The magnetopause marks the boundary where the pressure of the magnetosheath balances the magnetic pressure of Earth's magnetic field. Localized increases in magnetosheath pressure can therefore displace the magnetopause. One known plasma structure that exhibits such a local pressure increase is magnetosheath jets defined as transient dynamic pressure enhancements. These jets are particularly prominent downstream of the quasi-parallel bow shock, where they frequently interact with the magnetopause. To investigate the spatial and temporal characteristics of these interactions, we employ the 3D hybrid-kinetic plasma model AMITIS with a steady plasma inflow. Our results show that jets downstream of the quasi-parallel bow shock can generate magnetopause surface waves that propagate flankward. Interestingly, while jets appear to have a similar velocity as the surface waves and continuously drive them, the jets' apparent flankward motion does not align with the ion bulk velocity measured within the jets. This discrepancy may suggest ongoing jet generation at the bow shock, potentially linked to foreshock compressive structures.

The bow shock current (BSC) flows on the bow shock due to the compression of the interplanetary magnetic field (IMF) across the shock. Although previous studies have shown that the BSC can connect to magnetospheric current systems via the magnetosheath, it is still not known how this happens. For southward IMF, there is both numerical and observational evidence of BSC closure through the equatorial magnetosheath. For east-west IMF (IMF dominated by the By-component), the closure has instead been suggested to take place at higher latitudes, but this has yet to be investigated. In this paper we present the first hybrid-kinetic simulation results in support of BSC closure through the high-latitude magnetosheath, for east-west IMF. Our simulations indicate large-scale current closure away from (towards) the magnetosphere in the northern (southern) hemisphere, both in the dayside and nightside magnetosheath, for IMF By > 0. This is consistent with the north-to-south flowing BSC under such conditions. Moreover, our results suggest that the BSC primarily crosses the magnetosheath behind the quasi-perpendicular bow shock.

Over the past 25 years, several spacecraft have observed localized, high-pressure regions that sporadically appear in Earth’s magnetosheath, known as the “magnetosheath jets”. Despite previous analyses, the nature of these transient events remains elusive, marked by a range of uncertainties. These uncertainties mainly stem from the fact that oversimplified assumptions have been made in earlier analyses, where the jets are often portrayed as basic cylinder-like structures. This simplification is primarily because of two reasons: First, spacecraft observations in specific magnetosheath locations couldn't comprehensively cover and explore large spatial areas, providing only a limited perspective on the jets. Second, previous models used to study magnetosheath jets were either two-dimensional (2D) spatial models or three-dimensional (3D) with reduced scales of the Earth's magnetosphere to minimize computational complexity when dealing with Earth. In this study, we use Amitis, a high-performance, three-dimensional (3D in both configuration and velocity spaces), time-dependent hybrid-kinetic plasma model (kinetic ions, fluid electrons) that runs in parallel on Graphics Processing Units (GPUs). We present, for the first time, the global kinetic interaction between the solar wind and the entire magnetosphere of Earth using its true scales. Achieving this level of accuracy in kinetic modeling of the solar wind plasma interaction with Earth has been a long-standing challenge. Our 3D, time-dependent hybrid-kinetic simulations dispel the notion that the magnetosheath jets are simple cylinders. Instead, our simulations show that the magnetosheath jets exhibit complex and interconnected structures with dynamic 3D characteristics. As they move through the magnetosheath, they wrinkle, fold, merge, and split in complex ways before a subset reaches the magnetopause. Our findings are pivotal in advancing our understanding of magnetosheath jets and their significance in coupling between the solar wind and Earth's magnetosphere.

Magnetosheath jets, transient plasma structures of enhanced dynamic pressure, have been observed to trigger ultra‐low frequency (ULF) waves in the magnetosphere. These ULF waves contribute to energy transport in the magnetosphere‐ionosphere system. Therefore, there is a need to estimate the energy input into the ionosphere due to jet‐triggered ULF waves. In this study, we combine measurements from Magnetospheric Multiscale, ground‐based magnetometers, the EISCAT radar on Svalbard, and SuperDARN to estimate the Joule heating in the ionosphere resulting from jet impacts at the magnetopause. Focusing on three jets observed on 2016‐01‐07 we were able to calculate the Joule heating for two jets. We found an average Joule heating rate of mW/m 2 which is on par with other processes such as field line resonances. However, due to the short duration and spatial confinement of the jet‐induced ULF waves, the average energy input was only J. This suggests that the energy deposition of jet‐triggered ULF waves is small compared to other magnetospheric processes, and thus does not significantly impact the average energy budget of the magnetosphere.

The bow shock current (BSC) plays an important role in supplying the magnetosphere with solar wind energy, in particular during times of low solar wind magnetosonic Mach numbers. Since the magnetic pile‐up in the magnetosheath has to be maintained, the BSC cannot close locally, but must instead connect to magnetospheric current systems. However, the details of this closure remain poorly understood. For east–west interplanetary magnetic field (IMF) it has been hypothesized that the BSC partly closes to the high‐latitude ionosphere, as field‐aligned currents (FACs) on open field lines, but there is still no statistical evidence of this. In order to investigate this hypothesis, we use 9 years of Defense Meteorological Satellite Program (DMSP) data to construct normalized FAC maps of the northern hemisphere polar cap. We sort them according to different IMF clock angles, IMF magnitudes and magnetosonic Mach numbers. By separating opposite polarity FACs, we show that, on average, a unipolar FAC exists in the dayside polar cap when the IMF , regardless of the sign of the IMF . This current flows out of (into) the ionosphere in the northern hemisphere for IMF and is thus of the correct polarity to connect to the north–south component of the BSC. Moreover, it is strongest when the BSC flows predominantly in the north–south direction. These results constitute the first statistical evidence in support of at least a partial closure of the BSC to the ionosphere during non‐zero IMF .

Solar activity significantly influences the Earth's magnetosphere and ionosphere, causing current systems and space weather effects. The interaction between rapidly changing magnetic field and the Earth’s conductivity induces an electric field at the surface producing Geomagnetically Induced Currents (GICs) within critical human infrastructure, posing a risk of damage to power lines.GICs strongly depend on the ground conductivity. Sweden has large spatial variations and complexity in the underlying ground conductivity structure across the country. In order to better understand GICs and for the identification of the worst-case scenarios for Swedish power transmission lines, 3D simulations are essential.We present results from our GIC simulations, computed using our own 3D FDTD framework employing a Swedish ground conductivity model in high resolution. Compared to previous simulations of the Swedish power grid, ours is High Performance (runs on parallel GPUs), more flexible, and we can simulate the GICs in the time domain, instead of only the frequency domain as has been done before in simplistic approaches. This enables us to study GICs caused by much more realistic ionospheric source currents.

Abstract This study investigates the effects of non-zero IMF B y on the magnetotail B y and fast earthward ion convection (V ⊥ > 200 km/s, "⊥" indicates perpendicular to the magnetic field) in the near-lunar magnetotail plasma sheet using the plasma parameters and magnetic field detected by the ARTEMIS (Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon’s Interaction with the Sun) P1 satellite during the period 2011–2022. We find that the magnetotail B y with in the same direction as IMF B y dominates the entire region. The IMF B y influence is hemisphere-independent, but shows a dusk-dawn asymmetry with the IMF B y effect being weaker in the premidnight region than in the postmidnight region. We also find that the IMF B y influence on earthward fast convection results in an interhemispheric flow asymmetry and it is highly correlated with the direction of magnetotail B y. The statistical results indicate that occasionally localized dynamics can have a significant effect on magnetotail B y and V ⊥.

Magnetosheath jets, plasma structures with enhanced dynamic pressure, are frequently observed in the terrestrial magnetosheath. However, their mass, momentum, and energy content are still unknown. We utilize Amitis, a 3D hybrid-kinetic plasma simulation, to study the mass, momentum, and energy content of jets in the subsolar magnetosheath. We also analyze the kinetic, thermal, and electromagnetic energy flux associated with jets. Jets comprise up to 21% of the quasi-parallel magnetosheath and can carry up to half of the kinetic energy. Furthermore, jets convert kinetic energy to thermal energy. Our hybrid simulations also suggest that while jets can form downstream of the quasi-perpendicular shock, their volume and energy content are much small compared to jets downstream of the quasi-parallel bow shock. We conclude that magnetosheath jets play a vital role in heating up the magnetosheath and significantly influence the dynamics of the quasi-parallel magnetosheath.

Magnetic holes at the ion-to-electron kinetic scale (KSMHs) are one of the extremely small intermittent structures generated in turbulent magnetized plasmas. In recent years, the explorations of KSMHs have made substantial strides, driven by the ultra-high-precision observational data gathered from the Magnetospheric Multiscale (MMS) mission. This review paper summarizes the up-to-date characteristics of the KSMHs observed in Earth’s turbulent magnetosheath, as well as their potential impacts on space plasma. This review starts by introducing the fundamental properties of the KSMHs, including observational features, particle behaviors, scales, geometries, and distributions in terrestrial space. Researchers have discovered that KSMHs display a quasi-circular electron vortex-like structure attributed to electron diamagnetic drift. These electrons exhibit noticeable non-gyrotropy and undergo acceleration. The occurrence rate of KSMH in the Earth’s magnetosheath is significantly greater than in the solar wind and magnetotail, suggesting the turbulent magnetosheath is a primary source region. Additionally, KSMHs have also been generated in turbulence simulations and successfully reproduced by the kinetic equilibrium models. Furthermore, KSMHs have demonstrated their ability to accelerate electrons by a novel non-adiabatic electron acceleration mechanism, serve as an additional avenue for energy dissipation during magnetic reconnection, and generate diverse wave phenomena, including whistler waves, electrostatic solitary waves, and electron cyclotron waves in space plasma. These results highlight the magnetic hole’s impact such as wave-particle interaction, energy cascade/dissipation, and particle acceleration/heating in space plasma. We end this paper by summarizing these discoveries, discussing the generation mechanism, similar structures, and observations in the Earth’s magnetotail and solar wind, and presenting a future extension perspective in this active field.

Aims. We aim to quantify the width of the quasi-perpendicular Martian bow shock region to deepen the understanding of why the width is variable and which factors affect it, and to explore the implications on thermalization. Methods. To quantify the width, 2074 quasi-perpendicular bow shock crossings from a database were studied. Upstream conditions, such as Mach numbers, dynamic pressure, ion densities, and other factors, were considered. Furthermore, the difference between the downstream and upstream temperature was measured. Results. We found that the shock region width is correlated with the magnetosonic Mach number, the critical ratio, and the overshoot amplitude. The region was found to be anticorrelated with dynamic pressure. The width is not affected by the upstream ion density of the investigated species or by the upstream temperature. The difference between the downstream and upstream temperature is not affected by the shock region width. Conclusions. We found that the factors that affect the stand-off distance of the bow shock, such as the magnetosonic Mach number and dynamic pressure, also affect the width. The width is also positively correlated with the overshoot amplitude, indicating that the structures are coupled or that they are affected by largely the same conditions. The lack of a correlation with the ion temperature difference indicates that the shock region width does not affect the ion thermalization.

In astrophysics and space, supercritical shock is generated when an object interacts with an incoming supersonic plasma stream. Its downstream plasmas are highly turbulent, containing abundant vortices on all scales from magnetohydrodynamic to electron gyroscales. Understanding the production of these vortices is at the forefront, especially on the electron scale. Using ultrafast measurements of NASA's Magnetospheric Multiscale spacecraft, we report on the fortunate multi-spacecraft observation of the formation of an electron vortex directly generated inside the Earth's quasi-parallel bow shock transition and propagated to the downstream turbulent magnetosheath. The vortex is generated inside the shock transition by anisotropic similar to 100-600 eV electrons trapped in an ion-scale magnetic hole which could show a tornado-like magnetic morphology. Our results demonstrate that the electron vortex can develop not only as a product of the forward cascade but also from the shock transition into its downstream turbulence, which adds to the short-scale turbulence and dissipation. Turbulence is a ubiquitous process in fluids where nonlinear interactions take place to generate dynamically evolving vortex structures across a broad range of scales. It plays a leading role in the cascade of mass and energy transport to increasingly small scales until it is dissipated as heat. In ionized plasmas, turbulence is more complex when considering electromagnetic fields, different kinds of charged particles, waves, and dissipation mechanisms. For studying plasma turbulence, a readily available natural laboratory is the near-Earth environment. The solar wind plasma encounters the Earth's magnetosphere, generating a supercritical bow shock. The plasma downstream of the bow shock is highly turbulent and contains abundant plasma vortices from the macroscale to the electron gyroscale. Therefore, understanding the bow shock's role in vortex generation is crucial and essential to understanding the development of turbulence in collisionless magnetized plasmas. This paper presents a precise origin of electron-scale vortex for unpredictable and random plasma turbulence. The vortex can directly start inside the collisionless shock as a small-scale vortex before being transported downstream turbulence, instead of the popular belief that developing from the downstream turbulence and larger-scale vortices. Electron vortex can directly start inside the supercritical shock as a small-scale vortex before being transported downstream turbulence Evidence for its generation inside the shock transition is provided by identifying the energetic shock electron population as its source The vortex could show a tornado-like magnetic morphology, coupling with a magnetic hole and propagating to the downstream magnetosheath

Magnetosheath jets represent localized enhancements in dynamic pressure observed within the magnetosheath. These energetic entities, carrying excess energy and momentum, can impact the magnetopause and disrupt the magnetosphere. Therefore, they play a vital role in coupling the solar wind and terrestrial magnetosphere. However, our understanding of the morphology and formation of these complex, transient events remains incomplete over two decades after their initial observation. Previous studies have relied on oversimplified assumptions, considering jets as elongated cylinders with dimensions ranging from 0.1 RE to 5.0 RE (Earth radii). In this study, we present simulation results obtained from Amitis, a high-performance hybrid-kinetic plasma framework (particle ions and fluid electrons) running in parallel on Graphics Processing Units (GPUs) for fast and more environmentally friendly computation compared to CPU-based models. Considering realistic scales, we present the first global, three-dimensional (3D in both configuration and velocity spaces) hybrid-kinetic simulation results of the interaction between solar wind plasma and Earth. Our high-resolution kinetic simulations reveal the 3D structure of magnetosheath jets, showing that jets are far from being simple cylinders. Instead, they exhibit intricate and highly interconnected structures with dynamic 3D characteristics. As they move through the magnetosheath, they wrinkle, fold, merge, and split in complex ways before a subset reaches the magnetopause.

A common plasma feature which has been observed at comets during a relatively high outgassing activity is the presence of a magnetic field-free region, the so-called diamagnetic cavity. Observed for the first time at 1P/Halley, such structures have also been crossed many times at low relative speed at 67P/Churyumov-Gerasimenko by the ESA/Rosetta spacecraft.Many questions have been raised about the origin of this boundary. It is quite clear that, as one goes from an unmagnetised to a magnetised medium, one of the forces playing a role is the magnetic (pressure and tension) force. But what other force counter-balances the latter and helps form the boundary? For 1P/Halley, one formerly accepted explanation was the ion-neutral friction which has been investigated many times with magneto-hydrodynamic and hybrid simulations. However, the ion-neutral friction does not explain the observations at 67P/C-G as the outgassing rate was much lower than that of 1P/Halley.In this work, we investigate the balance between the electromagnetic forces at the boundary with a collisionless Particle-In-Cell 1D3V simulation and the open source code Smilei. It allows us to go down to scales which are not modelled by the more common MHD or hybrid simulations. In addition, this fully kinetic simulation give us access to the different moments (e.g., number density, mean velocity, pressure tensor) of the distribution function without extra assumptions (e.g., Ohm's law and adiabatic electrons). In particular, we investigate at the balance between the different forces at play on the electrons, i.e., the electron pressure gradient and the Lorentz force.For example, first results show that there is a sharp increase in the electric field at the boundary which decelerates ions coming from the diamagnetic cavity before reaching the magnetised part and being backstreamed towards the comet.

We investigate the magnetic forces (the magnetic pressure gradient force, the curvature force, and their sum the j × B ‐force) associated with earthward bursty bulk flows (BBFs) using Magnetospheric Multiscale (MMS) data from five tail seasons (2017–2021). For the first time, the magnetic forces are inferred downtail of XGSM = −20 R E and in the GSM XY and YZ planes. The results suggest that BBFs tend to be accelerated earthward by the magnetic pressure gradient force tailward of ∼19 R E and decelerated closer to that distance in the 2017–2018 data. The force magnitudes increase with distance. This is in accordance with earlier Cluster results. In the 2019–2021 data, the pressure gradient force magnitudes are generally smaller and no clear distance for the acceleration reversal can be determined. The curvature forces for both 2017–2018 and 2019–2021 BBFs indicate earthward acceleration independent of distance, consistent with the Cluster measurements. The sum, the j × B ‐force, suggests for the 2017–2018 BBFs earthward acceleration tailward of XGSM ∼15 R E and deceleration within that distance, also consistent with Cluster. In contrast, the 2019–2021 BBFs show general earthward acceleration by j × B independent of distance. In the GSM XY plane, the average ( j × B ) xy vectors are earthward, and in the premidnight and postmidnight dawnward for the 2017–2018 BBFs. For 2019–2021, the average ( j × B ) xy vectors have components toward the tail center. In the GSM YZ plane, the average ( j × B ) yz vectors are toward the neutral sheet.

During the long main phase of the St Patrick’s Day storm on March 17, 2015, we found three separate enhancements of the westward electrojet. These enhancements are observed in the ionospheric equivalent currents computed using geomagnetic data over Fennoscandia. Using data from the IMAGE magnetometer network, we identified localised field-aligned current (FAC) systems superimposed on the pre-existing ionospheric current system. We suggest that these localised current systems are wedgelets and that they can potentially contribute to a larger-scale structure of a substorm current wedge (SCW). Each wedgelet is associated with a negative B X spike. Each spike is recorded at a higher latitude than the former one and all three are very localised over Fennoscandia. The first spike occurred at 17:34 UT and was observed at Lycksele, Rørvik and Nurmijärvi, the second spike was recorded at 17:41 UT and located at Lycksele and Rørvik, whereas the last spike occurred at 17:47 UT and was observed at Kevo and Abisko. Simultaneous optical auroral data and electron injections at the geosynchronous orbit indicate that one or more substorms took place in the polar ionosphere at the time of the wedgelets. This study demonstrates the occurrence of small and short-lived structures such as wedgelets at different locations over a short time scale, 15 min in this case.

Plasma entities, known as magnetosheath jets, with higher dynamic pressure than the surrounding plasma, are often seen at Earth. They generate waves and contribute to energy transfer in the magnetosheath. Affecting the magnetopause, they cause surface waves and transfer energy into the magnetosphere, causing throat auroras and magnetic signatures detectable on the ground. We show that jets exist also beyond Earth’s environment in the magnetosheath of Mars, using data obtained by the MAVEN spacecraft. Thus, jets can be created also at Mars, which differs from Earth by its smaller bow shock, and they are associated with an increased level of magnetic field fluctuations. Jets couple large and small scales in magnetosheaths in the solar system and can play a similar part in astrophysical plasmas.

Spatio‐temporal variations of ionospheric currents cause rapid magnetic field variations at ground level and Geomagnetically Induced Currents (GICs) that can be harmful for human infrastructure. The risk for large excursions in the magnetic field time derivative, “dB/dt spikes”, is known to be high during geomagnetic storms and substorms. However, less is known about the occurrence of spikes during non‐stormy times. We use data from ground‐based globally covering magnetometers (SuperMAG database) from the years 1985–2021. We investigate the spike occurrence (|dB/dt| > 100 nT/min) as a function of magnetic local time (MLT), magnetic latitude (Mlat), and the solar cycle phases during non‐stormy times (−15 nT ≤ SYM‐H < 0). We sort our data into substorm (AL < 200 nT) intervals (“SUB”) and less active intervals between consecutive substorms (“nonSUB”). We find that spikes commonly occur in both SUBs and nonSUBs during non‐stormy times (3–23 spikes/day), covering 18–12 MLT and 65°–80° Mlat. This also implies a risk for infrastructure damage during non‐stormy times, especially when several spikes occur nearby in space and time, possibly causing infrastructure weathering. We find that spikes are more common in the declining phase of the solar cycle, and that the occurrence of SUB spikes propagates from one midnight to one morning hotspot with ∼10 min in MLT for each minute in universal time (UTC). Finally, we discuss causes for the spikes in terms of spatio‐temporal variations of ionospheric currents.

The magnetosheath is a region downstream of the bow shock filled with turbulent, decelerated solar wind plasma which is flowing earthwards. This solar wind flow sometimes shows signatures of localized structures with enhanced dynamic pressure, so called magnetosheath jets. These jets are often associated with low angles between the bow shock normal and the interplanetary magnetic field (IMF) direction, the so called quasi-parallel bow shock. Less often they are also found behind the quasi-perpendicular bow shock.As jets propagate through the magnetosheath, they interact with the surrounding plasma. Studying waves inside, and in the vicinity of, jets is a step towards understanding the interaction of jets with the surrounding plasma. So far whistler waves, electrostatic waves, waves in the lower hybrid frequency range as well as low frequency waves have been reported. However, the sources of these waves are unknown. In addition, further types of waves may be associated with the jets.We conduct a study on waves in magnetosheath jets using burst mode data of the Magnetospheric Multiscale (MMS) mission. The magnetic and electric field data are provided with a sampling rate of 8 kHz, while previous studies used data sets with much lower sampling rates. The high time resolution allows us to study different waves over a large frequency range and investigate properties of these waves. In addition, we discuss possible generation mechanisms.

In theory the width of the quasi-perpendicular bow shock ramp is on the scale of a few electron inertial lengths, but as this work will show the quasi-perpendicular bow shock at Mars is often wider. This is important because it implies that the conditions at Mars create a behaviour at the shock which cannot be described by current theory. Furthermore, the width could affect processes at the shock such as energy transfer of the ions and their subsequent thermalization. To investigate the cause of the width, two sets of quasi-perpendicular bow shock crossings measured by MAVEN are compared, one of unusual width (average 370 km or 5r$_{gi}$), and one of typical width (average 30 km or 0.7r$_{gi}$). These sets are labeled wide and thin shocks respectively. It is seen that the wide shocks have no distinct overshoot and have a higher level of magnetic field fluctuations than the thin shocks. Factors that are known to affect the standoff distance, such as the magnetosonic Mach number and mass loading of the solar wind by planetary species, were found not to affect the width of the bow shock. It is found that the temperature of the solar wind plasma increases more as it passes through a wide than a thin shock, indicating that ions are thermalized to a larger extent than at thin shocks. The larger-than-predicted by theory width of the Martian quasi-perpendicular bow shock indicate that there are conditions at Mars which we do not yet understand.