Anisotropic turbulence in rotating magnetoconvection

Numerical simulations of the 3D MHD-equations that describe rotating magnetoconvection in a Cartesian box have been performed using the code NIRVANA. The characteristics of large-scale quantities like the turbulence intensity and the turbulent heat flux that are caused by the average action of the small-scale fluctuations are computed directly from the fluctuating primitive variables. and the effects of the anisotropy induced by rotation and an external imposed magnetic field are quantified. The results confirm that the structure of the convection significant depends on the latitude and the rotation rate as well as on the magnetic field strength and direction. For faster rotation the influence of the Lorentz force on the flow becomes important at lower Elsässer number manifested in the change of the convection pattern and the domination of the azimuthal turbulence intensity. At the pole the turbulence intensity exhibits a slight maximum for an Elsässer number close to unity. No catastrophic quenching occurs as the turbulent quantities are significant suppressed only for field strengths above the typical values that are assumed to prevail within the fluid outer core of the Earth. In the presence of a horizontal magnetic field the vertical turbulent heat flux increases with increasing field strength so that cooling of the rotating system is facilitated. Horizontal transport of heat is always directed westwards and towards the poles. The latter might be a source of a large-scale meridional flow whereas the first in global simulations would be important in case of non-axisymmetric boundary conditions for the heat flux. The obtained results could serve as basic clues for the properties of turbulence models that might be applied in future simulations of the geodynamo.