Formulation of Turbulent Fluxes in the Stable Boundary Layer

Abstract

Abstract The mixing lengths for heat and momentum are computed from seven levels of eddy correlation data during the Cooperative Atmosphere–Surface Exchange Study-1999 (CASES-99). A number of formulations of the mixing length are evaluated, including surface layer similarity theory, several hybrid similarity theories, a formulation based on the Richardson number, and a formulation based on the local shear. A formulation of the mixing length is examined, which approaches z-less similarity for large z and surface layer similarity close to the ground surface. A generalized version includes a dependence on boundary layer depth, which approaches the usual boundary layer height dependence for neutral conditions. However, for many of the observational cases, a boundary layer did not exist in the usual sense, in that turbulence was generated primarily above the surface inversion layer and occasionally extended downward toward the surface. For these cases, inclusion of z-less turbulence is crucial.