New research shows unprecedented atmospheric changes during May's geomagnetic superstorm

On May 11, a gorgeous aurora surprised stargazers across the southern United States. That same weekend, a tractor guided by GPS missed its mark.

What do the visibility of the northern lights have in common with compromised farming equipment in the Midwest?

A uniquely powerful geomagnetic storm, according to two newly published papers co-authored by Virginia Tech's Scott England.

"The northern lights are caused by energetic, charged particles hitting our upper atmosphere, which are impacted by numerous factors in space, including the sun," said England, associate professor in the Kevin T. Crofton Department of Aerospace and Ocean Engineering. "During solar geomagnetic storms, there's a lot more of these energetic charged particles in the space around Earth, so we see a brightening of the northern lights and the region over which you can see them spreads out to include places like the lower 48 states that usually don't see this display."

England and a team of university and industry collaborators tracked the upper atmospheric event on May 11 using NASA's GOLD instrument. It turned out to be the strongest geomagnetic storm captured in the last 20 years. Their findings were recently published in Geophysical Research Letters in two studies, both co-authored by England. The first study, by first author Deepak Karan, from the University of Colorado, Boulder, showed unprecedented changes in location and spread of particles in the upper atmosphere. The second study, by first author and Virginia Tech alumnus J. Scott Evans '88, documented composition and temperature changes.

Among the collected data, England noted witnessing some "delightful swirly patterns" for the first time, and a dramatic motion of the air away from the aurora causing the formation of enormous vortices that moved air in a spiral larger than a hurricane. Specific observations included:

• Unpredictable movement of low energy charged particles from around the equator toward the aurora
• Charged particles that can be divided into two buckets: low energy and high energy, the latter of which can hurt humans working in space and damage electronics
• Changes in temperature and pressure that likely lead to the swirls and vortices seen
• Changes in locations and spread of low energy particles, which can negatively impact GPS, satellites, and even the electrical grid

"As the aurora intensifies, you see more lights, but along with that, there's more energy entering the atmosphere, so it makes the atmosphere near the poles very hot, which starts to push air away from the poles and towards the equator," England said. "This data poses a lot of questions like, did something really different happen during this geomagnetic storm than has happened previously, or do we just have better instruments to measure the changes?"

Furthermore, what could those changes mean for the human-made technology that orbits that region of the atmosphere?

More than a northern lights show

Earth's upper atmosphere, spanning from about 60 to 400 miles above us, borders space and is the hang-out zone for satellites and the International Space Station. The upper atmosphere is made up of some of the same particles as the lower atmosphere, where we live and breathe. But it also has another side, the ionosphere that can be thought of almost like an electric blanket -- highly charged and constantly fluctuating. These charged particles in the ionosphere are one thing that makes this region of space so dynamic. It's common for the temperature and composition of the upper atmosphere and ionosphere to change. In fact, it does so predictably during the day and night and even changes overtime with seasons.

England said the particles in earth's atmosphere are impacted by numerous factors in space, including the sun's activity. During a solar geomagnetic storm flare, an intense burst of radiation from the sun changes the composition and speed of the particles within the earth's atmosphere. So why in recent months all over the globe the northern lights have been visible in places where they've not been seen before now?

"The number of sunspots, flares, and storms changes with an 11-year cycle that we call the solar cycle," England said. "The number of flares we are seeing has been increasing gradually for the last couple of years as we move toward the peak of the solar cycle."

In addition to the visibility of the northern lights, geomagnetic storms have a range of impacts on our technology. Because radio and GPS signals travel through this constantly fluctuating "electric blanket," changes in this layer of the atmosphere can disrupt signals and impede navigation and communication systems such as GPS. Various factors from both earth's weather and space weather can impact this crucial layer, but there's much to be learned about why changes in the upper and lower atmosphere occur and how they might impact life as we know it.

"These storms can also increase electrical currents that flow around the Earth, which can impact technological devices that use very long wires. In recent years, there have been impacts to the power grid when too much current was flowing through the wires. During the largest geomagnetic storm ever recorded, the Carrington Event in 1859, these caused telegraph systems -- peak technology at that time -- to catch on fire," England said.

Scientists suspect that a storm similar to the 1859 Carrington Event, if it happened today, could cause an internet apocalypse, sending large numbers of people and businesses offline. While the May 11 storm did not cause drastic disruptions, with the peak of the solar cycle expected to reach in July 2025, we are still about a year away from knowing those potential effects.

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When is an aurora not an aurora?

The shimmering green, red and purple curtains of the northern and southern lights -- the auroras -- may be the best-known phenomena lighting up the nighttime sky, but the most mysterious are the mauve and white streaks called Steve and their frequent companion, a glowing green "picket fence."

First recognized in 2018 as distinct from the common auroras, Steve -- a tongue-in-cheek reference to the benign name given a scary hedge in a 2006 children's movie -- and its associated picket fence were nevertheless thought to be caused by the same physical processes. But scientists were left scratching their heads about how these glowing emissions were produced.

Claire Gasque, a University of California, Berkeley, graduate student in physics, has now proposed a physical explanation for these phenomena that is totally different from the processes responsible for the well-known auroras. She has teamed up with researchers at the campus's Space Sciences Laboratory (SSL) to propose that NASA launch a rocket into the heart of the aurora to find out if she's correct.

Vibrant auroras and glowing phenomena such as Steve and the picket fence are becoming more common as the sun enters the active period of its 11-year cycle, and November was a good month for Steve observations in the northern latitudes. Because all these transient luminous phenomena are triggered by solar storms and coronal mass ejections from the sun, the approaching solar maximum is an ideal time to study rare events like Steve and the picket fence.

Gasque described the physics behind the picket fence in a paper published last month in the journal Geophysical Research Letters and will discuss the results on Dec. 14 in an invited talk at the American Geophysical Union meeting in San Francisco.

She calculated that in a region of the upper atmosphere farther south than that in which auroras form, electric fields parallel to Earth's magnetic field could produce the color spectrum of the picket fence. If correct, this unusual process has implications for how physicists understand energy flow between Earth's magnetosphere, which surrounds and protects Earth from the solar wind, and the ionosphere at the edge of space.

"This would upend our modeling of what creates light and the energy in the aurora in some cases," Gasque said.

"The really interesting thing about Claire's paper is that we've known for a couple of years now that the Steve spectrum is telling us there's some very exotic physics going on. We just didn't know what it was," said Brian Harding, a co-author of the paper and an SSL assistant research physicist. "Claire's paper showed that parallel electric fields are capable of explaining this exotic spectrum."

The paper was a side project from Gasque's Ph.D. thesis, which is focused on the connection between events like volcanoes on Earth's surface and phenomena in the ionosphere 100 kilometers or more above our heads.

But after hearing about Steve -- which has now become an acronym for Strong Thermal Emission Velocity Enhancement -- at a conference in 2022, she couldn't resist looking into the physics behind Steve and the picket fence.

"It's really cool," she said. "It's one of the biggest mysteries in space physics right now."

The physics of Steve and picket fence

The common auroras are produced when the solar wind energizes particles in Earth's magnetosphere, often at altitudes higher than 1,000 kilometers above the surface. These energized particles spiral around Earth's magnetic field lines toward the poles, where they crash into and excite oxygen and nitrogen molecules in the upper atmosphere. When those molecules relax, oxygen emits specific frequencies of green and red light, while nitrogen generates a bit of red, but primarily a blue, emission line.

The colorful, shimmering curtains that result can extend for thousands of kilometers across the northern or southern latitudes.

Steve, however, displays not individual emission lines, but a broad range of frequencies centered around purple or mauve. And unlike auroras, neither Steve nor the picket fence emit blue light, which is generated when the most energetic particles hit and ionize nitrogen. Steve and the picket fence also occur at lower latitudes than the aurora, potentially even as far south as the equator.

Some researchers proposed that Steve is caused by ion flows in the upper atmosphere, referred to as subauroral ion drift, or SAID, though there's no well accepted physical explanation for how SAID could generate the colorful emissions.

Gasque's interest was sparked by suggestions that the picket fence's emissions could be generated by low-altitude electric fields parallel to Earth's magnetic field, a situation thought to be impossible because any electric field aligned with the magnetic field should quickly short out and disappear.

Using a common physical model of the ionosphere, Gasque subsequently showed that a moderate parallel electric field -- around 100 millivolts per meter -- at a height of about 110 km could accelerate electrons to an energy that would excite oxygen and nitrogen and generate the spectrum of light observed from the picket fence. Unusual conditions in that area, such as a lower density of charged plasma and more neutral atoms of oxygen and nitrogen, could potentially act as insulation to keep the electric field from shorting out.

"If you look at the spectrum of the picket fence, it's much more green than you would expect. And there's none of the blue that's coming from the ionization of nitrogen," Gasque said. "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."

Instead, she said, "the light from the picket fence is being created by particles that have to be energized right there in space by a parallel electric field, which is a completely different mechanism than any of the aurora that we've studied or known before."

She and Harding suspect that Steve itself may be produced by related processes. Their calculations also predict the type of ultraviolet emissions that this process would produce, which can be checked to verify the new hypothesis about the picket fence.

Though Gasque's calculations don't directly address the on-off glow that makes the phenomenon look like a picket fence, it's likely due to wavelike variations in the electric field, she said. And while the particles that are accelerated by the electric field are probably not from the sun, the scrambling of the atmosphere by solar storms probably triggers Steve and the picket fence, as it does the common aurora.

Enhanced auroras exhibit a picket fence-like glow

The next step, Harding said, is to launch a rocket from Alaska through these phenomena and measure the strength and direction of the electric and magnetic fields. SSL scientists specialize in designing and building instruments that do just that. Many of these instruments are on spacecraft now orbiting Earth and the sun.

Initially, the target would be what's known as an enhanced aurora, which is a normal aurora with picket fence-like emissions embedded in it.

"The enhanced aurora is basically this bright layer that's embedded in the normal aurora. The colors are similar to the picket fence in that there's not as much blue in them, and there's more green from oxygen and red from nitrogen. The hypothesis is that these are also created by parallel electric fields, but they are a lot more common than the picket fence," Gasque said.

The plan is not only "to fly a rocket through that enhanced layer to actually measure those parallel electric fields for the first time," she said, but also send a second rocket up to measure the particles at higher altitudes, "to distinguish the conditions from those that cause the auroras." Eventually, she hopes for a rocket that will fly directly through Steve and the picket fence.

Harding, Gasque and colleagues proposed just such a sounding rocket campaign to NASA this fall and expect to hear back regarding its selection in the first half of 2024. Gasque and Harding consider the experiment an important step in understanding the chemistry and physics of the upper atmosphere, the ionosphere and Earth's magnetosphere, and a proposal in line with the Low Cost Access to Space (LCAS) program sponsored by NASA for projects like this.

"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," Harding said. "We really don't know. Claire's paper is the first step in the chain of that understanding."

Gasque expressed appreciation for the input from people who study the middle ionosphere, or mesosphere, and the stratosphere, whose ideas helped her puzzle out the solution.

"With this collaboration, we were able to make some really cool progress in this field," she said. "Honestly, it was just following our nose and being excited about it."

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Uranus aurora discovery offers clues to habitable icy worlds

The presence of an infrared aurora on the cold, outer planet of Uranus has been confirmed for the first time by University of Leicester astronomers.

The discovery could shed light on the mysteries behind the magnetic fields of the planets of our solar system, and even on whether distant worlds might support life.

The team of scientists, supported by the Science and Technology Facilities Council (STFC), have obtained the first measurements of the infrared (IR) aurora at Uranus since investigations began in 1992. While the ultraviolet (UV) aurorae of Uranus has been observed since 1986, no confirmation of the IR aurora had been observed until now. The scientists' conclusions have been published in the journal Nature Astronomy.

The ice giants Uranus and Neptune are unusual planets in our solar system as their magnetic fields are misaligned with the axes in which they spin. While scientists have yet to find an explanation for this, clues may lie in Uranus's aurora.

Aurorae are caused by highly energetic charged particles, which are funnelled down and collide with a planet's atmosphere via the planet's magnetic field lines. On Earth, the most famous result of this process are the spectacles of the Northern and Southern Lights. At planets such as Uranus, where the atmosphere is predominately a mix of hydrogen and helium, this aurora will emit light outside of the visible spectrum and in wavelengths such as the infrared (IR).

The team used infrared auroral measurements taken by analysing specific wavelengths of light emitted from the planet, using the Keck II telescope. From this, they can analyse the light (known as emission lines) from these planets, similar to a barcode. In the infrared spectrum, the lines emitted by a charged particle known as H3+ will vary in brightness depending on how hot or cold the particle is and how dense this layer of the atmosphere is. Hence, the lines act like a thermometer into the planet.

Their observations revealed distinct increases in H3+ density in Uranus's atmosphere with little change in temperature, consistent with ionisation caused by the presence of an infrared aurora. Not only does this help us better understand the magnetic fields of the outer planets of our own solar system, but it may also help in identifying other planets that are suitable of supporting life.

Lead author Emma Thomas, a PhD student in the University of Leicester School of Physics and Astronomy, said: "The temperature of all the gas giant planets, including Uranus, are hundreds of degrees Kelvin/Celsius above what models predict if only warmed by the sun, leaving us with the big question of how these planets are so much hotter than expected? One theory suggests the energetic aurora is the cause of this, which generates and pushes heat from the aurora down towards the magnetic equator.

"A majority of exoplanets discovered so far fall in the sub-Neptune category, and hence are physically similar to Neptune and Uranus in size. This may also mean similar magnetic and atmospheric characteristics too. By analysing Uranus's aurora which directly connects to both the planet's magnetic field and atmosphere, we can make predictions about the atmospheres and magnetic fields of these worlds and hence their suitability for life.

"This paper is the culmination of 30 years of auroral study at Uranus, which has finally revealed the infrared aurora and begun a new age of aurora investigations at the planet. Our results will go on to broaden our knowledge of ice giant auroras and strengthen our understanding of planetary magnetic fields in our solar system, at exoplanets and even our own planet."

The results may also give scientists an insight into a rare phenomenon on Earth, in which the north and south pole switch hemisphere locations known as geomagnetic reversal.

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Physicists explain how type of aurora on Mars is formed

Physicists led by the University of Iowa have learned how a type of aurora on Mars is formed.

In a new study, the physicists studied discrete aurora, a light-in-the-sky display that occurs mostly during the night in the red planet's southern hemisphere. While scientists have known about discrete aurora on Mars-which also occur on Earth -- they did not know how they formed. That's because Mars does not have a global magnetic field like Earth, which is a main trigger for aurora, also called the northern and southern lights on our planet.

Instead, the physicists report, discrete aurora on Mars are governed by the interaction between the solar wind -- the constant jet of charged particles from the sun -- and magnetic fields generated by the crust at southern latitudes on Mars. It's the nature of this localized interaction between the solar wind and the crustal magnetic fields that lead to discrete aurora, the scientists find.

"We have the first detailed study looking at how solar wind conditions affect aurora on Mars," says Zachary Girazian, associate research scientist in the Department of Physics and Astronomy and the study's corresponding author. "Our main finding is that inside the strong crustal field region, the aurora occurrence rate depends mostly on the orientation of the solar wind magnetic field, while outside the strong crustal field region, the occurrence rate depends mostly on the solar wind dynamic pressure."

The findings come from more than 200 observations of discrete aurora on Mars by the NASA-led Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. One of the instruments used to make the observations, the Solar Wind Ion Analyzer, is led by Jasper Halekas, associate professor in the Department of Physics and Astronomy and a co-author on the study.

"Now is a very fruitful and exciting time for researching aurora at Mars. The database of discrete aurora observations we have from MAVEN is the first of its kind, allowing us to understand basic features of the aurora for the first time," Girazian says.

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Scientists connect the dots between Galilean moon, auroral emissions on Jupiter

On November 8, 2020, NASA's Juno spacecraft flew through an intense beam of electrons traveling from Ganymede, Jupiter's largest moon, to its auroral footprint on the gas giant. Southwest Research Institute scientists used data from Juno's payload to study the particle population traveling along the magnetic field line connecting Ganymede to Jupiter while, at the same time, remotely sensing the associated auroral emissions to unveil the mysterious processes creating the shimmering lights.

"Jupiter's most massive moons each create their own auroras on Jupiter's north and south poles," said Dr. Vincent Hue, lead author of a paper outlining the results of this research. "Each auroral footprint, as we call them, is magnetically connected to their respective moon, kind of like a magnetic leash connected to the moon glowing on Jupiter itself."

Like the Earth, Jupiter experiences auroral light around the polar regions as particles from its massive magnetosphere interact with molecules in the Jovian atmosphere. However, Jupiter's auroras are significantly more intense than Earth's, and unlike Earth, Jupiter's largest moons also create auroral spots. The Juno mission, led by SwRI's Dr. Scott Bolton, is circling Jupiter in a polar orbit and flew through the electron "thread" connecting Ganymede with its associated auroral footprint.

"Prior to Juno, we knew that these emissions can be quite complex, ranging from a single auroral spot to multiple spots, which sometimes trail an auroral curtain that we called the footprint tail," said Dr. Jamey Szalay, a co-author from Princeton University. "Juno, flying extremely close to Jupiter, revealed these auroral spots to be even more complex than previously thought."

Ganymede is the only moon in our solar system that has its own magnetic field. Its mini-magnetosphere interacts with Jupiter's massive magnetosphere, creating waves that accelerate electrons along the gas giant's magnetic field lines, which can be directly measured by Juno.

Two SwRI-led instruments on Juno, the Jovian Auroral Distributions Experiment (JADE) and the Ultraviolet Spectrometer (UVS) provided key data for this study, which was also supported by Juno's magnetic field sensor built at NASA's Goddard Space Flight Center.

"JADE measured the electrons traveling along the magnetic field lines, while UVS imaged the related auroral footprint spot," said SwRI's Dr. Thomas Greathouse, a co-author on this study.

In this way, Juno is both able to measure the electron "rain" and immediately observe the UV light it creates when it crashes into Jupiter. Previous Juno measurements showed that large magnetic perturbations accompanied the electron beams causing the auroral footprint. However, this time, Juno did not observe similar perturbations with the electron beam.

"If our interpretation is correct, this a confirmation of a decade-old theory that we put together to explain the morphology of the auroral footprints," said Dr. Bertrand Bonfond, a co-author of the study from the Liège University in Belgium. The theory suggests that electrons accelerated in both directions create the multi-spot dance of auroral footprints.

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Scientists solve 40-year mystery over Jupiter's X-ray aurora

A research team co-led by UCL (University College London) has solved a decades-old mystery as to how Jupiter produces a spectacular burst of X-rays every few minutes.

The X-rays are part of Jupiter's aurora -- bursts of visible and invisible light that occur when charged particles interact with the planet's atmosphere. A similar phenomenon occurs on Earth, creating the northern lights, but Jupiter's is much more powerful, releasing hundreds of gigawatts of energy, enough to briefly power all of human civilisation*.

In a new study, published in Science Advances, researchers combined close-up observations of Jupiter's environment by NASA's satellite Juno, which is currently orbiting the planet, with simultaneous X-ray measurements from the European Space Agency's XMM-Newton observatory (which is in Earth's own orbit).

The research team, led by UCL and the Chinese Academy of Sciences, discovered that X-ray flares were triggered by periodic vibrations of Jupiter's magnetic field lines. These vibrations create waves of plasma (ionised gas) that send heavy ion particles "surfing" along magnetic field lines until they smash into the planet's atmosphere, releasing energy in the form of X-rays.

Co-lead author Dr William Dunn (UCL Mullard Space Science Laboratory) said: "We have seen Jupiter producing X-ray aurora for four decades, but we didn't know how this happened. We only knew they were produced when ions crashed into the planet's atmosphere.

"Now we know these ions are transported by plasma waves -- an explanation that has not been proposed before, even though a similar process produces Earth's own aurora. It could, therefore, be a universal phenomenon, present across many different environments in space."

X-ray auroras occur at Jupiter's north and south poles, often with clockwork regularity -- during this observation Jupiter was producing bursts of X-rays every 27 minutes.

The charged ion particles that hit the atmosphere originate from volcanic gas pouring into space from giant volcanoes on Jupiter's moon, Io.

This gas becomes ionised (its atoms are stripped free of electrons) due to collisions in Jupiter's immediate environment, forming a donut of plasma that encircles the planet.

Co-lead author Dr Zhonghua Yao (Chinese Academy of Sciences, Beijing) said: "Now we have identified this fundamental process, there is a wealth of possibilities for where it could be studied next. Similar processes likely occur around Saturn, Uranus, Neptune and probably exoplanets as well, with different kinds of charged particles 'surfing' the waves."

Co-author Professor Graziella Branduardi-Raymont (UCL Mullard Space Science Laboratory) said: "X-rays are typically produced by extremely powerful and violent phenomena such as black holes and neutron stars, so it seems strange that mere planets produce them too.

"We can never visit black holes, as they are beyond space travel, but Jupiter is on our doorstep. With the arrival of the satellite Juno into Jupiter's orbit, astronomers now have a fantastic opportunity to study an environment that produces X-rays up close."

For the new study, researchers analysed observations of Jupiter and its surrounding environment carried out continuously over a 26-hour period by the Juno and XMM-Newton satellites.

They found a clear correlation between waves in the plasma detected by Juno and X-ray auroral flares at Jupiter's north pole recorded by X-MM Newton. They then used computer modelling to confirm that the waves would drive the heavy particles towards Jupiter's atmosphere.

Why the magnetic field lines vibrate periodically is unclear, but the vibration may result from interactions with the solar wind or from high-speed plasma flows within Jupiter's magnetosphere.

Jupiter's magnetic field is extremely strong -- about 20,000 times as strong as Earth's -- and therefore its magnetosphere, the area controlled by this magnetic field, is extremely large. If it was visible in the night sky, it would cover a region several times the size of our moon.

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Physicists report definitive evidence how auroras are created

The aurora borealis, or northern lights, that fill the sky in high-latitude regions have fascinated people for thousands of years. But how they're created, while theorized, had not been conclusively proven.

In a new study, a team of physicists led by University of Iowa reports definitive evidence that the most brilliant auroras are produced by powerful electromagnetic waves during geomagnetic storms. The phenomena, known as Alfven waves, accelerate electrons toward Earth, causing the particles to produce the familiar atmospheric light show.

The study, published online June 7 in the journal Nature Communications, concludes a decades-long quest to demonstrate experimentally the physical mechanisms for the acceleration of electrons by Alfven waves under conditions corresponding to Earth's auroral magnetosphere.

"Measurements revealed this small population of electrons undergoes 'resonant acceleration' by the Alfven wave's electric field, similar to a surfer catching a wave and being continually accelerated as the surfer moves along with the wave," says Greg Howes, associate professor in the Department of Physics and Astronomy at Iowa and study co-author.

Scientists have known that energized particles that emanate from the sun -- such as electrons racing at approximately 45 million miles per hour -- precipitate along the Earth's magnetic field lines into the upper atmosphere, where they collide with oxygen and nitrogen molecules, kicking them into an excited state. These excited molecules relax by emitting light, producing the colorful hues of the aurora.

The theory was supported by spacecraft missions that frequently found Alfven waves traveling Earthward above auroras, presumably accelerating electrons along the way. Although space-based measurements had supported the theory, limitations inherent to spacecraft and rocket measurements had prevented a definitive test.

The physicists were able to find confirmatory evidence in a series of experiments conducted at the Large Plasma Device (LPD) in UCLA's Basic Plasma Science Facility, a national collaborative research facility supported jointly by the U.S. Department of Energy and National Science Foundation.

"The idea that these waves can energize the electrons that create the aurora goes back more than four decades, but this is the first time we've been able to confirm definitively that it works," says Craig Kletzing, professor in the Department of Physics and Astronomy at Iowa and a study co-author. "These experiments let us make the key measurements that show that the space measurements and theory do, indeed, explain a major way in which the aurora are created."

The phenomenon of electrons "surfing" on the electric field of a wave is a theoretical process known as Landau damping, first proposed by Russian physicist Lev Landau in 1946. Through numerical simulations and mathematical modeling, the researchers demonstrated that the results of their experiment agreed with the predicted signature for Landau damping.

The agreement of experiment, simulation, and modeling provides the first direct evidence that Alfven waves can produce accelerated electrons, causing the aurora, says Troy Carter, professor of physics at UCLA and director of the UCLA Plasma Science and Technology Institute.

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Physicists describe new type of aurora

For millennia, humans in the high latitudes have been enthralled by auroras -- the northern and southern lights. Yet even after all that time, it appears the ethereal, dancing ribbons of light above Earth still hold some secrets.

In a new study, physicists led by the University of Iowa report a new feature to Earth's atmospheric light show. Examining video taken nearly two decades ago, the researchers describe multiple instances where a section of the diffuse aurora -- the faint, background-like glow accompanying the more vivid light commonly associated with auroras -- goes dark, as if scrubbed by a giant blotter. Then, after a short period of time, the blacked-out section suddenly reappears.

The researchers say the behavior, which they call "diffuse auroral erasers," has never been mentioned in the scientific literature. The findings appear in the Journal of Geophysical Research Space Physics.

Auroras occur when charged particles flowing from the sun -- called the solar wind -- interact with Earth's protective magnetic bubble. Some of those particles escape and fall toward our planet, and the energy released during their collisions with gases in Earth's atmosphere generate the light associated with auroras.

"The biggest thing about these erasers that we didn't know before but know now is that they exist," says Allison Jaynes, assistant professor in the Department of Physics and Astronomy at Iowa and study co-author. "It raises the question: Are these a common phenomenon that has been overlooked, or are they rare?

"Knowing they exist means there is a process that is creating them," Jaynes continues, "and it may be a process that we haven't started to look at yet because we never knew they were happening until now."

It was on March 15, 2002, that David Knudsen, a physicist at the University of Calgary, set up a video camera in Churchill, a town along Hudson Bay in Canada, to film auroras. Knudsen's group was a little disheartened; the forecast called for clear, dark skies -- normally perfect conditions for viewing auroras -- but no dazzling illumination was happening. Still, the team was using a camera specially designed to capture low-level light, much like night-vision goggles.

Though the scientists saw only mostly darkness as they gazed upward with their own eyes, the camera was picking up all sorts of auroral activity, including an unusual sequence where areas of the diffuse aurora disappeared, then came back.

Knudsen, looking at the video as it was being recorded, scribbled in his notebook, "pulsating 'black out' diffuse glow, which then fills in over several seconds."

"What surprised me, and what made me write it in the notebook, is when a patch brightened and turned off, the background diffuse aurora was erased. It went away," says Knudsen, a Fort Dodge, Iowa, native who has studied aurora for more than 35 years and is a co-author on the study. "There was a hole in the diffuse aurora. And then that hole would fill back in after a half-minute or so. I had never seen something like that before."

The note lay dormant, and the video unstudied, until Iowa's Jaynes handed it to graduate student Riley Troyer to investigate. Jaynes learned about Knudsen's recording at a scientific meeting in 2010 and referenced the eraser note in her doctoral thesis on diffuse aurora a few years later. Now on the faculty at Iowa, she wanted to learn more about the phenomenon.

"I knew there was something there. I knew it was different and unique," says Jaynes, assistant professor in the Department of Physics and Astronomy. "l had some ideas how it could be analyzed, but I hadn't done that yet. I handed it to Riley, and he went much further with it by figuring out his own way to analyze the data and produce some significant conclusions."

Troyer, from Fairbanks, Alaska, took up the assignment with gusto.

"I've seen hundreds of auroras growing up," says Troyer, who is in his third year of doctoral studies at Iowa. "They're part of my heritage, something I can study while keeping ties to where I'm from."

Troyer created a software program to key in on frames in the video when the faint erasers were visible. In all, he cataloged 22 eraser events in the two-hour recording.

"The most valuable thing we found is showing the time that it takes for the aurora to go from an eraser event (when the diffuse aurora is blotted out) to be filled or colored again," says Troyer, who is the paper's corresponding author, "and how long it takes to go from that erased state back to being diffuse aurora. Having a value on that will help with future modeling of magnetic fields."

Jaynes says learning about diffuse auroral erasers is akin to studying DNA to understand the entire human body.

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New research reveals secret to Jupiter's curious aurora activity

 Auroral displays continue to intrigue scientists, whether the bright lights shine over Earth or over another planet. The lights hold clues to the makeup of a planet's magnetic field and how that field operates.

New research about Jupiter proves that point -- and adds to the intrigue.

Peter Delamere, a professor of space physics at the University of Alaska Fairbanks Geophysical Institute, is among an international team of 13 researchers who have made a key discovery related to the aurora of our solar system's largest planet.

The team's work was published April 9, 2021, in the journal Science Advances. The research paper, titled "How Jupiter's unusual magnetospheric topology structures its aurora," was written by Binzheng Zhang of the Department of Earth Sciences at the University of Hong Kong; Delamere is the primary co-author.

Research done with a newly developed global magnetohydrodynamic model of Jupiter's magnetosphere provides evidence in support of a previously controversial and criticized idea that Delamere and researcher Fran Bagenal of the University of Colorado at Boulder put forward in a 2010 paper -- that Jupiter's polar cap is threaded in part with closed magnetic field lines rather than entirely with open magnetic field lines, as is the case with most other planets in our solar system.

"We as a community tend to polarize -- either open or closed -- and couldn't imagine a solution where it was a little of both," said Delamere, who has been studying Jupiter since 2000. "Yet in hindsight, that is exactly what the aurora was revealing to us."

Open lines are those that emanate from a planet but trail off into space away from the sun instead of reconnecting with a corresponding location in the opposite hemisphere.

On Earth, for example, the aurora appears on closed field lines around an area referred to as the auroral oval. It's the high latitude ring near -- but not at -- each end of Earth's magnetic axis.

Within that ring on Earth, however, and as with some other planets in our solar system, is an empty spot referred to as the polar cap. It's a place where magnetic field lines stream out unconnected -- and where the aurorae rarely appear because of it. Think of it like an incomplete electrical circuit in your home: No complete circuit, no lights.

Jupiter, however, has a polar cap in which the aurora dazzles. That puzzled scientists.

The problem, Delamere said, is that researchers were so Earth-centric in their thinking about Jupiter because of what they had learned about Earth's own magnetic fields.

The arrival at Jupiter of NASA's Juno spacecraft in July 2016 provided images of the polar cap and aurora. But those images, along with some captured by the Hubble Space Telescope, couldn't resolve the disagreement among scientists about open lines versus closed lines.

So Delamere and the rest of the research team used computer modeling for help. Their research revealed a largely closed polar region with a small crescent-shaped area of open flux, accounting for only about 9 percent of the polar cap region. The rest was active with aurora, signifying closed magnetic field lines.

Jupiter, it turns out, possesses a mix of open and closed lines in its polar caps.

"There was no model or no understanding to explain how you could have a crescent of open flux like this simulation is producing," he said. "It just never even entered my mind. I don't think anybody in the community could have imagined this solution. Yet this simulation has produced it."

"To me, this is a major paradigm shift for the way that we understand magnetospheres."

What else does this reveal? More work for researchers.

"It raises many questions about how the solar wind interacts with Jupiter's magnetosphere and influences the dynamics," Delamere said.

Jupiter's aurorally active polar cap could, for example, be due to the rapidity of the planet's rotation -- once every 10 hours compared to Earth's once every 24 hours -- and the enormity of its magnetosphere. Both reduce the impact of the solar wind, meaning the polar cap magnetic field lines are less likely to be torn apart to become open lines.

And to what extent does Jupiter's moon Io affect the magnetic lines within Jupiter's polar cap? Io is electrodynamically linked to Jupiter, something unique in our solar system, and as such is constantly stripped of heavy ions by its parent planet.

Read more at Science Daily

Scientists discover a new auroral feature on Jupiter

The SwRI-led Ultraviolet Spectrograph (UVS) orbiting Jupiter aboard NASA's Juno spacecraft has detected new faint aurora features, characterized by ring-like emissions, which expand rapidly over time. SwRI scientists determined that charged particles coming from the edge of Jupiter's massive magnetosphere triggered these auroral emissions.

"We think these newly discovered faint ultraviolet features originate millions of miles away from Jupiter, near the Jovian magnetosphere's boundary with the solar wind," said Dr. Vincent Hue, lead author of a paper accepted by the Journal of Geophysical Research: Space Physics. "The solar wind is a supersonic stream of charged particles emitted by the Sun. When they reach Jupiter, they interact with its magnetosphere in a way that is still not well understood."

Both Jupiter and Earth have magnetic fields that provide protection from the solar wind. The stronger the magnetic field, the larger the magnetosphere. Jupiter's magnetic field is 20,000 times stronger than Earth's and creates a magnetosphere so large it begins to deflect the solar wind 2-4 million miles before it reaches Jupiter.

"Despite decades of observations from Earth combined with numerous in-situ spacecraft measurements, scientists still do not fully understand the role the solar wind plays in moderating Jupiter's auroral emissions," said SwRI's Dr. Thomas Greathouse, a co-author on this study. "Jupiter's magnetospheric dynamics, the motion of charged particles within its magnetosphere, is largely controlled by Jupiter's 10-hour rotation, the fastest in the solar system. The solar wind's role is still debated."

One of the goals of the Juno mission, recently approved by NASA for an extension until 2025, is to explore Jupiter's magnetosphere by measuring its auroras with the UVS instrument. Previous observations with the Hubble Space Telescope and Juno have allowed scientists to determine that most of Jupiter's powerful auroras are generated by internal processes, that is the motion of charged particles within the magnetosphere. However, on numerous occasions, UVS has detected a faint type of aurora, characterized by rings of emissions expanding rapidly with time.

"The high-latitude location of the rings indicates that the particles causing the emissions are coming from the distant Jovian magnetosphere, near its boundary with the solar wind," said Bertrand Bonfond, a co-author on this study from Belgium's Liège University. In this region, plasma from the solar wind often interacts with the Jovian plasma in a way that is thought to form "Kelvin-Helmholtz" instabilities. These phenomena occur when there are shear velocities, such as at the interface between two fluids moving at different speeds. Another potential candidate to produce the rings are dayside magnetic reconnection events, where oppositely directed Jovian and interplanetary magnetic fields converge, rearrange and reconnect.

Read more at Science Daily

Jupiter's 'dawn storm' auroras are surprisingly Earth-like

 The storms, which consist of brightenings and broadenings of the dawn flank of an oval of auroral activity that encircles Jupiter's poles, evolve in a pattern surprisingly reminiscent of familiar surges in the aurora that undulate across Earth's polar skies, called auroral substorms, according to the authors.

The new study is the first to track the storms from their birth on the nightside of the giant planet through their full evolution. It was published today in AGU Advances, AGU's journal for high-impact, short-format reports with immediate implications spanning all Earth and space sciences.

During a dawn storm, Jupiter's quiet and regular auroral arc transforms into a complex and intensely bright auroral feature. It emits hundreds to thousands of Gigawatts of ultraviolet light into space as it rotates from the night side to the dawn side and ultimately to the day side of the planet over the course of 5-10 hours. A Gigawatt is the power produced by a typical modern nuclear reactor. This colossal brightness implies that at least ten times more energy was transferred from the magnetosphere to the upper atmosphere of Jupiter.

Previously, dawn storms had only been observed from ground-based telescopes on Earth or the Hubble Space Telescope, which can only offer side views of the aurora and cannot see the night side of the planet. Juno revolves around Jupiter every 53 days along a highly elongated orbit that brings it right above the poles every orbit.

"This is a real game changer," said Bertrand Bonfond, a researcher from the University of Liège and lead author of the new study. "We finally got to find out what was happening on the night side, where the dawn storms are born."

Familiar auroral sequences, different engines Polar auroras on Earth and on Jupiter are images of processes occurring in the magnetic fields that surround them. Both planets generate magnetic fields that capture charged particles.

Earth's magnetosphere is shaped by charged particles flowing out of the sun called the solar wind. Bursts of solar wind stretch Earth's magnetic field into a long tail on the nightside of the planet. When that tail snaps back, it fires charged particles into the nightside ionosphere, which appear as spectacular auroral light shows.

The new study found the timing of the dawn storms on Jupiter did not correlate with solar wind fluctuations. Jupiter's magnetosphere is mostly populated by particles escaping from its volcanic moon Io, which then get ionized and trapped around the planet by its magnetic field.

The sources of mass and energy fundamentally differ between these two magnetospheres, leading to auroras that usually look quite different. However, the dawn storms, as unraveled by Juno's ultraviolet spectrograph, looked familiar to the researchers.

"When we looked at the whole dawn storm sequence, we couldn't help but notice that the dawn storm auroras at Jupiter are very similar to a type of terrestrial auroras called substorms" said Zhonghua Yao, co-author of the study and scientific collaborator at the University of Liège.

The substorms result from the explosive reconfiguration of the tail of the magnetosphere. On Earth, they are strongly related to the variations of the solar wind and of the orientation of the interplanetary magnetic field. On Jupiter, such explosive reconfigurations are rather related to an overspill of the plasma originating from Io.

These findings demonstrate that, whatever their sources, particles and energy do not always circulate smoothly in planetary magnetospheres. They often accumulate until the magnetospheres collapse and generate substorm-like responses in the planetary aurorae.

Read more at Science Daily

First humans in Tasmania must have seen spectacular auroras

 Drilling a 270,000-year old core from a Tasmanian lake has provided the first Australian record of a major global event where the Earth's magnetic field 'switched '- and the opportunity to establish a precedent for developing new paleomagnetic dating tools for Australian archaeology and paleosciences.

"This is the first study of this kind in Australia since pioneering studies in the 1980s," said author Dr Agathe Lisé-Provonost, a McKenzie Fellow from the School of Earth Sciences at the University of Melbourne.

"Just two lakes in north-east Australia previously provided such "full-vector" record, where both the past directions and the past intensity of the Earth magnetic field are obtained from the same cores."

Published in the journal Quaternary Geochronology, Chronostratigraphy of a 270-ka sediment record from Lake Selina, Tasmania: Combining radiometric, geomagnetic and climatic dating, details how drilling into the 5.5 metre long Lake Selina core established that 41,000 years ago, people in Tasmania must have seen spectacular auroras when the Earth's magnetic field flipped, and for a few thousand years, north was south and south was north.

"During the geomagnetic 'excursion', the strength of the Earth's magnetic field almost vanished," said DrLisé-Provonost.

"This would lead to a big increase in cosmic and solar particles bombarding our planet because the magnetic field normally acts like a shield.

"We don't know when the next geomagnetic excursion will happen, but if one was to occur today, satellites would be rendered useless, smartphone navigation apps would fail, and there would be major disruptions of power distribution systems."

Research leading to that discovery got underway in 2014 when the author travelled to a small sub-alpine lake in western Tasmania with a team led by Associate Professor Michael-Shawn Fletcher, where a makeshift floating platform rigged to two inflatable rafts was used to drill down into the sediment.

With the core containing a climate, vegetation, and paleomagnetic record of the area, the team looked to first accurately date its layers finding evidence of the ecosystem changes that occurred as Tasmanian Aboriginals arrived 43,000 years ago and managed the land over thousands of years. Abrupt changes that occurred since the arrival of Europeans 200 years ago are also evidenced.

"Magnetic particles are eroded from rocks, making their way to a lake by wind or water, and settle down on the lake bottom," said Dr Lisé-Provonost.

"The magnetic particles act like tiny compass needles, aligning with the Earth's magnetic field. As these particles accumulate and become buried, they become locked in place, leaving a history of the Earth's magnetic field. The deeper we drill, the further back in time we go."

It's hoped the research will lead the way for more studies of the past geomagnetic field behavior from Australian lakes and other geological materials such as lava flows, cave deposits and fired archaeological artefacts, for developing new paleomagnetic dating tools and improving models of the Earth's magnetic field to, one day, maybe predict the next geomagnetic excursion.

Read more at Science Daily

Comet discovered to have its own northern lights

This composite is a mosaic comprising four individual NAVCAM images taken from 19 miles (31 kilometers) from the center of comet 67P/Churyumov-Gerasimenko on Nov. 20, 2014. The image resolution is 10 feet (3 meters) per pixel.

Data from NASA instruments aboard the ESA (European Space Agency) Rosetta mission have helped reveal that comet 67P/Churyumov-Gerasimenko has its own far-ultraviolet aurora. It is the first time such electromagnetic emissions in the far-ultraviolet have been documented on a celestial object other than a planet or moon. A paper on the findings was released today in the journal Nature Astronomy.

On Earth, aurora (also known as the northern or southern lights) are generated when electrically charged particles speeding from the Sun hit the upper atmosphere to create colorful shimmers of green, white, and red. Elsewhere in the solar system, Jupiter and some of its moons -- as well as Saturn, Uranus, Neptune, and even Mars -- have all exhibited their own version of northern lights. But the phenomena had yet to be documented in comets.

Rosetta is space exploration's most traveled and accomplished comet hunter. Launched in 2004, it orbited comet 67P/Churyumov-Gerasimenko (67P/C-G) from Aug. 2014 until its dramatic end-of-mission comet landing in Sept. 2016. The data for this most recent study is on what mission scientists initially interpreted as "dayglow," a process caused by photons of light interacting with the envelope of gas -- known as the coma -- that radiates from, and surrounds, the comet's nucleus. But new analysis of the data paints a very different picture.

"The glow surrounding 67P/C-G is one of a kind," said Marina Galand of Imperial College London and lead author of the study. "By linking data from numerous Rosetta instruments, we were able to get a better picture of what was going on. This enabled us to unambiguously identify how 67P/C-G's ultraviolet atomic emissions form."

The data indicate 67P/C-G's emissions are actually auroral in nature. Electrons streaming out in the solar wind -- the stream of charged particles flowing out from the Sun -- interact with the gas in the comet's coma, breaking apart water and other molecules. The resulting atoms give off a distinctive far-ultraviolet light. Invisible to the naked eye, far-ultraviolet has the shortest wavelengths of radiation in the ultraviolet spectrum.

Exploring the emission of 67P/C-G will enable scientists to learn how the particles in the solar wind change over time, something that is crucial for understanding space weather throughout the solar system. By providing better information on how the Sun's radiation affects the space environment they must travel through, such information could ultimately can help protect satellites and spacecraft, as well as astronauts traveling to the Moon and Mars.

"Rosetta is the gift that keeps on giving," said Paul Feldman, an investigator on Alice at the Johns Hopkins University in Baltimore and a co-author of the paper. "The treasure trove of data it returned over its two-year visit to the comet have allowed us to rewrite the book on these most exotic inhabitants of our solar system -- and by all accounts there is much more to come."

NASA Instruments Aboard ESA's Rosetta

NASA-supplied instruments contributed to this investigation. The Ion and Electron Sensor (IES) instrument detected the amount and energy of electrons near the spacecraft, the Alice instrument measured the ultraviolet light emitted by the aurora, and the Microwave Instrument for the Rosetta Orbiter (MIRO) measured the amount of water molecules around the comet (the MIRO instrument includes contributions from France, Germany, and Taiwan). Other instruments aboard the spacecraft used in the research were the Italian Space Agency's Visible and InfraRed Thermal Imaging Spectrometer (VIRTIS), the Langmuir Probe (LAP) provided by Sweden, and the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) provided by Switzerland.

Read more at Science Daily

Scientists discover what powers celestial phenomenon STEVE

Amateur astronomer's photograph used in the new research. The photograph was taken on May 8, 2016, in Keller, Wash. The major structures are two bands of upper atmospheric emissions 160 kilometers (100 miles) above the ground, a mauve arc and green picket fence. The black objects at the bottom are trees. The background star constellations include Gemini and Ursa Major.

The celestial phenomenon known as STEVE is likely caused by a combination of heating of charged particles in the atmosphere and energetic electrons like those that power the aurora, according to new research. In a new study, scientists found STEVE's source region in space and identified two mechanisms that cause it.

Last year, the obscure atmospheric lights became an internet sensation. Typical auroras, the northern and southern lights, are usually seen as swirling green ribbons spreading across the sky. But STEVE is a thin ribbon of pinkish-red or mauve-colored light stretching from east to west, farther south than where auroras usually appear. Even more strange, STEVE is sometimes joined by green vertical columns of light nicknamed the "picket fence."

Auroras are produced by glowing oxygen and nitrogen atoms in Earth's upper atmosphere, excited by charged particles streaming in from the near-Earth magnetic environment called the magnetosphere. Scientists didn't know if STEVE was a kind of aurora, but a 2018 study found its glow is not due to charged particles raining down into Earth's upper atmosphere.

The authors of the 2018 study dubbed STEVE a kind of "sky-glow" that is distinct from the aurora, but were unsure exactly what was causing it. Complicating the matter was the fact that STEVE can appear during solar-induced magnetic storms around Earth that power the brightest auroral lights.

Authors of a new study published in AGU's journal Geophysical Research Letters analyzed satellite data and ground images of STEVE events and conclude that the reddish arc and green picket fence are two distinct phenomena arising from different processes. The picket fence is caused by a mechanism similar to typical auroras, but STEVE's mauve streaks are caused by heating of charged particles higher up in the atmosphere, similar to what causes light bulbs to glow.

"Aurora is defined by particle precipitation, electrons and protons actually falling into our atmosphere, whereas the STEVE atmospheric glow comes from heating without particle precipitation," said Bea Gallardo-Lacourt, a space physicist at the University of Calgary and co-author of the new study. "The precipitating electrons that cause the green picket fence are thus aurora, though this occurs outside the auroral zone, so it's indeed unique."

Images of STEVE are beautiful in themselves, but they also provide a visible way to study the invisible, complex charged particle flows in Earth's magnetosphere, according to the study's authors. The new results help scientists better understand how particle flows develop in the ionosphere, which is important goal because such disturbances can interfere with radio communications and affect GPS signals.

Where does STEVE come from?

In the new study, researchers wanted to find out what powers STEVE and if it occurs in both the Northern and Southern Hemispheres at the same time. They analyzed data from several satellites passing overhead during STEVE events in April 2008 and May 2016 to measure the electric and magnetic fields in Earth's magnetosphere at the time.

The researchers then coupled the satellite data with photos of STEVE taken by amateur auroral photographers to figure out what causes the unusual glow. They found that during STEVE, a flowing "river" of charged particles in Earth's ionosphere collide, creating friction that heats the particles and causes them to emit mauve light. Incandescent light bulbs work in much the same way, where electricity heats a filament of tungsten until it's hot enough to glow.

Interestingly, the study found the picket fence is powered by energetic electrons streaming from space thousands of kilometers above Earth. While similar to the process that creates typical auroras, these electrons impact the atmosphere far south of usual auroral latitudes. The satellite data showed high-frequency waves moving from Earth's magnetosphere to its ionosphere can energize electrons and knock them out of the magnetosphere to create the striped picket fence display.

The researchers also found the picket fence occurs in both hemispheres at the same time, supporting the conclusion that its source is high enough above Earth to feed energy to both hemispheres simultaneously.

Public involvement has been crucial for STEVE research by providing ground-based images and precise time and location data, according to Toshi Nishimura, a space physicist at Boston University and lead author of the new study.

Read more at Science Daily

Shedding light on the science of auroral breakups

All-sky images of the auroral breakup that occurred around 2220 UT on June 30, 2017. Photographed at Syowa Station, Antarctica. Left: five minutes before the breakup. Right: right after the breakup.

Auroras, also known as Northern or Southern lights depending on whether they occur near the North or South Pole, are natural displays of light in the Earth's sky. Typically these lights are dimly present at night. However, sometimes these otherwise faint features explode in brightness and can even break up into separate glowing hallmarks, appearing as spectacular bursts of luminous manifestations. This striking and picturesque phenomenon is known as an auroral breakup.

Now, Japanese scientists have quantitatively confirmed how energetic this phenomenon can be. Using a combination of cutting-edge ground-based technology and new space-borne observations, they have demonstrated the essential role of an auroral breakup in ionizing the deep atmosphere. The research furthers our understanding of one of the most visually stunning natural phenomena.

The findings were published in Earth, Planets and Space on January 23, 2019.

The sun fires beams of charged particles, or plasma, toward Earth. Also referred to as solar winds, this plasma is mostly made up of electrons, protons and alpha particles. When these particles interact with the Earth's magnetic field, electrical currents are carried by electrons into the Earth's atmosphere. This reaction between the electrons and their atmospheric constituents emits light of varying color and complexity, visible as an aurora. However, little is known about how energetic the electrons can be when these lights explode into the stunning lightshows known as auroral breakups. So far, the assumption has been that electrons of a specific energy level are responsible for this rare phenomenon.

In the new study, the scientists report that, contrary to conventional thinking, a specific kind of electrons with much higher energy, called radiation belt electrons, are involved in the auroral breakup. Named after their location in the Earth's radiation belt, radiation belt electrons had not been clearly associated with auroral breakups before. The research team based their conclusions on a dataset collected via advanced technology and simulations.

"Radiation belt electrons are released from the Earth's magnetic field and charge the mesosphere during auroral breakup. This fact was quantitatively confirmed by both cutting-edge ground-based and new space-borne observations," adds Ryuho Kataoka, Ph.D., associate professor at the National Institute of Polar Research and the corresponding author. "This study also provides a good example how Arase satellite and PANSY radar can collaborate to understand the connection between space and atmosphere."

In their future research endeavors, the Professor Kataoka and his team hope to understand how the radiation belt electrons are released during the short-lasting period of auroral breakup. "The ultimate goal is to understand the interplay between auroras and radiation belts," Professor Kataoka adds.

Read more at Science Daily

New kind of aurora is not an aurora at all

The atmospheric phenomenon 'STEVE' which appears as a purple and green light ribbon in the sky.

Thin ribbons of purple and white light that sometimes appear in the night sky were dubbed a new type of aurora when brought to scientists' attention in 2016. But new research suggests these mysterious streams of light are not an aurora at all but an entirely new celestial phenomenon.

Amateur photographers had captured the new phenomenon, called STEVE, on film for decades. But the scientific community only got wind of STEVE in 2016. When scientists first looked at images of STEVE, they realized the lights were slightly different than light from typical auroras but were not sure what underlying mechanism was causing them.

In a new study, researchers analyzed a STEVE event in March 2008 to see whether it was produced in a similar manner as the aurora, which happens when showers of charged rain down into Earth's upper atmosphere. The study's results suggest STEVE is produced by a different atmospheric process than the aurora, making it an entirely new type of optical phenomenon.

"Our main conclusion is that STEVE is not an aurora," said Bea Gallardo-Lacourt, a space physicist at the University of Calgary in Canada and lead author of the new study in Geophysical Research Letters, a journal of the American Geophysical Union. "So right now, we know very little about it. And that's the cool thing, because this has been known by photographers for decades. But for the scientists, it's completely unknown."

The study authors have dubbed STEVE a kind of "skyglow," or glowing light in the night sky, that is distinct from the aurora.

Studying STEVE can help scientists better understand the upper atmosphere and the processes generating light in the sky, according to the authors.

"This is really interesting because we haven't figured it out and when you get a new problem, it's always exciting," said Joe Borovsky, a space physicist at the Space Science Institute in Los Alamos, New Mexico who was not connected to the new study. "It's like you think you know everything and it turns out you don't."

A different kind of light show

Auroras are produced when electrons and protons from Earth's magnetosphere, the region around Earth dominated by its magnetic field, rain down into the ionosphere, a region of charged particles in the upper atmosphere. When these electrons and protons become excited, they emit light of varying colors, most often green, red and blue.

A group of amateur auroral photographers brought STEVE to scientists' attention in 2016. A Facebook ground called the Alberta Aurora Chasers had occasionally noticed bright, thin streams of white and purple light running east to west in the Canadian night sky when they photographed the aurora.

Auroras are visible every night if viewing conditions are right, but the thin light ribbons of STEVE were only visible a few times per year. The light from STEVE was also showing up closer to the equator than the aurora, which can only be seen at high latitudes.

The photographers first thought the light ribbons were created by excited protons, but protons can only be photographed with special equipment. The light protons produce falls out of the range of wavelengths picked up by normal cameras.

The aurora chasers dubbed the light ribbon occurrences "Steve," a reference to the 2006 film Over the Hedge. When researchers presented data about the unusual lights at a 2016 scientific conference, a fellow space physicist proposed converting the name into the backronym STEVE, which stands for Strong Thermal Emission Velocity Enhancement, and the researchers adopted it.

Where does STEVE come from?

Scientists then started using data from satellites and images from ground-based observatories to try to understand what was causing the unusual light streaks. The first scientific study published on STEVE found a stream of fast-moving ions and super-hot electrons passing through the ionosphere right where STEVE was observed. The researchers suspected these particles were connected to STEVE somehow but were unsure whether they were responsible for producing it.

After that first study, of which Gallardo-Lacourt was a co-author, the researchers wanted to find out if STEVE's light is produced by particles raining down into the ionosphere, as typically happens with the aurora, or by some other process. In the new study, Gallardo-Lacourt and her colleagues analyzed a STEVE event that happened over eastern Canada on March 28, 2008, using images from ground-based cameras that record auroras over North America.

They coupled the images with data from NOAA's Polar Orbiting Environmental Satellite 17 (POES-17), which happened to pass directly over the ground-based cameras during the STEVE event. The satellite is equipped with an instrument that can measure charged particles precipitating into the ionosphere.

The study's results suggest STEVE is an entirely new phenomenon distinct from typical auroras. The POES-17 satellite detected no charged particles raining down to the ionosphere during the STEVE event, which means it is likely produced by an entirely different mechanism, according to the authors.

Read more at Science Daily

The Northern Lights Make Strange Sounds: Here's Why

For more than 15 years, a lone scientist in southern Finland has spent countless winter nights among the snowy fields and frozen lakes around his village, in pursuit of one of the most ephemeral mysteries of the heavens: the faint, almost phantasmagorical sounds heard during intense displays of the aurora borealis, or northern lights.

The epic study by acoustician Unto K. Laine includes the first audio recordings of the muffled crackling or popping sometimes heard overhead during spectacular aurora displays.

Over the years, the sounds of the northern lights have been explained as illusions, imagination, inebriation or even voices from the spiritual world.

But Laine has shown the sounds are real, and he thinks he has found what causes them: sparks of electricity discharging beneath the aurora in an inversion layer of the atmosphere that can form in clear and calm weather conditions.

Laine told Live Science that he became interested in the phenomenon of so-called auroral acoustics about 25 years ago, when he and his friends heard sounds from an aurora after a nighttime music gathering in Finnish Lapland, in the far north of the country.

"This experience never left me. We had to concentrate — we did not move or talk at all," he said. "A few of us did not hear it, because at that time, the aurora wasn't very strong, and it was a very low-intensity sound. I could never forget this experience; it was so strange."

In 2000, Laine started to keep a careful watch on space weather forecasts for reports of intense solar flares that could supercharge auroras over the following nights. Auroras are caused by charged particles from solar flares interacting with the Earth's magnetic field and raining into the upper atmosphere, where they excite the nitrogen and oxygen atoms of the air to create the dramatic and colorful light shows.

"During all these years, I have checked the space weather two to three times a day, so not to miss any aurora events — and always, when the weather conditions are good, I go," he said.

Sounds out of space

Laine's solitary hunt for the elusive sound of the northern lights demanded great patience. There have been few intense auroras over Finland in the past 16 years, thanks in part to the "solar minimum," a period of decreased activity in the sun's natural 11-year solar cycle. Between 2004 and 2007, the sun experienced a lull in activity, according to NASA, which meant fewer solar flares and fewer auroras. In 2011, as solar activity ramped up, Laine started using a VLF loop antenna to measure magnetic fields and a microphone array to triangulate the locations of crackles and pops in the ever-changing sounds from the aurora.

"The sounds are diverse and can vary quite a lot, and it is very possible that there are many different mechanisms creating the sounds," he said. "I have been concentrating more on the clapping, popping and crackling, because they are good for estimating the direction of the sound."

In September 2011, during an intense aurora overhead, Laine's microphone array was able to triangulate the locations of several distinct "clap" sounds from the celestial display. To his surprise, the results showed the sounds were originating just 230 feet (70 meters) above the ground — much lower than the auroras themselves, which occur at altitudes of up to 300 kilometers (185 miles).

Laine's unexpected discovery partly explained one of the mysteries of the acoustics of auroras: How can faint sounds from auroras so high in the atmosphere be heard at the surface of the Earth?

In a research paper published in 2012, which included the first recordings of auroral sounds ever made, Laine also ruled out a theory that the sounds could be made by trees, because his microphones had been set in open fields and beside frozen lakes.

The acoustics of auroras

Now, Laine thinks he may have discovered a mechanism in the atmosphere that explains at least some of the sounds caused by auroras.

During an intense display of the northern lights over southern Finland on March 17 and 18, 2013, when the temperature in the village of Fiskars was minus 4 degrees Fahrenheit (minus 20 degrees Celsius), Laine recorded hundreds of auroral sound events.

He also measured magnetic pulses that occurred immediately before each sound event, which corresponded in strength to the volume of the sounds.

Then, Laine matched his measurements to data from the Finnish Meteorological Institute for the same night, and found they had measured a thermal inversion layer in the atmosphere — a blanket of relatively warm air that traps cold air next to the ground in calm conditions — at the same altitude where the noises originated.

Read more at Discovery News