MODELING URBAN CANOPY AND TERRAIN FOR TRANSPORT-DIFFUSION SIMULATIONSAT SUB-MESOSCALES

Studies of the transport and dispersion of atmospheric pollutants at t he scale of a part or the whole of an urban agglomeration require nume rical simulations over domains between a few kilometres and a few tens of kilometres (sub-meso scale to meso-gamma scale). Current computer capabilities do not allow for a grid resolution sufficiently fine to e xplicitly simulate the flows at the scale of urban constructions (buil dings, streets, trees, etc.) which are known to have a large influence on the dynamics and thermodynamics of the lowest atmospheric layers. It is then necessary to replace the real soils and these constructions by 'apparent grounds'. In turn, this implies the development of param etric relationships to express the fluxes of momentum, sensible heat, and latent heat or water vapour, as a function of the characteristic p arameters of the apparent ground. In addition, it is necessary to deve lop methods and numerical tools to allow the generation of maps of the se ground fluxes over the city, from the analysis of these functions a nd the characteristics of the city quarters drawn from geographical/ge ometrical databanks.