龙卷发生环境与机理及灾情调查研究进展

Research advances on tornado environments,formation mechanisms and damage surveys

  • 摘要: 龙卷致灾性强、社会关注度高。文中回顾了龙卷机理研究、强度等级和灾害现场调查技术进展,给出了龙卷涡旋形成机制、现场调查需要注意的方面和强度估计存在的难点等,对未来进行了展望。通常认为中气旋龙卷的有利环境条件已非常明确,但不同环流背景下并不尽然,如冷涡背景下的大气低层湿度条件必要性、台风龙卷的对流有效位能作用等,以及龙卷爆发事件同一般龙卷事件的环境条件是否存在差异还有待深入研究。中气旋龙卷形成的关键是低层中气旋的形成、近地表涡旋小块的产生、组织和增强以及地表摩擦作用使得涡旋发展为具有涡旋边界层和拐角流区域的龙卷。地势分布对龙卷影响非常复杂;通常龙卷上坡会减弱、下坡会加强。不同龙卷的消亡机制可能不同。F等级、EF等级和T等级为常用的龙卷强度等级,目前得到广泛应用的是EF等级,中国国家标准的龙卷风强度等级与EF等级有明确对应关系。中国的风灾现场调查技术方法已发展较为成熟,获得了大量龙卷灾害调查数据;但综合应用多源精细遥感资料的龙卷灾害评估技术还有待进一步发展。龙卷的致灾机制非常复杂,强度估计有很大的不确定性。龙卷观测、现场调查、机理研究和预报、预警能力的精细度需要持续提升。

     

    Abstract: Tornado-induced disasters are intense and have been attracting great social attention. This article provides an overview of recent research on tornado mechanisms, tornado intensity classifications, and advances in damage surveys in China. It highlights the formation mechanisms of tornadic vortex, difficult aspects of field surveys and challenges in estimating tornado intensity and presents a prospect on future research. The favorable environmental conditions for mesocyclone tornadoes are quite clear, yet the necessity of low-level atmospheric humidity condition under cold vortex setting, the role of convective available potential energy in tropical cyclone tornado formation, and the favorable environmental conditions for tornado outbreak still require further studies. The formation of mesocyclone tornadoes is pivotal, involving the development of low-level mesocyclones, the generation and organization of near-surface vortex patches and their enhancement, and the influence of surface friction that leads to the development of tornadoes with vortex boundary layers and corner flow regions. The topographic influence on tornadoes is very complex. In general, tornadoes weaken when moving uphill and intensify when descending downhill. The dissipation mechanism of different tornadoes may be different, and any factors that are not favorable for the maintenance of tornadoes may cause their dissipation. Common tornado intensity scales include F-scale, EF-scale, and T-scale. The T-scale has the most detailed categorization with 11 levels, while the EF-scale is the most widely adopted. China’s national standard of tornado intensity classification is directly aligned with the EF-scale. The methods and steps for damage surveys of severe wind disasters have been developed significantly, and a substantial amount of tornado survey data has been collected in China. The disaster-causing mechanisms of tornadoes are complex, and great uncertainty remains in their intensity rating. On going advancements are needed in fine-scale observations and damage surveys, mechanism studies, and forecasting and warning capabilities for tornadoes.

     

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