An aurora named Steve

by Mary Caperton Morton
Tuesday, June 5, 2018

In 2015 and 2016, more than 30 reports of odd, purple-hued ribbons of light over southern Canada popped up in forums on Aurorasaurus, a citizen science project funded by NASA and the National Science Foundation that tracks the aurora borealis through user-submitted reports and tweets. The amateur astronomers nicknamed the strange phenomenon “Steve,” and in a new study, researchers have defined the new type of aurora.

Aurorae usually appear in dancing shades of green, blue and red as charged particles from the sun stream into Earth’s atmosphere and interact with our planet’s magnetic field, creating wavy light displays above the planet’s polar regions that can last for hours. The aurora borealis — seen in the northern hemisphere — occurs at high latitudes in an area known as the auroral zone, but Steve’s shorter-lived ribbons of purple light appeared at lower latitudes, as far south as southern Canada.

Using the European Space Agency’s Swarm satellites to track changes in Earth’s magnetic field, a team of scientists led by NASA’s Elizabeth MacDonald detected unusual levels of electron activity and westward ion flow in the ionosphere during Steve events. These observations suggest that Steve is an optical manifestation of a phenomenon called subauroral ion drift, which occurs when a fast-moving stream of extremely hot, charged particles from the sun interacts with Earth’s magnetosphere along lower-latitude magnetic field lines. Until recently, it had never been directly observed. “On the basis of the measured ion properties and original citizen science name, we propose to identify this arc as a Strong Thermal Emission Velocity Enhancement (STEVE),” the team wrote in Science Advances.

More sightings are needed to track and better define Steve. Sightings of Steve and other aurorae can be reported at or via the Aurorasaurus free mobile app available for Android and iOS.

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