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

大涡模拟（LES）是分析小尺度大气环流的一种重要计算方法。 根据计算网格的密度，LES可以精确地描绘尺度小到几米的涡流和漩涡。 在接近地面的高度上，更小的涡流变得越来越重要。 大涡模拟的一个基本问题是，在紧邻地面的表层中的涡旋不能被解析，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，必须近似亚网格尺度（SGS）过程的影响。 本研究的目标是开发改进的模型SGS过程中使用的大气表层。 该方法是分析在加州圣华金河谷进行的SGS 2000现场项目期间，采用专门设计的声波风速计阵列的数据。 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。 本文的主要目的是：（1）利用可分辨速度分量和可分辨温度、速度的联合概率函数，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、温度的关系。 总之，这些将识别SGS通量的特性，这些特性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.