Swarm reveals growing weak spot in Earth’s magnetic field

The Earth's magnetic field is vital to life on our planet. It is a complex and dynamic force that protects us from cosmic radiation and charged particles from the Sun.

It is primarily created by a global ocean of molten, spinning liquid iron that makes up the outer core about 3,000 km below our feet. Acting like a rotating conductor in a bicycle dynamo, it creates electrical currents, which in turn generate our ever-changing electromagnetic field – but in reality the processes that generate this field are much more complex.

Swarm, an Earth Explorer mission developed under ESA's Earth observation program FutureEOconsists 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.

Through this exceptional mission, scientists are gaining more information 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 back in the 19th century.

Today, the South Atlantic Anomaly is of particular interest to space security because satellites passing over the region encounter higher doses of incoming radiation. This could result in malfunction or damage to critical equipment and even power outages.

Published this month in Physics of the Earth and planetary interiors, latest results Data from the Swarm mission shows that while the South Atlantic Anomaly expanded steadily between 2014 and 2025, the Atlantic Ocean region southwest of Africa has seen an even more rapid weakening of the Earth's magnetic field since 2020.

“The South Atlantic Anomaly is not just one block,” says lead author Chris Finley, professor of geomagnetism at the Technical University of Denmark. “It changes differently in Africa than near South America. There's something special going on in that region that causes the field to weaken more intensely.”

This behavior is due to strange patterns in the magnetic field at the boundary between the Earth's liquid outer core and its rocky mantle, known as reflux patches.

Professor Finlay explains: “We normally expect to see magnetic field lines coming out of the core in the southern hemisphere. But underneath the South Atlantic Anomaly we are seeing unexpected areas where the magnetic field, instead of leaving the core, is returning back into the core. Thanks to the Swarm data, we can see one of these areas moving west over Africa, which is helping to weaken the South Atlantic Anomaly here.” region.”

Record 11 years of Swarm
The latest model of the magnetic field generated by the Earth's core marks a new milestone for ESA's Swarm satellites, which have provided the longest continuous record of magnetic field measurements from space to date.

The satellites were launched on November 22, 2013, as the fourth Earth Explorer mission. innovative satellites which form a key component of ESA's FutureEO programme.

Conceived as demonstrations of innovative Earth observation technologies, these missions have long outlived their original design life, become integral parts of long-term records, provided data for critical operational services, and paved the way for future generations of satellites.

The swarm data underpins global magnetic models used for navigation, monitoring space weather hazards and providing unprecedented insight into our Earth system from its core to the outer reaches of the Earth's atmosphere.

Earth's magnetic field strengthens over Siberia
Swarm's latest results highlight the dynamic nature of Earth's magnetism. For example, in the southern hemisphere there is one point where the magnetic field is especially strong, and in the northern hemisphere there are two – one around Canada, the other around Siberia.

“When you're trying to understand the Earth's magnetic field, it's important to remember that it's not just a dipole like a bar magnet. Only with satellites like Swarm can we fully map this structure and see how it changes,” Professor Finlay said.

However, since Swarm has been in orbit, the magnetic field over Siberia has strengthened and over Canada has weakened. The Canadian high field region shrank by 0.65% of the Earth's surface area, almost the size of India, while the Siberian region increased by 0.42% of the Earth's surface area, comparable to the size of Greenland.

This shift, caused by complex processes occurring in the Earth's turbulent core, is associated with The North Magnetic Pole is moving towards Siberia in recent years. This shift is important for navigation, which is affected by the dance between these two areas of strong magnetic field.

ESA's Swarm mission manager Anja Stromme said: “It's truly wonderful to see the big picture of our dynamic Earth thanks to Swarm's extended time series. All satellites are healthy and providing excellent data, so we hope to extend this record beyond 2030, when solar minimum will provide a more unprecedented view of our planet.”