The moisture torque

Abstract

A difference E − P of evaporation E and precipitation P per latitude belt implies an exchange of mass between the atmosphere and the underlying surface. In turn, a moisture torque is exerted on the axial angular momentum with sources (sinks) where E − P > 0 (< 0). the corresponding formulas are derived and data are used to show that the global moisture torque amounts to ∼ 1 − 2x1018 J. It is positive because evaporation exceeds precipitation in subtropical and tropical latitudes (except near the equator), where the earth's rotation velocity is larger than at midlatitudes where precipitation dominates. This moisture torque is small but not negligible in the angular momentum budget of the atmosphere.