If you’re planning to get out and see the aurora next time the Sun fires a blast our way, you might want to keep an eye out for a brand new type of sky glow that’s just been discovered. This short-lived phenomenon only appears after midnight and seems to be the inverse of something just spotted a few years ago.

The aurora are among the most spectacular natural phenomena we can see, but despite so many eyes on them for millennia, it looks like certain features can still slip through undetected. In 2017 a purple streak captured in images from the Alberta Aurora Chasers group turned out to be a completely different beast, called a sub-auroral ion drift. It was jokingly nicknamed “Steve” at the time, before being reverse-engineered into an awkward acronym standing for Strong Thermal Emission Velocity Enhancement.

On closer inspection, STEVE was found to be made up of a fast-flowing stream of gas that was heated to high temperatures. It was always seen moving towards the west and only before midnight, but scientists suspected that a similar phenomenon could occur after midnight, flowing east.

And sure enough, this anti-STEVE may now have been discovered in data from the Ramfjordmoen Research Station in the Norwegian Arctic. An image from December 28, 2021, contained a clear purple streak that extended for around 1,000 km (620 miles), which only appeared after midnight.

Some of 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.

STEVE’s late-night twin has yet to be given an official name, but our pitch is SAM (STEVE After Midnight).

The research was published in the journal Earth, Planets & Space.

Source: ESA