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In this study, we investigate the effects caused by interplanetary (IP) shock impact angles on the subsequent ground dB/dt variations during substorms. IP shock impact angles have been revealed as a major factor controlling the subsequent geomagnetic activity, meaning that shocks with small inclinations with the Sun‐Earth line are more likely to trigger higher geomagnetic activity resulting from nearly symmetric magnetospheric compressions. Such field variations are linked to the generation of geomagnetically induced currents (GICs), which couple to artificial conductors on the ground leading to deleterious consequences. We use a sub‐set of a shock data base with 237 events observed in the solar wind at L1 upstream of the Earth, and large arrays of ground magnetometers at stations located in North America and Greenland. The spherical elementary current system methodology is applied to the geomagnetic field data, and field‐aligned‐like currents in the ionosphere are derived. Then, such currents are inverted back to the ground and dB/dt variations are computed. Geographic maps are built with these field variations as a function of shock impact angles. The main findings of this investigation are: (a) typical dB/dt variations (5–10 nT/s) are caused by shocks with moderate inclinations; (b) the more frontal the shock impact, the more intense and the more spatially defined the ionospheric current amplitudes; and (c) nearly frontal shocks trigger more intense dB/dt variations with larger equatorward latitudinal expansions. Therefore, the findings of this work provide new insights for GIC forecasting focusing on nearly frontal shock impacts on the magnetosphere. Plain Language Summary: Space weather effects caused by solar perturbations can increase the intensity of electric currents flowing in the Earth's upper atmosphere. These currents in turn induce geoelectric currents on the ground that couple with ground infrastructure, such as power transmission lines, oil/gas pipelines, and railways, which further cause deleterious consequences. Recent studies have shown that the angle with which solar perturbations impact the Earth closely controls intensifications of electric currents in the upper atmosphere and the subsequent ground magnetic field perturbations causing geoelectric currents. When these space weather drivers impact Earth more frontally, the resulting atmospheric current enhancements and the subsequent ground magnetic field perturbations are generally more intense. In this study, we use a large amount of magnetic field data recorded in North America and Greenland. We find that the most intense geomagnetic field disturbances are caused by the impacts of nearly frontal solar perturbations on the Earth and cover large geographic areas reaching southern Canada and northern United States. The results of this work can be used by space weather forecasters when predicting events with significant magnetic field variations leading to intense geoelectric currents, particularly when tracking space weather drivers that are forecasted to impact Earth nearly frontally. Key Points: Typical substorm‐time ground dB/dt variations (5–10 nT/s) are caused by interplanetary shocks with moderate inclinations (140°–160°)The more frontal the shock, the more intense and the broader the ionospheric current amplitudesThe more frontal the shock, the more intense, larger the area coverage, and the lower the equatorward latitudinal extent of dB/dt variations [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]

Our current knowledge of the geomagnetic poleward and equatorward boundary dynamics is limited, particularly, how deep those two latitudinal boundaries can extend into lower geomagnetic latitudes during magnetic storms. We want to understand the motion of the boundary because it is important in terms of the location and magnitude of the effects of geomagnetic disturbances associated with storms on the ground. In this study we derive spherical elementary ionospheric currents from ground magnetometer arrays covering North America and Greenland during six magnetic storms in 2015 and 2018. With two dimensional maps of the auroral region current, we select the equatorward boundary of the region 2 currents by‐eye and fit the boundary with an ellipse to derive the location of the equatorward boundary at magnetic midnight. We have obtained over 500 boundaries and find that the midnight boundary location varies between 45° and 66° magnetic latitude. We examine the influence of the interplanetary magnetic field (IMF), solar wind plasma, and geomagnetic indices on the location of the magnetic midnight equatorial boundary and find that the equatorial boundary location is best correlated with the IMF Bz, VBz, and the Sym‐H index. We demonstrate that as the Bz component becomes more negative, the magnitude of VBz increases, and the magnitude of the Sym‐H index increases, the magnetic midnight equatorial boundary shifts equatorward during periods of moderate to high geomagnetic activity. Plain Language Summary: Our current knowledge of the geomagnetic poleward and equatorward boundary dynamics is limited, particularly, how deep the equatorward boundary of the auroral current system can extend into lower magnetic latitudes during magnetic storms. In this study we use two dimension ionospheric current maps derived from ground magnetometer arrays covering North America and Greenland during magnetic storms in 2015 and 2018 to understand the variability of the equatorward boundary of the auroral currents at magnetic midnight. We examine the influence of the interplanetary magnetic field (IMF), solar wind plasma, and geomagnetic indices on the location of the magnetic midnight equatorial boundary and find that the magnetic midnight equatorial boundary location is best correlated with the Bz component of the interplanetary magnetic field, the solar wind electric field (VBz), and the Sym‐H geomagnetic index. We demonstrate that as the Bz becomes more negative, the magnitude of VBz increases, and as the magnitude of the Sym‐H increases the magnetic midnight equatorial boundary moves equatorward. Key Points: We show the temporal and spatial development of the region 2 current system equatorward boundary during magnetic stormsWe show that the equatorward boundary at magnetic midnight varies in magnetic latitude between 45° and 71° MLatWe demonstrate a correlation between the equatorward boundary location and IMF Bz southward, VBz, Sym‐H, and the ε parameter [ABSTRACT FROM AUTHOR]