Scientists Finally Discover How Earth Experienced Its First ‘Polar Rain’ Auroras

The Northern Lights erupt in the skies like pulsating explosions of light energy, glowing in iridescent colors. But on December 25 and 26 in 2022, scientists captured an aurora that seemed too unusual, too eerie to be left unexplored. The “exceptionally gigantic aurora” was neither dancing nor pulsating nor moving. It appeared like a faint, greenish, featureless halo. After a series of delving into facts and studies, scientists discovered that the rare aurora was the result of a creepy phenomenon where the Sun spews a rainstorm of electrons into Earth’s magnetic field, generating the surreal glow, as they documented in research published in Science Advances.

Typically, an aurora, one of the most fascinating spectacles ever observed on Earth, is generated when the Sun ejects generous volleys of hot, flaring electrons. These electrons slam into the Earth’s magnetic field, which regrows again every time, per Space.com. When these electrons come in contact with the molecules swirling around in Earth’s atmosphere, their crashing results in the emission of dazzling glow, such as in purples, greens, blues, or pinks. The Sun’s core is punctuated with several coronal holes. In case of solar maximum or heightened solar energy, these holes release massive bursts of electrons in a process called “Coronal Mass Ejection (CME),” in which electrons can be observed flying for over 500 miles at a time.

When this happens, it lends a marvellously brilliant intensity to these glowing lights. When a team of researchers from Japan and the US analyzed this Christmas Day aurora, they were not just stunned; they were also puzzled. Initially, they used the All-Sky Electron Multiplying Charge-Coupled Device (EMCCD) camera in Longyearbyen in Norway to record the rare aurora. Then, Keisuke Hosokawa, the lead researcher from Tokyo, deployed the Special Sensor Ultraviolet Scanning Imager (SSUSI) to compare this faint, bland aurora with the ones seen on the polar-orbiting satellites of the Defense Meteorological Satellite Program (DMSP).

Tracing the source of this aurora from the Sun’s core, they realized it was triggered by a ferocious stream of excited electrons precipitating from the magnetosphere along the closed magnetic field lines of the planet. Once these electrons were ejected, they got stored inside a part called the “magnetotail.” Further energized by the force of blazing solar winds, they started raining into Earth’s atmosphere, triggering an aggressive tailspin of collisions. And as they crashed with the atmospheric molecules of nitrogen, carbon, and oxygen, they released this magnificent “calm” and “quiet” glow. They named this “suprathermal electrons” stream, coming from the Sun, as “polar rain.”

As Norwegians woke up to watch this glow blanketed upon the rugged mountains dusted with snow, scientists receiving data from the cameras in their laboratories noticed that the polar rain aurora continued to glow even when the solar winds disappeared. "When the solar wind disappeared, an intense flux of electrons with an energy of >1keV was observed by the DMSP, which made the polar rain aurora visible even from the ground as bright greenish emissions," said Hosokawa and his team in the study.