High-latitude field-aligned currents (FACs) reflect, in steady-state, the force balance between magnetospheric plasma dynamics and the collisional coupling of plasma to the neutral atmosphere in the ionosphere. Assessing the impact of high-latitude FACs at low latitudes is difficult for at least two reasons. First, FACs are primarily inferred from magnetometer measurements in low-Earth orbit by estimating the radial current using horizontal magnetic field perturbations and converting it to a FAC using a geometric factor. While this yields a locally correct estimate of the FAC density, the magnetic field generated by a radial current system differs from that generated by the corresponding FAC system when field lines are not radial. As a result, the magnetic field of the horizontal component of FACs, including their remote magnetic field observed at low latitudes, are neglected. Second, in many numerical simulations, FACs are coupled to the ionosphere only at high latitudes, while boundary conditions are imposed at lower latitudes, arguably making it difficult, from a fundamental physics perspective, to trace how high-latitude forcing influences low latitudes.Here we use AMPERE estimates of high-latitude FACs at 10-min resolution derived from magnetometer measurements on the Iridium satellite constellation to quantify their low-latitude impact. FACs in both polar regions are used to calculate the remote magnetic field using the integration method of Engels and Olsen (1998, https://doi.org/10.1016/S1364-6826(98)00094-7). A recently developed magnetosphere-ionosphere coupling model (Laundal et al. 2025, https://doi.org/10.5194/angeo-43-803-2025) is used to compute the associated penetration electric field. The resulting magnetic and electric fields are compared with observations at low latitudes.

Omega bands are an auroral structure which consist of upward and downward field aligned currents (FACs) which are formed in the boundary between the region 1 and region 2 FACs in the dawn sector. They are characterised by their wave-like structure, which is often described as looking like a chain of the Greek letter Ω, with luminous extensions of the aurora protruding poleward. Omega bands cause ground based perturbations as they drift eastward, which can have large dB/dt values and hence are a potential source of geomagnetically induced currents (GICs). GICs are a hazard to our infrastructure, as currents can be induced in power grids, railways and pipelines. In this study, we investigate several cases of omega bands using ground and spaced based observations to examine their properties. Observations from the European Incoherent SCATter (EISCAT) radar show enhancements in electron density, which alongside measurements of FACs from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) can be used to study the intensity of different events. We use the IMAGE magnetometer network across Scandinavia to explore the latitudinal extend of omega bands as well as see their drift speed and dB/dt strength. SuperDARN and DMSP ion drift meter measurements help us to determine if the omega bands are embedded in the convection flow. Data from the DMSP Special Sensor Ultraviolet Spectrographic Imager (SSUSI) show the auroral data associated with omega bands. We present a study of omega bands from 2010 onwards.

The 8 April 2024, total solar eclipse presented a unique opportunity to study ionospheric and magnetospheric responses to local changes in the solar illumination. As part of NASA’s citizen science initiative, we launched the EZIE-Mag Eclipse Measurement Campaign and deployed ultra low-cost, science-grade magnetometer kits operated by trained citizen scientists across diverse geographic locations. This grassroots decentralized approach enabled the collection of high-quality, distributed geomagnetic data. Observations from Muncie, Indiana, revealed a clear signal that is interpreted as being produced by eclipse-induced current system perturbations. This is an excellent example of complex electrodynamic coupling between the Sun and the magnetosphere-ionosphere-atmosphere environment. The results not only contribute to advancing Heliophysics research but also demonstrate the value of citizen science in enhancing space weather awareness and public education. The campaign’s inclusive approach in engaging participants from various backgrounds, underscores the potential for scalable, community-driven efforts to broaden participation and deepen public understanding of space weather phenomena.

The three Swarm satellites provide an optimum, low Earth orbit (LEO) and multi‐spacecraft platform, to explore for the first time the local correlation between field‐aligned currents (FACs), auroral electrojets, and magnetic perturbations at the Earth's surface. By combining Swarm and ground magnetic field data, one can investigate systematically the full correlation chain, whose final link controls the ground induced currents and related space weather effects. We introduce an integrated FAC product, the Sheet FAC (SFAC) index, as a convenient measure of the in‐situ FAC data, and explore the correlations SFAC‐AE, SFAC‐PEJ and SFAC‐dH, with AE the standard auroral electrojet index, PEJ the local, Swarm based, polar electrojet index, and dH the horizontal magnetic field perturbation at the Earth's surface. Given the good SFAC‐dH correlation, we also suggest an extension of SFAC to higher LEO satellites, which cannot observe any more the electrojet currents, but are fully capable to monitor SFAC.

The thermospheric composition (O/N2 ratio and NO) condition represents the state of the thermosphere. Significant changes in thermospheric composition and neutral wind are often observed during non-storm time (e.g. a weak substorm on May 29, 2023) due to continous energy and momentum input from solar wind to the geospace. It is challenging to find days when the solar wind impact is minimized and the geospace is at its ground state (super quiet) or undisturbed conditon. After a search of SuperMAG database over two decades (2002-2022), we finally identified a few super quiet intervals with (1) AE or SME < 50 nT, SymH > 0 nT), and (2) low auroral intensities (N2 LBHS (140-150 nm) < 500 R) over 48 consecutive hours or longer. We report one super quiet interval (November 6-7, 2009) with no O/N2 depletion or NO enhancment which represents a “geopace ground state”.

EZIE, the Electrojet Zeeman Imaging Explorer, is a NASA three-Cubesat Heliophysics mission scheduled to launch in late 2024 or early 2025. It employs four downward and cross-track looking miniaturized radiometers on each of the 6U CubeSat, flying in a pearls-on-a-string managed formation, to measure, for the first time, the two-dimensional structure and the temporal evolution of the electrojets flowing at altitudes of ~100–130 km. The four identical radiometers simultaneously measure polarimetric radiances of the molecular oxygen thermal emission at 118 GHz and employs the Zeeman sensing technique to obtain the current-induced magnetic field vectors at ~80 km, an altitude region very close to the electrojet. This measurement technique allows for the remote sensing of the meso-scale structure of the electrojets at four different cross-track locations simultaneously at altitudes notoriously difficult to measure in situ. The compact 118-GHz heterodyne spectropolarimeters leverage technologies demonstrated by NASA’s TEMPEST-D and CubeRRT missions and the CubeSat bus from RAVAN, CAT, TEMPEST-D, and CubeRRT. Differential drag maneuvers are used to manage satellite along-track temporal separation to within 2–10 minutes between adjacent satellite to record the electrojet temporal evolution without the need for on-board propulsion. The combination of the sensing technique, compact instrument and Cubesat technologies allow EZIE to cost-effectively obtain never-before “mesoscale” measurements needed to understand how the solar wind energies stored in the magnetosphere are transferred to the thermosphere and ionosphere. In this paper, we will present an overview of the EZIE mission, its science objectives, the Zeeman sensing technique employed, and the measurement products to be provided.

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 large dB / dt as 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.

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 degrees magnetic latitude. Rapid changes called geomagnetic disturbances (GMDs) in the Earth magnetic field can lead to currents flowing at the surface of the Earth. When these currents flow through infrastructure such as power grids and pipeline, damage can occur which can lead to a loss of services and impact society. It therefore important to understand the conditions necessary for these current to form. The rapid changes can be measured by ground magnetometers. A newly developed algorithm that uses 10 s data from 2010 to 2022, from SuperMAG magnetometers around the globe, has been developed. The GMDs are then places in context to the field aligned currents (FACs) measure by the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) that flow in the magnetosphere. A population that is found to occur at dawn lies equatorward of the FAC boundary. A population of GMDs found to occur at pre-midnight lie poleward of the FAC boundary. The latitude that the GMDs occur at is dependent on the FAC boundary. An algorithm has been developed to identify geomagnetic disturbances in 10 s magnetometer data Geomagnetic disturbances occur mainly in two populations, pre-midnight, on region 1 upward field-aligned currents (FACs) and dawn on the boundary The latitude that the geomagnetic disturbances occur at is dependent on the FAC boundary

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.

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 dB/dt $dB/dt$ 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 dB/dt $dB/dt$ 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.

Understanding of Earth’s geomagnetic environment is critical to mitigating the space weather impacts caused by disruptive geoelectric fields in power lines and other conductors on Earth’s surface. These impacts are the result of a chain of processes driven by the solar wind and linking Earth’s magnetosphere, ionosphere, thermosphere and Earth’s surface. Tremendous progress has been made over the last two decades in understanding the solar wind driving mechanisms, the coupling mechanisms connecting the magnetically controlled regions of near-Earth space, and the impacts of these collective processes on human technologies on Earth’s surface. Studies of solar wind drivers have been focused on understanding the responses of the geomagnetic environment to spatial and temporal variations in the solar wind associated with Coronal Mass Ejections, Corotating Interaction Regions, Interplanetary Shocks, High-Speed Streams, and other interplanetary magnetic field structures. Increasingly sophisticated numerical models are able to simulate the magnetospheric response to the solar wind forcing associated with these structures. Magnetosphere-ionosphere-thermosphere coupling remains a great challenge, although new observations and sophisticated models that can assimilate disparate data sets have improved the ability to specify the electrodynamic properties of the high latitude ionosphere. The temporal and spatial resolution needed to predict the electric fields, conductivities, and currents in the ionosphere is driving the need for further advances. These parameters are intricately tied to auroral phenomena—energy deposition due to Joule heating and precipitating particles, motions of the auroral boundary, and ion outflow. A new view of these auroral processes is emerging that focuses on small-scale structures in the magnetosphere and their ionospheric effects, which may include the rapid variations in current associated with geomagnetically induced currents and the resulting perturbations to geoelectric fields on Earth’s surface. Improvements in model development have paralleled the advancements in understanding, yielding coupled models that better replicate the spatial and temporal scales needed to simulate the interconnected domains. Many realizations of such multi-component systems are under development, each with its own limitations and advantages. Challenges remain in the ability of models to quantify uncertainties introduced by propagation of solar wind parameters, to account for numerical effects in model codes, and to handle the special conditions occurring during extreme events. The impacts to technical systems on the ground are highly sensitive to the local electric properties of Earth’s surface, as well as to the specific technology at risk. Current research is focused on understanding the characteristics of geomagnetic disturbances that are important for geomagnetically induced currents, the development of earth conductivity models, the calculation of geoelectric fields, and the modeling of induced currents in the different affected systems. Assessing and mitigating the risks to technical systems requires quantitative knowledge of the range of values to be expected under all possible geomagnetic and technical conditions. Considering the progress that has been made in studying the chain of events leading to hazardous geomagnetic disturbances, the path forward will require concerted efforts to reveal missing physics, improve modeling capabilities, and deploy new observational assets. New understanding should be targeted to accurately quantify solar wind driving, magnetosphere-ionosphere-thermosphere coupling, and the impacts on specific technologies. The research, modeling, and observations highlighted here provide a framework for constructing a plan by which the international science community can comprehensively address the growing threat to human technologies caused by geomagnetic disturbances.

Abstract Interplanetary (IP) shocks are perturbations observed in the solar wind. IP shocks correlate well with solar activity, being more numerous during times of high sunspot numbers. Earth‐bound IP shocks cause many space weather effects that are promptly observed in geospace and on the ground. Such effects can pose considerable threats to human assets in space and on the ground, including satellites in the upper atmosphere and power infrastructure. Thus, it is of great interest to the space weather community to (a) keep an accurate catalog of shocks observed near Earth, and (b) be able to forecast shock occurrence as a function of the solar cycle (SC). In this work, we use a supervised machine learning regression model to predict the number of shocks expected in SC25 using three previously published sunspot predictions for the same cycle. We predict shock counts to be around 275 ± 10, which is ∼47% higher than the shock occurrence in SC24 (187 ± 8), but still smaller than the shock occurrence in SC23 (343 ± 12). With the perspective of having more IP shocks on the horizon for SC25, we briefly discuss many opportunities in space weather research for the remainder years of SC25. The next decade or so will bring unprecedented opportunities for research and forecasting effects in the solar wind, magnetosphere, ionosphere, and on the ground. As a result, we predict SC25 will offer excellent opportunities for shock occurrences and data availability for conducting space weather research and forecasting.

Ultralight dark matter, such as kinetically mixed dark-photon dark matter (DPDM) or axion-like-particle dark matter (axion DM), can source an oscillating magnetic-field signal at Earth's surface. Previous work searched for this signal in a publicly available dataset of global magnetometer measurements maintained by the SuperMAG collaboration. This "low-fidelity" dataset reported measurements with a 1-min time resolution, allowing the search to set leading direct constraints on DPDM and axion DM with Compton frequencies f(DM) <= 1/(1 min) (corresponding to masses m(DM) <= 7 x 10(-17) eV). More recently, a dedicated experiment undertaken by the SNIPE Hunt collaboration has also searched for this same signal at higher frequencies f(DM) >= 0.5 Hz (or m(DM) >= 2 x 10(-1)5 eV). In this work, we search for this signal of ultralight DM in the SuperMAG "high-fidelity" dataset, which features a 1-sec time resolution, allowing us to probe the gap in parameter space between the low-fidelity dataset and the SNIPE Hunt experiment. The high-fidelity dataset exhibits lower geomagnetic noise than the low-fidelity dataset and features more data than the SNIPE Hunt experiment, making it a powerful probe of ultralight DM. Our search finds no robust DPDM or axion DM candidates. We set constraints on DPDM and axion DM parameter space for 10(-3) Hz <= fDM <= 0.98 Hz (or 4 x 10(-18) eV <= mDM <= 4 x 10(-15) eV). Our results are the leading direct constraints on both DPDM and axion DM in this mass range, and our DPDM constraint surpasses the leading astrophysical constraint in a narrow range around m(A ') approximate to 2 x 10(-15) eV.

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” in dB/dt, with 131,447 spikes in dB/dt exceeding 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 in dB/dt are 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%).

The joint European Space Agency and Chinese Academy of Sciences Solar wind Magnetosphere Ionosphere Link Explorer (SMILE) mission will explore global dynamics of the magnetosphere under varying solar wind and interplanetary magnetic field conditions, and simultaneously monitor the auroral response of the Northern Hemisphere ionosphere. Combining these large-scale responses with medium and fine-scale measurements at a variety of cadences by additional ground-based and space-based instruments will enable a much greater scientific impact beyond the original goals of the SMILE mission. Here, we describe current community efforts to prepare for SMILE, and the benefits and context various experiments that have explicitly expressed support for SMILE can of fer. A dedicated group of international scientists representing many different experiment types and geographical locations, the Ground-based and Additional Science Working Group, is facilitating these efforts. Preparations include constructing an online SMILE Data Fusion Facility, the discussion of particular or special modes for experiments such as coherent and incoherent scatter radar, and the consideration of particular observing strategies and spacecraft conjunctions. We anticipate growing interest and community engagement with the SMILE mission, and we welcome novel ideas and insights from the solarterrestrial community.

Utilizing magnetic field measurements made by the Iridium satellites and by ground magnetometers in North America we calculate the full ionospheric current system and investigate the substorm current wedge. The current estimates are independent of ionospheric conductance, and are based on estimates of the divergence‐free (DF) ionospheric current from ground magnetometers and curl‐free (CF) ionospheric currents from Iridium. The DF and CF currents are represented using spherical elementary current systems (SECS), derived using a new inversion scheme that ensures the current systems' spatial scales are consistent. We present 18 substorm events and find a typical substorm current wedge (SCW) in 12 events. Our investigation of these substorms shows that during substorm expansion, equivalent field‐aligned currents (EFACs) derived with ground magnetometers are a poor proxy of the actual FAC. We also find that the intensification of the westward electrojet can occur without an intensification of the FACs. We present theoretical investigations that show that the observed deviation between FACs estimated with satellite measurements and ground‐based EFACs are consistent with the presence of a strong local enhancement of the ionospheric conductance, similar to the substorm bulge. Such enhancements of the auroral conductance can also change the ionospheric closure of pre‐existing FACs such that the ground magnetic field, and in particular the westward electrojet, changes significantly. These results demonstrate that attributing intensification of the westward electrojet to SCW current closure can yield false understanding of the ionospheric and magnetospheric state.

Both the bow shock and magnetopause move in response to varying solar wind and magnetospheric conditions. Tracking their locations can provide important clues to the state of the solar wind-magnetosphere interaction, but is difficult with single spacecraft observations. This paper employs multipoint THEMIS observations of velocity gradients in the subsolar magnetosheath to remotely sense boundary locations on a continual basis for various solar wind conditions. We present three cases: (a) continuous northward IMF and no magnetopause motion; (b) southward IMF and no magnetopause motion with evidence of nightside activity; and (c) southward IMF and pressure increase with inward motion. When observing spacecraft are located near the Sun-Earth line, inferred boundary locations agree well with the predictions of the BATS-R-US global magnetohydrodynamic model, confirming the utility of both the new method and the models. Results show that boundaries often lie nearly at rest with amplitudes less than 0.5 RE. They provide evidence indicating that nightside reconnection and a strong sunward convection in the outer magnetosphere can counteract the magnetopause erosion expected when a southward interplanetary magnetic field (IMF) initiates reconnection on the dayside magnetopause. The velocity gradient method distinguishes between intervals when the subsolar bow shock and magnetopause move slowly or rapidly The velocity gradient method confirms the locations of the bow shock and magnetopause predicted by global magnetohydrodynamic simulations During quiet intervals, the amplitude of bow shock and magnetopause motion diminishes to less than 0.5 RE

Abrupt variations of auroral electrojets can induce geomagnetically induced currents, and the ability to model and forecast them is a pressing goal of space weather research. We report an auroral electrojet spike event that is extreme in magnitude, explosive in nature, and global in spatial extent that occurred on 24 April 2023. The event serves as a fundamental test of our understanding of the response of the geospace system to solar wind dynamics. Our results illustrate new and important characteristics that are drastically different from existing knowledge. Most important findings include (a) the event was only of similar to 5-min duration and was limited to a narrow (2 degrees-3 degrees) band of diffuse aurora; (b) the longitudinal span covered the entire nightside sector, possibly extending to the dayside; (c) the trigger seems to be a transient solar wind dynamic pressure pulse. In comparison, substorms usually last 1-2 hr and span almost the entire latitudinal width of the auroral oval. Magnetic perturbation events (MPEs) span hundreds km in radius. Both substorms and MPEs are mainly driven by disturbances in the magnetotail. A possible explanation is that the pressure pulse compresses the magnetosphere and enhances diffuse precipitation of electrons and protons from the inner plasma sheet, which elevates the ionospheric conductivity and intensifies the auroral electrojet. Therefore, the event exhibits a potentially new type of geomagnetic disturbance and highlights a solar wind driver that is enormously influential in driving extreme space weather events. Auroral electrojets are horizontal electric currents that flow in the auroral ionosphere, and extreme auroral electrojet activities can induce geomagnetically induced currents that damage high-voltage power transformers and increase steel corrosion of pipeline networks. Understanding what drives the extreme events is therefore a pressing goal of space weather research. We report an auroral electrojet spike event that is extreme in magnitude, explosive in nature, and global in spatial extent that occurred on 24 April 2023. The event serves as a fundamental test of our understanding of the response of the geospace system to solar wind dynamics. Most important findings include (a) the event was only of similar to 5-min duration and was limited to a narrow band of diffuse aurora; (b) the longitudinal span covered the entire nightside sector; (c) the trigger seems to be a transient solar wind dynamic pressure pulse. These features differ drastically from other widely known geomagnetic disturbances such as substorms or magnetic perturbation events, and signify a potentially new type of disturbance. A possible explanation is that the solar wind pressure pulse compresses the magnetosphere, enhances diffuse precipitation of particles into the ionosphere, and elevates the ionospheric conductivity. An abrupt and intense auroral electrojet enhancement occurred during the storm of 24 April 2023 This extreme event differs from typical geomagnetic disturbances in terms of magnitude, spatiotemporal extent, and physical driver The event was triggered by a solar wind pressure pulse, which enhanced diffuse auroral precipitation and ionospheric conductivity

In this work, we present a statistical study of substorms covering a five-year period 2016-2020. Substorm phases were identified from time series of the SuperMAG AL (SML) index using a list of 5,077 previously identified substorm onsets, the SML peak value marking transition from expansion to recovery phase, and the recovery identified as return to activity less than -100 nT in the SML index. Magnetic field observations from THEMIS, RBSP, and MMS missions were used to study the magnetotail characteristics during the substorm evolution. A superposed epoch analysis indicates that the substorm onset occurs almost simultaneously with a few minutes of uncertainty throughout the magnetotail, ranging from geostationary orbit to 20 RE. The onset in the transition region precedes the ground onset by a few minutes. The peak SML time coincides with the peak of the outer transition region Delta B-Z, which suggests that the field-aligned currents driving the SML activity arise from the outer transition region. Analysis of 2D maps of the tail magnetic field shows that the magnetotail current changes are limited to the center of the tail within |Y| < 10R(E). The substorm recovery is fastest in the inner transition region and lasts longer when moving further out. We did not find major asymmetries in the substorm signatures associated with IMF B-Y or B-Z.

We investigate the causes of large $dB/dt$ events observed by SuperMAG, by comparing with the time-series of different types of geomagnetic activity, or “convection state”, 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 $dB/dt$ 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 favours 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.