Radiative forcing of the Venus mesosphere: II. Thermal fluxes, cooling rates, and radiative equilibrium temperatures

Abstract

Results from the Pioneer Venus mission show that polar regions are up to 20°K warmer than the tropics at most levels in the Venus mesosphere (60–100 km). A radiative transfer model was used to determine how radiative forcing contributes to this feature. Global-mean radiative equilibrium temperatures were found at levels between 55 and 100 km and compared with observations. These experiments show how each opacity source contributes to the thermal structure, and indicate that computed global-mean temperatures are relatively insentive to uncertainties in the mesospheric optical properties. Latitude-dependent radiative equilibrium experiments show that meridional variations in radiative forcing act to destroy the observed mesospheric temperature gradients and produce polar temperatures which are up to 40°K cooler than those in the tropics. Net heating rates of 15°K/day (terrestrial solar day) are needed at levels in the polar mesosphere to maintain the observed thermal structure in the presence of the nominal radiative forcing.