Why The Earth's Magnetic Field Could Not Turn Around After All

    Abdulaziz Sobh

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    A gradual weakening in the geomagnetic field of the Earth has raised concerns that the field could turn around, reversing the magnetic north and south. But now, new research suggests that the field has been in a similar state before, without making a move.In a study published today in the Proceedings of the National Academy of Sciences (April 30), the researchers compared the current magnetic field, created by the shaking of the Earth's core, with the magnetic field of past eons. They discovered that current patterns do not resemble the two most extreme interruptions in the last 50,000 years when the magnetic field almost reversed. [7 ways in which the Earth changes in the blink of an eye]In contrast, the modern field seems similar to the field during two other periods, one makes 49,000 and another 46,000 years ago, when the field wobbled but did not change.Even a wobble, however, could have ramifications, the authors wrote. If the field continues to weaken, it could affect things like the electronics on board the low Earth orbit satellites, even without a total investment of magnetic north and south.Protection characteristicEarth's geomagnetic field protects the planet's surface from damaging charged particles in space, making it important for both life on Earth and the power grid. "Solar storms" that bombard the Earth with higher-than-normal levels of charged particles can cause problems with satellite communications and even the power grid, as happened in 2003 when "Halloween storms" forced a change in the direction of the aircraft and removed energy in parts of Sweden for an hour.Currently, magnetic north is very close to the North Pole, while the magnetic south is near the South Pole. That has been the case for approximately 780,000 years, the last time the geomagnetic field underwent a complete reversal, with magnetic changes in the north and south. But the field has been weakening by about 5 percent per century since direct observations began in 1840, and indirect observations hint that this weakening may have been occurring for at least 2,000 years, Maxwell Brown, who studies paleomagnetism at the University of Iceland, and his colleagues wrote in their new document. A particularly weak area called the South Atlantic Anomaly, which extends from South Africa to Chile, has been identified as a possible area of origin for a reversal of global polarity.Brown and his colleagues wanted to compare current conditions with the magnetic field of past years. They focused on two "excursions", which are large interruptions of the geomagnetic field that do not necessarily imply a global investment of magnetic north and south. One, the excursion to Laschamp, occurred approximately 41,000 years ago. During that excursion, the magnetic field was a complex confusion without a clear magnetic north and south. The other, the Mono Lake excursion, happened some 34,000 years ago and was marked by a very weak magnetic north and south.Natural variations researchers modeled these hypo geomagnetic discoveries and found that neither was very similar to field conditions at present. During the Laschamp excursion, the magnetic north and south weakened with increasing rapidity, and two large anomalies grew over Central America and Southeast Asia almost simultaneously. For thousands of years, patches appeared where the direction of magnetism reversed, and the intensity of the magnetic field fell very low.During the Mono Lake excursion, magnetic north and south weakened but for a shorter period of time, and many small patches of reverse magnetism appeared throughout the world. There were also many patches of altered intensity in the strength of the field, which appeared erratically and disappeared again. In a couple of thousand years, the field stopped wobbling and stabilized again with a strong north and south.Today's field is not as weak as the field during the Laschamp or Mono Lake excursions and has only one anomaly of intensity, the South Atlantic Anomaly. So, Brown and his co-authors argue that this is not enough to sow a global flip-flop. On the contrary, they wrote, a large excursion or magnetic field inversion probably requires many small core points around the globe. Supporting their argument, they found it twice 49,000 years ago and 46,000 years ago when the geomagnetic field was very similar to today's. In both cases, the field was recovered without any resulting extreme event.If the researchers are right and the magnetic field is not reversed, there could still be headaches for humans. Already, the South Atlantic Anomaly has occasionally caused electrical faults in the satellites, Brown and his colleagues wrote."[With] a continuous decrease in the intensity of the field," they continued, "problems like this will generalize."