One of the aims of the GAP project within MAP was to investigate the flow through the narrow pass at Brenner. As part of this investigation, 8 automatic weather stations were installed in a line through Brenner across the pass, up to the tops of the nearest mountains immediately to the east of west of the pass (up to 1000 m above the pass). A sodar was also located close to Brenner. Data from the automatic stations are available at 10 minute intervals and from the sodar at 30 minute intervals.

Analysis of the data was concentrated on reconstructing the potential temperature and wind speed cross-sections across the pass. The motivation comes from the fact that it has been shown that relative inclination of the potential temperature and wind speed surfaces can be directly related to the flux of potential vorticity through the pass (Schaer 1993). Thus, identification of these surfaces may provide evidence for the generation, at source, of PV banners (as opposed to detection of the banners downstream of the mountains).

Analysis of the potential temperature has demonstrated a persistent slope upwards towards the eastern side of the pass (i.e. the eastern side is colder). Although this could be due to local differences of radiative heating, it is equally true during day and nighttime. The result is also consistent with previous numerical modelling which suggests that tilting of the potential temperature surfaces is caused by the Coriolis effect. Analysis of the wind speed data suggests that sites in the mid-height of the valley sides are less windy than those on the valley floor or the mountain tops. Similar results exist for both northerly and southerly Foehn flows through the pass, suggesting that these features are not peculiarities of the local flow. When combined, the potential temperature and wind speed analyses lead to an estimate of the potential vorticity flux.