Updated on 2021/04/24

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 2

  1. ionosphere airglow TEC GPS GNSS

  2. 電離圏物理学

Research Areas 2

  1. Others / Others  / Aeronomy

  2. Natural Science / Space and planetary sciences

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 5

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

    2015.10

      More details

    Country:Japan

  2. 名古屋大学太陽地球環境研究所・准教授

    2011.11 - 2015.10

      More details

    Country:Japan

  3. 名古屋大学太陽地球環境研究所・助教

    2008.4 - 2011.10

      More details

    Country:Japan

  4. 名古屋大学太陽地球環境研究所・助手

    1999.9 - 2008.3

      More details

    Country:Japan

  5. COE (Center of Excellence) Researcher at Radio Atmospheric Science Center, Kyoto University

    1999.4 - 1999.8

      More details

    Country:Japan

Education 3

  1. Kyoto University   Graduate School, Division of Engineering

    1996.4 - 1999.3

      More details

    Country: Japan

  2. Kyoto University

    1994.4 - 1996.3

  3. Kyoto University   Faculty of Science

    1990.4 - 1994.3

      More details

    Country: Japan

Professional Memberships 4

  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

Awards 5

  1. 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  

     More details

    Country:Japan

  2. EPS Award

    2009.5   Earth, Planets and Space  

  3. 2009 Editors' Citations for Excellence in Refereeing, Geophysical Research Letters

    2010.9   American Geophysical Union  

  4. 2011 Editors' Citations for Excellence in Refereeing, Radio Science

    2011   American Geophysical Union  

  5. Excellent Reviewers 2020

    2021.1   Earth, Planets and Space  

 

Papers 359

  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

     More details

    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

     More details

    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

     More details

    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

     More details

    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

     More details

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

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

    Takahashi H., Wrasse C. M., Figueiredo C. A. O. B., Barros D., Paulino I., Essien P., Abdu M. A., Otsuka Y., Shiokawa K.

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

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

    Shinbori Atsuki, Otsuka Yuichi, Sori Takuya, Tsugawa Takuya, Nishioka Michi

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

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

    Sarudin I., Hamid N. S. A., Abdullah M., Buhari S. M., Shiokawa K., Otsuka Y., Yatini C. Y.

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

  9. 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

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

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

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

    Yadav Sneha, Shiokawa K., Oyama S., Otsuka Y.

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

  11. 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

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

    Balan N., Zhang Qing -He, Shiokawa K., Skoug R., Xing Zanyang, Ram S. Tulasi, Otsuka Y.

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

  13. 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

  14. 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

     More details

  15. 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

  16. 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

     More details

  17. 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

     More details

  18. 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

     More details

  19. 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

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

    Ozeki Yasuyuki, Otsuka Yoichi, Sato Shuya, Hashimoto Hiroyuki, Umemura Wataru, Sumimura Kazuhiko, Nishizawa Norihiko, Fukui Kiichi, Itoh Kazuyoshi

    MULTIPHOTON MICROSCOPY IN THE BIOMEDICAL SCIENCES XIII   Vol. 8588   2013

  21. 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

     More details

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

    Ozeki Yasuyuki, Umemura Wataru, Otsuka Yoichi, Satoh Shuya, Hashimoto Hiroyuki, Sumimura Kazuhiko, Nishizawa Norihiko, Fukui Kiichi, Itoh Kazuyoshi

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

  23. 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

  24. 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

  25. 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

  26. 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

  27. Significance of C4d deposition in antibody-mediated rejection

    Takeda Asami, Otsuka Yasuhiro, Horike Keiji, Inaguma Daijo, Hiramitsu Takahisa, Yamamoto Takayuki, Nanmoku Koji, Goto Norihiko, Watarai Yoshihiko, Uchida Kazuharu, Morozumi Kunio, Kobayashi Takaaki

    CLINICAL TRANSPLANTATION   Vol. 26   page: 43 - 48   2012.7

  28. 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

  29. 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

  30. 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

  31. 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

  32. 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

  33. Decay of polar cap patch

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

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 116   2011.5

  34. 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

  35. 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

  36. 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

  37. 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

  38. 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

  39. 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

  40. 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

  41. 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

  42. 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

  43. 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

  44. 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

  45. 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

  46. 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

     More details

  47. 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

     More details

  48. 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

     More details

  49. 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

     More details

  50. 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

     More details

  51. 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

     More details

  52. 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

     More details

  53. Northeastward motion of nighttime medium-scale traveling ionospheric disturbances at middle latitudes observed by an airglow imager

    Shiokawa K., Otsuka Y., Nishitani N., Ogawa T., Tsugawa T., Maruyama T., Smirnov S. E., Bychkov V. V., Shevtsov B. M.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 113 ( A12 )   2008.12

  54. Statistical study of relationship between medium-scale traveling ionospheric disturbance and sporadic E layer activities in summer night over Japan

    Otsuka Y., Tani T., Tsugawa T., Ogawa T., Saito A.

    JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS   Vol. 70 ( 17 ) page: 2196 - 2202   2008.12

  55. Decay of 3-m-scale ionospheric irregularities associated with a plasma bubble observed with the Equatorial Atmosphere Radar

    Saito Susumu, Fukao Shoichiro, Yamamoto Mamoru, Otsuka Yuichi, Maruyama Takashi

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 113 ( A11 )   2008.11

  56. Simultaneous appearance of isolated auroral arcs and Pc 1 geomagnetic pulsations at subauroral latitudes

    Sakaguchi K., Shiokawa K., Miyoshi Y., Otsuka Y., Ogawa T., Asamura K., Connors M.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 113 ( A5 )   2008.5

  57. Daytime 150-km echoes observed with the Equatorial Atmosphere Radar in Indonesia: First results

    Patra A. K., Yokoyama T., Otsuka Y., Yamamoto M.

    GEOPHYSICAL RESEARCH LETTERS   Vol. 35 ( 6 )   2008.3

  58. First three-dimensional simulation of the Perkins instability in the nighttime midlatitude ionosphere

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

    GEOPHYSICAL RESEARCH LETTERS   Vol. 35 ( 3 )   2008.2

  59. Optical and Radio Observations and AMIE/TIEGCM Modeling of Nighttime Traveling Ionospheric Disturbances at Midlatitudes During Geomagnetic Storms

    Shiokawa K., Tsugawa T., Otsuka Y., Ogawa T., Lu G., Saito A., Yamamoto M.

    MIDLATITUDE IONOSPHERIC DYNAMICS AND DISTURBANCES   Vol. 181   page: 271 - 281   2008

     More details

  60. Quantum dot sensitized solar cells

    Tachibana Yasuhiro, Akiyama Hitomi Y., Umekita Kazuya, Otsuka Yasuhide, Torimoto Tsukasa, Kuwabata Susumu

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

     More details

  61. Medium-scale traveling ionospheric disturbances detected with dense and wide TEC maps over North America

    Tsugawa T., Otsuka Y., Coster A. J., Saito A.

    GEOPHYSICAL RESEARCH LETTERS   Vol. 34 ( 22 )   2007.11

  62. Summer-winter hemispheric asymmetry of the sudden increase in ionospheric total electron content and of the O/N-2 ratio: Solar activity dependence

    Tsugawa T., Zhang S.-R., Coster A. J., Otsuka Y., Sato J., Saito A., Zhang Y., Paxton L. J.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 112 ( A8 )   2007.8

  63. Low-latitude total electron content enhancement at low geomagnetic activity observed over Japan

    Kutiev Ivan, Otsuka Yuichi, Saito Akinori, Tsugawa Takuya

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 112 ( A7 )   2007.7

  64. Simultaneous observations of nighttime medium-scale traveling ionospheric disturbances and E region field-aligned irregularities at midlatitude

    Otsuka Y., Onoma F., Shiokawa K., Ogawa T., Yamamoto M., Fukao S.

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

  65. Ground observation and AMIE-TIEGCM modeling of a storm-time traveling ionospheric disturbance

    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

  66. An intense gravity wave near the mesopause region observed by a Fabry-Perot interferometer and an airglow imager

    Shiokawa K., Suzuki S., Otsuka Y., Ogawa T., Nakamura T., Horinouchi T.

    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES   Vol. 112 ( D7 )   2007.4

  67. Simultaneous ground and satellite observations of an isolated proton arc at subauroral latitudes

    Sakaguchi K., Shiokawa K., Ieda A., Miyoshi Y., Otsuka Y., Ogawa T., Connors M., Donovan E. F., Rich F. J.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 112 ( A4 )   2007.4

  68. Medium-scale traveling ionospheric disturbances observed by GPS receiver network in Japan: a short review

    Tsugawa Takuya, Kotake Nobuki, Otsuka Yuichi, Saito Akinori

    GPS SOLUTIONS   Vol. 11 ( 2 ) page: 139 - 144   2007.3

  69. A concentric gravity wave structure in the mesospheric airglow images

    Suzuki S., Shiokawa K., Otsuka Y., Ogawa T., Nakamura K., Nakamura T.

    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES   Vol. 112 ( D2 )   2007.1

  70. Statistical study of medium-scale traveling ionospheric disturbances observed with the GPS networks in Southern California

    Kotake Nobuki, Otsuka Yuichi, Ogawa Tadahiko, Tsugawa Takuya, Saito Akinori

    EARTH PLANETS AND SPACE   Vol. 59 ( 2 ) page: 95 - 102   2007

     More details

  71. Summer-winter hemispheric asymmetry of sudden increase in ionospheric total electron content induced by solar flares: A role of O/N-2 ratio

    Tsugawa T., Sadakane T., Sato J., Otsuka Y., Ogawa T., Shiokawa K., Saito A.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 111 ( A11 )   2006.11

  72. Estimating drift velocity of polar cap patches with all-sky airglow imager at Resolute Bay, Canada

    Hosokawa K., Shiokawa K., Otsuka Y., Nakajima A., Ogawa T., Kelly J. D.

    GEOPHYSICAL RESEARCH LETTERS   Vol. 33 ( 15 )   2006.8

  73. A multi-instrument measurement of a mesospheric front-like structure at the equator

    Shiokawa Kazuo, Suzuki Shin, Otsuka Yuichi, Ogawa Tadahiko, Nakamura Takuji, Mlynczak Martin G., Russell James M. III

    JOURNAL OF THE METEOROLOGICAL SOCIETY OF JAPAN   Vol. 84A   page: 305 - 316   2006.7

     More details

  74. Equatorial ionospheric scintillations and zonal irregularity drifts observed with closely-spaced GPS receivers in Indonesia

    Otsuka Yuichi, Shiokawa Kazuo, Ogawa Tadahiko

    JOURNAL OF THE METEOROLOGICAL SOCIETY OF JAPAN   Vol. 84A   page: 343 - 351   2006.7

     More details

  75. Ionospheric disturbances over Indonesia and their possible association with atmospheric gravity waves from the troposphere

    Ogawa Tadahiko, Otsuka Yuichi, Shiokawa Kazuo, Saito Akinori, Nishioka Michi

    JOURNAL OF THE METEOROLOGICAL SOCIETY OF JAPAN   Vol. 84A   page: 327 - 342   2006.7

     More details

  76. Quasiperiodic southward moving waves in 630-nm airglow images in the equatorial thermosphere

    Shiokawa K., Otsuka Y., Ogawa T.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 111 ( A6 )   2006.6

  77. Characteristics and implications of Doppler spectra of E region quasi-periodic echoes observed by the multibeam middle and upper atmosphere radar

    Ogawa T, Otsuka Y, Yamamoto M

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 111 ( A5 )   2006.5

  78. Climatological study of GPS total electron content variations caused by medium-scale traveling ionospheric disturbances

    Kotake N, Otsuka Y, Tsugawa T, Ogawa T, Saito A

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 111 ( A4 )   2006.4

  79. Geomagnetic conjugate observations of large-scale traveling ionospheric disturbances using GPS networks in Japan and Australia

    Tsugawa T, Shiokawa K, Otsuka Y, Ogawa T, Saito A, Nishioka M

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 111 ( A2 )   2006.2

  80. GPS observations of post-storm TEC enhancements at low latitudes

    Kutiev Ivan, Otsuka Yuichi, Saito Akinori, Watanabe Shigeto

    EARTH PLANETS AND SPACE   Vol. 58 ( 11 ) page: 1479 - 1486   2006

     More details

  81. Observations of equatorial plasma bubbles using broadcast VHF radio waves

    Nakata H, Nagashima I, Sakata K, Otsuka Y, Akaike Y, Takano T, Shimakura S, Shiokawa K, Ogawa T

    GEOPHYSICAL RESEARCH LETTERS   Vol. 32 ( 17 )   2005.9

  82. Geomagnetic conjugate observation of nighttime medium-scale and large-scale traveling ionospheric disturbances: FRONT3 campaign

    Shiokawa K, Otsuka Y, Tsugawa T, Ogawa T, Saito A, Ohshima K, Kubota M, Maruyama T, Nakamura T, Yamamoto M, Wilkinson P

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 110 ( A5 )   2005.5

  83. Total electron content behavior over Japan during geomagnetic storms

    Kutiev I, Watanabe S, Otsuka Y, Saito A

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 110 ( A1 )   2005.1

  84. 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

     More details

  85. Relationship between propagation direction of gravity waves in OH and OI airglow images and VHF radar echo occurrence during the SEEK-2 campaign

    Onoma F, Otsuka Y, Shiokawa K, Ogawa T, Yamamoto M, Fukao S, Saito S

    ANNALES GEOPHYSICAE   Vol. 23 ( 7 ) page: 2385 - 2390   2005

     More details

  86. The first coordinated observations of mid-latitude E-region quasi-periodic radar echoes and lower thermospheric 557.7-nm airglow

    Ogawa T, Otsuka Y, Onoma F, Shiokawa K, Yamamoto M

    ANNALES GEOPHYSICAE   Vol. 23 ( 7 ) page: 2391 - 2399   2005

     More details

  87. Simultaneous ground- and satellite-based airglow observations of geomagnetic conjugate plasma bubbles in the equatorial anomaly

    Ogawa T, Sagawa E, Otsuka Y, Shiokawa K, Immel TI, Mende SB, Wilkinson P

    EARTH PLANETS AND SPACE   Vol. 57 ( 5 ) page: 385 - 392   2005

     More details

  88. Transition region of TEC enhancement phenomena during geomagnetically disturbed periods at mid-latitudes

    Unnikrishnan K, Saito A, Otsuka Y, Yamamoto M, Fukao S

    ANNALES GEOPHYSICAE   Vol. 23 ( 11 ) page: 3439 - 3450   2005

     More details

  89. Spatial relationship of equatorial plasma bubbles and field-aligned irregularities observed with an all-sky airglow imager and the Equatorial Atmosphere Radar

    Otsuka Y, Shiokawa K, Ogawa T, Yokoyama T, Yamamoto M, Fukao S

    GEOPHYSICAL RESEARCH LETTERS   Vol. 31 ( 20 )   2004.10

  90. Statistical characteristics of gravity waves observed by an all-sky imager at Darwin, Australia

    Suzuki S, Shiokawa K, Otsuka Y, Ogawa T, Wilkinson P

    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES   Vol. 109 ( D20 )   2004.8

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

    Otsuka Y, Shiokawa K, Ogawa T, Wilkinson P

    GEOPHYSICAL RESEARCH LETTERS   Vol. 31 ( 15 )   2004.8

  92. 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

  93. Comparison of OH rotational temperatures measured by the spectral airglow temperature imager (SATI) and by a tilting-filter photometer

    Shiokawa K, Otsuka Y, Ogawa T, Takahashi H, Nakamura T, Shimomai T

    JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS   Vol. 66 ( 11 ) page: 891 - 897   2004.7

  94. A statistical study of large-scale traveling ionospheric disturbances using the GPS network in Japan

    Tsugawa T, Saito A, Otsuka Y

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 109 ( A6 )   2004.6

  95. Simultaneous mesosphere/lower thermosphere and thermospheric F region observations during geomagnetic storms

    Balan N, Kawamura S, Nakamura T, Yamamoto M, Fukao S, Igarashi K, Maruyama T, Shiokawa K, Otsuka Y, Ogawa T, Alleyne H, Watanabe S, Murayama Y

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 109 ( A4 )   2004.4

  96. 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

  97. Generation of large-scale equatorial F-region plasma depletions during low range spread-F season

    Sahai Y, Fagundes PR, Abalde JR, Pimenta AA, Bittencourt JA, Otsuka Y, Rios VH

    ANNALES GEOPHYSICAE   Vol. 22 ( 1 ) page: 15 - 23   2004

     More details

  98. Time evolution of high-altitude plasma bubbles imaged at geomagnetic conjugate points

    Shiokawa K, Otsuka Y, Ogawa T, Wilkinson P

    ANNALES GEOPHYSICAE   Vol. 22 ( 9 ) page: 3137 - 3143   2004

     More details

  99. Optical and radio measurements of a 630-nm airglow enhancement over Japan on 9 September 1999

    Otsuka Y, Kadota T, Shiokawa K, Ogawa T, Kawamura S, Fukao S, Zhang SR

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 108 ( A6 )   2003.6

  100. Ground and satellite observations of nighttime medium-scale traveling ionospheric disturbance at midlatitude

    Shiokawa K, Otsuka Y, Ihara C, Ogawa T, Rich FJ

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 108 ( A4 )   2003.4

  101. Damping of large-scale traveling ionospheric disturbances detected with GPS networks during the geomagnetic storm

    Tsugawa T, Saito A, Otsuka Y, Yamamoto M

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 108 ( A3 )   2003.3

  102. 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

     More details

  103. Statistical study of nighttime medium-scale traveling ionospheric disturbances using midlatitude airglow images

    Shiokawa K, Ihara C, Otsuka Y, Ogawa T

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 108 ( A1 )   2003.1

  104. A two-channel Fabry-Perot interferometer with thermoelectric-cooled CCD detectors for neutral wind measurement in the upper atmosphere

    Shiokawa K, Kadota T, Otsuka Y, Ogawa T, Nakamura T, Fukao S

    EARTH PLANETS AND SPACE   Vol. 55 ( 5 ) page: 271 - 275   2003

     More details

  105. Simultaneous middle and upper atmosphere radar and ionospheric sounder observations of midlatitude E region irregularities and sporadic E layer

    Ogawa T, Takahashi O, Otsuka Y, Nozaki K, Yamamoto M, Kita K

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 107 ( A10 )   2002.10

  106. Annual and semiannual variations of the midlatitude ionosphere under low solar activity

    Kawamura S, Balan N, Otsuka Y, Fukao S

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 107 ( A8 )   2002.8

  107. Geomagnetic conjugate observations of equatorial airglow depletions

    Otsuka Y, Shiokawa K, Ogawa T, Wilkinson P

    GEOPHYSICAL RESEARCH LETTERS   Vol. 29 ( 15 )   2002.8

  108. 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

     More details

  109. A new technique for mapping of total electron content using GPS network in Japan

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

    EARTH PLANETS AND SPACE   Vol. 54 ( 1 ) page: 63 - 70   2002

     More details

  110. Imaging observations of the equatorward limit of midlatitude traveling ionospheric disturbances

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

    EARTH PLANETS AND SPACE   Vol. 54 ( 1 ) page: 57 - 62   2002

     More details

  111. 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

     More details

  112. Plasmaspheric electron content in the GPS ray paths over Japan under magnetically quiet conditions at high solar activity

    Balan N, Otsuka Y, Tsugawa T, Miyazaki S, Ogawa T, Shiokawa K

    EARTH PLANETS AND SPACE   Vol. 54 ( 1 ) page: 71 - 79   2002

     More details

  113. Observations of traveling ionospheric disturbances and 3-m scale irregularities in the nighttime F-region ionosphere with the MU radar and a GPS network

    Saito A, Nishimura M, Yamamoto M, Fukao S, Tsugawa T, Otsuka Y, Miyazaki S, Kelley MC

    EARTH PLANETS AND SPACE   Vol. 54 ( 1 ) page: 31 - 44   2002

     More details

  114. Observations and modeling of 630 nm airglow and total electron content associated with traveling ionospheric disturbances over Shigaraki, Japan

    Ogawa T, Balan N, Otsuka Y, Shiokawa K, Ihara C, Shimomai T, Saito A

    EARTH PLANETS AND SPACE   Vol. 54 ( 1 ) page: 45 - 56   2002

     More details

  115. Regional ionosphere map over Japanese Islands

    Ping J, Kono Y, Matsumoto K, Otsuka Y, Saito A, Shum C, Heki K, Kawano N

    EARTH PLANETS AND SPACE   Vol. 54 ( 12 ) page: E13 - E16   2002

     More details

  116. Three-channel imaging Fabry-Perot interferometer for measurement of mid-latitude airglow

    Shiokawa K, Kadota T, Ejiri MK, Otsuka Y, Katoh Y, Satoh M, Ogawa T

    APPLIED OPTICS   Vol. 40 ( 24 ) page: 4286 - 4296   2001.8

     More details

  117. 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

     More details

  118. Multi-point observation of short-period mesospheric gravity waves over Japan during the FRONT campaign

    Shiokawa K, Ejiri MK, Otsuka Y, Ogawa T, Kubota M, Igarashi K, Saito A, Nakamura T

    GEOPHYSICAL RESEARCH LETTERS   Vol. 27 ( 24 ) page: 4057 - 4060   2000.12

     More details

  119. Traveling ionospheric disturbances observed in the OI 630-nm nightglow images over Japan by using a multipoint imager network during the FRONT campaign

    Kubota M, Shiokawa K, Ejiri MK, Otsuka Y, Ogawa T, Sakanoi T, Fukunishi H, Yamamoto M, Fukao S, Saito A

    GEOPHYSICAL RESEARCH LETTERS   Vol. 27 ( 24 ) page: 4037 - 4040   2000.12

     More details

  120. MU radar observations of H+ ions in the topside ionosphere

    Kawamura S, Otsuka Y, Oliver WL, Balan N, Fukao S

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 103 ( A9 ) page: 20697 - 20704   1998.9

     More details

  121. Plasma temperature variations in the ionosphere over the middle and upper atmosphere radar

    Otsuka Y, Kawamura S, Balan N, Fukao S, Bailey GJ

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 103 ( A9 ) page: 20705 - 20713   1998.9

     More details

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

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

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

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

    Sivakandan Mani, Otsuka Yuichi, Ghosh Priyanka, Shinagawa Hiroyuki, Shinbori Atsuki, Miyoshi Yasunobu

    EARTH PLANETS AND SPACE   Vol. 73 ( 1 )   2021.2

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

    Otsuka Yuichi, Shinbori Atsuki, Tsugawa Takuya, Nishioka Michi

    EARTH PLANETS AND SPACE   Vol. 73 ( 1 )   2021.1

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

    Li Guozhu, Ning Baiqi, Otsuka Yuichi, Abdu Mangalathayil Ali, Abadi Prayitno, Liu Zhizhao, Spogli Luca, Wan Weixing

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

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

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

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 125 ( 10 )   2020.10

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

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

    GEOPHYSICAL RESEARCH LETTERS   Vol. 47 ( 13 )   2020.7

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

    Ghosh Priyanka, Otsuka Yuichi, Mani Sivakandan, Shinagawa Hiroyuki

    EARTH PLANETS AND SPACE   Vol. 72 ( 1 )   2020.7

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

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

    EARTH PLANETS AND SPACE   Vol. 72 ( 1 )   2020.5

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

    Abadi Prayitno, Otsuka Yuichi, Supriadi Slamet, Olla Angelikus

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

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

    Dao Tam, Minh Le Huy, Carter Brett, Que Le, Thanh Thuy Trinh, Bao Ngoc Phan, Otsuka Yuichi

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

  132. 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

     More details

    Publishing type:Research paper (scientific journal)   Publisher:American Geophysical Union ({AGU})  

    DOI: 10.1029/2019JA026839

    Web of Science

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

    Balan N., Zhang Qing-He, Xing Zanyang, Skoug R., Shiokawa K., Luehr H., Ram S. Tulasi, Otsuka Y., Zhao Lingxin

    ASTROPHYSICAL JOURNAL   Vol. 887 ( 1 )   2019.12

  134. 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 )   2019.12

     More details

    Publishing type:Research paper (scientific journal)  

    © 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

    Web of Science

    Scopus

    PubMed

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

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

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

  136. 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

  137. 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

  138. 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

  139. 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

     More details

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

    DOI: 10.3847/1538-4357/ab1b52

    Web of Science

  140. 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

  141. 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

     More details

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

    DOI: 10.23919/URSIAP-RASC.2019.8738444

    Web of Science

  142. 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

     More details

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

    DOI: 10.1016/j.asr.2018.03.024

    Web of Science

  143. 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

  144. 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

     More details

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

    DOI: 10.1029/2018JA026443

    Web of Science

  145. 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

  146. 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

     More details

  147. 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

     More details

  148. 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

  149. 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

  150. 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

     More details

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

    DOI: 10.1029/2018GL079615

    Web of Science

  151. 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

     More details

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

    DOI: 10.1186/s40645-018-0212-7

    Web of Science

  152. 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

     More details

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

    DOI: 10.1029/2018JA025438

    Web of Science

  153. 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

     More details

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

    DOI: 10.1029/2018JA025871

    Web of Science

  154. 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

     More details

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

    DOI: 10.1029/2018GL078723

    Web of Science

  155. 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

     More details

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

    DOI: 10.1029/2018JA025261

    Web of Science

  156. 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

     More details

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

    DOI: 10.1029/2018JA025585

    Web of Science

  157. 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

     More details

    Language:English   Publishing type:Research paper (scientific journal)   Publisher:American Geophysical Union ({AGU})  

    DOI: 10.1029/2018JA025491

    Web of Science

  158. 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

  159. 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

     More details

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

    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

    Web of Science

    Scopus

  160. 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

     More details

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

    Web of Science

  161. 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

  162. 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

     More details

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

    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

    Web of Science

  163. 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

     More details

    Language:English   Publishing type:Research paper (international conference proceedings)   Publisher:Institute of Electrical and Electronics Engineers Inc.  

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

    DOI: 10.1109/SPACES.2018.8316326

    Web of Science

    Scopus

  164. 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

     More details

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

    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

    Web of Science

  165. 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

     More details

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

    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

    Web of Science

    Scopus

  166. 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

     More details

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

    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

    Web of Science

    Scopus

  167. 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

     More details

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

    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

    Web of Science

    Scopus

  168. 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

     More details

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

    Web of Science

  169. 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

     More details

  170. 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

     More details

  171. 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

     More details

  172. 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

     More details

  173. 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

     More details

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

    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

    Web of Science

    Scopus

  174. 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: 11,257 - 11,264   2017.11

     More details

    Language:English   Publishing type:Research paper (scientific journal)   Publisher:American Geophysical Union ({AGU})  

    DOI: 10.1002/2017GL074678

    Web of Science

  175. 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

     More details

    Language:English   Publishing type:Research paper (international conference proceedings)   Publisher:Institute of Electrical and Electronics Engineers Inc.  

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

    DOI: 10.23919/URSIGASS.2017.8105106

    Web of Science

    Scopus

  176. 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

     More details

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

    DOI: 10.1186/s40623-017-0729-9

    Web of Science

  177. 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

     More details

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

    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

    Web of Science

  178. 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

     More details

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

    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

    Web of Science

    Scopus

  179. 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

     More details

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

    DOI: 10.1002/2017JA024589

    Web of Science

  180. 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

     More details

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

    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

    Web of Science

  181. 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

     More details

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

    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

    Web of Science

  182. 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

     More details

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

    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

    Web of Science

  183. 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

     More details

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

    DOI: 10.0002/2017JA023919

  184. 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

     More details

    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

    Web of Science

  185. 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

     More details

    Language:English   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

    Web of Science

  186. 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

     More details

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

    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

    Web of Science

  187. 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

     More details

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

    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

    Web of Science

  188. 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

     More details

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

    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

    Web of Science

  189. 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

     More details

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

    Web of Science

  190. 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

     More details

  191. 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

     More details

  192. 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

     More details

    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

    Web of Science

  193. 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

     More details

    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) <10) to the crest region (TECU>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

    Web of Science

  194. 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

     More details

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

    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

    Web of Science

  195. 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

     More details

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

    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

    Web of Science

  196. 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

     More details

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

    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

    Web of Science

  197. 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

     More details

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

    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

    Web of Science

  198. 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

     More details

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

    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

    Web of Science

  199. 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

     More details

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

    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

    Web of Science

  200. 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

     More details

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

    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 >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

    Web of Science

  201. 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

  202. 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

     More details

    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

    Web of Science

  203. 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

     More details

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

    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

    Web of Science

  204. 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

     More details

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

    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

    Web of Science

  205. 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

     More details

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

    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

    Web of Science

  206. 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

     More details

    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

    Web of Science

  207. 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

     More details

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

    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

    Web of Science

  208. 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

     More details

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

    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

    Web of Science

  209. 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

     More details

    Publishing type:Research paper (scientific journal)   Publisher:SPRINGER HEIDELBERG  

    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

    Web of Science

  210. 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

     More details

    Publishing type:Research paper (scientific journal)   Publisher:SPRINGER HEIDELBERG  

    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

    Web of Science

  211. 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

     More details

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

    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

    Web of Science

  212. 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

     More details

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

    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

    Web of Science

  213. 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

     More details

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

  214. 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

     More details

    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

    Web of Science

  215. 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

     More details

    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

    Web of Science

  216. 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

     More details

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

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

    Web of Science

  217. 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

     More details

    Publishing type:Research paper (scientific journal)   Publisher:SPRINGER HEIDELBERG  

    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

    Web of Science

  218. 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

     More details

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

    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) < -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

    Web of Science

  219. 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

     More details

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

    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

    Web of Science

  220. 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

     More details

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

    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

    Web of Science

  221. 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

     More details

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

    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

  222. 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

     More details

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

    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

    Web of Science

  223. 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

     More details

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

    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

  224. 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

     More details

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

  225. 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

     More details

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

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

    DOI: 10.1002/2013JA019732

    Web of Science

  226. 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

     More details

    Publisher:AMER GEOPHYSICAL UNION  

    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

    Web of Science

  227. 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

     More details

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

  228. 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

     More details

    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

  229. 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

     More details

    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

  230. 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

     More details

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

  231. 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

     More details

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

  232. 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

     More details

    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

  233. 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

     More details

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

  234. 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

     More details

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

    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

  235. 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

     More details

    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

  236. 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

     More details

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

    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

    Web of Science

  237. 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

     More details

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

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

    DOI: 10.1002/jgra.50581

    Web of Science

  238. 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

     More details

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

    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

    Web of Science

  239. 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

     More details

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

    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

    Web of Science

  240. 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

     More details

    Publishing type:Research paper (scientific journal)   Publisher:Blackwell Publishing Ltd  

    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

    Web of Science

    Scopus

  241. 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

     More details

    Publishing type:Research paper (scientific journal)   Publisher:Blackwell Publishing Ltd  

    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

  242. 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

     More details

    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

  243. 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

  244. 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

     More details

    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

  245. 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

     More details

    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

  246. 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

     More details

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

  247. 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

     More details

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

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

    Web of Science

  248. 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

     More details

    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

  249. 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

     More details

  250. 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

  251. 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

     More details

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

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

    DOI: 10.1029/2012JA017758

    Web of Science

  252. 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

     More details

    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

  253. 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

     More details

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

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

    DOI: 10.1029/2012JA017641

    Web of Science

  254. 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

     More details

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

    DOI: doi:10.1029/2012GL052286

  255. 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

     More details

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

    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

  256. 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

     More details

    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

  257. 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

     More details

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

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

    DOI: 10.1029/2011JA017423

    Web of Science

  258. 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

     More details

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

  259. 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

     More details

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

    DOI: doi:10.1155/2012/695793

  260. 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

     More details

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

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

    DOI: 10.1029/2011JA017241

    Web of Science

  261. 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

     More details

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

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

    DOI: 10.1029/2011JA016903

    Web of Science

  262. 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

     More details

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

    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

  263. 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

     More details

    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

  264. 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

     More details

    Language:English  

    J-GLOBAL

  265. 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

     More details

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

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

    DOI: 10.1029/2011JA017423

    Scopus

  266. Low-latitude mesosphere, thermosphere, and ionosphere Reviewed

    Y. Sahai, R. S. Dabas, Y. Otsuka, M. Klimenko

    International Journal of Geophysics   Vol. 2012   2012

     More details

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

    DOI: 10.1155/2012/671240

    Scopus

  267. 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

     More details

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

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

    DOI: 10.1029/2011JA016903

    Scopus

  268. 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

     More details

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

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

    DOI: 10.1029/2012JA017928

    Scopus

  269. 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

     More details

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

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

    DOI: 10.1029/2011JA017241

    Scopus

  270. 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

     More details

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

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

    DOI: 10.1029/2012JA017692

    Scopus

  271. 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

     More details

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

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

    DOI: 10.1029/2012JA017758

    Scopus

  272. 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

     More details

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

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

    DOI: 10.1029/2012JA017641

    Scopus

  273. 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

     More details

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

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

    DOI: 10.1155/2012/695793

    Scopus

  274. 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

     More details

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

    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

    Web of Science

  275. 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

     More details

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

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

    DOI: 10.1029/2011JA016797

    Web of Science

  276. 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

     More details

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

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

    DOI: 10.1029/2011JA016798

    Web of Science

  277. 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

     More details

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

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

    DOI: 10.1029/2011JA016607

    Web of Science

  278. 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

     More details

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

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

    DOI: 10.1029/2010JA016399

    Web of Science

  279. 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

     More details

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

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

    DOI: 10.1029/2010JA016297

    Web of Science

  280. 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

     More details

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

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

    DOI: 10.1029/2010JA016001

    Web of Science

  281. 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

     More details

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

    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

  282. 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

     More details

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

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

    DOI: 10.1029/2010JA015925

    Web of Science

  283. 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

     More details

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

    DOI: 10.1007/978-94-007-0326-1_21

    Web of Science

  284. 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

     More details

    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

  285. 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

     More details

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

    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

  286. 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

     More details

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

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

    DOI: 10.1029/2010JA016297

    Scopus

  287. 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

     More details

    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

  288. 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

     More details

    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

  289. 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

     More details

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

  290. 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

     More details

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

    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

  291. 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

     More details

    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

  292. 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

     More details

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

    DOI: 10.1541/ieejfms.131.983

  293. 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

     More details

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

  294. 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

     More details

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

    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'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

  295. 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

     More details

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

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

    DOI: 10.1029/2011JA016798

    Scopus

  296. 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

     More details

    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

  297. 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

     More details

    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

  298. 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

     More details

    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

  299. 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

     More details

    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

  300. 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

     More details

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

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

    DOI: 10.1029/2010JA015848

    Web of Science

  301. 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

     More details

    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

  302. 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

     More details

  303. 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

     More details

    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

  304. 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

     More details

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

    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

  305. 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

  306. 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

     More details

    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

  307. 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

     More details

    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

  308. 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

     More details

    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

  309. 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

     More details

    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

  310. 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

     More details

    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

  311. 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

     More details

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

    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 (∼300°E and ∼120°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°E to 120°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°, 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. © 2010 by the American Geophysical Union.

    DOI: 10.1029/2009JA014830

    Web of Science

    Scopus

  312. 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

     More details

    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

  313. 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

     More details

    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

  314. 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

     More details

    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

  315. 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

     More details

    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

  316. 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

     More details

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

  317. 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

     More details

    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

  318. 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

     More details

    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

  319. 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

     More details

    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

  320. 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   2009.7

  321. 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

     More details

    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'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

    Web of Science

  322. 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

     More details

    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

  323. 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

     More details

    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

  324. 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

     More details

  325. 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

  326. 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

     More details

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

    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

    Web of Science

  327. 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

  328. 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 )   2009.3

     More details

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

    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

    Scopus

  329. 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

     More details

    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

  330. 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

     More details

    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

  331. 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

     More details

    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

  332. 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

     More details

    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

  333. 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

     More details

    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

  334. 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

     More details

    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

  335. 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

     More details

    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

  336. 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

     More details

    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)

    Web of Science

  337. 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

     More details

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

    We present the characteristics of small-scale (< 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

  338. 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

     More details

    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

    Web of Science

  339. 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

     More details

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

    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

    Web of Science

  340. 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

     More details

    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

    Web of Science

  341. 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

     More details

    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

    Scopus

  342. 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

     More details

    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.

    Web of Science

  343. 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

     More details

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

    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

    Web of Science

  344. 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

     More details

    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

    Web of Science

  345. 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

     More details

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

  346. 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

     More details

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

  347. Equatorial ionospheric scintillations and zonal irregularity drifts observed with closely-spaced GPS receivers in Indonesia Reviewed

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

    J. Meteor. Soc. Japan   Vol. 84A   page: 343-351   2006

     More details

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

  348. A Statistical Study of Ionospheric Irregularities Observed with a GPS Network in Japan

    Y. Otsuka, T. Aramaki, T. Ogawa, A. Saito

    Recurrent Magnetic Storms: Corotating Solar Wind Streams   Vol. 167   page: 271 - +   2006

     More details

    © 2006 by the American Geophysical Union. All rights reserved. The Geographical Survey Institute of Japan has installed a network of about 1000 dual-frequency GPS receivers in Japan with their mutual distance of about 25 km. Phases and pseudo ranges of dual-frequency GPS signals are recorded every 30 s. The dense distribution of the GPS receivers allows us to reveal twodimensional structures of the ionospheric plasma density irregularities with scale sizes of the order of several kilometers. We analyzed TEC data obtained from the GPS network of Japan in 2000. It was found that the irregularity characteristics over Japan depended on latitude. The results are as follows: (1) at the northern part, the irregularities appeared only during geomagnetic storms. (2) At the middle part, they had the most frequent occurrence in summer nighttime and were usually accompanied by Medium-Scale Traveling Ionospheric Disturbances (MSTID). (3) At the southern part, they were associated with the equatorial plasma bubbles and their occurrences were highest in the equinoctial nighttime.

    DOI: 10.1029/167GM21

    Web of Science

    Scopus

  349. Spatial relationship of equatorial plasma bubbles and field-aligned irregularities observed with an all-sky airglow imager and the Equatorial Atmosphere Radar Reviewed

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

    Geophys. Res. Lett.   Vol. 31 ( L20802 ) page: 10.1029/2004GL020869   2004

     More details

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

    We report, for the first time, simultaneous two-dimensional observations of 630-nm airglow depletions and radar backscatter from field-aligned irregularities (FAI) associated with equatorial plasma bubbles. Spatial distributions of backscatter were obtained by performing
    east-west scans with the 47-MHz Equatorial Atmosphere Radar (EAR) in West Sumatra, Indonesia. A 630-nm airglow depletion, caused by a plasma bubble, was simultaneously
    observed with an all-sky airglow imager.
    Both the airglow depletion and backscatter region appeared as band-like structure elongated in the meridional direction with a zonal width of about 100 km. To compare the spatial structures of backscatter with that of airglow depletion,
    the backscatter was projected onto a horizontal plane at 250-km altitude. Backscatter was found to occur within the entire airglow-depleted region.

  350. Optical and radio measurements of a 630-nm enhancement over Japan on September 9, 1999 Reviewed

    Otsuka, Y., T. Kadota, K. Shiokawa, T. Ogawa, S. Kawamura,, S. Fukao, and S. -R. Zhang

    J. Geophys. Res.   Vol. 108(A6) ( 1252 ) page: doi:10.1029/2002JA009594   2003

     More details

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

    Using a comprehensive data set from optical and radio instruments, we investigate a midnight brightness wave that appeared in 630-nm airglow images over Japan on the night of September 9, 1999. This may be the first such observation of the brightness wave with an all-sky imager in the East-Asian longitudinal sector. The imager at Shigaraki (35.6N, 136.1E) tracked a north-northeastward propagation of the wave with an apparent velocity of 500 m/s after midnight. Ionosonde observations at five stations in Japan showed that rapid descent of the F2 layer propagated northward beyond 35N with decreasing amplitude. Incoherent scatter observations with the MU radar at Shigaraki also revealed that the F2 peak altitude decreased from 360 km to 280 km during the event. During the F2 layer descent, the altitude profile of the electron density became sharp, enhancing the F2 peak electron density. After the F2 layer altitude reached 280 km, electron density in the F2 layer rapidly decreased because of increased neutral density at low altitude. A Fabry-Perot interferometer (FPI) at Shigaraki observed northward neutral winds of 10--70 m/s during the event. A model calculation demonstrates that the meridional winds estimated from the MU radar electron density profiles are fairly well consistent with those observed with the FPI. From these results, we conclude that the observed northward wind enhancements, probably caused by the the midnight temperature maximum, pushed down the plasma in the F2 layer to lower altitudes along the geomagnetic field to cause the
    630-nm airglow intensity enhancement.

  351. Geomagnetic conjugate observations of equatorial airglow depletions Reviewed

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

    Geophys. Res. Lett.   Vol. 29   page: 10.1029/2002GL015347   2002

     More details

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

  352. The height of the maximum ionospheric electron density over the MU radar Reviewed

    Journal of Atmospheric and Solar-Terrestrial Physics   Vol. 61   page: 1367-83   1999

     More details

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

  353. Plasma temperature variations in the ionosphereover the middle and upper atmosphere radar Reviewed

    Journal of Geophysical Research   Vol. 103   page: 20,705-20,713   1998

     More details

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

  354. MU radar observations of H+ ions in the topside ionosphere Reviewed

    Journal of Geophysical Research   Vol. 103   page: 20,697-20,704   1998

     More details

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

  355. MST radar measurement of ionospheric F region winds:The "layer-wind" technique Reviewed

    Radio Science   Vol. 33   page: 941-948   1998

     More details

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

  356. Equinoctial asymmetries in the ionosphere and thermosphere observed by the MU radar Reviewed

    Journal of Geophysical Research   Vol. 103   page: 9,481-9,495   1998

     More details

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

  357. A climatology of F region gravity wave propagation over the middle and upper atmosphere radar Reviewed

    Journal of Geophysical Research   Vol. 102   page: 14,499-14,512   1997

     More details

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

  358. New aspects in the annual variation of the ionosphere observed by the MU radar Reviewed

    Geophysical Research Letters   Vol. 24   page: 2,287-2,290   1997

     More details

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

  359. Middle and upper atmosphere radar observations of the dispersion relation for ionospheric gravity waves Reviewed

    Journal of Geophysical Research   Vol. 100   page: 23,763-23,768   1995

     More details

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

▼display all

MISC 1

  1. 無人システムを利用したオーロラ現象の南極広域ネットワーク観測:共役点イベント解析(2)

    門倉昭, 山岸久雄, 岡田雅樹, 小川泰信, 田中良昌, 片岡龍峰, 内田ヘルベルト陽仁, 大塚雄一

    日本地球惑星科学連合大会予稿集(Web)   Vol. 2019   page: ROMBUNNO.PEM11‐23 (WEB ONLY)   2019

     More details

    Language:Japanese  

    J-GLOBAL

Presentations 48

  1. トロムソEISCAT サイトでのGPS シンチレーション観測

    大塚雄一、小川泰信、石井守、久保田実、津川卓也、塩川和夫、大山伸一郎

    第124回 地球電磁気・地球惑星圏学会 

     More details

    Event date: 2009.9

    Language:Japanese   Presentation type:Poster presentation  

    Country:Japan  

  2. ファブリ・ペロー干渉計観測による熱圏中性大気風速とMUレーダーによるF 領域プラズマドリフトの統計解析

    大塚雄一、塩川和夫、小川忠彦、深尾昌一郎

    第124回 地球電磁気・地球惑星圏学会 

     More details

    Event date: 2009.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Country:Japan  

  3. VHF Radar Observations of Nighttime F-Region Field-Aligned Irregularities Over Kototabang, Indonesia International conference

    Asia Oceania Geosciences Society (AOGS) 

     More details

    Event date: 2009.8

    Language:English   Presentation type:Oral presentation (invited, special)  

  4. Relationship between medium-scale traveling ionospheric disturbance and sporadic E layer activities in summer night over Japan International conference

    Asia Oceania Geosciences Society 2008 

     More details

    Event date: 2008.6

    Language:English   Presentation type:Oral presentation (general)  

  5. VHF Radar Observations of Nighttime F-Region Field-Aligned Irregularities Over Kototabang, Indonesia International conference

    Asia Oceania Geosciences Society 2008 

     More details

    Event date: 2008.6

    Language:English   Presentation type:Oral presentation (general)  

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

    12th International Symposium on Equatorial Aeronomy (ISEA-12) 

     More details

    Event date: 2008.5

    Language:English   Presentation type:Oral presentation (general)  

  7. Ionospheric variations observed by GPS-TEC and SuperDARN Hokkaido radar following large earthquakes International conference

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

     More details

    Event date: 2007.7

    Language:English   Presentation type:Oral presentation (general)  

    Country:Japan  

  8. Radar and Optical Observation of Medium-Scale Traveling Ionospheric Disturbances and Field-Aligned Irregularities in the F Region International conference

    IUGG XXIV General Assembly 

     More details

    Event date: 2007.7

    Language:English   Presentation type:Oral presentation (general)  

  9. Observations of ionospheric variations following the 13 January 2007 earthquake using GPS and Hokkaido HF radar International conference

    SuperDARN Workshop 2007 

     More details

    Event date: 2007.6

    Language:English   Presentation type:Oral presentation (general)  

    Country:Japan  

  10. Radar and Optical Observation of Medium-Scale Traveling Ionospheric Disturbances and Field-Aligned Irregularities in the F Region International conference

    AGU Joint Assembly, Acapulco 

     More details

    Event date: 2007.5

    Language:English   Presentation type:Oral presentation (invited, special)  

  11. 2007年1月13日の千島列島東方地震後にGPSと北海道-陸別HFレーダーで 観測された電離圏変動: 1. GPS

    大塚雄一、山矢優、西谷望、小川忠彦

    日本地球惑星科学連合2007年大会 

     More details

    Event date: 2007.5

    Language:Japanese   Presentation type:Poster presentation  

    Country:Japan  

  12. F領域沿磁力線不規則構造と中規模伝搬性電離圏擾乱のレーダー・光学同時観測

    大塚 雄一、横山 竜宏、塩川 和夫、小川 忠彦、山本 衛

    日本地球惑星科学連合2007年大会 

     More details

    Event date: 2007.5

    Language:Japanese   Presentation type:Poster presentation  

    Country:Japan  

  13. Radio and Optical Observations of Medium-scale Traveling Ionospheric Disturbances with the MU radar and All-Sky Airglow Imagers International conference

    the 2007 Taiwan Geosciences Assembly 

     More details

    Event date: 2007.5

    Language:English   Presentation type:Oral presentation (general)  

  14. Radar observations of F-region field-aligned irregularities over Indonesia International conference

    International Symposium on Coupling Processes in the Equatorial Atmosphere 

     More details

    Event date: 2007.3

    Language:English   Presentation type:Poster presentation  

    Country:Japan  

  15. GPSを用いたインドネシアにおける電離圏擾乱とドリフト速度の観測

    大塚雄一、 塩川 和夫、小川 忠彦

    CAWSES/IHY worskshop 

     More details

    Event date: 2007.3

    Language:Japanese   Presentation type:Poster presentation  

    Country:Japan  

  16. 2007年1月13日の千島列島東方地震後にGPSと北海道-陸別

    中緯度短波レーダー研究会 

     More details

    Event date: 2007.2

    Language:Japanese   Presentation type:Oral presentation (general)  

    Country:Japan  

  17. F領域沿磁力線不規則構造と中規模伝搬性電離圏 擾乱のレーダー・光学同時観測

    大塚雄一, 横山竜宏, 塩川和夫, 小川忠彦、齋藤昭則、山本衛

    大気圏シンポジウム 

     More details

    Event date: 2007.2

    Language:Japanese   Presentation type:Poster presentation  

    Country:Japan  

  18. Relationship between medium-scale traveling ionospheric disturbance and sporadic E layer activities in summer night over Japan International conference

    AGU Chapman Conference on Mid-latitude Ionospheric Dynamics and Disturbances 

     More details

    Event date: 2007.1

    Language:English   Presentation type:Oral presentation (general)  

  19. 赤道域電離圏擾乱と対流圏・MLT変動との関係 2

    「赤道大気上下結合」研究成果取まとめミニワークショップ 

     More details

    Event date: 2006.12

    Language:Japanese   Presentation type:Oral presentation (general)  

    Country:Japan  

  20. GPS全電子数を用いた赤道域電離圏擾乱の6-8日周期変動

    大塚 雄一、津川 卓也、横山 竜宏、他

    地球電磁気・地球惑星圏学会 

     More details

    Event date: 2006.11

    Language:Japanese   Presentation type:Oral presentation (general)  

    Country:Japan  

  21. Relationship between medium-scale traveling ionospheric disturbances and sporadic E layer over Japan International conference

    Asia Oceania Geosciences Society 3rd Annual Meeting, Singapore, Singapore 

     More details

    Event date: 2006.11

    Language:English   Presentation type:Oral presentation (invited, special)  

  22. 2004年12月26日のスマトラ沖地震後のGPS-TEC変動

    中間圏・熱圏・電離圏 (MTI) 研究集会 

     More details

    Event date: 2006.9

    Language:Japanese  

  23. GPS全電子数を用いた赤道域電離圏擾乱の6-8日周期変動

    大塚 雄一、津川 卓也、横山 竜宏、小川 忠彦、齊藤 昭則、西岡 未知

    特定領域研究「赤道大気上下結合」平成18年度公開ワークショップ 

     More details

    Event date: 2006.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Country:Japan  

  24. 中・低緯度における電離圏擾乱: 中規模伝搬性電離圏擾乱(MSTID)

    中間圏・熱圏・電離圏 (MTI) 研究集会 

     More details

    Event date: 2006.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Country:Japan  

  25. MTI衛星:サイエンス・電離圏

    中間圏・熱圏・電離圏 (MTI) 研究集会 

     More details

    Event date: 2006.9

    Language:Japanese  

  26. MTIP衛星の科学目標: 電離圏

    MTI小型衛星による大気圏・宇宙研観測ワークショップ 

     More details

    Event date: 2006.8

    Language:Japanese   Presentation type:Oral presentation (general)  

    Country:Japan  

  27. GPS及びイオノゾンデ観測による中規模伝搬性電離圏擾乱と スポラディックE層との関係の研究

    大塚雄一,谷貴行,津川卓也,小川忠彦,齊藤昭則

    日本地球惑星科学連合2006年大会 

     More details

    Event date: 2006.5

    Language:Japanese   Presentation type:Poster presentation  

    Country:Japan  

  28. MTI衛星を用いた電離圏・熱圏のサイエンス

    大塚雄一、MTI衛星検討グループ

    人工衛星からの電離圏・熱圏・中間圏撮像観測に関する研究集会 

     More details

    Event date: 2005.11

    Language:Japanese   Presentation type:Oral presentation (general)  

    Country:Japan  

  29. GPSを使った電離圏観測

    サイエンスワークショップ「太陽・地球・生命圏観測の現状と要素技術」 

     More details

    Event date: 2005.11

    Language:Japanese   Presentation type:Oral presentation (general)  

    Country:Japan  

  30. Optical and radio measurements of equatorial plasma bubbles over Indonesia International conference

     More details

    Event date: 2005.10

    Language:English   Presentation type:Poster presentation  

  31. GPS detection of total electron content variations over Indonesia and Thailand following the 26 December 2004 earthquake International conference

     More details

    Event date: 2005.9

    Language:English   Presentation type:Oral presentation (invited, special)  

    Country:Japan  

  32. 信楽のファブリ・ペロー干渉計で観測された熱圏中性大気風速の統計解析

    大塚雄一、塩川和夫、小川忠彦

    地球電磁気・地球惑星圏学会 

     More details

    Event date: 2005.9

    Language:Japanese   Presentation type:Poster presentation  

    Country:Japan  

  33. GPSで観測された2004年12月26日のスマトラ島西方沖地震後の電離圏変動

    大塚雄一、 小竹論季、 津川卓也、塩川和夫、小川忠彦、斎藤 享、川村眞文、丸山 隆、Effendy、N. Hemmakorn、T. Komolmis

    平成17年度「赤道大気上下結合」公開ワークショップ 

     More details

    Event date: 2005.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Country:Japan  

  34. GPSで観測された2004年12月26日のスマトラ島西方沖地震後の電離圏全電子数変動

    大塚雄一、 小竹論季、 津川卓也、塩川和夫、小川忠彦、斎藤 享、川村眞文、丸山 隆、Effendy、N. Hemmakorn、T. Komolmis

    CAWSES workshop (第6回宇宙天気/気候シンポジウム) 

     More details

    Event date: 2005.9

    Language:Japanese   Presentation type:Oral presentation (invited, special)  

    Country:Japan  

  35. Measurements of ionospheric irregularity drift using spaced GPS receivers in Indonesia International conference

    11th International Symposium on Equatorial Aeronomy and CAWSES Mini-Workshop 

     More details

    Event date: 2005.5

    Language:English   Presentation type:Oral presentation (general)  

  36. 2004年12月26日のスマトラ島西方沖地震後の電離圏全電子数変動

    大塚雄一、津川卓也、小竹論季、塩川和夫、小川忠彦

    地球惑星科学関連学会合同大会 

     More details

    Event date: 2005.5

    Language:Japanese   Presentation type:Poster presentation  

    Country:Japan  

  37. GPS detection of total electron content variations following the 26 December 2004 earthquake International conference

    11th International Symposium on Equatorial Aeronomy and CAWSES Mini-Workshop 

     More details

    Event date: 2005.5

    Language:English   Presentation type:Oral presentation (invited, special)  

  38. 2004年12月26日のスマトラ島西方沖地震後の電離圏全電子数変動

    大塚雄一、津川卓也、小竹論季、塩川和夫、小川忠彦

    全国共同利用化に向けた第9回生存圏シンポジウム「赤道大気レーダーによる電離圏研究とその広がり」 

     More details

    Event date: 2005.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Country:Japan  

  39. Total electron content variations during geomagnetic storms: From the dense GPS Network in Japan International conference

    Chapman Conference on Corotating Solar Wind Streams and Recurrent Geomagnetic Activity 

     More details

    Event date: 2005.2

    Language:English   Presentation type:Oral presentation (invited, special)  

  40. 中規模伝搬性電離圏擾乱のレーダー・光学観測

    大塚雄一、塩川和夫、小川忠彦、齊藤昭則、大島浩嗣、深尾昌一郎

    ISAS第19回大気圏シンポジウム 

     More details

    Event date: 2005.2

    Language:Japanese   Presentation type:Oral presentation (general)  

    Country:Japan  

  41. 衛星大気光観測・電離圏現象

    大塚雄一、塩川和夫、小川忠彦、斉藤昭則

    中間圏・熱圏・電離圏研究会 

     More details

    Event date: 2004.11

    Language:Japanese   Presentation type:Oral presentation (general)  

    Country:Japan  

  42. GPSによる赤道域電離圏イレギュラリティのドリフト速度観測

    大塚雄一、服部 誠、伊藤義訓、塩川和夫、小川忠彦

    中間圏・熱圏・電離圏研究会 

     More details

    Event date: 2004.11

    Language:Japanese   Presentation type:Poster presentation  

    Country:Japan  

  43. 第一回CPEAキャンペーン期間中におけるプラズマバブルの観測 - 速報-

    大塚雄一、服部 誠、塩川和夫、小川忠彦、深尾昌一郎、山本 衛、多山哲郎、丸山 隆、佐川永一、斎藤 享

    第116回SGEPSS 

     More details

    Event date: 2004.9

    Language:Japanese   Presentation type:Poster presentation  

    Country:Japan  

  44. GPS三点観測による赤道域F領域イレギュラリティのドリフト速度の測定

    第116回SGEPSS 

     More details

    Event date: 2004.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Country:Japan  

  45. Goemanetic conjugate observations of medium-scale traveling ionospheric disturbances with all-sky imagers International conference

    1st Asia Oceania Geosciences Society (AOGS) 

     More details

    Event date: 2004.7

    Language:English   Presentation type:Poster presentation  

  46. 大気光イメージャーによる電離圏の磁気共役点観測 International conference

     More details

    Event date: 2004.5

    Language:English   Presentation type:Poster presentation  

    Country:Japan  

  47. 大気光イメージャーによる中規模伝搬性電離圏擾乱の磁気共役点観測

    大塚雄一、塩川和夫、小川忠彦、斎藤昭則、大島浩嗣

    地球惑星科学関連学会合同大会 

     More details

    Event date: 2004.5

    Language:Japanese   Presentation type:Oral presentation (general)  

    Country:Japan  

  48. 観測点を増やした場合におけるSBASに対する効果

    大塚雄一、小川忠彦、星野尾一明、松永圭左、斎藤昭則

    地球惑星科学関連学会合同大会 

     More details

    Event date: 2004.5

    Language:Japanese   Presentation type:Poster presentation  

    Country:Japan  

▼display all

Research Project for Joint Research, Competitive Funding, etc. 2

  1. プラズマバブル測定用全天カメラの現地調整

    2005 - 2006.3

      More details

    Grant type:Competitive

    静止衛星型衛星航法補強システムの2周波対応に関する研究における電離圏シンチレーションの影響を調べるため、全天大気光カメラを与那国島に設置し、その原因であるプラズマバブルの発生特性を明らかにする。

  2. Development of all-sky airglow camera for plasma bubble observations

    2004.10 - 2005.3

      More details

    Grant type:Competitive

KAKENHI (Grants-in-Aid for Scientific Research) 32

  1. GPSシンチレーション観測による極域電離圏イレギュラリティの研究

    2011.4 - 2014.3

    科学研究費補助金  基盤研究(B)

    大塚雄一

      More details

    Authorship:Principal investigator 

  2. 電離圏・熱圏の春・秋非対称性

    2011.4 - 2014.3

    科学研究費補助金  基盤研究(C)

    大塚雄一

      More details

    Authorship:Principal investigator 

  3. 低緯度電離圏不規則構造のレーダー・イメージング観測

    2008.4 - 2011.3

    科学研究費補助金  若手研究(A)

    大塚 雄一

      More details

    Authorship:Principal investigator 

  4. GPS受信機網を用いた地震起源の電離圏変動に関する研究

    2006.4 - 2008.3

    科学研究費補助金 

      More details

    Authorship:Principal investigator 

  5. International study of equatorial ionosphere based on observations and models

    Grant number:20H00197  2020.4 - 2025.3

      More details

    Authorship:Coinvestigator(s) 

  6. Study of dynamical variation of particles and waves in the inner magnetosphere using ground-based network observations (PWING Project)

    Grant number:16H06286  2016.4 - 2021.3

      More details

    Authorship:Coinvestigator(s) 

  7. Observations of ionospheric scintillation at cusp and polar cap regions using satellite signals

    Grant number:16H05736  2016.4 - 2019.3

    Otsuka Yuichi

      More details

    Authorship:Principal investigator 

    Grant amount:\17290000 ( Direct Cost: \13300000 、 Indirect Cost:\3990000 )

    At polar and auroral regions, we have carried out measurements of ionospheric plasma structures and irregularities by receiving radio waves of Global Navigation Satellite System (GNSS) and low-Earth orbit satellites. We have revealed statistical characteristics of scintillation occurrence at polar and auroral regions, and estimated drift velocities of the ionospheric irregularities. We have found a new generation mechanism for the irregularities during magnetic storms.

  8. Understanding and prediction of geospace dynamics

    Grant number:15H05815  2015.6 - 2020.3

    Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)

    Miyoshi Yoshizumi

      More details

    Authorship:Coinvestigator(s) 

    This research group focused on "space radiation", "ionospheric disturbance", and "geomagnetically induced current" which are the most important space weather phenomena in geospace. The main achievements of this group are as follows. 1) Understanding of wave-particle interactions in the radiation belts that cause large flux enhancement and loss of energetic electrons by the Arase in-situ observations and newly developed simulations, 2) Development of forecast system that calculates ionospheric disturbances for a next few days, 3) Development of physical simulation codes for GIC in Japan islands, which calculates highly accurate GIC variations.

  9. 人工衛星-地上ネットワーク観測に基づく内部磁気圏の粒子変動メカニズムの研究

    Grant number:25247080  2013.4 - 2017.3

    塩川 和夫

      More details

    Authorship:Coinvestigator(s) 

    ・ロシアのZhigansk観測点において、誘導磁力計による定常観測を平成28年9月14日より開始し、良好なデータが取得できていることを確認した。ロシアのZhigansk観測点を管轄するヤクーツクのIKFIA研究所に、平成28年9月末にVLFアンテナ、高感度全天カメラを送付した(平成27年度の本計画の繰り越し分による実施)。また、関連機器による定常観測が行われている既存の観測点であるアサバスカ、トロムソ、マガダン、パラツンカ、レゾリュート、国内の母子里、陸別、信楽、鹿児島、佐多などの自動観測を維持・継続した。
    ・アサバスカ、マガダン、パラツンカの誘導磁力計による5年間の同時観測データを統計的に解析して、Pc1帯地磁気脈動の振幅変調の観測点ごとに違いの季節・太陽活動度・地方時・地磁気活動度などへの依存性を明らかにした。この結果から、この波動の振幅変調が磁気圏ではなく電離圏の伝搬中にうなりによって発生していることを示唆した。また、アサバスカで1年間に観測されたVLF/ELF帯波動の統計解析を行い、この波動の季節・地方時・地磁気活動度などへの依存性を明らかにした。これらの波動は、人工衛星に悪影響を及ぼす放射線帯粒子の加速や消失を引き起こしていることがわかっており、今回の結果は、この加速・消失過程の時間・空間変化に示唆を与えるものである。
    ・なお、本計画は、研究代表者が平成28年度から別の特別推進研究の代表者になったために、平成28年度途中で廃止になった。本計画で予定されていたカナダ中部のアサバスカ、カナダの東海岸、及び、ロシアのZhigansk観測点における光学・電磁場計測は、この特別推進研究によって引き続きおこなわれることになった。
    28年度が最終年度であるため、記入しない。
    28年度が最終年度であるため、記入しない。

  10. Study of relations between Equatorial Spread-F and ionospheric structures with Equatorial Atmosphere Radar and wide-area observation network

    Grant number:25302007  2013.4 - 2017.3

    Yamamoto Mamoru

      More details

    Authorship:Coinvestigator(s) 

    We aimed to elucidate the equatorial spread F phenomenon which is a strong instability phenomenon of the ionosphere, and the ionosphere structure. Specifically, (1) we studied statistical properties of ESF from long-term continuous observation with the equatorial atmosphere radar, (2) the time-space variation of ESF from the observation network developed in Southeast Asia and the ionosphere, and (3) tried further expansion of the satellite-beacon observation network and utilization of airglow observation from the International Space Station. This study project was successful as we published in total 26 articles in the peer-reviewed jounrnals.

  11. Coordinated observation of the mesospheric disturbances generated by the tropospheric activities using the coordinated observation from ground and the space

    Grant number:24403008  2012.4 - 2016.3

    Saito Akinori

      More details

    Authorship:Coinvestigator(s) 

    This study aimed to revel the effect of the tropospheric activities on the Mesosphere and the Thermosphere using the coordinated observation of ground-based imagers and ISS-IMAP/VISI (International Space Station - Ionosphere, Mesosphere upper Atmosphere, and Plasmasphere/ Visible-light and infrared spectrum imager) on the international space station. The calibration of ISS-IMAP/VISI by the comparison with simultaneous observation of the ground-based imager is another target of this study. An all-sky imager was installed on Hawaii Haleakala observatory of Tohoku University on March 2013, and the coordinated observation was carried out for about two and half years. The simultaneous observational data of the wave-like structures in the Mesosphere by the space-borne and the ground-based imaging was successfully obtained by this study. The characteristics of the atmospheric gravity waves that connect the Troposphere and the upper atmosphere were elucidated by this coordinated observation.

  12. Study of generation mechanism of middle-latitude ionospheric wave by rocket and ground-based observations

    Grant number:24340120  2012.4 - 2015.3

    YAMAMOTO Mamoru

      More details

    Authorship:Coinvestigator(s) 

    This study aimed to elucidate the generation mechanism of medium-scase traveling ionospheric disturbances (MSTID) by coordinated sounding rockets and ground-based observations. On July 20, 2013, sounding rockets S-520-27 and S-310-42 were successfully launched from JAXA Uchinoura Space Center (USC). We simultaneously carried out observations from aircraft and gound sites. In association to MSTID, large horizontal variation in electron density and electric field were observed. Sporadic E layer was present at the same time. Including the behavior of the neutral wind, we successfully demonstrated that MSTID is generated in the situation expected from the model that was proposed before the experiment. Also at the same time, we successfully photographed resonance scattering from the Lithium cloud under the full-moon and midnight condition from the aircraft and the ground, which was the world first Li-release experiment by using the moonlight.

  13. Equinoctial Asymmetry of the Ionosphere and Thermosphere

    Grant number:23540523  2011.4 - 2015.3

    OTSUKA Yuichi

      More details

    Authorship:Principal investigator 

    Grant amount:\4940000 ( Direct Cost: \3800000 、 Indirect Cost:\1140000 )

    Eddy diffusion coefficients have been estimated from long-term measurements of the mesospheric echo observed with the MU radar, which is a large atmospheric radar. We have found that the eddy diffusion coefficients are higher in Sep. equinox than Mar. equinox. According to the results obtained from the global simulation, this equinoctial asymmetry of the mesospheric eddy diffusion coefficients is responsible for that of the ionospheric plasma density. We have analyzed thermospheric neutral wind data obtained by Fabry Perot interferometer at Chiang Mai, Thailand, and show that equinoctial asymmetry of the meridional thermospheric winds is responsible for that of plasma bubble occurrence rate.

  14. Studies of Ionospheric Irregularities in the Polar Region by GPS Scintillation Observations

    Grant number:23403010  2011.4 - 2015.3

    OTSUKA Yuichi

      More details

    Authorship:Principal investigator 

    Grant amount:\20020000 ( Direct Cost: \15400000 、 Indirect Cost:\4620000 )

    We have installed 3 GNSS receivers at EISCAT radar site in Tromsoe, Norway and developed a system to measure phase and amplitude of the received radio waves at dual frequencies. With this system, we have observed fluctuations of the radio waves (scintillation) and compared them with aurora observed with optical instrument. Using more than 800 GNSS receivers in Europe, we have calculated total electron content and revealed statistical features of traveling ionospheric disturbances.

  15. Study of day-to-day variability of equatorial Spread-F based on large-area observations over India, southeast Asia, and Pacific

    Grant number:22403011  2010 - 2012

    YAMAMOTO Mamoru

      More details

    Authorship:Coinvestigator(s) 

    Equatorial Spread-F (ESF) is a one of the most intense ionospheric disturbance that causes severe scintillation to the satellite-ground communications, and degradation of the GPS locations. In this study we deployed large -area observation network of the ionosphere from Asia and Pacific regions by means of radars, nightglow imagers, and satellite-ground beacon receivers. We investigated yet-unknown day-to-day variability of ESF , and found that the ESF is generated from the enhanced Large -Scale Wave Structure (LSWS) of the ionosphere. We also found detailed behavior of ESF at post -midnight period that enhances under the low-solar conditions.

  16. A study of multi-scale ionospheric disturbances and their effects on GNSS using GPS receiver networks

    Grant number:22740326  2010 - 2011

    TSUGAWA Takuya

      More details

    Authorship:Other 

    Two-dimensional maps of ionospheric total electron content(TEC), rate of TEC change index(ROTI), loss-of-lock on GPS signals were derived using GPS receiver networks in Japan and the world. Using these data, ionospheric disturbances such as TIDs and plasma bubbles and their effects on GNSS were statistically studied. We have started realtime two-dimensional GPS-TEC observation in Japan and detected clear concentric ionospheric waves after the 2011 Tohoku earthquake.

  17. Development of wide-area plasma bubble monitoring by a passive radar technique with digital radio receivers

    Grant number:21740357  2009 - 2011

    SAITO Susumu

      More details

    Authorship:Other 

    A system to measure the propagation distance of HF broadcast radio waves was developed with digital software radio receivers by utilizing a passive radar technique. The propagation time of HF broadcast radio waves from Australia to Japan across the magnetic equator was measured by the system to derive propagation distance. A rrival angle s of the radio waves were measured simultaneously by an HF direction finder. It was suggested that more accurate position estimation of plasma bubbles and an effective wide-ar ea monitoring system of plasma bubbles would be achievable by measuring the distance and arrival angle of trans-equatorial HF radio wave propagation simultaneously.

  18. Study of the upper atmosphere dynamics using highly sensitive multi-point optical instruments

    Grant number:20244080  2008.4 - 2013.3

    SHIOKAWA Kazuo

      More details

    Authorship:Coinvestigator(s) 

    We have obtained various interesting results on the dynamical variations of the upper atmosphere at altitudes of 80-300 km using multi-point observation of nighttime airglow by 5 Fabry-Perot interferometers and more than 10 al-sky airglow imagers at Russia, Canada, Japan, Norway, Indonesia, Thailand, and Australia. Outstanding examples of the results are (1) various dynamical variations of medium-scale traveling ionospheric disturbances at subauroral latitudes, (2) evidence of duct propagation of small-scale gravity waves in the mesopause region, (3) evidence of a typhoon-induced small-scale gravity wave propagation to the mesopause region, and (4) relationship of eastward propagation of equatorial plasma bubbles and eastward thermospheric wind.

  19. Radar imaging observations of the field-aligned irregularities at low-latitude ionosphere

    Grant number:20684021  2008 - 2010

    OTSUKA Yuichi

      More details

    Authorship:Principal investigator 

    Grant amount:\22620000 ( Direct Cost: \17400000 、 Indirect Cost:\5220000 )

    We have analyzed E- and F-region field-aligned irregularities (FAIs) observed by a VHF backscatter radar with an operating frequency of 30.8 MHz in Indonesia and revealed statistically local time, seasonal, and solar activity variations of the FAI occurrence rates. Propagation characteristics and drift velocities of the FAIs are also investigated. Especially, we have studied the post-midnight F-region FAIs and suggested that the post-midnight FAIs are likely associated with either plasma bubbles or medium-scale traveling ionospheric disturbances (MSTIDs).

  20. Development of a whole atmosphere-ionosphere coupled model for the upper atmospheric research and prediction

    Grant number:20200047  2008 - 2010

    Grant-in-Aid for Scientific Research on Innovative Areas (Research a proposed research project)

    JIN Hidekatsu

      More details

    Authorship:Collaborating Investigator(s) (not designated on Grant-in-Aid) 

    We have developed a whole atmosphere-ionosphere coupled model, which can treat the Earth's entire atmospheric regions from the troposphere to the ionosphere. It has been found that the longitudinal dependences and day-to-day variations as recently observed in the upper atmosphere can be reproduced by the coupled model, and revealed that the effect of lower atmosphere is significant for the generation of the upper atmospheric variations. Further, we have incorporated meteorological reanalysis data into the coupled model, and the results suggested that the model and method can be useful for the future numerical prediction of the upper atmosphere.

  21. Study of the interaction between the ionospheric plasma and thermospheric neutral winds in the mid-and high-latitude region using the SuperDARN HF radar networ k

    Grant number:19340141  2007 - 2010

    NISHITANI Nozomu

      More details

    Authorship:Collaborating Investigator(s) (not designated on Grant-in-Aid) 

    The interaction between the ionospheric plasma and thermospheric neutral winds in the mid-and high-latitude region was investigated using the SuperDARN HF radar network. The main subjects of this project are : 1) dynamics of sub-auroral polarization streams, 2) large and medium scale traveling ionospheric disturbances, and 3) coseismic ionospheric disturbances.

  22. Ground-Satellite observation of geospace environment over Siberia and Japan

    Grant number:18403011  2006 - 2009

    SHIOKAWA Kazuo

      More details

    Authorship:Coinvestigator(s) 

    We installed all-sky cooled-CCD imagers and induction magnetometers at Magadan and Paratunka in Far-East Russia in 2007-2008. By combining pre-existing imagers and the SuperDARN Hokkaido radar and newly-installed induction magnetometers in Japan, we developed a latitudinal chain of ground-based stations to observe the upper atmosphere and geospace. Using these ground-based observations as well as satellite observations, we investigate storm-time broadband electron precipitation, which can cause low-latitude red auroras, and ionospheric disturbances in the subauroral region to middle latitudes.

  23. GPS受信機網を用いた地震起源の電離圏変動に関する研究

    Grant number:18654083  2006 - 2007

    萌芽研究

    大塚 雄一

      More details

    Authorship:Principal investigator 

    Grant amount:\2300000 ( Direct Cost: \2300000 )

    国内外のGPS観測データを収集し、電離圏における全電子数(Total Electron Content;TEC)を算出し、そのデータベースを作成することにより、以下の結果を得た。
    1.2000年1月から2007年10月までに日本で起きたマグニチュード6.0以上の地震(20例)について、地震発生後のTEC変動を調べた。このうち、2004年9月5日の紀伊半島沖地震、2007年1月13日の千島列島東方沖地震、2007年3月25日の能登半島地震、2007年7月16日の新潟県中越沖地震の4例において、地震発生から十数分後に震央の位置から遠ざかる方向に伝搬するTEC変動が観測された。さらに、そのうちの3例において、赤道向きに伝搬するTEC変動の振幅が他の方向に伝搬する場合よりも大きいことが明らかになった。この結果は、地震によるTEC変動は、地震に伴って発生した音波が原因であり、音波による中性大気の振動によって電離圏プラズマは磁力線平行方向にのみ動かされるため、このような震央に対する非等方的なTEC変動が起こる、と考えられる。本研究の結果は、地表付近の大気波動が超高層大気に与える影響は小さくないことを表しており、大気の上下結合を解明する重要性を示している。
    2.米国に設置されている1400台以上のGPS受信機を用いて、米国上空における電離圏全電子数の2次元マップを作成した。これまでに、中規模伝搬性電離圏擾乱や電離圏トラフの広域水平二次元構造が明らかになり、新たな観測結果が得られている。さらに、従来知られていない電離圏現象(例えば、線状に1,000km以上細長く伸びた領域でTECが増大・減少し、数10分で消滅する現象)も観測されており、電離圏の2次元観測の有効性が示された。

  24. Study of dynamic and elecimanagnetic conpling processes in the micilatifi vie. ionosphere

    Grant number:18340151  2006 - 2007

    YAMAMOTO Mamoru

      More details

    Authorship:Coinvestigator(s) 

    Coupling processes between plasma and neutral atmosphere is very important to understand the ionosphere. Inhomogeneity of plasma is the source of polarization electric field that maps very long along the geomagnetic field line. We obtained following results in our four research topics.
    Topic 1: Brainstorming for new studies of atmosphere ionosphere coupling processes
    International workshop was held in 2006 for intensive discussion on the topic. Future rocket experiment plan was made through the discussion. and is now proposed to JAXA/ISAS.
    Topic 2: F-region E-region coupling observations
    We conducted FERIX-2 observation campaign with the MU radar (F-region FAI observation), a portable radar in Sakata, Yamagata (E-region FAI observation), and an airglow imager (observation of neutral atmosphere density fluctuation), and directly compared FAIs in both regions. We found that F-region FAI has smaller scale structure that propagate northwestward along the wavefront of the larger structures. E-region FAIs tend to appear where F-region FAIs on the same field line are missing.
    Topic 3: Experiment of small-scale FAI structures with radar imaging technique
    We developed the radar imaging observations of FAIs with the MU radar. We found F- and E-region coupling relationship between the E-region FAIs and MSTID in GPS-TEC. First observations of midlatitude F-region FAIs were also successful. Radar imaging flout this topic was fully utilized in the FERIX-2 observation campaign.
    Topic 4: Ionosphere beacon experiment between satellite/rocket and ground
    We joined the ISAS sounding rocket observations in summer 2007, and conducted rocket-ground beacon experiment. We developed a new digital beacon receiver, and use it for the experiment.

  25. Super Rotation of Atmosphere/Plasma in Thermosphere-Cooperated Observations by Japan, India and Taiwan-

    Grant number:18340147  2006 - 2007

    WATANABE Shigeto

      More details

    Authorship:Coinvestigator(s) 

    In thermosphere where Space shuttle, Space station and satellites are flying, neutral atmosphere are ionized by Solar EUV and X-ray radiations with the ionization rate of 〜0.01%. Since the ionized ions and electrons, plasma, has a constrained motion by local geomagnetic field line, a large momentum transfer occurs between neutral atmosphere and plasma. Recent satellite observations indicated that the plasma controls the motion of neutral atmosphere in low latitude thermosphere, and the force is mapped along geomagnetic field line by ExB drift. The interaction may result in super rotation of neutral atmosphere in low latitude thermosphere. However, no simultaneous observation of neutral atmosphere and plasma has been carried out in the upper thermosphere.
    S520 rocket was launched from Uchinoura space center of JAXA at 19:25 JST on September 2, 2007. Lithium canisters and plasma instruments were equipped the rocket. Lithium gases with 〜1000 K were released three times at 230 km, 190 km and 140 km altitudes. Sunlight was scatted by the lithium gas with the resonance scattering at the wavelength of 670 nm, and was observed from 4 ground stations. We obtained, at the first time, neutral density and temperature profiles in thermosphere. An interaction process between neutral atmosphere and plasma will be made clear from the comparison with the data of plasma instruments. We also obtained the new technology to measure upper thermosphere by gas release, sensitive CCD camera on ground, and image processing.

  26. Observational Research on ionospheric response to EUV irradiance variation of solar flares

    Grant number:17540422  2005 - 2007

    MASUDA Satoshi

      More details

    Authorship:Coinvestigator(s) 

    In this research, we tried to reveal response of the ionosphere to solar activity based on observations. This research has the following four steps; (1) constitution of the database on solar flare X-rays data and EUV irradiance data, (2) observational studies on characteristics of solar flares, (3) development of the method of EUV data analysis and data analysis itself and (4) observational studies on increase of total numbers of electrons (so-called TEC) in the ionosphere due to solar flares. As for the step (1), we made a 10-year catalogue/database for solar flares observed with Yohkoh, including the information of X-ray light curves and flare images. By using this catalogue, we analyzed solar flares statistically for the next step (2). Then, we estimated the density of the solar atmosphere where hard X-rays are emitted. It is also shown that the density depends on energy of the X-ray photons. In the step (3), we developed a new method which estimates EUV flux from soft X-ray flux during solar flares. Because the time resolution is very bad while soft X-ray data are taken continuously. Thanks to this method, we can get virtual EUV flux data any time. In addition to this, we compared EUV flux, F10.7 index, tar (total solar irradiance), and soft X-ray data Then we hard that F10.7 index correlates EUV flux, but can not be used for In the final step (4), we compared zenith angle of the sun, flare intensity, and TEC statistically and revealed that increase of TEC linearly correlated EUV flux from solar flares. The good correlation between TEC derived inn GPS data and EUV flux, indicates that the F-layer of the ionosphere could affect GPS signals. Finally, we found an asymmetry of TEC variations bath in the summer and winter hemispheres. This result suggests that the ionospheric response to EUV flux variations depends on the background condition of the atmosphere

  27. Highly Sensitive Optical Observations of Aurcraand Upper Atmosphere in the Canadian Arctic

    Grant number:16403007  2004 - 2006

    OGAWA Tadahiko

      More details

    Authorship:Coinvestigator(s) 

    Two all-sky airglow/aurora imagers were installed at two Canadian stations at Resolute Bay(RSB)and Athabasca observed polar-cap plasma patches almost always(ATH))in 2005, At RSB, we always during southward IMF periods, From two-dimensional cross-correlation analyses, we determined velocity vectors of the patches, which indicates the ionospheric convection vector, that showed high correlation with the IMF-By and -Bz variations. At ATH, we often observed isolated proton arcs and Stable Auroral Red (SAR) arcs, which were located equatorward of the amoral oval The appearance of the isolated proton arcs was highly correlated with the Pc 1 geomagnetic pulsations measured simultaneously at ATH, suggesting interactions between the electromagnetic ion cyclotron (EMK) waves and protons in the vicinity of the plasmapause and the ring current. Similar interactions without waves were also suggested for the SAR arcs, which appeared after the substorm expansion phase even without geomagnetic storm. These observations show promising capability monitor magnetospheric processes from the ground stations, whit would contribute to the future satellite projects such as THEMES, ERG, and Scope/Xscale

  28. Study of generating mechanism of ionospheric E-region irregularities with rocket/radar simultaneous observations

    Grant number:14340145  2002 - 2003

    FUKAO Shoichiro

      More details

    Authorship:Coinvestigator(s) 

    Ionospheric irregularities in the mid-latitude E-region has been a study topics for more than ten years. The epoch was the discovery of the quasi-periodic (QP) structure in the E-region FAI (Field-Aligned Irregularity) echoes observed with the MU radar in Japan. The QP structures appear in the E-region FAI as a reflection of modulation pattern in the Sporadic-E (Es) layers. The structures are associated with polarization electric field, which suggests strong coupling process between the ionized and neutral atmosphere. In August 2002, we conducted SEEK-2 (Sporadic-E Experiment over Kyushu 2) campaign in Japan under collaboration with scientists from Japan, USA and Taiwan. The SEEK-2 consists of two sounding rockets of Institute of Space and Aeronautical Sciences that include in-situ experiment of electron density, electron temperature, electric field, plasma fluctuation and waves, and geomagnetic field as before. This research program is mainly dedicated to conduct the SEEK-2 ground-based observations. We operated two radars of 24.5 MHz and 31.6 MHz, ionosonde network of Japan, an MF radar, several airglow imagers, and a GPS scintillation-receiver system. We observed intense QP echoes with radars after 23 LT (= UT + 9 hours) on August 3, 2002, and launched rockets into the E-region at 2324 LT and 2339 LT. The operation of the SEEK-2 was very successful as we could, select a good event for the launches. All instruments on the rockets worked fine. We have found that the rockets detected multi-layered Es-layers at 103, 105 and 129 km altitudes, and intense electric fields that approach +-10 mV/m. In March 2003, we hosted the SEEK-2 workshop for data comparison and analysis. From this observation program we published more than 30 papers in the international journals. Numbers of oral presentations from the SEEK-2 results were 21 in international conferences, and 54 in domestic meetings.

  29. Study of the variation of the thermosphere by equatorial atmospheric energy

    Grant number:13136201  2001 - 2006

    OGAWA Tadahiko

      More details

    Authorship:Coinvestigator(s) 

    We have been conducted ground-based observations of the ionosphere and thermosphere in Indonesia, Japan, and Australia We paid special attention to 100-1000 km scale disturbances in the equatorial F-region ionosphere and thermosphere, i.e., medium-scale traveling ionospheric disturbances (MSTIDs) and plasma bubbles. MSTIDs detected with a 630-nm all-sky imager at Kototabang in Indonesia appear within and in the south of the equatorial F-region anomaly crest with a high occurrence in May and June, and have, on the average, a phase velocity of 300 m/s toward the south and a wavelength of 700 km. Plasma bubbles moving eastward at about 100 m/s have a scale of about 100 km with spacings of 200-250 km, and are embedded within plasma structures with an east-west scale of about 1000 km. MSTIDs and giant plasma bubbles can be simultaneously detected at lower midlatitudes in Japan and Australia that are connected by the geomagnetic field line, and are very identical in appearance in the both hemispheres. Equatorial ionospheric scintillations of GPS radio waves associated with plasma bubbles have been continuously monitored at Kototabang. They appear predominantly from sunset to midnight in equinoctial months, a characteristic of equatorial plasma bubble occurrences. To investigate possible dynamical coupling between the ionosphere/thermosphere and troposphere over the equator, we compare the scintillation activity and Earth's brightness temperature (Tbb) variation over the Indian Ocean. The results indicate the following: 1) the scintillation occurrence and Tbb variation are modulated by planetary waves with periods from a few days to several tens of days, and 2) the scintillation tend to be enhanced when high and low Tbb regions appear in the west of Kototabang, suggesting that plasma bubbles may be seeded by atmospheric gravity waves propagating upward from the troposphere.

  30. Geomagnetic conjugate observation of therinospheric waves at midlatitudes

    Grant number:13573006  2001 - 2004

    SHIOKAWA Kazuo

      More details

    Authorship:Coinvestigator(s) 

    (1)We have investigated a nighttime medium-scale traveling ionospheric disturbance(MSTID) observed by an airglow imager at Shigaraki, Japan. The structure was identified in the airglow images of OI (630.0 nm and 777.4 nm) as NW-SE band structures moving southwestward with a velocity of 50 m/s. We found that an electric field oscillation of -1.2 mV/m was sufficient to reproduce the observed airglow amplitudes. This modeled electric field was comparable to that observed by the DMSP F15 satellite as it passed over Shigaraki during our observing period. The DMSP ion drift data show that the oscillation of the polarization electric field correlated with the MSTID structure in the airglow image.
    (2)We found a large-scale equatorial F-region airglow depletions extending to low-midlatitudes in both hemispheres. The observational sites were located at low-midlatitude geomagnetic conjugate points. Clear depletions of 630.0-nm airglow intensity due to equaterial plasma bubbles were simultaneously observed with two all-sky imagers at Sata, Japan (magnetic latitude 24° N), and its geomagnetic conjugate point, Darwin, Australia (magnetic latitude 22° S). These observations indicate that plasma depletions in the equatorial ionosphere elongate along the geomagnetic field lines.
    (3)We report for the first time simultaneous observations of MSTIDs at geomagnetic conjugate points in both hemispheres, using two all-sky airglow imagers at midlatitudes. A 630-nm all-sky imager at Sata, Japan, detected MSTIDs with a wave front elongated from NW to SE. MSTIDs with a wave front 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 coincide closely with those in the Sata images. This result suggests that polarization electric field plays an important role in the generation of MSTIDs.

  31. Development of a data processing and distribution system for total electron content data of a GPS receiver network

    Grant number:12554016  2000 - 2001

    YAMAMOTO M

      More details

    Authorship:Coinvestigator(s) 

    A system to derive and distribute Total Electron Content (TEC) data over Japan was developed using the observational data of GEONET, a GPS receiver network operated by Geographical Survey Institute. GEONET obtains positioning data from GPS satellites in every 30 seconds at about 1000 receivers. The observed positioning data were converted to vertical TEC considering the geometry between the line-of-sight and the ionosphere. To reduce errors caused by this conversion, the data with low elevation angles were omitted in this process. Using this GEONET TEC data, two-dimensional distribution of TEC over Japan was derived with 30 seconds of temporal resolution and 0.15 degrees of spatial resolution in latitude and longitude. The accuracy of the derived TEC was estimated to be 2-4x10^<16> electron/m^2. Electrical biases inside of the transmitters and receivers were estimated and subtracted from the observed TEC data with the least-square fitting method. All of GEONET data since April in 1999 were processed with this method and newly obtained data are also processed every day. The derived TEC data are stored in a data base and can be accessed through WWW at http://stegps.kugi.kyoto-u.ac.jp/. Four types of data are provided in this data base : ATEC (absolute value of TEC for each receiver), TEC (TEC data for each receiver containing biases), AGRJD (two-dimensional distribution of absolute TEC over Japan) and GRID (two-dimensional distribution of perturbation TEC). Two-dimensional maps of TEC are also stored in the data base. The data base has interactive plot pages to make plots of TEC at any given dates and positions. Using this data base, several studies on the mid-latitude ionosphere were carried out. The medium-scale traveling ionospheric disturbances were detected by the GEONET TEC data and compared with the data by the other measurements, such as air-glow imagers and the MU radar. Ionospheric disturbances during the geomagnetic storm periods were studied in detail with GEONET TEC data.

  32. Three-dimensional imaging of atmospheric waves in the thermosphere using network observations over Japan

    Grant number:11440145  1999 - 2002

    OGAWA Tadahiko

      More details

    Authorship:Coinvestigator(s) 

    1) Routine observation of airglow image has been started since July 2000 at Sata (Kagoshima) and since October 2001 at Darwin (Australia) during this research period. Together with Rikubetsu (Hokkaido) and Shigaraki (Siga) (since October 1998), these four stations continue taking airglow images. Campaign observations were carried out at Okinawa (August, 1999) and Tanegashima (August 2002). A Fabry-Perot interferometer (FPI) measures mesospheric and thermospheric wind since October 2000 at Shigaraki. Quick-look plots of these routine measurements are available at http://stdb2.stelab.nagoya-u.ac.jp/omti/.
    2) Results for gravity waves in the mesopause region : a) Climatology (occurrence, propagation directions, and so on) of gravity waves were obtained from statistical study of airglow images at these Japanese and Australian stations. b) Localized (isolated) structure was found in the mesopause region. We suggest that nonlinear wave-wave interactions caused this structure. c) Heights of gravity waves and airglow emissions were determined by a triangulation technique using airglow images obtained at two nearby sites.
    3) Results for medium-scale traveling ionospheric disturbance (MSTID) : a) Climatology (occurrence, wavelength, propagation directions, and so on) of MSTIDs were obtained from statistical study of airglow images in Japan. b) Based on a comparison of satellite data and model calculations including background wind information from FPI, we show that the MSTIDs are not directly caused by gravity waves, but correspond to the electric field structure generated by some ionospheric instability. c) Based on simultaneous airglow imaging observations in Japan and Australia, we found that this electric field structure propagates along magnetic field line between the two hemispheres.
    4) Results for large-scale traveling ionospheric disturbance (LSTID) : LSTIDs were identified as 630-nm airglow enhancement during magnetic storms. We showed on the basis of model calculations and direct wind measurements that this LSTID was caused by poleward wind enhancement (propagating equatorward) in the thermosphere. We also argued from the observed auroral zone energy input that simple wind generation model in the auroral zone did not explain the observed LSTID features.
    5) Based on the simultaneous airglow imaging observations in Japan and Australia, we found symmetric plasma bubble structures between the two hemispheres.
    6) During the research period, we have succeeded observations of low-latitude aurora 11 times in the northern part of Japan (Hokkaido). Two of them were observed in the mainland of Japan (Shigaraki), making a record of lowest latitude of auroral measurement in Japan.
    7) From simultaneous measurement of mesospheric wind by the FPI and the MU radar, temporal variations of airglow emission height were estimated.

▼display all

 

Teaching Experience (On-campus) 6

  1. ionospheric physics

    2017

  2. ionospheric physics

    2016

  3. ionospheric physics

    2015

  4. ionospheric physics

    2014

  5. ionospheric physics

    2013

  6. ionospheric physics

    2012

▼display all

Teaching Experience (Off-campus) 1

  1. 中・低緯度電離圏擾乱の電波・光学観測

    2013.4 - 2014.3 Kyoto University)

 

Social Contribution 1

  1. 出前授業

    2015.11

     More details

    11月13日(金)に北海道陸別町の陸別小学校と陸別中学校で、本研究所及び北海道大学、北見工業大学の教員と大学院生による出前授業が実施されました。本研究所からは大塚雄一准教授と4名の大学院生が参加し、出前授業「夜空が光る?大気光について」によって、夕焼けが赤く見える仕組みなどを説明しました。また、翌14日(土)にはりくべつ宇宙地球科学館・銀河の森天文台において市民の皆さんを対象とした科学イベント「驚き!おもしろ科学実験2015」が実施され、直径1メートルの半球型スクリーンに地球や惑星の映像を投影する科学実験「動かしてみよう、四次元地球儀」を行いました。この事業は本研究所が事務局を務める陸別社会連携連絡協議会の活動の一環として、本学の総長裁量経費(地域貢献戦略枠)の支援のもとで実施されたものです。