Further Analysis of Near-surface Tornado Intensification

智力优点：强烈的风暴有时会产生猛烈的龙卷风，导致重大财产损失和人员伤亡。 了解什么条件导致龙卷风并控制其演变，结构和表面附近的破坏潜力是关键的研究目标，所涉及的现象范围和在该领域研究它们的困难使其复杂化。 这项研究的重点是一个关键的成分，涉及：与表面的涡流的相互作用。 主要研究人员和其他人以前的工作已经证明，这种相互作用可以：导致近地面风速超过准稳定条件下高空最大值的两倍，或者对于一类瞬态演变产生动态“拐角流崩溃”的情况下超过一个数量级;对近地面流入的特性高度敏感;并且可能受到小尺度碎片的吸收的显著影响（例如，泥土、沙子）。使用现有的大涡模拟（LES）龙卷风模型进行受控数值实验，以及更简单的分析模型，首席研究员将在重要方面扩展现有的结果，以更好地了解真实的大气涡旋的动态。 这将包括：将近地表强化分析推广到不对称涡流，如平移中气旋、龙卷风和次级“吸力涡流”;更系统地研究不对称角流崩溃;通过使用多种碎片种类，跟踪碎片的拾取和沉积，制作模拟损坏轨迹，绘制空气和碎片速度之间的差异，继续研究龙卷风如何在更现实的条件下对碎片负载作出反应;并尽可能将结果与现有的实地观察结果进行比较。更广泛的影响：这项研究将提供重要的成分，以帮助改善对龙卷风发生、行为和破坏潜力的预测，从而提高公共安全。 关于风结构和碎片运输的详细信息将有助于工程师设计能够承受可靠龙卷风条件的结构。 更好地了解龙卷风与地表的相互作用，可能有一天会导致在某些环境中减少强龙卷风破坏的可能性的策略。 本文所做的工作对含颗粒湍流的大涡模拟有很大的改进，在燃烧、化学处理和污染物扩散等领域也有广泛的应用。 该工作将对一名博士生进行深度培训。 鉴于公众对龙卷风的迷恋，它还将通过对大众媒体的贡献，促进科学教育和更广泛公众的兴趣。

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.