Modeling and Analysis of the Landfalling Hurricane Boundary Layer

该奖项由2009年美国复苏和再投资法案(公法111-5)资助。之前对飓风Fran(1996)期间收集的高分辨率移动多普勒雷达观测进行的分析表明，有证据表明有高度组织的亚千米尺度环流被称为边界层“卷”，它体现了围绕水平轴的有组织的旋转，并在某些风暴下的强切变风中发展。随着更广泛地认识到中涡的存在(通过围绕垂直轴的局部强烈旋转来确定)，这些有组织的特征叠加在飓风内强烈的、广泛的气旋式低层气流上，被认为有可能显著影响总体风暴强度(通过热量、水分和动量的垂直输送)，更局部地影响造成极端财产损失和生命损失的地面强风的持续时间和峰值强度。这项新的研究工作将使我们能够对国家科学基金会支持的“车轮上的多普勒”(DOW)移动雷达设施现有的大量数据进行详细检查，以了解最近几次飓风登陆的情况。结合针对低层风场内有组织特征的计算机数值表示的大涡模拟，这些分析将能够量化登陆飓风下的湍流结构、强度和所产生的通量。在可能的情况下，还将考虑对地面风速(如幸存的风速计)的辅助观测以及对树木和工程结构的时间标记破坏，以更好地将这些新的雷达观测与地球表面的条件联系起来。这项研究的学术价值在于改进了对飓风强度变化所涉及的低层(“边界层”)大气过程的文献记录和动力学理解，其空间尺度比以前观测到的要小得多，并将这些量与风暴强度/结构和下垫面的特征(例如，陆地-海洋对比、植被类型、已建建筑物的密度等)联系起来。将产生更广泛的影响，办法是加深对登陆热带气旋内湍流低空气流的了解，这可用于预报模式的改进和更准确地调整建筑规范，以及通过支持从代表性不足的群体中挑选的早期职业科学家。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Prior analysis of high-resolution mobile Doppler radar observations collected during Hurricane Fran (1996) has revealed evidence of highly organized sub-kilometer scale circulations termed boundary-layer "rolls," which embody organized rotation about a horizontal axis and develop within strongly sheared winds beneath some storms. Along with the more widely recognized presence of mesovortices (identified by locally-intense spin about a vertical axis), these organized features superposed on the intense, broadly cyclonic low-level airflow within hurricanes are thought to have potential to significantly influence overall storm intensity (via vertical transports of heat, moisture and momentum) and, more locally, to influence the duration and peak intensity of strong surface winds responsible for extreme property damage and loss of life. This new research effort will allow detailed examination of an extensive archive of existing data from the NSF-supported "Doppler on Wheels" (DOW) mobile radar facility for a number of more recent hurricane landfalls. In conjunction with large-eddy simulations aimed at the computer-based numerical representation of organized features within low-level wind fields, these analyses will allow quantification of turbulence structure, intensity and resultant fluxes beneath landfalling hurricanes. Where available, ancillary observations of surface wind speeds (as from surviving anemometers) and time-tagged damage to trees and engineered structures will also be considered to better relate these novel radar observations to conditions at the earth's surface. The intellectual merit of this study rests on improved documentation and dynamical understanding of the low-level ("boundary layer") atmospheric processes involved in hurricane intensity changes at far finer spatial scales than have previously been observed, and in relating these quantities both to storm intensity/structure and characteristics of the underlying surface (e.g., land-sea contrasts, type of vegetation, concentration of built structures etc.). Broader impacts will be derived through increased understanding of turbulent low-level airflows within landfalling tropical cyclones that can be implied to forecast model improvement and more accurately tuned building codes, as well as through support for an early-career scientist drawn from an underrepresented group.