Faculty Profiles - OTSUKA, Yuichi

Papers - OTSUKA, Yuichi

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

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

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

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

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

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

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

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

DOI： 10.1029/2019JA026783

Web of Science

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

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

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

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

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

EARTH PLANETS AND SPACE Vol. 71 ( 1 ) 2019.8

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

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

DOI： 10.1186/s40623-019-1072-0

Open Access

Web of Science

Direct Observations of Traveling Ionospheric Disturbances as Focusers of Solar Radiation: Spectral Caustics Reviewed Open Access

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

ASTROPHYSICAL JOURNAL Vol. 877 ( 2 ) 2019.6

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

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

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

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

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

DOI： 10.1029/2019SW002168

Web of Science

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

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

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

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

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

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

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

Sivavaraprasad G, Ratnam D. Venkata, Otsuka Yuichi

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

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

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

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

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

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

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

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

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

DOI： 10.1029/2018JA025634

Open Access

Web of Science

Visualization of rapid electron precipitation via chorus element wave–particle interactions Reviewed Open Access

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

Nature Communications Vol. 10 ( 1 ) 2019.1

Publishing type：Research paper (scientific journal)

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

DOI： 10.1038/s41467-018-07996-z

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

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

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

Rapid Loss of Relativistic Electrons by EMIC Waves in the Outer Radiation Belt Observed by Arase, Van Allen Probes, and the PWING Ground Stations Reviewed 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 Vol. 45 ( 23 ) page： 12720 - 12729 2018.12

Microscopic Observations of Pulsating Aurora Associated With Chorus Element Structures: Coordinated Arase Satellite-PWING Observations Reviewed 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, Nose, M, Nagatsuma, T, Connors, M, Nishitani, N, Katoh, Y, Hikishima, M, Kumamoto, A, Tsuchiya, F, Kadokura, A, Nishiyama, T, Inoue, T, Imamura, K, Matsuoka, A, Shinohara, I

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

Publishing type：Research paper (scientific journal)

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

DOI： 10.1029/2018GL079812

Web of Science

Scopus

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

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

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

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

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

DOI： 10.1029/2018GL079615

Open Access

Web of Science

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

Otsuka Yuichi

PROGRESS IN EARTH AND PLANETARY SCIENCE Vol. 5 2018.9

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

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

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

Storm-Enhanced Development of Postsunset Equatorial Plasma Bubbles Around the Meridian 120 degrees E/60 degrees W on 7-8 September 2017 Reviewed 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 Vol. 123 ( 9 ) page： 7985 - 7998 2018.9

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

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

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

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

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

DOI： 10.1029/2018GL078723

Web of Science

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Papers - OTSUKA, Yuichi