An observational study of the influence of large-scale mountains on air flow and lee cyclogenesis

  • Yong-Seung Chung


It was observed that large-scale topography induced significant orographic modifications in upper airflows. Only 14–26% of upper cold lows were recorded to cross major mountain systems, and the remainder of the cold lows passed them as cold troughs. In the course of prolonged upslope motions over a cordillera, upper-level contours were found to fan out laterally due to the generation of orographic mass-divergence and increased friction, etc. A weak upstream trough was also identified in the upslope side of mountains.

The upper-level windflows over the massifs, the Andes, the Rockies and the East Asian Mountains, tended to be weaker than those observed downstream and upstream, which is not what one would expect from many numerical/physical models. A careful examination indicated that the general decrease of wind flows was associated with orographic vertical motions, horizontal divergence and deflection, vertical shrinking, increased friction, blocking and splitting flows in the large-scale mountains. Jet streams appeared to form more frequently on the lee side than over mountain ranges. Some statistical evidence is shown for the influence of large-scale mountains on upper airflows.


Splitting Flow Major Mountain Asian Mountain Cold Trough Upslope Side 

Beobachtungen des Einflusses großer Gebirgszüge auf die Luftströmungen und auf Lee-Zyklogenese


Die großräumige Topographie kann die Höhenströmung in signifikanter Weise beeinflussen. Nur 14–26% der beobachteten Höhentiefdrucksysteme überquerten größere Gebirgszüge. Der Rest der Höhentiefs übersprang die Gebirge als kalte Tröge. Bei lang anhaltender Hangaufwärtsströmung breiteten sich die Konturlinien seitlich aus. Dies ist auf orographisch bedingte Massendivergenz und auf verstärkte Reibungseinflüsse zurückzuführen. Ein schwacher Trog auf der Luvseite des Gebirges konnte ebenfalls identifiziert werden.

Die Höhenwinde über den Gebirgsketten der Anden, der Rocky Mountains und der Berge Ostasiens waren im allgemeinen schwächer als die Winde stromaufwärts und stromabwärts der Gebirge, im Gegensatz zu den Aussagen numerischer und physikalischer Modelle. Sorgfältige Überprüfung der Daten zeigte, daß die Windabnahme mit orographischen Vertikalbewegungen, horizontaler Divergenz und Strömungsablenkung, vertikaler Kompression von Luftschichten, erhöhter Reibung und der Blockierung der Spaltung der Höhenströmung am Gebirgsmassiv im Zusammenhang stand. Strahlströme traten mit größerer Häufigkeit an der Leeseite der Gebirge auf. Einige statistische Folgerungen über den Einfluß von großen Gebirgszügen auf die Höhenströmung werden aufgezeigt.


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Copyright information

© Springer-Verlag 1977

Authors and Affiliations

  • Yong-Seung Chung
    • 1
  1. 1.Atmospheric Environment ServiceAtmospheric Research DirectorateTorontoCanada

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