In:
Physics of Fluids A: Fluid Dynamics, AIP Publishing, Vol. 3, No. 1 ( 1991-01-01), p. 155-162
Abstract:
Large-eddy simulations have shown that passive, conservative scalars emitted into the convective boundary layer (CBL) of the atmosphere have unusual diffusion properties. A species introduced through an area source at the layer top and having zero flux through the bottom (i.e., one undergoing ‘‘top-down’’ diffusion) has a well-behaved eddy diffusivity, but one introduced at the bottom, with zero flux at the top (‘‘bottom-up’’ diffusion) has a much different diffusivity profile in the same turbulence field. It is suggested that the roots of this transport asymmetry lie in the interaction between skewness of the transporting turbulence and the gradient of the flux of the transported scalar. A kinematic model is used to show that this interaction can indeed induce transport asymmetry in small-time-scale, homogeneous turbulence. The present simulations with a Lagrangian particle model confirm that this asymmetry extends to large-time-scale, inhomogeneous turbulence. A heuristic model of convective turbulence suggests that its asymmetric transport is also described by the kinematic model but with the small-time-scale restriction removed. In all cases the transport asymmetry effects scale with the parameter SσwTL/h, where S, σw, and TL are the skewness, standard deviation, and Lagrangian integral time scale of the transporting turbulence, and h is the layer depth; a scalar flux gradient is required as well.
Type of Medium:
Online Resource
ISSN:
0899-8213
Language:
English
Publisher:
AIP Publishing
Publication Date:
1991
detail.hit.zdb_id:
246807-4
detail.hit.zdb_id:
2130786-6
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