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Upstream effects of an Alpine-scale mountain ridge under various flow angles

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Numerical simulations are presented to investigate the upstream effects induced by an east-west-oriented, Alpine-scale mountain ridge under various flow angles. Due to the influence of the Coriolis force, the flow around the mountain is strongly asymmetric in the case of northerly flow, most of the air being deflected to the east. When the ambient flow turns eastward, the flow-splitting point also moves eastward, but this movement does not depend linearly on the large-scale flow direction. Surface friction induces a westward shift of the split point, which is consistent with the friction-induced wind turning in the boundary layer. The force balance in the vicinity of the split point shows that the low-level air flow is in approximate geostrophic balance when surface friction is neglected. The mass field adjusts such that the pressure increases (decreases) towards the mountain to the east (west) of the flow-splitting point, implying westerly (easterly) geostrophic wind.

In der vorliegenden Arbeit werden numerische Simulationen vorgestellt, in denen der stromaufwärtige Einfluss eines ost-west-gerichteten Bergmassivs von der Größenskala der Alpen untersucht wird. Dabei werden verschiedene Anströmwinkel betrachtet. Aufgrund des Einflusses der Corioliskraft ist die Umströmung des Berges bei Nordwind stark asymmetrisch, wobei der Großteil der Luft nach Osten abgelenkt wird. Dreht die Anströmung in Richtung Osten, verlagert sich auch der Stagnationspunkt ostwärts, jedoch hängt diese Verlagerung nicht linear von der Windrichtung ab. Bodenreibung bewirkt eine Verlagerung des Stagnationspunktes nach Westen, was aufgrund der reibungsbedingten Winddrehung in der Grenzschicht auch zu erwarten ist. Die Kräftebilanz in der Umgebung des Stagnationspunktes zeigt, dass die bodennahe Strömung im reibungsfreien Fall näherungsweise geostrophisch balanciert ist. Das Massenfeld stellt sich dabei so ein, dass der Druck östlich (westlich) des Stagnationspunktes zum Berg hin zunimmt (abnimmt), was westlichem (östlichem) geostrophischem Wind entspricht.
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Document Type: Research Article

Publication date: 2004-07-01

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  • Meteorologische Zeitschrift (originally founded in 1866) is the joint periodical of the meteorological societies of Austria, Germany and Switzerland. It accepts high-quality peer-reviewed manuscripts on all aspects of observational, theoretical and computational research out of the entire field of meteorology, including climatology. Meteorologische Zeitschrift represents a natural forum for the meteorological community of Central Europe and worldwide.
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