Testing the role of radiation in determining tropical cloud top temperature

A cloud-resolving model is used to test the hypothesis that radiative cooling by water vapor emission is the primary control on the temperature of tropical anvil clouds. The temperature of ice clouds in the model can be increased or decreased by changing only the emissivity of water vapor in the upper troposphere. The results agree with expectations from the Fixed Anvil Temperature (FAT) hypothesis proposed by Hartmann and Larson (2002). The model's fixed ozone profile influences upper tropospheric stability and creates a pressure-dependent inhibition of convection, leading to a small warming in cloud top temperature as sea surface temperature is increased. If only water vapor is included in the radiative calculation the cloud top temperature becomes independent of surface temperature as the FAT hypothesis predicts.