Cosmic Radiation at Flight Altitudes Increases When Solar Activity Declines

Commercial aircraft routinely cruise at altitudes where cosmic radiation can pose health risks to crew and passengers. A recent study employing high‑altitude balloon measurements over southern Israel has produced a detailed vertical profile of this radiation, revealing a counterintuitive pattern: levels at typical flight altitudes increase when solar activity declines. The research team collected data across a range of latitudes and altitudes, allowing them to disentangle the influence of solar modulation on the flux of high‑energy particles that penetrate the upper atmosphere.

The balloons carried sensitive dosimeters that recorded ionizing radiation from galactic cosmic rays and solar energetic particles. By correlating the measured fluxes with contemporaneous solar indices—such as sunspot number and solar radio flux—the investigators demonstrated that the heliosphere’s shielding effect weakens during solar minima, permitting more energetic particles to reach the stratosphere. The resulting radiation map shows a clear gradient: at 10–12 km the dose rate can rise by up to 30 % when solar activity drops from its peak to its trough.

These findings have practical implications for aviation safety and regulatory oversight. Airlines and flight‑planning agencies rely on accurate radiation exposure estimates to comply with occupational limits for crew and to assess cumulative passenger dose. The study’s evidence that solar cycles inversely affect in‑flight radiation suggests that exposure monitoring should be adjusted seasonally, and that flight routes at higher latitudes may require more stringent controls during periods of low solar activity.