Pressure-Driven Channeling Effects in Bent Valleys

M. Kossmann Department of Geography, University of Canterbury, Christchurch, New Zealand

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A. P. Sturman Department of Geography, University of Canterbury, Christchurch, New Zealand

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Abstract

Previous investigations of dynamic channeling of airflow in mountain valleys have been limited to straight valleys, where a constant along-valley component of the synoptic pressure gradient can be assumed. In nature, however, valleys are often curved or bent, that is, composed of segments of different orientations. In these valleys, the along-valley component of the synoptic-scale pressure gradient differs from one segment of the valley to another. This paper presents a simple conceptual model of the changes in wind speed and direction that will occur along the axis of a bent valley because of pressure-driven channeling when adjacent valley segments have a different orientation but constant width and depth. Special emphasis is given to horizontal flow convergence or divergence and compensatory lifting or subsidence within (and above) the valley. The processes are discussed for situations in which differently oriented but straight adjacent valley segments form a bent valley; however, the results can easily be adapted to smoothly curving valleys. The effects of the magnitude of the angle between segments (or, alternately, valley curvature) on the expected flow patterns in the valley are analyzed. The conceptual model derived for flow patterns in curved or bent valleys has a wide range of applications in mountainous terrain, including the dispersion of air pollutants, cloud formation and dissolution, precipitation, bushfire propagation, wind energy potential, and aviation.

Corresponding author address: Andrew P. Sturman, Department of Geography, Corner of Arts and Forestry Roads, University of Canterbury, Private Bag 4800, Christchurch, New Zealand. a.sturman@geog.canterbury.ac.nz

Abstract

Previous investigations of dynamic channeling of airflow in mountain valleys have been limited to straight valleys, where a constant along-valley component of the synoptic pressure gradient can be assumed. In nature, however, valleys are often curved or bent, that is, composed of segments of different orientations. In these valleys, the along-valley component of the synoptic-scale pressure gradient differs from one segment of the valley to another. This paper presents a simple conceptual model of the changes in wind speed and direction that will occur along the axis of a bent valley because of pressure-driven channeling when adjacent valley segments have a different orientation but constant width and depth. Special emphasis is given to horizontal flow convergence or divergence and compensatory lifting or subsidence within (and above) the valley. The processes are discussed for situations in which differently oriented but straight adjacent valley segments form a bent valley; however, the results can easily be adapted to smoothly curving valleys. The effects of the magnitude of the angle between segments (or, alternately, valley curvature) on the expected flow patterns in the valley are analyzed. The conceptual model derived for flow patterns in curved or bent valleys has a wide range of applications in mountainous terrain, including the dispersion of air pollutants, cloud formation and dissolution, precipitation, bushfire propagation, wind energy potential, and aviation.

Corresponding author address: Andrew P. Sturman, Department of Geography, Corner of Arts and Forestry Roads, University of Canterbury, Private Bag 4800, Christchurch, New Zealand. a.sturman@geog.canterbury.ac.nz

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  • Adrian, G. 1988. Synthetic wind climatology evaluated by the non-hydrostatic numerical mesoscale model KAMM. Environmental Meteorology, K. Grefen and J. Löbel, Eds., Kluwer Academic, 397–411.

    • Search Google Scholar
    • Export Citation
  • Eckman, R. M. 1998. Observations and numerical simulations of winds within a broad forested valley. J. Appl. Meteor. 37:206219.

  • Fiedler, F. 1983. Einige Charakteristika der Strömung im Oberrheingraben (Some characteristics of the airflow in the upper Rhine Valley). Wissenschaftliche Berichte des Meteorologischen Instituts der Universität Karlsruhe, Vol. 4, 113–123. [Available from Institut für Meteorologie und Klimaforschung, Universität Karlsruhe/Forschungszentrum Karlsruhe, Kaiserstrasse 12, D-76128 Karlsruhe, Germany.].

    • Search Google Scholar
    • Export Citation
  • Furger, M. 1992. The radiosoundings of Payerne: Aspects of the synoptic dynamic climatology of the wind field near mountain ranges. Theor. Appl. Climatol. 45:317.

    • Search Google Scholar
    • Export Citation
  • Geiger, R. 1961. Das Klima der bodennahen Luftschicht. Friedrich Vieweg and Sohn, 646 pp.

  • Kalthoff, N. and B. Vogel. 1992. Counter-current and channeling effect under stable stratification in the area of Karlsruhe. Theor. Appl. Climatol. 45:113126.

    • Search Google Scholar
    • Export Citation
  • Kaufmann, P. 1996. Regionale Windfelder über komplexer Topographie (Regional windfields over complex topography). Ph.D. dissertation. Paul Scherrer Institut, Villigen, Switzerland, 147 pp. [Available from Information Services, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland.].

    • Search Google Scholar
    • Export Citation
  • Kossmann, M. and A. P. Sturman. 2002. Dynamic airflow channelling effects in bent valleys. Preprints, 10th Conf. on Mountain Meteorology, Park City, UT, Amer. Meteor. Soc., 319–322.

    • Search Google Scholar
    • Export Citation
  • Smedman, A-S., H. Bergström, and U. Högström. 1996. Measured and modelled local wind fields over a frozen lake in a mountainous area. Contrib. Atmos. Phys. 69:501516.

    • Search Google Scholar
    • Export Citation
  • Vogel, B., G. Groß, and F. Wippermann. 1986. MESOKLIP (First special observation period): Observations and numerical simulation—a comparison. Bound.-Layer Meteor. 35:83102.

    • Search Google Scholar
    • Export Citation
  • Weber, R. O. and P. Kaufmann. 1998. Relationship of synoptic winds and complex terrain flows during the MISTRAL field experiment. J. Appl. Meteor. 37:14861496.

    • Search Google Scholar
    • Export Citation
  • Whiteman, C. D. 1990. Observations of thermally developed wind systems in mountainous terrain. Atmospheric Processes over Complex Terrain, Meteor. Monogr., No. 45, Amer. Meteor. Soc., 5–42.

    • Search Google Scholar
    • Export Citation
  • Whiteman, C. D. and J. C. Doran. 1993. The relationship between overlying synoptic-scale flows and winds within a valley. J. Appl. Meteor. 32:16691682.

    • Search Google Scholar
    • Export Citation
  • Wippermann, F. 1984. Air flow over and in broad valleys: Channelling and counter-current. Contrib. Atmos. Phys. 57:92105.

  • Wippermann, F. and G. Groß. 1981. On the construction of orographically influenced wind roses for given distributions for the large-scale wind. Contrib. Atmos. Phys. 54:492501.

    • Search Google Scholar
    • Export Citation
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