Venus cloud formation in the meridional circulation

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 H 2 SO 4 ‐H 2 O droplets in the upper atmosphere makes a thick cloud, since most of the H 2 SO 4 ‐H 2 O droplets photochemically produced are transported poleward by the meridional circulation. At low latitudes, the modeled large‐scale ascent of the concentrated H 2 SO 4 vapor forms a dense lower cloud in accord with observations by entry probes. The equatorward transport of H 2 SO 4 vapor below the cloud by the modeled meridional circulation and the sedimentation of droplets in the lower cloud leads to the accumulation of H 2 SO 4 vapor around the cloud base at low latitudes. The calculated H 2 SO 4 vapor distribution agrees with radio occultation observations. The middle cloud appears to be caused by the condensation of H 2 SO 4 vapor transported upward from below by convective mixing.