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Abstract Auroral substorms that move from auroral (<70°) to polar (>70°) magnetic latitudes (MLAT) are known to occur preferentially when a high‐speed solar wind stream passes by Earth. We report here on observations that occurred during a ∼75‐min interval with high‐speed solar wind on 28 November 2022 during which auroral arcs and very large geomagnetic disturbances (GMDs), also known as magnetic perturbation events (MPEs), with amplitude >9 nT/s = 540 nT/min moved progressively poleward at eight stations spanning a large region near and north of Hudson Bay, Canada shortly before midnight local time. Sustained GMD activity with amplitudes >3 nT/s appeared at each station for durations from 13 to 25 min. Spherical Elementary Currents Systems maps showed the poleward movement of a large‐scale westward electrojet as well as mesoscale electrojet structures and highly localized up/down pairs of vertical currents near these stations when the largest GMDs were observed. This study is consistent with other recent studies showing that very large poleward‐progressing GMDs can occur under high Vsw conditions, but is the first to document the sustained occurrence of large GMDs over such a wide high‐latitude region. 

Abstract Ultraviolet images of Earth's polar regions obtained by high altitude spacecraft have proved to be immensely useful for documenting numerous features of the aurora and understanding the coupling between Earth's magnetosphere and ionosphere. In this study we have examined images obtained by the far ultraviolet Spectrographic Imager camera on the IMAGE satellite during the first three years of its mission (2000–2002) for comparison with observations of large geomagnetic disturbances (GMDs) by ground‐based magnetometers in eastern Arctic Canada. To our knowledge, this is the first study to investigate the use of high‐altitude imager data to identify the global context of GMDs. We found that rapid auroral motions or localized intensifications visible in these images coincide with regions of largedB/dtas well as localized and closely spaced up/down vertical currents and increased equivalent ionospheric currents, but one of the two events presented did not appear to be related to substorm processes. These magnetic perturbations and currents can appear or disappear in a few tens of seconds, thus highlighting the importance of images with a high cadence. 

Abstract 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. 

Abstract 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/dtevents 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/dtidentified. 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/dtin the final data set. We examine the performance of our complete dB/dtsearch 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/dtevents and automated detection of magnetometer noise intervals in magnetic field databases. 

Abstract Large changes of the magnetic field associated with magnetic perturbation events (MPEs) with amplitudes |ΔB| of hundreds of nT and 5–10 min duration have been frequently observed within a few hours of midnight. This study compares the statistical location of nighttime MPEs with |dB/dt| ≥ 6 nT/s within the auroral current system observed during 2015 and 2017 at two stations, Cape Dorset and Kuujjuarapik, in Eastern Canada. Maps of the two dimensional nightside auroral current system were derived using the Spherical Elementary Current Systems (SECS) technique. Analyses were produced at each station for all events, and for premidnight and postmidnight subsets. We examine four MPE intervals in detail, two accompanied by auroral images, and show the varying associations between MPEs and overhead ionospheric current systems including electrojets and the field‐aligned like currents. We find 225 of 279 MPEs occurred within the westward electrojet and only 3 within the eastward electrojet. For the premidnight MPEs 100 of 230 events occurred within the Harang current system while many of the remainder occurred within either the downward region 1 current system or the upward region 2 current system. Many of the 49 postmidnight MPEs occurred in either the downward region 1 (11 events) or upward region 2 current system (27 events). These result suggest that the source of MPEs in the premidnight sector is somewhere between the inner to mid plasma sheet and the source for the MPEs in the postmidnight sector is somewhere between the inner magnetosphere and the inner plasma sheet. 

Abstract Rapid changes of magnetic fields associated with nighttime magnetic perturbation events (MPEs) with amplitudes |ΔB| of hundreds of nT and 5–10 min duration can induce geomagnetically induced currents (GICs) that can harm technological systems. Here we present superposed epoch analyses of large nighttime MPEs (|dB/dt| ≥ 6 nT/s) observed during 2015 and 2017 at five stations in Arctic Canada ranging from 64.7° to 75.2° in corrected geomagnetic latitude (MLAT) as functions of the interplanetary magnetic field (IMF), solar wind dynamic pressure, density, and velocity, and the SML, SMU, and SYM/H geomagnetic activity indices. Analyses were produced for premidnight and postmidnight events and for three ranges of time after the most recent substorm onset: (a) 0–30 min, (b) 30–60 min, and (c) >60 min. Of the solar wind and IMF parameters studied, only the IMF Bz component showed any consistent temporal variations prior to MPEs: a 1–2 h wide 1–3 nT negative minimum at all stations beginning ∼30–80 min before premidnight MPEs, and minima that were less consistent but often deeper before postmidnight MPEs. Median, 25th, and 75th percentile SuperMAG auroral indices SML (SMU) showed drops (rises) before pre‐ and post‐midnight type A MPEs, but most of the MPEs in categories B and C did not coincide with large‐scale peaks in ionospheric electrojets. Median SYM/H indices were flat near −30 nT for premidnight events and showed no consistent temporal association with any MPE events. More disturbed values of IMF Bz, Psw, Nsw, SML, SMU, and SYM/H appeared postmidnight than premidnight. 

Abstract 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 (|ΔB_x| > 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 fieldB_zthat 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.