![North Magnetic Poles](https://upload.wikimedia.org/wikipedia/commons/9/9c/North_Magnetic_Poles.svg)
The geomagnetic poles are
antipodal point
In mathematics, antipodal points of a sphere are those diametrically opposite to each other (the specific qualities of such a definition are that a line drawn from the one to the other passes through the center of the sphere so forms a true d ...
s where the axis of a best-fitting
dipole
In physics, a dipole () is an electromagnetic phenomenon which occurs in two ways:
*An electric dipole deals with the separation of the positive and negative electric charges found in any electromagnetic system. A simple example of this system i ...
intersects the surface of
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
. This ''theoretical'' dipole is equivalent to a powerful bar
magnet
A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nickel, ...
at the
center of Earth, and comes closer than any other point dipole model to describing the
magnetic field
A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...
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
Earth's outer core is a fluid layer about thick, composed of mostly iron and nickel that lies above Earth's solid inner core and below its mantle. The outer core begins approximately beneath Earth's surface at the core-mantle boundary and e ...
, 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.
The poles also swing in an oval of around in diameter daily due to
solar wind
The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between . The composition of the sola ...
deflecting the magnetic field.
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
aurora
An aurora (plural: auroras or aurorae), also commonly known as the polar lights, is a natural light display in Earth's sky, predominantly seen in high-latitude regions (around the Arctic and Antarctic). Auroras display dynamic patterns of bri ...
s can be observed. The
dipole model of the Earth's magnetic field
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 ina ...
consists of the location of geomagnetic poles and the dipole moment, which describes the strength of the field.
Definition
As a
first-order approximation
In science, engineering, and other quantitative disciplines, order of approximation refers to formal or informal expressions for how accurate an approximation is.
Usage in science and engineering
In formal expressions, the ordinal number used ...
, the
Earth's magnetic field
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 f ...
can be modeled as a simple
dipole
In physics, a dipole () is an electromagnetic phenomenon which occurs in two ways:
*An electric dipole deals with the separation of the positive and negative electric charges found in any electromagnetic system. A simple example of this system i ...
(like a bar magnet), tilted about 9.6° with respect to the
Earth's rotation
Earth's rotation or Earth's spin is the rotation of planet Earth around its own Rotation around a fixed axis, axis, as well as changes in the orientation (geometry), orientation of the rotation axis in space. Earth rotates eastward, in retrograd ...
axis (which defines the
Geographic North and
Geographic South Pole
The South Pole, also known as the Geographic South Pole, Terrestrial South Pole or 90th Parallel South, is one of the two points where Earth's axis of rotation intersects its surface. It is the southernmost point on Earth and lies antipod ...
s) and centered at the Earth's center.
The North and South Geomagnetic Poles are the
antipodal point
In mathematics, antipodal points of a sphere are those diametrically opposite to each other (the specific qualities of such a definition are that a line drawn from the one to the other passes through the center of the sphere so forms a true d ...
s 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).
If the Earth's magnetic field were a perfect dipole, the
field line
A field line is a graphical visual aid for visualizing vector fields. It consists of an imaginary directed line which is tangent to the field vector at each point along its length. A diagram showing a representative set of neighboring field l ...
s would be vertical to the surface at the Geomagnetic Poles, and they would align with the
North
North is one of the four compass points or cardinal directions. It is the opposite of south and is perpendicular to east and west. ''North'' is a noun, adjective, or adverb indicating Direction (geometry), direction or geography.
Etymology
T ...
and
South
South is one of the cardinal directions or Points of the compass, compass points. The direction is the opposite of north and is perpendicular to both east and west.
Etymology
The word ''south'' comes from Old English ''sūþ'', from earlier Pro ...
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.
Location
Like the
North Magnetic Pole
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 Earth's magnetic field, planet's magnetic field points vertically downward (in other words, if a magnetic comp ...
, the North Geomagnetic Pole attracts the north pole of a bar
magnet
A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nickel, ...
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
The interplanetary magnetic field (IMF), now more commonly referred to as the heliospheric magnetic field (HMF), is the component of the solar magnetic field that is dragged out from the solar corona by the solar wind flow to fill the Solar Syst ...
and provide a direct route for the
solar wind
The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between . The composition of the sola ...
to reach the
ionosphere
The ionosphere () is the ionized part of the upper atmosphere of Earth, from about to above sea level, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays an ...
. , it will be located at ,
on
Ellesmere Island
Ellesmere Island ( iu, script=Latn, Umingmak Nuna, lit=land of muskoxen; french: île d'Ellesmere) is Canada's northernmost and List of Canadian islands by area, third largest island, and the List of islands by area, tenth largest in the world. ...
,
Nunavut
Nunavut ( , ; iu, ᓄᓇᕗᑦ , ; ) is the largest and northernmost Provinces and territories of Canada#Territories, territory of Canada. It was separated officially from the Northwest Territories on April 1, 1999, via the ''Nunavut Act'' ...
,
Canada
Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...
, compared to 2015, when it was located at , also on Ellesmere Island.
[
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. , it is located at ,] whereas in 2005, it was calculated to be located at , near Vostok Station
Vostok Station (russian: :ru:Восток (антарктическая станция), ста́нция Восто́к, translit=stántsiya Vostók, , meaning "Station East") is a Russian Research stations in Antarctica, research station in ...
.
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
A compass is a device that shows the cardinal directions used for navigation and geographic orientation. It commonly consists of a magnetized needle or other element, such as a compass card or compass rose, which can pivot to align itself with ...
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 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 ...
in the Earth's crust
Earth's crust is Earth's thin outer shell of rock, referring to less than 1% of Earth's radius and volume. It is the top component of the lithosphere, a division of Earth's layers that includes the crust and the upper part of the mantle. The ...
also contribute to the local field.[
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
The International Geomagnetic Reference Field (IGRF) is a standard mathematical description of the large-scale structure of the Earth's main magnetic field and its secular variation. It was created by fitting parameters of a mathematical model of ...
(covering a wide time-span in history) or the U.S. World Magnetic Model
The World Magnetic Model (WMM) is a large spatial-scale representation of the Earth's magnetic field. It was developed jointly by the US National Geophysical Data Center and the British Geological Survey. The data and updates are issued by the ...
(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
Earth's outer core is a fluid layer about thick, composed of mostly iron and nickel that lies above Earth's solid inner core and below its mantle. The outer core begins approximately beneath Earth's surface at the core-mantle boundary and e ...
. (See 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 ...
.) 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.[
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.]
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
A geomagnetic reversal is a change in a planet's magnetic field such that the positions of magnetic north and magnetic south are interchanged (not to be confused with geographic north and geographic south). The Earth's field has alternated ...
. Evidence of geomagnetic reversals can be seen at mid-ocean ridge
A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics. It typically has a depth of about and rises about above the deepest portion of an ocean basin. This feature is where seafloor spreading takes place along a diverge ...
s where tectonic plate
Plate tectonics (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large te ...
s move apart. As magma
Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural sa ...
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
Remanence or remanent magnetization or residual magnetism is the magnetization left behind in a ferromagnetic material (such as iron) after an external magnetic field is removed. Colloquially, when a magnet is "magnetized", it has remanence. The ...
is called palaeomagnetism
Paleomagnetism (or palaeomagnetismsee ), is the study of magnetic fields recorded in rocks, sediment, or archeological materials. Geophysicists who specialize in paleomagnetism are called ''paleomagnetists.''
Certain magnetic minerals in rocks ...
. 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.
See also
* Earth's magnetic field
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 f ...
Notes
References
*
*
*{{cite book, last1=Merrill, first1= Ronald T., last2=McElhinny, first2=Michael W., last3=McFadden, first3=Phillip L., title=The magnetic field of the earth: Paleomagnetism, the core, and the deep mantle, publisher=Academic Press
Academic Press (AP) is an academic book publisher founded in 1941. It was acquired by Harcourt, Brace & World in 1969. Reed Elsevier bought Harcourt in 2000, and Academic Press is now an imprint of Elsevier.
Academic Press publishes reference ...
, year=1996, isbn=978-0-12-491246-5
External links
NOAA—Geomagnetic-related web resources
Geomagnetism
Orientation (geometry)