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Encyclopedia > Earth's magnetic field
The magnetosphere shields the surface of the Earth from the charged particles of the solar wind. It is compressed on the day (Sun) side due to the force of the arriving particles, and extended on the night side. (Image not to scale.)
The magnetosphere shields the surface of the Earth from the charged particles of the solar wind. It is compressed on the day (Sun) side due to the force of the arriving particles, and extended on the night side. (Image not to scale.)

Earth's magnetic field (and the surface magnetic field) is approximately a magnetic dipole, with one pole near the north pole (see Magnetic North Pole) and the other near the geographic south pole (see Magnetic South Pole). An imaginary line joining the magnetic poles would be inclined by approximately 11.3° from the planet's axis of rotation. The cause of the field is probably explained by dynamo theory. Image File history File links Download high resolution version (1200x656, 391 KB)Artists rendition of Earths magnetosphere. ... Image File history File links Download high resolution version (1200x656, 391 KB)Artists rendition of Earths magnetosphere. ... A magnetosphere is the region around an astronomical object in which phenomena are dominated or organized by its magnetic field. ... The plasma in the solar wind meeting the heliopause The solar wind is a stream of charged particles (i. ... This article is about Earth as a planet. ... This article is about the electromagnetic phenomenon. ... For other uses, see North Pole (disambiguation). ... This is about the geographic meaning of North Pole. ... For other uses, see South Pole (disambiguation). ... The ceremonial South Pole. ... The Dynamo theory proposes a mechanism by which a celestial body such as the Earth generates a magnetic field. ...


Magnetic fields extend infinitely, though they are weaker further from their source. The Earth's magnetic field, which effectively extends several tens of thousands of kilometres into space, is called the magnetosphere. “km” redirects here. ... Layers of Atmosphere - not to scale (NOAA)[1] Outer space, sometimes simply called space, refers to the relatively empty regions of the universe outside the atmospheres of celestial bodies. ... A magnetosphere is the region around an astronomical object in which phenomena are dominated or organized by its magnetic field. ...

Contents

Magnetic poles

Magnetic declination from true north in 2000.
Magnetic declination from true north in 1700
Magnetic declination from true north in 1700

Two different types of magnetic poles must be distinguished. There are the "magnetic poles" and the "geomagnetic poles". The magnetic poles are the two positions on the Earth's surface where the magnetic field is entirely vertical. Another way of saying this is that the inclination of the Earth's field is 90° at the North Magnetic Pole and -90° at the South Magnetic Pole. A typical compass that is allowed to swing only in the horizontal plane will point in random directions at either the South or North Magnetic Poles. This is about the geographic meaning of North Pole. ... The ceremonial South Pole. ... Image File history File links Size of this preview: 753 × 599 pixel Image in higher resolution (1010 × 804 pixel, file size: 66 KB, MIME type: image/gif)IGRF 2000 magnetic declination map. ... Image File history File links Size of this preview: 753 × 599 pixel Image in higher resolution (1010 × 804 pixel, file size: 66 KB, MIME type: image/gif)IGRF 2000 magnetic declination map. ... Magnetic declination. ...


The Earth's field is closely approximated by the field of a dipole positioned near the centre of the Earth. A dipole defines an axis. The two positions where the axis of the dipole that best fits the Earth's field intersect the Earth's surface are called the North and South geomagnetic poles. If the Earth's field were perfectly dipolar, the geomagnetic and magnetic poles would coincide. However, there are significant non-dipolar terms which cause the position of the two types of poles to be in different places.


The locations of the magnetic poles are not static but they wander as much as 15 km every year (Dr. David P. Stern, emeritus Goddard Space Flight Center, NASA[citation needed]). The pole position is usually not that which is indicated on many charts. The Geomagnetic Pole positions are usually not close to the position that commercial cartographers place "Magnetic Poles." "Geomagnetic Dipole Poles", "IGRF Model Dip Poles", and "Magnetic Dip Poles" are variously used to denote the magnetic poles.[1]


The Earth's field changes in strength and position. The two poles wander independently of each other and are not at directly opposite positions on the globe. Currently the magnetic south pole is farther from the geographic south pole than the magnetic north pole is from the geographic north pole.

Magnetic pole positions
North Magnetic Pole [2] (2001) 81°18′N 110°48′W / 81.3, -110.8 Wikimapia (2004 est) 82°18′N 113°24′W / 82.3, -113.4 Wikimapia (2005 est) 82°42′N 114°24′W / 82.7, -114.4 Wikimapia
South Magnetic Pole [3] (1998) 64°36′S 138°30′E / -64.6, 138.5 Wikimapia (2004 est) 63°30′S 138°00′E / -63.5, 138 Wikimapia

Field characteristics

The strength of the field at the Earth's surface ranges from less than 30 microteslas (0.3 gauss) in an area including most of South America and South Africa to over 60 microteslas (0.6 gauss) around the magnetic poles in northern Canada and south of Australia, and in part of Siberia.


The field is similar to that of a bar magnet, but this similarity is superficial. The magnetic field of a bar magnet, or any other type of permanent magnet, is created by the coordinated spins of electrons and nuclei within iron atoms. The Earth's core, however, is hotter than 1043 K, the Curie point temperature at which the orientations of spins within iron become randomized. Such randomization causes the substance to lose its magnetic field. Therefore the Earth's magnetic field is caused not by magnetized iron deposits, but mostly by electric currents in the liquid outer core. For other uses, see Magnet (disambiguation). ... In physics, spin refers to the angular momentum intrinsic to a body, as opposed to orbital angular momentum, which is the motion of its center of mass about an external point. ... For other uses, see Electron (disambiguation). ... The nucleus of an atom is the very small dense region, of positive charge, in its centre consisting of nucleons (protons and neutrons). ... Fe redirects here. ... For other uses, see Atom (disambiguation). ... For other uses, see Kelvin (disambiguation). ... The Curie point is a term in physics and materials science, named after Pierre Curie (1859-1906), and refers to a characteristic property of a ferromagnetic material. ... For other uses, see Temperature (disambiguation). ... In physics, spin refers to the angular momentum intrinsic to a body, as opposed to orbital angular momentum, which is the motion of its center of mass about an external point. ... This box:      Electric current is the flow (movement) of electric charge. ...


Convection of molten iron, within the outer liquid core, along with a Coriolis effect caused by the overall planetary rotation that tends to organize these "electric currents" in rolls aligned along the north-south polar axis. When conducting fluid flows across an existing magnetic field, electric currents are induced, which in turn creates another magnetic field. When this magnetic field reinforces the original magnetic field, a dynamo is created which sustains itself. This is called the "Dynamo Theory" and it explains how the earth's magnetic field is sustained. In the inertial frame of reference (upper part of the picture), the black object moves in a straight line. ... The Dynamo theory proposes a mechanism by which a celestial body such as the Earth generates a magnetic field. ...


Another feature that distinguishes the Earth magnetically from a bar magnet is its magnetosphere. At large distances from the planet, this dominates the surface magnetic field. Electric currents induced in the ionosphere also generate magnetic fields. Such a field is always generated near where the atmosphere is closest to the Sun, causing daily alterations which can deflect surface magnetic fields by as much as one degree. This article is about Earth as a planet. ... A magnetosphere is the region around an astronomical object in which phenomena are dominated or organized by its magnetic field. ... Relationship of the atmosphere and ionosphere The ionosphere is the uppermost part of the atmosphere, distinguished because it is ionized by solar radiation. ...


Inverse Squared Law of Magnetic Fields at close Distances

Close to one pole of a magnet, field strength diminishes as the inverse square of the distance. This is because it behaves as a "unipolar magnetic field" (that is, the close pole seems much stronger than the far pole, so the far pole can be ignored). Gravity is also a unipolar field, and it also diminishes as the inverse square of distance; but, unlike magnetic fields, gravitational fields always obey the inverse squared law.


Inverse Cubed Law of Magnetic Fields at far Distances

Far from a magnet, both poles appear to be practically at the same point. Mathematically, this "dipolar magnetic field" diminishes as the inverse cube of distance. Hence, far from Earth, the geomagnetic field diminishes as the inverse cube of distance. This article is about the electromagnetic phenomenon. ...


Magnetic field variations

Geomagnetic variations since last reversal.
Geomagnetic variations since last reversal.

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, the magnetic variations across the ocean floor have been mapped. The basalt — the iron-rich, volcanic rock making up the ocean floor — 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. 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. Image File history File links Approximate times of some of the most commonly reported geomagnetic excursions of the Brunhes Normal Polarity Chron. ... Image File history File links Approximate times of some of the most commonly reported geomagnetic excursions of the Brunhes Normal Polarity Chron. ... A magnetometer is a scientific instrument used to measure the strength and/or direction of the magnetic field in the vicinity of the instrument. ... In archaeology, an artifact or artefact is any object made or modified by a human culture, and often one later recovered by some archaeological endeavor. ... A midden, also known as kitchen middens, is a dump for domestic waste. ... Electrical resistance map of ancient Aphrodisias Archaeological geophysics most often refers to geophysical survey techniques used for archaeological imaging or mapping. ... A RNZAF P-3K Orion; the magnetic anomaly dectector protrudes from the tail to minimise interference from the aircrafts avionics. ... For the cities, see Basalt, Colorado and Basalt, Idaho. ... Magnetite is a ferrimagnetic mineral with chemical formula Fe3O4, one of several iron oxides and a member of the spinel group. ...


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. A magnetosphere is the region around an astronomical object in which phenomena are dominated or organized by its magnetic field. ... A solar flare observed by Hinode in the G-band. ... A geomagnetic storm is a temporary disturbance of the Earths magnetosphere. ... The Aurora Borealis, or Northern Lights, shines above Bear Lake Aurora Borealis as seen over Canada at 11,000m (36,000 feet) Red and green Aurora in Fairbanks, Alaska Aurora Borealis redirects here. ... The K-index quantifies disturbances in the horizontal component of earths magnetic field with an integer in the range 0-9 with 1 being calm and 5 or more indicating a geomagnetic storm. ...

See also Magnetic anomaly, South Atlantic Anomaly

The Van Allen radiation belts and the point of the South Atlantic Anomaly. ...

Magnetic field reversals

Main article: geomagnetic reversal

Based upon the study of lava flows of basalt throughout the world, it has been proposed that the Earth's magnetic field reverses at intervals, ranging from tens of thousands to many millions of years, with an average interval of approximately 250,000 years. The last such event, called the Brunhes-Matuyama reversal, is theorized to have occurred some 780,000 years ago. Recent geomagnetic reversals. ... For the cities, see Basalt, Colorado and Basalt, Idaho. ... A year (from Old English gēr) is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ... The Brunhes-Matuyama Reversal was a geologic event approximately 780,000 years ago when the Earths magnetic field last underwent reversal. ...


There is no clear theory as to how the geomagnetic reversals might have occurred. Some scientists have produced models for the core of the Earth wherein the magnetic field is only quasi-stable and the poles can spontaneously migrate from one orientation to the other over the course of a few hundred to a few thousand years. Other scientists propose that the geodynamo first turns itself off, either spontaneously or through some external action like a comet impact, and then restarts itself with the magnetic "North" pole pointing either North or South. External events are not likely to be routine causes of magnetic field reversals due to the lack of a correlation between the age of impact craters and the timing of reversals. Regardless of the cause, when magnetic "North" reappears in the opposite direction this is a reversal, whereas turning off and returning in the same direction is called a geomagnetic excursion. Artists impression of a major impact event. ... A geomagnetic excursion, like a geomagnetic reversal, is a significant change in the Earths magnetic field. ...


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. [4]


This has been found to be consistent, by measuring magnetism across ocean ridges. The molten lava (typically basalt or tholeiite) is extruded from volcanoes at well over the Curie temperature and then cools to adopt whatever magnetic field was present at the time. As time goes on more lava flows and bands of opposite magnetic fields are made present. Oceanic Ridge Oceanic crust is formed at an oceanic ridge, while the lithosphere is subducted back into the asthenosphere at trenches. ... Look up lava, Aa, pahoehoe in Wiktionary, the free dictionary. ... Tholeiite (or Tholeiitic basalt) is a type of basalt rock that is olivine-poor, and dominated by clinopyroxene, plagioclase, and iron ore. ... In physics, the Curie point, or Curie temperature, is the temperature above which a ferromagnet loses its ferromagnetic ability to possess a net (spontaneous) magnetization in the absence of an external magnetic field. ...


Using a magnetic detector (a variant of a compass), scientists have measured the historical direction of the Earth's magnetic field, by studying sequences of relatively iron-rich lava flows. Typically such layers have been found to record the direction of Earth's magnetic field when they cool (see paleomagnetism). They have found that the poles have shifted a number of times throughout the past. Paleomagnetism refers to the study of the record of the Earths magnetic field preserved in various magnetic minerals through time. ...


Citing oceanic basalt 3He/4He ratios [5] and other evidence, J. Marvin Herndon et al contend that the inner core of the Earth is not iron but much denser atoms. [6] Nuclear reactions as replicated in a fast breeder reactor are suggested to take place and this accounts for the change in the Earth's magnetic field [7] (see Georeactor). The fast breeder or fast breeder reactor (FBR) is a fast neutron reactor designed to breed fuel by producing more fissile material than it consumes. ... Since the 1970s, geochemistry has documented the origin and existence of naturally occurring slow fission reactors, specifically in geologic formations at Oklo in Gabon, Africa. ...


Magnetic field detection

The earth's magnetic field strength was measured by Carl Friedrich Gauss in 1835 and has been repeatedly measured since then, showing a relative decay of about 5% over the last 150 years [8] Johann Carl Friedrich Gauss (pronounced ,  ; in German usually Gauß, Latin: ) (30 April 1777 – 23 February 1855) was a German mathematician and scientist who contributed significantly to many fields, including number theory, statistics, analysis, differential geometry, geodesy, electrostatics, astronomy, and optics. ... | Come and take it, slogan of the Texas Revolution 1835 was a common year starting on Thursday (see link for calendar). ...


Governments sometimes operate units which specialise in the 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. This article is about Earth as a planet. ... The British Geological Survey is a publicly-funded body which aims to advance geoscientific knowledge of the United Kingdom landmass and its continental shelf by means of systematic surveying, monitoring and research. ... The British Geological Survey is a publicly-funded body which aims to advance geoscientific knowledge of the United Kingdom landmass and its continental shelf by means of systematic surveying, monitoring and research. ... The Eskdalemuir Observatory is located in Dumfries and Galloway, Scotland. ...


The military can take a keen interest in determining the characteristics of the local geomagnetic field, in order to detect anomalies in the natural background, which might be caused by the presence of 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. A RNZAF P-3K Orion; the magnetic anomaly dectector protrudes from the tail to minimise interference from the aircrafts avionics. ... The United Kingdom of Great Britain and Northern Ireland is a country in western Europe, and member of the Commonwealth of Nations, the G8, the European Union, and NATO. Usually known simply as the United Kingdom, the UK, or (inaccurately) as Great Britain or Britain, the UK has four constituent... The Nimrod is a maritime patrol aircraft developed in the United Kingdom. ...


Commercially, geophysical prospecting companies also use magnetic detectors to identify naturally occurring anomalies from ore bodies, such as the Kursk Magnetic Anomaly. Geophysics, the study of the earth by quantitative physical methods, especially by seismic reflection and refraction, gravity, magnetic, electrical, electromagnetic, and radioactivity methods. ... Prospecting is the physical search for minerals, fossils, precious metals or mineral specimens, and is also known as fossicking. ... For other uses, see Ore (disambiguation). ... Kursk Magnetic Anomaly (Russian: Курская магнитная аномалия) is a territory rich in iron ores located within Kursk Oblast, Belgorod Oblast, and Oryol Oblast, and constitutes a significant part of the Central Chernozyom Region. ...


Animals including birds and turtles can detect the Earth's magnetic field, and use the field to navigate during migration.[9]. For other uses, see Bird (disambiguation). ... For other uses, see Turtle (disambiguation). ...


References

  1. ^ "Problem with the "MAGNETIC" Pole Locations on Global Charts". Eos Vol. 77, No. 36, American Geophysical Union, 1996.
  2. ^ Geomagnetism, North Magnetic Pole. Natural Resources Canada, 2005-03-13.
  3. ^ South Magnetic Pole. Commonwealth of Australia, Australian Antarctic Division, 2002.
  4. ^ "New evidence for extraordinarily rapid change of the geomagnetic field during a reversal" (20 April 2002). Nature. 
  5. ^ Herndon, J. Marvin (2003). "Nuclear georeactor origin of oceanic basalt 3He/4He, evidence, and implications" (PDF). Proceedings of the National Academy of Sciences 100 (6): 3047-3050. 
  6. ^ Herndon, J. Marvin (1996). "Sub-structure of the inner core of the earth" (PDF). Proceedings of the National Academy of Sciences 93: 646-648. 
  7. ^ Hollenbach, D. F.; J. M. Herndon (2001). "Deep-earth reactor: nuclear fission, helium, and the geomagnetic field" (PDF). Proceedings of the National Academy of Sciences 98 (20): 11085-11090. 
  8. ^ Annual Review of Earth and Planetary Science, 1988 16 p.435 "Time Variations of the Earth's Magnetic Field: From Daily to Secular" by Vincent Courtillot and Jean Louis Le Mouel
  9. ^ Deutschlander M, Phillips J, Borland S (1999) "The case for light-dependent magnetic orientation in animals" Journal of Experimental Biology 202(8): 891-908

Further reading

  • Neil F. Comins (2001). Discovering the Essential Universe
  • J.N. Towle (1984). "The Anomalous Geomagnetic Variation Field and Geoelectric Structure Associated with the Mesa Butte Fault System, Arizona". In: Geological Society of America, Bulletin, 95:221, 1984.
  • US Dept of Energy (1999). Temperature of the Earth's core
  • James R. Wait (1954). "On the relation between telluric currents and the earth’s magnetic field", In: Geophysics, 19, 281-289.
  • Martin Walt (1994). Introduction to Geomagnetically Trapped Radiation by

One might be looking for Stephen Martin Walt (Political Science). ...

See also

Auroral kilometric radiation (AKR) is the intense radio radiation emitted in the acceleration zone (at a height of three times the radius of the Earth) of the polar lights. ... Dip circles are used the measure the angle between the horizon and the earth’s magnetic field (the dip angle). ... The Dynamo theory proposes a mechanism by which a celestial body such as the Earth generates a magnetic field. ... An Earth battery is composed of a pair of electrodes made of two dissimilar metals, such as iron and copper, which are buried in the soil or immersed in the sea. ... Earth Potential Rise (EPR) also called Ground Potential Rise (GPR) occurs when a large current flows to earth through an earth grid impedance. ... Earth radiation is a theoretical geophysical phenomenon described primarily by the German authors Manfred Curry and Ernst Hartmann. ... Jupiter has a very large and powerful magnetosphere. ... Plot showing a view from space of L-shells 1. ... Magnetic declination. ... See also Earths magnetic field The magnetic fieldof a rotating body of conductive gas or liquid develops self-amplifying electric currents, and thus a self-generated magnetic field, due to a combination of differential rotation (different angular velocity of different parts of body), Coriolis forces and induction. ... This is about the geographic meaning of North Pole. ... The ceremonial South Pole. ... Paleomagnetism refers to the study of the record of the Earths magnetic field preserved in various magnetic minerals through time. ... Van Allen radiation belts The Van Allen Radiation Belt is a torus of energetic charged particles (plasma) around Earth, held in place by Earths magnetic field. ... Christopher Columbus (1451–1506) was a navigator and an admiral for the Crown of Castile whose voyages to America greatly expanded European exploration and colonization of the continent (Vikings had previously had a colony at current New England, and there is significant support for Carthaginian pre-Columbian trans-Atlantic contact). ...

External links

Wikimedia Commons has media related to:
Earth's magnetic field
  • USGS Geomagnetism Program. Real time monitoring of the Earth's magnetic field. U.S. Department of the Interior, U.S. Geological Survey, February 17, 2005.
  • Geomagnetism. National Geophysical Data Center, NOAA. Apr-2005.
  • BGS Geomagnetism. Information on monitoring and modelling the geomagnetic field. British Geological Survey, August 2005.
  • William J. Broad, "Will Compasses Point South?". 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.
  • "3D Earth Magnetic Field Charged-Particle Simulator" Tool dedicated to the 3d simulation of charged particles in the magnetosphere.. [VRML Plug-in Required]
  • Stern, David P. (July 8, 2005). Exploration of the Earth's Magnetosphere. NASA. Retrieved on 2007-03-21.

The National Oceanic and Atmospheric Administration (NOAA) is a scientific agency of the United States Department of Commerce focused on the conditions of the oceans and the atmosphere. ... The New York Times is an internationally known daily newspaper published in New York City and distributed in the United States and many other nations worldwide. ... Not to be confused with Public Broadcasting Services in Malta. ... Artists conception of a white dwarf star accreting hydrogen from a larger companion A nova (pl. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 80th day of the year (81st in leap years) in the Gregorian calendar. ...

References

  • Herndon, J. Marvin (1996) Substructure of the inner core of the Earth Vol. 93, Issue 2, 646-648, January 23, 1996, PNAS
  • Hollenbach, D. F. and J. M. Herndon (2001) Deep-Earth reactor: Nuclear fission, helium, and the geomagnetic field Published online before print September 18, 2001, 10.1073/pnas.201393998, September 25, 2001, vol. 98, no. 20, PNAS


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