SULFUR-DIOXIDE IN THE ATMOSPHERE OF VENUS .2. MODELING RESULTS

We have analyzed the results from the UV sounding rocket observations of Venus made on 15 September 1988 and 29 March 1991 which obtained high-resolution spectra of Venus clouds from 190 to 230 nm. The albedo of Venus in this wavelength range is dominated by absorption features of sulfur dioxide and sulfur monoxide. We estimate that the mixing ratio of SO2 above the clouds of Venus is 80 +/- 40 ppb for 1988 and 120 +/- 60 ppb for 1991. The scale height of SO2 at the same altitude region is 3 +/- 1 km for both 1988 and 1991. These numbers are in good agreement with both Pioneer Venus and IUE observations made around the same time period, and indicate that no large change in SO2 above the clouds occurred from 1982 to 1991. In addition, the SO mixing ratio above the clouds derived from the 1991 observations is 12 +/- 5 ppb, and the scale height of SO above the clouds is close to that of the bulk atmosphere. Our analyses indicate that the mixing ratio of SO decreases sharply below the 64-km level, which is in good agreement with the photochemical models. The mixing ratio of SO, at the cloud top level derived from the 1988 observation ranges from 60 +/- 30 ppb at the equator to 300 +/- 150 ppb near 50 degrees S. The scale height of SO2 at the cloud top region ranges from about 3-4 km at the equator to similar to 2 km near 50 degrees S. Venera 15 observations show similar latitudinal variation of SO2. (C) 1994 Academic Press, Inc.