Collaborative Research: Measurements and Modeling of Subgrid-scale Turbulence in the Atmospheric Surface Layer

这项研究将在克莱姆森大学、宾夕法尼亚州立大学和国家大气研究中心合作进行。重点讨论了用大涡模拟(LES)预报大气边界层(ABL)统计量时遇到的问题。大涡模拟已成为反辐射导弹的有效研究工具，也可能是反辐射导弹最重要的仿真方法。在大涡模拟中，发生的尺度太小而不能被数值网格分辨的过程是基于可以被网格分辨的更大尺度的过程，使用次网格尺度(SGS)模式进行诊断。然而，在地面附近的大气近地面层，大涡模拟存在固有的低分辨率和较差的SGS模式性能。将进行一项综合研究计划，包括现场测量和数值模拟，以改善SGS模式的性能。本文利用野外观测资料，分析了SGS应力和通量的输送方程，以及SGS的速度和标量联合概率密度函数的输送方程，研究了SGS湍流对近地层可分辨尺度统计的影响。现场计划将使用在先前NSF支持的研究期间开发的阵列技术来测量可分辨和亚网格尺度的变量。它将首次包括对SGS应力和通量平流的测量，这对于研究SGS动力学和评估新的SGS模式是必不可少的。通过使用LES场作为模型输入来计算JPDF方程中的SGS变量，然后将其与观测值进行比较，从而获得模拟的SGS应力和通量，从而进一步分析观测结果。这项研究有望极大地促进对SGS应力和温度通量的动力学及其对可分辨尺度动力学的影响的理解。这项研究在几个领域产生了更广泛的影响。它将为两名研究生提供教育和研究机会。这项研究中开发的新的数据分析和处理方法将进一步了解阵列测量技术作为其他重要边界层应用的基本工具的潜力和局限性，例如面积平均通量测量。改进的大涡模拟对于改进应用于空气污染模拟、天气预报和陆地-大气相互作用模拟的预报工具将是重要的。这些改进的工具将极大地造福社会。

This research will be conducted collaboratively at Clemson University, the Pennsylvania State University, and the National Center for Atmospheric Research. It focuses on issues met in using large-eddy simulation (LES) to predict the statistics of the atmospheric boundary layer (ABL). LES has become an effective research tool for the ABL and probably the most important simulation method for it. In LES, processes occurring on scales too small to be resolved by the numerical grid are diagnosed based on larger scale processes that can be resolved by the grid, using a subgrid-scale (SGS) model. However, near the ground, in the atmospheric surface layer, LES suffers from inherent under-resolution and poor SGS model performance. An integrated research program will be conducted consisting of field measurements and numerical simulations to improve SGS model performance. This research investigates the impact of the SGS turbulence on the resolvable-scale statistics in the surface layer by using field measurements to analyze the transport equations of SGS stress and flux, and the transport equation of the joint probability density function (JPDF) of resolvable-scale velocity and scalars. The field program will employ the array technique developed during prior NSF-supported research to measure the resolvable- and subgrid-scale variables. It will, for the first time, include measurements of the advection of the SGS stress and flux, which is essential for studying the SGS dynamics and for evaluating the new SGS models. The observations will be further analyzed by obtaining modeled SGS stress and flux using LES fields as model inputs to compute the SGS variables in the JPDF equation, which then will be compared with observations. This research is expected to significantly advance the understanding of the dynamics of the SGS stress and temperature flux, and their impact on the resolvable-scale dynamics. The research has broader impacts in several areas. It will provide education and research opportunities for two graduate students. New data analyses and processing methods developed in this research will further the understanding of the potentials and limitations of the array measurement technique as an essential tool for other important boundary layer applications such as area-averaged flux measurements. Improved LES will be important for improving predictive tools for applications to air-pollution modeling, weather forecasting, and land-atmosphere interaction modeling. These improved tools will greatly benefit society.