研究者詳細 - 新堀　淳樹

Electrostatic electron cyclotron harmonic waves observed by the Akebono satellite near the equatorial region of the plasmasphere 査読有り

Generation mechanism of Z-mode waves in the equatorial plasmasphere 査読有り

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

EARTH PLANETS AND SPACE 59 巻 ( 9 ) 頁： 1027 - 1034 2007年

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

Earth, Planets and Space 59 巻 ( 6 ) 頁： 613 - 629 2007年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Earth, Planets and Space

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°) 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 fQn ESCH waves. We identified these plasma waves as the equatorial plasmasphere fQn waves (EP-fQn). The spectra of the EP-fQn waves are characterized by a narrow band structure and by a strong nature, with a wave intensity that ranges from 3.46 × 10-8 to 3.31 × 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-fQn 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-fQn 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. 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/BF03352723

Storm-time electric field distribution in the inner magnetosphere 査読有り

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

Geophysical Research Letters 33 巻 ( 22 ) 2006年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Geophysical Research Letters

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. Copyright 2006 by the American Geophysical Union.

DOI： 10.1029/2006GL027510

Enhancements of magnetospheric convection electric field in the inner magnetosphere associated with sudden commencements 査読有り

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年1月

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

新堀淳樹

Advances in space Research 38 頁： 1595 - 1607 2006年

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

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

ADVANCES IN SPACE RESEARCH 38 巻 ( 8 ) 頁： 1595 - 1607 2006年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Statistical studies of fast and slow Z-mode plasma waves in and beyond the equatorial plasmasphere based on long-term Akebono observations 査読有り

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

Earth, Planets and Space 58 巻 ( 3 ) 頁： 343 - 346 2006年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Electrodynamics in the duskside inner magnetosphere and plasmasphere during a super magnetic storm on March 13-15, 1989 査読有り

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

EARTH PLANETS AND SPACE 57 巻 ( 7 ) 頁： 643 - 659 2005年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

新堀淳樹

Earth, Planets and Space 56巻 56 巻 ( 2 ) 頁： 269 - 282 2004年

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

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 108 巻 ( A12 ) 2003年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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 Atsuki, Ono Takayuki, Iizima Masahide, Kumamoto Atsushi, Oya Hiroshi

Advances in polar upper atmosphere research 17 巻頁： 60 - 76 2003年9月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

Plasma wave phenomena associated with sudden commencements (SCs) were analyzed using the database of Akebono satellite observations that has been contributed to for more than 13 years, since March 1989. The plasma wave data from 263 satellite passages covering the onsets of SCs included 85 cases of auroral kilometric radiation (AKR) enhancement within a frequency range of 100kHz to 1.2MHz. The majority of the spectra of the SC-related AKR exhibited a two-banded structure with a harmonic relationship. The start time of the AKR enhancements tended to occur after the onset of the SCs, determined using the geomagnetic records of the Kakioka Magnetic Observatory, within a time range of 3 to 8min, with an average delay time of 5.26min. Based on this delay time feature, the magnetic disturbances associated with SCs were thought to propagate from the dayside magnetosphere to the nightside tail region where they compressed the plasma sheet. On the other hand, the data set reveals 19 cases of terrestrial hectometric radiation (THR) that were also associated with SCs appearing within a frequency range of 900kHz to 4MHz. The THR onset tended to occur 1 to 9min after the SC onset, with an average delay time of 5.84min.

DOI： 10.15094/00006362

CiNii Books

SC-triggered plasma waves observed by the Akebono satellite in the polar regions and the plasmasphere 査読有り

Shinbori Atsuki, Ono Takayuki, Oya Hiroshi

Advances in polar upper atmosphere research 16 巻頁： 126 - 135 2002年9月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：国立極地研究所

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

CiNii Books