1713号台风“天鸽”外围龙卷特征及成因分析

Analysis of the characteristics and causes of the peripheral tornado of NO.1713 Typhoon Hato

利用常规观测资料、多普勒天气雷达资料和区域加密自动站资料对1713号台风"天鸽"外围的龙卷过程进行分析,结果表明:(1)此次龙卷过程发生在台风外围螺旋云带前部,物理量分析表明广西东南部具有较大的不稳定度能量,抬升凝结高度较低,低层垂直风切变较大,具有利于龙卷发生的环境热力和动力条件。中尺度地面辐合线触发出新生对流单体,该对流单体在高温高湿和强不稳定状态环境中最终发展为龙卷。(2)此次龙卷为微超级单体风暴,具有低层有钩状回波、中高层回波悬垂和有界弱回波区(BWER)等典型超级单体特征,低层钩状回波的演变与龙卷的生消密切相关。(3)中气旋先于低层钩状回波出现,钩状回波形成于强中气旋附近。龙卷发生时中气旋底高在2㎞左右,TVS切变底部高度0.5㎞左右并且不断下降,与龙卷漏斗状云柱高度逐渐下降接地的趋势一致。

Using conventional observation data, Doppler weather radar, and regional encrypted automatic station data, the tornado process in NO.1713 typhoon Hato periphery was analyzed. The main conclusions of this paper were：（ 1） the tornado occurred in the front of the spiral cloud band in the typhoon periphery. Analysis of physical quantities showed that there was high instability energy in southeast Guangxi. The vertical wind shear in the middle-low level was large and the lifting condensation level was very low. These were the environmental conditions that conducive to the development of the tornado. The surface mesoscale convergence line triggered the generation of a new convection cell which eventually developed into a tornado with high temperature, high humidity, and strong instability.（ 2） This tornado was a micro-supercell storm with hook echo in the low level, echo overhung and bounded weak echo region（BWER） in the middle-upper level, which were typical supercell features. The evolution of the low-level hook echo was closely related to the occurrence and extinction of the tornado.（ 3） The mesocyclone appeared before the low-level hook echo and the hook echo appeared near the strong mesocyclone. When the tornado occurred, the bottom height of the mesocyclone was about 2 km, the bottom height of TVS shear was about 0. 5 km and continued to descend, which was consistent with the tornado funnel cloud that gradually descended to the ground.