Measurements of CH
            4
            and N
            2
            O fluxes at the landscape scale using micrometeorological methods

Flux gradient, eddy covariance and relaxed eddy accumulation methods were applied to measure CH 4 and N 2 O emissions from peatlands and arable land respectively. Measurements of N 2 O emission by eddy covariance using tunable diode laser spectroscopy provided fluxes ranging from 2 to 60 µ mol N 2 O m -2 h -1 with a mean value of 22 µ mol N 2 O m -2 h -1 from 320 h of continuous measurements. Fluxes of CH 4 measured above peatland in Caithness (U.K.) during May and June 1993 by eddy covariance and relaxed eddy accumulation methods were in the range 70 to 120 µ mol CH 4 m -2 h -1 with means of 14.7 µ mol CH 4 m -2 h -1 and 22.7 µ mol CH 4 m -2 h -1 respectively. Emissions of CH 4 from peatland changed with water table depth and soil temperature; increasing from 25 |Amol CH 4 m -2 h -1 at 5% pool area to 50 p.mol CH 4 m -2 h -1 with 30% within the flux footprint occupied by pools. A temperature response of 4.9 (xmol CH 4 m -2 h -1 °C -1 in the range 6-12 °C was also observed. The close similarity in average CH 4 emission fluxes reported for wetlands in Caithness, Hudson Bay and Alaska in the range 11 to 40 jamol CH 4 m -2 h -1 suggests that earlier estimates of CH 4 emission from high latitude wetlands were too large or that the area of high latitudes contributing to CH 4 emission has been seriously underestimated.

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A tool for evaluation of target area homogeneity at ecosystem stations employing eddy covariance method

10.5194/egusphere-egu21-8919 ◽

2021 ◽

Author(s):

Ladislav Šigut ◽

Thomas Wutzler ◽

Tarek El-Madany ◽

Milan Fischer ◽

Mirco Migliavacca

Keyword(s):

Eddy Covariance ◽

Water Cycle ◽

Source Area ◽

Mean Value ◽

Target Area ◽

Ministry Of Education ◽

Flux Footprint ◽

Eddy Covariance Method ◽

Additional Information ◽

Air Mixing

Our understanding of the carbon and water cycle was greatly improved through application of eddy covariance measurements in recent decades. Though powerful, this micrometeorological approach relies on a number of assumptions that can be affected by a selection of station location. Most importantly, terrain of the target area should be flat, target area should be homogeneous and adequate air mixing should be achieved. Although possible shortcomings can be reduced by careful site inspection before tower installation (flat terrain) or can be corrected for during data post-processing (filtering of periods with low mixing), preliminary assessment of target area homogeneity is difficult as well as correction of its impacts afterwards. The influence of such inhomogeneities can lead to a bias in the flux annual sums but also a bias in their relationships with environmental variables. Certain solutions were already proposed, but target area homogeneity was so far assessed only at a few selected sites. Here we aim to provide a suit of software tools that build on the existing software packages (REddyProc, Flux Footprint Prediction, openair, openeddy) and allow easy diagnosis of the situation at the given ecosystem station. We plan to provide directional analyses of variables of interest. This will allow to identify the wind sectors that show large deviations from the mean value of the whole target area. In a further step, we plan to combine footprint modeling with CO2 and energy flux measurements and thus provide attribution of mean (weighted) fluxes to their source area. Based on the differences with the directional analyses we will assess whether the higher computational expenses of footprint modeling are justified and bring additional information. Finally, we plan to separate the target area to a limited amount of wind sectors and attempt separate gap-filling and flux partitioning for areas identified by preceding homogeneity evaluation. The limitations and feasibility of this approach will be assessed.This work was supported by the Ministry of Education, Youth and Sports of CR within Mobility CzechGlobe2 (CZ.02.2.69/0.0/0.0/18_053/0016924).

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Eddy covariance flux measurements of momentum, heat and carbon dioxide in Hudson Bay at the onset of sea ice melt

10.5194/egusphere-egu21-15711 ◽

2021 ◽

Author(s):

Richard Sims ◽

Brian Butterworth ◽

Tim Papakyriakou ◽

Mohamed Ahmed ◽

Brent Else

Keyword(s):

Carbon Dioxide ◽

Gas Exchange ◽

Sea Ice ◽

Eddy Covariance ◽

Open Water ◽

The Arctic ◽

Gas Transfer ◽

Hudson Bay ◽

Flux Measurements ◽

Ice Fraction

Remoteness and tough conditions have made the Arctic Ocean historically difficult to access; until recently this has resulted in an undersampling of trace gas and gas exchange measurements. The seasonal cycle of sea ice completely transforms the air sea interface and the dynamics of gas exchange. To make estimates of gas exchange in the presence of sea ice, sea ice fraction is frequently used to scale open water gas transfer parametrisations. It remains unclear whether this scaling is appropriate for all sea ice regions. Ship based eddy covariance measurements were made in Hudson Bay during the summer of 2018 from the icebreaker CCGS Amundsen. We will present fluxes of carbon dioxide (CO2), heat and momentum and will show how they change around the Hudson Bay polynya under varying sea ice conditions. We will explore how these fluxes change with wind speed and sea ice fraction. As freshwater stratification was encountered during the cruise, we will compare our measurements with other recent eddy covariance flux measurements made from icebreakers and also will compare our turbulent CO2&#160;fluxes with bulk fluxes calculated using underway and surface bottle pCO2&#160;data.&#160;&#160;

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Exploring the variation in ecosystem scale methane fluxes and its drivers within a boreal mire complex

10.5194/egusphere-egu21-4489 ◽

2021 ◽

Author(s):

Koffi Dodji Noumonvi ◽

Joshua L. Ratcliffe ◽

Mats Öquist ◽

Mats B. Nilsson ◽

Matthias Peichl

Keyword(s):

Eddy Covariance ◽

Land Surface ◽

Chemical Properties ◽

Growing Season ◽

Small Scale ◽

Atmospheric Methane ◽

Flux Footprint ◽

Growing Season Length ◽

Methane Fluxes ◽

Northern Peatlands

Northern peatlands cover a small fraction of the earth&#8217;s land surface, and yet they are one of the most important natural sources of atmospheric methane. With climate change causing rising temperatures, changes in water balance and increased growing season length, peatland contribution to atmospheric methane concentration is likely to increase, justifying the increased attention given to northern peatland methane dynamics. Northern peatlands often occur as heterogeneous complexes characterized by hydromorphologically distinct features from < 1 m&#178; to tens of km&#178;, with differing physical, hydrological and chemical properties. The more commonly understood small-scale variation between hummocks, lawns and hollows has been well explored using chamber measurements. Single tower eddy covariance measurements, with a typical 95% flux footprint of < 0.5 km&#178;, have been used to assess the ecosystem scale methane exchange. However, how representative single tower flux measurements are of an entire mire complex is not well understood. To address this knowledge gap, the present study takes advantage of a network of four eddy covariance towers located less than 3 km apart at four mires within a typical boreal mire complex in northern Sweden. The variation of methane fluxes and its drivers between the four sites will be explored at different temporal scales, i.e. half-hourly, daily and at a growing-season scale.

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Fast response tunable diode laser spectroscopy for trace gas flux measurements

Infrared Physics & Technology ◽

10.1016/1350-4495(95)00114-x ◽

1996 ◽

Vol 37 (1) ◽

pp. 67-74 ◽

Cited By ~ 16

Author(s):

F.G. Wienhold ◽

H. Fischer ◽

G.W. Harris

Keyword(s):

Diode Laser ◽

Laser Spectroscopy ◽

Fast Response ◽

Tunable Diode Laser ◽

Trace Gas ◽

Gas Flux ◽

Tunable Diode Laser Spectroscopy ◽

Diode Laser Spectroscopy ◽

Flux Measurements

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A return to large-scale features of Pliocene climate: the Pliocene Model Intercomparison Project Phase 2

10.5194/cp-2019-145 ◽

2020 ◽

Cited By ~ 2

Author(s):

Alan M. Haywood ◽

Julia C. Tindall ◽

Harry J. Dowsett ◽

Aisling M. Dolan ◽

Kevin M. Foley ◽

...

Keyword(s):

Large Scale ◽

Climate Models ◽

Temperature Response ◽

Surface Air Temperature ◽

Co2 Concentration ◽

Mean Value ◽

System Response ◽

Phase 2 ◽

Model Intercomparison ◽

Intercomparison Project

Abstract. The Pliocene epoch has great potential to improve our understanding of the long-term climatic and environmental consequences of an atmospheric CO2 concentration near ~ 400 parts per million by volume. Here we present the large-scale features of Pliocene climate as simulated by a new ensemble of climate models of varying complexity and spatial resolution and based on new reconstructions of boundary conditions (the Pliocene Model Intercomparison Project Phase 2; PlioMIP2). As a global annual average, modelled surface air temperatures increase by between 1.4 and 4.7 °C relative to pre-industrial with a multi-model mean value of 2.8 °C. Annual mean total precipitation rates increase by 6 % (range: 2 %–13 %). On average, surface air temperature (SAT) increases are 1.3 °C greater over the land than over the oceans, and there is a clear pattern of polar amplification with warming polewards of 60° N and 60° S exceeding the global mean warming by a factor of 2.4. In the Atlantic and Pacific Oceans, meridional temperature gradients are reduced, while tropical zonal gradients remain largely unchanged. Although there are some modelling constraints, there is a statistically significant relationship between a model's climate response associated with a doubling in CO2 (Equilibrium Climate Sensitivity; ECS) and its simulated Pliocene surface temperature response. The mean ensemble earth system response to doubling of CO2 (including ice sheet feedbacks) is approximately 50 % greater than ECS, consistent with results from the PlioMIP1 ensemble. Proxy-derived estimates of Pliocene sea-surface temperatures are used to assess model estimates of ECS and indicate a range in ECS from 2.5 to 4.3 °C. This result is in general accord with the range in ECS presented by previous IPCC Assessment Reports.

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