Box simulations of rotating magnetoconvection

Spatiotemporal evolution

Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany

Corresponding author: uziegler@aip.de

Received: 31 July 2001
Accepted: 7 January 2002

Abstract

This paper reports 3D numerical simulations of compressible, thermal convection in a small rectilinear domain placed tangentially on a rotating sphere at latitude . The spatiotemporal evolution of convection is studied in an initially non-homogeneous toroidal magnetic field located at the interface of a 2-layer unstable/stable polytropic stratification. The effects from a variation of the rotation rate and magnetic field strength are explored. In weak field convection the solutions bear close resemblance to the field-free situation with the magnetic field treated as a passive ingredient. In this case a significant amount of magnetic energy is transported downwards into the stable layer by penetrative motions where the field is concentrated in small-scale tube-like features. In the case of a dominating magnetic field, the overall structure of convection changes dramatically towards a two-dimensional, more laminar flow with convective motions occurring in columnar cells aligned with the mean magnetic field. The latter quickly becomes flat in the convection zone due to magnetic buoyancy effects. Magnetic quenching of the flow heavily influences the mixing properties of convection, thereby, reducing the fluxes of kinetic energy and enthalpy and suppressing the downward transport of magnetic energy. Adding rotation in strong field convection generates streaming motions parallel to the mean field. These motions contain a large fraction of the total kinetic energy. The horizontally-averaged (mean) flows, on the other hand, are less energetic. In the presence of strong rotation the horizontal mean flows are triggered by inertial oscillations. Averaging the mean flows over time gives an estimate for steady flows persistent in a convection zone. Whereas the vertical flow component obtained in this way shows a systematic dependence on the rotation rate and field strength, the flows in the meridional and zonal directions depend in a more complex manner on these parameters. This includes reversals in their orientation when going from moderate to strong rotation and when increasing the magnetic field strength.