中文摘要：

用长江下游降水低频分量和南半球中纬度地区850 hPa低频经向风主成分,建立多变量时滞回归（multivariable lagged regression,MLR）模型,对2013年6—7月长江下游降水低频分量进行延伸期逐日变化预报试验。结果表明,20~30d时间尺度的长江下游低频降水预测时效可达25~30 d。进一步对2001—2012年资料分别构建的ML,R模型的历史回报预测试验表明,对于20~30 d振荡较强和正常的年份,南半球中纬度绕球遥相关（south circum global teleconnection,SCGT）波列是预测初夏长江下游低频降水未来30 d变化的显著信号。基于南半球SCGT的发展和演变,对于提前20 d以上预报长江下游地区2013年7月上旬持续强降水过程异常变化过程很有帮助,南半球热带外环流低频变化是影响初夏长江下游地区延伸期强降水变化的重要因子之一。

英文摘要：

Low-frequency rainfall over the lower reaches of Yangtze River Valley（LYRV） and the principal component of 850 hPa meridional wind anomalies over the extratropics of the Southern Hemisphere are employed to construct a multivariable lagged regressive（MLR） model,which is applied to the daily forecasting of low frequency rainfall over LYRV in June-July of 2013 for the extended range forecast.The result indicates that this method for the 20-30 d low-frequency rainfalls over LYRV has good predictive skill up to 25-30 d.By many hindcast experiments during the period of 2001-2012,this MLR model for the 20—30 d rainfalls over LYRV has good predictive skill up to about 30 days for the years with the stronger or normal 20-30 d oscillations.Based on the development and evolution of the southern circumglobal teleconnection（SCGT） wave train,it will help us to forecast the process of lasting heavy rainfall in early July of 2013 over LYRV over 20 days in advance.Hence,the low frequency variability of extratropics over the Southern Hemisphere is one of the main factor of the changes of the heavy rainfall over LYRV in early summer for the extended range.