Radiation inside an airliner can jump 60% when the Sun goes quiet

Radiation at commercial-aircraft altitude can rise by roughly 40% to 60% when the Sun is less active, according to a new analysis of high-altitude balloon measurements. The research team reported that the change is an extrapolation to solar-minimum conditions, not a direct measurement of every passenger’s dose, but it captures a real feature of the atmosphere above the weather.

That distinction is the useful place to start. The study does not say that a single flight suddenly becomes dangerous when solar activity ebbs. It says that the radiation environment at flight altitude changes with altitude, location and the solar cycle—important context for people who work repeatedly above the protective bulk of the lower atmosphere.

Six balloons climbed well above the airline cruising band

Dr. Roy Yaniv of Hebrew University of Jerusalem and Sheba Medical Center worked with Professor Yoav Yair of Reichman University and Professor Colin Price of Tel Aviv University on measurements from six balloon launches in southern Israel between 2014 and 2016. Their instruments climbed to about 35 kilometers, or 22 miles, giving the researchers a vertical view from near the ground to far above typical passenger-aircraft altitude.

Commercial aircraft commonly cruise at around 10 kilometers, or six miles. At that altitude, the team reported gamma-equivalent radiation dose rates of roughly 0.9 to 1.3 microsieverts per hour in its measurements. A microsievert is a very small unit used to express radiation dose; its value here is mainly comparative, showing that the environment aloft is not fixed even when the cabin experience feels routine.

The highest measured levels were above the usual flight path

The balloon data showed radiation increasing with altitude until it peaked around 17 to 20 kilometers, then declining again. Researchers call that region the Regener-Pfotzer maximum. It forms when high-energy cosmic rays entering the atmosphere collide with particles in the air and create cascades of secondary particles.

The finding is a reminder that a passenger jet is flying beneath the maximum, not outside the cosmic-ray environment altogether. The atmosphere still provides substantial shielding at cruise altitude, but less than it does at sea level. The exact exposure also varies by latitude because Earth’s magnetic field helps deflect charged particles, with the strength of that shielding changing by location.

A quieter Sun lets more galactic cosmic rays reach Earth

The Sun’s activity does more than produce visible sunspots and space-weather headlines. Its magnetic influence can help shield the solar system from galactic cosmic rays. When solar activity is high, that shielding is stronger. When activity drops, more energetic particles can reach Earth’s atmosphere.

The team found a negative correlation between solar activity and its radiation measurements, reported as r = -0.71. The authors cautioned that the limited number of observations makes that correlation indicative rather than statistically definitive. Their 40%–60% estimate for commercial aviation altitude is therefore best read as a modeled possibility for solar-minimum conditions, not a promise that every route will experience exactly the same jump.

Aircrew and frequent flyers are the clearest reason to keep measuring

The researchers’ concern is cumulative exposure, especially for pilots and cabin crew who spend far more time at altitude than an occasional traveler. It is also relevant to frequent flyers, although a study of atmospheric radiation is not a personal medical assessment. A route’s latitude, a plane’s altitude, the duration of a flight and the state of the solar cycle all change the setting.

One limitation deserves as much attention as the reported 40%–60% projection. The Geiger-Müller detectors used on the balloons were primarily sensitive to photons and charged particles, while the radiation field at flight altitude also includes neutrons. The researchers note that neutrons represent roughly 40% to 45% of modeled total ambient dose, so the reported direct measurements should not be treated as an all-in passenger dose.

That limitation does not erase the result; it defines its boundary. The balloon instruments supplied a reliable view of the electromagnetic component and agreed closely with the model for that component, generally within roughly 10% to 15%. The model then helped the researchers place those readings within a wider radiation field. Keeping those two layers separate is better science than treating one detector reading as a complete answer to a complicated exposure question.

The team said the atmosphere above aircraft is “continuously shaped by processes taking place far beyond Earth.” That is a precise way of describing why routine monitoring has value. Balloon observations paired with established models can show how conditions evolve without turning a solar lull into an alarm. The study’s central result is a measured relationship, a cautious 40%–60% solar-minimum projection and a reason to keep the aviation-radiation picture tied to data rather than assumption.

The study report is explicit that its 40%–60% figure is a projection. NASA’s space-weather overview explains the Sun’s changing influence on the near-Earth environment, while the FAA’s aeromedical radiation material addresses exposure at aviation altitude. The IAEA’s radiation-protection guidance supplies the wider measurement context. Those sources support a narrower conclusion than an alarmist reading: flight-altitude radiation is real, variable and best assessed through monitored conditions rather than a single headline number.

NOAA’s Space Weather Prediction Center provides the operational monitoring context for changing solar conditions.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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