李兆慧,王东海. 2017. 2015年10月4日佛山龙卷过程的观测分析[J]. 气象学报, ():-, doi:10.11676/qxxb2017.013
2015年10月4日佛山龙卷过程的观测分析
OBSERVATIONS OF OCTOBER 4TH 2015 FOSHAN TORNADO
投稿时间:2016-06-25  最后修改时间:2016-10-30
DOI:10.11676/qxxb2017.013
中文关键词:  强龙卷风  灾情调研  钩状回波  佛山
英文关键词:Severe tornado  damage survey  hook echo  Foshan
基金项目:
作者单位E-mail
李兆慧 佛山市气象局 li-zhao-hui@qq.com 
王东海 中国气象科学研究院 wangdh@camscma.cn 
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中文摘要:
      受1522号台风“彩虹”外围螺旋云带影响,2015年10月4日15时28分-16时(北京时)广东佛山出现了EF3级强龙卷并造成严重灾害。为了综合分析龙卷发生的多尺度环境背景场和龙卷的结构及强度变化等特点,本文进行了灾情调研,航拍龙卷灾情路径,走访龙卷目击者,确认龙卷路径及灾情级别,再结合多渠道获取的龙卷视频照片等资料以及观测资料进行分析研究,结果表明:(1)产生此次龙卷的超级单体存在于台风“彩虹”外围螺旋云带内;龙卷向西北偏北方向移动,触地时长为32分钟,受灾路径长度为31.7 km,最大灾情直径为577 m,平均时速约为60 km,具有“移动速度快,影响范围广,风力破坏强”的特点,其移动速度快慢似与超级单体强度和地面的粗糙度有关。(2)佛山地区中高层受偏南气流控制,水汽充足,地面有弱冷空气;珠三角喇叭口地形有利于气流的辐合与局地涡旋的产生; 抬升凝结高度低,垂直风切变大,有利于龙卷的生成。(3)地面自动站气象要素表现出受龙卷环流影响的特征。3 s极大风速的大值带和3 s最小气压的低值带以及1小时累计降水大值中心呈现出与龙卷走向一致的东南-西北向的带状分布;龙卷到来时其周围自动站气温和气压明显降低,风速明显增大,风向明显转变;降水在龙卷靠近前5-10分钟就开始明显增大,其大值中心位于龙卷路径的西侧。龙卷离开后气压比龙卷来临前有所升高,但气温较前降低。(4)龙卷出现在钩状回波前进方向的右后侧;降水大值区与雷达组合反射率大值区的落区基本一致。地面风场的辐合中心与龙卷触地的位置基本一致,并且钩状回波的入流区与地面偏东风区相对应。龙卷风暴单体发展高度在4 km左右,具有低重心对流的特点。其前部存在回波悬垂,一条很窄的向西北倾斜的回波大值带可能与龙卷漏斗云墙有关。对应径向速度剖面图上为一条向西北倾斜的正负速度交界区,构成一个逆时针旋转的涡旋带,切向剖面图上存在较强的辐合。(5)龙卷发展过程中伴随着龙卷风暴顶和风暴底的逐渐下降以及单体质心的下降,中气旋与龙卷涡旋特征TVS的顶和底也随之逐渐下降。TVS的顶高和底高都略低于中气旋,并在龙卷触地时降至最低。龙卷涡旋的切变值远远大于中气旋的切变值,且在龙卷强度最强时最大。综上所述,本文通过直接观测资料研究佛山龙卷的基本特征得到了一些有意义的结果,为龙卷等强天气的进一步研究提供了方法上的指导,对龙卷的预报预警提供了一定的技术支持。
英文摘要:
      A tornado, rated as a category 3 storm on the enhanced Fujita scale (EF3), touched down between 15:28 and 16:00 on October 4th 2015 in Foshan as part of Typhoon “Mujigae” (2015). This tornado destroyed a large number of factories and houses and lasted 32 minutes. The tornado swath was 31.7 km, with the largest tornado swath diameter reaching 577 m. The damaged photos and tornado videos were collected in the damage survey. In addition, the surface automatic weather station data, regular observed data, and Doppler radar data are used in this paper to analyze this tornado case. The tornado life cycle was divided into three stages: Developing stage, Mature stage and dissipating stage.The tornado moved faster in the developing and mature stage and slowed down in the dissipating stage because of the intensity of the supercell and differencial surface roughness. The large scale circulation was favorable for tornado genesis with obvious wind shear and high moisture in the lower levels. The cold air extended to the south as the small trough stretched southward in the surface layer, and the unstable layer with high SWEAT index, high K index and low lifting condensation level (LCL) were necessary environmental conditions for tornado genesis. The bell shape terrain of Pearl River Delta region helped the convergence and local vortex around the surface to genesis. The variables recorded by the surface automatic weather stations showed strong signals when the tornado passed by. The distribution of 3 s gust and 3 s minimum pressure was northwest-southeast, which was consistent with the tornado swath. The pressure and temperature dropped sharply while the wind speed increased dramatically when the tornado developed, and also the winds cyclonic convergenced around the tornado. The rainfall raised 5 to 10 min before the tornado arrived and the main rainfall zones located to the left of the tornado path indicated that the tornado was situated in the right-rear flank of the supercell. The pressure was higher and temperature was lower after the tornado left than that before the tornado came. The Tornadic Vortex Signature (TVS), the hook echo and bounded weak echo region were detected when the tornado touched down. The heights of the TVS''s top, base and centroid decreased as the storm strengthened and descende to the lowest when the tornado touched down on the ground. The wind shear was much higher than that of the detected mesocyclone, which also increased as well when the tornado touched down.
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