气候变暖背景下全球海温对中国东部夏季降水年代际转折的影响

针对1970年代末及1990年代初中国东部夏季降水（ECP）的年代际变化格局，采用EOF分解、相关分析、回归分析等统计方法诊断了全球海表面温度对ECP年代际变化前两个模态（EOF1、EOF2）的影响。发现大西洋多年代际振荡（AMO）序列，印度洋偶极子（DMI）序列，太平洋年代际振荡（PDO）序列与ECP前两个模态时间系数（PC1、PC2）相关性较好，结合各海温指数的年代际变化特征，发现ECP在1970年代末受PDO及DMI的影响在低纬及中纬度地区分别呈现EOF1、EOF2的正位相分布特征；而在1990年代初受AMO及PDO的影响主要呈现EOF1的特征。由各海温指数及PC1、PC2重建的ECP分布特征可知，AMO及DMI与PC1重建的ECP型相近，对ECP的影响范围集中在低纬地区。除去变暖影响的DMI及PC1回归的高度场中发现一个源起大西洋的波列，黄河以北为异常反气旋中心，以南为异常气旋中心，低层南风异常，水汽被输送到北方，导致中国北方降水增加，南方降水减少。PDO与PC2重建的ECP型相近，对ECP的影响集中在中纬度地区。二者回归得到中国东部低层北风异常，水汽在长江流域辐合，长江流域降水增加。 

THE IMPACTS OF GLOBAL SEA SURFACE TEMPERATURE ON DECADAL TRANSITIONS OF SUMMER PRECIPITATION OVER EASTERN CHINA AT GLOBAL WARMING TRANSITION POINTS

To analyze the decadal variability of the summer precipitation over eastern China (ECP) in the late 1970s and the early 1990s, the impacts of global sea surface temperature on the first two modes of the EOF decomposition of the ECP decadal change are diagnosed based on traditional statistical methods. The results show that there are considerable correlations between the Indian Ocean Dipole (DMI), the Atlantic Pacific Decadal Oscillation (PDO) and the time coefficients of the first and second EOF modes (PC1, PC2). According to the decadal variations of the DMI and PDO, the ECP mainly demonstrates the positive phase of first EOF mode (EOF1) and second EOF mode (EOF2) in the late 1970s due to DMI and PDO variations; the ECP shows the general first EOF mode (EOF1) in the early 1990s because of AMO and PDO variations. The reconstructed ECPs based on the AMO, DMI and PC1 are similar, mainly affecting the lower latitude of ECP. The wave trains originating from the Atlantic Ocean in the 500 hPa height fields regressed by PC1 and the IDMI-T (DMI removing the global warming effect) include an anomalous anticyclone center over the north of the Yellow River and a cyclone center to the south of the Yellow River, which generate low-level southerly anomalies and more water vapor transportation into northern China. As a result, summer rainfall increases over northern China and decreases over southern China. The reconstructed ECPs by the PDO and PC2 are similar and mainly affect the mid-latitude of ECP. Their regression fields lead to low-level north wind anomalies and water vapor convergence over the Yangtze-River Valley, which can explain the rainfall growth over the corresponding region and the decrease over north and south China.