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

Abstract

Some 36 years following its creation, the Deardorff 1980 (D80) subgrid turbulence 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) case from LES with realistic forcing using the original D80 scheme and the modified version of the scheme. 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, although 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 effects of stability in the considered flow case. The proposed modification offers a more straightforward and interpretable framework for the parametrization of subgrid turbulence in LES of atmospheric boundary layers.