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Abstract Geomagnetic disturbances (GMDs) are rapid fluctuations in the strength and direction of the magnetic field near the surface of the Earth which can cause electric currents to be induced in the ground. The geomagnetically induced currents (GICs) can cause damage to pipelines and power grids. A detection algorithm has been developed to identify rapid changes in 10 s averaged magnetometer data. This higher resolution data is important in capturing the most rapid changes associated with extreme GIC events. The algorithm has been used on an array of ground‐based magnetometers from SuperMAG data from 2010 to 2022, creating a new list of global GMDs. Data from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) is used to place the observed GMDs in the context of the global pattern of magnetosphere‐ionosphere field‐aligned currents (FACs). A dawn sector population of GMDs is found to lie near the boundary between the region 1 and region 2 FACs, while a pre‐midnight sector population is found to occur poleward of the FAC boundary on region 1 upward FACs. It is also shown that the latitude of the GMDs expands with the FAC boundary and their occurrence peaks around 77° magnetic latitude. 

Abstract During periods of increased geomagnetic activity, perturbations within the terrestrial magnetosphere are known to induce currents within conducting materials, at the surface of Earth through rapid changes in the local magnetic field over time (dB/dt). These currents are known as geomagnetically induced currents and have potentially detrimental effects on ground based infrastructure. In this study we undertake case studies of five geomagnetic storms, analyzing a total of 19 days of 1‐s SuperMAG data in order to better understand the magnetic local time (MLT) distribution, size, and occurrence of “spikes” indB/dt, with 131,447 spikes indB/dtexceeding 5 nT/s identified during these intervals. These spikes were concentrated in clusters over three MLT sectors: two previously identified pre‐midnight and dawn region hot‐spots, and a third, lower‐density population centered around 12 MLT (noon). The noon spike cluster was observed to be associated with pressure pulse impacts, however, due to incomplete magnetometer station coverage, this population is not observed for all investigated storms. The magnitude of spikes indB/dtare determined to be greatest within these three “hot‐spot” locations. These spike occurrences were then compared with field‐aligned current (FAC) data, provided by the Active Magnetospheric Planetary Electrodynamic Response Experiment. Spikes are most likely to be co‐located with upward FACs (56%) rather than downward FACs (30%) or no FACs (14%). 

Abstract A necessary condition for the generation of Geomagnetically Induced Currents (GICs) that can pose hazards for technological infrastructure is the occurrence of large, rapid changes in the magnetic field at the surface of the Earth. We investigate the causes of such events or “spikes” observed by SuperMAG at auroral latitudes, by comparing with the time‐series of different types of geomagnetic activity for the duration of 2010. Spikes are found to occur predominantly in the pre‐midnight and dawn sectors. We find that pre‐midnight spikes are associated with substorm onsets. Dawn sector spikes are not directly associated with substorms, but with auroral activity occurring within the westward electrojet region. Azimuthally‐spaced auroral features drift sunwards, producing Ps6 (10–20 min period) magnetic perturbations on the ground. The magnitude of is determined by the flow speed in the convection return flow region, which in turn is related to the strength of solar wind‐magnetospheric coupling. Pre‐midnight and dawn sector spikes can occur at the same time, as strong coupling favors both substorms and westward electrojet activity; however, the mechanisms that create them seem somewhat independent. The dawn auroral features share some characteristics with omega bands, but can also appear as north‐south aligned auroral streamers. We suggest that these two phenomena share a single underlying cause. The associated fluctuations in the westward electrojet produce quasi‐periodic negative excursions in the AL index, which can be mis‐identified as recurrent substorm intensifications. 

Abstract High‐Intensity Long‐Duration Continuous AE Activity (HILDCAA) intervals are driven by High Speed solar wind Streams (HSSs) during which the rapidly‐varying interplanetary magnetic field (IMF) produces high but intermittent dayside reconnection rates. This results in several days of large, quasi‐periodic enhancements in the auroral electrojet (AE) index. There has been debate over whether the enhancements in AE are produced by substorms or whether HILDCAAs represent a distinct class of magnetospheric dynamics. We investigate 16 HILDCAA events using the expanding/contracting polar cap model as a framework to understand the magnetospheric dynamics occurring during HSSs. Each HILDCAA onset shows variations in open magnetic flux, dayside and nightside reconnection rates, the cross‐polar cap potential, and AL that are characteristic of substorms. The enhancements in AE are produced by activity in the pre‐midnight sector, which is the typical substorm onset region. The periodicities present in the intermittent IMF determine the exact nature of the activity, producing a range of behaviors from a sequence of isolated substorms, through substorms which merge into one‐another, to almost continuous geomagnetic activity. The magnitude of magnetic fluctuations,dB/dt, in the pre‐midnight sector during HSSs is sufficient to produce a significant risk of Geomagnetically Induced Currents. 

Key Points Large dB / dt “spikes” in ground magnetometer data occur in three local time hotspots in the pre‐midnight, dawn, and pre‐noon sectors These are consistent with spikes produced by substorm onsets, omega bands, and the Kelvin‐Helmholtz instability, respectively Spike occurrence is controlled by solar activity, maximizing in the declining phase of the solar cycle, esp. solar cycle 23 

Abstract We comprehensively analyzed geomagnetic perturbations using ground magnetic records from over 400 stations spanning four solar cycles, from 1976 to 2023. We assess the perturbations in the three magnetic components separately. Our study covers low, middle, and high magnetic latitudes in the northern magnetic hemisphere, with the primary objective of quantifying extreme values and evaluating their variability on magnetic latitude, local time, and solar cycle phases “minimum, ascending, maximum, and declining.” Our findings reveal spatial patterns to be less discernible as perturbations intensify, with distinct responses at middle and high latitudes. The extreme values, defined as percentiles 0 and 100, were observed to be localized and randomly distributed in local time, especially in the east magnetic component. Additionally, we observed dusk‐dawn asymmetries in the magnitude of perturbations related to the auroral electrojets, indicating complex interactions between the magnetosphere and ionosphere. Furthermore, the results reveal a preference for the most significant extreme values to occur in the declining phase of the solar cycle. These insights deepen our understanding of geomagnetic perturbations and their variability, contributing to space weather forecasting and mitigation strategies. 

Key Points These indices are not totally interchangeable, consideration should be given to index choice in model validation or cross‐study comparison Hourly averaged SMR and SYM‐H return levels track Dst for return periods below 10 years. Above that they exceed Dst; at 100 years by >10% One minute cadence SMR and SYM‐H 5, 10, 50, and 100 year return levels exceed that of Dst by about 10%, 12%, 20%, and 25% respectively