RESULTS FOR 13-CM ABSORPTIVITY AND H2SO4 ABUNDANCE PROFILES FROM THE SEASON-10 (1986) PIONEER VENUS ORBITER RADIO OCCULTATION EXPERIMENT

Recent radio astronomical observations of Venus have suggested that the abundance and distribution of sulfur-bearing gases below the main cloud layer may vary significantly both in time and with position. To determine whether this is the case for sulfuric acid vapor (H2SO4), data from 23 Pioneer Venus Orbiter radio occultation experiments have been processed to obtain 13-cm absorptivity profiles. The data were obtained from radio occultation season 10 (late 1986 and early 1987). During the course of this season the occultation geometry allowed the spacecraft signal to probe the atmosphere over a wide range of latitudes in the northern hemisphere, and to altitudes as low as 39.4 km (above a mean radius of 6051.92 km). Since sulfuric acid vapor is the most opaque constituent in Venus' atmosphere at this wavelength, these profiles have been used to infer upper limits for abundance profiles of sulfuric acid vapor. Error bars have been placed on the absorptivity and abundance profiles by considering the propagation of statistical uncertainties through the steps of the signal inversion process (as per B. Lipa and G. L. Tyler, 1979, Icarus 39, 192-208). The results confirm the presence of statistically significant variations in the abundance and distribution of gaseous H2SO4 between the equatorial latitudes (11° to 25°N) and latitudes above 36°N. The results also suggest that the abundance of sulfuric acid vapor may have declined since the first Pioneer Venus radio occultation experiments in 1979, but additional work is needed to determine if the variations are statistically significant. © 1991.