Faculty Profiles - OTSUKA, Yuichi

Papers - OTSUKA, Yuichi

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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

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

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

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

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

Geophysical Research Letters Vol. 47 ( 13 ) 2020.7

Publishing type：Research paper (scientific journal)

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

DOI： 10.1029/2020GL087256

Open Access

Web of Science

Scopus

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 Vol. 72 ( 1 ) 2020.7

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

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

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

Publishing type：Research paper (scientific journal)

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

DOI： 10.1186/s40623-020-01187-1

Open Access

Web of Science

Scopus

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

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

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

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

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

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

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 Vol. 887 ( 1 ) 2019.12

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

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

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

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

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

DOI： 10.1029/2019JA027065

Open Access

Web of Science

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

Open Access

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

Open Access

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

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Papers - OTSUKA, Yuichi