我国西南地区秋季降水年际变化的空间差异及其成因

使用1980～2010年全国站点降水资料、ERA-Interim再分析环流资料、哈德莱海表温度资料,运用聚类分析和旋转经验正交函数分解,对西南地区的秋季降水按照其年际变化规律进行分区,进而分析影响各区域降水变化的物理过程和机理。结果表明:西南地区被分为东、西两个区域。西南东、西区域秋季降水的年际变化、显著周期、旱涝异常年份、相关的环流系统都有明显差异。西南东部秋季降水主要与热带海温异常有关,受低纬度环流影响。当赤道东太平洋为暖海温异常,热带印度洋为西正东负的偶极子型海温异常时,分别激发出西北太平洋反气旋和孟加拉反气旋,共同向西南东部输送水汽,造成西南东部降水偏多。西南西部降水在秋季三个月份与不同的环流形势对应:9月降水由中南半岛反气旋输送的暖湿气流决定;10月降水受高原以东反气旋环流和孟加拉湾低槽共同影响;11月降水主要受中高纬环流异常的影响,与斯堪的纳维亚遥相关存在显著负相关。

Spatial Pattern and Causes of Interannual Variability of Autumn Rainfall in Southwest China

Spatial pattern and mechanisms of interannual variability of autumn rainfall in Southwest China (SWC) are analyzed using rainfall data from weather stations in China and ERA-Interim reanalysis as well as Hadley Sea Surface Temperature (SST) data.Cluster analysis and Rotated Empirical Orthogonal Function have been applied in the present study.Based on differences in the interannual variability of autumn precipitation,SWC is divided into two parts:the eastern part and the western part.The interannual variability of rainfall,significant periods of oscillation,extremely dry or wet years and related atmospheric circulations are substantially different between the eastern and western SWC.The rainfall variability in the eastern SWC is closely related to tropical SST anomalies.The positive SST anomaly in the eastern Pacific Ocean can trigger anticyclonic circulation over the northwestern Pacific,while the dipole mode of SST anomaly in the tropical Indian Ocean with positive SST anomaly in the west and negative SST anomaly in the east can induce anticyclonic circulation over the Bay of Bengal.As a result,the atmospheric moisture transport to eastern SWC intensifies.However,the circulation patterns corresponding to rainfall anomalies in the western SWC in the three months of autumn are different.In September,the western SWC is under control of the anticyclone over the Indochina Peninsula.In October,the anticyclone to the east of the Tibetan Plateau and the low trough over the Bay of Bengal work together to determine precipitation in the western SWC.In November,anomalous atmospheric circulation over the mid-high latitudes plays an important role for rainfall in the western SWC,which is highly negatively correlated with the Scandinavian teleconnection index.