April 26, 2018: For the past 4 years, Spaceweather.com and Earth to Sky Calculus have been flying radiation sensors onboard airplanes to map the distribution of cosmic rays around our planet. Our database currently contains more than 17,000 GPS-tagged radiation measurements spanning 5 continents and 43,000 feet of altitude. Yesterday, we realized we could use this database to investigate a current event–namely, the possibility of a radiation leak from North Korea.
Above: Earth to Sky Calculus X-ray/gamma radiation sensors onboard a plane
North Korea recently surprised observers by announcing a suspension of its underground nuclear testing program. Geologists in China quickly offered an explanation: Mount Mantap, which sits atop of the test site, had collapsed. The mountain crumbled in Sept. 2017 minutes after the North Korean regime exploded a 100 kiloton prototype weapon. According to the South China Morning Post, the China Earthquake Administration believes the collapse may have created a “chimney” that allows the escape of radioactive materials.
Is there any sign of radioactivity in the air space around North Korea? Our database contains four flights near the Korean Peninsula–two in March 2016 (before the collapse), and two more in Feb. 2018 (after the collapse). These are shown in the map, below, where orange circles of 350 miles and 700 miles radius are centered on nuclear test site. During each flight we sampled X-rays and gamma-rays in the energy range 10 keV to 20 MeV at one minute intervals, accumulating more than 600 data points. Low energy X-rays have been used in the past to trace radioactive fallout from atomic tests, so our measurements may have some bearing on the question.
Above: Red dots show where we have collected radiation data in airspace near N. Korea.
And the answer is …. no. Comparing radiation levels pre-collapse vs. post-collapse, we found no significant difference. For instance, radiation dose rates in March 2016 at 31,500 feet were 0.9 uGy/hr (18 times the natural rate at sea level). Radiation dose rates in February 2018 at the same altitude were 1.0 uGy/hr (20 times sea level), a slight increase within the uncertainty of the measurements. If radiation is leaking from the collapsed mountain site, it is not having a detectable effect on aviation over neighboring countries.
April 20, 2018: An interplanetary shock wave hit Earth’s magnetic field on April 19th around 23:50 UT. When the disturbance arrived, the density of solar wind flowing around our planet abruptly quadrupled and a crack opened in Earth’s magnetic field. The resulting G2-class geomagnetic storm sparked unusual “electric blue” auroras.
“I’ve been flying airplanes for 20 years and photographing aurora for 10 years, but I’ve never seen anything like this before,” reports pilot Matt Melnyk who photographed the display from 39,000 feet:
“Electric blue auroras!” he says. “This was while on a red eye flight from Edmonton to Toronto around 4 am over northern Manitoba. Unbelievable sky. I was able to grab some hasty shots with a cell phone.”
Auroras are usually green–a sign of oxygen. Rare blue auroras are caused by nitrogen molecules. Energetic particles striking N2+ at the upper limits of Earth’s atmosphere can produce an azure glow during intense geomagnetic storms.
During the storm, Northern Lights spilled across the Canadian border into the United States as far south as Indiana. Hongming Zheng, a student at Purdue University, saw the blue glow just five miles from his dorm:
“I was preparing for bed at 1:32 am on April 20th when I read that there was an Interplanetary Shockwave,” says Zheng. “I immediately started driving north to see the show. A weak green wisp showed up at 2am and faded, but shortly after 5am a sudden outburst occurred. Purple pillars were easily visible to the naked eye. It’s funny how one minute you are in a humid dorm struggling to get the laundry door closed, and the next minute you are chasing one of the most spectacular phenomenon known to man.”
What is an interplanetary shock wave? It is a supersonic disturbance in the gaseous material of the solar wind. These waves are usually delivered by coronal mass ejections (CMEs). Indeed, this one might have been a minor CME that left the sun unrecognized earlier this week.
Alternately, it might have been an unusually sharp co-rotating interaction region (CIR). CIRs are transition zones between slow- and fast-moving streams of solar wind. They contain plasma density gradients and magnetic fields that often do a good job sparking auroras.
April 11, 2018: Yesterday, a G1-class geomagnetic storm was brewing over Canada as a stream of solar wind buffeted Earth’s magnetic field. Matthew Wheeler of Robson Valley, British Columbia, stepped outside to see what was up–and STEVE appeared. “My dog barked at it for the entire hour it was visible,” says Wheeler. “It was flowing like a river at astonishing speed.” Click to play his must-see video:
STEVE may look like an aurora, but it is not. For one thing, it is soft purple, not green like typical auroras. And it has its own special form–tightly collimated into a narrow ribbon that can bisect the entire sky.
Researchers are only beginning to understand the phenomenon–aided by a chance encounter between STEVE and a European satellite a few years ago. In situ measurements revealed that STEVE is a hot (3000 degrees C) ribbon of ionized gas slicing through Earth’s upper atmosphere some 300 km above the ground. It appears unpredictably during some, but not all, geomagnetic storms.
Another video–“my best yet,” says Wheeler–shows the beautiful interaction between the soft-purple ribbon and nearby green “picket fence” auroras:
“The purple ribbon was moving much faster than the green pickets,” says Wheeler. “And while their forms varied from smooth to ragged and back again, their path across the sky was almost constant for the whole hour–as it has since I first noticed STEVE over this valley in the 1980s.”
Does STEVE really make dogs bark? “Mine does,” says Wheeler. “In addition to barking at STEVE, my giant Akbash astronomy dog, Patch, has barked at the space station since he was a pup, and proudly seen it off the farm every time. He is also a valuable spotter of meteor showers. When I hear him barking upwards, it is time to go outside.”
Realtime Aurora Photo Gallery