Modelling of meteorological conditions at an urban scale for the PUMA campaigns

In this paper, a comparison of modelled and observed surface wind and temperature for two campaigns of the PUMA (Pollution of Urban Midlands Atmosphere) project is presented. The Regional Atmospheric Modelling System (RAMS) was configured for the West Midlands conurbation (WM), UK, to have two nested grids with a mesh size of 2 km for the inner grid which is embedded in the outer grid with a mesh size of 8 km. Statistical evaluation of the model results against observational data of wind speed, direction and temperature was conducted. In general, the model's performance is better in the summer campaign than in the winter campaign. The results suggest that the quality of the prediction is sensitive to whether or not cloud cover is captured by the model under winter conditions. Although the topography of the region is relatively flat, some spatial patterns of wind and temperature may exist under stagnant conditions during the summer and winter seasons. Under summer conditions, the spatial patterns are associated with convective eddies or rolls during daytime, while under winter conditions, the spatial patterns are closely linked to stability and topography. The modelled results of such winter conditions for the inner grid reveal subtle spatial patterns at a scale smaller than 10 km near hills and valleys with differences in elevation of a few hundred metres. Copyright (C) 2007 Royal Meteorological Society.