中文摘要：

使用WRF对发生在2010年4月28—29日一次广西前汛期回流暴雨过程进行了数值模拟,并通过诊断分析,研究了回流暴雨的形成机制。结果表明：冷空气受南岭、武夷山脉阻挡未能直接影响华南西部,其东移入海后,华南西部处入海高压后部,等压线呈＂东南—西北＂向,低层风向顺转为东南风,由于经南海回流的东南气流相对于孟加拉湾西南气流和越赤道气流是干冷的,不同性质气流汇合形成锋面、辐合线,提供了抬升条件,这是回流形势的形成过程;从θ_e和湿位涡诊断发现,边界层条件性对称不稳定和中低层对流性不稳定是此次暴雨中尺度对流系统发生发展的不稳定机制;边界层辐合和能量锋锋生是暴雨的主要触发条件;在暴雨增幅前不稳定能量有一个积累过程,边界层能量锋锋生和辐合抬升促使不稳定能量释放,使暴雨增幅;湿位涡负异常对暴雨预报具有指示意义,水平螺旋度正值增大与暴雨增幅有较好的对应关系;此次回流暴雨发生在边界层锋的两侧,边界层存在锋区表明此次回流暴雨在基本性质上仍属锋面降水。

英文摘要：

By using the model WRF,the Backflow rainstorm process that occurred in Guangxi during 28 —29 April 2010 was simulated.The formation mechanism of the backflow rainstorm was studied by diagnostic analysis.The results showed that,blocked by Wuyi Mountain and Nanling Mountains,the cold air can not directly affect the west of South China.When the cold air moves eastward into East China Sea,the west of South China is at the rear of high pressure.The isobaric line shows the trend of ＂southeast-northwest＂ and the wind direction in lower layers turns clockwisely to southeast.The southeast air of back flow,flowing through South China Sea,is dry and cold in comparison with the southwest airflow from Bengal Bay and the cross-equatorial airflow,so the airflows of different nature converge,forming the frontal surface and convergence line and providing lifting condition.This is the formation process of backflow situation.By diagnosing θ_e and moist potential vorticity（MPV）,we find that conditional symmetric instability（CSI） in boundary layers and convective instability in low-middle layers are the instability mechanisms of occurrence and development of this rainstorm MCS.Wind convergence and frontogenesis of energy front in boundary layers are the main triggering conditions of the convection.Before the increase of the torrential rain,there is a process of accumulation of convective instability energy.The frontogenesis of energy front and convergence lifting in boundary layers trigger the release of instability energy,leading to the increase of the rainstorm.The negative anomaly of MPV has indication for rainstorm forecasting,and the positive center of helicity has good relationships with the increase of the rainstorm.The rainstorm happens in both sides of the boundary-layer front.The existence of boundary-layer front means this backflow rainstorm belongs to frontal precipitation in nature.