We present a statistical study of large magnetic field vector residuals between Swarm observations and the 13th generation International Geomagnetic Reference Field (IGRF-13) model under quiet to moderate geomagnetic conditions. Since the vast majority of data are taken during these conditions, statistics of these large residuals are important for satellite operation when using IGRF-13 as reference, as well as for magnetosphere-ionosphere-thermosphere (MIT) studies. Residuals with magnitude of vector differences between observations and model estimations larger than 300 nT under Dst >-50 nT are studied from 2014 to 2020. All large residuals appear in the high-latitude auroral zone region peaking around 70° (-70°) magnetic latitude (MLAT) in the northern hemisphere (southern hemisphere) with also a secondary occurrence peak just below 80° (-80°) MLAT. However, the two hemispheres show clear asymmetries in the magnetic longitude (MLON) distribution where both hemispheres show high concentration of large residuals around the geographic poles. Since polar satellite’s orbits give rise to highly biased number of observations around the geographic poles, it results in a decrease in occurrence rate with respect to the total number of measurements. Identifying the source of large residuals under quiet to moderate geomagnetic conditions is helpful to better separate out geophysical current signatures from non-geophysical large residuals that arise due to hemispheric differences in the location of the IGRF-13 geomagnetic pole compared to the geographic pole. We suggest that near geographic pole observations of large residuals are not geophysical, but due to mapping uncertainties of the IGRF-13 geomagnetic coordinates to geographic coordinates.

Space-based in situ magnetic field measurements are often limited by spacecraft-generated interference, known as stray magnetic fields. These fields, generated by currents from spacecraft subsystems, are frequently several times stronger than the ambient magnetic field signals of interest. To mitigate this, strict magnetic cleanliness, long mechanical booms, and at least two magnetometers are typically necessary to eliminate the spacecraft-generated magnetic interference. When two magnetometers are placed collinearly on a boom, gradiometry can be performed by modeling the spacecraft’s field as a dipole and subtracting it from the magnetometer measurements. However, this technique requires careful preflight characterization of the spacecraft’s magnetic field to determine the dipole coupling coefficients and sufficient boom length. This process is time-intensive, costly, and prone to error due to the changing nature of a spacecraft magnetic field environment in operation. We propose a novel method for in situ calculation of the gradiometric coupling coefficients, called the Reduction Algorithm for Magnetometer Electromagnetic Noise (RAMEN). RAMEN utilizes single-source point analysis and the time-frequency content of the magnetometer signals to identify stray magnetic field signals and calculate the gradiometric coupling coefficients. Through two Monte Carlo simulations, we demonstrate that the RAMEN gradiometry algorithm matches gradiometry with preflight coupling coefficient estimation. Additionally, we apply the RAMEN algorithm to noisy magnetometer data from the Venus Express spacecraft to demonstrate its use. The RAMEN method enhances the fidelity of spaceborne magnetic field observations using gradiometry and reduces the burden of arduous preflight spacecraft magnetic characterization.

Magnetometers are essential instruments in space physics, but their measurements are often contaminated by various external interference sources. In this work, we present a comprehensive review of existing magnetometer interference removal methods and introduce MAGPRIME (MAGnetic signal PRocessing, Interference Mitigation, and Enhancement), an open-source Python library featuring a collection of state-of-the-art interference removal algorithms. MAGPRIME streamlines the process of interference removal in magnetic field data by providing researchers with an integrated, easy-to-use platform. We detail the design, structure, and functionality of the library, as well as its potential to facilitate future research by enabling rapid testing and customization of interference removal methods. Using the MAGPRIME Library, we present two Monte Carlo benchmark results to compare the efficacy of interference removal algorithms in different magnetometer configurations. In Benchmark A, the Underdetermined Blind Source Separation (UBSS) and traditional gradiometry algorithms surpass the uncleaned boom-mounted magnetometers, achieving improved correlation and reducing median error in each simulation. Benchmark B tests the efficacy of the suite of MAGPRIME algorithms in a boomless magnetometer configuration. In this configuration, the UBSS algorithm proves to significantly reduce median error, along with improvements in median correlation and signal to noise ratio. This study highlights MAGPRIME’s potential in enhancing magnetic field measurement accuracy in various spacecraft designs, from traditional gradiometry setups to compact, cost-effective alternatives like bus-mounted CubeSat magnetometers, thus establishing it as a valuable tool for researchers and engineers in space exploration and magnetism studies.

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.

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.

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.