研究者詳細 - 大塚　雄一

論文 - 大塚　雄一

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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

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

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

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

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

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

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.

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.

Web of Science

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.

Web of Science

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

Web of Science

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

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

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

Web of Science

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

Web of Science

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

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

MU radar observations of H+ ions in the topside ionosphere 査読有り

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

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

Web of Science

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