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P. E. Meade, M. A. Bullock, D. H. Grinspoon (SWRI)
We have adapted a standard cloud microphysics model to construct a self-consistent microphysical model of Venus’ cloud layer which reproduces and extends previous studies (e.g. James et al. 1997). Our model is based on the Community Aerosol and Radiation Model Atmosphere (CARMA), which is a widely used computer code for terrestrial cloud microphysics, derived from the work of Toon et al. (1988). The standard code has been adapted to treat H2O and H2SO4 as co-condensing vapor species onto aqueous H2SO4 cloud droplets, as well as the nucleation of condensation nuclei to droplets. Vapor condensation and evaporation follows the method of James et al. (1997). Microphysical processes included in this model include nucleation of condensation nuclei, condensation and evaporation of H2O and H2SO4 vapor, and droplet coagulation. Vertical transport occurs though advection, eddy diffusion, sedimentation for both droplets and condensation nuclei.
The cloud model is used to explore the sensitivity of Venus’ cloud layer to environmental changes. Observations of the Venus’ lower cloud from the Pioneer Venus, Venera, and Galileo spacecraft have suggested that the properties of the lower cloud may be time-variable, and at times may be entirely absent (Carlson et al. 1993, Grinspoon et al. 1993, Esposito et al. 1997). Our model explores the dependence of such behavior on environment factors such as variations in water or SO2 abundance. We have also calculated the optical properties of the model atmosphere using both the conventional optical constants for H2SO4 (Palmer and Williams, 1975), and the new data of Tisdale et al. (1998).
This work has been supported by NASA’s Exobiology Program.
References
Carlson, R.W., et al., 1993. Planetary and Space Science, 41, 477-486.
Esposito, L.W., et al., 1997. In Venus II, eds. S.W. Bougher et al., pp. 415-458, University of Arizona Press, Tucson.
Grinspoon, D.H., et al., 1993. Planetary and Space Science, 41 (July 1993), 515-542.
James, E. P., et al., 1997. Icarus, 129, 147-171.
Palmer, K.F., and D. Williams, 1975. Applied Optics, 14, 208-219.
Tisdale, R.T., et al., 1998. Journal of Geophysical Research, 103, 25,353-25,370.
Toon , O. B., et al., 1988. J. Atmos. Sci., 45, 2123-2143.
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.