Fumigation of pollutants into a growing convective boundary layer over an inhomogeneous surface: a large eddy simulation

Cai, Xiao Ming

doi:10.1016/s1352-2310(04)00335-8

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“…When heterogeneity scales (h) are much larger than the boundary-layer height (z i ) (h/z i 1), convective boundarylayer (CBL) characteristics are significantly altered Cai et al 2004;Patton et al 2005), which can trigger temporal oscillations (Schumann 1991;Hadfield et al 1991b;Letzel and Raasch 2003). The effect of surface heterogeneities at smaller scales (h/z i ≤ 1) is considerably reduced in the presence of a background wind (Hadfield et al 1991b;Hechtel et al 1990;Dörnbrack and Schumann 1993;Shen and Leclerc 1994;Avissar and Schmidt 1998;) compared to cases without a background wind (Hadfield et al 1991a).…”

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confidence: 99%

Characteristics of secondary circulations over an inhomogeneous surface simulated with large-eddy simulation

Prabha

Karipot

Binford

2006

Boundary-Layer Meteorol

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Large-eddy simulation is used to study secondary circulations in the convective boundary layer modulated as a result of horizontally varying surface properties and surface heat fluxes over flat terrain. The presence of heat flux heterogeneity and its alignment with respect to geostrophic wind influences the formation, strength and orientation of organized thermals. Results show boundary-attached roll formation along heat flux maxima in the streamwise direction. The streamwise organization of the updrafts and downdrafts formed downwind of heterogeneities leads to counter-rotating secondary circulations in the crosswind plane. The distribution of resolved-scale pressure deviations shows large pressure gradients in the crosswind plane. Spanwise and vertical velocity variances and heat flux profiles depict considerable spatial variability compared to a homogeneous forest simulation. Secondary circulations are observed for various ambient wind scenarios parallel and perpendicular to heterogeneities. In the presence of increased wind speed, thermals emerging from the heat flux heterogeneity are elongated, and organize along and downwind of large-scale heterogeneity in the streamwise direction. Simulation with a reduced heat flux shows a shallower circulation with a lower aspect ratio. Point measurements of heat flux inside the roll circulation could be overestimated by up to 15-25% compared to a homogeneous case.

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