Helium Content of the Stratosphere

Abstract

IT is often assumed that the absence of any systematic temperature gradient in the stratosphere is incompatible with large-scale mixing; winds, which in the troposphere ensure a constant composition of the permanent atmospheric constituents, are supposed to fall off rapidly as the boundary between the troposphere and stratosphere is passed, and above the level at which mixing ceases the composition of the atmosphere should therefore vary with the height. Over England, the boundary between troposphere and stratosphere lies between 10 km. and 11 km.; so far, however, we do not know where the large-scale mixing in the stratosphere becomes negligible. Chapman and Milne¹, therefore, in their well-known tables, provide for four cases in which effective mixing ceases and diffusion commences, at heights of 12 km., 20 km., 30 km., and 50 km. respectively. Maris² has suggested that effective mixing takes place up to about 100 km.