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

Clemson University, Clemson SC

Investigators

Abstract

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.