Further Analysis of Near-surface Tornado Intensification

智力价值：严重的风暴有时会产生猛烈的龙卷风，导致重大的财产损失和死亡。了解什么条件导致龙卷风并控制其在地表附近的演变、结构和破坏性潜力是关键的研究目标，因为涉及的现象范围很广，而且在实地研究它们的困难，这一目标变得更加复杂。这项研究的重点是其中的一个关键因素：涡旋与表面的相互作用。首席调查人员和其他人以前的工作已经证明，这种相互作用可导致近地表风速是准稳定条件下高空最大风速的两倍以上，或导致一类产生动态“拐角流坍塌”的瞬变演变的一个数量级以上；对近地表流入的性质高度敏感；并可受到小型碎片(例如泥土、沙子)吸收的极大影响。利用现有的用于受控数值试验的大涡模拟(LES)龙卷风模式和更简单的分析模式，首席调查者将以重要的方式扩展现有的结果，以更好地理解真实大气涡旋的动力学。这将包括：将近地表强化分析推广到非对称涡旋，例如转换中气旋、龙卷风和次生“吸力涡旋”；对非对称角流坍塌进行更系统的研究；继续调查龙卷风如何对更现实的条件下的碎片负荷作出反应，利用多种碎片种类，跟踪其拾取和沉积，以产生模拟的损害轨迹，绘制空气和碎片速度之间的差异图；并尽可能将结果与现有的实地观测结果相比较。更广泛的影响：这项研究将提供重要的成分，以帮助改进龙卷风发生、行为和破坏潜力的预测，从而提高公共安全。有关风结构和碎片运输的详细信息将有助于工程师尝试设计能够承受可信龙卷风条件的结构。更好地了解龙卷风与地表的相互作用，有朝一日可能会导致制定战略，减少某些环境中发生强烈龙卷风破坏的可能性。这项工作有望改善湍流颗粒流动的大涡模拟，在燃烧、化学处理或污染物扩散等其他领域具有广泛的应用前景。这项工作将对一名博士生进行深度培训。鉴于公众对龙卷风的痴迷，它还将通过对大众媒体的贡献，促进更广泛公众的科学教育和兴趣。

Intellectual Merit: Severe storms sometimes produce violent tornadoes leading to significant property damage and fatalities. Understanding what conditions lead to tornadoes and govern their evolution, structure and destructive potential near the surface are critical research goals, complicated by the range of phenomena involved and the difficulties of studying them in the field. This research focuses on one critical ingredient that is involved: the interaction of a vortex with the surface. Previous work by the Principal Investigators and others have demonstrated that this interaction can: lead to near-surface wind speeds more than double the maximums aloft for quasi-steady conditions or more than an order of magnitude greater for a class of transient evolutions producing a dynamic "corner flow collapse"; is highly sensitive to the properties of the near-surface inflow; and can be dramatically affected by the uptake of small-scale debris (e.g., dirt, sand). Using an existing large-eddy simulation (LES) tornado model for controlled numerical experiments together with simpler analytical models, the Principal Investigator will extend the existing results in important ways for better understanding the dynamics of real atmospheric vortices. This will include: generalizing the near-surface-intensification analysis to asymmetric vortices such as translating mesocyclones, tornadoes and secondary "suction vortices"; more systematic study of asymmetric corner flow collapse; continuing to investigate how tornadoes respond to debris loading for more realistic conditions by using multiple debris species, tracking their pickup and deposition to produce simulated damage tracks and mapping differences between air and debris velocities; and, to the degree possible, comparing the results with available field observations. Broader Impacts: The research will provide important ingredients to aid in improving predictions of tornado occurrence, behavior and destructive potential leading to increased public safety. Detailed information on wind structure and debris transport will aid engineers' attempts to design structures to withstand credible tornado conditions. Better understanding of the interaction of tornadoes with the surface may someday lead to strategies for reducing the likelihood of strong tornado damage in some environments. The improvements in LES of turbulent particle laden flows expected from this effort could have a wide range of application in other fields such as combustion, chemical processing or pollutant dispersal. The work will train one PhD student in depth. Given the public fascination with tornadoes it will also, through contributions to popular media, promote science education and interest among the broader public.