The refinement of a meteorological pre-processor for the urban environment

Abstract

The meteorological pre-processor used routinely at the Finnish Meteorological Institute (FMI) has been modified in order better to represent urban conditions. We have re-evaluated the roughness length, introduced the zero displacement height and divided the surface layer into a roughness sub-layer and an inertial sub-layer. The friction velocity and Monin-Obukhov length are evaluated using an empirically developed, exponential, Reynolds stress profile in the roughness sub-layer. The effect of these modifications has been studied by computing the dispersion parameters used in the urban dispersion modelling system UDM-FMI and comparing the revised parameters with the previous model computations.