Organizational Modes of Severe Wind-producing Convective Systems over North China

Severe weather reports and composite radar reflectivity data from 2010-14 over North China were used to analyze the distribution of severe convective wind（SCW） events and their organizational modes of radar reflectivity. The six organizational modes for SCW events（and their proportions） were cluster cells（35.4%）, squall lines（18.4%）, nonlinear-shaped systems（17.8%）, broken lines（11.6%）, individual cells（1.2%）, and bow echoes（0.5%）. The peak month for both squall lines and broken lines was June, whereas it was July for the other four modes. The highest numbers of SCW events were over the mountains, which were generally associated with disorganized systems of cluster cells. In contrast, SCW associated with linear systems occurred mainly over the plains, where stations recorded an average of less than one SCW event per year. Regions with a high frequency of SCW associated with nonlinear-shaped systems also experienced many SCW events associated with squall lines. Values of convective available potential energy, precipitable water, 0-3-km shear, and 0-6-km shear, were demonstrably larger over the plains than over the mountains, which had an evident effect on the organizational modes of SCW events. Therefore, topography may be an important factor in the organizational modes for SCW events over North China.

Initiation,organizational modes and environmental conditions of severe convective wind events during the warm season over North China

Based on the significant weather report,CG lightning,composite radar reflectivity,and ERA5 reanalysis data,we first studied the spatiotemporal distribution characteristics of four types(only severe convective wind(SCW);SCW and hail;SCW and short-duration heavy rainfall(SDHR);and SCW,hail,and SDHR)of convective weather events related to SCW during the warm season(May to September)from 2011 to 2018 in North China.Second,severe convective cases producing SCW were selected to statistically analyze the initiation,decay,lifetime,and organizational characteristics of convective systems.Finally,using ERA5 reanalysis data and conventional surface observation data,preconvective soundings were constructed to explore the differences in environmental conditions for initiating convective systems between SCW and non-SCW.The results indicate that mixed-type of SCW and SDHR events occur more frequently over plains,while other types of convective weather occur more frequently over mountains.The frequency peak of SCW occurs in June,while mixed convective weather peaks in July.The initiation time of convective systems is concentrated between 1000 and 1300 BST,with a peak at 1200 BST.Over mountains,the daily peaks of ordinary and significant SCW generally occur at 1700-1800 BST and 1600-1700 BST,respectively,while over plains,the peak of ordinary SCW typically lags behind that of mountains by 1-2 hours.Additionally,SCW systems are mainly initiated over mountains,with most lifetimes lasting 7–13 hours.Nonlinear convective systems produce the most SCW events,followed by trailing-stratiform convective systems.The convective available potential energy(CAPE),downdraft convective available potential energy,and the temperature difference between 850 and 500 hPa can all distinguish between SCW systems and non-SCW systems occurring over plains.Compared to non-SCW convective systems,SCW convective systems over mountains are more likely to occur in environments with less precipitable water,while SCW convective systems over plains are more likely to occur in environments with higher CAPE and stronger deep-layer wind shear.