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== Ozone layer ==
{{Further|Ozone layer}}
The mechanism describing the formation of the ozone layer was described by British mathematician [[Sydney Chapman (mathematician)|Sydney Chapman]] in 1930, and is known as the Chapman cycle or [[ozone–oxygen cycle]].<ref>{{Cite web|title=CHAPTER 10. STRATOSPHERIC OZONE|url=http://acmg.seas.harvard.edu/people/faculty/djj/book/bookchap10.html|access-date=2020-10-20|website=acmg.seas.harvard.edu|archive-date=2019-09-30|archive-url=https://web.archive.org/web/20190930034719/http://acmg.seas.harvard.edu/people/faculty/djj/book/bookchap10.html|url-status=dead}}</ref> Molecular oxygen absorbs high energy sunlight in the [[UV-C]] region, at wavelengths shorter than about 240 nm. Radicals produced from the homolytically split oxygen molecules combine with molecular oxygen to form ozone. Ozone in turn is [[photodissociation|photolysed]] much more rapidly than molecular oxygen as it has a stronger absorption that occurs at longer wavelengths, where the solar emission is more intense. Ozone (O<sub>3</sub>) photolysis produces O and O<sub>2</sub>. The oxygen atom product combines with atmospheric molecular oxygen to reform O<sub>3</sub>, releasing heat. The rapid photolysis and reformation of ozone heat the stratosphere, resulting in a temperature inversion. This increase of temperature with altitude is characteristic of the stratosphere; its resistance to vertical mixing means that it is stratified. Within the stratosphere temperatures increase with altitude ''(see [[temperature inversion]])''; the top of the stratosphere has a temperature of about 270 [[Kelvin|K]] (−3[[°C]] or 26.6[[°F]]).<ref>Seinfeld, J. H., and S. N.(2006), Atmospheric Chemistry and Physics: From Air Pollution to Climate Change 2nd ed, Wiley, New Jersey</ref>
This vertical [[Atmospheric stratification|stratification]], with warmer layers above and cooler layers below, makes the stratosphere dynamically stable: there is no regular [[convection]] and associated [[turbulence]] in this part of the atmosphere. However, exceptionally energetic convection processes, such as volcanic [[eruption column]]s and [[overshooting top]]s in severe [[Supercell|supercell thunderstorms]], may carry convection into the stratosphere on a very local and temporary basis. Overall, the attenuation of solar UV at wavelengths that damage DNA by the ozone layer allows life to exist on the surface of the planet outside of the ocean. All air entering the stratosphere must pass through the [[tropopause]], the temperature minimum that divides the troposphere and stratosphere. The rising air is literally freeze dried; the stratosphere is a very dry place. The top of the stratosphere is called the [[stratopause]], above which the temperature decreases with height.
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