The 4-Day Venus Circulation Driven by Periodic Thermal Forcing

Abstract

It has been proposed that the observed 4-day retrograde rotation of the Venus atmosphere is a zonal motion of at least the upper atmosphere driven by periodic solar thermal forcing. We have assessed the relative importance of periodic thermal forcing for the atmospheres of Venus, Earth, Mars, Jupiter, Saturn and Uranus. Periodic thermal forcing is likely to play a significant role only in the dynamics of the Venus atmosphere, principally because of the favorable overhead speed of the sun; this is 3 m sec?1, at least two orders of magnitude slower than the overhead solar speeds for the other planets. For a simplified channel flow problem we have examined the detailed mechanisms by which periodic induced circulations transport the momentum necessary to support a mean shear.