非ENSO年夏季西风带波包活动特征及其对长江中下游强降水事件的影响:以1993年为例

摘要

Using SST data from Hadley Centre,the NCEP/NCAR reanalysis data along with 740-station precipitation data in China,combined with the lag correlation and other methods,this paper analyzes the characteristics of summer precipitation in the Yangtze River Basin in non-ENSO years and investigates the characteristics of Rossby wave packets and their possible impacts on summer severe precipitation events in the Yangtze River Basin in nonENSO year 1993.Results show that there exist strong interannual and interdecadal variations for summer precipitation in the middle and lower reaches of the Yangtze River in non-ENSO years.Among non-ENSO years,1993 is a special year when the strongest flooding occurred in the Yangtze River Basin,which is chosen as the case for study.It is found that the wave packets in 1993 are originated from the south of Caspian Sea,propagating eastward to the middle and lower reaches of the Yangtze River.These wave packets disperse energy eastward,inducing accumulation of energy over China,facilitating the occurrence of summer severe precipitation in the Yangtze River Basin.A comparison is made for non-ENSO year 1993 and ENSO year 1983.It is found that the route along which the wave packets propagate in non-ENSO year 1993 locates more southern than that in ENSO year 1983.These results are helpful for us to understand the forming mechanism of summer severe rainfall events in the Yangtze River Basin in non-ENSO years.%利用Hadley中心海温资料、NCEP/NCAR再分析资料和中国740站逐日降水资料,运用一点滞后相关等方法,分析了非ENSO年长江流域夏季降水特征,并以1993年为例探讨了非ENSO年波包活动特征及其对长江流域夏季降水的影响.结果表明:非ENSO年长江中下游地区夏季降水年际和年代际变化明显,20世纪90年代初强降水事件多发.在1993年,波包起源于里海南侧,自西向东向长江中下游地区传播,为长江流域夏季降水的发生提供了必要的扰动能量积聚.通过非ENSO年和ENSO年波包活动个例的初步对比,发现非ENSO年的南支波导作用较为明显,波包主要表现为自西向东传至长江中下游地区;而作为ENSO年的1983年,则存在一支明显的偏北波导,使波包沿着西北—东南向的路径向下游传播,最终到达长江中下游地区.这些结果有利于深刻认识非ENSO年长江流域夏季强降水事件的形成机理.