Fifth Conference on Urban Environment


Further Evaluation of an Urban Canopy Parameterization Using VTMX and URBAN 2000 Data

Hung-Neng S. Chin, LLNL, Livermore, CA; and M. J. Leach

An urban canopy parameterization (UCP) is evaluated in a three-dimensional weather forecast model (COAMPS) to assess the urban impact on the structure of the lower atmosphere. This parameterization accounts for the effects of building drag, turbulent production, radiation balance, anthropogenic heating, and building rooftop heating and cooling. USGS land-use data with different resolutions (30m and 200m) are utilized to derive urban infrastructure and urban surface properties needed for driving the UCP. Both conventional surface station measurements and tracer concentration observations are used to gauge the performance of UCP on the sub-grid building effect. A series of sensitivity experiments are performed to gain understanding of the urban impact in the mesoscale model for an intensive observational period with stronger wind (IOP-10). Sensitivity experiments show that for this weak urban heat island case, the model horizontal grid resolution is important in simulating the elevated inversion layer. Results further reveal that the depth of the predicted urban boundary layer is about twice the urban canopy height and this ratio appears to be independent of the resolution of land-use data. The root mean square errors of the predicted wind and temperature with respect to urban surface station measurements exhibit large discrepancies in IOP-10. However, the close agreement of modeled tracer concentration with observations appears to support the modeled urban impact on the wind direction shift and wind drag effects. This result confirms the finding of an earlier observational study that an urban environment cannot be properly represented by single-station measurements. To generalize these urban effects, all IOPs with tracer releases (six in total) are used to evaluate the overall performance of UCP. Details of results will be presented in the meeting.

____________________________ This work was conducted under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract W-7405-Eng-48.

Corresponding author address: Dr. Chin, Lawrence Livermore National Laboratory, P. O. Box 808 (L-103), Livermore, CA 94551, Email:

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Session 16, canopy—atmosphere coupling
Thursday, 26 August 2004, 4:15 PM-5:00 PM

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