Venusian Cloud Distribution Simulated by a General Circulation Model

We construct a simple cloud model for a Venus general circulation model (GCM), which includes condensable gases of H2O and H2SO4 vapors, and condensation, evaporation, and sedimentation of sulfuric acid cloud particles. The zonally averaged mass loading of the cloud reproduced in the model takes its maximum and minimum in high and middle latitudes, respectively. This latitudinal distribution is consistent with the infrared measurements. The thick cloud is formed in high latitudes at 43-55 km altitudes by vertical winds associated with disturbances enhanced in the low static stability layer. The moderately thick cloud in low latitudes is attributed mainly to the transport of H2SO4 vapor by the mean meridional circulation. The horizontal cloud distribution in low latitudes has zonal wave numbers 1 and 2 structures, which change in time significantly. These characteristics of the low-latitude cloud would be associated with atmospheric waves in the cloud layer. The mixing ratio of H2O vapor increases with latitude in the cloud layer due to the vertical wind disturbances in the low static stability layer in high latitudes. This latitudinal trend is qualitatively consistent with the infrared measurements. The mixing ratio of H2SO4 vapor increases with latitude in the subcloud layer because a large amount of the cloud is evaporated there due to the sedimentation of cloud particles in the thick lower cloud in the polar region. The present results suggest that the Venus cloud distribution in the lower cloud layer is strongly affected by waves and/or disturbances as well as the mean meridional circulation. Plain Language Summary Venus is totally covered by thick clouds composed of concentrated sulfuric acid droplets. Although a lot of measurements of the Venus cloud have been conducted so far, the mechanism on how these thick clouds are generated and maintained in the Venus atmosphere has not been fully understood. In the present study, we constructed a simple cloud model for a Venus general circulation model (GCM) to investigate the three-dimensional distributions of the cloud and condensable gases. We succeeded in reproducing these distributions consistent with the previous observations, except for the sulfuric acid vapor mixing ratio in low latitudes. The present result elucidates that the cloud distribution is strongly affected by waves and/or disturbances as well as mean meridional circulation, and the lower cloud changes in time and space as shown in the infrared measurements. It is suggested that the atmospheric motions are crucial to understand how the Venus cloud is produced and maintained.