Monday, 9 June 2008
A highly urbanized (by use of the Martilli-Dupont-Taha surface, SBL, and PBL TKE schemes) version of MM5 has improved its performance in simulation of Houston and New York City (NYC) urban heat island (UHI) and PBL transport characteristics. In particular, the EPA version of MM5 (called uMM5 at SJSU) better simulates canopy-layer and PBL mean and turbulent met fields by use of a drag-force approach in lieu of typical Monin-Oblukov roughness-length theory. The model also accepts available fine-resolution input parameters obtained from a high resolution urban LU/LC data set collected by airborne lidar and analyzed by S. Burian at the University of Utah. The model was used with data from both the Texas2000 ozone field study and the NYC DHS/UDS MSG tracer releases. Results from the uMM5 and standard MM5 models showed more accurate UHIs and urban transport winds from the uMM5 simulations. In particular, the Houston low-speed results showed a stronger (and more accurate) daytime UHI, which was responsible for the observed convergence of ozone into the city. The high-speed NYC results showed no UHI, but a building induced barrier effect that produced divergent transport and downward vertical velocities over the city during the tracer release periods. The uMM5 met fields from the Houston results are being used as inputs into the CAMx photochemical model, while those from the NYC results will be used to provide time and space varying boundary conditions to a variety of rapid and CFD ER urban canopy and canyon flow and dispersion models.
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