Subgrid-scale (SGS) 2000: Analysis of Field Experimental Data to Elucidate Fundamental Physics in Parameterizations for Large-eddy Simulations

Johns Hopkins University, Baltimore MD

Investigators

Abstract

Large-eddy simulation (LES) is increasingly used to analyze land-atmosphere interactions at scales relevant to microscale and mesoscale meteorology. The goal of this project is to improve the understanding of subgrid-scale (SGS) motions - the turbulent velocity fluctuations too small to be resolved in LES models, which must be accounted for by some kind of parameterization. The approach is to use experimental data collected in the SGS2000 experiment, conducted in the summer of 2000 in the San Joaquin Valley. The analysis will employ novel ideas that have arisen from laboratory studies of turbulence. These include new statistical-geometrical tools to quantify alignments between SGS heat flux and temperature gradient vectors, the evaluation of spectral eddy viscosities and eddy diffusivities from the data, and the study of coherent structures such as sweeps and ejections. To extend the range of the scales that can be analyzed, a new field experiment will be planned that combines an array of hot-wire anemometers to measure the fine scales of turbulence with arrays of sonic anemometers to measure the larger scales. Details of the experiment design will depend on the outcome of the analysis of SGS2000 data. The field program will be undertaken in collaboration with the Atmospheric Technology and the Microscale and Mesoscale Meteorology Divisions of the National Center for Atmospheric Research.