Volcanic eruptions and earthquakes are clear signs that Earth’s interior is not calm, but there are also other, less obvious, dynamic processes going on deep below our feet. Scientists have identified an entirely new sort of magnetic wave that sweeps across the outermost region of Earth’s outer core every seven years using data from the ESA’s Swarm satellite mission. This interesting discovery provides a new window into a world we’ll never visit.

The magnetic field of the Earth acts as a giant shield, shielding us from cosmic radiation and charged particles carried by tremendous winds that escape the Sun’s gravitational pull and travel throughout the Solar System. Life as we know it would not exist without our magnetic field.

Understanding how and where our magnetic field is formed, why it fluctuates so much, how it interacts with solar wind, and why it is currently diminishing is not just of academic interest but also of societal importance. Solar storms, for example, can disrupt communication networks, navigation systems, and satellites, so while we can’t control changes in the magnetic field, understanding it can help us prepare.

The majority of the field is generated by a 3000 km deep ocean of superheated, whirling liquid iron that makes up Earth’s outer core. It generates electrical currents and a constantly changing electromagnetic field by acting like the spinning conductor in a bicycle dynamo.

The Swarm mission of the European Space Agency (ESA), which consists of three identical satellites, measures these magnetic signals as well as signals from the crust, seas, ionosphere, and magnetosphere.

Since the launch of the three Swarm satellites in 2013, scientists have been analyzing their data to learn more about a variety of Earth’s natural processes, ranging from space weather to the physics and dynamics of Earth’s tumultuous heart.

The only genuine way to probe deep into Earth’s core is to measure our magnetic field from space. Seismology and mineral physics provide information on the core’s material qualities, but they don’t reveal anything about the liquid outer core’s dynamo-generating motion.

However, scientists have discovered a hidden secret using data from the Swarm expedition.

A team of scientists discovered a new sort of magnetic wave that sweeps across the’surface’ of Earth’s outer core – where the core meets the mantle – according to a research published in the journal Proceedings of the National Academy of Sciences. This unexplained wave occurs every seven years and travels up to 1500 kilometers each year westward.

“Geophysicists have long theorised over the existence of such waves,” said Nicolas Gillet, lead author of the report, “but they were thought to take place over much longer time scales than our research has shown.”

“Measurements of the magnetic field from instruments based on the surface of Earth suggested that there was some kind of wave action, but we needed the global coverage offered by measurements from space to reveal what is actually going on.”

“We combined satellite measurements from Swarm, and also from the earlier German Champ mission and Danish Ørsted mission, with a computer model of the geodynamo to explain what the ground-based data had thrown up – and this led to our discovery.”

Due to the way the Earth spins, these waves line up in columns along the axis of rotation. The velocity and magnetic field changes caused by these waves are most pronounced in the core’s equatorial region.

While the research shows magneto-Coriolis waves with a seven-year period, the question of whether such waves exist at different intervals remains unanswered.

“Magnetic waves are likely to be triggered by disturbances deep within the Earth’s fluid core, possibly related to buoyancy plumes,” Dr. Gillet continued. “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 within the core.”

“Our research suggests that other such waves are likely to exist, probably with longer periods – but their discovery relies on more research.”

“This current research is certainly going to improve the scientific model of the magnetic field within Earth’s outer core,” said Ilias Daras, an ESA Swarm project scientist. “It may also give us new insight into the electrical conductivity of the lowermost part of the mantle and also of Earth’s thermal history.”

Image Credit: ESA

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