The South Atlantic Anomaly: Unraveling the Mystery Off the Coast of Africa

Nov 22, 2025 0

The South Atlantic Anomaly (SAA), a region marked by a peculiar magnetic field disturbance, has emerged as a significant subject of study among scientists. Located over the South Atlantic Ocean, this anomaly poses substantial risks to both terrestrial and space technology. As it continues to grow and shift, understanding its origins and implications becomes increasingly critical. Researchers are delving into the dynamics of Earth’s magnetic field to uncover the causes behind this mysterious phenomenon.

Magnetic field intensity at Earth's surface in 2014 (top) and 2025 (bottom), as measured by ESA's SWARM spacecraft. Source: ESA

The Nature of the South Atlantic Anomaly

The South Atlantic Anomaly is a region where Earth’s magnetic field is weaker than usual, allowing high levels of cosmic radiation to penetrate the atmosphere. This increase in radiation is particularly concerning for satellites and spacecraft, as it can disrupt electronic systems and potentially jeopardize missions. The International Space Station, orbiting with an inclination of 51.6°, requires extra shielding to deal with this problem.

Impact on Space Technology

The anomaly’s influence is particularly pronounced for spacecraft in low-Earth orbit, such as the International Space Station. As they pass through this region, they encounter a reduced magnetic shield, exposing them to high-energy protons from the Sun. Satellite operators must remain vigilant to mitigate the risks posed by the SAA. Routine shutdowns of spacecraft systems are often necessary to prevent significant data loss or permanent damage. The SAA is believed to have started a series of events leading to the destruction of the Hitomi, Japan's most powerful X-ray observatory.

Addressing the challenges posed by the SAA requires a comprehensive understanding of its behavior. Engineers and scientists are working to develop robust strategies to protect space missions from the anomaly’s effects. These efforts include designing spacecraft with improved shielding and developing predictive models to anticipate radiation spikes.

Evolution and Expansion

NASA’s observations indicate that the South Atlantic Anomaly is not only persisting but also expanding and altering its position. This growth raises alarms about its potential impacts on both space-based and ground-based technologies. The expanding SAA highlights the importance of ongoing research into Earth’s magnetic field. Scientists are focused on understanding the mechanisms driving this expansion and the accompanying weakening of the field.

Changes Over Time

The shape of the SAA changes over time. Since its initial discovery in 1958, the southern limits of the SAA have remained roughly constant while a long-term expansion has been measured to the northwest, the north, the northeast, and the east. Additionally, the shape and particle density of the SAA varies on a diurnal basis, with greatest particle density corresponding roughly to local noon.

Recent studies have revealed that the South Atlantic Anomaly is not a static feature. Instead, it is subject to dynamic changes in both size and shape. In 2016, NASA heliophysicist Ashley Greeley led a study that demonstrated the SAA’s slow drift across the Earth’s surface. Subsequent research using CubeSats confirmed the anomaly’s movement, providing valuable data for tracking its evolution. In 2020, researchers discovered that the anomaly seemed to be dividing, creating separate centers of minimum magnetic intensity. This finding raises questions about the future trajectory of the SAA and its long-term implications.

The highest intensity portion of the SAA drifts to the west at a speed of about 0.3° per year, and is noticeable in the references listed below. The drift rate of the SAA is very close to the rotation differential between the Earth's core and its surface, estimated to be between 0.3° and 0.5° per year. Current literature suggests that a slow weakening of the geomagnetic field is one of several causes for the changes in the borders of the SAA since its discovery.

Origins and Underlying Causes

To unravel the origins of the South Atlantic Anomaly, scientists are examining the dynamic processes occurring deep within Earth. The planet’s magnetic field is generated by the movement of molten iron and nickel in the outer core. One hypothesis attributes the anomaly to the African Large Low Shear Velocity Province, a substantial rock formation beneath Africa that influences the movement of molten materials in the outer core. Located about 1,800 miles below the surface, this geological feature contributes to the anomaly’s dramatic weakening effects. The tilt of Earth’s magnetic axis further complicates the field’s behavior. As a result, the SAA emerges as a region where the dipole field’s dominance is weakened. This interaction may lead to the observed reduction in magnetic field strength within the SAA region. This localized field, with its reversed polarity, creates a pocket of reduced magnetic intensity.

Read also: Unraveling South Africa Anomaly

Earth's Magnetic Field Lines

Implications for Earth's Future

The ongoing changes in the South Atlantic Anomaly have significant implications for Earth’s future. A weakening magnetic field increases susceptibility to solar storms and other space weather events, which can disrupt power grids, navigation systems, and communication networks.

Recent Findings and Research

Satellites detected a strange gravity signal off the coast of Africa nearly 20 years ago, suggesting something unusual had happened deep within the planet to distort its gravitational field, according to a recent study. The large gravitational anomaly lasted for about two years over the eastern Atlantic Ocean. It peaked in January 2007. The signal was a north-south-oriented gravity anomaly, stretching about 4,350 miles (7,000 kilometers) - close to the length of the entire African continent - from 2006 to 2008, according to the study.

The study authors suggested that the mass redistributions they attributed to the signal occurred as a result of a perovskite to post-perovskite phase transformation in this lower mantle section, whereby the structure of magnesium silicate changed under pressure, shifting mass deep within the Earth. Mandea noted that the main message of the study was that Earth is complex and that different datasets and methods are required to understand its internal processes.

NASA’s findings about the SAA’s growth underscore the importance of continued research into Earth’s magnetic field dynamics. As scientists strive to understand this complex phenomenon, the insights gained will guide the development of protective measures for technological systems and enhance our knowledge of Earth’s core processes.

Read also: Theories on Underwater Anomalies

As scientists continue to unravel the anomaly’s mysteries, they are left with more questions than answers. NASA’s commitment to monitoring the SAA underscores the importance of understanding this vast magnetic oddity. By studying its behavior and evolution, researchers can develop models and predictions that enhance our knowledge of Earth’s magnetic environment. The anomaly’s ongoing transformation emphasizes the need for ongoing missions and data collection.

As NASA diligently monitors the South Atlantic Anomaly, the scientific community remains captivated by its complexities. The anomaly’s dynamic nature and potential implications for Earth’s magnetic field pose a wealth of research opportunities.