Scalar fluxes in the planetary boundary layer — Theory,modeling, and measurement

I outline the general features of the vertical profile of the vertical flux of a conservative scalar in the planetary boundary layer, giving special emphasis to the convective case and emphasizing the importance of the Webb correction. After the influence of thermal stability on the structure of the turbulent eddies carrying this flux is reviewed, recent developments in parameterizing vertical transport in the convective boundary layer are discussed. I then survey three approaches to the numerical modeling of this transport — second-order closure, large-eddy simulation, and direct numerical simulation. Eddy-correlation, eddy-accumulation, and indirect techniques for measuring scalar fluxes are surveyed and contrasted. Finally, I discuss the physics of probe-induced flow distortion and its impact on scalar flux measurement, showing that it can be quite severe for trace species density fluxes measured from aircraft.Based on lectures given at the workshop Measurement and Parameterization of Land-Surface Evaporation Fluxes, Banyuls, France, October, 1988.The National Center for Atmospheric Research is sponsored by the National Science Foundation.