S. H. Derbyshire

Large-Eddy Simulation of the stably-stratified atmospheric boundary layer

Large-Eddy Simulation of stable boundary layers (SBLs) has been considered particularly difficult, indeed perhaps impossible with present computational resources. Here we present a new series of successful simulations of SBLs over uniform, flat terrain, using an approach previously successful for neutral and convective conditions, and showing that essentially the same model can handle all three main dry types of atmospheric boundary layer. We consider both technical requirements for successful and accurate SBL simulations and the observed characteristics of the simulated SBL. We discuss the evolution (in some cases to quasi-steady states) and compare with theory and experimental data. Effects of static-stability on the flow are analyzed using one-point and two-point statistics. Results show the development of a shear-driven SBL, with little sign of distinctively wavelike motions. The flow statistics are found to be consistent with local scaling, and that framework is used to compare with other data and theoretical models.

Stable Boundary-Layer Modelling: Established Approaches and Beyond

In the light of Large Eddy Simulation and other recent work, this paper discusses methods of stable boundary-layer modelling that are established in numerical weather prediction and potentially relevant to other applications, e.g., to dispersion. It is argued that classical scaling theory is best expressed in terms of the local Richardson numbers. The theory can then be extended to treat cases where classical assumptions break down. There are indications that Richardson number models with suitable boundary conditions can mimic, at least qualitatively, some features of the ‘very stable boundary layer’. Despite advances in research modelling, detailed observational validation remains essential.