Direct CO2 advection measurements and the night flux problem

Aubinet, Marc; Feigenwinter, Christian

doi:10.1016/j.agrformet.2010.03.007

Cited by 18 publications

(21 citation statements)

References 20 publications

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“…This suggests net assimilation of CO 2 by the forest vegetation at night, very unlikely in this ecosystem and therefore indicative of advection events, which are likely at this site under stable night-time conditions. Although there is no commonly agreed method to account for advection (Aubinet and Feigenwinter, 2010) our approach is consistent with the general logic of other methods. Other authors have recorded such errors with open-path setups (Lloyd, 2006;Hirata et al, 2007) and it is unlikely that such erroneous fluxes were caused solely by instrument error or interference by precipitation, with only 25 % of erroneous results removed by implementing LE and H thresholds for Wytham Woods data.…”

Section: Negative Night-time Fluxesmentioning

confidence: 51%

Carbon dioxide fluxes over an ancient broadleaved deciduous woodland in southern England

et al. 2011

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Abstract.We present results from a study of canopyatmosphere fluxes of carbon dioxide from 2007 to 2009 above a site in Wytham Woods, an ancient temperate broadleaved deciduous forest in southern England. Gapfilled net ecosystem exchange (NEE) data were partitioned into gross primary productivity (GPP) and ecosystem respiration (R e ) and analysed on daily, monthly and annual timescales. Over the continuous 24 month study period annual GPP was estimated to be 21.1 Mg C ha −1 yr −1 and R e to be 19.8 Mg C ha −1 yr −1 ; net ecosystem productivity (NEP) was 1.2 Mg C ha −1 yr −1 . These estimates were compared with independent bottom-up estimates derived from net primary productivity (NPP) and flux chamber measurements recorded at a plot within the flux footprint in 2008 (GPP = 26.5 ± 6.8 Mg C ha −1 yr −1 , R e = 24.8 ± 6.8 Mg C ha −1 yr −1 , biomass increment = ∼1.7 Mg C ha −1 yr −1 ). Over the two years the difference in seasonal NEP was predominantly caused by changes in ecosystem respiration, whereas GPP remained similar for equivalent months in different years. Although solar radiation was the largest influence on daily values of CO 2 fluxes (R 2 = 0.53 for the summer months for a linear regression), variation in R e appeared to be driven by temperature. Our findings suggest that this ancient woodland site is currently a substantial sink for carbon, resulting from continued growth that is probably a legacy of past management practices abandoned over 40 years ago. Our GPP and R e values are generally higher than other broadleaved temperate deciduous woodlands and may represent the influence of the UK's maritime climate, or the particular species composition of this site. The carbon sink value of Wytham Woods Correspondence to: Y. Malhi (yadvinder.malhi@ouce.ox.ac.uk) supports the protection and management of temperate deciduous woodlands (including those managed for conservation rather than silvicultural objectives) as a strategy to mitigate atmospheric carbon dioxide increases.

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Section: Negative Night-time Fluxesmentioning

confidence: 51%

Carbon dioxide fluxes over an ancient broadleaved deciduous woodland in southern England

et al. 2011

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“…While the eddy-covariance technique measures fluxes of momentum and scalars accurately in well-mixed convective boundary layer conditions, challenges in the measurement of net ecosystem exchange in the stable nocturnal boundary layer have been reported (Aubinet, 2010;Falge et al, 2001;Goulden et al, 1996;Karipot et al, 2008;Mahrt, 1999Mahrt, , 2010Mathieu et al, 2005). One challenge that must be encountered when conducting eddy-flux measurements in a stable boundary layer is the presence of wave-like disturbances (Nappo et al, 2008).…”

Section: Introductionmentioning

confidence: 99%

“…One challenge that must be encountered when conducting eddy-flux measurements in a stable boundary layer is the presence of wave-like disturbances (Nappo et al, 2008). Though the properties and propagation of wave-like disturbances in the boundary layer have been extensively studied (Chimonas, 1993(Chimonas, , 1999Finnigan, 1981, 1993;Einaudi et al, 1984;Finnigan and Einaudi, 1981;Hooke et al, 1973;Nappo, 2002), scant attention has been given to the impact of waves on turbulence and turbulent fluxes (Nappo et al, 2008;Viana et al, 2009;Zeri and Sa, 2010).…”

Section: Introductionmentioning

confidence: 99%

“…Waves are ubiquitous in the nocturnal boundary layer (Gossard and Hooke, 1975;Grivet-Talocia et al, 1999;Nappo, 2002;Rees et al, 2000) and can be generated by a number of mechanisms, including thunderstorms (Gedzelman, 1983), orographic excitation (terrain induced) (Chimonas, 1993), and shear instability (Emmanuel, 1973;Hooke et al, 1973). Ducted waves are bound between the ground surface and some atmospheric reflecting layer above or two reflecting critical layers aloft (Cooper et al, 2006;Fritts et al, 2003;Newsom and Banta, 2003;Rees and Mobbs, 1988), thus producing a wave guide allowing propagation to occur over long distances and time periods.…”

Section: Introductionmentioning

confidence: 99%

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On the impact of wave-like disturbances on turbulent fluxes and turbulence statistics in nighttime conditions: a case study

Durden

Nappo²,

Leclerc

et al. 2013

Biogeosciences

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Abstract. The interpretation of flux measurements in nocturnal conditions is typically fraught with challenges. This paper reports on how the presence of wave-like disturbances in a time series, can lead to an overestimation of turbulence statistics, errors when calculating the stability parameter, erroneous estimation of the friction velocity u * used to screen flux data, and errors in turbulent flux calculations. Using time series of the pressure signal from a microbarograph, wavelike disturbances at an AmeriFlux site are identified. The wave-like disturbances are removed during the calculation of turbulence statistics and turbulent fluxes. Our findings suggest that filtering eddy-covariance data in the presence of wave-like events prevents both an overestimation of turbulence statistics and errors in turbulent flux calculations. Results show that large-amplitude wave-like events, events surpassing three standard deviations, occurred on 18 % of the nights considered in the present study. Remarkably, on flux towers located in a very stably stratified boundary-layer regime, the presence of a gravity wave can enhance turbulence statistics more than 50 %. In addition, the presence of the disturbance modulates the calculated turbulent fluxes of CO 2 resulting in erroneous turbulent flux calculations of the order of 10 % depending on averaging time and pressure perturbation threshold criteria. Furthermore, the friction velocity u * was affected by the presence of the wave, and in at least one case, a 10 % increase caused u * to exceed the arbitrary 0.25 m s −1 threshold used in many studies. This results in an unintended bias in the data selected for analysis in the flux calculations. The impact of different averaging periods was also examined and found to be variable specific. These early case study results provide an insight into errors introduced when calculating "purely" turbulent fluxes. These results could contribute to improving modeling efforts by providing more accurate inputs of both turbulent kinetic energy, and isolating the turbulent component of u * for flux selection in the stable nocturnal boundary layer.

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“…Sensors on the tower above the canopy cannot measure the fluxes conducted by drainage flow because the layer above the canopy is decoupled from the drainage flow by the isolating super-stable layer. This advection problem is a well-known issue that has not yet been solved using eddy-flux measurements (Goulden et al, 1996;Aubinet et al, 2003;Staebler and Fitzjarrald, 2004;Sun et al, 2007;Yi et al, 2008;Montagnani et al, 2009;Feigenwinter et al, 2010;Aubinet and Feigenwinter, 2010;Queck and Bernhofer, 2010;Tóta et al, 2012;Siebicke et al, 2012).…”

Section: Xu Et Al: Stably Stratified Canopy Flow In Complex Terrainmentioning

confidence: 99%

Stably stratified canopy flow in complex terrain

Kutter

2015

Atmos. Chem. Phys.

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Abstract. Stably stratified canopy flow in complex terrain has been considered a difficult condition for measuring net ecosystem-atmosphere exchanges of carbon, water vapor, and energy. A long-standing advection error in eddy-flux measurements is caused by stably stratified canopy flow. Such a condition with strong thermal gradient and less turbulent air is also difficult for modeling. To understand the challenging atmospheric condition for eddy-flux measurements, we use the renormalized group (RNG) k-ε turbulence model to investigate the main characteristics of stably stratified canopy flows in complex terrain. In this twodimensional simulation, we imposed persistent constant heat flux at ground surface and linearly increasing cooling rate in the upper-canopy layer, vertically varying dissipative force from canopy drag elements, buoyancy forcing induced from thermal stratification and the hill terrain. These strong boundary effects keep nonlinearity in the two-dimensional NavierStokes equations high enough to generate turbulent behavior. The fundamental characteristics of nighttime canopy flow over complex terrain measured by the small number of available multi-tower advection experiments can be reproduced by this numerical simulation, such as (1) unstable layer in the canopy and super-stable layers associated with flow decoupling in deep canopy and near the top of canopy; (2) sub-canopy drainage flow and drainage flow near the top of canopy in calm night; (3) upward momentum transfer in canopy, downward heat transfer in upper canopy and upward heat transfer in deep canopy; and (4) large buoyancy suppression and weak shear production in strong stability.

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Direct CO2 advection measurements and the night flux problem

Cited by 18 publications

References 20 publications

Carbon dioxide fluxes over an ancient broadleaved deciduous woodland in southern England

Carbon dioxide fluxes over an ancient broadleaved deciduous woodland in southern England

On the impact of wave-like disturbances on turbulent fluxes and turbulence statistics in nighttime conditions: a case study

Stably stratified canopy flow in complex terrain

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