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

Abstract

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.

摘要

利用雷达组合反射率资料, 对2010-14年华北雷暴大风的对流组织进行分类研究.结果表明: 华北雷暴大风的六类对流组织类型所占比例分别为: 多单体(-35.4%),飑线(-18.4%),非线性对流(-17.8%),破碎线性对流(-11.6%),单体(-1.2%),弓形回波(-0.5%).飑线和破碎线性对流两类雷暴大风在6月份最多, 而其他四类对流组织峰值为7月份.华北山区发生雷暴大风多于平原地区.非线性对流和飑线两类雷暴大风高发区相似.海拔较高的山区雷暴大风的对流组织性较弱且多为多单体组织类型, 而平原地区的雷暴大风多由组织性较强的线性对流产生.这可能和山区和平原地区的大尺度环境配置有关, 因为平原地区雷暴大风的大气可降水量、对流有效位能及风垂直切变更强.因此, 地形是影响华北雷暴大风组织类型的一个重要原因.