Faculty Profiles - SHINBORI Atsuki

Papers - SHINBORI Atsuki

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Evolution of ring current and radiation belt particles under the influence of storm-time electric fields Reviewed Open Access

Y. Nishimura, A. Shinbori, T. Ono, M. Iizima, A. Kumamoto

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 112 ( A6 ) 2007.6

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

Electric field and potential distributions in the inner magnetosphere during geomagnetic storms have been investigated using the Akebono/EFD data. Using this electric field, we study injection of ring current particles and acceleration of radiation belt electrons by single-particle calculations. During the main phase, the dawn-dusk electric field is intensified especially in a range of 2 < L < 5 with a maximum amplitude of 6 mV/m on the duskside, and a two-cell convection pattern with a potential difference of 180 kV is identified. The convection pattern on the equatorial plane is significantly distorted with a large potential drop of 70 kV on the dawn and dusk sectors, indicating an intrinsic source of large-scale electric field in the inner magnetosphere. The plasma sheet ions are gathered into the dusk to premidnight sector in the inner magnetosphere in the region of enhanced electric field due to the strong E x B drift. The ions are transported into around 4 R-E with an acceleration of more than 1 order of magnitude within 40 min, conserving the first adiabatic invariants. Relativistic electrons with initial energy of some hundreds of kiloelectron volts at 5 R-E are energized to more than 100 keV for 3 hours. The energy spectrum during the recovery phase of 9 October 1990 geomagnetic storm observed by the CRRES satellite is reproduced without the radial diffusion or nonadiabatic acceleration by plasma waves. It is possible that this acceleration process is the inhomogeneity of the large-scale electric field, which corresponds to the del x E term along orbits of electrons around the Earth.

DOI： 10.1029/2006JA012177

Electrostatic electron cyclotron harmonic waves observed by the Akebono satellite near the equatorial region of the plasmasphere Reviewed Open Access

Shinbori A., Ono T., Iizima M., KUMAMOTO A., SHIRAI S., HANAOKA A., OKAMOTO K., OHASHI M., OYA H.

Earth, planets and space Vol. 59 ( 6 ) page： 613 - 629 2007.6

Electrostatic electron cyclotron harmonic waves observed by the Akebono satellite near the equatorial region of the plasmasphere Reviewed Open Access

新堀淳樹

Earth, Planets and Space (印刷中) 2007

Electrostatic electron cyclotron harmonic waves observed by the Akebono satellite near the equatorial region of the plasmasphere Reviewed Open Access

Shinbori A., Ono T., Iizima M., Kumarnot A., Shirai S., Hanaoka A., Okamoto K., Ohashi M., Oya H.

EARTH PLANETS AND SPACE Vol. 59 ( 6 ) page： 613 - 629 2007

Generation mechanism of Z-mode waves in the equatorial plasmasphere Reviewed Open Access

Yukitoshi Nishimura, T. Ono, M. Iizima, A. Shinbori, A. Kumamoto

Earth, Planets and Space Vol. 59 ( 9 ) page： 1027 - 1034 2007

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

In order to clarify the generation mechanism of Z-mode waves observed in the equatorial plasmasphere, the growth rate of Z-mode electromagnetic waves has been calculated under the higher-order cyclotron interaction process. Z-mode waves can interact with some tens of keV electrons with large pitch angles even in the dense cold background, and the amplitude is consistent with the Akebono plasma wave measurements. UHR and whistler mode waves are also excited by the same electron distribution, and this is also consistent with observations. The origin of these energetic electrons are identified as the ring current electrons injected into the plasmasphere by the intense large-scale electric field during geomagnetic storms, accelerated perpendicular to the ambient magnetic field and confined around the geomagnetic equator conserving the first and second adiabatic invariants. Since the intensity of Z-mode and UHR waves is associated with the development and decay of the ring current, ring current particles are most possible candidate for the free energy source of these waves. Copyright © The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS)
The Seismological Society of Japan
The Volcanological Society of Japan
The Geodetic Society of Japan
The Japanese Society for Planetary Sciences
TERRAPUB.

DOI： 10.1186/BF03352043

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Generation mechanism of Z-mode waves in the equatorial plasmasphere Reviewed Open Access

Nishimura Y., Ono T., Iizima M., Shinbori A., Kumamoto A.

EARTH PLANETS AND SPACE Vol. 59 ( 9 ) page： 1027 - 1034 2007

Electrostatic electron cyclotron harmonic waves observed by the Akebono satellite near the equatorial region of the plasmasphere Reviewed Open Access

A. Shinbori, T. Ono, M. Iizima, A. Kumarnot, S. Shirai, A. Hanaoka, K. Okamoto, M. Ohashi, H. Oya

EARTH PLANETS AND SPACE Vol. 59 ( 6 ) page： 613 - 629 2007

Language：English Publishing type：Research paper (scientific journal) Publisher：TERRA SCIENTIFIC PUBL CO

Analysis of the plasma wave observation data provided by the plasma waves and sounder experiment (PWS) on board the Akebono satellite frequently reveals the presence of electrostatic electron cyclotron harmonic (ESCH) waves in the low-latitude region (MLAT < 45 degrees) of the plasmasphere within an altitude range from about 3000 km to the apogee of the satellite (initial apogee was 10,500 km). Even at moderate or low geomagnetic activity, intense ESCH waves often appear near the equatorial region of the plasmasphere above the upper hybrid resonance (UHR) frequency at the lowest harmonic number branch of the f(Qn) ESCH waves. We identified these plasma waves as the equatorial plasmasphere f(Qn) waves (EP-f(Qn)). The spectra of the EP-f(Qn) waves are characterized by a narrow band structure and by a strong nature, with a wave intensity that ranges from 3.46 x 10(-8) to 3.31 X 10(-4) V/m. The maximum intensity is nearly coincident with the upper limit of the PWS receiver in the low-gain mode. Statistical analysis results reveal that the EP-f(Qn) waves are observable in all the local time sectors; however, the occurrence probability shows a clear enhancement in the early morning sector of 01-03 MLT in the plasmasphere. The EP-f(Qn) wave activities are suppressed within a period of strong magnetic disturbances as well as solar minimum phase. The linear dispersion relation analysis using a two-component plasma model reveals that supra-thermal plasma with the energy of about 750 eV and with a large temperature anisotropy (A = T-perp/T-parallel - 1 > 40) must be present in order to realize an appearance of a positive growth rate at the observed frequency and propagation angle of the ESCH waves. Since the hot plasma with such a high anisotropy has not been detected, the validity of the present two-component plasma model remains an open question. The occurrence feature of the ESCH waves showed that there is a constant activation or a constant flow-in of free energy to generate the strong plasma instability of ESCH waves near the post-midnight sector of the plasmasphere. The existence of ESCH waves revealed that the nature of the plasmaspheric plasma is more turbulent and active than has been believed.

DOI： 10.1186/BF03352723

Storm-time electric field distribution in the inner magnetosphere Reviewed Open Access

Y. Nishimura, A. Shinbori, T. Ono, M. Iizima, A. Kumamoto

GEOPHYSICAL RESEARCH LETTERS Vol. 33 ( 22 ) 2006.11

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

The distribution of the storm-time electric field in the inner magnetosphere has been investigated by using the Akebono/EFD data within a period from 1989 to 1995. During the main phase of geomagnetic storms, the strong electric field appears between L = 2 and L = 6 in both dawn and dusk sectors with the magnitude from 2 to 4 mV/m, and the maximum value appears at L = 3 in the dusk sector. During the recovery and weakly disturbed period, the region with intense electric field moves outward with decreasing the amplitude. This structure of the localized electric field is quite different from the Volland-Stern electric field model, suggesting the existence of another electric field source other than the large-scale convection electric field. During quiet periods, although the electric field fairly follows the corotation electric field, the distribution at L = 3.5 indicates a small deviation from pure corotation.

DOI： 10.1029/2006GL027510

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Enhancements of magnetospheric convection electric field in the inner magnetosphere associated with sudden commencements Reviewed

Shinbori, A, T. Ono, M. Iizima, A. Kumamoto

Advances in Space Research, Volume 38, Issue 8, 1595-1607, doi: 10.1016/j.asr.2005.05.082 2006.1

Enhancements of magnetospheric convection electric field associated with sudden commencements in the inner magnetosphere and plasmasphere regions Reviewed

新堀淳樹

Advances in space Research 38 page： 1595 - 1607 2006

Enhancements of magnetospheric convection electric field associated with sudden commencements in the inner magnetosphere and plasmasphere regions Reviewed

A. Shinbori, T. Ono, M. Iizima, A. Kumamoto, Y. Nishimura

ADVANCES IN SPACE RESEARCH Vol. 38 ( 8 ) page： 1595 - 1607 2006

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCI LTD

Electric field variations in the inner magnetosphere and plasmasphere regions associated with sudden commencements (SCs) are investigated by using the observation data of the Akebono satellite which has been carried out more than 15 years since 1989. 117 of 153 SC events in the low-latitude (MLAT < 45 degrees) region, which occurred within a period from March 1989 to January 1996, showed a shift of the magnetospheric convection electric field with the magnitude of 0.1-3.2 mV/m about 1 min after the electric field signature with a bi-polar waveform due to the passage of fast-mode hydromagnetic (HM) waves. The increase of the convection electric field takes place in the entire magnetic local time sector in the inner magnetosphere. The amplitude does not depend on L-value and magnetic local time but is proportional to the SC amplitude measured at Kakioka. The majority of the electric field enhancements persist for about 4-14 min. The origin of the convection electric field in the inner magnetosphere is a plasma motion caused by the compression of the magnetosphere due to the solar wind shock and discontinuity. (C) 2005 COSPAR. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.asr.2005.05.082

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Statistical studies of fast and slow Z-mode plasma waves in and beyond the equatorial plasmasphere based on long-term Akebono observations Reviewed Open Access

Yukitoshi Nishimura, T. Ono, M. Iizima, A. Shinbori, A. Kumamoto, H. Oya

Earth, Planets and Space Vol. 58 ( 3 ) page： 343 - 346 2006

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

In order to investigate spatial and temporal variations of fast and slow Z-mode waves frequently observed in the equatorial plasmasphere, statistical studies have been performed by using plasma wave observation data obtained by the Akebono satellite within a period from 1989 to 1995. It has been clarified that fast and slow Z-mode waves are intensified within ±5° of geomagnetic latitudes in an altitude range from 6000 km to the apogee (10500 km) of the satellite without obvious local time dependence. Long-term averaged intensity of fast Z-mode waves has almost the same orders of magnitude as that of slow Z-mode waves. These results indicate that significant part of fast Z-mode waves are not produced by the linear mode conversion process from slow Z-mode waves, but excited by more direct process. Furthermore, the region of intensified fast and slow Z-mode waves has been spread in a wider geomagnetic latitude range of ±10° during geomagnetic storms. These evidences suggest that one of the possible free energy sources is ring current particles injected into the equatorial region of the plasmasphere during geomagnetic storms. Copyright © The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS)
The Seismological Society of Japan
The Volcanological Society of Japan
The Geodetic Society of Japan
The Japanese Society for Planetary Sciences
TERRAPUB.

DOI： 10.1186/BF03351930

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Electrodynamics in the duskside inner magnetosphere and plasmasphere during a super magnetic storm on March 13-15, 1989 Reviewed Open Access

A Shinbori, Y Nishimura, T Ono, M Iizima, A Kumamoto, H Oya

EARTH PLANETS AND SPACE Vol. 57 ( 7 ) page： 643 - 659 2005

Language：English Publishing type：Research paper (scientific journal) Publisher：TERRA SCIENTIFIC PUBL CO

Variations of cold plasma density distribution and large-scale electric field in the inner magnetosphere and plasmasphere during a geomagnetic storm were investigated by using the observation data of the Akebono satellite which has been carried out for more than 15 yeas since March, 1989. We focus on the super geomagnetic storm on March 13-15, 1989, for which the maximum negative excursion of the Dst index was -589 nT. During the main phase of the magnetic storm, the strong convection electric field with a spatially inhomogeneous structure appears in the inner magnetosphere between L = 2.0 and 7.0. The averaged intensity of the electric field was in a range of about 2.5-9.2 mV/m. The spatial distribution in the magnetic equatorial region indicates that the magnitude within an L-value range of 2.2-7.0 is much larger than that observed at L = 7.0-10.0. Associated with the appearance of the strong convection electric field, the cold plasma density near the trough region around L = 3.0-6.0 was enhanced with one or two order magnitude, compared with that in the magnetically quiet condition. This implies that a mount of the ionospheric plasma may be supplied from the topside ionosphere into the trough and plasmasphere regions by the frictional heating due to the fast plasma convection in the ionosphere as pointed out by previous studies on the enhancements of plasma density in these regions, based on incoherent scatter radar and total electron content (TEC) observations (e.g., Yeh and Foster, 1990; Foster et al., 2004). During the recovery phase of the magnetic storm, the convection electric field observed in the inner magnetosphere and plasmasphere regions recovers within 3-4 days almost up to the level of the magnetically quiet condition.

DOI： 10.1186/BF03351843

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Effect of R2-FAC development on the ionospheric electric field pattern deduced by a global ionospheric potential solver Reviewed Open Access

Nakamizo, A. Y. Hiraki, Y. Ebihara, T. Kikuchi, K. Seki, T. Hori, A. Ieda, Y. Miyoshi, Y. Tsuji, Y. Nishimura, A. Shinbori

Journal of Geophysical Research, Volume 117, Issue A9, CiteID: A09231, doi: 10.1029/2012JA017669 Vol. 117 ( 9 ) 2004.4

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

Toward the understanding of the effect of the magnetosphere originated disturbances on the global ionospheric electric field and current system, we developed a two-dimensional ionospheric potential solver based on the so-called "thin shell model." The important extension from the previous studies is that our model covers the pole-to-pole ionosphere without placing any boundary at the equator. By using this solver, we investigate how the ionospheric electric field changes from undershielding condition to overshielding condition as the field aligned current (FAC) distribution changes. Calculations are performed by changing IR2/IR1 (the ratio of current intensities of region 2 (R2) and region 1 (R1) FACs) and by moving R2-FAC relative to the fixed R1-FAC. The results are summarized as follows: (1) The turning point, at which the ionosphere turns from undershielding to overshielding is IR2/IR1 = 0.7 ∼ 0.8. (2) With increasing the local time deference between the R1 and R2-FAC peaks, the efficiency of the shielding by R2-FAC increases but the associated potential skews to the nightside. (3) At the same time the shielding effect is weakened around noon, where the R1-potential intrudes to the low latitude region instead, but the R2-potential remains dominant at other local times. The result suggests that the overshielding or undershielding should be identified by observations not only in a limited local time sector but also in the overall ionosphere as much as possible. In order to accurately describe the ionospheric condition, we suggest new classification terms, "complete-overshielding" and "incomplete-overshielding. " © 2012. American Geophysical Union. All Rights Reserved.

DOI： 10.1029/2012JA017669

A Shinbori, T Ono, M Iizima, A Kumamoto

EARTH PLANETS AND SPACE Vol. 56 ( 2 ) page： 269 - 282 2004

Language：English Publishing type：Research paper (scientific journal) Publisher：TERRA SCIENTIFIC PUBL CO

Electric and magnetic field variations inside the plasmasphere associated with SCs identified on the ground are analyzed based on the Akebono satellite observations which have been carried out more than 13 years since March 1989. 126 electric field observation data corresponding to SCs show abrupt change of intensity as well as direction within a few minutes inside the plasmasphere. Temporal variations of the electric field showed a bipolar waveform with the amplitude range of 0.2-38 mV/m. The electric field signature is followed by a dumping oscillation with the period of Pc3-4 ranges. The magnetic field variations of 33 SCs also show an abrupt increase of 0.2-65 nT within a few minutes, which indicate the compression of the magnetosphere due to the discontinuity of solar wind. The initial excursion of the electric field during SCs tends to be directed westward. The amplitude does not show a dependence on magnetic local time that has been observed outside the plasmasphere. The magnitude of the electric field variations tends to be proportional with the power of 0.6 to the magnetic field variation in the plasmasphere. The Poynting vector of the initial SC impulse is directed toward the earth, which suggests that energy of magnetic disturbances associated with SCs propagates toward the earth inside the plasmasphere with the refraction due to the plasma density gradient. One of the most interesting results from the present study is that a DC offset of the Ey component of the electric field appears after the initial electric field impulse associated with SCs. This signature is interpreted to be a magnetospheric convection electric field penetration into the inner plasmasphere (L=2.5). The intensity of the offset of the Ey field gradually increases by 0.5-2.0 mV/m about 1-2 minutes after the onset of the initial electric field impulse and persists about 10-30 minutes.

DOI： 10.1186/BF03353409

Sudden commencements related plasma waves observed by the Akebono satellite in the polar region and inside the plasmasphere region Reviewed Open Access

A Shinbori, T Ono, M Iizima, A Kumamoto, H Oya

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 108 ( A12 ) 2003.12

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

Plasma wave phenomena associated with sudden commencements (SC) are analyzed using the database of the Akebono satellite observations that have been carried out for more than 13 years since March 1989. All the 719 data sets simultaneously observed in the periods of SC events show that plasma waves are enhanced with one-to-one correspondence to SCs in entire regions of the polar cap, auroral zone, and plasmasphere within a response time of +/-90 s. In the middle latitude and equatorial regions of the plasmasphere, intensification and frequency shift of electromagnetic whistler mode, LHR waves, and ion cyclotron harmonic waves are found. The electric field variations in this region also show clear response to the onset of SCs with the amplitude of 0.2-30 mV/m. The variations are observed in the nightside as well as dayside sectors, and no clear dependence of magnetic latitude, local time, and L shell is found. On the other hand, electrostatic whistler mode waves and electromagnetic ion cyclotron waves which show broadband spectra are generated in the high-latitude region. Spectra of low-energy particles observed simultaneously with the enhancement of these plasma waves show that electron fluxes are enhanced in all of pitch angle bins of the low-energy particle detector onboard the Akebono satellite. Near the cusp region, the ion fluxes are more enhanced in the upward direction than in the downward direction along the magnetic field lines. In about half of the cases of the high-latitude events, sudden appearance and intensification of AKR are also found after the onsets of SC. The delay time between the onsets of SC and AKR enhancement shows several minutes with the average time of 5.7 min. Time differences between the onsets of SC measured at Kakioka Magnetic Observatory and plasma wave enhancements observed by the Akebono satellite show positive correlation with possible delay time according to the propagation route of SC disturbances. Propagation character of SC disturbances shows two group signatures: one group takes a route which crosses the geomagnetic equator region with an average speed of 389.5 km/s. The speed is almost consistent with plasmaspheric fast-mode MHD wave velocity. The other group takes a route which starts from the dayside cusp region. In the second case, the SC disturbances propagate through the polar ionosphere region from the dayside to the nightside sectors with an average speed of 47 km/ s in the X-GSM coordinate corresponding to the ionospheric fast-mode MHD wave velocity.

DOI： 10.1029/2003JA009964

Shinbori, A, T. Ono, M. Izima, K. Kumamoto, H. Oya

Advances in polar upper atmosphere research Vol. 17 page： 60 - 76 2003.9

SC-triggered plasma waves observed by the Akebono satellite in the polar regions and the plasmasphere Reviewed Open Access

Shinbori, A, T. Ono, H. Oya

Advances in polar upper atmosphere research Vol. 16 page： 126 - 135 2002.9

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：National Institute of Polar Research

Plasma wave phenomena associated with sudden commencements (SCs) were analyzed based on observations conducted with the Akebono satellite, which has been collecting data for more than 13 years (since March 1989). Simultaneous plasma wave observation data for 257 SCs reveal that enhanced plasma waves are observed with an exact one-to-one correspondence with the SCs throughout the entire observation region, including the polar and plasmasphere regions. Electromagnetic whistler mode and ion cyclotron waves are enhanced in the low latitude plasmasphere, while electrostatic whistler mode and electromagnetic ion cyclotron waves are generated in the polar region. The onset times of the SC-triggered plasma waves exhibit a delay or lead time characteristic, compared with the onset times of SCs identified by the Kakioka Magnetic Observatory, with a time resolution of 1 s. By comparing the difference in SCs and enhanced electron plasma waves onset times, the propagation route of the SC disturbances can be identified in the plasmasphere.

DOI： https://doi.org/10.15094/00006352

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Papers - SHINBORI Atsuki