Ocean forcing to changes in global monsoon precipitation over the recent half-century

Previous examination of changes in global monsoon precipitation over land reveals an overall weakening over the recent half-century (1950-2000). The present study suggests that this significant change in global land monsoon precipitation is deducible from the atmosphere's response to the observed SST variations. When forced by historical sea surface temperatures covering the same period, the ensemble simulation with the NCAR Community Atmosphere Model, version 2 (CAM2) model successfully reproduced the weakening tendency of global land monsoon precipitation. This decreasing tendency was mainly caused by the warming trend over the central-eastern Pacific and the western tropical Indian Ocean. At the interannual time scale, the global land monsoon precipitation is closely correlated with ENSO. The simulated interannual variation of the global land monsoon index matches well with the observation, indicating that most monsoon precipitation variations arise from the ocean forcing. There are uncertainties between the GPCP and the CMAP data in describing the evolution of global ocean monsoon precipitation. There is very little correspondence between the simulated and the observed global monsoon index over the ocean area. Uncertainties in the satellite data and model deficiencies in describing the ocean monsoon domain are partly to blame. Among the components of global monsoon systems, the Asian-Australian monsoon system has the lowest reproducibility with prescribed SST forcing due to the neglect of air-sea feedback.