Stable boundary layers with low-level jets: what did we learn from the LES intercomparison within GABLS3?

Recently, the third intercomparison of single column and large-eddy models for atmospheric stable boundary layer simulations was organized under the auspices of the GEWEX atmospheric boundary layer study (GABLS). Eleven LES modeling groups from around the world participated in this intercomparison study to model a moderately stratified, baroclinic, mid-latitude nighttime boundary layer utilizing several LES subgrid-scale (SGS) models. The boundary layer was observed over Cabauw, Netherlands on July 1st, 2006. The initial condition for the LES intercomparison was created by synthetically merging the observed 200 m Cabauw tower data, wind profiler data, and a high-resolution sounding from DeBilt. Time-height-dependent geostrophic wind forcings were derived from a network of surface pressure stations in the Netherlands combined with analysis of a mesoscale weather forecasting model. In a similar fashion, time-height-dependent advection terms (for momentum, heat, and moisture) were also obtained from modeled mesoscale forecasts and observed trends at the 200 m level during nighttime. In this presentation, we discuss the performances of several dynamic and static (stability corrected) SGS models in capturing the characteristics of this moderately stable boundary layer. We will put a strong emphasis on the evolution of low-level jets (LLJs) and on the morning transition. A comparison with the first GABLS-LES study will also be given as well as a discussion on the important lessons for representing boundary layers in large scale models.