A mean electromotive force induced by magnetic buoyancy instabilities

Abstract

For a variety of reasons, based on results from magnetoconvection, self-consistent dynamo calculations and helioseismology, it seems plausible that the bulk of the solar magnetic field is located in the overshoot zone. Furthermore, it has also been suggested that the solar dynamo is operating in this region. The aim of this paper is then to show that it is possible to obtain a mean electromotive force (EMF), and hence an α-effect, in the convectively stable overshoot zone, which is driven by magnetic buoyancy instabilities. By investigating the stability of a layer of magnetic field embedded between two non-magnetic layers of plasma we are able to show the following: first, that magnetic buoyancy instabilities indeed give rise to a mean EMF and, secondly, that the electromotive force is largest in the region where the magnetic layer is unstable, i.e. where the field strength decreases fastest with height. Moreover, the influence of the rotation rate and the magnetic field strength on the magnetic buoyancy instability has been investigated in order to determine for which values of these parameters dynamo action might occur.