2011年梅雨期长江中下游地区两次暴雨过程数值模拟对比分析

Numerical Simulation and Comparison of Two Rainstorms in the Middle and Lower Reaches of the Yangtze River during Meiyu Period in 2011

基于WRF数值预报模式,对2011年梅雨期6月9—10日和14—15日长江中下游地区两次暴雨过程(分别简称"6·10"过程和"6·14"过程)进行数值模拟,重点对比分析了暴雨期间西南涡的活动与高低空急流耦合配置之间的关系。结果表明:1)西南涡的活动和高低空急流耦合配置与暴雨活动关系密切,是造成两次暴雨过程范围和强度差异的重要因素。2)"6·10"过程中,一个浅薄的西南涡系统受青藏高原浅槽东移北缩减弱影响,向东北方向移动,同时西南低空急流位置偏北,导致暴雨区位置偏北;"6·14"过程中,一个深厚的西南涡系统受高空浅槽东移发展加深影响,沿长江缓慢东移,伴随西南低空急流位置偏南,降水缓慢向东移动,导致暴雨区位置偏南。3)两次过程的强降水中心均位于高低空急流耦合区,"6·10"过程中,在长江中下游地区形成的高低空急流耦合区范围偏小且强度偏弱,因此辐合上升运动偏弱,不利于形成大范围的强降水;"6·14"过程中,在长江下游地区形成大范围高低空急流耦合的环流形势,强烈的辐合上升运动配合充足的水汽供应,最终形成大范围强降水。

Based on WRF numerical model,two rainstorms occurred during 2011 Meiyu period were simulated.Comparative analysis of their circulation and physical fields showed that：1）The movement of southwest vortex and the coupling of two jets at upper and lower levels were closely related to the rainstorms,which mainly caused the differences between two rainfalls.2）For the process of＂6·10＂,a flimsy southwest vortex system moved towards northeast as the weakened trough of Plateau moved eastward,and both of the southwest jet stream at lower level and the rainfall occurred at north;for the process of＂6·14＂,a deep southwest vortex moved slowly along the Yangtze river valley as the enhanced trough moved eastward,and both of the jet stream at lower level and the rainfall were located in the south.3）The strong precipitation centers of two proces-ses were in the coupling areas of jet streams at upper and lower levels.The range and intensity of the coupling area of＂6·10＂was smaller and weaker,thus the convergence ascending motion was also weaker,which could not cause heavy rain.On the contrary,during the process of＂6·14＂,the coupling area coverage of jet streams along the Yangtze River valley was larger,and the strong convergence ascending motion provided plenty of moisture,leading to the wide range and heavy rain.