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Earth's magnetic field

The Earth’s magnetic field is the magnetic field which surrounds the Earth. It is sometimes called the geomagnetic field.

The Earth’s magnetic field is created by the rotation of the Earth and Earth's core.[1] It shields the Earth against harmful particles in space. The field is unstable and has changed often in the history of the Earth.[2] As the Earth spins, the two parts of the core move at different speeds and this is thought to generate the magnetic field around the Earth as though it had a large bar magnet inside it.

The magnetic field creates magnetic poles that are near to the geographical poles. A compass uses the geomagnetic field to find directions. Many migratory animals also use the field when they travel long distances each spring and fall.[3]

Characteristics

The Earth’s geomagnetic field is created by two things. The convection in the liquid conducting core inside the center of the Earth is important for making the magnetic field.[2] When convection occurs in the electrical currents around the Earth, the magnetic field is created.[2] The Earth’s rotation is what keeps the magnetic field up. The interaction between the convective motions and the electrical currents creates a dynamo effect.

The intensity of the magnetic field is greatest near the magnetic poles[1] where it is vertical. The intensity of the field is weakest near the equator where it is horizontal. The magnetic field’s intensity is measured in gauss.[1]

The magnetic field has decreased in strength through recent years. In the early 21st century the field has decreased its strength 1.7%, on average.[2] In some areas of the field, the strength has decreased as much as 10%.[2] The reversal might happen in the next few thousand years. It has been shown that the movement of the magnetic poles is related to the decreasing strength of the magnetic field.[2]

A geomagnetic reversal is when the north magnetic pole and south magnetic pole trade places. This has happened a few times in the past few million years. The magnetic reversal happens after the strength of the field reaches zero.[3] When the strength begins to increase again, it will increase in the opposite direction, causing a reversal of the magnetic poles.[3] The time it takes the magnetic field to undergo a reversal is unknown, but can last up to ten thousand years.[3]

Magnetosphere

 
This figure shows the magnetosphere blocking solar wind caused by the sun.

The magnetosphere is created by the magnetic field. It is the area around the Earth that acts as a shield against the harmful particles in solar wind.[4] The magnetosphere has many different layers and structures, and solar wind shapes each of these layers.[4] The interaction of solar wind and the magnetosphere also causes the Northern and Southern Lights to appear.[5] The magnetosphere is very important in protecting the Earth against solar storms[4] which increase solar wind activity. Solar storms can cause geomagnetic storms which sometimes have serious affects on the Earth.

 
Movement of the north magnetic pole. It is expected to pass near the north geographic pole and continue its path to Siberia

The areas in between the north and south magnetic poles are the magnetic field lines. These lines leave the Earth from the vertical point of the South and reenters through the vertical point of the North. These two vertical points are called magnetic dip poles.[1] The magnetic dip poles are commonly referred to as the magnetic poles. The magnetic poles intersect the Earth at two points. The north magnetic pole intersects the Earth at 78.3 N latitude and 100 W longitude.[6] This places the north magnetic pole in the Arctic Circle. The south magnetic pole intersects the Earth at 78.3 S latitude and 142 E longitude.[6] This places the south magnetic pole in Antarctica. The magnetic poles are also where the magnetic fields are the strongest.[2]

Earth's magnetic poles

Like other magnetic fields, the Earth's magnetic field has magnetic poles.

The North Magnetic Pole is the point on the surface of Earth's northern hemisphere where the planet's magnetic field points vertically downwards. There is only one place where this occurs, near to (but distinct from) the Geographic North Pole.

Its southern hemisphere counterpart is the South Magnetic Pole. Since the Earth's magnetic field is not exactly symmetrical, a line drawn from one to the other does not pass through the geometric centre of the Earth.

The North Magnetic Pole moves over time due to magnetic changes in the Earth's core.[7] In 2001, it was near Ellesmere Island in northern Canada at 81°18′N 110°48′W / 81.3°N 110.8°W / 81.3; -110.8 (Magnetic North Pole 2001). As of 2015, the pole is thought to have moved east beyond the Canadian Arctic territorial claim to 86°18′N 160°00′W / 86.3°N 160.0°W / 86.3; -160.0 (Magnetic North Pole 2012 est).[8]

The Earth's North and South Magnetic Poles are also known as Magnetic Dip Poles, referring to the vertical "dip" of the magnetic field lines at those points.[9]

Migratory animals

Animals which take long migrations may depend on the magnetic field for a guide.[5]

Some migratory animals know their locations by the intensity of the field.[10] They know the time because of circadian rhythms the field produces. Migratory animals are born with a magnetic map in their head that allows them to migrate great distances safely.[11] Their ability to sense the magnetic field is because of magnetic particles. Other animals have a different mechanism.[12][13]

Earth's Magnetic Field Media

  • Computer simulation of Earth's field in a period of normal polarity between reversals.

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

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

  • The movement of Earth's North Magnetic Pole across the Canadian arctic

  • An artist's rendering of the structure of a magnetosphere. 1) Bow shock. 2) Magnetosheath. 3) Magnetopause. 4) Magnetosphere. 5) Northern tail lobe. 6) Southern tail lobe. 7) Plasmasphere.

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

  • Estimated declination contours by year, 1590 to 1990 (click to see variation)

  • Strength of the axial dipole component of Earth's magnetic field from 1600 to 2020

  • Geomagnetic polarity during the late Cenozoic Era. Dark areas denote periods where the polarity matches today's polarity, light areas denote periods where that polarity is reversed.

  • Variations in virtual axial dipole moment since the last reversal

  • Sea level magnetic fields observed by satellites (NASA)

References

  1. ↑ 1.0 1.1 1.2 1.3 Zvereva T.I. (2012). "Motion of the Earth's magnetic poles in the last decade". Geomagnetism and Aeronomy. 52 (2): 278–286. doi:10.1134/S0016793212020168. S2CID 121437116.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 Dergachev V.A.; et al. (2012). "Impact of the geomagnetic field and solar radiation on climate change". Geomagnetism and Aeronomy. 52 (8): 959–976. doi:10.1134/S0016793212080063. S2CID 121440857.
  3. ↑ 3.0 3.1 3.2 3.3 Markove, Marko S. (2011). "How living systems recognize applied electromagnetic fields". The Environmentalist. 31 (2): 89–96. doi:10.1007/s10669-011-9314-0. S2CID 123650418.
  4. ↑ 4.0 4.1 4.2 Dergachev V.A.; et al. (2011). "The connection between cosmic rays and changes in the geomagnetic field and the Earth's climate". Bulletin of the Russian Academy of Sciences:Physics. 75 (6): 847–850. doi:10.3103/S1062873811060128. S2CID 122598446.
  5. ↑ 5.0 5.1 Mikhailova G.A. & Smirnov S.E. (2011). "Effects of geomagnetic disturbances in the near Earth's atmosphere and possible biophysical mechanism of their influence on the human cardiovascular system". Izvestiya, Atmospheric and Oceanic Physics. 47 (7): 805–818. doi:10.1134/S0001433811070061. S2CID 122860566.
  6. ↑ 6.0 6.1 Bertolotti, Mario (2012). "The Earth's magnetic field and the geomagnetic effects". Celestial messengers: cosmic rays: the story of a scientific adventure. Astronomers' Universe. Springer. pp. 75–103. ISBN 978-3-642-28370-3.
  7. ↑ Merrill, Ronald T.; McElhinny, Michael W.; McFadden, Phillip L. (1996). "Chapter 8". The magnetic field of the earth: paleomagnetism, the core, and the deep mantle. Academic Pres]. ISBN 978-0-12-491246-5.
  8. ↑ World Data Center for Geomagnetism, Kyoto. "Magnetic North, Geomagnetic and Magnetic Poles". Retrieved 2012-07-03.
  9. ↑ "The Magnetic North Pole". Ocean bottom magnetology laboratory. Woods Hole Oceanographic Institution. Archived from the original on 2013-08-19. Retrieved 1 June 2012.
  10. ↑ Scott, Rebecca, Robert Marsh, and Graeme C. Hays (2012). "A little movement orientated to the geomagnetic field makes a big difference in strong flows". Marine Biology. 159 (3): 481–488. doi:10.1007/s00227-011-1825-1. S2CID 85973517.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  11. ↑ Wiltschicko, Wolfgang and Roswitha Witschko (2005). "Magnetic orientation and magnetoreception in birds and other animals". Journal of Comparative Physiology. 191 (8): 675–693. doi:10.1007/s00359-005-0627-7. PMID 15886990. S2CID 206960525.
  12. ↑ Gould J.L. (1984). "Magnetic field sensitivity in animals". Annual Review of Physiology. 46: 585–598. doi:10.1146/annurev.ph.46.030184.003101. PMID 6370118. Retrieved 25 February 2013.
  13. ↑ Lehikoinen, Aleksi and Kim Jaatinen (2011). "Delayed autumn migration in Northern European waterfowl" (PDF). Journal of Ornithology. 153 (2): 563–570. doi:10.1007/s10336-011-0777-z. S2CID 8805546. Retrieved 26 February 2013.[dead link]

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