Numerical simulations of the subsurface structure of sunspots

Details Numerical simulations of the subsurface structure of sunspots Numerical simulations of the subsurface structure of sunspots

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsh52b..02r&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #SH52B-02

Astronomy and Astrophysics

Astrophysics

[7522] Solar Physics, Astrophysics, And Astronomy / Helioseismology, [7524] Solar Physics, Astrophysics, And Astronomy / Magnetic Fields, [7529] Solar Physics, Astrophysics, And Astronomy / Photosphere

Scientific paper

Knowledge of the subsurface magnetic field and flow structure of sunspots is essential for understanding the processes involved in their formation, dynamic evolution and decay. Information on the subsurface structure can be obtained by either direct numerical modeling or helioseismic inversions. Numerical simulations have reached only in recent years the point at which entire sunspots or even active regions can be modeled including all relevant physical processes such as 3D radiative transfer and a realistic equation of state. We present in this talk results from a series of different models: from simulations of individual sunspots (with and without penumbrae) in differently sized computational domains to simulations of the active region formation process (flux emergence). It is found in all models that the subsurface magnetic field fragments on an intermediate scale (larger than the scale of sunspot fine structure such as umbral dots); most of these fragmentations become visible as light bridges or flux separation events in the photosphere. The subsurface field strength is found to be in the 5-10 kG range. The simulated sunspots are surrounded by large scale flows, the most dominant and robust flow component is a deep reaching outflow with an amplitude reaching about 50% of the convective RMS velocity at the respective depth. The simulated sunspots show helioseismic signatures (frequency dependent travel time shifts) similar to those in observed sunspots. On the other hand it is clear from the simulations that these signatures originate in the upper most 2-3 Mm of the convection zone, since only there substantial perturbations of the wave speed are present. The contributions from deeper layers are insignificant, in particular a direct comparison between an 8 Mm and 16 Mm deep simulation leads to indiscernible helioseismic differences. The National Center for Atmospheric Research is sponsored by the National Science Foundation. This work is in part supported through the NASA SDO Science Center.

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