Rocky Mountain Research Station Publications

**RMRS Online Publication - Journal
Articles, External Publications, and Special Reports
The fundamental equation of eddy covariance
and its application in flux measurements**

Gu, Lianhong; Massman, William J.; Leuning, Ray; Pallardy, Stephen G.; Meyers, Tilden; Hanson, Paul J.; Riggs, Jeffery S.; Hosman, Kevin P.; Yang, Bai. 2012.

The fundamental equation of eddy covariance and its application in flux measurements. Agricultural and Forest Meteorology. 152: 135-148.doi: 10.1016/j.agrformet.2011.09.014

A fundamental equation of eddy covariance (FQEC) is derived that allows the net ecosystem exchange (NEE) Ns of a specified atmospheric constituent s to be measured with the constraint of conservation of any other atmospheric constituent (e.g. N2, argon, or dry air). It is shown that if the condition [equation, see PDF] is true, the conservation of mass can be applied with the assumption of no net ecosystem source or sink of dry air and the FQEC is reduced to the following equation and its approximation for horizontally homogeneous mass fluxes: [equation, see PDF]. Here w is vertical velocity, c molar density, t time, h eddy flux measurement height, z vertical distance and [equation, see PDF] molar mixing ratio relative to dry air. Subscripts s, d and CO2 are for the specified constituent, dry air and carbon dioxide, respectively. Primes and overbars refer to turbulent fluctuations and time averages, respectively. This equation and its approximation are derived for non-steady state conditions that build on the steady-state theory of Webb, Pearman and Leuning (WPL; Webb et al., 1980. Quart. J. R. Meteorol. Soc. 106, 85100), theory that is widely used to calculate the eddy fluxes of CO2 and other trace gases.

Keywords:fundamental equation of eddy covariance, WPL corrections, no net ecosystem source or sink of dry air, effective change in storage

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**Title:** RMRS Other
Publications: The fundamental equation of eddy covariance and
its application in flux measurements

**Electronic Publish Date:** October 9, 2012

**Last Update:** October
9, 2012