A newly discovered feature of STEVE (Strong Thermal Emission Velocity Enhancement) that only occurs in the lower ionosphere has puzzled scientists about the ethereal lights again.
In a report released Oct. 1 in the journal AGU Advances, NASA researchers analyzed hundreds of hours of STEVE footage captured by citizen scientists to look for a mysterious new pattern dubbed "the streaks." These tiny green light stripes are sometimes seen stretching horizontally from the bottom of STEVE's green fence pickets, curving backward for about 20 to 30 seconds before disappearing.
If you don't know STEVE, you might know it from pictures. Unlike the famed Southern and Northern Lights, which coat the skies with ethereal green swirls around Earth's magnetic poles, STEVE appears as a purplish-white line of light cutting diagonally towards the horizon, extending through the atmosphere for hundreds of miles. It may appear closer to the equator than a standard aurora and is always followed by a "picket fence" of jagged green dots dancing alongside it.
Nobody knows what causes STEVE, but experts believe that it's not just an aurora. Auroras appear as the charged particles of the sun sail through space and break along Earth's magnetic field lines; STEVE, meanwhile, is a flow of thick, turbulent gas that appears independently of the solar weather. Researchers believe that this could be the result of a native process in the ionosphere-the level of the Earth's atmosphere that ranges between 50 and 600 miles above the Earth's surface, well below the magnetic field of the planet.
What's with the new streaks? As with all STEVE stuff, nobody really knows. But the latest paper sets forth certain fundamental characteristics. For instance, the long tube-like shape of the streaks may be an optical illusion; according to the experts, the streaks are more like tiny points of light that look elongated to us due to motion blur.
Each streak seems to have a physical link to the picket fence system above it the team discovered, and it travels over the same magnetic field lines. The streaks also seem to be picky on where they form; according to the team's estimates, the streaks occur only low in the ionosphere between 62 and 68 miles (100 to 110 km) above Earth. This makes the streaks "the lowest‐altitude and smallest‐scale optical feature associated with STEVE," the researchers wrote in the report.
The level of ambiguity is the same when it comes to STEVE, which was first identified by citizen scientists looking at the Canadian skies in July 2016. Astronomers continue to rely on observations from civilian photographers and stargazers-whose time and passion may exceed professional scientists-to unpack the mysterious river of light in our atmosphere.
