长江流域大范围旱涝与南亚高压的关系

THE LARGE AREA FLOOD AND DROUGHT OVER YANGTZE RIVER VALLEY AND ITS RELATION TO THE SOUTH ASIA HIGH

利用１９５８～１９９９年月平均气象资料，分析了４２ ａ以来长江流域大范围旱涝的时空分布特征， 发现长江流域降水具有非常明显的年代际变化，年代际的转折发生于２０世纪７０年代末，６０年 代的持续干旱和９０年代的多发性洪涝形成鲜明对比。依照降水标准差大小，从４２ ａ降水资料 中划分出６个严重涝年和５个严重旱年。合成分析表明旱涝年大气环流和全球海温均有明显差 异，涝年高 低层副热带高压偏南偏强，全球海温呈大范围正距平，旱年则相反。文中对比分析了南亚 高压和海温两个异常因子与夏季长江流域降水的关系，发现南亚高压强度指数与长江流域降 水有显著相关，二者的年代际变化趋势非常一致，２０世纪７０年代末当南亚高压由弱变强，长 江流域由相对干旱转为相对多雨。而赤道太平洋ＳＳＴＡ与长江流域降水的关系不甚确定。超前 ／滞后相关分析表明，前期冬春季１００ ｈＰａ副热带高压强度与夏季长江流域降水呈显著的正相 关，前期冬春季赤道东太平洋ＳＳＴＡ与长江流域降水也呈正相关，但相关不显著。分析结果表 明，由于中国特殊的地理环境、地形和海陆分布特征，将南亚高压作为一个异常强信号并加 以关注，对中国短期气候尤其是灾害性气候的预测具有重要意义。

The temporal and spatial distributions of the summertime precipitation over Yang tze River Valley are examined in this paper by employing monthly mean observatio n data from 1958 to 1999.There is a distinct interdecadal trend in precipitation and the transition occurs in late 1970s.The significant contrast can be found i n the persistent drought during 1960s and frequent occurrence of flood during 1990s.According to the standard deviation of the precipitation,the 6 severe flood yea rs and 5 severe drought years are identified during the past 42 years.The obvious differences between flood year and drought year are found in the troposphere and stratosphere circulations as well as in the global SSTA .The subtropica l high at both upper and lower troposphere shifts southward and becomes strengthened during the flood year,meanwhile the global SST exhibits large area positive anomalies ,and vice versa during the drought year.The sim ultaneous cor relation shows the significant positive correlation between SAH intensity index and precipitation anomalies in the Yangtze River Valley .When the SAH changes fr om a relat ive weak period to a strong period at the end of 1970s,the Yangtze River valley precipitation changs from a relative drought period to a flood period;whereas th e r elationship between the Yangtze River Valley precipitation and Equatorial Easter n Pacific SSTA is uncertain.The lead/lag correlation also shows the significant p ositive correlation between the intensity of winter/spring 100 hPa subtropical h igh and summertime Yangtze River Valley precipitation. The results of the paper suggest that due to the special geographic and land s ea distribution of China,the anomaly of the SAH has more direct impact on region al climate of China than that of ENSO.Thus we propose that the SAH should be con sidered as a strong anomalous signal and be paid more attention to.