document_title: Earth's magnetic field

question_text: what is the value of earth's magnetic field

question_tokens: what is the value of earth 's magnetic field

text: Earth's magnetic field

text: Importance[edit]

text: The Earth's magnetic field serves to deflect most of the solar wind, whose charged particles would otherwise strip away the ozone layer that protects the Earth from harmful ultraviolet radiation.[4] One stripping mechanism is for gas to be caught in bubbles of magnetic field, which are ripped off by solar winds.[5] Calculations of the loss of carbon dioxide from the atmosphere of Mars, resulting from scavenging of ions by the solar wind, indicate that the dissipation of the magnetic field of Mars caused a near total loss of its atmosphere.[6][7]

text: The study of past magnetic field of the Earth is known as paleomagnetism.[8] The polarity of the Earth's magnetic field is recorded in igneous rocks, and reversals of the field are thus detectable as "stripes" centered on mid-ocean ridges where the sea floor is spreading, while the stability of the geomagnetic poles between reversals has allowed paleomagnetists to track the past motion of continents. Reversals also provide the basis for magnetostratigraphy, a way of dating rocks and sediments.[9] The field also magnetizes the crust, and magnetic anomalies can be used to search for deposits of metal ores.[10]

text: Humans have used compasses for direction finding since the 11th century A.D. and for navigation since the 12th century.[11] Although the magnetic declination does shift with time, this wandering is slow enough that a simple compass remains useful for navigation. Using magnetoreception various other organisms, ranging from some types of bacteria to pigeons, use the Earth's magnetic field for orientation and navigation.

text: Main characteristics[edit]

text: Description[edit]

text: At any location, the Earth's magnetic field can be represented by a three-dimensional vector. A typical procedure for measuring its direction is to use a compass to determine the direction of magnetic North. Its angle relative to true North is the declination (D) or variation. Facing magnetic North, the angle the field makes with the horizontal is the inclination (I) or magnetic dip. The intensity (F) of the field is proportional to the force it exerts on a magnet. Another common representation is in X (North), Y (East) and Z (Down) coordinates.[12]

text: Intensity[edit]

text: The intensity of the field is often measured in gauss (G), but is generally reported in nanoteslas (nT), with 1 G = 100,000 nT. A nanotesla is also referred to as a gamma (γ).[13]   The tesla is the SI unit of the magnetic field, B.  The Earth's field ranges between approximately 25,000 and 65,000 nT (0.25–0.65 G). By comparison, a strong refrigerator magnet has a field of about 10,000,000 nanoteslas (100 G).[14]

text: A map of intensity contours is called an isodynamic chart. As the World Magnetic Model shows, the intensity tends to decrease from the poles to the equator. A minimum intensity occurs in the South Atlantic Anomaly over South America while there are maxima over northern Canada, Siberia, and the coast of Antarctica south of Australia.[15]

text: Inclination[edit]

text: The inclination is given by an angle that can assume values between -90° (up) to 90° (down). In the northern hemisphere, the field points downwards. It is straight down at the North Magnetic Pole and rotates upwards as the latitude decreases until it is horizontal (0°) at the magnetic equator. It continues to rotate upwards until it is straight up at the South Magnetic Pole. Inclination can be measured with a dip circle.

text: An isoclinic chart (map of inclination contours) for the Earth's magnetic field is shown below.

text: Declination[edit]

text: Declination is positive for an eastward deviation of the field relative to true north. It can be estimated by comparing the magnetic north/south heading on a compass with the direction of a celestial pole. Maps typically include information on the declination as an angle or a small diagram showing the relationship between magnetic north and true north. Information on declination for a region can be represented by a chart with isogonic lines (contour lines with each line representing a fixed declination).

text: Geographical variation[edit]

text: Components of the Earth's magnetic field at the surface from the World Magnetic Model for 2015.[15]

text:
Intensity

Inclination

Declination

text: Dipolar approximation[edit]

text: Near the surface of the Earth, its magnetic field can be closely approximated by the field of a magnetic dipole positioned at the center of the Earth and tilted at an angle of about 11° with respect to the rotational axis of the Earth.[13] The dipole is roughly equivalent to a powerful bar magnet, with its south pole pointing towards the geomagnetic North Pole.[16] This may seem surprising, but the north pole of a magnet is so defined because, if allowed to rotate freely, it points roughly northward (in the geographic sense). Since the north pole of a magnet attracts the south poles of other magnets and repels the north poles, it must be attracted to the south pole of Earth's magnet. The dipolar field accounts for 80–90% of the field in most locations.[12]

text: Magnetic poles[edit]

text: Historically, the north and south poles of a magnet were first defined by the Earth's magnetic field, not vice versa, since one of the first uses for a magnet was as a compass needle. Its North pole was defined as the pole that would be attracted by the Earth's North Magnetic Pole when the magnet was suspended so it could turn freely. Since opposite poles attract, the North Magnetic Pole of the Earth is really the south pole of its magnetic field (the place where the field is directed downward into the Earth).[17][18][19][20]

text: The positions of the magnetic poles can be defined in at least two ways: locally or globally.[21] The local definition is the point where the magnetic field is vertical.[22] This can be determined by measuring the inclination. The inclination of the Earth's field is 90° (downwards) at the North Magnetic Pole and -90° (upwards) at the South Magnetic Pole. The two poles wander independently of each other and are not directly opposite each other on the globe. They can migrate rapidly: movements of up to 40 kilometres (25 mi) per year have been observed for the North Magnetic Pole. Over the last 180 years, the North Magnetic Pole has been migrating northwestward, from Cape Adelaide in the Boothia Peninsula in 1831 to 600 kilometres (370 mi) from Resolute Bay in 2001.[23] The magnetic equator is the line where the inclination is zero (the magnetic field is horizontal).

text: The global definition of the Earth's field is based on a mathematical model. If a line is drawn through the center of the Earth, parallel to the moment of the best-fitting magnetic dipole, the two positions where it intersects the Earth's surface are called the North and South geomagnetic poles. If the Earth's magnetic field were perfectly dipolar, the geomagnetic poles and magnetic dip poles would coincide and compasses would point towards them. However, the Earth's field has a significant non-dipolar contribution, so the poles do not coincide and compasses do not generally point at either.

text: Magnetosphere[edit]

text: Earth's magnetic field, predominantly dipolar at its surface, is distorted further out by the solar wind. This is a stream of charged particles leaving the Sun's corona and accelerating to a speed of 200 to 1000 kilometres per second. They carry with them a magnetic field, the interplanetary magnetic field (IMF).[24]

text:
The solar wind exerts a pressure, and if it could reach Earth's atmosphere it would erode it. However, it is kept away by the pressure of the Earth's magnetic field. The magnetopause, the area where the pressures balance, is the boundary of the magnetosphere. Despite its name, the magnetosphere is asymmetric, with the sunward side being about 10 Earth radii out but the other side stretching out in a magnetotail that extends beyond 200 Earth radii.[25]
Sunward of the magnetopause is the bow shock, the area where the solar wind slows abruptly.[24]

text: Inside the magnetosphere is the plasmasphere, a donut-shaped region containing low-energy charged particles, or plasma. This region begins at a height of 60 km, extends up to 3 or 4 Earth radii, and includes the ionosphere. This region rotates with the Earth.[25] There are also two concentric tire-shaped regions, called the Van Allen radiation belts, with high-energy ions (energies from 0.1 to 10 million electron volts (MeV)). The inner belt is 1–2 Earth radii out while the outer belt is at 4–7 Earth radii. The plasmasphere and Van Allen belts have partial overlap, with the extent of overlap varying greatly with solar activity.[26]

text: As well as deflecting the solar wind, the Earth's magnetic field deflects cosmic rays, high-energy charged particles that are mostly from outside the Solar system. (Many cosmic rays are kept out of the Solar system by the Sun's magnetosphere, or heliosphere.[27]) By contrast, astronauts on the Moon risk exposure to radiation. Anyone who had been on the Moon's surface during a particularly violent solar eruption in 2005 would have received a lethal dose.[24]

text: Some of the charged particles do get into the magnetosphere. These spiral around field lines, bouncing back and forth between the poles several times per second. In addition, positive ions slowly drift westward and negative ions drift eastward, giving rise to a ring current. This current reduces the magnetic field at the Earth's surface.[24] Particles that penetrate the ionosphere and collide with the atoms there give rise to the lights of the aurorae and also emit X-rays.[25]

text: The varying conditions in the magnetosphere, known as space weather, are largely driven by solar activity. If the solar wind is weak, the magnetosphere expands; while if it is strong, it compresses the magnetosphere and more of it gets in. Periods of particularly intense activity, called geomagnetic storms, can occur when a coronal mass ejection erupts above the Sun and sends a shock wave through the Solar System. Such a wave can take just two days to reach the Earth. Geomagnetic storms can cause a lot of disruption; the "Halloween" storm of 2003 damaged more than a third of NASA's satellites. The largest documented storm occurred in 1859. It induced currents strong enough to short out telegraph lines, and aurorae were reported as far south as Hawaii.[24][28]

text: Time dependence[edit]

text: Short-term variations[edit]

text: The geomagnetic field changes on time scales from milliseconds to millions of years. Shorter time scales mostly arise from currents in the ionosphere (ionospheric dynamo region) and magnetosphere, and some changes can be traced to geomagnetic storms or daily variations in currents. Changes over time scales of a year or more mostly reflect changes in the Earth's interior, particularly the iron-rich core.[12]

text: Frequently, the Earth's magnetosphere is hit by solar flares causing geomagnetic storms, provoking displays of aurorae. The short-term instability of the magnetic field is measured with the K-index.[29]

text: Data from THEMIS show that the magnetic field, which interacts with the solar wind, is reduced when the magnetic orientation is aligned between Sun and Earth – opposite to the previous hypothesis. During forthcoming solar storms, this could result in blackouts and disruptions in artificial satellites.[30]

text: Secular variation[edit]

text: Changes in Earth's magnetic field on a time scale of a year or more are referred to as secular variation. Over hundreds of years, magnetic declination is observed to vary over tens of degrees.[12] A movie on the right shows how global declinations have changed over the last few centuries.[31]

text: The direction and intensity of the dipole change over time. Over the last two centuries the dipole strength has been decreasing at a rate of about 6.3% per century.[12] At this rate of decrease, the field would be negligible in about 1600 years.[32] However, this strength is about average for the last 7 thousand years, and the current rate of change is not unusual.[33]

text: A prominent feature in the non-dipolar part of the secular variation is a westward drift at a rate of about 0.2 degrees per year.[32] This drift is not the same everywhere and has varied over time. The globally averaged drift has been westward since about 1400 AD but eastward between about 1000 AD and 1400 AD.[34]

text: Changes that predate magnetic observatories are recorded in archaeological and geological materials. Such changes are referred to as paleomagnetic secular variation or paleosecular variation (PSV). The records typically include long periods of small change with occasional large changes reflecting geomagnetic excursions and reversals.[35]

text: Magnetic field reversals[edit]

text: Although generally Earth's field is approximately dipolar, with an axis that is nearly aligned with the rotational axis, occasionally the North and South geomagnetic poles trade places. Evidence for these geomagnetic reversals can be found in basalts, sediment cores taken from the ocean floors, and seafloor magnetic anomalies.[36] Reversals occur nearly randomly in time, with intervals between reversals ranging from less than 0.1 million years to as much as 50 million years. The most recent geomagnetic reversal, called the Brunhes–Matuyama reversal, occurred about 780,000 years ago.[23][37] A related phenomenon, a geomagnetic excursion, amounts to an incomplete reversal, with no change in polarity.[38][39] The Laschamp event is an example of an excursion, it having occurred during the last ice age (41,000 years ago).

text: The past magnetic field is recorded mostly by strongly magnetic minerals, particularly iron oxides such as magnetite, that can carry a permanent magnetic moment. This remanent magnetization, or remanence, can be acquired in more than one way. In lava flows, the direction of the field is "frozen" in small minerals as they cool, giving rise to a thermoremanent magnetization. In sediments, the orientation of magnetic particles acquires a slight bias towards the magnetic field as they are deposited on an ocean floor or lake bottom. This is called detrital remanent magnetization.[8]

text: Thermoremanent magnetization is the main source of the magnetic anomalies around mid-ocean ridges. As the seafloor spreads, magma wells up from the mantle, cools to form new basaltic crust on both sides of the ridge, and is carried away from it by seafloor spreading. As it cools, it records the direction of the Earth's field. When the Earth's field reverses, new basalt records the reversed direction. The result is a series of stripes that are symmetric about the ridge. A ship towing a magnetometer on the surface of the ocean can detect these stripes and infer the age of the ocean floor below. This provides information on the rate at which seafloor has spread in the past.[8]

text: Radiometric dating of lava flows has been used to establish a geomagnetic polarity time scale, part of which is shown in the image. This forms the basis of magnetostratigraphy, a geophysical correlation technique that can be used to date both sedimentary and volcanic sequences as well as the seafloor magnetic anomalies.[8]

text: Studies of lava flows on Steens Mountain, Oregon, indicate that the magnetic field could have shifted at a rate of up to 6 degrees per day at some time in Earth's history, which significantly challenges the popular understanding of how the Earth's magnetic field works.[40] This finding was later attributed to unusual rock magnetic properties of the lava flow under study, not rapid field change, by one of the original authors of the 1995 study.[41]

text: Temporary dipole tilt variations that take the dipole axis across the equator and then back to the original polarity are known as excursions.[39]

text: Earliest appearance[edit]

text: Paleomagnetic studies of Paleoarchean lava in Australia and conglomerate in South Africa have concluded that the magnetic field has been present since at least about 3,450 million years ago.[42][43][44]

text: Future[edit]

text: At present, the overall geomagnetic field is becoming weaker; the present strong deterioration corresponds to a 10–15% decline over the last 150 years and has accelerated in the past several years; geomagnetic intensity has declined almost continuously from a maximum 35% above the modern value achieved approximately 2,000 years ago. The rate of decrease and the current strength are within the normal range of variation, as shown by the record of past magnetic fields recorded in rocks.

text: The nature of Earth's magnetic field is one of heteroscedastic fluctuation. An instantaneous measurement of it, or several measurements of it across the span of decades or centuries, are not sufficient to extrapolate an overall trend in the field strength. It has gone up and down in the past for unknown reasons. Also, noting the local intensity of the dipole field (or its fluctuation) is insufficient to characterize Earth's magnetic field as a whole, as it is not strictly a dipole field. The dipole component of Earth's field can diminish even while the total magnetic field remains the same or increases.

text: The Earth's magnetic north pole is drifting from northern Canada towards Siberia with a presently accelerating rate—10 kilometres (6.2 mi) per year at the beginning of the 20th century, up to 40 kilometres (25 mi) per year in 2003,[23] and since then has only accelerated.[45]

text: Physical origin[edit]

text: The Earth's magnetic field is believed to be generated by electric currents in the conductive material of its core, created by convection currents due to heat escaping from the core.  However the process is complex, and computer models that reproduce some of its features have only been developed in the last few decades.

text: Earth's core and the geodynamo[edit]

text: The Earth and most of the planets in the Solar System, as well as the Sun and other stars, all generate magnetic fields through the motion of electrically conducting fluids.[47] The Earth's field originates in its core. This is a region of iron alloys extending to about 3400 km (the radius of the Earth is 6370 km). It is divided into a solid inner core, with a radius of 1220 km, and a liquid outer core.[48] The motion of the liquid in the outer core is driven by heat flow from the inner core, which is about 6,000 K (5,730 °C; 10,340 °F), to the core-mantle boundary, which is about 3,800 K (3,530 °C; 6,380 °F).[49]  The heat is generated by potential energy released by heavier materials sinking toward the core (planetary differentiation, the iron catastrophe) as well as decay of radioactive elements in the interior.  The pattern of flow is organized by the rotation of the Earth and the presence of the solid inner core.[50]

text: The mechanism by which the Earth generates a magnetic field is known as a dynamo.[47] The magnetic field is generated by a feedback loop: current loops generate magnetic fields (Ampère's circuital law); a changing magnetic field generates an electric field (Faraday's law); and the electric and magnetic fields exert a force on the charges that are flowing in currents (the Lorentz force).[51] These effects can be combined in a partial differential equation for the magnetic field called the magnetic induction equation,

text: where u is the velocity of the fluid; B is the magnetic B-field; and η=1/σμ is the magnetic diffusivity, which is inversely proportional to the product of the electrical conductivity σ and the permeability μ .[52]  The term ∂B/∂t is the time derivative of the field; ∇2 is the Laplace operator and ∇× is the curl operator.

text: The first term on the right hand side of the induction equation is a diffusion term. In a stationary fluid, the magnetic field declines and any concentrations of field spread out. If the Earth's dynamo shut off, the dipole part would disappear in a few tens of thousands of years.[52]

text:
In a perfect conductor (

σ
=
∞

{\displaystyle \sigma =\infty \;}

), there would be no diffusion. By Lenz's law, any change in the magnetic field would be immediately opposed by currents, so the flux through a given volume of fluid could not change. As the fluid moved, the magnetic field would go with it. The theorem describing this effect is called the frozen-in-field theorem. Even in a fluid with a finite conductivity, new field is generated by stretching field lines as the fluid moves in ways that deform it. This process could go on generating new field indefinitely, were it not that as the magnetic field increases in strength, it resists fluid motion.[52]

text: The motion of the fluid is sustained by convection, motion driven by buoyancy. The temperature increases towards the center of the Earth, and the higher temperature of the fluid lower down makes it buoyant. This buoyancy is enhanced by chemical separation: As the core cools, some of the molten iron solidifies and is plated to the inner core. In the process, lighter elements are left behind in the fluid, making it lighter. This is called compositional convection. A Coriolis effect, caused by the overall planetary rotation, tends to organize the flow into rolls aligned along the north-south polar axis.[50][52]

text: A dynamo can amplify a magnetic field, but it needs a "seed" field to get it started.[52] For the Earth, this could have been an external magnetic field. Early in its history the Sun went through a T-Tauri phase in which the solar wind would have had a magnetic field orders of magnitude larger than the present solar wind.[53] However, much of the field may have been screened out by the Earth's mantle. An alternative source is currents in the core-mantle boundary driven by chemical reactions or variations in thermal or electric conductivity. Such effects may still provide a small bias that are part of the boundary conditions for the geodynamo.[54]

text: The average magnetic field in the Earth's outer core was calculated to be 25 gausses, 50 times stronger than the field at the surface.[55]

text: Numerical models[edit]

text: Simulating the geodynamo requires numerically solving a set of nonlinear partial differential equations for the magnetohydrodynamics (MHD) of the Earth's interior. Simulation of the MHD equations is performed on a 3D grid of points and the fineness of the grid, which in part determines the realism of the solutions, is limited mainly by computer power. For decades, theorists were confined to creating kinematic dynamo computer models in which the fluid motion is chosen in advance and the effect on the magnetic field calculated. Kinematic dynamo theory was mainly a matter of trying different flow geometries and testing whether such geometries could sustain a dynamo.[56]

text: The first self-consistent dynamo models, ones that determine both the fluid motions and the magnetic field, were developed by two groups in 1995, one in Japan[57] and one in the United States.[1][58] The latter received attention because it successfully reproduced some of the characteristics of the Earth's field, including geomagnetic reversals.[56]

text: Currents in the ionosphere and magnetosphere[edit]

text: Electric currents induced in the ionosphere generate magnetic fields (ionospheric dynamo region). Such a field is always generated near where the atmosphere is closest to the Sun, causing daily alterations that can deflect surface magnetic fields by as much as one degree. Typical daily variations of field strength are about 25 nanoteslas (nT) (one part in 2000), with variations over a few seconds of typically around 1 nT (one part in 50,000).[59]

text: Measurement and analysis[edit]

text: Detection[edit]

text: The Earth's magnetic field strength was measured by Carl Friedrich Gauss in 1832[60] and has been repeatedly measured since then, showing a relative decay of about 10% over the last 150 years.[61] The Magsat satellite and later satellites have used 3-axis vector magnetometers to probe the 3-D structure of the Earth's magnetic field. The later Ørsted satellite allowed a comparison indicating a dynamic geodynamo in action that appears to be giving rise to an alternate pole under the Atlantic Ocean west of South Africa.[62]

text: Governments sometimes operate units that specialize in measurement of the Earth's magnetic field. These are geomagnetic observatories, typically part of a national Geological survey, for example the British Geological Survey's Eskdalemuir Observatory. Such observatories can measure and forecast magnetic conditions such as magnetic storms that sometimes affect communications, electric power, and other human activities.

text: The International Real-time Magnetic Observatory Network, with over 100 interlinked geomagnetic observatories around the world, has been recording the Earth's magnetic field since 1991.

text: The military determines local geomagnetic field characteristics, in order to detect anomalies in the natural background that might be caused by a significant metallic object such as a submerged submarine. Typically, these magnetic anomaly detectors are flown in aircraft like the UK's Nimrod or towed as an instrument or an array of instruments from surface ships.

text: Commercially, geophysical prospecting companies also use magnetic detectors to identify naturally occurring anomalies from ore bodies, such as the Kursk Magnetic Anomaly.

text: Crustal magnetic anomalies[edit]

text: Magnetometers detect minute deviations in the Earth's magnetic field caused by iron artifacts, kilns, some types of stone structures, and even ditches and middens in archaeological geophysics. Using magnetic instruments adapted from airborne magnetic anomaly detectors developed during World War II to detect submarines,[64] the magnetic variations across the ocean floor have been mapped. Basalt — the iron-rich, volcanic rock making up the ocean floor[65] — contains a strongly magnetic mineral (magnetite) and can locally distort compass readings. The distortion was recognized by Icelandic mariners as early as the late 18th century.[66] More important, because the presence of magnetite gives the basalt measurable magnetic properties, these magnetic variations have provided another means to study the deep ocean floor. When newly formed rock cools, such magnetic materials record the Earth's magnetic field.[66]

text: Statistical models[edit]

text: Each measurement of the magnetic field is at a particular place and time. If an accurate estimate of the field at some other place and time is needed, the measurements must be converted to a model and the model used to make predictions.

text: Spherical harmonics[edit]

text: The most common way of analyzing the global variations in the Earth's magnetic field is to fit the measurements to a set of spherical harmonics. This was first done by Carl Friedrich Gauss.[67] Spherical harmonics are functions that oscillate over the surface of a sphere. They are the product of two functions, one that depends on latitude and one on longitude. The function of longitude is zero along zero or more great circles passing through the North and South Poles; the number of such nodal lines is the absolute value of the order m. The function of latitude is zero along zero or more latitude circles; this plus the order is equal to the degree ℓ. Each harmonic is equivalent to a particular arrangement of magnetic charges at the center of the Earth. A monopole is an isolated magnetic charge, which has never been observed. A dipole is equivalent to two opposing charges brought close together and a quadrupole to two dipoles brought together. A quadrupole field is shown in the lower figure on the right.[12]

text: Spherical harmonics can represent any scalar field (function of position) that satisfies certain properties. A magnetic field is a vector field, but if it is expressed in Cartesian components X, Y, Z, each component is the derivative of the same scalar function called the magnetic potential. Analyses of the Earth's magnetic field use a modified version of the usual spherical harmonics that differ by a multiplicative factor. A least-squares fit to the magnetic field measurements gives the Earth's field as the sum of spherical harmonics, each multiplied by the best-fitting  Gauss coefficient gmℓ or hmℓ.[12]

text: The lowest-degree Gauss coefficient, g00, gives the contribution of an isolated magnetic charge, so it is zero. The next three coefficients – g10, g11, and h11 – determine the direction and magnitude of the dipole contribution. The best fitting dipole is tilted at an angle of about 10° with respect to the rotational axis, as described earlier.[12]

text: Radial dependence[edit]

text: Spherical harmonic analysis can be used to distinguish internal from external sources if measurements are available at more than one height (for example, ground observatories and satellites). In that case, each term with coefficient gmℓ or hmℓ can be split into two terms: one that decreases with radius as 1/rℓ+1 and one that increases with radius as rℓ. The increasing terms fit the external sources (currents in the ionosphere and magnetosphere). However, averaged over a few years the external contributions average to zero.[12]

text: The remaining terms predict that the potential of a dipole source (ℓ=1) drops off as 1/r2. The magnetic field, being a derivative of the potential, drops off as 1/r3. Quadrupole terms drop off as 1/r4, and higher order terms drop off increasingly rapidly with the radius. The radius of the outer core is about half of the radius of the Earth. If the field at the core-mantle boundary is fit to spherical harmonics, the dipole part is smaller by a factor of about 8 at the surface, the quadrupole part by a factor of 16, and so on. Thus, only the components with large wavelengths can be noticeable at the surface. From a variety of arguments, it is usually assumed that only terms up to degree 14 or less have their origin in the core. These have wavelengths of about 2,000 kilometres (1,200 mi) or less. Smaller features are attributed to crustal anomalies.[12]

text: Global models[edit]

text: The International Association of Geomagnetism and Aeronomy maintains a standard global field model called the International Geomagnetic Reference Field. It is updated every five years. The 11th-generation model, IGRF11, was developed using data from satellites (Ørsted, CHAMP and SAC-C) and a world network of geomagnetic observatories.[68] The spherical harmonic expansion was truncated at degree 10, with 120 coefficients, until 2000. Subsequent models are truncated at degree 13 (195 coefficients).[69]

text: Another global field model, called the World Magnetic Model, is produced jointly by the United States National Centers for Environmental Information (formerly the National Geophysical Data Center) and the British Geological Survey. This model truncates at degree 12 (168 coefficients) with an approximate spatial resolution of 3,000 kilometers. It is the model used by the United States Department of Defense, the Ministry of Defence (United Kingdom), the United States Federal Aviation Administration (FAA), the North Atlantic Treaty Organization (NATO), and the International Hydrographic Office as well as in many civilian navigation systems.[70]

text: A third model, produced by the Goddard Space Flight Center (NASA and GSFC) and the Danish Space Research Institute, uses a "comprehensive modeling" approach that attempts to reconcile data with greatly varying temporal and spatial resolution from ground and satellite sources.[71]

text: For users with higher accuracy needs, the United States National Centers for Environmental Information developed  the Enhanced Magnetic Model (EMM), which extends to degree and order 790 and resolves magnetic anomalies down to a wavelength of 56 kilometers. It was compiled from satellite, marine, aeromagnetic and ground magnetic surveys. As of  2018[update], the latest version, EMM2017, includes data from The European Space Agency's Swarm satellite mission.[72]

text: Biomagnetism[edit]

text: Animals including birds and turtles can detect the Earth's magnetic field, and use the field to navigate during migration.[73] Some researchers have found that cows and wild deer tend to align their bodies north-south while relaxing, but not when the animals are under high-voltage power lines, suggesting that magnetism is responsible.[74][75] Other researchers reported in 2011 that they could not replicate those findings using different Google Earth images.[76]

text: Researchers found out that very weak electromagnetic fields disrupt the magnetic compass used by European robins and other songbirds to navigate using the Earth's magnetic field. Neither power lines nor cellphone signals are to blame for the electromagnetic field effect on the birds;[77] instead, the culprits have frequencies between 2 kHz and 5 MHz. These include AM radio signals and ordinary electronic equipment that might be found in businesses or private homes.[78]


document_title: Courteney Cox

question_text: who got married in real life from friends

root

text: Courteney Cox

text: Early life[edit]

text: Cox was born and raised in Birmingham, Alabama.[3][4] She is a daughter of businessman Richard Lewis Cox (January 28, 1931 – September 3, 2001)[5] and Courteney Copeland (née Bass).[6][7] Cox has two older sisters, Virginia and Dorothy, and an older brother, Richard Jr. Her parents divorced in 1974 and her mother then married businessman Hunter Copeland (uncle to music promoter and business manager Ian Copeland).[8] After graduating from Mountain Brook High School, Cox left for Mount Vernon College in Washington, D.C., but did not complete her architecture course, opting instead to pursue a career in modeling and acting.[9] She has English ancestry.[10][11][12]

tag: p

text: Career[edit]

text: Early career[edit]

text: Cox appeared in the 1984 music video for Bruce Springsteen's "Dancing in the Dark" as the young woman pulled onstage at the St. Paul Civic Center to dance with Springsteen. Her early television work includes a starring role in the short-lived television series Misfits of Science (1985), and later in a recurring role as Lauren Miller, the girlfriend of Alex P. Keaton (Michael J. Fox) in the TV series Family Ties (1987–89). Her early film roles include Masters of the Universe (1987), Cocoon: The Return (1988), and I'll Be Home for Christmas (1988). She played Jewel Jagger, the hard-as-nails assistant of Larry Burrows (James Belushi), in Mr. Destiny (1990). In 1993, she co-starred in the short-lived CBS sitcom The Trouble with Larry with Bronson Pinchot and Perry King. The following year, shortly before the debut of the sitcom Friends, Cox appeared with Jim Carrey in Ace Ventura: Pet Detective and as Jerry Seinfeld's girlfriend, Meryl, in the Seinfeld episode "The Wife". In 1995, she was cast in Toad the Wet Sprocket's music video "Good Intentions". The song is also on the Friends soundtrack.

text: Friends[edit]

text: Later in 1994, Cox was asked to audition for the part of Rachel Green on a new sitcom, Friends; she was cast as Monica Geller, instead.[13]

text: At first the most famous cast member of the new show, Cox joined fellow castmates Jennifer Aniston (Rachel Green), Lisa Kudrow (Phoebe Buffay), Matt LeBlanc (Joey Tribbiani), Matthew Perry (Chandler Bing) and David Schwimmer (Ross Geller) for what became her most famous role, lasting for 10 seasons until 2004. According to the Guinness Book of World Records (2005), Cox (along with her female costars) became the highest-paid TV actress of all time, with her US$1 million-per-episode paycheck for the final two seasons of Friends.

text: Between seasons five and six, Cox married David Arquette, and changed her name to Courteney Cox Arquette. An in-joke reference to this is made in the beginning credits of the episode "The One After Vegas", where the rest of the cast has "Arquette" added to their names. The dedication "For Courteney and David, who did get married" – a reference to Monica and Chandler's decision not to marry in the episode – appears during the fade out to the tag scene.[14]

text: Film career[edit]

text: Cox also appeared in the high-profile Hollywood films, Scream (1996), Scream 2 (1997), and Scream 3 (2000), as reporter Gale Weathers. She met her husband, David Arquette, who played her on-screen love interest Dwight "Dewey" Riley, while filming the first Scream film. Both Cox and Arquette reprised their respective roles from the Scream trilogy in 2011's Scream 4. The film was released in theaters April 15, 2011.[15]

text: Her other films include Ace Ventura: Pet Detective with Jim Carrey (1994), The Runner (1999), 3000 Miles to Graceland (2001), and The Shrink Is In (2001). In late 2003, Cox and Arquette produced one season of the reality television series Mix It Up. The lifestyle show, which aired on the We cable channel, struggled with low ratings and was not renewed for a second season.

text: Later work[edit]

text: After the conclusion of Friends, Cox was producer Marc Cherry's first choice to be offered a starring role as Susan Mayer on Desperate Housewives, but Cox was unavailable due to her pregnancy and the role later went to Teri Hatcher.[16] A few years later, Cox signed a deal with ABC Studios (formerly Touchstone Television) to star in her own series.

text: After Friends, Cox starred in the independent film November (2005) which had a limited theatrical release; costarred with Tim Allen in the critically derided Zoom (2006), and cameoed in the big-budget remake of The Longest Yard (2005) as Lena, the girlfriend of Paul Crewe (Adam Sandler). She voiced Daisy in the animated film Barnyard (2006). A Friends reunion film was rumored to be in production following the success of Sex and the City (2008),[17] but this has been denied by Warner Bros. and others.

text: Cox starred as Lucy Spiller, a cynical tabloid editor, in Dirt (2007), a television drama for FX. Cox and her husband David Arquette were the executive producers of the series.[18] According to Cox, the series was canceled after the second season in 2008.[19] In July 2008, Entertainment Weekly announced that Cox had signed on to star in a three-episode arc for the television series Scrubs.[20]

text: In 2009, Cox began her roles as the star of the single-camera comedy series on ABC called Cougar Town, playing a newly single 40-year-old mother on the hunt for new experiences.[21][22][23] It is notably Cox's most successful work since Friends. The show's third season was to premiere in November 2011, but was moved to February 14, 2012. In the third season, Cox directed two of the show's 15 episodes of that season. The show's fourth season premiered on January 8, 2013. She also starred in a three-episode arc on former Friends co-star Lisa Kudrow's online web series Web Therapy (2009).

text: In June 2012, Cox directed and made a cameo appearance in a Lifetime television movie called Talhotblond, which premiered on the network on June 23, 2012.[24]

text: Personal life[edit]

text: Cox's previous boyfriends include rock promoter Ian Copeland,[25] Michael Keaton, and Adam Duritz of Counting Crows.

text: Cox married actor David Arquette on June 12, 1999.[26] Their daughter, Coco Riley Arquette, was born on June 13, 2004,[27][28][29] and Cox suffered from postpartum depression.[30] Her close friend Jennifer Aniston is Coco's godmother.[31] On October 11, 2010, it was announced that Cox and Arquette had separated, though they still maintain a close friendship and ongoing business relationship in Coquette Productions.[32][33][34] In June 2012, Arquette filed for divorce after nearly two years of separation from Cox.[35] The divorce became final in May 2013.[36]

text: Cox began dating Snow Patrol band member Johnny McDaid in late 2013.[37] The couple announced their engagement on Twitter on June 26, 2014.[38]

text: On the Season 9 premiere episode of the American genealogy documentary show Who Do You Think You Are?, it was discovered that Cox is descended from several key players involved in the deposing and likely murder of King Edward II of England, and also a direct descendant of William the Conqueror (her 26x great-grandfather).[39] Cox is practitioner of Budokan karate.[40][41]

text: Filmography[edit]

text: Film[edit]

text:
Year
Title
Role
Notes

1987
Down Twisted
Tarah
film debut

1987
Masters of the Universe
Julie Winston

1988
Cocoon: The Return
Sara

1990
Shaking the Tree
Kathleen

1990
Mr. Destiny
Jewel Jagger

1991
Blue Desert
Lisa Roberts

1992
The Opposite Sex and How to Live with Them
Carrie Davenport

1994
Ace Ventura: Pet Detective
Melissa Robinson

1996
Scream
Gale Weathers

1997
Commandments
Rachel Luce

1997
Scream 2
Gale Weathers

1999
The Runner
Karina

2000
Scream 3
Gale Weathers

2001
3000 Miles to Graceland
Cybil Waingrow

2001
The Shrink Is In
Samantha Crumb
also Executive Producer

2001
Get Well Soon
Lily Charles

2004
November
Sophie Jacobs

2005
The Longest Yard
Lena
uncredited

2006
Barnyard
Daisy the Cow
voice role

2006
Zoom
Marsha Holloway

2006
The Tripper
Dog Lover Hippie
credited as Courteney Cox-Arquette
also Executive Producer

2008
Alien Love Triangle
Alice
Short Film

2008
The Monday Before Thanksgiving
Cece
Short Film
also Director/Writer

2008
Bedtime Stories
Wendy

2008
The Butler's in Love

Short Film
Executive Producer

2011
Scream 4
Gale Weathers-Riley

2014
Just Before I Go

Director/Producer

2012
Got Rights
Celebrity
Short Film

2016
Mothers and Daughters
Beth

tag: table

text: Television[edit]

text:
Year
Title
Role
Notes

1984
As the World Turns
Bunny
television debut
Episode: "1.5000"

1985
Code Name: Foxfire
Flight Attendant
uncredited
Episode: "Slay It Again, Sam"

1985-1986
Misfits of Science
Gloria Dinallo
series regular; 16 episodes

1986
The Love Boat
Carol
Episode: "Daredevil/Picture Me a Spy/Sleeper"

1986
Sylvan in Paradise
Lucy Apple
Television Movie

1986
Murder, She Wrote
Carol Bannister
2 episodes

1987
If It's Tuesday, It Still Must Be Belgium
Hana Wyskocki
Television Movie

1987
I'll Be Home for Christmas
Nora Bundy
Television Movie

1987-1989
Family Ties
Lauren Miller
recurring role; 19 episodes

1989
Roxanne: The Prize Pulitzer
Jacquie Kimberly
Television Movie

1989
Till We Meet Again
Marie-Frederique 'Freddy' de Lancel
Television Miniseries
2 episodes

1990
Curiosity Kills
Gwen
Television Movie

1991
Morton & Hayes
Princess Lucy
Episode: "Oafs Overboard"

1992
Battling for Baby
Katherine
Television Movie

1992
Dream On
Alisha
Episode: "Come and Knock on Our Door..."

1993
The Trouble with Larry
Gabriella Easden
recurring role; 7 episodes

1994
Seinfeld
Meryl
Episode: "The Wife"

1994-2004
Friends
Monica Geller
series regular; 236 episodes

1995
Sketch Artist II: Hands That See
Emmy
Television Movie

1995
The Larry Sanders Show
Herself
Episode: "Larry's Big Idea"

1995
Saturday Night LIVE!
Herself
Host
Episode: "Courteney Cox/Dave Matthews Band"

1999
Happily Every After: Fairy Tales for Every Child
Emerald Salt Port
voice role
Episode: "Three Little Pigs"

2000
WCW Monday Nitro
Herself
credited as Courteney Cox-Arquette
Episode: "#5.33"

2003
MADtv
Herself
Episode: "#9.3"

2004
Mix It Up

4 episodes
Executive Producer

2005
Dirt Squirrel

Television Movie
Executive Producer

2005
Talk Show Diaries

Television Movie
Executive Producer

2005
The MidNightly News

Television Movie
Executive Producer

2005-2007
Daisy Does America

8 episodes
Executive Producer

2007-2008
Dirt
Lucy Spiller
series regular; 20 episodes
also Executive Producer

2009-2015
Cougar Town
Jules Cobb
series regular; 102 episodes
also Director/Executive Producer

2009
Scrubs
Dr. Maddox
3 episodes

2009
Web Therapy
Serena Duvall
Episode: "Psychic Analysis"

2011
Private Practice
Woman
uncredited
Episode: "Step One"

2012
TalhotBlond
Amanda
Television Movie
also Director/Producer

2013
Go On
Talia
Episode: "Matchup Problems"

2013
Tripaholics

Television Movie
Executive Producer

2014-2016
Drunk History
Edith Wilson
2 episodes

2014-2017
Celebrity Name Game
Herself
14 episodes
also Executive Producer

2015
Barley Famous
Herself
Episode: "Favorite Socks"

2016
Charity Case
Hailey
Television Movie
also Executive Producer

2016
Running Wild with Bear Grylls
Herself
Television Documentary
Episode: "Courteney Cox" S03E03

2017
Who Do You Think You Are?
Herself
Television Documentary
Episode: "Courteney Cox"

2017
Off Camera with Sam Jones
Herself
Episode: "Courteney Cox"

2017
The Gong Show
Herself
Guest Judge
Episode: "Will Arnett/Courteney Cox/Isla Fisher"

text: Other Work[edit]

text:
Year
Title
Role
Notes

1984
Bruce Springsteen: Dancing in the Dark
Woman
Music Video/Video Short

1996
Counting Crows: A Long Decemberr
Woman
Music Video/Video Short

2009
The Rembrandts: I'll Be There for You
Monica Geller
Music Video/Video Short

2009
Web Therapy
Serena DuVall
Web Series
3 episodes

text: Awards and Nominations[edit]

text: Courteney has received multiple awards and nominations throughout her career for her work in both film and television. Her most awarded role was as Monica Geller on the sitcom Friends (1994-2004), a role which she received a Screen Actors Guild award for Outstanding Performance by an Ensemble in a Comedy Series in 1996. Later she received a Golden Globe award nomination for her performance as Jules Cobb on the sitcom Cougar Town (2009-2015) for Best Lead Actress in a Television Series - Comedy or Musical in 2010.

text:
American Comedy awards

Year
Category
Title
Results
Lost to
Ref

1995
Funniest Supporting Female Performer in a Television Series
Friends
Nominated
Julia Louis-Dreyfus (Seinfeld)
[42]

1999
Nominated
Doris Roberts (Everybody Loves Raymond)
[43]

Blockbuster Entertainment awards

Year
Category
Title
Results
Lost to
Ref

1998
Favorite Actress - Horror
Scream 2
Nominated
Neve Campbell (Scream 2)
[44]

2001
Favorite Actress - Horror (Internet Only)
Scream 3
Nominated
Neve Campbell (Scream 3)
[45]

Critics Choice Television awards

Year
Category
Title
Results
Lost to
Ref

2011
Best Lead Actress in a Comedy Series
Cougar Town
Nominated
Tina Fey (30 Rock)
[46]

Gold Derby awards

Year
Category
Title
Results
Lost to
Ref

2010
Best Lead Actress in a Comedy Series
Cougar Town
Won

[47]

2011
Nominated
Amy Poehler (Parks and Recreation)
[48]

Golden Apple awards

Year
Category
Title
Results
Lost to
Ref

1995
Female Discovery of the Year

Won

[49]

Golden Globe awards

Year
Category
Title
Results
Lost to
Ref

2010
Best Lead Actress in a Television Series - Comedy or Musical
Cougar Town
Nominated
Toni Collette (United States of Tara)
[50]

Golden Raspberry awards

Year
Category
Title
Results
Lost to
Ref

2002
Worst Supporting Actress
3000 Miles to Graceland
Nominated
Estella Warren (Driven, Planet of the Apes)
[51]

Worst Screen Couple (shared with Kevin Costner)
Nominated
Tom Green (Freddy Got Fingered)

Online Film & Television Association awards

Year
Category
Title
Results
Lost to
Ref

1997
Best Ensemble in a Series
Friends
Nominated
Cast of (ER)
[52]

Best Ensemble in a Comedy Series
Won

1998
Best Ensemble in a Series
Nominated
Cast of (ER)
[53]

Best Ensemble in a Comedy Series
Nominated
Cast of (Ally McBeal)

1999
Nominated
[54]

2000
Nominated
Cast of (Will & Grace)
[55]

2001
Nominated
[56]

Nickelodeon Kid's Choice awards

Year
Category
Title
Results
Lost to
Ref

1997
Favorite Television Actress
Friends
Nominated
Tia & Tamera Mowry (Sister, Sister)
[57]

2000
Favorite Television Friends (shared with Jennifer Aniston, Lisa Kudrow)
Nominated
Ben Savage, Ryder Strong (Boy Meets World)
[58]

People's Choice awards

Year
Category
Title
Results
Lost to
Ref

1995
Favorite Performer in a New Television Program
Friends
Won

[59]

2011
Favorite Television Comedy Actress
Cougar Town
Nominated
Jane Lynch (Glee)
[60]

2012
Nominated
Lea Michele (Glee)
[61]

2014
Favorite Cable Television Actress
Nominated
Lucy Hale (Pretty Little Liars)
[62]

2015
Nominated
Angie Harmon (Rizzoli & Isles)
[63]

Saturn awards

Year
Category
Title
Results
Lost to
Ref

1998
Best Supporting Actress
Scream 2
Nominated
Gloria Stewart (Titanic)
[64]

Screen Actors Guild awards

Year
Category
Title
Results
Lost to
Ref

1996
Outstanding Performance by an Ensemble in a Comedy Series
Friends
Won

[65]

1999
Nominated
Cast of (Ally McBeal)
[66]

2000
Nominated
Cast of (Frasier)
[67]

2001
Nominated
Cast of (Will & Grace)
[68]

2002
Nominated
Cast of (Sex and the City)
[69]

2003
Nominated
Cast of (Everybody Loves Raymond)
[70]

2004
Nominated
Cast of (Sex and the City)
[71]

Teen Choice awards

Year
Category
Title
Results
Lost to
Ref

2000
Choice Movie - Chemistry (shared with David Arquette)
Scream 3
Won

[72]

2002
Choice TV Actress - Comedy
Friends
Nominated
Jennifer Aniston (Friends)
[73]

2003
Nominated
[74]

2005
Choice Movie - Hissy Fit
The Longest Yard
Nominated
Jon Heder (Napoleon Dynamite)
[75]

The Stinkers Bad Movie awards

Year
Category
Title
Results
Lost to
Ref

2001
Worst Supporting Actress
3000 Miles to Graceland
Nominated
Tori Spelling (Scary Movie 2)
[76]

Most Annoying Fake Accent - Female
Nominated
Jennifer Lopez (Angel Eyes)

2006
Worst Supporting Actress
Zoom
Nominated
Cindy Cheung (Lady in the Water)
[77]

The Streamy awards

Year
Category
Title
Results
Lost to
Ref

2010
Best Guest Star in a Web Series
Web Therapy
Nominated
Weird Al Yankovic (Know Your Meme)
[78]

TV Guide awards

Year
Category
Title
Results
Lost to
Ref

2000
Editor's Choice award
Friends
Won

[79]

TV Land awards

Year
Category
Title
Results
Lost to
Ref

2006
Most Wonderful Wedding (shared with Matthew Perry)
Friends
Nominated
Erin Moran, Scott Baio (Happy Days)
[80]

2007
Break-Up That Was So Bad It Was Good (shared with Michael J. Fox)
Family Ties
Nominated
Ted Danson, Shelley Long (Cheers)
[81]

Women in Film Crystal + Lucy awards

Year
Category
Title
Results
Lost to
Ref

2010
Lucy award

Won

[82]

Women's Image Network awards

Year
Category
Title
Results
Lost to
Ref

2010
Actress Comedy Series
Cougar Town
Nominated
Cheryl Hines (Curb Your Enthusiasm)
[83]