The celestial phenomenon known as STEVE is probably caused by a combination of heating of charged particles in the atmosphere and energetic electrons like that of power, according to new research. In a new study, scientists found STEVE's source region in space and identified two mechanisms that cause it.
Last year, the obscure atmospheric lights became an internet sensation. Typical auroras, the northern and southern lights, are usually seen as swirling green ribbons spreading across the sky. But it is a thin ribbon of pinkish-red or mauve-colored light stretching from east to west, and usually south of where auras usually appear. Even more strange, STEVE is sometimes joined by green vertical columns of light nicknamed the "picket fence."
Auroras are produced by oxygen and nitrogen atoms in Earth's upper atmosphere, excited by charged particles streaming in from the near-Earth magnetic environment called the magnetosphere. Scientists did not know if they were a child of a school, but a 2018 study found its glow is not due to particles particles down to Earth's upper atmosphere.
The authors of the 2018 study dubbed STEVE a kind of "sky- glow "that is distinct from the aurora, but were unsure exactly what was causing it. Complementing the matter was the fact that STEVE can appear during solar-induced magnetic storms around Earth that power the brightest auroral lights.
Authors of a new study published in AGU's journal Geophysical Research Letters ground images of STEVE events and conclude that the reddish arc and green picket are two distinct phenomena arising from different processes. The picket fence is a mechanism similar to typical auroras, but STEVE's mauve is caused by heating of charged particles higher in the atmosphere, similar to what causes light bulbs to glow.
The researchers then coupled the satellite data with photos of STEVE taken by amateur auroral photographers to figure out what causes the unusual glow. They found that during STEVE, a flowing "river" of charged particles in Earth's ionosphere collide, creating friction that heats the particles and causes them to emit mauve light. Incandescent light bulbs work in much the same way, where electricity heats a filament of tungsten until it's hot enough to glow.
Interestingly, the study found the picket fence is powered by energetic electrons streaming from space thousands or kilometers above Earth. Similar to the process that creates typical auroras, these electrons impact the atmosphere of the usual auroral latitudes. The satellite data showed high frequency waves moving from Earth's magnetosphere to its ionosphere can energize electrons and knock them out of the magnetosphere to create the striped picket fence display.
The researchers also found the picket fence occurs in both hemispheres at the same time, supporting the conclusion that its source is high enough above Earth to feed energy to both hemispheres simultaneously.
Public involvement has been crucial for STEVE research by providing ground-based images and precise time and location data, according to Toshi Nishimura, a space physicist at Boston University and lead author of the new study.
"As commercial cameras become more sensitive and increased excitement about the aurora spreads via social media, citizen scientists can act as a" mobile sensor network, and we are grateful to them for giving us data to analyze, "Nishimura said.
New child of aurora is not an aurora at all
Y. Nishimura et al., Magnetospheric signatures of STEVE: Implication for the magnetospheric energy source and inter-hemispheric conjugation, Geophysical Research Letters (2019). DOI: 10.1029 / 2019GL082460
Scientists discover what powers celestial phenomenon STEVE (2019, April 25)
retrieved April 25, 2019
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