南印度洋偶极型海温与中国西南地区初秋降水的关系

Relationship between the South Indian Ocean Dipole and the September Precipitation in Southwest China

利用1979年1月~2018年12月Hadley海表温度资料、CRU TS v4.03逐月格点降水资料,以及NCEP/NCAR再分析月平均资料,对南印度洋偶极型海温与中国西南地区初秋降水的关系进行了研究。结果表明:7~8月平均印度洋海表温度EOF第二模态表现为显著的东北—西南向偶极子模态,其东北和西南两侧的海表温度呈反相位变化特征,为典型的南印度洋偶极子(SIOD)分布,其时间系数表现为30a以上的周期变化并定义为新的SIOD指数;对应7~8月SIOD正异常,西南地区9月对流活动显著增强,负异常则对流活动显著受到抑制,且SIOD指数与中国西南地区初秋降水呈较强的正相关;SIOD影响中国初秋降水的主要途径是:印度洋东北部形成的越赤道气流在孟加拉湾以南上空分为两支,其中一支经孟加拉湾和中南半岛进入中国西南地区,将孟加拉湾水汽向该地区输送,并造成水汽在该地区辐合,有利于中国西南地区降水发生。该研究结果不仅对认识南印度洋海气系统对中国降水的可能影响,还对发展西南地区初秋降水预测模型有着重要的意义。

Using Hadley sea surface temperature data from January 1979 to December 2018,monthly grid precipitation data of CRU TS v4.03,and NCEP/NCAR re-analysis of monthly average data. The relationship between the dipolar sea temperature of the South Indian Ocean and the early autumn precipitation in southwestern my country was studied. The results show that the second mode of the average Indian Ocean sea surface temperature EOF from July to August shows a significant northeast-southwest dipole mode,and the sea surface temperature on both sides of the northeast and southwest shows an inverse phase change feature,which is typical. The distribution of the South Indian Ocean Dipole(SIOD),whose time coefficient is a periodic change of more than 30 years,is defined as a new SIOD index;Corresponding to the positive SIOD anomaly from July to August,the convective activity in Southwest China increased significantly in September,while the negative anomaly was significantly suppressed and the SIOD index was strongly positively correlated with the September precipitation in Southwest China. The main ways that SIOD affects China’s September precipitation are: The cross-equatorial air current formed in the northeastern Indian Ocean splits into two branches over the south of the Bay of Bengal. One of them enters southwestern China through the Bay of Bengal and the Indochina Peninsula. Precipitation occurs in southwest China. The results of this study are not only useful for understanding the possible impact of the South Indian Ocean air-sea system on precipitation in my country,but also for the development of early autumn precipitation prediction models in Southwest China.