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71-929: Some of the magnetic anomalies shown in the WDMAM generally relates to the altitude level of 5 kilometres (3.1 mi). Some of the significant features represented are of the Bangui Anomaly in the Central African Republic , the Chicxulub crater , the Thromsberg anomaly , the Richat Structure , the Atlantic ridge , the Bay of Biscay , the Sunda Arc and the Paris Basin . In evolving

142-810: 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, the Carrington Event , occurred in 1859. It induced currents strong enough to disrupt telegraph lines, and aurorae were reported as far south as Hawaii. The geomagnetic field changes on time scales from milliseconds to millions of years. Shorter time scales mostly arise from currents in

213-433: A Bouguer gravity anomaly of −120 mGal , a topographical surface feature shaped as a ring of 810 km (500 mi) diameter, rock features of Late Archean and Proterozoic periods in the central part of the anomaly, granulites , and charnockites rock formations supplemented by granites at the lower crust level, and greenstone belts, and metamorphosed basalts seen as rock exposures. A zone of thinner crust bounds

284-417: A lethal dose. 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. Particles that penetrate the ionosphere and collide with

355-449: 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

426-595: A magnet was as a compass needle. A magnet's North pole is defined as the pole that is attracted by the Earth's North Magnetic Pole when the magnet is suspended so it can 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). The positions of the magnetic poles can be defined in at least two ways: locally or globally. The local definition

497-401: A magnet. Another common representation is in X (North), Y (East) and Z (Down) coordinates. The intensity of the field is often measured in gauss (G) , but is generally reported in microteslas (μT), with 1 G = 100 μT. A nanotesla is also referred to as a gamma (γ). The Earth's field ranges between approximately 22 and 67 μT (0.22 and 0.67 G). By comparison,

568-560: A mixture of molten iron and nickel in Earth's outer core : these convection currents are caused by heat escaping from the core, a natural process called a geodynamo . The magnitude of Earth's magnetic field at its surface ranges from 25 to 65 μT (0.25 to 0.65 G). As an approximation, it is represented by a field of a magnetic dipole currently tilted at an angle of about 11° with respect to Earth's rotational axis, as if there were an enormous bar magnet placed at that angle through

639-413: 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

710-400: A presently accelerating rate—10 kilometres (6.2 mi) per year at the beginning of the 1900s, up to 40 kilometres (25 mi) per year in 2003, and since then has only accelerated. The Earth's magnetic field is believed to be generated by electric currents in the conductive iron alloys of its core, created by convection currents due to heat escaping from the core. The Earth and most of

781-563: A review, the NGDC candidate was chosen to form the basemap. Specified to a grid of three arcminutes, the WDMAM v1 was based on the NGDC's EMAG3 ( Earth Magnetic Anomaly Grid, 3 arcminute ) dataset. The EMAG has since been improved into EMAG2 at a resolution of two arcminutes and fitted into the Enhanced Magnetic Model . According to the BBC, the "global map shows the variation in strength of

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852-446: A significant non-dipolar contribution, so the poles do not coincide and compasses do not generally point at either. 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,

923-570: A strong refrigerator magnet has a field of about 10,000 μT (100 G). 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. The intensity of

994-420: 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

1065-439: 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. The animation shows how global declinations have changed over the last few centuries. 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. At this rate of decrease,

1136-460: Is a hindrance to studying trans-national tectonics, and could benefit from further satellite observational additions to improve its coverage. Several different models were put forward as candidates for WDMAM by groups from NASA, Leeds University, the Geological Survey of Finland, National Geophysical Data Center (NGDC) and GeoForschungszentrum Potsdam, all using the same base data. Following

1207-456: Is a local variation in the Earth's magnetic field centered at Bangui , the capital of the Central African Republic . The magnetic anomaly is roughly elliptical , about 700 km × 1,000 km (430 mi × 620 mi), and covers most of the country, making it one of the "largest and most intense crustal magnetic anomalies on the African continent". The anomaly was discovered in

1278-496: 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. 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

1349-404: 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. A dynamo can amplify a magnetic field, but it needs a "seed" field to get it started. 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

1420-431: Is called detrital remanent magnetization . 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

1491-472: Is incomplete. CHAMP , a German and Russian-built satellite which has been in orbit since 2001, has been of crucial importance to the map compilers. One of its principal achievements is that it has significantly improved the "pre-processing and the corrections applied to the CHAMP satellite measurements in order to obtain 'clean' satellite data compatible with ground data." However, it has some large gaps in data, which

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1562-589: 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. 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 . In 2024 researchers published evidence from Greenland for

1633-503: Is straight up at the South Magnetic Pole. Inclination can be measured with a dip circle . An isoclinic chart (map of inclination contours) for the Earth's magnetic field is shown below . 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

1704-417: Is the point where the magnetic field is vertical. 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. Movements of up to 40 kilometres (25 mi) per year have been observed for

1775-505: The Brunhes–Matuyama reversal , occurred about 780,000 years ago. A related phenomenon, a geomagnetic excursion , takes the dipole axis across the equator and then back to the original polarity. The Laschamp event is an example of an excursion, occurring during the last ice age (41,000 years ago). The past magnetic field is recorded mostly by strongly magnetic minerals , particularly iron oxides such as magnetite , that can carry

1846-478: The electrical conductivity σ and the permeability μ . The term ∂ B /∂ t is the partial derivative of the field with respect to time; ∇ is the Laplace operator , ∇× is the curl operator , and × is the vector product . 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

1917-422: The interplanetary magnetic field (IMF). 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

1988-431: The sea floor is spreading, while the stability of the geomagnetic poles between reversals has allowed paleomagnetism to track the past motion of continents. Reversals also provide the basis for magnetostratigraphy , a way of dating rocks and sediments. The field also magnetizes the crust, and magnetic anomalies can be used to search for deposits of metal ores . Humans have used compasses for direction finding since

2059-440: The 11th century A.D. and for navigation since the 12th century. Although the magnetic declination does shift with time, this wandering is slow enough that a simple compass 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. At any location, the Earth's magnetic field can be represented by

2130-493: The Central African Republic and Brazil. Earth%27s magnetic field Earth's magnetic field , also known as the geomagnetic field , is the magnetic field that extends from Earth's interior out into space, where it interacts with the solar wind , a stream of charged particles emanating from the Sun . The magnetic field is generated by electric currents due to the motion of convection currents of

2201-402: The Earth's dynamo shut off, the dipole part would disappear in a few tens of thousands of years. 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

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2272-467: The Earth's magnetic field related to deep Earth processes." 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

2343-465: 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. The magnetic equator is the line where the inclination is zero (the magnetic field is horizontal). The global definition of the Earth's field is based on a mathematical model. If

2414-518: The WDMAM the lithospheric data related to data acquired from satellites, data of aero-magnetic survey and marine survey, in-situ data gathered from field stations and observatories are to be collated analyzed together, and this would need an international joint effort. The map is the product of years of work, research and coordination by the International Association of Geomagnetism and Aeronomy (IAGA) and numerous small organizations around

2485-653: The anomaly after the city located at its center. The anomaly is sometimes called the Bangui negative anomaly, owing to its negative peak-to-trough difference, and is compared with the positive anomalies observed at the Benue Trough and Congo Basin where Lower Cambrian geological formations are exposed. The Bangui anomaly is bounded to the south by the Walvis Ridge , the north by the Cameroon–St. Helena volcanic line , and to

2556-679: The anomaly to the north and a zone of relatively thicker crust is on the southern edge. Two theories have been suggested for the origin of the Bangui anomaly, neither being conclusive. One theory points to a large igneous intrusion and the other to a meteorite impact in the Precambrian (before 540 Ma ). To support the latter theory, a connection was drawn with a meteorite impact that may have occurred in Brazil in Bahia state causing formation of carbonados (black diamond aggregates) which are found only in

2627-417: The atoms there give rise to the lights of the aurorae while also emitting X-rays . 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

2698-555: The center of Earth. The North geomagnetic pole ( Ellesmere Island , Nunavut , Canada) actually represents the South pole of Earth's magnetic field, and conversely the South geomagnetic pole corresponds to the north pole of Earth's magnetic field (because opposite magnetic poles attract and the north end of a magnet, like a compass needle, points toward Earth's South magnetic field. While the North and South magnetic poles are usually located near

2769-435: The current strength are within the normal range of variation, as shown by the record of past magnetic fields recorded in rocks. The nature of Earth's magnetic field is one of heteroscedastic (seemingly random) 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

2840-449: 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). Components of the Earth's magnetic field at the surface from the World Magnetic Model for 2020. Near the surface of the Earth, its magnetic field can be closely approximated by

2911-609: The diplomatic efforts needed to secure support and data contributions from these organizations." Diplomacy was needed to acquire data from the Russians, Indians, and Argentinians and so on. It is available through the Commission for the Geological Map of the World . The map is compiled from a jigsaw of aeromagnetic surveys, incorporating both ground-based, airborne and marine magnetic data, but

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2982-495: The earth composition, including the sea floor spreading under the oceans, and reserve deposits like iron ore at Kursk . It identifies some prominent magnetic anomalies on the African continent. The dominant factors for magnetic anomalies picked up on the map are "the thickness of the magnetised layer and the composition of the crust". Younger crust is typically thinner, and naturally has a lower number of magnetic materials. Bangui magnetic anomaly The Bangui magnetic anomaly

3053-460: The electric and magnetic fields exert a force on the charges that are flowing in currents (the Lorentz force ). These effects can be combined in a partial differential equation for the magnetic field called the magnetic induction equation , where u is the velocity of the fluid; B is the magnetic B-field; and η = 1/σμ is the magnetic diffusivity , which is the reciprocal of the product of

3124-429: The existence of the magnetic field as early as 3,700 million years ago. Starting in the late 1800s and throughout the 1900s and later, the overall geomagnetic field has become weaker; the present strong deterioration corresponds to a 10–15% decline and has accelerated since 2000; geomagnetic intensity has declined almost continuously from a maximum 35% above the modern value, from circa year 1 AD. The rate of decrease and

3195-423: 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. The dipole is roughly equivalent to a powerful bar magnet , with its south pole pointing towards the geomagnetic North Pole. 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

3266-900: The field would be negligible in about 1600 years. However, this strength is about average for the last 7 thousand years, and the current rate of change is not unusual. 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. 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. 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. A 1995 study of lava flows on Steens Mountain , Oregon appeared to suggest

3337-420: 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

3408-429: 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. The motion of

3479-522: The geographic poles, they slowly and continuously move over geological time scales, but sufficiently slowly for ordinary compasses to remain useful for navigation. However, at irregular intervals averaging several hundred thousand years, Earth's field reverses and the North and South Magnetic Poles abruptly switch places. These reversals of the geomagnetic poles leave a record in rocks that are of value to paleomagnetists in calculating geomagnetic fields in

3550-406: 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. 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

3621-405: The interior. The pattern of flow is organized by the rotation of the Earth and the presence of the solid inner core. The mechanism by which the Earth generates a magnetic field is known as a geodynamo . 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

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3692-432: 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 . Frequently, the Earth's magnetosphere is hit by solar flares causing geomagnetic storms, provoking displays of aurorae. The short-term instability of

3763-494: The ionosphere. This region rotates with the Earth. There are also two concentric tire-shaped regions, called the Van Allen radiation belts , with high-energy ions (energies from 0.1 to 10  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. As well as deflecting

3834-502: The late 1950s, explored in the 1970s, and named in 1982. Its origin remains unclear. In 1962, Raymond Godivier and Lucien Le Donche reported on a magnetic anomaly in the Central African Republic, which they identified by analyzing their surface magnetic activity data of 1956. These results were confirmed and built upon by the high-altitude aeromagnetic surveys carried out by the US Naval Oceanographic Office , as well as by

3905-422: 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). 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

3976-473: 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 . The study of the past magnetic field of the Earth is known as paleomagnetism. 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

4047-582: The magnetic field after the Earth's dipole field has been removed (Earth's dipole field varies from 35,000 nano- Tesla (nT) at the Equator to 70,000 nT at the poles). After removal of the dipole field, the remaining variations in the field (few hundreds of nT) are due to changes in the magnetic properties of the crustal rocks." The map is graphically represented by illustrating those landmarks of high magnetism in red to yellow hues and those of lower or negative magnetism in blue hues. It can pick up numerous aspects of

4118-451: The magnetic field is measured with the K-index . 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 . Changes in Earth's magnetic field on

4189-466: The magnetic field is subject to change over time. A 2021 paleomagnetic study from the University of Liverpool contributed to a growing body of evidence that the Earth's magnetic field cycles with intensity every 200 million years. The lead author stated that "Our findings, when considered alongside the existing datasets, support the existence of an approximately 200-million-year-long cycle in the strength of

4260-643: The magnetic field once shifted at a rate of up to 6° per day at some time in Earth's history, a surprising result. However, in 2014 one of the original authors published a new study which found the results were actually due to the continuous thermal demagnitization of the lava, not to a shift in the magnetic field. In July 2020 scientists report that analysis of simulations and a recent observational field model show that maximum rates of directional change of Earth's magnetic field reached ~10° per year – almost 100 times faster than current changes and 10 times faster than previously thought. Although generally Earth's field

4331-405: The other side stretching out in a magnetotail that extends beyond 200 Earth radii. Sunward of the magnetopause is the bow shock , the area where the solar wind slows abruptly. 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

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4402-418: 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. The Earth's magnetic north pole is drifting from northern Canada towards Siberia with

4473-399: The past. Such information in turn is helpful in studying the motions of continents and ocean floors. The magnetosphere is defined by the extent of Earth's magnetic field in space or geospace . It extends above the ionosphere , several tens of thousands of kilometres into space , protecting Earth from the charged particles of the solar wind and cosmic rays that would otherwise strip away

4544-417: 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. 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 . The motion of

4615-415: 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. Radiometric dating of lava flows has been used to establish a geomagnetic polarity time scale , part of which

4686-580: The satellite measurements conducted in 1964 with Cosmos 49 and in the 1970s with the Orbiting Geophysical Observatory at 350–500 kilometres (220–310 mi) altitudes. This data was combined in 1973 and yielded a spatial map of Earth's magnetic field, which was then updated after the launch of the Magsat satellite with an accuracy of 15  nT at an altitude of 400 kilometres (250 mi). In 1982, Robert D. Regan and Bruce D. Marsh named

4757-411: The solar wind would have had a magnetic field orders of magnitude larger than the present solar wind. 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

4828-522: 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 . 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

4899-429: The upper atmosphere, including the ozone layer that protects Earth from harmful ultraviolet radiation . Earth's magnetic field deflects most of the solar wind, whose charged particles would otherwise strip away the ozone layer that protects the Earth from harmful ultraviolet radiation. One stripping mechanism is for gas to be caught in bubbles of the magnetic field, which are ripped off by solar winds. Calculations of

4970-509: The west by the Mid-Atlantic Ridge . It is shaped approximately as an ellipse 700 km × 1,000 km (430 mi × 620 mi) in size. It has three sections, and the magnetic equator runs through its center. It has a short axis diameter of about 550 kilometres (340 mi), and its amplitude varies between –1000 nT at ground level and –20 nT at satellite altitude, about 400 kilometres (250 mi). Its features include

5041-459: The world including GETECH , a project of Leeds University , and Juha Korhonen of the Geological Survey of Finland have also been involved. International collaboration has been the key to the project. Mike Purucker of NASA said of the collaboration: "There are literally hundreds, perhaps thousands, of organisations around the world which hold this kind of data. One should not underestimate

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