梅雨期中国东部降水的时空变化及其与大气环流、海温的关系

Temporal and Spatial Variations of Precipitation in Eastern China During the Meiyu Period and Their Relationships with Circulation and Sea Surface Temperature

利用1961-2000年中国台站降水资料、NCEP／NCAR再分析资料以及扩展重建海平面温度（Extended Reconstructed Sea Surface Temperatures，ERSST）资料，采用EOF、小波变换、合成及相关方法探讨中国东部梅雨期降水的时空变化及其环流、水汽输送和海温异常特征。分析指出中国东部梅雨期（6月11日～7月10日）降水存在三种主要空间型：江南北部多雨型、长江流域多雨型和江淮平原多雨型。三种降水型都存在多时间尺度特征，由于年际和年代际振荡的周期和强度随时间的变化有不同表现，三种雨型旱涝年出现的年份有所不同。三种雨型对应的东亚夏季风环流各子系统的强度、位置、水汽输送等也存在明显差异。梅雨期三种雨型与冬季海温的研究表明：赤道东太平洋海温偏高有利于出现江南北部降水型；赤道印度洋、南海和西太平洋黑潮海温偏高有利于出现长江流域降水型；北太平洋中纬度海温偏高则有利于出现江淮平原降水型。

The observation shows that the main rain belt during the Meiyu period which may lead to flood is located in different areas in different years. But fewer works have been studied on such phenomena than on summer rainfall. However the rainfall during the Meiyu period often takes up half or more of total rainfall in summer of the year. So it is necessary to study the characteristics of rainfall during the Meiyu period. Based on the station rainfall in China, NCEP/NCAR reanalysis dataset and Extended Reconstructed Sea Surface Temperatures （ERSST）during 1961 - 2000, the temporal-spatial variations of precipitation in eastern China during the Meiyu period （11 June- 10 July） and accompanying circulation as well as pre-winter global sea surface temperature （SST） are studied by using the methods of empirical orthogonal function （EOF）, wavelet transform, composite and correlation analysis. It has been found that there are three main rain patterns in eastern China during the Meiyu period： the northern South China pattern, the Yangtze River pattern and the Yangtze- Huaihe plain pattern. They are all multi-scale phenomena and have three predominant oscillations： the quasi-biennial oscillation, the 3 - 5 year oscillation and the 10 year oscillation. But they are different from each other on amplitude and phase in the studying period. Furthermore their interdeeadal variation trends are different： for the Yangtze River pattern it is linearly increasing during the whole studying period and the sign varies from negative to positive around the end of the 1970s; while, for the other two, it is like a saddle back with the sign positive in the early and late studying period and negative in the mid studying period. It shows that the rainfall along the Yangtze River are increasing while rainfall over the northern South China and the Yangtze- Huaihe plain first decreased before the 1980s and then turned to increase after. Because these interannual and deeadal oscillations differ in period and intensity, the time of drought and flood occurring is different for the three rain patterns. It has been found that the East Asian monsoon circulation plays an important role in different rain patterns. Espeeially the western Pacific subtropical high, the Meiyu trough and the Okhotsk high are three most important circulation systems which have great influences on the precipitation in eastern China during the Meiyu period. The western Pacific subtropical high is more westward and southward than normal for the Yangtze River pattern while more northward and eastward than normal for the Yangtze- Huaihe plain pattern, and for the northern South China pattern it is similar to that for the Yangtze River pattern but somewhat more eastward than the latter. And the characters of water vapor transport for the three rain patterns are distinctly different too. The three rain patterns have a good correlation with pre-winter SST： the northern South China pattern has a high positive correlation with the tropical SST in the eastern Pacific, the Yangtze River pattern has a positive correlation with the tropical SST in the eastern Pacific and the eastern Indian Ocean and the subtropical SST in the northwestern Pacific, while the Yangtze- Huaihe plain pattern has a higher positive correlation with the subtropical SST in the North Pacific. It suggests that the rain pattern may be linked to the northward and eastward movement of the western Pacific subtropical high with the seasonal change and the different stages of ENSO cycle.