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  • Calculating Canopy Stomatal Conductance from Eddy Covariance Measurements, in Light of the Energy Budget Closure Problem
Title: Calculating Canopy Stomatal Conductance from Eddy Covariance Measurements, in Light of the Energy Budget Closure Problem
Canopy stomatal conductance (gsV) is commonly estimated from eddy covariance (EC) measurements of latent heat flux (LE) by inverting the Penman-Monteith (PM) equation. That method implicitly represents the sensible heat flux (H) as the residual of all other terms in the site energy budget – even though H is measured at least as accurately as LE at every EC site while the rest of the energy budget almost never is. We argue that gsV should instead be calculated from EC measurements of both H and LE, using the flux-gradient formulation that defines conductance and underlies the PM equation. The flux-gradient formulation dispenses with unnecessary assumptions, is conceptually simpler, and provides more accurate values of gsV for all plausible scenarios in which the measured energy budget fails to close, as is common at EC sites. The PM equation, on the other hand, contributes biases and erroneous spatial and temporal patterns to gsV, skewing its relationships with drivers such as light and vapor pressure deficit. To minimize the impact of the energy budget closure problem on the PM equation, it was previously proposed that the eddy fluxes should be corrected to close the long-term energy budget while preserving the Bowen ratio (B = H/LE). We show that such a flux correction does not fully remedy the PM equation but should produce accurate values of gsV when combined with the flux-gradient formulation.  more » « less
Award ID(s):
1754803
PAR ID:
10176566
Author(s) / Creator(s):
;
Date Published:
Journal Name:
Biogeosciences discussions
ISSN:
1810-6285
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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