H ₂ SO ₄ cycle in the Venusian tropical atmosphere as constrained by a microphysical cloud model

A one-dimensional microphysical model study revealed that vertical winds govern the H ₂ SO ₄ cycle in the equatorial cloud system of Venus. In the upper cloud region, photochemical production of H ₂ SO ₄ vapor leads to the formation of small droplets, which are blown off by the upward/poleward branck of the Hadley circulation. In the middle and lower cloud regions, H ₂ SO ₄ 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 H ₂ SO ₄ near the cloud base explains the observed accumulation of H ₂ SO ₄ 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 H ₂ SO ₄ vapor to condense onto condensation nuclei, thereby producing a large number of middle-size droplets.