The water vapour budget of the stratosphere studied using LIMS and SAMS satellite data

Monthly zonal mean observations of H 2 O and CH 4 made by the limb infrared monitor of the stratosphere (LIMS) and the stratospheric and mesospheric sounder (SAMS) instruments on Nimbus 7 have been used to investigate whether the H 2 O mixing ratios in the stratosphere are consistent with a source via the oxidation of CH 4 . While both sets of data show considerable seasonally varying structure, total hydrogen (neglecting molecular hydrogen) is relatively featureless with a mean value over the stratosphere of 6.0±0.35 p.p.m.v. (1σ) for the five‐month period studied. The uniformity of the total hydrogen fields points to the validity of the CH 4 oxidation hypothesis. The derived fields of total hydrogen are used to deduce a mean H 2 O mixing ratio for air as it enters the stratosphere of 2.7±0.35 p.p.m.v. (1σ) from which a desiccation temperature may be deduced (for example. −87.2°C at 60 mb).