On March 17, 2015, an arc of blood red light cut across the sky hundreds of miles above New Zealand. Over the next half hour, an amateur sky watcher observed that arc transform before his eyes into one of Earth’s most perplexing atmospheric mysteries – the strange strip of light known as STEVE – newly released images reveal.
STEVE, short for “Strong Thermal Velocity Enhancement,” is a strange atmospheric condition first described in 2018, after aurora aficionados saw a narrow stream of purple-gauze arc of light across the sky over northern Canada. Scientists who studied this phenomenon quickly confirmed that Steve was not twilight The multicolored glow that appears at high latitudes when solar particles collide with high atoms Earth atmosphere. Instead, STEVE was a separate and unique phenomenon.”completely unknown“You know.
Unlike the northern lights, which tend to flash in broad bands of green, blue, or reddish light depending on their altitude, STEVE typically appears as a single band of purplish white light that stabs straight up for hundreds of miles. Sometimes it is accompanied by a dashed green streak of lights known as the “pick-fence” phenomenon. Steve and his friend in the enclosure appear much lower in the sky than the typical aurora, in a part of the atmosphere known as the subcage region, where solar charged particles are unlikely to encroach.
Now, new research published in the journal Geophysical Research Letters STEVE linked to another structure under the cage, known as stable red auroral arches (SAR), for the first time.
In the new study, the authors compare footage from a New Zealand skywatcher in March 2015 with contemporary satellite observations and data from the all-sky imager at the Mount John Observatory of the nearby University of Canterbury. The combination of these three sources gave the researchers a comprehensive look at the unexpected appearance of STEVE that night.
The view of the sky that evening began with the appearance of a red SAR arc that swept at least 185 miles (300 km) over Dunedin, New Zealand. Satellite data showed that the arc’s appearance coincided with a strong geomagnetic storm – the falling of charged solar particles into Earth’s upper atmosphere – that lasted for about half an hour.
As the storm subsided, the red arc gradually gave way to STEVE’s distinctive violet streak, which pierced the sky at roughly the same place. Just before STEVE faded away, the green picket fence structure shone on the scene. According to the researchers, this is the first recorded event of all three structures appearing in the sky together, one after the other – possibly revealing new clues about the formation and evolution of STEVE.
“These phenomena differ from the aurora, in that their optical signatures appear to be caused by intense thermal and kinetic energy in Earth’s atmosphere, rather than being produced by energetic particles falling into our atmosphere,” the researchers wrote in the new study.
Satellite observations of the event suggest that a geomagnetic storm at night may have played a major role in this display of sky lights.
During the storm, the researchers wrote, a fast-moving jet of charged particles appeared alongside the SAR’s red arc. Known as sublabial ion drift (SAID), these streams of hot, fast particles occur typically in the subsonic region of the sky during geomagnetic storms. Satellite observations also showed that the current’s heat and velocity intensified when STEVE appeared about 30 minutes later.
According to the researchers, the “reasonable generation mechanism” of STEVE could be the interaction between fast-moving ion currents and nitrogen particles in the suboral region; When hot, charged particles collide with nitrogen molecules, the molecules become excited, emitting violet light to burn off their excess energy.
The new study highlights parts of the mysterious phenomenon, but more observations by Steve – from citizen scientists and professional researchers alike – are needed to further define this theory.
Originally published on Live Science.
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