Measurements of the Water Vapour, Tritium and Carbon-14 Content of the Middle Stratosphere over Southern England

Measurements of the water vapour, tritium and carbon-14 content of the stratosphere at heights of between 80,000 and 100,000 feet, made over England during the years 1956 to 1960, are described. The tritium and carbon-14 concentrations are greater than those expected from natural production due to the cosmic radiation. The bulk of these two isotopes, at present in the stratosphere, has been injected there during the course of thermonuclear explosions. Mass spectrometric analyses show that the deuterium/hydrogen ratio of the water and the carbon-13/carbon-12 and oxygen-16/oxygen-18 ratios of the carbon dioxide collected at these heights were the same, within the accuracy of measurement, as those for samples collected near the ground. The concentration of tritium at the heights of the measurements has not fallen since the termination of thermonuclear weapon testing in autumn 1958. There is poor correlation between the tritium concentration at 90,000 feet and that of particulate caesium-137 at 47,000 feet measured over the sampling period. The humidity above 80,000 feet is found to be greater than that in the lower stratosphere. It is concluded from these humidity and tritium results that the large scale meridional circulation in the stratosphere, first postulated by Brewer and Dobson, does not reach heights of 90,000 feet over temperate latitudes.