“The evidence generally comes from radar measurements. There are people who base their entire careers on studying turbulence in the ionospheric plasma formed by very rapid flows.” Semeter said. The green features are also moving more slowly than the structures in the purple emissions, and scientists speculate they could be caused by turbulence in the space particles – a brew of charged particles and magnetic field, called plasma – at these altitudes. The green emissions seem to be related to eddies, like the ones you might see forming in a river, moving more slowly than the other water around it. STEVE’s purple emissions are likely a result of ions moving at a supersonic speed. “The emissions are coming from mechanisms that we don’t fully understand just yet.” “STEVE in general appears to not conform well to either one of those categories,” Semeter said. These features are formed differently but also look different – airglow can occur across Earth, while auroras form in a broad ring around Earth’s magnetic poles. To be classified as an aurora, on the other hand, that release of light must be caused by electron bombardment. By studying the patterns in airglow, scientists can learn more about that area of the atmosphere, the ionosphere. When airglow occurs at night, atoms in the atmosphere recombine and release some of their stored energy in the form of light, creating bright swaths of color. ![]() Scientists tend to classify optical features in the sky into two categories: airglow and aurora. ![]() STEVE as a whole is something that scientists are still working to label. “You have other sequences where it looks like there is a tube-shaped structure that persists from image to image and doesn’t seem to conform to a moving point source, so we’re not really sure about that yet.”Ĭredit: Copyright Neil Zeller, used with permission ![]() “I’m not entirely sure about anything with respect to this phenomenon just yet,” Joshua Semeter, a professor at Boston University and first author on the paper, said. However, there are still a lot of questions to be answered – determining whether the green light is a point or indeed a line, is one extra clue to help scientists figure out what causes green light. The tip of the streak in one image will line up with the end of the tail in the next image, contributing to this speculation from the scientists. They suggest the streaks could be moving points of light – elongated in the images due to blur from the cameras. In a new paper for AGU Advances, researchers share their latest findings on these points. These “tiny little streaks” are extraordinarily small point-like features within the green picket fence of STEVE. In finding these tiny little streaks, we may be learning something fundamentally new in how green auroral light can be produced.” ![]() “STEVE is different than the usual aurora, but it is made of light and it is driven by the auroral system. “Often in physics, we build our understanding then test the extreme cases or test the cases in a different environment,” Elizabeth MacDonald, a space scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, explains. What they do know is that STEVE is not a normal aurora – some think maybe it’s not an aurora at all – and a new finding about the formation of streaks within the structure brings scientists one step closer to solving the mystery. Now named STEVE, or Strong Thermal Emission Velocity Enhancement, this phenomenon is still new to scientists, who are working to understand all its details. From 2015 to 2016, citizen scientists reported 30 instances of a purple ribbon in the sky, with a green picket fence structure underneath. In 2018, a new aurora-like discovery struck the world.
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