Some characteristics of magnetic field behavior in a model of MHD dynamo thermally driven in a rotating spherical shell

A model of three-dimensional self-consistent MHD dynamo in a rotating spherical shell is investigated through numerical simulations, in which a fully spectral scheme is used to guarantee precise computation in space. Generation mechanisms of the magnetic field and the structures of the magnetic and the velocity fields art then examined with emphasis on a fundamental process in the Earth's core. It turns oat that the magnetic field is confined in forward convective columns with respect to the drift direction of convection pattern. Detailed examination of generation mechanism of the magnetic field indicates that a strong toroidal magnetic field is generated by shear motion near the equatorial region close to the outer surface, whereas the poloidal magnetic field is rather maintained by fluid motion related to convective columns. Even when the magnetic and the velocity fields vary considerably, this relationship holds with some disruption during disordered states, and time variations of the magnetic field always show a time lag behind those of the velocity field. Although the so-called weak-field regime is investigated, fundamental phenomena shown in this paper should be of importance for understanding of the Earth and planetary dynamo processes. (C) 1999 Elsevier Science B.V. All rights reserved.