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 (FUV) Spectrographic Imager (SI) 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. Such GMDs are the physical drivers of geomagnetically induced currents (GICs) in susceptible technological infrastructure such as long-distance power lines and pipelines, but 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. 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.

A supervised convolutional neural network (CNN) was developed to automatically identify electromagnetic ion cyclotron (EMIC) wave events from spectrograms. These events have usually been identified manually, which can be a time-consuming process. Statistical analyses of larger datasets would be facilitated if this process were simplified. The neural network model was trained on spectrogram images from the Halley magnetometer station that had been manually identified as either containing or not containing an EMIC wave event anywhere in the spectrogram. This model was tested on an unseen set of spectrograms, achieving a perfect true positive rate of 1. Size, time, frequency, and pixel color information was extracted from each identified event and exported into a spreadsheet for easier analysis. This method has the capability of reducing time and effort required to identify important spectrogram features by hand. Such an automated method could be applied to other space weather data stored in spectrograms.

On 20 December 2015, three THEMIS spacecrafts detected a nightside magnetotail reconnection event at about 04:36 UT. The spacecrafts (P5, P4, and P3) had their footprints located over North America in the near vicinity of the Gillam ground magnetometer station in Canada. Multipoint observations, both in space and from the ground, allow for an examination of the spatiotemporal characteristics of the disturbance on the ground and the associated physical drivers in the magnetosphere and ionosphere. This study shows that the geomagnetic field dB/dt localization observed at Gillam ground magnetometer site was caused by an isolated substorm onset near that location driven by a nightside magnetotail reconnection event detected by three THEMIS spacecrafts that were located near the central plasma sheet. This event represents the first observation of ground dB/dt localization that is directly linked to nightside magnetotail fast flow bursts and reconnection event.

We explore the characteristics of EMIC waves generated in a non-dipole, compressed magnetic field at the minimum of the magnetic field. We conducted 2D full-wave simulations using the Petra-M code, focusing on a compressed dipole magnetic field line in the outer dayside magnetosphere for a range of L values ($L=8-10$). By comparing the simulation results with MMS observations, we aim to understand how the observed wave characteristics are affected by a shifting source region across different L-shells. Our findings indicate that the direction of the Poynting vector systematically changes depending on the local source location of the wave, which is consistent with the observations. EMIC waves propagate along the magnetic field line and reach both the northern and southern hemispheres; however, there is a notable difference in the power of EMIC waves between the two hemispheres, indicating seasonal asymmetries in their occurrence.

Geographic variability in Earth’s core magnetic field, measured at 400 km altitude but corrected for ionospheric and magnetospheric signals, correlates with electron flux levels measured by the RBSP spacecraft. Higher Earth’s |B| magnitude results in lower flux over L2-6. Over 20 eV – 2 MeV, at L2-4, this negative correlation is as large as -0.21, peaking at the 158 keV electrons, with the strongest effects in the 71 keV – 2 MeV electrons. Despite higher L shells being well above the 400 km field measure, statistically significant correlation with the core field was still seen in higher energy 1- 2 MeV electrons over L5-6. Controlling for Earth’s geographic |B| variability, particularly at lower L shells, results in stronger correlations between electron flux and solar wind, substorm, and ULF wave drivers. At L2, substorms (measured by the SME index), ULF waves, and solar wind velocity show increased correlations with electron flux (30, 100, and 175%, respectively) when Earth’s |B| is added as a covariate to ARMAX regression models. Modest increases in correlation of electron flux with these possible drivers were also seen at L3-6. This argues for the addition of Earth’s |B| as a covariate in models of electron response to drivers.

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 GMDs observed by ground magnetometers. We found six days during which one or more of these DFBs coincided 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. 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. This study is the first to connect spacecraft observations of DFBs in the magnetotail to intense (>6 nT/s) GMDs on the ground, and the results suggest DFBs could be an important driver of GICs.

Auroral substorms that move from auroral (<70°) to polar (>70°) magnetic latitudes (MLAT) are known to preferentially occur when a high-speed solar wind stream passes by Earth. We report here on observations that occurred during a ~75-min interval with high-speed solar wind on November 28, 2022 during which auroral arcs and very large geomagnetic disturbances (GMDs), also known as magnetic perturbation events (MPEs), with amplitude > 9 nT/s = 540 nT/min moved progressively poleward at eight stations spanning a large region near and north of Hudson Bay, Canada shortly before midnight local time. Sustained GMD activity with amplitudes > 3 nT/s appeared at each station with durations from 13 to 25 minutes. Spherical Elementary Currents Systems maps showed the poleward movement of a large-scale westward electrojet as well as mesoscale electrojet structures and highly localized up/down pairs of vertical currents near these stations when the largest GMDs were observed. This study is consistent with other recent studies showing that very large poleward-progressing GMDs can occur under high Vsw conditions, but is the first to document the sustained occurrence of large GMDs over such a wide high-latitude region.

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.

Rapid changes of magnetic fields associated with nighttime magnetic perturbation events (MPEs) with amplitudes |ΔB| of hundreds of nT and 5-10 min periods can induce geomagnetically-induced currents (GICs) that can harm technological systems. In this study we compare the occurrence and amplitude of nighttime MPEs with |dB/dt| ≥ 6 nT/s observed during 2015 and 2017 at five stations in Arctic Canada ranging from 75.2° to 64.7° in corrected geomagnetic latitude (MLAT) as functions of magnetic local time (MLT), the SME and SYM/H magnetic indices, and time delay after substorm onsets. Although most MPEs occurred within 30 minutes after a substorm onset, ~10% of those observed at the four lower latitude stations occurred over two hours after the most recent onset. A broad distribution in local time appeared at all 5 stations between 1700 and 0100 MLT, and a narrower distribution appeared at the lower latitude stations between 0200 and 0700 MLT. There was little or no correlation between MPE amplitude and the SYM/H index; most MPEs at all stations occurred for SYM/H values between -40 and 0 nT. SME index values for MPEs observed more than 1 hour after the most recent substorm onset fell in the lower half of the range of SME values for events during substorms, and dipolarizations in synchronous orbit at GOES 13 during these events were weaker or more often nonexistent. These observations suggest that substorms are neither necessary nor sufficient to cause MPEs, and hence predictions of GICs cannot focus solely on substorms.

We present a characterization of transient-large-amplitude (TLA) geomagnetic disturbances that occurred at six stations of the Magnetometer Array for Cusp and Cleft Studies throughout 2015. TLA events are defined as one or more short-timescale (< 60 seconds) dB/dt signature with magnitude > 6 nT/s. A semi-automated dB/dt search algorithm was developed to identify TLA events in ground magnetometer data and used to identify 40 TLA dB/dt events. We demonstrate the existence of large-amplitude dB/dt with timescale less than 10 seconds in nine of the events. The association of these events to sudden commencements is relatively weak, rather the events are more likely to occur in relation to substorm onsets. However, 15% of TLA events show no direct association to geomagnetic storms, substorms or nighttime magnetic impulse events.

We present a characterization of large amplitude, short-timescale geomagnetic disturbances that we refer to as transient induced current (TIC) events. TIC events are defined as one or more short-timescale (< 60 seconds) dB/dt signature with magnitude ≥ 6 nT/s. We identified 40 TIC events that occurred at six stations of the Magnetometer Array for Cusp and Cleft Studies throughout 2015 and we demonstrate the existence of large-amplitude dB/dt with timescale less than 10 seconds in nine of the events. The association of these events to sudden commencements is weaker than expected, rather the events are more likely to occur in relation to substorm onsets. However, 15% of TIC events show no direct association to geomagnetic storms, substorms or nighttime magnetic impulse events. Our findings suggest that the TICs have different properties than typical geomagnetically induced currents and may be hazardous to conductive components of the Internet of Things network.

Although lagged correlations have suggested influences of solar wind velocity (V) and number density (N), IMF Bz, ULF wave power, and substorms (as measured by AE) on MeV electron flux at geosynchronous orbit over an impressive number of hours and days, a satellite’s diurnal cycle can inflate correlations, associations between drivers may produce spurious effects, and correlations between all previous time steps may create an appearance of additive influence over many hours. Autoregressive-moving average transfer function (ARMAX) multiple regressions incorporating previous hours simultaneously can eliminate cycles and assess the impact of parameters, at each hour, while others are controlled. ARMAX influences are an order of magnitude lower than correlations. Most influence occurs within a few hours, not the many hours suggested by correlation. Over all hours, V and N show an initial negative impact, with longer term positive influences over the 9 (V) or 27 (N) h. Bz is initially a positive influence, longer term (6 h) negative effect. ULF waves impact flux in the first (positive) and second (negative) hour before the flux measurement, with further negative influences in the 12- 24 h before. AE (representing electron injection by substorms) shows only a short term (1 h) positive influence. However, when only recovery and after-recovery storm periods are considered (using stepwise regression), there are positive influences of ULF waves and V, negative influences of N and Bz, while AE shows no influence.