Abstract
We explore some of the underlying assumptions used to derive the density or WPL terms (Webb et al. (1980) Quart J Roy Meteorol Soc 106:85–100) required for estimating the surface exchange fluxes by eddy covariance. As part of this effort we recast the origin of the density terms as an assumption regarding the density fluctuations rather than as a (dry air) flux assumption. This new approach, which is similar to the expansion/compression approach of Liu (Boundary-Layer Meteorol 115:151–168, 2005), eliminates the dry-air mean advective vertical velocity from the development of the WPL terms and allows us to directly compare Liu’s assumptions for deriving the WPL terms with the analogous assumptions appropriate to the original expression of the WPL terms. We suggest, (i) that the main difference between these two approaches lies in the interpretation of the turbulent exchange flux, and (ii) that the original WPL formulation is the more appropriate approach. Given the importance of the WPL terms to accurate and reliable measurements of surface exchange fluxes, a careful analysis of their origins and their proper mathematical expression and interpretation is warranted.
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Baldocchi D, Falge E, Gu L, Olson R, Hollinger D, Running S, Anthoni P, Bernhofer Ch, Davis K, Evans R, Fuentes J, Goldstein A, Katul G, Law B, Lee X, Malhi Y, Meyers T, Munger W, Oechel W, Paw UKT, Pilegaard K, Schmid HP, Valentini R, Verma S, Vesala T, Wilson K, Wofsy S (2001) FLUXNET: a new tool to study the temporal and spatial variability of ecosystem-scale carbon dioxide, water vapor, and energy flux densities. Bull Amer Meteorol Soc 82:2415–2434
Fuehrer PL, Friehe CA (2002) Flux corrections revisited. Boundary-Layer Meteorol 102:415–457
Jacobson MZ (1999) Fundamentals of atmospheric modeling. Cambridge University Press, Cambridge, U.K., p 656
Leuning R (2004) Measurements of trace gas fluxes in the atmosphere using eddy covariance: WPL corrections revisited. In: Lee X, Massman WJ, Law BE (eds) Handbook of micrometeorology, a guide for surface flux measurement and analysis. Springer, Dordrecht, The Netherlands, pp 119–132
Liu H (2005) An alternative approach for CO2 flux correction caused by heat and water vapour transfer. Boundary-Layer Meteorol 115:151–168
Massman WJ (2004) Concerning the measurement of atmospheric trace gas fluxes with open- and closed-path eddy covariance systems: the WPL terms and spectral attenuation. In: Lee X, Massman WJ, Law BE (eds) Handbook of micrometeorology, a guide for surface flux measurement and analysis. Springer, Dordrecht, The Netherlands, pp 133–160
Massman WJ, Lee X (2002) Eddy covariance flux corrections and uncertainties in long-term studies of carbon and energy exchanges. Agric For Meteorol 113:121–144
Paw U KT, Baldocchi DD, Meyers TP, Wilson KB (2000) Correction of eddy-covariance measurements incorporating both advective effects and density fluxes. Boundary-Layer Meteorol 97:487–511
Webb EK, Pearman GI, Leuning R (1980) Correction of flux measurements for density effects due to heat and water vapour transfer. Quart J Roy Meteorol Soc 106:85–106
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Massman, W.J., Tuovinen, J.P. An Analysis and Implications of Alternative Methods of Deriving the Density (WPL) Terms for Eddy Covariance Flux Measurements. Boundary-Layer Meteorol 121, 221–227 (2006). https://doi.org/10.1007/s10546-006-9070-8
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DOI: https://doi.org/10.1007/s10546-006-9070-8