Characteristics of cloud radiative forcings over East Asia as simulated by the AGCMs in the CFMIP

Based on observational evidences from the satellitebased cloud and radiation retrievals, the authors evaluate the performances of ten current stateoftheart Atmospheric General Circulation Models (AGCMs) in simulating the cloud amount, cloud vertical structure, and cloud optical properties as well as its radiative characteristics over the East Asia domain. The simulations of ten AGCMs involved in the Cloud Feedback Model Intercomparison Program (CFMIP) are analyzed. The ISCCP simulator was employed in all models to facilitate the comparison between model results and satellite products. The results show that both the boreal winter and summer mean spatial patterns of cloud amount as well as cloud radiative characteristics are reasonably simulated by most of models. However, there still exist some discrepancies. Many AGCMs fail in capturing the boreal wintertime cloud maxima center on the lee side of Tibetan Plateau, and underestimate the middle-and low-level cloud amount around the East China Sea. The underestimate in total cloud amounts on the lee side of Tibetan Plateau and over the East China Sea are due to the underestimate of low- and middle- cloud amount. Many models are able to reasonably reproduce the total cloud maxima center over the Bay of Bengal and the southwestern China as well as a high cloud amount belt from southwest China to Japan in summer, but the amount of high level cloud is overpredicted and the middle-and low-level clouds are underpredicted over the cloudabounding region. The spatial pattern of simulated shortwave cloud radiative forcing resembles that of total cloud amount, while the spatial pattern of simulated longwave cloud forcing is similar to that of the high level cloud amount. However, the simulated cloud radiative forcing is better than the cloud amount both in spatial pattern and magnitude. The better simulation of shortwave cloud radiative forcing is resulted from the compensation of overestimated cloud optical thickness and underestimated cloud amount. In most models, the cloud optical depths at most levels are overestimated. The cloud radiative forcing is composited by the effects in both the cloudy and clear sky conditions. Besides cloud properties, the clear sky albedo is another cause to the discrepancy in shortwave cloud radiative forcing in boreal winter over land. The overestimate of clear sky surface albedo leads to a underestimate of shortwave cloud radiative forcing. The authors also propose whether the middle- and low-level cloud amount on the lee side of Tibetan Plateau can be properly reproduced in models is closely related to the fidelity of the simulated large scale circulation.