New aurora species discovered

Unusual Aurora phenomenon "Steve" gives researchers R tsel

Northern Lights "Steve" over Childs Lake in Canada. How these Auror arches are created is still puzzling. © Krista Trinder
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An aurora named "Steve": researchers have identified a new, very unusual kind of polar lights. These are narrow strips of reddish light, in which green structures light up for a short time - and which appear further to the south than would otherwise be typical for Aurors. Now, data from ESA's SWARM satellites are providing some clues to the causes of this "Steve" phenomenon. But they can not completely explain "Steve" yet.

Northern lights are among the most impressive phenomena of nature. They are caused by interactions of the solar wind with the complex magnetic protective cover of our planet. Depending on the particle and interaction, Aurors can have different colors and shapes. Some pulsate or flicker, others show sudden bursts of brightness. Another special case is proton arcs - delicate light stripes that pull upwards in an arc, which are created by collisions of high-energy protons with the gas particle.

Enigmatic bows

But there is another, previously unrecognized kind of polar lights. The first evidence of this provided a few years ago shots of Polarlicht photographers. At first glance, they show a proton arc, which is unusually bright, clearly set off and structured in addition. These arches often extend from the horizon above and seem to gradually wander west.

Unusually, too: These arches occur south of the 65th parallel - and thus at the edge and partly outside the classical polar light oval. Video recordings also show a changing structure of these Aurors: Although they are predominantly reddish in color, they still show minute-long color changes to green as well as greenish substructures, some of which resemble a picket fence.

"Steve" in action, shot in British Columbia. © Andy Witteman - @CNLastro

"Steve" does not fit into the scheme

Faced with these unusual features, polar scientists are mystified, as the phenomenon "baptized" by Steve did not seem to fit any of the known aurora species and their physical backgrounds. "Steve's different from traditional electron polar lights, " explain Elizabeth MacDonald of the NASA Goddard Space Flight Center at Greenbelt and her colleagues. But even to the proton bands do not fit this phenomenon. display

To get to the bottom of the riddle Steve, researchers have now analyzed hundreds of photos taken in 2015 and 2016 as part of a Citizen Science project in Canada. In addition, they evaluated the data from ESA's Swarm satellites, which had managed to catch Steve in the act.

A completely new kind

Now there is new knowledge about the mysterious "Steve". Based on the photos, the researchers confirm that "Steve" is actually a new form of polar light. Retaining his nickname, they now give him the official name: "Strong Thermal Emission Velocity Enhancement", short STEVE.

As the data from the Swarm sites shows, STEVE is associated with an abrupt increase in temperature and a strong westward flow of ions in the upper atmosphere. On the quator side of the Auror arc, they also registered a significant decrease in electron density, but on the polter side, there was an increase.

What's behind the auroral phenomenon "Steve"? NASA / GSFC, Genna Duberstein

Ion Jets and open questions

"All these features are in good agreement with those of a subauroral ion drift (SAID), " MacDonald and her colleagues report. "These phenomena, also known as polarization jets, are transient events in which ions race at supersonic speeds and in a narrow strip to the west." Similar to STEVE, these jets are also common also south of the normal polar light areas.

Strange, however: So far, these SAIDs were considered invisible optical phenomena have never before been observed in connection with these atmospheric ion currents. "The characteristic red and green colors that STEVE can develop within an hour can not be explained in the context of SAIDs yet, " say the researchers. So far, STEVE's secret has only partially been solved further research is needed. (Science Advances, 2018; doi: 10.1126 / sciadv.aaq0030)

(AAAS, 15.03.2018 - NPO)