||Realistic MHD Simulations of Solar Convection and Oscillations in Magnetic Regions: Mode Excitation and Effects of Acoustic Halos
||416, Solar-Stellar Dynamos as Revealed by Helio- and Asteroseismology: GONG 2008/SOHO 21
||Jacoutot, L.; Kosovichev, A. G.; Wray, A.; Mansour, N.
||We have used a 3D, compressible, non-linear radiative
magnetohydrodynamics code developed at the NASA Ames Research
Center to model solar convection and oscillations in magnetic
regions. This code takes into account several physical phenomena:
compressible fluid flow in a highly stratified medium, sub-grid
scale turbulence models, radiative energy transfer, and a real-gas
equation of state. We have studied the influence of the magnetic
field of various strength on the convective cells and on the
excitation mechanisms of the acoustic oscillations by calculating
spectral properties of the convective motions and oscillations.
The results reveal substantial changes of the granulation structure
with increased magnetic field, and a frequency-dependent reduction
in the oscillation power in a good agreement with solar observations.
The simulations provide a solution to the long-standing problem of
enhanced high-frequency acoustic emission at the boundaries of
active region ("acoustic halos"), suggesting that this phenomenon
is caused by the changes of the spatial-temporal spectrum of the
turbulent convection in magnetic field, resulting in turbulent
motions of smaller scales and higher frequencies than in quiet Sun
regions. These simulation results may have also important
implications for understanding high-frequency oscillations of