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The stratosphere (/, /) is the second major layer of Earth's atmosphere, just above the troposphere, and below the mesosphere. About 20% of the atmosphere's mass is contained in the stratosphere. The stratosphere is stratified in temperature, with warmer layers higher and cooler layers closer to the Earth. The increase of temperature with altitude, is a result of the absorption of the Sun's ultraviolet radiation by ozone. This is in contrast to the troposphere, near the Earth's surface, where temperatures decreases with altitude. The border between the troposphere and stratosphere, the tropopause, marks where this temperature inversion begins. Near the equator, the stratosphere starts at 18 km (59,000 ft; 11 mi); at mid latitudes, it starts at 10–13 km (33,000–43,000 ft; 6.2–8.1 mi) and ends at 50 km (160,000 ft; 31 mi); at the poles, it starts at about 8 km (26,000 ft; 5.0 mi). Temperatures vary within the stratosphere with the seasons, in particular with the polar night (winter). The greatest variation of temperature, takes place over the poles in the lower stratosphere; those variations are largely steady at lower latitudes and higher altitudes.
Ozone and temperature
Within this layer, temperature increases with altitude (see temperature inversion); the top of the stratosphere has a temperature of about 270 K (−3°C or 26.6°F). The increase of temperature within the stratosphere with altitude is due to the absorption of high energy ultraviolet (UVB and UVC) radiation from the Sun and the breaking of ozone (O3) into the atomic oxygen (O1) and common molecular oxygen (O2), hence, greater heating. At mid-stratosphere, there is less UV light, and as a result, less radiation energy able to break up ozone. As a result, O and O2 combine to O3, producing ozone at the lowest level of the stratosphere. It is the making and breaking of ozone that creates the stratification of temperatures in the stratosphere and protects life on Earth from the harmful effects of ultra-violet radiation. The result is an increase of temperature with altitude, despite the constant radiation of energy to space. The lower stratosphere receives very little UVC; thus atomic oxygen is not found here and ozone is not formed.[verification needed] This vertical 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. The top of the stratosphere is called the stratopause, above which the temperature decreases with height.
Methane (CH4), while not a direct cause of ozone destruction in the stratosphere, does lead to the formation of compounds that destroy ozone. Monatomic oxygen (O) in the upper stratosphere reacts with methane (CH4) to form a hydroxyl radical (OH·). This hydroxyl radical is then able to interact with non-soluble compounds like chlorofluorocarbons, and UV light breaks off chlorine radicals (Cl·). These chlorine radicals break off an oxygen atom from the ozone molecule, creating an oxygen molecule (O2) and a hypochloryl radical (ClO·). The hypochloryl radical then reacts with an atomic oxygen creating another oxygen molecule and another chlorine radical, thereby preventing the reaction of monatomic oxygen with O2 to create natural ozone.
Commercial airliners typically cruise at altitudes of 9–12 km (30,000–39,000 ft) which is in the lower reaches of the stratosphere in temperate latitudes. This optimizes fuel efficiency, mostly due to the low temperatures encountered near the tropopause and low air density, reducing parasitic drag on the airframe. Stated another way, it allows the airliner to fly faster for the same amount of drag. It also allows them to stay above the turbulent weather of the troposphere.
Because the temperature in the tropopause and lower stratosphere is largely constant with increasing altitude, very little convection and its resultant turbulence occurs there. Most turbulence at this altitude is caused by variations in the jet stream and other local wind shears, although areas of significant convective activity (thunderstorms) in the troposphere below may produce turbulence as a result of convective overshoot.
On October 24, 2014, Alan Eustace became the record holder for reaching the altitude record for a manned balloon at 135,890 ft (41,419 m). Mr Eustace also broke the world records for vertical speed reached with a peak velocity of 1,321 km/h (822 mph) and total freefall distance of 123,414 ft (37,617 m) - lasting four minutes and 27 seconds.
Circulation and mixing
The stratosphere is a region of intense interactions among radiative, dynamical, and chemical processes, in which the horizontal mixing of gaseous components proceeds much more rapidly than does vertical mixing.
An interesting feature of stratospheric circulation is the quasi-biennial oscillation (QBO) in the tropical latitudes, which is driven by gravity waves that are convectively generated in the troposphere. The QBO induces a secondary circulation that is important for the global stratospheric transport of tracers, such as ozone or water vapor.
During northern hemispheric winters, sudden stratospheric warmings, caused by the absorption of Rossby waves in the stratosphere, can be observed in approximately half of winters when easterly winds develop in the stratosphere. These events often precede unusual winter weather  and may even be responsible for the cold European winters of the 1960s.
Stratospheric warming of the polar vortex results in its weakening. When the vortex is strong, it keeps the cold, high pressure air masses "contained" in the arctic; when the vortex weakens, air masses move equatorward, and results in rapid changes of weather in the mid latitudes.
Bacterial life survives in the stratosphere, making it a part of the biosphere. In 2001 an Indian experiment, involving a high-altitude balloon, was carried out at a height of 41 kilometres and a sample of dust was collected with bacterial material inside.
Also, some bird species have been reported to fly at the lower levels of the stratosphere. On November 29, 1973, a Rüppell's vulture was ingested into a jet engine 11,552 m (37,900 ft) above the Ivory Coast, and bar-headed geese reportedly overfly Mount Everest's summit, which is 8,848 m (29,029 ft).
Léon Teisserenc de Bort from France and Richard Assmann from Germany, in separate publications and following years of observations, announced the discovery of an isothermal layer at around 11–14 km, which is the base of the lower stratosphere. This was based on temperature profiles from unmanned instrumented balloons.
- Le Grand Saut
- Lockheed U-2
- Paris Gun (first artificial object to reach stratosphere)
- Red Bull Stratos
- RQ-4 Global Hawk
- Service ceiling
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