The blue aurora borealis over Japan has puzzled scientists. Photo

Recently, Japan has witnessed unusual polar activity with the appearance of the aurora borealis in blue. This color has become a challenge for scientists.

To find out how the aurora could be this color, researchers used publicly available and scientific data for analysis. They discovered new structural details and potential formation mechanisms, challenging existing theories about the origin of the aurora, and concluded that it is the result of a strong magnetic storm, Scitech Daily writes.

In the new study, the researchers used video and images of the aurora borealis to map its extent, confirming their findings with spectrophotometric measurements.

The study, led by Sota Nanjo, a doctoral student at the Swedish Institute of Space Physics, and Professor Kazuo Shiokawa from the Institute of Space and Earth Environmental Research (ISEE) at Nagoya University, provided the first visualization of the spatial structure of the blue aurora during a storm. The researchers found that the aurorae had longitudinal structures that were aligned with magnetic field lines, and for the first time, they were identified in aurorae with a dominant blue color at low latitudes. The scientists also found that the aurora covered about 1200 km in longitude, consisted of three separate structures, and ranged in altitude from 400 to 900 km.

Nanjo and Shiokawa's discoveries could change the current understanding of the blue aurorae. The auroral current, a bagel-shaped region of charged particles surrounding the Earth, is thought to be the source of the energetic neutral atoms (ENAs) that create low-latitude auroras, including the red aurora. According to this model, the storm likely fueled the ENAs, creating the colorful light.

However, the team's discovery is not easily explained by this mechanism.

"This study revealed a structure several hundred kilometers across in the aurora with a blue dominant longitudinal color, which is difficult to interpret as ENA activity alone. In addition, it is unlikely that ENAs will create auroral structures aligned with magnetic field lines, as observed during our work," explains Shiokawa.

The results of the study may point to an interesting possibility of an unidentified process. "Our findings suggest that molecular nitrogen ions may have been accelerated upward by a certain mechanism and were responsible for the formation of the blue dominant aurora," the scientist said.

Shiokawa explained that it is not entirely clear today how molecular nitrogen ions with a large molecular weight can exist at such high altitudes. "Such ions cannot exist for a long time because of their large mass and short dissociative recombination time intervals, but they are observed at high altitudes. This process is shrouded in mystery," the scientist added.

Overall, repeated observations of blue-dominated auroras may provide clues to understanding the principle behind how nitrogen can be found at these altitudes. Since the process of outflow of molecular nitrogen ions into the magnetosphere is important in everything from understanding geomagnetic storms to the radiation environment in space, these discoveries can help us understand the processes that occur hundreds of kilometers above us.

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