THERMALLY DRIVEN MHD DYNAMO IN A ROTATING SPHERICAL-SHELL

In order to find a possible mechanism of the geodynamo the motion of a n electrically conducting Boussinesq fluid which is driven by the ther mal convection in a rotating spherical shell is investigated numerical ly. It is observed that the dynamo action can be effective when the Ro berts number is below a critical value and that the polarity of the ma gnetic dipole moment changes chaotically in time. The intensification mechanism of the magnetic field - the concentrate-and-stretch of the m agnetic lines - is clarified at the first time by a detailed compariso n of the spatial structures of the velocity and the magnetic fields.