When evaluating the Earth magnetic field, immediately the South Atlantic Anomaly becomes clear.
Wikipedia describes it this way: The South Atlantic Anomaly (SAA) is an area where the Earth’s inner Van Allen radiation belt comes closest to the Earth‘s surface, dipping down to an altitude of 200 kilometers (120 mi). This leads to an increased flux of energetic particles in this region and exposes orbiting satellites to higher-than-usual levels of radiation.
The effect is caused by the non-concentricity of the Earth and its magnetic dipole. The SAA is the near-Earth region where the Earth’s magnetic field is weakest relative to an idealized Earth-centered dipole field.
An asymmetrical intersection
The Van Allen radiation belts are symmetrical about the Earth’s magnetic axis, which is tilted with respect to the Earth’s rotational axis by an angle of approximately 11°. The intersection between the magnetic and rotation axes of the Earth is located not at the Earth’s center, but some 450 to 500 km (280 to 310 mi) away. Because of this asymmetry, the inner Van Allen belt is closest to the Earth’s surface over the south Atlantic Ocean where it dips down to 200 km (120 mi) in altitude, and farthest from the Earth’s surface over the north Pacific Ocean.
The Singapore antipodal point
If Earth’s magnetism is represented by a bar magnet of small size but the strong intensity (“magnetic dipole“), the SAA variation can be illustrated by placing the magnet, not in the plane of the Equator, but some small distance North shifted more or less in the direction of Singapore. As a result, over northern South America and the South Atlantic, near Singapore’s antipodal point, the magnetic field is relatively weak, resulting in a lower repulsion to trapped particles of the radiation belts there, and as a result, these particles reach deeper into the upper atmosphere than they otherwise would.
Changing over time
The shape of the SAA changes over time. Since its initial discovery in 1958, the southern limits of the SAA have remained roughly constant while a long-term expansion has been measured to the northwest, the north, the northeast, and the east. Additionally, the shape and particle density of the SAA varies on a diurnal basis, with greatest particle density corresponding roughly to local noon. At an altitude of approximately 500 km (310 mi), the SAA spans from −50° to 0° geographic latitude and from −90° to +40° longitude. The highest intensity portion of the SAA drifts to the west at a speed of about 0.3° per year and is noticeable in the references listed below. The drift rate of the SAA is very close to the rotation differential between the Earth’s core and its surface, estimated to be between 0.3° and 0.5° per year.
The geomagnetic field weakens
Current literature suggests that a slow weakening of the geomagnetic field is one of several causes for the changes in the borders of the SAA since its discovery. As the geomagnetic field continues to weaken, the inner Van Allen belt gets closer to the Earth, with a commensurate enlargement of the SAA at given altitudes.
A permanent magnetic field
This anomaly involves the bigger part of the South Atlantic, South America, Africa, and the Antarctic.
We know that the Earth magnetic field forms in the water of the abyss, in the earth’s core. The moon and the sun, with their magnetic interaction, move the inner salted waters engendering a dynamo effect. This is created due to a previous permanent magnetic field in the magnetite basin. In a very large zone of the Earth, this field weakens greatly.
Pillars sustaining the earth mantle
I already connected this situation to the presence of pillars that sustain the mantle and the crust layers over the abyssal waters. It is not a single column. It would be not enough. Not all columns are necessarily big the same, but we make the hypothesis that there are eight major columns under the mantle. These pillars connect the upper mantle with the lower basin. The material of these pillars is not magnetite, like the basin, but they are rock made with a composition similar to that of the mantle. If they were magnetite made there would be an increase in the magnetic field. But a diminishing is what we have.
Here you can see a picture with the possible position of the eight bigger pillars. There are possibly many other smaller ones.
A pillar in the center of the Atlantic Anomaly
As you can notice, a pillar comes to be exactly in the center of the Atlantic anomaly. I need to understand better the relationship between the pillars and the magnetic field. So I have to further analyze the connection between the surface tidal movements and the magnetic field. This connection (between the pillars and the magnetic field) is clear: where pillars stand, the magnetic field weakens. The magnetic field originates from the dynamo effect, hence from the motion of the abyssal waters. The motion is a consequence of the magnetic interaction of the moon and of the sun. This magnetic effect is obviously acting on the waters of the surface oceans.
Amphidromic points coincident with pillars
In a past article, I described the ocean’s tides as rotating around nodal points called amphidromic points. But what are these points? What happens there? Please, try a fast comparison between the map of the magnetic field and that of tides. You will easily perceive how every amphidromic point is coincident with the pillars position.
Pillars affecting tides
Pillars thus affect the tides and not only the abyssal ones. The magnetic interaction of waters with moon and sun starts up the movement of waters. The wave has a limited amplitude and thus the movement is limited to the circular zone around the pillar. The magnetic field of the tides generated in the abyssal basin acts on the upper waters of the oceans. Surface tides thus rotate around a nodal point due to the presence of a pillar under the mantle.
Everywhere, when you remark an amphidromic point, there is a pillar underground, big or small.
A conclusive summary
To make a summary, there is a bigger magnetic field in correspondence of the magnetite basin near the surface. I mean in the north and south directions, all along the south circumference.
In correspondence of the eight bigger pillars, the magnetic field weakens. The presence of a big or small pillar under the mantel gets manifest where there are amphidromic points. In these points, the possible presence of magnetite on the surface will cause a deviation of the field. Hence, the compass will not indicate north anymore. These anomalies are quite common in a number of places of the Earth, such as the Bermuda triangle.