Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Journal topic
Volume 15, issue 9
Biogeosciences, 15, 2945-2960, 2018
https://doi.org/10.5194/bg-15-2945-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Biogeosciences, 15, 2945-2960, 2018
https://doi.org/10.5194/bg-15-2945-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 16 May 2018

Research article | 16 May 2018

Footprint-weighted tile approach for a spruce forest and a nearby patchy clearing using the ACASA model

Kathrin Gatzsche1,2,a, Wolfgang Babel1,3,b, Eva Falge4,c, Rex David Pyles5, Kyaw Tha Paw U5, Armin Raabe2, and Thomas Foken1,3 Kathrin Gatzsche et al.
  • 1University of Bayreuth, formerly the Department of Micrometeorology, Bayreuth, Germany
  • 2University of Leipzig, Leipzig Institute for Meteorology, Leipzig, Germany
  • 3University of Bayreuth, Bayreuth Center of Ecology and Environmental Research (BayCEER), Bayreuth, Germany
  • 4Max Planck Institute of Chemistry, Biogeochemistry Department, Mainz, Germany
  • 5University of California, Department of Land, Air and Water Resources, Davis, California, USA
  • anow at: Leibniz Institute for Tropospheric Research (TROPOS), Department Modelling of Atmospheric Processes, Leipzig, Germany
  • bnow at: University of Bayreuth, Micrometeorology Group, Bayreuth, Germany
  • cnow at: German Meteorological Service, Agrometeorological Research Center, Braunschweig, Germany

Abstract. The ACASA (Advanced Canopy–Atmosphere–Soil Algorithm) model, with a higher-order closure for tall vegetation, has already been successfully tested and validated for homogeneous spruce forests. The aim of this paper is to test the model using a footprint-weighted tile approach for a clearing with a heterogeneous structure of the underlying surface. The comparison with flux data shows a good agreement with a footprint-aggregated tile approach of the model. However, the results of a comparison with a tile approach on the basis of the mean land use classification of the clearing is not significantly different. It is assumed that the footprint model is not accurate enough to separate small-scale heterogeneities. All measured fluxes are corrected by forcing the energy balance closure of the test data either by maintaining the measured Bowen ratio or by the attribution of the residual depending on the fractions of sensible and latent heat flux to the buoyancy flux. The comparison with the model, in which the energy balance is closed, shows that the buoyancy correction for Bowen ratios > 1.5 better fits the measured data. For lower Bowen ratios, the correction probably lies between the two methods, but the amount of available data was too small to make a conclusion. With an assumption of similarity between water and carbon dioxide fluxes, no correction of the net ecosystem exchange is necessary for Bowen ratios > 1.5.

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The ecosystem is a significant sink of carbon dioxide. To quantify this sink, very complex and validated models are required. However, the comparison of modeled and measured energy and matter fluxes in a heterogeneous landscape is still a challenge. On the one hand, models must be applied for various surface types, while on the other hand the comparison of the fluxes is only possible based on the flux source areas. This paper treats the potential aggregation of modeled fluxes and its validation.
The ecosystem is a significant sink of carbon dioxide. To quantify this sink, very complex and...
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