ESA spacecraft observe highest ground level enhancement of Solar Cycle 25 and subsequent geomagnetic storm

Authors: Laura Rodríguez-García, Matthew Taylor, Anja Stromme, Jorge Amaya, Daniel Müller, Miho Janvier, Olivier Witasse, Geraint Jones, Sebastien Besse, Domenico Trotta, Federica Guarnaccia, Anik De Groof, Andrew Walsh, Klaus Scipal, Raffaele Crapolicchio, Juha-Pekka Luntama, Hugh Evans, Beatriz Sánchez-Cano and the ESA Heliophysics group.

On 11 November 2025, a very powerful X5 solar flare erupted from active region NOAA (AR) 14274. It was recorded by the STIX instrument on Solar Orbiter, peaking around 10:04 UTC. At the same time, ESA’s SMOS spacecraft detected a large radio burst at 1.4 GHz, which persisted for approximately 30 minutes with peak intensities exceeding 12,000 solar flux units—roughly 100 times higher than those observed for a quiet Sun. The observations also included measurements of the circular polarisation of radio waves — a quantity only few instruments can observe. These space-borne observations are consistent with the radio bursts observed by radio spectrographs on the ground. Less than an hour later, a fast coronal mass ejection (CME) was released — a huge cloud of solar plasma racing through space at about 1800 km/s (6.5 million km/h), according to SOHO/LASCO coronagraph data. The CME reached Earth on 12 November around 18:00 UTC. Solar Orbiter, which was positioned closer to the Sun (0.82 au) and slightly west of Earth, encountered the CME about nine hours earlier.

During the event, several spacecraft measured high-energy particles. Solar Orbiter detected energetic electrons above 7 MeV, including penetrating ions above 400 MeV. BepiColombo, which had the best nominal magnetic connection to the eruption site on the Sun, measured protons above 70 MeV.  

On Earth, ground-based neutron monitors observed a rare Ground Level Enhancement (GLE), an event where exceptionally energetic particles from the Sun have sufficient energy to generate effects that can be measured at the Earth's surface. The particles that reached Earth arrived shortly after 10:00 UTC on 11 November. Its unusually large latitudinal spread indicates that the particles reached deep into the geomagnetic field, demonstrating that this was an extremely strong and highly energetic particle event. This was the strongest GLE of Solar Cycle 25 to date..

A few hours after the GLE detection, two earlier CMEs ejected from the same active region also arrived at Earth. Their combined effect triggered a geomagnetic storm, a temporary disturbance of the Earth's magnetosphere. ESA’s Swarm satellites, which monitor Earth’s magnetic field, recorded magnetic fluctuations up to ten times stronger than normal. Another exciting finding was that Swarm’s star trackers, which are normally used to correctly orient the satellites, detected a temporary enhancement of high energy protons at in the polar regions.