ESA’s Swarm satellite mission has detected a completely new type of magnetic wave that passes over the outermost part of the Earth’s outer core every seven years.
Nicolas Gillet, of the Université Université Grenoble Alpes and lead author of the paper, said: “Geophysicists have long theorized about the existence of such waves, but they were thought to occur over much longer timescales than our research has shown.
“Measurements of the magnetic field from instruments based on the Earth’s surface suggested there was some sort of wave action, but we needed the global coverage provided by measurements from space to reveal what’s really going on.
“We combined satellite measurements from Swarm, as well as from the earlier German Champ mission and Danish Ørsted mission, with a computer model of the geodynamo to explain what the ground data had yielded — and this led to our discovery.”
The Earth’s magnetic field is like a huge bubble that protects us from the onslaught of cosmic rays and charged particles carried by powerful winds that escape the sun’s gravity and flow through the solar system.
It could be important to understand exactly how and where our magnetic field is generated, why it constantly fluctuates, how it interacts with solar wind and, indeed, why it is currently weakening.
Most of the field is generated by an ocean of superheated, swirling liquid iron that forms the Earth’s outer core 3,000 kilometers below our feet.
Like the rotating conductor in a bicycle dynamo, it generates electric currents and the continuously changing electromagnetic field.
ESA’s Swarm mission, which consists of three identical satellites, measures these magnetic signals coming from the Earth’s core, as well as other signals coming from the crust, oceans, ionosphere and magnetosphere.
Measuring our magnetic field from space is the only real way to probe deep into the Earth’s core.
Seismology and mineral physics provide information about the material properties of the core, but do not shed light on the dynamo-generating motion of the liquid outer core.
But now, using data from the Swarm mission, scientists have uncovered a hidden secret.
A paper, published in the journal Proceedings of the National Academy of Sciences, describes how a team of scientists discovered a new type of magnetic wave that sweeps across the “surface” of Earth’s outer core — where the core meets the mantle.
This mysterious wave oscillates every seven years, propagating westward for up to 900 miles a year.
Due to the rotation of the earth, these waves come out 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 shows magneto-Coriolis waves close to a seven-year period, the question of whether such waves would oscillate at different periods remains.
dr. Gillet added: “Magnetic waves are likely caused by disturbances deep in the Earth’s fluid core, possibly related to buoyancy plumes.
“Each wave is specified by its period and typical length scale, and the period depends on characteristics of the forces at play. For magneto-Coriolis waves, the period is indicative of the intensity of the magnetic field in the core.
“Our research suggests that more such waves are likely to exist, likely with longer time periods — but their discovery depends on more research.”
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