Large-eddy simulation of the stable boundary layer with a focus on low-level jet and boundary layer depth
Bowen Zhou, University of California, Berkeley, Berkeley, CA; and F. K. Chow
Large-Eddy Simulation (LES) of the stably stratified atmospheric boundary layer is performed using an explicit filtering and reconstruction approach with a finite difference method. Turbulent stresses are split into the Resolvable Subfilter-Scale (RSFS) stresses and Subgrid-Scale (SGS) stresses. The former are recovered from a velocity reconstruction approach, and the latter are represented by a dynamic eddy-viscosity model. Subfilter-Scale (SFS) dissipation and backscatter events are statistically characterized, showing the ability of the RSFS/SGS framework to allow for energy exchange from small to large scales. A Low-Level Jet (LLJ) develops in the simulations, and wind shear in the jet is responsible for generating additional turbulent kinetic energy (TKE) around the top of the boundary layer. This elevated TKE is unexpected based on previous modeling results with traditional turbulence closures, but is in agreement with field observations under certain conditions. Boundary layer depth is an important parameter in the stable boundary layer (SBL) simulations. Unlike neutral or convective cases, where boundary layer depth is usually defined by the residual inversion layer, the SBL depth is formed in the simulation due to a self-developed over-capping inversion layer. The SBL depth is mainly affected by the strength of stratification, geostrophic wind forcing, and surface roughness. Many previous studies in the literature have shown a strong dependence of SBL depth on the turbulence model, and grid resolution. Higher grid resolution usually means a general decrease in boundary layer depth and an increase in jet strength. A grid refinement study using the reconstruction model is performed to compare with conventional eddy viscosity closures.
Poster Session 3, Stable Boundary Layers
Monday, 2 August 2010, 6:00 PM-7:30 PM, Castle Peak Ballroom
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