The GABLS Third Intercomparison Case for Boundary Layer Model Evaluation Part A: Case Selection and Set-up

A case is set-up to facilitate the intercomparison and evaluation of single-column models and large-eddy Simulation models. It is the third case defined in the context of the GEWEX Atmospheric Boundary Layer Studies (GABLS) and it utilize observations from Cabauw, The Netherlands. A relatively ideal, clear sky, baroclinic 24-hour period (1-2 July 2006) was selected from the multi-year data archive of Cabauw. The case has a geostrophic wind of approx. 7 m s-1. A pronounced low level jet develops due to inertial oscillation after decoupling of the atmosphere from the surface around sunset. Detailed initial conditions, surface conditions and dynamical forcings are prescribed on the basis of local observations and the outcome of a 3D-atmospheric model. It is shown that a very precise prescription of the forcings is a prerequisite to enable a meaningful evaluation of models against observational data