Equatorial magnetic dipole field intensification by convection vortices in a rotating spherical shell

Dynamo mechanism by thermal convection of an electrically conducting fluid in a rotating spherical shell is investigated by numerical simulation analysis of the MHD Boussinesq equations. The magnetic field is intensified, by stretching of magnetic field lines, along outgoing streamlines emanating from stagnation points in the convection velocity field so long as the magnetic field is weak. Once the magnetic field grows comparable in magnitude with the velocity field, however, the structure of the latter is deformed and the mechanism of magnetic field intensification is altered. The eastward drift of the convection vortices accelerated through the Lorentz torque creates a wavy zonal flow on which acceleration and deceleration are repeated periodically. The magnetic field is intensified, again through stretching of magnetic field lines, on the accelerating parts of the zonal flow predominantly near the equatorial plane. This establishes the magnetic dipole field with axis on the equatorial plane rotating around the rotation axis of the spherical shell. (C) 2002 Published by The Japan Society of Fluid Mechanics and Elsevier Science B.V. All rights reserved.