Structure and evolution of sunspots

A 2-D sunspot model is constructed which yields the temporal evolution of the magnetic field, the temperature distribution and the internal flow field. Transport coefficients such as magnetic diffusivity, edd viscosity and heat-conductivity are quenched by the basic magnetic field. The observational finding of a bright ring around the spot whose temperature excess runs with the spot area is clearly reproduced. The decay laws of the magnetic flux and the spot area are slightly parabolic also in accordance with observations.