Boundary Layer, Urban Meteorology and Land-Surface Processes

Sensitivity of turbulence statistics in the lower portion of a numerically simulated stable boundary layer to parameters of the Deardorff subgrid turbulence closure model

Dr. Jeremy Gibbs

Department of Mechanical Engineering, University of Utah
CIMMS, University of Oklahoma

15 October 2015, 2:30 PM

National Weather Center, Room 5930
120 David L. Boren Blvd.
University of Oklahoma
Norman, OK

The Deardorff 1980 (D80) subgrid turbulence closure model is perhaps still the most ubiquitous scheme used in large-eddy simulation (LES) studies of atmospheric boundary-layer flows. This model is often included as the default closure scheme in a variety of codes and numerical weather prediction models. In this study, we investigate the three commonly employed corrective adjustments of the D80 closure model. These include a stability-dependent length scale, the formulation for the subgrid turbulent Prandtl number, and the enhancement of near-surface dissipation. We implement a modified formulation of the D80 closure, then compare simulated flow statistics in the lower portion of a representative nocturnal stable boundary layer (SBL) for LES with realistic forcing using the original D80 scheme and the modified version.

LES data were compared with observations from the Southern Great Plains (SGP) site of the Atmospheric Radiation Measurement (ARM) Program in Lamont, Oklahoma. The modified scheme shows overall improvement in reproducing vertical profiles of wind speed and potential temperature in the near- surface region of the SBL. Conclusions regarding turbulence kinetic energy and friction velocity are not as definitive, though there are signs of improved agreement with measurement data. Examination of the stability parameter and near-surface sensible heat flux suggests the modified scheme better captures the nature of stability in the SBL. The proposed modification offers a more straightforward and interpretable framework for the parameterization of subgrid turbulence in LES of atmospheric boundary layers.

Boundary Layer, Urban Meteorology and Land-Surface Processes Seminar Series website