Velocity and magnetic fields in the Earth's core estimated from the geomagnetic field

Abstract

The velocity and the magnetic fields within the Earth's outer core are estimated from geomagnetic field data. This is performed by prescribing the radial dependence of the poloidal velocity field, into which the energy source for the geodynamo is implicitly incorporated, and by solving the Navier-Stokes and the magnetic induction equations. The conditions that time change of the velocity field is very slow and that the magnetic field and its time change must fit the observed geomagnetic field are imposed. The estimated velocity fields then have some common features with those estimated on the basis of the frozen-flux approximation. The toroidal magnetic field is stronger than the poloidal magnetic field, but both are of the same order of strength. Both generation balance in the induction equation and the strength of magnetic field in the core suggest that the geodynamo is likely to be of α 2 ω-type. Force balance in the core is estimated to be magnetostrophic.