Lower stratospheric radiative heating rates and sensitivities calculated from Antarctic balloon observations

Temperature, water vapor, and ozone profiles from balloon soundings at McMu rdo Station, Antarctica, during winter 1994 were used to calculate the diab atic heating rate in the lower stratosphere. These three variables represen t the necessary inputs to a clear-sky radiative heating rate calculation, A ccurate profiles of these variables without recourse to ancillary climatolo gical databases provide a means of testing the importance of realistic wate r vapor and ozone distributions to the lower stratospheric heating rate. Wa ter vapor at wavelengths greater than 17 mu m contributes as much cooling a s CO2 in the lower stratosphere during winter. Dehydration begins in midwin ter and causes a decrease in the cooling rate (increase in the heating rate ) by 30%. Ozone depletion affects both longwave and shortwave heating rates in the altitude region where the ozone loss occurs. The longwave heating d ecreases by 0.3 K d(-1) (potential temperature) and is comparable in magnit ude to that of the decrease in shortwave heating for a balloon sounding in early October. Significant longwave heating increases of 0.6 K d(-1) also o ccur above the region of ozone depletion as a result of higher penetration of upwelling radiation emitted by the surface. Sensitivity studies of the i mpact of tropospheric clouds at McMurdo show that the lower stratospheric h eating rates can decrease by 0.08 to 0.26 K d(-1) (vertically averaged) (18 to 60%), depending on the cloud parameterization used. Time series of the calculated heating rate at McMurdo show the effects of dehydration, ozone l oss, and the increase of the heating rate (decrease of the cooling rate) as the temperatures decrease and approach radiative equilibrium through the w inter.