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The action of high and steep mountains on quasi-geostrophic baroclinic instability and alpine cyclogenesis

Die Wirkung von hohen und steilen Gebirgen auf die quasigeostrophische barokline Instabilität und ihr Zusammenhang mit der alpinen Zyklogenese

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Summary

The modification induced on unstable baroclinic waves by high and steep bottom obstacles of limited horizontal extent is studied in some, mathematically tractable, limiting cases (obstacles with vertical lateral walls blocking the horizontal motion of the fluid). The model atmosphere is assumed quasi-geostrophic and the stability problem is dealt with in the two-level approximation. The results of such analysis show that the action of the obstacle can extend to the entire baroclinic wave unless strongly non-geostrophic effects, relaxing the “stiffness” of the quasi-geostrophic flow near the obstacle, are postulated. The weaknesses of this representation with respect to the problem of Alpine lee cyclogenesis are discussed.

Zusammenfassung

In einigen Fällen, die mathematisch behandelbar sind, wird die Modifikation der baroklinen instabilen Wellen durch hohe und steile Hindernisse von begrenzter horizontaler Ausdehnung untersucht. Für diese Untersuchung dient ein einfaches quasigeostrophisches Zweischichtenmodell. Die Hindernisse besitzen vertikale Wände, die die horizontale Strömung in der unteren Schicht blockieren. Die Ergebnisse derartiger Rechnungen zeigen, daß die Wirkung von Hindernissen auf die baroklinen Wellen in ihrer Gesamtheit ausgedehnt werden kann, falls nicht allzu starke ageostrophische Effekte, die die „Steifheit” der quasigeostrophischen Strömung in der Nähe des Hindernisses mildern, postuliert werden. Abschließend werden noch die Schwächen der Untersuchung im Hinblick auf eine alpine Leezyklogenese diskutiert.

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Speranza, A., Fantini, M. & Buzzi, A. The action of high and steep mountains on quasi-geostrophic baroclinic instability and alpine cyclogenesis. Arch. Met. Geoph. Biocl. A. 33, 245–261 (1985). https://doi.org/10.1007/BF02258477

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Keywords

  • Waste Water
  • Lateral Wall
  • Stability Problem
  • Horizontal Motion
  • Starke