Astronomy and Astrophysics – Astronomy
Scientific paper
May 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21621105r&link_type=abstract
American Astronomical Society, AAS Meeting #216, #211.05; Bulletin of the American Astronomical Society, Vol. 41, p.867
Astronomy and Astrophysics
Astronomy
Scientific paper
Sunspot fine structure has been modeled in the past by a combination of idealized magneto-convection simulations and simplified models that prescribe the magnetic field and flow structure to a large degree. Advancement in numerical methods and computing power has enabled recently 3D radiative MHD simulations of entire sunspots with sufficient resolution to address details of umbral dots and penumbral filaments. After a brief review of recent developments I will focus on the magneto-convective processes responsible for the complicated magnetic structure of the penumbra and the mechanisms leading to the driving of strong horizontal outflows (Evershed effect). Overturning convective motions are the central element for understanding sunspot fine structure. The expansion of upflowing plasma leads to a strong reduction of the magnetic field strength allowing for overturning convection, which weakens the magnetic field further due to flux expulsion. The latter has a stronger effect on the vertical magnetic field component, leading to the formation of elongated filaments with increased inclination angle. Strong horizontal outflows can be explained through a redistribution of kinetic energy preferring flows along the filaments. This redistribution is facilitated primarily through the Lorentz force, horizontal pressure gradients play only a minor role. In the near surface layers energy is primarily transported by convective motions turning over laterally, the contribution from large scale flows is negligible.
The National Center for Atmospheric Research is sponsored by the National Science Foundation.
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