Intercomparability of X_(CO_2) and X_(CH_4) from the United States TCCON sites

Creators: Hedelius, Jacob K.; Parker, Harrison; Wunch, Debra; Roehl, Coleen M.; Viatte, Camille; Newman, Sally; Toon, Geoffrey C.; Podolske, James R.; Hillyard, Patrick W.; Iraci, Laura T.; Dubey, Manvendra K.; Wennberg, Paul O.

Abstract

The Total Carbon Column Observing Network (TCCON) has become the standard for long-term column-averaged measurements of CO_2 and CH_4. Here, we use a pair of portable spectrometers to test for intra-network bias among the four currently operating TCCON sites in the United States (US). A previous analytical error analysis has suggested that the maximum 2σ site-to-site relative (absolute) bias of TCCON should be less than 0.2% (0.8ppm) in X_(CO_2) and 0.4% (7ppb) in X_(CH_4). We find here experimentally that the 95% confidence intervals for maximum pairwise site-to-site bias among the four US TCCON sites are 0.05–0.14% for X_(CO_2) and 0.08–0.24% for X_(CH_4). This is close to the limit of the bias we can detect using this methodology.

Additional Information

© Author(s) 2017. This work is distributed under the Creative Commons Attribution 3.0 License. Received: 25 Aug 2016 – Discussion started: 15 Sep 2016 – Revised: 04 Mar 2017 – Accepted: 24 Mar 2017 – Published: 20 Apr 2017. The MODIS Vegetation Indices products were retrieved from the online Data Pool, courtesy of the NASA EOSDIS Land Processes Distributed Active Archive Center (LP DAAC), USGS/Earth Resources Observation and Science (EROS) Center, Sioux Falls, South Dakota (https://lpdaac.usgs.gov/node/843). The nightlight data products (version 1 Nighttime VIIRS Day/Night Band composites) are generated by the Earth Observation Group, NOAA National Geophysical Data Center (http://ngdc.noaa.gov/eog/viirs/download_monthly.html). Ancillary surface meteorological data at Lamont were obtained from the Atmospheric Radiation Measurement (ARM) Program sponsored by the US Department of Energy, Office of Science, Office of Biological and Environmental Research, Climate and Environmental Sciences Division (Kyrouac and Holdridge, 1993). ERA-Interim data were supplied by ECMWF (European Centre for Medium-Range Weather Forecasts; http://www.ecmwf.int/). NAM12 (North American Mesoscale Forecast System, 12 km) data are a product of NOAA (NCEI DSI 6173, gov.noaa.ncdc: C00630). There are numerous people we wish to thank: Gregor Surawicz and Bruker Optics for assistance with the EM27/SUN firmware update; Matthias Frey for helpful discussions; Matthaeus Kiel for discussions on the air-mass-dependent correction factor; Heidi Boyden for her assistance at AFRC; Jeff Ayers for his on-site assistance at Park Falls; ARM SGP site for accommodations and Patrick Dowell and Kenneth Teske for their on-site assistance; Chris O'Dell for providing pTz profiles from MERRA-2 and GEOS5; and David Pollard for analysis of unassimilated sonde profiles. The authors gratefully acknowledge funding from the NASA Carbon Cycle Science program (grant number NNX14AI60G) and the Jet Propulsion Laboratory. Manvendra K. Dubey acknowledges funding from the NASA-CMS program for field observations and from the LANL-LDRD for the acquisition of the LANL EM27/SUN. The authors thank the referees for their comments. Edited by: J. Notholt. Reviewed by: F. Hase and one anonymous referee Data availability. TCCON data are currently hosted on the CDIAC and will also be available on the Caltech library data archive by the end of the year (Iraci et al., 2014; Wennberg et al., 2014a, b, c). Mobile FTS data are available upon request to the authors. The authors declare that they have no conflict of interest.

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