Simulation of flow and turbulence in the Phoenix area using a modified urbanized mesoscale model

Abstract

ABSTRACTThe urban canopy parameterization (UCP) of Dupont et al. implemented in the MM5v3.7 mesoscale meteorological modelling system (MM5‐UCP‐Basic) is evaluated against the non‐urbanized model (MM5‐NoUCP) using measurements taken in urban Phoenix during two field studies. In general, MM5‐UCP‐Basic improved the predictions of typical meteorological parameters. Nevertheless, significant discrepancies still exist between observations and the predictions of MM5‐UCP‐Basic, and new parameterizations and land‐use classes are introduced to improve the model performance. Anthropogenic heat flux from buildings and roadways is also included. The land‐use classes in the improved model (MM5‐UCP‐MOD) represent roadways and rivers, in addition to five classes of buildings identified in MM5‐UCP‐Basic. New parameterizations include those for momentum roughness, velocity decay during evening transition, and heat and momentum diffusivities for the nocturnal period that account for different heat and momentum transfer rates under stable atmospheric conditions. Five nested grid domains are used for simulations, with the highest resolution (1 km) implemented in the two UCP versions. In general, substantial improvements in the prediction of wind speed, temperature (especially during the night time), and momentum flux as well as a smaller improvement in the heat flux are noted, pointing to possible further enhancement to model performance by including improved physics in the model.