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Rare phenomenon recorded in Hokkaido exposes a little-noticed flaw in space weather forecasts and shows how weak auroras, captured by common cameras, can reveal greater risks for satellites in low Earth orbit.
Red auroras recorded in Hokkaido, northern Japan, indicate that some geomagnetic storms classified as moderate may have more intense effects than traditional space weather indices show.
The phenomenon was analyzed by researchers from Hokkaido University and the Okinawa Institute of Science and Technology.
The observations attracted attention because Hokkaido is at a low magnetic latitude for this type of phenomenon, usually associated with regions much closer to the poles.
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Even so, red and magenta lights appeared on four occasions in 2024 and were recorded again in March 2025.
Although most of these auroras were too weak to be perceived with the naked eye, long-exposure cameras managed to capture the glow on the northern horizon.
The images helped scientists identify a possible flaw in the way the intensity of certain solar storms is measured.
Red auroras in Hokkaido challenge forecasts
The island of Hokkaido does not usually appear on the aurora map during moderate geomagnetic storms.
For lights of this type to be seen there, under normal conditions, a stronger event would be expected, capable of pushing auroral activity to lower latitudes.
This logic was called into question when citizen scientists photographed auroras on June 28, August 4, September 12, and November 9, 2024.
A fifth record, on March 26, 2025, reinforced researchers’ interest in the observed pattern.
The study was led by Tomohiro M. Nakayama, affiliated with Hokkaido University, in collaboration with Ryuho Kataoka, from the Okinawa Institute of Science and Technology.
The team cross-referenced photographs taken by amateur observers with satellite data and solar wind measurements.
The images show reddish bands near the horizon and, in some cases, magenta rays with bluish variations at the top.
The shapes changed at short intervals, a characteristic compatible with an active geomagnetic storm.
Solar storm indices may underestimate risks
The usual classification of geomagnetic storms considers how the solar wind alters the Earth’s magnetic field.
In the four events of 2024, the main values indicated only moderate storms, which seemed inconsistent with visible auroras in Hokkaido.
Researchers observed, however, that indicators linked to the asymmetry of the magnetic disturbance showed higher values than conventional indices.
This suggests that the magnetosphere was significantly compressed, even though the standard classification did not reveal the full intensity of the process.
This compression can displace charged particles and alter the distribution of energy around the Earth.
Thus, a storm may seem less severe in the most commonly used metrics, while producing significant effects in the upper atmosphere and in low orbits.
The central point of the research is the density of the solar wind, that is, the number of charged particles arriving from the Sun.
In the 2024 events, this flow was not necessarily the fastest, but it carried a high concentration of particles per cubic centimeter.
Dense solar wind changes scientists’ interpretation
For a long time, the speed of the solar wind received greater emphasis in assessments of geomagnetic storms.
The Hokkaido cases indicate that density can also play a decisive role, especially when the magnetosphere is intensely compressed.
In the four episodes analyzed, the solar wind had significant density, with more than 30 particles per cubic centimeter at moderate speeds.
This combination helps explain why auroras appeared in a region considered too low for storms classified only as moderate.
The hypothesis discussed by researchers is that the compression of the magnetosphere and the heating of the upper atmosphere have raised the region where red auroras form.
Instead of occurring at the most common altitudes, they would have extended to much higher levels.
Red auroras usually form when energetic particles interact with oxygen atoms in rarefied layers of the atmosphere.
In the Japanese case, estimates indicate altitudes between approximately 500 and 800 kilometers, above the range normally expected for this type of glow.
Citizen science expands aurora observation in Japan
The investigation only advanced because observers scattered across Hokkaido recorded the phenomenon at different points on the island.
The images, many of them taken with smartphones and regular cameras, offered varied angles to reconstruct the position and height of the auroras.
This type of collaboration showed the importance of citizen science in events that are difficult to predict and observe with professional instruments.
On some nights, cloud cover or the limitation of formal stations would have left part of the phenomenon undocumented.
By comparing photographs with satellite data on the active aurora band, researchers were able to estimate the altitude of the red emissions.
The wide visual coverage allowed testing whether the brightness was local, followed coherent patterns, and corresponded to recorded geomagnetic activity.
Japan has started to gather an informal network of observers who monitor aurora alerts and share images on social media.
This mobilization provided an unusual volume of records for a phenomenon that, at lower latitudes, tends to be rare and discreet.
Low orbit satellites face greater drag
The discoveries are not limited to explaining the lights in the sky.
When geomagnetic storms heat and expand the upper atmosphere, low orbit satellites begin to face greater resistance, which can accelerate the loss of altitude.
This atmospheric drag increases fuel consumption, shortens the lifespan of equipment, and may require unplanned maneuvers.
In constellations with many satellites in low orbits, small variations in atmospheric density can have significant operational effects.
A frequently cited case occurred in February 2022, when dozens of Starlink satellites were lost after launch during a geomagnetic storm.
Subsequent studies associated the episode with increased drag caused by the expansion of the upper atmosphere.
Another analysis, published on the October 10, 2024 storm, pointed to a possible relationship between the geomagnetic event and the early reentry of a Starlink satellite.
The authors treated the case as a possible association, still dependent on further research for definitive confirmation.
Space weather demands new metrics for satellites
The results reinforce the need to include solar wind density with more weight in prediction models.
A slower but denser current may pose a greater risk than it appears when assessed only by traditional indices.
For satellite operators, this detail is relevant because the moderate classification of a storm may not reflect the full impact in low orbit.
The expansion of the upper atmosphere precisely affects the region where thousands of communication, observation, and navigation satellites circulate.
The study also shows that events not very visible to the public can carry important signals about the relationship between the Sun, magnetosphere, and Earth’s atmosphere.
In Hokkaido, faint lights captured by cameras revealed processes that could go unnoticed in conventional measurements.
The research was published in the Journal of Space Weather and Space Climate and adds new evidence to an increasingly strategic area.
With the growth of constellations in low orbit, understanding seemingly moderate solar storms is no longer just a scientific issue.
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