12.7
Apparent Interaction of Urban and Mesoscale Circulation in Salt Lake City during URBAN 2000
Martin J. Leach, LLNL, Livermore, CA; and F. J. Gouveia
The Chemical and Biological National Security Program (CBNP), United States Department of Energy, conducted a field campaign in Salt Lake City in October 2000. The field experiments were conducted in a downtown region of Salt Lake to gather data to evaluate models that are being developed in the CBNP, and spanned scales from the individual building scale to several blocks in the downtown area, to the urban basin in Salt Lake. Arrays of meteorological instruments and tracer samplers were deployed in several Intensive Observations Periods (IOPs) to characterize the thermodynamic and dynamic structure of the circulation, as well as gather data to evaluate dispersion models.
The IOPs during URBAN 2000 were conducted at night, during light wind conditions and with expected stable atmospheric conditions. Buildings, differential surface forcing, and the injection of heat from anthropogenic sources influence the circulation in an urban region. Buoyancy induced and shear generated turbulence due to these urban influences is expected to modify the mean circulation and thermal structure in the urban area. The circulation in the Salt Lake area is further complicated by the presence of complex terrain features in the region, with mountains to the east and southwest and the Great Salt Lake to the northwest of the urban center.
During IOP10, (the night of October 25th to the 26th), the winds were generally observed from the southeast, as expected from climatology. However a wave pattern with a period on the order of 70 to 90 minutes was observed in several of the sonic anemometers that were deployed around the downtown. It is hypothesized that the interaction of the mean flow with drainage flows coming down the canyons to the east and northeast of the city creates inertial gravity waves. The structure of these waves, the mean flow and the urban induced influences is discussed. The resulting wind field controls tracer transport. Observations indicate that the tracer material is transported more slowly in the mean wind direction with greater lateral spread than the modeled transport and dispersion. The relative importance of canopy effects and larger-scale waves in explaining this discrepancy is examined.
Session 12, Urban field projects: URBAN-VTMX
Thursday, 23 May 2002, 1:30 PM-3:44 PM
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