Large-Eddy Simulation of the Evolving Stable Boundary Layer Over Flat Terrain

Abstract

The stable boundary layer (SBL) in the atmosphere is of considerable interest because it is often the worse case scenario for air pollution studies and health effect assessments associated with the accidental release of toxic material. Traditional modeling approaches used in such studies do not simulate the non-steady character of the velocity field, and hence often overpredict concentrations while underpredicting spatial coverage of potentially harmful concentrations of airborne material. The challenge for LES is to be able to resolve the rather small energy-containing eddies of the SBL while still maintaining an adequate domain size. This requires that the subgrid-scale (SGS) parameterization of turbulence incorporate an adequate representation of turbulent energy transfer. Recent studies have shown that both upscale and downscale energy transfer can occur simultaneously, but that overall the net transfer is downscale. Including the upscale transfer of turbulent energy (energy backscatter) is particularly important near the ground and under stably-stratified conditions. The goal of this research is to improve the ability to realistically simulate the SBL. The large-eddy simulation (LES) approach with its subgrid-scale (SGS) turbulence model does a better job of capturing the temporally and spatially varying features of the SBL than do Reynolds-averaging models. The scientific objectivesmore » of this research are: (1) to characterize features of the evolving SBL structure for a range of meteorological conditions (wind speed and surface cooling), (2) to simulate realistically the transfer of energy between resolved and subgrid scales, and (3) to apply results to improve simulation of dispersion in the SBL.« less