Large-Eddy Simulation of Stably-Stratified Atmospheric Boundary Layers over Flat and Sloped Terrains*

Numerical studies of turbulent stably-stratified atmospheric boundary layer are known to pose significant challenges as a result of the smaller near-surface turbulence length scale caused by negative buoyancy effects when compared to neutral boundary layers. Due to advances in computing power, large-eddy simulation (LES) with fine spatial resolutions has emerged as a powerful tool to study the complex flow features in stably-stratified boundary layers; however, the quality of the predictions is strongly dependent on the subgrid-scale models and  the near-surface parameterization. Since, in addition to the buoyancy destruction of turbulence, gravity effects due to a nonzero terrain slope angle can also alter the near-surface flow structure, there is a major challenge for LES models to accurately account for unresolved flow-turbulence interactions in stably stratified boundary layers close to the surface. In the present work, a number of different models are applied to carry out LES of stably-stratified boundary layers over flat and sloped terrains to investigate the effects of terrain slope angle on the predictions and assess the performance of subgrid-scale models.