3.2
Further investigations of the "Ora del Garda" valley wind
Massimiliano de Franceschi, University of Trento, Trento, Italy; and G. Rampanelli and D. Zardi
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 very regularly during the summer season, when the thermal forcing is strong enough to produce a pressure imbalance originating along the shoreline of the Garda Lake from which the wind starts blowing in the late morning and then channels along the adjacent Sarca Valley and Lakes Valley till it reaches the Adige Valley north of Trento. The particular features of this wind have been the subject of earlier investigations by Austrian scientists at the beginning of the 20th century, as reported in the well known review by Wagner (1938). The flow structure in the ending part, investigated by means of balloons and double theodolite, appeared as a complex interaction between the upper flow blowing from the Lakes Valley and the Adige Valley wind.
In recent years the attention of the research group of atmospheric physics at the University of Trento has been concentrated at gaining a deeper understanding of the dynamics of the above wind.
After climatological analysis of data collected by meteorological networks operated by different institutions and the measurements performed using a light airplane, it appeared clearly that for a proper comprehension of the phenomenon - and a subsequent modelization - there was a loss of informations at a key site, namely at the end of the Lakes Valley, very close to the ridge from where the "Ora del Garda" flows down into the Adige Valley.
Therefore an additional wheather station has been located in the area where the flow jumps down in the Adige Valley, aimed at collecting useful informations where the maximum wind speed is to be expected. In addition two flights where performed in a fair wheather day when a fully developed diurnal cycle of the "Ora del Garda" was detected. The first flight investigated the whole Lakes Valley in the morning performing four cross-sections along the valley for a detailed picture of the morning evolution of the thermal structure of the flow. The second flight started in the early afternoon and explored the high turbulent region of the confluence where strong mixing was expected.
The results of this measurements are shown using both ground based as also airborne measurements, displaying a clear and regular diurnal cycle of the "Ora del Garda" which can be easily related to the different heating of the valley slopes during the day. Furthermore the data collected by the motorglider allowed a deeper comprehension of the complex thermal structure which occurs at the confluence of the two valleys.
Wagner, A., 1938, Theorie und Beobachtung der periodischen Gebirgswinde [Theory and Observation of Periodic Mountain Winds], Gerlands Beitr. Geophys., 52, 408-449. [English translation: C. D. Whiteman and E. Dreiseitl, 1984]
Session 3, PBL Structure and Circulations III
Monday, 17 June 2002, 1:30 PM-2:44 PM
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