欧亚遥相关型对印度夏季风与华北夏季降水间关系的影响

Effect on the relationship between Indian summer monsoon and North China summer rainfall by Eurasian teleconnection

利用国家气候中心160站月平均降水资料、印度热带气象研究所的全印度月平均降水资料和NCEP/NCAR的再分析资料,从年际和年代际角度分别研究了欧亚遥相关型(Eurasian teleconnection,EU)对印度夏季风与华北夏季降水关系的影响,并探究其物理机制。结果表明,EU与印度夏季风之间的相关系数只有-0.078,二者相互独立。印度夏季风与华北夏季降水有正相关关系(Indian Summer Monsoon and North China Summer Rainfall,ISM-NCSR),且在正EU位相时,ISM-NCSR关系较弱;负EU位相时,ISM-NCSR关系较强。这是由于EU负位相时,贝加尔湖右侧存在反气旋环流,有利于北风及冷空气南下。因此,强印度季风时北上的暖湿气流在华北地区与偏北风相遇形成锋面,有利于华北降水;弱印度季风时华北地区完全被强北风控制,水汽输送通道被阻断,不利于降水,从而导致ISM-NCSR关系强。正EU位相时与此相反,相关关系弱。

Based on the 160 stations monthly rainfall data provided by National Climate Center of China Meteorological Administration,the all-India monthly rainfall data provided by Indian Institute of Tropical Meteorology and the NCEP/NCAR reanalysis data,this study is made to investigate the summer Eurasian teleconnection(EU)effect on the relationship between the Indian summer monsoon(ISM)and North China summer rainfall(NCSR)from interannual and interdecadal scales respectively,as well as the associated mechanism.Based on the-0.078 correlation coefficient,the EU and ISM are independent of each other.When it comes to the positive EU phase,the relationship between the ISM and NCSR becomes weak,but strong when it comes to the negative EU phase.During negative EU phases,an anticyclonic circulation appears over Lake Baikal area which is extremely conducive to the northerly wind south of Lake Baikal area,thereby controlling the circulation over North China.As a result,when the ISM is strong,warm moist air from the southwest meets northerly winds and forms a front,which can give rise to North China's rainfall.However,during weak ISM,the circulation over North China is completely dominated by northerly winds,and the water vapor transport channel is completely blocked,which makes rainfall impossible.A strong relationship between ISM and NCSR has resulted from the negative EU phase.In contrast,the ISMR-NCSR relationship is weak during the positive EU phase.