The Urban Dispersion Model (UDM) calculates the time sequence of concentrations, sizes and positions of multiple dispersing puffs in urban areas. For speed and ease of use, each puff is approximated by a 3D gaussian concentration profile. The UDM operates as a standalone modelling capability or as a component of other modelling systems, e.g. the HPAC system developed by the US Defense Threat Reduction Agency (DTRA).

An extensive verification and validation programme for the UDM has been undertaken. Verification involves testing the implementation of the model equations in the software, while validation involves comparing model predictions against a comprehensive selection of measurements drawn from a database of field experimental trials. Preliminary validation results for the UDM were presented previously at this forum. The present paper describes further work in which model results have been compared against data obtained from two large-scale highly-instrumented field campaigns: the DOE CBNP-sponsored Urban 2000 trial held in Salt Lake City in October 2000(1); and the DTRA-sponsored Mock Urban Setting Trial (MUST) conducted at the Dugway Proving Ground, Utah, in September 2001. Details will also be given of comparisons between the experimental data and output from the HPAC system, incorporating UDM together with the SCIPUFF dispersion model.

Acknowledgements Data from the Urban 2000 experiment are being supplied by the participants, including Joe Shinn and Frank Gouveia (LLNL), Kirk Clawson (NOAA), Jerry Allwine (PNWL) and Chris Biltoft (DPG). Data from the MUST trial are being provided by the participants, including Chris Biltoft (DPG) and Eugene Yee (DRES, Canada).

References (1) Allwine, K. J., J. S. Shinn, G. E. Streit, K. L. Clawson, and M. Brown (2002), ‘An overview of URBAN 2000: A multi-scale field study of dispersion through an urban environment’, Bul. Amer. Meteor. Soc. (in review).