研究者詳細 - 大塚　雄一

論文 - 大塚　雄一

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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

Scopus

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

Web of Science

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

Web of Science

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

Web of Science

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

Web of Science

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