Wind Flow And Dispersion Modeling Over TerrainHigh Complexity

In a terrain of high complexity, such as mountain regions or local scale building structures, the topography is characterized by irregularities covering a wide range of dimensions and/or sizes. The irregularities can influence considerably the pressure gradients and induce mechanical effects on the wind systems. The air/ground interaction in terms of energy exchange can become highly variable due to rapid changes on surface orientation or altitude or even land use. As a sequence the wind system evolution is usually of multiscale character both in space and time especially in the case of thermally developed winds. A pollutant release advected by such multiscale wind systems can generate a quite complicated air pollution pattern. The present paper discusses the problems that a modeler has to face when treating applications with terrain of high complexity such as space resolution, ground discretization, subgrid modeling etc. The discussion is based on the extensive experience of the Environmental Research Laboratory of NCSR "DEMOKRITOS" in treating domains of this type, as reflected on the applications of the DEMOKRITOS Transport Code System (DETRACT) to specific problems.