ON THE DYNAMICS OF TOPOGRAPHICAL CORE-MANTLE COUPLING

We examine the dynamics of topographical core-mantle coupling, the pro cess by which angular momentum is exchanged between the Earth's fluid outer core and solid mantle through the action of pressure forces acti ng on topography on the core-mantle boundary. We show that methods for calculating the torque directly from observations based on the assump tion of tangentially geostrophic flow at the core surface should yield a zero torque if the mantle is an electrical insulator and the gravit ational acceleration is radial. We discuss the effect of relaxing thes e assumptions and argue that such methods remain incapable of determin ing the torque on the core, either due to violation of the underlying assumption of tangential geostrophy or the admission of larger non-top ographical torques.