Afterglow of thetroposphere (orange), thestratosphere (blue) and themesosphere (dark) at whichatmospheric entry begins, leavingcontrails, such as in this case of aspacecraft reentry.This image shows the temperature trend in the lower stratosphere as measured by a series of satellite-based instruments between January 1979 and December 2005. The lower stratosphere is centred around 18 kilometres above Earth's surface. The stratosphere image is dominated by blues and greens, which indicates a cooling over time.[1]Diagram showing the five primary layers of the Earth's atmosphere:exosphere,thermosphere,mesosphere, stratosphere, andtroposphere. The layers are not to scale.
Near theequator, the lower edge of the stratosphere is as high as 20 km (66,000 ft; 12 mi), at mid-latitudes around 10 km (33,000 ft; 6.2 mi), and at thepoles about 7 km (23,000 ft; 4.3 mi).[5] Temperatures range from an average of −51 °C (−60 °F; 220 K) near the tropopause to an average of −15 °C (5.0 °F; 260 K) near the mesosphere.[6] Stratospheric temperatures also vary within the stratosphere as theseasons change, reaching particularly low temperatures in thepolar night (winter).[7]Winds in the stratosphere can far exceed those in the troposphere, reaching near 60 m/s (220 km/h; 130 mph) in the Southernpolar vortex.[7]
In 1902,Léon Teisserenc de Bort from France andRichard Assmann from Germany, in separate but coordinated publications and following years of observations, published the discovery of an isothermal layer at around 11–14 km (6.8-8.7 mi), which is the base of the lower stratosphere. This was based on temperature profiles from mostly unmanned and a few manned instrumented balloons.[8]
The ozone layer in the stratosphere blocks harmful UV radiation from reaching the surface of the Earth. A gamma-ray burst would deplete the ozone layer, allowing UV radiation through.
The mechanism describing the formation of the ozone layer was described by British mathematician andgeophysicistSydney Chapman in 1930, and is known as the Chapman cycle orozone–oxygen cycle.[9] Molecular oxygen absorbs high energy sunlight in theUV-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 photolyzed 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 (O3) photolysis produces O and O2. The oxygen atom product combines with atmospheric molecular oxygen to reform O3, 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(seetemperature inversion); the top of the stratosphere has a temperature of about 270K (−3°C or 26.6°F).[10]
This verticalstratification, with warmer layers above and cooler layers below, makes the stratosphere dynamically stable: there is no regularconvection and associatedturbulence in this part of the atmosphere. However, exceptionally energetic convection processes, such as volcaniceruption columns andovershooting tops in severesupercell 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 planet's surface outside of the ocean. All air entering the stratosphere must pass through thetropopause, 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 thestratopause, above which the temperature decreases with height.
Sydney Chapman gave a correct description of the source of stratospheric ozone and its ability to generate heat within the stratosphere;[citation needed] he also wrote that ozone may be destroyed by reacting with atomic oxygen, making two molecules of molecular oxygen. We now know that there are additional ozone loss mechanisms and that these mechanisms are catalytic, meaning that a small amount of the catalyst can destroy a great number of ozone molecules. The first is due to the reaction ofhydroxyl radicals (•OH) with ozone. •OH is formed by the reaction of electrically excited oxygen atoms produced by ozone photolysis, with water vapor. While the stratosphere is dry, additional water vapour is produced in situ by the photochemical oxidation ofmethane (CH4). The HO2 radical produced by the reaction of OH with O3 is recycled to OH by reaction with oxygen atoms or ozone. In addition, solar proton events can significantly affect ozone levels viaradiolysis with the subsequent formation of OH.Nitrous oxide (N2O) is produced by biological activity at the surface and is oxidized to NO in the stratosphere; the so-called NOx radical cycles also deplete stratospheric ozone. Finally,chlorofluorocarbon molecules are photolyzed in the stratosphere releasing chlorine atoms that react with ozone giving ClO and O2. The chlorine atoms are recycled when ClO reacts with O in the upper stratosphere, or when ClO reacts with itself in the chemistry of the Antarctic ozone hole.
Paul J. Crutzen, Mario J. Molina and F. Sherwood Rowland were awarded the Nobel Prize in Chemistry in 1995 for their work describing the formation and decomposition of stratospheric ozone.[11]
Aircraft typically cruise at the stratosphere to avoidturbulence rampant in thetroposphere. The blue beam in this image is theozone layer, beaming further to themesosphere. Theozone heats the stratosphere, making conditions stable. The stratosphere is also the altitude limit of jets andweather balloons, as air is roughly a thousand times thinner there than at the troposphere.[12]
Commercialairliners 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.[13] This optimizesfuel efficiency, mostly due to the low temperatures encountered near the tropopause and low air density, reducingparasitic drag on theairframe. Stated another way, it allows the airliner to fly faster while maintaining lift equal to the weight of the plane. (The fuel consumption depends on the drag, which is related to the lift by thelift-to-drag ratio.) It also allows the airplane to stay above theturbulent weather of the troposphere.
TheConcorde aircraft cruised atMach 2 at about 60,000 ft (18 km), and theSR-71 cruised at Mach 3 at 85,000 ft (26 km), all within the stratosphere.
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 thejet stream and other local wind shears, although areas of significant convective activity (thunderstorms) in the troposphere below may produce turbulence as a result ofconvective 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).[14] Eustace also broke the world records for vertical speed skydiving, 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.[15]
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. The overall circulation of the stratosphere is termed asBrewer-Dobson circulation, which is a single-celled circulation, spanning from the tropics up to the poles, consisting of the tropical upwelling of air from the tropical troposphere and the extra-tropical downwelling of air. Stratospheric circulation is a predominantly wave-driven circulation in that the tropical upwelling is induced by the wave force by the westward propagatingRossby waves, in a phenomenon called Rossby-wave pumping.
Another large-scale feature that significantly influences stratospheric circulation is the breaking planetary waves[17] resulting in intense quasi-horizontal mixing in the midlatitudes. This breaking is much more pronounced in the winter hemisphere where this region is called the surf zone. This breaking is caused due to a highly non-linear interaction between the vertically propagating planetary waves and the isolated highpotential vorticity region known as thepolar vortex. The resultant breaking causes large-scale mixing of air and other trace gases throughout the midlatitude surf zone. The timescale of this rapid mixing is much smaller than the much slower timescales of upwelling in the tropics and downwelling in the extratropics.
During northern hemispheric winters,sudden stratospheric warmings, caused by the absorption ofRossby waves in the stratosphere, can be observed in approximately half of the winters when easterly winds develop in the stratosphere. These events often precede unusual winter weather[18] and may even be responsible for the cold European winters of the 1960s.[19]
Stratospheric warming of the polar vortex results in its weakening.[20] When the vortex is strong, it keeps the cold, high-pressure air massescontained in theArctic; when the vortex weakens, air masses move equatorward, and results in rapid changes of weather in the mid latitudes.
Upper-atmospheric lightning is a family of short-lived electrical breakdown phenomena that occur well above the altitudes of normallightning and storm clouds. Upper-atmospheric lightning is believed to be electrically induced forms of luminousplasma. Lightning extending above thetroposphere into the stratosphere is referred to asblue jet, and that reaching into themesosphere as redsprite.
Bacterial life survives in the stratosphere, making it a part of thebiosphere.[21] In 2001, dust was collected at a height of 41 kilometres in a high-altitude balloon experiment and was found to contain bacterial material when examined later in the laboratory.[22]
^Seinfeld, J. H.; Pandis, S. N. (2006).Atmospheric chemistry and physics: from air pollution to climate change (2nd ed.). Hoboken, NJ: Wiley. p. 8.ISBN978-0-471-72018-8.
