El Nio和La Nia事件对东亚冬、夏季风循环的影响

Impacts of El Nino and La Nina on the Cycle of the East Asian Winter and Summer Monsoon

通过合成的El Nino和La Nina的分析发现,一般一个El Nino或La Nina事件大致可以分成爆发前的冬季、发展期的夏季、盛期时的冬季和衰亡期的夏季四个阶段。在此基础上利用NCEP再分析环流资料和中国降水资料分析了东亚冬、夏季风对El Nino和LaNina的响应,结果发现,El Nino和 La Nina事件显著地影响了东亚冬、夏季风的循环。ElNino爆发前的冬季在东亚地区往往有异常强的北风;El Nino发展期的夏季,西太平洋副热带高压偏弱,同时影响我国的西南气流偏弱,从而江淮地区和南方沿海地区多雨,长江中游和华北地区少雨;El Nino盛期的冬季东亚地区则出现异常的南风;而El Nino衰亡期的夏季,西太平洋副热带高压偏强,同时影响我国的西南气流偏强,从而江淮地区少雨,华北、东北以及洞庭湖、鄱阳湖地区多雨。La Nina对东亚冬、夏季风循环的影响则与El Nino大致相反,但它的影响不如El Nino的影响显著。对强、弱东亚冬季风后的夏季中国降水异常的分析则表明,正是由于与El Nino或La Nina事件有关的海温异常对东亚冬、夏季风循环的影响才导致了东亚冬季风与随后的夏季风存在着紧密的联系;当冬季风异常不是由与ElNino或La Nina事件有关的海温异常所引起时,两者之间就缺少显著的联系。

Investigations of composite El Nino and La Nina suggest that an El Nino or La Nina events may be generally divided into 4 stages. They are the winter preceding the event, the summer during the developing phase, the winter during the mature phase and the summer during the decaying phase. Then the responses of East Asian winter and summer monsoon to El Nino and La Nina are analyzed with the NCEP reanalysis 'data and the rainfalls in China. The results indicate that the cycle of the East Asian winter and summer monsoons are significantly influenced by the El Nino and La Ninaevents. In the winter preceding an El Nino events, there are anomalous northerlies over the East Asian region. In the summer during the developing phase of an El Nino events, the western subtropical Pacific high tends to be weak, meanwhile the southwesterlies which affect China tend to be weak too. Thereby the rainfall is above normal in the Yangtze-Huaihe River Valley and the southern coastal area of China, and below normal in North China and the middle reaches of the Yangtze River. However, in the winter during the mature phase of an El Nino event, there are anomalous southerlies over the East Asian region. Besides, in the summer during the decaying phase of an El Nino events, the western subtropical Pacific high tends to be strong, meanwhile the southwesterlies which affect China tend to be strong too. Thereby the rainfall is below normal in the Yangtze-Huaihe River Valley, and above normal in North China, Northeast China and the area of the Dongting Lake and the Poyang Lake. The situations are approximately reverse for the impact of La Nina on the cycle of East Asian winter and summer monsoon, although the impact of La Nina is not significant as that of El Nino. Finally, the anomalous summer rainfall in China after strong and weak East Asian winter monsoon is analyzed. The result shows that the close linkage between the East Asian winter monsoon and the following summer monsoon is due to the impact of the SSTA associated with El Nino or La Nina events on the cycle of East Asian winter monsoon and summer monsoon. When the anomalous winter monsoon is not related to the SSTA associated with El Nino or La Nina events, there is no close linkage between them.