Delayed shear enhancement in mesoscale atmospheric dispersion

Conference · Sat Dec 31 04:00:00 EST 1994

OSTI ID:28727

Moran, M D ^[1]; Pielke, R A ^[2]

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1. Atmospheric Environment Service, Ontario (Canada)
2. Colorado State Univ., Fort Collins, CO (United States)

Mesoscale atmospheric dispersion (MAD) is more complicated than smaller-scale dispersion because the mean wind field can no longer be considered steady or horizontally homogeneous over mesoscale time and space scales. Wind shear also plays a much more important role on the mesoscale: horizontal dispersion can be enhanced and often dominated by vertical wind shear on these scales through the interaction of horizontal differential advection and vertical mixing. Just over 30 years ago, Pasquill suggested that this interaction need not be simultaneous and that the combination of differential horizontal advection with delayed or subsequent vertical mixing could maintain effective horizontal diffusion in spite of temporal or spatial reductions in boundary-layer turbulence intensity. This two-step mechanism has not received much attention since then, but a recent analysis of observations from and numerical simulations of two mesoscale tracer experiments suggests that delayed shear enhancement can play an important role in MAD. This paper presents an overview of this analysis, with particular emphasis on the influence of resolvable vertical shear on MAD in these two case studies and the contributions made by delayed shear enhancement.

• OSTI ID: 28727
• Report Number(s): CONF-940115--
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
AIR POLLUTION
ATMOSPHERIC CIRCULATION
CLIMATE MODELS
DIFFUSION
MIXING
SHEAR
WIND