A new source of solar flares is emerging over the sun's southeastern limb. On May 15th (1438 UT), it emitted a dramatic X3-class explosion, shown here in a movie from NASA's Solar Dynamics Observatory:

Extreme ultraviolet radiation from the flare ionized the top of Earth's atmosphere, causing a shortwave radio blackout over the Atlantic Ocean. Ham radio operators, aviators and mariners may have noticed a sudden loss of signal at all frequencies below 30 MHz.
The source of this flare will rotate over the sun's limb this week, making future explosions more squarely Earth-directed and potentially hurling CMEs in our direction. Stay tuned!
https://spaceweather.com/

Giant sunspot AR3664 is no longer facing Earth. That makes it extra dangerous. The Carrington-class sunspot is passing over the sun's western limb--a region of the sun that is magnetically connected to our planet. Indeed, we are feeling the effects of that connection right now; take a look at this map of ongoing radio blackouts:

Red zones in the map show where shortwave radio signals are being absorbed. Inside the Arctic Circle, frequencies below 30 MHz are almost completely blacked out, a nuisance for polar aviators and ham radio operators.
What's causing this? Protons accelerated by solar flares in the magnetic canopy of AR3664 are following the Parker Spiral back to Earth. Think of it as a magnetic superhighway. The arriving particles are funneled by our planet's magnetic field toward the poles where they ionize the atmosphere and interfere with the normal transmission of shortwave radio.
This polar cap absorption event could last for days, especially if it is boosted by more flares from AR3664. You can can monitor its progress here.
https://spaceweather.com/

Sunspot AR3664 just unleashed the strongest solar flare of the current solar cycle--an X8.7-category blast from beyond the sun's western limb. X marks the spot in this image of the flare from NASA's Solar Dynamics Observatory:

Because the sunspot is behind the edge of the solar disk, the flare was partially eclipsed. It was probably even stronger than it appeared. "X8.7" is almost certainly an underestimate of the flare's true strength.
Extreme ultraviolet radiation from the flare ionized the top of Earth's atmosphere, causing a deep shortwave radio blackout over the Americas. Ham radio operators, aviators and mariners may have noticed a sudden loss of signal at all frequencies below 30 MHz.
Subatomic debris from this event might soon reach Earth, guided toward our planet by the Parker Spiral. Also, a CME might be in the offing. Stay tuned for updates!
https://spaceweather.com/

NOAA models confirm that a Cannibal CME will strike our planet on Dec. 1st. Cannibal CMEs form when a fast CME sweeps up a slower CME ahead of it. The combination contains intense, tangled magnetic fields that can do a good job sparking auroras when they reach Earth. If a Cannibal CME strikes Earth on Dec. 1st, as predicted, geomagnetic storm levels could reach category G3 (Strong). If so, here's what we can expect. The last G3-class storm on Nov. 5th sparked not only bright auroras, but also deep-red SAR arcs around the world. Greg Redfern photographed this example from the Shenandoah National Park in Virginia:

"I didn't realize I had photographed an SAR arc until I processed my images the next day, stitching two of them together to reveal its shape," says Redfern.
SAR arcs look like auroras, but they are not. They are the glow of heat energy leaking into the upper atmosphere from Earth's ring current system–a donut-shaped circuit carrying millions of amps around our planet. During the Nov. 5th geomagnetic storm, these red arcs were observed as far south as Texas and California.
Auroras were observed as well -- "and they were INSANE," says Janne Maj Nagelsen, who watched the display from Stamnes, Vaksdal, Norway:

"I have never seen such strong auroras," says Nagelsen. "Not to mention the colors. I mean look at the picture! They were totally, literally insane."

Auroras are caused by charged particles raining from space down upon Earth's atmosphere. Unlike SAR arcs, which are pure red, auroras can have a rich and stunning variety of colors. Both phenomena may be photographed on Dec. 1, 2023, when a Cannibal CME is expected to hit Earth.
https://spaceweather.com/

If you're a satellite, this story is important. A series of geomagnetic storms in 2023 has pumped terawatts of energy into Earth's upper atmosphere, helping to push its temperature and height to a 20-year high. Air surrounding our planet is now touching satellites in Earth orbit and dragging them down.
"Blame the sun," says Martin Mlynczak of NASA Langley. "Increasing solar activity is heating the top of the atmosphere. The extra heat has no effect on weather or climate at Earth's surface, but it's a big deal for satellites in low Earth orbit."

Mlynczak is an expert on the temperature up there. For 20 years he has been using the SABER instrument on NASA's TIMED satellite to monitor infrared emissions from "the thermosphere," the uppermost layer of the atmosphere."Right now we’re seeing some of the highest readings in the mission's 21.5 year history," he says.
The thermosphere is exquisitely sensitive to solar activity, readily absorbing energy from solar flares and geomagnetic storms. These storms have been coming hard and fast with the recent rise of Solar Cycle 25.
"There have been five significant geomagnetic storms in calendar year 2023 that resulted in marked increases in the amount of infrared radiation (heat) in Earth's thermosphere," says Mlynczak. "They peaked on Jan. 15th (0.59 TW), Feb. 16th (0.62 TW), Feb. 27th (0.78 TW), Mar. 24th (1.04 TW), and April 24th (1.02 TW)."
The parenthetical values are TeraWatts (1,000,000,000,000 Watts) of infrared power observed by SABER during each storm. The sensor obtains these numbers by measuring infrared radiation emitted from nitric oxide and carbon dioxide molecules in the thermosphere.

"The two storms exceeding 1 TW are the seventh and eighth strongest storms observed by SABER over the past 21.5 years," he says. "It is interesting to note that each successive storm in 2023 is generally stronger than its predecessors."Actually, it doesn't take a strong storm to cause problems. In Feb. 2022, a minor geomagnetic storm dumped enough heat into the thermosphere that 38 newly launched Starlink satellites fell out of the sky. SpaceX has since started launching their Starlinks to higher initial altitudes to avoid the drag.
If current trends continue, the thermosphere will warm even more in 2023 and 2024. This is a matter of concern because Earth's population of active satellites has tripled since SpaceX started launching Starlinks in 2019. The growing constellation of 4100 Starlinks now provides internet service to more than a million customers. An extreme geomagnetic storm like the Halloween Storms of 2003 could shift the positions of these satellites by many 10s of kilometers, increasing the risk of collisions and causing some of the lowest ones to de-orbit.
Stay tuned as the warming continues.
https://spaceweather.com

BBC:  Sat, 27 May 2023 14:01 UTC

Much of northern England enjoyed a rare optical display on Sunday evening.  Thin, high cloud gave a spectacular show of halos, arcs and upside-down rainbows across the North East and Cumbria, not often seen together in the UK.  The phenomena are caused by sunlight reflecting and refracting through ice crystals high in the atmosphere.

BBC Look North weather presenter Jennifer Bartram said it was "very unusual".  "The particular angle at which the sunlight hits these high-up ice crystals form these patterns," she said.  "It's a real delight to see."

The rings around the Sun are known as halos and have a reddish tinge on the inner edge.

Though halos are not uncommon in the UK, the combination of other optical effects is more unusual.

One of the more unusual features spotted was an upside-down rainbow, known as a cirumzenithal arc.  It is also known as a Bravais' arc, and is formed when sunlight enters horizontal ice crystals and refracts through a side prism face, which causes the upside-down effect.

Also visible were a range of other effects, including parhelia - or sun dogs - which appear as bright patches either side of the sun.

A parhelic circle is an unforgettable sight. Thin and pale, it circles the zenith in a majestic arc, always keeping the same distance above the horizon. Two days ago, R. J Cobain saw this one over Conlig, Northern Ireland:

"I was shaking as I took as many photos as I could," says Corbin. "By combining 11 photos I was able to capture the full circle."
This was part of a great display of ice halos widely seen and reported across Northern Ireland and Northern England on May 28th. A weather system blanketed the region with a rare mixture of gem-like ice crystals in wispy cirrus clouds. Sunlight shining through the crystals produced a stunning variety of forms.
A full parhelic circle is among the rarest of ice halos. It requires as many as five internal reflections from millions of individual ice crytals, all catching sunbeams simultaneously. "This was by far the best display of atmospheric optics I have ever seen," Corbin says.
more images: from Alan Fitzsimmons of Belfast, Northern Ireland; from Mike Devenport of Gateshead, UK; from Ian Lee of Carlisle, Cumbria, UK.
https://spaceweather.com/

Chinese astrophotographer Jeff Dai has long dreamed of seeing auroras over his home country. "On April 24th, my dream came true," he says. A severe geomagnetic storm was underway when he drive to the countryside outside Karamay, Xinjiang, China, and photographed a sky full of Northern Lights:

"I could see them with my naked eye," he says. "It was truly spectacular!"
But there's more to the story. Only a fraction of the lights he saw were actual auroras. Note the red arc at the top of his photo. That's something else--an "SAR."
SARs are red arcs of light that ripple across the sky during some geomagnetic storms. They were discovered in 1956 at the beginning of the Space Age. Researchers didn’t know what they were and unwittingly gave them a misleading name: "Stable Auroral Red arcs" or SARs.
In fact, SARs are neither stable nor auroras. Auroras appear when charged particles rain down from space, hitting the atmosphere and causing it to glow like the picture tube of an old color TV. SARs form differently. They are a sign of heat energy leaking into the upper atmosphere from Earth’s ring current system--a donut-shaped circuit of plasma carrying millions of amps around our planet.

SARs are among the reddest things in the sky, with a monochromatic glow at 6300 Å that comes from atomic oxygen in the upper atmosphere. The human eye is relatively insensitive to light at this wavelength, but cameras record the color easily. Pro tip for photographers: Use a 6300 Å filter.
"Seeing auroras from China is very difficult," says Dai. "It happens maybe 1-2 times every 11 years." Seeing an SAR is even more rare. It was a dreamy night, indeed.
www.spaceweather.com

Pink auroras are rare. Pulsating auroras are rare, too. Last night in Abisko, Sweden, sky watchers witnessed both rarities at the same time. Hit PLAY to make the sky pulse:

"My guides who photographed the display couldn't believe their eyes," says Chad Blakley, the owner of Lights over Lapland. "They are all saying things like 'I have never seen anything like this before!' and one of them described it as 'a glitch in the Matrix.'"
Pulsating auroras are Blakley's favorite: "The best way to describe a pulsating aurora is to imagine the sky as a large checker board," he says. "As the pulsating begins, black squares on the board would illuminate as a green aurora. Then, in an instant, all the black squares lose their illumination and the red squares on the imaginary checkerboard immediately glow green."
In this case, however, the green was pink. Pink auroras appear when solar wind particles penetrate unusually deep in Earth's atmosphere, striking nitrogen molecules less than 100 km above our planet's surface. A crack in Earth's magnetic field on Oct. 3rd let the particles reach that level.
Pulsating auroras are so mysterious, NASA keeps launching rockets into them to learn what makes them tick. In 2018, researchers led by S. Kasahara of the University of Tokyo conclusively linked pulsating auroras to "chorus waves" in Earth's magnetosphere. Their findings explain everything -- except the shape of the 'squares' and why they blink so quickly. Keep launching rockets, NASA.
www.spaceweather.com

September 20, 2021 / Dr.Tony Phillips - NASA

Sept. 24, 2021: No solar storms? No problem. Earth has learned to make its own auroras. New results from NASA’s THEMIS-ARTEMIS spacecraft show that a type of Northern Lights called “diffuse auroras” comes from our own planet – no solar storms required.

Diffuse auroras look a bit like pea soup. They spread across the sky in a dim green haze, sometimes rippling as if stirred by a spoon. They’re not as flamboyant as auroras caused by solar storms. Nevertheless, they are important because they represent a whopping 75% of the energy input into Earth’s upper atmosphere at night. Researchers have been struggling to understand them for decades.

Above: Diffuse auroras and the Big Dipper,
photographed by Emmanuel V. Masongsong in Fairbanks, AK

“We believe we have found the source of these auroras,” says UCLA space physicist Xu Zhang, lead author of papers reporting the results in the Journal of Geophysical Research: Space Physics and Physics of Plasmas.

It is Earth itself.

Earth performs this trick using electron beams. High above our planet’s poles, beams of negatively-charged particles shoot upward into space, accelerated by electric fields in Earth’s magnetosphere. Sounding rockets and satellites discovered the beams decades ago. It turns out, they can power the diffuse auroras.

The video below shows how it works. The beams travel in great arcs through the space near Earth. As they go, they excite ripples in the magnetosphere called Electron Cyclotron Harmonic (ECH) waves. Turn up the volume and listen to the waves recorded by THEMIS-ARTEMIS:

Above: A great electrical circuit in space powering diffuse auroras. ECH waves were sonified by NASA’s HARP (Heliophysics Audified: Resonances in Plasmas) software.

ECH waves, in turn, knock other electrons out of their orbits, forcing them to fall back down onto the atmosphere. This rain of secondary electrons powers the diffuse auroras.

“This is exciting,” says UCLA professor Vassilis Angelopoulos, a co-author of the papers and lead of the THEMIS-ARTEMIS mission. “We have found a totally new way that particle energy can be transferred from Earth’s own atmosphere out to the magnetosphere and back again, creating a giant feedback loop in space.”

According to Angelopoulos, Earth’s polar electron beams1 sometimes weaken but they never completely go away2, not even during periods of low solar activity. This means Earth can make auroras without solar storms.

The sun is currently experiencing periods of quiet as young Solar Cycle 25 sputters to life. Pea soup, anyone?  [Note: Solar Cycle 25 is accelerating.  MS}

End Notes:

(1) Why do these electron beams exist? Earth’s magnetosphere is buzzing with energetic particles. Many of them are captured from the solar wind. When these particles strike the top of Earth’s atmosphere (the ionosphere), they dislodge electrons. Electric fields, which form naturally in Earth’s spinning magnetosphere, grab the liberated electrons and accelerate them skyward in collimated beams.

(2) Why don’t the beams ever go away? Short answer: because the solar wind never stops blowing. Even when the sun is quiet, Earth’s magnetosphere is jostled and energized by the ever-present solar wind. As a result, electrons are always being knocked off the top of Earth’s atmosphere as described in Note #1. Although solar storms are not required for this process, solar storms can help. For instance, when a CME strikes Earth’s magnetosphere, the contents of the magnetosphere become extra-energized. Lots of particles furiously strike the top of Earth’s atmosphere, liberating even more electrons than usual. Earth’s electron beams can thus become super-charged. When the storm subsides, the electron beams may weaken, but they never vanish because even the quiet sun produces solar wind.

References:

Zhang, X., Angelopoulos, V., Artemyev, A. V., Zhang, X.-J. (2021), Beam-driven ECH waves: A parametric study, Phys. Plasmas, 28, 072902, https://doi.org/10.1063/5.0053187

Zhang, X., Angelopoulos, V., Artemyev, A. V., Zhang, X.‐J., Liu, J. (2021). Beam‐driven electron cyclotron harmonic waves in Earth’s magnetotail. Journal of Geophysical Research: Space Physics, 126, e2020JA028743. https://doi.org/10.1029/2020JA028743s

https://spaceweatherarchive.com/2021/09/20/earth-can-makes-its-own-auroras/

Although STEVE is not an aurora, he has an aurora side-kick: the "picket fence." Evenly-spaced blobs of green light often appear alongside or underneath STEVE during geomagnetic storms. Alan Dyer photographed these specimens on March 13th:

"STEVE put on a great show, appearing first as the characteristic purple arc then developing green picket fence fingers rippling from east to west," says Dyer.
What are these green pickets? A team of researchers led by Toshi Nishimura of Boston University may have found the answer. Using data from NASA's THEMIS spacecraft, they pinpointed STEVE's power source. More than 22,000 km above Earth's surface, magnetic explosions called "substorms" hurl streams of hot plasma toward Earth. When the streams reach an altitude ~250 km above Earth's surface, they begin to emit a soft-purple light. This is STEVE.
The same explosions spray energetic electrons toward Earth. The electrons move even deeper into the atmosphere, all the way down to 100 km, where they ignite fingers of green auroras. This is the picket fence.
So when you see STEVE, look for his sidekick as well. Sometimes the picket fence appears first, so one can herald the other. Either way, it's a beautiful show.
www.spaceweather.com

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.

Above: An artists' concept of a mesospheric bore trapped in a high-altitude waveguide. [more]

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.
www.spaceweather.com

MIT Technology Review; Fri, 21 Jun 2019 18:43 UTC

The Tibetan Plateau is a vast elevated plain almost five kilometers above sea level, sometimes called the Roof of the World. It is bordered to the south by the world's highest mountain range and to the north by desert lands. It is one of the most isolated places on Earth.

But the extreme altitude makes it a useful place for scientists. In 1990, they built an observatory here to study the showers of subatomic particles that rain down from the upper atmosphere whenever it is hit by a high-energy cosmic ray. This work is better done at high altitude because there is less atmosphere to absorb the particles.

Since then, the so-called Tibet Air Shower Array has recorded vast numbers of high-energy cosmic rays, particles accelerated to huge energies by astrophysical phenomena such as supernovas, active galactic nuclei, and mysterious as-yet-unidentified sources.

But the array also picks up air showers caused by a different source - high-energy photons. These mysterious photons are also created by astrophysical phenomena such as the interaction between high-energy particles and the cosmic microwave background. Consequently, they can provide a unique insight into these processes and the environments in which they occur.

Over the years, the Tibet Air Shower Array has spotted plenty of these photons with energies up to dozens of teraelectronvolts (TeV 1012). That's roughly equivalent to the highest-energy photons that can be created on Earth. But nobody has ever observed more powerful photons.

Until now. Today, researchers from the Tibet Air Shower Gamma Collaboration say they have observed photons with energies above 100 TeV for the first time, including a remarkable photon with an energy of almost 500 TeV. This single photon has about the same energy as a falling Ping-Pong ball and is the highest-energy photon ever recorded.

The collaboration has also worked out where these photons are coming from: the Crab Nebula, the remnants of a supernova that occurred in 1054 AD in the Perseus Arm of the Milky Way, some 6,500 light-years from Earth.

.... read more at https://www.sott.net/article/415559-Earth-hit-by-highest-energy-photons-ever-recorded-from-the-Crab-Nebula

Friday night (April 5th) in Norway, researchers at the Andøya Space Center launched two sounding rockets into a minor geomagnetic storm. The results were out of this world. Aurora tour guide Kim Hartviksen photographed glowing blobs of blue and purple caused by the rockets dumping chemical powders into the storm:

"Residents for hundreds of miles were taken by surprise by these strange lights, which prompted calls to the police and 'The aliens are coming!' hysteria!" says Chris Nation who runs the Aurora Addicts guiding service.

When the night began, Nation, Hartviksen, and their clients were treated to a display of auroras, ignited by a stream of solar wind buffeting Earth's magnetic field. "As the auroras started to ebb away, our friends at Andøya launched their rockets into the fading lights," says Nation. "The show began anew as the rockets released their payload into the upper atmosphere."

An automated webcam operated by Chad Blakely of Lights over Lapland in Abisko, Sweden, caught the first puffs of powder emerging from the rockets. "It looked like an invasion of UFOs," says Blakley.

"Soon the glowing blobs evolved into more complicated structures--like two giant squid dancing in the northern sky with an impressive aurora display as its backdrop," decribes Blakley. "Our webcam has been taking a picture every five minutes for nearly 10 years. These images are by far the most exciting I've ever seen it record."

The name of the sounding rocket mission is AZURE--short for Auroral Zone Upwelling Rocket Experiment. Its goal is to measure winds and currents in the ionosphere, a electrically-charged layer of the Earth's atmosphere where auroras appear. Specifically, the researchers are interested in discovering how auroral energy might percolate down toward Earth to influence the lower atmosphere.

The twin rockets deployed two chemical tracers: trimethyl aluminum (TMA) and a barium/strontium mixture. These mixtures create colorful clouds that allow researchers to visually track the flow of neutral and charged particles, respectively. According to NASA, which funded the mission, the chemicals pose no hazard to residents in the region.

Update--a movie! "Here is my realtime video of the surprise rocket launch last night from NASA/ASC," reports Ole Salomonsen of Tromsø, Norway. "I was shocked when I saw this in the night sky facing north, I was not aware of the launch.
www.spaceweather.com

Last weekend, Nov. 10th, a stream of fast-moving solar wind hit Earth's magnetic field, igniting a ring of auroras around the South Pole. Minoru Yoneto saw the red-purple glow all the way from Queenstown, New Zealand:

"We were lucky to catch another Southern Lights display during my stargazing tour," says Yoneta. "Our guests were excited to photograph them using their own cameras."

Queenstown is at 45 degrees south latitude--a considerable distance from the South Pole. That's why the auroras looked red. Auroras circling the South Pole must reach very high above Earth's surface to be visible half a hemisphere away. At altitudes greater than ~200 km, auroras turn red. The ruby glow occurs when high energy particles from space hit oxygen atoms at the top of the atmosphere. Ionized molecular nitrogen adds a dash of purple to the high-altitude palette.

More red Southern Lights are possible on Nov. 18th or 19th when a new stream of solar wind is expected to arrive. The gaseous material is flowing from a relatively small hole in the sun's atmosphere. Queenstown stargazers, charge your cameras!
www.spaceweather.com