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Theoretical and Applied Climatology

, Volume 53, Issue 1–3, pp 49–58 | Cite as

Energy balance comparison of the Hartheim forest and an adjacent grassland site during the HartX experiment

  • W. Wicke
  • Ch. Bernhofer
Article

Summary

Energy balance components over a grassland surface were compared to those obtained above an adjacent, uniform Scots pine plantation during a five-day period of fine, sunny, spring weather. Soils were judged to contain ample water. Shortwave and total radiation flux densities were measured at both sites with pyranometers and total pyrradiometers. Soil heat flux densities were measured with heat flux plates at both sites, and additional storage changes were estimated for air and canopy at the forest site. The forest gained more shortwave energy than the grassland during daytime because of its lower albedo, but it lost more longwave radiation at night. The turbulent fluxes of sensible and latent energy were evaluated with the Bowen ratio energy balance (BREB) method at both sites. Temperature and humidity gradients were measured with fixed psychrometers at the grassland site, and with interchanging psychrometers at the forest site. Mean daily evapotranspiration (ET) averaged 2.26 mm over the five days for the Scots pine, or only 57 percent of the 3.94 mm measured at the grassland site. The mean Bowen ratios were 2.6 and 0.8, respectively.

An error analysis was carried out for the BREB estimates of latent heat flux at the two sites. For a given error in latent heat flux and at a specified Bowen ratio the demands on accuracy of dry- and wet-bulb temperature gradients above the rough forest canopy was found to be 10 times higher than above the smoother grassland. If additionally the observed differences in transpiration rates between the two sites were taken into account, the precision for temperature gradient measurements above the slowly transpiring forest becomes fortyfold greater than required above the rapidly transpiring grass. At present, BREB precision requirements for gradients above rougher, drier canopies appear achievable only through use of specialized instrumentation, such as measurement systems that incorporate interchangeable psychrometers into their design.

Keywords

Heat Flux Latent Heat Flux Forest Site Heat Flux Density Bowen Ratio 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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References

  1. Angus, D. E., Watts, P. J., 1984: Evapotranspiration — how good is the Bowen ratio Method?Agric. Water Managment 8, 133–150.Google Scholar
  2. Bernhofer, Ch., Gay, L. W., Laube W., Klug, W., 1992: Ein österreichisch-amerikanisches Bowenverhältnis-Energiebilanzmeßsystem.Wetter und Leben 44, 83–106.Google Scholar
  3. Bernhofer, Ch., 1992: Estimating forest evaporation at a nonideal site.Agric. Forest Meteorol. 60, 17–32.Google Scholar
  4. Bernhofer, Ch., Blanford, J. H., Siegwolf, R., Wedler, M., 1996: Applying single and two layer canopy models to derive conductances of a scots pine plantation from micrometeorological measurements.Theor. Appl. Climatol. 53, 95–104.Google Scholar
  5. Bowen, I. S., 1926: The ratio of heat losses by conduction and evaporation from any water surface.Phys. Rev. 27, 779–787.Google Scholar
  6. Brutsaert, W., 1982:Evaporation into the Atmosphere. Theory, History and Applications. Dordrecht: Reidel.Google Scholar
  7. Däke, C. U., 1972: Über ein neues Modell des Strahlungsbilanzmessers nach Schulze.Ber. Dtsch. Wetterdienst., 16 (126), Selbstverlag des Deutschen Wetterdienstes, 22 pp.Google Scholar
  8. Dirmhirn, I., 1964:Das Strahlungsfeld im Lebensraum. Frankfurt a. M.: Akademische Verlagsgesellschaft Frankfurt, 426 pp.Google Scholar
  9. Ernst, S., Wütherich, M., 1996: Spatial characteristics of surface and atmospheric properties during HartX.Theor. Appl. Climatol. 53, 59–67.Google Scholar
  10. Gay, L. W., 1988: A portable Bowen ratio system for ET measurements. Proc. Natl. Conf. on Irrigation and Drainage, Lincoln, NE. ASCE, New York, 625–632.Google Scholar
  11. Gay, L. W., Vogt, R., Bernhofer, Ch., Blanford, J. H., 1996: Flux agreement above a Scots pine plantation.Theor. Appl. Climatol. 53, 33–48.Google Scholar
  12. Gossmann, H., Saurer, H., Scheer, M., 1988: Oberflächentemperaturmessungen aus Satelliten als Beitrag zur Erfassung der Transport- und Depositionsbedingungen von Luftschadstoffen in Wäldern. Kernforschungszentrum Karlsruhe, KfK-PEF report no. 46, 63 pp.Google Scholar
  13. Halldin, S., 1991: Comments on ‘Corrections of errors associated with measurements of net all-wave radiation with double-domed radiometers’ by Oliver and Wright (1990).Bound. Layer Meteor. 57, 195–201.Google Scholar
  14. Halldin, S., Lindroth, A., 1992: Errors in net radiometry: comparison and evaluation of six radiometer designs.J. Atmos. Oceanic Technol. 9, 762–783.Google Scholar
  15. Iqbal, M., 1993:An Introduction to Solar Radiation. Toronto, New York, London: Academic Press, 390 pp.Google Scholar
  16. Jaeger, L., Kessler, A., 1996: The HartX period May 1992, seen against the background of twenty years of energy balance climatology at the Hartheim pine forest.Theor. Appl. Climatol. 53, 9–21.Google Scholar
  17. Kessler, A., 1985: Über die kurzwellige Albedo eines Kiefernwaldes. Eine klimatologische Langzeitstudie.Meteorol. Rdsch. 38, 82–91.Google Scholar
  18. Kessler, A., Jaeger, L., 1994: Mittlere Tages- und Jahresgänge der Strahlungsbilanz und ihrer Komponenten über einem südwestdeutschen Kiefernwald.Erdkunde 48, 14–33.Google Scholar
  19. Lee, R., 1980:Forest Hydrology. New York: Columbia University Press, 349 pp.Google Scholar
  20. Monteith, J. L. (ed.), 1976:Vegetation and the Atmosphere, Vol. 2. London: Academic Press, 439 pp.Google Scholar
  21. Ohmura, A., 1982: Objective criteria for rejecting data for Bowen ratio calculations.J. Appl. Meteorol. 21, 595–598.Google Scholar
  22. Parlow, E., 1996: The regional climate project REKLIP — an overview.Theor. Appl. Climatol. 53, 3–7.Google Scholar
  23. Sturm, N., Reber, S., Kessler, A., Tenhunen, J., 1996: Soil moisture variation and plant water stress at the Hartheim Scots pine forest.Theor. Appl. Climatol. 53, 123–133.Google Scholar
  24. Vogt, R., Bernhofer, Ch., Gay, L. W., Jaeger, L., Parlow, E., 1996: On the available energy during HartX: What's up for partitioning?Theor. Appl. Climatol. 53, 23–31.Google Scholar

Copyright information

© Springer-Verlag 1996

Authors and Affiliations

  • W. Wicke
    • 1
  • Ch. Bernhofer
    • 2
  1. 1.Meteorological InstituteUniversity of FreiburgGermany
  2. 2.Institute of Meteorology and Physics (IMP)Universität für BodenkulturViennaAustria

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