研究者詳細 - 新堀　淳樹

Observations of very-low-energy (<10 eV) ion outflows dominated by O<SUP>+</SUP> ions in the region of enhanced electron density in the polar cap magnetosphere during geomagnetic storms 査読有り Open Access

Kitamura, N; Nishimura, Y; Ono, T; Ebihara, Y; Terada, N; Shinbori, A; Kumamoto, A; Abe, T; Yamada, M; Watanabe, S; Matsuoka, A; Yau, AW

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 115 巻 ( 11 ) 2010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：Journal of Geophysical Research: Space Physics

Velocity distributions of upflowing ions in the polar ionosphere are crucial to understand their destinations. Natural plasma wave observations by the plasma wave and sounder experiments and thermal ion observations by the suprathermal ion mass spectrometer onboard the Akebono satellite at ∼9000 km altitude in the polar magnetosphere during the geomagnetic storms showed that ions in the region of enhanced electron density in the polar cap were dominated by very-low-energy O+ ions (∼85%) with upward velocities of 4-10 km s-1, corresponding to streaming energies of 1.3-8.4 eV. The fluxes of very-low-energy upflowing O+ ions exceeded 1 × 10 9 cm-2 s-1 (mapped to 1000 km altitude) across wide regions. These signatures are consistent with high-density plasma supplied by the cleft ion fountain mechanism. Trajectory calculations of O+ ions based on the Akebono observations as the initial condition showed the transport paths and accelerations of the O+ ions and indicated that the velocities of the very-low-energy upflowing O+ ions through the dayside polar cap are enough to reach the magnetosphere under strong convection. The calculations suggest the importance of the very-low-energy upflowing O + ions with large fluxes in the total O+ ion supply toward the magnetosphere, especially the near-Earth tail region and inner magnetosphere. The initially very-low-energy O+ ions can contribute significantly to the ring current formation during geomagnetic storms since some of the O+ ions were transported into the ring current region with typical energies of ring current ions (several tens of keV) in the trajectory calculations. Copyright 2010 by the American Geophysical Union.

DOI： 10.1029/2010JA015601

Anomalous occurrence features of the preliminary impulse of geomagnetic sudden commencement in the South Atlantic Anomaly region 査読有り Open Access

Shinbori, A; Nishimura, Y; Tsuji, Y; Kikuchi, T; Araki, T; Ikeda, A; Uozumi, T; Otadoy, RES; Utada, H; Ishitsuka, J; Trivedi, NB; Dutra, SLG; Schuch, NJ; Watari, S; Nagatsuma, T; Yumoto, K

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 115 巻 ( 8 ) 2010年8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：Journal of Geophysical Research: Space Physics

Occurrence features of the preliminary impulse (PI) of geomagnetic sudden commencement (SC) both in the Pacific Ocean and South Atlantic Anomaly (SAA) regions were investigated using the long-term magnetic field data obtained from the Circum-pan Pacific Magnetometer Network (CPMN) and NICT Space Weather Monitoring (NSWM) magnetometer networks. The low-latitude preliminary reverse impulse (PRI) at Okinawa (OKI: dip latitude = 37.97°) in the Pacific Ocean region appeared in all the magnetic local time (MLT) sectors with the peak occurrence rate of 40% around noon. On the other hand, the PRI occurrence rate at Santa Maria (SMA: dip latitude = -34.35°) near the center of the SAA region showed a significant enhancement in the daytime sector (0800-1600 h, MLT) with the peak value of 80%, which resembles the occurrence feature of the equatorial PRI. Moreover, the PRI amplitude around noon at SMA was about 3.0 times larger than that at OKI. From the calculation of the ionospheric conductivity derived from the IRI-2007 and NRLMSISE-00 models, it is shown that the height-integrated conductivity was more enhanced in the SAA region (SMA), where the ambient magnetic field intensity is weak, compared with that in the Pacific Ocean region (OKI). Therefore, the anomalous increase of the PRI occurrence and amplitude is caused by the significant enhancement of the ionospheric conductivity due to the weakness of the ambient magnetic field intensity in the SAA region. Copyright © 2010 by the American Geophysical Union.

DOI： 10.1029/2009JA015035

Temporal variations and spatial extent of the electron density enhancements in the polar magnetosphere during geomagnetic storms 査読有り

Anomalous Enhancement of Occurrence of the Preliminary Impulse of Geomagnetic Sudden Commencement (SC) at Low Latitude in the South Atlantic Anomaly (SAA) region 査読有り

Shinbori A, Y. Nishimura, Y. Tsuji, T. Kikuchi, T. Araki, A. Ikeda, T. Uozumi, R. Otadoy, H. Utada, J. Ishitsuka, N. Trivedi, S. Dutra, N. Schuch, S. Watari, T. Nagatsuma, K. Yumoto

Journal of Geophysical Research: Space Physics, Volume 115, Issue A8, CiteID: A08309, doi: 10.1029/2009JA015035 115 巻 ( A8 ) 2010年8月

Kitamura, N; Nishimura, Y; Ono, T; Kumamoto, A; Shinbori, A; Iizima, M; Matsuoka, A; Hairston, MR

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 115 巻 ( A7 ) 2010年7月

Penetration of magnetospheric electric fields to the equator and their effects on the low-latitude ionosphere during intense geomagnetic storms 査読有り

Veenadhari, B; Alex, S; Kikuchi, T; Shinbori, A; Singh, R; Chandrasekhar, E

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 115 巻 ( A3 ) 2010年3月

Development metadata database for upper atmosphere

Koyama, Y, Y.-M. Tanaka, T. Kouno, H. Hayashi, T. Hori, M. Kagitani, D. Yoshida, S. UeNo, S. Abe, A. Shinbori, N. Kaneda

Proceedings of CAWSES-II Kickoff Symposium in Japan 頁： 135-136 2010年

Scientific perspectives powered by IUGONET metadata database and integrated analysis tool

Hori, T, Y. Koyama, Y.-M. Tanaka, M. Kagitani, H. Hayashi, A. Shinbori, S. UeNo, D. Yoshida, S. Abe, T. Kouno, N. Kaneda, H. Tadokoro, IUGONET project members

Proceedings of CAWSES-II Kickoff Symposium in Japan 頁： 71-74 2010年

Response of convection electric fields in the magnetosphere to IMF orientation change 査読有り Open Access

Nishimura, Y; Kikuchi, T; Wygant, J; Shinbori, A; Ono, T; Matsuoka, A; Nagatsuma, T; Brautigam, D

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 114 巻 ( 9 ) 2009年9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：Journal of Geophysical Research: Space Physics

The transient response of convection electric fields in the inner magnetosphere to southward turning of the interplanetary magnetic field (IMF) is investigated using in-situ electric field observations by the CRRES and Akebono spacecraft. Electric fields earthward of the inner edge of the electron plasma sheet show quick responses simultaneously with change in ionospheric electric fields, which indicates the arrival of the first signal related to southward turning. A coordinated observation of the electric field by the CRRES and Akebono spacecraft separated by 5 RE reveals a simultaneous increase in the dawn-dusk electric field in a wide region of the inner magnetosphere. A quick response associated with the southward turning of the IMF is also identified in in-situ magnetic fields. It indicates that the southward turning of the IMF initiates simultaneous (less than 1 min) enhancements of ionospheric electric fields, convection electric fields in the inner magnetosphere, and the ring or tail current and region 2 FACs. In contrast, a quick response of convection electric fields is not identified in the electron plasma sheet. A statistical study using 161 events of IMF orientation change in 1991 confirms a prompt response within 5 min for 80% of events earthward of the electron plasma sheet, while a large time lag of more than 30 min is identified in electric fields in the electron plasma sheet. The remarkable difference in the response of electric fields indicates that electric fields in the electron plasma sheet are weakened by high conductance in the magnetically conjugated auroral ionosphere. Copyright 2009 by the American Geophysical Union.

DOI： 10.1029/2009JA014277

Magnetic latitude and local time dependence of the amplitude of geomagnetic sudden commencements 査読有り

Shinbori Atsuki, Tsuji Yuji, Kikuchi Takashi, Araki Tohru, Watari Shinichi

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 114 巻 2009年4月

Magnetic latitude and local time dependence of the amplitude of geomagnetic sudden commencements 査読有り

Shinbori A., Tsuji Y., Kikuchi T., Araki T., Watari S.

Journal of Geophysical Research: Space Physics 114 巻 ( 4 ) 2009年4月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Geophysical Research: Space Physics

Statistical analysis of the main impulse (MI) amplitude of geomagnetic sudden commencements (SCs) in a region from the middle latitudes to equator has been made using the long-term geomagnetic field data obtained from the Yap (geomagnetic latitude, θ = 0.38°), Guam (θ = 5.22°), Okinawa (θ = 16.54°), Kakioka (θ = 27.18°), Memanbetsu (θ = 35.16°), and St. Paratunka (θ = 45.58°) stations. The magnetic local time (MLT) dependence of SC amplitude in the middle latitudes showed magnetic field variations produced by two-cell ionospheric currents (DP 2-type currents) which are driven by the dawn-to-dusk electric field accompanying a pair of field-aligned currents (FACs). The effect of the DP 2-type currents at least expands to the low latitude (θ = 16.54°). In this region, the DL part of SC produced by the enhanced Chapman-Ferraro currents can be dominant, but the DP part of SC contaminated 7% of the DL one. On the other hand, at the daytime equator between 8:00 and 16:00 (MLT), the SC amplitude is considerably enhanced with its peak amplitude of 3.24 (normalized SYM-H value) around 11:00 (MLT) due to the Cowling effect. Another interesting point is that the SC amplitude in the nighttime sector was enhanced at all the stations again, and its peak value increases with increasing magnetic latitude. This result suggests that the effect of the FACs associated with the MI phase of SC expands to the equator. Copyright 2009 by the American Geophysical Union.

DOI： 10.1029/2008JA013871

Seasonal variations of the electron density distribution in the polar region during geomagnetically quiet periods near solar maximum 査読有り Open Access

Kitamura, N; Shinbori, A; Nishimura, Y; Ono, T; Iizima, M; Kumamoto, A

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 114 巻 ( A1 ) 頁： n/a - n/a 2009年1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：Journal of Geophysical Research: Space Physics

Meridional electron density distributions above 45 invariant latitude (ILAT) during geomagnetically quiet periods are statistically studied. Electron density data were obtained from plasma waves observed by the Akebono satellite from March 1989 to February 1991 (near solar maximum) in an altitude range of 274-10,500 km. Field-aligned electron density profiles were fitted by the sum of exponential and power law functions. The transition height, where the power law term equals the exponential term, is highest in the summer (at low solar zenith angle (SZA)) at ∼4000 km and lowest in the winter (at high SZA) at ∼1800 km in a region of ILAT ≥ 70; this is caused by the larger scale height in the summer (∼550 km) than that in the winter (∼250 km). The largest seasonal variation and SZA dependence of the electron density are found at an altitude of ∼2000 km with a factor of ∼50 (∼104 /cc in the summer, ∼103 /cc in the winter) in the trough, auroral, and polar cap regions. The seasonal variation and SZA dependence are smaller, about a factor of 5-10, above ∼5000 km. Day-night asymmetries in each season (within a factor of 5) are smaller than the seasonal variation. The scale height is larger in the dayside than in the nightside in each season. These results indicate that photoionization processes in the ionosphere strongly control electron density distributions up to at least ∼5000 km in the trough, auroral, and polar cap regions. Copyright 2009 by the American Geophysical Union.

DOI： 10.1029/2008JA013288

Magnetic latitude and local time dependence of the amplitude of geomagnetic sudden commencements 査読有り

A. Shinbori, Y. Tsuji, T. Kikuchi, T. Araki, S. Watari

Journal of Geophysical Research A: Space Physics 114 巻 ( 4 ) 2009年

SC-associated Ionospheric Electric Fields at Low Latitude : FM-CW Radar Observation

Ikeda Akihiro, Yumoto Kiyofumi, Shinohara Manabu, Nozaki Kenro, Yoshikawa Akimasa, Shinbori Atsuki

Memoirs of the Faculty of Science, Kyushu University. Series D, Earth and planetary sciences 32 巻 ( 1 ) 頁： 1 - 6 2008年2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：Faculty of Science, Kyushu University

We present the low-latitude ionospheric electric field during the main impulse (MI) phase of two geomagnetic sudden commencements (SCs), observed for the first time by an FM-CW radar. From our observation, the direction of the ionospheric electric field is eastward in the daytime and westward in the nighttime sectors. This difference indicates the penetration of the dawn-to-dusk polar electric field associated with the SCs into the low-latitude ionosphere.

DOI： 10.5109/11811

CiNii Research

SC-associated ionospheric electric fields at low latitude: FM-CW radar observation 査読有り

Ikeda, A, K. Yumoto, M. Shinohara, K. Nozaki, A. Yoshikawa, A. Shinbori

Mem. Fac. Sci., Kyushu Univ., Ser. D, Earth and Planet. Sci.,XXXII, 1-6 32 巻 ( 1 ) 頁： 1 - 6 2008年2月

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9月

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

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 112 巻 ( A6 ) 2007年6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：Journal of Geophysical Research: Space Physics

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 × 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 RE 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 ∇ × E term along orbits of electrons around the Earth. Copyright 2007 by the American Geophysical Union.

DOI： 10.1029/2006JA012177