Diurnal centroid of ecosystem energy and carbon fluxes at FLUXNET sites

Kell B. Wilson, Dennis Baldocchi, Eva Falge, Marc Aubinet, Paul Berbigier, Christian Bernhofer, Han Dolman, Chris Field, Allen Goldstein, Andre Granier, Dave Hollinger, Gabriel Katul, B. E. Law, Tilden Meyers, John Moncrieff, Russ Monson, John Tenhunen, Riccardo Valentini, Shashi Verma, Steve Wofsy

Research output: Contribution to journalArticlepeer-review

41 Scopus citations


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.

Original languageEnglish (US)
Pages (from-to)ACL 2-1 - ACL 2-13
JournalJournal of Geophysical Research: Atmospheres
Issue number21
StatePublished - Nov 16 2003


  • Diurnal
  • Energy flux
  • Evapotranspiration
  • Latent heat
  • Sensible heat

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Materials Chemistry
  • Polymers and Plastics
  • Physical and Theoretical Chemistry


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