Comparative measurements of water vapor fluxes over a tall forest using open- and closed-path eddy covariance system
Eddy covariance using infrared gas analyzes has been a useful tool for gas exchange measurements between soil, vegetation and the atmosphere. So far, comparisons between the open- and closed-path eddy covariance (CP) system have been extensively made on CO<sub>2</sub> flux estimations, w...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2015-10-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | http://www.atmos-meas-tech.net/8/4123/2015/amt-8-4123-2015.pdf |
| Summary: | Eddy covariance using infrared gas analyzes has been a useful tool for gas
exchange measurements between soil, vegetation and the atmosphere. So far,
comparisons between the open- and closed-path eddy covariance (CP) system
have been extensively made on CO<sub>2</sub> flux estimations, while lacking in
the comparison of water vapor flux estimations. In this study, the specific
performance of water vapor flux measurements of an open-path eddy covariance
(OP) system was compared against a CP system over a tall temperate forest in
northeastern China. The results show that the fluxes from the OP system
(<i>LE</i><sub>op</sub>) were generally greater than the <i>LE</i><sub>cp</sub> though the two systems
shared one sonic anemometer. The tube delay of closed-path analyzer depended
on relative humidity, and the fixed median time lag contributed to a
significant underestimation of <i>LE</i><sub>cp</sub> between the forest and atmosphere,
while slight systematic overestimation was also found for covariance
maximization method with single broad time lag search window. After the
optimized time lag compensation was made, the average difference between the
30 min <i>LE</i><sub>op</sub> and <i>LE</i><sub>cp</sub> was generally within 6.0 %. Integrated over
the annual cycle, the CP system yielded a 5.1 % underestimation of forest
evapotranspiration as compared to the OP system measurements (493 vs. 469 mm yr<sup>−1</sup>). This study indicates the importance to
estimate the sampling tube delay accurately for water vapor flux
calculations with closed-path analyzers, and it also suggests that some of
the imbalance of the surface energy budget in flux sites is possibly
caused by the systematic underestimation of water vapor fluxes measured with
closed-path eddy covariance systems. |
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| ISSN: | 1867-1381 1867-8548 |