Some aspects of the energy balance closure problem

Foken, Thomas; Wimmer, Florian; Mauder, Matthias; Thomas, Christoph; Liebethal, Claudia

doi:10.5194/acp-6-4395-2006

Cited by 284 publications

(147 citation statements)

References 26 publications

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“…The convention of positive values representing fluxes upward from the surface is used herein. The planar fit method of Wilczak et al (2001) was applied across the entire dataset in order to rotate sonic anemometer data into mean wind coordinates, and ogive analyses were prepared across the longest continuous measurement period (5.4 days) according to Foken et al (2006) in order to determine an appropriate flux averaging period. Quality control flags were calculated for each averaging period using the scheme of Foken et al (2004), and fluxes given a flag 2 were discarded from further analyses.…”

Section: Flux Instrumentation and Methodsmentioning

confidence: 99%

“…Though each scalar has its own unique sources and sinks (Foken et al, 2006), these results were taken to suggest that low-frequency contributions to GEM fluxes at this site were also minimal. The averaging period was set at 60 min, as this gave some smoothing to both flux and environmental data, allowing for greater comparison between the two that was not achievable using 20 min averaging.…”

Section: Gem Fluxes 321 Quality Controlmentioning

confidence: 99%

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Mercury fluxes over an Australian alpine grassland and observation of nocturnal atmospheric mercury depletion events

Howard

Edwards

2018

Atmos. Chem. Phys.

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Abstract. Aerodynamic gradient measurements of the airsurface exchange of gaseous elemental mercury (GEM) were undertaken over a 40 ha alpine grassland in Australia's Snowy Mountains region across a 3-week period during the late austral summer. Bi-directional GEM fluxes were observed throughout the study, with overall mean value of 0.2 ± 14.5 ng m −2 h −1 and mean nocturnal fluxes of −1.5 ± 7.8 ng m −2 h −1 compared to diurnal fluxes of 1.8 ± 18.6 ng m −2 h −1 . Deposition velocities ranged from −2.2 to 2.9 cm s −1 , whilst ambient GEM concentrations throughout the study were 0.59 ± 0.10 ng m −3 . Cumulative GEM fluxes correlated well with 24 h running mean soil temperatures, and one precipitation event was shown to have a positive impact on diurnal emission fluxes. The underlying vegetation had largely senesced and showed little stomatal control on fluxes. Nocturnal atmospheric mercury depletion events (NAMDEs) were observed concomitant with O 3 depletion and dew formation under shallow, stable nocturnal boundary layers. A mass balance box model was able to reproduce ambient GEM concentration patterns during NAMDE and non-NAMDE nights without invoking chemical oxidation of GEM throughout the column, indicating a significant role of surface processes controlling deposition in these events. Surface deposition was enhanced under NAMDE nights, though uptake to dew likely represents less than one-fifth of this enhanced deposition. Instead, enhancement of the surface GEM gradient as a result of oxidation at the surface in the presence of dew is hypothesised to be responsible for a large portion of GEM depletion during these particular events. GEM emission pulses following nights with significant deposition provide evidence for the prompt recycling of 17 % of deposited mercury, with the remaining portion retained in surface sinks. The long-term impacts of any sinks are however likely to be minimal, as cumulative GEM flux across the study period was close to zero.

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Section: Flux Instrumentation and Methodsmentioning

confidence: 99%

Section: Gem Fluxes 321 Quality Controlmentioning

confidence: 99%

Mercury fluxes over an Australian alpine grassland and observation of nocturnal atmospheric mercury depletion events

Howard

Edwards

2018

Atmos. Chem. Phys.

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“…Subsequently, surface flux estimates of CO 2 , sensible and latent heat were derived using ogive optimization (Sievers et al, 2015). The approach allows for separation of vertical turbulent flux and contributions from larger-scale motions by optimization of a model, ogive spectral distribution (Desjardins et al, 1989;Foken et al, 2006), to a density distribution of a large number of ogive spectral distributions, for which the data set length and detrending by running mean are varied simultaneously. Flux estimates are discarded only if an excessive number of gaps are present in the raw data set or if no theoretical model ogive distribution can be optimized sufficiently.…”

Section: Flux Measurements and Analysismentioning

confidence: 99%

Winter observations of CO<sub>2</sub> exchange between sea ice and the atmosphere in a coastal fjord environment

et al. 2015

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Abstract. Eddy covariance observations of CO 2 fluxes were conducted during March-April 2012 in a temporally sequential order for 8, 4 and 30 days, respectively, at three locations on fast sea ice and on newly formed polynya ice in a coastal fjord environment in northeast Greenland. CO 2 fluxes at the sites characterized by fast sea ice (ICEI and DNB) were found to increasingly reflect periods of strong outgassing in accordance with the progression of springtime warming and the occurrence of strong wind events: F ICE1 CO 2 = 1.73 ± 5 mmol m −2 day −1 and F DNB CO 2 = 8.64 ± 39.64 mmol m −2 day −1 , while CO 2 fluxes at the polynya site (POLYI) were found to generally reflect uptake F POLY1 CO 2 = −9.97 ± 19.8 mmol m −2 day −1 . Values given are the mean and standard deviation, and negative/positive values indicate uptake/outgassing, respectively. A diurnal correlation analysis supports a significant connection between site energetics and CO 2 fluxes linked to a number of possible thermally driven processes, which are thought to change the pCO 2 gradient at the snow-ice interface. The relative influence of these processes on atmospheric exchanges likely depends on the thickness of the ice. Specifically, the study indicates a predominant influence of brine volume expansion/contraction, brine dissolution/concentration and calcium carbonate formation/dissolution at sites characterized by a thick sea-ice cover, such that surface warming leads to an uptake of CO 2 and vice versa, while convective overturning within the sea-ice brines dominate at sites characterized by comparatively thin sea-ice cover, such that nighttime surface cooling leads to an uptake of CO 2 to the extent permitted by simultaneous formation of superimposed ice in the lower snow column.

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“…The problem of energy imbalance when measuring turbulent vertical fluxes at some height above the surface has been widely studied in the last few years (Culf et al, 2004;Foken et al, 2006Foken et al, , 2008Wilson et al, 2002;Tanaka et al, 2008;Barr et al, 2006;Oncley et al, 2007). The eddy-covariance (EC) method has become a standard tool in the study of the surface-atmosphere boundary layer interactions.…”

Section: Introductionmentioning

confidence: 99%

Analysis of the energy balance closure over a FLUXNET boreal forest in Finland

Sánchez

Caselles

Rubio

2010

Hydrol. Earth Syst. Sci.

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Abstract. The imbalance in the surface energy budget, when using eddy-covariance techniques to measure turbulent fluxes, is still an unresolved problem. Important progresses have been reported in recent years identifying potential reasons for this lack of energy balance closure. In this paper we focus on the data collected in a FLUXNET boreal forest site in Sodankylä, Finland. Using one month half-hourly data, an average Energy Balance Ratio (EBR) of 0.72 is obtained. The inclusion of the heat storage terms in the energy budget yields an improvement of about 6% in the total closure. The sensitivity of the energy balance closure to the turbulence intensity is analysed in terms of the friction velocity, and atmospheric stability/instability conditions. Significant better closure is obtained for high values of the friction velocity and unstable conditions. The mismatch in variable footprints for different fluxes is checked by analysing the dependence of the closure on wind direction. The inhomogeneities of the emplacement surrounding the flux tower induce a critical decrease in the EBR of up to 30% for specific wind directions. After filtering all unfavourable conditions, EBR=0.94. This is a reasonable good result for the energy balance closure. However there is still a 6% of the available energy unaccounted. Part of this remaining imbalance could be justified as the impossibility of the 30 min averaging time to capture the low frequency flux contributions, since the closure is improved by a 5% when the averaging time is expanded to 2 h.

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Some aspects of the energy balance closure problem

Cited by 284 publications

References 26 publications

Mercury fluxes over an Australian alpine grassland and observation of nocturnal atmospheric mercury depletion events

Mercury fluxes over an Australian alpine grassland and observation of nocturnal atmospheric mercury depletion events

Winter observations of CO<sub>2</sub> exchange between sea ice and the atmosphere in a coastal fjord environment

Analysis of the energy balance closure over a FLUXNET boreal forest in Finland

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Some aspects of the energy balance closure problem

Cited by 284 publications

References 26 publications

Mercury fluxes over an Australian alpine grassland and observation of nocturnal atmospheric mercury depletion events

Mercury fluxes over an Australian alpine grassland and observation of nocturnal atmospheric mercury depletion events

Winter observations of CO&lt;sub&gt;2&lt;/sub&gt; exchange between sea ice and the atmosphere in a coastal fjord environment

Analysis of the energy balance closure over a FLUXNET boreal forest in Finland

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Winter observations of CO<sub>2</sub> exchange between sea ice and the atmosphere in a coastal fjord environment