Pollutant Tansport and Dispersion in Highly Complex Terrain with a NWP – Particle Dispersion Model Combination

In the present study the sensitivity of pollutant dispersion in highly complex terrain to the turbulence parameterization is investigated. The modeling system is the COSMO numerical weather prediction model coupled with a Lagrangian Particle Dispersion Model (LPDM). The simulated cases are from the TRANSALP-89 tracer experiments, which took place within a narrow (bifurcating) alpine valley. In the normal mode the particle model receives the meteorological information from COSMO and determines the dispersion parameters using standard boundary layer scaling approaches based on turbulent kinetic energy. A new scaling approach by Weigel et al. (2007), which has been proposed for steep and narrow alpine valleys, is being tested in the present study. This new scaling approach is introduced in the interface between COSMO and LPDM. It is compared to results of a classical similarity theory approach and to the operational coupling type. First the ability of the COSMO model to simulate the valley wind system is assessed using several meteorological surface stations from the TRANSALP setup. The dispersion simulation is evaluated with the observed concentrations at 25 surface samplers. The sensitivity of the modeling system towards soil moisture, horizontal grid resolution, and boundary layer height determination is investigated. It is shown that if the flow field is correctly reproduced, the new scaling approach improves the tracer concentration simulation when compared to the classical coupling methods.