Secular increase of the vertical column abundance of methane derived from IR solar spectra recorded at the Jungfraujoch station

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Abstract
Using all of the pertinent infrared solar spectra recorded at the Jungfraujoch Station, Switzerland, in 1951, 1975, and in 1984–1987, the increase of the vertical column abundance of methane, CH4, above that station has been reevaluated. The results are based on equivalent widths measurements of both the R0 and the R5 transitions of the 2v3 band of CH4 at 6015.66 and 6067.09 cm−1 and on the CH4–v3 band absorption characteristics between 2905.0 and 2908.8 cm−1. The data between 1984 and 1987 provide a full seasonal cycle. They demonstrate a significant annual variation in the column abundance of CH4 of ±10% around the mean. They also show variability on shorter time scales. The mean cumulative rate of increase of the total vertical column abundance of CH4 above the Jungfraujoch is found to be (0.7 ± 0.1)% yr−1 between 1951 and 1986. Using a realistic CH4 concentration profile throughout the troposphere and the stratosphere, we deduce volume mixing ratios at the altitude of the Jungfraujoch, equal to 1.28±0.08 and 1.64±0.09 ppm, for 1951 and for 1985–1987, respectively.

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