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Researchers Reveal Possible Reason Behind The Recently Discovered ‘STEVE’ Aurora

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In 2017, a bunch of amateur night sky watchers discovered a new kind aurora, thin and purple/green, traveling from east to west in the northern sky. They technically weren't scientists, though they're vehement fans of auroras in general.

Researchers became aware of this new aurora when a Facebook group called Alberta Aurora Chasers started publishing photos of unusual purple-greenish streaks of light in the sky. Scientists contacted them and asked for pertinent information such as the time they witnessed the aurora, then corroborated it with Swarm satellite data from the European Space Agency.

STEVE Aurora

Now, nearly a year later, the researchers are officially proposing to name the phenomenon STEVE, which stands for Strong Thermal Emission Velocity. They also have an idea as to the conditions that cause it to appear. They also noted that the "citizen scientists" who discovered the aurora were of immense help.

"It's gratifying to show what citizen science can do," said Elizabeth MacDonald, from the NASA Goddard Space Flight Center, who led a study just published in the Science Advances journal. "Some people think it's just education and outreach, but it's actually real science, and people working together in ways that we never anticipated."

Auroras, for the uninitiated — also called southern lights and northern lights — are majestic displays of light formed when the planet's magnetic field guides charged particles from the sun around Earth and toward the upper atmosphere at its poles. There, these solar particles hit neutral ones, producing stunning streaks of light and color.

However, STEVE seems to operate differently.

To understand why STEVE occurs, scientists had to rely on their own measurements from the all-sky imagers at the University of Calgary, plus digital photographs from citizen scientists, in addition to the aforementioned Swarm data.

Subauroral Ion Drift

Synchronizing all their findings, the researchers now hypothesize that a phenomenon called the subauroral ion drift, or SAID, is the one that causes STEVE to appear in the sky. These are particles ebbing toward west, and they're faster than the speed of sound, and closer to the equator than the rest of the lights.

However, SAID typically doesn't come with light features, and those that do come with it remain as enigmas, the researchers noted in their paper. SAID emissions are also typically red, yet STEVE shows mostly green, so there are still a lot of loose ends to tie.

"There's an electric field in those regions that points poleward and a magnetic field that points downward, and those two together create this strong drift to the west," MacDonald said. The flow in our planet's ionosphere pulls charged solar particles to the west, and there they hit neutral particles, causing them to heat up. This produces vertically oriented light streaks that move toward west.

MacDonald reiterated how crucial citizen scientists' role were in studying STEVE, especially since aurora watchers can see auroras more distinctly than ground-based cameras. Macdonald also cites this discovery as an example of enhancing the communal bond between the scientific community and citizen scientists.

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