广东大冰雹风暴单体的多普勒天气雷达特征

Doppler Radar Features of Severe Hailstorms in Guangdong Province

选取2004—2012年广东省12个大冰雹风暴单体为样本,利用多普勒天气雷达资料,计算了最大反射率因子及其高度等多个雷达参数,分析了三体散射、旁瓣回波和环境温度层上回波特征以及大冰雹与非冰雹风暴单体间的反射率因子垂直廓线差异。结果表明:大冰雹风暴单体发展均非常旺盛,最大反射因子多超过65 dBZ,对应高度几乎都达到5 km。除受周围大范围雷达回波影响外,大冰雹风暴单体均观测到了三体散射或旁瓣回波特征,并具有一定的预报提前量;在0℃和-20℃层高度上的最大反射率因子均超过54 dBZ。大冰雹风暴单体与非冰雹风暴单体相比,低层回波迅速增加,强核心区垂直伸展更深厚,回波垂直递减率更小。

Doppler weather radar features of 12 severe hailstorms in Guangdong Province are studied. Firstly, radar echo characteristics including the maximum reflectivity, maximum reflectivityheight, the echo top, 45 dBZ echo height, the vertically integrated liquid （VIL） water, the VIL density and the vertical gradient of reflectivity are calculated. The maximum reflectivity of these 12 hailstorms are mostly over 65 dBZ with the highest value of 73 dBZ. The maximum echo heights are over 5 km with the highest being 9.2 km. Besides, all of 45 dBZ echo heights reach 9.7 km. The maximum VIL is 91 kg· m^-2 and only one storm＇s maximum VIL is less than 50 kg · m^-2. The average vertical gradient of reflectivity is 2.4 dB· km^-1 , and the minimum vertical gradient of reflectivity is 0.5 dB · km^-1. Secondly, three body scatter spike （TBSS） features, side-lobe echoes, and reflectivity distribution features in 0℃ and --20℃ environmental temperature layers of 12 sever hailstorms are analyzed. Side-lobe echoes and TBSS features are observed in 3 and 6 hailstorms, respectively, but they are found simultane- ously only in one severe hailstorm. Severe hails occur within 0--40 minutes after the first TBSS feather or the side-lobe echo appears, and the average forecast lead time is about 14 minutes. Average heights of the 0~C and --20~C environmental temperature layers around 12 severe hailstorms are 4502 m and 7682 m. All the maximum echoes of 12 severe hailstorms in 0℃ and -20℃ layers are over 54 dBZ, and the maximum values are 67 dBZ and 66 dBZ in different layers. Finally, vertical reflectivity profiles between severe hailstorms and non-hail storms are compared. For severe hailstorms, most of the maximum echoes exceed 65 dBZ, and their heights are between 5 km and 10 km. Radar echoes in hailstorms below 10 km are over 40 dBZ, and 30 dBZ echoes can extend to 15 km or higher. For non-hail storms in hailstorm days, the maximum echoes are about 60 dBZ, and correspond- ing heights are lower, located at 2--5 km levels. 40 dBZ echoes in storms are rarely above 10 km. It shows that these storms in hailstorm days can＇t generate large hail because of their weaker vertical updraft and weaker, reflectivity. For storms in non-hailstorm days, the maximum echoes vary from 55 dBZ to 68 dBZ, and heights of most of them are about 5 km. 40 dBZ echoes in some storms can extend to 10 km or higher, however, large hails don^t occur for these strong storms due to different environmental conditions.