STEVE (Strong Thermal Emission Speed Enhancement) is a thin ribbon of reddish-pink or mauve light that extends from east to west, further south than auroras usually appear. Even stranger, STEVE is sometimes accompanied by vertical green columns of light nicknamed about stakes. According to a new study, published in the journal Geophysical research chartsThe stakes of STEVE is caused by a mechanism similar to the typical aurora, but the mauve striations are caused by heating charged particles higher up in the Earth's atmosphere.
The auroras are produced by incandescent oxygen and nitrogen atoms in the upper atmosphere of the Earth, excited by charged particles from the magnetic environment near the Earth, the magnetosphere.
The researchers did not know if STEVE was a kind of aurora, but a 2018 study found that its brightness is not due to charged particles that fall into the upper atmosphere of the Earth.
"Aurora is defined by the precipitation of particles, electrons, and protons that actually fall into our atmosphere, while the atmospheric glow of STEVE comes from heating without precipitation of particles," said co-author Dr. Bea Gallardo-Lacourt, a physicist at the University of Calgary.
"The precipitating electrons that cause the green fence are therefore auroras, although this occurs outside the auroral zone, so it is really unique."
In the study, Dr. Gallardo-Lacourt and his colleagues wanted to find out what STEVE powers and whether it occurs in both the North and South hemispheres at the same time.
The team analyzed data from several satellites that passed over during STEVE events in April 2008 and May 2016 to measure the electric and magnetic fields in the Earth's magnetosphere at the time.
The scientists then joined the satellites data with STEVE photos taken by amateur dawn photographers to find out what causes unusual brightness.
They found that during STEVE, a stream of charged "particles" of charged particles in Earth's ionosphere collide, creating friction that heats the particles and causes them to emit mauve light.
Interestingly, they found that the picket fence is powered by energetic electrons that flow from space thousands of miles above the Earth. Although similar to the process that creates typical auroras, these electrons affect the atmosphere much to the south of the usual auroral latitudes.
Satellite data has shown that high-frequency waves traveling from Earth's magnetosphere to its ionosphere can energize the electrons and knock them off the magnetosphere to create a striped picket fence display.
The researchers also found that the picket fence occurs in both hemispheres at the same time, supporting the conclusion that its source is high enough above the Earth to feed energy to both hemispheres simultaneously.
"Public involvement has been crucial to STEVE research, providing ground imaging and accurate time and location data," said lead author Dr. Toshi Nishimura, a Boston University physicist.
"As commercial cameras become more sensitive and the heightened enthusiasm for the dawn spreads through social media, citizen scientists can act as a & # 39; mobile sensor network & # 39; and we are grateful to them for providing us with data for analysis. "
Y. Nishimura et al. STEVE magnetospheric signatures: Implication for magnetospheric energy source and interhemispheric conjugation. Geophysical research chartspublished online April 16, 2019; doi: 10.1029 / 2019GL082460