Scientists discover what enhances the celestial phenomenon STEVE.

Scientists discover what enhances the celestial phenomenon STEVE.

Photograph of the amateur astronomer used in the new research. The photograph was taken on May 8, 2016 in Keller, Washington. The main structures are two bands of atmospheric emissions greater than 160 kilometers (100 miles) above the ground, a mauve arch and a green fence. The black objects in the background are trees. Constellations of background stars include Gemini and the Big Dipper. Credit: Rocky Raybell.

The celestial phenomenon known as STEVE is probably caused by a combination of heating charged particles in the atmosphere and energetic electrons such as those that feed the aurora, according to new research. In a new study, scientists found the region of origin of STEVE in space and identified two mechanisms that cause it.

Last year, dark atmospheric lights became a sensation of the Internet. The typical auroras, the lights of the north and the south, are generally seen as green ribbons in swirls that extend across the sky. But STEVE is a thin ribbon of light pink or mauve red that extends from east to west, more to the south than where the auroras usually appear. Even more strange, sometimes STEVE is joined by vertical green light columns nicknamed "fence of stakes".

Auroras are produced by oxygen and nitrogen atoms in the Earth's upper atmosphere, excited by charged particles that flow from the near-Earth magnetic environment called the magnetosphere. Scientists did not know if STEVE was a species of aurora, but a 2018 study found that its brightness is not due to the charge of charged particles in Earth's upper atmosphere.

The authors of the 2018 study rated STEVE as a kind of "sky glow" that is different from the aurora, but they were not sure what exactly caused it. To complicate the matter, the fact that STEVE may appear during the sun-induced magnetic storms around the Earth that feed the brightest auroral lights.

Authors of a new study published in the magazine of AGU. Geophysical research letters badyzed the satellite data and images on the ground of STEVE events and concluded that the reddish arc and the green fence are two different phenomena that arise from different processes. The picket fence is caused by a mechanism similar to typical auroras, but the STEVE mauve stripes are caused by the heating of charged particles higher up in the atmosphere, similar to what makes the bulbs shine.

Scientists discover what enhances the celestial phenomenon STEVE.

Alberta Aurora Chasers captures STEVE, the top atmospheric science phenomenon, on the afternoon of April 10, 2018 in Prince George, British Columbia, Canada. Comrade Aurora Chaser, Robert Downie, kneels in the foreground, while photographer Ryan Sault captures the narrow ribbon of white-purple tones above. Credit: Ryan Sault.

"Aurora is defined by the precipitation of particles, electrons and protons really fall into our atmosphere, while the atmospheric brightness of STEVE comes from heating without precipitation of particles," said Bea Gallardo-Lacourt, space physicist at the University of Calgary and coauthor of the new study "The precipitating electrons that cause the green fence are, therefore, auroras, although this happens outside the auroral zone, so it is really unique".

The STEVE images are beautiful in themselves, but they also provide a visible way to study the flows of invisible and complex charged particles in the Earth's magnetosphere, according to the study's authors. The new results help scientists better understand how particle flows develop in the ionosphere, which is an important goal because these disturbances can interfere with radio communications and affect GPS signals.

Where does STEVE come from?

In the new study, the researchers wanted to find out what powers STEVE uses and if they occur in the northern and southern hemispheres at the same time. They badyzed data from several satellites that pbaded overhead during the STEVE events in April 2008 and May 2016 to measure the electric and magnetic fields in the Earth's magnetosphere at that time.

Then, the researchers coupled the satellite data with STEVE photos taken by amateur auroral photographers to discover what causes the unusual brightness. They found that during STEVE, a "river" that flows from charged particles in the Earth's ionosphere collides, creating a friction that heats the particles and causes them to emit mauve light. Incandescent bulbs work in the same way, where electricity heats a tungsten filament until it heats up enough to glow.

Scientists discover what enhances the celestial phenomenon STEVE.

The artistic representation of the magnetosphere during the appearance of STEVE, which represents the region of the plasma that falls within the auroral zone (green), the plasmasphere (blue) and the boundary between them, called plasmapause (red). The THEMIS and SWARM satellites (left and above) observed waves (red scribbles) that feed the STEVE atmospheric glow and the picket fence (inset), while the DMSP satellite (below) detected electron precipitation and a bright conjugate arc in the southern hemisphere. Credit: Emmanuel Masongsong, UCLA, and Yukitoshi Nishimura, BU / UCLA.

Interestingly, the study found that the stakes fence is powered by energetic electrons that are transmitted from space thousands of kilometers above the Earth. Although they are similar to the process that creates typical auroras, these electrons impact the atmosphere far to the south of the usual auroral latitudes. The satellite data showed that the high-frequency waves that move from the Earth's magnetosphere to its ionosphere can energize the electrons and remove them from the magnetosphere to create the screen of the striped picket fence.

The researchers also found that picket fence occurs in both hemispheres at the same time, supporting the conclusion that its source is high enough on Earth to power both hemispheres simultaneously.

According to Toshi Nishimura, a space physicist at Boston University and lead author of the new study, public participation has been crucial to STEVE's research in providing accurate terrestrial images and data on time and location.

"As commercial cameras become more sensitive and enthusiasm grows for the spread of the aurora through social networks, citizen scientists can act as a 'mobile sensor network', and we're grateful for providing us with data to badyze, "said Nishimura.

New kind of aurora is not an aurora at all

More information:
Y. Nishimura et al, STEVE magnetospheric signatures: implication for the source of magnetospheric energy and inter-hemispheric conjugation, Geophysical research letters (2019). DOI: 10.1029 / 2019GL082460

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American Geophysical Union

Scientists discover what power the celestial phenomenon STEVE (2019, April 25)
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