Abstract

One of the most improtant questions concerning dynamo action is the nature of the resulting force balance. For example, is a dynamo essentially “VAC”, with a balance between Viscous, Archimedean (buoyancy) and Coriolis forces, or, at the other extreme, “MAC”, where the magnetic forces enter the balance, but the viscous forces do not? Here we study plane-layer dynamos driven by rotating convection in the absence of inertia. This allows us to decompose the velocity into thermally- and magnetically-driven components. Through analysis of the soelnoidal projection of the forces—which is tantamount to considering the vorticity equation, but more tractable numerically—we can consider the various forces in terms of the thermal and magnetic velocitites. We are able to identify “weak field” solutions, whereby the predominant balance is VAC , and “strong field” solutions, in which the balance may be classified as “VMAC”. We do not attain true MAC solutions. This is joint work with Fausto Cattaneo of the University of Chicago.