Amazing new sightings unlock mysteries of rare blue auroras

NAGOYA, Japan — In May 2024, a once-in-a-generation solar storm painted the skies with an extraordinary and rarely seen celestial phenomenon: blue auroras that stretched across hundreds of miles of the night sky. This stunning display captured by citizen scientists in Japan didn’t just give us some great pictures, it’s offering a unique glimpse into the mysterious world of space weather and its breathtaking light shows.

The extreme geomagnetic storm, classified as a G5-level event — the most intense category — was triggered by multiple solar flares from sunspot region AR13664. These powerful eruptions sent coronal mass ejections hurtling toward Earth, creating a light show that was visible far further south than typical auroral displays.

What made this event particularly remarkable was the prevalence of blue auroras, a color rarely seen in low-latitude regions. Traditionally, auroras at these latitudes appear predominantly red or reddish-purple. The blue lights appeared in distinct vertical structures, almost like celestial curtains hanging across the night sky.

Two amateur photographers, armed with high-resolution digital cameras, captured this extraordinary event from different locations in Japan. One photographer shot images from the Noto Peninsula, while another photographed from Kiso in Nagano Prefecture. Their images revealed something scientists had never before documented so precisely: blue auroras with clear, structured formations extending from 400 to 900 kilometers above the Earth’s surface.

The researchers used sophisticated mathematical techniques to pinpoint the exact location and characteristics of these blue auroras. By comparing the images taken from different angles, they could triangulate the aurora’s position, altitude, and extent. Their calculations revealed the blue structures spanned approximately 1,200 kilometers — roughly the distance between San Francisco and Seattle — and appeared at a magnetic latitude of 40 degrees.

While scientists have observed blue emissions in auroras before, this event was unique. Previous blue auroras were typically associated with sunlit regions of the ionosphere, but these blue lights appeared during the middle of the night, synchronized with a substorm — a sudden burst of energy in Earth’s magnetosphere.

What’s actually creating these blue auroras remains somewhat mysterious. Researchers have proposed several potential explanations, including energetic neutral atoms (ENAs) from the Earth’s ring current or the resonant scattering of sunlight by nitrogen molecular ions. However, the precise vertical structures observed in this event suggest more complex processes might be at play.

“Our findings suggest that nitrogen molecular ions may have accelerated upward by some mechanism and were responsible for the formation of the blue-dominant aurora,” says Professor Kazuo Shiokawa from the Institute for Space-Earth Environmental Research (ISEE) at Nagoya University in a media release.

“To date, it is not well understood how nitrogen molecular ions with large molecular weight can exist at such high altitudes,” the study’s co-leader continues. “Such ions are not easily able to exist for long periods of time due to their heavy mass and short dissociative-recombination time intervals; however, they are observed at high altitudes. The process is shrouded in mystery.”  

This discovery provides valuable insights into space weather, solar-terrestrial interactions, and the complex dynamics of Earth’s magnetosphere. As solar activity is expected to increase in the coming years, these new observations could help scientists better understand these intricate atmospheric phenomena.

The study, published in the journal Earth Planets and Space, also highlights the growing importance of citizen scientists — amateur photographers and enthusiasts who contribute significantly to scientific research by capturing rare events with modern technology. Their high-resolution digital cameras and ability to be in multiple locations have opened new avenues for scientific observation.