北京市2018年“7·16”极端暴雨特征及成因分析

Analysis on characteristics and causes of the extreme rainstorm on 16 July 2018 in Beijing City

基于地面自动站、雷达及NCEP数据,采用标准化异常度方法,对北京市2018年7月15—16日出现的极端暴雨过程进行分析,结果表明:极端降雨发生在副热带高压和高空槽之间,低层有明显的西南急流,水汽充沛;暴雨发生时,环境条件标准化异常度均超过3σ,为此次极端降雨创造了极其有利的动力、水汽和不稳定条件;中尺度对流系统活动可分为对流系统触发和局地强降雨、对流系统组织化加强和强降雨区北移两个阶段,均伴有明显的“列车效应”,且降雨效率极高;低空西南急流利于大气不稳定层结的建立、水汽持续输送,地面辐合线方向与850 hPa低空急流方向、对流云团的移动方向均一致,是导致对流系统触发后增强的主要原因。

The extreme rainstorm process in Beijing from July 15 to 16,2018 was analyzed by using the data of automatic ground stations,radar and NCEP and the standardized anomaly method.The results show that:the extreme precipitation occurs between the subtropical high and the high trough,with obvious southwest jet in the lower layer and abundant water vapor;when the rainstorm occurs,the standardized anomaly of environmental conditions exceeds 3σ,which created the favorable dynamic,water vapor and unstable conditions for this extreme precipitation;meso-scale convective system activities can be divided into two stages,the convective system triggering and local heavy rainfall,and the convective system organization strengthening and northward movement of heavy rainfall area,both of which are accompanied by obvious train effect with very high precipitation efficiency;the low-level southwest jet is conducive to the establishment of atmospheric unstable stratification and the continuous transportation of water vapor.Meanwhile,the direction of the ground convergence line is consistent with the direction of the 850 hPa low-level jet and the movement direction of convective system,which is the main reason for the enhancement after the triggering of the convective system.