中文摘要：

利用中国160个站降水、NCEP再分析等资料和CCSM3模式,从对流层温度的角度,分析了影响6月长江中下游降水的因子和前兆信号。研究发现,反映对流层中高层纬向海-陆热力差异的亚洲-太平洋涛动异常可能是导致长江中下游地区降水异常的一个重要原因。观测统计和模式结果都表明,前期5月亚洲-太平洋涛动指数与其后6月长江中下游地区降水具有显著负相关关系,这一关系比前冬厄尔尼诺（拉尼娜）与6月降水的关系更为紧密,稳定性也相对更高。进一步分析发现,亚洲-太平洋涛动异常从5月至6月具有很好的持续性,5月亚洲-太平洋涛动可以通过影响后期6月西太平洋副热带高压的强度和位置、中国东南沿海的西南风以及中国东部中纬度地区的偏北风异常,进而影响长江中下游地区6月降水的多寡。此外,5月亚洲-太平洋涛动异常偏弱也是2011年6月长江流域出现降水异常偏多的一个重要原因。这些结果说明,对于6月长江流域降水,除了海温强迫作用外,对流层中高层异常也是一个重要的前期信号,因此,利用前期亚洲-太平洋涛动预测降水可能是一条值得尝试的途径。

英文摘要：

Using the precipitation data from the 160 stations of China and the NCEP reanalysis data and the CCSM3 simula- tions, influencing factors and precursory signals for anomalous precipitation over the middle and lower reaches of the Yangtze River are analyzed in terms of tropospheric temperature. The results show that the anomalous Asian-Pacific Oscillation （APO）, reflecting the anomalous zonal land-sea thermal contrast at the middle-upper troposphere, is an important factor for a- nomalous precipitation over the middle and lower reaches of the Yangtze River. Statistical observational and simulation results suggest that there is a significantly negative correlation between the May APO index and the following June precipitation over the middle and lower reaches of the Yangtze River. The relationship is closer than that between previous winter E1 Nino （La Nina） and June precipitation, and has a relatively higher stability. Further analyses indicate that APO has a good continuity from May to June, therefore May APO can modulate the intensity and location of the June western Pacific subtropical high, a- nomalous southwesterly winds over the southeastern coasts of China and anomalous northerly winds at the middle latitudes of eastern China, and eventually leads to anomalous June precipitation over the middle and lower reaches of the Yangtze River. In addition, a clearly weaker May APO is also a critical reason for the above-normal June precipitation over the middle and lower reaches of the Yangtze River in 2011. These results suggest that besides SST forcing, the middle-upper tropospheric anomalies should be considered as an important precursory influencing factor, and it seems worth trying to forecast precipitation using previous APO anomalies.