Local winds in the upper Rhone Valley |
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| Authors: | B Neininger and O Liechti |
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| Institution: | (1) Laboratory for Atmospheric Physics, Swiss Federal Institute of Technology, ETH Hoenggerberg, CH-8093 Zürich, Switzerland |
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| Abstract: | Balloon soundings during July and August 1979, 1981 and 1982 showed the vertical structure of the flow in the upper Rhone Valley. Between the low level winds up to a height of about 2000 m a s l and the gradient winds above 3000 m a s l, in 73 % of the 107 ascents, a counterflow was detected. It appeared more often in connection with down-valley flow (89 %) than with up-valley flow (38 %) above the ground. This flow pattern was found to be almost unaffected by the upper winds.The horizontal structure of the wind was studied with 3 ground weather stations that were separated 2 and 5 km along the valley axis. Up-valley winds occur in the average of 32 fair weather days only around noon. During the time of strongest up-slope winds, the valley wind is down-valley. That was already found in the climatic mean by Yoshino (1964) with wind shaped trees.As the wind recordings show, the down-valley flow develops first at the end of the valley and the resulting convergence zone moves down with about 2 m/s until it stops above a characteristic step near Fiesch (Fig 6).An explanation can be given by differential heating within the Rhone Valley itself and due to neighbouring valleys. The measured differences in the diurnal pressure changes of 5 stations is consistent with that hypothesis. |
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