South Atlantic Anomaly Expands Slightly, ESA Swarm Mission Reports

Researchers analysing data from the European Space Agency’s (ESA) Swarm mission have reported that the South Atlantic Anomaly (SAA) — the region of weakest intensity in Earth’s magnetic field — has expanded slightly since 2014, now covering 0.9% more of the Earth’s surface than a decade ago.

What is the South Atlantic Anomaly?

• The SAA is a region in Earth’s magnetic field where the field strength dips significantly, reaching an altitude of approximately 200 km (120 miles).
• This allows cosmic rays and charged particles to penetrate deeper into the atmosphere, increasing ionizing radiation exposure for spacecraft in Low Earth Orbit (LEO).

Cause of the Weak Spot

• Earth’s magnetic field is generated by the geodynamo — the motion of molten iron and nickel in the outer core.
• Uneven flow in the liquid core creates areas where the magnetic flux is concentrated and others where it spreads out.
• These weak regions, like the SAA, can expand, shrink, or migrate over decades without threatening the planet’s overall magnetic shield or signalling a magnetic reversal.

Swarm Mission and Observations

• Swarm is an Earth Explorer mission under ESA’s FutureEO programme, consisting of three identical satellites.
• The satellites precisely measure magnetic signals from:
  • Earth’s core, mantle, crust, and oceans
  • Ionosphere and magnetosphere
• Data from Swarm provides insight into natural variations of the geomagnetic field and the behaviour of regions like the SAA.

Significance

• Despite the SAA’s apparent expansion, scientists stress there is no reason for alarm.
• The changes are considered part of the natural variability of Earth’s geomagnetic field.
• Understanding the SAA is crucial for satellite safety, space weather monitoring, and geomagnetic research.

Source: ESA