References of "Aubinet, Marc"
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See detailRespiration of three Belgian crops: Partitioning of total ecosystem respiration in its heterotrophic, above- and below-ground autotrophic components
Suleau, Marie ULg; Moureaux, Christine ULg; Dufranne, Delphine ULg et al

in Agricultural and Forest Meteorology (2011), (151), 633-643

An experimental system combining an eddy covariance system, a micrometeorological station and soil chambers placed in planted areas and in root exclusion zones was installed during three successive years ... [more ▼]

An experimental system combining an eddy covariance system, a micrometeorological station and soil chambers placed in planted areas and in root exclusion zones was installed during three successive years in a production crop managed in a traditional way at the Lonzée experimental site (Belgium). Measurements were made successively on seed potato, winter wheat and sugar beet. The general objectives of the study were, first to evaluate the relative contributions to total ecosystem respiration (TER) of heterotrophic, above ground autotrophic and below ground autotrophic respiration over a succession of three agricultural crops (seed potato, winter wheat and sugar beet) cultivated on successive years at the same location and, secondly, to identify the driving variables of these contributions. Results showed that, during the observation periods, TER was dominated by autotrophic respiration (AR) (60–90%) and that AR was dominated by its above ground component (60–80%). HR was found to increase with temperature and to be independent of Gross Primary Production (GPP), whereas AR was driven by GPP and was mostly independent of temperature. The AR response to GPP was specific to the crop: not only AR intensity but also AR distribution between its above- (ARa) and below- (ARb) ground components were found to differ from one crop to another and, in the winter wheat, from one development stage to another. Generally, ARb contribution to AR was found larger when carbon allocation towards roots was more important. An uncertainty analysis was made and showed that the main sources of uncertainties on the estimates were the spatial variability for soil chamber measurements and uncertainties linked to the data gap filling method for eddy covariance measurements. [less ▲]

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See detailFirst space-based derivation of the global atmospheric methanol emission fluxes
Stavrakou, T.; Guenther, A.; Razavi, A. et al

in Atmospheric Chemistry and Physics (2011), 11

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See detailIsoprene and monoterpene emissions from a mixed temperate forest
Laffineur, Quentin ULg; Aubinet, Marc ULg; Schoon, N. et al

in Atmospheric Environment (2011), 45

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See detailLa respiration hétérotrophe dans les sols agricoles :description des facteurs importants et comparaison de modèles semi-mécanistes existants.
Buysse, Pauline ULg; Aubinet, Marc ULg

in Biotechnologie, Agronomie, Société et Environnement = Biotechnology, Agronomy, Society and Environment [=BASE] (2010), 14(4), 707-717

Soil heterotrophic respiration is a complex process which is governed by many biotic and abiotic factors. More specifically, in the agricultural ecosystems the influence of cultural practices and residue ... [more ▼]

Soil heterotrophic respiration is a complex process which is governed by many biotic and abiotic factors. More specifically, in the agricultural ecosystems the influence of cultural practices and residue management techniques is important. Global change impacts on the phenomenon are still unclear. Some studies suggest that a positive feedback may occur. Therefore, it is necessary to get to a better knowledge of the mechanisms involved. To reach this goal, many semimechanistic models have been developed. Compared to empiric models, they allow a better understanding of soil carbon dynamics by distributing total soil carbon content into several pools. This carbon allocation is based on carbon decomposition constants. However, these models work at very different spatial and temporal scales and many differences exist between them. These ones are put forward in this paper and the main biotic and abiotic soil heterotrophic respiration factors are also described. [less ▲]

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See detailThe carbon balance of European croplands: A cross-site comparison of simulation models
Wattenbach, Martin; Sus, Olivier; Vuichard, Nicolas et al

in Agriculture, Ecosystems & Environment (2010), 139(3), 419-453

Croplands cover approximately 45% of Europe and play an important role in the overall carbon budget of the continent. However, the estimation of their carbon balance remains uncertain due to the diversity ... [more ▼]

Croplands cover approximately 45% of Europe and play an important role in the overall carbon budget of the continent. However, the estimation of their carbon balance remains uncertain due to the diversity of crops and cropping systems together with the strong influence of human management. Here, we present a multi-site model comparison for four cropland ecosystem models namely theDNDC,ORCHIDEESTICS, CERES-EGC and SPA models. We compare the accuracy of the models in predicting net ecosystem exchange (NEE), gross primary production (GPP), ecosystem respiration (Reco) as well as actual evapotranspiration (ETa) for winter wheat (Triticum aestivum L.) and maize (Zea mays L.) derived from eddy covariance measurements on five sites along a gradient of climatic conditions from eastern to southwesterly Europe. The models are all able to simulate daily GPP. The simulation results for daily ETa and Reco are, however, less accurate. The resulting simulation of daily NEE is adequate except in some cases where models fail due to a lack in phase and amplitude alignment. ORCHIDEE-STICS and PAshowthe best performance. Nevertheless, they are not able to simulate full crop rotations or the multiple management practices used. CERES-EGC, and especially DNDC, although exhibiting a lower level of model accuracy, are able to simulate such conditions, resulting in more accurate simulation of annual cumulative NEE. [less ▲]

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See detailMeasurements necessary for assessing the net ecosystem carbon budget of croplands
Smith, Pete; Lanigan, Gary; Kutsch, Werner L. et al

in Agriculture, Ecosystems & Environment (2010), 139(3), 302-315

There are a number of methods that can be used to help assess carbon budgets at the site to continental scales. Eddy covariance (EC) networks have been developed over the last decade and have been used to ... [more ▼]

There are a number of methods that can be used to help assess carbon budgets at the site to continental scales. Eddy covariance (EC) networks have been developed over the last decade and have been used to make many advances in our understanding. However, eddy covariance measurements of CO2 and water vapour exchanges quantify the fluxes only on short time scales, but do not assess the impacts of long-term processes that contribute to biogeochemical cycling in croplands, such as harvest or residue removal and other management practices, so many other supplementary measurements are required to attribute different components of the carbon flux. Such methods include isotope studies, chamber flux measurements of C and other greenhouse gases, inventories of above- and below-ground biomass as well as management in- and outputs, book-keeping modelling, process modelling, experimental manipulation and earth observation (e.g. remote sensing). In this review, we summarise the component fluxes that make up the total cropland carbon budget, describe the key fluxes and methods used to estimate them, and examine how they need to be integrated to obtain the net ecosystem carbon budget of European croplands. We describe the uncertainties and difficulties inherent at each stage and how these can be minimised. [less ▲]

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See detailNight-time airflow in a forest canopy near a mountain crest
Sedlak, Pavel; Aubinet, Marc ULg; Heinesch, Bernard ULg et al

in Agricultural and Forest Meteorology (2010), 150(5), 736-744

Night-time airflow within a deep and dense canopy near the top of a mountain ridge is investigated based on measurements at Bily Kriz, Czech Republic. The site is characterized by a young Norway spruce ... [more ▼]

Night-time airflow within a deep and dense canopy near the top of a mountain ridge is investigated based on measurements at Bily Kriz, Czech Republic. The site is characterized by a young Norway spruce forest on a 13 degrees slope and the occurrence of almost exclusively upslope or downslope flows. The forest canopy reaches the ground surface. A decoupled two-layer structure of canopy flow typically develops at night. While the above-canopy flow is most frequently an upslope-directed larger-scale flow over the ridge, the lower-canopy flow is downslope (katabatic). However, the lower-canopy flow can be forced upslope when the wind speed above the canopy exceeds a well-defined limit. Less frequently, on the lee slope to the larger-scale flow, both the above-canopy and the lower-canopy flow are usually downslope, although a flow reversal in the lower canopy is also observed, accompanied with a large shear stress (friction velocity) above the canopy. The occurrence of opposing flows is not limited to sunset/sunrise transition periods. In a simplified modelling approach to the dynamics of the nocturnal lower-canopy flow decoupled from above, local equilibrium is assumed of solely two opposing driving forces - one induced by the negative buoyancy (due to radiative cooling of the canopy) and the other by the hydrodynamic pressure gradient (resulting from the larger-scale flow over the ridge) - and the canopy drag as a retarding force. The diagnostic model gives realistic values of the major driving terms for Bily Kriz, and the downslope or upslope direction and speed of the lower-canopy flow that agree well with the measurements. The model contributes to better interpretation of the experimental results, which are in accordance with recent publications on the flow patterns on forested hills. Knowledge of the lower-canopy flow behaviour and of the degree of its decoupling from the flow aloft is necessary for assessing the contribution of advection to the CO2 budget at sloping forest sites, and for analysis of the flux footprint. (C) 2010 Elsevier B.V. All rights reserved. [less ▲]

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See detailSpatiotemporal evolution of CO2 concentration, temperature, and wind field during stable nights at the Norunda forest site
Feigenwinter, Christian; Molder, Meelis; Lindroth, Anders et al

in Agricultural and Forest Meteorology (2010), 150(5), 692-701

Unusually high CO2 concentrations were frequently observed during stable nights in late summer 2006 at the CarboEurope-Integrated Project (CEIP) forest site in Norunda, Sweden. Mean CO2 concentrations in ... [more ▼]

Unusually high CO2 concentrations were frequently observed during stable nights in late summer 2006 at the CarboEurope-Integrated Project (CEIP) forest site in Norunda, Sweden. Mean CO2 concentrations in the layer below the height of the eddy-covariance measurement system at 30 m reached up to 500 mu mol mol(-1) and large vertical and horizontal gradients occurred, leading to very large advective fluxes with a high variability in size and direction. CO2 accumulation was found to build up in the second part of the night, when the stratification in the canopy sub-layer turned from stable to neutral. Largest vertical gradients of temperature and CO2 were shifted from close to the ground early in the night to the crown space of the forest late at night, decoupling the canopy sub-layer from the surface roughness layer. At the top of the canopy at 25 m CO2 concentrations up to 480 mu mol mol(-1) were observed at all four tower locations of the 3D cube setup and concentrations were still high (>400 mu mol mol(-1)) at the 100 m level of the Central tower. The vertical profiles of horizontal advective fluxes during the nights under investigation were similar and showed largest negative horizontal advection (equivalent to an additional CO2-sink) to occur in the crown space of the forest, and not, as usually expected, close to the ground. The magnitude of these fluxes was sometimes larger than 50 mu mol m(-2) s(-1)and they were caused by the large horizontal CO2 concentration gradients with maximum values of up to 1 mu mol mol(-1) m(-1). As a result of these high within canopy CO2 concentrations, the vertical advection also became large with frequent changes of direction according to the sign of the mean vertical wind component, which showed very small values scattering around zero. Inaccuracy of the sonic anemometer at such low wind velocities is the reason for uncertainty in vertical advection, whereas for horizontal advection, instrument errors were small compared to the fluxes. The advective fluxes during these nights were unusually high and it is not clear what they represent in relation to the biotic fluxes. Advection is most likely a scale overlapping process. With a control volume of about 100 m x 100 m x 30 m and the applied spatial resolution of the sensors, we obviously miss relevant information from processes in the mesoscale as well as in the turbulent scale. (C) 2009 Elsevier B.V. All rights reserved. [less ▲]

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See detailPlot-scale vertical and horizontal transport of CO2 modified by a persistent slope wind system in and above an alpine forest
Feigenwinter, Christian; Montagnani, Leonardo; Aubinet, Marc ULg

in Agricultural and Forest Meteorology (2010), 150(5), 665-673

Data from the flux tower site Renon/Ritten, Italy, located at 1735 m. a.s.l. on a south exposed steep (11 degrees) forested alpine slope, is analyzed. In spite of the complex terrain, a persistent slope ... [more ▼]

Data from the flux tower site Renon/Ritten, Italy, located at 1735 m. a.s.l. on a south exposed steep (11 degrees) forested alpine slope, is analyzed. In spite of the complex terrain, a persistent slope wind system prevailed at the site during most of the ADVEX campaign from April to September 2005. We describe in detail how CO2 is transported parallel to the slope and how this transport affects net ecosystem exchange (NEE) in the diurnal course. The local slope wind system may be strongly modified by two different large scale synoptic situations. The "Tramontana", a persistent strong wind from the north, amplified the drainage flow during nighttime and suppressed the upslope flow above the forest canopy during daytime. Vice versa, we observed periods with continuing flow from the south, which supported the local daytime upslope flow and partly suppressed the nighttime downslope flow. This led to periods of several hours with opposite flow directions in and above the canopy. Depending on the prevailing situation, the trunk space is coupled and/or decoupled with/from the roughness sublayer above the forest canopy. In particular, vertical and horizontal mixing of CO2 was strongly dependent on the dominating wind field with essential impact on the horizontal advective flux of CO2. The most common "Local" situation, dominated by the slope wind system, showed positive horizontal and vertical advection (with typical values around 7 and 3 mu mol m(-2) s(-1), respectively) together with downslope winds at night and slightly negative horizontal advection (typical values around 2 mu mol m(-2) s(-1)) together with upslope winds during the day. This pattern was amplified at night when the wind was consistently (day and night) blowing downslope (the "Tramontana" situation) and, vice versa, attenuated during the night, when the wind was blowing permanently upslope (the "Southerlies" situation). Taking into account these advective fluxes would significantly reduce the reported annual CO2 uptake of this forest. Related effects are expected to occur at flux tower sites with similar topography and vegetation. (C) 2009 Elsevier B.V. All rights reserved. [less ▲]

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See detailDirect advection measurements do not help to solve the night-time CO2 closure problem: Evidence from three different forests
Aubinet, Marc ULg; Feigenwinter, Christian; Heinesch, Bernard ULg et al

in Agricultural and Forest Meteorology (2010), 150(5), 655-664

The ADVEX project involved conducting extensive advection measurements at three sites, each with a different topography. One goal of the project was to measure the [CO2] balance under night-time ... [more ▼]

The ADVEX project involved conducting extensive advection measurements at three sites, each with a different topography. One goal of the project was to measure the [CO2] balance under night-time conditions, in an attempt to improve NEE estimates. Four towers were arranged in a square around a main tower, with the sides of the square about 100 m long. Equipped with 16 sonic anemometers and [CO2] sampling points, the towers were installed to measure vertical and horizontal advection of [CO2]. Vertical turbulent fluxes were measured by an eddy covariance system at the top of the main tower. The results showed that horizontal advection varied greatly from site to site and from one wind sector to another, the highest values being reached when there were large friction velocities and fairly unstable conditions. There was less variation in vertical advection, the highest values being reached when there were low friction velocities and stable conditions. The night-time NEE estimates deduced from the mass balance were found to be incompatible with biologically driven fluxes because (i) they varied strongly from one wind sector to another and this variation could not be explained in terms of a response of the biologic flux to climate, (ii) their order of magnitude was not realistic and (iii) they still showed a trend vs. friction velocity. From a critical analysis of the measurement and data treatment we concluded that the causes of the problem are related to the representativeness of the measurement (control volume size, sampling resolution) or the hypotheses underlying the derivation of the [CO2] mass balance (ignoring the horizontal turbulent flux divergence). This suggests that the improvement of eddy flux measurements by developing an advection completed [CO2] mass balance at night would be practically difficult. (C) 2010 Elsevier B.V. All rights reserved. [less ▲]

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See detailDirect CO2 advection measurements and the night flux problem
Aubinet, Marc ULg; Feigenwinter, Christian

in Agricultural and Forest Meteorology (2010), 150(5), 651-654

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See detailAnnual-scale adaptation of a soil heterotrophic respiration model to three agricultural sites in Belgium and South-Western France.
Buysse, Pauline ULg; Le Dantec, Valérie; Mordelet, Patrick et al

in Geophysical Research Abstracts (2010, May 06), 12

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See detailLong term carbon dioxide exchange above a mixed forest in the Belgian Ardennes: evaluation of different approaches to deduce total ecosystem respiration from Eddy covariance measurements
Jerome, Elisabeth ULg; Heinesch, Bernard ULg; Aubinet, Marc ULg

Poster (2010, May 05)

The general aim of this research is to analyze inter annual variability of carbon dioxide (CO2) fluxes exchanged by a mixed forest located at the Vielsalm experimental site in Belgium. At this site, CO2 ... [more ▼]

The general aim of this research is to analyze inter annual variability of carbon dioxide (CO2) fluxes exchanged by a mixed forest located at the Vielsalm experimental site in Belgium. At this site, CO2 flux measurements started in 1996 and are still going on. Thirteen complete years of measurements are thus available. Net Ecosystem Exchange (NEE) inter annual variability may be driven by gross primary productivity (GPP) or Total Ecosystem Respiration (TER), which should thus be both quantified. Using flux partitioning methods, TER is deduced from NEE measurements. GPP is then obtained by subtracting TER from NEE. Initially, a robust estimation of TER is required. This work seeks to compare two independent approaches to assess TER in order to quantify the implications on inter-annual variability. The comparison was performed on twelve complete years. TER estimates can be deduced by extrapolating to the whole day NEE measurements taken during selected night or day periods. In both case, the extrapolation is performed by using a respiration response to temperature. The first approach, referred as the night-time approach, consisted in calculating TER using a temperature response function derived from night-time data sets (Reichstein et al., 2005). The second approach, referred as the daytime approach, consisted in assessing TER from the intercept of the NEE/Photosynthetically Photon Flux Density (PPFD) response (Wohlfahrt et al., 2005). For each approach, different modalities were compared: the use of long term (annual) or short term (15 days) data sets for the night-time approach and the use of different types of regression for the daytime approach. In addition, the impact of the temperature choice was studied for each of the approaches. For the night-time approach, main results showed that air temperature sensitivity of ecosystem respiration derived from annual data did not reflect the short-term air temperature sensitivity. Vielsalm is a summer active ecosystem (annual temperature sensitivity larger than short-term temperature sensitivity). Results suggested also that, for both approaches, regressions based on soil temperature gave more robust results than those based on air temperature. Furthermore, the comparison showed that the night-time and the daytime approaches give disagreeing pictures of TER inter annual variability which suggested that the choice of the approach is critical in order to correctly depict TER inter annual variability. Finally, at this stage, TER inter annual variability cannot be explained by variability of climatic conditions. [less ▲]

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See detailVOC emissions from a temperate mixed forest in Belgium measured by eddy-covariance
Laffineur, Quentin ULg; Heinesch, Bernard ULg; Aubinet, Marc ULg et al

Poster (2010, May)

Forest ecosystems are known to be important emitters of Biogenic Volatile Organic Compounds (BVOC). They play an important role in the atmospheric chemistry and may contribute to the formation of ozone ... [more ▼]

Forest ecosystems are known to be important emitters of Biogenic Volatile Organic Compounds (BVOC). They play an important role in the atmospheric chemistry and may contribute to the formation of ozone and aerosols with consequences on air quality and on climate. In order to better understand the effects of environmental parameters on the emissions, micrometeorological flux measurements were carried out above a mixed forest (Fagus sylvatica, Pseudotsuga menziesii, Abies alba, Picea abies) at the Vielsalm experimental site (Belgium) from July to November 2009. The flux measurements were obtained by the eddy-covariance technique using proton transfer reaction mass spectrometry. In our first measurement campaign, among other VOC compounds, isoprene (m/z 69) and monoterpenoid compounds (m/z 137) have been measured continuously with a data coverage of 75 and 58 % respectively, allowing robust statistical analysis. In our analysis, we focused on these two main emissions. A footprint analysis showed that Fagus sylvatica seems to be the main emitter of m/z 137 and Abies alba seems to be the main emitter of m/z 69. BVOCs fluxes present an exponential response to temperature. This response is more pronounced for m/z 69 while it shows the strongest seasonal evolution for m/z 137. A light dependence of m/z 69 and m/z 137 fluxes was observed but the relationship did not exhibit the same behaviour before (hyperbolic relation) and after midday (linear relation). This behaviour difference induced a hysteresis effect on the daily evolution of averaged fluxes. A robust local minimum was also observed just before midday for m/z 69 (less obvious for m/z 137) during July-August period. This minimum is not observed in the CO2 fluxes which are also measured in Vielsalm. The light dependence of BVOC emissions suggests that m/z 69 and m/z 137 emissions are directly linked to the photosynthetic cycle but the presence of the midday local minimum suggests that other processes influence the measured BVOC fluxes. As for the relation with air temperature, a seasonal evolution of flux-light dependence was far more evident for m/z 137 than for m/z 69. This seasonal variation could be explained by a phenological effect. As Fagus sylvatica is the main m/z 137 emitter, its flux is probably influenced by leaves ageing while m/z 69, as mainly emitted by Abies alba, is less influenced by needles ageing. A wind speed dependence of BVOCs fluxes was also observed, the flux increasing linearly with wind speed. This surprising result will be discussed. [less ▲]

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See detailLes flux de CO2 en grandes cultures
Dufranne, Delphine ULg; Jerome, Elisabeth ULg; Moureaux, Christine ULg et al

Conference (2010, February 24)

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See detailLes grandes cultures et le cycle du carbone
Moureaux, Christine ULg; Aubinet, Marc ULg; Dufranne, Delphine ULg et al

in Livre Blanc Céréales (2010, February 24)

Le cycle du carbone et les flux de carbone dans une culture - Perspectives

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See detailModelling total soil respiration in agricultural soils.
Buysse, Pauline ULg; Goffin, Stéphanie; Carnol, Monique ULg et al

Poster (2010, January 12)

Soil respiration is a process which results in CO2 release from the soil to the atmosphere. It comprises two main components. The first one is heterotrophic respiration: CO2 is produced by soil ... [more ▼]

Soil respiration is a process which results in CO2 release from the soil to the atmosphere. It comprises two main components. The first one is heterotrophic respiration: CO2 is produced by soil microorganisms while decomposing the substrate. The second one is autotrophic respiration in which CO2 originates from roots and rhizospheric organisms. All the CO2 is then transported to the surface by diffusion (see Goffin et al., this session). Many biotic and abiotic factors play a role in soil respiration, making this process complex to analyze and understand. Temperature often appears as the most important driving variable. Besides that, interest in the future CO2 emissions from agricultural soils has been growing. Indeed, these ecosystems are a major concern from environmental, economic and social points of view. In particular, the choice of cultural practices and residue management techniques has a strong influence on CO2 emissions from agricultural systems. This work aims at getting to a better understanding of soil respiration in agricultural soils. To reach this goal, many semi-mechanistic models have been previously developed at very different spatio-temporal scales. We intend to adapt such an existing model to crop soils, within a spatial scale of a cultivated field and an annual temporal scale. The model will be validated by using flux measurements carried out at three different crop sites situated in the Hesbaye region in Belgium (Lonzée) and in the South West of France (Lamasquère, Auradé). The study was focused first on soil heterotrophic respiration. Within this part, short term sensitivity of this component to temperature was studied by means of a laboratory incubation experiment. This one was performed with soil samples taken at the Lonzée site. Among the many interesting results we got, it showed a clear sensitivity of soil heterotrophic respiration to short term temperature changes. In parallel, the soil heterotrophic model was calibrated on soil chamber measurements taken at the Lonzée site (Belgium). Next steps in this part of the work will be to calibrate the model using the data from the French sites, and finally to validate the model on the three sites. Afterwards, an autotrophic respiration submodel will be implemented and the results compared to field measurements carried out at the three sites. A further development could consist in simulating agricultural practices to take their impacts on CO2 emissions from crops into account. [less ▲]

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See detailNew Transfer Functions for Correcting Turbulent Water Vapour Fluxes
De Ligne, Anne ULg; Heinesch, Bernard ULg; Aubinet, Marc ULg

in Boundary-Layer Meteorology (2010), 137(2), 205-221

We address the problem of the high-frequency correction of water vapour fluxes measured by eddy covariance with a closed-path infrared gas analyser (IRGA). Different transfer functions are compared and ... [more ▼]

We address the problem of the high-frequency correction of water vapour fluxes measured by eddy covariance with a closed-path infrared gas analyser (IRGA). Different transfer functions are compared and evaluated at a forested (Vielsalm, Belgium) and an agricultural (Lonz,e, Belgium) site. Classical functions, usually applied to correct CO2 fluxes (Gaussian, Lorentzian), are found to be unsuited to water vapour cospectral corrections, being characterised by too sharp a decrease at high frequency. Two other functions characterised by a lower decreasing slope are found to better fit experimental transfer functions. They were calibrated and validated on experimental transfer functions and their dependency on air humidity is parameterised. On this basis, new correction coefficients are estimated. The coefficients are found to be larger than those based on the classical functions, even when the dependency of the latter on air humidity is taken into account. The difference amounts to 10 at the forested site and to 5 larger at the crop site. The study highlights the necessity of characterising the water transfer function shape and taking it into account in the correction factor at each site equipped with a closed path IRGA. [less ▲]

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