Geomagnetic pole

Last updated April 01, 2023

The geomagnetic poles are antipodal points where the axis of a best-fitting dipole intersects the surface of Earth. This theoretical dipole is equivalent to a powerful bar magnet at the center of Earth, and comes closer than any other point dipole model to describing the magnetic field observed at Earth's surface. In contrast, the magnetic poles of the actual Earth are not antipodal; that is, the line on which they lie does not pass through Earth's center.

Owing to motion of fluid in the Earth's outer core, the actual magnetic poles are constantly moving (secular variation). However, over thousands of years, their direction averages to the Earth's rotation axis. On the order of once every half a million years, the poles reverse (i.e., north switches place with south) although the time frame of this switching can be anywhere from every 10 thousand years to every 50 million years.^[2] The poles also swing in an oval of around 50 miles (80 km) in diameter daily due to solar wind deflecting the magnetic field.^[3]

Although the geomagnetic pole is only theoretical and cannot be located directly, it arguably is of more practical relevance than the magnetic (dip) pole. This is because the poles describe a great deal about the Earth's magnetic field, determining for example where auroras can be observed. The dipole model of the Earth's magnetic field consists of the location of geomagnetic poles and the dipole moment, which describes the strength of the field.^[3]

Recent locations of Earth's geomagnetic (auroral) poles, IGRF-13 fit^[4]
Year	1990 (definitive)	2000 (definitive)	2010 (definitive)	2020
North geomagnetic pole	79°12′N71°06′W / 79.2°N 71.1°W / 79.2; -71.1 (NGMP 1990)	79°36′N71°36′W / 79.6°N 71.6°W / 79.6; -71.6 (NGMP 2010)	80°06′N72°12′W / 80.1°N 72.2°W / 80.1; -72.2 (NGMP 2020)	80°42′N72°42′W / 80.7°N 72.7°W / 80.7; -72.7 (NGMP 2020) Coordinates: 80°42′N72°42′W / 80.7°N 72.7°W / 80.7; -72.7 (NGMP 2020)
South geomagnetic pole	79°12′S108°54′E / 79.2°S 108.9°E / -79.2; 108.9 (SGMP 1990)	79°36′S108°24′E / 79.6°S 108.4°E / -79.6; 108.4 (SGMP 2000)	80°06′S107°48′E / 80.1°S 107.8°E / -80.1; 107.8 (SGMP 2010)	80°42′S107°18′E / 80.7°S 107.3°E / -80.7; 107.3 (SGMP 2020)
Magnetic dipole moment (10²² A ⋅ m²)	7.84	7.79	7.75	7.71

Definition

As a first-order approximation, the Earth's magnetic field can be modeled as a simple dipole (like a bar magnet), tilted about 9.6° with respect to the Earth's rotation axis (which defines the Geographic North and Geographic South Poles) and centered at the Earth's center.^[5] The North and South Geomagnetic Poles are the antipodal points where the axis of this theoretical dipole intersects the Earth's surface. Thus, unlike the actual magnetic poles, the geomagnetic poles always have an equal degree of latitude and supplementary degrees of longitude respectively (2017: Lat. 80.5°N, 80.5°S; Long. 72.8°W, 107.2°E).^[4] If the Earth's magnetic field were a perfect dipole, the field lines would be vertical to the surface at the Geomagnetic Poles, and they would align with the North and South magnetic poles, with the North Magnetic Pole at the south end of dipole. However, the approximation is imperfect, and so the Magnetic and Geomagnetic Poles lie some distance apart.^[6]

Location

Like the North Magnetic Pole, the North Geomagnetic Pole attracts the north pole of a bar magnet and so is in a physical sense actually a magnetic south pole. It is the center of the 'open' magnetic field lines which connect to the interplanetary magnetic field and provide a direct route for the solar wind to reach the ionosphere. As of 2020^[update], it will be located at 80°39′N72°41′W / 80.65°N 72.68°W / 80.65; -72.68 (Geomagnetic North Pole 2020 est) ,^[7] on Ellesmere Island, Nunavut, Canada, compared to 2015, when it was located at 80°22′N72°37′W / 80.37°N 72.62°W / 80.37; -72.62 (Geomagnetic North Pole 2015 est) , also on Ellesmere Island.^[5]

The South Geomagnetic Pole is the point where the axis of this best-fitting tilted dipole intersects the Earth's surface in the southern hemisphere. As of 2020^[update], it is located at 80°39′S107°19′E / 80.65°S 107.32°E / -80.65; 107.32 (Geomagnetic South Pole 2020 est) ,^[7] whereas in 2005, it was calculated to be located at 79°44′S108°13′E / 79.74°S 108.22°E / -79.74; 108.22 (Geomagnetic South Pole 2005 est) , near Vostok Station.

Because the Earth's actual magnetic field is not an exact dipole, the (calculated) North and South Geomagnetic Poles do not coincide with the North and South Magnetic Poles. If the Earth's magnetic fields were exactly dipolar, the north pole of a magnetic compass needle would point directly at the North Geomagnetic Pole. In practice, it does not because the geomagnetic field that originates in the core has a more complex non-dipolar part, and magnetic anomalies in the Earth's crust also contribute to the local field.^[5]

The locations of geomagnetic poles are calculated by a statistical fit to measurements of the Earth's field by satellites and in geomagnetic observatories. This can be the International Geomagnetic Reference Field (covering a wide time-span in history)^[8] or the U.S. World Magnetic Model (only covering a five-year period).

Movement

The geomagnetic poles move over time because the geomagnetic field is produced by motion of the molten iron alloys in the Earth's outer core. (See geodynamo.) Over the past 150 years, the poles have moved westward at a rate of 0.05° to 0.1° per year and closer to the true poles at 0.01° per year.^[6]

Over several thousand years, the average location of the geomagnetic poles coincides with the geographical poles. Paleomagnetists have long relied on the geocentric axial dipole (GAD) hypothesis, which states that — aside from during geomagnetic reversals — the time-averaged position of the geomagnetic poles has always coincided with the geographic poles. There is considerable paleomagnetic evidence supporting this hypothesis.^[9]

Geomagnetic reversal

Over the life of the Earth, the orientation of Earth's magnetic field has reversed many times, with geomagnetic north becoming geomagnetic south and vice versa – an event known as a geomagnetic reversal. Evidence of geomagnetic reversals can be seen at mid-ocean ridges where tectonic plates move apart. As magma seeps out of the mantle and solidifies to become new ocean floor, the magnetic minerals in it are magnetized in the direction of the magnetic field. The study of this remanence is called palaeomagnetism. Thus, starting at the most recently formed ocean floor, one can read out the direction of the magnetic field in previous times as one moves farther away to older ocean floor.

Notes

↑ "Magnetic North, Geomagnetic and Magnetic Poles". wdc.kugi.kyoto-u.ac.jp. Retrieved 2019-12-18.
↑ "Is it true that Earth's magnetic field occasionally reverses its polarity?". www.usgs.gov. Retrieved 2021-09-16.
1 2 Nair, Manoj C. "Wandering of the Geomagnetic Poles | NCEI". www.ngdc.noaa.gov.
1 2 "Magnetic North: Geomagnetic and Magnetic Poles". World Data Center for Geomagnetism. Kyoto, Japan: Kyoto University. Retrieved 11 June 2018.
1 2 3 "Geomagnetism Frequently Asked Questions". National Geophysical Data Center. Retrieved 1 June 2016.
1 2 Merrill, McElhinny & McFadden 1996 , Chapter 2
1 2 "World Magnetic Model - Model Limitations". www.ngdc.noaa.gov. Retrieved 2020-01-17.
↑ IAGA Division V Working Group V-MOD. "International Geomagnetic Reference Field" . Retrieved 20 December 2016.
↑ Merrill, McElhinny & McFadden 1996 , Chapter 6

Related Research Articles

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Geophysics is a subject of natural science concerned with the physical processes and physical properties of the Earth and its surrounding space environment, and the use of quantitative methods for their analysis. Geophysicists, who usually study geophysics, physics, or one of the earth sciences at the graduate level, complete investigations across a wide range of scientific disciplines. The term geophysics classically refers to solid earth applications: Earth's shape; its gravitational, magnetic fields, and electromagnetic fields ; its internal structure and composition; its dynamics and their surface expression in plate tectonics, the generation of magmas, volcanism and rock formation. However, modern geophysics organizations and pure scientists use a broader definition that includes the water cycle including snow and ice; fluid dynamics of the oceans and the atmosphere; electricity and magnetism in the ionosphere and magnetosphere and solar-terrestrial physics; and analogous problems associated with the Moon and other planets.

The South Atlantic Anomaly (SAA) is an area where Earth's inner Van Allen radiation belt comes closest to Earth's surface, dipping down to an altitude of 200 kilometres (120 mi). This leads to an increased flux of energetic particles in this region and exposes orbiting satellites to higher-than-usual levels of ionizing radiation.

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 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.

In physics, the dynamo theory proposes a mechanism by which a celestial body such as Earth or a star generates a magnetic field. The dynamo theory describes the process through which a rotating, convecting, and electrically conducting fluid can maintain a magnetic field over astronomical time scales. A dynamo is thought to be the source of the Earth's magnetic field and the magnetic fields of Mercury and the Jovian planets.

Polar drift is a geological phenomenon caused by variations in the flow of molten iron in Earth's outer core, resulting in changes in the orientation of Earth's magnetic field, and hence the position of the magnetic north- and south poles.

<span class="mw-page-title-main">Paleomagnetism</span> Study of Earths magnetic field in past

Paleomagnetism is the study of magnetic fields recorded in rocks, sediment, or archeological materials. Geophysicists who specialize in paleomagnetism are called paleomagnetists.

A geomagnetic reversal is a change in a planet's magnetic field such that the positions of magnetic north and magnetic south are interchanged. The Earth's field has alternated between periods of normal polarity, in which the predominant direction of the field was the same as the present direction, and reverse polarity, in which it was the opposite. These periods are called chrons.

Geomagnetic latitude, or magnetic latitude (MLAT), is a parameter analogous to geographic latitude, except that, instead of being defined relative to the geographic poles, it is defined by the axis of the geomagnetic dipole, which can be accurately extracted from the International Geomagnetic Reference Field (IGRF).

The North Pole is the point in the Northern Hemisphere where the Earth's axis of rotation meets its surface.

South Pole or Southpole may refer to:

In geophysics, a magnetic anomaly is a local variation in the Earth's magnetic field resulting from variations in the chemistry or magnetism of the rocks. Mapping of variation over an area is valuable in detecting structures obscured by overlying material. The magnetic variation in successive bands of ocean floor parallel with mid-ocean ridges was important evidence for seafloor spreading, a concept central to the theory of plate tectonics.

Geomagnetic secular variation refers to changes in the Earth's magnetic field on time scales of about a year or more. These changes mostly reflect changes in the Earth's interior, while more rapid changes mostly originate in the ionosphere or magnetosphere.

The dipole model of the Earth's magnetic field is a first order approximation of the rather complex true Earth's magnetic field. Due to effects of the interplanetary magnetic field (IMF), and the solar wind, the dipole model is particularly inaccurate at high L-shells, but may be a good approximation for lower L-shells. For more precise work, or for any work at higher L-shells, a more accurate model that incorporates solar effects, such as the Tsyganenko magnetic field model, is recommended.

Apparent polar wander (APW) is the perceived movement of the Earth's paleo-magnetic poles relative to a continent while regarding the continent being studied as fixed in position. It is frequently displayed on the present latitude-longitude map as a path connecting the locations of geomagnetic poles, inferred at distinct times using paleomagnetic techniques.

Plate reconstruction is the process of reconstructing the positions of tectonic plates relative to each other or to other reference frames, such as the earth's magnetic field or groups of hotspots, in the geological past. This helps determine the shape and make-up of ancient supercontinents and provides a basis for paleogeographic reconstructions.

The north magnetic pole, also known as the magnetic north pole, is a point on the surface of Earth's Northern Hemisphere at which the planet's magnetic field points vertically downward. There is only one location where this occurs, near the geographic north pole. The geomagnetic north pole is the northern antipodal pole of an ideal dipole model of the Earth's magnetic field, which is the most closely fitting model of Earth's actual magnetic field.

The south magnetic pole, also known as the magnetic south pole, is the point on Earth's Southern Hemisphere where the geomagnetic field lines are directed perpendicular to the nominal surface. The Geomagnetic South Pole, a related point, is the south pole of an ideal dipole model of the Earth's magnetic field that most closely fits the Earth's actual magnetic field.

The following outline is provided as an overview of and topical guide to geophysics:

The history of geomagnetism is concerned with the history of the study of Earth's magnetic field. It encompasses the history of navigation using compasses, studies of the prehistoric magnetic field, and applications to plate tectonics.

References

McElhinny, Michael W.; McFadden, Phillip L. (2000). Paleomagnetism: Continents and Oceans. Academic Press. ISBN 0-12-483355-1.
Merrill, Ronald T. (2010). Our Magnetic Earth: The Science of Geomagnetism. University of Chicago Press. ISBN 978-0-226-52050-6.
Merrill, Ronald T.; McElhinny, Michael W.; McFadden, Phillip L. (1996). The magnetic field of the earth: Paleomagnetism, the core, and the deep mantle. Academic Press. ISBN 978-0-12-491246-5.

External links

NOAA—Geomagnetic-related web resources

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[1] "Magnetic North, Geomagnetic and Magnetic Poles". wdc.kugi.kyoto-u.ac.jp. Retrieved 2019-12-18.

[2] "Is it true that Earth's magnetic field occasionally reverses its polarity?". www.usgs.gov. Retrieved 2021-09-16.

[NDGCWA-3] 1 2 Nair, Manoj C. "Wandering of the Geomagnetic Poles | NCEI". www.ngdc.noaa.gov.

[WDCG-4] 1 2 "Magnetic North: Geomagnetic and Magnetic Poles". World Data Center for Geomagnetism. Kyoto, Japan: Kyoto University. Retrieved 11 June 2018.

[NGDC-5] 1 2 3 "Geomagnetism Frequently Asked Questions". National Geophysical Data Center. Retrieved 1 June 2016.

[Merrill1996ch2-6] 1 2 Merrill, McElhinny & McFadden 1996 , Chapter 2

[ndgc1-7] 1 2 "World Magnetic Model - Model Limitations". www.ngdc.noaa.gov. Retrieved 2020-01-17.

[IAGA2010-8] IAGA Division V Working Group V-MOD. "International Geomagnetic Reference Field" . Retrieved 20 December 2016.

[Merrill1996ch6-9] Merrill, McElhinny & McFadden 1996 , Chapter 6

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