The Coupling of the Core to the Precession of the Earth

The core follows the precession of the mantle by virtue of coupling to it. A simple model is presented which allows quantitative consideration of a superposition of both inertial and dissipative (electromagnetic) coupling torques. With the preferred value of the dissipative coupling coefficient, the dissipative mechanism accounts for only 2 or 3 per cent of the precessional coupling torque, but the dissipation amounts to about 3 times 10 Watts, which may suffice for a geomagnetic dynamo driven by precession. The dissipation itself is only weakly dependent upon the coupling coefficient and no assumption can lead to dissipation exceeding 10 W. This is much smaller than the loss of rotational energy by tidal friction; also it is hardly a significant contribution to the total core‐tomantle heat flux if we suppose that an adiabatic temperature gradient is maintained in the core, thus supporting the contention that the core contains potassium with a radioactive heat generation of order 10 W. Motion of the core is found to contribute to the semi‐annual terms of precession and nutation