Stratosphere

For other uses, see Stratosphere (disambiguation).
Space Shuttle Endeavour appears to straddle the stratosphere and mesosphere in this photo. "The orange layer is the troposphere, where all of the weather and clouds which we typically watch and experience are generated and contained. This orange layer gives way to the whitish Stratosphere and then into the Mesosphere."[1] (The shuttle is actually orbiting at more than 200 miles in altitude, far above this transition layer.)
Diagram of the atmosphere (layers to scale). Distance from the surface to the top of the stratosphere is just under 1% of Earth's radius.
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 centered around 18 kilometers above Earth's surface. The stratosphere image is dominated by blues and greens, which indicates a cooling over time.[2]

The stratosphere (/ˈstrætəˌsfɪər, -toʊ-/[3][4]) 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 farther down. This is in contrast to the troposphere, near the Earth's surface, which is cooler higher and warmer farther down. 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. The greatest variation takes place over the poles in the lower stratosphere, but are largely steady at lower latitudes and higher altitudes.

Ozone and temperature

Within this layer, temperature increases as altitude increases (see temperature inversion); the top of the stratosphere has a temperature of about 270 K (−3°C or 26.6°F), just slightly below the freezing point of water.[5] The stratosphere is layered in temperature because ozone (O3) here absorbs high energy ultraviolet (UVB and UVC) radiation from the Sun and is broken down into the allotropes of atomic oxygen (O1) and common molecular oxygen (O2). The mid stratosphere has less UV light passing through it; O and O2 are able to combine, and this is where the majority of natural ozone is produced. The two reactions with UV, the evolution of energy in the upper level with the breaking of ozone and absorption of energy at lower altitudes with the making of ozone, produces the temperature stratification of the stratosphere. The result is an increase of temperature with altitude, despite the constant radioactive energy loss to space. The lower stratosphere receives very low amounts of UVC; thus atomic oxygen is not found here and ozone is not formed. 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.

Aircraft flight

Commercial airliners typically cruise at altitudes of 9–12 km (30,000–39,000 ft) in temperate latitudes (in the lower reaches of the stratosphere).[6] This optimizes fuel burn, 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 hard weather (extreme turbulence).

Concorde cruised at mach 2 at about 18,000 m (59,000 ft), and the SR-71 cruised at mach 3 at 26,000 m (85,000 ft), 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 at these altitudes. Though most turbulence at this altitude is caused by variations in the jet stream and other local wind shears, 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.[7]

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[8] or water vapor.

In northern hemispheric winter, 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 [9] and may even be responsible for the cold European winters of the 1960s.[10]

Stratospheric warming of the polar vortex results in its weakening. When strong, the vortex keeps the cold, high pressure air masses "contained" in the arctic. When the vortex weakens air masses move equatorward. This results in rapid changes of weather in the mid latitudes.

Life

Bacteria

Bacterial life survives in the stratosphere, making it a part of the biosphere.[11] 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.[12]

Birds

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).[13][14]

Discovery

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.[15]

See also

References

  1. ↑ "ISS022-E-062672 caption". NASA. Retrieved 21 September 2012.
  2. ↑ "Atmospheric Temperature Trends, 1979-2005". NASA/Earth Observatory. 6 July 2007. Retrieved August 2015.
  3. ↑ Jones, Daniel (2003) [1917], Peter Roach, James Hartmann and Jane Setter, eds., English Pronouncing Dictionary, Cambridge: Cambridge University Press, ISBN 3-12-539683-2
  4. ↑ "Stratosphere". Merriam-Webster Dictionary.
  5. ↑ Seinfeld, J. H., and S. N.(2006), Atmospheric Chemistry and Physics: From Air Pollution to Climate Change 2nd ed, Wiley, New Jersey
  6. ↑ "Altitude of a Commercial Jet". Hypertextbook.com. Retrieved 2011-11-08.
  7. ↑ "Google's Alan Eustace beats Baumgartner's skydiving record". BBC News.
  8. ↑ N.Butchart, A.A. Scaife, J. Austin, S.H.E. Hare, J.R. Knight. Quasi-biennial oscillation in ozone in a coupled chemistry-climate model, Journal of Geophysical Research.
  9. ↑ M.P. Baldwin and T.J. Dunkerton. 'Stratospheric Harbingers of Anomalous Weather Regimes, Science Magazine.
  10. ↑ A.A. Scaife, J.R. Knight, G.K. Vallis, C.K. Folland. A stratospheric influence on the winter NAO and North Atlantic surface climate, Geophysical Research Letters.
  11. ↑ S. Shivaji et al, "Isolation of three novel bacterial strains, Janibacter hoylei sp. nov., Bacillus isronensis sp. nov. and Bacillus aryabhattai sp. nov. from cryotubes used for collecting air from upper atmosphere.", Int J Syst Evol Microbiol, 2009.
  12. ↑ M. M. Woolfson. Time, Space, Stars & Man: The Story of the Big Bang. World Scientific; 2013. ISBN 978-1-84816-933-3. p. 388.
  13. ↑ "Audubon: Birds". Audubonmagazine.org. Retrieved 2011-11-08.
  14. ↑ Thomas Alerstam, David A. Christie, Astrid Ulfstrand. Bird Migration (1990). Page 276.
  15. ↑ http://empslocal.ex.ac.uk/people/staff/gv219/classics.d/Hoinka-tropo97.pdf

External links

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