Gaoyuan qixiang (Jun 2023)
Case Study of Hail Size Distribution in Bayannur Area based on Two-Dimensional Video Disdrometer
Abstract
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.
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