DYNAMICS OF THE ATMOSPHERE OF VENUS.

Abstract

The wide range of radiative time scales in the Venus atmosphere, together with observations of temperature structure and winds, indicate that the atmosphere contains two distinct regimes. In the deep atmosphere, at altitudes below 40 km, diurnal effects are negligible, motions are weak, and the lapse rate is near-adiabatic. In the upper atmosphere, at altitudes above 70 km, diurnal effects are important, strong retrograde zonal motions occur, and the lapse rate is sub-adiabatic. The transition region between these two regimes is complicated by the presence of two layers of small-scale turbulence at altitudes of 45 and 60 km. Analytical and numerical studies show that the Hadley cell hypothesis for the circulations in the deep atmosphere is consistent with all the observations. Studies of the motions in the upper atmosphere are more ambiguous. Suggestions for explaining the strong zonal motions include the ″moving flame″ mechanism, the instability of diurnal convective cells to a mean shear, tidal forcing, momentum transport by internal gravity waves, and momentum transport by a Hadley cell.