不同年代际背景下南半球环流变化对中国夏季降水的影响

利用1951～2008年NCEP再分析资料和中国夏季降水观测资料,分析了南半球环流的年代际变化特征以及在不同年代际背景下南极涛动(AAO)对中国东部夏季降水的影响.结果表明,20世纪70年代末,南半球环流发生了年代际变化,东南太平洋和南大西洋副高减弱,而马斯克林高压(南印度洋副高)增强,绕南极低压带加深.在此背景下,AAO由负位相转变为正位相,对中国夏季降水的影响也随之发生改变.在春季AAO偏强的情况下,1976年之前,长江以南地区和华北地区降水偏多,江淮流域降水偏少；而在1976年之后,从华南沿海一直到江淮流域降水都偏多,华北到东北地区降水偏少.这说明AAO对中国夏季降水的影响与年代际背景有关,1976年之后,AAO对中国夏季降水的影响增强,影响范围更加偏北.在当前海温预报因子作用减弱的情况下,AAO有可能成为中国夏季降水预测的一个重要预报因子.

Influence of Southern Hemisphere Circulation on Summer Rainfall in China under Various Decadal Backgrounds

Using the NCEP reanalysis data and observed rainfall data in China from 1951 to 2008, the interdecadal variation in Southern Hemisphere (SH) circulation and the influence of Antarctic Oscillation (AAO) on summer rainfall in eastern China under the various decadal backgrounds was analyzed. The results indicate that interdecadal variation of SH circulation occurred during the late 1970s. While the subtropical highs in the southeastern Pacific and the southern Atlantic were weakened, the Mascarene high, also known as the Indian Ocean subtropical high, was intensified. In addition, the circumpolar low-pressure belt was deepened. The AAO with a negative phase was changed into a positive phase. The influence of AAO on summer rainfall in China was also changed. A stronger AAO in the boreal spring before 1976 related to more rainfall in the southern Yangtze River and in North China and less rainfall in the Yangtze-Huaihe River valley. Conversely, rainfall amounts were higher from south China to the Yangtze-Huaihe River valley and lower in northern and northeastern China after 1976. Therefore, the influence of AAO on summer rainfall in China is related to the decadal background. After 1976, the influence of AAO tended to intensify and extend more northward. When the effects of sea surface temperature are minimal, AAO can be used as an important tool for summer rainfall prediction in China.