Was Australia a sink or source of CO<sub>2</sub> in 2015? Data assimilation using OCO-2 satellite measurements

<p>In this study, we present the assimilation of data from the Orbiting Carbon Observatory-2 (OCO-2) (land nadir and glint data, version 9) to estimate the Australian carbon surface fluxes for the year 2015. To perform this estimation, we used both a regional-scale atmospheric transport–disper...

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Autores principales: Y. Villalobos, P. J. Rayner, J. D. Silver, S. Thomas, V. Haverd, J. Knauer, Z. M. Loh, N. M. Deutscher, D. W. T. Griffith, D. F. Pollard
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spelling oai:doaj.org-article:098ad9b128ef46a4bb5f39f9f8134edd2021-12-01T14:18:11ZWas Australia a sink or source of CO<sub>2</sub> in 2015? Data assimilation using OCO-2 satellite measurements10.5194/acp-21-17453-20211680-73161680-7324https://doaj.org/article/098ad9b128ef46a4bb5f39f9f8134edd2021-12-01T00:00:00Zhttps://acp.copernicus.org/articles/21/17453/2021/acp-21-17453-2021.pdfhttps://doaj.org/toc/1680-7316https://doaj.org/toc/1680-7324<p>In this study, we present the assimilation of data from the Orbiting Carbon Observatory-2 (OCO-2) (land nadir and glint data, version 9) to estimate the Australian carbon surface fluxes for the year 2015. To perform this estimation, we used both a regional-scale atmospheric transport–dispersion model and a four-dimensional variational assimilation scheme. Our results suggest that Australia was a carbon sink of <span class="inline-formula">−</span>0.41 <span class="inline-formula">±</span> 0.08 PgC yr<span class="inline-formula"><sup>−1</sup></span> compared to the prior estimate 0.09 <span class="inline-formula">±</span> 0.20 PgC yr<span class="inline-formula"><sup>−1</sup></span> (excluding fossil fuel emissions). Most of the carbon uptake occurred in northern Australia over the savanna ecotype and in the western region over areas with sparse vegetation. Analysis of the enhanced vegetation index (EVI) suggests that the majority of the carbon uptake over the savanna ecosystem was due to an increase of vegetation productivity (positive EVI anomalies) amplified by an anomalous increase of rainfall in summer. Further from this, a slight increase of carbon uptake in Western Australia over areas with sparse vegetation (the largest ecosystem in Australia) was noted due to increased land productivity in the area caused by positive rainfall anomalies. The stronger carbon uptake estimate in this ecosystem was partially due to the land surface model (CABLE-BIOS3) underestimating the gross primary productivity of the ecosystem. To evaluate the accuracy of our carbon flux estimates from OCO-2 retrievals, we compare our posterior concentration fields against the column-averaged carbon retrievals from the Total Carbon Column Observing Network (TCCON) and ground-based in situ monitoring sites located around our domain. The validation analysis against TCCON shows that our system is able to reduce bias mainly in the summer season. Comparison with surface in situ observations was less successful, particularly over oceanic monitoring sites that are strongly affected by oceanic fluxes and subject to less freedom by the inversion. For stations located far from the coast, the comparison with in situ data was more variable, suggesting difficulties matching the column-integrated and surface data by the inversion, most likely linked to model vertical transport. Comparison of our fluxes against the OCO-2 model intercomparison (MIP) was encouraging. The annual carbon uptake estimated by our inversion falls within the ensemble of the OCO-2 MIP global inversions and presents a similar seasonal pattern.</p>Y. VillalobosY. VillalobosY. VillalobosP. J. RaynerP. J. RaynerP. J. RaynerJ. D. SilverJ. D. SilverS. ThomasV. HaverdJ. KnauerZ. M. LohN. M. DeutscherD. W. T. GriffithD. F. PollardCopernicus PublicationsarticlePhysicsQC1-999ChemistryQD1-999ENAtmospheric Chemistry and Physics, Vol 21, Pp 17453-17494 (2021)
institution DOAJ
collection DOAJ
language EN
topic Physics
QC1-999
Chemistry
QD1-999
spellingShingle Physics
QC1-999
Chemistry
QD1-999
Y. Villalobos
Y. Villalobos
Y. Villalobos
P. J. Rayner
P. J. Rayner
P. J. Rayner
J. D. Silver
J. D. Silver
S. Thomas
V. Haverd
J. Knauer
Z. M. Loh
N. M. Deutscher
D. W. T. Griffith
D. F. Pollard
Was Australia a sink or source of CO<sub>2</sub> in 2015? Data assimilation using OCO-2 satellite measurements
description <p>In this study, we present the assimilation of data from the Orbiting Carbon Observatory-2 (OCO-2) (land nadir and glint data, version 9) to estimate the Australian carbon surface fluxes for the year 2015. To perform this estimation, we used both a regional-scale atmospheric transport–dispersion model and a four-dimensional variational assimilation scheme. Our results suggest that Australia was a carbon sink of <span class="inline-formula">−</span>0.41 <span class="inline-formula">±</span> 0.08 PgC yr<span class="inline-formula"><sup>−1</sup></span> compared to the prior estimate 0.09 <span class="inline-formula">±</span> 0.20 PgC yr<span class="inline-formula"><sup>−1</sup></span> (excluding fossil fuel emissions). Most of the carbon uptake occurred in northern Australia over the savanna ecotype and in the western region over areas with sparse vegetation. Analysis of the enhanced vegetation index (EVI) suggests that the majority of the carbon uptake over the savanna ecosystem was due to an increase of vegetation productivity (positive EVI anomalies) amplified by an anomalous increase of rainfall in summer. Further from this, a slight increase of carbon uptake in Western Australia over areas with sparse vegetation (the largest ecosystem in Australia) was noted due to increased land productivity in the area caused by positive rainfall anomalies. The stronger carbon uptake estimate in this ecosystem was partially due to the land surface model (CABLE-BIOS3) underestimating the gross primary productivity of the ecosystem. To evaluate the accuracy of our carbon flux estimates from OCO-2 retrievals, we compare our posterior concentration fields against the column-averaged carbon retrievals from the Total Carbon Column Observing Network (TCCON) and ground-based in situ monitoring sites located around our domain. The validation analysis against TCCON shows that our system is able to reduce bias mainly in the summer season. Comparison with surface in situ observations was less successful, particularly over oceanic monitoring sites that are strongly affected by oceanic fluxes and subject to less freedom by the inversion. For stations located far from the coast, the comparison with in situ data was more variable, suggesting difficulties matching the column-integrated and surface data by the inversion, most likely linked to model vertical transport. Comparison of our fluxes against the OCO-2 model intercomparison (MIP) was encouraging. The annual carbon uptake estimated by our inversion falls within the ensemble of the OCO-2 MIP global inversions and presents a similar seasonal pattern.</p>
format article
author Y. Villalobos
Y. Villalobos
Y. Villalobos
P. J. Rayner
P. J. Rayner
P. J. Rayner
J. D. Silver
J. D. Silver
S. Thomas
V. Haverd
J. Knauer
Z. M. Loh
N. M. Deutscher
D. W. T. Griffith
D. F. Pollard
author_facet Y. Villalobos
Y. Villalobos
Y. Villalobos
P. J. Rayner
P. J. Rayner
P. J. Rayner
J. D. Silver
J. D. Silver
S. Thomas
V. Haverd
J. Knauer
Z. M. Loh
N. M. Deutscher
D. W. T. Griffith
D. F. Pollard
author_sort Y. Villalobos
title Was Australia a sink or source of CO<sub>2</sub> in 2015? Data assimilation using OCO-2 satellite measurements
title_short Was Australia a sink or source of CO<sub>2</sub> in 2015? Data assimilation using OCO-2 satellite measurements
title_full Was Australia a sink or source of CO<sub>2</sub> in 2015? Data assimilation using OCO-2 satellite measurements
title_fullStr Was Australia a sink or source of CO<sub>2</sub> in 2015? Data assimilation using OCO-2 satellite measurements
title_full_unstemmed Was Australia a sink or source of CO<sub>2</sub> in 2015? Data assimilation using OCO-2 satellite measurements
title_sort was australia a sink or source of co<sub>2</sub> in 2015? data assimilation using oco-2 satellite measurements
publisher Copernicus Publications
publishDate 2021
url https://doaj.org/article/098ad9b128ef46a4bb5f39f9f8134edd
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