ANALYSIS OF A RARE SERIES OF TORNADOES IN THE NORTH CURRENTIN FRONT OF A TYPHOON
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摘要: 2008年8月6日下午，第9号台风“北冕”外围螺旋雨带中产生系列龙卷，先后袭击了广东省湛江市遂溪县界炮镇、北坡镇和港门镇。通过灾情及新一代雷达观测等资料的综合分析，确定这次龙卷强度为EF1级。利用观测资料对龙卷发生的环境场特征和雷达回波特征进行了分析，结果表明：产生龙卷的对流单体出现在台风移动路径前侧和台风中心西侧的强偏北急流中，龙卷发生在急流轴左前侧，其低层强的水汽辐合和对流不稳定、低层强辐合和高层强辐散、深厚的正涡度柱及整层强上升运动为龙卷的发生提供了有利的热力和动力条件；低的抬升凝结高度、强的低空0~1 km垂直风切变和较大的风暴相对螺旋度有利于超级单体风暴的发生发展。雷达观测表明，界炮镇龙卷和北坡镇龙卷为同一个低质心对流风暴产生，风暴具有热带对流回波特征；港门镇龙卷为另一个高质心微型超级单体风暴产生，风暴具有大陆性超级单体特征。龙卷均出现在微型超级单体风暴低层后侧入流缺口处、中等强度中气旋中心和TVS附近，TVS与龙卷几乎同时出现，对龙卷预警没有提前量，但中等强度中气旋较龙卷触地有约3个体扫的提前量，可以作为龙卷预警指标。Abstract: On the afternoon of August 6, 2008, a series of tornadoes were generated in the rain belt of No. 9 Typhoon Kammuri, which hit the Jiepao Town, Beipo Town and Gangmen Town in Suixi County of Zhanjiang Municipality, Guangdong Province. According to the comprehensive analysis of the disaster situation and observation data from new-generation radars, the intensity of the tornadoes was defined as EF1 level. The ambient conditions and radar characteristics of these tornadoes were analyzed using observation data. Results showed that: The micro-supercell that produced the tornadoes appeared in front of the typhoon path, which means it was in the northeast jet stream on the west of the typhoon center. Tornadoes occurred in the left front side of the north-northeast jet axis. Their strong low-level moisture convergence and strong convective instability, low-level convergence and high-level divergence, profound positive vorticity column and strong upward movement of the whole layer provided favorable thermodynamic and dynamic conditions for them. Low lifting condensation level, strong vertical wind shear at the low altitude of 0~1 km and large storm relative helicity were favorable to the occurrence and development of supercell storms. Radar observations showed that the tornadoes in Jiepao Town and Beipo Town were produced by the same low centroid convective storm, the radar characteristics of which were like those of tropical storms. The tornado at Gangmen was generated from a micro-supercell storm with higher centroid, the characteristics of which were similar to those of continental supper-cells. All the tornadoes appeared in the low-level inflows gap behind the micro-supercell storm, the center of the medium intensity mesocyclone and near the quasi-TVS. The quasi-TVS and tornadoes appeared almost at the same time, so there was no advance warning time for the tornadoes. However, the medium intensity cyclones occurred before the tornadoes reached the ground, which could be used as an indicator for tornado warning.
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图 3 2008年8月6日环流形势
a. 08:00高空形势综合图；b. 17:00地面形势；c. 14:00 500 hPa环流形势+850 hPa涡度(填色)；d. 20:00 500 hPa环流形势+850 hPa涡度(填色)。
图 5 2008年8月6日14—20时850 hPa水汽通量(填色，单位：g/(cm·hPa·s))和水汽通量散度(等值线，单位：10-5g/(cm2·hPa·s))(a，b)及850 hPa、700 hPa$\partial \theta_{\mathrm{se}} / \partial p$(单位：K/hPa)(c，d)
a、c. 14时；b、d. 20时。
图 7 2008年8月6日16:14—17:51湛江雷达0.5 °反射率因子(a)和径向速度图(b)及图b9的放大图(c)
黑三角形为龙卷触地位置，黑圈为中气旋，蓝圈为TVS，白圈为雷达识别的中气旋，白倒三角形为雷达识别的TVS。
表 1 2008年8月6日08时北海和阳江站探空站环境参数
环境参数 CAPE/(J/kg) CIN/(J/kg) LCL/m Wsr0~6 km/(m/s) Wsr0~1 km/(m/s) SRH/(m2/s2) 北海 1 679 59 523 12.2 10.5 83 阳江 138 64 500 15.9 12.0 235 
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