The weak spot in Earth’s magnetic field, a region over the South Atlantic where the field’s strength is significantly reduced compared to its surrounding area, has grown by an area nearly the size of the European continent over the past 11 years.
Using data from the European Space Agency’s (ESA) Swarm satellites, scientists revealed that the South Atlantic Anomaly has gotten much larger since 2014. In a recent study published in Physics of the Earth and Planetary Interiors, the team of scientists links the development to strange patterns at the boundary between Earth’s liquid layer, which lies above the solid inner core, and its rocky mantle, the layer between the crust and the outer core.
“The South Atlantic Anomaly is not just a single block,” Chris Finlay, professor of geomagnetism at the Technical University of Denmark and lead author of the study, said in a statement. “There’s something special happening in this region that is causing the field to weaken in a more intense way.”
That’s the spot
Earth’s magnetic field is essential to life on our planet. It protects Earth from cosmic radiation and acts as a shield against solar wind, keeping our atmosphere stable and preventing liquid water and other gases from being eroded by the stream of charged particles emitted by the Sun.
Scientists first identified the South Atlantic Anomaly, better known as the weak spot, in the late 1950s, when the first satellites began measuring Earth’s magnetic field. Early observations revealed that radiation levels were unusually high over one particular area over the South Atlantic, which meant that the magnetic field was weaker there compared to surrounding regions.
Swarm’s magnetic field measurements reveal changes in the weak spot. Credit: ESA
Satellites passing over the region experience higher doses of radiation compared to other areas, which makes studying the anomaly a crucial part of maintaining the safety of space missions, according to ESA.
“Normally we’d expect to see magnetic field lines coming out of the core in the southern hemisphere,” Finlay said. “But beneath the South Atlantic Anomaly we see unexpected areas where the magnetic field, instead of coming out of the core, goes back into the core.”
The Swarm data revealed that one of these areas is moving westward over Africa, which is contributing to the weakening of the South Atlantic Anomaly in this region. The data also highlights two points in the northern hemisphere where Earth’s magnetic field is particularly strong, one around Canada and the other around Siberia, that have experienced varying results since Swarm began its observations.
The strong spot around Canada has weakened, shrinking by 0.65% of Earth’s surface area, which is almost the size of India. On the other hand, the Siberian strong region has grown by 0.42% of Earth’s surface area, or about the size of Greenland.
“When you’re trying to understand Earth’s magnetic field, it’s important to remember that it’s not just a simple dipole, like a bar magnet,” Finlay said. “It’s only by having satellites like Swarm that we can fully map this structure and see it changing.”
ESA’s Swarm satellite constellation launched in 2013 to study the complexities of the magnetic field. The mission uses three satellites, named Alpha, Bravo, and Charlie, to measure magnetic signals originating from Earth’s core, as well as the planet’s crust, oceans, and parts of its atmosphere.
