Data from the European Space Agency's Swarm satellite mission reveals a significant expansion of a weak spot in Earth's magnetic field over the past decade. Known as the South Atlantic Anomaly, this region has grown by an area nearly the size of half of continental Europe since 2014, posing increased risks to satellites operating in low-Earth orbit.
The findings, based on 11 years of continuous observation, also show that the field is weakening at an accelerated rate in a specific area southwest of Africa. These changes are part of a larger, dynamic process within our planet that also affects the magnetic field's strength in the northern hemisphere.
Key Takeaways
- The South Atlantic Anomaly, a weak area in the magnetic field, has expanded significantly between 2014 and 2025.
- A specific region of the anomaly southwest of Africa has shown an accelerated weakening of the magnetic field since 2020.
- The changes are linked to unusual magnetic field patterns, known as reverse flux patches, at the boundary of Earth's core and mantle.
- Data also shows the magnetic field strengthening over Siberia while weakening over Canada, affecting the movement of the north magnetic pole.
The Growing South Atlantic Anomaly
Earth's magnetic field acts as a protective shield, deflecting harmful cosmic radiation and charged solar particles. However, this shield is not uniform. A large region of reduced magnetic intensity, the South Atlantic Anomaly (SAA), stretches from South America to southwest Africa.
A new study published in Physics of the Earth and Planetary Interiors analyzed over a decade of high-precision data from ESA's Swarm satellites. The results indicate that the SAA has been steadily growing, exposing a larger area to higher levels of radiation.
Why the Anomaly Matters
Satellites and spacecraft passing through the South Atlantic Anomaly are more vulnerable to radiation. This can cause temporary malfunctions, damage sensitive electronic components, or even lead to complete system blackouts. Understanding the anomaly's evolution is critical for space safety and mission planning.
The research highlights that the weakening is not uniform across the entire anomaly. Since 2020, a particular zone over the Atlantic Ocean, southwest of the African continent, has experienced a much faster decline in magnetic field strength.
“The South Atlantic Anomaly is not just a single block,” said lead author Chris Finlay, a Professor of Geomagnetism at the Technical University of Denmark. “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.”
Deep Earth Processes Driving the Change
The magnetic field is primarily generated by the movement of molten iron in Earth's outer core, approximately 3,000 kilometers below the surface. The complex dynamics of this liquid metal ocean create our planet's electromagnetic field.
Scientists believe the behavior of the SAA is linked to specific features at the core-mantle boundary. Professor Finlay's team used the Swarm data to identify strange patterns called reverse flux patches beneath the region.
“Normally we’d expect to see magnetic field lines coming out of the core in the southern hemisphere,” Finlay explained. “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 data suggests one of these reverse flux patches is moving westward over Africa. This movement is a key factor contributing to the intensified weakening of the magnetic field in that part of the anomaly.
Global Shifts in Magnetic Strength
The changes observed in the South Atlantic are part of a global pattern of magnetic field fluctuation. The latest Swarm data also reveals significant shifts in the northern hemisphere, where two points of particularly strong magnetic intensity exist: one over Canada and another over Siberia.
Northern Hemisphere Changes
- Canada: The strong field region has shrunk by 0.65% of Earth's surface area, an area nearly the size of India.
- Siberia: The strong field region has grown by 0.42% of Earth's surface area, comparable to the size of Greenland.
This redistribution of magnetic strength is directly related to the observed movement of the north magnetic pole, which has been drifting towards Siberia in recent years. This pole migration has practical implications, as it affects navigation systems that rely on magnetic field models.
“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,” said Professor Finlay. “It’s only by having satellites like Swarm that we can fully map this structure and see it changing.”
ESA's Swarm Mission Milestone
The new insights are possible thanks to the longevity and precision of ESA’s Swarm mission. Launched on November 22, 2013, the constellation of three identical satellites has now provided the longest continuous record of magnetic field measurements from space, spanning 11 years.
Developed as part of ESA’s FutureEO programme, Swarm was designed to measure magnetic signals from Earth’s core, mantle, crust, and oceans, as well as its ionosphere and magnetosphere. The mission has long outlived its original design lifetime and has become essential for long-term scientific records.
According to Anja Stromme, ESA’s Swarm Mission Manager, the satellites are in excellent health and continue to provide valuable data. “It’s really wonderful to see the big picture of our dynamic Earth thanks to Swarm’s extended timeseries,” she said. “We can hopefully extend that record beyond 2030, when the solar minimum will allow more unprecedented insights into our planet.”