Effect Of The Preceding Anomalous Sea Surface Temperature In Pacific Ocean And Indian Ocean On The Rainfall Around The Yangtze River And Its Southern Area In June

Based on the of NCEP/NCAR reanalysis data from 1951 to 2000, rainfall in the 160 stations in China from 1951to2000 and the Sea Surface Temperature Anomaly (SSTA) data provided by the NOAA-CIRES Climate Diagnostics Center. we examine the impact of the anomaly of the SSTA of tropical Indian ocean and tropical Pacific ocean on the rainfall in the Yangtze River and its south in June and the probable impacting mechanism is also studied. Then ,based upon the diagnostic results, we simulated the impact of the anomaly of the SSTA of the tropical Pacific ocean and tropical Indian ocean in the early Autumn using NCAR CAM3 atmospheric general circulation model (AGCM).Major conclusions are as follows:(1) The correlations between the Indian Ocean dipole index (IODI) and Nino3 index are different from seasons. The biggest correlation coefficient is 0.523 in autumn far beyond the 1% confidence level. Analysis the temporal variation of the monthly mean of the years when ENSO and Indian Ocean dipole both taken place in preceding autumn. we find that: Nino3 is stronger in December ;IODI is stronger in September ~November .Nino3 index's phase is not the same as IODI's ,IODI is about two months ahead of Nino3 index to be the maximum value .Define a new index(IODN3) which is the mix of Nino3 index and the IODI. IODN3 of preceding autumn is better correlated with the precipitation to the south of the middle and lower reaches of the Yangtze River in June in spite of the correlations associated with other two individual index with similar but the weaker features;(2) In Jun of the preceding autumn when positive phase events taken place the anomalies of 500hPa geopotential height, vertical velocity, vapor flux as well as anticyclonic circulation around the Philippine Island tends to maintain and stronger which contribute to the rainfall of Jun are almost opposite to these in Jun of the preceding autumn when negative phase events taken place.(3) the precipitation anomalies response to El Nino with different durations are different from each other, The anomalies of the model response are decreasing while the duration shorten. In a sense ,it's shown that strong SSTA in preceding Autumn is important to the rainfall around the Yangtze River and its southern area that corresponds with the former result of diagnostic analysis;the precipitation anomalies in the Yangtze River and its southern area are quite similar, a large area of positive precipitation anomalies, though the intensity of SSTA is different. It shows that the results of the model are stable and the results are believable;When the opposite SSTA is put in the model, the simulate results are not stable and not fully opposite to the results of the second experiments as well as different from the results of diagnostic analysis .(4) When a strong positive Indian Ocean dipole (IOD) event occurs in preceding Autumn,the anomalies precipitation in Jun around the Yangtze River and its southern area are positive and the results of the model are also stable and the results are believable;The results of the sensitive experiment showed that both of the positive SSTA in the tropical Pacific Ocean and positive IOD in the tropical Indian Ocean from early autumn to Jun could result in the significan"+ - +"pattern of 500hPa geopotential height anomaly over the mid-high latitude, and the influence of the former is larger;also these anomalies could make the subtropical high over West Pacific located in the west position, and the influende of the latter is larger.(5) When a strong positive IOD event simultaneously occurs with El Nino, the influence of them is different from the influence of a pure El Nino event occurs,the former could enhance the precipitation anomalousness in Jun around the Yangtze River and its southern area, and the results of the sensitive experiment are close to the fact, and the anticyclonic circulation around Philippine Island tends to maintain and stronger. Besides,the strong positive IOD may result in anomaly east wind from South China Sea to the Bay of Bengal.