FURTHER INVESTIGATIONS OF THE “ORA DEL GARDA” VALLEY WIND

*In the present work the results obtained from recent investigations concerning a local wind system, the so called "Ora del Garda", are presented. The latter flows regularly on sunny days during the summer season, when thermal forcing is strong enough to produce an appreciable pressure gradient throughout the valleys connecting the area North of the Garda Lake to the Adige Valley. The wind originates along the shoreline of Garda Lake (65 m a.m.s.l.) in the late morning, as a typical coast breeze, and then channels along the adjacent Sarca Valley and the Valle dei Laghi till it reaches the Adige Valley (whose floor is about 200 m a.s.l. high) North of Trento, flowing over an elevated saddle (about 600 m a.s.l.). The final stage of the wind results in a strong air mixing connecting the Valle dei Laghi to the Adige Valley. The particular features of this wind stimulated earlier investigations by Austrian scientists at the beginning of the 20th century, as reported in a well known review by Wagner (1938). The flow structure in the ending part, investigated by means of pilot balloons and double theodolite, appeared as a complex interaction between the upper flow blowing from the Valle dei Laghi and the Adige Valley diurnal wind (Figure 1). After climatological analysis of data collected by meteorological networks operated by different institutions (Baldi et al., 1999) and measurements performed using a light airplane, it appeared clearly that for a deeper understanding of the phenomenon and subsequent modelling further information were needed at a key site, namely at the end of the Valle dei Laghi, very close to the ridge from where the "Ora del Garda" flows down into the Adige Valley. Therefore an additional fully automated weather station has been located in that area (indicated with a star in Figure 1) where maximum wind speed was expected. The station provided measurement of wind speed and direction at 3 m above ground, air pressure, temperature and humidity, global and net radiation. All these quantities are collected as 10 minutes averages, also storing maximum and minimum value over the averaging period. In addition to ground based measurements, two flights were performed with an equipped light airplane during a fair weather day when a fully developed diurnal cycle of the "Ora del Garda" was detected. The