Faculty Profiles - SHIOKAWA, Kazuo

Papers - SHIOKAWA, Kazuo

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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 Reviewed Open Access

NM Gavrilov, K Shiokawa, T Ogawa

JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES Vol. 107 ( D24 ) page： ACL 7 - 1 2002.12

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

[1] 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 O-2 nightglow emissions at Shigaraki, Japan (35degreesN, 136degreesE) 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 O-2. 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.

DOI： 10.1029/2001JD001469

Web of Science

Scopus

Magnetospheric responses to sudden and quasiperiodic solar wind variations Reviewed Open Access

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 107 ( A11 ) 2002.11

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

[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 similar to3-10 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 Alfven waves excited by externally applied pressure changes as reported by previous studies.

DOI： 10.1029/2002JA009342

Web of Science

Scopus

New auroral spectrometer using an acousto-optic tunable filter Reviewed

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

Advances in polar upper atmosphere research Vol. 16 page： 146 - 156 2002.9

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

Y Otsuka, K Shiokawa, T Ogawa, P Wilkinson

GEOPHYSICAL RESEARCH LETTERS Vol. 29 ( 15 ) 2002.8

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

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 24degreesN), and its geomagnetic conjugate point, Darwin, Australia (magnetic latitude 22degreesS), 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

Web of Science

Scopus

Multiple auroral brightenings and associated Pi 2 pulsations Reviewed

K Shiokawa, K Yumoto, JV Olson

GEOPHYSICAL RESEARCH LETTERS Vol. 29 ( 11 ) page： 32 - 1 2002.6

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

[1] All-sky auroral data at Kotzebue (KOT, 64.4degrees 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

Web of Science

Scopus

A large-scale traveling ionospheric disturbance during the magnetic storm of 15 September 1999 Reviewed

K Shiokawa, Y Otsuka, T Ogawa, N Balan, K Igarashi, AJ Ridley, DJ Knipp, A Saito, K Yumoto

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 107 ( A6 ) 2002.6

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

[1] Using a comprehensive data set and model calculations, we have investigated a prominent large-scale traveling ionospheric disturbance (LSTID) observed in Japan (similar to37degrees-16degrees 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 f(o)F(2) (6 --> 8 MHz), and an enhancement of GPS total electron content (similar to1.0 x 10(16) m(-2)). Multipoint and imaging observations of these parameters show that the LSTID moved equatorward over Japan with a velocity of similar to400-450 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.

DOI： 10.1029/2001JA000245

Web of Science

A large-scale traveling ionospheric disturbance during the magnetic storm of 15 September 1999 Reviewed 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 Vol. 107 ( A6 ) 2002.6

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

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

GEOPHYSICAL RESEARCH LETTERS Vol. 29 ( 10 ) page： 85 - 1 2002.5

New auroral spectrometer using an aousto-optic tunable filter Reviewed

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

Adv. Polar Upper Atmos. Res. Vol. 16 page： 146 - 156 2002.1

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

Ogawa T, Balan N, Otsuka Y, Shiokawa K, Ihara C, Shimomai T, Saito A

EARTH PLANETS AND SPACE Vol. 54 ( 1 ) page： 45-56 2002

Imaging observations of the equatorward limit of midlatitude traveling ionospheric disturbances Reviewed

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

EARTH PLANETS AND SPACE Vol. 54 ( 1 ) page： 57 - 62 2002

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

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

EARTH PLANETS AND SPACE Vol. 54 ( 1 ) page： 71 - 79 2002

The wave2000 campaign: overview and preliminary results Reviewed

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 Vol. 64 ( 8-11 ) page： 1095 - 1104 2002

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

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 106 ( A11 ) page： 26091 - 26101 2001.11

Imaging observations of midlatitude ionospheric disturbances during the geomagnetic storm of February 12, 2000 Reviewed

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 106 ( A11 ) page： 24481 - 24492 2001.11

Small-scale gravity waves near the mesopause observed by four all-sky airglow imagers Reviewed

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

JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES Vol. 106 ( D19 ) page： 22793 - 22799 2001.10

Bi-directional electron distributions associated with near-tail flux transport Reviewed

Sergeev VA, Baumjohann W, Shiokawa K

GEOPHYSICAL RESEARCH LETTERS Vol. 28 ( 19 ) page： 3813 - 3816 2001.10

Three-channel imaging Fabry-Perot interferometer for measurement of mid-latitude airglow Reviewed

Shiokawa K, Kadota T, Ejiri MK, Otsuka Y, Katoh Y, Satoh M, Ogawa T

APPLIED OPTICS Vol. 40 ( 24 ) page： 4286-4296 2001.8

Clinical analysis and prognostic study of ossified ligamentum flavum of the thoracic spine Reviewed

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

JOURNAL OF NEUROSURGERY Vol. 94 ( 2 ) page： 221 - 226 2001.4

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

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 Vol. 28 ( 4 ) page： 689 - 692 2001.2

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Papers - SHIOKAWA, Kazuo