On March 17, 2015, a blood-red arc of light cut across the sky hundreds of miles above New Zealand. For the next half hour, an amateur sky observer observed that the arc was transforming before his eyes into one of the most puzzling atmospheric mysteries on Earth: the mysterious ribbon of light known as STEVE, the recently published images reveal.
STEVE, short for “strong improvement in thermal velocity,” is an atmospheric rarity first described in 2018, after amateur aurora hunters saw a narrow stream of gaseous purple light arc across the sky. in northern Canada. Scientists who studied the phenomenon soon confirmed that STEVE was not one aurora – the multicolored glow that appears at high latitudes when solar particles collide with high atoms of the Earth atmosphere. Rather, STEVE was a separate and unique phenomenon that is “completely unknown“in science.
Unlike auroras, which tend to glow in wide bands of green, blue, or reddish light depending on their altitude, STEVE usually appears as a single strip of purple-white light that goes upward for hundreds of miles. It is sometimes accompanied by a broken line of green light nicknamed the “fence” phenomenon. Both STEVE and his 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, a new research published in the journal Geophysical research letters has for the first time linked STEVE to another subauroral structure, known as stable auroral red arcs (SARs).
The complete set of auroral images taken by a citizen scientist, which show auroral objects through a series of color filters. (Image credit: Martinis et al.)
In the new study, the authors compared the March 2015 images of the New Zealand Sky Observer with satellite observations and contemporary data from a sky-wide image at the nearby Mount John Observatory at the University of New Zealand. Canterbury. The combination of these three sources gave researchers a complete view of the unexpected appearance of STEVE that night.
The spectacle of the sky that evening began with the appearance of a blood-red SAR arc that traveled at least 185 miles (300 kilometers) over Dunedin, New Zealand. Satellite data showed that the appearance of the arc coincided with a strong geomagnetic storm – a rain of charged solar particles in the Earth’s upper atmosphere – which lasted about half an hour.
As the storm subsided, the red bow gradually gave way to STEVE’s characteristic mauve stripe, which cut the sky almost exactly in the same place. Just before STEVE faded, the green structure of the fence gleamed in sight. According to researchers, this is the first recorded appearance of the three structures appearing in the sky together, one after the other, possibly revealing new clues about the formation and evolution of STEVE.
“These phenomena are different from auroras, as their optical signatures appear to be caused by extreme thermal and kinetic energy in the Earth’s atmosphere, rather than by energy particles raining down our atmosphere,” they wrote. the researchers in the new study.
Satellite observations of the event suggest that the geomagnetic storm of the night may have played a key role in this parade of sky lights.
During the storm, a rapid beam of charged particles appeared next to the red SAR arc, the researchers wrote. Known as subaural ion drift (SAID), these hot, fast particle currents often appear in the subaural zone of the sky during geomagnetic storms. Satellite observations also showed that heat and current speed intensified when STEVE appeared about 30 minutes later.
According to researchers, a “plausible generation mechanism” for STEVE could be the interaction between these fast-moving ionic currents and nitrogen molecules in the subauroral zone; when charged and hot particles collide with nitrogen molecules, the molecules are excited, emitting mauve light to burn their extra energy.
The new study sheds light on parts of the mysterious phenomenon, but more observations from STEVE, both citizen scientists and professional researchers, are needed to further refine this theory.
Originally published in Live Science.