Citizen Scientists Shed Light on the Mysteries of Blue Auroras in Low Latitudes
The Rare May 2024 Aurora Over Japan
On May 11, 2024, vibrant auroras graced Japan's Honshu and Hokkaido islands during an intense magnetic storm. While low-latitude auroras typically glow red from oxygen emission, the night showcased a rare salmon-pink aurora and an extraordinary, tall blue-dominant aurora near midnight.
The Role of Citizen Scientists in Documenting the Aurora
Scientists leveraged amateur photographs and smartphone recordings, combining public contributions with their research to study the phenomenon comprehensively.
Methodology and Key Findings
In their latest research, scientists examined visual data of the blue-dominant aurora to calculate its area, validating these calculations with spectrophotometric measurements.
The study, published in Earth, Planets and Space, was conducted under the leadership of Sota Nanjo, a postdoctoral researcher at the Swedish Institute of Space Physics, and Professor Kazuo Shiokawa from Nagoya University's ISEE.
Evidence of Blue-Dominant Aurora's Longitudinal Structures
Nanjo and Shiokawa's study offered the first visual evidence of the spatial configuration of blue-dominant auroras during a storm, revealing longitudinal structures aligned with magnetic field lines—a novel finding for low-latitude auroras.
Their analysis revealed that the aurora extended approximately 1,200 km longitudinally, comprised three distinct structures, and ranged in altitude between 400 and 900 km.
Challenging Existing Scientific Models
Nanjo and Shiokawa's research could redefine our understanding of blue auroras. The ring current, a toroidal zone of charged particles encircling Earth, is thought to generate energetic neutral atoms (ENAs) responsible for low-latitude auroras, such as red auroras. This model suggests the storm energized the ENAs, resulting in the vibrant light display.
Discrepancies with the ENA Mechanism
The team's findings, however, do not align neatly with this mechanism. Shiokawa noted, "Our study identified a longitudinal structure spanning several hundred kilometers in the blue-dominant aurora, which is challenging to explain solely through ENA activity. Moreover, ENA are unlikely to produce auroral formations aligned with magnetic field lines, as observed here."
Exploring Alternative Explanations
One alternative explanation involved resonant scattering of nitrogen molecular ions under sunlight irradiation. However, the researchers propose a different mechanism, as sunlight penetration reached only 700 km, not the observed 400 km.
An Unknown Mechanism at Play
The findings hint at the existence of an unknown mechanism. "Our research indicates that nitrogen molecular ions might have been accelerated upward by an unidentified process, leading to the blue-dominant aurora," Shiokawa explained.
"The mechanisms allowing nitrogen molecular ions, with their significant molecular weight, to persist at such high altitudes remain poorly understood," he stated. "These ions typically have brief lifespans due to their heavy mass and rapid dissociative-recombination rates, yet they are observed at elevated altitudes. This phenomenon remains enigmatic."
Implications for Future Research
Continued study of blue-dominant auroras, such as the one documented in Japan, might reveal critical information about the mechanisms behind nitrogen's occurrence at these heights.
Understanding the outflow of nitrogen molecular ions into the magnetosphere is critical for insights into geomagnetic storms and space radiation, and these findings provide valuable pers pectives on processes occurring hundreds of kilometers above Earth.
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