An Aurora of a Different Color

Meet STEVE, a purple and green, low-latitude, aurora-like phenomenon whose inner workings were uncovered with the help of citizen scientists.

Strong Thermal Emission Velocity Enhancement (STEVE) paints a green and purple streak across the sky from the bottom left to top right in the image above. In this image, this rare aurora-like event is crisscrossed by the dusty band of the Milky Way, which curves from the top left to bottom right.

STEVE, captured, in this instance, last year at Childs Lake in Manitoba, Canada, is not an aurora in the traditional sense: Instead of the oval-shaped, blue/green glow of more common types of auroras, STEVE appears as a thin, purple streak dangling a wavy, green picket fence structure. STEVEs always appear at the same time as normal auroras, but they occur at lower latitudes, in an area of the atmosphere called the subauroral zone.

Getting to Know STEVE

In recent years, dozens of STEVEs were cataloged by citizen scientists and shared in online forums. They called the phenomenon “Steve” simply for fun within their own group. In 2016, they shared their collection of Steve photos with the scientists running the Aurorasaurus citizen science project that tracks auroras through tweets and individual reports. The scientists eventually specially crafted the acronym “STEVE” to give a nod to the original name and its creators.

New insight into the origin and behavior of this rare atmospheric event became possible when, in 2016, a team of amateur and professional scientists used ground- and space-based cameras to image STEVE and a simultaneous normal aurora. By combining all of the available images, the team discovered that STEVEs and auroras form from a similar process—charged particles interacting with Earth’s magnetic field—but the particles that create STEVEs travel along magnetic field lines much closer to Earth than those that make ordinary auroras. That’s why STEVEs occur at lower latitudes than auroras.

In addition, the scientists were excited to discover that STEVEs are the visual counterpart to subauroral ion drift (SAID), a phenomenon studied since the 1970s. Finding out that SAIDs can have an accompanying visible feature suggests that there may be more going on in the subauroral zone of the atmosphere than scientists had thought, according to the scientific paper on this discovery, which the team published in Science Advances on 14 March.

The team is working with NASA on an ongoing campaign to collect more professional and amateur photos of STEVE, hoping to better understand these rare lights in the sky.