{{Short description|Gas layer surrounding Earth}}{{Redirect|Air}}{{Redirect-distinguish|Qualities of air|Air pollution{{!}}Air quality}}{{pp-semi-indef}}File:Top of Atmosphere.jpg|thumb|Blue light is scattered more than other wavelengths by the gases in the atmosphere, surrounding Earth in a visibly blue layer at the stratosphere, above the clouds of the troposphere, when seen from space on board the ISS at an altitude of {{cvt|335|km|mi}} (the weblink Gateway to Astonaut Photos of Earth, NASA, 2018-01-29, ">330x330pxThe atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth creates pressure, absorbs most meteoroids and ultraviolet solar radiation, warms the surface through heat retention (greenhouse effect), and reduces temperature extremes between day and night (the diurnal temperature variation), maintaining conditions allowing life and liquid water to exist on the Earth's surface.As of 2023, by mole fraction (i.e., by number of molecules), dry air contains 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.04% carbon dioxide, and small amounts of other gases.{{refn |name=total% |Two recent reliable sources cited here have total atmospheric compositions, including trace molecules, that exceed 100%. They are Allen's Astrophysical Quantities{{citation |editor-last=Cox |editor-first=Arthur N. |title=Allen's Astrophysical Quantities |edition=Fourth |year=2000 |publisher=AIP Press |pages=258â€“259 |isbn=0-387-98746-0}}, which rounds N{{sub|2}} and O{{sub|2}} to four significant digits without affecting the total because 0.004% was removed from N{{sub|2}} and added to O{{sub|2}}. It includes 20 constituents. (2000, 100.001241343%) and CRC Handbook of Chemistry and Physics{{citation |editor-last=Haynes |editor-first= H. M. |title=CRC Handbook of Chemistry and Physics |publisher=CRC Press |edition=97th |year=2016â€“2017 |page=14{{hyphen}}3 |isbn=978-1-4987-5428-6}}, which cites Allen's Astrophysical Quantities but includes only ten of its largest constituents. (2016â€“2017, 100.004667%), which cites Allen's Astrophysical Quantities. Both are used as references in this article. Both exceed 100% because their CO{{sub|2}} values were increased to 345 ppmv, without changing their other constituents to compensate. This is made worse by the April 2019 {{CO2}} value, which is 413.32 ppmv.{{citation |title=Trends in Atmospheric Carbon Dioxide |url=https://www.esrl.noaa.gov/gmd/ccgg/trends/ |website=Global Greenhouse Gas Reference Network, NOAA |year=2019 |access-date=2019-05-31}} Although minor, the January 2019 value for {{CH4}} is 1866.1 ppbv (parts per billion).{{citation |title=Trends in Atmospheric Methane |website=Global Greenhouse Gas Reference Network, NOAA |url=https://www.esrl.noaa.gov/gmd/ccgg/trends_ch4/ |year=2019 |access-date=2019-05-31}} Two older reliable sources have dry atmospheric compositions, including trace molecules, that total less than 100%: U.S. Standard Atmosphere, 1976{{citation |author=National Aeronautics and Space Administration |title=U.S. Standard Atmosphere, 1976 |url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19770009539.pdf |page=3 |year=1976}} (99.9997147%); and Astrophysical Quantities{{citation |last=Allen |first=C. W. |title=Astrophysical Quantities |url=https://archive.org/details/AstrophysicalQuantities/page/n127 |edition=Third |year=1976 |publisher=Athlone Press |page=119 |isbn=0-485-11150-0}} (1976, 99.9999357%).}} Air also contains a variable amount of water vapor, on average around 1% at sea level, and 0.4% over the entire atmosphere. Air composition, temperature, and atmospheric pressure vary with altitude. Within the atmosphere, air suitable for use in photosynthesis by terrestrial plants and breathing of terrestrial animals is found only in Earth's troposphere.{{citation needed|date=July 2021}}Earth's early atmosphere consisted of gases in the solar nebula, primarily hydrogen. The atmosphere changed significantly over time, affected by many factors such as volcanism, life, and weathering. Recently, human activity has also contributed to atmospheric changes, such as global warming, ozone depletion and acid deposition.The atmosphere has a mass of about 5.15{{e|18}} kg,Lide, David R. Handbook of Chemistry and Physics. Boca Raton, FL: CRC, 1996: 14â€“17 three quarters of which is within about {{convert|11|km|mi ft|abbr=on}} of the surface. The atmosphere becomes thinner with increasing altitude, with no definite boundary between the atmosphere and outer space. The KÃ¡rmÃ¡n line, at {{convert|100|km|mi|abbr=on}} 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 {{convert|120|km|mi|abbr=on}}. 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), and includes multiple subfields, such as climatology and atmospheric physics. Early pioneers in the field include LÃ©on Teisserenc de Bort and Richard Assmann.BOOK, VÃ¡zquez, M., Hanslmeier, A., Ultraviolet Radiation in the Solar System, Historical Introduction, Astrophysics and Space Science Library, 331,weblink 2006, Springer Science & Business Media, 978-1-4020-3730-6, 17, 2005ASSL..331.....V, 10.1007/1-4020-3730-9_1, The study of historic atmosphere is called paleoclimatology.

Composition

(File:Atmosphere gas proportions.svg|thumb|Composition of Earth's atmosphere by molecular count, excluding water vapor. Lower pie represents trace gases that together compose about 0.0434% of the atmosphere (0.0442% at August 2021 concentrations). Numbers are mainly from 2000, with {{CO2}} and methane from 2019, and do not represent any single source.)The three major constituents of Earth's atmosphere are nitrogen, oxygen, and argon. Water vapor accounts for roughly 0.25% of the atmosphere by mass. The concentration of water vapor (a greenhouse gas) varies significantly from around 10 ppm by mole fraction in the coldest portions of the atmosphere to as much as 5% by mole fraction in hot, humid air masses, and concentrations of other atmospheric gases are typically quoted in terms of dry air (without water vapor).Wallace, John M. and Peter V. Hobbs. Atmospheric Science: An Introductory Survey {{Webarchive|url=https://web.archive.org/web/20180728040037weblink |date=2018-07-28 }}. Elsevier. Second Edition, 2006. {{ISBN|978-0-12-732951-2}}. Chapter 1{{rp|8}} The remaining gases are often referred to as trace gases,WEB,weblink Trace Gases, Ace.mmu.ac.uk, 2010-10-16,weblink" title="web.archive.org/web/20101009044345weblink">weblink 9 October 2010, dead, among which are other greenhouse gases, principally carbon dioxide, methane, nitrous oxide, and ozone. Besides argon, already mentioned, other noble gases, neon, helium, krypton, and xenon are also present. Filtered air includes trace amounts of many other chemical compounds. Many substances of natural origin may be present in locally and seasonally variable small amounts as aerosols in an unfiltered air sample, including dust of mineral and organic composition, pollen and spores, sea spray, and volcanic ash. Various industrial pollutants also may be present as gases or aerosols, such as chlorine (elemental or in compounds), fluorine compounds and elemental mercury vapor. Sulfur compounds such as hydrogen sulfide and sulfur dioxide (SO2) may be derived from natural sources or from industrial air pollution.{| class="wikitable" style="text-align: center;"|+Major constituents of air, by mole fraction! colspan=4 | Dry air! colspan=2 | Gas! colspan=2 style="font-weight: normal;" | Mole fraction(A)

! style="width: 100px;" | Name! style="width: 50px;" | Formula! style="width: 100px; font-weight: normal;" | in ppm(B)! style="width: 100px;" | in %

Nitrogen| N2| 780,840| 78.084

Oxygen| O2| 209,460| 20.946

Argon| Ar| 9,340| 0.9340

Carbon dioxide(April 2022)(C)APRIL 2022>TITLE=VITAL SIGNS: CARBON DIOXIDE

ACCESS-DATE=16 MAY 2022, NASA Climate, | {{CO2}}| 417| 0.0417

Neon| Ne| 18.18| 0.001818

Helium| He| 5.24| 0.000524

Methane(2022)(C)APRIL 2022>TITLE=VITAL SIGNS: METHANE

ACCESS-DATE=2 FEB 2024, NASA Climate, | CH4| 1.91| 0.000191

Krypton| Kr| 1.14| 0.000114

! colspan=4 | If air is not dry:

Water vapor(D)| H2O| 0â€“30,000(D)| 0â€“3%(E)

! colspan=4 style="font-size: 0.85em; padding: 5px 2px 5px 10px; text-align: left; font-weight: normal;" | notes:

(A) Mole fraction is sometimes referred to as volume fraction; these are identical for an ideal gas only.
(B) ppm: parts per million by molecular count
- The total ppm above adds up to more than 1 million (currently 83.43 above it) due to experimental error.
(C) The concentration of {{CO2}} has been increasing in recent decades, as has that of {{CH4}}.
(D) Water vapor is about 0.25% by mass over full atmosphere
(E) Water vapor varies significantly locally

The average molecular weight of dry air, which can be used to calculate densities or to convert between mole fraction and mass fraction, is about 28.946Detlev MÃ¶ller: Luft: Chemie, Physik, Biologie, Reinhaltung, Recht. Walter de Gruyter, 2003, {{ISBN|3-11-016431-0}}, S. 173. (View in Google Books). or 28.96BOOK, Yunus Ã‡engel, Termodinamica e trasmissione del calore, WEB, Air - Molecular Weight and Composition,weblink 2021-04-27, www.engineeringtoolbox.com, g/mol. This is decreased when the air is humid.The relative concentration of gases remains constant until about {{convert|10000|m|ft|abbr=on|sigfig=2}}.WEB,weblink Air Composition, The Engineering ToolBox, The composition of air is unchanged until elevation of approximately 10.000 m, 2017-07-04,

Stratification

(File:Earth's atmosphere.svg|thumb|Earth's atmosphere. Lower four layers of the atmosphere in three dimensions as seen diagonally from above the exobase. Layers drawn to scale, objects within the layers are not to scale. Aurorae shown here at the bottom of the thermosphere can actually form at any altitude in this atmospheric layer.)In general, air pressure and density decrease with altitude in the atmosphere. However, the temperature has a more complicated profile with altitude, and may remain relatively constant or even increase with altitude in some regions (see the temperature section, below). Because the general pattern of the temperature/altitude profile, or lapse rate, is constant and measurable by means of instrumented balloon soundings, the temperature behavior provides a useful metric to distinguish atmospheric layers. In this way, Earth's atmosphere can be divided (called atmospheric stratification) into five main layers: troposphere, stratosphere, mesosphere, thermosphere, and exosphere.NEWS,weblink Earth's Upper Atmosphere, Zell, Holly, 2015-03-02, NASA, 2017-02-20, en, The altitudes of the five layers are as follows:

Exosphere: 700 to 10,000 km (440 to 6,200 miles)WEB, Exosphere - overview,weblink 2011, UCAR, April 19, 2015,weblink 17 May 2017, dead,
Thermosphere: 80 to 700 km (50 to 440 miles)WEB, Randy Russell, The Thermosphere, 2008,weblink 2013-10-18,
Mesosphere: 50 to 80 km (31 to 50 miles)
Stratosphere: 12 to 50 km (7 to 31 miles)
Troposphere: 0 to 12 km (0 to 7 miles)WEB,weblink The height of the tropopause, Das.uwyo.edu, 2012-04-18,

Exosphere

The exosphere is the outermost layer of Earth's atmosphere (though it is so tenuous that some scientists consider it to be part of interplanetary space rather than part of the atmosphere). It extends from the thermopause (also known as the "exobase") at the top of the thermosphere to a poorly defined boundary with the solar wind and interplanetary medium. The altitude of the exobase varies from about {{convert|500|km|mi ft}} to about {{convert|1000|km}} in times of higher incoming solar radiation.WEB, Exosphere - overview,weblink 2011, UCAR, April 19, 2015,weblink 17 May 2017, live, The upper limit varies depending on the definition. Various authorities consider it to end at about {{convert|10000|km}}WEB,weblink January 22, 2013, Earth's Atmospheric Layers, or about {{convert|190000|km|mi}}â€”about halfway to the moon, where the influence of Earth's gravity is about the same as radiation pressure from sunlight. The geocorona visible in the far ultraviolet (caused by neutral hydrogen) extends to at least {{convert|100000|km}}.This layer is mainly composed of extremely low densities of hydrogen, helium and several heavier molecules including nitrogen, oxygen and carbon dioxide closer to the exobase. The atoms and molecules are so far apart that they can travel hundreds of kilometres without colliding with one another. Thus, the exosphere no longer behaves like a gas, and the particles constantly escape into space. These free-moving particles follow ballistic trajectories and may migrate in and out of the magnetosphere or the solar wind. Every second, the Earth loses about 3 kg of hydrogen, 50 g of helium, and much smaller amounts of other constituents.David C. Catling and Kevin J. Zahnle, The Planetary Air Leak, Scientific American, May 2009, p. 26 (accessed 25 July 2012)The exosphere is too far above Earth for meteorological phenomena to be possible. However, Earth's aurorasâ€”the aurora borealis (northern lights) and aurora australis (southern lights)â€”sometimes occur in the lower part of the exosphere, where they overlap into the thermosphere. The exosphere contains many of the artificial satellites that orbit Earth.

Thermosphere

The thermosphere is the second-highest layer of Earth's atmosphere. It extends from the mesopause (which separates it from the mesosphere) at an altitude of about {{convert|80|km|mi ft|abbr=on|sigfig=2}} up to the thermopause at an altitude range of {{convert|500|-|1,000|km|mi ft|abbr=on|sigfig=2|comma=5}}. The height of the thermopause varies considerably due to changes in solar activity. Because the thermopause lies at the lower boundary of the exosphere, it is also referred to as the exobase. The lower part of the thermosphere, from {{convert|80|to|550|km}} above Earth's surface, contains the ionosphere.The temperature of the thermosphere gradually increases with height and can rise as high as {{convert|1,500|C|abbr=on|sigfig=2|comma=5}}, though the gas molecules are so far apart that its temperature in the usual sense is not very meaningful. The air is so rarefied that an individual molecule (of oxygen, for example) travels an average of {{convert|1|km|mi ft|comma=5}} between collisions with other molecules.Ahrens, C. Donald. Essentials of Meteorology. Published by Thomson Brooks/Cole, 2005. Although the thermosphere has a high proportion of molecules with high energy, it would not feel hot to a human in direct contact, because its density is too low to conduct a significant amount of energy to or from the skin.This layer is completely cloudless and free of water vapor. However, non-hydrometeorological phenomena such as the aurora borealis and aurora australis are occasionally seen in the thermosphere. The International Space Station orbits in this layer, between {{convert|350|and|420|km|mi|abbr=on|sigfig=2}}. It is this layer where many of the satellites orbiting the Earth are present.

Mesosphere

File:ISS-46 Soyuz TMA-17M reentry.jpg|thumb|upright=1.25|Afterglow of the troposphere (orange), the stratosphere (blue) and the mesosphere (dark) at which atmospheric entry begins, leaving smoke trails, such as in this case of a spacecraft spacecraftThe mesosphere is the third highest layer of Earth's atmosphere, occupying the region above the stratosphere and below the thermosphere. It extends from the stratopause at an altitude of about {{convert|50|km|mi ft|abbr=on|sigfig=2}} to the mesopause at {{convert|80|-|85|km|mi ft|abbr=on|sigfig=2}} above sea level.Temperatures drop with increasing altitude to the mesopause that marks the top of this middle layer of the atmosphere. It is the coldest place on Earth and has an average temperature around {{convert|-85|C|F K|abbr=on|lk=on|sigfig=2}}.JOURNAL, States, Robert J., Gardner, Chester S., Thermal Structure of the Mesopause Region (80â€“105 km) at 40Â°N Latitude. Part I: Seasonal Variations, Journal of the Atmospheric Sciences, 57, 1, 66â€“77, January 2000, 10.1175/1520-0469(2000)0572.0.CO;2, 2000JAtS...57...66S, free, WEB, Joe Buchdahl,weblink Atmosphere, Climate & Environment Information Programme, Ace.mmu.ac.uk, 2012-04-18, dead,weblink" title="web.archive.org/web/20100701030705weblink">weblink 2010-07-01, Just below the mesopause, the air is so cold that even the very scarce water vapor at this altitude can condense into polar-mesospheric noctilucent clouds of ice particles. These are the highest clouds in the atmosphere and may be visible to the naked eye if sunlight reflects off them about an hour or two after sunset or similarly before sunrise. They are most readily visible when the Sun is around 4 to 16 degrees below the horizon. Lightning-induced discharges known as transient luminous events (TLEs) occasionally form in the mesosphere above tropospheric thunderclouds. The mesosphere is also the layer where most meteors burn up upon atmospheric entrance. It is too high above Earth to be accessible to jet-powered aircraft and balloons, and too low to permit orbital spacecraft. The mesosphere is mainly accessed by sounding rockets and rocket-powered aircraft.

Stratosphere

The stratosphere is the second-lowest layer of Earth's atmosphere. It lies above the troposphere and is separated from it by the tropopause. This layer extends from the top of the troposphere at roughly {{convert|12|km|mi ft|abbr=on}} above Earth's surface to the stratopause at an altitude of about {{convert|50|to|55|km|mi ft|abbr=on}}.The atmospheric pressure at the top of the stratosphere is roughly 1/1000 the pressure at sea level. It contains the ozone layer, which is the part of Earth's atmosphere that contains relatively high concentrations of that gas. The stratosphere defines a layer in which temperatures rise with increasing altitude. This rise in temperature is caused by the absorption of ultraviolet radiation (UV) from the Sun by the ozone layer, which restricts turbulence and mixing. Although the temperature may be {{convert|-60|C|F K|abbr=on|sigfig=2}} at the tropopause, the top of the stratosphere is much warmer, and may be near 0 Â°C.WEB, Journal of the Atmospheric Sciences, stratopause, 1993,weblink 2013-10-18, 2013-10-19,weblink" title="web.archive.org/web/20131019124644weblink">weblink dead, The stratospheric temperature profile creates very stable atmospheric conditions, so the stratosphere lacks the weather-producing air turbulence that is so prevalent in the troposphere. Consequently, the stratosphere is almost completely free of clouds and other forms of weather. However, polar stratospheric or nacreous clouds are occasionally seen in the lower part of this layer of the atmosphere where the air is coldest. The stratosphere is the highest layer that can be accessed by jet-powered aircraft.

Troposphere

File:ISS-47_Islands_In_The_Sky,_Indonesia.jpg|thumb|upright=1.25|A picture of Earth's troposphere with its different cloud types of low to high altitudes casting shadows. Sunlight is reflected off the ocean, after it was filtered into a redish light by passing through much of the troposphere at sunset. The above lying stratosphere can be seen at the horizon as a band of its characteristic glow of blue scattered sunlight.]]The troposphere is the lowest layer of Earth's atmosphere. It extends from Earth's surface to an average height of about {{cvt|12|km|mi ft}}, although this altitude varies from about {{cvt|9|km|mi ft}} at the geographic poles to {{cvt|17|km|mi ft}} at the Equator, with some variation due to weather. The troposphere is bounded above by the tropopause, a boundary marked in most places by a temperature inversion (i.e. a layer of relatively warm air above a colder one), and in others by a zone that is isothermal with height.BOOK, Barry, R.G., Chorley, R.J., 1971, Atmosphere, Weather and Climate,weblink registration, London, Menthuen & Co Ltd., 65, 9780416079401, BOOK, Tyson, P.D., Preston-Whyte, R.A., 2013, The Weather and Climate of Southern Africa, 2nd, Oxford, Oxford University Press, 4, Although variations do occur, the temperature usually declines with increasing altitude in the troposphere because the troposphere is mostly heated through energy transfer from the surface. Thus, the lowest part of the troposphere (i.e. Earth's surface) is typically the warmest section of the troposphere. This promotes vertical mixing (hence, the origin of its name in the Greek word Ï„ÏÏŒÏ€Î¿Ï‚, tropos, meaning "turn"). The troposphere contains roughly 80% of the mass of Earth's atmosphere.BOOK, McGraw-Hill, Concise Encyclopedia of Science & Technology, 1984, Troposphere, It contains about four-fifths of the mass of the whole atmosphere., The troposphere is denser than all its overlying layers because a larger atmospheric weight sits on top of the troposphere and causes it to be most severely compressed. Fifty percent of the total mass of the atmosphere is located in the lower {{cvt|5.6|km|mi ft}} of the troposphere.Nearly all atmospheric water vapor or moisture is found in the troposphere, so it is the layer where most of Earth's weather takes place. It has basically all the weather-associated cloud genus types generated by active wind circulation, although very tall cumulonimbus thunder clouds can penetrate the tropopause from below and rise into the lower part of the stratosphere. Most conventional aviation activity takes place in the troposphere, and it is the only layer accessible by propeller-driven aircraft.

Other layers

(File:Msis_atmospheric_composition_by_height.svg|thumb|339x339px|The volume fraction of the main constituents of the Earth's atmosphere as a function of height, based on the MSIS-E-90 atmospheric model; the model only works above 85km)Within the five principal layers above, which are largely determined by temperature, several secondary layers may be distinguished by other properties:

The ozone layer is contained within the stratosphere. In this layer ozone concentrations are about 2 to 8 parts per million, which is much higher than in the lower atmosphere but still very small compared to the main components of the atmosphere. It is mainly located in the lower portion of the stratosphere from about {{convert|15|-|35|km|mi ft|abbr=on}}, though the thickness varies seasonally and geographically. About 90% of the ozone in Earth's atmosphere is contained in the stratosphere.
The ionosphere is a region of the atmosphere that is ionized by solar radiation. It is responsible for auroras. During daytime hours, it stretches from {{convert|50|to|1000|km|mi ft|abbr=on}} and includes the mesosphere, thermosphere, and parts of the exosphere. However, ionization in the mesosphere largely ceases during the night, so auroras are normally seen only in the thermosphere and lower exosphere. The ionosphere forms the inner edge of the magnetosphere. It has practical importance because it influences, for example, radio propagation on Earth.
The homosphere and heterosphere are defined by whether the atmospheric gases are well mixed. The surface-based homosphere includes the troposphere, stratosphere, mesosphere, and the lowest part of the thermosphere, where the chemical composition of the atmosphere does not depend on molecular weight because the gases are mixed by turbulence.WEB,weblink homosphere â€“ AMS Glossary, Amsglossary.allenpress.com, 2010-10-16,weblink" title="web.archive.org/web/20100914045832weblink">weblink 14 September 2010, live, This relatively homogeneous layer ends at the turbopause found at about {{convert|100|km|mi ft|abbr=on}}, the very edge of space itself as accepted by the FAI, which places it about {{convert|20|km|mi ft|abbr=on}} above the mesopause.

Above this altitude lies the heterosphere, which includes the exosphere and most of the thermosphere. Here, the chemical composition varies with altitude. This is because the distance that particles can move without colliding with one another is large compared with the size of motions that cause mixing. This allows the gases to stratify by molecular weight, with the heavier ones, such as oxygen and nitrogen, present only near the bottom of the heterosphere. The upper part of the heterosphere is composed almost completely of hydrogen, the lightest element.WEB,weblink The 4 Most Abundant Gases in Earth's Atmosphere, Anne Marie Helmenstine, PhD, June 16, 2018,

The planetary boundary layer is the part of the troposphere that is closest to Earth's surface and is directly affected by it, mainly through turbulent diffusion. During the day the planetary boundary layer usually is well-mixed, whereas at night it becomes stably stratified with weak or intermittent mixing. The depth of the planetary boundary layer ranges from as little as about {{convert|100|m|ft}} on clear, calm nights to {{convert |3000|m|ft|abbr=on}} or more during the afternoon in dry regions.

The average temperature of the atmosphere at Earth's surface is {{convert|14|C|F K|abbr=on}}WEB,weblink's_atmosphere.html, Earth's Atmosphere, dead,weblink" title="web.archive.org/web/20090614054213weblink">weblink 2009-06-14, or {{convert|15|C|F K|abbr=on}},WEB,weblink NASA â€“ Earth Fact Sheet, Nssdc.gsfc.nasa.gov, 2010-10-16,weblink" title="web.archive.org/web/20101030234253weblink">weblink 30 October 2010, live, depending on the reference.WEB,weblink weblink" title="web.archive.org/web/20090303233131weblink">weblink dead, 2009-03-03, Global Surface Temperature Anomalies, WEB,weblink weblink" title="web.archive.org/web/20050303202001weblink">weblink dead, 2005-03-03, Earth's Radiation Balance and Oceanic Heat Fluxes, WEB,weblink Coupled Model Intercomparison Project Control Run, dead,weblink" title="web.archive.org/web/20080528143343weblink">weblink 2008-05-28,

Physical properties

Pressure and thickness

The average atmospheric pressure at sea level is defined by the International Standard Atmosphere as {{convert|101325|Pa|Torr psi mmHg|lk=on|comma=off}}. This is sometimes referred to as a unit of standard atmospheres (atm). Total atmospheric mass is 5.1480Ã—1018 kg (1.135Ã—1019 lb),JOURNAL, The Mass of the Atmosphere: A Constraint on Global Analyses, Journal of Climate, 18, 6, 864, 1970-01-01, 10.1175/JCLI-3299.1, 2005JCli...18..864T, Trenberth, Kevin E., Smith, Lesley, 16754900, 10.1.1.727.6573, about 2.5% less than would be inferred from the average sea level pressure and Earth's area of 51007.2 megahectares, this portion being displaced by Earth's mountainous terrain. Atmospheric pressure is the total weight of the air above unit area at the point where the pressure is measured. Thus air pressure varies with location and weather.If the entire mass of the atmosphere had a uniform density equal to sea level density (about 1.2 kg per m3) from sea level upwards, it would terminate abruptly at an altitude of {{convert|8.50|km|ft|abbr=on}}.Air pressure actually decreases exponentially with altitude, dropping by half every {{convert|5.6|km|ft|abbr=on}} or by a factor of 1/e (0.368) every {{convert|7.64|km|ft|abbr=on}}, (this is called the scale height) -- for altitudes out to around {{convert|70|km|mi ft|abbr=on}}. However, the atmosphere is more accurately modeled with a customized equation for each layer that takes gradients of temperature, molecular composition, solar radiation and gravity into account. At heights over 100 km, an atmosphere may no longer be well mixed. Then each chemical species has its own scale height.In summary, the mass of Earth's atmosphere is distributed approximately as follows:Lutgens, Frederick K. and Edward J. Tarbuck (1995) The Atmosphere, Prentice Hall, 6th ed., pp. 14â€“17, {{ISBN|0-13-350612-6}}

50% is below {{convert|5.6|km|ft|abbr=on}}.
90% is below {{convert|16|km|ft|abbr=on}}.
99.99997% is below {{convert|100|km|mi ft|abbr=on}}, the KÃ¡rmÃ¡n line. By international convention, this marks the beginning of space where human travelers are considered astronauts.

By comparison, the summit of Mount Everest is at {{convert|8848|m|ft|abbr=on}}; commercial airliners typically cruise between {{convert|10|and|13|km|ft|abbr=on}} where the lower density and temperature of the air improve fuel economy; weather balloons reach {{convert|30.4|km|ft|abbr=on}} and above; and the highest X-15 flight in 1963 reached {{convert|108.0|km|ft|abbr=on}}.Even above the KÃ¡rmÃ¡n line, significant atmospheric effects such as auroras still occur. Meteors begin to glow in this region, though the larger ones may not burn up until they penetrate more deeply. The various layers of Earth's ionosphere, important to HF radio propagation, begin below 100 km and extend beyond 500 km. By comparison, the International Space Station and Space Shuttle typically orbit at 350â€“400 km, within the F-layer of the ionosphere where they encounter enough atmospheric drag to require reboosts every few months, otherwise, orbital decay will occur resulting in a return to Earth. Depending on solar activity, satellites can experience noticeable atmospheric drag at altitudes as high as 700â€“800 km.

Temperature

File:Atmospheric Temperature Trend.jpg|thumb|Temperature trends in two thick layers of the atmosphere as measured between January 1979 and December 2005 by microwave sounding units and advanced microwave sounding units on (NOAA]] weather satellites. The instruments record microwaves emitted from oxygen molecules in the atmosphere. Source:WEB,weblink Atmospheric Temperature Trends, 1979â€“2005 : Image of the Day, Earthobservatory.nasa.gov, 2000-01-01, 2014-06-10, )The division of the atmosphere into layers mostly by reference to temperature is discussed above. Temperature decreases with altitude starting at sea level, but variations in this trend begin above 11 km, where the temperature stabilizes over a large vertical distance through the rest of the troposphere. In the stratosphere, starting above about 20 km, the temperature increases with height, due to heating within the ozone layer caused by the capture of significant ultraviolet radiation from the Sun by the dioxygen and ozone gas in this region. Still another region of increasing temperature with altitude occurs at very high altitudes, in the aptly-named thermosphere above 90 km.

Speed of sound

Because in an ideal gas of constant composition the speed of sound depends only on temperature and not on pressure or density, the speed of sound in the atmosphere with altitude takes on the form of the complicated temperature profile (see illustration to the right), and does not mirror altitudinal changes in density or pressure.

Density and mass

File:Atmosphere model.png|thumb|Temperature and mass density against altitude from the NRLMSISE-00 standard atmosphere model (the eight dotted lines in each "decade" are at the eight cubes 8, 27, 64, ..., 729)]]The density of air at sea level is about 1.2 kg/m3 (1.2 g/L, 0.0012 g/cm3). Density is not measured directly but is calculated from measurements of temperature, pressure and humidity using the equation of state for air (a form of the ideal gas law). Atmospheric density decreases as the altitude increases. This variation can be approximately modeled using the barometric formula. More sophisticated models are used to predict the orbital decay of satellites.The average mass of the atmosphere is about 5 quadrillion (5{{e|15}}) tonnes or 1/1,200,000 the mass of Earth. According to the American National Center for Atmospheric Research, "The total mean mass of the atmosphere is 5.1480{{E|18}} kg with an annual range due to water vapor of 1.2 or 1.5{{E|15}} kg, depending on whether surface pressure or water vapor data are used; somewhat smaller than the previous estimate. The mean mass of water vapor is estimated as 1.27{{E|16}} kg and the dry air mass as 5.1352 Â±0.0003{{E|18}} kg."

Tabulated properties

Table of physical and thermal properties of air at atmospheric pressure:BOOK, Holman, Jack P.,weblink Heat transfer, McGraw-Hill Companies, Inc., 2002, 9780072406559, 9th, New York, NY, 600â€“606, English, 46959719, BOOK, Theodore L., Bergman, Adrienne S., Lavine, Frank P., Incropera, David P., DeWitt,weblink Fundamentals of heat and mass transfer., John Wiley and Sons, Inc., 2007, 9780471457282, 6th, Hoboken, NJ, 941â€“950, English, 62532755, {|class="wikitable mw-collapsible"Temperature [{{val>u=K}}]Density [{{val>u=kg/m3}}]Specific heat [{{val>u=J/(kgâ‹…Â°C)}}]Dynamic viscosity [{{val>u=kg/(mâ‹…s)}}]Kinematic viscosity [{{val>u=m2/s}}]Thermal conductivity [{{val>u=W/(mâ‹…Â°C)}}]Thermal diffusivity [{{val>u=m2/s}}]| Prandtl Number [1]Bulk modulus [{{val>u=Kâˆ’1}}]

100}}

3.601}}

1026.6}}

6.92E-06}}

1.92E-06}}

0.000925}}

2.50E-06}}

0.77}}

0.01}}

150}}

2.3675}}

1009.9}}

1.03E-05}}

4.34E-06}}

0.013735}}

5.75E-6}}

0.753}}

0.006667}}

200}}

1.7684}}

1006.1}}

1.33E-05}}

7.49E-06}}

0.01809}}

1.02E-05}}

0.738}}

0.005}}

250}}

1.4128}}

1005.3}}

1.60E-05}}

1.13E-05}}

0.02227}}

1.57E-05}}

0.722}}

0.004}}

300}}

1.1774}}

1005.7}}

1.85E-05}}

1.57E-05}}

0.02624}}

2.22E-05}}

0.708}}

0.003333}}

350}}

0.998}}

1009}}

2.08E-05}}

0.03003}}

2.98E-05}}

0.697}}

0.002857}}

400}}

0.8826}}

1014}}

2.29E-05}}

2.59E-05}}

0.03365}}

3.76E-05}}

0.689}}

0.0025}}

450}}

0.7833}}

1020.7}}

2.48E-05}}

3.17E-05}}

0.03707}}

4.22E-05}}

0.683}}

0.002222}}

500}}

0.7048}}

1029.5}}

2.67E-05}}

3.79E-05}}

0.04038}}

5.56E-05}}

0.68}}

0.002}}

550}}

0.6423}}

1039.2}}

2.85E-05}}

4.43E-05}}

0.0436}}

6.53E-05}}

0.68}}

0.001818}}

600}}

0.5879}}

1055.1}}

3.02E-05}}

5.13E-05}}

0.04659}}

7.51E-05}}

0.68}}

0.001667}}

650}}

0.543}}

1063.5}}

3.18E-05}}

5.85E-05}}

0.04953}}

8.58E-05}}

0.682}}

0.001538}}

700}}

0.503}}

1075.2}}

3.33E-05}}

6.63E-05}}

0.0523}}

9.67E-05}}

0.684}}

0.001429}}

750}}

0.4709}}

1085.6}}

3.48E-05}}

7.39E-05}}

0.05509}}

1.08E-04}}

0.686}}

0.001333}}

800}}

0.4405}}

1097.8}}

3.63E-05}}

8.23E-05}}

0.05779}}

1.20E-04}}

0.689}}

0.00125}}

850}}

0.4149}}

1109.5}}

3.77E-05}}

9.08E-05}}

0.06028}}

1.31E-04}}

0.692}}

0.001176}}

900}}

0.3925}}

1121.2}}

3.90E-05}}

9.93E-05}}

0.06279}}

1.43E-04}}

0.696}}

0.001111}}

950}}

0.3716}}

1132.1}}

4.02E-05}}

1.08E-04}}

0.06525}}

1.55E-04}}

0.699}}

0.001053}}

1000}}

0.3524}}

1141.7}}

4.15E-05}}

1.18E-04}}

0.06753}}

1.68E-04}}

0.702}}

0.001}}

1100}}

0.3204}}

1160}}

4.44E-05}}

1.39E-04}}

0.0732}}

1.97E-04}}

0.704}}

0.000909}}

1200}}

0.2947}}

1179}}

4.69E-05}}

1.59E-04}}

0.0782}}

2.25E-04}}

0.707}}

0.000833}}

1300}}

0.2707}}

1197}}

4.93E-05}}

1.82E-04}}

0.0837}}

2.58E-04}}

0.705}}

0.000769}}

1400}}

0.2515}}

1214}}

5.17E-05}}

2.06E-04}}

0.0891}}

2.92E-04}}

0.705}}

0.000714}}

1500}}

0.2355}}

1230}}

0.000054}}

2.29E-04}}

0.0946}}

3.26E-04}}

0.705}}

0.000667}}

1600}}

0.2211}}

1248}}

5.63E-05}}

2.55E-04}}

0.1}}

3.61E-04}}

0.705}}

0.000625}}

1700}}

0.2082}}

1267}}

5.85E-05}}

2.81E-04}}

0.105}}

3.98E-04}}

0.705}}

0.000588}}

1800}}

0.197}}

1287}}

6.07E-05}}

3.08E-04}}

0.111}}

4.38E-04}}

0.704}}

0.000556}}

1900}}

0.1858}}

1309}}

6.29E-05}}

3.39E-04}}

0.117}}

4.81E-04}}

0.704}}

0.000526}}

2000}}

0.1762}}

1338}}

0.000065}}

3.69E-04}}

0.124}}

5.26E-04}}

0.702}}

0.0005}}

2100}}

0.1682}}

1372}}

6.72E-05}}

4.00E-04}}

0.131}}

5.72E-04}}

0.7}}

0.000476}}

2200}}

0.1602}}

1419}}

6.93E-05}}

4.33E-04}}

0.139}}

6.12E-04}}

0.707}}

0.000455}}

2300}}

0.1538}}

1482}}

7.14E-05}}

4.64E-04}}

0.149}}

6.54E-04}}

0.71}}

0.000435}}

2400}}

0.1458}}

1574}}

7.35E-05}}

5.04E-04}}

0.161}}

7.02E-04}}

0.718}}

0.000417}}

2500}}

0.1394}}

1688}}

7.57E-05}}

5.44E-04}}

0.175}}

7.44E-04}}

0.73}}

0.0004}}

3000}}

0.1135}}

2.726}}

9.55E-05}}

8.41E-04}}

0.486}}

1.57E-03}}

0.536}}

0.0003333}}

Optical properties

{{See also|Sunlight}}Solar radiation (or sunlight) is the energy Earth receives from the Sun. Earth also emits radiation back into space, but at longer wavelengths that humans cannot see. Part of the incoming and emitted radiation is absorbed or reflected by the atmosphere.WEB, Absorption / reflection of sunlight,weblink 2023-06-13, Understanding Global Change, WEB, The Atmospheric Window,weblink 2023-06-13, National Oceanic and Atmospheric Administration, In May 2017, glints of light, seen as twinkling from an orbiting satellite a million miles away, were found to be reflected light from ice crystals in the atmosphere.NEWS, St. Fleur, Nicholas, Spotting Mysterious Twinkles on Earth From a Million Miles Away,weblink 19 May 2017, The New York Times, 20 May 2017, JOURNAL, Marshak, Alexander, VÃ¡rnai, TamÃ¡s, Kostinski, Alexander, Terrestrial glint seen from deep space: oriented ice crystals detected from the Lagrangian point, 15 May 2017, Geophysical Research Letters, 44, 10, 5197, 10.1002/2017GL073248, 2017GeoRL..44.5197M, 109930589,weblink 11603/13118, free,

Scattering

When light passes through Earth's atmosphere, photons interact with it through scattering. If the light does not interact with the atmosphere, it is called direct radiation and is what you see if you were to look directly at the Sun. Indirect radiation is light that has been scattered in the atmosphere. For example, on an overcast day when you cannot see your shadow, there is no direct radiation reaching you, it has all been scattered. As another example, due to a phenomenon called Rayleigh scattering, shorter (blue) wavelengths scatter more easily than longer (red) wavelengths. This is why the sky looks blue; you are seeing scattered blue light. This is also why sunsets are red. Because the Sun is close to the horizon, the Sun's rays pass through more atmosphere than normal before reaching your eye. Much of the blue light has been scattered out, leaving the red light in a sunset.

Absorption

File:Openstax Astronomy EM spectrum and atmosphere.jpg|thumb|Rough plot of Earth's atmospheric transmittance (or opacity) to various wavelengths of electromagnetic radiation, including visible light visible lightDifferent molecules absorb different wavelengths of radiation. For example, O2 and O3 absorb almost all radiation with wavelengths shorter than 300 nanometres. Water (H2O) absorbs at many wavelengths above 700 nm. When a molecule absorbs a photon, it increases the energy of the molecule. This heats the atmosphere, but the atmosphere also cools by emitting radiation, as discussed below.The combined absorption spectra of the gases in the atmosphere leave "windows" of low opacity, allowing the transmission of only certain bands of light. The optical window runs from around 300 nm (ultraviolet-C) up into the range humans can see, the visible spectrum (commonly called light), at roughly 400â€“700 nm and continues to the infrared to around 1100 nm. There are also infrared and radio windows that transmit some infrared and radio waves at longer wavelengths. For example, the radio window runs from about one centimetre to about eleven-metre waves.

Emission

{{Further|Emission spectrum}}Emission is the opposite of absorption, it is when an object emits radiation. Objects tend to emit amounts and wavelengths of radiation depending on their "black body" emission curves, therefore hotter objects tend to emit more radiation, with shorter wavelengths. Colder objects emit less radiation, with longer wavelengths. For example, the Sun is approximately {{convert|6000|K|lk=on}}, its radiation peaks near 500 nm, and is visible to the human eye. Earth is approximately {{convert|290|K|abbr=on}}, so its radiation peaks near 10,000 nm, and is much too long to be visible to humans.Because of its temperature, the atmosphere emits infrared radiation. For example, on clear nights Earth's surface cools down faster than on cloudy nights. This is because clouds (H2O) are strong absorbers and emitters of infrared radiation. This is also why it becomes colder at night at higher elevations.The greenhouse effect is directly related to this absorption and emission effect. Some gases in the atmosphere absorb and emit infrared radiation, but do not interact with sunlight in the visible spectrum. Common examples of these are {{CO2}} and H2O.

Refractive index

missing image!
- SB DouglasPreserve SunAtmosphericEffects 2017 3 cropped.jpg -
Distortive effect of atmospheric refraction upon the shape of the sun at the horizon

{{See also|Scintillation (astronomy)}}The refractive index of air is close to, but just greater than 1. Systematic variations in the refractive index can lead to the bending of light rays over long optical paths. One example is that, under some circumstances, observers on board ships can see other vessels just over the horizon because light is refracted in the same direction as the curvature of Earth's surface.The refractive index of air depends on temperature,JOURNAL, Bengt, EdlÃ©n, 1966, Metrologia, 2, 2, The refractive index of air, 71â€“80, 10.1088/0026-1394/2/2/002, 1966Metro...2...71E, giving rise to refraction effects when the temperature gradient is large. An example of such effects is the mirage.

Circulation

(File:AtmosphCirc2.png|thumb|right|An idealised view of three pairs of large circulation cells)Atmospheric circulation is the large-scale movement of air through the troposphere, and the means (with ocean circulation) by which heat is distributed around Earth. The large-scale structure of the atmospheric circulation varies from year to year, but the basic structure remains fairly constant because it is determined by Earth's rotation rate and the difference in solar radiation between the equator and poles.

{{anchor|History of Earth's atmosphere|Atmosphere of early Earth}}Evolution of Earth's atmosphere

{{anchor|First atmosphere}}Earliest atmosphere

The first atmosphere consisted of gases in the solar nebula, primarily hydrogen. There were probably simple hydrides such as those now found in the gas giants (Jupiter and Saturn), notably water vapor, methane and ammonia.JOURNAL, Zahnle, K., Schaefer, L., Laura K. Schaefer, Fegley, B., 10.1101/cshperspect.a004895, Earth's Earliest Atmospheres, Cold Spring Harbor Perspectives in Biology, 2, 10, a004895, 2010, 20573713, 2944365,

Second atmosphere

{{See also|Prebiotic atmosphere}}Outgassing from volcanism, supplemented by gases produced during the late heavy bombardment of Earth by huge asteroids, produced the next atmosphere, consisting largely of nitrogen plus carbon dioxide and inert gases. A major part of carbon-dioxide emissions dissolved in water and reacted with metals such as calcium and magnesium during weathering of crustal rocks to form carbonates that were deposited as sediments. Water-related sediments have been found that date from as early as 3.8 billion years ago.B. Windley: The Evolving Continents. Wiley Press, New York 1984About 3.4 billion years ago, nitrogen formed the major part of the then stable "second atmosphere". The influence of life has to be taken into account rather soon in the history of the atmosphere because hints of early life-forms appear as early as 3.5 billion years ago.J. Schopf: Earth's Earliest Biosphere: Its Origin and Evolution. Princeton University Press, Princeton, N.J., 1983 How Earth at that time maintained a climate warm enough for liquid water and life, if the early Sun put out 30% lower solar radiance than today, is a puzzle known as the "faint young Sun paradox".The geological record however shows a continuous relatively warm surface during the complete early temperature record of Earth â€“ with the exception of one cold glacial phase about 2.4 billion years ago. In the late Archean Eon an oxygen-containing atmosphere began to develop, apparently produced by photosynthesizing cyanobacteria (see Great Oxygenation Event), which have been found as stromatolite fossils from 2.7 billion years ago. The early basic carbon isotopy (isotope ratio proportions) strongly suggests conditions similar to the current, and that the fundamental features of the carbon cycle became established as early as 4 billion years ago.Ancient sediments in the Gabon dating from between about 2.15 and 2.08 billion years ago provide a record of Earth's dynamic oxygenation evolution. These fluctuations in oxygenation were likely driven by the Lomagundi carbon isotope excursion.JOURNAL, 2014, Timothy W. Lyons, Christopher T. Reinhard & Noah J. Planavsky, Atmospheric oxygenation three billion years ago, Nature, 10.1038/nature13068, 24553238, 2014Natur.506..307L, 506, 7488, 307â€“15, 4443958,

Third atmosphere

(File:Sauerstoffgehalt-1000mj2.png|thumb|Oxygen content of the atmosphere over the last billion yearsJOURNAL, Martin, Daniel, McKenna, Helen, Livina, Valerie, The human physiological impact of global deoxygenation, The Journal of Physiological Sciences, 67, 1, 97â€“106, 10.1007/s12576-016-0501-0, 27848144, 5138252, 1880-6546, 2016, Graph: Atmospheric Oxygen and CO2 vs Time)The constant re-arrangement of continents by plate tectonics influences the long-term evolution of the atmosphere by transferring carbon dioxide to and from large continental carbonate stores. Free oxygen did not exist in the atmosphere until about 2.4 billion years ago during the Great Oxygenation Event and its appearance is indicated by the end of the banded iron formations.Before this time, any oxygen produced by photosynthesis was consumed by the oxidation of reduced materials, notably iron. Free oxygen molecules did not start to accumulate in the atmosphere until the rate of production of oxygen began to exceed the availability of reducing materials that removed oxygen. This point signifies a shift from a reducing atmosphere to an oxidizing atmosphere. O2 showed major variations until reaching a steady state of more than 15% by the end of the Precambrian.Christopher R. Scotese, Back to Earth History : Summary Chart for the Precambrian, Paleomar Project The following time span from 539 million years ago to the present day is the Phanerozoic Eon, during the earliest period of which, the Cambrian, oxygen-requiring metazoan life forms began to appear.The amount of oxygen in the atmosphere has fluctuated over the last 600 million years, reaching a peak of about 30% around 280 million years ago, significantly higher than today's 21%. Two main processes govern changes in the atmosphere: Plants using carbon dioxide from the atmosphere and releasing oxygen, and then plants using some oxygen at night by the process of photorespiration while the remaining oxygen is used to break down organic material. Breakdown of pyrite and volcanic eruptions release sulfur into the atmosphere, which reacts with oxygen and hence reduces its amount in the atmosphere. However, volcanic eruptions also release carbon dioxide, which plants can convert to oxygen. The cause of the variation of the amount of oxygen in the atmosphere is not known. Periods with much oxygen in the atmosphere are associated with the rapid development of animals.

Air pollution

{{em|Air pollution}} is the introduction into the atmosphere of chemicals, particulate matter or biological materials that cause harm or discomfort to organisms.Starting from weblink Pollution â€“ Definition from the Merriam-Webster Online Dictionary Stratospheric ozone depletion is caused by air pollution, chiefly from chlorofluorocarbons and other ozone-depleting substances.Since 1750, human activity has increased the concentrations of various greenhouse gases, most importantly carbon dioxide, methane and nitrous oxide. This increase has caused an observed rise in global temperatures. Global average surface temperatures were {{Val|1.1|u=Â°C}} higher in the 2011â€“2020 decade than they were in 1850.BOOK, IPCC, IPCC AR6 WG1, 2021, 4â€“5, Summary for Policymakers, {{harvid, IPCC AR6 WG1 Summary for Policymakers, 2021, |author-link=IPCC|chapter-url=https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_SPM.pdf|access-date=2021-11-20|archive-date=2021-08-11|archive-url=https://web.archive.org/web/20210811205522weblink|url-status=dead}}File:Watching the Earth Breathe.ogv|thumb|Animation shows the buildup of tropospheric {{CO2}} in the Northern Hemisphere with a maximum around May. The maximum in the vegetation cycle follows in the late summer. Following the peak in vegetation, the drawdown of atmospheric {{CO2}} due to photosynthesis is apparent, particularly over the boreal forests boreal forests

Images from space

On October 19, 2015, NASA started a website containing daily images of the full sunlit side of Earth atweblink The images are taken from the Deep Space Climate Observatory (DSCOVR) and show Earth as it rotates during a day.WEB, Daily Views of Earth Available on New NASA Website,weblink NASA, 2015-10-21, Karen, Northon, 2015-10-19, {{Gallery|title=|width=160|height=170|align=leftEarth's night-side upper atmosphere appearing from the bottom as bands of afterglow illuminating the troposphere in orange with silhouettes of clouds, and the stratosphere in white and blue. Next the mesosphere (pink area) extends to the orange and faintly green line of the lowest airglow, at about one hundred kilometers at the edge of space and the lower edge of the thermosphere (invisible). Continuing with green and red bands of aurorae streching over several hundred kilometers.Limb view of Earth's atmosphere. Colors roughly denote the layers of the atmosphere.This image shows the Moon at the centre, with the limb of Earth near the bottom transitioning into the orange-colored troposphere. The troposphere ends abruptly at the tropopause, which appears in the image as the sharp boundary between the orange- and blue-colored atmosphere. The silvery-blue noctilucent clouds extend far above Earth's troposphere.Earth's atmosphere backlit by the Sun in an eclipse observed from deep space onboard Apollo 12 in 1969}}{{clear}}

References

External links

EB9, Atmosphere, III, Buchan, Alexander, Alexander Buchan (meteorologist), 28-36, 1,
Interactive global map of current atmospheric and ocean surface conditions.

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