研究者詳細 - 大塚　雄一

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

その他リンク： https://link.springer.com/article/10.1186/s40623-021-01486-1/fulltext.html

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

POLAR SCIENCE 28 巻 2021年6月

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

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 126 巻 ( 5 ) 2021年5月

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

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 126 巻 ( 5 ) 2021年5月

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

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 126 巻 ( 5 ) 2021年5月

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

Watanabe, K; Jin, H; Nishimoto, S; Imada, S; Kawai, T; Kawate, T; Otsuka, Y; Shinbori, A; Tsugawa, T; Nishioka, M

EARTH PLANETS AND SPACE 73 巻 ( 1 ) 2021年4月

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

Inaba, Y; Shiokawa, K; Oyama, S; Otsuka, Y; Connors, M; Schofield, I; Miyoshi, Y; Imajo, S; Shinbori, A; Gololobov, AY; Kazama, Y; Wang, SY; Tam, SWY; Chang, TF; Wang, BJ; Asamura, K; Yokota, S; Kasahara, S; Keika, K; Hori, T; Matsuoka, A; Kasahara, Y; Kumamoto, A; Matsuda, S; Kasaba, Y; Tsuchiya, F; Shoji, M; Kitahara, M; Nakamura, S; Shinohara, I; Spence, HE; Reeves, GD; Macdowall, RJ; Smith, CW; Wygant, JR; Bonnell, JW

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 126 巻 ( 4 ) 2021年4月

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

Narayanan, VL; Nozawa, S; Oyama, SI; Mann, I; Shiokawa, K; Otsuka, Y; Saito, N; Wada, S; Kawahara, TD; Takahashi, T

ATMOSPHERIC CHEMISTRY AND PHYSICS 21 巻 ( 4 ) 頁： 2343 - 2361 2021年2月

Comparison of seasonal and longitudinal variation of daytime MSTID activity using GPS observation and GAIA simulations Open Access

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

EARTH PLANETS AND SPACE 73 巻 ( 1 ) 2021年2月

On the Generation of an Unseasonal EPB Over South East Asia

Currie, JL; Carter, BA; Retterer, J; Dao, T; Pradipta, R; Caton, R; Groves, K; Otsuka, Y; Yokoyama, T; Hozumi, K; Le Truong, T; Terkildsen, M

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 126 巻 ( 2 ) 2021年2月

Multi-Wavelength Imaging Observations of STEVE at Athabasca, Canada Open Access

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 126 巻 ( 2 ) 2021年2月

Solar activity dependence of medium-scale traveling ionospheric disturbances using GPS receivers in Japan Open Access

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

EARTH PLANETS AND SPACE 73 巻 ( 1 ) 2021年1月

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

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

SURVEYS IN GEOPHYSICS 42 巻 ( 1 ) 頁： 201 - 238 2021年1月

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

Inaba, Y; Shiokawa, K; Oyama, S; Otsuka, Y; Oksanen, A; Shinbori, A; Gololobov, AY; Miyoshi, Y; Kazama, Y; Wang, SY; Tam, SWY; Chang, TF; Wang, BJ; Yokota, S; Kasahara, S; Keika, K; Hori, T; Matsuoka, A; Kasahara, Y; Kumamoto, A; Kasaba, Y; Tsuchiya, F; Shoji, M; Shinohara, I; Stolle, C

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 125 巻 ( 10 ) 2020年10月

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

Ram, ST; Ajith, KK; Yokoyama, T; Yamamoto, M; Hozumi, K; Shiokawa, K; Otsuka, Y; Li, G

GEOPHYSICAL RESEARCH LETTERS 47 巻 ( 13 ) 2020年7月

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

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

EARTH PLANETS AND SPACE 72 巻 ( 1 ) 2020年7月

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

Hosokawa, K; Takami, K; Saito, S; Ogawa, Y; Otsuka, Y; Shiokawa, K; Chen, CH; Lin, CH

EARTH PLANETS AND SPACE 72 巻 ( 1 ) 2020年5月

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

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

7TH INTERNATIONAL SEMINAR ON AEROSPACE SCIENCE AND TECHNOLOGY (ISAST 2019) 2226 巻 2020年

New observations of the total electron content and ionospheric scintillations over Ho Chi Minh city Open Access

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

VIETNAM JOURNAL OF EARTH SCIENCES 42 巻 ( 4 ) 頁： 320 - 333 2020年

Capability of Geomagnetic Storm Parameters to Identify Severe Space Weather Open Access

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

ASTROPHYSICAL JOURNAL 887 巻 ( 1 ) 2019年12月

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

Okoh, D; Seemala, G; Rabiu, B; Habarulema, JB; Jin, SG; Shiokawa, K; Otsuka, Y; Aggarwal, M; Uwamahoro, J; Mungufeni, P; Segun, B; Obafaye, A; Ellahony, N; Okonkwo, C; Tshisaphungo, M; Shetti, D

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 124 巻 ( 12 ) 頁： 10512 - 10532 2019年12月

Investigation of Spatiotemporal Morphology of Plasma Bubbles Based on EAR Observations 査読有り

Joshi, LM; Tsai, LC; Su, SY; Otsuka, Y; Yokoyama, T; Yamamoto, M; Sarkhel, S; Hozumi, K; Lu, CH

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 124 巻 ( 12 ) 頁： 10549 - 10563 2019年12月

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 査読有り Open Access

Tsuchiya, S; Shiokawa, K; Fujinami, H; Otsuka, Y; Nakamura, T; Connors, M; Schofield, I; Shevtsov, B; Poddelskiy, I

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 124 巻 ( 10 ) 頁： 8110 - 8124 2019年10月

Observation and characterization of traveling ionospheric disturbances induced by solar eclipse of 20 March 2015 using incoherent scatter radars and GPS networks 査読有り

Panasenko, SV; Otsuka, Y; van de Kamp, M; Chernogor, LF; Shinbori, A; Tsugawa, T; Nishioka, M

JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS 191 巻 2019年9月

Thermospheric wind variations observed by a Fabry-Perot interferometer at Tromso, Norway, at substorm onsets 査読有り Open Access

Xu, H; Shiokawa, K; Oyama, S; Otsuka, Y

EARTH PLANETS AND SPACE 71 巻 ( 1 ) 2019年8月

Direct Observations of Traveling Ionospheric Disturbances as Focusers of Solar Radiation: Spectral Caustics 査読有り Open Access

Koval, A; Chen, Y; Tsugawa, A; Otsuka, Y; Shinbori, A; Nishioka, M; Brazhenko, A; Stanislavsky, A; Konovalenko, A; Zhang, QH; Monstein, C; Gorgutsa, R

ASTROPHYSICAL JOURNAL 877 巻 ( 2 ) 2019年6月

Response of the Ionosphere-Plasmasphere Coupling to the September 2017 Storm:What Erodes the Plasmasphere so Severley? 査読有り Open Access

Obana, Y; Maruyama, N; Shinbori, A; Hashimoto, KK; Fedrizzi, M; Nosé, M; Otsuka, Y; Nishitani, N; Hori, T; Kumamoto, A; Tsuchiya, F; Matsuda, S; Matsuoka, A; Kasahara, Y; Yoshikawa, A; Miyoshi, Y; Shinohara, I

SPACE WEATHER-THE INTERNATIONAL JOURNAL OF RESEARCH AND APPLICATIONS 17 巻 ( 6 ) 頁： 861 - 876 2019年6月

Spatiotemporal development of pulsating auroral patch associated with discrete chorus elements: Arase and PWING observations 査読有り

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) 頁： 18776063 2019年6月

Development of multivariate ionospheric TEC forecasting algorithm using linear time series model and ARMA over low-latitude GNSS station 査読有り

Ratnam, DV; Otsuka, Y; Sivavaraprasad, G; Dabbakuti, JRKK

ADVANCES IN SPACE RESEARCH 63 巻 ( 9 ) 頁： 2848 - 2856 2019年5月

Multicomponent Analysis of Ionospheric Scintillation Effects Using the Synchrosqueezing Technique for Monitoring and Mitigating their Impact on GNSS Signals 査読有り

Sivavaraprasad, G; Ratnam, DV; Otsuka, Y

JOURNAL OF NAVIGATION 72 巻 ( 3 ) 頁： 669 - 684 2019年5月

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 査読有り

Huang, FQ; Otsuka, Y; Lei, JH; Luan, XL; Dou, XK; Li, GZ

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 124 巻 ( 3 ) 頁： 2312 - 2322 2019年3月

Observations of Low-Latitude Traveling Ionospheric Disturbances by a 630.0-nm Airglow Imager and the CHAMP Satellite Over Indonesia 査読有り Open Access

Moral, AC; Shiokawa, K; Suzuki, S; Liu, HX; Otsuka, Y; Yatini, CY

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 124 巻 ( 3 ) 頁： 2198 - 2212 2019年3月

Visualization of rapid electron precipitation via chorus element wave-particle interactions 査読有り Open Access

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

NATURE COMMUNICATIONS 10 巻 ( 1 ) 2019年1月

Implementation of Hybrid Ionospheric TEC Forecasting Algorithm Using PCA-NN Method 査読有り

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

IEEE JOURNAL OF SELECTED TOPICS IN APPLIED EARTH OBSERVATIONS AND REMOTE SENSING 12 巻 ( 1 ) 頁： 371 - 381 2019年1月

Rapid Loss of Relativistic Electrons by EMIC Waves in the Outer Radiation Belt Observed by Arase, Van Allen Probes, and the PWING Ground Stations 査読有り Open Access

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 45 巻 ( 23 ) 頁： 12720 - 12729 2018年12月

Microscopic Observations of Pulsating Aurora Associated With Chorus Element Structures: Coordinated Arase Satellite-PWING Observations 査読有り Open Access

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; Nosé, 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 45 巻 ( 22 ) 頁： 12125 - 12134 2018年11月

Statistical Analysis of SAR Arc Detachment From the Main Oval Based on 11-Year, AII-sky Imaging Observation at Athabasca, Canada 査読有り Open Access

Takagi, Y; Shiokawa, K; Otsuka, Y; Connors, M; Schofield, I

GEOPHYSICAL RESEARCH LETTERS 45 巻 ( 21 ) 頁： 11539 - 11546 2018年11月

Review of the generation mechanisms of post-midnight irregularities in the equatorial and low-latitude ionosphere 査読有り Open Access

Otsuka, Y

PROGRESS IN EARTH AND PLANETARY SCIENCE 5 巻 2018年9月

Investigation of Nighttime MSTIDS Observed by Optical Thermosphere Imagers at Low Latitudes: Morphology, Propagation Direction, and Wind Filtering 査読有り Open Access

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 123 巻 ( 9 ) 頁： 7843 - 7857 2018年9月

Storm-Enhanced Development of Postsunset Equatorial Plasma Bubbles Around the Meridian 120 degrees E/60 degrees W on 7-8 September 2017 査読有り Open Access

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 123 巻 ( 9 ) 頁： 7985 - 7998 2018年9月

Temporal and Spatial Variations of Storm Time Midlatitude Ionospheric Trough Based on Global GNSS-TEC and Arase Satellite Observations 査読有り

Shinbori, A; Otsuka, Y; Tsugawa, T; Nishioka, M; Kumamoto, A; Tsuchiya, F; Matsuda, S; Kasahara, Y; Matsuoka, A; Ruohoniemi, JM; Shepherd, SG; Nishitani, N

GEOPHYSICAL RESEARCH LETTERS 45 巻 ( 15 ) 頁： 7362 - 7370 2018年8月

On the Role of Thermospheric Winds and Sporadic E Layers in the Formation and Evolution of Electrified MSTIDs in Geomagnetic Conjugate Regions 査読有り Open Access

Narayanan V. L., Shiokawa K., Otsuka Y., Neudegg D.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 123 巻 ( 8 ) 頁： 6957 - 6980 2018年8月

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 査読有り Open Access

Tsuchiya, S; Shiokawa, K; Fujinami, H; Otsuka, Y; Nakamura, T; Yamamoto, M

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 123 巻 ( 8 ) 頁： 6930 - 6947 2018年8月

On the Solstice Maxima and Azimuth-Dependent Characteristics of the 150-km Echoes Observed Using the Equatorial Atmosphere Radar 査読有り

Chaitanya, PP; Patra, AK; Otsuka, Y; Yokoyama, T; Yamamoto, M

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 123 巻 ( 8 ) 頁： 6752 - 6759 2018年8月

Quantum criticality in the metal-superconductor transition of interacting Dirac fermions on a triangular lattice 査読有り Open Access

Otsuka Yuichi, Seki Kazuhiro, Sorella Sandro, Yunoki Seiji

PHYSICAL REVIEW B 98 巻 ( 3 ) 2018年7月

Equatorial plasma bubble seeding by MSTIDs in the ionosphere 査読有り Open Access

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

PROGRESS IN EARTH AND PLANETARY SCIENCE 5 巻 ( 1 ) 2018年6月

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 13 巻 ( 3 ) 頁： 535-545 2018年6月

Total Electron Content Observations by Dense Regional and Worldwide International Networks of GNSS 査読有り

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 13 巻 ( 3 ) 頁： 535 - 545 2018年6月

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 査読有り Open Access

Yamamoto, M; Otsuka, Y; Jin, H; Miyoshi, Y

PROGRESS IN EARTH AND PLANETARY SCIENCE 5 巻 2018年5月

Spatial and temporal characteristics of ionospheric total electron content over Indian equatorial and low-latitude GNSS stations 査読有り

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 2018- 巻頁： 105 - 108 2018年3月

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

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

DOI： 10.1109/SPACES.2018.8316326

Daily and seasonal variations in the linear growth rate of the Rayleigh-Taylor instability in the ionosphere obtained with GAIA 査読有り Open Access

Shinagawa, H; Jin, H; Miyoshi, Y; Fujiwara, H; Yokoyama, T; Otsuka, Y

PROGRESS IN EARTH AND PLANETARY SCIENCE 5 巻 2018年3月

Medium-Scale Traveling Ionospheric Disturbances Observed by Detrended Total Electron Content Maps Over Brazil 査読有り Open Access

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 123 巻 ( 3 ) 頁： 2215 - 2227 2018年3月

Daytime F-region irregularity triggered by rocket-induced ionospheric hole over low latitude 査読有り Open Access

Li, GZ; Ning, BQ; Abdu, MA; Wang, C; Otsuka, Y; Wan, WX; Lei, JH; Nishioka, M; Tsugawa, T; Hu, LH; Yang, GT; Yan, CX

PROGRESS IN EARTH AND PLANETARY SCIENCE 5 巻 ( 1 ) 2018年2月

Discovery of 1Hz Range Modulation of Isolated Proton Aurora at Subauroral Latitudes 査読有り Open Access

Ozaki, M; Shiokawa, K; Miyoshi, Y; Kataoka, R; Connors, M; Inoue, T; Yagitani, S; Ebihara, Y; Jun, CW; Nomura, R; Sakaguchi, K; Otsuka, Y; Uchida, HA; Schofield, I; Danskin, DW

GEOPHYSICAL RESEARCH LETTERS 45 巻 ( 3 ) 頁： 1209 - 1217 2018年2月

Observations of Ultrawideband Signals in GPS TEC Variations over Europe during Solar Eclipse 査読有り

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) 頁： 115 - 118 2018年

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

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

First Study on the Occurrence Frequency of Equatorial Plasma Bubbles over West Africa Using an All-Sky Airglow Imager and GNSS Receivers 査読有り Open Access

Okoh, D; Rabiu, B; Shiokawa, K; Otsuka, Y; Segun, B; Falayi, E; Onwuneme, S; Kaka, R

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 122 巻 ( 12 ) 頁： 12430 - 12444 2017年12月

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 査読有り Open Access

Shiokawa, K; Katoh, Y; Hamaguchi, Y; Yamamoto, Y; Adachi, T; Ozaki, M; Oyama, SI; Nosé, M; Nagatsuma, T; Tanaka, Y; Otsuka, Y; Miyoshi, Y; Kataoka, R; Takagi, Y; Takeshita, Y; Shinbori, A; Kurita, S; Hori, T; Nishitani, N; Shinohara, I; Tsuchiya, F; Obana, Y; Suzuki, S; Takahashi, N; Seki, K; Kadokura, A; Hosokawa, K; Ogawa, Y; Connors, M; Ruohoniemi, JM; Engebretson, M; Turunen, E; Ulich, T; Manninen, J; Raita, T; Kero, A; Oksanen, A; Back, M; Kauristie, K; Mattanen, J; Baishev, D; Kurkin, V; Oinats, A; Pashinin, A; Vasilyev, R; Rakhmatulin, R; Bristow, W; Karjala, M

EARTH PLANETS AND SPACE 69 巻 2017年11月

The Solar Flux Dependence of Ionospheric 150 km Radar Echoes and Implications 査読有り Open Access

Patra, AK; Chaitanya, PP; St-Maurice, JP; Otsuka, Y; Yokoyama, T; Yamamoto, M

GEOPHYSICAL RESEARCH LETTERS 44 巻 ( 22 ) 頁： 11257 - 11264 2017年11月

On the effect of thermospheric neutral winds on post-midnight field-aligned irregularities at low latitudes 査読有り

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 2017- 巻頁： 1 - 4 2017年11月

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

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

DOI： 10.23919/URSIGASS.2017.8105106

Geomagnetically conjugate observations of ionospheric and thermospheric variations accompanied by a midnight brightness wave at low latitudes (vol 69, 112, 2017) 査読有り Open Access

Fukushima, D; Shiokawa, K; Otsuka, Y; Kubota, M; Yokoyama, T; Nishioka, M; Komonjinda, S; Yatini, CY

EARTH PLANETS AND SPACE 69 巻 2017年11月

Characteristics of Seasonal Variation and Solar Activity Dependence of the Geomagnetic Solar Quiet Daily Variation 査読有り

Shinbori, A; Koyama, Y; Nosé, M; Hori, T; Otsuka, Y

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 122 巻 ( 10 ) 頁： 10796 - 10810 2017年10月

Geomagnetically conjugate observations of ionospheric and thermospheric variations accompanied by a midnight brightness wave at low latitudes 査読有り Open Access

Fukushima, D; Shiokawa, K; Otsuka, Y; Kubota, M; Yokoyama, T; Nishioka, M; Komonjinda, S; Yatini, CY

EARTH PLANETS AND SPACE 69 巻 2017年8月

Daytime zonal drifts in the ionospheric 150km and E regions estimated using EAR observations 査読有り

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 122 巻 ( 8 ) 頁： 9045 - 9055 2017年8月

Sixteen year variation of horizontal phase velocity and propagation direction of mesospheric and thermospheric waves in airglow images at Shigaraki, Japan 査読有り Open Access

Takeo, D; Shiokawa, K; Fujinami, H; Otsuka, Y; Matsuda, TS; Ejiri, MK; Nakamura, T; Yamamoto, M

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 122 巻 ( 8 ) 頁： 8770 - 8780 2017年8月

Equinoctial asymmetry in the zonal distribution of scintillation as observed by GPS receivers in Indonesia 査読有り Open Access

Abadi, P; Otsuka, Y; Shiokawa, K; Husin, A; Liu, HX; Saito, S

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 122 巻 ( 8 ) 頁： 8947 - 8958 2017年8月

Sixteen-year variation of horizontal phase velocity and propagation direction of mesospheric and thermospheric waves in airglow images at Shigaraki 査読有り Open Access

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

Journal of Geophysical Research -Atmospheres 122 巻頁： 8770-8780 2017年8月

記述言語：英語掲載種別：研究論文（学術雑誌）

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

DOI： 10.0002/2017JA023919

Explicit characteristics of evolutionary-type plasma bubbles observed from Equatorial Atmosphere Radar during the low to moderate solar activity years 2010-2012 査読有り

Coordinated observations of postmidnight irregularities and thermospheric neutral winds and temperatures at low latitudes 査読有り Open Access

Dao, T; Otsuka, Y; Shiokawa, K; Nishioka, M; Yamamoto, M; Buhari, SM; Abdullah, M; Husin, A

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 122 巻 ( 7 ) 頁： 7504 - 7518 2017年7月

Detection of Plasma Bubble in Ionosphere using GPS Receivers in Southeast Asia 査読有り Open Access

Buhari, SM; Abdullah, M; Otsuka, Y; Yokoyama, T; Nishioka, M; Hasbi, AM; Tsugawa, T

SAINS MALAYSIANA 46 巻 ( 6 ) 頁： 879 - 885 2017年6月

Measurement of thermospheric temperatures using OMTI Fabry-Perot interferometers with 70-mm etalon 査読有り Open Access

Nakamura, Y; Shiokawa, K; Otsuka, Y; Oyama, S; Nozawa, S; Komolmis, T; Komonjida, S; Neudegg, D; Yuile, C; Meriwether, J; Shinagawa, H; Jin, H

EARTH PLANETS AND SPACE 69 巻 2017年4月

Large-scale traveling ionospheric disturbances observed by GPS dTEC maps over North and South America on Saint Patrick's Day storm in 2015 査読有り Open Access

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 122 巻 ( 4 ) 頁： 4755 - 4763 2017年4月

Climatology of successive equatorial plasma bubbles observed by GPS ROTI over Malaysia 査読有り Open Access

Buhari, SM; Abdullah, M; Yokoyama, T; Otsuka, Y; Nishioka, M; Hasbi, AM; Bahari, SA; Tsugawa, T

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 122 巻 ( 2 ) 頁： 2174 - 2184 2017年2月

STATISTICAL ANALYSIS OF THE OCCURRENCES OF MSTIDs OBSERVED BY ALL-SKY IMAGER IN LOW MAGNETIC LATITUDE 査読有り

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

The first long-term all-sky imager observation of lunar sodium tail 査読有り

Nishino, MN; Shiokawa, K; Otsuka, Y

ICARUS 280 巻頁： 199 - 204 2016年12月

Three years of concentric gravity wave variability in the mesopause as observed by IMAP/VISI 査読有り

Perwitasari, S; Sakanoi, T; Nakamura, T; Ejiri, MK; Tsutsumi, M; Tomikawa, Y; Otsuka, Y; Yamazaki, A; Saito, A

GEOPHYSICAL RESEARCH LETTERS 43 巻 ( 22 ) 頁： 11528 - 11535 2016年11月

Ionospheric TEC Weather Map Over South America 査読有り Open Access

Takahashi, H; Wrasse, CM; Denardini, CM; Pádua, MB; de Paula, ER; Costa, SMA; Otsuka, Y; Shiokawa, K; Monico, JFG; Ivo, A; Sant'Anna, N

SPACE WEATHER-THE INTERNATIONAL JOURNAL OF RESEARCH AND APPLICATIONS 14 巻 ( 11 ) 頁： 937 - 949 2016年11月

On the fresh development of equatorial plasma bubbles around the midnight hours of June solstice 査読有り

Ajith, KK; Ram, ST; Yamamoto, M; Otsuka, Y; Niranjan, K

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 121 巻 ( 9 ) 頁： 9051 - 9062 2016年9月

Fast modulations of pulsating proton aurora related to subpacket structures of Pc1 geomagnetic pulsations at subauroral latitudes 査読有り Open Access

Ozaki, M; Shiokawa, K; Miyoshi, Y; Kataoka, R; Yagitani, S; Inoue, T; Ebihara, Y; Jun, CW; Nomura, R; Sakaguchi, K; Otsuka, Y; Shoji, M; Schofield, I; Connors, M; Jordanova, VK

GEOPHYSICAL RESEARCH LETTERS 43 巻 ( 15 ) 頁： 7859 - 7866 2016年8月

Enhanced ionospheric plasma bubble generation in more active ITCZ 査読有り Open Access

Li, GZ; Otsuka, Y; Ning, BQ; Abdu, MA; Yamamoto, M; Wan, WX; Liu, LB; Abadi, P

GEOPHYSICAL RESEARCH LETTERS 43 巻 ( 6 ) 頁： 2389 - 2395 2016年3月

Altitude development of postmidnight F region field-aligned irregularities observed using Equatorial Atmosphere Radar in Indonesia 査読有り Open Access

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

GEOPHYSICAL RESEARCH LETTERS 43 巻 ( 3 ) 頁： 1015 - 1022 2016年2月

Pulsating proton aurora caused by rising tone Pc1 waves 査読有り Open Access

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 121 巻 ( 2 ) 頁： 1608 - 1618 2016年2月

Duskside enhancement of equatorial zonal electric field response to convection electric fields during the St. Patrick's Day storm on 17 March 2015 査読有り Open Access

Ram, ST; Yokoyama, T; Otsuka, Y; Shiokawa, K; Sripathi, S; Veenadhari, B; Heelis, R; Ajith, KK; Gowtam, VS; Gurubaran, S; Supnithi, P; Le Huy, M

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 121 巻 ( 1 ) 頁： 538 - 548 2016年1月

ISS-IMAPによる大気光波状構造の観測 Open Access

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

第29回大気圏シンポジウム: 講演集録 2016年

TEC variation during high and low solar activities over South American sector 査読有り

Jonah, OF; de Paula, ER; Muella, MTAH; Dutra, SLG; Kherani, EA; Negreti, PMS; Otsuka, Y

JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS 135 巻頁： 22 - 35 2015年12月

A direct link between chorus emissions and pulsating aurora on timescales from milliseconds to minutes: A case study at subauroral latitudes 査読有り Open Access

Ozaki, M; Yagitani, S; Sawai, K; Shiokawa, K; Miyoshi, Y; Kataoka, R; Ieda, A; Ebihara, Y; Connors, M; Schofield, I; Katoh, Y; Otsuka, Y; Sunagawa, N; Jordanova, VK

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 120 巻 ( 11 ) 頁： 9617 - 9631 2015年11月

Coordinated airglow observations between IMAP/VISI and a ground-based all-sky imager on concentric gravity wave in the mesopause 査読有り Open Access

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 120 巻 ( 11 ) 頁： 9706 - 9721 2015年11月

Multi-instrument, high-resolution imaging of polar cap patch transportation 査読有り Open Access

Thomas, EG; Hosokawa, K; Sakai, J; Baker, JBH; Ruohoniemi, JM; Taguchi, S; Shiokawa, K; Otsuka, Y; Coster, AJ; St-Maurice, JP; McWilliams, KA

RADIO SCIENCE 50 巻 ( 9 ) 頁： 904 - 915 2015年9月

Plasma bubble monitoring by TEC map and 630 nm airglow image 査読有り Open Access

Takahashi, H; Wrasse, CM; Otsuka, Y; Ivo, A; Gomes, V; Paulino, I; Medeiros, AF; Denardini, CM; Sant'Anna, N; Shiokawa, K

JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS 130 巻頁： 151 - 158 2015年8月

Statistical study of auroral fragmentation into patches 査読有り Open Access

Hashimoto, A; Shiokawa, K; Otsuka, Y; Oyama, S; Nozawa, S; Hori, T; Lester, M; Johnsen, MG

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 120 巻 ( 8 ) 頁： 6207 - 6217 2015年8月

Fresh and evolutionary-type field-aligned irregularities generated near sunrise terminator due to overshielding electric fields 査読有り Open Access

Ram, ST; Ajith, KK; Yamamoto, M; Otsuka, Y; Yokoyama, T; Niranjan, K; Gurubaran, S

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 120 巻 ( 7 ) 頁： 5922 - 5930 2015年7月

Effects of pre-reversal enhancement of E x B drift on the latitudinal extension of plasma bubble in Southeast Asia 査読有り Open Access

Abadi, P; Otsuka, Y; Tsugawa, T

EARTH PLANETS AND SPACE 67 巻 2015年5月

Airglow-imaging observation of plasma bubble disappearance at geomagnetically conjugate points 査読有り Open Access

Shiokawa, K; Otsuka, Y; Lynn, KJW; Wilkinson, P; Tsugawa, T

EARTH PLANETS AND SPACE 67 巻頁： 1 - 12 2015年3月

Geomagnetically conjugate observation of plasma bubbles and thermospheric neutral winds at low latitudes 査読有り

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 120 巻 ( 3 ) 頁： 2222 - 2231 2015年3月

Ajith, KK; Ram, ST; Yamamoto, M; Yokoyama, T; Gowtam, VS; Otsuka, Y; Tsugawa, T; Niranjan, K

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 120 巻 ( 2 ) 頁： 1371 - 1382 2015年2月

CDF data archive and integrated data analysis platform for ERG-related ground data developed by ERG Science Center (ERG-SC) 査読有り

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

宇宙科学情報解析論文誌 JAXA-RR-14-009 巻頁： 75 - 90 2015年

GAST-D flight experiment results with disturbed and quiet ionospheric conditions 査読有り

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) 頁： 1494 - 1499 2015年

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

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

Direct observations of blob deformation during a substorm 査読有り

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

ANNALES GEOPHYSICAE 33 巻 ( 5 ) 頁： 525 - 530 2015年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Climatology of Equatorial Plasma Bubble Observed by MyRTKnet over the Years 2008-2013 査読有り

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) 頁： 101 - 105 2015年

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

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

DOI： 10.1109/IconSpace.2015.7283752

Airglow observations of nighttime medium-scale traveling ionospheric disturbances from Yonaguni: Statistical characteristics and low-latitude limit 査読有り

Long-term variation in the upper atmosphere as seen in the geomagnetic solar quiet daily variation 査読有り Open Access

Shinbori, A; Koyama, Y; Nose, M; Hori, T; Otsuka, Y; Yatagai, A

EARTH PLANETS AND SPACE 66 巻 2014年12月

CME front and severe space weather 査読有り Open Access

Balan, N; Skoug, R; Ram, ST; Rajesh, PK; Shiokawa, K; Otsuka, Y; Batista, IS; Ebihara, Y; Nakamura, T

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 119 巻 ( 12 ) 2014年12月

Continuous generation and two-dimensional structure of equatorial plasma bubbles observed by high-density GPS receivers in Southeast Asia 査読有り Open Access

Buhari, SM; Abdullah, M; Hasbi, AM; Otsuka, Y; Yokoyama, T; Nishioka, M; Tsugawa, T

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 119 巻 ( 12 ) 2014年12月

Narayanan, VL; Shiokawa, K; Otsuka, Y; Saito, S

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 119 巻 ( 11 ) 頁： 9268 - 9282 2014年11月

First spaceborne observation of the entire concentric airglow structure caused by tropospheric disturbance 査読有り Open Access

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

GEOPHYSICAL RESEARCH LETTERS 41 巻 ( 19 ) 頁： 6943 - 6948 2014年10月

Auroral fragmentation into patches 査読有り

Shiokawa, K; Hashimoto, A; Hori, T; Sakaguchi, K; Ogawa, Y; Donovan, E; Spanswick, E; Connors, M; Otsuka, Y; Oyama, SI; Nozawa, S; McWilliams, K

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 119 巻 ( 10 ) 頁： 8249 - 8261 2014年10月

Diagnostics of equatorial and low latitude ionosphere by TEC mapping over Brazil 査読有り

Takahashi, H; Costa, S; Otsuka, Y; Shiokawa, K; Monico, JFG; Paula, E; Nogueira, P; Denardini, CM; Becker-Guedes, F; Wrasse, CM; Ivo, AS; Gomes, VCF; Gargarela, W; Sant'Anna, N; Gatto, R

ADVANCES IN SPACE RESEARCH 54 巻 ( 3 ) 頁： 385 - 394 2014年8月

Observations of GPS scintillation during an isolated auroral substorm 査読有り

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

Progress in Earth and Planetary Sciencs 96693290710.1186/2197-4284-1-1 巻 2014年8月

Vertical ExB drifts from radar and C/NOFS observations in the Indian and Indonesian sectors: Consistency of observations and model 査読有り Open Access

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 119 巻 ( 5 ) 頁： 3777 - 3788 2014年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

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

Global imaging of polar cap patches with dual airglow imagers 査読有り Open Access

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

GEOPHYSICAL RESEARCH LETTERS 41 巻 ( 1 ) 頁： 1 - 6 2014年1月

赤道大気レーダーを用いた高度150km沿磁力線不規則構造のドリフト速度に関する研究査読有り Open Access

大塚雄一, 水谷徳仁, 塩川和夫, Amit Patra, 横山竜宏, 山本衛

南極資料頁：印刷中 2014年

The observation of equatorial plasma bubble using all sky imager and GPS TEC measurement 査読有り

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年

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

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

Vertical ExB drifts from radar and C/NOFS observations in the Indian and Indonesian sectors: Consistency of observations and model 査読有り Open Access

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

Journal of Geophysical Research: Space Physics 119 巻 ( 5 ) 頁： 3777 - 3788 2014年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Two-dimensional structure of equatorial plasma bubble observed using GPS networks in South East Asia region 査読有り

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

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

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

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

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年

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年

赤道大気レーダーを用いた高度150km沿磁力線不規則構造のドリフト速度に関する研究査読有り Open Access

大塚雄一, 水谷徳仁, 塩川和夫, Amit Patra, 横山竜宏, 山本衛

南極資料 57 巻 ( 3 ) 頁： 369-378 2013年11月

Typhoon-induced concentric airglow structures in the mesopause region 査読有り

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

Geophysical Research Letters 40 巻 ( 22 ) 頁： 5983 - 5987 2013年11月

記述言語：英語掲載種別：研究論文（学術雑誌）

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

DOI： 10.1002/2013GL058087

Typhoon-induced concentric airglow structures in the mesopause region 査読有り

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

GEOPHYSICAL RESEARCH LETTERS 40 巻 ( 22 ) 頁： 5983 - 5987 2013年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Two-dimensional simulation of ionospheric variations in the vicinity of the epicenter of the Tohoku-oki earthquake on 11 March 2011 査読有り

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

GEOPHYSICAL RESEARCH LETTERS 40 巻 ( 19 ) 頁： 5009 - 5013 2013年10月

Longitudinal characteristics of spread F backscatter plumes observed with the EAR and Sanya VHF radar in Southeast Asia 査読有り Open Access

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 118 巻 ( 10 ) 頁： 6544 - 6557 2013年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

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

Observation of nighttime medium-scale travelling ionospheric disturbances by two 630-nm airglow imagers near the auroral zone 査読有り

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

JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS 103 巻頁： 184 - 194 2013年10月

Ionogram-based range-time displays for observing relationships between ionosonde satellite traces, spread F and drifting optical plasma depletions 査読有り

Lynn, KJW; Otsuka, Y; Shiokawa, K

JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS 98 巻頁： 105 - 112 2013年6月

Physical mechanisms of the ionospheric storms at equatorial and higher latitudes during the recovery phase of geomagnetic storms 査読有り Open Access

Balan, N; Otsuka, Y; Nishioka, M; Liu, JY; Bailey, GJ

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 118 巻 ( 5 ) 頁： 2660 - 2669 2013年5月

Evidence of gravity wave ducting in the mesopause region from airglow network observations 査読有り Open Access

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

GEOPHYSICAL RESEARCH LETTERS 40 巻 ( 3 ) 頁： 601 - 605 2013年2月

GPS observations of medium-scale traveling ionospheric disturbances over Europe 査読有り Open Access

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

Ann. Geophys. 31 巻頁： 163-172 2013年2月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

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

DOI： doi:10.5194/angeo-31-163-2013

Drift velocities of 150-km field-aligned irregularities observed by the equatorial atmosphere radar 査読有り Open Access

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

Antarctic Record 57 巻 ( 3 ) 頁： 369 - 378 2013年

GPS observations of medium-scale traveling ionospheric disturbances over Europe 査読有り Open Access

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

ANNALES GEOPHYSICAE 31 巻 ( 2 ) 頁： 163 - 172 2013年

Longitudinal characteristics of spread F backscatter plumes observed with the EAR and Sanya VHF radar in Southeast Asia 査読有り Open Access

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

Journal of Geophysical Research: Space Physics 118 巻 ( 10 ) 頁： 6544 - 6557 2013年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

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年

Small-scale ionospheric delay variation associated with plasma bubbles studied with GNSS and optical measurements and its impact on GBAS 査読有り

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) 頁： 1869 - 1874 2013年

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

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

A comparative study of equatorial daytime vertical E x B drift in the Indian and Indonesian sectors based on 150 km echoes 査読有り Open Access

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 117 巻 2012年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Motion of high-latitude nighttime medium-scale traveling ionospheric disturbances associated with auroral brightening 査読有り Open Access

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 117 巻 2012年10月

Motion of high-latitude nighttime medium-scale traveling ionospheric disturbances associated with auroral brightening 査読有り Open Access

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 117 巻 2012年10月

Observation of equatorial nighttime medium-scale traveling ionospheric disturbances in 630-nm airglow images over 7 years 査読有り

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 117 巻 2012年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

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

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 査読有り

M. Nishioka, Y. Otsuka, K. Shiokawa, T. Tsugawa, Effendy, P. Supnithi, T. Nagatsuma, K. T. Murata

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 117 巻 2012年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Response of low-latitude ionosphere to medium-term changes of solar and geomagnetic activity 査読有り

Ivan Kutiev, Yuichi Otsuka, Dora Pancheva, Rod Heelis

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 117 巻 2012年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Overview of Nighttime Ionospheric Instabilities at Low- and Mid-Latitudes: Coupling Aspects Resulting in Structuring at the Mesoscale 査読有り

Disappearance of equatorial plasma bubble after interaction with mid-latitude medium-scale traveling ionospheric disturbance 査読有り Open Access

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

Geophys. Res. Lett. 39 巻 ( L14105 ) 2012年7月

Disappearance of equatorial plasma bubble after interaction with mid-latitude medium-scale traveling ionospheric disturbance 査読有り Open Access

Otsuka, Y; Shiokawa, K; Ogawa, T

GEOPHYSICAL RESEARCH LETTERS 39 巻 2012年7月

Makela, JJ; Otsuka, Y

SPACE SCIENCE REVIEWS 168 巻 ( 1-4 ) 頁： 419 - 440 2012年6月

GPS total electron content variations associated with poleward moving Sun-aligned arcs 査読有り Open Access

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 117 巻 2012年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

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

VHF Radar Observations of Post-Midnight F-Region Field-Aligned Irregularities over Indonesia during Solar Minimum 査読有り

Otsuka, Y., K. Shiokawa, M. Nishioka and Effendy

Indian Journal of Radio and Space Physics (IJRSP) ( 41 ) 頁： 199-207 2012年4月

VHF Radar Observations of Post-Midnight F-Region Field-Aligned Irregularities over Indonesia during Solar Minimum 査読有り

Otsuka, Y, K. Shiokawa, M. Nishioka, Effendy

Indian Journal of Radio and Space Physics (IJRSP) ( 41 ) 頁： 199-207 2012年4月

Seasonal and Local Time Variations of E-Region Field-Aligned Irregularities Observed with 30.8-MHz Radar at Kototabang, Indonesia 査読有り

Otsuka, Y.

International Journal of Geophysics 2012 巻 ( 695793 ) 2012年3月

Polarization of Pc1/EMIC waves and related proton auroras observed at subauroral latitudes 査読有り Open Access

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 117 巻 2012年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Ionospheric and thermospheric storms at equatorial latitudes observed by CHAMP, ROCSAT, and DMSP 査読有り Open Access

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 117 巻 2012年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

A comparative study of equatorial daytime vertical e × B drift in the Indian and Indonesian sectors based on 150 km echoes 査読有り Open Access

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

Journal of Geophysical Research: Space Physics 117 巻 ( 11 ) 2012年

記述言語：英語掲載種別：研究論文（学術雑誌）

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

DOI： 10.1029/2012JA018053

Development of low-cost sky-scanning Fabry-Perot interferometers for airglow and auroral studies 査読有り Open Access

Shiokawa, K; Otsuka, Y; Oyama, S; Nozawa, S; Satoh, M; Katoh, Y; Hamaguchi, Y; Yamamoto, Y; Meriwether, J

EARTH PLANETS AND SPACE 64 巻 ( 11 ) 頁： 1033 - 1046 2012年

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) 132nd 巻頁： ROMBUNNO.B005-18 2012年

GPS total electron content variations associated with poleward moving Sun-aligned arcs 査読有り Open Access

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 117 巻 ( 5 ) 2012年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Motion of high-latitude nighttime medium-scale traveling ionospheric disturbances associated with auroral brightening 査読有り Open Access

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

Journal of Geophysical Research: Space Physics 117 巻 ( 10 ) 2012年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Low-latitude mesosphere, thermosphere, and ionosphere 査読有り

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

International Journal of Geophysics 2012 巻 2012年

Ionospheric and thermospheric storms at equatorial latitudes observed by CHAMP, ROCSAT, and DMSP 査読有り Open Access

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

Journal of Geophysical Research: Space Physics 117 巻 ( 1 ) 2012年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Observation of equatorial nighttime medium-scale traveling ionospheric disturbances in 630-nm airglow images over 7 years 査読有り

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

Journal of Geophysical Research: Space Physics 117 巻 ( 10 ) 2012年

記述言語：英語掲載種別：研究論文（学術雑誌）

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

DOI： 10.1029/2012JA017758

Seasonal and local time variations of e -Region field-aligned irregularities observed with 30.8-mhz radar at kototabang, indonesia 査読有り

Y. Otsuka

International Journal of Geophysics 2012 巻 2012年

記述言語：英語掲載種別：研究論文（学術雑誌）

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

DOI： 10.1155/2012/695793

Response of low-latitude ionosphere to medium-term changes of solar and geomagnetic activity 査読有り

Ivan Kutiev, Yuichi Otsuka, Dora Pancheva, Rod Heelis

Journal of Geophysical Research: Space Physics 117 巻 ( 8 ) 2012年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Polarization of Pc1/EMIC waves and related proton auroras observed at subauroral latitudes 査読有り Open Access

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

Journal of Geophysical Research: Space Physics 117 巻 ( 2 ) 2012年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

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 査読有り

M. Nishioka, Y. Otsuka, K. Shiokawa, T. Tsugawa, Null Effendy, P. Supnithi, T. Nagatsuma, K. T. Murata

Journal of Geophysical Research: Space Physics 117 巻 ( 8 ) 2012年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Simultaneous observations at Darwin of equatorial bubbles by ionosonde-based range/time displays and airglow imaging 査読有り Open Access

Lynn, KJW; Otsuka, Y; Shiokawa, K

GEOPHYSICAL RESEARCH LETTERS 38 巻 2011年12月

On postmidnight low-latitude ionospheric irregularities during solar minimum: 1. Equatorial Atmosphere Radar and GPS-TEC observations in Indonesia 査読有り

T. Yokoyama, M. Yamamoto, Y. Otsuka, M. Nishioka, T. Tsugawa, S. Watanabe, R. F. Pfaff

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 116 巻 2011年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

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

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 116 巻 2011年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Equatorial electrodynamics and neutral background in the Asian sector during the 2009 stratospheric sudden warming 査読有り Open Access

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 116 巻 2011年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

New aspects of thermospheric and ionospheric storms revealed by CHAMP 査読有り Open Access

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 116 巻 2011年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

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

Decay of polar cap patch 査読有り

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 116 巻 2011年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

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

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 査読有り Open Access

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 116 巻 2011年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

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

First satellite-imaging observation of medium-scale traveling ionospheric disturbances by FORMOSAT-2/ISUAL 査読有り

Adachi, T; Otsuka, Y; Yamaoka, M; Yamamoto, M; Shiokawa, K; Chen, AB; Hsu, RR

GEOPHYSICAL RESEARCH LETTERS 38 巻 2011年2月

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

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 116 巻 2011年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Statistical Study of Medium-Scale Traveling Ionospheric Disturbances Observed with a GPS Receiver Network in Japan 査読有り

Otsuka, Y; Kotake, N; Shiokawa, K; Ogawa, T; Tsugawa, T; Saito, A

AERONOMY OF THE EARTH'S ATMOSPHERE AND IONOSPHERE 2 巻 ( 3 ) 頁： 291 - 299 2011年

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 査読有り Open Access

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 116 巻 ( 3 ) 2011年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Acoustic resonance and plasma depletion detected by GPS total electron content observation after the 2011 off the Pacific coast of Tohoku Earthquake 査読有り Open Access

Saito, A; Tsugawa, T; Otsuka, Y; Nishioka, M; Iyemori, T; Matsumura, M; Saito, S; Chen, CH; Goi, Y; Choosakul, N

EARTH PLANETS AND SPACE 63 巻 ( 7 ) 頁： 863 - 867 2011年

Decay of polar cap patch 査読有り

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

Journal of Geophysical Research: Space Physics 116 巻 ( 5 ) 2011年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Equatorial electrodynamics and neutral background in the Asian sector during the 2009 stratospheric sudden warming 査読有り Open Access

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 116 巻 ( 8 ) 2011年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Imaging observation of the Earth's mesosphere, thermosphere and ionosphere by VISI of ISS-IMAP on the International Space Station 査読有り

Sakanoi, T, Akiya, Y, Yamazaki, A, Otsuka, Y, Saito, A, Yoshikawa, I

IEEJ Transactions on Fundamentals and Materials 131 巻 ( 12 ) 頁： 983 - 988 2011年

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

We present the scientific targets, instrumental design, principle of measurement, and development of the Visible and near-Infrared Spectral Imager (VISI) which will be launched onto International Space Station (ISS) in January 2012. VISI is equipped with fast optics including a grism, and a high-sensitivity CCD to obtain airglow emissions at wavelengths of O (630 nm), OH Meinel band (650 nm) and O<sub>2</sub> (0-0) atmospheric band (762 nm). VISI has two field-of-views (FOVs), 45 degrees forward and 45 degrees backward to nadir, to subtract background contaminations. The data acquisition of VISI will be continuously performed with short exposure cycle less than several seconds when ISS is orbiting in the night side of the earth, and then provide the seamless line scanning images of the airglows with a spatial resolution better than 50 km. After manufacturing VISI, we checked its performance though optical and electric function tests as well as environmental tests that are necessary to be launched.

DOI： 10.1541/ieejfms.131.983

CiNii Research

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

New aspects of thermospheric and ionospheric storms revealed by CHAMP 査読有り Open Access

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

Journal of Geophysical Research: Space Physics 116 巻 ( 7 ) 2011年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Motion of polar cap arcs 査読有り

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

Journal of Geophysical Research 116 巻頁： doi:10.1029/2010JA015906 2011年

Long-distance propagation of ionospheric disturbance generated by the 2011 off the Pacific coast of Tohoku Earthquake 査読有り Open Access

Chen, CH; Saito, A; Lin, CH; Liu, JY; Tsai, HF; Tsugawa, T; Otsuka, Y; Nishioka, M; Matsumura, M

EARTH PLANETS AND SPACE 63 巻 ( 7 ) 頁： 881 - 884 2011年

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年

Ionospheric multiple stratifications and irregularities induced by the 2011 off the Pacific coast of Tohoku Earthquake 査読有り Open Access

Maruyama, T; Tsugawa, T; Kato, H; Saito, A; Otsuka, Y; Nishioka, M

EARTH PLANETS AND SPACE 63 巻 ( 7 ) 頁： 869 - 873 2011年

Ionospheric disturbances detected by GPS total electron content observation after the 2011 off the Pacific coast of Tohoku Earthquake 査読有り Open Access

Tsugawa, T; Saito, A; Otsuka, Y; Nishioka, M; Maruyama, T; Kato, H; Nagatsuma, T; Murata, KT

EARTH PLANETS AND SPACE 63 巻 ( 7 ) 頁： 875 - 879 2011年

Numerical simulations of atmospheric waves excited by the 2011 off the Pacific coast of Tohoku Earthquake 査読有り Open Access

Matsumura, M; Saito, A; Iyemori, T; Shinagawa, H; Tsugawa, T; Otsuka, Y; Nishioka, M; Chen, CH

EARTH PLANETS AND SPACE 63 巻 ( 7 ) 頁： 885 - 889 2011年

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 査読有り Open Access

Nishitani, N; Ogawa, T; Otsuka, Y; Hosokawa, K; Hori, T

EARTH PLANETS AND SPACE 63 巻 ( 7 ) 頁： 891 - 896 2011年

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

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

Journal of Geophysical Research: Space Physics 116 巻 ( 11 ) 2011年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

On postmidnight low-latitude ionospheric irregularities during solar minimum: 1. Equatorial Atmosphere Radar and GPS-TEC observations in Indonesia 査読有り

T. Yokoyama, M. Yamamoto, Y. Otsuka, M. Nishioka, T. Tsugawa, S. Watanabe, R. F. Pfaff

Journal of Geophysical Research: Space Physics 116 巻 ( 11 ) 2011年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

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

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

Journal of Geophysical Research: Space Physics 116 巻 ( 1 ) 2011年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Dynamic temporal evolution of polar cap tongue of ionization during magnetic storm 査読有り

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 115 巻 2010年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

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

Midnight latitude-altitude distribution of 630 nm airglow in the Asian sector measured with FORMOSAT-2/ISUAL 査読有り Open Access

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 115 巻 2010年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Large-scale traveling ionospheric disturbance observed by superDARN Hokkaido HF radar and GPS networks on 15 December 2006 査読有り

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 115 巻 2010年6月

Large-scale traveling ionospheric disturbance observed by superDARN Hokkaido HF radar and GPS networks on 15 December 2006 査読有り

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 115 巻 2010年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Nighttime-like quasi periodic echoes induced by a partial solar eclipse 査読有り Open Access

Thampi, SV; Yamamoto, M; Liu, HX; Saito, S; Otsuka, Y; Patra, AK

GEOPHYSICAL RESEARCH LETTERS 37 巻 2010年5月

Longitudinal development of low-latitude ionospheric irregularities during the geomagnetic storms of July 2004 査読有り Open Access

Li, GZ; Ning, BQ; Hu, LH; Liu, LB; Yue, XA; Wan, WX; Zhao, BQ; Igarashi, K; Kubota, M; Otsuka, Y; Xu, JS; Liu, JY

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 115 巻 ( 4 ) 2010年4月

A physical mechanism of positive ionospheric storms at low latitudes and midlatitudes 査読有り Open Access

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 115 巻 2010年2月

Reorganization of polar cap patches through shears in the background plasma convection 査読有り

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 115 巻 2010年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

A physical mechanism of positive ionospheric storms at low latitudes and midlatitudes 査読有り Open Access

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

Journal of Geophysical Research: Space Physics 115 巻 ( 2 ) 2010年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Dynamic temporal evolution of polar cap tongue of ionization during magnetic storm 査読有り

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

Journal of Geophysical Research: Space Physics 115 巻 ( 12 ) 2010年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Large-scale traveling ionospheric disturbance observed by superDARN Hokkaido HF radar and GPS networks on 15 December 2006 査読有り

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

Journal of Geophysical Research: Space Physics 115 巻 ( 6 ) 2010年

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

DOI： 10.1029/2009JA014297

Midnight latitude-altitude distribution of 630 nm airglow in the Asian sector measured with FORMOSAT-2/ISUAL 査読有り Open Access

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 115 巻 ( 9 ) 2010年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Lower-thermospheric wind fluctuations measured with an FPI during pulsating aurora at Tromso, Norway 査読有り Open Access

Oyama, S; Shiokawa, K; Kurihara, J; Tsuda, TT; Nozawa, S; Ogawa, Y; Otsuka, Y; Watkins, BJ

ANNALES GEOPHYSICAE 28 巻 ( 10 ) 頁： 1847 - 1857 2010年

Reorganization of polar cap patches through shears in the background plasma convection 査読有り

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

Journal of Geophysical Research: Space Physics 115 巻 ( 1 ) 2010年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

The STEL induction magnetometer network for observation of high-frequency geomagnetic pulsations 査読有り Open Access

Shiokawa, K; Nomura, R; Sakaguchi, K; Otsuka, Y; Hamaguchi, Y; Satoh, M; Katoh, Y; Yamamoto, Y; Shevtsov, BM; Smirnov, S; Poddelsky, I; Connors, M

EARTH PLANETS AND SPACE 62 巻 ( 6 ) 頁： 517 - 524 2010年

Thermospheric temperature and density variations 査読有り Open Access

Fujiwara, H; Miyoshi, Y; Jin, H; Shinagawa, H; Otsuka, Y; Saito, A; Ishii, M

SOLAR AND STELLAR VARIABILITY: IMPACT ON EARTH AND PLANETS ( 264 ) 頁： 310 - + 2010年

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年

Ionospheric and geomagnetic disturbances during the 2005 Sumatran earthquakes 査読有り

Hasbi, AM; Momani, MA; Ali, MAM; Misran, N; Shiokawa, K; Otsuka, Y; Yumoto, K

JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS 71 巻 ( 17-18 ) 頁： 1992 - 2005 2009年12月

On the gravity wave-driven instability of E layer at mid-latitude 査読有り

Shalimov, S; Ogawa, T; Otsuka, Y

JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS 71 巻 ( 17-18 ) 頁： 1943 - 1947 2009年12月

First observations of large-scale wave structure and equatorial spread F using CERTO radio beacon on the C/NOFS satellite 査読有り Open Access

Thampi, SV; Yamamoto, M; Tsunoda, RT; Otsuka, Y; Tsugawa, T; Uemoto, J; Ishii, M

GEOPHYSICAL RESEARCH LETTERS 36 巻 2009年9月

Coordinated observations of nighttime medium-scale traveling ionospheric disturbances in 630-nm airglow and HF radar echoes at midlatitudes 査読有り Open Access

Suzuki, S; Hosokawa, K; Otsuka, Y; Shiokawa, K; Ogawa, T; Nishitani, N; Shibata, TF; Koustov, AV; Shevtsov, BM

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 114 巻頁： A07312 2009年7月

First simultaneous observations of daytime MSTIDs over North America using GPS-TEC and DEMETER satellite data 査読有り Open Access

Onishi, T; Tsugawa, T; Otsuka, Y; Berthelier, JJ; Lebreton, JP

GEOPHYSICAL RESEARCH LETTERS 36 巻 2009年6月

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

Journal of Geophysical Research: Space Physics 114 巻 ( 5 ) 2009年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

VHF radar observations of nighttime F-region field-aligned irregularities over Kototabang, Indonesia 査読有り Open Access

Otsuka, Y., T. Ogawa, and Effendy

Earth Planets Space 61 巻頁： 431-437 2009年5月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

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.

DOI： 10.1186/BF03353159

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

J. Geophys. Res. 114 巻頁： A05302, doi:10.1029/2008JA013902 2009年5月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

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.

DOI： 10.1029/2008JA013902

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 114 巻 2009年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

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

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

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

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

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

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

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

Unusually elongated, bright airglow plume in the polar cap F region: Is it a tongue of ionization? 査読有り

Hosokawa, K; Tsugawa, T; Shiokawa, K; Otsuka, Y; Ogawa, T; Hairston, MR

GEOPHYSICAL RESEARCH LETTERS 36 巻 2009年4月

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 査読有り

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 114 巻 2009年3月

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 査読有り

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

Journal of Geophysical Research: Space Physics 114 巻 ( 3 ) 2009年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

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 査読有り Open Access

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

Journal of Geophysical Research: Space Physics 114 巻 ( 3 ) 2009年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Super plasma fountain and equatorial ionization anomaly during penetration electric field 査読有り Open Access

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

Journal of Geophysical Research: Space Physics 114 巻 ( 3 ) 2009年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Three-dimensional simulation of the coupled Perkins and es-layer instabilities in the nighttime midlatitude ionosphere 査読有り Open Access

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

Journal of Geophysical Research: Space Physics 114 巻 ( 3 ) 2009年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

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 査読有り Open Access

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 114 巻 2009年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

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

Super plasma fountain and equatorial ionization anomaly during penetration electric field 査読有り Open Access

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 114 巻 2009年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

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

Three-dimensional simulation of the coupled Perkins and E-s-layer instabilities in the nighttime midlatitude ionosphere 査読有り Open Access

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 114 巻 2009年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

Plasma 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

Medium-Scale Traveling Ionospheric Disturbances and Plasma Bubbles Observed by an All-Sky Airglow Imager at Yonaguni, Japan 査読有り

Ogawa, T; Otsuka, Y; Shiokawa, K; Tsugawa, T; Saito, A; Hoshinoo, K; Matunaga, K; Kubota, M; Ishii, M

TERRESTRIAL ATMOSPHERIC AND OCEANIC SCIENCES 20 巻 ( 1 ) 頁： 287 - 295 2009年2月

Effects observed in the ionospheric F region in the east Asian sector during the intense geomagnetic disturbances in the early part of November 2004 査読有り Open Access

Sahai Y., Becker-Guedes F., Fagundes P. R., de Jesus R., de Abreu A. J., Otsuka Y., Shiokawa K., Igarashi K., Yumoto K., Huang C. -S., Lan H. T., Saito A., Guarnieri F. L., Pillat V. G., Bittencourt J. A.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 114 巻 ( 3 ) 2009年1月

Characteristics of equatorial gravity waves derived from mesospheric airglow imaging observations 査読有り Open Access

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

ANNALES GEOPHYSICAE 27 巻 ( 4 ) 頁： 1625 - 1629 2009年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Equatorial GPS ionospheric scintillations over Kototabang, Indonesia and their relation to atmospheric waves from below 査読有り Open Access

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

EARTH PLANETS AND SPACE 61 巻 ( 4 ) 頁： 397 - 410 2009年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：TERRA SCIENTIFIC PUBL CO

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

Observations of the F-region ionospheric irregularities in the South American sector during the October 2003 'Halloween Storms' 査読有り Open Access

Sahai, Y; Becker-Guedes, F; Fagundes, PR; de Abreu, AJ; de Jesus, R; Pillat, VG; Abalde, JR; Martinis, CR; Brunini, C; Gende, M; Huang, CS; Pi, X; Lima, WLC; Bittencourt, JA; Otsuka, Y

ANNALES GEOPHYSICAE 27 巻 ( 12 ) 頁： 4463 - 4477 2009年

Relative effects of electric field and neutral wind on positive ionospheric storms 査読有り Open Access

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

Earth, Planets and Space 61 巻 ( 4 ) 頁： 439 - 445 2009年

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

Propagation characteristics of nighttime mesospheric and thermospheric waves observed by optical mesosphere thermosphere imagers at middle and low latitudes 査読有り Open Access

K. Shiokawa, Y. Otsuka, T. Ogawa

EARTH PLANETS AND SPACE 61 巻 ( 4 ) 頁： 479 - 491 2009年

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

The Optical Mesosphere Thermosphere Imagers (OMTIs) for network measurements of aurora and airglow 査読有り

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 1144 巻頁： 212 - + 2009年

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

Zonal asymmetry of daytime 150-km echoes observed by Equatorial Atmosphere Radar in Indonesia 査読有り Open Access

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

ANNALES GEOPHYSICAE 27 巻 ( 3 ) 頁： 967 - 974 2009年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

VHF radar observations of nighttime F-region field-aligned irregularities over Kototabang, Indonesia 査読有り Open Access

Y. Otsuka, T. Ogawa, Effendy

EARTH PLANETS AND SPACE 61 巻 ( 4 ) 頁： 431 - 437 2009年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：TERRA SCIENTIFIC PUBL CO

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

New observational deployments for SEALION-Airglow measurements using all-sky imagers

Minoru Kubota, Mamoru Ishii, Takuya Tsugawa, Jyunpei Uemoto, Hidekatsu Jin, Yuichi Otsuka, Kazuo Shiokawa

Journal of the National Institute of Information and Communications Technology 56 巻 ( 1-4 ) 頁： 299 - 307 2009年

記述言語：英語掲載種別：研究論文（学術雑誌）

An airglow all-sky imager (ASI)-a new monitoring instrument-is scheduled to be set up in February 2010 at Chiang Mai, Thailand, as part of the framework of the Southeast Asia Low-latitude Ionospheric Network (SEALION) being developed in the Southeast Asian region by the National Institute of Information and Communications Technology (NICT). The ASI images airglow having an emission layer near the ionospheric F-layer in order to observe the two-dimensional structure and time evolution of such ionospheric disturbances as plasma bubbles. In Southeast Asia, the Solar-Terrestrial Environment Laboratory (STE) of Nagoya University has been conducting ASI-based observations at Kototabang, Indonesia, ever since 2002. This paper provides detailed insight into the formation, growth and propagation of plasma bubbles as derived from observational data recorded using ASI at Kototabang and using SEALION ionoson-des and GPS receivers. The functional requirements for another ASI to be installed and ASI-based observation schemes are then discussed based on that insight.

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

Nighttime medium-scale traveling ionospheric disturbances detected by network GPS receivers in Taiwan 査読有り Open Access

Lee, CC; Liou, YA; Otsuka, Y; Chu, FD; Yeh, TK; Hoshinoo, K; Matunaga, K

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 113 巻 ( A12 ) 2008年12月

Shiokawa, K; Otsuka, Y; Nishitani, N; Ogawa, T; Tsugawa, T; Maruyama, T; Smirnov, SE; Bychkov, VV; Shevtsov, BM

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 113 巻 ( A12 ) 2008年12月

Nighttime medium-scale traveling ionospheric disturbances (MSTIDs) observed in 630-nm airglow images at middle latitudes are known to have a predominantly northwest-southeast phase surface and to move southwestward in the Northern Hemisphere of Earth. However, the mechanisms of MSTID generation and their systematic southwestward motion have not been clarified. In this paper, we report the "northeastward" motion of the MSTIDs observed at Paratunka, Far East Russia (52.97°N, 158.25°E), using an all-sky 630-nm airglow imager at 2000-2300 LT on 19 August 2007. The MSTIDs moved first southwestward but then back northeastward in the northern part of the images. The northeastward motion of the MSTIDs took place coincident with a F layer height decrease observed by an ionosonde at Paratunka. The F layer height decrease was also confirmed by an enhancement of the 630-nm airglow intensity, which seemed to propagate from northeast to southwest. This fact suggests that the F layer height decrease was caused by poleward wind enhancement rather than westward electric field. These observations imply that the F layer height decrease or the poleward thermospheric wind has some role in the northeastward turning of the MSTID propagation direction. Copyright 2008 by the American Geophysical Union.

DOI： 10.1029/2008JA013417

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

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

Otsuka, Y., T. Tani, T. Tsugawa, and T. Ogawa

J. Atmos. Solar-Terr. Phys. 70 巻頁： 2196-2202 2008年12月

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

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

JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS 70 巻 ( 17 ) 頁： 2196 - 2202 2008年12月

Decay of 3-m-scale ionospheric irregularities associated with a plasma bubble observed with the Equatorial Atmosphere Radar 査読有り Open Access

Saito, S; Fukao, S; Yamamoto, M; Otsuka, Y; Maruyama, T

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 113 巻 ( A11 ) 2008年11月

F-3 layer during penetration electric field 査読有り Open Access

Balan N., Thampi S. V., Lynn K., Otsuka Y., Alleyne H., Watanabe S., Abdu M. A., Fejer B. G.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 113 巻 2008年9月

Simultaneous appearance of isolated auroral arcs and Pc 1 geomagnetic pulsations at subauroral latitudes 査読有り Open Access

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 113 巻 ( A5 ) 2008年5月

Daytime 150-km echoes observed with the Equatorial Atmosphere Radar in Indonesia: First results 査読有り Open Access

Patra, AK; Yokoyama, T; Otsuka, Y; Yamamoto, M

GEOPHYSICAL RESEARCH LETTERS 35 巻 ( 6 ) 2008年3月

First three-dimensional simulation of the Perkins instability in the nighttime midlatitude ionosphere 査読有り

Yokoyama, T; Otsuka, Y; Ogawa, T; Yamamoto, M; Hysell, DL

GEOPHYSICAL RESEARCH LETTERS 35 巻 ( 3 ) 2008年2月

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

MIDLATITUDE IONOSPHERIC DYNAMICS AND DISTURBANCES 181 巻頁： 271 - 281 2008年

© 2008 by the American Geophysical Union. This paper summarizes our recent observations of storm-time traveling ionospheric disturbances (TIDs) over Japan. The storm-time TIDs, which are often referred as large-scale TIDs or traveling atmospheric disturbances, are generated at high-latitude auroral zone and propagate predominantly equatorward at midlatitudes as atmospheric waves in the thermosphere. The imaging measurements by airglow imagers and GPS networks give reliable wave parameters (wavelength, phase velocity, and amplitude) of TIDs. Comparison of imaging observations of TIDs between the northern and southern hemispheres revealed their nonconjugacy. Combinations of these imaging observations with vertical sounding measurements by ionosondes and radars provide a comprehensive description of TID structures at midlatitudes. Comparison between these observations and the assimilative mapping of the ionospheric electrodynamics technique with the thermosphere-ionosphere electrodynamics general circulation model results in several insights into the generation and propagation of TIDs at the high-latitude source region as well as limitations of the current global model.

DOI： 10.1029/181GM24

Discovery of anoumoulous stripes over the amazon by the PALSAR onboard ALOS satellite 査読有り

Masanobu Shimada, Yasushi Muraki, Yuichi Otsuka

International Geoscience and Remote Sensing Symposium (IGARSS) 2 巻 ( 1 ) 頁： II387 - II390 2008年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

We discovered anomalous stripes over the large area of Amazon when the region was scanned by the radar (PALSAR) onboard ALOS satellite. The stripes appeared on the local midnight along the geomagnetic field line with a typical characteristic width of 600m. ©2008 IEEE.

DOI： 10.1109/IGARSS.2008.4779009

Response of nighttime equatorial and low latitude F-region to the geomagnetic storm of August 18, 2003, in the Brazilian sector 査読有り

Medium-scale traveling ionospheric disturbances detected with dense and wide TEC maps over North America 査読有り Open Access

Tsugawa, T; Otsuka, Y; Coster, AJ; Saito, A

GEOPHYSICAL RESEARCH LETTERS 34 巻 ( 22 ) 2007年11月

Summer-winter hemispheric asymmetry of the sudden increase in ionospheric total electron content and of the O/N-2 ratio: Solar activity dependence 査読有り Open Access

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 112 巻 ( A8 ) 2007年8月

Low-latitude total electron content enhancement at low geomagnetic activity observed over Japan 査読有り Open Access

Kutiev, I; Otsuka, Y; Saito, A; Tsugawa, T

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 112 巻 ( A7 ) 2007年7月

Simultaneous observations of nighttime medium-scale traveling ionospheric disturbances and E region field-aligned irregularities at midlatitude 査読有り Open Access

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 112 巻 ( A6 ) 2007年6月

Ground observation and AMIE-TIEGCM modeling of a storm-time traveling ionospheric disturbance 査読有り Open Access

Shiokawa, K; Lu, G; Otsuka, Y; Ogawa, T; Yamamoto, M; Nishitani, N; Sato, N

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 112 巻 ( A5 ) 2007年5月

Simultaneous ground and satellite observations of an isolated proton arc at subauroral latitudes 査読有り Open Access

Sakaguchi, K; Shiokawa, K; Ieda, A; Miyoshi, Y; Otsuka, Y; Ogawa, T; Connors, M; Donovan, EF; Rich, FJ

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 112 巻 ( A4 ) 2007年4月

An intense gravity wave near the mesopause region observed by a Fabry-Perot interferometer and an airglow imager 査読有り Open Access

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

JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 112 巻 ( D7 ) 2007年4月

Medium-scale traveling ionospheric disturbances observed by GPS receiver network in Japan: a short review 査読有り

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

GPS SOLUTIONS 11 巻 ( 2 ) 頁： 139 - 144 2007年3月

A concentric gravity wave structure in the mesospheric airglow images 査読有り

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

JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 112 巻 ( D2 ) 2007年1月

Simultaneous observations of nighttime medium-scale traveling ionospheric disturbances and E-region field-aligned irregularities at midlatitude 査読有り

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

J. Geophys. Res 頁： doi:10.1029/2005JA011548 2007年

Statistical study of medium-scale traveling ionospheric disturbances observed with the GPS networks in Southern California 査読有り Open Access

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

EARTH PLANETS AND SPACE 59 巻 ( 2 ) 頁： 95 - 102 2007年

The ionospheric response in the Brazilian sector during the super geomagnetic storm on 20 November 2003 査読有り Open Access

Becker-Guedes, F; Sahai, Y; Fagundes, PR; Espinoza, ES; Pillat, VG; Lima, WLC; Basu, S; Basu, S; Otsuka, Y; Shiokawa, K; MacKenzie, EM; Pi, X; Bittencourt, JA

ANNALES GEOPHYSICAE 25 巻 ( 4 ) 頁： 863 - 873 2007年

Sahai, Y; Becker-Guedes, F; Fagundes, PR; Lima, WLC; Otsuka, Y; Huang, CS; Espinoza, ES; Pi, X; de Abreu, AJ; Bolzan, MJA; Pillat, VG; Abalde, JR; Pimenta, AA; Bittencourt, JA

ADVANCES IN SPACE RESEARCH 39 巻 ( 8 ) 頁： 1325 - 1334 2007年

Development of airglow temperature photometers with cooled-CCD detectors 査読有り Open Access

Shiokawa, K; Otsuka, Y; Suzuki, S; Katoh, T; Katohl, Y; Satoh, M; Ogawa, T; Takahashi, H; Gobbli, D; Nakamura, T; Williams, BP; She, CY; Taguchi, M; Shimomai, T

EARTH PLANETS AND SPACE 59 巻 ( 6 ) 頁： 585 - 599 2007年

Gravity wave momentum flux in the upper mesosphere derived from OH airglow imaging measurements 査読有り Open Access

Suzuki, S; Shiokawa, K; Otsuka, Y; Ogawa, T; Kubota, M; Tsutsumi, M; Nakamura, T; Fritts, DC

EARTH PLANETS AND SPACE 59 巻 ( 5 ) 頁： 421 - 428 2007年

Summer-winter hemispheric asymmetry of sudden increase in ionospheric total electron content induced by solar flares: A role of O/N-2 ratio 査読有り Open Access

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 111 巻 ( A11 ) 2006年11月

A fast-propagating, large-scale atmospheric gravity wave observed in the WAVE2004 campaign 査読有り

Kubota, M; Kawamura, S; Abo, M; Koizumi, Y; Murayama, Y; Yamamori, M; Shiokawa, K; Otsuka, Y; Uchiumi, M; Igarashi, K; Abe, T; Oyama, KI; Iwagami, N

JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 111 巻 ( D21 ) 2006年11月

Detection of ruptures of Andaman fault segments in the 2004 great Sumatra earthquake with coseismic ionospheric disturbances 査読有り Open Access

Heki, K; Otsuka, Y; Choosakul, N; Hemmakorn, N; Komolmis, T; Maruyama, T

JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH 111 巻 ( B9 ) 2006年9月

Estimating drift velocity of polar cap patches with all-sky airglow imager at Resolute Bay, Canada 査読有り

Hosokawa, K; Shiokawa, K; Otsuka, Y; Nakajima, A; Ogawa, T; Kelly, JD

GEOPHYSICAL RESEARCH LETTERS 33 巻 ( 15 ) 2006年8月

A multi-instrument measurement of a mesospheric front-like structure at the equator 査読有り Open Access

Shiokawa, K; Suzuki, S; Otsuka, Y; Ogawa, T; Nakamura, T; Mlynczak, MG; Russell, JM

JOURNAL OF THE METEOROLOGICAL SOCIETY OF JAPAN 84A 巻頁： 305 - 316 2006年7月

Equatorial ionospheric scintillations and zonal irregularity drifts observed with closely-spaced GPS receivers in Indonesia 査読有り Open Access

Otsuka, Y; Shiokawa, K; Ogawa, T

JOURNAL OF THE METEOROLOGICAL SOCIETY OF JAPAN 84A 巻頁： 343 - 351 2006年7月

Ionospheric disturbances over Indonesia and their possible association with atmospheric gravity waves from the troposphere 査読有り Open Access

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

JOURNAL OF THE METEOROLOGICAL SOCIETY OF JAPAN 84A 巻頁： 327 - 342 2006年7月

Quasiperiodic southward moving waves in 630-nm airglow images in the equatorial thermosphere 査読有り Open Access

Shiokawa, K; Otsuka, Y; Ogawa, T

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 111 巻 ( A6 ) 2006年6月

Characteristics and implications of Doppler spectra of E region quasi-periodic echoes observed by the multibeam middle and upper atmosphere radar 査読有り Open Access

Ogawa Tadahiko, Otsuka Yuichi, Yamamoto Mamoru

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 111 巻 ( A5 ) 2006年5月

Climatological study of GPS total electron content variations caused by medium-scale traveling ionospheric disturbances - art. no. A04306 査読有り

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 111 巻 ( A4 ) 2006年4月

Geomagnetic conjugate observations of large-scale traveling ionospheric disturbances using GPS networks in Japan and Australia - art. no. A02302 査読有り

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 111 巻 ( A2 ) 2006年2月

GPS detection of total electron content variations over Indonesia and Thailand following the 26 December 2004 earthquake 査読有り Open Access

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 58 巻頁： 159-165 2006年

Equatorial ionospheric scintillations and zonal irregularity drifts observed with closely-spaced GPS receivers in Indonesia 査読有り Open Access

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

J. Meteor. Soc. Japan 84A 巻頁： 343-351 2006年

A statistical study of ionospheric irregularities observed with a GPS network in Japan

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

RECURRENT MAGNETIC STORMS: COROTATING SOLAR WIND STREAMS 167 巻頁： 271 - + 2006年

© 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

GPS observations of post-storm TEC enhancements at low latitudes 査読有り Open Access

Kutiev, I; Otsuka, Y; Saito, A; Watanabe, S

EARTH PLANETS AND SPACE 58 巻 ( 11 ) 頁： 1479 - 1486 2006年

GPS detection of total electron content variations over Indonesia and Thailand following the 26 December 2004 earthquake 査読有り Open Access

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

EARTH PLANETS AND SPACE 58 巻 ( 2 ) 頁： 159 - 165 2006年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：The Seismological Society of Japan, Society of Geomagnetism and Earth, Planetary and Space Sciences, The Volcanological Society of Japan , The Geodetic Society of Japan , The Japanese Society for Planetary Sciences

We report the response of the ionosphere to the large earthquake 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. © 2006, The Seismological Society of Japan, Society of Geomagnetism and Earth, Planetary and Space Sciences, The Volcanological Society of Japan, The Geodetic Society of Japan, The Japanese Society for Planetary Sciences. All rights reserved.

DOI： 10.1186/BF03353373

Ionospheric variations at midlatitude detected by a dense GPS receiver array in Japan 査読有り

A. Saito, Y. Otsuka, T. Tsugawa, K. Matsunaga, K. Hoshinoo

Proceedings of the Annual Meeting - Institute of Navigation 頁： 425 - 428 2005年12月

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

Ionospheric variations over Japan were investigated with high spatial and temporal resolution data of GEONET, which consists of about 1,200 GPS receivers. Total Electron Content (TEC) data derived from GEONET clarified that various ionospheric phenomena cause the variation of the ionosphere in the region around 30 degrees of the geomagnetic latitude, and affect on the navigation system. The large day-to-day variation of TEC gradient over Japan was found to be attributed to the day-to-day variation of the Equatorial Ionization Anomaly (EIA) because Japan is located on the northern slope of EIA. The amplitude and location of EIA have large variability because they are controlled by a complex system among the neutral and the ionized atmospheres, lower and upper atmospheres, and low-latitude and high-latitude ionospheres. As a result, the variation of EIA is difficult to be predicted. Meso-scale ionospheric structures, such as medium-scale traveling ionospheric disturbances (MSTID) and plasma bubbles, drift in about 100m/s of velocity and cause variations of short temporal scale. They were often observed to be accompanied by smaller scale structures that generate phase and amplitude scintillations of the GPS radio waves. The activity of MSTID has maxima in summer and winter. During these maximum periods, they were detected by GEONET almost everyday. Plasma bubbles were detected in the lowest latitude area of Japan, and found to reach the central part of Japan in a few days in a year. Most of them were in the geomagnetically disturbed periods. The geomagnetic disturbances also generate large-scale traveling ionospheric disturbances and reduction of TEC.

Geomagnetic conjugate observation of nighttime medium-scale and large-scale traveling ionospheric disturbances: FRONT3 campaign - art. no. A05303 Open Access

Efficacy of STI571 for a patient with metastatic gastrointestinal stromal tumor 査読有り

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

HEPATO-GASTROENTEROLOGY 52 巻 ( 66 ) 頁： 1764 - 1767 2005年11月

Observations of equatorial plasma bubbles using broadcast VHF radio waves - art. no. L17110 査読有り Open Access

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

GEOPHYSICAL RESEARCH LETTERS 32 巻 ( 17 ) 2005年9月

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 110 巻 ( A5 ) 頁： doi:10.1029/2004JA010845 2005年5月

Total electron content behavior over Japan during geomagnetic storms - art. no. A01308 査読有り

Kutiev, I; Watanabe, S; Otsuka, Y; Saito, A

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 110 巻 ( A1 ) 2005年1月

Relationship between propagation direction of gravity waves in OH and OI airglow images and VHF radar echo occurrence during the SEEK-2 campaign 査読有り Open Access

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

ANNALES GEOPHYSICAE 23 巻 ( 7 ) 頁： 2385 - 2390 2005年

Simultaneous ground- and satellite-based airglow observations of geomagnetic conjugate plasma bubbles in the equatorial anomaly 査読有り Open Access

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

EARTH PLANETS AND SPACE 57 巻 ( 5 ) 頁： 385 - 392 2005年

The first coordinated observations of mid-latitude E-region quasi-periodic radar echoes and lower thermospheric 557.7-nm airglow 査読有り Open Access

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

ANNALES GEOPHYSICAE 23 巻 ( 7 ) 頁： 2391 - 2399 2005年

Transition region of TEC enhancement phenomena during geomagnetically disturbed periods at mid-latitudes 査読有り Open Access

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

ANNALES GEOPHYSICAE 23 巻 ( 11 ) 頁： 3439 - 3450 2005年

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

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

GEOPHYSICAL RESEARCH LETTERS 31 巻 ( 20 ) 2004年10月

Statistical characteristics of gravity waves observed by an all-sky imager at Darwin, Australia - art. no. D20S07 査読有り Open Access

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

JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 109 巻 ( D20 ) 頁： D20 - S07 2004年8月

Geomagnetic conjugate observations of medium-scale traveling ionospheric disturbances at midlatitude using all-sky airglow imagers - art. no. L15803 査読有り

Otsuka, Y; Shiokawa, K; Ogawa, T; Wilkinson, P

GEOPHYSICAL RESEARCH LETTERS 31 巻 ( 15 ) 2004年8月

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

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

JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS 66 巻 ( 11 ) 頁： 891 - 897 2004年7月

A statistical study of large-scale traveling ionospheric disturbances using the GPS network in Japan - art. no. A06302 査読有り Open Access

Tsugawa, T; Saito, A; Otsuka, Y

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 109 巻 ( A6 ) 頁： A06302 2004年6月

Simultaneous mesosphere/lower thermosphere and thermospheric F region observations during geomagnetic storms 査読有り

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 109 巻 ( A4 ) 2004年4月

*Geomagnetic conjugate observations of medium-scale traveling ionospheric disturbances at midlatitude using all-sky airglow imagers 査読有り

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

Geophys. Res. Lett. 31 巻 ( L15803 ) 頁： doi:10.1029/2004GL020262 2004年

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

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.

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

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

Geophys. Res. Lett. 31 巻 ( L20802 ) 頁： 10.1029/2004GL020869 2004年

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

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.

DOI： 10.1029/2004GL020869

Generation of large-scale equatorial F-region plasma depletions during low range spread-F season 査読有り Open Access

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

ANNALES GEOPHYSICAE 22 巻 ( 1 ) 頁： 15 - 23 2004年

Time evolution of high-altitude plasma bubbles imaged at geomagnetic conjugate points 査読有り Open Access

Shiokawa, K; Otsuka, Y; Ogawa, T; Wilkinson, P

ANNALES GEOPHYSICAE 22 巻 ( 9 ) 頁： 3137 - 3143 2004年

Ray-tracing Calculation of VHF Radio Waves Scattered by Field-aligned Irregularities Associated with Equatorial Plasma Bubbles 査読有り

Hiroyuki Nakata, Yoshiaki Akaike, Yuichi Otsuka, Toshiaki Takano, Satoshi Ujigawa, Ikuo Nagashima

IEEJ Transactions on Fundamentals and Materials 124 巻 ( 12 ) 頁： 1253 - 1254 2004年

記述言語：英語掲載種別：研究論文（学術雑誌）

In order to explain the propagation of VHF radio waves for TV broadcasting transmitted from Southeast Asia associated with equatorial plasma bubbles, we have examined ray paths of the radio waves scattered by field-aligned irregularities in equatorial plasma bubbles. In determining the ray paths of the radio waves, a ray tracing calculation combined with a model of the scattering by field-aligned irregularities is used. It is found that VHF radio waves transmitted from Philippines can propagate to Japan due to scattering by field-aligned irregularities located above the East China Sea. © 2004, The Institute of Electrical Engineers of Japan. All rights reserved.

DOI： 10.1541/ieejfms.124.1253

Ground and satellite observations of nighttime medium-scale traveling ionospheric disturbance at midlatitude - art. no. 1145 査読有り

Thermospheric wind during a storm-time large-scale traveling ionospheric disturbance - art. no. 1423 査読有り Open Access

Shiokawa, K; Otsuka, Y; Ogawa, T; Kawamura, S; Yamamoto, M; Fukao, S; Nakamura, T; Tsuda, T; Balan, N; Igarashi, K; Lu, G; Saito, A; Yumoto, K

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

Optical and radio measurements of a 630-nm airglow enhancement over Japan on 9 September 1999 - art. no. 1252 査読有り

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 108 巻 ( A6 ) 2003年6月

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 108 巻 ( A4 ) 2003年4月

Damping of large-scale traveling ionospheric disturbances detected with GPS networks during the geomagnetic storm - art. no. 1127 査読有り Open Access

Tsugawa, T; Saito, A; Otsuka, Y; Yamamoto, M

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 108 巻 ( A3 ) 2003年3月

Statistical study of nighttime medium-scale traveling ionospheric disturbances using midlatitude airglow images - art. no. 1052 査読有り Open Access

Shiokawa, K; Ihara, C; Otsuka, Y; Ogawa, T

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 108 巻 ( A1 ) 2003年1月

Optical and radio measurements of a 630-nm enhancement over Japan on September 9, 1999 査読有り

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

J. Geophys. Res. 108(A6) 巻 ( 1252 ) 頁： doi:10.1029/2002JA009594 2003年

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

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.

A two-channel Fabry-Perot interferometer with thermoelectric-cooled CCD detectors for neutral wind measurement in the upper atmosphere 査読有り Open Access

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

EARTH PLANETS AND SPACE 55 巻 ( 5 ) 頁： 271 - 275 2003年

Simultaneous middle and upper atmosphere radar and ionospheric sounder observations of midlatitude E region irregularities and sporadic E layer 査読有り

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 107 巻 ( A10 ) 2002年10月

Annual and semiannual variations of the midlatitude ionosphere under low solar activity - art. no. 1166 査読有り

Kawamura, S; Balan, N; Otsuka, Y; Fukao, S

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 107 巻 ( A8 ) 2002年8月

Geomagnetic conjugate observations of equatorial airglow depletions 査読有り

Otsuka, Y; Shiokawa, K; Ogawa, T; Wilkinson, P

GEOPHYSICAL RESEARCH LETTERS 29 巻 ( 15 ) 2002年8月

A large-scale traveling ionospheric disturbance during the magnetic storm of 15 September 1999 - art. no. 1088 査読有り Open Access

Shiokawa, K; Otsuka, Y; Ogawa, T; Balan, N; Igarashi, K; Ridley, AJ; Knipp, DJ; Saito, A; Yumoto, K

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 107 巻 ( A6 ) 2002年6月

Geomagnetic conjugate observations of equatorial airglow depletions 査読有り

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

Geophys. Res. Lett. 29 巻頁： 10.1029/2002GL015347 2002年

*A new technique for mapping of total electron content using GPS network in Japan 査読有り Open Access

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

Earth, Planets, and Space 54 巻頁： 63-70 2002年

A new technique for mapping of total electron content using GPS network in Japan 査読有り Open Access

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

EARTH PLANETS AND SPACE 54 巻 ( 1 ) 頁： 63 - 70 2002年

Imaging observations of the equatorward limit of midlatitude traveling ionospheric disturbances 査読有り Open Access

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

EARTH PLANETS AND SPACE 54 巻 ( 1 ) 頁： 57 - 62 2002年

Observations and modeling of 630 nm airglow and total electron content associated with traveling ionospheric disturbances over Shigaraki, Japan 査読有り Open Access

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

EARTH PLANETS AND SPACE 54 巻 ( 1 ) 頁： 45 - 56 2002年

Regional ionosphere map over Japanese Islands 査読有り Open Access

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

EARTH PLANETS AND SPACE 54 巻 ( 12 ) 頁： E13 - E16 2002年

Plasmaspheric electron content in the GPS ray paths over Japan under magnetically quiet conditions at high solar activity 査読有り Open Access

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

EARTH PLANETS AND SPACE 54 巻 ( 1 ) 頁： 71 - 79 2002年

Observations of traveling ionospheric disturbances and 3-m scale irregularities in the nighttime F-region ionosphere with the MU radar and a GPS network 査読有り Open Access

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

EARTH PLANETS AND SPACE 54 巻 ( 1 ) 頁： 31 - 44 2002年

Annual and semiannual variations of the midlatitude ionosphere under low solar activity 査読有り

S. Kawamura, N. Balan, Y. Otsuka, S. Fukao

Journal of Geophysical Research: Space Physics 107 巻 ( 8 ) 2002年

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

The annual and semiannual variations of the midlatitude ionosphere under low solar activity are studied using middle and upper (MU) radar (135°E, 35°N) incoherent scatter observations and Sheffield University plasmasphere-ionosphere model (SUPIM). The variations of the daytime electron density (Ne) and electron and ion temperatures (Te and Ti) at 200-600 km altitudes measured by the radar under low solar activity (F10.7 ≤ 120) are satisfactorily reproduced for the first time by incorporating the radar measured values of the magnetic meridional neutral wind velocity (U 0) and northward perpendicular plasma drift velocity (V ⊥) into SUPIM that uses mass spectrometer incoherent scatter 1986 (MSIS-86) for neutral densities and neutral temperatures. The study shows that the annual and semiannual variations of the midlatitude ionosphere during daytime at altitudes near and above the ionospheric peak under low solar activity depend more on the direct effect of the neutral wind arising through the changes in ionospheric height than on the indirect effect arising through the changes in thermospheric composition (or atomic to molecular concentration ratio)
the indirect effect, however, predominates on the variations at altitudes below the ionospheric peak. The electron temperature (Te) undergoes similar but almost opposite seasonal and semiannual variations as the electron density. The ion temperature (Ti) is closer to neutral temperature than to electron temperature at altitudes up to ∼400 km and shows comparatively weak annual and semiannual variations. Copyright 2002 by the American Geophysical Union.

DOI： 10.1029/2001JA000267

Imaging observations of midlatitude ionospheric disturbances during the geomagnetic storm of February 12, 2000 査読有り Open Access

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 106 巻 ( A11 ) 頁： 24481 - 24492 2001年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

Regular all-sky imaging observations of the F region OI 630 nm nightglow emission are carried out at Rikubetsu (43.5 degreesN) and Shigaraki (34.8 degreesN), Japan since 1998. In this paper, we present observations of the OI 630 nm emission images from these two sites with a cluster of other observations during the geomagnetic storm of February 12, 2000. The airglow observations were obtained between 1500 UT and 2000 UT (0000-0500 LT) on this night. Images from both Rikubetsu and Shigaraki show the presence of mesoscale-enhanced airglow bands moving slowly (similar to 20-30 m s(-1)) to the southwest direction. The mesoscale band structures were also detected by an extensive network of GPS signal observations over Japan. The airglow observations at Shigaraki also show intense OI 630 nm emission in the south with several small-scale intensity depletion structures. We suggest that these small-scale intensity depletion structures (scale size 30-50 km) are caused by possible nonlinear interaction between the mesoscale TIDs and enhanced regions of the equatorial ionospheric anomaly. The ionosonde observations from Wakkanai (45.4 degreesN) and Kokubunji (35.7 degreesN) show spread F signatures between 1130 and 2100 UT and 1215 and 1715 UT, respectively, whereas no spread F was observed at Yamagawa (31.2 degreesN) and Okinawa (26.3 degreesN). The phase fluctuations of GPS signal were observed at latitudes higher than 30 degreesN for 1400-1900 UT. These observations suggest enhanced storm time ionospheric disturbances were confined in the midlatitudes.

DOI： 10.1029/2000JA900169

Three-channel imaging Fabry-Perot interferometer for measurement of mid-latitude airglow 査読有り

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

APPLIED OPTICS 40 巻 ( 24 ) 頁： 4286 - 4296 2001年8月

Traveling ionospheric disturbances detected in the FRONT campaign 査読有り Open Access

Saito, A; Nishimura, M; Yamamoto, M; Fukao, S; Kubota, M; Shiokawa, K; Otsuka, Y; Tsugawa, T; Ogawa, T; Ishii, M; Sakanoi, T; Miyazaki, S

GEOPHYSICAL RESEARCH LETTERS 28 巻 ( 4 ) 頁： 689 - 692 2001年2月

Multi-point observation of short-period mesospheric gravity waves over Japan during the FRONT campaign 査読有り Open Access

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

GEOPHYSICAL RESEARCH LETTERS 27 巻 ( 24 ) 頁： 4057 - 4060 2000年12月

Traveling ionospheric disturbances observed in the OI 630-nm nightglow images over Japan by using a multipoint imager network during the FRONT campaign 査読有り Open Access

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

GEOPHYSICAL RESEARCH LETTERS 27 巻 ( 24 ) 頁： 4037 - 4040 2000年12月

Comprehensive imaging observations of midlatitude ionospheric disturbances during storm time substorms 査読有り Open Access

Shiokawa, K; Otsuka, Y; Ogawa, T; Igarashi, K; Miyazaki, S; Rich, FJ; Saito, A; Yumoto, Y

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 105 巻 ( A12 ) 頁： 27067 - 27080 2000年12月

A study of the forenoon ionospheric F-2 layer behavior over the middle and upper atmospheric radar 査読有り Open Access

Zhang, SR, WL Oliver, S Fukao, Y Otsuka

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 105 巻 ( A7 ) 頁： 15823 - 15833 2000年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

The middle and upper atmosphere (MU) radar incoherent Scatter observations of electron density N-e profiles for 1986-1995 at Shigaraki (34.85 degrees N, 136.10 degrees E) show a forenoon density depression (bite-out) in summer bo th on individual days and in statistical averages. The depression takes place generally between 0700 and 1200 LT, above the F-2 peak for low solar activity and around the F-2 peak for high solar activity. The maximum electron density NmF2 shows, in both percentage and time duration, a greater depression for low solar activity than for high solar activity. With increasing altitude, the forenoon N-e depression develops earlier for low solar activity. In combination with the MU radar observations of ion drifts and plasma; temperatures, our modeling indicates the following: (1) Transport processes such as the enhancement of electron temperature T-e, the poleward neutral wind, and the reduced upper boundary ionization density help to reduce N-e and result in a negative partial derivative N-e/partial derivative t in the morning hours in summer. Among those processes the morning enhancement of T-e is found to be most important for the presence of the forenoon bite-out, since it greatly increases the O+ diffusion such that ionization outflow is significantly intensified. (2) The forenoon bite-out occurs only in summer, not in other seasons, because the smaller atmospheric composition ratio [O]/[N-2] in summer leads to a smaller daytime background N-e and thus to an enhanced T-e, and the after-sunrise photochemical contributions (mainly the O+ production) are so small that partial derivative Ne/partial derivative t also tends to be smaller. These two conditions give prominence to the transport contributions. (3) The solar activity dependences of the forenoon bite-out can be explained basically in terms of the low-electron-density background. (4) The height of formation of the forenoon bite-out is also related to the sunrise effect on photoionization.

DOI： 10.1029/2000JA000007

A climatology of middle and upper atmosphere radar observations of thermospheric winds 査読有り Open Access

S Kawamura, Y Otsuka, Zhang, SR, S Fukao, WL Oliver

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 105 巻 ( A6 ) 頁： 12777 - 12788 2000年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

Shigaraki middle and upper atmosphere (MU) radar observations of horizontal thermospheric winds in the magnetic meridian plane over the period September 1986 to September 1996 are reported as climatological averages in the form of time-of-day variations for several combinations of seasonal and solar activity conditions and are compared with winds predicted by the horizontal wind model (HWM) anti with winds measured at Saint Santin and Millstone Hill. The dominant feature of the MU wind behavior is its mean diurnal variation of northward flow by day and southward flow by night, with the nighttime wind smoothly approaching and receding from a midnight maximum, while the daytime wind tends to show two peaks, a strong. one in the early daylight hours and a weak one in the afternoon-evening. HWM shows the same unimodal nighttime and bimodal daytime behavior, but the HWM pattern is shifted about 2 hours later in time. The amplitude of the diurnal harmonic decreases from 78 m/s at solar minimum to 45 m/s at solar maximum, while: HWM shows a corresponding increase from 53 to 62 m/s. The diurnal amplitude is remarkably stable with season but is superposed on a steady willd of 41 m/s southward in summer, 15 m/s northward in winter, and midway between these limits at the equinoxes. HWM shows a symmetric pattern of 30 m/s southward in summer and 30 m/s northward ill winter. Ion drag appears to be the main regulator of wind speed, and the seasonal wind patterns have a profound effect on the seasonal behavior of the ionosphere.

DOI： 10.1029/2000JA900013

The IRI's B parameters measured by the MU radar 査読有り

Zhang, SR, S Fukao, XY Huang, Y Otsuka

LOWER IONOSPHERE: MEASUREMENTS AND MODELS 25 巻 ( 1 ) 頁： 101 - 104 2000年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PERGAMON PRESS LTD

The IS measurements of power profile by the MU radar at Shigaraki (34.9 degrees N, 136.1 degrees E) are analyzed to give IRI's B-parameters, B0 B1 for 1986-1991. Empirical formulas are obtained to represent their variations as functions of local time and season at high solar activity. They are compared also with ionosonde ones for Wuchang (30.5 degrees N, 114.4 degrees E). (C) 1999 COSPAR. Published by Elsevier Science Ltd.

DOI： 10.1016/S0273-1177(99)00904-7

Annual variations of the ionosphere: A review based on MU radar observations 査読有り

N Balan, Y Otsuka, S Fukao, MA Abdu, GJ Bailey

LOWER IONOSPHERE: MEASUREMENTS AND MODELS 25 巻 ( 1 ) 頁： 153 - 162 2000年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PERGAMON PRESS LTD

A review of the annual variations of the ionosphere, which focuses on the physical mechanisms causing the well-known seasonal anomaly and equinoctial asymmetry, is presented. In this review, the electron density (Nc), electron and ion temperatures (Te and Ti). and field-parallel and field-perpendicular plasma velocities (V-parallel to and V-perpendicular to), measured by the MU radar in the 180-600 km altitude range during 1986-1994, are analysed to study the altitude dependence of the seasonal anomaly and equinoctial asymmetry. The meridional component of the thermospheric neutral wind velocity (U-theta) derived from V-parallel to and neutral densities obtained from MSIS-86 are used to investigate the relative importance of the chemical and dynamical processes causing the anomaly and asymmetry. The review concludes that, although the anomaly and asymmetry involve chemical and dynamical processes, the dynamical processes (mainly through the neutral wind) predominate in the asymmetry while the chemical processes predominate in the anomaly. (C) 1999 COSPAR. Published by Elsevier Science Ltd.

DOI： 10.1016/S0273-1177(99)00913-8

The height of the maximum ionospheric electron density over the MU radar 査読有り

Zhang, SR, S Fukao, WL Oliver, Y Otsuka

JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS 61 巻 ( 18 ) 頁： 1367 - 1383 1999年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD

Ionospheric F-2-layer peak height h(m)F(2) variations, as measured over 1986-1995 by the MU radar (34.85 degrees N, 136.1 degrees E) and as calculated with a theoretical model, are discussed. The diurnal variations of the measured peak height for different seasons and levels of solar activity are compared with those estimated from ionosonde M3000F(2) and IRI predictions. Also given are the measured ion drift velocities and meridional neutral winds needed to understand the dynamic behavior of the F-2-layer. It is found that: (1) h(m)F(2) is generally higher during periods of the solar maximum than during periods of the solar minimum, and higher in summer than in winter; (2) for the solar maximum, h(m)F(2) drops markedly in the morning and in the afternoon, while, for the solar minimum, the h(m)F(2) minimum occurs in the morning during summer and usually in the afternoon during winter. In general, the measured h(m)F(2) is well reproduced by our model when we use the observed drift velocities and plasma temperatures as inputs. Our modeling study shows that the neutral wind contributes strongly to the diurnal variation of h(m)F(2) in winter by lowering the ionization layer by day, particularly for the solar maximum; it also helps to enlarge the daynight difference of h(m)F(2) in summer. The northward electromagnetic drifts that usually cancel the neutral wind effect have only a minor effect for the location of the MU radar. Other features of the observed h(m)F(2) variations, e.g., the solar maximum-minimum difference, the summer-winter difference, and the morning and afternoon drops, are explained by the basic processes of O+ production, loss and diffusion, as influenced by the atomic oxygen concentration and neutral and plasma temperatures. (C) 2000 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S1364-6826(99)00088-7

The height of the maximum ionospheric electron density over the MU radar 査読有り

Journal of Atmospheric and Solar-Terrestrial Physics 61 巻頁： 1367-83 1999年

MU radar observations of H+ ions in the topside ionosphere 査読有り Open Access

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 103 巻 ( A9 ) 頁： 20697 - 20704 1998年9月

Plasma temperature variations in the ionosphere over the middle and upper atmosphere radar 査読有り

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 103 巻 ( A9 ) 頁： 20705 - 20713 1998年9月

MST radar measurement of ionospheric F region winds: The "layer wind" technique 査読有り Open Access

WL Oliver, Y Otsuka, S Fukao

RADIO SCIENCE 33 巻 ( 4 ) 頁： 941 - 948 1998年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

We develop an improved application of the mesosphere-stratospheretroposphere (MST) radar technique for the measurement of winds at ionospheric F region altitudes. While the experiment is basically one of incoherent scatter (IS), which yields very weak signals at the usual operating frequencies of MST radars, we develop an analysis technique that allows the signals to be integrated over the entire F region of the ionosphere to gain sufficient statistical accuracy to compute the "layer wind" accurately. This method is contrasted with the normal IS method of determining winds at discrete heights. The method is applied to data collected with the middle and upper atmosphere radar in Japan, though it is applicable to any MST radar having a comparable or even somewhat smaller power-aperture product and may also be adapted for improved results from mainline IS radars. Using this method, we are able to discuss confidently the geophysical behavior of the wind on individual days, whereas previously we were reluctant to discuss anything but climatological features from data averages.

DOI： 10.1029/98RS00658

Equinoctial asymmetries in the ionosphere and thermosphere observed by the MU radar 査読有り

N Balan, Y Otsuka, GJ Bailey, S Fukao

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 103 巻 ( A5 ) 頁： 9481 - 9495 1998年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

Annual variations of the ionosphere and thermosphere studied with the middle and upper atmosphere (MU) radar during the solar maximum period 1988-1992 show that the well-known seasonal anomaly in the electron density Ne exists only during daytime and at altitudes near the ionospheric peak and below. The observations also reveal the existence of equinoctial asymmetries in the ionosphere and thermosphere, with the asymmetry in the ionosphere changing its character with altitude during daytime. In the bottomside ionosphere the electron density Ne is slightly greater in September equinox than in March equinox. At higher altitudes the asymmetry reverses and becomes strong; the values of Ne in March equinox exceed those in September equinox by up to 100%. The electron temperature Te exhibits equinoctial asymmetries almost opposite those in Ne. The ion temperature Ti shows a weak asymmetry, in phase with the asymmetry in Ne. The field-aligned and field-perpendicular plasma velocities V-parallel to and V-perpendicular to are also different in the two equinoxes. In the thermosphere the neutral wind and composition show consistent equinoctial asymmetries. The meridional component of the daytime poleward wind velocity (U-theta) derived from the field-parallel plasma velocity is weaker in March equinox than in September equinox by up to 20 m s(-1), and the values of the daytime [O]/[N-2] ratio obtained from MSIS-86 are larger in September equinox than in March equinox by about 20%. Model calculations carried out by incorporating the measured V-perpendicular to and U-theta into the Sheffield University plasmasphere-ionosphere model that uses MSIS-86 for neutral atmosphere show that the equinoctial asymmetries in the ionosphere arise mainly from the corresponding asymmetries in the thermosphere, with major contributions from neutral winds and minor contributions from composition.

DOI： 10.1029/97JA03137

MU radar observations of H+ ions in the topside ionosphere 査読有り Open Access

Journal of Geophysical Research 103 巻頁： 20,697-20,704 1998年

MST radar measurement of ionospheric F region winds:The "layer-wind" technique 査読有り

Radio Science 33 巻頁： 941-948 1998年

Equinoctial asymmetries in the ionosphere and thermosphere observed by the MU radar 査読有り

Journal of Geophysical Research 103 巻頁： 9,481-9,495 1998年

Plasma temperature variations in the ionosphereover the middle and upper atmosphere radar 査読有り

Journal of Geophysical Research 103 巻頁： 20,705-20,713 1998年

New aspects in the annual variation of the ionosphere observed by the MU radar 査読有り

N Balan, Y Otsuka, S Fukao

GEOPHYSICAL RESEARCH LETTERS 24 巻 ( 18 ) 頁： 2287 - 2290 1997年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

Annual variations of the daytime ionosphere studied with the MU radar during a full solar cycle show equinoctial asymmetry in density, temperature, and plasma velocity. The electron density (Ne) in the bottomside ionosphere is slightly greater in September equinox compared to March equinox, which arises from the asymmetry in thermospheric composition. At higher altitudes, the asymmetry in Ne reverses and becomes strong; the values of Ne in March equinox exceed those in September equinox by up to 150%. The electron temperature (Te) shows an asymmetry, which is opposite to the asymmetry in Ne; the values of Te in the topside in March equinox are less than those in September equinox by up to 300K. The asymmetry in ion temperature (Ti) is weak (about 100K) and in phase with the asymmetry in Ne. The northward perpendicular plasma velocity (V-perpendicular to) is slightly greater in March equinox compared to September equinox. The meridional component of the thermospheric neutral wind velocity (U-theta), derived from the field-parallel plasma velocity V-parallel to, is up to 50% lower in March equinox compared to September equinox. The asymmetry in neutral winds accounts for the asymmetry in ionospheric density and temperature in the topside, with minor contribution from the asymmetry in plasma drifts.

DOI： 10.1029/97GL02184

A climatology of F region gravity wave propagation over the middle and upper atmosphere radar 査読有り Open Access

WL Oliver, Y Otsuka, M Sato, T Takami, S Fukao

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 102 巻 ( A7 ) 頁： 14499 - 14512 1997年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

By observing the ionospheric F region simultaneously in multiple beams with the middle and upper atmosphere radar, we have been able to track the passage of gravity waves and measure their propagation characteristics. Here we develop a climatology of wave propagation based on the observation of 58 daytime experiments conducted during 1986-1994. The thermosphere seems to be continuously swept by waves detectable by an incoherent scatter radar. These waves generally come for hours on end from a,consistent or slowly varying direction, which can be any direction on a given day. Statistically, the waves show a moderate preference for southward travel, with this preference being reduced or shifted to southeastward travel during disturbed times. On average, the horizontal phase trace speed remains near 240 m/s for all periods inspected (40-130 min). This speed matches the behavior expected for lossless waves with 150-200 km vertical wavelength. We find small variability in this relation for different times of day, seasons, solar and magnetic conditions, and directions of wave travel, though waves on disturbed days seem to travel moderately faster on solar minimum mornings.

DOI： 10.1029/97JA00491