山西高原大冰雹与小冰雹的环境参量对比分析

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

本文利用1956-2017年山西省109个气象站的逐日冰雹观测资料研究了山西冰雹的空间分布特征,发现全省冰雹日数由东北向西南依次减少,与海拔有很好的对应关系,山地冰雹发生日数高于盆地,冰雹频发区主要集中在北部和东部山区。以冰雹直径2 cm为阈值,将冰雹分为大冰雹与小冰雹两类,统计了2008-2019年山西两类冰雹站的比例,结果表明山西高原以小冰雹为主,大冰雹仅占3.9%,盆地大冰雹比山区多,大冰雹容易发生在陡峭山地与盆地或河谷的交界处。为了进一步研究大冰雹与小冰雹产生环境条件的差异,选了2008-2019年山西的23个大冰雹日和44个小冰雹日,基于订正的观测探空对表征冰雹天气的动力、热力和水汽等环境条件的多个环境参量进行了统计分析,以箱须图的形式给出了环境参量的分布。结果表明:大、小冰雹日的水汽差异最为显著,大冰雹日对流层低层水汽含量相对丰富,中层则比小冰雹更干,二者地面露点中位数分别是16℃和14℃,700~400 hPa之间的平均温度露点差中位数分别是14.8℃和12.7℃,整层可降水量中位数分别为26.7 mm和23.7 mm;二者的垂直温度直减率差异不明显,但850 hPa与500 hPa假相当位温差的差异很显著,这是由于假相当位温包含了水汽信息;二者的干球温度0℃层距离地面的高度差异不明显,但大冰雹日湿球温度0℃层距离地面的高度更高,说明大冰雹日干、湿球0℃层的差距更小,0℃层附近的湿度更大。大冰雹出现在更大的条件不稳定和更高的低层露点条件下,因而对应环境有更大的CAPE值,大冰雹与小冰雹的CAPE中位数分别是2099 J·kg^(-1)和1588 J·kg^(-1);大冰雹出现在更大的环境垂直风切变中,0~6 km垂直风切变中位数分别为16 m·s^(-1)和12 m·s^(-1)。

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.