Stable Boundary Layers and Subfilter-Scale Motions

Recent high-resolution large-eddy simulations (LES) of a stable atmospheric boundary layer (SBL) with mesh sizes (Formula presented.) or mesh spacings (Formula presented.) m are analyzed. The LES solutions are judged to be converged based on the good collapse of vertical profiles of mean winds, temperature, and low-order turbulence moments, i.e., fluxes and variances, with increasing N. The largest discrepancy is in the stably stratified region above the low-level jet. Subfilter-scale (SFS) motions are extracted from the LES with (Formula presented.) and are compared to sonic anemometer fields from the horizontal array turbulence study (HATS) and its sequel over the ocean (OHATS). The results from the simulation and observations are compared using the dimensionless resolution ratio (Formula presented.) where (Formula presented.) is the filter width and (Formula presented.) is a characteristic scale of the energy-containing eddies in vertical velocity. The SFS motions from the observations and LES span the ranges (Formula presented.) and are in good agreement. The small, medium, and large range of (Formula presented.) correspond to Reynolds-averaged Navier–Stokes (RANS), the gray zone (a.k.a. “Terra Incognita”), and fine-resolution LES. The gray zone cuts across the peak in the energy spectrum and then flux parameterizations need to be adaptive and account for partially resolved flux but also “stochastic” flux fluctuations that represent the turbulent correlation between the fluctuating rate of strain and SFS flux tensors. LES data with mesh 2048 (Formula presented.) will be made available to the research community through the web and tools provided by the Johns Hopkins University Turbulence Database.