Comparative Analysis on Two Rare and Continuous Rainfall Processes in Mid-and Lower-Reaches of Yangtze River

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.