Wandering of the Geomagnetic poles
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Geomagnetic poles
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Magnetic poles are defined in different ways. They are commonly
understood as positions on the Earth's surface
where the geomagnetic field is vertical (i.e., perpendicular) to the
ellipsoid. These north and south positions,
called dip poles, do not need to be (and are not currently) antipodal.
In principle the dip poles can be found by
conducting a magnetic survey to determine where the field is vertical.
Other definitions
of geomagnetic poles depend on the way the poles are computed from a
geomagnetic model. In practice the geomagnetic field is vertical
on oval-shaped loci traced on a daily basis, with considerable
variation from one day to the next.
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Experimental observations of dip poles
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It has been long understood that dip poles migrate over time. In 1831, James Clark Ross located the north dip pole position
in northern Canada. Natural Resources Canada (NRCan) tracked the North Magnetic Pole, which is slowly drifting across the
Canadian Arctic, by periodically carrying out magnetic surveys to reestablish the Pole's location from 1948 to 1994.
An international collaboration, led by a French fundraising association, Poly-Arctique, and involving NRCan,
Institut de Physique du Globe de Paris and Bureau de Recherche Geologique et Miniere, added two locations of the
North Magnetic Pole in 2001 and 2007. The most recent survey determined that the Pole is moving approximately
north-northwest at 55 km per year.
A web based portal is available to view both the experimental and modeled pole locations here.
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Observed north dip poles during 1831 – 2007 are yellow squares.
Modeled pole locations from 1590 to 2020 are circles progressing from
blue to yellow.
Observed south dip poles during 1903 – 2000 are yellow squares.
Modeled pole locations from 1590 to 2020 are circles progressing from
blue to yellow.
Model derived geomagnetic poles
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Geomagnetic field models can also define geomagnetic poles. The geomagnetic poles, or geocentric dipole, can be computed
from the first three Gauss coefficients from a main field model, such as the World Magnetic Model (WMM) or International
Geomagnetic Reference Field (IGRF). The WMM representation of the field includes a magnetic dipole at the center of the
Earth. This dipole defines an axis that intersects the Earth's surface at two antipodal points called geomagnetic poles.
Based on the WMM2015 coefficients for 2015.0 the geomagnetic north pole is at 72.62°W longitude and 80.31°N latitude,
and the geomagnetic south pole is at 107.38°E longitude and 80.31°S latitude. The axis of the dipole is currently
inclined at 9.69° to the Earth's rotation axis. The same dipole is the basis for the simple geomagnetic coordinate
system of geomagnetic latitude and longitude. Scientists, map makers and polar explorers have an interest in the
locations of the dip and geomagnetic poles. Although geomagnetic pole positions cannot be observed, they are arguably
of greater significance than the dip poles because the auroral ovals (approximate 5° latitude bands where the spectacular
aurora is likely visible) are closely centered on the geomagnetic poles. They are usually displaced slightly to the
night-side of the geomagnetic poles and greatly vary in size: bands of greatest activity occur between 15° and 25°
from the geomagnetic poles.
A software for computing the locations of geomagnetic pole is available here.
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Movement of magnetic poles from 1590 to 2020
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The magnetic poles or dip pole are computed from
all the Gauss coefficients using an iterative method. Magnetic poles derived in this fashion
are geographically closer to the experimentally observed poles. Based
on the current WMM model, the 2015 location of the north magnetic pole
is 86.27°N and 159.18°W and the south magnetic pole is 64.26°S and 136.59°E.
The locations of the poles (1590-2020) are
available for download here: North Pole ,
South Pole.
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