Comparative Analysis of Environmental Parameters of Severe and Less Severe Hail Events in Shanxi Plateau

Abstract

Based on the daily hail observation data of 109 meteorological stations in Shanxi Province from 1956 to 2017， the spatial distribution of hail in Shanxi is studied.It is found that the number of hail days decreases from northeast to southwest and is more in mountainous areas than in the basin， which has close correlation with the altitude.The hail prone areas were mainly concentrated in the northern and eastern mountainous areas.Taking the hail diameter of 2 cm as the threshold， the hail samples were divided into two groups， namely severe and less severe hail events.The proportion of the two groups of hail stations in Shanxi province from 2008 to 2019 is calculated.The results show that less severe hail events dominate in Shanxi Plateau and severe hail events account for only 3.9% of the total.Severe hail events are more inclined to occur in basins than in mountainous areas， and tend to occur at the junction of steep mountains and basins or valleys.In order to further study the difference of atmospheric environmental conditions between the two groups， 23 severe hail days and 44 less severe hail days during 2008-2019 in Shanxi are selected as samples.Based on the revised observational aerological sounding of those samples， several environmental parameters which represent the dynamic， thermal and moisture environmental conditions of hail weather are statistically analyzed.The results show that the difference of moisture conditions between severe and less severe hail days is significant.Severe hail cases are wetter in the lower troposphere and drier in the middle troposphere than the less severe hail cases.The median surface dew points of the two groups is 16 ℃ and 14 ℃， the median of average T-Td from 700 hPa to 400 hPa is 14.8 ℃ and 12.7 ℃， and the median total precipitable water is 26.7 mm and 23.7 mm respectively.There is no significant distinction in the vertical temperature lapse rate between the two groups， but the distinction in the pseudo equivalent temperature difference between 850 hPa and 500 hPa is very significant， which is because the pseudo-equivalent potential temperature contains moisture information.There is no significant distinction between the two groups in the height from the dry bulb 0 ℃ layer to ground， but the height from the wet bulb 0 ℃ layer to ground of severe hail cases is higher.It indicates that in severe hail cases， the difference between dry and wet bulb 0 ℃ layer is smaller and the humidity near 0 ℃ layer is larger.As severe hails occur in the conditions of greater instability and higher dew point in the lower troposphere， the corresponding environment of severe hail cases has a larger convective available potential energy （CAPE）.For severe and less severe hail cases， the median of CAPE was 2099 and 1588 J·kg-1 and the median of 0~6 km vertical wind shear was 16 m·s-1 and 12 m·s-1 respectively.Severe hail events tend to occur in the environment of stronger deep vertical wind shear.

Keywords

• severe hail events and less severe hail events
• spatial distribution
• comparison of environmental parameters