing and twisting flows may trigger
  instabilities of magnetic configurations that lead to flares and
  CMEs. We discuss the recent progress in the local helioseismology
  diagnostic tools and in our understanding of the subphotospheric
  dynamics and sources of variability.

---------------------------------------------------------
Title: High Degree Solar Oscillations in 3d Numerical Simulations
Authors: Georgobiani, D.; Stein, R. F.; Nordlund, Å.; Kosovichev,
   A. G.; Mansour, N. N.
2004ESASP.559..267G    Altcode: 2004soho...14..267G
  No abstract at ADS

---------------------------------------------------------
Title: The Current Status of Analyzing High-Degree Modes
Authors: Reiter, J.; Rhodes, E. J., Jr.; Kosovichev, A. G.; Schou, J.
2004ESASP.559...61R    Altcode: 2004soho...14...61R
  No abstract at ADS

---------------------------------------------------------
Title: Oscillation Spectra of Line Depth, Intensity and Velocity
    from Radiative Transfer Calculations
Authors: Wachter, R.; Haberreiter, M.; Kosovichev, A. G.
2004ESASP.559..668W    Altcode: 2004soho...14..668W
  No abstract at ADS

---------------------------------------------------------
Title: Turbulence Convection and Oscillations in the Sun
Authors: Mansour, N. N.; Kosovichev, A. G.; Georgobiani, D.; Wray,
   A.; Miesch, M.
2004ESASP.559..164M    Altcode: 2004soho...14..164M
  No abstract at ADS

---------------------------------------------------------
Title: Properties of the Acoustic Source Inferred from Nonadiabatic
    Oscillation Spectra
Authors: Wachter, R.; Kosovichev, A. G.
2004ESASP.559...55W    Altcode: 2004soho...14...55W
  No abstract at ADS

---------------------------------------------------------
Title: Probing Solar Dynamics in the Upper Convection Zone by
    Time-Distance Helioseismology
Authors: Zhao, J.; Kosovichev, A. G.
2004ESASP.559..672Z    Altcode: 2004soho...14..672Z
  No abstract at ADS

---------------------------------------------------------
Title: Erratum: “Looking for Gravity-Mode Multiplets with the GOLF
    Experiment aboard SOHO” (<A href="/abs/2004ApJ...604..455T">ApJ,
    604, 455 [2004]</A>)
Authors: Turck-Chièze, S.; García, R. A.; Couvidat, S.; Ulrich,
   R. K.; Bertello, L.; Varadi, F.; Kosovichev, A. G.; Gabriel, A. H.;
   Berthomieu, G.; Brun, A. S.; Lopes, I.; Pallé, P.; Provost, J.;
   Robillot, J. M.; Roca Cortés, T.
2004ApJ...608..610T    Altcode:
  As a result of an error at the Press, the second panel of Figure 9
  was repeated twice in the top row of the printed, black-and-white
  version of this figure, and the first panel was omitted. This error
  appears in the print edition and the PDF and postscript (PS) versions
  available with the electronic edition of the journal, although the
  panels of the color figure displayed in the electronic article itself
  are correct. Please see below for the corrected print version of Figure
  9. The Press sincerely regrets the error.

---------------------------------------------------------
Title: Sensitivity of Acoustic Wave Travel Times to Sound-Speed
    Perturbations in the Solar Interior
Authors: Birch, A. C.; Kosovichev, A. G.; Duvall, T. L., Jr.
2004ApJ...608..580B    Altcode:
  For time-distance helioseismology, it is important to establish the
  relationship between the travel times of acoustic waves propagating
  between different points on the solar surface through the solar interior
  and local perturbations to the sound speed in the propagation region. We
  use the Born approximation to derive a general expression for the
  linear sensitivity of travel times to local sound-speed perturbations
  in plane-parallel solar models with stochastic wave sources. The results
  show that the sensitivity of time-distance measurements to perturbations
  in sound speed depends on the details of the measurement procedure,
  such as the phase-speed filter used in typical time-distance data
  analysis. As a result, the details of the measurement procedure should
  be taken into account in the inversion of time-distance data. Otherwise,
  the inferred depths of perturbations may be incorrect.

---------------------------------------------------------
Title: On the Relationship between the Rotational Velocity and the
    Field Strength of Solar Magnetic Elements
Authors: Zhao, Junwei; Kosovichev, Alexander G.; Duvall, Thomas L., Jr.
2004ApJ...607L.135Z    Altcode:
  By tracking various solar surface tracers, previous studies have found
  that magnetic structures, such as plages and sunspots, rotate faster
  than the quiet solar regions. We investigate how the rotational speed of
  these magnetic features is related to their magnetic field strength. By
  use of near-surface horizontal velocities inferred from time-distance
  helioseismology, we have studied a few Carrington rotations covering
  the years 1997-2002, from near the solar minimum to the maximum. It
  is found that the residual rotational velocity of magnetic elements
  nearly linearly depends on their magnetic field strength: the stronger
  the magnetic field strength, the faster the magnetic elements rotate
  relative to the quiet solar regions. It is also found that the
  magnetic elements rotate faster in the solar maximum years than the
  elements of the same magnetic strength but in years with moderate solar
  activity. For all Carrington rotations studied, magnetic elements of the
  following polarity rotate faster than the leading polarity elements of
  the same magnetic strength. Possible interpretations of the observed
  relations are discussed. Prograde supergranular advection may cause
  the faster rotation of the following polarity elements.

---------------------------------------------------------
Title: Three-dimensional Inversion of Time-Distance Helioseismology
Data: Ray-Path and Fresnel-Zone Approximations
Authors: Couvidat, S.; Birch, A. C.; Kosovichev, A. G.; Zhao, J.
2004ApJ...607..554C    Altcode:
  Time-distance helioseismology has provided important new insight into
  the subphotospheric structure and dynamics of sunspots, active regions,
  supergranular cells, and large-scale flows. These inferences have been
  made by using either the ray-path or Fresnel-zone approximations. We
  present inversion results of travel-time perturbations of wavepackets
  propagating inside the Sun, using both ray-path and Fresnel-zone
  kernels for real and artificial data. The ray approximation was
  the first approximation used in time-distance helioseismology for
  deriving the sensitivity of travel times to perturbations in the solar
  interior. However, new types of sensitivity kernels are being developed
  to take into account finite-wavelength effects (such as kernels based
  on a Fresnel-zone approximation) and thus improve the resolution and
  accuracy of the inversions. Since many results have been obtained with
  the ray-path approximation, it is important to compare them with the
  new Fresnel-zone inversions to quantify their accuracy. We have applied
  the two approximations to artificial and real data and concluded that
  both approximations provide similar results for structures lying within
  the scope of the kernels. Nonetheless, the vertical structure can be
  inferred at greater depth with the Fresnel-zone kernels than with the
  ray-path ones, using the same travel-time data. Applying Fresnel-zone
  inversion to the MDI time-distance data of 1998 June 20 we confirm
  the two-part structure of the sunspots previously derived with the
  ray approximation.

---------------------------------------------------------
Title: Subphotospheric Dynamics During the Period of Massive Solar
    Flares
Authors: Kosovichev, A. G.; Duvall, T. L., Jr.
2004AAS...204.4703K    Altcode: 2004BAAS...36Q.737K
  Unstable coronal structures that lead to impulsive energy release in
  solar flares are created by magnetic flux emergence and by photospheric
  and subphotospheric motions shearing and twisting magnetic field
  lines. We present results of investigation of subsurface plasma flows
  and emerging structures associated with AR 10484, 10486, and 10488,
  which produced the majority of massive flares of October-November
  2003. The results representing 3-D maps of sound-speed perturbations
  and flow velocities are obtained from SOHO/MDI full-disk Doppler data
  by time-distance helioseismology with the horizontal resolution of 3
  Mm, vertical resolution of 0.7-4 Mm (in the depth range of 0-40 Mm),
  and temporal resolution of 8 hours. These maps are compared with the
  corresponding MDI magnetograms, and also with TRACE and RHESSI images
  to determine the role of subphotospheric dynamics in the development
  of the active regions and their flaring activity.

---------------------------------------------------------
Title: Structure Properties of Supergranulation and Granulation
Authors: Berrilli, F.; Del Moro, D.; Consolini, G.; Pietropaolo, E.;
   Duvall, T. L., Jr.; Kosovichev, A. G.
2004SoPh..221...33B    Altcode:
  We investigate spatial dislocation ordering of the solar structures
  associated with supergranulation and granulation scales. The
  supergranular and granular structures are automatically segmented
  from time-distance divergence maps and from broad-band images,
  respectively. The spatial dislocation ordering analysis is accomplished
  by applying the statistical method of Pair Correlation Function,
  g<SUB>2</SUB>(r), to segmented features in the solar fields. We
  compare the computed g<SUB>2</SUB>(r) functions obtained from both
  single and persistent, i.e., time-averaged, fields associated with
  supergranulation and granulation. We conclude that supergranulation
  and granulation patterns present a different topological order both
  in single and persistent fields. The analysis carried out on single
  fields suggests that the granulation behaves as an essentially random
  distribution of soft plasma features with a very broad distribution
  in size, while supergranulation behaves as a random distribution of
  close packed, coherent stiff features with a rather defined mean size.

---------------------------------------------------------
Title: Dynamics and Structure of Supergranulation
Authors: Del Moro, D.; Berrilli, F.; Duvall, T. L., Jr.; Kosovichev,
   A. G.
2004SoPh..221...23D    Altcode:
  In this paper we investigate the temporal evolution and geometric
  properties of solar supergranular features. For this purpose we apply
  an automatic feature-tracking algorithm to a 6-day time series of 18
  near-surface flowmaps containing 548 target objects. Lifetimes are
  calculated by measuring the time elapsing between the birth and death
  of each target. Using an exponential fit on the lifetime distribution
  of single supergranules we derived a mean lifetime of 22 hours. Based
  on the application of segmentation numerical procedures, we estimated
  characteristic geometric parameters such as area distributions of
  supergranular cells. We also derive the relationship between measured
  lifetime and the area of the supergranules.

---------------------------------------------------------
Title: Probing Plasma Structures and Dynamics Inside the Sun
Authors: Kosovichev, A. G.
2004AIPC..703..209K    Altcode:
  Helioseismology has provided tremendous amount of new information
  about the thermodynamic properties and dynamics of plasma in the Sun's
  interior. This gives us new insights into the basic physical processes
  inside the Sun, formation of magnetic structures in the solar plasma
  and mechanisms of solar and stellar activity. In particular, the new
  results have revealed the deep structure of sunspots and associated
  complicated patterns of plasma flows, the dynamics of the emerging
  magnetic flux and formation of active regions, the supergranular
  structure and dynamics of the upper convection zone, as well as
  the global structures and circulation patterns in the deep interior,
  evolving with the activity cycle. In addition, first attempts are made
  to find links between the internal dynamics and processes of magnetic
  energy release in the solar corona. Understanding of these results,
  often puzzling and counter-intuitive, represents a major challenge
  for MHD theories of astrophysical plasma.

---------------------------------------------------------
Title: Looking for Gravity-Mode Multiplets with the GOLF Experiment
    aboard SOHO
Authors: Turck-Chièze, S.; García, R. A.; Couvidat, S.; Ulrich,
   R. K.; Bertello, L.; Varadi, F.; Kosovichev, A. G.; Gabriel, A. H.;
   Berthomieu, G.; Brun, A. S.; Lopes, I.; Pallé, P.; Provost, J.;
   Robillot, J. M.; Roca Cortés, T.
2004ApJ...604..455T    Altcode:
  This paper is focused on the search for low-amplitude solar gravity
  modes between 150 and 400 μHz, corresponding to low-degree, low-order
  modes. It presents results based on an original strategy that looks
  for multiplets instead of single peaks, taking into consideration
  our knowledge of the solar interior from acoustic modes. Five years
  of quasi-continuous measurements collected with the helioseismic GOLF
  experiment aboard the SOHO spacecraft are analyzed. We use different
  power spectrum estimators and calculate confidence levels for the
  most significant peaks. This approach allows us to look for signals
  with velocities down to 2 mm s<SUP>-1</SUP>, not far from the limit
  of existing instruments aboard SOHO, amplitudes that have never been
  investigated up to now. We apply the method to series of 1290 days,
  beginning in 1996 April, near the solar cycle minimum. An automatic
  detection algorithm lists those peaks and multiplets that have a
  probability of more than 90% of not being pure noise. The detected
  patterns are then followed in time, considering also series of 1768 and
  2034 days, partly covering the solar cycle maximum. In the analyzed
  frequency range, the probability of detection of the multiplets
  does not increase with time as for very long lifetime modes. This is
  partly due to the observational conditions after 1998 October and the
  degradation of these observational conditions near the solar maximum,
  since these modes have a “mixed” character and probably behave as
  acoustic modes. Several structures retain our attention because of
  the presence of persistent peaks along the whole time span. These
  features may support the idea of an increase of the rotation in the
  inner core. There are good arguments for thinking that complementary
  observations up to the solar activity minimum in 2007 will be decisive
  for drawing conclusions on the presence or absence of gravity modes
  detected aboard the SOHO satellite.

---------------------------------------------------------
Title: Torsional Oscillation, Meridional Flows, and Vorticity
    Inferred in the Upper Convection Zone of the Sun by Time-Distance
    Helioseismology
Authors: Zhao, Junwei; Kosovichev, Alexander G.
2004ApJ...603..776Z    Altcode:
  By applying time-distance helioseismology measurements and inversions
  to Solar and Heliospheric Observatory (SOHO) Michelson Doppler Imager
  (MDI) dynamics campaign data, we obtain synoptic maps of subsurface
  plasma-flow fields at a depth of 0-12 Mm for seven solar Carrington
  rotations, covering the years 1996-2002, from solar-activity minimum to
  maximum. Vorticity distribution and both zonal and meridional flows are
  derived from such synoptic flow maps, which contain an enormous amount
  of information about solar dynamics. The results for the zonal flows
  agree well with previous results. The meridional flows of an order of 20
  m s<SUP>-1</SUP> are found to remain poleward during the whole period of
  observations. In addition to the poleward meridional flows observed at
  the solar minimum, extra meridional circulation cells of flow converging
  toward the activity belts are found in both hemispheres, which may imply
  plasma downdrafts in the activity belts. These converging flow cells
  migrate toward the solar equator together with the activity belts as
  the solar cycle evolves. The vorticity distributions are largely linear
  with latitude, and the deviations from the vorticity caused by the mean
  differential rotation are presented. Patterns of large-scale flows are
  investigated for a large active region at different depths. Converging
  flows toward the center of the active region are found near the solar
  surface, and divergent flows in this large active region are found
  to be rooted much deeper than similar flows observed in individual
  sunspots. We conclude that the extremely rich and complicated dynamics
  of the upper convection zone reveal remarkable organization on the
  large scale, which can be correlated with the magnetic activity zones.

---------------------------------------------------------
Title: Subphotospheric Structure of Sunspots and Active Regions
Authors: Kosovichev, Alexander G.
2004IAUS..223..171K    Altcode: 2005IAUS..223..171K
  New methods of local area helioseismology provide three-dimensional maps
  of sound-speed variations and mass flows in the upper convection zone,
  giving important insight into the internal structure and dynamics of
  sunspots and active regions. Most of these results are obtained from
  SOHO/MDI data using the method of time-distance helioseismology (or
  acoustic tomography). Robustness of this method has been significantly
  improved by incorporating most important wave propagation effects
  and stochastic properties of solar oscillations. Time-distance
  helioseismology reveals that developed sunspots have a two layer
  structure: a relatively thin sub-photospheric layer of lower sound
  speed, and a deeper layer of higher sound speed. The mass flows in the
  upper layer are typically converging and directed downward, while in the
  deeper interior the flows are mostly diverging. These results support
  the cluster model of sunspots suggested by Parker. New observations
  also provide interesting information about emerging magnetic flux,
  formation and evolution of active regions and complexes of activity,
  and allow us to investigate effects of sub-photospheric dynamics of
  active regions on the global circulation of the Sun and also small-scale
  rapid shear flows associated with flares and CME.

---------------------------------------------------------
Title: Multi-wavelength investigations of solar activity : proceedings
    of the 223th symposium of the International Astronomical Union held
    in Saint Petersburg, Russia, June 14-19, 2004
Authors: Stepanov, Alexander V.; Benevolenskaya, Elena E.; Kosovichev,
   Alexander G.
2004IAUS..223.....S    Altcode: 2005IAUS..223.....S
  No abstract at ADS

---------------------------------------------------------
Title: Probing Plasma Properties and Dynamics Inside the Sun
Authors: Kosovichev, A. G.
2004cosp...35.1908K    Altcode: 2004cosp.meet.1908K
  Helioseismology experiment MDI on board the SOHO spacecraft has provided
  tremendous amount of new information about the thermodynamic properties
  and dynamics of plasma in the Sun's interior, uncovering remarkable new
  perspectives for studying the complex interactions between turbulent
  convection, rotation and magnetism below the solar surface, and their
  relationship to solar irradiance variations and coronal activity. In
  particular, the new results have revealed the deep structure of
  sunspots and associated complicated patterns of plasma flows, the
  dynamics of the emerging magnetic flux and formation of active regions,
  the supergranular structure and dynamics of the upper convection zone,
  as well as the global structures and circulation patterns in the deep
  interior, evolving with the activity cycle. In addition, first attempts
  are made to find the links between the internal dynamics and processes
  of magnetic energy release in the solar corona. Understanding these
  results, often puzzling and counter-intuitive, is a major challenge
  for MHD theories of astrophysical plasma.

---------------------------------------------------------
Title: The Sub-surface Characteristics of Sunspots
Authors: Kosovichev, A. G.
2004cosp...35.1907K    Altcode: 2004cosp.meet.1907K
  New methods of helioseismology provide 3-D subphotospheric maps of
  sunspots, emerging magnetic structures and associated convective
  flows. This gives us new insights into the basic physical processes
  inside the Sun, formation of magnetic structures in the solar plasma
  and mechanisms of solar and stellar activity. The current results
  from the MDI instrument on SOHO reveal complicated stratification and
  flow patterns of solar plasma beneath sunspots, with a characteristic
  temperature increase in deeper layers and multiple vortex systems,
  providing evidence for a cluster model of sunspots. The helioseismic
  observations provide importants clues for understanding the mechanisms
  of formation of sunspots and active regions, and the subphotospheric
  dynamics of convective flows shearing and twisting magnetic fields in
  the corona.

---------------------------------------------------------
Title: The Sun's Surface and Subsurface. Investigating Shape and
    Irradiance
Authors: Kosovichev, Alexander
2004EOSTr..85...32K    Altcode:
  Since the Sun's radiative output establishes the Earth's thermal
  environment, knowing the source and nature of its variability
  is essential for understanding and predicting the interactions
  in the Earth-Sun system, among which are climate changes and the
  energy balance, photochemistry, and dynamics of the middle and upper
  atmosphere. The Sun's Surface and Subsurface brilliantly demonstrates
  how precise measurements of the Sun's properties, such as the solar
  diameter, oblateness, irradiance, and oscillation frequencies of
  normal modes provide insight into the structure and dynamics of the
  deep interior and the physical mechanisms of solar variability. This
  relatively compact book provides a comprehensive review of the
  basic principles, methodology, and tools for studying the solar
  variability. The main focus is on measurements and interpretation
  of the solar properties rather than on theory. It provides both an
  excellent introduction to the field and an exciting review of the
  recent advances in solar observations from the ground and space.

---------------------------------------------------------
Title: Sensitivity of Time-Distance Measurements to Local Changes
    in Sound Speed and Source Properties
Authors: Birch, A.; Kosovichev, A.
2003AGUFMSH21B0163B    Altcode:
  In order to interpret time-distance measurements of travel times it
  is important to understand the sensitivity of these measurements to
  different types of perturbations to a solar model. We will show example
  sensitivity functions for local perturbations to the sound-speed,
  source strength, and source correlation time. These examples show
  that the effect of a sound-speed perturbation on the time-distance
  travel-times depends on the details of the filtering. In particular,
  for narrow phase-speed filters, the sensitivity functions do not
  resemble the now traditional banana-doughnut kernels.

---------------------------------------------------------
Title: Solar Subsurface Synoptic Flow Maps by Time-Distance
    Helioseismology
Authors: Zhao, J.; Kosovichev, A. G.
2003AGUFMSH42B0537Z    Altcode:
  The synoptic flow maps have been made up to 12 Mm beneath the solar
  surface by use of time-distance helioseismology measurements and
  inversions. The study selects one Carrington rotation each year from
  1996 to 2002, covering from solar minimum to maximum. The synoptic flow
  map has a high spatial resolution of 0.24 heliographic degree per pixel,
  and supergranular flows are able to be shown. Zonal and meridional
  flows, as well as the vorticity distribution are derived from such
  maps. It is found that after the subtraction of the solar minimum data,
  the residual meridional flows converge toward the activity belts, and
  migrate toward the equator together with the sunspot zones. Results
  are to be compared with those obtained from previous studies such as
  frequency splitting and ring-diagram analysis.

---------------------------------------------------------
Title: Evolution of Active Regions in the Solar Interior
Authors: Kosovichev, A. G.; Duvall, T. L.
2003AGUFMSH22A0186K    Altcode:
  Using data from SOHO and TRACE, we investigate the emergence,
  evolution and dissipation of magnetic active regions in the
  solar interior and atmosphere by comparing 3D maps of subsurface
  structures and plasma flows, obtained by acoustic tomography, with the
  corresponding photospheric magnetograms and coronal EUV images. We
  find that the growth of active regions is characterized by multiple
  emergence of magnetic flux structures propagating very rapidly in the
  upper convection zone and by the formation of large-scale converging
  flows. During the decay, we have observed mostly diverging flows, and
  have attempted to detect submergence of magnetic flux. We look at some
  details of the dynamics of active regions, and discuss initial results
  of a search for the relationship between subphotospheric shearing flows,
  and changes in magnetic topology and flaring activity in the corona.

---------------------------------------------------------
Title: Time-Distance Helioseismology: How The Inversion Results
    Depend On The Approximation Used
Authors: Couvidat, S.; Birch, A. C.; Kosovichev, A. G.; Zhao, J.
2003AGUFMSH42B0534C    Altcode:
  During the last decade, time-distance helioseismology has provided
  important new insight into the solar sub-photospheric structure
  and dynamics of sunspots, active regions, supergranular cells, and
  large-scale flows. These results were based either on the ray-path or
  on the Fresnel-zone approximations. We present inversion results of
  travel-time perturbations of wavepackets propagating inside the Sun,
  using both ray-path and Fresnel-zone kernels for real and artificial
  data. The ray approximation was the first approximation in time-distance
  helioseismology for deriving the travel-times. However new types of
  kernels are being developed to take into account the finite-wavelength
  effects of the wavepackets (such as Fresnel-zone kernels), and thus
  improve the resolution and accuracy of the inversions. Since many
  results have been obtained with the ray-path approximation, it is
  important to compare them with the new Fresnel-zone inversions to
  quantify their accuracy.

---------------------------------------------------------
Title: Solar Seismic Models and the Neutrino Predictions
Authors: Couvidat, S.; Turck-Chièze, S.; Kosovichev, A. G.
2003ApJ...599.1434C    Altcode: 2002astro.ph..3107C
  This paper focuses on the solar neutrino fluxes, the g-mode predictions,
  and the possible impact of the magnetic fields on the neutrino emission
  and transport. The Solar and Heliospheric Observatory (SOHO) spacecraft
  has allowed astrophysicists to achieve a major breakthrough in the
  knowledge of the solar core. Both GOLF and MDI instruments on SOHO
  have significantly improved the accuracy of the sound speed profile,
  mainly by the detection of low-degree low-order p-modes. Our study
  (Turck-Chièze and coworkers) has lead to precise neutrino predictions
  through constructing a seismic solar model that is in good agreement
  with the sound speed profile inferred by helioseismology in the
  radiative interior of the Sun. In this paper we present the details
  of this study and investigate new solar models validated by the
  acoustic modes. These new models are primarily used to derive the
  emitted neutrino fluxes. We show that these fluxes do not depend
  strongly on the modified physics as far as the model is consistent
  with the helioseismic observations in the core. We also show that an
  internal large-scale magnetic field cannot exceed a maximum strength
  of ~=3×10<SUP>7</SUP> G in the radiative zone and may increase the
  emitted <SUP>8</SUP>B neutrino flux only by ~=2%. All the neutrino
  predictions here are compatible with the Sudbury Neutrino Observatory
  results, assuming three neutrino flavors. We deduce the electron and
  neutron radial densities that are needed to calculate the neutrino
  oscillation properties. Finally, we discuss how the magnetic fields
  may influence the neutrino transport through the RSFP process, for
  different values of Δm<SUP>2</SUP>.

---------------------------------------------------------
Title: Fast photospheric flows and magnetic fields  in a flaring
    active region
Authors: Meunier, N.; Kosovichev, A.
2003A&A...412..541M    Altcode:
  We present new results from the coordinated observations between
  the THEMIS telescope (in the multi-line spectropolarimetric mode)
  and Michelson Doppler Imager (MDI) on SOHO obtained in November 2000
  for active region NOAA 9236 which was the source of several X-class
  flares. The goal of these observations was twofold: to verify MDI
  measurements of the line-of-sight components of flow velocity and
  magnetic field, and to obtain more information about the photospheric
  flows and magnetic fields in flaring regions. Using the simultaneous
  observational data in several lines we have analyzed the structure and
  dynamics of this active region at the photospheric level before and
  after a X4.0 flare of November 26, the last major flare produced by
  this very active region. Vector magnetic field maps are computed from
  the THEMIS data by full inversion of the Stokes line profiles. In
  the Doppler velocity maps from THEMIS and MDI, we observe fast
  photospheric flows which appear to be supersonic in two regions
  located close to the region where the flare occurred. These flows
  seem to be long-lived (several hours at least). In one position,
  we observe a supersonic downflow strongly inclined with respect to
  the vertical (by 51<SUP>deg</SUP>), while in another position, a flow
  suggesting a strong shear with a supersonic component as well, although
  almost horizontal upflows and downflows cannot be ruled out in that
  case. These flows seem to be present at least 8 hours before the flare,
  and the amplitude in the second case appeared to be modified during
  the flare, especially, during the first minutes. In the MDI data, we
  observed strong permanent changes of the longitudinal magnetic flux,
  associated with the flare. The role of the strong flows and their
  interaction with the magnetic field in the development of the active
  region and the flare is not understood yet.

---------------------------------------------------------
Title: Analysis of relationship between flaring activity and
    subphotospheric flows in NOAA 9393
Authors: Kulinová, A.; Dzifcáková, E.; Duvall, T. L., Jr.;
   Kosovichev, A. G.
2003ESASP.535..125K    Altcode: 2003iscs.symp..125K
  The relationship between the subphotospheric flows and flaring activity
  is not well understood. It is believed that subphotospheric shearing
  flows play important role in creating unstable magnetic topology
  that leads to initiation of flares and CMEs. In this paper, we study
  subphotospheric flows and their relationship with two flares observed
  in active region NOAA 9393. One of the flares is connected with halo
  CME. SOHO/MDI and helioseismology data are used for determining the
  changes in morphology and are compared with changes of the topology
  as observed by TRACE. We find evidence of some connections between
  subphotospheric flows within 12 Mm below the photosphere and changes
  of photospheric magnetic fields and also the flaring activity.

---------------------------------------------------------
Title: Characterization of supergranular features via topological
    measures
Authors: Berrilli, F.; del Moro, D.; Giordano, S.; Consolini, G.;
   Kosovichev, A.
2003ESASP.535...47B    Altcode: 2003iscs.symp...47B
  The spatial configuration of enhanced magnetic field (active regions)
  in the outer layers of the Sun derives from the interaction between
  convective flows and solar magnetic field. Temporal evolution of
  active regions is considered the main responsible of radiative
  output variations. Particularly, solar irradiance variations are
  explained in terms of temporal and spatial evolution of solar
  surface magnetic fields. A key role in this evolution is played by
  supergranular convective flow that, advecting magnetic flux tubes,
  is also responsible of the creation of the magnetic network. This
  latter results located on the boundaries of supergranular cells. In
  order to measure both the spatial correlation length in supergranular
  structures and the degree of near neighbor order in such structures, we
  employ two topological analysis methods, the Pair Correlation Function
  g<SUB>2</SUB>(r) and the Information Entropy H'(l). More in detail,
  we apply these statistical methods to segmented images of divergence
  maps derived from the application of the time-distance technique to
  MDI/SOHO data. We assume that segmented images are representative of
  the mass flows associated to convective supergranular motions.

---------------------------------------------------------
Title: What helioseismology teaches us about the Sun
Authors: Kosovichev, A. G.
2003ESASP.535..795K    Altcode: 2003iscs.symp..795K
  Helioseismology uses observations of oscillations of the solar surface
  to determine the internal structure and dynamics of the Sun, providing
  critical knowledge about the mechanisms of solar variability and
  activity cycles. The recent advances based on observations from SOHO
  spacecraft and GONG network have allowed us to study both long-term
  changes of the global structure and circulation and short-term
  variations associated with developing active regions, sunspots
  and coronal activity. In particular, the global helioseismology
  results have revealed 1.3-year variations of the rotation rate in the
  tachocline, but found no indication of 11-year variations. Studies
  of the meridional circulation have shown formation of additional
  meridional cells of flows converging toward the activity belts, thus,
  questioning the flux-transport theories of the solar cycle. It is
  found that sunspots as cool objects appear to be only 4-5 Mm deep,
  but accumulate significant heat in the deeper layers, and also form
  converging downflows. Large active regions are formed as a result of
  multiple flux emergence, and no evidence of large-scale emerging Ω-loop
  has been found. This paper presents a brief review of these and some
  other results of helioseismology, analysis techniques, and perspectives.

---------------------------------------------------------
Title: Helioseismic Observation of the Structure and Dynamics of a
    Rotating Sunspot Beneath the Solar Surface
Authors: Zhao, Junwei; Kosovichev, Alexander G.
2003ApJ...591..446Z    Altcode:
  Time-distance helioseismology is applied to study the subphotospheric
  structures and dynamics of an unusually fast-rotating sunspot observed
  by the Michelson Doppler Imager on board SOHO in 2000 August. The
  subsurface sound speed structures and velocity fields are obtained for
  the sunspot region at different depths from 0 to 12 Mm. By comparing
  the subsurface sound speed variations with the surface magnetic field,
  we find evidence for structural twists beneath the visible surface of
  this active region, which may indicate that magnetic twists often seen
  at the photosphere also exist beneath the photosphere. We also report
  on the observation of subsurface horizontal vortical flows that extend
  to a depth of 5 Mm around this rotating sunspot and present evidence
  that opposite vortical flows may exist below 9 Mm. It is suggested that
  the vortical flows around this active region may build up a significant
  amount of magnetic helicity and energy to power solar eruptions. Monte
  Carlo simulation has been performed to estimate the error propagation,
  and in addition the sunspot umbra is masked to test the reliability of
  our inversion results. On the basis of the three-dimensional velocity
  fields obtained from the time-distance helioseismology inversions, we
  estimate the subsurface kinetic helicity at different depths for the
  first time and conclude that it is comparable to the current helicity
  estimated from vector magnetograms.

---------------------------------------------------------
Title: Optimal Masks for Solar g-Mode Detection
Authors: Wachter, R.; Schou, J.; Kosovichev, A. G.; Scherrer, P. H.
2003ApJ...588.1199W    Altcode:
  The detection of gravity (g) modes of solar oscillations is important
  for probing the physical conditions in the Sun's energy-generating
  core. We have developed a new method of spatial masks optimized to
  reveal solar g-modes of angular degree l=1-3 and applied it to Michelson
  Doppler Imager data in the frequency range of 50-500 μHz. These
  masks take into account the horizontal component of g-mode velocity
  eigenfunctions and the variations in the level of noise across the
  solar disk and adjust for the time-dependent mode projection properties
  caused by the inclination of the Sun's axis of rotation. They allow us
  to optimize the signal-to-noise ratio in the oscillation power spectra
  for potential g-modes of various angular order and degree. The peaks
  in the resulting spectra are analyzed in terms of their instrumental
  origin, long-term stability, and correspondence to the theoretically
  predicted g-mode spectrum. As a consequence of failing to detect
  any g-mode candidates, new upper limits for the surface amplitude of
  g-modes are obtained. The lowest upper limits in the range of 5-6 mm
  s<SUP>-1</SUP> are found for sectorial g-modes (l=m). These limits
  are an order of magnitude higher than the theoretical prediction of
  Kumar et al. in 1996.

---------------------------------------------------------
Title: Searching for Deep Changes of the Solar Structure
Authors: Kosovichev, A. G.
2003SPD....34.2611K    Altcode: 2003BAAS...35..856K
  A relation between normal-mode and multiple-reflection time-distance
  data is derived by applying the principle of stationary phase to
  solar acoustic oscillations. This relation links the global and local
  helioseismology data, and provides estimates of acoustic travel
  times in terms of mode frequencies. It is employed for searching
  solar-cycle variations in the tachocline, by using GONG and MDI data of
  1996-2002. The time-distance signature of magnetic field at the base
  of the convection zone recently reported by Chou and Serebryanskiy
  (2002) and the current precision of the deep changes are discussed.

---------------------------------------------------------
Title: Travel-Time Sensitivities for Time-Distance Helioseismology
Authors: Birch, A. C.; Kosovichev, A. G.
2003SPD....34.0807B    Altcode: 2003BAAS...35Q.823B
  Time-distance helioseismology is an important tool for studying the
  interior of the Sun in three dimensions. The primary data products in
  time-distance helioseismology are the times for wave packets (p mode
  or f mode) to travel between separate points on the solar surface. In
  order to invert travel times to obtain subsurface structure and flows
  it is necessary to understand the forward problem: the dependence
  of travel-times on small perturbations to conditions in the solar
  interior. We will present calculations, in the Born approximation,
  of the dependence of travel times on subsurface flows, perturbations
  to the sound speed, and spatial variations in source strength. We show
  that travel-time sensitivities can depend strongly on the details of
  the filtering that is performed during the data analysis.

---------------------------------------------------------
Title: Comparison of Solar Subsurface Weather Obtained with
    Time-Distance Tomography and Ring Analysis
Authors: Hindman, B. W.; Zhao, J.; Haber, D. A.; Kosovichev, A. G.;
   Toomre, J.
2003SPD....34.0806H    Altcode: 2003BAAS...35R.822H
  The near-surface shear layer exhibits a rich medley of flows that
  vary in size from granular and supergranular flows to flows of global
  scale. The largest of these flows have been dubbed Solar Surface Weather
  (SSW), and have been detected with both time-distance tomography and
  ring analysis. We present comparisons of synoptic maps of SSW flows
  obtained with both techniques from SOI-MDI Dynamics Program data. Both
  techniques provide measurements of the flows as a function of depth
  through inversion. The time-distance method utilizes only p-mode
  oscillations, while the ring analysis uses f modes as well. We find that
  the flows obtained with the two helioseismic techniques are remarkably
  similar, with common inflow and outflow sites as well as agreement in
  the general flow direction. At a depth of roughly 1.5 Mm the Spearman
  rank correlation coefficient between maps is on the order of 0.80. As
  the depth increases the correlation become weaker. The reduction in the
  correlation coefficient with depth is due to the increasing difference
  between the vertical resolution kernel of the two seismic techniques.

---------------------------------------------------------
Title: Synoptic Maps of Mass Flows Beneath the Solar Surface by
    Time-Distance Helioseismology
Authors: Zhao, J.; Kosovichev, A. G.
2003SPD....34.2609Z    Altcode: 2003BAAS...35..855Z
  We have derived the subsurface horizontal flow velocity fields
  for several solar Carrington rotations from 1996 to 2001, covering
  the period from the activity minimum to maximum of solar cycle 23,
  by analyzing SOHO/MDI Dynamics data. The synoptic flow maps have
  been made from the near-surface down to 12 megameters below the
  photosphere. The torsional oscillation and meridional flows, as well
  as the flow vorticity have been calculated from the flow maps as a
  function of latitude. It is found that after the subtraction of the
  solar minimum data, the residual meridional flows converge toward
  the activity belts, and migrate toward the equator together with
  the sunspot zones. In addition, the corresponding residual vorticity
  peaks in the activity belts, having the opposite signs in Northern
  and Southern hemispheres. Comparing the synoptic flow maps with the
  synoptic magnetic field maps, it is found that the solar plasma rotates
  faster where the photospheric magnetic field is stronger. An approximate
  linear relation between the magnetic strength and the rotational speed
  has been obtained from these data.

---------------------------------------------------------
Title: Inversions of artificial time-distance data using mainly Born
    approximation kernels and the MCD algorithm
Authors: Couvidat, S.; Birch, A. C.; Zhao, J.; Kosovichev, A. G.
2003SPD....34.0809C    Altcode: 2003BAAS...35..823C
  Local helioseismology, more specifically time-distance analysis,
  is a recent development in solar physics that gives us invaluable
  insight into the upper layers of the Sun. In this poster we show
  the results of a hare-and-hounds exercise concerning the inversion
  of time-distance data for perturbations to the sound-speed. We base
  our analysis on the Born approximation, which is expected to be more
  accurate than the usual ray-path approximation. We produce artificial
  time-distance data by solving the forward problem for travel times
  in the Born approximation. To invert these data, we apply the MCD
  (Multi-Channel Deconvolution) with Born approximation kernels, and
  the MCD and LSQR algorithms with ray theory kernels. We will present
  a detailed comparison between the different inversion results.

---------------------------------------------------------
Title: Autocorrelation analysis of MDI high-frequency data
Authors: Sekii, T.; Shibahashi, H.; Kosovichev, A. G.
2003ESASP.517..385S    Altcode: 2003soho...12..385S
  We have analyzed MDI data using time-distance autocorrelation function,
  in a high-frequency range above the acoustic cut-off frequency of the
  solar atmosphere. The MDI velocity, intensity and line-depth signals
  were looked at. The wave reflection rate at the photosphere has been
  found to be around 10 per cent for l = 125 and ν = 6.75mHz. The result
  is compared with a previous measurement.

---------------------------------------------------------
Title: Imaging of the solar interior: possibilities and limitations
Authors: Kosovichev, Alexander G.; Duvall, Thomas L., Jr.
2003SPIE.4853..327K    Altcode:
  Helioseismic tomography is a promising new method for probing
  3-D structures and flows beneath the solar surface. It is based on
  observation of solar acoustic waves, and provides great possibilities
  for studying the birth of active regions in the Sun's interior and
  for understanding the relation between the internal dynamics of
  active regions and chromospheric and coronal activity. We discuss
  observational requirements, challenges and limitations of this technique
  for investigating physical processes in the solar interior on their
  intrinsic spatial and temporal scales.

---------------------------------------------------------
Title: On the inference of supergranular flows by time-distance
    helioseismology
Authors: Zhao, Junwei; Kosovichev, Alexander G.
2003ESASP.517..417Z    Altcode: 2003soho...12..417Z
  We have attempted to derive the internal flow fields of supergranules
  by inverting time-distance helioseismology measurements based on the
  ray theoretical approximation. Due to the "cross-talk" effect between
  the contributions of the vertical flows and horizontal divergent flows
  and also due to the measurement errors propagation in the inversion,
  we can derive reliably only the horizontal velocity distribution in
  the supergranules, but the vertical velocity which is much smaller
  than the horizontal velocity is rather uncertain. The preliminary
  results from our inversion show that the divergent flows extend to
  a few megameters below solar surface, and also present evidence of
  converging flows at the depth of ~10Mm. A simple estimation gives
  the average depth of supergranules is approximately 15 Mm. Another
  inversion technique Multi-Channel Deconvolution is also developed. The
  subsurface flow fields of a sunspot derived from this technique are
  compared with the results from algorithm LSQR, and a correlation of 95%
  and above is found.

---------------------------------------------------------
Title: A search for the relationship between flaring activity and
    subphotospheric flows
Authors: Dzifcáková, E.; Kulinová, A.; Kosovichev, A. G.
2003ESASP.517..263D    Altcode: 2003soho...12..263D
  It is believed that subphotospheric shearing flows play important
  role in creating unstable magnetic topology that leads to initiation
  of flares and CME. However, the relationship between the flows and
  flaring activity is not well understood. Using the flow maps obtained
  by local helioseismology and magnetic and coronal data we attempt to
  search for this relationship. In particular, we study the evolution of
  active region NOAA 9393 in the context of changes in magnetic topology
  and flaring activity. SOHO/MDI and helioseismology data are used for
  determining the changes in morphology and are compared with changes
  of the topology as observed by TRACE.

---------------------------------------------------------
Title: Accurate measurements of SOI/MDI high-degree frequencies and
    frequency splittings
Authors: Reiter, J.; Kosovichev, A. G.; Rhodes, E. J., Jr.; Schou, J.
2003ESASP.517..369R    Altcode: 2003soho...12..369R
  We present accurate measurements of high-degree p-mode frequencies
  and frequency splittings obtained from the Full-Disk Program of
  the Michelson Doppler Imager (MDI) experiment onboard the Solar
  and Heliospheric Observatory (SOHO). The frequencies and frequency
  splittings are computed from unaveraged zonal, tesseral, and sectoral
  power spectra using a new fitting method of Reiter et al. (2002)
  based upon a maximum-likelihood fitting approach. In this method,
  both the spectral power distribution and contributions of the
  various observational and instrumental effects to the spatial leakage
  matrices are modelled accurately. We demonstrate that one of the most
  long-standing problems in high-degree helioseismology, viz. the jumps
  in the frequency splitting coefficients, can be solved by taking into
  account the distortion of the leakage matrix by the solar differential
  rotation. The results of inversion of the initial frequency set
  determined using this new method in the range of angular degree l =
  45-300 show a substantially better resolution of the subsurface layers
  compared to the previous studies with l below 220.

---------------------------------------------------------
Title: Granule and Supergranule properties derived from solar
    timeseries
Authors: Del Moro, D.; Berrilli, F.; Bonet, J. A.; Consolini, G.;
   Kosovichev, A.; Pietropaolo, E.
2003MmSAI..74..584D    Altcode:
  In this paper we mainly aim at the understanding of temporal evolution
  and spatial characterization of solar granular and supergranular
  features. For this purpose we apply an automatic feature-tracking
  algorithm to three different solar granulation timeseries and to a
  supergranular timeseries of near-surface divergence fields. The single
  lifetimes are calculated measuring the time elapsing between the birth
  and death of each target. In addition, we investigate spatial order of
  surface flows studying the g<SUB>2</SUB>(r) function of time-averaged
  supergranular fields.

---------------------------------------------------------
Title: Helioseismic tomography
Authors: Kosovichev, A. G.
2003dysu.book...78K    Altcode:
  Helioseismic tomography extends the capabilities of helioseismology
  by providing three-dimensional images of sound-speed variations and
  mass flows associated with sunspots, active regions, emerging magnetic
  flux, convective cells and other solar phenomena. The initial results
  reveal the structure of supergranulation and meridional flows beneath
  the solar surface as well as large-scale mass motions around sunspots
  and active regions, provide a clue for the mechanism of sunspots,
  and even show the presence of active regions on the far side of the Sun.

---------------------------------------------------------
Title: Telechronohelioseismology
Authors: Kosovichev, Alexander
2003safd.book..279K    Altcode:
  Telechronohelioseismology (or time-distance helioseismology) is a new
  diagnostic tool for three-dimensional structures and flows in the solar
  interior. Along with the other methods of local-area helioseismology,
  the ring diagram analysis, acoustic holography and acoustic imaging,
  it provides unique data for understanding turbulent dynamics of
  magnetized solar plasma. The technique is based on measurements
  of travel time delays or wave-form perturbations of wave packets
  extracted from the stochastic field of solar oscillations. It is
  complementary to the standard normal mode approach which is limited to
  diagnostics of two-dimensional axisymmetrical structures and flows. I
  discuss theoretical and observational principles of the new method,
  and present some current results on large-scale flows around active
  regions, the internal structure of sunspots and the dynamics of emerging
  magnetic flux.

---------------------------------------------------------
Title: Is Ni I 676.8 nm line affected by electron beams in flaring
    atmospheres?
Authors: Zharkova, V. V.; Kosovichev, A. G.
2002ESASP.506.1031Z    Altcode: 2002ESPM...10.1031Z; 2002svco.conf.1031Z
  Non-LTE simulations for a model Ni I atom in the ambient plasma with
  solar element abundances are carried out in order to investigate the
  effects of electron beams on the resulting Ni I 676.8 nm emission during
  solar flares. The Ni I 676.8 nm line profiles, source functions and
  departure coefficients were calculated for a period of 10 s after an
  injection of beams with a variety of their initial parameters. The Ni I
  676.8 nm line was found to decrease its depth in the core by about 30%
  in response to the increase of hydrodynamic heating of the atmosphere
  during the electron beam precipitation. At the maximum electron flux
  (6 s in our models), the line profile changes to emissive and stays
  as such for several seconds returning to the normal absorption profile
  after the beam is switched off (10 s). Therefore, the line measurements
  within a timescale of 1 min or longer are more likely not to be strongly
  affected by the line inversion while more precise (within seconds)
  temporal measurements on Ni 676.8 nm line profiles of the impulsive
  phase of flares have to be carefully investigated.

---------------------------------------------------------
Title: Evolution of Large-scale Coronal Structure with the Solar
    Cycle from EUV Data
Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Scherrer, P. H.
2002ASPC..277..419B    Altcode: 2002sccx.conf..419B
  No abstract at ADS

---------------------------------------------------------
Title: Solar cycle in the photosphere and corona
Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Scherrer, P. H.
2002ESASP.506..831B    Altcode: 2002svco.conf..831B; 2002ESPM...10..831B
  EIT/SOHO data in four EUV lines and MDI/SOHO (1996-2002), and soft X-ray
  YOHKOH data (1991-2001) are analyzed in the form of coronal synoptic
  maps for the investigation of solar cycle variations of the corona
  and magnetic field. The evolution of coronal structures is closely
  related to sunspot activity, photospheric magnetic field, and topology
  of the large-scale magnetic field. The coronal structures visible in
  extreme ultraviolet and soft X-rays as extended bright loops, reflect
  the non-axisymmetrical magnetic structure of the Sun, changing with the
  solar cycle. The long-living coronal structures are related to complexes
  of solar activity and display the quasiperiodic behavior (impulses of
  coronal activity) with periods of 1.0-1.5 year in the axisymmetrical
  distribution of EUV and X-ray fluxes during the current cycle.

---------------------------------------------------------
Title: Acoustic Tomography of the Sun's Interior with SDO:
    Possibilities and Limitations
Authors: Kosovichev, A. G.; Duvall, T. L.; Birch, A. C.; Gizon, L.;
   Zhao, J.; Sekii, T.; Shibahashi, H.
2002AGUFMSH21C..06K    Altcode:
  Helioseismic and Magnetic Imager on board SDO will significantly expand
  the possibilities for imaging plasma flows and structures in the solar
  interior. It will provide for the first time high-resolution data for
  continuous monitoring of emerging flux and developing active regions in
  the upper convection zone. It will also allow us to look for localized
  structures and flows in the tachocline region and deeper interior,
  and also investigate the near-polar regions. The expected results may
  give important clues of how the solar dynamo works and active regions
  develop. HMI will observe the entire spectrum of the solar acoustic
  and surface gravity waves, and provide the most comprehensive data
  for global and local helioseismology. The high-frequency part of the
  oscillation spectrum will be used for studying seismic properties of
  the solar atmosphere in the quiet Sun and active regions. The method
  of acoustic tomography or time-distance helioseismology is one of the
  primary tools of the HMI investigation. It is based on measurements and
  inversions of travel-time delays of solar waves, caused by plasma flows
  and variations of temperature and magnetic field. The data analysis
  requires deep understanding of the physics of wave propagation in the
  Sun and substantial computer resources. One of the important goals
  is to provide the flow and sound-speed maps of the upper convection
  zone in near-real time for space weather applications. We present the
  current status of the field, and discuss plans and challenges for the
  HMI data analyses and interpretation.

---------------------------------------------------------
Title: Inferring Subphotospheric Supergranular Flows by Time-Distance
    Helioseismology
Authors: Zhao, J.; Kosovichev, A. G.
2002AGUFMSH52A0460Z    Altcode:
  Time-distance helioseismology has provided us a tool to investigate
  the interior structures and flow fields of the Sun. Combining
  the measurements from surface- and deep-focusing schemes, we have
  attempted to derive the flow maps of supergranules by using the
  LSQR algorithm. The divergent horizontal flow fields are obtained
  near the surface, and there is evidence of converging flows below 12
  megameters or so. The main difficulty is in inferring the vertical
  component of the flow field because of strong cross-talk between the
  horizontal divergence and the vertical velocity in the travel-time
  data. A Multi-Channel Deconvolution technique was also employed to
  derive the velocity fields, and the results agree well with those from
  LSQR inversion. We discuss the systematic and random errors of the
  measurements, and implications of the initial results for understanding
  the supergranular convection.

---------------------------------------------------------
Title: Helioseismic observations of subphotospheric dynamics of
    sunspots and developing active regions
Authors: Kosovichev, A. G.; Duvall, T. L., Jr.; Zhao, Junwei
2002ESASP.505...79K    Altcode: 2002IAUCo.188...79K; 2002solm.conf...79K
  New methods of time-distance helioseismology provide us unique
  information about the structure and dynamics of sunspots and active
  regions in the upper convection zone. We present three-dimensional maps
  of the sound-speed perturbations and flow velocities obtained from the
  SOHO/MDI data for sunspots, emerging flux events and evolving active
  regions. The results reveal complex dynamics of magnetic structures
  below the solar surface, and shed light on the mechanisms of sunspots
  and active regions, and magnetic field dynamics. One interesting case
  that includes a fast spinning sunspot accompanied with subphotospheric
  vortex motions and twisting coronal loops represents an intriguing
  example of magnetic coupling between the subphotospheric processes and
  the atmospheric activity. The evolution of a large active region, NOAA
  9393, has been studied for almost 3 solar rotations in March-April 2001,
  including the periods of emergence, maximum activity and decay. It is
  concluded that this active region was formed by fragmented magnetic
  flux tubes emerging during an extended period of time rather than by
  a single large Ω-loop broken into smaller flux tubes near the surface.

---------------------------------------------------------
Title: Fast photospheric flows in a flaring active region
Authors: Meunier, N.; Kosovichev, A.
2002ESASP.505..505M    Altcode: 2002IAUCo.188..505M; 2002solm.conf..505M
  We present new results from coordinated observations with THEMIS
  (multi-line spectropolarimetric mode) and MDI/SOHO obtained in Nov
  2000. We observed active region AR 9236 using several photospheric
  lines before and after the last main flare produced by this very
  active region. Vector magnetic fields are computed from THEMIS data
  and a full inversion of the interesting profiles is performed. We
  observe fast flows which are probably supersonic in two regions located
  where this flare occurs. These flows seem to be long-lived structures
  (several hours). One of them is related to a strong shear with flows
  almost horizontal while the other is a downflow strongly inclined
  with respect to the vertical. They are present 9 hours before the
  flare, however their amplitude appears to be modified by the flare
  (especially during the first minutes).

---------------------------------------------------------
Title: Subsurface structure of sunspots
Authors: Kosovichev, A. G.
2002AN....323..186K    Altcode:
  The subsurface structure of sunspots is probed by measuring travel-time
  delays of acoustic waves propagating beneath the spots, and using
  a helioseismic inversion method to infer the internal sound-speed
  perturbations and mass flows. The initial results obtained from the
  MDI instrument on SOHO reveal under sunspots zones of the relatively
  low sound speed, extended to a depth of approximately 4 Mm. These zones
  are associated with cool areas of sunspots. In the deeper interior of
  sunspots the sound speed is higher than in the surrounding plasma. The
  regions of the higher sound speed are at least 60 Mm deep. These
  observations also show complicated flow patterns that include
  converging vortex flows in the upper 4 Mm deep layer. These flows play
  important role for maintaining the structure of sunspots. Developing
  active regions are associated with complicated evolving sound-speed
  perturbations beneath the surface, which are probably caused by
  multiple flux tubes emerging from the deep interior. A study of a
  rapidly rotating sunspot revealed strong shear flows beneath the spot.

---------------------------------------------------------
Title: Global low frequency acoustic modes after half a solar cycle
aboard SOHO: an improved view of the nuclear core
Authors: Turck-Chièze, S.; Garcí, R. A.; Couvidat, S.; Kosovichev,
   A. G.; Bertello, L.; Corbad, T.; Berthomieu, G.; Provost, J.;
   Eff-Darwich, A.
2002ESASP.508..593T    Altcode: 2002soho...11..593T
  Solar global oscillations have now been measured for more than 20
  years. The study of these modes has contributed to improve, along
  time, the description of the solar core. We have now a proper access
  to this part of the Sun, with ground networks observing for more than
  10 years and the three instruments aboard SOHO in a quasi continuous
  mode for now half a cycle. In this talk, we show the advantages of
  the global acoustic modes measured at low frequency. They are due to
  their longer lifetime and the reduced influence of the turbulent and
  variable surface effects. As a consequence, we have converged last
  year, after 30 years of unsuccess, to a boron-8 emitted neutrino flux
  in perfect agreement with the better understood detection of these
  neutrinos on earth. The splitting at low frequency is also now properly
  determined but the extracted rotation information is still limited in
  the core. It contains nevertheless the first dynamical vision of this
  part of the radiative zone. We will focus on it up to the end of the
  SOHO mission, together with the gravity mode region and the possible
  internal signature of the magnetic field. Some limits are given on
  these observables. Further improvements of their detectability are
  under study and will be mentioned.

---------------------------------------------------------
Title: Observations of solar-cycle effects by local- area
    helioseismology
Authors: Kosovichev, A. G.
2002ESASP.508..131K    Altcode: 2002soho...11..131K
  The local-area helioseismology is a set of new developing tools for
  3D acoustic imaging of the Sun's interior structure and dynamics. It
  considerably extends our capability for observing and understanding
  solar-cycle effects and dynamo processes of various scales inside
  the Sun. It also helps to interpret the solar-cycle variations
  that are observed in oscillation frequencies and other properties
  of global modes. Three basic tools: the ring-diagram analysis, the
  time-distance helioseismology and the acoustic holography, provide
  complementary diagnostics of the internal processes associated with
  solar activity. The ring-diagram analysis based on measurements of the
  local frequency-wavenumber dispersion relation for high-degree sound
  waves provides synoptic maps of large-scale subsurface flows. The
  time-distance helioseismology is capable of providing the synoptic
  maps for the interior sound-speed distribution in addition to the
  flow maps. This technique has also revealed intriguing images of
  developing active regions and sunspots and associated flow patterns
  in the upper convection zone. The method of acoustic holography
  has proved to be very efficient for mapping active regions on the
  far side of the Sun. Most results of the local-area helioseismology
  obtained so far deal with the solar-cycle effects in the upper half
  of the convection zone. However, there has been an attempt to obtain
  longitudinal synoptic maps of sound-speed variations in the tachocline
  by the time-distance technique. The recent major achievements of
  the local-area helioseismology also include studies of the meridional
  circulation and its variation with the solar cycle and an investigation
  of the relation between the torsional oscillations and large-scale flows
  around active regions. These results are obtained using Doppler-shift
  data from the MDI instrument on SOHO (Scherrer et al. 1995).

---------------------------------------------------------
Title: A new method for measuring frequencies and splittings of
    high-degree modes
Authors: Reiter, Johann; Rhodes, E. J., Jr.; Kosovichev, A. G.; Schou,
   J.; Scherrer, P. H.
2002ESASP.508...91R    Altcode: 2002soho...11...91R
  A novel peak-bagging method is presented that operates by fitting a
  theoretical profile (symmetric or asymmetric) to the separate peaks of
  each multiplet within each unaveraged power spectrum. This new approach
  allows a separate frequency, width, and amplitude to be obtained for
  each m value at each value of l, n. Hence, the frequency splittings
  due to solar rotation for each multiplet can be measured directly. We
  present some of our initial results obtained with this new method
  in the range 45 &lt;= l &lt;= 300, ν &lt;= 7 mHz when applied to
  data from the Michelson Doppler Imager (MDI) onboard the Solar and
  Heliospheric Observatory (SOHO). Also discussed are some instrumental
  and methodological problems of high-degree mode measurements.

---------------------------------------------------------
Title: The solar cycle dependence of low-degree p-mode parameters
Authors: Toutain, Thierry; Kosovichev, A. G.
2002ESASP.508..103T    Altcode: 2002soho...11..103T
  Thanks to the extension of the SOHO mission it is possible to analyze
  with a good accuracy the dependence of the low-degree p-mode parameters
  on the solar cycle. We have constructed from the LOI-proxy data
  (MDI) two time series of 784 days each, one taken at low activity
  and the other one at high activity. We have focused on analyzing the
  solar-cycle dependence of the linewidth, the splitting, the asymmetry
  and the frequency shift of the low-degree p modes. It turns out that
  some of these parameters exhibit a significant dependence on solar
  cycle moreover there is also a dependence on m the azimuthal order.

---------------------------------------------------------
Title: Effect of line asymmetry on determination of high-degree
    mode frequencies
Authors: Reiter, Johann; Rhodes, E. J., Jr.; Kosovichev, A. G.; Schou,
   J.; Scherrer, P. H.
2002ESASP.508...87R    Altcode: 2002soho...11...87R
  Accurate measurements of frequencies of high-degree p-modes are
  important for diagnostics of the structure and dynamics of the
  upper convective boundary layer, and understanding the nature of
  the solar-cycle variations detected in low- and medium-degree mode
  frequencies. Neglecting line asymmetry in the peak-bagging approach
  may lead to systematic errors in the determination of the mode
  characteristics and, hence, may affect the results of inversions. Here
  we demonstrate how the p-mode frequencies are systematically changed in
  the range of l &lt;= 1000, ν &lt;= 7mHz when line asymmetry is taken
  into account in the fitting of the spectral power peaks. The results
  reported are based upon spectra that were created from observations
  obtained from the MDI Full-Disk Program during the 1996 SOHO/MDI
  Dynamics Run.

---------------------------------------------------------
Title: Large-Scale Solar Coronal Structures in Soft X-Rays and Their
    Relationship to the Magnetic Flux
Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Lemen, J. R.;
   Scherrer, P. H.; Slater, G. L.
2002ApJ...571L.181B    Altcode:
  We have investigated the relationship between magnetic activity
  and coronal structures using soft X-ray data from the Yohkoh soft
  X-ray telescope and magnetic field data from the Kitt Peak Solar
  Observatory for the period of 1991-2001 and EUV data from the Solar
  and Heliospheric Observatory EUV Imaging Telescope for 1996-2001. The
  data are reduced to Carrington synoptic maps, which reveal two types of
  migrating structures of coronal activity at low and high latitudes in
  the time-latitudinal distribution. The low-latitude coronal structures,
  migrating equatorward, correspond to photospheric sunspot activity,
  and the high-latitude structures migrating toward the poles reflect
  polar activity of the Sun. We present the following new results:1. The
  migrating high-latitude coronal magnetic structures are revealed in the
  soft X-ray data as complete bright giant loops connecting the magnetic
  field of the following part of active regions with the polar field. They
  appear during the rising phase and maximum of the solar cycle and show
  quasi-periodic impulsive variations with a 1-1.5 yr period.2. The soft
  X-ray intensity of these loops has a strong power-law correlation with
  the photospheric magnetic flux. The power-law index, which on average
  is close to 2, shows variations with the solar cycle: it is higher
  for the period of the declining phase and minimum of solar activity
  than for the rising phase and maximum.

---------------------------------------------------------
Title: Large-scale coronal structures in EUV and soft X-rays in
    solar cycle 23
Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Scherrer, P. H.;
   Lemen, J. R.; Slater, G. L.
2002ESASP.508..367B    Altcode: 2002soho...11..367B
  We have analyzed the EIT/SOHO data in four EUV lines (171 Å, 195 Å,
  284 Å and 304 Å) and soft X-ray YOHKOH data in two filters (AlMg and
  Al) in the form of coronal synoptic maps for the period 1996 - 2001
  yrs. Two types of the bright structures have been detected in EUV in
  the axisymmetrically averaged synoptic maps. The structures of the first
  type migrate equatorward as the solar cycle progresses. They are related
  to complexes of sunspot activity and display the "butterfly"-type
  distribution. The structures of the second type migrate polarward
  and are associated with footpoints of giant coronal loops, which
  connect the polar regions and the following parts of the active
  complexes. These structures of coronal activity are also pronounced in
  the soft X-ray maps. However, the whole structure of the giant polar
  loops is visible in X-rays, and reveals connections to the low-latitude
  coronal structures. The relationship between the soft X-rays emission
  and the photospheric magnetic flux obtained from SOHO/MDI and Kitt
  Peak Solar Observatory has been investigated. It has been found that
  the relationship depends on the phase of the solar cycle. We discuss
  the role of the magnetic flux in the formation and evolution of the
  stable coronal structures during the rising phase of cycle 23.

---------------------------------------------------------
Title: Fast magnetic field variations associated with solar flares
Authors: Zharkova, V. V.; Kosovichev, A. G.
2002ESASP.508..159Z    Altcode: 2002soho...11..159Z
  The SOHO/MDI observations of fast magnetic field variations associated
  with flares reveal a close temporal correlation of the irreversible
  magnetic field changes occurring in the bipolar flare region with
  the temporal behaviour of hard and soft X-ray emission. These are
  expected to be accountable for a primary magnetic energy release in
  the flare while the released energy is about 1% of the estimated
  energy being stored in the magnetic rope structure reconstructed
  for this active region (Yan et al., 2001). There are also reversible
  changes of magnetic field, called earlier as "magnetic transients" or
  wave-like magnetic field variations, occurring in some unipolar flare
  regions. The "transient" magnetic field changes are accompanied by
  the Moreton waves in the chromosphere and EIT waves in the corona. In
  some flares the magnetic field variations measured with MDI look like
  waves following the Moreton wave's fronts. These changes are likely
  to reflect the mechanisms of energy transport into deeper atmospheric
  layers by charged particles (electrons and/or protons).

---------------------------------------------------------
Title: Optimal masks for g-mode detection in MIDI velocity data
Authors: Wachter, R.; Schou, J.; Kosovichev, A.; Scherrer, P. H.
2002ESASP.508..115W    Altcode: 2002soho...11..115W
  We are applying spatial masks to MDI velocity data that are optimized
  for revealing g-modes in the frequency range 50 through 500 μHz. These
  masks take into account the horizontal component of g-mode velocity
  eigenfunctions as well as the time dependent mode projection properties
  due to the changing solar B angle, and the varying noise level across
  the solar disk. The solar noise, which is likely to be caused by
  supergranulation in this frequency range is assumed to be uniformly
  distributed over the solar surface, consisting of a dominant horizontal
  component and a small radial component. The resulting time series are
  examined for possible g-mode candidates and new upper limits for the
  surface amplitude of g-modes are obtained.

---------------------------------------------------------
Title: Optimal masks for g-mode detection in MDI velocity data
Authors: Wachter, R.; Schou, J.; Kosovichev, A.; Scherrer, P. H.;
   Phoebus Team
2002AAS...200.0412W    Altcode: 2002BAAS...34..645W
  We are applying spatial masks for MDI velocity data that are optimized
  for revealing g-modes in the frequency range 50 through 500 μ
  Hz. These masks take into account the horizontal component of g-mode
  velocity eigenfunctions as well as the time dependent mode projection
  properties due to the changing solar B angle, and the varying noise
  level across the solar disk. The solar noise, which is likely to be
  caused by supergranulation in this frequency range is assumed to be
  uniformly distributed over the solar surface, consisting of a dominant
  horizontal component and a smaller radial component. The optimal masks
  are applied to the image and the resulting time series are examined
  for possible g-mode candidates. Because no mode peak has been detected,
  firm upper limits for the surface visibility of individual low degree
  modes can be given.

---------------------------------------------------------
Title: Helioseismic observations of developing active regions in
    the solar convection zone
Authors: Kosovichev, A.; Duvall, T., Jr.
2002AAS...200.8903K    Altcode: 2002BAAS...34Q.791K
  Time-distance helioseismology provides unique opportunities for studying
  the formation and evolution of regions of solar activity. The key
  questions are: How deep in the convection zone are the active regions
  formed? How fast do they erupt? What is the role of convective mass
  flows in the formation and evolution of active regions? Is there
  retraction of magnetic flux during the decay of active regions? Why
  do new active regions tend to appear in places where previous active
  regions existed? We discuss the current techniques for probing the
  subphotospheric structure and dynamics of active regions, uncertainties
  and limitations of these studies, and present results of observation of
  three developing active regions using Michelson Doppler Imager on SOHO.

---------------------------------------------------------
Title: Advances in Time-Distance Helioseismology
Authors: Duvall, T. L., Jr.; Beck, J. G.; Gizon, L.; Kosovichev, A. G.
2002AAS...200.7902D    Altcode: 2002BAAS...34..780D
  Time-distance helioseismology is a way to measure travel times between
  surface locations for waves traversing the solar interior. Coupling
  the travel time measurements with an extensive modeling effort has
  proven to be a powerful tool for measuring flows and other wave speed
  inhomogeneities in the solar interior. Problems receiving current
  attention include studying the time variation of the meridional
  circulation and torsional oscillation and active region emergence and
  evolution. Current results on these topics will be presented.

---------------------------------------------------------
Title: Study of a Rotating Sunspot and Statistics of Kinetic Helicity
    Near Sunspots' Surface By Local Helioseismology
Authors: Zhao, J.; Kosovichev, A.
2002AAS...200.0413Z    Altcode: 2002BAAS...34..645Z
  Time-distance helioseismology has provided a unique tool for studying
  interior structures of the Sun. The structure of sound speed variations
  and flow fields beneath the sunspot surface have been obtained by
  the use of inversion techniques in some previous studies. By applying
  time-distance measurements and an inversion technique to active region
  NOAA 9114 observed by SOHO/MDI, which showed unusual fast rotation
  around its center during its passage on the solar disk, we obtained
  the sound-speed structure and plasma flow fields up to 10 megameters
  below the photosphere. The subsurface sound-speed structure revealed
  apparent structural twists relative to the surface magnetic structure,
  which may suggest that the magnetic twists have existed below the
  visible surface. For the flow fields, strong vortical flows can be
  seen near the surface and opposite vortex was found about 10 megameters
  below the surface, which may provide an explanation of magnetic twists
  in sunspots. Same technique was applied to 86 active regions observed
  by SOHO/MDI in order to study the hemispherical preference of kinetic
  helicities of active regions. It was found that about 55% of active
  regions in northern hemisphere showed positive kinetic helicity,
  while 59% of southern hemisphere active regions showed negative
  kinetic helicity. This provides observational evidences to figure
  out where or how the observed surface magnetic helicity hemispherical
  preference forms.

---------------------------------------------------------
Title: A new insight into the energy release and transport in
    solar flares
Authors: Zharkova, V. V.; Kosovichev, A. G.
2002ESASP.477...35Z    Altcode: 2002scsw.conf...35Z
  The SOHO/MDI observations of fast magnetic field variations associated
  with flares reveal a close temporal correlation of the irreversible
  magnetic field changes occurring in the bipolar flare region with
  the temporal behaviour of hard and soft X-ray emission. These are
  expected to be accounted for a primary magnetic energy release during
  the flare event. There are also reversible changes of magnetic field,
  called earlier as "magnetic transients", occurring in some unipolar
  flare regions. These changes are likely to reflect the mechanisms of
  energy transport into deeper atmospheric layers by charged particles
  (electrons and/or protons). These "transient" magnetic field changes
  are also accompanied by Moreton waves in the chromosphere and EIT waves
  in the corona. The attempt to interpret these events using our previous
  kinetic models for beam electrons revealed that the energy momentum of
  electron beam delivered to the photospheric levels is marginally close
  to the limit derived from the recent solar quake observations. This
  encourages to consider a neutralised beam as the most possible source
  of both magnetic and helioseismic waves.

---------------------------------------------------------
Title: Coronal Patterns of Activity from Yohkoh and SOHO/EIT Data
Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Scherrer, P. H.;
   Lemen, J. R.; Slater, G. L.
2002mwoc.conf..329B    Altcode:
  We have studied the evolution of large-scale coronal structures using
  soft X-ray data from YOHKOH and EUV data from SOHO/EIT during the
  rising phase of the current solar cycle 23, and compared with the
  evolution of the photospheric magnetic field. During this period the
  distribution of the coronal structures generally reflects the evolution
  of the magnetic fields. However, the data from EIT and YOHKOH reveal
  large-scale magnetic connections in the corona which probably play
  significant role in the solar cycle. In particular, we have found that
  coronal structures such as high-latitude giant loops may be important
  for the topological evolution of magnetic structures during the solar
  cycle and for polar magnetic field reversals. We discuss possible
  mechanisms of the polar magnetic field reversals and their relations
  to the observed coronal structures.

---------------------------------------------------------
Title: Solar Coronal Activity and Evolution of the Magnetic Field
Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Scherrer, P. H.
2002stma.conf...27B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Active longitudes and coronal structures during the rising
    phase of the solar cycle
Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Scherrer, P. H.
2002AdSpR..29..389B    Altcode:
  The longitudinal structure of the solar corona has been investigated
  during the transition period between solar cycles 22 and 23 and at the
  beginning of the current cycle 23 using the SOHO/EIT data obtained
  in 171 Å, 195 Å, 284 Å and 304 Å EUV lines. The EIT images
  were transformed into synoptic maps for each of the spectral lines,
  and for the 195Å/171Å line ratio, which is an index of the coronal
  temperature. The synoptic maps reveal stable longitudinal structures in
  the coronal intensities and temperature, that are related to large-scale
  magnetic field structures. We discuss the relation between the coronal
  and photospheric magnetic structures obtained from the SOHO and Kitt
  Peak Solar Observatory data, and compare the rotation rates of these
  structures with the rotation profile of the solar interior in order
  to determine the possible origin of the coronal structures.

---------------------------------------------------------
Title: Local-area helioseismology as a diagnostic tool for solar
    variability
Authors: Kosovichev, A. G.; Duvall, T. L.; Birch, A. C.; Gizon, L.;
   Scherrer, P. H.; Zhao, Junwei
2002AdSpR..29.1899K    Altcode:
  Dynamical and thermal variations of the internal structure of the Sun
  can affect the energy flow and result in variations in irradiance
  at the surface. Studying variations in the interior is crucial for
  understanding the mechanisms of the irradiance variations. "Global"
  helioseismology based on analysis of normal mode frequencies, has helped
  to reveal radial and latitudinal variations of the solar structure
  and dynamics associated with the solar cycle in the deep interior. A
  new technique, - "local-area" helioseismology or heliotomography,
  offers additional potentially important diagnostics by providing
  three-dimensional maps of the sound speed and flows in the upper
  convection zone. These diagnostics are based on inversion of travel
  times of acoustic waves which propagate between different points on the
  solar surface through the interior. The most significant variations
  in the thermodynamic structure found by this method are associated
  with sunspots and complexes of solar activity. The inversion results
  provide evidence for areas of higher sound speed beneath sunspot regions
  located at depths of 4-20 Mm, which may be due to accumulated heat or
  magnetic field concentrations. However, the physics of these structures
  is not yet understood. Heliotomography also provides information about
  large-scale stable longitudinal structures in the solar interior,
  which can be used in irradiance models. This new diagnostic tool for
  solar variability is currently under development. It will require both
  a substantial theoretical and modeling effort and high-resolution
  data to develop new capabilities for understanding mechanisms of
  solar variability.

---------------------------------------------------------
Title: Noise reduction in helioseismic power spectra\ by
    non-orthogonal wavelets
Authors: Solanki, S. K.; Régulo, C.; Fligge, M.; Kosovichev, A. G.
2001A&A...379.1039S    Altcode:
  We present a method to reduce noise in helioseismic power spectra
  using a non-orthogonal wavelet transform based on quadratic spline
  functions. The quality of our method is tested by applying it to
  artificially generated time-series approximating solar p-modes. The
  mode frequencies and line widths obtained from least-squares fits to
  the smoothed spectra are compared with the corresponding parameters
  deduced from maximum likelihood fits to the original spectra. The
  results from both approaches are very similar and suggest that there
  is no major bias in either of these rather independent approaches. As a
  practical example we denoise parts of the power spectrum obtained from
  the two first years of operation of the GOLF instrument onboard SOHO.

---------------------------------------------------------
Title: The Largest Active Region of the Solar Cycle
Authors: Kosovichev, A. G.; Bush, R. I.; Duvall, T. L.; Scherrer, P. H.
2001AGUFMSH11C0730K    Altcode:
  The largest and most active sunspot region of the current solar
  cycle (known as AR 9393) was observed by the MDI instrument on SOHO
  continuously during three solar rotations in March-May 2001. On April
  2 this active region produced the largest solar flare of the last 25
  years. By using time-distance helioseismology we have investigated
  the development of the active region in the solar interior during that
  period starting from the processes of emergence. We present tomographic
  images of the sound-speed structures associated with this active region
  up to 100 Mm below the solar surface, and discuss their relation to
  the evolution of the surface magnetic field.

---------------------------------------------------------
Title: Accuracy of Born and Ray Approximations in Time-Distance
    Helioseismology
Authors: Price, G. H.; Birch, A. C.; Kosovichev, A. G.; Schlottmann,
   R. B.
2001AGUFMSH11B0709P    Altcode:
  Time-distance helioseismology attempts to infer localized departures
  from a nominal state of the solar interior from comparison of
  observed travel times of acoustic wave packets to those anticipated
  from the model. Until recently, such time-distance measurements
  have generally been modeled in the ray approximation, which neglects
  finite-wavelength effects. Concern that these effects can be important
  has prompted interest in the Born approximation, which is sensitive
  to them. In order to elucidate the ranges of validity of the ray and
  Born approximations and the nature of their limitations, we compare
  travel-time pertrubations calculated using these approximations to
  exact travel times for a simple problem, namely the propagation of
  adiabatic acoustic waves through the center of a spherically symmetric
  sound-speed perturbation to an otherwise uniform medium. We show that
  the Born and first-order ray approximations converge to the same result
  as the spatial scale of the medium perturbation becomes large compared
  to the first Fresnel zone, with a fractional error in the travel-time
  perturbation equal to the fractional strength of the perturbation,
  while a full ray calculation converges to the exact solution in this
  limit. For a uniform perturbation having a size the order of the
  first Fresnel zone, interference between direct and diffracted wave
  produces travel-time fluctuations that are entirely absent in the ray
  approximation; these fluctuations are only qualitatively replicated
  by the Born approximation for moderately weak (e.g., 5%) perturbation
  strengths. Such fluctuations are, however, largely suppressed for
  a smoothly-varying perturbation expected to be more representative
  of solar structures. The so-called banana-doughnut (here, ventilated
  cigar) form of the Born sensitivity kernels, i.e., a greatly reduced
  sensitivity of the travel-time perturbation to small-scale medium
  perturbations that fall near the unperturbed ray path that is absent
  in the ray approximation, is also shown to be consistent with the
  exact results.

---------------------------------------------------------
Title: Time-distance Helioseismology Study Over a Rotating Sunspot
Authors: Zhao, J.; Kosovichev, A. G.; Duvall, T. L.
2001AGUFMSH11B0708Z    Altcode:
  Time-distance helioseismology has provided a unique tool in studying
  interior structures of the Sun. The structure of sound speed variations
  and flow fields beneath the sunspot surface have been obtained by
  use of inversion technique in some previous studies. In this study
  we have applied the time-distance measurements from SOHO/MDI and the
  inversion technique to investigate a sunspot which showed unusually fast
  rotation around its center for a couple of days from Aug 7 to Aug 8,
  2000. The sound speed structure which is related to the magnetic field
  structures beneath the surface and associated temperature variations was
  obtained. The results revealed some twists in the sound-speed internal
  structure of the spot relative to the surface magnetic structure. This
  kind of subsurface twist was not seen 2 days after the start of
  rotation. This is consistent with the surface observation showing
  a reduction of transverse magnetic field twists after the surface
  rotation stopped. It could be explained as the magnetic field lines
  were twisted beneath the surface and the untwisting of field lines
  caused the surface rotation. Flow fields beneath the sunspot surface
  were also obtained. A strong vortex was found near the surface and
  a few megameters below the surface. Whether the subsurface vortical
  flows caused the magnetic field twists or the untwisting of field
  lines caused the subsurface vortical flows will be discussed.

---------------------------------------------------------
Title: Solar Coronal Structures in Extreme Ultraviolet and Soft
    X-rays and Their Relation to Magnetic Flux
Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Lemen, J. R.;
   Scherrer, P. H.; Slater, G. L.
2001AGUFMSH11C0720B    Altcode:
  The large-scale coronal structures are ultimately related to internal
  magnetic fields and thus provide important information about the solar
  dynamo. We have investigated the relationship between magnetic activity
  and coronal structures using EUV data from SOHO/EIT and X-ray data
  from Yohkoh/SXT, and magnetic field data from Kitt Peak and Wilcox
  Solar Observatories for the period 1996-2000 years. We discuss the
  non-uniform distribution of coronal heating and its connection with
  long-lived complexes of solar activity during the current cycle. EUV
  images reveal two sets of migrating structures of coronal activity
  in the time-latitudinal distribution of the EUV intensity in 171A,
  195A, 284A and 304A EIT wavelength channels. The low-latitude coronal
  structures, migrating equatorward, correspond to photospheric sunspot
  activity, and the high-latitude structures migrating towards the poles
  reflect polar activity of the sun. The polar branches are cooler then
  the equatorial branches. This is reflected in the time-latitudinal
  distribution of the soft X-rays in two filters (Al and AlMg). We
  discuss the physical properties and nature of these structures of
  coronal activity and their role in the solar cycle.

---------------------------------------------------------
Title: Probing Deep Structure of the Sun by Time-Distance
    Helioseismology
Authors: Birch, A. C.; Duvall, T. L.; Kosovichev, A. G.
2001AGUFMSH11B0710B    Altcode:
  Time-distance helioseismology is a method for inferring sound-speed
  perturbations and flow velocities by measuring the travel times for
  acoustic wave packets as they move between points on the solar surface
  through the solar interior. It has been successfully applied to infer
  structures and flows in the upper convection zone. However, probing
  the deep convection zone and, in particular, the tachocline region at
  the bottom of the convection zone where the solar dynamo is believed
  to be operating is quite challenging. Using the solar oscillation
  data from SOHO/MDI we have attempted to detect deep structures in
  a low-latitude band of the convection zone. For inversion of the
  travel-time measurements we used the theoretical sensitivity, in the
  first Born approximation, of travel times to sound speed inhomogeneities
  in the solar convection zone. We have obtained synoptic sound-speed maps
  for two solar rotations in 2000. The results show resolved structures
  in the lower convection zone. We compare the sound-speed maps with
  surface magnetic field synoptic maps and discuss possible relations
  between the deep structures and the surface field.

---------------------------------------------------------
Title: Observed and Predicted Ratios of the Horizontal and Vertical
    Components of the Solar p-Mode Velocity Eigenfunctions
Authors: Rhodes, Edward J., Jr.; Reiter, Johann; Schou, Jesper;
   Kosovichev, Alexander G.; Scherrer, Philip H.
2001ApJ...561.1127R    Altcode:
  We present evidence that the observed ratios of the horizontal
  and vertical components of the solar intermediate-degree p-mode
  velocity eigenfunctions closely match theoretical predictions of
  these ratios. This evidence comes from estimates of the observed
  eigenfunction component ratios that were obtained from the fitting
  of the p-mode oscillation peaks in low- and intermediate-degree
  (l&lt;=200) m-averaged power spectra computed from two different
  60.75 day time series of Global Oscillation Network Group (GONG)
  project Dopplergrams obtained in late 1996 and early 1998. These fits
  were carried out using a peak-fitting method in which we fitted each
  observed p-mode multiplet with a model profile that included both the
  target mode and its six nearest spatial sidelobes and which incorporated
  the effects of the incomplete observational time series through the
  convolution of the fitted profiles with the temporal window functions,
  which were computed using the two actual GONG observing histories. The
  fitted profile also included the effects of the spatial leakage of
  the modes of differing degrees into the target spectrum through the
  use of different sets of m-averaged spatial leakage matrices. In
  order to study the sensitivity of the estimated component ratios to
  the details of the computation of the m-averaged power spectra and of
  the image-masking schemes employed by the GONG project, we generated
  a total of 22 different sets of modal fits. We found that the best
  agreement between the predicted and inferred ratios came from the use
  of unweighted averaged power spectra that were computed using so-called
  n-averaged frequency-splitting coefficients, which had been computed
  by cross-correlating the 2l+1 zonal, tesseral, and sectoral power
  spectra at each l over a wide range of frequencies. This comparison
  yielded a total of 1906 pairs of predicted c<SUB>t,theory</SUB> and
  fitted c<SUB>t,fit</SUB> eigenfunction component ratios. A linear
  regression analysis of these pairs of ratios resulted in the following
  regression equation: c<SUB>t,fit</SUB>=(0.0088+/-0.0013)+(0.9940+/-
  0.0044)c<SUB>t,theory</SUB>. The resulting correlation coefficient
  was 0.9817. This agreement between the predicted and inferred ratios
  suggests that the predicted ratios should be used in the fitting of
  high-degree power spectra where the ratios cannot be inferred because
  of the blending together of individual modal peaks into broad ridges
  of power.

---------------------------------------------------------
Title: The Accuracy of the Born and Ray Approximations in
    Time-Distance Helioseismology
Authors: Birch, A. C.; Kosovichev, A. G.; Price, G. H.; Schlottmann,
   R. B.
2001ApJ...561L.229B    Altcode:
  Time-distance helioseismology measures the time for acoustic
  wave packets to travel, through the solar interior, from one
  location on the solar surface to another. Interpretation of travel
  times requires an understanding of their dependence on subsurface
  inhomogeneities. Traditionally, time-distance measurements have been
  modeled in the ray approximation. Recent efforts have focused on the
  Born approximation, which includes finite-wavelength effects. In order
  to understand the limitations and ranges of validity of the ray and Born
  approximations, we apply them to a simple problem-adiabatic acoustic
  waves in a uniform medium with a spherical inclusion-for which a
  numerical solution to the wave equation is computationally feasible. We
  show that, for perturbations with length scales large compared to
  the size of the first Fresnel zone, both the Born and first-order ray
  approximations yield the same result and that the fractional error in
  the travel time shift, computed by either approximation, is proportional
  to the fractional strength of the sound speed perturbation. Furthermore,
  we demonstrate that for perturbations with length scales smaller
  than the first Fresnel zone the ray approximation can substantially
  overestimate travel time perturbations while the Born approximation
  gives the correct order of magnitude. The main cause of the inaccuracy
  of the Born approximation travel times is the appearance of a diffracted
  wave. This wave, however, has not yet been observed in the solar data.

---------------------------------------------------------
Title: Time-distance helioseismology and the Solar Orbiter mission
Authors: Gizon, L.; Birch, A. C.; Bush, R. I.; Duvall, T. L., Jr.;
   Kosovichev, A. G.; Scherrer, P. H.; Zhao, Junwei
2001ESASP.493..227G    Altcode: 2001sefs.work..227G
  No abstract at ADS

---------------------------------------------------------
Title: Investigation of Mass Flows beneath a Sunspot by Time-Distance
    Helioseismology
Authors: Zhao, Junwei; Kosovichev, Alexander G.; Duvall, Thomas L., Jr.
2001ApJ...557..384Z    Altcode:
  A time-distance helioseismic technique is employed to analyze a set of
  high-resolution Dopplergram observations of a large sunspot by SOHO/MDI
  on 1998 June 18. A regularized, damped least-squares inversion is
  applied to the measurements of travel times to infer mass flows around
  the sunspot below the solar surface. Powerful converging and downward
  directed flows are detected at depths of 1.5-5 Mm, which may provide
  observational evidence for the downdrafts and vortex flows that were
  suggested by Parker for a cluster model of sunspots. Strong outflows
  extending more than 30 Mm are found below the downward and converging
  flows. It is suggested that the sunspot might be a relatively shallow
  phenomenon, with a depth of 5-6 Mm, as defined by its thermal and
  hydrodynamic properties. A strong mass flow across the sunspot is found
  at depths of 9-12 Mm, which may provide more evidence in support of the
  cluster model, as opposed to the monolithic sunspot model. We suggest
  that a new magnetic emergence that was found 5 hr after our analysis
  period is related to this mass flow.

---------------------------------------------------------
Title: Solar Neutrino Emission Deduced from a Seismic Model
Authors: Turck-Chièze, S.; Couvidat, S.; Kosovichev, A. G.; Gabriel,
   A. H.; Berthomieu, G.; Brun, A. S.; Christensen-Dalsgaard, J.; García,
   R. A.; Gough, D. O.; Provost, J.; Roca-Cortes, T.; Roxburgh, I. W.;
   Ulrich, R. K.
2001ApJ...555L..69T    Altcode:
  Three helioseismic instruments on the Solar and Heliospheric Observatory
  have observed the Sun almost continuously since early 1996. This
  has led to detailed study of the biases induced by the instruments
  that measure intensity or Doppler velocity variation. Photospheric
  turbulence hardly influences the tiny signature of conditions in the
  energy-generating core in the low-order modes, which are therefore very
  informative. We use sound-speed and density profiles inferred from GOLF
  and MDI data including these modes, together with recent improvements
  to stellar model computations, to build a spherically symmetric
  seismically adjusted model in agreement with the observations. The
  model is in hydrostatic and thermal balance and produces the present
  observed luminosity. In constructing the model, we adopt the best
  physics available, although we adjust some fundamental ingredients,
  well within the commonly estimated errors, such as the p-p reaction
  rate (+1%) and the heavy-element abundance (+3.5%); we also examine the
  sensitivity of the density profile to the nuclear reaction rates. Then,
  we deduce the corresponding emitted neutrino fluxes and consequently
  demonstrate that it is unlikely that the deficit of the neutrino fluxes
  measured on Earth can be explained by a spherically symmetric classical
  model without neutrino flavor transitions. Finally, we discuss the
  limitations of our results and future developments.

---------------------------------------------------------
Title: Detection of High-Latitude Waves of Solar Coronal Activity in
    Extreme-Ultraviolet Data from the Solar and Heliospheric Observatory
    EUV Imaging Telescope
Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Scherrer, P. H.
2001ApJ...554L.107B    Altcode:
  We present the results of an investigation of EUV coronal structures
  in 1996-2000 using the Solar and Heliospheric Observatory EIT data
  in 171, 195, 284, and 304 Å lines. During this period, poleward-
  and equatorward-migrating waves of solar activity have been found
  in axisymmetrical distributions of EUV intensity in all four
  lines. In the axisymmetrical distribution of the ratio of 195 Å
  to 171 Å intensities, which is a proxy of coronal temperature from
  1×10<SUP>6</SUP> to 2×10<SUP>6</SUP> K, the polar branches are less
  prominent. The high-latitude activity waves are caused by giant coronal
  magnetic loops connecting the polar magnetic field (formed during the
  preceding solar cycle) with the magnetic field of the “following”
  parts of active regions that emerged during the rising phase of the
  current cycle. We suggest that these coronal loops play an important
  role in the topological evolution of the magnetic structure of the
  Sun during the solar cycle.

---------------------------------------------------------
Title: Low-Degree Low-Order Solar p Modes As Seen By GOLF On
    board SOHO
Authors: García, R. A.; Régulo, C.; Turck-Chièze, S.; Bertello,
   L.; Kosovichev, A. G.; Brun, A. S.; Couvidat, S.; Henney, C. J.;
   Lazrek, M.; Ulrich, R. K.; Varadi, F.
2001SoPh..200..361G    Altcode:
  Data recovered from the GOLF experiment on board the ESA/NASA SOHO
  spacecraft have been used to analyze the low-order low-degree
  solar velocity acoustic-mode spectrum below ν=1.5 mHz (i.e.,
  1≤n≤9,l≤2). Various techniques (periodogram, RLAvCS,
  homomorphic-deconvolution and RLSCSA) have been used and compared to
  avoid possible biases due to a given analysis method. In this work,
  the acoustic resonance modes sensitive to the solar central region
  are studied. Comparing results from the different analysis techniques,
  10 modes below 1.5 mHz have been identified.

---------------------------------------------------------
Title: Studying Solar Variability by Local-Area Helioseismology
Authors: Kosovichev, A. G.
2001AGUSM..SP22A01K    Altcode:
  Local-area helioseismology provides diagnostics of 3D structures and
  flows in the solar interior. It substantially extends diagnostic
  capabilities of the `global' helioseismology which is based on
  normal mode frequencies and can recover only 2D azimuthally averaged
  structures and flows. Generally, very long time series of observations
  of solar oscillations are required to probe the deep interior. Recently
  developed approaches to the local-area helioseismology (time-distance
  helioseismology, acoustic imaging, holography, ring-diagram analysis)
  study evolution of particular regions on the Sun by tracking them with
  solar rotation. These methods use relatively short time series but so
  far have been limited to inferences in shallow subsurface layers of
  the Sun. Studying the deeper layers requires substantially longer time
  series, and represents a significant challenge for these techniques. I
  will discuss the current status and potentials of 3D diagnostics
  of internal processes inside the Sun, and their significance for
  understanding solar variability.

---------------------------------------------------------
Title: Polar Activity Wave in the Solar Corona
Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Scherrer, P. H.
2001AGUSM..SP61A05B    Altcode:
  We present the results of investigation of EUV coronal structures in
  1996-2000 using SOHO/EIT data in 171A, 195A, 284A and 304A. During
  this period polarward and equatorward migrating waves of activity
  have been found in axysymmetrical distributions of EUV intensity in
  all four lines. In the ratio of 195A and 171A intensities, which is
  a proxy of coronal temperature from 1 MK to 2 MK, the polar branch
  is not present. We discuss the physical nature of the polar wave
  of activity and conclude that it is related to dense plasma loops
  which are cooler then the loops related to the equatorward migrating
  wave. The latter reflects coronal structures connected with active
  regions and complexies of solar activity. The polar activity wave
  is caused by reconnection between the polar magnetic field and the
  magnetic field of `following' parts of active regions, and, probably,
  plays an important role in the solar cycle.

---------------------------------------------------------
Title: Deep Focusing in Time-Distance Helioseismology
Authors: Duvall, T. L.; Jensen, J. M.; Kosovichev, A. G.; Birch, A. C.
2001AGUSM..SP22A03D    Altcode:
  Much progress has been made by measuring the travel times of solar
  acoustic waves from a central surface location to points at equal arc
  distance away. Depth information is obtained from the range of arc
  distances examined, with the larger distances revealing the deeper
  layers. This method we will call surface-focusing, as the common
  point, or focus, is at the surface. To obtain a clearer picture of the
  subsurface region, it would, no doubt, be better to focus on points
  below the surface. Our first attempt to do this used the ray theory to
  pick surface location pairs that would focus on a particular subsurface
  point. This is not the ideal procedure, as Born approximation kernels
  suggest that this focus should have zero sensitivity to sound speed
  inhomogeneities. However, the sensitivity is concentrated below the
  surface in a much better way than the old surface-focusing method,
  and so we expect the deep-focusing method to be more sensitive. A
  large sunspot group was studied by both methods. Inversions based on
  both methods will be compared.

---------------------------------------------------------
Title: Mass Flows Beneath the Sunspot from Inversion of Time-distance
    Helioseismology
Authors: Zhao, J.; Kosovichev, A. G.; Duvall, T. L.
2001AGUSM..SP22A04Z    Altcode:
  Time-distance helioseismic technique has provided a useful tool to
  study the interior structure of the Sun. The inversion of time-distance
  measurements can help us reveal mass flows and sound speed perturbation
  beneath the solar surface. We have applied time-distance measurements
  to a set of high resolution Dopplergram observations of a sunspot by
  SOHO/MDI, and a regularized damped least-squares inversion was used
  to infer the mass flows beneath this sunspot. Powerful converging
  and downward flows are detected at a depth of 1.5 to 5 Mm, which may
  provide observational evidence for the cluster sunspot model. Strong
  outflows which extend more than 30Mm outside the center of the sunspot
  are found below 5Mm. A full disk observation of an interesting event in
  August 2000, an apparent spin of a sunspot, was also analyzed by the
  same approach but with lower resolution. For this event a vortex flow
  has been detected in subsurface layers. This may provide an insight
  into the study of helicity below the photosphere of the Sun.

---------------------------------------------------------
Title: Using a Wave-Theory Approach to Time-Distance Helioseismology
Authors: Birch, A. C.; Duvall, T. L.; Kosovichev, A. G.
2001AGUSM..SP31A21B    Altcode:
  Time-distance helioseismology is a method for measuring the travel
  times for acoustic wave packets as they move between points on the solar
  surface through the solar interior. In order to interpret travel times
  we derive, employing the Born approximation to the wave equation, a
  linear relationship between travel time variations and perturbations to
  a solar model; the results are essentially the "banana-doughnut" kernels
  familiar from geophysics. We show preliminary inversion results for
  large-scale structure inside the sun using these sensitivity kernels.

---------------------------------------------------------
Title: Challenges in High-Degree Helioseismology
Authors: Rhodes, E. J.; Reiter, J.; Schou, J.; Kosovichev, A. G.;
   Scherrer, P. H.
2001AGUSM..SP21C06R    Altcode:
  Some of the most exciting results that the field of helioseismology
  has provided in recent years have come from numerical inversions of
  different properties of the solar p-mode oscillations. Such inversions
  have been primarily of three types: 1) structural inversions which
  have employed tables of the frequencies of various p-modes and
  their associated uncertainties to infer different thermodynamic
  properties of the solar interior as functions of radius and latitude,
  2) rotational inversions which have employed tables of the frequency
  splittings of the modes of different azimuthal order to measure the
  internal angular velocity as functions of radius and latitude, and 3)
  horizontal flow inversions which have employed sets of frequencies
  of the rings that are observed in three-dimensional power spectra to
  infer sub-photospheric horizontal flow vectors as functions of depth,
  latitude and longitude. Unfortunately, the vast majority of such
  inversions have only included frequencies or frequency splittings
  of the low- and the intermediate-degree oscillations. Furthermore,
  the horizontal flow inversions have been somewhat limited by the
  difficulties in accurately fitting the rings of the higher-degree
  power spectra. These limitations have prevented helioseismologists from
  accurately inferring the sound speed, density, adiabatic gradient, and
  helium abundance in the outermost three to four percent (by radius)
  of the solar interior. In addition, the absence of high-l frequency
  splittings from most past rotational inversions has limited the
  accuracy with which we have been able to estimate the angular velocity
  of the solar surface layers. These limitations have mainly come about
  because for l&gt;= 200 the individual modal peaks blend together into
  broad ridges of power. Fitting such ridges requires knowledge of the
  amount of power which leaks into the sidelobes that are adjacent to
  the true spectral peaks. Such leakage information requires detailed
  knowledge of the spatial behavior of each different intrument, of
  the ratio of horizontal and vertical components of the solar p-mode
  eigenfunctions, and of the temporal window function of each dataset. In
  this presentation we will demonstrate the high-l frequencies which we
  have obtained from a new fitting technique which employs m-averaged
  power spectra, temporal window functions, and spatial leakage matrices
  to fit each mode or ridge with a total of seven peaks. We will also
  demonstrate that we have obtained evidence from the fitting of GONG
  power spectra that the true ratios of the eigenfunction components
  match the theoretical predictions of these ratios. Finally, we will
  also demonstrate that cross-correlations of the peaks and ridges in
  the 2l+1 individual spectra at each l result in systematic jumps in the
  frequency-splitting coefficients for l&gt;=200 due to the blending of
  the peaks into ridges. We will point out that, unless some method can
  be found which overcomes these detrimental effects of peak-blending,
  we will not be able to provide measures of the latitudinal behavior
  of the solar angular velocity close to the photosphere which will
  be independent of the horizontal flow mesurements obtained with the
  so-called “ring and trumpet” technique.

---------------------------------------------------------
Title: Resonant Vibrational Instabilities in Magnetized Stellar
    Atmospheres
Authors: Birch, A. C.; Kosovichev, A. G.; Spiegel, E. A.; Tao, L.
2001SoPh..199..291B    Altcode:
  We perform linear stability analysis on stratified, plane-parallel
  atmospheres in uniform vertical magnetic fields. We assume perfect
  electrical conductivity and we model non-adiabatic effects with Newton's
  law of radiative cooling. Numerical computations of the dispersion
  diagrams in all cases result in patterns of avoided crossings and
  mergers in the real part of the frequency. We focus on the case
  of a polytrope with a prevalent, relatively weak, magnetic field
  with overstable modes. The growth rates reveal prominent features
  near avoided crossings in the diagnostic diagram, as has been seen
  in related problems (Banerjee, Hasan, and Christensen-Dalsgaard,
  1997). These features arise in the presence of resonant oscillatory
  bifurcations in non-self adjoint eigenvalue problems. The onset of
  such bifurcations is signaled by the appearance of avoided crossings
  and mode mergers. We discuss the possible role of the linear stability
  results in understanding solar spicules.

---------------------------------------------------------
Title: Magnetic Energy Release and Transients in the Solar Flare of
    2000 July 14
Authors: Kosovichev, A. G.; Zharkova, V. V.
2001ApJ...550L.105K    Altcode:
  High-resolution observations of a large solar flare on 2000 July 14
  (“Bastille Day Flare”) from the Michelson Doppler Imager instrument
  on the SOHO spacecraft reveal rapid variations of the magnetic field in
  the lower solar atmosphere during the flare. Some of these variations
  were irreversible, occurred in the vicinity of magnetic neutral lines,
  and likely were related to magnetic energy release in the flare. A
  surprising result is that these variations happened very rapidly on the
  scale of 10-15 minutes in a large area of ~50 Mm<SUP>2</SUP> at the
  beginning of the flare. Other, more localized and impulsive magnetic
  field variations somewhat similar to “magnetic transients” observed by
  Zirin and coworkers were accompanied by impulses in continuum intensity
  and Doppler velocity. These impulses have dynamic characteristics
  similar to Ellerman's “bombs” and Severny's “mustaches” and were
  probably caused by high-energy particles bombarding the solar surface.

---------------------------------------------------------
Title: Probing Magnetic Structures in the Solar Interior by
    Helioseismic Tomography
Authors: Kosovichev, A. G.; Duvall, T. L., Jr.; Scherrer, P. H.
2001ASPC..248..169K    Altcode: 2001mfah.conf..169K
  No abstract at ADS

---------------------------------------------------------
Title: Heliotomography of the outer layers of the Sun
Authors: Kosovichev, A. G.; Duvall, T. L., Jr.; Birch, A. C.; Gizon,
   L.; Scherrer, P. H.; Zhao, Junwei
2001ESASP.464..701K    Altcode: 2001soho...10..701K
  Heliotomography offers important diagnostics of the solar interior
  by providing three-dimensional maps of the sound speed and flows in
  the upper convection zone. These diagnostics are based on inversion
  of travel times of acoustic waves which propagate between different
  points on the solar surface through the interior. The most significant
  variations in the thermodynamic structure found by this method
  are associated with sunspots and complexes of solar activity. The
  inversion results provide evidence for areas of higher sound speed
  beneath sunspot regions located at depths of 4 - 20 Mm, which may be
  due to accumulated heat or magnetic field concentrations. The results
  reveal structures and flows associated with active regions and sunspots
  at various stages of their evolution, and provide important constraints
  for theories of solar dynamics and activity.

---------------------------------------------------------
Title: Large-Scale Patterns of Solar Magnetic Field and Activity
    Cycles
Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Scherrer, P. H.
2001ASPC..248..135B    Altcode: 2001mfah.conf..135B
  No abstract at ADS

---------------------------------------------------------
Title: Local-area helioseismology by SOT on-board Solar-B
Authors: Sekii, T.; Shibahashi, H.; Kosovichev, A. G.; Duvall, T. L.,
   Jr.; Berger, T. E.; Bush, R.; Scherrer, P. H.
2001ESASP.464..327S    Altcode: 2001soho...10..327S
  Solar-B satellite, a successor to Yohkoh, will be launched
  in 2005. Placed in a sun-synchronous orbit, it will carry out
  multi-wavelength observation in optical, EUV and X-ray ranges. One of
  the instruments on Solar-B, Solar Optical Telescope (SOT), a Japan/US
  collaboration, aims at measuring the magnetic field and the Doppler
  velocity field in the solar photosphere. Although it is not specifically
  designed for helioseismic observations, the high-resolution Dopplergram
  produced by SOT is potentially a very powerful tool for detailed
  seismic investigation of subsurface magnetic and thermal structures
  and associated mass flows. If successful, these measurements will be
  an important contribution to the main goal of the Solar-B project:
  understanding the origin and dynamics of the basic magnetic structures
  and their effects on the solar corona. We discuss the prospect and
  challenges of local-area helioseismology by SOT.

---------------------------------------------------------
Title: Towards a Wave Theory Interpretation of Time-Distance
    Helioseismology Data
Authors: Birch, A. C.; Kosovichev, A. G.
2001IAUS..203..180B    Altcode:
  Time-distance helioseismology, which measures the time for acoustic
  waves to travel between points on the solar surface, has been used to
  study small-scale three-dimensional features in the sun, for example
  active regions, as well as large-scale features, for example meridional
  flow, that are not accessible by standard global helioseismology. The
  interpretation of travel times has typically been done in the
  ray approximation. The interaction of acoustic waves with features
  smaller than their wavelength, for example in active regions or in the
  tachocline, is not expected to be well represented by ray theory. In
  order to develop a wave interpretation of time-distance data we employ
  the first Born approximation, which takes into account finite-wavelength
  effects and allows a single scattering between the source and receiver
  of the acoustic wave. We show the sensitivity of travel times to flows
  and structure perturbations and compare the results with ray theory.

---------------------------------------------------------
Title: The Born approximation in time-distance helioseismology
Authors: Birch, A. C.; Kosovichev, A. G.
2001ESASP.464..187B    Altcode: 2001soho...10..187B
  Time-distance helioseismology, which measures the time for acoustic
  waves to travel between points on the solar surface, has been used to
  study small-scale three-dimensional features in the sun, for example
  active regions, as well as large-scale features, for example meridional
  flow, that are not accessible by standard global helioseismology. The
  interpretation of travel times has typically been done in the ray
  approximation. The interaction of acoustic waves with features smaller
  than their wavelength, such as in active regions or in the tachocline,
  is not expected to be well represented by ray theory. In order to
  develop a wave interpretation of time-distance data we employ the
  first Born approximation, which takes into account finite-wavelength
  effects and allows a single scattering between the source and receiver
  of the acoustic wave. We show that in the case of spherically symmetric
  perturbations the Born approximation can be easily related to normal
  mode perturbation theory. The Born approximation agrees with ray theory
  when applied to large scale perturbations, and performs better than
  ray theory when applied to perturbations with small spatial scale. We
  show, via an example OLA inversion of artificial data, that reasonable
  averaging kernels can be built from Born approximation kernels.

---------------------------------------------------------
Title: Active Longitudinal Structures of the Sun from MDI and EIT
    Observations
Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Scherrer, P. H.
2001IAUS..203..251B    Altcode:
  Using data from the EIT and MDI instruments on SOHO and from Kitt
  Peak Observatory we have studied the non-axisymmetrical structure
  and dynamics of solar activity at different levels of the solar
  atmosphere. The data were reduced to synoptic maps of the photospheric
  magnetic field and coronal structures in the EUV lines: 171Å, 195Å,
  284Å, and 304Å. In addition, the coronal temperature maps were
  obtained using the ration of the 171Å and 195Å lines. The results
  reveal long-living longitudinal structures in the photosphere and
  corona during the transition from Cycle 22 to 23 and the rising
  phase of Cycle 23. We have found the Hale magnetic field polarity
  reversal first occured at the active longitudes. Thus, the stable
  longitudinal structures play an important role in the mechanism of
  the solar cycle. These structures are also revealed in the large-scale
  structure of the corona. We study the relation between the magnetic and
  coronal longitudinal structures, and their role in formation of coronal
  holes. We discuss the relations between rotation of the longitudinal
  structures in the photosphere and corona and compare with the rotation
  rate of the solar interior using helioseismic data. This work was
  carried out in the collaboration with J. T. Hoeksema, A. G. Kosovichev
  and P. H. Scherrer of Stanford University.

---------------------------------------------------------
Title: Solar Active Longitudes and Their Rotations Using SOHO-MDI Data
(CD-ROM Directory: contribs/benevo2)
Authors: Benevolenskaya, E. E.; Hoeksema, J. T.; Kosovichev, A. G.;
   Scherrer, P. H.
2001ASPC..223..583B    Altcode: 2001csss...11..583B
  No abstract at ADS

---------------------------------------------------------
Title: Low-degree p-mode parameters: the solar-cycle dependence
Authors: Toutain, T.; Kosovichev, A. G.
2001ESASP.464..123T    Altcode: 2001soho...10..123T
  Using the LOI-proxy data of the MDI instrument we have studied the
  solar-cycle dependence of the low-degree (l=0-3) p modes between May
  1996 and August 2000. In addition to the usual frequency shift we have
  also found that mode linewidths increase by about 15% from the solar
  minimum to the solar maximum. Within the accuracy we have, the other
  parameters: rotational splitting and asymmetry do not exhibit any
  dependence with the solar cycle, except the a<SUB>2</SUB> coefficient
  which seems to increase as well with activity. Thought the mode energy
  does not also vary much, this analysis indicates an unexplained maximum
  of energy in the first half of year 1998.

---------------------------------------------------------
Title: New Developments in Local Area Helioseismology
Authors: Duvall, T. L., Jr.; Kosovichev, A. G.
2001IAUS..203..159D    Altcode:
  Several techniques are used to study local areas in helioseismology,
  including time-distance helioseismology, acoustic imaging/holography,
  and ring diagram analysis. These techniques can be used to study flows,
  magnetic fields, and temperature inhomogeneities. The "local" area
  studied can be as small as a supergranule, or as large as the entire
  convection zone in the case of meridional circulation as studied
  by Giles and colleagues. Active regions have been studied with some
  interesting results, with complicated flow patterns below sunspots
  and detectable sound speed inhomogeneitities in the 10 Mm below the
  spots. Another interesting result is the detection of sunspots on
  the back side of the Sun by Lindsey and Braun using the holography
  technique. A confirmation of their result using the time-distance
  technique will be discussed.

---------------------------------------------------------
Title: Helioseismic Tomography of Solar Active Regions (CD-ROM
Directory: contribs/kosovich)
Authors: Kosovichev, A. G.
2001ASPC..223...99K    Altcode: 2001csss...11...99K
  No abstract at ADS

---------------------------------------------------------
Title: The physics of the solar core deduced from GOLF and MDI
    acoustic modes
Authors: Turck-Chièze, S.; Kosovichev, A. G.; Couvidat, S.; García,
   R. A.; Nghiem, P.; Pérez Hernández, F.; Turcotte, S.
2001ESASP.464..485T    Altcode: 2001soho...10..485T
  We use the recent results on solar acoustic modes coming from GOLF
  and MDI, to demonstrate that we improve the quality of the inversion
  of the sound speed and the density by avoiding several biases coming
  from the turbulent surface. The present accuracy allows a quantitative
  discussion on the physics of the solar nuclear core. We now exclude
  several phenomena which are incompatible with the present observations:
  central turbulent mixing or large modification of the pp chain nuclear
  reaction rates. We propose a solution to the difference between the
  Sun and solar models only in terms of turbulence at the base of the
  convective zone, an increase of the weak interaction p-p reaction
  rate by 2% in the framework of intermediate Mitler screening, and
  an underestimate of CNO composition of no more than 3%. Even if this
  solution is probably not unique, it allows a prediction of neutrino
  fluxes induced by helioseismology. We also note that nowadays,
  helioseismology puts just a few constraints on the reaction rates of
  the CNO cycle, and let place for lower high energy neutrino predictions.

---------------------------------------------------------
Title: Helioseismic and magnetic waves as signatures of energy
    transport mechanisms in solar flares
Authors: Zharkova, V. V.; Kosovichev, A. G.
2001ESASP.464..259Z    Altcode: 2001soho...10..259Z
  Recently reported helioseismic waves caused by a X-class solar flare
  propagating in the solar interior and observed in a form of ripples
  at the photosphere as well as magnetic field variations in the lower
  atmosphere associated with another X-class flares revived an interest
  to the problem of energy release and transport in solar flares. A
  comparison of simulations with the seismic observations revealed that
  a starting time of the wave coincides with the onset of the X-ray
  flare while the wave's amplitude corresponds to the energy momentum
  higher by half of order of the magnitude than the one observed. In
  the current paper electron beams are considered as alternative agents
  delivering energy directly to the photosphere. Depth variations of
  a momentum and energy deposition by beam electrons with the energy
  power law precipitating from the corona into a flaring atmosphere
  are calculated using the time-dependent kinetic solutions. A momentum
  brought by weak beams to lower chromospheric levels was found not to
  exceed of 10<SUP>18</SUP> - 10<SUP>19</SUP> whereas moderately intense
  and hard beams can deliver the momentum of (5 - 10)×10<SUP>22</SUP>
  g cm/s. Energy deposition functions are also shown to increase with
  depths by about an order of magnitude at the lower chromosphere if
  Ohmic losses are included in addition to pure Coulomb collisions.

---------------------------------------------------------
Title: g-mode detection: Where do we stand?
Authors: Appourchaux, T.; Andersen, B.; Berthomieu, G.; Chaplin, W.;
   Elsworth, Y.; Finsterle, W.; Frölich, C.; Gough, D. O.; Hoeksema,
   T.; Isaak, G.; Kosovichev, A.; Provost, J.; Scherrer, P.; Sekii, T.;
   Toutain, T.
2001ESASP.464..467A    Altcode: 2001soho...10..467A
  We review the recent developments in determining the upper limits to
  g-mode amplitudes obtained by SOHO instruments, GONG and BiSON. We
  address how this limit can be improved by way of new helioseismic
  instruments and/or new collaborations, hopefully providing in the not
  too distant future unambiguous g-mode detection.

---------------------------------------------------------
Title: Solar Interior: Rotation
Authors: Kosovichev, A.
2000eaa..bookE2010K    Altcode:
  The Sun rotates differentially, i.e. the solar rotation rate varies with
  both latitude and radius. The differential rotation is particularly
  prominent in the convection zone where equatorial zones rotate almost
  30% faster than near-polar regions. There are also strong variations
  of the rotation rate with radius near the surface and at the bottom
  of the convection zone (rotational shear layers). I...

---------------------------------------------------------
Title: Signatures of the Rise of Cycle 23
Authors: Dziembowski, W. A.; Goode, P. R.; Kosovichev, A. G.; Schou, J.
2000ApJ...537.1026D    Altcode:
  During the rise of Cycle 23, we have found a sizable, systematic
  evolution of the Solar and Heliospheric Observatory/Michelson Doppler
  Imager solar oscillation frequencies implying significant changes in the
  spherically symmetric structure of the Sun's outer layers as well as in
  its asphericity up to a P<SUB>18</SUB> Legendre distortion. We conducted
  a search for corresponding asymmetries in Ca II K data from Big Bear
  Solar Observatory. We found tight temporal and angular correlations of
  the respective asphericities up through P<SUB>10</SUB>. This result
  emphasizes the role of the magnetic field in producing the frequency
  changes. We carried out inversions of the frequency differences and
  the splitting coefficients assuming that the source of the evolving
  changes is a varying stochastic magnetic field. With respect to the
  most recent activity minimum, we detected a significant perturbation in
  the spherical part at a depth of 25-100 Mm, which may be interpreted
  as being a result of a magnetic perturbation, &lt;B<SUP>2</SUP>&gt;,
  of about (60KG)<SUP>2</SUP> and/or a relative temperature perturbation
  of about 1.2×10<SUP>-4</SUP>. Larger, although less statistically
  significant, perturbations of the interior structure were found in
  the aspherical distortion.

---------------------------------------------------------
Title: Observational Upper Limits to Low-Degree Solar g-Modes
Authors: Appourchaux, T.; Fröhlich, C.; Andersen, B.; Berthomieu, G.;
   Chaplin, W. J.; Elsworth, Y.; Finsterle, W.; Gough, D. O.; Hoeksema,
   J. T.; Isaak, G. R.; Kosovichev, A. G.; Provost, J.; Scherrer, P. H.;
   Sekii, T.; Toutain, T.
2000ApJ...538..401A    Altcode:
  Observations made by the Michelson Doppler Imager (MDI) and Variability
  of solar IRradiance and Gravity Oscillations (VIRGO) on the Solar and
  Heliospheric Observatory (SOHO) and by the ground-based Birmingham
  Solar Oscillations Network (BiSON) and Global Oscillations Network
  Group (GONG) have been used in a concerted effort to search for solar
  gravity oscillations. All spectra are dominated by solar noise in the
  frequency region from 100 to 1000 μHz, where g-modes are expected to be
  found. Several methods have been used in an effort to extract any g-mode
  signal present. These include (1) the correlation of data-both full-disk
  and imaged (with different spatial-mask properties)-collected over
  different time intervals from the same instrument, (2) the correlation
  of near-contemporaneous data from different instruments, and (3) the
  extraction-through the application of complex filtering techniques-of
  the coherent part of data collected at different heights in the solar
  atmosphere. The detection limit is set by the loss of coherence
  caused by the temporal evolution and the motion (e.g., rotation)
  of superficial structures. Although we cannot identify any g-mode
  signature, we have nevertheless set a firm upper limit to the amplitudes
  of the modes: at 200 μHz, they are below 10 mm s<SUP>-1</SUP> in
  velocity, and below 0.5 parts per million in intensity. The velocity
  limit corresponds very approximately to a peak-to-peak vertical
  displacement of δR/R<SUB>solar</SUB>=2.3×10<SUP>-8</SUP> at the
  solar surface. These levels which are much lower than prior claims,
  are consistent with theoretical predictions.

---------------------------------------------------------
Title: Identification of Solar Acoustic Modes of Low Angular Degree
    and Low Radial Order
Authors: Bertello, L.; Varadi, F.; Ulrich, R. K.; Henney, C. J.;
   Kosovichev, A. G.; García, R. A.; Turck-Chièze, S.
2000ApJ...537L.143B    Altcode:
  We present evidence for the detection of low radial order (n&lt;10)
  acoustic modes of low angular degree, l=0-2, in the 759 day long
  Global Oscillations at Low Frequency and Michelson Doppler Imager time
  series. We used Random-Lag Singular Cross-Spectrum Analysis, which
  searches for simultaneous oscillatory components in two or more time
  series. We have determined 11 modes in the range n=3-9, of which eight
  modes confirm the previous measurements by Toutain et al. and three
  modes of l=0 and n=3, 5, and 6 are reliably measured for the first
  time. The errors of frequency determination are also significantly
  reduced for several previously identified modes. New sound speed
  inversion results suggest that the effect of inhomogeneous initial
  composition of the Sun should be included in the standard solar model.

---------------------------------------------------------
Title: Comparison of the 1998 April 29 M6.8 and 1998 November 5
    M8.4 Flares
Authors: Wang, Haimin; Goode, Philip R.; Denker, Carsten; Yang, Guo;
   Yurchishin, Vasyl; Nitta, Nariaki; Gurman, Joseph B.; St. Cyr, Chris;
   Kosovichev, Alexander G.
2000ApJ...536..971W    Altcode:
  We combined, and analyzed in detail, the Hα and magnetograph data
  from Big Bear Solar Observatory (BBSO), full-disk magnetograms from
  the Michelson Doppler Imager (MDI) on board Solar and Heliospheric
  Observatory (SOHO), coronagraph data from the Large Angle Spectrometric
  Coronagraph (LASCO) of SOHO, Fe XII 195 Å data from the Extreme
  ultraviolet Imaging Telescope (EIT) of SOHO, and Yohkoh soft X-ray
  telescope (SXT) data of the M6.8 flare of 1998 April 29 in National
  Oceanic and Atmospheric Administration (NOAA) region 8375 and the
  M8.4 flare of 1998 November 5 in NOAA region 8384. These two flares
  have remarkable similarities:1. Partial halo coronal mass ejections
  (CMEs) were observed for both events. For the 1998 April 29 event,
  even though the flare occurred in the southeast of the disk center,
  the ejected material moved predominantly across the equator, and the
  central part of the CME occurred in the northeast limb. The direction
  in which the cusp points in the postflare SXT images determines the
  dominant direction of the CMEs.2. Coronal dimming was clearly observed
  in EIT Fe XII 195 Å for both but was not observed in Yohkoh SXT for
  either event. Dimming started 2 hr before the onset of the flares,
  indicating large-scale coronal restructuring before both flares.3. No
  global or local photospheric magnetic field change was detected from
  either event; in particular, no magnetic field change was found in the
  dimming areas.4. Both events lasted several hours and, thus, could be
  classified as long duration events (LDEs). However, they are different
  in the following important aspects. For the 1998 April 29 event,
  the flare and the CME are associated with an erupting filament in
  which the two initial ribbons were well connected and then gradually
  separated. SXT preflare images show the classical S-shape sheared
  configuration (sigmoid structure). For the 1998 November 5 event, two
  initial ribbons were well separated, and the SXT preflare image shows
  the interaction of at least two loops. In addition, no filament eruption
  was observed. We conclude that even though these two events resulted
  in similar coronal consequences, they are due to two distinct physical
  processes: eruption of sheared loops and interaction of two loops.

---------------------------------------------------------
Title: Comparison of Frequencies and Rotational Splittings of Solar
    Acoustic Modes of Low Angular Degree from Simultaneous MDI and
    GOLF Observations
Authors: Bertello, L.; Henney, C. J.; Ulrich, R. K.; Varadi, F.;
   Kosovichev, A. G.; Scherrer, P. H.; Roca Cortés, T.; Thiery, S.;
   Boumier, P.; Gabriel, A. H.; Turck-Chièze, S.
2000ApJ...535.1066B    Altcode:
  During the years 1996 through 1998 the Michelson Doppler Imager (MDI)
  and the Global Oscillations at Low Frequency (GOLF) experiments on the
  Solar and Heliospheric Observatory (SOHO) mission have provided unique
  and nearly uninterrupted sequences of helioseismic observations. This
  paper describes the analysis carried out on power spectra from 759
  days of calibrated disk-averaged velocity signals provided by these two
  experiments. The period investigated in this work is from 1996 May 25
  to 1998 June 22. We report the results of frequency determination of
  low-degree (l&lt;=3) acoustic modes in the frequency range between 1.4
  mHz and 3.7 mHz. Rotational splittings are also measured for nonradial
  modes up to 3.0 mHz. The power spectrum estimation of the signals
  is performed using classical Fourier analysis and the line-profile
  parameters of the modes are determined by means of a maximum likelihood
  method. All parameters have been estimated using both symmetrical and
  asymmetrical line profile-fitting formula. The line asymmetry parameter
  of all modes with frequency higher than 2.0 mHz is systematically
  negative and independent of l. This result is consistent with the
  fact that both MDI and GOLF data sets investigated in this paper are
  predominantly velocity signals, in agreement with previous results. A
  comparison of the results between the symmetric and asymmetric fits
  shows that there is a systematic shift in the frequencies for modes
  above 2.0 mHz. Below this frequency, the line width of the modes
  is very small and the time base of the data does not provide enough
  statistics to reveal an asymmetry. In general, the results show that
  frequency and rotational splitting values obtained from both the
  MDI and GOLF signals are in excellent agreement, and no significant
  differences exist between the two data sets within the accuracy of the
  measurements. Our results are consistent with a uniform rotation of
  the solar core at the rate of about 435 nHz and show only very small
  deviations of the core structure from the standard solar model.

---------------------------------------------------------
Title: Diagnostics of Solar Magnetic Fields by Time-Distance
    Helioseismology
Authors: Zhao, J.; Duvall, T. L., Jr.; Kosovichev, A. G.
2000SPD....31.0120Z    Altcode: 2000BAAS...32..804Z
  Sunspot seismology has been developed in recent years, and the
  time-distance analysis plays an important role in it. Most of the
  current inferences for interior structures were made by measuring
  perturbations of the acoustic wave speed which is due to both
  temperature and magnetic field variations. An important problem
  of the time-distance seismology is to disentangle the effects of
  temperature and magnetic field. The standard technique for the travel
  time measurements is to divide annuli for given wave travel distances
  into four sectors to get both the wave speed and flow velocity under the
  surface. Here, we consider the inhomogeneity caused by the magnetic
  field of sunspots. By dividing the annuli into eight sectors and
  analyzing the travel time of each octants, we can obtain the direction
  and the magnitude of the magnetic field in sunspot regions. Scattering
  and absorption of incoming waves in each different direction may also
  play an important role in these measurements.

---------------------------------------------------------
Title: Active Longitudes in Solar Corona
Authors: Benevolenskaya, E. E.; Kosovichev, A. G.; Scherrer, P. H.
2000SPD....31.0226B    Altcode: 2000BAAS...32..815B
  We present the results of the investigation of the large-scale
  structure of the solar corona during the transition period between
  solar cycles 22 and 23 and at the beginning of the current cycle 23
  using the SOHO/EIT EUV data obtained in 171 Angstroms, 195 Angstroms,
  284 Angstroms and 304 Angstroms lines. For this analysis the data
  were transformed into synoptic maps for each of the spectral lines,
  and for the 195 Angstroms/171 Angstroms line ratio which is an
  index of the coronal temperature. The synoptic maps reveal stable
  longitudinal structures in the coronal intensities and temperature,
  which are related to large-scale magnetic field structures. We discuss
  the relation between the coronal and photospheric magnetic structures
  obtained from the SOHO/MDI data, and compare the rotation rates of
  these structures with the rotation profile of the solar interior in
  order to determine the possible origin of the coronal structures.

---------------------------------------------------------
Title: Heliotomography: what happens just below the surface?
Authors: Kosovichev, A. G.; Duvall, T. L., Jr.
2000SPD....31.0601K    Altcode: 2000BAAS...32..838K
  Heliotomography (or time-distance helioseismology) is a relatively
  new tool for diagnostics of internal structures and dynamics of
  the Sun. It is based on inversion of travel times of acoustic
  wave packets propagating through the solar interior and bouncing
  back to the surface. The travel times provide information about the
  variations of temperature, magnetic fields and flow velocities along
  the wave paths. These properties of the solar interior are inferred
  from the travel times by tomographic inversions. Heliotomography has
  provided a three-dimensional view of the interior, not accessible by
  traditional helioseismology based on mode frequencies. This method has
  been applied to study both large-scale flows (meridional circulation,
  North-South asymmetry of solar rotation) and small-scale phenomena
  (supergranulation, sunspots, emerging magnetic flux). The results
  reveal very dynamical and complicated structures below the surface,
  associated with convection and magnetic fields, and shed new light
  on the formation and evolution of active regions and sunspots. We
  discuss the current limits for the temporal and spatial resolution and
  recent achievements. Most inversion results provide the results to
  a depth of 20 Mm. It has been demonstrated that with this method we
  can measure the solar flows to the base of the convection zone which
  is 200 Mm deep. However, resolving deep and small-scale features is
  very challenging, and requires concentrated efforts for developing
  both the measurement techniques and theoretical interpretations. We
  review the recent progress in developing a wave-theory approach to
  heliotomographic inversions, and perspectives for the diagnostics of
  the physical processes below the Sun's surface.

---------------------------------------------------------
Title: Observations of Magnetic Energy Release in Solar Flares
Authors: Kosovichev, A. G.; Zharkova, V. V.
2000SPD....31.0259K    Altcode: 2000BAAS...32..821K
  We report on direct observations of magnetic energy release in
  solar flares using Michelson Doppler Imager (MDI) instrument on SOHO
  spacecraft. Continuous monitoring a solar active region in May 1998
  with high-quality magnetograms taken every minute has allowed us to
  detect sudden decreases of the magnetic energy of the active region
  during two moderate-class flares. The most rapid energy release occurred
  near the maxima of the flare soft X-ray emission recorded by the GOES
  satellite. After the flares the magnetic energy of the active region is
  restored to nearly preflare values. We have also detected irreversible
  changes in the magnetic energy distribution for this and other active
  regions during solar flares.

---------------------------------------------------------
Title: Optimal Masks for Low-Degree Solar Acoustic Modes
Authors: Toutain, T.; Kosovichev, A. G.
2000ApJ...534L.211T    Altcode: 2000astro.ph..4153T
  We suggest a solution to an important problem in observational
  helioseismology of the separation of lines of solar acoustic (p) modes
  of low angular degree in oscillation power spectra by constructing
  optimal masks for Doppler images of the Sun. Accurate measurements
  of oscillation frequencies of low-degree modes are essential for the
  determination of the structure and rotation of the solar core. However,
  these measurements for a particular mode are often affected by leakage
  of other p-modes arising when the Doppler images are projected on to
  spherical harmonic masks. The leakage results in overlapping peaks
  corresponding to different oscillation modes in the power spectra. In
  this Letter, we present a method for calculating optimal masks for a
  given (target) mode by minimizing the signals of other modes appearing
  in its vicinity. We apply this method to time series of 2 yr obtained
  from the Michelson Doppler Imager instrument on board the Solar and
  Heliospheric Observatory space mission and demonstrate its ability to
  reduce efficiently the mode leakage.

---------------------------------------------------------
Title: Sunspots: Frontside and Backside Measurements with
    Time-Distance Helioseismology
Authors: Duvall, T. L., Jr.; Kosovichev, A. G.; Scherrer, P. H.
2000SPD....31.0505D    Altcode: 2000BAAS...32..837D
  In time-distance helioseismology, travel times measured between
  different surface locations are used to infer subsurface flows,
  temperature inhomogeneities and magnetic fields. It has been suggested
  that most of the travel time reduction near sunspots may be due to the
  lowered reflection layer associated with the Wilson depression. This
  will be examined by looking at rays that travel below the sunspot but do
  not begin or end in the spot. A time-distance method of imaging sunspots
  on the backside will be compared with that of Lindsey and Braun.

---------------------------------------------------------
Title: Sunspots: frontside and backside measurements with
    time-distance helioseismology.
Authors: Duvall, T. L., Jr.; Kosovichev, A. G.; Scherrer, P. H.
2000BAAS...32Q.837D    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Heliotomography: what happens just below the surface?
Authors: Kosovichev, A. G.; Duvall, T. L., Jr.
2000BAAS...32..837K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: A Wave-Theory Approach to Time-Distance Helioseismology
Authors: Birch, A. C.; Kosovichev, A. G.
2000SPD....31.0107B    Altcode: 2000BAAS...32R.802B
  Time-distance helioseismology, which measures the time for acoustic
  waves to travel between points on the solar surface, has been
  used to study small-scale three-dimensional features in the sun,
  for example active regions, as well as large-scale features, for
  example meridional flow, that are not accessible by standard global
  helioseismology. The interpretation of travel times has typically
  been done in the ray approximation. The interaction of acoustic waves
  with features smaller than their wavelength, for example in active
  regions or in the tachocline, is not expected to be well represented
  by ray theory. In order to develop a wave-based interpretation of
  time-distance data we employ the first Born approximation, which takes
  into account finite-wavelength effects and allows a single scattering
  between the source and receiver of the acoustic wave. We calculate the
  sensitivity functions, the solar equivalent of the 'banana-doughnut'
  kernels from terrestrial seismology, for the wave travel times and
  study the dependence of travel times on perturbations to a solar
  model. The wave travel times are compared with ray theory. This work
  was supported by NASA grant NAG-3077.

---------------------------------------------------------
Title: Observations of magnetic energy release in solar flares.
Authors: Kosovichev, A. G.; Zharkova, V. V.
2000BAAS...32Q.821K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The Magnetic Connectivity of Moss Regions
Authors: Zhao, X. P.; Hoeksema, J. T.; Kosovichev, A. G.; Bush, R.;
   Scherrer, P. H.
2000SoPh..193..219Z    Altcode:
  A novel emission feature resembling moss was first identified in
  high-resolution TRACE Fe ix/x 171 Å images by Berger et al. (1999). The
  moss emission is characterized by dynamic arc-second scale, bright
  elements surrounding dark inclusions in images of solar active
  regions. Patches of moss elements, called moss regions, have a scale
  of 20-30 Mm. Moss regions occur only above some of magnetic plages
  that underlie soft X-ray coronal loops. Using the potential field
  extrapolation of the photospheric magnetic field into the corona, we
  find that the magnetic field lines in moss-associated magnetic plages
  connect with adjacent plages with opposite polarity; however, all field
  lines from mossless plages end in surrounding `quiet regions'. This
  result is consistent with the idea that the TRACE moss is the emission
  from the upper transition region due to heating of low-lying plasma
  by field-aligned thermal conduction from overlying hot plasma (Berger
  et al., 1999).

---------------------------------------------------------
Title: Helioseismic diagnostics of solar convection and activity. Part
    1, 2. Proceedings. SOHO-9 Workshop, Stanford, CA (USA), 12 - 15
    Jul 1999.
Authors: Švestka, Z.; Harvey, J. W.; Kosovichev, A. G.; Duvall,
   T. L., Jr.
2000SoPh..192....1S    Altcode:
  The following topics were dealt with: theories of solar convection,
  rotation and activity, helioseismic tomography, acoustic imaging and
  holography, ring-diagram analysis, magnetic fields and oscillations,
  solar cycle variations of the internal structure and rotation, solar
  convective structures and oscillations.

---------------------------------------------------------
Title: Travel Time Sensitivity Kernels
Authors: Birch, A. C.; Kosovichev, A. G.
2000SoPh..192..193B    Altcode:
  We derive, following the standard first Born approximation approach
  used in the geophysics literature, an expression for the travel time
  perturbation caused by a perturbation to sound speed. In our simple
  model we employ a point source at one point and calculate the time
  taken for a wave packet created at the source to move to a second
  point. In the first Born approximation the travel time delay caused
  by a perturbation to the background model can be expressed as the
  integral over the whole sun of some function, called the travel time
  sensitivity kernel, multiplied by the perturbation. The sensitivity
  kernels are zero along the geometrical ray connecting the two points
  and have maximum weight in a tube around the ray; they are the solar
  equivalent of `the banana-doughnut' kernels discussed in the geophysics
  literature. Calculating sensitivity kernels that are more accurate
  than those derived from ray theory is important for the future of
  inversions done with time-distance helioseismology data as they will
  allow greater confidence in the results as well as increased resolution.

---------------------------------------------------------
Title: Time-Distance Inversion Methods and Results - (Invited Review)
Authors: Kosovichev, A. G.; Duvall, T. L. _Jr., Jr.; Scherrer, P. H.
2000SoPh..192..159K    Altcode:
  The current interpretations of the travel-time measurements in quiet
  and active regions on the Sun are discussed. These interpretations
  are based on various approximations to the 3-D wave equation such as
  the Fermat principle for acoustic rays and the Born approximation. The
  ray approximation and its modifications have provided the first view
  of the 3-D structures and flows in the solar interior. However, more
  accurate and computationally efficient approximations describing the
  relation between the wave travel times and the internal properties
  are required to study the structures and flows in detail. Inversion
  of the large three-dimensional datasets is efficiently carried
  out by regularized iterative methods. Some results of time-distance
  inversions for emerging active regions, sunspots, meridional flows and
  supergranulation are presented. An active region which emerged on the
  solar disk in January 1998, was studied from SOHO/MDI for eight days,
  both before and after its emergence at the surface. The results show
  a complicated structure of the emerging region in the interior, and
  suggest that the emerging flux ropes travel very quickly through the
  depth range of our observations. The estimated speed of emergence is
  about 1.3 km s<SUP>−1</SUP>. Tomographic images of a large sunspot
  reveal sunspot `fingers' - long narrow structures at a depth of about
  4 Mm, which connect the sunspot with surrounding pores of the same
  polarity.

---------------------------------------------------------
Title: Numerical Simulations of Oscillation Modes of the Solar
    Convection Zone
Authors: Georgobiani, D.; Kosovichev, A. G.; Nigam, R.; Nordlund,
   Å.; Stein, R. F.
2000ApJ...530L.139G    Altcode: 1999astro.ph.12485G
  We use the three-dimensional hydrodynamic code of Stein &amp; Nordlund
  to realistically simulate the upper layers of the solar convection zone
  in order to study physical characteristics of solar oscillations. Our
  first result is that the properties of oscillation modes in the
  simulation closely match the observed properties. Recent observations
  from the Solar and Heliospheric Observatory (SOHO)/Michelson Doppler
  Imager (MDI) and Global Oscillations Network Group have confirmed the
  asymmetry of solar oscillation line profiles, initially discovered
  by Duvall et al. In this Letter, we compare the line profiles in
  the power spectra of the Doppler velocity and continuum intensity
  oscillations from the SOHO/MDI observations with the simulation. We
  also compare the phase differences between the velocity and intensity
  data. We have found that the simulated line profiles are asymmetric
  and have the same asymmetry reversal between velocity and intensity
  as observed. The phase difference between the velocity and intensity
  signals is negative at low frequencies, and phase jumps in the vicinity
  of modes are also observed. Thus, our numerical model reproduces the
  basic observed properties of solar oscillations and allows us to study
  the physical properties which are not observed.

---------------------------------------------------------
Title: Helioseismic Waves and Magnetic Field Variations Induced by
    Solar Flares as Probes of Energy Transport Mechanisms
Authors: Zharkova, V. V.; Kosovichev, A. G.
2000ASPC..206...77Z    Altcode: 2000hesp.conf...77Z
  No abstract at ADS

---------------------------------------------------------
Title: Observation of Shock Waves Associated with Coronal Mass
    Ejections from SOHO/LASCO
Authors: Stepanova, T. V.; Kosovichev, A. G.
2000AdSpR..25.1855S    Altcode:
  Theoretical models of coronal mass ejections (CME) predict formation
  of shock waves in front of eruptive magnetic structures, loops and
  arches. These shock waves have been detected in the solar wind at large
  distances from the Sun. However, their observation at short distances in
  the solar corona has been difficult. We have attempted to identify the
  shocks in the LASCO data by comparing the radial intensity profiles in
  limb CMEs with a theoretical model (Stepanova and Kosovichev, 1993). We
  demonstrate that the shock scan be identified at least in some cases of
  CME of the simple loop-like geometry. The LASCO observations indicate
  a turbulent structure for the flows associated with the shocks. We
  have determined the velocity of such shocks and expanding loops and
  compared with our model. In most cases, the observed expansion speed
  was rather slow possibly meaning that no significant disturbances on
  the solar surface were involved in initiating the eruptions

---------------------------------------------------------
Title: Solar tomography
Authors: Kosovichev, A. G.; Duvall, T. L., Jr.
1999CSci...77.1467K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: New and Old Magnetic Fluxes at the Beginning of Solar Cycle 23
Authors: Benevolenskaya, E. E.; Hoeksema, J. T.; Kosovichev, A. G.;
   Scherrer, P. H.
1999ESASP.448...69B    Altcode: 1999ESPM....9...69B; 1999mfsp.conf...69B
  No abstract at ADS

---------------------------------------------------------
Title: Variations of Photospheric Magnetic Field Associated with
    Flares and CMEs
Authors: Kosovichev, A. G.; Zharkova, V. V.
1999SoPh..190..459K    Altcode:
  Using high-cadence magnetograms from the SOHO/MDI we have investigated
  variations of the photospheric magnetic field during solar flares
  and CMEs. In the case of a strong X-class flare of May 2, 1998, we
  have detected variations of magnetic field in a form of a rapidly
  propagating magnetic wave. During the impulsive phase of the flare we
  have observed a sudden decrease of the magnetic energy in the flare
  region. This provides direct evidence of magnetic energy release in
  solar flares. We discuss the physics of the magnetic field variations,
  and their relations to the Moreton Hα waves and the coronal waves
  observed by the EIT.

---------------------------------------------------------
Title: Structure and Dynamics of Interconnecting Loops and Coronal
    Holes in Active Longitudes
Authors: Benevolenskaya, Elena E.; Kosovichev, A. G.; Scherrer, P. H.
1999SoPh..190..145B    Altcode:
  Using SOHO/MDI and SOHO/EIT data we study properties and dynamics
  of interconnected active regions, and the relations between the
  photospheric magnetic fields and coronal structures in active longitudes
  during the beginning of solar cycle 23. The emergence of new magnetic
  flux results in appearance of new interconnecting loops. The existence
  of stable coronal structures strongly depends on the photospheric
  magnetic fluxes and their variations. We present some initial results
  for a complex of solar activity observed in April 1997, and discuss
  the role of reconnection in the formation of the interconnected loops
  and coronal holes.

---------------------------------------------------------
Title: Detection of Magnetic Wave Associated with Solar Flares and CME
Authors: Zharkova, V. V.; Kosovichev, A. G.
1999ESASP.446..755Z    Altcode: 1999soho....8..755Z
  Using high-cadence magnetograms from the SOHO/MDI we have investigated
  variations of the photospheric magnetic field during solar flares and
  CME. For most investigated events there was no significant change in
  the magnetic fields. However, in the case of a strong X-class flare
  we have detected a rapidly propagating magnetic wave. We discuss the
  physics of this new phenomenon, and its relation to the Moreton H-alpha
  waves and the coronal waves observed by the EIT.

---------------------------------------------------------
Title: Frequencies and splittings of low-degree acoustic modes:
    a comparison between MDI and GOLF observations
Authors: Bertello, L.; Henney, C. J.; Ulrich, R. K.; Varadi, F.;
   Kosovichev, A. G.; Roca Cortes, T.; Garcia, R. A.; Scherrer, P. H.
1999AAS...19410805B    Altcode:
  During the years 1996 through 1998 the MDI and GOLF experiments on the
  SOHO mission have provided unique and nearly uninterrupted sequences of
  helioseismic observations. This paper describes the analysis carried out
  on power spectra from 759 days of calibrated velocity signals provided
  by these two experiments. The time series investigated in this work are
  from 25 May, 1996 to 22 June, 1998. We report the results of frequency
  and splitting determination of low-degree (l &lt; 4) acoustic modes
  in the frequency range between 1.5 mHz and 4.0 mHz. The power spectrum
  estimation of the signals is performed using classical Fourier analysis
  and the line-profile parameters of the modes are determined by means of
  a maximum likelihood method. All parameters have been estimated using
  both symmetrical and asymmetrical line profile-fitting formula. The
  line asymmetry parameter of all modes with frequency higher than 2.0
  mHz is systematically negative and independent from l. This result is
  consistent with the fact that both MDI and GOLF data sets investigated
  in this paper are predominantly velocity signals. A comparison of the
  results between symmetric fit and asymmetric one shows that there
  is a systematic shift in the eigenfrequencies for modes above 2.0
  mHz. The results show that eigenfrequency and rotational splitting
  values obtained from both the MDI and GOLF signals are in excellent
  agreement, and no significant differences exist between the two data
  sets within the indetermination of the measurement.

---------------------------------------------------------
Title: Frequencies and splittings of low-degree acoustic modes:
    a comparison between MDI and GOLF observations.
Authors: Bertello, L.; Henney, C. J.; Ulrich, R. K.; Varadi, F.;
   Kosovichev, A. G.; Roca Cortes, T.; Garcia, R. A.; Scherrer, P. H.
1999BAAS...31.1242B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Oscillations in Active Regions - Diagnostics and Seismology
Authors: Kosovichev, A. G.
1999ASPC..184..151K    Altcode:
  Oscillations in solar active regions provide a unique tool for
  probing the structure and dynamics of the active regions in the
  solar interior. The oscillations are excited stochastically by
  turbulent convection and also by strong localized events, such as
  flares. Oscillation power maps of stochastically excited waves show
  a deficit of acoustic power in the frequency range 2-5 mHz, and
  enhanced power at higher frequencies. These power variations are
  stronger in regions with stronger magnetic field, and, probably,
  are due to transformation of lower-frequency acoustic waves into
  higher-frequency MHD waves. An impulsive excitation event was observed
  as a result of a solar flare on July 9, 1996, from SOHO/MDI. The
  amplitude of the seismic waves on the surface was sufficiently high
  to determine the characteristics of the energy and momentum impact,
  and also to construct time-distance diagrams of the seismic response
  and to detect the deviation from the axial symmetry. This deviation
  probably resulted from the interaction with sunspots. Thus, in
  principle, the flare seismic waves can be used to probe the structure
  of active regions by time-distance helioseismology. The current
  methods of seismic diagnostics, acoustic imaging and time-distance
  tomography, are based on accumulating the seismic signal by averaging
  stochastically excited waves over a period of several hours. These
  methods have provided interesting information about the structure and
  evolution of active regions in the Sun's interior. As an example, I
  present the results of acoustic imaging of sunspots, and helioseismic
  tomography for large-scale imaging of active complexes of January 1991,
  and for an active region which emerged near the center of the solar
  disk in July 1996 and which studied from SOHO/MDI for nine days, both
  before and after its emergence at the surface. The initial results
  show complicated structures of the emerging regions in the interior,
  and suggest that the emerging flux ropes travel very quickly through
  the depth range of these observations.

---------------------------------------------------------
Title: Inversion methods in helioseismology and solar tomography.
Authors: Kosovichev, A. G.
1999JCoAM.109....1K    Altcode:
  Basic methods by which the internal structure and dynamics of the
  Sun can be inferred from observed frequencies of solar oscillations
  and acoustic travel times are discussed. The methods for inverting
  the oscillation frequencies are based on a variational formulation of
  the adiabatic eigenvalue problem for a star. The inversion technique
  formulated in terms of linear integral constraints provides estimates
  of localized averages of properties of the solar structure, such as
  density and sound speed, helium abundance in the convection zone for
  a given equation of state, and, in addition, the estimates for the
  internal rotation rate. The method of inverting acoustic travel times
  employs a geometrical ray approximation and provides 3D images of
  solar convective cells, active regions and sunspots. The information
  about the global and local structures and flow velocities in the solar
  interior is important for understanding solar evolution and mechanisms
  of solar activity. The high-resolution helioseismology projects from
  space provide a tremendous amount of data, the interpretation of which
  is increasingly challenging and requires the development of efficient
  inversion methods and algorithms.

---------------------------------------------------------
Title: The Interaction of New and Old Magnetic Fluxes at the Beginning
    of Solar Cycle 23
Authors: Benevolenskaya, E. E.; Hoeksema, J. T.; Kosovichev, A. G.;
   Scherrer, P. H.
1999ApJ...517L.163B    Altcode: 1999astro.ph..3404B
  The 11 yr cycle of solar activity follows Hale's law by reversing
  the magnetic polarity of leading and following sunspots in bipolar
  regions during the minima of activity. In the 1996-1997 solar minimum,
  most solar activity emerged in narrow longitudinal zones--“active
  longitudes” but over a range in latitude. Investigating the
  distribution of solar magnetic flux, we have found that the Hale
  sunspot polarity reversal first occurred in these active zones. We have
  estimated the rotation rates of the magnetic flux in the active zones
  before and after the polarity reversal. Comparing these rotation rates
  with the internal rotation inferred by helioseismology, we suggest
  that both “old” and “new” magnetic fluxes were probably generated
  in a low-latitude zone near the base of the solar convection zone. The
  reversal of active region polarity observed in certain longitudes at the
  beginning of a new solar cycle suggests that the phenomenon of active
  longitudes may give fundamental information about the mechanism of
  the solar cycle. The nonrandom distribution of old-cycle and new-cycle
  fluxes presents a challenge for dynamo theories, most of which assume
  a uniform longitudinal distribution of solar magnetic fields.

---------------------------------------------------------
Title: Imaging of Emerging Magnetic Flux by Time-Distance
    Helioseismology
Authors: Kosovichev, A. G.; Duvall, T. L., Jr.; Scherrer, P. H.
1999AAS...194.5901K    Altcode: 1999BAAS...31..917K
  We have used measurements of acoustic travel time in the convection
  zone to infer local perturbations of the sound speed and 3D flow
  velocities associated with emerging active regions in July 1996 and
  January 1998. Both regions were observed with the MDI instrument on
  SOHO before and after emergence continuously for 9 days. The first
  active region emerged in a long-lived complex of activity and produced
  a strong X-class flare. The second active region was a high-latitude
  region of the new solar cycle. The time-distance inversion results show
  complicated dynamics of the magnetic flux in the convection zone, and
  indicate that the emerging flux travels faster in the convection zone
  than predicted by theory. We discuss the differences in the dynamics
  of these active regions.

---------------------------------------------------------
Title: Solar Internal Rotation as Measured by the SOHO SOI/MDI
    Full-Disk Program
Authors: Rhodes, E. J., Jr.; Reiter, J.; Kosovichev, A. G.; Schou,
   J.; Scherrer, P. H.
1999AAS...194.5602R    Altcode: 1999BAAS...31..911R
  We present estimates of the solar internal angular velocity obtained
  from p-mode frequency splittings computed from observations of the
  SOHO SOI/MDI Experiment's Full-Disk Program. Specifically, a time
  series of full-disk Dopplergrams which was obtained during the 61-day
  long 1996 Dynamics Run of the SOI/MDI Experiment were converted into
  time series of spherical harmonic coeffificients for degrees ranging
  up to 1000. These time series of spherical harmonic coefficients
  were then converted into 1001 sets of zonal, sectoral, and tesseral
  power spectra. Estimates of the rotationally-induced p-mode frequency
  splittings for every degree between 1 and 1000 were then obtained from
  these sets of power spectra through a cross-correlation of the 2l+1
  spectra within each set. Because this cross-correlation was carried
  out between the frequency limits of 1800 to 4800 mu Hz for each set
  of spectra, the resulting splitting coefficients were effectively
  averaged over the radial order, n, at each degree. Due to the blending
  of individual p-mode spectral peaks for degrees above 200, the raw
  frequency splitting coefficients for all degrees between 200 and 1000
  had to be corrected before an inversion could be performed. We will
  describe the method we adopted for correcting the raw splittings and
  we will present both the raw and corrected splitting coefficients. We
  will also present a two-dimensional inversion of the corrected
  coefficients. Finally, we will also demonstrate how the inclusion of
  the high-degree splittings allows us to obtain better estimates of the
  solar internal angular velocity in the shallow sub-photospheric part
  of the solar convection zone than have been possible in past studies
  which included only the splittings of the low- and intermediate-degree
  p-modes.

---------------------------------------------------------
Title: The SOI-MDI Dynamics Program: Observing the Solar Cycle
Authors: Bush, R. I.; Beck, J. G.; Bogart, R. S.; Hoeksema, J. T.;
   Kosovichev, A. G.; Scherrer, P. H.; Schou, J.; Sommers, J.; Duvall,
   T. L.
1999AAS...194.9205B    Altcode: 1999BAAS...31..987B
  The Michelson Doppler Imager instrument on the SOHO spacecraft has been
  observing the Sun over the last three years. The MDI Dynamics Program
  provides nearly continuous full disk Doppler measurements of the solar
  photosphere with 4 arc-second resolution for periods of 60 to 90 days
  each year. Three of these Dynamics periods have been completed: 23 May
  to 24 July 1996, 13 April to 14 July 1997, 9 January to 10 April 1998. A
  fourth Dynamics observing period began on 13 March and is scheduled to
  continue through mid July. These observations provide a unique view
  of the evolution of the Sun in the early part of the solar cycle,
  both from interior flows deduced by helioseimic analysis and changes
  in large scale surface motion. Details of the Dynamics programs will
  be presented along with an overview of current results. This research
  is supported by the SOI-MDI NASA grant NAG5-3077 at Stanford University.

---------------------------------------------------------
Title: SONAR - Solar Near-surface Active Region Rendering
Authors: Scherrer, P. H.; Hoeksema, J. T.; Kosovichev, A. G.; Duvall,
   T. L.; Schrijver, K. J.; Title, A. M.
1999AAS...194.7606S    Altcode: 1999BAAS...31Q.957S
  The processes in the top 20,000-km of the Sun's convection zone govern
  the growth and decay of active regions and provide the magnetic flux and
  energy for the active phenomena of the upper solar atmosphere. The MDI
  experiment on SOHO has demonstrated that this region is now accessible
  to study by means of local helioseismology. However, SOHO provides
  neither the temporal nor spatial resolution and coverage necessary
  to exploit these techniques to study the eruption and evolution of
  active region magnetic structures. The SONAR mission with moderate
  resolution full disk Doppler and vector magnetic field observations,
  and atmospheric magnetic connectivity observations via EUV imaging
  can provide the necessary data. The science motivation and general
  instrumentation requirements for the mission are presented.

---------------------------------------------------------
Title: Three-dimensional simulations of solar oscillations: line
    profiles and asymmetries
Authors: Georgobiani, D. G.; Nigam, R.; Kosovichev, A. G.; Stein,
   R. F.; Nordlund, A.
1999AAS...194.5605G    Altcode: 1999BAAS...31..912G
  In order to study spectral characteristics of the solar oscillations,
  we use the Stein-Nordlund 3d hydrodynamic code to generate lond
  temporal sequencies of realistically simulated upper layers of the
  solar convective zone. The simulation domain ranges from 0.5 Mm above
  the surface of tau =1 to 2.5 Mm below this surface, and is 6 Mm by
  6 Mm wide. We have generated 24 hours of solar time. We calculate
  power spectra of the vertical velocity and temperature at different
  heights and the emergent intensity at the surface. Here, we present the
  profiles of velocity, intensity and temperature for both radial (l = 0)
  and first nonradial (l = 700) mode. We compare line profiles from the
  simulation with the power spectra of the Doppler velocity and continuum
  intensity from the SOHO/MDI observations. Both simulated and observed
  profiles demonstrate similar types of asymmetry, and the asymmetry
  reversal between the local quantities like velocity and temperature, and
  emergent intensity profiles is also present in the simulated data. The
  preliminary results are promising as they allow us to establish a
  connection between the observational data and realistic simulations,
  and enable us to understand better the physics of solar oscillations.

---------------------------------------------------------
Title: New Views of Active Regions
Authors: Duvall, T. L., Jr.; Kosovichev, A. G.; Scherrer, P. H.
1999AAS...194.4203D    Altcode: 1999BAAS...31..882D
  3-d acoustic tomography of the region below the photosphere is providing
  qualitatively new insights about solar active regions. This tomography
  is based on the measurement of travel times between different surface
  locations and is sensitive to subsurface flows and to wave-speed
  inhomogeneities caused by temperature and magnetic field variations. A
  flow cell has been seen below sunspots similar to the model of Parker
  (Ap.J. 230,905-913,1979) in which there is a horizontal inflow near
  the top of the convection zone, a downflow directly below the sunspot
  and a horizontal outflow below. This flow may be what stabilizes the
  sunspot. A wave-speed reduction is seen in the 2 Mm below the surface
  sunspot and a wave-speed enhancement is seen below to at least 10 Mm
  depth for a reasonably large spot. At 10 Mm depth, a wave-speed increase
  of 3% could be caused by a 10 kG magnetic field or a temperature
  excess of 6%. At present we cannot distinguish between temperature
  and magnetic field effects on the wave speed, but we will present a
  comparison between the wave speed as predicted from a sunspot model
  and that measured with the tomography. This research is supported by
  NASA contract NAG5-3077 at Stanford University.

---------------------------------------------------------
Title: Instability of Nonadiabatic Oscillations in a Magnetized
    Polytrope
Authors: Birch, A. C.; Kosovichev, A. G.; Spiegel, E. A.; Tao, L.
1999AAS...194.9307B    Altcode: 1999BAAS...31S.989B
  We apply linear stability analysis to a stratified plane parallel
  perfectly conducting atmosphere with a vertical magnetic field and
  Newton's law of cooling. For the case of a polytropically stratified
  atmosphere we find that there are overstable modes. The instability is
  due to the background temperature gradient combined with the cooling. We
  show perturbation results for the case of the cooling time much longer
  or much shorter than the oscillation period. Numerical calculations of
  the dispersion relations are shown for the weak and strong magnetic
  field cases, for long and short cooling times, and for polytrope
  and isothermal atmospheres. Generically the k-omega diagrams show a
  complicated pattern of avoided crossings. The damping or growth rates
  in general show features where branches undergo avoided crossings. The
  results, in particular the existence of overstable modes in the
  polytrope atmosphere, may be significant to the investigation of MHD
  phenomena in solar and stellar atmospheres, for example solar spicules.

---------------------------------------------------------
Title: A New Technique for Inversion of Helioseismic Data
Authors: Larsen, R. M.; Kosovichev, A. G.; Schou, J.
1999AAS...194.5604L    Altcode: 1999BAAS...31..912L
  Inversions of rotational frequency splittings derived from helioseismic
  data obtained by the MDI instrument and the GONG network have given a
  detailed picture of the differential rotation in the convection zone
  (Schou et al. 1998). However, features associated with sharp gradients
  of the rotation rate such as jets, near surface shear layers (torsional
  oscillations) as well as the transition layer to the radiative interior
  (the "tachocline") are usually not well resolved. This is due to the
  smoothing applied by traditional inversion methods such as Regularized
  Least Squares (RLS) and Optimally Localized Averages (OLA). In this work
  we show how a generalized version of the method proposed by Thompson
  (1990) can used be to study these features by inverting directly
  for the radial or latitudinal derivative of the rotation rate. This
  research is supported by the SOI-MDI NASA grant NAG5-3077 at Stanford
  University. References: G.I. Marchuk, Methods of Numerical Mathematics,
  New York, Springer-Verlag, 1975. Schou, J. et al., 1998, Astrophys J.,
  505, 390. Thompson, M. J., 1990, Sol. Phys., 125, 1.

---------------------------------------------------------
Title: The Magnetic Structure of the Sun at the Beginning of Solar
    Cycle 23
Authors: Benevolenskaya, E. E.; Hoeksema, J. T.; Kosovichev, A. G.;
   Scherrer, P. H.
1999AAS...194.9201B    Altcode: 1999BAAS...31R.986B
  The 11-year cycle of solar activity follows Hale's law by reversing the
  magnetic polarity of leading and following sunspots in bipolar regions
  during the minima of activity. In the 1996-97 solar minimum, most solar
  activity emerged in narrow longitudinal zones - `active longitudes'
  but over a range in latitude. Investigating the distribution of solar
  magnetic flux, we have found that the Hale sunspot polarity reversal
  first occurred in these active zones. We have estimated the rotation
  rates of the magnetic flux in the active zones before and after the
  polarity reversal. Comparing these rotation rates with the internal
  rotation inferred by helioseismology, we suggest that both `old' and
  `new' magnetic fluxes were probably generated in a low-latitude zone
  near the base of the solar convection zone. The reversal of active
  region polarity observed in certain longitudes at the beginning of
  a new solar cycle suggests that the phenomenon of active longitudes
  may give fundamental information about the mechanism of the solar
  cycle. The non-random distribution of old-cycle and new-cycle fluxes
  presents a challenge for dynamo theories, most of which assume a
  uniform longitudinal distribution of solar magnetic fields. We have
  used accurate measurements of solar oscillation frequencies from the
  GONG and SOHO/MDI to infer the latitudinal dependence of the solar
  structure associated with magnetic fields beneath the surface. The
  results show significant variations of the aspherical structure of
  the Sun at the beginning of the new cycle. These variations correlate
  with the latitudinal distribution of the surface magnetic flux. We
  discuss possible variations at the base of the convection zone and
  their relation to the dynamo mechanism.

---------------------------------------------------------
Title: Subsurface Observations of Sunspots and Solar Supergranulation
Authors: Duvall, T. L., Jr.; Kosovichev, A. G.; Scherrer, P. H.
1999AAS...194.5606D    Altcode: 1999BAAS...31..912D
  3-d acoustic tomography of the region below the photosphere is providing
  new insights into sunspots and the apparently convective flow observed
  at the surface called supergranulation. The tomography is based on
  the measurement of travel times between different surface locations
  and is sensitive to subsurface flows and to wave-speed inhomogeneities
  caused by temperature and magnetic field variations. This study uses
  dopplergrams from the MDI instrument on the SOHO spacecraft. A flow
  cell has been seen below sunspots similar to the model of Parker
  (Ap.J. 230,905-913,1979) in which there is a horizontal inflow near
  the top of the convection zone, a downflow directly below the sunspot
  and a horizontal outflow below. The depth of the supergranulation
  flow will be discussed. This research is supported by NASA contract
  NAG5-3077 at Stanford University.

---------------------------------------------------------
Title: The Global View of the Solar Interior
Authors: Kosovichev, A. G.
1999AAS...194.4201K    Altcode: 1999BAAS...31Q.882K
  The Michelson Doppler Imager (MDI) instrument on SOHO, GONG and other
  space and ground-based helioseismic experiments provide a unique
  opportunity for continuous monitoring of the internal structure
  and dynamics of the Sun. The new data reveal spatial and temporal
  complexity of internal phenomena such as mixing beneath the base
  of the convection zone, the subsurface zonal and meridional flows,
  sound-speed asphericity, polar vortex and others. The exploration of
  these phenomena by helioseismology is important for understanding the
  physics of our nearest star. I discuss progress in the diagnostics
  of the solar interior, based on 2 years of MDI and 4 years of GONG
  observations. Accurately measured frequencies of solar oscillation
  modes have provided detailed information about rotation and structure
  in the radiative core, the transition region between the convective and
  radiative zones and the upper convective boundary layer. Substantial
  progress has been made in achieving better latitudinal and radial
  resolution in structure and rotation inversions. In addition, new
  information about the turbulent convection and internal magnetic
  field is obtained from f-mode data. Further progress in helioseismology
  crucially depends on understanding the physics of solar oscillations, in
  particular, the properties of modal lines and ridges in the oscillation
  power spectra.

---------------------------------------------------------
Title: Source of Solar Acoustic Modes
Authors: Nigam, R.; Kosovichev, A. G.
1999ApJ...514L..53N    Altcode:
  Solar acoustic modes are found to be excited in a thin superadiabatic
  layer of turbulent convection (about 75+/-50 km below the photosphere)
  beneath the Sun's surface. Comparing the theoretical power spectra
  of both velocity and pressure oscillations of medium angular degree
  with that obtained from the Michelson Doppler Imager instrument on
  board the Solar and Heliospheric Observatory, we find that a composite
  source consisting of a monopole, which corresponds to mass or entropy
  fluctuations, and a quadrupole, which consists of the Reynolds stress,
  excites these oscillations. The dominant source is of a monopole
  type since it provides the best match to the observed velocity and
  intensity oscillation power spectra. For the above source to match the
  observed asymmetry in intensity, a part of the background is found to be
  correlated with the pressure perturbation. The sign of the correlation
  is found to be negative, which suggests that there is photospheric
  darkening prior to the occurrence of the localized acoustic event,
  in agreement with the previous finding of P. R. Goode and coworkers.

---------------------------------------------------------
Title: Computing 3 D Dynamo Models with Observed Solar Data
Authors: Franklin, Joel; Kosovichev, Alexander
1999soho....9E..57F    Altcode:
  We look at finite difference approaches to the three dimensional
  solar dynamo problem using differential rotation and diffusivity data
  from observation. As a model problem to test the finite difference
  formulation and code, we attempt to numerically solve the axisymmetric,
  2 D induction equations with alpha-effect.

---------------------------------------------------------
Title: Phase and Amplitude Difference between Velocity and Intensity
    Helioseismic Spectra
Authors: Nigam, R.; Kosovichev, A. G.
1999ApJ...510L.149N    Altcode:
  An explanation for the phase and amplitude difference between velocity
  and intensity oscillations of the Sun is provided. The phase difference
  along the modal lines in the power spectra was originally observed
  by Deubner and coworkers in 1989. From a simple adiabatic theory of
  solar oscillations, one expects this phase difference to be 90° for
  modes below the acoustic cutoff frequency (bound states) and zero for
  modes above the acoustic cutoff frequency (scattered states). But,
  surprisingly, from observations, the bound states show a phase
  difference that is below 90° along modal lines, and the scattered
  states also show a nonzero phase difference. We compute the phase
  difference between the velocity and intensity oscillations using
  medium angular degree data obtained from the Michelson Doppler Imager
  instrument on board the Solar and Heliospheric Observatory and confirm
  Deubner's result. We conclude that the unusual phase characteristics
  of the solar oscillations can be attributed to the fact that a part of
  the background is correlated to the source responsible for exciting
  the waves. The idea of the correlated background also explains why
  the high-frequency modes above the acoustic cutoff frequency are
  stronger in intensity than in the velocity power spectrum relative to
  the uncorrelated background, while at frequencies below the acoustic
  cutoff the velocity power relative to the uncorrelated background
  is stronger compared to the intensity. In addition, this explains
  the relative shift of the maxima in the velocity and intensity
  high-frequency power spectra.

---------------------------------------------------------
Title: Helioseismic Diagnostics of Solar Convection and Activity
Authors: Duvall, T. L., Jr.; Kosovichev, A. G.
1999soho....9E....D    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Time-distance helioseismology
Authors: Kosovichev, A. G.; Duvall, T. L.; Scherrer, P. H.
1999AdSpR..24..163K    Altcode:
  The time-distance helioseismology (or helioseismic tomography) is a new
  promising method for probing 3-D structures and flows beneath the solar
  surface, which is potentially important for studying the birth of active
  regions in the sun's interior and for understanding the relation between
  the internal dynamics of active regions and chromospheric and coronal
  activity. In this method, the time for waves to travel along subsurface
  ray paths is determined from the temporal cross correlation of signals
  at two separated surface points. By measuring the times for many
  pairs of points from Dopplergrams covering the visible hemisphere, a
  tremendous quantity of information about the state of the solar interior
  is derived. As an example, we present the results for supergranular
  flows and for an active region which emerged near the center of the
  solar disk in July 1996, and was studied from SOHO/MDI for nine days,
  both before and after its emergence at the surface. Initial results
  show a complicated structure of the emerging region in the interior,
  and suggest that the emerging flux ropes travel very quickly through
  the depth range of our observations.

---------------------------------------------------------
Title: The Effect of Line-of-Sight Projection on Travel Time
    Measurements
Authors: Birch, A. C.; Kosovichev, A. G.
1999soho....9E..44B    Altcode:
  We calculate the theoretical cross-correlation between line-of-sight
  velocity signals derived from a spherically symmetric model
  sun. The vertical and horizontal velocity eigenfunctions combined
  with line-of-sight projection are included in the model. We show
  that the travel time between two points depends not only on their
  separation but also on their positions on the disk, as a result of
  the correlation between the projections of the horizontal and radial
  velocities. Variations of up to a minute in the travel time can occur
  at separations on order of the solar radius. This apparent travel time
  perturbation may be important in time-distance investigations of the
  structure of the base of the convection zone and other problems. This
  research is supported by NASA grant NAG5-3077 at Stanford University.

---------------------------------------------------------
Title: Solar P-Mode Spectrum Asymmetries: Testing Theories With
    Numerical Simulations
Authors: Georgobiani, Dali; Nigam, Rakesh; Kosovichev, Alexander G.;
   Stein, Robert F.
1999soho....9E..58G    Altcode:
  We use a 36 hour sequence of 3-D hydrodynamic simulations of solar
  convection to study the line profiles of the acoustic modes and their
  asymmetries. We construct power spectra of the emergent intensity
  and the vertical velocity at a fixed height of 200 km above the t = 1
  surface, as well as their phase differences. We compare the synthetic
  results with those obtained from the SOHO/MDI observations. The
  simulations and observations show similar direction of asymmetry
  and reversal of asymmetry between the velocity and intensity. Our
  preliminary results confirm the theoretical model of Nigam (Nigam et
  al. 1998). To make the simulation results more realistic, the intensity
  and velocity will in future be obtained from the synthetic NiI 6768
  line used in the observations.

---------------------------------------------------------
Title: Helioseismic Studies of the Solar Tachocline
Authors: Larsen, R. M.; Kosovichev, A. G.; Schou, J.
1999soho....9E..69L    Altcode:
  Accurate determinations of the depth and width of the solar tachocline
  provide important observational constraints on theoretical models of
  solar convection and the solar dynamo, which drives the Sun's magnetic
  field. We present the tachocline parameters obtained from inversions
  of frequency splittings from MDI, GONG and LOWL and compare this with
  previously published results. Finally we invert frequency splittings
  for individual GONG months and a number of 72 days sets from MDI, in
  order to see if any variation can be seen in the tachocline parameters
  with the solar cycle. Briefly, our method consists in inverting
  the frequency splittings directly for the radial derivative of the
  solar rotation rate using a full 2D SOLA technique. Subsequently the
  radial derivative of a parametric model of the rotation profile in
  the tachocline is convolved with the averaging kernels from the SOLA
  inversion, and the parameters in the models are adjusted to obtain a
  chi-squared fit of the model to the inversion result. This research
  is supported by NASA grant NAG5-3077 at Stanford University.

---------------------------------------------------------
Title: Time-Distance Inversion Methods and Results
Authors: Kosovichev, A. G.
1999soho....9E..20K    Altcode:
  The current interpretations of the travel-time measurements in quiet
  and active regions on the Sun will be discussed. These interpretations
  are based on various approximations to the 3D wave equation such as the
  Fermat principle for acoustic rays and the Born approximation. The ray
  approximation and its modifications have provided the first view of the
  3-D structures and flows in the solar interior. However, more accurate
  and computationally efficient approximations describing the relation
  between the wave travel times and the internal properties are required
  to study the structures and flows in detail. Inversion of the large
  three-dimensional datasets can be efficiently carried out by regularized
  iterative methods. The results of time-distance inversions for emerging
  active regions, sunspots and supergranulation will be presented. This
  research is supported by NASA contract NAG5-3077 at Stanford University.

---------------------------------------------------------
Title: Latitudinal Variation of Solar Subsurface Rotation
Authors: Kosovichev, A. G.; Birch, A. C.
1998AAS...19310004K    Altcode: 1998BAAS...30Q1397K
  Analysis of p-mode frequency splittings as measured by the Solar
  Oscillations Investigation-Michelson Doppler Imager (SOI-MDI) on board
  the Solar and Heliospheric Observatory (SOHO) and the ground-based
  Global Oscillations Network Group (GONG) experiment reveals that the
  symmetric component of the solar rotation rate, radially averaged
  over the upper 28 Mm of the convection zone and closer than 15 deg
  to the poles, is roughly 310 nHz (corresponding to a period of 37.3
  days), which is slower than the 320 nHz (corresponding to a period
  of 36.2 days) estimated from surface measurements. The slow polar
  rotation is sometimes interpreted as a polar vortex and is important
  for understanding solar dynamics. In addition, zonal flows, previously
  inferred from the SOI-MDI f-mode splittings, are seen with both SOI-MDI
  and GONG p-mode splittings. The GONG data provide strong support for
  the findings of Schou and colleagues. We discuss possible physical
  mechanisms for the slow rotation of the polar regions.

---------------------------------------------------------
Title: A Nonlinear Model for Solar Spicules
Authors: Birch, A. C.; Spiegel, E. A.; Tao, L.; Kosovichev, A. G.
1998AAS...19310001B    Altcode: 1998BAAS...30.1397B
  We develop a weakly nonlinear theory for the growth of optically thin
  perturbations to a plane-parallel chromosphere-like layer described
  by the MHD equations in an attempt to explain the dynamics of solar
  spicules. Damping of the perturbations is by Newton's law of cooling
  and the magnetic field is assumed to be vertical. The theory leads to
  a nonlinear PDE that describes the time evolution of perturbations to
  the layer. Numerical results are presented.

---------------------------------------------------------
Title: Solar Cycle Onset Seen in SOHO Michelson Doppler Imager
    Seismic Data
Authors: Dziembowski, W. A.; Goode, P. R.; di Mauro, M. P.; Kosovichev,
   A. G.; Schou, J.
1998ApJ...509..456D    Altcode:
  We have analyzed time changes in centroid frequencies and multiplet
  frequency splittings of solar oscillations determined with the Michelson
  Doppler Imager instrument (MDI) on SOHO. The data were divided into
  five consecutive 72 day sets covering the period from 1996 May 1
  through 1997 April 25. We have detected a significant trend in the
  a<SUB>4</SUB> and a<SUB>6</SUB> frequency splitting coefficients,
  which reflects a decrease in the P<SUB>4</SUB> distortion (described by
  the fourth-degree Legendre polynomial of colatitude) and an increase
  in the P<SUB>6</SUB> distortion. The rise of the latter distortion
  seems to coincide precisely with the rise in the number of new cycle
  sunspots. Such sharp and detailed clues to activity onset are new and do
  not exist in splitting data from the rising phase of the last cycle. The
  relative differences among the solar radii inferred from the f-mode
  frequencies from the five sets (at most 6 × 10<SUP>-6</SUP> or 4 km)
  are formally significant, reaching a minimum during the observed period.

---------------------------------------------------------
Title: The Source of Solar Oscillations
Authors: Nigam, R.; Kosovichev, A. G.
1998AAS...19310002N    Altcode: 1998BAAS...30.1397N
  In this study the role of line asymmetry and phase difference between
  velocity and intensity helioseismic spectra for understanding the
  excitation of solar oscillations is discussed. The solar intensity
  and velocity oscillations are usually observed from variations in
  an absorption line. These variations consist of two parts: solar
  oscillation modes and granulation noise. Because the oscillation
  modes are excited by granulation, we argue that the granulation signal
  (noise) is partially correlated with the oscillations. The data from
  the Michelson Doppler Imager (MDI) instrument on board the Solar and
  Heliospheric Observatory (SOHO) have clearly revealed a reversal of
  asymmetry between velocity and intensity power spectra. We have shown
  that the cause of reversal in asymmetry between velocity and intensity
  power spectra is due to the presence of the correlated noise in the
  intensity data. This noise is also responsible for the high-frequency
  shift in the two spectra at and above the acoustic cutoff frequency. Our
  theory also explains the deviation of the observed phase difference
  between velocity and intensity from that predicted by simple adiabatic
  theory of solar oscillations. The observed phase, jumps in the vicinity
  of an eigenfrequency, but theory does not explain such jumps. We
  studied different types of excitation sources at various depths and
  found that monopole and quadrupole acoustic sources when placed in the
  superadiabatic layer (at a depth of 75 km below the photosphere) match
  the observations. For these source types, the sign of the correlation is
  negative corresponding to photospheric darkening. Finally, an asymmetric
  fitting formula is used to determine the eigenfrequencies of solar
  oscillations by fitting both the velocity and intensity power spectra.

---------------------------------------------------------
Title: Asymmetry and Frequencies of Low-Degree p-Modes and the
    Structure of the Sun's Core
Authors: Toutain, T.; Appourchaux, T.; Fröhlich, C.; Kosovichev,
   A. G.; Nigam, R.; Scherrer, P. H.
1998ApJ...506L.147T    Altcode:
  An accurate determination of the frequencies of low-degree solar
  p-modes is an important task of helioseismology. Using 679 days of
  solar oscillation data observed in Doppler velocity and continuum
  intensity from two Solar and Heliospheric Observatory instruments
  (the Michelson Doppler Imager and the SunPhotoMeter), we show that
  fitting the spectra with Lorentzian profiles leads to systematic
  differences between intensity and velocity frequencies as large as
  0.1 μHz for angular degrees l=0, 1, and 2 because of the opposite
  asymmetry between intensity and velocity. We use a physics-based
  asymmetrical line shape to fit p-mode lines, and we demonstrate
  that their asymmetry is statistically significant and that frequency
  differences are considerably reduced. These measurements provide more
  accurate estimates of the solar eigenfrequencies. We discuss inferences
  of the structure of the solar core.

---------------------------------------------------------
Title: Helioseismic Studies of Differential Rotation in the Solar
    Envelope by the Solar Oscillations Investigation Using the Michelson
    Doppler Imager
Authors: Schou, J.; Antia, H. M.; Basu, S.; Bogart, R. S.; Bush,
   R. I.; Chitre, S. M.; Christensen-Dalsgaard, J.; Di Mauro, M. P.;
   Dziembowski, W. A.; Eff-Darwich, A.; Gough, D. O.; Haber, D. A.;
   Hoeksema, J. T.; Howe, R.; Korzennik, S. G.; Kosovichev, A. G.;
   Larsen, R. M.; Pijpers, F. P.; Scherrer, P. H.; Sekii, T.; Tarbell,
   T. D.; Title, A. M.; Thompson, M. J.; Toomre, J.
1998ApJ...505..390S    Altcode:
  The splitting of the frequencies of the global resonant acoustic modes
  of the Sun by large-scale flows and rotation permits study of the
  variation of angular velocity Ω with both radius and latitude within
  the turbulent convection zone and the deeper radiative interior. The
  nearly uninterrupted Doppler imaging observations, provided by the
  Solar Oscillations Investigation (SOI) using the Michelson Doppler
  Imager (MDI) on the Solar and Heliospheric Observatory (SOHO) spacecraft
  positioned at the L<SUB>1</SUB> Lagrangian point in continuous sunlight,
  yield oscillation power spectra with very high signal-to-noise ratios
  that allow frequency splittings to be determined with exceptional
  accuracy. This paper reports on joint helioseismic analyses of
  solar rotation in the convection zone and in the outer part of the
  radiative core. Inversions have been obtained for a medium-l mode set
  (involving modes of angular degree l extending to about 250) obtained
  from the first 144 day interval of SOI-MDI observations in 1996. Drawing
  inferences about the solar internal rotation from the splitting data
  is a subtle process. By applying more than one inversion technique
  to the data, we get some indication of what are the more robust
  and less robust features of our inversion solutions. Here we have
  used seven different inversion methods. To test the reliability and
  sensitivity of these methods, we have performed a set of controlled
  experiments utilizing artificial data. This gives us some confidence
  in the inferences we can draw from the real solar data. The inversions
  of SOI-MDI data have confirmed that the decrease of Ω with latitude
  seen at the surface extends with little radial variation through much
  of the convection zone, at the base of which is an adjustment layer,
  called the tachocline, leading to nearly uniform rotation deeper
  in the radiative interior. A prominent rotational shearing layer in
  which Ω increases just below the surface is discernible at low to
  mid latitudes. Using the new data, we have also been able to study the
  solar rotation closer to the poles than has been achieved in previous
  investigations. The data have revealed that the angular velocity
  is distinctly lower at high latitudes than the values previously
  extrapolated from measurements at lower latitudes based on surface
  Doppler observations and helioseismology. Furthermore, we have found
  some evidence near latitudes of 75° of a submerged polar jet which
  is rotating more rapidly than its immediate surroundings. Superposed
  on the relatively smooth latitudinal variation in Ω are alternating
  zonal bands of slightly faster and slower rotation, each extending
  some 10° to 15° in latitude. These relatively weak banded flows
  have been followed by inversion to a depth of about 5% of the solar
  radius and appear to coincide with the evolving pattern of “torsional
  oscillations” reported from earlier surface Doppler studies.

---------------------------------------------------------
Title: Random Damping and Frequency Reduction of the Solar F Mode
Authors: Duvall, T. L., Jr.; Kosovichev, A. G.; Murawski, K.
1998ApJ...505L..55D    Altcode:
  We present observations showing that the frequency of the high-degree
  f-mode is significantly lower than the frequency given by the simple
  dispersion relation, ω<SUP>2</SUP>=gk , and that the line width grows
  with the wavenumber k. We attempt to explain that this behavior is
  the result of the interaction with granulation, which we model as a
  random flow. Because the f-mode spends more time propagating against
  the flow than with the flow, its effective speed and, consequently,
  frequency are reduced. Additionally, an eddy viscosity introduces the
  negative imaginary part of frequency. This negative imaginary part
  represents the damping of the coherent field due to scattering. The
  line width is proportional to the magnitude of the imaginary part
  of the frequency. We apply an analytical perturbation technique and
  numerical methods to estimate the line width and the frequency shift,
  and we show that the results are consistent with the properties of the
  f-mode obtained from the high-resolution Michelson Doppler Imager data
  from the Solar and Heliospheric Observatory.

---------------------------------------------------------
Title: Measuring the Sun's Eigenfrequencies from Velocity and
Intensity Helioseismic Spectra: Asymmetrical Line Profile-fitting
    Formula
Authors: Nigam, R.; Kosovichev, A. G.
1998ApJ...505L..51N    Altcode:
  Solar eigenfrequencies are generally determined by fitting a Lorentzian
  to the spectral lines in the power spectrum. This assumes that the
  spectral line is symmetric. Recent observations from the Michelson
  Doppler Imager (MDI) on board the Solar and Heliospheric Observatory
  have indicated that the power spectra of p-modes show varying amounts
  of asymmetry. Line asymmetry is an intrinsic property of solar
  oscillations and depends on the properties of the excitation source
  and the background noise correlated with the oscillations. Neglecting
  asymmetry leads to systematic errors in the determination of frequencies
  and thus affects the results of inversions. In this Letter, we use a
  simple physical model to derive a new fitting formula that incorporates
  the effects of asymmetry. It is then tested on artificial and real
  solar MDI data. A comparison of the results of a symmetric fit with
  those of an asymmetric one shows that there is a systematic shift in
  the eigenfrequencies. Our formula will yield more accurate estimates
  of the solar eigenfrequencies, which is important for improving the
  accuracy of helioseismic inversions.

---------------------------------------------------------
Title: Latitudinal Variation of Solar Subsurface Rotation Inferred
    from p-Mode Frequency Splittings Measured with SOI-MDI and GONG
Authors: Birch, A. C.; Kosovichev, A. G.
1998ApJ...503L.187B    Altcode:
  Analysis of p-mode frequency splittings as measured by the Solar
  Oscillations Investigation-Michelson Doppler Imager (SOI-MDI) on
  board the Solar and Heliospheric Observatory and the ground-based
  Global Oscillations Network Group (GONG) experiment reveal that
  the symmetric component of the solar rotation rate in the upper 4%
  by radius and closer than 20° to the poles is approximately 10 nHz
  slower than would be expected from a three-term fit, of the form
  traditionally used to express the main components of latitudinal
  differential rotation, to the inferred subsurface rotation rate. The
  slow polar rotation is important for understanding solar dynamics. In
  addition, zonal flows, previously inferred from the SOI-MDI f-mode
  splittings by Kosovichev &amp; Schou, are seen with both SOI-MDI and
  GONG p-mode frequency splittings. These results were obtained with a
  one-dimensional latitudinal inversion technique that provides better
  angular resolution near the poles, at the expense of decreased radial
  resolution, than the standard two-dimensional inversions. Both of
  these findings confirm and extend the findings of Schou and colleagues
  (1998) from SOI-MDI data. The agreement found between the different
  helioseismic experiments, SOI-MDI and GONG, gives confidence in the
  current inferences of the differential rotation in the Sun's subsurface
  layers. The physics of the slow polar rotation is not understood yet.

---------------------------------------------------------
Title: The Adiabatic Exponent in the Solar Core
Authors: Elliott, J. R.; Kosovichev, A. G.
1998ApJ...500L.199E    Altcode:
  We present helioseismic inversions of solar p-mode frequencies
  obtained by the Michelson Doppler Imager instrument of the Solar
  Oscillation Investigation project on board SOHO, which indicate a
  lower central value for the adiabatic exponent Γ<SUB>1</SUB> in the
  Sun than in current models. We show how the inclusion of relativistic
  effects in the equation of state removes the discrepancy and allows
  almost perfect agreement in Γ<SUB>1</SUB> between the models and
  the Sun. This increases our confidence both in the reliability of the
  equation-of-state calculation and the determination of solar p-mode
  frequencies.

---------------------------------------------------------
Title: X-ray flare sparks quake inside Sun
Authors: Kosovichev, A. G.; Zharkova, V. V.
1998Natur.393..317K    Altcode:
  Solar flares involve a release of the Sun's magnetic energy as
  X-radiation, particle beams and high-speed plasma flows. But
  we have discovered, using data from the Solar and Heliospheric
  Observatory (SOHO), that these flares also affect the Sun's interior,
  generating seismic waves similar to earthquakes. For example, a
  three-kilometre-high seismic wave was caused by a moderate X-ray flare
  that occurred on 9 July 1996 and propagated at about 50 kilometres
  per second to a distance 120,000 kilometres from the flare site.

---------------------------------------------------------
Title: Initial High-Degree p-Mode Frequencies and Rotational Frequency
    Splittings from the SOHO SOI/MDI Experiment
Authors: Rhodes, E. J., Jr.; Reiter, J.; Kosovichev, A. G.; Schou,
   J.; Scherrer, P. H.
1998AAS...192.1901R    Altcode: 1998BAAS...30..845R
  We present the first high-degree p-mode frequencies and
  rotationally-induced frequency splittings obtained from the Full-Disk
  Program of the SOHO Solar Oscillation Investigation/Michelson
  Doppler Imager experiment. The frequencies and splittings which we
  present here were computed from power spectra obtained during the
  1996 SOI/MDI Dynamics Run. Specifically, a 60.75-day time series of
  full-disk Dopplergrams was converted into sets of zonal, tesseral,
  and sectoral power spectra covering the degree range of 0 through
  1000. Estimates of the n-averaged frequency splittings were computed
  for the frequency range of 1800 to 4800 microhertz at each degree and
  these averaged splitting coefficients were then employed to compute an
  average power spectrum for that degree. From these 1001 average power
  spectra estimates were made of the frequencies, frequency uncertainties,
  widths, peak power densities, and background power densities of a total
  of 13664 separate peaks in the set of 1001 average power spectra. A
  total of 2554 of these peaks were isolated enough in their respective
  spectra to be fit as single p-modes. However, for the remaining 11110
  peaks (mostly those above l =200), the individual p-mode peaks and
  their spatial sidelobes were located so close together in frequency
  that they appeared as ridges rather than as isolated modal peaks in the
  average power spectra. For these p-mode ridges we obtained so-called
  “ridge-fit” parameter estimates. Observed asymmetries in the p-mode
  ridge shapes altered the fitted peak frequencies from their “true”
  values and required that we correct the raw ridge-fit frequencies. Forty
  sets of these power spectra were also processed to yield estimates of
  the rotational splitting coefficients for individual p-mode ridges
  for every 25th degree between l =25 and 1000. For l between 25
  and 175 we will compare these Full-Disk program splittings with the
  previously-published splittings from the 1996 SOI/MDI Medium-l Program
  (Kosovichev et al., Solar Physics, 170, 43-61,1997).

---------------------------------------------------------
Title: Asymmetry in Velocity and Intensity Helioseismic Spectra:
    A Solution to a Long-standing Puzzle
Authors: Nigam, R.; Kosovichev, A. G.; Scherrer, P. H.; Schou, J.
1998ApJ...495L.115N    Altcode:
  We give an explanation for the opposite sense of asymmetry of the
  solar acoustic mode lines in velocity and intensity oscillation
  power spectra, thereby solving the half-decade-old puzzle of Duvall
  and coworkers. The solution came after comparing the velocity and
  intensity oscillation data of medium angular degree l obtained from the
  Michelson Doppler Imager instrument on board the Solar and Heliospheric
  Observatory with the theoretical power spectra. We conclude that the
  solar noise in the velocity and intensity spectra is made up of two
  components: one is correlated to the source that is responsible for
  driving the solar p-modes, and the other is an additive uncorrelated
  background. The correlated component of the noise affects the line
  profiles. The asymmetry of the intensity spectrum is reversed because
  the correlated component is of a sufficiently large level, while the
  asymmetry of the velocity spectrum remains unreversed because the
  correlated component is smaller. This also explains the high-frequency
  shift between velocity and intensity at and above the acoustic cutoff
  frequency. A composite source consisting of a monopole term (mass term)
  and a dipole term (force due to Reynolds stress) is found to explain
  the observed spectra when it is located in the zone of superadiabatic
  convection at a depth of 75+/-50 km below the photosphere.

---------------------------------------------------------
Title: Asymmetry and Fitting of Velocity and Intensity Power Spectra
    from SOHO/MDI
Authors: Nigam, R.; Kosovichev, A. G.
1998ESASP.418..945N    Altcode: 1998soho....6..945N
  The line profiles of solar modes show marked asymmetry at frequencies
  less than the acoustic cut-off frequency. Observations from the
  Michelson Doppler Imager instrument on board the Solar and Heliospheric
  Observatory have revealed a reversal of asymmetry between velocity
  and intensity power spectra of medium angular degree. We have
  argued that the cause of reversal in asymmetry between velocity and
  intensity power spectra is due to the presence of correlated noise,
  whose level happens to be more in the intensity data, hence reverses
  its asymmetry (Nigam et al., 1998). The correlated noise is also
  responsible for the high-frequency shift in the two spectra at and
  above the acoustic cut-off frequency. It is found that the asymmetry
  depends on the type and depth of the source that excites the solar
  acoustic modes. By studying line asymmetry an insight into the
  physics of excitation of solar oscillations can be gained. Finally,
  a fitting formula incorporating line asymmetry is developed. This
  is used to simultaneously fit the two spectra. For the theoretical
  spectra, the fits yield the same fitted frequency, which is close
  to the eigenfrequency computed from the solar model. The frequency
  corrections will have an impact on the inversions.

---------------------------------------------------------
Title: Observation of seismic effects of solar flares from the SOHO
    Michelson Doppler Imager
Authors: Kosovichev, A. G.; Zharkova, V. V.
1998IAUS..185..191K    Altcode:
  Solar flares are the most strong seismic localized disturbances on
  the solar surface. During the impulsive phase a high-energy electron
  beam heats the chromosphere, resulting in explosive evaporation of
  chromospheric plasma at supersonic velocities. This upward motion is
  balanced by recoil of the lower part of the chromosphere downward into
  the Sun that excites propagating waves in the solar interior. We report
  on first observations of the seismic effect of solar flares from the
  Michelson Doppler Imager (MDI) Dynamics data, and compare the results
  with theoretical models. Observations of seismic response to solar
  flares provide important information about the flare mechanism and
  about the subphotospheric structure of active regions.

---------------------------------------------------------
Title: The Comparison of Simultaneous SOI/MDI and Mt. Wilson 60-foot
    Tower Power Spectra and p-Mode Parameters
Authors: Rhodes, E. J., Jr.; Reiter, J.; Kosovichev, A. G.; Schou,
   J.; Scherrer, P. H.; Rose, P. J.; Irish, S.; Jones, A. R.
1998ESASP.418..311R    Altcode: 1998soho....6..311R
  We present the results of the first detailed comparison between the
  1996 SOHO SOI/MDI Dynamics Run program of full-disk Ni I Dopplergram
  observations and a simultaneous time series of ground-based
  observations obtained in the Na D lines at the 60-Foot Solar Tower
  of the Mt. Wilson Observatory (MWO). Specifically, we will compare
  sets of simultaneously-observed SOHO/MDI and MWO power spectra and
  the high-degree p-mode frequencies, frequency splittings, widths, and
  power densities which we obtained by fitting these two sets of power
  spectra. Beginning on May 23, 1996, the SOI/MDI experiment began its
  first high duty cycle run of 1024x1024 pixel images. this was the
  1996 Dynamics Run. On all but three of the days of this 60.75-day
  time series a second time series of simultaneous 1024x1024 pixel
  full-disk Dopplergrams was obtained at MWO. From these simultaneous MWO
  observations we have computed 601 sets of zonal, tesseral, and sectoral
  power spectra which covered the degree range of 0 to 600. These sets
  of power spectra were then analyzed in two different ways to yield
  both frequencies and frequency splittings. First, estimates of the
  frequency splittings were computed for the frequency range of 1800 to
  4800 microhertz at each degree and these n-averaged splittings were
  employed to compute an average power spectrum for that degree. Estimates
  were then made of the frequencies, frequency uncertainties, widths, peak
  power densities, and background power densities of the set of peaks in
  these 601 average power spectra. As is described in our companion paper
  on the MDI ridge-fit frequency measurements (Rhodes et al.,1998), we
  also had to correct our raw MWO ridge-fit frequencies for the effects
  the merger of individual p-mode peaks and sidelobes into ridges. We
  could also directly compare the frequency dependence of the observed
  power density in both the MDI and MWO power spectra. We have found
  that there is a systematic difference such that the power density in
  the chromospheric-level power spectra from MWO tends to be below that
  of the photosheric-level MDI spectra at low frequencies and to rise
  above the MDI power density as the frequency increases. All but the l
  = 0 MWO power spectra were also processed to yield estimates of the
  rotational splitting coefficients for individual p-mode ridges for
  every degree between l = 4 and 600. We will compare these splittings
  with both the previously-published splittings from the 1996 SOI/MDI
  Medium-l Program (Kosovichev et al., 1997) and with the MDI high-degree
  splittings presented in our companion MDI paper.

---------------------------------------------------------
Title: Line Asymmetry of VIRGO and MDI Low-Degree p Modes
Authors: Toutain, T.; Appourchaux, T.; Frohlich, C.; Kosovichev, A.;
   Rakesh, N.; Scherrer, P.
1998ESASP.418..973T    Altcode: 1998soho....6..973T
  Using continuous time series of 610 days of velocity (MDI, LOI-proxy)
  and intensity (VIRGO, SPM and LOI) we show that Lorentzian profiles as
  a model of low-degree p-mode line leads to systematic differences in
  the determination of intensity and velocity mode frequencies. These
  differences, as large as 0.1 muHz for degrees l = 0, 1, 2 and 3,
  are frequency-dependent. The use of a physics-based asymmetrical line
  shape (Rakesh et al., 1998) to fit the same lines has allowed us to
  significantly reduce differences in the frequency determination. P-mode
  lines in velocity exhibit a significant negative asymmetry (excess
  of power in the left wing) whereas p-modes lines in intensity have a
  positive asymmetry (excess of power in the right wing). The magnitude
  and sign of this asymmetry are directly related to the location of
  the source of p-mode excitation and to the correlation between mode
  and solar noise.

---------------------------------------------------------
Title: Comparison of SOHO-SOI/MDI and GONG Spectra
Authors: Komm, R. W.; Anderson, E.; Hill, F.; Howe, R.; Kosovichev,
   A. G.; Scherrer, P. H.; Schou, J.; Fodor, I.; Stark, P.
1998ESASP.418..253K    Altcode: 1998soho....6..253K
  We compare solar p-mode parameters, such as central frequency, width,
  and amplitude, derived from GONG and SOHO-SOI/MDI Medium-l Program
  time series obtained during the same time period. With the excellent
  data available now from GONG and SOHO-SOI/MDI, there exist data
  sets long enough to make such a comparison useful. For this study,
  we have chosen time series of three ell values (ell = 30, 65, and 100)
  corresponding to GONG month 16 (Oct 28 -- Dec 2, 1996). For each time
  series, we calculated multitaper power spectra using generalized
  sine tapers to reduce the influence of the gap structure, which is
  different for the two data sets. Then, we applied the GONG peakfitting
  algorithm to the spectra to derive mode parameters and selected `good'
  fits common to both MDI and GONG spectra, according to three selection
  criteria. Preliminary results show that mode frequencies determined
  from MDI spectra are essentially the same as the frequencies from
  GONG spectra and that the difference is, in general, well within one
  formal error bar. The background slope at frequencies above 5mHz is
  different between MDI and GONG spectra depending on ell. At present,
  we are analyzing 3-month time series of ell = 0 to ell = 150. We intend
  to present the results of the on-going comparison.

---------------------------------------------------------
Title: Damping and Frequency Shift of the Solar f-mode Due to the
    Interaction with Turbulent Convection
Authors: Murawski, K.; Duvall, T. L., Jr.; Kosovichev, A. G.
1998ESASP.418..825M    Altcode: 1998soho....6..825M
  Observations indicate that the frequency of the high-degree f-mode
  is substantially smaller that the frequency given by the simple
  dispersion relation, ω<SUP>2</SUP> = gk, and that the line width
  grows with the wavenumber k. We attempt to explain this behaviour as
  a result of interaction with granulation which we model as a random
  flow. Because of buffeting from the random flow the f-mode wave
  speed and consequently frequency are reduced. Additionally, a random
  flow makes an appearance of the negative imaginary part of frequency,
  ω<SUB>i</SUB>. This negative complex part represents the damping of the
  mean field, i. e. the generation of random field at the expense of the
  mean field energy. The line width is proportional to the magnitude of
  the imaginary part of the frequency. We apply an analytical perturbation
  technique and numerical methods to estimate the imaginary part and
  the frequency shift, and show that the results are consistent with
  the properties of the f-mode obtained from the high-resolution MDI data.

---------------------------------------------------------
Title: Initial SOI/MDI High-Degree Frequencies and Frequency
    Splittings
Authors: Rhodes, E. J., Jr.; Reiter, J.; Kosovichev, A. G.; Schou,
   J.; Scherrer, P. H.
1998ESASP.418...73R    Altcode: 1998soho....6...73R
  We present the first high-degree p-mode frequencies and frequency
  splittings obtained from the Full-Disk Program of the SOHO Solar
  Oscillation Investigation/Michelson Doppler Imager experiment. The
  frequencies and splittings which we present here were computed
  from power spectra obtained during the 1996 SOI/MDI Dynamics
  Run. Specifically, a time series of full-disk Dopplergrams, which
  began on May 23, 1996, and which covered 87480 minutes (60.75 days),
  was converted into sets of zonal, tesseral, and sectoral power spectra
  covering the degree range of 0 through 1000. These sets of power spectra
  were then analyzed in two different ways to yield both frequencies and
  frequency splittings. First, estimates of the frequency splittings
  were computed for the frequency range of 1800 to 4800 microhertz at
  each degree and these n-averaged splittings were employed to compute an
  average power spectrum for that degree. Estimates were then made of the
  frequencies, frequency uncertainties, widths, peak power densities,
  and background power densities of a total of 13664 separate peaks
  in these 1001 average power spectra. A total of 2554 of these peaks
  were isolated enough in their respective spectra to be fit as single
  p-modes. However, for the remaining 11110 peaks (mostly those above l
  = 200), the individual p-mode peaks and their spatial sidelobes were
  located so close together in frequency that they appeared as ridges
  rather than as isolated modal peaks in the average power spectra. For
  these cases we were forced to employ a wider fitting range for our
  frequency-estimation code and in so doing we obtained so-called
  “ridge-fit” parameter estimates. Due to a degree-dependence in
  the measured velocity power density, the observed p-mode ridges were
  asymmetric in shape. These asymmetries in the p-mode ridge shapes,
  which are in addition to the intinsic asymmetries caused by the
  excitation mechanism of the p-modes themselves, alter the fitted peak
  frequencies from their “true” values. For this reason, we had to
  develop a mechanism which we then used to correct the raw ridge-fit
  frequencies. Forty sets of these power spectra were also processed to
  yield estimates of the rotational splitting coefficients for individual
  p-mode ridges for every 25th degree between l = 25 and 1000. For l
  between 25 and 175 we will compare these Full-Disk program splittings
  with the previously-published splittings from the 1996 SOI/MDI Medium-l
  Program (Kosovichev et al., Solar Physics, 170, 43-61,1997).

---------------------------------------------------------
Title: Splittings of MDI Low-Degree p Modes
Authors: Toutain, T.; Kosovichev, A. G.
1998ESASP.418..349T    Altcode: 1998soho....6..349T
  Applying an optimal mask technique (Toutain et al, 1997) to an
  uninterruped &gt; time series of 610 days of MDI/LOI-proxy Doppler
  velocity data we produce cleaned m- ν diagrams for degrees l = 1,
  2, 3. We derive p-mode parameter assuming a diagonal leakage matrix
  but taking into account the correlation of noise between different
  m-spectra (Schou,J., 1992 and Appourchaux et al., 1997). This fitting
  technique allows an unbiased determination of the p-mode parameters
  (Appourchaux et al., 1997). We fit the a<SUB>1</SUB> coefficient using
  a Lorentzian profile and an asymmetrical profile as described by Rakesh
  et al, 1998. The inversion results will be presented at the meeting.

---------------------------------------------------------
Title: Line asymmetry and excitation mechanism of solar oscillations
Authors: Nigam, R.; Kosovichev, A. G.; Scherrer, P. H.
1998IAUS..185..195N    Altcode:
  The width and asymmetry of lines in the power spectrum of solar
  oscillations, obtained from the Michelson Doppler Imager (MDI) data,
  on board the Solar and Heliospheric Observatory (SOHO), are used to
  study the physics of excitation and damping of the oscillations. A
  theoretical model for solar oscillations is developed. In this model,
  the asymmetry is an effect of interference between the trapped waves
  from the source that pass through the region of wave propagation in the
  Sun's interior. From this the power spectrum is computed for different
  values of the source location and for various values of the angular
  degree l. It is seen that there is marked line asymmetry below the
  acoustic cut-off frequency, which corresponds to the asymmetry of
  bound states in quantum mechanics. The asymmetry is reduced above
  the acoustic cut-off frequency, which corresponds to the asymmetry
  of scattered states, which is a result of interference between an
  outward direct wave from the source and corresponding inward untrapped
  waves. The asymmetry is found to depend strongly on the source location
  and on the value of l. We discuss the properties of the solar acoustic
  source inferred from the MDI data.

---------------------------------------------------------
Title: Solar Asymmetries from SOHO/MDI Splitting Data
Authors: Goode, P. R.; Dziembowski, W. A.; DiMauro, M. P.; Kosovichev,
   A. G.; Schou, J.
1998ESASP.418..887G    Altcode: 1998soho....6..887G
  No abstract at ADS

---------------------------------------------------------
Title: Latitudinal Dependence of the Solar Rotation Rate in the
    Upper Convection Zone
Authors: Birch, A. C.; Kosovichev, A. G.
1998ESASP.418..679B    Altcode: 1998soho....6..679B
  Analysis of p-mode frequency splittings as measured by the Solar
  Oscillations Investigation-Michelson Doppler Imager (SOI-MDI) on board
  the Solar and Heliospheric Observatory (SOHO) and the ground-based
  Global Oscillations Network Group (GONG) experiment reveals that the
  symmetric component of the solar rotation rate, radially averaged
  over the upper 28 Mm of the convection zone and closer than 15-circ
  to the poles, is roughly 310 nHz (corresponding to a period of 37.3
  days), which is slower than the 320 nHz (corresponding to a period
  of 36.2 days) estimated from surface measurements (e.g. Snodgrass,
  1984). The slow polar rotation is sometimes interpreted as a polar
  vortex and is important for understanding solar dynamics. In addition,
  zonal flows, previously inferred from the SOI-MDI f-mode splittings
  (Kosovichev and Schou, 1997), are seen with both SOI-MDI and GONG p-mode
  splittings. The GONG data provide strong support for the findings of
  Schou and colleagues (Schou et al., 1998). We discuss possible physical
  mechanisms for the slow rotation of the polar regions.

---------------------------------------------------------
Title: Improved SOLA Inversions of MDI Data
Authors: Larsen, R. M.; Christensen-Dalsgaard, J.; Kosovichev, A. G.;
   Schou, J.
1998ESASP.418..813L    Altcode: 1998soho....6..813L
  We present a new version of 2d-SOLA, where the target functions have
  been modified to match the behavior of the mode kernels near the
  rotation axis and to minimize near-surface contributions. Inversion
  of artificial data show that these modifications significantly improve
  the effective resolution near the pole, which allows us to assess the
  reliability of the high-latitude features seen by other inversion
  methods. Most importantly, our new inversions seem to confirm the
  detection of a submerged polar jet previously seen in the 2d-RLS
  inversions reported by Schou et al. 1998. A test of the robustness of
  the improved method is carried out by inverting artificial data from
  the MDI Hare and Hounds exercise. We analyze the averaging kernels and
  error propagation of the method, and also describe the error-correlation
  between different points in the solution, the latter being a potential
  source of spurious features in the solutions as pointed out by Howe
  and Thompson, 1996. So far, helioseismic datasets given in the form of
  a-coefficients have been inverted under the assumption that the errors
  in different a-coefficients are uncorrelated. The MDI peak-bagging
  procedure, however, does produce estimates of the error-correlation
  between a-coefficients within the same multiplet. Here we investigate
  the effect of including this knowledge in the inversions.

---------------------------------------------------------
Title: Seismic Response to Solar Flares Observed SOHO/MDI
Authors: Zharkova, V. V.; Kosovichev, A. G.
1998ESASP.418..661Z    Altcode: 1998soho....6..661Z
  First observations with the SOHO Michelson Doppler Imager (MDI) of
  seismic effects in the solar atmosphere in response to solar flares
  are investigated in the complex environment using X-ray (Yohkoh),
  white light (LASCO) and magnetographic observations. Solar flares are
  found to produce the outgoing circular waves which can be detected on
  MDI dopplergrams visually. The time-distance diagrams for the first
  three azimuthal components of the flare seismogram are constructed from
  1 minute velocity differences. These observations were compared with
  the theoretical models of a seismic response to solar flares using the
  thick target model with electron beam injection. Some discrepancies
  were found as for the energy momentum of flare's shock waves being
  able to produce a noticeable seismic response, so for the observed
  travel time of seismic waves in comparison with the theoretical
  predictions. Possible mechanisms of such discrepancies are discussed.

---------------------------------------------------------
Title: Tests of Convective Frequency Effects with SOI/MDI High-Degree
    Data
Authors: Rosenthal, C. S.; Christensen-Dalsgaard, J.; Kosovichev,
   A. G.; Nordlund, A. A.; Reiter, J.; Rhodes, E. J., Jr.; Schou, J.;
   Stein, R. F.; Trampedach, R.
1998ESASP.418..521R    Altcode: 1998astro.ph..7066R; 1998soho....6..521R
  Advances in hydrodynamical simulations have provided new insight into
  the effects of convection on the frequencies of solar oscillations. As
  more accurate observations become available, this may lead to an
  improved understanding of the dynamics of convection and the interaction
  between convection and pulsation (Rosenthal et al. 1999). Recent
  high-resolution observations from the SOI/MDI instrument on the
  SOHO spacecraft have provided the so-far most-detailed observations
  of high-degree modes of solar oscillations, which are particularly
  sensitive to the near-surface properties of the Sun. Here we present
  preliminary results of a comparison between these observations and
  frequencies computed for models based on realistic simulations of
  near-surface convection. Such comparisons may be expected to help
  in identifying the causes for the remaining differences between the
  observed frequencies and those of solar models.

---------------------------------------------------------
Title: Spherical and aspherical structure of the sun: First year of
    SOHO/MDI observations
Authors: Kosovichev, A. G.; Schou, J.; Scherrer, P. H.; Goode, P. H.;
   Dziembowski, W. A.; Rhodes, E. J., Jr.; SOI Structure Inversion Team
1998IAUS..185..157K    Altcode:
  We report the results of one year of continuous observations of the
  Sun's internal structure using data from the Medium-l Program of
  the Michelson Doppler Imager (MDI) on board SOHO. The data provide
  continuous coverage of p modes of angular degree l from 0 to 250,
  and the f mode from l=100 to 250. The striking stability of solar
  Dopplergrams measured by MDI, without an intervening atmosphere,
  substantially decreases the noise in the solar oscillations power
  spectrum compared with ground-based observations. This permits
  detection of lower amplitude oscillations, extending the range and
  precision of measured normal mode frequencies. We present new inversion
  results for the radial and latitudinal seismic solar structures with
  particular attention to zonal asphericity inferred with the high
  angular resolution from the data. Using f-mode frequency splitting
  we estimate the large-scale structure of the subsurface magnetic
  fields. The variations of the solar structure observed during the
  first year of MDI observations are also discussed.

---------------------------------------------------------
Title: Solar Asymmetries from SOHO/MDI Splitting Data
Authors: Dziembowski, W. A.; Goode, P. R.; Di Mauro, M. P.; Kosovichev,
   A. G.; Schou, J.
1998ESASP.418..887D    Altcode: 1998soho....6..887D
  Systematic changes in p-mode frequencies through the solar cycle
  have been discovered during the previous high activity phase. Most
  significant changes were found in the even-a coefficients of
  the fine structure in the oscillation spectra (Kuhn, 1988;
  and Libbrecht and Woodard, 1990). We analyzed time changes in
  frequencies determined with the SOHO/MDI instrument. The data were
  divided into five 72-day sets covering (1) 5/1/96-7/11/96, (2)
  7/12/96-9/21/96, (3) 9/22/96-12/2/96, (4) 12/3/96-2/12/97, and (5)
  2/13/97-4/25/97. The splitting coefficients a<SUB>k</SUB> are defined by
  nuv<SUB>los</SUB>ell,n,m-bar nu<SUB>ell,n</SUB> = sum<SUB>{k = 1}</SUB>
  a<SUB>k</SUB> {cal P}<SUB>k</SUB><SUP>ell</SUP>(m), where {cal P} are
  are orthogonal polynomials (see Ritzwoller and Lavely 1991 and Schou,
  et al. 1994). We analyzed behavior of the even order coefficients,
  a<SUB>2k</SUB>, which arise from the respective, P<SUB>2k</SUB>
  (cos θ), distortion of the Sun's structure. We found a significant
  trend in behavior of the a<SUB>4</SUB> and a<SUB>6</SUB> coefficients,
  which reflects a decrease of the P<SUB>4</SUB> and an increase of the
  P<SUB>6</SUB> distortions. This trend is the same as seen in the BBSO
  data (Libbrecht and Woodard, 1990) between 1986 and 1988 i.e. at the
  onset of the previous activity phase. The trend in a<SUB>2</SUB> is
  not so apparent. The centroid frequencies, bar nu<SUB>ell,n</SUB>, as
  already reported by Kosovichev et al. (1998), exhibit small nonmonotonic
  variations. The relative differences in solar radius inferred from the
  f-mode frequencies in the five sets (at most 5 times 10<SUP>-6</SUP>)
  are formally significant, but again there is no trend.

---------------------------------------------------------
Title: Observational Upper Limits for Low-Degree Solar g-modes
Authors: Fröhlich, C.; Finsterle, W.; Andersen, B.; Appourchaux, T.;
   Chaplin, W. J.; Elsworth, Y.; D. O. Gough; Hoeksema, J. T.; Isaak,
   G. R.; Kosovichev, A. G.; Provost, J.; Scherrer, P. H.; Sekii, T.;
   Toutain, T.
1998ESASP.418...67F    Altcode: 1998soho....6...67F
  No abstract at ADS

---------------------------------------------------------
Title: Observation of low-degree modes from SOHO/MDI using optimal
    masks
Authors: Toutain, T.; Kosovichev, A. G.
1998IAUS..185..179T    Altcode:
  The overlap of peaks of low-degree p-mode split multiplets in
  oscillation power spectra significantly affects the measurements of
  the rotational frequency splitting, and, thus, contributes to the
  uncertainty of the rotation rate of the solar core. We have developed
  optimal masks to isolate individual components of the multiplets, and
  discuss the advantages of the optimal-mask method over the integrated
  disk observations and projection onto spherical harmonics. The method
  has been applied to the Michelson Doppler Imager Low-l data, and the
  results of the measurements of the mode frequencies, linewidth, line
  asymmetry and amplitude are reported.

---------------------------------------------------------
Title: Relativistic Effects in the Solar Equation of State
Authors: Elliott, J. R.; Kosovichev, A. G.
1998ESASP.418..453E    Altcode: 1998soho....6..453E
  We present helioseismic inversions of solar p-mode frequencies
  obtained by the Michelson Doppler Imager (MDI) instrument of the Solar
  Oscillation Investigation (SOI) project on board SOHO, indicating that
  a lower central value for the adiabatic exponent Γ<SUB>1</SUB> in the
  sun than in current models. We show how the inclusion of relativistic
  effects in the equation of state removes the discrepancy and allows
  almost perfect agreement in Γ<SUB>1</SUB> between the models and
  the sun. This increases our confidence both in the reliability of the
  equation of state calculation and the determination of solar p-mode
  frequencies.

---------------------------------------------------------
Title: Solar rotation and large-scale flows determined by
    time-distance helioseismology MDI
Authors: Giles, P. M.; Duvall, T. L., Jr.; Kosovichev, A. G.
1998IAUS..185..149G    Altcode:
  We use differences of reciprocal travel time of acoustic waves
  propagating along parallels and meridians to determine variations of
  solar rotation and large-scale flows beneath the Sun's surface. This
  new technique can provide an effective measure of the antisymmetric
  component of the differential rotation and meridional flows that are not
  determined by the traditional helioseismic techniques based on inversion
  of frequency splitting of normal modes. We investigate resolution and
  precision of the time-distance measurements using the Michelson Doppler
  Imager (MDI) Medium-l data. The first results show a clear picture of
  the latitudinal differential rotation and its variation with depth. We
  discuss preliminary results of the meridional flow measurements.

---------------------------------------------------------
Title: Some Numerical Simulations of Oscillations in the Solar
    Atmosphere
Authors: Andreev, A. S.; Kosovichev, A. G.
1998ESASP.418...87A    Altcode: 1998soho....6...87A
  The new results, obtained by simulations of atmospheric oscillations are
  presented. The details of quasi-periodic shock waves, which are produced
  by photospheric and subphotospheric oscillations and spread up into the
  upper chromosphere and corona, as well as their interaction with the
  transition region between chromosphere and corona are considered. The
  results show agreement with cooperative studies of the phenomena,
  using observations from MDI and SOHO coronal instruments.

---------------------------------------------------------
Title: Numerical model for coronal shock waves formation in two-fluid
    approximation
Authors: Kosovichev, A. G.; Stepanova, T. V.
1998PAICz..88..167K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Some results of numerical modeling of solar atmospheric
    oscillations.
Authors: Andreev, A. S.; Kosovichev, A. G.
1998BCrAO..94..123A    Altcode:
  The nonlinear response of the solar atmosphere to a single
  subphotospheric wave disturbance, one part of the energy of which is
  spent on exciting internal p-modes and the other generates traveling
  oscillations in the chromosphere and corona, is examined. The latter,
  reaching the upper chromosphere and corona, are transformed into
  quasi-periodic shock waves as a result of the so-called wave wake
  effect. Results of one-dimensional calculations of this process on
  the basis of observations made during the MDI and SOHO projects are
  presented.

---------------------------------------------------------
Title: Comparative Studies of Low-Order and Low-Degree Solar p Modes
Authors: Appourchaux, T.; Andersen, B.; Chaplin, W.; Elsworth, Y.;
   Finsterle, W.; Frohlich, C.; Gough, D.; Hoeksema, J. T.; Isaak, G.;
   Kosovichev, A.; Provost, J.; Scherrer, P.; Sekii, T.; Toutain, T.
1998ESASP.418...95A    Altcode: 1998soho....6...95A
  The amplitudes of solar p-modes decrease steeply with decreasing
  radial order below about 17. The background solar signal (solar noise)
  in general increases steadily with decreasing frequency. For the
  irradiance and radiance measurements with VIRGO or SOI/MDI on SOHO this
  combination makes it difficult to detect low degree modes below about
  1.8 mHz. The solar noise as observed in velocity with SOI/MDI or the
  ground based BISON network is significantly lower in this region than
  in intensity measurements. This allows low degree modes to be observed
  close to 1 mHz. We present results of detection and charaterization
  of the lowest order observable p-modes both in velocity and intensity
  measurements. Where applicable the properties of the modes observed
  with the two methods are compared.

---------------------------------------------------------
Title: Acoustic tomography of solar convective flows and structures
Authors: Kosovichev, A. G.; Duvall, T. L., Jr.
1997ASSL..225..241K    Altcode: 1997scor.proc..241K; 2018arXiv180603273K
  We present a new method for helioseismic diagnostics of the
  three-dimensional structure of sound speed, magnetic fields and flow
  velocities in the convection zone by inversion of acoustic travel-time
  data. The data are measurements of the time for acoustic waves to
  travel between points on the solar surface and surrounding annuli
  obtained from continuous observations at the South Pole in 1991 and
  from high-resolution observations from the Solar and Heliospheric
  Observatory (SOHO) in 1996. The travel time of the waves depends
  primarily on the sound speed perturbations and the velocity of flow
  along the ray paths. The effects of the sound speed perturbations
  and flows can be separated by measuring the travel time of waves
  propagating in opposite directions along the same ray paths. Magnetic
  fields result in anisotropy of the wave speed. A 3D inversion method
  based on Fermat's Principle and a regularized least-squares technique
  have been applied to infer the properties of convection in the quiet
  Sun and in active regions.

---------------------------------------------------------
Title: Probing the Internal Structure of the Sun with the SOHO
    Michelson Doppler Imager
Authors: Kosovichev, A. G.; Nigam, R.; Scherrer, P. H.; Schou, J.;
   Reiter, J.; Rhodes, E. J., Jr.; Toutain, T.
1997AAS...191.7311K    Altcode: 1997BAAS...29R1322K
  The inference of the thermodynamic structure of the Sun from the
  observed properties of the solar normal modes of oscillation is a
  principal goal of helioseismology. We report the results of the first
  year of continuous observations of the Sun's internal structure using
  data from the Medium-l Program of the Michelson Doppler Imager (MDI)
  on board ESA/NASA spacecraft SOHO. The data provide continuous coverage
  of the acoustic (p) modes of angular degree l from 0 to 250, and the
  fundamental (f) mode of the Sun from l=100 to 250. During two 2-month
  intervals, the high-degree modes, up to l=1000, have been observed. The
  great stability of solar Dopplergrams measured by MDI permits detection
  of lower amplitude oscillations, extending the range and precision of
  measured normal mode frequencies, and thus substantially increasing
  the resolution and precision of helioseismic inversions. We present
  new inversion results for the radial and latitudinal seismic solar
  structures with particular attention to the transition region between
  the radiative and convection zones and to the energy-generating core. We
  discuss evidence for convective overshoot at the base of the convection
  zone, and the significance of deviations in the core structure from
  the standard evolutionary model. Comparing the f-mode frequencies
  with the corresponding frequencies of the standard solar models, we
  argue that the apparent photospheric solar radius (695.99 Mm) used to
  calibrate the models should be reduced by approximately 0.3 Mm. The
  discrepancy between the `seismic' and apparent photospheric radii is
  not explained by the known systematic errors in the helioseismic and
  photospheric measurements. If confirmed, this discrepancy represents
  a new interesting challenge to theories of solar convection and solar
  modeling. Using f-mode frequency splitting we estimate the large-scale
  structure of the subsurface magnetic fields. The variations of the solar
  oscillation frequencies during the first year of MDI observations are
  also discussed.

---------------------------------------------------------
Title: Rotation and Zonal Flows in the Solar Envelope from the
    SOHO/MDI Observations
Authors: Scherrer, P. H.; Schou, J.; Bogart, R. S.; Bush, R. I.;
   Hoeksema, J. T.; Kosovichev, A. G.; Antia, H. M.; Chitre, S. M.;
   Christensen-Dalsgaard, J.; Larsen, R. M.; Pijpers, F. P.; Eff-Darwich,
   A.; Korzennik, S. G.; Gough, D. O.; Sekii, T.; Howe, R.; Tarbell,
   T.; Title, A. M.; Thompson, M. J.; Toomre, J.
1997AAS...191.7310S    Altcode: 1997BAAS...29.1322S
  We report on the latest inferences concerning solar differential
  rotation that have been drawn from the helioseismic data that are now
  available from the Solar Oscillations Investigation (SOI) using the
  Michelson Doppler Imager (MDI) on the Solar and Heliospheric Observatory
  (SOHO). That spacecraft is positioned in a halo orbit near the Sun-Earth
  Lagrangian point L_1, in order to obtain continuous Doppler-imaged
  observations of the sun with high spatial fidelity. Doppler velocity,
  intensity and magnetic field images are recorded, based on modulations
  of the 676.8 nm Ni I solar absorption line. The high spatial resolution
  of MDI thereby permits the study of many millions of global resonant
  modes of solar oscillation. Determination and subsequent inversion
  of the frequencies of these modes, including the degeneracy-splitting
  by the rotation of the sun, enables us to infer how the sun's angular
  velocity varies throughout much of the interior. The current MDI data
  are providing substantial refinements to the helioseismic deductions
  that can be made about differential rotation both within the convection
  zone and in its transition to the radiative interior. The shearing
  layer evident in the angular velocity Omega just below the solar
  surface is becoming better defined, as is the adjustment layer or
  tachocline near the base of the convection zone. The MDI data are also
  revealing a prominent decrease in Omega at high latitudes from the
  rotation rate expressed by a simple three-term expansion in latitude
  that was originally deduced from surface Doppler measurements. Further,
  there are indications that a submerged polar vortex involving somewhat
  faster Omega than its surroundings exists at about 75(deg) in latitudes.

---------------------------------------------------------
Title: Determination of the Sun's Seismic Radius from the SOHO
    Michelson Doppler Imager
Authors: Schou, J.; Kosovichev, A. G.; Goode, P. R.; Dziembowski, W. A.
1997ApJ...489L.197S    Altcode:
  Dopplergrams from the Michelson Doppler Imager (MDI) instrument on board
  the SOHO spacecraft have been used to accurately measure frequencies of
  the Sun's fundamental (f) mode in the medium angular degree range, l =
  88--250. The comparison of these frequencies with the corresponding
  frequencies of the standard solar models suggests that the apparent
  photospheric solar radius (695.99 Mm) used to calibrate the models
  should be reduced by approximately 0.3 Mm. The precise value of the
  seismologically determined solar radius depends on the description
  of the subsurface layer of superadiabatic convection. The discrepancy
  between the "seismic" and apparent photospheric radii is not explained
  by the known systematic errors in the helioseismic and photospheric
  measurements. If confirmed, this discrepancy represents an interesting
  new challenge to theories of solar convection and solar modeling.

---------------------------------------------------------
Title: Measurements of Frequencies of Solar Oscillations from the
    MDI Medium-l Program
Authors: Rhodes, E. J., Jr.; Kosovichev, A. G.; Schou, J.; Scherrer,
   P. H.; Reiter, J.
1997SoPh..175..287R    Altcode:
  Inversions of solar internal structure employ both the frequencies
  and the associated uncertainties of the solar oscillation modes
  as input parameters. In this paper we investigate how systematic
  errors in these input parameters may affect the resulting inferences
  of the sun's internal structure. Such systematic errors are likely
  to arise from inaccuracies in the theoretical models which are used
  to represent the spectral lines in the observational power spectra,
  from line blending, from asymmetries in the profiles of these lines,
  and from other factors. In order to study such systematic effects we
  have employed two different duration observing runs (one of 60 days
  and the second of 144 days) obtained with the Medium-l Program of the
  Michelson Doppler Imager experiment onboard the SOHO spacecraft. This
  observing program provides continuous observations of solar oscillation
  modes having angular degrees, l, ranging from 0 to ∼ 300. For this
  study intermediate- and high-degree p-mode oscillations having degrees
  less than 251 were employed.

---------------------------------------------------------
Title: Tri-Phonic Helioseismology: Comparison of Solar P Modes
    Observed by the Helioseismology Instruments Aboard SOHO
Authors: Toutain, T.; Appourchaux, T.; Baudin, F.; Fröhlich, C.;
   Gabriel, A.; Scherrer, P.; Andersen, B. N.; Bogart, R.; Bush, R.;
   Finsterle, W.; García, R. A.; Grec, G.; Henney, C. J.; Hoeksema,
   J. T.; Jiménez, A.; Kosovichev, A.; Roca Cortés, T.; Turck-Chièze,
   S.; Ulrich, R.; Wehrli, C.
1997SoPh..175..311T    Altcode:
  The three helioseismology instruments aboard SOHO observe solar p modes
  in velocity (GOLF and MDI) and in intensity (VIRGO and MDI). Time series
  of two months duration are compared and confirm that the instruments
  indeed observe the same Sun to a high degree of precision. Power
  spectra of 108 days are compared showing systematic differences between
  mode frequencies measured in intensity and in velocity. Data coverage
  exceeds 97% for all the instruments during this interval. The weighted
  mean differences (V-I) are −0.1 µHz for l=0, and −0.16 µHz for
  l=1. The source of this systematic difference may be due to an asymmetry
  effect that is stronger for modes seen in intensity. Wavelet analysis
  is also used to compare the shape of the forcing functions. In these
  data sets nearly all of the variations in mode amplitude are of solar
  origin. Some implications for structure inversions are discussed.

---------------------------------------------------------
Title: Studying the temporal behavior of the Evershed flow from
    SOHO/MDI
Authors: Burnette, A. B.; Kosovichev, A. G.
1997BAAS...29.1120B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Asymptotic Latitudinal Inversion of Frequency Splitting Data
Authors: Birch, A. C.; Kosovichev, A. G.
1997BAAS...29Q1121B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Detection of Zonal Shear Flows beneath the Sun's Surface from
    f-Mode Frequency Splitting
Authors: Kosovichev, A. G.; Schou, J.
1997ApJ...482L.207K    Altcode:
  We report on the first successful measure of the zonal variations of
  the Sun's differential rotation (so-called torsional oscillations) by
  helioseismology. Using new helioseismic data from the Michelson Doppler
  Imager on board SOHO, we have detected zonal flow bands with velocity
  variation of 5 m s<SUP>-1</SUP> at a depth of 2-9 Mm beneath the
  surface. The subsurface flow is inferred from rotational splitting of
  frequencies of the fundamental mode of solar oscillations in the range
  of angular degree l from 120 to 250, using a 144 day uninterrupted time
  series of the Sun's Doppler velocities. The structure of the subsurface
  shear flow resembles the pattern of the torsional oscillations observed
  on the surface. Comparing with previous surface measurements, we found
  evidence for migration of the flow bands towards the equator.

---------------------------------------------------------
Title: Solar Meridional Circulation and Rotation Determined by
    Time-Distance Helioseismology using MDI Data From SOHO
Authors: Giles, P. M.; Duvall, T. L., Jr.; Kosovichev, A. G.; Scherrer,
   P. H.
1997SPD....28.1002G    Altcode: 1997BAAS...29..914G
  Using the technique of time-distance helioseismology, acoustic wave
  travel times can be measured between pairs of points on the solar
  surface. The travel time of the waves depends primarily on the wave
  group velocity and on the component of flow velocity which is parallel
  to the direction of wave propagation. By choosing pairs of points which
  share a common longitude, it is possible to use these waves to probe
  the meridional flow beneath the surface. Any flows present will cause
  a difference between the northward and southward travel times along
  the meridian. Varying the distance between points allows isolation
  of waves which propagate to different depths beneath the surface,
  and thus the flow velocity can be measured as a function of latitude
  and depth. Similarly, by choosing pairs of points which share a common
  latitude it is possible to measure the effects of solar rotation using
  an analogous procedure. This technique could provide high resolution
  in latitude and allows study of the northern and southern hemispheres
  independently. Using velocity images taken by the Michelson Doppler
  Imager during June 1996, we have detected meridional flows in the
  uppermost layers of the sun. Measurements of this flow velocity
  and of the rotation rate as functions of latitude and depth will be
  presented. This research is supported by NASA contract NAG5-3077 at
  Stanford University.

---------------------------------------------------------
Title: Analysis of Velocity and Intensity Helioseismic Spectra
    from SOHO/MDI
Authors: Nigam, R.; Kosovichev, A. G.; Scherrer, P. H.; Schou, J.
1997SPD....28.0904N    Altcode: 1997BAAS...29..913N
  We give an explanation for the cause of the asymmetry of spectral lines
  of solar oscillation power spectrum. We also explain the cause of the
  opposite sense of asymmetry in velocity and intensity oscillation power
  spectra, thereby resolving a half-decade old puzzle. The motivation for
  the investigation came after comparing the velocity and intensity data
  obtained from the Michelson Doppler Imager (MDI) instrument on board the
  Solar and Heliospheric Observatory (SOHO). The analysis is based on a
  theoretical model of wave excitation with viscous damping in conjunction
  with a spherically symmetric solar model. Neglecting asymmetry can
  lead to systematic errors in the eigenfrequency measurements, which
  in turn leads to errors in inversion. This research was supported by
  NASA grant NAG5-3077 at Stanford University.

---------------------------------------------------------
Title: Spherical and Aspherical Structure of the Sun
Authors: Kosovichev, A. G.; SOI Structure Inversion Team
1997SPD....28.0902K    Altcode: 1997BAAS...29..913K
  The striking stability of solar Dopplergrams measured by SOHO,
  without an intervening atmosphere, substantially decreases the noise
  in the solar oscillations power spectrum compared with ground-based
  observations. This permits detection of lower amplitude oscillations,
  extending the range and precision of measured normal mode frequencies
  and frequency splitting for inferring the internal structure of the
  Sun. We report on new inversion results for the radial and latitudinal
  seismic solar structures with particular attention to zonal asphericity
  inferred with the high angular resolution. The frequency splitting of
  the fundamental mode is used to estimate the large-scale structure of
  the subsurface magnetic fields. The sound-speed profile inferred from
  the mean frequencies of mode multiplets gives evidence for significant
  deviations from a standard solar model in the upper convective boundary
  layer, in a thin layer just beneath the convection zone and in the
  energy-generating core. This research is supported by the SOI-MDI NASA
  contract NAG5-3077 at Stanford University.

---------------------------------------------------------
Title: Performance of the Michelson Doppler Imager Instrument on SOHO
Authors: Scherrer, P.; Bogart, R.; Bush, R.; Duvall, T.; Hoeksema,
   J. T.; Kosovichev, A.; Schou, J.; Morrison, M.; Tarbell, T.; Title, A.
1997SPD....28.0207S    Altcode: 1997BAAS...29..894S
  Launched on SOHO in December 1995, the MDI instrument took its 10
  millionth filtergram in early April, 1997. The instrument and spacecraft
  have performed admirably since commissioning, providing over a year
  of virtually uninterrupted time series of velocity and intensity
  measurements at moderate resolution, a continuous 60-day time series
  of full disk 4" velocity and line depth maps, monthly 72+ hour time
  series in various observables, a host of daily 8-hour campaigns, and
  full-disk magnetograms every 96 minutes. Another uninterrupted 90-day
  interval of nearly full data recovery is scheduled to be completed in
  mid July. Various scientific results using MDI data are being presented
  at this meeting. About a dozen terabytes of data sets have been created
  and archived and normal pipeline processing is now completed soon after
  retrieving the data, typically less than a month after the observations
  are made. Most of the data products are generally available on the WWW,
  see http://soi.stanford.edu. Selected data are available in near real
  time. The SOI team welcomes collaborations. Routine and extraordinary
  calibrations along with analysis of scientific data sets allow us to
  make good estimates of the noise and understand many of the sources
  of systematic errors in the instrument. In almost every respect the
  instrument performs as well or better than expected before launch,
  the primary limitations being photon noise on the short term and
  fixed or slowly varying offsets on the long term. We have found that
  the Michelsons are somewhat more sensitive to operational temperature
  variations than was expected, adding some additional constraints on
  our observing sequences.

---------------------------------------------------------
Title: The Effects of Systematic Errors in the Estimation of p-Mode
    Frequencies on the Inversion of Solar Internal Structure
Authors: Rhodes, E. J., Jr.; Appourchaux, T.; Bachmann, K.; Kosovichev,
   A. G.; Scherrer, P. H.; Schou, J.; Reiter, J.
1997SPD....28.0901R    Altcode: 1997BAAS...29..913R
  The frequencies and associated uncertainties of the low-, intermdeiate-,
  and high-degree p-mode oscillations are the input quantities for the
  inversion programs which infer the thermodynamic structure of the solar
  interior. In this review we will attempt to demonstrate the different
  possible systematic errors that are currently present in our estimation
  of both the modal frequencies and their uncertainties. We will also
  demonstrate the effects of some of these errors upon the inferred
  radial profile of the solar internal sound speed. Among the different
  possible systematic errors which we will discuss are the effects of:
  1)the asymmetric shapes of the peaks in observational power spectra,
  2)the realization noise which is present in the case of the low-degree
  modes, 3)the different frequency estimation methods used on different
  types of power spectra (i.e., on either tesseral power spectra or
  on m-averaged power spectra), 4) the differences in the frequencies
  which are estimated from velocity- and intensity-based power spectra,
  5) the blending of individual p-modes into so-called "ridges" of
  observed power at both high degrees and high frequencies, and 6) the
  spatial and temporal aliasing which occurs at both high degrees and
  at high frequencies. We will demonstrate these different errors using
  results obtained with the VIRGO and MDI experiments onboard the SOHO
  spacecraft. We will also compare some of these space-based results
  with the results of similar estimates obtained from co-temporaneous
  ground-based observations, such as from the Mt. Wilson 60-Foot Solar
  Tower. We will include the results from different structural inversions
  carried out with different sets of input frequencies and uncertainties
  in order to demonstrate the effects of these different systematic
  errors upon the inverted internal sound speed profile.

---------------------------------------------------------
Title: Structure and Rotation of the Solar Interior: Initial Results
    from the MDI Medium-L Program
Authors: Kosovichev, A. G.; Schou, J.; Scherrer, P. H.; Bogart, R. S.;
   Bush, R. I.; Hoeksema, J. T.; Aloise, J.; Bacon, L.; Burnette, A.; de
   Forest, C.; Giles, P. M.; Leibrand, K.; Nigam, R.; Rubin, M.; Scott,
   K.; Williams, S. D.; Basu, Sarbani; Christensen-Dalsgaard, J.; Dappen,
   W.; Rhodes, E. J., Jr.; Duvall, T. L., Jr.; Howe, R.; Thompson, M. J.;
   Gough, D. O.; Sekii, T.; Toomre, J.; Tarbell, T. D.; Title, A. M.;
   Mathur, D.; Morrison, M.; Saba, J. L. R.; Wolfson, C. J.; Zayer, I.;
   Milford, P. N.
1997SoPh..170...43K    Altcode:
  The medium-l program of the Michelson Doppler Imager instrument on board
  SOHO provides continuous observations of oscillation modes of angular
  degree, l, from 0 to ∽ 300. The data for the program are partly
  processed on board because only about 3% of MDI observations can be
  transmitted continuously to the ground. The on-board data processing,
  the main component of which is Gaussian-weighted binning, has been
  optimized to reduce the negative influence of spatial aliasing of the
  high-degree oscillation modes. The data processing is completed in a
  data analysis pipeline at the SOI Stanford Support Center to determine
  the mean multiplet frequencies and splitting coefficients. The initial
  results show that the noise in the medium-l oscillation power spectrum
  is substantially lower than in ground-based measurements. This enables
  us to detect lower amplitude modes and, thus, to extend the range of
  measured mode frequencies. This is important for inferring the Sun's
  internal structure and rotation. The MDI observations also reveal the
  asymmetry of oscillation spectral lines. The line asymmetries agree
  with the theory of mode excitation by acoustic sources localized in the
  upper convective boundary layer. The sound-speed profile inferred from
  the mean frequencies gives evidence for a sharp variation at the edge
  of the energy-generating core. The results also confirm the previous
  finding by the GONG (Gough et al., 1996) that, in a thin layer just
  beneath the convection zone, helium appears to be less abundant than
  predicted by theory. Inverting the multiplet frequency splittings from
  MDI, we detect significant rotational shear in this thin layer. This
  layer is likely to be the place where the solar dynamo operates. In
  order to understand how the Sun works, it is extremely important to
  observe the evolution of this transition layer throughout the 11-year
  activity cycle.

---------------------------------------------------------
Title: Internal structure and rotation of the Sun: First results
    from MDI data
Authors: Kosovichev, A. G.; Schou, J.; Scherrer, P. H.; Bogart, R. S.;
   Bush, R. I.; Hoeksema, J. T.; Aloise, J.; Bacon, L.; Burnette, A.;
   De Forest, C.; Giles, P. M.; Leibrand, K.; Nigam, R.; Rubin, M.;
   Scott, K.; Williams, S. D.; Basu, Sarbani; Christensen-Dalsgaard,
   J.; Däppen, W.; Rhodes, E. J., Jr.; Duvall, T. L., Jr.; Howe, R.;
   Thompson, M. J.; Gough, D. O.; Sekii, T.; Toomre, J.; Tarbell, T. D.;
   Title, A. M.; Mathur, D.; Morrison, M.; Saba, J. L. R.; Wolfson,
   C. J.; Zayer, I.; Milford, P. N.
1997IAUS..181..203K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: New Time-distance helioseismology results from the SOI/MDI
    experiment
Authors: Duvall, T., Jr.; Kosovichev, A. G.; Scherrer, P. H.
1997IAUS..181...83D    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Time-Distance Helioseismology with the MDI Instrument:
    Initial Results
Authors: Duvall, T. L., Jr.; Kosovichev, A. G.; Scherrer, P. H.;
   Bogart, R. S.; Bush, R. I.; de Forest, C.; Hoeksema, J. T.; Schou,
   J.; Saba, J. L. R.; Tarbell, T. D.; Title, A. M.; Wolfson, C. J.;
   Milford, P. N.
1997SoPh..170...63D    Altcode:
  In time-distance helioseismology, the travel time of acoustic waves
  is measured between various points on the solar surface. To some
  approximation, the waves can be considered to follow ray paths that
  depend only on a mean solar model, with the curvature of the ray
  paths being caused by the increasing sound speed with depth below the
  surface. The travel time is affected by various inhomogeneities along
  the ray path, including flows, temperature inhomogeneities, and magnetic
  fields. By measuring a large number of times between different locations
  and using an inversion method, it is possible to construct 3-dimensional
  maps of the subsurface inhomogeneities. The SOI/MDI experiment on SOHO
  has several unique capabilities for time-distance helioseismology. The
  great stability of the images observed without benefit of an intervening
  atmosphere is quite striking. It has made it possible for us to detect
  the travel time for separations of points as small as 2.4 Mm in the
  high-resolution mode of MDI (0.6 arc sec pixel<SUP>-1</SUP>). This has
  enabled the detection of the supergranulation flow. Coupled with the
  inversion technique, we can now study the 3-dimensional evolution of
  the flows near the solar surface.

---------------------------------------------------------
Title: Frequencies of solar oscillations and the seismic structure
    of the Sun from SOHO/MDI.
Authors: Rhodes, E. J., Jr.; Kosovichev, A. G.; Scherrer, P. H.;
   Schou, J.; Reiter, J.
1997AGAb...13..163R    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Inferences of element abundances from helioseismic data
Authors: Kosovichev, Alexander G.
1997AIPC..385..159K    Altcode: 1997recs.conf..159K
  The abundance of helium in the Sun's interior is estimated by the
  method of `model-oriented' helioseismic inversion of solar oscillation
  frequencies. In this method, the equations of state and thermal
  balance are used in addition to the hydrostatic equation. By inverting
  the observed p-mode frequencies, direct evidence for gravitational
  settling of helium has been obtained. However, the helium settling
  cannot account for the anomalously low helium abundance of the solar
  corona and wind. The ratio of the helium to hydrogen densities in the
  convection zone inferred from the helioseismic data [1,2] using the
  most recent equation of state [3] is 8.5%+/-0.2% suggesting that the
  separation of helium and hydrogen predominantly occurs in the solar
  atmosphere and corona.

---------------------------------------------------------
Title: The seismic structure of the Sun from GONG
Authors: Anderson, E.; Antia, H. M.; Basu, S.; Chaboyer, B.; Chitre,
   S. M.; Christensen-Dalsgaard, J.; Eff-Darwich, A.; Elliott, J. R.;
   Giles, P. M.; Gough, D. O.; Guzik, J. A.; Harvey, J. W.; Hill,
   F.; Leibacher, J. W.; Kosovichev, A. G.; Monteiro, M. J. P. F. G.;
   Richard, O.; Sekii, T.; Shibahashi, H.; Takata, M.; Thompson, M. J.;
   Toomre, J.; Vauclair, S.; Vorontsov, S. V.
1997IAUS..181..151A    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Observation of solar convection with the MDI instrument
    on SOHO.
Authors: Kosovichev, A. G.; Scherrer, P. H.; Duvall, T. L., Jr.
1996BAAS...28.1298K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: New Views of the Sun's Interior from the SOHO/MDI Space
    Experiment
Authors: Scherrer, P. H.; Bogart, R. S.; Bush, R. I.; Hoeksema, J. T.;
   Kosovichev, A. G.; Nigam, R.; Schou, J.; Duvall, T. L., Jr.
1996AAS...189.1803S    Altcode: 1996BAAS...28.1298S
  The strking stability of solar Dopplergrams measured by the Michelson
  Doppler Imager (MDI) instrument on the SOHO spacecraft, without an
  intervening atmosphere, substantially decreases the noise in the solar
  oscillations power spectrum compared with groundbased observations. This
  permits detection of lower amplitude oscillations, extending the range
  of measured normal mode frequencies. This is important for improving
  resolution and precision of helioseismic inferences about the Sun's
  internal structure and dynamics. The MDI observations also reveal the
  asymmetries of oscillation spectral lines that until now have been
  largely hidden in noise. The line asymmetries agree with a theory of
  excitation of solar oscillations by acoustic sources localized in the
  upper convective boundary layer. High-resolution MDI images make it
  possible to measure the travel time of acoustic waves propagating
  inside the Sun by comparing points on the surface as close as 2.4
  Mm. This is sufficient to detect supergranulation flows beneath the
  surface. Coupled with tomographic inversion techniques, we can now study
  the 3-dimensional evolution of the flows near the photosphere. The
  sound-speed profile inferred from normal modes frequencies shows a
  sharp variation at the edge of the energy-generating core, something
  not accounted for by the standard evolution theory. The analysis also
  confirms recent GONG results suggesting that helium is less abundant
  than theory predicts in a thin layer just beneath the convection
  zone. Inversion of the multiplet frequency splittings shows significant
  rotational shear in this thin layer. This shear flow probably generates
  turbulence that mixes the plasma in the upper radiative zone. This layer
  is likely to be the place where the solar dynamo operates. Continuous
  observation of the evolution of this transition layer during the entire
  11-year activity cycle will be extremely important for understanding
  the mechanisms of solar activity.

---------------------------------------------------------
Title: Helioseismic Constraints on the Gradient of Angular Velocity
    at the Base of the Solar Convection Zone
Authors: Kosovichev, A. G.
1996ApJ...469L..61K    Altcode:
  The layer of transition from the nearly rigid rotation of the radiative
  interior to the latitudinal differential rotation of the convection zone
  plays a significant role in the internal dynamics of the Sun. Using
  rotational splitting coefficients of the p-mode frequencies, obtained
  during 1986--1990 at the Big Bear Solar Observatory, we have found that
  the thickness of the transitional layer is 0.09 +/- 0.04 solar radii
  (63 +/- 28 Mm), and that most of the transition occurs beneath the
  adiabatically stratified part of the convection zone, as suggested by
  the dynamo theories of the 22 yr solar activity cycle.

---------------------------------------------------------
Title: Helioseismic measurements of elemental abundances in the
    sun's interior
Authors: Kosovichev, A. G.
1996BASI...24..355K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Study of solar high-frequency modes near the acoustic cut-off
    frequency
Authors: Nigam, R.; Kosovichev, A. G.
1996BASI...24..195N    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Determination of 3D internal structure and flows by tomographic
    inversion
Authors: Kosovichev, A. G.
1996BASI...24..191K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The MDI Structure Program: Continuous Monitoring of the
    Solar Interior
Authors: Bush, R. I.; Bogart, R. S.; Hoeksema, J. T.; Kosovichev,
   A. G.; Scherrer, P. H.; Mathur, D.; Morrison, M.; Tarbell, T. D.
1996AAS...188.3708B    Altcode: 1996BAAS...28..878B
  The Structure Program for the Michelson Doppler Imager instrument
  on SOHO is designed to provide valuable helioseismic observations
  through a continuously operating 5 kbps telemetry channel. Only about
  3% of the total MDI raw data can be transmitted without interruption
  to the ground. Therefore, extensive data processing must be performed
  by the MDI instrument in order produce data products that will fit
  into the restricted telemetry and to meet the scientific observing
  requirements. The Structure Program consists of five observing programs:
  the Medium-l Velocity, Low-l (LOI) Velocity and Intensity, Limb Figure,
  Flux Budget, and Magnetic Proxy. These programs generate spatial
  and temporal averages of three of the MDI full disk observables:
  the velocity, computed continuum intensity, and the computed line
  depth. The performance of these filters will be described. The
  goal of the Medium-l Program is to provide reliable measurements
  of solar p-modes in the range of the angular degree, l, from 0 to
  300, by generating a 23,000 bin spatial average of the full disk
  velocity. The Low-l Program re-bins the velocity and continuum intensity
  images into 180 bins, with the intent of observing long period global
  oscillations. The other three Structure Observations are averaged over
  24 minutes with a 12 minute sample time. The Limb Figure extracts a 14
  arcsecond annulus at the Sun's limb in order to study long wavelength
  oscillations in the observed limb. The Flux Budget and Magnetic Proxy
  are 128 by 128 pixel re-bins of the continuum intensity and line depth
  observables respectively, to study the solar luminosity and large
  scale features. Extensive tests of the individual components of the
  Structure Program have been performed during the commissioning phase of
  the SOHO operation. Uninterrupted operation started in April 1996. This
  research is supported by NASA contract NAG5-3077 at Stanford University.

---------------------------------------------------------
Title: The Current State of Solar Modeling
Authors: Christensen-Dalsgaard, J.; Dappen, W.; Ajukov, S. V.;
   Anderson, E. R.; Antia, H. M.; Basu, S.; Baturin, V. A.; Berthomieu,
   G.; Chaboyer, B.; Chitre, S. M.; Cox, A. N.; Demarque, P.; Donatowicz,
   J.; Dziembowski, W. A.; Gabriel, M.; Gough, D. O.; Guenther, D. B.;
   Guzik, J. A.; Harvey, J. W.; Hill, F.; Houdek, G.; Iglesias, C. A.;
   Kosovichev, A. G.; Leibacher, J. W.; Morel, P.; Proffitt, C. R.;
   Provost, J.; Reiter, J.; Rhodes, E. J., Jr.; Rogers, F. J.; Roxburgh,
   I. W.; Thompson, M. J.; Ulrich, R. K.
1996Sci...272.1286C    Altcode:
  Data from the Global Oscillation Network Group (GONG) project and
  other helioseismic experiments provide a test for models of stellar
  interiors and for the thermodynamic and radiative properties, on which
  the models depend, of matter under the extreme conditions found in the
  sun. Current models are in agreement with the helioseismic inferences,
  which suggests, for example, that the disagreement between the predicted
  and observed fluxes of neutrinos from the sun is not caused by errors in
  the models. However, the GONG data reveal subtle errors in the models,
  such as an excess in sound speed just beneath the convection zone. These
  discrepancies indicate effects that have so far not been correctly
  accounted for; for example, it is plausible that the sound-speed
  differences reflect weak mixing in stellar interiors, of potential
  importance to the overall evolution of stars and ultimately to estimates
  of the age of the galaxy based on stellar evolution calculations.

---------------------------------------------------------
Title: Detection of Subsurface Supergranulation Structure and Flows
    from MDI High-Resolution Data using Time-Distance Techniques
Authors: Duvall, T. L., Jr.; Kosovichev, A. G.; Scherrer, P. H.;
   Milford, P. N.
1996AAS...188.4908D    Altcode: 1996BAAS...28Q.898D
  The supergranulation is seen at the surface of the sun in the doppler
  shift of spectrum lines as an apparent cellular convection pattern
  with a scale of about 4% of the solar radius. This scale is about
  30 times larger than the granulation, seen in white light. Why these
  distinct scales would be present (and possibly a third intermediate
  scale mesogranulation) is somewhat of a mystery. Also unknown is
  the depth structure of the convection. We have used acoustic wave
  measurements from the MDI experiment on SOHO to address these
  questions. By crosscorrelating the signal at one location with
  that on annuli centered on the location, it is possible to measure
  times for waves to travel over known subsurface ray paths. With some
  variations on this theme, it is possible to measure horizontal and
  vertical flows and sound speed variations. Of course, the resulting
  measurements refer to quantities integrated along these ray paths. An
  inversion technique based on Fermat's principle has been developed
  and used to map the flow velocities and sound speed variations as
  a function of horizontal position and depth. The MDI experiment on
  SOHO makes doppler shift maps with 1Kx1K points in two choices of
  image scale, 2 and 0.6 arcsec/pixel. For the present study, we have
  used the higher resolution mode to observe 8.5 hours of doppler maps
  sampled once per minute. In order to average enough crosscorrelations
  to see time-distance effects, the resultant time-distance maps are
  reduced in resolution by a factor of 10 from the initial data. This
  still yields about 7 samples across a single supergranulation cell,
  or 49 over the area of a square cell. Our initial inversions based
  on the ray theory suggest that the supergranulation flow extends at
  least to 0.5% of the solar radius below the surface. This research is
  supported by the SOI-MDI NASA contract NAG5-3077 at Stanford University.

---------------------------------------------------------
Title: The Seismic Structure of the Sun
Authors: Gough, D. O.; Kosovichev, A. G.; Toomre, J.; Anderson,
   E.; Antia, H. M.; Basu, S.; Chaboyer, B.; Chitre, S. M.;
   Christensen-Dalsgaard, J.; Dziembowski, W. A.; Eff-Darwich, A.;
   Elliott, J. R.; Giles, P. M.; Goode, P. R.; Guzik, J. A.; Harvey,
   J. W.; Hill, F.; Leibacher, J. W.; Monteiro, M. J. P. F. G.; Richard,
   O.; Sekii, T.; Shibahashi, H.; Takata, M.; Thompson, M. J.; Vauclair,
   S.; Vorontsov, S. V.
1996Sci...272.1296G    Altcode:
  Global Oscillation Network Group data reveal that the internal
  structure of the sun can be well represented by a calibrated standard
  model. However, immediately beneath the convection zone and at the
  edge of the energy-generating core, the sound-speed variation is
  somewhat smoother in the sun than it is in the model. This could be a
  consequence of chemical inhomogeneity that is too severe in the model,
  perhaps owing to inaccurate modeling of gravitational settling or to
  neglected macroscopic motion that may be present in the sun. Accurate
  knowledge of the sun's structure enables inferences to be made about
  the physics that controls the sun; for example, through the opacity,
  the equation of state, or wave motion. Those inferences can then be
  used elsewhere in astrophysics.

---------------------------------------------------------
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.
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: The Internal Structure of the Sun
Authors: Gough, D. O.; Kosovichev, A. G.; GONG Structure Inversions
   Team
1996AAS...188.5303G    Altcode: 1996BAAS...28..903G
  The principal first inferences that have been drawn from the GONG data
  concerning the internal structure of the Sun will be reported. After
  explaining briefly the procedures by which the inferences have been
  drawn, deviations of the spherically averaged structure of the Sun
  from that of standard solar models will be presented. Those deviations
  occur predominantly near the base of the convection zone, and perhaps
  in the energy-generating core. There is also evidence for a deviation
  from spherical symmetry, principally near the surface. The possible
  physical implications of our findings will be discussed.

---------------------------------------------------------
Title: The Solar Acoustic Spectrum and Eigenmode Parameters
Authors: Hill, F.; Stark, P. B.; Stebbins, R. T.; Anderson, E. R.;
   Antia, H. M.; Brown, T. M.; Duvall, T. L., Jr.; Haber, D. A.;
   Harvey, J. W.; Hathaway, D. H.; Howe, R.; Hubbard, R. P.; Jones,
   H. P.; Kennedy, J. R.; Korzennik, S. G.; Kosovichev, A. G.; Leibacher,
   J. W.; Libbrecht, K. G.; Pintar, J. A.; Rhodes, E. J., Jr.; Schou, J.;
   Thompson, M. J.; Tomczyk, S.; Toner, C. G.; Toussaint, R.; Williams,
   W. E.
1996Sci...272.1292H    Altcode:
  The Global Oscillation Network Group (GONG) project estimates
  the frequencies, amplitudes, and linewidths of more than 250,000
  acoustic resonances of the sun from data sets lasting 36 days. The
  frequency resolution of a single data set is 0.321 microhertz. For
  frequencies averaged over the azimuthal order m, the median formal
  error is 0.044 microhertz, and the associated median fractional error
  is 1.6 x 10<SUP>-5</SUP>. For a 3-year data set, the fractional error
  is expected to be 3 x 10<SUP>-6</SUP>. The GONG m-averaged frequency
  measurements differ from other helioseismic data sets by 0.03 to 0.08
  microhertz. The differences arise from a combination of systematic
  errors, random errors, and possible changes in solar structure.

---------------------------------------------------------
Title: Diagnostics of Shallow Convective Structures by Time-Distance
    Helioseismology
Authors: Kosovichev, A. G.; Duvall, T. L., Jr.; Scherrer, P. H.
1996AAS...188.3709K    Altcode: 1996BAAS...28R.878K
  We present a new method of 3D helioseismic diagnostics to study
  subphotospheric flow and thermal and magnetic structure associated with
  turbulent convection. The main difference from the previous studies
  by Duvall et al. (1996, Nature, 379, 235) and by Kosovichev (1996,
  ApJL, 461, L55) is that the new method can be applied for measuring
  solar properties in the shallow layer just beneath the surface. The
  shallow layer of superadiabatic convection, which is only few thousand
  kilometers deep, is the region of the greatest uncertainty in our
  knowledge of the Sun's interior. Recent numerical simulations have
  demonstrated substantial deviations of the structure of this layer from
  the mixing-length theory commonly used in modeling stellar structure
  and evolution. The uncertainty in the physics of turbulent convection
  also affects helioseismic inferences about the deep interior. Our method
  of 3D diagnostics is based on measuring and inverting anomalies of the
  sound-wave travel time between two areas on the solar surface. Because
  of the stochastic nature of solar waves, these two areas must
  be sufficiently large to provide a good signal-to-noise ratio. In
  practice, the travel time can be measured from the cross-correlation
  function averaged over several thousand cross-correlations between
  individual points on the surface. Therefore, it is essential to have
  stable high-resolution series of Doppler images. Such data have been
  obtained from the Michelson Doppler Imager instrument on SOHO. In this
  paper, we present some details of the cross-correlation time-distance
  analysis, and the technique to invert the travel-time measurements using
  the optical ray approximation. The travel time of the waves depends
  primarily on the wave group velocity and on the velocity of flow along
  the ray paths. The effects of the wave speed structure and of flows are
  separated by measuring the travel time of waves propagating in opposite
  directions along the same ray paths. The effects of magnetic fields are
  measured through anisotropy of the wave speed. We discuss the limits
  for observing small-scale features beneath the surface. This research is
  supported by the SOI-MDI NASA contract NAG5-3077 at Stanford University.

---------------------------------------------------------
Title: Tomographic Imaging of the Sun's Interior
Authors: Kosovichev, A. G.
1996ApJ...461L..55K    Altcode:
  A new method is presented of determining the three-dimensional
  sound-speed structure and flow velocities in the solar convection
  zone by inversion of the acoustic travel-time data recently obtained
  by Duvall and coworkers. The initial inversion results reveal
  large-scale subsurface structures and flows related to the active
  regions, and are important for understanding the physics of solar
  activity and large-scale convection. The results provide evidence
  of a zonal structure below the surface in the low-latitude area of
  the magnetic activity. Strong converging downflows, up to 1.2 km s-1,
  and a substantial excess of the sound speed are found beneath growing
  active regions. In a decaying active region, there is evidence for
  the lower than average sound speed and for upwelling of plasma.

---------------------------------------------------------
Title: Helelioseismic constraints on the properties of the solar
    core and on the solar neutrino fluxes.
Authors: Kosovichev, A.
1996sube.conf..171K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The Solar Oscillations Investigation - Michelson Doppler Imager
Authors: Scherrer, P. H.; Bogart, R. S.; Bush, R. I.; Hoeksema, J. T.;
   Kosovichev, A. G.; Schou, J.; Rosenberg, W.; Springer, L.; Tarbell,
   T. D.; Title, A.; Wolfson, C. J.; Zayer, I.; MDI Engineering Team
1995SoPh..162..129S    Altcode:
  The Solar Oscillations Investigation (SOI) uses the Michelson Doppler
  Imager (MDI) instrument to probe the interior of the Sun by measuring
  the photospheric manifestations of solar oscillations. Characteristics
  of the modes reveal the static and dynamic properties of the
  convection zone and core. Knowledge of these properties will improve
  our understanding of the solar cycle and of stellar evolution. Other
  photospheric observations will contribute to our knowledge of the
  solar magnetic field and surface motions. The investigation consists
  of coordinated efforts by several teams pursuing specific scientific
  objectives.

---------------------------------------------------------
Title: Probing the Sun's Interior Structure and Flows By Tomographic
    Inversion
Authors: Kosovichev, A. G.
1995AAS...18710111K    Altcode: 1995BAAS...27.1427K
  I present results of inversion of travel-time maps recently obtained
  by Duvall, Jefferies and Harvey (1995, BAAS, v.25, 950). The maps
  represent measurements of the time for acoustic waves to travel between
  points on a solar surface and surrounding annuli. The measurements
  are sensitive to perturbations of the sound speed and flows along the
  ray pathes. A 3D inversion method based on Fermat's Principle and a
  conjugate-gradient technique has been applied to infer the sound speed
  and the velocity of flows from the observations obtained by Duvall
  et al. at the South Pole Jan. 4-5 1991. The spatial resolution of the
  inversion is 1.75 degree in both longitude and latitude, and 15 Mm in
  depth. The results reveal large-scale subsurface structures and flows
  related to the active regions, and are important for understanding
  the physics of solar activity and large-scale convection.

---------------------------------------------------------
Title: Non-linear effects at tidal capture of stars by a massive
    black hole - II. Compressible affine models and tidal interaction
    after capture
Authors: Diener, P.; Kosovichev, A. G.; Kotok, E. V.; Novikov, I. D.;
   Pethick, C. J.
1995MNRAS.275..498D    Altcode:
  This paper continues our investigations published in Paper I. The
  tidal interaction of stars with a massive black hole after tidal
  capture is investigated in the framework of the ellipsoidal `affine'
  stellar model proposed by Carter &amp; Luminet. We investigate the
  influence of the orientation of the ellipsoidal stellar model and
  the influence of the phase and amplitude of the oscillations on the
  subsequent passages. Finally a parametrization of the probability for
  a star to lose (or gain) energy during subsequent passages is found
  for a compressible model.

---------------------------------------------------------
Title: Helioseismic measurement of element abundances in the solar
    interior
Authors: Kosovichev, A. G.
1995AdSpR..15g..95K    Altcode: 1995AdSpR..15...95K
  Inversions of the current solar data give a value for the helium
  abundance in the convection zone, which is significantly lower than
  the value in standard solar models, thus suggesting that gravitational
  settling of helium takes place in the Sun. This is consistent with the
  inversion results in the radiative interior, where evidence is found
  for large-scale material redistribution. There is also indication
  of variations of the helium abundance in the energy-generating core,
  which are not described by standard solar evolution theory.

---------------------------------------------------------
Title: Coronal Manifestations of Oscillations: a Numerical Model
Authors: Andreev, A. S.; Kosovichev, A. G.
1995ESASP.376b.471A    Altcode: 1995help.confP.471A; 1995soho....2..471A
  No abstract at ADS

---------------------------------------------------------
Title: Structure of the Solar Core: Inversion of Recent Low-Degree
    Data
Authors: Kosovichev, A. G.
1995ESASP.376b..21K    Altcode: 1995soho....2...21K; 1995help.confP..21K
  The deviations of the property, u ≡ p/ρ, in the Sun's interior from
  a standard solar model have been studied by inverting six different
  sets of frequencies of low-degree modes, obtained from space- and
  ground-based observations. The results from the IPHIR space experiment,
  the IRIS network and from the LOI ground-based observations indicate
  an increase of the deviation δu towards the center. The inversions
  of the three datasets from BISON, corresponding to low, high and mean
  levels of solar activity, show complicated changes of δu in the core
  among the datasets, with the average tendency of decreasing towards
  the center. The reason of the inconsistency between BISON and the
  other datasets remains unknown. Nevertheless, property u (or the speed
  of sound) in the central core inferred from each of the datasets is
  higher than in a solar model with gravitational settling of helium,
  which is currently the closest to the inversion results.

---------------------------------------------------------
Title: An Attempt to Measure Latitudinal Variation of the Depth of
    the Convection Zone
Authors: Gough, D. O.; Kosovichev, A. G.
1995ESASP.376b..47G    Altcode: 1995help.confP..47G; 1995soho....2...47G
  The location of the base of the convection zone coincides with the
  sharp variation of the slope of the relative difference in the quantity
  u = p/ρ between the Sun and a solar model, provided that the zone
  of adiabatic convection is deeper in the model than in the Sun. The
  authors have determined the difference δu/u as a function of radius at
  various latitudes between the Sun and a spherically symmetrical solar
  model by inverting the BBSO data (Libbrecht and Woodard, 1993). The
  results offer evidence that the convection zone may be somewhat deeper
  at the equator than it is at the poles. The variation of the depth,
  however, does not exceed 0.2 R<SUB>sun</SUB>.

---------------------------------------------------------
Title: Seismic Response to Solar Flares: Theoretical Predictions
Authors: Kosovichev, A. G.; Zharkova, V. V.
1995ESASP.376b.341K    Altcode: 1995help.confP.341K; 1995soho....2..341K
  No abstract at ADS

---------------------------------------------------------
Title: Constrained Estimates of Low-Degree Mode Frequencies and the
    Determination of the Interior Structure of the Sun
Authors: Gough, D. O.; Kosovichev, A. G.; Toutain, T.
1995SoPh..157....1G    Altcode:
  Low-degreep-modes penetrate to the solar centre and provide direct
  information about the core. However, the high observational accuracy
  that is required to resolve the details of the structure of the core
  is difficult to achieve because the oscillation power spectrum is
  significantly distorted by stochastic forcing of the oscillations,
  which appears as multiplicative noise. Here, an attempt is reported to
  reduce uncertainties of spectral parameter estimation by incorporating
  constraints imposed by smooth behaviour of some of the parameters
  (e.g., linewidths, background noise, rotational splitting) over a
  group of lines. Instead of estimating these parameters independently
  for each line, we determine them as smooth functions of frequency. It
  is expected that this procedure gives more accurate estimates of the
  average frequencies of any multiplet in the power spectrum, to which
  we have applied no constraints. We give some examples of the procedure
  for whole-disk measurements by the IPHIR space experiment. It is shown
  that the additional constraints do not result in significant changes
  in the frequency estimates, except for one mode whose peak in the power
  spectrum has the lowest signal-to-noise ratio. However, the uncertainty
  in the frequency of that mode does not influence substantially the
  results of the structure inversion in the core. Inversions of the IPHIR
  datasets are compared with corresponding inversions of data from the
  Birmingham Solar Oscillation Network (BISON). The IPHIR data indicate
  a sharp increase towards the centre of the deviation of the squared
  sound speed of the sun from that of a standard solar model, whereas the
  BISON data show a decrease. The difference between the IPHIR and BISON
  inversions is significant, preventing any definite conclusion about
  the deviation of the structure of the solar core from that of the model.

---------------------------------------------------------
Title: Solar Cycle Variations of the Internal Rotation: a Search
    for Dynamo Waves
Authors: Kosovichev, A. G.
1995SPD....26..405K    Altcode: 1995BAAS...27..955K
  No abstract at ADS

---------------------------------------------------------
Title: Testing the Statistical Significance of the Asymmetries of
p-Mode Line Profiles: Application to the IPHIR Data
Authors: Appourchaux, T.; Toutain, T.; Gough, D. O.; Kosovichev, A.
1995ASPC...76..314A    Altcode: 1995gong.conf..314A
  No abstract at ADS

---------------------------------------------------------
Title: The Upper Convective Boundary Layer
Authors: Kosovichev, A. G.
1995ESASP.376a.165K    Altcode: 1995soho....1..165K; 1995heli.conf..165K
  Reviews the progress that has been made in our understanding of
  the physics of the upper boundary layer of the Sun, its influence on
  frequencies of five-minute oscillations, and its role in excitation of
  the oscillations. The author also discusses approaches to seismological
  diagnosis of the properties of the layer, important information about
  which will be obtained from MDI high-resolution data.

---------------------------------------------------------
Title: Constraints on Oblique Rotation of the Solar Core from
    Low-Degree Modes
Authors: Gough, D. O.; Kosovichev, A. G.; Toutain, T.
1995ASPC...76...55G    Altcode: 1995gong.conf...55G
  No abstract at ADS

---------------------------------------------------------
Title: Working Group 9 - Interior Structure and Inversions
Authors: Kosovichev, A. G.; Basu, S.; Christensen-Dalsgaard, J.;
   Eff-Darwich, A.; Gough, D. O.; Iglesias, C. A.; Pérez-Hernández,
   F.; Rogers, F.; Sekii, T.; Shibahashi, H.
1995ESASP.376a.211K    Altcode: 1995heli.conf..211K
  No abstract at ADS

---------------------------------------------------------
Title: Prediction of g-Mode Frequencies
Authors: Kosovichev, A. G.; Gavryuseva, E. A.
1995ASPC...76..180K    Altcode: 1995gong.conf..180K
  No abstract at ADS

---------------------------------------------------------
Title: Inversions of BBSO Rotational Splitting Data
Authors: Sekii, T.; Gough, D. O.; Kosovichev, A. G.
1995ASPC...76...59S    Altcode: 1995gong.conf...59S
  No abstract at ADS

---------------------------------------------------------
Title: Frequencies of Low-Degree Modes and the Structure of the
    Solar Core
Authors: Gough, D. O.; Kosovichev, A. G.; Toutain, T.
1995ASPC...76..176G    Altcode: 1995gong.conf..176G
  No abstract at ADS

---------------------------------------------------------
Title: Seismic Effects of North-South Asymmetry of Sun's Rotation
Authors: Gough, D. O.; Kosovichev, A. G.
1995ASPC...76...63G    Altcode: 1995gong.conf...63G
  No abstract at ADS

---------------------------------------------------------
Title: Determination of Interior Structure by Inversion
Authors: Kosovichev, A. G.
1995ASPC...76...89K    Altcode: 1995gong.conf...89K
  No abstract at ADS

---------------------------------------------------------
Title: Numerical modeling of macrospicules and mass ejections in
    the corona
Authors: Andreev, A. S.; Kosovichev, A. G.
1994ESASP.373..179A    Altcode: 1994soho....3..179A
  No abstract at ADS

---------------------------------------------------------
Title: Modelling UV spectral lines from solar coronal transients
Authors: Kosovichev, A. G.; Spadaro, D.; Stepanova, T. V.; Ventura, R.
1994ESASP.373..159K    Altcode: 1994soho....3..159K
  No abstract at ADS

---------------------------------------------------------
Title: Helioseismological measurements of the distribution of helium
    inside the Sun
Authors: Kosovichev, A. G.
1994AAS...18512301K    Altcode: 1994BAAS...26.1522K
  Helioseismology provides a unique tool for investigating chemical
  composition of the interior of the Sun. There are two basic ways of
  obtaining the information. The first one is to calibrate theoretical
  solar models by comparing either the observed oscillation frequencies
  with the eigenfrequencies of the models, or primary seismic parameters
  (e.g. the sound speed, the density and the adiabatic exponent) inverted
  from the observed frequencies with the corresponding parameters of
  the solar models. The second approach is to measure abundances by
  direct (`secondary') inversions of the frequencies, incorporating
  additional equations of the stellar structure into the helioseismic
  inverse problem. The additional equation to estimate composition of
  the convection zone is the equation of state which relates variations
  of the adiabatic exponent in zones of ionization of elements to their
  abundances. In the radiative interior where the most abundant elements
  are almost totally ionized, the energy equations together with equations
  of the energy generation rate and the opacity are used to relate primary
  seismic parameters with abundances. Inversions of the current solar
  data give a value for the helium abundance in the convection zone,
  which is significantly lower than the value in standard solar models,
  thus suggesting that gravitational settling of helium takes place
  in the Sun. This is consistent with the inversion results in the
  radiative interior, where evidence is found for large-scale material
  redistribution. There is also indication of variations of the helium
  abundance in the energy-generating core, which are not described by
  standard solar evolution theory. It is anticipated that the new data
  from the GONG and SOI will substantially improve accuracy of the
  measurements of the helium abundance.

---------------------------------------------------------
Title: Modeling of dynamic evolution of roconal loops
Authors: Stepanova, T. V.; Kosovichev, A. G.
1994SSRv...70..171S    Altcode:
  Parameters of expanding magnetic loops and arches and of mass flows
  generated by them in the corona have been computed in a 1D two-fluid
  approximation. Two possible trigger mechanisms of the coronal transients
  have been considered: (i) sudden increase of the background magnetic
  field strength, and (ii) heating and compression plasma inside these
  magnetic structures. We discuss the formation of shock waves and their
  dependence on dynamics and geometry of the magnetic structures.

---------------------------------------------------------
Title: Numerical simulations of spicule driving mechanisms
Authors: Andreev, A. S.; Kosovichev, A. G.
1994SSRv...70...53A    Altcode:
  Spicules are known as one of the most prevalent small-scale
  dynamic phenomena on the sun, which are likely to give considerable
  contribution to coronal heating and mass supply. We discuss a model
  of the spicules driven by a train of slow MHD shock waves propagating
  along a vertical expanding magnetic flux tube. The shocks are initiated
  due to compression of the tube by the increasing external pressure
  in the lower chromosphere. Downflow of spicular material depends on
  radiative cooling and other dissipative processes.

---------------------------------------------------------
Title: On a mechanism of spicule formation by shock waves in
    magnetic tubes
Authors: Andreev, A. S.; Kosovichev, A. G.
1994AstL...20..323A    Altcode: 1994PAZh...20..383A
  No abstract at ADS

---------------------------------------------------------
Title: A new estimate of the solar core rotation from IPHIR.
Authors: Toutain, T.; Kosovichev, A. G.
1994A&A...284..265T    Altcode:
  The effect of a rigidly rotating core on frequency splitting is shown
  to be approximately the same for all the observed low-degree modes. It
  is suggested that, in analysing poorly resolved rotationally split
  multiplets in oscillation power spectra, one should first determine
  a single value for the splitting instead of estimating the splitting
  for individual modes separately. By using this technique for fitting
  lines with l=1, 2 of the IPHIR spectra, a mean sidereal splitting of
  0.468+/-0.036 and of 0.427+/-0.046 μHz has been obtained for the green
  and red channels of the IPHIR photometer, respectively. The average
  value of these measurements, 0.452+/-0.020 μHz, suggests that the
  central core of the sun rotates with the same period of approximately
  26 days as the outer part of the radiative zone.

---------------------------------------------------------
Title: Helioseismic evidence for mixing in the radiative interior
Authors: Kosovichev, A. G.
1994LNP...432...47K    Altcode: 1994LNPM...11...47K
  Results are presented of a determination of the hydrostatic parameters
  of the solar structure, namely density, sound speed, and a parameter
  of convectioe stability, by direct inversion of solar oscillation
  frequencies. The analysed data sets include frequencies of acoustic
  modes of intermediate degree (l = 4 - 140, observed by Libbrecht et
  al. (1990, and those of low degree (l = 0 - 2), obtained from the IPHIR
  space experiment (Toutain and Fröhlich 1992. The low-degree data sets
  are of particular importance for resolving the structure of the solar
  core. The inversion results show that the overall structure of the solar
  interior is consistent with a non-standard solar model constructed by
  Christensen-Dalsgaard et al. (1993 by increasing opacities beneath the
  convection zone in accordance with Rogers and Iglesias (1992, and by
  taking into account gravitational settling of helium. The inversions
  give also evidence for an overshoot beneath the convection zone and
  for a moderate localized mixing in the energy-generating core.

---------------------------------------------------------
Title: Seismic measurements of the helium abundance and the depth
    of stellar convection zones
Authors: Kosovichev, A. G.
1993MNRAS.265.1053K    Altcode:
  A new inversion technique is presented for measuring the depth of
  stellar convection zones and the helium abundance from oscillation
  frequencies of low-degree modes. It is based on a linearized variational
  principle for stellar oscillations, reformulated in terms of a parameter
  of convective stability (which is proportional to the radial gradient
  of the specific entropy) and the helium abundance, by using the
  equations of hydrostatic support of stellar structure and the equation
  of state. In addition, it is assumed that the parameter of convective
  stability is close to zero in the zones of adiabatic convection. It
  is then possible to locate the lower boundary of the convection zone
  in the envelope by applying a regularized least-squares fit to the
  oscillation frequencies. It is demonstrated that the technique works
  for low-degree data alone, such as can be obtained from full-disk
  measurements. The technique has been applied to solar data obtained
  from the IPHIR instrument on the Phobos spacecraft. The estimates of
  the solar helium abundance and the depth of the convection zone so
  obtained are discussed.

---------------------------------------------------------
Title: The Influence of Low-Degree P-Mode Frequencies on the
    Determination of the Structure of the Solar Interior
Authors: Gough, D. O.; Kosovichev, A. G.
1993MNRAS.264..522G    Altcode:
  Accurate measurements of the frequencies of low-degree acoustic
  oscillations provide valuable information about the structure of the
  solar core. We determine the radial resolution that can be achieved by
  direct inversions of frequency data sets recently obtained by various
  observers to find the hydrostatic parameters density, sound speed and
  a parameter of convective stability. The outcome of those inversions
  indicates that the outer part of the radiative zone of the Sun is
  similar to that of a solar model that takes account of helium settling
  against microscopic diffusion. From the two data sets with lowest
  estimated errors (those by Toutain &amp; Fröhlich and Anguera Gubau
  et al.) there is some evidence for an error in the modelling of the
  energy-generating core, which could be accounted for by local material
  redistribution in the core. Another data set by Elsworth et al.,
  however, is almost compatible with the core of the theoretical model.

---------------------------------------------------------
Title: Interplanetary shocks generated by expanding magnetic loops
Authors: Stepanova, T. V.; Kosovichev, A. G.
1993AdSpR..13f..51S    Altcode: 1993AdSpR..13...51S
  We present a self-consistent numerical model of shock wave formation in
  the heliosphere by an expanding magnetic loop. In the model a coronal
  mass ejection is initiated by a loss of magnetohydrostatic equilibrium
  of the loop as a result of an increase of underlying magnetic field
  strength. The expanding magnetic loops produce propagating shock
  waves. <P />The plasma motions are described by a system of two-fluid
  Navier-Stokes equations taking account of modified coefficients for
  electron and ion heat conduction, ion viscosity and energy exchange
  between ions and electrons. <P />We obtain shock wave parameters in the
  outer heliosphere vs initial perturbations of the magnetic loops, and
  show that the shocks can be divided into two types, depending on their
  intensity. In the case of relatively weak shocks a typical feature
  is formation of a dense and cold layer (“piling-up” of material)
  near the upper boundary of the loop. In the case of strong shocks
  large-scale turbulence and viscous heating in the relaxation zone
  behind the front play an important role, and no appreciable piling-up
  of plasma occurs. <P />We demonstrate that expanding magnetic loops,
  which are observed as magnetic clouds in the outer heliosphere, can
  effectively drive transient shocks ahead.

---------------------------------------------------------
Title: Helioseismic Test of the Standard Solar Model
Authors: Kosovichev, A. G.
1993BAAS...25.1219K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Seismic evidence of modulation of the structure and angular
    velocity of the Sun associated with the solar cycle
Authors: Gough, D. O.; Kosovichev, A. G.; Sekii, T.; Libbrecht, K. G.;
   Woodard, M. F.
1993ASPC...40...93G    Altcode: 1993IAUCo.137...93G; 1993ist..proc...93G
  No abstract at ADS

---------------------------------------------------------
Title: On the Influence of Treatment of Heavy Elements in the Equation
    of State on the Resulting Values of the Adiabatic Exponent
Authors: Däppen, W.; Gough, D. O.; Kosovichev, A. G.; Rhodes,
   E. J., Jr.
1993ASPC...40..304D    Altcode: 1993ist..proc..304D
  No abstract at ADS

---------------------------------------------------------
Title: The High-Frequency P-Mode Spectrum
Authors: Milford, P. N.; Scherrer, P. H.; Frank, Z.; Kosovichev,
   A. G.; Gough, D. O.
1993ASPC...42...97M    Altcode: 1993gong.conf...97M
  No abstract at ADS

---------------------------------------------------------
Title: The Form of the Angular Velocity in the Solar Convection Zone
Authors: Gough, D. O.; Kosovichev, A. G.; Sekii, T.; Libbrecht, K. G.;
   Woodard, M. F.
1993ASPC...42..213G    Altcode: 1993gong.conf..213G
  No abstract at ADS

---------------------------------------------------------
Title: Initial asteroseismic inversions
Authors: Gough, D. O.; Kosovichev, A. G.
1993ASPC...40..541G    Altcode: 1993IAUCo.137..541G; 1993ist..proc..541G
  No abstract at ADS

---------------------------------------------------------
Title: Seismic Analysis of Stellar P-Mode Spectra
Authors: Gough, D. O.; Kosovichev, A. G.
1993ASPC...42..351G    Altcode: 1993gong.conf..351G
  No abstract at ADS

---------------------------------------------------------
Title: It is possible to determine whether a star is rotating about
    a unique axis?
Authors: Gough, D. O.; Kosovichev, A. G.
1993ASPC...40..566G    Altcode: 1993IAUCo.137..566G; 1993ist..proc..566G
  No abstract at ADS

---------------------------------------------------------
Title: Plans for MT.WILSON - Crimean Observatory High-Degree
    Helioseismology Network
Authors: Rhodes, E. J., Jr.; Cacciani, A.; Dappen, W.; Didkovsky,
   L. V.; Hill, F.; Korzennik, S. G.; Kosovichev, A. G.; Kotov, V. A.;
   Scherrer, P. H.
1993ASPC...42..477R    Altcode: 1993gong.conf..477R
  No abstract at ADS

---------------------------------------------------------
Title: Sources of uncertainty in direct seismological measurements
    of the solar helium abundance
Authors: Kosovichev, A. G.; Christensen-Dalsgaard, J.; Daeppen, W.;
   Dziembowski, W. A.; Gough, D. O.; Thompson, M. J.
1992MNRAS.259..536K    Altcode:
  The methods by which Dappen et al. (1988, 1990, 1991) and Dziembowski
  et al. (1990, 1991, 1992) recently obtained discrepant estimates of
  the helium abundance in the solar convection zone are compared. The
  aim of the investigation reported in this paper is to identify the
  main source of the discrepancy. Using as proxy data eigenfrequencies
  of a set of modes of a theoretical solar model, computed with the
  same physics as were the frequencies of a reference model with which
  these data are compared, the two methods yield similar results. Thus
  we ascertain that the principal source of the discrepancy is not in
  the inversions themselves, which yield essentially a measure of the
  variation of the adiabatic exponent gamma of the material in the He II
  ionization zone. Instead it is in the approximations adopted in the
  treatment of heavy elements in the equation of state used to relate
  the variation of gamma to chemical composition. We obtain acceptably
  consistent results when inverting solar data by two methods using the
  same equation of state. We attempt to identify the likely residual
  sources of uncertainty.

---------------------------------------------------------
Title: A numerical model of interaction of coronal transients with
    the solar wind.
Authors: Stepanova, Tatiana V.; Kosovichev, A. G.
1992ESASP.348..209S    Altcode: 1992cscl.work..209S
  The authors consider loss of hydrostatic equilibrium of a coronal
  magnetic loop as a result of an increase of the magnetic field under
  the loop and as a result of a flare-induced heating of plasma inside
  the loop. The expanding magnetic loops act as a piston on coronal
  plasma and produce shock waves propagating in the solar wind. The
  shock waves are computed in a one-dimensional, two-fluid approximation,
  taking into account the processes of turbulent dissipation. The authors
  describe two regimes of the process: i) almost monotonic expansion of
  a magnetic loop with a strong shock ahead of it, when magnetic forces
  are dominant; ii) oscillatory expansion of a loop with multiple shocks
  in the ambient plasma, if the magnetic forces can be balanced by the
  gravity force when there is a significant mass input into the loop.

---------------------------------------------------------
Title: Non-linear effects at tidal capture of stars by a massive
    black hole. I - Incompressible affine model
Authors: Kosovichev, A. G.; Novikov, I. D.
1992MNRAS.258..715K    Altcode:
  Non-linear effects of the tidal interaction of a star with a massive
  black hole are discussed on the basis of an ellipsoidal 'affine' stellar
  model proposed by Carter and Luminet. The effects are considered for an
  incompressible stellar model. We compute the amount of energy deposited
  into the star from the orbital motion by tidal forces and determine
  an effective Roche limit of tidal disruption for a parabolic orbit. A
  comparison between the non-linear affine model and a linear theory of
  small perturbations is made, and the limits of their applicability are
  found. The dynamics of the tidal interactions at subsequent pericenter
  passages after the tidal capture are considered, and it is shown that
  the non-linear effects significantly reinforce the absorption of the
  orbital energy by the star, and result in tidal disruptions far beyond
  the Roche limit.

---------------------------------------------------------
Title: Numerical model for coronal shock wave formation in two-fluid
    approximation
Authors: Kosovichev, A. G.; Stepanova, T. V.
1992sws..coll...61K    Altcode:
  We present results of modeling of shock waves, generated by coronal
  transients and expanding flare loops. We consider loss of hydrostatic
  equilibrium of a magnetic loop as a result of an increase of the
  magnetic field under the loop and as a result of a flare-induced
  heating of plasma inside the loop. The expanding magnetic loops act
  as a piston on coronal plasma and produce shock waves propagating
  in the solar wind. The shock waves are computed in one-dimensional,
  two-fluid approximation, by taking into account the processes of
  turbulent dissipation. The corresponding gas-dynamic equations are
  solved simultaneously with equations of motion of the magnetic tube
  to provide a self-consistent picture of the shock formation by the
  transients.

---------------------------------------------------------
Title: Numerical simulation of shock waves in the heliosphere
Authors: Kosovichev, A. G.; Stepanova, T. V.
1991AZh....68.1283K    Altcode:
  Results of calculations of shock waves generated by coronal transients
  and expanding flare loops are presented. The expanding magnetic
  loops act as a piston on the coronal plasma and produce shock waves
  propagating in the solar wind. The shock waves are computed in a 1D
  two-fluid approximation, taking turbulent dissipation processes into
  account. Shock wave parameters are obtained as functions of the initial
  perturbations of the magnetic loops.

---------------------------------------------------------
Title: Numerical Simulation of Shocks in the Heliosphere
Authors: Kosovichev, A. G.; Stepanova, T. V.
1991SvA....35..646K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Construction of a Seismic Model of the Sun
Authors: Kosovichev, A. G.; Fedorova, A. V.
1991SvA....35..507K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: A New Inversion for the Hydrostatic Stratification of the Sun
Authors: Däppen, W.; Gough, D. O.; Kosovichev, A. G.; Thompson, M. J.
1991LNP...388..111D    Altcode: 1991ctsm.conf..111D
  Inversions for the spherically symmetric component of the hydrostatic
  stratification of the Sun are presented. These employ the Backus-Gilbert
  optimally localized averaging procedure applied to oscillation multiplet
  frequencies in the range 1.5 - 3 mHz of modes with 4 l 140 determined
  by Libbrecht et al. (1990) from observations carried out in 1986. We
  also obtain an estimate of the helium abundance in the solar convective
  envelope.

---------------------------------------------------------
Title: Oscillations and Tidal Resonance Phenomena in the Beta-Lyrae
    System
Authors: Kosovichev, A. G.; Skulskii, M. Y.
1990SvAL...16..103K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Oscillation and tidal resonant phenomena in beta-Lyrae.
Authors: Kosovichev, A. G.; Skulsky, M. Yu.
1990PAZh...16..240K    Altcode:
  In the Beta Lyrae system, oscillations in H-alpha emission lines
  and magnetic field variations with a period of 1.85 d have been
  observed. It is suggested that these oscillations and variations are
  related to the excitation of quadrupole fundamental eigenmodes in the
  bright component of the binary system. This excitation is the result
  of a resonant interaction between the modes and the tidal wave, due
  to asynchronized orbital and rotational periods.

---------------------------------------------------------
Title: Helioseismological Determination of Stratification and Dynamic
    Processes in the Solar Core
Authors: Kosovichev, A. G.
1990IAUS..142...56K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Structure of the Solar Core Inferred from Inversion of
    Frequencies of Low-Degree p-Modes
Authors: Kosovichev, A. G.
1990LNP...367..319K    Altcode: 1990psss.conf..319K
  Results of estimations of density and a parameter of convective
  stability in the central regions of the Sun from observed frequencies
  of 5-min modes are presented.

---------------------------------------------------------
Title: Using Helioseismic Data to Probe the Hydrogen Abundance in
    the Solar Core
Authors: Gough, D. O.; Kosovichev, Alexander G.
1990ASSL..159..327G    Altcode: 1990IAUCo.121..327G; 1990insu.conf..327G
  No abstract at ADS

---------------------------------------------------------
Title: An attempt to understand the stanford p-mode data.
Authors: Gough, Douglas O.; Kosovichev, A. G.
1988ESASP.286..195G    Altcode: 1988ssls.rept..195G
  The p-mode frequencies reported by Henning and Scherred (1986),
  showing anomalous behavior at degree 5 and frequencies below 2
  mHz were investigated. No plausible solar model is consistent with
  them. A density inversion including the low-degree 5 min data of
  Jimenez et al. (1988) implies that the density of the solar core
  is 10 percent greater than it is in the standard solar model 1 of
  Christensen-Dalsgaard (1982). Although that result is in keeping with
  previous suggestions either that the Sun has a greater evolutionary
  age than is usually supposed or that there is a cloud of weakly
  interacting massive particles in the solar core and its environs,
  the behavior of the sound speed in the core is not consistent with
  either hypothesis. Both the inferred sound-speed variation, and a
  secondary inversion for hydrogen abundance (relying on an assumption of
  thermal balance), provide evidence for material redistribution in the
  energy-generating core. A sound-speed inversion for the entire radiative
  interior, using also frequencies of low and intermediate degree compiled
  by Duvall et al. (1988), confirms the earlier finding that the sound
  speed in the Sun exceeds that of a standard solar model by up to 1
  percent in a region extending 30 percent of the solar radius and centred
  at r = 0.4R. That is consistent with, though does not necessarily
  imply, that the opacity in the outer layers of the radiative interior
  at temperatures of up to 4 million K is underestimated by 20 percent.

---------------------------------------------------------
Title: The effect of a nonspherical sound speed on the acoustic
    frequency spectrum of the Sun.
Authors: Kosovichev, A. G.; Perdang, J.
1988ESASP.286..539K    Altcode: 1988ssls.rept..539K
  The authors study the effect on the solar acoustic frequency spectrum
  of a localised deviation from spherical symmetry concentrated near the
  outer convective zone of the sun. The local asymmetry is modelled by
  an angular-dependent contribution to the sound speed. Calculations of
  the acoustic frequencies in the range 1500 to 4000 μHz have been made
  for a nonspherical deformation of relative amplitude ɛ varying from
  0 to 0.1. For ɛ &gt; 0.02 all acoustic frequencies of this range are
  strongly and irregularly displaced (quantum chaos). For lower values of
  ɛ only a small fraction of the frequencies are irregularly shifted. The
  deviation of the frequency spectrum of the deformed solar model with
  respect to the spectrum of a spherically symmetric model is measured by
  a relative scatter σ(ɛ). The relative scatter σ<SUB>obs</SUB> of the
  current observed solar frequencies with respect to the frequencies of
  a standard spherically symmetric solar model is found to correspond to
  an amplitude of the disturbance ɛ = 0.025. The results are indicative
  that even slight local asymmetries influence the precise positions
  of the frequencies. They suggest the possibility of a diagnosis of
  nonspherical effects in the structure of the sun.

---------------------------------------------------------
Title: Determination of the solar speed by an asymptotic inversion
    technique.
Authors: Kosovichev, A. G.
1988ESASP.286..533K    Altcode: 1988ssls.rept..533K
  A new asymptotic inversion technique is developed using a weighted
  least-squares bicubic spline fit to the observational data. The accuracy
  of the asymptotic approach is discussed, and it is shown that the
  asymptotic theory is adequate to determine the sound speed in the
  solar interior between 0.4 and 0.9 R. The inversion of the data of
  Duval et al. (1988) shows that the sound speed between 0.4 and 0.7
  R is about 1% greater than it is in the standard solar model 1 of
  Christensen-Dalsgaard (1982); this result is in agreement with the
  previous asymptotic inversion of Christensen-Dalsgaard et al. (1985)
  and also that of Christensen-Dalsgaard et al. (1988). It is also
  consistent with the inversions presented by Gough and Kosovichev (1988)
  using a kernel function approach.

---------------------------------------------------------
Title: An Asymptotic Solution of the Inverse Problem of
    Helioseismology for the Internal Differential Rotation of the Sun
Authors: Kosovichev, A. G.; Parchevskii, K. V.
1988SvAL...14..201K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The Structure of Thermal Waves in High-Temperature Solar-Flare
    Plasma
Authors: Kosovichev, A. G.
1988SvAL...14..243K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The structure of thermal waves in a high temperature flare
    plasma
Authors: Kosovichev, A. G.
1988PAZh...14..569K    Altcode:
  A numerical simulation of thermal waves which have been observed
  in the high-temperature plasma (T<SUB>e</SUB> ≡ 10<SUP>7</SUP>K,
  n<SUB>e</SUB> ≡ 10<SUP>10</SUP>cm<SUP>-3</SUP>) are carried
  out. Heat flow saturation and ion heating have been taken into
  account. It is shown that in the case of high energy input rate (with
  the characteristic time τ<SUB>0</SUB> ⪉ 1 s) the thermal wave is
  a running temperature pulse with a steep front. Otherwise, in the
  case of gradual energy input (τ<SUB>0</SUB> ⪆ 3 s), the thermal
  wave with a monotonous temperature profile is formed. The calculated
  velocities of the thermal waves correspond to the observed values of
  (900 - 1600) km/s at the energy input of 3×10<SUP>30</SUP>erg on the
  timescale τ<SUB>0</SUB> = (7 - 10) s.

---------------------------------------------------------
Title: An asymptotic solution to the inverse problem of
    helioseismology for determining the internal differential rotation
    of the sun
Authors: Kosovichev, A. G.; Parchevskii, K. V.
1988PAZh...14..473K    Altcode:
  The dependence of angular velocity versus radius and latitude in the
  solar interior can be obtained from the frequency splitting of 5 minute
  oscillations by solving two-dimensional integral Abels equation, if
  the observational data are presented as a function of (l+1/2)/σ and
  (l+1/2)/m.

---------------------------------------------------------
Title: The determination of the angular velocity of the sun's inner
    rotation using helioseismological data
Authors: Kosovichev, A. G.
1988PAZh...14..344K    Altcode:
  Duvall and Harvey's (1984) and Brown and Morrow's (1987) data of the
  rotational frequency splitting between solar acoustic ("5-minute")
  modes were analyzed. The author determined the angular velocity near
  the equatorial plane for 0.06 ≤ r/R ≤ 0.9 and radial variations
  of the latitudinal differential rotation for 0.4 ≤ r/R ≤ 0.9. The
  latitudinal differential rotation is found to be much smaller in
  the radiative zone than in the convective zone. A method for the
  observational data reduction is suggested providing a more accurate
  determination of the solar rotation.

---------------------------------------------------------
Title: The Internal Rotation of the Sun from Helioseismological Data
Authors: Kosovichev, A. G.
1988SvAL...14..145K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Conditions of plasma layers formation with enhanced electric
    current density and temperature in the Sun's atmosphere
Authors: Boiko, A. Ya.; Kosovichev, A. G.; Popov, Yu. P.; Sokolov,
   V. S.
1988BCrAO..79....9B    Altcode: 1990BCrAO..79....9B
  A finite-difference numerical method is used to study nonlinear
  development of MHD thermal instability (or superheating instability)
  in one-dimensional approximation. The authors consider: (1) growth of
  small perturbations in unstable quasistationary current layers, and
  (2) the development of instability occurring due to interaction of a
  shock wave with the magnetic field (in case of strong perturbation). It
  is found that the intensive Joule heating in the perturbations leads
  to self-supported high-temperature current layers (so-called T-layers
  ). Under conservation of total magnetic flux the instability leads to
  more than hundredfold increase of temperature of plasma in a free-force
  magnetic field. The authors suggest that this is the case in solar
  flares. It has been found that typical thickness of the T-layers is
  about 10<SUP>3</SUP> - 10<SUP>5</SUP>cm, assuming an isotropic Coulomb
  resistivity. Thus, the authors suggest that high resistivity of solar
  plasma inferred from observations can be caused by turbulence resulting
  from the MHD thermal instability.

---------------------------------------------------------
Title: Nonlinear mode coupling in oscillating stars. III. Amplitude
    limitingeffect of the rotation in the Delta Scuti stars.
Authors: Dziembowski, W.; Krolikowska, M.; Kosovichev, A.
1988AcA....38...61D    Altcode:
  The authors derive the amplitude equations describing the three-mode
  coupling in the presence of rotation. The formalism is applied to
  calculate the amplitudes of the low order acoustic modes at the onset
  of the parametric instability to the growth of gravity modes. Numerical
  calculations made for a ZAMS star model show that significant lowering
  of these amplitudes occurs for V<SUB>rot</SUB> &gt; 20 km/s. This
  may explain observed absence of high amplitude pulsators in rapidly
  rotating stars.

---------------------------------------------------------
Title: An Attempt to Determine the Structure of the Solar Core from
    Observed G-Mode Frequencies
Authors: Kosovichev, A. G.
1988IAUS..123..141K    Altcode:
  Useful information about the stratification of the solar core (0 &lt;
  r &lt; 0.3 R) can be obtained from inversions of g-mode frequencies
  (a range of periods 100 - 200 min) using Tikhonov's standard form of
  regularization theory.

---------------------------------------------------------
Title: Inertial Modes Trapped in the Solar Convective Envelope
Authors: Dziembowski, W.; Kosovichev, A.; Kozlowski, M.
1988IAUS..123..117D    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Asymptotic Solution Of The Inverse Problem Of Helioseismology
    For Determining The Internal Differential Rotation Of The Sun
Authors: Kosovichev, A. G.; Parchevsky, K. V.
1988AZh....14..473K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: On conditions of plasma layers formation with enhanced electric
    current density and temperature in the atmosphere of the Sun.
Authors: Bojko, A. Ya.; Kosovichev, A. G.; Popov, Yu. P.; Sokolov,
   V. S.
1988IzKry..79...11B    Altcode:
  A finite-difference numerical method is used to study the nonlinear
  development of a MHD thermal instability (or superheating instability)
  in one-dimensional approximation. The authors consider: (1) growth of
  small perturbations in unstable quasi-stationary current layers, and (2)
  the development of instability occurring due to interaction of a shock
  wave with the magnetic field (in case of strong perturbation). It
  is found that the intensive Joule heating in the perturbations
  leads to self-supported high-temperature current layers (so called
  T-layers). Under conservation of total magnetic flux the instability
  leads to more than hundredfold increase of temperature of plasma in a
  force-free magnetic field. The authors suggest that this is the case in
  solar flares. It has been found that typical thickness of the T-layers
  is about 10<SUP>3</SUP> - 10<SUP>5</SUP> cm, assuming an isotropic
  Coulomb resistivity. Thus, it is suggested that high resistivity of
  solar plasma inferred from observations can be caused by turbulence
  resulting from the MHD thermal instability.

---------------------------------------------------------
Title: Spatial structure of normal-mode solar oscillations
Authors: Gorkin, L. B.; Kosovichev, A. G.
1988BCrAO..80..151G    Altcode: 1990BCrAO..80..151G
  The physical properties and geometric structure of normal hydrodynamic
  modes of three types - acoustic (p), internal gravity (g), and
  inertial (r) - are described qualitatively. Regions in which
  they are trapped inside the Sun and properties of the frequency
  spectra are indicated. Distributions of the radial velocities of the
  oscillations are plotted in projection onto the Sun's disk, and the
  spatial frequencies that characterize the oscillation sensitivity
  of observations of spectral-line Doppler shifts in the whole-disk
  emission and the Doppler-signal difference between a central zone and
  limb zones symmetric about the center of the disk are calculated.

---------------------------------------------------------
Title: Determining the internal rotation of the Sun from the frequency
    splitting of acoustic modes
Authors: Kosovichev, A. G.
1988BCrAO..80..167K    Altcode: 1990BCrAO..80..167K
  A method for determination of the Sun's angular velocity of rotation
  as a function of radius and latitude has been developed on the basis of
  the WKB approximation and Abel's inversion. Existing observational data
  were used to find the angular velocities in the plane of the equator at
  0.06 ≤ r/R ≤0.9 and the latitudinal differential rotation at 0.4
  ≤ r/R ≤0.9. It is established that the latitudinal differential
  rotation decreases in the radiative zone and that a criterion of
  hydrodynamic instability of the rotation is satisfied in the outer
  part of the radiative zone.

---------------------------------------------------------
Title: Heat-source energetics in high-temperature flare plasma
Authors: Andreev, A. S.; Kosovichev, A. G.
1988BCrAO..78..153A    Altcode: 1989BCrAO..78..153A
  The release and transfer of energy in the high-temperature
  plasma (T<SUB>e</SUB> ≡ 10<SUP>7</SUP>K, n<SUB>e</SUB> ≡
  10<SUP>10</SUP>cm<SUP>-3</SUP>) during solar flares is modeled
  numerically in a one-dimensional nonstationary approximation with
  allowance for heat flux saturation effects and heating of the ion
  component of the plasma. It is shown that when energy release is rapid
  with a characteristic time τ<SUB>0</SUB> ⪉ 1 sec, thermal energy
  propagates in the form of a traveling temperature pulse with a steep
  leading edge. In the case of gradual energy release (τ<SUB>0</SUB>
  ⪆ 3 sec), a thermal wave with a monotonic temperature distribution
  is formed. The average propagation velocities of the wave are found
  as functions of the amount of energy and the release rate. It is found
  that the 900 - 1600 km sec<SUP>-1</SUP> velocities measured are obtained
  when an energy of (2.3 - 3.5)·10<SUP>30</SUP>erg is released during 6 -
  10 sec. A qualitative comparison is made with observations of certain
  characteristics of the plasma's X-ray emission.

---------------------------------------------------------
Title: Spatial structures of normal modes of solar oscillations.
Authors: Gorkin, L. B.; Kosovichev, A. G.
1988IzKry..80..157G    Altcode:
  Physical properties and geometrical structures of three kinds of
  hydrodynamic oscillations: acoustic (p), internal gravity (g) and
  inertial (r) modes are discussed. Resonant cavities in the solar
  interior and characteristics of frequency spectra of the modes are
  described. Patterns of Doppler velocities, projected onto the solar
  disk, are considered. Spatial filter functions, characterizing the
  sensitivity of the whole disk observations and the differential velocity
  measurements are calculated.

---------------------------------------------------------
Title: Energetics of heat source in high-temperature plasma of
    solar flares.
Authors: Andreev, A. S.; Kosovichev, A. G.
1988IzKry..78..140A    Altcode:
  A numerical simulation of energy input and transfer in high-temperature
  plasma (T<SUB>e</SUB> ≡ 10<SUP>7</SUP>K, n<SUB>e</SUB> ≡
  10<SUP>10</SUP>cm<SUP>-3</SUP>) are carried out by using one-dimensional
  non-stationary approximation. Heat flow saturation and ion heating have
  been taken into account. It is shown that in the case of high input
  rate (with the characteristic time τ<SUB>0</SUB> ⪉ 1 s) thermal
  energy is transferred by a running temperature pulse with a steep
  front. Otherwise, in the case of gradual energy input (τ<SUB>0</SUB>
  ⪆ 3 s), the thermal wave with a monotonous temperature profile is
  formed. The average velocity of thermal wave as a function of total
  energy and input rate was calculated. The observed velocities 900 -
  1600 km s<SUP>-1</SUP> correspond to a total energy input (2.5 -
  3.5)×10<SUP>30</SUP>erg during 7 - 10 s. A qualitative comparison
  is made between the numerical results and the observed parameters of
  X-ray radiation during solar flares.

---------------------------------------------------------
Title: Nonlinear effects of acoustic oscillations in the Sun
Authors: Kosovichev, A. G.
1987BCrAO..76..188K    Altcode: 1989BCrAO..76..188K
  No abstract at ADS

---------------------------------------------------------
Title: Low frequency oscillations in slowly rotating stars. I. General
    properties.
Authors: Dziembowski, W.; Kosovichev, A.
1987AcA....37..313D    Altcode:
  The case of general nonuniform rotation is considered. Some of the
  results, however, are applicable only to spherical rotation. Partial
  differential equations for adiabatic oscillations are reduced to a
  system of ordinary equations by means of a truncated spherical-harmonic
  expansion. Asymptotic solutions are obtained and used in the discussion
  of mode properties and classification. These solutions are also
  employed in the numerical method of a quantitative treatment of the
  problem. It is pointed out that approximations used in previous studies
  of quasi-toroidal modes are not generally valid in whole stellar models,
  and this refers also to the case of the uniform rotation.

---------------------------------------------------------
Title: On the possibility of rapid rotation of the solar core.
Authors: Kotov, V. A.; Kosovichev, A. G.
1987IzKry..77...72K    Altcode:
  The authors discuss a conjecture that the central core of the Sun
  rotates plausibly with very short period near 160<SUP>m</SUP>. The
  rotational splitting of low degree p-modes oscillations was calculated
  for the standard solar model, but with the inner core of various size
  spinning with the 160<SUP>m</SUP> period. The results of calculations
  agree with the actual splitting of l = 1, 2 and 3 modes inferred by
  Duvall et al. (1984) from observations of 5<SUP>m</SUP>-oscillations,
  if one assumes that the radius of a rapidly spinning core is less than
  0.08 R_sun;. Such small core contains about 6% of the total solar
  mass. The resulting gravitational quadrupole moment J<SUB>2</SUB>
  of the Sun, ⪉4×10<SUP>-6</SUP>, does not contradict the results of
  observational data on solar oblateness.

---------------------------------------------------------
Title: Low Frequency Oscillations in Slowly Rotating Stars - Part
    Two - Inertial Modes in the Solar Convective Envelope
Authors: Dziembowski, W.; Kosovichev, A.; Kozlowski, M.
1987AcA....37..331D    Altcode:
  Due to their efficient trapping in the outer layers the inertial
  oscillations may reach observable amplitudes even if they have energies
  as low as those of the individual "five minute" modes. The authors
  present results of eigenfrequencies and eigenvectors calculations that
  should facilitate spectroscopic search for such oscillations.

---------------------------------------------------------
Title: Nonlinear effects of acoustic oscillations in the Sun.
Authors: Kosovichev, A. G.
1987IzKry..76..179K    Altcode:
  A finite-difference method for the adiabatic equations of gas dynamics
  was used to study nonlinear interactions of radial acoustic modes
  (p<SUB>1_0</SUB> - p<SUB>30</SUB>) in the Sun. It is shown that
  nonlinear effects generate a low frequency oscillation and high
  frequency oscillations whose frequencies are the sums of the acoustic
  mode frequencies. It has been found that although the period of
  low frequency oscillation may be close to 160 min, the amplitudes
  of acoustic modes must be 10<SUP>2</SUP> - 10<SUP>3</SUP> times the
  observed ones independently of the number of interacting modes and their
  phases. Thus the author tends to conclude that the 160-min oscillation
  cannot be explained in terms of nonlinear effects of acoustic mode
  oscillations in the Sun.

---------------------------------------------------------
Title: Numeric calculations of thermal waves in the solar corona
Authors: Andreev, A. S.; Kosovichev, A. G.
1987BCrAO..76..195A    Altcode: 1989BCrAO..76..195A
  No abstract at ADS

---------------------------------------------------------
Title: Numerical calculations of thermal waves in the solar corona.
Authors: Andreev, A. S.; Kosovichev, A. G.
1987IzKry..76..186A    Altcode:
  A numerical simulation of thermal waves observed in high-temperature
  coronal plasma during solar flares has been carried out. A heat
  flux saturation and energy transfer from electrons to ions are
  shown to be two principal physical factors responsible fot thermal
  waves propagation. The former prevails, mainly, during the first few
  second of flare energy release, the latter is more significant in the
  succedding period of time. The dependence of thermal wave velocity on
  initial thermodynamic state of plasma has been determined. It is found
  that the mean velocity depends on density rather than on the intitial
  temperature. The calculations show a good qualitative agreement with
  the observational data, and make it possible to estimate the parameters
  of coronal plasma in magnetic arch structures.

---------------------------------------------------------
Title: Low Frequency Oscillations in Slowly Rotating Stars - Part
    Three - Kelvin-Helmholtz Instability
Authors: Dziembowski, W.; Kosovichev, A.
1987AcA....37..341D    Altcode:
  Adiabatic instabilities of stellar rotation to nonaxisymmetric
  perturbations are investigated. Exact instability criteria are obtained
  assuming various forms of the longitudinal differential rotation. It
  is shown that the forms determined for the sun imply an instability,
  but limitation of the formalism when applied to the convective zone
  are pointed out.

---------------------------------------------------------
Title: On the possibility of rapid rotation of the solar core
Authors: Kotov, V. A.; Kosovichev, A. G.
1987BCrAO..77...80K    Altcode: 1989BCrAO..77...80K
  No abstract at ADS

---------------------------------------------------------
Title: Interpretations of the 160-minute solar oscillation
Authors: Kosovichev, A. G.; Severnyj, A. B.
1986PAZh...12..238K    Altcode:
  Identification of solar oscillation with the 160-min period as a
  non-radial mode of the sun has been considered on the basis of the
  observational data recently available from several observatories. The
  amplitudes and phases observed allow the most probable identification
  of such an oscillation as a mode with degree l = 3 of a spherical
  harmonic. On the other hand however, the observed rotational splitting
  of the eigenfrequency due to solar rotation gives l = 1. New methods
  for future observations are considered to permit more reliable
  identification of the 160-min oscillations.

---------------------------------------------------------
Title: Interpretations of the 160-MINUTE Solar Oscillation
Authors: Kosovichev, A. G.; Severnyi, A. B.
1986SvAL...12...97K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Possible effects on the sun and close binary systems from
    background gravitational radiation with period 160 min.
Authors: Kosovichev, A. G.
1986BCrAO..75...30K    Altcode: 1987BCrAO..75...30K
  No abstract at ADS

---------------------------------------------------------
Title: Solution of an inverse helioseismological problem from
    observations on solar gravitational oscillations.
Authors: Kosovichev, A. G.
1986BCrAO..75...36K    Altcode: 1987BCrAO..75...36K
  No abstract at ADS

---------------------------------------------------------
Title: Processing photodiode-array solar-oscillation observations.
Authors: Kosovichev, A. G.
1986BCrAO..75...19K    Altcode: 1987BCrAO..75...19K
  No abstract at ADS

---------------------------------------------------------
Title: Solution of the inverse problem of helioseismology on the
    basis of observations of gravity-mode oscillations of the sun.
Authors: Kosovichev, A. G.
1986IzKry..75...40K    Altcode:
  A technique for inverting the observed frequencies of solar
  g-mode oscillations is considered. The inversion procedure gives
  a change in density distribution with respect to an original solar
  model. Calculations based on the Crimean solar oscillations data show
  possible fine-scale density structures in the solar core. However, at
  present one cannot draw a final conclusion on the solar core structure
  by reason of low accuracy of the data. The results of calculations
  with an artificial data set argue that significant corrections to the
  original solar model will be possible, when the more extensive and
  precise data are available on the g-modes.

---------------------------------------------------------
Title: Simulating thermal and gasdynamic processes in solar-flare
    pulse phases
Authors: Kosovichev, A. G.
1986BCrAO..75....6K    Altcode: 1987BCrAO..75....6K; 1986BuCri..75....6K
  No abstract at ADS

---------------------------------------------------------
Title: Mathematical method of analysis of solar oscillation data
    obtained from a photodiode array.
Authors: Kosovichev, A. G.
1986IzKry..75...22K    Altcode:
  A method is presented for the determination of eigenmodes of
  oscillation of the sun in the brightness fluctuations which can be
  measured by a photodiode array. Two cases of the observations are
  considered. First, the solar disc image covers all pixels of the square
  diode array. Second, the array covers the entire solar disc, in which
  case a part of the array is used to measure the brightness. It is shown
  that the second scheme is more suitable for detection of the modes
  of oscillation of the sun. The selection of the modes specified by a
  spherical harmonic is carried out. The optimal sets of the coefficients
  for a diode array of 16×16 pixels and the spherical harmonics with
  degree l ≤ 20 are calculated. Resolving powers of the method are
  determined for some harmonics.

---------------------------------------------------------
Title: On possible effects of background gravitational waves with
    a period of 160 min on the sun and close binaries.
Authors: Kosovichev, A. G.
1986IzKry..75...33K    Altcode:
  The resonant effect of background (cosmological) gravitational
  radiation on the sun and binary systems is calculated. The upper
  limits to the amplitude of the 160-min solar pulsation and to the
  changes in the periods of the orbital rotation of the binary systems
  are established. When the energy density of the gravitational radiation
  does not exceed that of a closed Universe, the effects associated with
  the gravitational waves are much less than the ones observed.

---------------------------------------------------------
Title: Numerical simulations of gas-dynamical and thermal processes
    in the impulsive phase of solar flares.
Authors: Kosovichev, A. G.
1986IzKry..75....8K    Altcode:
  Nonlinear time-dependent numerical simulation of the gas-dynamical
  and thermal processes in the solar atmosphere heated by non-thermal
  electrons is carried out. The structure of the shock wave in the
  chromosphere and the thermal instability of hot flare plasma are
  investigated. A thin zone of thermal relaxation (with thickness Δz
  ≈ 2×10<SUP>5</SUP>cm) is found to be formed behind the shock
  front. In this zone the temperature and density of plasma vary
  from T ≈ 3×10<SUP>5</SUP>K, n ≈ 10<SUP>13</SUP>cm<SUP>-3</SUP>
  to T ≈ 9×10<SUP>3</SUP>K, n ≈ 10<SUP>15</SUP>cm<SUP>-3</SUP>
  because of strong radiative energy losses. During the relaxation
  process thin cold condensations (Δz ≈ 10<SUP>3</SUP>cm) arise
  behind the shock front as a result of thermal instability. The life
  time of these structures approximately equals to 10<SUP>-2</SUP>s. They
  disappear when the thermal balance is set in the surrounding plasma. The
  formation of a cold and dense structure (Δz ≈ 5×10<SUP>5</SUP>cm,
  T ≈ 9×10<SUP>3</SUP>K, n ≈ 2×10<SUP>13</SUP>cm<SUP>-3</SUP>) in
  high-temperature plasma due to the thermal instability is investigated
  in detail.

---------------------------------------------------------
Title: Excitation of oscillations in a stellar encounter
Authors: Kosovichev, A. G.; Severnyi, A. B.
1985BCrAO..70...13K    Altcode: 1987BCrAO..70...13K
  No abstract at ADS

---------------------------------------------------------
Title: Chemical composition effects on the stability of the Sun's
    natural gravitational oscillations.
Authors: Kosovichev, A. G.; Severnyj, A. B.
1985BCrAO..72..162K    Altcode: 1985BuCri..72..162K; 1987BCrAO..72..162K
  No abstract at ADS

---------------------------------------------------------
Title: Excitation of stellar oscillations during close encounters
Authors: Kosovichev, A. G.; Severnyi, A. B.
1985IzKry..70...14K    Altcode:
  The oscillations arising at close encounters of stars are considered
  with the aid of numerical methods in linear adiabatic approximation. It
  is shown that two types of oscillatory motions appear due to the
  action of tidal force. The first one is a normal mode described by
  a spherical harmonic of degree l = 2 and order m = 0. The second one,
  the more important type of oscillation of several times higher amplitude
  (l = 2, m = +2) is a running wave propagating in the direction of the
  parabolic motion of the disturbing star. The spectral distribution
  of amplitudes is investigated for polytropic stellar models with
  the index of polytropes N = 2, 2.5, 3, 3.25, 3.5 and for different
  periastron distances. It is suggested that the 160-min oscillations
  of the sun can be a relict phenomenon of encounter of the sun with a
  star, or a cloud, of small (1/5 of solar) mass at the earlier stages
  of solar evolution when it was among the stars of an early-type star
  cluster. It is also pointed out that the oscillations arising at close
  encounters are very similar to those of β Cep stars.

---------------------------------------------------------
Title: Influence of the chemical composition on the stability of
    solar gravity mode oscillations.
Authors: Kosovichev, A. G.; Severnyi, A. B.
1985IzKry..72..188K    Altcode:
  Solar models with low heavy elements abundance interior (model C) and
  with mixing in the core are calculated. It is suggested that mixing
  leads to more homogeneous distribution of hydrogen concentration in the
  core compared with the standard model. The non-radial oscillations
  stability of these models are investigated by quasi-adiabatic
  approximation. For models C g<SUB>1</SUB>- and g<SUB>2</SUB>-modes
  belonging to dipole (l = 1) oscillations are found unstable due to
  the ɛ-mechanism. It means that the mechanism of nonlinear resonance
  excitation of long-period (over the range 120 - 200<SUP>m</SUP>)
  solar oscillations for this model is confirmed. The instability of a
  gravity mode is also revealed in the mixing models when the ratio of
  hydrogen abundance at the centre and the surface equals approximately
  to 0.7 - 0.8. It is pointed out that only the models with low Z are
  in agreement with the solar neutrino experiment and the observed solar
  gravity mode oscillations.

---------------------------------------------------------
Title: On the influence of gravitational radiation on the 160-min
    solar oscillation.
Authors: Kosovichev, A. G.
1985IzKry..73...15K    Altcode:
  The resonance amplitude of solar oscillations forced by gravitational
  waves is calculated in connection with the recent idea, that the 160-min
  oscillation might be caused by gravitational waves from the nearby
  binary system Geminga. It is found that the maximum possible amplitude
  of the oscillation is at least 10<SUP>3</SUP> times smaller than the
  observed value. The author concludes that the 160-min oscillation in
  the sun cannot be excited by gravitational waves emitted from the binary
  system Geminga but by any other source. He calculates the gravitational
  wave luminosity of the sun due to the 160-min oscillation and finds
  that the influence of the gravitational radiation on the damping of
  the oscillation is negligible.

---------------------------------------------------------
Title: The Effects of Gravitational Radiation on the Solar 160-Min
    Pulsations
Authors: Kosovichev, A. G.
1985BCrAO..72...13K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The stability of solar gravity-mode oscillations and the
    structure of the sun
Authors: Kosovichev, A. G.; Severnyj, A. B.
1984PAZh...10..679K    Altcode:
  The g-mode oscillations stability for the interior of solar models
  with low heavy-element abundances and models with turbulent diffusion
  mixing inside is investigated by a quasi-adiabatic approximation. The
  models with low Z are found to be most unstable. It is pointed out that
  only the models with low Z are in agreement with the solar neutrino
  experiment and the observed solar gravity mode oscillations.

---------------------------------------------------------
Title: The stability of solar gravity-mode oscillations and the
    structure of the sun
Authors: Kosovichev, A. G.; Severnyj, A. B.
1984SvAL...10..284K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Instability of non-radial g-mode oscillations of the sun with
    low-Z interior
Authors: Kosovichev, A. G.; Severnyi, A. B.
1984MmSAI..55..129K    Altcode:
  A quasi-adiabatic approximation is used to calculate the stability of
  nonradial g-mode oscillations in evolutionary solar models with initial
  heavy-element abundances (Z0) = 0.02 and 0.001. The model parameters
  and the calculated periods and damping times are presented in tables,
  and a graph of the evolution of growth rates is provided. In the
  model with Z0 = 0.02, low g-modes with l = 1 are unstable during the
  main-sequence phase from 250 Myr to 3.8 Gyr, but all modes are stable
  (except for the l = 1 g2-mode) in the present. In the model with Z0 =
  0.001, however, the g1 and g2 modes with l = 1 are unstable due to a
  destabilization epsilon mechanism, and the amplitude growth time is
  of the order 10 Myr. These results suggest that high-degree g-modes
  are resonantly excited.

---------------------------------------------------------
Title: The 160-minute solar pulsations are not excited by
    gravitational waves
Authors: Kosovichev, A. G.
1984PAZh...10..457K    Altcode:
  Theoretical calculations are carried out of solar oscillations caused
  by gravitational waves from a binary system such as the gamma ray
  emitter Geminga. The waves would raise tides in the sun as they
  passed through it. The analytical model describes fluctuations in
  the curvature tensor, due to the gravitational waves. The waves are
  treated in terms of a time delayed reduced quadrupole mass-moment
  tensor emitted from the center of mass of the binary system. Account is
  taken of the complex spherical harmonics in the waves. An equation is
  obtained for the forced adiabatic solar oscillation and its amplitude,
  and to dissipation of the pulsational energy in the sun. It is shown
  that the peak amplitude of the projected oscillation will be at least
  a thousand times smaller than that of the solar 160 min oscillations,
  so Geminga cannot be causing the oscillations.

---------------------------------------------------------
Title: The 160-MINUTE Solar Pulsations are not Excited by
    Gravitational Waves
Authors: Kosovichev, A. G.
1984SvAL...10..190K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: On the Stability of Solar Gravity Mode Oscillations and the
    Structure of the Sun
Authors: Kosovichev, A. G.; Severny, A. B.
1984LIACo..25..278K    Altcode: 1984tpss.conf..278K; 1984trss.conf..278K
  No abstract at ADS

---------------------------------------------------------
Title: Numerical Analysis of Nonlinear Radial Pulsations of Stars
Authors: Kosovichev, A. G.
1984BCrAO..69..101K    Altcode: 1986BCrAO..69...93B
  No abstract at ADS

---------------------------------------------------------
Title: A method for the numerical calculation of the nonlinear radial
    pulsations of stars
Authors: Kosovichev, A. G.
1984IzKry..69..108K    Altcode:
  The use of the finite difference method to calculate the nonlinear
  radial pulsations of stars is examined. The mathematical model of these
  pulsations is described by equations of time-dependent gravitational
  gas dynamics in the one-dimensional (spherically symmetric) case. A
  two-parameter family of fully conservative difference schemes is
  obtained; these schemes provide for a more precise calculation of
  nonlinear flows with shocks than other difference schemes of the same
  order of approximation. Methods for the numerical solution of implicit
  (absolutely stable) difference schemes from the family considered
  are discussed.

---------------------------------------------------------
Title: Stellar oscillations triggered by close encounters
Authors: Kosovichev, A. G.; Severnyj, A. B.
1983PAZh....9..424K    Altcode:
  The oscillations arising at close encounters of stars are considered
  with the aid of numerical methods in linear adiabatic approximations. It
  is shown that two types of oscillatory motions appear due to the action
  of tidal forces. The first is a normal mode described by the spherical
  harmonic of degree l = 2 and of order m = 0. The second more important
  type of oscillation, with a several times higher amplitude (l = 2, |m| =
  2) is a running wave, propagating in the direction of parabolic motion
  of the disturbing star. It is suggested that the 160-min oscillations
  of the sun can be a relict phenomenon of encounter of the sun with a
  low-mass star or a cloud at the earlier stage of solar evolution. It
  is also pointed out that the oscillations arising at close encounters
  are very similar to those of β Cephei stars.

---------------------------------------------------------
Title: Stellar Oscillations Triggered by Close Encounters
Authors: Kosovichev, A. G.; Severnyi, A. B.
1983SvAL....9..223K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: On the Excitation of Oscillations of the Sun - Numerical Models
Authors: Kosovichev, A. G.; Severny, A. B.
1983SoPh...82..323K    Altcode: 1983IAUCo..66..323K
  Numerical solutions of the general time-dependent gas-dynamical
  equations in linear adiabatic approximation are given for initial
  conditions imitating: (a) a central perturbation, (b) a boundary
  perturbation (in the convective envelope), and (c) a `shrinking' of
  the Sun as a whole. For a variety of models of the Sun it is found
  that at the surface the radial component v<SUB>r</SUB> of velocity is
  much greater than the tangential component v<SUB>t</SUB>, and that the
  period T of stationary oscillations does not exceed 131<SUP>m</SUP>. The
  appearance at the surface of a g mode with period 160<SUP>m</SUP>
  is found to be improbable.

---------------------------------------------------------
Title: The Optical Continuum of Solar and Stellar Flares
Authors: Livshits, M. A.; Badalian, O. G.; Kosovichev, A. G.; Katsova,
   M. M.
1981SoPh...73..269L    Altcode:
  A further development of the Kostyuk-Pikelner's model is presented. The
  response of the chromosphere heated by non-thermal electrons of
  the power-law energy spectrum has been studied on the basis of the
  numerical solution of the one-dimensional time-dependent equations
  of gravitational gas dynamics. The ionization and energy loss for
  the emissions in the Lyman and Balmer lines have been determined
  separately for the optically thin and thick Lα-line layers. Due to
  the initial heating, a higher-pressure region is formed. From this
  region, disturbances propagate upwards (a shock wave with a velocity
  of more than 1000 km s<SUP>-1</SUP>) and downwards. A temperature
  jump propagates downwards, and a shock is formed in front of the
  thermal wave. During a period of several seconds after the beginning
  of this process, the temperature jump intensifies the downward shock
  wave and the large radiative loss gives rise to the high density jump
  (ϱ<SUB>2</SUB>/ϱ<SUB>1</SUB> ∼ 100). The numerical solution has
  been analyzed in detail for the case heating of the ionized and neutral
  plasma, and a value of this heating is close to the upper limit of the
  admissible values. In this case, the condensation located between the
  temperature jump and the shock wave front, may emit in the observed
  optical continuum.

---------------------------------------------------------
Title: On the excitation of oscillations in the sun
Authors: Kosovichev, A. G.; Severnyj, A. B.
1981PAZh....7..304K    Altcode:
  The nonstationary equations of gas dynamics are solved numerically to
  analyze radial adiabatic oscillations of the sun that result from local
  perturbations of the thermodynamic parameters in the energy-generating
  core region of the sun. Calculations are performed for a polytropic
  sphere and a standard solar model. Results show that a spherical
  wave produced by the perturbation will travel from the center to the
  surface and back, while undergoing successive reflections from the lower
  boundary of the atmosphere and from the center of the sun. Calculated
  oscillations in the radiation flux and the oscillation power spectrum
  are compared with observed solar pulsations.

---------------------------------------------------------
Title: On the Excitation of Oscillations in the Sun
Authors: Kosovichev, A. G.; Severnyi, A. B.
1981SvAL....7..168K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Origin of the optical continuum of flares on red dwarfs
Authors: Katsova, M. M.; Kosovichev, A. G.; Livshits, M. A.
1981Afz....17..285K    Altcode:
  Gas dynamic processes in the chromosphere of a red dwarf, on which
  a beam of accelerated electrons with a power spectrum is incident
  for 10 sec, are considered. The ionization and radiation losses of
  hydrogen are determined separately for layers that are transparent
  and opaque in the line L-alpha. A discontinuity of the temperature
  propagates downward in the chromosphere, and a shock wave with high
  compression is formed in front of it. A dense region is formed at a
  height of about 1500 km with a density greater than 10 to the 15th/cu
  cm and a T of 9000 K; this region expands from a thickness of 1 km
  to 10 km. White radiation in the flares results when the dense region
  becomes strongly opaque in the Balmer lines. The Balmer losses cannot
  compensate for the heating, and a rise in the temperature in the dense
  region leads to the appearance of the optical continuum.

---------------------------------------------------------
Title: Origin of the Optical Continuum of Flares on Red Dwarfs
Authors: Katsova, M. M.; Kosovichev, A. G.; Livshits, M. A.
1981Ap.....17..156K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Quasiperiodic oscillations in the solar atmosphere
Authors: Kosovichev, A. G.; Popov, Yu. P.
1981BCrAO..63...15K    Altcode: 1981BuCri..63...15K
  No abstract at ADS

---------------------------------------------------------
Title: On quasi-periodic oscillations in the solar atmosphere.
Authors: Popov, Iu. P.; Kosovichev, A. G.
1981IzKry..63...15P    Altcode:
  A numerical solution of the nonlinear equations of one-dimensional
  gas dynamics is used to examine the propagation of perturbations in
  the convective zone and atmosphere of the sun. The inhomogeneity of
  the solar plasma in the gravitational field leads to the generation
  of oscillations in the atmosphere with a period of approximately 300
  sec. The effect of nonlinearity on the character of the oscillations is
  clarified, and the present results are compared with experimental data.

---------------------------------------------------------
Title: The nature of the optical continuum of red-dwarf flares
Authors: Katsova, M. M.; Kosovichev, A. G.; Livshits, M. A.
1980PAZh....6..498K    Altcode:
  The gas-dynamical processes that would result from heating of
  a partially ionized, hydrogen stellar chromosphere by accelerated
  electrons are investigated numerically. The radiative energy loss in the
  optically thick layer is estimated. A condensation should, according
  to the calculation, be propagated downward in the chromosphere: it
  would have a density n = 10 to the 15th - 10 to the 16th per cu cm,
  temperature T = 900 K, thickness 1-10 km, and optical depth tau (4500)
  = 1. The luminosity, color indices, and Balmer jump for the optical
  continuum of this condensation are consistent with observations of
  flares in red dwarf stars.

---------------------------------------------------------
Title: The Nature of the Optical Continuum of Red Dwarf Flares
Authors: Katsova, M. M.; Kosovichev, A. G.; Livshits, M. A.
1980SvAL....6..275K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Calculation of one-dimensional unsteady-state problems of
    gravitational gasdynamics
Authors: Kosovichev, A. G.; Popov, Iu. P.
1979ZVMMF..19.1253K    Altcode:
  Some features of the numerical solution of one-dimensional
  unsteady-state problems of gasdynamics in the presence of gravity
  are examined. The problem of shock wave propagation in the solar
  atmosphere is analyzed, showing the effectiveness of applying completely
  conservative finite-difference schemes to problems of this type. The
  process of periodic generation of shock waves in the atmosphere in
  the presence of monotonic dynamic effects at its lower boundary is
  identified.

---------------------------------------------------------
Title: Gas-dynamical processes under the action of heating of the
    chromosphere by accelerated electrons.
Authors: Kosovichev, A. G.; Livshits, M. A.; Badalyan, O. G.
1979ATsir1069....1K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Nonlinear stage of instability due to local Joule-overheating
    in the solar active regions.
Authors: Sokolov, V. S.; Kosovichev, A. G.
1978SoPh...57...73S    Altcode:
  The numerical solution by a computer of the system of
  magnetohydrodynamics equations in the one-dimensional approximation
  serves as the basis for studying the non-linear stage of the instability
  due to local Joule-overheating of zones with large values of magnetic
  field gradients in the active regions of the Sun. We have demonstrated
  the formation of a system of current layers responsible for efficient
  transformation of magnetic energy into Joule heat and kinetic energy
  of the macroscopic motion. The specific features of quasi-stationary
  skinning of magnetic field with gravitation have been noted.

---------------------------------------------------------
Title: Skinning process stability of the magnetic field in the solar
    active regions.
Authors: Sokolov, V. S.; Katsnel'Son, S. S.; Katsnelson, S. S.;
   Kosovichev, A. G.; Slavin, V. S.
1977SoPh...51..293S    Altcode:
  Skinning process stability of the magnetic field in homogeneous
  plasma is studied. A set of magnetohydrodynamic equations is
  used. Dependence of electrical conductivity on the plasma parameters
  and radiation intensity in grey-body approximation are taken into
  account. The investigation is carried out on the model problems
  in linear approximation and by means of numerical solution of MHD
  equations. Threshold of stability and critical gradient of magnetic
  field in skin-layer are obtained. The model of the phenomenon proposed
  in the paper indicates on overheating instability of plasma with
  electric current in large gradient magnetic field zones as a possible
  trigger mechanism of solar flare origin.

---------------------------------------------------------
Title: On a model of chromospheric flares on the sun.
Authors: Sokolov, V. S.; Kosovichev, A. G.; Slavin, V. S.
1977mmns.conf..216S    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: On the stability of the magnetic field skin zone in the solar
    lower chromosphere plasma.
Authors: Kosovichev, A. G.; Sokolov, V. S.
1975AehIs...5...17K    Altcode:
  No abstract at ADS