GEOEFFECTIVENESS OF DIFFERENT SOLAR DRIVERS (CYCLES 22–25)

We investigate the geoeffectiveness of three primary types of solar wind structures: high-speed streams from coronal holes (HSS/CIR), coronal mass ejections (CMEs) exhibiting a magnetic cloud (MC) structure, and CMEs without a clear flux-rope signature (non-MC CMEs). We analyze data spanning four solar cycles (22–25) to examine each driver’s occurrence frequency, typical solar wind parameters (speed and magnetic field), and resulting effects on the global geomagnetic indices Kp and Dst. The results confirm that MC-type CMEs are the most efficient producers of intense storms (Dst ≤ –100 nT) due to prolonged intervals of southward magnetic fields. However, in weaker solar cycles (e.g., cycle 24), the average intensity and geoeffectiveness of MC events decline, reducing the overall contribution of CME-driven storms. In contrast, HSS/CIR events tend to induce moderate geomagnetic storms (Dst in the –50 to –80 nT range) coupled with elevated Kp for several consecutive days. These streams become the dominant source of geomagnetic activity during the declining phase of the solar cycle, when persistent coronal holes remain active while strong CMEs become less frequent. Preliminary data from the rising phase of cycle 25 already suggest a rebound in CME geoeffectiveness compared to the unusually weak cycle 24. These findings underscore the importance of accounting for solar cycle phase in space weather forecasting, as different solar drivers dominate at different times and affect Earth’s magnetosphere in distinct ways.