Observations of anomalous peaks in atmospheric ionizing radiation below 10 km

Scientists have performed different kind of measurements with various experimental setups for more than 100 years in order to explore in detail the atmospheric ionizing radiation (AIR) profile. The common feature of all previous AIR measurements is the presence of continuous intensity increase of ionizing components along the atmospheric vertical profiles up to the well-known Regener-Pfotzer (RP) maximum appearing between 16–25 km altitudes. In this study, measured vertical ionization profile showed a peaking in ionizing radiation intensity in the atmosphere registered below 10 km altitude, exceeding more than 20 times the values at these heights from previous measurements by meteorological balloons (or in any other way lifted detectors into the atmosphere). We confirmed these findings by three independent measurements performed by detectors equipped with ultra-thin mica windows. The registered peaking in ionizing radiation intensity was observed at altitude ranging from 5-8 km, in a very narrow altitude region (∼300 m). Furthermore, Monte Carlo simulations of propagation of cosmic rays through the atmosphere were performed, searching for possible increase in number of detected events at certain altitudes (10 km, 8 km, and 5 km) due to air-shower developments. Unlike our experimental results, the simulation results did not show an enhance in the number of cosmic ray-produced secondary particles at certain altitudes (5 km or 8 km) relative to the 10 km altitude. A form of anomaly in atmospheric ionizing radiation field at lower altitudes has been seen in ARMAS (Automated Radiation Measurements for Aerospace Safety) data and measurements performed by the National University Corporation, Fukushima University. The presented results in this study will have broad impact on the better understanding of the ionizing radiation production mechanism in the atmosphere, as well as on its dose consequences. © 2025 COSPAR