Turbopause
From Glossary of Meteorology
turbopause
The surface that separates the homosphere, in which the constituents of the atmosphere are well mixed by turbulence, from the heterosphere, in which constituents adopt their individual distributions with height as the result of molecular diffusion.
The turbopause is not very clearly marked, but usually lies at a height of about 100 km, near the base of the thermosphere.
