Introduction Geomagnetically induced currents (GICs) pose a critical space weather hazard to ground-based conductive infrastructure. Previous studies have commonly identified large GIC events using daily maximum amplitudes exceeding 10 A, a criterion that may obscure the detailed temporal structure of GIC disturbances. Methods In this study, we apply an improved identification criterion to systematically select 81 large GIC disturbance events from high-resolution (10 s) measurements at the Mäntsälä compressor station of the Finnish natural gas pipeline between 1999 and 2020, covering nearly two solar cycles. We investigated the statistical relationships between these events, geomagnetic storms, and interplanetary drivers. Results The analysis revealed that multiple large GIC disturbances can be triggered by a single intense geomagnetic storm. Statistically, 67 of the 81 large GIC events were associated with 39 intense geomagnetic storms (SymH ≤ −100 nT), confirming that intense storms are the primary driver. Notably, 14 events were associated with one weak and 13 moderate storms, demonstrating that lower-intensity storms are also capable of generating significant GICs. Furthermore, we examined the corresponding interplanetary sources and found that interplanetary coronal mass ejections (ICMEs) dominated, accounting for 72.84% of events and producing the most intense GIC disturbances. Discussion Stream interaction regions (SIRs), interactions between ICMEs and SIRs, and high-speed solar wind streams also contributed to the occurrence of large GIC disturbances.
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