Schneising, O. and Bergamaschi, P. and Bovensmann, H. and Buchwitz, M. and Burrows, J. P. and Deutscher, N. M. and Griffith, D. W. T. and Heymann, J. and Macatangay, R. and Messerschmidt, J. and Notholt, J. and Rettinger, M. and Reuter, M. and Sussman, R. and Velazco, V. A. and Warneke, T. and Wennberg, P. O. and Wunch, D. (2012) Atmospheric greenhouse gases retrieved from SCIAMACHY: comparison to ground-based FTS measurements and model results. Atmospheric Chemistry and Physics, 12 (3). pp. 1527-1540. ISSN 1680-7316 http://resolver.caltech.edu/CaltechAUTHORS:20120321-101605257
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SCIAMACHY onboard ENVISAT (launched in 2002) enables the retrieval of global long-term column-averaged dry air mole fractions of the two most important anthropogenic greenhouse gases carbon dioxide and methane (denoted XCO_2 and XCH_4). In order to assess the quality of the greenhouse gas data obtained with the recently introduced v2 of the scientific retrieval algorithm WFM-DOAS, we present validations with ground-based Fourier Transform Spectrometer (FTS) measurements and comparisons with model results at eight Total Carbon Column Observing Network (TCCON) sites providing realistic error estimates of the satellite data. Such validation is a prerequisite to assess the suitability of data sets for their use in inverse modelling. It is shown that there are generally no significant differences between the carbon dioxide annual increases of SCIAMACHY and the assimilation system CarbonTracker (2.00 ± 0.16 ppm yr^(−1) compared to 1.94 ± 0.03 ppm yr−1 on global average). The XCO_2 seasonal cycle amplitudes derived from SCIAMACHY are typically larger than those from TCCON which are in turn larger than those from CarbonTracker. The absolute values of the northern hemispheric TCCON seasonal cycle amplitudes are closer to SCIAMACHY than to CarbonTracker and the corresponding differences are not significant when compared with SCIAMACHY, whereas they can be significant for a subset of the analysed TCCON sites when compared with CarbonTracker. At Darwin we find discrepancies of the seasonal cycle derived from SCIAMACHY compared to the other data sets which can probably be ascribed to occurrences of undetected thin clouds. Based on the comparison with the reference data, we conclude that the carbon dioxide data set can be characterised by a regional relative precision (mean standard deviation of the differences) of about 2.2 ppm and a relative accuracy (standard deviation of the mean differences) of 1.1–1.2 ppm for monthly average composites within a radius of 500 km. For methane, prior to November 2005, the regional relative precision amounts to 12 ppb and the relative accuracy is about 3 ppb for monthly composite averages within the same radius. The loss of some spectral detector pixels results in a degradation of performance thereafter in the spectral range currently used for the methane column retrieval. This leads to larger scatter and lower XCH_4 values are retrieved in the tropics for the subsequent time period degrading the relative accuracy. As a result, the overall relative precision is estimated to be 17 ppb and the relative accuracy is in the range of about 10–20 ppb for monthly averages within a radius of 500 km. The derived estimates show that the SCIAMACHY XCH_4 data set before November 2005 is suitable for regional source/sink determination and regional-scale flux uncertainty reduction via inverse modelling worldwide. In addition, the XCO2 monthly data potentially provide valuable information in continental regions, where there is sparse sampling by surface flask measurements.
|Additional Information:||© 2012 The Author(s). This work is distributed under the Creative Commons Attribution 3.0 License. Published by Copernicus Publications on behalf of the European Geosciences Union. Received: 18 September 2011; Published in Atmos. Chem. Phys. Discuss.: 26 October 2011; Revised: 27 January 2012; Accepted: 30 January 2012; Published: 9 February 2012. We thank ESA and DLR for providing us with the SCIAMACHY Level 1 data and the SCIAMACHY calibration team (DLR, SRON, University of Bremen, ESA, and others) for continuously improving the quality of the spectra. TCCON data were obtained from the TCCON Data Archive, operated by the California Institute of Technology from the website at http: //tccon.ipac.caltech.edu/. CarbonTracker 2010 results were provided by NOAA ESRL, Boulder, Colorado, USA from the website at http://carbontracker.noaa.gov. The research leading to these results has received funding from the ESA project CARBONGASES, which is part of The Changing Earth Science Network, the ESA projects GHG-CCI, ADVANSE, and ALANIS Methane, the European Union’s Seventh Framework Programme (FP7/2007–2013) under Grant Agreement no. 218793 and 212095 (MACC and CityZen), the DLR grant SADOS, and from the University and the State of Bremen. The Park Falls and Lamont TCCON stations are funded by NASA grants NNX11AG01G, NAG5-12247, NNG05-GD07G, and NASA’s Orbiting Carbon Observatory Program. We are grateful to the DOE ARM program for technical support in Lamont and Jeff Ayers for technical support in Park Falls. The TCCON sites at Białystok and Orl´eans are financially supported by the Senate of Bremen and the EU projects IMECC and GEOmon. We acknowledge maintenance and logistical work provided by AeroMeteo Service (Białystok) and RAMCES team at LSCE (Gif-sur-Yvette, France). Edited by: B. N. Duncan|
|Official Citation:||Schneising, O., Bergamaschi, P., Bovensmann, H., Buchwitz, M., Burrows, J. P., Deutscher, N. M., Griffith, D. W. T., Heymann, J., Macatangay, R., Messerschmidt, J., Notholt, J., Rettinger, M., Reuter, M., Sussmann, R., Velazco, V. A., Warneke, T., Wennberg, P. O., and Wunch, D.: Atmospheric greenhouse gases retrieved from SCIAMACHY: comparison to ground-based FTS measurements and model results, Atmos. Chem. Phys., 12, 1527-1540, doi:10.5194/acp-12-1527-2012, 2012.|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Jason Perez|
|Deposited On:||28 Mar 2012 18:54|
|Last Modified:||26 Dec 2012 14:58|
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