First intercalibration of column-averaged methane from the Total Carbon Column Observing Network and the Network for the Detection of Atmospheric Composition Change

Citation:	Sussmann, R., A. Ostler, F. Forster (more) , 2013: First intercalibration of column-averaged methane from the Total Carbon Column Observing Network and the Network for the Detection of Atmospheric Composition Change. Atmospheric Measurement Techniques, 6, 379-418, DOI: 10.5194/amt-6-397-2013.
UCAR/NCAR/UCP Authors:	Hannigan, J. , Atmospheric Chemistry Division (ACD)
Other Authors:	Sussmann, R. Ostler, A. Forster, F. Rettinger, M. Deutscher, N.M. Griffith, D.W. Jones, N. Patra, P.K.
UCAR Affiliations:	Atmospheric Chemistry Division (ACD)
Full Text:	Download osgc-000-000-012-230.pdf size: 7868 KB
Abstract:	We present the first 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° N, 11.06° E, 743 m a.s.l.), and Wollongong, Australia (34.41° S, 150.88° 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 y-intercept that is statistically different from zero, and the MIR/NIR intercalibration factor is found to be close to ideal within 2-σ 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-σ uncertainty. At Wollongong the seasonal cycle of methane is less pronounced and corresponding smoothing errors are not as significant, enabling standard MIR and NIR retrievals to be used directly, without correction to a common a priori. View More
Classification:	Refereed
Resource Type:	Article
Date Published	2013-02-20
Relations:	http://dx.doi.org/10.5194/amt-6-397-2013
Published Version:	10.5194/amt-6-397-2013
Copyright Notice:	Copyright Author(s) 2013. This work is distributed under the Creative Commons Attribution 3.0 License
Citable URL:	http://nldr.library.ucar.edu/repository/collections/OSGC-000-000-012-230