华东一次极端冰雹天气过程雷达回波特征的比较分析

Comparative Analysis of Radar Echo Characteristics of An Extreme Hail Storm Process in East China

2005年6月14日到15日凌晨,受东北冷涡影响,华东出现了一次历史上罕见的冰雹天气过程,最大冰雹直径达15~18 cm,并伴有雷暴大风和龙卷。本文利用2005年6月14日08:00(北京时,下同)至15日08:00新一代多普勒天气雷达资料,统计分析了这次过程中江苏沭阳、江苏泗阳、安徽固镇三地极端冰雹的雷达回波特征,结果如下:(1)极端冰雹过程是由不同超级单体造成,由于环境CAPE、深层垂直风切变和低层相对风暴螺旋度都很强,导致三个超级单体都具有强中气旋,而强中气旋与环境相互作用导致向上的扰动气压梯度力,使得超级单体上升气流大大增强并强烈发展。(2)三地超级单体雹暴回波最大反射率因子超过70 dBZ,60 dBZ以上强回波持续时间超过3 h,60 dBZ最大高度超过11 km。比较而言,沭阳超级单体持续时间最长,泗阳超级单体回波强度最大,固镇超级单体雹暴60 dBZ以上的反射率因子垂直扩展高度最高。从上述雹暴例子初步得到线索:当最大反射率因子超过68 dBZ、60 dBZ回波扩展高度在10 km以上预示有极端冰雹出现。(3)有界弱回波区(BWER)或弱回波区(WER)以及位于其上的回波悬垂是超级单体雹暴的典型结构。泗阳雹暴显示有WER和宽广的回波悬垂,沭阳和固镇雹暴则显示出BWER和宽广的回波悬垂,固镇雹暴中气旋切变值的持续上升伴随着雹暴的强盛发展。(4)三个超级单体雹暴的垂直液态水含量(VIL)异常高,分别为88 kg·m^(-2)、102 kg·m^(-2)、89 kg·m^(-2),远超过6月大冰雹的VIL阈值65 kg·m^(-2)。固镇雹暴显示出强烈的风暴顶辐散特征,辐散速度差值最高达80 m·s^(-1)。(5)固镇雹暴出现近1 h的三体散射长钉(TBSS),沭阳、固镇雹暴出现旁瓣回波,都表明雹暴中存在大冰雹。

From June 14 to the early morning of June 15,2005,affected by the northeast cold vortex,a hail weather process rarely seen in history occurred in Shandong,northwest Jiangsu and northeast Anhui.The maximum hail diameter was 15~18 cm.Based on the new generation doppler weather radar data of 08:00(Beijing time)from June 14 to 15,2005,this paper compares and analyzes the radar echo characteristics of extreme hail in Shuyang,Jiangsu,Siyang and Guzhen,Anhui.Results showed that:(1)The extreme hail process in the three regions is caused by different supercells,due to the strong environmental CAPE,deep vertical wind shear and low-level relative storm helicity,the three supercells formed successively and all had strong and mosocyclones.The interaction between strong and mosocyclones and the environment leads to an upward disturbance of the pressure gradient force,which greatly increases the updraft intensity of the supercell and strong development itself.(2)The radar echo shows that the supercell causing extreme hail in the three places has high echo starting height and strong echo intensity.The maximum reflectivity factor is more than 70 dBZ,and the strong echo lasted more than 3 hours.The maximum height of 60 dBZ is higher than 11 km.In comparison,Shuyang supercell has the longest duration;Siyang supercell has the largest echo intensity;The Guzhen supercell hailstorm has the highest vertical expansion height of reflectivity factor above 60 dBZ.Preliminary clues are obtained from the above three supercell hailstorm examples:when the maximum reflectivity factor exceeds 68 dBZ and the echo expansion height of 60 dBZ is above 10 km,it indicates that extreme hail appears.(3)The bounded weak echo area(BWER)or weak echo area(WER)and the overhangs of echoes above it are the typical hailstorm structure of a supercell storm.The Siyang hailstorm showed WER and broad echo overhang,while the Shuyang and Guzhen hailstorms showed BWER and broad echo overhang.The continuous increase of mesocyclone shear value in Guzhen hailstorm is accompanied by the strong development of hailstorm.(4)The vertical integration of liquid water content(VIL)based on cells is abnormally high,reaching 88 kg·m^(-2),102 kg·m^(-2) and 89 kg·m^(-2) respectively,far exceeding the VIL threshold of 65 kg·m^(-2) corresponding to large hail in June.The Guzhen hailstorm showed a strong storm top divergence,and the divergence velocity difference was as high as 80 m·s^(-1)(5)There are three-body scattering spike(TBSS)in guzhen hailstorm for nearly 1 hour,and there are obvious side-lobe echo characteristics in Shuyang and Guzhen hailstorms,all indicated the existence of large hails.