scholarly journals Relative Humidity Effect on the High-Frequency Attenuation of Water Vapor Flux Measured by a Closed-Path Eddy Covariance System

2009 ◽  
Vol 26 (9) ◽  
pp. 1856-1866 ◽  
Author(s):  
Ivan Mammarella ◽  
Samuli Launiainen ◽  
Tiia Gronholm ◽  
Petri Keronen ◽  
Jukka Pumpanen ◽  
...  
Keyword(s):  
Water Vapor ◽  
Relative Humidity ◽  
Eddy Covariance ◽  
High Frequency ◽  
Humidity Effect ◽  
Water Vapor Flux ◽  
Sampling Tube ◽  
Vapor Flux ◽  
Eddy Covariance System ◽  
Relative Humidity Effect

Abstract In this study the high-frequency loss of carbon dioxide (CO2) and water vapor (H2O) fluxes, measured by a closed-path eddy covariance system, were studied, and the related correction factors through the cospectral transfer function method were calculated. As already reported by other studies, it was found that the age of the sampling tube is a relevant factor to consider when estimating the spectral correction of water vapor fluxes. Moreover, a time-dependent relationship between the characteristic time constant (or response time) for water vapor and the ambient relative humidity was disclosed. Such dependence is negligible when the sampling tube is new, but it becomes important already when the tube is only 1 yr old and increases with the age of the tube. With a new sampling tube, the correction of water vapor flux measurements over a Scots pine forest in Hyytiälä, Finland, amounted on average to 7%. After 4 yr the correction increased strongly, ranging from 10%–15% during the summer to 30%–40% in wintertime, when the relative humidity is typically high. For this site the effective correction improved the long-term energy and water balance. Results suggest that the relative humidity effect on high-frequency loss of water vapor flux should be taken into account and that the effective transfer function should be estimated experimentally at least once per year. On the other hand, this high correction can be avoided by a correct choice and periodic maintenance of the eddy covariance system tube, for example, by cleaning or changing it at least once per year.

Improved eddy covariance flux based transpiration estimates at high relative humidity and comparison to sap flux

2021 ◽  
Author(s):  
Weijie Zhang ◽  
Jacob A. Nelson ◽  
Rafael Poyatos ◽  
Diego Miralles ◽  
Mirco Migliavacca ◽  
...  
Keyword(s):  
Water Vapor ◽  
Relative Humidity ◽  
Eddy Covariance ◽  
High Frequency ◽  
High Relative Humidity ◽  
Closed Path ◽  
Sap Flux ◽  
Water Vapor Flux ◽  
Vapor Flux ◽  
Flux Measurements

<p>Eddy covariance (EC) directly measures evapotranspiration (ET), which consists of transpiration and evaporation (E) from the soil and other surfaces. For process understanding it is pivotal to separate ET into its components. Yet, its computation is highly sensitive to the methodology used to estimate T. Among the multiple methods proposed in recent years, T has been estimated from EC via the Transpiration Estimation Algorithm (TEA, Nelson et al., 2020), and from the sap flux measurement network SAPFLUXNET (Poyatos et al., 2020). These methods are applicable to a large number of measurement sites worldwide, and can help constrain the global estimates of the ratio of T to ET, T/ET. While EC measures water and carbon fluxes across ecosystems globally, water vapor flux measurements can be underestimated at high relative humidity (Ibrom et al., 2007; Mammarella et al., 2009) causing errors in the measured ET and propagating into the predicted T.</p><p>Here we report a method to detect and correct the high relative humidity error caused by attenuation of high frequency in water vapor measurements of a closed-path EC system. Our results of the comparison between present water use efficiency (WUE) with previous TEA-based WUE show that the corrected WUE is lower at high relative humidity than that derived from previous TEA at the sub-daily scale. Besides, we compare the corrected T estimates from EC to concurrent SAPFLUXNET sites to show an improved relationship between sap flux and EC based T, T/ET, and WUE. Finally, we explore the main abiotic factors, such as vapor pressure deficit, air temperature, and precipitation, influencing WUE estimated from different T estimation methodologies. These results provide an improved data-driven approach to the ongoing research on ET partitioning and the factors influencing the WUE across ecosystems globally.</p><p> </p><p>Ibrom, A. et al. (2007) ‘Strong low-pass filtering effects on water vapour flux measurements with closed-path eddy correlation systems’, Agricultural and Forest Meteorology. doi.org/10.1016/j.agrformet.2007.07.007.</p><p>Mammarella, I. et al. (2009) ‘Relative humidity effect on the high-frequency attenuation of water vapor flux measured by a closed-path eddy covariance system’, Journal of Atmospheric and Oceanic Technology. doi.org/10.1175/2009JTECHA1179.1.</p><p>Nelson, J. A. et al. (2020) ‘Ecosystem transpiration and evaporation: Insights from three water flux partitioning methods across FLUXNET sites’, Global Change Biology. doi: 10.1111/gcb.15314.</p><p>Poyatos, R. et al. (2020) ‘Global transpiration data from sap flow measurements: the SAPFLUXNET database’, Earth System Science Data. doi:10.5194/essd-2020-227.</p>

scholarly journals Comparative measurements of water vapor fluxes over a tall forest using open- and closed-path eddy covariance system

2015 ◽  
Vol 8 (5) ◽  
pp. 4711-4736
Author(s):  
J. B. Wu ◽  
X. Y. Zhou ◽  
A. Z. Wang ◽  
F. H. Yuan
Keyword(s):  
Water Vapor ◽  
Eddy Covariance ◽  
Time Lag ◽  
Sonic Anemometer ◽  
Co2 Flux ◽  
Closed Path ◽  
Water Vapor Flux ◽  
Vapor Flux ◽  
Flux Measurements ◽  
Eddy Covariance System

Abstract. Eddy covariance using infrared gas analyses has been a useful tool for gas exchange measurements between soil, vegetation and atmosphere. So far, comparisons between the open- and closed-path eddy covariance (CP) system have been extensively made on CO2 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 Northeast China. The results show that the fluxes from the OP system (LEop) were generally greater than the (LEcp though the two systems shared one sonic anemometer. The tube delay of closed-path analyser depended on relative humidity, and the fixed median time lag contributed to a significant underestimation of (LEcp 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 (LEop and (LEcp was generally within 6%. 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−1). This study indicates the importance to estimate the sampling tube delay accurately for water vapor flux calculations with closed-path analysers, and it also suggests that when discuss the energy balance closure problem in flux sites with closed-path eddy covariance systems, it has to be aware that some of the imbalance is possibly caused by the systematic underestimation of water vapor fluxes.

scholarly journals Comparative measurements of water vapor fluxes over a tall forest using open- and closed-path eddy covariance system

2015 ◽  
Vol 8 (10) ◽  
pp. 4123-4131 ◽  
Author(s):  
J. B. Wu ◽  
X. Y. Zhou ◽  
A. Z. Wang ◽  
F. H. Yuan
Keyword(s):  
Water Vapor ◽  
Eddy Covariance ◽  
Time Lag ◽  
Sonic Anemometer ◽  
Co2 Flux ◽  
Surface Energy Budget ◽  
Closed Path ◽  
Water Vapor Flux ◽  
Vapor Flux ◽  
Flux Measurements

Abstract. 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 CO2 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 (LEop) were generally greater than the LEcp 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 LEcp 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 LEop and LEcp 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−1). 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.

scholarly journals First-time lidar measurement of water vapor flux in a volcanic plume

2011 ◽  
Vol 284 (5) ◽  
pp. 1295-1298 ◽  
Author(s):  
Luca Fiorani ◽  
Francesco Colao ◽  
Antonio Palucci ◽  
Davod Poreh ◽  
Alessandro Aiuppa ◽  
...  
Keyword(s):  
Water Vapor ◽  
Volcanic Plume ◽  
Lidar Measurement ◽  
Water Vapor Flux ◽  
Vapor Flux ◽  
First Time

Estimation of the precipitable water and water vapor flux using MAX-DOAS in two typical  cities of China

2021 ◽  
Author(s):  
Hongmei Ren ◽  
Ang Li ◽  
Pinhua Xie ◽  
Zhaokun Hu ◽  
Jin Xu ◽  
...  
Keyword(s):  
Water Vapor ◽  
Precipitable Water ◽  
Reanalysis Data ◽  
Vapor Transport ◽  
Water Vapor Transport ◽  
Optical Absorption Spectroscopy ◽  
Water Vapor Flux ◽  
Vapor Flux ◽  
The North ◽  
Two Cities

<p>      Water vapor transport affects regional precipitation and climate change. The measurement of precipitable water and water vapor flux is of great significance to the study of precipitation and water vapor transport. In the study, a new method of computing the precipitable water and estimating the water vapor transport flux using multi-axis differential optical absorption spectroscopy (MAX-DOAS) were presented. The calculated precipitable water and water vapor flux were compared to the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis data and the correlation coefficient of the precipitable water, the zonal and meridional water vapor flux and ECMWF are r≥0.92, r=0.77 and r≥0.89, respectively. The seasonal and diurnal climatologies of precipitable water and water vapor flux in the coastal (Qingdao) and inland (Xi’an) cities of China using this method were analyzed from June 1, 2019 to May 31, 2020. The results indicated that the seasonal and diurnal variation characteristics of the precipitable water in the two cities were similar. The zonal fluxes of the two cities were mainly transported from west to east, Qingdao's meridional flux was mainly transported to the south, and Xi'an was mainly transported to the north. The results also indicated that the water vapor flux transmitting belts appear near 2km and 1.4km above the surface in Qingdao and appeared around 2.8km, 1.6km and 1.0km in Xi'an. </p>

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