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| Titel |
Assessing 5 years of GOSAT Proxy XCH4 data and associated uncertainties |
| VerfasserIn |
R. J. Parker, H. Boesch, K. Byckling, A. J. Webb, P. I. Palmer, L. Feng, P. Bergamaschi, F. Chevallier, J. Notholt, N. Deutscher, T. Warneke, F. Hase, R. Sussmann, S. Kawakami, R. Kivi, D. W. T. Griffith, V. Velazco |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 8, no. 11 ; Nr. 8, no. 11 (2015-11-17), S.4785-4801 |
| Datensatznummer |
250116684
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| Publikation (Nr.) |
 copernicus.org/amt-8-4785-2015.pdf |
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| Zusammenfassung |
| We present 5 years of GOSAT XCH4 retrieved using the
"proxy" approach. The Proxy XCH4 data are validated against
ground-based TCCON observations and are found to be of high quality
with a small bias of 4.8 ppb (∼ 0.27 %) and
a single-sounding precision of 13.4 ppb (∼ 0.74 %). The station-to-station bias (ameasure of the relative
accuracy) is found to be 4.2 ppb. For the first time the
XCH4 / XCO2 ratio component of the Proxy
retrieval is
validated (bias of 0.014 ppb ppm−1 (∼ 0.30 %),
single-sounding precision of 0.033 ppb ppm−1 (∼
0.72 %)).
The uncertainty relating to the model XCO2 component of the
Proxy XCH4 is assessed through the use of an ensemble of
XCO2 models. While each individual XCO2 model is found to
agree well with the TCCON validation data (r = 0.94–0.97), it is
not possible to select one model as the best from our
comparisons. The median XCO2 value of the ensemble has
a smaller scatter against TCCON (a standard deviation of
0.92 ppm) than any of the individual models whilst
maintaining a small bias (0.15 ppm). This model median
XCO2 is used to calculate the Proxy XCH4 with the maximum
deviation of the ensemble from the median used as an estimate of the
uncertainty.
We compare this uncertainty to the a posteriori retrieval error (which is assumed to reduce with sqrt(N)) and
find typically that the model XCO2 uncertainty becomes
significant during summer months when the a posteriori error is at
its lowest due to the increase in signal related to increased
summertime reflected sunlight.
We assess the significance of these model and retrieval
uncertainties on flux inversion by comparing the GOSAT XCH4
against modelled XCH4 from TM5-4DVAR constrained by NOAA
surface observations (MACC reanalysis scenario S1-NOAA). We find
that for the majority of regions the differences are much larger
than the estimated uncertainties. Our findings show that useful
information will be provided to the inversions for the majority of
regions in addition to that already provided by the assimilated surface
measurements. |
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