Microphysics of Venusian clouds in rising tropical air

As the global distribution of Venusian H₂SO₄-H₂O clouds is strongly related to the global circulation of H₂SO₄ governed by wind transport and sedimentation of droplets, the circulation of H₂SO₄ in the Tropics was studied by simultaneously solving advection and cloud microphysics equations using a one-dimensional model that includes a weak upwelling representing the rising branch of Hadley circulation near the equator. H₂SO₄ vapor in the upper cloud region is supplied by photochemical production and condenses into cloud droplets that are removed from the tropical atmosphere by Hadley circulation, whereas in middle and lower cloud regions, dynamical processes supply H₂SO₄ vapor from below such that resultant droplets are large and fall against the upwelling. The combination of the mean upward advection of vapor and the sedimentation of droplets leads to accumulation of H₂SO₄ and H₂O vapor near the cloud base: an observed phenomenon. A separate model run was performed to investigate the effect of transient strong winds on condensational growth, with results indicating that transient winds produce a variety of size distributions similar to those observed. Variation in cloud thickness associated with such events is thought to explain large opacity variations in near-infrared observations.