Superposed Epoch Analysis of Extreme Geomagnetic Disturbances at Auroral Zone Latitudes Over a Solar Cycle

Abstract Intense and rapidly changing electrical currents in near‐Earth space produce geomagnetic disturbances (GMDs) with large magnetic field rates of change (dB/dt) and in turn large geomagnetically induced currents (GICs) in nearby power lines and pipelines. This study builds on the work of Engebretson, Yang, et al. (2024, https://doi.org/10.1029/2023ja031643 ), designated as Paper 1, that presented observations of large and extreme geomagnetic disturbances (GMDs) with amplitude >20 nT/s in Eastern Arctic Canada over a full solar cycle. Here we present a superposed epoch analysis of the temporal context of these events from 2 hr before to 1 hr after each GMD with respect to the Polar Cap North (PCN) index, an indicator of solar wind driving of Earth's space environment, the SuperMAG SML index, an indicator of the intensity of westward auroral zone ionospheric currents, and the occurrences of substorm onsets identified in three substorm lists accessible at the SuperMAG web site. When sorted by categories of solar wind driving, nearly 90% of these events were found to occur when the solar wind velocity was >450 km/s. Postmidnight events were associated with CME and Corotating Interaction Regions storms and possibly with omega bands, while GMDs at earlier local times occurred not as substorm onsets but as intensifications of ongoing substorms. The PCN traces showed very similar temporal patterns before and during most premidnight extreme GMD events: a slow, gradual rise beginning ∼1 hr before and continuing during the GMD event, a slightly higher maximum 10–30 min later, and then a slight drop.