“Daytime Auroras” … a.k.a. Polar Stratospheric Clouds

Feb. 15, 2017: On Feb. 13th, something amazing happened in the stratosphere over the Arctic Circle. Normally, the air 60,000+ feet above Earth’s surface is dry and utterly transparent.  On the eve of Valentine’s Day, however, the Arctic stratosphere filled with a gossamer haze of crystalline ice, and when sunlight hit the freezing crystals, the sky filled with clouds of intense iridescent color.

“Our guests referred to the clouds as ‘daytime auroras,'” reports Chad Blakley, who operates the Lights over Lapland tour guide service in Abisko, Sweden. One of them, Champ Cameron (@champcameron on Instagram), snapped this picture of the display:

“Champ was participating in our Sami And Reindeer Experience outside of Abisko yesterday afternoon,” explains Blakley. “The roads were very icy due to a freak rain storm and warm weather (+9 degrees C) so we nearly canceled the trip. But we heard that there were incredible clouds in the sky so we chose to brave the weather and push on.”

Good thing. They witnessed an exceptional display of polar stratospheric clouds (PSCs). PSCs are a sign of very cold temperatures in the stratosphere. For ice crystals to form in the normally arid stratosphere, temperatures must drop to around -85º C. So while it was strangely warm on the ground below, it was incredibly cold up above.

Longtime observers say PSCs are becoming more common and more intense. “I’ve been living here all my life (33 years),” says Mia Stålnacke of Kiruna, Sweden, who also photographed the colorful outbreak. “I definitely feel that these clouds are appearing more often then they used to. I remember seeing them a few times/year since I was a kid, but these last couple of years we’ve had them much more often–sometimes for almost a week straight. Others seem to feel the same way; I see local groups on Facebook flooded with photos of PSCs and comments on how often they’re appearing now.”

“Our bus driver, a longtime resident of the area, described it as the best PSC display he had ever seen,” relays Blakley. “We were overwhelmed by the natural beauty.” The clouds were so intense, they remained visible even after the sun set:

“We saw these clouds all day long, and they continued into the night,” says photographer Lars Lehnert of Abisko, Sweden. ” I’ve never seen anything quite like it.”

Once thought to be mere curiosities, some PSCs are now known to be associated with the destruction of ozone. Indeed, an ozone hole formed over the UK in Feb. 2016 following an outbreak of ozone-destroying Type 1 PSCs.

To investigate these clouds further, Spaceweather.com and the students of Earth to Sky Calculus will travel to Abisko Sweden for a week in March 2017.  We plan to launch a series of space weather balloons into the Arctic stratosphere, measuring temperature, air pressure, and ambient radiation.  If PSCs are present, our sensors will pass directly through them, and our cameras can photograph the colorful clouds at point blank range. Stay tuned!

Realtime PSC Photo Gallery

Polar Stratospheric Clouds at Night

Feb. 14, 2017: Arctic nights are usually colored by the aurora borealis. Last night was different. The colors came from polar stratospheric clouds (PSCs). Lars Lehnert photographed the display from Abisko, Sweden:

“We saw these clouds all day long,” says Lenart, “and they continued into the night. I’ve never seen anything quite like it.”

In Kiruna, Sweden, longtime PSC photographer Mia Stålnacke saw them, too: “This was a first for me!” she says. “The polar stratospheric clouds which lit up the Arctic skies in daylight are still here. Now they are beautifully lit up by the Moon instead!”

This is a remarkable episode of PSCs–the best in many years according to some longtime residents of northern Sweden. Arctic sky watchers should remain alert for more, both day and night, as this unusual winter continues.

Realtime PSC Photo Gallery

An Outbreak of Polar Stratospheric Clouds

Feb. 13, 2017: Around the Arctic Circle, observers are reporting an outbreak of polar stratospheric clouds (PSCs). “Today, Feb. 13th, the sky was filled with their brilliant colors from sunrise to sunset,” says Mia Stålnacke, who sends this picture from Kiruna, Sweden:

These clouds are newsworthy because normally the stratosphere has no clouds at all. Home to the ozone layer, the stratosphere is arid and almost always transparent. Yet, Stålnacke says, “we’ve been seeing stratospheric clouds very often this winter and last.”

According to multiple longtime residents of the area, the Feb 13th display was exceptional. “Everyone I spoke to agrees it was the best they had ever seen,” says Chad Blakley, who operates the Lights over Lapland tour guide service in Abisko, Sweden.

“I’ve been living here all my life (33 years),” says Stålnacke. “I definitely feel that these clouds are appearing more often then they used to. I remember seeing them a few times/year since I was a kid, but these last couple of years we’ve had them much more often–sometimes for almost a week straight. Others seem to feel the same way; I see local groups on Facebook flooded with photos of PSCs and comments on how often they’re appearing now.”

“The clouds were all over Finland, too,” says Matti Helin who took this picture on Feb. 13th:

What’s going on up there?

PSCs are a sign of very cold temperatures in the stratosphere.  The clouds are made of ice. Indeed, that is the source of their remarkable color: High-altitude sunlight shining through tiny ice particles ~10µm across produce a bright iridescent glow.  For ice crystals to form in the very dry stratosphere, temperatures must drop to around -85º C.

Once thought to be mere curiosities, some PSCs are now known to be associated with the destruction of ozone. Indeed, an ozone hole formed over the UK in Feb. 2016 following an outbreak of ozone-destroying Type 1 PSCs.

To investigate these clouds further, Spaceweather.com and the students of Earth to Sky Calculus will travel to Abisko Sweden for a week in March 2017.  We plan to launch a series of space weather balloons into the Arctic stratosphere, measuring temperature, air pressure, and ambient radiation.  If PSCs are present, our sensors will pass directly through them, and our cameras can photograph the colorful clouds at point blank range. Stay tuned!

Green Comet Approaches Earth

Feb. 7,2017: A small comet named “45P/Honda-Mrkos-Pajdusakova” (45P for short) is approaching Earth.  At closest approach on Feb. 11th, the comet will be 7.4 million miles from our planet, visible in binoculars and small telescopes. This is what it looks like:

Michael Jäger of Stixendorf, Austria, took the picture on Dec. 31, 2016, just as the comet was swinging around the sun en route to Earth. Since then 45P’s icy nucleus has been heated by solar radiation, causing it to spew brightening jets of gas into the comet’s green atmosphere.  Why green? Because the comet’s vaporizing nucleus emits diatomic carbon, C2, a gas which glows green in the near-vacuum of space.

According to the Minor Planet Center, this is the 8th closest pass of any comet in the modern era (since ~1950, when modern technology started being used to study comets). It will only be 31 times farther from Earth than the Moon. Interestingly, 45P made an even closer approach on its previous orbit (23 lunar distances), so it is also on the list as the 5th closest.

Proximity makes the comet bright despite its small size. Forecasters say 45P could be on the verge of naked eye visibility (6th magnitude) when it emerges into the pre-dawn sky later this week. The best time to look is during the dark hours before sunrise between Feb 9th and 12th. The comet will be racing through the constellation Hercules high in the eastern sky. Sky maps: Feb. 9, 10, 11, 12.

Got a great picture? First, submit it to Spaceweather.com. Next, send it to the Planetary Science Institute, which is collecting amateur images to help professional researchers study Comet 45P.  More resources: 3D Orbit, Ephemeris.

Realtime Comet Photo Gallery

Radiation Clouds at Aviation Altitudes

Jan. 20, 2017: A new study published in the peer-reviewed journal Space Weather reports the discovery of radiation “clouds” at aviation altitudes. When airplanes fly through these clouds, dose rates of cosmic radiation normally absorbed by air travelers can double or more.

“We have flown radiation sensors onboard 264 research flights at altitudes as high as 17.3 km (56,700 ft) from 2013 to 2017,” says Kent Tobiska, lead author of the paper and PI of the NASA-supported program Automated Radiation Measurements for Aerospace Safety (ARMAS). “On at least six occasions, our sensors have recorded surges in ionizing radiation that we interpret as analogous to localized clouds.”

The fact that air travelers absorb radiation is not news.  Researchers have long known that cosmic rays crashing into Earth’s atmosphere create a spray of secondary particles such as neutrons, protons, electrons, X-rays and gamma-rays that penetrate aircraft.  100,000 mile frequent flyers absorb as much radiation as 20 chest X-rays—and even a single flight across the USA can expose a traveler to more radiation than a dental X-ray.

Conventional wisdom says that dose rates should vary smoothly with latitude and longitude and the height of the aircraft.  Any changes as a plane navigates airspace should be gradual.  Tobiska and colleagues have found something quite different, however: Sometimes dose rates skyrocket for no apparent reason.

“We were quite surprised to see this,” says Tobiska.

All of the surges they observed occurred at relatively high latitudes, well above 50 degrees in both hemispheres. One example offered in their paper is typical: On Oct 3, 2015, an NSF/NCAR research aircraft took off from southern Chile and flew south to measure the thickness of the Antarctic ice shelf.  Onboard, the ARMAS flight module recorded a 2x increase in ionizing radiation for about 30 minutes while the plane flew 11 km (36,000 feet) over the Antarctic Peninsula.  No solar storm was in progress.  The plane did not abruptly change direction or altitude.  Nevertheless, the ambient radiation environment changed sharply. Similar episodes have occurred off the coast of Washington state.

Above: Radiation measurements made by ARMAS while flying over Antarctica. The colored points are from ARMAS. The black points are from a NASA computer model (NAIRAS) predicting radiation dose rates. Throughout the flight, ARMAS observed higher dose rates than predicted by the model, including a surge highlighted in pink.

What’s going on?

“We’re not sure,” says Tobiska, “but we have an idea.”

Earth’s magnetic field, he explains, traps many cosmic rays and solar energetic particles in structures called “magnetic bottles.”  These bottles can be leaky.  Even minor gusts of solar wind can cause the trapped particles to squirt out the ends of the bottle, sending beams of particles down toward the Earth below.

“Basically, we think we might be flying through some of these leaky particle beams,” says Tobiska.

Tobiska notes that a team of South Korean researchers has observed similar variations in radiation while flying sensors onboard a military aircraft near the border between the two Koreas (Lee et al 2015).  If the phenomena are the same, the Korean measurements would suggest that “radiation clouds” may exist at middle latitudes, too.

The ARMAS program has a busy flight schedule in 2017. “We’ll be looking carefully for more ‘clouds’ as we continue to characterize the radiation environment at aviation altitudes,” says Tobiska.

Stay tuned for updates and, meanwhile, read Tobiska et al’s original research at this URL:  http://onlinelibrary.wiley.com/doi/10.1002/2016SW001419/abstract

Sunspots Vanish, Space Weather Continues

Jan 11, 2017: So far in 2017, the big story in space weather is sunspots–or rather, the lack thereof. The sun has been blank more than 90% of the time.  Only one very tiny spot observed for a few hours on Jan. 3rd interrupted a string of spotless days from New Years through Jan. 11th. Devoid of dark cores, yesterday’s sun is typical of the year so far:

The last time the sun produced a similar string of spotless days was May of 2010, almost 7 years ago. That was near the end of the previous deep Solar Minimum.  The current stretch is a sign that Solar Minimum is coming again. Sunspot numbers rise and fall with an ~11-year period, slowly oscillating between Solar Max and Solar Min. In 2017, the pendulum is swinging toward the bottom.

Contrary to popular belief, space weather does not stop when sunspots vanish.  Recent nights are proof: Bright auroras have been dancing around the Arctic Circle. Tom Arne Moldenaes of Groetfjord, Norway, recorded this eruption (“like green lava from a volcano,” he says) on Jan. 5th when the face of the sun was completely spotless:

The auroras were sparked by a stream of solar wind flowing from a large hole in the sun’s atmosphere. Such “coronal holes” are common during Solar Minimum.

Sunspots are an important source of space weather. They can unleash solar flares, cause radio blackouts and geomagnetic storms. However, equally interesting things happen when sunspots vanish. For instance, the extreme ultraviolet output of the sun plummets. This causes the upper atmosphere of Earth to cool and collapse. With less air “up there” to cause orbital decay, space junk accumulates around our planet.

Also during Solar Minimum, the heliosphere shrinks, bringing interstellar space closer to Earth. Galactic cosmic rays penetrate the inner solar system with relative ease. Indeed, a cosmic ray surge is already underway, with implications for astronauts and even ordinary air travelers.

Stay tuned for updates as we enter a new phase of the solar cycle.

Realtime Aurora Photo Gallery

Aurora “Blaster Fire” Recorded in Sweden

Dec. 29, 2016: For centuries, Arctic sky watchers have occasionally reported strange sounds filling the air as Northern Lights danced overhead. Hisses, crackles, and even loud “claps” have been heard and recorded. It may be time to add a new sound to the menagerie: blaster fire.

Photographer Oliver Wright sends this report from inside the Arctic Circle: “On Christmas Night 2016, I was standing beneath an intense display of auroras in Abisko, Sweden, when I heard something that sounded like Star Wars blasters.” As the lights danced overhead, a series of rat-a-tat ‘swooshes’ emanated from a nearby set of power lines.  “Other bystanders heard it, too,” he says. “I rushed closer to the power lines and was able to record a sample using my iPhone.”

To listen, click on the photo–and don’t forget to turn up the volume:

Wright says that the sounds waxed and waned in sync with the auroras overhead; the brighter the lights, the louder the sounds. Distance mattered, too:  “The sounds grew louder as I approached the power lines, and fainter as I moved away.”

Wright is a veteran tour guide working for Lights over Lapland, and he has heard these sounds before–”three times in total. Each time I was standing near power lines.” He recalls a particularly intense outburst of “blaster fire” during the powerful St. Patrick’s Day Storm of March 2015. In each case, guests and/or friends heard the sounds as well.

What’s going on?

“Aurora sounds” have long been a controversial topic.  Some researchers insist that they exist only in the imagination of the listener, but there is growing evidence that they are real.


Twas the night before Christmas. Read Oliver Wright’s aurora blog.

Perhaps the most commonly reported aurora sounds are “hissing” and “crackling,” a bit like static on a radio.  These are thought to come from electric fields causing spark discharges at the pointy ends of objects like pine needles or even strands of dry hair.  Aurora “claps” have been recorded as well.  A researcher in Finland spent 15 years studying this phenomenon and published his results in 2012.  He found that a temperature inversion layer in the atmosphere about 70 meters above the ground could cause a separation of + and – charges in the air. During strong geomagnetic storms, the charge separation breaks down, causing air to move and a “clap” to be heard.

The sounds Wright recorded may be a result of “electrophonic transduction”–that is, the conversion of electromagnetic energy into mechanical motion. At the time of the Christmas aurora outburst, magnetic fields around Abisko were seething with activity.  Physics 101: Unsettled magnetic fields can cause currents to flow in power lines.  Strong low-frequency currents can literally shake objects, launching acoustic vibrations into the air.  Wright may have recorded the unique sound of those power lines swaying in response to the magnetic storm.

“This discussion feels poignant with the passing of Carrie Fisher as she was my childhood love and the sound is very reminiscent of Star Wars,” notes Wright.

Indeed, “Carrie’s Crackles” might be a good name for these heavenly sounds. Around Abisko, people will be listening for more as the next magnetic storm approaches.  Stay tuned!

I’m Dreaming of a … Pink Christmas?

Dec. 26, 2016: Christmas Day 2016 brought a fantastic display of auroras to the Arctic Circle. A great many of them were pink. James Helmericks sends this picture from the Colville River Delta in northern Alaska:

“This was the brightest pink display I have ever seen, at one time even giving the snow a pink tinge,” he says.

The pink color is probably a sign of nitrogen. Most auroras are green–a verdant glow caused by energetic particles from space hitting oxygen atoms 100 km to 300 km above Earth’s surface. Seldom-seen pink appears when the energetic particles descend lower than usual, striking nitrogen molecules at the 100 km level and below.

On the days and nights around Christmas 2016, the pinks became so intense, they appeared white, not only to cameras, “but also to the naked eye,” says Sarah Skinner, who witnessed the strange colors several nights in a row from Abisko, Sweden. “It looked like someone had photoshopped the sky!” she says.

It is worth noting that these remarkable auroras appeared during a lull in solar activity. For three days centered on Christmas, the face of the sun was completely blank. There were no sunspots, no solar flares, and no CMEs. Instead, the display was caused by a high-speed solar wind stream blowing out of a large hole in the sun’s atmosphere. Such atmospheric holes are common during Solar Minimum, so we can expect many similar displays as the sunspot cycle crashes in the years ahead.

Realtime Aurora Photo Gallery

Evolution of a Coronal Hole

Dec. 26, 2016: Christmas 2016 was special for sky watchers around the Arctic Circle.  The skies filled with some of the best Northern Lights of the year, including rare outbursts of white and pink. The source of the display: A giant “coronal hole” in the sun’s atmosphere sprayed our planet with solar wind. The hole opened up in July 2016 and it has been strobing Earth with solar wind every ~28 days ever since as the hole pirouettes with the slowly rotating sun.

Spaceweather.com reader Stuart Green has prepared a plot showing the evolution of the coronal hole and the effect it has had on the magnetic field at his private observatory in Preston, England.  Click on the image to inspect the full 6 months:

Inset images come from NASA’s Solar Dynamics Observatory. The coronal hole is the giant dark region, starting small in July, then growing and shape-shifting as the year unfolds.

The background strip chart recording shows the instability of the magnetic field around Green’s private observatory. When the coronal hole is facing Earth, big changes are measured.

“I’ve been recording geomagnetic activity over the past three years using a home built/ home designed magnetometer,” says Green. “The sensor is buried in my garden about 0.5m below the surface in an East/West orientation to allow very sensitive (sub nanotesla) measurements of magnetic declination during geomagnetic storms. The plots show the change in magnetic flux density in nanotesla occurring between readings every 2.5 minutes.”

Green’s presentation suggests that this yawning hole is a long-lived feature on the sun, and it will probably be back as potent as ever 28 days from now.  Stay tuned for magnetic unrest–and more Arctic auroras–in January.

White Auroras

Dec. 25, 2016: Auroras are usually green. Occasionally, other colors appear: red, purple, blue. One color that never shows itself, however, is white–that is, not until last night. “I saw white auroras over Tromsø, Norway!” reports veteran observer Markus Varik. He recorded the phenomenon in this photo:

“I’ve been working more than 400 nights as a Northern Lights guide, and although sometimes I think I’ve seen it all, never I have witnessed white auroras like that,” says Varik. “It was amazing to see it unravel white like that in front of my eyes. Pure magic!”

Auroras get their colors from specific elements in Earth’s upper atmosphere. Green auroras, for instance, come from atomic oxygen; blue is associated with molecular nitrogen. No element produces white. So where did it come from?

An important clue: Elsewhere in Scandinavia, intense ribbons of pale pink appeared. Here is a specimen recorded by an automated auroracam in Abisko, Sweden:

Sarah Skinner, a tour guide with Lights over Lapland, saw the display: “OMG, it was the pinkest aurora ever!”

The ‘white auroras’ Varik photographed might actually be pink auroras filtered and paled by low-hanging clouds. Indeed, there is a strong hint of pink in Varik’s photo.

Pink auroras are somewhat rare, but hardly unprecedented. They appear when  energetic particles from space descend lower than usual, striking nitrogen molecules at the 100 km level and below. Look for more in the aurora photo gallery:

Realtime Aurora Photo Gallery