澳大利亚东侧环流及海温异常与长江中下游夏季旱涝的关系

利用NCEP/NCAR再分析资料、NOAA的SST资料和1951～2005年中国160站月降水总量资料，研究了南极涛动，特别是澳大利亚东侧的环流及局地海温异常与长江中下游夏季旱涝的关系。研究发现，澳大利亚东侧位势高度异常与长江中下游夏季降水存在显著正相关，并由此定义了一个澳大利亚东侧位势高度指数（GHIEA）。当GHIEA指数偏大（小） 时，也即澳大利亚东侧位势高度偏高（偏低），这种气压异常扰动可能通过Rossby波传播到北半球副热带地区，形成南北半球高度场的遥相关，使我国南海至菲律宾北部副热带地区位势高度增加（减小），也即副高较强（弱）且偏南西伸（偏北偏东），从而造成长江中下游地区降水偏多（少）。夏季南极涛动与长江中下游夏季降水的显著相关的原因主要是澳大利亚东侧局地位势高度异常造成的。澳大利亚东侧位势高度偏高（低），南极涛动指数（IAO） 也随之偏大（小），澳大利亚东侧位势高度异常通过南北半球高度场遥相关影响到北半球副热带地区的大气环流， 进而使长江中游夏季降水偏多（少）。另外，从局地海温异常角度也能部分解释澳大利亚东侧位势高度异常与长江中下游夏季降水存在显著正相关的可能成因:当澳大利亚东侧局地海域SST偏高（低）时，对应GHIEA指数偏高（低），也即澳大利亚东侧位势高度偏高（低）。同时，当澳大利亚东侧局地海域SST偏高（低）时，南海地区SST也易于偏高（低），使西太平洋副高较强并偏南西伸（较弱并偏北偏东），从而造成长江中下游降水偏多（少）。

The Relationship between Circulation and SST Anomaly East of Australia and the Summer Rainfall in the Middle and Lower Reaches of the Yangtze River

There are many factors influencing the summer rainfall in the middle and lower reaches of the Yangtze River.Except for the direct influence of the Northern Hemisphere atmospheric circulation systems,the indirect influence of many atmospheric circulation systems of the Southern Hemisphere also plays an important role in the summer rainfall in the middle and lower reaches of the Yangtze River,for example,the Antarctic Oscillation.In this paper,based on the NCEP/NCAR reanalysis data,sea surface temperature(SST) from NOAA and the precipitation data from 160 stations in China,the relationship between the flood/ drought in the middle and lower reaches of the Yangtze River and the Antarctic Oscillation(in particular,the atmospheric circulation and SST east of Australia) is studied.The result indicates that,the geopotential height anomaly east of Australia is significantly positively correlated with the summer rainfall in the middle and lower reaches of the Yangtze River.According to this positive correlation,an index,the Geopotential Height Index East of Australia(GHIEA) is defined to characterize the influence on the rainfall in the middle and lower reaches of the Yangtze River.While the GHIEA,namely,the geopotential height east of Australia is stronger(weaker),the geopotential height from the South China Sea to the north of Philippines is stronger(weaker).The western Pacific Subtropical High is stronger(weaker) and extends southward and westward(northward and eastward).Therefore the rainfall in the middle and lower reaches of the Yangtze River is more(less) corresponding to the variation of the subtropical high.Below is the reason that the GHIEA in the Southern Hemisphere can lead the anomaly of the summer rainfall in the middle and lower reaches of the Yangtze River: the geopotential height anomaly disturbances may propagate from the area east of Australia to the subtropical area of the Northern Hemisphere by means of Rossby wave,so that the teleconnection between the Northern Hemisphere and the Southern Hemisphere occurs.The teleconnection associates the GHIEA with the summer rainfall in the middle and lower reaches of the Yangtze River.Mainly for the geopotential height anomaly east of Australia,the Antarctic Oscillation in summer(June-August) is closely related to the summer rainfall in the middle and lower reaches of the Yangtze River.While the GHIEA is stronger(weaker),the Antarctic Oscillation Index(AAO) is stronger(weaker).The summer rainfall in the middle and lower reaches of the Yangtze River is more(less).In addition,the local SST anomaly can partly explain the significantly positive correlation between the GHIEA and the summer rainfall in the middle and lower reaches of the Yangtze River.If the local SST east of Australia is greater(lower),the GHIEA,as well as the geopotential height east of Australia is stronger (weaker).While the SST anomaly east of Australia is positive(negative),the SST over the South China Sea is greater(lower).The positive(negative) SST anomaly over the South China Sea may result in the anomaly of the western Pacific subtropical high.It makes the subtropical high stronger(weaker) and western and southern(northern and eastern),so the summer rainfall in the middle and lower reaches of the Yangtze River is more(less).