DEVELOPMENT OF THE NEW CCC/GCM LONGWAVE RADIATION MODEL FOR EXTENSION INTO THE MIDDLE ATMOSPHERE

A new infrared (IR) radiation scheme for extending the CCC/GCM (Canadian Climate Center General Circulation Model) into the middle atmosphere is proposed. It combines the previous CCC/GCM radiation scheme including the effects of H2O, CO2, O-3, CH4, N2O, CFC11 and CFC12, clouds and aerosols, with a new computationally efficient matrix parameterization for the cooling rate in the middle atmosphere for both LTE (local thermodynamic equilibrium) and non-LTE layers. The matrix parameterization includes the effects of both the 15 mu m CO2 and the 9.6 mu m O-3 bands and provides a proper lower boundary condition for the non-LTE recurrence formula. The new scheme shows satisfactory agreement with line-by-line calculations. The absolute error does nor exceed 0.8 K day(-1) for vastly different atmospheric conditions. Introducing the new radiation module into the CCC/GCM results in deviations of the simulated temperature from the CIRA-1986 model of not more than 10 K throughout most of the altitude-latitude domain.