A new study by the University of Leeds and the University of California, San Diego shows that changes in the direction of the Earth's magnetic field can occur 10 times faster than previously thought.
Their study provides new insights into the swirling flow of iron 2,800 kilometers below the planet's surface and how it has affected the movement of the magnetic field over the past hundred thousand years.
Our magnetic field is created and maintained by the convective flow of molten metal that forms the Earth's outer core. The movement of liquid iron creates electrical currents that feed the field, which not only helps orient navigation systems, but also helps protect us from harmful extraterrestrial radiation and keeps our atmosphere in place.
The magnetic field is constantly changing. Satellites now provide new means for measuring and tracking its current shifts, but the field has existed long before artificial recording devices were invented. To capture the evolution of the field backward through geological time, scientists analyze magnetic fields recorded by precipitation, lava flows and artificial artifacts. Accurately tracking the signal from the Earth's main field is extremely challenging, and therefore the rate of field change assessed by these types of analyzes is still debated.
Now Dr. Chris Davis, Associate Professor at Leeds and Professor Catherine Constable of the H. Scripps, University of California, San Diego, took a different approach. They combined computer simulations of the field generation process with a recently published reconstruction of the Earth's magnetic field changes over the past 100,000 years.
Their study, published in Nature Communications, shows that changes in the direction of the Earth's magnetic field have reached speeds that are 10 times the fastest current fluctuation of up to one degree per year.
They demonstrate that these rapid changes are associated with localized weakening of the magnetic field. This means that these changes usually occurred at times when the field changed polarity, or during geomagnetic deviations, when the axis of the dipole, corresponding to the lines of force that arise at one magnetic pole and converge at the other, moves far from places to the north and south. geographic poles.
The most striking example of this in their study is the abrupt change in the direction of the geomagnetic field by about 2.5 degrees per year 39,000 years ago. This shift was associated with locally weak field strengths in a confined spatial region off the west coast of Central America and followed the global Lashamp hike - a short change in the Earth's magnetic field about 41,000 years ago.
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Such events are revealed by computer simulations of the field, which can reveal much more details of their physical origin than a limited paleomagnetic reconstruction.
Their detailed analysis shows that the fastest changes in direction are associated with the movement of backflow spots along the surface of the liquid core. These spots are more common at lower latitudes, suggesting that future searches for rapid changes in direction should focus on these areas.
Dr. Davis of the Earth and Environment School said: “We have a very incomplete knowledge of our magnetic field until 400 years ago. Because these rapid changes represent some of the more extreme properties of the liquid core, they can provide important insights into the behavior of the Earth's interior.”
Prof Constable said: “Understanding whether computer simulations of a magnetic field accurately reflect the physical behavior of the geomagnetic field as indicated by geological data can be very difficult.
“But in this case, we managed to reach mutual understanding both on the rate of change and on the general location of the most extreme events in a number of computer simulations. Further study of the evolution of dynamics in these simulations offers a useful strategy for documenting how such rapid changes occur and whether they are also detected during times of stable magnetic polarity, such as what we experience today.