On March 17, 2015, an arc of blood-red light streaked across the sky hundreds of miles above New Zealand. Over the next half hour, an amateur skywatcher watched this arc as it transformed before his eyes into one of Earth’s most puzzling atmospheric mysteries – the strange ribbon of light known as STEVE’s name – reveal newly released images.
STEVE, short for “Strong Thermal Velocity Enhancer”, is an atmospheric oddity first described in 2018, after amateur aurora hunters saw a narrow arcing stream of wispy purple light in the sky above. over northern Canada. Scientists who studied the phenomenon quickly confirmed that STEVE was not a dawn – the multicolored glow that appears at high latitudes when solar particles collide with atoms of high Earth atmosphere. On the contrary, STEVE was a distinct and unique phenomenon that is “completely unknown“to science.
Unlike the Northern Lights, which tend to flicker in broad bands of green, blue, or reddish light depending on their altitude, STEVE typically appears as a single purplish-white ribbon of light that stabs upward for hundreds of miles. Sometimes it is accompanied by a dashed green line of lights dubbed the “palisade” phenomenon. STEVE and his friend the palisade 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 Research Letters linked STEVE to another subauroral structure, known as stable auroral red arcs (SARs), for the first time.
In the new study, the authors compared New Zealand skywatcher images from March 2015 with contemporary satellite observations and data from an all-sky imager at the nearby University of Canterbury’s Mount John Observatory. The combination of these three sources gave researchers complete insight into STEVE’s unexpected appearance that night.
This evening’s sky spectacle began with the appearance of a blood-red SAR arc that hovered over Dunedin, New Zealand, at least 185 miles (300 kilometers) away. 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 – which lasted about half an hour.
As the storm subsided, the red arc gradually gave way to STEVE’s signature purple streak, which crossed the sky at almost the exact same spot. Just before STEVE disappeared, the green structure of the palisade shimmered. According to the researchers, this is the first recorded occurrence 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 because their optical signatures appear to be triggered by extreme thermal and kinetic energy in Earth’s atmosphere, rather than produced by energetic particles raining down our atmosphere,” the researchers wrote in the new study. .
Satellite observations of the event suggest that the night’s geomagnetic storm may have played a key role in this parade of sky lights.
During the storm, a fast jet of charged particles appeared along the red SAR arc, the researchers wrote. Known as subauroral ion drift (SAID), these streams of hot, fast-moving particles typically appear in the subauroral zone of the sky during geomagnetic storms. Satellite observations also showed that the heat and speed of the flow 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 ion fluxes and nitrogen molecules of the subauroral zone; when charged, hot particles collide with nitrogen molecules, the molecules become excited, emitting purple light to burn off their extra energy.
The new study sheds light on parts of the mysterious phenomenon, but more STEVE observations – from citizen scientists and professional researchers – are needed to explore this theory further.
Originally posted on Live Science.