How Do Friction and Pressure Torques Affect the Relative and Ω Angular Momenta of the Atmosphere?

Abstract

The axial Ω and relative angular momenta, MΩ and Mr, depend on the meridional mass distribution and relative zonal velocity, respectively. According to the conventional formulation, the time rate of change of MΩ is determined by the Coriolis conversion induced by meridional velocity, C, whereas Mr is accelerated by C and the friction and pressure torques. This note decomposes C into three components, according to different ways of distributing mass in meridional direction. It is shown that the first two components are identical to the pressure and friction torque, respectively, and the last one equals the conversion induced by the ageostrophic meridional flow, Ca. The decomposition identifies Ca as the only forcing of Mr. The resulting budgets suggest that the torques change the angular momentum of a rotating fluid with the aid of mass transports, rather than by directly accelerating the rotation speed, as in the case of a rigid body.