Observations of CH4 and N2O by the NIMBUS 7 SAMS: A comparison with in situ data and two-dimensional numerical model calculations


  • R. L. Jones,

  • J. A. Pyle


Monthly mean, zonal mean measurements of CH4 and N2O for 1979 made by the stratospheric and mesospheric sounder (SAMS) on the NIMBUS 7 satellite are presented for the first time. Comparison with in situ and other available data confirms a general pattern of mixing ratios decreasing with height and of maxima, at a given pressure level, in low latitudes. The SAMS data, by virtue of its extensive coverage, reveals new features. These include during certain months a “double peak” when, along a constant pressure surface, mixing ratio maxima are found in low latitudes of both hemispheres with a local minimum at the equator. In the upper stratosphere are found regions of weak and strong horizontal gradients. Comparison with a two-dimensional model shows many areas of agreement, especially for CH4, and the model is used to interpret atmospheric behavior. The model overestimates the observed N2O in the upper stratosphere. This is investigated in terms of a possible underestimation of the photochemical sink. We believe strongly, however, that uncertainties in transport representation cannot be ruled out.