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Since the origin of the Earth, the magnetic field that surrounds it has never ceased to vary, while ensuring over billions of years its protective function against solar winds. These variations can go up to complete reversals of the magnetic poles. This process has been repeated many times over the course of geological time. It is, so to speak, a trivial phenomenon, which occurs on average every 200,000 years, even if it is difficult to observe any regularity.

An anomaly, but no program reversal!

Currently, we are able to measure the intensity and orientation of the magnetic field terrestrial and follow its evolution. However, the scientists observe that, for about 180 years, the strength of the magnetic field has decreased by about 10%. An area of ​​weakened magnetic field has also started forming in the South Atlantic off the South American coast. The presence of this anomaly raised the idea that a reverse polarity it could be imminent. This could be the first reversal documented directly by man.

However, a new study, published in PNAS, proves that this is not the case. This type of anomaly would in fact be a recurring phenomenon in the last 9,000 years, in connection with the normal variations of the magnetic field that is generated by complex convective movements inside the outer core of the Earth.

The researchers’ modeling then led to the conclusion that the South Atlantic anomaly could likely disappear within the next 300 years, without causing a magnetic field reversal.

Does the South Atlantic Magnetic Anomaly herald an imminent magnetic reversal?

Is a magnetic reversal of the Earth’s poles imminent? Maybe so … or maybe not. To try to find out, paleomagnetics searched the archives of volcanic rocks of 34 past eruptions on the island of Sainte-Hélène, in the heart of the South Atlantic magnetic anomaly.

Article of Laurent Saccopublished on 22 August 2020

The phenomenon of pole reversal is fascinating, all the more so because it involves a strong temporary weakening of the intensity of the Earth’s magnetic shield. Nevertheless, magnetic reversals discovered more than a century ago they have happened many times in the history of the Earth and there is no convincing evidence that it has, each time, profoundly changed climate or the biosphere. Nothing really special seems to happen when the Blue Planet’s magnetic field is at its maximum, at least as long as it remains very temporary on the geological scale, which counts as a unit of time one million years. Fortunately, therefore, Mergerthe Anglo-American science fiction disaster film directed by Jon Amiel and released in 2003 is destined to remain on the screens.

However, there has long been a decrease in the overall strength of the Earth’s magnetic field as well it is debated whether this is an indication of an impending magnetic reversal. If the phenomenon occurred today, it would certainly upset our technologically advanced civilization, based on electricity, electronics and satellites, especially in the case of storm violent sun.

We understand quite well that the Earth’s magnetic field is the joint product of its rotation and its convection turbulent part of its core League from iron and nickel that is liquid. L’VKS experience (Von Karman Sodium) also allows to reproduce the self-exciting dynamo thus produced and the magnetic reversalsbut we do not yet know how to make good predictions on the evolution of magnetosphere how would we do for the climate and theatmosphereeven if we still succeeded some skill in this direction.

The magnetic anomaly of the South Atlantic and the memory of the Sant’Elena volcano

Some have long wondered if the famous South Atlantic Magnetic Anomaly, which Futura discussed in the previous article below, was not a precursor to magnetic pole reversal. Recall that this is a region of the Atlantic where there is a noticeable weakening of the intensity of the earth’s magnetic field, which is normally roughly dipolar, like that of a magnetic bar made of materials ferromagnetic. Also note that it is associated with malfunctions of nearby satellites above this region.

In an effort to better understand the nature and significance of this anomaly, paleomagnetics have excavated the geomagnetic records of the Earth preserved in the volcanic rocks emitted on the island of St. Helena which lies in the middle of the Atlantic Anomaly. They just published the results of their work in a famous article Proceedings of the National Academy of Sciences (PNA).

Here’s what Yael Engbers, a PhD student at the University of Liverpool and lead author of the article, says PNAS : “Our study provides the first long-term analysis of the magnetic field in this region dating back millions of years. It reveals that the South Atlantic magnetic field anomaly is not a singular anomaly, similar anomalies existed eight to eleven million years ago. This is the first time that the erratic behavior of the geomagnetic field in the South Atlantic region has been shown on such a long time scale. This suggests that the South Atlantic anomaly is a recurring feature and probably not a sign of an impending turnaround. Our work also strengthens previous studies that suggested a link between the South Atlantic anomaly and anomalous seismic characteristics in the coat lower and outer core. This brings us closer to establishing a direct link between the behavior of the geomagnetic field and the characteristics of the interior of the Earth. “.

Why is Earth’s magnetic field weakening in the South Atlantic?

Article of Emma Hollen published on 05/26/2020

the Earth’s magnetic field gradually weakens south of the Atlantic, a phenomenon that confuses more than a geophysicist. While some will argue that this is the work of the Atlanteans, scientists are appealing to heaven.

Although invisible to ours eyesthe Earth’s magnetic field plays an essential role in the preservation of life on our Blue Planet. All at once magnet and shield, deflects the deadly particles of solar winds, the last remnants of which bloom northern Lights and southern to the poles of the planet. However, this is decreasing in a region that stretches between Africa and South America, a region so well known for its magnetic anomalies that it is the subject of its own myths. To understand this amazing phenomenon, scientists turned to Swarma constellation of three minisatellites launched by ESA on 22 November 2013 to study our magnetosphere.

Cluster, a magnetic anomaly in the Atlantic

The magnetic field arises from the convection movements of the outer core of the Earth: surrounding the inner core, solidthis sphere of metal liquid, composed mainly of iron and nickel, acts as a real dynamo. The electric currents generates changes and changes. Thus, recent studies have observed the displacements of the magnetic North Pole for several tens of kilometers per year. But the South Atlantic Magnetic (or Cluster) Anomaly is somewhat different and has questioned scientists for many decades.

Although the overall strength of the Earth’s magnetic field has declined over the past two centuries, the Cluster appears to be following its own course. Between 1970 and 2020, the intensity of the field dropped from 24,000 to 22,000 nanotesla in this region, as the anomaly continues to move west at a rate of 20 kilometers per year. More recently, in the past five years, a second foyer low intensity appears to have emerged in southwestern Africa, suggesting that the anomaly could separate into two separate cells.

This visualization illustrates the evolution of the South Atlantic Magnetic Anomaly as recorded by the Swarm over the past five years. © Swarm, ESA

Polarity reversal?

The existence of the Cluster calls into question the reductionist conception that one could have of the mechanics at the origin of the Earth’s magnetic field. A simple dipole model, which describes an Earth acting as a magnet, not enough to explain L’emergency of these anomalies. That is why, in November 2013, ESA launched the Swarm mission, with the aim of exploring our magnetosphere. ” We are lucky to have the Swarm satellites orbit to study the development of the South Atlantic anomaly, comments Jürgen Matzkaof the German Center for Geoscience Research. The challenge now is to understand the processes that cause these changes at the heart of the Earth.

The currently prevailing hypothesis is that of a polarity reversal, an event that occurs on average every 250,000 years. The last occurred almost 780,000 years ago, perhaps a new reversal is on the agenda. Whatever happens, the strange behaviors of the Earth’s magnetic field do not portend anything alarming for us on Earth. The only ones affected will be the satellites in low orbit, which could present malfunctions during their passage over this mysterious area as yet misunderstood.

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