中文摘要：

2000年以来长江流域未见到很典型的梅雨暴雨,尽管如此,所谓＂不典型＂的区域性致洪暴雨仍时有发生,甚至造成严重洪涝。利用NCEP资料、常规和SCHeREX计划期间的6h一次的高空探测资料和大量的地面自动站资料、多普勒雷达、FY-2C卫星黑体温度资料及NOAA的CMORPH资料,分析了2009年6月29日00：00（协调世界时,下同）至30日00：00引发武汉严重洪涝的强降水。结果表明,尽管中高纬环流和槽脊系统有＂错位＂现象,但东亚地区鞍形场的存在有利于高原东侧中尺度低压（扰动）的发生发展。随着高原槽东移和西太平洋副热带高压突然西伸,在四川—重庆地区诱生出中尺度涡旋及明显的低空急流,同时上层冷干、下层暖湿空气叠置而形成较强的位势不稳定层结,在低层辐合场的触发下,使致洪暴雨得以发生。该年有较好的水汽输送条件,主要源地在南中国海。因此,即使在大尺度环流不是非常＂典型＂的情况下,一旦武汉地区存在有利的天气尺度和中尺度系统,且有足够的水汽供应,暴雨仍有可能发生。

英文摘要：

Since 2000, the main Meiyu front rainband moved northward to the Huaihe River basin. The poor or no Meiyu occurred in the Yangtze River very often, due to the anomaly of the atmospheric circulation. However, in poor Meiyu season, a heavy rainfall still occurred in Wuhan area during 0000 UTC 29 June–0000 UTC 30 June 2009. The mentioned above case is diagnosed by using NCEP data, operational observation from China Meteorological Administration, four times per day SCHeREX sounding, automatic weather stations data, radar data, FY-2C Black Body Temperature （TBB）, and CMORPH data. It is noticed that the Baikal trough as cold air source favorable the heavy rainfall occurrence has been replaced by the ridge. However, the other favorable factors still benefit the precipitation. They have been noticed that： 1） Existance of col pressure field in East Asia provided the important condition for formation of mesoscale disturbance to the eastern part of the Tibetan Plateau. 2） Eastward shifting trough from the Tibetan Plateau intensified the vertical motion in the middle reaches of the Yangtze River and a meso low formed between Chongqing City and Hubei Province which was very helpful for heavy rainfall in Wuhan. 3） Westward extending of the West Pacific Subtropical High forced the low level jet to intensify in Jiangxi and Hunan provinces and Low Level Jet （LLJ） transported very rich moisture to the Wuhan area. 4） Overlaying of the cold and dry in upper troposphere on the warm and moist in low troposphere produced the significant potential instability. High Convective Available Potential Energy （CAPE） value was released and the convection was initiated due to the triggering of the mesoscale disturbance. 5） The small meso-β scale convective systems relating directly with the heavy rainfall in Wuhan have been revealed.