On the consequences of the energy imbalance for calculating surface conductance to water vapour.
The Penman-Monteith combination equation, which is most frequently used to derive the surface conductance to water vapour (Gs), implicitly assumes the energy balance to be closed. Any energy imbalance (positive or negative) will thus affect the calculated Gs. Using eddy covariance energy flux data from a temperate grassland and a desert shrub ecosystem we explored five possible approaches of closing the energy imbalance and show that calculated Gsmay differ considerably between these five approaches depending on the relative magnitudes of sensible and latent heat fluxes, and the magnitude and sign of the energy imbalance. Based on our limited understanding of the nature of the energy imbalance, we tend to favour an approach which preserves the Bowen-ratio and closes the energy balance on a larger time scale.
Institut für Ökologie, Universität Innsbruck, Sternwartestr. 15, 6020 Innsbruck, AUSTRIA.
Georg
G
Wohlfahrt
Institut für Ökologie, Universität Innsbruck, Sternwartestr. 15, 6020 Innsbruck, AUSTRIA.
Alois
A
Haslwanter
Institut für Ökologie, Universität Innsbruck, Sternwartestr. 15, 6020 Innsbruck, AUSTRIA.
Lukas
L
Hörtnagl
Division of Earth and Ecosystem Sciences, Desert Research Institute, 2215 Raggio Parkway, Reno NV 89512, USA.
Richard L
RL
Jasoni
Division of Earth and Ecosystem Sciences, Desert Research Institute, 755 E. Flamingo Road, Las Vegas NV 89119, USA.
Lynn F
LF
Fenstermaker
Division of Earth and Ecosystem Sciences, Desert Research Institute, 2215 Raggio Parkway, Reno NV 89512, USA.
John A
JA
Arnone
Institut für Ökologie, Universität Innsbruck, Sternwartestr. 15, 6020 Innsbruck, AUSTRIA.
Albin
A
Hammerle
Penman-Monteith combination equation; eddy covariance; energy balance closure