ON A PHYSICALLY REALISTIC FAST DYNAMO

As a step towards a physically realistic model of a fast dynamo, we st udy numerically a kinematic dynamo driven by convection in a rapidly r otating cylindrical annulus. Convection maintains the quasi-geostrophi c balance whilst developing more complicated time-dependence as the Ra yleigh number is increased. We incorporate the effect ol Ekman suction and investigate dynamo action resulting from a chaotic pow obtained i n this manner. We examine the growth rate as a function of magnetic Pr andtl number Pm, which is proportional to the magnetic Reynolds number . Even for the largest value of Pm considered a clearly identifiable a symptotic behaviour is not established. Nevertheless the available evi dence strongly suggests a fast dynamo process.