Author name code: ustyugov ADS astronomy entries on 2022-09-14 author:"Ustyugov, Sergey D." ------------------------------------------------------------------------ Title: Dust-Polarization Maps for Local Interstellar Turbulence Authors: Kritsuk, Alexei G.; Flauger, Raphael; Ustyugov, Sergey D. Bibcode: 2018PhRvL.121b1104K Altcode: 2017arXiv171111108K We show that simulations of magnetohydrodynamic turbulence in the multiphase interstellar medium yield an E /B ratio for polarized emission from Galactic dust in broad agreement with recent Planck measurements. In addition, the B -mode spectra display a scale dependence that is consistent with observations over the range of scales resolved in the simulations. The simulations present an opportunity to understand the physical origin of the E /B ratio and a starting point for more refined models of Galactic emission of use for both current and future cosmic microwave background experiments. Title: The structure and statistics of interstellar turbulence Authors: Kritsuk, A. G.; Ustyugov, S. D.; Norman, M. L. Bibcode: 2017NJPh...19f5003K Altcode: 2017arXiv170501912K We explore the structure and statistics of multiphase, magnetized ISM turbulence in the local Milky Way by means of driven periodic box numerical MHD simulations. Using the higher order-accurate piecewise-parabolic method on a local stencil (PPML), we carry out a small parameter survey varying the mean magnetic field strength and density while fixing the rms velocity to observed values. We quantify numerous characteristics of the transient and steady-state turbulence, including its thermodynamics and phase structure, kinetic and magnetic energy power spectra, structure functions, and distribution functions of density, column density, pressure, and magnetic field strength. The simulations reproduce many observables of the local ISM, including molecular clouds, such as the ratio of turbulent to mean magnetic field at 100 pc scale, the mass and volume fractions of thermally stable Hi, the lognormal distribution of column densities, the mass-weighted distribution of thermal pressure, and the linewidth-size relationship for molecular clouds. Our models predict the shape of magnetic field probability density functions (PDFs), which are strongly non-Gaussian, and the relative alignment of magnetic field and density structures. Finally, our models show how the observed low rates of star formation per free-fall time are controlled by the multiphase thermodynamics and large-scale turbulence. Title: Realistic Magnetohydrodynamical Simulation of Solar Local Supergranulation Authors: Ustyugov, S. D. Bibcode: 2012ASPC..454...73U Altcode: Three-dimensional numerical simulations of solar surface magnetoconvection using realistic model physics are conducted. The thermal structure of convective motions into the upper radiative layers of the photosphere, the main scales of convective cells and the penetration depths of convection are investigated. We take part of the solar photosphere with size of 60×60 Mm in horizontal direction and by depth 20 Mm from level of the visible solar surface. We use a realistic initial model of the Sun and apply equation of state and opacities of stellar matter. The equations of fully compressible radiation magnetohydrodynamics with dynamical viscosity and gravity are solved. We apply:

1) Piecewise Parabolic Method on a Local Stecil (PPML) for the magnetohydrodynamics,

2) conservative method of characteristic for the radiative transfer,

3) dynamical viscosity from subgrid scale modeling.

In simulation we take uniform two-dimesional grid in gorizontal plane and nonuniform grid in vertical direction with number of cells 600×600×204. We use 512 processors with distributed memory multiprocessors on supercomputer MVS-100k in the Joint Computational Centre of the Russian Academy of Sciences. Title: The Two States of Star-forming Clouds Authors: Collins, David C.; Kritsuk, Alexei G.; Padoan, Paolo; Li, Hui; Xu, Hao; Ustyugov, Sergey D.; Norman, Michael L. Bibcode: 2012ApJ...750...13C Altcode: 2012arXiv1202.2594C We examine the effects of self-gravity and magnetic fields on supersonic turbulence in isothermal molecular clouds with high-resolution simulations and adaptive mesh refinement. These simulations use large root grids (5123) to capture turbulence and four levels of refinement to follow the collapse to high densities, for an effective resolution of 81923. Three Mach 9 simulations are performed, two super-Alfvénic and one trans-Alfvénic. We find that gravity splits the clouds into two populations, one low-density turbulent state and one high-density collapsing state. The low-density state exhibits properties similar to non-self-gravitating in this regime, and we examine the effects of varied magnetic field strength on statistical properties: the density probability distribution function is approximately lognormal, the velocity power spectral slopes decrease with decreasing mean field strength, the alignment between velocity and magnetic field increases with the field, and the magnetic field probability distribution can be fitted to a stretched exponential. The high-density state is well characterized by self-similar spheres: the density probability distribution is a power law, collapse rate decreases with increasing mean field, density power spectra have positive slopes, P(ρ, k)vpropk, thermal-to-magnetic pressure ratios are roughly unity for all mean field strengths, dynamic-to-magnetic pressure ratios are larger than unity for all mean field strengths, the magnetic field distribution follows a power-law distribution. The high Alfvén Mach numbers in collapsing regions explain the recent observations of magnetic influence decreasing with density. We also find that the high-density state is typically found in filaments formed by converging flows, consistent with recent Herschel observations. Possible modifications to existing star formation theories are explored. The overall trans-Alfvénic nature of star-forming clouds is discussed. Title: Comparing Numerical Methods for Isothermal Magnetized Supersonic Turbulence Authors: Kritsuk, Alexei G.; Nordlund, Åke; Collins, David; Padoan, Paolo; Norman, Michael L.; Abel, Tom; Banerjee, Robi; Federrath, Christoph; Flock, Mario; Lee, Dongwook; Li, Pak Shing; Müller, Wolf-Christian; Teyssier, Romain; Ustyugov, Sergey D.; Vogel, Christian; Xu, Hao Bibcode: 2011ApJ...737...13K Altcode: 2011arXiv1103.5525K Many astrophysical applications involve magnetized turbulent flows with shock waves. Ab initio star formation simulations require a robust representation of supersonic turbulence in molecular clouds on a wide range of scales imposing stringent demands on the quality of numerical algorithms. We employ simulations of supersonic super-Alfvénic turbulence decay as a benchmark test problem to assess and compare the performance of nine popular astrophysical MHD methods actively used to model star formation. The set of nine codes includes: ENZO, FLASH, KT-MHD, LL-MHD, PLUTO, PPML, RAMSES, STAGGER, and ZEUS. These applications employ a variety of numerical approaches, including both split and unsplit, finite difference and finite volume, divergence preserving and divergence cleaning, a variety of Riemann solvers, and a range of spatial reconstruction and time integration techniques. We present a comprehensive set of statistical measures designed to quantify the effects of numerical dissipation in these MHD solvers. We compare power spectra for basic fields to determine the effective spectral bandwidth of the methods and rank them based on their relative effective Reynolds numbers. We also compare numerical dissipation for solenoidal and dilatational velocity components to check for possible impacts of the numerics on small-scale density statistics. Finally, we discuss the convergence of various characteristics for the turbulence decay test and the impact of various components of numerical schemes on the accuracy of solutions. The nine codes gave qualitatively the same results, implying that they are all performing reasonably well and are useful for scientific applications. We show that the best performing codes employ a consistently high order of accuracy for spatial reconstruction of the evolved fields, transverse gradient interpolation, conservation law update step, and Lorentz force computation. The best results are achieved with divergence-free evolution of the magnetic field using the constrained transport method and using little to no explicit artificial viscosity. Codes that fall short in one or more of these areas are still useful, but they must compensate for higher numerical dissipation with higher numerical resolution. This paper is the largest, most comprehensive MHD code comparison on an application-like test problem to date. We hope this work will help developers improve their numerical algorithms while helping users to make informed choices about choosing optimal applications for their specific astrophysical problems. Title: Magnetic Fields in Molecular Clouds Authors: Padoan, Paolo; Lunttila, Tuomas; Juvela, Mika; Nordlund, Åke; Collins, David; Kritsuk, Alexei; Normal, Michael; Ustyugov, Sergey Bibcode: 2011IAUS..271..187P Altcode: Supersonic magneto-hydrodynamic (MHD) turbulence in molecular clouds (MCs) plays an important role in the process of star formation. The effect of the turbulence on the cloud fragmentation process depends on the magnetic field strength. In this work we discuss the idea that the turbulence is super-Alfvénic, at least with respect to the cloud mean magnetic field. We argue that MCs are likely to be born super-Alfvénic. We then support this scenario based on a recent simulation of the large-scale warm interstellar medium turbulence. Using small-scale isothermal MHD turbulence simulation, we also show that MCs may remain super-Alfvénic even with respect to their rms magnetic field strength, amplified by the turbulence. Finally, we briefly discuss the comparison with the observations, suggesting that super-Alfvénic turbulence successfully reproduces the Zeeman measurements of the magnetic field strength in dense MC clouds. Title: Validated helioseismic inversions for 3D vector flows Authors: Švanda, M.; Gizon, L.; Hanasoge, S. M.; Ustyugov, S. D. Bibcode: 2011A&A...530A.148S Altcode: 2011arXiv1104.4083S Context. According to time-distance helioseismology, information about internal fluid motions is encoded in the travel times of solar waves. The inverse problem consists of inferring three-dimensional vector flows from a set of travel-time measurements. While only few tests of the inversions have been done, it is known that the retrieval of the small-amplitude vertical flow velocities is problematic. A thorough study of biases and noise has not been carried out in realistic conditions.
Aims: Here we investigate the potential of time-distance helioseismology to infer three-dimensional convective velocities in the near-surface layers of the Sun. We developed a new subtractive optimally localised averaging (SOLA) code suitable for pipeline pseudo-automatic processing. Compared to its predecessor, the code was improved by accounting for additional constraints in order to get the right answer within a given noise level. The main aim of this study is to validate results obtained by our inversion code.
Methods: We simulate travel-time maps using a snapshot from a numerical simulation of solar convective flows, realistic Born travel-time sensitivity kernels, and a realistic model of travel-time noise. These synthetic travel times are inverted for flows and the results compared with the known input flow field. Additional constraints are implemented in the inversion: cross-talk minimization between flow components and spatial localization of inversion coefficients.
Results: Using modes f, p1 through p4, we show that horizontal convective flow velocities can be inferred without bias, at a signal-to-noise ratio greater than one in the top 3.5 Mm, provided that observations span at least four days. The vertical component of velocity (vz), if it were to be weak, is more difficult to infer and is seriously affected by cross-talk from horizontal velocity components. We emphasise that this cross-talk must be explicitly minimised in order to retrieve vz in the top 1 Mm. We also show that statistical averaging over many different areas of the Sun allows for reliably measuring of average properties of all three flow components in the top 5.5 Mm of the convection zone.

Figures 16-28 are available in electronic form at http://www.aanda.org Title: Interstellar Turbulence and Star Formation Authors: Kritsuk, Alexei G.; Ustyugov, Sergey D.; Norman, Michael L. Bibcode: 2011IAUS..270..179K Altcode: 2010arXiv1011.2177K We provide a brief overview of recent advances and outstanding issues in simulations of interstellar turbulence, including isothermal models for interior structure of molecular clouds and larger-scale multiphase models designed to simulate the formation of molecular clouds. We show how self-organization in highly compressible magnetized turbulence in the multiphase ISM can be exploited in simple numerical models to generate realistic initial conditions for star formation. Title: Realistic magnetohydrodynamical simulation of solar local supergranulation Authors: Ustyugov, Sergey D. Bibcode: 2010PhST..142a4031U Altcode: 2009arXiv0906.5232U Three-dimensional numerical simulations of solar surface magnetoconvection using realistic model physics are conducted. The thermal structure of convective motions into the upper radiative layers of the photosphere, the main scales of convective cells and the penetration depths of convection are investigated. We take part of the solar photosphere with a size of 60×60 Mm2 in the horizontal direction and of depth 20 Mm from the level of the visible solar surface. We use a realistic initial model of the sun and apply the equation of state and opacities of stellar matter. The equations of fully compressible radiation magnetohydrodynamics (MHD) with dynamical viscosity and gravity are solved. We apply (i) the conservative total variation diminishing (TVD) difference scheme for MHD, (ii) the diffusion approximation for radiative transfer and (iii) dynamical viscosity from subgrid-scale modeling. In simulation, we take a uniform two-dimensional grid in the horizontal plane and a nonuniform grid in the vertical direction with the number of cells being 600×600×204. We use 512 processors with distributed memory multiprocessors on the supercomputer MVS-100k at the Joint Computational Centre of the Russian Academy of Sciences. Title: Self-organization in Turbulent Molecular Clouds: Compressional Versus Solenoidal Modes Authors: Kritsuk, A. G.; Ustyugov, S. D.; Norman, M. L.; Padoan, P. Bibcode: 2010ASPC..429...15K Altcode: 2009arXiv0912.0546K We use three-dimensional numerical simulations to study self-organization in supersonic turbulence in molecular clouds. Our numerical experiments describe decaying and driven turbulent flows with an isothermal equation of state, sonic Mach numbers from 2 to 10, and various degrees of magnetization. We focus on properties of the velocity field and, specifically, on the level of its potential (dilatational) component as a function of turbulent Mach number, magnetic field strength, and scale. We show how extreme choices of either purely solenoidal or purely potential forcing can reduce the extent of the inertial range in the context of periodic box models for molecular cloud turbulence. We suggest an optimized forcing to maximize the effective Reynolds number in numerical models. Title: MHD Turbulence In Star-Forming Clouds Authors: Padoan, P.; Kritsuk, A. G.; Lunttila, T.; Juvela, M.; Nordlund, A.; Norman, M. L.; Ustyugov, S. D. Bibcode: 2010AIPC.1242..219P Altcode: Supersonic magneto-hydrodynamic (MHD) turbulence in molecular clouds (MCs) plays an important role in the process of star formation. The effect of the turbulence on the cloud fragmentation process depends on the magnetic field strength. In this work we discuss the idea that the turbulence is super-Alfvénic, at least with respect to the cloud mean magnetic field. We argue that MCs are likely to be born super-Alfvénic. We then support this scenario based on a recent simulation of the large-scale warm interstellar medium turbulence. Using small-scale isothermal MHD turbulence simulation, we also show that MCs may remain super-Alfvénic even with respect to their rms magnetic field strength, amplified by the turbulence. Finally, we briefly discuss the comparison with the observations, suggesting that super-Alfvénic turbulence successfully reproduces the Zeeman measurements of the magnetic field strength in dense MC clouds. Title: Realistic Magnetohydrodynamical Simulations of Local Solar Supergranulation Authors: Ustyugov, S. D. Bibcode: 2009ASPC..416..427U Altcode: Three-dimensional numerical simulations of solar surface magnetoconvection using realistic model physics are conducted. The thermal structure of convective motions into the upper radiative layers of the photosphere, the main scales of convective cells and the penetration depths of convection are investigated. We take a part of the solar photosphere with horizontal size 60 × 60 Mm by depth 20 Mm from the level of the visible solar surface. We use a realistic initial model of the Sun and apply the equation of state with the opacities of stellar matter. The equations of fully compressible radiative magnetohydrodynamics with dynamical viscosity and gravity are solved. We apply 1) a conservative TVD difference scheme for the magnetohydrodynamics, 2) the diffusion approximation for radiative transfer, and 3) dynamical viscosity from subgrid-scale modeling. In the simulations, we take a uniform two-dimensional grid in the horizontal plane and a nonuniform grid in depth with 600 × 600 × 204 pixels. We use 512 processors with distributed-memory multiprocessors on supercomputer MVS-100k in the Joint Computational Center of the Russian Academy of Sciences. Title: Piecewise parabolic method on a local stencil for magnetized supersonic turbulence simulation Authors: Ustyugov, Sergey D.; Popov, Mikhail V.; Kritsuk, Alexei G.; Norman, Michael L. Bibcode: 2009JCoPh.228.7614U Altcode: 2009arXiv0905.2960U Stable, accurate, divergence-free simulation of magnetized supersonic turbulence is a severe test of numerical MHD schemes and has been surprisingly difficult to achieve due to the range of flow conditions present. Here we present a new, higher order-accurate, low dissipation numerical method which requires no additional dissipation or local “fixes” for stable execution. We describe PPML, a local stencil variant of the popular PPM algorithm for solving the equations of compressible ideal magnetohydrodynamics. The principal difference between PPML and PPM is that cell interface states are evolved rather that reconstructed at every timestep, resulting in a compact stencil. Interface states are evolved using Riemann invariants containing all transverse derivative information. The conservation laws are updated in an unsplit fashion, making the scheme fully multidimensional. Divergence-free evolution of the magnetic field is maintained using the higher order-accurate constrained transport technique of Gardiner and Stone. The accuracy and stability of the scheme is documented against a bank of standard test problems drawn from the literature. The method is applied to numerical simulation of supersonic MHD turbulence, which is important for many problems in astrophysics, including star formation in dark molecular clouds. PPML accurately reproduces in three-dimensions a transition to turbulence in highly compressible isothermal gas in a molecular cloud model. The low dissipation and wide spectral bandwidth of this method make it an ideal candidate for direct turbulence simulations. Title: Simulating supersonic turbulence in magnetized molecular clouds Authors: Kritsuk, Alexei G.; Ustyugov, Sergey D.; Norman, Michael L.; Padoan, Paolo Bibcode: 2009JPhCS.180a2020K Altcode: 2009arXiv0908.0378K We present results of large-scale three-dimensional weakly magnetized supersonic turbulence simulations with an isothermal equation of state at grid resolutions up to 10243 cells with the Piecewise Parabolic Method on a Local Stencil. The turbulence is driven by a large-scale isotropic solenoidal force in a periodic computational domain and fully develops in a few flow crossing times. We then evolve the flow for a number of flow crossing times and analyze various statistical properties of the saturated turbulent state. We show that the energy transfer rate in the inertial range of scales is surprisingly close to a constant, indicating that Kolmogorov's phenomenology for incompressible turbulence can be extended to magnetized supersonic flows. We also discuss numerical dissipation effects and convergence of different turbulence diagnostics as grid resolution refines from 2563 to 10243 cells. Title: Simulations of Supersonic Turbulence in Molecular Clouds: Evidence for a New Universality Authors: Kritsuk, A. G.; Ustyugov, S. D.; Norman, M. L.; Padoan, P. Bibcode: 2009ASPC..406...15K Altcode: 2009arXiv0902.3222K We use three-dimensional simulations to study the statistics of supersonic turbulence in molecular clouds. Our numerical experiments describe driven turbulent flows with an isothermal equation of state, Mach numbers around 10, and various degrees of magnetization. We first support the so-called 1/3-rule of \cite{kritsuk...07a} with our new data from a larger 20483 simulation. We then attempt to extend the 1/3-rule to supersonic MHD turbulence and get encouraging preliminary results based on a set of 5123 simulations. Our results suggest an interesting new approach to tackle universal scaling relations and intermittency in supersonic MHD turbulence. Title: Simulations of Supersonic Turbulence in Magnetized Molecular Clouds Authors: Kritsuk, Alexei; Ustyugov, S. D.; Norman, M. L.; Padoan, P. Bibcode: 2009AAS...21348510K Altcode: 2009BAAS...41R.457K We report first results from three-dimensional numerical simulations of supersonic magnetohydrodynamic (MHD) turbulence with the Piecewise Parabolic Method on Local Stencil (PPML, Popov & Ustyugov 2008). PPML is a multi-dimensional higher-order Godunov scheme that preserves monotonicity of solutions in the vicinity of strong discontinuities, and maintains zero divergence of the magnetic field through a constrained transport approach. The method is very accurate, extremely low-dissipation, and perfectly stable for super-Alfv'enic turbulence, where many other MHD schemes experience difficulties.

We solve the equations of ideal MHD in a periodic domain on Cartesian grids of up to 1024^3 points. Our models describe driven turbulence at Mach 10 and assume an isothermal equation of state to mimic the conditions in molecular clouds. We start with uniform gas density and uniform magnetic field aligned with one of the coordinate directions and apply large-scale solenoidal force to develop a saturated turbulent state in a statistical equilibrium. Depending on the initial field strength, B_0, a saturation is reached within three-to-six dynamical times of driving. We then collect the turbulence statistics and compare those for different models.

As predicted by Kritsuk et al. (2007), for weak initial fields we get Kolmogorov spectra for the density-weighted velocities ρ^{1/3}u. With stronger fields, the spectra tend to get shallower, but the -5/3 scaling still appears to hold (even in these highly compressible, magnetized flows) for a combination of kinetic and magnetic variables constructed in the spirit of Politano & Pouquet (1998). We compare PDFs, structure functions, and power spectra from runs with different B_0 and discuss the signature of magnetic field in the statistical properties of molecular cloud turbulence and their role in overall flow dynamics.

This research was partially supported by NSF grants AST0607675, AST0808184, and by NRAC allocation MCA07S014. We utilized computing resources provided by NICS, TACC, and SDSC. Title: Realistic Simulation of Local Solar Supergranulation Authors: Ustyugov, Sergey D. Bibcode: 2008AIPC.1043..234U Altcode: 2008arXiv0806.1337U I represent results three-dimensional numerical simulation of solar surface convection on scales local supergranulation with realistic model physics. I study thermal structure of convective motions in photosphere, the range of convection cell sizes and the penetration depths of convection. A portion of the solar photosphere extending 100×100 Mm horizontally and from 0 Mm down to 20 Mm below the visible surface is considered. I take equation of state and opacities of stellar matter and distribution with radius of all physical variables from Solar Standard Model. The equations of fully compressible radiation hydrodynamics with dynamical viscosity and gravity are solved. The high order conservative PPML difference scheme for the hydrodynamics, the method of characteristic for the radiative transfer and dynamical viscosity from subgrid scale modeling are applied. The simulations are conducted on a uniform horizontal grid of 1000×1000, with 168 nonuniformly spaced vertical grid points, on 256 processors with distributed memory multiprocessors on supercomputer MVS5000 in Computational Center of Russian Academy of Sciences. Title: Large Eddy Simulation of Solar Photosphere Convection with Realistic Physics Authors: Ustyugov, S. D. Bibcode: 2008ASPC..383...43U Altcode: 2007arXiv0710.3023U Three-dimensional large eddy simulations of solar surface convection using realistic model physics are conducted. The thermal structure of convective motions into the upper radiative layers of the photosphere, the range of convection cell sizes, and the penetration depths of convection are investigated. A portion of the solar photosphere and the upper layers of the convection zone, a region extending 60× 60 Mm horizontally from 0 Mm down to 20 Mm below the visible surface, is considered. We start from a realistic initial model of the Sun with an equation of state and opacities of stellar matter. The equations of fully compressible radiation hydrodynamics with dynamical viscosity and gravity are solved. We use: 1) a high order conservative TVD scheme for the hydrodynamics, 2) the diffusion approximation for the radiative transfer, 3) dynamical viscosity from subgrid scale modeling. The simulations are conducted on a uniform horizontal grid of 600× 600, with 168 nonuniformly spaced vertical grid points, on 144 processors with distributed memory multiprocessors on supercomputer MBC-1500 in the Computational Centre of the Russian Academy of Sciences. Title: Numerical Simulation of Solar Magnetoconvection with Realistic Physics Authors: Ustyugov, Sergey D. Bibcode: 2007AIPC..895..109U Altcode: Three-dimensional magnetohydrodynamics numerical simulation of solar surface convection on scale of supergranulation using realistic model physics is conducted. The effects of magnetic fields on thermal structure of convective motions into radiative layers, the range of convection cell sizes and penetration depths of convection are investigated. We simulate a part of the solar photosphere and the upper layers of the convection zone, a region extending on 30 × 30 Mm horizontally from 0 Mm down to 18 Mm below the visible surface. Equations of the compressible radiation magnetohydrodynamics with dynamical viscosity and gravity are solved. We used: 1) distribution by radius of all variables from realistic model of Sun, 2) equation of state and opacities of matter for stellar conditions, 3) high order conservative TVD scheme for solution of the magnetohydrodynamics equations, 4) diffusion approximation for radiative transfer solution, 5) calculation dynamical viscosity applying subgrid scale modelling. Simulations are conducted on horizontal uniform grid of 320 × 320 and with 144 nonuniformly spaced vertical grid points on the 128 processors of super-computer with distributed memory multiprocessors in Russian Academy of Sciences in Moscow. Title: Mechanisms of supernova explosions Authors: Chechetkin, V. M.; Popov, M. V.; Ustyugov, S. D. Bibcode: 2007acag.conf..179C Altcode: No abstract at ADS Title: Magnetohydrodynamic Simulation of Solar Supergranulation Authors: Ustyugov, S. D. Bibcode: 2006ASPC..359..226U Altcode: 2006astro.ph..5627U Three-dimensional magnetohydrodynamical large eddy simulations of solar surface convection using realistic model physics are conducted. The effects of magnetic fields on the thermal structure of convective motions into radiative layers, the range of convection cell sizes and penetration depths of convection are investigated. We simulate a portion of the solar photosphere and the upper layers of the convection zone, a region extending 30× 30 Mm horizontally from 0 Mm down to 18 Mm below the visible surface. We solve equations of the fully compressible radiation magnetohydrodynamics with dynamical viscosity and gravity. For numerical simulation we use: 1) realistic initial model of Sun and equation of state and opacities of stellar matter, 2) high order conservative TVD scheme for solution magnetohydrodynamics, 3) diffusion approximation for radiative transfer 4) dynamical viscosity from subgrid scale modeling. Simulations are conducted on a horizontal uniform grid of 320 × 320 and with 144 nonuniformly spaced vertical grid points on 128 processors of a supercomputer MBC-1500 with distributed memory multiprocessors in Russian Academy of Sciences. Title: Three Dimensional Numerical Simulation of MHD Solar Convection on Multiproccesor Supercomputer Systems Authors: Ustyugov, S. D. Bibcode: 2006ASPC..354..115U Altcode: Three-dimensional magnetohydrodynamical large eddy simulations of solar surface convection using realistic model physics are conducted. The effects of magnetic fields on the thermal structure of convective motions into radiative layers, the range of convection cell sizes and the penetration depths of convection are investigated. We simulate a portion of the solar photosphere and the upper layers of the convection zone, a region extending 18 × 18 Mm horizontally from 0 Mm down to 18 Mm below the visible surface. We solve the equations of fully compressible radiation magnetohydrodynamics with dynamical viscosity and gravity. We use: 1) a high order conservative TVD scheme for the magnetohydrodynamics, 2) the diffusion approximation for the radiative transfer, 3) dynamical viscosity from subgrid scale modeling. We start from a realistic initial model of Sun with an equation of state and opacities of stellar matter. The simulations are conducted on a uniform horizontal grid of 192 × 192, with 144 nonuniformly spaced vertical grid points, on 64 processors with distributed memory multiprocessors. Title: Subsurface flows from numerical simulations compared with flows from ring analysis Authors: Ustyugov, S.; Komm, R.; Burtseva, O.; Howe, R.; Kholikov, S. Bibcode: 2006ESASP.624E..54U Altcode: 2006soho...18E..54U No abstract at ADS Title: Three Dimensional Numerical Simulation of Solar Convection on Multiproccesors Supercomputer Systems Authors: Ustyugov, S. D. Bibcode: 2005ASPC..346..357U Altcode: Three-dimensional large eddy simulations of solar surface convection using realistic model physics is conducted. Thermal structure of convective motions into radiative layers and the range of convection cell sizes is investigated. We simulate a some portion of the solar photosphere and the upper layers of the convection zone, a region extending 18 x 18 Mm horizontally from 0 Mm down to 18 Mm below the visible surface. We solve equations of the fully compressible radiation hydrodynamics with dynamical viscosity and gravity. For numerical simulation we use: 1) realistic initial model of Sun and equation of state and opacities of stellar matter, 2) high order conservative TVD scheme for solution hydrodynamics, 3) diffusion approximation for solution radiative transfer in convective layers of Sun, 4) calculation dynamical viscosity from subgrid scale modelling. Simulations are conducted on horizontal uniform grid of 192 x 192 and with 144 non-uniformly spaced vertical grid points on the 64 processors of supercomputer with distributed memory multiprocesseres (two Alpha 21264/667 MHz in node, memory 1 Gb in node, SAN Myrinet to communication, 512 nodes). Title: Boundary Conditions for Simulations of the Thermal Outburst of a Type Ia Supernova Authors: Popov, M. V.; Ustyugov, S. D.; Chechetkin, V. M. Bibcode: 2005ARep...49..450P Altcode: We present a technique to calculate the boundary conditions for simulations of the development of large-scale convective instability in the cores of rotating white-dwarf progenitors of type Ia supernovae. The hydrodynamical equations describing this situation are analyzed. We also study the impact of the boundary conditions on the development of the thermal outburst. Title: Numerical Simulation of Hydrodynamic Instability in a Rotating Protoneutron Star by Supernova Explosion II Type Authors: Ustyugov, S. D. Bibcode: 2005tsra.conf..567U Altcode: Large-scale convective instability owing to the neutronization of matter in a protoneutron star during the collapse of star with low initial entropy are considered. The 3D hydrodynamic calculation on nested grids with three level shows that large-scale bubbles of hot matter with size 106 cm arise to surface neutrinosphere. When the bubbles reaches low density, the neutrinos contained in matter freely escape from it in the regime of volume radiation. The characteristic time of this process is equalled to 3.5 ms. The shock from the initial bounce when the collapse in the stellar core stops will then be supported by the neutrino emission, resulting in the ejection of an envelope. In rotating protoneutron star the large scale bubbles come to the surface of the stellar core along the axis of rotation. Neutrino with energy 30-50 MeV are contained in the bubbles. Calculations shows that time of neutrino emission form such bubble is equal near 1 ms with mean energy of neutrino 30-40 MeV. Title: Development of the Geometric Structure of the Thermonuclear-Deflagration Front in Type Ia Supernovae Authors: Popov, M. V.; Ustyugov, S. D.; Chechetkin, V. M. Bibcode: 2004ARep...48..921P Altcode: Three-dimensional hydrodynamical simulations of the development of a large-scale instability accompanying deflagration in the degenerate cores of rotating white dwarfs—progenitors of type-Ia supernovae—are presented. The numerical algorithm used is described in detail. An explicit, conservative, Godunov-type TVD difference scheme was employed for the computations. Large-scale convective processes are important as the deflagration front propagates. The supernova explosion is strongly nonspherically symmetric; a large-scale front structure emerges and propagates most rapidly along the rotational axis. The arrival of fresh thermonuclear fuel to the central region of the core can result in flares and the destruction of the core. Title: Three Dimensional Numerical Simulations of Near Surface Solar Convection with Realistic Physics Authors: Ustyugov, S. D. Bibcode: 2004ESASP.559..660U Altcode: 2004soho...14..660U No abstract at ADS Title: Numerical simulation of large-scale convection in type-II supernovae explosion Authors: Chechetkin, V. M.; Popov, M. V.; Ustyugov, S. D. Bibcode: 2002NCimB.117.1027C Altcode: No abstract at ADS Title: Simulation of Neutrino Transport by Large-Scale Convective Instability in a Proto-Neutron Star Authors: Suslin, V. M.; Ustyugov, S. D.; Chechetkin, V. M.; Churkina, G. P. Bibcode: 2001ARep...45..241S Altcode: Neutrino transfer via convective flow to the surface of a proto-neutron star is numerically simulated. The evolution of the neutrino distribution in a heated region rising from the center of the proto-neutron star to its surface is simulated using a kinetic equation with a Uehling-Uhlenbeck collision integral in a uniform, isotropic approximation. The composition of the matter in the region under consideration changes due to the “burning” of electrons and protons by beta processes. The simulation results enable the estimation of the characteristic time required for the rising medium to become optically thin to neutrinos and the characteristic spectrum of the neutrinos that are emitted. Title: Supernovae explosions in the presence of large-scale convective instability in a rotating protoneutron star Authors: Ustyugov, S. D.; Chechetkin, V. M. Bibcode: 1999ARep...43..718U Altcode: No abstract at ADS Title: Gravitational radiation from a rotating protoneutron star Authors: Sazhin, M. V.; Ustyugov, S. D.; Chechetkin, V. M. Bibcode: 1998JETP...86..629S Altcode: No abstract at ADS Title: On the neutrino mechanism of supernova explosions Authors: Chechetkin, V. M.; Ustyugov, S. D.; Gorbunov, A. A.; Polezhaev, V. I. Bibcode: 1997AstL...23...30C Altcode: 1997PAZh...23...34C No abstract at ADS Title: Gravity waves accompanying supernova explosions Authors: Sazhin, M. V.; Ustyugov, S. D.; Chechetkin, V. M. Bibcode: 1996JETPL..64..871S Altcode: No abstract at ADS Title: Gravity waves accompanying supernova explosions Authors: Sazhin, M. V.; Ustyugov, S. D.; Chechetkin, V. M. Bibcode: 1996ZhPmR..64..817S Altcode: No abstract at ADS Title: On the Minimal Critical Mass of Magnetic Interstellar Clouds Authors: Dudorov, A. E.; Ustyugov, S. D. Bibcode: 1990ATsir1546....7D Altcode: No abstract at ADS