Improved Constraints on Northern Extratropical CO₂ Fluxes Obtained by Combining Surface-Based and Space-Based Atmospheric CO₂ Measurements

Creators: Byrne, B.; Liu, J.; Lee, M.; Baker, I.; Bowman, K. W.; Deutscher, N. M.; Feist, D. G.; Griffith, D. W. T.; Iraci, L. T.; Kiel, M.; Kimball, J. S.; Miller, C. E.; Morino, I.; Parazoo, N. C.; Petri, C.; Roehl, C. M.; Sha, M. K.; Strong, K.; Velazco, V. A.; Wennberg, P. O.; Wunch, D.

Abstract

Top‐down estimates of CO₂ fluxes are typically constrained by either surface‐based or space‐based CO₂ observations. Both of these measurement types have spatial and temporal gaps in observational coverage that can lead to differences in inferred fluxes. Assimilating both surface‐based and space‐based measurements concurrently in a flux inversion framework improves observational coverage and reduces sampling related artifacts. This study examines the consistency of flux constraints provided by these different observations and the potential to combine them by performing a series of 6‐year (2010–2015) CO₂ flux inversions. Flux inversions are performed assimilating surface‐based measurements from the in situ and flask network, measurements from the Total Carbon Column Observing Network (TCCON), and space‐based measurements from the Greenhouse Gases Observing Satellite (GOSAT), or all three data sets combined. Combining the data sets results in more precise flux estimates for subcontinental regions relative to any of the data sets alone. Combining the data sets also improves the accuracy of the posterior fluxes, based on reduced root‐mean‐square differences between posterior flux‐simulated CO₂ and aircraft‐based CO₂ over midlatitude regions (0.33–0.56 ppm) in comparison to GOSAT (0.37–0.61 ppm), TCCON (0.50–0.68 ppm), or in situ and flask measurements (0.46–0.56 ppm) alone. These results suggest that surface‐based and GOSAT measurements give complementary constraints on CO₂ fluxes in the northern extratropics and can be combined in flux inversions to improve constraints on regional fluxes. This stands in contrast with many earlier attempts to combine these data sets and suggests that improvements in the NASA Atmospheric CO₂ Observations from Space (ACOS) retrieval algorithm have significantly improved the consistency of space‐based and surface‐based flux constraints.

Additional Information

© 2020 The Authors. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. Issue Online: 26 July 2020; Version of Record online: 26 July 2020; Accepted manuscript online: 24 June 2020; Manuscript accepted: 13 June 2020; Manuscript revised: 05 May 2020; Manuscript received: 08 November 2019. BB was supported by an appointment to the NASA Postdoctoral Program at the Jet Propulsion Laboratory, administered by Universities Space Research Association under contract with NASA. JL was supported by the NASA OCO2/3 science team program NNH17ZDA001N‐OCO2. KWB was supported by the NASA Carbon Monitoring System (CMS) project (NNH16ZDA001N‐CMS). The research carried out at the Jet Propulsion Laboratory, California Institute of Technology, was under a contract with the National Aeronautics and Space Administration. Resources supporting this work were provided by the NASA High‐End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center. Odiac project is supported by Greenhouse Gas Observing SATellite (GOSAT) project, National Institute for Environmental Studies (NIES), Japan. We thank S. Basu for providing downscaled ODIAC emissions. We thank T. Machida, H. Matsueda, Y. Sawa, and Y. Niwa for providing CONTRAIL measurements. The TCCON site at Reunion Island is operated by the Royal Belgian Institute for Space Aeronomy with financial support in 2014, 2015, 2016, 2017, 2018, and 2019 under the EU project ICOS‐Inwire and the ministerial decree for ICOS (FR/35/IC2) and local activities supported by LACy/UMR8105 Universit de La Reunion. The TCCON project for Rikubetsu site is supported in part by the GOSAT series project. The Ascension Island TCCON station has been supported by the European Space Agency (ESA) under grant 4000120088/17/I‐EF and by the German Bundesministerium fur Wirtschaft und Energie (BMWi) under grants 50EE1711C and 50EE1711E. We thank the ESA Ariane Tracking Station at North East Bay, Ascension Island, for hosting and local support. Data Availability Statement: TCCON data were obtained from the TCCON Data Archive, hosted by CaltechDATA (http://tccondata.org). FLUXCOM products were obtained from the Data Portal of the Max Planck Institute for Biochemistry [https://www.bgc-jena.mpg.de]. MERRA‐2 products were downloaded from MDISC (https://gmao.gsfc.nasa.gov/reanalysis/MERRA-2/), managed by the NASA Goddard Earth Sciences (GES) Data and Information Services Center (DISC). GOSAT OCFP v7.1 urn:x-wiley:jgrd:media:jgrd56355:jgrd56355-math-0041 retrievals were downloaded from the Copernicus Climate Change Service website (https://cds.climate.copernicus.eu). Version 4.1 of the GLOBALVIEW plus package was downloaded from http://www.esrl.noaa.gov/gmd/ccgg/obspack/. ESA CCI soil moisture data was downloaded from https://www.esa-soilmoisture-cci.org/. Odiac emissions data set was provided by T. Oda of Colorado State University, Fort Collins CO, USA/Global Monitoring Division, NOAA Earth System Research Laboratory, Boulder CO, USA. GOSAT and OCO‐2 ACOS retrievals were downloaded from the CO2 virtual science data environment: https://co2.jpl.nasa.gov/. Prior and posterior NEE and Ocean fluxes presented in this study will be available for download from https://data.nas.nasa.gov and https://cmsflux.jpl.nasa.gov/. The JR‐STATION data set is available from the Global Environmental Database, hosted by Center for Global Environmental Research (CGER), National Institute for Environmental Studies (NIES) (http://db.cger.nies.go.jp/portal/geds/atmosphericAnd OceanicMonitoring).

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