STEVE over Alberta, Canada

Ribbons of coloured light occasionally seen in the night sky have different origins than an aurora, according to measurements of charged particles in the atmosphere. Credit: Neil Zeller

Atmospheric science

The aurora named STEVE is not an aurora

The charged particles that cause a true aurora are uncommon during the dazzling display named STEVE.

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.