Simple Inclusion of z-less Turbulence within and above the Modeled Nocturnal Boundary Layer

Abstract

In simple models, the nocturnal boundary layer is generally formulated in terms of eddy diffusivities, which are functions of height above ground and boundary layer depth. This approach is modified in this study to include ?z-less? turbulence, which is formulated in terms of a stability-dependent mixing length and a Prandtl number, which are not tied to the existence of a boundary layer depth. These modifications have been guided by analysis of nocturnal boundary layer data from the Cooperative Atmospheric-Surface Exchange Study?1999. The modeled turbulence sometimes exhibits an upside-down structure with turbulence generated by shear associated with nocturnal flow acceleration at higher levels. The modified model produces a more realistic smoother wind speed maximum (nocturnal jet) and generates layers of turbulence above the boundary layer. Remaining shortcomings of the new model are discussed.