Modelisation of the Three-Dimensional Wind Field above the Alpine Region

Abstract

Dispersion and transport of atmospheric pollutants over complex terrain have been recognized as an important research item in the frame of EUROTRAC. The transboundary transport evaluated by conventional models (e.g. EMEP) is largely uncertain particularly for the Alpine countries where orographic barriers of an average height of 3500 m (Western Alps) strongly modify the air masses circulation. The frequent decoupling of the low-level circulation from the synoptic-scale flow is a well known fact in the Po valley and in its adjacent pre-Alpine region (Giuliacci, 1985; Ambrosetti et al.,1987). The closed low-level circulation, particularly downwind of the Western Alps which include the highest summits, can lead to high concentrations of pollutants, especially during periods of thermal inversion in the winter. The presence of densely populated areas on both sides of the Alps and this particular climatology were some of the motivations of a research proposal named TRANSALP (Transport of air trace constituents over the Italian-Swiss Alps) including contributions from laboratories of Italy, Switzerland, West Germany and Denmark; this proposal has been very recently accepted among the EUROTRAC projects.