Observations and scaling of the atmospheric boundary layer

One of the areas of research that Reg Clarke took a particular interest in was the atmospheric boundary layer (ABL). In this review we examine observations of the structure of the ABL based on a framework of similarity scaling. This includes: the Monin–Obukhov surface layer; the free-convection layer; the near-neutral upper layer; the mixed layer; the stable layer scaled by local fluxes; and the stable inter-mittent layer. Limitations of this framework are illustrated for the horizontal wind variances in the surface layer and the moisture flux in the mixed layer. Recent developments in prescribing surface layer stable profiles, top-down bottom-up scaling for the mixed layer, free-convection fluxes, generalised Rossby number similarity theory, and treatment of inhomogeneous surfaces are emphasised.