Geomagnetic pole
The geomagnetic poles are
Owing to motion of fluid in the Earth's
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]
Year | 1990 (definitive) | 2000 (definitive) | 2010 (definitive) | 2020 |
---|---|---|---|---|
North geomagnetic pole | 79°12′N 71°06′W / 79.2°N 71.1°W | 79°36′N 71°36′W / 79.6°N 71.6°W | 80°06′N 72°12′W / 80.1°N 72.2°W | 80°42′N 72°42′W / 80.7°N 72.7°W |
South geomagnetic pole | 79°12′S 108°54′E / 79.2°S 108.9°E | 79°36′S 108°24′E / 79.6°S 108.4°E | 80°06′S 107°48′E / 80.1°S 107.8°E | 80°42′S 107°18′E / 80.7°S 107.3°E |
Magnetic dipole moment |
7.84 | 7.79 | 7.75 | 7.71 |
Definition
As a
Location
Like the
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′S 107°19′E / 80.65°S 107.32°E,[7] whereas in 2005, it was calculated to be located at 79°44′S 108°13′E / 79.74°S 108.22°E, 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
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
See also
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.
- ^ a b Nair, Manoj C. "Wandering of the Geomagnetic Poles | NCEI". www.ngdc.noaa.gov.
- ^ a b "Magnetic North: Geomagnetic and Magnetic Poles". World Data Center for Geomagnetism. Kyoto, Japan: Kyoto University. Retrieved 11 June 2018.
- ^ a b c "Geomagnetism Frequently Asked Questions". National Geophysical Data Center. Retrieved 1 June 2016.
- ^ a b Merrill, McElhinny & McFadden 1996, Chapter 2
- ^ a b "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
References
- McElhinny, Michael W.; McFadden, Phillip L. (2000). Paleomagnetism: Continents and Oceans. ISBN 0-12-483355-1.
- Merrill, Ronald T. (2010). Our Magnetic Earth: The Science of Geomagnetism. 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. ISBN 978-0-12-491246-5.