Summary
An investigation is undertaken of the boundary-layer structure of the late afternoon and evening wind profiles above a gently sloped incline of a valley on the Swiss Plateau. Wind maxima of up to 6 m/s are observed at height of the order of 100–150 m above the surface. From a comparison with other related studies it is concluded that these maxima cannot be attributed entirely to the gravity drainage flow. In addition, a good correlation is found between the simplified Scorer parameter,\(l = N\sqrt u \), and the difference between wind maximum and windspeed above the crest height for the late afternoon. Therefore it is argued that mechanical interaction of the hills with the mesoscale wind-field dominates the observed wind structure. The need of an adequate representation of this phenomenon in PBL-models for complex topography is stressed.
Zusammenfassung
Die Struktur spätnachmittäglicher und abendlicher Windprofile in der planetaren Grenzschicht über einem schwachgeneigten Hang eines Tales des Schweizerischen Mittellandes wird untersucht. Es werden Windmaxima mit einer Stärke bis zu 6 m/s in einer Höhe von 100–150 m über Grund beobachtet. Ein Vergleich mit Ergebnissen, die sich in der Literatur finden, zeigt, daß these Maxima nicht ausschließlich dem thermisch induzierten Kaltluftabfluß zugeordnet werden können. Im weiteren wird festgestellt, daß spätnach-mittags eine gute Korrelation besteht zwischen dem vereinfachten Scorer-Parameter\(l = N\sqrt u \) und der Differenz zwischen Windstärkemaximum und der Windgeschwindigkeit oberhalb Kretenhöhe. Es wird daher geschlossen, daß die mechanische Wechselwirkung zwischen den Hügelzügen und dem mesoskaligen Windfeld im wesentlichen die Windstruktu rbestimmt. Es wird betont, dasB in Modellen der planetaren Grenzschicht fiber komplexem Gelände dieser Sachverhalt angemessene Berücksichtigung finden sollte.
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Gygax, H.A. Evidence for mechanical induced downslope wind in the lee of gently sloped hills. Arch. Met. Geoph. Biocl. A. 34, 167–177 (1985). https://doi.org/10.1007/BF02277446
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DOI: https://doi.org/10.1007/BF02277446