Author name code: kitiashvili
ADS astronomy entries on 2022-09-14
author:"Kitiashvili, Irina N." 
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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
Bibcode: 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.

Title: Using 3D Realistic Modeling of Solar-Type Stars to Characterize
    Stellar Jitter
Authors: Kitiashvili, Irina; Wray, Alan; Granovsly, Samuel
Bibcode: 2022cosp...44..587K
Altcode:
  Detection of Earth-mass exoplanets orbiting solar-type stars requires a
  procedure to extract weak variations in the radial velocity signals,
  which are significantly weaker than the background noise induced
  by dynamics of the stellar photospheres. We use the 3D radiative MHD
  "StellarBox" code to characterize this noise to obtain realistic stellar
  (magneto)convection models based on first physical principles. We
  performed a series of high-resolution numerical simulations of
  solar-type stars to obtain disk-integrated synthetic observations by
  computing Fe I lines using the radiative transfer "Spinor" code. We
  present the stellar jitter modeling results for selected target stars
  and discuss the origin of the noise and perspectives of this effort.

Title: Characterization of Stellar Jitter Using 3D Realistic Modeling
    of Solar-Type Stars
Authors: Kitiashvili, Irina; Granovsky, Samuel; Wray, Alan; Kosovichev,
   Alexander
Bibcode: 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.

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
Bibcode: 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.

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.
Bibcode: 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.

Title: Modeling Stellar Jitter for the Detection of Earth-Mass
    Exoplanets via Precision Radial Velocity Measurements
Authors: Granovsky, Samuel; Kitiashvili, Irina N.; Wray, Alan
Bibcode: 2022arXiv220207087G
Altcode:
  The detection of Earth-size exoplanets is a technological and data
  analysis challenge. Future progress in Earth-mass exoplanet detection
  is expected from the development of extreme precision radial velocity
  measurements. Increasing radial velocity precision requires developing
  a new physics-based data analysis methodology to discriminate planetary
  signals from host-star-related effects, taking stellar variability and
  instrumental uncertainties into account. In this work, we investigate
  and quantify stellar disturbances of the planet-hosting solar-type
  star HD121504 from 3D radiative modeling obtained with the StellarBox
  code. The model has been used for determining statistical properties of
  the turbulent plasma and obtaining synthetic spectroscopic observations
  for several Fe I lines at different locations on the stellar disk to
  mimic high-resolution spectroscopic observations.

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
Bibcode: 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.

Title: 3D Radiative MHD Modeling of the Solar Atmospheric Dynamics
    and Structure
Authors: Kitiashvili, Irina; Sadykov, Viacheslav; Wray, Alan;
   Kosovichev, Alexander
Bibcode: 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.

Title: Dynamical Coupling of the Solar Subsurface Shear Layer and
    the Atmosphere
Authors: Kitiashvili, Irina; Sadykov, Viacheslav; Kosovichev,
   Alexander; Wray, Alan
Bibcode: 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.

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
Bibcode: 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: Effects of observational data shortage on accuracy of global
    solar activity forecast
Authors: Kitiashvili, Irina N.
Bibcode: 2021MNRAS.505.6085K
Altcode: 2020arXiv200109376K
  Building a reliable forecast of solar activity is a long-standing
  problem that requires an accurate description of past and current
  global dynamics. Relatively recently, synoptic observations of magnetic
  fields and subsurface flows have become available. In this paper,
  we present an investigation of the effects of short observational
  data series on the accuracy of solar cycle prediction. This analysis
  is performed using the annual sunspot number time-series applied to
  the Parker-Kleeorin-Ruzmaikin dynamo model and employing the Ensemble
  Kalman Filter (EnKF) data assimilation method. The testing of cycle
  prediction accuracy is performed for the last six cycles (for Solar
  Cycles 19-24) by sequentially shortening the observational data series
  to predict a target cycle and evaluate the resulting prediction accuracy
  according to specified criteria. According to the analysis, reliable
  activity predictions can be made using relatively short time-series
  of the sunspot number. The accuracy of the solar activity has a weak
  dependence on the length of available observations. It is demonstrated
  that at least three cycles of observations are needed to obtain robust
  forecasts.

Title: Dynamics and Structure of Main-Sequence Stars with Shallow
    Convection Zones
Authors: Kitiashvili, I. N.; Wray, A. A.
Bibcode: 2021tsc2.confE.132K
Altcode:
  A dramatic increase in observational data from NASA's Kepler, K2, and
  TESS missions and supporting ground-based observatories have opened
  new opportunities to investigate the internal structure, dynamics,
  and evolution of stars and their atmospheres. We present 3D radiative
  MHD simulations for several main-sequence stars with masses from 1.4
  to 1.5 Msun. The simulations are performed using the "StellarBox" code
  developed for modeling stellar turbulent convection and atmospheres with
  a high degree of realism. This presentation discusses similarities and
  differences between 3D realistic-type and 1D mixing-length models with
  regard to structural, thermodynamic, and turbulent property variations
  from the radiative zone to the convection zone and photosphere.

Title: Probing Stellar Cores by Asteroseismic Inversions
Authors: Kosovichev, Alexander; Kitiashvili, Irina
Bibcode: 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: 3D Modeling of Solar-Type Stars to Characterize Stellar Jitter
Authors: Kitiashvili, I. N.; Wray, A. A.; Granovsky, S.
Bibcode: 2021tsc2.confE.135K
Altcode:
  Detection of Earth-mass planets requires measurements of radial velocity
  with extreme precision. To capture the tiny disturbances caused by a
  planet's motion, it is necessary to understand and characterize the
  host star's turbulent dynamics in order to apply proper filtering to
  the observational data. We take advantage of current computational
  and technological capabilities to develop 3D realistic models of the
  stellar subsurface convection and atmospheres and thereby estimate
  the photospheric jitter. We have identified an initial set of target
  stars, obtained initial conditions using the MESA code, and obtained
  initial 3D radiative models of the stellar surfaces and atmospheres
  with a spatial resolution of 50km. We present initial 3D radiative
  hydrodynamic model results of the planet-hosting star HD209458.

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
Bibcode: 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: Influence of Center-to-Limb Effects on Observations of the
    Solar Atmosphere
Authors: Kitiashvili, I. N.; Sadykov, V. M.; Wray, A. A.
Bibcode: 2021AAS...23811313K
Altcode:
  The complexity of the highly dynamical atmospheric layers of
  the Sun in the presence of inhomogeneous magnetic fields makes
  it challenging to correctly interpret observations from space
  and ground-based instruments. In particular, the center-to-limb
  variations of spectro-polarimetric properties may lead to significant
  misinterpretations of helioseismic and magnetic observables. To
  address these challenges and study the physical processes behind
  observations of various types, we use 3D MHD radiative models, which
  reproduce the dynamics and observational properties with high-degree
  realism. To study the center-to-limb effects, we obtained series of
  synthetic spectropolarimetric and intensity imaging data that mimic
  observations from different space instruments: HMI and AIA (SDO), SOT
  (Hinode), and IRIS, as well as upcoming DKIST ground observations. In
  the presentation, we discuss the influence of observations at different
  angular distances from the solar disk center on the resulting properties
  of the magnetic field, atmospheric structure and dynamics, and acoustic
  and surface gravity waves.

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.
Bibcode: 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: 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
Bibcode: 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: 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
Bibcode: 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: Effects of Rotation on Internal Structure and Dynamics of
    Main-Sequence Stars
Authors: Kitiashvili, Irina N.; Wray, Alan A.
Bibcode: 2021csss.confE..17K
Altcode:
  Current state-of-the-art computer simulations allow us to build 3D
  dynamical and radiative models of stars from physical first principles
  with a high degree of realism. The radiative 3D dynamical stellar
  models obtained with the StellarBox code take into account the effects
  of turbulence, stellar abundances, a realistic equation of state, and
  radiative energy transport. In this talk, I will discuss the effects
  of rotation on the turbulent dynamics and surface structure for a 1.47
  Msun star for rotational periods of 1 and 14 days. The simulations
  are performed with the computational domain at various latitudes. The
  models reproduce stellar granulation, the subsurface shear layer,
  structural changes in 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 and
  meridional circulation.

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.
Bibcode: 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: 3D Realistic Modeling of Main-Sequence Stars with Shallow
    Outer Convection Zone
Authors: Kitiashvili, I. N.; Wray, A. A.; Kosovichev, A. G.
Bibcode: 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: Radiation Data Portal: Integration of Radiation Measurements at
    the Aviation Altitudes and Solar-Terrestrial Environment Observations
Authors: Sadykov, V. M.; Kitiashvili, I. N.; Tobiska, W. K.;
   Guhathakurta, M.
Bibcode: 2021SpWea..1902653S
Altcode: 2021arXiv210307604S
  The impact of radiation dramatically increases at high altitudes in
  the Earth's atmosphere and in space. Therefore, monitoring and access
  to radiation environment measurements are critical for estimating
  the radiation exposure risks of aircraft and spacecraft crews and the
  impact of space weather disturbances on electronics. Addressing these
  needs requires convenient access to multisource radiation environment
  data and enhancement of visualization and search capabilities. The
  Radiation Data Portal represents an interactive web-based application
  for search and visualization of in-flight radiation measurements. The
  portal enhances the exploration capabilities of various properties of
  the radiation environment and provides measurements of dose rates along
  with information on space weather-related conditions. The Radiation
  Data Portal back-end is a MySQL relational database that contains
  the radiation measurements obtained from the Automated Radiation
  Measurements for Aerospace Safety (ARMAS) device and the soft X-ray
  and proton flux measurements from the Geostationary Operational
  Environmental Satellite. The implemented application programming
  interface and Python routines allow a user to retrieve the database
  records without interaction with the web interface. As a use case of
  the Radiation Data Portal, we examine ARMAS measurements during an
  enhancement of the solar proton (SP) fluxes, known as solar proton
  events, and compare them to measurements during SP-quiet periods.

Title: Radiation Portal: Connection of Radiation Measurements on
    Airplane Flights with Observations of Solar-Terrestrial Environment
Authors: Sadykov, V. M.; Kitiashvili, I.; Tobiska, W. K.; Guhathakurta,
   M.
Bibcode: 2020AGUFMSH0030002S
Altcode:
  The impact of solar radiation dramatically increases at high altitudes
  in the Earth's atmosphere and in space. Therefore, continuous monitoring
  of the radiation environment is critical for the safety of aircraft
  and spacecraft crews and passengers. Addressing the problem requires
  a complex approach of integration of different data sources and
  enhancement of the visualization and search capabilities. The Radiation
  Portal Database represents an interactive web-based application for
  convenient search and visualization of in-flight radiation measurements
  and exploration of various properties related to the radiation
  environment. The primary element of the Radiation Portal back-end
  is a MySQL relational database that currently contains the radiation
  measurements obtained from the Automated Radiation Measurements for
  Aerospace Safety (ARMAS) device, and soft X-ray and proton fluxes
  from Geostationary Orbiting Environmental Satellite (GOES). The
  developed Application Programming Interface (API) and related Python
  routines allow a user to retrieve the database records directly and
  efficiently, without interaction with the web interface. As a use case
  of the Radiation Portal, we examine the properties of the ARMAS flights
  taken during the enhanced Solar Proton (SP) fluxes and compare them to
  the flights of similar time and location taken during SP-quiet periods.

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.
Bibcode: 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.
Bibcode: 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: 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
Bibcode: 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: 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.
Bibcode: 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: Application of Synoptic Magnetograms to Global Solar Activity
    Forecast
Authors: Kitiashvili, I. N.
Bibcode: 2020ApJ...890...36K
Altcode: 2019arXiv191000820K
  Synoptic magnetograms provide us with knowledge about the evolution of
  magnetic fields on the solar surface and present important information
  for forecasting future solar activity. In this work, poloidal and
  toroidal magnetic field components derived from synoptic magnetograms
  are assimilated, using the Ensemble Kalman Filter method, into a
  mean-field dynamo model based on Parker's migratory dynamo theory
  complemented by magnetic helicity conservation. It was found that
  the predicted toroidal field is in good agreement with observations
  for almost the entire following solar cycle. However, poloidal field
  predictions agree with observations only for the first 2-3 yr of
  the predicted cycle. The results indicate that the upcoming Solar
  Maximum of Cycle 25 (SC25) is expected to be weaker than the current
  Cycle 24. The model results show that a deep extended solar activity
  minimum is expected during 2019-2021, and that the next solar maximum
  will occur in 2024-2025. The sunspot number at the maximum will be
  about 50 with an error estimate of 15%-30%. The maximum will likely
  have a double peak or show extended periods (for 2-2.5 yr) of high
  activity. According to the hemispheric prediction results, SC25 will
  start in 2020 in the southern hemisphere, and will have a maximum in
  2024 with a sunspot number of about 28. In the northern hemisphere
  the cycle will be delayed for about 1 yr (with an error of ±0.5 yr),
  and reach a maximum in 2025 with a sunspot number of about 23.

Title: Resolving Power of Asteroseismic Inversion of the Kepler
    Legacy Sample
Authors: Kosovichev, Alexander G.; Kitiashvili, Irina N.
Bibcode: 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: Global evolution of solar magnetic fields and prediction of
    activity cycles
Authors: Kitiashvili, Irina N.
Bibcode: 2020IAUS..354..147K
Altcode: 2020arXiv200304563K
  Prediction of solar activity cycles is challenging because physical
  processes inside the Sun involve a broad range of multiscale dynamics
  that no model can reproduce and because the available observations
  are highly limited and cover mostly surface layers. Helioseismology
  makes it possible to probe solar dynamics in the convective zone, but
  variations in differential rotation and meridional circulation are
  currently available for only two solar activity cycles. It has been
  demonstrated that sunspot observations, which cover over 400 years,
  can be used to calibrate the Parker-Kleeorin-Ruzmaikin dynamo model,
  and that the Ensemble Kalman Filter (EnKF) method can be used to link
  the modeled magnetic fields to sunspot observations and make reliable
  predictions of a following activity cycle. However, for more accurate
  predictions, it is necessary to use actual observations of the solar
  magnetic fields, which are available only for the last four solar
  cycles. In this paper I briefly discuss the influence of the limited
  number of available observations on the accuracy of EnKF estimates
  of solar cycle parameters, the criteria to evaluate the predictions,
  and application of synoptic magnetograms to the prediction of solar
  activity.

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.
Bibcode: 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: 3D Modeling of the Structure and Dynamics of a Main-Sequence
    F-type Star
Authors: Kitiashvili, Irina N.; Wray, Alan A.
Bibcode: 2020IAUS..354...86K
Altcode: 2021arXiv210712575K
  Current state-of-the-art computational modeling makes it possible to
  build realistic models of stellar convection zones and atmospheres
  that take into account chemical composition, radiative effects,
  ionization, and turbulence. The standard 1D mixing-length-based
  evolutionary models are not able to capture many physical processes of
  the stellar interior dynamics. Mixing-length models provide an initial
  approximation of stellar structure that can be used to initialize 3D
  radiative hydrodynamics simulations which include realistic modeling
  of turbulence, radiation, and other phenomena.

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.
Bibcode: 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.
Bibcode: 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: Long-Term Prediction of Solar Activity Using Magnetogram Data
    and Ensemble Kalman Filter
Authors: Kitiashvili, Irina; Kosovichev, Alexander G.
Bibcode: 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: 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.
Bibcode: 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: New Frontiers for Terrestrial-sized to Neptune-sized Exoplanets
    In the Era of Extremely Large Telescopes
Authors: Wang, Ji; Meyer, Michael; Boss, Alan; Close, Laird; Currie,
   Thayne; Dragomir, Diana; Fortney, Jonathan; Gaidos, Eric; Hasegawa,
   Yasuhiro; Kitiashvili, Irina; Konopacky, Quinn; Lee, Chien-Hsiu;
   Lewis, Nikole K.; Liu, Michael; Lupu, Roxana; Mawet, Dimitri; Melis,
   Carl; Lopez-Morales, Mercedes; Morley, Caroline V.; Packham, Chris;
   Peretz, Eliad; Skemer, Andy; Ulmer, Mel
Bibcode: 2019BAAS...51c.200W
Altcode: 2019arXiv190307556W; 2019astro2020T.200W
  Detecting and characterizing terrestrial- to Neptune-sized planets
  (1 &lt; R &lt; 4 R<SUB>Earth</SUB>) around nearby stars holds the
  key to understanding the diversity of exoplanets and will ultimately
  address the ubiquitousness of life in the universe. Here we provide
  an overview of the challenge and promise of success.

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.
Bibcode: 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: Reconstructing Extreme Space Weather From Planet Hosting Stars
Authors: Airapetian, Vladimir; Adibekyan, V.; Ansdell, M.; Alexander,
   D.; Barklay, T.; Bastian, T.; Boro Saikia, S.; Cohen, O.; Cuntz,
   M.; Danchi, W.; Davenport, J.; DeNolfo, G.; DeVore, R.; Dong, C. F.;
   Drake, J. J.; France, K.; Fraschetti, F.; Herbst, K.; Garcia-Sage,
   K.; Gillon, M.; Glocer, A.; Grenfell, J. L.; Gronoff, G.; Gopalswamy,
   N.; Guedel, M.; Hartnett, H.; Harutyunyan, H.; Hinkel, N. R.; Jensen,
   A. G.; Jin, M.; Johnstone, C.; Kahler, S.; Kalas, P.; Kane, S. R.;
   Kay, C.; Kitiashvili, I. N.; Kochukhov, O.; Kondrashov, D.; Lazio, J.;
   Leake, J.; Li, G.; Linsky, J.; Lueftinger, T.; Lynch, B.; Lyra, W.;
   Mandell, A. M.; Mandt, K. E.; Maehara, H.; Miesch, M. S.; Mickaelian,
   A. M.; Mouschou, S.; Notsu, Y.; Ofman, L.; Oman, L. D.; Osten, R. A.;
   Oran, R.; Petre, R.; Ramirez, R. M.; Rau, G.; Redfield, S.; Réville,
   V.; Rugheimer, S.; Scheucher, M.; Schlieder, J. E.; Shibata, K.;
   Schnittman, J. D.; Soderblom, David; Strugarek, A.; Turner, J. D.;
   Usmanov, A.; Van Der Holst, B.; Vidotto, A.; Vourlidas, A.; Way, M. J.;
   Wolk, Scott J.; Zank, G. P.; Zarka, P.; Kopparapu, R.; Babakhanova,
   S.; Pevtsov, A. A.; Lee, Y.; Henning, W.; Colón, K. D.; Wolf, E. T.
Bibcode: 2019BAAS...51c.564A
Altcode: 2019astro2020T.564A; 2019arXiv190306853A
  The goal of this white paper is to identify and describe promising key
  research goals to aid the theoretical characterization and observational
  detection of ionizing radiation from quiescent and flaring upper
  atmospheres of planet hosts as well as properties of stellar coronal
  mass ejections (CMEs) and stellar energetic particle (SEP) events.

Title: Stellar Characterization Necessary to Define Holistic Planetary
    Habitability
Authors: Hinkel, Natalie; Kitiashvili, Irina; Young, Patrick;
   Youngblood, Allison
Bibcode: 2019BAAS...51c.435H
Altcode: 2019arXiv190401089H; 2019astro2020T.435H
  It is a truism that "to know the planet, you must know the star." We
  discuss important stellar characteristics that require attention in
  upcoming ground- and space-based missions, such that their processes
  can be either detangled from that of the planet, correlated with
  the presence of a planet, or utilized in lieu of direct planetary
  observations.

Title: Application of Synoptic Magnetograms for Prediction of Solar
    Activity Using Ensemble Kalman Filter
Authors: Kitiashvili, Irina N.
Bibcode: 2019shin.confE.215K
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.

Title: Constraining Stellar Photospheres as an Essential Step for
    Transmission Spectroscopy of Small Exoplanets
Authors: Rackham, Benjamin; Pinhas, Arazi; Apai, Dániel; Haywood,
   Raphaëlle; Cegla, Heather; Espinoza, Néstor; Teske, Johanna;
   Gully-Santiago, Michael; Rau, Gioia; Morris, Brett M.; Angerhausen,
   Daniel; Barclay, Thomas; Carone, Ludmila; Cauley, P. Wilson; de Wit,
   Julien; Domagal-Goldman, Shawn; Dong, Chuanfei; Dragomir, Diana;
   Giampapa, Mark S.; Hasegawa, Yasuhiro; Hinkel, Natalie R.; Hu, Renyu;
   Jordán, Andrés; Kitiashvili, Irina; Kreidberg, Laura; Lisse,
   Carey; Llama, Joe; López-Morales, Mercedes; Mennesson, Bertrand;
   Molaverdikhani, Karan; Osip, David J.; Quintana, Elisa V.
Bibcode: 2019BAAS...51c.328R
Altcode: 2019astro2020T.328R; 2019arXiv190306152R
  Transmission spectra probe the atmospheres of transiting exoplanets, but
  these observations are also subject to signals introduced by magnetic
  active regions on host stars. We outline scientific opportunities in
  the next decade for providing useful constraints on stellar photospheres
  for the purposes of exoplanet transmission spectroscopy.

Title: The Need for Laboratory Measurements and Ab Initio Studies
    to Aid Understanding of Exoplanetary Atmospheres
Authors: Fortney, Jonathan; Robinson, Tyler D.; Domagal-Goldman,
   Shawn; Genio, Anthony D. Del; Gordon, Iouli E.; Gharib-Nezhad,
   Ehsan; Lewis, Nikole; Sousa-Silva, Clara; Airapetian, Vladimir;
   Drouin, Brian; Hargreaves, Robert J.; Huang, Xinchuan; Karman,
   Tijs; Ramirez, Ramses M.; Rieker, Gregory B.; Tennyson, Jonathan;
   Wordsworth, Robin; Yurchenko, Sergei N.; Johnson, Alexandria V.;
   Lee, Timothy J.; Marley, Mark S.; Dong, Chuanfei; Kane, Stephen;
   López-Morales, Mercedes; Fauchez, Thomas; Lee, Timothy; Sung, Keeyoon;
   Haghighipour, Nader; Horst, Sarah; Gao, Peter; Kao, Der-you; Dressing,
   Courtney; Lupu, Roxana; Savin, Daniel Wolf; Fleury, Benjamin; Venot,
   Olivia; Ascenzi, Daniela; Milam, Stefanie; Linnartz, Harold; Gudipati,
   Murthy; Gronoff, Guillaume; Salama, Farid; Gavilan, Lisseth; Bouwman,
   Jordy; Turbet, Martin; Benilan, Yves; Henderson, Bryana; Batalha,
   Natalie; Jensen-Clem, Rebecca; Lyons, Timothy; Freedman, Richard;
   Schwieterman, Edward; Goyal, Jayesh; Mancini, Luigi; Irwin, Patrick;
   Desert, Jean-Michel; Molaverdikhani, Karan; Gizis, John; Taylor, Jake;
   Lothringer, Joshua; Pierrehumbert, Raymond; Zellem, Robert; Batalha,
   Natasha; Rugheimer, Sarah; Lustig-Yaeger, Jacob; Hu, Renyu; Kempton,
   Eliza; Arney, Giada; Line, Mike; Alam, Munazza; Moses, Julianne; Iro,
   Nicolas; Kreidberg, Laura; Blecic, Jasmina; Louden, Tom; Mollière,
   Paul; Stevenson, Kevin; Swain, Mark; Bott, Kimberly; Madhusudhan,
   Nikku; Krissansen-Totton, Joshua; Deming, Drake; Kitiashvili, Irina;
   Shkolnik, Evgenya; Rustamkulov, Zafar; Rogers, Leslie; Close, Laird
Bibcode: 2019astro2020T.146F
Altcode: 2019arXiv190507064F
  We are now in the new era of the characterization of exoplanet
  atmospheres. However, atmosphere models are often limited by
  insufficiencies in the laboratory and theoretical data that serve
  as critical inputs. Here we provide descriptions of areas where
  new investigations could fill critical gaps in our ability to model
  exoplanet atmospheres.

Title: Statistical Properties of Soft X-Ray Emission of Solar Flares
Authors: Sadykov, Viacheslav M.; Kosovichev, Alexander G.; Kitiashvili,
   Irina N.; Frolov, Alexander
Bibcode: 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.
Bibcode: 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: Realistic Radiative 3D MHD Modeling of Outer Convection Zones
    and Atmospheres of Moderate-Mass Stars
Authors: Kitiashvili, Irina
Bibcode: 2019atp..prop..132K
Altcode:
  Scientific Goals and Objectives: The primary scientific goal of the
  proposed study is to understand and characterize the internal structure
  and turbulent dynamics of the outer convection zones, photospheres,
  and chromospheres of moderate-mass main-sequence stars using advanced 3D
  radiative MHD models that are built from first physical principles and
  take into account the effects of radiation, metallicity, turbulence,
  and magnetic fields. The primary objectives are: 1) investigate the
  structural, dynamic, energetic, and turbulent properties of the outer
  convection zones and atmospheres, including convective overshooting,
  effects of magnetic fields, and metallicity in solar-type stars;
  2) investigate the process of excitation of stellar oscillations and
  their interaction with turbulent convection and magnetic fields, and 3)
  generate series of synthetic stellar spectra to link the 3D models with
  observations. The proposed methodology is based on high-resolution 3D
  radiative MHD simulations for several stars over the spectral range from
  F to A with masses from 1.4 to 2 M_Sun by using the StellarBox code,
  which was specially developed for modeling stellar turbulent convection
  and atmospheres with a high degree of realism. The computational domain
  will include layers from the upper radiative zone, through the whole
  convection zone, and into the low atmosphere. We will investigate the
  effects of background magnetic fields of various strength and fields
  spontaneously generated by local dynamo processes. The proposed
  approach to stellar magnetoconvection modeling is based on first
  physical principles where the initial conditions for each selected
  target star are calculated by the stellar evolution code MESA. The
  synthetic spectral data will be generated from the output of the 3D
  simulations using available radiative transfer codes: the SPECTRUM
  code to calculate broad-band spectra of stars, and the SPINOR code
  for high-resolution spectra of LTE lines. Perceived significance of
  the proposed work to the objectives of the solicitation and to NASA
  interests and programs: The proposed study is important and very
  timely because it will provide a solid background for interpretation
  of currently available observations from the Kepler, K2 and TESS
  missions and will provide theoretical support to achieve the mission
  goals and increase their scientific output. The improved methodologies
  for characterizing the internal dynamic properties of stars and their
  surfaces are also important for exoplanet detection, because they
  provide estimates of stellar noise and radial velocity jitter . The
  proposed study addresses NASA s Strategic goal: expand the frontiers of
  knowledge, capability, and opportunity in space ; and NASA s Strategic
  Objective: Discover how the universe works, explore how it began and
  evolved, and search for life on planets around other stars .

Title: Physics-Based Approach to Predict the Solar Activity Cycles
Authors: Kitiashvili, Irina N.
Bibcode: 2018shin.confE.155K
Altcode:
  Observations of the complex highly non-linear dynamics of global
  turbulent flows and magnetic fields are currently available only from
  Earth-side observations. Recent progress in helioseismology has provided
  us some additional information about the subsurface dynamics, but its
  relation to the magnetic field evolution is not yet understood. These
  limitations cause uncertainties that are difficult take into account,
  and perform proper calibration of dynamo models. The current dynamo
  models have also uncertainties due to the complicated turbulent physics
  of magnetic field generation, transport and dissipation. Because of the
  uncertainties in both observations and theory, the data assimilation
  approach is natural way for the solar cycle prediction and estimating
  uncertainties of this prediction. The data assimilation approach
  combining information from both models and observations together with
  estimation possible errors has been developed in a large number of
  different methodologies. In this presentation I will compare results
  from four such methodologies: the Ensemble Kalman Filter method, the
  Extended Kalman Filter, the Ensemble Kalman Filter Smoother, and the
  Ensemble Adjustment Kalman Filter, for predicting sunspot cycles using
  a low-order solar dynamo model that takes into account the effects of
  magnetic helicity balance. I will discuss the prediction results for
  the upcoming Solar Cycle 25 and their uncertainties.

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
Bibcode: 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: 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
Bibcode: 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: Using Data Assimilation Methods for Physics-Based Capabilities
    to Predict Solar Activity Cycles
Authors: Kitiashvili, Irina
Bibcode: 2018tess.conf31603K
Altcode:
  Difficulties of building reliable forecasts of the strength and duration
  of solar activity cycles are associated with numerous problems from
  both observations and dynamo models. Utilization of the mathematical
  data assimilation approach, in which a theoretical model is 'trained'
  by observational data, allows us to improve the model solution according
  to available observations in an optimal way by taking into uncertainties
  in both observations and model. The data assimilation approach covers
  a large number of different methods, as well as their parameters that
  may affect predictive capabilities. In this presentation I will compare
  application of four data assimilation methodologies: Ensemble Kalman
  Filter method, Extended Kalman Filter, Ensemble Kalman Filter Smoother
  and Ensemble Adjustment Kalman Filter for predicting the sunspot cycles
  using a low-order solar dynamo that takes into account effects of the
  magnetic helicity balance, and discuss the prediction results for the
  next solar cycle.

Title: Advances in Realistic MHD Simulations of the Sun and Stars
Authors: Kitiashvili, Irina N.
Bibcode: 2018vsss.book...63K
Altcode:
  No abstract at ADS

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

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.
Bibcode: 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: 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.
Bibcode: 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: Data Assimilation and Uncertainties in Early Solar Cycle
    Predictions
Authors: Kitiashvili, Irina
Bibcode: 2017SPD....4830602K
Altcode:
  Stochastic nature of solar activity variations together with our
  limited knowledge of the dynamo mechanism and subsurface dynamics
  causes uncertainty in predictions of the solar cycle. For improving the
  physics-based predictions we can take advantage of the mathematical
  data assimilation approach that allows us to take into account both,
  observational errors and model uncertainties, and provide estimates of
  the next solar cycle along with prediction uncertainties. In this study
  we use the Parker's migratory dynamo model together with the equation
  of magnetic helicity balance, which reproduces main properties of
  the sunspot cycles and allow us to minimize discrepancies between the
  observed global activity variations and the model solution. The test
  simulation runs show that a reliable prediction can be obtained for two
  phases of preceding solar cycle: 1) if the polar field reversals shortly
  after the solar maxima (strong toroidal field and weak poloidal field),
  and 2) during the solar minima (strongest poloidal and weak toroidal
  fields). The early estimate of Cycle 25 obtained by this method shows
  that this cycle will start in 2019 - 2020, reach the maximum in 2023 -
  2024, and that the mean sunspot number at the maximum will be about 90
  (for the v2.0 sunspot number series).

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.
Bibcode: 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: 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.
Bibcode: 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.

Title: Using Data Assimilation Methods for Prediction of Solar
    Activity
Authors: Kitiashvili, Irina N.; Collins, Nancy S.
Bibcode: 2017shin.confE..59K
Altcode:
  The variability of solar magnetic activity known as the 11-year solar
  cycles has the longest history of observations. These solar cycles
  dramatically affect conditions in the heliosphere and the Earth's
  space environment. Our current understanding of the physical processes
  that make up global solar dynamics and the dynamo that generates the
  magnetic fields is sketchy, resulting in unrealistic descriptions in
  theoretical and numerical models of the solar cycles. The absence of
  long-term observations of solar interior dynamics and photospheric
  magnetic fields hinders development of accurate dynamo models and
  their calibration. In such situations, mathematical data assimilation
  methods provide an optimal approach for combining the available
  observational data and their uncertainties with theoretical models
  in order to estimate the state of the solar dynamo and predict future
  cycles. In this presentation, we will discuss the implementation and
  performance of an Ensemble Kalman Filter data assimilation method based
  on the Parker migratory dynamo model complemented by the equation of
  magnetic helicity conservation and long-term sunspot data series. This
  approach has allowed us to reproduce the general properties of the solar
  cycles and has already demonstrated a good predictive capability for the
  current cycle, 24. We will discuss further development of this approach,
  which includes a more sophisticated dynamo model, synoptic magnetogram
  data, and employs the DART Data Assimilation Research Testbed.

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.
Bibcode: 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.

Title: Data Assimilation Approach for Forecast of Solar Activity
    Cycles
Authors: Kitiashvili, Irina N.
Bibcode: 2016ApJ...831...15K
Altcode:
  Numerous attempts to predict future solar cycles are mostly based
  on empirical relations derived from observations of previous cycles,
  and they yield a wide range of predicted strengths and durations of
  the cycles. Results obtained with current dynamo models also deviate
  strongly from each other, thus raising questions about criteria to
  quantify the reliability of such predictions. The primary difficulties
  in modeling future solar activity are shortcomings of both the
  dynamo models and observations that do not allow us to determine
  the current and past states of the global solar magnetic structure
  and its dynamics. Data assimilation is a relatively new approach to
  develop physics-based predictions and estimate their uncertainties
  in situations where the physical properties of a system are not
  well-known. This paper presents an application of the ensemble
  Kalman filter method for modeling and prediction of solar cycles
  through use of a low-order nonlinear dynamo model that includes the
  essential physics and can describe general properties of the sunspot
  cycles. Despite the simplicity of this model, the data assimilation
  approach provides reasonable estimates for the strengths of future
  solar cycles. In particular, the prediction of Cycle 24 calculated
  and published in 2008 is so far holding up quite well. In this paper,
  I will present my first attempt to predict Cycle 25 using the data
  assimilation approach, and discuss the uncertainties of that prediction.

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.
Bibcode: 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.

Title: Early Solar Cycle Prediction with the Data Assimilation
Approach: Uncertainties and Future Challenges
Authors: Kitiashvili, Irina N.
Bibcode: 2016shin.confE..27K
Altcode:
  Solar variability is primarily driven by the evolution of magnetic
  fields on both local and global scales. Because of the coupled
  multi-scale nature of the solar magnetism the current dynamo models
  cannot realistically describe these interactions, limiting our
  predictive capabilities. An additional limitation lays in our poor
  knowledge of the structure and dynamics of magnetic fields in the solar
  convection zone, because observations cover only the solar surface. To
  overcome these limitations and obtain a more reliable picture of
  the global evolution of the solar magnetic activity I develop a
  synergetic analysis that combines of a theoretical dynamo model and
  observations by applying a data assimilation approach. <P />Data
  assimilation is a relatively new approach to develop physics-based
  predictions and estimate their uncertainties in situations when the
  physical properties of a system are not well known. Specifically,
  I will present an application of the Ensemble Kalman Filter method to
  modeling and prediction of solar cycles by using a low-order non-linear
  dynamo model, which includes the essential physics and can describe
  general properties of the sunspot cycles. Despite the simplicity
  of this model, the data assimilation approach provides reasonable
  estimates for the strengths of future solar cycles. In particular,
  the prediction of Cycle 24 calculated and published in 2008 is so far
  holding quite well. I will present my first attempt to predict the
  Solar Cycle 25 using the data assimilation approach and will discuss
  the uncertainties of this prediction.

Title: 3D Radiative MHD Modeling of Quiet-Sun Magnetic Activity
Authors: Kitiashvili, Irina
Bibcode: 2016SPD....47.1205K
Altcode:
  Quiet-Sun regions that cover most of the solar surface represent a
  background state that plays an extremely important role in the dynamics
  and energetics of the solar atmosphere. A clear understanding of these
  regions is required for accurate interpretation of solar activity
  events such as emergence of magnetic flux, sunspot formation,
  and eruptive dynamics. Modern high-resolution observations from
  ground and space telescopes have revealed a complicated dynamics of
  turbulent magnetoconvection and its effects in the solar atmosphere
  and corona, showing intense interactions across different temporal
  and spatial scales. Interpretation of the observed complex phenomena
  and understanding of their origins is impossible without advanced
  numerical models. I will present new results of realistic-type 3D
  radiative MHD simulations of the upper turbulent convective layer and
  atmosphere of the Sun. The results reveal the mechanism of formation
  and properties of the Sun’s “magnetic carpet” controlled by
  subsurface small-scale dynamo processes, and demonstrate interaction
  between the subsurface layers and the atmosphere via spontaneous
  small-scale eruptions and wave phenomena. To link the simulations to
  solar data the spectro-polarimetric radiative transfer code SPINOR is
  used to convert the simulated data into the Stokes profiles of various
  spectral lines, including the SDO and Hinode observables. The results
  provide a detailed physical understanding of the quiet-Sun dynamics,
  and show potential for future observations with the DKIST and other
  large solar telescopes.

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.
Bibcode: 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.

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.
Bibcode: 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 Dynamo on Small and Global Scales
Authors: Kitiashvili, I.; Kosovichev, A. G.; Mansour, N. N.; Wray,
   A. A.
Bibcode: 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: The Sun's Photospheric Convection Spectrum
Authors: Hathaway, David H.; Teil, Thibaud; Norton, Aimee A.;
   Kitiashvili, Irina
Bibcode: 2015ApJ...811..105H
Altcode: 2015arXiv150803022H
  Spectra of the cellular photospheric flows are determined from
  full-disk Doppler velocity observations acquired by the Helioseismic
  and Magnetic Imager (HMI) instrument on the Solar Dynamics Observatory
  spacecraft. Three different analysis methods are used to separately
  determine spectral coefficients representing the poloidal flows, the
  toroidal flows, and the radial flows. The amplitudes of these spectral
  coefficients are constrained by simulated data analyzed with the same
  procedures as the HMI data. We find that the total velocity spectrum
  rises smoothly to a peak at a wavenumber of about 120 (wavelength of
  about 35 Mm), which is typical of supergranules. The spectrum levels
  off out to wavenumbers of about 400, and then rises again to a peak
  at a wavenumber of about 3500 (wavelength of about 1200 km), which
  is typical of granules. The velocity spectrum is dominated by the
  poloidal flow component (horizontal flows with divergence but no curl)
  at wavenumbers above 30. The toroidal flow component (horizontal flows
  with curl but no divergence) dominates at wavenumbers less than 30. The
  radial flow velocity is only about 3% of the total flow velocity at
  the lowest wavenumbers, but increases in strength to become about 50%
  at wavenumbers near 4000. The spectrum compares well with the spectrum
  of giant cell flows at the lowest wavenumbers and with the spectrum
  of granulation from a 3D radiative-hydrodynamic simulation at the
  highest wavenumbers.

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
Bibcode: 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: Radiative 3D MHD simulations of the spontaneous small-scale
    eruptions in the solar atmosphere
Authors: Kitiashvili, Irina N.
Bibcode: 2015IAUGA..2258477K
Altcode:
  Studying non-linear turbulent dynamics of the solar atmosphere
  is important for understanding mechanism of the solar and stellar
  brightness variations. High-resolution observations of the quiet
  Sun reveal ubiquitous distributions of high-speed jets, which are
  transport mass and energy into the solar corona and feeding the
  solar wind. However, the origin of these eruption events is still
  unknown. Using 3D realistic MHD 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 and shows that 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. I will discuss about properties
  of these eruptions, their effects on brightness and spectral variations
  and comparison with observations.

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.
Bibcode: 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: Scaling properties of turbulent flows on the Sun and stars
Authors: Kitiashvili, Irina N.
Bibcode: 2015IAUGA..2258535K
Altcode:
  Understanding dynamics of the solar and stellar plasmas is not
  possible without characterization of turbulent spectral properties
  by using numerical simulations and observations. Recent progress in
  observational and computational capabilities allows us to investigate
  variations of these properties under different physical conditions. I
  will present analysis of scaling properties of solar and stellar
  magnetoconvection using results of 3D radiative MHD simulations of
  the Sun and several main-sequence stars with various masses, and
  compare with observations. I will discuss a synergy of turbulent
  scaling properties of convection on different stars and effects of
  magnetic field.

Title: Realistic Modeling of Local Dynamo Processes on the Sun
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Mansour, N. N.; Wray,
   A. A.
Bibcode: 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: Numerical simulations of magnetoconvection and helioseismology
Authors: Kitiashvili, I. N.
Bibcode: 2015exse.book..238K
Altcode:
  No abstract at ADS

Title: Using Realistic MHD Simulations for Modeling and Interpretation
    of Quiet-Sun Observations with the Solar Dynamics Observatory
    Helioseismic and Magnetic Imager
Authors: Kitiashvili, I. N.; Couvidat, S.; Lagg, A.
Bibcode: 2015ApJ...808...59K
Altcode: 2014arXiv1407.2663K
  The solar atmosphere is extremely dynamic, and many important phenomena
  develop on small scales that are unresolved in observations with
  the Helioseismic and Magnetic Imager (HMI) instrument on the Solar
  Dynamics Observatory. For correct calibration and interpretation of
  the observations, it is very important to investigate the effects
  of small-scale structures and dynamics on the HMI observables,
  such as Doppler shift, continuum intensity, spectral line depth,
  and width. We use 3D radiative hydrodynamics simulations of the
  upper turbulent convective layer and the atmosphere of the Sun, and
  a spectro-polarimetric radiative transfer code to study observational
  characteristics of the Fe i 6173 Å line observed by HMI in quiet-Sun
  regions. We use the modeling results to investigate the sensitivity
  of the line Doppler shift to plasma velocity, and also sensitivities
  of the line parameters to plasma temperature and density, and
  determine effective line formation heights for observations of solar
  regions located at different distances from the disk center. These
  estimates are important for the interpretation of helioseismology
  measurements. In addition, we consider various center-to-limb effects,
  such as convective blueshift, variations of helioseismic travel-times,
  and the “concave” Sun effect, and show that the simulations can
  qualitatively reproduce the observed phenomena, indicating that these
  effects are related to a complex interaction of the solar dynamics
  and radiative transfer.

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.
Bibcode: 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: Advances in Realistic MHD Simulation
Authors: Kitiashvili, I.
Bibcode: 2014AGUFMSH31C..03K
Altcode:
  Modern high-resolution observations from ground and space telescopes
  reveal a complicated dynamics of turbulent magnetoconvection and its
  effects in the solar atmosphere and corona, showing intense interactions
  across different temporal and spatial scales. Interpretation of
  the observed complex phenomena and understanding of their origins
  is impossible without advanced numerical models. The rapid growth of
  computational capabilities has made possible 3D radiative MHD numerical
  simulations that reproduce solar conditions with a high degree of
  realism. Such simulations allow us to determine physical processes
  hidden from direct observations. They also provide synthetic data for
  calibration of observational data and for developing and testing ideas
  for improved diagnostics. In the talk I will discuss current advances
  and challenges of modeling multi-scale turbulent magnetoconvection,
  magnetic self-organization phenomena in the photosphere, their
  dynamical interaction with the chromospheric layers, and modeling of
  spectro-polarimetric observations for different instruments.

Title: Spectro-polarimetric properties of small-scale plasma eruptions
    driven by magnetic vortex tubes
Authors: Kitiashvili, Irina N.
Bibcode: 2014PASJ...66S...8K
Altcode: 2014arXiv1407.2295K; 2014PASJ..tmp..112K
  The highly turbulent nature of convection on the Sun causes strong
  multi-scale interaction of subsurface layers with the photosphere and
  chromosphere. According to realistic 3D radiative magnetohydrodynamic
  numerical simulations, ubiquitous small-scale vortex tubes are generated
  by turbulent flows below the visible surface and concentrated in the
  intergranular lanes. The vortex tubes can capture and amplify magnetic
  field, penetrate into chromospheric layers and initiate quasi-periodic
  flow eruptions that generate Alfvénic waves, and transport mass and
  energy into the solar atmosphere. The simulations revealed high-speed
  flow patterns, and complicated thermodynamic and magnetic structures
  in the erupting vortex tubes. The spontaneous eruptions are initiated
  and driven by strong pressure gradients in the near-surface layers,
  and accelerated by the Lorentz force in the low chromosphere. In this
  paper, the simulation data are used to further investigate the dynamics
  of the eruptions, their spectro-polarimetric characteristics for the
  Fe I 6301.5 and 6302.5 Å spectral lines, and demonstrate expected
  signatures of the eruptions in the Hinode Spectro-Polarimeter (SP)
  data. We found that the complex dynamical structure of vortex tubes
  (downflows in the vortex core and upflows on periphery) can be captured
  by the Stokes I profiles. During an eruption, the ratio of down and
  upflows can suddenly change, and this effect can be observed in the
  Stokes V profile. Also, during the eruption the linear polarization
  signal increases, and this also can be detected with Hinode SP.

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.
Bibcode: 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: Radiative 3D Modeling of Convection of Main-Sequence Stars
Authors: Kitiashvili, Irina
Bibcode: 2014AAS...22440402K
Altcode:
  Recent progress in observational capabilities, and particularly,
  the large amount of photometric data from Kepler, require the
  development of realistic numerical simulations for data interpretation
  and validation of theoretical models. Current state-of-the-art of
  computational modeling based on first principles makes it possible to
  build realistic models of stellar convection zones and atmospheres,
  which can take into account chemical composition, effects of radiation,
  ionization and turbulence. I present large-scale 3D time-dependent
  radiative hydrodynamics simulations for a series of Kepler-target
  stars with masses from 1.01 Ms to 1.52 Ms and effective temperature
  varying from 5780 K to 6982 K, and investigate the properties of
  convection, the surface structure and oscillations. For massive A-type
  stars, the simulations include the whole outer convection layer and
  the overshoot region at the interface with the radiative zone. The
  simulations reveal that in stars that are more massive than the Sun,
  turbulent convection is highly supersonic and produces multiscale
  granulation patterns on the surface. These simulation results also
  show that contrary to current paradigm, turbulent convection plays
  a very important role in the surface dynamics of A-type stars, and
  leads to stochastic excitation of acoustic oscillations observed by
  Kepler. I will also discuss the dynamics of the overshooting region
  and excitation of internal gravity waves.

Title: Realistic Modeling of Spontaneous Flow Eruptions in the
    Quiet Sun
Authors: Kitiashvili, Irina; Yoon, Seokkwan S
Bibcode: 2014AAS...22432302K
Altcode:
  Ground and space observations reveal that the solar surface is
  covered by high-speed jets transporting mass and energy into the solar
  corona and feeding the solar wind. The origin and driving forces of
  the observed eruptions are still unknown. Using realistic numerical
  simulations we find that small-scale plasma eruptions can be produced
  by ubiquitous magnetized vortex tubes generated in the Sun's turbulent
  convection. The vortex tubes (resembling tornadoes) penetrate into
  the solar atmosphere, capture and strengthen the background magnetic
  field, and push surrounding material up, generating impulses of Alfven
  waves and shocks. Our simulations reveal complicated high-speed flows,
  thermodynamic, and magnetic structures in the erupting vortex tubes. We
  find that the eruptions are initiated in the subsurface layers, and
  initially are driven by high-pressure gradients in the subphotosphere
  and photosphere, and are accelerated by the Lorentz force in the
  higher atmospheric layers. The eruptions are often quasi-periodic
  with a characteristic period of 2-5 min. These vortex eruptions have
  a complicated flow helical pattern, with predominantly downward flows
  in the vortex tube cores and upward flows in their surroundings. For
  comparison with observations we calculate full Stokes profiles in
  different wavelength for different space and ground instruments,
  such as HMI/SDO, Hinode, NST/BBSO, IMaX/Sunrise. In particular, we
  find that the observed eruption events are not always associated with
  strong magnetic field concentrations, and that strong field patches
  can be a source of several simultaneous eruptions.

Title: Modeling of SDO/HMI spectro-polarimetric data and
    center-to-limb variation effects with 3D MHD simulations
Authors: Kitiashvili, Irina; Couvidat, Sebastien
Bibcode: 2014AAS...22442207K
Altcode:
  Observations with the Solar Dynamics Observatory (SDO), and, in
  particular, Helioseismic and Magnetic Imager (HMI) provide a unique
  opportunity to investigate various phenomena simultaneously over the
  whole solar disk. Current state-of-the-art numerical simulations allow
  us to model the observational data with a high degree of realism,
  and use the artificial data for interpretation of observed properties
  ("observables") in terms of the physical conditions, for the testing of
  new data analysis techniques and the improvement of data calibration. In
  the current study we use realistic-type 3D radiative MHD simulations
  of the upper turbulent convective layer and atmosphere of the Sun,
  obtained with the SolarBox code, and employ the spectro-polarimetric
  radiative transfer code SPINOR to convert the simulated data into
  Stokes profiles of the HMI Fe I 6173 A line for different conditions
  in the solar atmosphere. For testing the HMI calibration the synthetic
  Stokes profiles are processed through the SDO/JSOC simplified data
  analysis pipeline. We investigate properties of the HMI observables
  for various solar features, variations of the line formation height
  for different angular distances from the disk center, effects of the
  spatial resolution and iron abundance, and pay particular attention
  to the center-to-limb variations effects playing important role in
  local helioseismology measurements.

Title: Multiscale Properties of the Local Dynamo on the Sun
Authors: Kitiashvili, Irina; Kosovichev, Alexander G.; Mansour,
   Nagi N; Wray, Alan A
Bibcode: 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: Radiative hydrodynamic simulations of turbulent convection
    and pulsations of Kepler target stars
Authors: Kitiashvili, Irina N.
Bibcode: 2014IAUS..301..193K
Altcode:
  The problem of interaction of stellar pulsations with turbulence
  and radiation in stellar convective envelopes is central to our
  understanding of excitation mechanisms, oscillation amplitudes
  and frequency shifts. Realistic (``ab initio'') numerical
  simulations provide unique insights into the complex physics of
  pulsation-turbulence-radiation interactions, as well as into the
  energy transport and dynamics of convection zones, beyond the standard
  evolutionary theory. 3D radiative hydrodynamics simulations have been
  performed for several Kepler target stars, from M- to A-class along
  the main sequence, using a new `StellarBox' code, which takes into
  account all essential physics and includes subgrid scale turbulence
  modeling. The results reveal dramatic changes in the convection and
  pulsation properties among stars of different mass. For relatively
  massive stars with thin convective envelopes, the simulations allow
  us to investigate the dynamics the whole envelope convection zone
  including the overshoot region, and also look at the excitation of
  internal gravity waves. Physical properties of the turbulent convection
  and pulsations, and the oscillation spectrum for two of these targets
  are presented and discussed in this paper. In one of these stars,
  with mass 1.47 M <SUB>⊙</SUB>, we simulate the whole convective
  zone and investigate the overshoot region at the boundary with the
  radiative zone.

Title: Mechanism of local dynamo action on the Sun
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Mansour, N. N.; Wray,
   A. A.
Bibcode: 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.
Bibcode: 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: Mechanisms of formation ofsolar pores and sunspots
Authors: Kitiashvili, Irina N.
Bibcode: 2013IAUS..294..269K
Altcode:
  Spontaneous formation of self-organized magnetic structures, such as
  sunspots and pores, is one of intriguing and oldest problems, which
  represents a complicated interaction of convection and magnetic fields
  on different scales. Observations of sunspots and pores formation reveal
  a fast process of accumulation of emerging magnetic field into stable
  long-living magnetic structures. However, the physical mechanisms
  of the flux accumulation into the compact magnetic structures with
  high field strength and their stability are not clear. Development of
  observational capabilities, theory, and realistic-type MHD numerical
  simulations open a new level of our understanding of the turbulent
  processes of the magnetic field accumulation. I discuss the recent
  progress in observations and radiative MHD simulations that provide
  important clues for possible mechanisms of formation and stability of
  sunspots and pores, and their links to the dynamo process.

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.
Bibcode: 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: Spin rotation, Chandler wobble and free core nutation of
    isolated multi-layer pulsars
Authors: Gusev, Alexander; Kitiashvili, Irina
Bibcode: 2013IAUS..291..392G
Altcode:
  At present time there are investigations of precession and nutation
  for very different celestial multi-layer bodies: the Earth (Getino
  1995), Moon (Gusev 2010), planets of Solar system (Gusev 2010) and
  pulsars (Link et al. 2007). The long-periodic precession phenomenon
  was detected for few pulsars: PSR B1828-11, PSR B1557-50, PSR 2217+47,
  PSR 0531+21, PSR B0833-45, and PSR B1642-03. Stairs, Lyne &amp; Shemar
  (2000) have found that the arrival-time residuals from PSR B1828-11
  vary periodically with a different periods. According to our model,
  the neutron star has the rigid crust (RC), the fluid outer core (FOC)
  and the solid inner core (SIC). The model explains generation of four
  modes in the rotation of the pulsar: two modes of Chandler wobble
  (CW, ICW) and two modes connecting with free core nutation (FCN, FICN)
  (Gusev &amp; Kitiashvili 2008). We are propose the explanation for all
  harmonics of Time of Arrival (TOA) pulses variations as precession of
  a neutron star owing to differential rotation of RC, FOC and crystal
  SIC of the pulsar PSR B1828-11: 250, 500, 1000 days. We used canonical
  method for interpretation TOA variations by Chandler Wobble (CW)
  and Free Core Nutation (FCN) of pulsar.

Title: Using realistic MHD simulations for modeling HMI observables
Authors: Kitiashvili, I.; Couvidat, S.; Mansour, N.; Wray, A.;
   Kosovichev, A.
Bibcode: 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: 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.
Bibcode: 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: 3D MHD Simulations of Spontaneous Flow Ejections by Turbulent
    Convection into the Chromosphere
Authors: Kitiashvili, I.; Kosovichev, A. G.; Mansour, N.; Wray, A.
Bibcode: 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: Self-organization of the Solar Turbulent Convection in
    Magnetic Field
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Mansour, N. N.; Wray,
   A. A.
Bibcode: 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.
Bibcode: 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: 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.
Bibcode: 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: Fine-scale Magnetic Structures and Flows in Sunspot Simulations
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Wray, A. A.; Mansour,
   N. N.
Bibcode: 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: Vortex tubes of turbulent solar convection
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Mansour, N. N.; Lele,
   S. K.; Wray, A. A.
Bibcode: 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: Simulations and Observational Signatures of Mass Ejections,
    Alfven Waves and Shocks Driven by Turbulent Magnetized Vortex Tubes
Authors: Kitiashvili, Irina N.
Bibcode: 2012shin.confE.105K
Altcode:
  The mass and energy supply from the Sun into the solar wind is driven
  by turbulent convection in the near-surface layers. Therefore, the
  dynamics of subsurface turbulent processes and their connections to
  the atmosphere are a key to understanding the energy transport, heating
  of the atmosphere, corona and wind, and mass eruptions. I present new
  results of radiative 3D MHD simulations that reveal a fundamental role
  of small-scale magnetized vortex tubes generated near the solar surface
  by turbulent convection and penetrating into the higher atmospheric
  layers, potentially providing the mass and energy for the solar wind in
  open magnetic field structures.The advanced, realistic type, numerical
  simulations included most important effects, such as sub-grid scale
  turbulence, magnetic field, radiation, ionization and excitation
  of all abundant spices, realistic EOS and initial solar model. The
  MHD simulations revealed formation of ubiquitous small-scale vortex
  tubes mostly concentrated in the intergranular lanes, which capture
  and twist magnetic field lines and penetrate into the high atmospheric
  layers. This process leads to spontaneous generation of shock and Alfven
  waves, and is accompanied by small-scale mass ejections. I discuss
  spectro-polarimetric diagnostics of the vortex tubes and eruptions,
  and their signatures in recent high-resolution observations.

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.
Bibcode: 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: Dynamics of Magnetized Vortex Tubes in the Solar Chromosphere
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Mansour, N. N.; Wray,
   A. A.
Bibcode: 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.
Bibcode: 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: Effects of vortex tube dynamics in the chromosphere
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Lele, S. K.; Mansour,
   N. N.; Wray, A. A.
Bibcode: 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.
Bibcode: 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: 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.
Bibcode: 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: Data Assimilation for Dynamo Modeling and Solar Cycle
    Prediction
Authors: Kitiashvili, I. N.
Bibcode: 2011AGUFMSH54A..02K
Altcode:
  Incredible growth of space technologies makes them more and more
  vulnerable to solar impacts. From this point of view accurate
  predictions of solar activity on various time scales are critical
  for planning future space missions, space experiments, and also
  important for reducing these impacts on ground services. Observed
  cyclic variations of solar activity are a result of a complicated
  non-linear dynamo process in the convection zone that is not
  fully understood. Therefore dynamo models cannot be used for direct
  predictions. Also, the information about convective flows is usually
  limited to surface observations, and only recently we have started
  measurements of interior flows by helioseismology. Data assimilation
  methods combine the available observational data and models for an
  efficient and accurate estimation of physical properties of the dynamo
  process, which cannot be observed directly. This approach allows us to
  make predictions even when our knowledge of a system is incomplete. It
  has been successfully used in meteorology, but is relatively new in the
  solar activity studies. I will discuss the general methodology of data
  assimilation methods for the solar dynamo modeling, its implementation
  for short and long term predictions of the sunspot cycles, and also
  limitations and uncertainties of this approach.

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.
Bibcode: 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: 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.
Bibcode: 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: Numerical simulations of magnetic structures
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Wray, A. A.; Mansour,
   N. N.
Bibcode: 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: Realistic MHD simulations of magnetic self-organization in
    solar plasma
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Wray, A. A.; Mansour,
   N. N.
Bibcode: 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.
Bibcode: 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: A Mechanism of the Solar Acoustic Emission
Authors: Kitiashvili, Irina; Kosovichev, A. G.; Lele, S. K.; Mansour,
   N. N.; Wray, A. A.
Bibcode: 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: 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.
Bibcode: 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: 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.
Bibcode: 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.
Bibcode: 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: Modeling and Prediction of Solar Cycles Using Data Assimilation
    Methods
Authors: Kitiashvili, Irina N.; Kosovichev, Alexander G.
Bibcode: 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: Subsurface structure of the Evershed flows in sunspots
Authors: Kitiashvili, Irina N.; Kosovichev, Alexander G.; Mansour,
   Nagi N.; Wray, Alan A.
Bibcode: 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: 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.
Bibcode: 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.
Bibcode: 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: 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.
Bibcode: 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.
Bibcode: 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: Mechanism of Spontaneous Formation of Stable Magnetic
    Structures on the Sun
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Wray, A. A.; Mansour,
   N. N.
Bibcode: 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: Rotational evolution of planetary systems under the action
    of gravitational and magnetic perturbations
Authors: Kitiashvili, I. N.; Gusev, A. V.
Bibcode: 2010CosRe..48..335K
Altcode:
  Dynamics of planets around other stars that demonstrate a variety
  of possible characteristics is of interest from the point of view
  of realization of new scenarios of evolution which have not been
  realized in the Solar System. We consider the rotational evolution
  of exoplanets under the action of gravitational perturbations and
  magnetic disturbances using the methods of quality analysis and theory
  of bifurcation of multiparametric differential equations that describe
  evolution of non-resonant rotation of a dynamically symmetric planet
  magnetized along its symmetry axis. We analyze 64 phase portraits
  describing the evolution of angular momentum vector L for all possible
  values of planet parameters. The values of parameters are determined
  for the case when the direct rotation of a planet is changed for its
  retrograde rotation.

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.
Bibcode: 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: 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.
Bibcode: 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.
Bibcode: 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: 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.
Bibcode: 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: 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.
Bibcode: 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: Prediction of solar activity cycles by assimilating sunspot
    data into a dynamo model
Authors: Kitiashvili, Irina N.; Kosovichev, Alexander G.
Bibcode: 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: Implementation of Data Assimilation Methods for Dynamo Models
    to Predict Solar Activity
Authors: Kitiashvili, I.; Kosovichev, A.
Bibcode: 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: The Origin of High-Speed Evershed Flows in Sunspots
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Wray, A. A.; Mansour,
   N. N.
Bibcode: 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.
Bibcode: 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: 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.
Bibcode: 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.
Bibcode: 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: Realistic 3D MHD Simulations of the Evershed Effect
Authors: Kitiashvili, Irina; Kosovichev, A. G.; Wray, A. A.; Mansour,
   N. N.
Bibcode: 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: Prediction of solar magnetic cycles by a data assimilation
    method
Authors: Kitiashvili, Irina N.; Kosovichev, Alexander G.
Bibcode: 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 and tidal interactions in spin evolution of exoplanets
Authors: Kitiashvili, Irina N.
Bibcode: 2009IAUS..259..303K
Altcode:
  The axis-rotational evolution of exoplanets on close orbits strongly
  depends on their magnetic and tidal interactions with the parent
  stars. Impulsive perturbations from a star created by periodical
  activity may accumulate with time and lead to significant long-term
  perturbations of the planet spin evolution. I consider the spin
  evolution for different conditions of gravitational, magnetic and tidal
  perturbations, orbit eccentricity and different angles between the
  planetary orbit plane and the reference frame of a parent star. In this
  report I present a summary of analytical and numerical calculations
  of the spin evolution, and discuss the problem of the star-planet
  magnetic interaction.

Title: Nonlinear dynamical modeling of solar cycles using dynamo
    formulation with turbulent magnetic helicity
Authors: Kitiashvili, I. N.; Kosovichev, A. G.
Bibcode: 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: Using Data Assimilation Methods for Modeling and Predicting
    Solar Activity Cycles
Authors: Kitiashvili, I. N.; Kosovichev, A. G.
Bibcode: 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: Application of Data Assimilation Method for Predicting
    Solar Cycles
Authors: Kitiashvili, I.; Kosovichev, A. G.
Bibcode: 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: Inner core wobble and free core nutation of pulsar PSR B1828-11
Authors: Kitiashvili, I.; Gusev, A.
Bibcode: 2008AdSpR..42.1391K
Altcode:
  PSR B1828-11 has long-term, highly periodic and correlated variations in
  pulse shape and a slow-down rate with period variations of approximately
  1000, 500 and 250 days [Stairs, I.H., Lyne, A.G., Shemar, S.L. Evidence
  for free precession in a pulsar. Nature 406, 484-486, 2000]. There
  are three potential explanations of pulses time-of-arrival from a
  pulsar. These are related to the interior of the neutron star, planetary
  bodies, free precession and nutation. We use the Hamiltonian canonical
  method of Getino (1995) for analyzing the dynamically symmetric pulsar
  PSR B1828-11, consisting of a rigid crust, elliptical liquid outer
  core and solid inner core. Using the theory of differential rotation
  of a pulsar, we investigate the dependence on Chandler wobble period,
  inner core wobble, retrograde free core nutation and prograde free
  inner core nutation from ellipticity of the inner crystal core, outer
  liquid core and total pulsar.

Title: Quasi-periodical variations of pulsars spin as mimicry of
    differential rotation
Authors: Kitiashvili, I.; Gusev, A.
Bibcode: 2008epsc.conf..507K
Altcode:
  ABSTRACT Observation of pulsars is a powerful source of information for
  studying the dynamics and internal structure of neutron stars. Known
  about quasi-periodical fluctuations of the time-of-arrival of
  radiation(TOA) for some pulsars, which we explain as Chandler wobble,
  Free core nutation, Free inner core nutation and Inner core wobble in
  case three layer model. Using hamilton approximation to theory rotation
  of multilayer celestial bodies we estimate dynamical flattening for
  different layers for PSR B1828-11. It is known that an innate feature
  of pulsar radiation is high stability of the time-of-arrival (TOA)
  of pulses, and therefore the analysis of TOA fluctuations can reflect
  subtle effects of neutron stars dynamics. TOA variations of pulsars can
  be interpreted by three reasons: gravitational perturbation of pulsar
  by planetary bodies, peculiarities of a pulsar interior like Tkachenko
  oscillations and free precession motion, when axis of rotation do not
  coincide with vectors of the angular moment of solid crust, liquid outer
  core and crystal core. The radial velocity of a star is obtained by
  measuring the magnitude of the Doppler effect in its spectrum. Stars
  showing a small amplitude variation of the radial velocity can be
  interpreted as systems having planetary companions. Assuming that
  the pulsar PSR B1257+12 has a mass of 1:35M¯, the Keplerian orbital
  radii are 0.9, 1.4 and 2.1 AU and with masses are 3:1M©=sin(i),
  10:2M©=sin(i), 4:6M©=sin(i), where i is the orbital inclination
  [7]. In 2000, Stairs, Lyne and Shemar reported about their discovery
  of long-term, highly-periodic and correlated variations of pulse
  shape and the rate of slow-down of the pulsar PSR B182811 with period
  variations approximately 1000, 500, 250 and 167 days, which may be
  a result of the spin axis caused by an asymmetry in the shape of the
  pulsar. The long-periodic precession phenomenon was also detected for
  a few pulsars: PSR 2217+47, PSR 0531+21, PSR B083345, PSR B182811,
  PSR B164203 [2,3,6,]. The rotation of the terrestrial planets having
  rigid mantle, outer liquid and inner solid cores is characterized by
  Chandler wobble, Inner core wobble, Free Core Nutation, Free Inner
  Core Nutation. Like the Earth, a neutron star can undergo a free
  precession [4]. The period of precession is defined by deformation of
  a pulsar and tension in crust and mantle. If the crust and the core
  of pulsar have differential rotation then axis of a pulsar rotation
  will be precess, because axis of deformation will not coincide with
  axis of rotation. The three-layer model is more complicated than the
  previous case therefore classical methods fail. Escapa, Getino and
  Ferrandiz [1] developed a canonical formulation for an three-layer
  Earth model. We research model of pulsar, which includes three layers
  (fig. 1): an axis symmetrical rigid mantle, a fluid outer core (FOC)
  and a solid inner core (SIC). Flattened of the pulsar, it's FOC
  and SIC are Here A;C;Af ;Cf ;As;Cs;Ac;Cc are moments of inertia of
  the pulsar, FOC, SIC and total core accordingly; e, ef , ec are the
  flattening of total pulsar, FOC, core and SIC accordingly. In case
  rotation of a three-layer neutron star we have variations of next
  types: the Chandler Wobble (CW) is a motion of the pulsar rotation
  axis around its dynamical figure due to the bulges of the pulsar
  (it is the only global rotational mode for completely solid pulsar);
  the Free Core Nutation (FCN) is a differential rotation of the liquid
  core relatively the crust rotation; This mode does exist only if the
  core is liquid; the Free Inner Core Nutation (FICN) is a mode related
  to the differential rotation of the inner core with respect to the
  other layers of the pulsar. The mode exists only if the pulsar has
  two-layer core contains outer liquid and inner solid components; the
  Inner Core Wobble (ICW) is a differential rotation of the figure axis
  of the pulsar core with respect to the rotation axis of the pulsar and
  is due to the flattened of the inner core, having an excess of density
  with respect to the liquid core. This mode does exist only if there is
  an ellipsoidal solid inner core inside a liquid core in the pulsar. We
  propose the explanation for four harmonics of TOA pulses variations as
  precession of a neutron star owing to differential rotation of crust,
  outer liquid core and inner crystal core of the pulsar PSR B1828-11. In
  the frame of the three-layer model we investigate the free rotation
  of dynamically-symmetrical PSR B1828-11 by Hamilton methods proposed
  Getino [1]. The model explains generation of four modes in the rotation
  of the pulsar: two modes of Chandler wobbles (CW, ICW) and two modes
  connecting with free core nutation (FCN, FICN). The neutron star has
  rigid the crust, the fluid outer core and the solid inner core. We
  consider four models of an internal structure of pulsars (tabl. 1)
  in the frame of three-layer approximation. We are used three models of
  pulsar (tabl. 1, M1 - M3) for modeling of inner, outer cores flattening
  and total pulsar. The periods of variations can be described in next
  way where ± is a small parameter has the analytical expression [6]
  here Cb f and Ab f are the principal inertia moments corresponding to
  a spherical layer in the FOC with radius equal to the major semiaxia
  of the SIC which encloses the solid inner core [1]. The observation of
  PSR B1828-11 has revealed the existence of four periodic variations
  TOA pulses. In the frame of the three-layer model we proposed the
  explanation for all pulse fluctuations by differential rotation crust,
  outer core and inner core of the neutron star. We received estimations
  of dynamical flattening of the inner and outer cores for pulsar. We
  have offered the realistic model of the dynamical pulsar structure and
  two explanations of the feature of flattened of the crust, the outer
  core and the inner core of the pulsar. (Kitiashvili and Gusev, 2008)
  References [1] Escapa, A. et al. (2001), J.Geoph.Res., 106, B6,
  11387. [2] Kitiashvili, I. (2004) PhD thesis, Moscow University. [3]
  Kitiashvili, I.N. and Gusev, A.V. (2008) Astronomy Reports, 52(1),
  61. [4] Pines, D. and Shaham J. (1974), Nature, 248, 483. [5] Stairs,
  I.H. et al. (2000), Nature, 406, 484. [6] Suleymanova, S.A. and Shitov,
  Y.P. (1994), ApJ.Lett., 422, 17. [7] Wolszczan A. (1997), Celest. &amp;
  Dyn. Astr., 68, 13.

Title: Modeling of evolution of the rotational axis of “hot
    Jupiter” planets under tidal perturbations
Authors: Kitiashvili, Irina
Bibcode: 2008IAUS..249..197K
Altcode: 2007IAUS..249..197K
  In this report, we present results of analytical and numerical
  calculations of evolution the axis of rotation of planets moving at
  very close orbits. We consider the evolution of the axis of rotation
  caused by tidal perturbations of a parent star and obtain estimates
  of the principal moment of inertia and the dynamical flattening for
  nine exoplanets. From analysis of evolutionary equations, we obtain the
  critical values of the kinetic momentum vector, $\vec L$, for different
  values of orbital eccentricity. We find a general tendency of vector
  $\vec L$ to evolve to the direction perpendicular to the orbital plane.

Title: Application of Data Assimilation Methods to Non-Linear Dynamo
    Models of Solar Cycle
Authors: Kitiashvili, I.; Kosovichev, A.
Bibcode: 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: Rotational evolution of exoplanets under the action of
    gravitational and magnetic perturbations
Authors: Kitiashvili, Irina N.; Gusev, Alexander
Bibcode: 2008CeMDA.100..121K
Altcode: 2008CeMDA.tmp....5K
  We investigate the evolution of the rotational axes of exoplanets under
  the action of gravitational and magnetic perturbations. The planet is
  assumed to be dynamically symmetrical and to be magnetised along its
  dynamical-symmetry axis. By qualitative methods of the bifurcation
  theory of multiparametric PDEs, we have derived a gallery of 69 phase
  portraits. The portraits illustrate evolutionary trajectories of the
  angular momentum {ěc L} of a planet for a variety of the initial
  conditions, for different values of the ratio between parameters
  describing gravitational and magnetic perturbations, and for different
  rates of the orbital evolution. We provide examples of the phase
  portraits, that reveal the differences in topology and the evolutionary
  track of {ěc L} in the vicinity of an equilibrium state. We determine
  the bifurcation properties, i.e., the way of reorganisation of phase
  trajectories in the vicinities of equilibria; and we point out the
  combinations of parameters’ values that permit ip-overs from a
  prograde to a retrograde spin mode.

Title: Application of Data Assimilation Methods to Non-Linear Solar
    Dynamo Models
Authors: Kitiashvili, I.
Bibcode: 2008ASPC..383..255K
Altcode:
  Prediction of parameters of the 11-year solar cycles is one the
  most interesting problems of solar physics, in which helioseismology
  observations play an important role. However, the knowledge of the
  underlying processes is incomplete, and this makes predictions of the
  solar cycles difficult. The data assimilation approach developed
  in meteorology and Earth science makes possible efficient and
  accurate estimations of physical properties, which cannot be observed
  directly. To a first approximation, the solar dynamo models can be
  described in terms of simple, Lorenz-type, dynamical systems. The
  application of data assimilation to this type of models and the initial
  results are discussed in this paper.

Title: Long-period variations of pulsar emission and the dynamical
    ellipticity of neutron stars
Authors: Kitiashvili, I. N.; Gusev, A. V.
Bibcode: 2008ARep...52...61K
Altcode: 2008AZh....85...69K
  Assuming that the observed periodic variations of pulsar emission
  are due to the free precession of the spin axis, we investigate
  the evolution of the rotation of a two-layer neutron star using the
  Hamiltonian method of Getino. We model the dynamical characteristics of
  a rotating neutron star using the observed variations of the emission
  of seven pulsars. We estimate the dependence of the period of the
  Chandler wobble, the period of precession of the spin axis, and the
  dynamical ellipticity of a neutron star on the model used to describe
  the super-dense neutron matter and the mass of the star.

Title: Dynamical Flattening of Crust, Fluid Outer Core and Solid
    Inner Core for PSR B1828-11
Authors: Kitiashvili, I.; Gusev, A.
Bibcode: 2006IAUJD...6E..11K
Altcode:
  An investigation of rotation variations allows studying a structure
  of a neutron star. Analysis of the time-of-arrival (TOA) pulses
  fluctuations can be reflection of thin effects of neutron stars
  rotational dynamics. In observations of radiation from some pulsars:
  PSR 2217+47, PSR 0531+21, PSR B0833-45, PSR B1828-11, PSR B1642-03
  a long periodic fluctuations of TOA pulses with period from 25 to
  6136 days were detected. PSR B1828-11 has long-term, highly periodic
  and correlated variations pulse shape and of the rate of slow-down
  with period variations approximately 1000, 500, 250 and 167 days. TOA
  variations of pulsars can be interpreted by three reasons: gravitational
  perturbation by planetary bodies, peculiarities of a pulsar interior
  like Tkachenko oscillations and free precession motion, when axis of
  rotation do not coincide with vectors of the angular moment of solid
  crust, liquid outer core and crystal core. We use the Hamiltonian
  canonical method of Getino for the dynamically symmetrical three-layer
  model of the pulsar PSR B1828-11. We explane four harmonics of pulses
  variations as precessions and nutations of a neutron star owing to
  differential rotation of crust, fluid outer core (FOC) and solid inner
  core (SIC) by Chandler wobble (CW), Inner Chandler Wobble (ICW), Free
  Core Nutation (FCN) and Free Inner Core Nutation (FICN). We have got
  the estimates of dynamical flattening of the crust, the FOC and the
  SIC of the pulsar (~10^-9) for known periodic variations of the TOA
  pulse from PSR B1828-11: P[CW] = 167 days, P[ICW] = 500 days, P[FCN] =
  250 days, P[FICN] = 1000 days. With increase of pulsar radius on 1.1 km
  the dynamical flattening of crust grows in 5.5 times, and flattening of
  fluid outer core increases only in 1.5 times. Changing of the radius
  of the inner core (from 0.6 to 1.1 km) almost does not influence to
  dynamical flattening of the solid inner core. We have estimates the
  flateness of crust ~ 0.3 · 10^-9, flateness of FOC ~ 0.6 · 10^-9 and
  flateness of SIC is ~ 4.7 · 10^-9. We have offered the realistic model
  of the dynamical pulsar structure and two explanations of the feature
  of flattening of the crust, the outer fluid core and the inner solid
  core of the pulsar.

Title: Normal Modes in Rotation of Two/Three Layers Planets
Authors: Gusev, A.; Petrova, N.; Kitiashvili, I.
Bibcode: 2006IAUJD..10E..36G
Altcode:
  In many theoretical investigations the normal modes of the linearized
  equations of rotation are computed, yielding both the periods and
  the eigenspaces of three librations. The modern view of internal
  structure of the planet takes into account a complex two- or three-layer
  model. For a planet with a solid inner core and a liquid outer core,
  there are four rotational normal modes. This numbers is reduced to two
  for a planet without inner core, and to one for a planet without liquid
  core. All types of modes are result of non-coincidence of rotation axes
  and of the main inertia moments of mantle, outer and inner core. For
  the Earth and the nearest planets - Mars and Moon - there is a wide
  spectrum of observations and theoretical speculations about parameters
  of the planet's deep interior. For instance, the most interesting data
  on dynamics and internal structure of the Moon are already accumulated
  as a result of the different observations and space experiments. The
  Japanese space experiments Lunar A, SELENE-missions, Luna Glob (Russia)
  planed for 2007 - 2012 years will contribute significantly to the
  information about the Moon: qualitative parameter Q, Love number k[2],
  core's radius R[c], core's density etc. In a case of free rotation
  of the two- or three-layer planet the two or four modes in its polar
  motion might be observed. The evaluations of the periods were made:
  periods of the Free Core Nutation (FCN) were obtained for Mercury
  (P[FCN] = 597 yrs) and first time for Venus (P[FCN] = 1534 yrs). For
  the Moon the period of Free Inner Core Nutation (FICN) P[FICN]= 515
  - 634 yrs and the period of Inner Core Wobble (ICW) P[ICW]= 101 -
  108 yrs were computed for different models of the lunar core. The
  main tendency of behavior of two new periods (P [FICN ]and P[ICW])
  is preliminary revealed: a) the FICN-period decreases both with the
  increasing of the core's radius and of the thick of fluid shell; b)
  conversely, the ICW-period have the direct ratio to radius of a core
  and thickness of a liquid layer.

Title: Astronomy in the Russian Scientific-Educational Project:
    "KAZAN-GEONA-2010"
Authors: Gusev, A.; Kitiashvili, I.
Bibcode: 2006IAUSS...2E..38G
Altcode:
  The European Union promotes the Sixth Framework Programme. One of the
  goals of the EU Programme is opening national research and training
  programs. A special role in the history of the Kazan University was
  played by the great mathematician Nikolai Lobachevsky - the founder
  of non-Euclidean geometry (1826). Historically, the thousand-year
  old city of Kazan and the two-hundred-year old Kazan University
  carry out the role of the scientific, organizational, and cultural
  educational center of the Volga region. For the continued successful
  development of educational and scientific-educational activity of
  the Russian Federation, the Republic Tatarstan, Kazan was offered
  the national project: the International Center of the Sciences
  and Internet Technologies "GeoNa" (Geometry of Nature - GeoNa -
  is wisdom, enthusiasm, pride, grandeur). This is a modern complex
  of conference halls including the Center for Internet Technologies,
  a 3D Planetarium - development of the Moon, PhysicsLand, an active
  museum of natural sciences, an oceanarium, and a training complex
  "Spheres of Knowledge". Center GeoNa promotes the direct and effective
  channel of cooperation with scientific centers around the world. GeoNa
  will host conferences, congresses, fundamental scientific research
  sessions of the Moon and planets, and scientific-educational actions:
  presentation of the international scientific programs on lunar research
  and modern lunar databases. A more intense program of exchange between
  scientific centers and organizations for a better knowledge and planning
  of their astronomical curricula and the introduction of the teaching
  of astronomy are proposed. Center GeoNa will enable scientists and
  teachers of the Russian universities with advanced achievements in
  science and information technologies to join together to establish
  scientific communications with foreign colleagues in the sphere of the
  high technology and educational projects with world scientific centers.

Title: Precession of inner crystal core and free nutation of outer
    liquid core of a pulsar
Authors: Gusev, Alexander; Kitiashvili, Irina
Bibcode: 2006GrCo...12...59G
Altcode:
  No abstract at ADS

Title: Transition from a direct rotation to the reverse rotation of
    exoplanets by action of the basic perturbations
Authors: Gusev, A.; Kitiashvili, I.
Bibcode: 2006epsc.conf..260G
Altcode:
  The discovery of 188 planets, around the main sequence stars and around
  the pulsars, has attracted considerable interest to the cosmogonical
  problems connected with the formation and early evolution of
  planets. The process of planetary formation is significantly determined
  by the orbital-rotational characteristics of exoplanets. Researches of
  transition from direct rotation to the reverse rotation of a planet
  in Solar system by action of tidal interaction have been investigated
  Beletsky (1995), Laskar et al. (2003). For short-periodic exoplanetary
  systems a reverse rotation of planets are also possible for a special
  combination of gravitational, magnetic perturbations and evolutions of
  an orbital plane without of planetary tidal evolution. We investigated
  possibilities of transition from direct rotation to reverse rotation of
  exoplanet by action of gravitational (γ), magnetic (α) perturbations
  and evolutions of an orbital plane by methods of the qualitative
  analysis and the theory bifurcations the multipleparameter differential
  equations. We constructed gallery of phase portraits, which describe
  rotary evolution exoplanet for a wide range of values of perturbed
  parameters. We described bifurcation surfaces, which show topological
  reorganization of phase trajectories in a vicinity of equilibrium
  states (ES) and selected combination of parameters. In gallery of
  phase portraits exists two basic types of bifurcations: 1) formation
  of a topologically complex saddle in result of mixing of two centers
  and a simple saddle; 2) transition from a complex saddle of ES to the
  center. The first type of bifurcation will be for transition from a
  condition |α| &lt; |γ| to |α| = |γ|. Bifurcations of the second
  type are possible, if a ratio of parameters from |α| = |γ| will pass
  to |α| &gt; |γ|. If gravitational perturbations are dominant, then
  on the phase sphere exist three areas: 1. area of reverse rotation
  of exoplanet; 2. area of direct rotation with an opportunity the
  realization of regime with periodic change of direct rotation of a
  planet to reverse rotation; and 3. area libration motion of a vector
  of kinetic momentum with periodic change of direct rotation to reverse
  motion. When magnetic field is absent, the trace structure illustrates
  a precession of the vector of kinetic moment of a planet around the
  normal to the orbital plane. Phase portraits demonstrate behaviour
  of the vector of kinetic moment of a planet in dependence on the all
  possible values of parameters planetary systems. The investigations
  have support by the grant MK-2736.2005.2 of the President of the
  Russian Federation for the state support young Russian scientists.

Title: Qualitative and bifurcation analysis of gravi-magnetic
    interactions for the spin-orbit evolution of extra-solar systems
Authors: Kitiashvili, I.; Gusev, A.
Bibcode: 2006epsc.conf..256K
Altcode:
  Detection of extra-solar planets has expanded ours representations
  about possibilities for realization of different regimes of planetary
  dynamics. Now are discovered 188 exoplanets in 146 planetary systems
  about main sequence stars and 4 planets about pulsars PSR B1257+12 and
  PSR B1620-26. Among open planetary systems 18 are multiplanetary, into
  their structure are including 41 exoplanets and 3 brown dwarfs. 1. In
  connection with a diversity of dynamical characteristics of exoplanets
  we investigate a spin evolution of planets for a wide spectrum of
  parameters of gravitational, magnetic perturbations and effects of
  orbit evolution. Structure of planetary systems depends on the effects
  of their own rotation. 2. Known, that the Sun and some planets of
  the Solar system have own magnetic field. The reason of formation
  coplanar planetary orbits and observable distribution of the moment
  of motion is the influence of electromagnetic forces at early stages
  of evolution of Solar system. Magnetization of the central body of
  planetary system is a necessary condition of formation of planets. We
  investigate not resonant rotation of the magnetized along an axis of
  symmetry a dynamically symmetrical exoplanet (A = B) in a magnetic
  field of a star under action of the gravitational (γ) and magnetic
  (α) moments, take into consideration also effects of evolution of
  orbit. Structure of phase portraits and their evolution are described by
  the following properties: 1. exists two or four states of equilibrium
  (ES) depending on a ratio of parameters; 2. in result of confluence
  of two centers and saddle located between them appear a topological
  saddle or a center; 3. during migration or bifurcation of ES, one of
  equilibrium states is constant. Separatrixes of saddle break a surface
  of sphere on three areas containing one center. In result of reduction
  of γ parameter and increase α, two centers migrate to ES of type
  "saddle". When γ = α, two centers will merge with transformation ES
  from a simple saddle to topological complex saddle. When α &gt; γ,
  the new formed topological saddle will disappear with formation on its
  place the center. We obtained gallery from 64 phase portraits on a plane
  and on sphere for all values of parameters of evolutionary system of
  the equations under action of the basic perturb moments. The analysis
  of the phase portraits gallery gives a wide spectrum of evolutionary
  tracks of rotation exoplanets. Variation of gravitational and magnetic
  fields due to planetary evolution causes displacement and change of
  ES kind. The investigations have support by the grant MK-2736.2005.2
  of the President of the Russian Federation for the state support young
  Russian scientists.

Title: Precession of inner core and free nutation of outer core of
    pulsar PSR B1828-11
Authors: Kitiashvili, I.; Gusev, A.
Bibcode: 2006cosp...36.2037K
Altcode: 2006cosp.meet.2037K
  Observation of pulsars is a powerful source of the information for
  research of dynamics and internal structure of neutron stars Analysis
  of the time-of-arrival pulses fluctuations can be reflection of
  thin effects of neutron stars rotational dynamics The long-periodic
  precession phenomenon was detected for pulsars PSR 2217 47 PSR 0531
  21 PSR B0833-45 PSR B1828-11 PSR B1642-03 with period from 25 to
  6136 days PSR B1828-11 has long-term highly periodic and correlated
  variations pulse shape and of the rate of slow-down with period
  variations approximately 1000 500 250 and 167 days We explane for all
  harmonics of pulses variations as precession of a neutron star owing
  to differential rotation of crust outer liquid core and inner crystal
  core of the pulsar We use the Hamiltonian canonical method of Getino
  for the dynamically symmetrical three-layer model of the pulsar PSR
  B1828-11 We investigated dependence flateness of crust outer and inner
  cores of pulsar from periods Chandler wobble Inner Chandler Wobble Free
  Core Nutation and Free Inner Core Nutation from ellipticity of inner
  crystal core outer liquid core and total pulsar We have estimates the
  flateness of crust and outer core are sim 1 8 10 -11 and flateness of
  inner core is sim 1 5 10 -8

Title: The Moon in the Russian scientific-educational project:
    Kazan-GeoNa-2010
Authors: Gusev, A.; Kitiashvili, I.; Petrova, N.
Bibcode: 2006cosp...36.2040G
Altcode: 2006cosp.meet.2040G
  Historically thousand-year Kazan city and the two-hundred-year Kazan
  university Russia carry out a role of the scientific-organizational and
  cultural-educational center of Volga region For the further successful
  development of educational and scientific-educational activity of
  the Russian Federation the Republic Tatarstan Kazan is offered the
  national project - the International Center of the Science and the
  Internet of Technologies bf GeoNa bf Geo metry of bf Na ture - bf
  GeoNa is developed - wisdom enthusiasm pride grandeur which includes a
  modern complex of conference halls up to 4 thousand places the Center
  the Internet of Technologies 3D Planetarium - development of the Moon
  PhysicsLand an active museum of natural sciences an oceanarium training
  a complex Spheres of Knowledge botanical and landscape oases In center
  bf GeoNa will be hosted conferences congresses fundamental scientific
  researches of the Moon scientific-educational actions presentation
  of the international scientific programs on lunar research modern
  lunar databases exhibition Hi-tech of the equipment the extensive
  cultural-educational tourist and cognitive programs Center bf GeoNa
  will enable scientists and teachers of the Russian universities to
  join to advanced achievements of a science information technologies to
  establish scientific communications with foreign colleagues in sphere
  of the high technology and educational projects with world space centers

Title: Chandler Wobble and Free Core Nutation of Neutron Stars
Authors: Gusev, A.; Kitiashvili, I.
Bibcode: 2004IAUS..218...45G
Altcode:
  Extending the theory of core-mantle differential rotation of a planet,
  we have obtained the periods P<SUB>CW</SUB> and P<SUB>FCN</SUB> for
  different pulsars in the second approximation. We have investigated
  the dependence of these periods on the equation of state of neutron
  liquid, flatness of mantle and crust of the neutron star.

Title: Early evolution of the planetary system around PSR B1257+12
Authors: Gusev, Alexander; Kitiashvili, Irina
Bibcode: 2004IAUS..202..187G
Altcode:
  No abstract at ADS

Title: Extra-solar planets: from direct rotation into reverse rotation
Authors: Kitiashvili, Irina; Gusev, Alexander
Bibcode: 2004IAUS..202..205K
Altcode:
  No abstract at ADS

Title: Inner chandler wobble and free core nutation of pulsar
Authors: Gusev, A.; Kitiashvili, I.
Bibcode: 2004cosp...35.3301G
Altcode: 2004cosp.meet.3301G
  PSR B1828-11 have long-term, highly periodic and correlated
  variations pulse shape and of the rate of slow-down with period
  variations approximately 1000, 500 and 250 days (Stairs et al.,
  2000). There are three potential explanations of time of arrival
  pulses from pulsar concerned with the interior of the neutron star,
  planetary bodies and free precession and nutation. The rotation of
  the terrestrial planets having rigid mantle, outer liquid and inner
  crystal cores are characterized by Chandler Wobble (CW), Inner
  Chandler Wobble (ICW), Free Core Nutation (FCN), Free Inner Core
  Nutation (FICN). We use the Hamiltonian canonical technique of Getino
  (1997) for dynamically symmetrical pulsar composed of the rigid crust,
  elliptical liquid mantle and crystal core. Correctly extending theory
  of core-mantle-crust differential rotation of a body, we have obtained
  the periods of P<SUB>CW</SUB>, P<SUB>ICW</SUB>, P<SUB>FCN</SUB> and
  P<SUB>FICN</SUB> for different pulsars. We investigated dependence of
  period CW and FCN from the state equation of neutron liquid, flatness
  of mantle and crust of the neutron star. Detection the CW, ICW, FCN
  and FICN of the pulsar and its periods allow: to determine crust,
  mantle and core radiuses and it's flattening; to determine density
  jump at the Crust-Mantle Boundary and Core-Mantle Boundary.

Title: Research of protoplanetary disks of the young pulsars
Authors: Kitiashvili, I.; Gusev, A.
Bibcode: 2004cosp...35.3290K
Altcode: 2004cosp.meet.3290K
  At present time is known approximately 750 radiopulsars, from them 27
  pulsars is observed in other bands and only seven are observed in the
  optical band. Discovery exoplanets around PSR B1257+12 and PSR B1828-11
  gave strong push for search and investigation of planets around neutron
  stars. At the early stages of planet evolution the tidal and magnetic
  interactions of exoplanet with disk takes a principal role: the tidal
  effects lead to the capture into resonance rotation of the planet, the
  analyses of gravi-magnetic interaction has shown that a direct rotation
  of the planet may be passed into reverse rotation and vice versa for
  a rather broad range of the parameters. The dynamical structure of
  protoplanetary disk are reviewed. Investigation of protoplanetary disk
  around the optic pulsar by VLTI for combination of observed periodic
  delays in the arrival times of pulsar pulses are proposed. Measurements
  of the near-IR sizes of the central regions of the young neutron stars,
  with high-resolution interferometric studies of protoplanetary disks
  should help clarify how disk structure affects formation and migration
  of exoplanet.

Title: Orbital resonances in exoplanetary systems
Authors: Gusev, A.; Kitiashvili, I.
Bibcode: 2003EAEJA.....8390G
Altcode:
  Now opening of 88 planetary systems, that include 104 planets: 101
  are Jupiter's type near main sequence stars and 3 are terrestrial type
  near pulsar, has generated huge interest to fundamental questions of
  cosmogony, to formation and early evolution of Earth-type planets,
  stability of planetary systems in the extreme conditions, influence
  gravitational, magnetic fields and tidal effects on formation of
  resonant structures in the universe. Among all extra-solar planets 41
  exoplanets are short-periodic (before 180 days), 35 are middle-periodic
  and 28 long-periodic (more 1000 days) planets with the revolution
  periods P are varied from 2.99 days (HD 83443) to 5360 days (55 Cnc);
  planetary masses therewith lie in the range 0.015 M<SUB>⊕</SUB>
  (PSR 1257+12) and 11 M<SUB>J</SUB>; the main semi-axes a lie between
  0.038 AU (HD 83443) and 5.9 AU (55 Cnc), eccentricity of the planets
  varies from 0.0 (15 planets) to 0.927 in HD80606; inclination for five
  planetary systems are 85.2<SUP>0</SUP> for HD 209458, 46<SUP>0</SUP>
  for ɛ Eridani, 25<SUP>0</SUP> for 55 Cnc, 37<SUP>0</SUP> for Gliese
  876, 84.3<SUP>0</SUP> for BD -10 3166; six planets Ups And, Gl 777A,
  HD 114783, HR810, HD 27442, HD 28185 circulate in habitable zone a ∼
  0.5 - 3 AU, P ∼ 240 - 500 days, e &lt; 0.2. From known multiplanetary
  systems we can see class of planetary systems with resonances: HD 82943
  (2:1), Gliese 876 (2:1), 55 Cnc (3:1), PSR 1257+12 (2:3), 47 Uma (3:7),
  HD 12661 (2:11). At the early stages of planet evolution the tidal
  and magnetic interactions takes a principal role - the tidal effects
  lead to the capture into resonance rotation of the planet, while the
  gravi-magnetic interaction shows that a direct rotation of the planet
  may be passed into reverse rotation and vice versa for a rather broad
  range of the parameters. We investigate the equations describing the
  evolution of the kinetic momentum vector for dynamically symmetrical
  planets by action of gravitational, magnetic and tidal interaction with
  the central star. The obtained gallery of more twenty phase portraits
  of kinetic momentum evolution illustrates the various regimes of the
  planetary systems evolution.

Title: Exoplanets around pulsars
Authors: Kitiashvili, I.; Gusev, A.
Bibcode: 2003EAEJA.....6227K
Altcode:
  Surprise discovery of thrid planets and cometary body (!?) near the
  pulsar PSR~B1257+12 (Wolszczan and Frail, 1992) posed the problems
  of describing their moving around pulsar, their origin and early
  rotation. At the present time the question whether there exist another
  three pulsars in the planetary systems is under discussion: PSR 0329+54
  (1 planet), PSR B1620--26 (1 planet) and PSR 1828--11 (3 planets,
  Stairs et al., 2000) . It is known the time scale of pulsars is very
  stable, then in some cases the periodical fluctuation in time of
  arrival may be provoked motion of planetary bodies, free precession or
  concerned with the interior of the neutron star. Discovery exoplanets
  around PSR~B1257+12 gave strong push for search and investigate
  planets around neutron stars. Dust disks around stars still retain
  information about the formation processes of the exoplanetary systems
  as they are formed by collisions of planetesimals or protoplanets.The
  conventional explanation for the formation gas giant planets, core
  accretion, presumes that a gaseous envelope collapses upon a roughly
  10 M<SUB>⊕</SUB>, solid core that was formed by the collisional
  accumulation of planetary embryos orbiting in a gaseous disk (Boss,
  2002). Small protoplanets torque the disk at the Lindblad and
  corotation resonances, and the resulting back-torque can propel a
  planet into the star (Ward, 1997). We investigate the equations of
  the magneto-rotational instability of the Keplerian disk in linear
  approximation by qualitative and bifurcation methods. The separation
  of 3-dimensional parameter space of dynamical system by bifurcation
  surfaces is obtained. The obtained gallery of more ten phase portraits
  of disk evolution illustrates the various regimes of the planetary
  systems evolution. Investigation of a matter around young pulsars
  will allow us to answer about a possibility of birth of planets after
  explosion of a supernova star.

Title: Spin-Orbital Evolution of Exoplanets
Authors: Gusev, A.; Kitiashvili, I.
Bibcode: 2003EAS.....6..281G
Altcode:
  We investigated the equation describing the evolution of the kinetic
  momentum vector of planets by the action of gravitational and magnetic
  interaction. The obtained gallery of portraits of the kinetic
  momentum evolution illustrates the various regimes of planetary
  system evolution. We are going to investigate a fine structure
  of protoplanetary disk around the pulsar by VLTI for detection of
  extrasolar planets on early time of formation.

Title: Through Kazan ASPERA to Modern Projects
Authors: Gusev, Alexander; Kitiashvili, Irina; Petrova, Natasha
Bibcode: 2003IAUSS...4E..48G
Altcode:
  Now the European Union form the Sixth Framework Programme. One of
  its the objects of the EU Programme is opening national researches and
  training programmes. The Russian PhD students and young astronomers have
  business and financial difficulties in access to modern databases and
  astronomical projects and so they has not been included in European
  overview of priorities. Modern requirements to the organization
  of observant projects on powerful telescopes assumes painstaking
  scientific computer preparation of the application. A rigid competition
  for observation time assume preliminary computer modeling of target
  object for success of the application. Kazan AstroGeoPhysics Partnership

Title: Free core nutation and Chandler wobble of pulsar
Authors: Kitiashvili, I.; Gusev, A.
Bibcode: 2002cosp...34E1352K
Altcode: 2002cosp.meetE1352K
  In 2000 year Stairs, Lyne and Shemar reported the discovery of the
  long-term, highly periodic and correlated variations pulse shape
  and of the rate of slow-down of the pulsar PSR B1828-11 with period
  variations approximately 1000, 500 and 250 days. According to Stairs
  et al. (2000), probably, the precession of the spin axis is caused
  by asymmetry in the shape of the pulsar. It is known that rotation of
  the terrestrial planets having rigid mantle and elliptical liquid core
  is characterized by Free Core Nutation (FCN). Therewith any celestial
  body whose rotation axis does not coincide with the main inertia axis
  is characterized by Chandler Wobble (CW). These phenomena of FCN and CW
  are manifested as periodical oscillations of rotation axis of the planet
  in inertial reference system. For rotating pulsar we deal with the case
  of modulation of pulses emitted around the direction of the magnetic
  axis of a pulsar whose symmetry axis does not coincide with the angular
  velocity vector. We have obtained the periods of PC W and PF C N for
  different pulsars, correctly extending for neutron star the theory of
  core-mantle differential rotation of the planets (Petrova &amp;Gusev,
  2001). It was made in the frame of Hamiltonian approach for description
  of rotation of two-layer pulsar having rigid crust and liquid mantle.

