研究者詳細 - 大塚　雄一

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