Geomagnetic secular variation, core motions and implications for the Earth's wobbles

Abstract

Motions at the top of the core are known to be responsible for the secular variation of the Earth's magnetic field. If this flow is supposed geostrophic, the associated pressure field can have an appropriate geometry to exert a pressure torque upon the elliptical core-mantle boundary and, besides, to alter the elastic products of inertia in such a way as to excite the Earth's and core wobbles. We consider some schematic excitation functions and the resulting amplitudes of the Earth's and core rotational motions. The proposed mechanism is shown to be efficient for exciting the long-period Markowitz wobble of the rotation axis and also the Chandler wobble if the variations in the pressure field have the right time scales, as indeed suggested by the available secular variation data.