北印度夏季风与中国河套及邻近地区盛夏降水的联系

Relationships between North Indian Summer Monsoon and Midsummer Rainfall in Hetao and Its Vicinity Regions of China

利用印度热带气象研究所和中国气象局分别提供的1951-2006年印度各分区和中国160个站点的逐月降水资料,NCEP/NCAR逐月再分析资料以及NOAA提供的逐月海表温度资料,对印度各分区降水与中国区域降水之间的联系进行了分析。结果发现盛夏7-8月印度西北部和北部山区降水与中国河套及邻近地区降水呈显著的正相关关系,由此将7-8月印度西北部与北部山区降水定义为北印度夏季风指数。进一步通过遥相关和水汽输送揭示了北印度夏季风强弱与中国河套盛夏降水的联系途径。当北印度夏季风偏强时,中国河套受异常低压系统前部气流控制,系统从低层到高层向西倾斜,低压前部、高压后部的偏南气流带来南方暖湿气流,有助于河套降水的产生。北印度夏季风强盛年亦有助于输送到中国河套地区的三条水汽通道的加强。北印度夏季风偏弱时,情况相反。北印度夏季风异常偏强/弱,若从前期冬季开始伴随有一次La Nia/El Nio过程,赤道东太平洋SST异常通过与北印度夏季风相联系引起的水汽异常输送对中国河套降水产生更显著影响,而北印度夏季风即使不受到赤道东太平洋SST异常影响,对河套降水的影响仍然是显著的。

Based on monthly rainfall series of seven homogeneous zones in India and 160 observational stations in China during 1951 to 2006,as well as monthly mean reanalysis data from NCEP / NCAR and NOAA,the relationships between rainfall in each subregions over India and China are investigated. The results showthat rainfall in July and August over the northwest and north mountains of India and Hetao and its vicinity areas（ Hetao for short） of China exhibit a significant positive correlation,thus defining the midsummer rainfall of the northwest and North Mountains of India as North Indian summer monsoon（ NISM）. To further reveal the relevant mechanism of the NISMon the rainfall of Hetao,we discuss the relation from two aspects of teleconnection and water vapor transport. It is indicated that when the NISMis strong,Hetao is controlled by the southerly stream in front of abnormal depression,which is located to the southeast of Lake Baikal and tilts westward with the increase of altitude. In addition,the enhancement of NISMalso induces the reinforcement of water vapor transporting to Hetao,which is favorable for more rainfall there than normal,and vice versa. Strong / weak NISMis often companied by a La Nia / El Nio event. Eastern equatorial Pacific anomalous SST plays an important role on Hetao rainfall through NISM,while NISMis still significantly correlated with the rainfall of Hetao after excluding the effect of eastern equatorial Pacific SST anomalies.