珠江三角洲台风龙卷的活动特征及环境条件分析

Analysis of Typhoon-Tornado Activity Characteristics and Environmental Condition in the Pearl River Delta

利用常规观测、自动气象站、多普勒雷达等资料分析珠江三角洲台风龙卷的活动特征及其产生的环境条件。结果表明:台风龙卷发生在6-10月,时间多为10-20时,出现在台风登陆后1.3~21.3 h的时段内;多数龙卷位于台风中心的东北象限,台风中心在广东湛江一广西东南部或北部湾附近时是珠江三角洲龙卷发生的高风险期。高层辐散、低层辐合及中低空强东南急流在珠江口附近叠加是龙卷产生的有利环流背景。强或弱龙卷环境条件的共同特征为低抬升凝结高度、强深层和低层垂直风切变及较大风暴相对螺旋度(SRH),主要差异是强龙卷的深层和低层垂直风切变与SRH更大;相似台风路径下,有/无龙卷环境条件的明显差异在于0~1 km低层垂直风切变和SRH,两值越大出现超级单体或中气旋的可能性越大,龙卷发生概率也就越高。台风龙卷风暴母体属于低质心的微型超级单体风暴;低层有强或中等强度中气旋,有时强中气旋中心伴有龙卷涡旋特征(TVS);龙卷出现在钩状回波顶端或TVS附近。与西风带超级单体龙卷相比,台风龙卷中气旋的尺度更小、垂直伸展高度更低。

Based on the data of conventional observation, automatic weather station and Doppler weather radar, this paper analyzes the activity characteristics and environmental condition of the typhoon-tornadoes in the Pearl River Delta. T h e results show that tornadoes occur from June to October and the time is concentrated in the period from 10 : 00 BT to 20 : 00 BT. Tornadoes occur between 1. 3 h and 21. 3 h after ty phoon landfall. A strong preference for tornado occurrence is in the no rth east quadrant with respect to land-falling typhoon center. High risk periods of tornado genesis in the Pearl River Delta correspond to the typhoon center locating between Zhanjiang of Guangdong and southeast Guangxi or Beibu Gulf. Thesyn - optic situation of upper-level divergence, low-level convergence, and superimposition of strong southeasterly jets at mid- and low-layer over the Pearl River Delta are conducive to the w eath er background of tornadoes. The common environm ental conditions for strong or weak tornado genesis appear to be low LCL , strong deep-layer and low-level vertical wind shear ( VWS) and high sto rm relative helicity (SRH). The major difference betw een weak and strong tornado cases is that the latter has stro n g er deep-layer and low-level VWS and greater SRH . The significant diversities are VWS at 0 - 1 km and SRH betw een tornadic and nontornadic environm ental conditions under the similar typhoon tracks. With the higher values of VW Sand SRH , the possibility of supercells and mesocyclones increases, thus tornadoes are most likely to be detected. Tornado storms are mini supercell storms with low centriod. Strong or moderate mesocyclones are likely to be detected through the radial velocity data of the CINRAD/SA radar at low level, and significant tornadic vortex signature ( TVS ) may be found in the center of mesocyclones. The tornadoes lie in the interior of the hook echo or near TVS . Compared w ith the supercell tornadoes in the westerlies, mesocyclones of typhoon tornadoes are sm aller in scale and lower in stretching height.