Stratosphere

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.)

Atmosphere diagram showing stratosphere. The layers are to scale: from Earth's surface to the top of the stratosphere (50km) is just under 1% of Earth's radius. (click to enlarge)

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. Source:

The stratosphere /ˈstrætəsfɪər/ is the second major layer of Earth's atmosphere, just above the troposphere, and below the mesosphere. It is stratified in temperature, with warmer layers higher up and cooler layers farther down. This is in contrast to the troposphere near the Earth's surface, which is cooler higher up and warmer farther down. The border of the troposphere and stratosphere, the tropopause, is marked by where this inversion begins, which in terms of atmospheric thermodynamics is the equilibrium level. At moderate latitudes the stratosphere is situated between about 10–13 km (30,000–40,000 ft; 6–8 mi) and 50 km (160,000 ft; 31 mi) altitude above the surface, while at the poles it starts at about 8 km (30,000 ft; 5 mi) altitude, and near the equator it may start at altitudes as high as 18 km (59,000 ft; 11 mi).

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 29.6°F), just slightly below the freezing point of water.^[2] The stratosphere is layered in temperature because ozone (O₃) here absorbs high energy UVB and UVC energy waves from the Sun and is broken down into atomic oxygen (O) and diatomic oxygen (O₂). Atomic oxygen is found prevalent in the upper stratosphere due to the bombardment of UV light and the destruction of both ozone and diatomic oxygen. The mid stratosphere has less UV light passing through it, O and O₂ are able to combine, and is where the majority of natural ozone is produced. It is when these two forms of oxygen recombine to form ozone that they release the heat found in the stratosphere. The lower stratosphere receives very low amounts of UVC, thus atomic oxygen is not found here and ozone is not formed (with heat as the byproduct). 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. Monoatomic 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 monoatomic 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).^[3] 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 would cruise at mach 2 at about 18,000 m (59,000 ft), and the SR-71 would cruise at mach 3 at 26,000 m (85,000 ft), all still in the stratosphere.

Because the temperature in the tropopause and lower stratosphere remains constant (or slightly decreases) with increasing altitude, very little convective 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 convective overshoot.

Although a few gliders have achieved great altitudes in the powerful thermals in thunderstorms ,^{[citation needed]} this is dangerous. Most high altitude flights by gliders use lee waves from mountain ranges and were used to set the current record of 15,447 m (50,679 ft).

On October 14, 2012, Felix Baumgartner became the record holder for both reaching the altitude record for a manned balloon and highest skydive ever from 39.04 km (128,100 ft).^[4]

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 in 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^[5] 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 ^[6] and may even be responsible for the cold European winters of the 1960s ^[7]

Life

Bacteria

Bacterial life survives in the stratosphere, making it a part of the biosphere.^[8] 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.^[9]

Birds

Also, some bird species have been reported to fly at the lower levels of the stratosphere. On November 29, 1975, 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).^[10][11]

See also

• Le Grand Saut
• Léon Teisserenc de Bort and Richard Assmann (the discoverers of the stratosphere)
• Lockheed U-2
• Paris Gun (first artificial object to reach stratosphere)
• Red Bull Stratos
• RQ-4 Global Hawk
• Service ceiling

References

External links

• The dictionary definition of stratosphere at Wiktionary