10 1002_2016JD025263_published.pdf (1.84 MB)
CH4 concentrations over the Amazon from GOSAT consistent with in situ vertical profile data
journal contributionposted on 2016-11-14, 11:54 authored by Alex J. Webb, Hartmut Bösch, Robert J. Parker, L. V. Gatti, E. Gloor, P. I. Palmer, L. S. Basso, M. P. Chipperfield, C. S. C. Correia, L. G. Domingues, L. Feng, S. Gonzi, J. B. Miller, T. Warneke, C. Wilson
The Amazon Basin contains large wetland ecosystems which are important sources of methane (CH4). Spaceborne observations of atmospheric CH4 can provide constraints on emissions from these remote ecosystems, but lack of validation precludes robust estimates. We present the first validation of CH4 columns in the Amazon from the Greenhouse gases Observing SATellite (GOSAT) using aircraft measurements of CH4 over five sites across the Amazon Basin. These aircraft profiles, combined with stratospheric results from the TOMCAT chemical transport model, are vertically integrated allowing direct comparison to the GOSAT XCH4 measurements (the column-averaged dry air mole fraction of CH4). The measurements agree within uncertainties or show no significant difference at three of the aircraft sites, with differences ranging from -1.9 ppb to 6.6 ppb, while at two sites GOSAT XCH4 is shown to be slightly higher than aircraft measurements, by 8.1 ppb and 9.7 ppb. The seasonality in XCH4 seen by the aircraft profiles is also well captured (correlation coefficients from 0.61 to 0.90). GOSAT observes elevated concentrations in the northwest corner of South America in the dry season and enhanced concentrations elsewhere in the Amazon Basin in the wet season, with the strongest seasonal differences coinciding with regions in Bolivia known to contain large wetlands. Our results are encouraging evidence that these GOSAT CH4 columns are generally in good agreement with in situ measurements, and understanding the magnitude of any remaining biases between the two will allow more confidence in the application of XCH4 to constrain Amazonian CH4 fluxes.
We thank JAXA and NIES for providing access and support for GOSAT data. We thank the NERC and FAPESP for their joint funding of the Amazonian Carbon Observatory Project (NERC Reference: NE/J016284/1). A. Webb is funded by the UK Natural Environment Research Council (NERC). H. Bösch and R. Parker are supported by the NERC National Centre for Earth Observation (NCEO) and the ESA Climate Change Initiative (GHG-CCI). Parker is also funded via an ESA Living Planet Fellowship. M. Gloor was financially supported by the NERC consortium grant AMAZONICA (NE/F005806/1) which we also thank for providing access to additional aircraft profiles. We thank BADC for providing ECMWF data. Research at the University of Edinburgh is funded by the NERC grant NE/J016195/1. P. Palmer acknowledges his Royal Society Wolfson Research Merit Award. The University of Leicester GOSAT data are freely available through the ESA GHG-CCI website (www.esa-ghg-cci.org). ACO data will be made available through the British Atmospheric Data Centre (BADC) (www.badc.nerc.ac.uk/data/), and AMAZONICA data are available upon request by L. V. Gatti (email@example.com). ECMWF ERA-Interim data are available through the ECMWF website (http://apps.ecmwf.int/datasets/). Access to the MACC-II data can be requested from the ECMWF MARS data server (experiment ID g4om, www.ecmwf.int/en/forecasts/datasets). Paramaribo-FTS data are available upon request from T. Warneke (firstname.lastname@example.org). GEOS-Chem model and metadata are freely available upon request by P. Palmer (email@example.com). TOMCAT model output can be requested from M. Chipperfield (M.Chipperfield@leeds.ac.uk), who acknowledges his Royal Society Wolfson Research Merit award. This research used the SPECTRE and ALICE High Performance Computing Facilities at the University of Leicester. The TOMCAT model was run on the Archer national supercomputer. We thank CEDA for use of the JASMIN supercomputer system on which we run the NAME model.
CitationJournal of Geophysical Research: Atmospheres, 2016, 121, 11,006–11,020
Author affiliation/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy
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