Mysterious twin of STEVE aurora discovered in Norway

A new auroral phenomenon, potentially a twin of the STEVE — a mysterious ribbon of purple light in the night sky, was photographed over Norway on December 28, 2021. The finding, confirmed by ESA’s Swarm satellite data, reveals an eastward stream of hot gases at dawn, similar to the westward stream seen at dusk.

A new auroral phenomenon, potentially a dawn-side twin of the mysterious STEVE, has been discovered in Norway.

This finding was made possible through the collaborative efforts of scientists and citizen scientists, leveraging data from the European Space Agency’s (ESA) Swarm satellites and images from an all-sky digital camera at the Ramfjordmoen Research Station.

STEVE, a sub-auroral ion drift or strong thermal emission velocity enhancement, was initially discovered by the Alberta Aurora Chasers Facebook group in 2016.

It’s a mysterious atmospheric phenomenon that appears as a purple ribbon of light in the night sky, moving westward at dusk. Unlike the traditional aurora borealis, which displays green, blue, and red hues, STEVE’s mauve appearance and brief duration intrigued scientists since its discovery.

Now a new study, involving researchers from the University of Electro-Communications in Japan, the Swedish Institute of Space Physics, the Arctic University of Norway, and Hofstra, suggests the existence of a similar phenomenon occurring at dawn — STEVE’s twin.

Whilst looking through images of aurora above the Norwegian Arctic captured by all-sky digital camera at the Ramfjordmoen Research Station, photographer Gabriel Arne Hofstra stumbled across something peculiar, something STEVE-like but not STEVE, in an image from December 28, 2021.

Their finding has been confirmed by ESA’s Swarm constellation of satellites.

While Swarm satellites did not fly directly through the arc at the precise time of the event, data from their electric field instruments measured conditions in the purple region before, during, and after the observation, indicating an eastward ion flow.

“Our findings not only open new avenues in auroral physics but also underscore the importance of continuous collaboration between scientists and photographers. Such efforts are particularly crucial in the coming years as solar activity approaches its peak, when we may encounter extraordinary phenomena,” said Sota Nanjo of the University of Electro-Communications.

The ability of digital cameras to capture high-contrast images of auroral events played a crucial role in this discovery. As solar activity peaks in the coming year, such collaborations are expected to uncover more extraordinary phenomena. The recent geomagnetic storm on May 10, 2024, one of the most documented aurora events, highlighted the value of citizen science in advancing our understanding of space weather.

“The combination of millions of images taken worldwide, along with data from the satellites of ESA’s heliophysics observatory, like Swarm, will give us an even better understanding of how space weather affects Earth’s atmosphere,” said Anja Strømme, Swarm Mission Manager.

References:

¹ Post-midnight purple arc and patches appeared on the high latitude part of the auroral oval: Dawnside counterpart of STEVE? – Nanjo, S., Hofstra, G.A., Shiokawa, K. et al. -Earth Planets Space 76, 55 (2024). DOI: https://doi.org/10.1186/s40623-024-01995-9

² Swarm helps discover Steve’s long-lost twin – ESA – June 3, 2024

Featured image: STEVES twin captured by the all-sky digital camera at the Ramfjordmoen Research Station in Norway. Credit: Ramfjordmoen Research Station