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Tropospheric CH4 signals as observed by NDACC FTIR at globally distributed sites and comparison to GAW surface in situ measurements

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Author Sepúlveda E., Schneider M., Hase F., Barthlott S., Dubravica D., García O. E., Gomez-Pelaez A., González Y., Guerra J. C., Gisi M., Kohlhepp R., Dohe S., Blumenstock T., Strong K., Weaver D., Palm M., Sadeghi A., Deutscher N. M., Warneke T., Notholt J., Jones N., Griffith D. W. T., Smale D., Brailsford G. W., et al. ,
Project ICOS-CH: Integrated Carbon Observation System in Switzerland
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Original article (peer-reviewed)

Journal Atmospheric Measurement Techniques
Volume (Issue) 7(7)
Page(s) 2337 - 2360
Title of proceedings Atmospheric Measurement Techniques
DOI 10.5194/amt-7-2337-2014

Open Access

URL http://doi.org/10.5194/amt-7-2337-2014
Type of Open Access Publisher (Gold Open Access)

Abstract

We present lower/middle tropospheric column-averaged CH4 mole fraction time series measured by nine globally distributed ground-based FTIR (Fourier transform infrared) remote sensing experiments of the Network for the Detection of Atmospheric Composition Change (NDACC). We show that these data are well representative of the tropospheric regional-scale CH4 signal, largely independent of the local surface small-scale signals, and only weakly dependent on upper tropospheric/lower stratospheric (UTLS) CH4 variations. In order to achieve the weak dependency on the UTLS, we use an a posteriori correction method. We estimate a typical precision for daily mean values of about 0.5% and a systematic error of about 2.5%. The theoretical assessments are complemented by an extensive empirical study. For this purpose, we use surface in situ CH 4 measurements made within the Global Atmosphere Watch (GAW) network and compare them to the remote sensing data. We briefly discuss different filter methods for removing the local small-scale signals from the surface in situ data sets in order to obtain the in situ regional-scale signals. We find good agreement between the filtered in situ and the remote sensing data. The agreement is consistent for a variety of timescales that are interesting for CH4 source/sink research: day-to-day, monthly, and inter-annual. The comparison study confirms our theoretical estimations and proves that the NDACC FTIR measurements can provide valuable data for investigating the cycle of CH4 .
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