A two-scale mixing formulation for the atmospheric boundary layer

Abstract

This study compares different simple mixing schemes for one-dimensional models and then focuses on the two-scale mixing approach. Two-scale mixing consists of local diffusion between adjacent grid levels and nonlocal mixing over the bulk of the boundary layer (nonlocal mixing). The latter represents nonlocal mixing by the boundary-layer scale eddies. A common example of two-scale mixing is the formulation of the turbulent heat transport in terms of an eddy diffusivity to represent small-scale diffusion and a “countergradient correction” to represent boundary-layer scale transport. Most existing two-scale approaches are applied to heat and moisture transport while momentum transport is simultaneously parameterized only in terms of a local diffusivity without nonlocal mixing. This study attempts to correct this inconsistency.