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

2011年4月27日的龙卷风爆发引发了三场长距离龙卷风，穿越了森林茂密的地区和山区。 其中一场龙卷风的等级为EF-4，经过大烟山国家公园的西部，另外两场龙卷风的等级分别为EF-2和EF-3，穿越北方格鲁吉亚的查特胡奇国家森林。 鉴于此次龙卷风的爆发给国家造成了严重的经济和人员损失，因此必须进行及时和彻底的科学调查。本项目将复杂地形下观测到的森林破坏与模拟涡旋相结合，试图重建龙卷风通过期间的近地面风场。目标是：1）回顾性地描述三个强的，长轨迹龙卷风在茂密的森林景观的表面风场，和2）确定崎岖地形的方面，可能会影响低层风场的强大和相对罕见的龙卷风在山区。 这些目标将允许一个假设，即显着的地形变化影响的强度和行为的tornadoes.Intellectual优点：由于固有的困难，在获得直接或遥感观测龙卷风在山区，替代方法，回顾近地表风场的特点，必须寻求。 这一罕见而值得注意的事件提供了一个独特而宝贵的机会，以评估龙卷风沿着的整个路径龙卷风风场在一个茂密的森林和山区。 每一个龙卷风穿过国家森林的轨迹都创造了一个由成千上万棵树组成的研究机会，每一棵树都提供了它坠落时环境风速和方向的信息。 结合物理环境的信息，如坡度，地形位置，土壤类型和表面海拔，这些树木在各种各样的环境提供了一个完美的场景，以实现风场重建。迄今为止，没有研究将地形纳入低层龙卷风动力学的数值模式。 因此，观测研究的重要性，在复杂地形的近地面龙卷风风场的特点仍然是至关重要的。 损害调查依赖于航空摄影，并在研究区域的一部分进行地面调查确认，将揭示树木的特征，位置和方向数据，作为输入到一个理想化的漩涡和树木之间的相互作用的模拟。研究结果可能有助于保险业、应急管理人员和森林管理部门进行风险评估。这些分析可能会突出山区更容易受到龙卷风袭击的地区，从而为学校、风暴避难所或拖车公园制定未来的结构工程和地理位置指南。树木损害模型可以揭示树木的特点，最终可能导致改进的增强藤田规模的植被损害指标。 最后，PI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，重点是强烈的龙卷风可以而且确实发生在山区。 这项工作将提高公众对龙卷风威胁的普遍认识，因为公众可能没有意识到龙卷风的危险。此外，这项研究还将对研究生和本科生进行培训。 PI和学生将参加各种国家会议和研讨会。 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.