Updated on 2024/04/08

写真a

 
OTSUKA, Yuichi
 
Organization
Institute for Space-Earth Environmental Research Division for Ionospheric and Magnetospheric Research Associate professor
Graduate School
Graduate School of Science
Title
Associate professor
Contact information
メールアドレス
External link

Degree 1

  1. Doctor of Engineering ( 1999.3   Kyoto University ) 

Research Interests 3

  1. ionosphere airglow TEC GPS GNSS

  2. 電離圏物理学

  3. 超高層大気物理学

Research Areas 3

  1. Others / Others  / Aeronomy

  2. Natural Science / Space and planetary sciences

  3. Others / Others  / Aeronomy

Current Research Project and SDGs 2

  1. A study of low- and mid-latitude ionosphere using GPS, radar and optical observations

  2. Study of ionospheric effects on GNSS

Research History 1

  1. Institute for Space-Earth Environmental Research, Associate Professor

    2015.10

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    Country:Japan

Education 2

  1. Kyoto University   Graduate School, Division of Engineering

    1996.4 - 1999.3

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    Country: Japan

  2. Kyoto University

    1996.4 - 1998.3

Professional Memberships 5

  1. The Society of Geomagnetism and Earth, Planetaryand Space Sciences

  2. American Geophysical Union

  3. The Institute of Positioning, Navigation and Timing of Japan

  4. THE INSTITUTE OF POSITIONING

  5. SOCIETY OF GEOMAGNETISM AND EARTH

Awards 13

  1. Excellent Reviewers 2021

    2022.1   Earth, Planets and Space  

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    Award type:Honored in official journal of a scientific society, scientific journal 

  2. Excellent Reviewers 2020

    2021.1   Earth, Planets and Space  

  3. Advances in Space Research: Top Reviewer 2019

    2020.6   Committee on Space Research  

  4. Tanakadate Award

    2019.10   Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS)  

  5. AGU’s Outstanding Reviewers of 2018, Radio Science

    2019.5   American Geophysical Union (AGU)  

  6. Advances in Space Research: Top Reviewers of 2017

    2018.8  

  7. Editors' Citations for Excellence in Refereeing, Radio Science

    2012.10   American Geophysical Union (AGU)  

    OTSUKA, Yuichi

  8. 2011 Editors' Citations for Excellence in Refereeing, Radio Science

    2011   American Geophysical Union  

  9. 2009 Editors' Citations for Excellence in Refereeing, Geophysical Research Letters

    2010.9   American Geophysical Union  

  10. Editors' Citations for Excellence in Refereeing, Geophysical Research Letters

    2010.5   American Geophysical Union (AGU)  

    OTSUKA, Yuichi

  11. EPS Award

    2009.5   Earth, Planets and Space (EPS)  

    OTSUKA, Yuichi

  12. 地球電磁気・地球惑星圏学会 大林奨励賞

    2005.9   地球電磁気・地球惑星圏学会  

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    Country:Japan

  13. Obayashi Early Career Scientist Award

    2005.9   Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS)   熱圏電離圏における大気・プラズマ結合の研究

    OTSUKA, Yuichi

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Papers 466

  1. Spatial relationship of nighttime medium-scale traveling ionospheric disturbances and F region field-aligned irregularities observed with two spaced all-sky airglow imagers and the middle and upper atmosphere radar Reviewed

    Otsuka, Y., K. Shiokawa, T. Ogawa, T. Yokoyama, and M. Yamamoto

    J. Geophys. Res.   Vol. 114   page: A05302, doi:10.1029/2008JA013902   2009.5

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    Authorship:Lead author   Language:English   Publishing type:Research paper (scientific journal)  

    We report simultaneous observations of medium-scale traveling ionospheric disturbances (MSTIDs) and field-aligned irregularities (FAIs) in the F region by using two all-sky airglow imagers and the MU radar. MSTIDs propagating southwestward were observed simultaneously in 630-nm airglow images over Sakata (39.0N, 139.9E) and Shigaraki (34.9N, 136.1E), Japan on the night of June 16, 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 intense (weak) signal-to-noise ratio (SNR) 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 NW-SE 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.

  2. VHF radar observations of nighttime F-region field-aligned irregularities over Kototabang, Indonesia Reviewed

    Otsuka, Y., T. Ogawa, and Effendy

    Earth Planets Space   Vol. 61   page: 431-437   2009.5

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    Authorship:Lead author   Language:English   Publishing type:Research paper (scientific journal)  

    We report the response of the ionosphere to the large erthquake that occurred in West Sumatra, Indonesia, at 0058 UT on December 26, 2004. We have analyzed Global Positioning System (GPS) data obtained at two sites in Sumatra and at three sites in Thailand to investigate total electron content (TEC) variations. Between 14 and 40 min after the earthquake,
    TEC enhancements of 1.6--6.9 TEC units (TECU) were observed
    at subionospheric points located 360-2000 km north of the epicenter. From the time delays of the observed TEC enhancements, we find that the TEC enhancements propagated northward from the epicenter. The time delays between the earthquake and rapid increases in TEC, which occurred near the epicenter, are consistent with the idea that acoustic waves generated by the earthquake propagated into the ionosphere at the speed of sound to cause the TEC variations.
    A small TEC enhancement of 0.6 TECU was observed south of the epicenter, while no TEC enhancements were seen east of the epicenter. From a model calculation, we find that this directivity of the TEC variations with respect to the azimuth from the epicenter could be caused partially by the directivity in the response of the electron density variation
    to the acoustic waves in the neutral atmosphere.

  3. GPS detection of total electron content variations over Indonesia and Thailand following the 26 December 2004 earthquake Reviewed

    Otsuka, Y., N. Kotake, T. Tsugawa, K. Shiokawa, T. Ogawa, Effendy, S. Saito, M. Kawamura, T. Maruyama, N. Hemmakorn, and T. Komolmis

    Earth, Planets and Space   Vol. 58   page: 159-165   2006

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    Authorship:Lead author   Language:English   Publishing type:Research paper (scientific journal)  

  4. *Geomagnetic conjugate observations of medium-scale traveling ionospheric disturbances at midlatitude using all-sky airglow imagers Reviewed

    Otsuka, Y., K. Shiokawa, T. Ogawa, and P. Wilkinson

    Geophys. Res. Lett.   Vol. 31 ( L15803 ) page: doi:10.1029/2004GL020262   2004

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    Authorship:Lead author   Language:English   Publishing type:Research paper (scientific journal)  

    We report for the first time simultaneous observations of medium-scale traveling ionospheric disturbances (MSTIDs) at geomagnetic conjugate points in both hemispheres, using two all-sky airglow imagers at midlatitudes. A 630-nm all-sky CCD imager at Sata, Japan, detected MSTIDs with a wavefront elongated from NW to SE on the night of August 9, 2002. During this event, MSTIDs with a wavefront elongated from SW to NE were observed at the geomagnetic conjugate point, Darwin, Australia. The MSTID structures mapped from Darwin to its magnetic conjugate points along the geomagnetic field lines B coincide closely with those in the Sata images. This result suggests that polarization electric field (Ep) plays an important role in the generation of MSTIDs. Ep maps along B and moves the F region plasma upward or downward by ExB drifts, causing plasma density perturbations with structures mirrored in the northern and southern hemispheres.

  5. *A new technique for mapping of total electron content using GPS network in Japan Reviewed

    Otsuka, Y., T. Ogawa, A. Saito, T. Tsugawa, S. Fukao, and S. Miyazaki

    Earth, Planets, and Space   Vol. 54   page: 63-70   2002

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    Authorship:Lead author   Language:English   Publishing type:Research paper (scientific journal)  

  6. Performance of the double-thin-shell approach for studying nighttime medium-scale traveling ionospheric disturbances using two dense GNSS observation networks in Japan

    Fu, WZ; Otsuka, Y; Shinbori, A; Nishioka, M; Perwitasari, S

    EARTH PLANETS AND SPACE   Vol. 76 ( 1 )   2024.1

  7. Statistical Analysis of Global and Regional Ionospheric Total Electron Content (TEC) Using Extreme Value Distributions

    Emmela, S; Ratnam, DV; Otsuka, Y; Shinbori, A; Sori, T; Nishioka, M; Perwitasari, S

    IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING   Vol. 62   2024

  8. Assessing the potential of ionosonde for forecasting post-sunset equatorial spread F: an observational experiment in Southeast Asia

    Abadi, P; Ahmad, UA; Otsuka, Y; Jamjareegulgarn, P; Almahi, A; Perwitasari, S; Supriadi, S; Harjupa, W; Septiawan, RR

    EARTH PLANETS AND SPACE   Vol. 75 ( 1 )   2023.12

  9. An Extreme Value Analysis of Long-Term GNSS Ionospheric Total Electron Content Data Observed at Japan Grid Point Location (34.95° N and 134.05° E) Reviewed

      Vol. 20   2023.11

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  10. Equinoctial asymmetry of plasma bubble occurrence and electric field at evening: GPS and ionosonde measurements in Southeast Asia Reviewed

    Otsuka, Y; Abadi, P; Hozumi, K; Almahi, A

    JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS   Vol. 252   2023.11

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

    DOI: 10.1016/j.jastp.2023.106136

    Web of Science

  11. Daytime Medium Scale Traveling Ionospheric Disturbances (MSTIDS) Over the Andes Mountains at Equatorial and Low Magnetic Latitudes

    Figueiredo, CAOB; Wrasse, CM; Vadas, S; Takahashi, H; Otsuka, Y; Nyassor, PK; Shiokawa, K; Paulino, I; Barros, D

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 128 ( 10 )   2023.10

  12. Responses of the African-European equatorial-, low-, mid-, and high-latitude ionosphere to geomagnetic storms of 2013, 2015 St Patrick's Days, 1 June 2013, and 7 October 2015 Reviewed

      Vol. 72 ( 3 ) page: 775 - 789   2023.8

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  13. Equatorial plasma bubble intensities across longitudinal sectors of the globe using GNSS observations Reviewed

      Vol. 249   2023.8

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  14. Ionospheric disturbances over South America related to Tonga volcanic eruption Reviewed

      Vol. 75 ( 1 )   2023.5

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  15. Day-to-day variability of the equatorial ionosphere in Asian sector during August-October 2019 Reviewed

      Vol. 10   2023.5

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  16. First Detection of Midlatitude Plasma Bubble by SuperDARN During a Geomagnetic Storm on May 27 and 28, 2017 Reviewed

      Vol. 128 ( 4 )   2023.4

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    Language:English  

    DOI: 10.1029/2022JA031157

    Web of Science

  17. Multi-Event Conjugate Measurements of the SAR Arc Detachment From the Auroral Oval Using DMSP Satellites and an All-Sky Camera at Athabasca, Canada Reviewed

      Vol. 128 ( 4 )   2023.4

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    Language:English  

    DOI: 10.1029/2022JA030544

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  18. Dependence of Ionospheric Responses on Solar Wind Dynamic Pressure During Geomagnetic Storms Using Global Long-Term GNSS-TEC Data Reviewed

      Vol. 128 ( 3 )   2023.3

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    Language:English  

    DOI: 10.1029/2022JA030913

    Web of Science

  19. Solved and unsolved riddles about low-latitude daytime valley region plasma waves and 150-km echoes Reviewed

      Vol. 10   2023.2

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  20. Tandem Observations of Nighttime Mid-Latitude Topside Ionospheric Perturbations Reviewed

      Vol. 21 ( 2 )   2023.2

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    Language:English  

    DOI: 10.1029/2022SW003312

    Web of Science

  21. Ionospheric Modulation by EMIC Wave-Driven Proton Precipitation: Observations and Simulations

    Tian, XB; Yu, YQ; Gong, F; Ma, LX; Cao, JB; Solomon, SC; Shreedevi, PR; Shiokawa, K; Otsuka, Y; Oyama, S; Miyoshi, Y

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 128 ( 1 )   2023.1

  22. Relationship between geomagnetic storms and occurrence of ionospheric irregularities in the west sector of Africa during the peak of the 24th solar cycle

    Ondede, GO; Rabiu, AB; Okoh, D; Baki, P; Olwendo, J; Shiokawa, K; Otsuka, Y

    FRONTIERS IN ASTRONOMY AND SPACE SCIENCES   Vol. 9   2022.11

  23. Localized mesospheric ozone destruction corresponding to isolated proton aurora coming from Earth's radiation belt

    Ozaki Mitsunori, Shiokawa Kazuo, Kataoka Ryuho, Mlynczak Martin, Paxton Larry, Connors Martin, Yagitani Satoshi, Hashimoto Shion, Otsuka Yuichi, Nakahira Satoshi, Mann Ian

    SCIENTIFIC REPORTS   Vol. 12 ( 1 )   2022.10

  24. Three-Dimensional Fourier Analysis of Atmospheric Gravity Waves and Medium-Scale Traveling Ionospheric Disturbances Observed in Airglow Images in Hawaii Over Three Years

    Naito Hideto, Shiokawa Kazuo, Otsuka Yuichi, Fujinami Hatsuki, Tsuboi Takuma, Sakanoi Takeshi, Saito Akinori, Nakamura Takuji

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 127 ( 10 )   2022.10

  25. Statistical Study of Subauroral Arc Detachment at Athabasca, Canada: New Insights on STEVE

    Yadav, S; Shiokawa, K; Otsuka, Y; Connors, M

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 127 ( 9 )   2022.9

  26. Geomagnetic conjugacy of plasma bubbles extending to mid-latitudes during a geomagnetic storm on March 1, 2013

    Sori, T; Otsuka, Y; Shinbori, A; Nishioka, M; Perwitasari, S

    EARTH PLANETS AND SPACE   Vol. 74 ( 1 )   2022.8

  27. Electromagnetic conjugacy of ionospheric disturbances after the 2022 Hunga Tonga-Hunga Ha'apai volcanic eruption as seen in GNSS-TEC and SuperDARN Hokkaido pair of radars observations

    Shinbori Atsuki, Otsuka Yuichi, Sori Takuya, Nishioka Michi, Perwitasari Septi, Tsuda Takuo, Nishitani Nozomu

    EARTH PLANETS AND SPACE   Vol. 74 ( 1 )   2022.7

  28. A confirmation of vertical acoustic resonance and field-aligned current generation just after the 2022 Hunga Tonga Hunga Ha'apai volcanic eruption

    Iyemori, T; Nishioka, M; Otsuka, Y; Shinbori, A

    EARTH PLANETS AND SPACE   Vol. 74 ( 1 )   2022.6

  29. On the Role of E-F Region Coupling in the Generation of Nighttime MSTIDs During Summer and Equinox: Case Studies Over Northern Germany

    Sivakandan, M; Martinis, C; Otsuka, Y; Chau, JL; Norrell, J; Mielich, J; Conte, JF; Stolle, C; Rodríguez-Zuluaga, J; Shinbori, A; Nishioka, M; Tsugawa, T

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 127 ( 5 )   2022.5

  30. Modeling Post-Sunset Equatorial Spread-F Occurrence as a Function of Evening Upward Plasma Drift Using Logistic Regression, Deduced from Ionosondes in Southeast Asia

    Abadi, P; Ahmad, UA; Otsuka, Y; Jamjareegulgarn, P; Martiningrum, DR; Faturahman, A; Perwitasari, S; Saputra, RE; Septiawan, RR

    REMOTE SENSING   Vol. 14 ( 8 )   2022.4

  31. Statistical Behavior of Large-Scale Ionospheric Disturbances From High Latitudes to Mid-Latitudes During Geomagnetic Storms Using 20-yr GNSS-TEC Data: Dependence on Season and Storm Intensity

    Shinbori, A; Otsuka, Y; Sori, T; Tsugawa, T; Nishioka, M

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 127 ( 1 )   2022.1

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    Language:Japanese  

    DOI: 10.1029/2021JA029687

    Web of Science

  32. Variations of Zonal Wind Velocity in the Thermosphere Observed at Southeast Asian Sector During Quiet and Active Geomagnetic Days

    Sarudin, I; Hamid, NSA; Abdullah, M; Rusli, FNSM; Otsuka, Y; Shiokawa, K; Yatini, C; Komonjinda, S; Somboon, E

    JURNAL FIZIK MALAYSIA   Vol. 43 ( 1 ) page: 10025 - 10035   2022

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  33. Xtend, the Soft X-ray Imaging Telescope for the X-ray Imaging and Spectroscopy Mission (XRISM)

    Mori, K; Tomida, H; Nakajima, H; Okajima, T; Noda, H; Tanaka, T; Uchida, H; Hagino, K; Kobayashi, SB; Suzuki, H; Yoshida, T; Murakami, H; Uchiyama, H; Nobukawa, M; Nobukawa, KK; Yoneyama, T; Matsumoto, H; Tsuru, TG; Yamauchi, M; Hatsukade, I; Ishida, M; Maeda, Y; Hayashi, T; Tamura, K; Boissay-Malaquin, R; Sato, T; Hiraga, J; Kohmura, T; Yamaoka, K; Dotani, T; Ozaki, M; Tsunemi, H; Kanemaru, Y; Sato, J; Takaki, T; Terada, Y; Miyazaki, K; Kusunoki, K; Otsuka, Y; Yokosu, H; Yonemaru, W; Asahina, Y; Asakura, K; Yoshimoto, M; Ode, Y; Sato, J; Hakamata, T; Aoyagi, M; Aoki, Y; Tsunomachi, S; Doi, T; Aoki, D; Fujisawa, K; Kitajima, M; Hayashida, K

    SPACE TELESCOPES AND INSTRUMENTATION 2022: ULTRAVIOLET TO GAMMA RAY   Vol. 12181   2022

  34. An experimental investigation into the possible connections between the zonal neutral wind speeds and equatorial plasma bubble drift velocities over the African equatorial region

    Okoh, DI; Rabiu, AB; Shiokawa, K; Otsuka, Y; Wu, Q; Seemala, GK; Katamzi-Joseph, ZT

    JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS   Vol. 220   2021.9

  35. Preface to the Special Issue on recent advances in the study of Equatorial Plasma Bubbles and Ionospheric Scintillation

    Otsuka, Y; Spogli, L; Ram, ST; Li, GZ

    EARTH AND PLANETARY PHYSICS   Vol. 5 ( 5 ) page: 365 - 367   2021.9

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    Language:Japanese  

    DOI: 10.26464/epp2021050

    Web of Science

  36. Plasma depletions lasting into daytime during the recovery phase of a geomagnetic storm in May 2017: Analysis and simulation of GPS total electron content observations

    Otsuka, Y; Shinbori, A; Sori, T; Tsugawa, T; Nishioka, M; Huba, JD

    EARTH AND PLANETARY PHYSICS   Vol. 5 ( 5 ) page: 427 - 434   2021.9

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    DOI: 10.26464/epp2021046

    Web of Science

  37. Multi-instrument study of longitudinal wave structures for plasma bubble seeding in the equatorial ionosphere

    Takahashi, H; Essien, P; Figueiredo, CAO; Wrasse, CM; Barros, D; Abdu, MA; Otsuka, Y; Shiokawa, K; Li, GZ

    EARTH AND PLANETARY PHYSICS   Vol. 5 ( 5 ) page: 368 - 377   2021.9

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    DOI: 10.26464/epp2021047

    Web of Science

  38. L-Band Synthetic Aperture Radar Observation of Ionospheric Density Irregularities at Equatorial Plasma Depletion Region

    Sato, H; Kim, JS; Otsuka, Y; Wrasse, CM; de Paula, ER; de Souza, JR

    GEOPHYSICAL RESEARCH LETTERS   Vol. 48 ( 16 )   2021.8

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    DOI: 10.1029/2021GL093541

    Web of Science

  39. PSTEP: project for solar-terrestrial environment prediction

    Kusano, K; Ichimoto, K; Ishii, M; Miyoshi, Y; Yoden, S; Akiyoshi, H; Asai, A; Ebihara, Y; Fujiwara, H; Goto, TN; Hanaoka, Y; Hayakawa, H; Hosokawa, K; Hotta, H; Hozumi, K; Imada, S; Iwai, K; Iyemori, T; Jin, H; Kataoka, R; Katoh, Y; Kikuchi, T; Kubo, Y; Kurita, S; Matsumoto, H; Mitani, T; Miyahara, H; Miyoshi, Y; Nagatsuma, T; Nakamizo, A; Nakamura, S; Nakata, H; Nishizuka, N; Otsuka, Y; Saito, S; Saito, S; Sakurai, T; Sato, T; Shimizu, T; Shinagawa, H; Shiokawa, K; Shiota, D; Takashima, T; Tao, C; Toriumi, S; Ueno, S; Watanabe, K; Watari, S; Yashiro, S; Yoshida, K; Yoshikawa, A

    EARTH PLANETS AND SPACE   Vol. 73 ( 1 )   2021.8

  40. Characteristics of Medium-Scale Traveling Ionospheric Disturbances and Ionospheric Irregularities at Mid-Latitudes Revealed by the Total Electron Content Associated With the Beidou Geostationary Satellite

    Huang, F; Lei, J; Otsuka, Y; Luan, X; Liu, Y; Zhong, J; Dou, X

    IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING   Vol. 59 ( 8 ) page: 6424 - 6430   2021.8

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    DOI: 10.1109/TGRS.2020.3032741

    Web of Science

  41. What controls the luminosity of polar cap airglow patches?: Implication from airglow measurements in Eureka, Canada in comparison with SuperDARN convection pattern

    Hosokawa, K; Nagata, M; Shiokawa, K; Otsuka, Y

    POLAR SCIENCE   Vol. 28   2021.6

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  42. Statistical study of medium-scale traveling ionospheric disturbances in low-latitude ionosphere using an automatic algorithm

    Cheng, PH; Lin, C; Otsuka, Y; Liu, HL; Rajesh, PK; Chen, CH; Lin, JT; Chang, MT

    EARTH PLANETS AND SPACE   Vol. 73 ( 1 )   2021.5

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  43. The Occurrence Feature of Plasma Bubbles in the Equatorial to Midlatitude Ionosphere During Geomagnetic Storms Using Long-Term GNSS-TEC Data

    Sori, T; Shinbori, A; Otsuka, Y; Tsugawa, T; Nishioka, M

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 126 ( 5 )   2021.5

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    DOI: 10.1029/2020JA029010

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  44. Simultaneous Observation of Two Isolated Proton Auroras at Subauroral Latitudes by a Highly Sensitive All-Sky Camera and Van Allen Probes

    Nakamura, K; Shiokawa, K; Otsuka, Y; Shinbori, A; Miyoshi, Y; Connors, M; Spence, H; Reeves, G; Funsten, HO; MacDowall, R; Smith, C; Wygant, J; Bonnell, J

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 126 ( 5 )   2021.5

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    DOI: 10.1029/2020JA029078

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  45. Influence of Zonal Wind Velocity Variation on Equatorial Plasma Bubble Occurrences Over Southeast Asia

    Sarudin, I; Hamid, NSA; Abdullah, M; Buhari, SM; Shiokawa, K; Otsuka, Y; Hozumi, K; Jamjareegulgarn, P

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 126 ( 5 )   2021.5

  46. Multi-Wavelength Imaging Observations of STEVE at Athabasca, Canada

    Yadav, S; Shiokawa, K; Otsuka, Y; Connors, M; St Maurice, JP

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 126 ( 2 )   2021.2

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    DOI: 10.1029/2020JA028622

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  47. Medium-Scale Traveling Ionospheric Disturbances

    Otsuka, Y

    IONOSPHERE DYNAMICS AND APPLICATIONS   Vol. 260   page: 421 - 437   2021

  48. Equatorial Plasma Bubble Occurrence Under Propagation of MSTID and MLT Gravity Waves

    Takahashi, H; Wrasse, CM; Figueiredo, CAOB; Barros, D; Paulino, I; Essien, P; Abdu, MA; Otsuka, Y; Shiokawa, K

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 125 ( 9 )   2020.9

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    DOI: 10.1029/2019JA027566

    Web of Science

  49. Temporal and Spatial Variations of Total Electron Content Enhancements During a Geomagnetic Storm on 27 and 28 September 2017

    Shinbori, A; Otsuka, Y; Sori, T; Tsugawa, T; Nishioka, M

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 125 ( 7 )   2020.7

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    DOI: 10.1029/2019JA026873

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  50. Equatorial Plasma Bubble Zonal Drift Velocity Variations in Response to Season, Local Time, and Solar Activity across Southeast Asia

    Sarudin, I; Hamid, NSA; Abdullah, M; Buhari, SM; Shiokawa, K; Otsuka, Y; Yatini, CY

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 125 ( 3 )   2020.3

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    DOI: 10.1029/2019JA027521

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  51. Wavenumber Spectra of Atmospheric Gravity Waves and Medium-Scale Traveling Ionospheric Disturbances Based on More Than 10-Year Airglow Images in Japan, Russia, and Canada

    Satoshi Tsuchiya, Kazuo Shiokawa, Yuichi Otsuka, Takuji Nakamura, Mamoru Yamamoto, Martin Connors, Ian Schofield, Boris Shevtsov, Igor Poddelsky

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 125 ( 3 )   2020.3

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

    We have studied atmospheric gravity waves (AGWs) and nighttime medium-scale traveling ionospheric disturbances (MSTIDs) by applying three-dimensional spectral analysis technique to 557.7- and 630.0-nm airglow images at Shigaraki (SGK) (35 degrees N, 136 degrees E, 1999-2017) and Rikubetsu (RIK) (44 degrees N, 144 degrees E, 1999-2017), Japan, Athabasca (ATH), Canada, (55 degrees N, 247 degrees E, 2005-2017), and Magadan (MGD), Russia (60 degrees N, 151 degrees E, 2008-2017), focusing on their horizontal wavenumber spectra. For the AGWs in 557.7-nm images, the power spectra in summer are stronger than in other seasons, probably due to stronger tropospheric convection. The highest energy content of the waves are mostly at wavelengths between 20 and 300 km at MGD, ATH, and RIK, while it is above 200 km at SGK. The largest power spectral density is obtained at RIK at wavelengths of 30-100 km and then ATH. The slopes of the horizontal wavenumber spectra varies from -2.77 to -3.22. From the MSTIDs in 630.0-nm images, the power spectra in summer at RIK and SGK are stronger than those in other seasons regardless of solar activity. The power spectra in solar quiet time are stronger than those in solar active time at all four stations. These features can be explained by the Perkins instability with coupling between sporadic E and F layers. The spectral slope decreases with increasing latitudes. Weak positive correlations were obtained between the daily wave power of AGWs in 557.7-nm images and MSTIDs in 630.0-nm images, suggesting that the MSTIDs in the thermosphere may be partially generated by the AGWs from the mesopause region.Plain Language Summary In this paper we study atmospheric gravity waves (AGWs) and nighttime medium-scale traveling ionospheric disturbances (MSTIDs) observed at four stations in Japan, Canada, and Russia, in 557.7- and 630.0-nm airglow images over more than 10 years. The 557.7-nm airglow has an emission layer at altitudes of 90-100 km (mesopause region). The waves seen in the 557.7-nm airglow images mainly indicates AGWs. The 630.0-nm airglow has an emission layer at altitudes of 200-300 km (bottomside ionosphere). The waves seen in the 630.0-nm airglow images mainly indicates MSTIDs in the ionosphere. The AGWs in the mesopause region are the main driver of global atmospheric circulation in the middle atmosphere. The MSTIDs in the bottomside ionosphere are one of the causes of the satellite positioning error. We show typical energy content, propagation direction, and wavelengths of these waves at these two altitudes and discuss possible reason of the observed characteristics. These results contribute to our understanding of generation and propagation of AGWs and MSTIDs in the upper atmosphere.

    DOI: 10.1029/2019JA026807

    Web of Science

  52. Multievent Analysis of Oscillatory Motion of Medium-Scale Traveling Ionospheric Disturbances Observed by a 630-nm Airglow Imager Over Tromso

    Yadav, S; Shiokawa, K; Oyama, S; Otsuka, Y

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 125 ( 3 )   2020.3

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    DOI: 10.1029/2019JA027598

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  53. Characteristics of GNSS Total Electron Content Enhancements Over the Midlatitudes During a Geomagnetic Storm on 7 and 8 November 2004

    Sori, T; Shinbori, A; Otsuka, Y; Tsugawa, T; Nishioka, M

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 124 ( 12 ) page: 10376 - 10394   2019.12

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    DOI: 10.1029/2019JA026713

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  54. Adjuvant therapy with nivolumab versus ipilimumab after complete resection of stage III/IV melanoma: Japanese subgroup analysis from the phase 3 CheckMate 238 study

    Yokota, K; Uchi, H; Uhara, H; Yoshikawa, S; Takenouchi, T; Inozume, T; Ozawa, K; Ihn, H; Fujisawa, Y; Qureshi, A; de Pril, V; Otsuka, Y; Weber, J; Yamazaki, N

    JOURNAL OF DERMATOLOGY   Vol. 46 ( 12 ) page: 1197 - 1201   2019.12

  55. IpsDst of Dst Storms Applied to Ionosphere-Thermosphere Storms and Low-Latitude Aurora

    Balan, N; Zhang, QH; Shiokawa, K; Skoug, R; Xing, ZY; Ram, ST; Otsuka, Y

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 124 ( 11 ) page: 9552 - 9565   2019.11

  56. Statistical Study of Auroral/Resonant-Scattering 427.8-nm Emission Observed at Subauroral Latitudes Over 14 Years

    Shiokawa, K; Otsuka, Y; Connors, M

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 124 ( 11 ) page: 9293 - 9301   2019.11

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    DOI: 10.1029/2019JA026704

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  57. Japanese Surveillance of Neuroendovascular Therapy in JR-NET - Part II. Japanese Registry of NeuroEndovascular Treatment 3. Main Report

    Sakai, N; Uchida, K; Iihara, K; Satow, T; Ezura, M; Hyodo, A; Miyachi, S; Miyamoto, S; Nagai, Y; Nishimura, K; Toyoda, K; Yoshimura, S; Imamura, H; Sakai, C; Matsumaru, Y; Sakai, N; Iihara, K; Satow, T; Ezura, M; Hyodo, A; Miyachi, S; Miyamoto, S; Nagai, Y; Nishimura, K; Toyoda, K; Fujinaka, T; Higashi, T; Hirohata, M; Ishii, A; Imamura, H; Ito, Y; Kuwayama, N; Oishi, H; Matsumaru, Y; Matsumoto, Y; Nakahara, I; Sakai, C; Sugiu, K; Terada, T; Yoshimura, S; Sakai, N; Adachi, H; Ueno, Y; Yamagami, H; Imamura, H; Kunieda, T; Koyanagi, M; Kuramoto, Y; Todo, K; Ishikawa, T; Shigematsu, T; Yamamoto, S; Sato, S; Asai, K; Arimura, K; Tani, S; Mineharu, Y; Narumi, O; Ishii, A; Sakai, C; Ikeda, H; Kono, T; Matsumoto, Y; Kondo, R; Furui, E; Suzuki, I; Takahashi, T; Akiyama, T; Endo, H; Sato, K; Kageyama, Y; Ssawa, S; Niizuma, K; Yazawa, Y; Itabashi, R; Ezura, M; Kimura, N; Tsuboi, K; Sato, K; Nishimura, S; Sato, K; Osawa, S; Suzuki, I; Sugiu, K; Terai, Y; Tokunaga, K; Katsumata, A; Kusaka, N; Nishida, A; Kawada, S; Watanabe, K; Hishikawa, T; Hirashita, K; Itami, H; Ota, S; Sekihara, Y; Shimizu, N; Maeda, K; Matsumaru, Y; Izumoto, H; Tsuruta, W; Nakane, Y; Okumura, H; Hayakawa, M; Hirota, Y; Sato, M; Kamiya, Y; Watanabe, A; Amano, T; Aoki, M; Hyuga, T; Watanabe, D; Mori, K; Seida, M; Osanai, T; Hirohata, M; Takeuchi, M; Tsutsumi, M; Nii, K; Eto, H; Kazekawa, K; Aikawa, H; Onizuka, M; Yoshida, H; Sakamoto, K; Mizokami, T; Oishi, H; Iko, M; Nakai, K; Kin, S; Nonaka, T; Yonemasu, Y; Takahashi, A; Onda, T; Kogure, S; Ueda, R; Shimizu, T; Nomura, T; Yamamura, A; Hayashi, S; Nakahara, I; Nakamura, M; Furuichi, S; Iwamuro, Y; Ohta, T; Toyota, S; Furui, E; Watanabe, Y; Matsumoto, S; Ishibashi, R; Urabe, Y; Gomi, M; Fukushima, Y; Saka, M; Nakazawa, T; Matsuda, Y; Hyodo, A; Hori, Y; Shirato, M; Suzuki, K; Suzuki, S; Takigawa, T; Shimizu, N; Tanaka, Y; Takano, I; Satow, T; Iihara, K; Okazaki, T; Morita, K; Yamagami, H; Ito, K; Sugata, S; Hayakawa, M; Matsushige, T; Ishii, D; Ishikawa, T; 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Makiuchi, T; Hashimoto, K; Asai, T; Hyogo, T; Kataoka, T; Ogino, T; Imai, K; Takegami, T; Hamanaka, M; Yamada, T; Ikeda, N; Okamoto, T; Kano, T; Toi, H; Matsubara, S; Murao, K; Nakazawa, K; Takahashi, A; Nakajima, N; Iwamuro, Y; Ohta, T; Aketa, S; Takabatake, N; Kunieda, T; Fukuda, H; Takemoto, K; Miyake, K; Morioka, J; Yukawa, H; Akiyama, T; Konno, H; Nakahara, K; Nishio, M; Hiramatsu, H; Shibanai, K; Nishio, A; Yamauchi, S; Kondo, K; Hayasaki, K; Mitsuhashi, Y; Kawakami, T; Yamauchi, S; Mizuguchi, A; Demura, K; Satoh, K; Hanaoka, M; Manabe, S; Tamura, T; Kinouchi, T; Tsurukiri, J; Horie, N; Morikawa, M; Hayashi, K; Higashi, T; Morofuji, Y; Nakai, Y; Irie, S; Tsuruta, W; Takigawa, T; Matsumaru, Y; Sato, M; Ikeda, G; Nakazawa, K; Ayabe, J; Akaji, K; Iwai, T; Naito, I; Dembo, T; Ueda, R; Ishimori, H; Kimura, H; Suzuki, K; Fujinaka, T; Kajikawa, R; Nishida, T; Ohara, N; Sakaguchi, M; Nakamura, H; Tone, O; Shigeta, K; Yatsushige, H; Mohri, M; Uchiyama, N; Hamada, J; Misaki, K; Toma, N; Shibata, M; 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Ogata, A; Takase, Y; Takada, T; Otsuka, Y; Ueda, T; Nogoshi, S; Takeuchi, H; Arakawa, H; Sugawara, T; Ozaki, S; Ichikawa, T; Okamoto, T; Munemitsu, T; Saiki, M; Ueba, Y; Yoshida, Y; Kominami, S; Suzuki, M; Watanabe, A; Kikuchi, O; Wada, H; Sakurai, J; Takata, H; Shiraga, S; Terada, T; Morishima, H; Koyama, S; Wakui, D; Onodera, H; Ooshima, K; Tsuji, A; Tanaka, T; Higuchi, K; Uchida, K; Shirakawa, M; Maeno, K; Tanaka, Y; Kojima, A; Suzuki, M; Watanabe, A; Srivatanakul, K; Tanoue, S; Okahara, M; Kashiwagi, J; Kiyosue, H; Sagara, Y; Shimada, R; Yoshioka, T; Sambongi, Y; Negoro, M; Miyasaki, A; Hamasaki, O; Takabatake, Y; Handa, A; Higuchi, K; Hamada, K; Ichihashi, T; Fukazawa, S; Nonaka, Y; Shojima, M; Kato, T; Kaku, Y; Sakai, H; Fukui, K; Mina-Mide, H; Suyama, T; Kobayashi, J; Ohara, N; Takeda, N; Ota, S; Arai, M; Uemura, A; Fukui, N; Fujimura, N; Uchiyama, N; Mohri, M; Higashi, R; Misaki, K; Sugiura, Y; Watanabe, K; Yamazaki, S; Munemitsu, T; Murai, N; Miyakoshi, A; Yamao, Y; Yoshida, Y; Yamaura, I; Minami, H; Matsumoto, H; Masuda, A; Hara, Y; Iihara, K; Suyama, Y; Yamasaki, H; Ishii, Y; Wakabayashi, S; Tanoue, S; Kubo, T; Tsutsumi, M; Shimada, A; Oura, Y; Fujita, A; Kimoto, A; Abe, H; Takemoto, H; Okada, H; Yoshimura, R; Obata, Y; Yoshino, Y; Kawano, Y; Matsumoto, K; Mutoh, T; Dehara, M; Kubota, T; Kawarabuki, K; Shirato, M; Asano, T; Sagara, Y; Shibuya, T; Suma, T; Amari, K; Oishi, H; Yamamoto, M; Iihoshi, S; Miyata, K; Fukasaku, K; Tamaki, R; Nishio, M; Kojima, T; Maekawa, H; Yanaka, M; Okawa, M; Iwaasa, M; Goda, M; Kubo, T; Hirai, M; Yamada, M; Yoshino, Y; Nemoto, S; Kuwayama, N; Yamamoto, H; Akioka, N; Nakayama, H; Nakabayashi, K

    NEUROLOGIA MEDICO-CHIRURGICA   Vol. 59 ( 3 ) page: 106 - 115   2019.3

  58. Spatiotemporal development of pulsating auroral patch associated with discrete chorus elements: Arase and PWING observations

    Ozaki M., Shiokawa K., Miyoshi Y., Hosokawa K., Oyama S., Yagitani S., Kasahara Y., Kasaba Y., Matsuda S., Kataoka R., Ebihara Y., Ogawa Y., Otsuka Y., Kurita S., Moore R. C., Tanaka Y. -M., Nose M., Nagatsuma T., Connors M., Nishitani N., Hikishima M., Kumamoto A., Tsuchiya F., Kadokura A., Nishiyama T., Inoue T., Imamura K., Matsuoka A., Shinohara I.

    2019 URSI ASIA-PACIFIC RADIO SCIENCE CONFERENCE (AP-RASC)     2019

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  59. Spatial and Temporal Characteristics of Ionospheric Total Electron Content over Indian Equatorial and Low-Latitude GNSS Stations

    Sivavaraprasad G., Otsuka Yuichi, Tripathi Nitin Kumar, Chowdhary V. Rajesh, Ratnam D. Venkata, Khan Mohammed Afzal

    2018 CONFERENCE ON SIGNAL PROCESSING AND COMMUNICATION ENGINEERING SYSTEMS (SPACES)     page: 105 - 108   2018

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  60. Observations of Ultrawideband Signals in GPS TEC Variations over Europe during Solar Eclipse

    Panasenko Sergii V., Chernogor Leonid F., Lazorenko Oleg V., Otsuka Yuichi, van de Kamp Max

    2018 9TH INTERNATIONAL CONFERENCE ON ULTRAWIDEBAND AND ULTRASHORT IMPULSE SIGNALS (UWBUSIS)     page: 115 - 118   2018

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  61. Temporal and spatial variations of mid-latitude ionospheric trough during a geomagnetic storm based on global GNSS-TEC and Arase satellite observations

    Shinbori Atsuki, Otsuka Yuichi, Tsugawa Takuya, Nishioka Michi, Kumamoto Atsushi, Tsuchia Fuminori, Matsuda Shoya, Kasahara Yoshiya

    2018 2ND URSI ATLANTIC RADIO SCIENCE MEETING (AT-RASC)     2018

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  62. STATISTICAL ANALYSIS OF THE OCCURRENCES OF MSTIDs OBSERVED BY ALL-SKY IMAGER IN LOW MAGNETIC LATITUDE

    Ednofri, Wu Falin, Otsuka Yuichi, Ishii Mamoru, Marlia Dessi, Zhao Yan

    2017 IEEE INTERNATIONAL GEOSCIENCE AND REMOTE SENSING SYMPOSIUM (IGARSS)     page: 4425 - 4428   2017

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  63. On the effect of thermospheric neutral winds on post-midnight field-aligned irregularities at low latitudes

    Dao Tam, Otsuka Yuichi, Shiokawa Kazuo, Nishioka Michi, Yamamoto Mamoru, Buhari Suhaila M., Abdullah Mardina, Husin Asnawi

    2017 XXXIIND GENERAL ASSEMBLY AND SCIENTIFIC SYMPOSIUM OF THE INTERNATIONAL UNION OF RADIO SCIENCE (URSI GASS)     2017

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  64. Early Phase Arterial Reaction Following Drug-Eluting and Bare-Metal Stent Implantation in Patients With ST-Segment Elevation Myocardial Infarction Optical Coherence Tomography Assessment at 2 Weeks

    Nishio, R; Shinke, T; Morino, Y; Tanabe, K; Furuya, J; Takizawa, K; Ako, J; Kozuma, K; Hibi, K; Ishii, H; Hirohata, A; Otsuka, Y; Otake, H; Takaya, T; Hirata, K

    INTERNATIONAL HEART JOURNAL   Vol. 56 ( 4 ) page: 389 - 394   2015.7

  65. Micro-source development for XMASS experiment

    Kim, NY; Abe, K; Hieda, K; Hiraid, K; Hirano, S; Kishimoto, Y; Kobayashi, K; Moriyama, S; Nakagawa, K; Nakahata, M; Nishiie, H; Ogawa, H; Oka, N; Sekiya, H; Shinozaki, A; Suzuki, Y; Takeda, A; Takachio, O; Ueshima, K; Umemoto, D; Yamashita, M; Yang, BS; Tasaka, S; Liu, J; Martens, K; Hosokawa, K; Miuchi, K; Murata, A; Onishi, Y; Otsuka, Y; Takeuchi, Y; Kim, YH; Lee, KB; Lee, MK; Lee, JS; Fukuda, Y; Itow, Y; Nishitani, Y; Masuda, K; Takiya, H; Uchida, H; Kim, YD; Kusaba, F; Motoki, D; Nishijima, K; Fujii, K; Murayama, I; Nakamura, S

    NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT   Vol. 784   page: 499 - 503   2015.6

  66. Climatology of Equatorial Plasma Bubble Observed by MyRTKnet over the Years 2008-2013

    Buhari S. M., Abdullah M., Yokoyama T., Hasbi A. M., Otsuka Y., Nishioka M., Bahari S. A., Tsugawa T.

    2015 INTERNATIONAL CONFERENCE ON SPACE SCIENCE AND COMMUNICATION (ICONSPACE)     page: 101 - 105   2015

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  67. Direct observations of blob deformation during a substorm

    Ishida T., Ogawa Y., Kadokura A., Hosokawa K., Otsuka Y.

    ANNALES GEOPHYSICAE   Vol. 33 ( 5 ) page: 525 - 530   2015

  68. GAST-D flight experiment results with disturbed and quiet ionospheric conditions

    Saito Susumu, Yoshihara Takayuki, Kezuka Atsushi, Saitoh Shinji, Fukushima Sonosuke, Otsuka Yuichi

    PROCEEDINGS OF THE 28TH INTERNATIONAL TECHNICAL MEETING OF THE SATELLITE DIVISION OF THE INSTITUTE OF NAVIGATION (ION GNSS+ 2015)     page: 1494 - 1499   2015

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  69. Search for Bosonic Superweakly Interacting Massive Dark Matter Particles with the XMASS-I Detector

    Abe, K; Hieda, K; Hiraide, K; Hirano, S; Kishimoto, Y; Ichimura, K; Kobayashi, K; Moriyama, S; Nakagawa, K; Nakahata, M; Ogawa, H; Oka, N; Sekiya, H; Shinozaki, A; Suzuki, Y; Takeda, A; Takachio, O; Umemoto, D; Yamashita, M; Yang, BS; Tasaka, S; Liu, J; Martens, K; Hosokawa, K; Miuchi, K; Murata, A; Onishi, Y; Otsuka, Y; Takeuchi, Y; Kim, YH; Lee, KB; Lee, MK; Lee, JS; Fukuda, Y; Itow, Y; Masuda, K; Takiya, H; Uchida, H; Kim, NY; Kim, YD; Kusaba, F; Nishijima, K; Fujii, K; Murayama, I; Nakamura, S

    PHYSICAL REVIEW LETTERS   Vol. 113 ( 12 )   2014.9

  70. Search for inelastic WIMP nucleus scattering on Xe-129 in data from the XMASS-I experiment

    Uchida H., Abe K., Hieda K., Hiraide K., Hirano S., Ichimura K., Kishimoto Y., Kobayashi K., Moriyama S., Nakagawa K., Nakahata M., Ogawa H., Oka N., Sekiya H., Shinozaki A., Suzuki Y., Takeda A., Takachio O., Umemoto D., Yamashita M., Yang B. S., Tasaka S., Liu J., Martens K., Hosokawa K., Miuchi K., Murata A., Onishi Y., Otsuka Y., Takeuchi Y., Kim Y. H., Lee K. B., Lee M. K., Lee J. S., Fukuda Y., Itow Y., Masuda K., Nishitani Y., Takiya H., Kim N. Y., Kim Y. D., Kusaba F., Nishijima K., Fujii K., Murayama I., Nakamura S.

    PROGRESS OF THEORETICAL AND EXPERIMENTAL PHYSICS   Vol. 2014 ( 6 )   2014.6

  71. The observation of equatorial plasma bubble using all sky imager and GPS TEC measurement

    Buhari Suhaila M., Abdullah Mardina, Hasbi Alina Marie, Otsuka Yuichi, Bahari Siti Aminah, Mokhtar Mohd Hezri, Nishioka Michi, Tsugawa Takuya

    2014 XXXITH URSI GENERAL ASSEMBLY AND SCIENTIFIC SYMPOSIUM (URSI GASS)     2014

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  72. Two-dimensional structure of equatorial plasma bubble observed using GPS networks in South East Asia region

    Buhari Suhaila M., Abdullah Mardina, Hasbi Alina Marie, Otsuka Yuichi

    2014 INTERNATIONAL CONFERENCE ON ELECTRONICS, INFORMATION AND COMMUNICATIONS (ICEIC)     2014

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  73. Typhoon-induced concentric airglow structures in the mesopause region

    Suzuki S., Vadas S. L., Shiokawa K., Otsuka Y., Kawamura S., Murayama Y.

    GEOPHYSICAL RESEARCH LETTERS   Vol. 40 ( 22 ) page: 5983 - 5987   2013.11

  74. XMASS detector

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    NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT   Vol. 716   page: 78 - 85   2013.7

  75. Light WIMP search in XMASS

    Abe, K; Hieda, K; Hiraide, K; Hirano, S; Kishimoto, Y; Kobayashi, K; Moriyama, S; Nakagawa, K; Nakahata, M; Ogawa, H; Oka, N; Sekiya, H; Shinozaki, A; Suzuki, Y; Takeda, A; Takachio, O; Ueshima, K; Umemoto, D; Yamashita, M; Yang, BS; Tasaka, S; Liu, J; Martens, K; Hosokawa, K; Miuchi, K; Murata, A; Onishi, Y; Otsuka, Y; Takeuchi, Y; Kim, YH; Lee, KB; Lee, MK; Lee, JS; Fukuda, Y; Itow, Y; Masuda, K; Nishitani, Y; Takiya, H; Uchida, H; Kim, NY; Kim, YD; Kusaba, F; Motoki, D; Nishijima, K; Fujii, K; Murayama, I; Nakamura, S

    PHYSICS LETTERS B   Vol. 719 ( 1-3 ) page: 78 - 82   2013.2

  76. Label-free observation of tissues by high-speed stimulated Raman spectral microscopy and independent component analysis

    Ozeki, Y; Otsuka, Y; Sato, S; Hashimoto, H; Umemura, W; Sumimura, K; Nishizawa, N; Fukui, K; Itoh, K

    MULTIPHOTON MICROSCOPY IN THE BIOMEDICAL SCIENCES XIII   Vol. 8588   2013

  77. Small-scale ionospheric delay variation associated with plasma bubbles studied with GNSS and optical measurements and its impact on GBAS

    Saito S., Yoshihara T., Otsuka Y.

    PROCEEDINGS OF THE 26TH INTERNATIONAL TECHNICAL MEETING OF THE SATELLITE DIVISION OF THE INSTITUTE OF NAVIGATION (ION GNSS 2013)     page: 1869 - 1874   2013

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  78. High-speed molecular spectral imaging of tissue with stimulated Raman scattering

    Ozeki, Y; Umemura, W; Otsuka, Y; Satoh, S; Hashimoto, H; Sumimura, K; Nishizawa, N; Fukui, K; Itoh, K

    NATURE PHOTONICS   Vol. 6 ( 12 ) page: 844 - 850   2012.12

  79. A comparative study of equatorial daytime vertical E x B drift in the Indian and Indonesian sectors based on 150 km echoes

    Patra A. K., Chaitanya P. Pavan, Mizutani N., Otsuka Y., Yokoyama T., Yamamoto M.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 117   2012.11

  80. Observation of equatorial nighttime medium-scale traveling ionospheric disturbances in 630-nm airglow images over 7 years

    Fukushima D., Shiokawa K., Otsuka Y., Ogawa T.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 117   2012.10

  81. Motion of high-latitude nighttime medium-scale traveling ionospheric disturbances associated with auroral brightening

    Shiokawa K., Mori M., Otsuka Y., Oyama S., Nozawa S.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 117   2012.10

  82. Response of low-latitude ionosphere to medium-term changes of solar and geomagnetic activity

    Kutiev Ivan, Otsuka Yuichi, Pancheva Dora, Heelis Rod

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 117   2012.8

  83. Significance of C4d deposition in antibody-mediated rejection

    Takeda, A; Otsuka, Y; Horike, K; Inaguma, D; Hiramitsu, T; Yamamoto, T; Nanmoku, K; Goto, N; Watarai, Y; Uchida, K; Morozumi, K; Kobayashi, T

    CLINICAL TRANSPLANTATION   Vol. 26   page: 43 - 48   2012.7

  84. GPS total electron content variations associated with poleward moving Sun-aligned arcs

    Jayachandran P. T., Hosokawa K., Shiokawa K., Otsuka Y., Watson C., Mushini S. C., MacDougall J. W., Prikryl P., Chadwick R., Kelly T. D.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 117   2012.5

  85. Polarization of Pc1/EMIC waves and related proton auroras observed at subauroral latitudes

    Nomura R., Shiokawa K., Sakaguchi K., Otsuka Y., Connors M.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 117   2012.2

  86. Ionospheric and thermospheric storms at equatorial latitudes observed by CHAMP, ROCSAT, and DMSP

    Balan N., Liu J. Y., Otsuka Y., Ram S. Tulasi, Luehr H.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 117   2012.1

  87. On postmidnight low-latitude ionospheric irregularities during solar minimum: 2. C/NOFS observations and comparisons with the Equatorial Atmosphere Radar

    Yokoyama T., Pfaff R. F., Roddy P. A., Yamamoto M., Otsuka Y.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 116   2011.11

  88. New aspects of thermospheric and ionospheric storms revealed by CHAMP

    Balan N., Yamamoto M., Liu J. Y., Otsuka Y., Liu H., Luehr H.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 116   2011.7

  89. Decay of polar cap patch

    Hosokawa K., Moen J. I., Shiokawa K., Otsuka Y.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 116   2011.5

  90. Vertical connection from the tropospheric activities to the ionospheric longitudinal structure simulated by a new Earth's whole atmosphere-ionosphere coupled model

    Jin H., Miyoshi Y., Fujiwara H., Shinagawa H., Terada K., Terada N., Ishii M., Otsuka Y., Saito A.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 116   2011.1

  91. Dynamic temporal evolution of polar cap tongue of ionization during magnetic storm

    Hosokawa K., Tsugawa T., Shiokawa K., Otsuka Y., Nishitani N., Ogawa T., Hairston M. R.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 115   2010.12

  92. Midnight latitude-altitude distribution of 630 nm airglow in the Asian sector measured with FORMOSAT-2/ISUAL

    Adachi Toru, Yamaoka Masashi, Yamamoto Mamoru, Otsuka Yuichi, Liu Huixin, Hsiao Chun-Chieh, Chen Alfred B., Hsu Rue-Ron

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 115   2010.9

  93. Finite-Temperature Properties across the Charge Ordering Transition-Combined Bosonization, Renormalization Group, and Numerical Methods-

    Yoshioka, H; Tsuchiizu, M; Otsuka, Y; Seo, H

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 79 ( 9 )   2010.9

  94. Large-scale traveling ionospheric disturbance observed by superDARN Hokkaido HF radar and GPS networks on 15 December 2006

    Hayashi H., Nishitani N., Ogawa T., Otsuka Y., Tsugawa T., Hosokawa K., Saito A.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 115   2010.6

  95. A physical mechanism of positive ionospheric storms at low latitudes and midlatitudes

    Balan N., Shiokawa K., Otsuka Y., Kikuchi T., Lekshmi D. Vijaya, Kawamura S., Yamamoto M., Bailey G. J.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 115   2010.2

  96. Reorganization of polar cap patches through shears in the background plasma convection

    Hosokawa K., St-Maurice J. -P., Sofko G. J., Shiokawa K., Otsuka Y., Ogawa T.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 115   2010.1

  97. Spatial relationship of nighttime medium-scale traveling ionospheric disturbances and F region field-aligned irregularities observed with two spaced all-sky airglow imagers and the middle and upper atmosphere radar

    Otsuka Y., Shiokawa K., Ogawa T., Yokoyama T., Yamamoto M.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 114   2009.5

  98. Motion of polar cap patches: A statistical study with all-sky airglow imager at Resolute Bay, Canada

    Hosokawa K., Kashimoto T., Suzuki S., Shiokawa K., Otsuka Y., Ogawa T.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 114   2009.4

  99. Medium-scale traveling ionospheric disturbances observed with the SuperDARN Hokkaido radar, all-sky imager, and GPS network and their relation to concurrent sporadic E irregularities

    Ogawa T., Nishitani N., Otsuka Y., Shiokawa K., Tsugawa T., Hosokawa K.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 114   2009.3

  100. Super plasma fountain and equatorial ionization anomaly during penetration electric field

    Balan N., Shiokawa K., Otsuka Y., Watanabe S., Bailey G. J.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 114   2009.3

  101. Relationship between polar cap patches and field-aligned irregularities as observed with an all-sky airglow imager at Resolute Bay and the PolarDARN radar at Rankin Inlet

    Hosokawa K., Shiokawa K., Otsuka Y., Ogawa T., St-Maurice J. -P., Sofko G. J., Andre D. A.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 114   2009.3

  102. Three-dimensional simulation of the coupled Perkins and E-s-layer instabilities in the nighttime midlatitude ionosphere

    Yokoyama Tatsuhiro, Hysell David L., Otsuka Yuichi, Yamamoto Mamoru

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 114   2009.3

  103. Characteristics of equatorial gravity waves derived from mesospheric airglow imaging observations

    Suzuki S., Shiokawa K., Liu A. Z., Otsuka Y., Ogawa T., Nakamura T.

    ANNALES GEOPHYSICAE   Vol. 27 ( 4 ) page: 1625 - 1629   2009

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  104. Equatorial GPS ionospheric scintillations over Kototabang, Indonesia and their relation to atmospheric waves from below

    Ogawa Tadahiko, Miyoshi Yasunobu, Otsuka Yuichi, Nakamura Takuji, Shiokawa Kazuo

    EARTH PLANETS AND SPACE   Vol. 61 ( 4 ) page: 397 - 410   2009

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  105. Propagation characteristics of nighttime mesospheric and thermospheric waves observed by optical mesosphere thermosphere imagers at middle and low latitudes

    Shiokawa K., Otsuka Y., Ogawa T.

    EARTH PLANETS AND SPACE   Vol. 61 ( 4 ) page: 479 - 491   2009

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  106. Relative effects of electric field and neutral wind on positive ionospheric storms

    Balan N., Alleyne H., Otsuka Y., Lekshmi D. Vijaya, Fejer B. G., McCrea I.

    EARTH PLANETS AND SPACE   Vol. 61 ( 4 ) page: 439 - 445   2009

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  107. The Optical Mesosphere Thermosphere Imagers (OMTIs) for network measurements of aurora and airglow

    Shiokawa K., Hosokawa K., Sakaguchi K., Ieda A., Otsuka Y., Ogawa T., Connors M.

    FUTURE PERSPECTIVES OF SPACE PLASMA AND PARTICLE INSTRUMENTATION AND INTERNATIONAL COLLABORATIONS   Vol. 1144   page: 212 - +   2009

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  108. Zonal asymmetry of daytime 150-km echoes observed by Equatorial Atmosphere Radar in Indonesia

    Yokoyama T., Hysell D. L., Patra A. K., Otsuka Y., Yamamoto M.

    ANNALES GEOPHYSICAE   Vol. 27 ( 3 ) page: 967 - 974   2009

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  109. VHF radar observations of nighttime F-region field-aligned irregularities over Kototabang, Indonesia

    Otsuka Y., Ogawa T., Effendy

    EARTH PLANETS AND SPACE   Vol. 61 ( 4 ) page: 431 - 437   2009

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  110. Prospective multicenter trial comparing repeated immunosuppressive therapy with stem-cell transplantation from an alternative donor as second-line treatment for children with severe and very severe aplastic anemia

    Kosaka, Y; Yagasaki, H; Sano, K; Kobayashi, R; Ayukawa, H; Kaneko, T; Yabe, H; Tsuchida, M; Mugishima, H; Hara, A; Morimoto, A; Otsuka, Y; Ohga, S; Bessho, F; Nakahata, T; Tsukimoto, I; Kojima, S

    BLOOD   Vol. 111 ( 3 ) page: 1054 - 1059   2008.2

  111. Quantum dot sensitized solar cells

    Tachibana, Y; Akiyama, HY; Umekita, K; Otsuka, Y; Torimoto, T; Kuwabata, S

    2008 2ND IEEE INTERNATIONAL NANOELECTRONICS CONFERENCE, VOLS 1-3     page: 160 - +   2008

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  112. Efficacy of STI571 for a patient with metastatic gastrointestinal stromal tumor

    Sasaki, Y; Niwa, Y; Ando, N; Otsuka, Y; Ohmiya, N; Hirooka, Y; Itoh, A; Furuta, S; Goto, H

    HEPATO-GASTROENTEROLOGY   Vol. 52 ( 66 ) page: 1764 - 1767   2005.11

  113. Inhibition of platelet adherence to mononuclear cells by alpha-tocopherol - Role of P-selectin

    Murohara T, Ikeda H, Otsuka Y, Aoki M, Haramaki N, Katoh A, Takajo Y, Imaizumi T

    CIRCULATION   Vol. 110 ( 2 ) page: 141 - 148   2004.7

  114. Usefulness of magnifying endoscopy in the diagnosis of early gastric cancer

    Otsuka, Y; Niwa, Y; Ohmiya, N; Ando, N; Ohashi, A; Hirooka, Y; Goto, H

    ENDOSCOPY   Vol. 36 ( 2 ) page: 165 - 169   2004.2

  115. Novel gene encoding a Ca2+-binding protein and under hexokinase-dependent sugar regulation

    Otsuki S, Ikeda A, Sunako T, Muto S, Yazaki J, Nakamura K, Fujii F, Shimbo K, Otsuka Y, Yamamoto K, Sakata K, Sasaki T, Kishimoto N, Kikuchi S, Yamaguchi J

    BIOSCIENCE BIOTECHNOLOGY AND BIOCHEMISTRY   Vol. 67 ( 2 ) page: 347 - 353   2003.2

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  116. Vitamin E inhibits lysophosphatidylcholine-induced endothelial dysfunction and platelet activation

    Murohara, T; Ikeda, H; Katoh, A; Takajo, Y; Otsuka, Y; Haramaki, N; Imaizumi, T

    ANTIOXIDANTS & REDOX SIGNALING   Vol. 4 ( 5 ) page: 791 - 798   2002.10

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  117. Platelet GPIIb/IIIa is activated and platelet-leukocyte coaggregates formed in vivo during hemodialysis

    Kawabata, K; Nakai, S; Miwa, M; Sugiura, T; Otsuka, Y; Shinzato, T; Hiki, Y; Tomimatsu, I; Ushida, Y; Hosono, F; Maeda, K

    NEPHRON   Vol. 90 ( 4 ) page: 391 - 400   2002.4

  118. Changes in Mac-1 and CD14 expression on monocytes and serum soluble CD14 level during push/pull hemodiafiltration

    Kawabata, K; Nakai, S; Miwa, M; Sugiura, T; Otsuka, Y; Shinzato, T; Hiki, Y; Tomimatsu, I; Ushida, Y; Hosono, F; Maeda, K

    NEPHRON   Vol. 90 ( 3 ) page: 273 - 281   2002.3

  119. Numerical simulation of gas flow through sand core

    Maeda, Y; Nomura, H; Otsuka, Y; Tomishige, H; Mori, Y

    INTERNATIONAL JOURNAL OF CAST METALS RESEARCH   Vol. 15 ( 4 ) page: 441 - 444   2002

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  120. Imaging observations of midlatitude ionospheric disturbances during the geomagnetic storm of February 12, 2000

    Sahai Y, Shiokawa K, Otsuka Y, Ihara C, Ogawa T, Igarashi K, Miyazaki S, Saito A

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 106 ( A11 ) page: 24481 - 24492   2001.11

  121. CD31 expression on leukocytes is downregulated in vivo during hemodialysis

    Kawabata, K; Nakai, S; Miwa, M; Sugiura, T; Otsuka, Y; Shinzato, T; Hiki, N; Tomimatsu, I; Ushida, Y; Hosono, F; Maeda, K

    NEPHRON   Vol. 89 ( 2 ) page: 153 - 160   2001.10

  122. The assessment of vertical and lateral invasion of early gastric cancer by magnifying endoscopy

    Otsuka, Y; Goto, H; Niwa, Y; Ohmiya, N; Kamiya, K; Sakata, T; Ando, N; Ito, B; Sasaki, Y; Hayakawa, T

    GASTROINTESTINAL ENDOSCOPY   Vol. 53 ( 5 ) page: AB212 - AB212   2001.4

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  123. The assessment of vertical and lateral invasion of early gastric cancer by magnifying endoscopy

    Otsuka Y, Goto H, Niwa Y, Ohmiya N, Kamiya K, Sakata T, Ando N, Ito B, Sasaki Y, Hayakawa T

    GASTROINTESTINAL ENDOSCOPY   Vol. 53 ( 5 ) page: AB212 - AB212   2001.4

  124. Diagnosis of gastrointestinal stromal tumor using endscopic ultrasonography-guided fine needle aspiration biopsy.

    Ando, N; Goto, H; Niwa, Y; Hirooka, Y; Koijima, S; Hosoi, T; Shinkai, M; Sakata, T; Otsuka, Y; Hayakawa, T

    GASTROINTESTINAL ENDOSCOPY   Vol. 51 ( 4 ) page: AB162 - AB162   2000.4

  125. Statistical Analysis of the Horizontal Phase Velocity Distribution of Atmospheric Gravity Waves and Medium-Scale Traveling Ionospheric Disturbances in Airglow Images Over Sata (31.0°N, 130.7°E), Japan Reviewed

    Takuma Tsuboi, Kazuo Shiokawa, Yuichi Otsuka, Hatsuki Fujinami, Takuji Nakamura

    Journal of Geophysical Research: Space Physics   Vol. 128 ( 12 )   2023.12

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

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

  126. Machine learning approach for ionospheric scintillation prediction on ROTI parameter over the African region during solar cycle 24 Reviewed

    Stephen Tete, Yuichi Otsuka, Waheed K. Zahra, Ayman Mahrous

    Advances in Space Research     2023.12

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

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

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

  127. New aspects of the upper atmospheric disturbances caused by the explosive eruption of the 2022 Hunga Tonga–Hunga Ha’apai volcano Invited Reviewed

    A. Shinbori, Y. Otsuka, T. Sori, M. Nishioka, S. Perwitasari, T. T. Tsuda, N. Nishitani, A. Kumamoto, F. Tsuchiya, S. Matsuda, Y. Kasahara, A. Matsuoka, S. Nakamura, Y. Miyoshi, I. Shinohara

    Earth Planets Space   Vol. 75 ( 1 ) page: 175   2023.11

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

    DOI: 10.1186/s40623-023-01930-4

    Web of Science

  128. Periodic oscillations of Doppler frequency excited by the traveling ionospheric disturbances associated with the Tonga eruption in 2022 Reviewed

    Hiroyuki Nakata, Keisuke Hosokawa, Susumu Saito, Yuichi Otsuka, Ichoro Tomizawa

    Earth, Planets and Space   Vol. 75 ( 1 )   2023.10

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    Abstract

    The explosive eruption of the Hunga Tonga-Hunga Ha’apai volcano on 15 January 2022 generated atmospheric waves traveling around the Earth, which caused ionospheric disturbances on various spatio-temporal scales. A HF Doppler sounding system in Japan detected characteristic ionospheric disturbances showing periodic oscillations in the Doppler frequency with a period of ~ 4 min. In this study, such periodic oscillations were examined by comparing Doppler frequency data with Total Electron Content data obtained by Global Navigation Satellite System. The observed periodic oscillations in the Doppler frequency were characterized by a sawtooth or S-letter shaped variation, implying the passage of the traveling ionospheric disturbances through the reflection points of the HF Doppler sounding system. It was also found that the periodic oscillations occurred prior to the arrival of the tropospheric Lamb wave excited by the Tonga eruption. From the total electron content data, the traveling ionospheric disturbances causing the periodic oscillations were excited by the tropospheric Lamb waves at the conjugate point in the southern hemisphere, namely, the electric field perturbations due to the Lamb waves in the southern hemisphere mapped onto the sensing area of the HF Doppler sounding system in the northern hemisphere along the magnetic field lines. The periodic oscillations were observed only in the path between Chofu transmitter and Sarobetsu receiver, whose the radio propagation path is almost aligned in the north–south direction. This suggests that the traveling ionospheric disturbance has a structure elongating in the meridional direction. The variation in the Doppler frequency was reproduced by using a simple model of the propagation of the traveling ionospheric disturbances and the resultant motion of the reflection point. As a result, the vertical motion of the reflection point associated with the periodic oscillations was estimated to be about 1 km. It is known that 4-min period variations are sometimes observed in association with earthquakes, which is due to resonances of acoustic mode waves propagating between the ground and the lower ionosphere. Therefore, a similar resonance structure in the southern hemisphere is a plausible source of the traveling ionospheric disturbances detected in the northern hemisphere.

    Graphical Abstract

    DOI: 10.1186/s40623-023-01914-4

    Web of Science

    Other Link: https://link.springer.com/article/10.1186/s40623-023-01914-4/fulltext.html

  129. Statistical Analysis of the Horizontal Phase Velocity Distribution of Atmospheric Gravity Waves and Medium-Scale Traveling Ionospheric Disturbances in Airglow Images Over Darwin (12.4°S, 131.0°E) Reviewed International coauthorship

    Takuma Tsuboi, Kazuo Shiokawa, Yuichi Otsuka, Hatsuki Fujinami, Takuji Nakamura, David Neudegg

    Journal of Geophysical Research: Space Physics   Vol. 128 ( 8 )   2023.8

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

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

    Other Link: https://doi.org/10.1029/2022JA030769

  130. Spatio-Temporal Characteristics of IPDP-Type EMIC Waves on April 19, 2017: Implications for Loss of Relativistic Electrons in the Outer Belt Reviewed

    Asuka Hirai, Fuminori Tsuchiya, Takahiro Obara, Yuto Katoh, Yoshizumi Miyoshi, Kazuo Shiokawa, Yasumasa Kasaba, Hiroaki Misawa, Chae Woo Jun, Satoshi Kurita, Martin G. Connors, Aaron T. Hendry, Atsuki Shinbori, Yuichi Otsuka, Takuya Tsugawa, Michi Nishioka, Septi Perwitasari, Jerry W. Manweiler

    Journal of Geophysical Research: Space Physics   Vol. 128 ( 8 )   2023.8

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    To understand the mechanism of the increased frequency of intervals of pulsations of diminishing periods (IPDPs), we analyzed IPDP-type electromagnetic ion cyclotron (EMIC) waves that occurred on 19 April 2017, using ground and satellite observations. Observations by low-altitude satellites and ground-based magnetometers indicate that the increased IPDP frequency is caused by an inward (i.e., Earthward) shift of the EMIC wave source region. The EMIC wave source region moves inward along the mid-latitude trough, which we used as a proxy for the plasmapause location. A statistical analysis shows that increases in the IPDP frequency showed a positive correlation with polar cap potentials. These results suggest an enhanced convection electric field causes an inward shift of the source region. The inward shift of the source region allows EMIC waves to scatter relativistic electrons over a wide range of radial distances during the IPDP event. This mechanism suggests that IPDP-type EMIC waves are more likely to scatter relativistic electrons than other EMIC waves. We also show that the decreased phase-space density of relativistic electrons in the outer radiation belt is consistent with the extent of the source region and the resonant energy of EMIC waves, implying a possible contribution of EMIC waves to outer radiation belt loss during the main phase of geomagnetic storms.

    DOI: 10.1029/2023JA031479

    Web of Science

    Scopus

  131. Generation of equatorial plasma bubble after the 2022 Tonga volcanic eruption Reviewed

    A. Shinbori, T. Sori, Y. Otsuka, M. Nishioka, S. Perwitasari, T. T. Tsuda, A. Kumamoto, F. Tsuchiya, S. Matsuda, Y. Kasahara, A. Matsuoka, S. Nakamura, Y. Miyoshi, I. Shinohara

    Sci. Rep.   Vol. 13 ( 1 ) page: 6450   2023.5

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    Equatorial plasma bubbles are a phenomenon of plasma density depletion with small-scale density irregularities, normally observed in the equatorial ionosphere. This phenomenon, which impacts satellite-based communications, was observed in the Asia-Pacific region after the largest-on-record January 15, 2022 eruption of the Tonga volcano. We used satellite and ground-based ionospheric observations to demonstrate that an air pressure wave triggered by the Tonga volcanic eruption could cause the emergence of an equatorial plasma bubble. The most prominent observation result shows a sudden increase of electron density and height of the ionosphere several ten minutes to hours before the initial arrival of the air pressure wave in the lower atmosphere. The propagation speed of ionospheric electron density variations was ~ 480–540 m/s, whose speed was higher than that of a Lamb wave (~315 m/s) in the troposphere. The electron density variations started larger in the Northern Hemisphere than in the Southern Hemisphere. The fast response of the ionosphere could be caused by an instantaneous transmission of the electric field to the magnetic conjugate ionosphere along the magnetic field lines. After the ionospheric perturbations, electron density depletion appeared in the equatorial and low-latitude ionosphere and extended at least up to ±25° in geomagnetic latitude.

    DOI: 10.1038/s41598-023-33603-3

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    PubMed

  132. Statistical analysis for EUV dynamic spectra and their impact on the ionosphere during solar flares Reviewed

    Shohei Nishimoto, Kyoko Watanabe, Hidekatsu Jin, Toshiki Kawai, Shinsuke Imada, Tomoko Kawate, Yuichi Otsuka, Atsuki Shinbori, Takuya Tsugawa, Michi Nishioka

    Earth, Planets and Space   Vol. 75 ( 1 )   2023.3

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:Springer Science and Business Media LLC  

    Abstract

    The X-rays and extreme ultraviolet (EUV) emitted during solar flares can rapidly change the physical composition of Earth’s ionosphere, causing space weather phenomena. It is important to develop an accurate understanding of solar flare emission spectra to understand how it affects the ionosphere. We reproduced the entire solar flare emission spectrum using an empirical model and physics-based model, and input it into the Earth’s atmospheric model, GAIA to calculate the total electron content (TEC) enhancement due to solar flare emission. We compared the statistics of nine solar flare events and calculated the TEC enhancements with the corresponding observed data. The model used in this study was able to estimate the TEC enhancement due to solar flare emission with a correlation coefficient greater than 0.9. The results of this study indicate that the TEC enhancement due to solar flare emission is determined by soft X-ray and EUV emission with wavelengths shorter than 35 nm. The TEC enhancement is found to be largely due to the change in the soft X-ray emission and EUV line emissions with wavelengths, such as Fe XVII 10.08 nm, Fe XIX 10.85 nm and He II 30.38 nm.

    Graphical Abstract

    DOI: 10.1186/s40623-023-01788-6

    Web of Science

    Other Link: https://link.springer.com/article/10.1186/s40623-023-01788-6/fulltext.html

  133. Multi-Event Analysis of Magnetosphere-Ionosphere Coupling of Nighttime Medium-Scale Traveling Ionospheric Disturbances From the Ground and the Arase Satellite Reviewed

    K. Kawai, K. Shiokawa, Y. Otsuka, S. Oyama, M. G. Connors, Y. Kasahara, Y. Kasaba, S. Nakamura, F. Tsuchiya, A. Kumamoto, A. Shinbori, A. Matsuoka, I. Shinohara, Y. Miyoshi

    Journal of Geophysical Research: Space Physics   Vol. 128 ( 2 )   2023.2

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    Kawai et al. (2021) reported the first ground-satellite conjugate observation of nighttime medium-scale traveling ionospheric disturbances (MSTIDs), by analyzing measurements from an airglow imager at Gakona (geographic latitude: 62.39°N, geographic longitude: 214.78°E, magnetic latitude: 63.60°N) and the Arase satellite in the magnetosphere on 3 November 2018. The Arase satellite observed variations in both the polarization electric field and the electron density as the Arase footprint passed through the MSTID structures in the ionosphere. In this study, we investigated whether these electric field and density variations associated with MSTIDs at subauroral latitudes are always observed by Arase in the magnetosphere. We used three airglow imagers installed at Gakona, Athabasca (geographic latitude: 54.60°N, geographic longitude: 246.36°E, magnetic latitude: 61.10°N), and Kapuskasing (geographic latitude: 49.39°N, geographic longitude: 277.81°E, magnetic latitude: 58.70°N) and the Arase satellite. We found eight observations of MSTIDs conjugate with Arase. They indicate that electric field and density variations associated with MSTIDs are not always observed in the magnetosphere. These variations tend to be observed in the magnetosphere during geomagnetically quiet times and when the amplitude of the MSTID is large. We categorized the MSTIDs into those caused by plasma instabilities and gravity waves and found that the electric field and density variations can be observed in the magnetosphere for both types of MSTIDs.

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  134. A Statistical Study of Longitudinal Extent of Pc1 Pulsations Using Seven PWING Ground Stations at Subauroral Latitudes Reviewed

    Jie Liu, Kazuo Shiokawa, Shin‐Ichiro Oyama, Yuichi Otsuka, Chae‐Woo Jun, Masahito Nosé, Tsutomu Nagatsuma, Kaori Sakaguchi, Akira Kadokura, Mitsunori Ozaki, Martin Connors, Dmitry Baishev, Nozomu Nishitani, Alexey Oinats, Vladimir Kurkin, Tero Raita

    Journal of Geophysical Research: Space Physics   Vol. 128 ( 1 )   2023.1

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    DOI: 10.1029/2021JA029987

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  135. Generation Mechanisms of Plasma Density Irregularity in the Equatorial Ionosphere During a Geomagnetic Storm on 21–22 December 2014

    T. Sori, A. Shinbori, Y. Otsuka, T. Tsugawa, M. Nishioka, A. Yoshikawa

    Journal of Geophysical Research: Space Physics   Vol. 127 ( 5 )   2022.5

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    The equatorial ionosphere endured plasma density irregularities during a geomagnetic storm on 21–22 December 2014. To understand the underlying mechanism, we analyzed the rate of the total electron content change (ROTI) data obtained from a global navigation satellite system, along with solar wind, interplanetary magnetic field (IMF), geomagnetic indices, Jicamarca incoherent scatter radar, and magnetometer data. The results indicate that the ROTI enhancement related to plasma density irregularities (plasma bubbles) occurred three times in the equatorial and low latitude regions of the American sector during the geomagnetic storm. The first, second, and third enhancements which have a longitudinal extent of ∼20° appeared in the post-sunset, pre-midnight, and post-midnight sectors, respectively. The second enhancement occurred during the recovery phase of the storm-time substorm even though the IMF remained southward. During this period, the direction of the dayside equatorial electrojet (EEJ) changed from eastward to westward, while the nightside upward plasma velocity at Jicamarca increased to 28.8 m/s. The response of the EEJ and upward ion drift implies that the westward and eastward electric fields were intensified on the dayside and nightside, respectively. Therefore, these results suggest that an over-shielding electric field penetrates the dayside/nightside equator simultaneously in association with a substorm recovery phase, and that the electric field generates plasma bubbles by the Rayleigh-Taylor instability mechanism. Plasma bubbles induced by the penetration of an over-shielding electric field due to substorm activity have not previously been reported.

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  136. Propagation characteristics of sporadic E and medium-scale traveling ionospheric disturbances (MSTIDs): statistics using HF Doppler and GPS-TEC data in Japan

    Ryo Matsushima, Keisuke Hosokawa, Jun Sakai, Yuichi Otsuka, Mitsumu K. Ejiri, Michi Nishioka, Takuya Tsugawa

    EARTH PLANETS AND SPACE   Vol. 74 ( 1 )   2022.4

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    We carried out a statistical analysis of the propagation characteristics of Es and Medium-Scale Traveling Ionospheric Disturbances (MSTIDs) by combining data of HF Doppler (HFD) sounder and Total Electron Content (TEC) obtained from the GPS receivers of GEONET (GPS-TEC) for 4 years from 2014 to 2017. We made use of Es reflection data from the HFD receivers in Sugito, Saitama (36.0 degrees N, 139.7 degrees E), Fujisawa, Kanagawa (35.3 degrees N, 139.5 degrees E), and Sugadaira, Nagano (36.4 degrees N, 138.3 degrees E) in Japan. By using this triangle observation, we succeeded in deriving the horizontal speed and direction of the motion of Es. In addition, we estimated the phase velocity of MSTIDs observed in the simultaneously obtained maps of GPS-TEC with the same triangle observation procedure. The speeds of Es and MSTIDs were commonly less than 100 m/s in most cases and their propagation direction was predominantly southwestward. This result is consistent with the statistical characteristics of nighttime MSTIDs observed in the previous studies. More importantly, good correspondence between the propagation characteristics of the two phenomena at two different altitudes confirms that Es and MSTIDs move in tandem with each other, further suggesting that Es in the E region plays an important role in the generation and propagation of MSTIDs in the F region.

    DOI: 10.1186/s40623-022-01616-3

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  137. Propagation direction analyses of medium‐scale traveling ionospheric disturbances observed over North America with GPS‐TEC perturbation maps by three‐dimensional spectral analysis method

    Septi Perwitasari, Takuji Nakamura, Takuya Tsugawa, Michi Nishioka, Yoshihiro Tomikawa, Mitsumu K. Ejiri, Masaru Kogure, Yuichi Otsuka, Atsuki Shinbori, Hidekatsu Jin, Chihiro Tao

    Journal of Geophysical Research: Space Physics   Vol. 127 ( 1 )   2022.1

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    DOI: 10.1029/2020JA028791

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  138. Propagation Mechanism of Medium Wave Broadcasting Waves Observed by the Arase Satellite: Hectometric Line Spectra

    Kozo Hashimoto, Atsuki Shinbori, Yuichi Otsuka, Fuminori Tsuchiya, Atsushi Kumamoto, Yoshiya Kasahara, Ayako Matsuoka, Isamu Nagano, Yoshizumi Miyoshi, Tatsuhiro Yokoyama

    Journal of Geophysical Research: Space Physics   Vol. 126 ( 11 )   2021.11

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    A new type of terrestrial line spectra found by the Arase satellite was reported in 2018. These spectra are called “hectometric line spectra (HLS)”. They primarily consist of constant frequency narrowband components at frequencies between 525 kHz and 1,700 kHz, which originate and are sometimes amplified from AM broadcasting waves. In addition to these, other generated emissions are observed. Entrances and the mode conversion of the AM broadcasting waves into the equatorial and low-latitude ionosphere with plasma density depletion called plasma bubbles are observed. Electron density profiles and equatorial plasma bubbles are examined through Global Positioning System (GPS)-Total electron content (TEC) analyses. As a result, the Arase satellite which observed the HLS passed through the TEC depression region near the equatorial ionosphere associated with plasma bubbles. The scenario based on the mode conversion of the L-O mode to the Z mode and vice versa was confirmed with observations and GPS-TEC analyses. Another entrance when foF2 estimated from TEC is lower than 1,000 kHz instead of a plasma bubble is also found. No mode conversion is necessary, then.

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  139. Isolated Proton Aurora Driven by EMIC Pc1 Wave: PWING, Swarm, and NOAA POES Multi-Instrument Observations

    Hyangpyo Kim, Kazuo Shiokawa, Jaeheung Park, Yoshizumi Miyoshi, Yukinaga Miyashita, Claudia Stolle, Hyunju Kim Connor, Junga Hwang, Stephan Buchert, Hyuck Jin Kwon, Satoko Nakamura, Kohki Nakamura, Shin Ichiro Oyama, Yuichi Otsuka, Tsutomu Nagatsuma, Kaori Sakaguchi

    Geophysical Research Letters   Vol. 48 ( 18 )   2021.9

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    We report the concurrent observations of F-region plasma changes and field-aligned currents (FACs) above isolated proton auroras (IPAs) associated with electromagnetic ion cyclotron Pc1 waves. Key events on March 19, 2020 and September 12, 2018 show that ground magnetometers and all-sky imagers detected concurrent Pc1 wave and IPA, during which NOAA POES observed precipitating energetic protons. In the ionospheric F-layer above the IPA zone, the Swarm satellites observed transverse Pc1 waves, which span wider latitudes than IPA. Around IPA, Swarm also detected the bipolar FAC and localized plasma density enhancement, which is occasionally surrounded by wide/shallow depletion. This indicates that wave-induced proton precipitation contributes to the energy transfer from the magnetosphere to the ionosphere.

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  140. First Simultaneous Observation of a Night Time Medium‐Scale Traveling Ionospheric Disturbance From the Ground and a Magnetospheric Satellite

    K. Kawai, K. Shiokawa, Y. Otsuka, S. Oyama, Y. Kasaba, Y. Kasahara, F. Tsuchiya, A. Kumamoto, S. Nakamura, A. Matsuoka, S. Imajo, Y. Kazama, S.‐Y. Wang, S. W. Y. Tam, T. F. Chang, B. J. Wang, K. Asamura, S. Kasahara, S. Yokota, K. Keika, T. Hori, Y. Miyoshi, C. Jun, M. Shoji, I. Shinohara

    Journal of Geophysical Research: Space Physics   Vol. 126 ( 9 )   2021.9

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    DOI: 10.1029/2020JA029086

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  141. Coupled investigations of ionosphere variations over European and Japanese regions: observations, comparative analysis, and validation of models and facilities

    Sergii V. Panasenko, Dmytro V. Kotov, Yuichi Otsuka, Mamoru Yamamoto, Hiroyuki Hashiguchi, Philip G. Richards, Vladimir Truhlik, Oleksandr V. Bogomaz, Maryna O. Shulha, Taras G. Zhivolup, Igor F. Domnin

    Progress in Earth and Planetary Science   Vol. 8 ( 1 )   2021.8

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    This paper presents the results of a coordinated measurement campaign with ground based and satellite observations over European and Japanese regions during September 5–6, 2017. Two incoherent scatter radars, two satellite missions, International Reference Ionosphere (IRI-2016) empirical model, and Field Line Interhemispheric Plasma (FLIP) physical model were employed to examine the regular behavior of the F2-layer peak height and density and the topside ionosphere electron density, electron, and ion temperatures as well as traveling ionospheric disturbances (TIDs). The daily ionospheric variations over Kharkiv and Shigaraki exhibited similar behavior qualitatively and quantitatively. The results show that none of the empirical IRI-2016 models of F2-layer peak height, topside electron density, and temperature can be preferred for predicting the key qualitative features of variations in ionospheric plasma parameters over Kharkiv and Shigaraki. The likely reason is rapid day to day changes in solar activity and series of moderate enhancements of magnetic activity occurring in the observation period and preceding days. Compared with IRI-2016 model, the FLIP physical model was shown to provide the best agreement with the observations when constrained to follow the observed diurnal variations of F2-layer peak height both over Europe and Japan. This paper presents the first direct comparison of the mid-latitude electron density measured by the Swarm satellite with incoherent scatter radar data and it confirms the high quality of the space-borne data. For the first time, evidence of the possible need to increase the neutral hydrogen density in NRLMSISE-00 model by at least a factor of 2 was obtained for the Asian longitudinal sector. The TIDs, which have predominant periods of about 50 min over Europe and 80 min over Japan, were detected, likely caused by passage of the solar terminator. Such a difference in the periods could indicate regional features and is the topic for further research.

    DOI: 10.1186/s40645-021-00441-8

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  142. Model-based reproduction and validation of the total spectra of a solar flare and their impact on the global environment at the X9.3 event of September 6, 2017

    Kyoko Watanabe, Hidekatsu Jin, Shohei Nishimoto, Shinsuke Imada, Toshiki Kawai, Tomoko Kawate, Yuichi Otsuka, Atsuki Shinbori, Takuya Tsugawa, Michi Nishioka

    Earth, Planets and Space   Vol. 73 ( 1 )   2021.4

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    <title>Abstract</title>We attempted to reproduce the total electron content (TEC) variation in the Earth's atmosphere from the temporal variation of the solar flare spectrum of the X9.3 flare on September 6, 2017. The flare spectrum from the Flare Irradiance Spectral Model (FISM), and the flare spectrum from the 1D hydrodynamic model, which considers the physics of plasma in the flare loop, are used in the GAIA model, which is a simulation model of the Earth's whole atmosphere and ionosphere, to calculate the TEC difference. We then compared these results with the observed TEC. When we used the FISM flare spectrum, the difference in TEC from the background was in a good agreement with the observation. However, when the flare spectrum of the 1D-hydrodynamic model was used, the result varied depending on the presence or absence of the background. This difference depending on the models is considered to represent which extreme ultraviolet (EUV) radiation is primarily responsible for increasing TEC. From the flare spectrum obtained from these models and the calculation result of TEC fluctuation using GAIA, it is considered that the enhancement in EUV emission by approximately 15<bold>–</bold>35 nm mainly contributes in increasing TEC rather than that of X-ray emission, which is thought to be mainly responsible for sudden ionospheric disturbance. In addition, from the altitude/wavelength distribution of the ionization rate of Earth's atmosphere by GAIA (Ground-to-topside Atmosphere and Ionosphere model for Aeronomy), it was found that EUV radiation of approximately 15<bold>–</bold>35 nm affects a wide altitude range of 120<bold>–</bold>300 km, and TEC enhancement is mainly caused by the ionization of nitrogen molecules.

    DOI: 10.1186/s40623-021-01376-6

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  143. Multi‐Event Analysis of Plasma and Field Variations in Source of Stable Auroral Red (SAR) Arcs in Inner Magnetosphere During Non‐Storm‐Time Substorms

    Yudai Inaba, Kazuo Shiokawa, Shin‐ichiro Oyama, Yuichi Otsuka, Martin Connors, Ian Schofield, Yoshizumi Miyoshi, Shun Imajo, Atsuki Shinbori, Artem Yu Gololobov, Yoichi Kazama, Shiang‐Yu Wang, Sunny W. Y. Tam, Tzu‐Fang Chang, Bo‐Jhou Wang, Kazushi Asamura, Shoichiro Yokota, Satoshi Kasahara, Kunihiro Keika, Tomoaki Hori, Ayako Matsuoka, Yoshiya Kasahara, Atsushi Kumamoto, Shoya Matsuda, Yasumasa Kasaba, Fuminori Tsuchiya, Masafumi Shoji, Masahiro Kitahara, Satoko Nakamura, Iku Shinohara, Harlan E. Spence, Geoff D. Reeves, Robert J. Macdowall, Charles W. Smith, John R. Wygant, John W. Bonnell

    Journal of Geophysical Research: Space Physics   Vol. 126 ( 4 )   2021.4

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    DOI: 10.1029/2020JA029081

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  144. Formation of an additional density peak in the bottom side of the sodium layer associated with the passage of multiple mesospheric frontal systems

    Viswanathan Lakshmi Narayanan, Satonori Nozawa, Shin-Ichiro Oyama, Ingrid Mann, Kazuo Shiokawa, Yuichi Otsuka, Norihito Saito, Satoshi Wada, Takuya D. Kawahara, Toru Takahashi

    ATMOSPHERIC CHEMISTRY AND PHYSICS   Vol. 21 ( 4 ) page: 2343 - 2361   2021.2

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    We present a detailed investigation of the formation of an additional sodium density peak at altitudes of 79-85 km below the main peak of the sodium layer based on sodium lidar and airglow imager measurements made at Ramfjordmoen near Tromso, Norway, on the night of 19 December 2014. The airglow imager observations of OH emissions revealed four passing frontal systems that resembled mesospheric bores, which typically occur in ducting regions of the upper mesosphere. For about 1.5 h, the lower-altitude sodium peak had densities similar to that of the main peak of the layer around 90 km. The lower-altitude sodium peak weakened and disappeared soon after the fourth front had passed. The fourth front had weakened in intensity by the time it approached the region of lidar beams and disappeared soon afterwards. The column-integrated sodium densities increased gradually during the formation of the lower-altitude sodium peak. Temperatures measured with the lidar indicate that there was a strong thermal duct structure between 87 and 93 km. Furthermore, the temperature was enhanced below 85 km. Horizontal wind magnitudes estimated from the lidar showed strong wind shears above 93 km. We conclude that the combination of an enhanced stability region due to the temperature profile and intense wind shears have provided ideal conditions for evolution of multiple mesospheric bores revealed as frontal systems in the OH images. The downward motion associated with the fronts appeared to have brought air rich in H and O from higher altitudes into the region below 85 km, wherein the temperature was also higher. Both factors would have liberated sodium atoms from the reservoir species and suppressed the reconversion of atomic sodium into reservoir species so that the lower-altitude sodium peak could form and the column abundance could increase. The presented observations also reveal the importance of mesospheric frontal systems in bringing about significant variation of minor species over shorter temporal intervals.

    DOI: 10.5194/acp-21-2343-2021

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  145. Comparison of seasonal and longitudinal variation of daytime MSTID activity using GPS observation and GAIA simulations

    Sivakandan, M; Otsuka, Y; Ghosh, P; Shinagawa, H; Shinbori, A; Miyoshi, Y

    EARTH PLANETS AND SPACE   Vol. 73 ( 1 )   2021.2

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  146. On the Generation of an Unseasonal EPB Over South East Asia

    J. L. Currie, B. A. Carter, J. Retterer, T. Dao, R. Pradipta, R. Caton, K. Groves, Y. Otsuka, T. Yokoyama, K. Hozumi, T. Le Truong, M. Terkildsen

    Journal of Geophysical Research: Space Physics   Vol. 126 ( 2 )   2021.2

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    An unseasonal equatorial plasma bubble (EPB) event over South-East Asia was observed on July 22, 2014 that has not been studied before. An investigation into this event is presented with the 26th July, 2014 as a comparison, non-bubble day. The 22nd July EPB event occurred in the late post-sunset sector and was associated with a small upward plasma drift. This event was highlighted using a new filter on the SCINDA S4 data. Ionosonde data show that sporadic E was present during the growth period for the EPB event. Modeling results from Thermosphere-Ionosphere Electrodynamics (TEC) Global Circulation Model were used to conduct a numerical experiment investigating the direct effect of sporadic E on the linear R-T growth rate. It was shown that sporadic E located in the correct latitude and local time can increase the linear growth rate. The seeding conditions were investigated using TEC data from Patumwan, Thailand. Wave-like structures were observed for both days of interest, with larger amplitudes on 22nd July compared with the 26th July. Finally, simulations using the high-resolution model PBMOD showed that for forcing from above conditions similar to the days of interest, EPBs would form in the presence of large seed perturbations. Therefore, it is likely that this unseasonal event was caused by large seed perturbations in TEC.

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  147. Solar activity dependence of medium-scale traveling ionospheric disturbances using GPS receivers in Japan

    Otsuka, Y; Shinbori, A; Tsugawa, T; Nishioka, M

    EARTH PLANETS AND SPACE   Vol. 73 ( 1 )   2021.1

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  148. Challenges to Equatorial Plasma Bubble and Ionospheric Scintillation Short-Term Forecasting and Future Aspects in East and Southeast Asia

    Li, GZ; Ning, BQ; Otsuka, Y; Abdu, MA; Abadi, P; Liu, ZZ; Spogli, L; Wan, WX

    SURVEYS IN GEOPHYSICS   Vol. 42 ( 1 ) page: 201 - 238   2021.1

  149. Plasma and Field Observations in the Magnetospheric Source Region of a Stable Auroral Red (SAR) Arc by the Arase Satellite on 28 March 2017

    Yudai Inaba, Kazuo Shiokawa, Shin‐ichiro Oyama, Yuichi Otsuka, Arto Oksanen, Atsuki Shinbori, Artem Yu Gololobov, Yoshizumi Miyoshi, Yoichi Kazama, Shiang‐Yu Wang, Sunny W. Y. Tam, Tzu‐Fang Chang, Bo‐Jhou Wang, Shoichiro Yokota, Satoshi Kasahara, Kunihiro Keika, Tomoaki Hori, Ayako Matsuoka, Yoshiya Kasahara, Atsushi Kumamoto, Yasumasa Kasaba, Fuminori Tsuchiya, Masafumi Shoji, Iku Shinohara, Claudia Stolle

    Journal of Geophysical Research: Space Physics   Vol. 125 ( 10 )   2020.10

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    DOI: 10.1029/2020JA028068

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  150. Dilatory and Downward Development of 3-m Scale Irregularities in the Funnel-Like Region of a Rapidly Rising Equatorial Plasma Bubble

    S. Tulasi Ram, K. K. Ajith, T. Yokoyama, M. Yamamoto, K. Hozumi, K. Shiokawa, Y. Otsuka, G. Li

    Geophysical Research Letters   Vol. 47 ( 13 )   2020.7

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    The equatorial plasma bubbles, once developed, grow nonlinearly into topside ionosphere, and simultaneous secondary instabilities lead to the development of shorter scale irregularities. The altitudinal growth and generation of smaller scale irregularities determine the spatio-temporal occurrence and the intensity of ionospheric scintillations at wide spectrum of radio waves and have significant implications on the GNSS/Satellite Based Augmentation Systems. In this letter, we present a unique equatorial plasma bubble observation from equatorial atmosphere radar that provides hitherto undisclosed evidence for the smaller (3-m) scale irregularities initially developing at higher altitudes and subsequently developing to lower altitudes in a narrow funnel-like structure. The responsible mechanisms for early development of shorter scale irregularities in the topside and their subsequent development at lower altitudes are discussed in light of difference between the time scales of altitudinal growth and cascading rate of secondary instabilities through high-resolution bubble model simulations.

    DOI: 10.1029/2020GL087256

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  151. Day-to-day variation of pre-reversal enhancement in the equatorial ionosphere based on GAIA model simulations

    Ghosh, P; Otsuka, Y; Mani, S; Shinagawa, H

    EARTH PLANETS AND SPACE   Vol. 72 ( 1 )   2020.7

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  152. Observations of equatorial plasma bubbles using a low-cost 630.0-nm all-sky imager in Ishigaki Island, Japan

    Keisuke Hosokawa, Kohei Takami, Susumu Saito, Yasunobu Ogawa, Yuichi Otsuka, Kazuo Shiokawa, Chia Hung Chen, Chien Hung Lin

    Earth, Planets and Space   Vol. 72 ( 1 )   2020.5

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    © 2020, The Author(s). Here, we introduce a low-cost airglow imaging system developed for observing plasma bubble signatures in 630.0-nm airglow emission from the F region of the ionosphere. The system is composed of a small camera, optical filter, and fish-eye lens, and is operated using free software that automatically records video from the camera. A pilot system was deployed in Ishigaki Island in the southern part of Japan (Lat 24.4, Lon 124.4, Mlat 19.6) and was operated for ~ 1.5 years from 2014 to 2016 corresponding to the recent solar maximum period. The pilot observations demonstrated that it was difficult to identify the plasma bubble signature in the raw image captured every 4 s. However, the quality of the image could be improved by reducing the random noise of instrumental origin through an integration of 30 consecutive raw images obtained in 2 min and further by subtracting the 1-h averaged background image. We compared the deviation images to those from a co-existing airglow imager of OMTIs, which is equipped with a back-illuminated cooled CCD camera with a high quantum efficiency of ~ 90%. It was confirmed that the low-cost airglow imager is capable of imaging the spatial structure of plasma bubbles, including their bifurcating traces. The results of these pilot observations in Ishigaki Island will allow us to distribute the low-cost imager in a wide area and construct a network for monitoring plasma bubbles and their space weather impacts on satellite navigation systems.[Figure not available: see fulltext.].

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  153. Probability of Ionospheric Plasma Bubble Occurrence as a Function of Pre-Reversal Enhancement Deduced from Ionosondes in Southeast Asia

    Abadi, P; Otsuka, Y; Supriadi, S; Olla, A

    7TH INTERNATIONAL SEMINAR ON AEROSPACE SCIENCE AND TECHNOLOGY (ISAST 2019)   Vol. 2226   2020

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    DOI: 10.1063/5.0002321

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  154. New observations of the total electron content and ionospheric scintillations over Ho Chi Minh city

    Dao, T; Huy, ML; Carter, B; Le, Q; Trinh, TT; Phan, BN; Otsuka, Y

    VIETNAM JOURNAL OF EARTH SCIENCES   Vol. 42 ( 4 ) page: 320 - 333   2020

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  155. Capability of Geomagnetic Storm Parameters to Identify Severe Space Weather

    Balan, N; Zhang, QH; Xing, ZY; Skoug, R; Shiokawa, K; Lühr, H; Ram, ST; Otsuka, Y; Zhao, LX

    ASTROPHYSICAL JOURNAL   Vol. 887 ( 1 )   2019.12

  156. A Neural Network-Based Ionospheric Model Over Africa From Constellation Observing System for Meteorology, Ionosphere, and Climate and Ground Global Positioning System Observations

    Daniel Okoh, Gopi Seemala, Babatunde Rabiu, John Bosco Habarulema, Shuanggen Jin, Kazuo Shiokawa, Yuichi Otsuka, Malini Aggarwal, Jean Uwamahoro, Patrick Mungufeni, Bolaji Segun, Aderonke Obafaye, Nada Ellahony, Chinelo Okonkwo, Mpho Tshisaphungo, Dadaso Shetti

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 124 ( 12 ) page: 10512 - 10532   2019.12

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    The first regional total electron content (TEC) model over the entire African region (known as AfriTEC model) using empirical observations is developed and presented. Artificial neural networks were used to train TEC observations obtained from Global Positioning System receivers, both on ground and onboard the Constellation Observing System for Meteorology, Ionosphere, and Climate satellites for the African region from years 2000 to 2017. The neural network training was implemented using inputs that enabled the networks to learn diurnal variations, seasonal variations, spatial variations, and variations that are connected with the level of solar activity, for quiet geomagnetic conditions (-20 nT <= Dst <= 20 nT). The effectiveness of three solar activity indices (sunspot number, solar radio flux at 10.7-cm wavelength [F10.7], and solar ultraviolet [UV] flux at 1 AU) for the neural network trainings was tested. The F10.7 and UV were more effective, and the F10.7 was used as it gave the least errors on the validation data set used. Equatorial anomaly simulations show a reduced occurrence during the June solstice season. The distance of separation between the anomaly crests is typically in the range from about 11.5 +/- 1.0 degrees to 16.0 +/- 1.0 degrees. The separation is observed to widen as solar activity levels increase. During the December solstice, the anomaly region shifts southwards of the equinox locations; in year 2012, the trough shifted by about 1.5 degrees and the southern crest shifted by over 2.5 degrees.

    DOI: 10.1029/2019JA027065

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  157. Investigation of Spatiotemporal Morphology of Plasma Bubbles Based on EAR Observations Reviewed

    L.M. Joshi, L.‐C. Tsai, S.‐Y. Su, Y. Otsuka, T. Yokoyama, M. Yamamoto, S. Sarkhel, K. Hozumi, C.‐H. Lu

    Journal of Geophysical Research: Space Physics   Vol. 124 ( 12 ) page: 10549 - 10563   2019.12

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    DOI: 10.1029/2019JA026839

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  158. Three-Dimensional Fourier Analysis of the Phase Velocity Distributions of Mesospheric and Ionospheric Waves Based on Airglow Images Collected Over 10 Years: Comparison of Magadan, Russia, and Athabasca, Canada Reviewed

    Tsuchiya Satoshi, Shiokawa Kazuo, Fujinami Hatsuki, Otsuka Yuichi, Nakamura Takuji, Connors Martin, Schofield Ian, Shevtsov Boris, Poddelskiy Igor

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 124 ( 10 ) page: 8110 - 8124   2019.10

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    We studied atmospheric gravity waves (AGWs) and nighttime medium-scale traveling ionospheric disturbances (MSTIDs) using a three-dimensional spectral analysis technique for airglow images at wavelengths of 557.7 nm (altitude: 90-100 km for AGWs) and 630.0 nm (200-300 km for MSTIDs), obtained from Athabasca (ATH), Canada (55 degrees N, 247 degrees E, 2005-2017), and Magadan (MGD), Russia (60 degrees N, 151 degrees E, 2008-2017), over 10-13 years. The AGW propagation direction in summer was from northwestward to northward in ATH and northeastward in MGD with phase speeds of 20-60 m/s. In winter at ATH, they are more omnidirectional with weak preference from northwestward to southward with a speed less than 40 m/s, while another weaker power exists from northeastward to southeastward from 70 to 120 m/s. In winter at MGD, there was no dominant direction in the phase-velocity spectra with spectral power an order smaller than ATH. We suggest that these AGW characteristics were caused by wind filtering and intensity and locations of tropospheric sources. The MSTIDs at ATH propagated southwestward in spring and winter and northeastward in summer and fall. The MSTIDs at MGD propagated northeastward, eastward, and westward in spring, fall, and winter, respectively, with weaker power than that at ATH. The phase speeds are mostly less than 100 m/s except for fall. The propagation direction tends to change from south-southwestward in the evening to north-northeastward after the midnight at both ATH and MGD. We discuss possible reasons for these MSTID characteristics at high latitudes based on Perkins and E-F coupling instabilities, high-latitude plasma convection, and thermospheric neutral winds.

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  159. Observation and characterization of traveling ionospheric disturbances induced by solar eclipse of 20 March 2015 using incoherent scatter radars and GPS networks Reviewed

    Panasenko Sergii V, Otsuka Yuichi, van de Kamp Max, Chernogor Leonid F, Shinbori Atsuki, Tsugawa Takuya, Nishioka Michi

    JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS   Vol. 191   2019.9

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  160. Thermospheric wind variations observed by a Fabry-Perot interferometer at Tromso, Norway, at substorm onsets Reviewed

    Xu Heqiucen, Shiokawa Kazuo, Oyama Shin-ichiro, Otsuka Yuichi

    EARTH PLANETS AND SPACE   Vol. 71 ( 1 )   2019.8

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    Energy input from the magnetosphere during substorms can strongly affect the high-latitude thermosphere. The ionospheric current caused by thermospheric wind variations may also provide a feedback to the magnetosphere. In this study, we investigate the characteristics of high-latitude thermospheric wind variations at local substorm onsets at Tromso, Norway, as well as the possibility of such feedback mechanism. A Fabry-Perot interferometer (FPI) at Tromso provided wind measurements estimated from the Doppler shift of red-line emission (630.0 nm) of aurora and airglow. We analyzed wind data in 2009 with a time resolution of similar to 13 min. We first carefully identified the onset times of isolated local substorms at Tromso and extracted four wind measurements from red-line emission. All these events showed increases of eastward components at local substorm onsets. For northward components, these events showed decreases except for those at midnight. The observed wind variations at local substorm onsets were less than 49 m/s. These values are much smaller than the typical plasma convection speed in the auroral zone. We speculate that the ionospheric current caused by thermospheric wind variations at local substorm onsets does not provide strong feedback to the development of substorm expansion phase in the magnetotail. We discuss the possible causes of these wind variations in the context of plasma convection, diurnal tides, and arc-associated electric field.

    DOI: 10.1186/s40623-019-1072-0

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  161. Direct Observations of Traveling Ionospheric Disturbances as Focusers of Solar Radiation: Spectral Caustics Reviewed

    Koval Artem, Chen Yao, Tsugawa Akuya, Otsuka Yuichi, Shinbori Atsuki, Nishioka Michi, Brazhenko Anatoliy, Stanislaysky Aleksander, Konovalenko Aleksander, Zhang Qing-He, Monstein Christian, Gorgutsa Roman

    ASTROPHYSICAL JOURNAL   Vol. 877 ( 2 )   2019.6

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    DOI: 10.3847/1538-4357/ab1b52

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  162. Response of the Ionosphere-Plasmasphere Coupling to the September 2017 Storm:What Erodes the Plasmasphere so Severley? Reviewed

    Obana Yuki, Maruyama Naomi, Shinbori Atsuki, Hashimoto Kumiko K, Fedrizzi Mariangel, Nose Masahito, Otsuka Yuichi, Nishitani Nozomu, Hori Tomoaki, Kumamoto Atsushi, Tsuchiya Fuminori, Matsuda Shoya, Matsuoka Ayako, Kasahara Yoshiya, Yoshikawa Akimasa, Miyoshi Yoshizumi, Shinohara Iku

    SPACE WEATHER-THE INTERNATIONAL JOURNAL OF RESEARCH AND APPLICATIONS   Vol. 17 ( 6 ) page: 861 - 876   2019.6

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    We report an extreme erosion of the plasmasphere arising from the September 2017 storm. The cold electron density is identified from the upper limit frequency of upper hybrid resonance waves observed by the Plasma Wave Experiment instrument onboard the Exploration of energization and Radiation in Geospace/Arase satellite. The electron density profiles reveal that the plasmasphere was severely eroded during the recovery phase of the storm and the plasmapause was located at L = 1.6-1.7 at 23 UT 8 September 2017. This is the first report of deep erosion of the plasmasphere (L-pp < 2) with the in situ observation of the electron density. The degree of the severity is much more than what is expected from the relatively moderate value of the SYM-H minimum (-146 nT). We attempt to find a possible explanation for the observed severe depletion by using both observational evidence and numerical simulations. Our results suggest that the middle latitude electric field had penetrated from the high-latitude storm time convection for several hours. Such an unusually long-lasting penetration event can cause this observed degree of severity.Plain Language Summary The plasmasphere is the region of cold, relatively dense ionized gas (mostly protons and helium ions) that resides on the magnetic field lines close to the Earth. It is understood that the plasmasphere is threaded by magnetic field flux tubes that are persistently "closed," so that plasma from the Earth's ionosphere has filled the flux tubes. The typical location of the outer boundary of the plasmasphere, known as the plasmapause, is usually 40,000-50,000 km from the Earth. Here we report that a magnetic storm during 7-10 September 2017 dramatically displaced the outer boundary of the plasmasphere inwards, to only similar to 4,000 km from Earth's surface. Our study suggests that the remarkable deformation is caused by the unusually long-lasting leakage of the convection electric field deep within the plasmasphere.

    DOI: 10.1029/2019SW002168

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  163. Spatiotemporal development of pulsating auroral patch associated with discrete chorus elements: Arase and PWING observations Reviewed

    Ozaki, M, K. Shiokawa, Y. Miyoshi, K. Hosokawa, S. Oyama, S. Yagitani, Y. Kasahara, Y. Kasaba, S. Matsuda, R. Kataoka, Y. Ebihara, Y. Ogawa, Y. Otsuka, S. Kurita, R. C. Moore, Y.-M. Tanaka, M. Nosé, T. Nagatsuma, M. Connors, N. Nishitani, M. Hikishima, A. Kumamoto, F. Tsuchiya, A. Kadokura, T. Nishiyama, T. Inoue, K. Imamura, A. Matsuoka, I. Shinohara

    2019 URSI ASIA-PACIFIC RADIO SCIENCE CONFERENCE (AP-RASC)     page: 18776063   2019.6

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    DOI: 10.23919/URSIAP-RASC.2019.8738444

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  164. Development of multivariate ionospheric TEC forecasting algorithm using linear time series model and ARMA over low-latitude GNSS station Reviewed

    Ratnam D. Venkata, Otsuka Yuichi, Sivavaraprasad G, Dabbakuti J, R. K. Kumar

    ADVANCES IN SPACE RESEARCH   Vol. 63 ( 9 ) page: 2848 - 2856   2019.5

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    DOI: 10.1016/j.asr.2018.03.024

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  165. Multicomponent Analysis of Ionospheric Scintillation Effects Using the Synchrosqueezing Technique for Monitoring and Mitigating their Impact on GNSS Signals Reviewed

    Sivavaraprasad G, Ratnam D. Venkata, Otsuka Yuichi

    JOURNAL OF NAVIGATION   Vol. 72 ( 3 ) page: 669 - 684   2019.5

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    DOI: 10.1017/S0373463318000929

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  166. Daytime Periodic Wave-like Structures in the Ionosphere Observed at Low Latitudes over the Asian-Australian Sector Using Total Electron Content from Beidou Geostationary Satellites Reviewed

    Huang Fuqing, Otsuka Yuichi, Lei Jiuhou, Luan Xiaoli, Dou Xiankang, Li Guozhu

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 124 ( 3 ) page: 2312 - 2322   2019.3

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    DOI: 10.1029/2018JA026443

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  167. Observations of Low-Latitude Traveling Ionospheric Disturbances by a 630.0-nm Airglow Imager and the CHAMP Satellite Over Indonesia Reviewed

    Moral Aysegul Ceren, Shiokawa Kazuo, Suzuki Shin, Liu Huixin, Otsuka Yuichi, Yatini Clara Yoko

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 124 ( 3 ) page: 2198 - 2212   2019.3

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    We report the first comparison of ground and satellite measurements of low-latitude traveling ionospheric disturbances (TIDs). Three TID events were simultaneously observed by a 630.0-nm airglow imager and the CHAllenging Minisatellite Payload (CHAMP) satellite at Kototabang, Indonesia (geographic coordinates: 0.2 degrees S, 100.3 degrees E, geomagnetic latitude: 10.6 degrees S). In 630.0-nm airglow images of all three events, there are clear southward-moving structures. Events 1 and 2 are a single pulse with horizontal scales of similar to 500-1,000 km. Event 3 shows five wave fronts with a horizontal scale size of 500-1,000 km. All three TIDs are medium-scale TIDs. Horizontal wavelengths of both airglow intensity at an average emission altitude of 250 km and CHAMP neutral density variations measured at 400 km are estimated by fitting a sinusoidal function to the observed data. The estimated horizontal wavelengths for airglow and neutral density data are 1,031 and 880 km for event 1 and 560 and 420 km for event 3, respectively. These values between airglow and CHAMP are comparable, suggesting both instruments are observing the same wave. For event 1, the CHAMP electron density mapped along the geomagnetic field line onto the airglow altitude does not show wave structure similar to the airglow variation. For events 2 and 3, the plasma density did not show wavy structures similar to the waves seen in the airglow image and CHAMP neutral density. These results suggest that the TIDs observed in airglow images are not caused by ionospheric plasma instability but by gravity waves in the thermosphere.

    DOI: 10.1029/2018JA025634

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  168. Visualization of rapid electron precipitation via chorus element wave–particle interactions Reviewed

    Mitsunori Ozaki, Yoshizumi Miyoshi, Kazuo Shiokawa, Keisuke Hosokawa, Shin ichiro Oyama, Ryuho Kataoka, Yusuke Ebihara, Yasunobu Ogawa, Yoshiya Kasahara, Satoshi Yagitani, Yasumasa Kasaba, Atsushi Kumamoto, Fuminori Tsuchiya, Shoya Matsuda, Yuto Katoh, Mitsuru Hikishima, Satoshi Kurita, Yuichi Otsuka, Robert C. Moore, Yoshimasa Tanaka, Masahito Nosé, Tsutomu Nagatsuma, Nozomu Nishitani, Akira Kadokura, Martin Connors, Takumi Inoue, Ayako Matsuoka, Iku Shinohara

    Nature Communications   Vol. 10 ( 1 )   2019.1

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    © 2019, The Author(s). Chorus waves, among the most intense electromagnetic emissions in the Earth’s magnetosphere, magnetized planets, and laboratory plasmas, play an important role in the acceleration and loss of energetic electrons in the plasma universe through resonant interactions with electrons. However, the spatial evolution of the electron resonant interactions with electromagnetic waves remains poorly understood owing to imaging difficulties. Here we provide a compelling visualization of chorus element wave–particle interactions in the Earth’s magnetosphere. Through in-situ measurements of chorus waveforms with the Arase satellite and transient auroral flashes from electron precipitation events as detected by 100-Hz video sampling from the ground, Earth’s aurora becomes a display for the resonant interactions. Our observations capture an asymmetric spatial development, correlated strongly with the amplitude variation of discrete chorus elements. This finding is not theoretically predicted but helps in understanding the rapid scattering processes of energetic electrons near the Earth and other magnetized planets.

    DOI: 10.1038/s41467-018-07996-z

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  169. Implementation of Hybrid Ionospheric TEC Forecasting Algorithm Using PCA-NN Method Reviewed

    Mallika, IL, Ratnam, DV, Ostuka, Y, Sivavaraprasad, G, Raman, S

    IEEE JOURNAL OF SELECTED TOPICS IN APPLIED EARTH OBSERVATIONS AND REMOTE SENSING   Vol. 12 ( 1 ) page: 371 - 381   2019.1

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  170. Rapid Loss of Relativistic Electrons by EMIC Waves in the Outer Radiation Belt Observed by Arase, Van Allen Probes, and the PWING Ground Stations Reviewed

    Kurita, S, Miyoshi, Y, Shiokawa, K, Higashio, N, Mitani, T, Takashima, T, Matsuoka, A, Shinohara, I, Kletzing, CA, Blake, JB, Claudepierre, SG, Connors, M, Oyama, S, Nagatsuma, T, Sakaguchi, K, Baishev, D, Otsuka, Y

    GEOPHYSICAL RESEARCH LETTERS   Vol. 45 ( 23 ) page: 12720 - 12729   2018.12

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    DOI: 10.1029/2018GL080262

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    Other Link: https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2018GL080262

  171. Microscopic Observations of Pulsating Aurora Associated With Chorus Element Structures: Coordinated Arase Satellite-PWING Observations Reviewed

    Ozaki, M, Shiokawa, K, Miyoshi, Y, Hosokawa, K, Oyama, S, Yagitani, S, Kasahara, Y, Kasaba, Y, Matsuda, S, Kataoka, R, Ebihara, Y, Ogawa, Y, Otsuka, Y, Kurita, S, Moore, RC, Tanaka, YM, Nose, M, Nagatsuma, T, Connors, M, Nishitani, N, Katoh, Y, Hikishima, M, Kumamoto, A, Tsuchiya, F, Kadokura, A, Nishiyama, T, Inoue, T, Imamura, K, Matsuoka, A, Shinohara, I

    GEOPHYSICAL RESEARCH LETTERS   Vol. 45 ( 22 ) page: 12125 - 12134   2018.11

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    Rapid (<1 s) intensity modulation of pulsating auroras is caused by successive chorus elements as a response to wave-particle interactions in the magnetosphere. Here we found that a pulsating auroral patch responds to the time spacing for successive chorus elements and possibly to chorus subpacket structures with a time scale of tens of milliseconds. These responses were identified from coordinated Arase satellite and ground (Gakona, Alaska) observations with a high-speed auroral imager (100 Hz). The temporal variations of auroral intensity in a few-hertz frequency range exhibited a spatial concentration at the lower-latitude edge of the auroral patch. The spatial evolution of the auroral patch showed repeated expansion/contraction with tens of kilometer scales in the ionosphere, which could be spatial behaviors in the wave-particle interactions. These observations indicate that chorus elements evolve coherently within the auroral patch, which is approximately 900 km in the radial and longitudinal directions at the magnetic equator.

    DOI: 10.1029/2018GL079812

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  172. Statistical Analysis of SAR Arc Detachment From the Main Oval Based on 11-Year, AII-sky Imaging Observation at Athabasca, Canada Reviewed

    Takagi Yuki, Shiokawa Kazuo, Otsuka Yuichi, Connors Martin, Schofield Ian

    GEOPHYSICAL RESEARCH LETTERS   Vol. 45 ( 21 ) page: 11539 - 11546   2018.11

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    We report the first statistical analysis of stable auroral red (SAR) arc detachments from the main auroral oval, using 630-nm all-sky cooled-Charge Coupled Device images obtained at Athabasca (magnetic latitude = 61.7 degrees N), Canada. SAR arc detachments from the main oval can be an important way of monitoring the characteristics of ring current particle injection in the inner magnetosphere. We analyzed all-sky images obtained for 11 years from 2006 to 2016 and found 163 SAR arc detachment events. The SAR arc detachments tend to occur in the premidnight sector, indicating the ring current ion drift to the dusk sector. The SAR arc detachments also tend to occur at the beginning of the substorm recovery phase, suggesting that the SAR arcs detach from the main oval as the main auroral oval returns to higher latitudes. The equatorward velocities of detached SAR arcs are from -100 m/s (poleward) to +200 m/s (equatorward), corresponding to magnetospheric electric fields from -1 to +2 mV/m.Plain Language, Summary Stable auroral red (SAR) arcs are the optical emissions caused by low-energy electron precipitation into the ionosphere from the inner magnetosphere close to the earth. In this paper, we report the first statistical analysis of SAR arc detachments from the main auroral oval, using all-sky cooled-Charge Coupled Device images measured at a wavelength of 630.0 nm obtained at Athabasca, Canada, which is located at latitudes just lower than the auroral zone latitudes. SAR arc detachments from the main oval can be an important way of monitoring the characteristics of high-energy particle injection in the inner magnetosphere. We analyzed 11-year all-sky images from 2006 to 2016 and found 163 SAR arc detachment events. The SAR arc detachments tend to occur premidnight, indicating the high-energy ion drift to the dusk sector. We also found that the SAR arc detachments tend to occur at the beginning of the substorm recovery phase. This likely indicates that the SAR arcs detach from the high-latitude aurora as the main aurora returns to higher latitudes at the beginning of the recovery phase. The equatorward velocities of detached SAR arcs are also estimated from the analysis.

    DOI: 10.1029/2018GL079615

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  173. Review of the generation mechanisms of post-midnight irregularities in the equatorial and low-latitude ionosphere Reviewed

    Otsuka Yuichi

    PROGRESS IN EARTH AND PLANETARY SCIENCE   Vol. 5   2018.9

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    DOI: 10.1186/s40645-018-0212-7

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  174. Investigation of Nighttime MSTIDS Observed by Optical Thermosphere Imagers at Low Latitudes: Morphology, Propagation Direction, and Wind Filtering Reviewed

    Figueiredo, CAOB, Takahashi, H, Wrasse, CM, Otsuka, Y, Shiokawa, K, Barros, D

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 123 ( 9 ) page: 7843 - 7857   2018.9

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    DOI: 10.1029/2018JA025438

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  175. Storm-Enhanced Development of Postsunset Equatorial Plasma Bubbles Around the Meridian 120 degrees E/60 degrees W on 7-8 September 2017 Reviewed

    Li Guozhu, Ning Baiqi, Wang Chi, Abdu M. A, Otsuka Yuichi, Yamamoto M, Wu Jian, Chen Jinsong

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 123 ( 9 ) page: 7985 - 7998   2018.9

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    DOI: 10.1029/2018JA025871

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  176. Temporal and Spatial Variations of Storm Time Midlatitude Ionospheric Trough Based on Global GNSS-TEC and Arase Satellite Observations Reviewed

    Shinbori Atsuki, Otsuka Yuichi, Tsugawa Takuya, Nishioka Michi, Kumamoto Atsushi, Tsuchiya Fuminori, Matsuda Shoya, Kasahara Yoshiya, Matsuoka Ayako, Ruohoniemi J. Michael, Shepherd Simon G, Nishitani Nozomu

    GEOPHYSICAL RESEARCH LETTERS   Vol. 45 ( 15 ) page: 7362 - 7370   2018.8

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    Temporal and spatial variations of the midlatitude ionospheric trough during a geomagnetic storm on 4 April 2017 have been investigated using Global Navigation Satellite System total electron content data together with Arase satellite observations. After the geomagnetic storm commencement, the trough minimum location moves equatorward from 60 to 48 degrees in geomagnetic latitude within 4 hr. The trough minimum location identified from the Global Navigation Satellite System total electron content data is located near the footprint of an abrupt drop of electron density detected by the Arase High-Frequency Analyzer instrument. The longitudinal variation of the trough minimum location shows a significant variation with a scale of 1,000-2,500 km during both storm and quiet times. This phenomenon has not yet been reported by previous studies. After the onset of the storm recovery phase, the trough minimum location rapidly moves poleward back to the quiet time location within 4 hr.Plain Language Summary Geomagnetic storms lead to a sever change in the plasma environment in the ionosphere and magnetosphere. Because their storm time disturbances in these regions cause an enhancement of positioning error and satellite anomaly due to the ionospheric electron density variation and magnetospheric high-energy particles, to clarify the characteristics of storm time variation of plasma environment and its physical mechanism is essential for prediction of the Geospace environmental change as space weather. In this study, we analyzed global positioning system total electron content data and Arase satellite observations in the inner magnetosphere to monitor a storm time change in the shape of the plasmasphere that controls the generation and propagation of plasma waves. Our analysis results show that the location of the midlatitude trough minimum identified from the total electron content data rapidly moves equatorward and poleward within 4 hr during the main and recovery phases. The location of the midlatitude trough minimum almost corresponds to that of the plasmapause detected by the Arase satellite. The longitudinal distribution of the midlatitude trough minimum shows a significant variation with its scale of 1,000-2,500 km. This feature is also seen during a geomagnetically quiet time. This phenomenon has not yet been reported by previous works.

    DOI: 10.1029/2018GL078723

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  177. On the Role of Thermospheric Winds and Sporadic E Layers in the Formation and Evolution of Electrified MSTIDs in Geomagnetic Conjugate Regions Reviewed

    Narayanan, VL, Shiokawa, K, Otsuka, Y, Neudegg, D

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 123 ( 8 ) page: 6957 - 6980   2018.8

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    DOI: 10.1029/2018JA025261

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  178. On the Solstice Maxima and Azimuth-Dependent Characteristics of the 150-km Echoes Observed Using the Equatorial Atmosphere Radar Reviewed

    P. Pavan Chaitanya, A. K. Patra, Y. Otsuka, T. Yokoyama, M. Yamamoto

    Journal of Geophysical Research: Space Physics   Vol. 123 ( 8 ) page: 6752 - 6759   2018.8

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    DOI: 10.1029/2018JA025491

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  179. Statistical Analysis of the Phase Velocity Distribution of Mesospheric and Ionospheric Waves Observed in Airglow Images Over a 16-Year Period: Comparison Between Rikubetsu and Shigaraki, Japan Reviewed

    Tsuchiya Satoshi, Shiokawa Kazuo, Fujinami Hatsuki, Otsuka Yuichi, Nakamura Takuji, Yamamoto Mamoru

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 123 ( 8 ) page: 6930 - 6947   2018.8

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    Atmospheric gravity waves (AGWs) in the mesopause region and medium-scale traveling ionospheric disturbances (MSTIDs) in the thermosphere from 1999 through 2014 were studied by applying a three-dimensional spectral analysis technique to airglow images at wavelengths of 557.7 (emission altitudes: 90-100 km) and 630.0 nm (emission altitudes: 200-300 km) obtained at Rikubetsu (43.5 degrees N, 143.8 degrees E) and Shigaraki (34.8 degrees N, 136.1 degrees E), Japan. To our knowledge, such a long-term multipoint analysis of AGWs and MSTIDs using airglow images has not been reported previously. The propagation direction of mesospheric AGWs seen in 557.7-nm airglow images at both stations was northeastward in summer and southwestward in winter, probably due to wind filtering of these waves by the mesospheric jet. In winter, the propagation direction of AGWs shifted from southwestward to northwestward as time progressed from evening to morning at both stations, which can also be explained by the wind filtering effect. The propagation direction of AGWs changed from southwestward to northeastward at Rikubetsu during a zonal wind reversal at 60 degrees N at 10 hPa, caused by stratospheric sudden warming (SSW). No such a SSW-associated change was identified at Shigaraki, indicating that the effect of SSW wind reversal reached only the Rikubetsu latitudes. For MSTIDs, the major propagation direction was southwestward with a minor northeastward peak for all seasons at both stations. A negative correlation was found between the yearly variation in power spectral density and solar F10.7 flux. This negative correlation can be explained by considering the linear growth rate of the Perkins instability.

    DOI: 10.1029/2018JA025585

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  180. Quantum criticality in the metal-superconductor transition of interacting Dirac fermions on a triangular lattice Reviewed

    Otsuka Yuichi, Seki Kazuhiro, Sorella Sandro, Yunoki Seiji

    PHYSICAL REVIEW B   Vol. 98 ( 3 )   2018.7

  181. Equatorial plasma bubble seeding by MSTIDs in the ionosphere Reviewed

    Hisao Takahashi, Cristiano Max Wrasse, Cosme Alexandre Oliveira Barros Figueiredo, Diego Barros, Mangalathayil Ali Abdu, Yuichi Otsuka, Kazuo Shiokawa

    Progress in Earth and Planetary Science   Vol. 5 ( 1 )   2018.6

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    Occurrences of equatorial plasma bubbles (EPBs) and medium-scale traveling ionospheric disturbances (MSTIDs) were studied using GPS satellite data-based total electron content mapping, ionograms, and 630 nm all-sky airglow images observed over the South American continent during the period of 2014–2015. In many cases, we observed a close relationship between the inter-bubble distance and the horizontal wavelength of the MSTIDs. The MSTIDs followed by EPBs occurred primarily in the afternoon to evening period under strong tropospheric convective activities (cold fronts and/or intertropical convergence zones). The close relationship between EPBs and MSTIDs suggests that MSTIDs could be one of the seeding sources of EPBs. [Figure not available: see fulltext.].

    DOI: 10.1186/s40645-018-0189-2

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  182. Total Electron Content Observations by Dense Regional and Worldwide International Networks of GNSS

    Tsugawa Takuya, Nishioka Michi, Ishii Mamoru, Hozumi Kornyanat, Saito Susumu, Shinbori Atsuki, Otsuka Yuichi, Saito Akinori, Buhari Suhaila M., Abdullah Mardina, Supnithi Pornchai

    JOURNAL OF DISASTER RESEARCH   Vol. 13 ( 3 ) page: 535-545   2018.6

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  183. Total Electron Content Observations by Dense Regional and Worldwide International Networks of GNSS Reviewed

    Tsugawa Takuya, Nishioka Michi, Ishii Mamoru, Hozumi Kornyanat, Saito Susumu, Shinbori Atsuki, Otsuka Yuichi, Saito Akinori, Buhari Suhaila M, Abdullah Mardina, Supnithi Pornchai

    JOURNAL OF DISASTER RESEARCH   Vol. 13 ( 3 ) page: 535 - 545   2018.6

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    Two-dimensional ionospheric total electron content (TEC) maps have been derived from ground- based Global Navigation Satellite System (GNSS) receiver networks and applied to studies of various ionospheric disturbances since the mid-1990s. For the purpose of monitoring and researching ionospheric conditions and ionospheric space weather phenomena, we have developed TEC maps of areas over Japan using the dense GNSS network, GNSS Earth Observation NETwork (GEONET), which consists of about 1300 stations and is operated by the Geospatial Information Authority of Japan (GSI). Currently, we are providing high-resolution, two-dimensional maps of absolute TEC, detrended TEC, rate of TEC change index (ROTI), and loss-of-lock on GPS signal over Japan on a real- time basis. Such high-resolution TEC maps using dense GNSS receiver networks are one of the most effective ways to observe, on a scale of several 100 km to 1000 km, ionospheric variations caused by traveling ionospheric disturbances and/or equatorial plasma bubbles, which can degrade single-frequency and differential GNSS positioning/navigation. We have collected all the available GNSS receiver data in the world to expand the TEC observation area. Currently, however, dense GNSS receiver networks are available in only limited areas, such as Japan, North America, and Europe. To expand the two-dimensional TEC observation with high resolution, we have conducted the Dense Regional and Worldwide International GNSS TEC observation (DRAWING- TEC) project, which is engaged in three activities: (1) standardizing GNSSTEC data, (2) developing a new high-resolution TEC mapping technique, and (3) sharing the standardized TEC data or the information of GNSS receiver network. We have developed a new standardized TEC format, GNSS-TEC EXchange (GTEX), which is included in the Formatted Tables of ITU-R SG 3 Data-banks related to Recommendation ITU-R P. 311. Sharing the GTEX TEC data would be easier than sharing the GPS/GNSS data among those in the international ionospheric researcher community. The DRAWINGTEC project would promote studies of medium-scale ionospheric variations and their effect on GNSS.

    DOI: 10.20965/jdr.2018.p0535

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  184. Relationship between day-to-day variability of equatorial plasma bubble activity from GPS scintillation and atmospheric properties from Ground-to-topside model of Atmosphere and Ionosphere for Aeronomy (GAIA) assimilation Reviewed

    Mamoru Yamamoto, Yuichi Otsuka, Hidekatsu Jin, Yasunobu Miyoshi

    PROGRESS IN EARTH AND PLANETARY SCIENCE   Vol. 5   2018.5

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    The relationship between day-to-day variability of equatorial plasma bubbles (EPBs) and the neutral atmosphere is studied. This study is based on the previous study in which the GPS scintillation index and the tropospheric cloud-top temperature are used as proxies for EPB activity and atmospheric perturbations, respectively, and a correlation was found between their day-to-day variations. In this paper, we maintained the same GPS scintillation data but substituted the atmospheric data via an assimilation run of the Ground-to-topside model of Atmosphere and Ionosphere for Aeronomy (GAIA). Cross-correlation between the EPB activity and the atmospheric temperature is similar to the results in Ogawa et al. (Earth Planets Space 61: 397-410, 2009). The new findings from our study include (1) an enhanced correlation between the EPB activity and the neutral atmosphere is found in horizontally and vertically large areas, (2) the longitudinal disturbance of atmospheric temperature and wind velocity during the EPB-active days is enhanced, and (3) the enhancement of atmospheric disturbance during the EPB-active days shows a similarity to the characteristics of large-scale wave structures in the ionosphere. These results more clearly support couplings between EPBs and the neutral atmosphere.

    DOI: 10.1186/s40645-018-0184-7

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  185. Spatial and temporal characteristics of ionospheric total electron content over Indian equatorial and low-latitude GNSS stations Reviewed

    G. Sivavaraprasad, Yuichi Otsuka, Nitin Kumar Tripathi, V Rajesh Chowdhary, D Venkata Ratnam, Mohammed Afzal Khan

    2018 Conference on Signal Processing And Communication Engineering Systems, SPACES 2018   Vol. 2018-   page: 105 - 108   2018.3

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    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

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  186. Daily and seasonal variations in the linear growth rate of the Rayleigh-Taylor instability in the ionosphere obtained with GAIA Reviewed

    Shinagawa, Hiroyuki, Jin, Hidekatsu, Miyoshi, Yasunobu, Fujiwara, Hitoshi, Yokoyama, Tatsuhiro, Otsuka, Yuichi

    PROGRESS IN EARTH AND PLANETARY SCIENCE   Vol. 5   2018.3

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    The linear growth rates of the Rayleigh-Taylor (R-T) instability in the ionosphere from 2011 to 2013 were obtained with a whole atmosphere-ionosphere coupled model GAIA (ground-to-topside model of atmosphere and ionosphere for aeronomy). The effects of thermospheric dynamics driven by atmospheric waves propagating from below on the R-T growth rate are included in the model by incorporating meteorological reanalysis data in the region below 30 km altitude. The daily maximum R-T growth rates for these periods are compared with the observed occurrence days of the equatorial plasma bubble (EPB) determined by the Equatorial Atmosphere Radar (EAR) and Global Positioning System (GPS) in West Sumatra, Indonesia. We found that a high R-T growth rate tends to correspond to the actual EPB occurrence, suggesting the possibility of predicting EPB occurrences with numerical models.

    DOI: 10.1186/s40645-018-0175-8

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  187. Medium-Scale Traveling Ionospheric Disturbances Observed by Detrended Total Electron Content Maps Over Brazil Reviewed

    C. A.O.B. Figueiredo, H. Takahashi, C. M. Wrasse, Y. Otsuka, K. Shiokawa, D. Barros

    Journal of Geophysical Research: Space Physics   Vol. 123 ( 3 ) page: 2215 - 2227   2018.3

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    A ground-based network of Global Navigation Satellite Systems receivers has been used to monitor medium-scale traveling ionospheric disturbances (MSTIDs). MSTIDs were studied using total electron content perturbation maps and keograms over south-southeast of Brazil during the period from December 2012 to February 2016. In total, 826 MSTIDs were observed mainly in daytime, thus presenting median values of horizontal wavelength, period, and horizontal phase velocity of 452 ± 107 km, 24 ± 4 min. and 323 ± 81 m/s, respectively. The direction of propagation varies on the season: during the winter (June–August), the waves preferentially propagated to north-northeast, while in the other seasons the waves propagated to other directions. The anisotropy observed in the MSTID propagation direction could be associated with the region of the gravity wave generation that takes place in the troposphere. We also found that the MSTIDs were observed most frequently during the daytime, between 11 and 15 local time in winter and near to dusk solar terminator (17–19 local time) in the other seasons. Furthermore, the occurrence of MSTIDs was higher in winter. We suggest that atmospheric gravity waves in the thermosphere, mesosphere, and troposphere could play an important role in generating the MSTIDs and the propagation direction may depend on location of the wave sources.

    DOI: 10.1002/2017JA025021

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  188. Daytime F-region irregularity triggered by rocket-induced ionospheric hole over low latitude Reviewed

    Guozhu Li, Baiqi Ning, M. A. Abdu, Chi Wang, Yuichi Otsuka, Weixing Wan, Jiuhou Lei, Michi Nishioka, Takuya Tsugawa, Lianhuan Hu, Guotao Yang, Chunxiao Yan

    Progress in Earth and Planetary Science   Vol. 5 ( 1 )   2018.2

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    Unexpected daytime F-region irregularities following the appearance of an ionospheric hole have been observed over low latitude. The irregularities developed initially above the F-region peak height (~ 360 km) with a thickness of about 30 km and an east-west extension of more than 200 km around 1057 LT and then expanded upward to 500 km altitude behaving like the equatorial spread-F (ESF) irregularities of the nighttime ionosphere. These daytime F-region irregularities cannot be explained on basis of an earlier suggestion that the F-region irregularities observed during daytime are the continuation of the irregularities initially generated on the previous night. Based on the coincidence, both in space and time, with the appearance of an ionospheric hole, which was generated after the passage of a rocket, we conclude that the daytime F-region irregularities must have been artificially generated locally through a manifestation of plasma instability triggered by the rocket exhaust-induced ionospheric hole over low latitude. [Figure not available: see fulltext.].

    DOI: 10.1186/s40645-018-0172-y

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  189. Discovery of 1 Hz Range Modulation of Isolated Proton Aurora at Subauroral Latitudes Reviewed

    M. Ozaki, K. Shiokawa, Y. Miyoshi, R. Kataoka, M. Connors, T. Inoue, S. Yagitani, Y. Ebihara, C. W. Jun, R. Nomura, K. Sakaguchi, Y. Otsuka, H. A. Uchida, I. Schofield, D. W. Danskin

    Geophysical Research Letters   Vol. 45 ( 3 ) page: 1209 - 1217   2018.2

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    Isolated proton aurora (IPA) is a manifestation of the wave-particle interaction visible at subauroral latitudes, with activity on many timescales. We herein present the first observational evidence of rapid luminous modulation of IPA correlated with simultaneously observed Pc1 waves observed on the ground, which are equivalent to the electromagnetic ion cyclotron (EMIC) waves in the magnetosphere. The fastest luminous modulation of IPA was observed in the 1 Hz frequency range, which was twice the frequency of the related Pc1 waves. The time lag between variations of Pc1 wave power and the IPA luminosity suggests that the source regions of IPA are distributed near the magnetic equator, suggesting an EMIC wave-energetic (a few tens of keV) proton or relativistic (MeV or sub-MeV) electron interaction. The generation mechanism of this 1 Hz luminous modulation remains an open issue, but this study supports the importance of nonlinear pitch angle scattering via wave-particle interactions.

    DOI: 10.1002/2017GL076486

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  190. Observations of Ultrawideband Signals in GPS TEC Variations over Europe during Solar Eclipse Reviewed

    Panasenko Sergii V, Chernogor Leonid F, Lazorenko Oleg V, Otsuka Yuichi, van de Kamp Max

    2018 9TH INTERNATIONAL CONFERENCE ON ULTRAWIDEBAND AND ULTRASHORT IMPULSE SIGNALS (UWBUSIS)     page: 115 - 118   2018

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  191. Temporal and spatial variations of mid-latitude ionospheric trough during a geomagnetic storm based on global GNSS-TEC and Arase satellite observations Reviewed

    2018 2ND URSI ATLANTIC RADIO SCIENCE MEETING (AT-RASC)     2018

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  192. First Study on the Occurrence Frequency of Equatorial Plasma Bubbles over West Africa Using an All-Sky Airglow Imager and GNSS Receivers Reviewed

    Daniel Okoh, Babatunde Rabiu, Kazuo Shiokawa, Yuichi Otsuka, Bolaji Segun, Elijah Falayi, Sylvester Onwuneme, Rafiat Kaka

    Journal of Geophysical Research: Space Physics   Vol. 122 ( 12 ) page: 12430 - 12444   2017.12

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    This is the first paper that reports the occurrence frequency of equatorial plasma bubbles and their dependences of local time, season, and geomagnetic activity based on airglow imaging observations at West Africa. The all-sky imager, situated in Abuja (Geographic: 8.99°N, 7.38°E
    Geomagnetic: 1.60°S), has a 180° fisheye view covering almost the entire airspace of Nigeria. Plasma bubbles are observed for 70 nights of the 147 clear-sky nights from 9 June 2015 to 31 January 2017. Differences between nighttime and daytime ROTIs were also computed as a proxy of plasma bubbles using Global Navigation Satellite Systems (GNSS) receivers within the coverage of the all-sky imager. Most plasma bubble occurrences are found during equinoxes and least occurrences during solstices. The occurrence rate of plasma bubbles was highest around local midnight and lower for hours farther away. Most of the postmidnight plasma bubbles were observed around the months of December to March, a period that coincides with the harmattan period in Nigeria. The on/off status of plasma bubble in airglow and GNSS observations were in agreement for 67.2% of the total 768 h, while we suggest several reasons responsible for the remaining 32.8% when the airglow and GNSS bubble status are inconsistent. A majority of the plasma bubbles were observed under relatively quiet geomagnetic conditions (Dst ≥ −40 and Kp ≤ 3), but there was no significant pattern observed in the occurrence rate of plasma bubbles as a function of geomagnetic activity. We suggest that geomagnetic activities could have either suppressed or promoted the occurrence of plasma bubbles.

    DOI: 10.1002/2017JA024602

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  193. Ground-based instruments of the PWING project to investigate dynamics of the inner magnetosphere at subauroral latitudes as a part of the ERG-ground coordinated observation network Reviewed

    Kazuo Shiokawa, Yasuo Katoh, Yoshiyuki Hamaguchi, Yuka Yamamoto, Takumi Adachi, Mitsunori Ozaki, Shin-Ichiro Oyama, Masahito Nose, Tsutomu Nagatsuma, Yoshimasa Tanaka, Yuichi Otsuka, Yoshizumi Miyoshi, Ryuho Kataoka, Yuki Takagi, Yuhei Takeshita, Atsuki Shinbori, Satoshi Kurita, Tomoaki Hori, Nozomu Nishitani, Iku Shinohara, Fuminori Tsuchiya, Yuki Obana, Shin Suzuki, Naoko Takahashi, Kanako Seki, Akira Kadokura, Keisuke Hosokawa, Yasunobu Ogawa, Martin Connors, J. Michael Ruohoniemi, Mark Engebretson, Esa Turunen, Thomas Ulich, Jyrki Manninen, Tero Raita, Antti Kero, Arto Oksanen, Marko Back, Kirsti Kauristie, Jyrki Mattanen, Dmitry Baishev, Vladimir Kurkin, Alexey Oinats, Alexander Pashinin, Roman Vasilyev, Ravil Rakhmatulin, William Bristow, Marty Karjala

    EARTH PLANETS AND SPACE   Vol. 69   2017.11

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    The plasmas (electrons and ions) in the inner magnetosphere have wide energy ranges from electron volts to mega-electron volts (MeV). These plasmas rotate around the Earth longitudinally due to the gradient and curvature of the geomagnetic field and by the co-rotation motion with timescales from several tens of hours to less than 10 min. They interact with plasma waves at frequencies of mHz to kHz mainly in the equatorial plane of the magnetosphere, obtain energies up to MeV, and are lost into the ionosphere. In order to provide the global distribution and quantitative evaluation of the dynamical variation of these plasmas and waves in the inner magnetosphere, the PWING project (study of dynamical variation of particles and waves in the inner magnetosphere using ground-based network observations, http://www.isee.nagoya-u.ac.jp/dimr/PWING/) has been carried out since April 2016. This paper describes the stations and instrumentation of the PWING project. We operate all-sky airglow/aurora imagers, 64-Hz sampling induction magnetometers, 40-kHz sampling loop antennas, and 64-Hz sampling riometers at eight stations at subauroral latitudes (similar to 60 degrees geomagnetic latitude) in the northern hemisphere, as well as 100-Hz sampling EMCCD cameras at three stations. These stations are distributed longitudinally in Canada, Iceland, Finland, Russia, and Alaska to obtain the longitudinal distribution of plasmas and waves in the inner magnetosphere. This PWING longitudinal network has been developed as a part of the ERG (Arase)-ground coordinated observation network. The ERG (Arase) satellite was launched on December 20, 2016, and has been in full operation since March 2017. We will combine these ground network observations with the ERG (Arase) satellite and global modeling studies. These comprehensive datasets will contribute to the investigation of dynamical variation of particles and waves in the inner magnetosphere, which is one of the most important research topics in recent space physics, and the outcome of our research will improve safe and secure use of geospace around the Earth.

    DOI: 10.1186/s40623-017-0745-9

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  194. The Solar Flux Dependence of Ionospheric 150 km Radar Echoes and Implications Reviewed

    A. K. Patra, P. Pavan Chaitanya, J.‐P. St.‐Maurice, Y. Otsuka, T. Yokoyama, M. Yamamoto

    Geophysical Research Letters   Vol. 44 ( 22 ) page: 11257 - 11264   2017.11

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    DOI: 10.1002/2017GL074678

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  195. On the effect of thermospheric neutral winds on post-midnight field-aligned irregularities at low latitudes Reviewed

    Tam Dao, Yuichi Otsuka, Kazuo Shiokawa, Michi Nishioka, Mamoru Yamamoto, Suhaila M. Buhari, Mardina Abdullah, Asnawi Husin

    2017 32nd General Assembly and Scientific Symposium of the International Union of Radio Science, URSI GASS 2017   Vol. 2017-   page: 1 - 4   2017.11

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    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

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  196. Geomagnetically conjugate observations of ionospheric and thermospheric variations accompanied by a midnight brightness wave at low latitudes (vol 69, 112, 2017) Reviewed

    D. Fukushima, K. Shiokawa, Y. Otsuka, M. Kubota, T. Yokoyama, M. Nishioka, S. Komonjinda, C. Y. Yatini

    EARTH PLANETS AND SPACE   Vol. 69   2017.11

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    DOI: 10.1186/s40623-017-0729-9

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  197. Characteristics of Seasonal Variation and Solar Activity Dependence of the Geomagnetic Solar Quiet Daily Variation Reviewed

    Atsuki Shinbori, Yukinobu Koyama, Masahito Nosé, Tomoaki Hori, Yuichi Otsuka

    Journal of Geophysical Research: Space Physics   Vol. 122 ( 10 ) page: 10796 - 10810   2017.10

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    Characteristics of seasonal variation and solar activity dependence of the X and Y components of the geomagnetic solar quiet (Sq) daily variation at Memambetsu in midlatitudes and Guam near the equator have been investigated using long-term geomagnetic field data with 1 h time resolution from 1957 to 2016. The monthly mean Sq variation in the X and Y components (Sq-X and Sq-Y) shows a clear seasonal variation and solar activity dependence. The amplitude of seasonal variation increases significantly during high solar activities and is proportional to the solar F10.7 index. The pattern of the seasonal variation is quite different between Sq-X and Sq-Y. The result of the correlation analysis between the solar F10.7 index and the Sq-X and Sq-Y shows an almost linear relationship, but the slope of the linear fitted line varies as a function of local time and month. This implies that the sensitivity of Sq-X and Sq-Y to the solar activity is different for different local times and seasons. The pattern of the local time and seasonal variations of Sq-Y at Guam shows good agreement with that of a magnetic field produced by interhemispheric field-aligned currents (FACs), which flow from the summer to winter hemispheres in the dawn and dusk sectors and from the winter to summer hemispheres in the prenoon to afternoon sectors. The direction of the interhemispheric FAC in the dusk sector is opposite to the concept of Fukushima's model.

    DOI: 10.1002/2017JA024342

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  198. Geomagnetically conjugate observations of ionospheric and thermospheric variations accompanied by a midnight brightness wave at low latitudes Reviewed

    D. Fukushima, K. Shiokawa, Y. Otsuka, M. Kubota, T. Yokoyama, M. Nishioka, S. Komonjinda, C. Y. Yatini

    EARTH PLANETS AND SPACE   Vol. 69   2017.8

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    We conducted geomagnetically conjugate observations of 630-nm airglow for a midnight brightness wave (MBW) at Kototabang, Indonesia [geomagnetic latitude (MLAT): 10.0 degrees S], and Chiang Mai, Thailand (MLAT: 8.9 degrees N), which are geomagnetically conjugate points at low latitudes. An airglow enhancement that was considered to be an MBW was observed in OI (630-nm) airglow images at Kototabang around local midnight from 2240 to 2430 LT on February 7, 2011. This MBW propagated south-southwestward, which is geomagnetically poleward, at a velocity of 290 m/s. However, a similar wave was not observed in the 630-nm airglow images at Chiang Mai. This is the first evidence of an MBW that does not have geomagnetic conjugacy, which also implies generation of MBW only in one side of the hemisphere from the equator. We simultaneously observed thermospheric neutral winds observed by a co-located Fabry-Perot interferometer at Kototabang. The observed meridional winds turned from northward (geomagnetically equatorward) to southward (geomagnetically poleward) just before the wave was observed. This indicates that the observed MBW was generated by the poleward winds which push ionospheric plasma down along geomagnetic field lines, thereby increasing the 630-nm airglow intensity. The bottomside ionospheric heights observed by ionosondes rapidly decreased at Kototabang and slightly increased at Chiang Mai. We suggest that the polarization electric field inside the observed MBW is projected to the northern hemisphere, causing the small height increase observed at Chiang Mai. This implies that electromagnetic coupling between hemispheres can occur even though the original disturbance is caused purely by the neutral wind.

    DOI: 10.1186/s40623-017-0698-z

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  199. Daytime zonal drifts in the ionospheric 150 km and E regions estimated using EAR observations Reviewed

    P. Pavan Chaitanya, A. K. Patra, Y. Otsuka, T. Yokoyama, M. Yamamoto, R. A. Stoneback, R. A. Heelis

    Journal of Geophysical Research: Space Physics   Vol. 122 ( 8 ) page: 9045 - 9055   2017.8

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    DOI: 10.1002/2017JA024589

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  200. Sixteen year variation of horizontal phase velocity and propagation direction of mesospheric and thermospheric waves in airglow images at Shigaraki, Japan Reviewed

    D. Takeo, K. Shiokawa, H. Fujinami, Y. Otsuka, T. S. Matsuda, M. K. Ejiri, T. Nakamura, M. Yamamoto

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 122 ( 8 ) page: 8770 - 8780   2017.8

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    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 degrees N, 136.1 degrees E, dip angle: 49 degrees) over similar to 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 the propagation direction of MSTIDs is mainly southwestward with a minor northeastward component throughout the 16 years. A clear negative correlation is seen between the yearly power spectral density of MSTIDs and F-10.7 solar flux. This negative correlation with solar activity may be explained by the linear growth rate of the Perkins instability and secondary wave generation of gravity waves in the thermosphere.

    DOI: 10.1002/2017JA023919

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  201. Equinoctial asymmetry in the zonal distribution of scintillation as observed by GPS receivers in Indonesia Reviewed

    P. Abadi, Y. Otsuka, K. Shiokawa, A. Husin, Huixin Liu, S. Saito

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 122 ( 8 ) page: 8947 - 8958   2017.8

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    We investigate the azimuthal distribution of amplitude scintillation observed by Global Positioning System (GPS) ground receivers at Pontianak (0.0 degrees S, 109.3 degrees E; magnetic latitude: 9.8 degrees S) and Bandung (6.9 degrees S, 107.6 degrees E; magnetic latitude: 16.7 degrees S) in Indonesia in March and September from 2011 to 2015. The scintillation is found to occur more to the west than to the east in March at both stations, whereas no such zonal difference is found in September. We also analyze the zonal scintillation drift as estimated using three closely spaced single-frequency GPS receivers at Kototabang (0.2 degrees S, 100.3 degrees E; magnetic latitude: 9.9 degrees S) in Indonesia during 2003-2015 and the zonal thermospheric neutral wind as measured by the CHAMP satellite at longitudes of 90 degrees-120 degrees E during 2001-2008. We find that the velocities of both the zonal scintillation drift and the neutral wind decrease with increasing latitudes. Interestingly, the latitudinal gradients of both the zonal scintillation drift and the neutral wind are steeper in March than in September. These steeper March gradients may be responsible for the increased westward altitudinal and latitudinal tilting of plasma bubbles in March. This equinoctial asymmetry could be responsible for the observed westward bias in scintillation in March, because the scintillation is more likely to occur when radio waves pass through longer lengths of plasma irregularities in the plasma bubbles.

    DOI: 10.1002/2017JA024146

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  202. Sixteen-year variation of horizontal phase velocity and propagation direction of mesospheric and thermospheric waves in airglow images at Shigaraki Reviewed

    Takeo, D, K. Shiokawa, H. Fujinami, Y. Otsuka, T. S. Matsuda, M. K. Ejiri, T. Nakamura, M. Yamamoto

    Journal of Geophysical Research -Atmospheres   Vol. 122   page: 8770-8780   2017.8

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    DOI: 10.0002/2017JA023919

  203. Coordinated observations of postmidnight irregularities and thermospheric neutral winds and temperatures at low latitudes Reviewed

    Tam Dao, Yuichi Otsuka, Kazuo Shiokawa, Michi Nishioka, Mamoru Yamamoto, Suhaila M. Buhari, Mardina Abdullah, Asnawi Husin

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 122 ( 7 ) page: 7504 - 7518   2017.7

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

    We investigated a postmidnight field-aligned irregularity (FAI) event observed with the Equatorial Atmosphere Radar at Kototabang (0.2 degrees S, 100.3 degrees E, dip latitude 10.4 degrees S) in Indonesia on the night of 9 July 2010 using a comprehensive data set of both neutral and plasma parameters. We examined the rate of total electron content change index (ROTI) obtained from GPS receivers in Southeast Asia, airglow images detected by an all-sky imager, and thermospheric neutral winds and temperatures obtained by a Fabry-Perot interferometer at Kototabang. Altitudes of the F layer (h'F) observed by ionosondes at Kototabang, Chiang Mai, and Chumphon were also surveyed. We found that the postmidnight FAIs occurred within plasma bubbles and coincided with kilometer-scale plasma density irregularities. We also observed an enhancement of the magnetically equatorward thermospheric neutral wind at the same time as the increase of h'F at low-latitude stations, but h'F at a station near the magnetic equator remained invariant. Simultaneously, a magnetically equatorward gradient of thermospheric temperature was identified at Kototabang. The convergence of equatorward neutral winds from the Northern and Southern Hemispheres could be associated with a midnight temperature maximum occurring around the magnetic equator. Equatorward neutral winds can uplift the F layer at low latitudes and increase the growth rate of Rayleigh-Taylor instabilities, causing more rapid extension of plasma bubbles. The equatorward winds in both hemispheres also intensify the eastward Pedersen current, so a large polarization electric field generated in the plasma bubble might play an important role in the generation of postmidnight FAIs.

    DOI: 10.1002/2017JA024048

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  204. Detection of Plasma Bubble in Ionosphere using GPS Receivers in Southeast Asia Reviewed

    Suhaila M. Buhari, Mardina Abdullah, Yuichi Otsuka, Tatsuhiro Yokoyama, Michi Nishioka, Alina Marie Hasbi, Takuya Tsugawa

    SAINS MALAYSIANA   Vol. 46 ( 6 ) page: 879 - 885   2017.6

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    Language:Malay   Publishing type:Research paper (scientific journal)   Publisher:UNIV KEBANGSAAN MALAYSIA  

    The equatorial ionosphere most often shows a nighttime plasma irregularity that is commonly referred as equatorial plasma bubble (PBB). The occurrence of PBB could cause rapid fluctuations in the amplitude and phase of the propagation radio signals and crucial to communication and navigation systems. The PBB normally occur successively where one structure rising after another during the sunset time. However, the onset time and location of the PBB are ubiquitous because the seed of the initial perturbation is not completely understood. Although various observation systems have been developed to capture the EPB, each of the measurement is limited with space and time resolution. This study aims to observe 2D structure of the PBB using high-density GPS receivers in Southeast Asia. GPS data was collected from 127 GPS receivers in Southeast Asia with the spacing distances of 30-120 km from each other. Total electron content (TEC) was derived from the difference between two signals from each GPS satellite. The signature of the PBB was detected using rate of TEC change index (ROTI) for all the available satellites to receiver paths. The 2D structure of the PBB was obtained by averaging GPS ROTI into 0.45 degrees latitude x 0.45 degrees longitude grid and projected at 300 km altitude. A case study on the night of 18 Mac 2011 showed the births of six PBB structures during the passage of the solar terminator along the 95 degrees E to 120 degrees E longitude. The separation distance between the PBB structures varied from 300 to 600 km. The separation distance between the EPB structures play an important role in determining the source of the seeding mechanism that believed in a form of wavelike structure.

    DOI: 10.17576/jsm-2017-4606-06

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  205. Measurement of thermospheric temperatures using OMTI Fabry-Perot interferometers with 70-mm etalon Reviewed

    Y. Nakamura, K. Shiokawa, Y. Otsuka, S. Oyama, S. Nozawa, T. Komolmis, S. Komonjida, Dave Neudegg, Colin Yuile, J. Meriwether, H. Shinagawa, H. Jin

    EARTH PLANETS AND SPACE   Vol. 69   2017.4

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    Fabry-Perot interferometer (FPI) is an instrument that can measure the temperature and wind velocity of the thermosphere through observations of airglow emission at a wavelength of 630.0 nm. The Solar-Terrestrial Environment Laboratory/Institute for Space-Earth Environmental Research, Nagoya University, has recently developed four new ground-based FPIs. One of those FPIs, possessing a large-aperture etalon (diameter: 116 mm), was installed in Tromso (FP01), Norway, in 2009. The other three small FPIs, using 70-mm-diameter etalons, were installed in Thailand (FP02), Indonesia (FP03) and Australia (FP04) in 2010-2011. They use highly sensitive cooled-CCD cameras with 1024 x 1024 pixels to obtain interference fringes. However, appropriate temperature has not been obtained from the interference fringes using these new small-aperture FPIs. In the present study we improved the analysis procedure of temperature determination using these FPIs. Each of FPIs measures north, south, east and west directions repeatedly by rotating two mirrors mounted on top of the FPI. We estimated center pixel of laser fringe and airglow fringes for each direction and found significant differences in the center pixel locations (a few pixels) among the measurement directions. These differences are considered to be caused by movement of the scanning mirror on the top of the optics, resulting in mechanical distortion of the optics body. By calculating the fringe center separately for each direction, we could correct these center pixel variations and determine the temperature with random errors of 10-40 K. This new method was employed to the all measurements from four FPIs after 2009 and provided temperatures with reasonably small errors. However, we found that temperatures below 400 K were obtained associated with weak airglow intensities and concluded using a model calculation that they are due to contamination of OH line emissions in the upper mesosphere. By defining an appropriate threshold of the fringe peak count, we successfully eliminated these unrealistic temperature values, and the corrected temperature values became comparable to those provided by the MSIS-90E and GAIA models.

    DOI: 10.1186/s40623-017-0643-1

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  206. Large-scale traveling ionospheric disturbances observed by GPS dTEC maps over North and South America on Saint Patrick's Day storm in 2015 Reviewed

    C. A. O. B. Figueiredo, C. M. Wrasse, H. Takahashi, Y. Otsuka, K. Shiokawa, D. Barros

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 122 ( 4 ) page: 4755 - 4763   2017.4

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    Large-scale traveling ionospheric disturbances (LSTIDs) were detected in both Northern and Southern Hemispheres over American sector during the geomagnetic storm on 17-18 March 2015, also known as the Saint Patrick's Day storm. Detrended total electronic content (dTEC) maps were made using dense GNSS network receiver data. The retrieved LSTIDs showed wavelengths of 1000 to 2000 km, phase velocity of similar to 300-1000 m/s, and period of similar to 30-50 min. Among them, three couples of LSTIDs were observed propagating from the polar regions to low latitudes. Two wave events observed in daytime showed the propagation direction of southwest in the Northern Hemisphere and northeast in the Southern Hemisphere, which means an asymmetric propagation against the geographic equator. The other wave event observed during the evening hour showed symmetric propagation direction, i.e., southwest in the Northern Hemisphere and northwest in the Southern Hemisphere, whereas their wavelength and phase velocity are significantly different between NH and SH. These observations indicate that the two groups of LSTID have different propagation conditions from polar to low-latitude regions. The observed asymmetric/symmetric propagation forms suggest asymmetric/symmetric auroral current activity between the northern and southern polar regions.

    DOI: 10.1002/2016JA023417

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  207. Climatology of successive equatorial plasma bubbles observed by GPS ROTI over Malaysia Reviewed

    S. M. Buhari, M. Abdullah, T. Yokoyama, Y. Otsuka, M. Nishioka, A. M. Hasbi, S. A. Bahari, T. Tsugawa

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 122 ( 2 ) page: 2174 - 2184   2017.2

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    The occurrence rate of the equatorial plasma bubble (EPB) with season, solar activity, and geomagnetic conditions are investigated using long-term data sets of Malaysia Real-Time Kinematics Network (MyRTKnet) from 2008 to 2013. The rate of TEC (total electron content) change index (ROTI) in 5 min was derived from MyRTKnet data to detect the EPB with scale sizes around tens of kilometers. Then, the daily east-west cross sections of 2-D ROTI maps were used to examine the EPB features over 100 degrees E-119 degrees E longitudes. The EPBs tend to occur successively in one night along the observational coverage of MyRTKnet during equinoxes in high solar activity years. The perturbations in a form of wavelike structures along the observed longitudes might be responsible for the development of successive EPBs due to high growth rate of the Rayleigh-Taylor instability (RTI) process. On the contrary, the occurrence of successive EPBs is infrequent and the occurrence day of EPB remains active during equinoctial months in low solar activity years. The small growth rate of the RTI process during low solar activity years might require a strong seed perturbation to generate the EPB structure. The occurrence probability of the EPB was found to be similar during quiet and disturbed geomagnetic conditions. The results imply that the strong perturbations play an important role in the development of the EPB in low solar activity years. Nonetheless, the high growth rate of the RTI could cause the successive occurrence of the EPB in high solar activity years.

    DOI: 10.1002/2016JA023202

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  208. STATISTICAL ANALYSIS OF THE OCCURRENCES OF MSTIDs OBSERVED BY ALL-SKY IMAGER IN LOW MAGNETIC LATITUDE Reviewed

    2017 IEEE INTERNATIONAL GEOSCIENCE AND REMOTE SENSING SYMPOSIUM (IGARSS)     page: 4425 - 4428   2017

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  209. The first long-term all-sky imager observation of lunar sodium tail Reviewed

    Masaki N. Nishino, Kazuo Shiokawa, Yuichi Otsuka

    ICARUS   Vol. 280   page: 199 - 204   2016.12

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:ACADEMIC PRESS INC ELSEVIER SCIENCE  

    The Moon possesses a long tail of neutral sodium atoms that are emitted from the lunar surface and transported anti-sunward by the solar radiation pressure. Since the earth crosses the lunar sodium tail for a few days around the new moon, the resonant light emission from sodium atoms can be detected from the ground. Here we show the first long-term (16 years) observation of the lunar sodium tail, using an all-sky imager at Shigaraki Observatory (35 degrees N, 136 degrees E), Japan. We have surveyed our database of all-sky sodium images at a wavelength of 5893 nm to find more than 20 events in which a bright spot emerges around the anti-lunar point during the new moon periods. We could not find any clear correlation between the sodium brightness and solar wind parameters (density, speed, dynamic pressure, and F10.7 index). In particular, no enhancement of the sodium spot brightness is detected even under very high density solar wind conditions (70 cm(-3); an order-of-magnitude higher than usual), which means that solar wind sputtering is not a principal mechanism of the formation of the lunar sodium tail. (C) 2016 Elsevier Inc. All rights reserved.

    DOI: 10.1016/j.icarus.2016.08.004

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  210. Three years of concentric gravity wave variability in the mesopause as observed by IMAP/VISI Reviewed

    S. Perwitasari, T. Sakanoi, T. Nakamura, M. K. Ejiri, M. Tsutsumi, Y. Tomikawa, Y. Otsuka, A. Yamazaki, A. Saito

    GEOPHYSICAL RESEARCH LETTERS   Vol. 43 ( 22 ) page: 11528 - 11535   2016.11

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    We report a statistical study on concentric gravity waves (CGWs) in the mesopause (similar to 95 km) using 3 years nightglow data obtained by Ionosphere, Mesosphere, upper Atmosphere and Plasmasphere/Visible and near-Infrared Spectral Imager. The 235 CGWs events were found with horizontal wavelength ranging from 40 to 250 km and maximum radius of 200 to 3000 km. The latitudinal distribution of the CGWs centers had peaks in mid latitude (40 degrees N and 40 degrees S) and minimum at low latitudes (10 degrees S). More events were found in the summer hemisphere midlatitudes, with a rapid transition between northern and Southern Hemisphere around the equinoxes. The occurrence probability was significantly higher during nonsolstice months (February-May and August-November) than solstice months (June-July and December-January), suggesting that there was a little breaking or critical level absorption so the waves could reach the mesopause more often during these periods. The global distribution showed several preferable regions but very few events over tropical convective regions.

    DOI: 10.1002/2016GL071511

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  211. Ionospheric TEC Weather Map Over South America Reviewed

    H. Takahashi, C. M. Wrasse, C. M. Denardini, M. B. Padua, E. R. de Paula, S. M. A. Costa, Y. Otsuka, K. Shiokawa, J. F. Galera Monico, A. Ivo, N. Sant'Anna

    SPACE WEATHER-THE INTERNATIONAL JOURNAL OF RESEARCH AND APPLICATIONS   Vol. 14 ( 11 ) page: 937 - 949   2016.11

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

    Ionospheric weather maps using the total electron content (TEC) monitored by ground-based Global Navigation Satellite Systems (GNSS) receivers over South American continent, TECMAP, have been operationally produced by Instituto Nacional de Pesquisas Espaciais's Space Weather Study and Monitoring Program (Estudo e Monitoramento Brasileiro de Clima Especial) since 2013. In order to cover the whole continent, four GNSS receiver networks, (Rede Brasileiro de Monitoramento Continuo) RBMC/Brazilian Institute for Geography and Statistics, Low-latitude Ionospheric Sensor Network, International GNSS Service, and Red Argentina de Monitoreo Satelital Continuo, in total similar to 140 sites, have been used. TECMAPs with a time resolution of 10min are produced in 12h time delay. Spatial resolution of the map is rather low, varying between 50 and 500km depending on the density of the observation points. Large day-to-day variabilities of the equatorial ionization anomaly have been observed. Spatial gradient of TEC from the anomaly trough (total electron content unit, 1TECU=10(16)elm(-2) (TECU) &lt;10) to the crest region (TECU&gt;80) causes a large ionospheric range delay in the GNSS positioning system. Ionospheric plasma bubbles, their seeding and development, could be monitored. This plasma density (spatial and temporal) variability causes not only the GNSS-based positioning error but also radio wave scintillations. Monitoring of these phenomena by TEC mapping becomes an important issue for space weather concern for high-technology positioning system and telecommunication.

    DOI: 10.1002/2016SW001474

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  212. On the fresh development of equatorial plasma bubbles around the midnight hours of June solstice Reviewed

    K. K. Ajith, S. Tulasi Ram, M. Yamamoto, Y. Otsuka, K. Niranjan

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 121 ( 9 ) page: 9051 - 9062   2016.9

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    Using the 47MHz Equatorial Atmosphere Radar (EAR) at Kototabang, Indonesia, the nocturnal evolution of equatorial plasma bubbles (EPBs) was examined during the moderate solar activity years 2011-2012. While the evolution of EPBs was mostly (86%) confined to post sunset hours (1900-2100LT) during equinoxes, in contrast, the majority of EPBs (similar to 71%) in June solstice found evolve around the midnight hours (2200-0300LT). The mechanisms behind the fresh evolution of summer time midnight EPBs were investigated, for the first time, through SAMI2 model simulations with a realistic input of background ExB drift variation derived from CINDI IVM on board C/NOFS satellite. The term-by-term analysis of linear growth rate of RT instability indicates that the formation of high flux tube electron content height gradient (K-F) (steep vertical gradient) region at higher altitudes is the key factor for the enhanced growth rate of RT instability. The responsible factors are discussed in light of relatively weak westward zonal electric field in the presence of equatorward neutral wind and bottomside recombination around the midnight hours of June solstice. The effects of neutral winds and weak westward electric fields on the uplift of equatorial F layer were examined separately using controlled SAMI2 simulations. The results indicate that relatively larger linear growth rate is more likely to occur around midnight during June solstice because of relatively weak westward electric field than other local times in the presence of equatorward meridional wind.

    DOI: 10.1002/2016JA023024

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  213. Fast modulations of pulsating proton aurora related to subpacket structures of Pc1 geomagnetic pulsations at subauroral latitudes Reviewed

    M. Ozaki, K. Shiokawa, Y. Miyoshi, R. Kataoka, S. Yagitani, T. Inoue, Y. Ebihara, C. -W Jun, R. Nomura, K. Sakaguchi, Y. Otsuka, M. Shoji, I. Schofield, M. Connors, V. K. Jordanova

    GEOPHYSICAL RESEARCH LETTERS   Vol. 43 ( 15 ) page: 7859 - 7866   2016.8

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    To understand the role of electromagnetic ion cyclotron (EMIC) waves in determining the temporal features of pulsating proton aurora (PPA) via wave-particle interactions at subauroral latitudes, high-time-resolution (1/8s) images of proton-induced N-2(+) emissions were recorded using a new electron multiplying charge-coupled device camera, along with related Pc1 pulsations on the ground. The observed Pc1 pulsations consisted of successive rising-tone elements with a spacing for each element of 100s and subpacket structures, which manifest as amplitude modulations with a period of a few tens of seconds. In accordance with the temporal features of the Pc1 pulsations, the auroral intensity showed a similar repetition period of 100s and an unpredicted fast modulation of a few tens of seconds. These results indicate that PPA is generated by pitch angle scattering, nonlinearly interacting with Pc1/EMIC waves at the magnetic equator.

    DOI: 10.1002/2016GL070008

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  214. Enhanced ionospheric plasma bubble generation in more active ITCZ Reviewed

    Guozhu Li, Yuichi Otsuka, Baiqi Ning, M. A. Abdu, M. Yamamoto, Weixing Wan, Libo Liu, Prayitno Abadi

    GEOPHYSICAL RESEARCH LETTERS   Vol. 43 ( 6 ) page: 2389 - 2395   2016.3

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    A close link between the atmospheric Intertropical Convergence Zone (ITCZ) and ionospheric plasma bubble has been proposed since the last century. But this relationship has often appeared to be less than convincing due to the simultaneous roles played by several other factors in shaping the global distribution of ionospheric bubbles. From simultaneous collaborative radar multibeam steering measurements at Kototabang (0.2 degrees S, 100.3 degrees E) and Sanya (18.4 degrees N, 109.6 degrees E), conducted during September-October of 2012 and 2013, we find that the total numbers of nights with bubble (i.e., occurrence rates) at the two closely located longitudes (Kototabang and Sanya) are comparable. But interestingly, the total number of nights with locally generated bubble (i.e., generation rate) over Kototabang is clearly more than that over Sanya. Further analysis reveals that a more active ITCZ is situated around the longitude of Kototabang. We surmise that the enhanced ionospheric bubble generation at Kototabang longitude could be caused by a higher gravity wave activity associated with the more active ITCZ.

    DOI: 10.1002/2016GL068145

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  215. Altitude development of postmidnight F region field-aligned irregularities observed using Equatorial Atmosphere Radar in Indonesia Reviewed

    Tam Dao, Yuichi Otsuka, Kazuo Shiokawa, S. Tulasi Ram, Mamoru Yamamoto

    GEOPHYSICAL RESEARCH LETTERS   Vol. 43 ( 3 ) page: 1015 - 1022   2016.2

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    For the first time, vertical rise velocities of postmidnight field-aligned irregularities (FAIs) at low geomagnetic latitudes have been examined near the June solstice by using two-dimensional maps of F region FAI echoes observed with the Equatorial Atmosphere Radar in Indonesia for 3years starting in May 2010. We found 15 freshly growing FAIs at postmidnight between May and August during the 3years. The rise velocities of FAIs are smaller at postmidnight than at postsunset, and most postmidnight FAIs do not exceed an altitude of 450km. Based on the rise velocities, a lower limit for the creation time of the postmidnight FAIs is estimated to be between 21:30LT and 02:00LT for 14 of the 15 events, indicating that this class of FAIs is distinct from the postsunset FAIs.

    DOI: 10.1002/2015GL067432

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  216. Pulsating proton aurora caused by rising tone Pc1 waves Reviewed

    R. Nomura, K. Shiokawa, Y. Omura, Y. Ebihara, Y. Miyoshi, K. Sakaguchi, Y. Otsuka, M. Connors

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 121 ( 2 ) page: 1608 - 1618   2016.2

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    We found rising tone emissions with a dispersion of approximate to 1Hz per several tens of seconds in the dynamic spectrum of a Pc1 geomagnetic pulsation (Pc1) observed on the ground. These Pc1 rising tones were successively observed over approximate to 30min from 0250UT on 14 October 2006 by an induction magnetometer at Athabasca, Canada (54.7 degrees N, 246.7 degrees E, magnetic latitude 61.7 degrees N). Simultaneously, a Time History of Events and Macroscale Interactions during Substorms panchromatic (THEMIS) all-sky camera detected pulsations of an isolated proton aurora with a period of several tens of seconds, approximate to 10% variations in intensity, and fine structures of 3 degrees in magnetic longitudes. The pulsations of the proton aurora close to the zenith of ATH have one-to-one correspondences with the Pc1 rising tones. This suggests that these rising tones scatter magnetospheric protons intermittently at the equatorial region. The radial motion of the magnetospheric source, of which the isolated proton aurora is a projection, can explain the central frequency increase of Pc1, but not the shorter period (tens of seconds) frequency increase of approximate to 1Hz in Pc1 rising tones. We suggest that EMIC-triggered emissions generate the frequency increase of Pc1 rising tones on the ground and that they also cause the Pc1 pearl structure, which has a similar characteristic time.

    DOI: 10.1002/2015JA021681

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  217. Duskside enhancement of equatorial zonal electric field response to convection electric fields during the St. Patrick's Day storm on 17 March 2015 Reviewed

    S. Tulasi Ram, T. Yokoyama, Y. Otsuka, K. Shiokawa, S. Sripathi, B. Veenadhari, R. Heelis, K. K. Ajith, V. S. Gowtam, S. Gurubaran, P. Supnithi, M. Le Huy

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 121 ( 1 ) page: 538 - 548   2016.1

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    The equatorial zonal electric field responses to prompt penetration of eastward convection electric fields (PPEF) were compared at closely spaced longitudinal intervals at dusk to premidnight sectors during the intense geomagnetic storm of 17 March 2015. At dusk sector (Indian longitudes), a rapid uplift of equatorial F layer to &gt;550km and development of intense equatorial plasma bubbles (EPBs) were observed. These EPBs were found to extend up to 27.13 degrees N and 25.98 degrees S magnetic dip latitudes indicating their altitude development to similar to 1670km at apex. In contrast, at few degrees east in the premidnight sector (Thailand-Indonesian longitudes), no significant height rise and/or EPB activity has been observed. The eastward electric field perturbations due to PPEF are greatly dominated at dusk sector despite the existence of background westward ionospheric disturbance dynamo (IDD) fields, whereas they were mostly counter balanced by the IDD fields in the premidnight sector. In situ observations from SWARM-A and SWARM-C and Communication/Navigation Outage Forecasting System satellites detected a large plasma density depletion near Indian equatorial region due to large electrodynamic uplift of F layer to higher than satellite altitudes. Further, this large uplift is found to confine to a narrow longitudinal sector centered on sunset terminator. This study brings out the significantly enhanced equatorial zonal electric field in response to PPEF that is uniquely confined to dusk sector. The responsible mechanisms are discussed in terms of unique electrodynamic conditions prevailing at dusk sector in the presence of convection electric fields associated with the onset of a substorm under southward interplanetary magnetic field B-z.

    DOI: 10.1002/2015JA021932

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  218. ISS-IMAPによる大気光波状構造の観測

    齊藤昭則, 穂積裕太, 坂野井健, S. Perwitasari, 吉川一朗, 山崎敦, 大塚雄一, 山本衛

        2016

  219. TEC variation during high and low solar activities over South American sector Reviewed

    O. F. Jonah, E. R. de Paula, M. T. A. H. Muella, S. L. G. Dutra, E. A. Kherani, P. M. S. Negreti, Y. Otsuka

    JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS   Vol. 135   page: 22 - 35   2015.12

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:PERGAMON-ELSEVIER SCIENCE LTD  

    Using dual frequency GPS receivers in the South American sector, the measurement of absolute ionospheric Total Electron Content (TEC) has been estimated applying the Nagoya ionospheric model for both the years of 2009 and 2001, which represent low and high solar activities, respectively. The diurnal, day-to-day, monthly, seasonal, latitudinal and longitudinal variations of TEC were studied for equatorial and low latitude regions of South America. The strength and characteristics of the Equatorial Ionization Anomaly (EIA) were equally analyzed. The analyses reveal the diurnal, seasonal and semidiurnal TEC variation, as well as the nighttime variability during the low and high solar activities. Wavelet power spectra analysis was employed to check the periodicities of the TEC data, F10.7 and zonal and meridional wind velocities measured by Meteor radar at similar to 100 km altitude. Periods such as 27, 16, 8-10, 1-5 days were found to be dominant in the zonal and meridional wind velocity corresponding with those of TEC periodicities. Hence, besides the solar radiation, we suggest that there are contributions of tides and planetary waves in spatial and temporal TEC enhancement and variations during the geomagnetic quiet periods of both solar activities. (C) 2015 Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.jastp.2015.10.005

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  220. A direct link between chorus emissions and pulsating aurora on timescales from milliseconds to minutes: A case study at subauroral latitudes Reviewed

    Mitsunori Ozaki, Satoshi Yagitani, Kaoru Sawai, Kazuo Shiokawa, Yoshizumi Miyoshi, Ryuho Kataoka, Akimasa Ieda, Yusuke Ebihara, Martin Connors, Ian Schofield, Yuto Katoh, Yuichi Otsuka, Naoki Sunagawa, Vania K. Jordanova

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 120 ( 11 ) page: 9617 - 9631   2015.11

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    A correlation was observed between chorus emissions and pulsating aurora (PA) from observations at Athabasca (L approximate to 4.3) in Canada at 9: 00-9: 20 UT on 7 February 2013, using an electron multiplying charge-coupled device camera and a VLF loop antenna with sampling rates of 110 Hz and 100 kHz, respectively. Pulsating aurora having a quasiperiodic variation in luminosity and a few hertz modulation was observed together with chorus emissions consisting of a group of successive rising-tone elements. The repetition period and modulation frequency of the PA are in good agreement with those of the modulated chorus. After 9: 11 UT, the temporal features of the aurora became aperiodic PA of indistinct modulation. Simultaneously, the rising-tone chorus turned into chorus emissions consisting of numerous rising-tone elements. The equatorial geomagnetic field inhomogeneity calculated using the Tsyganenko 2002 model shows a decreasing trend during the period. This result is consistent with nonlinear wave growth theory having a small geomagnetic field inhomogeneity, which contributes to a decrease in the threshold amplitude to trigger discrete chorus elements. These observations show a close connection between chorus emissions and PA on timescales from milliseconds for generation of discrete chorus elements on the microphysics of wave-particle interaction to minutes for the variations of the geomagnetic field inhomogeneity related with the substorm activity.

    DOI: 10.1002/2015JA021381

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  221. Coordinated airglow observations between IMAP/VISI and a ground-based all-sky imager on concentric gravity wave in the mesopause Reviewed

    S. Perwitasari, T. Sakanoi, A. Yamazaki, Y. Otsuka, Y. Hozumi, Y. Akiya, A. Saito, K. Shiokawa, S. Kawamura

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 120 ( 11 ) page: 9706 - 9721   2015.11

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    We present a study of concentric gravity waves (CGWs) event from the coordinated observation between Ionosphere, Mesosphere, upper Atmosphere, and Plasmasphere mapping (IMAP)/Visible and near-Infrared Spectral Imager (VISI), all-sky camera at Rikubetsu, Multi-functional Transport Satellite (MTSAT), Tropical Rainfall Measuring Mission, and MF radar at Wakkanai combined with Modern-Era Retrospective Analysis for Research and Application data. IMAP/VISI is the first space-based imager that capable of imaging the airglow in the mesosphere and lower thermosphere region in the nadir-looking direction. Therefore, it has a unique ability to observe a great extend of CGWs propagation. Arc-like shaped, part of CGWs pattern was observed around themesopause (similar to 95 km) in the O-2 762 nm airglow emission obtained by IMAP/VISI at 1204 UT on 18 October 2012. Similar patterns were also observed by the all-sky imager at Rikubetsu (43.5 degrees N, 143.8 degrees E) in OI 557.7 nm and OH band airglow emissions from similar to 1100 to 1200 UT. Horizontal wavelengths of the observed small-scale gravity waves are similar to 50 km (OH band and OI 557.7nm) and similar to 67 km (O-2 762 nm). The source is suggested to be a deep convective activity over Honshu Island which likely was an enhanced convective activity related to a typhoon in the south of Japan. The data showed that the CGWs could propagate up to similar to 1400-1500km horizontally from the source to the mesopause but not farther away. Using atmospheric temperature profiles obtained by Thermospheric Ionosphere Mesosphere Energetics Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry, we conclude that this long-distance propagation of the waves could be caused by thermal duct in the middle atmosphere. The arc-like shaped instead of full circle pattern points out that the wind filtering effect is significant for the particular direction of wave propagation.

    DOI: 10.1002/2015JA021424

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  222. Multi-instrument, high-resolution imaging of polar cap patch transportation Reviewed

    E. G. Thomas, K. Hosokawa, J. Sakai, J. B. H. Baker, J. M. Ruohoniemi, S. Taguchi, K. Shiokawa, Y. Otsuka, A. J. Coster, J. -P. St.-Maurice, K. A. McWilliams

    RADIO SCIENCE   Vol. 50 ( 9 ) page: 904 - 915   2015.9

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    Transionospheric radio signals in the high-latitude polar cap are susceptible to degradation when encountering sharp electron density gradients associated with discrete plasma structures, or patches. Multi-instrument measurements of polar cap patches are examined during a geomagnetic storm interval on 22 January 2012. For the first time, we monitor the transportation of patches with high spatial and temporal resolution across the polar cap for 1-2 h using a combination of GPS total electron content (TEC), all-sky airglow imagers (ASIs), and Super Dual Auroral Radar Network (SuperDARN) HF radar backscatter. Simultaneous measurements from these data sets allow for continuous tracking of patch location, horizontal extent, and velocity despite adverse observational conditions for the primary technique (e.g., sunlit regions in the ASI data). Spatial collocation between patch-like features in relatively coarse but global GPS TEC measurements and those mapped by high-resolution ASI data was very good, indicating that GPS TEC can be applied to track patches continuously as they are transported across the polar cap. In contrast to previous observations of cigar-shaped patches formed under weakly disturbed conditions, the relatively narrow dawn-dusk extent of patches in the present interval (500-800 km) suggests association with a longitudinally confined plasma source region, such as storm-enhanced density (SED) plume. SuperDARN observations show that the backscatter power enhancements corresponded to the optical patches, and for the first time we demonstrate that the motion of the optical patches was consistent with background plasma convection velocities.

    DOI: 10.1002/2015RS005672

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  223. Plasma bubble monitoring by TEC map and 630 nm airglow image Reviewed

    H. Takahashi, C. M. Wrasse, Y. Otsuka, A. Ivo, V. Gomes, I. Paulino, A. F. Medeiros, C. M. Denardini, N. Sant'Anna, K. Shiokawa

    JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS   Vol. 130   page: 151 - 158   2015.8

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:PERGAMON-ELSEVIER SCIENCE LTD  

    Equatorial ionosphere plasma bubbles over the South American continent were successfully observed by mapping the total electron content (TECMAP) using data provided by ground-based GNSS receiver networks. The TECMAP could cover almost all of the continent within 4000 km distance in longitude and latitude, monitoring TEC variability continuously with a time resolution of 10 min. Simultaneous observations of OI 630 nm all-sky image at Cachoeira Paulista (22.7 degrees S, 45.0 degrees W) and Cariri (7.4 degrees S, 36.5 degrees W) were used to compare the bubble structures. The spatial resolution of the TECMAP varied from 50 km to 1000 km, depending on the density of the observation sites. On the other hand, optical imaging has a spatial resolution better than 15 km, depicting the fine structure of the bubbles but covering a limited area (similar to 1600 km diameter). TECMAP has an advantage in its spatial coverage and the continuous monitoring (day and night) form. The initial phase of plasma depletion in the post-sunset equatorial ionization anomaly (PS-EIA) trough region, followed by development of plasma bubbles in the crest region, could be monitored in a progressive way over the magnetic equator. In December 2013 to January 2014, periodically spaced bubble structures were frequently observed. The longitudinal spacing between the bubbles was around 600-800 km depending on the day. The periodic form of plasma bubbles may suggest a seeding process related to the solar terminator passage in the ionosphere. (C) 2015 Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.jastp.2015.06.003

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  224. Statistical study of auroral fragmentation into patches Reviewed

    Ayumi Hashimoto, Kazuo Shiokawa, Yuichi Otsuka, Shin-ichiro Oyama, Satonori Nozawa, Tomoaki Hori, Mark Lester, Magnar Gullikstad Johnsen

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 120 ( 8 ) page: 6207 - 6217   2015.8

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    The study of auroral dynamics is important when considering disturbances of the magnetosphere. Shiokawa et al. (2010, 2014) reported observations of finger-like auroral structures that cause auroral fragmentation. Those structures are probably produced by macroscopic instabilities in the magnetosphere, mainly of the Rayleigh-Taylor type. However, the statistical characteristics of these structures have not yet been investigated. Here based on observations by an all-sky imager at TromsO (magnetic latitude=67.1 degrees N), Norway, over three winter seasons, we statistically analyzed the occurrence conditions of 14 large-scale finger-like structures that developed from large-scale auroral regions including arcs and 6 small-scale finger-like structures that developed in auroral patches. The large-scale structures were seen from midnight to dawn local time and usually appeared at the beginning of the substorm recovery phase, near the low-latitude boundary of the auroral region. The small-scale structures were primarily seen at dawn and mainly occurred in the late recovery phase of substorms. The sizes of these large- and small-scale structures mapped in the magnetospheric equatorial plane are usually larger than the gyroradius of 10keV protons, indicating that the finger-like structures could be caused by magnetohydrodynamic instabilities. However, the scale of small structures is only twice the gyroradius of 10keV protons, suggesting that finite Larmor radius effects may contribute to the formation of small-scale structures. The eastward propagation velocities of the structures are -40 to +200m/s and are comparable with those of plasma drift velocities measured by the colocating Super Dual Auroral Radar Network radar.

    DOI: 10.1002/2015JA021000

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  225. Fresh and evolutionary-type field-aligned irregularities generated near sunrise terminator due to overshielding electric fields Reviewed

    S. Tulasi Ram, K. K. Ajith, M. Yamamoto, Y. Otsuka, T. Yokoyama, K. Niranjan, S. Gurubaran

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 120 ( 7 ) page: 5922 - 5930   2015.7

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    The unusual evolution of fresh and intense field-aligned irregularities (FAI) near sunrise terminator which further sustained for more than 90min of postsunrise period was observed by Equatorial Atmosphere Radar at Kototabang during a minor geomagnetic storm period. These FAI echoes were initially observed around 250-350km altitudes, growing upward under eastward polarization electric fields indicating the plasma bubbles that are fully depleted along the flux tube. The background low-latitude F layer dynamics that lead to the development of these dawn time FAI have been investigated from two ionosondes at near magnetic conjugate low-latitude locations. A minor geomagnetic storm was in progress which did not appear to cause any large electric field perturbations at preceding postsunset to midnight period over Indonesian sector. However, the prompt penetration of overshielding electric fields associated with sudden northward turning of interplanetary magnetic field B-z caused spectacular ascent of F layer and development of fresh, intense, and upward evolutionary plasma bubbles near sunrise terminator.

    DOI: 10.1002/2015JA021427

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  226. Effects of pre-reversal enhancement of E x B drift on the latitudinal extension of plasma bubble in Southeast Asia Reviewed

    Prayitno Abadi, Yuichi Otsuka, Takuya Tsugawa

    EARTH PLANETS AND SPACE   Vol. 67   2015.5

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    We investigated the effects of the F region bottomside altitude (h'F), maximum upward E x B drift velocity, duration of pre-reversal enhancement and the integral of upward E x B drift on the latitudinal extension of equatorial plasma bubbles in the Southeast Asian sector using the observations recorded by three GPS receivers and two ionosondes. The GPS receivers are installed at Kototabang (0.2 degrees S, 100.3 degrees E; 9.9 degrees S magnetic latitude), Pontianak (0.02 degrees S, 109.3 degrees E; 9.8 degrees S magnetic latitude) and Bandung (6.9 degrees S, 107.6 degrees E; 16.7 degrees S magnetic latitude) in Indonesia. The ionosondes are installed at magnetically equatorial stations, Chumphon (10.7 degrees N, 99.4 degrees E; 0.86 degrees N magnetic latitude) in Thailand and Bac Lieu (9.3 degrees N, 105.7 degrees E; 0.62 degrees N magnetic latitude) in Vietnam. We analysed those observations acquired in the equinoctial months (March, April, September and October) in 2010-2012, when the solar activity index F-10.7 was in the range from 75 to 150. Assuming that plasma bubbles are the major source of scintillations, the latitudinal extension of the bubbles was determined according to the S4 index. We have found that the peak of h'F, maximum upward E x B drift and the integral of upward E x B drift during the pre-reversal enhancement period are positively correlated with the maximum latitude extension of plasma bubbles, but that duration of pre-reversal enhancement does not show correlation. The plasma bubbles reached magnetic latitudes of 10 degrees-20 degrees in the following conditions: (1) the peak value of h'F is greater than 250-450 km, (2) the maximum upward E x B drift is greater than 10-70 m/s and (3) the integral of upward E x B drift is greater than 50-250 m/s. These results suggest that the latitudinal extension of plasma bubbles is controlled mainly by the magnitude of pre-reversal enhancement and the peak value of h'F at the initial phase of development of plasma bubbles (or equatorial spread F) rather than by the duration of pre-reversal enhancement.

    DOI: 10.1186/s40623-015-0246-7

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  227. Airglow-imaging observation of plasma bubble disappearance at geomagnetically conjugate points Reviewed

    Kazuo Shiokawa, Yuichi Otsuka, Kenneth J. W. Lynn, Philip Wilkinson, Takuya Tsugawa

    EARTH PLANETS AND SPACE   Vol. 67   page: 1 - 12   2015.3

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    We report the first observation of the disappearance of a plasma bubble over geomagnetically conjugate points. It was observed by airglow imagers at Darwin, Australia (magnetic latitude: -22 degrees N) and Sata, Japan (21 degrees N) on 8 August 2002. The plasma bubble was observed in 630-nm airglow images from 1530 (0030 LT) to 1800 UT (0300 LT) and disappeared equatorward at 1800 to 1900 UT (0300 to 0400 LT) in the field of view. The ionograms at Darwin and Yamagawa (20 km north of Sata) show strong spread-F signatures at approximately 16 to 21 UT. At Darwin, the F-layer virtual height suddenly increased from approximately 200 to approximately 260 km at the time of bubble disappearance. However, a similar F-layer height increase was not observed over the conjugate point at Yamagawa, indicating that this F-layer rise was caused not by an eastward electric field but by enhancement of the equatorward thermospheric wind over Darwin. We think that this enhancement of the equatorward neutral wind was caused by an equatorward-propagating large-scale traveling ionospheric disturbance, which was identified in the north-south keogram of 630-nm airglow images. We speculate that polarization electric field associated with this equatorward neutral wind drive plasma drift across the magnetic field line to cause the observed bubble disappearance.

    DOI: 10.1186/s40623-015-0202-6

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  228. Geomagnetically conjugate observation of plasma bubbles and thermospheric neutral winds at low latitudes Reviewed

    D. Fukushima, K. Shiokawa, Y. Otsuka, M. Nishioka, M. Kubota, T. Tsugawa, T. Nagatsuma, S. Komonjinda, C. Y. Yatini

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 120 ( 3 ) page: 2222 - 2231   2015.3

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    This is the first paper that reports simultaneous observations of zonal drift of plasma bubbles and the thermospheric neutral winds at geomagnetically conjugate points in both hemispheres. The plasma bubbles were observed in the 630nm nighttime airglow images taken by using highly sensitive all-sky airglow imagers at Kototabang, Indonesia (geomagnetic latitude (MLAT): 10.0 degrees S), and Chiang Mai, Thailand (MLAT: 8.9 degrees N), which are nearly geomagnetically conjugate stations, for 7h from 13 to 20UT (from 20 to 03LT) on 5 April 2011. The bubbles continuously propagated eastward with velocities of 100-125m/s. The 630nm images at Chiang Mai and those mapped to the conjugate point of Kototabang fit very well, which indicates that the observed plasma bubbles were geomagnetically connected. The eastward thermospheric neutral winds measured by two Fabry-Perot interferometers were 70-130m/s at Kototabang and 50-90m/s at Chiang Mai. We compared the observed plasma bubble drift velocity with the velocity calculated from the observed neutral winds and the model conductivity, to investigate the F region dynamo contribution to the bubble drift velocity. The estimated drift velocities were 60-90% of the observed velocities of the plasma bubbles, suggesting that most of the plasma bubble velocity can be explained by the F region dynamo effect.

    DOI: 10.1002/2014JA020398

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  229. Explicit characteristics of evolutionary-type plasma bubbles observed from Equatorial Atmosphere Radar during the low to moderate solar activity years 2010-2012 Reviewed

    K. K. Ajith, S. Tulasi Ram, M. Yamamoto, T. Yokoyama, V. Sai Gowtam, Y. Otsuka, T. Tsugawa, K. Niranjan

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 120 ( 2 ) page: 1371 - 1382   2015.2

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    Using the fan sector backscatter maps of 47MHz Equatorial Atmosphere Radar (EAR) at Kototabang (0.2 degrees S geographic latitude, 100.3 degrees E geographic longitude, and 10.4 degrees S geomagnetic latitude), Indonesia, the spatial and temporal evolution of equatorial plasma bubbles (EPBs) were examined to classify the evolutionary-type EPBs from those which formed elsewhere and drifted into the field of view of radar. A total of 535 EPBs were observed during the low to moderate solar activity years 2010-2012, out of which about 210 (similar to 39%) are of evolving type and the remaining 325 (similar to 61%) are drifting-in EPBs. In general, both the evolving-type and drifting-in EPBs exhibit predominance during the postsunset hours of equinoxes and December solstices. Interestingly, a large number of EPBs were found to develop even a few minutes prior to the apex sunset during equinoxes. Further, the occurrence of evolving-type EPBs exhibits a clear secondary peak around midnight (2300-0100 LT), primarily, due to higher rate of occurrence during the postmidnight hours of June solstices. A significant number (similar to 33%) of postmidnight EPBs generated during June solstices did not exhibited any clear zonal drift, while about 14% of EPBs drifted westward. Also, the westward drifting EPBs are confined only to June solstices. The responsible mechanisms for the genesis of fresh EPBs during postmidnight hours were discussed in light of equatorward meridional winds in the presence of weak westward electric fields.

    DOI: 10.1002/2014JA020878

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  230. CDF data archive and integrated data analysis platform for ERG-related ground data developed by ERG Science Center (ERG-SC) Reviewed

    Hori, T, Y. Miyashita, Y. Miyoshi, K. Seki, T. Segawa, Y.-M. Tanaka, K. Keika, M. Shoji, I. Shinohara, K. Shiokawa, Y. Otsuka, S. Abe, A. Yoshikawa, K. Yumoto, Y. Obana, N. Nishitani, A. S. Yukimatu, T. Nagatsuma, M. Kunitake, K. Hosokawa, Y. Ogawa, K. T. Murata, M. Nosé, H. Kawano, T. Sakanoi

    Journal of Space Science Informatics Japan   Vol. JAXA-RR-14-009   page: 75 - 90   2015

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  231. Climatology of Equatorial Plasma Bubble Observed by MyRTKnet over the Years 2008-2013 Reviewed

    S. M. Buhari, M. Abdullah, T. Yokoyama, A. M. Hasbi, Y. Otsuka, M. Nishioka, S. A. Bahari, T. Tsugawa

    2015 INTERNATIONAL CONFERENCE ON SPACE SCIENCE AND COMMUNICATION (ICONSPACE)     page: 101 - 105   2015

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    Language:English   Publishing type:Research paper (international conference proceedings)   Publisher: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

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  232. Direct observations of blob deformation during a substorm Reviewed

    T. Ishida, Y. Ogawa, A. Kadokura, K. Hosokawa, Y. Otsuka

    ANNALES GEOPHYSICAE   Vol. 33 ( 5 ) page: 525 - 530   2015

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

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  233. GAST-D flight experiment results with disturbed and quiet ionospheric conditions Reviewed

    Susumu Saito, Takayuki Yoshihara, Atsushi Kezuka, Shinji Saitoh, Sonosuke Fukushima, Yuichi Otsuka

    PROCEEDINGS OF THE 28TH INTERNATIONAL TECHNICAL MEETING OF THE SATELLITE DIVISION OF THE INSTITUTE OF NAVIGATION (ION GNSS+ 2015)     page: 1494 - 1499   2015

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    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.

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  234. Long-term variation in the upper atmosphere as seen in the geomagnetic solar quiet daily variation Reviewed

    Atsuki Shinbori, Yukinobu Koyama, Masahito Nose, Tomoaki Hori, Yuichi Otsuka, Akiyo Yatagai

    EARTH PLANETS AND SPACE   Vol. 66   2014.12

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    Characteristics of long-term variation in the amplitude of solar quiet (Sq) geomagnetic field daily variation have been investigated using 1-h geomagnetic field data obtained from 69 geomagnetic observation stations within the period of 1947 to 2013. The Sq amplitude observed at these geomagnetic stations showed a clear dependence on the 10- to 12-year solar activity cycle and tended to be enhanced during each solar maximum phase. The Sq amplitude was the smallest around the minimum of solar cycle 23/24 in 2008 to 2009. The relationship between the solar F10.7 index and Sq amplitude was approximately linear but about 53% of geomagnetic stations showed a weak nonlinear relation to the solar F10.7 index. In order to remove the effect of solar activity seen in the long-term variation of the Sq amplitude, we calculated a linear or second-order fitting curve between the solar F10.7 index and Sq amplitude during 1947 to 2013 and examined the residual Sq amplitude, which is defined as the deviation from the fitting curve. As a result, the majority of trends in the residual Sq amplitude that passed through a trend test showed negative values over a wide region. This tendency was relatively strong in Europe, India, the eastern part of Canada, and New Zealand. The relationship between the magnetic field intensity at 100-km altitude and residual Sq amplitude showed an anti-correlation for about 71% of the geomagnetic stations. Furthermore, the residual Sq amplitude at the equatorial station (Addis Ababa) was anti-correlated with the absolute value of the magnetic field inclination. This implies movement of the equatorial electrojet due to the secular variation of the ambient magnetic field.

    DOI: 10.1186/s40623-014-0155-1

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  235. CME front and severe space weather Reviewed

    N. Balan, R. Skoug, S. Tulasi Ram, P. K. Rajesh, K. Shiokawa, Y. Otsuka, I. S. Batista, Y. Ebihara, T. Nakamura

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 119 ( 12 )   2014.12

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    Thanks to the work of a number of scientists who made it known that severe space weather can cause extensive social and economic disruptions in the modern high-technology society. It is therefore important to understand what determines the severity of space weather and whether it can be predicted. We present results obtained from the analysis of coronal mass ejections (CMEs), solar energetic particle (SEP) events, interplanetary magnetic field (IMF), CME-magnetosphere coupling, and geomagnetic storms associated with the major space weather events since 1998 by combining data from the ACE and GOES satellites with geomagnetic parameters and the Carrington event of 1859, the Quebec event of 1989, and an event in 1958. The results seem to indicate that (1) it is the impulsive energy mainly due to the impulsive velocity and orientation of IMF B-z at the leading edge of the CMEs (or CME front) that determine the severity of space weather. (2) CMEs having high impulsive velocity (sudden nonfluctuating increase by over 275 km s(-1) over the background) caused severe space weather (SvSW) in the heliosphere (failure of the solar wind ion mode of Solar Wind Electron Proton Alpha Monitor in ACE) probably by suddenly accelerating the high-energy particles in the SEPs ahead directly or through the shocks. (3) The impact of such CMEs which also show the IMF B-z southward from the leading edge caused SvSW at the Earth including extreme geomagnetic storms of mean Dst(MP) &lt; -250 nT during main phases, and the known electric power outages happened during some of these SvSW events. (4) The higher the impulsive velocity, the more severe the space weather, like faster weather fronts and tsunami fronts causing more severe damage through impulsive action. (5) The CMEs having IMF B-z northward at the leading edge do not seem to cause SvSW on Earth, although, later when the IMF B-z turns southward, they can lead to super geomagnetic storms of intensity (Dst(min)) less than even -400 nT.

    DOI: 10.1002/2014JA020151

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  236. Continuous generation and two-dimensional structure of equatorial plasma bubbles observed by high-density GPS receivers in Southeast Asia Reviewed

    S. M. Buhari, M. Abdullah, A. M. Hasbi, Y. Otsuka, T. Yokoyama, M. Nishioka, T. Tsugawa

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 119 ( 12 )   2014.12

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    High-density GPS receivers located in Southeast Asia (SEA) were utilized to study the two-dimensional structure of ionospheric plasma irregularities in the equatorial region. The longitudinal and latitudinal variations of tens of kilometer-scale irregularities associated with equatorial plasma bubbles (EPBs) were investigated using two-dimensional maps of the rate of total electron content change index (ROTI) from 127 GPS receivers with an average spacing of about 50-100 km. The longitudinal variations of the two-dimensional maps of GPS ROTI measurement on 5 April 2011 revealed that 16 striations of EPBs were generated continuously around the passage of the solar terminator. The separation distance between the subsequent onset locations varied from 100 to 550 km with 10 min intervals. The lifetimes of the EPBs observed by GPS ROTI measurement were between 50 min and over 7 h. The EPBs propagated 440-3000 km toward the east with velocities of 83-162 m s(-1). The longitudinal variations of EPBs by GPS ROTI keogram coincided with the depletions of 630 nm emission observed using the airglow imager. Six EPBs were observed by GPS ROTI along the meridian of Equatorial Atmosphere Radar (EAR), while only three EPBs were detected by the EAR. The high-density GPS receivers in SEA have an advantage of providing time continuous descriptions of latitudinal/longitudinal variations of EPBs with both high spatial resolution and broad geographical coverage. The spatial periodicity of the EPBs could be associated with a wavelength of the quasiperiodic structures on the bottomside of the F region which initiate the Rayleigh-Taylor instability.

    DOI: 10.1002/2014JA020433

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  237. Airglow observations of nighttime medium-scale traveling ionospheric disturbances from Yonaguni: Statistical characteristics and low-latitude limit Reviewed

    V. Lakshmi Narayanan, K. Shiokawa, Y. Otsuka, S. Saito

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 119 ( 11 ) page: 9268 - 9282   2014.11

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    The characteristics of nighttime medium-scale traveling ionospheric disturbance (MSTID) features observed over Yonaguni (24.5 degrees N, 123.0 degrees E; 19.3 degrees N dip latitude), Japan are studied using all-sky imaging of OI 630.0nm airglow emission. The uniqueness of these observations is that the area observed by the imager covers the transition region between low to middle latitudes in the ionosphere. Typical low-latitude limit of midlatitude-type nighttime MSTIDs possessing phase front alignments along the northwest to the southeast occurs in this region. These MSTID features are rarely sighted at dip latitudes below 15 degrees. We selected 2 year period for analysis in which 1 year corresponded to the solar minimum conditions and another year to the solar maximum conditions. The MSTIDs were observed to extend to farther lower latitudes during the solar minimum conditions than during the solar maximum periods. Their observed range of wavelengths, phase velocities, phase front alignment, and propagation directions are similar to those observed at typical midlatitude sites. However, on many occasions the phase fronts of the observed MSTIDs did not extend over the whole field of view of the imager indicating that some process inhibits their extension to further lower latitudes. Detailed investigation suggests that the poleward propagating enhancement of airglow intensity, probably associated with the midnight pressure bulge, causes the MSTID features to disappear when they reach lower latitudes later in the night. When the MSTIDs reach lower latitudes well before midnight, they are found to be inhibited by the equatorial ionization anomaly crest region.

    DOI: 10.1002/2014JA020368

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  238. First spaceborne observation of the entire concentric airglow structure caused by tropospheric disturbance Reviewed

    Y. Akiya, A. Saito, T. Sakanoi, Y. Hozumi, A. Yamazaki, Y. Otsuka, M. Nishioka, T. Tsugawa

    GEOPHYSICAL RESEARCH LETTERS   Vol. 41 ( 19 ) page: 6943 - 6948   2014.10

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    Spaceborne imagers are able to observe the airglow structures with wide field of views regardless of the tropospheric condition that limits the observational time of the ground-based imagers. Concentric wave structures of the O-2 airglow in 762 nm wavelength were observed over North America on 1 June 2013 from the International Space Station. This was the first observation in which the entire image of the structure was captured from space, and its spatial scale size was determined to be 1200 km radius without assumptions. The apparent horizontal wavelength was 80 km, and the amplitude in the intensity was approximately 20% of the background intensity. The propagation velocity of the structure was derived as 125 +/- 62 m/s and atmospheric gravity waves were estimated to be generated for 3. 5 +/- 1. 7 h. Concentric structures observed in this event were interpreted to be generated by super cells that caused a tornado in its early phase.

    DOI: 10.1002/2014GL061403

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  239. Auroral fragmentation into patches Reviewed

    Kazuo Shiokawa, Ayumi Hashimoto, Tomoaki Hori, Kaori Sakaguchi, Yasunobu Ogawa, Eric Donovan, Emma Spanswick, Martin Connors, Yuichi Otsuka, Shin-Ichiro Oyama, Satonori Nozawa, Kathryn McWilliams

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 119 ( 10 ) page: 8249 - 8261   2014.10

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    Auroral patches in diffuse auroras are very common features in the postmidnight local time. However, the processes that produce auroral patches are not yet well understood. In this paper we present two examples of auroral fragmentation which is the process by which uniform aurora is broken into several fragments to form auroral patches. These examples were observed at Athabasca, Canada (geomagnetic latitude: 61.7 degrees N), and TromsO, Norway (67.1 degrees N). Captured in sequences of images, the auroral fragmentation occurs as finger-like structures developing latitudinally with horizontal-scale sizes of 40-100 km at ionospheric altitudes. The structures tend to develop in a north-south direction with speeds of 150-420 m/s without any shearing motion, suggesting that pressure-driven instability in the balance between the earthward magnetic-tension force and the tailward pressure gradient force in the magnetosphere is the main driving force of the auroral fragmentation. Therefore, these observations indicate that auroral fragmentation associated with pressure-driven instability is a process that creates auroral patches. The observed slow eastward drift of aurora during the auroral fragmentation suggests that fragmentation occurs in low-energy ambient plasma.

    DOI: 10.1002/2014JA020050

    Web of Science

  240. Diagnostics of equatorial and low latitude ionosphere by TEC mapping over Brazil Reviewed

    H. Takahashi, S. Costa, Y. Otsuka, K. Shiokawa, J. F. G. Monico, E. Paula, P. Nogueira, C. M. Denardini, F. Becker-Guedes, C. M. Wrasse, A. S. Ivo, V. C. F. Gomes, W. Gargarela, N. Sant'Anna, R. Gatto

    ADVANCES IN SPACE RESEARCH   Vol. 54 ( 3 ) page: 385 - 394   2014.8

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    The total electron content (TEC) in the equatorial and low-latitude ionosphere over Brazil was monitored in two dimensions by using 2011 data from the ground-based global navigation satellite system (GNSS) receiver network operated by the Brazilian Institute for Geography and Statistics. It was possible to monitor the spatial and temporal variations in TEC over Brazil continuously during both day and night with a temporal interval of 10 mm and a spatial resolution of about 400 km. The daytime equatorial ionization anomaly (ETA) and post-sunset plasma enhancement (PS-ETA) were monitored over an area corresponding to a longitudinal extension of 4000 km in South America. Considerable day-to-day variation was observed in ETA and PS-ETA. A large latitudinal and longitudinal gradient of TEC indicated a significant ionospheric range error in application of the GNSS positioning system. Large-scale plasma bubbles after sunset were also mapped over a wide range. Depletions with longitudinally separated by more than 800 km were observed. They were extended by more than 2000 km along the magnetic field lines and drifted eastward. It is expected that 2-dimensional TEC mapping can serve as a useful tool for diagnosing ionospheric weather, such as temporal and spatial variation in the equatorial plasma trough and crest, and particularly for monitoring the dynamics of plasma bubbles. (C) 2014 COSPAR. Published by Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.asr.2014.01.032

    Web of Science

  241. Observations of GPS scintillation during an isolated auroral substorm Reviewed

    Hosokawa, K, Y. Otsuka, Y. Ogawa, T. Tsugawa

    Progress in Earth and Planetary Sciencs   Vol. 96693290710.1186/2197-4284-1-1   2014.8

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  242. Vertical ExB drifts from radar and C/NOFS observations in the Indian and Indonesian sectors: Consistency of observations and model Reviewed

    A. K. Patra, P. Pavan Chaitanya, Y. Otsuka, T. Yokoyama, M. Yamamoto, R. A. Stoneback, R. A. Heelis

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 119 ( 5 ) page: 3777 - 3788   2014.5

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    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

  243. Global imaging of polar cap patches with dual airglow imagers Reviewed

    K. Hosokawa, S. Taguchi, K. Shiokawa, Y. Otsuka, Y. Ogawa, M. Nicolls

    GEOPHYSICAL RESEARCH LETTERS   Vol. 41 ( 1 ) page: 1 - 6   2014.1

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    During a 2 h interval from 2240 to 2440 UT on 12 November 2012, regions of increased 630.0 nm airglow emissions were simultaneously detected by dual all-sky imagers in the polar cap, one at Longyearbyen, Norway (78.1 degrees N, 15.5 degrees E) and the other at Resolute Bay, Canada (74.7 degrees N, 265.1 degrees E). The Resolute Bay incoherent scatter radar observed clear enhancements of the F region electron density up to 10(12) m(-3) within these airglow structures which indicates that these are optical manifestations of polar cap patches propagating across the polar cap. During this interval of simultaneous airglow imaging, the nightside/dawnside (dayside/duskside) half of the patches was captured by the imager at Longyearbyen (Resolute Bay). This unique situation enabled us to estimate the dawn-dusk extent of the patches to be around 1500 km, which was at least 60-70% of the width of the antisunward plasma stream seen in the Super Dual Auroral Radar Network convection maps. In contrast to the large extent in the dawn-dusk direction, the noon-midnight thickness of each patch was less than 500 km. These observations demonstrate that there exists a class of patches showing cigar-shaped structures. Such patches could be produced in a wide range of local time on the dayside nearly simultaneously and spread across many hours of local time soon after their generation.

    DOI: 10.1002/2013GL058748

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  244. Drift Velocities of 150-km Field-Aligned Irregularities Observed by the Equatorial Atmosphere Radar Reviewed

    Otsuka Y., Mizutani, N., Shiokawa, K., Patra, A., Yokoyama, T., and Yamamoto

    Antarctic Record     page: 印刷中   2014

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  245. The observation of equatorial plasma bubble using all sky imager and GPS TEC measurement Reviewed

    Suhaila M. Buhari, Mardina Abdullah, Alina Marie Hasbi, Yuichi Otsuka, Siti Aminah Bahari, Mohd Hezri Mokhtar, Michi Nishioka, Takuya Tsugawa

    2014 XXXITH URSI GENERAL ASSEMBLY AND SCIENTIFIC SYMPOSIUM (URSI GASS)     2014

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    Language:English   Publishing type:Research paper (international conference proceedings)   Publisher: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

  246. 国際宇宙ステーションからの超高層大気撮像観測ミッションISS-IMAPの現状

    齊藤 昭則, 秋谷祐亮, 穂積裕太, 山崎 敦, 阿部 琢美, 鈴木 睦, 村上豪, 坂野井 健, 吉川 一朗, 大塚 雄一, 藤原 均, 田口 真, 山本 衛, 中村 卓司, 江尻 省, 菊池 雅行, 河野 英昭, Huixin Liu, 石井 守, 久保田 実, 津川 卓也, 星野尾 一明, 坂野井 和代, IMAPワーキンググループ

    第14回宇宙科学シンポジウム 講演集     2014

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  247. 国際宇宙ステーションからの大気光観測による赤道域電離圏擾乱の研究

    山田貴宣, 大塚雄一, 坂野井健, 山崎敦, 齊藤昭則, 秋谷祐亮

    第28回大気圏シンポジウム講演集     2014

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    Language:Japanese   Publishing type:Research paper (other academic)  

  248. Vertical ExB drifts from radar and C/NOFS observations in the Indian and Indonesian sectors: Consistency of observations and model Reviewed

    A. K. Patra, P. Pavan Chaitanya, Y. Otsuka, T. Yokoyama, M. Yamamoto, R. A. Stoneback, R. A. Heelis

    Journal of Geophysical Research: Space Physics   Vol. 119 ( 5 ) page: 3777 - 3788   2014

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

  249. Two-dimensional structure of equatorial plasma bubble observed using GPS networks in South East Asia region Reviewed

    Suhaila M. Buhari, Mardina Abdullah, Alina Marie Hasbi, Yuichi Otsuka

    2014 International Conference on Electronics, Information and Communications (ICEIC)     2014

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    Language:English   Publishing type:Research paper (international conference proceedings)   Publisher: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

  250. Drift Velocities of 150-km Field-Aligned Irregularities Observed by the Equatorial Atmosphere Radar Reviewed

    Otsuka Y., Mizutani, N., Shiokawa, K., Patra, A., Yokoyama, T., and Yamamoto, M.

      Vol. 57 ( 3 ) page: 369-378   2013.11

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  251. Typhoon-induced concentric airglow structures in the mesopause region Reviewed

    S. Suzuki, S. L. Vadas, K. Shiokawa, Y. Otsuka, S. Kawamura, Y. Murayama

    Geophysical Research Letters   Vol. 40 ( 22 ) page: 5983 - 5987   2013.11

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    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

  252. Typhoon-induced concentric airglow structures in the mesopause region Reviewed

    S. Suzuki, S. L. Vadas, K. Shiokawa, Y. Otsuka, S. Kawamura, Y. Murayama

    GEOPHYSICAL RESEARCH LETTERS   Vol. 40 ( 22 ) page: 5983 - 5987   2013.11

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

  253. Two-dimensional simulation of ionospheric variations in the vicinity of the epicenter of the Tohoku-oki earthquake on 11 March 2011 Reviewed

    H. Shinagawa, T. Tsugawa, M. Matsumura, T. Iyemori, A. Saito, T. Maruyama, H. Jin, M. Nishioka, Y. Otsuka

    GEOPHYSICAL RESEARCH LETTERS   Vol. 40 ( 19 ) page: 5009 - 5013   2013.10

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    Unusual ionospheric variations were observed in the M9.0 Tohoku-oki earthquake on 11 March 2011. Among various kinds of features in the ionosphere, significant depletion of total electron content (TEC) near the epicenter was observed after the earthquake. Although previous studies have suggested that the coseismic ionospheric variations are associated with atmospheric perturbation caused by vertical displacement of the sea surface, the mechanism of the TEC depletion has not been fully understood. In this paper, a two-dimensional nonlinear nonhydrostatic compressible atmosphere-ionosphere model is employed to investigate the ionospheric variations in the vicinity of the epicenter. The simulation results reveal that an impulsive pressure pulse produced by a sudden uplift of the sea surface leads to local atmospheric expansion in the thermosphere and that the expansion of the thermosphere combined with the effect of inclined magnetic field lines in the ionosphere causes the sudden TEC depletion above the epicenter region.

    DOI: 10.1002/2013GL057627

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  254. Longitudinal characteristics of spread F backscatter plumes observed with the EAR and Sanya VHF radar in Southeast Asia Reviewed

    Guozhu Li, Baiqi Ning, M. A. Abdu, Yuchi Otsuka, T. Yokoyama, M. Yamamoto, Libo Liu

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 118 ( 10 ) page: 6544 - 6557   2013.10

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    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

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  255. Observation of nighttime medium-scale travelling ionospheric disturbances by two 630-nm airglow imagers near the auroral zone Reviewed

    K. Shiokawa, M. Mori, Y. Otsuka, S. Oyama, S. Nozawa, S. Suzuki, M. Connors

    JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS   Vol. 103   page: 184 - 194   2013.10

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    This is the first statistical study of high-latitude nighttime medium-scale traveling ionospheric disturbances (MSTIDs) observed by all-sky airglow imagers in the European and Canadian longitudinal sectors. We investigate the MSTIDs observed in the 630-nm airglow imagers at Tromso (magnetic latitude: 67.1 degrees N), Norway, for two winters, and at Athabasca (61.7 degrees N), Canada, for 2 years. At both stations, the MSTIDs were observed mostly before midnight with an occurrence rate of more than 50% of clear observation hours at Tromso and similar to 30% at Athabasca. The average wavelengths, phase velocities, and periods of the observed MSTIDs were 150-200 km, 50-80 m/s, and 30-60 min, respectively. We found that MSTIDs at Tromso tend to show eastward motion in addition to the typical westward and southwestward motion at middle latitudes. At Athabasca, westward and southwestward motions prevail except for the summer when characteristic northward-moving MSTIDs with larger wavelengths and faster phase velocities were observed. At both stations, some MSTIDs showed characteristic changes of their phase velocity and directions in association with auroral activity, suggesting that they are plasma structures affected by auroral electric field. Vertical wavelengths of gravity waves were estimated by using simultaneous thermospheric wind data obtained at Tromso, showing that most of these MSTIDs can exist as gravity waves in the thermosphere. On the basis of these results, we conclude that the high-latitude nighttime MSTIDs are caused mainly by the Perkins and E-F coupling instabilities similar to those at middle latitudes and that an additional source by atmospheric gravity waves from lower altitudes also comes into play. (C) 2013 Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.jastp.2013.03.024

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  256. Ionogram-based range-time displays for observing relationships between ionosonde satellite traces, spread F and drifting optical plasma depletions Reviewed

    K. J. W. Lynn, Y. Otsuka, K. Shiokawa

    JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS   Vol. 98   page: 105 - 112   2013.6

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    A form of range-time plots derived from ionograms taken from a standard digital ionosondes, situated at the low latitude sites of Vanimo, Port Moresby and Darwin, exhibit bursts of spread F at the center of descending and ascending off-angle reflectors. This particular type of event has since been identified with the passage of optically imaged ionospheric plasma depletions (bubbles) over a Darwin ionosonde. This paper describes the process for producing this form of range-time display and its relationship to ionospheric height, satellite traces and range spread F as seen on individual ionograms. First hop satellite traces are proposed to be via direct reflection from the steep electron density gradients at the base of bubbles while second hop satellite traces then involve a single additional ground reflection. Measurements of night equatorial drift velocity were made from the range-time displays and found to be in the range 20-220 m/s peaking at approximately 90-100 m/s in good agreement with values derived from drift measurements made by a variety of other types of equipment. (C) 2013 Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.jastp.2013.03.020

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  257. Physical mechanisms of the ionospheric storms at equatorial and higher latitudes during the recovery phase of geomagnetic storms Reviewed

    N. Balan, Y. Otsuka, M. Nishioka, J. Y. Liu, G. J. Bailey

    Journal of Geophysical Research: Space Physics   Vol. 118 ( 5 ) page: 2660 - 2669   2013.5

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    The paper studies the physical mechanisms of the ionospheric storms at equatorial and higher latitudes, which are generally opposite both during the main phase (MP) and recovery phase (RP) of geomagnetic storms. The mechanisms are based on the natural tendency of physical systems to occupy minimum energy state which is most stable. The paper first illustrates the recent developments in the understanding of the mechanisms during daytime MPs when generally negative ionospheric storms (in Nmax and TEC) develop at equatorial latitudes and positive storms occur at higher latitudes, including why the storms are severe only in some cases. The paper then investigates the relative importance of the physical mechanisms of the positive ionospheric storms observed at equatorial latitudes (within ±15°) during daytime RPs when negative storms occur at higher latitudes using CHAMP Ne and GPS-TEC data and Sheffield University Plasmasphere Ionosphere Model. The results indicate that the mechanical effect of the storm-time equatorward neutral winds that causes plasma convergence at equatorial F region could be a major source for the positive storms, with the downwelling effect of the winds and zero or westward electric field, if present, acting as minor sources. Key PointsPositive ionospheric storms during RPs due to plasma convergencePhysical mechanisms based on stable minimum energy stateSevere space weather seems to be due to the rate of energy release during CMEs ©2013. American Geophysical Union. All Rights Reserved.

    DOI: 10.1002/jgra.50275

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    Scopus

  258. Evidence of gravity wave ducting in the mesopause region from airglow network observations Reviewed

    S. Suzuki, K. Shiokawa, Y. Otsuka, S. Kawamura, Y. Murayama

    Geophysical Research Letters   Vol. 40 ( 3 ) page: 601 - 605   2013.2

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    We present observational evidence of gravity wave ducting and show, for the first time, that the ducting occurs over large horizontal distances in the mesopause region. An optical network of four all-sky imagers in Japan identified two-dimensional patterns of small-scale gravity wave bands in OH airglow images on 13 June 2004. The wave signatures clearly showed northward propagation of more than 1800 km over a wide range of latitudes. The horizontal wavelength, horizontal phase speed, and wave period were estimated from the airglow data as 33.4 km, 42.8 m s&lt
    sup&gt
    -1&lt
    /sup&gt
    , and 13.4 min, respectively. The wave structure lasted for the whole 5-h airglow observation period. Simultaneous MF radar wind data and TIMED/SABER measurements suggested that the wave was trapped and ducted at the airglow height. The ducting likely contributed to the remarkable coherence of the wave as it propagated northward. Key Points An airglow imaging network in Japan provides gravity wave ducting signatures Gravity wave bands appear over a horizontal extent of more than 1800 km Simultaneous winds and temperature are consistent with gravity wave ducting © 2012. American Geophysical Union. All Rights Reserved.

    DOI: 10.1029/2012GL054605

    Web of Science

    Scopus

  259. GPS observations of medium-scale traveling ionospheric disturbances over Europe Reviewed

    Otsuka, Y., Suzuki, K., Nakagawa, S., Nishioka, M., Shiokawa, K., and Tsugawa, T.

    Ann. Geophys.   Vol. 31   page: 163-172   2013.2

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    Authorship:Lead author   Language:English   Publishing type:Research paper (scientific journal)  

    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

  260. Drift velocities of 150-km field-aligned irregularities observed by the equatorial atmosphere radar Reviewed

    Otsuka Y, Mizutani N, Shiokawa K, Patra A, Yokoyama T, Yamamoto M

    Antarctic Record   Vol. 57 ( 3 ) page: 369 - 378   2013

  261. IMAP-WG国際宇宙ステーションからの地球超高層大気撮像観測ISS-IMAPミッションの初期成果

    齊藤昭則, 山崎 敦, 阿部琢美, 鈴木 睦, 坂野井 健, 吉川一朗, 大塚雄一, 藤原 均, 田口 真, 山本 衛, 中村卓司, 江尻 省, 菊池雅行, 河野英昭, Huixin Liu, 石井 守, 久保田 実, 津川卓也, 星野尾一明, 坂野井和代

    第13回宇宙科学シンポジウム     2013

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  262. GPS observations of medium-scale traveling ionospheric disturbances over Europe Reviewed

    Y. Otsuka, K. Suzuki, S. Nakagawa, M. Nishioka, K. Shiokawa, T. Tsugawa

    ANNALES GEOPHYSICAE   Vol. 31 ( 2 ) page: 163 - 172   2013

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:COPERNICUS GESELLSCHAFT MBH  

    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: 10.5194/angeo-31-163-2013

    Web of Science

  263. Longitudinal characteristics of spread F backscatter plumes observed with the EAR and Sanya VHF radar in Southeast Asia Reviewed

    Guozhu Li, Baiqi Ning, M. A. Abdu, Yuchi Otsuka, T. Yokoyama, M. Yamamoto, Libo Liu

    Journal of Geophysical Research: Space Physics   Vol. 118 ( 10 ) page: 6544 - 6557   2013

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

  264. Small-scale ionospheric delay variation associated with plasma bubbles studied with GNSS and optical measurements and its impact on GBAS Reviewed

    S. Saito, T. Yoshihara, Y. Otsuka

    PROCEEDINGS OF THE 26TH INTERNATIONAL TECHNICAL MEETING OF THE SATELLITE DIVISION OF THE INSTITUTE OF NAVIGATION (ION GNSS 2013)     page: 1869 - 1874   2013

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    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

  265. A comparative study of equatorial daytime vertical E x B drift in the Indian and Indonesian sectors based on 150 km echoes Reviewed

    A. K. Patra, P. Pavan Chaitanya, N. Mizutani, Y. Otsuka, T. Yokoyama, M. Yamamoto

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 117   2012.11

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

  266. Motion of high-latitude nighttime medium-scale traveling ionospheric disturbances associated with auroral brightening Reviewed

    Shiokawa, K, Mori, M, Otsuka, Y, Oyama, S, Nozawa, S

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 117   2012.10

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  267. Motion of high-latitude nighttime medium-scale traveling ionospheric disturbances associated with auroral brightening Reviewed

    Shiokawa K, Mori M, Otsuka Y, Oyama S, Nozawa S

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 117   2012.10

  268. Observation of equatorial nighttime medium-scale traveling ionospheric disturbances in 630-nm airglow images over 7 years Reviewed

    D. Fukushima, K. Shiokawa, Y. Otsuka, T. Ogawa

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 117   2012.10

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    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

  269. On post-midnight field-aligned irregularities observed with a 30.8-MHz radar at a low latitude: Comparison with F-layer altitude near the geomagnetic equator Reviewed

    M. Nishioka, Y. Otsuka, K. Shiokawa, T. Tsugawa, Effendy, P. Supnithi, T. Nagatsuma, K. T. Murata

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 117   2012.8

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

  270. Response of low-latitude ionosphere to medium-term changes of solar and geomagnetic activity Reviewed

    Ivan Kutiev, Yuichi Otsuka, Dora Pancheva, Rod Heelis

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 117   2012.8

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    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

  271. Disappearance of equatorial plasma bubble after interaction with mid-latitude medium-scale traveling ionospheric disturbance Reviewed

    Otsuka, Y., K. Shiokawa, and T. Ogawa

    Geophys. Res. Lett.   Vol. 39 ( L14105 )   2012.7

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    DOI: doi:10.1029/2012GL052286

  272. Disappearance of equatorial plasma bubble after interaction with mid-latitude medium-scale traveling ionospheric disturbance Reviewed

    Y. Otsuka, K. Shiokawa, T. Ogawa

    GEOPHYSICAL RESEARCH LETTERS   Vol. 39   2012.7

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    We report simultaneous observations of an equatorial plasma bubble and a Medium-Scale Traveling Ionospheric Disturbance (MSTID) in 630-nm airglow images taken with an all-sky airglow imager at Shigaraki (34.9 degrees N, 136.1 degrees E; dip angle of the geomagnetic field similar to 49 degrees), Japan. Clear depletion of the 630-nm airglow intensity was observed as the equatorial plasma bubble propagated eastward, whereas the MSTID, which had a wavefront aligned from northwest to southeast, propagated southwestward. This result indicates that MSTIDs do not propagate at the same velocity as the ambient plasma, which is clearly shown by the eastward motion of the plasma bubbles. We found that the airglow depletion caused by the plasma bubble disappeared when the plasma bubble encountered the MSTID. The plasma depletion could be filled with ambient rich plasma that moved into the plasma-depleted region by E x B drift associated with the MSTID, indicating that MSTIDs are accompanied by electric field perturbations.

    DOI: 10.1029/2012GL052286

    Web of Science

  273. Overview of Nighttime Ionospheric Instabilities at Low- and Mid-Latitudes: Coupling Aspects Resulting in Structuring at the Mesoscale Reviewed

    Jonathan J. Makela, Yuichi Otsuka

    SPACE SCIENCE REVIEWS   Vol. 168 ( 1-4 ) page: 419 - 440   2012.6

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    Language:English   Publisher:SPRINGER  

    We present a review of the current state of understanding regarding two classes of irregularities causing mesoscale structuring (hundreds of kilometers) in the nighttime ionosphere at low- and mid-latitudes. Additionally, current state of understanding of equatorial plasma bubbles at low latitudes, and medium-scale traveling ionospheric disturbances at mid latitudes and their relationship to possible seeding from lower altitudes are described. In each case, well-developed linear theories exist to explain the general properties of the irregularities. However, these linear theories have growth rates too low to explain the actual observations, giving rise to the need to invoke seeding mechanisms. We describe the observational databases that have been compiled over the decades and discuss possible coupling and seeding mechanisms that would overcome the low growth rate and explain the observed structuring at the mesoscale. Future research directions are also briefly discussed.

    DOI: 10.1007/s11214-011-9816-6

    Web of Science

  274. GPS total electron content variations associated with poleward moving Sun-aligned arcs Reviewed

    P. T. Jayachandran, K. Hosokawa, K. Shiokawa, Y. Otsuka, C. Watson, S. C. Mushini, J. W. MacDougall, P. Prikryl, R. Chadwick, T. D. Kelly

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 117   2012.5

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    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 (&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 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

  275. VHF Radar Observations of Post-Midnight F-Region Field-Aligned Irregularities over Indonesia during Solar Minimum Reviewed

    Otsuka, Y., K. Shiokawa, M. Nishioka and Effendy

    Indian Journal of Radio and Space Physics (IJRSP)   ( 41 ) page: 199-207   2012.4

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  276. VHF Radar Observations of Post-Midnight F-Region Field-Aligned Irregularities over Indonesia during Solar Minimum Reviewed

    Otsuka, Y, K. Shiokawa, M. Nishioka, Effendy

    Indian Journal of Radio and Space Physics (IJRSP)   ( 41 ) page: 199-207   2012.4

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  277. Seasonal and Local Time Variations of E-Region Field-Aligned Irregularities Observed with 30.8-MHz Radar at Kototabang, Indonesia Reviewed

    Otsuka, Y.

    International Journal of Geophysics   Vol. 2012 ( 695793 )   2012.3

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    DOI: doi:10.1155/2012/695793

  278. Polarization of Pc1/EMIC waves and related proton auroras observed at subauroral latitudes Reviewed

    R. Nomura, K. Shiokawa, K. Sakaguchi, Y. Otsuka, M. Connors

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 117   2012.2

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    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

  279. Ionospheric and thermospheric storms at equatorial latitudes observed by CHAMP, ROCSAT, and DMSP Reviewed

    N. Balan, J. Y. Liu, Y. Otsuka, S. Tulasi Ram, H. Luehr

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 117   2012.1

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    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

  280. A comparative study of equatorial daytime vertical e × B drift in the Indian and Indonesian sectors based on 150 km echoes Reviewed

    A. K. Patra, P. Pavan Chaitanya, N. Mizutani, Y. Otsuka, T. Yokoyama, M. Yamamoto

    Journal of Geophysical Research: Space Physics   Vol. 117 ( 11 )   2012

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    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

  281. Development of low-cost sky-scanning Fabry-Perot interferometers for airglow and auroral studies Reviewed

    K. Shiokawa, Y. Otsuka, S. Oyama, S. Nozawa, M. Satoh, Y. Katoh, Y. Hamaguchi, Y. Yamamoto, J. Meriwether

    EARTH PLANETS AND SPACE   Vol. 64 ( 11 ) page: 1033 - 1046   2012

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

    We have developed new Fabry-Perot interferometers (FPIs) that are designed to measure thermospheric winds and temperatures as well as mesospheric winds through the airglow/aurora emissions at wavelengths of 630.0 nm and 557.7 nm, respectively. One FPI (FP01), possessing a large aperture etalon (diameter: 116 mm), was installed at the EISCAT Tromso site in 2009. The other FPIs, using 70-mm diameter etalons, were installed in Thailand, Indonesia, and Australia in 2010-2011 (FP02-FP04) by the Solar-Terrestrial Environment Laboratory, and in Peru (Nazca and Jicamarca) and Alaska (Poker Flat) by Clemson University. The FPIs with 70-mm etalons are low-cost compact instruments, suitable for multipoint network observations. All of these FPIs use low-noise cooled-CCD detectors with 1024 x 1024 pixels combined with a 4-stage thermoelectric cooling system that can cool the CCD temperature down to -80 degrees C. The large incident angle (maximum: 1.3 degrees-1.4 degrees) to the etalon achieved by the use of multiple orders increases the throughput of the FPIs. The airglow and aurora observations at Tromso by FP01 show wind velocities with typical random errors ranging from 2 to 13 m s(-1) and from 4 to 27 m s(-1) for mesosphere (557.7 nm) and thermosphere (630.0 nm) measurements, respectively. The 630.0-nm airglow observations at Shigaraki, Japan, by FP02-FP04 and by the American FPI instruments give thermospheric wind velocities with typical random errors that vary from 2 m s(-1) to more than 50 m s(-1) depending on airglow intensity.

    DOI: 10.5047/eps.2012.05.004

    Web of Science

  282. GPS total electron content variations associated with poleward moving Sun-aligned arcs Reviewed

    P. T. Jayachandran, K. Hosokawa, K. Shiokawa, Y. Otsuka, C. Watson, S. C. Mushini, J. W. MacDougall, P. Prikryl, R. Chadwick, T. D. Kelly

    Journal of Geophysical Research: Space Physics   Vol. 117 ( 5 )   2012

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    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

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  283. Early observation and future plan of the Ionosphere, Mesosphere, upper Atmosphere, and Plasmasphere mapping observation mission

    SAITO Akinori, YAMAZAKI Atsushi, SAKANOI Takeshi, YOSHIKAWA Ichiro, ABE Takumi, OTSUKA Yuichi, TAGUCHI Makoto, SUZUKI Makoto, KIKUCHI Masayuki, NAKAMURA Takuji, YAMAMOTO Mamoru, KAWANO Hideaki, LIU Huixin, ISHII Mamoru, TSUGAWA Takuya, SAKANOI Kazuyo, FUJIWARA Hitoshi, KUBOTA Minoru, EJIRI Mitsumu K, SAITO Akinori

    地球電磁気・地球惑星圏学会総会及び講演会予稿集(CD-ROM)   Vol. 132nd   page: ROMBUNNO.B005-18   2012

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  284. Ionospheric and thermospheric storms at equatorial latitudes observed by CHAMP, ROCSAT, and DMSP Reviewed

    N. Balan, J. Y. Liu, Y. Otsuka, S. Tulasi Ram, H. Lühr

    Journal of Geophysical Research: Space Physics   Vol. 117 ( 1 )   2012

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    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

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  285. Observation of equatorial nighttime medium-scale traveling ionospheric disturbances in 630-nm airglow images over 7 years Reviewed

    D. Fukushima, K. Shiokawa, Y. Otsuka, T. Ogawa

    Journal of Geophysical Research: Space Physics   Vol. 117 ( 10 )   2012

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    [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

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  286. Motion of high-latitude nighttime medium-scale traveling ionospheric disturbances associated with auroral brightening Reviewed

    K. Shiokawa, M. Mori, Y. Otsuka, S. Oyama, S. Nozawa

    Journal of Geophysical Research: Space Physics   Vol. 117 ( 10 )   2012

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    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

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  287. Low-latitude mesosphere, thermosphere, and ionosphere Reviewed

    Y. Sahai, R. S. Dabas, Y. Otsuka, M. Klimenko

    International Journal of Geophysics   Vol. 2012   2012

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    DOI: 10.1155/2012/671240

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  288. On post-midnight field-aligned irregularities observed with a 30.8-MHz radar at a low latitude: Comparison with F-layer altitude near the geomagnetic equator Reviewed

    M. Nishioka, Y. Otsuka, K. Shiokawa, T. Tsugawa, Null Effendy, P. Supnithi, T. Nagatsuma, K. T. Murata

    Journal of Geophysical Research: Space Physics   Vol. 117 ( 8 )   2012

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    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

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  289. Seasonal and local time variations of e -Region field-aligned irregularities observed with 30.8-mhz radar at kototabang, indonesia Reviewed

    Y. Otsuka

    International Journal of Geophysics   Vol. 2012   2012

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    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

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  290. Response of low-latitude ionosphere to medium-term changes of solar and geomagnetic activity Reviewed

    Ivan Kutiev, Yuichi Otsuka, Dora Pancheva, Rod Heelis

    Journal of Geophysical Research: Space Physics   Vol. 117 ( 8 )   2012

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    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

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  291. Polarization of Pc1/EMIC waves and related proton auroras observed at subauroral latitudes Reviewed

    R. Nomura, K. Shiokawa, K. Sakaguchi, Y. Otsuka, M. Connors

    Journal of Geophysical Research: Space Physics   Vol. 117 ( 2 )   2012

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    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

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  292. Simultaneous observations at Darwin of equatorial bubbles by ionosonde-based range/time displays and airglow imaging Reviewed

    K. J. W. Lynn, Y. Otsuka, K. Shiokawa

    GEOPHYSICAL RESEARCH LETTERS   Vol. 38   2011.12

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    Airglow observations of ionospheric electron density depletions made at Darwin, Australia have demonstrated that the tree-like structure of bubbles developed at the magnetic equator are mapped along magnetic field lines with considerable accuracy to the base of the ionosphere at higher latitudes. Ionosonde range-time displays made at Darwin and other equatorial sites in the Australian region show characteristic approaching and receding echoes which converge on a typical spread-F event. These off-angle echoes have often been referred to in the literature as satellite traces and associated with spread F with little recognition of their true significance. All four optical depletions previously reported in the literature as being seen at Darwin are found in this paper to be accompanied by such typical off-angle/spread F events. The zonal drift velocity of the moving reflectors can be measured from the speed at which such echoes approach and recede. Since digital ionosondes in equatorial sites have existed for many years, existing ionogram data, when suitably processed into range-time displays, may allow the occurrence of such events over several sunspot cycles to be found. A question remains as to whether all or only some of such equatorial range-time events correspond to electron density depletions. Citation: Lynn, K. J. W., Y. Otsuka, and K. Shiokawa (2011), Simultaneous observations at Darwin of equatorial bubbles by ionosonde-based range/time displays and airglow imaging, Geophys. Res. Lett., 38, L23101, doi:10.1029/2011GL049856.

    DOI: 10.1029/2011GL049856

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  293. On postmidnight low-latitude ionospheric irregularities during solar minimum: 1. Equatorial Atmosphere Radar and GPS-TEC observations in Indonesia Reviewed

    T. Yokoyama, M. Yamamoto, Y. Otsuka, M. Nishioka, T. Tsugawa, S. Watanabe, R. F. Pfaff

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 116   2011.11

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    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

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  294. On postmidnight low-latitude ionospheric irregularities during solar minimum: 2. C/NOFS observations and comparisons with the Equatorial Atmosphere Radar Reviewed

    T. Yokoyama, R. F. Pfaff, P. A. Roddy, M. Yamamoto, Y. Otsuka

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 116   2011.11

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    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

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  295. Equatorial electrodynamics and neutral background in the Asian sector during the 2009 stratospheric sudden warming Reviewed

    Huixin Liu, Mamoru Yamamoto, S. Tulasi Ram, Takuya Tsugawa, Yuichi Otsuka, Claudia Stolle, Eelco Doornbos, Kiyohumi Yumoto, Tsutomu Nagatsuma

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 116   2011.8

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    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

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  296. New aspects of thermospheric and ionospheric storms revealed by CHAMP Reviewed

    N. Balan, M. Yamamoto, J. Y. Liu, Y. Otsuka, H. Liu, H. Luehr

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 116   2011.7

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    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

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  297. Decay of polar cap patch Reviewed

    K. Hosokawa, J. I. Moen, K. Shiokawa, Y. Otsuka

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 116   2011.5

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    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

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  298. A statistical study of the response of the dayside equatorial F-2 layer to the main phase of intense geomagnetic storms as an indicator of penetration electric field Reviewed

    N. Balan, M. Yamamoto, V. Sreeja, I. S. Batista, K. J. W. Lynn, M. A. Abdu, S. Ravindran, T. Kikuchi, Y. Otsuka, K. Shokawa, S. Alex

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 116   2011.3

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    The response of the dayside equatorial F-2 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 B-z; the storms include 15 superstorms (Dst &lt; -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

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  299. First satellite-imaging observation of medium-scale traveling ionospheric disturbances by FORMOSAT-2/ISUAL Reviewed

    Toru Adachi, Yuichi Otsuka, Masashi Yamaoka, Mamoru Yamamoto, Kazuo Shiokawa, Alfred B. Chen, Rue-Ron Hsu

    GEOPHYSICAL RESEARCH LETTERS   Vol. 38   2011.2

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    On the night of May 16, 2007, a satellite limb imager of FORMOSAT-2/ISUAL observed wave-like structures of the 630-nm airglow simultaneously with an all-sky imager deployed at Darwin in Australia. The height of the airglow layer was estimated as 220 km, and the structures were aligned in the northeast-southwest orientation with a wavelength of similar to 300 km and propagated toward the northwest with a phase velocity of similar to 100 m s(-1), showing typical characteristics of the nighttime medium-scale traveling ionospheric disturbances (MSTIDs). We conclude that ISUAL for the first time succeeded in observing the airglow layer altitude and airglow structures modulated by MSTID from space. Such a satellite limb airglow imaging could be a new tool to characterize ionospheric irregularities on a global level. Citation: Adachi, T., Y. Otsuka, M. Yamaoka, M. Yamamoto, K. Shiokawa, A. B. Chen, and R.-R. Hsu (2011), First satellite-imaging observation of medium-scale traveling ionospheric disturbances by FORMOSAT-2/ISUAL, Geophys. Res. Lett., 38, L04101, doi:10.1029/2010GL046268.

    DOI: 10.1029/2010GL046268

    Web of Science

  300. Vertical connection from the tropospheric activities to the ionospheric longitudinal structure simulated by a new Earth's whole atmosphere-ionosphere coupled model Reviewed

    H. Jin, Y. Miyoshi, H. Fujiwara, H. Shinagawa, K. Terada, N. Terada, M. Ishii, Y. Otsuka, A. Saito

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 116   2011.1

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    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

  301. Statistical Study of Medium-Scale Traveling Ionospheric Disturbances Observed with a GPS Receiver Network in Japan Reviewed

    Otsuka, Y, Kotake, N, Shiokawa, K, Ogawa, T, Tsugawa, T, Saito, A

    AERONOMY OF THE EARTH'S ATMOSPHERE AND IONOSPHERE   Vol. 2 ( 3 ) page: 291 - 299   2011

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    DOI: 10.1007/978-94-007-0326-1_21

    Web of Science

  302. A statistical study of the response of the dayside equatorial F2 layer to the main phase of intense geomagnetic storms as an indicator of penetration electric field Reviewed

    N. Balan, M. Yamamoto, V. Sreeja, I. S. Batista, K. J.W. Lynn, M. A. Abdu, S. Ravindran, T. Kikuchi, Y. Otsuka, K. Shokawa, S. Alex

    Journal of Geophysical Research: Space Physics   Vol. 116 ( 3 )   2011

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

  303. Acoustic resonance and plasma depletion detected by GPS total electron content observation after the 2011 off the Pacific coast of Tohoku Earthquake Reviewed

    A. Saito, T. Tsugawa, Y. Otsuka, M. Nishioka, T. Iyemori, M. Matsumura, S. Saito, C. H. Chen, Y. Goi, N. Choosakul

    EARTH PLANETS AND SPACE   Vol. 63 ( 7 ) page: 863 - 867   2011

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    Two-dimensional structures of the ionospheric variations generated by the acoustic resonance between the ground surface and the lower thermosphere was observed for the first time near the epicenter after the M 9.0 Tohoku earthquake on March 11, 2011. A short-period oscillation of total electron content was observed by a GPS receiver array after the earthquake for four hours in the vicinity of the epicenter. It was centered in the east of the epicenter where the tsunami was estimated to commence. The frequency of the dominant mode of the oscillation was 4.5 mHz, 222 seconds of period, while there were minor oscillations whose frequency were 3.7 mHz and 5.3 mHz. These periods are consistent with the periods of the acoustic resonance between the ground surface and the lower thermosphere, predicted by a numerical model. The amplitude of the TEC oscillation showed a gradual change of the amplitude. The two-dimensional distributions of TEC variations generated by this resonance had wave frontal structures that extended from northwest to southeast. The resonant oscillation of the TEC was accompanied by a depletion of TEC whose duration was about 60 minutes. The area of this depletion also centered on the epicenter.

    DOI: 10.5047/eps.2011.06.034

    Web of Science

  304. Decay of polar cap patch Reviewed

    K. Hosokawa, J. I. Moen, K. Shiokawa, Y. Otsuka

    Journal of Geophysical Research: Space Physics   Vol. 116 ( 5 )   2011

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    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

  305. Imaging observation of the Earth's mesosphere, thermosphere and ionosphere by VISI of ISS-IMAP on the International Space Station Reviewed

    Sakanoi, T, Akiya, Y, Yamazaki, A, Otsuka, Y, Saito, A, Yoshikawa, I

    IEEJ Transactions on Fundamentals and Materials   Vol. 131 ( 12 ) page: 983 - 988   2011

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher: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 O<sub>2</sub> (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

    Other Link: https://jlc.jst.go.jp/DN/JALC/00383579674?from=CiNii

  306. Equatorial electrodynamics and neutral background in the Asian sector during the 2009 stratospheric sudden warming Reviewed

    Huixin Liu, Mamoru Yamamoto, S. Tulasi Ram, Takuya Tsugawa, Yuichi Otsuka, Claudia Stolle, Eelco Doornbos, Kiyohumi Yumoto, Tsutomu Nagatsuma

    Journal of Geophysical Research: Space Physics   Vol. 116 ( 8 )   2011

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

  307. Ionospheric disturbances detected by GPS total electron content observation after the 2011 off the Pacific coast of Tohoku Earthquake Reviewed

    T. Tsugawa, A. Saito, Y. Otsuka, M. Nishioka, T. Maruyama, H. Kato, T. Nagatsuma, K. T. Murata

    EARTH PLANETS AND SPACE   Vol. 63 ( 7 ) page: 875 - 879   2011

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

    All the details of ionospheric disturbances following the 2011 Tohoku Earthquake were first revealed by the high-resolution GPS total electron content observation in Japan. The initial ionospheric disturbance appeared as sudden depletions following small impulsive TEC enhancements similar to 7 minutes after the earthquake onset, near the epicenter. Then, concentric waves appeared to propagate in the radial direction with a velocity of 138-3,457 m/s. Zonally-extended enhancements of the TEC also appeared in the west of Japan. In the vicinity of the epicenter, short-period oscillations with a period of similar to 4 minutes were observed. This paper focuses on the concentric waves. The concentric pattern indicates that they had a point source. The center of these structures, termed the "ionospheric epicenter", was located about 170 km from the epicenter in the southeast direction. According to the propagation characteristics, these concentric waves could be caused by atmospheric waves classified into three types: acoustic waves generated from a propagating Rayleigh wave, acoustic waves from the ionospheric epicenter, and atmospheric gravity waves from the ionospheric epicenter. The amplitude of the concentric waves was not uniform and was dependent on the azimuth of their propagation direction, which could not be explained by previously-proposed theory.

    DOI: 10.5047/eps.2011.06.035

    Web of Science

  308. Numerical simulations of atmospheric waves excited by the 2011 off the Pacific coast of Tohoku Earthquake Reviewed

    M. Matsumura, A. Saito, T. Iyemori, H. Shinagawa, T. Tsugawa, Y. Otsuka, M. Nishioka, C. H. Chen

    EARTH PLANETS AND SPACE   Vol. 63 ( 7 ) page: 885 - 889   2011

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:SPRINGER HEIDELBERG  

    Numerical simulations are performed to simulate atmospheric perturbations observed at ionospheric heights just after the 2011 off the Pacific coast of Tohoku Earthquake. A time-dependent, two-dimensional, nonlinear, non-hydrostatic, compressible and neutral, numerical model is developed to reproduce the atmospheric perturbations. An impulsive upward surface motion is assumed as the source of the perturbations. Simulated atmospheric perturbations at 300-km altitude show remarkable agreement with oscillations observed in the ionospheric total electron content (TEC) when the source width is about 250 km. In the vicinity of the source, the acoustic resonance modes between the ground surface and the lower thermosphere are dominant. They have three dominant frequencies for the interval between 20 and 60 min after the impulsive input. The perturbation with the maximum amplitude has a frequency of 4.4 mHz. The other dominant modes have frequencies of 3.6 and 5.1 mHz. The beats between the dominant modes are also seen. In the distance, the gravity modes are dominant. The horizontal phase velocities are about 220 to 300 m/s, and the horizontal wavelengths are about 200 to 400 km. The good agreement between the simulation and the observations indicates that ionospheric oscillations generated by the earthquake are mainly due to the motion of the neutral atmosphere.

    DOI: 10.5047/eps.2011.07.015

    Web of Science

  309. New aspects of thermospheric and ionospheric storms revealed by CHAMP Reviewed

    N. Balan, M. Yamamoto, J. Y. Liu, Y. Otsuka, H. Liu, H. Lühr

    Journal of Geophysical Research: Space Physics   Vol. 116 ( 7 )   2011

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

  310. Motion of polar cap arcs Reviewed

    Hosokawa, K, J. I. Moen, K. Shiokawa, Y. Otsuka

    Journal of Geophysical Research   Vol. 116   page: doi:10.1029/2010JA015906   2011

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  311. Long-distance propagation of ionospheric disturbance generated by the 2011 off the Pacific coast of Tohoku Earthquake Reviewed

    C. H. Chen, A. Saito, C. H. Lin, J. Y. Liu, H. F. Tsai, T. Tsugawa, Y. Otsuka, M. Nishioka, M. Matsumura

    EARTH PLANETS AND SPACE   Vol. 63 ( 7 ) page: 881 - 884   2011

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:SPRINGER HEIDELBERG  

    Propagation of the initial ionospheric total electron content (TEC) disturbances generated by the 2011 off the Pacific coast of Tohoku Earthquake at 05: 46: 23 UT on March 11, 2011, was investigated with ground-based Global Positioning System (GPS) receivers in the east-Asian region. It was found that the initial ionospheric disturbance formed a zonal wave front after the earthquake occurrence. Four zonal wave fronts of this initial ionospheric disturbance were observed to travel southward from Japan to Taiwan with a velocity of about 1,0001,700 m/s. This study further found that the direction of the wave vector rotated from the south-southwest to the south-southeast as it traveled from Japan to Taiwan. The meridional propagation of the coseismic ionospheric disturbances is consistent with those observed after previous intense earthquakes. The temporal evolutions of initial ionospheric disturbances, after the earthquake, near the epicenter was observed in two-dimensions. The directivity of the disturbances was caused by a geomagnetic field effect.

    DOI: 10.5047/eps.2011.06.026

    Web of Science

  312. ISS-IMAPミッションによって明らかになる超高層大気の姿

    斎藤昭則, 山崎敦, 阿部琢美, 鈴木睦, 坂野井健, 藤原均, 吉川一朗, 大塚雄一, 田口真, 山本衛, 中村卓司, 江尻省, 菊池雅行, 河野英昭, 石井守, 久保田実, 星野尾一明, 坂野井和代

    第25回大気圏シンポジウム     2011

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  313. Ionospheric multiple stratifications and irregularities induced by the 2011 off the Pacific coast of Tohoku Earthquake Reviewed

    Takashi Maruyama, Takuya Tsugawa, Hisao Kato, Akinori Saito, Yuichi Otsuka, Michi Nishioka

    EARTH PLANETS AND SPACE   Vol. 63 ( 7 ) page: 869 - 873   2011

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    A strong earthquake with a magnitude of 9.0 occurred at 1446: 23 JST on March 11, 2011, in Japan. Ionospheric disturbances were detected at 1500 JST at four ionosonde stations. An irregular distortion of echo trace was observed at Kokubunji, which is the nearest station to the epicenter and is 440 km from it. Multiple-cusp-type trace indicating extra stratification was observed at Wakkanai and Yamagawa, which are 870 and 1410 km away from the epicenter. A small wavy fluctuation was observed at Okinawa 1910 km away from the epicenter. The real height analysis of the ionograms showed a vertical structure with a scale size of 20 similar to 30 km.

    DOI: 10.5047/eps.2011.06.008

    Web of Science

  314. On postmidnight low-latitude ionospheric irregularities during solar minimum: 1. Equatorial Atmosphere Radar and GPS-TEC observations in Indonesia Reviewed

    T. Yokoyama, M. Yamamoto, Y. Otsuka, M. Nishioka, T. Tsugawa, S. Watanabe, R. F. Pfaff

    Journal of Geophysical Research: Space Physics   Vol. 116 ( 11 )   2011

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

  315. Propagation of large amplitude ionospheric disturbances with velocity dispersion observed by the SuperDARN Hokkaido radar after the 2011 off the Pacific coast of Tohoku Earthquake Reviewed

    Nozomu Nishitani, Tadahiko Ogawa, Yuichi Otsuka, Keisuke Hosokawa, Tomoaki Hori

    EARTH PLANETS AND SPACE   Vol. 63 ( 7 ) page: 891 - 896   2011

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    Ionospheric responses to the 2011 off the Pacific coast of Tohoku Earthquake are studied using the SuperDARN Hokkaido radar, which is located at (43.5 degrees N, 143.6 degrees E) and which monitors the ionosphere over a wide horizontal area. The radar observed an oscillation of the vertical motion of the ionosphere with a period of about 1 to 2 min. The disturbance propagated northward, away from the epicenter with the velocity of about 6.2, 4.5, 3.9 and 3.5 km/s. The latter three values are basically consistent with the propagation of the Earth&apos;s surface waves reported in several previous studies. The propagation velocities decreased with time, which has not been reported in previous studies for this propagation velocity range. The peak-to-peak amplitudes of Doppler velocities of ground/sea scatter echoes observed by the radar were up to 200 m/s, which is considerably larger than previously-reported values using HF Doppler measurements, although they are not extremely large for this historical earthquake (M = 9.0). This is the first time that ionospheric data have been obtained with high temporal (8 s) and spatial (22.5 km) resolutions following a giant earthquake, which enables us to discuss the detailed characteristics of the propagation of coseismic ionospheric disturbances.

    DOI: 10.5047/eps.2011.07.003

    Web of Science

  316. On postmidnight low-latitude ionospheric irregularities during solar minimum: 2. C/NOFS observations and comparisons with the Equatorial Atmosphere Radar Reviewed

    T. Yokoyama, R. F. Pfaff, P. A. Roddy, M. Yamamoto, Y. Otsuka

    Journal of Geophysical Research: Space Physics   Vol. 116 ( 11 )   2011

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    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

  317. Vertical connection from the tropospheric activities to the ionospheric longitudinal structure simulated by a new Earth's whole atmosphere-ionosphere coupled model Reviewed

    H. Jin, Y. Miyoshi, H. Fujiwara, H. Shinagawa, K. Terada, N. Terada, M. Ishii, Y. Otsuka, A. Saito

    Journal of Geophysical Research: Space Physics   Vol. 116 ( 1 )   2011

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

  318. Dynamic temporal evolution of polar cap tongue of ionization during magnetic storm Reviewed

    K. Hosokawa, T. Tsugawa, K. Shiokawa, Y. Otsuka, N. Nishitani, T. Ogawa, M. R. Hairston

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 115   2010.12

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    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

  319. Midnight latitude-altitude distribution of 630 nm airglow in the Asian sector measured with FORMOSAT-2/ISUAL Reviewed

    Toru Adachi, Masashi Yamaoka, Mamoru Yamamoto, Yuichi Otsuka, Huixin Liu, Chun-Chieh Hsiao, Alfred B. Chen, Rue-Ron Hsu

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 115   2010.9

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

  320. Large-scale traveling ionospheric disturbance observed by superDARN Hokkaido HF radar and GPS networks on 15 December 2006 Reviewed

    Hayashi, H, Nishitani, N, Ogawa, T, Otsuka, Y, Tsugawa, T, Hosokawa, K, Saito, A

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 115   2010.6

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  321. Large-scale traveling ionospheric disturbance observed by superDARN Hokkaido HF radar and GPS networks on 15 December 2006 Reviewed

    H. Hayashi, N. Nishitani, T. Ogawa, Y. Otsuka, T. Tsugawa, K. Hosokawa, A. Saito

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 115   2010.6

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

  322. Nighttime-like quasi periodic echoes induced by a partial solar eclipse Reviewed

    Smitha V. Thampi, Mamoru Yamamoto, Huixin Liu, Susumu Saito, Yuichi Otsuka, Amit Kumar Patra

    GEOPHYSICAL RESEARCH LETTERS   Vol. 37   2010.5

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    The first observations of solar eclipse induced mid-latitude plasma irregularities using the middle and upper atmosphere radar (MU radar) at Shigaraki (34.85 degrees N, 136.1 degrees E, 25.0 degrees N geomagnetic) are presented. The observations were done during the partial solar eclipse on 22 July, 2009. The observations show that the sudden withdrawal of solar radiation could deplete the background E-region densities, thereby unmasking the long-lived metallic ions within the strong and patchy Sporadic E-layers. As a result of this, Quasi-Periodic (QP) echoes were generated, which were detected by the MU radar. These echoes resemble the normal post-sunset QP echoes observed over mid-latitudes as revealed by the multi-channel interfereometry imaging. This example shows that over mid-latitudes E-region plasma irregularities can be generated during a partial solar eclipse, revealing a hitherto unobserved aspect of mid-latitude ionospheric responses to eclipses. Citation: Thampi, S. V., M. Yamamoto, H. Liu, S. Saito, Y. Otsuka, and A. K. Patra (2010), Nighttime-like quasi periodic echoes induced by a partial solar eclipse, Geophys. Res. Lett., 37, L09107, doi: 10.1029/2010GL042855.

    DOI: 10.1029/2010GL042855

    Web of Science

  323. Longitudinal development of low-latitude ionospheric irregularities during the geomagnetic storms of July 2004 Reviewed

    Guozhu Li, Baiqi Ning, Lianhuan Hu, Libo Liu, Xinan Yue, Weixing Wan, Biqiang Zhao, K. Igarashi, Minoru Kubota, Yuichi Otsuka, J. S. Xu, J. Y. Liu

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 115 ( 4 )   2010.4

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    During the period 22-28 July 2004, three geomagnetic storms occurred due to a sequence of coronal mass ejections. In this paper we present and discuss the ionospheric observations from a set of in situ satellites and ground-based GPS total electron content and scintillation receivers, a VHF radar, and two chains of ionosondes (similar to 300 degrees E and similar to 120 degrees E, respectively) that provide the evolutionary characteristics of equatorial and low-latitude ionospheric irregularities versus longitude during these storm periods. It is found that the irregularities occurred over a wide longitudinal range, extending from around 300 degrees E to 120 degrees E on storm days 25 and 27 July 2004. On 25 July plasma bubbles (PBs) began premidnight in America and postmidnight in Southeast Asia. On 27 July the occurrence of irregularities followed the sunset terminator and was observed sequentially after sunset from American to Southeast Asian longitudes. Past studies have reported that storm-time low-latitude ionospheric irregularities are mostly confined to a narrower longitude range, &lt;90 degrees, after sunset hours and are associated with the prompt penetration of eastward electric fields (PPEFs) into low latitudes. In June solstice months the occurrence of range-type spread F or PBs is very low in Southeast Asian and South American sectors. In contrast, the present results indicate that geomagnetic storms triggered the wide longitudinal development of PBs. In the American sector this was probably due to the effects of PPEFs on both storm days. However, in the Southeast Asian sector the PBs on the 2 days probably arose from disturbance dynamo electric field (DDEF), PPEF, and gravity wave seeding effects. This study further shows that under complex storm conditions, besides the long duration or multiple penetrations, the combined effects of PPEFs and DDEFs could result in a wide longitude extent of ionospheric irregularities at times.

    DOI: 10.1029/2009JA014830

    Web of Science

    Scopus

  324. A physical mechanism of positive ionospheric storms at low latitudes and midlatitudes Reviewed

    Balan N, Shiokawa K, Otsuka Y, Kikuchi T, Lekshmi D. Vijaya, Kawamura S, Yamamoto M, Bailey G. J

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 115   2010.2

  325. Reorganization of polar cap patches through shears in the background plasma convection Reviewed

    K. Hosokawa, J. -P. St-Maurice, G. J. Sofko, K. Shiokawa, Y. Otsuka, T. Ogawa

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 115   2010.1

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

  326. A physical mechanism of positive ionospheric storms at low latitudes and midlatitudes Reviewed

    N. Balan, K. Shiokawa, Y. Otsuka, T. Kikuchi, D. Vijaya Lekshmi, S. Kawamura, M. Yamamoto, G. J. Bailey

    Journal of Geophysical Research: Space Physics   Vol. 115 ( 2 )   2010

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

  327. Dynamic temporal evolution of polar cap tongue of ionization during magnetic storm Reviewed

    K. Hosokawa, T. Tsugawa, K. Shiokawa, Y. Otsuka, N. Nishitani, T. Ogawa, M. R. Hairston

    Journal of Geophysical Research: Space Physics   Vol. 115 ( 12 )   2010

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

  328. Large-scale traveling ionospheric disturbance observed by superDARN Hokkaido HF radar and GPS networks on 15 December 2006 Reviewed

    H. Hayashi, N. Nishitani, T. Ogawa, Y. Otsuka, T. Tsugawa, K. Hosokawa, A. Saito

    Journal of Geophysical Research: Space Physics   Vol. 115 ( 6 )   2010

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

  329. Midnight latitude-altitude distribution of 630 nm airglow in the Asian sector measured with FORMOSAT-2/ISUAL Reviewed

    Toru Adachi, Masashi Yamaoka, Mamoru Yamamoto, Yuichi Otsuka, Huixin Liu, Chun-Chieh Hsiao, Alfred B. Chen, Rue-Ron Hsu

    Journal of Geophysical Research: Space Physics   Vol. 115 ( 9 )   2010

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

  330. Lower-thermospheric wind fluctuations measured with an FPI during pulsating aurora at Tromso, Norway Reviewed

    S. Oyama, K. Shiokawa, J. Kurihara, T. T. Tsuda, S. Nozawa, Y. Ogawa, Y. Otsuka, B. J. Watkins

    ANNALES GEOPHYSICAE   Vol. 28 ( 10 ) page: 1847 - 1857   2010

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:COPERNICUS GESELLSCHAFT MBH  

    Simultaneous observations were conducted with a Fabry-Perot Interferometer (FPI) at a wavelength of 557.7 nm, an all-sky camera at a wavelength of 557.7 nm, and the European Incoherent Scatter (EISCAT) UHF radar during the Dynamics and Energetics of the Lower Thermosphere in Aurora 2 (DELTA-2) campaign in January 2009. This paper concentrated on two events during periods of pulsating aurora. The lower-thermospheric wind velocity measured with the FPI showed obvious fluctuations in both vertical and horizontal components. Of particular interest is that the location of the fluctuations was found in a darker area that appeared within the pulsating aurora. During the same time period, the EISCAT radar observed sporadic enhancements in the F-region backscatter echo power, which suggests the presence of low-energy electron (1 keV or lower) precipitation coinciding with increase in amplitude of the electromagnetic wave (at the order of 10 Hz or higher). While we have not yet identified the dominant mechanism causing the fluctuations in FPI-derived wind velocity during the pulsating aurora, the frictional heating energy dissipated by the electric-field perturbations may be responsible for the increase in ionospheric thermal energy thus modifying the local wind dynamics in the lower thermosphere.

    DOI: 10.5194/angeo-28-1847-2010

    Web of Science

  331. Reorganization of polar cap patches through shears in the background plasma convection Reviewed

    K. Hosokawa, J. P. St-Maurice, G. J. Sofko, K. Shiokawa, Y. Otsuka, T. Ogawa

    Journal of Geophysical Research: Space Physics   Vol. 115 ( 1 )   2010

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

  332. The STEL induction magnetometer network for observation of high-frequency geomagnetic pulsations Reviewed

    K. Shiokawa, R. Nomura, K. Sakaguchi, Y. Otsuka, Y. Hamaguchi, M. Satoh, Y. Katoh, Y. Yamamoto, B. M. Shevtsov, S. Smirnov, I. Poddelsky, M. Connors

    EARTH PLANETS AND SPACE   Vol. 62 ( 6 ) page: 517 - 524   2010

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:SPRINGER HEIDELBERG  

    The Solar-Terrestrial Environment Laboratory (STEL) induction magnetometer network has been developed to investigate the propagation characteristics of high-frequency geomagnetic pulsations in the Pc1 frequency range (0.2-5 Hz). Five induction magnetometers were installed in the period 2005-2008 at Athabasca in Canada, Magadan and Paratunka in Far East Russia, and Moshiri and Sata in Japan. The sensitivity of these magnetometers is between 0.3 and 13 V/nT at turnover frequencies of 1.7-5.5 Hz. GPS time pulses are used for accurate triggering of the 64-Hz data sampling. We show examples of PiB/Pc1 magnetic pulsations observed at these five stations, as well as the harmonic structure of ionospheric Alfven resonators observed at Moshiri. We found that the Pc1 packets are slightly modulated as they propagate from high to low latitudes in the ionospheric duct. These network observations are expected to contribute to our understanding of Pc1-range magnetic pulsations and their interaction with relativistic electrons by combining the obtained results with future satellite missions that observe radiation belt particles.

    DOI: 10.5047/eps.2010.05.003

    Web of Science

  333. 国際宇宙ステーションJEM曝露部からの超高層大気撮像観測計画ISS-IMAP

    齊藤昭則, 阿部琢美, 山崎敦, 鈴木睦, 坂野井健, 藤原均, 吉川一朗, 大塚雄一, 田口真, 山本衛, 中村卓司, 菊池雅行, 江尻省, 河野英昭, 石井守, 久保田実, 星野尾一明, 坂野井和代

    第10回宇宙科学シンポジウム講演集     2010

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  334. Thermospheric temperature and density variations Reviewed

    Hitoshi Fujiwara, Yasunobu Miyoshi, Hidekatsu Jin, Hiroyuki Shinagawa, Yuichi Otsuka, Akinori Saito, Mamoru Ishii

    SOLAR AND STELLAR VARIABILITY: IMPACT ON EARTH AND PLANETS   ( 264 ) page: 310 - +   2010

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    Language:English   Publishing type:Research paper (international conference proceedings)   Publisher:CAMBRIDGE UNIV PRESS  

    The thermosphere is the transition region from the atmosphere to space. Both the solar ultraviolet radiation and the solar wind energy inputs have caused significant thermospheric variations from past to present. In order to understand thermospheric/ionospheric disturbances in association with changes in solar activity, observational and modelling efforts have been made by many researchers. Recent satellite observations, e.g., the satellite CHAMP, have revealed mass density variations in the upper thermosphere. The thermospheric temperature, wind, and composition variations have been also investigated with general/global circulation models (GCMs) which include forcings due to the solar wind energy inputs and the lower atmospheric effects. In particular, we have developed a GCM which covers all the atmospheric regions, troposphere, stratosphere, mesosphere, and thermosphere, to describe variations of the thermospheric temperature and density caused by both effects from the lower atmosphere and the magnetosphere. GCM simulations represent global and localized temperature and density structures, winch vary from hour to hour, depending on forcings due to the lower atmosphere, solar and geomagnetic activities. This modelling attempt will enable us to describe the thermospheric weather influenced by solar activity in cooperation with ground-based and satellite observations.

    DOI: 10.1017/S1743921309992857

    Web of Science

  335. Ionospheric and geomagnetic disturbances during the 2005 Sumatran earthquakes Reviewed

    Alina Marie Hasbi, Mohammed Awad Momani, Mohd Alauddin Mohd Ali, Norbahiah Misran, Kazuo Shiokawa, Yuichi Otsuka, Kiyohumi Yumoto

    JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS   Vol. 71 ( 17-18 ) page: 1992 - 2005   2009.12

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:PERGAMON-ELSEVIER SCIENCE LTD  

    This paper investigates the ionospheric and geomagnetic responses during the 28 March 2005 and 14 May 2005 Sumatran earthquakes using GPS and magnetometer stations located in the near zone of the epicenters. These events occurred during low solar and geomagnetic activity. TEC oscillations with periods of 5-10 min were observed about 10-24 min after the earthquakes and have horizontal propagation velocities of 922-1259 m/s. Ionospheric disturbances were observed at GPS stations located to the northeast of the epicenters, while no significant disturbances were seen relatively east and south of the epicenters. The magnetic field measurements show rapid fluctuations of 4-5 s shortly after the earthquake, followed by a Pc5 pulsation of 4.8 min about 11 min after the event. The correlation between the ionospheric and geomagnetic responses shows a good agreement in the period and time lag of the peak disturbance arrival, i.e. about 11-13 min after the earthquake. (C) 2009 Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.jastp.2009.09.004

    Web of Science

  336. On the gravity wave-driven instability of E layer at mid-latitude Reviewed

    S. Shalimov, T. Ogawa, Y. Otsuka

    JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS   Vol. 71 ( 17-18 ) page: 1943 - 1947   2009.12

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:PERGAMON-ELSEVIER SCIENCE LTD  

    The plasma instability process during internal gravity wave propagation through the ionospheric E region is considered. The growth rate of the instability has been found and it has been shown that it depends on perturbation wavelength, gravity wave parameters and direction of propagation. The conditions for the instability are favorable when the vorticity of the associated neutral motion becomes antiparallel to the geomagnetic field. In the proposed instability mechanism plasma irregularities could seed the large-scale sporadic E layer structuring because they are generated in situ as a part of the same neutral wind structure that serves to initiate the formation of the layer. (C) 2009 Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.jastp.2009.08.004

    Web of Science

  337. First observations of large-scale wave structure and equatorial spread F using CERTO radio beacon on the C/NOFS satellite Reviewed

    Smitha V. Thampi, Mamoru Yamamoto, Roland T. Tsunoda, Yuichi Otsuka, Takuya Tsugawa, Jyunpei Uemoto, Mamoru Ishii

    GEOPHYSICAL RESEARCH LETTERS   Vol. 36   2009.9

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

    First observations of large-scale wave structure (LSWS) and the subsequent development of equatorial spread F (ESF), using total electron content (TEC) derived from the ground based reception of beacon signals from the CERTO (Coherent Electromagnetic Radio Tomography) radio beacon on board C/NOFS (Communications/Navigation Outage Forecasting System) satellite, are presented. Selected examples of TEC variations, using measurements made during January 2009 from Bac Lieu, Vietnam (9.2 degrees N, 105.6 degrees E geographic, 1.7 degrees N magnetic dip latitude) are presented to illustrate two key findings: (1) LSWS appears to play a more important role in the development of ESF than the post-sunset rise (PSSR) of the F-layer, and (2) LSWS can appear well before E region sunset. Other findings, that LSWS does not have significant zonal drift in the initial stages of growth, and can have zonal wavelengths of several hundred kilometers, corroborate earlier reports. Citation: Thampi, S. V., M. Yamamoto, R. T. Tsunoda, Y. Otsuka, T. Tsugawa, J. Uemoto, and M. Ishii (2009), First observations of large-scale wave structure and equatorial spread F using CERTO radio beacon on the C/NOFS satellite, Geophys. Res. Lett., 36, L18111, doi: 10.1029/2009GL039887.

    DOI: 10.1029/2009GL039887

    Web of Science

  338. Coordinated observations of nighttime medium-scale traveling ionospheric disturbances in 630-nm airglow and HF radar echoes at midlatitudes Reviewed

    Suzuki S, Hosokawa K, Otsuka Y, Shiokawa K, Ogawa T, Nishitani N, Shibata T. F, Koustov A. V, Shevtsov B. M

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 114   page: A07312   2009.7

  339. First simultaneous observations of daytime MSTIDs over North America using GPS-TEC and DEMETER satellite data Reviewed

    Tatsuo Onishi, Takuya Tsugawa, Yuichi Otsuka, Jean-Jacques Berthelier, Jean-Pierre Lebreton

    GEOPHYSICAL RESEARCH LETTERS   Vol. 36   2009.6

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

    We present simultaneous observations of daytime medium-scale traveling ionospheric disturbances (MSTIDs) over North America, using measurements of the Total Electron Content (TEC) by the US GPS network and ionospheric plasma data from the DEMETER microsatellite. Several events show latitudinal variations of the plasma parameters at satellite altitude corresponding to the MSTID structures revealed on 2D TEC maps. In a case study with a very well defined MSTID, quasi periodic variations of the plasma density and of the ion velocity parallel to the Earth&apos;s magnetic field are observed along the satellite orbit that match the signature of the MSTID on the TEC maps. We believe it is the first simultaneous observation of parallel plasma motion in the topside ionosphere and propagating MSTID structures in the F-region. An initial analysis of this event is performed in the light of results from simple model of ionospheric disturbances associated with Atmospheric Gravity Waves (AGWs). Citation: Onishi, T., T. Tsugawa, Y. Otsuka, J.-J. Berthelier, and J.-P. Lebreton (2009), First simultaneous observations of daytime MSTIDs over North America using GPS-TEC and DEMETER satellite data, Geophys. Res. Lett., 36, L11808, doi:10.1029/2009GL038156.

    DOI: 10.1029/2009GL038156

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  340. Spatial relationship of nighttime medium-scale traveling ionospheric disturbances and F region field-aligned irregularities observed with two spaced all-sky airglow imagers and the middle and upper atmosphere radar Reviewed

    Y. Otsuka, K. Shiokawa, T. Ogawa, T. Yokoyama, M. Yamamoto

    Journal of Geophysical Research: Space Physics   Vol. 114 ( 5 )   2009.5

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

  341. Spatial relationship of nighttime medium-scale traveling ionospheric disturbances and F region field-aligned irregularities observed with two spaced all-sky airglow imagers and the middle and upper atmosphere radar Reviewed

    Y. Otsuka, K. Shiokawa, T. Ogawa, T. Yokoyama, M. Yamamoto

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 114   2009.5

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

  342. Motion of polar cap patches: A statistical study with all-sky airglow imager at Resolute Bay, Canada Reviewed

    Hosokawa, K, Kashimoto, T, Suzuki, S, Shiokawa, K, Otsuka, Y, Ogawa, T

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 114   2009.4

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  343. Motion of polar cap patches: A statistical study with all-sky airglow imager at Resolute Bay, Canada Reviewed

    Hosokawa K, Kashimoto T, Suzuki S, Shiokawa K, Otsuka Y, Ogawa T

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 114   2009.4

  344. Unusually elongated, bright airglow plume in the polar cap F region: Is it a tongue of ionization? Reviewed

    K. Hosokawa, T. Tsugawa, K. Shiokawa, Y. Otsuka, T. Ogawa, M. R. Hairston

    GEOPHYSICAL RESEARCH LETTERS   Vol. 36   2009.4

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    We report an event of unusually elongated, bright airglow plume, which is considered as an optical manifestation of tongue of ionization (TOI) in the central polar cap. This optical structure was detected with an all-sky airglow imager at Resolute Bay (74.73 degrees N, 265.07 degrees E) during a large magnetic storm on December 15, 2006. The absolute optical intensity of the plume was approximate to 1 kR, which is much brighter than that of non-stormtime polar cap patches. Two-dimensional imaging capability of the all-sky imager demonstrates that some meso-scale structures (approximate to 250-600 km) were embedded within the plume. Simultaneous ion density and drift measurements with the DMSP spacecraft strongly suggest that the plume was extending from the dayside as a narrow stream of dense plasma and thus is an optical manifestation of polar cap TOI. The DMSP data also implies that the possible source of the plume is a narrow stream of storm enhanced density (SED) transported from lower latitudes. The DMSP auroral particle observation demonstrates that the polar cap extremely expanded equatorward during this interval. This extreme expansion allowed the anti-sunward convection to capture plasmas within the SED and deliver them deep into the polar cap as a luminous airglow plume. This observation claims that the plasma transport from the dayside lower latitudes plays an important role in controlling the plasma environment in the polar cap ionosphere during magnetic storms. Citation: Hosokawa, K., T. Tsugawa, K. Shiokawa, Y. Otsuka, T. Ogawa, and M. R. Hairston (2009), Unusually elongated, bright airglow plume in the polar cap F region: Is it a tongue of ionization?, Geophys. Res. Lett., 36, L07103, doi:10.1029/2009GL037512.

    DOI: 10.1029/2009GL037512

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  345. Medium-scale traveling ionospheric disturbances observed with the SuperDARN Hokkaido radar, all-sky imager, and GPS network and their relation to concurrent sporadic E irregularities Reviewed

    Ogawa T, Nishitani N, Otsuka Y, Shiokawa K, Tsugawa T, Hosokawa K

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 114   2009.3

  346. Medium-scale traveling ionospheric disturbances observed with the SuperDARN Hokkaido radar, all-sky imager, and GPS network and their relation to concurrent sporadic E irregularities Reviewed

    T. Ogawa, N. Nishitani, Y. Otsuka, K. Shiokawa, T. Tsugawa, K. Hosokawa

    Journal of Geophysical Research: Space Physics   Vol. 114 ( 3 )   2009.3

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:Blackwell Publishing Ltd  

    We present midlatitude medium-scale traveling ionospheric disturbances (MSTIDs) observed with a Super Dual Auroral Radar Network (SuperDARN) HF radar at around 10 MHz in Hokkaido, Japan, in combination with a 630-nm all-sky imager and a GPS network (GEONET) that provides total electron content (TEC) data. MSTIDs propagating southward from high latitudes are detected at first with the HF radar and then with the imager and GEONET. We analyze two MSTID events, one in winter (event 1) and the other in summer (event 2), to find that MSTIDs appear simultaneously, at least, at 55°-25°N. It is shown that nighttime MSTIDs propagate toward the southwest over a horizontal distance of about 4000 km, and daytime MSTIDs do so toward the southeast. Daytime radar echoes are due to ground/sea surface (GS) scatter, while nighttime echoes in event 1 return from 15-m-scale F region field-aligned irregularities (FAIs) and those in event 2 are due to GS scatter. Doppler velocities of the nighttime F region FAI echoes in event 1 are negative (motion away from the radar) within strong echo regions and are positive (motion toward the radar) within weak echo regions. This fact suggests that the strong (weak) echoes return from suppressed (enhanced) airglow/TEC areas, in line with previous observations over central Japan. The nighttime MSTIDs in events 1 and 2 are often accompanied by concurrent coherent echoes from FAIs in sporadic E (Es) layers. The Es echo areas in event 2 rather coincide with suppressed airglow/TEC areas in the F region that are connected with the echo areas along the geomagnetic field, indicating the existence of E and F region coupling at night. Copyright 2009 by the American Geophysical Union.

    DOI: 10.1029/2008JA013893

    Scopus

  347. Relationship between polar cap patches and field-aligned irregularities as observed with an all-sky airglow imager at Resolute Bay and the PolarDARN radar at Rankin Inlet Reviewed

    K. Hosokawa, K. Shiokawa, Y. Otsuka, T. Ogawa, J. P. St-Maurice, G. J. Sofko, D. A. Andre

    Journal of Geophysical Research: Space Physics   Vol. 114 ( 3 )   2009.3

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:Blackwell Publishing Ltd  

    Simultaneous two-dimensional observations of airglow enhancement and radar backscatter from field-aligned irregularities (FAIs) associated with polar cap patches were conducted. The spatial structure of 630 nm airglow from polar cap patches was imaged using an all-sky airglow imager at Resolute Bay, Canada, while backscatter echoes from decameter-scale FAIs were observed using the newly constructed HF Polar Dual Auroral Radar Network (PolarDARN) radar at Rankin Inlet, Canada. Both the airglow enhancement and the radar backscatter appeared within a structured region with the spatial extent of about 500-1000 km. The decameter-scale FAIs were found to extend over the entire region of airglow enhancement associated with polar cap patches, indicating that the polar patch plasma became almost fully structured soon after initiation (within approximately 2025 min). These findings imply that some rapid structuring process of the entire patch area is involved in addition to the primary gradient-drift instabilities. Copyright 2009 by the American Geophysical Union.

    DOI: 10.1029/2008JA013707

    Scopus

  348. Super plasma fountain and equatorial ionization anomaly during penetration electric field Reviewed

    N. Balan, K. Shiokawa, Y. Otsuka, S. Watanabe, G. J. Bailey

    Journal of Geophysical Research: Space Physics   Vol. 114 ( 3 )   2009.3

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:Blackwell Publishing Ltd  

    Relative importance of diffusion, electric field, and neutral wind on equatorial plasma fountain and equatorial ionization anomaly (EIA) during a strong daytime eastward prompt penetration electric field (PPEF) event are evaluated using the Sheffield University Plasmasphere Ionosphere Model and the recorded PPEF during the super geomagnetic storm of 9 November 2004. The fountain rapidly develops into a super fountain during the PPEF event. The super fountain becomes strong with less poleward turning of the velocity vectors in the presence of an equatorward wind that reduces (or stops) the downward velocity component due to diffusion and raises the ionosphere to high altitudes of reduced chemical loss. The EIA crests in peak electron density and total electron content shift rapidly to higher than normal latitudes during the PPEF event. However, the crests become stronger than normal only in the presence of an equatorward wind. The results suggest that the presence of an equatorward neutral wind is required to produce a strong positive ionospheric storm during, a daytime eastward PPEF event. The equatorward neutral wind need not be a storm time wind though stronger wind can lead to stronger ionospheric storms. Copyright 2009 by the American Geophysical Union.

    DOI: 10.1029/2008JA013768

    Scopus

  349. Three-dimensional simulation of the coupled Perkins and es-layer instabilities in the nighttime midlatitude ionosphere Reviewed

    Tatsuhiro Yokoyama, David L. Hysell, Yuichi Otsuka, Mamoru Yamamoto

    Journal of Geophysical Research: Space Physics   Vol. 114 ( 3 )   2009.3

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:Blackwell Publishing Ltd  

    Plasma density structures and associated irregularities in the nighttime midlatitude ionosphere are frequently observed as frontal structures elongated from northwest to southeast (NW-SE) in the Northern Hemisphere. The frontal structures and the coupling process between the E and F regions are studied with a three-dimensional numerical model, which can simulate two instability mechanisms: Perkins instability in the F-region and sporadic-E (E s)-layer instability in the E region. The fastest growth of the coupled instability occurs when the unstable conditions on NW-SE perturbation are satisfied in both regions. The perturbation of F-region integrated conductivity grows much faster than the isolated Perkins instability. The meridional component of a rotational wind shear blows an existing E5 layer southward, and the F-region structure follows the E-region drift velocity. The NW-SE structure in the E region can be formed from random perturbation regardless of the F-region condition. When the F region is unstable on the NW-SE perturbation, however, the NW-SE structure is formed in both regions with a common scale length. We conclude that (1) the Es-layer instability plays a major role in seeding NW-SE structure in the F region, and the Perkins instability is required to amplify its perturbation
    (2) the rotational wind shear in the E region produces southwestward phase propagation of the NW-SE structure in both the E and F regions
    and (3) the coupling process has a significant effect on the scale of the Es-layer perturbation rather than the growth rate of the Es-layer instability. Copyright 2009 by the American Geophysical Union.

    DOI: 10.1029/2008JA013789

    Scopus

  350. Relationship between polar cap patches and field-aligned irregularities as observed with an all-sky airglow imager at Resolute Bay and the PolarDARN radar at Rankin Inlet Reviewed

    K. Hosokawa, K. Shiokawa, Y. Otsuka, T. Ogawa, J. -P. St-Maurice, G. J. Sofko, D. A. Andre

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 114   2009.3

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

    Simultaneous two-dimensional observations of airglow enhancement and radar backscatter from field-aligned irregularities (FAIs) associated with polar cap patches were conducted. The spatial structure of 630 nm airglow from polar cap patches was imaged using an all-sky airglow imager at Resolute Bay, Canada, while backscatter echoes from decameter-scale FAIs were observed using the newly constructed HF Polar Dual Auroral Radar Network (PolarDARN) radar at Rankin Inlet, Canada. Both the airglow enhancement and the radar backscatter appeared within a structured region with the spatial extent of about 500-1000 km. The decameter-scale FAIs were found to extend over the entire region of airglow enhancement associated with polar cap patches, indicating that the polar patch plasma became almost fully structured soon after initiation (within approximately 20-25 min). These findings imply that some rapid structuring process of the entire patch area is involved in addition to the primary gradient-drift instabilities.

    DOI: 10.1029/2008JA013707

    Web of Science

  351. Super plasma fountain and equatorial ionization anomaly during penetration electric field Reviewed

    N. Balan, K. Shiokawa, Y. Otsuka, S. Watanabe, G. J. Bailey

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 114   2009.3

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

    Relative importance of diffusion, electric field, and neutral wind on equatorial plasma fountain and equatorial ionization anomaly (EIA) during a strong daytime eastward prompt penetration electric field (PPEF) event are evaluated using the Sheffield University Plasmasphere Ionosphere Model and the recorded PPEF during the super geomagnetic storm of 9 November 2004. The fountain rapidly develops into a super fountain during the PPEF event. The super fountain becomes strong with less poleward turning of the velocity vectors in the presence of an equatorward wind that reduces (or stops) the downward velocity component due to diffusion and raises the ionosphere to high altitudes of reduced chemical loss. The EIA crests in peak electron density and total electron content shift rapidly to higher than normal latitudes during the PPEF event. However, the crests become stronger than normal only in the presence of an equatorward wind. The results suggest that the presence of an equatorward neutral wind is required to produce a strong positive ionospheric storm during a daytime eastward PPEF event. The equatorward neutral wind need not be a storm time wind though stronger wind can lead to stronger ionospheric storms.

    DOI: 10.1029/2008JA013768

    Web of Science

  352. Three-dimensional simulation of the coupled Perkins and E-s-layer instabilities in the nighttime midlatitude ionosphere Reviewed

    Tatsuhiro Yokoyama, David L. Hysell, Yuichi Otsuka, Mamoru Yamamoto

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 114   2009.3

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

    Plasma density structures and associated irregularities in the nighttime midlatitude ionosphere are frequently observed as frontal structures elongated from northwest to southeast (NW-SE) in the Northern Hemisphere. The frontal structures and the coupling process between the E and F regions are studied with a three-dimensional numerical model, which can simulate two instability mechanisms: Perkins instability in the F-region and sporadic-E (E-s)-layer instability in the E region. The fastest growth of the coupled instability occurs when the unstable conditions on NW-SE perturbation are satisfied in both regions. The perturbation of F-region integrated conductivity grows much faster than the isolated Perkins instability. The meridional component of a rotational wind shear blows an existing E-s layer southward, and the F-region structure follows the E-region drift velocity. The NW-SE structure in the E region can be formed from random perturbation regardless of the F-region condition. When the F region is unstable on the NW-SE perturbation, however, the NW-SE structure is formed in both regions with a common scale length. We conclude that (1) the E-s-layer instability plays a major role in seeding NW-SE structure in the F region, and the Perkins instability is required to amplify its perturbation; (2) the rotational wind shear in the E region produces southwestward phase propagation of the NW-SE structure in both the E and F regions; and (3) the coupling process has a significant effect on the scale of the E-s-layer perturbation rather than the growth rate of the E-s-layer instability.

    DOI: 10.1029/2008JA013789

    Web of Science

  353. Medium-Scale Traveling Ionospheric Disturbances and Plasma Bubbles Observed by an All-Sky Airglow Imager at Yonaguni, Japan Reviewed

    Tadahiko Ogawa, Yuichi Otsuka, Kazuo Shiokawa, Takuya Tsugawa, Akinori Saito, Kazuaki Hoshinoo, Keisuke Matunaga, Minoru Kubota, Mamoru Ishii

    TERRESTRIAL ATMOSPHERIC AND OCEANIC SCIENCES   Vol. 20 ( 1 ) page: 287 - 295   2009.2

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:CHINESE GEOSCIENCE UNION  

    We report on nighttime airglow imaging observations of the low latitude ionosphere by means of a 630-m all-sky imager installed in March 2006 at Yonaguni, Japan (24.5 degrees N, 123.0 degrees E; 14.6 degrees N geomagnetic), about 100 kin east of Taiwan. The imager detected medium-scale traveling ionospheric disturbances (MSTIDs) for about 7 hours on the night of 26 May 2006. A dense GPS network in Japan also observed the same MSTID event on this night. The imager and GEONET data indicate that most of the MSTIDs propagated southwestward from the north of Japan to the south of Yonaguni and Taiwan over 4000 kin, with a southern limit of 19 degrees N (geomagnetic latitude 9 degrees N) or lower. On the night of 10 November 2006, the imager observed two weak emission bands that were embedded on the F-region anomaly crest to the south of Yonaguni. The simultaneous electron density profiles from the FORMOSAT-3/COSMIC mission demonstrate that the weak emission bands are due to density depletions in equatorial plasma bubbles. These case studies suggest that the Yonaguni imager in collaboration with other instruments is very suitable for the study of ionospheric disturbances in and around the northern F-region anomaly crest.

    DOI: 10.3319/TAO.2007.12.06.02(F3C)

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  354. Effects observed in the ionospheric F region in the east Asian sector during the intense geomagnetic disturbances in the early part of November 2004 Reviewed

    Y. Sahai, F. Becker-Guedes, P. R. Fagundes, R. De Jesus, A. J. De Abreu, Y. Otsuka, K. Shiokawa, K. Igarashi, K. Yumoto, C. S. Huang, H. T. Lan, A. Saito, F. L. Guarnieri, V. G. Pillat, J. A. Bittencourt

    Journal of Geophysical Research: Space Physics   Vol. 114 ( 3 )   2009.1

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    The Sun was very active in the early part of November 2004. During the period of 8-10 November 2004, intense geomagnetic disturbances with two superstorms were observed. In a companion paper (hereinafter referred to as paper 1), the effects observed in the F region during the intense geomagnetic disturbances in the early part of November 2004 in the Latin American sector were presented. In the present paper, we investigate the effects observed in the F region during the intense geomagnetic disturbances in the early part of November 2004 in the east Asian sector. We have used the ionospheric sounding observations at Ho Chi Minh City (Vietnam) and Okinawa, Yamagawa, Kokubunji, and Wakkanai (Japan) in the present investigations. Also, GPS observations in the east Asian sector (several longitude zones) have been used to study the effect in the F region during the intense geomagnetic disturbances. The ion density versus latitudinal variations obtained by the DMSP F15 satellite orbiting at about 800 km altitude in the east Asian sector and the magnetic field data obtained at several stations in the Japanese meridian are also presented. Several important features from these observations in both the sectors during this extended period of intense geomagnetic disturbances are presented. The east Asian sector showed very pronounced effects during the second superstorm, which was preceded by two storm enhancements. It should be mentioned that around the beginning of the night on 10 November, ionospheric irregularities propagating from higher midlatitude region to low-latitude region were observed in the Japanese sector. The most intense geomagnetic field H component in that sector was observed on 10 November at L = 2.8, indicating that the auroral oval and the heating got further to low latitudes and the ionospheric irregularities observed in the Japanese sector on this night are midlatitude ionospheric disturbances associated with the second superstorm. The absence of ionospheric irregularities in the Japanese sector during the 8 November superstorm suggests that the magnetosphere-ionosphere system was possibly preconditioned (primed) when the second interplanetary structure impacted the magnetosphere. Copyright 2009 by the American Geophysical Union.

    DOI: 10.1029/2008JA013053

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    Scopus

  355. Characteristics of equatorial gravity waves derived from mesospheric airglow imaging observations Reviewed

    S. Suzuki, K. Shiokawa, A. Z. Liu, Y. Otsuka, T. Ogawa, T. Nakamura

    ANNALES GEOPHYSICAE   Vol. 27 ( 4 ) page: 1625 - 1629   2009

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:COPERNICUS GESELLSCHAFT MBH  

    We present the characteristics of small-scale (&lt; 100 km) gravity waves in the equatorial mesopause region derived from OH airglow imaging observations at Kototabang (100.3 degrees E, 0.2 degrees S), Indonesia, from 2002 to 2005. We adopted a method that could automatically detect gravity waves in the airglow images using two-dimensional cross power spectra of gravity waves. The propagation directions of the waves were likely controlled by zonal filtering due to stratospheric mean winds that show a quasi-biennial oscillation (QBO) and the presence of many wave sources in the troposphere.

    DOI: 10.5194/angeo-27-1625-2009

    Web of Science

  356. Equatorial GPS ionospheric scintillations over Kototabang, Indonesia and their relation to atmospheric waves from below Reviewed

    Tadahiko Ogawa, Yasunobu Miyoshi, Yuichi Otsuka, Takuji Nakamura, Kazuo Shiokawa

    EARTH PLANETS AND SPACE   Vol. 61 ( 4 ) page: 397 - 410   2009

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

    Using Global Positioning System (GPS) satellites. we have been conducting equatorial ionospheric scintillation observations at Kototabang, Indonesia since January 2003. Scintillations caused by equatorial plasma bubbles appear between 2000 and 0 100 LT in equinoctial months with a seasonal asymmetry, and their activity decreases with decreasing solar activity. A comparison between scintillation index (S-4) and Earth's brightness temperature variations suggests that file scintillation activity call be related to tropospheric disturbances over file Indian Ocean to the west of Kototabang. TO Understand better the reasons of day-to-day variability of S-4, we analyze S-4. T-bb and lower thermospheric neutral wind ((mu'(2)) over bar) data. The results show that S-4 fluctuates with periods of about 2.5, 5, 8, 14 and 25 days, possibly due to atmospheric waves from below and that similar periods are also found in the T-bb and (mu'(2)) over tilde variations. Using a general circulation model, we made numerical simulations to determine the behavior of neutral wind in the equatorial thermosphere. The results indicate the following: (1) 2- to 20-day waves dissipate rapidly above about an altitude of 125 km, and 0.5- to 3-hour waves become predominant above 100 km, (2) zonal winds above 200 km altitude are, on the whole, eastward during sunset-sunrise, (3) zonal wind patterns due to short-period (1-4 h) atmospheric gravity waves (AGWs) above 120 km altitude change day by day, exhibit wavy structures with scale lengths of about 30-1000 km and, as it whole, move eastward in about 100(-1) while changing patterns over time. These simulations suggest that the Rayleigh-Taylor instability responsible for plasma bubble generation call be seeded by AGWs with short periods of about 0.5-3 h, and that background conditions necessary for this instability are modulated by planetary-scale atmospheric waves propagating up to an altitude of about 120 km front below.

    DOI: 10.1186/BF03353157

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  357. Observations of the F-region ionospheric irregularities in the South American sector during the October 2003 'Halloween Storms' Reviewed

    Y. Sahai, F. Becker-Guedes, P. R. Fagundes, A. J. de Abreu, R. de Jesus, V. G. Pillat, J. R. Abalde, C. R. Martinis, C. Brunini, M. Gende, C. -S. Huang, X. Pi, W. L. C. Lima, J. A. Bittencourt, Y. Otsuka

    ANNALES GEOPHYSICAE   Vol. 27 ( 12 ) page: 4463 - 4477   2009

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    The response of the ionospheric F-region in the South American sector during the super geomagnetic storms on 29 and 30 October 2003 is studied in the present investigation.
    In this paper, we present ionospheric sounding observations during the period 29-31 October 2003 obtained at Palmas (a near equatorial location) and Sao Jose dos Campos (a location under the southern crest of the equatorial ionospheric anomaly), Brazil, along with observations during the period 27-31 October 2003 from a chain of GPS stations covering the South American sector from Imperatriz, Brazil, to Rio Grande, Argentina. Also, complementary observations that include sequences of all-sky images of the OI 777.4 and 630.0 nm emissions observed at El Leoncito, Argentina, on the nights of 28-29 (geomagnetically quiet night) and 29-30 (geomagnetically disturbed night) October 2003, and ion densities observed in the South American sector by the DMSP F13, F14 and F15 satellites orbiting at about 800 km on 29 and 30 October 2003 are presented. In addition, global TEC maps derived from GPS observations collected from the global GPS network of International GPS Service (IGS) are presented, showing widespread and drastic TEC changes during the different phases of the geomagnetic disturbances. The observations indicate that the equatorial ionospheric irregularities or plasma bubbles extend to the Argentinean station Rawson (geom. Lat. 33.1 degrees S) and map at the magnetic equator at an altitude of about 2500 km.

    DOI: 10.5194/angeo-27-4463-2009

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  358. Propagation characteristics of nighttime mesospheric and thermospheric waves observed by optical mesosphere thermosphere imagers at middle and low latitudes Reviewed

    K. Shiokawa, Y. Otsuka, T. Ogawa

    EARTH PLANETS AND SPACE   Vol. 61 ( 4 ) page: 479 - 491   2009

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:SPRINGER HEIDELBERG  

    We review measurements of nighttime atmospheric/ionospheric wave in the upper atmosphere in Japan. Indonesia. and Australia. using all-sky airglow imagers of optical mesosphere thermosphere imagers (OMTIs). The imagers observe two-dimensional patterns of airglow emissions from oxygen (wavelength: 557.7 nm) and hydorxyl (OH) (near-infrared band) in the mesopause region (80-100 km) and from oxygen (630.0 nm) in the thermosphere/ionosphere (200-300 km). Several statistical studies were done to investigate propagation characteristics of small-scale (less than 100 km) gravity waves in the mesopause region and medium-scale traveling ionospheric disturbances (MSTIDs. similar to 100-1,000 km) in the thermosphere/ionosphere. Clear seasonal variations of occurrence and propagation directions were reported for these waves. The propagation directions in the mesopause region are controlled by wind filtering, ducting processes and relative location to the wave sources in the troposphere. On the other hand, systematic equatorward and westward motions were observed for all seasons for nighttime MSTIDs in the midlatitude ionosphere with geomagnetic conjugacy between the northern and Southern hemispheres. Ionospheric instabilities may play important role for the generation and propagation of these MSTIDs. We also give an example of simultaneous observation of quasi-periodic southward-moving waves in the mesopause and in the thermosphere at the geographic equator, From these results, we discuss mean wind acceleration by mesospheric gravity waves and penetration of gravity waves from the mesosphere to the thermosphere.

    DOI: 10.1186/BF03353165

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  359. Relative effects of electric field and neutral wind on positive ionospheric storms Reviewed

    N. Balan, H. Alleyne, Y. Otsuka, D.Vijaya Lekshmi, B. G. Fejer, I. McCrea

    Earth, Planets and Space   Vol. 61 ( 4 ) page: 439 - 445   2009

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    Language:English   Publishing type:Research paper (international conference proceedings)   Publisher:Springer Berlin  

    The paper studies the relative importance of penetrating eastward electric field (PEEF) and direct effects of equatorward neutral wind in leading to positive ionospheric storms at low-mid latitudes using observations and modeling. The observations show strong positive ionospheric storms in total electron content (TEC) and peak electron density (Nmax) at low-mid latitudes in Japan longitudes (≈125°E-145°E) during the first main phase (started at sunrise on 08 November) of a super double geomagnetic storm during 07-11 November 2004. The model results obtained using the Sheffield University Plasmashpere Ionosphere Model (SUPIM) show that the direct effects of storm-time equatorward neutral wind (that reduce poleward plasma flow and raise the ionosphere to high altitudes of reduced chemical loss) can be the main driver of positive ionospheric storms at low-mid latitudes except in Nmax around the equator. The equatorward wind without PEEF can also result in stronger positive ionospheric storms than with PEEF. Though PEEF on its own is unlikely to cause positive ionospheric storms, it can lead to positive ionospheric storms in the presence of an equatorward wind. Copyright © The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS).

    DOI: 10.1186/BF03353160

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  360. The Optical Mesosphere Thermosphere Imagers (OMTIs) for network measurements of aurora and airglow Reviewed

    K. Shiokawa, K. Hosokawa, K. Sakaguchi, A. Ieda, Y. Otsuka, T. Ogawa, M. Connors

    FUTURE PERSPECTIVES OF SPACE PLASMA AND PARTICLE INSTRUMENTATION AND INTERNATIONAL COLLABORATIONS   Vol. 1144   page: 212 - +   2009

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    Language:English   Publishing type:Research paper (international conference proceedings)   Publisher:AMER INST PHYSICS  

    The Optical Mesosphere Thermosphere Imagers (OMTIs) currently consist of eight all-sky cooled-CCD imagers and several interferometers and spectrometers. They are making routine observations of aurora and airglow in Japan, Australia, Indonesia, and Canada. Here we show recent results of OMTIs particularly from. the two Canadian stations at Resolute Bay (RSB) and Athabasca (ATH). At RSB, we observe polar-cap plasma patches almost always during southward IMF periods. From two-dimensional cross-correlation analyses, we determine velocity vectors of the patches, which indicates the ionospheric convection vector, showing high correlation with the IMF-By and -Bz variations. At ATH, we often observe isolated proton arcs and Stable Auroral Red (SAR) arcs, which are located equatorward of the auroral oval. The appearance of the isolated proton arcs is highly correlated with the Pc I geomagnetic pulsations measured simultaneously at ATH, suggesting interactions between the electromagnetic ion cyclotron (EMIC) waves and protons in the vicinity of the plasmapause and the ring current. Similar interactions without waves are also suggested for the SAR arcs, which appear after the substorm expansion phase even without geomagnetic storms. These observations show promising capability to monitor magnetospheric processes from the ground stations, which would contribute to the future satellite projects, such as THEMIS, ERG, and Scope/Xscale.

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  361. Zonal asymmetry of daytime 150-km echoes observed by Equatorial Atmosphere Radar in Indonesia Reviewed

    T. Yokoyama, D. L. Hysell, A. K. Patra, Y. Otsuka, M. Yamamoto

    ANNALES GEOPHYSICAE   Vol. 27 ( 3 ) page: 967 - 974   2009

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:COPERNICUS GESELLSCHAFT MBH  

    Multi-beam observations of the daytime ionospheric E-region irregularities and the so-called 150-km echoes with the 47-MHz Equatorial Atmosphere Radar (EAR) in West Sumatra, Indonesia (0.20 degrees S, 100.32 degrees E, 10.36 degrees S dip latitude) are presented. 150-km echoes have been frequently observed by the EAR, and their characteristics are basically the same as the equatorial ones, except for an intriguing zonal asymmetry; stronger echoes in lower altitudes in the east directions, and weaker echoes in higher altitudes in the west. The highest occurrence is seen at 5.7 degrees east with respect to the magnetic meridian, and the altitude gradually increases as viewing from the east to west. Arc structures which return backscatter echoes are proposed to explain the asymmetry. While the strength of radar echoes below 105 km is uniform within the wide coverage of azimuthal directions, the upper E-region (105-120 km) echoes also show a different type of zonal asymmetry, which should be generated by an essentially different mechanism from the lower E-region and 150-km echoes.

    DOI: 10.5194/angeo-27-967-2009

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  362. VHF radar observations of nighttime F-region field-aligned irregularities over Kototabang, Indonesia Reviewed

    Y. Otsuka, T. Ogawa, Effendy

    EARTH PLANETS AND SPACE   Vol. 61 ( 4 ) page: 431 - 437   2009

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    We report, for the first time, continuous observations of the nighttime F-region field-aligned irregularities (FAIs) over Indonesia. A VHF radar with operating frequency of 30.8 MHz and peak power of 20 kW has been operated at Kolotabang (0.20 degrees S, 100.32 degrees E; dip latitude 10.4 degrees S), Indonesia since February 2006. Five beams were allocated between +/- 54 degrees in azimuth around geographic South (126 degrees-234 degrees). From the Continuous observation from February 2006 to November 2007, we found that FAIs appeared frequently at pre-midnight between March and May and Lit post-midnight between May and August. The pre-midnight FAIs coincided well with GPS scintillation observed at the same site. Seasonal and local time variations of the pre-midnight FAI Occurrence are consistent with those of equatorial plasma bubbles reported in previous studies (e.g., Maruyama and Matuura, 1984). These results indicate that the pre-midnight FAIs could be associated with the equatorial plasma bubbles. On the other hand, seasonal and local time variations of the post-midnight FAIs were inconsistent with those of the plasma bubbles. The features of the post-midnight FAIs can be summarized as follows: (1) The post-midnight FAIs are not accompanied by GPS scintillations. (2) Most of the post-midnight FAI regions do not show propagation, but some of them propagate westward. (3) Echo intensity of the post-midnight FAIs was weaker than that of the pre-midnight FAIs. These features are similar to those of the FAI echoes that have been observed at mid-latitude (e.g., Fukao et, al., 1991). At Kototabang, Fukao et al. (2004) have firstly observed FAIs that resemble those Lit mid-latitude. The present paper reports statistical characteristics of the mid-latitude-type FAIs observed at Kototabang.

    DOI: 10.1186/BF03353159

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  363. Nighttime medium-scale traveling ionospheric disturbances detected by network GPS receivers in Taiwan Reviewed

    C. C. Lee, Y. A. Liou, Y. Otsuka, F. D. Chu, T. K. Yeh, K. Hoshinoo, K. Matunaga

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 113 ( A12 )   2008.12

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

    [1] The nighttime medium-scale traveling ionospheric disturbances (MSTIDs) are detected by the network GPS receivers in Taiwan for the first time. The two-dimensional mapping technique (a spatial resolution of 0.05 degrees x 0.05 degrees in latitude and longitude with 5 x 5 pixels smoothing) is applied on the data of TEC perturbations (TECp) and GPS phase fluctuations (Delta TEC/min). The results show that the MSTIDs move southwestward to latitude of 20.5 degrees N with a horizontal velocity between 100 and 160 m/s and a wavelength of about 500 km. The wavefronts of the MSTIDs are aligned along the northwest-southeast direction. Furthermore, the greater vertical bar Delta TEC/min vertical bar values are corresponding to the wave peak and trough of TECp. This coincidence indicates that the MSTIDs play an important role for the generation of F region irregularities in the low-latitude ionosphere.

    DOI: 10.1029/2008JA013250

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  364. Northeastward motion of nighttime medium-scale traveling ionospheric disturbances at middle latitudes observed by an airglow imager

    K. Shiokawa, Y. Otsuka, N. Nishitani, T. Ogawa, T. Tsugawa, T. Maruyama, S. E. Smirnov, V. V. Bychkov, B. M. Shevtso

    Journal of Geophysical Research: Space Physics   Vol. 113 ( A12 )   2008.12

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    Nighttime medium-scale traveling ionospheric disturbances (MSTIDs) observed in 630-nm airglow images at middle latitudes are known to have a predominantly northwest-southeast phase surface and to move southwestward in the Northern Hemisphere of Earth. However, the mechanisms of MSTID generation and their systematic southwestward motion have not been clarified. In this paper, we report the &quot;northeastward&quot; motion of the MSTIDs observed at Paratunka, Far East Russia (52.97°N, 158.25°E), using an all-sky 630-nm airglow imager at 2000-2300 LT on 19 August 2007. The MSTIDs moved first southwestward but then back northeastward in the northern part of the images. The northeastward motion of the MSTIDs took place coincident with a F layer height decrease observed by an ionosonde at Paratunka. The F layer height decrease was also confirmed by an enhancement of the 630-nm airglow intensity, which seemed to propagate from northeast to southwest. This fact suggests that the F layer height decrease was caused by poleward wind enhancement rather than westward electric field. These observations imply that the F layer height decrease or the poleward thermospheric wind has some role in the northeastward turning of the MSTID propagation direction. Copyright 2008 by the American Geophysical Union.

    DOI: 10.1029/2008JA013417

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  365. Statistical study of relationship between medium-scale traveling ionospheric disturbance and sporadic E layer activities in summer night over Japan Reviewed

    Otsuka, Y., T. Tani, T. Tsugawa, and T. Ogawa

    J. Atmos. Solar-Terr. Phys.   Vol. 70   page: 2196-2202   2008.12

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  366. Statistical study of relationship between medium-scale traveling ionospheric disturbance and sporadic E layer activities in summer night over Japan Reviewed

    Y. Otsuka, T. Tani, T. Tsugawa, T. Ogawa, A. Saito

    JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS   Vol. 70 ( 17 ) page: 2196 - 2202   2008.12

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:PERGAMON-ELSEVIER SCIENCE LTD  

    We investigate the relationship between medium-scale traveling ionospheric disturbance (MSTID) and sporadic E (E-s) layer activities in summer nights by analyzing total electron content (TEC) data obtained from a global positioning system (GPS) network in Japan and ionosonde data obtained at Kokubunji, Japan during May-August in 2001-2005. MSTID activity is defined as delta I/($) over bar, where delta I is standard deviation of the TEC perturbations over Kokubunji within 1 h, and 7 is the background TEC. By analyzing nighttime-averaged (19-02 LT) values of MSTID activity and E, layer parameters, we find that the MSTID activity is closely correlated with f(0)E(s) and f(0)E(s) -f(b)E(s). This result suggests that MSTID and the spatial structures of E, layer could be generated by an electro-dynamical coupling process between the Es layer and F region through polarization electric fields. Furthermore, we suggest that the appearance of the E, layer in the summer hemisphere could play an important role in generating MSTIDs in both hemispheres. (C) 2008 Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.jastp.2008.07.008

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  367. Decay of 3-m-scale ionospheric irregularities associated with a plasma bubble observed with the Equatorial Atmosphere Radar Reviewed

    Susumu Saito, Shoichiro Fukao, Mamoru Yamamoto, Yuichi Otsuka, Takashi Maruyama

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 113 ( A11 )   2008.11

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

    We investigated the decay processes of 3-m-scale ionospheric irregularities associated with plasma bubbles by multi-instrument observations. The observations were made using the Equatorial Atmosphere Radar (EAR), a 630-nm airglow imager, and ionosondes. The EAR&apos;s electronic beam steering capability allowed us to see the temporal evolution of 3-m-scale irregularities associated with plasma bubbles in two-dimensional views. Around midnight on 28 and 31 March 2006, the EAR detected plasma bubbles that drifted into its field of view. When their eastward drift motion slowed and they finally stopped moving eastward, the 3-m-scale irregularities decayed. These results suggest that instability driven by the eastward neutral wind kept the 3-m-scale irregularities in matured plasma bubbles, which are in the well-developed stage, active for several hours after sunset. The stagnated plasma bubbles drifted downward with the ambient westward electric field. This drift resulted in the backscatter echo patterns seen in the range-time-intensity (RTI) plots which look like those associated with mid-latitude plumes.

    DOI: 10.1029/2008JA013118

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  368. F-3 layer during penetration electric field Reviewed

    Balan, N, Thampi, SV, Lynn, K, Otsuka, Y, Alleyne, H, Watanabe, S, Abdu, MA, Fejer, BG

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 113   2008.9

  369. Simultaneous appearance of isolated auroral arcs and Pc 1 geomagnetic pulsations at subauroral latitudes Reviewed

    K. Sakaguchi, K. Shiokawa, Y. Miyoshi, Y. Otsuka, T. Ogawa, K. Asamura, M. Connors

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 113 ( A5 )   2008.5

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    We have been conducting observations of aurora and geomagnetic pulsations at Athabasca, Canada, located at a subauroral latitude ( magnetic latitude: 62 degrees, L similar to 4.6), using an all-sky imager and an induction magnetometer. Isolated auroral arcs at wavelengths of 557.7 nm, 630.0 nm, and 486.1 nm ( H-beta) were often observed at latitudes separated equatorward from the main auroral oval. From a 1-year observation ( 4 September 2005 to 3 September 2006), we found 13 isolated arc events. All these isolated arcs occurred coincidentally with Pc 1 geomagnetic pulsations, although there were nine other Pc 1 events without isolated arcs in the field of view of the imager. The arcs were observed in both pre- and post-midnight sectors and tended to appear during the late recovery phase of geomagnetic storms. The isolated arcs had limited latitudinal and longitudinal widths of less than 230 km and 250 - 800 km, respectively. We found that as isolated arcs moved equatorward ( poleward), the frequencies of the simultaneous Pc 1 pulsations increased ( decreased). Using the Tsyganenko-02 magnetic field model, the observed Pc 1 frequencies were almost the same as the frequencies of He+ electromagnetic ion cyclotron ( EMIC) waves at the equatorial plane connected to observed isolated arcs. These results indicate that interactions of spatially localized EMIC waves with ring current ions cause high-energy ion precipitation and associated isolated auroras at subauroral latitudes. These results also imply that the dynamics and instabilities in the inner magnetosphere can be monitored as low-latitude auroral emissions away from the ordinary auroral oval.

    DOI: 10.1029/2007JA012888

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  370. Daytime 150-km echoes observed with the Equatorial Atmosphere Radar in Indonesia: First results Reviewed

    A. K. Patra, T. Yokoyama, Y. Otsuka, M. Yamamoto

    GEOPHYSICAL RESEARCH LETTERS   Vol. 35 ( 6 )   2008.3

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

    Results of the daytime 150-km echoes from 10.36 degrees S magnetic latitude observed using the Equatorial Atmosphere Radar (EAR), which are first of its kind from magnetic southern hemisphere, are presented. The echoing region of 145-165 km shows forenoon descent and afternoon ascent with signal intensity modulation with time resembling a necklace and the Doppler spectra are narrow, which are quite similar to those reported earlier from other locations. Westward and upward/southward irregularity drifts are found to be consistent with daytime background electric fields, providing a tool to investigate low latitude daytime electrodynamics. Detectability of these echoes suggests the absence of strong latitudinal dependence in contrast to the earlier belief, suggesting a possibility of their detection at mid-latitudes. Also the echoes show zonal anisotropy that is opposite to that observed over Pohnpei. The implications of these observations are discussed in the light of present understanding of 150-km echoing phenomenon.

    DOI: 10.1029/2007GL033130

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  371. First three-dimensional simulation of the Perkins instability in the nighttime midlatitude ionosphere Reviewed

    Tatsuhiro Yokoyama, Yuichi Otsuka, Tadahiko Ogawa, Mamoru Yamamoto, David L. Hysell

    GEOPHYSICAL RESEARCH LETTERS   Vol. 35 ( 3 )   2008.2

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

    A three-dimensional numerical simulation in the nighttime midlatitude ionosphere is developed for the first time and applied to the Perkins instability in the midlatitude F region. Growth of the Perkins instability is successfully reproduced under nighttime condition, and the numerical results basically agree with a linear theory and previous two-dimensional numerical studies. Northwest-southeast (NW-SE) alignment of density perturbations is generated from random seeding by applying a southeastward neutral wind. The perturbations are dominant at altitudes of 200 300 km where a steep density gradient exists, which is consistent with the altitude of 630-nm airglow emission that often shows NW-SE alignment. Further simulation in terms of the E-F coupling can be done in the near future.

    DOI: 10.1029/2007GL032496

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  372. Optical and radio observations and AMIE/TIEGCM modeling of nighttime traveling ionospheric disturbances at midlatitudes during geomagnetic storms

    K. Shiokawa, T. Tsugawa, T. Tsugawa, Y. Otsuka, T. Ogawa, G. Lu, A. Saito, M. Yamamoto

    Geophysical Monograph Series   Vol. 181   page: 271 - 281   2008

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    © 2008 by the American Geophysical Union. This paper summarizes our recent observations of storm-time traveling ionospheric disturbances (TIDs) over Japan. The storm-time TIDs, which are often referred as large-scale TIDs or traveling atmospheric disturbances, are generated at high-latitude auroral zone and propagate predominantly equatorward at midlatitudes as atmospheric waves in the thermosphere. The imaging measurements by airglow imagers and GPS networks give reliable wave parameters (wavelength, phase velocity, and amplitude) of TIDs. Comparison of imaging observations of TIDs between the northern and southern hemispheres revealed their nonconjugacy. Combinations of these imaging observations with vertical sounding measurements by ionosondes and radars provide a comprehensive description of TID structures at midlatitudes. Comparison between these observations and the assimilative mapping of the ionospheric electrodynamics technique with the thermosphere-ionosphere electrodynamics general circulation model results in several insights into the generation and propagation of TIDs at the high-latitude source region as well as limitations of the current global model.

    DOI: 10.1029/181GM24

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  373. Discovery of anoumoulous stripes over the amazon by the PALSAR onboard ALOS satellite Reviewed

    Masanobu Shimada, Yasushi Muraki, Yuichi Otsuka

    International Geoscience and Remote Sensing Symposium (IGARSS)   Vol. 2 ( 1 ) page: II387 - II390   2008

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    We discovered anomalous stripes over the large area of Amazon when the region was scanned by the radar (PALSAR) onboard ALOS satellite. The stripes appeared on the local midnight along the geomagnetic field line with a typical characteristic width of 600m. ©2008 IEEE.

    DOI: 10.1109/IGARSS.2008.4779009

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  374. Medium-scale traveling ionospheric disturbances detected with dense and wide TEC maps over North America Reviewed

    T. Tsugawa, Y. Otsuka, A. J. Coster, A. Saito

    GEOPHYSICAL RESEARCH LETTERS   Vol. 34 ( 22 )   2007.11

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

    Nighttime and daytime medium- scale traveling ionospheric disturbances ( MSTIDs) are detected with dense and wide detrended total electron content ( TEC) maps over North America using multiple GPS receiver networks. The TEC maps cover a wide region of 60-130 degrees W and 24 - 54 degrees N (30-65 degrees N in geomagnetic latitude), and have a spatial resolution of 1.05 degrees x1.05 degrees in latitude and longitude (0.15 degrees x0.15 degrees with 7x7 pixel smoothing) and a temporal resolution of 30 seconds. The TEC maps reveal, for the first time, that the nighttime MSTIDs propagate southwestward with 200 - 500 km wavelengths over North America and have wavefronts longer than similar to 2,000 km. We also observe that daytime MSTIDs with 300 - 1,000 km wavelengths propagate southeastward until mid-afternoon and southwestward in the late afternoon. In the mid-to-late afternoon, these MSTIDs propagating in the different directions are superimposed. The TEC maps can be a new powerful tool to investigate the MSTIDs.

    DOI: 10.1029/2007GL031663

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  375. Summer-winter hemispheric asymmetry of the sudden increase in ionospheric total electron content and of the O/N2 ratio: Solar activity dependence Reviewed

    T. Tsugawa, S. R. Zhang, A. J. Coster, Y. Otsuka, J. Sato, A. Saito, Y. Zhang, L. J. Paxton

    Journal of Geophysical Research: Space Physics   Vol. 112 ( A8 )   2007.8

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:Blackwell Publishing Ltd  

    The solar activity dependence of the summer-winter hemispheric asymmetry (SWHA) of the sudden increase in total electron content (SITEC) due to solar flares and of the O/N2 ratio is statistically analyzed using global GPS-total electron content data and TIMED Global Ultraviolet Imager column O/N2 ratio data. We focus on observations with nonnegligible residuals of the solar zenith angle (SZA) dependency of SITEC. We examined 109 SITEC events associated with flares larger than M5 X-ray class flare from 2000 through 2006 and compared the residual SITEC (δ) to the O/N2 ratio. We observed that the latitude gradient of δ has not only an annual variation but also a year-to-year variation that is similar to those of the O/N2 ratio. The SWHA magnitude (defined as the annual maximum of latitude gradient) of both δ and O/N2 decreases as the solar activity declines toward its minimum. The correlation coefficient between the annual SWHA magnitudes of δ and those of O/N2 is 0.92, indicating strongly that the SWHA of O/N2 is responsible for that of SITEC in both the annual and year-to-year variations. The X-ray classes of the solar flares have no clear correlation with the solar activity, F10.7 index. We observe that the SWHA magnitude of δ does not depend on the magnitude of solar flare but rather on the background solar activity through the SWHA magnitude of the O/N2. Copyright 2007 by the American Geophysical Union.

    DOI: 10.1029/2007JA012415

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  376. Low-latitude total electron content enhancement at low geomagnetic activity observed over Japan Reviewed

    Ivan Kutiev, Yuichi Otsuka, Akinori Saito, Takuya Tsugawa

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 112 ( A7 )   2007.7

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    [1] Numerous total electron content (TEC) values derived from GPS signals are averaged within 1.5 degrees x 1.5 degrees cells in a 1-hour time frame, and the relative deviations of these average values from corresponding monthly medians are used to produce latitude-time plots over Japan. The paper analyzes the appearance and development of enhancements of TEC of equatorial origin (ETEs), occurring outside initial and main phases of geomagnetic storms. ETE structures appear mainly as single-crest structures in the evening hours local time, with TEC peak around 1900 LT. TEC usually decreases with latitude, and the structures disappear below 40 degrees N. In some cases the TEC peak is found above the plot boundary of 24 degrees N, as depletions toward the equator are also observed. The observed enhanced structures are linked to the well-known evening prereversal enhancement of ion drift in the equatorial F region. Double-crest ETEs are also observed, with the second peak occurring in early morning hours. Most of the ETE events appear in periods of low geomagnetic activity, 1-3 days after the main phase of the storms. In some cases the time of rising of ETE structures coincides with the increase of interplanetary electric field (IEF), a fact showing the importance of directly penetrating electric field in formation of ETEs. Often, ETEs appear repeatedly in 2 or 3 consecutive days. It is supposed that planetary atmospheric waves are responsible for this phenomenon. Most of the observed features of ETEs can be explained by the published results of simulations of the coupled thermosphere-ionosphere-plasmasphere (CTIP) model and the thermosphere/ionosphere/electrodynamic general circulation model (TIEGCM). It is suggested that ETE structures are produced mainly by a disturbance winds dynamo electric field, built up after the main phase of the storms. Some ETE events, appearing at the end of a prolonged period of low geomagnetic activity, can be linked to directly penetrating IEF in equatorial ionosphere. The intensity of these electric fields is much smaller than is needed to explain the observations.

    DOI: 10.1029/2007JA012385

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  377. Simultaneous observations of nighttime medium-scale traveling ionospheric disturbances and E region field-aligned irregularities at midlatitude Reviewed

    Y. Otsuka, F. Onoma, K. Shiokawa, T. Ogawa, M. Yamamoto, S. Fukao

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

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    [1] We report on simultaneous observations of very high frequency ( VHF) radar backscatter from field-aligned irregularities (FAI) in the E region and medium-scale traveling ionospheric disturbances (MSTID) in 630-nm airglow images. On the night of 6 August 2002, the powerful 46.5-MHz middle and upper atmosphere ( MU) radar with five beam directions at Shigaraki, Japan, observed typical quasiperiodic (QP) echoes from FAI in the E region. During this QP echo event, an all-sky charge-coupled device imager at the MU radar site detected MSTID in 630-nm airglow images. The MSTID also propagated southwestward at 80 m/s with fluctuation amplitudes of 50% from the background intensity and a wavelength of 380 km. Period of the MSTID was almost same as that of the Doppler velocity in the QP echoes. The airglow enhancement ( depletion) caused by the MSTID coincided with southeastward ( northwestward) velocity in the QP echo. These results indicate that the electric fields associated with the F region MSTID could be closely coupled to those associated with QP echoes in the E region.

    DOI: 10.1029/2005JA011548

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  378. Ground observation and AMIE-TIEGCM modeling of a storm-time traveling ionospheric disturbance Reviewed

    Shiokawa, K, Lu, G, Otsuka, Y, Ogawa, T, Yamamoto, M, Nishitani, N, Sato, N

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 112 ( A5 )   2007.5

  379. Simultaneous ground and satellite observations of an isolated proton arc at subauroral latitudes Reviewed

    K. Sakaguchi, K. Shiokawa, A. Ieda, Y. Miyoshi, Y. Otsuka, T. Ogawa, M. Connors, E. F. Donovan, F. J. Rich

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 112 ( A4 )   2007.4

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

    [1] We observed an isolated proton arc at the Athabasca station (MLAT: 62 degrees N) in Canada on 5 September 2005, using a ground-based all-sky imager at wavelengths of 557.7 nm, 630.0 nm, and 486.1 nm (H beta). This arc is similar to the detached proton arc recently observed by the IMAGE satellite [Immel et al., 2002]. The arc appeared at 0500-0640 UT (2100-2240 MLT), coincident with strong Pc 1 geomagnetic pulsations in the frequency range of the electromagnetic ion cyclotron (EMIC) wave. The isolated arc did not change its structure and intensity during the late growth and expansive phases of a small substorm that occurred at 0550 UT. From particle data obtained by the NOAA 17 satellite, we found that the isolated arc was associated with the localized enhancement of ion precipitation fluxes at an energy range of 30-80 keV at L similar to 4. Trapped ion flux enhancements ( ring current ions) were also observed at two latitudinally separated regions. The localized ion precipitation was located at the outer boundary of the inner ring current ions. The DMSP F13 satellite observed signatures of an ionospheric plasma trough near the conjugate point of the arc in the Southern Hemisphere. The trough is considered to be connected to the plasmapause. These results indicate that the source region of the isolated arc was located near the plasmapause and in the ring current. We conclude that the observed isolated proton arc at subauroral latitudes was caused by the EMIC waves, which were generated near the plasmapause and resonantly scattered the ring current protons into the loss cone.

    DOI: 10.1029/2006JA012135

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  380. An intense gravity wave near the mesopause region observed by a Fabry-Perot interferometer and an airglow imager Reviewed

    K. Shiokawa, S. Suzuki, Y. Otsuka, T. Ogawa, T. Nakamura, T. Horinouchi

    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES   Vol. 112 ( D7 )   2007.4

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    [1] We report an intense gravity wave event observed at Shigaraki, Japan, at 1500 - 2000 UT (0000 - 0500 LT) on 22 December 2001 using a Fabry-Perot interferometer, which measures the Doppler shift of nocturnal airglow emission at a wavelength of 557.7 nm (emission altitude: 90 - 100 km). The wave had a period of 1.5 hours and a peak-to-peak amplitude of 68 m/s in the horizontal wind velocity. The hodograph of the east-west and north-south wind oscillations showed a polarization direction of the wave of ENE-WSW. An all-sky airglow imager at Shigaraki also recorded a similar southwestward moving wave with a period of similar to 1.5 hours and a velocity of 146 m/s in the 557.7-nm airglow images. The horizontal wavelength was estimated to be 790 km from the images. These facts indicate that the wave was generated in the northeast of Japan, where a well-developed low-pressure cell (968 hPa) and a distortion of the jet stream were observed in the troposphere. However, the large horizontal wavelength, the fast phase velocity, and the possible source location apart from the exit of the jet streak are different from those predicted from previous numerical simulations.

    DOI: 10.1029/2006JD007385

    Web of Science

  381. Medium-scale traveling ionospheric disturbances observed by GPS receiver network in Japan: a short review Reviewed

    Takuya Tsugawa, Nobuki Kotake, Yuichi Otsuka, Akinori Saito

    GPS SOLUTIONS   Vol. 11 ( 2 ) page: 139 - 144   2007.3

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    Medium-scale traveling ionospheric disturbances (MSTID) are wave-like perturbations of the ionospheric plasma with wavelengths of several hundred kilometres and velocities of several hundred metres per second. MSTID is one of the most common ionospheric phenomena that generally induce the perturbations of ionospheric total electron content (TEC) by similar to 10(16) electron/m(2), which corresponds to -54 ns (16.2 cm) delay at GPS L1 signal. In the past decade, several new characteristics on MSTIDs have been revealed by the TEC observations using the dense GPS receiver network in Japan. In this paper, we provide a short review of these new observations and summarize the morphological characteristics of MSTIDs in Japan.

    DOI: 10.1007/s10291-006-0045-5

    Web of Science

  382. A concentric gravity wave structure in the mesospheric airglow images Reviewed

    S. Suzuki, K. Shiokawa, Y. Otsuka, T. Ogawa, K. Nakamura, T. Nakamura

    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES   Vol. 112 ( D2 )   2007.1

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    A concentric gravity wave pattern was observed by an all-sky airglow imager located at Shigaraki, Japan (34.9 degrees N, 136.1 degrees E) on 3 October 2002. The wave pattern was identified over 2.5 hours (1330-1600 UT or 2230-0100 LT) both in the OI (557.7 nm) and OH (720-910 nm) band images. It had a wavelength of about 35 km and propagated concentrically northeastward with a horizontal phase velocity of about 80 m/s. The wave had a short period of about 7 min and a momentum flux of 2.2 m(2)/s(2). We identified the source of the waves as a cumulonimbus in the satellite cloud images and in radar precipitation images near the center of the concentric pattern. We conclude that this rare wave pattern was caused by a weak wind system that extended from the stratosphere to the mesopause region in an autumn transition.

    DOI: 10.1029/2005JD006558

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  383. Simultaneous observations of nighttime medium-scale traveling ionospheric disturbances and E-region field-aligned irregularities at midlatitude Reviewed

    Otsuka, Y., F. Onoma, K. Shiokawa, T. Ogawa, M. Yamamoto, and S. Fukao

    J. Geophys. Res     page: doi:10.1029/2005JA011548   2007

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  384. Statistical study of medium-scale traveling ionospheric disturbances observed with the GPS networks in Southern California Reviewed

    Nobuki Kotake, Yuichi Otsuka, Tadahiko Ogawa, Takuya Tsugawa, Akinori Saito

    EARTH PLANETS AND SPACE   Vol. 59 ( 2 ) page: 95 - 102   2007

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    Using global positioning system (GPS) data taken from 350 dual-frequency GPS receivers in Southern California in 2002, we investigated two-dimensional maps of total electron content (TEC) perturbations with a time resolution of 30 s and a spatial resolution of 0.15 degrees x0.15 degrees in longitude and latitude to reveal statistical characteristics of medium-scale traveling ionospheric disturbances (MSTIDs). We found that MSTIDs can be categorized into three types. One type is daytime MSTIDs, which frequently occur in winter and equinoxes. Since most of the daytime MSTIDs propagated southeastward, we speculate that the daytime MSTIDs could be caused by atmospheric gravity waves in the thermosphere. A second type is nighttime MSTIDs, which frequently occur in summer. Nighttime MSTIDs propagate southwestward. This propagation direction is consistent with the idea that polarization electric fields could play an important role in generating nighttime MSTIDs. The third is dusk MSTIDs, which frequently occur in summer and propagate northwestward. Dusk MSTIDs could be caused by gravity waves originating from the sunset terminator because they have wavefronts almost parallel to the sunset terminator.

    DOI: 10.1186/BF03352681

    Web of Science

  385. The ionospheric response in the Brazilian sector during the super geomagnetic storm on 20 November 2003 Reviewed

    F. Becker-Guedes, Y. Sahai, P. R. Fagundes, E. S. Espinoza, V. G. Pillat, W. L. C. Lima, Su. Basu, Sa. Basu, Y. Otsuka, K. Shiokawa, E. M. MacKenzie, X. Pi, J. A. Bittencourt

    ANNALES GEOPHYSICAE   Vol. 25 ( 4 ) page: 863 - 873   2007

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    A very intense geomagnetic storm (superstorm) began with storm sudden commencement (SSC) at 08:03 UT on 20 November 2003, as a result of the coronal mass ejection (CME) by sunspot 484 hurled into space on 18 November 2003. The geomagnetic storm attained vertical bar D-st vertical bar(max)=472 nT at 20:00 UT (20 November). In this paper we present the simultaneous ionospheric sounding observations, using the Canadian Advanced Digital Ionosondes (CADIs), carried out from Palmas (PAL; 10.2 degrees S, 48.2 degrees W; dip latitude 5.5 degrees S; a near equatorial station) and Sao Jose dos Campos (SJC; 23.2 degrees S. 45.9 degrees W; dip latitude 17.6 degrees S; station located under the crest of equatorial ionospheric anomaly), Brazil. In addition, total electron content (TEC) measurements from several GPS receiving stations in the Brazilian sector during this storm are presented. The simultaneous ionospheric sounding observations carried out at SJC and PAL, and TEC observations on 3 consecutive days viz., 19 November (quiet), 20 November (disturbed) and 21 November (recovery phase) are presented. Salient features from the ionospheric observations in the Brazilian sector during the superstorm are discussed. The difference in the observed ionospheric response at the two stations (PAL and SJC) is considerable. This is not surprising given that PAL is close to the magnetic equator and SJC is near the crest of the equatorial ionospheric anomaly (EIA). It should be pointed out that soon after the SSC (about 4 h later), the F-region critical frequency (foF2), the F-region peak height (hpF2), and variations of virtual heights at different frequencies (iso-frequency plots) all show wavelike oscillations of the F-region during daytime at both the ionospheric sounding stations. Unusual rapid uplifting of F-region at PAL was observed during both the main and recovery phases of the storm.

    DOI: 10.5194/angeo-25-863-2007

    Web of Science

  386. Response of nighttime equatorial and low latitude F-region to the geomagnetic storm of August 18, 2003, in the Brazilian sector Reviewed

    Y. Sahai, F. Becker-Guedes, P. R. Fagundes, W. L. C. Lima, Y. Otsuka, C. -S. Huang, E. S. Espinoza, X. Pi, A. J. de Abreu, M. J. A. Bolzan, V. G. Pillat, J. R. Abalde, A. A. Pimenta, J. A. Bittencourt

    ADVANCES IN SPACE RESEARCH   Vol. 39 ( 8 ) page: 1325 - 1334   2007

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    This paper presents an investigation of geomagnetic storm effects in the equatorial and low latitude F-region in the Brazilian sector during the intense geomagnetic storm on 18 August, 2003 (SSC 14:21 UT on 17/08; Sigma Kp = 52+; Ap = 108; vertical bar Dst vertical bar(max) = 168 at 1600 UT on 18/08). Simultaneous ionospheric sounding measurements from two stations, viz., Palmas (10.2 degrees S, 48.2 degrees W; dip latitude 5.7 degrees S) and Sao Jose dos Campos (23.2 degrees S, 45.9 degrees W; dip latitude 17.6 degrees S), Brazil, are presented for the nights of 16-17, 17-18 and 18-19 August, 2003 (quiet, disturbed and recovery phases). Both stations are equipped with the Canadian Advanced Digital Ionosonde (CADI). Quiet and disturbed conditions of the F-region ionosphere are compared using data collected from the two stations. The relationship between magnetospheric disturbance and low-latitude ionospheric dynamics, and generation of ionospheric irregularities are discussed. On the disturbed nights (17-18 and 18-19 August), the low latitude station S. J. Campos showed strong enhancements in the F-region critical frequency (foF2), whereas the near equatorial station Palmas showed strong uplifting of the F-layer about 1 h earlier. Normally during the June solstice months (May-August) in the Brazilian sector, large-scale ionospheric irregularities in form of plasma bubbles are rarely observed. On the night of 17-18 August, ionsospheric sounding observations at Palmas showed the presence of bottomside spread-F, whereas on the night of 18-19 August, the observations at Palmas and S. J. Campos showed the presence of plasma bubbles when the storm recovery phase had just started. The complementary GPS data available from several stations in the "Rede Brasileira de MonitoramentoContinuo de GPS (Brazilian Network for Continuous GPSMonitoring)" are used to obtain the vertical total electron content (VTEC) and the rate of change of TEC per minute on UT days 18 and 19 August, 2003 and presented. Also, several global ionospheric TEC maps from the worldwide network of GPS receivers are presented, showing widespread latitudinal and longitudinal TEC changes during the different phases of the storm. All the observations (local ionospheric sounding and GPS network measurements, and global GPS measurements) presented in this investigation related to the geomagnetic storm on 18 August indicate that the equatorial and low latitude region in the Brazilian sector had much stronger effect during the recovery phase compared with the main phase. A comparison of the observed disturbance drifts with the Fejer-Scherliess storm-time model drifts indicate that the modeled drifts are not consistent with the present observations. (C) 2007 COSPAR. Published by Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.asr.2007.02.064

    Web of Science

  387. Development of airglow temperature photometers with cooled-CCD detectors Reviewed

    K. Shiokawa, Y. Otsuka, S. Suzuki, T. Katoh, Y. Katohl, M. Satoh, T. Ogawa, H. Takahashi, D. Gobbli, T. Nakamura, B. P. Williams, C.-Y. She, M. Taguchi, T. Shimomai

    EARTH PLANETS AND SPACE   Vol. 59 ( 6 ) page: 585 - 599   2007

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    We have developed three airglow temperature photometers with cooled-CCD detectors. The photometers measure rotational temperatures using the airglow emissions of OH and 02 near the mesopause region (altitude: 80-100 km). The photometers also measure six other airglow and auroral lines at wavelengths of 55.7, 630.0, 777.4, 589.3, 427.8, and 486.1 nm. The CCD detectors are used to distinguish the emission lines in these airglow bands, similarly to those used by the Spectral Airglow Temperature Imagers (SATI). In this paper, we describe the configuration of the photometers, their calibration, the data processing to extract rotational temperatures and emission intensities from the measured airglow spectra, as well as the initial deployment at Platteville, Colorado (40.2 degrees N, 255 degrees E), when their observations were compared with the concurrent and nearly collocated observations by a sodium lidar. We obtain a good correlation and some systematic difference of temperatures from the photometers and the lidar, and discuss possible causes of the temperature difference.

    DOI: 10.1186/BF03352721

    Web of Science

  388. Gravity wave momentum flux in the upper mesosphere derived from OH airglow imaging measurements Reviewed

    Shin Suzuki, Kazuo Shiokawa, Yuichi Otsuka, Tadahiko Ogawa, Minoru Kubota, Masaki Tsutsumi, Takuji Nakamura, David C. Fritts

    EARTH PLANETS AND SPACE   Vol. 59 ( 5 ) page: 421 - 428   2007

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    We report procedures to identify small-scale (20-100 km) atmospheric gravity wav