Results of radio occultation of the neutral atmosphere of Venus and bistatic radar determination of surface relief with the aid of the Venera 9 and 10 satellites

In radio occultation experiments conducted on the Venusian atmosphere with the Venera 9 and 10 satellites, three regions of approximatelly constant temperature gradient were observed in the night-side atmosphere. At altitudes 43-50 km, the temperature gradient of about 9.8 K/km is close to a dry adiabatic gradient for a CO2 atmosphere. Transition from a dry to a moist adiabatic atmosphere occurred at about 59 km at a temperature of about 270 K. A regular nightside minimum of about 166 K is observed at around 88 km. Three regions of constant temperature gradient are also observed in the dayside atmosphere. Temperature inversions are noted at altitudes 62-72 km. Distributions of relative relief heights and near-surface pressure for two regions are given.