Scientists say there may be good opportunities to see STEVE in the night sky as solar activity increases over the next few years
April 1, 2023 at 7:00 am EDT
“It’s this pink arch, and at times, it reaches above me,” said Lach, who is based in the Canadian community of Plumas, Manitoba. “I really don’t know what it is.”
He sees something rarer than the aurora. It’s STEVE.
STEVE is not an aurora, but you can think of it as a shy, distant cousin. It looks like it’s part of the family, but it has its own unique style. The phenomenon usually appears as a long, thin purple-and-white arc, sometimes accompanied by a structure that looks like a green picket fence. It is fainter and narrower, and occurs at lower latitudes and higher altitudes than most auroras. It’s also harder to predict. (Then there’s the name, which we’ll get to in a moment.)
Seeing STEVE could be a matter of space physics serendipity. Lach has managed to photograph STEVE more than 20 times since the first sighting in 2015 — possibly the most of any individual on record — and has probably even seen the ribbon of light. Many top researchers in the field have never even seen the light phenomenon once.
Citizen scientists like Lach, in addition to satellite data and sky cameras, have become valuable resources for researchers investigating STEVE — when it formed and how to identify it. A citizen-science project, called Aurorasaurus, allows the public to report sightings and connects amateur photographers with scientists. Since STEVE’s formal identification in 2018, researchers, photographers, and citizen scientists have learned what makes STEVE special. (A note: In a previous job at NASA, the reporter worked part time for Aurorasaurus and wrote news releases related to the discovery, though he did not previously work with any of the researchers mentioned in this piece.)
Solar activity is expected to increase over the next few years, researchers say, so there may be a good chance for the public to see STEVE. During an intense geomagnetic storm last week, at least three people photographed the phenomenon.
“Someone without a degree here can still contribute to scientific learning,” said Lach, who recently retired as a school administrative assistant and now manages a farm.
Giving “Steve” a streak of light might seem a bit random, and it is.
Around 2015, Lach and several aurora chasers began sharing photos of a strange, thin aurora-like structure running from east to west. He and others also posted about the strange mauve arc online and in Facebook groups and thought it might be a well-known phenomenon called the proton aurora, a type of aurora that is broad and diffuse and invisible to the naked eye, which requires instruments such as a camera to view you. But scientists have refuted that identification because this phenomenon appears bright, narrow and structured.
In an effort to call it something besides a purple-y ribbon-y thing, Chris Ratzlaff, an aurora chaser and photographer around Calgary, Alberta, suggested something a little different: “Steve.” He took the name from the children’s animated film “Over the Hedge,” which he recently watched with his children. In one scene, the animal characters are frightened by an unfamiliar trimmed bush and decide to call it Steve.
As scientists began to look at satellite data and images in more detail, they determined that this thin ribbon of light was actually a high-speed stream of particles in the upper atmosphere experiencing a superheated glow. A team of space physicists and citizen scientists published the introductory study recognizing Steve in 2018.
Scientists have given the phenomenon a backronym: Strong Thermal Emission Velocity Enhancement.
What are some side effects of STEVE?
Even if you haven’t seen STEVE, Earthlings can experience its effects in a different way.
STEVE researcher Toshi Nishimura recounts at least one instance where the radio signal from a radar network disappeared for 30 minutes when STEVE appeared, but then returned once the ghostly light left the area , suggesting that the phenomenon can interfere with such signals. Similar blackouts can occur in space weather associated with the aurora, but he said STEVE occurs in different regions than an aurora and will affect different satellites and networks.
STEVE is important because the Earth’s magnetic field “does something out of the ordinary. … We still don’t understand why,” said Nishimura, who recently published a study in STEVE’s mysteries. He had never seen the phenomenon in person.
How do you know if what you see is STEVE?
STEVE has gained popularity in the past decade, but observations have been thought to date back to the 1880s. Of course, it wasn’t known as STEVE back then. Photographs were also not available in advance, so sightings were sometimes described through text or sketches.
In a study published in 1891, one observer described a “bright band stretching east and west,” like the straight tail of a large comet. In 1933, aurora pioneer Carl Stormer took an early photograph of the phenomenon at a black-and-white photo.
A few weeks after STEVE was formally identified in 2018, citizen-scientist Michael Hunnekuhl began searching through previous studies and compiled a list of these historical and recent observations. He has created a database of more than 1,000 observations, which he says is probably the largest STEVE database in the world.
STEVE has been observed on every continent, including Antarctica. The highest number of reports come from Canada, Finland and parts of the United States, but that may be a result of high awareness of the phenomenon in those locations.
“Steve’s appearance rate and observation rate can be different, especially if you go back a few years, because people don’t know Steve,” Hunnekuhl said. The weather may also influence reporting rates, he said, because people may be more likely to go outside in certain conditions.
However, several trends emerged in the data: STEVE appeared most often in March and September near the equinoxes (which is when aurora activity usually peaks). The visible arc lasts about 30 minutes and is very rare after midnight.
STEVE is seen in conjunction with an aurora, although it is usually physically separated. It appears about 30 minutes after the aurora begins to brighten. Lach says he found STEVE by looking at the western edge of the aurora. STEVE can be blocked out by a bright aurora, though, especially if it’s close to it. Lach said he usually sees STEVE when the aurora is dull or solar activity is relatively low.
STEVE can also take slightly different forms. It may appear as a short arc just to the west of the aurora or extend across the sky from east to west. Large displays also show deeper colors — a deep red at the top, mauve in the middle and white at the bottom.
As the STEVE arc continues, a green picket fence may appear. Sometimes the arch disappears and the green picket fence remains.
How is STEVE different from aurora?
STEVE and the aurora are both ghostly light phenomena in the atmosphere, but that’s where the similarities end.
NASA researcher Bea Gallardo-Lacourt, who has been part of STEVE research since the inaugural paper in 2018, summarizes some of the differences in their creation: Auroras involve a physical mechanism, with electrons and ions raining down in our upper atmosphere and exciting atoms. The STEVE arc is a hot band of gas that involves a chemical reaction, producing a glow in the ionosphere (higher than auroras).
Gallardo-Lacourt, who has never seen STEVE, explained that the arc is associated with a very fast flow of particles — about five times faster than that seen in auroras. One proposed mechanism is that this powerful plasma flow stimulates nitrogen molecules in the atmosphere which then interact with oxygen molecules, creating nitric oxide. This nitric oxide, which is otherwise rare in our atmosphere, is energetic and glowing, emitting light in the violet range of the visible light spectrum about 280 miles above Earth’s surface.
Their sources are also different. The creation of an aurora begins when the sun sends a surge of energy to Earth, such as through a solar flare called a coronal mass ejection, and triggers a large-scale geomagnetic storm. However, STEVE occurred with and without geomagnetic storms.
Nishimura, a researcher at Boston University, said that STEVE always seems to occur during localized and brief disturbances in the Earth’s magnetic field, called substorms. Substorms can occur without a major geomagnetic storm and occur daily. But despite all the substorms, researchers are puzzled as to why STEVE sightings are still relatively rare compared to the aurora.
With each photo and report, people are gaining a better understanding of this relatively unexplored part of our atmosphere, and its connection to the sun. If you see STEVE, contact any of the researchers – or share your finds with us on Twitter.
