In episode 45, Liz MacDonald from the NASA’s Goddard Space Flight Center, discusses in her research into STEVE, a previously unrecorded atmospheric phenomenon discovered by citizen scientists in late 2016 that appears as a ribbon of flickering purple and green light in the night sky. Her open-access article “New science in plain sight: Citizen scientists lead to the discovery of optical structure in the upper atmosphere” was published on March 18, 2018 in Science Advances, and was co-authored with multiple professional and citizen scientists.
- Aurorasaurus citizen science project
- Liz on Twitter
- Liz talking about “glitter bombs” on NPR’s Science Friday
- “Mystery of Purple Lights in Sky Solved With Help From Citizen Scientists“
- Origin of backronym STEVE
News and Media
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Hosts / Producers
Doug Leigh & Ryan Watkins
How to Cite
Leigh, D., Watkins, R., & MacDonald, E.. (2019, March 20). Parsing Science – The Wonder of STEVE. figshare. https://doi.org/10.6084/m9.figshare.7885070
What’s The Angle? by Shane Ivers
Liz McDonald: The scientists, we, eventually figured out that that was a thing called the subauroral ion drift.
Ryan Watkins: This is parsing science. The unpublished stories behind the world’s most compelling science as told by the researchers themselves. I’m Ryan Watkins…
Doug Leigh: And I’m Doug Leigh. Today, in episode 45 of Parsing Science we’ll talk with Liz McDonald from NASA’s Goddard Space Flight Center in Greenbelt Maryland about her research in the STEVE, a previously unreported atmospheric phenomena discovered by citizen scientists in late 2016 which appears as a ribbon of flickering purple and green light in the night sky. Here is Liz McDonald.
McDonald: Hello! I’m Liz McDonald, and I’m a space plasma physicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. I study the aurora in all kinds of different forms, both from kind of satellite observations and observations of the beautiful lights from the ground, from scientific cameras. And so what I do is kind of called space weather. Much like the usual weather, it’s very hard to predict, much more hard to predict than even our terrestrial weather. So the sun gives us not just light but also charged particles which are the fourth state of matter, known as plasma, and that’s always changing what intensity and kinds of particles are coming from the sun, and that’s what drives the visibility of the aurora.
Liz’s interest in space weather and physics
Watkins: If you’re anything like us, witnessing the Northern Lights is high on your bucket list. So imagine having a job where studying these long-known but only recently-understood phenomenon is a day-to-day thing. We began our conversation by asking Liz how she became interested in the physics and weather of space, as well as when she first saw an aurora herself.
McDonald: I went to the University of New Hampshire for graduate school, and there I studied aurora’s from an experiment that flew on a rocket above the Northern Lights. NASA flies rockets to take measurements of the particles that are causing the lights, and my thesis experiment was measuring a certain type of those particles during the aurora. So I got to go up to Alaska when we launched the rocket and see my first aurora there. But I had gotten interested in this field as an undergraduate at the University of Washington, where I had a NASA space grant scholarship, and just happened to be matched with a mentor in this field of space physics. And even though I was just a freshman and I pretty much hated physics, my mentor, she really opened my eyes as far as what physics research actually was, and what physicists actually did, and introduced me to this whole beautiful complex world of the aurora. And I just kept taking one more physics class and one more physics class, and eventually decided to keep going in grad school, and keep studying the aurora.
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What auroras are
Leigh: Auroras take their name from the Roman goddess of the dawn, who heralded in the arrival of the sun each morning by flying across the sky in a chariot drawn by winged horses. We asked Liz to explain where the atmospheric phenomenon are typically located, what they can look like, and what causes their famous dancing glow.
McDonald: The usual aurora occurs in kind of an oval region centered around the earth’s magnetic pole, and it has a variety of different forms that are mostly these very tall curtains of light that swirl around. They are primarily green colored, sometimes when they’re very strong some pink on the lower border, and then some red at the very highest altitudes, and they look different depending on your perspective, and then the different colors come from the different elements in the very upper atmosphere. This is above about 60 miles up in the atmosphere, so very high above where planes and where regular weather occurs. And what you have is primarily like oxygen and nitrogen particles up there. And so the oxygen is what causes the green glow as well as the the red, that’s even higher altitude. But basically you have particles from the space environment, raining down on these particles in the upper atmosphere, and then causing them to glow. So it’s really kind of a multi-step chain reaction that starts at the sun, and the glow that you see in the upper atmosphere is like the last step, and many different things happen from the sun sending out these charged particles. So the earth’s magnetic field looks like a bar magnet basically, it’s a dipole, has north and a south pole, and the interaction of the sun’s magnetic fields with the earth’s magnetic field is what transfers the energy from the particles coming from the sun to the earth’s magnetic field environment, which traps them and swirls them around. And then there’s different types of aurora, and different colors and different forms depending on all kinds of different physics that happens in the earth’s magnetic field environment.
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Where auroras are
Watkins: While aurora borealis are sometimes seen at lower latitudes, they’re far more common at higher ones, such as in the north of Canada and Europe. Liz describes next how sightings of aurora below this zone in which they are typically seen led to the discovery of STEVE, for which “Strong Thermal Emission Velocity Enhancement” is a backronym.
McDonald: People were seeing lights at lower than usual latitudes, further south than the usual aurora when you’re in the northern hemisphere. So there were these aurora chasers out there and they know what they’re looking at, they know what aurora is, either overhead or far to the northern horizon. But they were taking these photographs, and seeing something else that was typically overhead at latitudes like Calgary Alberta, and it was quaint colorless to the naked eye, maybe kind of gray, but with their cameras they were able to pick up a neat kind of purple mauve color to this very narrow ribbon that was overhead. And so it was kind of purple, and it sometimes had these little green discreet sort of picket fence features along with it, and both of those were really indications that it was a different kind of light process like aurora, but not the traditional auroral arc.
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Citizen scientists and STEVE, pt. 1
Leigh: In 2016, what citizen scientists around Alberta Canada were posting online caught the attention of many professional scientists, including Liz, who four years earlier had set up the website Aurorasaurus to provide real-time maps of aurora visibility. So we asked her to tell us how it was that this previously undescribed phenomenon came to get its unusual name.
McDonald: Most of the aurora actually is driven by electrons. So the regular aurora, all the green stuff, is actually mostly driven by electrons that rained down on the upper atmosphere, and then there’s also something called proton aurora, which is typically quite dim, quite diffuse, and kind of red, but that occurs further south than the usual aurora, what we call the sub latitudes of a rural zone. So that was where the term kind of came from, the citizen scientists who first photographed this. We’re calling it a proton arc and when their photographs were shared with scientists, who are experts in proton aurora, those folks were adamant that this was not proton aurora. Then we had something that was being regularly photographed, the citizen scientists were bringing it to us at aurora source and asking what is this, and we didn’t have a good answer for it. So one of the folks from the Alberta aurora chasers, a guy named Chris Ratliff, came up with kind of a placeholder name for it. He was like just call it STEVE, which is actually a reference to this movie called: “Over the Hedge,” in which it’s this kind of animated characters and woodland creatures, and they one day come upon a hedge in their forest and they don’t know what it is, and they’re really cute, and they just like: oh just call it STEVE. And so that was where the name STEVE came for a minute, just kind of stuck.
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Citizen scientists and STEVE, pt. 2
Watkins: Collaborating with citizen scientists photographers in Canada, professional scientists use satellite imaging to monitor the storm. This allowed Liz and her colleagues to determine the origin of these unique Northern Lights, as she describes after this short break.
Watkins: Here again is Liz McDonald.
McDonald: What eventually happened was that the citizen scientists kept taking observations and the professional scientists, especially up in Calgary and other places, were looking in our traditional data, both from a very extensive array of cameras across Canada as well as satellites that monitor the charged particle environment, and seeing if we could capture this at the same time as a STEVE was occurring, and one of those events came together in 2016. So that’s what led to the discovery, and the discovery is actually that when you look at the satellite data from a European Space Agency satellite, called Swarm, that flew through a STEVE event in 2016 and actually the particular data came from a particle instrument that was built by the University of Calgary. And what we saw was that the particles were very hot, the electrons were very hot, and the ions were actually flowing to the west. So there was a really strong flow of particles, like a big spike of particles, because the satellites fly through this STEVE event, which is this narrow east-west ribbon satellites fly north-south. So they’re kind of cutting straight across it really quickly, so you see a big spike in flow, and an increased temperature, and that’s actually been seen before by satellites. And so the scientists, we, eventually figured out that that was a thing called a subauroral ion drift, and those of us who were first looking at the Swarm data were not that familiar with subaurora ion drifts, but we were looking at this and looking at the past observations, and basically the STEVE event looks like a particularly strong subauroral ion drift. So these things have been seen for 40 years, although there’s still some questions about how they occur, but they were never predicted to have a visible signature to produce light. And so when you have this really strong flow and these heated particles, there wasn’t and there still isn’t a full explanation of how that light is occurring. But what we’re seeing is that there’s a little bit of light and it’s this characteristic thing called STEVE.
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Leigh: There’s a story about a scientist who made an aurora detector by stringing a few hundred feet of wire between two metal rods he’d driven it into the ground so that when voltage changed along the wire, a bell rang. Then he’d pull on his boots and head outside to take photographs of them. The Aurorasaurus website is a decidedly more modern undertaking combining real time space physics data with aurora sightings made by citizen scientists. So Ryan and I were curious to learn more about how the project came about.
McDonald: So aurora source is the citizen science project and I actually got the idea for this project way back in 2011 when there was a large storm of aurora. I was in New Mexico at the time and I was kind of watching — there’s certain satellites that you watched the incoming particles and how strong they are — and I was looking at the data and thinking: well maybe this event would be strong enough to be seen, even into New Mexico. But you can’t quite tell, you can’t really tell until those particles reach the earth environment. And what happened was I actually got on Twitter that night because the storm was very well timed with nightfall on the eastern seaboard. It was back in 2011 and I’m not the first adopter of any technology really, so I hadn’t ever gotten on Twitter before, but I had kind of been hearing about it, and I got on Twitter and saw in fact that people all over the eastern seaboard down to as far south as Alabama were actually seeing the Northern Lights and were tweeting about it. And so the idea was that we need to put these observations on a map, because you can then better show people where this visibility is actually occurring, and where people have seen it. That was the kernel of the idea in 2011, and then I began learning about what citizen science was as well. So we decided to take kind of a hybrid approach, between like, basically crowdsourcing these observations from Twitter, where they are fairly plentiful. During events you can maybe have one tweet per second about the aurora — it widely varies, but that was just kind of what I saw in this first large storm — and then there’s many people who are actually enthusiasts of aurora and regularly go out and chase it, and take photographs and those folks may or may not be on Twitter. But that was the population that we wanted to target for contributing those observations for science as well. And so when you do citizen science, the public can participate, you’re asking volunteers to contribute their data and you’re archiving that data. You have proper terms and conditions for people’s data so that you’re taking care of it. All we really need to know is when and where exactly you were when you saw the aurora, or if you didn’t see the aurora that’s also useful information to help improve our models. You can also submit a photo, if you like, and then we have a few simple questions about what kind of aurora you might have seen, and how fast it was moving, and that sort of thing. So we built the website in 2013 mostly, we got a larger grant from the National Science Foundation that was for interdisciplinary innovative work. We were collaborating with informal educators as well as human-computer interactions professionals academics from Penn State University, who study how people interact with technology. And then we got this larger grants, and we built apps and a better website, and that launched in late 2014, just in time for the aurora to really be active and more frequently visible further south or further from the poles than it usually is.
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Watkins: The sun has a heartbeat: every 11 years sunspot activity and solar winds peak, resulting in increased a rural activity in the upper atmosphere. Leading up to the latest of these, Liz partnered with a number of professional and citizen scientists to better observe and understand STEVE. Doug and I were curious to hear more about the opportunities this offered.
McDonald: That was around the maximum of this recent solar cycle. This being the first solar maximum with social media, these observations were totally new, not previously available during the last solar maximum. The aurora is less frequent now, we’re sort of in the declining phase of the solar cycle, but we’ve built a audience and, most importantly, citizen scientist contributors have grown and during every enhancement of aurora where it can be seen, you know, maybe once a month to the US-Canadian border, that varies quite a bit, but folks are out and submitting observations when that occurs.
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STEVEs’ picket fences
Leigh: STEVEs commonly have a unique feature not seen in other related phenomena: a series of green lines which may propagate toward one hand of the main structure. Ryan and I were curious to learn what Liz and her team were able to learn about these features, which have been described as looking like green picket fences.
McDonald: We haven’t worked out all of the details of the directionality of these picket fence structures, they’re a different color. So you have the STEVE, which is at about 200 kilometers altitude and it’s this purple ribbon that’s fairly static, it’s flowing east to west, it’s kind of holding its shape more or less, and then you have these picket fence features that are either slightly to the north or slightly below at a lower altitude. And then they come and go, and they have different alignments, and so it’s very difficult to describe their alignment from just one video or one point of view. And so one thing that we’re trying to do with more citizen science observations is to triangulate these structures, and actually even citizen scientists themselves have started to do this, to get the altitude from multiple points of view, and then you have to correlate that with the magnetic field. It’s a little more complicated at these subauroral latitudes because it’s not simply vertical. If you’re in a place like Alaska, you can basically approximate the magnetic field direction, as you know, straight into the earth there whereas. If you’re at the equator, it’s basically horizontally out, you know, it’s 90 degrees to that. But if you’re at these several latitudes it’s tilted, and so then all of the space plasma physics you have blows of the particles perpendicular to the magnetic field, and then you have electric fields that point in the third direction and things are really crazy. So we’re still figuring that out.
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Watkins: Our understanding of STEVE largely comes from an opportunity in 2016 when one coincided with the European Space Agency satellite passing overhead. The fact that the satellite passed close to STEVE led us to wonder, could you feel a STEVE if, like the goddess aurora, you were flying through one yourself?
McDonald: If you were a satellite and say you were a conducting metal object, you could feel it in the sense that more charged particles would be hitting the metal and that causes it to charge up and effects the spacecraft charging. So spacecraft charging is something that always happens to any kind of body in space on satellites. And so satellites feel these particles, and there can be some negative effects from that similar to, you know, if you’re getting a little static shock from walking across the carpet something like that, if you build up a lot of charge in a certain place on a satellite and it discharges somewhere else that can zap different electronics. And so satellites feel it but these particles are so tenuous, they’re not very dense even though it’s hot and, you know, it’s not something you would feel.
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Leigh: Ryan and I were hooked, and wanted to know how we might see a STEVE, either when traveling up to higher latitudes sometime or when one of the less common lower latitude aurora show up on Aurorasaurus. Here’s what Liz suggests.
McDonald: So you don’t need a telescope, just a normal point-and-shoot camera or a fancier digital camera can take really nice observations of the aurora. And I would recommend the Aurorasaurus website or apps whereby you can contribute your observations of the aurora, because they might have some kind of rare new discovery of something like STEVE, and so every data point basically contributes to a better understanding of the dynamics of the aurora and improving our models of it. So we offer alerts of when the aurora will be visible for people all over the world so you can sign up for alert and then you can also contribute your observations. And then there is more software that can be used to kind of get into different research aspects on your own, but that’s something that some of the enthusiast communities are starting to do and we haven’t formalized too much yet. But it doesn’t need to be formalized because people are just doing it, because they’re interested.
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Links to article, bonus audio and other materials
Watkins: That was Liz McDonald discussing her article: “New science in plain sight: Citizen scientists lead to the discovery of optical structure in the upper atmosphere” published with 15 professional and citizen scientists in Science Advances. You’ll find a link to their open access paper at: parsingscience.org/e45 along with bonus audio and other materials we discussed during the episode.
Leigh: Thanks to everyone who participated in Parsing Sciences drawing for free access to our archive of bonus clips from previous episodes, as well as those of future guests for all of 2019. We hope that our five winners are enjoying the material, and plan to run another giveaway later this year. In the meantime, for as little as $1 a month you too can get unlimited access to hours of unreleased audio from our conversations with scientists from around the world, and help support what we hope is one of your favorite science shows.
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Preview of next episode
Leigh: Next time on Parsing Science, we’ll be joined by Neera Jain from Purdue University’s School of Mechanical Engineering. She’ll talk with us about her experiments into how to make the machines that humans collaborate with more trustworthy by measuring and responding to changes in our bodies and minds.
Neera Jain: If we can come up with quantitative models that describe all these things, we now have this really cool ability to do things, like to be able to feed information to a machine that helps it understand whether or not a human is trusting or not, and based on that, that machine can change the information or modify how it’s delivering information to that human to help the human, for example, do their job better.
Watkins: We hope that you’ll join us again.
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