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

We propose a mechanism for the formation of the horse-collar auroral configuration during periods of strongly northwards interplanetary magnetic field, invoking the action of dual-lobe reconnection (DLR). Auroral observations are provided by the Imager for Magnetopause-to-Auroras Global Exploration (IMAGE) satellite and spacecraft of the Defense Meteorological Satellite Program (DMSP). We also use ionospheric flow measurements from DMSP and polar maps of field-aligned currents (FACs) derived from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE). Sunward convection is observed within the dark polar cap, with antisunwards flows within the horse-collar auroral region, together with the NBZ FAC distribution expected to be associated with DLR. We suggest that newly-closed flux is transported antisunwards and to dawn and dusk within the reverse lobe cell convection pattern associated with DLR, causing the polar cap to acquire a teardrop shape and weak auroras to form at high latitudes. If the process continues, the cusp-aligned arcs auroral configuration ensues. Horse-collar auroras and cusp-aligned arcs are a common feature of the quiet magnetosphere, and this model provides a first understanding of their formation, resolving several outstanding questions regarding the nature of DLR and the magnetospheric structure and dynamics during northwards IMF. The model can also provide insights into the trapping of solar wind plasma by the magnetosphere and the formation of a low-latitude boundary layer and cold, dense plasma sheet.

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.

We examine a 6-day traversal of the magnetotail by the ARTEMIS satellites during an interval of prolonged northward IMF. The electrostatic analyzer (ESA) onboard the ARTEMIS spacecraft measures high ion and electron fluxes at approximately 60 RE downtail in regions of the magnetotail which would normally be the magnetotail lobe, containing open flux evacuated of plasma. We interpret these observations as trapped plasma on closed magnetic flux indicating that the magnetotail is closed or partially closed but extends at least as far as similar to 60 RE downtail. We find that the occurrence of plasma in the magnetotail and the closure of the magnetosphere results in distinct changes to the magnetotail structure including a reduction in the magnetic field strength and pressure as well as a narrowing of the tail by approximately 20 RE. The interplanetary magnetic field (IMF) interacts with the Earth's magnetic field which can dramatically alter the structure of the Earth's magnetosphere. When the IMF and the Earth's magnetic field are oppositely directed (i.e., southward) the magnetosphere has regions of both closed magnetic field lines near the equator where both ends of the field line connect to Earth and open magnetic field lines at the magnetic poles where one end connects to the Earth and one end connects to the IMF. Plasma populations get trapped in closed field regions and can be accelerated down to the atmosphere where they cause the aurora. Plasma populations on open field lines tend to escape out of the magnetosphere. When the IMF direction is aligned with the Earth's magnetic field (i.e., northward) the open magnetic field regions become more closed, trapping plasma. In this study, we observe trapped plasma populations 60 Earth radii down the magnetotail which coincide with observations of trapped plasma nearer to Earth indicating that the regions of closed magnetic field extend 60 Earth radii down the magnetotail. We examine a far magnetotail traversal (similar to 60 RE) by ARTEMIS during a period of prolonged northward IMF ARTEMIS/ESA observes high density plasma similar to 60 RE downtail coincident with high density plasma observed by Cluster/CIS We interpret these observations as trapped plasma on closed field lines

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%).

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.

During the long main phase of the St Patrick’s Day storm on March 17, 2015, we found three separate enhancements of the westward electrojet. These enhancements are observed in the ionospheric equivalent currents computed using geomagnetic data over Fennoscandia. Using data from the IMAGE magnetometer network, we identified localised field-aligned current (FAC) systems superimposed on the pre-existing ionospheric current system. We suggest that these localised current systems are wedgelets and that they can potentially contribute to a larger-scale structure of a substorm current wedge (SCW). Each wedgelet is associated with a negative B X spike. Each spike is recorded at a higher latitude than the former one and all three are very localised over Fennoscandia. The first spike occurred at 17:34 UT and was observed at Lycksele, Rørvik and Nurmijärvi, the second spike was recorded at 17:41 UT and located at Lycksele and Rørvik, whereas the last spike occurred at 17:47 UT and was observed at Kevo and Abisko. Simultaneous optical auroral data and electron injections at the geosynchronous orbit indicate that one or more substorms took place in the polar ionosphere at the time of the wedgelets. This study demonstrates the occurrence of small and short-lived structures such as wedgelets at different locations over a short time scale, 15 min in this case.

We investigate a 15‐day period in October 2011. Auroral observations by the Special Sensor Ultraviolet Spectrographic Imager instrument onboard the Defense Meteorological Satellite Program F16, F17, and F18 spacecraft indicate that the polar regions were covered by weak cusp‐aligned arc (CAA) emissions whenever the interplanetary magnetic field (IMF) clock angle was small, |θ| < 45°, which amounted to 30% of the time. Simultaneous observations of ions and electrons in the tail by the Cluster C4 and Geotail spacecraft showed that during these intervals dense (≈1 cm−3) plasma was observed, even as far from the equatorial plane of the tail as |ZGSE| ≈ 13 RE. The ions had a pitch angle distribution peaking parallel and antiparallel to the magnetic field and the electrons had pitch angles that peaked perpendicular to the field. We interpret the counter‐streaming ions and double loss‐cone electrons as evidence that the plasma was trapped on closed field lines, and acted as a source for the CAA emission across the polar regions. This suggests that the magnetosphere was almost entirely closed during these periods. We further argue that the closure occurred as a consequence of dual‐lobe reconnection. Our finding forces a significant re‐evaluation of the magnetic topology of the magnetosphere during periods of northwards IMF.

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.

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 sixteen 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 behaviours 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, which can be detrimental to power-grids and pipelines.

The polar cap can become teardrop shaped through the poleward expansion of the dusk and dawn sectors of the auroral oval, to form what is called horse collar aurora (HCA). The formation of HCA has been linked to dual-lobe reconnection (DLR) where magnetic flux is closed at the dayside magnetopause. A prolonged period of northward IMF is required for the formation of HCA. HCA have previously been identified in UV images captured by the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) instrument on-board the Defense Meteorological Satellite Program (DMSP) spacecraft F16, F17 and F18. Events that have concurrent 630.0 nm all-sky camera (ASC) data from the Redline Geospace Observatory (REGO) Resolute Bay site are now studied in more detail, making use of the higher cadence of the ASC images compared to DMSP/SSUSI. 11 HCA events are studied and classified based on the IMF conditions at the end of the event. Five of the events were found to end via a southward turning of the IMF, two end with positive B-y dominated IMF and four with negative B-y dominance. Under positive (negative) B-y the arcs move duskward (dawnward) in the northern hemisphere with the opposite true in the southern hemisphere. Under a southward turning the arcs move equatorward. One event is of particular interest as it occurred while there was a transpolar arc (TPA) also present. Understanding the evolution of HCA will allow DLR to be studied in more detail.

We investigate a fifteen-day period in October 2011. Auroral observations by the SSUSI instrument onboard the DMSP F16, F17, and F18 spacecraft indicate that the polar regions were covered by weak cusp-aligned arc emissions whenever the IMF clock angle was small, |θ|<45°, which amounted to 30% of the time. Simultaneous observations of ions and electrons in the tail by the Cluster C4 and Geotail spacecraft showed that during these intervals dense (1 cm-3) plasma was observed, even as far from the equatorial plane of the tail as |ZGSE| = 13 RE. The ions had a pitch angle distribution peaking parallel and antiparallel to the magnetic field and the electrons had pitch angles that peaked perpendicular to the field. We interpret the counter-streaming ions and double loss-cone electrons as evidence that the plasma was trapped on closed field lines, and acted as a source for the cusp-aligned arc emission across the polar regions. This suggests that the magnetosphere was almost entirely closed during these periods. We further argue that the closure occured as a consequence of dual-lobe reconnection at the dayside magnetopause. Our finding forces a significant re-evaluation of the magnetic topology of the magnetosphere during periods of northwards IMF.

Horse collar aurora (HCA) are an auroral feature where the dawn and dusk sector auroral oval moves polewards and the polar cap becomes teardrop shaped. They form during prolonged periods of northward interplanetary magnetic field (IMF), when the IMF clock angle is small. Their formation has been linked to dual‐lobe reconnection (DLR) closing magnetic flux at the dayside magnetopause. The conditions necessary for DLR are currently not well‐understood therefore understanding HCA statistics will allow DLR to be studied in more detail. We have identified over 600 HCA events between 2010 and 2016 in UV images captured by the Special Sensor Ultraviolet Spectrographic Imager instrument on‐board the Defense Meteorological Satellite Program spacecraft F16, F17 and F18. As expected, there is a clear preference for HCA occurring during northward IMF. We find no clear seasonal dependence in their occurrence, with an average of 8 HCA events per month. The occurrence of HCA events does not appear to depend on the B x component of the IMF. Considering the average radiance intensity across the dusk‐dawn meridian shows the HCA as a separate bulge inside the auroral oval and that the dawn side arc of the HCA is usually brighter than the dusk in the Lyman‐Birge‐Hopfield short band. We relate this to the expected field aligned current pattern of HCA formation. We further suggest that transpolar arcs observed in the dawn sector simultaneously in both northern and southern hemispheres are misidentified HCA.

Upstream solar wind measurements from near the L1 Lagrangian point are commonly used to investigate solar wind‐magnetosphere coupling. The off‐Sun‐Earth line distance of such solar wind monitors can be large, up to 100 R E . We investigate how the correlation between measurements of the interplanetary magnetic field and associated ionospheric responses deteriorates as the off‐Sun‐Earth line distance increases. Specifically, we use the magnitude and polarity of the dayside region 0 field‐aligned currents (R0 FACs) as a measure of interplanetary magnetic field (IMF) B Y ‐associated magnetic tension effects on newly‐reconnected field lines, related to the Svalgaard‐Mansurov effect. The R0 FACs are derived from Advanced Magnetosphere and Planetary Electrodynamics Response Experiment measurements by a principal component analysis, for the years 2010–2016. We perform cross‐correlation analyses between time‐series of IMF B Y , measured by the Wind spacecraft and propagated to the nose of the bow shock by the OMNI technique, and these R0 FAC measurements. Typically, in the summer hemisphere, cross‐correlation coefficients between 0.6 and 0.9 are found. However, there is a reduction of order 0.1–0.15 in correlation coefficient between periods when Wind is close to (within 45 R E ) and distant from (beyond 70 R E ) the Sun‐Earth line. We find a time‐lag of around 17 min between predictions of the arrival of IMF features at the bow shock and their effect in the ionosphere, irrespective of the location of Wind.

Transpolar arcs (TPAs) are auroral features that occur polewards of the main auroral oval suggesting that the magnetosphere has acquired a complicated magnetic topology. They are primarily a northward interplanetary magnetic field (IMF) auroral phenomenon, and their formation and evolution have no single explanation that is unanimously agreed upon. An automated detection algorithm has been developed to detect the occurrence of TPAs in UV images captured from the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) instrument onboard the Defense Meteorological Satellite Program (DMSP) spacecraft, in order to further study their occurrence. Via this detection algorithm TPAs are identified as a peak in the average radiance intensity poleward of 12.5° colatitude, in two or more of the wavelengths/bands sensed by SSUSI. Using the detection algorithm for the years 2010 to 2016, over 5000 images containing TPAs are identified. The occurrence of these TPAs shows a seasonal dependence, with more arcs being visible in the winter hemisphere. The orbital plane of DMSP has been investigated as a possible explanation of the dependences in the results of the detection algorithm. For the spacecraft of interest this leads to a preferential observation of the northern hemisphere with the detection algorithm missing TPAs in the southern hemisphere around 01–06 UT. No seasonal bias has been found for these spacecraft. We discuss the ramifications of these findings in terms of proposed TPA generation mechanisms and suggest reasons for the seasonal dependence including it being a reflection of probability of seeing TPAs due to visibility.

Following the St. Patrick's Day (17 March) geomagnetic storm of 2013, the interplanetary magnetic field had near‐zero clock angle for almost two days. Throughout this period multiple cusp‐aligned auroral arcs formed in the polar regions; we present observations of, and provide a new explanation for, this poorly understood phenomenon. The arcs were observed by auroral imagers onboard satellites of the Defense Meteorological Satellite Program. Ionospheric flow measurements and observations of energetic particles from the same satellites show that the arcs were produced by inverted‐V precipitation associated with upward field‐aligned currents (FACs) at shears in the convection pattern. The large‐scale convection pattern revealed by the Super Dual Auroral Radar Network and the corresponding FAC pattern observed by the Active Magnetosphere and Planetary Electrodynamics Response Experiment suggest that dual‐lobe reconnection was ongoing to produce significant closure of the magnetosphere. However, we propose that once the magnetosphere became nearly closed complicated lobe reconnection geometries arose that produced interleaving of regions of open and closed magnetic flux and spatial and temporal structure in the convection pattern that evolved on timescales shorter than the orbital period of the DMSP spacecraft. This new model naturally explains many features of cusp‐aligned arcs, including why they focus in from the nightside toward the cusp region.

We quantify the contributions of different convection states to the magnetic flux through-put of the magnetosphere during 2010. To do this we provide a continuous classification of convection state for the duration of 2010 based upon observations of the solar wind and interplanetary magnetic field, geomagnetic indices, and field-aligned currents measured by the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE). Convection states are defined as 1) quiet and 2) weak activity, substorm 3) growth, 4) expansion, and 5) recovery phases, 6) substorm driven phase (when relatively steady magnetospheric convection occurs), 7) recovery bays (when recovery phase is accompanied by a negative excursion of the AL electrojet index), and 8) periods of multiple intensifications (storm-time periods when continuous short-period AL activity occur). The magnetosphere is quiet for 46% of the time, when very little convection takes place. The majority of convection occurs during growth and driven phases (21% and 38%, respectively, of open magnetic flux accumulation by dayside reconnection). We discuss these results in the context of the expanding/contracting polar cap model of convection, and describe a framework within which isolated substorms and disturbances during periods of more continuous solar wind-magnetosphere driving can be understood.

We propose a mechanism for the formation of the horse-collar auroral configuration common during periods of strongly northwards interplanetary magnetic field, invoking the action of dual-lobe reconnection (DLR). Auroral observations are provided by the Imager for Magnetopause-to-Auroras Global Exploration (IMAGE) satellite and spacecraft of the Defense Meteorological Satellite Program (DMSP). We also use ionospheric flow measurements from DMSP and polar maps of field-aligned currents (FACs) derived from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE). Sunward convection is observed within the dark polar cap, with antisunwards flows within the horse-collar auroral region, together with the NBZ FAC distribution expected to be associated with DLR. We suggest that newly-closed flux is transported antisunwards and to dawn and dusk within the reverse lobe cell convection pattern associated with DLR, causing the polar cap to acquire a teardrop shape and weak auroras to form at high latitudes. Horse-collar auroras are a common feature of the quiet magnetosphere, and this model provides a first understanding of their formation, resolving several outstanding questions regarding the nature of DLR and the magnetospheric structure and dynamics during northwards IMF. The model can also provide insights into the trapping of solar wind plasma by the magnetosphere and the formation of a low-latitude boundary layer and cold, dense plasma sheet. We speculate that prolonged DLR could lead to a fully closed magnetosphere, with the formation of horse-collar auroras being an intermediate step.

Earth and Space Science Open Archive This preprint has been submitted to and is under consideration at Journal of Geophysical Research - Space Physics. ESSOAr is a venue for early communication or feedback before peer review. Data may be preliminary.Learn more about preprints preprintOpen AccessYou are viewing the latest version by default [v1]Magnetospheric flux transport in the Dungey cycle during 2010Authors Stephen E. Milan iD Jennifer Alyson Carter iD Harneet Sangha iD Gemma E. Bower iD Brian J. Anderson iDSee all authors Stephen E. MilaniDCorresponding Author• Submitting AuthorUniversity of LeicesteriDhttps://orcid.org/0000-0001-5050-9604view email addressThe email was not providedcopy email addressJennifer Alyson CarteriDUniversity of LeicesteriDhttps://orcid.org/0000-0002-0981-2895view email addressThe email was not providedcopy email addressHarneet SanghaiDUniversity of LeicesteriDhttps://orcid.org/0000-0003-2857-7162view email addressThe email was not providedcopy email addressGemma E. BoweriDUniversity of LeicesteriDhttps://orcid.org/0000-0002-5141-7012view email addressThe email was not providedcopy email addressBrian J. AndersoniDJohn Hopkins Univ.iDhttps://orcid.org/0000-0003-2543-0149view email addressThe email was not providedcopy email address