STEVE, the mysterious purple lights unraveled


Citizen scientists are an important community for scientific discoveries and that has been proven once again through unraveling of secrets behind 'Steve' - the mysterious purple lights.

The strange purple lights phenomenon during northern lights - 'Steve' has long been observed and studied but scientists were not able to figure out the reason behind these strange lights. While initially the name 'Steve' caught on without any scientific basis, it now stands short for Strong Thermal Emission Velocity Enhancement.

The team behind the latest unravel run a project called Aurorasaurus that track the aurora borealis through user-submitted reports and tweets. This team conferred to determine the identity of Steve by talking with main contributors of these images, amateur photographers in a Facebook group called Alberta Aurora Chasers. While Steve has been studied for quite some time there hasn't been any definitive answer to what it was.

This changed with Notanee Bourassa, an IT technician in Regina, Canada, snapped photographs of Steve outside of his home on July 25, 2016, around midnight, during a 20 minute period when Steve appeared. Bourassa wasn't the only one observing Steve as ground-based cameras called all-sky cameras, run by the University of Calgary and University of California, Berkeley, took pictures of large areas of the sky and captured Steve and the auroral display far to the north. From space, ESA's (the European Space Agency) Swarm satellite just happened to be passing over the exact area at the same time and documented Steve.

This effectively gave scientists ground and satellite views of Steve. Scientists have now learned, despite its ordinary name, that Steve may be an extraordinary puzzle piece in painting a better picture of how Earth's magnetic fields function and interact with charged particles in space. The findings are published in a study released today in Science Advances.

The study highlights one key quality of Steve: Steve is not a normal aurora. Auroras occur globally in an oval shape, last hours and appear primarily in greens, blues and reds. Citizen science reports showed Steve is purple with a green picket fence structure that waves. It is a line with a beginning and end. People have observed Steve for 20 minutes to 1 hour before it disappears.

If anything, auroras and Steve are different flavors of an ice cream, said MacDonald. They are both created in generally the same way: Charged particles from the Sun interact with Earth's magnetic field lines.

The uniqueness of Steve is in the details. While Steve goes through the same large-scale creation process as an aurora, it travels along different magnetic field lines than the aurora. All-sky cameras showed that Steve appears at much lower latitudes. That means the charged particles that create Steve connect to magnetic field lines that are closer to Earth's equator, hence why Steve is often seen in southern Canada.

Perhaps the biggest surprise about Steve appeared in the satellite data. The data showed that Steve comprises a fast moving stream of extremely hot particles called a sub auroral ion drift, or SAID. Scientists have studied SAIDs since the 1970s but never knew there was an accompanying visual effect. The Swarm satellite recorded information on the charged particles' speeds and temperatures, but does not have an imager aboard.

Steve is an important discovery because of its location in the sub auroral zone, an area of lower latitude than where most auroras appear that is not well researched. For one, with this discovery, scientists now know there are unknown chemical processes taking place in the sub auroral zone that can lead to this light emission.

Second, Steve consistently appears in the presence of auroras, which usually occur at a higher latitude area called the auroral zone. That means there is something happening in near-Earth space that leads to both an aurora and Steve. Steve might be the only visual clue that exists to show a chemical or physical connection between the higher latitude auroral zone and lower latitude sub auroral zone, said one of the researchers.

The team can learn a lot about Steve with additional ground and satellite reports, but recording Steve from the ground and space simultaneously is a rare occurrence. Each Swarm satellite orbits Earth every 90 minutes and Steve only lasts up to an hour in a specific area. If the satellite misses Steve as it circles Earth, Steve will probably be gone by the time that same satellite crosses the spot again.

In the end, capturing Steve becomes a game of perseverance and probability.