基于二维雨滴谱仪的巴彦淖尔地区降雹谱个例分析

Case Study of Hail Size Distribution in Bayannur Area based on Two-Dimensional Video Disdrometer

布设在内蒙古自治区巴彦淖尔市五原县气象局的二维雨滴谱仪(2DVD)在2020年7月27日观测到一次含雹混合降水事件,基于粒子直径与本地下落末速度对2DVD数据质控后,分析了此次过程不同直径-速度和不同直径-轴比下的粒子数量分布以及粒子谱、中值体积直径、质量加权平均直径、粒子数浓度和降水强度等参数随时间的演变。结果表明:(1)直径0.1~0.5 mm的雨滴实测下落末速度偏大于经验公式计算的下落末速度,直径5~10.4 mm的冰雹粒子下落速度为5.5~11.6 m·s^(-1),直径小于6 mm的冰雹粒子下落速度分布较广。直径0.1~2 mm的小雨滴轴比为0.9~1.1,直径2~5 mm的大雨滴轴比为0.7~1.0,直径5~10.4 mm的冰雹粒子轴比为0.5~1。(2)本次降雹类型为先雨后雹,雹雨混降,雹后持续降雨,冰雹谱谱宽为10.4 mm。逐分钟降水粒子谱存在3个直径极大值,在降水和降雹之间存在短暂的无降水,谱宽和粒子数浓度随时间同时增大和减小,并在降雹阶段,各参数陡增至峰值。(3)冰雹谱分布呈单调递减型,通过M-P分布函数分段模拟了降雹时段的雨滴谱和冰雹谱,模拟的粒子谱大于2DVD实测的粒子谱,且模拟雨滴谱与实测谱的数浓度对数均方根误差为1.02,模拟冰雹谱与实测谱的数浓度均方根误差为2.21。

A hail event with rainfall was observed on July 27,2020 using a two-dimensional video distrometer(2DVD)deployed at Wuyuan National Meteorological Station,Wuyuan County,Bayannur City,Inner Mongolia.After quality controlled of the 2DVD data based on the relationship between particle diameter and empirical local particle terminal fall velocity are used then for the analysis of,the particle number distribution(ND)under different diameter-velocity and different diameter-axis ratios,and the evolution of parameters such as particle spectrum,median volume diameter,mass-weighted average diameter,total number of particles density and precipitation intensity during this precipitation process have been analyzed.The results show that:(1)The measured terminal falling velocity of raindrops with a diameter of 0.1~0.5 mm is larger than the terminal falling velocity calculated by the empirical formula,and the falling velocity of hail with diameter of 5.0~10.4 mm is 7.2~9.0 m·s^(-1),which is less than the local particle terminal velocity.The axial ratio of small raindrops with a diameter of 0.1~2.0 mm is 0.9~1.1,the axial ratio of big raindrops with a diameter of 2~5 mm is 0.7~1.0,and the axial ratio of hail particles with a diameter of 5.0~10.4 mm is 0.5~1.0.(2)By the 2DVD observation,the event discussed in this paper is a precipitation process of rain followed by hail,hail-rain mixture and then rain again.The hail-spectrum width is 10.4 mm.There are three maximum diameters in the minute-by-minute precipitation particle spectrum.And there is a short period of no precipitation between rainfall and hail.The spectrum width and particle number concentration increase and decrease simultaneously with time.During the hailfall stage,each parameter increases sharply to the peak.(3)The M-P distribution is used to simulate the raindrop spectrum and hail spectrum during the hailfall period,the simulated spectrum is larger than that observed by 2DVD.The logarithmic root mean square error between the simulated raindrop spectrum and the measured one is 1.02,and the root mean square error between the simulated hail spectrum and the measured spectrum is 2.21.