极端雷暴大风的环境参量特征

Environmental Parameter Characteristics of Severe Wind with Extreme Thunderstorm

为了研究极端雷暴大风天气环境要素特点,选取2002-2017年中国各地区极端雷暴大风个例95个和不伴随强对流的普通雷暴个例95个,通过两者间关键环境参数的对比,揭示极端雷暴大风事件的关键环境参数特征。结果表明:极端雷暴大风天气发生在对流层中层相对干的环境下,表现为400～700 hPa极端雷暴大风对应的单层最大温度露点差和平均温度露点差平均值分别为25.7℃和13. 6℃,而普通雷暴的相应值分别为16. 2℃和6.5℃。统计结果表明:尽管产生极端雷暴大风的对流风暴和普通雷达对应的地面露点差异并不大,但前者相应的大气可降水量(平均值为37 mm)明显低于后者(平均值为51 mm),差异突出表现在两者湿层厚度的不同上;相对于普通雷暴事件,极端雷暴大风事件对应的对流有效位能值(平均值为1820 J·kg^(-1))明显高于普通雷暴事件的对应值(平均值为470 J·kg^(-1));此外,极端雷暴大风事件对应的对流层中下层垂直温度递减率、下沉有效位能、夹卷层平均风速和0～6 km,0～3 km垂直风切变均明显大于普通雷暴事件对应的相应值。

Cases of severe wind with extreme thunderstorm and ordinary thunderstorm without strong convection in various regions of China are analyzed to study characteristics of environmental element of the severe wind, and 95 cases are selected for each type from 2002 to 2017. The comparison of key environmental parameters of severe wind with extreme thunderstorm and ordinary thunderstorm reveal the key environmental parameter characteristics. Results show that severe wind occurs in a relatively dry environment in the middle troposphere. The single-layered maximum depression of dew point of severe wind is 25. 7℃ and the average depression of dew point is 13. 6℃ when those of ordinary thunderstorm are 16. 2℃ and 6. 5℃, respectively. Differences between their ground dew point temperature are not significant, when the mean ground dew point temperature of severe wind is 20. 2℃, and the mean of ordinary thunderstorm is 21℃.However, the average precipitable water of the former is 37 mm, significantly lower than that of the latter which is 51 mm due to the discrepancy in moisture layer. The moisture layer thickness of the former is below 2 km in most of cases, obviously shallower than the average thickness of ordinary thunderstorm moisture layer, which is 3. 6 km. The mean vertical temperature lapse rate in the middle and lower troposphere of severe wind is larger than that of ordinary thunderstorm. Its average temperature difference between850 hPa and 500 hPa is 28. 2℃, obviously larger than that of ordinary events, which is 23. 3℃. At the same time, as the ground dew point temperature is not much different, the mean convective available potential energy of severe wind is 1820 J · kg^(-1), larger than the average of ordinary thunderstorm which is only 470 J · kg^(-1). The convective inhibition for two types of thunderstorms are not significantly different,the average convective inhibition of severe wind is 79 J · kg^(-1), comparing to 55 J · kg^(-1) of ordinary thunderstorms. 0-6 km vertical wind shear of severe wind is 18. 1 m · s^(-1) and 0-3 km vertical wind shear is13. 2 m · s^(-1) comparing to 14. 3 m · s^(-1) and 10. 5 m · s^(-1),respectively. The convective available potential energy of downdraft of severe wind is larger whose average value is 1110 J · kg^(-1) while the mean convective available potential energy of downdraft of ordinary thunderstorm is 620 J · kg^(-1). And the median entrainment zone mean wind speed of severe wind is 14 m · s^(-1). It is slightly larger than that of ordinary thunderstorm, which is 12 m · s^(-1). In addition, there is also discrepancy in the height of characteristic layer of severe wind with extreme thunderstorm and ordinary thunderstorm, such as 0℃ layer,-20℃layer, and the lifting condensation level.