Meridional Circulation and the Maintenance of the Venus Atmospheric Rotation

Abstract

A meridional cell, with rising motion near the equator and sinking near the poles, transports angular momentum upward in an atmosphere whenever equatorial regions of the atmosphere have an angular momentum surplus relative to polar regions. This process way contribute to the maintenance of the Venus atmospheric super-rotation. Super-rotation by this process is exhibited in a simple analytical model. The super-rotation ratio in the model is derived to be exp (HD2/vvm), where H is depth in scale heights, D the mean scale height, vv the vertical eddy diffusivity, and tm the meridional overturning time. For the mechanism to work, some eddy process must maintain an angular momentum surplus in equatorial regions. Vorticity mixing is suggested. It is also demonstrated that if the Richardson number is large in a cyclostrophic atmosphere, the mean thermal structure is given by global radiative equilibrium, and local deviations from equilibrium are balanced by adiabatic cooling or warming associated with vertical motions.