Those who travel to the polar regions hope not only for great experiences and pictures of the wildlife and landscape. To be able to see and photograph auroras is also high up on the wish list. Watching the seemingly magical lights dance in the sky has always fascinated people. But auroras are not the only celestial phenomena. Rarer and more mysterious is one called STEVE, which appeared in the Antarctic sky in mid-August.
During the polar night in Antarctica, people employed at the year-round stations like to be outside to observe and photograph the southern aurora. Among them is Australian weather observer Barry Becker, who spent the past austral winter on Australia’s Casey Station. An avid aurora fan and photographer, as the Australian Antarctic Division describes him, he spent a lot of time outside photographing the night sky and the auroras that kept appearing over the station. He was also outside on August 17 this year, in the middle of the Antarctic winter. “I noticed the sky was different from other nights viewing aurora – the colouring was visible as a grey/white and pinkish band, extending right across the celestial dome, from north-east to south-west,” Becker explained. What he then saw and photographed over the next twenty minutes is one of the most rarely investigated celestial phenomena, namely a STEVE.
STEVE stands for Strong Thermal Emission Velocity Enhancement and was first properly publicized in 2016 by a Facebook group of aurora photographers. Before that, photographers had observed similar phenomena for decades. But it was only thanks to the group that a physicist became aware of the phenomenon and investigations into it began, especially from NASA Goddard Space Flight Center. The current state of knowledge is that STEVE is not an auroral phenomenon, but a jet of plasma (extremely hot charged particles that have a temperature of about 3,000°C) flowing in an approximate east-west direction at an altitude of about 450 kilometers at speeds of up to 6 km/s. The latest study, of which there are only a few, suggests that this is not an aurora phenomenon in which solar winds “rain down” particles into the ionosphere, but may be a previously unknown mechanism.
So-called “picket fence” auroras, green choppy auroras, have been observed right next to the ribbon during many STEVE apparitions. But researchers, after analyzing the data to date, conclude that the two phenomena are not necessarily related. However, studies on STEVE are currently scarce, mainly due to the fact that it is not known when and where a STEVE will occur. This is because the phenomenon is not limited to Antarctica, but has also been observed and documented in the northern hemisphere.
Researchers and institutions such as NASA or the Australian Antarctic Division are aware of the difficulties of trying to better understand this phenomenon, which has hardly been studied to date, without having any idea when it will next occur and where. Therefore, they call upon aurora photographers and all enthusiasts to report corresponding observations as “Citizen Scientists” with all necessary information and image material. Barry Becker’s images are already very helpful in this regard, as atmospheric physicist Dr. John French of the Australian Antarctic Division notes. “This is a great capture of a STEVE and associated ‘picket fence’ aurora, and will contribute to the scientific knowledge of this poorly understood thermal emission. These types of citizen science observations are remarkably valuable to record and document atmospheric phenomena, and occasionally reveal new processes in fields that were generally thought to be well understood.” Although further attempts by Becker to observe this phenomenon have so far failed. But the hunt for STEVE continues in any case.
Dr Michael Wenger, PolarJournal
Contributed image: STEVE via Casey, image by Barry Becker via AAD.
Link to study: Gallardo-LAcourt, B et all (2018) Geophys Res Let 45 (16) On the Origin of STEVE: Particle precipitation or ionospheric sky glow?; doi.org/10.1029/2018GL078509
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