Mean Profiles and Similarity in a Stationary and Horizontally-Uniform ABL

In this chapter the so-called flux-profile relationships are presented for specific humidity, and other relevant quantities such as wind speed and temperature in the different sublayers of the ABL. Because of the above-mentioned difficulties of closure, these relationships are not derived by the solution of the transport equations; rather they are arrived at by invoking similarity, through the application of dimensional analysis. Thus, after the relevant physical quantities are identified from the governing equations or simply by inspection, they are organized into a reduced number of dimensionless quantities. Dimensional analysis only establishes the possible existence of a functional relationship between these dimensionless quantities; however, the function itself must usually be determined by experiment. Still, in some cases the functional form of the relationship may be inferred theoretically by means of a conceptual transport model or by applying a plausible closure assumption to the transport equations, and only some unknown constants need be determined experimentally. Especially in recent years numerous similarity models for the ABL have been proposed in the literature. This chapter does not present an exhaustive review but only the more important schemes that appear applicable in the determination of water vapor transport.