齋藤 義文

© 2020 us. © 2020 American Physical Society. American Physical Society. The first-order Fermi acceleration of electrons requires an injection of electrons into a mildly relativistic energy range. However, the mechanism of injection has remained a puzzle both in theory and observation. We present direct evidence for a novel stochastic shock drift acceleration theory for the injection obtained with Magnetospheric Multiscale observations at the Earth's bow shock. The theoretical model can explain electron acceleration to mildly relativistic energies at high-speed astrophysical shocks, which may provide a solution to the long-standing issue of electron injection.

© Cambridge University Press 2020. The deviation from thermodynamic equilibrium of the ion velocity distribution functions (VDFs), as measured by the Magnetospheric Multiscale (MMS) mission in the Earth's turbulent magnetosheath, is quantitatively investigated. Making use of the unprecedented high-resolution MMS ion data, and together with Vlasov-Maxwell simulations, this analysis aims at investigating the relationship between deviation from Maxwellian equilibrium and typical plasma parameters. Correlations of the non-Maxwellian features with plasma quantities such as electric fields, ion temperature, current density and ion vorticity are found to be similar in magnetosheath data and numerical experiments, with a poor correlation between distortions of ion VDFs and current density, evidence that questions the occurrence of VDF departure from Maxwellian at the current density peaks. Moreover, strong correlation has been observed with the magnitude of the electric field in the turbulent magnetosheath, while a certain degree of correlation has been found in the numerical simulations and during a magnetopause crossing by MMS. This work could help shed light on the influence of electrostatic waves on the distortion of the ion VDFs in space turbulent plasmas.

©2019. American Geophysical Union. All Rights Reserved. The magnetotail current sheet carries the current responsible for the largest fraction of the energy storage in the magnetotail, the magnetic energy in the lobes. It is thus inextricably linked with the dynamics and evolution of many magnetospheric phenomena, such as substorms. The magnetotail current sheet structure and stability depend mostly on the kinetic properties of the plasma populating the magnetotail. One of the most underinvestigated properties of this plasma is electron temperature anisotropy, which may contribute a large fraction of the total current. Using observations from five missions in the magnetotail, we examine the electron temperature anisotropy, Te‖/Te⊥, and its potential contribution to the current density, quantified by the firehose parameter (βe‖−βe⊥)/2, across y∈[−20,20]RE and x∈[−100,−10]RE. We find that a significant fraction (>30%) of all current sheets have an anisotropic electron current density >10% of the total current. These current sheets form two distinct groups: (1) near-Earth (<30 RE) accompanied by weak plasma flows (<100 km/s) and enhanced equatorial magnetic field (>3 nT) and (2) middle tail (>40 RE) accompanied by fast plasma flows (>300 km/s) and small equatorial magnetic field (≤1 nT). For a significant number of near-Earth current sheets, the anisotropic electron current can be >25% of the total current density. Our findings suggest that electron temperature anisotropy should be included in current sheet models describing realistic magnetotail structure and dynamics.

The Moon interacts with the incident solar wind plasma in various ways, and most of these interactions are accompanied by variations of the interplanetary magnetic field (IMF) around the Moon. Here we first report decreases of the IMF strength observed at 100 km altitude on the lunar dayside and over the polar region, comparing upstream solar wind data from ACE with Kaguya (SELENE) data. We note that the magnetic field decreases are observed above non-magnetized regions or very weakly magnetized regions. In one event the IMF is weakened in the dayside northern hemisphere when the IMF is roughly anti-parallel to the solar wind flow. We estimate that the decrease in the magnetic pressure can be partly compensated by the thermal pressure of the back-scattered solar wind protons, which suggests that the magnetic field decrease is interpreted as diamagnetic effect by the back-scattered protons. In another event an IMF decrease is continuously detected from the northern polar region to the dayside mid-latitude region, which is not fully explained by the thermal pressure of the back-scattered protons. We also discuss the diamagnetic current system in the upstream (fore-moon) solar wind region formed by the back-scattered protons.

© 2019. American Geophysical Union. All Rights Reserved. Plasma heating during the magnetic reconnection is not well understood, particularly in terms of adiabaticity, heating rate, and electron-ion temperature ratio. This study focuses on macroscopic profiles of Ti, Te, and Ti/Te in the near-Earth magnetotail, using data obtained from Magnetospheric Multiscale. Observation points are categorized into three different regions: low-beta/high-beta inflow region, the reconnection sites, and magnetic pileup regions. From low-beta inflow region to high-beta inflow region, both Ti and Te increase and electron entropy is constant. Ion entropy, on the other hand, increases across the transition. Inside the reconnection site, Ti and Te increase, and entropies remain constant. From the outflow region to the pileup region, electrons are selectively heated. Electron entropy increases in the transition. This statistical study suggests that nonadiabatic heating occurs around the plasma sheet boundary layer for ions and at the early stage of magnetic field pileup for electrons.

© 2019. The Authors. We present an overview of the ionospheric conditions during the launch of the Investigation of Cusp Irregularities 3 (ICI-3) sounding rocket. ICI-3 was launched from Ny-Ålesund, Svalbard, at 7:21.31 UT on 3 December 2011. The objective of ICI-3 was to intersect the reversed flow event (RFE), which is thought to be an important source for the rapid development of ionospheric irregularities in the cusp ionosphere. The interplanetary magnetic field was characterized by strongly negative Bz and weakly negative By. The EISCAT Svalbard radar (ESR) 32-m beam was operating in a fast azimuth sweep mode between 180° (south) and 300° (northwest) at an elevation angle of 30°. The ESR observed a series of RFEs as westward flow channels that were opposed to the large-scale eastward plasma flow in the prenoon sector. ICI-3 intersected the first RFE in the ESR field of view and observed flow structures that were consistent with the ESR observations. Furthermore, ICI-3 revealed finer-scale flow structures inside the RFE. The high-resolution electron density data show intense fluctuations at all scales throughout the RFE. The ionospheric pierce point of the GPS satellite PRN30, which was tracked at Hornsund, intersected the RFE at the same time. The GPS scintillation data show moderate phase scintillations and weak amplitude scintillations. A comparison of the power spectra reveals a good match between the ground-based GPS carrier phase measurements and the spectral slope of the in situ electron density data in the lower frequency range. It demonstrates the possibility of modelling GPS scintillations from high-resolution in situ electron density data.

©2019. American Geophysical Union. All Rights Reserved. We present a new method for determining the main relevant features of the local magnetic field configuration, based entirely on the knowledge of the magnetic field gradient four-spacecraft measurements. The method, named “magnetic configuration analysis” (MCA), estimates the spatial scales on which the magnetic field varies locally. While it directly derives from the well-known magnetic directional derivative and magnetic rotational analysis procedures (Shi et al., 2005, htpps://doi.org/10.1029/2005GL022454; Shen et al., 2007, https://doi.org/10.1029/2005JA011584), MCA was specifically designed to address the actual magnetic field geometry. By applying MCA to multispacecraft data from the Magnetospheric Multiscale (MMS) satellites, we perform both case and statistical analyses of local magnetic field shape and dimensionality at very high cadence and small scales. We apply this technique to different near-Earth environments and define a classification scheme for the type of configuration observed. While our case studies allow us to benchmark the method with those used in past works, our statistical analysis unveils the typical shape of magnetic configurations and their statistical distributions. We show that small-scale magnetic configurations are generally elongated, displaying forms of cigar and blade shapes, but occasionally being planar in shape like thin pancakes (mostly inside current sheets). Magnetic configurations, however, rarely show isotropy in their magnetic variance. The planar nature of magnetic configurations and, most importantly, their scale lengths strongly depend on the plasma β parameter. Finally, the most invariant direction is statistically aligned with the electric current, reminiscent of the importance of electromagnetic forces in shaping the local magnetic configuration.

© 2019, The Author(s), under exclusive licence to Springer Nature Limited. Change history: In this Letter, the y-axis values in Fig. 3f should go from 4 to −8 (rather than from 4 to −4), the y-axis values in Fig. 3h should appear next to the major tick marks (rather than the minor ticks), and in Fig. 1b, the arrows at the top and bottom of the electron-scale current sheet were going in the wrong direction; these errors have been corrected online.

©2019. American Geophysical Union. All Rights Reserved. We report Magnetospheric Multiscale observations of reconnection in a thin current sheet at the interface of interlinked flux tubes carried by converging reconnection jets at Earth's magnetopause. The ion skin depth-scale width of the interface current sheet and the non-frozen-in ions indicate that Magnetospheric Multiscale crossed the reconnection layer near the X-line, through the ion diffusion region. Significant pileup of the reconnecting component of the magnetic field in this and three other events on approach to the interface current sheet was accompanied by an increase in magnetic shear and decrease in Δβ, leading to conditions favorable for reconnection at the interface current sheet. The pileup also led to enhanced available magnetic energy per particle and strong electron heating. The observations shed light on the evolution and energy release in 3-D systems with multiple reconnection sites.

©2018. American Geophysical Union. All Rights Reserved. We present results from the reconstruction of the electron diffusion region of magnetotail reconnection observed by the Magnetospheric Multiscale (MMS) spacecraft on 11 July 2017. In the event, the conditions were suited for the reconstruction technique, developed by Sonnerup et al. (2016, https://doi.org/10.1002/2016JA022430), that produces magnetic field and electron streamline maps based on a two-dimensional, time-independent, inertialess form of electron magnetohydrodynamic equation, assuming an approximately symmetric current sheet and negligible guide magnetic field. For such a two-dimensional and steady structure, the X line orientation can be estimated from a method based on Ampère's law using single-spacecraft measurements of the magnetic field and electric current density. Our reconstruction results indicate that although the X point was not captured inside its tetrahedron, MMS approached the X point as close as one electron inertial length ~27 km. The opening angle of the recovered separatrix field line, combined with theory, suggests that the dimensionless reconnection rate was 0.17, which is consistent with the measured reconnection electric field 2–4 mV/m. The stagnation point of the reconstructed electron flow is shifted earthward of the X point by ~90 km, one possible interpretation of which is discussed. The energy conversion rate j · E′ in the electron frame tends to be higher near the stagnation point, consistent with earlier observations and simulations, and is not correlated with the amplitude of broadband electrostatic waves observed in the upper-hybrid frequency range. The latter suggests that the waves did not contribute to energy dissipation in this particular electron diffusion region.

© 2018 American Association for the Advancement of Science. All rights reserved. Magnetic reconnection is an energy conversion process that occurs in many astrophysical contexts including Earth’s magnetosphere, where the process can be investigated in situ by spacecraft. On 11 July 2017, the four Magnetospheric Multiscale spacecraft encountered a reconnection site in Earth’s magnetotail, where reconnection involves symmetric inflow conditions. The electron-scale plasma measurements revealed (i) super-Alfvénic electron jets reaching 15,000 kilometers per second; (ii) electron meandering motion and acceleration by the electric field, producing multiple crescent-shaped structures in the velocity distributions; and (iii) the spatial dimensions of the electron diffusion region with an aspect ratio of 0.1 to 0.2, consistent with fast reconnection. The well-structured multiple layers of electron populations indicate that the dominant electron dynamics are mostly laminar, despite the presence of turbulence near the reconnection site.

© 2018 American Association for the Advancement of Science. All Rights Reserved. Particle acceleration by plasma waves and spontaneous wave generation are fundamental energy and momentum exchange processes in collisionless plasmas. Such wave-particle interactions occur ubiquitously in space. We present ultrafast measurements in Earth’s magnetosphere by the Magnetospheric Multiscale spacecraft that enabled quantitative evaluation of energy transfer in interactions associated with electromagnetic ion cyclotron waves. The observed ion distributions are not symmetric around the magnetic field direction but are in phase with the plasma wave fields. The wave-ion phase relations demonstrate that a cyclotron resonance transferred energy from hot protons to waves, which in turn nonresonantly accelerated cold He+ to energies up to ~2 kilo–electron volts. These observations provide direct quantitative evidence for collisionless energy transfer in plasmas between distinct particle populations via wave-particle interactions.

©2018. American Geophysical Union. All Rights Reserved. We investigate the average location of magnetic reconnection on the Earth's dayside magnetopause, based on spatial distributions of northward and southward reconnection jets observed by the THEMIS spacecraft at the near-noon (10–14 magnetic local time) magnetopause. A total of 711 reconnection jets were identified by applying the Walén relation, the tangential stress balance relation to be satisfied for a reconnected (rotational discontinuity) magnetopause, to magnetopause crossings identified from 10 years of THEMIS observations. The directions and positions of jets indicate that during southward interplanetary magnetic field (IMF) conditions, the dayside X-line location shifts from the subsolar point toward the winter hemisphere by about 6 Earth radii under the largest tilt of the geomagnetic dipole axis. The X-line location also shifts northward (southward) by at most 2.5 Earth radii when the IMF is predominantly radial and its x component is positive (negative). The dipole tilt effect on the shift of the X-line location becomes smaller for higher solar wind Alfvén Mach numbers. The dipole tilt effect being larger than the IMF Bx effect suggests that the X-line location has a seasonal dependence. Since models and theory show that the reconnection rate away from the subsolar magnetopause is lower than that at the subsolar magnetopause, the dipole tilt dependence of the X-line location suggests that the efficiency of solar wind energy transfer into the magnetosphere may decrease under larger dipole tilt; this may partially account for seasonal variations of geomagnetic activity, which is known to decrease under larger dipole tilts.

©2018. American Geophysical Union. All Rights Reserved. We investigated characteristics of slow-mode shocks in the dayside magnetopause based on Magnetospheric Multiscale observations from September 2015 to February 2017. We analyzed 99 magnetopause crossings with reconnection jets and high time resolution data, out of which 20 crossings showed slow-mode shock signatures. Out of these crossings, one crossing showed slow-mode shock signature on both sides, and the rest had slow-mode shock signatures on one side, six (13) on magnetosphere (magnetosheath). The detection probability of slow-mode shocks in the magnetopause is ~20%, which is greater than that reported in the magnetotail. We also found 12 rotational discontinuities in these slow-mode shock events. The results also show that the observation of magnetosphere side slow-mode shock is favored when the number density ratio of magnetosheath to magnetosphere is small. No clear dependence of the existence of slow-mode shocks on other parameters such as, plasma beta, temperature anisotropy, and jet velocity, was found.

© 2018 Macmillan Publishers Ltd., part of Springer Nature. Magnetic reconnection in current sheets is a magnetic-to-particle energy conversion process that is fundamental to many space and laboratory plasma systems. In the standard model of reconnection, this process occurs in a minuscule electron-scale diffusion region 1,2 . On larger scales, ions couple to the newly reconnected magnetic-field lines and are ejected away from the diffusion region in the form of bi-directional ion jets at the ion Alfvén speed 3-5 . Much of the energy conversion occurs in spatially extended ion exhausts downstream of the diffusion region 6 . In turbulent plasmas, which contain a large number of small-scale current sheets, reconnection has long been suggested to have a major role in the dissipation of turbulent energy at kinetic scales 7-11 . However, evidence for reconnection plasma jetting in small-scale turbulent plasmas has so far been lacking. Here we report observations made in Earth's turbulent magnetosheath region (downstream of the bow shock) of an electron-scale current sheet in which diverging bi-directional super-ion-Alfvénic electron jets, parallel electric fields and enhanced magnetic-to-particle energy conversion were detected. Contrary to the standard model of reconnection, the thin reconnecting current sheet was not embedded in a wider ion-scale current layer and no ion jets were detected. Observations of this and other similar, but unidirectional, electron jet events without signatures of ion reconnection reveal a form of reconnection that can drive turbulent energy transfer and dissipation in electron-scale current sheets without ion coupling.

© 2018 Author(s). Microprocesses associated with plasma inhomogeneities are studied on the basis of data from the Investigation of Cusp Irregularities (ICI-3) sounding rocket. The ICI-3 rocket is devoted to investigating a reverse flow event in the cusp F region ionosphere. By numerical stability analysis, it is demonstrated that inhomogeneous-energy-density-driven (IEDD) instability can be a mechanism for the excitation of small-scale plasma inhomogeneities. The Local Intermittency Measure (LIM) method also applied the rocket data to analyze irregular structures of the electric field during rocket flight in the cusp. A qualitative agreement between high values of the growth rates of the IEDD instability and the regions with enhanced LIM is observed. This suggests that IEDD instability is connected to turbulent non-Gaussian processes.

©2018. American Geophysical Union. All Rights Reserved. This paper describes the generation and initial utilization of a database containing 80 vector and scalar quantities, for a total of 8,670 magnetopause and magnetosheath current sheet crossings by MMS1, using plasma and magnetic field data from the Fast Plasma Investigation, Fluxgate Magnetometer, and Hot Plasma Composition Analyzer instruments, augmented by solar wind and interplanetary magnetic field data from CDAWeb. Based on a determination of the current sheet width, measured and calculated vector and scalar quantities are stored for the two sides of the current sheet and for selected times within the current sheet. The only manual operations were the classification of the current sheets according to the type of boundary, the character of the magnetic field transition, and the quality of the current sheet fit. To characterize the database, histograms of selected key quantities are presented. We then give the statistics for the duration, motion, and thicknesses of the magnetopause current sheet, using single-spacecraft techniques for the determination of the normal velocities, obtaining median results of 12.9 s, 38.5 km/s, and 705.4 km, respectively. When scaled to the ion inertial length, the median thickness became 12.6; there were no thicknesses less than one. Next, we apply the Walén relation to find crossings that are rotational discontinuities and thus may indicate ongoing magnetic reconnection. For crossings where the velocities in the outflow region exceed the velocity on the magnetosheath side by at least 250 km/s, 47% meet our rotational discontinuity criteria. If we require the outflow to exceed 250 km/s along the L direction, then the percentage rises to 68%.

©2018. American Geophysical Union. All Rights Reserved. The occurrence of spatially and temporally variable reconnection at the Earth's magnetopause leads to the complex interaction of magnetic fields from the magnetosphere and magnetosheath. Flux transfer events (FTEs) constitute one such type of interaction. Their main characteristics are (1) an enhanced core magnetic field magnitude and (2) a bipolar magnetic field signature in the component normal to the magnetopause, reminiscent of a large-scale helicoidal flux tube magnetic configuration. However, other geometrical configurations which do not fit this classical picture have also been observed. Using high-resolution measurements from the Magnetospheric Multiscale mission, we investigate an event in the vicinity of the Earth's magnetopause on 7 November 2015. Despite signatures that, at first glance, appear consistent with a classic FTE, based on detailed geometrical and dynamical analyses as well as on topological signatures revealed by suprathermal electron properties, we demonstrate that this event is not consistent with a single, homogenous helicoidal structure. Our analysis rather suggests that it consists of the interaction of two separate sets of magnetic field lines with different connectivities. This complex three-dimensional interaction constructively conspires to produce signatures partially consistent with that of an FTE. We also show that, at the interface between the two sets of field lines, where the observed magnetic pileup occurs, a thin and strong current sheet forms with a large ion jet, which may be consistent with magnetic flux dissipation through magnetic reconnection in the interaction region.

© 2018 U.S. Government. Turbulence is a fundamental physical process through which energy injected into a system at large scales cascades to smaller scales. In collisionless plasmas, turbulence provides a critical mechanism for dissipating electromagnetic energy. Here, we present observations of plasma fluctuations in low-β turbulence using data from NASA's Magnetospheric Multiscale mission in Earth's magnetosheath. We provide constraints on the partitioning of turbulent energy density in the fluid, ion-kinetic, and electron-kinetic ranges. Magnetic field fluctuations dominated the energy density spectrum throughout the fluid and ion-kinetic ranges, consistent with previous observations of turbulence in similar plasma regimes. However, at scales shorter than the electron inertial length, fluctuation power in electron kinetic energy significantly exceeded that of the magnetic field, resulting in an electron-motion-regulated cascade at small scales. This dominance is highly relevant for the study of turbulence in highly magnetized laboratory and astrophysical plasmas.

©2018. American Geophysical Union. All Rights Reserved. Narrowband electromagnetic ion cyclotron waves first discovered by the Apollo 15 and 16 Lunar Surface Magnetometers were surveyed in the magnetic field data obtained by the Kaguya satellite at an altitude of ∼100 km above the Moon in the tail lobe and plasma sheet boundary layer of the Earth's magnetosphere. The frequencies of the waves were typically 0.7 times the local proton cyclotron frequency, and 75% of the waves were left hand polarized with respect to the background magnetic field. They had a significant compressional component and comprised several discrete packets. They were detected on the dayside, nightside, and above the terminator of the Moon, irrespective of the lunar magnetic anomaly, or the magnetic connection to the lunar surface. The waves with the same characteristics were detected by Geotail in the absence of the Moon in the magnetotail. The most likely energy source of the electromagnetic ion cyclotron waves is the ring beam ions in the plasma sheet boundary layer.

©2018. The Authors. We report Magnetospheric Multiscale observations of electron pressure gradient electric fields near a magnetic reconnection diffusion region using a new technique for extracting 7.5 ms electron moments from the Fast Plasma Investigation. We find that the deviation of the perpendicular electron bulk velocity from E × B drift in the interval where the out-of-plane current density is increasing can be explained by the diamagnetic drift. In the interval where the out-of-plane current is transitioning to in-plane current, the electron momentum equation is not satisfied at 7.5 ms resolution.

©2017. American Geophysical Union. All Rights Reserved. Mirror mode waves are ubiquitous in the Earth's magnetosheath, in particular behind the quasi-perpendicular shock. Embedded in these nonlinear structures, intense lion roars are often observed. Lion roars are characterized by whistler wave packets at a frequency ∼100 Hz, which are thought to be generated in the magnetic field minima. In this study, we make use of the high time resolution instruments on board the Magnetospheric MultiScale mission to investigate these waves and the associated electron dynamics in the quasi-perpendicular magnetosheath on 22 January 2016. We show that despite a core electron parallel anisotropy, lion roars can be generated locally in the range 0.05–0.2fce by the perpendicular anisotropy of electrons in a particular energy range. We also show that intense lion roars can be observed up to higher frequencies due to the sharp nonlinear peaks of the signal, which appear as sharp spikes in the dynamic spectra. As a result, a high sampling rate is needed to estimate correctly their amplitude, and the latter might have been underestimated in previous studies using lower time resolution instruments. We also present for the first-time 3-D high time resolution electron velocity distribution functions in mirror modes. We demonstrate that the dynamics of electrons trapped in the mirror mode structures are consistent with the Kivelson and Southwood (1996) model. However, these electrons can also interact with the embedded lion roars: first signatures of electron quasi-linear pitch angle diffusion and possible signatures of nonlinear interaction with high-amplitude wave packets are presented. These processes can lead to electron untrapping from mirror modes.

©2017. American Geophysical Union. All Rights Reserved. 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.

©2017. The Authors. In this paper we use the full armament of the MMS (Magnetospheric Multiscale) spacecraft to study magnetic reconnection in the turbulent magnetosheath downstream of a quasi-parallel bow shock. Contrarily to the magnetopause and magnetotail cases, only a few observations of reconnection in the magnetosheath have been reported. The case study in this paper presents, for the first time, both fluid-scale and kinetic-scale signatures of an ongoing reconnection in the turbulent magnetosheath. The spacecraft are crossing the reconnection inflow and outflow regions and the ion diffusion region (IDR). Inside the reconnection outflows D shape ion distributions are observed. Inside the IDR mixing of ion populations, crescent-like velocity distributions and ion accelerations are observed. One of the spacecraft skims the outer region of the electron diffusion region, where parallel electric fields, energy dissipation/conversion, electron pressure tensor agyrotropy, electron temperature anisotropy, and electron accelerations are observed. Some of the difficulties of the observations of magnetic reconnection in turbulent plasma are also outlined.

A scaffold-hopping strategy towards a new pyrazolo[1,5-a]pyridine based core using molecular hybridization of two structurally distinct EP1 antagonists, followed by structure-activity relationship guided optimization, resulted in the identification of potent EP1 antagonists exemplified by 4c, 4f, and 4j, which were shown to reduce pathological intravesical pressure in rats when administered at 1 mg/kg iv. (C) 2017 Published by Elsevier Ltd.

© 2017 Elsevier Inc. There forms a tenuous region called the wake behind the Moon in the solar wind, and plasma entry/refilling into the wake is a fundamental problem of the lunar plasma science. High-energy ions and electrons in the foreshock of the Earth's magnetosphere were detected at the lunar surface in the Apollo era, but their effects on the lunar night-side environment have never been studied. Here we show the first observation of bow-shock reflected protons by Kaguya (SELENE) spacecraft in orbit around the Moon, confirming that solar wind plasma reflected at the terrestrial bow shock can easily access the deepest lunar wake when the Moon stays in the foreshock (We name this mechanism ‘type-3 entry’). In a continuous type-3 event, low-energy electron beams from the lunar night-side surface are not obvious even though the spacecraft location is magnetically connected to the lunar surface. On the other hand, in an intermittent type-3 entry event, the kinetic energy of upward-going field-aligned electron beams decreases from ∼ 80 eV to ∼ 20 eV or electron beams disappear as the bow-shock reflected ions come accompanied by enhanced downward electrons. According to theoretical treatment based on electric current balance at the lunar surface including secondary electron emission by incident electron and ion impact, we deduce that incident ions would be accompanied by a few to several times higher flux of an incident electron flux, which well fits observed downward fluxes. We conclude that impact by the bow-shock reflected ions and electrons raises the electrostatic potential of the lunar night-side surface.

© Published under licence by IOP Publishing Ltd. Planetary plasma and atmospheres have been challenged by space missions of Japanese science community from 1990s, with ISAS and JAXA. The first trial, a Martian orbiter Nozomi, was launched in July 1998. At the departure from Earth in Dec. 1998, she met an engine trouble but we struggled and found a narrow and long path connecting to the Dec 2003 arrival, which is the simultaneous arrival with ESA Mars Express. Unfortunately, we had an additional power trouble in Apr. 2002 associated with a solar flare event, and we gave up the trial at the gate of Mars in Dec. 2003. In parallel to the Kaguya Lunar orbiter in 2007-2009, a next trial to planets, the Akatsuki orbiter to Venus, was prepared. She departed from Earth in May 2010. However, she got an engine trouble at the arrival to Venus in Dec. 2010, and we again endured another long path, but this road was at last ended by a success of the orbit entry in Dec. 2015. We also created the UV/EUV space telescope, Hisaki, using the sensor and optics technologies extracted from Nozomi. It is going well after the launch in 2013 and actively looking planetary thin atmospheres collaborating with other space missions. This paper summarizes the Hisaki and Akatsuki missions which are now on orbit, with the next missions, Arase (ERG), BepiColombo, JUICE, and beyond.

© 2017. The American Astronomical Society. All rights reserved. Electrons are accelerated to non-Thermal energies at shocks in space and astrophysical environments. While different mechanisms of electron acceleration have been proposed, it remains unclear how non-Thermal electrons are produced out of the thermal plasma pool. Here, we report in situ evidence of pitch-Angle scattering of non-Thermal electrons by whistler waves at Earth's bow shock. On 2015 November 4, the Magnetospheric Multiscale (MMS) mission crossed the bow shock with an Alfvén Mach number ∼11 and a shock angle ∼84°. In the ramp and overshoot regions, MMS revealed bursty enhancements of non-Thermal (0.5-2 keV) electron flux, correlated with high-frequency (0.2-0.4 , where is the cyclotron frequency) parallel-propagating whistler waves. The electron velocity distribution (measured at 30 ms cadence) showed an enhanced gradient of phase-space density at and around the region where the electron velocity component parallel to the magnetic field matched the resonant energy inferred from the wave frequency range. The flux of 0.5 keV electrons (measured at 1 ms cadence) showed fluctuations with the same frequency. These features indicate that non-Thermal electrons were pitch-Angle scattered by cyclotron resonance with the high-frequency whistler waves. However, the precise role of the pitch-Angle scattering by the higher-frequency whistler waves and possible nonlinear effects in the electron acceleration process remains unclear.

©2017. American Geophysical Union. All Rights Reserved. We present first results of the reconstruction of the electron diffusion region (EDR) based on a two-dimensional, incompressible, and inertialess version of the electron magnetohydrodynamics equations. The method is applied to 30 ms resolution magnetic field, and electron moments data taken when the Magnetospheric Multiscale (MMS) spacecraft observed an EDR of near-antiparallel magnetopause reconnection on 16 October 2015. An X-type magnetic field configuration and quadrupolar Hall fields, consistent with the electron inflow and outflow, are successfully recovered. While MMS encountered a region of significant energy dissipation on the magnetospheric side of the sub-ion-scale current sheet, the reconstructions show that the MMS tetrahedron missed the X line by a distance of a few kilometers (~2 electron inertial lengths). The estimated reconnection electric field is 0.42–0.98 mV/m, equivalent to the dimensionless reconnection rate of 0.11–0.25. Signatures of three-dimensional structures and/or time-dependent processes are also identified.

© 2017 The Author(s). Alfvén waves are fundamental plasma wave modes that permeate the universe. At small kinetic scales, they provide a critical mechanism for the transfer of energy between electromagnetic fields and charged particles. These waves are important not only in planetary magnetospheres, heliospheres and astrophysical systems but also in laboratory plasma experiments and fusion reactors. Through measurement of charged particles and electromagnetic fields with NASA's Magnetospheric Multiscale (MMS) mission, we utilize Earth's magnetosphere as a plasma physics laboratory. Here we confirm the conservative energy exchange between the electromagnetic field fluctuations and the charged particles that comprise an undamped kinetic Alfvén wave. Electrons confined between adjacent wave peaks may have contributed to saturation of damping effects via nonlinear particle trapping. The investigation of these detailed wave dynamics has been unexplored territory in experimental plasma physics and is only recently enabled by high-resolution MMS observations.

© 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved. For five days of each lunar orbit, the Moon is shielded from solar wind bombardment by the Earth's magnetosphere, which is filled with terrestrial ions. Although the possibility of the presence of terrestrial nitrogen and noble gases in lunar soil has been discussed based on their isotopic composition 1, complicated oxygen isotope fractionation in lunar metal 2,3 (particularly the provenance of a 16 O-poor component) reÂ-mains an enigma 4,5. Here, we report observations from the Japanese spacecraft Kaguya of significant numbers of 1-10 keV O + ions, seen only when the Moon was in the Earth's plasma sheet. Considering the penetration depth into metal of O + ions with such energy, and the 16 O-poor mass-independent fractionation of the Earth's upper atmosphere 6, we conclude that biogenic terrestrial oxygen has been transported to the Moon by the Earth wind (at least 2.6 × 10 4 ions cm â '2 s â '1) and implanted into the surface of the lunar regolith, at around tens of nanometres in depth 3,4. We suggest the possibility that the Earth's atmosphere of billions of years ago may be preserved on the present-day lunar surface.

© 2017. The American Astronomical Society. All rights reserved. We present a statistical study of coherent structures at kinetic scales, using data from the Magnetospheric Multiscale mission in the Earth's magnetosheath. We implemented the multi-spacecraft partial variance of increments (PVI) technique to detect these structures, which are associated with intermittency at kinetic scales. We examine the properties of the electron heating occurring within such structures. We find that, statistically, structures with a high PVI index are regions of significant electron heating. We also focus on one such structure, a current sheet, which shows some signatures consistent with magnetic reconnection. Strong parallel electron heating coincides with whistler emissions at the edges of the current sheet.

©2017. American Geophysical Union. All Rights Reserved. The time resolution of low-energy charged particle measurements is becoming higher and higher. In order to realize high time resolution measurements, a 1-D circular delay line anode has been developed as a high-speed microchannel plate (MCP) anode. The maximum count rate of the 1-D circular delay line anode is around 1 × 107/s/360°, which is much higher than the widely used resistive anode, whose maximum count rate is around 1 × 106/s/360°. In order to achieve much higher speeds, an MCP anode with application-specific integrated circuit (ASIC) has been developed. We have decided to adopt an anode configuration in which a discrete anode is formed on a ceramic substrate, and a bare ASIC chip is installed on the back of the ceramic. It has been found that the anode can detect at a high count rate of 2 × 108/s/360°. Developments in both delay line and discrete anodes, as well as readout electronics, will be reviewed.

©2016. American Geophysical Union. All Rights Reserved. The role and properties of lower hybrid waves in the ion diffusion region and magnetospheric inflow region of asymmetric reconnection are investigated using the Magnetospheric Multiscale (MMS) mission. Two distinct groups of lower hybrid waves are observed in the ion diffusion region and magnetospheric inflow region, which have distinct properties and propagate in opposite directions along the magnetopause. One group develops near the ion edge in the magnetospheric inflow, where magnetosheath ions enter the magnetosphere through the finite gyroradius effect and are driven by the ion-ion cross-field instability due to the interaction between the magnetosheath ions and cold magnetospheric ions. This leads to heating of the cold magnetospheric ions. The second group develops at the sharpest density gradient, where the Hall electric field is observed and is driven by the lower hybrid drift instability. These drift waves produce cross-field particle diffusion, enabling magnetosheath electrons to enter the magnetospheric inflow region thereby broadening the density gradient in the ion diffusion region.

© 2016 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the http://creativecommons.org/licenses/by/3.0/ Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Collisionless shock nonstationarity arising from microscale physics influences shock structure and particle acceleration mechanisms. Nonstationarity has been difficult to quantify due to the small spatial and temporal scales. We use the closely spaced (subgyroscale), high-time-resolution measurements from one rapid crossing of Earth's quasiperpendicular bow shock by the Magnetospheric Multiscale (MMS) spacecraft to compare competing nonstationarity processes. Using MMS's high-cadence kinetic plasma measurements, we show that the shock exhibits nonstationarity in the form of ripples.

©2016. American Geophysical Union. All Rights Reserved. Localized kinetic-scale regions of strong current are believed to play an important role in plasma thermalization and particle acceleration in turbulent plasmas. We present a detailed study of a strong localized current, 4900 nA m−2, located at a fast plasma jet observed in the magnetosheath downstream of a quasi-parallel shock. The thickness of the current region is ∼3 ion inertial lengths and forms at a boundary separating magnetosheath-like and solar wind-like plasmas. On ion scales the current region has the shape of a sheet with a significant average normal magnetic field component but shows strong variations on smaller scales. The dynamic pressure within the magnetosheath jet is over 3 times the solar wind dynamic pressure. We suggest that the current sheet is forming due to high velocity shears associated with the jet. Inside the current sheet we observe local electron acceleration, producing electron beams, along the magnetic field. However, there is no clear sign of ongoing reconnection. At higher energies, above the beam energy, we observe a loss cone consistent with part of the hot magnetosheath-like electrons escaping into the colder solar wind-like plasma. This suggests that the acceleration process within the current sheet is similar to the one that occurs at shocks, where electron beams and loss cones are also observed. Therefore, electron beams observed in the magnetosheath do not have to originate from the bow shock but can also be generated locally inside the magnetosheath.

©2016. American Geophysical Union. All Rights Reserved. We report in situ measurements of plasma irregularities associated with a reverse flow event (RFE) in the cusp F region ionosphere. The Investigation of Cusp Irregularities 3 (ICI-3) sounding rocket, while flying through a RFE, encountered several regions with density irregularities down to meter scales. We address in detail the region with the most intense small-scale fluctuations in both the density and in the AC electric field, which were observed on the equatorward edge of a flow shear, and coincided with a double-humped jet of fast flow. Due to its long-wavelength and low-frequency character, the Kelvin-Helmholtz instability (KHI) alone cannot be the source of the observed irregularities. Using ICI-3 data as inputs, we perform a numerical stability analysis of the inhomogeneous energy-density-driven instability (IEDDI) and demonstrate that it can excite electrostatic ion cyclotron waves in a wide range of wave numbers and frequencies for the electric field configuration observed in that region, which can give rise to the observed small-scale turbulence. The IEDDI can seed as a secondary process on steepened vortices created by a primary KHI. Such an interplay between macroprocesses and microprocesses could be an important mechanism for ion heating in relation to RFEs.

©2016. American Geophysical Union. All Rights Reserved. The Magnetospheric Multiscale mission has demonstrated the frequent presence of reconnection exhausts at thin current sheets within Kelvin-Helmholtz (KH) waves at the flank magnetopause. Motivated by these recent observations, we performed a statistical analysis of the boundary layers on the magnetosheath side of all KH current sheets on 8 September 2015. We show 86% consistency between the exhaust flows and particle leakage in the magnetosheath boundary layers but further highlight the very frequent presence of additional boundary layer signatures that do not come from the locally observed reconnection exhausts. These additional electron and ion boundary layers, of various durations and at various positions with respect to the leading and trailing boundaries of the KH waves, signal connections to reconnection sites at other locations. Based on the directionality and extent of these layers, we provide an interpretation whereby complex magnetic topologies can arise within KH waves from the combination of reconnection in the equatorial plane and at midlatitudes in the Southern and Northern Hemispheres, where additional reconnection sites are expected to be triggered by the three-dimensional field lines interweaving induced by the KH waves at the flanks (owing to differential flow and magnetic field shear with latitude). The present event demonstrates that the three-dimensional development of KH waves can induce plasma entry (through reconnection at both midlatitude and equatorial regions) already sunward of the terminator where the instability remains in its linear stage.

©2016. American Geophysical Union. All Rights Reserved. Ion velocity distribution functions (VDFs) from a particle-in-cell simulation of asymmetric reconnection are investigated to reveal a two-scale structure of the ion diffusion region (IDR). Ions bouncing in the inner IDR are trapped mainly by the electric field normal to the current sheet (N direction), while those reaching the outer IDR are turned back mainly by the magnetic force. The resulting inner layer VDFs have counter-streaming populations along N with decreasing counter-streaming speeds away from the midplane while maintaining the out-of-plane speed, and the outer layer VDFs exhibit crescent shapes toward the out-of-plane direction. Observations of the above VDF features and the normal electric fields provide evidence for the two-scale meandering motion.

©2016. American Geophysical Union. All Rights Reserved. Observations by the four Magnetospheric Multiscale spacecraft are used to investigate the Hall physics of a magnetopause magnetic reconnection separatrix layer. Inside this layer of currents and strong normal electric fields, cold (eV) ions of ionospheric origin can remain frozen-in together with the electrons. The cold ions reduce the Hall current. Using a generalized Ohm's law, the electric field is balanced by the sum of the terms corresponding to the Hall current, the v × B drifting cold ions, and the divergence of the electron pressure tensor. A mixture of hot and cold ions is common at the subsolar magnetopause. A mixture of length scales caused by a mixture of ion temperatures has significant effects on the Hall physics of magnetic reconnection.

©2016. American Geophysical Union. All Rights Reserved. We present observations of asymmetric magnetic reconnection showing evidence of electron demagnetization in the electron outflow. The observations were made at the magnetopause by the four Magnetospheric Multiscale (MMS) spacecraft, separated by ∼15 km. The reconnecting current sheet has negligible guide field, and all four spacecraft likely pass close to the electron diffusion region just south of the X line. In the electron outflow near the X line, all four spacecraft observe highly structured electron distributions in a region comparable to a few electron gyroradii. The distributions consist of a core with T∥>T⊥ and a nongyrotropic crescent perpendicular to the magnetic field. The crescents are associated with finite gyroradius effects of partly demagnetized electrons. These observations clearly demonstrate the manifestation of finite gyroradius effects in an electron-scale reconnection current sheet.

©2016. American Geophysical Union. All Rights Reserved. Although the effects of magnetic reconnection in magnetospheres can be observed at planetary scales, reconnection is initiated at electron scales in a plasma. Surrounding the electron diffusion region, there is an Ion-Decoupling Region (IDR) of the size of the ion length scales (inertial length and gyroradius). Reconnection at the Earth's magnetopause often includes cold magnetospheric (few tens of eV), hot magnetospheric (10 keV), and magnetosheath (1 keV) ions, with different gyroradius length scales. We report observations of a subregion inside the IDR of the size of the cold ion population gyroradius (∼15 km) where the cold ions are demagnetized and accelerated parallel to the Hall electric field. Outside the subregion, cold ions follow the E × B motion together with electrons, while hot ions are demagnetized. We observe a sharp cold ion density gradient separating the two regions, which we identify as the cold and hot IDRs.

©2016. American Geophysical Union. All Rights Reserved. Observations from the MESSENGER spacecraft have considerably enhanced our understanding of the plasma environment at Mercury. In particular, measurements from the Fast Imaging Plasma Spectrometer provide evidences of a variety of ion species of planetary origin (He+, O+, and Na+) in the northern dayside cusp and in the nightside plasma sheet. A more comprehensive view of Mercury's plasma environment will be provided by the BepiColombo mission that will be launched in 2018. On board the BepiColombo MMO spacecraft, the Mercury Plasma/Particle Experiment consortium gathers different sensors dedicated to particle measurements. Among these sensors, the Mass Spectrum Analyzer (MSA) is the instrument dedicated to plasma composition analysis. It consists of a top hat for energy analysis followed by a time-of-flight (TOF) chamber to derive the ion mass. Taking advantage of the spacecraft rotation, MSA will measure three-dimensional distribution functions in one spin (4 s), from energies characteristic of exospheric populations (in the eV range) up to plasma sheet energies (up to ~38 keV/q). A notable feature of the MSA instrument is that the TOF chamber is polarized with a linear electric field that leads to isochronous TOFs and enhanced mass resolution (typically, m/∆m ≈ 40 for ions with energies up to 13 keV/q). At Mercury, this capability is of paramount importance to thoroughly characterize the wide variety of ion species originating from the planet surface. It is thus anticipated that MSA will provide unprecedented information on ion populations in the Hermean environment and hence improve our understanding of the coupling processes at work.

©2016. American Geophysical Union. All Rights Reserved. The four Magnetospheric Multiscale (MMS) spacecraft recorded the first direct evidence of reconnection exhausts associated with Kelvin-Helmholtz (KH) waves at the duskside magnetopause on 8 September 2015 which allows for local mass and energy transport across the flank magnetopause. Pressure anisotropy-weighted Walén analyses confirmed in-plane exhausts across 22 of 42 KH-related trailing magnetopause current sheets (CSs). Twenty-one jets were observed by all spacecraft, with small variations in ion velocity, along the same sunward or antisunward direction with nearly equal probability. One exhaust was only observed by the MMS-1,2 pair, while MMS-3,4 traversed a narrow CS (1.5 ion inertial length) in the vicinity of an electron diffusion region. The exhausts were locally 2-D planar in nature as MMS-1,2 observed almost identical signatures separated along the guide-field. Asymmetric magnetic and electric Hall fields are reported in agreement with a strong guide-field and a weak plasma density asymmetry across the magnetopause CS.

©2016. American Geophysical Union. All Rights Reserved. The Kelvin-Helmholtz (KH) instability at the Earth's magnetopause is predominantly excited during northward interplanetary magnetic field (IMF). Magnetic reconnection due to KH waves has been suggested as one of the mechanisms to transfer solar wind plasma into the magnetosphere. We investigate KH waves observed at the magnetopause by the Magnetospheric Multiscale (MMS) mission; in particular, we study the trailing edges of KH waves with Alfvénic ion jets. We observe gradual mixing of magnetospheric and magnetosheath ions at the boundary layer. The magnetospheric electrons with energy up to 80 keV are observed on the magnetosheath side of the jets, which indicates that they escape into the magnetosheath through reconnected magnetic field lines. At the same time, the low-energy (below 100 eV) magnetosheath electrons enter the magnetosphere and are heated in the field-aligned direction at the high-density edge of the jets. Our observations provide unambiguous kinetic evidence for ongoing reconnection due to KH waves.

©2016. American Geophysical Union. All Rights Reserved. We present Magnetospheric Multiscale observations of an electron-scale current sheet and electron outflow jet for asymmetric reconnection with guide field at the subsolar magnetopause. The electron jet observed within the reconnection region has an electron Mach number of 0.35 and is associated with electron agyrotropy. The jet is unstable to an electrostatic instability which generates intense waves with E∥ amplitudes reaching up to 300 mV m−1 and potentials up to 20% of the electron thermal energy. We see evidence of interaction between the waves and the electron beam, leading to quick thermalization of the beam and stabilization of the instability. The wave phase speed is comparable to the ion thermal speed, suggesting that the instability is of Buneman type, and therefore introduces electron-ion drag and leads to braking of the electron flow. Our observations demonstrate that electrostatic turbulence plays an important role in the electron-scale physics of asymmetric reconnection.