Investigation of Subgrid-Scale Turbulence in the Atmospheric Surface Layer Using Field Measurement Data

大涡模拟是分析小尺度大气环流的重要计算方法。根据计算网格的密度，大涡模拟可以精确地描绘出尺度小至几米的涡旋和涡旋。在接近地面的高度，更小的涡流变得越来越重要。大涡模拟的一个基本问题是，紧邻地面的近地面层中的涡旋不能被分解，必须被参数化--也就是说，在计算近地面大气中的热量和动量通量时，必须近似次网格尺度(SGS)过程的影响。这项研究的目标是开发用于大气表层的SGS过程的改进模式。该方法是分析在加利福尼亚州圣华金山谷进行的SGS2000现场项目期间使用特殊设计的声波风速计阵列获取的数据。这些数据以高分辨率提供了关于近地面风的时间和空间结构的独特信息。本工作的目的是(1)利用可分辨速度分量和可分辨温度和速度的联合概率函数来研究SGS通量对可分辨过程的影响；(2)了解SGS通量与可分辨速度和温度的关系。总而言之，这些将确定SGS通量的特征，这些特征对于可解析的过程非常重要，并直接对大涡模拟做出贡献。湍流模拟的进展不仅对气象学，而且对其他地球物理和工程应用都具有重要意义。

Large-eddy simulation (LES) is an important computational method for analyzing small-scale atmospheric circulations. Depending on the density of the computational grid, LES can accurately depict eddies and vortices with scales as small as a few meters. Still smaller eddies become increasingly important at altitudes close to the ground. A fundamental problem with LES is that the eddies in the surface layer immediately next to the ground cannot be resolved and must be parameterized - that is, in calculations of the heat and momentum flux in the atmosphere near the ground, the effects of subgrid-scale (SGS) processes must be approximated. The goal of this research is to develop improved models of SGS processes for use in the atmospheric surface layer. The approach is to analyze data taken with a specially designed array of sonic anemometers during the SGS2000 field project conducted in the San Joaquin Valley, California. These data provide unique information on the time and space structure of the wind near the ground with high resolution. The objectives of the work are (1) to investigate the effects of SGS fluxes on resolvable processes by use of joint probability functions of the resolvable velocity components and the resolvable temperature and velocity; (2) to understand the relationship between SGS fluxes and the resolvable velocity and temperature. Together, these will identify characteristics of the SGS flux that are important for resolvable processes and contribute directly to LES modeling. Progress in turbulence modeling is important not only for meteorology but also for other geophysical and engineering applications.