Citizen scientists chasing the aurora help discover a new feature in STEVE

In 2018, a new aurora-like discovery hit the world. From 2015 to 2016, citizen scientists reported 30 cases of a purple ribbon in the sky, with a green fence structure underneath. Now called STEVE, or Strong Thermal Emission Velocity Enhancement, this phenomenon is still new to scientists, who are working to understand all the details. What they do know is that STEVE is no ordinary aurora – some think it may not be an aurora at all – and a new discovery about the formation of streaks within the structure takes scientists one step closer to solving the mystery.

“Often in physics, we build our understanding and then test extreme cases or test cases in a different environment,” says Elizabeth MacDonald, a space scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “STEVE is different from the usual aurora, but it is made of light and is guided by the auroral system. By finding these tiny streaks, we could learn something fundamentally new about how green auroral light can be produced.”

These “tiny streaks” are extraordinarily small pinpoint features within STEVE’s green fence. In a new article for AGU advances, the researchers share their latest findings on these points. They suggest that the streaks could be moving points of light, stretched in images due to camera blur. The tip of the strip in one image will line up with the tip of the tail in the next image, contributing to this speculation by scientists. However, there are still many questions to be answered: determining whether green light is a dot or even a line is one more clue to help scientists understand what causes green light.

“I’m still not entirely sure about this phenomenon,” said Joshua Semeter, a professor at Boston University and first author of the paper. “You have other sequences where there appears to be a tube-like structure that persists from image to image and doesn’t seem to conform to a moving point source, so we’re not sure yet.”

STEVE as a whole is something scientists are still trying to label. Scientists tend to classify the optical features in the sky into two categories: airglow and aurora. When the air glow occurs at night, the atoms in the atmosphere recombine and release some of their stored energy in the form of light, creating bright streaks of color. By studying the patterns in the air flare, scientists can learn more about that area of ​​the atmosphere, the ionosphere. To be classified as an aurora, however, that release of light must be caused by the electron bombardment. These features form differently but also look different: air flare can occur on Earth, while auroras form in a large ring around the Earth’s magnetic poles.

“STEVE in general doesn’t seem to fit well into any of these categories,” Semeter said. “The emissions come from mechanisms that we don’t fully understand yet.”

STEVE’s purple emissions are likely the result of ions moving at supersonic speed. Green emissions appear to be related to eddies, such as those you might see forming in a river, moving slower than other waters around it. Green features also move slower than structures in purple emissions, and scientists speculate that they could be caused by turbulence in space particles – a mixture of charged particles and a magnetic field, called plasma – at these altitudes.

“We know this type of turbulence occurs. There are people who base their entire careers on studying the turbulence in ionospheric plasma formed by very rapid flows.” Semeter said. “The evidence generally comes from radar measurements. We never have an optical signature.” Semeter suggests that when it comes to STEVE’s appearance, the flows in these cases are so extreme that we can actually see them in the atmosphere.

“This paper is the tip of the iceberg in this new area of ​​these tiny little bits of fence. Something we do in physics is try to crumble to increase our understanding,” MacDonald said. “This paper establishes the altitude range and some of the techniques we can use to identify these features, so they can be better resolved in other observations.”

To establish the altitude range and identify these characteristics, scientists extensively used photos and videos captured by citizen scientists.

“Citizen scientists are the ones who brought the STEVE phenomenon to the attention of scientists. Their photos are typically longer than our traditional scientific observations,” MacDonald said. “Citizen scientists don’t get into the patterns that scientists are in. They do things differently. They are free to move the camera and take whatever exposure they want.” However, to make this new discovery of the points within STEVE, photographers actually took photographs with shorter exposures to capture this movement.

To get those photographs, citizen scientists spend hours in the freezing cold, late at night, waiting for a sunrise – or hopefully STEVE – to appear. While the data may indicate whether an aurora will appear, the indicators for STEVE have not yet been identified. However, the aurora hunters show up and take the photos anyway.

Neil Zeller, a photographer and co-author of the paper, says he originally had no intention of becoming a citizen scientist. “It was just for the beauty,” Zeller explained. Zeller has been involved in the discovery of STEVE from the very beginning. He showed a photo of STEVE to MacDonald years ago, kicking off the first research on the phenomenon. He is now a co-author of this article.

“It’s an honor, it really is,” Zeller said of contributing to this research. “I tend to take a step back from the scientists who do the work. They are out there for its beauty and for capturing these phenomena in the sky.”

This paper also used another valuable contribution from citizen scientist: a voluntary database of STEVE observations. Michael Hunnekuhl, another author of the article, maintains this database and has contributed to STEVE’s findings in the past. Hunnekuhl noticed the streaks in the photographs independently of the scientists on the paper, and his detailed documentation and triangulation techniques were instrumental in this research.

Zeller and other city scientists plan to continue taking and examining those images, capturing the beauty of Earth’s atmosphere, and MacDonald, Semeter, and other scientists will continue to study them, learning more about this new phenomenon.