Boundary-Layer Meteorology

, Volume 74, Issue 1–2, pp 131–161 | Cite as

Modification of air flow over an escarpment — Results from the Hjardemål experiment

  • Stefan Emeis
  • Helmut P. Frank
  • Franz Fiedler
Article

Abstract

Mean flow, turbulence, and surface pressure measurements over an escarpment are presented. The speed-up in the mean wind field shows the known dependence on stratification. Cross-sections of the standard deviation of horizontal and vertical wind components and of the friction velocity are derived from the data and compare favorably with the numerical model of Zeman and Jensen (1987). The modification of turbulent power spectra at intermediate frequencies can be explained by rapid distortion theory. At very low frequencies, there is a quasi-stationary response to the disturbance. Except for speed-up and standard deviations of the wind components, which are also shown for downslope wind, all results in this paper refer to upslope winds.

An analysis of the vertical momentum flux reveals that upstream of the escarpment, most of the flux is transported in sweeps of fast, sinking motion to the ground. Downstream of the escarpment, ejections of slow, rising motion dominate the turbulent transport.

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References

  1. Adrian, G. and Fiedler, F.: 1991 ‘Simulation of Unstationary Wind and Temperature Fields over Complex Terrain and Comparison with Observations’,Beitr. Phys. Atmosph. 64, 27–48.Google Scholar
  2. Astley, R. J.: 1977, ‘A Finite Element Frozen Vorticity Solution for Two-Dimensional Wind Flow over Hills’,6th Australasian Conf. on Hydraulics and Fluid Mechanics, Adelaide, Australia, 443–446.Google Scholar
  3. Batchelor, G. K. and Proudman, I.: 1954, ‘The Effect of Rapid Distortion of a Fluid in Turbulent Motion’,Q. J. Mech. Appl. Math. 7, 83–103.Google Scholar
  4. Bowen, A. J.: 1979, ‘Full Scale Measurements of the Atmospheric Turbulence over Two Escarpments’, in J. E. Cermak (ed.),Wind Engineering: Proc. 5th Internat. Conf., Fort Collins, Pergamon, 161–172.Google Scholar
  5. Bowen, A. J. and Lindley, D.: 1974 ‘Measurements of the Mean Wind Flow Over Various Escarpment Shapes’,5th Australasian Conf. on Hydraulics and Fluid Mechanics, Canterbury, New Zealand, 211–219.Google Scholar
  6. Bowen, A. J. and Lindley, D.: 1977, ‘A Wind-Tunnel Investigation of the Wind Speed and Turbulence Characteristics Close to the Ground over Various Escarpment Shapes’,Boundary-Layer Meteorol. 12, 259–271.Google Scholar
  7. Britter, R. E., Hunt, J. C. R. and Mumford, J. C.: 1979, ‘The Distortion of Turbulence by a Circular Cylinder’,J. Fluid Mech. 92, 269–301.Google Scholar
  8. Chen, F.: 1990, ‘Turbulent Characteristics over a Rough Natural Surface Part II: Responses of Profiles to Turbulence’,Boundary-Layer Meteorol. 52, 301–311.Google Scholar
  9. Courtney, M., Højstrup, J., and Jensen, N. O.: 1990, A Field Study of Flow over an Escarpment’,9th Symposium on Turbulence and Diffusion, AMS, Roskilde (DK), April 30–May 3, 1990, 363–366.Google Scholar
  10. Emeis, S., Courtney, M. S., Højstrup, J., and Jensen, N. O.: 1993,Hjardemål Experiment Data Report, Risø National Laboratory, Risø-M-2289(EN), and Sonderforschungsbereich 210, Univ. Karlsruhe, Germany, Nr. SFB210/E/77, 126 pp. (available from Risø National Laboratory, Library, P.O. Box 49, DK-4000 Roskilde)Google Scholar
  11. Fiedler, F.: 1975, ‘Turbulenter Spannungs-und Deformationstensor in der Prandtl-Schicht’,Beitr. Phys. Atmosph. 48, 290–300.Google Scholar
  12. Frank, H., Heldt, K., Emeis, S., and Fiedler, F.: 1993, ‘Flow over an Embankment: Speed-up and Pressure Perturbation’,Boundary-Layer Meteorol. 63, 163–182.Google Scholar
  13. Horst, T. W.: 1973, ‘Corrections for Response Errors in a Three-Component Propeller Anemometer’,J. Appl. Meteorol. 12, 716–725.Google Scholar
  14. Jackson, P. S. and Hunt, J. C. R.: 1975, ‘Turbulent Wind Flow over a Low Hill’,Q. J. R. Meteorol. Soc. 101, 929–955.Google Scholar
  15. Jensen, N. O.: 1983, ‘Escarpment Induced Flow Perturbations, a Comparison of Measurements and Theory’,J. Wind Eng. Ind. Aerodyn. 15, 243–251.Google Scholar
  16. Jensen, N. O., Troen, I., and Højholt, P.: 1990, ‘Model Comparisons with Flow over an Escarpment’,9th Symposium on Turbulence and Diffusion, AMS, Roskilde (DK), April 30–May 3, 1990, 413–416.Google Scholar
  17. Kaimal, J. C., Wyngaard, J. C., Izumi, Y., and Coté, O. R.: 1972, ‘Spectral Characteristics of Surfacelayer Turbulence’,Q. J. R. Meteorol. Soc. 98, 563–589.Google Scholar
  18. Kreyszig, E.: 1988,Statistische Methoden und ihre Anwendungen, 7. ed., Vandenhoek & Ruprecht, Göttingen, 462 pp.Google Scholar
  19. Mason, P. J.: 1986, ‘Flow over the Summit of an Isolated Hill’,Boundary-Layer Meteorol. 37, 385–405.Google Scholar
  20. Mason, P. J. and King, J. C.: 1985, ‘Measurements and Predictions of Flow and Turbulence over an Isolated Hill of Moderate Slope’,Q. J. R. Meteorol. Soc. 111, 617–640.Google Scholar
  21. McBean, G. A.: 1974, ‘The Turbulent Transfer Mechanisms: A Time Domain Analysis’,Q. J. R. Meteorol. Soc. 100, 53–66.Google Scholar
  22. Olesen, H. R., Larsen, S. E., and Højstrup, J.: 1984, ‘Modelling Velocity Spectra in the Lower Part of the Planetary Boundary Layer’,Boundary-Layer Meteorol. 29, 285–312.Google Scholar
  23. Panofsky, H. A., Larko, D., Lipschutz, R., Stone, G., Bradley, E. F., Bowen, A. J., and Højstrup, J.: 1982, ‘Spectra of Velocity Components over Complex Terrain’,Q. J. R. Meteorol. Soc. 108, 215–230.Google Scholar
  24. Panofsky, H. A. and Dutton, J. A.: 1984,Atmospheric Turbulence, Models and Methods for Engineering Applications, Wiley Interscience, John Wiley & Sons, New York, 397 pp.Google Scholar
  25. Taylor, P. A., Mason, P. J., and Bradley, E. F.: 1987, ‘Boundary Layer Flow over Hills’,Boundary-Layer Meteorol. 39, 107–132.Google Scholar
  26. Townsend, A. A.: 1976,The Structure of Turbulent Shear Flow, 2nd ed., Cambridge Univ. Press, 429 pp.Google Scholar
  27. Zenman, O. and Jensen, N. O.: 1987, ‘Modification of Turbulence Characteristics in Flow over Hills’,Q. J. R. Meteorol. Soc. 113, 55–80.Google Scholar

Copyright information

© Kluwer Academic Publishers 1995

Authors and Affiliations

  • Stefan Emeis
    • 1
  • Helmut P. Frank
    • 1
  • Franz Fiedler
    • 1
  1. 1.Institut für Meteorologie und Klimaforschung Kernforschungszentrum Karlsruhe/UniversitätKarlsruheGermany

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