Venera-15: Water Vapor at Altitudes of 55-65 km

Spectra of Venus outgoing thermal radiation were measured in 1983 onboard the Venera-15 spacecraft (Venusʹ artificial satellite) in the 6-40 Jim range at different latitudes and longitudes. Results of a new analysis of these spectra are presented, which have been elaborated in order to revise the water vapor content estimates resulting from them. Higher quality spectra have been selected, obtained from the ground-based processing of interferograms, and new approaches are taken to their analysis. Two latitude zones are separated (A from approximately 20° to 50° and B from 60° to 80° north latitude) with different levels, where optical thickness in the aerosol continuum in the H(2)O longwave band is equal to ~l (about 62 and 56 km, respectively). Mean ratios of the water vapor mixture near this level are almost identical (10 and 8 ppm, respectively), although partial pressures and densities differ by ~2-4 times. A modest increase of the mixture ratio is detected in daytime. Essential differences in the latitude dependence between different measurement runs exist. On the average, water content decreases with increasing latitudes in latitudes (phi) > 55°, and at (phi) > 70°, a large dispersion of the reconstructed values of water content is observed, which is essentially greater than the errors. These variations are connected with dynamic structures, such as the "cold collar" and "hot dipole." The water content in the form of vapor, at least in the A zone, is greater than the liquid water content in the sulphuric acid solution (in particles), and, apparently, the main source of water in the cloud layer is from deeper atmosphere layers.