Mesoscale circulation across the Alps: Preliminary simulation of transalp 1990 observations

This paper describes the simulation of the most important characteristics of the flow and temperature fields observed during the tracer release of the 1990 TRANSALP campaign. The goal of the campaign was to follow the tracer from Leventina Valley to the other side of the Alpine range to investigate whether a re-circulation process could occur due to the valley and mountain breezes. Model output is compared with observations of wind and temperature over an entire day (29 September 1990). Meteorological measurements were obtained at a number of ground stations. Vertical wind and temperature profiles were also available. Model initialization was performed using airborne meteorological measurements and profiles from the synoptic station of Payerne. RAMS results correctly describe the generation of the drainage flow during the night and the successive formation of the valley breeze due to the difference in temperature gradients in the various valleys of the domain. Simulated windfields are in general more accurate during the daytime than during the night hours, since vertical variability in stable conditions is more difficult to reproduce.