Relationships Between Rainfall In The Southern Part Of China And SSTA Of Both Tropical Indian Ocean And South China Sea

Using the monthly mean data from SODA, GISST 2.3b, NCEP/NCAR reanalysis, CMAP and Willmott precipitation datasets, we have investigated the relationships between the summer rainfall in southern part of China and the SSTA of the tropical Indian Ocean along with the South China Sea. The results are summarized as follows:(1) The dipole pattern is observed in the sea surface height and the depth of 20℃ when a dipole event occurs in the tropical Indian Ocean as observed in SSTA. The winds near the ocean surface in the central equatorial Indian Ocean blow towards west during positive dipole events. In the Pacific ENSO years, the IOD pattern is not observed in either surface height or depth of 20 ℃ isoline in the tropical Indian Ocean. These results reconfirm that the IOD is independent of ENSO. The surface height dipole index (SHDMI), depth of 20℃ index (ZDMI) and surface zonal wind-stress dipole index (UDND) have been defined to indicate the IOD signals, which involves the oceanic dynamic processes. These indices are consistent with each other and have strong correlations with the SSTA IOD index.(2) By defining the pure Indian Ocean Dipole (IOD) index and pure NIN03 index, we have demonstrated that both the IOD and the tropical middle Indian Ocean SSTA from Jun to August have significant positive correlations with South China summer rainfall. About 60% of summer rainfall anomalies in South China can be explained by the interannual variations of tropical Indian Ocean SSTA in May, which is a very useful clue to rainfall prediction. When the IOD index is positive (negative), South China summer rainfall enhances (reduces), caused by the anomalous ascent (subsidence) and the water vapor convergence (divergence) over South China.(3) The JJA mean SST of South China Sea (SCS) is increased apparently from 1950 to 1999. The anomalous low temperatures have been observed before 1980s, whereas the anomalous high temperatures after 1990s. The abrupt change as detected in the time series of SSTA begins from later of 1980s. The SST changes with periods of 3-5 years, quasi-seven years and quasi-ten years.The SSTA exhibits two distinct patterns. The one shows the same-signed SSTA over the entire SCS basin. The other shows the dipole-like distribution with the oppositely signed SSTA in the southern and the northern part of SCS respectively. The variance of the same-signed SSTA is prominent, while the dipole like SSTA pattern appeared around 10% times of the 50 study years. The correlation reaches its maximum when SCS SSTA lags equatorial Pacific SSTA by 7 months. The same-signed SSTA in SCS has positive (negative) correlation with both the tropical southeast (southwest) Pacific SSTA and the tropical Indian Ocean. The oppositely signed SSTA pattern in SCS is to some extent related to the IOD other than the Pacific ENSO. These results reconfirm that IOD is an ocean-atmosphere coupled phenomenon in the tropical Indian Ocean.(4) Both the simultaneous and lag correlations of the South China summer rainfall with the SCS same-signed SSTA are significant. When SSTA of the whole SCS are warm, the water vapor converges in South China, causing excessive rainfall in Yangtze River valley and Sichuan province, whereas rainfall decreases in Shandong province, southern part of Fujian province and eastern part of Guangdong province. When SSTA in the northern (southern) part of the basin in summertime is positive (negative), excessive rainfall is received in the southern Yangtze River valley, while less rainfall is received in large part of Huaihe River valley.