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Structures in compressible magnetoconvection & the nature of umbral dots

Structures in compressible magnetoconvection & the nature of umbral dots. C. Tian & K. Petrovay ELTE, Budapest. Outline. Introduction N umerical model Selected r esults C omparison s with observation s Discussion & Summary. Introduction --UD.

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Structures in compressible magnetoconvection & the nature of umbral dots

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  1. Structures in compressible magnetoconvection & the nature of umbral dots C. Tian & K. Petrovay ELTE, Budapest

  2. Outline • Introduction • Numerical model • Selected results • Comparisons with observations • Discussion & Summary

  3. Introduction--UD • Sunspot is associated with the most intense phase of solar active region. • Umbral dots (UD) • size: 700~200km • lifetime: 10m~1hr

  4. Introduction--Numerical studies • Along with the development of Computer science, numerical simulations become the most promising tool to study UDs. • Current existing numerical studies of Sunspots: • Realistic simulations (Shussler,Rempel,Cheung ...) • Parametric simulations: (Weiss et al. ) Shussler & Vogler 2006 Apj 641 Cheung et al 2010 Apj Wiess et al 2002 MNRS Rempel et al 2009 Science

  5. Numerical Model • An ideal gas • contained in a cubic box with periodic sides • aspect ratio 5:1. • Initial conditions: • two layers polytropic gas stratified under gravity. • non-magneto convection+ vertical uniform magnetic fields • Boundary conditions: • solid upper lid, opened bottom; • vertical BCs for magnetic fields • Turbulence model: Sub-grid scale Smagorinsky model • Numerical scheme: • gas-kinetic BGK-MHD (Tian 2010)

  6. Initial Statistical Steady State thermodynamically relaxed non-magnetic convection, is taken as the initial conditions formagnetoconvection

  7. Results --Granulation pattern • we recovered the results of Weiss et al • intermittent field • flux separation (Tao, Wiess) • small scale convection

  8. Results -- Anisotropic turbulence • grouped into three categories

  9. Results--Evolution • the small scale convection pulsates with time • multifold convective cells show up small-scale convection flux-separation intermittent fields

  10. Results-something new • CASE G: B0=3.1Be Be~900Gauss

  11. Comparisons with observation • Structure of UDs (Bharti et al 2007 Apj 665) ~1 arcsec ~0.5 arcsec ~10 arcsec

  12. Comparisons with observation • time evolution from observation Bharti,Joshi & Jaaffrey ApJ 699, 2007 G-band image of NOAA 10930 by SOT FOV: 1.57Mm^2 time interval: 2 m • time evolution from simulation

  13. Summary & Discussion • consistent with earlier study, particularly those of Wiess et al: • small-scale convection; flux separation; intermittent field • morphologicallymore closer to the observation • Limitations: • resolution; size; • boundary conditions, radiation transfer; • Future plan: boundary conditions >> radiation transfer >> ... ...

  14. The end Thanks!

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