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Diurnal centroid of ecosystem energy and carbon fluxes at FLUXNET sites
Atmospheric Turbulence and Diffusion Division, NOAA, Oak Ridge, Tennessee, USA
ESPM, University of California at Berkeley, Berkeley, California, USA
Pflanzen-ekologie, University Bayreuth, Bayreuth, Germany
Unite de Physique, Faculte des Sciences Agronomiques de Gembloux, Gembloux, Belgium
Unite de Bioclimatologie, INRA Bourdeaux, Gazinet, France
Insitute fur Hydrologie und Meteorologie, Tharandt, Germany
Department of GeoEnvironmental Sciences, Faculty of Earth and Life Sciences, Vrije Universiteit, Amsterdam, Netherlands
Department of Plant Biology, Carnegie Institution of Washington, Stanford, California, USA
ESPM, University of California at Berkeley, Berkeley, California, USA
Unite Ecophysiologie Forestieres, Institut Nationale de la Recherche Agronomique, Champenoux, France
USDA Forest Service, Northeastern Forest Experiment Station, Durham, New Hampshire, USA
School of the Environment, Duke University, Durham, North Carolina, USA
College of Forestry, Oregon State University, Corvallis, Oregon, USA
Atmospheric Turbulence and Diffusion Division, NOAA, Oak Ridge, Tennessee, USA
Department of Ecology and Environmental Research, University of Edinburgh, Edinburgh, UK
DEPOB, University of Colorado, Boulder, Colorado, USA
Pflanzen-ekologie, University Bayreuth, Bayreuth, Germany
Department of Forest Science and Resources, University of Tuscia, Viterbo, Italy
School of Natural Resource Sciences, University of Nebraska, Lincoln, Nebraska, USA
Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA
Data from a network of eddy covariance stations in Europe and North America (FLUXNET) were analyzed to examine the diurnal patterns of surface energy and carbon fluxes during the summer period across a range of ecosystems and climates. Diurnal trends were quantified by assessing the time of day surface fluxes and meteorological variable reached peak values, using the “diurnal centroid” method; the diurnal centroid enabled us to discern whether the peak activity of the variable of interest is weighted more toward the morning or afternoon. In this paper, diurnal centroid estimates were used to diagnose which atmospheric and physiological processes controlled carbon dioxide, water vapor, and sensible heat fluxes across different ecosystems and climates. Sensitivity tests suggested that the diurnal centroids for latent (LE) and sensible (H) heat flux depend on atmospheric resistance, static stability in the free atmosphere, stomatal response to vapor pressure deficit, and advection. With respect to diurnal trends of surface energy fluxes at FLUXNET sites, maximum LE occurred later in the day relative to H at most tall forests with continental climates. The lag between LE and H was reduced or reversed at sites that were influenced by advection or by afternoon stomatal closure. The time of peak carbon uptake of temperate forests occurred earlier relative to the temporal peak of photosynthetically active radiation, as compared to boreal forests. The timing of this peak occurred earlier during periods with low soil water content, as it did during the summer in Mediterranean climates. In this case, the diurnal centroid for the CO2 flux was influenced by the response of respiration and photosynthesis to increasing afternoon temperature and by afternoon stomatal closure.
Received 2 October 2001; accepted 21 May 2003; published 6 November 2003.
Citation: (2003), Diurnal centroid of ecosystem energy and carbon fluxes at FLUXNET sites, J. Geophys. Res., 108(D21), 4664, doi:10.1029/2001JD001349.
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