Assessment of the Canadian urban modeling system using Joint Urban 2003 observations over Oklahoma City

The new Canadian urban modeling system developed at Environment Canada to better represent surface and boundary layer processes in urban environments, includes the Town Energy Balance urban canopy parameterization. The new modeling system has been run over Oklahoma City (OK, United States) within the framework of the Joint Urban 2003 field experiment (July 2003). Simulations with 250-m grid sizes have been performed for daytime and nighttime intensive observational periods (IOP6 and IOP9) of the experiment. An extensive evaluation against near-surface and upper-air observations indicates a realistic simulation of the urban micro-climate for various urban areas, in particular the positive urban heat island (UHI) effect during the night as well as the negative UHI in the morning. Sensitivity tests highlight the impact of dry soil conditions in and around Oklahoma City on the evolution of the daytime convective boundary layer, and also underline the role of the nocturnal low-level jet in vertically extending the UHI and developing a mixed layer in the first 200 meters above Oklahoma City.