Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

Both solar wind and ionospheric sources contribute to the magnetotail plasma sheet, but how their contribution changes during a geomagnetic storm is an open question. The source is critical because the plasma sheet properties control the enhancement and decay rate of the ring current, the main cause of the geomagnetic field perturbations that define a geomagnetic storm. Here we use the solar wind composition to track the source and show that the plasma sheet source changes from predominantly solar wind to predominantly ionospheric as a storm develops. Additionally, we find that the ionospheric plasma during the storm main phase is initially dominated by singly ionized hydrogen (H⁺), likely from the polar wind, a low energy outflow from the polar cap, and then transitions to the accelerated outflow from the dayside and nightside auroral regions, identified by singly ionized oxygen (O⁺). These results reveal how the access to the magnetotail of the different sources can change quickly, impacting the storm development.

DOI： 10.1038/s41467-023-41735-3

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PubMed

Other Link： https://www.nature.com/articles/s41467-023-41735-3

Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

Abstract

Although many substorm‐related observations have been made, we still have limited insight into propagation of the plasma and field perturbations in Pi2 frequencies (∼7–25 mHz) in association with substorm aurora, particularly from the auroral source region in the inner magnetosphere to the ground. In this study, we present conjugate observations of a substorm brightening aurora using an all‐sky camera and an inner‐magnetospheric satellite Arase at L ∼ 5. A camera at Gakona (62.39°N, 214.78°E), Alaska, observed a substorm auroral brightening on 28 December 2018, and the footprint of the satellite was located just equatorward of the aurora. Around the timing of the auroral brightening, the satellite observed a series of quasi‐periodic variations in the electric and magnetic fields and in the energy flux of electrons and ions. We demonstrate that the diamagnetic variations of thermal pressure and medium‐energy ion energy flux in the inner magnetosphere show approximately one‐to‐one correspondence with the oscillations in luminosity of the substorm brightening aurora and high‐latitudinal Pi2 pulsations on the ground. We also found their anti‐correlation with low‐energy electrons. Cavity‐type Pi2 pulsations were observed at mid‐ and low‐latitudinal stations. Based on these observations, we suggest that a wave phenomenon in the substorm auroral source region, like ballooning type instability, play an important role in the development of substorm and related auroral brightening and high‐latitude Pi2, and that the variation of the auroral luminosity was directly driven by keV electrons which were modulated by Alfven waves in the inner magnetosphere.

DOI： 10.1029/2023ja031648

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Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

Abstract

Using Arase observations of the inner magnetosphere during 26 CIR‐driven geomagnetic storms with minimum Sym‐H between ‐33 and ‐86 nT, we investigated ring current pressure development of ions (H⁺, He⁺, O⁺) and electron during prestorm, main, early recovery and late recovery phases as a function of L‐shell and magnetic local time. It is found that during the main and early recovery phase of the storms the ion pressure is asymmetric in the inner magnetosphere, leading to a strong partial ring current. The ion pressure becomes symmetric during the late recovery phase. H⁺ ions with energies of ∼20‐50 keV and ∼50‐100 keV contribute more to the ring current pressure during the main phase and early/late recovery phase, respectively. O⁺ ions with energies of ∼10‐20 keV contribute significantly during main and early recovery phase. These are consistent with previous studies. The electron pressure was found to be asymmetric during the main, early recovery and late recovery phase. The electron pressure peaks from midnight to the dawn sector. Electrons with energy of <50 keV contribute to the ring current pressure during the main and early recovery phase of the storms. Overall, the electron contribution to the total ring current is found to be ∼11% during the main and early recovery phases. However, the electron contribution is found to be significant (∼22%) in the 03‐09 MLT sector during the main and early recovery phase. The results indicate an important role of electrons in the ring current build up.

This article is protected by copyright. All rights reserved.

DOI： 10.1029/2023ja031756

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Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

Abstract

A physical mechanism to produce pulsating aurora (PsA) has been considered to be the interaction of the electron and the chorus wave generated near the equatorial plane of the magnetosphere. A recent observation of high temporal resolution of chorus waves by the Arase satellite revealed that the presence or absence of the internal modulation of PsA, which is a characteristic sub‐second scintillation at 3 ± 1 Hz within each optical pulsation, is closely related to the discreteness of the element structure of the chorus wave. However, it is still unclear what parameters (or conditions) control the discreteness of the element and the existence of the internal modulation of PsA. In this study, we discuss parameters that determine the presence or absence of the internal modulation of PsA and element structure of chorus by showing a conjugate observation of PsA/chorus by ground‐based cameras and the Arase satellite. During the event, the occurrence of internal modulation increased temporally. The wave data from the satellite show that the repetitive frequency of elements was ∼6 Hz when the internal modulation was indistinct, while the repetitive frequency was ∼3 Hz when the internal modulation was distinct. The particle measurements suggest that this difference was caused by changes in the density and the temperature anisotropy of the hot electron. The internal modulation was clearly observed when the density of hot electrons decreased and the temperature anisotropy relaxed after the injection. Observations of internal modulations from the ground might allow us to estimate the parameters such as energetic electron density and temperature anisotropy in the magnetosphere.

DOI： 10.1029/2023ja031499

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Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

DOI： 10.1029/2022ja031131

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Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

DOI： 10.1029/2022ja030992

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Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2022JA030992

Publishing type：Research paper (scientific journal)  

Auroral brightening is one of the most common phenomena that occur during substorm onset and is usually recognized as a projection of the substorm-associated magnetospheric plasma dynamics to the ionosphere. However, electromagnetic fields and plasma features associated with the substorm brightening arc have not been well understood. In this study, we present a comprehensive observation of the source plasma and field variations of a substorm brightening aurora in the inner magnetosphere. We performed a unique conjugate observation of a substorm brightening auroral arc observed by a ground-based camera and by the Arase satellite in the magnetospheric source region at L ∼ 6. The event was observed at Tromsø (69.6°N, 19.2°E), Norway, on 12 October 2017. The brightening arc indicates east-west structures with longitudinal scales of ∼0.5°–2.0°. Field-aligned bi-directional electrons with an energy range between 66 and 1,800 eV were detected by the satellite, simultaneously with the appearance of the brightening arc in the camera. These electrons were probably supplied from the auroral brightening region in the ionosphere, indicating that the satellite was on the same field line of the brightening aurora. The magnetic and electric field data show characteristic fluctuations and earthward Poynting flux around the time that the satellite crossed the aurora. Anti-phase oscillations between the thermal pressure and the magnetic pressure are also reported. Based on these observations, we suggest the possibility that a ballooning instability occurred in the source region of the substorm brightening arc in the inner magnetosphere at L ∼ 6.

DOI： 10.1029/2021JA030072

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DOI： 10.3389/fspas.2022.1020815

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Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

DOI： 10.1029/2022gl099655

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PubMed

Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2022GL099655

Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

DOI： 10.1029/2022ja030545

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：FRONTIERS MEDIA SA  

During July to October of 2019, a sequence of isolated Corotating Interaction Regions (CIRs) impacted the magnetosphere, for four consecutive solar rotations, without any interposed Interplanetary Coronal Mass Ejections. Even though the series of CIRs resulted in relatively weak geomagnetic storms, the net effect of the outer radiation belt during each disturbance was different, depending on the electron energy. During the August-September CIR group, significant multi-MeV electron enhancements occurred, up to ultra-relativistic energies of 9.9 MeV in the heart of the outer Van Allen radiation belt. These characteristics deemed this time period a fine case for studying the different electron acceleration mechanisms. In order to do this, we exploited coordinated data from the Van Allen Probes, the Time History of Events and Macroscale Interactions during Substorms Mission (THEMIS), Arase and Galileo satellites, covering seed, relativistic and ultra-relativistic electron populations, investigating their Phase Space Density (PSD) profile dependence on the values of the second adiabatic invariant K, ranging from near-equatorial to off equatorial mirroring populations. Our results indicate that different acceleration mechanisms took place for different electron energies. The PSD profiles were dependent not only on the mu value, but also on the K value, with higher K values corresponding to more pronounced local acceleration by chorus waves. The 9.9 MeV electrons were enhanced prior to the 7.7 MeV, indicating that different mechanisms took effect on different populations. Finally, all ultra-relativistic enhancements took place below geosynchronous orbit, emphasizing the need for more Medium Earth Orbit (MEO) missions.

DOI： 10.3389/fspas.2022.949788

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Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

DOI： 10.1029/2022ja030362

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Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2022JA030362

Publishing type：Research paper (scientific journal)  

The auroral acceleration region plays an important role in the magnetosphere-ionosphere coupling system. In this study, signatures of an auroral U-shaped potential structure were found for the first time in the near-equatorial inner magnetosphere by the Arase satellite at ∼6.0 RE geocentric distance and 11° magnetic latitude. The observed magnetic and electric field variations corresponded to the equatorward motion of the upward field-aligned current and converging perpendicular electric field. Examining the three-dimensional velocity distribution function of H+ and O+ ions, we demonstrate that upflowing ion beams were significantly deflected in an east-west direction with a perpendicular velocity up to ∼80 km/s, which is consistent with the ExB drift velocity. A simple particle drift model with the inferred auroral perpendicular potential presents a new kink-like drift path of ions from the magnetotail, implying that the auroral potential structure has a great impact on particle dynamics in the near-earth plasma sheet.

DOI： 10.1029/2022GL098105

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Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

DOI： 10.1029/2022ja030271

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DOI： 10.1029/2021JA029965

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Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

DOI： 10.1029/2021ja030008

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

Energetic electron precipitation from Earth’s outer radiation belt heats the upper atmosphere and alters its chemical properties. The precipitating flux intensity, typically modelled using inputs from high-altitude, equatorial spacecraft, dictates the radiation belt’s energy contribution to the atmosphere and the strength of space-atmosphere coupling. The classical quasi-linear theory of electron precipitation through moderately fast diffusive interactions with plasma waves predicts that precipitating electron fluxes cannot exceed fluxes of electrons trapped in the radiation belt, setting an apparent upper limit for electron precipitation. Here we show from low-altitude satellite observations, that ~100 keV electron precipitation rates often exceed this apparent upper limit. We demonstrate that such superfast precipitation is caused by nonlinear electron interactions with intense plasma waves, which have not been previously incorporated in radiation belt models. The high occurrence rate of superfast precipitation suggests that it is important for modelling both radiation belt fluxes and space-atmosphere coupling.

DOI： 10.1038/s41467-022-29291-8

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PubMed

Other Link： https://www.nature.com/articles/s41467-022-29291-8

Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

DOI： 10.1029/2021gl095194

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Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union ({AGU})  

DOI： 10.1029/2021JA029786

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Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2021JA029786

Publishing type：Research paper (scientific journal)   Publisher：EDP Sciences  

Many studies have been conducted about the impact of energetic charged particles on the atmosphere during geomagnetically active times, while quiet time effects are poorly understood. We identified two energetic electron precipitation (EEP) events during the growth phase of moderate substorms and estimated the mesospheric ionization rate for an EEP event for which the most comprehensive dataset from ground-based and space-born instruments was available. The mesospheric ionization signature reached below 70 km altitude and continued for ~15 min until the substorm onset, as observed by the PANSY radar and imaging riometer at Syowa Station in the Antarctic region. We also used energetic electron flux observed by the Arase and POES 15 satellites as the input for the air-shower simulation code PHITS to quantitatively estimate the mesospheric ionization rate. The calculated ionization level due to the precipitating electrons is consistent with the observed value of cosmic noise absorption. The possible spatial extent of EEP is estimated to be ~8 h MLT in longitude and ~1.5° in latitude from a global magnetohydrodynamic simulation REPPU and the precipitating electron observations by the POES satellite, respectively. Such a significant duration and spatial extent of EEP events suggest a non-negligible contribution of the growth phase EEP to the mesospheric ionization. Combining the cutting-edge observations and simulations, we shed new light on the space weather impact of the EEP events during geomagnetically quiet times, which is important to understand the possible link between the space environment and climate.

DOI： 10.1051/swsc/2022012

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Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

<title>Abstract</title>
Magnetic field line reconnection is a universal plasma process responsible for the conversion of magnetic field energy to plasma heating and charged particle acceleration. Solar flares and Earth's magnetospheric substorms are two of the most investigated dynamical systems where global magnetic field reconfiguration is accompanied by energization of plasma populations. Such a reconfiguration includes formation of a long-living current system connecting the primary energy release region and cold dense conductive plasma of the photosphere/ionosphere. In both flares and substorms the evolution of this current system correlates with the formation and dynamics of energetic particle fluxes (although energy ranges can be different for these systems). Our study is focused on the similarity between flares and substorms. Using a wide range of data sets available for flare and substorm investigations, we qualitatively compare the dynamics of currents and energetic particle fluxes for one flare and one substorm. We show that there is a clear correlation between energetic particle precipitations (associated with energy release due to magnetic reconnection seen from riometer and hard X-ray measurements) and magnetic field reconfiguration/formation of the current system, whereas the long-term current system evolution correlates better with hot plasma fluxes (seen from in situ and soft X-ray measurements). We then discuss how data sets of in situ measurements of magnetospheric substorms can help interpret solar flare data.

DOI： 10.3847/1538-4357/ac2dfc

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Other Link： https://iopscience.iop.org/article/10.3847/1538-4357/ac2dfc/pdf

Publishing type：Research paper (scientific journal)  

After publication of this article (Matsuda et al. 2021), it is noticed the 8th author’s name is incorrect. The name should be corrected from “Jun Chae-Woo” to “Chae-Woo Jun”. The name has been revised in this Correction and the original article has been updated as well.

DOI： 10.1186/s40623-021-01450-z

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Publishing type：Research paper (scientific journal)  

We present observations of an equatorward detachment of the auroral arc from the main oval and magnetically conjugate measurements made by the Arase satellite in the inner magnetosphere. The all-sky imager at Gakona (magnetic latitude = 63.6°N), Alaska, shows the detachment of the auroral arc in both red and green lines at local midnight (∼0130–0230 MLT) on 30 March 2017. The electron density derived from the Arase in-situ observations shows that this arc occurred outside the plasmapause. At the arc crossing, the electron flux of energies ∼0.1–2 keV is found to be locally enhanced at L∼4.3–4.5. We estimated auroral intensities for both red and green lines by using the Arase low-energy (0.1–19 keV) electron flux data. The peak latitude of the estimated intensity shows reasonably good correspondence with the observed intensity mapped at the ionospheric footprints of the Arase satellite. These findings indicate that the observed arc detachment at Gakona was associated with the localized enhancement of low-energy electrons (∼0.1–2 keV) at the inner edge of the electron plasma sheet. Further, we employ the simulation results of the Community Coordinated Modeling Center (CCMC), the BATS-R-US–CIMI 3-D MHD code to understand the conditions in the inner magnetosphere around the time of detachment. Although the simulation could not reproduce the lower-energy component responsible for the arc detachment, it successfully reproduced two earthward convection events at the lower radial distance (R) (R ≤ ∼4) around the time of arc detachment and the features of enhanced convection in similarity with the observations.

DOI： 10.1029/2020JA029080

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Scopus

Publishing type：Research paper (scientific journal)  

DOI： 10.1186/s40623-021-01532-y

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PubMed

Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

DOI： 10.1029/2020ja028972

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Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2020JA028972

Publishing type：Research paper (scientific journal)  

Resonant interactions of energetic electrons with electromagnetic whistler-mode waves (whistlers) contribute significantly to the dynamics of electron fluxes in Earth's outer radiation belt. At low geomagnetic latitudes, these waves are very effective in pitch angle scattering and precipitation into the ionosphere of low equatorial pitch angle, tens of keV electrons and acceleration of high equatorial pitch angle electrons to relativistic energies. Relativistic (hundreds of keV), electrons may also be precipitated by resonant interaction with whistlers, but this requires waves propagating quasi-parallel without significant intensity decrease to high latitudes where they can resonate with higher energy low equatorial pitch angle electrons than at the equator. Wave propagation away from the equatorial source region in a non-uniform magnetic field leads to ray divergence from the originally field-aligned direction and efficient wave damping by Landau resonance with suprathermal electrons, reducing the wave ability to scatter electrons at high latitudes. However, wave propagation can become ducted along field-aligned density peaks (ducts), preventing ray divergence and wave damping. Such ducting may therefore result in significant relativistic electron precipitation. We present evidence that ducted whistlers efficiently precipitate relativistic electrons. We employ simultaneous near-equatorial and ground-based measurements of whistlers and low-altitude electron precipitation measurements by ELFIN CubeSat. We show that ducted waves (appearing on the ground) efficiently scatter relativistic electrons into the loss cone, contrary to non-ducted waves (absent on the ground) precipitating only (Formula presented.) keV electrons. Our results indicate that ducted whistlers may be quite significant for relativistic electron losses; they should be further studied statistically and possibly incorporated in radiation belt models.

DOI： 10.1029/2021JA029851

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Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

DOI： 10.1029/2020ja029086

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Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2020JA029086

Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

DOI： 10.1029/2020ja029095

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Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2020JA029095

Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

DOI： 10.1029/2021ja029168

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

<title>Abstract</title>Pulsating aurorae (PsA) are caused by the intermittent precipitations of magnetospheric electrons (energies of a few keV to a few tens of keV) through wave-particle interactions, thereby depositing most of their energy at altitudes ~ 100 km. However, the maximum energy of precipitated electrons and its impacts on the atmosphere are unknown. Herein, we report unique observations by the European Incoherent Scatter (EISCAT) radar showing electron precipitations ranging from a few hundred keV to a few MeV during a PsA associated with a weak geomagnetic storm. Simultaneously, the Arase spacecraft has observed intense whistler-mode chorus waves at the conjugate location along magnetic field lines. A computer simulation based on the EISCAT observations shows immediate catalytic ozone depletion at the mesospheric altitudes. Since PsA occurs frequently, often in daily basis, and extends its impact over large MLT areas, we anticipate that the PsA possesses a significant forcing to the mesospheric ozone chemistry in high latitudes through high energy electron precipitations. Therefore, the generation of PsA results in the depletion of mesospheric ozone through high-energy electron precipitations caused by whistler-mode chorus waves, which are similar to the well-known effect due to solar energetic protons triggered by solar flares.

DOI： 10.1038/s41598-021-92611-3

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PubMed

Other Link： http://www.nature.com/articles/s41598-021-92611-3

Publishing type：Research paper (scientific journal)  

This study investigates the characterization and calibration of the high-energy electron experiments (HEP) instrument onboard the exploration of energization and radiation in geospace (ERG). Two detector modules, HEP-L and HEP-H, which employ stacks of multichannel silicon strip detectors, detect electrons in the energy ranges of 70 keV–1 MeV and 700 keV–2 MeV, respectively. The detector response to electron irradiation needs to be assessed to obtain accurate electron fluxes from these detectors. In this study, we perform Monte Carlo simulations using the Geant4 particle simulation tool to reconstruct incident electron fluxes from detected count rates. Based on the simulation results, we investigate the response characteristics of the detectors when electrons with a certain range of energy are irradiated onto them. A response function is constructed by combining the simulation results for different incident energies. A response matrix is calculated by binning the response function according to the energy channels of the detector, and an inverse matrix derived from the response matrix is used to calibrate the observational data. Compared with the data obtained from another electron instrument onboard the Arase satellite (MEP-e), whose energy range overlaps with that of the HEP, the differential flux data for the overlapping energy range (85–95 keV) are consistent with each other. The basic characteristics of the HEP detectors are thus confirmed to provide well-calibrated data.

DOI： 10.1029/2021JA029110

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Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

DOI： 10.1029/2020ja028929

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Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

DOI： 10.1029/2020ja028633

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Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

DOI： 10.1029/2020ja029091

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Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

DOI： 10.1029/2021ja029109

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Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2021JA029109

Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union ({AGU})  

DOI： 10.1029/2020JA028951

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Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2020JA028951

Publishing type：Research paper (scientific journal)  

Stable auroral red (SAR) arcs are optical events with dominant 630.0-nm emission caused by low-energy electron heat flux into the topside ionosphere from the inner magnetosphere. SAR arcs are observed at subauroral latitudes and often occur during the recovery phase of magnetic storms and substorms. Past studies concluded that these low-energy electrons were generated in the spatial overlap region between the outer plasmasphere and ring-current ions and suggested that Coulomb collisions between plasmaspheric electrons and ring-current ions are more feasible for the SAR-arc generation mechanism rather than Landau damping by electromagnetic ion cyclotron waves or kinetic Alfvén waves. This work studies three separate SAR-arc events with conjunctions, using all-sky imagers and inner magnetospheric satellites (Arase and Radiation Belt Storm Probes [RBSP]) during non-storm-time substorms on December 19, 2012 (event 1), January 17, 2015 (event 2), and November 4, 2019 (event 3). We evaluated for the first time the heat flux via Coulomb collision using full-energy-range ion data obtained by the satellites. The electron heat fluxes due to Coulomb collisions reached ∼10  eV/cm /s for events 1 and 2, indicating that Coulomb collisions could have caused the SAR arcs. RBSP-A also observed local enhancements of 7–20-mHz electromagnetic wave power above the SAR arc in event 2. The heat flux for the freshly detached SAR arc in event 3 reached ∼10  eV/cm /s, which is insufficient to have caused the SAR arc. In event 3, local flux enhancement of electrons (<200 eV) and various electromagnetic waves were observed, these are likely to have caused the freshly detached SAR arc. 9 2 8 2

DOI： 10.1029/2020JA029081

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Publishing type：Research paper (scientific journal)  

The temporal variation of the energetic electron flux distribution caused by whistler mode chorus waves through the cyclotron resonant interaction provides crucial information on how electrons are accelerated in the Earth's inner magnetosphere. This study employs a data-driven test-particle simulation which demonstrates that the rapid change of energetic electron distribution observed by the Arase satellite cannot be simply explained by a quasi-linear diffusion mechanism, but is essentially caused by nonlinear scattering: the phase trapping and the phase dislocation. In response to upper-band whistler chorus bursts, multiple nonlinear interactions finally achieve an efficient flux enhancement of electrons on a time scale of the chorus burst. A quasi-linear diffusion model tends to underestimate the flux enhancement of energetic electrons as compared with a model based on the realistic dynamic frequency spectrum of whistler waves. It is concluded that the nonlinear phase trapping plays an important role in the rapid flux enhancement of energetic electrons observed by Arase.

DOI： 10.1029/2020JA028979

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Publishing type：Research paper (scientific journal)  

In situ electron density profiles obtained from Arase in the night magnetic local time (MLT) sector and from RBSP-B covering all MLTs are used to study the small-scale density irregularities present in the plasmasphere and near the plasmapause. Electron density perturbations with amplitudes >10% from background density and with time-scales less than 30-min are investigated here as the small-scale density irregularities. The statistical survey of the density irregularities is carried out using nearly 2 years of density data obtained from RBSP-B and 4 months of data from Arase satellites. The results show that density irregularities are present globally at all MLT sectors and L-shells both inside and outside the plasmapause, with a higher occurrence at L > 4. The occurrence of density irregularities is found to be higher during disturbed geomagnetic and interplanetary conditions. The case studies presented here revealed: (1) The plasmaspheric density irregularities observed during both quiet and disturbed conditions are found to coexist with the hot plasma sheet population. (2) During quiet periods, the plasma waves in the whistler-mode frequency range are found to be modulated by the small-scale density irregularities, with density depletions coinciding well with the decrease in whistler intensity. Our observations suggest that different source mechanisms are responsible for the generation of density structures at different MLTs and geomagnetic conditions.

DOI： 10.1029/2020JA027917

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Publishing type：Research paper (scientific journal)  

Whistler mode chorus waves scatter magnetospheric electrons and cause precipitation into the Earth's atmosphere. Previous measurements showed that nightside chorus waves are indeed responsible for diffuse/pulsating aurora. Although chorus waves and electron precipitation have also been detected on the dayside, their link has not been illustrated (or demonstrated) in detail compared to the nightside observations. Conventional low-altitude satellite observations do not well resolve the energy range of 10–100 keV, hampering verification on resonance condition with chorus waves. In this paper we report observations of energetic electrons with energies of 30–100 keV that were made by the electron sensor installed on the NASA's sounding rocket RockSat-XN. It was launched from the Andøya Space Center on the dayside (MLT ∼ 11 h) at the L-value of ∼7 on January 13, 2019. Transient electron precipitation was observed at ∼50 keV with the duration of <100 s. The VLF receiver of a ground station at Kola peninsula in Russia near the rocket's footprint observed intermittent emissions of whistler-mode waves at the VLF frequency range simultaneously with the rocket observations. The energy of precipitating electrons is consistent with those derived from the quasilinear theory of pitch angle scattering by chorus waves through cyclotron resonance, assuming a typical dayside magnetospheric electron density. Precise interaction region is discussed based on the obtained energy spectrum below 100 keV.

DOI： 10.1029/2020JA028477

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Publishing type：Research paper (scientific journal)  

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 kilometres . 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. 1

DOI： 10.1038/s41598-020-79665-5

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PubMed

Publishing type：Research paper (scientific journal)  

We have been operating remote high frequency (HF) wave receivers for the SuperDARN Hokkaido East radar in Nagoya (1092 km away from the radar) and Rikubetsu (a few tens of m away from the radar antenna) since 2014 to monitor the ionospheric environment and its changes. One receiver set consists of a USRP-N210 receiver unit, Ubuntu Linux PC and dipole/loop antenna. Using the remote receiver data it is possible to monitor the upward/downward motion of the ionosphere at the ionospheric reflection point of the HF radar backlobe beams emitted toward the Nagoya area. The usage of the SuperDARN (backlobe) beams has the following advantages over other instruments such as HF Doppler systems: (1) SuperDARN Backlobe beams also have high directivity, so that it is possible to observe strong echoes at the remote area more than 1000 km away from the radar. (2) Since the SuperDARN radars emit pulse waves instead of continuous waves, it is possible to identify the travel time from the radar to the receiver. The initial results of the observation of ionospheric perturbations using the remote HF wave receiver of the SuperDARN Hokkaido East radar are described.

DOI： 10.1016/j.polar.2021.100669

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Scopus

Publishing type：Research paper (scientific journal)  

A stable auroral red (SAR) arc is an aurora with a dominant 630 nm emission at subauroral latitudes. SAR arcs have been considered to occur due to the spatial overlap between the plasmasphere and the ring-current ions. In the overlap region, plasmaspheric electrons are heated by ring-current ions or plasma waves, and their energy is then transferred down to the ionosphere where it causes oxygen red emission. However, there have been no study conducted so far that quantitatively examined plasma and electromagnetic fields in the magnetosphere associated with SAR arc. In this paper, we report the first quantitative evaluation of conjugate measurements of a SAR arc observed at 2204 UT on 28 March 2017 and investigate its source region using an all-sky imager at Nyrölä (magnetic latitude: 59.4°N), Finland, and the Arase satellite. The Arase observation shows that the SAR arc appeared in the overlap region between a plasmaspheric plume and the ring-current ions and that electromagnetic ion cyclotron waves and kinetic Alfven waves were not observed above the SAR arc. The SAR arc was located at the ionospheric trough minimum identified from a total electron content map obtained by the GNSS receiver network. The Swarm satellite flying in the ionosphere also passed the SAR arc at ~2320 UT and observed a decrease in electron density and an increase in electron temperature during the SAR-arc crossing. These observations suggest that the heating of plasmaspheric electrons via Coulomb collision with ring-current ions is the most plausible mechanism for the SAR-arc generation.

DOI： 10.1029/2020JA028068

Web of Science

Scopus

Publishing type：Research paper (scientific journal)  

Auroral arcs and diffuse auroras are common phenomena at high latitudes, though characteristics of their source plasma and fields have not been well understood. We report the first observation of fields and particles including their pitch-angle distributions in the source region of auroral arcs and diffuse auroras, using data from the Arase satellite at L ~ 6.0–6.5. The auroral arcs appeared and expanded both poleward and equatorward at local midnight from ~0308 UT on 11 September 2018 at Nain (magnetic latitude: 66°), Canada, during the expansion phase of a substorm, while diffuse auroras covered the whole sky after 0348 UT. The top part of auroral arcs was characterized by purple/blue emissions. Bidirectional field-aligned electrons with structured energy-time spectra were observed in the source region of auroral arcs, while source electrons became isotropic and less structured in the diffuse auroral region afterwards. We suggest that structured bidirectional electrons at energies below a few keV were caused by upward field-aligned potential differences (upward electric field along geomagnetic field) reaching high altitudes (~30,000 km) above Arase. The bidirectional electrons above a few keV were probably caused by Fermi acceleration associated with the observed field dipolarization. Strong electric-field fluctuations and earthward Poynting flux were observed at the arc crossing and are probably also caused by the field dipolarization. The ions showed time-pitch-angle dispersion caused by mirror reflection. These results indicate a clear contrast between auroral arcs and diffuse auroras in terms of source plasma and fields and generation mechanisms of auroral arcs in the inner magnetosphere.

DOI： 10.1029/2019JA027310

Web of Science

Scopus

Publishing type：Research paper (scientific journal)  

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 (Formula presented.) of its original level.

DOI： 10.1029/2019GL086040

Web of Science

Scopus

Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

<title>Abstract</title>A technique for estimating a plasma drift velocity distribution in the ionosphere is presented. This technique is based on a framework for representing a global vector field on a sphere by using a set of localized basis functions which is newly derived as a variant of the spherical elementary current system (SECS). A vector field on a sphere can be divided into its divergence-free (DF) component and curl-free (CF) component. The DF and CF components can then be represented by weighted sums of the DF and CF vector-valued basis functions, respectively. While the SECS basis functions have a singular point, the new basis functions do not diverge over a sphere. This property of the new basis function allows us to achieve robust prediction of the drift velocity at any point in the ionosphere. Assuming that the ionospheric plasma drift velocity has no divergence, its distribution can be represented by a weighted sum of the DF basis functions. The proposed technique estimates the ionospheric plasma drift velocity distribution from the SuperDARN data by using the DF basis functions. Since there are some wide gaps in the spatial coverage of the SuperDARN, an empirical convection model is combined with the framework based on the new basis functions. It is demonstrated that the proposed technique is useful for the estimation and modeling of the ionospheric plasma velocity distribution.

DOI： 10.1186/s40623-020-01168-4

Web of Science

Scopus

Other Link： http://link.springer.com/article/10.1186/s40623-020-01168-4/fulltext.html

Language：English   Publisher：THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES  

The high-energy electron experiments (HEP) instrument on board the Arase satellite employs two sensors, HEP-L and HEP-H, and was designed to measure electrons with energies from 70 keV to 2 MeV. The recent Van Allen Probes observations indicate that MeV electron flux is very small in the inner radiation belt, while the HEP has detected significant counts at MeV energy channels in the inner radiation belt. Counts in the inner radiation belt are registered similarly at different energy channels of HEP-H and higher energy channels of HEP-L, and show no clear energy dependence. Their properties suggest contamination of high-energy protons that populate densely the inner radiation belt. In order to identify the energy of the penetrating protons we compare the spatial distribution of the HEP counts with NASA's AP9 mean model. We find that the primary peak of the count distribution measured with HEP in MeV energy range is located at L = 1.5 at the magnetic equator, which in in agreement of > 60 MeV inner belt protons of AP9 mean model. The secondary distribution is also found at higher L values, which can be attributed to MeV protons. We have been conducting Geant4 simulation for penetrating protons into the HEP. Our result of the simulation is consistent with suggestions of analysis on the spatial distribution.

DOI： 10.2322/tastj.18.398

Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

DOI： 10.1029/2019ja027061

Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2019JA027061

Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1186/s40623-019-0999-5

Web of Science

Other Link： http://link.springer.com/article/10.1186/s40623-019-0999-5/fulltext.html

Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

DOI： 10.1029/2019gl085499

Web of Science

Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2019GL085499

Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union ({AGU})  

©2019. American Geophysical Union. All Rights Reserved. We report the electron flux modulations without corresponding magnetic fluctuations from unique multipoint satellite observations of the Arase (Exploration of Energization and Radiation in Geospace) and the Van Allen Probe (Radiation Belt Storm Probe [RBSP])-B satellites. On 30 March 2017, both Arase and RBSP-B observed periodic fluctuations in the relativistic electron flux with energies ranging from 500 keV to 2 MeV when they were located near the magnetic equator in the morning and dusk local time sectors, respectively. Arase did not observe Pc5 pulsations, while they were observed by RBSP-B. The clear dispersion signature of the relativistic electron fluctuations observed by Arase indicates that the source region is limited to the postnoon to the dusk sector. This is confirmed by RBSP-B and ground-magnetometer observations, where Pc5 pulsations are observed to drift-resonate with relativistic electrons on the duskside. Thus, Arase observed the drift-resonance signatures “remotely,” whereas RBSP-B observed them “locally.”.

DOI： 10.1029/2019GL084379

Web of Science

Scopus

Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union ({AGU})  

©2019. American Geophysical Union. All Rights Reserved. Molecular ions in the magnetosphere can be a tracer of fast ion outflows from the deep ionosphere. Statistical properties of molecular ions (O2+/NO+/N2+) in the ring current are investigated based on ion composition measurements (<180 keV/q) by medium-energy particle experiments-electron analyzer and low-energy particle experiments-ion mass analyzer instruments on board the Arase (Exploration of energization and Radiation in Geospace, ERG) satellite. The investigated period from late March to December 2017 includes 11 geomagnetic storms with the minimum Dst index less than −40 nT. The molecular ions are observed in the region of L = 2.5–6.6 and clearly identified at energies above ~12 keV during most magnetic storms. During quiet times, molecular ions are not observed. The average energy density ratio of the molecular ions to O+ is ~3%. The ratio tends to increase with the size of magnetic storms. Existence of molecular ions even during small magnetic storms suggests that the fast ion outflow from the deep ionosphere occurs frequently during geomagnetically active periods.

DOI： 10.1029/2019GL084163

Scopus

Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

DOI： 10.1029/2019ja026682

Web of Science

Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2019JA026682

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union ({AGU})  

We report an extreme erosion of the plasmasphere arising from the September 2017 storm. The cold electron density is identified from the upper limit frequency of upper hybrid resonance waves observed by the Plasma Wave Experiment instrument onboard the Exploration of energization and Radiation in Geospace/Arase satellite. The electron density profiles reveal that the plasmasphere was severely eroded during the recovery phase of the storm and the plasmapause was located at L = 1.6-1.7 at 23 UT 8 September 2017. This is the first report of deep erosion of the plasmasphere (L-pp < 2) with the in situ observation of the electron density. The degree of the severity is much more than what is expected from the relatively moderate value of the SYM-H minimum (-146 nT). We attempt to find a possible explanation for the observed severe depletion by using both observational evidence and numerical simulations. Our results suggest that the middle latitude electric field had penetrated from the high-latitude storm time convection for several hours. Such an unusually long-lasting penetration event can cause this observed degree of severity.Plain Language Summary The plasmasphere is the region of cold, relatively dense ionized gas (mostly protons and helium ions) that resides on the magnetic field lines close to the Earth. It is understood that the plasmasphere is threaded by magnetic field flux tubes that are persistently "closed," so that plasma from the Earth's ionosphere has filled the flux tubes. The typical location of the outer boundary of the plasmasphere, known as the plasmapause, is usually 40,000-50,000 km from the Earth. Here we report that a magnetic storm during 7-10 September 2017 dramatically displaced the outer boundary of the plasmasphere inwards, to only similar to 4,000 km from Earth's surface. Our study suggests that the remarkable deformation is caused by the unusually long-lasting leakage of the convection electric field deep within the plasmasphere.

DOI： 10.1029/2019SW002168

Web of Science

DOI： 10.1186/s40645-019-0270-5

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGEROPEN  

Transient mesospheric echo in the VHF range was detected at an altitude of 65-70km 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 >100keV 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 >100keV, rather than X-rays from the auroral electrons, played a dominant role in the transient and deep (65-70km) mesospheric ionization during the observed auroral breakup.

DOI： 10.1186/s40623-019-0989-7

Web of Science

© 2019, The Author(s). With the advent of the Heliophysics/Geospace System Observatory (H/GSO), a complement of multi-spacecraft missions and ground-based observatories to study the space environment, data retrieval, analysis, and visualization of space physics data can be daunting. The Space Physics Environment Data Analysis System (SPEDAS), a grass-roots software development platform (www.spedas.org), is now officially supported by NASA Heliophysics as part of its data environment infrastructure. It serves more than a dozen space missions and ground observatories and can integrate the full complement of past and upcoming space physics missions with minimal resources, following clear, simple, and well-proven guidelines. Free, modular and configurable to the needs of individual missions, it works in both command-line (ideal for experienced users) and Graphical User Interface (GUI) mode (reducing the learning curve for first-time users). Both options have “crib-sheets,” user-command sequences in ASCII format that can facilitate record-and-repeat actions, especially for complex operations and plotting. Crib-sheets enhance scientific interactions, as users can move rapidly and accurately from exchanges of technical information on data processing to efficient discussions regarding data interpretation and science. SPEDAS can readily query and ingest all International Solar Terrestrial Physics (ISTP)-compatible products from the Space Physics Data Facility (SPDF), enabling access to a vast collection of historic and current mission data. The planned incorporation of Heliophysics Application Programmer’s Interface (HAPI) standards will facilitate data ingestion from distributed datasets that adhere to these standards. Although SPEDAS is currently Interactive Data Language (IDL)-based (and interfaces to Java-based tools such as Autoplot), efforts are under-way to expand it further to work with python (first as an interface tool and potentially even receiving an under-the-hood replacement). We review the SPEDAS development history, goals, and current implementation. We explain its “modes of use” with examples geared for users and outline its technical implementation and requirements with software developers in mind. We also describe SPEDAS personnel and software management, interfaces with other organizations, resources and support structure available to the community, and future development plans.

DOI： 10.1007/s11214-018-0576-4

Web of Science

Scopus

PubMed

Other Link： http://orcid.org/0000-0001-8451-6941

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Berlin Heidelberg  

The Exploration of energization and Radiation in Geospace (ERG) Science Center serves as a hub of the ERG project, providing data files in a common format and developing the space physics environment data analysis software and plug-ins for data analysis. The Science Center also develops observation plans for the ERG (Arase) satellite according to the science strategy of the project. Conjugate observations with other satellites and ground-based observations are also planned. These tasks contribute to the ERG project by achieving quick analysis and well-organized conjugate ERG satellite and ground-based observations.[Figure not available: see fulltext.]

DOI： 10.1186/s40623-018-0867-8

Web of Science

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union ({AGU})  

©2018. American Geophysical Union. All Rights Reserved. Super Dual Auroral Radar Network (SuperDARN) observations show that ionospheric flow fluctuations of millihertz or lower-frequency range with horizontal velocities of a few hundred meters per second appeared in the subauroral to midlatitude region during a magnetic storm on 27 March 2017. A set of the radars have provided the first ever observations that the fluctuations propagate azimuthally both westward and eastward simultaneously, showing bifurcated phase propagation associated with substorm expansion. Concurrent observations near the conjugate site in the inner magnetosphere made by the Arase satellite provide evidence that multiple drifting clouds of electrons in the near-Earth equatorial plane were associated with the electric field fluctuations propagating eastward in the ionosphere. We interpret this event in terms of mesoscale pressure gradients carried by drifting ring current electrons that distort field lines one after another as they drift through the inner magnetosphere, causing eastward propagating ionospheric electric field fluctuations.

DOI： 10.1029/2018GL079777

Web of Science

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGEROPEN  

Understanding of underlying mechanisms of drastic variations of the near-Earth space (geospace) is one of the current focuses of the magnetospheric physics. The science target of the geospace research project Exploration of energization and Radiation in Geospace (ERG) is to understand the geospace variations with a focus on the relativistic electron acceleration and loss processes. In order to achieve the goal, the ERG project consists of the three parts: the Arase (ERG) satellite, ground-based observations, and theory/modeling/integrated studies. The role of theory/modeling/integrated studies part is to promote relevant theoretical and simulation studies as well as integrated data analysis to combine different kinds of observations and modeling. Here we provide technical reports on simulation and empirical models related to the ERG project together with their roles in the integrated studies of dynamic geospace variations. The simulation and empirical models covered include the radial diffusion model of the radiation belt electrons, GEMSIS-RB and RBW models, CIMI model with global MHD simulation REPPU, GEMSIS-RC model, plasmasphere thermosphere model, self-consistent wave-particle interaction simulations (electron hybrid code and ion hybrid code), the ionospheric electric potential (GEMSIS-POT) model, and SuperDARN electric field models with data assimilation. ERG (Arase) science center tools to support integrated studies with various kinds of data are also briefly introduced.

DOI： 10.1186/s40623-018-0785-9

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER HEIDELBERG  

This paper introduces ISEE_3D, an interactive visualization tool for three-dimensional plasma velocity distribution functions, developed by the Institute for Space-Earth Environmental Research, Nagoya University, Japan. The tool provides a variety of methods to visualize the distribution function of space plasma: scatter, volume, and isosurface modes. The tool also has a wide range of functions, such as displaying magnetic field vectors and two-dimensional slices of distributions to facilitate extensive analysis. The coordinate transformation to the magnetic field coordinates is also implemented in the tool. The source codes of the tool are written as scripts of a widely used data analysis software language, Interactive Data Language, which has been widespread in the field of space physics and solar physics. The current version of the tool can be used for data files of the plasma distribution function from the Geotail satellite mission, which are publicly accessible through the Data Archives and Transmission System of the Institute of Space and Astronautical Science (ISAS)/Japan Aerospace Exploration Agency (JAXA). The tool is also available in the Space Physics Environment Data Analysis Software to visualize plasma data from the Magnetospheric Multiscale and the Time History of Events and Macroscale Interactions during Substorms missions. The tool is planned to be applied to data from other missions, such as Arase (ERG) and Van Allen Probes after replacing or adding data loading plug-ins. This visualization tool helps scientists understand the dynamics of space plasma better, particularly in the regions where the magnetohydrodynamic approximation is not valid, for example, the Earth's inner magnetosphere, magnetopause, bow shock, and plasma sheet.

DOI： 10.1186/s40623-017-0761-9

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER HEIDELBERG  

This paper summarizes the specifications and initial evaluation results of Wire Probe Antenna (WPT) and Electric Field Detector (EFD), the key components for the electric field measurement of the Plasma Wave Experiment (PWE) aboard the Arase (ERG) satellite. WPT consists of two pairs of dipole antennas with similar to 31-m tip-to-tip length. Each antenna element has a spherical probe (60 mm diameter) at each end of the wire (15 m length). They are extended orthogonally in the spin plane of the spacecraft, which is roughly perpendicular to the Sun and enables to measure the electric field in the frequency range of DC to 10 MHz. This system is almost identical to the WPT of Plasma Wave Investigation aboard the BepiColombo Mercury Magnetospheric Orbiter, except for the material of the spherical probe (ERG: Al alloy, MMO: Ti alloy). EFD is a part of the EWO (EFD/WFC/OFA) receiver and measures the 2-ch electric field at a sampling rate of 512 Hz (dynamic range: +/- 200 mV/m) and the 4-ch spacecraft potential at a sampling rate of 128 Hz (dynamic range: +/- 100 V and +/- 3 V/m), with the bias control capability of WPT. The electric field waveform provides (1) fundamental information about the plasma dynamics and accelerations and (2) the characteristics of MHD and ion waves in various magnetospheric statuses with the magnetic field measured by MGF and PWE-MSC. The spacecraft potential provides information on thermal electron plasma variations and structure combined with the electron density obtained from the upper hybrid resonance frequency provided by PWE-HFA. EFD has two data modes. The continuous (medium-mode) data are provided as (1) 2-ch waveforms at 64 Hz (in apoapsis mode, L &gt; 4) or 256 Hz (in periapsis mode, L &lt; 4), (2) 1-ch spectrum within 1-232 Hz with 1-s resolution, and (3) 4-ch spacecraft potential at 8 Hz. The burst (high-mode) data are intermittently obtained as (4) 2-ch waveforms at 512 Hz and (5) 4-ch spacecraft potential at 128 Hz and downloaded with the WFC-E/B datasets after the selection. This paper also shows the initial evaluation results in the initial observation phase.

DOI： 10.1186/s40623-017-0760-x

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Blackwell Publishing Ltd  

We examine magnetic and electric field perturbations associated with a sudden commencement (SC), caused by an interplanetary (IP) shock passing over the Earth's magnetosphere on 16 February 2013. The SC was identified in the magnetic and electric field data measured at Time History of Events and Macroscale Interactions during Substorms (THEMIS-E
THE-E: magnetic local time (MLT) = 12.4, L = 6.3), Van Allen Probe-A (VAP-A: MLT = 3.2, L = 5.1), and Van Allen Probe-B (VAP-B: MLT = 0.2. L = 4.9) in the magnetosphere. During the SC interval, THE-E observed a dawnward-then-duskward electric (E) field perturbation around noon, while VAP-B observed a duskward E field perturbation around midnight. VAP-A observed a dawnward-then-duskward E field perturbation in the postmidnight sector, but the duration and magnitude of the dawnward E perturbation are much shorter and weaker than that at THE-E. That is, the E field signature changes with local time during the SC interval. The Super Dual Auroral Radar Network radar data indicate that the ionospheric plasma motions during the SC are mainly due to the E field variations observed in space. This indicates that the SC-associated E field in space plays a significant role in determining the dynamic variations of the ionospheric convection flow. By comparing previous SC MHD simulations and our observations, we suggest that the E field variations observed at the spacecraft are produced by magnetospheric convection flows due to deformation of the magnetosphere as the IP shock sweeps the magnetopause.

DOI： 10.1002/2017JA024611

Web of Science

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER HEIDELBERG  

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, http://www.isee.nagoya-u.ac.jp/dimr/PWING/) 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 (similar to 60 degrees 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.

DOI： 10.1186/s40623-017-0745-9

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Blackwell Publishing Ltd  

Characteristics of seasonal variation and solar activity dependence of the X and Y components of the geomagnetic solar quiet (Sq) daily variation at Memambetsu in midlatitudes and Guam near the equator have been investigated using long-term geomagnetic field data with 1 h time resolution from 1957 to 2016. The monthly mean Sq variation in the X and Y components (Sq-X and Sq-Y) shows a clear seasonal variation and solar activity dependence. The amplitude of seasonal variation increases significantly during high solar activities and is proportional to the solar F10.7 index. The pattern of the seasonal variation is quite different between Sq-X and Sq-Y. The result of the correlation analysis between the solar F10.7 index and the Sq-X and Sq-Y shows an almost linear relationship, but the slope of the linear fitted line varies as a function of local time and month. This implies that the sensitivity of Sq-X and Sq-Y to the solar activity is different for different local times and seasons. The pattern of the local time and seasonal variations of Sq-Y at Guam shows good agreement with that of a magnetic field produced by interhemispheric field-aligned currents (FACs), which flow from the summer to winter hemispheres in the dawn and dusk sectors and from the winter to summer hemispheres in the prenoon to afternoon sectors. The direction of the interhemispheric FAC in the dusk sector is opposite to the concept of Fukushima's model.

DOI： 10.1002/2017JA024342

Web of Science

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER HEIDELBERG  

We examined the morphological signatures of 315 omega band aurora events observed using the Time History of Events and Macroscale Interactions during Substorm ground-based all-sky imager network over a period of 8 years. We find that omega bands can be classified into the following three subtypes: (1) classical (O-type) omega bands, (2) torch or tongue (T-type) omega bands, and (3) combinations of classical and torch or tongue (O/T-type) omega bands. The statistical results show that T-type bands occur the most frequently (45%), followed by O/T-type bands (35%) and O-type bands (18%). We also examined the morphologies of the omega bands during their formation, from the growth period to the declining period through the maximum period. Interestingly, the omega bands are not stable, but rather exhibit dynamic changes in shape, intensity, and motion. They grow from small-scale bumps (seeds) at the poleward boundary of preexisting east-west-aligned auroras, rather than via the rotation or shear motion of preexisting east-west-aligned auroras, and do not exhibit any shear motion during the periods of auroral activity growth. Furthermore, the auroral luminosity is observed to increase during the declining period, and the total time from the start of the growth period to the end of the declining period is found to be about 20 min. Such dynamical signatures may be important in determining the mechanism responsible for omega band formation.

DOI： 10.1186/s40623-017-0688-1

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

We investigate spatial and temporal evolution of large-scale electric fields in the magnetosphere and ionosphere associated with sudden commencements (SCs) using multipoint equatorial magnetospheric (THEMIS, RBSP, and GOES) and ionospheric (C/NOFS) satellites with radars (SuperDARN). A distinct SC event on 17 March 2013 shows that the magnetospheric electric field in the equatorial plane propagates from dayside toward nightside as a fast-mode wave. The ionospheric electric field responds similar to 41s after the onset of dayside magnetospheric electric field, which can be explained by the propagation of the Alfven wave along magnetic field lines. The wavelet analysis shows that the Alfven wave is dominant in the plasmasphere. Poynting fluxes toward the ionosphere support these propagations. From a statistical analysis of response time, tailward propagation speed is estimated at about 1000-1100km/s. We also statistically derive a spatial distribution and time evolution of the magnetospheric electric field in the dawn-dusk direction (E-y). Our result shows that negative E-y (dawnward) propagates from noon toward the magnetotail, followed by positive E-y (duskward). The propagation characteristics of electric fields in the equatorial plane depend on magnetic local time. At noon, negative E-y lasts for about 1min, and positive E-y becomes dominant about 2min after the SC onset. Negative E-y soon attenuates in the nightside region, while the positive E-y propagates fairly well to the premidnight or postmidnight regions while maintaining a certain amplitude. The enhancement of positive E-y is due to the enhancement of magnetospheric convection associated with the main impulse of SCs.

DOI： 10.1002/2017JA023990

Web of Science

Language：Japanese   Publishing type：Research paper (scientific journal)  

(accepted)

DOI： 10.20637/JAXA-RR-16-007/0003

Language：English  

Language：English   Publishing type：Research paper (scientific journal)  

The Exploration of energization and Radiation in Geospace project Science Center (ERG-SC) has developed the science data file archive and integrated data analysis tool for the ground network observation data of the ERG project. We have organized data design consortiums to develop and elaborate the standard metadata and data variable sets for each type of the ERG-related ground data being archived as Common Data Format (CDF) files. The integrated data analysis software for the project has also been developed on the basis of the Space Physics Environment Data Analysis Software (SPEDAS) which works in concert with the CDF data file repository. The software tools, which are provided as plug-in libraries for SPEDAS, are made available to the international science community so that scientists and students are ready to proceed to integrated studies combining the ground data with other satellite and simulation data seamlessly. The integrated data analysis software can make scientific activities more productive and help the ERG project achieve the scientific goals.

Publishing type：Research paper (scientific journal)  

DOI： 10.1002/2015JA021000

Publishing type：Research paper (scientific journal)  

DOI： 10.1002/2015JA021382

Publishing type：Research paper (scientific journal)  

DOI： 10.1186/s40623-015-0299-7

Publishing type：Research paper (scientific journal)  

DOI： 10.1186/s40623-015-0360-6

Language：Japanese   Publishing type：Research paper (scientific journal)  

In order to understand the mechanism of global-scale phenomena in the upper atmosphere, multidisciplinary researches using many kinds of data are important. An infrastructure to access to many kinds of data on the Internet is one of the keys to the multidisciplinary researches. The Inter-university Upper atmosphere Global Observation NETwork (IUGONET) project solved this problem by developing a metadata database to provide information such as URL of database or each data .le, which are managed dispersively by several institutes. Because the metadata database covers a wide scienti.c .eld, it is likely that non-specialized users can not easily select a right search phrase. We connected an associative search engine which is called GETAssoc with the metadata database, in order to get the related words and to generate re-query phrases by using them automatically. We collected metadata from SAO/NASA Astrophysics Data System to create the dictionary for associative search. We show that the prepared dictionary gives the related terms as expected for generating re-query phrases.

Publishing type：Research paper (scientific journal)  

DOI： 10.1002/2014JA020665

Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.cpc.2014.08.011

Publishing type：Research paper (scientific journal)  

DOI： 10.1186/s40623-014-0155-1

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

DOI： 10.1002/2014JA020050

Language：Japanese   Publishing type：Research paper (scientific journal)  

This paper reports on the benchmark test of the metadata management system developed by the Inter-university Upper atmosphere Global Observation NETwork (IUGONET) project. The IUGONET metadata management system consists of the metadata reception module based on file repositories of Git, which is a widely-used version control software, and the metadata import module to register metadata to the metadata database using the DSpace commands. We made the performance assessments for these two modules in terms of the processing speed for registering/importing metadata both on a native Linux platform and a virtualized Linux platform. As a result, the metadata reception module processes properly eve millions of registered metadata within several minutes at most, showing roughly the similar performance for the native and virtualized platform. On the other hand, the metadata import module needs much longer processing times of several to a few tens of hours for the same amount of metadata. As compared with the virtualized platform, the native platform gives a four times faster speed for updating indices for the built-in search engine based on Lucene. From a perspective of the regular operation of the metadata management system, the metadata import module runs more efficiently on the native Linux platform and it is estimated by our performance test that it takes about 5 hours to newly import 105 metadata files and subsequently takes about 21 hours to update the Lucene indices for the registered metadata of 5 × 106 in total.

Language：Japanese   Publishing type：Research paper (scientific journal)  

In the IUGONET (Inter-university Upper atmosphere Global Observation NETwork) project, we have developed UDAS (iUgonet Data Analysis Software), which is a software to visualize and analyze various kinds of upper atmospheric data distributed by five universities/institutes (Tohoku Univ., Nagoya Univ., Kyoto Univ., Kyushu Univ., and NIPR). UDAS is a plug-in software of TDAS (THEMIS Data Analysis Software suite) written in IDL (Interactive Data Language), and thus can call useful routines to visualize and analyze time series data and GUI included in TDAS. We released a beta version of UDAS at the IUGONET website in May, 2011, and a formal version in February, 2012. We are planning to incorporate UDAS into TDAS and release it from the THEMIS software website after September, 2012. Automatic test tools for the UDAS programs were developed to reduce the workload for the development team. Furthermore, we built an executable file of TDAS that can run on the IDL Virtual Machine environment without any IDL licenses and released it for public testing. These developments will contribute to the promotion of the use of the UDAS and the ground-based observational data distributed by the IUGONET institutions.

Publishing type：Research paper (scientific journal)  

DOI： 10.2481/dsj.WDS-030

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.3724/SP.J.1085.2013.00069

Publishing type：Research paper (scientific journal)  

DOI： 10.1002/jgra.50450

Language：Japanese   Publishing type：Research paper (scientific journal)  

This paper reports on the common metadata format and the metadata management system developed by the Inter-university Upper atmosphere Global Observation NETwork (IUGONET) project. The IUGONET common metadata format has been designed on the basis of the Space Physics Archive Search and Extract (SPASE) data model/metadata format, which has been developed by the SPASE consortium, with some modifications made by IUGONET to accommodate metadata for the various kinds of ground observational data produced by the IUGONET institutes and universities. We have also developed the registration/management system for metadata XML files using GIT, which is a widely-used version control software. With the designed metadata format and the metadata management system, IUGONET continues to generate and archive metadata for the observational data of Japanese Solar-Terrestrial physics community.

Language：Japanese   Publishing type：Research paper (scientific journal)  

This paper describes an overview of the Inter-university Upper atmosphere Global Observation NETwork (IUGONET) project and briefly mentions important products to be developed in the project. It is an inter-university program by the National Institute of Polar Research, Tohoku University, Nagoya University, Kyoto University, and Kyushu University to build a database of metadata for ground-based observations of the upper atmosphere. The metadata database will be of great help to researchers in efficiently finding and obtaining observational data spread over the universities and institutes. This should also facilitate synthetic analysis of multi-disciplinary data, which will lead to new types of research in the upper atmosphere. The IUGONET development team designs its metadata format based on the SPASE (Space Physics Archive Search and Extract) data model. Some modifications depending on characteristics of ground-based observations of the upper atmosphere are added. The metadata database system is built on the platform of DSpace with customizations according to the IUGONET metadata. In addition, an analysis software for the observational data provided by the IUGONET institutions is developed based on the TDAS (THEMIS Data Analysis Software suite) library written in IDL (Interactive Data Language).

Language：Japanese   Publishing type：Research paper (scientific journal)  

In this paper we report an outline of data analysis software developed by the IUGONET (Inter-university Upper atmosphere Global Observation NETwork) project. UDAS (iUgonet Data Analysis Software) is the software to visualize and analyze the upper atmospheric data distributed by five universities/institutes (Tohoku Univ., Nagoya Univ., Kyoto Univ., Kyushu Univ., and NIPR) that belong to the IUGONET project. The UDAS is a plug-in software of TDAS (THEMIS Data Analysis Software suite) that is written in IDL (Interactive Data Language) and has many useful routines to visualize and analyze time series data. In addition, the UDAS provides the GUI (Graphical User Interface) for beginners of IDL. A beta version of the UDAS was released at the IUGONET website in May, 2011. Furthermore, future perspectives of the UDAS are described.

Language：Japanese   Publishing type：Research paper (scientific journal)  

We have been building the metadata database of the gound-based observational data for upper atmosphere as developers of the Inter-university Uppear atmosphere Global Observation NETwork (IUGONET) project which is a six year research project from fiscal 2009 by the five Japanese universities and institutes. The main purpose of the metadata database to facilitate access is the improvement of accessibility to the various kinds of the observational data which are distributed to many databases in the various institutes. We designed the IUGONET common metadata format which is based on the SPASE data model/metadata format developed by the SPASE Consortium. Then we customized DSpace, a free repository software, which handles the Dublin Core metadata format by default, to handle the IUGONET common metadata. In this paper, we describe the IUGONET metadata database as a case example of metadata database adaptation for geoscience.

Language：Japanese   Publishing type：Research paper (scientific journal)  

We have developed European incoherent scatter (EISCAT) database which contains ionospheric parameters (electron density, electron and ion temperatures, and ion velocity) measured with EISCAT radars located in northern Scandinavia and Svalbard. The EISCAT database provides valuable information for studies on upper atmospheric physics in the polar region. In addition, combinations of the EISCAT database and other in-situ and ground-based databases are essential to understand dynamics of the interaction between polar mesosphere, thermosphere, ionosphere, and magnetosphere. In this paper, we explain the current status of data analysis and visualization of the EISCAT database, and discuss their application to a next generation imaging radar project named EISCAT_3D.

Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2012JA017669

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DOI： 10.1029/2012GM001304

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DOI： 10.1029/2011JA017459

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DOI： 10.1029/2012JA017871

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DOI： 10.1029/2012JA018093

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DOI： 10.5047/eps.2011.01.003

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DOI： 10.1029/2010JA015975

Publishing type：Research paper (scientific journal)  

DOI： 10.5047/eps.2011.07.003

Publishing type：Research paper (scientific journal)  

DOI： 10.5194/angeo-29-367-2011

Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2010JA016032

Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2010JA015491

Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2010JA015832

Language：English   Publishing type：Research paper (scientific journal)  

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DOI： 10.1029/2008SW000417

Publishing type：Research paper (scientific journal)  

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DOI： 10.1029/2008JA013586

Publishing type：Research paper (scientific journal)  

DOI： 10.1142/6494-vol8

Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2006GL027024

Publishing type：Research paper (scientific journal)  

DOI： 10.1007/s11214-006-5669-9

Language：English   Publishing type：Research paper (scientific journal)  

Language：English  

DOI： 10.1016/S0964-2749(05)80029-0

Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2004JA010449

Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2004GL021891

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Publishing type：Research paper (scientific journal)  

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Publishing type：Research paper (scientific journal)  

DOI： 10.1029/1999GL003737

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/GM105p0001

Publishing type：Research paper (scientific journal)  

Event date： 2023.9

Language：English   Presentation type：Poster presentation  

Venue：Sendai   Country：Japan  

Event date： 2023.5

Language：English   Presentation type：Poster presentation  

Venue：Makuhari   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：Nagoya University, Nagoya  

Language：English   Presentation type：Oral presentation (general)  

Language：English   Presentation type：Poster presentation  

Language：Japanese   Presentation type：Oral presentation (general)  

Language：English   Presentation type：Oral presentation (general)  

Language：English   Presentation type：Poster presentation  

Language：English   Presentation type：Poster presentation  

Venue：Nagoya University, Nagoya  

Language：Japanese   Presentation type：Poster presentation  

Language：English   Presentation type：Oral presentation (invited, special)  

Language：Japanese   Presentation type：Oral presentation (general)  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：National Institute of Information and Communications Technology, Koganei, Tokyo  

Language：Japanese   Presentation type：Poster presentation  

Venue：Institute of Space and Astronautical Science, Sagamihara, Kanagawa  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Tohoku University, Sendai  

Language：English   Presentation type：Oral presentation (invited, special)  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Nagoya University, Nagoya  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Tohoku University, Sendai