However, two different mechanisms are responsible for the formation of Venus' clouds (Rossow 1977). Photo-A numerical microphysical model that treats one-dimensional vertical transport of sulfuric acid/water solution aerosols, chemistry leads to the formation of cloud droplets near their nucleation, growth/evaporation, coagulation, and sedicloud top (ศ70 km), but near cloud bottom (ศ50 km), the mentation, is applied to the condensational middle and lower cloud is formed by condensation of a chemically stable Venus clouds. The model predicts the vertical profiles of sulfuric sulfuric acid vapor on hydrated sulfuric acid particles. The acid gas and water vapor, cloud microphysical properties, and sulfuric acid vapor is supplied by dynamical motions from the acid concentration of the aerosol particles. Results of model the abundant reservoir beneath the clouds (Jenkins and simulations agree favorably with Pioneer Venus particle size Steffes 1991, Jenkins et al. 1994). Thus, the lower part of spectrometer data, extinction and backscattering coefficients the Venus cloud is similar to terrestrial stratus clouds which measured by Pioneer Venus and Venera probes, in situ and are formed when water vapor condenses in uprising air.
remote observations of cloud optical depth, and sulfuric acid vapor abundances retrieved from Magellan radio occultation
In situ probe measurements detected three cloud laydata. It is found that the lower Venus cloud is formed as a ers-upper, middle, and lower-based on distinctive cloud consequence of a large upward flux of sulfuric acid vapor from particle size distributions (Esposito et al. 1983). While the the evaporation region below the cloud base. The mechanism upper cloud is essentially uniform, the middle and lower of lower cloud formation is probably heterogeneous nucleation clouds undergo significant spatial and temporal variations of sulfuric acid and water vapors on soluble nuclei. Model (Esposito et al. 1983, Crisp et al. 1991, Carlson et al. 1993, altitude profiles of the abundances of water vapor and gaseous Grinspoon et al. 1993). The patchy structure of the lower sulfuric acid demonstrate the control of these vapors by the and middle Venus cloud layers, with thick opaque cloud condensational cloud. Cloud processes account for the observed regions neighboring bright cloudless spots, is especially decline in concentration of water vapor with altitude, from ศ30 clearly observed on Galileo and ground-based near-infrappm below the clouds to ศ10 ppm at 60-km altitude. The structure of the lower and middle clouds is strongly dependent red images of Venus' nightside (Crisp et al. 1989, Bell et on the eddy diffusion coefficient. Hence, changes in transport al. 1991, Carlson et al. 1993, Grinspoon et al. 1993). The rates may explain the variations in cloud properties revealed variability of the middle and lower clouds may be a conseby the Pioneer Venus and Venera probe in situ measurements quence of the influence of atmospheric dynamics on the as well as by Earth-based and Galileo near-infrared observamicrophysical processes involved in the formation of these tions of the lower part of the Venus cloud.