Articles | Volume 7, issue 7
Atmos. Meas. Tech., 7, 2337–2360, 2014
Atmos. Meas. Tech., 7, 2337–2360, 2014

Research article 31 Jul 2014

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. Sepúlveda2,1, 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. Deutscher6,5, 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 E. Sepúlveda et al.
  • 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.