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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union

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Atmos. Meas. Tech., 7, 2337-2360, 2014
© Author(s) 2014. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
31 Jul 2014
Tropospheric CH4 signals as observed by NDACC FTIR at globally distributed sites and comparison to GAW surface in situ measurements
E. Sepúlveda1,2, M. Schneider3, F. Hase3, S. Barthlott3, D. Dubravica3, O. E. García1, A. Gomez-Pelaez1, Y. González1, J. C. Guerra2, M. Gisi3,*, R. Kohlhepp3,**, S. Dohe3, T. Blumenstock3, K. Strong4, D. Weaver4, M. Palm5, A. Sadeghi5, N. M. Deutscher5,6, T. Warneke5, J. Notholt5, N. Jones6, D. W. T. Griffith6, D. Smale7, G. W. Brailsford7, J. Robinson7, F. Meinhardt8, M. Steinbacher9, T. Aalto10, and D. Worthy11 1Izaña Atmospheric Research Center, Agencia Estatal de Meteorología (AEMET), Tenerife, Spain
2Department of Physics, University of La Laguna (ULL), Tenerife, Spain
3Institute for Meteorology and Climate Research, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
4Department of Physics, University of Toronto (UofT), Toronto, Canada
5Institute of Environmental Physics, University of Bremen (UB), Bremen, Germany
6Centre for Atmospheric Chemistry, University of Wollongong (UOW), Wollongong, Australia
7National Institute of Water and Atmospheric Research (NIWA), Lauder, New Zealand
8Federal Environmental Agency Germany (UBA), Dessau-Roßlau, Germany
9Swiss Federal Laboratories for Materials Science and Technology (EMPA), Dübendorf, Switzerland
10Climate Change Research, Finnish Meteorological Institute (FMI), Helsinki, Finland
11Climate Research Division, Environment Canada (EC), Wellington, Canada
*now at: Bruker Optics GmbH, Ettlingen, Germany
**now at: Deutscher Wetterdienst, Offenbach, Germany
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 CH4 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.

Citation: 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., Robinson, J., Meinhardt, F., Steinbacher, M., Aalto, T., and Worthy, D.: Tropospheric CH4 signals as observed by NDACC FTIR at globally distributed sites and comparison to GAW surface in situ measurements, Atmos. Meas. Tech., 7, 2337-2360, doi:10.5194/amt-7-2337-2014, 2014.
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