Profile Information
- Affiliation
- Professor, Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency
- Degree
- Ph.D(The University of Tokyo)
- J-GLOBAL ID
- 200901025081752002
- researchmap Member ID
- 5000018897
Research Interests
4Research Areas
3Education
2Papers
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Direct Evidence for Electron Pitch Angle Scattering Driven by Electrostatic Cyclotron Harmonic WavesGeophysical Research Letters, 52(5), Feb 28, 2025Abstract Electrostatic Cyclotron Harmonic (ECH) waves have been considered a potential cause of pitch angle scattering of electrons in the energy range from a few hundred eV to tens of keV. Theoretical studies have suggested that scattering by ECH waves is enhanced at lower pitch angles near the loss cone. Due to the insufficient angular resolution of particle detectors, it has been a great challenge to reveal ECH‐driven scattering based on electron measurements. This study reports on variations in electron pitch angle distributions associated with ECH wave activity observed by the Arase satellite. The variation is characterized by a decrease in fluxes near the loss cone, and energy and pitch angle dependence of the flux decrease is consistent with the region of enhanced pitch angle scattering rates predicted by the quasi‐linear diffusion theory. This study provides direct evidence for energy‐pitch angle dependence of pitch angle scattering driven by ECH waves.
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Geophysical Research Letters, 52(3), Feb 10, 2025Abstract We report a statistical result of electrons inside the loss cone with energies of 67 eV–88 keV using electron measurements obtained in situ by the Arase satellite in the inner magnetosphere around the magnetic equator for 60 months. Loss cone electrons are found with a high occurrence probability from the nightside to the dawnside at approximately L = 6. For 641 eV–88 keV electrons, the high‐occurrence region shifts toward later magnetic local times (MLTs) with increasing loss cone electron energy. The spatial distribution of the occurrence probability around MLT = 22–3 at L = 5–6 is consistent with the calculated average resonance energy distribution of whistler mode chorus waves near the magnetic equator. These results suggest that pitch angle scattering driven by chorus waves plays the main role in electron precipitation in this region.
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Journal of Geophysical Research: Space Physics, 130(2), Feb 6, 2025Abstract Strong Thermal Emission Velocity Enhancement (STEVE) is a latitudinally narrow, purple‐band emission observed at subauroral latitudes. Stable Auroral Red (SAR) arcs characterized by major red emission, and red/green arcs with both red and green emissions also occur at subauroral latitudes. Characteristics of magnetospheric source plasma and electromagnetic fields of these three types of arcs have not been fully understood because of the limited conjugate observations between magnetosphere and the ground. In this study, we report 11 conjugate observations (2 STEVEs, 7 SAR arcs, and 2 red/green arcs), using all‐sky images obtained at seven ground stations over more than four years from January 2017 to April 2021 and magnetospheric satellites (Arase and Van Allen Probes). We found that, in the inner magnetosphere, the source region of STEVEs and red/green arcs were located outside the plasmasphere, and that of the SAR arc was in the region of spatial overlap between the plasmasphere and ring current region. Electromagnetic waves at frequencies below 1 Hz were observed for STEVEs and red/green arcs. SuperDARN radar data showed a strong westward plasma flow in the ionosphere, especially during STEVE events, whereas the plasma flows associated with SAR arcs and red/green arcs were generally weaker and variable. The STEVE and SAR arc can appear simultaneously at slightly different latitudes and STEVEs and red/green arcs can transform into SAR arcs. These first comprehensive ground‐satellite measurements of three types of subauroral‐latitude auroras increase our understanding on similarlity, differences, and coupling of these auroras in the ionosphere and the magnetosphere.
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Scientific Reports, 15(1), Jan 14, 2025
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Journal of Geophysical Research: Space Physics, 129(12), Dec 13, 2024Abstract We investigate the dynamics of relativistic electrons in the Earth's outer radiation belt by analyzing the interplay of several key physical processes: electron losses due to pitch angle scattering from electromagnetic ion cyclotron (EMIC) waves and chorus waves, and electron flux increases from chorus wave‐driven acceleration of 100–300 keV seed electrons injected from the plasma sheet. We examine a weak geomagnetic storm on 17 April 2021, using observations from various spacecraft, including GOES, Van Allen Probes, ERG/ARASE, MMS, ELFIN, and POES. Despite strong EMIC‐ and chorus wave‐driven electron precipitation in the outer radiation belt, trapped 0.1–1.5 MeV electron fluxes actually increased. We use theoretical estimates of electron quasi‐linear diffusion rates by chorus and EMIC waves, based on statistics of their wave power distribution, to examine the role of those waves in the observed relativistic electron flux variations. We find that a significant supply of 100–300 keV electrons by plasma sheet injections together with chorus wave‐driven acceleration can overcome the rate of chorus and EMIC wave‐driven electron losses through pitch angle scattering toward the loss cone, explaining the observed net increase in electron fluxes. Our study emphasizes the importance of simultaneously taking into account resonant wave‐particle interactions and modeled local energy gradients of electron phase space density following injections, to accurately forecast the dynamical evolution of trapped electron fluxes.
Misc.
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Text for GPS/GNSS Symposium, 2023, 2023
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地球電磁気・地球惑星圏学会総会及び講演会(Web), 154th, 2023
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地球電磁気・地球惑星圏学会総会及び講演会(Web), 154th, 2023
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地球電磁気・地球惑星圏学会総会及び講演会(Web), 146th, 2019
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日本地球惑星科学連合大会予稿集(Web), 2019, 2019
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2019 EUROPEAN SPACE POWER CONFERENCE (ESPC), 2019We found that the solar panel output current of JAXA's Venus explorer Akatsuki is below values expected from percentage of shadow during penumbras. We also found that a similar phenomenon occurs in JAXA's Van Allen radiation belts explorer Arase during Earth shadow penumbra. However, during a Lunar shadow penumbra, solar panel output current decreased in proportion to percentage of shadow. We consider that sunlight attenuated by the planetary atmosphere caused this decrease in current. As in the transit spectroscopy technique, planetary atmospheres could be characterized by trends in solar panel output current.
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International Journal of Astronomy and Astrophysics, 8 306-322, Nov 14, 2018 Peer-reviewed
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宇宙科学技術連合講演会講演集(CD-ROM), 62nd, 2018
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宇宙科学技術連合講演会講演集(CD-ROM), 62nd ROMBUNNO.3C19, 2018
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2018 2ND URSI ATLANTIC RADIO SCIENCE MEETING (AT-RASC), 45(24) 13199-13205, 2018
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宇宙科学技術連合講演会講演集(CD-ROM), 61st, 2017
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地球電磁気・地球惑星圏学会総会及び講演会(Web), 142nd, 2017
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地球電磁気・地球惑星圏学会総会及び講演会(Web), 142nd, 2017
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日本地球惑星科学連合大会予稿集(Web), 2017, 2017
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日本地球惑星科学連合大会予稿集(Web), 2017, 2017
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日本地球惑星科学連合大会予稿集(Web), 2017, 2017
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応用物理学会春季学術講演会講演予稿集(CD-ROM), 63rd ROMBUNNO.20P‐KD‐7, Mar 3, 2016
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地球電磁気・地球惑星圏学会総会及び講演会(Web), 140th, 2016
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Journal of Plasma and Fusion Research, 90(5) 277-288, May, 2014
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(13) 43-46, Mar 31, 201410th Spacecraft Environment Symposium (December 2-3, 2013, Science Museum), Tokyo JapanPhysical characteristics: Original contains color illustrations
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Proceedings of JSST2012 International Conference on Simulation Technology, 562-565, Sep, 2012 Peer-reviewed
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JAXA Research and Development Memorandum, JAXA-RM-11-019, Mar, 2012
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48th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit 2012, 2012 Peer-reviewedA magnetoplasma sail (MPS) spacecraft produces an artificial magnetosphere to reflect the solar wind particles approaching the coil, and the corresponding repulsive force exerts on the coil to accelerate the spacecraft in the solar wind direction. In this paper, plasma equilibrium in an artificial magnetosphere in interplanetary space is numerically studied to apply the idea of plasma equilibrium for MPS. It is numerically shown that releasing a lowvelocity plasma from an MPS spacecraft excites an equatorial ring-current, which makes a larger magnetosphere and correspondingly a larger thrust level becomes possible. Thrust gain, which is defined as a thrust ratio between MPS and pure magnetic sail without releasing plasma, was found to be as much as 20; this thrust gain is predicted from a limited model describing the interaction between a dipole magnetic field and ions. Also, some preliminary numerical simulations, including a solar wind to magnetosphere interaction as well as plasma equilibrium in a magnetosphere, were conducted to indicate a thrust gain as much as 3.3 is possible in an MHD regime. © 2012 by Ikkoh Funaki.
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2011(9) 71-76, Aug 26, 2011
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(10) 169-177, Feb 28, 20117th Spacecraft Enivironment Symposium (October 19-20, 2010, Tokyo International Forum), Tokyo JapanPhysical characteristics: Original contains color illustrations
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日本惑星科学会秋期講演会予稿集, 2010 44-44, Oct 6, 2010
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Meeting abstracts of the Physical Society of Japan, 65(2) 193-193, Aug 18, 2010
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46th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, AIAA-2010-6773, Jul, 2010 Peer-reviewed
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(9), Feb 26, 20106th Spacecraft Enivironment Symposium (February 29-30, 2009. Kitakyushu International Conference Center)Physical characteristics: Original contains color illustrations
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(9) 211-214, Feb 26, 20106th Spacecraft Enivironment Symposium (February 29-30, 2009. Kitakyushu International Conference Center)Physical characteristics: Original contains color illustrations
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JAXA research and development report, 9 11-18, Feb, 2010A three-dimensional electrostatic full Particle-In-Cell code has been developed to analyze spacecraft-plasma interactions quantitatively. We adopted the code to evaluate the correlation between the floating potential of a spacecraft and the photoelectron current in the magnetospheric plasma environment by comparing the computation results and the observation ones by the GEOTAIL spacecraft. The numerical model of the velocity distribution function of the photoelectron described as double Maxwellian was proposed to consider the correlation and the space charge effect of the photoelectron that affects to the current collection onto a spacecraft was also discussed.
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宇宙航空研究開発機構研究開発報告, 9, Feb, 2010
Research Projects
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Grants-in-Aid for Scientific Research, Japan Society for the Promotion of Science, Apr, 2023 - Mar, 2028
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科学研究費助成事業 基盤研究(B), 日本学術振興会, Apr, 2020 - Mar, 2023
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Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (S), Japan Society for the Promotion of Science, May, 2017 - Mar, 2022
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Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A), Japan Society for the Promotion of Science, Apr, 2017 - Mar, 2021
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Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B), Japan Society for the Promotion of Science, Apr, 2014 - Mar, 2018