February 3, 2009
China Monsoon Rainfall Prediction
The Monsoon and Environment Research Group of Peking University submitted a report to Chinese Science Bulletin, recently, showed that regional summer monsoon rainfall in China can be predicted by 1-2 seasons ahead by using the signals of the sea surface temperature anomaly (SSTA) and the subsurface temperature anomaly (STA) in the central equatorial Pacific (CEP). Several new facts have been revealed as follows.
(1) The strongest center of SSTA along the equatorial Pacific has migrated westward from the eastern equatorial Pacific (EEP, NINO3 region) to the CEP (NINO3.4 or NINO4 region) in the last half century. Regular inter-annual oscillations or variation frequency of SSTA in the equatorial Pacific are modulated by intensive La NiÃ±a events for about decadal interval. The winter phase-lock feature for warming events is commonly found at different intervals but warming places are also modulated by intensive La NiÃ±a events. The positive SSTA along the equatorial zone results from exposing positive STA which appears about 3 months earlier than SSTA. This is a precursory signal for indicating the future warming or cooling event in the equatorial Pacific.
(2) The subtropical summer monsoon rainfall in China has had a long-term rising trend for the last two decades. The long-term increasing trend is still continued in the central China (Huaihe) region but a deducing trend has been observed since 1998 in southern regions. A typical biennial oscillation of summer rainfall anomaly has been found in central China and biennial oscillation of SSTA has also been observed in the CEP since the early 21st century.
(3) Since the beginning of the 21st century, three warm events in winter occurring in the CEP have been accompanied with more summer rainfall in central China and less summer rainfall in southern China. The warm SSTA indicated that the winter phase-lock SSTA had a determined relationship with the summer rainfall anomalies in central China and southern China respectively. This relationship shows that the more summer rainfall in central China follows the winter-spring warm water in the CEP while the more summer rainfall in southern China may follow the winter-spring cool water in recent years. A cold water event was observed in 2008 so that the more summer rainfall has been successfully predicted in southern China.
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