长江中下游持续性异常降水的天气学特征分析

针对长江中下游持续性降水的研究多为个例诊断,很少从合成的角度考虑,利用长江中下游地区89站的1961~2011年的逐日降水资料和NCEP/NCAR逐日再分析资料,采用数理统计和合成分析的方法,统计长江中下游地区夏季持续性降水事件,并合成分析了其环流特征。结果表明:1961~2011年,长江中下游地区夏季持续性异常降水事件发生了50次,主要集中在6月和7月,长江中下游地区持续性异常降水事件平均每2~3年发生一次。厄尔尼诺次年多有持续性异常降水发生;长江中下游地区持续性异常事件发生时,总伴有环流场的异常调整,低纬西太平洋副热带高压西伸,南北经向风在长江流域交汇,高层上,南亚高压东移,长江中下游地区出现强的辐散中心,为异常降水提供了重要条件。水汽来源主要是索马里越赤道气流途径暖湿的阿拉伯海,孟加拉湾和我国南海北部,进入长江中下游地区。

Synoptic Features of Continuous Abnormal Rain in the Middle-lower Reach of the Yangtze River in Summer

Because the most researches of continuous abnormal rain in the middle-lower reach of the Yangtze River are case diagnosis,few from the synthetic point of view.Using daily observed precipitation data in the middle-lower reach of the Yangtze River and NCEP/NCAR daily reanalysis data during the period 1961-2011,continuous abnormal rain is defined in this paper.Based on the definition,characteristics of continuous abnormal rain in this area in summer are studied as well as features of the circulation during the rain period.The results are as shown：During 1961-2011,continuous abnormal rain happened 50 times in the middle-lower reach of the Yangtze River which concentrated in June and July and they almost happened in the next year of El-Nino year.During continuous abnormal rain period,subtropical high in the Westem Pacific is more powerful and locate in the South China Sea.Dry and cold north wind meets wet and warm south wind in the Yangtze River area.The main source of water vapor is that Somali cross-equatorial flow pathways Arabian Sea,Bay of Bengal and the northern part of the South China Sea,and then into the Yangtze River region.