受賞国：日本国

DOI： 10.1186/s40623-023-01956-8

Web of Science

DOI： 10.1109/TGRS.2023.3338513

Web of Science

DOI： 10.1186/s40623-023-01941-1

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記述言語：英語  

DOI： 10.1109/LGRS.2023.3292593

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.jastp.2023.106136

Web of Science

DOI： 10.1029/2023JA031477

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記述言語：英語  

DOI： 10.1016/j.asr.2022.10.029

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記述言語：英語  

DOI： 10.1016/j.jastp.2023.106097

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記述言語：英語  

DOI： 10.1186/s40623-023-01844-1

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記述言語：英語  

DOI： 10.3389/fspas.2023.1198739

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記述言語：英語  

DOI： 10.1029/2022JA031157

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記述言語：英語  

DOI： 10.1029/2022JA030544

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記述言語：英語  

DOI： 10.1029/2022JA030913

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記述言語：英語  

DOI： 10.3389/fspas.2023.1091319

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記述言語：英語  

DOI： 10.1029/2022SW003312

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DOI： 10.1029/2022JA030983

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DOI： 10.3389/fspas.2022.969235

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DOI： 10.1038/s41598-022-20548-2

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DOI： 10.1029/2022JA030346

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DOI： 10.1029/2021JA029856

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DOI： 10.1186/s40623-022-01682-7

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DOI： 10.1186/s40623-022-01665-8

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DOI： 10.1186/s40623-022-01653-y

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DOI： 10.1029/2021JA030159

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DOI： 10.3390/rs14081896

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記述言語：日本語  

DOI： 10.1029/2021JA029687

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DOI： 10.1117/12.2626894

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DOI： 10.1016/j.jastp.2021.105663

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記述言語：日本語  

DOI： 10.26464/epp2021050

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記述言語：日本語  

DOI： 10.26464/epp2021046

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記述言語：日本語  

DOI： 10.26464/epp2021047

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記述言語：日本語  

DOI： 10.1029/2021GL093541

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DOI： 10.1186/s40623-021-01486-1

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記述言語：日本語  

DOI： 10.1109/TGRS.2020.3032741

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記述言語：日本語  

DOI： 10.1016/j.polar.2020.100608

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記述言語：日本語  

DOI： 10.1186/s40623-021-01432-1

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記述言語：日本語  

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記述言語：日本語  

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記述言語：日本語  

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DOI： 10.1002/9781119815617.ch18

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記述言語：日本語  

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記述言語：日本語  

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DOI： 10.1029/2019JA027521

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2019JA026807

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記述言語：日本語  

DOI： 10.1029/2019JA027598

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記述言語：日本語  

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DOI： 10.1111/1346-8138.15103

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PubMed

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記述言語：日本語  

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DOI： 10.2176/nmc.oa.2018-0267

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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PubMed

DOI： 10.1016/j.nima.2014.11.012

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PubMed

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PubMed

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DOI： 10.1182/blood-2007-08-099168

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PubMed

DOI： 10.1161/01.CIR.0000134485.30393.63

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DOI： 10.1055/s-2004-814184

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PubMed

Web of Science

記述言語：日本語  

DOI： 10.1089/152308602760598945

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PubMed

DOI： 10.1159/000054726

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DOI： 10.1159/000049063

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DOI： 10.1029/2000JA900169

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DOI： 10.1159/000046062

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PubMed

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DOI： 10.1016/S0016-5107(00)14387-1

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： https://doi.org/10.1029/2023JA031600

DOI： https://doi.org/10.1029/2023JA031600

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： https://doi.org/10.1016/j.asr.2023.12.026

DOI： https://doi.org/10.1016/j.asr.2023.12.026

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1186/s40623-023-01930-4

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1186/s40623-023-01914-4

Web of Science

その他リンク： https://link.springer.com/article/10.1186/s40623-023-01914-4/fulltext.html

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： https://doi.org/10.1029/2022JA030769

DOI： https://doi.org/10.1029/2022JA030769

その他リンク： https://doi.org/10.1029/2022JA030769

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2023JA031479

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Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1038/s41598-023-33603-3

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Scopus

PubMed

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1186/s40623-023-01788-6

Web of Science

その他リンク： https://link.springer.com/article/10.1186/s40623-023-01788-6/fulltext.html

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2022JA030542

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Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2021JA029987

Web of Science

その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2021JA029987

掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2021JA030240

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1186/s40623-022-01616-3

Web of Science

掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2020JA028791

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2021JA029813

Web of Science

Scopus

掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2021GL095090

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Scopus

掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2020JA029086

Web of Science

その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2020JA029086

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1186/s40645-021-00441-8

Web of Science

その他リンク： https://link.springer.com/article/10.1186/s40645-021-00441-8/fulltext.html

掲載種別：研究論文（学術雑誌）  

DOI： 10.1186/s40623-021-01376-6

Web of Science

その他リンク： https://link.springer.com/article/10.1186/s40623-021-01376-6/fulltext.html

掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2020JA029081

Web of Science

その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2020JA029081

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.5194/acp-21-2343-2021

Web of Science

記述言語：日本語  

DOI： 10.1186/s40623-021-01369-5

Web of Science

掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2020JA028724

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Scopus

記述言語：日本語  

DOI： 10.1186/s40623-020-01353-5

Web of Science

DOI： 10.1007/s10712-020-09613-5

Web of Science

掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2020JA028068

Web of Science

その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2020JA028068

掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2020GL087256

Web of Science

Scopus

記述言語：日本語  

DOI： 10.1186/s40623-020-01228-9

Web of Science

掲載種別：研究論文（学術雑誌）  

DOI： 10.1186/s40623-020-01187-1

Web of Science

Scopus

記述言語：日本語  

DOI： 10.15625/0866-7187/42/4/15281

Web of Science

記述言語：日本語  

DOI： 10.1063/5.0002321

Web of Science

DOI： 10.3847/1538-4357/ab5113

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2019JA027065

Web of Science

掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2019JA026839

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2019JA026783

Web of Science

記述言語：日本語  

DOI： 10.1016/j.jastp.2019.05.015

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1186/s40623-019-1072-0

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/ab1b52

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2019SW002168

Web of Science

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

DOI： 10.23919/URSIAP-RASC.2019.8738444

Web of Science

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.asr.2018.03.024

Web of Science

記述言語：日本語  

DOI： 10.1017/S0373463318000929

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2018JA026443

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2018JA025634

Web of Science

掲載種別：研究論文（学術雑誌）  

DOI： 10.1038/s41467-018-07996-z

Web of Science

Scopus

PubMed

DOI： 10.1109/JSTARS.2018.2877445

掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2018GL080262

Web of Science

その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2018GL080262

掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2018GL079812

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2018GL079615

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1186/s40645-018-0212-7

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2018JA025438

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2018JA025871

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2018GL078723

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2018JA025261

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2018JA025585

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2018JA025491

Web of Science

DOI： 10.1103/PhysRevB.98.035126

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1186/s40645-018-0189-2

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.20965/jdr.2018.p0535

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1186/s40645-018-0184-7

Web of Science

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Institute of Electrical and Electronics Engineers Inc.  

The study and understanding of the intermittent characteristics of equatorial and low latitude ionosphere is crucial for modelling and forecasting the ionosphere and space weather conditions. The performance of space-based navigation systems such as Global Positioning System (GPS) is affected by the sporadic temporal and spatial variations of ionospheric Total Electron Content (TEC). The variability of ionospheric electron density over Indian low latitude sector is difficult to model due to Equatorial Ionization Anomaly (EIA). In this paper, Multi-fractal aspects of the GPS measured TEC is investigated during both high and low solar activity periods of 24th solar cycle. The vertical TEC (VTEC) data sets are obtained from two Indian low latitude stations namely, Bangalore (Geographical Latitude: 13.020 N, Geographical Longitude: 77.57o E), and Lucknow (Geographical Latitude: 26.830 N, Geographical Longitude: 80.92o E) for two year long period 2013 and 2015. The experimental results shows that the respective geographic sites have important scaling differences as well as similarities when their Multi-fractal signatures for VTEC are compared. These differences and similarities are interpreted in terms of the EIA conditions, where this phenomenon is an important source of intermittence due to the presence of the VTEC peaks at ±300 geomagnetic latitudes. During the high solar activity period, the intermittence characteristics of VTEC over EIA region (Lucknow) are relatively more complex than equatorial (Bengaluru) station, whereas during low solar activity period the scenario is reciprocal.

DOI： 10.1109/SPACES.2018.8316326

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1186/s40645-018-0175-8

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/2017JA025021

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1186/s40645-018-0172-y

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/2017GL076486

Web of Science

Scopus

Web of Science

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/2017JA024602

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/2017GL074678

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1186/s40623-017-0745-9

Web of Science

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Institute of Electrical and Electronics Engineers Inc.  

We investigated a post-midnight Field-Aligned Irregularities (FAIs) event observed with the Equatorial Atmosphere Radar (EAR) at Kototabang (0.2°S, 100.3°E, dip lat. 10.4°S) in Indonesia on the night of 9 July 2010, using a comprehensive dataset of both neutral and plasma parameters. We compared FAI echoes collocated with 630 nm airglow depletion detected by an all-sky imager. The thermospheric neutral winds and temperatures obtained by a Fabry-Perot interferometer at Kototabang and the altitudes of F-layer (h'F) observed with ionosondes at Kototabang, Chiang Mai, and Chumphon were also examined. We found that the 3-m scale post-midnight FAIs occurred within plasma bubbles. The convergence of the equatorward neutral winds happened in this particular event related to midnight temperature maximum (MTM) and that the equatorward winds in both northern and southern hemispheres could be responsible for the growth of plasma bubbles around midnight. The uplift of F-layer at low latitudes could increase the growth rate of the Rayleigh-Taylor instability. Eastward electric currents driven by the equatorward winds could also contribute to the generation of the irregularities at post-midnight.

DOI： 10.23919/URSIGASS.2017.8105106

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1186/s40623-017-0729-9

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/2017JA024342

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1186/s40623-017-0698-z

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/2017JA024589

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/2017JA023919

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/2017JA024146

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We analyzed the horizontal phase velocity of gravity waves and medium-scale traveling ionospheric disturbances (MSTIDs) by using the three-dimensional fast Fourier transform method developed by Matsuda et al. (2014) for 557.7 nm (altitude: 90–100 km) and 630.0 nm (altitude: 200–300 km) airglow images obtained at Shigaraki MU Observatory (34.8°N, 136.1°E, dip angle: 49°) over ∼16 years from 16 March 1999 to 20 February 2015. The analysis of 557.7 nm airglow images shows clear seasonal variation of the propagation direction of gravity waves in the mesopause region. In spring, summer, fall, and winter, the peak directions are northeastward, northeastward, northwestward, and southwestward, respectively. The difference in east-west propagation direction between summer and winter is probably caused by the wind filtering effect due to the zonal mesospheric jet. Comparison with tropospheric reanalysis data shows that the difference in north-south propagation direction between summer and winter is caused by differences in the latitudinal location of wave sources due to convective activity in the troposphere relative to Shigaraki. The analysis of 630.0 nm airglow images shows that t

DOI： 10.0002/2017JA023919

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/2017JA024048

Web of Science

記述言語：マレー語   掲載種別：研究論文（学術雑誌）  

DOI： 10.17576/jsm-2017-4606-06

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1186/s40623-017-0643-1

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/2016JA023417

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/2016JA023202

Web of Science

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.icarus.2016.08.004

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/2016GL071511

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/2016SW001474

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/2016JA023024

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/2016GL070008

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/2016GL068145

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/2015GL067432

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/2015JA021681

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/2015JA021932

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.jastp.2015.10.005

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/2015JA021381

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/2015JA021424

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/2015RS005672

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.jastp.2015.06.003

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/2015JA021000

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/2015JA021427

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1186/s40623-015-0246-7

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1186/s40623-015-0202-6

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/2014JA020398

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/2014JA020878

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：COPERNICUS GESELLSCHAFT MBH  

Ionospheric blobs are localized plasma density enhancements, which are mainly produced by the transportation process of plasma. To understand the deformation process of a blob, observations of plasma parameters with good spatial-temporal resolution are desirable. Thus, we conducted the European Incoherent Scatter radar observations with high-speed meridional scans (60-80 s) during October and December 2013, and observed the temporal evolution of a blob during a substorm on 4 December 2013. This paper is the first report of direct observations of blob deformation during a substorm. The blob deformation arose from an enhanced plasma flow shear during the substorm expansion phase, and then the blob split into two smaller-scale blobs, whose scale sizes were more than similar to 100 km in latitude. Our analysis indicates that the Kelvin-Helmholtz instability and dissociative recombination could have deformed the blob structure.

DOI： 10.5194/angeocom-33-525-2015

Web of Science

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

Malaysia Real-Time Kinematics GNSS Network (MyRTKnet) which consists of 78 GPS receivers was used to investigate the occurrence of equatorial plasma bubble (EPB) along 96 degrees E - 120 degrees E longitude. In this study, we present the monthly occurrence rate of EPB along the geographical longitudes of 96 degrees E - 120 degrees E for a half of solar cycle period (2008 - 2013). A 2D map of rate of TEC change index (ROTI) projected at 300 km altitude was derived from the signal paths between GPS satellites and the receivers. A ROTI keogram for one day period was obtained from the east-west cross section of the 2D ROTI maps at 4 degrees N for every 5 min. The occurrence day of EPB was determined from the keogram by the existence of ROTI larger than 0.1 TECU/min within the 96 degrees E - 120 degrees E longitude. The results show that the occurrence of EPB along the 96 degrees E - 120 degrees E has maximum during equinoctial months and is consistent with previous studies. The occurrence rate of EPB during equinoctial months shows similar characteristics in low and high solar activity due to the broad observational coverage of the MyRTKnet. In contrast, the occurrence rate of EPB during solstice months shows significant relation with solar activity. Solstice months recorded high occurrence rate of EPB in high solar activity that might be attributed to post-midnight irregularities.

DOI： 10.1109/IconSpace.2015.7283752

Web of Science

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：INST NAVIGATION  

GAST-D ground prototype and and GAST-D airborne experimental subsystem have been developed. The GAST-D ground prototype was installed at New Ishigaki Airport located in the low magnetic latitude region. With the ground prototype and the airborne experimental system, GAST-D flight experiments in the low magnetic latitude region under ionospheric quiet and disturbed conditions for the first time in the world.
Two flight campaigns were conducted in March and September 2014. In the campaign carried out in September 2014, the vertical error performances were comparable between ionospheric quiet and disturbed condition. However, availability degradation during the severely disturbed condition is an issue. The DSIGMA monitor which is one of the airborne integrity monitors was confirmed by all-sky airglow measurements to react ionospheric disturbance.
The next steps of the study include parameter tuning of the ground prototype and airborne experimental system to enhance service availability during ionospheric disturbed conditions.

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1186/s40623-014-0155-1

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/2014JA020151

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/2014JA020433

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/2014JA020368

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/2014GL061403

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/2014JA020050

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.asr.2014.01.032

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

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  

In this paper, we analyze vertical ExB drifts obtained from the Doppler shifts of the daytime 150km radar echoes from two radar stations located off the magnetic equator, namely, Gadanki in India and Kototabang in Indonesia, and compare those with corresponding Coupled Ion Neutral Dynamics Investigation (CINDI) observations onboard the C/NOFS satellite and the Scherliess-Fejer model in an effort to understand to what extent the low-latitude vertical ExB drifts of the 150km region represent the F region vertical ExB drifts. The radar observations were made during 9-16 LT in January, June, July, and December 2009. A detailed comparison reveals that vertical ExB drifts observed by the radars at both locations agree well with those of CINDI and differ remarkably from those of the model. Importantly, the model and observed drifts show large disagreement when the observed drifts are either large or downward. Further, while the CINDI as well as the radar observations from the two longitudes are found to agree with each other on the average, they differ remarkably on several occasions when compared on a one-to-one basis. The observed difference in detail is due to measurements made in different volumes linked with latitudinal and/or longitudinal differences and underlines the role of neutral dynamics linked with tides and gravity waves in the two longitude sectors on the respective vertical ExB drifts. The results presented here are the first of their kind and are expected to have wider applications in furthering our understanding on fine-scale longitudinal variabilities in the ionosphere in general and ionospheric electrodynamics in the Indian and Indonesian sectors in particular.

DOI： 10.1002/2013JA019732

Web of Science

記述言語：英語  

DOI： 10.1002/2013GL058748

Web of Science

担当区分：筆頭著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

In this study, the two-dimensional horizontal structure of EPB was observed using GPS total electron content (TEC) measurement in South East Asia region. Rate of TEC index (ROTI) is calculated from GPS TEC measurement and plotted onto two-dimensional map in geographic coordinate. Depletion of The OI 630.0 nm emission is completely coincided with ROTI enhancement region from GPS TEC measurement. Therefore, the observation using GPS TEC measurement is able to provide spatial and temporal properties of EPB in SEA region.

Web of Science

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

Malaysia is located at equatorial region, which is from 3 degrees to 8 degrees South of the magnetic equator where equatorial plasma bubbles (EPBs) frequently occur. EPBs could disrupt radio communication and navigational systems in this region. We present the two-dimensional structure of EPBs observed using GPS networks over South East Asia (SEA) near the equatorial region. 59 days with EPB structure were observed using GPS networks in 2011. The results show that; 1) the initial EPBs onset time occurs mostly after post-sunset between 1900 to 2100 local time (LT); 2) the duration of the occurrences of EPB is mostly from 3 to 6 hours; 3) the GPS networks in SEA region are able to observe east-west size of EPBs from 50 km to 650 km with accuracy +/-50 km.

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Blackwell Publishing Ltd  

In this paper, we analyze vertical ExB drifts obtained from the Doppler shifts of the daytime 150 km radar echoes from two radar stations located off the magnetic equator, namely, Gadanki in India and Kototabang in Indonesia, and compare those with corresponding Coupled Ion Neutral Dynamics Investigation (CINDI) observations onboard the C/NOFS satellite and the Scherliess-Fejer model in an effort to understand to what extent the low-latitude vertical ExB drifts of the 150 km region represent the F region vertical ExB drifts. The radar observations were made during 9-16 LT in January, June, July, and December 2009. A detailed comparison reveals that vertical ExB drifts observed by the radars at both locations agree well with those of CINDI and differ remarkably from those of the model. Importantly, the model and observed drifts show large disagreement when the observed drifts are either large or downward. Further, while the CINDI as well as the radar observations from the two longitudes are found to agree with each other on the average, they differ remarkably on several occasions when compared on a one-to-one basis. The observed difference in detail is due to measurements made in different volumes linked with latitudinal and/or longitudinal differences and underlines the role of neutral dynamics linked with tides and gravity waves in the two longitude sectors on the respective vertical ExB drifts. The results presented here are the first of their kind and are expected to have wider applications in furthering our understanding on fine-scale longitudinal variabilities in the ionosphere in general and ionospheric electrodynamics in the Indian and Indonesian sectors in particular. Key Points First comparison of 150 km echo and C/NOFS ExB drifts over India and Indonesia These observations agree at both locations and show some longitudinal difference Radar and C/NOFS observations differ remarkably from model ©2014. American Geophysical Union. All Rights Reserved.

DOI： 10.1002/2013JA019732

Scopus

記述言語：日本語   掲載種別：研究論文（その他学術会議資料等）  

記述言語：日本語   掲載種別：研究論文（その他学術会議資料等）  

担当区分：筆頭著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We present the first reported gravity wave patterns in the mesopause region caused by a typhoon in the troposphere. On 10 December 2002, concentric rings of gravity waves in OH airglow were observed simultaneously by all-sky imagers in the Optical Mesosphere and Thermosphere Imager system in Japan, located at Rikubetsu (43.5°N, 143.8°E), Shigaraki (34.9°N, 136.1°E), and Sata (31.0°N, 130.7°E). The airglow structures, which were well defined and formed a coherent wave pattern expanding concentrically, were identified over 8 h (2135-2947 LT). We estimate the horizontal wavelength, horizontal phase speed, and wave period as 34.5 km, 50.2 m s-1, and 11.5 min, respectively. Infrared cloud images from the Geostationary Meteorological Satellite show that the center of the rings estimated from the airglow data corresponds to a spiral band of Typhoon Pongsona (T0226). This unique event provides new insight into coupling between the lower and upper atmosphere. ©2013. American Geophysical Union. All Rights Reserved.

DOI： 10.1002/2013GL058087

Scopus

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  

We present the first reported gravity wave patterns in the mesopause region caused by a typhoon in the troposphere. On 10 December 2002, concentric rings of gravity waves in OH airglow were observed simultaneously by all-sky imagers in the Optical Mesosphere and Thermosphere Imager system in Japan, located at Rikubetsu (43.5 degrees N, 143.8 degrees E), Shigaraki (34.9 degrees N, 136.1 degrees E), and Sata (31.0 degrees N, 130.7 degrees E). The airglow structures, which were well defined and formed a coherent wave pattern expanding concentrically, were identified over 8 h (2135-2947 LT). We estimate the horizontal wavelength, horizontal phase speed, and wave period as 34.5 km, 50.2 m s(-1), and 11.5 min, respectively. Infrared cloud images from the Geostationary Meteorological Satellite show that the center of the rings estimated from the airglow data corresponds to a spiral band of Typhoon Pongsona (T0226). This unique event provides new insight into coupling between the lower and upper atmosphere.

DOI： 10.1002/2013GL058087

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/2013GL057627

Web of Science

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  

The development of equatorial plasma irregularity plumes can be well recorded by steerable backscatter radars operated at and off the magnetic equator due to the fact that the vertically extended plume structures are tracers of magnetically north-south aligned larger scale structures. From observations during March 2012, using two low latitude steerable backscatter radars in Southeast Asia, the Equatorial Atmosphere Radar (EAR) (0.2 degrees S, 100.3 degrees E; dip lat 10.4 degrees S) and the Sanya VHF radar (18.4 degrees N, 109.6 degrees E; dip lat 12.8 degrees N), the characteristics of backscatter plumes over the two sites separated in longitude by similar to 1000 km were simultaneously investigated. The beam steering measurements reveal frequent occurrences of multiple plumes over both radar sites, of which two cases are analyzed here. The observations on 30 March 2012 show plume structures initiated within the radar scanned area, followed by others drifting from the west of the radar beam over both stations. A tracing analysis on the onset locations of plasma plumes reveals spatially well-separated backscatter plumes, with a maximum east-west wavelength of about 1000 km, periodically generated in longitudes between 85 degrees E and 110 degrees E. The postsunset backscatter plumes seen by the Sanya VHF radar are found to be due to the passage of sunset plumes initiated around the longitude of EAR. Most interestingly, the EAR measurements on the night of 21 March 2012 show multiple plume structures that developed successively in the radar scanned area with east-west separation of similar to 50 km, with however no sunset plasma plume over Sanya. Colocated ionogram measurements show that spread F irregularities occurred mainly in the bottomside F region at Sanya, whereas satellite traces in ionograms that are indications of large-scale wave structures were observed on that night at both stations. Possible causes for the longitudinal difference in the characteristics of radar backscatter plumes are discussed.

DOI： 10.1002/jgra.50581

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.jastp.2013.03.024

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.jastp.2013.03.020

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/jgra.50275

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2012GL054605

Web of Science

Scopus

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

Two-dimensional structures of medium-scale traveling ionospheric disturbances (MSTIDs) over Europe have been revealed, for the first time, by using maps of the total electron content (TEC) obtained from more than 800 GPS receivers of the European GPS receiver networks. From statistical analysis of the TEC maps obtained 2008, we have found that the observed MSTIDs can be categorized into two groups: daytime MSTID and nighttime MSTID. The daytime MSTID frequently occurs in winter. Its maximum occurrence rate in monthly and hourly bin exceeds 70% at lower latitudes over Europe, whereas it is approximately 45% at higher latitudes. Since most of the daytime MSTIDs propagate southward, we speculate that they could be caused by atmospheric gravity waves in the thermosphere. The nighttime MSTIDs also frequently occur in winter but most of them propagate southwestward, in a direction consistent with the theory that polarization electric fields play an important role in generating the nighttime MSTIDs. The nighttime MSTID occurrence rate shows distinct latitudinal difference: The maximum of the occurrence rate in monthly and hourly bin is approximately 50% at lower latitudes in Europe, whereas the nighttime MSTID was rarely observed at higher latitudes. We have performed model calculations of the plasma density perturbations caused by a gravity wave and an oscillating electric field to reproduce the daytime and nighttime MSTIDs, respectively. We find that TEC perturbations caused by gravity waves do not show dip angle dependencies, while those caused by the oscillating electric field have a larger amplitude at lower latitudes. These dip angle dependencies of the TEC perturbation amplitude could contribute to the latitudinal variation of the MSTID occurrence rate. Comparing with previous studies, we discuss the longitudinal difference of the nighttime MSTID occurrence rate, along with the E- and F-region coupling processes. The seasonal variation, of the nighttime MSTID occurrence rate in Europe, is not consistent with the theory that the longitudinal and seasonal variations of the nighttime MSTID occurrence could be attributed to those of the Es layer occurrence.

DOI： doi:10.5194/angeo-31-163-2013

DOI： 10.15094/00009711

Scopus

J-GLOBAL

その他リンク： http://orcid.org/0000-0001-8392-6455

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.5194/angeo-31-163-2013

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Blackwell Publishing Ltd  

The development of equatorial plasma irregularity plumes can be well recorded by steerable backscatter radars operated at and off the magnetic equator due to the fact that the vertically extended plume structures are tracers of magnetically north-south aligned larger scale structures. From observations during March 2012, using two low latitude steerable backscatter radars in Southeast Asia, the Equatorial Atmosphere Radar (EAR) (0.2°S, 100.3°E
dip lat 10.4°S) and the Sanya VHF radar (18.4°N, 109.6°E
dip lat 12.8°N), the characteristics of backscatter plumes over the two sites separated in longitude by ~1000 km were simultaneously investigated. The beam steering measurements reveal frequent occurrences of multiple plumes over both radar sites, of which two cases are analyzed here. The observations on 30 March 2012 show plume structures initiated within the radar scanned area, followed by others drifting from the west of the radar beam over both stations. A tracing analysis on the onset locations of plasma plumes reveals spatially well-separated backscatter plumes, with a maximum east-west wavelength of about 1000 km, periodically generated in longitudes between 85°E and 110°E. The postsunset backscatter plumes seen by the Sanya VHF radar are found to be due to the passage of sunset plumes initiated around the longitude of EAR. Most interestingly, the EAR measurements on the night of 21 March 2012 show multiple plume structures that developed successively in the radar scanned area with east-west separation of ~50 km, with however no sunset plasma plume over Sanya. Colocated ionogram measurements show that spread F irregularities occurred mainly in the bottomside F region at Sanya, whereas satellite traces in ionograms that are indications of large-scale wave structures were observed on that night at both stations. Possible causes for the longitudinal difference in the characteristics of radar backscatter plumes are discussed. Key Points Simultaneous measurements of ESF plumes by two closely located radars Sunset plume onset and post-sunset periodic plumes are detected by both radars Smaller scale longitudinal differences in the plume occurrence are presented ©2013. American Geophysical Union. All Rights Reserved.

DOI： 10.1002/jgra.50581

Scopus

記述言語：日本語   掲載種別：研究論文（その他学術会議資料等）  

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：INST NAVIGATION  

For differential GNSS systems such as the ground-based augmentation system (GBAS), spatial variation (or spatial gradient) in ionospheric delay is a critical issue.
In the low latitude region, the dominant ionospheric disturbance is the plasma bubble. Plasma bubbles are local ionospheric depletions that often occur after sunset. They accompany ionospheric irregularities with various scale sizes from 100 km down to a meter. However, the characteristics of the low latitude ionospheric variations in teens of a specific threat to GBAS have not been well studied yet.
This paper studies the spatial relationship between the ionospheric delay gradients and the large-scale plasma bubble structure. The ionospheric delay gradients are measured with spaced receivers at Ishigaki, Japan. Large-scale plasma bubble structures are measured with an all-sky airglow images observed at Yonaguni, Japan.
The ionospheric delay gradients are shown to have large values at the edges of plasma bubbles, and theeir directions are consistent with the direction of the electron density gradient inferred from the airglow images as well as the expectation that the gradient.
In some cases, however, the ionospheric delay gradients have large values had large values at locations other than the plasma bubble edges. The absolute ionospheric delay with dual-frequency measurements and the drift velocity will be analyzed to investigate the scale size and the amplitude of the irregularities that cause the ionospheric delay gradients. Co-site observations of the ionospheric delay gradient and the airglow at Ishigaki to have nearly common line of sights for both the measurements.

Web of Science

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  

In this paper, we study for the first time the daytime vertical E x B drift velocities from Gadanki and Kototabang using the Doppler shifts of the 150-km echoes observed during 2008-2010, a period of low solar activity. Drift velocities are mostly positive and confined to 35 m s(-1) at both the locations, except for Gadanki where on a few occasions negative drift velocities have been observed in the afternoon hours. Drift velocities generally show a decreasing trend with local time and the largest drift is generally observed in the forenoon hours consistent with extensively reported observations and models of E x B drift. Drift velocities from Gadanki and Kototabang compared exceeding well on some days and differed remarkably on many days despite the fact that they are longitudinally separated by only 20 degrees. The day-to-day variation in the drift velocity could be as high as 15 m s(-1) at Gadanki and 7 m s(-1) at Kototabang. Seasonal mean drifts over Gadanki are found to be generally larger than those of Kototabang. The observations have been compared in detail with those reported earlier based on ground- and satellite- based observations and also with the Scherliess-Fejer model. The observed differences in the drifts at the two locations, including the downward drifts, have been discussed in the light of current understanding of the longitudinal variability of E x B drift.

DOI： 10.1029/2012JA018053

Web of Science

DOI： 10.1029/2012JA017928

DOI： 10.1029/2012JA017928

Web of Science

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  

We report on nighttime medium- scale traveling ionospheric disturbances (MSTIDs) observed at Kototabang, Indonesia (geographic longitude: 100.3 degrees E; geographic latitude: 0.2 degrees S; and geomagnetic latitude: 10.6 degrees S) during a 7-year period from October 2002 to October 2009. MSTIDs were observed in 630-nm nighttime airglow images by using a highly sensitive all-sky airglow imager at Kototabang. The averages and standard deviations of horizontal phase velocity, period, and horizontal wavelength of MSTIDs observed during the 7 years were 320 +/- 170 m/s, 42 +/- 11 min, and 790 +/- 440 km, respectively. The occurrence rate of the observed MSTIDs decreased with decreasing solar activity. The average horizontal wavelength of MSTIDs increased with decreasing solar activity. Southward MSTIDs were dominant throughout the 7 years of observations. These facts are consistent with the hypothesis that the observed MSTIDs are caused by gravity waves in the thermosphere. Moreover, we compared the propagation directions of the observed MSTIDs with the locations of tropospheric convection activity for the events where gravity waves producing the observed MSTIDs could have existed in the lower atmosphere. Strong tropospheric convection was found within +/- 30 degrees from the source directions of MSTIDs in 81% of the MSTID events. In such events, gravity waves were possibly generated from deep convection in the troposphere and directly propagated into the thermosphere.

DOI： 10.1029/2012JA017758

Web of Science

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  

We investigated the relationship between post-midnight F-region field aligned irregularities (FAIs) and F-layer altitude by analyzing data of a 30.8-MHz radar installed 5at Kototabang, Indonesia (0.2 degrees S, 100.3 degrees E; geomagnetic latitude 10.4 degrees S) and an ionosonde installed at Chumphon, Thailand (10.7 degrees N, 99.4 degrees E; geomagnetic latitude 3.3 degrees N). Chumphon is located near the geomagnetic equator on approximately the same meridian as Kototabang. Case studies show that the altitude of the F-layer rose at Chumphon a half hour before the post-midnight FAIs appeared at Kototabang. The Doppler velocity of the E-region FAIs observed simultaneously by the 30.8-MHz radar was downward, indicating that the F-layer uplift was not caused by the electric field. We also investigated seasonal variations of the post-midnight FAI occurrence and the F-layer altitude. Both the post-midnight FAIs and the uplift of the F-layer were frequently seen around midnight between May and August. The seasonal variation of the midnight F-layer uplift around the geomagnetic equator coincided with that of the post-midnight FAI occurrence at Kototabang. These results suggest that the uplift of the F-layer would play an important role in the generation of post-midnight FAIs. We evaluated the linear growth rate of the Rayleigh-Taylor instability based on the altitude of the F-layer observed at Chumphon. The result shows that the uplift of the F-layer can enhance the growth rate because gravity-driven eastward electric current increases. Therefore, we interpret that the observed FAIs were accompanied by plasma bubble, the growth rate of which was reinforced by the uplifted F-layer.

DOI： 10.1029/2012JA017692

Web of Science

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  

The paper presents the medium-term quasi periodic (similar to 9-27 day) response of middle and low-latitude ionosphere to solar [F10.7) and geomagnetic (Kp-index) forcing. The ionospheric response is examined by wavelet analysis of the relative deviations of TEC over Japan for the period of time 2000-2008. It is found that the similar to 27-day rTEC oscillations correlate well with the same oscillations of the solar index F10.7 particularly in the solar maximum and its early declining phase (2001-2005). During the declining phase of solar activity (for example, year of 2005) the Kp-index variability exhibits additionally strong oscillations with periods 13.5- and 9-days. Similar oscillations are found in rTEC as well but they do not follow the geomagnetic forcing as faithfully as those associated with F10.7. During solar minimum the quasi periodic rTEC variability is shaped mainly by the recurrent geomagnetic activity. An attempt is made to investigate the latitudinal dependence of the similar to 9-27-day rTEC response over Japan as well as the phase relationship between the forcing and response.

DOI： 10.1029/2012JA017641

Web of Science

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： doi:10.1029/2012GL052286

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2012GL052286

Web of Science

記述言語：英語  

DOI： 10.1007/s11214-011-9816-6

Web of Science

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  

GPS total electron content (TEC) has shown quasiperiodic oscillations of varying amplitude associated with poleward moving Sun-aligned arcs. The amplitude of TEC variations showed a maximum of similar to 3 TECU and seemed to decrease as the arcs moved poleward from the source/generation region. Simultaneous DMSP data showed that fluctuations in TEC and optical intensification were caused by precipitation of high-energy (>500 eV) particles. Concurrent ionosonde observations also exhibited quasiperiodic variations (within limit of the resolution of the data) in peak ionospheric electron density of the ionosphere. Bottom height of the ionospheric layers produced by precipitating particles varied between 130 km (upper E region) and 300 km (F region), indicating variable particle precipitation energy. Frequency analysis of high-resolution TEC data showed a broad range of discrete frequency components from 1.60 mHz to 22.80 mHz present in the TEC oscillations, which may provide insight into the energization/modulation of precipitating particles by these oscillations. A broad distribution of equivalent vertical thickness of arcs was calculated using GPS TEC and ionosonde measurements of peak electron density. This distribution showed a minimum thickness of 21 km, a maximum of 84 km, and an average of 49 km. The equivalent vertical thickness also showed a linear relationship with bottomside height of the ionospheric layer (auroral arc). The relationship showed an increase in the vertical thickness with an increase in bottomside height of the layer. This relationship is a consequence of variations in the energy of the precipitating particles causing different ionospheric production profiles.

DOI： 10.1029/2011JA017423

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： doi:10.1155/2012/695793

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  

We have investigated the polarization of Pc1 geomagnetic pulsations and related proton auroras at subauroral latitudes, using an induction magnetometer and an all-sky camera at Athabasca, Canada (54.7 degrees N, 246.7 degrees E, magnetic latitude (mlat) 61.7 degrees N). Isolated proton auroras often appear in association with Pc1 pulsations, because of proton scattering by electromagnetic ion cyclotron (EMIC) waves in the magnetosphere. We used the proton aurora as a proxy for the location and size of the Pc1 ionospheric source. For 27 Pc1 events with simultaneously observed proton auroras over 4 years from September 7, 2005 to September 6, 2009, we calculated the distances between the Pc1 ionospheric source and the observation site, normalized by the scale size of the source. We tried three different definitions of the scale size of Pc1 ionospheric source to calculate the normalized distances. We found that the rotation angle theta between the Pc1 polarization ellipse and the direction to the proton aurora changes from 90 degrees to 0 degrees as the normalized distance increases. For the definition of the scale sizes that gives most clear theta-transition from 90 degrees to 0 degrees, the transition occurs at the normalized distance similar to 2.0-4.0, while it was similar to 1.0-2.0 by the model calculation of Fujita and Tamao (1988). The averaged major axes tend to point toward the proton aurora at larger distances. The difference of the transition location may imply that the Pc1 ionospheric sources are larger than the isolated proton auroras, or that the inhomogenuity of the ionospheric conductivity by the proton precipitation affects the transition distances.

DOI： 10.1029/2011JA017241

Web of Science

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  

Analysis of the dayside electron density (Ne) and neutral mass density (N) at 400 km height measured by CHAMP during 12 intense geomagnetic storms in 2000-2004, and ion densities at 600 km and 840 km heights measured by ROCSAT and DMSP during a few of the intense storms, reveal some new aspects. Thermospheric storms (change of N) reach the equator within 1.5 to 3 hours from the main phase (MP) onset of intense storms having short and steady MPs. The responses of the equatorial ionosphere (at CHAMP) to both MPs and RPs (recovery phases) of the storms are generally opposite to those at higher latitudes. In addition to the known opposite responses during MPs, the analysis reveals that positive ionospheric storms develop at equatorial latitudes (within about +/- 15 degrees magnetic latitudes) during daytime RPs, while conventional negative storms occur at higher latitudes. Ionospheric storms also extend to the topside ionosphere beyond 850 km height and are generally positive (at DMSP), especially during MPs. The positive storms around the equatorial ionospheric peak during RPs are interpreted in terms of the potential sources such as (1) zero or westward electric fields due to disturbance dynamo and/or prompt penetration, (2) plasma convergence due to the mechanical effects of storm-time equatorward neutral winds and waves, (3) increase of atomic oxygen density and decrease of molecular nitrogen density due to the downwelling effect of the winds, and (4) photoionization. The positive storms in the topside ionosphere during MPs involve the rapid upward drift of plasma due to eastward PPEFs, reduction in the downward diffusion of plasma along the field lines, and plasma convergence due to equatorward winds and waves.

DOI： 10.1029/2011JA016903

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

In this paper, we study for the first time the daytime vertical E × B drift velocities from Gadanki and Kototabang using the Doppler shifts of the 150-km echoes observed during 2008-2010, a period of low solar activity. Drift velocities are mostly positive and confined to 35 m s-1 at both the locations, except for Gadanki where on a few occasions negative drift velocities have been observed in the afternoon hours. Drift velocities generally show a decreasing trend with local time and the largest drift is generally observed in the forenoon hours consistent with extensively reported observations and models of E × B drift. Drift velocities from Gadanki and Kototabang compared exceeding well on some days and differed remarkably on many days despite the fact that they are longitudinally separated by only 20. The day-to-day variation in the drift velocity could be as high as 15 m s-1 at Gadanki and 7 m s-1 at Kototabang. Seasonal mean drifts over Gadanki are found to be generally larger than those of Kototabang. The observations have been compared in detail with those reported earlier based on ground-and satellite-based observations and also with the Scherliess-Fejer model. The observed differences in the drifts at the two locations, including the downward drifts, have been discussed in the light of current understanding of the longitudinal variability of E × B drift.

DOI： 10.1029/2012JA018053

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.5047/eps.2012.05.004

Web of Science

記述言語：英語  

J-GLOBAL

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Blackwell Publishing Ltd  

GPS total electron content (TEC) has shown quasiperiodic oscillations of varying amplitude associated with poleward moving Sun-aligned arcs. The amplitude of TEC variations showed a maximum of ∼3 TECU and seemed to decrease as the arcs moved poleward from the source/generation region. Simultaneous DMSP data showed that fluctuations in TEC and optical intensification were caused by precipitation of high-energy (&gt
500 eV) particles. Concurrent ionosonde observations also exhibited quasiperiodic variations (within limit of the resolution of the data) in peak ionospheric electron density of the ionosphere. Bottom height of the ionospheric layers produced by precipitating particles varied between 130km (upper E region) and 300km (F region), indicating variable particle precipitation energy. Frequency analysis of high-resolution TEC data showed a broad range of discrete frequency components from 1.60 mHz to 22.80 mHz present in the TEC oscillations, which may provide insight into the energization/modulation of precipitating particles by these oscillations. A broad distribution of equivalent vertical thickness of arcs was calculated using GPS TEC and ionosonde measurements of peak electron density. This distribution showed a minimum thickness of 21km, a maximum of 84km, and an average of 49km. The equivalent vertical thickness also showed a linear relationship with bottomside height of the ionospheric layer (auroral arc). The relationship showed an increase in the vertical thickness with an increase in bottomside height of the layer. This relationship is a consequence of variations in the energy of the precipitating particles causing different ionospheric production profiles. Copyright 2012 by the American Geophysical Union.

DOI： 10.1029/2011JA017423

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1155/2012/671240

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Blackwell Publishing Ltd  

Analysis of the dayside electron density (Ne) and neutral mass density (N) at 400km height measured by CHAMP during 12 intense geomagnetic storms in 2000-2004, and ion densities at 600km and 840km heights measured by ROCSAT and DMSP during a few of the intense storms, reveal some new aspects. Thermospheric storms (change of N) reach the equator within 1.5 to 3 hours from the main phase (MP) onset of intense storms having short and steady MPs. The responses of the equatorial ionosphere (at CHAMP) to both MPs and RPs (recovery phases) of the storms are generally opposite to those at higher latitudes. In addition to the known opposite responses during MPs, the analysis reveals that positive ionospheric storms develop at equatorial latitudes (within about ±15° magnetic latitudes) during daytime RPs, while conventional negative storms occur at higher latitudes. Ionospheric storms also extend to the topside ionosphere beyond 850km height and are generally positive (at DMSP), especially during MPs. The positive storms around the equatorial ionospheric peak during RPs are interpreted in terms of the potential sources such as (1) zero or westward electric fields due to disturbance dynamo and/or prompt penetration, (2) plasma convergence due to the mechanical effects of storm-time equatorward neutral winds and waves, (3) increase of atomic oxygen density and decrease of molecular nitrogen density due to the downwelling effect of the winds, and (4) photoionization. The positive storms in the topside ionosphere during MPs involve the rapid upward drift of plasma due to eastward PPEFs, reduction in the downward diffusion of plasma along the field lines, and plasma convergence due to equatorward winds and waves.

DOI： 10.1029/2011JA016903

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Blackwell Publishing Ltd  

We report for the first time the rapid oscillating motion of nighttime medium-scale traveling ionospheric disturbances (MSTIDs) based on airglow imaging observations at Troms (magnetic latitude: 67.1N), Norway on 8 December, 2009. The MSTIDs appeared in 630-nm airglow images at 1530 UT as wave-like structures south of Troms with a horizontal wavelength of ∼200km and a phase surface of north to south. They moved eastward with velocities of 30-60m/s. The velocity was faster in the poleward-side of the MSTIDs, forming a northeast-southwest phase surface at later times. This phase surface direction is opposite to that of midlatitude MSTIDs. The MSTIDs show sudden oscillations and phase jump in the east-west direction with a timescale of ∼10min at 1730 UT. The oscillations were associated with an auroral brightening observed at the poleward edge of the images and small magnetic field perturbations observed by ground magnetometers. The Doppler measurement of the 630-nm airglow by a Fabry-Perot interferometer at Troms showed a stable southeastward thermospheric wind with a velocity of ∼150m/s. These observations indicate that the MSTID oscillations were linked to auroral electric field in the ionosphere, implying that the observed MSTIDs are ionospheric plasma structures. We suggest that the observed MSTIDs were created by atmospheric gravity waves at the beginning, left as fossil plasma structures even after the gravity wave packet dissipated in the thermosphere, moved eastward according to the background electric field driven by the F-region dynamo, and oscillated associated with the auroral electric field. © 2012. American Geophysical Union. All Rights Reserved.

DOI： 10.1029/2012JA017928

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Blackwell Publishing Ltd  

We have investigated the polarization of Pc1 geomagnetic pulsations and related proton auroras at subauroral latitudes, using an induction magnetometer and an all-sky camera at Athabasca, Canada (54.7°N, 246.7°E, magnetic latitude (mlat) 61.7°N). Isolated proton auroras often appear in association with Pc1 pulsations, because of proton scattering by electromagnetic ion cyclotron (EMIC) waves in the magnetosphere. We used the proton aurora as a proxy for the location and size of the Pc1 ionospheric source. For 27 Pc1 events with simultaneously observed proton auroras over 4years from September 7, 2005 to September 6, 2009, we calculated the distances between the Pc1 ionospheric source and the observation site, normalized by the scale size of the source. We tried three different definitions of the scale size of Pc1 ionospheric source to calculate the normalized distances. We found that the rotation angle θ between the Pc1 polarization ellipse and the direction to the proton aurora changes from 90° to 0° as the normalized distance increases. For the definition of the scale sizes that gives most clear θ-transition from 90° to 0°, the transition occurs at the normalized distance ∼2.0-4.0, while it was ∼1.0-2.0 by the model calculation of Fujita and Tamao (1988). The averaged major axes tend to point toward the proton aurora at larger distances. The difference of the transition location may imply that the Pc1 ionospheric sources are larger than the isolated proton auroras, or that the inhomogenuity of the ionospheric conductivity by the proton precipitation affects the transition distances. Copyright 2012 by the American Geophysical Union.

DOI： 10.1029/2011JA017241

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Blackwell Publishing Ltd  

We investigated the relationship between post-midnight F-region field aligned irregularities (FAIs) and F-layer altitude by analyzing data of a 30.8-MHz radar installed 5at Kototabang, Indonesia (0.2S, 100.3E
geomagnetic latitude 10.4S) and an ionosonde installed at Chumphon, Thailand (10.7N, 99.4E
geomagnetic latitude 3.3N). Chumphon is located near the geomagnetic equator on approximately the same meridian as Kototabang. Case studies show that the altitude of the F-layer rose at Chumphon a half hour before the post-midnight FAIs appeared at Kototabang. The Doppler velocity of the E-region FAIs observed simultaneously by the 30.8-MHz radar was downward, indicating that the F-layer uplift was not caused by the electric field. We also investigated seasonal variations of the post-midnight FAI occurrence and the F-layer altitude. Both the post-midnight FAIs and the uplift of the F-layer were frequently seen around midnight between May and August. The seasonal variation of the midnight F-layer uplift around the geomagnetic equator coincided with that of the post-midnight FAI occurrence at Kototabang. These results suggest that the uplift of the F-layer would play an important role in the generation of post-midnight FAIs. We evaluated the linear growth rate of the Rayleigh-Taylor instability based on the altitude of the F-layer observed at Chumphon. The result shows that the uplift of the F-layer can enhance the growth rate because gravity-driven eastward electric current increases. Therefore, we interpret that the observed FAIs were accompanied by plasma bubble, the growth rate of which was reinforced by the uplifted F-layer. © 2012. American Geophysical Union. All Rights Reserved.

DOI： 10.1029/2012JA017692

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

[1] We report on nighttime medium-scale traveling ionospheric disturbances (MSTIDs) observed at Kototabang, Indonesia (geographic longitude: 100.3°E
geographic latitude: 0.2°S
and geomagnetic latitude: 10.6°S) during a 7-year period from October 2002 to October 2009. MSTIDs were observed in 630-nm nighttime airglow images by using a highly sensitive all-sky airglow imager at Kototabang. The averages and standard deviations of horizontal phase velocity, period, and horizontal wavelength of MSTIDs observed during the 7 years were 320 ±170 m/s, 42 ±11 min, and 790 ± 440 km, respectively. The occurrence rate of the observed MSTIDs decreased with decreasing solar activity. The average horizontal wavelength of MSTIDs increased with decreasing solar activity. Southward MSTIDs were dominant throughout the 7 years of observations. These facts are consistent with the hypothesis that the observed MSTIDs are caused by gravity waves in the thermosphere. Moreover, we compared the propagation directions of the observed MSTIDs with the locations of tropospheric convection activity for the events where gravity waves producing the observed MSTIDs could have existed in the lower atmosphere. Strong tropospheric convection was found within ±30 degrees from the source directions of MSTIDs in 81% of the MSTID events. In such events, gravity waves were possibly generated from deep convection in the troposphere and directly propagated into the thermosphere. © 2012. American Geophysical Union. All Rights Reserved.

DOI： 10.1029/2012JA017758

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Blackwell Publishing Ltd  

The paper presents the medium-term quasi periodic (∼9-27 day) response of middle and low-latitude ionosphere to solar [F10.7) and geomagnetic (Kp-index) forcing. The ionospheric response is examined by wavelet analysis of the relative deviations of TEC over Japan for the period of time 2000-2008. It is found that the ∼27-day rTEC oscillations correlate well with the same oscillations of the solar index F10.7 particularly in the solar maximum and its early declining phase (2001-2005). During the declining phase of solar activity (for example, year of 2005) the Kp-index variability exhibits additionally strong oscillations with periods 13.5- and 9-days. Similar oscillations are found in rTEC as well but they do not follow the geomagnetic forcing as faithfully as those associated with F10.7. During solar minimum the quasi periodic rTEC variability is shaped mainly by the recurrent geomagnetic activity. An attempt is made to investigate the latitudinal dependence of the ∼9-27-day rTEC response over Japan as well as the phase relationship between the forcing and response. © 2012. American Geophysical Union. All Rights Reserved.

DOI： 10.1029/2012JA017641

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A VHF backscatter radar with operating frequency 30.8 MHz has been operated at Kototabang (0.20°S, 100.32°E
dip latitude 10.36°S), Indonesia, since February 2006. We analyzed E-region field-aligned irregularities (FAIs) observed by this radar through a year of 2007 and found that the E-region FAI observed at Kototabang can be classified into two groups. One is "descending FAI". Altitude of the FAI echo region descends with time from 102 km to 88 km altitude during 0700-1000 and 1900-0000 LT in June solstice season. The other is "low-altitude FAI", which is observed in an altitude range from 88 to 94 km mainly during nighttime. The observed Doppler velocity show distinct local time and altitude dependence. The seasonally averaged zonal velocity above (below) approximately 94 km altitude is westward (eastward) during daytime and eastward (westward) during nighttime. Meridional/vertical velocity perpendicular to the geomagnetic fields is upward during daytime and downward during nighttime. The direction of the FAI velocity above approximately 94 km altitude is consistent with that of the background E × B plasma drifts reported previously. © 2012 Y. Otsuka.

DOI： 10.1155/2012/695793

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2011GL049856

Web of Science

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  

Using the 47 MHz Equatorial Atmosphere Radar (EAR) in West Sumatra, Indonesia (10.36 degrees S dip latitude), it is shown that postmidnight irregularities during solar minimum are morphologically different from those detected during solar maximum and are quite similar to those observed with the middle and upper atmosphere (MU) radar in midlatitudes (29.3 degrees N dip latitude). Utilizing the rapid beam-steering capability of the EAR, the spatial structure of the postmidnight irregularities is clearly presented for the first time. It is found that they usually propagate westward and can be categorized into two types. One shows sharp upwelling plumes near local midnight, which should not be a mere passage of fossil plasma bubbles. The other has successive tilted structures which have the same orientation as medium-scale traveling ionospheric disturbances typically observed at midlatitudes. We suggest that the convergence of the equatorward thermospheric wind which is believed to be responsible for the midnight temperature maximum may be an important factor to produce a preferable condition for the upwelling plumes in the postmidnight sector. The displacement between geographic and magnetic equators may also be important for seasonal/longitudinal variation of the postmidnight irregularities.

DOI： 10.1029/2011JA016797

Web of Science

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  

A detailed comparison between the observations of the Communication/Navigation Outage Forecasting System (C/NOFS) satellite and the 47 MHz Equatorial Atmosphere Radar (EAR) in West Sumatra, Indonesia (10.36 degrees S dip latitude) on the postmidnight irregularities is presented. The zonal and meridional E x B drift velocities measured by the vector electric field instrument on the C/NOFS are consistent with the westward propagation of backscatter echoes and the line-of-sight Doppler velocities observed with the EAR, respectively. The plasma density depletions are observed in the postmidnight sector for several consecutive orbits, which suggests the depletions grow slowly during the premidnight period and reach the spacecraft altitude around local midnight. The convergence of the equatorward wind which could be responsible for the midnight temperature maximum may produce a preferable condition for the growth of the Rayleigh-Taylor instability around midnight. Electric field fluctuations of medium-scale traveling ionospheric disturbances may play an important role in seeding the instability. Both equatorial and midlatitude-type plasma instabilities could be operational at the EAR latitude sector, which together would foster a high occurrence of postmidnight irregularities during solar minimum.

DOI： 10.1029/2011JA016798

Web of Science

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  

Using ground observations of total electron content (TEC) and equatorial electrojet (EEJ) in the Asian sector, along with plasma and neutral densities obtained from the CHAMP satellite, we investigate the ionospheric electrodynamics and neutral background in this longitude sector during the major stratospheric sudden warming (SSW) in January 2009. Our analysis reveals the following prominent features. First, the TEC response in tropical regions is strongly latitude dependent, with monotonic depletion at the dip equator but a semidiurnal perturbation at low latitudes. Second, the TEC semidiurnal perturbation possesses a significant hemispheric asymmetry in terms of onset date and magnitude. It starts on the same day as the SSW peak in the Northern Hemisphere but 2 days later in the Southern Hemisphere. Its magnitude is twice as strong in the north than in the south. Third, strong counter electrojet occurs in the afternoon, following the strengthening of the eastward EEJ in the morning. Fourth, semidiurnal perturbation in both TEC and EEJ possesses a phase shift, at a rate of about 0.7 h/day. Comparisons with results reported in the Peruvian sector reveal clear longitude dependence in the amplitude and hemispheric asymmetry of the semidiurnal perturbation. Finally, thermospheric density undergoes similar to 25% decrease at low latitudes in the afternoon local time sector during the SSW, indicating significant cooling effects in the tropical upper thermosphere.

DOI： 10.1029/2011JA016607

Web of Science

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  

The neutral mass density N and electron density Ne at 400 km height measured by CHAMP during nine intense geomagnetic storms bring out some new aspects of the thermospheric and ionospheric storms. The thermospheric storms (increase of N) develop with the onset of the main phases (MP) of the geomagnetic storms and reach their peak phases before or by the end of the MPs. The ionospheric storms (change of Ne) in general undergo an initial negative phase (with the equatorial ionization anomaly (EIA) crests shifting poleward) before turning positive, and the positive storms reach their peak strengths (or phases) centered at +/- 25 degrees-30 degrees magnetic latitudes; in some (4) cases the positive storms develop without an initial negative phase and with the EIA crests shifting equatorward; in all cases the positive storms reach their peak phases before the end of the MPs and turn to conventional negative storms by the end of the MPs. The observations agree with the different aspects of a physical mechanism of the positive storms. The observations also reveal that the Halloween storms of 30 October 2003 with a short MP without fluctuations produced the strongest positive ionospheric storms through impulsive response, and there is strong equinoctial asymmetry in the ionosphere and thermosphere during geomagnetic storms.

DOI： 10.1029/2010JA016399

Web of Science

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  

We report an event in which a polar cap patch was detected with an all-sky imager (ASI) at Resolute Bay, Canada (74.73 degrees N, 265.07 degrees E; AACGM latitude 82.9 degrees), on the nightside. The patch stopped its antisunward motion associated with a northward turning of interplanetary magnetic field and stayed within the field of view of the ASI for more than 1 h. When the patch stagnated, its luminosity decreased gradually, which allows us to investigate how the patch plasma decayed in a quantitative manner. The decay of the patch can be quantitatively explained by the loss through recombinations of O(+) with ambient N(2) and O(2) molecules, if we assume the altitude of the optical patch to be around 295 km. The derived altitude of the patch around 295 km is much higher than the nominal value at 235 km obtained from the MSIS-E90 and IRI-2007 models, indicating that climatological models such as IRI are not suitable for describing the actual density profile of patches. This is probably because the loss process was much faster in the lower-altitude part of the patch; thus, the peak altitude of the patch increased as it traveled across the polar cap because of rapid recombination at the bottomside of the F region. This suggests that we should employ higher emission altitude when we investigate optical patches transported deep into the nightside polar cap. Such information is important when we compare the optical data with other instruments such as coherent radars and GPS scintillation measurements by mapping the all-sky image on the geographic coordinate system with an assumption of the patch emission altitude.

DOI： 10.1029/2010JA016297

Web of Science

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  

The response of the dayside equatorial F-2 layer to the main phases of the 22 intense geomagnetic storms (Dst < -150 nT) in 1998-2008 is investigated using the digital ionosonde data from the equatorial stations in Brazilian, Indian, and Australian longitudes together with equatorial electrojet strength and IMF B-z; the storms include 15 superstorms (Dst < -200 nT). The observations show that there is a period during all MPs when the F-2 layer peak rises (and falls) rapidly with large peak electron density (Nmax) reduction, the rise velocity strongly correlates with the intensity (Dst) of the storms, and the duration of the Nmax reduction corresponds to that of strong eastward electrojet when IMF Bz remains highly negative. The observations indicate the occurrence of strong eastward prompt penetration electric fields (PPEF) during the rapid F-2 layer response. The PPEF drives the F-2 layer peak rapidly upward, which reduces Nmax due to vertical expansion and diffusion. The results therefore suggest that the rapid F-2 layer response (rapid rise (and fall) of peak height (hmax) with large Nmax reduction) observed by ionosondes can be used to detect the occurrence of the daytime eastward PPEF during intense geomagnetic storms irrespective of season and level of solar activity. The data also show two rare events of strong daytime westward electric fields due to disturbance dynamo and/or prompt penetration. The results are important when radars are not available to monitor the occurrence of the PPEF.

DOI： 10.1029/2010JA016001

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2010GL046268

Web of Science

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  

This paper introduces a new Earth's atmosphere-ionosphere coupled model that treats seamlessly the neutral atmospheric region from the troposphere to the thermosphere as well as the thermosphere-ionosphere interaction including the electrodynamics self-consistently. The model is especially useful for the study of vertical connection between the meteorological phenomena and the upper atmospheric behaviors. As an initial simulation using the coupled model, we have carried out a 30 day consecutive run in September. The result reveals that the longitudinal structure of the F-region ionosphere varies on a day-to-day basis in a highly complex way and that a four-peak structure of the daytime equatorial ionization anomaly (EIA) similar to the recent observations appears as an averaged feature. The simulation reproduces and thus confirms the vertical coupling processes proposed so far with respect to the formation of the averaged EIA longitudinal structure; the excitation of solar nonmigrating tides in the troposphere, their propagation through the middle atmosphere, and the modulation of ionospheric dynamo, which in turn affects EIA generation. The simulation result indicates that not only the ionospheric averaged longitudinal structure but also the day-to-day variation can be modulated significantly by the lower atmospheric effect.

DOI： 10.1029/2010JA015925

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1007/978-94-007-0326-1_21

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Blackwell Publishing Ltd  

The response of the dayside equatorial F2 layer to the main phases of the 22 intense geomagnetic storms (Dst &lt
-150 nT) in 1998-2008 is investigated using the digital ionosonde data from the equatorial stations in Brazilian, Indian, and Australian longitudes together with equatorial electrojet strength and IMF Bz
the storms include 15 superstorms (Dst &lt
-200 nT). The observations show that there is a period during all MPs when the F2 layer peak rises (and falls) rapidly with large peak electron density (Nmax) reduction, the rise velocity strongly correlates with the intensity (Dst) of the storms, and the duration of the Nmax reduction corresponds to that of strong eastward electrojet when IMF Bz remains highly negative. The observations indicate the occurrence of strong eastward prompt penetration electric fields (PPEF) during the rapid F2 layer response. The PPEF drives the F2 layer peak rapidly upward, which reduces Nmax due to vertical expansion and diffusion. The results therefore suggest that the rapid F2 layer response (rapid rise (and fall) of peak height (hmax) with large Nmax reduction) observed by ionosondes can be used to detect the occurrence of the daytime eastward PPEF during intense geomagnetic storms irrespective of season and level of solar activity. The data also show two rare events of strong daytime westward electric fields due to disturbance dynamo and/or prompt penetration. The results are important when radars are not available to monitor the occurrence of the PPEF. Copyright 2011 by the American Geophysical Union.

DOI： 10.1029/2010JA016001

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.5047/eps.2011.06.034

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Blackwell Publishing Ltd  

We report an event in which a polar cap patch was detected with an all-sky imager (ASI) at Resolute Bay, Canada (74.73° N, 265.07° E
AACGM latitude 82.9°), on the nightside. The patch stopped its antisunward motion associated with a northward turning of interplanetary magnetic field and stayed within the field of view of the ASI for more than 1 h. When the patch stagnated, its luminosity decreased gradually, which allows us to investigate how the patch plasma decayed in a quantitative manner. The decay of the patch can be quantitatively explained by the loss through recombinations of O+ with ambient N2 and O2 molecules, if we assume the altitude of the optical patch to be around 295 km. The derived altitude of the patch around 295 km is much higher than the nominal value at 235 km obtained from the MSIS-E90 and IRI-2007 models, indicating that climatological models such as IRI are not suitable for describing the actual density profile of patches. This is probably because the loss process was much faster in the lower-altitude part of the patch
thus, the peak altitude of the patch increased as it traveled across the polar cap because of rapid recombination at the bottomside of the F region. This suggests that we should employ higher emission altitude when we investigate optical patches transported deep into the nightside polar cap. Such information is important when we compare the optical data with other instruments such as coherent radars and GPS scintillation measurements by mapping the all-sky image on the geographic coordinate system with an assumption of the patch emission altitude. Copyright 2011 by the American Geophysical Union.

DOI： 10.1029/2010JA016297

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Blackwell Publishing Ltd  

Using ground observations of total electron content (TEC) and equatorial electrojet (EEJ) in the Asian sector, along with plasma and neutral densities obtained from the CHAMP satellite, we investigate the ionospheric electrodynamics and neutral background in this longitude sector during the major stratospheric sudden warming (SSW) in January 2009. Our analysis reveals the following prominent features. First, the TEC response in tropical regions is strongly latitude dependent, with monotonic depletion at the dip equator but a semidiurnal perturbation at low latitudes. Second, the TEC semidiurnal perturbation possesses a significant hemispheric asymmetry in terms of onset date and magnitude. It starts on the same day as the SSW peak in the Northern Hemisphere but 2 days later in the Southern Hemisphere. Its magnitude is twice as strong in the north than in the south. Third, strong counter electrojet occurs in the afternoon, following the strengthening of the eastward EEJ in the morning. Fourth, semidiurnal perturbation in both TEC and EEJ possesses a phase shift, at a rate of about 0.7 h/day. Comparisons with results reported in the Peruvian sector reveal clear longitude dependence in the amplitude and hemispheric asymmetry of the semidiurnal perturbation. Finally, thermospheric density undergoes ∼25% decrease at low latitudes in the afternoon local time sector during the SSW, indicating significant cooling effects in the tropical upper thermosphere. Copyright © 2011 by the American Geophysical Union.

DOI： 10.1029/2011JA016607

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：The Institute of Electrical Engineers of Japan  

We present the scientific targets, instrumental design, principle of measurement, and development of the Visible and near-Infrared Spectral Imager (VISI) which will be launched onto International Space Station (ISS) in January 2012. VISI is equipped with fast optics including a grism, and a high-sensitivity CCD to obtain airglow emissions at wavelengths of O (630 nm), OH Meinel band (650 nm) and O₂ (0-0) atmospheric band (762 nm). VISI has two field-of-views (FOVs), 45 degrees forward and 45 degrees backward to nadir, to subtract background contaminations. The data acquisition of VISI will be continuously performed with short exposure cycle less than several seconds when ISS is orbiting in the night side of the earth, and then provide the seamless line scanning images of the airglows with a spatial resolution better than 50 km. After manufacturing VISI, we checked its performance though optical and electric function tests as well as environmental tests that are necessary to be launched.

DOI： 10.1541/ieejfms.131.983

CiNii Books

その他リンク： https://jlc.jst.go.jp/DN/JALC/00383579674?from=CiNii

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.5047/eps.2011.06.026

Web of Science

記述言語：日本語   掲載種別：研究論文（その他学術会議資料等）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.5047/eps.2011.06.008

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.5047/eps.2011.06.035

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.5047/eps.2011.07.003

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Blackwell Publishing Ltd  

A detailed comparison between the observations of the Communication/ Navigation Outage Forecasting System (C/NOFS) satellite and the 47 MHz Equatorial Atmosphere Radar (EAR) in West Sumatra, Indonesia (10.36S dip latitude) on the postmidnight irregularities is presented. The zonal and meridional E × B drift velocities measured by the vector electric field instrument on the C/NOFS are consistent with the westward propagation of backscatter echoes and the line-of-sight Doppler velocities observed with the EAR, respectively. The plasma density depletions are observed in the postmidnight sector for several consecutive orbits, which suggests the depletions grow slowly during the premidnight period and reach the spacecraft altitude around local midnight. The convergence of the equatorward wind which could be responsible for the midnight temperature maximum may produce a preferable condition for the growth of the Rayleigh-Taylor instability around midnight. Electric field fluctuations of medium-scale traveling ionospheric disturbances may play an important role in seeding the instability. Both equatorial and midlatitude-type plasma instabilities could be operational at the EAR latitude sector, which together would foster a high occurrence of postmidnight irregularities during solar minimum. Copyright 2011 by the American Geophysical Union.

DOI： 10.1029/2011JA016798

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Blackwell Publishing Ltd  

Using the 47 MHz Equatorial Atmosphere Radar (EAR) in West Sumatra, Indonesia (10.36S dip latitude), it is shown that postmidnight irregularities during solar minimum are morphologically different from those detected during solar maximum and are quite similar to those observed with the middle and upper atmosphere (MU) radar in midlatitudes (29.3N dip latitude). Utilizing the rapid beam-steering capability of the EAR, the spatial structure of the postmidnight irregularities is clearly presented for the first time. It is found that they usually propagate westward and can be categorized into two types. One shows sharp upwelling plumes near local midnight, which should not be a mere passage of fossil plasma bubbles. The other has successive tilted structures which have the same orientation as medium-scale traveling ionospheric disturbances typically observed at midlatitudes. We suggest that the convergence of the equatorward thermospheric wind which is believed to be responsible for the midnight temperature maximum may be an important factor to produce a preferable condition for the upwelling plumes in the postmidnight sector. The displacement between geographic and magnetic equators may also be important for seasonal/longitudinal variation of the postmidnight irregularities. © 2011 by the American Geophysical Union.

DOI： 10.1029/2011JA016797

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.5047/eps.2011.07.015

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Blackwell Publishing Ltd  

The neutral mass density N and electron density Ne at 400 km height measured by CHAMP during nine intense geomagnetic storms bring out some new aspects of the thermospheric and ionospheric storms. The thermospheric storms (increase of N) develop with the onset of the main phases (MP) of the geomagnetic storms and reach their peak phases before or by the end of the MPs. The ionospheric storms (change of Ne) in general undergo an initial negative phase (with the equatorial ionization anomaly (EIA) crests shifting poleward) before turning positive, and the positive storms reach their peak strengths (or phases) centered at 25-30 magnetic latitudes
in some (4) cases the positive storms develop without an initial negative phase and with the EIA crests shifting equatorward
in all cases the positive storms reach their peak phases before the end of the MPs and turn to conventional negative storms by the end of the MPs. The observations agree with the different aspects of a physical mechanism of the positive storms. The observations also reveal that the Halloween storms of 30 October 2003 with a short MP without fluctuations produced the strongest positive ionospheric storms through impulsive response, and there is strong equinoctial asymmetry in the ionosphere and thermosphere during geomagnetic storms. Copyright 2011 by the American Geophysical Union.

DOI： 10.1029/2010JA016399

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Blackwell Publishing Ltd  

This paper introduces a new Earth's atmosphere-ionosphere coupled model that treats seamlessly the neutral atmospheric region from the troposphere to the thermosphere as well as the thermosphere-ionosphere interaction including the electrodynamics self-consistently. The model is especially useful for the study of vertical connection between the meteorological phenomena and the upper atmospheric behaviors. As an initial simulation using the coupled model, we have carried out a 30 day consecutive run in September. The result reveals that the longitudinal structure of the F-region ionosphere varies on a day-to-day basis in a highly complex way and that a four-peak structure of the daytime equatorial ionization anomaly (EIA) similar to the recent observations appears as an averaged feature. The simulation reproduces and thus confirms the vertical coupling processes proposed so far with respect to the formation of the averaged EIA longitudinal structure
the excitation of solar nonmigrating tides in the troposphere, their propagation through the middle atmosphere, and the modulation of ionospheric dynamo, which in turn affects EIA generation. The simulation result indicates that not only the ionospheric averaged longitudinal structure but also the day-to-day variation can be modulated significantly by the lower atmospheric effect. Copyright 2011 by the American Geophysical Union.

DOI： 10.1029/2010JA015925

Scopus

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  

During a magnetic storm on 14-16 December 2006, a polar cap tongue of ionization (TOI) was detected by an all-sky imager (ASI) at Resolute Bay, Canada (74.73 degrees N, 265.07 degrees E). We investigate the temporal evolution and spatial structure of the TOI in detail by combining the optical data with other observations (e. g., solar wind, GPS total electron content, SuperDARN, and DMSP and NOAA POES satellites). The TOI was observed as a bright and elongated 630 nm airglow plume for 4 h during the main phase of the storm. This interval corresponded to a period of prolonged stable large-amplitude southward IMF during a coronal mass ejection (CME). One to one and a half hours before the appearance of TOI, the polar cap boundary expanded rapidly far equatorward, and a positive ionospheric storm occurred. This implies that both the "expansion of the high-latitude plasma convection" and "build up of the source plasma in the midlatitudes" are necessary conditions for the formation of a TOI. Because both of them were triggered by a major southward turning of the IMF, the prolonged large-amplitude southward IMF orientation in the trailing part of the CME was primarily responsible for the generation of TOI. After its appearance, the TOI exhibited dynamic motion in the dawn to dusk direction. Simultaneous SuperDARN data suggest that a longitudinal progression of subauroral polarization stream controlled this dynamic motion. The optical TOI was found to be a continuous stream elongated in the noon-midnight direction although it contained some mesoscale patterns. Absence of large-scale temporal changes in the cusp plasma flow during the stable IMF period allowed the TOI to remain continuous without being broken into polar cap patches. The mesoscale structures within the TOI were probably produced by small-scale velocity fluctuations in the cusp plasma flow. The TOI as visualized with the all-sky airglow imager was found to be much more dynamic and much more complicated than we ever thought. The current study indicates that such a behavior of the TOI was presumably caused by a combination of temporal variations in the global-scale plasma circulation system, expansion and contraction of the polar cap area, and plasma density changes in the dayside low to midlatitudes.

DOI： 10.1029/2010JA015848

Web of Science

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  

The Imager for Sprites and Upper Atmospheric Lightning (ISUAL) payload on board the FORMOSAT-2 satellite carried out the first limb imaging observation of 630 nm airglow for the purpose of studying physical processes in the F region ionosphere. For a total of 14 nights in 2006-2008, ISUAL scanned the midnight latitude-altitude distribution of 630 nm airglow in the Asian sector. On two nights of relatively active conditions (Sigma Kp = 26, 30+) we found several bright airglow regions, which were highly variable each night in terms of luminosity and location. In relatively quiet conditions (Sigma Kp = 4-20) near May/June we found two bright regions which were stably located in the midlatitude region of 40 degrees S-10 degrees S (50 degrees S-20 degrees S magnetic latitude (MLAT)) and in the equatorial region of 0 degrees-10 degrees N (10 degrees S-0 degrees MLAT). On one of the quiet nights, FORMOSAT-3/COSMIC and CHAMP simultaneously measured the plasma density in the same region where ISUAL observed airglow. The plasma density data generally show good agreement, suggesting that plasma enhancements were the primary source of these two bright airglow regions. From detailed comparison with past studies we explain that the airglow in the equatorial region was due to the midnight brightness wave produced in association with the midnight temperature maximum, while that in the midlatitude region was due to the typical plasma distribution usually formed in the midnight sector. The fact that the equatorial airglow was much brighter than the midlatitude airglow and was observed on most nights during the campaign period strongly suggests the importance of further studies on the MTM/MBW phenomenology, which is not well reproduced in the current general circulation model.

DOI： 10.1029/2009JA015147

Web of Science

DOI： 10.1029/2009JA014297

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  

On 15 December 2006, during the main phase of a relatively large storm, Doppler velocity data from the Super Dual Aural Radar Network (SuperDARN) Hokkaido radar, together with total electron content (TEC) data from the GPS Earth Observation Network (GEONET), recorded daytime large-scale traveling ionospheric disturbances (LSTIDs). We studied two disturbances propagating southward and one disturbance propagating northward between 0000 and 0600 UT on 15 December 2006. The former disturbances were LSTIDs typical of those reported in many previous studies, whereas the latter was confirmed as an LSTID propagating from the Southern into the Northern Hemisphere, reported in a few past studies. From comparisons of SuperDARN Hokkaido radar Doppler velocity and GEONET TEC, we found a positive correlation between downward ionospheric motion and increasing TEC. This relationship is consistent with results of model calculation. This is the first observation of LSTIDs ranging from high to low latitude combining simultaneous SuperDARN HF radar and GPS network observations.

DOI： 10.1029/2009JA014297

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2010GL042855

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2009JA014830

Web of Science

Scopus

DOI： 10.1029/2009JA014515

Web of Science

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  

On the night of December 20, 2006, 630 nm airglow images obtained by an all-sky camera at Resolute Bay, Canada (74.73 degrees N, 265.07 degrees E; altitude adjusted corrected geomagnetic (AACGM) latitude 82.9 degrees) showed the passage of successive polar cap patches. Shortly after convection came to a temporary halt, one of the patches was reorganized into two substructures in approximately 8 min. The two-dimensional background ionospheric convection pattern measured using the newly deployed PolarDARN radar at Rankin Inlet (62.82 degrees N, 93.11 degrees W; AACGM latitude 72.96 degrees) showed that a velocity shear of approximately 120 m s(-1)/340 km suddenly appeared in the vicinity of the patch at the time of reorganization. A qualitative analysis of the relationship between the magnitude of the velocity shear and the distance between the divided patches indicates that the shear in the background plasma convection velocity significantly contributed to the reorganization of the patch. This shear structure appeared soon after a southward turning of the interplanetary magnetic field (IMF) and was probably associated with the reconfiguration of the convection pattern from a pre-existing northward-oriented IMF pattern to a southward-oriented one. The present observations indicate that the reconfiguration/deformation of patches because of a shear in the background convection field, especially reorganization of patches into smaller substructures, may play an important role in the rapid structuring of patches.

DOI： 10.1029/2009JA014599

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Blackwell Publishing Ltd  

[1] A physical mechanism of the positive ionospheric storms at low latitudes and midlatitudes is presented through multi-instrument observations, theoretical modeling, and basic principles. According to the mechanism, an equatorward neutral wind is required to produce positive ionospheric storms. The mechanical effects of the wind (1) reduce (or stop) the downward diffusion of plasma along the geomagnetic field lines, (2) raise the ionosphere to high altitudes of reduced chemical loss, and hence (3) accumulate the plasma at altitudes near and above the ionospheric peak centered at around ±30° magnetic latitudes. Daytime eastward prompt penetration electric field (PPEF), if it occurs, also shifts the equatorial ionization anomaly crests to higher than normal latitudes, up to approximately ±30° latitudes. The positive ionospheric storms are most likely in the longitudes where the onset of the geomagnetic storms falls in the ionization production dominated morning-noon local time sector when the plasma accumulation due to the mechanical effects of the wind largely exceeds the plasma loss due to the chemical effect of the wind. The mechanism agrees with the multi-instrument observations made during the supergeomagnetic storm of 7-8 November 2004, with 18 h long initial phase (IP) and 10 h long main phase (MP). The observations, which are mainly in the Japanese-Australian longitudes where the MP onset was in the morning (0600 LT, 2100 UT), show (1) strong positive ionospheric storms (in Ne, Nmax, hmax, Global Positioning System-total electron content (GPS-TEC), and 630 nm airglow intensity) in both Northern and Southern hemispheres started at the morning (0600 LT) MP onset and lasted for a day, (2) repeated occurrence of strong eastward PPEF events penetrated after the MP onset and superposed with westward electric field started before the MP onset, and (3) storm time equatorward neutral winds (inferred from 1 and 2). Repeated occurrence of an unusually strong F3 layer with large density depletions around the equator was also observed during the morning-noon MP. Copyright 2010 by the American Geophysical Union.

DOI： 10.1029/2009JA014515

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Blackwell Publishing Ltd  

During a magnetic storm on 14-16 December 2006, a polar cap tongue of ionization (TOI) was detected by an all-sky imager (ASI) at Resolute Bay, Canada (74.73°N, 265.07°E). We investigate the temporal evolution and spatial structure of the TOI in detail by combining the optical data with other observations (e.g., solar wind, GPS total electron content, SuperDARN, and DMSP and NOAA POES satellites). The TOI was observed as a bright and elongated 630 nm airglow plume for 4 h during the main phase of the storm. This interval corresponded to a period of prolonged stable large-amplitude southward IMF during a coronal mass ejection (CME). One to one and a half hours before the appearance of TOI, the polar cap boundary expanded rapidly far equatorward, and a positive ionospheric storm occurred. This implies that both the "expansion of the high-latitude plasma convection" and "build up of the source plasma in the midlatitudes" are necessary conditions for the formation of a TOI. Because both of them were triggered by a major southward turning of the IMF, the prolonged large-amplitude southward IMF orientation in the trailing part of the CME was primarily responsible for the generation of TOI. After its appearance, the TOI exhibited dynamic motion in the dawn to dusk direction. Simultaneous SuperDARN data suggest that a longitudinal progression of subauroral polarization stream controlled this dynamic motion. The optical TOI was found to be a continuous stream elongated in the noon-midnight direction although it contained some mesoscale patterns. Absence of large-scale temporal changes in the cusp plasma flow during the stable IMF period allowed the TOI to remain continuous without being broken into polar cap patches. The mesoscale structures within the TOI were probably produced by small-scale velocity fluctuations in the cusp plasma flow. The TOI as visualized with the all-sky airglow imager was found to be much more dynamic and much more complicated than we ever thought. The current study indicates that such a behavior of the TOI was presumably caused by a combination of temporal variations in the global-scale plasma circulation system, expansion and contraction of the polar cap area, and plasma density changes in the dayside low to midlatitudes. Copyright 2010 by the American Geophysical Union.

DOI： 10.1029/2010JA015848

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Blackwell Publishing Ltd  

On 15 December 2006, during the main phase of a relatively large storm, Doppler velocity data from the Super Dual Aural Radar Network (SuperDARN) Hokkaido radar, together with total electron content (TEC) data from the GPS Earth Observation Network (GEONET), recorded daytime large-scale traveling ionospheric disturbances (LSTIDs). We studied two disturbances propagating southward and one disturbance propagating northward between 0000 and 0600 UT on 15 December 2006. The former disturbances were LSTIDs typical of those reported in many previous studies, whereas the latter was confirmed as an LSTID propagating from the Southern into the Northern Hemisphere, reported in a few past studies. From comparisons of SuperDARN Hokkaido radar Doppler velocity and GEONET TEC, we found a positive correlation between downward ionospheric motion and increasing TEC. This relationship is consistent with results of model calculation. This is the first observation of LSTIDs ranging from high to low latitude combining simultaneous SuperDARN HF radar and GPS network observations. Copyright © 2010 by the American Geophysical Union.

DOI： 10.1029/2009JA014297

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.5194/angeo-28-1847-2010

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Blackwell Publishing Ltd  

The Imager for Sprites and Upper Atmospheric Lightning (ISUAL) payload on board the FORMOSAT-2 satellite carried out the first limb imaging observation of 630 nm airglow for the purpose of studying physical processes in the F region ionosphere. For a total of 14 nights in 2006-2008, ISUAL scanned the midnight latitude-altitude distribution of 630 nm airglow in the Asian sector. On two nights of relatively active conditions (ΣKp = 26, 30+) we found several bright airglow regions, which were highly variable each night in terms of luminosity and location. In relatively quiet conditions (ΣKp = 4-20) near May/June we found two bright regions which were stably located in the midlatitude region of 40°S-10°S (50°S-20°S magnetic latitude (MLAT)) and in the equatorial region of 0°-10°N (10°S-0° MLAT). On one of the quiet nights, FORMOSAT-3/COSMIC and CHAMP simultaneously measured the plasma density in the same region where ISUAL observed airglow. The plasma density data generally show good agreement, suggesting that plasma enhancements were the primary source of these two bright airglow regions. From detailed comparison with past studies we explain that the airglow in the equatorial region was due to the midnight brightness wave produced in association with the midnight temperature maximum, while that in the midlatitude region was due to the typical plasma distribution usually formed in the midnight sector. The fact that the equatorial airglow was much brighter than the midlatitude airglow and was observed on most nights during the campaign period strongly suggests the importance of further studies on the MTM/MBW phenomenology, which is not well reproduced in the current general circulation model. Copyright 2010 by the American Geophysical Union.

DOI： 10.1029/2009JA015147

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Blackwell Publishing Ltd  

On the night of December 20, 2006, 630 nm airglow images obtained by an all-sky camera at Resolute Bay, Canada (74.73°N, 265.07°E
altitude adjusted corrected geomagnetic (AACGM) latitude 82.9°) showed the passage of successive polar cap patches. Shortly after convection came to a temporary halt, one of the patches was reorganized into two substructures in approximately 8 min. The two-dimensional background ionospheric convection pattern measured using the newly deployed PolarDARN radar at Rankin Inlet (62.82°N, 93.11°W
AACGM latitude 72.96°) showed that a velocity shear of approximately 120 m s-1/340 km suddenly appeared in the vicinity of the patch at the time of reorganization. A qualitative analysis of the relationship between the magnitude of the velocity shear and the distance between the divided patches indicates that the shear in the background plasma convection velocity significantly contributed to the reorganization of the patch. This shear structure appeared soon after a southward turning of the interplanetary magnetic field (IMF) and was probably associated with the reconfiguration of the convection pattern from a pre-existing northward-oriented IMF pattern to a southward-oriented one. The present observations indicate that the reconfiguration/deformation of patches because of a shear in the background convection field, especially reorganization of patches into smaller substructures, may play an important role in the rapid structuring of patches. Copyright 2010 by the American Geophysical Union.

DOI： 10.1029/2009JA014599

Scopus

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

DOI： 10.1017/S1743921309992857

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.5047/eps.2010.05.003

Web of Science

記述言語：日本語   掲載種別：研究論文（その他学術会議資料等）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.jastp.2009.09.004

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.jastp.2009.08.004

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2009GL039887

Web of Science

DOI： 10.1029/2008JA013963

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2009GL038156

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Blackwell Publishing Ltd  

We report simultaneous observations of medium-scale traveling ionospheric disturbances (MSTIDs) and field-aligned irregularities (FAls) in the F region using two all-sky airglow imagers and the middle and upper atmosphere (MU) radar. MSTIDs propagating southwestward were observed simultaneously in 630-nm airglow images over Sakata (39.0°N, 139.9°E) and Shigaraki (34.90N, 136.1°E), Japan, on the night of 16 June 2004. By using all-sky images over both sites, we estimated the altitude of the airglow layer to be 260 km by the triangulation method. During the MSTID event, FAIs in the F region were observed by making multibeam measurements with the MU radar at Shigaraki. In order to investigate the spatial relationship between the MSTIDs and FAIs, the FAIs were mapped onto the 630-nm airglow layer (altitude, 260 km) along the geomagnetic field lines. We found that FAIs with an intense (weak) signal-to-noise ratio coincided with the airglow depletion (enhancement) caused by the MSTIDs. FAI velocity obtained from a combination of the Doppler velocities on the three radar beams oscillated in the northwest-southeast direction, with an amplitude of approximately 82 m/s. The FAI velocity was northwestward (southeastward) at the airglow depletion (enhancement). The directions of the FAI velocity were consistent with those of the ExB drifts caused by the polarized electric fields associated with the MSTIDs. The northeastward polarized electric field at the airglow depletion region strengthened the background eastward effective electric field and drove the gradient drift instability generating FAIs. This might be the reason why the FAIs preferred to occur at the airglow depletion region. Copyright 2009 by the American Geophysical Union.

DOI： 10.1029/2008JA013902

Scopus

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  

We report simultaneous observations of medium-scale traveling ionospheric disturbances (MSTIDs) and field-aligned irregularities (FAIs) in the F region using two all-sky airglow imagers and the middle and upper atmosphere (MU) radar. MSTIDs propagating southwestward were observed simultaneously in 630-nm airglow images over Sakata (39.0 degrees N, 139.9 degrees E) and Shigaraki (34.9 degrees N, 136.1 degrees E), Japan, on the night of 16 June 2004. By using all-sky images over both sites, we estimated the altitude of the airglow layer to be 260 km by the triangulation method. During the MSTID event, FAIs in the F region were observed by making multibeam measurements with the MU radar at Shigaraki. In order to investigate the spatial relationship between the MSTIDs and FAIs, the FAIs were mapped onto the 630-nm airglow layer (altitude, 260 km) along the geomagnetic field lines. We found that FAIs with an intense (weak) signal-to-noise ratio coincided with the airglow depletion (enhancement) caused by the MSTIDs. FAI velocity obtained from a combination of the Doppler velocities on the three radar beams oscillated in the northwest-southeast direction, with an amplitude of approximately 82 m/s. The FAI velocity was northwestward (southeastward) at the airglow depletion (enhancement). The directions of the FAI velocity were consistent with those of the E x B drifts caused by the polarized electric fields associated with the MSTIDs. The northeastward polarized electric field at the airglow depletion region strengthened the background eastward effective electric field and drove the gradient drift instability generating FAIs. This might be the reason why the FAIs preferred to occur at the airglow depletion region.

DOI： 10.1029/2008JA013902

Web of Science

DOI： 10.1029/2008JA014020

DOI： 10.1029/2008JA014020

Web of Science