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Based on Your Reading of the Text, What Is the Origin of Earthã¢â‚¬â„¢s Magnetic Field? Quizlet

Written By Wednesday, 9 March 2022 Add Comment Edit

Magnetic field that extends from the Earth's outer and inner core to where it meets the solar wind

Computer simulation of Globe's field in a period of normal polarity betwixt reversals.[1] The lines represent magnetic field lines, blue when the field points towards the center and yellowish when away. The rotation axis of Earth is centered and vertical. The dumbo clusters of lines are inside Globe's core.[2]

Earth'south magnetic field, also known every bit the geomagnetic field, is the magnetic field that extends from World'south interior out into infinite, where it interacts with the solar wind, a stream of charged particles emanating from the Sun. The magnetic field is generated past electric currents due to the motion of convection currents of a mixture of molten atomic number 26 and nickel in World'south outer cadre: these convection currents are caused by estrus escaping from the core, a natural procedure called a geodynamo. The magnitude of Globe's magnetic field at its surface ranges from 25 to 65 μT (0.25 to 0.65 Yard).[3] Every bit an approximation, information technology is represented by a field of a magnetic dipole currently tilted at an angle of virtually 11° with respect to Earth's rotational axis, equally if there were an enormous bar magnet placed at that angle through the center of Earth. The North geomagnetic pole actually represents the Southward pole of World's magnetic field, and conversely the S geomagnetic pole corresponds to the n pole of Globe's magnetic field (because opposite magnetic poles attract and the north cease of a magnet, like a compass needle, points toward Earth's South magnetic field, i.e., the Due north geomagnetic pole near the Geographic Due north Pole). Equally of 2015, the North geomagnetic pole was located on Ellesmere Island, Nunavut, Canada.

While the North and Due south magnetic poles are normally located well-nigh the geographic poles, they slowly and continuously movement over geological time scales, but sufficiently slowly for ordinary compasses to remain useful for navigation. Yet, at irregular intervals averaging several hundred grand years, Earth's field reverses and the North and Southward Magnetic Poles respectively, abruptly switch places. These reversals of the geomagnetic poles leave a record in rocks that are of value to paleomagnetists in computing geomagnetic fields in the by. Such information in turn is helpful in studying the motions of continents and sea floors in the process of plate tectonics.

The magnetosphere is the region above the ionosphere that is divers by the extent of World's magnetic field in space. It extends several tens of thousands of kilometres into space, protecting Earth from the charged particles of the solar wind and catholic rays that would otherwise strip away the upper atmosphere, including the ozone layer that protects Earth from the harmful ultraviolet radiation.

Significance [edit]

Earth's magnetic field deflects most of the solar wind, whose charged particles would otherwise strip abroad 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 temper of Mars, resulting from scavenging of ions by the solar current of air, point that the dissipation of the magnetic field of Mars caused a near total loss of its atmosphere.[6] [7]

The study of the past magnetic field of the Earth is known as paleomagnetism.[eight] The polarity of the Earth'southward 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 immune paleomagnetism to track the past move of continents. Reversals also provide the basis for magnetostratigraphy, a way of dating rocks and sediments.[ix] The field also magnetizes the chaff, and magnetic anomalies tin can be used to search for deposits of metallic ores.[ten]

Humans have used compasses for direction finding since the 11th century A.D. and for navigation since the 12th century.[xi] Although the magnetic declination does shift with time, this wandering is slow enough that a simple compass tin can remain 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.

Characteristics [edit]

At whatsoever location, the Earth's magnetic field tin exist represented by a three-dimensional vector. A typical procedure for measuring its direction is to use a compass to determine the management of magnetic North. Its angle relative to truthful Northward is the declination ( D ) or variation. Facing magnetic Northward, 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 (E) and Z (Down) coordinates.[12]

Common coordinate systems used for representing the Earth's magnetic field.

Intensity [edit]

The intensity of the field is oftentimes measured in gauss (Thousand), only is more often than not reported in microteslas (μT), with ane One thousand = 100 μT. A nanotesla is too referred to as a gamma (γ). The World's field ranges betwixt approximately 25 and 65 μT (0.25 and 0.65 Grand).[13] By comparison, a stiff fridge magnet has a field of virtually 10,000 μT (100 G).[fourteen]

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 Southward America while there are maxima over northern Canada, Siberia, and the coast of Antarctica south of Australia.[fifteen]

The intensity of the magnetic field is subject to change over time. A 2021 paleomagnetic written report from the Academy of Liverpool contributed to a growing trunk of show that the Earth'southward magnetic field cycles with intensity every 200 meg years. The pb author stated that "Our findings, when considered alongside the existing datasets, back up the existence of an approximately 200-meg-year-long bicycle in the force of the World's magnetic field related to deep Earth processes."[16]

Inclination [edit]

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

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

Declination [edit]

Declination is positive for an due east deviation of the field relative to true north. It tin be estimated by comparing the magnetic due north–south heading on a compass with the direction of a angelic pole. Maps typically include data on the declination every bit an bending or a small diagram showing the relationship between magnetic north and true north. Information on declination for a region can be represented by a nautical chart with isogonic lines (profile lines with each line representing a fixed declination).

Geographical variation [edit]

Components of the Globe'southward magnetic field at the surface from the Globe Magnetic Model for 2015.[15]

  • Intensity

  • Inclination

  • Declination

Dipolar approximation [edit]

Relationship between Earth'southward poles. A1 and A2 are the geographic poles; B1 and B2 are the geomagnetic poles; C1 (south) and C2 (n) are the magnetic poles.

Virtually 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 Globe and tilted at an angle of most eleven° with respect to the rotational axis of the Globe.[13] The dipole is roughly equivalent to a powerful bar magnet, with its southward pole pointing towards the geomagnetic North Pole.[17] This may seem surprising, but the north pole of a magnet is and so defined considering, if immune to rotate freely, it points roughly northward (in the geographic sense). Since the north pole of a magnet attracts the southward poles of other magnets and repels the north poles, it must be attracted to the southward pole of Globe's magnet. The dipolar field accounts for 80–ninety% of the field in virtually locations.[12]

Magnetic poles [edit]

The movement of Globe's Due north Magnetic Pole across the Canadian arctic.

Historically, the north and southward poles of a magnet were first defined by the Globe's magnetic field, not vice versa, since one of the first uses for a magnet was every bit a compass needle. A magnet's North pole is defined equally the pole that is attracted by the Earth'due south Due north Magnetic Pole when the magnet is suspended so it can turn freely. Since contrary poles attract, the Due north Magnetic Pole of the Globe is really the due south pole of its magnetic field (the place where the field is directed down into the Earth).[18] [nineteen] [20] [21]

The positions of the magnetic poles tin can be divers in at least two ways: locally or globally.[22] The local definition is the point where the magnetic field is vertical.[23] This tin can be determined by measuring the inclination. The inclination of the Earth'south field is ninety° (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 straight contrary each other on the globe. Movements of up to twoscore kilometres (25 mi) per yr have been observed for the Due north Magnetic Pole. Over the terminal 180 years, the North Magnetic Pole has been migrating northwestward, from Greatcoat Adelaide in the Boothia Peninsula in 1831 to 600 kilometres (370 mi) from Resolute Bay in 2001.[24] The magnetic equator is the line where the inclination is nothing (the magnetic field is horizontal).

The global definition of the World's field is based on a mathematical model. If a line is drawn through the heart of the Earth, parallel to the moment of the all-time-fitting magnetic dipole, the two positions where it intersects the Earth'southward surface are called the Northward and South geomagnetic poles. If the World'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 pregnant non-dipolar contribution, and so the poles do not coincide and compasses do not by and large indicate at either.

Magnetosphere [edit]

An artist's rendering of the structure of a magnetosphere. 1) Bow shock. ii) Magnetosheath. iii) Magnetopause. 4) Magnetosphere. 5) Northern tail lobe. 6) Southern tail lobe. 7) Plasmasphere.

Earth's magnetic field, predominantly dipolar at its surface, is distorted farther out by the solar wind. This is a stream of charged particles leaving the Sun'south corona and accelerating to a speed of 200 to 1000 kilometres per 2d. They carry with them a magnetic field, the interplanetary magnetic field (IMF).[25]

The solar wind exerts a pressure, and if it could reach Earth'due south atmosphere it would erode it. However, it is kept abroad past the pressure of the World'southward magnetic field. The magnetopause, the area where the pressures remainder, is the purlieus of the magnetosphere. Despite its name, the magnetosphere is asymmetric, with the sunward side being almost 10 World radii out merely the other side stretching out in a magnetotail that extends beyond 200 Earth radii.[26] Sunward of the magnetopause is the bow stupor, the area where the solar current of air slows abruptly.[25]

Inside the magnetosphere is the plasmasphere, a donut-shaped region containing low-energy charged particles, or plasma. This region begins at a meridian of 60 km, extends upwards to 3 or 4 Globe radii, and includes the ionosphere. This region rotates with the Earth.[26] There are besides two concentric tire-shaped regions, chosen the Van Allen radiations belts, with high-energy ions (energies from 0.1 to 10 MeV). The inner chugalug is i–2 Globe radii out while the outer belt is at iv–7 Earth radii. The plasmasphere and Van Allen belts take fractional overlap, with the extent of overlap varying profoundly with solar action.[27]

As well as deflecting the solar current of air, the World'southward magnetic field deflects cosmic rays, high-energy charged particles that are more often than not from outside the Solar Arrangement. Many catholic rays are kept out of the Solar Organization by the Sun's magnetosphere, or heliosphere.[28] By contrast, astronauts on the Moon risk exposure to radiation. Anyone who had been on the Moon'southward surface during a peculiarly violent solar eruption in 2005 would accept received a lethal dose.[25]

Some of the charged particles exercise become into the magnetosphere. These spiral effectually field lines, billowy back and forth between the poles several times per second. In addition, positive ions slowly migrate westward and negative ions drift east, giving rise to a ring current. This current reduces the magnetic field at the Earth's surface.[25] Particles that penetrate the ionosphere and collide with the atoms in that location give rise to the lights of the aurorae and also emit X-rays.[26]

The varying conditions in the magnetosphere, known every bit space weather condition, are largely driven by solar action. If the solar current of air is weak, the magnetosphere expands; while if it is strong, information technology compresses the magnetosphere and more of information technology gets in. Periods of specially intense activity, called geomagnetic storms, can occur when a coronal mass ejection erupts to a higher place the Sunday and sends a shock wave through the Solar System. Such a wave can take just two days to reach the Earth. Geomagnetic storms can crusade a lot of disruption; the "Halloween" storm of 2003 damaged more than a tertiary of NASA'due south satellites. The largest documented storm, the Carrington Event, occurred in 1859. It induced currents strong enough to disrupt telegraph lines, and aurorae were reported as far southward every bit Hawaii.[25] [29]

Time dependence [edit]

Short-term variations [edit]

Background: a set of traces from magnetic observatories showing a magnetic tempest in 2000.
Globe: map showing locations of observatories and contour lines giving horizontal magnetic intensity in μ T.

The geomagnetic field changes on time scales from milliseconds to millions of years. Shorter fourth dimension 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 yr or more than mostly reverberate changes in the Globe'due south interior, particularly the atomic number 26-rich core.[12]

Often, the World's magnetosphere is hit by solar flares causing geomagnetic storms, provoking displays of aurorae. The curt-term instability of the magnetic field is measured with the K-index.[30]

Data from THEMIS show that the magnetic field, which interacts with the solar current of air, is reduced when the magnetic orientation is aligned between Sun and Globe – reverse to the previous hypothesis. During forthcoming solar storms, this could outcome in blackouts and disruptions in artificial satellites.[31]

Secular variation [edit]

Estimated declination contours by yr, 1590 to 1990 (click to run into variation).

Force of the centric dipole component of Earth'southward magnetic field from 1600 to 2020.

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] The animation shows how global declinations take changed over the last few centuries.[32]

The direction and intensity of the dipole change over time. Over the last two centuries the dipole force has been decreasing at a rate of about 6.3% per century.[12] At this rate of decrease, the field would exist negligible in about 1600 years.[33] Still, this strength is nigh boilerplate for the terminal 7 yard years, and the electric current charge per unit of change is non unusual.[34]

A prominent feature in the non-dipolar part of the secular variation is a westward drift at a rate of about 0.2° per year.[33] This drift is not the same everywhere and has varied over time. The globally averaged drift has been w since about 1400 AD but east betwixt most thou Advertising and 1400 Advertising.[35]

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 modify with occasional large changes reflecting geomagnetic excursions and reversals.[36]

In July 2020 scientists report that analysis of simulations and a recent observational field model show that maximum rates of directional change of Earth'due south magnetic field reached ~10° per year – almost 100 times faster than current changes and 10 times faster than previously idea.[37] [38]

Studies of lava flows on Steens Mountain, Oregon, indicate that the magnetic field could take shifted at a charge per unit of up to 6° per twenty-four hours at some time in Globe'southward history, which significantly challenges the popular understanding of how the Earth's magnetic field works.[39] This finding was later attributed to unusual rock magnetic backdrop of the lava flow under study, not rapid field change, by one of the original authors of the 1995 study.[xl]

Magnetic field reversals [edit]

Geomagnetic polarity during the late Cenozoic Era. Nighttime areas announce periods where the polarity matches today'southward polarity, lite areas denote periods where that polarity is reversed.

Although more often than not Globe's field is approximately dipolar, with an axis that is near 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.[41] Reversals occur nearly randomly in time, with intervals between reversals ranging from less than 0.i million years to as much equally 50 million years. The near recent geomagnetic reversal, called the Brunhes–Matuyama reversal, occurred virtually 780,000 years ago.[24] [42] A related phenomenon, a geomagnetic excursion, takes the dipole axis across the equator and and then dorsum to the original polarity.[43] [44] The Laschamp event is an instance of an excursion, occurring during the final water ice age (41,000 years agone).

The past magnetic field is recorded more often than not 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 manner. In lava flows, the management of the field is "frozen" in pocket-size minerals equally they cool, giving rising to a thermoremanent magnetization. In sediments, the orientation of magnetic particles acquires a slight bias towards the magnetic field equally they are deposited on an bounding main floor or lake bottom. This is called detrital remanent magnetization.[8]

Thermoremanent magnetization is the chief source of the magnetic anomalies around mid-ocean ridges. As the seafloor spreads, magma wells upwards from the pall, cools to form new basaltic chaff on both sides of the ridge, and is carried away from it by seafloor spreading. As it cools, it records the direction of the Globe'due south 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 bounding main 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 by.[8]

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

Earliest appearance [edit]

Paleomagnetic studies of Paleoarchean lava in Commonwealth of australia and conglomerate in South Africa have ended that the magnetic field has been nowadays since at least about 3,450 million years agone.[45] [46] [47]

Future [edit]

Variations in virtual axial dipole moment since the final reversal.

At nowadays, 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 ii,000 years ago. The rate of decrease and the current force are within the normal range of variation, as shown by the record of past magnetic fields recorded in rocks.

The nature of World's magnetic field is one of heteroscedastic fluctuation. An instantaneous measurement of information technology, or several measurements of information technology 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. Likewise, noting the local intensity of the dipole field (or its fluctuation) is insufficient to narrate Earth'due south magnetic field as a whole, as it is not strictly a dipole field. The dipole component of Earth'south field tin diminish even while the total magnetic field remains the same or increases.

The World's magnetic n pole is drifting from northern Canada towards Siberia with a shortly accelerating rate—10 kilometres (six.2 mi) per twelvemonth at the beginning of the 20th century, up to forty kilometres (25 mi) per year in 2003,[24] and since then has merely accelerated.[48] [49]

Concrete origin [edit]

Earth's core and the geodynamo [edit]

The World'southward magnetic field is believed to be generated by electrical currents in the conductive fe alloys of its cadre, created past convection currents due to oestrus escaping from the core.

A schematic illustrating the human relationship between motion of conducting fluid, organized into rolls by the Coriolis force, and the magnetic field the movement generates.[50]

The Earth and most of the planets in the Solar System, as well every bit the Sun and other stars, all generate magnetic fields through the motion of electrically conducting fluids.[51] The Globe'south field originates in its core. This is a region of atomic number 26 alloys extending to almost 3400 km (the radius of the Earth is 6370 km). Information technology is divided into a solid inner core, with a radius of 1220 km, and a liquid outer core.[52] The movement of the liquid in the outer core is driven by heat catamenia from the inner core, which is nearly 6,000 Thousand (5,730 °C; 10,340 °F), to the core-mantle purlieus, which is well-nigh three,800 K (3,530 °C; six,380 °F).[53] The heat is generated by potential energy released by heavier materials sinking toward the core (planetary differentiation, the iron catastrophe) as well equally disuse of radioactive elements in the interior. The pattern of menses is organized by the rotation of the World and the presence of the solid inner core.[54]

The machinery by which the Earth generates a magnetic field is known as a dynamo.[51] 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 strength on the charges that are flowing in currents (the Lorentz force).[55] These effects tin can be combined in a partial differential equation for the magnetic field called the magnetic induction equation,

∂ B ∂ t = η ∇ 2 B + ∇ × ( u × B ) , {\displaystyle {\frac {\fractional \mathbf {B} }{\partial t}}=\eta \nabla ^{2}\mathbf {B} +\nabla \times (\mathbf {u} \times \mathbf {B} ),}

where u is the velocity of the fluid; B is the magnetic B-field; and η=i/σμ is the magnetic diffusivity, which is inversely proportional to the production of the electrical conductivity σ and the permeability μ .[56] The term ∂B/∂t is the time derivative of the field; ∇two is the Laplace operator and ∇× is the scroll operator.

The kickoff term on the right hand side of the consecration 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.[56]

In a perfect conductor ( σ = ∞ {\displaystyle \sigma =\infty \;} ), there would be no diffusion. By Lenz'due south law, any modify in the magnetic field would be immediately opposed by currents, then the flux through a given volume of fluid could not change. Equally the fluid moved, the magnetic field would go with it. The theorem describing this result is called the frozen-in-field theorem. Even in a fluid with a finite conductivity, new field is generated past stretching field lines as the fluid moves in ways that deform it. This process could go on generating new field indefinitely, were information technology not that as the magnetic field increases in strength, it resists fluid motion.[56]

The motion of the fluid is sustained past convection, motion driven by buoyancy. The temperature increases towards the center of the Globe, and the college temperature of the fluid lower down makes information technology buoyant. This buoyancy is enhanced by chemical separation: As the core cools, some of the molten atomic number 26 solidifies and is plated to the inner core. In the process, lighter elements are left behind in the fluid, making information technology lighter. This is called compositional convection. A Coriolis effect, acquired by the overall planetary rotation, tends to organize the period into rolls aligned along the north–south polar centrality.[54] [56]

A dynamo can amplify a magnetic field, but it needs a "seed" field to become it started.[56] For the World, 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 take had a magnetic field orders of magnitude larger than the present solar air current.[57] 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 chemic reactions or variations in thermal or electric conductivity. Such effects may yet provide a small bias that are part of the boundary conditions for the geodynamo.[58]

The boilerplate magnetic field in the Globe's outer core was calculated to be 25 gauss, 50 times stronger than the field at the surface.[59]

Numerical models [edit]

Simulating the geodynamo by computer requires numerically solving a gear up of nonlinear fractional differential equations for the magnetohydrodynamics (MHD) of the Earth'south interior. Simulation of the MHD equations is performed on a 3D filigree of points and the fineness of the grid, which in part determines the realism of the solutions, is limited mainly by computer ability. For decades, theorists were bars to creating kinematic dynamo computer models in which the fluid motility is chosen in advance and the consequence on the magnetic field calculated. Kinematic dynamo theory was mainly a affair of trying different menstruum geometries and testing whether such geometries could sustain a dynamo.[60]

The beginning self-consistent dynamo models, ones that determine both the fluid motions and the magnetic field, were developed past ii groups in 1995, one in Japan[61] and ane in the United States.[1] [62] The latter received attention considering it successfully reproduced some of the characteristics of the Earth's field, including geomagnetic reversals.[60]

Effect of body of water tides [edit]

The oceans contribute to Earth's magnetic field. Seawater is an electric conductor, and therefore interacts with the magnetic field. Equally the tides bicycle around the sea basins, the bounding main water substantially tries to pull the geomagnetic field lines along. Because the salty h2o is slightly conductive, the interaction is relatively weak: the strongest component is from the regular lunar tide that happens about twice per twenty-four hour period (M2). Other contributions come from ocean swell, eddies, and even tsunamis.[63]

The strength of the interaction depends also on the temperature of the bounding main water. The entire heat stored in the sea can now exist inferred from observations of the Earth's magnetic field.[64] [63]

Currents in the ionosphere and magnetosphere [edit]

Electric currents induced in the ionosphere generate magnetic fields (ionospheric dynamo region). Such a field is e'er generated nigh where the atmosphere is closest to the Sun, causing daily alterations that can deflect surface magnetic fields by equally much as 1°. Typical daily variations of field strength are near 25 nT (one part in 2000), with variations over a few seconds of typically around 1 nT (one function in 50,000).[65]

Measurement and analysis [edit]

Detection [edit]

The Earth's magnetic field forcefulness was measured by Carl Friedrich Gauss in 1832[66] and has been repeatedly measured since then, showing a relative disuse of nigh 10% over the last 150 years.[67] The Magsat satellite and afterward satellites accept used 3-axis vector magnetometers to probe the 3-D structure of the Earth's magnetic field. The afterwards 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.[68]

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 tin can mensurate and forecast magnetic conditions such every bit magnetic storms that sometimes affect communications, electric power, and other human activities.

The International Real-fourth dimension Magnetic Observatory Network, with over 100 interlinked geomagnetic observatories around the earth, has been recording the Earth'south magnetic field since 1991.

The military determines local geomagnetic field characteristics, in lodge to detect anomalies in the natural background that might be acquired past a pregnant metal object such every bit a submerged submarine. Typically, these magnetic anomaly detectors are flown in aircraft like the United kingdom of great britain and northern ireland'due south Nimrod or towed as an instrument or an array of instruments from surface ships.

Commercially, geophysical prospecting companies also use magnetic detectors to place naturally occurring anomalies from ore bodies, such every bit the Kursk Magnetic Anomaly.

Crustal magnetic anomalies [edit]

A model of brusque-wavelength features of Earth's magnetic field, attributed to lithospheric anomalies[69]

Magnetometers detect minute deviations in the Earth's magnetic field caused by iron artifacts, kilns, some types of stone structures, and fifty-fifty ditches and middens in archaeological geophysics. Using magnetic instruments adapted from airborne magnetic anomaly detectors developed during World War Ii to notice submarines,[70] the magnetic variations across the bounding main floor accept been mapped. Basalt — the iron-rich, volcanic rock making up the body of water floor[71] — contains a strongly magnetic mineral (magnetite) and can locally distort compass readings. The distortion was recognized by Icelandic mariners equally early every bit the late 18th century.[72] More of import, because the presence of magnetite gives the basalt measurable magnetic backdrop, these magnetic variations have provided another means to report the deep ocean floor. When newly formed stone cools, such magnetic materials record the Earth'southward magnetic field.[72]

Statistical models [edit]

Each measurement of the magnetic field is at a particular place and time. If an authentic 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 brand predictions.

Spherical harmonics [edit]

Schematic representation of spherical harmonics on a sphere and their nodal lines. P ℓ m is equal to 0 along k great circles passing through the poles, and along ℓ-m circles of equal breadth. The role changes sign each ℓtime it crosses i of these lines.

Example of a quadrupole field. This tin can too be synthetic by moving 2 dipoles together.

The most mutual way of analyzing the global variations in the Globe's magnetic field is to fit the measurements to a set of spherical harmonics. This was first done past Carl Friedrich Gauss.[73] Spherical harmonics are functions that oscillate over the surface of a sphere. They are the production of two functions, one that depends on latitude and one on longitude. The office of longitude is zippo forth cipher or more cracking circles passing through the Due north and Southward Poles; the number of such nodal lines is the accented value of the order 1000 . The role of latitude is zero along zilch or more latitude circles; this plus the guild is equal to the degree ℓ. Each harmonic is equivalent to a particular arrangement of magnetic charges at the centre of the Earth. A monopole is an isolated magnetic accuse, which has never been observed. A dipole is equivalent to ii 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]

Spherical harmonics can represent any scalar field (function of position) that satisfies sure properties. A magnetic field is a vector field, just if information technology is expressed in Cartesian components X, Y, Z , each component is the derivative of the same scalar function chosen 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 Globe's field as the sum of spherical harmonics, each multiplied past the all-time-plumbing equipment Gauss coefficient yardm ℓ or hg ℓ .[12]

The lowest-degree Gauss coefficient, k 0 0 , gives the contribution of an isolated magnetic accuse, so it is zero. The next three coefficients – thousand 1 0 , g one 1 , and h 1 i – make up one's mind the direction and magnitude of the dipole contribution. The best fitting dipole is tilted at an bending of about x° with respect to the rotational axis, as described earlier.[12]

Radial dependence [edit]

Spherical harmonic analysis can be used to distinguish internal from external sources if measurements are bachelor at more one height (for example, basis observatories and satellites). In that case, each term with coefficient gthousand ℓ or hg ℓ can be split into two terms: i that decreases with radius every bit one/r ℓ+1 and one that increases with radius equally r ℓ . The increasing terms fit the external sources (currents in the ionosphere and magnetosphere). All the same, averaged over a few years the external contributions average to zero.[12]

The remaining terms predict that the potential of a dipole source (ℓ=ane) drops off as 1/r 2 . The magnetic field, being a derivative of the potential, drops off as ane/r 3 . Quadrupole terms drib off as 1/r 4 , and college order terms drop off increasingly rapidly with the radius. The radius of the outer core is near half of the radius of the Globe. If the field at the core-pall boundary is fit to spherical harmonics, the dipole function is smaller by a factor of about viii at the surface, the quadrupole function by a factor of 16, and then on. Thus, merely the components with large wavelengths can exist noticeable at the surface. From a diversity of arguments, it is normally assumed that only terms upwardly to degree xiv or less accept their origin in the core. These have wavelengths of about 2,000 km (ane,200 mi) or less. Smaller features are attributed to crustal anomalies.[12]

Global models [edit]

The International Clan of Geomagnetism and Aeronomy maintains a standard global field model called the International Geomagnetic Reference Field (IGRF). Information technology is updated every v years. The 11th-generation model, IGRF11, was developed using data from satellites (Ørsted, Champ and SAC-C) and a globe network of geomagnetic observatories.[74] The spherical harmonic expansion was truncated at degree 10, with 120 coefficients, until 2000. Subsequent models are truncated at degree 13 (195 coefficients).[75]

Another global field model, called the Globe Magnetic Model, is produced jointly by the Usa National Centers for Environmental Information (formerly the National Geophysical Data Eye) and the British Geological Survey. This model truncates at caste 12 (168 coefficients) with an approximate spatial resolution of 3,000 kilometers. Information technology is the model used by the United States Department of Defense, the Ministry building of Defense force (United Kingdom), the Us Federal Aviation Administration (FAA), the Northward Atlantic Treaty Organization (NATO), and the International Hydrographic Organization equally well as in many noncombatant navigation systems.[76]

The to a higher place models only take into account the "chief field" at the cadre-mantle boundary. Although by and large good enough for navigation, higher-accuracy use cases crave smaller-calibration magnetic anomalies and other variations to exist considered. Some examples are (meet geomag.us ref for more):[77]

  • The "comprehensive modeling" (CM) appproach by the Goddard Space Flight Center (NASA and GSFC) and the Danish Space Research Institute. CM attempts to reconcile data with greatly varying temporal and spatial resolution from ground and satellite sources. The latest version every bit of 2022 is CM5 of 2016. It provides separate components for chief field plus lithosphere (crustal), M2 tidal, and main/induced magnetosphere/ionosphere variations.[78]
  • The US National Centers for Ecology Information developed the Enhanced Magnetic Model (EMM), which extends to degree and order 790 and resolves magnetic anomalies downwardly to a wavelength of 56 kilometers. It was compiled from satellite, marine, aeromagnetic and basis magnetic surveys. As of 2018[update], the latest version, EMM2017, includes information from The European Infinite Agency's Swarm satellite mission.[79]

For historical data well-nigh the principal field, the IGRF may exist used back to twelvemonth 1900.[75] A specialized GUFM1 model estimates dorsum to year 1590 using ship'south logs.[80] Paleomagnetic inquiry has produced models dating dorsum to 10,000 BCE.[81]

Biomagnetism [edit]

Animals, including birds and turtles, tin detect the Earth'due south magnetic field, and employ the field to navigate during migration.[82] Some researchers have establish that cows and wild deer tend to marshal their bodies north–south while relaxing, only not when the animals are nether loftier-voltage power lines, suggesting that magnetism is responsible.[83] [84] Other researchers reported in 2011 that they could not replicate those findings using unlike Google Earth images.[85]

Very weak electromagnetic fields disrupt the magnetic compass used past European robins and other songbirds, which apply the Earth's magnetic field to navigate. Neither power lines nor cellphone signals are to blame for the electromagnetic field consequence on the birds;[86] 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.[87]

Encounter besides [edit]

  • Geomagnetic wiggle
  • Geomagnetic latitude
  • Magnetotellurics
  • Operation Argus

References [edit]

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Farther reading [edit]

  • Campbell, Wallace H. (2003). Introduction to geomagnetic fields (2nd ed.). New York: Cambridge University Press. ISBN978-0-521-52953-2.
  • Comins, Neil F. (2008). Discovering the Essential Universe (Fourth ed.). W. H. Freeman. ISBN978-1-4292-1797-two.
  • Gramling, Carolyn (1 Feb 2019). "Earth's core may have hardened merely in fourth dimension to save its magnetic field". Science News . Retrieved 3 February 2019.
  • Herndon, J. K. (1996-01-23). "Substructure of the inner cadre of the Earth". PNAS. 93 (2): 646–648. Bibcode:1996PNAS...93..646H. doi:10.1073/pnas.93.2.646. PMC40105. PMID 11607625.
  • Hollenbach, D. F.; Herndon, J. Thousand. (2001-09-25). "Deep-World reactor: Nuclear fission, helium, and the geomagnetic field". PNAS. 98 (twenty): 11085–90. Bibcode:2001PNAS...9811085H. doi:10.1073/pnas.201393998. PMC58687. PMID 11562483.
  • Love, Jeffrey J. (2008). "Magnetic monitoring of Globe and space" (PDF). Physics Today. 61 (ii): 31–37. Bibcode:2008PhT....61b..31H. doi:10.1063/ane.2883907.
  • Luhmann, J. G.; Johnson, R. E.; Zhang, M. H. 1000. (1992). "Evolutionary impact of sputtering of the Martian atmosphere by O+ pickup ions". Geophysical Research Letters. xix (21): 2151–2154. Bibcode:1992GeoRL..xix.2151L. doi:x.1029/92GL02485.
  • Merrill, Ronald T. (2010). Our Magnetic Earth: The Science of Geomagnetism. University of Chicago Press. ISBN978-0-226-52050-half dozen.
  • Merrill, Ronald T.; McElhinny, Michael Due west.; McFadden, Phillip L. (1996). The magnetic field of the earth: paleomagnetism, the core, and the deep pall. Academic Press. ISBN978-0-12-491246-five.
  • "Temperature of the World's core". NEWTON Ask a Scientist. 1999. Archived from the original on 2010-09-08. Retrieved 2006-01-21 .
  • Tauxe, Lisa (1998). Paleomagnetic Principles and Practice. Kluwer. ISBN978-0-7923-5258-7.
  • Towle, J. N. (1984). "The Anomalous Geomagnetic Variation Field and Geoelectric Structure Associated with the Mesa Butte Fault System, Arizona". Geological Guild of America Message. 9 (2): 221–225. Bibcode:1984GSAB...95..221T. doi:10.1130/0016-7606(1984)95<221:TAGVFA>2.0.CO;two.
  • Look, James R. (1954). "On the relation betwixt telluric currents and the world's magnetic field". Geophysics. 19 (two): 281–289. Bibcode:1954Geop...19..281W. doi:10.1190/1.1437994. S2CID 51844483.
  • Walt, Martin (1994). Introduction to Geomagnetically Trapped Radiation. Cambridge University Press. ISBN978-0-521-61611-9.

External links [edit]

  • Geomagnetism & Paleomagnetism background material. American Geophysical Union Geomagnetism and Paleomagnetism Section.
  • National Geomagnetism Plan. United States Geological Survey, March eight, 2011.
  • BGS Geomagnetism. Information on monitoring and modeling the geomagnetic field. British Geological Survey, August 2005.
  • William J. Broad, Will Compasses Indicate South?. The New York Times, July 13, 2004.
  • John Roach, Why Does Earth's Magnetic Field Flip?. National Geographic, September 27, 2004.
  • Magnetic Storm. PBS NOVA, 2003. (ed. about pole reversals)
  • When North Goes South. Projects in Scientific Computing, 1996.
  • The Great Magnet, the Earth, History of the discovery of Earth's magnetic field by David P. Stern.
  • Exploration of the Earth's Magnetosphere, Educational spider web site by David P. Stern and Mauricio Peredo
  • International Geomagnetic Reference Field 2011
  • Global evolution/bibelot of the Globe's magnetic field Archived 2016-06-24 at the Wayback Automobile Sweeps are in 10° steps at 10 years intervals. Based on information from: The Constitute of Geophysics, ETH Zurich
  • Patterns in Earth'due south magnetic field that evolve on the social club of ane,000 years Archived 2018-07-twenty at the Wayback Automobile. July 19, 2017
  • Chree, Charles (1911). "Magnetism, Terrestrial". In Chisholm, Hugh (ed.). Encyclopædia Britannica. Vol. 17 (11th ed.). Cambridge University Printing. pp. 353–385. (with dozens of tables and several diagrams)

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