When you hear the term "jet stream," you probably think of the powerful winds that encircle the Earth, high up in the atmosphere.
But now, scientists have used observations by the European Space Agency's Swarm satellites to identify another sort of jet stream, one that's made of molten metal instead of air and is located 1,865 miles beneath the Earth's surface, stretching from Siberia to Alaska.
The findings, contained in an article just published in the online edition of Nature Geoscience, depict a previously unknown geological feature that may yield secrets about the Earth's inner workings.
The jet stream inside the Earth is located along the border of two regions of the Earth's core, and it's about 261 miles in width. It moves about 25 miles in the course of a year. That's far slower than the hundreds of miles per hour at which the atmospheric jet streams travel, but three times faster than other parts of the outer core and hundreds of thousands of times faster than the Earth's tectonic plates. The interior jet stream gradually is accelerating, according to the scientists' findings.
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"What's most surprising about the jet is that it's likely been in the core for many years and no-one has seen it before - not even with previous satellite missions," lead researcher Phil Livermore, an associate professor in the School of Earth and the Environment at the University of Leeds, said in an email. "The jet is likely to have been around in the core for some hundreds of millions of years, and we've only just glimpsed it through the technical-revolution of the Swarm mission."
Swarm, launched in 2013, uses a trio of satellites rather than just one probe to produce extremely high-resolution images of the Earth's magnetic field and how it moves. By analyzing that data, scientists essentially can peer inside the planet.
"Swarm measures the magnetic field in space, from which it is possible to create an image of the magnetic field at the edge of the Earth's core," Livermore said. "Although the mantle is solid rock, the magnetic field can 'see' inside, and hence produce an x-ray view of the inside of our planet. At high latitude, at the edge of the core, there are patches of intense magnetic field that we can track over time. it is these features that allows us to infer that the iron in the core is moving in a jet. We cannot see the jet itself, but we can see its effect by the fact that it drags around magnetic features."
Livermore described the jet stream as "a very significant" feature of the core, and said that gaining knowledge about it will help scientists to better understand the interior workings of the planet.
"The jet stream probably doesn't have any immediate impacts for us on the Earth surface, but it may shed light on the dynamical state of the liquid core," he said. "The more we know about how the core operates, the more chance we will have in, for example, being able to predict whether the current weakening of the magnetic field is a precursor to a global reversal."
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The jet stream inside the Earth doesn't form a ring around the planet, as the ones in the atmosphere do. Instead, it's a boundary within the core, separating two regions with different dynamics. Technical University of Denmark senior scientist Chris Finlay, one of the study's co-authors, described the internal jet stream in an email as existing "around an imaginary cylinder that sits around the inner core and is parallel to Earth's rotation axis."
"If fluid is forced towards the boundary from both sides, it has nowhere to go but sideways - and hence forms the jet," Livermore said.
The jet stream's direction and magnitude are likely caused by the core's internal magnetic field, Livermore said. That could mean that as the magnetic field changes over time, the direction and magnitude of the jet also will change.
Image: Magnetic field data gathered by European Space Agency's Swarm satellites show a river of molten metal deep inside the Earth. Credit: ESA.
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