1822号“山竹”台风龙卷过程观测与预警分析

AN ANALYSIS ON THE OBSERVATIONS AND WARNINGS OF TORNADO INDUCED BY TYPHOON MANGKHUT

2018年9月17日09:37—10:00,在登陆台风“山竹”外围螺旋雨带中,广东省佛山市三水区到肇庆市四会区发生了EF2级强龙卷,龙卷路径长度18km,持续时间23min,平均时速47km/h,导致不少建筑物损毁。本次过程佛山市进行了龙卷预警试验,提前37min发布了龙卷预警,龙卷没有造成人员伤亡。利用观测资料对产生强龙卷的环境场特征、地面自动站和雷达观测的中小尺度特征以及龙卷预警试验进行了分析,结果表明:产生龙卷的微型超级单体出现在台风外围和副高边缘之间的强东南急流中,具有低层辐合、高层辐散、水汽充足等典型台风外围龙卷环流形势特征;强的低空0~1km垂直风切变、大的风暴相对螺旋度和低的抬升凝结高度等环境条件利于龙卷的生成;龙卷影响时,邻近地面自动气象站观测要素表现出明显的信号,瞬时大风和最低气压的极值区呈东南至西北向带状分布,与龙卷路径一致,龙卷过境前后,单站气压“漏斗”明显,5min降压/升压幅度达-2.5hPa/+2.1hPa;广州多普勒天气雷达探测到龙卷母体风暴的低层钩状回波和入流缺口特征,以及低层强中气旋和类TVS特征。预警试验初步表明,对台风龙卷高发区,在环境场有利情况下,若低层出现中等或以上强度中气旋,其底高在1km以下,可以考虑发布龙卷预警。

In an outer rainband of the landfalling typhoon Mangkhut,an EF2 tornado struck Sanshui District of Foshan City and Sihui District of Zhaoqing City,Guangdong Province from 9:37 to 10:00 on 17 September 2018.The tornado lasted for 23 minutes,produced an 18-km long ground damage track.Its average velocity was 47 km/h.As Foshan Weather Service was then conducting a tornado warning test,tornado warnings were issued 37 minutes in advance,and thus no people were injured or killed.Based on the data of observations,this paper focuses on the synoptic background,mesoscale characteristics of automatic weather stations and doppler radar and warning test of the tornado.The results show that miniature supercell spawned tornado formed in the southeast jets between typhoon and subtropical high.The features of low-level convergence,upper level divergence and high moisture in lower levels are typical tornado synoptic environment with the outer region of typhoon circulation.The environmental conditions,such as strong vertical wind shear at 0~1 km,high storm relative helicity and low lifting condensation level were favorable for tornado genesis.Significant signals were recorded by the adjacent automatic weather stations when tornado passed by.The distribution of extreme variables of gust and pressure extended from southeast to northwest which was consistent with the tornado track.The pressure showed a clear funnel and dropped sharply by-2.5 hPa/5min and increased sharply by 2.1 hPa/5min during the tornado influencing period.The hook echo,FIN,low-level strong mesocyclone and similar TVS were detected by Guangzhou doppler radar.Preliminary examination of tornado warning test indicated that tornado warnings could be issued to those areas with high tornadoes frequency when the bottom height of low-level moderate or greater mesocyclone is lower than 1 km and the synoptic environmental conditions are favorable for tornado genesis.