Why is STEVE not an aurora?
Answers
As of March 2018, STEVE has only been spotted in the presence of an aurora. STEVE was not observed from October 2016 to February 2017, or from October 2017 to February 2018, leading NASA to believe that STEVE may only appear in certain seasons.
Answer:
A vivid light show in the night sky popularly called ‘the aurora named STEVE’ might not be an aurora after all.
For decades, amateurs have photographed narrow purple and white ribbons of light that occasionally appear in the night sky at high latitudes. The phenomenon was dubbed STEVE, which scientists converted to an acronym for Strong Thermal Emission Velocity Enhancement. Researchers proposed that it is a type of aurora, a light display generated when ions and other charged particles from space slam into Earth’s magnetic field.
Beatriz Gallardo-Lacourt at the University of Calgary in Canada and her colleagues measured electrons and ions in the upper atmosphere during a STEVE event for the first time. The team found that the number of charged particles associated with a STEVE event was at least two orders of magnitude less than the number typically found in an aurora. This particular STEVE occurrence, and possibly others, formed through an unknown process in the layer of the atmosphere called the ionosphere, the scientists conclude.
Geo. Res. Lett. (2018)