“山竹”(1822)台风外围佛山强龙卷天气过程观测分析

Analysis of Tornado Weather Process of No.1822 Typhoon“Mangkhut”

利用地面气象观测、多普勒天气雷达、风廓线雷达及现场灾调等资料,对2018年9月17日上午发生在佛山的“山竹”台风(1822)外围强龙卷天气过程进行分析。结果表明:龙卷发生在台风登陆后前进方向右前侧的东北象限,强度为EF2级。低层急流汇合与高层辐散相互配合提供了有利的环流背景,环境场表现为中等偏弱的对流有效位能、弱的对流抑制能量、低的抬升凝结高度、大的风暴相对螺旋度和0—1 km强垂直风切变等特征。地面气象要素受龙卷影响表现出明显的信号,龙卷过境前后单站气压降低/升高明显,风向出现明显气旋式旋转。产生龙卷的风暴为低质心微超级单体,龙卷出现在雷达钩状回波的弱回波区附近,雷达低仰角速度图上出现强中气旋和龙卷涡旋特征,中气旋尺度小、伸展高度低,且在龙卷发生前其最强切变突然增强。当环境条件有利时,在台风龙卷的高发区,当雷达低仰角速度图上出现中等强度以上中气旋,且底高在1 km以下时,可以考虑发布龙卷预警。

Based on the conventional observation data of surface automatic weather station,Doppler radar,wind profile data,network videos,disaster investigation and so on,the environmental background and radar echo characteristics of typhoon occurrence and development were discussed.The results showed that the tornado was generated in the northeast jet convergence area between the right forward quadrant of Typhoon“Mangkhut”(1822)and the subtropical high edge,and the intensity was EF2.The divergence of upper level and the convergence of lower level provided a favorable weather background of the tornado occurrence.The typhoon-tornado occurred in an environmental field with weak convective available potential energy(CAPE)and convective inhibitory energy,low elevation condensation height(LCL),strong low-level vertical wind shear and large storm relative helicity(SRH).The pressure dropped sharply when the tornado came and rose rapidly as the tornado was far away,and the cyclonic convergent wind circled under the impact of the tornado.The tornado was generated by mini supercell storm with low center of mass.The tornado appeared at the edge of the strongest echo gradient region near the weak echo area.Strong mesocyclone was detected in the lower layer of the velocity chart and the duration of mesocyclone was about 1 hour.The mesocyclone center was accompanied by TVS.The mesocyclone became smaller and the vertical extension height decreased.In the high risk area of the typhoon tornado,when environmental conditions were favorable and moderate mesocyclone was detected as well as the mesocyclone base below 1 km,the early warning of tornado may be considered.