Dept. of Solar System Sciences
基本情報
経歴
5-
2026年4月 - 現在
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2017年4月 - 現在
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2014年4月 - 2017年3月
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2011年4月 - 2014年3月
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2008年4月 - 2011年3月
学歴
3-
2008年4月 - 2011年3月
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2006年4月 - 2008年3月
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2002年4月 - 2006年3月
主要な受賞
8-
2011年3月
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2011年3月
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2008年3月
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2007年9月
論文
159-
Journal of Geophysical Research: Space Physics 131(5) 2026年4月30日Abstract We studied a coronal mass ejection (CME) structure that propagated through the inner heliosphere in October 2021, which was observed by BepiColombo, Solar Orbiter, PSP, STEREO‐A, and DSCOVR spacecraft located at different radial distances and heliospheric longitudes. Notably, four of the five spacecraft detected a dip‐like signature in the magnetic field embedded within the CME. We investigated the cause of the dip‐like signature on the basis of both in situ solar wind data and solar surface data. We examined the flare‐triggering structure of the M1.6 flare, which probably caused the CME; however, there was no conclusive evidence found linking the flare to the dip‐like signature observed in the ejected CME. We applied the minimum variance analysis (MVA) to the in situ magnetic field data to determine whether the dip‐like signature could represent a planar magnetic structure (PMS) embedded in the CME‐driven shock sheath. Our MVA results confirmed that the magnetic field associated with the dip‐like structure lies along a plane perpendicular to the minimum variance direction, consistent with the characteristics of the PMS previously reported in the literature. Additionally, we examined the shock parameters and found that the CME‐driven shock developed more rapidly than usual, probably because of the passage of a stream interaction region (SIR) during the initial phase of its propagation. This fact suggests that the interaction between the CME and the SIR played a significant role in the formation of the PMS, resulting in the observation of dip‐like structure downstream at most of the spacecraft.
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Earth, Planets and Space 78(1) 2026年3月16日Abstract We analyze a unique solar energetic particle event observed simultaneously by the BepiColombo and STEREO-A spacecraft on March 30, 2022. The two spacecraft at heliocentric distances of 0.6 and 1.0 AU are expected to be aligned approximately along the same magnetic field line, providing a valuable opportunity to investigate particle transport processes in the inner heliosphere. Protons with energies above 1.0 MeV exhibit velocity dispersion during the rise phase, suggesting that the energetic particles are produced close to the Sun, possibly associated with a coronal mass ejection. In contrast, protons during the decay phase are characterized by long-lasting time profiles with longer time scales at 1.0 AU than at 0.6 AU, suggesting that the particles deviate from ballistic propagation. By assimilating these multi-spacecraft observation data into numerical simulations of the focused transport equation, for the first time, we estimate the mean free path parallel to the magnetic field as a time series. The inferred mean free path decreases over time and approaches around 0.5–1.0 AU at the STEREO-A location during the decay phase, suggesting an increasing influence of scattering on particle transport. This interpretation is qualitatively supported by independent STEREO-A observations that showed increasing magnetic field fluctuations, suggesting the connection between the particle transport and the local field fluctuations. However, only a fraction of these fluctuations is expected to contribute to particle scattering, which may be due to the multidimensional nature of magnetic field fluctuations. Graphical abstract
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2026年3月14日Life-environmentology, Astronomy, and PlanetarY Ultraviolet Telescope Assembly (LAPYUTA) is a future ultraviolet (UV) space telescope that is selected as a candidate for JAXA's 6th M-class mission. Launch is planned for the early 2030s. LAPYUTA will perform spectroscopic and imaging observations in the far-ultraviolet spectral range (110-190 nm) with a large effective area (>300 cm2) and a high spatial resolution (0.1 arcsec). LAPYUTA has the following four objectives: (1) atmospheres of solar system planets, (2) atmospheres of exoplanets around the habitable zone, (3) structures of present-day galaxies, and (4) synthesis process of heavy elements from observations of neutron star mergers. The key to addressing these scientific goals is the measurement of the physical state of hydrogen, oxygen, and carbon. These elements are common in the universe and are involved in understanding the structure and evolution of the universe at various spatial scales, from planets to stars to galaxies, and UV spectral measurement is adequate for measuring the physical state of the elements. LAPYUTA aims to achieve resolution and sensitivity in the far-UV wavelength range comparable to the Hubble Space Telescope (HST) while using JAXA’s small scientific satellite. The mission part consists of a Cassegrain telescope with a 60 cm aperture primary mirror, four focal plane instruments, a medium dispersion spectrograph (MRS), a high dispersion spectrograph (HRS), a UV slit imager (UVSI), and a wide-field fine guide sensor (FGS). To achieve a highly effective area and high angular resolution, we are developing three key technologies: UV mirror deposition, a large high-precision detector, and a pointing disturbance correction function, as well as studying the concept of the telescope structure. The key technologies for ultraviolet observations developed here will serve as a stepping stone for Japan's participation in the Habitable Worlds Observatory (HWO).
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The Astrophysical Journal 997(1) 2-2 2026年1月13日 査読有りAbstract Interplanetary coronal mass ejections (ICMEs) cause “Forbush decreases” (FDs), which are local decreases in background galactic cosmic rays (GCRs). Even though FDs can be observed with simple particle instruments, their amplitude and shape provide physical profiles of passing ICMEs. However, in some cases, previous statistical studies of the heliocentric distance dependence of FD changes associated with ICME propagation have found no strong correlation. We need the criteria for evaluating the relationship between ICME structure and FDs, necessary for the FD’s statistical analysis. This study investigates the effect of the evolution and interactions of ICMEs on FD profiles in the inner solar system using multipoint comparisons. We focus on multipoint ICME observations by Solar Orbiter, BepiColombo, and near-Earth spacecraft from 2022 March 10 to 16, when these spacecraft were ideally located for studying the radial and longitudinal evolution of ICMEs and accompanying FDs. We compared GCR variations with the multiple in situ data and ICME model, clarifying the correspondence between the evolution of each ICME structure in the radial and azimuthal directions and the depth and gradients of the FD. The radial comparison revealed decreases in FD intensities and gradients associated with the expansion of the ICME. The longitudinal difference found in FD intensity indicates longitudinal variations of the ICME’s shielding effect. These results suggest that accurate multipoint FD comparisons require determining the relationship between the observer’s position and the inner structure of the passing ICMEs.
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NATURE COMMUNICATIONS 17(1) 2026年1月1日 査読有り
MISC
134-
Proceedings of the SPIE 13093 2024年8月21日
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Abstract EGU 2023 2023年5月15日 招待有りHisaki is an earth orbiting extreme ultraviolet spectroscope dedicated for observing solar system planets. Thanks to its monitoring capability, Hisaki has carried out unprecedented continuous observation of Io plasma torus, Jovian aurora, and Mars and Venus upper atmosphere since December 2013. One of notable phenomena observed by Hisaki is significant enhancements of neutral gas (sodium and oxygen) from Io occurred in the spring of 2015. Hisaki revealed that not only the plasma source, but transport, heating, and loss processes of magnetospheric plasma were influenced by the variation in the neutral source input. The presentation will include related topics from recent Hisaki publication. Since the autumn of 2016, the Juno spacecraft was in the orbit around Jupiter. Hisaki monitored activities of Jovian aurora and the plasma torus in the Juno era. These datasets will provide opportunities to compare in-situ observation by Juno with the global view by Hisaki. JAXA approved the Hisaki mission period by the end of March 2023. As a future remote observation platform, we are going to propose a UV space telescope, LAPYUTA (Life-environmentology, Astronomy, and PlanetarY Ultraviolet Telescope Assembly), a Japanese-leading mission using heritages of UV instruments for planetary science (e.g., Hisaki) and space telescope techniques for astronomy. One of goals of this mission is dynamics of our solar system planets and moons as the most quantifiable archetypes of extraterrestrial habitable environments in the universe. Water plume that gushes from the subsurface ocean of Galilean moons and tenuous atmosphere which is generated by bombardment of energetic charged particles to the surface are primary targets of LAPYUTA. As the plume activity and the atmosphere are not stable, continuous monitoring with high spatial resolution is essential. The icy moon's plume and ambient space will be deeply explored with the spacecraft by NASA's and ESA's icy moon missions in 2020s-2030s. The complementary remote sensing by LAPYUTA will visualize their global structure and temporal dynamics.
共同研究・競争的資金等の研究課題
13-
日本学術振興会 科学研究費助成事業 2024年4月 - 2028年3月
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日本学術振興会 科学研究費助成事業 2023年4月 - 2026年3月
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日本学術振興会 科学研究費助成事業 国際共同研究加速基金(国際共同研究強化(B)) 2020年10月 - 2024年3月
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日本学術振興会 科学研究費助成事業 基盤研究(B) 2020年4月 - 2023年3月
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宇宙航空研究開発機構 搭載機器基礎開発研究費 2020年5月 - 2021年3月
