Speaker
Description
We present a preliminary analysis of two recent periods of quasi-extreme space weather driven by strong interplanetary (IP) shocks. In November 2025, four fast CMEs occurred within five days, each associated with an X-class flare. Although the third event had the highest soft X- ray peak flux and CME speed, giving rise to a ground level enhancement (GLE) event, it was the shock wave from the second eruption that was more surprising. It arrived much earlier than expected, causing not only a G5 geomagnetic storm but also a very rare energetic storm particle (ESP) event extending beyond 100 MeV. In January 2026, an apparently isolated CME (also associated with an X1.9 flare) drove a shock wave that remained strong when it arrived at 1 AU. The resulting ESP event reached the >10 MeV flux levels not observed since 1991 March 22 but its spectrum was very soft, in sharp contrast to the November 2025 event. This shock was again responsible for a G5 (Kp=9-) geomagnetic storm. We evaluate the relative roles of intrinsic CME properties and interplanetary preconditioning for producing these quasi-extreme radiation storm conditions of different kinds. Comparing them with other historical events that showed very high >10 MeV proton fluxes, we discuss the possible solar cycle dependence of how CME-driven shock waves evolve in the heliosphere.