Jan. 29, 2020: A new type of aurora is rippling across Arctic skies. Citizen scientists who discovered it nicknamed it “The Dunes” because of its resemblance to desert sand dunes. A paper published in the Jan. 28th issue of AGU Advances describes the new form and the unexpected physics that causes it.

Dune-shaped auroras form in a narrow altitude range 80 km to 120 km above Earth’s surface. Turns out, this is an extremely hard-to-study layer of Earth’s atmosphere. It’s too high for weather balloons, and too low for rockets.

“Due to the difficulties in measuring atmospheric phenomena between 80 and 120 km, we sometimes call this region ‘the ignorosphere‘,” says Minna Palmroth, Professor of Computational Space Physics at the University of Helsinki and the lead author of the study.

Sky watchers in the Arctic have been seeing Dunes for years without understanding what they were. A breakthrough came on Oct. 7, 2018, when multiple groups photographed the dunes from widely separated locations in Finland. Maxime Grandin, a postdoctoral researcher in Palmroth’s team, analyzed the images, using triangulation techniques to decipher the Dune’s geometry.

Conclusion: Dunes are located ~100 km high–smack-dab in the middle of the ignorosphere–and have a pure, monochromatic wavelength of about 45 km.

The research team believes the Dunes are a “mesospheric bore”–a type of atmospheric gravity wave that springs up from the surface below and gets caught in a thermal waveguide ~100 km high. When solar wind particles rain down on the bore, they illuminate its rippling structure.

The discovery of Dunes may allow researchers to study the ignorosphere as never before. Monitoring Dunes can reveal previously hidden waves and waveguides at the boundary between Earth and space. Aurora photographers, have you seen a Dune? Submit your photos here.

Note: This research was made possible by ordinary people paying close attention to the sky. The first report of aurora dunes in Oct. 2015 came from Mikko Peussa, an aurora photographer in Finland. Next, Matti Helin learned of the phenomenon and managed to get researchers interested. Helin participated in subsequent breakthrough observations, and joined 6 other amateurs (P. Koski, A. Oksanen, M. A. Glad, R. Valonen, K. Saari and E. Bruus ) on the AGU Advances paper.

Jan. 16, 2019: Yes, there are explosions in Earth’s magnetic field. They happen all the time. Gusts of solar wind press against Earth’s magnetosphere, squeezing lines of magnetic force together. The lines criss-cross and reconnect, literally exploding and propelling high energy particles toward Earth.  Auroras are the afterglow of this process.

On Dec. 20, 2015, one such explosion occurred closer to Earth than anyone had seen before.  It has taken researchers 4 years to fully wrap their minds around what happened, and the results were published just this week in the Jan. 13, 2020, edition of Nature Physics.

Lead author Vassilis Angelopoulos of UCLA explains: “Usually, these explosions happen at least 100,000 miles from Earth, far downstream in our planet’s magnetic tail. On Dec. 20, 2015, however, we observed a reconnection event only 30,000 miles away–more than 3 times closer than normal.”

It was a case of good luck and perfect timing. NASA’s swarm of three THEMIS spacecraft were passing through the area, and they were able to pinpoint the explosion’s location “right on the doorstep” of the geosynchronous satellite belt. This showed reconnection events may pose a previously overlooked threat to Earth-orbiting satellites. The nearby blast caused a strong G2-class geomagnetic storm and intense auroras around the Arctic Circle.

Angelopoulos estimated the energy involved. “The explosion and subsequent storm delivered as much as ~88 PetaJoules of energy to the near-Earth environment. That’s more than 10 times the energy of the largest US nuclear bomb and about 20 times the energy of a magnitude 7 earthquake.”

Before this event, many researchers felt that reconnection at such proximity was impossible. Earth’s nearby magnetic field was too stable for such explosions … or so the thinking went.

“Now we know better,” Angelopoulos says. “The THEMIS multipoint observations are iron-clad. It really happened, and this is going to make a big impact on future studies of geomagnetic storms.”

The original research in Nature Physics may be found here.

 

Jan. 10, 2020: One day, perhaps in our lifetimes, perhaps a million years from now, the red giant Betelgeuse will dim a little–and then explode. The resulting supernova will rival the full Moon and cast shadows after dark, completely transforming the night skies of Earth. No wonder astronomers are closely tracking the current “fainting of Betelgeuse.”

“Fainting” is an actual astronomical term. It means dimming, the opposite of brightening. And right now, Betelgeuse is definitely fainting.

Edward Guinan of Villanova University and colleagues caused a minor sensation last month when they reported “[Betelgeuse] has been declining in brightness since October 2019, now reaching a modern all-time low of V = +1.12 mag on 07 December 2019 UT. Currently this is the faintest the star has been during our 25+ years of continuous monitoring.”

Little did they know when they issued their telegram in December that Betelgeuse was about to become even fainter. “On 06 January 2020 UT, the magnitude of Betelgeuse was V = +1.37,” reports Guinan. That’s 20% dimmer than the “modern all-time low” registered last month.

This 3-year plot of the Villanova team’s data shows Betelgeuse’s rapid decline:

The horizontal axis is Heliocentric Julian Date (HJD). For reference, Jan. 6, 2020, the date of the most recent measurement, has an HJD of 2458855.

The fainting is easy to see with the naked eye. Not too long ago, Betelgeuse was the 10th brightest star in the sky. Now it is the 21st. Observers of Orion rising in the east after sunset can’t help but notice that the Hunter’s shoulder is dimmer than it used to be.

Astronomers have long known that Betelgeuse is on the precipice of an energy crisis. It’s about to run out of fuel in its core. When that happens, the star will collapse and rebound explosively, producing the first bright supernova in the Milky Way since 1604. Experts in stellar evolution believe Betelgeuse could die at any time during the next 100,000 years or so–a blink of an eye on time scales of astronomy.

Does the current dimming herald that final blast? Probably not. Betelgeuse is a slowly variable star, and this is probably no more than an episode of deeper-than-usual dimming. Of course, one day astronomers will think the same thing … and then the night sky will change forever.

Stay tuned for updates.

Jan. 9, 2020: The finest outbreak of polar stratospheric clouds (PSCs) in decades is still going strong. “We witnessed a wonderful display this evening (Jan. 8th),” reports Alex Conu, who photographed the clouds drawing a crowd in Oslo, Norway:

“The cloud’s bright pastel colors looked fabulous alongside Venus in the evening sky,” he says.

Polar stratospheric clouds are rare. Normally, the stratosphere has no clouds at all. A few times each winter, however, icy clouds form when the temperature in the stratosphere drops below -85C. Such staggeringly-low temperatures are required to help sparse water molecules stick together. This winter, the clouds have been appearing daily since late December, a sign of unusually cold conditions in the stratosphere.

Stratospheric clouds are widely regarded as the most beautiful clouds on Earth. Because of their intense colors (caused by high-altitude sunlight hitting tiny ice crystals), novice sky watchers sometimes mistake the clouds for auroras. This picture from P-M Hedén of Tänndalen, Sweden, shows why:

“On Jan. 4th, the colors got so strong that the snow turned red,” marvels Hedén. “I have been seeing these crazy displays at both sunrise and sunset from my cabin in the Swedish mountains.”

Stay tuned for updates as the outbreak continues.

Jan. 7, 2019: Yesterday, Jan. 6th, something unexpected happened in the soil of northern Norway. “Electrical currents started flowing,” reports Rob Stammes, who monitors ground currents at the Polarlightcenter geophysical observatory in Lofoten. This chart recording shows the sudden surge around 1930 UT:

“It seemed to be some kind of shockwave,” says Stammes. “My instruments detected a sudden, strong variation in both ground currents and our local magnetic field. It really was a surprise.”

NASA’s ACE spacecraft detected something as well. About 15 minutes before the disturbance in Norway, the interplanetary magnetic field (IMF) near Earth abruptly swung around 180 degrees, and the solar wind density jumped more than 5-fold. Earth may have crossed through a fold in the heliospheric current sheet–a giant, wavy membrane of electrical current rippling through the solar system. Such crossings can cause these kind of effects.

While currents flowed through the ground, auroras filled the sky. Rayann Elzein photographed the corresponding outburst of lights from Utsjoki, Finland:

“What a surprise!” says Elzein. “The auroras were sudden and dynamic, with fast-moving green needles and several purple fringes!”

The auroras and ground currents were caused by the same thing: Rapidly changing magnetic fields. High above Earth’s surface, magnetic vibrations shook loose energetic particles, which rained down on the upper atmosphere, creating auroras where they struck. Just below Earth’s surface, magnetic vibrations caused currents to flow, triggering Rob Stammes’ ground sensors.

“We couldn’t see the auroras in northern Norway because of cloud cover,” says Stammes, a little ruefully. “We had to be satisfied with the electricity underfoot.”

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Jan. 1, 2020: A spectacular display of polar stratospheric clouds (PSCs) that began two days ago is still going strong around the Arctic Circle. This picture, taken on Dec. 31st by Per-Anders Gustavsson in Jukkasjärvi, Sweden, shows why some onlookers mistake them for daytime auroras:

“The colors were amazing,” says Gustavsson, who drives a tour bus for Visit Abisko. “I was driving by the world-famous Ice Hotel when we saw the clouds. We just had to stop for pictures.”

“I’ve seen a lot of beautiful things during my years in the Arctic,” he adds. “This was easily one of the greatest displays I have ever seen.”

Polar stratospheric clouds are newsworthy because normally the stratosphere has no clouds at all. The stratosphere is arid and almost always transparent. Only when the temperature drops to a staggeringly cold -85C can sparse water molecules assemble themselves into icy stratospheric clouds. PSCs are far more rare than auroras.

The clouds are even visible at night, as shown in this Dec. 31st photo taken by Fredrik Broms in Kvaløya, Norway:

“Better than New Year fireworks – by far!” says Broms. “What an amazing way to end 2019.”

“This really is a rare event,” says Chad Blakley, who runs the Lights over Lapland aurora tour service in Abisko, Sweden. “Local villagers in both Abisko and Kiruna who are more than 70 years old confirmed they have never seen anything of the size, scale, or intensity. At one point I would say that close to 25% of the sky was filled with the clouds. PSCs we have seen in previous winters have been closer to 1% or 2%.”

Polar stratospheric clouds are intensely colorful because they are made of a special type of ice. High-altitude sunlight shining through microscopic crystals only ~10µm across produce a bright iridescent glow unlike the lesser iridescence of ordinary tropospheric clouds.

Stay tuned for updates as the outbreak continues.