Inferring regional sources and sinks of atmospheric CO<sub>2</sub> from GOSAT XCO<sub>2</sub> data
We have examined the utility of retrieved column-averaged, dry-air mole fractions of CO<sub>2</sub> (XCO<sub>2</sub>) from the Greenhouse Gases Observing Satellite (GOSAT) for quantifying monthly, regional flux estimates of CO<sub>2</sub>, using the GEOS-Chem four...
| Main Authors: | , , , , , , , , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2014-04-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/14/3703/2014/acp-14-3703-2014.pdf |
| Summary: | We have examined the utility of retrieved column-averaged, dry-air mole
fractions of CO<sub>2</sub> (XCO<sub>2</sub>) from the Greenhouse Gases Observing Satellite
(GOSAT) for quantifying monthly, regional flux estimates of CO<sub>2</sub>, using the
GEOS-Chem four-dimensional variational (4D-Var) data assimilation system. We
focused on assessing the potential impact of biases in the GOSAT CO<sub>2</sub> data
on the regional flux estimates. Using different screening and bias correction
approaches, we selected three different subsets of the GOSAT XCO<sub>2</sub> data for
the 4D-Var inversion analyses, and found that the inferred global fluxes were
consistent across the three XCO<sub>2</sub> inversions. However, the GOSAT
observational coverage was a challenge for the regional flux estimates. In
the northern extratropics, the inversions were more sensitive to North
American fluxes than to European and Asian fluxes due to the lack of
observations over Eurasia in winter and over eastern and southern Asia in
summer. The regional flux estimates were also sensitive to the treatment of
the residual bias in the GOSAT XCO<sub>2</sub> data. The largest differences obtained
were for temperate North America and temperate South America, for which the
largest spread between the inversions was 1.02 and 0.96 Pg C,
respectively. In the case of temperate North America, one inversion suggested
a strong source, whereas the second and third XCO<sub>2</sub> inversions produced a
weak and strong sink, respectively. Despite the discrepancies in the regional
flux estimates between the three XCO<sub>2</sub> inversions, the a posteriori
CO<sub>2</sub> distributions were in good agreement (with a mean difference between
the three inversions of typically less than 0.5 ppm) with independent data
from the Total Carbon Column Observing Network (TCCON), the surface flask
network, and from the HIAPER Pole-to-Pole Observations (HIPPO) aircraft
campaign. The discrepancy in the regional flux estimates from the different
inversions, despite the agreement of the global flux estimates suggests the
need for additional work to determine the minimum spatial scales at which we
can reliably quantify the fluxes using GOSAT XCO<sub>2</sub>. The fact that the a
posteriori CO<sub>2</sub> from the different inversions were in good agreement with
the independent data although the regional flux estimates differed
significantly, suggests that innovative ways of exploiting existing data sets,
and possibly additional observations, are needed to better evaluate the
inferred regional flux estimates. |
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| ISSN: | 1680-7316 1680-7324 |