Simulating solar MHD

Two aspects of solar MHD are discussed in relation to the work of the MHD simulation group at KIS. Photospheric magneto-convection, the nonlinear interaction of magnetic ®eld and convection in a strongly strati®ed, radiating ̄uid, is a key process of general astrophysical relevance. Comprehensive numerical simulations including radiative transfer have significantly improved our understanding of the processes and have become an important tool for the interpretation of observational data. Examples of ®eld intensi®cation in the solar photosphere (`convective collapse') are shown. The second line of research is concerned with the dynamics of ̄ux tubes in the convection zone, which has far-reaching implications for our understanding of the solar dynamo. Simulations indicate that the ®eld strength in the region where the ̄ux is stored before erupting to form sunspot groups is of the order of 10 G, an order of magnitude larger than previous estimates based on equipartition with the kinetic energy of convective ̄ows.