我国江淮地区5-7月降水异常的区域特征

采用旋转经验正交展开(REOF)方法，对我国江淮地区50a5—7月降水标准化距平场进行客观分区，并分析了南北两区5—7月降水异常的长期变化趋势及其周期的变化。结果表明，江淮地区5—7月降水方差场可以分为2个区域，各区降水量异常有明显的季节变化，降水异常峰值出现在6月和7月，基本呈单峰型分布；南部区变化趋势比北部区明显，均具有显著的年际和年代际变化特征：南北两区都存在3a的主周期，南部和北部分别有21a和15a的年代际周期；江淮南、北区的降水在降水偏多、偏少年都与全国大部分地区呈同位相分布，但江淮北区的降水始终都与华南地区呈反位相分布；副热带季风系统的强弱及副高南北位置的变化直接影响江淮5—7月降水。

Regional Features of Rainfall Anomalies in the Jianghuai Valley during the May to July Period

Using the rotated empirical orthogonal function (REOF) method,the normalized rainfall field during the May to July period in the Jianghuai Valley is divided objectively into the north and south regions.Based on this,the long-term trend and periodic variations of each region rainfall anomalies are analyzed.It is found that in the Jianghuai Valley,the peaks of precipitation anomalies in the south and north regions appear separately in June and July respectively.The trend of variations in the south region of the Jianghuai Valley is obvious in comparison with that in the north region,but the two regions have remarkable characteristics of interannual and interdecadal changes in the recent 50 years;There mainly exist 3-year interannual periods both in the south and north regions and a 21-year interdecadal period in the south region and a 15-year interdecadal period in the north region.Precipitation departures during the May to July period in the Jianghuai Valley is in phase with those in many areas of China in the wet and dry years,but the precipitation departure in the north region is always out of phase with that in south China.Further more,the rainfall anomaly in the Jianghuai Valley is directly influenced by the variations of the latitude of the subtropical high ridge and the intensity of the subtropical monsoon system.