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

摘要

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.