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Elevated uptake of CO2 over Europe inferred from GOSAT XCO2 retrievals: a real phenomenon or an artefact of the analysis?

Journal Article


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Abstract


  • Estimates of the natural CO2 flux over Europe inferred from in situ measurements

    of atmospheric CO2 mole fraction have been used previously to check top-down flux

    estimates inferred from space-borne dry-air CO2 column (XCO2

    ) retrievals. Recent work

    has shown that CO2 fluxes inferred from XCO2

    5 data from the Japanese Greenhouse

    gases Observing SATellite (GOSAT) have a larger seasonal amplitude and a more

    negative annual net CO2 balance than those inferred from the in situ data. The causes

    of this enhanced European CO2 uptake have since become the focus of recent studies.

    We show this elevated uptake over Europe could largely be explained by mis-fitting

    10 data due to regional biases. We establish a reference in situ inversion that uses an

    Ensemble Kalman Filter (EnKF) to assimilate surface flask data and the XCO2

    data

    from the surface-based Total Carbon Column Observing Network (TCCON). The same

    EnKF system is also used to assimilate two, independent versions of GOSAT XCO2

    data. We find that the GOSAT-inferred European terrestrial biosphere uptake peaks

    15 during the summer, similar to the reference inversion, but the net annual flux is 1.18-

    0.1GtCa-1 compared to a value of 0.56-0.1GtCa-1 for our control inversion that

    uses only in situ data. To reconcile these two estimates, we have performed a series of

    numerical experiments that assimilate observations with biases or assimilate synthetic

    observations for which part or all of the GOSAT XCO2 data are replaced with model

    20 data. We find that 50–80% of the elevated European uptake in 2010 inferred from

    GOSAT data is due to retrievals outside the immediate European region, while most

    of the remainder can be explained by a sub-ppm retrieval bias over Europe. We have

    used data assimilation techniques to estimate monthly GOSAT XCO2

    biases from the

    joint assimilation of in situ observations and GOSAT XCO2

    retrievals. We find a monthly

    25 varying bias of up to 0.5 ppm can explain an overestimate of the annual sink of up to

    0.18 GtCa-1.

UOW Authors


  •   Feng, L (external author)
  •   Palmer, Paul I. (external author)
  •   Parker, Robert J. (external author)
  •   Deutscher, Nicholas
  •   Feist, Dietrich G. (external author)
  •   Kivi, Rigel (external author)
  •   Morino, Isamu (external author)
  •   Sussmann, Ralf (external author)

Publication Date


  • 2015

Citation


  • Feng, L., Palmer, P. I., Parker, R. J., Deutscher, N. M., Feist, D. G., Kivi, R., Morino, I. & Sussmann, R. (2015). Elevated uptake of CO2 over Europe inferred from GOSAT XCO2 retrievals: a real phenomenon or an artefact of the analysis?. Atmospheric Chemistry and Physics, 15 (3), 1989-2011.

Ro Full-text Url


  • http://ro.uow.edu.au/cgi/viewcontent.cgi?article=4763&context=smhpapers

Ro Metadata Url


  • http://ro.uow.edu.au/smhpapers/3740

Number Of Pages


  • 22

Start Page


  • 1989

End Page


  • 2011

Volume


  • 15

Issue


  • 3

Place Of Publication


  • Germany

Abstract


  • Estimates of the natural CO2 flux over Europe inferred from in situ measurements

    of atmospheric CO2 mole fraction have been used previously to check top-down flux

    estimates inferred from space-borne dry-air CO2 column (XCO2

    ) retrievals. Recent work

    has shown that CO2 fluxes inferred from XCO2

    5 data from the Japanese Greenhouse

    gases Observing SATellite (GOSAT) have a larger seasonal amplitude and a more

    negative annual net CO2 balance than those inferred from the in situ data. The causes

    of this enhanced European CO2 uptake have since become the focus of recent studies.

    We show this elevated uptake over Europe could largely be explained by mis-fitting

    10 data due to regional biases. We establish a reference in situ inversion that uses an

    Ensemble Kalman Filter (EnKF) to assimilate surface flask data and the XCO2

    data

    from the surface-based Total Carbon Column Observing Network (TCCON). The same

    EnKF system is also used to assimilate two, independent versions of GOSAT XCO2

    data. We find that the GOSAT-inferred European terrestrial biosphere uptake peaks

    15 during the summer, similar to the reference inversion, but the net annual flux is 1.18-

    0.1GtCa-1 compared to a value of 0.56-0.1GtCa-1 for our control inversion that

    uses only in situ data. To reconcile these two estimates, we have performed a series of

    numerical experiments that assimilate observations with biases or assimilate synthetic

    observations for which part or all of the GOSAT XCO2 data are replaced with model

    20 data. We find that 50–80% of the elevated European uptake in 2010 inferred from

    GOSAT data is due to retrievals outside the immediate European region, while most

    of the remainder can be explained by a sub-ppm retrieval bias over Europe. We have

    used data assimilation techniques to estimate monthly GOSAT XCO2

    biases from the

    joint assimilation of in situ observations and GOSAT XCO2

    retrievals. We find a monthly

    25 varying bias of up to 0.5 ppm can explain an overestimate of the annual sink of up to

    0.18 GtCa-1.

UOW Authors


  •   Feng, L (external author)
  •   Palmer, Paul I. (external author)
  •   Parker, Robert J. (external author)
  •   Deutscher, Nicholas
  •   Feist, Dietrich G. (external author)
  •   Kivi, Rigel (external author)
  •   Morino, Isamu (external author)
  •   Sussmann, Ralf (external author)

Publication Date


  • 2015

Citation


  • Feng, L., Palmer, P. I., Parker, R. J., Deutscher, N. M., Feist, D. G., Kivi, R., Morino, I. & Sussmann, R. (2015). Elevated uptake of CO2 over Europe inferred from GOSAT XCO2 retrievals: a real phenomenon or an artefact of the analysis?. Atmospheric Chemistry and Physics, 15 (3), 1989-2011.

Ro Full-text Url


  • http://ro.uow.edu.au/cgi/viewcontent.cgi?article=4763&context=smhpapers

Ro Metadata Url


  • http://ro.uow.edu.au/smhpapers/3740

Number Of Pages


  • 22

Start Page


  • 1989

End Page


  • 2011

Volume


  • 15

Issue


  • 3

Place Of Publication


  • Germany