Venus cloud formation in the meridional circulation

Abstract

A two‐dimensional model study revealed that the meridional circulation can have a large influence on the distributions of the cloud and condensable gases on Venus. In our model, the generally observed depression of near‐infrared optical thickness at midlatitude is reproduced as a result of the enhancement of cloud thickness at low and high latitudes. At high latitudes, the modeled poleward transport of H2SO4‐H2O droplets in the upper atmosphere makes a thick cloud, since most of the H2SO4‐H2O droplets photochemically produced are transported poleward by the meridional circulation. At low latitudes, the modeled large‐scale ascent of the concentrated H2SO4 vapor forms a dense lower cloud in accord with observations by entry probes. The equatorward transport of H2SO4 vapor below the cloud by the modeled meridional circulation and the sedimentation of droplets in the lower cloud leads to the accumulation of H2SO4 vapor around the cloud base at low latitudes. The calculated H2SO4 vapor distribution agrees with radio occultation observations. The middle cloud appears to be caused by the condensation of H2SO4 vapor transported upward from below by convective mixing.