It is very important for the study of hail cloud and its suppression to learn the characteristic parameters of hail such as number concentration, the maximum diameter, terminal velocity. Based on the data collected by Parsivel precipitation particle spectrometer in a hail process occurred on 22 May 2013 in Weibei area of Shaanxi Province, combing the data of radar reflectivity and minute precipitation data from the automatic station, the temporal evolution of physical parameters was analyzed that include the rainfall intensity, rainfall amount, maximum hail diameter, number concentration, spectral distribution and hail velocity. The results are shown as follows:(1)The average particle spectrum distributions of rain and hail were calculated for this hail process, and fitted by the Marshall-Palmer exponential distribution. The correlation coefficient of fitting is 0.95 for raindrop with diameter of 0.3~4.75 mm, and 0.99 for hail with diameter of 5.5~11 mm; (2) The number concentrations of hail are 0.3% of the total precipitation particles, and its precipitation accounts for 37% of the total precipitation; (3) During the hail process, the number concentration of raindrop and hail increases or decreases simultaneously. The maximum number concentrations of hail and raindrop are 5 m-3 and 1 423 m-3 in one minute, respectively; (4) This is the first time that the terminal velocity of hail was measured in situ in China. The empirical formula of the average hail velocity is obtained by fitting the measured terminal velocities with the hail diameter, and its relative error is 2.8% in respect to the measured average terminal velocity of hail. This study will be a firm foundation for the further learning the features of hailstorm and the effect of artificial hail suppression in this area, and will be a good reference for the development of explicit cloud physics scheme of numerical model.
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