Contrasting Space Weather Drivers of Two Geomagnetically Induced Current Events in Alberta, Canada During the May 2024 Superstorm

Strong geomagnetic disturbances (GMDs) caused by intense space storms induce geomagnetically induced currents (GICs) in the Earth and within long conductive infrastructure, potentially posing risks to electricity transmission systems. Here, we investigate the solar wind conditions and magnetospheric processes responsible for two significant GIC events observed in Alberta, Canada, during the intense May 2024 geomagnetic storm. Though no outages or damages were documented by Alberta utilities, transformer neutral-to-ground (TNG) measurements, provided by AltaLink LP, recorded GIC exceeding 150 A flowing through three transformers. The first GIC event during the studied interval, 08:00 to 11:00 UT, reached 20 A at 08:53 UT, measured at a southern Alberta substation, and was driven by substorm-related activity with an onset at unusually low sub-auroral latitudes. The second GIC event resulted from magnetospheric compression triggered by a rapid increase in solar wind density, leading to a stronger and more global GMD, resulting in a measured peak GIC of 165 A at 09:41 UT in central Alberta and 38 A at 09:38 in southern Alberta, with the period of intense GIC lasting around 10 min. Further, a strong correlation was seen between the GIC predicted by a data-driven DC-equivalent network model and the observed GIC at both the transformer neutral and in the power line, the latter measured using the differential magnetometer method. Despite the large-scale nature of event 2, the GIC model demonstrates the importance of grid topology for determining where the largest GIC occur within the Alberta Interconnected Electric System.