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Yansen Wang, Cheryl L. Klipp, Dennis M. Garvey, David A. Ligon, Chatt C. Williamson, Sam S. Chang, Rob K. Newsom, and Ronald Calhoun

) also computed several morphological parameters using methods proposed by Grimmond and Oke (1999) . The frontal area index, defined as the total area of buildings projected into the plane normal to the approaching wind direction divided by the horizontal projected plan area of the study site, ranges from 0.3 to 0.4 from the four cardinal directions. The complete aspect ratio, defined as the ratio of the surface area of buildings to the horizontal projected plane area, is 1.5–12 in the CBD area. The

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P. Ramamurthy, E. R. Pardyjak, and J. C. Klewicki

building height in scale-model cities immersed in a neutral stability flow. For neutral conditions over a large range of building frontal and plan areas, Macdonald et al. (2002) have identified the basic shapes for mean and turbulence profiles within and above regular, idealized arrays of buildings. During stable conditions, many questions still exist regarding the effect of upstream stability on flow within cities. This is likely a result of the high variability of urban morphologies, land uses, and

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M. A. Nelson, E. R. Pardyjak, J. C. Klewicki, S. U. Pol, and M. J. Brown

canyon was approximately 50 m (based on the buildings bounding the canyon) with a corresponding canyon width S 1 of approximately 25 m and canyon length S 2 of approximately 150 m, yielding a height to separation ratio ( HS −1 1 ) of approximately 2. An analysis of the building morphology data in the urban core of OKC performed by Burian et al. (2005) found the plan area fraction λ p to be 0.35 and the frontal area index λ f to range between 0.14 and 0.22 depending on wind direction. A λ f

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Donald A. Burrows, Eric A. Hendricks, Steve R. Diehl, and Robert Keith

, J. S. Shinn , R. P. Hosker , J. F. Bowers , and J. C. Pace , 2004 : Overview of Joint Urban 2003—An atmospheric dispersion study in Oklahoma City. Preprints, Symp. on Planning, Nowcasting, and Forecasting in the Urban Zone and Eighth Symp. on Integrated Observing and Assimilation Systems for Atmosphere, Oceans, and Land Surface, Seattle, WA, Amer. Meteor. Soc., J7.1 . Baik , J-J. , J-J. Kim , and H. J. S. Fernando , 2003 : A CFD model for simulating urban flow and

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M. A. Nelson, E. R. Pardyjak, M. J. Brown, and J. C. Klewicki

. Burian et al. (2005) found the OKC urban core to have a plan area fraction λ p of 0.35 and a frontal area index λ f that ranged between 0.14 and 0.22 depending on wind direction. A λ f of 0.14 corresponded to winds out of the east and 0.19 for winds out of the north. The largest value of 0.22 corresponded to winds that were oblique to the orientation of the streets in the urban core (i.e., nominally winds coming from the northwest, northeast, southwest, or southeast). These values characterize

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Stevens T. Chan and Martin J. Leach

that to simulate urban dispersion scenarios successfully under light and highly variable winds it is necessary to use appropriate time-dependent forcing and turbulence from the larger-scale flow through the inflow boundary. Their results also indicate that inflow turbulence is as important, if not more so, than building-induced mechanical turbulence in dispersion scenarios under the above conditions. Although high-resolution CFD models are very useful for emergency planning, vulnerability analyses

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Julia E. Flaherty, David Stock, and Brian Lamb

standards. However, improperly sited monitoring stations may report less-than-typical concentrations, allowing urban populations to unknowingly experience unhealthy levels of pollutant. Alternately, monitors may report higher-than-typical concentrations, which cause cities to invest unnecessary funds into attainment plans. As computing power has become more affordable, computational fluid dynamics (CFD) has become an increasingly valuable tool for studying urban flow. These models explicitly account for

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Eric A. Hendricks, Steve R. Diehl, Donald A. Burrows, and Robert Keith

dispersion study in Oklahoma City. Preprints, Symp. on Planning, Nowcasting, and Forecasting in the Urban Zone and Eighth Symp. on Integrated Observing and Assimilation Systems for Atmosphere, Oceans, and Land Surface, Seattle, WA, Amer. Meteor. Soc., J7.1 . Arya , S. P. , 2001 : Introduction to Micrometeorology . Academic Press, 415 pp . Brown , M. J. , 2004 : Urban dispersion—Challenges for fast response modeling. Preprints, Fifth Conf. on the Urban Environment, Vancouver, BC, Canada, Amer

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Steve R. Diehl, Donald A. Burrows, Eric A. Hendricks, and Robert Keith

2003—An atmospheric dispersion study in Oklahoma City. Preprints, Symp. on Planning, Nowcasting, and Forecasting in the Urban Zone and Eighth Symp. on Integrated Observing and Assimilation Systems for Atmosphere, Oceans, and Land Surface, Seattle, WA, Amer. Meteor. Soc., CD-ROM, J7.1 . Brook , D. R. , N. V. Felton , C. M. Clem , D. C. H. Strickland , I. H. Griffiths , R. D. Kingdon , D. J. Hall , and J. M. Hargrave , 2003 : Validation of the urban dispersion model (UDM

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Julia E. Flaherty, Brian Lamb, K. Jerry Allwine, and Eugene Allwine

, K. J. , J. H. Shinn , G. E. Streit , K. L. Clawson , and M. Brown , 2002 : Overview of Urban 2000: A multiscale field study of dispersion through an urban environment. Bull. Amer. Meteor. Soc. , 83 , 521 – 536 . Allwine , K. J. , M. J. Leach , L. W. Stockham , J. S. Shinn , R. P. Hosker , J. F. Bowers , and J. C. Pace , 2004 : Overview of Joint Urban 2003—An atmospheric dispersion study in Oklahoma City. Preprints, Symp. on Planning, Nowcasting, and

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