In the year 2003, the first large-eddy simulation (LES) intercomparison of stable boundary layers was organized under the auspices of the GEWEX atmospheric boundary layer study (GABLS). More than ten LES modeling groups around the world participated in this intercomparison study. They modeled a weakly stable barotropic boundary layer utilizing several LES subgrid-scale (SGS) models. This intercomparison study highlighted that LES of weakly stable boundary layers is quite feasible. However, some of the key turbulence statistics were found to be sensitive to SGS models even at relatively fine resolutions, which is not desirable.
Quite a few novel SGS models have been proposed in the atmospheric boundary layer literature in the past few years. The existing SGS models have also evolved quite dramatically during this period. The GABLS community believes that the time is opportune for another LES intercomparison in order to re-evaluate the capabilities of the SGS models - in the context of moderately stratified flows.
The GABL3 LES intercomparison case is based on a moderately stratified, baroclinic, mid-latitude boundary layer observed over Cabauw, the Netherlands on July 1st, 2006. During the course of this intercomparison study, the GABLS community will probe into the performances of several SGS models in capturing the characteristics of this modertately stable boundary layer. They will also put strong emphasis on the evolution of low-level jets and early morning transition.
Lastly, this new intercomparison exercise will also attempt to address some of the outstanding questions related to stable boundary layer turbulence (see ScienceQ for details).