On dynamic geodynamo models with imposed velocity as energy source

The first step of a project to study three-dimensional numerical dynamo mod els in a rapidly rotating sphere is reported. We aim at finding solutions i n the magnetostrophic regime, where the Taylor's condition is obeyed. Visco us terms, including the Ekman suction at the boundary, are discarded. At th is stage, our project consists of investigating the coupling of the momentu m and induction equations. The energy equation is ignored and an imposed ve locity provides the energy source. We present our code and we show that the algorithm to calculate the geostrophic velocity is stable. (C) 1999 Elsevi er Science B.V. All rights reserved.