Numerical simulations of the influence of the Vancouver metropolitan area on summertime atmospheric circulations during EPiCC

In the context of the Environmental Prediction in Canadian Cities (EPiCC) project the Canadian Urban Modeling System is used to investigate the influence of urban environments on mesoscale atmospheric circulations and other meteorological phenomena and processes. Those processes are of particular importance for communication with dwellers about their health and security, such as air quality assessment. The present study focuses on a typical summer event (14-15 August 2008) occurring in the metropolitan area of Vancouver, Canada. The local atmospheric circulations over this city are complex due to its particular geography : the large urban area is surrounded by mountains and by an heterogeneous seashore landscape. Numerical simulations are performed using three nested grids at 2.5km, 1km and 250m over the urban area. Synoptic forcings and intial conditions are provided by the regional operational weather forecast model at the resolution of 15km. Results are compared with surface measurements (energy fluxes sites) and ground based atmospheric soundings, such as measurements from a ceilometer, a tethered balloon deployed during 24 hours, from a Lidar, and from a microwave radiometer. The influence of the city on local circulations (including sea breeze) is analysed using an additional simulation for which the urban surface is removed.