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An urban airshed model

Pitts, Robert Owen (1991) An urban airshed model. PhD thesis, Murdoch University.

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Abstract

A numerical mesoscale model, originally developed by Pielke (1974), is validated and applied to simulating the mesoscale meteorology of the Swan coastal plain of Western Australia as the basis for an urban airshed model. Since the only radiosonde profile available to initialise the model is influenced by downslope flow from the nearby asymmetric Darling Scarp, the validation incorporates model comparisons with aircraft cross-sections of temperature and humidity across the coastal plain.

These observations highlight topographically induced hydraulic jumps, lee waves or vertically propagating hydrostatic waves depending on the upwind stability and wind profile. The vertically propagating waves and hydraulic jump were observed to produce accelerated flow down the escarpment. Two of these hydrostatically dominated days were modelled and shown to reproduce the essential features of wave overturning and the development of a shooting hydraulic flow. This response is dependent on the wind profile but not on the existence of a critical level.

The high backsheared environment leads to a high ratio of Brunt-Vaisala frequency to wind speed throughout the profile, resulting in short wavelengths, high nonlinearity and overturning. With the ratio of the halfwidth of the topography to the boundary layer depth being small, the flow fields are shown to be sensitive to the boundary layer.

Further validation of the model was conducted over the change in surface conditions encounted at the coast. In particular, these validations addressed the parameterization of the subgrid scale fluxes within the model and established its ability to simulate the mesoscale meteorology of the region under a variety of conditions.

Having validated the meteorological component of the model, the major emission source within the region (motor vehicles) is incorporated. Automotive emissions are derived from driving characteristics and vehicle emissions based on speed and acceleration to produce spatially and temporally varying emissions across the Perth region.

A simple Langevin scheme is incorporated into the mesoscale model to simulate the dispersal of both point and area sources. The scheme is shown to satisfy the well mixed criterion and illustrates good agreement with previous laboratory and field studies. With the incorporation of the predicted emissions, the model is shown to reproduce the measured concentrations for a selected case study and its potential as an urban airshed model is highlighted.

Item Type: Thesis (PhD)
Murdoch Affiliation: School of Biological and Environmental Sciences
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: repository@murdoch.edu.au. Thank you.
Supervisor(s): Lyons, Tom and Scott, Bill
URI: http://researchrepository.murdoch.edu.au/id/eprint/51350
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