【摘要】 利用中尺度数值模式MM5和实况资料,对比分析了分别发生在2008年秋季和2009年春季长江中下游历史罕见的强连阴雨天气过程。结果表明,欧亚地区500 hPa"两槽一脊"型是长江中下游春、秋季出现强连阴雨过程的典型环流形势。连阴雨过程低空急流异常活跃,存在风向、风速的辐合。比较该两次过程显示,2009年春季连阴雨过程低层风速辐合明显,而2008年秋季则风向辐合明显。两次连阴雨过程都存在宽广而强大的水汽输送带,其北侧是与之相平行的θse锋区。水汽输送范围越广,强度越强,θse锋区的强度越强,越容易在连阴雨过程中产生强对流天气。连阴雨过程的水汽源于孟加拉湾、南海和西太平洋。该两过程湿层深厚,中层存在湿中性层结。θse等值线都出现类似于鞍形场的结构,水汽通量的大值区出现在鞍形场中间部位,与大降水的发生位置吻合。两次连阴雨过程辐合上升运动明显,强中心位于600 hPa高度。更多还原

【Abstract】 Using the mesoscale numerical model MM5 and the observed data,the characteristics of the two rare and continuous rainfall processes in the mid-and lower-reaches of Yangtze River in autumn of 2008 and spring of 2009 were analyzed.The results show that the continuously heavy rain process is associated with the specialy circulation pattern,i.e.,two troughs located respectively at Urals mountain and East Asia and a ridge located at Northern China.There was active low level jet in continuous rainfall process.There were strong speed convergence in spring and wind direction convergence in autumn.Water vapour transfer belt was strong and wide and there was θse front in its north.Water vapour came from the South China Sea(SCS) and the Bay of Bengal in spring and came from SCS and the western Pacific.There were humid neutral stratification on middle level.θse isoline appeared saddle-shaped structure.There were strong ascending motion and convergence in continuous rainfall process.The maximum value of ascending motion was on 600 hPa.Continuous rainfall in spring was stronger in convection and energy than in autumn.更多还原