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The 21st century is the time of complexity. We delineate it and its importance as necessary to solve ‘wicked problems.’ Inherently transdisciplinary, trans-scale, and interconnected to living systems, the solution to Heliophysics’ identity crisis and to unlock the next generation of scientific discovery may be to embrace complexity. With the right foresight, direction, and incentive over the next ten years, Heliophysics can become a beacon for how all of society thinks about and does complexity science.

Extended periods of northward interplanetary magnetic field (IMF) lead to the formation of a cold, dense plasma sheet due to the entry of solar wind plasma into the magnetosphere. Identifying the paths that the solar wind takes to enter the magnetosphere, and their relative importance has remained elusive. Any theoretical model of entry must satisfy observational constraints, such as the overall entry rate and the dawn‐dusk asymmetry observed in the cold, dense plasma sheet. We model, using a combination of global magnetohydrodynamic and test particle simulations, solar wind ion entry into the magnetosphere during northward IMF and compare entry facilitated by the Kelvin‐Helmholtz instability to cusp reconnection. For Kelvin‐Helmholtz entry we reproduce transport rates inferred from observation and kinetic modeling and find that intravortex reconnection creates buoyant flux tubes, which provides, through interchange instability, a mechanism of filling the central plasma sheet with cold magnetosheath plasma. For cusp entry we show that an intrinsic dawn‐dusk asymmetry is created during entry that is the result of alignment of the westward ion drift with the dawnward electric field typically observed during northward IMF. We show that both entry mechanisms provide comparable mass but affect entering plasma differently. The flank‐entering plasma is cold and dawn‐dusk symmetric, whereas the cusp‐entering plasma is accelerated and preferentially deflected toward dawn. The combined effect of these entry mechanisms results in a plasma sheet population that exhibits dawn‐dusk asymmetry in the manner that is seen in nature: a two‐component (hot and cold) dusk flank and hotter, broadly peaked dawn population., Key Points Global MHD model with kinetic test particles shows comparable solar wind entry from KH vortices and cusp reconnection under northward IMFSolar wind entry exhibits intrinsic dawn‐dusk asymmetry due to the preferential energization and dawnward deflection of cusp‐entering ionsCombined flank‐ and cusp‐entering solar wind ions recreates observed two‐component (hot and cold) dusk and broad‐peaked dawn population

The role a geospace plume in influencing the efficiency of magnetopause reconnection is an open question with two contrasting theories being debated. A local‐control theory suggests that a plume decreases both local and global reconnection rates, whereas a global‐control theory argues that the global reconnection rate is controlled by the solar wind rather than local physics. Observationally, limited numbers of point measurements from spacecraft cannot reveal whether a local change affects the global reconnection. A distributed observatory is hence needed to assess the validity of the two theories. We use THEMIS and Los Alamos National Laboratory spacecraft to identify the occurrence of a geospace plume and its contact with the magnetopause. Global evolution and morphology of the plume is traced using GPS measurements. SuperDARN is then used to monitor the distribution and the strength of dayside reconnection. Two storm‐time geospace plume events are examined and show that as the plume contacts the magnetopause, the efficiency of reconnection decreases at the contact longitude. The amount of local decrease is 81% and 68% for the two events, and both values are consistent with the mass loading effect of the plume if the plume's atomic mass is ∼4 amu. Reconnection in the surrounding is enhanced, and when the solar wind driving is stable, little variation is seen in the cross polar cap potential. This study illuminates a pathway to resolve the role of cold dense plasma on solar wind‐magnetosphere coupling, and the observations suggest that plumes redistribute magnetopause reconnection activity without changing the global strength substantially., Key Points We strategically coordinate measurements made by THEMIS and Los Alamos National Laboratory spacecraft, GPS network, and SuperDARN to investigate geospace plumesPlumes decrease the local reconnection rate at the plume longitude and increase the reconnection rate in regions adjacent to the plumeWhen the solar wind is stable, the global reconnection remains unchanged in presence of plumes, supporting a global‐control theory

Based on global hybrid simulation results, we predict that foreshock turbulence can reach the magnetopause and lead to reconnection as well as Earth‐sized indents. Both the interplanetary magnetic field (IMF) and solar wind are constant in our simulation, and hence, all dynamics are generated by foreshock instabilities. The IMF in the simulation is mostly Sun‐Earth aligned with a weak northward and zero dawn‐dusk component, such that subsolar magnetopause reconnection is not expected without foreshock turbulence modifying the magnetosheath fields. We show a reconnection example to illustrate that the turbulence can create large magnetic shear angles across the magnetopause to induce local bursty reconnection. Magnetopause reconnection and indents developed from the impact of foreshock turbulence can potentially contribute to dayside loss of planetary plasmas., Key Points Foreshock turbulence can reach the magnetopause under a northward quasi‐radial interplanetary magnetic field with zero dawn‐dusk componentThe turbulence can create large magnetic shear angles across the magnetopause, leading to local bursty reconnectionBombardments of the turbulence cause Earth‐sized magnetopause indents under constant interplanetary magnetic field and solar wind

The LEXI and SMILE missions will provide soft X‐ray images of the Earth's magnetosheath and cusps after their anticipated launch in 2023 and 2024, respectively. The IBEX mission showed the potential of an Energetic Neutral Atom (ENA) instrument to image dayside magnetosheath and cusps, albeit over the long hours required to raster an image with a single pixel imager. Thus, it is timely to discuss the two imaging techniques and relevant science topics. We simulate soft X‐ray and low‐ENA images that might be observed by a virtual spacecraft during two interesting solar wind scenarios: a southward turning of the interplanetary magnetic field and a sudden enhancement of the solar wind dynamic pressure. We employ the OpenGGCM global magnetohydrodynamics model and a simple exospheric neutral density model for these calculations. Both the magnetosheath and the cusps generate strong soft X‐rays and ENA signals that can be used to extract the locations and motions of the bow shock and magnetopause. Magnetopause erosion corresponds closely to the enhancement of dayside reconnection rate obtained from the OpenGGCM model, indicating that images can be used to understand global‐scale magnetopause reconnection. When dayside imagers are installed with high‐ENA inner‐magnetosphere and FUV/UV aurora imagers, we can trace the solar wind energy flow from the bow shock to the magnetosphere and then to the ionosphere in a self‐standing manner without relying upon other observatories. Soft X‐ray and/or ENA imagers can also unveil the dayside exosphere density structure and its response to space weather., Key Points Soft X‐ray and Energetic Neutral Atom (ENA) imaging instruments provide an innovative way to visualize the global solar wind‐magnetosphere interactionHigh‐cadence, wide field‐of‐view soft X‐ray, and ENA images can capture the motion of the bow shock and magnetopauseThe magnetopause motion can reveal the magnetopause reconnection mode on a global scale

A sequence of discrete solar wind structures within the sheath region of an interplanetary coronal mass ejection on November 6, 2015, caused a series of compressions and releases of the dayside magnetosphere. Each compression resulted in a brief adiabatic enhancement of ions (electrons) driving bursts of electromagnetic ion cyclotron (EMIC; whistler mode chorus) wave growth across the dayside magnetosphere. Fine‐structured rising tones were observed in the EMIC wave bursts, resulting in nonlinear scattering of relativistic electrons in the outer radiation belt. Multipoint observations allow us to study the spatial structure and evolution of these sheath structures as they propagate Earthward from L1 as well as the spatio‐temporal characteristics of the magnetospheric response. This event highlights the importance of fine‐scale solar wind structure, in particular within complex sheath regions, in driving dayside phenomena within the inner magnetosphere., Key Points A sequence of discrete structures within an interplanetary coronal mass ejection sheath are tracked via multipoint measurementsEach structure results in magnetospheric compression, adiabatic enhancement of ions and electrons, and cyclotron wave growthThis event highlights the importance of fine‐scale solar wind structure and sheath regions for driving dayside magnetospheric phenomena

In this study, the ion composition of flux transfer events (FTEs) observed within the magnetosheath proper is examined. These FTEs were observed just upstream of the Earth's postnoon magnetopause by the National Aeronautics and Space Administration (NASA) Magnetospheric Multiscale (MMS) spacecraft constellation. The minor ion characteristics are described using energy spectrograms, flux distributions, and ion moments as the constellation encountered each FTE. In conjunction with electron data and magnetic field observations, such observations provide important contextual information on the formation, topologies, and evolution of FTEs. In particular, minor ions, when combined with the field‐aligned streaming of electrons, are reliable indicators of FTE topology. The observations are also placed (i) in context of the solar wind magnetic field configuration, (ii) the connection of the sampled flux tube to the ionosphere, and (iii) the location relative to the modeled reconnection line at the magnetopause. While protons and alpha particles were often depleted within the FTEs relative to the surrounding magnetosheath plasma, the He+ and O+ populations showed clear enhancements either near the center or near the edges of the FTE, and the bulk plasma flow directions are consistent with magnetic reconnection northward of the spacecraft and convection from the dayside toward the flank magnetopause., Key Points Long‐duration magnetosheath FTEs observed under at postnoon local times and under similar solar wind conditions are compared and contrastedMinor ions from the magnetosphere are observed at higher energies at the edges than at the center of the FTEsThe cores of the magnetosheath FTEs are on closed field lines

At the Earth's low‐latitude magnetopause, clear signatures of the Kelvin‐Helmholtz (KH) waves have been frequently observed during periods of the northward interplanetary magnetic field (IMF), whereas these signatures have been much less frequently observed during the southward IMF. Here, we performed the first 3‐D fully kinetic simulation of the magnetopause KH instability under the southward IMF condition. The simulation demonstrates that fast magnetic reconnection is induced at multiple locations along the vortex edge in an early nonlinear growth phase of the instability. The reconnection outflow jets significantly disrupt the flow of the nonlinear KH vortex, while the disrupted turbulent flow strongly bends and twists the reconnected field lines. The resulting coupling of the complex field and flow patterns within the magnetopause boundary layer leads to a quick decay of the vortex structure, which may explain the difference in the observation probability of KH waves between northward and southward IMF conditions., Key Points Three‐dimensional fully kinetic simulation of Kelvin‐Helmholtz instability at the Earth's magnetopause under the southward IMF condition is performedFast reconnection causes a rapid decay of the nonlinear vortex structure in the early nonlinear growth phase of the instabilityThe vortex decay can lead to a lower probability of observing magnetopause Kelvin‐Helmholtz waves/vortices during southward IMF periods

The Geospace Environmental Modelling (GEM) community offers a framework for collaborations between modelers, observers, and theoreticians in the form of regular challenges. In many cases, these challenges involve model‐data comparisons to provide wider context to observations or validate model results. To perform meaningful comparisons, a statistical approach is often adopted, which requires the extraction of a large number of measurements from a specific region. However, in complex regions such as the magnetosheath, compiling these data can be difficult. Here, we provide the statistical context of compiling statistical data for the southward IMF GEM challenge initiated by the “Dayside Kinetic Processes in Global Solar Wind‐Magnetosphere Interaction” focus group. It is shown that matching very specific upstream conditions can severely impact the statistical data if limits are imposed on several solar wind parameters. We suggest that future studies that wish to compare simulations and/or single events to statistical data should carefully consider at an early stage the availability of data in context with the upstream criteria. We also demonstrate the importance of how specific IMF conditions are defined, the chosen spacecraft, the region of interest, and how regions are identified automatically. The lessons learnt in this study are of wide context to many future studies as well as GEM challenges. The results also highlight the issue where a global statistical perspective has to be balanced with its relevance to more‐extreme, less‐frequent individual events, which is typically the case in the field of space weather., Key Points We provide technical guidelines for compiling large‐scale magnetosheath statistical dataThe availability of data for specific simulation/event conditions should be considered in the early planning stages of future studiesThe limits and manner in which solar wind criteria are defined play a major role in compiling statistical datasets

The Interstellar Boundary Explorer (IBEX) mission provides global energetic neutral atom (ENA) observations from the heliosphere and the Earth's magnetosphere, including spatial, temporal, and energy information. IBEX views the magnetosphere from the sides and almost always perpendicular to noon‐midnight plane. We report the first ENA images of the energization process in the Earth's ion foreshock and magnetosheath regions. We show ENA flux and spectral images of the dayside magnetosphere with significant energization of ENA plasma sources (above ~2.7 keV) in the region magnetically connected to the Earth's bow shock (BS) in its quasi‐parallel configuration of the interplanetary magnetic field (IMF). We also show that the ion energization increases gradually with decreasing IMF‐BS angle, suggesting more efficient suprathermal ion acceleration deeper in the quasi‐parallel foreshock., Key Points We present the first remote‐sensing global images of ion energization in the Earth's foreshockWe provide ion energization profile as a function of bow shock obliquityWe quantify the difference of energization in magnetosheath and its magnetically connected counterpart in the upstream foreshock

The solar wind is slowed, deflected, and heated as it encounters Venus's induced magnetosphere. The importance of kinetic plasma processes to these interactions has not been examined in detail, due to a lack of constraining observations. In this study, kinetic‐scale electric field structures are identified in the Venusian magnetosheath, including plasma double layers. The double layers may be driven by currents or mixing of inhomogeneous plasmas near the edge of the magnetosheath. Estimated double‐layer spatial scales are consistent with those reported at Earth. Estimated potential drops are similar to electron temperature gradients across the bow shock. Many double layers are found in few high cadence data captures, suggesting that their amplitudes are high relative to other magnetosheath plasma waves. These are the first direct observations of plasma double layers beyond near‐Earth space, supporting the idea that kinetic plasma processes are active in many space plasma environments., Key Points Plasma double layers are detected near the Venusian bow shockMultiple double layers are identified in a small amount of burst dataKinetic processes may help mediate interaction between the solar wind and induced magnetospheres

Energetic neutral atoms (ENAs) created by charge‐exchange of ions with the Earth's hydrogen exosphere near the subsolar magnetopause yield information on the distribution of plasma in the outer magnetosphere and magnetosheath. ENA observations from the Interstellar Boundary Explorer (IBEX) are used to image magnetosheath plasma and, for the first time, low‐energy magnetospheric plasma near the magnetopause. These images show that magnetosheath plasma is distributed fairly evenly near the subsolar magnetopause; however, low‐energy magnetospheric plasma is not distributed evenly in the outer magnetosphere. Simultaneous images and in situ observations from the Magnetospheric Multiscale (MMS) spacecraft from November 2015 (during the solar cycle declining phase) are used to derive the exospheric density. The ~11–17 cm−3 density at 10 RE is similar to that obtained previously for solar minimum. Thus, these combined results indicate that the exospheric density 10 RE from the Earth may have a weak dependence on solar cycle., Key Points ENA cameras image both magnetosheath and magnetospheric plasmas in the vicinity of the subsolar magnetopauseMagnetospheric plasma is not distributed evenly across the dayside near the magnetopauseThe exospheric hydrogen density near the magnetopause may have a weak dependence on solar F10.7

Forecasting the geomagnetic effects of solar storms, known as coronal mass ejections (CMEs), is currently severely limited by our inability to predict the magnetic field configuration in the CME magnetic core and by observational effects of a single spacecraft trajectory through its 3‐D structure. CME magnetic flux ropes can lead to continuous forcing of the energy input to the Earth's magnetosphere by strong and steady southward‐pointing magnetic fields. Here we demonstrate in a proof‐of‐concept way a new approach to predict the southward field B z in a CME flux rope. It combines a novel semiempirical model of CME flux rope magnetic fields (Three‐Dimensional Coronal ROpe Ejection) with solar observations and in situ magnetic field data from along the Sun‐Earth line. These are provided here by the MESSENGER spacecraft for a CME event on 9–13 July 2013. Three‐Dimensional Coronal ROpe Ejection is the first such model that contains the interplanetary propagation and evolution of a 3‐D flux rope magnetic field, the observation by a synthetic spacecraft, and the prediction of an index of geomagnetic activity. A counterclockwise rotation of the left‐handed erupting CME flux rope in the corona of 30° and a deflection angle of 20° is evident from comparison of solar and coronal observations. The calculated Dst matches reasonably the observed Dst minimum and its time evolution, but the results are highly sensitive to the CME axis orientation. We discuss assumptions and limitations of the method prototype and its potential for real time space weather forecasting and heliospheric data interpretation., Key Points A new semiempirical model (3DCORE) for simulating the propagation of coronal mass ejection magnetic flux ropes is introduced3DCORE is able to model the observations of a coronal mass ejection on 9–13 July 2013 observed at MESSENGER and WindSolar, coronagraph, and MESSENGER observations are used as constraints, resulting in a good match of the modeled and observed Dst index

International audience; Soft X-rays are emitted when highly charged solar wind particles like O7+ and O8+ exchange electrons with neutral hydrogens. This process is called solar wind charge exchange (SWCX). The Earth's magnetosheath and cusps are expected to emit strong SWCX emissions due to high abundances of both solar wind particles and exospheric hydrogen atoms in these regions. The Solar wind - Magnetosphere - Ionosphere Link Explorer (SMILE) mission, selected by ESA and China with launch in 2023, will image the Earth's dayside system in soft X-rays. To support the SMILE mission, we conduct a statistical study on the near-Earth SWCX signals using the XMM-Newton astrophysics observations. XMM-Newton is a European X-ray telescope launched in 1999 and has observed cosmic X-ray sources for nearly 18 years. At times, its line-of-sight passes the dayside magnetosheath, and the telescope detects near-Earth SWCX emissions in addition to X-ray light sources like stars and galaxies, diffuse astronomical X-ray backgrounds like interstellar and intergalactic clouds, diffuse heliospheric SWCX signals, and particle backgrounds from the telescope's own glow. We introduce how to extract near-Earth SWCX signals from the XMM-Newton's raw observation data. Then, we investigate the relation of near-Earth X-ray emissions to the solar irradiance, solar wind flux, and abundances of X-ray source particles in solar wind.

The subsolar magnetosheath is penetrated by transient enhancements in dynamic pressure. These enhancements, also called high‐speed jets, can propagate to the magnetopause, causing large‐amplitude yet localized boundary indentations on impact. Possible downstream consequences of these impacts are, e.g., local magnetopause reconnection, impulsive penetration of magnetosheath plasma into the magnetosphere, inner magnetospheric and boundary surface waves, drop outs and other variations in radiation belt electron populations, ionospheric flow enhancements, and magnetic field variations observed on the ground. Consequently, jets can be geoeffective. The extend of their geoeffectiveness is influenced by the amount of mass, momentum, and energy they transport, i.e., by how large they are. Their overall importance in the framework of solar wind‐magnetosphere coupling is determined by how often jets of geoeffective size hit the dayside magnetopause. In this paper, we calculate such jet impact rates for the first time. From a large data set of Time History of Events and Macroscale Interactions during Substorms (THEMIS) multispacecraft jet observations, we find distributions of scale sizes perpendicular and parallel to the direction of jet propagation. They are well modeled by an exponential function with characteristic scales of 1.34R E (perpendicular) and 0.71R E (parallel direction), respectively. Using the distribution of perpendicular scale sizes, we derive an impact rate of jets with cross‐sectional diameters larger than 2R E on a reference area of about 100RE2 of the subsolar magnetopause. That rate is about 3 per hour in general, and about 9 per hour under low interplanetary magnetic field cone angle conditions (, Key Points First determination of magnetosheath high‐speed jet cross‐sectional scale size distributionFirst determination of geoeffective jet impact rates on the subsolar magnetopauseImpact rates of large jets are much higher than occurrence rates of other dayside transients

We investigate the plasmaspheric influence on the resonant mode coupling of magnetospheric ultralow frequency (ULF) waves using the Lyon‐Fedder‐Mobarry (LFM) global magnetohydrodynamic (MHD) model. We present results from two different versions of the model, both driven by the same solar wind conditions: one version that contains a plasmasphere (the LFM coupled to the Rice Convection Model, where the Gallagher plasmasphere model is also included) and another that does not (the stand‐alone LFM). We find that the inclusion of a cold, dense plasmasphere has a significant impact on the nature of the simulated ULF waves. For example, the inclusion of a plasmasphere leads to a deeper (more earthward) penetration of the compressional (azimuthal) electric field fluctuations, due to a shift in the location of the wave turning points. Consequently, the locations where the compressional electric field oscillations resonantly couple their energy into local toroidal mode field line resonances also shift earthward. We also find, in both simulations, that higher‐frequency compressional (azimuthal) electric field oscillations penetrate deeper than lower frequency oscillations. In addition, the compressional wave mode structure in the simulations is consistent with a radial standing wave oscillation pattern, characteristic of a resonant waveguide. The incorporation of a plasmasphere into the LFM global MHD model represents an advance in the state of the art in regard to ULF wave modeling with such simulations. We offer a brief discussion of the implications for radiation belt modeling techniques that use the electric and magnetic field outputs from global MHD simulations to drive particle dynamics., Key Points Magnetosphere responds as a resonant waveguide to ULF fluctuations in solar wind dynamic pressureInclusion of a plasmasphere has a substantial impact on the nature of the simulated ULF wavesInclusion of a plasmasphere leads to a deeper penetration of azimuthal electric field oscillations

Studies of Saturn's magnetosphere with the Cassini mission have established the importance of Enceladus as the dominant mass source for Saturn's magnetosphere. It is well known that the ionosphere is an important mass source at Earth during periods of intense geomagnetic activity, but lesser attention has been dedicated to study the ionospheric mass source at Saturn. In this paper we describe a case study of data from Saturn's magnetotail, when Cassini was located at ≃ 2200 h Saturn local time at 36 R S from Saturn. During several entries into the magnetotail lobe, tailward flowing cold electrons and a cold ion beam were observed directly adjacent to the plasma sheet and extending deeper into the lobe. The electrons and ions appear to be dispersed, dropping to lower energies with time. The composition of both the plasma sheet and lobe ions show very low fluxes (sometimes zero within measurement error) of water group ions. The magnetic field has a swept‐forward configuration which is atypical for this region, and the total magnetic field strength is larger than expected at this distance from the planet. Ultraviolet auroral observations show a dawn brightening, and upstream heliospheric models suggest that the magnetosphere is being compressed by a region of high solar wind ram pressure. We interpret this event as the observation of ionospheric outflow in Saturn's magnetotail. We estimate a number flux between (2.95 ± 0.43) × 109 and (1.43 ± 0.21) × 1010 cm−2 s−1, 1 or about 2 orders of magnitude larger than suggested by steady state MHD models, with a mass source between 1.4 ×102 and 1.1 ×103 kg/s. After considering several configurations for the active atmospheric regions, we consider as most probable the main auroral oval, with associated mass source between 49.7 ±13.4 and 239.8 ±64.8 kg/s for an average auroral oval, and 10 ±4 and 49 ±23 kg/s for the specific auroral oval morphology found during this event. It is not clear how much of this mass is trapped within the magnetosphere and how much is lost to the solar wind., Key Points Tailward observation of ionospheric plasma in the magnetotail lobeEvidence for simultaneous reconnection in the plasma sheetFirst observational estimate at Saturn of mass source rate from the ionosphere to the magnetotail

For over 10 years, the Cassini spacecraft has patrolled Saturn's magnetosphere and observed its magnetopause boundary over a wide range of prevailing solar wind and interior plasma conditions. We now have data that enable us to resolve a significant dawn‐dusk asymmetry and find that the magnetosphere extends farther from the planet on the dawnside of the planet by 7 ± 1%. In addition, an opposing dawn‐dusk asymmetry in the suprathermal plasma pressure adjacent to the magnetopause has been observed. This probably acts to reduce the size asymmetry and may explain the discrepancy between the degree of asymmetry found here and a similar asymmetry found by Kivelson and Jia (2014) using MHD simulations. Finally, these observations sample a wide range of season, allowing the “intrinsic” polar flattening (14 ± 1%) caused by the magnetodisc to be separated from the seasonally induced north‐south asymmetry in the magnetopause shape found theoretically (5 ± 1% when the planet's magnetic dipole is tilted away from the Sun by 10–17°)., Key Points Saturn's magnetosphere extends farther at dawn than dusk by 7%The degree of asymmetry departs from MHD predictions, likely due to the suprathermal plasma pressureAn intrinsic polar flattening of 14% is found with an additional seasonally induced component

In this data report we discuss reprocessing of the Space Technology 5 (ST5) magnetometer database for inclusion in NASA's Coordinated Data Analysis Web (CDAWeb) virtual observatory. The mission consisted of three spacecraft flying in elliptical orbits, from 27 March to 27 June 2006. Reprocessing includes (1) transforming the data into the Modified Apex Coordinate System for projection to a common reference altitude of 110 km, (2) correcting gain jumps, and (3) validating the results. We display the averaged magnetic perturbations as a keogram, which allows direct comparison of the full‐mission data with the solar wind values and geomagnetic indices. With the data referenced to a common altitude, we find the following: (1) Magnetic perturbations that track the passage of corotating interaction regions and high‐speed solar wind; (2) unexpectedly strong dayside perturbations during a solstice magnetospheric sawtooth oscillation interval characterized by a radial interplanetary magnetic field (IMF) component that may have enhanced the accompanying modest southward IMF; and (3) intervals of reduced magnetic perturbations or “calms,” associated with periods of slow solar wind, interspersed among variable‐length episodic enhancements. These calms are most evident when the IMF is northward or projects with a northward component onto the geomagnetic dipole. The reprocessed ST5 data are in very good agreement with magnetic perturbations from the Defense Meteorological Satellite Program (DMSP) spacecraft, which we also map to 110 km. We briefly discuss the methods used to remap the ST5 data and the means of validating the results against DMSP. Our methods form the basis for future intermission comparisons of space‐based magnetometer data., Key Points ST5 Magnetic Perturbations Have Been ReprocessedReprocessed data at 100 km compare well to DMSP dataKeogram view of data show response to several solar wind drivers

Magnetic reconnection has been established as the dominant mechanism by which magnetic fields in different regions change topology to create open magnetic field lines that allow energy and momentum to flow into the magnetosphere. One of the persistent problems of magnetic reconnection is the question of whether the process is continuous or intermittent and what input condition(s) might favor one type of reconnection over the other. Observations from imagers that record FUV emissions caused by precipitating cusp ions demonstrate the global nature of magnetic reconnection. Those images show continuous ionospheric emissions even during changing interplanetary magnetic field conditions. On the other hand, in situ observations from polar‐orbiting satellites show distinctive cusp structures in flux distributions of precipitating ions, which are interpreted as the telltale signature of intermittent reconnection. This study uses a modification of the low‐velocity cutoff method, which was previously successfully used to determine the location of the reconnection site, to calculate for the cusp ion distributions the “time since reconnection occurred.” The “time since reconnection” is used to determine the “reconnection time” for the cusp magnetic field lines where these distributions have been observed. The profile of the reconnection time, either continuous or stepped, is a direct measurement of the nature of magnetic reconnection at the reconnection site. This paper will discuss a continuous and pulsed reconnection event from the Polar spacecraft to illustrate the methodology., Key Points Methodology to distinguish pulsed form continuous reconnectionDetermine the reconnection time for cusp magnetic field linesDetermine the reconnection location simultaneously

Ultralow frequency (ULF) waves play a fundamental role in the dynamics of the inner magnetosphere and outer radiation belt during geomagnetic storms. Broadband ULF wave power can transport energetic electrons via radial diffusion, and discrete ULF wave power can energize electrons through a resonant interaction. Using observations from the Magnetospheric Multiscale mission, we characterize the evolution of ULF waves during a high‐speed solar wind stream (HSS) and moderate geomagnetic storm while there is an enhancement of the outer radiation belt. The Automated Flare Inference of Oscillations code is used to distinguish discrete ULF wave power from broadband wave power during the HSS. During periods of discrete wave power and utilizing the close separation of the Magnetospheric Multiscale spacecraft, we estimate the toroidal mode ULF azimuthal wave number throughout the geomagnetic storm. We concentrate on the toroidal mode as the HSS compresses the dayside magnetosphere resulting in an asymmetric magnetic field topology where toroidal mode waves can interact with energetic electrons. Analysis of the mode structure and wave numbers demonstrates that the generation of the observed ULF waves is a combination of externally driven waves, via the Kelvin‐Helmholtz instability, and internally driven waves, via unstable ion distributions. Further analysis of the periods and toroidal azimuthal wave numbers suggests that these waves can couple with the core electron radiation belt population via the drift resonance during the storm. The azimuthal wave number and structure of ULF wave power (broadband or discrete) have important implications for the inner magnetospheric and radiation belt dynamics., Key Points ULF wave power is systematically characterized as discrete or broadband, and the azimuthal wave number of discrete ULF waves is determinedStorm time discrete ULF waves can couple with the core radiation belt electron population via the drift resonanceStorm time ULF waves are the result of both external (Kelvin‐Helmholtz) and internal (plasma instabilities) generation mechanisms

Observations from Magnetospheric MultiScale (~8 Re) and Van Allen Probes (~5 and 4 Re) show that the initial dayside response to a small interplanetary shock is a double‐peaked dawnward electric field, which is distinctly different from the usual bipolar (dawnward and then duskward) signature reported for large shocks. The associated E × B flow is radially inward. The shock compressed the magnetopause to inside 8 Re, as observed by Magnetospheric MultiScale (MMS), with a speed that is comparable to the E × B flow. The magnetopause speed and the E × B speeds were significantly less than the propagation speed of the pulse from MMS to the Van Allen Probes and GOES‐13, which is consistent with the MHD fast mode. There were increased fluxes of energetic electrons up to several MeV. Signatures of drift echoes and response to ULF waves also were seen. These observations demonstrate that even very weak shocks can have significant impact on the radiation belts., Key Points Magnetospheric response to small shocks not typical bipolar electric field pulse seen for large shocksPropagation of compression on VAP, MMS, and GOES‐13 is consistent with fast mode speed; large‐scale structure is not fast modeElectric field pulse associated with small shock energizes electrons to >50 keV; flux enhancements seen up to several MeV

New Magnetospheric Multiscale (MMS) observations of small‐scale (~7 ion inertial length radius) flux transfer events (FTEs) at the dayside magnetopause are reported. The 10 km MMS tetrahedron size enables their structure and properties to be calculated using a variety of multispacecraft techniques, allowing them to be identified as flux ropes, whose flux content is small (~22 kWb). The current density, calculated using plasma and magnetic field measurements independently, is found to be filamentary. Intercomparison of the plasma moments with electric and magnetic field measurements reveals structured non‐frozen‐in ion behavior. The data are further compared with a particle‐in‐cell simulation. It is concluded that these small‐scale flux ropes, which are not seen to be growing, represent a distinct class of FTE which is generated on the magnetopause by secondary reconnection., Key Points Ion‐scale flux ropes are observed during magnetopause reconnectionThe largely force‐free flux ropes exhibit filamentary currents and nonideal ion behaviorSmall flux content and comparison with simulation indicate a secondary reconnection origin

Two of the largest geomagnetic storms of the last decade were witnessed in 2015. On 17 March 2015, a coronal mass ejection‐driven event occurred with a Dst (storm time ring current index) value reaching −223 nT. On 22 June 2015 another strong storm (Dst reaching −204 nT) was recorded. These two storms each produced almost total loss of radiation belt high‐energy (E ≳ 1 MeV) electron fluxes. Following the dropouts of radiation belt fluxes there were complex and rather remarkable recoveries of the electrons extending up to nearly 10 MeV in kinetic energy. The energized outer zone electrons showed a rich variety of pitch angle features including strong “butterfly” distributions with deep minima in flux at α = 90°. However, despite strong driving of outer zone earthward radial diffusion in these storms, the previously reported “impenetrable barrier” at L ≈ 2.8 was pushed inward, but not significantly breached, and no E ≳ 2.0 MeV electrons were seen to pass through the radiation belt slot region to reach the inner Van Allen zone. Overall, these intense storms show a wealth of novel features of acceleration, transport, and loss that are demonstrated in the present detailed analysis., Key Points March and June 2015 storms offer insight into ultrarelativistic electron dynamicsImpenetrable barrier can be pushed inward, still isolates high‐E electrons from inner zoneMulti‐MeV electrons take 1‐2 days to appear following these strong driving events.

It is known that the correction of the Kyoto Dst index for the secular variation of the Earth's internal field produces a discontinuity in the Kyoto Dst index at the end of each year. We show that this secular correction also introduces a significant baseline error to the Kyoto Dst index that leads to an underestimate of the solar cycle variation of geomagnetic activity and of the strength of the ring current as measured by the Kyoto Dst index. Thus, the average value of the Kyoto Dst index would be approximately 13 nT more negative for the active year 2003 compared to quiet years 2006 and 2009 if the Kyoto Dst index properly measured the effects of the ring current and other currents that influence the Dst observatories. Discontinuities in the Kyoto Dst index at the end of each year have an average value of about 5 nT, but the discontinuity at the end of year 2002 was approximately 12 nT, and the discontinuity at the end of year 1982 may have been as large as 20 nT., Key Points Kyoto Dst index underestimates the solar cycle variation of magnetic activityLong‐term averages of the Kyoto Dst index should be used with cautionQuiet time currents produce a depression of the surface equatorial magnetic field of 15–30 nT

International audience; Velocity shear driven vortices associated to the Kelvin-Helmholtz instability (KHI) have been detected by in-situ observations at the Earth[1], Saturn[2] and Mercury[3] magnetospheres' boundary due to the interaction with the solar wind[4]. KHI in magnetized plasmas have been widely studied numerically in the framework of a fluid and hybrid descriptions, while only very few studies have focused on the physics of electrons[5,6] because of computational constraints. In this work we present a full kinetic particle in cell study of the KHI spanning a range of scales going from fluid to electron scales. The simulation is initialized with an extended fluid equilibrium[7] including finite ion Larmor radius effects. Our large-scale configuration includes two-possible alignment of the vorticity with the background magnetic field each one corresponding to the interaction of the solar wind with the dawn and dusk side of a planet. We discuss electron heating and acceleration by the wave and turbulent activity as well as magnetic reconnection induced by vortex dynamics. Two-fluid simulations have suggested that KHI instability can lead to the formation of coherent structures resulting from the saturation of the mirror instability[8]. Our full kinetic approach confirms such hypothesis. We investigate the formation, the properties and the electron distribution functions of the mirror modes in our simulations and in complementary dedicated ones. [1] J. E. Stawarz, S. Eriksson, et al., Journal of Geophysical Research: Space Physics, 121, 2016, 11,021-11,034 [2] A. Masters, N. Achilleos, et al., Journal of Geophysical Research: Space Physics, 115, 2010, 7225 [3] T. Sundberg, S. A. Boardsen, et al., Planetary and Space Sciences, 59, 2011, 2051-2057 [4] M. Faganello, F. Califano, Journal of Plasma Physics, 83, 2017, 535830601 [5] P. Henri, S. S. Cerri, F. Califano, F. Pegorago, et al., Physics of Plasmas, 20, 2013, 102118 [6] W. Daughton, T. K. M. Nakamura, et al., Physics of Plasmas, 21, 2014, 252307. [7] S. S. Cerri, P. Henri, F. Califano, et al., Physics of Plasmas, 20, 2013, 112112 [8] S. De Camillis, S. S. Cerri, F. Califano, and F. Pegoraro, Plasma Physics and Controlled Fusion, 28, 2016, 045007