A city can strongly modify the boundary layer structure. The two most important causes are mechanical (drag and turbulence induced by buildings), and thermal (shadowing and trapping of radiation in urban canyons as well as thermal properties of the urban materials). A correct parameterization of these effects in mesoscale models is crucial for a good reproduction of pollutant dispersion.Aim of this contribution is, firstly, to show that a detailed urban parameterization implemented in a mesoscale model is able to reproduce the observed nocturnal structure of the urban boundary layer, and, then, to use the model as a tool to understand the importance of different parameters (wind speed, urban morphology, rural soil moisture) and the mutual interactions between mechanical and thermal factors, using the technique of Stein and Alpert (1993).
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