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，LES可以精确地描绘小到几米的漩涡和漩涡。在接近地面的高度，更小的涡流变得越来越重要。LES的一个基本问题是，紧挨着地面的表层涡旋无法解决，必须参数化——也就是说，在计算近地面大气中的热量和动量通量时，必须近似计算亚网格尺度（SGS）过程的影响。本研究的目标是开发用于大气表层的改进的SGS过程模型。该方法是分析在加利福尼亚州圣华金河谷进行的SGS2000现场项目中使用特殊设计的声波风速计阵列所获得的数据。这些数据提供了独特的、高分辨率的近地风时空结构信息。本文的研究目标是：(1)利用可分解速度分量与可分解温度和速度的联合概率函数，研究SGS通量对可分解过程的影响；(2)了解SGS通量与可分辨速度和温度的关系。总之，这些将确定SGS通量的特征，这些特征对可解析过程很重要，并直接有助于LES建模。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很重要。

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.