Tropospheric methane in the mid-latitudes of the Southern Hemisphere |
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| Authors: | P J Fraser M A K Khalil R A Rasmussen L P Steele |
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| Institution: | (1) Cooperative Institute for Research in Environmental Sciences, University of Colorado/NOAA, 80309 Boulder, CO, U.S.A.;(2) Present address: Division of Atmospheric Research, CSIRO, Station Street, 3195 Aspendale, Victoria, Australia;(3) Department of Environmental Science, Oregon Graduate Center, 19600 NW Walker Road, 97006 Beaverton, OR, U.S.A.;(4) Geophysical Monitoring for Climatic Change, Air Resources Laboratory/NOAA, 325 Broadway, 80303 Boulder, CO, U.S.A. |
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| Abstract: | Results of more than 800 new measurements of methane (CH4) concentrations in the Southern Hemisphere troposphere (34–41° S, 130–150° E) are reported. These were obtained between September 1980 and March 1983 from the surface at Cape Grim, Tasmania, through the middle (3.5–5.5 km) to the upper troposphere (7–10 km). The concentration of CH4 increased throughout the entire troposphere over the measurement period, adding further support to the view that CH4 concentrations are currently increasing on a global scale. For data averaged vertically through the troposphere the rate of increase found was 20 ppbv/yr or 1.3%/yr at December 1981. In the surface CH4 data a seasonal cycle with a peak to peak amplitude of approximately 28 ppbv is seen, with the minimum concentration occurring in March and the maximum in September–October. A cycle with the same phase as that seen at the surface, but with a significantly decreased amplitude, is apparent in the mid troposphere but no cycle is detected in the upper tropospheric data. The phase and amplitude of the cycle are qualitatively in agreement with the concept that the major sink for methane is oxidation by hydroxyl radicals. Also presented is evidence of a positive vertical gradient in methane, with a suggestion that the magnitude of this gradient has changed over the period of measurements. |
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| Keywords: | Methane troposphere southern hemisphere trend annual cycle vertical gradient |
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