Overview: A Growing Magnetic Weak Spot
The European Space Agency’s Swarm mission has delivered a striking finding: the South Atlantic Anomaly (SAA), a region where Earth’s magnetic field is unusually weak, has expanded by nearly half the size of continental Europe since 2014. Using 11 years of magnetic field measurements from the Swarm satellite trio, scientists are gaining new insight into how our planet’s magnetosphere changes and why some areas weaken more quickly than others. The discovery has practical implications for space operations, aviation, and our understanding of the geodynamo that powers Earth’s protective shield.
What Swarm Is and Why It Matters
Swarm is an Earth Explorer mission from the European Space Agency designed to sense magnetic signals arising from Earth’s core, mantle, crust, oceans, ionosphere, and magnetosphere. The constellation’s precise measurements have created the longest continuous record of space-based magnetic data, enabling researchers to model how magnetic field sources evolve over time. This knowledge is essential for navigation systems, space weather forecasting, and the broader study of Earth’s interior dynamics.
South Atlantic Anomaly: Expansion and Body of Change
The SAA was first identified in the 19th century as a weak magnetic pocket near southeast South America. Since 2014, the region’s area has grown steadily, and since 2020 a distinct sector southwest of Africa has weakened at an even faster rate. Lead author Chris Finlay, a professor of geomagnetism at the Technical University of Denmark, notes that the SAA is not a uniform block but a composite of shifting zones. “It’s changing differently towards Africa than it is near South America,” he explains. “There’s something special happening in this region that is causing the field to weaken more intensely.”
Mechanisms Behind the Weakening
The latest model attributes the SAA’s behavior to complex patterns at the boundary where Earth’s liquid outer core meets the solid mantle. Specifically, reverse flux patches—areas where magnetic field lines re-enter the core instead of emanating from it—play a significant role. Swarm data reveal a westward-moving patch beneath Africa that contributes to the regional weakening. These insights underscore that Earth’s magnetic field is not a simple dipole but a dynamic, evolving system shaped by core processes and mantle interactions.
Regional Shifts and Global Implications
Beyond the SAA, Swarm data show notable regional variations: the magnetic field strengthens in Siberia while weakening in Canada, signaling a broader redistribution of field strength across the globe. The Siberian region has grown by roughly the size of Greenland in terms of affected area, while Canada’s strong-field region diminished by about the area of India. These shifts are linked to the Northern Hemisphere’s magnetic pole moving toward Siberia and underscore the magmatic and fluid dynamics at Earth’s core–mantle boundary.
Why This Matters for Space and Society
As the SAA expands and regional magnetic patterns shift, satellites passing over the weak region are exposed to higher radiation doses, increasing the risk of onboard electronics failure or degraded sensors. This has practical consequences for satellite operators, aviation, and even ground-based technologies reliant on precise magnetic field models. Swarm’s extended time series supports improved magnetic models used for navigation, space weather monitoring, and operational services that rely on accurate field maps.
The Path Forward for Swarm
ESA’s Swarm mission has already exceeded its original design lifetime, continuing to deliver high-quality data that illuminate the Earth’s interior and near-space environment. As the solar cycle evolves and data accumulate, scientists hope to extend the record beyond 2030, deepening our understanding of how the core drives magnetic field changes. The Swarm results remind us that Earth’s magnetic shield remains a dynamic, living system—one that scientists are only beginning to fully map.
Quoted Insight
“It’s really wonderful to see the big picture of our dynamic Earth thanks to Swarm’s extended timeseries,” says ESA Swarm Mission Manager Anja Stromme. “We can hopefully extend that record beyond 2030 for more unprecedented insights.”
