Blue auroras are a fascinating but extremely rare phenomenon. While green and red auroras can often be seen over the polar regions, the blue glow only appears under special conditions. Now, for the first time, Japanese scientists have precisely measured the altitude at which this rare light occurs – and obtained a result that has surprised even experts.
In October 2023, a team led by Katsumi Ida from Japan’s National Fusion Research Institute in Kiruna, northern Sweden, made an extraordinary observation. Using a specially developed hyperspectral camera that can separate light of different wavelengths, they analyzed the blue aurora in detail. This technique made it possible for the first time to separate the actual glow of the aurora from the disturbing scattered light of the sun. Th…
Blue auroras are a fascinating but extremely rare phenomenon. While green and red auroras can often be seen over the polar regions, the blue glow only appears under special conditions. Now, for the first time, Japanese scientists have precisely measured the altitude at which this rare light occurs – and obtained a result that has surprised even experts.
In October 2023, a team led by Katsumi Ida from Japan’s National Fusion Research Institute in Kiruna, northern Sweden, made an extraordinary observation. Using a specially developed hyperspectral camera that can separate light of different wavelengths, they analyzed the blue aurora in detail. This technique made it possible for the first time to separate the actual glow of the aurora from the disturbing scattered light of the sun. This is particularly important as blue auroras usually occur during twilight, when the sun is still slightly illuminating the upper layers of the atmosphere.
The results were surprising: The maximum of the blue aurora was not, as theoretically predicted, at an altitude of around 125 kilometers, but significantly higher, at around 200 kilometers. This is an area in which the atmosphere is already very thin. Under these conditions, there should actually be too few nitrogen molecules to generate such intense light emission.
Scientists are therefore faced with a new puzzle. How does a sufficiently high density of ionized nitrogen molecules arise at this altitude? Ida’s team suspects two possible explanations. Either ionized particles are transported upwards from lower layers of the atmosphere, or there is an exchange between oxygen and nitrogen ions in which energy and charge are transferred. Both processes could explain why the blue glow occurs at such high altitudes.
Blue auroras occur when high-energy particles from the solar wind penetrate the upper atmosphere and ionize nitrogen molecules there. These molecules emit light in the blue spectrum as they fall back to their ground state. As these processes require a lot of energy, they occur much less frequently than the greenish or red auroras produced by oxygen atoms.
Thanks to the hyperspectral camera, the researchers were able to break down the light into tiny wavelength ranges and precisely determine the altitude from which it originated. This made it possible for the first time to determine the exact altitude at which the blue aurora originated – a technological advance that could provide further insights into the dynamics of the upper atmosphere in the future.
The result is of great importance for research. If it is confirmed that blue auroras regularly occur at an altitude of around 200 kilometers, existing models of ionospheric chemistry will have to be revised. This is because it was previously assumed that there were hardly any high-energy nitrogen ions at this altitude.
The scientists are therefore planning further observations in Scandinavia and North America to find out more about the conditions under which the blue auroras occur. In particular, they want to carry out new measurements during twilight, when the transitions between sunlight and darkness change the ionosphere.
Conclusion
The new measurements reveal that blue auroras occur at much higher altitudes than previously assumed. This indicates that previously unknown processes are taking place in the upper atmosphere. This rare phenomenon is therefore an important key to better understanding the physical interactions between the sun, magnetic field and atmosphere. One thing is certain: the mystery of the blue glow in the sky is far from being solved.
Source: Scinexx.de