一次冰雹过程的多源资料观测特征分析

Analysis of the characteristics of a hail event with multi-source data

为认识降雹不同阶段对流系统的回波、微物理参量和热动力演变特征,利用多普勒天气雷达、激光雨滴谱仪、微波辐射计、自动气象观测站等观测资料,对2017年7月9日天津地区一次冰雹天气的回波特征、雨滴谱差异、温湿度及水汽变化进行研究。结果表明:(1)850 hPa切变线东侧的暖湿气流与500 hPa冷空气叠加,有利于不稳定能量积累及对流天气触发。降雹临近时,环境大气不稳定性显著增强。(2)冰雹云发展演变阶段观测到两次地面降雹,均发生在对流单体合并加强过程中。(3)降雹时段,粒子最大直径、质量加权平均直径和中值体积直径达到峰值,中大滴对降水雨强的贡献率达94.56%,该时段平均谱谱宽最大;降雹后,直径小于1.0 mm的小滴对雨强贡献率增大,在不超过1.0 mm的粒子区间平均谱呈双峰特征,第一峰和第二峰分别出现在0.3 mm、0.6 mm附近。(4)降雹前水汽出现缓慢持续积累,积分水汽、液态水含量在降雹前1 h出现明显跃增,低层逆温的存在使高层干冷、低层暖湿的现象更为明显;降雹结束后整层大气水汽有所回落。

To understand the evolution characteristics of radar echo,microphysical parameters,and thermal dynamics of the convective systems during different stages of hailstorms,observations from Doppler weather radar,laser raindrop spectrometer,microwave radiometer,and automatic meteorological stations were used to investigate the radar echo characteristics,raindrop spectrum difference,temperature,humidity and water vapor variation characteristics of a hailstorm occurred in Tianjin on July 9,2017.The results are as follows.(1)The warm and wet air on the east side of the shear line at 850 hPa is superimposed with the cold air at 500 hPa,which is conducive to the accumulation of unstable energy and triggering of convective weather.With hail approaching,the instability of the ambient atmosphere increased significantly.(2)During the evolution stage of the hail cloud,two hailfall events were observed,both of which occurred during the strengthening and merging processes of the convective cells.(3)During the hailfall stage,the maximum diameter,mass-weighted mean diameter,and median volume diameter of the precipitation particles reached their peak values.The contribution rate of medium and large droplets to precipitation intensity reached 94.56%,and the average spectral width during the hailfall stage was the largest.While after hailfall,the contribution rate of particles with a diameter less than 1.0 mm increased.The mean spectrum of particles within the range of less than 1.0 mm showed a bimodal pattern,with the first peak and the second peak occurring near 0.3 mm and 0.6 mm,respectively.(4)Before the hailfall,the water vapor accumulated slowly but continuously.The integrated water vapor and liquid water content showed an obvious increase in 1 h before hailfall.Due to the existence of temperature inversion,the upper layers were dryer and colder,while the lower layers were warmer and wetter.Note that the water vapor content in the whole atmosphere started to decrease after the hailfall.