A new study published in the peer-reviewed journal Space Weather reports the discovery of radiation "clouds" at aviation altitudes. When airplanes fly through these clouds, dose rates of cosmic radiation normally absorbed by air travelers can double or more. "We have flown radiation sensors onboard 264 research flights at altitudes as high as 17.3 km (56,700 ft) from 2013 to 2017," says Kent Tobiska, lead author of the paper and PI of the NASA-supported program Automated Radiation Measurements for Aerospace Safety (ARMAS). "On at least six occasions, our sensors have recorded surges in ionizing radiation that we interpret as analogous to localized clouds." 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