2017年7月延庆地区一次强对流天气成因分析

Causes Analysis on a Strong Convective Weather in Yanqing July 2017

本文采用欧洲中心再分析资料(ERA5)与加密地面观测资料、风廓线雷达和多普勒雷达以及云图资料,分析了2017年7月7日延庆地区一次强对流天气过程,并由此讨论了基层预报预警服务工作的难点。结果表明:1) 此次强对流天气出现前大尺度环境条件有利于对流天气发展,高空受到低涡底部冷空气影响,低层存在切变线和西南急流,地面上受到气旋影响。2) 午后对流不稳定度进一步加强,CAPE达到2000 J/kg,同时0~3 km存在中等到强的垂直风速切变(16~22 m/s),0℃和?20℃高度适宜冰雹发展,中小尺度环境场有利于对流单体发展为超级单体风暴;此外,地面上中尺度辐合线和露点锋是此次强对流发展的重要触发机制。3) 雷达回波结构分析表明,对流单体南下到怀来北部盆地区域时加强发展为超级单体风暴,卫星云图表现出“V”形风雹云的特征,风廓线雷达监测表明超级单体开始影响延庆西部时,延庆城区低层出现强的东南风上升气流。

By using the ERA5 reanalysis data and intensive ground observation data, the wind profile and Doppler radar data, and the satellite cloud data, a strong convective weather process in Yanqing on 7th July 2017 has been analyzed, and the challenges of the forecast and early warning service at primary station were also discussed. The results showed that: 1) the severe convective weather process occurred at a favorable synoptic-scale background, with a cold vortex in 500hPa, a convergence line and jet stream in 850 hPa, and a frontal cyclone on the ground surface. 2) In the afternoon, the convective instability developed significantly, with the convective available potential energy (CAPE) increasing from 200 J/kg to 2000 J/kg. At the same time, a moderate-to-strong intensity of the vertical wind shear (16 - 22 m/s) existed at 0 - 3 km, and the height of 0?C and ?20?C were highly suitable for hail development, all of which means the meso-scale environment was inclined to the developing of supercell storms. Furthermore, the ground mesoscale convergence line and dew point front was the trigger mechanism. 3) Radar echo displayed that the convective cells strengthened into the Supercell storms when they reached the northern basin area of Huailai, and the satellite cloud picture showed “V” shape feature which imply to the hailstorm clouds, and wind profile radar detected a strong southeasterly updraft in the lower level when the supercells reached the western part of Yanqing.