H2SO4 cycle in the Venusian tropical atmosphere as constrained by a microphysical cloud model Original Research Article

A one-dimensional microphysical model study revealed that vertical winds govern the H2SO4 cycle in the equatorial cloud system of Venus. In the upper cloud region, photochemical production of H2SO4 vapor leads to the formation of small droplets, which are blown off by the upward/poleward branch of the Hadley circulation. In the middle and lower cloud regions, H2SO4 vapor is supplied from below by dynamical processes and condenses into large droplets, which fall against the upwelling of the Hadley circulation. The local circulation of H2SO4 near the cloud base explains the observed accumulation of H2SO4 vapor beneath the equatorial cloud. It was also revealed that the transient strong vertical winds associated with transient eddies can explain the contradictory results for the particle size distribution observed by entry probes: the adiabatic cooling in an updraft forces H2SO4 vapor to condense onto condensation nuclei, thereby producing a large number of middle-size droplets.