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| Titel |
Intercalibration of column-averaged methane from the Total Carbon Column Observing Network and the Network for the Detection of Atmospheric Composition Change: An Update |
| VerfasserIn |
Andreas Ostler, Ralf Sussmann, Frank Forster, Markus Rettinger, Thomas Blumenstock, Nicholas Deutscher, Susanne Dohe, David Griffith, James Hannigan, Frank Hase, Nicholas Jones, Prabir Patra |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250078865
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| Zusammenfassung |
| We present the intercalibration of dry-air column-averaged mole fractions of methane
(XCH4) retrieved from solar Fourier transform infrared (FTIR) measurements of the
Network for the Detection of Atmospheric Composition Change (NDACC) in the
mid-infrared (MIR) versus near-infrared (NIR) soundings from the Total Carbon
Column Observing Network (TCCON). The study uses multi-annual quasi-coincident
MIR and NIR measurements from the stations Garmisch, Germany (47.48 Ë N,
11.06 Ë E, 743 m a.s.l.) and Wollongong, Australia (34.41 Ë S, 150.88 Ë E, 30 m
a.s.l.).
Direct comparison of the retrieved MIR and NIR XCH4 time series for Garmisch shows a
quasi-periodic seasonal bias leading to a standard deviation (stdv) of the difference time
series (NIR-MIR) of 7.2 ppb. After reducing time dependent a priori impact by using realistic
site- and time-dependent ACTM-simulated profiles as a common prior, the seasonal bias is
reduced (stdv = 5.2 ppb). A linear fit to the MIR-NIR scatter plot of monthly means based on
same-day coincidences does not show a significant intercept, and the MIR/NIR
intercalibration factor is found to be close to ideal within 2 sigma uncertainty, i.e. 0.9996(8).
The difference time series (NIR-MIR) do not show a significant trend. The same basic
findings hold for Wollongong. In particular an overall MIR/NIR intercalibration factor
close to the ideal 1 is found within 2 sigma uncertainty. Differently to Garmisch,
the original Wollongong MIR and NIR data can be jointly used without using a
common a priori because of the less pronounced (southern-hemisphere) seasonal
cycle.
In addition the study has been extended by the MIR and NIR measurements of the
stations Karlsruhe, Germany (49.1 Ë N, 910 Ë E, 110 m a.s.l.) and Izana, Spain (28.30 Ë N,
16.48 Ë W, 2370 m a.s.l.).
Our results suggest that it is possible to set up a harmonized NDACC and TCCON XCH4
data set which can be exploited for joint trend studies, satellite validation, or the inverse
modeling of sources and sinks. |
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