Cloud radiative forcing over South America: Comparison of CPTEC/COLA AGCM output with SRB data

Cloud radiative forcing (CRF) as well as cloud radiative forcing ratio (CRFR) are useful parameters for studying the effects of clouds on the Earth's radiation budget. By its definition, CRF is the difference between the radiative fluxes in the cloudy and clear-sky conditions while CRFR is the ratio between them. Comparison of CRF or CRFR values simulated by AGCM with those measured helps to verify cloud and radiation parameterizations employed in the models. In order to verify cloudiness impact on the surface solar radiative fluxes simulated by CPTEC/COLA AGCM in the different regions of South America, we compared seasonal variations of cloud radiative forcing ratio obtained as output from 10-year run (1985-1996) of CPTEC/COLA AGCM with the CRFR data provided by First WCRP Surface Radiation Budget Global Data Set (1985-1988). Strong change of seasonal variations of CRFR with latitude over South America has been found in both data sets. Also the monthly mean values of CRFR simulated by CPTEC/COLA AGCM in Brazil's Amazonia were compared with the CRFR data obtained from the ground-based solar irradiance measurements taken at the six ABRACOS observational sites from 1991 to 1995. The better or worse agreement between simulated and measured monthly mean CRFR values has been obtained for the various regions of South America providing information about the needed changes in the model parameterizations of cloudiness.