Geodynamo a-effect from box simulations of magnetoconvection

点击翻译按钮获取中文摘要

Employing the code NIRVANA (Ziegler 1998, 1999) a local model of weakly compressible, rotating magnetoconvection for the outer core of the Earth is developed. The d-effect correlating the turbulent electromotive force due to small-scale motions with the large-scale magnetic field is estimated. The d-effect is fundamental in mean-field dynamo theory and should exist in a rotating, stratified turbulent fluid. Since the density stratification in the Earth's core is much smaller than in stellar convection zones it is, however, not clear whether its magnitude is sufficiently high to allow dynamo action. The present project contributes to our understanding of the geodynamo phenomenon in that it provides a parametrization of the d-effect on the strength of the mean magnetic field and on the position given by the latitudinal angle the Cartesian computational box is placed tangentially on the sphere. The characteristic properties of the geodynamo d-effect (amplitude, anisotropy, quenching behavior) are investigated. Strong magnetic fields are considered consistent with the idea of a magnetically-dominated outer core.