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Data from the European Space Agency’s Swarm satellite mission, released in October 2025, show that the South Atlantic Anomaly (SAA) — a region of unusually weak magnetic field over South America and the southern Atlantic Ocean — has grown considerably over the past decade. The weakened field exposes satellites and high‑altitude aircraft to more intense charged‑particle radiation.
Background
Earth’s magnetic field is generated by convection of molten iron in the outer core. It deflects solar wind and cosmic rays, protecting our atmosphere and life. The field is not uniform; some areas are stronger, while others, like the SAA, are weaker.
- Expansion and weakening: According to Swarm measurements, the area of the SAA has expanded by roughly half the size of continental Europe since 2014. Magnetic intensity within it has also decreased.
- Multiple weak patches: Scientists previously thought the anomaly was a single large region, but Swarm data reveal at least two weak spots. One patch is drifting westward, while another near southwest Africa has weakened markedly since 2020. These variations suggest complex core dynamics beneath the Atlantic.
- Possible causes: One hypothesis links the anomaly to the African Large Low‑Shear‑Velocity Province — a giant hot blob at the core‑mantle boundary that disrupts the flow of liquid iron. Changes in the outer core can alter field lines, causing them to bend or reverse locally.
- Impacts: Satellites passing through the SAA experience higher radiation doses, which can damage electronics or cause data glitches. Mission planners often switch off instruments during transit. High‑altitude aircraft crews are also exposed to slightly higher radiation levels.
Outlook
Despite the anomaly’s expansion, scientists note that the overall magnetic field is still strong and there is no evidence of an imminent pole reversal. The north magnetic pole continues to drift towards Siberia, while the field weakens over Canada. Continuous monitoring by missions like Swarm, ground observatories and high‑altitude balloons will help researchers understand core dynamics and predict future changes.
Source: ScienceAlert · SA