Top-down and bottom-up diffusion of a scalar in the convective boundary layer.

Abstract

The vertical diffusion of a passive, conservative scalar through the convective PBL is actually the superposition of what we call 'top-down' and 'bottom-up' processes. We argue that the vertical asymmetry in the buoyant production of the turbulent kinetic energy should cause the top-down and bottom-up diffusivities to differ. If so, we show that the diffusivity for the total process is poorly behaved; it depends on the scalar flux profile and can have singularities. -from Authors