Earth’s sky fills with lovely dancing lights when the Sun gets boisterous.
Vibrant auroral streams dance and flare across the sky around the poles. But as one approaches the equator, another empyrean glow emerges: the mauve-pink, blushing STEVE and his accompanying green-striped picket fence.
It’s a mystery what these lights are and why they show up in our sky. Although they resemble auroras, scientists have previously speculated that they might be connected. However, the mechanics underlying the occurrence have remained mysterious.
A recent research puts out a novel theory, stating that STEVE and the picket fence are clearly not auroras but rather something else entirely.
A team led by physicist Claire Gasque of the University of California Berkeley claims that STEVE and the picket fence are created by electric fields parallel to the magnetic field lines, at lower latitudes than the aurora, rather than magnetic fields like those that cause auroras.
Should this be true, it would have a significant impact on our comprehension of the Earth’s atmosphere, magnetosphere, interactions, and underlying physics.
The STEVE spectrum has been indicating to us for a few years now that some pretty unusual physics is occurring. We simply didn’t know what it was,” UC Berkeley physicist Brian Harding explains. “Claire’s paper showed that parallel electric fields are capable of explaining this exotic spectrum.”
One of the most breathtaking views that the Earth has to offer is an aurora. They have a very intriguing physics explanation as well. They happen when solar particles—such as those released in a strong solar wind or during a massive eruption like a flare—are propelled toward Earth and into space.
Most of them simply bounce off of Earth’s shielding magnetosphere, but some are caught and speed up along magnetic field lines to higher latitudes where they are hurled down into the upper atmosphere. There, they crash against molecules and atoms in the atmosphere, briefly igniting them and making them glow.
This is the aurora, and depending on which atoms are being ionized, it can seem green, yellow, pink, red, or purple. Oxygen is green. Nitrogen is either purple or blue. One of the less common forms, blood red, is indeed oxygen, although it only appears very high in the atmosphere and only during the strongest solar events.
And then there’s Steve, dressed in an odd mauve-and-white combination, occasionally joined by a green feature with stripes called a picket fence. Strong Thermal Emission Velocity Enhancement, or STEVE, was formally recognized as a distinct phenomenon in 2018, and researchers have been attempting to understand it for a long time.
“It’s pretty awesome,” remarks Gasque. “It’s one of the biggest mysteries in space physics right now.”
Researchers hypothesized that STEVE might have originated from a subauroral ion drift, or SAID, a stream of ionized atoms in the high atmosphere that doesn’t shower down particles like auroral particles do. Particles falling out of a STEVE were assumed to be the cause of the picket fence.
However, experts are unsure about how a SAID, which is typically unrelated to a STEVE, might cause the STEVE-like glow. Furthermore, Gasque and her group believed that there might be an additional reason for the picket fence.
The picket fence’s spectrum reveals a lot more green than one may anticipate. Furthermore, none of the blue that results from nitrogen ionization is present,” she says.
“What that’s telling us is that there’s only a specific energy range of electrons that can create those colors, and they can’t be coming from way out in space down into the atmosphere, because those particles have too much energy.”
Rather than descending from a higher altitude to a lower one, as previously thought, Gasque and her team have now demonstrated that the particles in the picket fence are being energized locally by an electric field. This is a completely different mechanism than the one responsible for aurora.
Additionally, their work shows that a similar approach could yield STEVE.
There’s a reliable method to find out. To test it firsthand, the researchers believe we should launch a rocket into STEVE or the picket fence. The initial goal might be an enhanced aurora, which are areas of brighter light that occasionally emerge embedded in an aurora. However, given how uncommon the phenomenon is, that could be challenging. Their hues closely resemble those of the picket fence.
Electric fields are also suggested to cause these properties. Additionally, enhanced aurora present a more approachable potential because they are more common than STEVE.
“It’s fair to say that there’s going to be a lot of study in the future about how those electric fields got there, what waves they are or aren’t associated with, and what that means for the larger energy transfer between Earth’s atmosphere and space,” adds Harding. It’s really unknown to us. The first link in the chain of that knowledge is Claire’s paper.”
The research has been published in Geophysical Research Letters.
