STEVE (the Strong Thermal Emissions Velocity Enhancement) is a spectacular and colorful celestial phenomenon that was first spotted in 2016. Scientists have studied the particles associated with STEVE for decades, but only recently have they witnessed the phenomenon in the sky. This past summer, a research team led by University of Calgary researcher D.M. Gillies confirmed that, despite its colorful appearance, STEVE isn’t a type of aurora but something entirely unique.
In May, researchers confirmed that STEVE is not an aurora. But this new research expands our understanding of the strange phenomenon even further.
“The big thing is, we can clearly say now it’s [a] not regular aurora,” study co-author Don Hampton, a researcher at the University of Alaska Fairbanks, said in a statement. “It’s a new phenomenon; that’s pretty exciting.”
One characteristic that distinguishes STEVE is its mauve hues, which are different from the typically green, purple, blue and yellow beams of auroras. Additionally, STEVE is visible from latitudes much farther south than auroras usually are.
The researchers used a spectrograph, which they built at the Geophysical Institute at the University of Alaska Fairbanks, to study the light coming from STEVE which they observed on April 10, 2018 at Lucky Lake in Saskatchewan, Canada. They analyzed its emissions to determine its wavelengths, patterns and other properties. A spectrum acts as an identifier, so by determining STEVE’s spectrum, the team hopes to further understand and categorize the phenomenon.
“We need to understand what the spectrum looks like and therefore understand the physics behind it,” Hampton said in the statement.
Green optical structures, often described as “picket fence” structures because of their distinctive shape, can be seen jutting through STEVE at lower altitudes, and in studying the wavelengths of the emissions from STEVE and these green structures, the team found that the green emissions have a much different spectrum from STEVE.
The team determined that the green columns which appear alongside STEVE are caused by particle precipitation, which occurs when energetic particles like electrons, protons, neutrons and ions are accelerated through the atmosphere. This makes these green streaks a type of aurora very similar to a typical auroral structure. However, because they have a very different spectrum, STEVE is in a category of its own, the researchers concluded.
The team found that STEVE isn’t caused by particle collisions in the atmosphere but rather some sort of warm atmospheric emission.
“When we looked at the spectrum of STEVE, it had none of those distinct wavelengths … Instead, it’s a very broad band of light,” Hampton said in the statement. “When you turn your electric stove on, those coils get red hot, right? If you look at it with a spectrograph, you would see broadband emissions … So this is like very, very warm atmosphere emissions of some sort.”
Scientists will continue to study STEVE, what exactly it is and what causes it. Understanding STEVE is more than just an important scientific pursuit, however. Phenomena in the atmosphere can disrupt radio communications between spacecraft and humans back on Earth, so understanding this strange, pink phenomenon could have immediate, practical applications.
Journal article: https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019GL083272