17. Numerical and Experimental Simulations of Local Winds

Local circulation dynamics have a strong impact on the climate evolution as they contribute to the redistribution of energy and scalars from the regional to the global scale. Mesoscale phenomena are driven by surface heat, momentum and moisture fluxes; the intensity and distribution of these forcings can be significantly modified by the urbanization. The present work describes numerical and experimental investigations of the flow over an urban area. The circulation arises from the temperature difference between the city and the suburbs, called the Urban Heat Island (UHI) phenomenon. The three-dimensional non-hydrostatic meteorological model WRF has been used to perform Large Eddy Simulations of the UHI flow and its evolution during the complete day-night cycle. The domain is assumed to be planar in the cross-flow direction and periodic lateral boundary conditions are imposed. The laboratory experiments are conducted in a thermally controlled water tank to simulate an initially stably stratified environment and an electric heater solidal with the bottom of the tank mimics the urban site. Image analysis techniques have been used to reconstruct the velocity fields, while temperatures are acquired by multiple thermocouple arrays. The high resolution of both the numerical and laboratory experiments allows a detailed characterization of both mean and turbulent properties of the UHI circulation. Present numerical and laboratory results, normalized by similarity theory scaling parameters, compare well with literature data.