Using information from ESA’s Swarm satellite mission, scientists have discovered a completely new type of magnetic wave that sweeps across the outermost part of Earth’s outer core every seven years and propagates westward at up to 1 500 km (932 miles) a year. The discovery offers a way to probe the cylindrical radial component of the magnetic field inside Earth’s core.
Since the trio of Swarm satellites was launched in 2013, scientists have been analyzing their data to gain new insight into many of Earth’s natural processes, from space weather to the physics and dynamics of Earth’s stormy heart.
Measuring our magnetic field from space is the only real way of probing deep down to Earth’s core. Seismology and mineral physics provide information about the material properties of the core, but they do not shed any light on the dynamo-generating motion of the liquid outer core.
But now, using data from the Swarm mission, scientists have unearthed a hidden secret.
“Geophysicists have long theorized over the existence of such waves, but they were thought to take place over much longer time scales than our research has shown,” said lead author Nicolas Gillet from the University Université Grenoble Alpes.
“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.”
Owing to Earth’s rotation, these waves align in columns along the axis of rotation. The motion and magnetic field changes associated with these waves are strongest near the equatorial region of the core.
While the research exhibits magneto-Coriolis waves near a seven-year period, the question of the existence of such waves that would oscillate at different periods, however, remains.
“Magnetic waves are likely to be triggered by disturbances deep within 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 within the core,” Gillet added.
“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. 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,” said Ilias Daras, ESA’s Swarm mission scientist.
1 Swarm unveils magnetic waves deep down – ESA – May 23, 2022
2 Satellite magnetic data reveal interannual waves in Earth’s core – Nicolas Gillet et al. – PNAS – March 21, 2022 – https://doi.org/10.1073/pnas.211525811
Featured image credit: University Université Grenoble Alpes, ESA
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