Microwave absorptivity by sulfuric acid in the Venus atmosphere: First results from the Venus Express Radio Science experiment VeRa

Abstract

The Venus Express (VEX) Radio Science experiment VeRa utilizes radio occultation techniques to investigate the Venus atmosphere over a wide range of latitudes. Radio attenuation measurements with the VEX 3.6cm (X-band) signal provide information on the absorptivity distribution within the Venus cloud deck. The combined results from 6years of occultation measurements reveal a distinct latitudinal variation in absorptivity in the altitude range from 50 to 55km. Enhanced absorptivity is observed at equatorial and mid-latitudes (0–50°S), exceeding 0.008dB/km on the dayside and 0.01dB/km on the nightside of the southern hemisphere. Poleward of 50°S latitude a decrease in the absorptivity is observed, reaching minimal values at polar latitudes (>70°S), where the absorptivity did not exceed 0.005dB/km on the dayside and 0.004dB/km on the nightside. The main absorber of radio waves in the Venus atmosphere, gaseous sulfuric acid, can serve as a tracer for atmospheric motions. The inferred absorptivity was used to determine the abundance of gaseous sulfuric acid. Abundances of about 1–2ppm are found between 0°S and 70°S latitude in the altitude range from 50 to about 52km, sometimes increasing to values of about 3ppm on the dayside and 5ppm on the nightside near 50km. The abundance at polar latitudes (>70°S) did not exceed 1ppm within the considered altitude range. The absorptivity and gaseous sulfuric acid height profiles are compared with previous measurements.