The role of meridional motions for the solar dynamo

Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany

Abstract

The dynamo equation is solved for the solar convection zone with the given ("observed") rotation law and positive α-effect. If the latter exists in the entire convection zone the resulting dynamo shows strong toroidal field belts in the polar region migrating equatorwards. The same happens for α concentrated at the bottom of the convection zone but then we get too many belts with higher amplitude. The cycle period is always too short. Including meridional circulation which is directed equatorwards at the bottom of the convection zone (where the eddy diffusivity is reduced), the amplitude of the toroidal field grows and the butterfly diagram reaches low-latitudes. The cycle time approaches the solar value. The dynamo regime is highly sensitive to the interplay between flow and diffusivity at the bottom of the convection zone. Stationary solutions are not very seldom. For less active stars a slight increase of the cycle period with the rotation period is observed in agreement with the decrease of the meridional flow for faster rotation.