渝西一次强对流风暴过程的中尺度特征分析

Analysis on mesoscale characteristics of a severe convective storm event in western Chongqing on 23 July 2011

利用常规观测资料、地面加密自动站资料、ADTD地闪资料和天气雷达资料,分析了2011年7月23日重庆西部一次强对流风暴过程的中尺度特征。结果显示:(1)此次强对流天气是在"两高一低"环流背景下发生的,强的层结不稳定、低层水汽充足、大的下沉不稳定能量及0—6 km中等强度垂直风切变为其提供了有利的环境条件。(2)地面灾害性大风主要集中在地面强降水及地闪密度中心附近,地面观测到与地面大风相联系的辐合线、辐散区、冷池及雷暴高压等中尺度特征,地闪以负地闪为主,负、正地闪之比约为101:1。(3)造成极端大风和短时强降水的强对流风暴在雷达回波图上具有明显的阵风锋、回波悬垂、弱回波区和有界弱回波区等特征;在径向速度图上,具有明显的中气旋、辐散区、大风区、前侧入流、高层辐散和低层辐合等特征,这些特征对地面灾害性大风具有一定的监测预警意义。

Based on data from conventional observations, intensive network of automatic weather stations （AWS）, ADTD lightning instru-ment and weather radar, we analyzed the mesoscale characteristics of a severe convective storm event occurred in western Chongqing on 23 July 2011. The main results are as follows. （1） The event occurred under the condition of a cold low circulation between the Tibet high and the subtropical high. Several factors such as strong unstable stratification, sufficient water vapor in the low level, large downdraft convective avail-able potential energy （DCAPE） and moderate vertical shear in 0-6 km are favorable to the development of the storm. （2） The disastrous gale is mainly located in the center and its surrounding areas of surface heavy rainfall and high density of ground lightning. Mesoscale characteristics associated with the ground gale, such as convergence line, convergence zone, cold pool and thunder high, are observed by AWS. Negative cloud-to-ground （CG） lightening dominated in the event, and the ratio of negative to positive CG is approximately 101：1. （3） The gust fronts, echo hanging, weak echo region （WER） and boundary weak echo region （BWER） are quite clear on the PPI and RHI charts of radar reflectiv-ity factors, and features such as mesosyclone, divergence on low tilts, large radial velocity region, inflow flows, divergence in the upper level and convergence in the low level are also evident in the radial velocity chart. The above characteristics are of significant importance in disas-trous gale detection and its early warning.