RADIATIVE-CONVECTIVE MODEL WITH AN EXPLICIT HYDROLOGIC-CYCLE .1. FORMULATION AND SENSITIVITY TO MODEL PARAMETERS

A hydrological cycle is explicitly included in a one-dimensional radia tive-convective equilibrium model which is coupled to a ''swamp'' surf ace and tested with various cumulus convection schemes: the hard and s oft convective adjustment schemes, the Kuo scheme, the Goddard Institu te for Space Studies (GISS) (1974) model 1 scheme, the GISS (1983) mod el 2 scheme, and the Emanuel scheme. The essential difference between our model and other radiative-convective models is that in our model t he moisture profile (but not cloudiness) is interactively computed by the cumulus convection scheme. This has a crucial influence on the com putation of the radiative fluxes throughout the atmosphere and therefo re on the model's sensitivities. Using the Emanuel scheme, we show tha t the climate equilibrium is very sensitive to cloud microphysical pro cesses. Clouds with high precipitation efficiency produce cold and dry climates. Clouds with low precipitation efficiency lead to moist and warm climates. Since climate equilibrium can be very sensitive to the cloud microphysical processes, any cumulus convection scheme adequate for use in general circulation models (GCMs) should be strongly based on them. The cumulus convection schemes currently in use in GCMs bypas s the microphysical processes by making arbitrary moistening assumptio ns. We suggest that they are inadequate for climate change studies.