Authors: Alessandro Bruno (NASA/GSFC & CUA)

The solar eruptions of 11 November 2025 and 18 January 2026 produced two of the most remarkable space weather events of Solar Cycle 25, yet their impacts differed dramatically despite both being associated with fast coronal mass ejections (CMEs) and X-class flares. The November event produced the major Ground Level Enhancement (GLE) 77 and was followed by a complex energetic storm particle (ESP) enhancement driven by interacting solar-wind structures associated with preceding eruptions. In contrast, the January event produced exceptionally intense low-energy solar energetic particle (SEP) fluxes, a pronounced Forbush decrease, yet lacked a high-energy component. Both periods caused a severe geomagnetic storm. In this scene-setter presentation, I compare these two events using remote-sensing observations, in situ particle and solar wind measurements, and neutron monitor observations to investigate the physical drivers that led to these divergent outcomes. The analysis highlights how the combined effects of the solar eruption mechanisms, CME evolution, magnetic connectivity, heliospheric preconditioning, and interplanetary transport shaped the observed SEP characteristics and their geospace impacts, emphasizing the importance of these factors for understanding and forecasting extreme space weather events.