Near-surface Tornado Intensification

近地表龙卷风增强

• 批准号: 0236667
• 负责人: David Lewellen
• 金额: $ 32.82万
• 依托单位: West Virginia University Research Corporation
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-03-01 至 2006-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0236667&HistoricalAwards=false
• 关键词: Near; surface; Tornado; Intensification

One of the ultimate goals of tornado research is to predict tornado occurrence and strength as a function of the environments which give rise to them, a goal made extremely difficult by the range of physical scales and phenomena involved and the complexity of the interactions between them. The objective of this research project is an improved understanding of one critical ingredient of this problem: the phenomenon of near-surface intensification. Prior work by the Principal Investigators (PIs) and others has demonstrated that the turbulent interaction of a vortex with the surface can produce maximum wind speeds more than double those well above the surface and an order of magnitude greater intensification for short periods. Changes in the near-surface inflow can make the difference between extreme near-surface intensification or none at all. The PIs have identified a corner flow swirl ratio and a dimensionless time rate of change of low-swirl flux as two critical parameters governing this behavior. Near-surface intensification is expected to be important on both the mesocylone scale and the tornado scale, but much remains to be done to clarify its role in both tornadogenesis and determining tornado intensity, and to determine how to approximate this phenomenon in subgrid/surface parameterizations for storm scale simulations. This research will use and extend the PI's existing high-resolution, three?dimensional, unsteady, numerical model of tornado vortices. Controlled, limited-domain, numerical experiments will focus on identifying the dynamical relationships involved in near-surface intensification during transient vortex evolution. The approach complements observational case studies and storm model simulations and should prove useful in interpreting the results of both. The code will be modified to include buoyancy generated by latent heat released in the core and debris loading to allow initial estimates of their effects on the near-surface flow. Adding the funnel and debris clouds to the simulations will also foster more direct comparisons with field observations of tornadoes, such as videos and fine-scale Doppler radar measurements. Society will benefit through increased public safety, if improvements can be made in forecasting which radar detected mesocyclones will generate a tornado and what the damage potential might be. This research, which will include providing results to the research community through publications, meetings, graduate student education, and personal interaction, is designed to provide a necessary ingredient for such improvements. Also, detailed information on the tornado wind structure and debris transport should aid engineer's attempts to design structures to withstand tornado conditions.

龙卷风研究的最终目标之一是预测龙卷风的发生和强度，作为产生它们的环境的函数，由于所涉及的物理尺度和现象的范围以及它们之间相互作用的复杂性，这一目标非常困难。 该研究项目的目标是更好地了解这个问题的一个关键因素：近地表强化现象。 主要研究人员（PI）和其他人先前的工作已经证明，涡旋与表面的湍流相互作用可以产生最大风速，其最大风速是表面上方风速的两倍以上，并且在短时间内增强一个数量级。 近地表入流的变化可以决定极端近地表强化或根本没有强化。 PI已经确定了角流旋流比和低旋流通量的无量纲时间变化率作为控制这种行为的两个关键参数。 近地表强化预计是重要的中气旋尺度和龙卷风尺度，但仍有很多工作要做，以澄清其在龙卷风的作用，并确定龙卷风强度，并确定如何近似这种现象的亚网格/表面参数化风暴尺度模拟。 本研究将使用和扩展PI现有的高分辨率，三？三维，非定常，数值模型的龙卷风漩涡。 受控的有限域数值试验将集中于确定瞬态涡旋演化过程中近地面强化所涉及的动力学关系。 该方法补充了观测案例研究和风暴模型模拟，并应证明有助于解释两者的结果。将对该代码进行修改，以包括堆芯释放的潜热和碎片装载产生的浮力，从而能够初步估计其对近地表流动的影响。 在模拟中加入漏斗云和碎片云也将促进与龙卷风的实地观测（如视频和精细尺度多普勒雷达测量）进行更直接的比较。如果能够在预测哪些雷达探测到的中气旋将产生龙卷风以及可能造成的破坏方面有所改进，那么社会将通过增加公共安全而受益。 这项研究，这将包括通过出版物，会议，研究生教育和个人互动，研究社区提供的结果，旨在为这种改进提供必要的成分。 此外，关于龙卷风风结构和碎片运输的详细信息应有助于工程师设计结构以承受龙卷风条件。