Faculty Profiles - OTSUKA, Yuichi

Papers - OTSUKA, Yuichi

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Efficacy of STI571 for a patient with metastatic gastrointestinal stromal tumor Reviewed

Sasaki, Y, Niwa, Y, Ando, N, Otsuka, Y, Ohmiya, N, Hirooka, Y, Itoh, A, Furuta, S, Goto, H

HEPATO-GASTROENTEROLOGY Vol. 52 ( 66 ) page： 1764 - 1767 2005.11

Observations of equatorial plasma bubbles using broadcast VHF radio waves Reviewed Open Access

H Nakata, Nagashima, I, K Sakata, Y Otsuka, Y Akaike, T Takano, S Shimakura, K Shiokawa, T Ogawa

GEOPHYSICAL RESEARCH LETTERS Vol. 32 ( 17 ) 2005.9

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

The propagation of VHF radio waves affected by field-aligned irregularities within equatorial plasma bubbles is examined. Continuous observation of VHF radio waves at Tateyama, Japan, shows that broadcast radio waves transmitted from Southeast Asia propagate to Japan. Using a ray-tracing calculation combined with a model of scattering by field-aligned irregularities, we determined scatter points suitable for the reception of these radio waves. The results of the calculation show that radio waves transmitted from the Philippines can propagate to Japan owing to field-aligned irregularities within equatorial plasma bubbles located west of Japan. Comparing with all-sky imager data observed at Sata, Japan, we found that the radio waves are received at Tateyama when the plasma bubbles are observed at Sata. The results of this study show that the reception of these radio waves is closely correlated with the equatorial plasma bubbles.

DOI： 10.1029/2005GL023243

Open Access

Web of Science

Geomagnetic conjugate observation of nighttime medium-scale and large-scale traveling ionospheric disturbances: FRONT3 campaign - art. no. A05303 Open Access

Shiokawa, K; Otsuka, Y; Tsugawa, T; Ogawa, T; Saito, A; Ohshima, K; Kubota, M; Maruyama, T; Nakamura, T; Yamamoto, M; Wilkinson, P

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 110 ( A5 ) page： doi:10.1029/2004JA010845 2005.5

Total electron content behavior over Japan during geomagnetic storms Reviewed Open Access

Kutiev, I, S Watanabe, Y Otsuka, A Saito

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 110 ( A1 ) 2005.1

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

[ 1] The total electron content (TEC) obtained from GPS signals is used to study ionospheric dynamics over Japan during geomagnetically disturbed conditions. The numerous TEC measurements are averaged in cells with a size 1.5degrees x 1.5degrees geographic scale and formatted as time series within the years 2000 - 2002. To extract the storm time changes of TEC, the diurnal and 27-day periodicities are subsequently removed. Diurnal variations are removed by replacing absolute TEC values in each cell with their relative deviations (RTEC) from medians. The hourly RTEC values from all cells within the central 4degrees-wide band over Japan area are then approximated by a plane surface. This surface is represented by two parameters: its value at the center (rt) and the slope (b) along the main axis, taken as constants of the linear regression. The 27-day periodicity was approximated by Fourier waves with main period of 640 hours and two harmonics separately for rt and b and subtracted from them. The analysis of rt and b behavior during a number of geomagnetic storms allowed us to reveal several repeatable features of average TEC behavior. It was found that TEC behavior during the storms is similar to that of f(o)F(2) at the F region and was local time - dependent. A marked poleward expansion of the equatorial ionosphere ( crest region) at the end of recovery phase is persistently observed feature, produced probably by intensified eastward zonal winds. Such an expansion of equatorial ionosphere is observed also during isolated substorms, outside main geomagnetic storms. An oscillation-like change of positive and negative disturbances with period of 24 hours is observed during a 4-day period, following a moderate storm. In the absence of geomagnetic activity driver that effect is probably caused by the alternative expansion and contraction of equatorial ionosphere.

DOI： 10.1029/2004JA010586

Open Access

Web of Science

Relationship between propagation direction of gravity waves in OH and OI airglow images and VHF radar echo occurrence during the SEEK-2 campaign Reviewed Open Access

F Onoma, Y Otsuka, K Shiokawa, T Ogawa, M Yamamoto, S Fukao, S Saito

ANNALES GEOPHYSICAE Vol. 23 ( 7 ) page： 2385 - 2390 2005

Language：English Publishing type：Research paper (scientific journal) Publisher：EUROPEAN GEOSCIENCES UNION

We report simultaneous observations of atmospheric gravity waves (AGW) in OI (557.7 nm) and OH air-glow images and VHF radar backscatter from field-aligned irregularities (FAI) in the E-region during the SEEK-2 (Sporadic-E Experiment over Kyushu 2) campaign period from 29 July to 9 August 2002. An all-sky imager was operated at Nishino-Omote (30.5 degrees N, 130.1 degrees E), Japan. On 14 nights. 17 AGW events were detected in OI and OH air-glow images. AGW propagated mostly toward the northeast or southeast. From comparison with the E-region FAI occurrence, which is detected by a nearby VHF radar (31.57 MHz), we found that AGW tended to propagate southeastward during FAI events. This result suggests that the interaction between AGW and E-region plasma plays an important role in generating FAI. Furthermore, polarization electric fields generated directly by AGW may contribute to the FAI generation.

DOI： 10.5194/angeo-23-2385-2005

Open Access

Web of Science

Simultaneous ground- and satellite-based airglow observations of geomagnetic conjugate plasma bubbles in the equatorial anomaly Reviewed Open Access

T Ogawa, E Sagawa, Y Otsuka, K Shiokawa, TI Immel, SB Mende, P Wilkinson

EARTH PLANETS AND SPACE Vol. 57 ( 5 ) page： 385 - 392 2005

Language：English Publishing type：Research paper (scientific journal) Publisher：TERRA SCIENTIFIC PUBL CO

We compare, for the first time, geomagnetically-conjugate plasma bubbles observed by ground-based 01 630.0-nm all-sky imagers at Shigaraki, Japan (34.8 degrees N, 136.1 degrees E; magnetic latitude 25.4 degrees N) and Darwin, Australia (12.4 degrees S, 131.0 degrees E; magnetic latitude 22.0 degrees S), with global-scale plasma structures (similar to 10,000 km in longitude) in the equatorial anomaly simultaneously detected with an OI 135.6-nm imager on the IMAGE satellite at similar to 7 earth radii. As found previously, global-scale plasma structures in both hemisphere imaged by IMAGE consist of an array of geomagnetically-conjugate small- to medium-scale (a few hundreds to 1000 km in longitude) wavy structures that move to the east at similar to 100 in s(-1). We find the following: 1) plasma bubbles detected with the all-sky imagers reach an apex altitude of 1800 km over the geomagnetic equator while moving to the east at - 100 m s(-1) with spacings of 200-250 km. 2) Bubbles observed with the all-sky imagers and IMAGE are embedded within the small- to medium-scale wavy structures, and some of them are located near the crest of ail enhanced electron density region associated with the wavy structures. 3) The bubbles and wavy structures that are generated near sunset slant to the west with increasing latitude in both hemispheres, and tilts do not change with longitude (i.e., local time). The results suggest that the generation and evolution of plasma bubbles are closely related to those of the small- to medium-scale plasma structures.

DOI： 10.1186/BF03351822

Open Access

Web of Science

The first coordinated observations of mid-latitude E-region quasi-periodic radar echoes and lower thermospheric 557.7-nm airglow Reviewed Open Access

T Ogawa, Y Otsuka, F Onoma, K Shiokawa, M Yamamoto

ANNALES GEOPHYSICAE Vol. 23 ( 7 ) page： 2391 - 2399 2005

Language：English Publishing type：Research paper (scientific journal) Publisher：EUROPEAN GEOSCIENCES UNION

We present the first coordinated observations of quasi-periodic (QP) radar echoes from sporadic-E (E-S) field-aligned irregularities (FAIs), OI 557.7-nm airglow, and neutral winds in a common volume over Shigaraki, Japan (34.9 degrees N. 136.1 degrees E) on the night of 5 August 2002 during the SEEK-2 campaign. QP echo altitudes of 90-110 km were lower than usual by 10 km, enabling us to make a detailed comparison among QP echoes, airglow intensity, and neutral wind at around 96 km altitude. Eastward movement of the QP echo regions is consistent with the motions of neutral winds, airglow structures, and FAIs, suggesting that the electrodynamics of E-S-layers is fundamentally controlled by the neutral atmospheric dynamics. During the QP echo event, the echo altitudes clearly went up (down) in harmony with an airglow enhancement (subsidence) that also moved to the east. This fact suggests that the eastward-moving enhanced airglow region included an upward (downward) component of neutral winds to raise (lower) the altitude of the wind-shear node responsible for the E-S formation. The airglow intensity, echo intensity, and Doppler velocity of FAIs at around 96km altitude fluctuated with periods from 10min to 1 h, indicating that these parameters were modulated with short-period atmospheric disturbances. Some QP echo regions below 100 km altitude contained small-scale QP structures in which very strong neutral winds exceeding 100 m/s existed. The results are compared with recent observations, theories, and simulations of QP echoes.

DOI： 10.5194/angeo-23-2391-2005

Open Access

Web of Science

Transition region of TEC enhancement phenomena during geomagnetically disturbed periods at mid-latitudes Reviewed Open Access

K Unnikrishnan, A Saito, Y Otsuka, M Yamamoto, S Fukao

ANNALES GEOPHYSICAE Vol. 23 ( 11 ) page： 3439 - 3450 2005

Language：English Publishing type：Research paper (scientific journal) Publisher：EUROPEAN GEOSCIENCES UNION

Large-scale TEC perturbations/enhancements observed during the day sectors of major storm periods, 1213 February 2000, 23 September 1999, 29 October 2003, and 21 November 2003, were studied using a high resolution GPS network over Japan. TEC enhancements described in the present study have large magnitudes (>= 25 x 10(16) electrons/m(2)) compared to the quiet-time values and long periods (>= 120 min). The sequential manner of development and the propagation of these perturbations show that they are initiated at the northern region and propagate towards the southern region of Japan, with velocities > 350 m/s. On 12 February 2000, remarkably high values of TEC and background content are observed at the southern region, compared to the north, because of the poleward expansion of the equatorial anomaly crest, which is characterized by strong latitudinal gradients near 35 degrees N (26 degrees N geomagnetically). When the TEC enhancements, initiating at the north, propagate through the region 39-34 degrees N (30-25 degrees N geomagnetically), they undergo transitions characterized by a severe decrease in amplitude of TEC enhancements. This may be due to their interaction with the higher background content of the expanded anomaly crest. However, at the low-latitude region, below 34 degrees N, an increase in TEC is manifested as an enhanced ionization pattern (EIP). This could be due to the prompt penetration of the eastward electric field, which is evident from high values of the southward Interplanetary Magnetic Field component (IMF B-z) and AE index. The TEC perturbations observed on the other storm days also exhibit similar transitions, characterized by a decreasing magnitude of the perturbation component, at the region around 39-34 degrees N. In addition to this, on the other storm days, at the low-latitude region, below 34 degrees N, an increase in TEC (EIP feature) also indicates the repeatability of the above scenario. It is found that, the latitude and time at which the decrease in magnitude of the perturbation component/amplitude of the TEC enhancement are matching with the latitude and time of the appearance of the high background content. In the present study, on 12 February 2000, the F-layer height increases at Wakkanai and Kokubunji, by exhibiting a typical dispersion feature of LSTID, or passage of an equator-ward surge, which is matching with the time of occurrence of the propagating TEC perturbation component. Similarly, on 29 October 2003, the increase in F-layer heights by more than 150 km at Wakkanai and 90 km at Kokubunji around 18:00 JST, indicates the role of the equatorward neutral wind. On that day, TEC perturbation observed at the northern region, after 18:30 JST, which propagates towards south, could be caused mainly by the equatorward neutral wind, leading to an F-layer height increase. These observations imply the role of the equatorward neutral wind, which increases the F-layer height, by lifting the ionization to the regions of lower loss during daytime, when production is still taking place, which, in turn, increases the TEC values.
Large-scale traveling ionospheric disturbances (LSTIDs) are considered as ionospheric manifestations of the passage of Atmospheric Gravity Waves (AGWs) that are generated at the high latitude by energy input from the magnetosphere to the low-latitude ionosphere. This study shows that large-scale TEC perturbations observed here are produced at the northern region due to the combined effects of the equatorward neutral wind, the subsequent F-layer height increase, and LSTIDs. When these perturbation components propagate through the region, 39-34 degrees N, they undergo transitions characterised by a decrease in magnitude. Also, at the low-latitude region, below 34 degrees N, an increase in the TEC exhibits EIP feature, due to the prompt penetration of the eastward electric field.

DOI： 10.5194/angeo-23-3439-2005

Open Access

Web of Science

Spatial relationship of equatorial plasma bubbles and field-aligned irregularities observed with an all-sky airglow imager and the Equatorial Atmosphere Radar Reviewed Open Access

Y Otsuka, K Shiokawa, T Ogawa, T Yokoyama, M Yamamoto, S Fukao

GEOPHYSICAL RESEARCH LETTERS Vol. 31 ( 20 ) 2004.10

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

We report, for the first time, simultaneous two-dimensional observations of 630-nm airglow depletions and radar backscatter from field-aligned irregularities (FAI) associated with equatorial plasma bubbles. Spatial distributions of backscatter were obtained by performing east-west scans with the 47-MHz Equatorial Atmosphere Radar (EAR) in West Sumatra, Indonesia. A 630-nm airglow depletion, caused by a plasma bubble, was simultaneously observed with an all-sky airglow imager. Both the airglow depletion and backscatter region appeared as band-like structure elongated in the meridional direction with a zonal width of about 100 km. To compare the spatial structures of backscatter with that of airglow depletion, the backscatter was projected onto a horizontal plane at 250-km altitude. Backscatter was found to occur within the entire airglow-depleted region.

DOI： 10.1029/2004GL020869

Open Access

Web of Science

Statistical characteristics of gravity waves observed by an all-sky imager at Darwin, Australia Reviewed Open Access

Shin Suzuki, K. Shiokawa, Y. Otsuka, T. Ogawa, P. Wilkinson

Journal of Geophysical Research D: Atmospheres Vol. 109 ( D20 ) page： D20 - S07 2004.8

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

An all-sky airglow imager with a cooled charge-coupled device camera in place at Darwin (12.4°S, 131.0°E), Australia, since October 2001 has been used to obtain two-dimensional gravity wave images in the mesopause region. Using airglow images of the OI (557.7 nm, emission altitude ∼96 km) and OH band (720-910 nm, ∼86 km) emissions obtained for October 2001 to August 2002, we investigated the wavelengths, phase velocities, and propagation directions of gravity waves. Wave occurrence in OH images (60-90%) is higher than in OI images (30-70%) for all seasons. The waves have wavelengths of less than 90 km (peak: 30-50 km) and phase velocities ofless than 90 m/s (peak: 30-60 m /s). Most of the waves propagate in the meridional direction, and the directionality strongly depends on the season. In winter, waves propagate both poleward and equatorward, while in summer almost all waves propagate poleward. An examination of airglow-imaging statistics at Adelaide (35°S, 138°E), Australia, obtained by Walterscheid et al. [1999], leads us to conclude that this clear directionality is caused by the location of the wave sources and by the wave ducting processes
that is, poleward waves in summer come from an equatorial convective source through a thermal duct structure. The effect of wind filtering on the waves is also discussed for zonal wave propagation. Copyright 2004 by the American Geophysical Union.

DOI： 10.1029/2003JD004336

Open Access

Web of Science

Scopus

Geomagnetic conjugate observations of medium-scale traveling ionospheric disturbances at midlatitude using all-sky airglow imagers Reviewed Open Access

Y Otsuka, K Shiokawa, T Ogawa, P Wilkinson

GEOPHYSICAL RESEARCH LETTERS Vol. 31 ( 15 ) 2004.8

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

We report for the first time simultaneous observations of medium-scale traveling ionospheric disturbances (MSTIDs) at geomagnetic conjugate points in both hemispheres, using two all-sky airglow imagers at midlatitudes. A 630-nm all-sky CCD imager at Sata, Japan, detected MSTIDs with a wavefront elongated from NW to SE on the night of August 9, 2002. During this event, MSTIDs with a wavefront elongated from SW to NE were observed at the geomagnetic conjugate point, Darwin, Australia. To investigate geomagnetic conjugacy of the MSTID structures, the Darwin images were mapped The MSTID structures mapped from Darwin to its magnetic conjugate points along the geomagnetic field lines ( B) coincide closely with those in the Sata images. This result suggests that polarization electric field (E-p) plays an important role in the generation of MSTIDs. E-p maps along B and moves the F region plasma upward or downward by E x B drifts, causing plasma density perturbations with structures mirrored in the northern and southern hemispheres.

DOI： 10.1029/2004GL020262

Open Access

Web of Science

Comparison of OH rotational temperatures measured by the spectral airglow temperature imager (SATI) and by a tilting-filter photometer Reviewed

K Shiokawa, Y Otsuka, T Ogawa, H Takahashi, T Nakamura, T Shimomai

JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS Vol. 66 ( 11 ) page： 891 - 897 2004.7

Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD

Measurements of OH rotational temperatures have been carried out at Shigaraki, Japan(34.8degreesN, 136.1degreesE), for 8 nights in September-December:2000, using the Spectral Airglow Temperature Imager (SATI) and a tilting-filter zenith photometer (MC4), simultaneously. Clear positive correlation was obtained between the two temperatures. However, the absolute temperatures obtained by SATI were unusually low (similar to130-180 K) with differences of similar to60 K from the MC4 temperatures. We discuss possible causes of the temperature differences, particularly for SATI, which newly uses OH(6-2) Q-branch lines (MC4 uses OH(6-2) P-branch lines) and imaging optics for the temperature measurement. (C) 2004 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jastp.2004.03.003

Web of Science

A statistical study of large-scale traveling ionospheric disturbances using the GPS network in Japan Reviewed Open Access

Tsugawa, T, Saito, A, Otsuka, Y

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 109 ( A6 ) page： A06302 2004.6

Simultaneous mesosphere/lower thermosphere and thermospheric F region observations during geomagnetic storms Reviewed

Balan, N, Kawamura, S, Nakamura, T, Yamamoto, M, Fukao, S, Igarashi, K, Maruyama, T, Shiokawa, K, Otsuka, Y, Ogawa, T, Alleyne, H, Watanabe, S, Murayama, Y

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 109 ( A4 ) 2004.4

*Geomagnetic conjugate observations of medium-scale traveling ionospheric disturbances at midlatitude using all-sky airglow imagers Reviewed

Otsuka, Y., K. Shiokawa, T. Ogawa, and P. Wilkinson

Geophys. Res. Lett. Vol. 31 ( L15803 ) page： doi:10.1029/2004GL020262 2004

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

We report for the first time simultaneous observations of medium-scale traveling ionospheric disturbances (MSTIDs) at geomagnetic conjugate points in both hemispheres, using two all-sky airglow imagers at midlatitudes. A 630-nm all-sky CCD imager at Sata, Japan, detected MSTIDs with a wavefront elongated from NW to SE on the night of August 9, 2002. During this event, MSTIDs with a wavefront elongated from SW to NE were observed at the geomagnetic conjugate point, Darwin, Australia. The MSTID structures mapped from Darwin to its magnetic conjugate points along the geomagnetic field lines B coincide closely with those in the Sata images. This result suggests that polarization electric field (Ep) plays an important role in the generation of MSTIDs. Ep maps along B and moves the F region plasma upward or downward by ExB drifts, causing plasma density perturbations with structures mirrored in the northern and southern hemispheres.

Spatial relationship of equatorial plasma bubbles and field-aligned irregularities observed with an all-sky airglow imager and the Equatorial Atmosphere Radar Reviewed

Otsuka, Y., K. Shiokawa, T. Ogawa, T. Yokoyama, M. Yamamoto, and S. Fukao

Geophys. Res. Lett. Vol. 31 ( L20802 ) page： 10.1029/2004GL020869 2004

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

We report, for the first time, simultaneous two-dimensional observations of 630-nm airglow depletions and radar backscatter from field-aligned irregularities (FAI) associated with equatorial plasma bubbles. Spatial distributions of backscatter were obtained by performing
east-west scans with the 47-MHz Equatorial Atmosphere Radar (EAR) in West Sumatra, Indonesia. A 630-nm airglow depletion, caused by a plasma bubble, was simultaneously
observed with an all-sky airglow imager.
Both the airglow depletion and backscatter region appeared as band-like structure elongated in the meridional direction with a zonal width of about 100 km. To compare the spatial structures of backscatter with that of airglow depletion,
the backscatter was projected onto a horizontal plane at 250-km altitude. Backscatter was found to occur within the entire airglow-depleted region.

DOI： 10.1029/2004GL020869

Generation of large-scale equatorial F-region plasma depletions during low range spread-F season Reviewed Open Access

Y Sahai, PR Fagundes, Abalde, JR, AA Pimenta, JA Bittencourt, Y Otsuka, VH Rios

ANNALES GEOPHYSICAE Vol. 22 ( 1 ) page： 15 - 23 2004

Language：English Publishing type：Research paper (scientific journal) Publisher：EUROPEAN GEOPHYSICAL SOC

All-sky imaging observations of the F-region OI 630nm nightglow emission allow us to visualize large-scale equatorial plasma depletions, generally known as trans- equatorial plasma bubbles. Strong range type spread-F is the radio signature of these (magnetically) north-south aligned plasma depletions. An extensive database of the 01 630nm emission all-sky imaging observations has been obtained at Cachoeira Paulista (22.7degreesS, 45.0degreesW; dip latitude similar to16degreesS), Brazil, between the years 1987 and 2000. An analysis of these observations revealed that relatively few large-scale ionospheric plasma depletions occur during the months of May to August (southern winter, June solstice) in the Brazilian sector. Of the few that are observed during, these months, some occur in association with geomagnetic storms and some do not. In this paper, a detailed analysis of the events when large-scale ionospheric plasma depletions were initiated and evolved during the June solstice periods are presented and discussed.

DOI： 10.5194/angeo-22-15-2004

Open Access

Web of Science

Time evolution of high-altitude plasma bubbles imaged at geomagnetic conjugate points Reviewed Open Access

K Shiokawa, Y Otsuka, T Ogawa, P Wilkinson

ANNALES GEOPHYSICAE Vol. 22 ( 9 ) page： 3137 - 3143 2004

Language：English Publishing type：Research paper (scientific journal) Publisher：EUROPEAN GEOSCIENCES UNION

Temporal and spatial evolution of two high-altitude plasma bubbles (evening and midnight) was observed on 4 April 2002, at geomagnetic conjugate points at Sata, Japan (magnetic latitude 24degrees N), and Darwin, Australia (magnetic latitude 22degrees S), using two 630-nm airglow imagers. The apex height of the bubbles reached similar to1500km. The upward velocity of the evolution was faster in the evening (similar to170m/s at 20:00-21:00 LT) than around midnight (similar to28 m/s at 23:00-00:00 LT). Bifurcating features of the bubbles into a smaller scale size of similar to50 km were clearly seen for both the evening and midnight bubbles, showing fairly good conjugacy between the Northern and Southern Hemispheres.

DOI： 10.5194/angeo-22-3137-2004

Open Access

Web of Science

Ray-tracing Calculation of VHF Radio Waves Scattered by Field-aligned Irregularities Associated with Equatorial Plasma Bubbles Reviewed Open Access

Hiroyuki Nakata, Yoshiaki Akaike, Yuichi Otsuka, Toshiaki Takano, Satoshi Ujigawa, Ikuo Nagashima

IEEJ Transactions on Fundamentals and Materials Vol. 124 ( 12 ) page： 1253 - 1254 2004

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

In order to explain the propagation of VHF radio waves for TV broadcasting transmitted from Southeast Asia associated with equatorial plasma bubbles, we have examined ray paths of the radio waves scattered by field-aligned irregularities in equatorial plasma bubbles. In determining the ray paths of the radio waves, a ray tracing calculation combined with a model of the scattering by field-aligned irregularities is used. It is found that VHF radio waves transmitted from Philippines can propagate to Japan due to scattering by field-aligned irregularities located above the East China Sea. © 2004, The Institute of Electrical Engineers of Japan. All rights reserved.

DOI： 10.1541/ieejfms.124.1253

Open Access

Scopus

Thermospheric wind during a storm-time large-scale traveling ionospheric disturbance Reviewed Open Access

K Shiokawa, Y Otsuka, T Ogawa, S Kawamura, M Yamamoto, S Fukao, T Nakamura, T Tsuda, N Balan, K Igarashi, G Lu, A Saito, K Yumoto

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 108 ( A12 ) 2003.12

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

[1] A prominent large-scale traveling ionospheric disturbance (LSTID) was observed in Japan during the major magnetic storm (Dst similar to -358 nT) of 31 March 2001. It was detected as enhancements of the 630-nm airglow and foF2, GPS-TEC variations, and a decrease in F-layer virtual height at 1700 - 1900 UT (0200 - 0400 LT). It moved equatorward with a speed of similar to600 m/s. The decrease in the F-layer height was also detected by the MU radar at Shigaraki. Thermospheric wind variations were observed by the MU radar through ion drift measurement and by a Fabry-Perot interferometer (FPI) through a Doppler shift of the 630-nm airglow line at Shigaraki. The wind data show a turn of the meridional wind from -94 m/s (equatorward) to + 44 m/s (poleward) during the LSTID, indicating that an intense poleward wind in the thermosphere passed over Shigaraki as an atmospheric gravity wave and caused the observed ionospheric features of the LSTID. Intense poleward wind was also detected at mesospheric altitudes (95 - 100 km) by the MU radar ( through meteor echoes) and by the FPI ( through the 558-nm airglow) with a delay of similar to2 hours from the thermospheric wind, indicating downward phase progression of the wave. Generation of the observed poleward wind in the auroral zone was investigated using magnetic field data and auroral energy input estimated by the assimilative mapping of ionospheric electrodynamics (AMIE) technique. We suggest that simple atmospheric heating and/or the Lorentz force in the auroral zone do not explain the observed poleward wind enhancement.

DOI： 10.1029/2003JA010001

Open Access

Web of Science

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Papers - OTSUKA, Yuichi