Comparative Analysis of Occurrence and Development of Multiple β-Meso Scale Convective Systems During a Localized Severe Torrential Rain Event in North China
Based on the conventional surface and upper-air observations,Doppler radar products,wind-profiling radar data,VDRAS and NCEP reanalysis data,the triggering and development mechanisms of multiple β-meso scale convective systems under the influence of subtropical high in North China from 5 to 6 August 2018 are analyzed.The results show that this severe torrential rain occurred under the control of subtropi-cal high,in a high temperature and high humidity air mass,with extremely unstable atmospheric stratifica-tion.The torrential rain was caused by multiple successive developing mesoscale convective systems,namely MCS-Ⅰ,MCS-Ⅱ,MCS-Ⅲ and MCS-Ⅳ,which were quasi-stationary β-meso scale systems on the windward slope of Taihang Mountains in southwest-northeast direction,in Baoding Area of North China Plain in north-south direction,near Baoding to Bazhou in the southwest-northeast direction and centered on Xiong'an New Area in east-west direction,respectively.In a similar environment,different mesoscale convective systems had significant differences in triggering mechanisms.MCS-Ⅰ on the windward slope of Taihang Mountains was triggered by near-surface easterly warm and humid airflow converging and lifting on the windward slope with mountain wind.After being influenced by MCS-Ⅰ,the local cold pool formed by radiation difference and earlier-stage severe precipitation was strengthened again.Its outflow formed two surface convergence lines with environmental wind,which triggered MCS-Ⅱ and MCS-Ⅲ and organ-ized convection along convergence line into band-like development.The enhanced easterly wind at ultra-low altitude superimposed the outflow of the cold pool,promoting further uplift of the warm and humid air mass along the mountain under the effect of terrain uplift,triggering MCS-Ⅰ reconstruction.MCS-Ⅳ de-veloped most vigorously and lasted longest,and was the direct maker of the severe torrential rain center.On one hand,the two merger processes of MCS-Ⅱ and MCS-Ⅲ,MCS-Ⅰ and MCS-Ⅳ were important rea-sons for the strengthening and persistence of MCS-Ⅳ.On the other hand,the boundary layer easterly jet provided favorable conditions such as water vapor and unstable energy for MCS-Ⅳ's development,and also promoted the development of mesoscale vortex in its left front side,resulting in a significant increase of cyclonic vorticity in MCS-Ⅳ's location,enhancing the vertical secondary circulation development centered on jet axis,causing MCS-Ⅳ's continuous maintenance,and forming an east-west severe torrential rain belt centered at Xiong'an New Area in North China Plain.
万方数据
维普
