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.