The first of two new rare sky glow phenomena was videoed in 2017, over Southwest Canada. It appeared closer to the equator than where auroras normally occur, and was a different color……purple! Auroras are red, blue, and green. This first new sky glow was dubbed STEVE, for Strong Thermal Emission Velocity Enhancement. After deeper investigation and observation, it was determined that STEVE was a plasma stream of charged particles, or “sub-auroral ion drift,” a fast-flowing stream of gas at high temperatures. STEVE only flows West and before midnight. More information on STEVE can be found here.
In 2021, Norwegian Arctic researchers discovered another mysterious, non-aurora purple sky glow that flows East only after midnight. This similar but different phenomenon doesn’t have an official name yet, but in some ways, it is an anti-STEVE. European Space Agency (ESA) ’s Swarm satellites were able to measure the conditions in the purple part of the phenomenon before, during, and after it appeared. This showed that the ions were likely flowing eastward. More information on the anti-STEVE can be found here.
Top image: 2022 ALAN DYER/AMAZINGSKY.COM
Image: Nanjo, S., Hofstra, G.A., Shiokawa, K. et al. Post-midnight purple arc and patches appeared on the high latitude part of the auroral oval: Dawnside counterpart of STEVE?. Earth Planets Space 76, 55 (2024). https://doi.org/10.1186/s40623-024-01995-9
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