Energy balance closure at FLUXNET sites

• Published in: Agricultural and Forest Meteorology
• Main Authors: Wilson, K.B., Goldstein, A., Falge, E., Aubinet, M., Baldocchi, D.D., Berbigier, P., Bernhofer, C., Ceulemans, R., Dolman, A.J., Field, C., Grelle, A., Ibrom, A., Law, B.E., Kowalski, A., Meyers, T., Monchieff, J., Monson, R., Oechel, W., Tenhunen, J., Valentini, R., Verma, S.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2002
• Subjects: Arctic
• Online Access: https://research.vu.nl/en/publications/e42397dd-5a3e-4377-b86a-ebe5b6b901d1; https://doi.org/10.1016/S0168-1923(02)00109-0

A comprehensive evaluation of energy balance closure is performed across 22 sites and 50 site-years in FLUXNET, a network of eddy covariance sites measuring long-term carbon and energy fluxes in contrasting ecosystems and climates. Energy balance closure was evaluated by statistical regression of turbulent energy fluxes (sensible and latent heat (LE)) against available energy (net radiation, less the energy stored) and by solving for the energy balance ratio, the ratio of turbulent energy fluxes to available energy. These methods indicate a general lack of closure at most sites, with a mean imbalance in the order of 20%. The imbalance was prevalent in all measured vegetation types and in climates ranging from Mediterranean to temperate and arctic. There were no clear differences between sites using open and closed path infrared gas analyzers. At a majority of sites closure improved with turbulent intensity (friction velocity), but lack of total closure was still prevalent under most conditions. The imbalance was greatest during nocturnal periods. The results suggest that estimates of the scalar turbulent fluxes of sensible and LE are underestimated and/or that available energy is overestimated. The implications on interpreting long-term CO