An economical method for computing the radiative energy transfer in circulation models

Abstract

Abstract Based on the methodology of a two‐stream approximation (Kerschgens et al. 1978) the transfer of radiative energy in model atmospheres can now be calculated with high economy and sufficient accuracy. In this model the number of spectral intervals has been minimized to four (solar spectrum) and six (infrared spectrum) for which new effective transmission functions have been computed, where standard aerosol profiles and absorption and scattering coefficients are incorporated. The concentrations of major atmospheric gases (water vapour, carbon dioxide, ozone), the cloud cover and cloud liquid water content of each layer can be changed freely. Thus this model could be used in any numerical circulation model. In the first part of this paper we discuss the basic principles of the method and results obtained for cloudless model atmospheres. The accuracy of computed flux densities is better than 5% and of flux divergences better than 20% in the worst cases. In the second part this method will be applied to total and partial cloud cover in each layer.