Boundary-Layer Meteorology

, Volume 47, Issue 1–4, pp 349–377

Observation of organized structure in turbulent flow within and above a forest canopy

  • W. Gao
  • R. H. Shaw
  • K. T. Paw U


Ramp patterns of temperature and humidity occur coherently at several levels within and above a deciduous forest as shown by data gathered with up to seven triaxial sonic anemometer/thermometers and three Lyman-alpha hygrometers at an experimental site in Ontario, Canada. The ramps appear most clearly in the middle and upper portion of the forest. Time/height cross-sections of scalar contours and velocity vectors, developed from both single events and ensemble averages of several events, portray details of the flow structures associated with the scalar ramps. Near the top of the forest they are composed of a weak ejecting motion transporting warm and/or moist air out of the forest followed by strong sweeps of cool and/or dry air penetrating into the canopy. The sweep is separated from the ejecting air by a sharp scalar microfront. At approximately twice the height of the forest, ejections and sweeps are of about equal strength.

In the middle and upper parts of the canopy, sweeps conduct a large proportion of the overall transfer between the forest and the lower atmosphere, with a lesser contribution from ejections. Ejections become equally important aloft. During one 30-min run, identified structures were responsible for more than 75% of the total fluxes of heat and momentum at mid-canopy height. Near the canopy top, the transition from ejection of slow moving fluid to sweep bringing fast moving air from above is very rapid but, at both higher and lower levels, brief periods of upward momentum transfer occur at or immediately before the microfront.


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  1. Antonia, R. A., Chambers, A. J., Friehe, C. A., and Van Atta, C. W.: 1979, ‘Temperature Ramps in the Atmospheric Surface Layer’, J. Atmos. Sci. 36, 99–108.Google Scholar
  2. Baldocchi, D. D. and Meyers, T. P.: 1988, ‘Turbulence Structure in a Deciduous Forest’, Boundary-Layer Meteorol. 43, 345–364.Google Scholar
  3. Bogard, D. G. and Tiederman, W. G.: 1986, ‘Burst Detection with Single-point Velocity Measurements’, J. Fluid Mech. 162, 389–413.Google Scholar
  4. Busch, N. E.: 1973, ‘On the Mechanics of Atmospheric Turbulence’, in D. A. Haugen (ed.), Workshop on Micrometeorology, Amer. Meteorol. Soc., Boston, pp. 1–65.Google Scholar
  5. Chen, C. P. and Blackwelder, R. F.: 1978, ‘Large-scale Motion in a Turbulent Boundary Layer: a Study Using Temperature Contamination’, J. Fluid Mech. 89, 1–31.Google Scholar
  6. Chiba, O.: 1978, ‘Stability Dependence of the Vertical Velocity Skewness in the Atmospheric Surface Layer’, J. Meteorol. Soc. Japan. 56, 140–142.Google Scholar
  7. Corino, E. R. and Brodkey, R. S.: 1969, ‘A Visual Investigation of the Wall Region in Turbulent Flow’, J. Fluid Mech. 37, 1–30.Google Scholar
  8. Denmead, O. T. and Bradley, E. F.: 1987, ‘On Scalar Transport in Plant Canopies’, Irrigation Sci. 8, 131–149.Google Scholar
  9. Finnigan, J. J.: 1979a, ‘Turbulence in Waving Wheat. I Mean Statistics and Honami’, Boundary-Layer Meteorol. 16, 181–211.Google Scholar
  10. Finnigan, J. J.: 1979b, ‘Turbulence in Waving Wheat. II Structure of Momentum Transfer’, Boundary-Layer Meteorol. 16, 213–236.Google Scholar
  11. Kaimal, J. C.: 1974, ‘Translation Speed of Convective Plumes in the Atmospheric Surface Layer’, Quart. J. Roy. Meteorol. Soc. 100, 46–52.Google Scholar
  12. Kaimal, J. C. and Businger, J. A.: 1970, ‘Case Studies of a Convective Plume and a Dust Devil’, J. Appl. Meteorol. 9, 612–620.Google Scholar
  13. Kline, S. J., Reynolds, W. C., Schraub, F. A., and Rundstadler, P. W.: 1967, ‘The Structure of Turbulent Boundary Layers’, J. Fluid Mech. 30, 741–773.Google Scholar
  14. Legg, B. J. and Monteith, J. L.: 1975, ‘Heat and Mass Transfer in Plant Canopies’, in D. A. De Vries and N. H. Afgan (eds.), Heat and Mass Transfer in the Biosphere, Wiley, New York, pp. 167–186.Google Scholar
  15. Meyers, T. P. and Paw, U. K. T.: 1986, ‘Testing of a Higher-order Closure Model for Airflow within and above Plant Canopies’, Boundary-Layer Meteorol. 37, 297–311.Google Scholar
  16. Meyers, T. P. and Paw, U. K. T.: 1987, ‘Modelling the Plant Canopy Micrometeorology with Higher-order Closure Principles’, Agric. Forest. Meteorol. 41, 143–163.Google Scholar
  17. Neumann, H. H., den Hartog, G., and Shaw, R. H.: 1988, ‘Leaf Area Measurements During Leaf-fall for a Deciduous Forest Based on Hemispheric Photographs and Leaf-litter Collection’, Agric. Forest Meteorol., in press.Google Scholar
  18. Offen, G. R. and Kline, S. J.: 1975, ‘A Proposed Model of the Bursting Process in Turbulent Boundary Layers’, J. Fluid Mech. 70, 209–228.Google Scholar
  19. Praturi, A. K. and Brodkey, R. S.: 1978, ‘A Stereoscopic Visual Study of Coherent Structures in Turbulent Shear Flow’, J. Fluid Mech. 89, 251–272.Google Scholar
  20. Priestley, C. H. B.: 1959, Turbulent Transfer in the Lower Atmosphere, University of Chicago Press, Chicago, pp. 53–72.Google Scholar
  21. Rajagopalan, S. and Antonia, R. A.: 1980, ‘Interaction between Large and Small Scale Motions in a Two-dimensional Turbulent Flow Duct’, Phys. Fluids 23, 1101–1110.Google Scholar
  22. Raupach, M. R.: 1981, ‘Conditional Statistics of Reynolds Stress in Rough-wall and Smooth-wall Turbulent Boundary Layers’, J. Fluid Mech. 108, 363–382.Google Scholar
  23. Raupach, M. R.: 1987, ‘A Lagrangian Analysis of Scalar Transfer in Vegetation Canopies’, Q. J. Roy. Meteorol. Soc. 113, 107–120.Google Scholar
  24. Raupach, M. R. and Thom, A. S.: 1981, ‘Turbulence in and above Plant Canopies’, Ann. Rev. Fluid Mech. 13, 97–129.Google Scholar
  25. Schols, J. L. J.: 1984, ‘The Detection and Measurement of Turbulent Structures in the Atmospheric Surface Layer’, Boundary-Layer Meteorol. 29, 39–58.Google Scholar
  26. Shaw, R. H., den Hartog, G., and Neumann, H. H.: 1988, ‘Influence on Foliar Density and Thermal Stability on Profiles of Reynolds Stress and Turbulence Intensity in a Deciduous Forest’, Boundary-Layer Meteorol. 45, 391–409.Google Scholar
  27. Shaw, R. H., Tavangar, J., and Ward, D. P.: 1983, ‘Structure of the Reynolds Stress in a Canopy Layer’, J. Clim. Appl. Meteorol. 22, 1922–1931.Google Scholar
  28. Shaw, R. H. and Seginer, I.: 1987, ‘Calculation of Velocity Skewness in Real and Artificial Plant Canopies’, Boundary-Layer Meteorol. 39, 315–332.Google Scholar
  29. Subramanian, C. S., Rajagopalan, S., Antonia, R. A., and Chambers, A. J.: 1982, ‘Comparison of Conditional Sampling and Averaging Techniques in a Turbulent Boundary Layer’, J. Fluid Mech. 123, 335–362.Google Scholar
  30. Talmon, A. M., Kunen, J. M. G., and Ooms, G.: 1986, ‘Simultaneous Flow Visualization and Reynolds-stress Measurement in a Turbulent Boundary Layer’, J. Fluid Mech. 163, 459–478.Google Scholar
  31. Taylor, R. J.: 1958, ‘Thermal Structures in the Lowest Layer of the Atmosphere’, Australian J. Phys. 11, 168–176.Google Scholar
  32. Thomas, A. S. and Bull, M. K.: 1983, ‘On the Role of the Wall-Pressure Fluctuations in Deterministic Motions in the Turbulent Boundary Layer’, J. Fluid Mech. 128, 283–322.Google Scholar
  33. Wallace, J. M., Eckelmann, H., and Brodkey, R. S.: 1972, ‘The Wall Region in Turbulent Shear Flow’, J. Fluid Mech. 54, 39–48.Google Scholar
  34. Wilczak, J. M.: 1984, ‘Large-scale Eddies in the Unstably Stratified Atmospheric Surface Layer. Part I: Velocity and Temperature Structure’, J. Atmos. Sci. 41, 3537–3550.Google Scholar
  35. Wilczak, J. M. and Businger, J. A.: 1984, ‘Large-scale Eddies in the Unstably Stratified Atmospheric Surface Layer. Part II: Turbulent Pressure Fluctuations and the Budgets of Heat Flux, Stress and Turbulent Kinetic Energy’, J. Atmos. Sci. 41, 3551–3567.Google Scholar
  36. Wilczak, J. M. and Tillman, J. E.: 1980, ‘The Three-dimensional Structure of Convection in the Atmospheric Surface Layer’, J. Atmos. Sci. 37, 2424–2443.Google Scholar
  37. Wilson, N. R. and Shaw, R. H.: 1977, ‘A Higher Order Closure Model for Canopy Flow’, J. Appl. Meteorol. 16, 1197–1205.Google Scholar

Copyright information

© Kluwer Academic Publishers 1989

Authors and Affiliations

  • W. Gao
    • 1
  • R. H. Shaw
    • 1
  • K. T. Paw U
    • 1
  1. 1.Department of Land, Air and Water ResourcesUniversity of CaliforniaDavisUSA

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