On October 3, 2015, a National Science Foundation Gulfstream V research jet recorded a massive increase in atmospheric radiation while flying over the South Atlantic between Antarctica and the tip of South America. For 11 minutes, its onboard radiation detector watched levels double, as if the aircraft had flown through a cloud of radiation.
That 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 have raised important questions, most notably about the risks to aircrews and the safe operation of airborne electronic devices. But most of all, scientists want to know what causes these bursts of radiation.
Today we have an answer thanks to the work of Kent Tobiska at Space Environment Technologies in California, and colleagues who have studied the incidents and believe they know the source of the radiation.
Their work raises important questions about the safety of frequent flyers, such as aircrews, and how to protect them from events that “are analogous to planes flying through clouds of radiation,” say Tobiska and company.
Space scientists have long known that Earth is bombarded from space by a constant stream of high-energy radiation from beyond the Solar System, called Galactic Cosmic Rays, and by more sporadic bursts from the Sun called Solar Energetic Particles. This radiation generally takes the form of high-energy electrons, protons, and alpha particles.
Earth is protected from these particles by the Sun’s magnetic field, which slows much of the incoming galactic radiation, and by its own magnetic field high above the atmosphere, which funnels charged particles toward the poles.
However, the high-energy particles still reach the upper atmosphere at about 100 km, where they collide with oxygen and nitrogen atoms, creating lower-energy electrons and photons that cascade in chain reactions to the lower atmosphere. These cascades reach a maximum intensity at altitudes of about 20 km, but are constantly absorbed at lower altitudes by the thicker atmosphere.
Commercial aircraft operate at altitudes of up to about 10 km and therefore experience a higher dose of this radiation than on the ground. The concern is that this type of radiation can ionize atoms and tear DNA, which could cause health problems such as cancer. It can also interfere with electronic instruments.
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 continuously monitor it on a global scale. So, in 2012, various US agencies began developing a real-time global monitoring system to measure levels. The system was called the Automated Radiation Measurements for Aerospace Safety (ARMAS) program and Tobiska’s company, Space Environment Technologies, has played a key role in it.
Since then, the program has made hundreds of thousands of radiation measurements during 599 flights around the world.
It soon became clear that the level of background radiation is not constant at all, but several surveillance aircraft experienced sudden and rapid increases in radiation that would subside relatively quickly.
Tobiska and company focus their analysis on 57 events of this type.
They first compared the radiation bursts with background readings elsewhere on the planet to rule out the possibility that a solar storm or an increase in galactic cosmic rays was to blame. They found no increase in activity elsewhere.
Clearly this radiation was being generated closer to home and only in small areas. Judging from the speed of the aircraft, these radiation patches cover areas no larger than 1,000 km in diameter.
catch 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-altitude ocean of plasma. Like any other ocean, this plasma is affected by environmental conditions. — space weather in the form of changes in the sun’s magnetic field and by solar storms.
This generates turbulence and sets up powerful plasma waves. It is these plasma waves, called electromagnetic ion cyclotron waves, that Tobiska and his colleagues believe are the source of the radiation bursts.
This is because charged particles can ride on cyclotron waves of electromagnetic ions and be greatly accelerated. Any particles that do escape do so as powerful bursts of high-energy radiation. Indeed, plasma wave accelerators are an emerging technology for next-generation particle colliders.
But the bursts only go down toward the Earth’s surface, where Earth’s magnetic field begins to point toward the surface. And this only happens at high latitudes. It turns out that one of the characteristics of the observed radiation spikes is that they only occur at high latitudes.
The team also found that radiation spikes tended to coincide with periods of turbulent space weather, which promote conditions in which electromagnetic ion cyclotron waves can form. It is also possible to see evidence of these waves from the ground.
“The evidence points to the [radiation] The beam is produced at higher altitudes by incident relativistic electrons coming from the Van Allen radiation belts and generated by the electromagnetic ion cyclotron wave,” say Tobiska and co.
The consequences are significant. For many years, scientists have calculated background radiation rates at high altitudes and set safe limits on the time aircrew must spend in these conditions. This allows them to operate safely.
But this new source of radiation threatens to upset these calculations, particularly for those flying more northerly routes.
“The net effect on aircraft crew and frequent flyers on these routes will be an increase in monthly and annual exposures, which may have career-limiting health consequences,” say Tobiska and company.
That conclusion is likely to send shock waves through the aviation industry. The significance of this additional exposure has yet to be calculated, but this work should be given the highest priority. At the same time, this should be designed to provide clarity to the many men and women who will be concerned about the effect of this radiation on their health.
Ref: Radiation Enhancement Events Discovered at Commercial Aviation Altitudes: