Cellular dynamo in a rotating spherical shell

Magnetoconvection in a rotating spherical shell is simulated numerically using a code developed by Tilgner and Busse. The thermal stratification is convectively unstable in the outer part and stable in the inner part of the shell. Regimes are found in which the convective flow is weakly affected by rotation and preserves its cellular structure. The dipolar component of the large-scale magnetic field exhibits undamped oscillations. It appears that convection cells slightly modified by rotation can be building blocks of the global dynamo. The generation of the magnetic field is thus due to regular "macroscopic" flows, and their structure itself may ensure the presence of the a effect responsible for the action of the dynamo. Such dynamos can be called deterministic, in contrast to those in which the maintenance of the magnetic field is related to the statistical predominance of a certain sign of helicity in the turbulent velocity field. Investigation of conditions under which dynamos of this sort can operate could suggest a more definite answer to the question of the origin of solar and stellar magnetic fields. (c) 2005 WILEY-VCH Verlag GmbH M Co. KGaA, Weinheim.