Large and small scale motions in Kinematic dynamos

Abstract

Abstract Kinematic, axisymmetric mean field dynamos are examined for a number of models in order to study the cooperation between small scale turbulent motions (α-affect) and the large scale motions (ω-effect and meridional flow). For a spherical dynamo we show that it is more difficult to excite an α2-dynamo with dipolar parity in the presence of differential rotation, which increases with increasing depth, when the magnitude of the toroidal shearing effect is too small. Meridional streaming in the absence of differential rotation has an inhibitory effect on α2-dynamos. For dynamos in spheres the ease with which a dynamo is excited when the combined effects of differential rotation and meridional flow are present depends on the model for ω(r,θ). For a model where the maximum in the toroidal shearing is towards the edge of the region enclosing the streamlines a small amount of meridional flow enhances dynamo action. For dynamos confined to a spherical shell the effect of a small amount of single cell meri...