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.

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.

This paper presents a novel approach and algorithm to the problem of magnetic field interference cancellation of time-varying interference using distributed magnetometers and spacecraft telemetry with particular emphasis on the constrained computational and power requirements of CubeSats. The traditional approach to enable space-based low-amplitude and low-noise magnetometry is to develop a spacecraft magnetic cleanliness design and place the magnetometer sensor at the end of a boom far enough away from the bus to minimize remaining stray magnetic fields. In addition, secondary magnetometers are often placed partway along the boom to apply magnetic field gradiometry to clean the data further (e.g., NASA MMS has 8 meter booms with a sensor half-way down and another at the end). We employ a different approach taking advantage of low-cost chip-based magnetometers that can be placed throughout the satellite bus instead of utilizing a boom. The spacecraft magnetic field interference cancellation problem that we solve involves estimation of noise when the number of interfering sources far exceeds the number of sensors required to decouple the noise from the signal. The proposed approach models this as a contextual bandit learning problem and the proposed algorithm learns to identify the optimal low-noise combination of distributed magnetometers based on indirect information gained on spacecraft currents through telemetry. The algorithmic behaviors are tested with synthetically modeled spacecraft data and on real world data generated in a lab-based setting with telemetry and currents collected from the GRIFEX CubeSat and provides a way for accurate magnetic field measurements with CubeSats.

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.

Disturbances in the magnetosphere-ionosphere system cause changes in the geomagnetic field that result in ground induced currents (GICs) that are potentially hazardous to electrical systems on Earth. Harmful GICs are driven by magnetic field fluctuations with timescales generally falling in the range of 1-10 minutes; much less attention has been placed on geomagnetic field fluctuations with short timescales (< 60 seconds) because they cause transient induced currents (TICs) that have not been considered to pose a legitimate threat to electrical systems since they are similar to electrical transients due to lightning. On the contrary, short-timescale magnetic field fluctuations have been found to be capable of coupling directly to power grids and electrical systems, inducing substantial voltages without first flowing in the ground. This ionospheric current coupling poses a potential threat to any of these systems, especially electronic equipment with low operating voltage or that does not have surge protection. Transmitting devices that are at risk by such currents are becoming increasingly more prevalent in society with the growth of the Internet of Things (IoT) network. Our characterization of transient magnetic field perturbations provides detail on short-timescale changes of the magnetosphere-ionosphere coupled system and supports the assessment of possible hazards to technological infrastructure on Earth. This research is enabled by modern magnetometers, both ground- and space-based, with high sampling rate capabilities that allow for the measurement of transient surface magnetic field fluctuations with short-timescales. We present the characteristics of transient magnetic field changes observed by the MACCS array in Arctic Canada by selecting events recorded on the ground and analyzing the behavior of the electromagnetic fluctuations within the ionosphere and magnetosphere during such events.

Sudden Impulse (SI) events and Sudden Storm Commencements (SSC) are rapid geomagnetic variations associated with a compression of the magnetic field. Starting in 2006 Ebre Observatory, the IAGA international database on rapid magnetic variations, began to differentiate SI events from SSCs. These events have different magnetic characteristics depending on local time and latitude. Starting in 2006 and ending with the last definitive published dataset, the module SeaPy within Python is used to perform a superposed epoch analysis on SI events and SSCs for high latitude stations and low latitude stations. In relation to low latitude station onset times, we find systematic behavior of the total field strength and North-South component of the magnetic field at high latitudes. Specifically, the SI and SSC signatures are delayed and the compression signature can be highly variable from event to event.

Nearly all studies of impulsive magnetic perturbation events (MPEs) with large magnetic field variability (dB/dt) that can produce dangerous geomagnetically-induced currents (GICs) have used data from the northern hemisphere. Here we present details of four large-amplitude MPE events (|DBx|> 900 nT and |dB/dt| > 10 nT/s in at least one component) observed between 2015 and 2018 in conjugate high latitude regions (65 - 80° corrected geomagnetic latitude), using magnetometer data from (1) Pangnirtung and Iqaluit in eastern Arctic Canada and the magnetically conjugate South Pole Station in Antarctica and (2) the Greenland West Coast Chain and two magnetically conjugate chains in Antarctica, AAL-PIP and BAS LPM. From 1 to 3 different isolated MPEs localized in corrected geomagnetic latitude were observed during 3 pre-midnight events; many were simultaneous within 3 min in both hemispheres. Their conjugate latitudinal amplitude profiles, however, matched qualitatively at best. During an extended post-midnight interval, which we associate with an interval of omega bands, multiple highly localized MPEs occurred independently in time at each station in both hemispheres. These nighttime MPEs occurred under a wide range of geomagnetic conditions, but common to each was a negative IMF Bz that exhibited at least a modest increase at or near the time of the event. A comparison of perturbation amplitudes to modeled ionospheric conductivities in conjugate hemispheres clearly favored a current generator model over a voltage generator model for 3 of the 4 events; neither model provided a good fit for the pre-midnight event that occurred near vernal equinox.

Rapid changes of magnetic fields associated with nighttime magnetic perturbation events (MPEs) with amplitudes |ΔB| of hundreds of nT and 5-10 min duration can induce geomagnetically-induced currents (GICs) that can harm technological systems. Here we present superposed epoch analyses of large nighttime MPEs (|dB/dt| ≥ 6 nT/s) observed during 2015 and 2017 at five stations in Arctic Canada ranging from 64.7° to 75.2° in corrected geomagnetic latitude (MLAT) as functions of the interplanetary magnetic field (IMF), solar wind dynamic pressure, density, and velocity, and the SML, SMU, and SYM/H geomagnetic activity indices. Analyses were produced for premidnight and postmidnight events and for three ranges of time after the most recent substorm onset: A) 0-30 min, B) 30-60 min, and C) >60 min. Of the solar wind and IMF parameters studied, only the IMF Bz component showed any consistent temporal variations prior to MPEs: a 1-2 hour wide 1-3 nT negative minimum at all stations beginning ~30 to 80 min before premidnight MPEs, and minima that were less consistent but often deeper before postmidnight MPEs. Median, 25th, and 75th percentile SuperMAG auroral indices SML (SMU) showed drops (rises) before pre- and post-midnight type A MPEs, but most of the MPEs in categories B and C did not coincide with large-scale peaks in ionospheric electrojets. Median SYM/H indices were flat near -30 nT for premidnight events and showed no consistent temporal association with any MPE events. More disturbed values of IMF Bz, Psw, Nsw, SML, SMU, and SYM/H appeared postmidnight than premidnight.

The rapid changes of magnetic fields associated with nighttime magnetic perturbations with amplitudes |ΔB| of hundreds of nT and 5-10 min periods can induce bursts of geomagnetically-induced currents that can harm technological systems. Recent studies of these events in eastern Arctic Canada, based on data from four ground magnetometer arrays and augmented by observations from auroral imagers and high-altitude spacecraft in the nightside magnetosphere, showed them to be highly localized, with largest |dB/dt| values within a ~275 km half-maximum radius that was associated with a region of shear between upward and downward field-aligned currents, and usually but not always associated with substorms. In this study we look in more detail at the field-aligned currents associated with these events using AMPERE data, and compare the context and characteristics of events not associated with substorms (occurring from 60 min to over two days after the most recent substorm onset) to those occurring within 30 min of onset. Preliminary results of this comparison, based on events with |dB/dt|≥ 6 nT/s observed during 2015 and 2017 at Repulse Bay (75.2° CGMLAT), showed that the SYM/H distributions for both categories of events were similar, with 85% between -40 and 10 nT, and the SME values during non-substorm events coincided with the lower half of the range of SME values for events during substorms (200 – 700 nT). Dipolarizations of ≥ 20 nT amplitude at GOES 13 occurred within 45 minutes prior to 73% of the substorm events but only 29% of the non-substorm events. These observations suggest that predictions of GICs cannot focus solely on the occurrence of intense substorms.

The accurate determination of the Field Line Resonance (FLR) frequency of a resonating geomagnetic field line is necessary to remotely monitor the plasmaspheric mass density during geomagnetic storms and quiet times alike. Under certain assumptions the plasmaspheric mass density at the equator is inversely proportional to the square of the FLR frequency. The most common techniques to determine the FLR frequency from ground magnetometer measurements are the amplitude ratio and phase difference techniques, both based on geomagnetic field observations at two latitudinally separated ground stations along the same magnetic meridian. Previously developed automated techniques have used statistical methods to pinpoint the FLR frequency using the amplitude ratio and phase difference calculations. We now introduce a physics-based automated technique, using non-linear least square fitting of the ground magnetometer data to the analytical resonant wave equations, that reproduces the wave characteristics on the ground, and from those determine the FLR frequency. One of the advantages of the new technique is the estimation of physics-based errors of the FLR frequency, and as a result of the equatorial plasmaspheric mass density. We present analytical results of the new technique, and test it using data from the Inner-Magnetospheric Array for Geospace Science (iMAGS) ground magnetometer chain along the coast of Chile and the east coast of the United States. We compare the results with the results of previously published statistical automated techniques.