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We examined rapid variations in the electron zebra stripe patterns, specifically at L= 1.5, over a three‐month duration, using twin Van Allen Probes within Earth's inner magnetosphere. During geomagnetically quiet intervals, these stripes exhibit a peak‐to‐valley ratio (Δj) ∼1.25 in detrended electron fluxes. However, during geomagnetic storms, they became highly prominent, with Δj> 2.5. The correlation between Δjand net field‐aligned currents (FACs) is observed to be high (0.70). Global magnetohydrodynamic (MHD) simulation results indicate that the westward electric field at midnight at low latitudes in the deep inner magnetosphere correlates well with net FACs. An increase in net FACs could amplify the dawn‐to‐dusk electric field in the deep inner magnetosphere, thereby causing the inward transport of electrons. Given that FACs are linked to the interaction between solar wind and the magnetosphere, our findings emphasize the importance of solar wind‐magnetosphere coupling in the deeper regions of the inner magnetosphere. The intensity of hundreds of keV electron fluxes displays a distinctive pattern in the energy versus L‐value spectrogram, characterized by periodic valleys and peaks, commonly referred to as zebra stripes. These patterns have been observed in the magnetospheres of multiple planets, including Earth, Jupiter, and Saturn. Our study reveals that during geomagnetically quiet intervals, Earth's inner magnetospheric zebra stripes exhibit well‐defined banded features. However, these bands become highly pronounced during geomagnetic storms. The peak‐to‐valley ratio (Δj) of detrended electron fluxes shows a correlation with net field‐aligned currents (FACs), and these FACs, in turn, align with the westward component of the electric field at midnight. Consequently, FACs play a significant role in controlling electron flux dynamics deep within the inner magnetosphere. This research illuminates the solar wind‐magnetosphere‐ionosphere couplings. Electron zebra stripes are a persistent feature in Earth's inner magnetosphere, although they become intensified during geomagnetic stormsPeak‐valley ratio (Δj) in detrended electron flux within the zebra stripes enhances by ≥1 factor at L= 1.5 during three geomagnetic stormsΔjis well correlated with the net field‐aligned current (FAC) in polar region, suggesting the dominant role of convection driven by FAC Electron zebra stripes are a persistent feature in Earth's inner magnetosphere, although they become intensified during geomagnetic storms Peak‐valley ratio (Δj) in detrended electron flux within the zebra stripes enhances by ≥1 factor at L= 1.5 during three geomagnetic storms Δjis well correlated with the net field‐aligned current (FAC) in polar region, suggesting the dominant role of convection driven by FAC

Orbiting Earth's dayside outer magnetosphere on 29 September 2015, the Magnetospheric Multiscale (MMS) satellites measured plasma composition, simultaneous electromagnetic ion cyclotron waves, and intermittent fast plasma flows consistent with ultralow frequency waves or convection. Such flows can accelerate typically unobservable low‐energy plasma into a measurable energy range of spacecraft plasma instrumentation. We exploit the flow occurrence to ensure measurement of cold ion species alongside the hot particles—consisting of ionospheric heavy ions and solar wind He++—during a subinterval of wave emissions with spectral properties previously described as peculiar. Through application of the composition and multisatellite wave vector data to linear theory, we demonstrate the emissions are in fact consistent with theory, growing naturally in the He++band with sufficient free energy. Electromagnetic ion cyclotron waves are a special class of plasma waves observed in space near Earth or in other magnetized plasmas. They emit electromagnetic energy near the local ion cyclotron frequencies, a relationship that has been studied extensively through theory. But investigations in space via satellite observations have been hindered by an observational problem. Spacecraft charge positive in sunlight due to interactions between sunlight and spacecraft surfaces. Because of this, positively charged ion species with very low energy are invisible to spacecraft plasma instruments. These invisible low‐energy ions are critical to measure to fully understand their effects on the wave emissions. Luckily, electric fields induced by sudden ambient magnetic field changes sometimes provide extra acceleration to these low‐energy ions, helping them enter plasma instrument apertures and be observed. We investigate the electromagnetic waves during one such acceleration interval and use comprehensive plasma instrument measurements to show waves thought to be peculiar are instead behaving consistent with theory. Exploring other times and regions of space under similar measurement conditions may improve our understanding of how the electromagnetic waves are generated and their evolution in space and time. Convection flows enabled direct measurement of comprehensive plasma composition during observations of EMIC waves with peculiar propertiesSingle‐spacecraft and multispacecraft measurements were applied to modeling and tests of linear kinetic theoryThe multiple heavy ion populations, even with low abundances, help sustain wave growth and explain the wave properties

We examine the statistical distribution of large‐scale Birkeland currents measured by the Active Magnetosphere and Planetary Electrodynamics Response Experiment in four unique categories of geomagnetic activity for the first time: quiet times, storm times, quiet‐time substorms, and storm‐time substorms. A novel method is employed to sort data into one of these four categories, and the categorizations are provided for future research. The mean current density is largest during substorms and its standard deviation is largest during geomagnetic storms. Current densities which are above a low threshold are more likely during substorms, but extreme currents are far more likely during geomagnetic storms, consistent with a paradigm in which geomagnetic storms represent periods of enhanced variability over quiet times. We demonstrate that extreme currents are most likely to flow within the Region 2 current during geomagnetic storms. This is unexpected in a paradigm of the current systems in which Region 1 current is generally larger. We take measurements from a set of 66 spacecraft orbiting Earth to look at electric currents that flow along Earth's magnetic field lines. We look at different types of space weather called “geomagnetic storms” and “substorms,” and combine methods to detect when those types of space weather happen. We use our combined method to separate our measurements into the different types of space weather, and then we look at how strong the currents are during each type of space weather. We plot histograms of the strengths and then use those histograms to work out the underlying mathematics of the strengths: we can then plot further graphs showing how those underlying mathematics change. We then work out when the very strongest currents are likely to flow, and during which type of space weather this occurs, which is useful both for understanding the system and for mitigating against the risks of space weather. Geomagnetic storms are more likely than substorms to drive extreme field‐aligned current densitiesExtreme current densities are most likely on the dayside and least likely within 3 hr of midnightThe highest probabilities of extreme current densities occur in Region 2 currents during geomagnetic storms Geomagnetic storms are more likely than substorms to drive extreme field‐aligned current densities Extreme current densities are most likely on the dayside and least likely within 3 hr of midnight The highest probabilities of extreme current densities occur in Region 2 currents during geomagnetic storms

We analyze the local dynamics of magnetotail reconnection onset using Magnetospheric Multiscale (MMS) data. In conjunction with MMS, the macroscopic dynamics of this event were captured by a number of other ground and space‐based observatories, as is reported in a companion paper. We find that the local dynamics of the onset were characterized by the rapid thinning of the cross‐tail current sheet below the ion inertial scale, accompanied by the growth of flapping waves and the subsequent onset of electron tearing. Multiple kinetic‐scale magnetic islands were detected coincident with the growth of an initially sub‐Alfvénic, demagnetized tailward ion exhaust. The onset and rapid enhancement of parallel electron inflow at the exhaust boundary was a remote signature of the intensification of reconnection Earthward of the spacecraft. Two secondary reconnection sites are found embedded within the exhaust from a primary X‐line. The primary X‐line was designated as such on the basis that (a) while multiple jet reversals were observed in the current sheet, only one reversal of the electron inflow was observed at the high‐latitude exhaust boundary, (b) the reconnection electric field was roughly five times larger at the primary X‐line than the secondary X‐lines, and (c) energetic electron fluxes increased and transitioned from anti‐field‐aligned to isotropic during the primary X‐line crossing, indicating a change in magnetic topology. The results are consistent with the idea that a primary X‐line mediates the reconnection of lobe magnetic field lines and accelerates electrons more efficiently than its secondary X‐line counterparts. Magnetotail reconnection onset was triggered by electron tearing during a solar wind pressure pulseOnset was characterized by the rapid collapse of the current sheet thickness and kinetic‐scale flux rope formationA primary X‐line was established within minutes of the onset Magnetotail reconnection onset was triggered by electron tearing during a solar wind pressure pulse Onset was characterized by the rapid collapse of the current sheet thickness and kinetic‐scale flux rope formation A primary X‐line was established within minutes of the onset

We analyze a magnetotail reconnection onset event on 3 July 2017 that was observed under otherwise quiescent magnetospheric conditions by a fortuitous conjunction of six space and ground‐based observatories. The study investigates the large‐scale coupling of the solar wind–magnetosphere system that precipitated the onset of the magnetotail reconnection, focusing on the processes that thinned and stretched the cross‐tail current layer in the absence of significant flux loading during a 2‐hr‐long preconditioning phase. It is demonstrated with data in the (a) upstream solar wind, (b) at the low‐latitude magnetopause, (c) in the high‐latitude polar cap, and (d) in the magnetotail that the typical picture of solar wind‐driven current sheet thinning via flux loading does not appear relevant for this particular event. We find that the current sheet thinning was, instead, initiated by a transient solar wind pressure pulse and that the current sheet thinning continued even as the magnetotail and solar wind pressures decreased. We suggest that field line curvature‐induced scattering (observed by magnetospheric multiscale) and precipitation (observed by Defense Meteorological Satellite Program) of high‐energy thermal protons may have evacuated plasma sheet thermal energy, which may require a thinning of the plasma sheet to preserve pressure equilibrium with the solar wind. Magnetotail reconnection onset was observed during a fortuitous multiscale conjunction of the heliophysics observatoriesA transient solar wind pressure pulse triggered thinning and stretching of the cross‐tail current sheet without significant flux loadingA second solar wind pressure pulse caused the thinned current sheet to rapidly collapse and reconnect Magnetotail reconnection onset was observed during a fortuitous multiscale conjunction of the heliophysics observatories A transient solar wind pressure pulse triggered thinning and stretching of the cross‐tail current sheet without significant flux loading A second solar wind pressure pulse caused the thinned current sheet to rapidly collapse and reconnect

We present Magnetospheric Multiscale mission (MMS) observations of Hall physics in the magnetotail, which compared to dayside Hall physics is a relatively unexplored topic. The plasma consists of electrons, moderately cold ions (T∼1.5 keV) and hot ions (T∼20 keV). MMS can differentiate between the cold ion demagnetization region and hot ion demagnetization regions, which suggests that MMS was observing multiscale Hall physics. The observed Hall electric field is compared with a generalized Ohm's law, accounting for multiple ion populations. The cold ion population, despite its relatively high initial temperature, has a significant impact on the Hall electric field. These results show that multiscale Hall physics is relevant over a much larger temperature range than previously observed and is relevant for the whole magnetosphere as well as for other astrophysical plasma. MMS multispacecraft observation of Hall electric fields during a deep partial plasma sheet crossingMixing of hot (20 keV) and moderately cold (1.5 keV) ions generate multiscale Hall electric fieldsElectron and cold/hot ion demagnetization boundaries are observed near their predicted locations

The Magnetospheric Multiscale (MMS) spacecraft obtained unprecedented high‐time resolution multipoint particle and field measurements of an interplanetary shock event on 8 January 2018. The spacecraft encountered the supercritical forward shock of a forward/reverse shock pair in the pristine solar wind upstream of the bow shock near the subsolar point as they neared apogee at ~25 RE. The high‐time resolution measurements from the four spacecraft, separated by only ~20 km, allowed direct measurement of particle distributions revealing evidence of electron heating and near specularly reflected ions. The cross‐shock potential is calculated directly from 3‐D electric field measurements. This is the first reported direct high temporal resolution (<1 s) observation at an interplanetary shock of near specularly reflected ions. Calculation of the cross‐shock potential yields a potential jump significant enough to reflect at least some of the protons from the incident solar wind beam. The cross‐shock potential calculated here is consistent with previous estimations based on particle measurements and numerical/analytical simulations. The ambipolar contribution to the cross‐shock potential calculated from the four‐spacecraft divergence of the electron pressure tensor is somewhat higher than that inferred form the Liouville‐mapped electron energy gain across the shock. Furthermore, the high‐time‐resolution 3‐D electric field measurements reported here reveal small‐scale nonlinear structures embedded in the shock layer that contribute to the nonmonotonic shock transition. MMS observed a supercritical IP shock in the upstream pristine solar wind, directly resolving near specularly reflected ionsThe cross‐shock potential jump calculated from 3‐D E‐field measurements is consistent with the observed electron heating and ion reflectionThe high‐temporal‐resolution 3‐D electric field measurements revealed small‐scale nonlinear structures embedded within the shock front

The occurrence and impacts of magnetopause processes at outer planets, particularly magnetic reconnection and the Kelvin‐Helmholtz instability (KHI), remains unresolved. From a list of 2,114 magnetopause crossings at Saturn spanning the full duration of the Cassini mission, magnetic field and low‐energy plasma properties are analyzed for each crossing to determine the likelihood of particular dynamical processes at Saturn's magnetopause. Using Cassini magnetic field data, crossings are categorized as (a) those with signatures of possible magnetic reconnection, (b) those near/inside a magnetopause surface wave or vortex arising from KHI, and (c) those during quiescent conditions (i.e., lacking signatures indicative of magnetic reconnection or KH waves). Of magnetopause crossings with valid intervals on both sides of the boundary, nearly half of the crossings met criteria for signatures of reconnection, with little dependence on local time or latitude of the magnetopause crossing location. Crossings identified as associated with KHI are found to more likely occur toward the dawn sector as compared to other local times, but with both flanks likely being quasi‐unstable to the instability. Magnetopause properties for crossings with available low‐energy electron data from Cassini are further explored to provide insight into the local plasma conditions that may be conducive to magnetic reconnection and/or KH waves. This investigation reveals that certain dynamics along the magnetopause of Saturn may be more prevalent than previously considered, and provides a basis for a more comprehensive understanding of magnetopause dynamics and plasma transport at the outer planets. We analyze Cassini data encompassing 2,114 magnetopause crossings to determine the occurrence of dynamical processes at Saturn's magnetopauseThe occurrence of reconnection is prevalent at Saturn's magnetopause and is independent of Saturn local time and latitudeObservationally, we find more Kelvin‐Helmholtz signatures at dawn, but both dawn and dusk can be conducive to Kelvin‐Helmholtz instability We analyze Cassini data encompassing 2,114 magnetopause crossings to determine the occurrence of dynamical processes at Saturn's magnetopause The occurrence of reconnection is prevalent at Saturn's magnetopause and is independent of Saturn local time and latitude Observationally, we find more Kelvin‐Helmholtz signatures at dawn, but both dawn and dusk can be conducive to Kelvin‐Helmholtz instability

The development of large‐scale Birkeland currents is examined using the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE), which measures global Birkeland currents continuously on 10‐min time scales. The integrated current was used to identify onsets of at least 1 MA preceded by periods of quiescence lasting at least 3 hr. The Region 1 currents do not fully form without Region 2. Rather, they develop together, first on the dayside, then on the nightside, and lastly, they fill in and intensify at all local times to form the nominal statistical pattern. The onsets are closely correlated with enhancements of magnetospheric forcing as indicated by the solar wind electric field and the orientation of the interplanetary magnetic field. Nightside onsets correspond to intensifications of the auroral electrojet as reflected in the AE index; they are delayed by ~40 min relative to the increase of the dayside current and are 2.8 times more rapid than the dayside current increase. After nightside onset, Birkeland currents expand toward dawn and dusk and merge with the dayside currents while also intensifying at all local times. The dayside current pattern depends on the sign of the interplanetary magnetic field BY. The nightside current distributions are the same for positive and negative BYand display a Harang discontinuity independent of the sign of BY. The predominant development and intensification of Birkeland currents occur after nightside onset at all local times with roughly 75% of the total current, both Regions 1 and 2, appearing after nightside onset. This study uses data from the 66 Iridium Communications satellites to track the development of electric currents that drive aurora. These currents can turn on in less than about an hour. However, the currents can only be measured from satellites orbiting the Earth above the atmosphere, and in those orbits, satellites take about 100 min to orbit the Earth. With the Iridium constellation, we remeasure these currents every 10 min and are able to track where they start and how they grow. This happens in two steps: Currents appear first in the day where they remain. About 30 min later, new currents start near midnight and then spread toward dawn and dusk and increase until they completely encircle the poles in an oval pattern. The total current finally reaches millions of Amperes. The two‐step process implies that explosive dynamics in the magnetic tail of the Earth play a key role in creating and generating the auroral currents. This study shows that the effects they have on the temporal sequence of activity onset need to be included to predict the effects of the solar wind and solar storms on the Earth's ionosphere and upper atmosphere. Analysis of Birkeland current growth following extended intervals of low current reveals the development sequence of the global systemCurrents begin on the dayside with both Regions 1 and 2 and do not appear on the nightside until a sudden onset about 30 min laterAt onset, nightside Regions 1 and 2 appear together, intensify, and expand to the dayside forming the complete system after about an hour

The Whole Heliosphere and Planetary Interactions initiative was established to leverage relatively quiet intervals during solar minimum to better understand the interconnectedness of the various domains in the heliosphere. This study provides an expansive mosaic of observations spanning from the Sun, through interplanetary space, to the magnetospheric response and subsequent effects on the ionosphere‐thermosphere‐mesosphere (ITM) system. To accomplish this, a diverse set of observational datasets are utilized from 2019 July 26 to October 16 (i.e., over three Carrington rotations, CR2220, CR2221, and CR2222) with connections of these observations to the more focused studies submitted to this special issue. Particularly, this study focuses on two long‐lived coronal holes and their varying impact in sculpting the heliosphere and driving of the magnetospheric system. As a result, the evolution of coronal holes, impacts on the inner heliosphere solar wind, glimpses at mesoscale solar wind variability, magnetospheric response to these evolving solar wind drivers, and resulting ITM phenomena are captured to reveal the interconnectedness of this system‐of‐systems. The field of Heliophysics research spans a large range of plasma regimes and disciplines that are all linked through the complex interactions each system has with one another. To better explore the interconnected nature of the heliosphere, this study combines observations from across the sub‐domains of Heliophysics to construct snapshots of the Sun, solar wind, and the magnetospheric and ionospheric systems at Earth over three revolutions of the Sun. This allows for a unique vantage point to put these systems in perspective of one another and understand how they impact one another. The evolution and impacts of two coronal holes are investigated over three Carrington rotationsThe evolution of the coronal hole led to changes in the solar wind throughout the inner solar systemSubsequent geospace response differed with each passage due to both changes in the solar wind and preconditioning within the systems The evolution and impacts of two coronal holes are investigated over three Carrington rotations The evolution of the coronal hole led to changes in the solar wind throughout the inner solar system Subsequent geospace response differed with each passage due to both changes in the solar wind and preconditioning within the systems

An extended interval of perturbed magnetospheric conditions in November 2016 supported increased convection and sunward transport of plasmaspheric material. During this period of time the Magnetospheric Multiscale satellites, with their apogees along Earth's dusk‐side outer magnetosphere, encountered several cold plasma density structures at the same time as plasma bulk flows capable of accelerating hidden cold plasma occurred. Investigating the charged particle and fields data during two subintervals showed that the satellites made direct measurements of cold plasmaspheric ions embedded within multicomponent hot plasmas as well as electromagnetic emissions consistent with electromagnetic ion cyclotron (EMIC) waves. The complex in situ ion composition measurements were applied to linear wave modeling to interpret the impacts of cold and hot ion species on wave growth and band structure. Although the waves for both intervals were predicted to have peak growth rate below ΩHe+, substantial differences were observed among all other dispersive properties. The modeling also showed EMIC waves generated in the presence of heavy ions had growth rates and unstable wave numbers always smaller than predicted for a pure proton‐electron plasma. The results provide implications for future investigation of EMIC wave generation with and without direct measurements of the cold and hot plasma composition as well as of subsequent wave‐particle interactions. Electromagnetic ion cyclotron (EMIC) waves occur throughout our solar system. The waves have been observed near Earth and are more likely to achieve large amplitudes in the magnetized plasma that exists in a region of space called Earth's dusk‐side magnetosphere. Multiple plasma populations exist in this region that can be organized into groups of cold or hot plasmas. Although the hot plasmas can be measured most of the time, the cold plasmas are usually hidden from plasma sensors due to positive spacecraft charging issues; cold plasmas are therefore usually unavailable to help provide a detailed understanding of why dusk‐side EMIC waves are generated. The purpose of our study was to investigate measurements made by the NASA Magnetospheric Multiscale satellites to during a time period when the cold plasma species were not hidden and apply these measurements to improve understanding of these dusk‐side EMIC waves. The results showed why comprehensive measurements are needed to continue advancing our understanding of EMIC waves as seen by other spacecraft in different regions in Earth's magnetosphere, and how these waves impact other plasma populations. Plasma bulk flows enabled direct measurement of cold plasmaspheric ions during dusk‐side EMIC wave activityThe cold and hot plasma composition data supported accurate tests of local linear wave growthThe presence and variability of heavy ions impact wave growth and band structure, and can influence subsequent wave‐particle interactions Plasma bulk flows enabled direct measurement of cold plasmaspheric ions during dusk‐side EMIC wave activity The cold and hot plasma composition data supported accurate tests of local linear wave growth The presence and variability of heavy ions impact wave growth and band structure, and can influence subsequent wave‐particle interactions

Using a three‐dimensional (3‐D) global‐scale hybrid code, the Magnetospheric Multiscale (MMS) reconnection event around 02:13 UT on 18 November 2015, highlighted in the Geospace Environment Modeling (GEM) Dayside Kinetic Challenge, is simulated, in which the interplanetary magnetic field (IMF) points southward and the geomagnetic field has a −27° dipole tilt angle. Strong southward plasma jets are found near the magnetopause as a result of the dayside reconnection. Our results indicate that the subsolar magnetopause reconnection X line shifts from the subsolar point toward the Northern Hemisphere due to the effect of the tilted geomagnetic dipole angle, consistent with the MMS observation. Subsequently, the reconnection X lines or sites and reconnection flux ropes above the equator propagate northward along the magnetopause. The formation and global distribution of the X lines and the structure of the magnetopause reconnection are investigated in detail with the simulation. Mirror mode waves are also found in the middle of the magnetosheath downstream of the quasi‐perpendicular shock where the plasma properties are consistent with the mirror instability condition. As a special outcome of the GEM challenge event, the spatial and temporal variations in reconnection, the electromagnetic power spectra, and the associated D‐shaped ion velocity distributions in the simulated reconnection event are compared with the MMS observation. Subsolar magnetopause X lines shift toward the Northern Hemisphere due to the effect of the negative tilted geomagnetic dipole angleThe hybrid simulation magnetic fields and plasma date match MMS3 observations well during the magnetopause crossingMirror mode waves appear in the middle of the magnetosheath downstream of the quasi‐perpendicular shock

Field‐aligned currents from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) were combined with simultaneous and coincident observations of ionospheric conductivities made by the Poker Flat Incoherent Scatter Radar (PFISR) in Alaska for 20 geomagnetically active days. The height‐integrated conductivities (conductances) were determined from the electron densities measured by the radar between 80 and 200 km altitude. Binning and averaging the data by field‐aligned current density and magnetic local time, we find that the currents correlate with conductances in both upward and downward current regions over some magnetic local times. The strongest correlation is seen in the late evening and morning sectors, with the Hall conductances two to three times larger than the Pedersen conductances for the same values of the field‐aligned current. The observed correlations reflect the mean energy of auroral precipitation, the contributions from electrons and protons to producing enhanced conductances, and the availability of charge carriers on auroral field lines. We apply linear fitting and smoothing to the correlations to construct an empirical model for specifying auroral conductances globally from AMPERE field‐aligned current maps. The energy fluxes from precipitating particles derived from the model conductances compare well with those derived using AMPERE data combined with satellite‐based measurements of far ultraviolet emissions, suggesting the results obtained at Poker Flat may be applicable to all high latitude locations. The ability to estimate conductances from AMPERE field‐aligned current maps provides the means to develop a global conductance model for the auroral ionosphere. Simultaneous and coincident field‐aligned current and conductance data are used to study correlations between the two quantitiesThe correlations between parallel currents and conductances are strongest from late evening to morning magnetic local timesThe correlations can be used to model auroral conductances from field‐aligned current measurements