(ORDO NEWS) — While volcanic eruptions and earthquakes serve as direct reminders that the Earth’s inner life is not peaceful, there are other, more subtle dynamics going on deep below the Earth.
Using information from ESA’s Swarm satellite, scientists have discovered a completely new type of magnetic wave that travels through the outermost part of the Earth’s outer core every seven years. Presented at the ESA Living Planet Symposium, this exciting discovery opens a new window into a world we may never see.
The Earth’s magnetic field is like a huge bubble protecting us from the onslaught of cosmic radiation and charged particles carried by powerful winds, which, avoiding the gravitational pull of the Sun, sweep 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 constantly fluctuates, how it interacts with the solar wind, and moreover, why it is currently weakening is not only of academic interest, but also of social benefit.
For example, solar storms can damage communications networks, navigation systems, and satellites, so while there’s nothing we can do about changes in the magnetic field, understanding this invisible force helps us be prepared.
Much of the field is generated by the ocean of superheated, swirling liquid iron that makes up the Earth’s outer core 3,000 km below our feet. Acting like a rotating conductor in a bicycle dynamo, it generates electrical currents and a constantly changing electromagnetic field.
The ESA Swarm mission, which consists of three identical satellites, measures magnetic signals from the Earth’s core, as well as other signals from the crust, oceans, ionosphere and magnetosphere.
Since the launch of a trio of Swarm satellites in 2013, scientists have been analyzing their data to gain new insights into many of Earth’s natural processes, from space weather to the physics and dynamics of Earth’s turbulent heart.
Measuring our magnetic field from space is the only real way to get deep into the Earth’s core. Seismology and mineral physics provide information about the properties of the core material, but they do not shed light on the dynamics of the fluid outer core.
But now, using data from the Swarm mission, scientists have uncovered a hidden secret.
An article published in the journal Proceedings of the National Academy of Sciences describes how a team of scientists has discovered a new type of magnetic wave traveling along the “surface” of the Earth’s outer core, where the core meets the mantle. This enigmatic wave oscillates every seven years and travels westward at speeds of up to 1,500 kilometers a year.
Nicolas Gillet of the University of Grenoble-Alpes and the paper’s lead author said: “Geophysicists have long suspected the existence of such waves, but they were thought to occur on much longer time scales than our study showed.”
Measurements of the magnetic field with instruments on the surface of the Earth suggested that there was some kind of wave action, but we needed the global coverage provided by measurements from space to find out what was really happening.
“We combined the Swarm satellite measurements, as well as the earlier German Champ mission and the Danish Ørsted mission with a geodynamo computer model to explain what the ground data showed that led to our discovery.”
Due to the rotation of the Earth, these waves line up in columns along the axis of rotation. The movement and changes in the magnetic field associated with these waves are strongest near the equatorial region of the core.
Although the study demonstrates magnetic-Coriolis waves near a seven-year period, the question of the existence of such waves that would oscillate with different periods, nevertheless, remains open.
Dr. Gillett added: “Magnetic waves are likely caused by disturbances deep within the Earth’s liquid core, possibly associated with buoyancy plumes. Each wave is characterized by a period and a typical length scale, with the period depending on the characteristics of the forces involved. For magneto-Coriolis waves, the period indicates the intensity of the magnetic field inside the nucleus.
“Our research indicates that there are likely other similar waves, possibly with longer periods, but their detection depends on further research.”
ESA Swarm mission scientist Ilias Daras said: “The current study will certainly improve the scientific model of the magnetic field in the Earth’s outer core. It may also give us new insights into the electrical conductivity of the lowest part of the mantle, as well as the Earth’s thermal history.”
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