Do dynamo-waves propagate along isorotation surfaces?

Abstract

It is shown that the basic rule of the dynamo theory on the propagation of dynamo-waves along surfaces of constant angular velocity is restricted to the case of isotropic magnetic diffusion. The influence of rotation on convective turbulence induces an anisotropy in the eddy diffusivity. The anisotropy makes the direction of travel of the dynamo wave deviate from the isorotation surfaces. The deviation is towards the equator for solar conditions. This finding may help to resolve the old problem of solar dynamo theory concerning the incompatibility between the helioseismological rotation law and equatorward migration of solar activity. A qualitative explanation for the inclined propagation is suggested. The derived properties of the dynamo waves are illustrated by 2D dynamo models in spherical geometry. The model with anisotropic diffusion shows a pronounced equatorial drift of toroidal fields even with a depth independent rotation.