Convection in the atmospheric boundary layer

Abstract

Recent advances in the study of clear and partly cloudy convective boundary layers are reviewed. The techniques and results of observational studies of the structure and dynamics of convective elements are discussed. These findings have important consequences for pollution dispersion. They also form the basis for a test of LES dispersion models which is more discriminating than those based on replication of observed turbulence statistics. Several new approaches to CBL similarity theory and parameterization have appeared. They avoid some of the problems associated with the over-simplification of previous techniques. Particularly noteworthy is the ability to handle counter-gradient fluxes with relatively simple models. Progress towards parameterization of CBL turbulence in the presence of horizontal inhomogeneity of the atmosphere or surface has been slower. Efforts to locate the limits of validity of the assumption of horizontal homogeneity have been more successful than the efforts to develop parameterizations which do not rely upon it. Mesoscale models need CBL parameterizations which are valid over complex terrain and in the presence of strong differential advection and mean vertical motion. LES models may prove useful in producing the data sets on which such parameterizations could be based.