On Christmas Day of 2022, observers across the Arctic were treated to an extraordinary sight—a unique aurora caused by a ‘rainstorm’ of electrons from the sun. This fascinating phenomenon has been the focus of joint research by scientists from Japan and the United States, who have spent months, and even years, unraveling the mysteries of this rare event. This was the first time such an aurora was visible from the ground during a period when solar wind gusts were notably weak.
Typically, the auroras we observe, such as those seen in Norway, exhibit dynamic patterns and pulsating lights with distinct shapes across the sky. These natural light displays are powered by electrons carried from the sun by the solar wind, becoming trapped within Earth’s magnetotail—an extension of our planet’s magnetic field.
During more intense solar events, these trapped electrons travel along Earth’s magnetic field lines toward the poles, where they collide with atmospheric molecules, causing the characteristic glow of auroras in hues of blue, green, or red.
However, the Christmas Day aurora of 2022 stood out as it appeared as a faint, featureless glow that spanned an impressive 4,000 kilometers without any of the usual structure or variation in brightness. This remarkable event marked a historical first, as no similar space phenomenon had been observed from Earth before.
The conditions for this unique aurora were set by the dwindling solar winds, which allowed an intense flux of electrons to penetrate the atmosphere, creating what is known as a polar rain aurora. According to Keisuke Hosokawa from the Center for Space Science and Radio Engineering at the University of Electro-Communications in Tokyo, “When the solar wind disappeared, an intense flux of electrons with an energy of >1keV was observed by the DMSP, making the polar rain aurora visible from the ground as bright greenish emissions.”
The size of the magnetic funnel through which the electrons traveled was also unusual, opening at about 7,500 kilometers when projected at Earth’s distance from the sun, explaining the smooth appearance of the aurora. This unprecedented event not only added a magical touch to the holiday celebrations but also provided valuable insights into the behavior of our planet’s magnetic field and its interaction with solar activity.