Publications

2017

• Examining Energetic Particle Injections and the Effects on the Inner Magnetosphere with Multiple Spacecraft/Missions
  
  • Leonard T. W.
  • Baker D. N.
  • Blake J. B.
  • Burch J. L.
  • Cohen I. J.
  • Ergun R.
  • Fennell J. F.
  • Gershman D. J.
  • Giles B. L.
  • Jaynes A. N.
  • Le Contel Olivier
  • Mauk B.
  • Russell C. T.
  • Strangeway R. J.
  • Torbert R. B.
  • Turner D. L.
  • Wilder F. D.
  , 2017, 32. The Magnetospheric Multiscale (MMS) Fly's Eye Energetic Particle Spectrometer (FEEPS) instrument has observed a multitude of particle injection events since its launch in 2014. These injections often lead to enhancements observed by the Van Allen Probes MagEIS instrument, as well as other elements of the modern-day Heliophysics System Observatory. The high spatial resolution and unprecedented time scales of the MMS observations provide a microscope view of the plasma physical properties in Earth's neighborhood while the combination with other missions in the Heliophysics System Observatory provides a telescope view of the larger Sun-Earth system. Past studies have found a relationship between substorm activity, which can be more powerful during high speed solar wind stream events, and enhancements of the outer radiation belt electrons. In this study, we examine several distinct particle injection events with dipolarization front characteristics observed by MMS and multiple complementary missions. In particular, cases involving multiple injection events are compared to singular injection events for their effectiveness of creating radiation belt enhancements.
• Plasma Waves and Structures Associated with Magnetic Reconnection
  
  • Ergun R.
  • Wilder F. D.
  • Ahmadi N.
  • Goodrich K. A.
  • Holmes J.
  • Newman D. L.
  • Burch J. L.
  • Torbert R. B.
  • Le Contel Olivier
  • Giles B. L.
  • Strangeway R. J.
  • Lindqvist P. A.
  , 2017, 21. Space observations of magnetic reconnection indicate a variety of plasma wave modes and structures in the vicinity of the electron diffusion region including electromagnetic whistler waves, quasi-electrostatic whistler waves, electron phase-space holes, double layers, electron acoustic waves, lower hybrid waves, upper hybrid waves, and electromagnetic drift waves. These waves and plasma structures are seen in magnetotail reconnection and subsolar reconnection. The MMS mission has the unique ability to unequivocally identify the electron diffusion region and distinguish waves in the EDR from those in the extended separatrix. Such a distinction is critical since some of the observed waves may be involved the reconnection process while others may result from subsequent or associated events and do not directly influence the reconnection process. For example, some of the largest amplitude (> 100 mV/m) electrostatic waves have been identified as electron acoustic waves and upper hybrid waves. These waves are likely generated as a result of reconnection and do not appear to strongly influence the reconnection process. On the other hand, large-amplitude electrostatic whistler waves have been observed very near the X-line, are seen in simulations, and may be participating in reconnection physics. Electromagnetic drift waves almost always appear in cases of asymmetric reconnection and may lead to a more turbulent process. We summarize wave observations by MMS and discuss the relative their possible role in magnetic reconnection physics, concentrating on recent magnetotail observations.
• 3D ion-scale dynamics of BBFs and their associated emissions in Earth's magnetotail using 3D hybrid simulations and MMS multi-spacecraft observations
  
  • Breuillard Hugo
  • Aunai N.
  • Le Contel Olivier
  • Catapano F.
  • Alexandrova Alexandra
  • Retinò Alessandro
  • Cozzani Giulia
  • Gershman D. J.
  • Giles B. L.
  • Khotyaintsev Y. V.
  • Lindqvist P. A.
  • Ergun R.
  • Strangeway R. J.
  • Russell C. T.
  • Magnes W.
  • Plaschke F.
  • Nakamura R.
  • Fuselier S. A.
  • Turner D. L.
  • Schwartz S. J.
  • Torbert R. B.
  • Burch J. L.
  , 2017, pp.SM44A-08. Transient and localized jets of hot plasma, also known as Bursty Bulk Flows (BBFs), play a crucial role in Earth's magnetotail dynamics because the energy input from the solar wind is partly dissipated in their vicinity, notably in their embedded dipolarization front (DF). This dissipation is in the form of strong low-frequency waves that can heat and accelerate energetic particles up to the high-latitude plasma sheet. The ion-scale dynamics of BBFs have been revealed by the Cluster and THEMIS multi-spacecraft missions. However, the dynamics of BBF propagation in the magnetotail are still under debate due to instrumental limitations and spacecraft separation distances, as well as simulation limitations. The NASA/MMS fleet, which features unprecedented high time resolution instruments and four spacecraft separated by kinetic-scale distances, has also shown recently that the DF normal dynamics and its associated emissions are below the ion gyroradius scale in this region. Large variations in the dawn-dusk direction were also observed. However, most of large-scale simulations are using the MHD approach and are assumed 2D in the XZ plane. Thus, in this study we take advantage of both multi-spacecraft observations by MMS and large-scale 3D hybrid simulations to investigate the 3D dynamics of BBFs and their associated emissions at ion-scale in Earth's magnetotail, and their impact on particle heating and acceleration.
• MMS Observations of Langmuir Collapse and Emission?
  
  • Boardsen S. A.
  • Che H.
  • Wilder F. D.
  • Ergun R.
  • Le Contel Olivier
  • Gershman D. J.
  • Giles B. L.
  • Moore T. E.
  • Paterson W. R.
  , 2017, 11. Through the two stream instability, electron beams accelerated by solar flares and nanoflares are believed to be responsible for several types of solar radio bursts observed in the corona and interplanetary medium, including flare-associated coronal Type J, U, and Type III radio bursts, and nanoflare-associated weak coronal type III bursts. However the duration of these radio bursts is several orders of magnitude longer than the linear saturation time of the electron two-stream instability. This discrepancy has been a long-standing puzzle. Recently Che et al. [2017, doi: 10.1073/pnas.1614055114] proposed a mechanism in which the plasma coherent emission is maintained by the cyclic Langmuir collapse. Wave coupling between Langmuir waves and electrostatic whistler waves is the key process necessary to close the feedback loop. In the magnetosphere, electron beams are commonly produced by acceleration processes such as magnetic reconnection, during which both whistlers and Langmuir waves are observed and thus provide possible in-situ observations to test and study the emission process near the acceleration source region. The high spatial and time resolution MMS fields and particle data are used to test aspects of this mechanism. In this presentation, we will present some preliminary results from MMS observations of electron beams near a reconnection region. We investigate, in the regions where the electron beams are observed, the coupling between high frequency Langmuir waves and low frequency electrostatic whistler waves, and the associated electromagnetic emissions, along with other possible specific features predicted by this model.
• Turbulent energy cascade in the inner heliosphere: a universal process underlying different turbulent patterns
  
  • Verdini Andrea
  • Grappin Roland
  • Montagud-Camps Victor
  , 2017, 11, pp.SH11B-2455. Direct measurements of the rate of turbulent energy cascade at 1 AU via structure functions (e.g., Starwarz et al 2009) indicate that the cascade rate is comparable to the level required to obtain the observed slow radial decrease of proton temperature observed in the inner heliosphere (Totten et al 1995). This is in contrast with the diversity of turbulent anisotropy (Dasso et al 2005, Verdini Grappin 2015) observed, as well as the systematicchange in spectral slope when passing from slow, cold flows to fast, hot flows.We want here to isolate initial conditions around 0.2 AU that can show at the same time the observed universal temperature gradient and the variety of turbulent patterns found in fast and slow winds. Direct numerical simulations of turbulent evolution including solar wind expansion are done allowing to measure directly the turbulent heating between 0.2 and 1 AU. When starting at 0.2 AU with large scale excitation of wavenumbers mainly perpendicular to the mean field, that is, corresponding to the 2D configuration characteristic of slow winds (Dasso et al 2005), we find a radial proton temperature gradient close to the 1/R profile observed, when adopting reasonable values of the Mach number and expansion rate. The fast/hot wind case is discussed.
• Magnetic Reconnection as Revealed by the Magnetospheric Multiscale Mission
  
  • Burch J. L.
  • Torbert R. B.
  • Moore T. E.
  • Giles B. L.
  • Phan T.
  • Le Contel Olivier
  • Webster J.
  • Genestreti K.
  • Ergun R.
  • Chen L. J.
  • Wang S.
  • Dorelli J. C.
  • Rager A. C.
  • Graham Daniel B.
  • Gershman D. J.
  , 2017, 21. The NASA Magnetospheric Multiscale (MMS) mission has completed its prime mission observations and has now entered an extended mission phase. During the two-year prime mission MMS made fundamental advances in our understanding of magnetic reconnection as enabled by its unprecedentedly high-resolution plasma and field measurements, which were made from 4 identical spacecraft in tetrahedral formations ranging down to 7 km. The primary objective of MMS is to understand reconnection at the electron scale, and this objective was accomplished by detailed analysis of 32 electron diffusion regions at the dayside magnetopause and a significant number in the magnetotail, which are still being captured and analyzed. Significant interplay between theory and experiment has occurred throughout the mission leading to the discovery of agyrotropic "crescent-shaped" electron velocity-space distributions, which carry the out-of-plane current; the electron pressure tensor divergence, which produces the reconnection electric field; standing oblique whistler waves, which produce intense dissipation in sub-gyroscale regions near the X-line and electron stagnation point; beam-plasma interactions leading to whistler-mode and Langmuir waves; electromagnetic drift waves leading to corrugated magnetopause current sheets, and numerous other new reconnection-related phenomena. In this talk the many new aspects of reconnection discovered by MMS will be placed into context and used to evaluate our current level of understanding of this universally important space plasma phenomenon.
• Radio and Plasma Wave Observations During Cassini's Grand Finale
  
  • Kurth W. S.
  • Bostrom R.
  • Canu Patrick
  • Cecconi B.
  • Cornilleau-Wehrlin Nicole
  • Farrell W. M.
  • Fischer G.
  • Galopeau Patrick H. M.
  • Gurnett D. A.
  • Gustafsson G.
  • Hospodarsky G. B.
  • Lamy L.
  • Lecacheux A.
  • Louarn P.
  • Macdowall R. J.
  • Menietti J. D.
  • Modolo Ronan
  • Morooka M.
  • Pedersen A.
  • Persoon A. M.
  • Sulaiman A. H.
  • Wahlund J. E.
  • Ye S.
  • Zarka P. M.
  , 2017, pp.abstract #U22A-07. Cassini ends its 13-year exploration of the Saturnian system in 22 high inclination Grand Finale orbits with perikrones falling between the inner edge of the D ring and the upper limits of Saturn's atmosphere. The Cassini Radio and Plasma Wave Science (RPWS) instrument makes a variety of observations in these unique orbits including Saturn kilometric radiation, plasma waves such as auroral hiss associated with Saturn's auroras, dust via impacts with Cassini, and the upper reaches of Saturn's ionosphere. This paper will provide an overview of the RPWS results from this final phase of the Cassini mission with the unique opportunities afforded by the orbit. Based on early Grand Finale orbits, we can already say that the spacecraft has passed through cyclotron maser source regions of the Saturn kilometric radiation a number of times, found only small amounts of micron-sized dust in the equatorial region, and observed highly variable densities of cold plasma of order 1000 cm-3 in the ionosphere at altitudes of a few thousand km.
• Analyzing the magnetopause internal structure: new possibilities offered by MMS
  
  • Belmont Gérard
  • Manuzzo Roberto
  • Rezeau Laurence
  • Aunai N.
  • Dargent Jérémy
  , 2017, 2017, pp.SM11A-2292.
• Circuit de lecture d'un magnétomètre à induction pour l'étude de plasmas atmosphériques sur la mission JUICE
  
  • Varizat Laurent
  , 2017. Les magnétomètres à induction sont utilisés dans de nombreux domaines d'exploration scientifique de la géophysique à l'astrophysique. Dans ces deux domaines l'étude des composantes magnétiques des ondes électromagnétiques naturelles requiert des instruments particulièrement performants: sensibles et présentant de faibles bruits intrinsèques pour accéder à des champs magnétiques de quelques fT/ . Dans le cas d'instruments scientifiques embarqués à bord de satellites, des contraintes en température, consommation, encombrement et de tenue en radiation s'ajoutent aux autres contraintes. Les technologies de circuits intégrés permettent une rupture technologique qui se traduit par une réduction de la taille des circuits électroniques embarqués d'un facteur supérieur à 1000 tout en améliorant les performances électriques et instrumentales (réduction de la consommation, des sources de bruit, augmentation de la bande passante et durcissement de l'électronique). Une première thèse au L2E (A. Rhouni) a montré la pertinence d'une technologie CMOS pour ce type d'instrumentation. Dans la présente thèse est décrite l'étude menée sur les circuits intégrés soumis à des environnements contraignants liés aux futures missions dans lesquelles ce type d'instrument doit être embarqué (Mission JUICE de l'ESA). Ces contraintes devenant de plus en plus sévères (dose de radiations supérieure à 300krad, température inférieure à 100 Kelvin ...), leur prise en compte dans tout le processus de conception est nécessaire. Une modélisation des effets de ces contraintes sur les composants de la technologie cible de circuits intégrés a été réalisée afin de pouvoir prendre en compte ces effets dès la conception. Enfin, ces modèles ont servi à la conception d'un circuit de lecture d'un magnétomètre à induction pour l'astrophysique.
• Determining the Thickness and the Sub-Structure Details of the Magnetopause from MMS Data
  
  • Manuzzo Roberto
  • Belmont Gérard
  • Rezeau Laurence
  • Califano F.
  , 2017.
• Multi-scale observations of magnetic reconnection: Cluster and MMS measurements of the reconnecting magnetopause at the subsolar region and dusk sector
  
  • Toledo-Redondo Sergio
  • Escoubet C. Philippe
  • Lavraud B.
  • Andre M.
  • Coxon J.
  • Fear R. C.
  • Aunai N.
  • Hwang K.-J.
  • Li W.
  • Fuselier S. A.
  • Giles B. L.
  • Russell C. T.
  • Burch J. L.
  , 2017, 13, pp.SM13D-2401. Magnetic reconnection is a fundamental plasma process that couples the shocked solar wind to the Earth's magnetosphere, allowing the interchange of energy and mass. The X line of magnetic reconnection lies along the magnetopause but its extent and orientation are only partially understood, despite its importance for understanding global solar wind - magnetosphere coupling. We have identified a series of conjunctions between the MMS and Cluster missions where they crossed simultaneously the magnetopause at locations separated by several Earth radii: MMS spacecraft were in the subsolar region while Cluster were in the dusk flank. We identify signatures of reconnection at both spacecraft, allowing us to draw new conclusions about the extent, orientation and time variations of the X line along the magnetopause.
• MMS Observations of Harmonic Electromagnetic Cyclotron Waves
  
  • Usanova M.
  • Ahmadi N.
  • Ergun R.
  • Trattner K. J.
  • Fuselier S. A.
  • Torbert R. B.
  • Mauk B.
  • Le Contel Olivier
  • Giles B. L.
  • Russell C. T.
  • Burch J. L.
  • Strangeway R. J.
  , 2017, 42. Harmonically related electromagnetic ion cyclotron waves with the fundamental frequency near the O cyclotron frequency were observed by the four MMS spacecraft on May 20, 2016. The wave activity was detected by the spacecraft on their inbound passage through the Earth's morning magnetosphere during generally quiet geomagnetic conditions but enhanced solar wind dynamic pressure. It was also associated with an enhancement of energetic H and O ions. The waves are seen in both magnetic and electric fields, formed by over ten higher order harmonics, most pronounced in the electric field. The wave activity lasted for about an hour with some wave packets giving rise to short-lived structures extending from Hz to kHz range. These observations are particularly interesting since they suggest cross-frequency coupling between the lower and higher frequency modes. Further work will focus on examining the nature and role of these waves in the energetic particle dynamics from a theoretical perspective.
• The "Alfvén" proposal for the European Space Agency M5 Mission Call
  
  • Berthomier Matthieu
  • Fazakerley A.
  , 2017, 41, pp.SM41A-2678. The Alfvén mission objective is to elucidate the particle acceleration processes and their consequences for electromagnetic radiation and energy transport in strongly magnetised plasmas. The Earth's Auroral Acceleration Region is a unique laboratory for investigating these processes. The only way to distinguish between the models describing acceleration processes at the heart of Magnetosphere-Ionosphere Coupling is to combine high-time resolution in situ measurements (as pioneered by FAST), multi-point measurements (as pioneered by CLUSTER), and auroral arc imaging in one mission. Charged particle acceleration in strongly magnetized plasmas requires the conversion of electromagnetic energy into magnetic-field-aligned particle kinetic energy. Alfvén will measure for the first time the occurrence and distribution of small scale parallel electric fields in space and time. In order to determine the relative efficiency of the different conversion mechanisms, Alfvén will also measure the corresponding particle energy fluxes locally and into the aurora. Alfvén will discover how electromagnetic radiation is generated in the acceleration region and how it escapes. Alfvén will make key measurements of Auroral Kilometric Radiation needed to test competing models of wave generation, mode conversion and escape from their source region. These will reveal the mode conversion processes and which information is ultimately carried by the polarization of radio waves reaching free space. Alfvén will discover the global impact of particle acceleration on the dynamic coupling between a magnetized object and its plasma environment. Dual spacecraft measurements offer the unique opportunity to unambiguously determine which part of the energy flowing into the ionosphere is eventually dissipated in this collisional plasma and which part is transmitted to outflowing ions of ionospheric origin. The Alfvén mission design involves use of two simple identical spacecraft, a comprehensive suite of inter-calibrated particles and fields instruments, cutting edge auroral imaging, easily accessible orbits that frequently visit the region of scientific interest and straightforward operations.
• Ion dynamics in the magnetospheric flanks of Mercury
  
  • Aizawa Sae
  • Delcourt Dominique
  • Terada N.
  , 2017, 51, pp.P51G-05. Because of a large velocity shear in the flanks of Mercury's magnetosphere, Kelvin-Helmholtz (KH) instability is expected to develop and to play a role in mass and momentum transport across the magnetopause. Using single particle simulations in field configurations obtained from MHD simulations, we investigate the dynamics of ions in this region. We focus on heavy ions of planetary origin (e.g., Na , K , Mg ) that may be found on either side of the magnetopause, due to the ionization of exospheric neutrals. Because characteristic spatial and temporal scales of KH instability at Mercury are comparable to or smaller than typical ion scales, we show that under such conditions the guiding center approximation is invalid and that planetary ions may be transported in a non-adiabatic (magnetic moment violation) manner. In this study, we focus on the effect of the electric field that develops within KH vortices. We show that the intensification rather than the change of orientation of this electric field is responsible for large (up to hundreds of eVs or a few keVs) energization of heavy planetary ions. This energization occurs systematically for particles with low initial energies in the perpendicular direction, the energy realized being of the order of the energy corresponding to the maximum ExB drift speed, εmax, in a like manner to a pickup ion process. It is also found that particles that have initial energies comparable to εmax may be decelerated depending upon gyration phase. Finally, we find that particles with initial perpendicular energies much larger than εmax are little affected during transport through KH vortices. We suggest that the development of KH instabilities in Mercury's magnetospheric flanks may lead to significant ion energization and pitch angle diffusion, and may thus play a prominent role in plasma mixing at the magnetopause.
• Electrostatic Turbulence and Anomalous Effects in Reconnection Diffusion Region
  
  • Khotyaintsev Y. V.
  • Graham D. B.
  • Norgren C.
  • Vaivads A.
  • Li W.
  • Divin A. V.
  • Andre M.
  • Markidis S.
  • Lindqvist P. A.
  • Peng I. B.
  • Argall M. R.
  • Ergun R.
  • Le Contel Olivier
  • Magnes W.
  • Russell C. T.
  • Giles B. L.
  • Torbert R. B.
  • Burch J. L.
  , 2017, 11. Magnetic reconnection is a fundamental process whereby microscopicplasma processes cause macroscopic changes in magnetic field topology,so that initially separated plasmas become magnetically connected.Waves can produce particle diffusion, and anomalous resistivity, aswell as heat the plasma and accelerate plasma particles, all of whichcan impact ongoing reconnection. We report electrostatic turbulencedeveloping within the diffusion region of asymmetric magnetopausereconnection using observations by the Magnetospheric Multiscalemission and large-scale particle-in-cell simulations, and characterizeanomalous effects and plasma heating within the diffusion region. Ourobservations demonstrate that electrostatic turbulence plays animportant role in the electron-scale physics of asymmetricreconnection.
• Fire Hose Instability in the Multiple Magnetic Reconnection
  
  • Alexandrova Alexandra
  • Retinò Alessandro
  • Divin A. V.
  • Le Contel Olivier
  • Matteini L.
  • Breuillard Hugo
  • Deca J.
  • Catapano F.
  • Cozzani Giulia
  • Nakamura R.
  • Panov E. V.
  • Vörös Z.
  , 2017, 2017, pp.SM11C-2321. We present observations of multiple reconnection in the Earth's magnetotail. In particular, we observe an ion temperature anisotropy characterized by large temperature along the magnetic field, between the two active X-lines. The anisotropy is associated with right-hand polarized waves at frequencies lower than the ion cyclotron frequency and propagating obliquely to the background magnetic field. We show that the observed anisotropy and the wave properties are consistent with linear kinetic theory of fire hose instability. The observations are in agreement with the particle-in-cell simulations of multiple reconnection. The results suggest that the fire hose instability can develop during multiple reconnection as a consequence of the ion parallel anisotropy that is produced by counter-streaming ions trapped between the X-lines.
• Reconnection properties in Kelvin-Helmholtz instabilities
  
  • Vernisse Y.
  • Lavraud B.
  • Eriksson S.
  • Gershman D. J.
  • Dorelli J. C.
  • Pollock C. J.
  • Giles B. L.
  • Aunai N.
  • Avanov L. A.
  • Burch J. L.
  • Chandler Michael O.
  • Coffey V. N.
  • Dargent Jérémy
  • Ergun R.
  • Farrugia C. J.
  • Genot V. N.
  • Graham Daniel B.
  • Hasegawa H.
  • Jacquey C.
  • Kacem I.
  • Khotyaintsev Y. V.
  • Li W.
  • Magnes W.
  • Marchaudon A.
  • Moore T. E.
  • Paterson W. R.
  • Penou E.
  • Phan T.
  • Retinò Alessandro
  • Schwartz S. J.
  • Saito Y.
  • Sauvaud J.-A.
  • Schiff C.
  • Torbert R. B.
  • Wilder F. D.
  • Yokota S.
  , 2017, 2017, pp.SM13B-2377. Kelvin-Helmholtz instabilities are particular laboratories to study strong guide field reconnection processes. In particular, unlike the usual dayside magnetopause, the conditions across the magnetopause in KH vortices are quasi-symmetric, with low differences in beta and magnetic shear angle. We study these properties by means of statistical analysis of the high-resolution data of the Magnetospheric Multiscale mission. Several events of Kelvin-Helmholtz instabilities pas the terminator plane and a long lasting dayside instabilities event where used in order to produce this statistical analysis. Early results present a consistency between the data and the theory. In addition, the results emphasize the importance of the thickness of the magnetopause as a driver of magnetic reconnection in low magnetic shear events.
• The « 3-D donut » electrostatic analyzer for millisecond timescale electron measurements in the solar wind
  
  • Berthomier Matthieu
  • Techer Jean-Denis
  , 2017, 44, pp.SH44A-05. Understanding electron acceleration mechanisms in planetary magnetospheres or energy dissipation at electron scale in the solar wind requires fast measurement of electron distribution functions on a millisecond time scale. Still, since the beginning of space age, the instantaneous field of view of plasma spectrometers is limited to a few degrees around their viewing plane. In Earth's magnetosphere, the NASA MMS spacecraft use 8 state-of-the-art sensor heads to reach a time resolution of 30 milliseconds. This costly strategy in terms of mass and power consumption can hardly be extended to the next generation of constellation missions that would use a large number of small-satellites. In the solar wind, using the same sensor heads, the ESA THOR mission is expected to reach the 5ms timescale in the thermal energy range, up to 100eV. We present the « 3-D donut » electrostatic analyzer concept that can change the game for future space missions because of its instantaneous hemispheric field of view. A set of 2 sensors is sufficient to cover all directions over a wide range of energy, e.g. up to 1-2keV in the solar wind, which covers both thermal and supra-thermal particles. In addition, its high sensitivity compared to state of the art instruments opens the possibility of millisecond time scale measurements in space plasmas. With CNES support, we developed a high fidelity prototype (a quarter of the full « 3-D donut » analyzer) that includes all electronic sub-systems. The prototype weights less than a kilogram. The key building block of the instrument is an imaging detector that uses EASIC, a low-power front-end electronics that will fly on the ESA Solar Orbiter and on the NASA Parker Solar Probe missions.
• Study of Plasma Waves Observed onboard Rosetta in the 67P/ChuryumovGerasimenko Comet Environment Using High Time Resolution Density Data Inferred from RPC-MIP and RPC-LAP Cross-calibration
  
  • Breuillard Hugo
  • Henri P.
  • Vallieres X.
  • Eriksson A. I.
  • Odelstad E.
  • Johansson F. L.
  • Richter I.
  • Goetz C.
  • Wattieaux Gaëtan
  • Tsurutani B. T.
  • Hajra R.
  • Le Contel Olivier
  , 2017, 51, pp.P51D-2631. During two years, the groundbreaking ESA/Rosetta mission was able to escort comet 67P where previous cometary missions were only limited to flybys. This enabled for the first time to make in-situ measurements of the evolution of a comet's plasma environment. The density and temperature measured by Rosetta are derived from RPC-Mutual Impedance Probe (MIP) and RPC-Langmuir Probe (LAP). On one hand, low time resolution electron density are calculated using the plasma frequency extracted from the MIP mutual impedance spectra. On the other hand, high time resolution density fluctuations are estimated from the spacecraft potential measured by LAP. In this study, using a simple spacecraft charging model, we perform a cross-calibration of MIP plasma density and LAP spacecraft potential variations to obtain high time resolution measurements of the electron density. These results are also used to constrain the electron temperature. Then we make use of these new dataset, together with RPC-MAG magnetic field measurements, to investigate for the first time the compressibility and the correlations between plasma and magnetic field variations, for both singing comet waves and steepened waves observed, respectively during low and high cometary outgassing activity, in the plasma environment of comet 67P.
• Kinetic Studies of Thin Current Sheets at Magnetosheath Jets
  
  • Eriksson E.
  • Vaivads A.
  • Khotyaintsev Y. V.
  • Graham D. B.
  • Yordanova E.
  • Hietala H.
  • Markidis S.
  • Giles B. L.
  • André M.
  • Russell C. T.
  • Le Contel Olivier
  • Burch J. L.
  , 2017, 11. In near-Earth space one of the most turbulent plasma environments is the magnetosheath (MSH) downstream of the quasi-parallel shock. The particle acceleration and plasma thermalization processes there are still not fully understood. Regions of strong localized currents are believed to play a key role in those processes. The Magnetospheric Multiscale (MMS) mission has sufficiently high cadence to study these processes in detail. We present details of studies of two different events that contain strong current regions inside the MSH downstream of the quasi-parallel shock. In both cases the shape of the current region is in the form of a sheet, however they show internal 3D structure on the scale of the spacecraft separation (15 and 20 km, respectively). Both current sheets have a normal magnetic field component different from zero indicating that the regions at the different sides of the current sheets are magnetically connected. Both current sheets are boundaries between two different plasma regions. Furthermore, both current sheets are observed at MSH jets. These jets are characterized by localized dynamic pressure being larger than the solar wind dynamic pressure. One current sheet does not seem to be reconnecting while the other shows reconnection signatures. Inside the non-reconnecting current sheet we observe locally accelerated electron beams along the magnetic field. At energies above the beam energy we observe a loss cone consistent with part of the hot MSH-like electrons escaping into the colder solar wind-like plasma. This suggests that the acceleration process within this current sheet is similar to the one that occurs at the bow shock, where electron beams and loss cones are also observed. Therefore, we conclude that electron beams observed in the MSH do not have to originate from the bow shock, but can also be generated locally inside the MSH. The reconnecting current sheet also shows signs of thermalization and electron acceleration processes that are discussed in detail.
• MMS Observations of Protons and Heavy Ions Acceleration at Plasma Jet Fronts
  
  • Catapano F.
  • Retinò Alessandro
  • Zimbardo G.
  • Cozzani Giulia
  • Breuillard Hugo
  • Le Contel Olivier
  • Alexandrova Alexandra
  • Mirioni Laurent
  • Cohen I. J.
  • Turner D. L.
  • Perri S.
  • Greco A.
  • Mauk B.
  • Torbert R. B.
  • Russell C. T.
  • Khotyaintsev Y. V.
  • Lindqvist P. A.
  • Ergun R.
  • Giles B. L.
  • Fuselier S. A.
  • Moore T. E.
  • Burch J. L.
  , 2017, pp.SM22B-08. Plasma jet fronts in the Earth's magnetotail are kinetic-scale boundaries separating hot fast plasma jets, generally attributed to reconnection outflows, from colder ambient plasma. Jet fronts are typically associated with a sharp increase of the vertical component of the magnetic field Bz, an increase of the plasma temperature and a drop of plasma density. Spacecraft observations and numerical simulations indicate that jet fronts are sites of major ion acceleration. The exact acceleration mechanisms as well as the dependence of such mechanisms on ion composition are not fully understood, yet. Recent high-resolution measurements of ion distribution functions in the magnetotail allow for the first time to study the acceleration mechanisms in detail. Here, we show several examples of jet fronts and discuss ion acceleration therein. We show fronts that propagate in the mid-tail magnetotail both as isolated laminar boundaries and as multiple boundaries embedded in strong magnetic fluctuations and turbulence. We also show fronts in the near-Earth jet braking region, where they interact with the dipolar magnetic field and are significantly decelerated/diverted. Finally, we study the acceleration of different ion species (H , He , O ) at different types of fronts and we discuss possible different acceleration mechanisms and how they depend on the ion species.
• Estimation of the Chorus Group Velocity from THEMIS Wave Observations
  
  • Taubenschuss U.
  • Santolik O.
  • Le Contel Olivier
  • Bonnell J. W.
  , 2017, 51. Chorus waves can play an important role for the energy budget of Earth's radiation belts. Some nonlinear analytical models describing chorus generation and energy transfer between waves and energetic electrons need the wave group velocity as a model parameter. The group velocity is the propagation velocity of the amplitude envelope of a wave packet. Theoretically, its absolute value is derived from a derivative of frequency (om) with respect to wave number (k), i.e. v_g = dₒm/dₖ. It is difficult, if not impossible, to infer this quantity directly from electromagnetic wave observations in space. We propose to take a "detour" over the Poynting velocity (vₚ), which is related to the Poynting vector (S) and the average wave energy density (W). Both, S and W can be inferred from a combination of electric and magnetic signals measured by triaxial antenna systems. We demonstrate the concept and show first results from an application to chorus observations made by the THEMIS spacecraft.
• Multi-scale multi-point observation of dipolarization in the near-Earth's magnetotail
  
  • Nakamura R.
  • Varsani A.
  • Genestreti K.
  • Nakamura T.
  • Baumjohann W.
  • Birn Joachim
  • Le Contel Olivier
  • Nagai T.
  , 2017, 43. We report on evolution of the dipolarization in the near-Earth plasma sheet during two intense substorms based on observations when the four spacecraft of the Magnetospheric Multiscale (MMS) together with GOES and Geotail were located in the near Earth magnetotail. These multiple spacecraft together with the ground-based magnetogram enabled to obtain the location of the large- scale substorm current wedge (SCW) and overall changes in the plasma sheet configuration. MMS was located in the southern hemisphere at the outer plasma sheet and observed fast flow disturbances associated with dipolarizations. The high time-resolution measurements from MMS enable us to detect the rapid motion of the field structures and the flow disturbances separately and to resolve signatures below the ion-scales. We found small-scale transient field-aligned current sheets associated with upward streaming cold plasmas and Hall-current layers in the fast flow shear region. Observations of these current structures are compared with simulations of reconnection jets.
• Thin current sheets observation by MMS during a near-Earth's magnetotail reconnection event
  
  • Nakamura R.
  • Varsani A.
  • Nakamura T.
  • Genestreti K.
  • Plaschke F.
  • Baumjohann W.
  • Nagai T.
  • Burch J. L.
  • Cohen I. J.
  • Ergun R.
  • Fuselier S. A.
  • Giles B. L.
  • Le Contel Olivier
  • Lindqvist P. A.
  • Magnes W.
  • Schwartz S. J.
  • Strangeway R. J.
  • Torbert R. B.
  , 2017, 22. During summer 2017, the four spacecraft of the Magnetospheric Multiscale (MMS) mission traversed the nightside magnetotail current sheet at an apogee of 25 RE. They detected a number of flow reversal events suggestive of the passage of the reconnection current sheet. Due to the mission's unprecedented high-time resolution and spatial separation well below the ion scales, structure of thin current sheets is well resolved both with plasma and field measurements. In this study we examine the detailed structure of thin current sheets during a flow reversal event from tailward flow to Earthward flow, when MMS crossed the center of the current sheet . We investigate the changes in the structure of the thin current sheet relative to the X-point based on multi-point analysis. We determine the motion and strength of the current sheet from curlometer calculations comparing these with currents obtained from the particle data. The observed structures of these current sheets are also compared with simulations.
• Generation of Electron Whistler Waves at the Mirror Mode Magnetic Holes: MMS Observations and PIC Simulation
  
  • Ahmadi N.
  • Wilder F. D.
  • Usanova M.
  • Ergun R.
  • Argall M. R.
  • Goodrich K. A.
  • Eriksson S.
  • Germaschewski K.
  • Torbert R. B.
  • Lindqvist P. A.
  • Le Contel Olivier
  • Khotyaintsev Y. V.
  • Strangeway R. J.
  • Schwartz S. J.
  • Giles B. L.
  • Burch J. L.
  , 2017, 24. The Magnetospheric Multiscale (MMS) mission observed electron whistler waves at the center and at the gradients of magnetic holes on the dayside magnetosheath. The magnetic holes are nonlinear mirror structures which are anti-correlated with particle density. We used expanding box Particle-in-cell simulations and produced the mirror instability magnetic holes. We show that the electron whistler waves can be generated at the gradients and the center of magnetic holes in our simulations which is in agreement with MMS observations. At the nonlinear regime of mirror instability, the proton and electron temperature anisotropy are anti-correlated with the magnetic hole. The plasma is unstable to electron whistler waves at the minimum of the magnetic field structures. In the saturation regime of mirror instability, when magnetic holes are dominant, electron temperature anisotropy develops at the edges of the magnetic holes and electrons become isotropic at the magnetic field minimum. We investigate the possible mechanism for enhancing the electron temperature anisotropy and analyze the electron pitch angle distributions and electron distribution functions in our simulations and compare it with MMS observations.