by 
On March 17, 2015, a blood-red arc of light pierced the sky hundreds of miles above New Zealand. For the next half hour, an amateur skywatcher watched that arc as it transformed before their eyes into one of Earth’s most puzzling atmospheric mysteries: the mysterious ribbon of light known as STEVE, newly released images reveal.
STEVE, short for “strong thermal velocity enhancement,” is an atmospheric oddity first described in 2018, after amateur aurora hunters spotted a narrow stream of diaphanous purple arc light in the sky over northern California. Canada. Scientists who studied the phenomenon soon confirmed that STEVE was not a dawn — the multicolored glow that appears at high latitudes when solar particles collide with atoms of high from the earth atmosphere. Rather, STEVE was a separate and unique phenomenon that is “completely unknown“ (opens in a new tab) To science
Unlike the Northern Lights, which tend to glow in broad bands of green, blue, or reddish light depending on their altitude, STEVE typically appears as a single ribbon of purplish-white light that rises in a straight line for hundreds of miles. It is sometimes accompanied by a dashed green line of lights dubbed the “picket fence” phenomenon. Both STEVE and his picket fence friend appear much lower in the sky than a typical aurora, in a part of the atmosphere known as the subauroral region, where charged solar particles are unlikely to enter.
Now, new research published in the journal Geophysical Investigation Letters (opens in a new tab) has linked STEVE with another subauroral structure, known as stable auroral red arches (SARs), for the first time.
In the new study, the authors compared New Zealand Skywatcher’s March 2015 images with contemporary satellite observations and data from an all-sky imager at the University of Canterbury’s nearby Mount John Observatory. Combining these three sources gave investigators a complete picture of STEVE’s unexpected appearance that night.
That night’s sky spectacle began with the appearance of a blood-red SAR arc that swooped at least 300 kilometers (185 miles) over Dunedin, New Zealand. Satellite data showed that the arc’s appearance coincided with a strong geomagnetic storm, a shower of charged solar particles in Earth’s upper atmosphere, that lasted about half an hour.
As the storm abated, the red arc gradually gave way to STEVE’s signature mauve streak, which streaked across the sky in almost exactly the same spot. Just before STEVE faded away, the green fence structure flashed into view. According to the researchers, this is the first recorded appearance of the three structures appearing together in the sky, one after the other, possibly revealing new clues about the formation and evolution of STEVE.
“These phenomena are distinct from auroras in that their optical signatures appear to be caused by extreme thermal and kinetic energy in Earth’s atmosphere, rather than by energetic particles falling into our atmosphere,” the researchers wrote in the new studio.
Satellite observations of the event suggest that the night’s geomagnetic storm may have played a key role in this parade of lights in the sky.
During the storm, a fast jet of charged particles appeared alongside the red SAR arc, the researchers wrote. Known as subauroral ion drift (SAID), these streams of hot, fast particles often appear in the subauroral part of the sky during geomagnetic storms. Satellite observations also showed that the heat and speed of the current intensified when STEVE appeared about 30 minutes later.
According to the researchers, a “plausible generation mechanism” for STEVE could be the interaction between these fast-moving ion currents and nitrogen (opens in a new tab) molecules in the subauroral zone; when hot, charged particles collide with nitrogen molecules, the molecules become excited and emit a mauve light to burn off their extra energy.
The new study illuminates parts of the mysterious phenomenon, but more observations of STEVE are needed, both from citizen scientists and professional researchers, to further pin down this theory.
Originally published on Live Science.
