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AIM: Large amplitude narrowband obliquely propagating whistler-mode waves at frequencies of ~0.2 fce (electron cyclotron frequency) are commonly observed at 1 AU, and are most consistent with the whistler heat flux fan instability. We want to determine whether similar whistler-mode waves occur inside 0.2 AU, and how their properties compare to those at 1 AU. METHODS: We utilize the waveform capture data from the Parker Solar Probe Fields instrument to develop a data base of narrowband whistler waves. The SWEAP instrument, in conjunction with the quasi-thermal noise measurement form Fields, provides the electron heat flux, beta, and other electron parameters. RESULTS: Parker Solar Probe observations inside ~0.3 AU show that the waves are more intermittent than at 1 AU, and are often interspersed with electrostatic whistler/Bernstein waves at higher frequencies. This is likely due to the more variable solar wind observed closer to the Sun. The whistlers usually occur within regions when the magnetic field is more variable and often with small increases in the solar wind speed. The near-sun whistler-mode waves are also narrowband and large amplitude, and associated with beta greater than 1. Wave angles are sometimes highly oblique (near the resonance cone), but angles have been determined for only a small fraction of the events. The association with heat flux and beta is generally consistent with the whistler fan instability although there are intervals where the heat flux is significantly lower than the instability limit. Strong scattering of strahl energy electrons is seen in association with the waves, providing evidence that the waves regulate the electron heat flux..

We present the first evidence of sub-proton-scale magnetic holes in the Venusian magnetosheath. Depressions in magnetic field strength, commonly referred to as magnetic holes, are observed ubiquitously in space plasmas. Magnetic holes with spatial scales larger than the local proton gyroradius (ρ) are usually attributed to the mirror instability. Those smaller than or on the order of ρ, termed "sub-proton-scale" magnetic holes, are likely supported by electron currents vortices, rotating perpendicular to the ambient magnetic field. While there are numerous accounts of sub-proton-scale magnetic holes within the Earth's magnetosphere, there are no reported observations in other space plasma environments. During Parker Solar Probe's first Venus Gravity Assist, the spacecraft crossed the planet's bow shock and subsequently observed the Venusian magnetosheath. The FIELDS instrument suite onboard the spacecraft achieved magnetic and electric field measurements of magnetic hole structures. The electric field associated with magnetic depressions are consistent with electron current vortices with amplitudes on the order of 1μA/m2. This observation suggests sub-proton-scale magnetic holes are signatures of a universal process in space plasmas.

During its first 174 days at heliocentric distances less than 0.5 au, Parker Solar Probe encountered hundreds of narrowband electromagnetic wave bursts in the whistler frequency range. These events typically lasted on the order of minutes, although narrowband storms lasting longer than one hour were observed as well. The FIELDS instrument measures two components of the electric field and two components of the magnetic field of each wave - here we describe an analysis method for determining polarization and propagation direction with this limited information. The waves are shown to be circularly polarized and to rotate in a right-handed sense around the background magnetic field, confirming their identification as whistlers. Their propagation directions are shown to be approximately collinear with the background magnetic field, although ambiguity remains as to whether they are anti-parallel or parallel. Future data will allow the analysis method to resolve this ambiguity, which is a critical step toward identifying Doppler-shifted cyclotron resonances between the waves and strahl electrons.

Over the last two years, and six near-Sun encounter orbits, the Parker Solar Probe spacecraft has provided the first in-situ observations of interplanetary dust closer than ~0.3 AU from the Sun. Dust is detected by the FIELDS instrument via impact ionization and subsequent perturbations to the plasma environment close to the spacecraft. FIELDS observations yield count rates, impact amplitudes, and impact directionality information. Interpreting these data to arrive at new understanding of dust dynamics of the inner heliosphere requires combining state-of-the-art modeling and theory with detailed FIELDS instrument knowledge. In this talk, we describe recent results related to the near-Sun dust environment, including: bounding the location and rate of beta-meteoroid production, the interaction of debris streams with near-Sun dust, the density of near-circular dust near the Sun, hints of dust sublimation close to the Sun, and the effects of instrument operation on dust impact detection. The Parker Solar Probe FIELDS data provide an in-situ window into stellar processing of dust in the near-Sun plasma environment, and we are beginning to understand what we see.

The induced magnetosphere of Venus presents an obstacle to the solar wind. At the flow-obstacle interface, plasma is slowed, deflected, and heated. Based on observations of Earth's bow shock and magnetosheath, kinetic plasma processes are expected to play an important role in these dynamics at Venus. However, these processes have gone largely undetected at Venus due to the small number of measurements at sufficiently high sampling cadences. Using data from a Parker Solar Probe encounter with Venus, this study demonstrates the existence of kinetic-scale electric field structures, including plasma double layers, at the outer edge of the Venusian magnetosheath. Many of the double layers have signatures of developed two-stream instabilities and phase space holes. Double layer spatial scales are consistent with those reported at Earth. Estimated potential drops are similar to the electron temperature change across the bow shock, consistent with double layers driven by mixing of inhomogeneous plasmas at the magnetosheath boundary. A large number of distinct double layers are found in few burst captures, implying that double layers, and the waves that they drive, have higher amplitudes relative to other high frequency bow shock and magnetosheath waves at Venus as compared to Earth. These are the first direct observations of plasma double layers beyond near-Earth space, demonstrating that kinetic plasma processes are active in diverse plasma environments, and can be identified when high cadence observations are available.

著者人数: 48名, Accepted: 2017-10-10, 資料番号: SA1170207000

Interplanetary Dust Particles (IDPs) consist of the pummeled remnants of asteroids and comets, trapped in high velocity orbits around the Sun. When these fast moving particles (>20km/s) collide with a spacecraft, they explode into a plasma cloud. These events cause voltage spikes in electric field instrument data on missions such as Voyager, Cassini, STEREO, MAVEN, WIND and Parker Solar Probe. When a dust impact occurs, the electric field antennas register a voltage spike with the highest amplitude on the antenna nearest to the impact. Prior to the August 2018 launch of Parker Solar Probe, IDP within 0.3 AU of the Sun had never been measured in-situ, and predictions for its distribution vary by orders of magnitude. Now that Parker Solar Probe data are available, we are developing algorithms to identify dust impacts and to observe IDP at distances closer to the Sun than ever before. Dust impacts have been successfully identified in different electric field instrument data products using independent detection algorithms. This provides good evidence that the identification method is reliable. The first two orbits of Parker Solar Probe data were examined and dust impact data were compared with a model which predicts the flux and direction of IDP close the the Sun. The dust populations considered in the model include particles shed by Jupiter-family comets and asteroids. Specifically, the model predicts the most likely direction of dust impacts on Parker Solar Probe. By comparing the amplitudes of dust impacts on each antenna, we used the data to determine the direction of observed impacts. During closest approach to the Sun, the model predicts that most impacts will be on the ram side of the spacecraft. The data show that antenna V4, located in the ram direction, does see the most high-amplitude impact signatures near perihelion. This, and other comparisons convey good agreement between the model and data.

During its first solar encounters, the Parker Solar Probe mission discovered that the near-Sun solar wind is teeming with plasma waves and instabilities. One prominent plasma wave type appears Sunward of 50 solar radii, where intervals of significant plasma wave power near the electron cyclotron frequency (fce) are detected. Most of this wave power is concentrated near 0.7 fce, with strong harmonics extending above fce often observed. At least two distinct concurrent wave modes are identified (electron Bernstein waves and electrostatic whistler-mode waves). Wave intervals range in duration from a few seconds to hours. The amplitude and occurrence of these near-fce waves increases significantly with decreasing distance to the Sun, suggesting that they play an important role in the evolution of electron populations in the near-Sun plasma environment. Correlations are observed between the occurrence of these waves and properties of the population of electrons escaping the solar corona (the strahl), implying that these waves play a role in regulating the heat flux carried by these electrons. Finally, the occurrence of these near-fce waves is strongly correlated with specific solar wind magnetic field configurations and the level of magnetic turbulence at the location of the spacecraft, offering new insight into the macro-scale structure of the near-Sun solar wind.

The Parker Solar Probe (PSP) mission serves as an opportunity to understand the connection between turbulent dissipation and particle heating and solar wind acceleration. Though inherently connected to plasma kinetic scales, the physical dynamics and in-situ observational signatures of dissipation typically depend on macroscale properties of the mean magnetic field. In order to observe anisotropic characteristics of magnetic field fluctuations at inertial and dissipation scales, a merged dataset consisting of fluxgate and search-coil magnetometer measurements has been developed for PSP/FIELDS. This work reports first observations from the PSP merged magnetic field data, focusing on anisotropic properties of dissipation scale phenomena: coherent electromagnetic ion cyclotron waves, spectral power distributions, intermittency, and magnetic helicity. Analyzing these observational signatures at kinetic scales will largely constrain the physical processes responsible for coronal heating and solar wind acceleration.

The NASA Parker Solar Probe mission has made its first set of solar encounters at 35.7 solar radii. The first encounters reveal a solar wind rich in instabilities and kinetic physics. The FIELDS instrument on PSP measures copious, intermittent burstsof electron plasma (Langmuir) waves throughout Encounters 1 and 2. These waves are purely electrostatic, to the sensitivity of the measurement, and have wave (electric field) vectors aligned with the solar wind magnetic field. We suggest that these Langmuir waves are generated on a Landau resonance by electron beams with beam speeds of 5-10 v_th. The duration of the bursts suggests beams of ~100-10000 km across the magnetic field. We examine the statistics and occurence conditions. Langmuir waves during Encounter 1 are definitively not associated with solar type III radio bursts. FIELDS also measures signatures of ion cyclotron waves and kinetic scale turbulence, with indications for energy exchange processes in the inner corona.

Measurements from the FIELDS and SWEAP instrument suites on Parker Solar Probe (PSP) are presented in order to investigate disparate aspects of the large scale structure of the solar wind and its associated Poynting and ion energy flux. The observations are obtained during a 30 day period beginning 10/31/2018 over radial distances from 36 to 130 Rs . We focus primarily on phenomena over time scales of >1 minutes, although, we do include some discussion of the contribution of short duration magnetic field, velocity, and Poynting flux spikes (switchbacks) (Bale et al., 2019, Mozer et al. this session) to longer term averages of ion energy flux and Poynting flux. Some of the observations include 1) PSP observed three fast solar wind streams with enhanced ion energy flux and Poynting flux falling with distance between 35 and 130 Rs over the 30 day period. These same streams were observed at 1 AU providing one of the largest baseline measurements of high-speed streams. 2) In a different study near perihelion, because of shifts between retrograde and prograde motion of the spacecraft relative to the solar surface, PSP explored features on the sun at the same Carrington longitude as many as three times. This leads to the observation that the reported CMEs observation on 10/31 and 11/11 occur at the same longitude of 327o and are arguably manifestations of the same long-term " evolving structure'. 3) Finally, with regard to energy flow, PSP also has phases of its trajectory lasting ~2 days when it moves ~6 Rs (38 to 46 Rs) in radial distance while moving less than 10 in longitude. These orbital configurations have been exploited to provide estimates of the average Poynting flux and ion energy flux over radial distance. When the Poynting flux (Sr) from 1 Hz to >30 minutes is averaged over 0.5 hours, the radial Poynting flux (~2) is ~ an order of magnitude smaller than the steady state ion energy flux (8 mW/m2) and it's associated spatial or temporal variations. Evaluating the entire data base, the observed energy fluxes decrease strongly with radial distance with a major effect being the radial expansion of the solar wind. To model this expansion, we normalize Poynting flux as Sr(R/Rs)2 and also Sr(Br(Rs/Br(R) (analogous to cross helicity) and similarly normalize ion energy flux, and (as yet) find no obvious systematic dependence on radial distance.

The Poynting flux, measured on the Parker Solar Probe during 10 days surrounding the perihelion pass on April 4, 2019, was large (~20,000 μwatts/m2) at 35 solar radii and nearly zero before and after perihelion at 50 solar radii. Its spatial divergence means that electromagnetic energy was converted to plasma energy that heated and accelerated the solar wind. Because the Poynting flux, which is electromagnetic energy flow, was comparable in magnitude to the kinetic energy flow, 0.5nmv3, near perihelion, the Poynting flux was adequate for performing this acceleration task. Properties of the MHD waves that comprised the Poynting flux are discussed, including their correlation with magnetic field switchbacks.

In order for the Parker Solar Probe (PSP) mission to study the solar corona, it will fly closer to the sun than any spacecraft ever has by performing seven gravity assists at Venus. These gravity assists provide a rare opportunity to study the induced magnetosphere and solar-wind interaction at Venus using the plasma instrumentation aboard PSP. Venus's upper atmosphere hosts several atomic species such as hydrogen, helium, oxygen, carbon, and argon, some of which are energized in the upper atmosphere to escape energies or ionized and carried away from the planet. What is special about Venus, as opposed to Mars, is that virtually all significant present-day atmospheric escape of heavy constituents is in the form of ions. Using the Fields experiment (FIELDS) and Solar Wind Electrons Alphas and Protons Investigation (SWEAP), we will present plasma observations from the first PSP Venus gravity assist, including the first in-situ electric field observations to ever have been measured at Venus. We will also use the solar wind measurements as initial inputs into a magnetohydrodynamic (MHD) model and present a global picture of the induced Venusian magnetosphere and the subsequent ion precipitation, escape, and magnetic topology throughout the first flyby. Finally, we will compare the PSP Venus flyby during the deep minimum of solar cycle 24 to previous observations downtail with Venus Express and Pioneer Venus Orbiter.

Convection and rotation drive the solar dynamo and, ultimately, provide the mechanical energy flux required to heat the solar corona and accelerate the solar wind. However, the way in which energy is then dissipated to heat the corona and wind are not well understood. Some energization models invoke non-thermal energy flux imparted by plasma Alfvén waves, while others rely on a carpet of small nano-flares as energy input, however these models have been unconstrained by direct measurements of the solar wind near its origin. Here we use in situ measurements from the FIELDS instrument suite during the first solar encounter (E1) at 35.7 solar radii (Rs) of the NASA Parker Solar Probe (PSP) mission to reveal the magnetic structure and kinetics of slow Alfvénic solar wind emerging from a small, equatorial coronal hole. Our measurements show that, at solar minimum, the slow wind can escape from above the low-lying, complex magnetic structures of the equatorial streamer belt, carrying a magnetic field that is highly dynamic, exhibiting polarity reversals on timescales from seconds to hours. These rapidly oscillating field structures are associated with clustered radial jets of plasma in which the energy flux is dramatically enhanced and turbulence levels are higher. Time intervals between groups of jets indicate a solar wind that is steady with a mostly radial magnetic field and relatively low levels of Alfvénic turbulent fluctuations. This 'quiet' wind however shows clear signatures of plasma micro-instabilities associated with ion and electron beams and velocity-space structure.

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著者人数: 39名, Accepted: 2016-05-13, 資料番号: SA1160088000

著者人数: 28名, Accepted: 2016-05-09, 資料番号: SA1160079000

著者人数: 50名, Accepted: 2017-11-21, 資料番号: SA1170269000

International audience; 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.

International audience; 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.

The Magnetospheric Multiscale mission is employed to examine intense Poynting flux directed along the background magnetic field toward Earth, which reaches amplitudes of nearly 2 mW/m(2). The event is located within the plasma sheet but likely near the boundary at a geocentric distance of 9 RE in association with bulk flow signatures. The fluctuations have wavelengths perpendicular to the magnetic field of 124-264 km (compared to an ion gyroradius of 280 km), consistent with highly kinetic Alfven waves. While the wave vector remains highly perpendicular to the magnetic field, there is substantial variation of the direction in the perpendicular plane. The field-aligned Poynting flux may be associated with kinetic Alfven waves released along the separatrix by magnetotail reconnection and/or the radiation of waves excited by bursty bulk flow braking and may provide a means through which energy released by magnetic reconnection is transferred to the auroral region.

International audience; Observations of magnetic reconnection at Earth's magnetopause often display asymmetric structures that are accompanied by strong magnetic field (B) fluctuations and large-amplitude parallel electric fields (E||). The B turbulence is most intense at frequencies above the ion cyclotron frequency and below the lower hybrid frequency. The B fluctuations are consistent with a thin, oscillating current sheet that is corrugated along the electron flow direction (along the X line), which is a type of electromagnetic drift wave. Near the X line, electron flow is primarily due to a Hall electric field, which diverts ion flow in asymmetric reconnection and accompanies the instability. Importantly, the drift waves appear to drive strong parallel currents which, in turn, generate large-amplitude ( 100 mV/m) E|| in the form of nonlinear waves and structures. These observations suggest that turbulence may be common in asymmetric reconnection, penetrate into the electron diffusion region, and possibly influence the magnetic reconnection process.

International audience; We show observations of whistler mode waves in both the low-latitude boundary layer (LLBL) and on closed magnetospheric field lines during a crossing of the dayside reconnecting magnetopause by the Magnetospheric Multiscale (MMS) mission on 11 October 2015. The whistlers in the LLBL were on the electron edge of the magnetospheric separatrix and exhibited high propagation angles with respect to the background field, approaching 40°, with bursty and nonlinear parallel electric field signatures. The whistlers in the closed magnetosphere had Poynting flux that was more field aligned. Comparing the reduced electron distributions for each event, the magnetospheric whistlers appear to be consistent with anisotropy-driven waves, while the distribution in the LLBL case includes anisotropic backward resonant electrons and a forward resonant beam at near half the electron-Alfvén speed. Results are compared with the previously published observations by MMS on 19 September 2015 of LLBL whistler waves. The observations suggest that whistlers in the LLBL can be both beam and anisotropy driven, and the relative contribution of each might depend on the distance from the X line.

International audience; We analyze two ion scale dipolarization fronts associated with field-aligned currents detected by the Magnetospheric Multiscale mission during a large substorm on 10 August 2016. The first event corresponds to a fast dawnward flow with an antiparallel current and could be generated by the wake of a previous fast earthward flow. It is associated with intense lower hybrid drift waves detected at the front and propagating dawnward with a perpendicular phase speed close to the electric drift and the ion thermal velocity. The second event corresponds to a flow reversal: from southwward/dawnward to northward/duskward associated with a parallel current consistent with a brief expansion of the plasma sheet before the front crossing and with a smaller lower hybrid drift wave activity. Electromagnetic electron phase-space holes are detected near these low-frequency drift waves during both events. The drift waves could accelerate electrons parallel to the magnetic field and produce the parallel electron drift needed to generate the electron holes. Yet we cannot rule out the possibility that the drift waves are produced by the antiparallel current associated with the fast flows, leaving the source for the electron holes unexplained.

We report the observations of an electron vortex magnetic hole corresponding to a new type of coherent structures in the magnetosheath turbulent plasma using the Magnetospheric Multiscale (MMS) mission data. The magnetic hole is characterized by a magnetic depression, a density peak, a total electron temperature increase (with a parallel temperature decrease but a perpendicular temperature increase), and strong currents carried by the electrons. The current has a dip in the center of the magnetic hole and a peak in the outer region of the magnetic hole. The estimated size of the magnetic hole is about 0.23 \r{ho}i (~ 30 \r{ho}e) in the circular cross-section perpendicular to its axis, where \r{ho}i and \r{ho}e are respectively the proton and electron gyroradius. There are no clear enhancement seen in high energy electron fluxes, but an enhancement in the perpendicular electron fluxes at ~ 90{\deg} pitch angles inside the magnetic hole is seen, implying that the electron are trapped within it. The variations of the electron velocity components Vem and Ven suggest that an electron vortex is formed by trapping electrons inside the magnetic hole in the circular cross-section (in the M-N plane). These observations demonstrate the existence of a new type of coherent structures behaving as an electron vortex magnetic hole in turbulent space plasmas as predicted by recent kinetic simulations., Comment: 19 pages, 4 figures

International audience; Previous observations of the terrestrial bow shock have frequently shown large-amplitude fluctuations in the parallel electric field. These parallel electric fields are seen as both nonlinear solitary structures, such as double layers and electron phase-space holes, and short-wavelength waves, which can reach amplitudes greater than 100 mV/m. The Magnetospheric Multi-Scale (MMS) Mission has crossed the Earth's bow shock more than 200 times. The parallel electric field signatures observed in these crossings are seen in very discrete packets and evolve over time scales of less than a second, indicating the presence of a wealth of kinetic-scale activity. The high time resolution of the Fast Particle Instrument (FPI) available on MMS offers greater detail of the kinetic-scale physics that occur at bow shocks than ever before, allowing greater insight into the overall effect of these observed electric fields. We present a characterization of these parallel electric fields found in a single bow shock event and how it reflects the kinetic-scale activity that can occur at the terrestrial bow shock.

International audience; Whistler-mode waves have been observed at the subsolar magnetopause in association with magnetic reconnection, including near the electron diffusion region (EDR) and near the separatrices. Observations by the Magnetospheric Multiscale (MMS) mission have shown oblique whistler-mode waves at the electron edge of the reconnection layer that are coincident with time-domain structures such as double layers and electrostatic solitary waves, as well as intense Langmuir oscillations. Additionally, large amplitude non-linear parallel oscillations often coincide with these waves, and may be the result of interactions between the whistler-mode waves and electron-acoustic waves, similar to what has been observed in the radiation belts. We present results of an investigation by MMS into the non-linear evolution of these whistlers and their effects on the local plasma population. Preliminary results suggest that the waves are less common near EDR candidates than on the separatrices and that, via non-linear parallel electric fields, they contribute to direct acceleration of electrons.

International audience; During the first year of the Magnetospheric Multiscale Mission (MMS) there have been multiple observations of large amplitude parallel electric fields, as high as 100 mV/m, associated with magnetic reconnection along the terrestrial magnetopause. These electric fields have been observed as a variety of different wave phenomena and plasma structures. One distinct and rare type of plasma structures are unipolar, high amplitude, parallel electric field pulses which are observed directly adjacent to the electron diffusion region and are thought to represent secondary reconnection. Intense parallel plasma waves are interpreted to be ion acoustic waves, electron acoustic waves or beam mode, indicative of cold plasma mixing. Nonlinear structures commonly associated with Alfvénic turbulence on the magnetospheric side of the magnetopause are also reported. We present examples of these three parallel electric field signatures and examine their possible implications on magnetic reconnection.

International audience; Magnetic reconnection occurs in thin current sheets that form in turbulent plasmas. It leads to particle heating and acceleration and is thought to play an important role for the turbulent dissipation at kinetic scales, energy. However, in situ observations are scarce and the extent of its contribution to turbulent dissipation has yet to be determined. The MMS mission allows us to closely study kinetic-scale intermittent structures that form in turbulent plasma as well as to detect thin reconnecting current sheets and examine their properties. We present the results of MMS observations in the turbulence of the Earth's magnetosheath. We performed a statistical study of small-scale intermittent structures and their role in heating and accelerating electrons. We examined one current sheet in detail which shows evidence of reconnection, focusing on the mechanisms that drive the observed heating and acceleration within it and the role of wave-particle interactions.

International audience; The Magnetospheric MultiScale mission (MMS) has observed several instances of asymmetric reconnection at Earth's magnetopause, where plasma from the magnetosheath encounters that of the magnetosphere. On Earth's dayside, the magnetosphere is often made up of a two-component distribution of cold (<< 10 eV) and hot ( 1 keV) plasma, sometimes including the cold ion plume. Magnetosheath plasma is primarily warm ( 100 eV) post-shock solar wind. Where they meet, magnetopause reconnection alters the magnetic topology such that these two populations are left cohabiting a field line and rapidly mix. There have been several events observed by MMS where the Fast Plasma Instrument (FPI) clearly shows cold ions near the diffusion region impinging upon the warm magnetosheath population. In many of these, we also see patches of strong electrostatic waves parallel to the magnetic field - a smoking gun for rapid mixing via nonlinear processes. Cold ions alone are too slow to create the same waves; solving for roots of a simplified dispersion relation shows the electron population damps out the ion modes. From this, we infer the presence of cold electrons; in one notable case found by Wilder et al. 2016 (in review), they have been observed directly by FPI. Vlasov simulations of plasma mixing for a number of these events closely reproduce the observed electric field signatures. We conclude from numerical analysis and direct MMS observations that cold plasma mixing, including cold electrons, is the primary driver of parallel electrostatic waves observed near the electron diffusion region in asymmetric magnetic reconnection.

©2016. American Geophysical Union. All Rights Reserved.We report observations from the Magnetospheric Multiscale satellites of large-amplitude, parallel, electrostatic waves associated with magnetic reconnection at the Earths magnetopause. The observed waves have parallel electric fields (E||) with amplitudes on the order of 100 mV/m and display nonlinear characteristics that suggest a possible net E||. These waves are observed within the ion diffusion region and adjacent to (within several electron skin depths) the electron diffusion region. They are in or near the magnetosphere side current layer. Simulation results support that the strong electrostatic linear and nonlinear wave activities appear to be driven by a two stream instability, which is a consequence of mixing cold (

著者人数: 39名, Accepted: 2016-05-03, 資料番号: SA1160372000

International audience; In this letter, first observations of ion-scale magnetic island from the Magnetospheric Multiscale mission in the magnetosheath turbulent plasma are presented. The magnetic island is characterized by bipolar variation of magnetic fields with magnetic field compression, strong core field, density depletion, and strong currents dominated by the parallel component to the local magnetic field. The estimated size of magnetic island is about 8 di, where di is the ion inertial length. Distinct particle behaviors and wave activities inside and at the edges of the magnetic island are observed: parallel electron beam accompanied with electrostatic solitary waves and strong electromagnetic lower hybrid drift waves inside the magnetic island and bidirectional electron beams, whistler waves, weak electromagnetic lower hybrid drift waves, and strong broadband electrostatic noise at the edges of the magnetic island. Our observations demonstrate that highly dynamical, strong wave activities and electron-scale physics occur within ion-scale magnetic islands in the magnetosheath turbulent plasma.

International audience; Spatial and high-time-resolution properties of the velocities, magnetic field, and 3-D electric field within plasma turbulence are examined observationally using data from the Magnetospheric Multiscale mission. Observations from a Kelvin-Helmholtz instability (KHI) on the Earth's magnetopause are examined, which both provides a series of repeatable intervals to analyze, giving better statistics, and provides a first look at the properties of turbulence in the KHI. For the first time direct observations of both the high-frequency ion and electron velocity spectra are examined, showing differing ion and electron behavior at kinetic scales. Temporal spectra exhibit power law behavior with changes in slope near the ion gyrofrequency and lower hybrid frequency. The work provides the first observational evidence for turbulent intermittency and anisotropy consistent with quasi two-dimensional turbulence in association with the KHI. The behavior of kinetic-scale intermittency is found to have differences from previous studies of solar wind turbulence, leading to novel insights on the turbulent dynamics in the KHI.

International audience; Dipolarization fronts (DFs), embedded in bursty bulk flows, play a crucial role in Earth's plasma sheet dynamics because the energy input from the solar wind is partly dissipated in their vicinity. This dissipation is in the form of strong low-frequency waves that can heat and accelerate energetic electrons up to the high-latitude plasma sheet. However, the dynamics of DF propagation and associated low-frequency waves in the magnetotail are still under debate due to instrumental limitations and spacecraft separation distances. In May 2015 the Magnetospheric Multiscale (MMS) mission was in a string-of-pearls configuration with an average intersatellite distance of 160 km, which allows us to study in detail the microphysics of DFs. Thus, in this letter we employ MMS data to investigate the properties of dipolarization fronts propagating earthward and associated whistler mode wave emissions. We show that the spatial dynamics of DFs are below the ion gyroradius scale in this region (˜500 km), which can modify the dynamics of ions in the vicinity of the DF (e.g., making their motion nonadiabatic). We also show that whistler wave dynamics have a temporal scale of the order of the ion gyroperiod (a few seconds), indicating that the perpendicular temperature anisotropy can vary on such time scales.

International audience; Plasma jets aka bursty bulk flows play a crucial role in Earth's magnetosphere dynamics, in particular during substorms where they can penetrate down to the geosynchronous orbit. The energy input from the solar wind is partly dissipated in jet fronts (also called dipolarization fronts) in the form of strong whistler waves that can heat and accelerate energetic electrons. The ratio of the energy transported during jets to the substorm energy consumption can reach one third or more due to kinetic-scale phenomena, that are still under debate due to instrumental limitations. The recently-launched Magnetospheric Multiscale (MMS) mission has already detected numerous plasma jet events, and evolves in a tetrahedral configuration (with an average inter- satellite distance of 160 km and unprecedent resolutions up to 16,000 samples/s) that allows to study in detail the microphysics of these phenomena. Thus in this study we employ MMS data to investigate the energy dissipated in jet fronts related to the generation of whistler waves, and the interaction of such waves with energetic electrons in the vicinity of the flow/jet braking region near the equatorial boundary between tail and inner magnetosphere. We also make use of ray tracing simulations to evaluate their propagation properties, as well as their impact on particles in the off-equatorial magnetosphere.

International audience; Bursty Bulk Flows (BBFs), thought to result from reconnection in the near Earth plasma sheet, transfer a significant amount of mass and energy to the inner magnetosphere. The BBF braking region occurs at roughly 10 RE as the flow encounters the dipolar field near Earth and must slow significantly and/or deflect. Previous studies using the THEMIS spacecraft observed electron phase space holes and double-layers in the BBF braking region and speculated that strong field-aligned currents generated by turbulence within the region created these structures. While evidence supporting the existence of turbulence within the region was found, the lack of small-scale spatial information from THEMIS made it difficult to characterize the turbulence and currents within the region. In the present study, BBF braking region observations from the recently launched Magnetospheric Multiscale (MMS) mission are examined. Characteristics of the turbulence are examined through statistical methods such as spatial and temporal correlation functions. Individual structures within the turbulence will also be examined using multi-spacecraft techniques to better characterize the currents, which may contribute to the formation of kinetic structures and dissipation of turbulent energy.

International audience; One of the major challenges in understanding magnetic reconnection is determining the role of processes operating at electron spatial scales within the diffusion region and separatrices. Currently, the processes operating at these scales are difficult to identify and characterize, but are crucial for enabling magnetic fields to reconnect. However, the recently launched Magnetospheric Multiscale (MMS) mission is specifically designed to investigate these electron scale processes. We use MMS data to investigate the type of electrostatic and electromagnetic instabilities present in the diffusion region and separatrices of asymmetric reconnection at the magnetopause. The waves are characterized using polarization analyses and interferometry techniques. Of particular interest are whistler waves and electrostatic solitary waves, which have a large range of observed properties. We investigate the generation mechanisms of the waves as well as their role in plasma heating and anomalous resistivity, using high time resolution wave and particle measurements.

International audience; The phenomenon of magnetic reconnection, especially at electron scales, is still poorly understood. One process that warrants further investigation is the role of wave phenomenon in mediating magnetic reconnection. Previous observations have shown the presence of electrostatic solitary waves (ESWs) as well as whistler mode waves near the dayside reconnection site. Additionally, recent simulations have suggested that whistler waves might be generated by electron phase space holes associated with ESWs as they propagate along the magnetic separatrix towards the diffusion region. Other observations have shown ESWs with distinct speeds and time scales, suggesting that different instabilities generate the ESWs. NASA's recently launched Magnetospheric Multiscale (MMS) mission presents a unique opportunity to investigate the roles of wave phenomena, such as ESWs and whistlers, in asymmetric reconnection at the dayside magnetopause. We will present 3-D electric and magnetic field data from magnetopause crossings by MMS during its first dayside science phase. Burst mode wave data and electron distributions from all four spacecraft will be analyzed to investigate the origin of these wave phenomena, as well as their impact on the reconnection electric field.

International audience; We present MMS observations of particle and wave activity in the Earth's Bursty Bulk Flow (BBF) Braking region (6 - 12 Earth radii tailward). This region, previously examined by the THEMIS spacecraft, has shown evidence of bursty, high velocity, Earthward particle flows, turbulent magnetic fields, and large amplitude electric field signatures (amplitudes can, at times, exceed 100 mV/m). Kinetic features such as double layers, electron phase-space holes, and magnetic holes have been observed frequently throughout this region. The Magnetospheric Multi-scale (MMS) spacecraft, launched March 2015, are currently orbiting the Earth with the objective of observing the microphysics of magnetic reconnection. During its commissioning phase (March 2015 - August 2015), all four spacecraft apogees were primarily in the BBF Braking region. The presence of MMS in this region can offer higher spatial and temporal resolution of the BBF Braking region than ever before. We examine MMS observations kinetic structures (double layers, electron phase-space and magnetic holes) to further characterize the BBF braking region and its overall effects on the Earth space environment.

International audience; We use multi-spacecraft observations by MMS and Cluster in the magnetotail and 3D PIC simulations to investigate conversion of electromagnetic energy at the front of a plasma jet. In PIC simulations the plasma jets (fast localized plasma flows) are produced by magnetic reconnection, while in observations we study bursty bulk flows (BBFs). Jet fronts are known to have a sharp increase of magnetic field (referred to as dipolarization fronts in the magnetospheric physics) as well as sharp gradients in plasma density and temperature. These sharp gradients at the front generate broadband turbulence in the lower-hybrid frequency range, which have amplitudes several times larger than the convective field, wave potential comparable to electron thermal energy, and perpendicular wavelength of the order of several electron gyro-scales. Despite the large wave amplitudes, we find only moderate dissipation due to these waves in the front reference frame, which goes into heating of electrons. We find that the major dissipation is happening in the Earth (laboratory) frame and it is related to reflection and acceleration of ions from the jet front. This dissipation operates at scales of the order several ion inertial lengths, and the primary contribution to E*J is coming from the convective electric field of the front (E=Vfront_x B) and the current flowing at the front.

Purpose: This work compared peripheral nerve stimulation (PNS) thresh-olds for the MRI scanner body gradients (BODY), a head/neck insert gradient (INSERT),and the combination of both gradient sets used simultaneously (COMPOSITE).Methods:For BODY, INSERT and COMPOSITE gradients, PNS thresholds were determined byexposing subject volunteers to stepped increases in gradient strength. For COMPOSITEmode, the INSERT was applied at equal (experiment 1) or double (experiment 2) theBODY gradient strength. Results: The locations and thresholds of peripheral nerve stimu-lation depended on the gradient system configuration, gradient axis, and gradientstrength. Stimulation in the body occurred when using the BODYY-gradient axis eithersingly (110 T/m/s) or in COMPOSITE mode (315 T/m/s experiment 2) and adding theinsert gradient had negligible effect on stimulation. Stimulation in the head/sinus areagenerally occurred when using the INSERTX-gradient either singly (213 T/m/s) or inCOMPOSITE mode (320 T/m/s) and adding the body gradient had negligible effect onstimulation. In the COMPOSITE mode, both the location of stimulation and the limitinggradient strength matched location and strength of the limiting component gradient.Conclusion: Stimulation, to a first-order approximation, is independent for the two gradi-ent systems. In COMPOSITE mode, PNS can be dominated by either of the individualgradient components, indicating that the contribution of each component can beincreased until the threshold limit of each component gradient is reached. COMPOSITEgradients provide increased gradient performance with PNS thresholds higher than eithercomponent gradient system operating alone

International audience; We use multi-spacecraft observations by MMS and Cluster in the magnetotail and 3D PIC simulations to investigate conversion of electromagnetic energy at the front of a plasma jet. In PIC simulations the plasma jets (fast localized plasma flows) are produced by magnetic reconnection, while in observations we study bursty bulk flows (BBFs). Jet fronts are known to have a sharp increase of magnetic field (referred to as dipolarization fronts in the magnetospheric physics) as well as sharp gradients in plasma density and temperature. These sharp gradients at the front generate broadband turbulence in the lower-hybrid frequency range, which have amplitudes several times larger than the convective field, wave potential comparable to electron thermal energy, and perpendicular wavelength of the order of several electron gyro-scales. Despite the large wave amplitudes, we find only moderate dissipation due to these waves in the front reference frame, which goes into heating of electrons. We find that the major dissipation is happening in the Earth (laboratory) frame and it is related to reflection and acceleration of ions from the jet front. This dissipation operates at scales of the order several ion inertial lengths, and the primary contribution to E*J is coming from the convective electric field of the front (E=Vfront_x B) and the current flowing at the front.

International audience

International audience; Bursty Bulk Flows (BBFs), thought to be ejecta from reconnection in the near-Earth magnetotail, are an important means of mass, energy, and magnetic flux transport in the magnetosphere. Understanding how this energy is redirected within the braking region, where the flow impinges on the dipolar field near Earth, is an important question. In this study, properties of the small-scale currents in the BBF braking region are examined with particular emphasis on the nature of the field-aligned component of the currents. Previous studies have suggested that the instability of field-aligned currents associated with turbulence may generate double layers and electron phase space holes observed in the region, thereby providing a collisionless dissipation mechanism for the turbulence. However, direct information about these small-scale currents was inaccessible with the previous data sets. A campaign of burst data collection including Fast Plasma Investigation data from the magnetotail focused on BBF events during August of 2016 has made the present study possible. The work provides insights into the process of energy dissipation by turbulence in the BBF braking region.

International audience; Since the 9th of July, the MMS fleet of four satellites have evolved into a tetrahedral configuration with an average inter-satellite distance of 160 km and an apogee of 12 earth radii on the dusk side. In this study we report on ultra-low (1 mHz to ~10 Hz) and very-low (10 Hz to ~ 4 kHz) frequency wave activity measured by the four satellites during several crossings of the dusk equatorial magnetopause. Since the Larmor radius of magnetosheath protons is of the order of 50 km, this inter-satellite distance allows us to investigate in detail the physics of the magnetopause at proton scales including current structures related to Kelvin-Helmholtz instability as well as other energy transfer processes. From wave polarization analysis, we characterize the different types of emissions and discuss different mechanisms of heating and acceleration of particles. In particular, we focus on the electron heating by kinetic Alfvén waves and lower hybrid waves and the electron acceleration by oblique whistler mode waves, which have been suggested as possible mechanisms from previous Cluster and THEMIS measurements.

Telomerase is the ribonucleoprotein enzyme responsible for the replication of chromosome ends in most eukaryotes. In the ciliate Euplotes aediculatus, the protein p43 biochemically co-purifies with active telomerase and appears to be stoichiometric with both the RNA and the catalytic protein subunit of this telomerase complex. Here we describe cloning of the gene for p43 and present evidence that it is an authentic component of the telomerase holoenzyme. Comparison of the nucleotide sequence of the cloned gene with peptide sequences of the protein suggests that production of full-length p43 relies on a programmed ribosomal frameshift, an extremely rare translational mechanism. Anti-p43 antibodies immunodeplete telomerase RNA and telomerase activity from E.aediculatus nuclear extracts, indicating that the vast majority of mature telomerase complexes in the cell are associated with p43. The sequence of p43 reveals similarity to the La autoantigen, an RNA-binding protein involved in maturation of RNA polymerase III transcripts, and recombinant p43 binds telomerase RNA in vitro. By analogy to other La proteins, p43 may function in chaperoning the assembly and/or facilitating nuclear retention of telomerase.