Convective Dynamos with Penetration, Rotation, and Shear

We investigate the dynamo properties of Boussinesq, penetrative convection in the presence of rotation and large-scale velocity shear flows. Several numerical experiments are conducted in a local Cartesian computational domain in which the relative stability of the lower stable layer, the rotation rate, the supercriticality of the convection, and the strength of the imposed shear flow are varied. Once a statistically steady hydrodynamic state is achieved for any set of parameters, a weak seed magnetic field is added and the subsequent dynamo evolution is followed. In all cases studied, the weak seed field is initially amplified exponentially and then eventually saturates in a stationary magnetohydrodynamic (MHD) state. Even in the presence of penetration, rotation, and shear, the field is predominantly small-scale. We analyze the reasons for this and make suggestions as to possible further mechanisms that may lead to large-scale field generation.