Seasonal and latitudinal variation of atmospheric methane: A ground‐based and ship‐borne solar IR spectroscopic study

Column‐averaged volume mixing ratios of CH 4 were retrieved with a precision of better than 0.5% from infrared solar absorption spectra obtained at Ny‐Alesund (Spitsbergen, 79°N) between 1997 and 2004 and during two ship cruises (54°N–34°S) on the Atlantic in 2003. The retrieval has been performed in a spectral region available to all operational FTIR (Fourier Transform InfraRed) spectrometers performing solar absorption measurements. The seasonality and the long‐term increase of the tropospheric volume‐mixing ratio, derived from the infrared measurements agree well with data from surface sampling at this site. The latitudinal variation of ship‐borne measurements between 54°N and 34°S is in agreement with inverse model simulations which are optimized vs. the global NOAA/ESRL measurements.