2019年4月13日广东徐闻强龙卷天气分析

Analysis of the 13 April 2019 Strong Tornado in Xuwen County,Guangdong Province

利用常规高空地面观测、广东省区域加密自动站、湛江多普勒雷达以及FY-4A高分辨可见光云图等资料对2019年4月13日广东省湛江市徐闻县EF3级强龙卷过程进行分析。结果表明:强龙卷发生在低纬地区海岸带附近,路径长约16 km,历经"三次陆上、两次海上"的复杂过程,持续约36 min。产生龙卷超级单体的中尺度对流系统出现在地面暖低压槽前、中低层显著西南气流和偏南急流汇合处;环境条件表现为强的垂直风切变、低的抬升凝结高度、大的风暴相对螺旋度和能量螺旋度,地面存在触发对流的中尺度辐合线和小尺度涡旋。龙卷罕见地经过徐闻县和安镇政府自动站,该站受到龙卷涡旋不同部位影响,风向随时间呈顺转—逆转—顺转的变化特征,并测到15级强风;气压和气温陡降,平均气压、平均气温最大降幅分别为2.6 hPa·(5 min)^(-1)、1.7℃·(5 min)^(-1)。龙卷发生在一个主要伴随正地闪、高质心的超级单体风暴中,钩状回波和回波悬垂特征明显,并伴有低层强中气旋和龙卷涡旋特征;中气旋强度和顶高呈反位相变化,3次(2次)强度峰值(谷值)和3次(2次)顶高谷值(峰值)正好与龙卷3次(2次)陆上(入海)活动时间对应,龙卷在陆地上(海面上)时,中气旋较强(较弱)、顶高较低(较高)。龙卷出现在钩状回波顶端、β中尺度对流系统上风侧TBB梯度最大处、水汽羽之下和中气旋底高低于500 m期间。

An EF3 strong tornado in Xuwen County of Zhanjiang City,Guangdong Province on 13 April 2019 was analyzed by using observation data,automatic weather station data,Zhanjiang Doppler Radar data and FY-4A satellite high resolution visible cloud images.The results show that this strong tornado occurred near the coastal zone in the low latitude area,with a path length of about 16 km.It experienced a complex process of“three times on land and two times on sea”,lasting for about 36 minutes.The mesoscale convective system producing tornado supercell appeared in front of the warm and low pressure trough,where the southwest air flow and southerly jet flow converged significantly in the middle and lower layers.The environmental conditions were characterized by strong vertical wind shear,low lifting condensation height,large storm relative helicity and large energy helicity.There were mesoscale convergence lines and smallscale vortex triggering convection on the ground.The tornado passed through the automatic weather station of Hean Town Government of Xuwen County,which was affected by different parts of the tornado vortex.The wind direction of the tornado changed from clockwise to reverse to clockwise,and the wind force got to Grade 15.The average pressure and temperature dropped sharply by 2.6 hPa·(5 min)^(-1) min and 1.7℃·(5 min)^(-1),respectively.The tornado occurred in a supercell storm with positive cloud-to-ground lightning and high cell centroid.The hook echo and echo pendency were obviously accompanied by low-level strong mesocyclone and tornado vortex signature.The intensity and top height of the mesocyclone changed in inverse phases,and the three(two)peak value(valley value)of the intensity and three(two)valley value(peak value)of top height exactly corresponded to the time of the three(two)land(sea)activities of the tornado.When the tornado was on the land(sea),the mesocyclone was stronger(weaker)and the top height was lower(higher).The tornado occurred near the top of the hook echo and at the maximum TBB gradient on the windward side of meso-βscale convective system,under the water vapor plume and during the period when the height of the bottom of the mesocyclone was lower than 500 m.