江西省夏季降水年际变化的机理研究

The mechanism research of interannual variation of summer precipitation in Jiangxi Province

通过对观测资料和大气再分析资料的诊断分析,研究了影响江西省夏季降水变率的物理机制。结果表明江西省夏季降水存在显著的年际变率。极端条件下,降水偏多的夏季可达降水偏少的夏季的降水量的三倍。中纬度地区的准静止波列和热带关键海区的海温异常是造成江西夏季降水异常的主要原因。当江西省夏季降水偏多时,欧亚大陆地区存在“正—负—正”的准正压Rossby波列结构,位于贝加尔湖的正活动中心能引导干冷空气南下,从而有利于江南地区的锋生和江西降水的增加。此外,当江西省夏季降水偏多时,前期冬季中东太平洋地区有El Niño事件的活动,并能通过大气桥在夏季印度洋地区形成正海温异常。通过“印度洋电容器”机制,印度洋的暖海温能激发向东传播的Kelvin波,引起菲律宾地区降水的减少。菲律宾地区抑制的降水能激发向北传播的EAP/PJ波列,使得西太平洋副热带高压西伸增强,从而有利于水汽向江南地区的输送,并造成江西夏季的降水增加。

Based on observation and reanalysis datasets,the physical mechanism of summer rainfall variabilities in Jiangxi Province was analyzed.Results show that the summer rainfall in Jiangxi presents significant interannual variability.The rainfall amount in the wettest summer can be about triple of that in the driest summer.The stationary Rossby wave in the middle latitudes and Sea Surface Temperature(SST)anomaly in the key tropical ocean are responsible for the summer rainfall variabilities.When the summer rainfall is above normal,an positive-negative-positive equivalent-barotropic Rossby wave persists in the Eurasia.The high-pressure action center near the Lake Baikal favors cold and dry air moving southward,thus lead to the frontogenesis and more rainfall in Jiangxi.In addition,when the summer rainfall in Jiangxi is enhanced,El Niño events also persist over the eastern and central Pacific in the preceding winter.The positive SST anomalies over the eastern and central Pacific can induce positive summertime SST anomalies over the Indian Ocean through atmosphere bridge.The positive SST anomalies in the Indian Ocean can emanate eastward propagating Kelvin wave through the Indian Ocean capacitor mechanism and reduce the convective activities in the Philippines.The reduced rainfall in the Philippines can excite northward propagating EAP/PJ wave train and cause westward shift and the strengthening of western Pacific subtropical high.As a result,the water vapor transporting to the southern China enhances and the summer rainfall in Jaingxi increases.