Magnetic poles

Magnetic poles

Earth´s magnetic field (and the surface magnetic field) is approximately a magnetic dipole, with one pole near the north pole and the other near the geographic south pole. An imaginary line joining te magnetic poles would be inclined by approximately 11.3o from the planet’s axis of rotation. The cause of the field is probably explained by dynamo theory. The magnetic field extends several tens of thousands of kilometers into space as the magnetosphere.

Magnetic poles

Magnetic declination from true north in 2000. The locations of the magnetic poles are not static but wander as much as 15km every year (Dr. David P. Stern, emeritus Goddard Space Flight Center, NASA). The pole position is usually not that indicated on many charts and many magnetic pole marking brings a confusion as to what is being located at the given positions.

The geomagnetic pole position are usually not close to the position that commercial cartographers place “geomagnetic dipole poles”, “IGRF model dip poles”, and “magnetic dip poles ” are variously used to denote the magnetic poles.

The Earth’s field is changing in size and position. The two poles wander independently of each other and are not at directly opposite positions on the globe. Currently the sount magnetic pole is farther from the geographic south pole than the north magnetic pole is from the north geographic pole

Field characteristics

The field is similar to that of a bar magnet, but this similarity is superficial. The magnetic field of a bar magnet, or any other type of permanent magnet, is created by the coordinated motions of electrons (negatively charged particles) within iron atoms. The Earth’s core, however, is hotter than 1043 K, the curie point Temperature at which the orientations of electron orbits within iron become randomized. Such randomization tends to cause the substance to lose its magnetic field. Therefore the Earth’s magnetic field is caused not by magnetized iron deposits, but mostly by electric currents in the liquid outer core.

Another feature that distinguishes the earth magnetically from a bar magnet is its magnetosphere. At large distances from the planet, this dominates the surface magnetic field. Electric currents induced in the ionosphere also generate magnetic fields, such a field is always generated near where the atmosphere is closest to the sun, causing daily alterations whish can deflect surface magnetic fields by as much as one degree.

Magnetic field variations

The strength of the field at the earth’s surface ranges from less than 30 microteslas (0.3 gauss) in an area including most of south America and south Africa to ever 60 microteslas (0.6 gauss) around the magnetic poles in the northern Canada an south of Australia, and in part of Siberia.

Magnetometers detect minute deviations in the Earth’s field caused by iron artifacts, kilns, some types of structures, and even ditches and middens in geophysical survey. Using the magnetic intruments adapted from airborne devices developed during world War II to detect submarines, the magnetic variations across the ocean floor have been mapped. The basalt – the iron-rich, volcanic rock making up the ocean floor – contains a strongly magnetic mineral (magnetite) and can locally distort compass readings. The distortion was recognized by Icelandic mariners as early as the late 18th century. More important, because the presence of magnetite gives the basalt measurable magnetic properties, these magnetic variations have provided another means to study the deep ocean floor. when newly formed rock cools, such magnetic materials record the earth’s magnetic field.

A geomagnetic reversal is a change in the orientation of earth’s magnetic field such that the positions of magnetic north and magnetic south become interchanged. These events, which typically last a few hundred to a few

...