Solar Storm Pushed Flight Radiation Past Safety Limits With No Alert

Radiation from the strongest solar radiation storm in nearly 20 years climbed to around 1000 times the normal ground-level background in the air high above Shetland, at the northern tip of the UK, according to a study in the journal Space Weather. Hours after the peak, levels crossed international aviation safety thresholds, yet no aviation advisory went out.

The research, led by Fraser Baird and Ben Clewer of the University of Surrey and reported by Physics World, looked at a single event: a storm labeled GLE 77 that struck on Nov. 11, 2025.

How a solar outburst reached the ground

Cosmic rays always add a little radiation to Earth’s atmosphere. In a Ground Level Enhancement, or GLE, the Sun throws out particles with enough energy to raise that background all the way down to the surface. The dose grows with altitude, so aircraft are more exposed than people on the ground.

GLE 77 started at 10:05 UTC with an X5-class flare (a large eruption on the Sun) and a coronal mass ejection, a cloud of material thrown into space. Particles arrived at nearly the speed of light, and ground monitors picked up the rise at around 10:15 UTC. At Lerwick in Shetland, the ground count more than doubled.

Balloons, ground monitors and two passenger jets

Within an hour of the storm’s start, the Met Office began launching weather balloons carrying radiation detectors from Shetland. The team combined those readings with four neutron monitors on the ground across the UK and with radiation monitors on two passenger aircraft. The balloons rose as high as 106,000 feet, above the altitudes where supersonic jets fly.

Baird told Physics World the balloon data gave him the biggest surprise. The readings also showed how quickly the effect dropped off to the south: Camborne, near the southern end of the UK, saw only a 12% increase at ground level.

Part of that gap comes from Earth’s magnetic field, which shields less near the poles. The rest comes from anisotropy, meaning the particles arrived mostly from one part of the sky. Baird compared it to a torch beam aimed at Earth. The magnetic field bends that beam, so places close to each other can get particles from different directions, and hotspots form where the risk is highest. The storm also had two separate radiation peaks, which Baird said points to particles being accelerated long after the visible flare had faded.

What it means for flights

Several hours after the peak, radiation over Lerwick passed the International Civil Aviation Organization’s “moderate” threshold at business-jet altitudes and its “severe” threshold at supersonic altitudes. Baird called the missing warning the study’s main finding and said aviation space weather alerts “can be improved upon.”

The trouble is that GLEs cannot yet be forecast. Forecasters rely on nowcasts, estimates built from live measurements, and this event showed those still fall short.

One London-to-New York flight that departed during the storm logged radiation exposure 46% above normal. That route crosses high northern latitudes, where the magnetic field protects aircraft least, and the researchers note that more flights now use such routes. A second flight to New York, leaving about six hours later, recorded no significant rise. The aircraft readings came after the strongest hotspots had passed, which is why the on-demand balloon launches mattered so much.

For passengers, the dose was small. Baird estimates that someone flying through the peak picked up extra radiation equal to about two additional flights. The larger worry is aircraft electronics, which radiation can disrupt; Physics World notes that Airbus recently grounded around 6000 aircraft to fix a radiation-induced fault.

Limits of one modest storm

The findings rest on one event, and by historical standards it was modest. A 1956 storm was about 50 times more intense. Concorde, which made the first GLE observation ever recorded from an aircraft, carried radiation monitors on every flight, and Baird would like all aircraft, especially supersonic ones, to do the same.

What the team is doing next

The Surrey group is now measuring how narrow the particle beam was, working on better nowcasts and adding monitors to aircraft and balloons, so that a stronger storm can be tracked at every altitude.

Source: Physics World