Mesosphere

The mesosphere (/ˈmɛsoʊsfɪər/; from Greek mesos "middle" ) is the layer of the Earth's atmosphere that is directly above the stratosphere and directly below the thermosphere. In the mesosphere, temperature decreases as the altitude increases. This characteristic is used to define its limits: it begins at the top of the stratosphere (sometimes called the stratopause), and ends at the mesopause, which is the coldest part of Earth's atmosphere with temperatures below −143 °C (−225 °F; 130 K). The exact upper and lower boundaries of the mesosphere vary with latitude and with season (higher in winter and at the tropics, lower in summer and at the poles), but the lower boundary is usually located at heights from 50 to 65 kilometres (164,000 to 213,000 ft; 31 to 40 mi) above the Earth's surface and the upper boundary (mesopause) is usually around 85 to 100 kilometres (53 to 62 mi).[2][3][4][5]

The stratosphere and the mesosphere are collectively referred to as the "middle atmosphere",[6] which spans heights from approximately 10 kilometres (33,000 ft; 6.2 mi) to 100 kilometres (62 mi; 330,000 ft). The mesopause, at an altitude of 80–90 km (50–56 mi), separates the mesosphere from the thermosphere—the second-outermost layer of the Earth's atmosphere. This is also around the same altitude as the turbopause, below which different chemical species are well mixed due to turbulent eddies. Above this level the atmosphere becomes non-uniform; the scale heights of different chemical species differ by their molecular masses.

The term near space is also sometimes used. This term does not have a technical definition, but typically refers the region of the atmosphere up to 100 km (65,000 and 328,000 feet), roughly between the Armstrong limit (above which humans need a pressure suit to survive) up to the Kármán line where astrodynamics must take over from aerodynamics in order to achieve flight. The definition of near space can vary depending on the source, but in general near space comprises the altitudes above where commercial airliners fly but below orbiting satellites. Some sources distinguish between the terms "near space" and "upper atmosphere," so that only the layers closest to the Karman line are called near space.

Endeavour silhouette STS-130
Space Shuttle Endeavour appears to straddle the stratosphere and mesosphere in this photo. The troposphere, which contains clouds, appears orange in this photo.[1]
EarthAtmosphereBig
Diagram showing the five primary layers of the Earth's atmosphere: exosphere, thermosphere, mesosphere, stratosphere, and troposphere. The layers are to scale. From Earth's surface to the top of the stratosphere (50km) is just under 1% of Earth's radius.

Temperature

Within the mesosphere, temperature decreases with increasing height, due to decreasing absorption of solar radiation by the rarefied atmosphere and increasing cooling by CO2 radiative emission. The top of the mesosphere, called the mesopause, is the coldest part of Earth's atmosphere.[7] Temperatures in the upper mesosphere fall as low as −101 °C (172 K; −150 °F),[8] varying according to latitude and season.

Dynamic features

The main dynamic features in this region are strong zonal (East-West) winds, atmospheric tides, internal atmospheric gravity waves (commonly called "gravity waves"), and planetary waves. Most of these tides and waves start in the troposphere and lower stratosphere, and propagate to the mesosphere. In the mesosphere, gravity-wave amplitudes can become so large that the waves become unstable and dissipate. This dissipation deposits momentum into the mesosphere and largely drives global circulation. This helps the Earth.

Noctilucent clouds are located in the mesosphere. The upper mesosphere is also the region of the ionosphere known as the D layer. The D layer is only present during the day when some ionization occurs with nitric oxide being ionized by Lyman series-alpha hydrogen radiation. The ionization is so weak that when night falls, and the source of ionization is removed, the free electron and ion form back into a neutral molecule. The mesosphere has been called the "ignorosphere" because it is poorly studied relative to the stratosphere (which can be accessed with high-altitude balloons) and the thermosphere (in which satellites can orbit).[9]

A 5 km (3.1 mi; 16,000 ft) deep sodium layer is located between 80–105 km (50–65 mi; 262,000–344,000 ft). Made of unbound, non-ionized atoms of sodium, the sodium layer radiates weakly to contribute to the airglow. The sodium has an average concentration of 400,000 atoms per cubic centimetre. This band is regularly replenished by sodium sublimating from incoming meteors. Astronomers have begun utilizing this sodium band to create "guide stars" as part of the adaptive optical correction process used to produce ultra-sharp ground-based observations.[10] Other metal layers, e.g. iron and potassium, exist in the upper mesosphere/lower thermosphere region as well.

Millions of meteors enter the Earth's atmosphere, averaging 40 tons per year.[11] The ablated material, called meteoric smoke, is thought to serve as condensation nuclei for noctilucent clouds.

Exploration and uses

The mesosphere lies above altitude records for aircraft,[12] while only the lowest few kilometers are accessible to balloons, for which the altitude record is 53.0 km.[13] Meanwhile, the mesosphere is below the minimum altitude for orbital spacecraft due to high atmospheric drag.[14][15][16] It has only been accessed through the use of sounding rockets, which are only capable of taking mesospheric measurements for a few minutes per mission.[17] As a result, it is the least-understood part of the atmosphere, resulting in the humorous moniker ignorosphere.[18] The presence of red sprites and blue jets (electrical discharges or lightning within the lower mesosphere), noctilucent clouds, and density shears within this poorly understood layer are of current scientific interest.

Near space was first explored in the 1930s. The early flights flew to the edge of space without computers, spacesuits, and with only crude life support systems. Notable people who flew in near space were Jean Piccard and his wife Jeannette, on the nearcraft The Century of Progress. Later exploration was mainly carried out by unmanned craft, although there have been skydiving attempts made from high-altitude balloons.

The area is of interest for military surveillance purposes, scientific study, as well as to commercial interests for communications, and tourism. Craft that fly in near space include high-altitude balloons, non-rigid airships, rockoons, sounding rockets, and the Lockheed U-2 aircraft. The region has been of interest to space travel. Early attempts used a craft known as a rockoon to reach extreme altitudes and orbit. These are still used today for sounding rockets.

High-altitude platform stations have been proposed for applications such as communications relays. There has been a resurgence of interest in near space to launch manned spacecraft by man. Groups like ARCASPACE, as well as the da Vinci Project are planning on launching manned suborbital space vehicles from high-altitude balloons. JP Aerospace has a proposal for a spaceport in near space, as part of their Airship to Orbit program.

High-altitude balloons

Picture taken at aprox. 100,000 feet above Oregon by Justin Hamel and Chris Thompson
The Earth from approximately 100,000 ft (30,000 m) above Oregon, United States.

Near space has long been used for scientific ballooning, for applications such as submillimetre astronomy. High-altitude balloons are often flown by students and by amateur groups to altitudes on the order of 100,000 ft (30,000 m), for both scientific and educational purposes.[19][20][21]

Phenomena in mesosphere and near space

See also

References

  1. ^ "ISS022-E-062672 caption". NASA. Retrieved 21 September 2012.
  2. ^ "Middle atmosphere". www.antarctica.gov.au. Retrieved 17 June 2018.
  3. ^ Venkat Ratnam, M.; Patra, A. K.; Krishna Murthy, B. V. (25 March 2010). "Tropical mesopause: Is it always close to 100 km?". Journal of Geophysical Research. 115 (D6). doi:10.1029/2009jd012531. ISSN 0148-0227.
  4. ^ "The Mesosphere - overview | UCAR Center for Science Education". scied.ucar.edu. Retrieved 17 June 2018.
  5. ^ von Zahn, U.; Höffner, J.; Eska, V.; Alpers, M. (1 November 1996). "The mesopause altitude: Only two distinctive levels worldwide?". Geophysical Research Letters. 23 (22): 3231–3234. doi:10.1029/96gl03041. ISSN 0094-8276.
  6. ^ "Middle Atmosphere Meteorology". atmos.washington.edu. Retrieved 19 December 2018.
  7. ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006–) "mesosphere". doi:10.1351/goldbook.M03855
  8. ^ Mesosphere (Wayback Machine Archive), Atmosphere, Climate & Environment Information ProgGFKDamme (UK Department for Environment, Food and Rural Affairs), archived from the original on 1 July 2010, retrieved 14 November 2011
  9. ^ "Upper atmosphere may hold clues in Columbia mystery". 6 February 2003.
  10. ^ Martin Enderlein et al., ESO's Very Large Telescope sees four times first light, Laser Focus World, July 2016, pp. 22-24
  11. ^ Leinert C.; Gruen E. (1990). "Interplanetary Dust". Physics and Chemistry in Space (R. Schwenn and E. Marsch eds.). Springer-Verlag. pp. 204-275
  12. ^ "Powered Aeroplanes World Records". Fédération Aéronautique Internationale. Archived from the original on 11 September 2016. Retrieved 31 August 2016.
  13. ^ "Research on Balloon to Float over 50km Altitude". Institute of Space and Astronautical Science, JAXA. Retrieved 29 September 2011.
  14. ^ "IADC Space Debris Mitigation Guidelines" (PDF). Inter-Agency Space Debris Coordination Committee. 15 October 2002.
  15. ^ "NASA Safety Standard 1740.14, Guidelines and Assessment Procedures for Limiting Orbital Debris" (PDF). Office of Safety and Mission Assurance. 1 August 1995. Archived from the original (PDF) on 15 February 2013.
  16. ^ "100 km Altitude Boundary for Astronautics". Fédération Aéronautique Internationale.
  17. ^ "NASA Sounding Rocket Program Overview". NASA Sounding Rocket Program. NASA. 24 July 2006. Retrieved 10 October 2006.
  18. ^ "Reusable Rockets Set to Explore the 'Ignorosphere'". Discover Magazine. 1 September 2016. Retrieved 2 April 2018.
  19. ^ GSBC, What is a High Altitude Balloon (accessed August 8, 2016)
  20. ^ UKHAS, A Beginners Guide to High Altitude Ballooning (accessed August 8, 2016)
  21. ^ DIY Space Exploration, Introduction to High Altitude Balloons (accessed August 8, 2016)

External links

Aeronomy

Aeronomy is the meteorological science of the upper region of the Earth's or other planetary atmospheres, which relates to the atmospheric motions, its chemical composition and properties, and the reaction to it from the environment from space. The term aeronomy was introduced by Sydney Chapman in a Letter to the Editor of Nature entitled Some Thoughts on Nomenclature in 1946. Studies within the subject also investigate the causes of dissociation or ionization processes.Today the term also includes the science of the corresponding regions of the atmospheres of other planets. Aeronomy is a branch of atmospheric physics. Research in aeronomy requires access to balloons, satellites, and sounding rockets which provide valuable data about this region of the atmosphere. Atmospheric tides dominate the dynamics of the mesosphere and lower thermosphere, essential to understanding the atmosphere as a whole. Other phenomena studied are upper-atmospheric lightning discharges, such as red sprites, sprite halos or blue jets.

Aeronomy of Ice in the Mesosphere

The Aeronomy of Ice in the Mesosphere (AIM) is a satellite to conduct a 26-month study of noctilucent clouds (NLCs). It is the ninetieth Explorer program mission and is part of the NASA-funded Small Explorer program (SMEX). On April 25, 2007 AIM was boosted into a 600 km (370 mi) high polar orbit by a Pegasus-XL rocket, which was air-launched from the Lockheed L-1011 Stargazer aircraft operated by Orbital Sciences.

Air current

Air currents are concentrated areas of winds. They are mainly due to differences in pressure and/or temperature. They are divided into horizontal and vertical currents: both are present at mesoscale while horizontal ones dominate at synoptic scale. Air currents are not only found in the troposphere, but extend to the stratosphere and mesosphere.

Apache Mesos

Apache Mesos is an open-source project to manage computer clusters. It was developed at the University of California, Berkeley.

Atmosphere of Earth

The atmosphere of Earth is the layer of gases, commonly known as air, that surrounds the planet Earth and is retained by Earth's gravity. The atmosphere of Earth protects life on Earth by creating pressure allowing for liquid water to exist on the Earth's surface, absorbing ultraviolet solar radiation, warming the surface through heat retention (greenhouse effect), and reducing temperature extremes between day and night (the diurnal temperature variation).

By volume, dry air contains 78.09% nitrogen, 20.95% oxygen, 0.93% argon, 0.04% carbon dioxide, and small amounts of other gases. Air also contains a variable amount of water vapor, on average around 1% at sea level, and 0.4% over the entire atmosphere. Air content and atmospheric pressure vary at different layers, and air suitable for use in photosynthesis by terrestrial plants and breathing of terrestrial animals is found only in Earth's troposphere and in artificial atmospheres.

The atmosphere has a mass of about 5.15×1018 kg, three quarters of which is within about 11 km (6.8 mi; 36,000 ft) of the surface. The atmosphere becomes thinner and thinner with increasing altitude, with no definite boundary between the atmosphere and outer space. The Kármán line, at 100 km (62 mi), or 1.57% of Earth's radius, is often used as the border between the atmosphere and outer space. Atmospheric effects become noticeable during atmospheric reentry of spacecraft at an altitude of around 120 km (75 mi). Several layers can be distinguished in the atmosphere, based on characteristics such as temperature and composition.

The study of Earth's atmosphere and its processes is called atmospheric science (aerology). Early pioneers in the field include Léon Teisserenc de Bort and Richard Assmann.

List of heliophysics missions

This is a list of missions supporting heliophysics, including solar observatory missions, solar orbiters, and spacecraft studying the solar wind.

MOZART (model)

MOZART (Model for OZone And Related chemical Tracers) is a chemistry transport model (CTM) developed jointly by the (US) National Center for Atmospheric Research (NCAR), the Geophysical Fluid Dynamics Laboratory (GFDL), and the Max Planck Institute for Meteorology (MPI-Met) to simulate changes in ozone concentrations in the Earth's atmosphere. MOZART was designed to simulate tropospheric chemical and transport processes, but has been extended into the stratosphere and mesosphere. It can be driven by standard meteorological fields from, e.g.,

the National Centers for Environmental Prediction (NCEP)

the European Centre for Medium-Range Weather Forecasts (ECMWF)

the Global Modeling and Assimilation Office (GMAO)or by fields generated from general circulation models.

Mesopause

The mesopause is the point of minimum temperature at the boundary between the mesosphere and the thermosphere atmospheric regions. Due to the lack of solar heating and very strong radiative cooling from carbon dioxide, the mesosphere is the coldest region on Earth with temperatures as low as -100 °C (-148 °F or 173 K). The altitude of the mesopause for many years was assumed to be at around 85 km (53 mi.), but observations to higher altitudes and modeling studies in the last 10 years have shown that in fact the mesopause consists of two minima - one at about 85 km and a stronger minimum at about 100 km (62 mi).Another feature is that the summer mesopause is cooler than the winter (sometimes referred to as the mesopause anomaly). It is due to a summer-to-winter circulation giving rise to upwelling at the summer pole and downwelling at the winter pole. Air rising will expand and cool resulting in a cold summer mesopause and conversely downwelling air results in compression and associated increase in temperature at the winter mesopause. In the mesosphere the summer-to-winter circulation is due to gravity wave dissipation, which deposits momentum against the mean east-west flow, resulting in a small north-south circulation.In recent years the mesopause has also been the focus of studies on global climate change associated with increases in CO2. Unlike the troposphere, where greenhouse gases result in the atmosphere heating up, increased CO2 in the mesosphere acts to cool the atmosphere due to increased radiative emission. This results in a measurable effect - the mesopause should become cooler with increased CO2. Observations do show a decrease of temperature of the mesopause, though the magnitude of this decrease varies and is subject to further study. Modeling studies of this phenomenon have also been carried out.

Mesosphere, Inc.

Mesosphere is an American technology company based in San Francisco, California which develops software for data centers based on Apache Mesos.

It calls its product Datacenter Operating System.

Mesosphere (mantle)

In geology, the mesosphere refers to the part of the Earth's mantle below the lithosphere and the asthenosphere, but above the outer core. The upper boundary is defined by the sharp increase in seismic wave velocities and density at a depth of 660 kilometers (410 mi). At a depth of 660 km, ringwoodite (gamma-(Mg,Fe)2SiO4) decomposes into Mg-Si perovskite and magnesiowüstite. This reaction marks the boundary between upper mantle and lower mantle. This measurement is estimated from seismic data and high-pressure laboratory experiments.

The base of the mesosphere includes the D'' zone which lies just above the core-mantle boundary at approximately 2,700 to 2,890 km (1,678 to 1,796 mi). The base of the lower mantle is at about 2700 km."Mesosphere" (not to be confused with mesosphere, a layer of the atmosphere) is derived from “mesospheric shell”, coined by Reginald Aldworth Daly, a Harvard University geology professor. In the pre-plate tectonics era, Daly (1940) inferred that the outer Earth consisted of three spherical layers: lithosphere (including the crust), asthenosphere, and mesospheric shell. Daly’s hypothetical depths to the lithosphere–asthenosphere boundary ranged from 80 to 100 km (50 to 62 mi), and the top of the mesospheric shell (base of the asthenosphere) were from 200 to 480 km (124 to 298 mi). Thus, Daly’s asthenosphere was inferred to be 120 to 400 km (75 to 249 mi) thick. According to Daly, the base of the solid Earth mesosphere could extend to the base of the mantle (and, thus, to the top of the core). The term mesosphere has largely been replaced by the term lower mantle in the scientific literature.

A derivative term, mesoplates, was introduced as a heuristic, based on a combination of "mesosphere" and "plate", for postulated reference frames in which mantle hotspots apparently exist.

Noctilucent cloud

Noctilucent clouds, or night shining clouds, are tenuous cloud-like phenomena in the upper atmosphere of Earth. They consist of ice crystals and are only visible during astronomical twilight. Noctilucent roughly means "night shining" in Latin. They are most often observed during the summer months from latitudes between 50° and 70° north and south of the Equator. They are visible only during local summer months and when the Sun is below the observer's horizon, but while the clouds are still in sunlight. Recent studies suggests that increased atmospheric methane emissions produce additional water vapor once the methane molecules reach the mesosphere - creating, or reinforcing existing noctilucent clouds.They are the highest clouds in Earth's atmosphere, located in the mesosphere at altitudes of around 76 to 85 km (47 to 53 mi). They are too faint to be seen in daylight, and are visible only when illuminated by sunlight from below the horizon while the lower layers of the atmosphere are in Earth's shadow.

Polar mesospheric summer echoes

Polar mesospheric summer echoes (PMSE) is the phenomenon of anomalous radar echoes found between 80-90 km in altitude from May through early August in the Arctic, and from November through to February in the Antarctic. These strong radar echoes are associated with the extremely cold temperatures that occur above continental Antarctica during the summer. Rocket and radar measurements indicate that a partial reflection from a multitude of ion layers and constructive interference causes at least some of the PMSE.

Generally PMSE exhibits dramatic variations in height and intensity as well as large variations in Doppler shift. PMSE exhibit strong signal power enhancements of scattering cross section at VHF radar frequencies in the range 50 MHz to 250 MHz, at times even to over 1 GHz, that occur in summer at high latitudes. The peak PMSE height is slightly below the summer mesopause temperature minimum at 88 km, and above the noctilucent cloud (NLC) and/or polar mesospheric cloud (PMC) layer at 83–84 km. The usual instrument for observing PMSE is a VHF Mesosphere-Stratosphere-Troposphere (MST) radar, although LIDARs and sounding rockets have also been used.

PMSE is believed to be caused by structural irregularities in the ionospheric electron density at lower altitudes. The exact cause of PMSE is not yet known, although theorists have proposed steep electron density gradients, heavy positive ions, dressed aerosols, gravity waves and turbulence as possible explanations.

PMSE occurs in both the Arctic and Antarctic regions, and is sometimes accompanied by noctilucent clouds.

Solar Mesosphere Explorer

The Solar Mesosphere Explorer (also known as Explorer 64) was a United States unmanned spacecraft to investigate the processes that create and destroy ozone in Earth's upper atmosphere. The mesosphere is a layer of the atmosphere extending from the top of the stratosphere to an altitude of about 80 kilometers (50 mi). The spacecraft carried five instruments to measure ozone, water vapor and incoming solar radiation.

Launched on October 6, 1981, on a Delta rocket from Vandenberg Air Force Base, in California, the satellite returned data until April 4, 1989. The spacecraft reentered Earth's atmosphere on March 5, 1991.

Managed for NASA by the Jet Propulsion Laboratory, the Solar Mesosphere Explorer was built by Ball Space Systems and operated by the Laboratory for Atmospheric and Space Physics of the University of Colorado where one hundred undergraduate and graduate students were involved.

Mass: 437 kilograms (963 pounds)

Power: Solar panels which charged NiCad batteries

Configuration: Cylinder 1.25 meter (4.1 ft) diameter by 1.7 meter (5.6 ft) high

Science instruments: Ultraviolet ozone spectrometer, 1.27 micrometre spectrometer, nitrogen dioxide spectrometer, four-channel infrared radiometer, solar ultraviolet monitor, solar proton alarm detector

Stratopause

The stratopause (formerly Mesopeak) is the level of the atmosphere which is the boundary between two layers: the stratosphere and the mesosphere. In the stratosphere the temperature increases with altitude, and the stratopause is the region where a maximum in the temperature occurs.

This atmospheric feature is not only associated with Earth: it occurs on any other planet or moon that has an atmosphere as well.On Earth, the stratopause is 50 to 55 kilometres (31–34 mi) high above the Earth's surface. The atmospheric pressure is around 1/1000 of the pressure at sea level. The temperature in the stratopause is -15 degrees Celsius (5 degrees Fahrenheit).

Stratosphere

The stratosphere () is the second major layer of Earth's atmosphere, just above the troposphere, and below the mesosphere. The stratosphere is stratified (layered) in temperature, with warmer layers higher and cooler layers closer to the Earth; this increase of temperature with altitude is a result of the absorption of the Sun's ultraviolet radiation by the ozone layer. This is in contrast to the troposphere, near the Earth's surface, where temperature 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 as high as 20 km (66,000 ft; 12 mi), around 10 km (33,000 ft; 6.2 mi) at midlatitudes, and at about 7 km (23,000 ft; 4.3 mi) at the poles. 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. Stratospheric temperatures also vary within the stratosphere as the seasons change, reaching particularly low temperatures in the polar night (winter). Winds in the stratosphere can far exceed those in the troposphere, reaching near 60 m/s (220 km/h; 130 mph) in the Southern polar vortex.

TIMED

The TIMED (Thermosphere Ionosphere Mesosphere Energetics and Dynamics) is an orbiter mission dedicated to study the dynamics of the Mesosphere and Lower Thermosphere (MLT) portion of the Earth's atmosphere. The mission was launched from Vandenberg Air Force Base in California on December 7, 2001 aboard a Delta II rocket launch vehicle. The project is sponsored and managed by NASA, while the spacecraft was designed and assembled by the Applied Physics Laboratory at Johns Hopkins University. The mission has been extended several times, and has now collected data over an entire solar cycle, which helps in its goal to differentiate the Sun's effects on the atmosphere from other effects.

Thermosphere

The thermosphere is the layer in the Earth's atmosphere directly above the mesosphere and below the exosphere. Within this layer of the atmosphere, ultraviolet radiation causes photoionization/photodissociation of molecules, creating ions in the ionosphere. Taking its name from the Greek θερμός (pronounced thermos) meaning heat, the thermosphere begins at about 80 km (50 mi) above sea level. At these high altitudes, the residual atmospheric gases sort into strata according to molecular mass (see turbosphere). Thermospheric temperatures increase with altitude due to absorption of highly energetic solar radiation. Temperatures are highly dependent on solar activity, and can rise to 1,700 °C (3,100 °F) or more. Radiation causes the atmosphere particles in this layer to become electrically charged (see ionosphere), enabling radio waves to be refracted and thus be received beyond the horizon. In the exosphere, beginning at about 600 km (375 mi) above sea level, the atmosphere turns into space, although by the criteria set for the definition of the Kármán line, the thermosphere itself is part of space.

The highly diluted gas in this layer can reach 2,500 °C (4,530 °F) during the day. Despite the high temperature, an observer or object will experience cold temperatures in the thermosphere, because the extremely low density of gas (practically a hard vacuum) is insufficient for the molecules to conduct heat. A normal thermometer will read significantly below 0 °C (32 °F), at least at night, because the energy lost by thermal radiation would exceed the energy acquired from the atmospheric gas by direct contact. In the anacoustic zone above 160 kilometres (99 mi), the density is so low that molecular interactions are too infrequent to permit the transmission of sound.

The dynamics of the thermosphere are dominated by atmospheric tides, which are driven by the very significant diurnal heating. Atmospheric waves dissipate above this level because of collisions between the neutral gas and the ionospheric plasma.

The International Space Station orbits the Earth within the middle of the thermosphere, between 330 and 435 kilometres (205 and 270 mi).

Turbopause

The turbopause marks the altitude in the Earth's atmosphere below which turbulent mixing dominates. The region below the turbopause is known as the homosphere, where the chemical constituents are well mixed and display identical height distributions; in other words, the chemical composition of the atmosphere remains constant in this region for chemical species which have long mean residence times. Highly reactive chemicals tend to exhibit great concentration variability throughout the atmosphere, whereas unreactive species will exhibit more homogeneous concentrations. The region above the turbopause is the heterosphere, where molecular diffusion dominates and the chemical composition of the atmosphere varies according to chemical species.

The turbopause lies near the mesopause, at the intersection of the mesosphere and the thermosphere, at an altitude of roughly 100 km.

Upper-atmospheric models

Upper-atmospheric models are simulations of the Earth's atmosphere between 20 and 100 km (65,000 and 328,000 feet) that comprises the stratosphere, mesosphere, and the lower thermosphere. Whereas most climate models simulate a region of the Earth's atmosphere from the surface to the stratopause, there also exist numerical models which simulate the wind, temperature and composition of the Earth's tenuous upper atmosphere, from the mesosphere to the exosphere, including the ionosphere. This region is affected strongly by the 11 year Solar cycle through variations in solar UV/EUV/Xray radiation and solar wind leading to high latitude particle precipitation and aurora. It has been proposed that these phenomena may have an effect on the lower atmosphere, and should therefore be included in simulations of climate change. For this reason there has been a drive in recent years to create whole atmosphere models to investigate whether or not this is the case.

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