Geomagnetic core-mantle coupling

The electrically conducting lower mantle is penetrated by changing magnetic fields originating in the earth's core. The Lorentz force (j×B) interaction of these fields with the electrical currents there produces a mechanical torque on the mantle. By using the Maxwell stress representation the expression for this torque is shown to reduce to the surface integral −1/μ ∫ (r×B) BrdS over the core-mantle boundary. The result is important in the study of possible changes in the length of day and the geographical position of the pole, due to angular momentum transfer between the electromagnetically coupled core and mantle.