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Kinetic aspects of the ion current layer at the center of a reconnection outflow exhaust near the X-type region are investigated by a two-dimensional particle-in-cell (PIC) simulation. The layer consists of magnetized electrons and unmagnetized ions that carry a perpendicular electric current. The ion fluid appears to be nonideal, sub-Alfvénic, and nondissipative. The ion velocity distribution functions contain multiple populations, such as global Speiser ions, local Speiser ions, and trapped ions. The particle motion of the local Speiser ions in an appropriately rotated coordinate system explains the ion fluid properties very well. The trapped ions are the first demonstration of the regular orbits in the chaotic particle dynamics [Chen and Palmadesso, J. Geophys. Res. 91, 1499 (1986)] in self-consistent PIC simulations. They would be observational signatures in the ion current layer near reconnection sites. [ABSTRACT FROM AUTHOR]

The high-specification computational power of Japan Aerospace Exploration Agency's new supercomputer system, called Fujitsu FX1 cluster, enables us to perform really macroscale 3-D situations with full particle plasma simulation [particle-in-cell (PIC) method]. A fully 3-D kinetic approach to collisionless shock problems, which is one of the most important problems in the space plasma science, is possible, and a challenging run is being executed for a pioneering study of the topic. About 0.4 billion grids are allocated for the electromagnetic fields, and about 0.1 trillion particles are loaded into the simulation run. The computational efficiency of the PIC code is about 8% of the peak performance (4.6 Tflops) using 5776 CPU cores (57 Tflops). The simulation parameters were selected to simulate ESA's Cluster-II spacecraft observational result reported by Seki (in 2009). The full mass ratio mi/me = 1840 was taken for this simulation, and almost one ion inertia length square could be allocated for the simulation. In this simulation, a quite complicated wave activity is found in the shock foot region. In this paper, comparing 3-D results with 2-D simulation results, a 3-D nature of shock transition region of quasi-perpendicular shock is reported. [ABSTRACT FROM AUTHOR]

Previous studies have shown that auroral kilometric radiation (AKR) can play an important role in the magnetosphere‐atmosphere coupling and has the right‐handed extraordinary (R‐X), left‐handed ordinary (L‐O) and left‐handed extraordinary (L‐X) modes. However, the L‐X mode has not been directly observed in the lower latitude magnetosphere yet, probably because of its very limited frequency range. Here, using observations of the Arase satellite on 6 September 2018, we present an AKR event with two distinct bands (8–20 and 300–1000 kHz) around the location: L = 8 and latitude = −37°. The low (high) band is identified as the L‐X (R‐X) mode based on the polarization and frequency ranges. Simulations of 3‐D ray tracing show that most of ray paths with 14 (11 and 18) kHz pass (miss) the location of Arase, basically consistent with observations. Our study provides direct evidence that the L‐X mode can propagate from high latitudes downward to lower latitudes. Plain Language Summary: Auroral kilometric radiation (AKR) is a widely existing radio emission with kilometric wavelength at the Earth, contributing to the magnetosphere‐atmosphere coupling. Similar emissions have been observed on all magnetic planets of the solar system. Previous studies have shown that AKR primarily occurs in the R‐X mode, with a small contribution in the L‐O and L‐X modes. The L‐X mode at lower latitudes has not been directly observed so far, most likely due to its extremely limited frequency range. Here, we present an L‐X mode (peak frequency ∼14 kHz) in the lower latitude magnetosphere observed by the Arase satellite. Using the 3‐D ray tracing method, we simulate ray paths with different initial wave parameters and source locations. Simulations show that ray paths with 14 (11 and 18) kHz pass (miss) the location of the Arase satellite and are highly dependent on initial wave parameters and the location of source. Our results provide a direct evidence that the L‐X mode from high latitude source regions can propagate downward to lower latitudes under suitable conditions. This study enriches the understanding of AKR propagation characteristics in the magnetosphere. Key Points: An auroral kilometric radiation (AKR) event with two distinct bands (8–20 kHz and 300–1000 kHz) is observed around the location: L = 8 and latitude = −37°Based on the polarization and frequency ranges, the low (high) band AKR is identified as the L‐X (R‐X) mode3‐D ray tracing simulations show that L‐X mode can propagate downward to lower latitudes, basically consistent with observations [ABSTRACT FROM AUTHOR]

Plasmaspheric hiss waves are important to shape the Earth's electron radiation belt. These waves are commonly envisioned to have a long lifetime which allows them to permeate the global plasmasphere from a spatially restricted source. However, this hypothesis has not been experimentally confirmed yet, because of the challenging observational requirements in terms of location and timing. With wave and particle measurements from five magnetospheric satellites and detailed modeling, we present the first report of long lifetime (∼42 s) hiss rays in the substorm‐disturbed plasmasphere. The low‐frequency hiss waves are found to originate from the middle piece of the plasmaspheric plume, bounce between two hemispheres, and eventually drift into the plasmaspheric core. These hiss rays can travel through ∼3 hr magnetic local time and ∼4 magnetic shell. Such a long‐time and large‐scale permeation of hiss rays could benefit from the ducting process by plasmaspheric field‐aligned density irregularities. Plain Language Summary: Earth's plasmasphere is populated by a type of whistler‐mode wave named plasmaspheric hiss which is able to shape the electron radiation belt. Hiss waves were commonly envisioned to have a long lifetime which allows them to permeate the global plasmasphere from a spatially restricted source. Although there have been numerous studies on the source of plasmaspheric hiss waves, the hypothesis regarding their long lifetime remains not experimentally confirmed yet because of the challenging observational requirements in terms of location and timing. On the basis of wave and particle measurements from five magnetospheric satellites covering the entire plasmasphere and detailed modeling, we show that the hiss rays can survive at least 42 s in the plasmasphere disturbed by substorms. Within the survival period, these hiss rays migrated from the middle piece of the plasmaspheric plume to the plasmaspheric core, whose path lengths reached 25 Earth radii. Such a long‐time and large‐scale permeation of hiss rays from the plasmaspheric plume to the plasmaspheric core could benefit from the ducting process by plasmaspheric field‐aligned density irregularities. Key Points: Low‐frequency hiss waves were excited by energetic electrons inside the dayside plasmaspheric plume following substormsLow‐frequency hiss rays survived at least 42 s, allowing themselves to migrate from the plasmaspheric plume to the plasmaspheric corePlasmaspheric density ducts facilitated the permeation of hiss rays from the plasmaspheric plume to the plasmaspheric core [ABSTRACT FROM AUTHOR]

The Arase (ERG) satellite is possible to observe higher L-value plasma sheet close to the plasma sheet boundary because of its characteristic orbit, and, actually, Arase has observed several lobe entry events just outside of the outer radiation belt. In some of these events, we found that energetic electron bursts up to (sometimes, over) 300 keV appear at the plasma sheet boundary. The purpose of this study is to address where do the energetic electron bursts at higher latitude come from and what is the contribution of magnetotail reconnection and its associated acceleration process to the generation of the energetic electron bursts. However, the observed energetic electron bursts look quite similar to typical dispersionless substorm injection events. If the observed electron bursts are due to the substorm injection, the observation cannot be explained by the standard understanding of the injection because (1) the injection occurs associated with local magnetic field dipolarizations in downstream of the magnetotail reconnection jets (in deep inside of the plasma sheet) and (2) energetic electrons observed at the plasma sheet boundary are thought to be directly accelerated from magnetotail reconnection sites. Since the pitch angle distribution of 100-200 keV electron shows enhancement both of parallel and perpendicular fluxes, the observed results suggest the coexistence of (1) and (2). In this presentation, we will discuss the physical meanings of the observed electron bursts. The discussion is important to address the relationship between magnetotail reconnection and injections, and the results might contribute to a better understanding of electron acceleration processes and energy input to the inner magnetosphere. [ABSTRACT FROM AUTHOR]

The hazardous plasma environment surrounding Earth poses risks to satellites due to internal charging and surface charging effects. Accurate predictions of these risks are crucial for minimizing damage and preparing for system failures of satellites. To forecast the plasma environment, it is essential to know the current state of the system, as the accuracy of the forecast depends on the accuracy of the initial condition of the forecast. In this study, we use data assimilation techniques to combine observational data and model predictions, and present the first global validation of a data-assimilative electron ring current nowcast during a geomagnetic storm. By assimilating measurements from one satellite and validating the results against another satellite in a different magnetic local time sector, we assess the global response and effectiveness of the data assimilation technique for space weather applications. Using this method, we found that the simulation accuracy can be drastically improved at times when observations are available while eliminating almost all of the bias previously present in the model. These findings contribute to the construction of improved operational models in estimating surface charging risks and providing realistic 'source' populations for radiation belt simulations. [ABSTRACT FROM AUTHOR]

Variations of relativistic electron fluxes (E ≥ 1 MeV) and wave activity in the Earth magnetosphere are studied to determine the contribution of different acceleration mechanisms of the outer radiation belt electrons: ULF mechanism, VLF mechanism, and adiabatic acceleration. The electron fluxes were measured by Arase satellite and geostationary GOES satellites. The ULF power index is used to characterize the magnetospheric wave activity in the Pc5 range. To characterize the VLF wave activity in the magnetosphere, we use data from PWE instrument of Arase satellite. We consider some of the most powerful magnetic storms during the Arase era: May 27–29, 2017; September 7–10, 2017; and August 25–28, 2018. Also, non-storm intervals with a high solar wind speed before and after these storms for comparison are analyzed. Magnitudes of relativistic electron fluxes during these magnetic storms are found to be greater than that during non-storm intervals with high solar wind streams. During magnetic storms, the flux intensity maximum shifts to lower L-shells compared to intervals without magnetic storms. For the considered events, the substorm activity, as characterized by AE index, is found to be a necessary condition for the increase of relativistic electron fluxes, whereas a high solar wind speed alone is not sufficient for the relativistic electron growth. The enhancement of relativistic electron fluxes by 1.5–2 orders of magnitude is observed 1–3 days after the growth of the ULF index and VLF emission power. The growth of VLF and ULF wave powers coincides with the growth of substorm activity and occurs approximately at the same time. Both mechanisms operate at the first phase of electron acceleration. At the second phase of electron acceleration, the mechanism associated with the injection of electrons into the region of the magnetic field weakened by the ring current and their subsequent betatron acceleration during the magnetic field restoration can work effectively. [ABSTRACT FROM AUTHOR]

The Hunga Tonga–Hunga Ha'apai (HTHH) undersea volcanic eruption that occurred at 04:15 UT on 15 January 2022 is one of the most explosive events in the modern era, and a vertical plume reached approximately 55 km, corresponding to a height of the lower mesosphere. The intense explosion and subsequent plume generated acoustic and atmospheric gravity waves detected by ground-based instruments worldwide. Because a global-scale atmospheric and ionospheric response to the large volcanic eruption has not yet been observed, it provides a unique opportunity to promote interdisciplinary studies of coupling processes in lithosphere–atmosphere–ionosphere with ground-based and satellite observations and modeling. Further, this event allows us to elucidate the propagation and occurrence features of traveling ionospheric disturbances, the generation of equatorial plasma bubbles, the cause of electron density holes around the volcano, and the magnetic conjugacy of magnetic field perturbations. The most notable point among these studies is that the medium-scale travelling traveling ionospheric disturbances (MSTIDs) have magnetic conjugacy even in the daytime ionosphere and are generated by an external electric field, such as an E-region dynamo field, due to the motions of neutrals in the thermosphere. This advocates a new generation mechanism of MSTIDs other than the neutral oscillation associated with atmospheric gravity waves and electrified MSTIDs, which are frequently observed during daytime and nighttime, respectively. This paper reviews the recent studies of atmospheric and ionospheric disturbances after the HTHH volcanic eruption and summarizes what we know from this extreme event analysis. Further, we analyzed new datasets not shown in previous studies to give some new insights to understanding of some related phenomena. As a result, we also found that 4-min plasma flow oscillations caused by the acoustic resonance appeared with the amplitude of approximately 30 m/s in the northern hemisphere a few hours before the initial arrival of the air pressure waves. The propagation direction was westward, which is the same as that of the daytime MSTIDs with a magnetic conjugate feature. This result suggests that the 4-min oscillations are generated by an external electric field transmitted to the northern hemisphere along magnetic field lines. [ABSTRACT FROM AUTHOR]

The Exploration of energization and Radiation in Geospace (ERG) project explores the acceleration, transport, and loss of relativistic electrons in the radiation belts and the dynamics for geospace storms. This project consists of three research teams for satellite observation, ground-based network observation, and integrated data analysis/simulation. This synergetic approach is essential for obtaining a comprehensive understanding of the relativistic electron generation/loss processes of the radiation belts as well as geospace storms through cross-energy/cross-regional couplings, in which different plasma/particle populations and regions are strongly coupled with each other. This paper gives an overview of the ERG project and presents the initial results from the ERG (Arase) satellite. [ABSTRACT FROM AUTHOR]

Equatorial plasma bubbles are a phenomenon of plasma density depletion with small-scale density irregularities, normally observed in the equatorial ionosphere. This phenomenon, which impacts satellite-based communications, was observed in the Asia-Pacific region after the largest-on-record January 15, 2022 eruption of the Tonga volcano. We used satellite and ground-based ionospheric observations to demonstrate that an air pressure wave triggered by the Tonga volcanic eruption could cause the emergence of an equatorial plasma bubble. The most prominent observation result shows a sudden increase of electron density and height of the ionosphere several ten minutes to hours before the initial arrival of the air pressure wave in the lower atmosphere. The propagation speed of ionospheric electron density variations was ~ 480–540 m/s, whose speed was higher than that of a Lamb wave (~315 m/s) in the troposphere. The electron density variations started larger in the Northern Hemisphere than in the Southern Hemisphere. The fast response of the ionosphere could be caused by an instantaneous transmission of the electric field to the magnetic conjugate ionosphere along the magnetic field lines. After the ionospheric perturbations, electron density depletion appeared in the equatorial and low-latitude ionosphere and extended at least up to ±25° in geomagnetic latitude. [ABSTRACT FROM AUTHOR]

Recent studies have shown that auroral kilometric radiation (AKR) can propagate from the polar source cavity into the equatorial radiation belt but there is no direct evidence yet. By examining 19‐month data from Arase satellite and Van Allen Probes, we report a unique event that distinct AKR emissions are observed simultaneously at high and low latitudes, with the peak wave spectra in the frequency 300–400 kHz. Using the three‐dimensional ray tracing method, we simulate the AKR ray paths at three typical frequencies (220, 350, and 550 kHz), and show that more ray paths for 350 kHz can propagate downward through the locations of Arase satellite and Van Allen Probe B than those for other two frequencies. This result can successfully explain the observation and provides a direct evidence that AKR can propagate to low latitude radiation belt under suitable conditions. Plain Language Summary: Auroral kilometric radiation (AKR) is a widely existing electromagnetic wave in the magnetosphere and has potential for acceleration or precipitation loss of energetic electrons, yielding serious damage to orbiting space systems or ozone destruction in the atmosphere. Previous observation and numerical simulation have shown that AKR originated from the polar cavity region can be presented in the low latitude even in the equator. However, there is no direct observational evidence yet due to lack of the correlated data at higher and lower latitudes. Here, we examine observations of Arase satellite and Van Allen Probes from 25 March 2017 to 30 October 2018, and find a unique AKR event detected simultaneously by the Arase satellite (at high latitude) and Probe B (at low latitude). Using 3‐D ray tracing method, we simulate AKR paths for different frequencies (220, 350, and 550 kHz) with suitable wave normal angles and azimuthal angles. We show that more ray paths for 350 kHz can pass through the locations of Arase satellite and Probe B than those for other two frequencies, consistent with the observations. The current result provides a direct evidence that AKR can propagate to low latitude radiation belt under suitable conditions. Key Points: A unique auroral kilometric radiation (AKR) event is reported simultaneously by Arase satellite and Van Allen Probes during 19‐month observationsSimulations show that more AKR for 350 kHz pass the locations of two satellites, consistent with observationsAKR raypaths are highly dependent on wave frequency, initial wave normal angles and azimuthal angles [ABSTRACT FROM AUTHOR]

Auroral kilometric radiation (AKR) is generated at high latitudes and can propagate down to low latitudes. Due to the lack of direct observations, the characteristics of AKR in the middle and low latitudes of two hemispheres have not been studied so far. Here, using observations of the Arase satellite from 23 March 2017 to 31 July 2019, we present the first statistical study of AKR distribution in the northern (Magnetic latitude Mlat = 0°–40°) and southern (Mlat = −40°–0°) hemispheres. Results (totally 30,353 samples) show that relatively high occurrence rates (>30%) of AKR in the northern (southern) hemisphere primarily stay in the region of magnetic local time MLT = 17–24 (MLT = 21–05). About 60% of wave samples in the northern (southern) hemisphere are observed in the frequency range of ≤300 kHz (>300 kHz). The asymmetric distribution in two hemispheres can further enrich our understanding of AKR. Plain Language Summary: Auroral kilometric radiation (AKR) is a strong radio emission with kilometric wavelength at the Earth. They have a potential for accelerating electrons to relativistic energies or scattering electrons into the atmosphere, leading to serious damage to spacecrafts or ozone destruction. Because the parallel electric field contributing to AKR generation should be different in the northern and southern hemispheres, it is necessary to study the distribution characteristics of AKR in two hemispheres. Here, we examine the data of Arase satellite from 23 March 2017 to 31 July 2019, and find that the distributions of AKR samples in two hemispheres are asymmetric. The occurrence rate in the southern hemisphere is greater than that in the northern hemisphere. More AKR samples in the northern (southern) hemisphere occur from dusk to midnight (pre‐midnight to dawn). More AKR samples in the northern (southern) hemisphere are observed in the frequency range of ≤300 kHz (>300 kHz). This study provides more information about AKR in the magnetosphere. Key Points: The distribution characteristics of Auroral kilometric radiation (AKR) in two hemispheres are presented for the first time based on observations from Arase satelliteAKR samples in the northern (southern) hemisphere are observed relatively frequently in the region of magnetic local time = 17–24 (MLT = 21–05)More AKR samples in the northern (southern) hemisphere stay in the low (high) frequency range [ABSTRACT FROM AUTHOR]

Very low frequency (VLF) waves (about 3–30 kHz) in the Earth's magnetosphere interact strongly with energetic electrons and are a key element in controlling dynamics of the Van Allen radiation belts. Bistatic very low frequency (VLF) transmission experiments have recently been conducted in the magnetosphere using the high-power VLF transmitter on the Air Force Research Laboratory's Demonstration and Science Experiments (DSX) spacecraft and an electric field receiver onboard the Japan Aerospace Exploration Agency's Arase (ERG) spacecraft. On 4 September 2019, the spacecraft came within 410 km of each other and were in geomagnetic alignment. During this time, VLF signals were successfully transmitted from DSX to Arase, marking the first successful reception of a space-to-space VLF signal. Arase measurements were consistent with field-aligned propagation as expected from linear cold plasma theory. Details of the transmission event and comparison to VLF propagation model predictions are presented. The capability to directly inject VLF waves into near-Earth space provides a new way to study the dynamics of the radiation belts, ushering in a new era of space experimentation. [ABSTRACT FROM AUTHOR]

Magnetopause reconnection would be characterized by the density jump across the current sheet, the flow shear across the boundary, and nonzero guide field. While effects of each of these elements have been studied, the effects arising from the combination of these are still unexplored. Two-dimensional full-particle simulations show that the combination of shear flow and/or guide field with density asymmetry induces the sliding motion of the X-line along the magnetopause. The direction of the X-line motion is controlled either by the ion flow at the X-line when the shear flow effects dominate or by the electron flow at the X-line when the guide field effects dominate. The shear flow effects and the guide field effects may counteract each other in determining the direction of the X-line motion and, in the close proximity of the subsolar region where the flow is slow, the X-line motion can be opposite to the flow direction. [ABSTRACT FROM AUTHOR]

Counterstreaming ions embedded in hot isotropic ions are found at the front of fast earthward plasma flows in the recovery phase of substorms in the Earth's magnetotail. The counterstreaming ions are present only when the northward component of the magnetic field increases in the equatorial plane. Hybrid simulations of magnetic reconnection have been carried out. It is found that counterstreaming ions form in the leading edge of jetting plasmas produced with magnetic reconnection, where the magnetic field lines pile up due to the pre-existing stationary plasmas. These counterstreaming ions originate from cold ions on the northern and southern tail lobe field lines, and earthward transport of the reconnected field lines makes these cold ions flow into the equatorial plane. The present observations provide strong evidence of magnetic reconnection in the recovery phase of substorms at the kinetic level. [ABSTRACT FROM AUTHOR]

The wedge‐like and nose‐like ion spectral structures, named after their characteristic shapes in the energy‐time spectrograms, appear to be distinctively different structures in the Earth's inner magnetosphere. Here. we present a case study with conjugate observations from the Arase spacecraft and the twin Van Allen Probes on July 1 and 2, 2017, which displayed the characteristic signatures of the wedge‐like and nose‐like ion structures, respectively. When the spacecraft nearly intersected at L = 2.8, the two structures overlapped with enhanced ion fluxes in the energy range of 1–10 keV. These observations suggest that the wedge‐like and nose‐like spectral signatures are merely the manifestations of one single structure along different spacecraft trajectories. This finding is further validated by the reproduction of both structures from a particle‐tracing model, which also indicates their formation processes associated with the intermittent substorm injections in the nightside magnetosphere. Plain Language Summary: In recent decades, a variety of magnetospheric missions have observed many different kinds of ion dispersion signatures in the inner magnetosphere, including nose‐like, wedge‐like, trunk‐like structures, etc. They are named after the shapes of enhanced ion fluxes in the energy‐time (or energy‐L shell) spectrogram. In previous studies, the source and formation mechanism of these structures were independently investigated so that their mutual relationships are still unknown. Using the joint observations from Arase and two Van Allen Probes, we first reveal the relationship between the wedge‐like and nose‐like structures. We find that these two structures are merely the manifestations of a single structure along different spacecraft trajectories and their formation is subject to the accessibility of the injected ions associated with the intermittent substorm activities in the near‐Earth tail. This study also demonstrates that the joint observations of different ion structures and their comparisons with modeling simulations can shed new light on the understanding of the interplay between ions and fields in the inner magnetosphere and the promotion of the empirical electric field models. Key Points: The wedge‐like and nose‐like ion structures were observed by Arase and twin Van Allen Probes in the inner magnetosphere, respectivelyTwo structures overlapped at the intersection of spacecraft trajectories, indicating they are merely manifestations of a single structureThe observational characteristics are reproduced by a particle‐tracing simulation, with ions originating from the substorm injection region [ABSTRACT FROM AUTHOR]

The wedge‐like and nose‐like ion spectral structures, named after their characteristic shapes in the energy‐time spectrograms, appear to be distinctively different structures in the Earth's inner magnetosphere. Here. we present a case study with conjugate observations from the Arase spacecraft and the twin Van Allen Probes on July 1 and 2, 2017, which displayed the characteristic signatures of the wedge‐like and nose‐like ion structures, respectively. When the spacecraft nearly intersected at L = 2.8, the two structures overlapped with enhanced ion fluxes in the energy range of 1–10 keV. These observations suggest that the wedge‐like and nose‐like spectral signatures are merely the manifestations of one single structure along different spacecraft trajectories. This finding is further validated by the reproduction of both structures from a particle‐tracing model, which also indicates their formation processes associated with the intermittent substorm injections in the nightside magnetosphere. Plain Language Summary: In recent decades, a variety of magnetospheric missions have observed many different kinds of ion dispersion signatures in the inner magnetosphere, including nose‐like, wedge‐like, trunk‐like structures, etc. They are named after the shapes of enhanced ion fluxes in the energy‐time (or energy‐L shell) spectrogram. In previous studies, the source and formation mechanism of these structures were independently investigated so that their mutual relationships are still unknown. Using the joint observations from Arase and two Van Allen Probes, we first reveal the relationship between the wedge‐like and nose‐like structures. We find that these two structures are merely the manifestations of a single structure along different spacecraft trajectories and their formation is subject to the accessibility of the injected ions associated with the intermittent substorm activities in the near‐Earth tail. This study also demonstrates that the joint observations of different ion structures and their comparisons with modeling simulations can shed new light on the understanding of the interplay between ions and fields in the inner magnetosphere and the promotion of the empirical electric field models. Key Points: The wedge‐like and nose‐like ion structures were observed by Arase and twin Van Allen Probes in the inner magnetosphere, respectivelyTwo structures overlapped at the intersection of spacecraft trajectories, indicating they are merely manifestations of a single structureThe observational characteristics are reproduced by a particle‐tracing simulation, with ions originating from the substorm injection region [ABSTRACT FROM AUTHOR]

A study using Arase data gives the first observational evidence that the frequency drift of electromagnetic ion cyclotron (EMIC) waves is caused by cyclotron trapping. EMIC emissions play an important role in planetary magnetospheres, causing scattering loss of radiation belt relativistic electrons and energetic protons. EMIC waves frequently show nonlinear signatures that include frequency drift and amplitude enhancements. While nonlinear growth theory has suggested that the frequency change is caused by nonlinear resonant currents owing to cyclotron trapping of the particles, observational evidence for this has been elusive. We survey the wave data observed by Arase from March, 2017 to September 2019, and find the best falling tone emission event, one detected on 11th November, 2017, for the wave particle interaction analysis. Here, we show for the first time direct evidence of the formation of a proton hill in phase space indicating cyclotron trapping. The associated resonance currents and the wave growth of a falling tone EMIC wave are observed coincident with the hill, as theoretically predicted. [ABSTRACT FROM AUTHOR]

We have developed ISEE_Wave (Institute for Space-Earth Environmental Research, Nagoya University - Plasma Wave Analysis Tool), an interactive plasma wave analysis tool for electric and magnetic field waveforms observed by the plasma wave experiment aboard the Arase satellite. ISEE_Wave provides an integrated wave analysis environment on a graphical user interface, where users can visualize advanced wave properties, such as the electric and magnetic field wave power spectra, wave normal polar angle, polarization ellipse, planarity of polarization, and Poynting vector angle. Users can simply select a time interval for their analysis, and ISEE_Wave automatically downloads the waveform data, ambient magnetic field data, and spacecraft attitude data from the data archive repository of the ERG Science Center, and then performs necessary coordinate transformation and spectral matrix calculation. The singular value decomposition technique is used as the core technique for the wave property analysis of ISEE_Wave. On-demand analysis is possible by specifying the parameters of the wave property analysis as well as the plot styles using the graphical user interface of ISEE_Wave. The results can be saved as image files of plots and/or a tplot save file. ISEE_Wave aids in the identification of fine structures of observed plasma waves, wave mode identification, and wave propagation analysis. These properties can be used to understand plasma wave generation, propagation, and wave-particle interaction in the inner magnetosphere. ISEE_Wave can also be applied to general waveform data observed by other spacecraft by using the plug-in procedures to load the data. [ABSTRACT FROM AUTHOR]

Auroral kilometric radiations (AKR) are strong radio emission phenomena, and can produce significant acceleration or scattering of radiation belt electrons. The variation of AKR wave amplitude with the latitude (λ) has not been reported so far owing to lack of measurements. Here, using observations of the Arase satellite and Van Allen Probes from March 23, 2017 to July 31, 2019, we present the first statistical study on the AKR electric field amplitude (Et) in the radiation belts for |λ| = 0° − 40° and L‐shell L = 3.0–6.2. Results (totally 14,770 samples) show that Et can be described by a concise formula: Et(λ) = E0 exp(ξ sin |λ|), decreasing with decreasing latitude. Fitting parameters E0 and ξ are limited in the ranges: E0 = 0.054–0.340 mV/m and ξ = 3.0–4.2. Wave amplitudes are greater (smaller) under intense (weak) geomagnetic conditions. This study helps to better quantify the gyroresonance between AKR and radiation belt electrons. Plain Language Summary: Auroral kilometric radiation (AKR) is a strong radio emission phenomenon which is generated in the low density polar cavity. They can propagate downward into radiation belts and produce significant acceleration or pitch angle scattering of energetic electrons. Those electrons can yield serious damage to spacecraft or ozone destruction. Because wave‐particle interaction generally occurs at each point along the field line and diffusion coefficients are directly proportional to the square of wave amplitude, it is necessary to specify the field‐aligned wave amplitude. However, previous calculations of AKR‐electron interaction were based on the assumption of the constant field‐aligned wave amplitude. Here, using observations of the Arase satellite and Van Allen Probes from March 23, 2017 to July 31, 2019, we report a field‐aligned distribution of AKR wave amplitude for the first time. Gaussian fitting for the electric field power spectral density is performed to obtain the wave amplitude of each AKR sample. We calculate averaged wave amplitudes of total 14,770 samples on the dayside and nightside. Results show that wave amplitude can be described by a concise formula, decreasing obviously with decreasing latitude. Wave amplitudes are greater (smaller) under intense (weak) geomagnetic condition. This paper provides the further understanding of AKR‐electron interaction. Key Points: The field‐aligned distribution of AKR wave amplitude is presented for the first time based on Arase satellite and Van Allen ProbesWave amplitudes can be approximately described by a concise exponential formula and decrease obviously with decreasing latitudeThe AKR sample and amplitude are roughly symmetric around the equator, wave amplitudes increase with increasing geomagnetic activities [ABSTRACT FROM AUTHOR]

Bright, discrete, thin auroral arcs are a typical form of auroras in nightside polar regions. Their light is produced by magnetospheric electrons, accelerated downward to obtain energies of several kilo electron volts by a quasi-static electric field. These electrons collide with and excite thermosphere atoms to higher energy states at altitude of ~ 100 km; relaxation from these states produces the auroral light. The electric potential accelerating the aurora-producing electrons has been reported to lie immediately above the ionosphere, at a few altitudes of thousand kilometres1. However, the highest altitude at which the precipitating electron is accelerated by the parallel potential drop is still unclear. Here, we show that active auroral arcs are powered by electrons accelerated at altitudes reaching greater than 30,000 km. We employ high-angular resolution electron observations achieved by the Arase satellite in the magnetosphere and optical observations of the aurora from a ground-based all-sky imager. Our observations of electron properties and dynamics resemble those of electron potential acceleration reported from low-altitude satellites except that the acceleration region is much higher than previously assumed. This shows that the dominant auroral acceleration region can extend far above a few thousand kilometres, well within the magnetospheric plasma proper, suggesting formation of the acceleration region by some unknown magnetospheric mechanisms. [ABSTRACT FROM AUTHOR]

Plasmaspheric hiss is an important whistler‐mode emission shaping the Van Allen radiation belt environment. How the plasmaspheric hiss waves are generated, propagate, and dissipate remains under intense debate. With the five spacecraft of Van Allen Probes, Exploration of energization and Radiation in Geospace (Arase), and Geostationary Operational Environmental Satellites missions at widely spaced locations, we present here the first comprehensive observations of hiss waves growing from the substorm‐injected electron instability, spreading within the plasmasphere, and dissipating over a large spatial scale. During substorms, hot electrons were injected energy‐dispersively into the plasmasphere near the dawnside and, probably through a combination of linear and nonlinear cyclotron resonances, generated whistler‐mode waves with globally drifting frequencies. These waves were able to propagate from the dawnside to the noonside, with the frequency‐drifting feature retained. Approximately 5 hr of magnetic local time away from the source region in the dayside sector, the wave power was dissipated to e−4 of its original level. Plain Language Summary: A noisy band of electromagnetic waves with frequencies ranging from tens of hertz to several kilohertz in the Earth's plasmasphere is termed plasmaspheric hiss. These waves are recognized to shape the Van Allen radiation belt environment and then affect the spacecraft survivability and lifetime. How the plasmaspheric hiss waves are generated, propagate, and dissipate has been a fundamental unanswered question since their discovery. With three space missions scattered in the inner magnetosphere, we present here the first comprehensive observations of hiss waves growing from the substorm‐injected electron instability, spreading within the plasmasphere, and dissipating over a large spatial scale. These findings have significant implications for the modeling of the plasmaspheric hiss waves and the Van Allen radiation belt dynamics. Key Points: Near the dawnside, energy‐dispersively injected electrons generated plasmaspheric hiss with globally drifting frequenciesThe frequency drift feature allowed tracing the plasmaspheric hiss propagation from the dawnside to the noonsideThe dayside plasmaspheric hiss dissipated away roughly within a magnetic local time span of 5 hr [ABSTRACT FROM AUTHOR]

Plasmaspheric hiss is an important whistler‐mode emission shaping the Van Allen radiation belt environment. How the plasmaspheric hiss waves are generated, propagate, and dissipate remains under intense debate. With the five spacecraft of Van Allen Probes, Exploration of energization and Radiation in Geospace (Arase), and Geostationary Operational Environmental Satellites missions at widely spaced locations, we present here the first comprehensive observations of hiss waves growing from the substorm‐injected electron instability, spreading within the plasmasphere, and dissipating over a large spatial scale. During substorms, hot electrons were injected energy‐dispersively into the plasmasphere near the dawnside and, probably through a combination of linear and nonlinear cyclotron resonances, generated whistler‐mode waves with globally drifting frequencies. These waves were able to propagate from the dawnside to the noonside, with the frequency‐drifting feature retained. Approximately 5 hr of magnetic local time away from the source region in the dayside sector, the wave power was dissipated to e−4 of its original level. Plain Language Summary: A noisy band of electromagnetic waves with frequencies ranging from tens of hertz to several kilohertz in the Earth's plasmasphere is termed plasmaspheric hiss. These waves are recognized to shape the Van Allen radiation belt environment and then affect the spacecraft survivability and lifetime. How the plasmaspheric hiss waves are generated, propagate, and dissipate has been a fundamental unanswered question since their discovery. With three space missions scattered in the inner magnetosphere, we present here the first comprehensive observations of hiss waves growing from the substorm‐injected electron instability, spreading within the plasmasphere, and dissipating over a large spatial scale. These findings have significant implications for the modeling of the plasmaspheric hiss waves and the Van Allen radiation belt dynamics. Key Points: Near the dawnside, energy‐dispersively injected electrons generated plasmaspheric hiss with globally drifting frequenciesThe frequency drift feature allowed tracing the plasmaspheric hiss propagation from the dawnside to the noonsideThe dayside plasmaspheric hiss dissipated away roughly within a magnetic local time span of 5 hr [ABSTRACT FROM AUTHOR]

The extremely high-energy electron experiment (XEP) onboard the Arase (ERG) satellite is designed to measure high-energy electrons in the Earth’s radiation belts. The XEP was developed by taking advantage of our technical heritage of high-energy particle detectors that are onboard Earth observation satellites of the Japan Aerospace Exploration Agency (JAXA) as the radiation monitor. The main target of the XEP is to precisely measure variations of relativistic electrons in the outer radiation belt even during magnetic storms. The measurement is scientifically required to address physical mechanisms of electron acceleration and loss. The XEP consists of five solid-state silicon detectors (SSDs) and a single-crystal inorganic scintillator of cerium-doped gadolinium orthosilicate (GSO) to measure electrons in the energy range of 0.4-20 MeV and has a 20° single field of view (FOV). It is also equipped with a plastic scintillator that surrounds the GSO scintillator to prevent particles from entering the detectors from outside the FOV. The XEP has started its observation of relativistic electrons and has successfully observed dynamic variations of relativistic electron fluxes in the outer radiation belt during magnetic storms. This paper describes the instrumentation of the XEP and presents an example of initial observation results. [ABSTRACT FROM AUTHOR]

Abstract: We present observational evidence of drift resonance between westward propagating odd mode standing ultralow frequency waves and energetic protons. Compressional ∼13 mHz (Pc4 band) waves and proton flux oscillations at >50 keV were detected at ∼03 hr magnetic local time by the Arase satellite on 15 April 2017. The azimuthal wave number (m number) is estimated to be ∼−50 from ground observations, while the theory of drift resonance gives m ∼− 49 for odd mode waves and ∼110‐keV protons, providing evidence that the drift resonance indeed took place in this event. We also found a steep earthward gradient of proton phase space density, which can quantitatively explain the wave excitation. The observed waves show typical features of giant pulsations (Pgs), regarding local time, m number, and flux oscillations. This study, therefore, has great implications to the field line mode structure and excitation mechanism of Pgs. [ABSTRACT FROM AUTHOR]

We describe the principles of the Wave-Particle Interaction Analyzer (WPIA) and the implementation of the Software-type WPIA (S-WPIA) on the Arase satellite. The WPIA is a new type of instrument for the direct and quantitative measurement of wave-particle interactions. The S-WPIA is installed on the Arase satellite as a software function running on the mission data processor. The S-WPIA on board the Arase satellite uses an electromagnetic field waveform that is measured by the waveform capture receiver of the plasma wave experiment (PWE), and the velocity vectors of electrons detected by the medium-energy particle experiment-electron analyzer (MEP-e), the high-energy electron experiment (HEP), and the extremely high-energy electron experiment (XEP). The prime objective of the S-WPIA is to measure the energy exchange between whistler-mode chorus emissions and energetic electrons in the inner magnetosphere. It is essential for the S-WPIA to synchronize instruments to a relative time accuracy better than the time period of the plasma wave oscillations. Since the typical frequency of chorus emissions in the inner magnetosphere is a few kHz, a relative time accuracy of better than 10 μs is required in order to measure the relative phase angle between the wave and velocity vectors. In the Arase satellite, a dedicated system has been developed to realize the time resolution required for inter-instrument communication. Here, both the time index distributed over all instruments through the satellite system and an S-WPIA clock signal are used, that are distributed from the PWE to the MEP-e, HEP, and XEP through a direct line, for the synchronization of instruments within a relative time accuracy of a few μs. We also estimate the number of particles required to obtain statistically significant results with the S-WPIA and the expected accumulation time by referring to the specifications of the MEP-e and assuming a count rate for each detector. [ABSTRACT FROM AUTHOR]

The plasmas (electrons and ions) in the inner magnetosphere have wide energy ranges from electron volts to mega-electron volts (MeV). These plasmas rotate around the Earth longitudinally due to the gradient and curvature of the geomagnetic field and by the co-rotation motion with timescales from several tens of hours to less than 10 min. They interact with plasma waves at frequencies of mHz to kHz mainly in the equatorial plane of the magnetosphere, obtain energies up to MeV, and are lost into the ionosphere. In order to provide the global distribution and quantitative evaluation of the dynamical variation of these plasmas and waves in the inner magnetosphere, the PWING project (study of dynamical variation of particles and waves in the inner magnetosphere using ground-based network observations, ) has been carried out since April 2016. This paper describes the stations and instrumentation of the PWING project. We operate all-sky airglow/aurora imagers, 64-Hz sampling induction magnetometers, 40-kHz sampling loop antennas, and 64-Hz sampling riometers at eight stations at subauroral latitudes (~ 60° geomagnetic latitude) in the northern hemisphere, as well as 100-Hz sampling EMCCD cameras at three stations. These stations are distributed longitudinally in Canada, Iceland, Finland, Russia, and Alaska to obtain the longitudinal distribution of plasmas and waves in the inner magnetosphere. This PWING longitudinal network has been developed as a part of the ERG (Arase)-ground coordinated observation network. The ERG (Arase) satellite was launched on December 20, 2016, and has been in full operation since March 2017. We will combine these ground network observations with the ERG (Arase) satellite and global modeling studies. These comprehensive datasets will contribute to the investigation of dynamical variation of particles and waves in the inner magnetosphere, which is one of the most important research topics in recent space physics, and the outcome of our research will improve safe and secure use of geospace around the Earth. [ABSTRACT FROM AUTHOR]

Solar wind interaction with a kinetic scale magnetosphere and the resulting momentum transfer process are investigated by 2.5-dimensional full kinetic particle-in-cell simulations. The spatial scale of the considered magnetosphere is less than or comparable to the ion inertial length and is relevant for magnetized asteroids or spacecraft with mini-magnetosphere plasma propulsion. Momentum transfer is evaluated by studying the Lorentz force between solar wind plasma and a hypothetical coil current density that creates the magnetosphere. In the zero interplanetary magnetic field (IMF) limit, solar wind interaction goes into a steady state with constant Lorentz force. The dominant Lorentz force acting on the coil current density is applied by the thin electron current layer at the wind-filled front of the magnetosphere. Dynamic pressure of the solar wind balances the magnetic pressure in this region via electrostatic deceleration of ions. The resulting Lorentz force is characterized as a function of the scale of magnetosphere normalized by the electron gyration radius, which determines the local structure of the current layer. For the finite northward IMF case, solar wind electrons flow into the magnetosphere through the reconnecting region. The inner electrons enhance the ion deceleration, and this results in temporal increment of the Lorentz force. It is concluded that the momentum transfer of solar wind plasma could take place actively with variety of kinetic plasma phenomena, even in a magnetosphere with a small scale of less than the ion inertial length. [ABSTRACT FROM AUTHOR]

The system size dependence of electron acceleration during large-scale magnetic island coalescence is studied via a two-dimensional particle-in-cell simulation. Using a simulation box that is larger than those used in previous studies, injection by merging line acceleration and subsequent reacceleration inside a merged island are found to be the mechanisms for producing the most energetic electrons. This finding and knowledge of the reacceleration process enable us to predict that the high energy end of the electron energy spectrum continues to expand as the merged island size increases. Both the merging line acceleration and the reacceleration within a merged island require the island coalescence process to be so dynamic as to involve fast in-flow toward the center of a merged island. Once this condition is met in an early stage of the coalescence, it is likely to stay in the subsequent phase. In other words, if the thin elongated current sheet is initially able to host the dynamic magnetic island coalescence process, it will be a site where repeated upgrades in the maximum energy of electrons occur in a systematic manner. [ABSTRACT FROM AUTHOR]

In a thin elongated current sheet, it is likely that more than one X-line forms and thus multiple magnetic islands are produced. The islands are then subject to merging. By simulating such a case with a two-dimensional full-particle code, we show that a merger forming a large island produces the most energetic electron population in the system. By setting the lateral extent of the simulation box to be as large as ∼100 ion inertial lengths, we introduce many (16) small islands in the initial thin current sheet (∼1 ion inertial length thickness). Merging of these islands proceeds to leave only two islands in the system. Then, strong electron acceleration is seen upon the final merger that produces the single island in the large simulation box. The most energetic electrons in the system are accelerated at the merging line. The merging line acceleration dominates because the reverse-reconnection facilitating the final merger is in such a strongly driven manner that the associated electric field is an order of magnitude larger than those available upon normal reconnection. Combining the results from additional runs enables us to obtain a scaling law, which suggests a non-negligible role played by merging lines in the observed electron acceleration phenomena. [ABSTRACT FROM AUTHOR]

Recent advancement in numerical techniques for Vlasov simulations and their application to cross-scale coupling in the plasma universe are discussed. Magnetohydrodynamic (MHD) simulations are now widely used for numerical modeling of global and macroscopic phenomena. In the framework of the MHD approximation, however, diffusion coefficients such as resistivity and adiabatic index are given from empirical models. Thus there are recent attempts to understand first-principle kinetic processes in macroscopic phenomena, such as magnetic reconnection and the Kelvin–Helmholtz (KH) instability via full kinetic particle-in-cell and Vlasov codes. In the present study, a benchmark test for a new four-dimensional full electromagnetic Vlasov code is performed. First, the computational speed of the Vlasov code is measured and a linear performance scaling is obtained on a massively parallel supercomputer with more than 12 000 cores. Second, a first-principle Vlasov simulation of the KH instability is performed in order to evaluate current status of numerical techniques for Vlasov simulations. The KH instability is usually adopted as a benchmark test problem for guiding-center Vlasov codes, in which a cyclotron motion of charged particles is neglected. There is not any full electromagnetic Vlasov simulation of the KH instability; this is because it is difficult to follow Evector ×Bvector drift motion accurately without approximations. The present first-principle Vlasov simulation has successfully represented the formation of KH vortices and its secondary instability. These results suggest that Vlasov code simulations would be a powerful approach for studies of cross-scale coupling on future Peta-scale supercomputers. [ABSTRACT FROM AUTHOR]

Correction to: Earth Planets Space (2021) 73:110 https://doi.org/10.1186/s40623-021-01430-3 After publication of this article (Matsuda et al. [1]), it is noticed the 8th author's name is incorrect. Reference 1 Matsuda S, Miyoshi Y, Nakamura S, Kitahara M, Shoji M, Hori T, Imajo S, Jun C-W, Kurita S, Kasahara Y, Matsuoka A, Shinohara I. ISEE Wave: interactive plasma wave analysis tool. Correction to: ISEE Wave: interactive plasma wave analysis tool. [Extracted from the article]

Substorm-associated electron injection, starting on Apr. 5, 2017, was observed by the ERG (Arase), GOES-15 and GOES-13 spacecraft. ERG successfully observed a clear and sufficient extent of manifestations of the dispersionless injection and the successive drift echoes at radial distances shorter than geosynchronous orbit (GEO) during a unique period of the satellite mission. The GOES-15 and GOES-13 measured the drift echoes of the event as well. The observations provided constraints to study the event and opportunities to make adjustments to the previous substorm injection models. Models built on an impulsive earthward-propagating electromagnetic field have been proposed to simulate substorm injections. So far such models showed good results of dispersionless features compared to spacecraft observations, but could only produce drift echoes with periods somewhat different from geosynchronous observations. To study the substorm injection event and produce drift echoes with better periods, we modify an existing model in the literature. ERG and GOES spacecraft measured tens to a few hundred keV electrons injected during the substorm, providing important seed population for ring current and radiation belts. Since the electron energies of interest are comparable to the rest mass energy, our work further provides the relativistic form of the previous model and employs a semiempirical model as background field instead of a dipole-based one in the previous study. Our work shows that the main features of the substorm injection event are successfully reproduced with the drift echoes periods showing a better fit to the observations of this event when relativistic effects are considered. Despite possible deviation of the model magnetic fields from reality, the relativistic computations still show dominant effect on the drift echoes periods. The substorm injection expanding earthward farther than GEO was observed by ERG, and the event can be better simulated by the further-developed model shown in this work. [ABSTRACT FROM AUTHOR]

Transient mesospheric echo in the VHF range was detected at an altitude of 65-70 km during the auroral breakup that occurred from 2220 to 2226 UT on June 30, 2017. During this event, the footprint of the Arase satellite was located within the field of view of the all-sky imagers at Syowa Station in the Antarctic. Auroral observations at Syowa Station revealed the dominant precipitation of relatively soft electrons during the auroral breakup. A corresponding spike in cosmic noise absorption was also observed at Syowa Station, while the Arase satellite observed a flux enhancement of > 100 keV electrons and a broadband noise without detecting chorus waves or electromagnetic ion cyclotron waves. A general-purpose Monte Carlo particle transport simulation code was used to quantitatively evaluate the ionization in the middle atmosphere. Results of this study indicate that the precipitation of energetic electrons of > 100 keV, rather than X-rays from the auroral electrons, played a dominant role in the transient and deep (65-70 km) mesospheric ionization during the observed auroral breakup. [ABSTRACT FROM AUTHOR]

Auroral substorms, dynamic phenomena that occur in the upper atmosphere at night, are caused by global reconfiguration of the magnetosphere, which releases stored solar wind energy. These storms are characterized by auroral brightening from dusk to midnight, followed by violent motions of distinct auroral arcs that suddenly break up, and the subsequent emergence of diffuse, pulsating auroral patches at dawn. Pulsating aurorae, which are quasiperiodic, blinking patches of light tens to hundreds of kilometres across, appear at altitudes of about 100 kilometres in the high-latitude regions of both hemispheres, and multiple patches often cover the entire sky. This auroral pulsation, with periods of several to tens of seconds, is generated by the intermittent precipitation of energetic electrons (several to tens of kiloelectronvolts) arriving from the magnetosphere and colliding with the atoms and molecules of the upper atmosphere. A possible cause of this precipitation is the interaction between magnetospheric electrons and electromagnetic waves called whistler-mode chorus waves. However, no direct observational evidence of this interaction has been obtained so far. Here we report that energetic electrons are scattered by chorus waves, resulting in their precipitation. Our observations were made in March 2017 with a magnetospheric spacecraft equipped with a high-angular-resolution electron sensor and electromagnetic field instruments. The measured quasiperiodic precipitating electron flux was sufficiently intense to generate a pulsating aurora, which was indeed simultaneously observed by a ground auroral imager. [ABSTRACT FROM AUTHOR]

In the inner magnetosphere, the Arase spacecraft has observed electromagnetic ion cyclotron (EMIC) emissions with both rising and falling frequencies. The instantaneous frequency analyses on the electromagnetic fields of the EMIC rising tone emission have been performed by the Hilbert‐Huang transform. The time variation of the instantaneous frequency shows a good agreement with the nonlinear theory for the frequency evolutions. Rapid instantaneous frequency modulation is also found during the rising tone emission. We estimate the peak‐to‐peak time of the fluctuation in the frequency and find that the fluctuation is caused around a half of the particle trapping time. From the motion of the phase‐bunched particle around the resonant velocity, it is expected that the nonlinear resonant current, which induces the falling frequency is formed in half the trapping time. Plain Language Summary: The Arase spacecraft observed nonlinear EMIC rising and falling tone emissions in the inner magnetosphere. Instantaneous frequency of nonlinear EMIC rising tone emission is analyzed by Hilbert‐Huang Transformation. Fast frequency modulation of the rising tone emission is found in the instantaneous frequency, which can be caused by the phase‐bunched particles in the phase space. Key Points: Typical nonlinear EMIC rising and falling tone emissions have been observed by the electric and magnetic field detectors onboard AraseInstantaneous frequency of a rising tone emission is analyzed and compared with the nonlinear growth theoryEMIC waves have short‐time frequency modulations caused by phase‐bunched ion motion in the phase space [ABSTRACT FROM AUTHOR]

The Exploration of energization and Radiation in Geospace (ERG) project aims to study acceleration and loss mechanisms of relativistic electrons around the Earth. The Arase (ERG) satellite was launched on December 20, 2016, to explore in the heart of the Earth’s radiation belt. In the present paper, we introduce the specifications of the Plasma Wave Experiment (PWE) on board the Arase satellite. In the inner magnetosphere, plasma waves, such as the whistler-mode chorus, electromagnetic ion cyclotron wave, and magnetosonic wave, are expected to interact with particles over a wide energy range and contribute to high-energy particle loss and/or acceleration processes. Thermal plasma density is another key parameter because it controls the dispersion relation of plasma waves, which affects wave-particle interaction conditions and wave propagation characteristics. The DC electric field also plays an important role in controlling the global dynamics of the inner magnetosphere. The PWE, which consists of an orthogonal electric field sensor (WPT; wire probe antenna), a triaxial magnetic sensor (MSC; magnetic search coil), and receivers named electric field detector (EFD), waveform capture and onboard frequency analyzer (WFC/OFA), and high-frequency analyzer (HFA), was developed to measure the DC electric field and plasma waves in the inner magnetosphere. Using these sensors and receivers, the PWE covers a wide frequency range from DC to 10 MHz for electric fields and from a few Hz to 100 kHz for magnetic fields. We produce continuous ELF/VLF/HF range wave spectra and ELF range waveforms for 24 h each day. We also produce spectral matrices as continuous data for wave direction finding. In addition, we intermittently produce two types of waveform burst data, “chorus burst” and “EMIC burst.” We also input raw waveform data into the software-type wave-particle interaction analyzer (S-WPIA), which derives direct correlation between waves and particles. Finally, we introduce our PWE observation strategy and provide some initial results. [ABSTRACT FROM AUTHOR]

We developed the onboard processing software for the Plasma Wave Experiment (PWE) onboard the Exploration of energization and Radiation in Geospace, Arase satellite. The PWE instrument has three receivers: Electric Field Detector, Waveform Capture/Onboard Frequency Analyzer (WFC/OFA), and the High-Frequency Analyzer. We designed a pseudo-parallel processing scheme with a time-sharing system and achieved simultaneous signal processing for each receiver. Since electric and magnetic field signals are processed by the different CPUs, we developed a synchronized observation system by using shared packets on the mission network. The OFA continuously measures the power spectra, spectral matrices, and complex spectra. The OFA obtains not only the entire ELF/VLF plasma waves’ activity but also the detailed properties (e.g., propagation direction and polarization) of the observed plasma waves. We performed simultaneous observation of electric and magnetic field data and successfully obtained clear wave properties of whistler-mode chorus waves using these data. In order to measure raw waveforms, we developed two modes for the WFC, ‘chorus burst mode’ (65,536 samples/s) and ‘EMIC burst mode’ (1024 samples/s), for the purpose of the measurement of the whistler-mode chorus waves (typically in a frequency range from several hundred Hz to several kHz) and the EMIC waves (typically in a frequency range from a few Hz to several hundred Hz), respectively. We successfully obtained the waveforms of electric and magnetic fields of whistler-mode chorus waves and ion cyclotron mode waves along the Arase’s orbit. We also designed the software-type wave-particle interaction analyzer mode. In this mode, we measure electric and magnetic field waveforms continuously and transfer them to the mission data recorder onboard the Arase satellite. We also installed an onboard signal calibration function (onboard SoftWare CALibration; SWCAL). We performed onboard electric circuit diagnostics and antenna impedance measurement of the wire-probe antennas along the orbit. We utilize the results obtained using the SWCAL function when we calibrate the spectra and waveforms obtained by the PWE. [ABSTRACT FROM AUTHOR]