2020年广西南宁一次极端暴雨特征及预报偏差分析

Analysis on the characteristics and forecast deviation of an extreme rainstorm in Nanning city in 2020

利用常规观测数据,对2020年6月24—25日广西南宁的极端暴雨过程进行分析。结果表明,极端暴雨发生于大陆副热带高压和西太平洋副热带高压对峙、西南季风活跃的有利背景下,高空槽缓慢东移引导切变线、弱冷空气南下,西太平洋副热带高压西北侧的低空急流为强降水的发生提供了异常充足的水汽、不稳定能量条件;此次过程的雨带分布和雨团活动与两个阶段的中尺度对流系统(MCS)发展演变有关,不同阶段的强回波都具有后向传播、低质心的特征,列车效应明显;极端短时强降水出现在TBB≤-90℃附近;欧洲中期天气预报中心高分辨率模式(ECMWF_HR)预报强降水落区偏北、强度偏弱,ECMWF_HR模式对于天气系统预报偏北是导致暴雨预报偏差的主要原因。

Based on conventional observation data, the extreme rainstorm process in Nanning City, Guangxi from June 24 to 25, 2020 was analyzed. The results showed that the extreme rainstorm occurred in the favorable background of the confrontation between the subtropical high and the continental high, and the active southwest monsoon. The upper-layer trough slowly moved eastward to guide the shear line and the weak cold air to move southward. The low-level jet on the northwest side of the subtropical high provided abnormally sufficient water vapor and unstable energy conditions for the occurrence of heavy precipitation. The results of satellite cloud images and radar observation showed that the distribution of rain bands and the activity of rain clusters were related to the development and evolution of MCS in two stages. The strong echoes in different stages had the characteristics of backward propagation and low mass center, and its train effect was obvious. The extreme shorttime severe precipitation occurred nearby the region of TBB≤-90℃.Compared with the observation, the rainfall area and the rainfall intensity predicted by the large-scale ECMWF_HR model was more northerly and more weak respectively, which were mainly due to the relatively northerly weather systems predicted by ECMWF_HR model.