Effects of Topography on Turbulent Fluxes in Stable Boundary Layers Using a New Generation Large-Eddy Simulation

大气模拟模式（例如，数值天气预报和气候模式）对区域尺度动量和热量通量的预测存在重大误差，这与我们考虑亚网格尺度地形和大气稳定性综合影响的有限能力有关。特别是，由于地形诱导的形式阻力和重力波而引起的湍流通量的增强不能通过常用的基于相似性的参数化来适当地捕获，这些参数化严格地只适用于均匀平坦表面上的边界层流动。为了产生物理上真实的结果，这些模型需要稳定性修正，这是“在模型性能上的启发”，几乎没有科学基础。在这个项目中，将进行风洞实验、现场测量和大涡模拟（LES）的新颖组合，以获得有关自然地形与稳定分层大气边界层湍流之间复杂相互作用的物理见解。首先，将创建一个框架来评估新一代LES在复杂地形上的性能（包括最近在无调谐动态亚网格尺度模型方面的进展）。然后，新一代LES将用于模拟不同地形上的稳定边界层，以获得研究控制陆地-大气相互作用的物理所需的高分辨率3-D瞬态信息。多尺度小波分析将用于量化地形、大气稳定性和湍流通量之间相互作用的主要尺度。这将旨在发展基于物理的相似性理论修正，包括与地形和热分层相关的时间和空间尺度。这些结果有可能大大改善区域尺度通量的参数化，从而提高天气和气候模式的准确性。这项研究的智力价值在于它使用了独特而全面的风洞实验、现场测量、最先进的大涡模拟技术和统计工具，以更好地了解地形对稳定边界层湍流通量的影响。这项研究有可能为我们对陆地-大气相互作用的理解和参数化能力提供新的线索。更广泛的影响包括大气边界层通量参数化方面的实质性改进，从而提高了大气模拟模式的精度。一种新的基于网络的教育工具将被开发，以利用大涡模拟场的可视化/动画的教育潜力。新工具将用于由首席研究员教授的本科和研究生课程以及针对高中生的外展活动。此外，两名研究生将作为研究助理接受指导，并将参与该教育工具的开发和实施。

Prediction of regional-scale fluxes of momentum and heat in atmospheric simulation models (e.g., numerical weather prediction and climate models) is subject to substantial errors associated with our limited ability to account for the combined effects of subgrid-scale topography and atmospheric stability. In particular, enhancement of turbulent fluxes due to topographically-induced form drag and gravity waves cannot be properly captured by commonly-used similarity-based parameterizations, which are strictly only valid for boundary layer flow over homogeneous flat surfaces. In order to produce physically realistic results these models require stability corrections, which are "inspired in model performance" and have little or no scientific foundation. In this project, a novel combination of wind tunnel experiments, field measurements and large-eddy simulations (LES) will be carried out to gain physical insight concerning the complex interactions between natural topography and stably stratified atmospheric boundary layer turbulence. First, a framework will be created to evaluate the performance of the new generation LES (including recent advances in tuning-free dynamic subgrid-scale models) over complex terrain. The new-generation LES will then be used to simulate stable boundary layers over different topographies to obtain high-resolution 3-D transient information needed to study the physics governing land-atmosphere interaction. Multiscale wavelet analysis will be used to quantify the dominant scales of interaction between topography, atmospheric stability and turbulent fluxes. This will be aimed at developing physically-based modifications to similarity theory that include relevant temporal and spatial scales associated with both topography and thermal stratification. These results have the potential to substantially improve the parameterization of regional-scale fluxes and, therefore, the accuracy of weather and climate models. The intellectual merit of the research lies in its use of a unique and comprehensive combination of wind tunnel experiments, field measurements, state-of-the-art large-eddy simulation techniques, and statistical tools needed to better understand the effects of topography on turbulent fluxes in stable boundary layers. The research has the potential to shed new light on our understanding of, and ability to parameterize, land-atmosphere interactions.The broader impacts include substantial improvement in the parameterization of atmospheric boundary layer fluxes and, as a result, improved accuracy of atmospheric simulation models. A new web-based educational tool will be developed to take advantage of the educational potential of visualizations/animations of large-eddy simulation fields. The new tool will be used in undergraduate and graduate courses taught by the principal investigator as well as outreach activities for high school students. Furthermore, two graduate students will be mentored as research assistants and will also participate in the development and implementation of the educational tool.