Laboratory simulations of the atmospheric mixed-layer in flow over complex topography

Abstract

A laboratory study of the influence of complex terrain on the interface between a well-mixed boundary layer and an elevated stratified layer was conducted in the towing-tank facility of the U.S. Environmental Protection Agency. The height of the mixed layer in the daytime boundary layer can have a strong influence on the concentration of pollutants within this layer. Deflections of streamlines at the height of the interface are primarily a function of hill Froude number (Fr), the ratio of mixed-layer height (z i ) to terrain height (h), and the crosswind dimension of the terrain. The magnitude of the deflections increases as Fr increases and z i /h decreases. For mixing-height streamlines that are initially below the terrain top, the response is linear with Fr; for those initially above the terrain feature the response to Fr is more complex. Once Fr exceeds about 2, the terrainrelated response of the mixed layer interface decreases somewhat with increasing Fr (toward more neutral flow). Deflections are also shown to increase as the crosswind dimensions of the terrain increase. Comparisons with numerical modeling, limited field data, and other laboratory measurements reported in the literature are favorable. Additionally, visual observations of dye streamers suggest that the flow structure exhibited for our elevated inversions passing over three dimensional hills is similar to that reported in the literature for continuously stratified flow over two-dimensional hills. * Retired.

Emissions and topographic effects on column CO2 () variations, with a focus on the Southern California Megacity

“…Though the ML may fluctuate by a few hundred meters over a distance of several kilometers due to updrafts [ Nielsen‐Gammon et al , ], these are averaged out with downdrafts over an hour or so. Over smaller areas, average variations in the ML height pressure are smoother than changes in surface pressure as noted by streamlines over topographic features [ Perry and Snyder , ]. Maps of the average surface pressure p s and ML are shown in Figure .…”

Anabatic Flow along a Uniformly Heated Slope Studied through Large-Eddy Simulation

“…On the other hand, pioneer field experiments have paved the way for key studies on the comprehension of the local processes driving the onset of the anabatic flows [26], the evolution of the anabatic layer [9] and its unsteadiness [27]. Laboratory experiments have delved into the initial development of the slope flow [11,28,29] and the implication of a later development on air quality [30]. Of more recent interest is the evaluation of rising plumes and flow separation from the slope due to the surface heating.…”