turbopause

{{Short description|Altitude in the Earth's atmosphere below which turbulent mixing dominates}}

The turbopause, also called the homopause, marks the altitude in an atmosphere below which turbulent mixing dominates. Mathematically, it is defined as the point where the coefficient of Eddy diffusion is equal to the coefficient of molecular diffusion.{{cite book |last=Atreya|first=Sushil K. |chapter=Vertical Mixing |date=1986 |pages=66–79 |editor-last=Atreya |editor-first=Sushil K. |title=Atmospheres and Ionospheres of the Outer Planets and Their Satellites |volume=15 |series=Physics and Chemistry in Space |publisher=Springer Berlin Heidelberg |language=en |doi=10.1007/978-3-642-71394-1_4 |isbn=9783642713941}} The region below the turbopause is known as the homosphere, where the atmosphere is well mixed for chemical species which have long mean residence times. Highly reactive chemicals tend to have variable concentration throughout the atmosphere, while unreactive species have more homogeneous concentrations. The region above the turbopause is the heterosphere, where molecular diffusion dominates and the chemical composition of the atmosphere varies according to chemical species and their atomic weight.

Earth's turbopause lies near the mesopause, at the intersection of the mesosphere and the thermosphere, at an altitude of roughly {{cvt|90|km|mi}}.{{cite web |url=https://glossary.ametsoc.org/wiki/turbopause |title=turbopause |website=AMS Glossary (glossary.ametsoc.org) |publisher=American Meteorological Society |access-date=2019-06-01}} Some other turbopauses in the Solar System that are known include Venus' turbopause at about {{cvt|130|–|135|km|mi}}, Mars' at about {{cvt|130|km|mi}}, Jupiter's at roughly {{cvt|385|km|mi}}, and Titan's at around {{cvt|800|–|850|km|mi}}.{{cite book |title=Atmospheric Evolution on Inhabited and Lifeless Worlds?|last1=Catling|first1=David |last2=Kasting|first2=James |publisher=Cambridge University Press |year=2017 |isbn=9780521844123 |page=6}}

It was discovered by French scientists following the firing of two Véronique sounding rockets on 10 and 12 March 1959.{{cite web |first=Philippe|last=Varnoteaux |url=https://air-cosmos.com/article/il-y-a-60-ans-vronique-agi-emmenait-la-france-dans-lespace-partie-1-la-campagne-de-tirs-490 |language=fr |title=Il y a 60 ans, Véronique AGI emmenait la France dans l'espace – PARTIE 1 : La campagne de tirs |access-date=2019-08-31}}