Correcting eddy-covariance flux underestimates over a grassland.

Journal Article · Thu Jun 08 04:00:00 EDT 2000 · Agricult. For. Meteor.

DOI:https://doi.org/10.1016/S0168-1923(00)00123-4· OSTI ID:942842

Twine, T E; Kustas, W P; Norman, J M; Cook, D R; Houser, P R; Meyers, T P; Prueger, J H; Starks, P J; Wesely, M L; DOE,

Independent measurements of the major energy balance flux components are not often consistent with the principle of conservation of energy. This is referred to as a lack of closure of the surface energy balance. Most results in the literature have shown the sum of sensible and latent heat fluxes measured by eddy covariance to be less than the difference between net radiation and soil heat fluxes. This under-measurement of sensible and latent heat fluxes by eddy-covariance instruments has occurred in numerous field experiments and among many different manufacturers of instruments. Four eddy-covariance systems consisting of the same models of instruments were set up side-by-side during the Southern Great Plains 1997 Hydrology Experiment and all systems under-measured fluxes by similar amounts. One of these eddy-covariance systems was collocated with three other types of eddy-covariance systems at different sites; all of these systems under-measured the sensible and latent-heat fluxes. The net radiometers and soil heat flux plates used in conjunction with the eddy-covariance systems were calibrated independently and measurements of net radiation and soil heat flux showed little scatter for various sites. The 10% absolute uncertainty in available energy measurements was considerably smaller than the systematic closure problem in the surface energy budget, which varied from 10 to 30%. When available-energy measurement errors are known and modest, eddy-covariance measurements of sensible and latent heat fluxes should be adjusted for closure. Although the preferred method of energy balance closure is to maintain the Bowen-ratio, the method for obtaining closure appears to be less important than assuring that eddy-covariance measurements are consistent with conservation of energy. Based on numerous measurements over a sorghum canopy, carbon dioxide fluxes, which are measured by eddy covariance, are underestimated by the same factor as eddy covariance evaporation measurements when energy balance closure is not achieved.

• Research Organization: Argonne National Laboratory (ANL)
• Sponsoring Organization: SC; NASA; USDA
• DOE Contract Number: AC02-06CH11357
• OSTI ID: 942842
• Report Number(s): ANL/ER/JA-35183
• Journal Information: Agricult. For. Meteor., Journal Name: Agricult. For. Meteor. Journal Issue: 3 ; Jun. 8, 2000 Vol. 103; ISSN 0168-1923
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

54 ENVIRONMENTAL SCIENCES
CARBON DIOXIDE
ENERGY
ENERGY BALANCE
ERRORS
EVAPORATION
HEAT
HEAT FLUX
HYDROLOGY
PLATES
RADIATIONS
RADIOMETERS
RANGELANDS
SOILS
SORGHUM
SURFACE ENERGY
USA