A remarkably smooth and mysterious Christmas Day Aurora observed over the Arctic in 2022 was the result of a “rain storm”. electrons directly from sunsay Japanese and American researchers.
It is the first time a rare aurora of this kind has been seen from the ground, at a time when gusts solar storm it almost completely fell away, leaving a region of calm around the Earth.
Normally, the aurora borealis, like the one seen around the world, is displayed in Maythey move and pulsate with clearly discernible shapes in the sky. These auroras are powered by electrons from the solar wind—the stream of charged particles that flow from the sun—that become trapped in the extension Earth’s magnetic field called a magnetotail. When space weather becomes extreme as when a coronal mass ejection (CME) — a large ejection of plasma and magnetic field from the sun — is released, the magnetotail can be chipped off (don’t worry, it will grow back). Electrons trapped there flow down Earthmagnetic field lines to the poles. In doing so, they encounter molecules Earth’s atmospherehe collided with them and urged them to light up the colors of the aurora borealis (blue for nitrogen emissions, green or red for oxygen depending on its altitude).
Smooth aurora from 25-26 however, December 2022 was very different. Captured by the All-Sky Electron Multiplying Charge-Coupled Device (EMCCD) camera in Longyearbyen, Norway, the aurora was a faint, indistinct glow spanning 2,485 miles (4,000 kilometers) in extent. It had no texture, no pulsation or variable brightness. No type of aurora ever seen from Earth before.
To solve the mystery, a team led by Keisuke Hosokawa of the Center for Space Science and Radio Engineering at Tokyo University of Electro-Communications compared this faint aurora with that of the SSUSI (Special Sensor Ultraviolet Scanning Imager) in polar orbit. Defense Meteorological Satellite Program (DMSP) satellites have seen. The DMSP is operated by the National Oceanic and Atmospheric Administration and the US A cosmic force on behalf of the US Department of Defense.
Satellites saw the aurora from above and found that it had all the hallmarks of a rare type of aurora called an aurora borealis that had only been seen from space until now.
The normal solar wind moves about 250 miles (400 km) per second. However, the sun is shining corona it is full of holes, especially at higher solar latitudes, where the exceptionally “fast” solar wind flows, moving at speeds of up to 800 km per second. Sometimes these coronal holes can appear at lower latitudes, and this happened at Christmas 2022, coinciding with the cessation of the regular solar wind.
In the place of coronal holes, the magnetic field lines of the Sun are open – they do not slide back to the solar surface, the photosphere. As open magnetic field lines expand into space, the coronal hole forms the base of a magnetic funnel from which high-energy electrons flow.
In the case of the aurora borealis, these electrons traveled through space and the open magnetic field lines combined with the Earth’s magnetic field above the North Pole, allowing the electrons to rain directly onto the poles rather than being trapped inside the magnetotail.
Normally we don’t notice this because normal polar wind particles scatter the fast wind electrons coming out of the coronal hole. On this occasion, however, the pressure of the solar wind was reduced to the point where it was negligible, and the electrons of the fast wind could reach Earth undisturbed.
Furthermore, the diameter of this magnetic funnel opening is about 4,600 miles (7,500 km) when projected onto Earth’s distance from the Sun. That’s why the aurora borealis seemed so smooth; open tubes of magnetic flux emanating from the Sun covered a wider area than the northern polar cap of the Earth. Because the electrons had high energy, the aurora borealis was pure green rather than red, because it takes more energy to ionize oxygen deeper in the atmosphere.
The clear evidence was that the DMSP satellites saw polar rain only over the Earth’s north magnetic pole, which is tilted toward the Sun during the Northern Hemisphere winter.
“When the solar wind disappeared, DMSP observed an intense flow of electrons with energies >1keV, making the aurora borealis visible even from the ground as a bright greenish emission,” Hosokawa’s team said in their published research paper.
Polar rain itself has previously been studied in depth using particle detectors satellites in orbit, but such studies are few. These smooth auroras are not normally visible to the naked eye on the ground. As such, until now, no one knew what the smooth, bland aurora that turned the sky green on Christmas 2022 was. For the full explanation, check out the June 21 issue of the magazine Scientific advances.