explanation blue bibcodes open ADS page with paths to full text
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
2022cosp...44.3232K Altcode:
Forecasting space weather on different temporal scales is a problem that
requires the development of advanced physics-based models, algorithms,
and data analysis approaches for a variety of observations and their
inferences. We take advantage of currently available computational
capabilities to model solar dynamics from the deep interior to
the corona and investigate mechanisms that may drive space weather
conditions. Comparison of the synthetic observables obtained from
numerical simulations and actual observations allows us to uncover
physical processes associated with observed phenomena. To facilitate a
transition from modeling short-term physical phenomena to developing a
reliable forecast-oriented model, we suggest using the data assimilation
approach. It allows us to cross-analyze dynamo model solutions and
observations and to consider possible uncertainties and errors. Our
results demonstrate promising potential for modeling upcoming solar
activity combined with observations. In this presentation, we briefly
summarize current multi-scale modeling capabilities and results
and discuss ongoing developments to build a reliable physics-based
forecast-oriented model of solar activity.
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Title: Using 3D Realistic Modeling of Solar-Type Stars to Characterize
Stellar Jitter
Authors: Kitiashvili, Irina; Wray, Alan; Granovsly, Samuel
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.
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Title: Characterization of Stellar Jitter Using 3D Realistic Modeling
of Solar-Type Stars
Authors: Kitiashvili, Irina; Granovsky, Samuel; Wray, Alan; Kosovichev,
Alexander
2022AAS...24041702K Altcode:
Recent progress in the ab-initio modeling of solar magnetoconvection
makes it possible to simulate the surface dynamics of solar-type
stars with a high degree of realism. These simulations can be used
to characterize stellar photospheric disturbances which contaminate
the radial velocity signal and limit our capabilities to detect
Earth-mass exoplanets. We use the 3D radiative MHD "StellarBox" code
to obtain realistic stellar (magneto)convection models and characterize
photospheric noise. The initial conditions for the numerical simulations
are generated using the MESA stellar evolution code. The computational
domain covers the upper layers of the convection zone and the lower
atmosphere. We present numerical models of solar-type planet-host stars,
disk-integrated synthetic observations, and observables such as line
profiles, Doppler shift, etc. Synthesis of observations performed for
a list of FeI lines using the radiative transfer "Spinor" code. We
present the stellar jitter modeling results for selected target stars,
discuss the origin of the noise and compare with high-resolution
HARPS observations.
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Title: Leptocline as a Shallow Substructure of Near-Surface Shear
Layer in 3D Radiative Hydrodynamic Simulations
Authors: Kitiashvili, Irina N.; Kosovichev, Alexander G.; Wray,
Alan A.; Sadykov, Viacheslav M.; Guerrero, Gustavo
2022arXiv220301484K Altcode:
Understanding effects driven by rotation in the solar convection zone
is essential for many problems related to solar activity, such as
the formation of differential rotation, meridional circulation, and
others. We analyze realistic 3D radiative hydrodynamics simulations
of solar subsurface dynamics in the presence of rotation in a local
domain 80 Mm wide and 25 Mm deep, located at 30 degrees latitude. The
simulation results reveal the development of a shallow 10-Mm deep
substructure of the Near-Surface Shear Layer (NSSL), characterized
by a strong radial rotational gradient and self-organized meridional
flows. This shallow layer ("leptocline") is located in the hydrogen
ionization zone associated with enhanced anisotropic overshooting-type
flows into a less unstable layer between the H and HeII ionization
zones. We discuss current observational evidence of the presence of
the leptocline and show that the radial variations of the differential
rotation and meridional flow profiles obtained from the simulations
in this layer qualitatively agree with helioseismic observations.
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Title: Revisiting the Solar Research Cyberinfrastructure Needs:
A White Paper of Findings and Recommendations
Authors: Nita, Gelu; Ahmadzadeh, Azim; Criscuoli, Serena;
Davey, Alisdair; Gary, Dale; Georgoulis, Manolis; Hurlburt, Neal;
Kitiashvili, Irina; Kempton, Dustin; Kosovichev, Alexander; Martens,
Piet; McGranaghan, Ryan; Oria, Vincent; Reardon, Kevin; Sadykov,
Viacheslav; Timmons, Ryan; Wang, Haimin; Wang, Jason T. L.
2022arXiv220309544N Altcode:
Solar and Heliosphere physics are areas of remarkable data-driven
discoveries. Recent advances in high-cadence, high-resolution
multiwavelength observations, growing amounts of data from realistic
modeling, and operational needs for uninterrupted science-quality data
coverage generate the demand for a solar metadata standardization and
overall healthy data infrastructure. This white paper is prepared as
an effort of the working group "Uniform Semantics and Syntax of Solar
Observations and Events" created within the "Towards Integration of
Heliophysics Data, Modeling, and Analysis Tools" EarthCube Research
Coordination Network (@HDMIEC RCN), with primary objectives to discuss
current advances and identify future needs for the solar research
cyberinfrastructure. The white paper summarizes presentations and
discussions held during the special working group session at the
EarthCube Annual Meeting on June 19th, 2020, as well as community
contribution gathered during a series of preceding workshops and
subsequent RCN working group sessions. The authors provide examples
of the current standing of the solar research cyberinfrastructure, and
describe the problems related to current data handling approaches. The
list of the top-level recommendations agreed by the authors of the
current white paper is presented at the beginning of the paper.
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Title: Modeling Stellar Jitter for the Detection of Earth-Mass
Exoplanets via Precision Radial Velocity Measurements
Authors: Granovsky, Samuel; Kitiashvili, Irina N.; Wray, Alan
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.
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Title: Physical Properties of the Solar Atmosphere Derived from
Comparison of Spectro-Polarimetric SDO/HMI Observables with 3D
Radiative MHD Simulations
Authors: Sadykov, Viacheslav; Kitiashvili, Irina; Kosovichev,
Alexander; Wray, Alan
2021AGUFMSH44A..06S Altcode:
In this study, we compare the SDO/HMI line-of-sight observables
(magnetic field, velocity, continuum intensity, and line depth) with
the related physical properties for dynamo simulations performed using
the StellarBox 3D Radiative MHD code. The modeling of the Fe I 6173 A
Stokes profiles is performed using the SPINOR radiative transfer code in
the LTE approximation. The reproduced SDO/HMI line-of-sight pipeline is
applied to the modeled spectra, and the observables are synthesized with
high (numerical) and SDO/HMI (instrumental) resolutions. Correlations
between the observables and the physical properties at various
heights in the atmosphere are studied for a set of view angles (0,
30, 45, 60, 70, and 80 degrees away from the solar disk center). It
is found that SDO/HMI velocity and magnetic field (less prominently)
observables are correlated with physical parameters at certain heights
of the solar atmosphere. These heights increase from about 100-150 km
above the photosphere for the disk center case to 300-600 km above the
photosphere for the 80-degree case, however, are almost the same for
the 0-60 degree projection angles. The integrated unsigned magnetic
flux calculated from the observables underestimates the actual magnetic
flux at strongest correlation heights for about 40% on average. The
integrated continuum intensity as calculated from the observables
is about 4-8% larger with respect to its actual values. In addition,
we discuss a problem of contribution of unresolved magnetic elements
to solar brightness based on the modeling data. The results improve
physics-based interpretations of the SDO/HMI observables and provide a
better understanding of the physical properties of the solar atmosphere.
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Title: 3D Radiative MHD Modeling of the Solar Atmospheric Dynamics
and Structure
Authors: Kitiashvili, Irina; Sadykov, Viacheslav; Wray, Alan;
Kosovichev, Alexander
2021AGUFMSH45B2370K Altcode:
Dramatic dynamical phenomena accompanied by strong thermodynamic
and magnetic structuring are the primary drivers of great interest
in studying the solar atmosphere with high spatial and temporal
resolutions. Using current computational capabilities, it became
possible to model the magnetized solar plasma in different regimes
with a high degree of realism. To study the fine structuring of the
solar atmosphere and dynamics, we use 3D MHD radiative models covering
all layers from the upper convection zone to the corona. Realistic 3D
radiative MHD modeling of the solar magnetoconvection and atmosphere
allows us to generate synthetic observables that directly link the
physical properties of the solar plasma to spectroscopic observables. We
calculate series of synthetic spectropolarimetric imaging data that
model observations from different space instruments: HMI and AIA (SDO),
SOT (Hinode), and IRIS, as well as for the upcoming DKIST ground
observations, and investigate how the observational data are linked
to physical processes in the solar atmosphere. In the presentation,
we discuss qualitative and quantitative changes of the atmospheric
structure and dynamics at different layers of the solar atmosphere,
properties of acoustic and surface gravity waves, sources of the local
heating in the chromosphere-corona transition region, formation of
shocks, and high-frequency oscillations in the corona, as well as
manifestation of these phenomena in the modeled observables.
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Title: Dynamical Coupling of the Solar Subsurface Shear Layer and
the Atmosphere
Authors: Kitiashvili, Irina; Sadykov, Viacheslav; Kosovichev,
Alexander; Wray, Alan
2021AGUFMSH53C..01K Altcode:
The dynamical coupling of subsurface and surface layers of the Sun is
crucial for understanding how phenomena observed in the solar atmosphere
reflect the evolution of subsurface plasma flows in the present
global-scale rotation. In this work, we use long time-series (over
100-hours) of high-resolution 3D radiative hydrodynamic simulations
obtained for an 80-Mm wide and 25-Mm deep computational domain, using
the SolarBox code, to investigate the formation and dynamics of the
Subsurface Shear Layer (SSL) and observational manifestations. The
solar rotation is modeled in the f-plane approximation at 30 degrees
latitude. The simulation results reveal the formation of the SSL, and
meridional circulation. To compare the simulation results with the
SDO/HMI observations, we generate synthetic time series of the Fe I
(6173A) line profile for different locations on the solar disk, using
the SPINOR radiative transfer code. The line-profile data are converted
into the SDO/HMI observables using an HMI pipeline emulator and analyzed
for both the modeled and instrumental resolutions. The analysis results
reproduce the photospheric structure and dynamics as well as various
helioseismic properties such as rotational frequency splitting, ring-
and time-distance diagrams, and the center-to-limb effect. This work
provides a basis for a deeper understanding of the solar subsurface
dynamics and physical interpretation of observational data.
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Title: Simulating Exoplanet Host Star -Horologii from the Surface
to the Bottom of the Convection Zone
Authors: Guerrero, Gustavo; Kitiashvili, Irina; Bonanno, Alfio;
Kosovichev, Alexander
2021AGUFM.U44B..02G Altcode:
The G0 type, planet-hosting, star -Horologii has been observed for
several years through different techniques. While there is still some
debate about its rotational period (4-8 days), it seems conclusive that
it exhibits a magnetic cycle of ~1.6 years. This short period allowed
for constructing the first butterfly diagram for a star different from
the Sun. The detailed study of this object provides unique opportunities
to understand the dynamo operating in solar-like stars. In this work,
we present realistic 3D radiative hydrodynamics simulations (RHD) of
surface and subsurface convection of this star. The depth reached by
these models connects with anelastic global MHD simulations (AMHD) of
the -Horologiis dynamo. The RHD models provide an understanding of the
structure and signal of surface convection and its spectra, allowing for
direct comparison with high-resolution spectroscopic observations. The
AMHD simulations enlighten the magnetic contribution to this signal. In
addition, we provide predictions of the star differential rotation,
meridional circulation and the alpha-Omega dynamo sustaining its
magnetic field.
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Title: Effects of observational data shortage on accuracy of global
solar activity forecast
Authors: Kitiashvili, Irina N.
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.
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Title: Dynamics and Structure of Main-Sequence Stars with Shallow
Convection Zones
Authors: Kitiashvili, I. N.; Wray, A. A.
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.
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Title: Probing Stellar Cores by Asteroseismic Inversions
Authors: Kosovichev, Alexander; Kitiashvili, Irina
2021tsc2.confE.130K Altcode:
Precision asteroseismology data from Kepler and TESS provide a unique
opportunity to investigate the interior structure of stars at various
stages of stellar evolution. Detection of mixed acoustic-gravity
oscillation modes has opened perspectives for probing the properties
of energy-generating cores. Most of the previous analysis was focused
on fitting standard evolutionary stellar models using mode frequency
splitting and scaling laws for oscillation properties. We present
direct asteroseismic inversions using the method of optimally localized
averages, which effectively eliminates the surface effects and attempts
to resolve the stellar core structure.
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Title: 3D Modeling of Solar-Type Stars to Characterize Stellar Jitter
Authors: Kitiashvili, I. N.; Wray, A. A.; Granovsky, S.
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.
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Title: Prediction of Solar Proton Events with Machine Learning:
Comparison with Operational Forecasts and "All-Clear" Perspectives
Authors: Sadykov, Viacheslav; Kosovichev, Alexander; Kitiashvili,
Irina; Oria, Vincent; Nita, Gelu M; Illarionov, Egor; O'Keefe, Patrick;
Jiang, Yucheng; Fereira, Sheldon; Ali, Aatiya
2021arXiv210703911S Altcode:
Solar Energetic Particle events (SEPs) are among the most dangerous
transient phenomena of solar activity. As hazardous radiation, SEPs may
affect the health of astronauts in outer space and adversely impact
current and future space exploration. In this paper, we consider the
problem of daily prediction of Solar Proton Events (SPEs) based on
the characteristics of the magnetic fields in solar Active Regions
(ARs), preceding soft X-ray and proton fluxes, and statistics of solar
radio bursts. The machine learning (ML) algorithm uses an artificial
neural network of custom architecture designed for whole-Sun input. The
predictions of the ML model are compared with the SWPC NOAA operational
forecasts of SPEs. Our preliminary results indicate that 1) for the
AR-based predictions, it is necessary to take into account ARs at
the western limb and on the far side of the Sun; 2) characteristics
of the preceding proton flux represent the most valuable input for
prediction; 3) daily median characteristics of ARs and the counts of
type II, III, and IV radio bursts may be excluded from the forecast
without performance loss; and 4) ML-based forecasts outperform SWPC
NOAA forecasts in situations in which missing SPE events is very
undesirable. The introduced approach indicates the possibility of
developing robust "all-clear" SPE forecasts by employing machine
learning methods.
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Title: Influence of Center-to-Limb Effects on Observations of the
Solar Atmosphere
Authors: Kitiashvili, I. N.; Sadykov, V. M.; Wray, A. A.
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.
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Title: Physical Properties of the Solar Atmosphere Derived from
Comparison of Spectro-Polarimetric SDO/HMI Observables with 3D
Radiative MHD Simulations
Authors: Sadykov, V.; Kitiashvili, I.; Kosovichev, A.; Wray, A.
2021AAS...23832804S Altcode:
In this study, we compare the SDO/HMI line-of-sight observables
(magnetic field, velocity, continuum intensity, and line depth) with the
related physical properties for several dynamo simulation runs performed
using the "StellarBox" 3D Radiative MHD code. The modeling of the Fe I
6173 Å Stokes profiles is performed using the SPINOR radiative transfer
code in the LTE approximation. The reproduced SDO/HMI line-of-sight
pipeline is applied to the modeled spectra, and the observables
are synthesized with high (numerical) and SDO/HMI (instrumental)
resolutions. Correlations between the observables and the physical
properties at various heights in the atmosphere are studied for a set
of view angles (0, 30, 45, 60, 70, and 80 degrees away from the solar
disk center). It is found that the SDO/HMI magnetic field and velocity
measurements are unambiguously correlated with physical parameters
at certain heights of the solar atmosphere. These heights increase
from about 100 km above the photosphere for the disk center case to
300-600 km above the photosphere for the 80-degree case. The heights
are found to be slightly lower in regions where stronger magnetic
fields are found. The comparison of the photospheric magnetic flux and
integrated continuum intensity derived from the SDO/HMI observables and
high-resolution observations and spectra is discussed. The results
of our study improve physics-based interpretations of the SDO/HMI
observables and provide a better understanding of the physical
properties of the solar atmosphere.
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Title: Understanding the Consequences Of Fields and Flows in the
Interior and Exterior of the Sun (COFFIES)
Authors: Hoeksema, J. T.; Brummell, N.; Bush, R.; Hess Webber, S.;
Kitiashvili, I.; Komm, R.; Kosovichev, A.; Mendez, B.; Scherrer, P.;
Upton, L.; Wray, A.; Zevin, D.; The Coffies Team
2021AAS...23811322H Altcode:
The solar activity cycle is the Consequence Of Fields and Flows in the
Interior and Exterior of the Sun (COFFIES). As a Phase-1 NASA DRIVE
Science Center (DSC), COFFIES ultimately aims to develop a data-driven
model of solar activity. To attain this goal COFFIES members are
learning to work together effectively to perform the investigations
needed to answer five primary science questions: <P />1) What drives
varying large-scale motions in the Sun? <P />2) How do flows interact
with the magnetic field to cause varying activity cycles? <P />3) Why
do active regions emerge when and where they do? <P />4) What do the
manifestations of activity and convection reveal about the internal
processes? <P />5) How does our understanding of the Sun as a star
inform us more generally about activity dynamics and structure? <P />The
virtual COFFIES center brings together a broad spectrum of observers,
data analysts, theorists, computational scientists, and educators
who collaborate through interacting working groups of four principal
science teams. The principal objectives of the four primary science
teams are to 1) understand the generation of quasi-periodic stellar
magnetic cycles, 2) further develop 3D physical models of interior
dynamics and convection, 3) establish clear physical links between solar
flow fields and near-surface observations, and 4) develop more robust
helioseismic techniques to resolve solar interior flows. Additional
cross-team activities are facilitated by teams for numerical modeling,
center effectiveness, outreach and eduction, and diversity, equity,
inclusion and access (DEIA).
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Title: Compression of Solar Spectroscopic Observations: a Case Study
of Mg II k Spectral Line Profiles Observed by NASA's IRIS Satellite
Authors: Sadykov, Viacheslav M; Kitiashvili, Irina N; Sainz Dalda,
Alberto; Oria, Vincent; Kosovichev, Alexander G; Illarionov, Egor
2021arXiv210307373S Altcode:
In this study we extract the deep features and investigate the
compression of the Mg II k spectral line profiles observed in quiet
Sun regions by NASA's IRIS satellite. The data set of line profiles
used for the analysis was obtained on April 20th, 2020, at the
center of the solar disc, and contains almost 300,000 individual
Mg II k line profiles after data cleaning. The data are separated
into train and test subsets. The train subset was used to train the
autoencoder of the varying embedding layer size. The early stopping
criterion was implemented on the test subset to prevent the model from
overfitting. Our results indicate that it is possible to compress the
spectral line profiles more than 27 times (which corresponds to the
reduction of the data dimensionality from 110 to 4) while having a 4 DN
average reconstruction error, which is comparable to the variations in
the line continuum. The mean squared error and the reconstruction error
of even statistical moments sharply decrease when the dimensionality of
the embedding layer increases from 1 to 4 and almost stop decreasing
for higher numbers. The observed occasional improvements in training
for values higher than 4 indicate that a better compact embedding may
potentially be obtained if other training strategies and longer training
times are used. The features learned for the critical four-dimensional
case can be interpreted. In particular, three of these four features
mainly control the line width, line asymmetry, and line dip formation
respectively. The presented results are the first attempt to obtain
a compact embedding for spectroscopic line profiles and confirm the
value of this approach, in particular for feature extraction, data
compression, and denoising.
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Title: Effects of Rotation on Internal Structure and Dynamics of
Main-Sequence Stars
Authors: Kitiashvili, Irina N.; Wray, Alan A.
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.
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Title: Connecting Atmospheric Properties and Synthetic Emission of
Shock Waves Using 3D RMHD Simulations of the Quiet Sun
Authors: Sadykov, Viacheslav M.; Kitiashvili, Irina N.; Kosovichev,
Alexander G.; Wray, Alan A.
2021ApJ...909...35S Altcode: 2020arXiv200805995S
We analyze the evolution of shock waves in high-resolution 3D radiative
MHD simulations of the quiet Sun and their synthetic emission
characteristics. The simulations model the dynamics of a 12.8 ×
12.8 × 15.2 Mm quiet-Sun region (including a 5.2 Mm layer of the
upper convection zone and a 10 Mm atmosphere from the photosphere
to corona) with an initially uniform vertical magnetic field of
10 G, naturally driven by convective flows. We synthesize the Mg
II and C II spectral lines observed by the Interface Region Imaging
Spectrograph (IRIS) satellite and extreme ultraviolet emission observed
by the Solar Dynamics Observatory (SDO)/AIA telescope. Synthetic
observations are obtained using the RH1.5D radiative transfer code and
temperature response functions at both the numerical and instrumental
resolutions. We found that the Doppler velocity jumps of the C II 1334.5
Å IRIS line and a relative enhancement of the emission in the 335 Å
SDO/AIA channel are the best proxies for the enthalpy deposited by shock
waves into the corona (with Kendall's τ correlation coefficients of
0.59 and 0.38, respectively). The synthetic emission of the lines and
the extreme ultraviolet passbands are correlated with each other during
the shock-wave propagation. All studied shocks are mostly hydrodynamic
(i.e., the magnetic energy carried by horizontal fields is ≤2.6%
of the enthalpy for all events) and have Mach numbers >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.
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Title: 3D Realistic Modeling of Main-Sequence Stars with Shallow
Outer Convection Zone
Authors: Kitiashvili, I. N.; Wray, A. A.; Kosovichev, A. G.
2021AAS...23741505K Altcode:
Our current state-of-the-art computer simulations allow us to build
3D dynamical and radiation models of F-type stars from physical first
principles. Using the stellar interior's structure from the MESA
stellar evolution code as initial conditions, we generate models of
main-sequence stars with the mass from 1.4 Msun to 2 Msun for various
metallicity composition, in the range of [Fe/H] from -0.3 to 0.2. The
radiative 3D dynamical stellar models obtained with the StellarBox
code take into account the effects of turbulence, stellar abundances,
and radiation. We investigate the turbulent dynamics from the radiative
zone to the outer convection zone and the lower atmosphere for these
stars and compare their turbulent properties. <P />Also, we investigate
the effects of stellar rotation for a 1.47Msun star for rotational
periods of 1 and 14 days. The simulations are performed for the
different latitudinal location of the computation domain. The models
reproduce the subsurface shear layer, structural changes of convection,
and the tachocline, which is the interface between the inner radiative
zone and the outer convection zone and plays a crucial role in stellar
variability. In particular, the model results reveal the formation of
differential rotation of an anti-solar type. The simulation results shed
light on differential rotation properties, the excitation of oscillation
modes, the tachocline's dynamics and structure, and support analysis
and interpretation of observational data from Kepler and TESS missions.
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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.
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.
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.
2020AGUFMSH007..04K Altcode:
Uninterrupted helioseismic observations from the SoHO/MDI, SDO/HMI and
GONG instruments for more than two decades provide unique observational
data for studying the solar-cycle variations of the differential
rotation, large-scale and meridional flows. The data also allows
us to investigate changes in the thermodynamic structure associated
with dynamo-generated magnetic fields. The wealth of global and local
helioseismic data provides theoretical constraints on the solar dynamics
and dynamo models. The synergy of helioseismic inferences with advanced
MHD modeling sheds light on the origin of the solar activity cycles. It
helps to understand better the physical processes that control the
strength and duration of the cyclic magnetic activity and leads to
new physics-based approaches for prediction of the solar cycles. We
briefly overview the current status, discuss the solar dynamical
structure and evolution revealed by helioseismic inversions and the
forward-modeling method, and focus on the most critical points of the
problem. In particular, we discuss recent advances in measurements and
modeling of the solar-cycle variations of the meridional circulation
and migrating zonal flows (torsional oscillations) on the solar surface
and in the subsurface layers, the deep convection zone, and the solar
tachocline. The relationships between the internal dynamics and the
evolution of global magnetic fields lead to new ideas of how magnetic
fields are generated and affect the solar flows and structure.
---------------------------------------------------------
Title: Multi-Wavelength Modeling and Analysis of the Center-to-Limb
Effects of Solar Spectroscopy and Helioseismology
Authors: Kitiashvili, I.; Zhao, J.; Sadykov, V. M.; Criscuoli, S.;
Kosovichev, A. G.; Wray, A. A.
2020AGUFMSH0020003K Altcode:
An accurate interpretation of observed solar dynamics with different
instruments requires modeling solar magnetoconvection in different
regimes, as well as taking into account center-to-limb effects,
magnetic fields, and turbulence. Realistic 3D radiative MHD modeling
of the solar magnetoconvection and atmosphere allows us to generate
synthetic observables that directly link the physical properties of
the solar plasma to spectroscopic and helioseismic observables. In
this work, we investigate the influence of the center-to-limb effects
for a wide range of wavelengths, which correspond to the operational
lines of HMI/SDO, Hinode, DKIST, and other instruments. In particular,
we discuss the wavelength-dependency of the center-to-limb helioseismic
observations of acoustic travel times that are used for diagnostics of
the deep meridional circulation, as well as 'concave' Sun effect. The
presented study will support interpretation of helioseismic inversion
results by taking into account realistic coupling of subsurface and
atmosphere, and geometry-related effects. In particular, it allows us
to improve accuracy of solar subsurface measurements from the SoHO and
SDO missions, and resolve the long-standing problem of the meridional
circulation and evolution with the solar cycle.
---------------------------------------------------------
Title: Machine Learning in Heliophysics and Space Weather Forecasting:
A White Paper of Findings and Recommendations
Authors: Nita, Gelu; Georgoulis, Manolis; Kitiashvili, Irina; Sadykov,
Viacheslav; Camporeale, Enrico; Kosovichev, Alexander; Wang, Haimin;
Oria, Vincent; Wang, Jason; Angryk, Rafal; Aydin, Berkay; Ahmadzadeh,
Azim; Bai, Xiaoli; Bastian, Timothy; Filali Boubrahimi, Soukaina; Chen,
Bin; Davey, Alisdair; Fereira, Sheldon; Fleishman, Gregory; Gary, Dale;
Gerrard, Andrew; Hellbourg, Gregory; Herbert, Katherine; Ireland,
Jack; Illarionov, Egor; Kuroda, Natsuha; Li, Qin; Liu, Chang; Liu,
Yuexin; Kim, Hyomin; Kempton, Dustin; Ma, Ruizhe; Martens, Petrus;
McGranaghan, Ryan; Semones, Edward; Stefan, John; Stejko, Andrey;
Collado-Vega, Yaireska; Wang, Meiqi; Xu, Yan; Yu, Sijie
2020arXiv200612224N Altcode:
The authors of this white paper met on 16-17 January 2020 at the New
Jersey Institute of Technology, Newark, NJ, for a 2-day workshop that
brought together a group of heliophysicists, data providers, expert
modelers, and computer/data scientists. Their objective was to discuss
critical developments and prospects of the application of machine and/or
deep learning techniques for data analysis, modeling and forecasting
in Heliophysics, and to shape a strategy for further developments in
the field. The workshop combined a set of plenary sessions featuring
invited introductory talks interleaved with a set of open discussion
sessions. The outcome of the discussion is encapsulated in this white
paper that also features a top-level list of recommendations agreed
by participants.
---------------------------------------------------------
Title: Response of SDO/HMI Observables to Heating of the Solar
Atmosphere by Precipitating High-energy Electrons
Authors: Sadykov, Viacheslav M.; Kosovichev, Alexander G.; Kitiashvili,
Irina N.; Kerr, Graham S.
2020ApJ...893...24S Altcode: 2019arXiv190610788S
We perform an analysis of the line-of-sight (LOS) observables of the
Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics
Observatory (SDO) for models of the solar atmosphere heated by
precipitating high-energy electrons during solar flares. The radiative
hydrodynamic (RADYN) flare models are obtained from the F-CHROMA
database. The Stokes profiles for the Fe 6173 Å line observed by
SDO/HMI are calculated using the radiative transfer code RH1.5D,
assuming statistical equilibrium for atomic level populations,
and imposing uniform background vertical magnetic fields of various
strengths. The SDO/HMI observing sequence and LOS data processing
pipeline algorithm are applied to derive the observables (continuum
intensity, line depth, Doppler velocity, LOS magnetic field). Our
results reveal that the strongest deviations of the observables from
the actual spectroscopic line parameters are found for the model with
a total energy deposited of E<SUB>total</SUB> = 1.0 × 10<SUP>12</SUP>
erg cm<SUP>-2</SUP>, injected with a power-law spectral index of δ =
3 above a low-energy cutoff of E<SUB>c</SUB> = 25 keV. The magnitudes
of the velocity and magnetic field deviations depend on the imposed
magnetic field, and can reach 0.35 km s<SUP>-1</SUP> for LOS velocities,
90 G for LOS magnetic field, and 3% for continuum enhancement for the
1000 G imposed LOS magnetic field setup. For E<SUB>total</SUB> ≥
3.0 × 10<SUP>11</SUP> erg cm<SUP>-2</SUP> models, the velocity and
magnetic field deviations are most strongly correlated with the energy
flux carried by ∼50 keV electrons, and the continuum enhancement
is correlated with the synthesized ∼55-60 keV hard X-ray photon
flux. The relatively low magnitudes of perturbations of the observables
and absence of magnetic field sign reversals suggest that the considered
RADYN beam heating models augmented with the uniform vertical magnetic
field setups cannot explain the strong transient changes found in the
SDO/HMI observations.
---------------------------------------------------------
Title: Application of Synoptic Magnetograms to Global Solar Activity
Forecast
Authors: Kitiashvili, I. N.
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.
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.
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.
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.
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.
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&k 2796 Å & 2803 Å and transition
region C II 1334 Å & 1335 Å lines using the realistic 3D RMHD
simulations of the quiescent solar atmosphere (using StellarBox and
RH1.5 codes). K-Means clustering algorithm is applied separately
to the observed or synthetic spectroscopic line profiles, as well
as to their statistical moments (intensity maxima, Doppler shifts,
line widths etc). The average silhouette width maximization technique
for the K-Means algorithm is utilized to obtain optimal numbers of
clusters. We discuss applications of the line profile clustering method
to 1) visualizations of computational and observational spectroscopic
imaging data; 2) understanding of evolutionary trends and behavior
patterns; 3) recognition of heating events and shock waves.
---------------------------------------------------------
Title: Solar activity modeling: from subgranular scales to the
solar cycles
Authors: Kitiashvili, I.; Wray, A. A.; Sadykov, V. M.; Kosovichev,
A. G.; Mansour, N. N.
2019AGUFMSH31E3350K Altcode:
Dynamical effects of solar magnetoconvection span a wide range
spatial and temporal scales that extends from the interior to the
corona and from fast turbulent motions to the global-Sun magnetic
activity. To study the solar activity on short temporal scales (from
minutes to hours), we use 3D radiative MHD simulations that allow
us to investigate complex turbulent interactions that drive various
phenomena, such as plasma eruptions, spontaneous formation of magnetic
structures, funnel-like structures and magnetic loops in the corona,
and others. In particular, we focus on multi-scale processes of energy
exchange across the different layers, which contribute to the corona
heating and eruptive dynamics, as well as interlinks between different
layers of the solar interior and atmosphere. <P />For modeling the
global-scale activity we use the data assimilation approach that has
demonstrated great potential for building reliable long-term forecasts
of solar activity. In particular, it has been shown that the Ensemble
Kalman Filter (EnKF) method applied to the Parker-Kleeorin-Ruzmakin
dynamo model is capable of predicting solar activity up to one
sunspot cycle ahead in time, as well as estimating the properties of
the next cycle a few years before it begins. In this presentation,
using the available magnetogram data, we discuss development of
the methodology and forecast quality criteria (including forecast
uncertainties and sources of errors). We demonstrate the influence
of observational limitation on the prediction accuracy. We present
the EnKF predictions of the upcoming Solar Cycle 25 based on both
the sunspot number series and observed magnetic fields, and discuss
the uncertainties and potential of the data assimilation approach for
modeling and forecasting the solar activity.
---------------------------------------------------------
Title: Long-Term Prediction of Solar Activity Using Magnetogram Data
and Ensemble Kalman Filter
Authors: Kitiashvili, Irina; Kosovichev, Alexander G.
2019AAS...23440101K Altcode:
Solar activity predictions using the data assimilation approach have
demonstrated great potential to build reliable long-term forecasts of
solar activity. In particular, it has been shown that the Ensemble
Kalman Filter (EnKF) method applied to a non-linear dynamo model is
capable of predicting solar activity up to one sunspot cycle ahead
in time, as well as estimating the properties of the next cycle a
few years before it begins. These developments assume an empirical
relationship between the mean toroidal magnetic field flux and the
sunspot number. Estimated from the sunspot number series, variations
of the toroidal field have been used to assimilate the data into the
Parker-Kleeorin-Ruzmakin (PKR) dynamo model by applying the EnKF
method. The dynamo model describes the evolution of the toroidal
and poloidal components of the magnetic field and the magnetic
helicity. Full-disk magnetograms provide more accurate and complete
input data by constraining both the toroidal and poloidal global
field components, but these data are available only for the last four
solar cycles. In this presentation, using the available magnetogram
data, we discuss development of the methodology and forecast quality
criteria (including forecast uncertainties and sources of errors). We
demonstrate the influence of limited time series observations on the
accuracy of solar activity predictions. We present EnKF predictions of
the upcoming Solar Cycle 25 based on both the sunspot number series and
observed magnetic fields and discuss the uncertainties and potential
of the data assimilation approach. The research is funded by the NSF
SHINE program AGS-1622341.
---------------------------------------------------------
Title: 3D Realistic Modeling of Chromospheric and Coronal Heating
and Self-Organization
Authors: Kitiashvili, Irina; Wray, Alan A.; Kosovichev, Alexander G.;
Sadykov, Viacheslav M.; Mansour, Nagi N.
2019AAS...23410615K Altcode:
Turbulent magnetoconvection is a primary driver of the dynamics and
structure of the solar atmosphere and corona. Realistic high-resolution
radiative MHD simulations reveal a complex multiscale structuring
and dynamics above the photosphere. We present a detailed study of
dynamical links between small-scale magnetic fields generated by
local dynamo action and properties of the chromosphere and corona,
as well as effects of coherent self-organized magnetic structures. In
particular, we discuss formation of coherent structures, eruptive
dynamics, and contributions of multi-scale structuring and highly
non-linear dynamics to heating of the chromosphere and corona.
---------------------------------------------------------
Title: 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
2019BAAS...51c.200W Altcode: 2019arXiv190307556W; 2019astro2020T.200W
Detecting and characterizing terrestrial- to Neptune-sized planets
(1 < R < 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.
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&k
3969A&3934A, Mg II h&k 2796A&2803A), and transition region
(C II 1334A&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.
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
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.
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.
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
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
2019ApJ...874...19S Altcode: 2018arXiv181005610S
We present a statistical analysis of properties of Soft X-Ray (SXR)
emission, plasma temperature (T), and emission measure (EM), derived
from Geostationary Operational Environmental Satellite observations
of flares in 2002-2017. The temperature and EMs are obtained using
the Temperature and EM-based Background Subtraction algorithm, which
delivers reliable results together with uncertainties even for weak
B-class flare events. More than 96% of flares demonstrate a sequential
appearance of T, SXR, and EM maxima, in agreement with the expected
behavior of the chromospheric evaporation process. The relative number
of such flares increases with increasing the SXR flux maximum. The
SXR maximum is closer in time to the T maximum for B-class flares than
for ≥C-class flares, while it is very close to the EM maximum for M-
and X-class flares. We define flares as “T-controlled” if the time
interval between the SXR and T maxima is at least two times shorter than
the interval between the EM and SXR maxima, and as “EM-controlled”
if the time interval between the EM and SXR maxima is at least two
times shorter than the interval between the SXR and T maxima. For
any considered flare class range, the T-controlled events compared
to EM-controlled events have: (a) higher EM but lower T; (b) longer
durations and shorter relative growth times; and (c) longer FWHM and
characteristic decay times. Interpretation of these statistical results
based on analysis of a single loop dynamics suggests that for flares
of the same class range, the T-controlled events can be developed in
longer loops than the EM-controlled events.
---------------------------------------------------------
Title: The Origin of Deep Acoustic Sources Associated with Solar
Magnetic Structures
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Mansour, N. N.; Wray,
A. A.; Sandstrom, T. A.
2019ApJ...872...34K Altcode: 2018arXiv181006133K
It is generally accepted that solar acoustic (p) modes are excited
by near-surface turbulent motions, in particular by downdrafts and
interacting vortices in intergranular lanes. Recent analysis of Solar
Dynamics Observatory data by Zhao et al. (2015) revealed fast-moving
waves around sunspots, which are consistent with magnetoacoustic waves
excited approximately 5 Mm beneath the sunspot. We analyzed 3D radiative
MHD simulations of solar magnetoconvection with a self-organized
pore-like magnetic structure, and identified more than 600 individual
acoustic events both inside and outside this structure. By performing
a case-by-case study, we found that acoustic sources surrounding
the magnetic structure are associated with downdrafts. Their depth
correlates with downdraft speed and magnetic field strength. The
sources often can be transported into deeper layers by downdrafts. The
wave front shape, in the case of a strong or inclined downdraft,
can be stretched along the downdraft. Inside the magnetic structure,
excitation of acoustic waves is driven by converging flows. Frequently,
strong converging plasma streams hit the structure boundaries, causing
compressions in its interior that excite acoustic waves. Analysis
of the depth distribution of acoustic events shows the strongest
concentration at 0.2-1 Mm beneath the surface for the outside sources
and mostly below 1 Mm inside the magnetic region, that is, deeper than
their counterparts outside the magnetic region.
---------------------------------------------------------
Title: Realistic Radiative 3D MHD Modeling of Outer Convection Zones
and Atmospheres of Moderate-Mass Stars
Authors: Kitiashvili, Irina
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.
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
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
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
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.
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.
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.
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.
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
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
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.
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
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
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
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
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
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.
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.
2013arXiv1312.0982K Altcode:
In the quiet Sun, magnetic fields are usually observed as small-scale
magnetic elements, `salt and pepper', covering the entire solar
surface. By using 3D radiative MHD numerical simulations we demonstrate
that these fields are a result of local dynamo action in the top layers
of the convection zone, where extremely weak `seed' magnetic fields can
locally grow above the mean equipartition field (e.g., from a $10^{-6}$
G `seed' field to more than 1000 G magnetic structures). We find that
the local dynamo action takes place only in a shallow, about 500 km
deep, subsurface layer, from which the generated field is transported
into deeper layers by convection downdrafts. We demonstrate that the
observed dominance of vertical magnetic fields at the photosphere
and the horizontal fields above the photosphere can be explained by
multi-scale magnetic loops produced by the dynamo.
---------------------------------------------------------
Title: Turbulent Hydrodynamics and Oscillations of Moderate-Mass Stars
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Lele, S. K.; Mansour,
N. N.; Wray, A. A.
2013ASPC..479..377K Altcode:
The solar-type pulsators are characterized by acoustic oscillation
modes excited by turbulent convection in the upper convective boundary
layer. As the stellar mass increases the convection zone shrinks, the
scale and intensity of the turbulent motions increases, providing more
energy for excitation of acoustic modes. When the stellar mass reaches
about 1.6 solar masses the upper convection zone consists of two very
thin layers corresponding to H and He ionization, and in addition to
the acoustic modes the stars show strong internal gravity modes. The
thin convection zone is often considered insignificant for the stellar
dynamics and variability. We use three-dimensional (3D) numerical
radiative hydrodynamics simulations to study convective and oscillation
properties of Main Sequence stars from the solar-type stars to more
massive stars. We present simulation results for some of the target
stars selected for the Kepler Guest Observer project “Transition
in Variable Stars: From Solar-Type Stars to Gamma-Doradus Stars.”
For the moderate-mass (A-type) stars the simulations reveal supersonic
granular-type convection of a scale significantly larger than the solar
granulation scale, and strong overshooting plumes penetrating into the
stable radiative zone, that can affect the oscillation properties of
these stars.
---------------------------------------------------------
Title: Mechanisms of formation ofsolar pores and sunspots
Authors: Kitiashvili, Irina N.
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.
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
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 & 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 & 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.
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.
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.
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.
2012ASPC..462..382K Altcode:
Observations of the solar surface show a highly turbulent behavior
of convection, and reveal coherent structures in distributed magnetic
fields. We present results of realistic radiation magneto-hydrodynamics
(MHD) simulations in three dimensions (3D) of the solar subsurface
layers, and investigate properties of magneto-convection for various
magnetic field topologies and strengths. In particular, we discuss the
filamentary structure and dynamics of sunspot penumbra, spontaneous
formation of pore-like and small-scale magnetic structures, and compare
the simulation results with observations.
---------------------------------------------------------
Title: Radiation Hydrodynamics Simulations of Turbulent Convection
for Kepler Target Stars
Authors: Kitiashvili, I. N.; Guzik, J. A.; Kosovichev, A. G.; Mansour,
N. N.; Saio, H.; Shibahashi, H.; Wray, A. A.
2012ASPC..462..378K Altcode:
The solar-type pulsators are characterized by acoustic oscillation
modes excited by turbulent granular convection in the upper convective
boundary layer. As the stellar mass increases the convection zone
shrinks, the scale and intensity of the turbulent motions increases,
providing more energy for excitation of acoustic modes. When the stellar
mass reaches about 1.6 solar masses the upper convection zone consists
of two very thin layers corresponding to H and He ionization, and in
addition to the acoustic modes the stars show strong internal gravity
modes The thin convection zone is often considered insignificant for
the stellar dynamics and variability. We use numerical radiation
transfer simulations in three dimensions (3D) to study convective
and oscillation properties of main-sequence stars from the solar-type
stars to more massive stars. In the simulations we used models of the
stellar interior, calculated for individual Kepler mission targets. The
3D radiation hydrodynamics simulations reveal supersonic granular-type
convection on a scale significantly larger than the solar granulation,
and strong overshooting plumes penetrating into the stable radiative
zone, which can affect oscillation properties of a star.
---------------------------------------------------------
Title: Detection of Small-scale Granular Structures in the Quiet
Sun with the New Solar Telescope
Authors: Abramenko, V. I.; Yurchyshyn, V. B.; Goode, P. R.;
Kitiashvili, I. N.; Kosovichev, A. G.
2012ApJ...756L..27A Altcode: 2012arXiv1208.4337A
Results of a statistical analysis of solar granulation are presented. A
data set of 36 images of a quiet-Sun area on the solar disk center was
used. The data were obtained with the 1.6 m clear aperture New Solar
Telescope at Big Bear Solar Observatory and with a broadband filter
centered at the TiO (705.7 nm) spectral line. The very high spatial
resolution of the data (diffraction limit of 77 km and pixel scale of
0farcs0375) augmented by the very high image contrast (15.5% ± 0.6%)
allowed us to detect for the first time a distinct subpopulation of
mini-granular structures. These structures are dominant on spatial
scales below 600 km. Their size is distributed as a power law with an
index of -1.8 (which is close to the Kolmogorov's -5/3 law) and no
predominant scale. The regular granules display a Gaussian (normal)
size distribution with a mean diameter of 1050 km. Mini-granular
structures contribute significantly to the total granular area. They are
predominantly confined to the wide dark lanes between regular granules
and often form chains and clusters, but different from magnetic bright
points. A multi-fractality test reveals that the structures smaller
than 600 km represent a multi-fractal, whereas on larger scales the
granulation pattern shows no multi-fractality and can be considered
as a Gaussian random field. The origin, properties, and role of the
population of mini-granular structures in the solar magnetoconvection
are yet to be explored.
---------------------------------------------------------
Title: Fine-scale Magnetic Structures and Flows in Sunspot Simulations
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Wray, A. A.; Mansour,
N. N.
2012ASPC..454..253K Altcode:
One of most intriguing processes on the Sun is the formation and
dynamics of sunspots and active regions, where magneto-convective
conditions are very different from quiet Sun regions. High-resolution
observations from Hinode and numerical simulations shed light into these
processes. In our 3D radiative MHD simulations we take into account
real-gas equation of state, ionization and excitation of all abundant
spices, turbulent and magnetic effects. We present recent results of
numerical simulations of a top layer of the convective zone and the
photosphere in the presence of magnetic field of various strength and
inclination. The simulation results explain the filamentary organization
of penumbra, reveal the mechanisms of the Evershed effect and the
sea-serpent behavior of magnetic field lines, and show the subsurface
dynamics of umbral dots as a natural consequence of magnetoconvection
processes.
---------------------------------------------------------
Title: Vortex tubes of turbulent solar convection
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Mansour, N. N.; Lele,
S. K.; Wray, A. A.
2012PhyS...86a8403K Altcode: 2011arXiv1112.5925K
The investigation of the turbulent properties of solar convection is
important for understanding the multi-scale dynamics observed on the
solar surface. In particular, recent high-resolution observations have
revealed ubiquitous vortical structures, and numerical simulations have
demonstrated links between vortex tube dynamics and the magnetic field
organization. Simulations have shown the importance of vortex tube
interactions in mechanisms of acoustic wave excitation on the Sun. In
this paper, we investigate the mechanisms of formation of vortex tubes
in highly turbulent convective flows near the solar surface by using
realistic radiative hydrodynamic large-eddy simulations. Analysis of
data from the simulations indicates two basic processes of vortex tube
formation: (i) the development of small-scale convective instability
inside convective granules and (ii) a Kelvin-Helmholtz-type instability
of shearing flows in intergranular lanes. Our analysis shows that
vortex stretching during these processes is a primary source of the
generation of small-scale vorticity on the Sun.
---------------------------------------------------------
Title: Simulations and Observational Signatures of Mass Ejections,
Alfven Waves and Shocks Driven by Turbulent Magnetized Vortex Tubes
Authors: Kitiashvili, Irina N.
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.
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.
2012ApJ...751L..21K Altcode: 2012arXiv1201.5442K
We use three-dimensional radiative MHD simulations to investigate the
formation and dynamics of small-scale (less than 0.5 Mm in diameter)
vortex tubes spontaneously generated by turbulent convection in
quiet-Sun regions with an initially weak (10 G) mean magnetic
field. The results show that the vortex tubes penetrate into the
chromosphere and substantially affect the structure and dynamics
of the solar atmosphere. The vortex tubes are mostly concentrated
in intergranular lanes and are characterized by strong (near sonic)
downflows and swirling motions that capture and twist magnetic field
lines, forming magnetic flux tubes that expand with height and attain
magnetic field strengths ranging from 200 G in the chromosphere to more
than 1 kG in the photosphere. We investigate in detail the physical
properties of these vortex tubes, including thermodynamic properties,
flow dynamics, and kinetic and current helicities, and conclude that
magnetized vortex tubes provide an important path for energy and
momentum transfer from the convection zone into the chromosphere.
---------------------------------------------------------
Title: Convection-Chromosphere Coupling due to Vortex Tube Dynamic
Authors: Kitiashvili, Irina; Kosovichev, A.; Mansour, N.; Wray, A.
2012AAS...22012405K Altcode:
Ubiquitous distribution of small-scale vortex tubes on the solar surface
was found both in observations and simulations. Complicated dynamics
of the turbulent vortex tubes is a source of various observed effects
such as acoustic waves excitation and processes of self-organization
in magnetized solar plasma. We use realistic-type radiative 3D MHD
simulations to investigate in detail different mechanisms of the
vortex tube formation by granular flows in the upper convection zone,
appearance of vortex tubes on the surface and their interaction with
the atmosphere. The simulation results reveal new interesting effects of
penetration of the vortex tubes from the turbulent subphotosphere into
the chromosphere, interaction between these layers, and influence of
the helical motions on thermodynamic properties of the chromosphere. In
the presence of background magnetic field, the vortex tubes lead to
formation of compact magnetic flux tubes, playing important role in
the mass and energy flux into the chromosphere. We discuss implication
of the simulation results for future high-resolution observations.
---------------------------------------------------------
Title: Effects of vortex tube dynamics in the chromosphere
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Lele, S. K.; Mansour,
N. N.; Wray, A. A.
2012decs.confE..96K Altcode:
Investigation of the solar atmosphere dynamics cannot be complete
without understanding coupling, and mass and energy exchange between
the strongly-turbulent subphotosphere and the chromosphere. Modern
computational capabilities allow us to construct realistic dynamical
models, which take into account dynamical, chemical and radiative
properties of the solar plasma. Such simulations based on first physical
principles and accurate modeling of effects of magnetic field and
small-scale turbulence, coupled with spectro-polarimetric line formation
calculations, provide synthetic multi-wavelength observables, and are
very important for interpretation of observational data. The simulations
allow us to study physical processes and phenomena that have not been
resolved in observations. In this talk we will present our recent
results of high-resolution 3D radiative MHD numerical simulations of
top layers of the convective zone and the chromosphere. The simulations
reveal ubiquitous distribution of small-scale swirling motions in
quiet-Sun and magnetic regions, forming vortex tubes extending from
the subphosphere into the chromosphere. Our results show that these
small-scale vortex tubes that originally formed in subsurface layer
and penetrate into the chromosphere provide an efficient coupling
of the turbulent convective layers with the atmosphere. They play
important role in various processes, such as shearing instabilities,
wave excitation, formation of magnetic flux tubes and transport
of energy, mass, momentum and also turbulent properties from the
convection zone into the chromosphere. In the presentation, we will
focus on the physical aspects of the vortex tube formation, penetration
into the atmosphere, interaction with magnetic fields, their role in
the energy exchange, and on observational diagnostics and comparison
with observational data.
---------------------------------------------------------
Title: Links between photospheric and chromospheric oscillations
Authors: Kosovichev, A. G.; Kitiashvili, I. N.; Mitra-Kraev, U.;
Sekii, T.
2012decs.confE..97K Altcode:
Oscillations excited by turbulent convection play important in the
dynamics and energetics of the solar atmosphere. Oscillations below the
acoustic cut-off frequency form photospheric resonant modes trapped
in the interior but also penetrating into the chromosphere. Above
the frequency cut-off, the oscillations represent traveling waves
in the chromosphere that form pseudo-modes due to interference with
waves coming from the interior. The physics of the chromospheric
oscillations, their coupling to the photospheric oscillations, and
their role in the chromospheric dynamics and energetics are not fully
understood. The observed oscillation properties strongly depend on
the excitation mechanism, interaction with turbulence and radiation,
and local structure and dynamics of the chromosphere. Significant
advances can be made through multi-wavelength observations of
atmospheric oscillations and realistic numerical radiative hydrodynamics
simulations. Using Hinode/SOT data we investigate the basic properties
of solar oscillations observed at two levels in the solar atmosphere,
in the G-band (formed in the photosphere) and in the CaII H line
(chromospheric emission). We analyzed the data by calculating the
individual power spectra as well as the cross-spectral properties,
i.e., coherence and phase shift. The observational properties are
compared with theoretical models and numerical simulations. The
results reveal significant frequency shifts between the CaII H and
G-band spectra, in particular above the acoustic cutoff frequency for
pseudo-modes. The cross-spectrum phase shows peaks associated with
the acoustic oscillation (p-mode) lines, and begins to increase with
frequency around the acoustic cut-off. However, we find no phase shift
for the (surface gravity wave) f-mode. The observed properties for
the p-modes are qualitatively reproduced in a model that includes a
correlated background due to radiative effects. Our results show that
multi-wavelength observations of solar oscillations, in combination
with radiative hydrodynamics modeling, help to understand the coupling
between photospheric and chromospheric oscillations.
---------------------------------------------------------
Title: Vortex tubes of solar convection: formation, properties
and dynamics
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Lele, S. K.; Mansour,
N. N.; Wray, A. A.
2011AGUFMSH43A1927K Altcode:
Turbulent convection of the Sun demonstrates very complicated dynamics,
which is often associated with different scales of self-organization. In
particular, vortex tube structures have been identified initially in
numerical simulations and then in high-resolution observations. We
present new results of 3D radiative MHD simulations of a top layer of
the convective zone that reveal the important role of turbulent vortex
tubes in various solar processes: acoustic waves excitation, convective
downdrafts, spontaneous formation of stable magnetic structures and
others. We consider various aspects of the vortex tubes dynamics,
including their formation, identification, physical characteristics, and
links to phenomena observed in the quiet Sun and magnetic regions. We
compare the simulation results with observational data from SDO/HMI,
Hinode and large ground-based telescope.
---------------------------------------------------------
Title: Data Assimilation for Dynamo Modeling and Solar Cycle
Prediction
Authors: Kitiashvili, I. N.
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.
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.
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.
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.
2011IAUS..274..120K Altcode:
Filamentary structure is a fundamental property of the magnetized solar
plasma. Recent high-resolution observations and numerical simulations
have revealed close links between the filamentary structures and
plasma dynamics in large-scale solar phenomena, such as sunspots and
magnetic network. A new emerging paradigm is that the mechanisms
of the filamentary structuring and large-scale organization are
natural consequences of turbulent magnetoconvection on the Sun. We
present results of 3D radiative MHD large-eddy simulations (LES) of
magnetic structures in the turbulent convective boundary layer of the
Sun. The results show how the initial relatively weak and uniformly
distributed magnetic field forms the filamentary structures, which
under certain conditions gets organized on larger scales, creating
stable long-living magnetic structures. We discuss the physics of
magnetic self-organization in the turbulent solar plasma, and compare
the simulation results with observations.
---------------------------------------------------------
Title: High-resolution 3D Radiative MHD Simulations Of Turbulent
Convection And Spectro-polarimetric Properties
Authors: Kitiashvili, Irina; Kosovichev, A. G.; Mansour, N. N.;
Stenflo, J. O.; Wray, A. A.
2011SPD....42.1708K Altcode: 2011BAAS..43S.1708K
Realistic numerical simulations of solar magnetoconvection play a
key role for our understanding of the basic physical phenomena in
the subsurface convective boundary layer and the atmosphere. For the
accurate modeling of the turbulent processes on the Sun it is important
to perform the simulations with the highest possible resolution. Our
results have revealed significant changes in properties of the
turbulent motions when the resolution is increased. It is particularly
interesting that small-scale vortex motions in the intergranular
lanes become ubiquitous and strong, and play a critical role in the
large-scale organization of the solar dynamics. For the comparison
with observational data it is necessary to investigate relationships
between the physical and spectro-polarimetric properties in various
conditions of the quiet-Sun and magnetic regions, and model the observed
parameters. By using the radiative line formation code, SPINOR/STOPRO,
we have calculated the Stokes profiles and other characteristics
for the spectral line of the Hinode/SOT and SDO/HMI instruments,
and compared the simulation results with the observational data.
---------------------------------------------------------
Title: A Mechanism of the Solar Acoustic Emission
Authors: Kitiashvili, Irina; Kosovichev, A. G.; Lele, S. K.; Mansour,
N. N.; Wray, A. A.
2011SPD....42.1701K Altcode: 2011BAAS..43S.1701K
Understanding the mechanism of acoustic waves excitation in the
turbulent surface layer is very important for the interpretation of
helioseismology data and development of new methods of helioseismic
diagnostics of the solar interior, as well as for understanding of
the role of the acoustic flux in the energy transport. A substantial
progress is being made from the analysis of high-resolution
observational data, particularly from Hinode, Sunrise, and SDO/HMI,
and also from high-resolution realistic numerical simulations. The
simulations take into account all essential turbulent and other
physical properties of the solar plasma, and allow us to look at the
scales that cannot be resolved in observations, and also compare the
data and models. We present new results of 3D radiative hydrodynamics
simulations of the upper convection zone and atmosphere, and show that
one of the possible mechanisms of the acoustic waves generation is a
result of interaction two and more vortex tubes. The process of a vortex
annihilation, which produces acoustic waves, the properties of these
waves and vortices, and comparison with the available observational
data will be discussed.
---------------------------------------------------------
Title: Numerical MHD Simulations of Solar Magnetoconvection and
Oscillations in Inclined Magnetic Field Regions
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Mansour, N. N.; Wray,
A. A.
2011SoPh..268..283K Altcode: 2010SoPh..tmp..239K; 2010arXiv1011.5527K
The sunspot penumbra is a transition zone between the strong vertical
magnetic field area (sunspot umbra) and the quiet Sun. The penumbra
has a fine filamentary structure that is characterized by magnetic
field lines inclined toward the surface. Numerical simulations of
solar convection in inclined magnetic field regions have provided an
explanation of the filamentary structure and the Evershed outflow in
the penumbra. In this article, we use radiative MHD simulations to
investigate the influence of the magnetic field inclination on the
power spectrum of vertical velocity oscillations. The results reveal a
strong shift of the resonance mode peaks to higher frequencies in the
case of a highly inclined magnetic field. The frequency shift for the
inclined field is significantly greater than that in vertical-field
regions of similar strength. This is consistent with the behavior of
fast MHD waves.
---------------------------------------------------------
Title: LES of turbulent convection in solar-type stars and formation
of large-scale magnetic structures
Authors: Rogachevskii, I.; Kleeorin, N.; Kitiashvili, I. N.;
Kosovichev, A. G.; Wray, A. A.; Mansour, N. N.
2011arXiv1102.1206R Altcode:
In this study we investigate the effects of turbulent convection on
formation of large-scale inhomogeneous magnetic structures by means of
Large-Eddy Simulation (LES) for convection in solar-type stars. The
main idea of this study is the implementation of a new subgrid-scale
model for the effective Lorentz force in a three-dimensional nonlinear
radiative magnetohydrodynamics (MHD) code developed for simulating
the upper solar convection zone and lower atmosphere. To this end we
derived the energy budget equations, which include the effects of the
subgrid-scale turbulence on the Lorentz-force, and implemented the
new subgrid-scale turbulence model (TELF-Model) in a three-dimensional
nonlinear MHD LES code. Using imposed initial vertical and horizontal
uniform magnetic fields in LES with the TELF-Model, we have shown that
the magnetic flux tubes formation is started when the initial mean
magnetic field is larger than a threshold value (about 100 G). This is
in agreement with the theoretical studies by Rogachevskii and Kleeorin
(2007). We have determined the vertical profiles of the velocity and
magnetic fluctuations, total MHD energy and anisotropy of turbulent
magneto-convection, kinetic and current and cross helicities.
---------------------------------------------------------
Title: Excitation of Acoustic Waves by Vortices in the Quiet Sun
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Mansour, N. N.; Wray,
A. A.
2011ApJ...727L..50K Altcode: 2010arXiv1011.3775K
The five-minute oscillations are one of the basic properties of solar
convection. Observations show a mixture of a large number of acoustic
wave fronts propagating from their sources. We investigate the process
of acoustic waves excitation from the point of view of individual
events, by using a realistic three-dimensional radiative hydrodynamic
simulation of the quiet Sun. The results show that the excitation events
are related to the dynamics of vortex tubes (or swirls) in intergranular
lanes of solar convection. These whirlpool-like flows are characterized
by very strong horizontal velocities (7-11 km s<SUP>-1</SUP>) and
downflows (≈7 km s<SUP>-1</SUP>), and are accompanied by strong
decreases of temperature, density, and pressure at the surface and
0.5-1 Mm below the surface. High-speed whirlpool flows can attract
and capture other vortices. According to our simulation results the
processes of vortex interaction, such as vortex annihilation, can
cause excitation of acoustic waves on the Sun.
---------------------------------------------------------
Title: Modeling and Prediction of Solar Cycles Using Data Assimilation
Methods
Authors: Kitiashvili, Irina N.; Kosovichev, Alexander G.
2011LNP...832..121K Altcode:
Variations of solar activity are a result of a complicate dynamo process
in the convection zone. We consider this phenomenon in the context
of sunspot number variations, which have detailed observational data
during the past 23 solar cycles. However, despite the known general
properties of the solar cycles a reliable forecast of the 11-year
sunspot number is still a problem. The main reasons are imperfect
dynamo models and deficiency of the necessary observational data. To
solve this problem we propose to use data assimilation methods. These
methods combine observational data and models for best possible,
efficient and accurate estimates of physical properties that cannot be
observed directly. The methods are capable of providing a forecast of
the system future state. It is demonstrated that the Ensemble Kalman
Filter (EnKF) method can be used to assimilate the sunspot number data
into a non-linear α{-}Upomega mean-field dynamo model, which takes
into account dynamics of turbulent magnetic helicity. We apply this
method for characterization of the solar dynamo properties and for
prediction of the sunspot number.
---------------------------------------------------------
Title: Subsurface structure of the Evershed flows in sunspots
Authors: Kitiashvili, Irina N.; Kosovichev, Alexander G.; Mansour,
Nagi N.; Wray, Alan A.
2011JPhCS.271a2076K Altcode:
The radial outflows in sunspot penumbrae, known as the Evershed
effect, are of significant interest for understanding the dynamics
of sunspots. Local helioseismology has not been able to determine
the depth of these flows nor their relationship to mass circulation
in sunspots. Recent radiative MHD simulations have provided a
convincing explanation of the Evershed flow as a natural consequence
of magnetoconvection in the strongly inclined magnetic field region of
the penumbra. The simulations reproduce many observational features of
penumbra dynamics, including the filamentary structure, the high-speed
non-stationary "Evershed clouds", and the "sea-serpent" behavior
of magnetic field lines. We present the subsurface structure of the
Evershed effect, obtained from numerical simulations, and determine the
depth of the radial outflows for various magnetic field strengths and
inclinations. The simulations predict that Evershed flows are rather
shallow and concentrated in the top 0.5 - 1 Mm layer of the convection
zone. This prediction can be tested by local helioseismology methods.
---------------------------------------------------------
Title: Realistic MHD Simulations of Formation of Sunspot-like
Structures and Comparison with Observations
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Mansour, N. N.; Wray,
A. A.
2010AGUFMSH31A1782K Altcode:
The process of formation of magnetic structures such as sunspot and
pores in the turbulent convection zone is still enigma. However,
the recent progress in numerical radiative MHD simulations provides
clues about the possible mechanism of magnetic field accumulation in
spontaneously formed stable structures. Implementation of sub-grid
turbulent models in our "SolarBox" code, gives us the possibility
to model more accurately turbulent properties, and reproduce the
dynamics of the magnetized plasma. The code takes into account
non-ideal (tabular) EOS, effects of ionization, chemical composition,
radiation, turbulence and magnetic field. Our simulation results show
an important role of vortices, which create local cavity of pressure
and are associated with strong converging flows under the surface,
during the initial stage of the spontaneous structure formation. The
resulting structure represents a compact self-organized concentration
of strong magnetic field, reaching ~6 kG in the interior, and ~1.5 kG
on the surface. It has a cluster-like internal structurization, and
is maintained by strong downdrafts extending into the deep layers. We
discuss the role of turbulent MHD dynamics in this mechanism, and
compare the simulation results with observations of the sunspot
formation process during a magnetic flux emergence, from the Solar
Dynamics Observatory and Hinode.
---------------------------------------------------------
Title: Cross-helicity turbulence model: Application to MHD phenomena
from solar convection zone to heliosphere
Authors: Yokoi, N.; Kitiashvili, I. N.; Kosovichev, A. G.
2010AGUFMSH31A1793Y Altcode:
Cross helicity (velocity-magnetic field correlation) is expected
to play a key role in several geo/astrophysical processes including
dynamo action, suppression of turbulent transport, etc. We discuss the
relevance of the cross-helicity effects with the aid of the turbulence
model. A turbulence model with the cross-helicity effects incorporated
may be called the “cross-helicity turbulence model”. This model is
applied to several MHD phenomena ranging from the formations of magnetic
fields and plasma motions in the solar convection zone to the solar-wind
evolution in the heliosphere. Generation of turbulence quantities
depends on the inhomogeneity of large-scale fields, and turbulence
in turn determines the configuration of the mean fields through the
turbulent transport. Such nonlinear interactions between the mean- and
fluctuation-fields are explored with the aid of numerical simulations
with cross-helicity turbulence model. Through the comparisons to the
observation, validity of the turbulence model is examined. Examinations
include (i) A large-eddy simulation of the sunspot flow reveals how and
how much cross helicity is generated there; (ii) A eddy-viscosity-type
turbulence model shows how the turbulence quantities evolves under
the influence of the large-scale velocity and magnetic-field shears.
---------------------------------------------------------
Title: A Precise Asteroseismic Age and Radius for the Evolved Sun-like
Star KIC 11026764
Authors: Metcalfe, T. S.; Monteiro, M. J. P. F. G.; Thompson, M. J.;
Molenda-Żakowicz, J.; Appourchaux, T.; Chaplin, W. J.; Doǧan, G.;
Eggenberger, P.; Bedding, T. R.; Bruntt, H.; Creevey, O. L.; Quirion,
P. -O.; Stello, D.; Bonanno, A.; Silva Aguirre, V.; Basu, S.; Esch,
L.; Gai, N.; Di Mauro, M. P.; Kosovichev, A. G.; Kitiashvili, I. N.;
Suárez, J. C.; Moya, A.; Piau, L.; García, R. A.; Marques, J. P.;
Frasca, A.; Biazzo, K.; Sousa, S. G.; Dreizler, S.; Bazot, M.; Karoff,
C.; Frandsen, S.; Wilson, P. A.; Brown, T. M.; Christensen-Dalsgaard,
J.; Gilliland, R. L.; Kjeldsen, H.; Campante, T. L.; Fletcher, S. T.;
Handberg, R.; Régulo, C.; Salabert, D.; Schou, J.; Verner, G. A.;
Ballot, J.; Broomhall, A. -M.; Elsworth, Y.; Hekker, S.; Huber, D.;
Mathur, S.; New, R.; Roxburgh, I. W.; Sato, K. H.; White, T. R.;
Borucki, W. J.; Koch, D. G.; Jenkins, J. M.
2010ApJ...723.1583M Altcode: 2010arXiv1010.4329M
The primary science goal of the Kepler Mission is to provide
a census of exoplanets in the solar neighborhood, including the
identification and characterization of habitable Earth-like planets. The
asteroseismic capabilities of the mission are being used to determine
precise radii and ages for the target stars from their solar-like
oscillations. Chaplin et al. published observations of three bright
G-type stars, which were monitored during the first 33.5 days of science
operations. One of these stars, the subgiant KIC 11026764, exhibits a
characteristic pattern of oscillation frequencies suggesting that it
has evolved significantly. We have derived asteroseismic estimates of
the properties of KIC 11026764 from Kepler photometry combined with
ground-based spectroscopic data. We present the results of detailed
modeling for this star, employing a variety of independent codes and
analyses that attempt to match the asteroseismic and spectroscopic
constraints simultaneously. We determine both the radius and the age
of KIC 11026764 with a precision near 1%, and an accuracy near 2%
for the radius and 15% for the age. Continued observations of this
star promise to reveal additional oscillation frequencies that will
further improve the determination of its fundamental properties.
---------------------------------------------------------
Title: Realistic MHD numerical simulations of solar convection and
oscillations in inclined magnetic field regions
Authors: Kitiashvili, Irina N.; Kosovichev, Alexander G.; Wray,
Alan A.; Mansour, Nagi N.
2010HiA....15..348K Altcode:
It is known that physical properties of solar turbulent convection and
oscillations strongly depend on magnetic field. In particular, recent
observations from SOHO/MDI revealed significant changes of the wave
properties in inclined magnetic field regions of sunspots, which affect
helioseismic inferences. We use realistic 3D radiative MHD numerical
simulations to investigate solar convection and oscillations and their
relationship in the presence of inclined magnetic field. In the case of
highly inclined and strong 1-1.5 kG field the solar convection develops
filamentary structure and high-speed flows (Fig. 1a), which provide an
explanation to the Evershed effect in sunspot penumbra (Kitiashvili,
et al. 2009).
---------------------------------------------------------
Title: Mechanism of Spontaneous Formation of Stable Magnetic
Structures on the Sun
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Wray, A. A.; Mansour,
N. N.
2010ApJ...719..307K Altcode: 2010arXiv1004.2288K
One of the puzzling features of solar magnetism is formation of
long-living compact magnetic structures, such as sunspots and
pores, in the highly turbulent upper layer of the solar convective
zone. We use realistic radiative three-dimensional MHD simulations
to investigate the interaction between magnetic field and turbulent
convection. In the simulations, a weak vertical uniform magnetic
field is imposed in a region of fully developed granular convection,
and the total magnetic flux through the top and bottom boundaries is
kept constant. The simulation results reveal a process of spontaneous
formation of stable magnetic structures, which may be a key to
understanding the magnetic self-organization on the Sun and formation
of pores and sunspots. This process consists of two basic steps: (1)
formation of small-scale filamentary magnetic structures associated with
concentrations of vorticity and whirlpool-type motions, and (2) merging
of these structures due to the vortex attraction, caused by converging
downdrafts around magnetic concentration below the surface. In the
resulting large-scale structure maintained by the converging plasma
motions, the magnetic field strength reaches ~1.5 kG at the surface
and ~6 kG in the interior, and the surface structure resembles solar
pores. The magnetic structure remains stable for the whole simulation
run of several hours with no sign of decay.
---------------------------------------------------------
Title: Rotational evolution of planetary systems under the action
of gravitational and magnetic perturbations
Authors: Kitiashvili, I. N.; Gusev, A. V.
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.
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.
2010AAS...21631706K Altcode: 2010BAAS...41..899K
Recent high-resolution spectro-polarimetric observations of a sunspot
detected formation of bipolar magnetic patches in the mid penumbra and
propagation of these patches toward the outer penumbral boundary. The
observations have been interpreted as an evidence of sea-serpent field
lines near the solar surface. Using a radiative 3D MHD code, we model
the behavior of solar magnetoconvection in strongly inclined magnetic
field of penumbra. The numerical simulation results reproduce the
moving bipolar magnetic elements observed in high-resolution SOHO/MDI
and Hinode/SOT data and also their physical properties, supporting the
sea-serpent model. The simulations explain the sea-serpent structure
and dynamics of the penumbral field as a consequence of turbulent
magnetoconvection in a highly inclined, strong magnetic field,
which forms filamentary structures and has properties of traveling
convective wave. The model also shows that the appearance of the
sea-serpent magnetic field lines is closely related to high-speed
patches ("Evershed clouds") of the penumbra radial outflow.
---------------------------------------------------------
Title: Observations of Emerging Active Regions and Sunspot Formation
from SDO/HMI
Authors: Kitiashvili, Irina; Kosovichev, A. G.; Mansour, N. N.; Wray,
A. A.
2010AAS...21640233K Altcode:
Continuous high-resolution data of magnetic fields, Doppler velocity
and intensity from the Helioseismic and Magnetic Imager (HMI) on
SDO provide an excellent opportunity to investigate the process of
formation of sunspots and active regions and compare with theoretical
models. We analyze the HMI observations of an emerging active
region and formation of sunspots. The results show that the sunspot
formation involves accumulation of small-scale magnetic elements
into a large-scale magnetic structure and substantial changes of the
properties of convection in the region of flux emergence. We discuss
the HMI capabilities for studying these processes, and compare the
observations with results of numerical MHD simulations.
---------------------------------------------------------
Title: Radiative Hydrodynamic Simulations of Turbulent Convection
and Oscillations from Solar-Type to A-Type Stars
Authors: Kitiashvili, Irina; Kosovichev, A. G.; Saio, H.; Shibahashi,
H.; Wray, A. A.; Mansour, N. N.
2010AAS...21640012K Altcode: 2010BAAS...41..856K
We use 3D numerical radiative hydrodynamic simulations to study
convective and oscillation properties of main sequence stars from
the solar-type stars to more massive stars. The solar-type pulsators
are characterized by acoustic oscillation modes excited by turbulent
granular convection in the upper convective boundary layer. As the
stellar mass increases the convection zone shrinks, the scale and
intensity of the turbulent motions increases, providing more energy for
excitation of acoustic modes. When the stellar mass reaches about 1.6
solar masses the upper convection zone consists of two very thin layers
corresponding to H and He ionization, and in addition to the acoustic
modes the stars show strong internal gravity modes The thin convection
zone is often considered insignificant for the stellar dynamics and
variability. However, the 3D radiative hydrodynamics simulations reveal
supersonic granular-type convection of the scale significantly larger
than the solar granulation, and strong overshooting plumes penetrating
into the stable radiative zone. These plumes may contribute to the
excitation of oscillation in A-type stars.
---------------------------------------------------------
Title: The Asteroseismic Potential of Kepler: First Results for
Solar-Type Stars
Authors: Chaplin, W. J.; Appourchaux, T.; Elsworth, Y.; García,
R. A.; Houdek, G.; Karoff, C.; Metcalfe, T. S.; Molenda-Żakowicz,
J.; Monteiro, M. J. P. F. G.; Thompson, M. J.; Brown, T. M.;
Christensen-Dalsgaard, J.; Gilliland, R. L.; Kjeldsen, H.; Borucki,
W. J.; Koch, D.; Jenkins, J. M.; Ballot, J.; Basu, S.; Bazot, M.;
Bedding, T. R.; Benomar, O.; Bonanno, A.; Brandão, I. M.; Bruntt,
H.; Campante, T. L.; Creevey, O. L.; Di Mauro, M. P.; Doǧan,
G.; Dreizler, S.; Eggenberger, P.; Esch, L.; Fletcher, S. T.;
Frandsen, S.; Gai, N.; Gaulme, P.; Handberg, R.; Hekker, S.; Howe,
R.; Huber, D.; Korzennik, S. G.; Lebrun, J. C.; Leccia, S.; Martic,
M.; Mathur, S.; Mosser, B.; New, R.; Quirion, P. -O.; Régulo, C.;
Roxburgh, I. W.; Salabert, D.; Schou, J.; Sousa, S. G.; Stello, D.;
Verner, G. A.; Arentoft, T.; Barban, C.; Belkacem, K.; Benatti, S.;
Biazzo, K.; Boumier, P.; Bradley, P. A.; Broomhall, A. -M.; Buzasi,
D. L.; Claudi, R. U.; Cunha, M. S.; D'Antona, F.; Deheuvels, S.;
Derekas, A.; García Hernández, A.; Giampapa, M. S.; Goupil, M. J.;
Gruberbauer, M.; Guzik, J. A.; Hale, S. J.; Ireland, M. J.; Kiss,
L. L.; Kitiashvili, I. N.; Kolenberg, K.; Korhonen, H.; Kosovichev,
A. G.; Kupka, F.; Lebreton, Y.; Leroy, B.; Ludwig, H. -G.; Mathis, S.;
Michel, E.; Miglio, A.; Montalbán, J.; Moya, A.; Noels, A.; Noyes,
R. W.; Pallé, P. L.; Piau, L.; Preston, H. L.; Roca Cortés, T.;
Roth, M.; Sato, K. H.; Schmitt, J.; Serenelli, A. M.; Silva Aguirre,
V.; Stevens, I. R.; Suárez, J. C.; Suran, M. D.; Trampedach, R.;
Turck-Chièze, S.; Uytterhoeven, K.; Ventura, R.; Wilson, P. A.
2010ApJ...713L.169C Altcode: 2010arXiv1001.0506C
We present preliminary asteroseismic results from Kepler on three G-type
stars. The observations, made at one-minute cadence during the first
33.5 days of science operations, reveal high signal-to-noise solar-like
oscillation spectra in all three stars: about 20 modes of oscillation
may be clearly distinguished in each star. We discuss the appearance of
the oscillation spectra, use the frequencies and frequency separations
to provide first results on the radii, masses, and ages of the stars,
and comment in the light of these results on prospects for inference
on other solar-type stars that Kepler will observe.
---------------------------------------------------------
Title: Prediction of solar activity cycles by assimilating sunspot
data into a dynamo model
Authors: Kitiashvili, Irina N.; Kosovichev, Alexander G.
2010IAUS..264..202K Altcode:
Solar activity is a determining factor for space climate of the
Solar system. Thus, predicting the magnetic activity of the Sun is
very important. However, our incomplete knowledge about the dynamo
processes of generation and transport of magnetic fields inside
Sun does not allow us to make an accurate forecast. For predicting
the solar cycle properties use the Ensemble Kalman Filter (EnKF)
to assimilate the sunspot data into a simple dynamo model. This
method takes into account uncertainties of both the dynamo model and
the observed sunspot number series. The method has been tested by
calculating predictions of the past cycles using the observed annual
sunspot numbers only until the start of these cycles, and showed a
reasonable agreement between the predicted and actual data. After this,
we have calculated a prediction for the upcoming solar cycle 24, and
found that it will be approximately 30% weaker than the previous one,
confirming some previous expectations. In addition, we have investigated
the properties of the dynamo model during the solar minima, and their
relationship to the strength of the following solar cycles. The results
show that prior the weak cycles, 20 and 23, and the upcoming cycle,
24, the vector-potential of the poloidal component of magnetic field
and the magnetic helicity substantial decrease. The decrease of the
poloidal field corresponds to the well-known correlation between the
polar magnetic field strength at the minimum and the sunspot number at
the maximum. However, the correlation between the magnetic helicity and
the future cycle strength is new, and should be further investigated.
---------------------------------------------------------
Title: Implementation of Data Assimilation Methods for Dynamo Models
to Predict Solar Activity
Authors: Kitiashvili, I.; Kosovichev, A.
2009ASPC..416..511K Altcode:
Cyclic variations of solar activity are a result of a complicated
dynamo process in the convection zone. Despite the regular cyclic
variations of solar activity, the chaotic variations of sunspot number
from cycle to cycle are difficult to predict. The main reasons are the
imperfect dynamo models and deficiency of the necessary observational
data. Data assimilation methods iterate observational data and models
for possible efficient and accurate estimations of physical properties,
which cannot be observed directly. We apply the Ensemble Kalman Filter
method for assimilation of the sunspot data into a non-linear mean-field
dynamo model, which takes into variations of magnetic helicity and
parameters of the solar convection zone from helioseismology. We
present the results of application of this data assimilation method
for representation of the solar cycles and prediction of variations
of the sunspot number, and discuss potentials of data assimilation
methods for solar dynamo modeling.
---------------------------------------------------------
Title: The Origin of High-Speed Evershed Flows in Sunspots
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Wray, A. A.; Mansour,
N. N.
2009AGUFMSH23B1534K Altcode:
Radial outflow of magnetized plasma in sunspot penumbrae, the
Evershed effect, has a long history of observations and modeling,
since its discovery in 1909. There are several different approaches
for explaining this phenomenon, but these models cannot describe
various observational facts. We have carried out 3D radiative MHD
simulations of solar convection in the presence of magnetic field
of different strength and inclination. The simulation results show
that when the magnetic field is strong (1-2 kG) and highly inclined
towards the surface (by 80-85 degrees) the granular convective cells
transform into filamentary, flux-tube like structures with strong
horizontal velocities. In addition, the convective process takes the
form of traveling waves with convective cells moving in the direction
of the field inclination. The combination of these two effects, the
filamentary structure and the traveling convective waves, result in
high-speed, 4-6 km/s, plasma streams, identified in observations as
"Evershed clouds". In the case of a very strong magnetic field the
streams form coherent structures across the field. The simulation
results reproduce many observed features of the Evershed effect,
and allow us to establish links with the previous models.
---------------------------------------------------------
Title: Realistic Numerical Modeling of Solar Magnetoconvection
and Oscillations
Authors: Kitiashvili, I.; Jacoutot, L.; Kosovichev, A.
2009ASPC..415...83K Altcode: 2009arXiv0901.4369K
We have developed 3D, compressible, non-linear radiative MHD simulations
to study the influence of magnetic fields of various strengths and
geometries on the turbulent convective cells and on the excitation
mechanisms of the acoustic oscillations. The results reveal substantial
changes of the granulation structure with increased magnetic field,
and a frequency-dependent reduction in the oscillation power. These
simulation results reproduce the enhanced high-frequency acoustic
emission observed at the boundaries of active region (“acoustic halo”
phenomenon). In the presence of inclined magnetic field the solar
convection develops filamentary structure with flows concentrated
along magnetic filaments, and also exhibits behavior of running
magnetoconvective waves, resembling recent observations of the sunspot
penumbra dynamics from Hinode/SOT.
---------------------------------------------------------
Title: Numerical Modeling of Solar Convection and Oscillations in
Magnetic Regions
Authors: Kitiashvili, I. N.; Jacoutot, L.; Kosovichev, A. G.; Wray,
A. A.; Mansour, N. N.
2009AIPC.1170..569K Altcode:
Solar observations show that the spectra of turbulent convection
and oscillations significantly change in magnetic regions, resulting
in interesting phenomena, such as high-frequency “acoustic halos”
around active regions. In addition, recent observations from SOHO/MDI
revealed significant changes of the wave properties in inclined magnetic
field regions of sunspots, which affect helioseismic inferences. We
use realistic 3D radiative MHD numerical simulations to investigate
properties of solar convection and excitation and propagation of
oscillations in magnetic regions. A new feature of these simulations is
implementation of a dynamic sub-grid turbulence model, which allows more
accurate description of turbulent dissipation and wave excitation. We
present the simulation results for a wide range of the field strength
and inclination in the top 6 Mm layer of the convection zone. The
results show interesting and unexpected effects in the dynamics and
large-scale organization of the magnetoconvection (including traveling
waves and shearing flows), and also changes in the excitation properties
and spectrum of oscillations, suggesting an explanation of the acoustic
“halos” observed above the acoustic cut-off frequency.
---------------------------------------------------------
Title: Traveling Waves of Magnetoconvection and the Origin of the
Evershed Effect in Sunspots
Authors: Kitiashvili, I. N.; Kosovichev, A. G.; Wray, A. A.; Mansour,
N. N.
2009ApJ...700L.178K Altcode: 2009arXiv0904.3599K
Discovered in 1909, the Evershed effect represents strong mass outflows
in sunspot penumbra, where the magnetic field of sunspots is filamentary
and almost horizontal. These flows play an important role in sunspots
and have been studied in detail using large ground-based and space
telescopes, but the basic understanding of its mechanism is still
missing. We present results of realistic numerical simulations of
the Sun's subsurface dynamics, and argue that the key mechanism of
this effect is in nonlinear magnetoconvection that has properties
of traveling waves in the presence of a strong, highly inclined
magnetic field. The simulations reproduce many observed features of
the Evershed effect, including the high-speed "Evershed clouds," the
filamentary structure of the flows, and the nonstationary quasiperiodic
behavior. The results provide a synergy of previous theoretical models
and lead to an interesting prediction of a large-scale organization
of the outflows.
---------------------------------------------------------
Title: Realistic 3D MHD Simulations of the Evershed Effect
Authors: Kitiashvili, Irina; Kosovichev, A. G.; Wray, A. A.; Mansour,
N. N.
2009SPD....40.0906K Altcode:
Effect of the horizontal radial outflow in a sunspot penumbra (called
"Evershed effect") has a 100-year history of investigations, but its
physical nature is not clear yet. The Evershed flows begin at bright
penumbral grains and propagate outward along penumbra filaments
with the mean velocity of 1 - 2 km/s. High-resolution observations
reveal that the Evershed flows are non-stationary, and that the
strongest, 4 - 5 km/s, flows appear in quasi-periodic patches,
"Evershed clouds". To study the nature of the Evershed effect we
simulate behavior of convective motions in the presence strong
inclined magnetic field. We use a 3D radiative non-linear MHD code,
which describes realistic physical properties: compressible fluid
flow in a highly stratified and magnetized plasma, 3D multi-group
radiative energy transfer, a real-gas equation of state, and sub-grid
scale turbulence models. We present a set of numerical experiments,
which include the upper solar convection zone and lower atmosphere for
different magnetic field strength (600 - 2000 Gauss) and inclination
(0 - 90 degrees). The results show the development of filamentary
magnetic structures and systematic flows in the direction of field
inclination, strongly resembling the Evershed effect in penumbra. In
particular, the simulations reproduce the high-speed "Evershed clouds",
relationships between the flow velocity and the field strength and
inclination, and other observational characteristics. We discuss the
simulation results in the context of previously models, such as the
embedded flux tube model, the magnetic gap model and the overturning
magnetoconvection model, and argue that the physical mechanism of
the Evershed effect is in a non-linear interaction between the narrow
overturning convective motions and traveling magnetoconvection waves,
formed in highly inclined strong magnetic field regions.
---------------------------------------------------------
Title: Prediction of solar magnetic cycles by a data assimilation
method
Authors: Kitiashvili, Irina N.; Kosovichev, Alexander G.
2009IAUS..259..235K Altcode:
We consider solar magnetic activity in the context of sunspot number
variations, as a result of a non-linear oscillatory dynamo process. The
apparent chaotic behavior of the 11-year sunspot cycles and undefined
errors of observations create uncertainties for predicting the
strength and duration of the cycles. Uncertainties in dynamo model
parameters create additional difficulties for the forecasting. Modern
data assimilation methods allow us to assimilate the observational
data into the models for possible efficient and accurate estimations
of the physical properties, which cannot be observed directly, such as
the internal magnetic fields and helicity. We apply the Ensemble Kalman
Filter method to a low-order non-linear dynamo model, which takes into
account variations of the turbulent magnetic helicity and reproduces
basic characteristics of the solar cycles. We investigate the predictive
capabilities of this approach, and present test results for prediction
of the previous cycles and a forecast of the next solar cycle 24.
---------------------------------------------------------
Title: Magnetic and tidal interactions in spin evolution of exoplanets
Authors: Kitiashvili, Irina N.
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.
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.
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.
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.
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.
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. &
Dyn. Astr., 68, 13.
---------------------------------------------------------
Title: Modeling of evolution of the rotational axis of “hot
Jupiter” planets under tidal perturbations
Authors: Kitiashvili, Irina
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.
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
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.
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.
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.
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.
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.
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
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.
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| < |γ| to |α| = |γ|. Bifurcations of the second
type are possible, if a ratio of parameters from |α| = |γ| will pass
to |α| > |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.
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 > 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.
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
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Title: The Moon in the Russian scientific-educational project:
Kazan-GeoNa-2010
Authors: Gusev, A.; Kitiashvili, I.; Petrova, N.
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.
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
2004IAUS..202..187G Altcode:
No abstract at ADS
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Title: Extra-solar planets: from direct rotation into reverse rotation
Authors: Kitiashvili, Irina; Gusev, Alexander
2004IAUS..202..205K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Inner chandler wobble and free core nutation of pulsar
Authors: Gusev, A.; Kitiashvili, I.
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.
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.
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 < 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.
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.
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
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.
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 &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.
