Quantifying Cloud Radiative Effects based on Cloudsat and Calipso Profiles

Our limited knowledge about clouds and their horizontal and vertical structure, and the resulting influence of clouds on the radiation budget, present one of the largest uncertainties in our understanding of the climate system. The A-Train satellite constellation, and in particular the CLOUDSAT cloud radar and CALIPSO cloud and aerosol lidar, offer a unique source of data to study this aspect of climate.

We present a modelling framework for calculating vertically resolved profiles of shortwave and longwave radiative fluxes and heating rates from CLOUDSAT and CALIPSO operational products. The radiation calculations are carried out with the Rapid Radiative Transfer Model for GCM applications (RRTMG), which has recently been adopted by a variety of atmospheric models. It is based on a two-stream solver of the radiative transfer equation and a correlated-k scheme for absorption by relevant atmospheric cases. Aerosol effects are included using Calipso-retrieved aerosol optical depth at 532nm, and the spectral dependence of their optical properties is obtained from the OPAC aerosol properties library.

A comparison of radiative fluxes and heating rates calculated by our scheme with the official 2B-FLXHR product is presented. In particular, focus is given to the impacts of aerosols, which are not included in the 2B-FLXHR product. Also, different strategies for combining CLOUDSAT and CALIPSO data are evaluated, and the resulting uncertainties are discussed.