赤道印度洋偶极子对重庆夏季降水的影响分析

利用重庆34个气象台站1961—2017年夏季降水量、NCEP/NCAR的再分析月平均高度场资料和海面温度资料,分析发现,上年秋季尤其是11月的赤道(热带)印度洋偶极子(tropical Indian Ocean dipole,TIOD)模态与重庆夏季降水存在正相关关系。通过前期海面温度对大气环流的影响分析,结果表明:上年11月TIOD和夏季500 hPa高度场的相关与重庆夏季降水和高度场的相关一致,显示出从高纬度到低纬度"+、-、+"的相关分布,反映出当上年11月TIOD正位相(负位相)时,次年夏季环流场表现出乌拉尔山阻塞高压明显(不明显)、中纬度30°～37°N低值系统活跃(不活跃),西太平洋副热带高压偏强(弱)、位置偏南(北)的重庆夏季典型的降水偏多环流特征;前期赤道太平洋ENSO暖事件和前期TIOD事件同时发生时,两个事件的作用相互叠加,使得西太平洋副热带高压加强西伸并且位置偏南,造成重庆夏季降水的异常偏多。

Impact analysis of equatorial Indian Ocean dipole on summer precipitation in Chongqing

Based on the summer precipitation data of 34 meteorological stations in Chongqing from 1961 to 2017 and NCEP/NCAR reanalysis data of monthly average height and SST, it is found that there is positive correlation between the tropical Indian Ocean dipole (TIOD) mode of the last autumn, especially November, and summer precipitation in Chongqing. The impact of SST on the atmospheric circulation is analyzed and shown below. 1) The correlation between TIOD of the last November and height field at 500 hPa in summer is consistent with that between the summer precipitation in Chongqing and height field, showing a distribution of "+, -, +" from high latitudes to low latitudes. When TIOD of the last November is in positive (negative) phase, the summer circulation in the next year is characterized by obvious (unobvious) Ural blocking high, active (inactive) low value system in middle latitudes between 30°N and 37°N, stronger (weaker) western Pacific subtropical high, and more typical southward (northward) summer precipitation in Chongqing. 2) When the warm phase of ENSO in the equatorial Pacific occurs at the same time with the TIOD event previously, the two events overlap with each other, causing the western Pacific subtropical high to be intensified and stretch westward and southward and resulting in anomalously more summer precipitation in Chongqing.