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Results from a third-order turbulence closure scheme model and from experimental studies are used to improve the Eddy Kinetic Energy (EKE) model for the Planetary Boundary Layer (PBL).It is proposed to use two different lengths, one for mixing and one for dissipation, as well as a temperature counter-gradient in the heat flux parameterization and a corrective term in the gradient-type relation for the computation of EKE flux. Such refinements do not lead to any increase in computing cost nor to any particular difficulty for the model implementation. They however allow for significantly better results, which are in close agreement with those of much more sophisticated models, at least in the case of the convective PBL, which is mainly considered here.

Land-use practices such as deforestation or agricultural management may affect regional climate, ecosystems and water resources. The present study investigates the impact of surface heterogeneity on the behaviour of the atmospheric boundary layer (ABL), at a typical spatial scale of 1 km. Large-eddy simulations, using an interactive soil–vegetation–atmosphere surface scheme, are performed to document the structure of the three-dimensional flow, as driven by buoyancy forces, over patchy terrain with different surface characteristics (roughness, soil moisture, temperature) on each individual patch. The patchy terrain consists of striped and chessboard patterns. The results show that the ABL strongly responds to the spatial configuration of surface heterogeneities. The stripe configuration made of two patches with different soil moisture contents generates the development of a quasi- two-dimensional inland breeze, whereas a three-dimensional divergent flow is induced by chessboard patterns. The feedback of such small-scale atmospheric circulations on the surface fluxes appears to be highly non-linear. The surface sensible and latent heat fluxes averaged over the 25-km2 domain may vary by 5% with respect to the patch arrangement

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