DISPERSION MODELING IN COMPLEX TERRAIN USING WIND CLIMATOLOGIES

If annual mean values of concentration in complex terrain have to be d etermined, a representative wind climatology, which reflects local flo w characteristics, is needed. This gives rise to two problems. First, observational data representative of the dispersion area are frequentl y not to hand. Second, the flow in the dispersion area itself may show a significant spatial structure, so transport is affected by varying wind speeds and directions. Both problems may be overcome by determini ng local wind climatologies by numerical modelling. The concept is to deduce terrain-dependent wind climatologies near the ground from the g eostrophic wind climatology valid for the source region. Surface obser vations from the model area may also be included if available. If resu lting surface wind climatologies are similar to each other within the dispersion area, then the variation of flow caused by the terrain stru cture need not be considered when modelling dispersion. In this case, Gaussian plume modelling may be used. If, however, the calculated wind climatologies differ significantly within the model area, then disper sion modelling has to take into account the spatial structure of the f low. This requires a Eulerian or a Lagrangian approach, because simple r methods of dispersion modelling are not capable of considering three -dimensional flow characteristics.