Interannual And Interdecadal Variations Of Summer Rainfall In South China And Their Relationships With Sea Surface Temperature In The Tropical Indian Ocean In Recent20Years

Interannual and interdecadal variations of summer (July-August) rainfall in South China in recent20years are investigated based on rainfall data from GPCP and China’s160stations. The observed global and tropical Indian ocean sea surface temperature (SST) are used to drive the NCAR CAM5.1global atmospheric circulation model for multi-group long-term integrations respectively, and then the changes of summer precipitation in South China and its relationship with tropical Indian Ocean SST anomaly are investigated through the comparison of model outputs with ERA-Interim reanalyses The main results are as follows:(1) Interdecadal weakening of summer rainfall in South China occured in the early2000s, which is possibly due to the changes of the North-Western Pacific Subtropical High (NWPSH) and the South Asia High (SAH). After the early2000s, the NWPSH strengthens and extends westward, and the SAH also enhances and extends eastward, producing an anomaly cyclone in the lower troposphere and an anomaly sinking motion over South China, which is unfavorable to induce rainfall overthere. Consistence of numerical simulations with observations indicate that the SST changes in tropical Indian Ocean exert important impacts upon the interdecadal variability of summer rainfall in South China. Interdecadal decreasing of summer rainfall in South China happened in the early2000s is possibly closely related to the interdecadal reduction of typhoon rainfall over there.(2) In recent20years, there exists a significant negative correlation between the summer (July-August) rainfall in South China and (May-June) SST in tropical Indian Ocean at the interannual scale, showing marked. negative relationship. When SST in the tropical Indian Ocean warmer than normal, the SAH will be stronger than normal and extend eastward, and the NWPSH will enhance and extend westward, producing anomaly cyclonic circulation, sinking motion over South China and thereby reducing rainfall over there. The results of numerical simulations indicate that the May-June SST anomaly in tropical Indian Ocean exerts important impacts upon the interannual variability of summer rainfall in South China.(3) The relationship between summer (July-August) rainfall in South China and (May-June) SST in tropical Indian Ocean becomes significantly negative from less significant after in the mid-1990s. Further analysis shows that the relationship of (May-June) SST in tropical Indian Ocean and (May-June) SST in tropical Western Pacific Ocean is strengthened, the relationship between the July-August North-Western Pacific Subtropical High (NWPSH) and July-August SST in tropical Western Pacific Ocean is also enhanced, at the same time The relationship between summer (July-August) rainfall in South China and the July-August NWPSH is increased, as well These factors may be the main cause of the strengthen relationship between summer (July-August) rainfall in South China and (May-June) SST in tropical Indian Ocean after the mid-1990s.