广东一次超级单体强龙卷的形成环境和观测特征分析

ANALYSIS OF FORMATION ENVIRONMENT AND CHARACTERISTICS OF A SUPERCELL STRONG TORNADO IN GUANGDONG PROVINCE

2016年5月9日,广东省佛山市三水区遭受龙卷风袭击,通过现场灾情调查等资料确定龙卷造成的最强地面灾害强度为EF3级。利用S波段双偏振雷达、探空和高密度自动气象站等多种资料分析此次强龙卷发生的环境条件和中尺度特征,结果表明:产生强龙卷的中尺度对流系统发生在高空槽前、低层切变线南侧、低空和超低空偏南急流交汇处及地面静止锋南侧的中尺度辐合线附近;龙卷发生前环境大气具备了强的对流不稳定能量、低的抬升凝结高度、强的深层和低空垂直风切变及大的风暴相对螺旋度等有利于超级单体风暴发生发展的所有环境条件,而极大的能量螺旋度对超级单体强龙卷的发生有较好的指示意义;龙卷涡旋影响时,附近地面测站风速突增、风向气旋性转变、气压陡降/陡升、气温急降、无降水,龙卷涡旋远离后出现明显降水;产生龙卷的母体风暴源于三个多单体风暴先后合并加强形成的高质心超级单体强雹暴,≥65dBZ强反射率达到7.5km以上,偏振雷达探测到明显低层钩状回波、强中气旋、TVS和中高层悬垂回波中的冰雹增长,冰雹区对应CC低值区和ZDR小值区,龙卷涡旋位置出现速度谱宽大值区;龙卷位于超级单体风暴钩状回波内侧的弱回波区、中气旋中心和TVS附近,伴随中气旋尺度紧缩、底高下降等特征。

A tornado struck Sanshui District,Foshan City,Guangdong Province on 9 May 2016.According to the on-site disaster investigation and other data,the strongest ground disaster intensity caused by the tornado was rated EF3.The environmental conditions and mesoscale characteristics of the strong tornado are analyzed by using the data of S-band dual-polarization doppler radar,sounding and high-density automatic weather stations.The results show that the mesoscale convective system producing strong tornado occurred in front of the high-level trough,in the south of the low-level shear line,near the intersection of the low-level and ultra-low level southerly jets,and near the mesoscale convergence line in the south side of the surface stationary front.Before the tornado formed,the ambient atmosphere had all the environmental conditions that were conducive to the occurrence and development of supercell storm,such as strong convective instability energy,low lifting condensation level,strong deep-and low-level vertical wind shear,and high storm relative helicity.The extreme energy helicity is a good indicator of the occurrence of the supercell strong tornado.Under the influence of tornado vortex,the wind speed recorded by nearby ground stations increased sharply,the wind direction changed cyclonically,the pressure dropped/rose steeply,the temperature dropped significantly,and there was no precipitation.After the tornado vortex left and became far away,significant precipitation occurred.The parent storm of the tornado was three multicell storms merging and strengthening to form a high-centroid supercell strong hailstorm.The strong reflectivity of≥65 dBZ extended above 7.5 km.The polarization radar detected obvious low-level hook echo,strong mesocyclone,TVS and growth of hail in the hanging echo of middle and upper layers.The hail area corresponded to the low value area of CC and the small value area of ZDR,and there was a velocity spectrum width high value area in the tornado vortex.Accompanied by mesocyclone scale contraction and bottom height decline,the tornado was in the weak echo area inside the hook echo of the supercell storm and was near the center of mesocyclone and TVS.