强西南急流背景下南岭山脉一次暖区大暴雨数值模拟分析

NUMERICAL SIMULATION OF WARM-SECTOR HEAVY RAINFALL PROCESS OVER NANLING MOUNTAINS UNDER STRONG LOW-LEVEL SOUTHWEST JET

利用常规观测资料、卫星FY-2G逐时TBB资料,采用WRF中尺度数值模式,对2016年5月5日湘桂粤边界南岭山脉的一次强西南急流背景下预报失败的暖区大暴雨过程(简称16·5过程,下同)进行数值模拟和诊断分析,研究了南岭山脉特殊地形对此次暖区降水过程的动力结构、水汽输送和云降水微物理机制的影响。结果表明,中低层西南气流由于受到南岭多处山脉地形的阻挡、侧摩擦和峡谷等效应的影响反复出现强烈辐合区,导致连续出现超强的水汽辐合中心,造成了湘桂粤边界暖区大暴雨的发生;在南岭特殊地形导致的动力、水汽条件下和有利于云内微物理过程发展的环境下,局地对流云系强烈发展与大尺度西南气流引导的深厚高层冰相云系结合后,云内的过冷云水在强盛的上升气流作用下抬升,丰富的过冷云水有利于贝吉隆过程和结凇进程,促进云内固态粒子增长,这是导致此次暖区大暴雨发生的重要云微物理内因。

Based on conventional observational data and the hourly black body temperature(TBB) data from FY-2G satellite, a warm-sector heavy rainfall process under strong low-level southwest jet, which failed to be predicted in practice, is numerically simulated and diagnosed using the WRF mesoscale numerical model. The process occurred over Nanling Mountains(the border of Hunan, Guangxi and Guangdong) on May 5, 2016(referred to as 16·5 process). The effects of special topography of Nanling Mountains on the dynamic structure, water vapor transport and cloud and precipitation microphysical mechanism of 16·5 process are studied. The results show that due to the blocking of mountain terrains,lateral friction and canyon effects in the Nanling Mountains, strong convergence areas repeatedly appear in the middle and lower levels of the southwest airflow, causing continuous occurrences of super-strong watervapor convergence centers and leading to heavy rainfalls in the warm sector at the border of Hunan,Guangxi and Guangdong. Under the dynamic and water-vapor conditions caused by the special topography of Nanling Mountains and the environment conducive to the development of cloud microphysical processes, the strong development of local convective cloud system is combined with the deep high-level ice cloud system guided by large-scale southwest jet. Thus, the super-cold water in the cloud rises under the action of strong updraft. Abundant super-cold water is conducive to the process of Bergeron, the rime formation process, and the growing of solid particles in the cloud, which is an important internal cause of the occurrence of the 16·5 process.