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

  • Yong-Seung Chung
Article

Summary

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.

Keywords

Splitting Flow Major Mountain Asian Mountain Cold Trough Upslope Side 

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

Zusammenfassung

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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References

  1. 1.
    Bjerknes, V., J. Bjerknes, H. Solberg, and T. Bergeron: Physikalische Hydrodynamik, S. 488–493. Berlin: Springer. 1933.Google Scholar
  2. 2.
    Bolin, B.: On the Influence of the Earth's Orography on the General Character of the Westerlies, Tellus,2, 184–195 (1950).Google Scholar
  3. 3.
    Chung, Y.-S.: On the Behaviour of Upper Airflows in Large-Scale Mountains. Presented at the Symposium 18-GARP 1 st Objective: Weather Predictability, 16th Gen. Ass., IUGG, Grenoble, 1975.Google Scholar
  4. 4.
    Chung, Y.-S.: On the Orographic Influence and Lee Cyclogenesis in the Andes, the Rockies and the East Asian Mountains. Arch. Met. Geoph. Biokl., Ser. A,26, 1–12 (1977).Google Scholar
  5. 5.
    Chung, Y.-S., and E. R. Reinelt: On Cyclogenesis in the Lee of the Canadian Rocky Mountains. Arch. Met. Geoph. Biokl., Ser. A,22, 205–226 (1973).Google Scholar
  6. 6.
    Chung, Y.-S., K. D. Hage, and E. R. Reinelt: On Lee Cyclogenesis and Airflow in the Canadian Rocky Mountains and the East Asian Mountains. Mon. Wea. Rev.,104, 879–891 (1976).CrossRefGoogle Scholar
  7. 7.
    Crutcher, H. L., and J. M. Meserve: Selected Level Heights, Temperature and Dew Points for the Northern Hemisphere. NAVAIR 50-IC-52. U. S. Naval Wea. Serv., 1970.Google Scholar
  8. 8.
    Edelmann, W.: An Analytical Solution for Stationary Barotrophic Flow Crossing a Meridional Mountain Barrier. Beitr. Phys. Atm.,45, 87–120 (1972).Google Scholar
  9. 9.
    Egger, J.: Numerical Experiments on Lee Cyclogenesis. Mon. Wea. Rev.102, 847–860 (1974).CrossRefGoogle Scholar
  10. 10.
    Hage, K. D.: On Summer Cyclogenesis in Western Canada Associated With Upper Cold Lows. Sci. Report No. 1 Contract No. AF 19(604)-2179. The Univ. of Chicago, 1957.Google Scholar
  11. 11.
    Holmboe, J., G. E. Forsythe, and W. Gustin: Dynamic Meteorology, pp. 326–328. New York: John Wiley, and Sons Inc. 1945.Google Scholar
  12. 12.
    Jenne, R. L., H. L. Crutcher, H. van Loon, and J. J. Taljaard: Climate of the Upper Air: Southern Hemisphere, Vol. III. Vector Mean Geostrophic Winds. NCAR-NT/STR-58, 1971.Google Scholar
  13. 13.
    Joint GARP Organizing Committee (ICSU/WMO): Final Report of the Study Conference on the Air Flow Over and Around Mountains (J. Charney et al.). Belgrade, 1976.Google Scholar
  14. 14.
    Kasahara, A.: The Dynamical Influences of Orography on the Large-Scale Motion of the Atmosphere. J. Atmos. Sci.,23, 259–271 (1966).CrossRefGoogle Scholar
  15. 15.
    Kawata, Y.: The Influence of the Rocky Mountains on Non-Steady Isobaric Height Patterns. J. Meteor. Soc. Japan.35, 174–183 (1957).Google Scholar
  16. 16.
    Lester, P. F.: A Study of the Structure and Behaviour of Jet Streams Over the Western United States. Colorado State Univ., Fort Collins, 1969.Google Scholar
  17. 17.
    Manabe, S., and T. B. Terpstra: The Effects of Mountains on the General Circulation of the Atmosphere as Identified by Numerical Experiments. J. Atmos. Sci.,31, 3–42 (1974).CrossRefGoogle Scholar
  18. 18.
    Meteorological Institute: Eursia Historical Weather Maps for Jan.-Oct. 1958 and Nov.-Dec. 1959. Central Weather Bureau, Peking, 1964.Google Scholar
  19. 19.
    Meteorological Office: Daily Aerological Cross-Sections at Latitude 30°N, During the International Geophysical Year Period. March, June, September and December 1958. Met. O. 766 d, London, 1968.Google Scholar
  20. 20.
    Namias, J., and P. F. Clapp: Confluence Theory of the High-Tropospheric Jet Stream. J. Meteor.,6, 330–336 (1949).Google Scholar
  21. 21.
    Nicholls, J. M.: The Airflow Over Mountains, Research 1958–1972. W. M. O. Tech. Note No. 127, 1973.Google Scholar
  22. 22.
    Queney, P.: The Problem of Airflow Over Mountains. A Summary of Theoretical Studies. Bull. Amer. Meteor. Soc.,29, 16–26 (1948).Google Scholar
  23. 23.
    Reiter, E. R.: Jet-Stream Meteorology, Ch. 6 and 7, pp. 324–409. Chicago: Univ. Press. 1963.Google Scholar
  24. 24.
    Scorer, R. S.: Theory of Waves in the Lee of Mountains. Quart. J. R. Met. Soc.,75, 41–56 (1949).Google Scholar

Copyright information

© Springer-Verlag 1977

Authors and Affiliations

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

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