 |
| Titel |
Attenuation correction of water vapor fluxes from closed-path eddy-covariance systems |
| VerfasserIn |
B. R. K. Runkle, C. Wille, T. Sachs, L. Kutzbach |
| Konferenz |
EGU General Assembly 2012
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250063621
|
|
|
|
|
|
| Zusammenfassung |
| In recent work we have investigated errors that are prevalent and systematic in the
closed-path eddy-covariance measurement of latent heat flux: the attenuation of
fluxes through dampened cospectral power at high frequencies. This process is
especially pronounced during periods of high relative humidity through the adsorption
and desorption of water vapor along the tube walls. These effects are additionally
amplified during lower air temperature conditions. Fortunately, such effects can
be identified using the lag time of the cross-correlation peak between the water
vapor and vertical wind velocity signals, and can be modeled by computing the
cospectral attenuation relative to the cospectral power of simultaneous sensible
heat-flux measurements. This work found that including the role of temperature
in modifying the attenuation–humidity relationship is essential for unbiased flux
correction, and that physically based cospectral attenuation methods are effective
characterizers of closed-path instrument signal loss relative to the unattenuated flux
value.
In this presentation, we demonstrate the large magnitude of this effect on the vertical H2O
flux. Using an H2O-CO2 eddy covariance dataset taken during the 2006 growing season in a
polygonal tundra ecosystem in the Lena River Delta in Northern Siberia (72Ë 22’ N, 126Ë
30’ E), we quantify under-estimation of the water vapor flux by the closed-path
measurement system. Because environmental conditions at this site are both humid and
relatively low in temperature throughout nearly the entire year, these effects are
greater here than in other ecosystems. The water vapor flux derived without proper
accounting of the tube-based attenuation “misses” 45% of the actual water vapor flux as
corrected for the tube adsorption effects. The ecological consequences of such a
measurement correction are substantial, as site evapotranspiration is tightly coupled to the
vertical fluxes of CO2 and CH4, and the water use efficiency of plant species could be
overestimated. |
|
|
|
|
|
|