STEVE (Strong Thermal Emission Velocity Enhancement) is an intriguing atmospheric phenomenon that has captured the attention of scientists and aurora enthusiasts alike. Unlike traditional auroras, which are known for their shimmery green ribbons, STEVE appears as a mauve band of light that stretches east to west, often accompanied by vertical green stripes known as the “picket fence.”
The complex physics behind STEVE has been a subject of extensive research and discussion. A high-resolution video captured in August 2022 revealed smaller structures in STEVE’s purple glow, which were not observable in long-exposure photos. This video showed a clumpy, speckled stream of purple moving westward at about 9 kilometers per second, with variations in brightness that lasted mere seconds. The leading theory suggests that this purple light is due to nitric oxide excited by a fast plasma stream. However, the short-lived granular bursts of brightness within STEVE add complexity to this explanation.
Another aspect of STEVE’s formation involves its relationship with another atmospheric phenomenon called a stable auroral red (SAR) arc. In some instances, STEVE has been observed to emerge from a SAR arc’s red glow, transforming into its distinctive purple streak. This transition is not always consistent, as not all SAR arcs mutate into STEVE, and at times, STEVE and SAR arcs have been seen alongside each other but appearing independent.
The formation of STEVE’s purple smear is attributed to a westward-flowing stream of plasma in the atmosphere. Charged particles within this plasma flow heat other atmospheric particles through friction, causing them to emit purple light. The specific wavelengths of light from the picket fence suggest that it is not a typical aurora. Instead, it’s thought to be created by different atmospheric processes, possibly involving parallel electric fields and the ionosphere’s interaction with space weather.
Researchers continue to study STEVE to understand its formation better and its implications for space weather prediction. The study of STEVE is not only a fascinating glimpse into atmospheric phenomena but also contributes to our broader understanding of the Earth’s magnetosphere and ionosphere.