The Parameterization of Shortwave and Longwave Radiative Fluxes for Use in Zonally Averaged Climate Models

Abstract

The shortwave and longwave fluxes at the top of the atmosphere (TOA) and at the surface are parameterized in term of solar constant, solar zenith angle, cloud parameters (amount, optical depth, height, and emissivity), surface albedo, surface air temperature, surface temperature, and atmospheric CO2 concentration. Detailed radiative models are used to calculate up- and downward radiative fluxes at TOA and at the surface with input from standard vertical atmospheric profiles of temperature, water vapor, and ozone. Expressions for clear-sky and completely overcast conditions are presented. It is shown that there is reasonably good agreement between the radiative fluxes calculated with this parameterization, with the detailed radiation models and with standard radiation codes (ICRCCM). Furthermore, it is shown that the parameterization is able to produce with reasonable accuracy several aspects of the latitudinally and seasonally varying, zonally averaged shortwave and longwave radiative fluxes at TOA and at the surface. The effect of clouds on the radiative fluxes as calculated with the parameterization compares reasonably well with observations, which is an important aspect for climate modeling studies. The radiation parameterization presented here is particularly useful in zonal average climate models (such as energy balance climate models) that treat the atmosphere as one bulk layer, since it is computationally efficient.