On overestimation of tropical precipitation by an atmospheric GCM with prescribed SST

We investigate how an atmospheric general circulation model (AGCM) can reproduce atmospheric aspects of climate, when the boundary conditions are prescribed. The AGCM is integrated with sea surface temperature (SST) specified from an integration of a coupled general circulation model (CGCM). A systematic difference in the mean climate is found between the AGCM and the CGCM in the tropical Pacific. This difference is apparent when and where local SST is warmest. In the CGCM, precipitation does not last long due to SST and cloud-radiation feedback. Precipitation in the AGCM, however, tends to persist longer. Results of this experiment imply that caution is needed when using an AGCM with boundary conditions derived from a CGCM for climate change studies.