Geoeffectiveness of Interplanetary Storm Drivers during Solar Cycle 25 through June 2026: A Comparative Study of ICMEs, Sheath Regions, and Corotating Interaction Regions

Abstract

This study presents a cycle-to-date classification and geoeffectiveness analysis of the interplanetary drivers of geomagnetic storms during Solar Cycle 25 (SC25), from December 2019 to 24 June 2026. Hourly OMNI solar-wind plasma and interplanetary magnetic-field data were analysed together with the Dst, Kp, and AE indices. A total of 111 storms with minimum Dst <= -50 nT were identified and assigned to interplanetary coronal mass-ejection (ICME) ejecta or magnetic clouds, sheath regions, combined sheath-plus-ejecta (S+E) structures, or corotating interaction region/high-speed-stream (CIR/HSS) drivers. The catalogue contains 86 moderate, 19 intense, five superintense, and one extreme storm. S+E structures account for 65 storms and 23 of the 25 storms at intense or stronger levels (92%), including all six superintense-or-extreme events. CIR/HSS storms (n = 28) are almost exclusively moderate. Across the full sample, minimum Dst is most strongly associated with peak southward IMF Bz (r = 0.85) and maximum dynamic pressure (|r| = 0.80); the Bz-Dst relationship is tighter for S+E events (r = 0.87) than for CIR/HSS events (r = 0.52). The relative CIR/HSS contribution increases during the declining phase, while ICME-related activity remains substantial. A constant-coefficient linear Burton-type model provides limited pooled hindcast skill, particularly for CIR/HSS storms. A nonlinear threshold-injection formulation with driver-dependent decay scaling, calibrated on pre-2025 storms and evaluated on 2025-2026 storms, yields correlations of r = 0.86-0.91 and prediction efficiencies of 0.74-0.81 across the principal driver classes. Storm-level cross-validation and sensitivity testing indicate that these cycle-to-date conclusions are not driven by a single fitting split or by the uncertain classification of moderate storms. Because the analysis concerns one incomplete solar cycle and relatively few extreme events, the inferred S+E dominance should be treated as an SC25-specific finding requiring confirmation across additional cycles.