Although volcanic eruptions and earthquakes immediately remind people that the interior of the earth is not calm, there are other more elusive dynamic processes taking place deep under our feet. Using information from the ESA swarm mission, scientists have discovered a new kind of magnetic wave that sweeps the outermost part of the earth's outer core every seven years.
The discovery presented at the living palnet Symposium of ESA a few days ago has opened a new window for a world we will never see.
The earth's magnetic field is like a giant bubble, which protects us from cosmic radiation and charged particles carried by strong winds that escape the sun's gravity and flow through the solar system. Without our magnetic field, life as we know it would not exist.
Understanding how and where our magnetic field is generated, why it fluctuates, how it interacts with the solar wind, and why it is weakening is not only of academic significance, but also of benefit to society. For example, solar storms will damage communication networks, navigation systems and satellites. Therefore, although we can do nothing about changes in the magnetic field, understanding this invisible force will help us prepare.
It is understood that most of the magnetic field is generated by the overheated and rotating liquid iron ocean 3000 kilometers under our feet, which constitutes the outer core of the earth. Like a rotating conductor in a bicycle generator, it generates current and a constantly changing electromagnetic field.
ESA's swarm mission consists of three identical satellites, which measure these magnetic signals from the earth's core and other signals from the crust, ocean, ionosphere and magnetosphere.
Since the launch of the three swarm satellites in 2013, scientists have been analyzing their data to gain new insights into many of the earth's natural processes, from space weather to the physics and dynamics of the earth's storm heart.
Measuring our magnetic field from space is the only real way to probe the depths of the earth's core. Seismology and mineral physics provide information about the properties of the earth's core material, but they do not provide any enlightenment for the dynamic generation of the liquid outer core.
But now, by using data from the swarm mission, scientists have discovered a hidden secret.
A paper published in the proceedings of the National Academy of Sciences describes how a team of scientists has detected a new type of magnetic wave, which sweeps across the "surface" of the earth's outer core, that is, the intersection of the earth's core and mantle. This mysterious wave oscillates every seven years and travels westward at a speed of up to 1500 kilometers per year.
Nicolas Gillet from Grenoble Alps university is the first author of the paper, He pointed out: "Geophysicists have been doing theoretical research on the existence of such waves for a long time, but they are believed to occur on a much longer time scale than our research shows. The measurement of magnetic field by instruments based on the earth's surface shows that there is a certain wave effect, but we need the global coverage provided by the measurement from space to reveal the actual situation. We will use the satellite measurement from swarm and the measurement from champ in early Germany The measurements of Wu and the Danish Ø rsted mission were combined with the computer model of geodynamics to explain what the ground data showed - which led to our discovery. "
As the earth rotates, these waves line up along the axis of rotation. The motion and magnetic field changes associated with these waves are strongest near the equatorial region of the core.
Although the study shows that the magnetic Coriolis wave is close to the seven-year period, the question remains whether there is such a wave that will oscillate in different periods.
Dr Gillet added: "Magnetic waves are likely to be caused by interference deep in the earth's fluid core, which may be related to buoyancy plumes. Each wave is defined by its period and typical length scale, and the period depends on the characteristics of the force at work. For magnetic Coriolis waves, the period indicates the strength of the magnetic field in the earth's core. Our research shows that other such waves may exist and may have longer periods - but their discovery depends on For more research. "
Ilias daras, a swarm mission scientist at ESA, said: "the current study will certainly improve the scientific model of the magnetic field in the outer core of the earth. It may also enable us to have a new understanding of the conductivity of the lowest mantle and the thermal history of the earth."