On October 3, 2015, a National Science Foundation Gulfstream V research aircraft recorded a massive spike in atmospheric radiation as it flew over the South Atlantic Ocean between Antarctica and the tip of South America. For 11 minutes, the radiation detector on board watched the levels double, as if the plane had flown through a cloud of radiation.
This was not the only incident. Since 2013, airborne detectors have recorded 57 similar bursts of radiation, each lasting between ten minutes and an hour.
The observations raised important questions, not least about the risks to cabin crew and the safe operation of airborne electronics. But most of all, scientists want to know what causes these radioactive explosions.
Today we have an answer thanks to the work of Kent Tobiska at Space Environment Technologies in California, and colleagues, who have studied accidents and believe they know where the radiation is coming from.
Their work raises important questions about the safety of frequent flyers such as aircrews and how to protect them from events that “like aircraft flying through radioactive clouds,” Topeska and colleagues say.
Space scientists have long known that Earth is being bombarded from space by a steady stream of high-energy radiation from outside the solar system, called galactic cosmic rays, and by more sporadic outbursts from the sun called solar particles. This radiation generally takes the form of high-energy electrons, protons, and alpha particles.
Earth is shielded from these particles by the sun’s magnetic field, which slows much of the galaxy’s incoming radiation, and by its own magnetic field high above the atmosphere, which directs charged particles toward the poles.
However, the high-energy particles still reach the upper atmosphere about 100 km away where they collide with oxygen and nitrogen atoms resulting in low-energy electrons and photons flowing in a chain reaction in the lower atmosphere. These waterfalls reach their maximum at altitudes of about 20 km, but are steadily absorbed at lower altitudes by the thick atmosphere.
Commercial aircraft operate at altitudes of about 10 kilometers and are therefore exposed to a higher dose of this radiation than those on the ground. The concern is that this type of radiation could ionize atoms and rip DNA, which could cause health problems such as cancer. It can also interfere with electronic instruments.
So any new source of ionizing radiation is a major concern.
Although radiation has been a well-known problem at high altitudes for decades, there has been no attempt to consistently monitor it on a global scale. So in 2012, several US agencies began developing a global, real-time monitoring system to measure levels. The system was called the Automated Radiation Measurements Program for Aerospace Safety (ARMAS) and Topesca’s company, Space Environment Technologies, played a key role in it.
Since then, the program has made hundreds of thousands of radioactive measurements during 599 flights around the world.
It soon became clear that the background radiation level is not at all constant. Instead, the various observation planes experienced rapid and sudden increases in radiation that would disappear relatively quickly.
Tobiska and colleagues focused their analysis on 57 such events.
They first compared the radiation blasts to background readings elsewhere on the planet to rule out the possibility that a solar storm or an increase in galactic cosmic rays was the cause. They found no increase in activity anywhere else.
It is clear that this radiation was generated near the house and only in small areas. Depending on the speed of the aircraft, these radiation spots cover areas with a diameter of no more than 1,000 km.
arrest the culprit
The obvious culprit was Earth’s Van Allen radiation belts, the part of the magnetosphere that traps high-energy charged particles creating a high ocean of plasma. Like any other ocean, this plasma is exposed to environmental conditions – Space weather in the form of changes in the magnetic field of the Sun and solar storms.
This generates turbulence and creates powerful plasma waves. Topeska and his colleagues believe that these plasmonic waves, called electromagnetic cyclotron ion waves, are the source of the radioactive explosions.
That’s because charged particles can surf on electromagnetic cyclotron-ion waves, and become exponentially accelerated. Any particles that survive do so as powerful bursts of high-energy radiation. In fact, plasma wave accelerators are an emerging technology for the next generation of particle colliders.
But the bursts only head down, toward the Earth’s surface, as the Earth’s magnetic field begins to point back toward the surface. And this only happens at higher latitudes. As it turned out, a feature of the observed radiation spikes is that they occur only at higher latitudes.
The team also found that radiation spikes tend to coincide with periods of turbulent space weather, enhancing the conditions under which electromagnetic cyclotron ion waves can form. It is also possible to see evidence of these waves from Earth.
Evidence points to [radiation] A beam that is produced at higher altitudes by incident relativistic electrons coming from the Van Allen radiation belts and generated by the electromagnetic ion cyclotron wave,” Topeska and colleagues say.
The consequences are dire. Over the course of many years, scientists have calculated background rates of radiation at high altitudes and set safe limits for the time flight crews should spend in these conditions. This allows them to work safely.
But this new source of radiation threatens to turn these calculations upside down, especially for those traveling on northern trails.
“The net effect on cabin crew and frequent flyers of these routes would be an increase in monthly and annual exposure, which could have career-limiting health consequences,” Topeska and colleagues say.
That conclusion would likely send shock waves through the airline industry. The significance of this additional exposure has not yet been calculated but this work should be given the highest priority. Essentially, this should be designed to give clarity to the many men and women who will be concerned about the effect this radiation has on their health.
Reference: Increased radioactive events detected at commercial flight altitudes: https://arxiv.org/abs/2209.05599