Statistical study of intense geomagnetic storms and their solar origins over the period 1996 ─ 2025

Abstract

Using in situ geomagnetic and solar wind observations, we present a comprehensive list of intense geomagnetic storms (GMSs) that occurred between 1996 and 2025, covering Solar Cycles (SCs) 23, 24, and the ongoing SC 25. The study focuses on storms with (Dst ≤ −100 nT), primarily driven by interplanetary coronal mass ejections (ICMEs), with the main objective of identifying and characterizing their solar source regions. Remote-sensing observations from the Solar and Heliospheric Observatory (SOHO), Solar TErrestrial RElations Observatory (STEREO), and Solar Dynamics Observatory (SDO) across multiple wavelengths are used to trace GMSs back to their solar origins. A total of 139 intense storms are identified, of which 120 are ICME-driven and 19 are associated with corotating interaction regions (CIRs). ICME-driven storms reach significantly larger intensities (Dst = −422 nT) compared to CIR-driven storms (Dst = −130 nT). With six cases being linked to stealth CMEs, this list of storms captures two super storms during SC 25, including the May 2024 event (Dst = −406 nT), the strongest in two decades. The following statistical conclusions are drawn: i) Storm occurrence and intensity are found to correspond well with solar cycle strength and sunspot number, with SC 23 producing the 87 storms, including 10 super storms, SC 24 producing 26 without super storms, and SC 25 producing 26 storms with two super storms. ii) The CME source regions exhibit a pronounced east–west asymmetry, with a majority (69%) originating from the western solar hemisphere. iii) Storm intensity shows weak dependence on flare strength and CME speed, although extreme storms are associated with higher average CME speeds and large flare strengths. iv) The Dst index has a strong correlation (0.74) with peak southward Bz, total magnetic field strength, and a linear fit arrives at the statistical relation that the Dst is five times the peak Bz. v) The Dst index has a significant correlation with the electric field Ey , with a linear relation Dst = 6.1×Ey −89.3. These results reinforce the dominant role of ICME magnetic structure in driving severe geomagnetic activity and provide an updated perspective on the solar origins and geoeffectiveness of intense geomagnetic storms across the solar cycles.