Arctic Space Weather Balloon Launch

March 3, 2017: is going to Sweden–and we’re taking a team of student researchers from Earth to Sky Calculus with us. For a week beginning on March 9th we plan to launch a series of space weather balloons equipped with cosmic ray sensors and cameras into the stratosphere above the Arctic Circle. At the same time, Earth to Sky launch teams in Chile and California will be sending up identical payloads, forming an intercontinental balloon network:

We’re doing this for three reasons:

1. To understand Earth’s changing radiation environment: Regular monitoring of the stratosphere over California shows that cosmic rays have intensified more than 10% since 2015.  Because of a recent decline in the solar cycle, more and more cosmic rays are reaching the inner solar system and penetrating the atmosphere of our planet. Earth’s magnetic field should protect us against these rays, but geomagnetism is weakening. Globally, Earth’s magnetic field has declined in strength by 10% since the 19th century with changes accelerating in recent years, according to measurements by Europe’s SWARM satellites. To understand Earth’s global response to these changes, we must launch balloons and sample radiation from widely-spaced locations.  The upcoming network launch will span three continents, more than 14,000 km of linear distance, and 90+ degrees of latitude.

Above: Satellite data show that Earth’s magnetic field is changing: full story.

2. To photograph the Northern Lights: We will be launching balloons from Abisko, Sweden, 250 km inside the Arctic Circle. Abisko is famous for spectacular auroras. One of our payloads will carry a low-light camera capable of photographing these lights from the stratosphere. Even at 120,000 feet, the balloon will be well below the auroras, but we will be a lot closer than any camera on the ground

3. To sample polar stratospheric clouds: During winter months, the stratosphere above the Arctic Circle sometimes fills with icy clouds so colorful, they are likened to the aurora borealis. Polar stratospheric clouds (PSCs) are a sign of extremely cold temperatures in the stratosphere and some types of PSCs are responsible for ozone destruction. Our space weather balloons can fly right through these clouds, sampling their temperature, pressure, and ambient levels of radiation.  We can also photograph them from the inside–a possible first!

Above: Polar stratospheric clouds over Kiruna, Sweden, on Feb. 14. Credit: Mia Stålnacke

Stay tuned for daily updates beginning March 9th.

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

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

Autumn is Aurora Season

by Dr.Tony Phillips (
Sept. 4, 2016

Summer is ending in the northern hemisphere.  That’s good news for sky watchers because autumn is “aurora season.” Autumn is special in part because lengthening nights and crisp pleasant evenings tempt stargazers outside; they see things they ordinarily wouldn’t. But there’s more to it than that: autumn really does produce a surplus of geomagnetic storms–almost twice the annual average.

see captionIn fact, both spring and autumn are good aurora seasons. Winter and summer are poor. This is a puzzle for researchers because auroras are triggered by solar activity. The Sun doesn’t know what season it is on Earth–so how could one season yield more auroras than another?

Left: Geomagnetic activity from 1875 to 1927, from “Semiannual Variation of Geomagnetic Activity” by C.T. Russell and R.L. McPherron, JGR, 78(1), 92, 1973. See also this analysis by NASA solar physicist David Hathaway.

To understand the answer, we must first understand what causes auroras themselves.

Auroras appear during geomagnetic storms–that is, when Earth’s magnetic field is vibrating in response to a solar wind gust. Such gusts pose no danger to people on the ground because our magnetic field forms a bubble around Earth called the magnetosphere, which protects us. The magnetosphere is filled with electrons and protons. “When a solar wind gust hits the magnetosphere, the impact knocks loose some of those trapped particles,” explains space physicist Tony Lui of Johns Hopkins University. “They rain down on Earth’s atmosphere and cause the air to glow where they hit–like the picture tube of a color TV.”

Below: Still frames from a digital movie show how solar wind gusts rattle Earth’s magnetosphere and trigger auroras. Click to view the 750 kb Quicktime animation created by Digital Radiance, Inc.

see caption
Some solar wind gusts (“coronal mass ejections”) are caused by explosions near sunspots, others are caused by holes in the Sun’s atmosphere (“coronal holes”) that spew solar wind streams into interplanetary space. These gusts sweep past Earth year-round, which returns us to the original question: why do auroras appear more often during spring and autumn?

The answer probably involves the Sun’s magnetic field near Earth. The Sun is a huge magnet, and all the planets in the solar system orbit within the Sun’s cavernous magnetosphere. Earth’s magnetosphere, which spans about 50,000 km from side to side, is tiny compared to the Sun’s.

The outer boundary of Earth’s magnetosphere is called the magnetopause–that’s where Earth’s magnetic field bumps into the Sun’s and fends off the solar wind. Earth’s magnetic field points north at the magnetopause. If the Sun’s magnetic field tilts south near the magnetopause, it can partially cancel Earth’s magnetic field at the point of contact.

see caption“At such times the two fields (Earth’s and the Sun’s) link up,” says Christopher Russell, a Professor of Geophysics and Space Physics at UCLA. “You can then follow a magnetic field line from Earth directly into the solar wind.” Researchers call the north-south component of the Sun’s nearby magnetic field “Bz” (pronounced “Bee-sub-Zee”). Negative (south-pointing) Bz‘s open a door through which energy from the solar wind can reach Earth’s inner magnetosphere. Positive (north-pointing) Bz‘s close the door.

Above: Coronal holes spewing solar windappear as dark areas in ultraviolet and x-ray images of the Sun.

In the early 1970’s Russell and colleague R. L. McPherron recognized a connection between Bz and Earth’s changing seasons. “It’s a matter of geometry,” explains Russell. Bz is the component of the Sun’s magnetic field near Earth which is parallel to Earth’s magnetic axis. As viewed from the Sun, Earth’s tilted axis seem to wobble slowly back and forth with a one-year period. The wobbling motion is what makes Bz wax and wane in synch with the seasons.

In fact, Bz is always fluttering back and forth between north and south as tangled knots of solar magnetic field drift by Earth. What Russell and McPherron realized is that the average size of the flutter is greatest in spring and fall. When Bz turns south during one of those two seasons, it really turns south and “opens the door wide” for the solar wind.

see captionLeft: A solar wind gust triggered these bright auroras in Finland on Sept. 7, 2002. Photo credit: Martti Tenhunen. [more]

Mystery solved? Not yet. In a Geophysical Research Letter (28, 2353-2356, June15, 2001), Lyatsky et al argued that Bz and other known effects account for less than one-third of the seasonal ups-and-downs of geomagnetic storms. “This is an area of active research,” remarks Lui. “We still don’t have all the answers because it’s a complicated problem.”

But not too complicated to enjoy. Dark nights, bright stars, an occasional meteor–and the promise of Northern Lights. Perhaps scientists haven’t figured out why auroras prefer autumn, but it’s easy to understand why sky watchers do….

What lies inside Jupiter?

July 5, 2016: Jupiter’s swirling clouds can be seen through any department store telescope. With no more effort than it takes to bend over an eyepiece, you can witness storm systems bigger than Earth navigating ruddy belts that stretch hundreds of thousands of kilometers around Jupiter’s vast equator. It’s fascinating.

It’s also vexing. According to many researchers, the really interesting things–from the roots of monster storms to stores of exotic matter–are located at depth. The clouds themselves hide the greatest mysteries from view.

NASA’s Juno probe, which went into orbit on July 4,2016, could change all that. The goal of the mission is to answer the question, What lies inside Jupiter?

juno crop for ICYMI 160701

“Our knowledge of Jupiter is truly skin deep,” says Juno’s principal investigator, Scott Bolton of the SouthWest Research Institute in San Antonio, TX. “Even the Galileo probe, which dived into the clouds in 1995, penetrated no more than about 0.2% of Jupiter’s radius.”

There are many basic things researchers would like to know—like how far down does the Great Red Spot go? How much water does Jupiter hold? And what is the exotic material near the planet’s core?

Juno will lift the veil without actually diving through the clouds. Bolton explains how: “Swooping as low as 5000 km above the cloudtops, Juno will spend a full year orbiting nearer to Jupiter than any previous spacecraft. The probe’s flight path will cover all latitudes and longitudes, allowing us to fully map Jupiter’s gravitational field and thus figure out how the interior is layered.”

Jupiter is made primarily of hydrogen, but only the outer layers may be in gaseous form. Deep inside Jupiter, researchers believe, high temperatures and crushing pressures transform the gas into an exotic form of matter known as liquid metallic hydrogen–a liquid form of hydrogen akin to the slippery mercury in an old-fashioned thermometer. Jupiter’s powerful magnetic field almost certainly springs from dynamo action inside this vast realm of electrically conducting fluid.

“Juno’s magnetometers will precisely map Jupiter’s magnetic field,” says Bolton. “This will tell us a great deal about the planet’s inner magnetic dynamo and the role liquid metallic hydrogen plays in it.”

diagram of Jupiter's interior.

Juno will also probe Jupiter’s atmosphere using a set of microwave radiometers.

“Our sensors can measure the temperature and water content at depths where the pressure is 50 times greater than what the Galileo probe experienced,” says Bolton.

Jupiter’s water content is of particular interest. There are two leading theories of Jupiter’s origin: One holds that Jupiter formed more or less where it is today, while the other suggests Jupiter formed at greater distances from the sun, later migrating to its current location. (Imagine the havoc a giant planet migrating through the solar system could cause.) The two theories predict different amounts of water in Jupiter’s interior, so Juno should be able to distinguish between them—or rule out both.

Finally, Juno will get a grand view of the most powerful Northern Lights in the Solar System.

“Juno’s polar orbit is ideal for studying Jupiter’s auroras,” explains Bolton. “They are really strong, and we don’t fully understand how they are created.”

Auroras on JupiterUnlike Earth, which lights up in response to solar activity, Jupiter makes its own auroras. The power source is the giant planet’s own rotation. Although Jupiter is ten times wider than Earth, it manages to spin around 2.5 times as fast as our little planet. As any freshman engineering student knows, if you spin a magnet—and Jupiter is a very big magnet—you’ve got an electric generator. Induced electric fields accelerate particles toward Jupiter’s poles where the aurora action takes place. Remarkably, many of the particles that rain down on Jupiter’s poles appear to be ejecta from volcanoes on Io. How this complicated system actually works is a puzzle.

It’s a puzzle that members of the public will witness at close range thanks to JunoCam—a public outreach instrument modeled on the descent camera for Mars rover Curiosity. When Juno swoops low over the cloudtops, JunoCam will go to work, snapping pictures better than the best Hubble images of Jupiter.

“JunoCam will show us what you would see if you were an astronaut orbiting Jupiter,” says Bolton. “I am looking forward to that.”