magnetic pole

magnetic pole the two nearly opposite ends of the planet where the earth's magnetic intensity is the greatest, as the north and south magnetic poles. For the magnetic north, it is the direction from any point on the earth's surface linking the horizontal component of the magnetic lines of force with the observer and north magnetic pole; it is similar for magnetic south. The north magnetic pole, first located (1831) by British explorer Sir James C. Ross , is now about 78°N and 104°W in the Queen Elizabeth Islands of northern Canada. The south magnetic pole, reached (1909) by Australian geologists Sir T. W. E. David and Sir Douglas Mawson , is now about 66°S and 139°E on the Adélie Coast of Antarctica. The magnetic poles are not fixed but follow circular paths with diameters of about 100 miles (160 km). Studies of paleomagnetism also indicate that the earth's magnetic field has reversed its polarity many times in the geologic past. The best hypothesis to date for the origin of terrestrial magnetism is the self-exciting dynamo theory, where the earth's magnetic field is generated by the interaction of motion and electrical currents in the earth's liquid outer core.

magnetic pole The north and south magnetic poles are two special locations on the Earth's surface near the geographic poles, where a horizontally pivoted compass needle shows a vertical orientation with respect to the Earth's surface (see geomagnetism: main field, secular variation, and westward drift for the difference between the terms ‘magnetic’ and ‘geomagnetic’). There are in fact many places on the Earth where a compass needle may show a vertical magnetic inclination because of the effect of strong local geological or cultural sources; thus, to qualify for a magnetic pole, the orientation of the compass needle must gradually become vertical over a very long distance. Magnetic poles have no particular scientific significance. Finding their location has, however, been historically important as a test of human endurance in Arctic and Antarctic climates—perhaps also as symbols of the human spirit of exploration of the unknown. On the other hand, the locations of the geomagnetic poles (the places where the axis of the geocentric magnetic dipole that best fits the main field intersect the Earth's surface) and the geomagnetic latitudes are considerably more important because many ionospheric phenomena in polar regions are related to geomagnetic latitudes and field lines. Magnetic latitudes are, however, scientifically more critical in the equatorial– mid-latitude regions.

Dhananjay Ravat

mag·net·ic pole • n. each of the points near the extremities of the axis of rotation of the earth or another celestial body where a magnetic needle dips vertically. ∎  each of the two points or regions of an artificial or natural magnet to and from which the lines of magnetic force are directed.