Near-surface Tornado Intensification

龙卷风研究的最终目标之一是作为产生龙卷风的环境的函数来预测龙卷风的发生和强度，这一目标由于涉及的物理规模和现象的范围以及它们之间相互作用的复杂性而变得极其困难。这一研究项目的目的是更好地了解这一问题的一个关键因素：近地表强化现象。首席调查员和其他人之前的工作表明，涡旋与地面的湍流相互作用可以产生远高于地面两倍以上的最大风速，并在短时间内增强一个数量级。近地表流入的变化可能会造成极端的近地表强化或根本不强化。PI已确定角流旋流比和低旋流通量的无量纲时间变化率是控制这一行为的两个关键参数。预计近地面强化在中气旋尺度和龙卷风尺度上都是重要的，但仍有许多工作要做，以澄清其在龙卷风发生和确定龙卷风强度方面的作用，并确定如何在风暴尺度模拟的次网格/地面参数化中近似这一现象。这项研究将使用和扩展PI现有的高分辨率、三维、非定常的龙卷风涡旋数值模式。受控、有限区域的数值试验将集中于确定瞬变涡旋演变过程中近地表强化所涉及的动力学关系。该方法是对观测案例研究和风暴模型模拟的补充，在解释两者的结果方面应该是有用的。将对代码进行修改，以包括由岩心释放的潜热和碎片负载产生的浮力，以便对其对近地表水流的影响进行初步估计。将漏斗和碎片云添加到模拟中也将促进与龙卷风的现场观测进行更直接的比较，例如视频和精细尺度的多普勒雷达测量。如果能够改进对哪些雷达探测到的中气旋将产生龙卷风以及可能造成什么破坏的预测，社会将受益于增加的公共安全。这项研究将包括通过出版物、会议、研究生教育和个人互动向研究社区提供结果，旨在为此类改进提供必要的成分。此外，关于龙卷风结构和碎片运输的详细信息应该有助于工程师尝试设计能够承受龙卷风条件的结构。

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.