A dent in Earth’s magnetic field is messing with aurorae
Abizarre dent in Earth’s magnetic field above the southern Atlantic Ocean weakens the southern lights. The South Atlantic Anomaly is a large, oval-shaped region over South America and the southern Atlantic Ocean where Earth’s magnetic field is weakest. The anomaly is already well known for allowing charged particles from the Sun to dip close to Earth’s surface, exposing satellites orbiting above to high levels of ionising radiation.
A recent study has found that this weak region also affects southern aurorae, the glowing lights in the upper atmosphere that can be seen at high latitudes. The southern lights occur over and around Antarctica and are the equivalent of the northern lights that dance over the Arctic and subarctic. Aurorae are caused by solar particles interacting with gas molecules in Earth’s atmosphere and are usually considered largely under the control of the Sun. But the new research highlights the two-way nature of the relationship.
“Our discovery highlights the significance of Earth-related factors, such as anomalies in Earth’s intrinsic magnetic field that rotate with the Earth,” said Zhi-yang Liu, a researcher at the Institute of Space Physics and Applied Technology at Peking University in China. The researchers used data from an instrument aboard the Feng-yun 3E satellite, launched in 2021, that measures magnetic field variations. They found a ‘substantial weakening’ of magnetic fluctuations in the aurora australis, or southern lights, where it overlaps with the South Atlantic Anomaly.
To confirm the findings, ultraviolet light was also analysed from this region of the aurorae using data from the US Defense Meteorological Satellite Program, which showed a weakening in the southern lights in the area of the anomaly. It’s likely this weakening is even visible to the naked eye. There are fewer aurorae reported from China’s Great Wall Station and other research stations on King George Island than in other Antarctic regions. Research suggests that the ultraviolet and visible light in aurorae behave similarly, Liu said, so it’s likely that the visible light of the aurorae is weakened by the South Atlantic Anomaly, too.
The weakened magnetic fluctuations of the anomaly seem to reduce the amount of energy that can be put into the atmosphere by solar particles, but the physics of the weakened aurorae aren’t entirely understood. There may be feedback effects between the atmosphere and solar energy that further complicate the picture. Future research will also investigate whether a similar phenomenon occurs on other planets.