Abstract
Six levels of simultaneously sampled ultrasonic data are used to analyse the turbulence structure within a mixed forest of 13 m height on a steep slope (35°) in an alpine valley. The data set is compared to other studies carried out over forests in more ideal, flat terrain. The analysis is carried out for 30-min mean data, joint probability distributions, length scales and spectral characteristics.
Thermally induced upslope winds and cold air drainage lead to a wind speed maximum within the trunk space. Slope winds are superimposed on valley winds and the valley-wind component becomes stronger with increasing height. Slope and valley winds are thus interacting on different spatial and time scales leading to a quite complex pattern in momentum transport that differs significantly from surface-layer characteristics. Directional shear causes lateral momentum transports that are in the same order or even larger than the longitudinal ones. In the canopy, however, a sharp attenuation of turbulence is observed. Skewed distributions of velocity components indicate that intermittent turbulent transport plays an important role in the energy distribution.
Even though large-scale pressure fields lead to characteristic features in the turbulent structure that are superimposed on the canopy flow, it is found that many statistical properties typical of both mixing layers and canopy flow are observed in the data set.
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References
Barry, R. G.: 1992, Mountain Weather & Climate, 2nd edn., Routledge, London and New York, 402 pp.
Christen, A., van Gorsel, E., Andretta, M., Calanca, P., Rotach, M. W., and Vogt, R.: 2000, 'Intercomparison of Ultrasonic Anemometers during the MAP-Riviera Project', in Ninth Conference on Mountain Meteorology, Aspen, CO, August 7-11, 2000, American Meteorological Society, 45 Beacon St., Boston, MA, pp. 130-131.
Christen, A., van Gorsel, E., Vogt, R., Andretta, M., and Rotach, M. W.: 2001, 'Ultrasonic Anemometer Instrumentation at Steep Slopes: Wind Tunnel Study-Field Intercomparison-Measurements', in MAP Meeting Schliersee, in MAP Newsletter 15, May 14-16, pp. 206-209.
De Bruin, H. A. R., Kohsiek, W., and van den Hurk, B. J. J. M.: 1993, 'A Verification of Some Methods to Determine the Fluxes of Momentum, Sensible Heat, and Water Vapour using Standard Deviation and Structure Parameter of Scalar Meteorological Quantities', Boundary-Layer Meteorol. 63, 231-257.
Egger, J.: 1990, 'Thermally Forced Flows: Theory', in W. Blumen (ed.), Atmospheric Processes over Complex Terrain, 23, American Meteorological Society, Boston, MA, pp. 43-57.
Finnigan, J.: 2000, 'Turbulence in Plant Canopies', Annu. Rev. Fluid Mech. 32, 519-571.
Finnigan, J. J. and Brunet, Y.: 1995, 'Turbulent Airflow in Forests on Flat and Hilly Terrain', in M. P. Coutts and J. Grace (eds.), Wind and Trees, Cambridge Universtiy Press, Cambridge, pp. 3-40.
Kaimal, J. C.: 1978, 'Horizontal Velocity Spectra in an Unstable Surface Layer', J. Atmos. Sci. 35, 18-24.
Kaimal, J. C. and Finnigan, J. J.: 1994, Atmospheric Boundary Layer Flows, Oxford University Press, Oxford, 289 pp.
Kruijt, B., Malhi, Y., Lloyd, J., Nobre, A. D., Miranda, A. C., and Pereira, M. G. P.: 2000, 'Turbulence Statistics above and within Two Amazon Rain Forest Canopies', Boundary-Layer Meteorol. 94, 297-331.
Maitani, T. and Shaw, R. H.: 1990, 'Joint Probability Analysis of Momentum and Heat Fluxes at a Deciduous Forest', Boundary-Layer Meteorol. 52, 283-300.
Mazzoni, R.: 1996, Turbulenzstruktur im gestörten Nachlauf einer künstlichen Oberflächenmodifikation. Ein Feldexperiment, Ph.D. Dissertation, ETH Zürich, Zürich, 133 pp.
Panofsky, H. A. and Dutton, J. A.: 1984, Atmospheric Turbulence-Models and Methods for Engineering Applications, J. Wiley, New York, 397 pp.
Peltier, L. J., Wyngaard, J. C., Khanna, S., and Brasseur, J.: 1996, 'Spectra in the Unstable Surface Layer', J. Atmos. Sci. 53, 49-61.
Rannik, Ñ. and Vesala, T.: 1999, 'Autoregressive Filtering versus Linear Detrending in Estimation of Fluxes by the Eddy Covariance Method', Boundary-Layer Meteorol. 91, 259-280.
Raupach, M. R.: 1988, 'Canopy Transport Processes', in W. L. Steffen and O. T. Denmead (eds.), Flow and Transport in the Natural Environment: Advances and Applications, Springer, Berlin, pp. 95-127.
Raupach, M. R. and Finnigan, J. J.: 1997, 'The Influence of Topography on Meteorological Variables and Surface-Atmosphere Interactions', J. Hydrol. 190, 182-213.
Raupach, M. R. and Thom, A. S.: 1981, 'Turbulence in and above Plant Canopies', Annu. Rev. Fluid Mech. 13, 97-129.
Raupach, M. R., Finnigan, J. J., and Brunet, Y.: 1996, 'Coherent Eddies and Turbulence in Vegetation Canopies: The Mixing-Layer Analogy', Boundary-Layer Meteorol. 78, 351-382.
Rotach, M.W., Calanca, C., Vogt, R., Steyn, D. G., Graziani, G., and Gurtz, J.: 2000, 'The Turbulence Structure and Exchange Processes in an Alpine Valley: TheMAP-Riviera Project', in Ninth Conference on Mountain Meteorology, Aspen, CO, August 7-11, American Meteorological Society, 45 Beacon St., Boston, MA, pp. 231-234.
Shaw, R. H., Brunet, Y., Finnigan, J. J., and Raupach, M. R.: 1995, 'A Wind Tunnel Study of Air Flow inWaving Wheat: Two Point Velocity Statistics', Boundary-Layer Meteorol. 76, 349-376.
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.
Vogt, R.: 1995, Theorie, Technik und Analyse der experimentellen Flussbestimmung am Beispiel des Hartheimer Kiefernwaldes, Ph.D. Dissertation, University of Basel, Basel, 101 pp.
Whiteman, C. D.: 1990, 'Observations of Thermally Developed Wind Systems in Mountinous Terrain', in W. Blumen (ed.), Atmospheric Processes over Complex Terrain, 23, American Meteorological Society, Boston, MA, pp. 5-42.
Whiteman, C. D. and Allwine, K. J.: 1989, 'Deep Valley Radiation and Surface Energy Budget Microclimates. Part I: Radiation', J. Appl. Meteorol. 28, 414-426.
Wood, N.: 2000, 'Windflow over Complex Terrain: A Historical Perspective and the Prospect for Large-Eddy Modelling', Boundary-Layer Meteorol. 96, 11-32.
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Van Gorsel, E., Christen, A., Feigenwinter, C. et al. Daytime Turbulence Statistics above a Steep Forested Slope. Boundary-Layer Meteorology 109, 311–329 (2003). https://doi.org/10.1023/A:1025811010239
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DOI: https://doi.org/10.1023/A:1025811010239