Observations of Atmospheric Radiation Increases During GLE 77 From New Airborne and Ground Level Instruments

Abstract

On 11 November 2025, at approximately 10:20 UTC, the 77th Ground Level Enhancement (GLE) occurred. This paper presents a comprehensive data set encompassing observations from ground‐level neutron monitors across the United Kingdom (UK), radiation monitors on radiosonde flights from the UK and the Netherlands, and radiation monitors onboard transatlantic flights from London‐Heathrow to New York. The ground level observations reveal a strong anisotropy in the event intensity and time profile across the UK, where a strong peak was observed in the north at the beginning of the event, and a second weaker peak was observed in the south approximately 1 hr later. Data from radiosondes launched from the northern extremity of the UK show that the threshold for an International Civil Aviation Organisation (ICAO) moderate radiation threshold was exceeded at business jet altitudes several hours after the event peak, and at supersonic altitudes the severe threshold was exceeded by a factor of two. Other radiosonde flights from the south of the UK and the Netherlands did not show a significant increase in radiation levels. One Heathrow‐New York (JFK) flight, departing at 11:45 UTC, experienced a 42.6 % increase in total ambient dose equivalent exposure, compared to typical background conditions, but did not observe any ICAO thresholds being exceeded. The second flight, (Heathrow‐Newark) departing at 17:45 UTC did not observe any significant increase in radiation exposure.