Abstract: Based on the ground meteorological monitoring information, NCEP/NCAR reanalysis data and wind profiler radar data, a heavy fog process induced by a rainfall event in southern Jiangsu Province on 2 April 2016 was analyzed comprehensively. The results indicate that the high surface air temperature accelerated water vapor evaporation before the rainfall, which prompted the decrease of visibility, while the water vapor was condensed to cooling fog under the influence of weak cold air at the later stage of rainfall weakening, and resulted in sharply decreasing of visibility to the minimum value, which was the main reason of the inconsistency of occurrence time between the lowest visibility and the biggest rainfall intensity. Warm advection and positive variable temperature were obvious before the rainfall, which was beneficial to the construction of inverse temperature structure during the rainfall. The low height of inversion layer and the strong reverse temperature played an important role for decreasing of visibility. The vertical wind speed in lower layer sharply increased at the strongest stage of rainfall, so the urgent wind speed, strong rainfall and low visibility caused the occurrence of traffic accident.

Key words: precipitation, heavy fog, visibility, warm advection, variable temperature

摘要： 利用地面气象常规观测资料、NCEP/NCAR再分析资料和风廓线雷达数据，针对2016年4月2日江苏南部地区一次降水诱发的大雾过程进行综合诊断分析。结果表明：降水之前地面气温高加速了水汽蒸发，促使能见度下降，而降水减弱后期，弱冷空气使得水汽凝结形成冷却雾，致使能见度下降至最低，这是最低能见度与最大雨强出现时间不一致的主要原因。降水之前明显的暖平流、正变温，有利于降水过程中逆温结构的形成，逆温层高度低、逆温强度大是能见度下降的重要条件。雨强最强阶段，垂直方向上低层风速突增，风急、雨强、能见度低引发了交通事故的发生。

关键词: 降水, 大雾, 能见度, 暖平流, 变温