Perspectives on the non-stationarity of the relationship between Indian and East Asian summer rainfall variations

The relationship between Indian and East Asian summer rainfall variations is non-stationary in observations as well as in historical simulations of climate models. Is this non-stationarity due to changes in effects of external forcing or internal atmospheric processes? Whilst ENSO is an important oceanic forcing of Indian and East Asian summer rainfall variations, its impacts cannot explain the observed long-term changes in the Indian–East Asian summer rainfall relationship. Monte Carlo test indicates that the role of random processes cannot be totally excluded in the observed long-term changes of the relationship. Analysis of climate model outputs shows that the Indian–North China summer rainfall relationship displays obvious temporal variations in both individual and ensemble mean model simulations and large differences among model simulations. This suggests an important role played by atmospheric internal variability in changes of the Indian–East Asian summer rainfall relationship. This point of view is supported by results from a 100-years AGCM simulation with climatological SST specified in the global ocean. The correlation between Indian and North China or southern Japan summer rainfall variations displays large fluctuations in the AGCM simulation