中文摘要：

利用常规观测资料、多普勒天气雷达资料、地面自动站加密资料、NCEP 1°×1°的再分析资料等对2014年7月18日发生在湘赣地区一次台前飑线过程的环境条件及多普勒天气雷达特征进行研究。结果表明：台前飑线产生前,对流层低层较好的水汽条件、条件不稳定层结以及两者结合形成的高CAPE值均为其发生发展提供了良好的条件;台风倒槽是此次台前飑线过程主要影响系统,露点锋、地面辐合线为其提供了抬升触发和维持加强机制;台前飑线西移北上的过程中出现＂弓形＂回波、中层径向辐合（MARC）、速度大值区、阵风锋。本次台前飑线和以往研究的西风带飑线存在以下差异：本次飑线低层垂直风切变主要是以风速差为主;中高层的冷空气侵入并不明显;在成熟阶段,气压场上也没有明显的雷暴高压,但有明显正变压;本次飑线过程是发生在暖湿的环境条件下,后侧入流为相对湿度较大的东南急流,雨水蒸发并没有西风带飑线强烈;雷达速度图上虽有MARC特征但最大正负速度差值并不是很大（15-27 m/s）。上述特征可能是该台前飑线过境湖南过程中没有造成极端大风的主要原因之一。

英文摘要：

Based on the routine observational data, SWAN networking charts, radar data of Changsha Station, intensive automatic weather station data and 1°×1° NCEP 6 h reanalysis data, the circulation pattern of the squall line in front of a typhoon on 18 July 2014 in Hunan and Jiangxi Province and the Doppler radar characteristics are analyzed. The results show that： the preferable vapor conditions in the lower atmosphere, the unstable thermal stratification, the high lapse rate of temperature gradient, and high CAPE provided favorable potential conditions for the development of the squall line before generation; the inverted typhoon trough was the main influential system of the squall lines, and the front and the surface convergence line triggered the squall line; the bow-shaped echo, mid-altitude radial convergence （MARC）, high-speed value zones, gust fronts, etc. appeared during the westward and northward movement of the squall line. The squall line in front of typhoons are different from westerly ones： at the low levels the vertical wind shear is mainly dominated by wind velocity differences; the cold air invasion is not as obvious as in the middle and upper levels; there is no evident thunderstorm high at the mature stage, but distinct positive pressure variation is detected; the squall line process happened in warm and humid environmental conditions, with influx of southeast jet stream on its rear side, and its evaporation of rainfall was weaker than that of westerly squall lines. The characteristics of MARC on the velocity diagram were apparent, yet without massive differences between positive and negative velocities （15 to 27 m/s）, which are the reasons why the squall line went through Hunan Province without bringing severe disasters.