Reconstruction of Near-Surface Tornado Wind Fields from Forest Damage Patterns in Complex Terrain

2011年4月27日最近爆发的龙卷风产生了三个长轨道龙卷风，穿过森林茂密的地区和山区。一个等级为EF-4的龙卷风经过大烟山国家公园的西部，另外两个等级为EF-2和EF-3的龙卷风穿过乔治亚州北部查塔胡奇国家森林的山脉。鉴于这次龙卷风的爆发给国家造成了严重的经济和人员损失，迅速和彻底的科学调查势在必行。本项目将观测到的复杂地形下的森林破坏与模拟涡相结合，重建龙卷风通过时的近地面风场。目标是1)回顾性地描述在茂密的森林景观中三种强、长路径龙卷风的地面风场特征，以及2)确定崎岖地形可能影响山区强且相对罕见的龙卷风的低层风场的各个方面。这些目标将允许对重大地形变化影响龙卷风强度和行为的假设进行检验。知识价值：由于在山区获得龙卷风的直接或遥感观测所固有的困难，必须寻求对近地面风场进行回顾性表征的替代方法。这一罕见而引人注目的事件提供了一个独特而宝贵的机会，可以评估在森林茂密的山区沿着龙卷风的整个路径的龙卷风风场。每一个经过国家森林的龙卷风轨迹都创造了一个由数万棵树组成的研究机会，每棵树都提供了它降落时周围风速和风向的信息。结合物理环境的信息，如坡度、地形位置、土壤类型和地表海拔，这些树木在各种各样的环境中为实现风场重建提供了一个完美的场景。到目前为止，还没有研究将地形纳入低层龙卷风动力学的数值模型。因此，在复杂地形中对近地面龙卷风风场进行观测研究的重要性仍然是至关重要的。依靠航空摄影的损害调查，以及部分研究区域的地面调查的确认，将揭示树木的特征、位置和方向数据，作为模拟理想涡旋和树木之间相互作用的输入。更广泛的影响：对社会的更广泛的好处是丰富的。研究结果可能有助于保险业、应急管理人员和森林当局进行风险评估。这些分析可能会突出山区中更容易受到龙卷风袭击的地区，从而形成未来的结构工程和学校、风暴避难所或拖车停车场的地理位置指导方针。树木损害模型可能揭示树木的特征，最终导致增强藤田尺度的植被损害指标的改善。最后，ppi希望通过在线和当地新闻发布来教育公众关于这项研究及其结果，重点是强龙卷风可能而且确实发生在山区。这一努力将提高公众对龙卷风威胁的普遍认识，这些地区的公众可能没有认识到这种危险。此外，该研究将培养研究生和本科生。pi和学生将参加各种全国性的会议和研讨会。该项目还将促进气象学、林业、生态学、环境工程、地理学和社会科学等领域的跨学科合作。

The recent 27 April 2011 tornado outbreak spawned three long-track tornadoes that passed across heavily forested landscapes and mountainous regions. One tornado rated EF-4 passed over the western portion of the Great Smoky Mountains National Park, and two other tornadoes, rated EF-2 and EF-3, crossed the mountains of northern Georgia in the Chattahoochee National Forest. Given that this tornado outbreak caused severe economic and human losses to the nation, a prompt and thorough scientific investigation is imperative.This project combines observed forest damage in complex terrain with simulated vortices in an effort to reconstruct the near-surface wind field during the passage of tornadoes. The objectives are to 1) retrospectively characterize surface wind fields for three strong, long-track tornadoes in heavily-forested landscapes, and 2) determine the aspects of rugged topography that may influence the low-level wind field of strong and relatively rare tornadoes in the mountains. These objectives will allow a test of the hypothesis that significant topographic variations influence the strength and behavior of tornadoes.Intellectual merit:Because of the difficulties inherent in obtaining direct or remotely-sensed observations of tornadoes in the mountains, alternative approaches that retrospectively characterize the near-surface wind fields must be sought. This rare and notable event provides a unique and valuable opportunity to assess a tornadic wind field along the entire path of the tornado in a heavily forested and mountainous area. Each tornado track through a national forest creates a research opportunity consisting of tens of thousands of trees, each of which provides information on the ambient wind speed and direction when it fell. Combined with information on the physical surroundings, such as slope, topographic position, soil types, and surface elevation, these trees in a tremendous variety of surroundings provide a perfect scenario with which to implement a wind field reconstruction.To date, no studies incorporate terrain into numerical models of low-level tornado dynamics. Thus, the importance of observational studies that characterize the near-surface tornadic wind field in complex topography remains paramount. Damage surveys relying on aerial photography, with confirmation by ground surveys in a portion of the study area, will reveal tree characteristics, location, and orientation data for use as input to a simulation of the interaction between an idealized vortex and trees.Broader impacts:The broader benefits to society are plentiful. Results of the research may aid risk assessments by the insurance industry, emergency managers, and forest authorities. The analyses may highlight areas that are more vulnerable to tornadoes in the mountains and will thus shape future structural engineering and geographical placement guidelines for schools, storm shelters, or trailer parks. The tree damage model may reveal characteristics of trees that could eventually lead to improvements in vegetation damage indicators for the Enhanced Fujita scale. Lastly, the PIs expect to educate the general public through online and local news releases regarding the study and its results, with emphasis on the fact that strong tornadoes can and do occur in the mountains. This effort will enhance general awareness of the threat of tornadoes in areas where the public may not recognize the dangers.In addition, the research will train both graduate and undergraduate students. The PIs and students will participate in various national conferences and workshops. The project will also promote interdisciplinary collaborations from areas such as meteorology, forestry, ecology, environmental engineering, geography, and social sciences.