Nearly all studies of impulsive magnetic perturbation events (MPEs) with large magnetic field variability (dB/dt) that can produce dangerous geomagnetically induced currents (GICs) have used data from the Northern Hemisphere. Here we present details of four large‐amplitude MPE events (|ΔBx| > 900 nT and |dB/dt| > 10 nT/s in at least one component) observed between 2015 and 2018 in conjugate high‐latitude regions (65–80° corrected geomagnetic latitude), using magnetometer data from (1) Pangnirtung and Iqaluit in eastern Arctic Canada and the magnetically conjugate South Pole Station in Antarctica and (2) the Greenland West Coast Chain and two magnetically conjugate chains in Antarctica, AAL‐PIP and BAS LPM. From one to three different isolated MPEs localized in corrected geomagnetic latitude were observed during three premidnight events; many were simultaneous within 3 min in both hemispheres. Their conjugate latitudinal amplitude profiles, however, matched qualitatively at best. During an extended postmidnight interval, which we associate with an interval of omega bands, multiple highly localized MPEs occurred independently in time at each station in both hemispheres. These nighttime MPEs occurred under a wide range of geomagnetic conditions, but common to each was a negative interplanetary magnetic field Bz that exhibited at least a modest increase at or near the time of the event. A comparison of perturbation amplitudes to modeled ionospheric conductances in conjugate hemispheres clearly favored a current generator model over a voltage generator model for three of the four events; neither model provided a good fit for the premidnight event that occurred near vernal equinox.

Space weather events occur due to the interaction of active solar wind with near-Earth space, activating magnetohydrodynamic (MHD) and electromagnetic transfer processes that propagate throughout the magnetosphere-ionosphere (M-I) system down to the surface of Earth. Perhaps the most critical concern regarding space weather is the threat of large geomagnetically induced currents (GIC) to technological infrastructure on Earth. Flowing through man-made conductors on Earth like railways, pipelines and power grids, GICs can be large enough to cause damage to transformers resulting in major power outages and costly equipment damage (Boteler et al., 1998;Pulkkinen et al., 2017). GICs are the result of a horizontal surface electric field E induced in Earth's surface that is driven by large changes of the surface magnetic field, dB/dt, via Faraday's law of induction. Hazardous GICs associated with large, rapid magnetic disturbances often result from the most disruptive geomagnetic storms and auroral substorms. Therefore, significant efforts of the geophysical community are aimed at developing global MHD models of geomagnetic storm and substorm activity and incorporating the magnetotelluric response of the Earth to compute GICs (Pulkkinen et al., 2015;Zhang et al., 2012). However, beyond the largest space weather events, several studies suggest that there are more rapid, small-scale and localized processes involved in generating some extreme GICs (

Space weather events occur due to the interaction of active solar wind with near-Earth space, activating magnetohydrodynamic (MHD) and electromagnetic transfer processes that propagate throughout the magnetosphere-ionosphere (M-I) system down to the surface of Earth. Perhaps the most critical concern regarding space weather is the threat of large geomagnetically induced currents (GIC) to technological infrastructure on Earth. Flowing through man-made conductors on Earth like railways, pipelines and power grids, GICs can be large enough to cause damage to transformers resulting in major power outages and costly equipment damage (Boteler et al., 1998;Pulkkinen et al., 2017). GICs are the result of a horizontal surface electric field E induced in Earth's surface that is driven by large changes of the surface magnetic field, dB/dt, via Faraday's law of induction. Hazardous GICs associated with large, rapid magnetic disturbances often result from the most disruptive geomagnetic storms and auroral substorms. Therefore, significant efforts of the geophysical community are aimed at developing global MHD models of geomagnetic storm and substorm activity and incorporating the magnetotelluric response of the Earth to compute GICs (Pulkkinen et al., 2015;Zhang et al., 2012). However, beyond the largest space weather events, several studies suggest that there are more rapid, small-scale and localized processes involved in generating some extreme GICs (

Extreme (≥ 20 nT/s) geomagnetic disturbances (GMDs, also denoted as MPEs - magnetic perturbation events) – impulsive nighttime disturbances with time scale ~5-10 min, have sufficient amplitude to cause bursts of geomagnetically induced currents (GICs) that can damage technical infrastructure. In this study we present occurrence statistics for extreme GMD events from five stations in the MACCS and AUTUMNX magnetometer arrays in Arctic Canada at magnetic latitudes ranging from 65° to 75°. We report all large (≥ 6 nT/s) and extreme GMDs from these stations from 2011 through 2022 to analyze variations of GMD activity over a full solar cycle and compare them to those found in three earlier studies. GMD activity between 2011 and 2022 did not closely follow the sunspot cycle, but instead was lowest during its rising phase and maximum (2011-2014) and highest during the early declining phase (2015-2017). Most of these GMDs, especially the most extreme, were associated with high-speed solar wind streams (Vsw > 600 km/s) and steady solar wind pressure. All extreme GMDs occurred within 80 min after substorm onsets, but few within 5 min. Multistation data often revealed a poleward progression of GMDs, consistent with a tailward retreat of the magnetotail reconnection region. These observations indicate that extreme GIC hazard conditions can occur for a variety of solar wind drivers and geomagnetic conditions, not only for fast-coronal mass ejection driven storms.

We present an automated method to identify high‐frequency geomagnetic disturbances in ground magnetometer data and classify the events by the source of the perturbations. We developed an algorithm to search for and identify changes in the surface magnetic field, dB/dt, with user‐specified amplitude and timescale. We used this algorithm to identify transient‐large‐amplitude (TLA) dB/dt events that have timescale less than 60 s and amplitude >6 nT/s. Because these magnetic variations have similar amplitude and time characteristics to instrumental or man‐made noise, the algorithm identified a large number of noise‐type signatures as well as geophysical signatures. We manually classified these events by their sources (noise‐type or geophysical) and statistically characterized each type of event; the insights gained were used to more specifically define a TLA geophysical event and greatly reduce the number of noise‐type dB/dt identified. Next, we implemented a support vector machine classification algorithm to classify the remaining events in order to further reduce the number of noise‐type dB/dt in the final data set. We examine the performance of our complete dB/dt search algorithm in widely used magnetometer databases and the effect of a common data processing technique on the results. The automated algorithm is a new technique to identify geomagnetic disturbances and instrumental or man‐made noise, enabling systematic identification and analysis of space weather related dB/dt events and automated detection of magnetometer noise intervals in magnetic field databases.