Advancing Understanding of the Tornado Vortex through Numerical Simulations of Increasing Complexity and Evaluation of Observing Systems

对龙卷风核心的风的结构和变化的详细了解仍然不完整。虽然观测技术的最新进展（特别是多普勒雷达）已经揭示了主要切向环流的内部核心结构，但关于次要环流（径向和垂直）仍然存在很大的不确定性，而且关于地表附近（低于50米）的流动的信息仍然缺乏，而龙卷风的大部分流入都位于地表以下。以前对龙卷风产生的超级单体的模拟描绘了地表附近龙卷风可信的、详细的结构，但它们固有的复杂性阻碍了对龙卷风最基本动力学的理解。更简单的龙卷风室型模拟有助于理解，但几乎所有先前的模拟都使用了规定的流入和流出边界条件，这些条件排除了龙卷风与产生龙卷风的更大环境之间的相互作用。该项目的研究将弥合理论（主要来自高度理想化、低雷诺数、轴对称模拟）、上述更为复杂的风暴尺度模拟和观测（总是具有有限的空间和时间覆盖）之间的差距。广泛使用的数值模型（cm2）将用于模拟越来越复杂的类似龙卷风的涡旋，从具有无滑移下边界条件和恒定涡流粘度的轴对称模拟到具有真实表面粗糙度的三维大涡流模拟（LES）。此外，选择高分辨率直接数值模拟（DNS）将用于评估亚网格湍流参数化的准确性，特别是在地表附近。这些模拟的结果也将用于评估当前（也许是未来）的仪器和分析程序能够从有限的观测数据重建三维风场的程度。这项工作的广泛影响将包括改进对龙卷风近地面风场的评估，作为旋涡大小、强度和不同地面条件下的函数，这反过来将有助于指导收集分析过去和未来现场活动的数据。将评估从最近的野外活动（如VORTEX2）获得的数据能够准确诊断龙卷风风场的程度，从而更好地分析过去活动的数据，并为未来的活动提供更好的设计。该项目将支持一名博士后的教育指导和职业发展。

Detailed understanding of the structure and variability of winds in the core of tornadoes remains incomplete. While recent advances in observational technology (particularly Doppler radars) have revealed the inner-core structure of the primary tangential circulation, large uncertainties remain regarding the secondary (radial and vertical) circulations, and there remains a paucity of information concerning flow near the surface (below 50 meters) where most of the inflow to tornadoes resides. Previous simulations of tornado-producing supercells portray believable, detailed structures of the tornado near the surface, but their inherent complexity has inhibited understanding of the most basic dynamics of tornadoes. Simpler tornado-chamber-type simulations facilitate understanding, but almost all previous simulations have used prescribed inflow and outflow boundary conditions that preclude interactions between the tornado and the larger environment that creates it. The research in this project will bridge the gaps between theory (primarily from highly idealized, low-Reynolds-number, axisymmetric simulations), aforementioned storm-scale simulations that are far more complex, and observations (which always have limited spatial and temporal coverage). A widely-used numerical model (CM1) will be used to perform simulations of tornado-like vortices of increasing complexity, ranging from axisymmetric simulations with no-slip lower boundary conditions and constant eddy viscosity to three-dimensional large eddy simulation (LES) with realistic surface roughness. In addition, select high resolution direct numerical simulations (DNS) will be used to assess the accuracy of subgrid turbulence parameterizations, especially near the surface. Output from these simulations will also be used to assess the extent to which current (and perhaps future) instruments and analysis procedures are capable of reconstructing three-dimensional wind fields from limited observational data.Broader impacts of this effort will include improved assessment of the near-surface wind fields of tornadoes as a function of vortex size, intensity, and over different surface conditions, which will in-turn help to guide the collection analysis of data from past and future field campaigns. The extent to which data obtained from recent field campaigns (such as VORTEX2) can accurately diagnose tornado wind fields will be evaluated, leading to better analyses of data from past campaigns and better designs for future campaigns. The project will support education mentoring and career development of a post-doctoral fellow.