Solar storm images illuminate mystery of red aurora glow

Earth experienced a significant magnetic storm on 10 May 2024, the second most powerful since 1958, following a strong solar event. This resulted in vibrant auroras visible even at mid-latitudes, prompting stargazers and researchers to observe and photograph the phenomenon.

“I’ve seen many auroras at higher latitudes. Above Göttingen, they’re a rarity. I absolutely wanted to photograph them. I wasn’t originally interested in using the photos for scientific purposes,” stated Sami Solanki, director of the Max Planck Institute for Solar System Research in Germany.

Images from both scientists and amateur photographers revealed a reddish glow above the typical green auroras, characterized by bright rays extending downwards. The key observation of these rays physically linking the red glow to the green aurora has been crucial in deciphering the underlying mechanism.

While red auroras have been observed at middle latitudes during intense magnetic storms at altitudes of 80 to 200km, the process behind their formation has been unclear due to a lack of satellite data in the region.

Previous theories suggested the red glow might be caused by heat or waves accelerating electrons. However, the 2024 event’s photographic evidence has provided new insights.

“Rays continuously connecting the red aurora above to the green aurora below have not been reported in any scientific paper,” explained Bruce Tsurutani, author of a study published in Annales Geophysicae.

The research team compared the aurora images with data on solar wind and Earth’s magnetic field disturbances, alongside existing knowledge of green auroras.

Green auroras are typically produced when fast electrons travel along the Earth’s magnetic field lines to altitudes of 130 to 85km, triggering collisions that cause oxygen atoms to glow green. A similar process occurs with red auroras, but at significantly higher altitudes, ranging from 200 to 800km.

At these extreme altitudes, electrons collide with sparse oxygen particles, producing a red glow. As the electrons descend into denser atmospheric layers, they trigger the familiar green aurora.

Researchers believe there may be multiple types of red auroras and are seeking additional photographs with short exposure times to better analyze the streaks and use stars as reference points.

Despite the Sun moving away from its peak activity cycle, further strong solar events and auroral displays are still possible in the coming months and years. “Anyone who takes photos of the aurora with a smartphone or camera can contribute to their study,” added Yasuhito Narita, another author of the study from the Technical University of Braunschweig in Germany.