# Earth's magnetic field

(Redirected from Geomagnetic)

The Earth’s magnetic field is the magnetic field that 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 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. The magnetic poles will trade places during a magnetic reversal.[3]

## Characteristics

The Earth’s geomagnetic field is created because of two things. The convective motions in the liquid conducting core inside the center of the Earth are important for making the magnetic field.[2] When the convective motions occur with 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 past twenty-two years, the field has decreased its strength 1.7%, on average.[2] In some areas of the field, the strength has decreased up to 10%.[2] The fast strength decrease of the field is a sign that the magnetic field might be reversing. 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 history of the Earth. 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] The Earth’s magnetic reversals are recorded in rocks, especially in basalt. Scientists believed that the last geomagnetic reversal occurred 780,000 years ago.[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

### North magnetic pole

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. 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.[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 chemical compass based on a radical pair mechanism.[12][13]

## References

1. Zvereva T.I. (2012). "Motion of the Earth's magnetic poles in the last decade". Geomagnetism and Aeronomy 52 (2): 278-286.
2. Dergachev V.A. et al. (2012). "Impact of the geomagnetic field and solar radiation on climate change". Geomagnetism and Aeronomy 52 (8): 959-976.
3. Markove, Marko S. (2011). "How living systems recognize applied electromagnetic fields". The Environmentalist 31 (2): 89-96.
4. 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.
5. 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.
6. 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. `|access-date=` requires `|url=` (help)
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. Retrieved June 2012. Check date values in: `|accessdate=` (help)
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.
11. Wiltschicko, Wolfgang and Roswitha Witschko (2005). "Magnetic orientation and magnetoreception in birds and other animals". Journal of Comparative Physiology 191 (8): 675-693.
12. Gould J.L. (1984). "Magnetic field sensitivity in animals". Annual Review of Physiology 46: 585-598.
13. Lehikoinen, Aleksi and Kim Jaatinen (2011). "Delayed Autumn migration in northern european waterfowl". Journal of Ornithology 153 (2): 563-570. Retrieved 26 February 2013.