研究者詳細 - 塩川　和夫

論文 - 塩川　和夫

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Seasonal variations of medium-scale gravity wave parameters in the lower thermosphere obtained from spectral airglow temperature imager observations at Shigaraki, Japan 査読有り Open Access

Gavrilov, NM; Shiokawa, K; Ogawa, T

JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 107 巻 ( D24 ) 頁： ACL 7 - 1 2002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：Journal of Geophysical Research Atmospheres

A method of statistical analysis is used to study parameters of the medium-scale internal gravity waves (IGWs) from the data of the spectral airglow temperature imager (SATI) observations of the OH and O2 nightglow emissions at Shigaraki, Japan (35°N, 136°E) during April 1998 to May 2001. Average relative magnitudes of spectral components of airglow variations are 1.8-2.4% for the emission rates and 0.5-1% for the rotational temperature in different seasons. Distributions of periods, horizontal wavelengths, and phase speeds have the main maxima at 0.5-2 hours, 100-500 km, and 50-150 m/s, respectively. In winter, the distributions of propagation azimuths are broad with a dominance in the northwest sector and in the southern half of the sky for OH and in the northwest and southeast sectors for O2. In spring and summer, IGWs propagate mainly to the northern half of the sky with larger occurrence in the northeast sector for OH emission. Seasonal variations of the average and median IGW magnitudes do not exceed 20-30% and are not stable. In winter, IGWs have maximum occurrence with larger magnitudes, horizontal wavelengths, and phase speeds, particularly at azimuths of 90-210 deg. These results are compared with previous studies. Copyright 2002 by the American Geophysical Union.

DOI： 10.1029/2001JD001469

Web of Science

Scopus

Magnetospheric responses to sudden and quasiperiodic solar wind variations 査読有り Open Access

Kim, KH; Cattell, CA; Lee, DH; Takahashi, K; Yumoto, K; Shiokawa, K; Mozer, FS; Andre, M

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 107 巻 ( A11 ) 2002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：Journal of Geophysical Research: Space Physics

[1] On April 13 (day 103), 2001, 0700-1400 UT, the Polar satellite experienced different plasma regimes (i.e., magnetosphere, magnetosheath, and solar wind) because of the solar wind dynamic pressure variations and its high orbital inclination near the subsolar magnetopause meridian. When Polar was in the magnetosheath, quasiperiodic spacecraft potential (SP) variations, corresponding to density variations, with a recurrence time of ~3-10 min were observed. Using simultaneous solar Wind observations, it was confirmed that the magnetosheath SP variations were inherent in the solar wind. We observed an almost one-to-one correspondence between the SP variations and the geomagnetic field perturbations at lower latitudes (L = 1.1-2.8) on the nightside. At higher latitudes (L = 2.9-6.1) on the dayside, however, the field perturbations are more complicated than the magnetosheath SP variations. This suggests that if the magnetospheric perturbations produced by the external source (solar wind/magnetosheath pressure variations) deeply penetrate into the magnetosphere, the lower-latitude data on the nightside are important to monitor the external source variations. In addition, we observed the radial electric field oscillations excited nearly simultaneously with the magnetic field enhancement, associated with a sudden increase in the solar wind dynamic pressure, when Polar was in the magnetosphere. These oscillations may be considered as transient standing Alfvén waves excited by externally applied pressure changes as reported by previous studies. Copyright 2002 by the American Geophysical Union.

DOI： 10.1029/2002JA009342

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New auroral spectrometer using an acousto-optic tunable filter 査読有り

Shiokawa Kazuo, Katoh Yasuo, Satoh Mitsugi, Ogawa Tadahiko, Taguchi Makoto, Yamagishi Hisao

Advances in polar upper atmosphere research 16 巻頁： 146 - 156 2002年9月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：National Institute of Polar Research

This paper reports the performance and capability of a newly developed zenith spectrometer (for measurements of airglow and aurora) that uses an acousto-optic tunable filter (AOTF). The AOTF can scan the pass-band of the spectrometer between 450 and 700 nm with a bandwidth of 2-3 nm by changing the RF driver frequency from 180 to 100 MHz. The absolute sensitivity of the spectrometer is 〜0.1-1.5 counts/Rayleigh/s per spectral step. The spectrometer is fully automated. The O I (557.7 nm) airglow line can be clearly identified in test observations of midlatitude airglow performed at Shigaraki Observatory, Japan. Based on an estimate of the signal-to-noise ratio, we conclude that the full auroral spectrum (450-700) nm can be measured by the AOTF spectrometer with a time resolution of 〜100 s and a signal-to-noise ratio of 〜100 for an auroral emission intensity of 10 kR. An example of the auroral spectra is shown for observations made at Syowa Station in Antarctica.

CiNii Research

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

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Geophysical Research Letters

We report for the first time large-scale equatorial F-region airglow depletions extending to low-midlatitudes in both hemispheres. The observational sites were located at low-midlatitude geomagnetic conjugate points. Clear depletions of 630.0-nm airglow intensity due to equatorial plasma bubbles were simultaneously observed with two all-sky imagers at Sata, Japan (magnetic latitude 24°N), and its geomagnetic conjugate point, Darwin, Australia (magnetic latitude 22°S), on the night of November 12, 2001. Airglow depletion regions with east-west scale sizes of 40-100 km extend poleward. The maximum apex altitude of the plasma bubbles is about 1,700 km over the geomagnetic equator. The depletions move eastward at about 100 m/s, without changing their structures. The Darwin depletion structures mapped onto the northern hemisphere along the geomagnetic field coincide closely with structures in the Sata images, even for the 40-km structure. These observations indicate that plasma depletions in the equatorial ionosphere elongate along the geomagnetic field lines.

DOI： 10.1029/2002GL015347

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Scopus

Multiple auroral brightenings and associated Pi 2 pulsations 査読有り

Shiokawa K, Yumoto K, Olson JV

GEOPHYSICAL RESEARCH LETTERS 29 巻 ( 11 ) 頁： 32 - 1 2002年6月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Geophysical Research Letters

All-sky auroral data at Kotzebue (KOT, 64.4° MLAT). Alaska, and magnetic field data from both high- and low-latitude stations are used to demonstrate the relation between multiple auroral brightenings and Pi 2 magnetic pulsations during an isolated substorm. At least five Pi 2 wave packets are identified in the magnetic field data around the end of the growth phase. Auroral luminosity variations do not show oscillations in the Pi 2 frequency range, though each Pi 2 wave packet has good correspondence with each small-scale auroral brightening and poleward motion. This fact may contradict the idea of high-latitude Pi 2 generation by oscillations of substorm field-aligned currents. We discuss possible reasons of this discrepancy from localization of the Pi 2 current system and low-energy electrons as the current carrier.

DOI： 10.1029/2001GL014583

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Scopus

A large-scale traveling ionospheric disturbance during the magnetic storm of 15 September 1999 査読有り

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

A large-scale traveling ionospheric disturbance during the magnetic storm of 15 September 1999 査読有り Open Access

Shiokawa K., Otsuka Y., Ogawa T., Balan N., Igarashi K., Ridley A.J., Knipp D.J., Saito A., Yumoto K.

Journal of Geophysical Research: Space Physics 107 巻 ( A6 ) 2002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：Journal of Geophysical Research: Space Physics

[1] Using a comprehensive data set and model calculations, we have investigated a prominent large-scale traveling ionospheric disturbance (LSTID) observed in Japan (∼37°-16° MLAT) on 15 September 1999, during a recovery phase of sequential storms. The LSTID was detected at 2300-2400 LT (1400-1500 UT) as an enhancement of the 630-nm airglow intensity (50→350 R), a decrease in the F layer virtual height (at 2 MHz, 360→200 km), an enhancement of FoF2 (6→8 MHz), and an enhancement of GPS total electron content (∼1.0 x 1016 m-2). Multipoint and imaging observations of these parameters show that the LSTID moved equatorward over Japan with a velocity of ∼400-450 m/s. From a comparison with the Sheffield University Plasmasphere-Ionosphere Model (SUPIM) we conclude that an enhancement (250-300 m/s) of poleward neutral wind (that is propagating equatorward) caused these observational features of the LSTID at midlatitudes. To investigate generation of the LSTID by auroral energy input, we have used auroral images obtained by the Polar UVI instrument, magnetic field variations obtained at multipoint ground stations, and the empirical Joule heating rate calculated by the assimilative mapping of ionospheric electrodynamics (AMIE) technique. Intense auroral energy input was observed at 0800-1100 UT (4-6 hours before the LSTID), probably causing equatorward neutral wind at lower latitudes. It is likely that the poleward wind pulse that caused the observed LSTID was generated associated with the cessation of this equatorward wind. The effect of Lorentz force is also discussed. Copyright 2002 by the American Geophysical Union.

DOI： 10.1029/2001JA000245

Open Access

Scopus

Dual-site imaging observations of small-scale wave structures through OH and OI nightglow emissions 査読有り

Ejiri MK, Shiokawa K, Ogawa T, Kubota M, Nakamura T, Tsuda T

GEOPHYSICAL RESEARCH LETTERS 29 巻 ( 10 ) 頁： 85 - 1 2002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：Geophysical Research Letters

Four all-sky CCD imagers have been simultaneously operated at Shingaraki (34.9°N, 136.1°E) and Murou (34.6°N, 136.0°E), Japan from January to March 1998 to obtain OH and OI (557.7 nm) nightglow images. We determined height of observed small-scale wave structures (horizontal wavelengths of ∼7-9 km) by a triangulation technique. For an event of January 26, the structures seen in both nightglow images are estimated to have existed at around 91 km, suggesting that the structures occur at altitudes where these emission layers overlap. For another event of January 30, the structures with a height of 82 km were observed only in the OH images. These results indicate that the height extent of the small-scale wave structures is fairly small, suggesting that such structures are instability features rather than gravity waves. Even if we assume that the structures are gravity waves, their vertical wavelengths estimated by using the dispersion relation are very small.

DOI： 10.1029/2001GL014257

Web of Science

Scopus

New auroral spectrometer using an aousto-optic tunable filter 査読有り

Shiokawa, K, Y. Katoh, M. Satoh, T. Ogawa, M. Taguchi, H. Yamagishi

Adv. Polar Upper Atmos. Res. 16 巻頁： 146 - 156 2002年1月

Observations and modeling of 630 nm airglow and total electron content associated with traveling ionospheric disturbances over Shigaraki, Japan 査読有り

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

Imaging observations of the equatorward limit of midlatitude traveling ionospheric disturbances 査読有り

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

Plasmaspheric electron content in the GPS ray paths over Japan under magnetically quiet conditions at high solar activity 査読有り

Balan N, Otsuka Y, Tsugawa T, Miyazaki S, Ogawa T, Shiokawa K

EARTH PLANETS AND SPACE 54 巻 ( 1 ) 頁： 71 - 79 2002年

The wave2000 campaign: overview and preliminary results 査読有り

Iwagami N, Shibaki T, Suzuki T, Yamada Y, Onishi H, Takahashi Y, Yamamoto H, Sekiguchi H, Mori K, Sano Y, Kubota M, Murayama Y, Ishii M, Oyama KI, Yoshimura R, Shimoyama M, Koizumi Y, Shiokawa K, Takegawa N, Nakamura T

JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS 64 巻 ( 8-11 ) 頁： 1095 - 1104 2002年

A stable auroral red arc observed over Japan after an interval of very weak solar wind 査読有り

Shiokawa K, Ogawa T, Oya H, Rich FJ, Yumoto K

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 106 巻 ( A11 ) 頁： 26091 - 26101 2001年11月

Imaging observations of midlatitude ionospheric disturbances during the geomagnetic storm of February 12, 2000 査読有り

Sahai Y, Shiokawa K, Otsuka Y, Ihara C, Ogawa T, Igarashi K, Miyazaki S, Saito A

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 106 巻 ( A11 ) 頁： 24481 - 24492 2001年11月

Small-scale gravity waves near the mesopause observed by four all-sky airglow imagers 査読有り

Ejiri MK, Shiokawa K, Ogawa T, Nakamura T, Maekawa R, Tsuda T, Kubota M

JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 106 巻 ( D19 ) 頁： 22793 - 22799 2001年10月

Bi-directional electron distributions associated with near-tail flux transport 査読有り

Sergeev VA, Baumjohann W, Shiokawa K

GEOPHYSICAL RESEARCH LETTERS 28 巻 ( 19 ) 頁： 3813 - 3816 2001年10月

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

Clinical analysis and prognostic study of ossified ligamentum flavum of the thoracic spine 査読有り

K Shiokawa, J Hanakita, H Suwa, M Saiki, M Oda, M Kajiwara

JOURNAL OF NEUROSURGERY 94 巻 ( 2 ) 頁： 221 - 226 2001年4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 ASSOC NEUROLOGICAL SURGEONS

Object. A variety of factors may affect surgery-related outcome in patients with ossification of the ligamentum flavum (OLF) of the thoracic spine. The aim of this study was to determine these factors on the basis of preoperative clinical and radiological findings.
Methods. The authors treated 31 cases of symptomatic thoracic OLF between 1988 and 1999. The following factors were retrospectively studied: patient age, sex, morbidity level, initial symptoms, chief complaint, duration of symptoms, patellar reflex, Achilles reflex, computerized tomography (CT) finding, presence of intramedullary change determined by magnetic resonance imaging, coexistent spinal lesions, preoperative grade, and postoperative grade.
A decompressive laminectomy was performed in all cases. In 29 patients (94%) improved symptoms were demonstrated postoperatively. In terms of functional prognosis, the preoperative duration of symptoms was significantly shorter in the group of patients with excellent outcomes than in those with fair outcomes (p < 0.05).
No significant difference was observed in the correlation between other factors. To evaluate the degree of preoperative thoracic stenosis and the severity/extent of OLF-induced spinal compression, we used an original OLF CT scoring system. A score of excellent on the CT scale tended to indicate an excellent prognosis (p < 0.01).
Conclusions. Thoracic OLF frequently develops in the lower-thoracic spine in middle-aged men, and it is complicated by various spinal lesions in many cases. Early diagnosis and treatment are important for understanding the clinical symptoms and imaging diagnosis because the present findings suggest that a delay in diagnosis and treatment correlates with the functional prognosis postoperatively.

DOI： 10.3171/spi.2001.94.2.0221

Web of Science

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

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