The atmosphere of Jupiter: An analysis of the Voyager radio occultation measurements

Abstract

Coherently related S (2.3 GHz) and X band (8.4 GHz) signals transmitted from Voyager 1 and 2 have been used to probe the Jovian atmosphere during occultations of the spacecraft by Jupiter. The observations have yielded profiles in height of the gas refractivity, molecular number density, pressure, temperature, and microwave absorption in the troposphere and stratosphere of Jupiter at latitudes ranging from 0° to about 70°S. The data cover a pressure range from 1000 to 1 mbar over a height interval of 160 km. At the 1000‐mbar level, the temperature was 165±5 K, and the lapse rate was equal to the adiabatic value of 2.1 K/km, within the resolution of the measurements. The ammonia abundance in this region of the atmosphere was about 0.022±0.008%, in approximate agreement with the value derived from cosmic abundance considerations. The tropopause, which was detected near the 140‐mbar level, had a temperature of 110 K. Above the tropopause, the temperature increased with increasing altitude, reaching 160±20 K in the 10‐ to 1‐mbar region of the stratosphere. Significant horizontal density variations were detected in the stratosphere. This may imply a nonuniform temperature and aerosol distribution across the Jovian disk or high‐ and low‐pressure regions due to local atmospheric dynamics. The zenoid or gravity equipotential surface which best fits the 100‐mbar isobaric surface has an equatorial radius of 71,541±4 km and a polar radius of 66,896±4 km.