NASA Goddard
Map of the South Atlantic Anomaly
According to the most recent data from three satellites monitoring our planet, the enormous depression in Earth’s magnetic field continues to expand. There is something special happening in this region, which is weakening the field more intensely, scientists say.
A South Atlantic Anomalyor SAA, stretches across the gulf that separates Africa from South America, and the most recent data suggests that its size increased into something like half the size of Europe since 2014 — at the same time as its magnetic intensity decreases.
The ocean of molten iron in the Earth’s outer core, responsible for generating the planetary magnetic field, it is not static and calm, but turbulent and complex, with behaviors that can alter the external field on temporal scales just a few years oldexplains .
The Earth’s magnetic field is a vast network of field lines generated by dynamo of the planet’s core: the conducting, convective, rotating fluid in the outer core, which converts kinetic energy into magnetic energy.
This field stretches across spaceforming an invisible structure around the planet that helps retain the atmosphere and deflect cosmic rays.
Over millennia, the magnetic field has fluctuated in intensityeven reaching polar reversals. These events do not pose a direct danger to life on the surface, but there are other reasons to study them.
Some navigation systems depend on the magnetic field of Earth, for example. The magnetic field also deflects charged particlesand a weaker magnetic field makes satellites more vulnerable the accumulation of dangerous loads.
Furthermore, the magnetic field deflects solar and cosmic radiationmeaning astronauts and passengers on high-altitude flights are exposed to higher doses of radiation where the magnetic field is weaker.
Understanding changes in the magnetic field could reveal what’s going on in the planet’s deep interior, which in turn could help scientists create more accurate predictive models about their future behavior and mitigating these problems.
The South Atlantic Anomaly is known for less since the 1960sbut there were no detailed studies and continued on it until the launch of the ESA Swarm missionin 2013, which placed three satellites into orbit designed to work together on mapping the geomagnetic field.
The most recent results from the Swarm mission, which were presented in a publication in the journal Physics of the Earth and Planetary Interiors, represent the longest continuous monitoring of Earth’s magnetic field to date — and now reveal new complexities at SAA.
“The South Atlantic Anomaly It’s not just a single block,” says the geophysicist Chris Finlayresearcher at the Technical University of Denmark and first author of the article, in ESA. “It’s changing differently towards Africa than towards South America. There’s something special happening in this region that is weakening the field more intensely.”
The scientists do not know exactly what causes the anomalybut they know that the magnetic field inside the planet, below this region, does not behave as expected.
The Earth’s magnetic field is approximately dipolar; the magnetic north pole is where field lines dip into the planet, and the magnetic south pole is where they emerge.
This is a very simplified version; the magnetic field as a whole is much more complexbut, in general terms, this model describes how the field is expected to behave. In SAA, part of the magnetic flux beneath the Earth’s surface is curiously reversed.
“Normally we would expect to see magnetic field lines coming out of the core in the southern hemisphere. But beneath the South Atlantic Anomaly we see unexpected areas where the magnetic field, instead of leaving the core, dips back into it,” explains Finlay.
“Thanks to Swarm data, we can observe one of these areas moving west over Africa, which contributes to the weakening of the SAA in this region”, explains the researcher.
This inversion of magnetic flux could be linked to a great and mysterious mass of superheated material outside the Earth’s coreknown as the African Large Low-Shear-Velocity Province (LLSVP) under the SAA.
This mass could disrupt core convectionthus changing the behavior of the magnetic field above it. This is believed to be a normal Earth behavior; we simply didn’t have the tools to study it until recently.
Other changes observed by Swarm in Earth’s magnetic field include a slight weakening over Canada and a slight strengthening over Siberia, associated with a change in the magnetic structure beneath North America.
“It’s really wonderful to see the whole picture of our dynamic Earth thanks to Swarm’s extended time series,” says Anja Strommemanager of the Swarm mission at ESA.
“The satellites are all in good condition and provide exceptional data, so we hope to be able to extend this record beyond 2030, when the solar minimum will allow us to obtain unprecedented information about our planet”, concludes Stromme.
