甘肃中部一次冷锋后高架雷暴天气过程综合诊断

Comprehensive Analysis of an Elevated Thunderstorm Process Behind Cold Front in the Central of Gansu Province

利用常规气象观测资料、ECMWF再分析资料和多普勒天气雷达资料等,从环流特征、天气系统配置以及动力、热力条件等方面,对2017年10月8-9日甘肃中部地区的一次冷锋后高架雷暴天气过程进行综合诊断分析。结果表明:冷锋、700 hPa切变线、西南急流以及500 hPa高空槽是本次高架雷暴天气发生发展的主要天气系统。北方南下的冷空气在近地面形成冷垫,暖湿气流沿锋区倾斜爬升,在逆温层顶触发了高架雷暴天气。本次过程逆温层深厚,逆温层及其附近垂直方向上存在3个0℃层。受过程前降水和西南暖湿气流影响,大气层结呈"上干、下湿"结构,且具有"上下冷、中间暖"的特征。对流层中低层垂直风切变、低层辐合与高层辐散,是促使暖湿空气抬升的重要动力,而中低层高能舌和最大对流有效位能值能够较好地反映过程中的不稳定能量。高架雷暴过程中,兰州及附近地区出现降雨(雪)及冰雹天气,并伴有大范围东北-西南向雷电;雷达强回波高度达8 km以上,具有典型的冰雹回波特征。

Based on the conventional meteorological observation data, ECMWF reanalysis data and reflectivity factor data of Doppler radar, the circulation situations, weather systems configuration, dynamic and thermal conditions of an elevated thunderstorm weather process behind cold front in the central of Gansu Province from October 8 to 9, 2017 were diagnosed synthetically. The results show that the weather systems affecting the occurrence and development of the elevated thunderstorm weather were mainly cold front, 700 hPa shear line, southwestern jet and 500 hPa upper-level trough. The cold air moving southward formed a cold pad near the ground, and the warm and humid airflow climbed along cold front, which triggered the elevated thunderstorm weather at the inversion layer top near 620 hPa. The inversion layer of the elevated thunderstorm weather was deep, and there were three 0 ℃ layers in vertical direction. Under the influence of rainfall before the occurrence of the elevated thunderstorm process and southwest warm and moist airflow, the atmosphere was dry in upper layer and humid in lower layer, and it was cold in upper and lower layers and warm in middle layer, which indicated the atmospheric stratification was instability. The vertical wind shear in middle and lower levels of troposphere, convergence in lower level and divergence in upper level prompted the uplift of warm and humid air. The high energy tongue and BCAPE in middle and lower levels could reflect unstable energy conditions well during the process. During the elevated thunderstorms process, the rainfall(snowfall) and hail weather accompanying wide-range and northeast-southwest thunder and lightning appeared over Lanzhou and its surrounding. The strong echo height of radar reflectivity factor exceeded 8 km, and the echo characteristic of hail was typical.