1California Institute of Technology, Pasadena, CA, USA
2Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
3Old Dominion University, Norfolk, VA, USA
4University of Waterloo, Waterloo, Ontario, Canada
5BC Consulting, Ltd., Alexandra, New Zealand
6University of Wollongong, Wollongong, Australia
7University of Bremen, Bremen, Germany
8Finnish Meteorological Institute, Sodankylä, Finland
9Karlsruhe Institute of Technology, Karlsruhe, Germany
10National Institute of Water and Atmospheric Research, Wellington, New Zealand
Received: 15 Feb 2014 – Discussion started: 07 Apr 2014
Abstract. The Total Carbon Column Observing Network (TCCON) is a global ground-based network of Fourier transform spectrometers that produce precise measurements of column-averaged dry-air mole fractions of atmospheric methane (CH4). Temporal variability in the total column of CH4 due to stratospheric dynamics obscures fluctuations and trends driven by tropospheric transport and local surface fluxes that are critical for understanding CH4 sources and sinks. We reduce the contribution of stratospheric variability from the total column average by subtracting an estimate of the stratospheric CH4 derived from simultaneous measurements of hydrogen fluoride (HF). HF provides a proxy for stratospheric CH4 because it is strongly correlated to CH4 in the stratosphere, has an accurately known tropospheric abundance (of zero), and is measured at most TCCON stations. The stratospheric partial column of CH4 is calculated as a function of the zonal and annual trends in the relationship between CH4 and HF in the stratosphere, which we determine from ACE-FTS satellite data. We also explicitly take into account the CH4 column averaging kernel to estimate the contribution of stratospheric CH4 to the total column. The resulting tropospheric CH4 columns are consistent with in situ aircraft measurements and augment existing observations in the troposphere.
Revised: 18 Jul 2014 – Accepted: 06 Aug 2014 – Published: 10 Sep 2014
Saad, K. M., Wunch, D., Toon, G. C., Bernath, P., Boone, C., Connor, B., Deutscher, N. M., Griffith, D. W. T., Kivi, R., Notholt, J., Roehl, C., Schneider, M., Sherlock, V., and Wennberg, P. O.: Derivation of tropospheric methane from TCCON CH4 and HF total column observations, Atmos. Meas. Tech., 7, 2907-2918, doi:10.5194/amt-7-2907-2014, 2014.