Earth Hit by Year's Strongest Geomagnetic Storm, a G4 Event Triggering Auroras Across 21 U.S. States

Between Wednesday, November 12, and Thursday, November 13, 2025, the Earth’s environment was impacted by an exceptionally powerful geomagnetic storm. This celestial event achieved a G4 classification on the NOAA scale, officially registering as the most intense solar disturbance recorded during the current year. Although the storm did not reach the maximum anticipated G5 level, it peaked with Kp indices ranging significantly between G4.3 and G4.7. The initial trigger for this massive disturbance was a sequence of intense solar eruptions, including a notable X1.7 class flare that had occurred on November 9.

Researchers at the Laboratory of Solar Astronomy IKI RAS and ISZF SB RAS determined that the anomalous severity of the storm resulted from a critical “double impact.” This phenomenon involved two distinct Coronal Mass Ejections (CMEs), which were launched from the Sun on November 9 and November 10, respectively, merging while in transit. The second, faster ejection overtook the earlier cloud of plasma, compressing and accelerating it. This fusion created a single, far denser, and quicker structure, dramatically intensifying the subsequent interaction with the planet's magnetosphere. Consequently, the actual storm dynamics exceeded the initial forecasts, which had predicted a less severe G3–G4 level.

The cosmic phenomenon yielded spectacular visual consequences. The resulting expansion of the auroral oval meant that the Northern Lights (Aurora Borealis) became visible in latitudes where such occurrences are extremely rare. Notably, Stable Auroral Red (SAR) arcs, which are highly atypical for mid-latitudes, were successfully documented in Catalonia, Spain. Within the United States, the aurora was observed in a minimum of 21 states, painting the skies across a vast geographical area stretching from Alaska to the southern reaches of Florida and Alabama.

In addition to the visual spectacle, both the European Space Agency (ESA) and NOAA issued critical advisories regarding potential risks to technological infrastructure. Geomagnetic disturbances classified at the G4 level significantly elevate the likelihood of interference with satellite navigation systems. Moreover, these powerful fluctuations can induce failures or disruptions in terrestrial power grids, particularly those operating in higher northern latitudes. NOAA specialists maintained continuous, rigorous monitoring throughout the event, given the persistent possibility that the storm might have escalated to the maximum G5 level.

While the storm presented technological threats, it carried no direct biological danger to the general population. Nevertheless, individuals sensitive to meteorological changes, especially those managing chronic cardiovascular and nervous system conditions, may have experienced related symptoms, such as headaches and fluctuations in blood pressure. Scientists confirmed that activity began a steady decline after the peak intensity was reached on November 12. A long-term stabilization of the magnetosphere is now expected, as the active centers on the Sun have rotated out of the direct Sun-Earth line. Infrastructure operators and the public are urged to maintain awareness, although the probability of further strong disturbances occurring before the end of November is considered low.