Decoding mysterious aurora-like phenomenon STEVE seen after surprise solar storm
Southern Canada witnessed a strange phenomenon after a surprise solar storm hit Earth's ionosphere on August 7. The collision of charged particles resulted in bizarre, thin ribbons of green and mauve light called STEVE (strong thermal velocity enhancement). According to astronomy writer and photographer Alan Dyer, the mysterious phenomenon lasted for about 40 minutes. That leads to the question, what is STEVE?
- It looks like an aurora, but it isn't one. We call it STEVE.
- Since 2016, the scientific community has been scratching its head to identify what causes STEVE. Yes, we have made some progress, but this wispy combination of mauve light with its green fingers is still shrouded in mystery.
- While science tries to unravel STEVE, let's simply bask in its glory.
The recent appearance of STEVE was captured by Alan Dyer in southern Alberta at 12:30 am MDT (12:30 pm IST) on August 8. The phenomenon started late night on August 7. He wrote, "STEVE was 'discovered' here so he likes appearing here more than anywhere else!" This time, STEVE also appeared farther south than its usual pastures.
A great showing of @STEVEPhenomena last night, Aug 7-8, arcing across the sky, and showing his green fingers briefly for about 2 minutes. STEVE lasted about 40 minutes, appearing as the Kp5 aurora to the north subsided. This was 12:30 am MDT from southern Alberta. @TweetAurora pic.twitter.com/EtKF6udfFk— Alan Dyer (@amazingskyguy) August 8, 2022
STEVE is usually composed of a long ribbon of mauve-colored light that lasts for an hour or more, and a "picket fence" of green light that usually disappears in a few minutes. The strange aerial glow was first identified in 2016 by Canadian citizen scientists and aurora hunters. It looks like an aurora but was completely unknown to science until its discovery.
STEVE is a long, thin line of hot gas. It traverses the sky for hundreds of miles. Satellite observations have shown that the hot air inside STEVE can move roughly 500 times faster than the air on both sides. It can also flame up at more than 3,000 degree Celsius. STEVE appears in the subauroral zone, much lower than where auroras are found.
Auroras, which are found in Earth's upper atmosphere, are caused by high-energy electrons from the sun hitting Earth's ionosphere. The electrons are fired from the sun during solar storms and coronal mass ejections (CME). Therefore, the presence of STEVE in the subauroral zone likely means that it is not caused by solar storms. Interestingly though, STEVE almost always appears during solar storms.
There are several hypotheses on STEVE's origin. One suggests that it is caused by the clash of charged particles higher in the atmosphere during solar storms that lead to a sudden burst of thermal and kinetic energy. The National Oceanic and Atmospheric Administration attributes STEVE's birth to a stream of hot gas ejected from the sun during solar storms and CMEs.
According to a research published in the Geophysical Research Letters journal in 2019, when a flowing river of plasma particles collides in Earth's ionosphere, it causes friction. This friction heats the particles and causes them to emit STEVE's purple light. The researchers attributed the green pattern to something called "energetic particle precipitation." This happens when high-frequency waves move Earth's magnetosphere to its ionosphere.