Spectroscopic observations of the water‐vapour content of the stratosphere

The water‐vapour content of the stratosphere has been deduced from records of the solar spectrum observed from a Canberra aircraft at altitudes up to 48,000 ft. The spectral region 3,790‐3,860 cm −1 in the 2·7 μ band has been separated into four groups of absorption lines whose rates of growth have been studied. Measurements in an altitude chamber of the absorption of very small paths of water vapour have been used to interpret the aircraft measurements in terms of absolute values of (pressure X quantity of water vapour) ½ . Spectroscopic observations have been compared with measurements made by the frost‐point hygrometer. The overall results show that the water‐vapour content in a vertical column above 45,000 ft over southern England is about 4·5 μ, corresponding to a mixing ratio of 3 × 10 −6 , if this is assumed constant above the height of observation.