The Building of the Ark; the Flood (v. 21-32; cf. Gen. vi. 13-viii. 19).

21. And He commanded Noah to make him an ark, that he might save himself from the waters of the flood. 2 22. And Noah made the ark in all respects as He commanded him, in the twenty-seventh jubilee 1307 A.M. of years, in the fifth week in the fifth year (on the new moon of the first month). 23. And he entered in the sixth (year) thereof, in the second month, on 1308 A.M. the new moon of the second month, till the sixteenth; and he entered, and all that we brought to him, into the ark, and the Lord closed 3 it from without on the seventeenth 4 evening.

24. And the Lord opened seven flood-gates 5 of heaven,And the mouths of the fountains of the great deep, seven mouths in number.

25. And the flood-gates began to pour down water from the heaven forty days and forty nights,And the fountains of the deep also sent up waters, until the whole world was full of water.

26. And the waters increased upon the earthFifteen cubits did the waters rise above all the high mountains, p. 60And the ark was lift up above the earth,And it moved upon the face of the waters. 1

27. And the water prevailed on the face of the earth five months-one hundred and fifty days. 2 28. And the ark went and rested on the top of Lûbâr, one of the mountains of Ararat. 3 29. And (on the new moon) in the fourth month the fountains of the great deep were closed and the flood-gates of heaven were restrained; and on the new moon of the seventh month all the mouths of the abysses of the earth were opened, and the water began to descend into the deep 1309 A.M. below. 4 30. And on the new moon of the tenth month the tops of the mountains were seen, and on the new moon of the first month the earth became visible. 5 31. And the waters disappeared from above the earth in the fifth week in the seventh year thereof, and on the seventeenth 6 day in the second month the earth was dry. 32. And on the twenty-seventh thereof he opened the ark, and sent forth from it beasts, and cattle, and birds, and every moving thing. 7

Today, it is known that the world's atmosphere consists of different layers that lie on top of each other.19 Based on the criteria of chemical contents or air temperature, the definitions made have determined the atmosphere of the earth as seven layers.20 According to the "Limited Fine Mesh Model (LFMMII)," a model of atmosphere used to estimate weather conditions for 48 hours, the atmosphere is also 7 layers. According to the modern geological definitions the seven layers of atmosphere are as follows:

1. Troposphere

2. Stratosphere

3. Mesosphere

4. Thermosphere

5. Exosphere

6. Ionosphere

7. Magnetosphere

Atmosphere of EarthFrom Wikipedia, the free encyclopedia (Redirected from Earth's atmosphere)"Air" redirects here. For other uses, see Air (disambiguation).

"Qualities of air" redirects here. It is not to be confused with Air quality.

This animation shows the buildup of tropospheric CO2 in the Northern Hemisphere with a maximum around May. The maximum in the vegetation cycle follows, occurring in the late summer. Following the peak in vegetation, the drawdown of atmospheric CO2 due to photosynthesis is apparent, particularly over the Boreal Forests.

Blue light is scattered more than other wavelengths by the gases in the atmosphere, giving the Earth a blue halo when seen from space.

Limb view, of the Earth's atmosphere. Colours roughly denote the layers of the atmosphere.

This image shows the moon at centre, with the limb of Earth near the bottom transitioning into the orange-coloured troposphere, the lowest and most dense portion of the Earth's atmosphere. The troposphere ends abruptly at the tropopause, which appears in the image as the sharp boundary between the orange- and blue- coloured atmosphere. The silvery-blue noctilucent clouds extend far above the Earth's troposphere.

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 atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention (greenhouse effect), and reducing temperature extremes between day and night (the diurnal temperature variation).Atmospheric stratification describes the structure of the atmosphere, dividing it into distinct layers, each with specific characteristics such as temperature or composition. The atmosphere has a mass of about 5×1018 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. An altitude of 120 km (75 mi) is where atmospheric effects become noticeable during atmospheric reentry of spacecraft. The Kármán line, at 100 km (62 mi), also is often regarded as the boundary between atmosphere and outer space.Air is the name given to the atmosphere used in breathing and photosynthesis. Dry air contains roughly (by volume) 78.09% nitrogen, 20.95% oxygen, 0.93% argon, 0.039% carbon dioxide, and small amounts of other gases. Air also contains a variable amount of water vapor, on average around 1%. While air content and atmospheric pressure vary at different layers, air suitable for the survival of terrestrial plants and terrestrial animals is currently only known to be found in Earth's troposphere and artificial atmospheres.

Contents [hide] 1 Composition2 Structure of the atmosphere2.1 Principal layers2.1.1 Exosphere2.1.2 Thermosphere2.1.3 Mesosphere2.1.4 Stratosphere2.1.5 Troposphere2.2 Other layers3 Physical properties3.1 Pressure and thickness3.2 Temperature and speed of sound3.3 Density and mass4 Optical properties4.1 Scattering4.2 Absorption4.3 Emission4.4 Refractive index5 Circulation6 Evolution of Earth's atmosphere6.1 Earliest atmosphere6.2 Second atmosphere6.3 Third atmosphere6.4 Air pollution7 See also8 References9 External linksComposition

Main article: Atmospheric chemistry

Composition of Earth's atmosphere. The lower pie represents the trace gases which together compose 0.039% of the atmosphere. Values normalized for illustration. The numbers are from a variety of years (mainly 1987, with CO2 and methane from 2009) and do not represent any single source.

Mean atmospheric water vaporAir is mainly composed of nitrogen, oxygen, and argon, which together constitute the major gases of the atmosphere. The remaining gases are often referred to as trace gases,[2] among which are the greenhouse gases such as water vapor, carbon dioxide, methane, nitrous oxide, and ozone. Filtered air includes trace amounts of many other chemical compounds. Many natural substances may be present in tiny amounts in an unfiltered air sample, including dust, pollen and spores, sea spray, and volcanic ash. Various industrial pollutants also may be present, such as chlorine (elementary or in compounds), fluorine compounds, elemental mercury, and sulfur compounds such as sulfur dioxide [SO2].Composition of dry atmosphere, by volume[3]ppmv: parts per million by volume (note: volume fraction is equal to mole fraction for ideal gas only, see volume (thermodynamics))Gas VolumeNitrogen (N2) 780,840 ppmv (78.084%)Oxygen (O2) 209,460 ppmv (20.946%)Argon (Ar) 9,340 ppmv (0.9340%)Carbon dioxide (CO2) 394.45 ppmv (0.039445%)Neon (Ne) 18.18 ppmv (0.001818%)Helium (He) 5.24 ppmv (0.000524%)Methane (CH4) 1.79 ppmv (0.000179%)Krypton (Kr) 1.14 ppmv (0.000114%)Hydrogen (H2) 0.55 ppmv (0.000055%)Nitrous oxide (N2O) 0.325 ppmv (0.0000325%)Carbon monoxide (CO) 0.1 ppmv (0.00001%)

Xenon (Xe) 0.09 ppmv (9×10−6%) (0.000009%)Ozone (O3) 0.0 to 0.07 ppmv (0 to 7×10−6%)Nitrogen dioxide (NO2) 0.02 ppmv (2×10−6%) (0.000002%)Iodine (I2) 0.01 ppmv (1×10−6%) (0.000001%)Ammonia (NH3) traceNot included in above dry atmosphere:Water vapor (H2O) ~0.40% over full atmosphere, typically 1%–4% at surfaceStructure of the atmosphere

Principal layers

Layers of the atmosphere (not to scale)In general, air pressure and density decrease in the atmosphere as height increases. However, 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 is constant and recognizable through means such as balloon soundings, the temperature behavior provides a useful metric to distinguish between atmospheric layers. In this way, Earth's atmosphere can be divided (called atmospheric stratification) into five main layers. From highest to lowest, these layers are:ExosphereMain article: ExosphereThe outermost layer of Earth's atmosphere extends from the exobase upward. It is mainly composed of hydrogen and helium. The particles are so far apart that they can travel hundreds of kilometers without colliding with one another. Since the particles rarely collide, the atmosphere no longer behaves like a fluid. These free-moving particles follow ballistic trajectories and may migrate into and out of the magnetosphere or the solar wind.ThermosphereMain article: ThermosphereTemperature increases with height in the thermosphere from the mesopause up to the thermopause, then is constant with height. Unlike in the stratosphere, where the inversion is caused by absorption of radiation by ozone, in the thermosphere the inversion is a result of the extremely low density of molecules. The temperature of this layer can rise to 1,500 °C (2,700 °F), though the gas molecules are so far apart that temperature in the usual sense is not well defined. The air is so rarefied that an individual molecule (of oxygen, for example) travels an average of 1 kilometer between collisions with other molecules.[4] The International Space Station orbits in this layer, between 320 and 380 km (200 and 240 mi). Because of the relative infrequency of molecular collisions, air above the mesopause is poorly mixed compared with air below. While the composition from the troposphere to the mesosphere is fairly constant, above a certain point, air is poorly mixed and becomes compositionally stratified. The point dividing these two regions is known as the turbopause. The region below is the homosphere, and the region above is the heterosphere. The top of the thermosphere is the bottom of the exosphere, called the exobase. Its height varies with solar activity and ranges from about 350–800 km (220–500 mi; 1,100,000–2,600,000 ft).[citation needed]MesosphereMain article: MesosphereThe mesosphere extends from the stratopause to 80–85 km (50–53 mi; 260,000–280,000 ft). It is the layer where most meteors burn up upon entering the atmosphere. Temperature decreases with height in the mesosphere. The mesopause, the temperature minimum that marks the top of the mesosphere, is the coldest place on Earth and has an average temperature around −85 °C (−120 °F; 190 K).[5] At the mesopause, temperatures may drop to −100 °C (−150 °F; 170 K).[6] Due to the cold temperature of the mesosphere, water vapor is frozen, forming ice clouds (or Noctilucent clouds). A type of lightning referred to as either sprites or ELVES, form many miles above thunderclouds in the troposphere.StratosphereMain article: StratosphereThe stratosphere extends from the tropopause to about 51 km (32 mi; 170,000 ft). Temperature increases with height due to increased absorption of ultraviolet radiation by the ozone layer, which restricts turbulence and mixing. While the temperature may be −60 °C (−76 °F; 210 K) at the tropopause, the top of the stratosphere is much warmer, and may be near freezing[citation needed]. The stratopause, which is the boundary between the stratosphere and mesosphere, typically is at 50 to 55 km (31 to 34 mi; 160,000 to 180,000 ft). The pressure here is 1/1000 sea level.TroposphereMain article: TroposphereThe troposphere begins at the surface and extends to between 9 km (30,000 ft) at the poles and 17 km (56,000 ft) at the equator,[7] with some variation due to weather. The troposphere is mostly heated by transfer of energy

from the surface, so on average the lowest part of the troposphere is warmest and temperature decreases with altitude. This promotes vertical mixing (hence the origin of its name in the Greek word "τροπή", trope, meaning turn or overturn). The troposphere contains roughly 80% of the mass of the atmosphere.[8] The tropopause is the boundary between the troposphere and stratosphere.Other layersWithin the five principal layers determined by temperature are several layers determined 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 15–35 km (9.3–22 mi; 49,000–110,000 ft), though the thickness varies seasonally and geographically. About 90% of the ozone in our atmosphere is contained in the stratosphere.The ionosphere, the part of the atmosphere that is ionized by solar radiation, stretches from 50 to 1,000 km (31 to 620 mi; 160,000 to 3,300,000 ft) and typically overlaps both the exosphere and the thermosphere. It forms the inner edge of the magnetosphere. It has practical importance because it influences, for example, radio propagation on the Earth. It is responsible for auroras.The homosphere and heterosphere are defined by whether the atmospheric gases are well mixed. In the homosphere the chemical composition of the atmosphere does not depend on molecular weight because the gases are mixed by turbulence.[9] The homosphere includes the troposphere, stratosphere, and mesosphere. Above the turbopause at about 100 km (62 mi; 330,000 ft) (essentially corresponding to the mesopause), the 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.The planetary boundary layer is the part of the troposphere that is nearest the Earth's surface and is directly affected by it, mainly through turbulent diffusion. During the day the planetary boundary layer usually is well-mixed, while at night it becomes stably stratified with weak or intermittent mixing. The depth of the planetary boundary layer ranges from as little as about 100 m on clear, calm nights to 3000 m or more during the afternoon in dry regions.The average temperature of the atmosphere at the surface of Earth is 14 °C (57 °F; 287 K)[10] or 15 °C (59 °F; 288 K),[11] depending on the reference.[12][13][14]Physical properties

Comparison of the 1962 US Standard Atmosphere graph of geometric altitude against air density, pressure, the speed of sound and temperature with approximate altitudes of various objects.[15]Pressure and thicknessMain article: Atmospheric pressureThe average atmospheric pressure at sea level is about 1 atmosphere (atm)=101.3 kPa (kilopascals)=14.7 psi (pounds per square inch)=760 torr=29.92 inches of mercury (symbol Hg). Total atmospheric mass is 5.1480×1018 kg (1.135×1019 lb),[16] about 2.5% less than would be inferred from the average sea level pressure and the Earth's area of 51007.2 megahectares, this portion being displaced by the 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 atmosphere had a uniform density, it would terminate abruptly at an altitude of 8.50 km (27,900 ft). It actually decreases exponentially with altitude, dropping by half every 5.6 km (18,000 ft) or by a factor of 1/e every 7.64 km (25,100 ft), the average scale height of the atmosphere below 70 km (43 mi; 230,000 ft). 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.In summary, the mass of the earth's atmosphere is distributed approximately as follows:[17]50% is below 5.6 km (18,000 ft).90% is below 16 km (52,000 ft).99.99997% is below 100 km (62 mi; 330,000 ft), the Kármán line. By international convention, this marks the beginning of space where human travelers are considered astronauts.By comparison, the summit of Mt. Everest is at 8,848 m (29,029 ft); commercial airliners typically cruise between 10 km (33,000 ft) and 13 km (43,000 ft) where the thinner air improves fuel economy; weather balloons reach 30.4 km (100,000 ft) and above; and the highest X-15 flight in 1963 reached 108.0 km (354,300 ft).Even above the Kármán 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 the 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 350–400 km, within the F-layer

of the ionosphere where they encounter enough atmospheric drag to require reboosts every few months. Depending on solar activity, satellites can still experience noticeable atmospheric drag at altitudes as high as 700–800 km.Temperature and speed of soundMain articles: Atmospheric temperature and Speed of soundThe 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 through 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 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.Because in an ideal gas of constant composition the speed of sound depends only on temperature and not on the gas 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

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)Main article: Density of airThe density of air at sea level is about 1.2 kg/m3 (1.2 g/L). 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 orbital decay of satellites.The average mass of the atmosphere is about 5 quadrillion (5×1015) 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 5.1480×1018 kg with an annual range due to water vapor of 1.2 or 1.5×1015 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 1.27×1016 kg and the dry air mass as 5.1352 ±0.0003×1018 kg."Optical properties

See also: SunlightSolar radiation (or sunlight) is the energy the Earth receives from the Sun. The Earth also emits radiation back into space, but at longer wavelengths that we cannot see. Part of the incoming and emitted radiation is absorbed or reflected by the atmosphere.ScatteringMain article: ScatteringWhen light passes through our 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 to reach your eye. Much of the blue light has been scattered out, leaving the red light in a sunset.AbsorptionMain article: Absorption (electromagnetic radiation)Different molecules absorb different wavelengths of radiation. For example, O2 and O3 absorb almost all wavelengths shorter than 300 nanometers. Water (H2O) absorbs many wavelengths above 700 nm. When a molecule absorbs a photon, it increases the energy of the molecule. We can think of this as heating the atmosphere, but the atmosphere also cools by emitting radiation, as discussed below.

Rough plot of Earth's atmospheric transmittance (or opacity) to various wavelengths of electromagnetic radiation, including visible light.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 400–700 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 centimeter to about eleven-meter waves.EmissionMain article: Emission (electromagnetic radiation)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 6,000 K (5,730 °C; 10,340 °F), its radiation peaks near 500 nm, and is visible to the human eye. The Earth is approximately 290 K (17 °C; 62 °F), 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 the 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 atmosphere acts as a "blanket" to limit the amount of radiation the Earth loses into space.The greenhouse effect is directly related to this absorption and emission (or "blanket") effect. Some chemicals in the atmosphere absorb and emit infrared radiation, but do not interact with sunlight in the visible spectrum. Common examples of these chemicals are CO2 and H2O. If there are too much of these greenhouse gases, sunlight heats the Earth's surface, but the gases block the infrared radiation from exiting back to space. This imbalance causes the Earth to warm, and thus climate change.Refractive indexThe refractive index of air is close to, but just greater than 1. Systematic variations in refractive index can lead to the bending of light rays over long optical paths. One example is that, under some circumstances, observers onboard ships can see other vessels just over the horizon because light is refracted in the same direction as the curvature of the Earth's surface.The refractive index of air depends on temperature, giving rise to refraction effects when the temperature gradient is large. An example of such effects is the mirage.See also: Scintillation (astronomy)Circulation

Main article: Atmospheric circulation

An idealised view of three 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 the Earth. The large-scale structure of the atmospheric circulation varies from year to year, but the basic structure remains fairly constant as it is determined by the Earth's rotation rate and the difference in solar radiation between the equator and poles.Evolution of Earth's atmosphere

See also: History of Earth and PaleoclimatologyEarliest atmosphereThe first atmosphere would have consisted of gases in the solar nebula, primarily hydrogen. In addition there would probably have been simple hydrides such as are now found in gas-giant planets like Jupiter and Saturn, notably water vapor, methane and ammonia. As the solar nebula dissipated these gases would have escaped, partly driven off by the solar wind.[18]Second atmosphereThe next atmosphere, consisting largely of nitrogen plus carbon dioxide and inert gases, was produced by outgassing from volcanism, supplemented by gases produced during the late heavy bombardment of Earth by huge asteroids.[18] A major rainfall led to the buildup of a vast ocean. A major part of carbon dioxide exhalations were soon dissolved in water and built up carbonate sediments.Water-related sediments have been found dating from as early as 3.8 billion years ago.[19] About 3.4 billion years ago, nitrogen was the major part of the then stable "second atmosphere". An influence of life has to be taken into account rather soon in the history of the atmosphere, since hints of early life forms are to be found as early as 3.5 billion years ago.[20] The fact that this is not perfectly in line with the 30% lower solar radiance (compared to today) of the early Sun has been described as the "faint young Sun paradox".The geological record however shows a continually relatively warm surface during the complete early temperature record of the Earth with the exception of one cold glacial phase about 2.4 billion years ago. In the late Archaean eon an oxygen-containing atmosphere began to develop, apparently from photosynthesizing algae which have been found as stromatolite fossils from 2.7 billion years ago. The early basic carbon isotopy (isotope ratio proportions) is very much in line with what is found today,[21] suggesting that the fundamental features of the carbon cycle were established as early as 4 billion years ago.

Third atmosphere

Oxygen content of the atmosphere over the last billion years. This diagram in more detailThe accretion of continents about 3.5 billion years ago[22] added plate tectonics, constantly rearranging the continents and also shaping long-term climate evolution by allowing the transfer of carbon dioxide to large land-based carbonate stores. Free oxygen did not exist until about 1.7 billion years ago and this can be seen with the development of the red beds and the end of the banded iron formations. The Earth had a lot of iron in the beginning, and higher amounts of oxygen was not available in the atmosphere until all the iron had been oxidized. This signifies a shift from a reducing atmosphere to an oxidizing atmosphere. O2 showed major ups and downs until reaching a steady state of more than 15%.[23] The following time span was the Phanerozoic eon, during which oxygen-breathing metazoan life forms began to appear.The amount of oxygen in the atmosphere has gone up and down during the last 600 million years. There was a peak 280 million years ago, when the amount of oxygen was about 30%, much higher than today. Two main processes govern changes in the atmosphere: Plants converts carbon dioxide into the bodies of the plants, which emits oxygen into the atmosphere, and break down of pyrite rocks cause sulphur to be added to the oceans. Volcanos cause this sulphur to be oxidized, reducing the amount of oxygen in the atmosphere. But volcanos also emit carbon dioxide, so that plants can convert this to oxygen. The exact cause of the variation of oxygen in the atmosphere is not known. Periods with much oxygen in the atmosphere are believed to cause rapid development of animals. Even though the atmosphere today has only 21 percent oxygen, today is still regarded as a period with rapid development of animals because of a high amount of oxygen in the atmosphere.[24]Currently, anthropogenic greenhouse gases are increasing in the atmosphere. According to the Intergovernmental Panel on Climate Change, this increase is the main cause of global warming.[25]Air pollutionMain article: Air pollutionAir pollution is the introduction of chemicals, particulate matter, or biological materials that cause harm or discomfort to organisms into the atmosphere.[26] Stratospheric ozone depletion is believed to be caused by air pollution (chiefly from chlorofluorocarbons).[citation needed]See also

Atmosphere portalEnvironment portal

Aerial perspectiveAir glowAirshedAtmosphere (for information on atmospheres in general)Atmospheric dispersion modelingAtmospheric electricityAtmospheric modelsAtmospheric Radiation Measurement (ARM) (in the U.S.)Atmospheric stratificationAviationBiosphereCarbon dioxide in Earth's atmosphereCompressed airEnvironmental impact of aviationGlobal dimmingHistorical temperature recordHydrosphereHypermobility (travel)Kyoto ProtocolLeaching (agriculture)LithosphereStandard Dry AirCOSPAR international reference atmosphere (CIRA)U.S. Standard AtmosphereWarm periodWater vapor in Earth's atmosphereReferences

^ "ISS022-E-062672 caption". NASA. Retrieved 21 September 2012.

^ "Trace Gases". Ace.mmu.ac.uk. Archived from the original on 9 October 2010. Retrieved 2010-10-16.^ Source for figures: Carbon dioxide, NOAA Earth System Research Laboratory, (updated 2012.03). Methane, IPCC TAR table 6.1, (updated to 1998). The NASA total was 17 ppmv over 100%, and CO2 was increased here by 15 ppmv. To normalize, N2 should be reduced by about 25 ppmv and O2 by about 7 ppmv.^ Ahrens, C. Donald. Essentials of Meteorology. Published by Thomson Brooks/Cole, 2005.^ States, Robert J.; Gardner, Chester S. (January 2000). "Thermal Structure of the Mesopause Region (80–105 km) at 40°N Latitude. Part I: Seasonal Variations". Journal of the Atmospheric Sciences 2000 57: 66–77. Bibcode 2000JAtS...57...66S. doi:10.1175/1520-0469(2000)057<0066:TSOTMR>2.0.CO;2.^ Joe Buchdahl. "Atmosphere, Climate & Environment Information Programme". Ace.mmu.ac.uk. Retrieved 2012-04-18.^ "The height of the tropopause". Das.uwyo.edu. Retrieved 2012-04-18.^ McGraw-Hill Concise Encyclopedia of Science & Technology. (1984). Troposhere. "It contains about four-fifths of the mass of the whole atmosphere."^ "''homosphere''—AMS Glossary". Amsglossary.allenpress.com. Archived from the original on 14 September 2010. Retrieved 2010-10-16.^ "Earth's Atmosphere".^ "NASA — Earth Fact Sheet". Nssdc.gsfc.nasa.gov. Archived from the original on 30 October 2010. Retrieved 2010-10-16.^ "Global Surface Temperature Anomalies".^ "Earth's Radiation Balance and Oceanic Heat Fluxes".^ "Coupled Model Intercomparison Project Control Run".^ Geometric altitude vs. temperature, pressure, density, and the speed of sound derived from the 1962 U.S. Standard Atmosphere.^ "The Mass of the Atmosphere: A Constraint on Global Analyses". Ams.allenpress.com. 1970-01-01. Retrieved 2010-10-16.^ Lutgens, Frederick K. and Edward J. Tarbuck (1995) The Atmosphere, Prentice Hall, 6th ed., pp14-17, ISBN 0-13-350612-6^ a b Zahnle, K.; Schaefer, L.; Fegley, B. (2010). "Earth's Earliest Atmospheres". Cold Spring Harbor Perspectives in Biology 2 (10): a004895. doi:10.1101/cshperspect.a004895. PMID 20573713. edit^ B. Windley: The Evolving Continents. Wiley Press, New York 1984^ J. Schopf: Earth's Earliest Biosphere: Its Origin and Evolution. Princeton University Press, Princeton, N.J., 1983^ Celestial climate driver: a perspective from 4 billion years of the carbon cycle Geoscience Canada, March, 2005 by Jan Veizer^ Veizer in B. F. Windley (ed.), The Early History of the Earth, John Wiley and Sons, London, p. 569., 1976^ Christopher R. Scotese, Back to Earth History : Summary Chart for the Precambrian, Paleomar Project^ Peter Ward:[1] Out of Thin Air]: Dinosaurs, Birds, and Earth's Ancient Atmosphere^ "Summary for Policymakers" (PDF). Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Intergovernmental Panel on Climate Change. 5 February 2007.^ Starting from [2] Pollution — Definition from the Merriam-Webster Online DictionaryExternal links

Wikimedia Commons has media related to: Earth's atmosphereNASA atmosphere modelsNASA's Earth Fact SheetAmerican Geophysical Union: Atmospheric SciencesOutreach of the GEOmon project See how Earth atmosphere is observed and monitored by a European project that combines many approaches.Stuff in the Air Find out what the atmosphere contains.Layers of the AtmosphereAnswers to several questions of curious kids related to Air and AtmosphereThe AMS Glossary of MeteorologyPaul Crutzen Interview Free video of Paul Crutzen Nobel Laureate for his work on decomposition of ozone talking to Harry Kroto Nobel Laureate by the Vega Science Trust.

TroposphereFrom Wikipedia, the free encyclopediaFor the Congolese experimental rocket family, see Troposphere (rocket family).

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]

Earth atmosphere diagram showing the exosphere and other layers. The layers are to scale. From Earth's surface to the top of the stratosphere (50km) is just under 1% of Earth's radius.The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 80% of the atmosphere's mass and 99% of its water vapor and aerosols.[2] The average depth of the troposphere is approximately 17 km (11 mi) in the middle latitudes. It is deeper in the tropics, up to 20 km (12 mi), and shallower near the polar regions, at 7 km (4.3 mi) in summer, and indistinct in winter. The lowest part of the troposphere, where friction with the Earth's surface influences air flow, is the planetary boundary layer. This layer is typically a few hundred meters to 2 km (1.2 mi) deep depending on the landform and time of day. The border between the troposphere and stratosphere, called the tropopause, is a temperature inversion.[3]The word troposphere derives from the Greek: tropos for "turning" or "mixing," reflecting the fact that turbulent mixing plays an important role in the troposphere's structure and behavior. Most of the phenomena we associate with day-to-day weather occur in the troposphere.[3]Contents [hide] 1 Pressure and temperature structure1.1 Composition1.2 Pressure1.3 Temperature1.4 Tropopause2 Atmospheric flow2.1 Zonal Flow2.2 Meridional flow2.3 Three-cell model3 Synoptic scale observations and concepts3.1 Forcing3.2 Divergence and Convergence4 References5 External links[edit]Pressure and temperature structure

A view of Earth's troposphere from an airplane.

Atmospheric circulation shown with three large cells.[edit]CompositionThe chemical composition of the troposphere is essentially uniform, with the notable exception of water vapor. The source of water vapor is at the surface through the processes of evaporation and transpiration. Furthermore the temperature of the troposphere decreases with height, and saturation vapor pressure decreases strongly as temperature drops, so the amount of water vapor that can exist in the atmosphere decreases strongly with height. Thus the proportion of water vapor is normally greatest near the surface and decreases with height.[edit]PressureThe pressure of the atmosphere is maximum at sea level and decreases with higher altitude. This is because the atmosphere is very nearly in hydrostatic equilibrium, so that the pressure is equal to the weight of air above a given point. The change in pressure with height, therefore can be equated to the density with this hydrostatic equation:[4]

where:gn is the standard gravity

ρ is the densityz is the altitudep is the pressureR is the gas constantT is the thermodynamic (absolute) temperaturem is the molar massSince temperature in principle also depends on altitude, one needs a second equation to determine the pressure as a function of height, as discussed in the next section.*[edit]TemperatureMain article: Lapse rateThe temperature of the troposphere generally decreases as altitude increases. The rate at which the temperature decreases, , is called the environmental lapse rate (ELR). The ELR is nothing more than the difference in temperature between the surface and the tropopause divided by the height. The reason for this temperature difference is the absorption of the sun's energy occurs at the ground which heats the lower levels of the atmosphere, and the radiation of heat occurs at the top of the atmosphere cooling the earth, this process maintaining the overall heat balance of the earth.As parcels of air in the atmosphere rise and fall, they also undergo changes in temperature for reasons described below. The rate of change of the temperature in the parcel may be less than or more than the ELR. When a parcel of air rises, it expands, because the pressure is lower at higher altitudes. As the air parcel expands, it pushes on the air around it, doing work; but generally it does not gain heat in exchange from its environment, because its thermal conductivity is low (such a process is called adiabatic). Since the parcel does work and gains no heat, it loses energy, and so its temperature decreases. (The reverse, of course, will be true for a sinking parcel of air.) [3]Since the heat exchanged is related to the entropy change by , the equation governing the temperature as a function of height for a thoroughly mixed atmosphere is

where S is the entropy. The rate at which temperature decreases with height under such conditions is called the adiabatic lapse rate.For dry air, which is approximately an ideal gas, we can proceed further. The adiabatic equation for an ideal gas is [5]

where is the heat capacity ratio (=7/5, for air). Combining with the equation for the pressure, one arrives at the dry adiabatic lapse rate,[6]

If the air contains water vapor, then cooling of the air can cause the water to condense, and the behavior is no longer that of an ideal gas. If the air is at the saturated vapor pressure, then the rate at which temperature drops with height is called the saturated adiabatic lapse rate. More generally, the actual rate at which the temperature drops with altitude is called the environmental lapse rate. In the troposphere, the average environmental lapse rate is a drop of about 6.5 °C for every 1 km (1,000 meters) in increased height.[3]The environmental lapse rate (the actual rate at which temperature drops with height, ) is not usually equal to the adiabatic lapse rate (or correspondingly, ). If the upper air is warmer than predicted by the adiabatic lapse rate (), then when a parcel of air rises and expands, it will arrive at the new height at a lower temperature than its surroundings. In this case, the air parcel is denser than its surroundings, so it sinks back to its original height, and the air is stable against being lifted. If, on the contrary, the upper air is cooler than predicted by the adiabatic lapse rate, then when the air parcel rises to its new height it will have a higher temperature and a lower density than its surroundings, and will continue to accelerate upward.[3][4]Temperatures decrease at middle latitudes from an average of 15°C at sea level to about -55°C at the top of the tropopause. At the poles, the troposphere is thinner and the temperature only decreases to -45°C, while at the equator the temperature at the top of the troposphere can reach -75°C.[citation needed][edit]TropopauseMain article: TropopauseThe tropopause is the boundary region between the troposphere and the stratosphere.Measuring the temperature change with height through the troposphere and the stratosphere identifies the location of the tropopause. In the troposphere, temperature decreases with altitude. In the stratosphere, however, the temperature remains constant for a while and then increases with altitude. The region of the atmosphere where the lapse rate changes from positive (in the troposphere) to negative (in the stratosphere), is defined as the tropopause.[3] Thus, the tropopause is an inversion layer, and there is little mixing between the two layers of the atmosphere.[edit]Atmospheric flow

The flow of the atmosphere generally moves in a west to east direction. This however can often become interrupted, creating a more north to south or south to north flow. These scenarios are often described in meteorology as zonal or meridional. These terms, however, tend to be used in reference to localised areas of atmosphere (at a synoptic scale)). A fuller explanation of the flow of atmosphere around the Earth as a whole can be found in the three-cell model.[edit]Zonal FlowA zonal flow regime is the meteorological term meaning that the general flow pattern is west to east along the Earth's latitude lines, with weak shortwaves embedded in the flow.[7] The use of the word "zone" refers to the flow being along the Earth's latitudinal "zones". This pattern can buckle and thus become a meridional flow.[edit]Meridional flow

Meridional Flow pattern of October 23, 2003. Note the amplified troughs and ridges in this 500 hPa height pattern.When the zonal flow buckles, the atmosphere can flow in a more longitudinal (or meridional) direction, and thus the term "meridional flow" arises. Meridional flow patterns feature strong, amplified troughs and ridges, with more north-south flow in the general pattern than west-to-east flow.[8][edit]Three-cell modelMain article: Atmospheric circulationThe three cells model attempts to describe the actual flow of the Earth's atmosphere as a whole. It divides the Earth into the tropical (Hadley cell), mid latitude (Ferrel cell), and polar (polar cell) regions, dealing with energy flow and global circulation. Its fundamental principle is that of balance - the energy that the Earth absorbs from the sun each year is equal to that which it loses back into space, but this however is not a balance precisely maintained in each latitude due to the varying strength of the sun in each "cell" resulting from the tilt of the Earth's axis in relation to its orbit. It demonstrates that a pattern emerges to mirror that of the ocean - the tropics do not continue to get warmer because the atmosphere transports warm air poleward and cold air equatorward, the purpose of which appears to be that of heat and moisture distribution around the planet.[9][edit]Synoptic scale observations and concepts

[edit]ForcingForcing is a term used by meteorologists to describe the situation where a change or an event in one part of the atmosphere causes a strengthening change in another part of the atmosphere. It is usually used to describe connections between upper, middle or lower levels (such as upper-level divergence causing lower level convergence in cyclone formation), but can sometimes also be used to describe such connections over distance rather than height alone. In some respects, tele-connections could be considered a type of forcing.[edit]Divergence and ConvergenceAn area of convergence is one in which the total mass of air is increasing with time, resulting in an increase in pressure at locations below the convergence level (recall that atmospheric pressure is just the total weight of air above a given point). Divergence is the opposite of convergence - an area where the total mass of air is decreasing with time, resulting in falling pressure in regions below the area of divergence. Where divergence is occurring in the upper atmosphere, there will be air coming in to try to balance the net loss of mass (this is called the principle of mass conservation), and there is a resulting upward motion (positive vertical velocity). Another way to state this is to say that regions of upper air divergence are conducive to lower level convergence, cyclone formation, and positive vertical velocity. Therefore, identifying regions of upper air divergence is an important step in forecasting the formation of a surface low pressure area.[edit]References

^ "ISS022-E-062672 caption". NASA. Retrieved 21 September 2012.^ McGraw-Hill Concise Encyclopedia of Science & Technology. (1984). Troposhere. "It contains about four-fifths of the mass of the whole atmosphere."^ a b c d e f Danielson, Levin, and Abrams, Meteorology, McGraw Hill, 2003^ a b Landau and Lifshitz, Fluid Mechanics, Pergamon, 1979^ Landau and Lifshitz, Statistical Physics Part 1, Pergamon, 1980^ Kittel and Kroemer, Thermal Physics, Freeman, 1980; chapter 6, problem 11^ "American Meteorological Society Glossary - Zonal Flow". Allen Press Inc.. June 2000. Retrieved 2006-10-03.^ "American Meteorological Society Glossary - Meridional Flow". Allen Press Inc.. June 2000. Retrieved 2006-10-03.^ "Meteorology - MSN Encarta, "Energy Flow and Global Circulation"". Encarta.Msn.com. Archived from the original on 2009-10-31. Retrieved 2006-10-13.[edit]External links

Look up troposphere in Wiktionary, the free dictionary.Composition of the Atmosphere, from the University of Tennessee Physics dept.Chemical Reactions in the Atmospherehttp://encarta.msn.com/encyclopedia_761571037_3/Meteorology.html#s12 (Archived 2009-10-31)[hide] v t eEarth's atmosphereTroposphere Stratosphere Mesosphere Thermosphere ExosphereTropopause Stratopause Mesopause Thermopause / ExobaseOzone layer Turbopause IonosphereView page ratingsRate this pageWhat's this?TrustworthyObjectiveCompleteWell-writtenI am highly knowledgeable about this topic (optional)

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StratosphereFrom Wikipedia, the free encyclopediaFor other uses, see Stratosphere (disambiguation).

This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (October 2010)

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]

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)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. The stratosphere is situated between about 10 km (6 mi) and 50 km (30 mi) altitude above the surface at moderate latitudes, while at the poles it starts at about 8 km (5 mi) altitude.Contents [hide] 1 Ozone and temperature2 Aircraft flight3 Circulation and mixing4 Life5 See also6 References[edit]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)[verification needed]. 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 hypochlorite radical (ClO·). The hypochlorite radical then reacts with an atomic oxygen creating another oxygen molecule and another chlorine radical, thereby preventing the reaction of a monoatomic oxygen with O2 to create natural ozone.[edit]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 thanks to the low temperatures encountered near the tropopause and low air density, reducing parasitic drag on the airframe. It also allows them to stay above hard weather (extreme turbulence).Concorde would cruise at mach 2 at about 18,000 m (60,000 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 increases) 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 39km (128,097 feet).[4][edit]Circulation and mixing

This section does not cite any references or sources. (June 2009)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 or water vapor.In northern hemispheric winter, sudden stratospheric warmings, caused by the absorption of Rossby waves in the stratosphere, can often be observed.[edit]Life

Bacterial life survives in the stratosphere, making it a part of the biosphere.[5] 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 reportedly ingested into a jet engine 11,552 m (37,900 ft) above the Ivory Coast, and Bar-headed geese routinely overfly Mount Everest's summit, which is 8,848 m (29,029 ft).[6][7][edit]See also

Look up stratosphere in Wiktionary, the free dictionary.Léon Teisserenc de Bort and Richard Assmann (the discoverers of the stratosphere)Paris Gun (first artificial object to reach stratosphere)SR-71 BlackbirdConcordeLockheed U-2RQ-4 Global HawkService ceilingLe Grand SautFelix BaumgartnerRed Bull Stratos[edit]References

^ "ISS022-E-062672 caption". NASA. Retrieved 21 September 2012.^ Seinfeld, J. H., and S. N. Pandis, (2006), Atmospheric Chemistry and Physics: From Air Pollution to Climate Change 2nd ed, Wiley, New Jersey^ "Altitude of a Commercial Jet". Hypertextbook.com. Retrieved 2011-11-08.^ LLORCA, JUAN CARLOS (October 15, 2012). "Skydiver Felix Baumgartner hits 833.9 mph in record jump". Associated Press. Retrieved 2012-10-15.^ 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.^ "Audubon: Birds". Audubonmagazine.org. Retrieved 2011-11-08.^ Thomas Alerstam, David A. Christie, Astrid Ulfstrand. Bird Migration (1990). Page 276.[hide] v t eEarth's atmosphereTroposphere Stratosphere Mesosphere Thermosphere ExosphereTropopause Stratopause Mesopause Thermopause / ExobaseOzone layer Turbopause IonosphereView page ratingsRate this pageWhat's this?TrustworthyObjectiveCompleteWell-writtenI am highly knowledgeable about this topic (optional)

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MesosphereFrom Wikipedia, the free encyclopedia

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]

Earth atmosphere diagram showing the exosphere and other layers. The layers are to scale. From Earth's surface to the top of the stratosphere (50 km or 31 mi) is just under 1% of Earth's radius.

This article is about the atmospheric mesosphere, for the Earth's mantle see Mesosphere (mantle).The mesosphere (/ˈmɛsoʊsfɪər/; from Greek mesos = middle and sphaira = ball) is the layer of the Earth's atmosphere that is directly above the stratosphere and directly below the thermosphere. In the mesosphere temperature decreases with increasing height. The upper boundary of the mesosphere is the mesopause, which can be the coldest naturally occurring place on Earth with temperatures below 130 K. The exact upper and lower boundaries of the mesosphere vary with latitude and with season, but the lower boundary of the mesosphere is usually located at heights of about 50 km above the Earth's surface and the mesopause is usually at heights near 100 km, except at middle and high latitudes in summer where it descends to heights of about 85 km.The stratosphere, mesosphere and lowest part of the thermosphere are collectively referred to as the "middle atmosphere", which spans heights from approximately 10 to 100 km. 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.Contents [hide] 1 Temperature2 Dynamic features3 Uncertainties4 Meteors5 References6 External links[edit]Temperature

Within the mesosphere, temperature decreases with increasing altitude. This is due to decreasing solar heating and increasing cooling by CO2 radiative emission. The top of the mesosphere, called the mesopause, is the coldest part of Earth's atmosphere.[2] Temperatures in the upper mesosphere fall as low as −100 °C (173 K; −148 °F),[3] varying according to latitude and season.[edit]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 are excited in the troposphere and lower stratosphere, and propagate upward 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.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.A 5 km (3.1 mi) deep sodium layer is located between 80–105 km (50–65 mi). Made of unbound, non-ionized atoms of sodium, the sodium layer radiates weakly to contribute to the airglow.[edit]Uncertainties

The mesosphere lies above the maximum altitude for aircraft and below the minimum altitude for orbital spacecraft. It has only been accessed through the use of sounding rockets. As a result, it is the most poorly understood part of the atmosphere. The presence of red sprites and blue jets (electrical discharges or lightning within the lower mesosphere), noctilucent clouds and density shears within the poorly understood layer are of current scientific interest.[edit]Meteors

Millions of meteors enter the atmosphere, an average of 40 tons per year.[4] Within the mesosphere most melt or vaporize as a result of collisions with the gas particles contained there. This results in a higher concentration of iron and other refractory materials reaching the surface.[citation needed][edit]References

^ "ISS022-E-062672 caption". NASA. Retrieved 21 September 2012.^ Nic, M.; Jirat, J.; Kosata, B., eds. (2006–). "mesosphere". IUPAC Compendium of Chemical Terminology (Online ed.). doi:10.1351/goldbook.M03855. ISBN 0-9678550-9-8.^ Mesosphere, retrieved 2011-11-14^ Leinert C.; Gruen E. (1990). "Interplanetary Dust". Physics and Chemistry in Space (R. Schwenn and E. Marsch eds.). Springer-Verlag. pp. 204-275[edit]External links

Description with links to other atmospheric topics

ThermosphereFrom Wikipedia, the free encyclopedia

Earth atmosphere diagram showing the exosphere and other layers. The layers are to scale. From Earth's surface to the top of the stratosphere (50 kilometres (31 mi)) is just under 1% of Earth's radius.The thermosphere is the layer of the Earth's atmosphere directly above the mesosphere and directly below the exosphere. Within this layer, ultraviolet radiation (UV) causes ionization. Called from the Greek θερμός (pronounced thermos) meaning heat, the thermosphere begins about 85 kilometres (53 mi) above the Earth.[1] 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 2,000 °C (3,630 °F). Radiation causes the atmosphere particles in this layer to become electrically charged (see ionosphere), enabling radio waves to bounce off and be received beyond the horizon. In the exosphere, beginning at 500 to 1,000 kilometres (310 to 620 mi) above the Earth's surface, the atmosphere turns into space.The highly diluted gas in this layer can reach 2,500 °C (4,530 °F) during the day. Even though the temperature is so high, one would not feel warm in the thermosphere, because it is so near vacuum that there is not enough contact with the few atoms of gas to transfer much heat. A normal thermometer would read significantly below 0 °C (32 °F), 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. Atmospherics waves dissipate above this level because of collisions between the neutral gas and the ionospheric plasma.The International Space Station has a stable orbit within the middle of the thermosphere, between 320 and 380 kilometres (200 and 240 mi). Auroras also occur in the thermosphere.Contents [hide] 1 History2 Neutral gas constituents3 Energy input3.1 Energy budget3.2 Solar XUV radiation3.3 Solar wind3.4 Atmospheric waves4 Dynamics5 Thermospheric storms6 References[edit]History

Prior to the space age, the only indirect access to the height region above about 100 km altitudes came from ionospheric and geomagnetic research. Electromagnetic waves below the VHF-range (VHF = very high frequencies; 30 - 300 MHz) reflected and attenuated in the ionospheric D-, E-, and F- layers depending on frequency, time of day, geographic location, and solar activity can be observed on the ground.[2] The geomagnetic activity, likewise observed on the ground, was attributed to upper atmospheric electric currents, known today as currents flowing within the ionospheric dynamo region and the magnetosphere.[3] With the advent of the Russian satellite Sputnik in 1957, observations of the Doppler effect of the satellite signal overhead allowed for the first time to determine continuously the orbital decay of the satellite and thus the atmospheric drag from which the variations of the thermospheric density could be derived. Mainly involved in these early measurements were L.G. Jacchia and J.W. Slowey (USA), D.G. King-Hele (Great Britain), and W. Priester and H.K. Pätzold (Germany). They discovered for the first time the large daily variations of the atmospheric density, its reaction on geomagnetically disturbanced conditions, etc. Today, an array of satellites measures directly the various components of the atmospheric gas. A full summary of early and present observations was presented by G. W. Prölss in 2011 .[4][edit]Neutral gas constituents

It is convenient to separate the atmospheric regions according to the two temperature minima at about 12 km altitude (the tropopause) and at about 85 km (the mesopause) (Figure 1). The thermosphere (or the upper atmosphere) is the height region above 85 km, while the region between the tropospause and the mesopause is the middle atmosphere (stratosphere and mesosphere) where absorption of solar UV radiation generates the temperature maximum near 45 km altitude and causes the ozone layer.

Figure 1. Nomenclature of atmospheric regions based on the profiles of electric conductivity (left), temperature (middle), and electron density (right)

The density of the Earth's atmosphere decreases nearly exponentially with altitude. The total mass of the atmosphere is M = ρA H 1 kg/cm2 within a column of one square centimeter above the ground (with ρA = ≃1.29 kg/m3 the atmospheric density on the ground at z = 0 m altitude, and H 8 km the average atmospheric ≃scale height). 80% of that mass is already concentrated within the troposphere. The mass of the thermosphere above about 85 km is only 0.002% of the total mass. Therefore, no significant energetic feedback from the thermosphere to the lower atmospheric regions can be expected.Turbulence causes the air within the lower atmospheric regions below the turbopause at about 110 km to be a mixture of gases that does not change its composition. Its mean molecular weight is 29 g/mol with molecular oxygen (O2) and nitrogen (N2) as the two dominant constituents. Above the turbopause, however, diffusive separation of the various constituents is significant, so that each constituent follows its own barometric height structure with a scale height inversely proportional to its molecular weight. The lighter constituents atomic oxygen (O), helium (He), and hydrogen (H) successively dominate above about 200 km altitude and vary with geographic location, time, and solar activity. The ratio N2/O which is a measure of the electron density at the ionospheric F region is highly affected by these variations.[5] These changes follow from the diffusion of the minor constituents through the major gas component during dynamic processes.[edit]Energy input

[edit]Energy budgetThe thermospheric temperature can be determined from density observations as well as from direct satellite measurements. The temperature vs. altitude z in Fig. 1 can be simulated by the so-called Bates profile [6](1) T = T∞ - (T∞ - To) exp{-s (z - zo)}with T∞ the exospheric temperature above about 400 km altitude, To = 355 K, and zo = 120 km reference temperature and height, and s an empirical parameter depending on T∞ and decreasing with T∞. That formula is derived from a simple equation of heat conduction. One estimates a total heat input of qo 0.8 to 1.6 mW/m2 ≃above zo = 120 km altitude. In order to obtain equilibrium conditions, that heat input qo above zo is lost to the lower atmospheric regions by heat conduction.The exospheric temperature T∞ is a fair measurement of the solar XUV radiation. Since solar radio emission F at 10.7 cm wavelength is a good indicator of solar activity, on can apply the empirical formula for quiet magnetospheric conditions.[7](2) T∞ 500 + 3.4 Fo≃with T∞ in K, Fo in 10- 2 W m−2 Hz−1 (the Covington index) a value of F averaged over several solar cycles. The Covington index varies typically between 70 and 250 during a solar cycle, and never drops below about 50. Thus, T∞ varies between about 740 and 1350 K. During very quiet magnetospheric conditions, the still continuously flowing magnetospheric energy input contributes by about 250 K to the residual temperature of 500 K in eq.(2). The rest of 250 K in eq.(2) can be attributed to atmospheric waves generated within the troposphere and dissipated within the lower thermosphere.[edit]Solar XUV radiationThe solar X-ray and extreme ultraviolet radiation (XUV) at wavelengths < 170 nm is almost completely absorbed within the thermosphere. This radiation causes the various ionospheric layers as well as a temperature increase at these heights (Figure 1). While the solar visible light (380 to 780 nm) is nearly constant with a variability of not more than about 0.1% of the solar constant,[8] the solar XUV radiation is highly variable in time and space. For instance, X-ray bursts associated with solar flares can dramatically increase their intensity over preflare levels by many orders of magnitude over a time span of tens of minutes. In the extreme ultraviolet, the Lyman α line at 121.6 nm represents an important source of ionization and dissociation at ionospheric D layer heights.[9] During quiet periods of solar activity, it alone contains more energy than the rest of the spectrum at lower wavelengths. Quasi-periodic changes of the order of 100% and more with period of 27 days and 11 years belong to the prominent variations of solar XUV radiation. However, irregular fluctuations over all time scales are present all the time.[10] During low solar activity, about one half of the total energy input into the thermosphere is thought to be solar XUV radiation. Evidently, that solar XUV energy input occurs only during daytime conditions, maximizing at the equator during equinox.[edit]Solar windA second source of energy input into the thermosphere is solar wind energy which is transferred to the magnetosphere by mechanisms that are not completely understood. One possible way to transfer energy is via a hydrodynamic dynamo process. Solar wind particles penetrate into the polar regions of the magnetosphere where the geomagnetic field lines are essentially vertically directed. An electric field is generated, directed from dawn to dusk. Along the last closed geomagnetic field lines with their footpoints within the auroral zones, field aligned electric currents can flow into the ionospheric dynamo region where they are closed by electric Pedersen and Hall currents. Ohmic losses of the Pedersen currents heat the lower thermosphere (see e.g., Magnetospheric electric convection field). In addition, penetration of high energetic particles from the magnetosphere into the auroral regions enhance drastically the electric conductivity, further increasing the electric currents and thus Joule heating. During quiet magnetospheric activity, the magnetosphere contributes perhaps by a quarter to the

energy budget of the thermosphere.[11] This is about 250 K of the exospheric temperature in eq.(2). During very large activity, however, this heat input can increase substantially, by a factor of four or more. That solar wind input occurs mainly in the auroral regions during the day as well as during the night.[edit]Atmospheric wavesTwo kinds of large scale atmospheric waves within the lower atmosphere exist: internal waves with finite vertical wavelengths which can transport wave energy upward and external waves with infinitely large wavelengths which cannot transport wave energy.[12] Atmospheric gravity waves and most of the atmospheric tides generated within the troposphere belong to the internal waves. Their density amplitudes increase exponentially with height, so that at the mesopause these waves become turbulent and their enery is dissipated (similar to breaking of ocean waves at the coast), thus contributing to the heating of the thermosphere by about 250 K in eq.(2). On the other hand, the fundamental diurnal tide labelled (1, -2) which is most efficiently excited by solar irradiance is an external wave and plays only a marginal role within lower and middle atmosphere. However, at thermospheric altitudes, it becomes the predominant wave. It drives the electric Sq-current within the ionospheric dynamo region between about 100 and 200 km height.Heating, predominately by tidal waves, occurs mainly at lower and middle latitudes. The variability of this heating depends in general on the meteorological conditions within troposphere and middle atmosphere, and may not exceed about 50%.[edit]Dynamics

Figure 2. Schematic meridian-height cross-section of circulation of (a) symmetric wind component (P20), (b) of antisymmetric wind component (P10), and (d) of symmetric diurnal wind component (P11) at 3 h and 15 h local time. Upper right pannel (c) shows the horizontal wind vectors of the diurnal component in the northern hemisphere depending on local timeWithin the thermosphere above about 150 km height, all atmospheric waves successively become external waves, and no signifiant vertical wave structure is visible. The atmospheric wave modes degenerate to the spherical functions Pnm with n a meridional wave number and m the zonal wave number (m = 0: zonal mean flow; m = 1: diurnal tides; m = 2: semidiunal tides; etc.). The thermophere becomes a damped oscillator system with low pass filter characteristics. This means that smaller scale waves (greater numbers of (n,m)) and higher frequencies are suppressed in favor of large scale waves and lower frequencies. If one considers very quiet magnetospheric disturbances and a constant mean exospheric temperature (averaged over the sphere), the observed temporal and spatial distribution of the exospheric temperature distribution can be described by a sum of spheric functions:[13](3) T(φ,λ,t) = T∞{1 + ΔT20 P20(φ) + ΔT10 P10(φ) cos[ωa(t - ta)] + ΔT11 P11(φ) cos(τ - τd) + . . .}Here, it is φ latitude, λ longitude, and t time, ωa the angular frequency of one year, ωd the angular frequency of one solar day, and τ = ωdt + λ the local time. ta = June, 21 is the time of northern summer solstice, and τd = 15:00 is the local time of maximum diurnal temperature.The first term in (3) on the right is the global mean of the exospheric temperature (of the order of 1000 K). The second term [with P20 = 0.5(3 sin2(φ)- 1)] represents the heat surplus at lower latitudes and a corresponding heat deficit at higher latitudes (Fig. 2a). A thermal wind system develops with winds toward the poles in the upper level and wind away from the poles in the lower level. The coefficient ΔT20 ≈ 0.004 is small because Joule heating in the aurora regions compensates that heat surplus even during quiet magnetospheric conditions. During disturbed conditions, however, that term becomes dominant changing sign so that now heat surplus is transported from the poles to the equator. The third term (with P10 = sin φ) represents heat surplus on the summer hemisphere and is responsible for the transport of excess heat from the summer into the winter hemisphere (Fig. 2b). Its relative amplitude is of the order ΔT10 0.13. The fourth term (with P11(φ) = cos φ) is the dominant ≃diurnal wave (the tidal mode (1,-2)). It is responsible for the transport of excess heat from the day time hemisphere into the night time hemisphere (Fig. 2d). Its relative amplitude is ΔT11 0.15, thus of the order of ≃150 K. Additional terms (e.g., semiannual, semidiurnal terms and higher order terms) must be added to eq.(3). They are, however, of minor importance. Corresponding sums can be developed for density, pressure, and the various gas constituents.[7][14][edit]Thermospheric storms

Contrary to solar XUV radiation, magnetospheric disturbances, indicated on the ground by geomagnetic variations, show an unpredictable impulsive character, from short periodic disturbances of the order of hours to long standing giant storms of several day's duration. The reaction of the thermosphere to a large magnetospheric storm is called thermospheric storm. Since the heat input into the thermosphere occurs at high latitudes (mainly into the auroral regions), the heat transport represented by the term P20 in eq.(3) is reversed. In addition, due to the impulsive form of the disturbance, higher order terms are generated which, however, possess short decay times and thus quickly disappear. The sum of these modes determines the "travel time" of the disturbance to the

lower latitudes, and thus the response time of the thermosphere with respect to the magnetospheric disturbance. Important for the development of a ionospheric storm is the increase of the ratio N2/O during a thermospheric storm at middle and higher latitude.[4] An increase of N2 increases the loss process of the ionospheric plasma and causes therefore a decrease of the electron density within the ionospheric F-layer (negative ionospheric storm).[edit]References

^ Duxbury & Duxbury. Introduction to the World's Oceans. 5ed. (1997)^ Rawer, K., "Wave Propagation in the Ionosphere", Kluwer, Dordrecht, 1993^ Chapman, S. and J. Bartels, "Geomagnetism", Clarendon Press, New York,1951^ a b Prölss, G.W., Density perturbations in the upper atmosphere caused by dissipation of solar wind energy, Surv. Geophys., 32, 101, 2011^ Prölss, G.W. and M. K. Bird, "Physics of the Earth's Space Environment", Springer Verlag, Heidelberg, 2010^ Rawer, K., Modelling of neutral and ionized atmospheres, in Flügge, S. (ed): Encycl. Phys., 49/7, Springer Verlag, Heidelberg, 223^ a b Hedin,A.E., A revised thermospheric model based on mass spectrometer and incoherent scatter data: MSIS-83 J. Geophys. Res., 88, 10170, 1983^ Willson, R.C., Measurements of the solar total irradiance and its variability, Space Sci. Rev., 38, 203, 1984^ Brasseur, G., and S. Salomon, "Aeronomy of the Middle Atmosphere", Reidel Pub., Dordrecht, 1984^ Schmidtke, G., Modelling of the solar radiation for aeronomical applications, in Flügge, S. (ed), Encycl. Phys. 49/7, Springer Verlag, Heidelberg, 1^ Knipp, D.J., W.K. Tobiska, and B.A. Emery, Direct and indirect thermospheric heating source for solar cycles, Solar Phys., 224, 2506, 2004^ Volland, H., "Atmospheric Tidal and Planetary Waves", Kluwer, Dordrecht, 1988^ Köhnlein, W., A model of thermospheric temperature and composition, Planet. Space Sci. 28, 225, 1980^ von Zahn, U., et al., ESRO-4 model of global thermospheric composition and temperatures during low solar activity, Geophy. Res. Lett., 4, 33, 1977

ExosphereFrom Wikipedia, the free encyclopedia

Earth atmosphere diagram showing the exosphere and other layers. The layers are to scale. From Earth's surface to the top of the stratosphere (50km) is just under 1% of Earth's radius.The exosphere (Ancient Greek: ἔξω éxō "outside, external, beyond", Ancient Greek: σφαῖρα sphaĩra "sphere") is the uppermost layer of Earth's atmosphere. In the exosphere the density is so low that particles collide only rarely. That makes it possible for energetic particles to escape Earth's gravity altogether. Here, the Earth's atmosphere gradually thins out and merges with interplanetary space.Several moons, such as Earth's moon and the Galilean satellites, have exospheres without denser atmospheres. These consist of atoms and molecules which are ejected from surface rocks and follow a parabolic trajectory until the collide with the surface. Generally each of these atoms and molecules has an independent trajectory. Authors differ as to whether such moons are considered to have atmospheres or not. Smaller bodies such as asteroids, in which the atoms emitted from the surface escape to space, are not considered to have exospheres.Contents [hide] 1 Earth's exosphere1.1 Lower boundary1.2 Upper boundary2 References[edit]Earth's exosphere

The main gases within the Earth's exosphere are the lightest atmospheric gases, mainly hydrogen, with some helium, carbon dioxide, and atomic oxygen near the exobase. Since there is no clear boundary between outer space and the exosphere, the exosphere is sometimes considered a part of outer space.[edit]Lower boundaryMain article: ThermopauseThe lower boundary of the exosphere is known as exobase; it is also called the thermopause as in Earth's atmosphere the atmospheric temperature becomes nearly a constant above this altitude. Before the term exobase was established this boundary was also called the critical level where barometric law no longer applies.[1] The

altitude of the exobase ranges from about 500 to 1,000 kilometres (310 to 620 mi) depending on solar activity.[citation needed]The exobase can defined in one of two ways:The height above which there are negligible atomic collisions between the particles (free molecular flow) andThe height above which constituent atoms are on purely ballistic trajectories.If we define the exobase as the height at which upward traveling molecules experience one collision on average, then at this position the mean free path of a molecule is equal to one pressure scale height. This is shown in the following. Consider a volume of air, with horizontal area and height equal to the mean free path , at pressure and temperature . For an ideal gas, the number of molecules contained in it is:

where is the universal gas constant. From the requirement that each molecule traveling upward undergoes on average one collision, the pressure is:

where is the mean molecular mass of the gas. Solving these two equations gives:

which is the equation for the pressure scale height. As the pressure scale height is almost equal to the density scale height of the primary constituent, and since the Knudsen number is the ratio of mean free path and typical density fluctuation scale, this means that the exobase lies in the region where .The fluctuation in the height of the exobase is important because this provides atmospheric drag on satellites, eventually causing them to fall from orbit if no action is taken to maintain the orbit.[edit]Upper boundaryIn principle, the exosphere covers all distances where particles are still gravitationally bound to Earth, i.e. particles still have ballistic orbits that will take them back towards Earth. Theoretically, the upper boundary of the exosphere can be defined as the distance at which the influence of solar radiation pressure on atomic hydrogen exceeds that of the Earth’s gravitational pull. This happens at half the distance to the Moon (190,000 kilometres (120,000 mi)). The exosphere observable from space as the geocorona is seen to extend to at least 100,000 kilometres (62,000 mi) from the surface of the Earth. The exosphere is a transitional zone between Earth’s atmosphere and interplanetary space.[edit]References

^ Bauer & Lammer, Planetary Aeronomy: Atmosphere Environments in Planetary Systems, Springer, 2004.Gerd W. Prolss: Physics of the Earth's Space Environment: An Introduction. ISBN 3-540-21426-7[hide] v t eEarth's atmosphereTroposphere Stratosphere Mesosphere Thermosphere ExosphereTropopause Stratopause Mesopause Thermopause / ExobaseOzone layer Turbopause Ionosphere

IonosphereFrom Wikipedia, the free encyclopedia (Redirected from Ionospheric)The ionosphere is a part of the upper atmosphere, from about 85 km to 600 km altitude, comprising portions of the mesosphere, thermosphere and exosphere, distinguished because it is ionized by solar radiation. It plays an important part in atmospheric electricity and forms the inner edge of the magnetosphere. It has practical importance because, among other functions, it influences radio propagation to distant places on the Earth.[1]

Relationship of the atmosphere and ionosphereContents [hide] 1 Geophysics2 The ionospheric layers2.1 D layer2.2 E layer2.3 Es2.4 F layer2.5 Ionospheric model3 Anomalies to the "ideal" model3.1 Winter anomaly3.2 Equatorial anomaly

3.3 Equatorial electrojet4 Ionospheric perturbations4.1 X-rays: sudden ionospheric disturbances (SID)4.2 Protons: polar cap absorption (PCA)4.3 Geomagnetic storms4.4 Lightning5 Radio application5.1 Mechanism of refraction6 Other applications7 Measurements7.1 Ionograms7.2 Incoherent scatter radars7.3 Solar flux7.4 Scientific research on ionospheric propagation8 Ionospheres on other planets and Titan9 History10 See also11 Notes12 References13 External links[edit]Geophysics

The ionosphere is a shell of electrons and electrically charged atoms and molecules that surrounds the Earth, stretching from a height of about 50 km to more than 1000 km. It owes its existence primarily to ultraviolet radiation from the Sun.The lowest part of the Earth's atmosphere, the troposphere extends from the surface to about 10 km (6.2 mi). Above 10 km is the stratosphere, followed by the mesosphere. In the stratosphere incoming solar radiation creates the ozone layer. At heights of above 80 km (50 mi), in the thermosphere, the atmosphere is so thin that free electrons can exist for short periods of time before they are captured by a nearby positive ion. The number of these free electrons is sufficient to affect radio propagation. This portion of the atmosphere is ionized and contains a plasma which is referred to as the ionosphere. In a plasma, the negative free electrons and the positive ions are attracted to each other by the electrostatic force, but they are too energetic to stay fixed together in an electrically neutral molecule.Ultraviolet (UV), X-Ray and shorter wavelengths of solar radiation are ionizing, since photons at these frequencies contain sufficient energy to dislodge an electron from a neutral gas atom or molecule upon absorption. In this process the light electron obtains a high velocity so that the temperature of the created electronic gas is much higher (of the order of thousand K) than the one of ions and neutrals. The reverse process to Ionization is recombination, in which a free electron is "captured" by a positive ion, occurs spontaneously. This causes the emission of a photon carrying away the energy produced upon recombination. As gas density increases at lower altitudes, the recombination process prevails, since the gas molecules and ions are closer together. The balance between these two processes determines the quantity of ionization present.Ionization depends primarily on the Sun and its activity. The amount of ionization in the ionosphere varies greatly with the amount of radiation received from the Sun. Thus there is a diurnal (time of day) effect and a seasonal effect. The local winter hemisphere is tipped away from the Sun, thus there is less received solar radiation. The activity of the Sun is associated with the sunspot cycle, with more radiation occurring with more sunspots. Radiation received also varies with geographical location (polar, auroral zones, mid-latitudes, and equatorial regions). There are also mechanisms that disturb the ionosphere and decrease the ionization. There are disturbances such as solar flares and the associated release of charged particles into the solar wind which reaches the Earth and interacts with its geomagnetic field.[edit]The ionospheric layers

Ionospheric layers.At night the F layer is the only layer of significant ionization present, while the ionization in the E and D layers is extremely low. During the day, the D and E layers become much more heavily ionized, as does the F layer, which develops an additional, weaker region of ionisation known as the F1 layer. The F2 layer persists by day and night and is the region mainly responsible for the refraction of radio waves.[edit]D layerThe D layer is the innermost layer, 60 km to 90 km above the surface of the Earth. Ionization here is due to Lyman series-alpha hydrogen radiation at a wavelength of 121.5 nanometre (nm) ionizing nitric oxide (NO). In

addition, with high Solar activity hard X-rays (wavelength < 1 nm) may ionize (N2, O2). During the night cosmic rays produce a residual amount of ionization. Recombination is high in the D layer, the net ionization effect is low, but loss of wave energy is great due to frequent collisions of the electrons (about ten collisions every msec). As a result high-frequency (HF) radio waves are not reflected by the D layer but suffer loss of energy therein. This is the main reason for absorption of HF radio waves, particularly at 10 MHz and below, with progressively smaller absorption as the frequency gets higher. The absorption is small at night and greatest about midday. The layer reduces greatly after sunset; a small part remains due to galactic cosmic rays. A common example of the D layer in action is the disappearance of distant AM broadcast band stations in the daytime.During solar proton events, ionization can reach unusually high levels in the D-region over high and polar latitudes. Such very rare events are known as Polar Cap Absorption (or PCA) events, because the increased ionization significantly enhances the absorption of radio signals passing through the region. In fact, absorption levels can increase by many tens of dB during intense events, which is enough to absorb most (if not all) transpolar HF radio signal transmissions. Such events typically last less than 24 to 48 hours.[edit]E layerThe E layer is the middle layer, 90 km to 120 km above the surface of the Earth. Ionization is due to soft X-ray (1-10 nm) and far ultraviolet (UV) solar radiation ionization of molecular oxygen (O2). Normally, at oblique incidence, this layer can only reflect radio waves having frequencies lower than about 10 MHz and may contribute a bit to absorption on frequencies above. However, during intense Sporadic E events, the Es layer can reflect frequencies up to 50 MHz and higher. The vertical structure of the E layer is primarily determined by the competing effects of ionization and recombination. At night the E layer rapidly disappears because the primary source of ionization is no longer present. After sunset an increase in the height of the E layer maximum increases the range to which radio waves can travel by reflection from the layer.This region is also known as the Kennelly-Heaviside Layer or simply the Heaviside layer. Its existence was predicted in 1902 independently and almost simultaneously by the American electrical engineer Arthur Edwin Kennelly (1861–1939) and the British physicist Oliver Heaviside (1850–1925). However, it was not until 1924 that its existence was detected by Edward V. Appleton.[edit]EsThe Es layer (sporadic E-layer) is characterized by small, thin clouds of intense ionization, which can support reflection of radio waves, rarely up to 225 MHz. Sporadic-E events may last for just a few minutes to several hours. Sporadic E propagation makes radio amateurs very excited, as propagation paths that are generally unreachable can open up. There are multiple causes of sporadic-E that are still being pursued by researchers. This propagation occurs most frequently during the summer months when high signal levels may be reached. The skip distances are generally around 1,640 km (1,020 mi). Distances for one hop propagation can be as close as 900 km (560 mi) or up to 2,500 km (1,600 mi). Double-hop reception over 3,500 km (2,200 mi) is possible.[edit]F layerThe F layer or region, also known as the Appleton layer extends from about 200 km to more than 500 km above the surface of Earth. It is the densest point of the ionosphere, which implies signals penetrating this layer will escape into space. At higher altitudes the amount of oxygen ions decreases and lighter ions such as hydrogen and helium become dominant, this layer is the topside ionosphere. Here extreme ultraviolet (UV, 10–100 nm) solar radiation ionizes atomic oxygen. The F layer consists of one layer at night, but during the day, a deformation often forms in the profile that is labeled F1. The F2 layer remains by day and night responsible for most skywave propagation of radio waves, facilitating high frequency (HF, or shortwave) radio communications over long distances.From 1972 to 1975 NASA launched the AEROS and AEROS B satellites to study the F region.[2][edit]Ionospheric modelAn ionospheric model is a mathematical description of the ionosphere as a function of location, altitude, day of year, phase of the sunspot cycle and geomagnetic activity. Geophysically, the state of the ionospheric plasma may be described by four parameters: electron density, electron and ion temperature and, since several species of ions are present, ionic composition. Radio propagation depends uniquely on electron density.Models are usually expressed as computer programs. The model may be based on basic physics of the interactions of the ions and electrons with the neutral atmosphere and sunlight, or it may be a statistical description based on a large number of observations or a combination of physics and observations. One of the most widely used models is the International Reference Ionosphere (IRI)[3] (IRI 2007), which is based on data and specifies the four parameters just mentioned. The IRI is an international project sponsored by the Committee on Space Research (COSPAR) and the International Union of Radio Science (URSI).[4] The major data sources are the worldwide network of ionosondes, the powerful incoherent scatter radars (Jicamarca, Arecibo, Millstone Hill, Malvern, St. Santin), the ISIS and Alouette topside sounders, and in situ instruments on several satellites and rockets. IRI is updated yearly. IRI is more accurate in describing the variation of the electron density from bottom of the ionosphere to the altitude of maximum density than in describing the total electron content (TEC).Since 1999 this model is "International Standard" for the terrestrial ionosphere (standard TS16457).

[edit]Anomalies to the "ideal" model

Ionograms allow deducing, via computation, the true shape of the different layers. Nonhomogeneous structure of the electron/ion-plasma produces rough echo traces, seen predominantly at night and at higher latitudes, and during disturbed conditions.[edit]Winter anomalyAt mid-latitudes, the F2 layer daytime ion production is higher in the summer, as expected, since the Sun shines more directly on the Earth. However, there are seasonal changes in the molecular-to-atomic ratio of the neutral atmosphere that cause the summer ion loss rate to be even higher. The result is that the increase in the summertime loss overwhelms the increase in summertime production, and total F2 ionization is actually lower in the local summer months. This effect is known as the winter anomaly. The anomaly is always present in the northern hemisphere, but is usually absent in the southern hemisphere during periods of low solar activity.[edit]Equatorial anomaly

Electric currents created in sunward ionosphere.Within approximately ± 20 degrees of the magnetic equator, is the equatorial anomaly. It is the occurrence of a trough of concentrated ionization in the F2 layer. The Earth's magnetic field lines are horizontal at the magnetic equator. Solar heating and tidal oscillations in the lower ionosphere move plasma up and across the magnetic field lines. This sets up a sheet of electric current in the E region which, with the horizontal magnetic field, forces ionization up into the F layer, concentrating at ± 20 degrees from the magnetic equator. This phenomenon is known as the equatorial fountain.[edit]Equatorial electrojetThe worldwide solar-driven wind results in the so-called Sq (solar quiet) current system in the E region of the Earth's ionosphere (ionospheric dynamo region) (100–130 km altitude). Resulting from this current is an electrostatic field directed E-W (dawn-dusk) in the equatorial day side of the ionosphere. At the magnetic dip equator, where the geomagnetic field is horizontal, this electric field results in an enhanced eastward current flow within ± 3 degrees of the magnetic equator, known as the equatorial electrojet.[edit]Ionospheric perturbations

[edit]X-rays: sudden ionospheric disturbances (SID)When the Sun is active, strong solar flares can occur that will hit the sunlit side of Earth with hard X-rays. The X-rays will penetrate to the D-region, releasing electrons that will rapidly increase absorption, causing a High Frequency (3 - 30 MHz) radio blackout. During this time Very Low Frequency (3 – 30 kHz) signals will be reflected by the D layer instead of the E layer, where the increased atmospheric density will usually increase the absorption of the wave and thus dampen it. As soon as the X-rays end, the sudden ionospheric disturbance (SID) or radio black-out ends as the electrons in the D-region recombine rapidly and signal strengths return to normal.[edit]Protons: polar cap absorption (PCA)Associated with solar flares is a release of high-energy protons. These particles can hit the Earth within 15 minutes to 2 hours of the solar flare. The protons spiral around and down the magnetic field lines of the Earth and penetrate into the atmosphere near the magnetic poles increasing the ionization of the D and E layers. PCA's typically last anywhere from about an hour to several days, with an average of around 24 to 36 hours.[edit]Geomagnetic stormsA geomagnetic storm is a temporary intense disturbance of the Earth's magnetosphere.During a geomagnetic storm the F2 layer will become unstable, fragment, and may even disappear completely.In the Northern and Southern pole regions of the Earth aurorae will be observable in the sky.[edit]LightningLightning can cause ionospheric perturbations in the D-region in one of two ways. The first is through VLF (Very Low Frequency) radio waves launched into the magnetosphere. These so-called "whistler" mode waves can interact with radiation belt particles and cause them to precipitate onto the ionosphere, adding ionization to the D-region. These disturbances are called "lightning-induced electron precipitation" (LEP) events.Additional ionization can also occur from direct heating/ionization as a result of huge motions of charge in lightning strikes. These events are called Early/Fast.In 1925, C. F. Wilson proposed a mechanism by which electrical discharge from lightning storms could propagate upwards from clouds to the ionosphere. Around the same time, Robert Watson-Watt, working at the Radio Research Station in Slough, UK, suggested that the ionospheric sporadic E layer (Es) appeared to be enhanced as a result of lightning but that more work was needed. In 2005, C. Davis and C. Johnson, working at the Rutherford Appleton Laboratory in Oxfordshire, UK, demonstrated that the Es layer was indeed enhanced as a result of lightning activity. Their subsequent research has focussed on the mechanism by which this process can occur.[edit]Radio application

DX communication, popular among amateur radio enthusiasts, is a term given to communication over great distances. Thanks to the property of ionized atmospheric gases to refract high frequency (HF, or shortwave) radio waves, the ionosphere can be utilized to "bounce" a transmitted signal down to ground. Transcontinental HF-connections rely on up to 5 bounces, or hops. Such communications played an important role during World War II. Karl Rawer's most sophisticated prediction method[1] took account of several (zig-zag) paths, attenuation in the D-region and predicted the 11-year solar cycle by a method due to Wolfgang Gleißberg.[edit]Mechanism of refractionWhen a radio wave reaches the ionosphere, the electric field in the wave forces the electrons in the ionosphere into oscillation at the same frequency as the radio wave. Some of the radio-frequency energy is given up to this resonant oscillation. The oscillating electrons will then either be lost to recombination or will re-radiate the original wave energy. Total refraction can occur when the collision frequency of the ionosphere is less than the radio frequency, and if the electron density in the ionosphere is great enough.The critical frequency is the limiting frequency at or below which a radio wave is reflected by an ionospheric layer at vertical incidence. If the transmitted frequency is higher than the plasma frequency of the ionosphere, then the electrons cannot respond fast enough, and they are not able to re-radiate the signal. It is calculated as shown below:

where N = electron density per m3 and fcritical is in Hz.The Maximum Usable Frequency (MUF) is defined as the upper frequency limit that can be used for transmission between two points at a specified time.

where = angle of attack, the angle of the wave relative to the horizon, and sin is the sine function.The cutoff frequency is the frequency below which a radio wave fails to penetrate a layer of the ionosphere at the incidence angle required for transmission between two specified points by refraction from the layer.[edit]Other applications

The open system electrodynamic tether, which uses the ionosphere, is being researched. The space tether uses plasma contactors and the ionosphere as parts of a circuit to extract energy from the Earth's magnetic field by electromagnetic induction.[edit]Measurements

[edit]IonogramsIonograms show the virtual heights and critical frequencies of the ionospheric layers and which are measured by an ionosonde. An ionosonde sweeps a range of frequencies, usually from 0.1 to 30 MHz, transmitting at vertical incidence to the ionosphere. As the frequency increases, each wave is refracted less by the ionization in the layer, and so each penetrates further before it is reflected. Eventually, a frequency is reached that enables the wave to penetrate the layer without being reflected. For ordinary mode waves, this occurs when the transmitted frequency just exceeds the peak plasma, or critical, frequency of the layer. Tracings of the reflected high frequency radio pulses are known as ionograms. Reduction rules are given in: "URSI Handbook of Ionogram Interpretation and Reduction", edited by William Roy Piggott and Karl Rawer, Elsevier Amsterdam, 1961 (translations into Chinese, French, Japanese and Russian are available).[edit]Incoherent scatter radarsIncoherent scatter radars operate above the critical frequencies. Therefore the technique allows to probe the ionosphere, unlike ionosondes, also above the electron density peaks. The thermal fluctuations of the electron density scattering the transmitted signals lack coherence, which gave the technique its name. Their power spectrum contains information not only on the density, but also on the ion and electron temperatures, ion masses and drift velocities.[edit]Solar fluxSolar flux is a measurement of the intensity of solar radio emissions at a frequency of 2800 MHz made using a radio telescope located in Dominion Radio Astrophysical Observatory, Penticton, British Columbia, Canada.[5] Known also as the 10.7 cm flux (the wavelength of the radio signals at 2800 MHz), this solar radio emission has been shown to be proportional to sunspot activity. However, the level of the Sun's ultraviolet and X-ray emissions is primarily responsible for causing ionization in the Earth's upper atmosphere. We now have data from the GOES spacecraft that measures the background X-ray flux from the Sun, a parameter more closely related to the ionization levels in the ionosphere.The A and K indices are a measurement of the behavior of the horizontal component of the geomagnetic field. The K index uses a scale from 0 to 9 to measure the change in the horizontal component of the geomagnetic field. A new K index is determined at the Boulder Geomagnetic Observatory 40°08′15″N 105°14′16″W.The geomagnetic activity levels of the Earth are measured by the fluctuation of the Earth's magnetic field in SI units called teslas (or in non-SI gauss, especially in older literature). The Earth's magnetic field is measured around the planet by many observatories. The data retrieved is processed and turned into measurement indices.

Daily measurements for the entire planet are made available through an estimate of the ap index, called the planetary A-index (PAI).[edit]Scientific research on ionospheric propagationScientists also are exploring the structure of the ionosphere by a wide variety of methods, including passive observations of optical and radio emissions generated in the ionosphere, bouncing radio waves of different frequencies from it, incoherent scatter radars such as the EISCAT, Sondre Stromfjord, Millstone Hill, Arecibo, and Jicamarca radars, coherent scatter radars such as the Super Dual Auroral Radar Network (SuperDARN) radars, and using special receivers to detect how the reflected waves have changed from the transmitted waves.A variety of experiments, such as HAARP (High Frequency Active Auroral Research Program), involve high power radio transmitters to modify the properties of the ionosphere. These investigations focus on studying the properties and behavior of ionospheric plasma, with particular emphasis on being able to understand and use it to enhance communications and surveillance systems for both civilian and military purposes. HAARP was started in 1993 as a proposed twenty year experiment, and is currently active near Gakona, Alaska.The SuperDARN radar project researches the high- and mid-latitudes using coherent backscatter of radio waves in the 8 to 20 MHz range. Coherent backscatter is similar to Bragg scattering in crystals and involves the constructive interference of scattering from ionospheric density irregularities. The project involves more than 11 different countries and multiple radars in both hemispheres.Scientists are also examining the ionosphere by the changes to radio waves, from satellites and stars, passing through it. The Arecibo radio telescope located in Puerto Rico, was originally intended to study Earth's ionosphere.[edit]Ionospheres on other planets and Titan

The atmosphere of Titan includes an ionosphere.[6] It ranges from about 1100 to 1300 km in altitude, and contains carbon compounds.Planets with ionospheres (incomplete list):Ionosphere of VenusIonosphere of Uranus[edit]History

Guglielmo Marconi received the first trans-Atlantic radio signal on December 12, 1901, in St. John's, Newfoundland (now in Canada) using a 152.4 m (500 ft) kite-supported antenna for reception. The transmitting station in Poldhu, Cornwall used a spark-gap transmitter to produce a signal with a frequency of approximately 500 kHz and a power of 100 times more than any radio signal previously produced. The message received was three dits, the Morse code for the letter S. To reach Newfoundland the signal would have to bounce off the ionosphere twice. Dr. Jack Belrose has recently contested this, however, based on theoretical and experimental work.[7] However, Marconi did achieve transatlantic wireless communications beyond a shadow of doubt in Glace Bay, Nova Scotia one year later.In 1902, Oliver Heaviside proposed the existence of the Kennelly-Heaviside Layer of the ionosphere which bears his name. Heaviside's proposal included means by which radio signals are transmitted around the Earth's curvature. Heaviside's proposal, coupled with Planck's law of black body radiation, may have hampered the growth of radio astronomy for the detection of electromagnetic waves from celestial bodies until 1932 (and the development of high frequency radio transceivers). Also in 1902, Arthur Edwin Kennelly discovered some of the ionosphere's radio-electrical properties.In 1912, the U.S. Congress imposed the Radio Act of 1912 on amateur radio operators, limiting their operations to frequencies above 1.5 MHz (wavelength 200 meters or smaller). The government thought those frequencies were useless. This led to the discovery of HF radio propagation via the ionosphere in 1923.In 1926, Scottish physicist Robert Watson-Watt introduced the term ionosphere in a letter published only in 1969 in Nature:We have in quite recent years seen the universal adoption of the term ‘stratosphere’..and..the companion term ‘troposphere’... The term ‘ionosphere’, for the region in which the main characteristic is large scale ionisation with considerable mean free paths, appears appropriate as an addition to this series.

Edward V. Appleton was awarded a Nobel Prize in 1947 for his confirmation in 1927 of the existence of the ionosphere. Lloyd Berkner first measured the height and density of the ionosphere. This permitted the first complete theory of short wave radio propagation. Maurice V. Wilkes and J. A. Ratcliffe researched the topic of radio propagation of very long radio waves in the ionosphere. Vitaly Ginzburg has developed a theory of electromagnetic wave propagation in plasmas such as the ionosphere.In 1962 the Canadian satellite Alouette 1 was launched to study the ionosphere. Following its success were Alouette 2 in 1965 and the two ISIS satellites in 1969 and 1971, further AEROS -A and -B in 1972 and 1975, all for measuring the ionosphere.[edit]See also

GeophysicsVan Allen radiation beltSchumann resonancesInternational Reference IonosphereMagnetospheric electric convection fieldionospheric dynamo regionRadioSfericsEarth-Ionosphere waveguideFadingLine-of-sight propagationIonospheric absorptionRelatedTether propulsionCanadian Geospace MonitoringPioneer Venus projectNozomiNew HorizonsSoft gamma repeaterTIMED (Thermosphere Ionosphere Mesosphere Energetics and Dynamics)International Geophysical YearUpper Atmospheric LightningListsList of astronomical topicsList of electronics topicsList of plasma (physics) articles[edit]Notes

^ a b K. Rawer. Wave Propagation in the Ionosphere. Kluwer Acad.Publ., Dordrecht 1993. ISBN 0-7923-0775-5^ Yenne, Bill (1985). The Encyclopedia of US Spacecraft. Exeter Books (A Bison Book), New York. ISBN 0-671-07580-2.p.12 AEROS^ D.Bilitza:International Reference Ionosphere 2000.Radio Sci.36,#2,261-275 2001^ "International Reference Ionosphere". Ccmc.gsfc.nasa.gov. Retrieved 2011-11-08.^ "F10.7 Solar Flux Forecast Verification". Swpc.noaa.gov. 2007-10-01. Retrieved 2011-11-08.^ NASA/JPL: Titan's upper atmosphere Accessed 2010-08-25^ John S. Belrose, "Fessenden and Marconi: Their Differing Technologies and Transatlantic Experiments During the First Decade of this Century". International Conference on 100 Years of Radio -- 5–7 September 1995.[edit]References

Corum, J. F., and Corum, K. L., "A Physical Interpretation of the Colorado Springs Data". Proceedings of the Second International Tesla Symposium. Colorado Springs, Colorado, 1986.Davies, Kenneth (1990). Ionospheric Radio. IEE Electromagnetic Waves Series #31. London, UK: Peter Peregrinus Ltd/The Institution of Electrical Engineers. ISBN 0-86341-186-X.Grotz, Toby, "The True Meaning of Wireless Transmission of power". Tesla : A Journal of Modern Science, 1997.Hargreaves, J. K., "The Upper Atmosphere and Solar-Terrestrial Relations". Cambridge University Press, 1992,Kelley, M. C, and Heelis, R. A., "The Earth's Ionosphere: Plasma Physics and Electrodynamics". Academic Press, 1989.Leo F. McNamara. (1994) ISBN 0-89464-804-7 "Radio Amateurs Guide to the Ionosphere".Rawer,K.:"Wave Propagation in the Ionosphere". Kluwer Academic Publ., Dordrecht 1993 ISBN 0-7923-0775-5.D. Bilitza, "International Reference Ionosphere 2000,".Radio Science 36, #2, pp 261–275, 2001.J. Lilensten et P.-L. Blelly: Du Soleil à la Terre, Aéronomie et météorologie de l'espace, Collection Grenoble Sciences, Université Joseph Fourier Grenoble I, 2000. ISBN 978-2-86883-467-6P.-L. Blelly and D. Alcaydé, Ionosphere, in: Y. Kamide/A. Chian, Handbook of the Solar-Terrestrial Environment, Springer-Verlag Berlin Heidelberg, pp. 189–220, 2007. doi:10.1007/11367758_8H. Volland, Atmospheric Electrodynamics, Springer Verlag, Berlin, 1984.[edit]External links

Wikimedia Commons has media related to: Ionosphere

Look up ionosphere in Wiktionary, the free dictionary.Gehred, Paul, and Norm Cohen, SWPC's Radio User's Page.Amsat-Italia project on Ionospheric propagation (ESA SWENET website)NZ4O Solar Space Weather & Geomagnetic Data ArchiveNZ4O 160 Meter (Medium Frequency)Radio Propagation Theory Notes Layman Level Explanations Of "Seemingly" Mysterious 160 Meter (MF/HF) Propagation OccurrencesUSGS Geomagnetism ProgramEncyclopaedia Britannica, Ionosphere and magnetosphereCurrent Space Weather ConditionsCurrent Solar X-Ray FluxSuper Dual Auroral Radar NetworkEuropean Inchorent Scatter radar systemMillstone Hill incoherent scatter radar[hide] v t eEarth's atmosphereTroposphere Stratosphere Mesosphere Thermosphere ExosphereTropopause Stratopause Mesopause Thermopause / ExobaseOzone layer Turbopause Ionosphere

MagnetosphereFrom Wikipedia, the free encyclopedia

Magnetic field lines represent the magnetic field surrounding Earth.

Artistic rendition of a magnetosphere. Sizes are not to scale.A magnetosphere is formed when a stream of charged particles, such as the solar wind, interacts with and is deflected by the magnetic field of a planet or similar body. Earth is surrounded by a magnetosphere, as are the other planets with intrinsic magnetic fields: Mercury, Jupiter, Saturn, Uranus, and Neptune. Jupiter's moon Ganymede has a small magnetosphere, but it is situated entirely within the magnetosphere of Jupiter, leading to complex interactions. The ionospheres of weakly magnetized planets such as Venus and Mars set up currents that partially deflect the solar wind flow, but do not have magnetospheres, per se. The magnetosphere is caused by the movement of electrical currents in the outer core of the earth. The outer core is of a liquid state while the inner core is of a solid state due to the immense amount of pressure it experiences. The Magnetosphere is nothing but the magnetic field that prevents the solar winds, or highly energetic particles that come from the sun's corona from completely depriving the earth of its oxygen. If the magnetosphere did not exist, then Earth would not be able to sustain life.Contents [hide] 1 History of magnetospheric physics2 Earth's magnetosphere3 General properties4 Radiation belts5 Magnetic tails6 Electric currents in space7 Classification of magnetic fields8 Magnetic substorms and storms9 Other bodies10 See also11 References12 External links[edit]History of magnetospheric physics

Main article: Magnetosphere historyTheories about the solar plasma stream and its interaction with Earth were published as early as 1931. During the next several decades multiple scientists, including Sydney Chapman and Hannes Alfvén, proposed a variety of

mechanisms and explanations.[1] The Earth's magnetosphere was first measured in 1958 by Explorer 1 with instruments designed by James A. Van Allen of The University of Iowa during the research performed for the International Geophysical Year.[2][3] In August and September 1958, Project Argus was performed to test a theory about the formation of radiation belts that may have tactical use in war.In 1959 Thomas Gold proposed the name "magnetosphere" when he wrote:"The region above the ionosphere in which the magnetic field of the earth has a dominant control over the motions of gas and fast charged particles is known to extend out to a distance of the order of 10 earth radii; it may appropriately be called the 'magnetosphere'."[4][edit]Earth's magnetosphere

Schematic of Earth's magnetosphere. The solar wind flows from left to right.The magnetosphere of Earth is a region in space whose shape is determined by the Earth's internal magnetic field, the solar wind plasma, and the interplanetary magnetic field (IMF).[5] The boundary of the magnetosphere ("magnetopause") is roughly bullet shaped, about 15 RE abreast of Earth and on the night side (in the "magnetotail" or "geotail") approaching a cylinder with a radius 20-25 RE. The tail region stretches well past 200 RE, and the way it ends is not well known.The outer neutral gas envelope of Earth, or geocorona, consists mostly of the lightest atoms, hydrogen and helium, and continues beyond 4-5 RE, with diminishing density. The hot plasma ions of the magnetosphere acquire electrons during collisions with these atoms and create an escaping "glow" of energetic neutral atoms (ENAs)[6] that have been used to image the hot plasma clouds by the IMAGE[7] and TWINS[8] missions.The upward extension of the ionosphere, known as the plasmasphere, also extends beyond 4-5 RE with diminishing density, beyond which it becomes a flow of light ions called the polar wind that escapes out of the magnetosphere into the solar wind. Energy deposited in the ionosphere by auroras strongly heats the heavier atmospheric components such as oxygen and molecules of oxygen and nitrogen, which would not otherwise escape from Earth's gravity. Owing to this highly variable heating, however, a heavy atmospheric or ionospheric outflow of plasma flows during disturbed periods from the auroral zones into the magnetosphere, extending the region dominated by terrestrial material, known as the fourth or plasma geosphere, at times out to the magnetopause.Earth’s magnetosphere protects the ozone layer from the solar wind. The ozone layer protects the Earth (and life on it) from dangerous ultraviolet radiation.[9][edit]General properties

This section does not cite any references or sources. (September 2011)

Density and temperature of plasma in the magnetosphere and other areas of space. Density increases upwards, temperature increases towards the right. The free electrons in a metal may be considered an electron plasma[10]Two factors determine the structure and behavior of the magnetosphere: (1) The internal field of the Earth, and (2) The solar wind.The internal field of the Earth (its "main field") appears to be generated in the Earth's core by a dynamo process, associated with the circulation of liquid metal in the core, driven by internal heat sources. Its major part resembles the field of a bar magnet ("dipole field") inclined by about 10° to the rotation axis of Earth, but more complex parts ("higher harmonics") also exist, as first shown by Carl Friedrich Gauss. The dipole field has an intensity of about 30,000-60,000 nanoteslas (nT) at the Earth's surface, and its intensity diminishes as the inverse of the cube of the distance, i.e. at a distance of 2 Earth radii it only amounts to 1/8 of the surface field in the same direction. Higher harmonics diminish faster, like higher powers of 1/R, making the dipole field the only important internal source in most of the magnetosphere.The solar wind is a fast outflow of hot plasma from the sun in all directions. Above the sun's equator it typically attains 400 km/s; above the sun's poles, up to twice as much. The flow is powered by the million-degree temperature of the sun's corona, for which no generally accepted explanation exists yet. Its composition resembles that of the Sun—about 95% of the ions are protons, about 4% helium nuclei (alpha particles), with 1% of heavier matter (C, N, O, Ne, Si, Mg...up to Fe) and enough electrons to keep charge neutrality. At Earth's orbit its typical density is 6 ions/cm3 (variable, as is the velocity), and it contains a variable interplanetary magnetic field (IMF) of (typically) 2–5 nT. The IMF is produced by stretched-out magnetic field lines originating on the Sun, a process described in the article Geomagnetic storm.Physical reasons make it difficult for solar wind plasma with its embedded IMF to mix with terrestrial plasma whose magnetic field has a different source. The two plasmas end up separated by a boundary, the magnetopause, and the Earth's plasma is confined to a cavity inside the flowing solar wind, the magnetosphere. The isolation is not complete, thanks to secondary processes such as magnetic reconnection—otherwise it would

be hard for the solar wind to transmit much energy to the magnetosphere—but it still determines the overall configuration.An additional feature is a collision-free bow shock which forms in the solar wind ahead of Earth, typically at 13.5 RE on the sunward side. It forms because the solar velocity of the wind exceeds (typically 2–3 times) that of Alfvén waves, a family of characteristic waves with which disturbances propagate in a magnetized fluid. In the region behind the shock ("magnetosheath") the velocity drops briefly to the Alfvén velocity (and the temperature rises, absorbing lost kinetic energy), but the velocity soon rises back as plasma is dragged forward by the surrounding solar wind flow.To understand the magnetosphere, one needs to visualize its magnetic field lines, that everywhere point in the direction of the magnetic field—e.g., diverging out near the magnetic north pole (or geographic southpole), and converging again around the magnetic south pole (or the geographic northpole), where they enter the Earth. They can be visualized like wires which tie the magnetosphere together—wires that also guide the motions of trapped particles, which slide along them like beads (though other motions may also occur).[edit]Radiation belts

This section does not cite any references or sources. (September 2011)When the first scientific satellites were launched in the first half of 1958—Explorers 1 and 3 by the US, Sputnik 3 by the Soviet Union—they observed an intense (and unexpected) radiation belt around Earth, held by its magnetic field. "My God, space is radioactive!" exclaimed one of Van Allen's colleagues, when the meaning of those observations was realized. That was the "inner radiation belt" of protons with energies in the range 10-100 MeV (megaelectronvolts), attributed later to "albedo neutron decay," a secondary effect of the interaction of cosmic radiation with the upper atmosphere. It is centered on field lines crossing the equator about 1.5 RE from the Earth's center.Later a population of trapped ions and electrons was observed on field lines crossing the equator at 2.5–8 RE. The high-energy part of that population (about 1 MeV) became known as the "outer radiation belt", but its bulk is at lower energies (peak about 65 keV) and is identified as the ring current plasma.The trapping of charged particles in a magnetic field can be quite stable. This is particularly true in the inner belt, because the build-up of trapped protons from albedo neutrons is quite slow, requiring years to reach observed intensities. In July 1962, the United States tested a thermonuclear weapon high over the South Pacific at around 400 km in the upper atmosphere, in this region, creating an artificial belt of high-energy electrons, and some of them were still around 4–5 years later (such tests are now banned by treaty).The outer belt and ring current are less persistent, because charge-exchange collisions with atoms of the geocorona (see above) tends to remove their particles. That suggests the existence of an effective source mechanism, continually supplying this region with fresh plasma. It turns out that the magnetic barrier can be broken down by electric forces, as discussed in Magnetic Storms and Plasma Flows (MSPF). If plasma is pushed hard enough, it generates electric fields which allow it to move in response to the push, often (not always) deforming the magnetic field in the process.[edit]Magnetic tails

This section does not cite any references or sources. (September 2011)

A view from the IMAGE satellite showing Earth's plasmasphere using its Extreme Ultraviolet (EUV) imager instrument.A magnetic tail or magnetotail is formed by pressure from the solar wind on a planet's magnetosphere. The magnetotail can extend great distances away from its originating planet. Earth's magnetic tail extends at least 200 Earth radii in the anti-sunward direction well beyond the orbit of the Moon at about 60 Earth radii, while Jupiter's magnetic tail extends beyond the orbit of Saturn. On occasion Saturn is immersed inside the Jovian magnetosphere.The extended magnetotail results from the energy stored in the planet's magnetic field. At times this energy is released and the magnetic field becomes temporarily more dipole-like. As it does so that stored energy goes to energize plasma trapped on the involved magnetic field lines. Some of that plasma is driven tailward and into the distant solar wind. The rest is injected into the inner magnetosphere where it results in the aurora and the ring current plasma population. The resulting energetic plasma and electric currents can disrupt spacecraft operations, communication and navigation.[edit]Electric currents in space

This section does not cite any references or sources. (September 2011)Magnetic fields in the magnetosphere arise from the Earth's internal magnetic field as well as from electric currents that flow in the magnetospheric plasma: the plasma acts as an electromagnet. Magnetic fields from currents that circulate in the magnetospheric plasma extend the Earth's magnetism much further in space than

would be predicted from the Earth's internal field alone. Such currents also determine the field's structure far from Earth, creating the regions described in the introduction above.Unlike in a conventional resistive electric circuit, where currents are best thought of as arising as a response to an applied voltage, currents in the magnetosphere are better seen as caused by the structure and motion of the plasma in its associated magnetic field. For instance, electrons and positive ions trapped in the dipole-like field near the Earth tend to circulate around the magnetic axis of the dipole (the line connecting the magnetic poles) in a ring around the Earth, without gaining or losing energy (this is known as Guiding center motion). Viewed from above the magnetic north pole (geographic south), ions circulate clockwise, electrons counterclockwise, producing a net circulating clockwise current, known (from its shape) as the ring current. No voltage is needed—the current arises naturally from the motion of the ions and electrons in the magnetic field.Any such current will modify the magnetic field. The ring current, for instance, strengthens the field on its outside, helping expand the size of the magnetosphere. At the same time, it weakens the magnetic field in its interior. In a magnetic storm, plasma is added to the ring current, making it temporarily stronger, and the field at Earth is observed to weaken by up to 1-2%.The deformation of the magnetic field, and the flow of electric currents in it, are intimately linked, making it often hard to label one as cause and the other as effect. Frequently (as in the magnetopause and the magnetotail) it is intuitively more useful to regard the distribution and flow of plasma as the primary effect, producing the observed magnetic structure, with the associated electric currents just one feature of those structures, more of a consistency requirement of the magnetic structure.As noted, one exception (at least) exists, a case where voltages do drive currents. That happens with Birkeland currents, which flow from distant space into the near-polar ionosphere, continue at least some distance in the ionosphere, and then return to space. (Part of the current then detours and leaves Earth again along field lines on the morning side, flows across midnight as part of the ring current, then comes back to the ionosphere along field lines on the evening side and rejoins the pattern.) The full circuit of those currents, under various conditions, is still under debate. Because the ionosphere is an ohmic conductor of sorts, such flow will heat it up. It will also create secondary Hall currents, and accelerate magnetospheric particles—electrons in the arcs of the polar aurora, and singly ionized oxygen ions (O+) which contribute to the ring current.Two kinds of global-scale magnetospheric electric fields can be identified:a) a magnetospheric electric convection field, which originates from the interaction between the solar wind plasma and the polar geomagnetic field. It is directed from dawn to dusk, andb) a co-rotation field, which is generated in a co-rotating frame of reference in order to compensate for the Lorentz force.The thermal plasma within the inner magnetosphere corotates with the Earth and therefore reacts to the sum of these two fields. The configuration of the sum of both electric potentials has a torus-like inner region of closed electric potential lines in which ionized particles of thermal energy are trapped (plasmasphere). Outside the last closed electric potential shell (the plasmapause), the ionized particles are lost to space.The electric convection field causes charge separation at the magnetopause. Therefore, discharging currents flow via electric field-aligned currents (Birkeland currents) into the auroral regions of the ionosphere on the morning side and out of the ionosphere on the evening side. The electric circuit is closed within the ionospheric dynamo region (about 100 to 200 km above the ground). These currents are the DP1 current (the auroral electrojet) and the polar DP2 current. Their magnetic manifestations can be observed on the ground. Joule heating due to the varying electric currents heats the neutral gas of the thermosphere causing thermospheric disturbances.[11][edit]Classification of magnetic fields

This section does not cite any references or sources. (September 2011)

Schematic view of the different current systems which shape the Earth's magnetosphereRegardless of whether they are viewed as sources or consequences of the magnetospheric field structure, electric currents flow in closed circuits. That makes them useful for classifying different parts of the magnetic field of the magnetosphere, each associated with a distinct type of circuit. In this way the field of the magnetosphere is often resolved into 5 distinct parts, as follows.The internal field of the Earth ("main field") arising from electric currents in the core. It is dipole-like, modified by higher harmonic contributions.The ring current field, carried by plasma trapped in the dipole-like field around Earth, typically at distances 3–8 RE (less during large storms). Its current flows (approximately) around the magnetic equator, mainly clockwise when viewed from north. (A small counterclockwise ring current flows at the inner edge of the ring, caused by the fall-off in plasma density as Earth is approached.)The field confining the Earth's plasma and magnetic field inside the magnetospheric cavity. The currents responsible for it flow on the magnetopause, the interface between the magnetosphere and the solar wind, described in the introduction. Their flow, again, may be viewed as arising from the geometry of the magnetic

field (rather than from any driving voltage), a consequence of "Ampére's law" (embodied in Maxwell's equations) which in this case requires an electric current to flow along any interface between magnetic fields of different directions and/or intensities. The system of tail currents. The magnetotail consists of twin bundles of oppositely directed magnetic field (the "tail lobes"), directed earthwards in the northern half of the tail and away from Earth in the southern half. In between the two exists a layer ("plasma sheet") of denser plasma (0.3-0.5 ions/cm3 versus 0.01-0.02 in the lobes), and because of the difference between the adjoining magnetic fields, by Ampére's law an electric current flows there too, directed from dawn to dusk. The flow closes (as it must) by following the tail magnetopause—part over the northern lobe, part over the southern one.The Birkeland current field (and its branches in the ionosphere and ring current), a circuit is associated with the polar aurora. Unlike the 3 preceding current systems, it does require a constant input of energy, to provide the heating of its ionospheric path and the acceleration of auroral electrons and of positive ions. The energy probably comes from a dynamo process, meaning that part of the circuit threads a plasma moving relative to Earth, either in the solar wind and in "boundary layer" flows which it drives just inside the magnetopause, or by plasma moving earthward in the magnetotail, as observed during substorms (below).[edit]Magnetic substorms and storms

This section does not cite any references or sources. (September 2011)Earlier it was stated that, "if plasma is pushed hard enough, it generates electric fields which allow it to move in response to the push, often (not always) deforming the magnetic field in the process." Two examples of such "pushing" are particularly important in the magnetosphere. The THEMIS mission is a NASA program to study in detail the physical processes involved in substorms.The more common one occurs when the north-south component Bz of the interplanetary magnetic field (IMF) is appreciable and points southward. In this state field lines of the magnetosphere are relatively strongly linked to the IMF, allowing energy and plasma to enter it at relatively high rates. This swells up the magnetotail and makes it unstable. Ultimately the tail's structure changes abruptly and violently, a process known as a magnetic substorm.

Magnetic reconnection in the near-Earth magnetotail, producing a disconnected "plasmoid"One possible scenario (the subject is still debated) is as follows. As the magnetotail swells, it creates a wider obstacle to the solar wind flow, causing its widening portion to be squeezed more by the solar wind. In the end, this squeezing breaks apart field lines in the plasma sheet ("magnetic reconnection"), and the distant part of the sheet, no longer attached to the Earth, is swept away as an independent magnetic structure ("plasmoid"). The near-Earth part snaps back earthwards, energizing its particles and producing Birkeland currents and bright auroras. As observed in the 1970s by the ATS satellites at 6.6 RE, when conditions are favorable that can happen up to several times a day.Substorms generally do not substantially add to the ring current. That happens in magnetic storms, when following an eruption on the sun (a "coronal mass ejection" or a "solar flare"—details are still debated, see MSPF) a fast-moving plasma cloud hits the Earth. If the IMF has a southward component, this not only pushes the magnetopause boundary closer to Earth (at times to about half its usual distance), but it also produces an injection of plasma from the tail, much more vigorous than the one associated with substorms.The plasma population of the ring current may now grow substantially, and a notable part of the addition consists of O+ oxygen ions extracted from the ionosphere as a by-product of the polar aurora. In addition, the ring current is driven earthward (which energizes its particles further), temporarily modifying the field around the Earth and thus shifting the aurora (and its current system) closer to the equator. The magnetic disturbance may decay within 1–3 days as many ions are removed by charge exchange, but the higher energies of the ring current can persist much longer.[edit]Other bodies

Mars, with little or no magnetic field is thought to have lost much of its former oceans and atmosphere to space in part due to the direct impact of the solar wind. Venus with its thick atmosphere is thought to have lost most of its water to space in large part owing to solar wind ablation.[12]Due to the size of Jupiter's magnetosphere there is a possibility of very weak and very brief seasonal head-tail interaction between Earth's and Jupiter's magnetospheres[citation needed]. The magnetospheres of the outer gas planets may weakly interact, although their magnetospheres are much smaller than Jupiter's.[edit]See also

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Io's interaction with Jupiter's magnetosphereInternational Magnetospheric StudyMagnetic sail for applications in spacecraft propulsionPlasma physicsList of plasma (physics) articles[edit]References

^ Akasofu, Syun-Ichi (23 August 2011). "The Scientific Legacy of Sydney Chapman". Eos 92 (34): 281–282. Bibcode 2011EOSTr..92..281A. doi:10.1029/2011EO340001.^ Axford, W. I., "Discovering the Earth's Magnetosphere" (1982) Advances in Space Research, v. 2, Issue 1, p. 11-12.^ Van Allen, James A., Origins of Magnetospheric Physics, Smithsonian Institution Press (1983) ISBN 0-87474-940-9^ Gold, T. (1959), Motions in the Magnetosphere of the Earth, J. Geophys. Res., 64(9), 1219–1224, doi:10.1029/JZ064i011p01665^ Parks, George K. (1991). "1". Physics of Space Plasmas: An Introduction. Addison-Wesley. ISBN 0-201-50821-4.^ Brandt, P.C.; Mitchell, D.G.; Roelof, E.C.; Krimigis, S.M.; Paranicas, C.P.; Mauk, B.H.; Saur, J.; DeMajistre, R. (2005). "ENA Imaging: Seeing the Invisible". Johns Hopkins APL Technical Digest 26 (2): 143–155. Retrieved 27 September 2011.^ "NAI imaging: science background". IMAGE: Imager for Magnetopause-to-Aurora Global Exploration. Southwest Research Institute. Retrieved September 2011.^ "Two Wide-angle Imaging Neutral-atom Spectrometers". Southwest Research Institute. Retrieved September 2011.^ Quirin Shlermeler (3 March 2005). "Solar wind hammers the ozone layer". naturenews. doi:10.1038/news050228-12. Retrieved 27 September 2011.^ After Peratt, A. L., "Advances in Numerical Modeling of Astrophysical and Space Plasmas" (1966) Astrophysics and Space Science, v. 242, Issue 1/2, p. 93-163.^ Volland, Hans,(1988), "Atmospheric Tidal and Planetary Waves", Kluwer, Dordrecht^ "Polar Substorm". NASA Science News. 2009-03-02. Retrieved 2010-12-28.Walt, Martin, Introduction to Geomagnetically Trapped Radiation, Cambridge University Press (1994) ISBN 978-0-521-61611-9Carlowicz, M. and R. Lopez, Storms from the Sun, National Academies Press (2002) ISBN 978-0-309-07642-5Hess, Wilmot N. (1968). The Radiation Belt and Magnetosphere. Blaisdell Pub. Co..D. P. Stern, M. Peredo (2004-09-28). "The Exploration of the Earth's Magnetosphere". NASA. Retrieved 2006-08-22.Volland, Hans, Atmospheric Electrodynamics, Kluwer, Dordrecht, 1984[edit]External links

USGS Geomagnetism ProgramAurora borealisStorms from the Sun - The Emerging Science of Space WeatherMagnetosphere: Earth's Magnetic Shield Against the Solar WindPhysics of the Aurora"3D Earth Magnetic Field Charged-Particle Simulator" Tool dedicated to the 3d simulation of charged particles in the magnetosphere.. [VRML Plug-in Required]"Exploration of the Earth's Magnetosphere", Educational web site by David P. Stern and Mauricio Peredo[hide] v t eMagnetosphericsSubmagnetosphereGeosphere Earth's magnetic field Aurora Polar wind Atmospheric circulation Jet streamEarth's magnetosphereIonosphere Plasmasphere Magnetosphere Magnetopause Magnetosphere particle motion Ring current Van Allen radiation belt Birkeland current Magnetosheath Magnetosphere chronologySolar windInterplanetary magnetic field Heliosphere Heliopause Solar flare Geomagnetic storm Coronal mass ejection Heliospheric current sheet Space weatherSatellitesFull list Cluster Double Star GEOTAIL IMAGE MMS (launch due 2014) Polar THEMIS Van Allen Probes WINDResearch projects

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