geomagnetism

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geomagnetism:

see magnetismmagnetism,
force of attraction or repulsion between various substances, especially those made of iron and certain other metals; ultimately it is due to the motion of electric charges.
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geomagnetism

(jee-oh-mag -nĕ-tiz-ăm) The Earth's magnetic field (or its study), which at the Earth's surface approximates that of a bar magnet at the center of the Earth with its axis inclined by 11.4° to the Earth's rotation axis and somewhat off-centered: the north magnetic and geographical poles are much closer together than the south poles. Both sets of poles wander in position. The strength of the magnetic field varies from 0.6 gauss near the magnetic poles to 0.3 gauss near the equator, i.e. from 60–30 microtesla, but can depart by up to 20% from the average without any correlation with major surface features. The dipole field changes only slowly with time but there are larger local variations in strength and direction. Violent short-term fluctuations occur during geomagnetic storms. Studies of magnetized rocks show that the entire magnetic field has reversed in direction about twice every million years in the past 165 million years. Complete reversals (i.e. north pole switching from pointing toward geographic north to pointing south, or vice versa) can occur within a few thousand years. The source of the geomagnetic field is believed to lie in a complex dynamo action in the Earth's liquid iron-rich outer core. Convective motion in this rotating electrically conducting fluid, in the presence of a magnetic field, generates electric currents; these in turn induce a magnetic field. Hence the Earth's field has been maintained. The field existed since at least 2.5, probably 3.5, thousand million years ago. See also magnetosphere; ring current.

geomagnetism

[¦jē·ō′mag·nə‚tiz·əm]
(geophysics)
The magnetism of the earth. Also known as terrestrial magnetism.
The branch of science that deals with the earth's magnetism.
References in periodicals archive ?
As for Hydro-Quebec, because NASA's satellite wasn't available in 1989, the company had to resort to the more expensive alternative, investing millions to install devices in its transmission lines that block the geomagnetically induced currents, says Butler.
Voltage regulation can be affected as undesired relay operations occur on important system equipment, and new areas of vulnerability are exposed from the interaction of geomagnetically induced currents (GIC) with equipment that has been added to the grid.
Also deployed was a low-light television camera, which recorded the images produced as the geomagnetically trapped and spiraling electrons fired in pulses by the gun ionized neutral atoms of the upper atmosphere.
Geomagnetically induced currents (GIC) are produced when shocks from severe magnetic storms interrupt the Earth's normally stable magnetic field.
When the Earth's magnetic field captures ionized particles carried by the solar wind, geomagnetically induced currents can flow through the power system, entering and exiting the many grounding points on a transmission network.
Igneous rock has a high level of electrical resistance, which encourages geomagnetically induced currents to flow in the power-transmission lines situated above the rock.