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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 19, issue 5
Ann. Geophys., 19, 581–587, 2001
https://doi.org/10.5194/angeo-19-581-2001
© Author(s) 2001. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 19, 581–587, 2001
https://doi.org/10.5194/angeo-19-581-2001
© Author(s) 2001. This work is distributed under
the Creative Commons Attribution 3.0 License.

  31 May 2001

31 May 2001

Quantifying the coupling degree between land surface and the atmospheric boundary layer with the coupled vegetation-atmosphere model HIRVAC

V. Goldberg and Ch. Bernhofer V. Goldberg and Ch. Bernhofer
  • Dresden University of Technology, Institute for Hydrology and Meteorology, Department of Meteorology, Pienner Str. 9, 01737 Tharandt, Germany

Abstract. In the present study, the ability of different indices to quantify the coupling degree between a vegetated surface and the atmospheric boundary layer is tested. For this purpose, a one-and-a-half dimensional atmospheric boundary layer model, including a high resolved vegetation canopy, was applied (HIRVAC) and indices, such as the decoupling factor Ω, as well as other measures derived from model out-put were used. The aim of the study was to show that the quite complex coupling and feedback mechanisms can be described with these relatively simple measures. Model results illustrate that the vegetation and the atmosphere are well coupled (expressed by a lower Ω) under conditions of a tall and dense canopy, as well as under strong dynamic forcing. This better aerodynamic coupling leads to an increase in evapotranspiration, as well as an increase in the evaporative fraction. This fact was also shown by the second coupling measure: the relative changes in daily model evapotranspiration. This measure was inspired by the assumption that these changes are primarily dependent on the coupling degree between the surface and the atmosphere, if the other boundary conditions in the model are fixed. A third sensitivity measure was used according to Jacobs and de Bruin (1992). It shows that the sensitivity of evaporative fraction to stomata resistance is much higher with a better aerodynamic coupling. The results of the factor Ω; are in a good agreement with the findings of Jacobs and de Bruin: they stress that it is a valuable strategy to group vegetation into two simple categories (smooth and rough) for the understanding of vegetation-atmosphere coupling.

Key words. Atmospheric composition and structure (biosphere- atmosphere interactions) – Hydrology (evapotranspiration; hydroclimatology)

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