ESA’s Swarm Satellites Discovers STEVE’s Twin That Appears at Dawn [Study]

ESA's Swarm Satellites Discovers STEVE's Twin That Appears at Dawn [Study]
(Photo: Wikimedia Commons/NASA Goddard Space Flight Center)

Citizen scientists helped researchers find STEVE's long-lost twin, and ESA's trio of magnetic-field monitoring Swarm satellites played a part in the discovery.

ESA's Swarm Satellites Found STEVE's Twin

Strong Thermal Emission Velocity Enhancement (STEVE) was initially mistaken as auroras because of its close resemblance to the northern lights. It turns out that STEVE has a twin.

STEVE is the westward stream's visual effect at nightfall. Due to this, experts wonder if there's a corresponding eastward stream with a similar impact at dawn, which could probably be its twin.

A new study by photographer Gabriel Arne Hofstra, the Swedish Institute of Space Physics, the Arctic University of Norway, and the University of Electro-Communications in Japan suggests that researchers and citizen scientists may have just found it.

The group created an application that uses the Ramfjordmoen Research Station's all-sky digital camera to capture pictures of the aurora's daily dances above the Norwegian Arctic.

While searching through its data files, Gabriel Arne Hofstra saw something strange, something STEVE-like, in a photograph from Dec. 28, 2021.

However, there were some significant distinctions from Steve. After midnight, the 1000 km-long arc emerged on the dawn side, pointing poleward from the nearby green aurora.

Even though none of the three Swarm satellites operated by ESA passed through the arc precisely at the moment and location shown in the all-sky picture, the electric field instruments on two satellites could gauge the conditions in the purple area before, during, and following the event.

The purple area of the data displayed the characteristics of an eastward ion movement.

"It's great to see yet another example of successful citizen science," said Swarm Mission Manager Anja Strømme. "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."

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What Is STEVE?

STEVE is associated with intense sub-auroral ion drift (SAID). At lower latitudes, it is seen as a mauve-colored light streak with distinguishable green bands, often referred to as a picket fence.

STEVE is one of those annoyingly elusive characters. It is not often found with auroras. Finding STEVE could occasionally depend on luck, as Manitoba-based Canadian photographer Donna Lach noted.

Space physicist Elizabeth MacDonald of NASA's Goddard Space Flight Center had never seen the event before until about eight years ago, when she was in Calgary, Alberta, for a seminar. At the time, it had no name either.

STEVE, identified by its occurrence closer to the equator than auroras, is a rare night sky phenomenon that few scientists studying northern lights or auroras have witnessed. With its purple-pink arch and green vertical stripes, STEVE is as vibrant as an aurora.

In 2015, citizen scientist Neil Zeller said they referred to it as a proton arc. However, a University of Calgary professor, Dr. Eric Donovan, argued that it was "misidentified" because a proton arc is "subvisual, broad, and diffuse." Nevertheless, Donovan, who was with MacDonald that day at the Kilkenny Irish Pub, assured Zeller that the one she saw was "visually bright, narrow, and structured."

They agreed not to refer to the phenomena as a proton arc anymore. The name "STEVE" was proposed by fellow aurora chaser Chris Ratzlaff in 2016. The 2006 DreamWorks animated picture "Over the Hedge," served as the inspiration for the moniker.