Using 11 years of magnetic field measurements from the European Space Agency's (ESA) Swarm constellation of satellites, scientists have discovered that the weak region in Earth's magnetic field over the South Atlantic – known as the South Atlantic Anomaly – has expanded since 2014 to an area almost half the size of continental Europe.
As ESA states in a statement, the Earth's magnetic field is vital for life on our planet. It is a complex and dynamic agent that protects us from cosmic radiation and charged particles from the Sun.
It is largely produced by an ocean of molten, swirling liquid iron that forms the outer core about 3000 km below Earth's surface. Acting like a rotating conductor, it creates electric currents, which in turn produce our ever-changing electromagnetic field, but in reality the processes that produce the field are much more complex.
Swarm, an Earth Explorer mission developed under ESA's Earth Observation FutureEO programme, consists of a constellation of three identical satellites that precisely measure magnetic signals emanating from the Earth's core, mantle, crust and oceans, as well as the ionosphere and magnetosphere.
Thanks to this mission, scientists are gaining more knowledge about the different sources of magnetism to understand how and why the magnetic field weakens in some places and strengthens in others. The South Atlantic Weak Field Anomaly was first identified southeast of South America in the 19th century.
Today, the South Atlantic Anomaly is of particular interest to space safety, as satellites passing through the region face higher doses of incoming radiation.
This can lead to malfunctions or damage to critical hardware, and even power outages.
The latest findings from the Swarm mission reveal that while the South Atlantic Anomaly expanded steadily between 2014 and 2025, a region of the Atlantic Ocean southwest of Africa is experiencing an even faster weakening of the Earth's magnetic field from 2020.
The South Atlantic Anomaly, says lead author Chris Finley, professor of Geomagnetism at the Technical University of Denmark, changes in a different way toward Africa than near South America. There's something special going on in that region that causes the field to weaken more sharply, he notes.
This behavior is linked to strange patterns in the magnetic field at the boundaries between Earth's liquid outer core and its rocky mantle, known as reversal spots.
Professor Finlay explains: “We would normally expect to see magnetic field lines emanating from the core in the southern hemisphere. But beneath the South Atlantic Anomaly we see unexpected regions where the magnetic field, instead of coming from the core, is returning to the core. Thanks to the Swarm data, we can see one of these regions moving west over Africa, which is contributing to the weakening of the South Atlantic Anomaly in that region.”
