Characteristics and Cause Analysis of Local Rainstorms When Subtropical High Moving North

Using conventional meteorological observation data, automatic weather station data, radar data and Final Operational Global Analysis (FNL) data, and focusing on the local rainstorms of Hebei province in the process of subtropical high moving north on 20-22 July 2017, the meso-scale characteristics and reasons are analyzed in this paper. Firstly, the local rainstorms belong to the heavy rain caused by summer monsoon moving north, and the distribution of rainfall is extremely uneven, with 3 strong rainfall centers located in Qinhuangdao, Shijiazhuang, and Langfang. Secondly, the difference of heat and water vapor causes the different characteristics of 3 centers: local rainstorm in Qinhuangdao are accompanied by large-scale energy front and water vapor transportation, and radar echoes are banded and mixed; while local rainstorms in Shijiazhuang and Langfang occur at high temperature and moisture environment without large-scale water vapor transportation, and the radar echoes are dense block convective echoes. Lastly, the trigger mechanisms of the 3 strong rainfall centers are different: the local rainstorm in Qinhuangdao is triggered by the shear lines in middle and low level, and multiple convective cells affect successively resulting in “train effect”; while the local rainstorms generated by meso-scale convective systems in Shijiazhuang and Langfang are triggered by the northeast or east wind in the boundary layer. Keywords—subtropical high moving north, local rainstorm, radar characteristics, trigger mechanism 摘要—利用常规气象观测资料、自动站资料、雷达和 FNL 再分析资料,对 2017 年 7 月 20-22 日副高持续北抬过程中的 河北省局地暴雨中尺度特征进行了深入分析,并就其成因进 行了探讨。首先,本次局地暴雨属于夏季风北上产生的暴 雨,雨量分布极为不均,有 3 个强降水中心,分别位于秦皇 岛、石家庄、廊坊。其次,环境热力和水汽的差异导致 3 个 强降水中心的特征不同:秦皇岛的局地暴雨伴随有天气尺度 的能量锋和水汽输送,雷达回波呈带状混合性回波;石家庄 和廊坊的局地暴雨发生在高温高湿的环境中,没有天气尺度 的水汽输送,雷达回波为结构密实的块状对流回波。最后,3 个强降水中心的触发机制不同:秦皇岛局地暴雨由中低层切 变线触发,多个对流单体相继影响,造成列车效应;石家庄 和廊坊的局地暴雨由边界层东北风或偏东风渗透触发中尺度