William R. Pendergrass

Dispersion in neutral boundary layer over a step change in surface roughness—I. Mean flow and turbulence structure

In this study we have compared two quite different simulated boundary layers over homogeneous surfaces with an internal boundary layer (IBL) developed over a step change in surface roughness. The two simulated boundary layers are representative of rural and urban type environments under neutral conditions (Counihan, 1975), which are characterized by different power-law profiles, ratios of shear stress to freestream velocity and ratios of boundary-layer height to roughness parameter. For the change-in-roughness case, the need to incorporate the displacement height in evaluation of the IBL height (hi) is identified. The growth of hi with distance x from the location of roughness change is well described by Elliotts formula hi/Z02 = a(x/Z02)p, with p = 0.8 and a ≅ 0.35, and agrees with that observed in the field by Bradley (1968). The shear-stress measurements show considerable overshooting at the location of the roughness change before slowly settling down to their new surface equilibrium values further downstream. The overshooting of near-surface values is also present in σu, σv and σw measurements. Ignoring the initial phase of overshooting of the surface stress measurements, the lowest portion (∼ 13) of the IBL can be identified as an equilibrium layer, in which flow properties are essentially in equilibrium with the underlying surface. The variations of the non-dimensional wind shear and the ratio of shear stress to turbulent kinetic energy in the IBL are also studied.

THE EFFECTIVENESS OF STATIONARY AUTOMOBILES AS SHELTERS IN ACCIDENTAL RELEASES OF TOXIC MATERIALS

Abstract The protection offered occupants of stationary automobiles against airborne gases and respirable particles, such as might result from an accidental release, was measured and found to be substantial. For the four autos tested with the air conditioning (AC) system on and in recirculate position, the equilibrium ratios of inside/outside concentrations ( I / O ) for 2-μm diameter particles were less than 0.2, and some ratios were as small as 0.014. With both the AC compressor and the system fan off, the I / O for five autos ranged from 0.04 to 0.18. These low ratios are primarily a result of deposition within the autos. However, three of the five autos had substantially higher I / O ratios when the AC fan was on than when off, indicating that for some autos the AC caused significant added intake of outside air. Air exchange rates for the five stationary autos were on the order of 0.5h −1 with AC off, and 2.5 h −1 with AC on.

Urban Turbulence in Space and in Time

AbstractThe utility of aggregating data from near-surface meteorological networks for initiating dispersion models is examined by using data from the “WeatherBug” network that is operated by Earth Networks, Inc. WeatherBug instruments are typically mounted 2–3 m above the eaves of buildings and thus are more representative of the immediate surroundings than of conditions over the broader area. This study focuses on subnetworks of WeatherBug sites that are within circles of varying radius about selected stations of the DCNet program. DCNet is a Washington, D.C., research program of the NOAA Air Resources Laboratory. The aggregation of data within varying-sized circles of 3–10-km radius yields average velocities and velocity-component standard deviations that are largely independent of the number of stations reporting—provided that number exceeds about 10. Given this finding, variances of wind components are aggregated from arrays of WeatherBug stations within a 5-km radius of selected central DCNet locatio...

On the Micrometeorology of the Southern Great Plains 1: Legacy Relationships Revisited

Data from a 32-m tower located near Ocotillo, Texas (

On the Relevance of \(\ln (z_{0} /z_{0T})= kB^{-1}\)

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An integrated WRF/HYSPLIT modeling approach for the assessment of PM2.5 source regions over the Mississippi Gulf Coast region

32.12050∘N;

On the Micrometeorology of the Southern Great Plains. 2: Turbulence Statistics

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