Ground Level Enhancement in Hydrological Neutron Sensors: Coordination and Analysis (GLEHNSCAN)

On November 11th 2025, the level of ionising radiation in the atmosphere, recorded at ground level, suddenly increased; at Lerwick, radiation levels doubled in 10 minutes. Such an increase is called a Ground Level Enhancement (GLE), and the event in question, denoted GLE 77, was the largest in almost 20 years. GLEs are caused by space weather events, specifically by high energy protons  accelerated at the Sun during solar flares and coronal mass ejections. Travelling close to the speed of light, on reaching the Earth they interact with Earth’s atmosphere creating cascades of subatomic particles including protons, neutrons, and muons. While such cascades are always present due to galactic cosmic rays, their number can increase by orders of magnitude during a GLE. Such events are a particular hazard for aviation since they increase the radiation dose received by passengers and crew as well as increasing the risk of malfunctions in safety-critical on-board electronic flight control units. This risk was recently highlighted by the grounding of around 6000 Airbus A320s following the discovery of vulnerabilities to “intense solar radiation” in the avionics. Other critical infrastructure at ground level, including nuclear power controls and autonomous vehicles, can be affected in similar ways.
The great complicating factor of GLEs is their anisotropy. That is to say that their intensity varies significantly with location on Earth. This can result in localised radiation hotspots, the scale of which is not fully understood. Measuring atmospheric radiation levels is therefore critical to mitigating the risk associated with GLEs. They have been observed in the ground-level neutron monitor network since 1949, but this is geographically sparse and has declined to around 50 monitors worldwide. The consequence of this combination of a highly anisotropic phenomenon and a sparse observation network is that, during any given GLE, there is great uncertainty as to the true...