Geodynamo α-effect derived from box simulations of rotating magnetoconvection

The equations for compressible rotating magnetoconvection are numerically solved in a Cartesian box assuming conditions roughly suitable for the geodynamo. The mean electromotive force describing the generation of mean magnetic flux by convective turbulence in the rotating fluid is directly calculated from the simulations and the corresponding α-coefficients are derived. Due to the very weak density stratification, the α-effect changes its sign in the middle of the box. It is positive at the top and negative at the bottom of the convective instable layer. For strong magnetic fields we also find a clear downward advection of the mean magnetic field. Finally the quenching behavior of the α-effect in dependence of the imposed magnetic field strength is presented.