SUMMARY
A number of tracer experiments were conducted in the Alpine region around the Gothard Pass, both from South to North (1989-1990 campaigns) and from North to South to study the transport and dispersion of trace gas in the atmosphere in complex topography. Model simulations were then applied to reproduce the measured meteorological observations and tracer concentration data.
TRANSALP consisted of 3 tracer field experiments carried out in the Ticino area (southern Switzerland) in the years 1989, 1990 and 1991. The experiments were designed to study the transport and diffusion of trace gases over the very complex Alpine topography. In September 1989, the first campaign was performed under thermally induced up-valleys flow. In the second experiment (September-October 1990), the overflow of the tracer plume over the first alpine barrier at the Gotthard, Lucomagno and Nufenen passes was studied in the S-N direction. The third campaign (September 1991) was focussed on the N-S air flow across the Alps, over an area that was considerably larger than in the previous campaigns. The results and knowledge gained from each experiment were used to improve logistics and design of the following experiment . The data collected are stored in a data bank, which is available to evaluate mesoscale atmospheric transport and dispersion models in complex terrain. The results of the experiments gave evidence of the occurrence of a transalpine exchange of air constituents, both in N-S and S-N directions. Some significant results obtained in the simulation of the flow field and tracer concentration during some of the experiments are included. They prove the model capability of reproducing the main features of the tracer gases dispersion. However, the very complex topography limits the interpretation and extrapolation of some of the results. Further, only limited investigation of the nocturnal drainage flow was performed during the campaigns. These drawbacks indicate that a larger number of measurements would have been required, in particular for the analysis of the 3-D turbulence field and its temporal evolution.
PARTICIPANTS
JRC-Ispra; Germany: KfK Karlsruhe; Switzerland: P.S. Institute; Italy: CNR Torino, ENEL