研究者業績
基本情報
- 所属
- 国立研究開発法人宇宙航空研究開発機構 宇宙科学研究所 教授 (副所長)
- 学位
- 理学博士(1992年3月 東京大学)
- 連絡先
- fujimoto.masaki
jaxa.jp - J-GLOBAL ID
- 200901003508985603
- researchmap会員ID
- 1000203981
2006年より、JAXA宇宙科学研究所に所属。それまでの宇宙プラズマ物理の研究に加え、太陽系探査の企画推進にも関わるように。その立場で貢献してきたものとして、JUICE, ひさき、ERG、はやぶさ２，MMX、DESTINY+。宇宙プラズマ研究において多体系の物理への興味が高かったこと、JAXAが得意とする小天体とのリンクが強いことから、N体計算からの惑星系形成論も研究テーマに追加した。また、太陽系探査以外の宇宙科学計画の国際協力調整にも携わる。
経歴
3-
2006年4月 - 現在
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1996年4月 - 2006年3月
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1992年4月 - 1996年3月
学歴
2-
- 1992年
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- 1987年
受賞
5-
2004年
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2004年
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1996年
論文
163-
Journal of Astronomical Telescopes, Instruments, and Systems 9(03) 2023年9月12日
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NATURE ASTRONOMY 6(2) 214-+ 2022年2月Abstract C-type asteroids1 are considered to be primitive small Solar System bodies enriched in water and organics, providing clues to the origin and evolution of the Solar System and the building blocks of life. C-type asteroid 162173 Ryugu has been characterized by remote sensing2–7 and on-asteroid measurements8,9 with Hayabusa2 (ref. 10). However, the ground truth provided by laboratory analysis of returned samples is invaluable to determine the fine properties of asteroids and other planetary bodies. We report preliminary results of analyses on returned samples from Ryugu of the particle size distribution, density and porosity, spectral properties and textural properties, and the results of a search for Ca–Al-rich inclusions (CAIs) and chondrules. The bulk sample mainly consists of rugged and smooth particles of millimetre to submillimetre size, confirming that the physical and chemical properties were not altered during the return from the asteroid. The power index of its size distribution is shallower than that of the surface boulder observed on Ryugu11, indicating differences in the returned Ryugu samples. The average of the estimated bulk densities of Ryugu sample particles is 1,282 ± 231 kg m−3, which is lower than that of meteorites12, suggesting a high microporosity down to the millimetre scale, extending centimetre-scale estimates from thermal measurements5,9. The extremely dark optical to near-infrared reflectance and spectral profile with weak absorptions at 2.7 and 3.4 μm imply a carbonaceous composition with indigenous aqueous alteration, matching the global average of Ryugu3,4 and confirming that the sample is representative of the asteroid. Together with the absence of submillimetre CAIs and chondrules, these features indicate that Ryugu is most similar to CI chondrites but has lower albedo, higher porosity and more fragile characteristics.
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Space Science Reviews 217(5) 2021年8月
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SPACE TELESCOPES AND INSTRUMENTATION 2020: ULTRAVIOLET TO GAMMA RAY 11444 2021年GEO-X (GEOspace X-ray imager) is a 50 kg-class small satellite to image the global Earth's magnetosphere in X-rays via solar wind charge exchange emission. A 12U CubeSat will be injected into an elliptical orbit with an apogee distance of similar to 40 Earth radii. In order to observe the diffuse soft X-ray emission in 0.3-2 keV and to verify X-ray imaging of the dayside structures of the magnetosphere such as cusps, magnetosheaths and magnetopauses which are identified statistically by in-situ satellite observations, an original light-weight X-ray imaging spectrometer (similar to 10 kg, similar to 10 W, similar to 10x10x30 cm) will be carried. The payload is composed of a ultra light-weight MEMS Wolter type-I telescope (similar to 4x4 deg(2) FOV, <10 arcmin resolution) and a high speed CMOS sensor with a thin optical blocking filter (similar to 2x2 cm(2), frame rate similar to 20 ms, energy resolution <80 eV FWHM at 0.6 keV). An aimed launch year is 2023-25 corresponding to the 25th solar maximum.
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Space Science Reviews 216(7) 2020年10月
MISC
108-
2018年9月7日The surface of the Martian moon Phobos exhibits two distinct geologic units, known as the red and blue units. The provenance of these regions is uncertain yet crucial to understanding the origin of the Martian moon and its interaction with the space environment. Here we show that Phobos' orbital eccentricity can cause sufficient grain motion to refresh its surface, suggesting that space weathering is the likely driver of the dichotomy on the moon's surface. In particular, we predict that blue regions are made up of pristine endogenic material that can be uncovered in steep terrain subject to large variations in the tidal forcing from Mars. The predictions of our model are consistent with current spacecraft observations which show that blue units are found near these regions.
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METEORITICS & PLANETARY SCIENCE 52 A393-A393 2017年8月
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第49回月・惑星シンポジウム = Proceedings of the 49th ISAS Lunar and Planetary Symposium 2016年7月第49回月・惑星シンポジウム (2016年7月20-21日. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS)), 相模原市, 神奈川県著者人数: 17名資料番号: SA6000059007
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Geophysical Research Letters 43(11) 5536-5544 2016年6月16日©2016. American Geophysical Union. All Rights Reserved. We report evidence for reconnection between colliding reconnection jets in a compressed current sheet at the center of a magnetic flux rope at Earth's magnetopause. The reconnection involved nearly symmetric inflow boundary conditions with a strong guide field of two. The thin (2.5 ion-skin depth (di) width) current sheet (at ~12 di downstream of the X line) was well resolved by MMS, which revealed large asymmetries in plasma and field structures in the exhaust. Ion perpendicular heating, electron parallel heating, and density compression occurred on one side of the exhaust, while ion parallel heating and density depression were shifted to the other side. The normal electric field and double out-of-plane (bifurcated) currents spanned almost the entire exhaust. These observations are in good agreement with a kinetic simulation for similar boundary conditions, demonstrating in new detail that the structure of large guide field symmetric reconnection is distinctly different from antiparallel reconnection.
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第16回宇宙科学シンポジウム 講演集 = Proceedings of the 16th Space Science Symposium 2016年1月第16回宇宙科学シンポジウム (2016年1月6日-7日. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS)相模原キャンパス), 相模原市, 神奈川県資料番号: SA6000046246レポート番号: S4-009
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METEORITICS & PLANETARY SCIENCE 50 2015年8月
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Earth, planets and space 64(2) 83-92 2012年2月1日
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日本物理学会講演概要集 65(2) 193-193 2010年8月18日
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FUTURE PERSPECTIVES OF SPACE PLASMA AND PARTICLE INSTRUMENTATION AND INTERNATIONAL COLLABORATIONS 1144 40-+ 2009年Using electron and magnetic field data obtained from the Cluster satellites, we identify the spatial distribution of highly accelerated electron distributions up to 10 keV. They are generally isotropic and form flat-top distributions in the phase space. These distributions are observed in the vicinity of the X line associated with the quadrupole-like magnetic field and energetic ions, throughout the plasma sheet. In some cases, these distributions are quasi-stable, continuously observed for a few minutes with a stable B, polarity and low current density in the center of the plasma sheet.
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JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 112(A4) A04213 2007年4月[1] We present first results of a novel technique for producing a two-dimensional (2-D) map of the velocity field from single-spacecraft observations of the bulk plasma parameters and magnetic field. For flow transverse to a unidirectional magnetic field, the MHD equations of motion can be reduced to a Grad-Shafranov- type (GS-type) equation for the stream function (Sonnerup et al., 2006), provided that the plasma structure is 2-D and time-independent when seen in its proper frame. We show how this equation can be used to recover the flow field in regions surrounding a spacecraft path, as was first done in the GS reconstruction of the magnetic field by Sonnerup and Guo ( 1996). The new method is benchmarked by use of an exact solution of the GS-type equation and further by use of synthetic data from 2-D MHD simulations of the Kelvin-Helmholtz instability (KHI). Streamline maps of reasonable accuracy can be generated even when temporal evolution during the KHI development expected at the flank magnetopause is present. Application of the technique to a Geotail encounter with a train of KH waves in the low-latitude flank boundary layer indicates that a chain of vortices ( each of size similar to 3 R-E by 1 R-E) existed and moved tailward along the magnetopause.
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J. Geophys. Res.-Space Phys. 111(A9) A09203-A09203 2006年
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日本物理学会講演概要集 60(1) 248-248 2005年3月4日
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日本物理学会講演概要集 60 207-207 2005年
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26pXA-5 磁気圏プラズマにおけるスケール間結合と次期磁気圏観測衛星計画SCOPEの概要(プラズマ宇宙物理(MHD現象3),領域2(プラズマ基礎・プラズマ科学・核融合プラズマ・プラズマ宇宙物理))日本物理学会講演概要集 60 231-231 2005年
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NATURE 430(7001) 755-758 2004年8月Establishing the mechanisms by which the solar wind enters Earth's magnetosphere is one of the biggest goals of magnetospheric physics, as it forms the basis of space weather phenomena such as magnetic storms and aurorae(1). It is generally believed that magnetic reconnection is the dominant process, especially during southward solar-wind magnetic field conditions when the solar-wind and geomagnetic fields are antiparallel at the low-latitude magnetopause(2). But the plasma content in the outer magnetosphere increases during northward solar-wind magnetic field conditions(3,4), contrary to expectation if reconnection is dominant. Here we show that during northward solar-wind magnetic field conditions - in the absence of active reconnection at low latitudes - there is a solar-wind transport mechanism associated with the nonlinear phase of the Kelvin - Helmholtz instability(5). This can supply plasma sources for various space weather phenomena.
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NATURE 430(7001) 755-758 2004年8月Establishing the mechanisms by which the solar wind enters Earth's magnetosphere is one of the biggest goals of magnetospheric physics, as it forms the basis of space weather phenomena such as magnetic storms and aurorae(1). It is generally believed that magnetic reconnection is the dominant process, especially during southward solar-wind magnetic field conditions when the solar-wind and geomagnetic fields are antiparallel at the low-latitude magnetopause(2). But the plasma content in the outer magnetosphere increases during northward solar-wind magnetic field conditions(3,4), contrary to expectation if reconnection is dominant. Here we show that during northward solar-wind magnetic field conditions - in the absence of active reconnection at low latitudes - there is a solar-wind transport mechanism associated with the nonlinear phase of the Kelvin - Helmholtz instability(5). This can supply plasma sources for various space weather phenomena.
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JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 109(A5) doi:10.1029-2003JA010174 2004年5月We report on the transient strong flow shear (large northward/southward electric field) events accompanied by energetic ion beams and localized field-aligned currents observed at the boundary of the premidnight plasma sheet by Cluster in the Northern Hemisphere and Geotail in the Southern Hemisphere. The events took place associated with plasma sheet expansion during a substorm interval, with the main positive bay onset at 1155 UT on 10 October 2001. Typical timescales of these events were 1-5 minutes. Cluster multipoint analysis showed that the field-aligned currents consist of upward and downward current layers, the latter located at the outermost edge of the plasma sheet and concentrated in a region with a thickness of 1600 km. Low-energy proton flow suggested that the electric field was southward at the outer part and northward at the inner part, with a magnitude exceeding 10 mV/m. The electric field reversal region also corresponds to the boundary between beam-like electrons and more isotropic electron distributions. Geotail observed corresponding plasma and field disturbances simultaneously inside the plasma sheet. We suggest that the strong bipolar electric fields could be related to the Hall effect of the transient reconnection process tailward of Cluster and Geotail and to the leading edge of the plasma flow jetting Earthward from the reconnection region.
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JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 109(A5) doi:10.1029-2003JA010174 2004年5月We report on the transient strong flow shear (large northward/southward electric field) events accompanied by energetic ion beams and localized field-aligned currents observed at the boundary of the premidnight plasma sheet by Cluster in the Northern Hemisphere and Geotail in the Southern Hemisphere. The events took place associated with plasma sheet expansion during a substorm interval, with the main positive bay onset at 1155 UT on 10 October 2001. Typical timescales of these events were 1-5 minutes. Cluster multipoint analysis showed that the field-aligned currents consist of upward and downward current layers, the latter located at the outermost edge of the plasma sheet and concentrated in a region with a thickness of 1600 km. Low-energy proton flow suggested that the electric field was southward at the outer part and northward at the inner part, with a magnitude exceeding 10 mV/m. The electric field reversal region also corresponds to the boundary between beam-like electrons and more isotropic electron distributions. Geotail observed corresponding plasma and field disturbances simultaneously inside the plasma sheet. We suggest that the strong bipolar electric fields could be related to the Hall effect of the transient reconnection process tailward of Cluster and Geotail and to the leading edge of the plasma flow jetting Earthward from the reconnection region.
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PHYSICAL REVIEW LETTERS 92(14) 145001 2004年4月We have simulated nonlinear development of MHD-scale Kelvin-Helmholtz (KH) vortices by a two-dimensional two-fluid system including finite electron inertial effects. In the presence of moderate density jump across a shear layer, in striking contrast to MHD results, MHD KH vortices are found to decay by the time one eddy turnover is completed. The decay is mediated by smaller vortices that appear within the parent vortex and stays effective even when the shear layer width is made larger. It is shown that the smaller vortices are basically of MHD nature while the seeding for these is achieved by the electron inertial effect. Application of the results to the magnetotail boundary layer is discussed.
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PHYSICAL REVIEW LETTERS 92(14) 145001 2004年4月We have simulated nonlinear development of MHD-scale Kelvin-Helmholtz (KH) vortices by a two-dimensional two-fluid system including finite electron inertial effects. In the presence of moderate density jump across a shear layer, in striking contrast to MHD results, MHD KH vortices are found to decay by the time one eddy turnover is completed. The decay is mediated by smaller vortices that appear within the parent vortex and stays effective even when the shear layer width is made larger. It is shown that the smaller vortices are basically of MHD nature while the seeding for these is achieved by the electron inertial effect. Application of the results to the magnetotail boundary layer is discussed.
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GEOPHYSICAL RESEARCH LETTERS 31(6) doi:10.1029-2003GL019120 2004年3月The ion behavior in the low-latitude boundary region is studied based on Geotail data accumulated over several years, toward understanding the formation mechanism of the cold-dense plasma sheet under prolonged northward interplanetary magnetic field (IMF). A statistical survey shows that, during extended northward IMF, (1) dense magnetosheath-like ions appear far more often, especially on the flanks, (2) the dense ions are mostly stagnant, in contrast to those in the classical low-latitude boundary layer (LLBL), (3) a substantial fraction of the dense and stagnant ions is spatially mixed with hot magnetospheric ions, and (4) the mixed ion population has magnetic local time dependence in ion mixing state in energy space. Based on these findings, we argue that, under extended northward IMF, a significant transfer of the solar wind/LLBL ions onto the magnetospheric field lines occurs on the flanks, and the transport/heating process of the entrant ions is different for different local times.
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GEOPHYSICAL RESEARCH LETTERS 31(3) doi:10.1029-2003GL018955 2004年2月Dependence of tearing mode saturation state on the current sheet thickness is investigated by two-dimensional (2-D) full particle simulations. When the system length L-x is taken to be the wavelength of the maximum growth mode L-x = lambda(max) = 12D (D: half-thickness of the current sheet), the instability is found to saturate without producing significant reconnection if D > D-cr(1st) = 3.5 lambda(e), where lambda(e) is the electron inertial length. When the system length is doubled Lx = 2lambda(max), only insignificant effects are available for D > D-cr(2nd) = 2.7lambda(h), where lambda(h) is the ion-electron hybrid inertial length. Comparing these 2-D results with a recent 3-D result, it is shown clearly that a three-dimensional effect reduces the current sheet thickness and thus leads to quick production of substantial reconnection even if D > D-cr(1st).
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GEOPHYSICAL RESEARCH LETTERS 31(3) doi:10.1029-2003GL018955 2004年2月Dependence of tearing mode saturation state on the current sheet thickness is investigated by two-dimensional (2-D) full particle simulations. When the system length L-x is taken to be the wavelength of the maximum growth mode L-x = lambda(max) = 12D (D: half-thickness of the current sheet), the instability is found to saturate without producing significant reconnection if D > D-cr(1st) = 3.5 lambda(e), where lambda(e) is the electron inertial length. When the system length is doubled Lx = 2lambda(max), only insignificant effects are available for D > D-cr(2nd) = 2.7lambda(h), where lambda(h) is the ion-electron hybrid inertial length. Comparing these 2-D results with a recent 3-D result, it is shown clearly that a three-dimensional effect reduces the current sheet thickness and thus leads to quick production of substantial reconnection even if D > D-cr(1st).
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Geophys. Res. Lett. 31 doi:10.1029-2003GL019120 2004年
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JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 108(A10) doi:10.1029-2003JA009900 2003年10月[1] The spacecraft Geotail has observed the Hall current system in the vicinity of the magnetic reconnection site of the near-Earth magnetotail for substorm onsets. In the outermost region near the plasma sheet/tail lobe boundary, field-aligned currents flow out of the magnetic reconnection site. In the adjacent region, just inside the outflowing current layer, field-aligned currents flow into the magnetic reconnection site. Hence, the Hall current circuit forms a thin double-sheet structure near the separatrix layer.
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JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 108(A10) doi:10.1029-2003JA009900 2003年10月[1] The spacecraft Geotail has observed the Hall current system in the vicinity of the magnetic reconnection site of the near-Earth magnetotail for substorm onsets. In the outermost region near the plasma sheet/tail lobe boundary, field-aligned currents flow out of the magnetic reconnection site. In the adjacent region, just inside the outflowing current layer, field-aligned currents flow into the magnetic reconnection site. Hence, the Hall current circuit forms a thin double-sheet structure near the separatrix layer.
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GEOPHYSICAL RESEARCH LETTERS 30(10) 10.1029-2003GL016885 2003年5月[1] On March 18, 2002, under northward interplanetary magnetic field (IMF) and high (similar to15 nPa) solar wind dynamic pressure conditions, Cluster observed reconnection signatures and the passage of an X-line at the large (similar to175degrees) magnetic-shear high-latitude magnetopause (MP). The observations are consistent with the occurrence of a reconnection site tailward of the cusp and in the vicinity of the spacecraft. At the same time IMAGE observed a bright spot poleward of the dayside auroral oval resulting from precipitating protons into the atmosphere. The intensity of the proton spot is consistent with the energy flux contained in the plasma jets observed by Cluster. Using the Tsyganenko-01 magnetic field model with enhanced solar wind pressure, the Cluster MP location is mapped to the vicinity of the IMAGE proton spot. Mapping the auroral spot out to the MP implies an X-line of at least 3.6 R-E in y(GSM). In addition to confirming the reconnection source of the dayside auroral proton spot, the Cluster observations also reveal sub-Alfvenic flows and a plasma depletion layer in the magnetosheath next to the MP, in a region where gas dynamic models predict super-Alfvenic flows.
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GEOPHYSICAL RESEARCH LETTERS 30(10) 10.1029-2003GL016885 2003年5月[1] On March 18, 2002, under northward interplanetary magnetic field (IMF) and high (similar to15 nPa) solar wind dynamic pressure conditions, Cluster observed reconnection signatures and the passage of an X-line at the large (similar to175degrees) magnetic-shear high-latitude magnetopause (MP). The observations are consistent with the occurrence of a reconnection site tailward of the cusp and in the vicinity of the spacecraft. At the same time IMAGE observed a bright spot poleward of the dayside auroral oval resulting from precipitating protons into the atmosphere. The intensity of the proton spot is consistent with the energy flux contained in the plasma jets observed by Cluster. Using the Tsyganenko-01 magnetic field model with enhanced solar wind pressure, the Cluster MP location is mapped to the vicinity of the IMAGE proton spot. Mapping the auroral spot out to the MP implies an X-line of at least 3.6 R-E in y(GSM). In addition to confirming the reconnection source of the dayside auroral proton spot, the Cluster observations also reveal sub-Alfvenic flows and a plasma depletion layer in the magnetosheath next to the MP, in a region where gas dynamic models predict super-Alfvenic flows.
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GEOPHYSICAL RESEARCH LETTERS 30(10) 10.1029-2003GL016885 2003年5月[1] On March 18, 2002, under northward interplanetary magnetic field (IMF) and high (similar to15 nPa) solar wind dynamic pressure conditions, Cluster observed reconnection signatures and the passage of an X-line at the large (similar to175degrees) magnetic-shear high-latitude magnetopause (MP). The observations are consistent with the occurrence of a reconnection site tailward of the cusp and in the vicinity of the spacecraft. At the same time IMAGE observed a bright spot poleward of the dayside auroral oval resulting from precipitating protons into the atmosphere. The intensity of the proton spot is consistent with the energy flux contained in the plasma jets observed by Cluster. Using the Tsyganenko-01 magnetic field model with enhanced solar wind pressure, the Cluster MP location is mapped to the vicinity of the IMAGE proton spot. Mapping the auroral spot out to the MP implies an X-line of at least 3.6 R-E in y(GSM). In addition to confirming the reconnection source of the dayside auroral proton spot, the Cluster observations also reveal sub-Alfvenic flows and a plasma depletion layer in the magnetosheath next to the MP, in a region where gas dynamic models predict super-Alfvenic flows.
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GEOPHYSICAL RESEARCH LETTERS 30(10) 10.1029-2003GL016885 2003年5月[1] On March 18, 2002, under northward interplanetary magnetic field (IMF) and high (similar to15 nPa) solar wind dynamic pressure conditions, Cluster observed reconnection signatures and the passage of an X-line at the large (similar to175degrees) magnetic-shear high-latitude magnetopause (MP). The observations are consistent with the occurrence of a reconnection site tailward of the cusp and in the vicinity of the spacecraft. At the same time IMAGE observed a bright spot poleward of the dayside auroral oval resulting from precipitating protons into the atmosphere. The intensity of the proton spot is consistent with the energy flux contained in the plasma jets observed by Cluster. Using the Tsyganenko-01 magnetic field model with enhanced solar wind pressure, the Cluster MP location is mapped to the vicinity of the IMAGE proton spot. Mapping the auroral spot out to the MP implies an X-line of at least 3.6 R-E in y(GSM). In addition to confirming the reconnection source of the dayside auroral proton spot, the Cluster observations also reveal sub-Alfvenic flows and a plasma depletion layer in the magnetosheath next to the MP, in a region where gas dynamic models predict super-Alfvenic flows.
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Geotail observations of the dayside low-latitude boundary layer: IMF control and dawn-dusk asymmetryJ. Geophys. Res. 108 10.1029-2002JA009667 2003年
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Geotail observations of the dayside low-latitude boundary layer: IMF control and dawn-dusk asymmetryJ. Geophys. Res. 108 0.1029-2002JA009667 2003年
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Geotail observations of the dayside low-latitude boundary layer: IMF control and dawn-dusk asymmetryJ. Geophys. Res. 108 10.1029-2002JA009667 2003年
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Geotail observations of the dayside low-latitude boundary layer: IMF control and dawn-dusk asymmetryJ. Geophys. Res. 108 0.1029-2002JA009667 2003年
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JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 107(A10) 10.1029-2002JA009246 2002年10月[1] The latter half of the magnetic cloud event on 10-11 January 1997 is studied in the context of the cold-dense plasma sheet. A fortuitous distribution of spacecraft in key regions allows us to relate the plasma sheet status transition with the boundary layer process. When the interplanetary magnetic field (IMF) was strongly northward and the solar wind density returned to a nominal value from an anomalously large one, two spacecraft, Geotail and Interball-Tail, were in the dusk-flank region and detected a change in the plasma sheet status from hot and tenuous to cold and dense. The change seen by these spacecraft making in situ observations is confirmed to be a global feature by DMSP observations at low altitude. Just around this time, Interball-Aurora and Polar were crossing the dusk-auroral oval, monitoring globally the dynamics of the dusk-flank magnetopause at its footpoint. Injection of magnetosheath-like ions was detected by these spacecraft. We try to relate these observations with the processes that transport the magnetosheath plasma onto the magnetospheric field lines. Three candidate processes are discussed, but none of them turn out to be convincing, indicating the need for further study on this issue.
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JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 107(A10) 10.1029-2002JA009246 2002年10月[1] The latter half of the magnetic cloud event on 10-11 January 1997 is studied in the context of the cold-dense plasma sheet. A fortuitous distribution of spacecraft in key regions allows us to relate the plasma sheet status transition with the boundary layer process. When the interplanetary magnetic field (IMF) was strongly northward and the solar wind density returned to a nominal value from an anomalously large one, two spacecraft, Geotail and Interball-Tail, were in the dusk-flank region and detected a change in the plasma sheet status from hot and tenuous to cold and dense. The change seen by these spacecraft making in situ observations is confirmed to be a global feature by DMSP observations at low altitude. Just around this time, Interball-Aurora and Polar were crossing the dusk-auroral oval, monitoring globally the dynamics of the dusk-flank magnetopause at its footpoint. Injection of magnetosheath-like ions was detected by these spacecraft. We try to relate these observations with the processes that transport the magnetosheath plasma onto the magnetospheric field lines. Three candidate processes are discussed, but none of them turn out to be convincing, indicating the need for further study on this issue.
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GEOPHYSICAL RESEARCH LETTERS 29(8) 10.1029-2001GL013780 2002年4月[1] Three-dimensional structures of reconnection jets are investigated by hybrid simulations. Magnetic reconnection is initiated by ad-hoc anomalous resistivity, which is uniform in the cross-tail direction but localized within the meridian plane. At the interface between the reconnection jet and the pre-existing plasma sheet ahead of it, the reconnected field lines are piled up and the plasma density is enhanced by compression. The interface becomes unstable to an interchange instability and deforms itself into a wavy shape. In the non-linear growth phase, the wavy perturbations grow into magnetic bubbles into which the field lines are converged and the bubbles move faster than the other parts. It is suggested that this instability can generate localized channels with a cross-tail extent of a few R-E, in which plasma and magnetic field transports are achieved, and thus may well be related to the formation of the bursty bulk flows in the magnetotail.
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GEOPHYSICAL RESEARCH LETTERS 29(8) 10.1029-2001GL013780 2002年4月[1] Three-dimensional structures of reconnection jets are investigated by hybrid simulations. Magnetic reconnection is initiated by ad-hoc anomalous resistivity, which is uniform in the cross-tail direction but localized within the meridian plane. At the interface between the reconnection jet and the pre-existing plasma sheet ahead of it, the reconnected field lines are piled up and the plasma density is enhanced by compression. The interface becomes unstable to an interchange instability and deforms itself into a wavy shape. In the non-linear growth phase, the wavy perturbations grow into magnetic bubbles into which the field lines are converged and the bubbles move faster than the other parts. It is suggested that this instability can generate localized channels with a cross-tail extent of a few R-E, in which plasma and magnetic field transports are achieved, and thus may well be related to the formation of the bursty bulk flows in the magnetotail.
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COMPARATIVE RECONNECTION STUDIES AT THE SUN AND IN PLANETARY MAGNETOSPHERES 29(7) 1125-1128 2002年When a reconnection jet encounters a pre-existing plasma sheet standing ahead of it, the interface between the two where both plasma and magnetic field are compressed becomes unstable and develops a bubblelike structure. We have conducted three-dimensional hybrid simulations (ions as particles and electrons as massless charge neutralizing fluid) of this instability. We suggest that this instability generates a variety of plasma flows and field configurations which may have relevance to some magnetospheric phenomena. (C) 2002 COSPAR. Published by Elsevier Science Ltd, All rights reserved.
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DYNAMIC PROCESSES IN THE CRITICAL MAGNETOSPHERIC REGIONS AND RADIATION BELT MODELS, PROCEEDINGS 30(12) 2663-2666 2002年Current sheet instabilities having wavenumber vectors parallel to the current direction are studied as a linear eigenvalue problem in a two-fluid system where electrons are treated as a finite-mass charge neutralizing component. Focusing on ion-scale current sheets, we show that a hybrid scale current sheet kink instability (CSKI) is one of the major instabilities to appear. The hybrid scale CSKI in a magnetotail-like situation has a wavelength much shorter than the well-studied drift-kink instability (DKI). While most of the previous studies have focused on the long-wavelength range, a full-particle simulation with much larger ion-to-electron mass ratio (R-M = 400) shows the growth of the hybrid scale CSKI as predicted by linear analyses. We also show that the CSKI has large growth rates in a magnetopause-like situation. (C) 2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved.
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ADVANCES IN GLOBAL MAGNETOSPHERIC STRUCTURE, DYNAMICS, AND REGION COUPLING, PROCEEDINGS 30(10) 2279-2288 2002年Cold-dense plasma sheet (CDPS) is known to appear during extended northward IMF periods. Its appearance suggests enhanced entry of the solar wind into the magnetosphere during the times when it is supposed to be most closed, in a manner totally different from active times, and that on to closed field lines. To understand the CDPS formation mechanism, which still remains open, anatomy of CDPS is performed in this study. By inspecting the ion spectrum characteristics CDPS is classified into three categories. Dawn-dusk asymmetry is revealed as the spatial distributions of the three categories are plotted separately, which indicates that different heating/transport processes are operative on different sides of the magnetotail. On dawnside a group of data characterized by the highest temperature from one of the CDPS categories is distributed at the plasma sheet inner-edge and is connected to the hot-dense ions (HDIs) at the further inner region. An independent analysis indicates that HDIs not associated with elevated solar wind dynamic pressure appear in the dawnside inner-magnetosphere during extended northward IMF. Both studies points to the idea that HDIs are the inner-magnetosphere extension of dawnside CDPS and that there is significant dawn-dusk asymmetry in heating and transport in the magnetotail under northward IMF. (C) 2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved.
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COMPARATIVE RECONNECTION STUDIES AT THE SUN AND IN PLANETARY MAGNETOSPHERES 29(7) 1125-1128 2002年When a reconnection jet encounters a pre-existing plasma sheet standing ahead of it, the interface between the two where both plasma and magnetic field are compressed becomes unstable and develops a bubblelike structure. We have conducted three-dimensional hybrid simulations (ions as particles and electrons as massless charge neutralizing fluid) of this instability. We suggest that this instability generates a variety of plasma flows and field configurations which may have relevance to some magnetospheric phenomena. (C) 2002 COSPAR. Published by Elsevier Science Ltd, All rights reserved.
書籍等出版物
14Works(作品等)
1共同研究・競争的資金等の研究課題
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日本学術振興会 科学研究費助成事業 2019年11月 - 2022年3月
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日本学術振興会 科学研究費助成事業 2017年4月 - 2020年3月
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日本学術振興会 科学研究費助成事業 2015年4月 - 2018年3月
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日本学術振興会 科学研究費助成事業 2014年4月 - 2018年3月
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日本学術振興会 科学研究費助成事業 2012年4月 - 2015年3月
