Takuya Usami
The distinct longitudinal structures and altitude at which these auroras occurred suggest that there is an unknown mechanism behind the phenomenon.
On May 11, 2024, Japan witnessed a rare celestial phenomenon, when auroras of salmon pink and blue tones lit up the skies of Honshu and Hokkaido. Unlike typical red auroras caused by oxygen emissions, these vibrant displays resulted from a powerful magnetic storm and revealed intriguing new details about aurora formation.
The researchers, led by Sota Nanjo of the Swedish Institute of Space Physics and Professor Kazuo Shiokawa of the Institute for Space-Earth Environmental Research at Nagoya University, used a combination of amateur photographs, smartphone videos and scientific measurements to investigate this event. Their findings, out December 5 in the journal Earth, Planets and Space, highlight groundbreaking observations about the auroras with blue predominance.
The blue aurora, which appeared unusually tall and stretched about 1200 km long, presented distinct longitudinal structures aligned with the Earth’s magnetic field lines. This alignment, observed for the first time in low-latitude blue auroras, challenges traditional models of aurora formation. The researchers also noted that the altitude of the auroras varied between 400 and 900 km, with sunlight unable to reach the lower levels observed, suggesting the existence of an unknown mechanism.
Current theories attribute low-latitude auroras to energetic neutral atoms (ENAs) produced in Earth’s ring current. However, this explanation is not sufficient to explain the structured patterns and alignment observed in this case. Another hypothesis, involving nitrogen molecular ions illuminated by sunlight, also proved to be insufficient due to altitude limitations.
The team’s findings propose that molecular nitrogen ions were likely accelerated upward by a unidentified processforming the dominant blue auroras. This revelation raises questions about how these ions, with their large molecular weight and short lifespan, can exist at such high altitudes, explains .
Professor Shiokawa highlighted the importance of these discoveries, stating that understanding this process could have implications for study of geomagnetic stormsspace radiation environments and the dynamics of the magnetosphere in general.
Future observations of similar auroral events could provide valuable insights into the mechanisms underlying nitrogen ion activity at high altitudes. These studies could ultimately reshape our understanding of the science of the aurora borealis and the complex interactions that occur in Earth’s upper atmosphere.
