A dynamo model interpretation of geomagnetic field structures

Abstract

We present numerical dynamo models which qualitatively reproduce some structural characteristics of the present-day geomagnetic field. Time-dependent convection in an electrically conducting, rotating spherical shell at Ekman numbers 1-3×10-4 generates dipole-dominated magnetic fields, which exhibit distinct bundles of strong radial flux at high latitudes, low flux over the poles, and paired spots of reversed flux near the equator, suggestive of the geomagnetic field pattern at the core-mantle boundary. In our model these structures result from high magnetic Reynolds number, helical convection in columns parallel to the spin axis and rising plumes near the poles.