An intercomparison of large-eddy simulations of the stable boundary layer

Results are presented from the first intercomparison of Large-eddy simulation (LES) models for the stable boundary layer (SBL), as part of the GABLS (Global Energy and Water Cycle Experiment Atmospheric Boundary Layer Study) initiative. A moderately stable case is used, based on Arctic observations. All models produce successful simulations, since they reflect many of the results from local scaling theory and observations. There is more spread between the output than found for previous LES of the convective boundary layer, and significant sensitivity to resolution. Simulations performed at 1m resolution show only small changes in the mean profiles compared to coarser resolutions; simulations at higher than 12.5m resolution do not laminarise spuriously. Also, sensitivity to sub-grid models for individual models highlights their importance in SBL simulation, particularly at moderate resolution (6.25m). Stability functions are derived from the LES using typical mixing lengths used in Numerical Weather Prediction (NWP) and climate models. The functions are significantly less than those used in NWP, but become larger when smaller asymptotic mixing lengths are used. There is also support for the use of K-profile similarity in parametrizations. Thus, the results provide improved understanding and motivate future developments of the parametrization of the SBL.