中文摘要：

根据1954—2005年江淮地区梅雨期间的逐日降水资料,采用旋转经验正交函数分解法（REOF）分析得到,江淮梅雨具有江淮型、江南型、淮河型和两湖型4种优势降水型,都存在着6—7年和准20年的周期振荡,20世纪90年代后表现为江南梅雨型减少、而淮河梅雨型增加的趋势。进一步采用系统聚类法对江淮梅雨期逐年降水场进行客观分型得到,江淮梅雨分为全流域丰梅型、全流域枯梅型、南丰北枯型、北丰南枯型和南北丰中间枯型共5种雨型。全流域丰梅型具有入梅早、出梅晚、梅雨期长、梅雨量大和梅雨强的特点,而全流域枯梅型正好与之相反。雨带型中,以南北（北）丰中间（南）枯型入梅早（晚）,南（北）丰北（南）枯型出梅早（晚）,这些特征与雨带的地理位置相对应。江淮各梅雨型均具有明显的年代际变化,20世纪90年代主要对应全流域丰梅型和南丰北枯型,而2000年以后以全流域枯梅型、北丰南枯型和南北丰中间枯型为主。近52年中20世纪60年代（90年代）梅雨期最短（长）、梅雨量最少（多）、梅雨强度最弱（强）。最后,从南亚高压位置、高空东、西风急流、西太平洋副热带高压和阻塞高压的位置及维持、垂直速度、季风气流的水汽输送6个方面对比了不同梅雨降水型所对应的大气环流特征及主要差异。

英文摘要：

According to the daily meiyu period precipitation data from 1954 to 2005,the distribution of the predominant precipitation patterns in the Yangtze-Huaihe region is analyzed by the rotated empirical orthogonal function（REOF） method.The results show that there mainly are four kind meiyu precipitation modes in the region,namely,the Yangtze-Huaihe-type,south of the Yangtze River-type,Huaihe River-type,as well as Dongting Lake and Poyang Lake-type.During the recent 52 years,the occurrence probability of the precipitation modes of the Huaihe River-type becomes increasing and the probability of the other three modes is almost the same as each other.All of them are of 6-7-year and quasi-20-year periodical oscillations as suggested by use of the method of the maximum entropy spectrum with the Dongting Lake and the Poyang Lake-type having an additional 2-3-year period.It is worthwhile to note that the south of the Yangtze River-type tends to decrease while the Huaihe River-type to increase since 1990.Based further on the REOF,the subdivision of the precipitation distribution pattern has been obtained by use of the method of the system-cluster analysis.The precipitation distribution of the Yangtze-Huaihe-type meiyu can be divided into 5 categories of pattern.The first and the second precipitation categories are the rich and poor meiyu pattern in the whole Yangtze-Huaihe region,respectively.The other three categories are characterized by rich in the south and poor in the north（RMSPN）,rich in the north and poor in the south（RMNPS）,rich in the south and north and poor in the middle （RMSNPM）,respectively.They account for 15.4%,40.4%,15.4%,19.2%and 9.6%of the total years,respectively.And each precipitation pattern has its different meiyu parameter characteristics.For example,the earlier onset date,later end date, longer meiyu duration and stronger rainfall are characteristic of the rich meiyu pattern,but the reverse conditions are of the poor one.As long as the rain-belt pattern is concerned,the RMSNPM shows an e