Gravity, Oceanic Angular Momentum, and the Earth’s Rotation

Abstract

The angular momentum of the oceans changes as both the distribution of mass within the oceans changes and as the direction and speed of oceanic currents change. Since, in the absence of external torques, the angular momentum of the solid Earth-atmosphere-ocean system is conserved, the changing oceanic angular momentum will cause the solid Earth’s angular momentum to change, or, in other words, will cause the Earth’s rotation to change. The changing distribution of mass within the oceans also causes the Earth’s gravitational field to change, an effect that will soon be measured by the CHAMP and GRACE satellite missions. By measuring changes in the second-degree spherical harmonic coefficients of the Earth’s gravitational field, which are related to the elements of the Earth’s inertia tensor, CHAMP and GRACE will, in effect, be directly measuring changes in the Earth’s rotation caused by mass redistribution.