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Boundary-Layer Meteorology

, Volume 136, Issue 2, pp 193–218 | Cite as

Energy Balance Closure Using Eddy Covariance Above Two Different Land Surfaces and Implications for CO2 Flux Measurements

  • Joe Kidston
  • Christian Brümmer
  • T. Andrew Black
  • Kai Morgenstern
  • Zoran Nesic
  • J. Harry McCaughey
  • Alan G. Barr
Article

Abstract

Components of the surface energy balance of a mature boreal jack pine forest and a jack pine clearcut were analysed to determine the causes of the imbalance that is commonly observed in micrometeorological measurements. At the clearcut site (HJP02), a significant portion of the imbalance was caused by: (i) the overestimation of net radiation (R n ) due to the inclusion of the tower in the field of view of the downward facing radiometers, and (ii) the underestimation of the latent heat flux (λE) due to the damping of high frequency fluctuations in the water vapour mixing ratio by the sample tube of the closed-path infrared gas analyzer. Loss of low-frequency covariance induced by insufficient averaging time as well as systematic advection of fluxes away from the eddy-covariance (EC) tower were discounted as significant issues. Spatial and temporal distributions of the total surface-layer heat flux (T), i.e. the sum of sensible heat flux (H) and λE, were well behaved and differences between the relative magnitudes of the turbulent fluxes for several investigated energy balance closure (C) classes were observed. Therefore, it can be assumed that micrometeorological processes that affected all turbulent fluxes similarly did not cause the variation in C. Turbulent fluxes measured at the clearcut site should not be forced to close the energy balance. However, at the mature forest site (OJP), loss of low-frequency covariance contributed significantly to the systematic imbalance when a 30-min averaging time was used, but the application of averaging times that were long enough to capture all of the low-frequency covariance was inadequate to resolve all of the high-frequency covariance. Although we found qualitative similarity between T and the net ecosystem exchange (NEE) of carbon dioxide (CO2), forcing T to closure while retaining the Bowen ratio and applying the same factor to CO2 fluxes (F C ) cannot be generally recommended since it remains uncertain to what extent long wavelength contributions affect the relationship between T, F C and C.

Keywords

Available energy flux Eddy covariance Energy balance closure High-frequency loss Latent heat flux Low-frequency loss Sampling-tube attenuation Sensible heat flux Turbulent flux cospectra 

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Copyright information

© Springer Science+Business Media B.V. 2010

Authors and Affiliations

  • Joe Kidston
    • 1
    • 2
  • Christian Brümmer
    • 1
    • 3
  • T. Andrew Black
    • 1
  • Kai Morgenstern
    • 1
  • Zoran Nesic
    • 1
  • J. Harry McCaughey
    • 4
  • Alan G. Barr
    • 5
  1. 1.Faculty of Land and Food SystemsUniversity of British ColumbiaVancouverCanada
  2. 2.National Institute of Water and Atmospheric Research (NIWA)WellingtonNew Zealand
  3. 3.Johann Heinrich von Thünen-Institut (vTI)Institute of Agricultural Climate Research (AK)BraunschweigGermany
  4. 4.Department of GeographyQueen’s UniversityKingstonCanada
  5. 5.Climate Research DivisionEnvironment CanadaSaskatoonCanada

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