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

Polar Stratospheric Clouds

Dec. 9, 2016: The stratosphere above the Arctic Circle is getting cold … very cold.  That’s the only way to explain these colorful clouds that materialized over Kiruna, Sweden, on Dec. 9th:

“Polar stratospheric clouds are back in the subarctic,” reports photographer Mia Stålnacke. “They were brilliantly beautiful today.”

Icy polar stratospheric clouds (PSCs) form in the lower stratosphere when temperatures drop to around -85ºC. That’s how cold it has to be for ice crystals to form in the very dry stratosphere. High-altitude sunlight shining through tiny ice particles ~10µm across produce the characteristic bright iridescent colors.

“Once seen they are never forgotten,” says atmospheric optics expert Les Cowley. “Polar stratospheric clouds have much more vivid colors than ordinary iridescent clouds, which are very much poor relations and seen frequently all over the world.”

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.

“Last winter we had these clouds almost daily for long periods of time,” says Stålnacke. Arctic sky watchers are encouraged to be alert for more in the days ahead. The best time to look is just before sunrise or after sunset.

Mesospheric Bore

Nov. 29, 2016: This month, a lot is happening in the mesosphere. The mesosphere is a layer of Earth’s atmosphere above the stratosphere; it is the realm of sprites, noctilucent clouds (NLCs), and airglow. Starting on Nov. 17th, NASA’s AIM spacecraft spotted bright noctilucent clouds forming in the mesosphere above Antarctica. Then, in an apparently unrelated development on Nov. 24th, the normal dome of airglow over China split in two. Xiao Shuai photographed the event from Mount Balang in Sichuan:

This is called a “mesospheric bore”–and not because it’s dull.  A bore is a type of atmospheric wave with deep ripples at its leading edge.  Indeed, you can see the ripples in Shuai’s photo separating the zone of airglow from clear sky.

Bores fall into the category of “gravity waves”—so called because gravity acts as the restoring force essential to wave motion. Analogy: Boats in water. When a boat goes tearing across a lake, water in front of the boat is pushed upward. Gravity pulls the water back down again and this sets up a wave.

In this case, instead of water, rarefied air is the medium through which the wave propagates.  The sudden boundary in the airglow layer is probably akin to a hydraulic jump.  But what created the disturbance in the first place?  (What is the ‘boat’?) No one knows.

“There may be updates in the coming days as scientists from NASA and the Chinese Academy of Science check data from satellites to learn more about this event,” says Jeff Dai, who has been helping Xiao Shuai process and communicate his extraordinary images. “Also, we encourage other photographers from Thailand, Myanmar, Bangladesh and India to submit their images of the wave.”

Realtime Space Weather Photo Gallery

Noctilucent Clouds Appear over Antarctica

Nov. 24, 2016: This just in from NASA’s AIM spacecraft: The sky above Antarctica is glowing electric blue. A ring of bright noctilucent clouds (NLCs) has formed around the South Pole, shown here in a Nov. 24th image taken by the spacecraft’s Cloud Imaging and Particle Size (CIPS) Instrument:

“This season started on Nov. 17th, and is tied with 2013 for the earliest southern hemisphere season in the CIPS data record,” says Cora Randall, a member of the AIM science team at the University of Colorado.

NLCs are Earth’s highest clouds. They form more than 80 km above Earth’s surface. Indeed, they are a mixture of Earth and space:  Wisps of summertime water vapor rising from the planet below wrap themselves around meteoroids, forming tiny crystals of ice. Emphasis on summertime; NLCs appear on the eve of summer in both hemispheres.

There is growing evidence that noctilucent clouds are boosted by climate change.  In recent years they have been sighted at lower latitudes than ever before, and they often get started in earlier months as well.

“The early start of the 2016 season was not at all a surprise,” says Randall. “The southern hemisphere polar stratospheric winds switched to their summer-like state quite early this year.”

Readers, you can monitor developments over Antarctica right here on Spaceweather.com. “Daily daisies” from NASA’s AIM spacecraft are automatically posted every 24 hours, showing the dance of electric-blue around the frozen continent.

Realtime Noctilucent Cloud Photo Gallery

Cosmic Rays Continue to Intensify

Nov. 15, 2016: As the sunspot cycle declines, we expect cosmic rays to increase. Is this actually happening? The answer is “yes.” Spaceweather.com and the students of Earth to Sky Calculus have been monitoring radiation levels in the stratosphere with frequent high-altitude balloon flights over California. Here are the latest results, current as of Nov. 11, 2016:

Data show that cosmic ray levels are intensifying with an 11% increase since March 2015.

Cosmic rays are high-energy photons and subatomic particles accelerated in our direction by distant supernovas and other violent events in the Milky Way. Usually, cosmic rays are held at bay by the sun’s magnetic field, which envelops and protects all the planets in the Solar System. But the sun’s magnetic shield is weakening as the solar cycle shifts from Solar Max to Solar Minimum. As the sunspot cycle goes down, cosmic rays go up.

The sensors we send to the stratosphere measure X-rays and gamma-rays which are produced by the crash of primary cosmic rays into Earth’s atmosphere. In this way we are able to track increasing levels of radiation. The increase is expected to continue for years to come as solar activity plunges toward a deep Solar Minimum in 2019-2020.

Recently, we have expanded the scope of our measurements beyond California with launch sites in three continents: North America, South America and soon above the Arctic Circle in Europe. This Intercontinental Space Weather Balloon Network will allow us to probe the variable protection we receive from Earth’s magnetic field and atmosphere as a function of location around the globe.