Consistent regional fluxes of CH4 and CO2 inferred from
GOSAT proxy XCH4:XCO2 retrievals, 2010–2014
Liang Feng1, Paul I. Palmer1, Hartmut Bösch2, Robert J . Parker2, Alex J. Webb2, Caio S. C. Correia3, Nicholas M. Deutscher4,5, Lucas G. Domingues3, Dietrich G. Feist6, Luciana V. Gatti3, Emanuel Gloor7, Frank Hase8, Rigel Kivi9, Yi Liu10, John B. Miller11,12, Isamu Morino13, Ralf Sussmann14, Kimberly Strong15, Osamu Uchino13, Jing Wang10, and Andreas Zahn161National Centre for Earth Observation, School of GeoSciences, University of Edinburgh, UK 2National Centre for Earth Observation, Department of Physics and Astronomy, University of Leicester, UK 3Instituto de Pesquisas Energéticas e Nucleares (IPEN) -Comissao Nacional de Energia Nuclear (CNEN) – Atmospheric Chemistry Laboratory, Cidade Universitaria, Sao Paulo, Brazil 4Institute of Environmental Physics, University of Bremen, Germany 5Centre for Atmospheric Chemistry, University of Wollongong, Australia 6Max Planck Institute for Biogeochemistry, Jena, Germany 7School of Geography, University of Leeds, Leeds, UK 8Karlsruhe Institute of Technology (KIT), IMK-ASF, 76021 Karlsruhe, Germany 9FMI-Arctic Research Center, Sodankylä, Finland 10Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China 11Global Monitoring Division, Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, Colorado, USA 12Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, Boulder, Colorado, USA 13National Institute for Environmental Studies (NIES), Tsukuba, Japan 14Karlsruhe Institute of Technology (KIT), Institute of Meteorology and Climate Research – Atmospheric Environmental Research (IMK-IFU), 82467 Garmisch-Partenkirchen, Germany 15Department of Physics, University of Toronto, Toronto, M5S 1A7, Canada 16Karlsruhe Institute of Technology (KIT), Institute of Meteorology and Climate Research (IMK), 76344 Eggenstein-leopoldshafen, Germany
Received: 28 Sep 2016 – Accepted for review: 21 Oct 2016 – Discussion started: 24 Oct 2016
Abstract. We use the GEOS-Chem global 3-D model of atmospheric chemistry and transport and an ensemble Kalman filter to simultaneously infer regional fluxes of methane (CH4) and carbon dioxide (CO2) directly from GOSAT retrievals of XCH4:XCO2, using sparse ground-based CH4 and CO2 mole fraction data to anchor the ratio. This work builds on previously reported theory that takes advantage that: (1) these ratios are less prone to systematic error than either the full physics data products or the proxy CH4 data products; and (2) the resulting CH4 and CO2 fluxes are self-consistent. We show that a posteriori fluxes inferred from the GOSAT data generally outperform the fluxes inferred only from in situ data, as expected. GOSAT CH4 and CO2 fluxes are consistent with global growth rates for CO2 and CH4 reported by NOAA, and with a range of independent data including in particular new profile measurements (0–7 km) over the Amazon basin that were collected specifically to help validate GOSAT over this geographical region. We find that large-scale multi-year annual a posteriori CO2 fluxes inferred from GOSAT data are similar to those inferred from the in situ surface data but with smaller uncertainties, particularly over the tropics. GOSAT data are consistent with smaller peak-to-peak seasonal amplitudes of CO2 than either a priori or the in situ inversion, particularly over the tropics and the southern extra-tropics. Over the northern extra-tropics, GOSAT data show larger uptake than the a priori but less than the in situ inversion, resulting in small net emissions over the year. We also find evidence that the carbon balance of tropical South America was perturbed following the droughts of 2010 and 2012 with net annual fluxes not returning to an approximate annual balance until 2013. In contrast, GOSAT data significantly changed the a priori spatial distribution of CH4 emission with a 40 % increase over tropical South America and tropical Asia and smaller decrease over Eurasia and temperate South America. We find no evidence from GOSAT that tropical South American CH4 fluxes were dramatically affected by the two large-scale Amazon droughts. However, we find that GOSAT data are consistent with double seasonal peaks in fluxes that are reproduced over the five years we studied: a small peak in January to April and a larger peak in June to October, which is likely due to superimposed emissions from different geographical regions.
Feng, L., Palmer, P. I., Bösch, H., Parker, R. J., Webb, A. J., Correia, C. S. C., Deutscher, N. M., Domingues, L. G., Feist, D. G., Gatti, L. V., Gloor, E., Hase, F., Kivi, R., Liu, Y., Miller, J. B., Morino, I., Sussmann, R., Strong, K., Uchino, O., Wang, J., and Zahn, A.: Consistent regional fluxes of CH4 and CO2 inferred from
GOSAT proxy XCH4:XCO2 retrievals, 2010–2014, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-868, in review, 2016.