Radiation “clouds” at aviation altitudes have been recently discovered by scientists.
When airplanes fly through these clouds, dose rates of cosmic radiation normally absorbed by air travelers can double or more.
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: Sometimes dose rates skyrocket for no apparent reason. They have flown radiation sensors onboard 264 research flights at altitudes as high as 17.3 km (56,700 ft) from 2013 to 2017. On at least six occasions, the sensors have recorded surges in ionizing radiation that scientists interpreted as analogous to localized clouds. Quite a surprise!
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.
What’s going on?
Scientists are not sure about the mechanisms behind this mysterious clouds…
Earth’s magnetic field 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. So did the planes fly through some of these leaky particle beams?
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. If the phenomena are the same, the Korean measurements would suggest that “radiation clouds” may exist at middle latitudes, too.