In this paper,we report on the results of an investigation into inter-decadal changes in moisture transport and divergence in East Asia for the two periods 1980-2001 and 1958-1979.The aim is to explore the mechanism of summer rainfall change in the region after abrupt changes.The relevant changes are calculated using ERA-40 daily reanalysis datasets.The results show that both stationary and transient eddy moisture transports to the Chinese mainland have declined since the abrupt change in atmospheric general circulation in the late 1970s,leading to more rainfall in South China and less in the North.The anomalous rainfall pattern coincides well with anomalous large-scale moisture divergence in the troposphere,of which stationary-wave or monsoon transport is dominant,in comparison with the contribution of the transient eddies.Furthermore,their divergences are found to be in opposite phases.In addition,meridional divergence is more important than its zonal counterpart,with an opposite phase in East Asia.Abnormal zonal moisture convergences appear in northwestern and northeastern parts of China,and are related to the excess rainfalls in these regions.An increase in transient eddy activity is one of the major mechanisms for excess rainfall in northern Xinjiang.Consequently,the anomalous rainfall pattern in East Asia results from a decline of the East Asian monsoon after the abrupt change,while the rainfall increase in northwestern China involves anomalies of both stationary waves and transient eddies on boreal westerly over the midand high latitudes.
[Objective] The research aimed to establish the regression model which was used to predict the precipitation in the flood season in China.[Method] Based on statistical model,North Atlantic oscillation index and the sea surface temperature index in development and declining stages of ENSO were used to predict East Asian summer monsoon index.After the stations were divided into 16 zones,the same factors were used to establish the regression model predicting the station precipitation in the flood season in China.Moreover,it was compared with the model that predicted firstly the monsoon index and estimated the precipitation.[Result] The prediction results of summer precipitation during 2005-2009 by every model were contrasted.It was found that the model that the factor predicted indirectly the regional precipitation was better than that predicted indirectly the station precipitation.Meanwhile,the model that the factor predicted directly the regional precipitation was better than that predicted indirectly the regional precipitation.The prediction score P of optimum model that three factors predicted directly the regional precipitation reached averagely 74.2,and the anomaly correlation coefficient ACC was averagely 0.219.Seen from the comparison situation of positive and negative zone distribution of precipitation anomaly percentage between the predicted and observed values in 5 years,the prediction effects in the south and east of Northeast China,some areas in the south of Yangtze River,the coast of South China and most areas of Xinjiang were good.The predicted positive/negative distribution of precipitation anomaly percentage tallied with that of observation.[Conclusion] The model could predict well summer precipitation in China.
CHENG Zhi1,2 1.College of Atmospheric Sciences,Lanzhou University,Lanzhou 730000,China
