New data from the European Space Agency's Swarm satellites reveal that the South Atlantic Anomaly, a weak spot in Earth's magnetic field, has grown by nearly half the size of continental Europe since 2014. A region southwest of Africa is weakening even faster in recent years. This expansion highlights unusual activity in Earth's molten outer core.
Earth's magnetic field, which shields the planet from cosmic radiation and solar particles, originates from the motion of molten iron in the outer core, about 3,000 kilometers below the surface. The South Atlantic Anomaly, first identified in the 19th century southeast of South America, poses risks to satellites passing through it, exposing them to higher radiation levels that can cause malfunctions and hardware damage.
Analysis of 11 years of data from the Swarm satellite constellation, launched on November 22, 2013, shows the anomaly expanded steadily from 2014 to 2025. Since 2020, the area southwest of Africa has experienced accelerated weakening. Lead author Chris Finlay, Professor of Geomagnetism at the Technical University of Denmark, noted, "The South Atlantic Anomaly is not just a single block. It's changing differently towards Africa than it is near South America. There's something special happening in this region that is causing the field to weaken in a more intense way."
This behavior links to reverse flux patches at the core-mantle boundary, where magnetic field lines unexpectedly re-enter the core in the southern hemisphere. Finlay explained, "Thanks to the Swarm data we can see one of these areas moving westward over Africa, which contributes to the weakening of the South Atlantic Anomaly in this region."
Meanwhile, the magnetic field has strengthened over Siberia, expanding by 0.42% of Earth's surface area—comparable to Greenland—while the strong region over Canada has shrunk by 0.65%, roughly the size of India. These shifts relate to the northern magnetic pole's gradual movement toward Siberia, impacting navigation systems.
Swarm's extended observations, now the longest continuous space-based record of Earth's magnetic field, aid in modeling global magnetism for navigation and space weather tracking. ESA's Swarm Mission Manager Anja Stromme said, "The satellites are all healthy and providing excellent data, so we can hopefully extend that record beyond 2030."
The findings appear in Physics of the Earth and Planetary Interiors.