An extreme geomagnetic storm brought spectacular auroral displays on the night of May 10–11, 2024, which were photographed as far south as Mexico, Florida, and Algeria. In the Southern Hemisphere, the “Aurora Australis” reached unusually far north, being visible from Australia, Argentina, Chile, and New Zealand. The storm was triggered by a so-called “cannibal CME” – a phenomenon that occurs when a later, faster coronal mass ejection (CME) overtakes and collides with an earlier one, compressing plasma density and velocity into a massive shock front.

We observed the aurora from Schwarzenberg, Ore Mountains, Germany (50° 32′ 43″ N, 12° 46′ 45″ E). By the end of twilight, faint reddish beams were already visible, intensifying as darkness fell and sweeping from north to west, where the waxing crescent Moon appeared to be “dancing” within the auroral glow. Around 22:45 local time, the characteristic rays gave way to a diffuse crimson glow that stretched photographically far into the southern sky. A further outburst shortly after midnight sent red-violet rays to the zenith, where they converged in a Corona. In the south, green patches pulsed with vivid intensity, with upward-shooting red rays fanning out like flower petals – a breathtaking sight unlike anything we had ever seen before.

This rare event was identified as a RAGDA (Red Arc with Green Diffuse Aurora), a phenomenon occurring at the southern edge of the auroral oval and characterized by deep red arcs accompanied by green, pulsating spots. However, the sharply defined, upward-shooting rays we observed have not been described in connection with RAGDA before.

Research led by Toshi Nishimura in collaboration with Finnish amateur astronomers has shed light on this phenomenon. While typical auroras are caused by solar-wind electrons, RAGDA is driven by solar-wind protons colliding with atmospheric atoms, initiating a chain reaction. These collisions liberate electrons, which then excite other particles, producing the distinctive two-tone auroral display and, occasionally, transient rays such as those we captured. To date, this specific phenomenon has only been documented twice, and in both cases the rays were more diffuse and less sharply defined. Intriguingly, these rays appear to suppress the green diffuse glow while leaving the red arc intact. (→ Link to article)

There are now several dedicated reporting platforms for unusual auroral forms. Such reports are scientifically valuable, as they have revealed that some auroral emissions are not solely driven by particles from solar storms but also by protons originating within Earth’s magnetosphere, funneled downward along magnetic field lines. A key indicator is that aurora-producing particles often carry hundreds to thousands of times more energy than particles within a CME striking Earth. Anyone who photographs unusual auroras is encouraged to share their images with scientists—precise time and location metadata are more important than precise classification.

Aurora Reporting Platforms for Scientific Collaboration:

• Project Solarmax: www.solarmaxmission.com
• Skywarden (Finland): www.taivaanvahti.fi
• Aurorasaurus: www.aurorasaurus.org