中文摘要：

利用长江中下游地区66个气象站逐日降水资料，通过经验正交函数分解分析中雨以上日数极端降水指数及形成的原因。结果表明：长江中下游中雨以上日数主要表现为全区一致型、南北反向型，且两种分布形势均存在准2a周期的年际变化和年代际变化；中雨以上日数在1990s开始显著增长，2000s以来，长江以北地区偏多，长江以南地区偏少；2000--2011年，我国东部经向上仍旧存在“反气旋一气旋”水汽输送异常，蒙古高原反气旋型水汽输送加强，引起雨带停滞在长江以北，造成长江以南地区中雨以上日数偏少。

英文摘要：

Based on the daily precipitation data of 66 meteorological stations over the middle and lower reaches of the Yangtze River, the Empirical Orthogonal Function （EOF） decomposition was used to analyze the extreme precipitation index of the moderate or above rain days and its formation reasons. Re- sults show that the moderate or above rainy days over middle and lower reaches of the Yangtze River can be classified into the same anomaly pattern in the whole area and the reverse anomaly pattern in the south and north, but the both present interannual and interdecadal variation of the quasi-biennial period . The moderate or above days began to rise significantly in 1990s, and since 2000s, the north area of the Yan- gtze River exceeded the south; during 2000-2011, there still was ＂anticyclonic-cyclonic＂ anomaly of water vapor transportation in the meridional direction in the East China, and the anticyclonic water vapor transportation in Mongolia plateau was strengthened enough to cause the rain belt to stagnate in the north of the Yangtze River, and made the moderate or above rainy days in the south of the Yangtze River relatively less.