厄尔尼诺事件对中国夏季水汽输送和降水分布影响的新研究

基于1961-2016年中国地面台站降水观测资料和多种再分析资料，分析了东部型和中部型两类厄尔尼诺事件对中国夏季水汽输送和降水的不同影响。结果表明：（1）厄尔尼诺事件对中国夏季降水的影响在发生当年和次年有明显的不同，主要影响是在其发生的次年，中国大部分地区的夏季降水明显偏多。（2）东部型厄尔尼诺事件当年夏季，西北太平洋副热带高压（副高）偏东偏弱，水汽输送条件较弱，不利于中国大范围降水的发生；中部型事件当年夏季，低纬度印度洋和西太平洋蒸发异常偏强，来自阿拉伯海、孟加拉湾和西北太平洋向华南地区的水汽输送和净水汽收支增加，有利于华南地区降水的异常增多。（3）东部型厄尔尼诺事件次年夏季，副热带太平洋蒸发异常偏强，副高西伸，由于东亚-太平洋（EAP）遥相关型的建立，副高西侧的强西南气流将来自太平洋蒸发的大量水汽持续输送至中国中东部地区。此外，在东亚-太平洋遥相关型影响下中高纬度地区建立了亚洲双阻型环流，其间的低槽冷涡与上游阻高之间的强偏北气流有利于北冰洋的水汽持续输送到西北和华北北部地区，中国大部分地区净水汽收支均增加，中国北方和南方地区的降水均产生了明显的同步性增多响应，形成了南北两条异常雨带。中部型厄尔尼诺事件次年夏季，副高较常年偏西且偏北，来自太平洋蒸发的大量水汽输送到江淮地区，使其净水汽收支增加和降水偏多。因此，厄尔尼诺事件的发生不仅对长江流域和淮河流域等南方地区的降水有重要影响，对华北、东北和西北地区的降水异常也有相当的作用。

A new study of El Niño impacts on summertime water vapor transport and rainfall in China

Based on observed precipitation data and multiple reanalysis datasets from 1961 to 2016, different impacts of eastern Pacific (EP) El Niño and central Pacific (CP) El Niño events on summertime moisture transport and rainfall in China have been investigated. Results suggest that:(1) the impacts of El Niño events on summertime rainfall in China are significantly different in the El Niño developing summer and decaying summer. The main impacts occur in the El Niño-decaying summer when obvious rainfall signals are found in most areas; (2) in the summer of EP El Niño developing, the western North Pacific (WNP) subtropical high (SH) tends to retreat eastward and becomes weak. The weak moisture transport conditions are not conductive to the occurrence of rainfall in most areas. In the summer of CP El Niño developing, evaporation over the western Pacific Ocean and low latitudes of the Indian Ocean becomes stronger. Abundant moisture originating from the Arabian Sea, the Bay of Bengal and the western Pacific Ocean is transported to South China and the net moisture income increase, tending to induce positive rainfall anomalies in South China; (3) in the El Niño decaying summer, extra tropical Pacific evaporation increases significantly. The westward expansion of the WNPSH and the establishment of East Asia/Pacific (EAP) teleconnection are favorable for the southwesterly winds along the western side of the WNPSH to carry abundant water vapor from the Pacific to central-eastern China. Meanwhile, the double-blocking set up in Eurasia high-mid latitudes and the northerly flow between the low trough and upstream blocking high tend to carry more water vapor from the Arctic Ocean to Northwest China and northern part of North China. The positive net moisture income anomalies are found in most areas in China, providing favorable moisture conditions for rainfall. Two rain belts form in southern and northern China, respectively. In the CP El Niño decaying summer, the WNPSH tends to extend westward and northward, which is favorable for the transport of water vapor originating from the strong Pacific evaporation to Jianghuai region, leading to increases in net moisture income in Jianghuai region. Hence, El Niño events not only influence rainfall anomalies in Yangtze River valley and Huai River valley, but also influence rainfall anomalies in North China, Northeast China and Northwest China.