A parametrization of solar energy disposition in the climate system

Abstract

During the past decade a class of climate models of reduced complexity, called Earth system Models of Intermediate Complexity (EMICs), has been developed. Some of these models employ an energy and moisture balance model (EMBM) as the atmospheric component. However, the solar energy disposition (SED) in the subcomponents of these climate models using an EMBM has never been parametrized in a systematic manner. In this paper, the SED, which is a measure of the amount of solar radiation absorbed in the atmosphere, absorbed at the surface and reflected to space, is first expressed as functions of the surface albedo and the integrated atmospheric reflectivity, transmissivity, absorptivity and cloud amount for a one‐layer atmosphere which includes a cloud region and aerosols. Then an atmospheric radiative‐convective model is used to parametrize the integrated atmospheric reflectivity and transmissivity in terms of cloud optical depth, aerosol optical depth, precipitable water, and solar zenith angle. Next, the presentday climatology of the SED is calculated using the climatological data (for cloud amount and optical depth, aerosol optical depth, precipitable water and surface albedo) from the International Satellite Cloud Climatology Project (ISCCP ), ECMWF 15‐year Reanalysis (ERA‐15) and the Pathfinder Atmosphere (PATMOS). Since cloud amount data are used from three independent sources, three SEDs are in fact calculated and tested against the SED derived from satellite data. The calculated SEDs are in good agreement with the SED derived from satellite data; thus the parametrized SED presented here is recommended for use in climate models which employ an EMBM or a one‐layer atmosphere model.