Important variations in the magnetic field, observed by satellites in certain areas of the globe, could herald an inversion of the poles. This phenomenon has already come about several times in the history of the planet. Is the Earth losing its compass? This is what a study by the Department of Geomagnetism and Paleomagnetism of the Paris Geophysical Institute (l’Institut de physique du globe de Paris [IPG]) would have us believe.
We are all contained by the Earth’s magnetic field without really noticing it. We become aware of it only when we use a compass to find our way. This is the most obvious manifestation of the Earth’s magnetism, which has existed for 3 billion years and is generated 3,000 kilo-meters under our feet by the stirring of our planet’s liquid iron core. This liquid iron core causes the Earth to act like a giant magnet; the magnetic lines are organized on a bipolar basis, more or less in alignment with the Earth’s rotational axis.
This bipolar configuration, however, is not permanent. It varies with the movement of the Earth’s liquid core, and in the past, the positions of the magnetic poles have been known to switch entirely. These phenomena were verified by paleomagnetic studies on ancient volcanic basalts. The latter contain magnetic grains that kept both the orientation and strength of the Earth’s magnetic field when they became solid.
The Earth’s magnetosphere is a close- to-spherical magnetic field that surrounds our planet. As a matter of fact, this magnetosphere shields us from the constant bombardment that our globe suffers as a consequence of t its exposition to the Sun. It is estimated that the Sun is blowing several radiation particles, in many directions, around 1 billion kilograms of electrons, protons and other forms of dense matter per second.
There is a spot in this magnetic shielding that actually plays as a hole letting the incoming solar wind to penetrate close to our ground and release a larger radiation dose comparatively to other areas where the magnetosphere shows a more uniform profile. That dip is said to be caused by the eccentric displacement of the center of the
magnetic field from the geographical center of the Earth as well as the displacement between the magnetic and geographic poles. This dip is dubbed the South Atlantic magnetic anomaly (SAMA). It is occupying the area between Southeast Brazil and South Africa.
The minimum value, of the total geomagnetic field F of about 22,850 nT is found around 26° South and 54° West, which agrees well with the International Geomagnetic Reference Field (IGRF) model for the year 2000. The F field strength within the radius of about 1000 km around the F minimum point is less than 23,000 nT. It can be noted that the anomaly is dynamic, the center of the anomaly, that is the area of F minimum, has traveled in the last century from near Rio de Janeiro (23°.0 S, 43°.0 W) to Rio Grande do Sul (29°.0 S, 54°.0 W). These locations are determined from a combination of the magnetic maps prepared by the Brazilian National Observatory, Ministry of Science and Technology, Rio de Janeiro and the IGRF models Marins (2002). The center of F minimum and location of magnetic equator both have undergone a large secular variation unseen elsewhere. It is thought that this westward drift of the center of the anomaly and magnetic equator may be related to the westward drift of the geomagnetic axis of the Earth. The present value of F at São Martinho da Serra (SMS) (29°.43 S, 53°.80 W) is 22,883 nT and it is decreasing at the rate of 28 nT/year.
If the South Atlantic magnetic anomaly (SAMA) is taken as signal of an imminent reversal of our planet´s magnetic poles, how imminent is the reversal occurrence?
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