2019年8月16日山东诸城一次罕见强雹暴结构和大雹形成的观测分析

为研究雹暴结构和大冰雹的形成机制，利用潍坊CINRAD/SA新一代天气雷达、青岛S波段双偏振多普勒天气雷达探测数据，结合探空、地面气象观测站观测和实地冰雹调查资料，对2019年8月16日发生在山东诸城的一次罕见强雹暴过程的天气背景、风雹灾害、雷达回波演变、雹云结构及大冰雹形成机制进行分析。结果表明，受冷涡天气系统影响，鲁中山区、鲁东南地区低层暖湿、高层干冷，0—6 km高度风矢量差为30.3 m/s，十分有利于强雹暴的发展。雹云发展迅速，历经发生、跃增、酝酿、降雹和消亡等5个阶段，在发生阶段即观测到中气旋、有界弱回波区等结构并不断增强，长时间维持；降雹阶段的雹云具有典型的有界弱回波区—悬垂回波—回波墙和“S”型水平流场等特征，有界弱回波区与旋转上升气流和水平速度为0的“0线”结构相关联，“0线”穿过悬垂回波和有界弱回波区顶部强回波区，指向雹云对流上冲云顶，具有特定的成雹功能；强降雹时段，雹云有界弱回波区北侧回波墙及其上方强回波区的水平反射率因子大于60 dBz，对应的差分反射率因子大多为?1—0 dB，表明为大冰雹的聚集区。依据对成熟阶段雹云雷达回波形态、径向速度和三维风场的分析，给出了实例雹云内主上升气流框架和具有成雹功能的“0线”结构示意图，有助于理解“0线”结构在大雹循环增长中的可能作用机理。 

Observational analysis of a rare and severe hailstorm cloud structure and large hailstones formation on 16 August 2019 in Zhucheng，Shandong province

A rare and severe hailstorm occurred on 16 August 2019 in Zhucheng, Shandong province is analyzed to investigate the structure of the hailstorm and the formation mechanism of large hailstones. Radar observations from Weifang CINRAD-SA (China New Generation Radar, S-band) and Qingdao S-band dual polarization Doppler weather radar, soundings and surface observations collected at various meteorological stations, and hail information obtained from field surveys are analyzed to reveal the weather background, the storm disaster situation, the evolution of radar echoes, the structure of the hailstorm and the formation mechanism of large hailstones. The results show that under the influence of a cold vortex system, the low levels are warm and wet while the upper levels are dry and cold over the central mountainous area and the southeast of Shandong province. Strong vertical wind shear of around 30.3 m/s from surface to 6 km altitude is conducive to the development of strong hailstorm. The hailstorm developed rapidly and went through five stages: Initiation, leap increase, brewing, hail fall and extinction. In the initiation stage, mesocyclone and Bounded Weak Echo Region (BWER) could be observed, which continuously strengthened and maintained for a long time. In the hail fall stage, the hailstorm showed characteristic structures such as BWER–overhang echo–echo wall and S-type horizontal circulation field. Furthermore, the BWER was associated with the configuration of the rotating updraft and the "0 line" structure where the horizontal velocity was zero. The "0 line" crossed the overhang echo and the strong echo region above the BWER and pointed to the top of the clouds with a specific hail forming function. In the heavy hail fall stage, the horizontal reflectivity factor (Z_H) in the echo wall to the north of BWER and the strong echo region in the upper hail clouds was greater than 60 dBz, and differential reflectivity (Z_DR) values were mostly between ?1—0 dB, indicating it was the accumulation area of hailstones. Based on the shape of the radar echo, radial velocity and three-dimensional circulation field in the mature stage of the hailstorm, the framework of the main updraft in the hailstorm and the schematic diagram of the "0 line" structure with hailstorm forming function are revealed in the present study. The results are helpful for better understanding possible mechanisms of the "0 line" structure in the growth of large hailstorms.