Magnetic Fields and the Rotation of the Solar Convection Zone

Abstract

Arguments are presented in favour of the conjecture that magnetic fields in the convection zone are concentrated, highly fragmented and passive to velocity fields (convection, rotation) with the only exception of the uppermost layers, where buoyancy becomes dominant. The concept of an “anchor” or “coupling depth” is given some basis. It is concluded that large active regions have their origin in a region of dominating differential rotation at the lower boundary layer of the convection zone from where they are injected into the convection zone proper. It is shown that this view is consistent with observations of the evolution of active regions and favours the cluster model of sunspots. Information from magnetic fields about the rotation of deep layers of the convection zone can only be derived from observations of the very early phases of large active region evolution. These indicate that the rotation rate increases with depth in the upper layers of the convection zone but that the rotation of the source region of magnetic fields is slower than the surface value. It is argued that the observed rotation of magnetic tracers can be related to phase velocities of convective patterns as well as to real plasma velocities. Consequences for our picture of the solar dynamo are discussed briefly.

Mitteilungen aus dem Kiepenheuer-Institut Nr. 266