Optical and particle observations by the DMSP satellites in both hemispheres. (A) UV image from the SSUSI on board the DMSP F17 satellite in the Northern Hemisphere (B) UV image from the SSUSI on board the DMSP F17 satellite in the Southern Hemisphere (C and D) Energy-time spectrogram of ions (C) and electrons (D) recorded by the particle instruments on board the DMSP F17 satellite during the period shown in (A). (E and F) Energy-time spectrogram of ions (E) and electrons (F) recorded by the particle instruments on board the DMSP F17 satellite during the period shown in (B). Image credit: Scientific advances (2024). DOI: 10.1126/sciadv.adn5276
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Optical and particle observations by the DMSP satellites in both hemispheres. (A) UV image from the SSUSI on board the DMSP F17 satellite in the Northern Hemisphere (B) UV image from the SSUSI on board the DMSP F17 satellite in the Southern Hemisphere (C and D) Energy-time spectrogram of ions (C) and electrons (D) recorded by the particle instruments on board the DMSP F17 satellite during the period shown in (A). (E and F) Energy-time spectrogram of ions (E) and electrons (F) recorded by the particle instruments on board the DMSP F17 satellite during the period shown in (B). Image credit: Scientific advances (2024). DOI: 10.1126/sciadv.adn5276
A small team of astronomers from various institutions in Japan, in collaboration with two colleagues in the United States, have solved the mystery of the unusually smooth aurora that appeared in the Arctic sky in December 2022.
In her in Advances in science, The group describes how they studied in detail both the ground-based data recorded during the event and the satellite observations and the insights they gained.
In December 2020, a ground-based camera in Norway recorded what was then described as a remarkable auroral event in the night sky, extending 4,000 kilometers across the polar cap. It was considered unusually uniform and covered a much larger part of the night sky than normal.
For two years, the source of the monster remained a mystery. In this new study, the research team was finally able to clarify the circumstances that led to this unusual event.
The team examined camera images of the event and then compared them with satellite images from 75 magnetic latitudes. They discovered a suprathermal stream of electrons originating from the solar corona. Its emission patterns were strikingly similar to images of polar rain auroras – in which electrons from the solar corona travel through the Earth’s atmosphere above one of the polar regions.
Convinced that they were on the right track, they conducted further investigations – this time to find out why the aurora could last so long. They found that this unique event had occurred during an unusually quiet period of the solar wind.
When the polar rain auroras filled the night sky in December, the solar wind density dropped to as little as 0.5 cm-3– something that almost never happens. The research team notes that polar rain auroras are usually invisible to the naked eye. The reason the 2022 auroras were visible with a regular camera was the absence of solar wind.
It has been noted that auroral research has been greatly supported by citizen scientists, who were instrumental in determining the source of the purple lights that appeared in Canadian skies in 2016.
More information:
Keisuke Hosokawa et al., Extraordinarily gigantic auroras in the polar cap on a day when the solar wind had almost disappeared, Scientific advances (2024). DOI: 10.1126/sciadv.adn5276
Information about the magazine:
Scientific advances
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