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An interplanetary shock can abruptly compress the magnetosphere, excite magnetospheric waves and field-aligned currents, and cause a ground magnetic response known as a sudden commencement (SC). However, the transient (

Dipolarizing flux bundles (DFBs) have been suggested to transport energy and momentum from regions of reconnection in the magnetotail to the high latitude ionosphere, where they can generate localized ionospheric currents that can produce large nighttime geomagnetic disturbances (GMDs). In this study we identified DFBs observed in the midnight sector from ~7 to ~10 RE by THEMIS A, D, and E during days in 2015-2017 whose northern hemisphere magnetic footpoints mapped to regions near Hudson Bay, Canada, and have compared them to isolated GMDs observed by ground magnetometers. We found 6 days during which one or more of these DFBs coincided to within ±3 min with ≥6 nT/s GMDs observed by latitudinally closely spaced ground-based magnetometers located near those footpoints. Spherical elementary current systems (SECS) maps and all-sky imager data provided further characterization of two events, showing short-lived localized intense upward currents, auroral intensifications and/or streamers, and vortical perturbations of a westward electrojet. On all but one of these days the coincident DFB--GMD pairs occurred during intervals of high-speed solar wind streams but low values of SYM/H. The observations reported here indicate that isolated DFBs generated under these conditions influence only limited spatial regions nearer Earth. In some events, in which the DFBs were observed closer to Earth and with lower Earthward velocities, the GMDs occurred slightly earlier than the DFBs, suggesting that braking had begun before the time of the DFB observation. [ABSTRACT FROM AUTHOR]

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. Plain Language Summary: Geomagnetically induced currents (GICs) can give rise to the most extreme space weather impact of disrupting electric power distribution. GICs can be driven by extreme geomagnetic disturbances (GMDs) that are observed as large amplitude (several hundred nT amplitude) and rapid (5–10 min period) changes in the geomagnetic field. We found that extreme high‐latitude GMDs occur throughout the solar cycle, but are preferentially observed during the declining phase of the solar cycle (the several year interval just past solar maximum) and in conjunction with high‐speed solar wind streams. They also all occur within 80 min of a geomagnetic substorm, but are not directly related to its explosive onset. These GMDs are most often observed to propagate poleward consistent with tailward retreat of magnetotail reconnection regions. These results show that extreme GMDs and hence large GICs can be driven by a variety of solar wind conditions and not just fast coronal mass ejections. Key Points: Most large (6 nT/s) and extreme (>20 nT/s) high latitude geomagnetic disturbances (GMDs) occurred during the declining phase of the sunspot cycleMost extreme GMDs occurred during high‐speed solar wind streams and often within 25 min after a substorm onset, but seldom within 5 minMany extreme GMDs showed a poleward progression, consistent with the tailward retreat of the magnetotail reconnection region [ABSTRACT FROM AUTHOR]

A predictive model for the variation of ionospheric currents is of great scientific and practical importance to our modern industrial society. To study the response of ionospheric currents to external drivers including geomagnetic indices and solar radiation, we developed a feedforward neural network model trained on the Equivalent Ionospheric Current (EIC) data from 1st January 2007 to 31st December 2019. Due to the highly imbalanced nature of the ionospheric currents data, which means that the data of extreme events are much less than those of quiet times, we utilized different loss functions to improve the model performance. Our model demonstrates the potential to predict the active events of ionospheric currents reasonably well (e.g., EICs during substorms) within a timescale of a few minutes. Although the data used for training are measurements over the North American and Greenland sectors, our model is not only able to predict EICs within this region, but is also able to provide a promising out‐of‐sample prediction on a global scale. Plain Language Summary: Studying the ionospheric current system is important for our modern society, since its drastic change can impact the ground‐based facilities such as power grid. We used a neural network model to predict the influence of geomagnetic activities and upstream condition on the variation of ionospheric currents over the North American and Greenland regions during a whole solar cycle period. Because the data set of ionospheric currents is highly imbalanced, we used different loss function to optimize our model. We found that our model can reasonably well predict the ionospheric current events which are related to the magnetospheric activities. We also found that our model can provide predictions beyond the North American and Greenland regions. Key Points: A neural network is trained to predict the response of Equivalent Ionospheric Currents (EIC) to geomagnetic indicesA comparative study between the mean square error and focal loss has been made to address the EIC's imbalance regression problemOur model can spatially and temporally predict the eastward‐westward EIC component [ABSTRACT FROM AUTHOR]

We have examined the most intense external (magnetospheric and ionospheric) and internal (induced) | d H /dt | (amplitude of the 10 s time derivative of the horizontal geomagnetic field) events observed by the high-latitude International Monitor for Auroral Geomagnetic Effects (IMAGE) magnetometers between 1994 and 2018. While the most intense external | d H /dt | events at adjacent stations typically occurred simultaneously, the most intense internal (and total) | d H /dt | events were more scattered in time, most likely due to the complexity of induction in the conducting ground. The most intense external | d H /dt | events occurred during geomagnetic storms, among which the Halloween storm in Oct 2003 featured prominently, and drove intense geomagnetically induced currents (GIC). Events in the prenoon local time sector were associated with sudden commencements (SC) and pulsations, and the most intense | d H /dt | values were driven by abrupt changes in the eastward electrojet due to solar wind dynamic pressure increase or decrease. Events in the premidnight and dawn local time sectors were associated with substorm activity, and the most intense | d H /dt | values were driven by abrupt changes in the westward electrojet, such as weakening and poleward retreat (premidnight) or undulation (dawn). Despite being associated with various event types and occurring at different local time sectors, there were common features among the drivers of most intense external | d H /dt | values: pre-existing intense ionospheric currents (SC events were an exception) that were abruptly modified by sudden changes in the magnetospheric magnetic field configuration. While proper description of the fast changes during SC events appears to require 1 s data, pulsations and substorms may be sufficiently described by 10 s | d H /dt |. 1 min data, however, significantly underestimates the | d H /dt | peaks. Our results contribute towards the ultimate goal of reliable forecasts of d H /dt and GIC. [ABSTRACT FROM AUTHOR]