广西地区一次强雷暴天气过程雷达特征及环境场分析

Analysis of radar features and environmental background during a severe thunderstorm in early summer 2014 in Guangxi Zhuang Autonomous Region

利用常规气象观测资料、区域自动站观测资料、多普勒雷达探测资料、NCEP的1.0°×1.0°和2.5°×2.5°再分析资料,采用天气学诊断的方法对2014年6月5日广西区域性强雷暴天气过程的雷达特征和环境场进行了分析。结果表明:广西地区此次强雷暴天气过程是在500 h Pa前倾槽与地面静止锋配合的有利天气背景下,由两个弓形回波造成的。广西北部地区的弓形回波强度较弱,移动较慢,呈低质心和垂直上升结构,属强降水雷暴系统,造成了短时强降水重复出现,导致大范围暴雨;广西南部地区的弓形回波强度较强,移动较快,具有前侧和后侧入流缺口、前倾结构、中层径向辐合等雷暴大风的典型特征,造成大范围雷暴大风和局地短时强降水。中层环境湿度及垂直风切变的差异是造成广西北部和南部地区雷暴天气类型差异的环境背景原因。广西南部地区中层干区是由副热带高压环流内的干空气在西南急流作用下向北输送造成的。850—500 h Pa西南急流和较强的垂直风切变则是由高空槽与副热带高压快速靠近导致的强气压梯度造成的。

The radar features and environmental background during a regional severe thunderstorm on June 5,2014 in Guangxi Zhuang Autonomous Region were investigated using methods of a synoptic meteorology and a diagnostic analysis with conventional meteorological data,observations from regional automatic weather stations and Doppler radar,as well as the NCEP reanalysis data with resolution of 1. 0° × 1. 0°and 2. 5° × 2. 5°. The results indicate that the severe thunderstorm is caused by two bow echoes according to the radar detection. The forward-tilting trough at 500 hPa and quasi-stationary front at the surface provide favorable conditions for the formation of the thunderstorms. The intensity of the bow echo in the northern Guangxi Zhuang Autonomous Region is weak and it moves slowly,with a low barycenter and vertical upward structure,which causes repeatedly short-time heavy rainfall and ultimately leads to a large-scale rainstorm. However, the intensity of the bow echo in the southern Guangxi Zhuang Autonomous Region is relatively stronger and it moves faster,with typical characteristics of thunderstorm gale, such as front and rear inflows, inclined structure and mid-altitude radial convergence（ MARC）. This bow echo causes the regional gale and local short-time heavy rainfall. Mid-level humidity and vertical wind shear are background reasons for the different weather types in the northern and southern Guangxi Zhuang Autonomous Region,respectively. The dry air,controlled by the subtropical high,moves to the north along southwesterly jet,and makes dry air advection over the southern Guangxi Zhuang Autonomous Region. The 500 hPa trough moves rapidly toward the area of the subtropical high,which leads to a greater pressure gradient and generates southwesterly jet between 850 and 500 hPa as well as strong vertical wind shear.