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The Earth’s magnetosheath is a dynamic region and its properties strongly depend on the angle between the bow shock normal and the solar wind magnetic field (θbn). If the shock is quasi-parallel (θbn < 45°), the magnetosheath is magnetically connected to the foreshock, causing strong fluctuations and structures propagating from upstream to downstream. A quasi-perpendicular shock (θbn > 45°) produces a less structured and more stationary magnetosheath characterized by compression and high ion temperature anisotropy. These distinct configurations make it possible to study how different plasma environments affect various processes such as turbulence, heating, and wave-particle interactions. Therefore, such studies require an accurate classification of the magnetosheath. This is not easily achieved, especially close to the magnetopause where the shock crossing for the plasma of interest cannot be observed.Previously, Karlsson et al. (2021) used data from the Cluster mission to propose a promising classification method using local measurements of the magnetic field standard deviation, high-energy ion flux, and ion temperature anisotropy. In this work, we are building on this study and extending it to the Magnetospheric Multiscale (MMS) mission, having a different orbit than Cluster. We compare this local classification to θbn estimated from upstream conditions and well-known bow shock models, and discuss the advantages and disadvantages of the different methods. Reference: Karlsson, T., Raptis, S., Trollvik, H., & Nilsson, H. (2021). Classifying the magnetosheath behind the quasi-parallel and quasi-perpendicular bow shock by local measurements. Journal of Geophysical Research: Space Physics, 126, e2021JA029269.

Collisionless shocks exist across diverse plasma environments. Examples are supernova remnants, comets, near planets, and interplanetary (IP) shocks in the solar wind. As the shock Mach number increases, so does the complexity of the ion distribution functions at the shock front due to features such as whistler precursors, ion reflection, shock ripples, and nonstationarity. Experimental studies of ion dynamics at supercritical high Mach (>5) number shocks are typically conducted using planetary bow shock crossings since the Mach number of these shocks are higher while the shock speeds with respect to the observing spacecraft are lower. As a result, it is easier to resolve complex features in the ion velocity distribution function. For these reasons, studies concentrating on ion reflection at IP shocks are rare. However, comparisons with IP shocks are interesting since they have a much larger curvature radius and can be accompanied by more energetic particles.In this work, we analyze a quasi-perpendicular shock observed by Solar Orbiter (SolO) on 30 October 2021 with a Mach number of around 7; this is much higher than the typical values of SolO IP shocks, which are between 1-3. For this event, we observed clear signatures in the upstream ion distribution function of reflected ions with energies extending to around 15 keV, which is lower than reported by other studies. The shock also demonstrates a non-planar feature, which may indicate shock rippling. In addition, whistler precursors are also found immediately upstream locally within the shock foot. We present these experimental results and a comparison with test-particle analysis and numerical modeling results.

The Earth's Magnetospheric System is the complex and highly dynamic environment in near-Earth space where plasma gets actively energized and transport of large amounts of energy occurs, due to the interaction of the solar wind with the Earth's magnetic field. Understanding plasma energization and energy transport is an open challenge of space plasma physics, with important implications for space weather science as well as for the understanding of distant astrophysical plasmas. Plasma energization and energy transport are related to fundamental processes such as shocks, magnetic reconnection, turbulence and waves, plasma jets and instabilities, which are at the core of the current space plasma physics research. ESA/Cluster and NASA/MMS four-point constellations, as well as the large-scale multipoint mission NASA/THEMIS, have greatly improved over the last two decades our understanding of plasma processes at individual scales compared to earlier single-point measurements. Despite the large amount of available observations, we still do not fully understand the physical mechanisms which give rise to plasma energization and energy transport. The reason is that the fundamental physical processes governing plasma energization and energy transport operate across multiple scales ranging from the large fluid to the smaller kinetic scales. Here we present the Plasma Observatory (PO) multiscale mission concept which is tailored to study plasma energization and energy transport within the Earth's Magnetospheric System. PO baseline is comprised of one mothercraft (MSC) and six identical smallsat daughtercraft (DSC) in an HEO 8 RE X 18 RE orbit, covering all the key regions of the Magnetospheric System where strong energization and transport occur: the foreshock, bow shock, magnetosheath, magnetopause, magnetotail current sheet, and the transition region. MSC payload provides a complete characterization of electromagnetic fields and plasma particles in a single point with time resolution sufficient to resolve kinetic physics at sub-ion scales. The DSCs have identical payload which is much simpler than on the MSC, yet giving a full characterization of the plasma at the ion and fluid scales. Going beyond Cluster, THEMIS and MMS, PO will permit us to resolve for the first time the coupling between ion and fluid scales as well as the non-planarity and non-stationarity of plasma structures at those scales. PO is one of the five ESA M7 candidates to be launched around 2037 and is currently undergoing a competitive Phase 0 at ESA for further downselection to Phase A at the end of 2023.

Ion-acoustic waves are often observed in the solar wind along the Solar Orbiter’s orbit. These electrostatic waves are generated via ion-ion or current-driven instabilities below the local proton plasma frequency. Due to the Doppler shift, they are typically observed in the frequency range between the local electron and proton plasma frequency in the spacecraft frame. Ion-acoustic waves often accompany large-scale solar wind structures and play a role in the energy dissipation in the propagating solar wind. Time Domain Sampler (TDS) receiver, a part of the Radio and Plasma Waves (RPW) instrument, is sampling wave emissions at frequencies below 200 kHz almost continuously from the beginning of the mission. Almost three years of observations allow us to perform a detailed study of ion-acoustic waves in the solar wind under variable plasma conditions. The emission tends to be observed when proton density and temperature are highly perturbed. A detailed analysis of the proton velocity distribution and wave generation using solar wind data from a Proton and Alpha particle Sensor (PAS) of the Solar Wind Analyzer (SWA) is shown.

High-speed electron flows play an important role in the energy dissipation and conversion in the terrestrial magnetosphere and are widely observed in regions related to magnetic reconnection, e.g., the vicinity of electron diffusion regions (EDRs), and separatrix layers. NASA’s Magnetospheric Multiscale mission was designed to resolve the electron-scale kinetic processes of Earth’s magnetosphere. Here, we perform a systematic survey of high-speed electron flows in the terrestrial magnetotail using the MMS observations from 2017 to 2021. The high-speed electron flows are characterized by electron bulk speeds larger than 5000 km/s. We identified 649 events. Those events demonstrate unambiguous dawn-dusk asymmetry, and 73% of them locate in the dusk magnetotail. The selected events are found in EDRs, the reconnection separatrix boundary layer, and the lobe region. More than 70% of the events are identified in the separatrix boundary layer and the lobe region and are aligned with the ambient magnetic field. 75 cases, with magnetic field magnitude smaller than 5 nT, locate near the plasma-sheet neutral line. Approximately 20 cases among them have EDR signatures, and those high-speed electron flows are directed arbitrarily with respect to the ambient magnetic field. We also show other statistical properties of the events, including electron bulk speed, electron number density, and temperature anisotropy.

We report an event of intermittent reconnection from the terrestrial magnetotail observed by the Magnetospheric MultiScale mission. First, magnetic reconnection is active, inferred from a field-aligned off-equatorial plasma jet. Over 40 seconds, this jet is replaced by a quiet time interval with dusk-ward diamagnetic ion flow carried by a hot population that persists for about two minutes. During this interval, we observe signs of current sheet thickening followed by thinning. The change in the dawn-dusk current associated with the inferred thickening is provided by changes in the electron flux, and we argue this is a result of momentum conservation. Thereafter, we observe an equatorial jet of hot plasma that gradually builds up before the spacecraft encounter a dipolarization front about 20 seconds later. This first dipolarization front is associated with a transition from a hot pre-existing plasma sheet, to colder plasma of lobe origin. This event showcases behavior during intermittent magnetic reconnection and may help us understand the spatiotemporal evolution of reconnecting regions.

​​The Earth’s magnetosheath is a turbulent plasma region where the interplay between coherent structures and various plasma waves affect the particle dynamics and energy transfer. The properties of the magnetosheath are controlled by the upstream conditions. Magnetosheath plasma downstream of a quasi-parallel bow shock (the angle between the shock normal and the interplanetary magnetic field being less than 45°) tends to have stronger fluctuations while a quasi-perpendicular shock leads to a more stationary magnetosheath. These two geometries create different environments for processes such as wave generation. One example is whistler waves that can be excited by non-Maxwellian electron velocity distributions formed in local magnetic structures. Whistler waves have been observed throughout the magnetosheath. As previous statistical studies have considered the region as a whole, it is yet unexplored which magnetosheath geometry creates more favorable conditions for whistler wave generation.In this work, we address this issue and investigate how the occurrence and properties of whistler waves depend on the magnetosheath configuration. We detect whistler waves using data from the Magnetospheric Multiscale (MMS) mission. We compare whistler wave occurrence to the shock normal angle estimated from upstream conditions, as well as local conditions which are typically different between the quasi-parallel and quasi-perpendicular geometries. The results give an indication of the conditions needed for the whistler waves to efficiently dissipate energy in the turbulent magnetosheath.

MMS can resolve the fine structure of the shock ramp, which often shows holes in reduced ion-phase space distributions (integrated along the tangential plane of the shock). This is possible due to the high temporal resolutions of FPI/DIS. Such holes have been associated with ripples propagating along the shock surface but also can be related to the shock reformation. We statistically characterize the ion phase-space holes at the Earth’s bow shock using MMS observations. We establish a systematic procedure to find the shocks exhibiting the phase-space holes. We apply the procedure to ~500 shock crossings for which the burst data necessary to identify the holes is available. We identify phase-space holes for 66% of the crossings. We note that the actual occurrence is likely higher, as the holes are not resolved for fast shock crossings. We characterize the occurrence of the holes as a function of shock parameters such as Mach number and geometry. We find that the holes are widespread at the bow shock and are present for a wide range of shock geometries and Mach numbers (MA) studied. Their occurrence has no dependence on the shock geometry and increases with the Mach number, MA. The highest occurrence (70% probability) is for MA above 5. These results are essential to understanding the non-stationary behavior of collisionless shocks.

The process of electron heating across collisionless shocks is not fully understood. Their heating is believed to be an interplay between adiabatic large scale, DC electric and magnetic fields across the shock and non-adiabatic large amplitude AC electromagnetic and electrostatic waves. In this work we use the database developed by Lalti et al. 2022 to select 426 quasi-perpendicular shock crossings by MMS spacecraft, each of which exhibiting a clean upstream and downstream region. For each shock we calculate the various shock and plasma parameters such as θBn, MA, βe, cross shock potential, electron temperature parallel and perpendicular to the magnetic field. We investigate the various correlations between those parameters in order to understand the general character of electron heating, and to what extent non-adiabatic effects contribute to the process. Lalti, A., Khotyaintsev, Y. V., Dimmock, A. P., Johlander, A., Graham, D. B., and Olshevsky, V., “A Database of MMS Bow Shock Crossings Compiled Using Machine Learning”, Journal of Geophysical Research (Space Physics), vol. 127, no. 8, 2022. doi:10.1029/2022JA030454.

Identifying collisionless shock crossings in data sent from spacecraft has so far been done manually. It is a tedious job that shock physicists have to go through if they want to conduct case studies or perform statistical studies. We use a machine learning approach to automatically identify shock crossings from the Magnetospheric Multiscale (MMS) spacecraft. We compile a database of those crossings including various spacecraft related and shock related parameters for each event. Furthermore, we show that the shocks in the database have properties that are spread out both in real space and parameter space. We also present a possible science application of the database by looking for correlations between ion acceleration efficiency at shocks and different shock parameters such as the shock geometry and the Mach number.

Langmuir waves (electrostatic waves near the electron plasma frequency) are often observed in the solar wind, playing an important role in the energy dissipation of electrons. The largest amplitude waves are typically associated with type II and III solar radio bursts and planetary foreshocks. However, Langmuir waves not connected with radio bursts are also found in the solar wind. The causes of these Langmuir waves are not well understood. Langmuir waves are also found around magnetic holes, a localised depression of the magnetic field strength. This study aims to investigate the relationship between Langmuir waves and magnetic holes in the solar wind using electric and magnetic field measurements performed by the Solar Orbiter’s RPW and MAG instruments during 2020 and 2021. We identified a large set of Langmuir wave events from the RPW/TDS (Time Domain Sampler) waveform data using the plasma density estimated from the spacecraft’s potential obtained by RPW, showing that ~7% of them have been spotted inside magnetic holes. We will compare these events with local plasma conditions analysing the electron distribution functions, and discuss the mechanisms that may lead to the generation of Langmuir waves associated with magnetic holes in the solar wind.

In the present work, we consider 49 dipolarization fronts (DF) detected by the Magnetospheric Multiscale (MMS) mission on 2017, near the Earth’s magnetotail equator (Bx0) ahead or at the DF. For the second subcategory, we found the same behavior ahead or at the DF whereas it is the opposite (J·E0) only occurs behind the front for the second subcategory. The possible origin of these two subcategories is discussed.

On November 27, 2021, Solar Orbiter completed its only flyby of Earth on its way to the following Sun’s encounter in March 2022. Although this fast flyby was performed primarily to decrease the spacecraft’s velocity and change orbit to get closer to the Sun, the Radio and Plasma Wave (RPW) instrument had the opportunity to perform high cadence measurements in the Earth’s magnetosphere. We review the main observation of the Time Domain Sampler (TDS) receiver, a part of the RPW instrument, made during this flyby at frequencies below 200 kHz. The TDS receiver operated in a high cadence mode providing us with the regular waveform snapshot with 62 ms length every ten seconds for two electric components. Besides the regular captures, we have got more than five hundred onboard classified snapshots and the statistical products with a sixteen-second cadence. Before entering the terrestrial magnetosphere around 02:30UT, the spacecraft wandered through the foreshock region, registering intense bursts of Langmuir waves. After the bowshock crossing, Solar Orbiter was for more than two hours in the morning sector of the magnetosphere, recording various plasma wave modes. The closest approach was reached at 04:30UT above North Africa at an altitude of 460 km. Then the spacecraft continued into the Earth’s tail and entered the magnetosheath around 13:00UT. After 15:00UT, the Solar Orbiter crossed the bowshock, and bursts of Langmuir waves were detected again pointing out to the deep downstream foreshock region. Further from the Earth, intense Auroral Kilometric Radiation (AKR) at frequencies above 100 kHz was also detected.

We investigate the polarization of Langmuir waves observed by the Time Domain Sampler (TDS) module of the Radio and Plasma Waves instrument on Solar Orbiter during several extensive Type III burst events. During its two-year-long cruise phase, Solar orbiter often crossed the source region of the Type III radio emission and observed the Langmuir waves generated by solar energetic electrons. The waves are known to exhibit complex modulation and often non-trivial elliptical polarization which sometimes rapidly changes on the timescales of tens of milliseconds. We show that the observed waveforms are typically composed of multiple sub-packets with a relatively short coherence length. We investigate the correlation between the polarization of the waves, simultaneously observed energetic electrons beams and other plasma properties.

Collisionless shocks are ubiquitous throughout the universe in near-Earth and astrophysical plasma environments. The behavior of collisionless shocks in terms of their structure and energy dissipation has been the subject of extensive research over many decades, but many open questions remain. Recent studies have demonstrated that the Earth's bow shock can exhibit ripples that propagate along the shock surface. However, their occurrence, dependence on shock parameters, and their role in shock dynamics is still under investigation. One signature of rippling is the presence of phase space holes in reduced ion distribution (integrated along the tangential plane of the shock). Such ion phase space holes are also observed in association with the shock reformation. It is unclear at what part of the parametric space these ion phase space holes are expected. In this study, we have focused on characterizing ion phase space holes at the Earth’s bow shock using MMS observations. We analyze more than 500 shock crossings observed by the MMS spacecraft and establish a systematic procedure to find the shocks exhibiting phase space holes. We investigate the key shock physical processes responsible for the existence of these phase space holes (e.g. ripples and reformation) and study the association to shock parameters such as Mach number and geometry. We present the first statistical study of this nature, and these results are important to understanding the non-stationary behavior of collisionless shocks.

Broadband waves near and below the lower-hybrid frequency have been observed at the magnetopause for a long time. In recent years NASA's multi-spacecraft mission Magnetospheric Multiscale (MMS) has enabled the waves to be analysed in much greater detail.Previous case studies have shown that these waves can cause plasma diffusion across the magnetopause, leading to the broadening of current layers. It has also been argued that the waves might contribute to parallel electron heating and anomalous resistivity.In this study we analyze the aforementioned waves at the magnetopause using multi-spacecraft analysis methods and data from the MMS mission. We investigate the properties of these waves on a statistical level, using several months of data. In particular, we present the relation between the waves and ambient plasma properties such as density gradients and the corresponding gradient length-scale, and to magnetic reconnection.

High frequency electrostatic oscillations are one of the most fundamental players in energy conversion in collisionless plasmas. Whether at collisionless shocks, turbulence energy cascades or reconnection, small scale Debye length processes are at the heart of irreversible energy exchange between particles and fields. MMS is one of the most advanced still active spacecraft, with high resolution field and particle instruments. The electric field instrument (EDP) on board of MMS is formed of 3 axial double probes positioned in a perpendicular configuration allowing for the measurement of the 3D electric field. In this study we probe the limitations of the EDP instrument in measuring Debye-scale electrostatic oscillations. In particular we show that at such small wavelengths the electric field is attenuated due to the finite probe-to-probe separation. Furthermore, we propose a method to correct for the electric field attenuation based on the single spacecraft interferometry technique which will allow us to properly determine the observed wave modes.

Collisionless shock waves are important for particle heating and acceleration in space. Electron heating at shocks is a combination of adiabatic heating due to large-scale electric and magnetic fields and scattering by high-frequency oscillations. Electron heating and scattering at the shock is still poorly understood but the scales at which heating happens can hint to which physical processes are taking place. Here, we study electron heating scales with the Magnetospheric Multiscale (MMS) spacecraft at Earth’s quasi-perpendicular bow shock. We utilize the small tetrahedron formation and rapid plasma measurements of MMS to directly measure the electron temperature gradient inside the shock. From this, we reconstruct the electron temperature profile inside the shock ramps of a number of shock crossings with varying shock parameters. We find that most of the electron temperature increase takes place on a scale of tens of electron inertial lengths. Further, we investigate the electron distribution functions and attempt to disentangle the effects of the large-scale adiabatic heating and scattering by high-frequency waves.

Whistler waves, right-hand polarized waves with frequencies below the electron cyclotron frequency, are common in many space plasma regions such as the Earth’s magnetosheath. They can be generated by electron temperature anisotropy, in which case the instability grows through cyclotron resonance. A common way to determine the stability of an electron distribution function is to compare the parallel and perpendicular temperature (with respect to the background magnetic field) to stability thresholds. However, such an approach based on the moments of the distribution function can potentially leave out some properties of the distribution which are important for wave generation.In this work, we investigate the features of the electron distribution functions measured by MMS in the turbulent magnetosheath downstream of a quasi-parallel shock. We show that even though statistically whistler waves tend to occur close to the regions where the stability threshold is exceeded, they are also observed in regions predicted to be stable to wave generation. For such waves we observe that the electron pitch angle distribution often has the so-called butterfly shape (with minima in both the parallel and perpendicular directions) and is located in magnetic field minima. Using a linear numerical dispersion solver (WHAMP), we show that the butterfly distribution is unstable to whistler wave generation even though the instability threshold based on the associated moments is not exceeded. Comparison between the numerical results and waves measured by the MMS spacecraft indicate that the observed whistler waves are generated by the butterfly distribution. This phenomenon has previously been observed in mirror modes and large scale magnetic holes. Our findings show that it also occurs on smaller scales (~1 ion inertial length) in more turbulent environments, such as the quasi-parallel magnetosheath.

We investigate the Venusian magnetotail and its boundaries utilising magnetic field and density measurements that cover a wide range of radial distances, from the two geometrically similar Solar Orbiter Venus flybys on 27 December 2020 and 9 August 2021. We look at the magnetic field components along the spacecraft trajectory in an attempt to identify boundary crossings, as well as the extent and intensity of the bowshock deep in the magnetotail. We compare these observations with results of a simulation of the induced magnetosphere and magnetotail of Venus, where the initial upstream conditions are provided by Solar Orbiter measurements, to examine in what degree the simulation representation agrees with the observations. The model encloses a massive volume of 80RV x 60RV x 60RV in which we look at magnetic field and proton density variations. Additionally, we vary the rotation of the clock angle in order to find for which rotation angle we get the best match with the observations during the different steps of the spacecraft's trajectory.

The primary scientific goal of ICARUS (Investigation of Coronal AcceleRation and heating of solar wind Up to the Sun), a mother-daughter satellite mission, proposed in response to the ESA “Voyage 2050” Call, will be to determine how the magnetic field and plasma dynamics in the outer solar atmosphere give rise to the corona, the solar wind, and the entire heliosphere. Reaching this goal will be a Rosetta Stone step, with results that are broadly applicable within the fields of space plasma physics and astrophysics. Within ESA’s Cosmic Vision roadmap, these science goals address Theme 2: “How does the Solar System work?” by investigating basic processes occurring “From the Sun to the edge of the Solar System”. ICARUS will not only advance our understanding of the plasma environment around our Sun, but also of the numerous magnetically active stars with hot plasma coronae. ICARUS I will perform the first direct in situ measurements of electromagnetic fields, particle acceleration, wave activity, energy distribution, and flows directly in the regions in which the solar wind emerges from the coronal plasma. ICARUS I will have a perihelion altitude of 1 solar radius and will cross the region where the major energy deposition occurs. The polar orbit of ICARUS I will enable crossing the regions where both the fast and slow winds are generated. It will probe the local characteristics of the plasma and provide unique information about the physical processes involved in the creation of the solar wind. ICARUS II will observe this region using remote-sensing instruments, providing simultaneous, contextual information about regions crossed by ICARUS I and the solar atmosphere below as observed by solar telescopes. It will thus provide bridges for understanding the magnetic links between the heliosphere and the solar atmosphere. Such information is crucial to our understanding of the plasma physics and electrodynamics of the solar atmosphere. ICARUS II will also play a very important relay role, enabling the radio-link with ICARUS I. It will receive, collect, and store information transmitted from ICARUS I during its closest approach to the Sun. It will also perform preliminary data processing before transmitting it to Earth. Performing such unique in situ observations in the area where presumably hazardous solar energetic particles are energized, ICARUS will provide fundamental advances in our capabilities to monitor and forecast the space radiation environment. Therefore, the results from the ICARUS mission will be extremely crucial for future space explorations, especially for long-term crewed space missions.

When analyzing plasma waves, a key parameter to determine is the phase velocity. It enables us to, for example, compute wavelengths, wave potentials, and determine the energy of resonant particles. The phase velocity of a wave, observed by a single spacecraft equipped with electric field probes, can be determined using interferometry techniques. While several methods have been developed to do this, they have not been documented in detail. In this study, we use an analytical model to analyze and compare three interferometry methods applied on the probe geometry of the Magnetospheric Multiscale spacecraft. One method relies on measured probe potentials, whereas the other two use different E-field measurements: one by reconstructing the E-field between two probes and the spacecraft, the other by constructing four pairwise parallel E-field components in the spacecraft spin-plane. We find that the potential method is sensitive both to how planar the wave is, and to spacecraft potential changes due to the wave. The E-field methods are less affected by the spacecraft potential, and while the reconstructed E-field method is applicable in some cases, the second E-field method is almost always preferable. We conclude that the potential based interferometry method is useful when spacecraft potential effects are negligible and the signals of the different probes are very well correlated. The method using two pairs of parallel E-fields is practically always preferable to the reconstructed E-field method and produces the correct velocity in the spin-plane, but it requires knowledge of the propagation direction to provide the full velocity., 35 pages, 9 figures, 1 table

We present recent high time resolution observations from an oblique (43 deg) shock crossing from the Magnetospheric Multiscale mission. Short-duration bursts between 10 and 100 ms of ion acoustic waves are observed in this event alongside a persistent reflected ion population. High time resolution (150 ms) particle measurements show strongly varying ion distributions between successive measurements, implying that they are bursty and impulsive by nature. Such signatures are consistent with ion bursts that are impulsively reflected at various points within the shock. We find that, after instability analysis using a Fried-Conte dispersion solver, the insertion of dispersive ion bursts into an already stable ion distribution can lead to wave growth in the ion acoustic mode for short durations of time. We find that impulsively reflected ions are a plausible mechanism for ion acoustic wave growth in the terrestrial bow shock and, furthermore, suggest that wave growth can lead to a small but measurable momentum exchange between the solar wind ions and the reflected population.

The recently released spacecraft potential measured by the RPW instrument onboard Solar Orbiter has been used to estimate the solar wind electron density in the inner heliosphere. Selected intervals have been extracted to study and quantify the properties of turbulence. Empirical Mode Decomposition was used to obtain the generalized marginal Hilbert spectrum, equivalent to the structure functions analysis, additionally reducing issues typical of nonstationary time series. Results show the presence of a well defined inertial range with Kolmogorov scaling. However, the turbulence shows intermittency only in part of the samples, while other intervals have homogeneous scale-dependent fluctuations. These are observed predominantly during intervals of ion-frequency wave activity. Comparisons with compressible magnetic field intermittency (from the MAG instrument) and with an estimate of the solar wind velocity (using electric and magnetic field) are also provided to provide general context and help determine the cause for the absence of intermittency.

Wakes behind scientific spacecraft caused by supersonic drifting ions is common in collisionless plasmas. Such wakes change the local plasma conditions and disturb in situ observations of the geophysical plasma parameters. We concentrate on observations of the electric field with double-probe instruments. Sometimes the wake effects are caused by the spacecraft body, are minor and easy to detect, and can be compensated for in a reasonable way. We show an example from the Cluster spacecraft in the solar wind. Sometimes the effects are caused by an electrostatic structure around a positively charged spacecraft causing an enhanced wake and major effects on the local plasma. Here observations of the geophysical electric field with the double-probe technique becomes impossible. Rather, the wake can be used to detect the presence of cold positive ions. Together with other instruments, also the cold ion flux can be estimated. We discuss such examples from the Cluster spacecraft in the magnetospheric lobes. For an intermediate range of parameters, when the drift energy of the ions is comparable to the equivalent charge of the spacecraft, also the charged wire booms of a double-probe instrument must be taken into account to extract useful information from the observations. We show an example from the MMS spacecraft near the magnetopause. With understanding of the physics causing wakes behind spacecraft, the local effects can sometimes be compensated for. When this is not possible, sometimes entirely new geophysical parameters can be estimated. An example is the flux of cold positive ions, constituting a major part of the mass outflow from planet Earth, using electric and magnetic field instruments on a spacecraft charged due to photoionization

International audience; Processes driven by unsteady reconnection can efficiently accelerate particles in many astrophysical plasmas. An example is the reconnection jet fronts in an outflow region. We present evidence of suprathermal ion acceleration between two consecutive reconnection jet fronts observed by the Magnetospheric Multiscale mission in the terrestrial magnetotail. An earthward propagating jet is approached by a second faster jet. Between the jets, the thermal ions are mostly perpendicular to magnetic field, are trapped, and are gradually accelerated in the parallel direction up to 150 keV. Observations suggest that ions are predominantly accelerated by a Fermi-like mechanism in the contracting magnetic bottle formed between the two jet fronts. The ion acceleration mechanism is presumably efficient in other environments where jet fronts produced by variable rates of reconnection are common and where the interaction of multiple jet fronts can also develop a turbulent environment, e.g., in stellar and solar eruptions.

Magnetic nulls are ubiquitous in space plasmas, and are of interest as sites of localized energy dissipation or magnetic reconnection. As such, a number of methods have been proposed for detecting nulls in both simulation data and in situ spacecraft data from Earth's magnetosphere. The same methods can be applied to detect stagnation points in flow fields. In this paper we describe a systematic comparison of different methods for finding magnetic nulls. The Poincare index method, the first-order Taylor expansion (FOTE) method, and the trilinear method are considered. We define a magnetic field containing fourteen magnetic nulls whose positions and types are known to arbitrary precision. Furthermore, we applied the selected techniques in order to find and classify those nulls. Two situations are considered: one in which the magnetic field is discretized on a rectangular grid, and the second in which the magnetic field is discretized along synthetic `spacecraft trajectories' within the domain. At present, FOTE and trilinear are the most reliable methods for finding nulls in the spacecraft data and in numerical simulations on Cartesian grids, respectively. The Poincare index method is suitable for simulations on both tetrahedral and hexahedral meshes. The proposed magnetic field configuration can be used for grading and benchmarking the new and existing tools for finding magnetic nulls and flow stagnation points., Reproduced with permission from Astronomy & Astrophysics, \c{opyright} ESO

Compressive plasma turbulence is investigated at sub-ion scales in the solar wind using both the Fast Plasma Investigation (FPI) instrument on the Magnetospheric MultiScale mission (MMS), as well as using calibrated spacecraft potential data from the Spin Plane Double Probe (SDP) instrument. The data from FPI allow a measurement down to the sub-ion scale region ($f_{sc}\gtrsim 1$ Hz) to be investigated before the instrumental noise becomes significant at a spacecraft frame frequency of $f_{sc}\approx 3$Hz, whereas calibrated spacecraft potential allows a measurement up to $f_{sc}\approx 40$Hz. In this work, we give a detailed description of density estimation in the solar wind using the spacecraft potential measurement from the SDP instrument on MMS. Several intervals of solar wind plasma have been processed using the methodology described which are made available. One of the intervals is investigated in more detail and the power spectral density of the compressive fluctuations is measured from the inertial range to the sub-ion range. The morphology of the density spectra can be explained by either a cascade of Alfv\'en waves and slow waves at large scales and kinetic Alfv\'en waves at sub-ion scales, or more generally by the Hall effect. Using electric field measurements the two hypotheses are discussed., Comment: Accepted to APJS

International audience

Flapping motions of current sheets are commonly observed in the magnetotail. Various wave modes can correspond to these oscillations such as kink-like flapping or steady flapping (e.g Wei2019). The period of such oscillating phenomena is usually longer than 100s and a typical observations consist only of a few crossings (e.g. Zhang2002). Here, we present a short period (T≈25s) flapping event observed by Magnetospheric Multiscale (MMS) mission at the dusk side plasmasheet on September 14, 2019. Using the multispacecraft observations, the direction of flapping as well as the direction of propagation of the current sheet are determined using the minimum variance, the timing method and the spatiotemporal derivative (Shi2005). It appears that the three methods give similar results with a direction of propagation of the current sheet which mainly lies in the ecliptic plane with a flapping velocity up to 500km/s. Based on the obtained wavelength and the variations of the direction of propagation we discuss which of the wave modes can explain the flapping.

The Radio and Plasma Wave instrument (RPW) for Solar Orbiter includes a Time Domain Sampler sub-unit (TDS) designed to capture electromagnetic waveform measurements of high-frequency plasma waves and antenna voltage spikes associated with dust impacts. TDS will digitize three components of the electric field and one magnetic component at 524 kHz sampling rate and scan the obtained signal for plasma waves and dust impact signatures. The main science target of TDS are Langmuir waves observed in the solar wind in association with Type II and Type III solar bursts, interplanetary shocks, magnetic holes, and other phenomena. In this poster, we present the scientific data products provided by the TDS instrument and discuss the first data obtained during the commissioning phase. The first data will be used to evaluate the actual performance of the RPW TDS instrument.

Separatrices of magnetic reconnection host intense perpendicular Hall electric fields produced by decoupling of ion and electron components and associated with the in-plane electrostatic potential drop between inflow and outflow regions. The width of these structures is several local electron inertial lengths, which is small enough to demagnetize ions as they cross the layer. We investigate temperature dependence of ion acceleration at separatrices by means of 2D Particle-in-Cell (PIC) simulations of magnetic reconnection with only cold or hot ion background population. The separatrix Hall electric field is balanced by the inertia term in cold background simulations, the effect indicative of the quasi-steady local perpendicular acceleration. The electric field introduces a cross-field beam of unmagnetized particles which makes the temperature strongly non-gyrotropic and susceptible to sub-ion scale instabilities. This acceleration mechanism nearly vanishes for hot ion background simulations. Particle-in-cell simulations are complemented by one-dimensional test particle calculations, which show that the hot ion particles experience scattering in energies after crossing the accelerating layer, whereas cold ions are uniformly energized up to the energies comparable to the electrostatic potential drop between the inflow and outflow regions.

Plasma waves are one of the important products of the magnetic reconnection process. Plasma waves can produce particle heating, diffusion, and anomalous effects, which can potentially affect magnetic reconnection. We investigate the evolution and properties of plasma waves during a multiple X-line reconnection event at the magnetopause using measurements from the Magnetospheric Multiscale (MMS) mission. Both whistler waves and large-amplitude electrostatic waves were observed around the reconnecting current sheet. In these regions, the electron velocity distribution functions consist of a combination of a cold beam at low energies with an anisotropic population or a loss-cone at high energies. The electrostatic waves corresponded to regions where the cold beams are accelerated, while the whistlers corresponded to regions with significant anisotropies or loss cones. When the cold beams were accelerated to higher energies, the whistlers disappeared since the anisotropy or loss-cone distributions became less apparent. These results present the detailed evolution of the plasma waves reflecting the electron dynamics during magnetic reconnection.

Lower hybrid waves are investigated at the magnetosheath separatrix region in asymmetric guide-field reconnection at Earth’s magnetopause by using MMS observations. These waves are found in a limited region, depending on the density gradient across the separatrix, and they are driven by the lower hybrid drift instability. Properties of these waves are presented: (1) the waves propagate towards the x-line due to the out-of-plane magnetic field, consistent with the electron drift direction; (2) the wave potential is about 20% of the electron temperature. These drift waves effectively produce cross-field particle diffusion, enabling the entry of magnetosheath electrons into the exhaust region.

The process of transforming the bulk kinetic energy of solar wind into the random motion of the plasma particles is still an open question. One of the proposed mechanisms for energy dissipation in such shocks is wave-particle interactions. Specifically reflected ions at the foot of the shock could interact with the solar wind plasma in an unstable way causing an increase in the temperature of the upstream plasma. Phase standing Whistler precursor waves upstream of the shock front could play a major role in enhancing energy dissipation. We analyze multiple shock crossing events encountered by the Magnetospheric Multiscale (MMS) multi-spacecraft Mission, with Alfvenic Mach numbers around 4 and a θBn around 80 degrees. We use these events to study the effect of such waves on energy dissipation at quasi perpendicular shocks. Using spectral analysis and by calculating the poynting flux of the waves, we investigate the upstream shock energy transport by whistler waves, then we discuss the consequences of these results on the wave particle interaction as a mechanism for stabilizing such high Mach number shocks.

We discuss the importance to determine the structure and composition of the upper atmospheres and ionospheres of the Icy Giants (Uranus & Neptune) as well as Triton’s ionosphere in the light of numerous recently obtained Cassini results. The ionizing radiation and charging environment within the upper atmospheres of Saturn and Titan creates a very complex organic chemistry leading to charged sub-nm-sized to 100 nm-sized aerosols. The charged dust has a profound effect on the ionospheric structure and related chemistry, enhancing the ion number density well above photochemical equilibrium levels, while the electrons tend to become attached to the dust population. The organic chemistry leads to compounds reaching above 50,000 amu diffusing downward and possibly creating a pre-biotic chemistry. This process, involving nitrogen, methane and water may very well be a more general process, also applicable for the cases of Uranus, Neptune and Triton, were all have these starting species abundant in their upper atmospheres. We therefore propose that a future mission to the Ice Giants and the moon Triton has Langmuir probe, electron spectrometer, dust, ion- and neutral mass spectrometers onboard to make detailed in-situ measurements on both the orbiter and atmospheric probe in order to investigate this fundamental chemistry and aerosol formation.

At Earth’s bow shock electrons can be reflected and accelerated along magnetic fields lines, which can then form electron beams and excite Langmuir and beam-mode waves. These electron beams form when the shock normal angle is close to 90 degrees. However, recent observations have shown that quasi-perpendicular shocks can be non-stationary and exhibit ripples, which can modify the local shock-normal angle and cross-shock potential. We use Magnetospheric Multiscale (MMS) data to investigate the effects of shock ripples on the accelerated electrons observed in the electron foreshock. We compare the results with test-particle simulations to determine the effect of shock ripples on electron acceleration. We discuss the implications of these results for the generation of plasma frequency waves and radio emission in the electron foreshock region.

Using spacecraft potential observations with and without active spacecraft potential control (on/off) from the Magnetospheric Multiscale (MMS) mission, we estimate the average photoelectron emissio ...

Particle injections in the magnetosphere transport electrons and ions from the magnetotail to the radiation belts. Here we consider generation mechanisms of dispersionless injections, namely, those with simultaneous increase of the particle flux over a wide energy range. In this study we take advantage of multisatellite observations which simultaneously monitor Earth's magnetospheric dynamics from the tail toward the radiation belts during a substorm event. Dispersionless injections are associated with instabilities in the plasma sheet during the growth phase of the substorm, with a dipolarization front at the onset and with magnetic flux pileup during the expansion phase. They show different spatial spread and propagation characteristics. Injection associated with the dipolarization front is the most penetrating. At geosynchronous orbit (6.6R(E)), the electron distributions do not have a classic power law fit but instead a bump on tail centered on similar to 120keV during dispersionless electron injections. However, electron distributions of injections associated with magnetic flux pileup in the magnetotail (13R(E)) do not show such a signature. We surmise that an additional resonant acceleration occurs in between these locations. We relate the acceleration mechanism to the electron drift resonance with ultralow frequency waves localized in the inner magnetosphere.

Magnetic reconnection—the process responsible for many explosive phenomena in both nature and laboratory—is efficient at dissipating magnetic energy into particle energy. To date, exactly how this dissipation happens remains unclear, owing to the scarcity of multipoint measurements of the “diffusion region” at the sub-ion scale. Here we report such a measurement by Cluster—four spacecraft with separation of 1/5 ion scale. We discover numerous current filaments and magnetic nulls inside the diffusion region of magnetic reconnection, with the strongest currents appearing at spiral nulls (O-lines) and the separatrices. Inside each current filament, kinetic-scale turbulence is significantly increased and the energy dissipation, E′ ⋅ j, is 100 times larger than the typical value. At the jet reversal point, where radial nulls (X-lines) are detected, the current, turbulence, and energy dissipations are surprisingly small. All these features clearly demonstrate that energy dissipation in magnetic reconnection occurs at O-lines but not X-lines.

We investigate the properties of the ion sky maps produced by the Dual Ion Spectrometers (DIS) from the Fast Plasma Investigation (FPI). We have trained a convolutional neural network classifier to predict four regions crossed by the MMS on the dayside magnetosphere: solar wind, ion foreshock, magnetosheath, and magnetopause using solely DIS spectrograms. The accuracy of the classifier is >98%. We use the classifier to detect mixed plasma regions, in particular to find the bow shock regions. A similar approach can be used to identify the magnetopause crossings and reveal regions prone to magnetic reconnection. Data processing through the trained classifier is fast and efficient and thus can be used for classification for the whole MMS database., Accepted to JGR: Space Physics

Shock ripples are ion-inertial-scale waves propagating within the front region of magnetized quasi-perpendicular collisionless shocks. The ripples are thought to influence particle dynamics and acceleration at shocks. With the four magnetospheric multiscale (MMS) spacecraft, it is for the first time possible to fully resolve the small scale ripples in space. We use observations of one slow crossing of the Earth’s non-stationary bow shock by MMS. From multi-spacecraft measurements we show that the non-stationarity is due to ripples propagating along the shock surface. We find that the ripples are near linearly polarized waves propagating in the coplanarity plane with a phase speed equal to the local Alfvén speed and have a wavelength close to 5 times the upstream ion inertial length. The dispersive properties of the ripples resemble those of Alfvén ion cyclotron waves in linear theory. Taking advantage of the slow crossing by the four MMS spacecraft, we map the shock-reflected ions as a function of ripple phase and distance from the shock. We find that ions are preferentially reflected in regions of the wave with magnetic field stronger than the average overshoot field, while in the regions of lower magnetic field, ions penetrate the shock to the downstream region. QC 20190710