Transport and Storage of Magnetic Field by Overshooting Turbulent Compressible Convection

Abstract

We present the results of a series of numerical experiments that investigate the transport of magnetic fields by turbulent penetrative compressible convection. We find that magnetic flux is preferentially transported downward out of a turbulent convecting region and stored in a stably stratified region below. This pumping mechanism is believed to be a crucial component for the operation of a large-scale solar interface dynamo since it may be responsible for the transport of flux from the solar convection zone to the stable overshoot region. The high-resolution three-dimensional simulations show that efficient pumping occurs as a result of the action of strong coherent downflowing plumes. The properties of the transport are evaluated as a function of magnetic field strength, rotation rate, supercriticality, stiffness of the interface, and configuration. The turbulent pumping of magnetic flux is remarkably robust and more efficient than its laminar counterpart. The turbulent convection naturally amplifies magnetic energy from any existing mean field. The transport of flux from the convection zone removes the source for this local amplification there, and thus the peak magnetic energy also comes to reside in the stable region. This is important for an effective interface dynamo.