Magnetic Rossby waves in the stratified ocean of the core, and topographic core-mantle coupling

Abstract

A new model of the stably stratified layer at the top of the core is proposed. The existence of a stably stratified layer (we name it the stratified ocean) at the top of the core makes possible the propagation of the waves akin to the Rossby waves (also named “planetary waves”), well known in oceanology and meteorology. These waves are modified and experience significant decay, due to the core’s magnetic field. The “magnetic Rossby waves” are considered here, using a simple planar model, to reveal their qualitative features without going into significant mathematical complications. The core-mantle coupling, which originates from the interaction of the surface flow with the topography of the core-mantle boundary, is strongly influenced by the stably stratified layer. We consider the topographic core-mantle coupling arising due to generation of motion resembling the magnetic Rossby waves in the stably stratified layer. A simple expression is obtained for the topographic tangential stress on the core-mantle boundary.