Relative impact of two urban canopy parameterizations on coastal urban processes

The impact of two different urban canopy parameterizations (UCP) on coastal urban processes is examined for a sea-breeze event in the New York City area using the Coupled Ocean Atmosphere Mesoscale Prediction System* (COAMPSŪ) developed by the Naval Research Laboratory (NRL). The two parameterizations are the simpler, single-level UCP originally developed by Brown and Williams (1998) and a more sophisticated drag-force and thermodynamic canopy approach of Dupont et al. (2003).

COAMPSŪ is a complete three-dimensional mesoscale prediction system that has been used for operational mesoscale forecasting since 1996. It consists of atmospheric and ocean data assimilation with data quality control, analysis, initialization, and a nonhydrostatic atmospheric forecast model with an imbedded passive tracer model. Because urban infrastructure can significantly modify surface and atmospheric dynamic and thermodynamic properties, effects due to building drag, turbulent production, radiation balance, and anthropogenic and rooftop heating should be included in a mesoscale model. The impacts of parameterized urban processes affect the accuracy of mesoscale prediction, and hence will be assessed relative to the degree of sophistication required for each parameterization, as well as the level of complexity required for the urban databases.

COAMPSŪ is configured with 5-nests centered on Manhattan with highest horizontal resolution of 0.444 km. High-resolution (250-m) databases are used to determine building morphology. Analyzed sea surface temperatures are determined on the native grids from the COAMPSŪ Ocean Data Assimilation (CODA) using standard MCSST, ship, and profile observations. In addition, high-resolution time-varying (hourly) sea surface temperatures provided by the Stevens Institute of Technology New York Harbor Observing and Prediction System (NYHOPS) have been prepared for nest 4 (1.33 km resolution) and nest 5.

Simulations with COAMPSŪ at 0.444-km horizontal resolution with the two different parameterizations of urban processes are compared to available surface observations to assess the impacts of the UCP on sea breeze initiation, evolution and modification. The impact of the urban canopy layer on mesoscale plume transport, as well as its development and evolution, will be shown using COAMPSŪ simulations with the imbedded passive tracer model. Model tracer releases occurring both within and above the urban canopy will be compared to assess the impact of coastal urban boundary layer structure on plume transport. --------------- *COAMPSŪ is a registered trademark of the Naval Research Laboratory.