MECHANICAL CORE-MANTLE COUPLING AND DYNAMO MODELING

Mechanical core-mantle coupling is first investigated in the absence o f magnetic forces. Two different expressions for the pressure at the c ore surface are derived for the two symmetries with respect to the equ ator. It is shown that the modified Taylor's condition (for a non-sphe rical volume in the absence of magnetic forces) can be read as a condi tion on the surface pressure, which had been previously derived in a s tudy of the topographic torque. The equation governing the time evolut ion of the geostrophic velocity in dynamo models is modified to take i nto account the distortion of geostrophic contours by small bumps. Fin ally, study of the time changes in the zonal velocity at the core surf ace seems to indicate that the observed core-mantle coupling is a by-p roduct of torsional oscillations riding inside the Earth's fluid core.