Analysis of geomagnetically induced currents (GICs) during the May 2024 Gannon storm

The May 2024 Gannon storm, one of the most intense geomagnetic disturbances (GMDs) in two decades, provides a valuable opportunity to examine geomagnetically induced currents (GICs), their drivers, and impacts on bulk power system resilience. We analyzed GICs over the United States using direct measurements from three North American Electric Reliability Corporation (NERC) monitoring devices, magnetometer-derived proxy indices, and continuous wavelet transform (CWT). The storm featured multiple substorm onsets, supersubstorms (SSSs), and westward electrojet (WEJ). Results show that during the sudden storm commencement on 10 May, magnetic field variations, d H / d t reached 80 nT/min at ∼54° MLAT with GICs of up to 70 A recorded by device 10659 (∼54° MLAT) at about 17:08 UT. During the main phase on 10 May, GICs peaked at 128 A at device 10659 around 21:44 UT due to substorm activity in conjunction with Ps6 pulsations. Furthermore, the substorm onset at ∼02:00 UT on 11 May was associated with an enhanced d H / d t of 437 nT/min at ∼56° MLAT and the largest GIC response to this GMD with a peak of 176 A (device 10659) at 02:04 UT. CWT analysis further suggests that Ps6 magnetic pulsations contributed as secondary driving mechanisms. The recovery phase was characterized by significant GICs up to 120 A at the same device around 08:41 UT, related to coupled magnetospheric drivers, including Pc5 magnetic pulsations and a SSS under magnetic cloud conditions. This storm phase further featured a GIC of 91 A (at 04:32 UT) associated with substorm activity detected during the high-speed stream on 12 May. The study highlights the role of substorms, SSSs, and associated localized magnetic disturbances driven by distinct ICME features, in generating substantial GICs during the recovery phase of intense storms, emphasizing their critical impact on space-weather hazards.