研究者詳細 - 塩川　和夫

論文 - 塩川　和夫

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The Upper Atmosphere and Plasma Imager/the Telescope of Visible Light (UPI/TVIS) onboard the Kaguya spacecraft 査読有り

Taguchi M., Sakanoi T., Okano S., Kagitani M., Kikuchi M., Ejiri M., Yoshikawa I., Yamazaki A., Murakami G., Yoshioka K., Kameda S., Miyake W., Nakamura M., Shiokawa K.

EARTH PLANETS AND SPACE 61 巻 ( 12 ) 頁： XVII - XXIII 2009年

Possible influence of ultra-fast Kelvin wave on the equatorial ionosphere evening uplifting 査読有り

Takahashi H., Abdu M. A., Wrasse C. M., Fechine J., Batista I. S., Pancheva D., Lima L. M., Batista P. P., Clemesha B. R., Shiokawa K., Gobbi D., Mlynczak M. G., Russell J. M.

EARTH PLANETS AND SPACE 61 巻 ( 4 ) 頁： 455 - 462 2009年

Northeastward motion of nighttime medium-scale traveling ionospheric disturbances at middle latitudes observed by an airglow imager

Shiokawa K., Otsuka Y., Nishitani N., Ogawa T., Tsugawa T., Maruyama T., Smirnov S. E., Bychkov V. V., Shevtsov B. M.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 113 巻 ( A12 ) 2008年12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：Journal of Geophysical Research: Space Physics

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

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Precipitation of radiation belt electrons by EMIC waves, observed from ground and space 査読有り

Miyoshi Y., Sakaguchi K., Shiokawa K., Evans D., Albert J., Connors M., Jordanova V.

GEOPHYSICAL RESEARCH LETTERS 35 巻 ( 23 ) 2008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：Geophysical Research Letters

We show evidence that left-hand polarised electromagnetic ion cyclotron (EMIC) plasma waves can cause the loss of relativistic electrons into the atmosphere. Our unique set of ground and satellite observations shows coincident precipitation of ions with energies of tens of keV and of relativistic electrons into an isolated proton aurora. The coincident precipitation was produced by wave-particle interactions with EMIC waves near the plasmapause. The estimation of pitch angle diffusion coefficients supports that the observed EMIC waves caused coincident precipitation of both ions and relativistic electrons. This study clarifies that ions with energies of tens of keV affect the evolution of relativistic electrons in the radiation belts via cyclotron resonance with EMIC waves, an effect that was first theoretically predicted in the earlv 1970's. Copyright 2008 by the American Geophysical Union.

DOI： 10.1029/2008GL035727

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Simultaneous THEMIS in situ and auroral observations of a small substorm 査読有り

Donovan E., Liu W., Liang J., Spanswick E., Voronkov I., Connors M., Syrjasuo M., Baker G., Jackel B., Trondsen T., Greffen M., Angelopoulos V., Russell C. T., Mende S. B., Frey H. U., Keiling A., Carlson C. W., McFadden J. P., Glassmeier K. -H., Auster U., Hayashi K., Sakaguchi K., Shiokawa K., Wild J. A., Rae I. J.

GEOPHYSICAL RESEARCH LETTERS 35 巻 ( 17 ) 2008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 present ground-based and in situ observations from March 13, 2007. The THEMIS satellites were in the evening sector conjugate to THEMIS ground-based imagers. At ∼0507 UT there was an optical onset on inner CPS field lines. This involved near-simultaneous brightening of 1 MLT hour longitudinal segment of the onset arc. The part of the arc that brightened was that closest to the equatorward boundary of the diffuse (proton) aurora. Within one minute, a dipolarization front moved across four THEMIS satellites. Based on their locations, the order in which they detected the dipolarization front, and the auroral evolution, we assert that the expansion phase began earthward of the four satellites and evolved radially outwards. We conclude that this onset occurred in an azimuthally localized region of highly stretched field lines. Copyright 2008 by the American Geophysical Union.

DOI： 10.1029/2008GL033794

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Particle and field characteristics of broadband electrons observed by the FAST satellite during geomagnetic storms: A multievent study 査読有り Open Access

Nakajima, A; Shiokawa, K; Seki, K; McFadden, JP; Carlson, CW; Strangeway, RJ; Yumoto, K

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 113 巻 ( A6 ) 2008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

During geomagnetic storms, remarkable electron-flux enhancements (>1012 eV cm-2 s-1) over a broadband energy range (∼0.05-10 keV) are sometimes observed near the equatorward edge of the auroral oval. We call such electron flux enhancements broadband electrons (BBEs). In this paper, we identified 12 BBE events from the electron-energy spectra obtained by the Fast Auroral Snapshot (FAST) satellite during 81 large geomagnetic storms (minimum Dst index <-90 nT) between September 1996 and March 2004. Ground-based magnetic field data show that the BBEs are observed ∼6-28 min after the onset of substorms during the main phase of large storms. During these events, the pitch angle distributions of electrons show isotropic features at a higher energy range above ∼1 keV, except for an upward loss cone. At a lower energy range below ∼1 keV, field-aligned downward electron fluxes are most intense, and perpendicular fluxes are weakest. These results imply that a higher-energy part of BBEs originates from higher altitudes in the inner magnetosphere and that a lower-energy part is accelerated parallel to the local magnetic field at lower altitudes near the satellite. Intense fluctuations of electric and magnetic fields and enhanced lower-frequency (0.1 Hz to 16 kHz) waves are observed during the BBEs. These characteristics are common for all BBE events. We compared lower-energy (<1 keV) electron fluxes with field-aligned Poynting fluxes of the waves at 0.06-4 Hz during the BBEs. The Poynting fluxes are systematically downward with intensity comparable to that of the lower-energy electron fluxes, suggesting downward acceleration of lower-energy electrons by the observed low-frequency waves. Copyright 2008 by the American Geophysical Union.

DOI： 10.1029/2007JA013001

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Correlation of substorm injections, auroral modulations, and ground Pi2 査読有り

Keiling A., Angelopoulos V., Larson D., Lin R., McFadden J., Carlson C., Bonnell J. W., Mozer F. S., Glassmeier K. -H., Auster H. U., Magnes W., Mende S., Frey H., Roux A., LeContel O., Frey S., Phan T., Donovan E., Russell C. T., Mann I., Liu W., Li X., Fillingim M., Parks G., Shiokawa K., Raeder J.

GEOPHYSICAL RESEARCH LETTERS 35 巻 ( 17 ) 2008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：Geophysical Research Letters

In this case study we report a substorm, 23 March 2007, which exhibited oscillations with a period of ∼135 s in three substorm phenomena all of which were one-to-one correlated. The in-situ observations are from one THEMIS spacecraft (8.3 RE geocentric distance) and the geosynchronous LANL-97A spacecraft. The focus here is on the intensification phase during which THEMIS was conjugate to the region of auroral brightening and its foot point was near the high-latitude ground station Kiana. The following results will be demonstrated: (1) THEMIS and LANL-97A (time-delayed)recorded periodic ion injections (>100 keV). (2) Near-conjugate high-latitude ground magnetometer data show very large Pi2 (δH∼150 nT) with a 6-s time delay compared to the THEMIS ion injections. (3) Low-latitude ground magnetometer data also show Pi2 with the same waveform as the high-latitude Pi2 but with longer time delays (20-31 s). (4) Auroral luminosity was periodically modulated during the intensification phase. (5) All three signatures (ion injections, ground Pi2, optical modulation) had the same periodicity of ∼135 s but with various time delays with respect to the THEMIS ion injections. These observations demonstrate that the three substorm phenomena had a common source which controlled the periodicity. Copyright 2008 by the American Geophysical Union.

DOI： 10.1029/2008GL033969

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プラズマバブルの発生位置の同定査読有り

木下佳紀, 中田裕之, 大塚雄一, 鷹野敏明, 島倉信, 塩川和夫, 小川忠彦

大気電気学会誌 2 巻 ( 1 ) 頁： 147 - 148 2008年5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

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

We have been conducting observations of aurora and geomagnetic pulsations at Athabasca, Canada, located at a subauroral latitude (magnetic latitude: 62°, L ∼ 4.6), using an all-sky imager and an induction magnetometer. Isolated auroral arcs at wavelengths of 557.7 nm, 630.0 nm, and 486.1 nm (H β) were often observed at latitudes separated equatorward from the main auroral oval. From a 1-year observation (4 September 2005 to 3 September 2006), we found 13 isolated arc events. All these isolated arcs occurred coincidentally with Pc 1 geomagnetic pulsations, although there were nine other Pc 1 events without isolated arcs in the field of view of the imager. The arcs were observed in both pre- and post-midnight sectors and tended to appear during the late recovery phase of geomagnetic storms. The isolated arcs had limited latitudinal and longitudinal widths of less than 230 km and 250-800 km, respectively. We found that as isolated arcs moved equatorward (poleward), the frequencies of the simultaneous Pc 1 pulsations increased (decreased). Using the Tsyganenko-02 magnetic field model, the observed Pc 1 frequencies were almost the same as the frequencies of He+ electromagnetic ion cyclotron (EMIC) waves at the equatorial plane connected to observed isolated arcs. These results indicate that interactions of spatially localized EMIC waves with ring current ions cause high-energy ion precipitation and associated isolated auroras at subauroral latitudes. These results also imply that the dynamics and instabilities in the inner magnetosphere can be monitored as low-latitude auroral emissions away from the ordinary auroral oval. Copyright 2008 by the American Geophysical Union.

DOI： 10.1029/2007JA012888

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Atmospheric gravity waves identified by ground-based observations of the intensity and rotational temperature of OH airglow 査読有り

Suzuki H., Shiokawa K., Tsutsumi M., Nakamura T., Taguchi M.

Polar Science 2 巻 ( 1 ) 頁： 1 - 8 2008年3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：Polar Science

Spectroscopic observations of OH airglow undertaken on May 2, 2006 at Uji, Japan reveal variations in intensity and rotational temperature related to the passage of an atmospheric gravity wave. The variations exhibit a period of approximately 1 h and magnitudes of 2-6% in intensity and 0.5-2% in rotational temperature. The vertical wavelength and intrinsic frequency of the atmospheric gravity wave were determined from the horizontal wavelength derived by an OH airglow imager, the background horizontal wind velocity obtained by the middle and upper atmosphere (MU) radar, and the dispersion relationship. The observed variations are consistent with the values calculated using the model of Liu, A.Z., Swenson, G.R. [2003. A modeling study of O2 and OH airglow perturbations induced by atmospheric gravity waves. J. Geophys. Res. 108 (No. D4), 4151. doi:10.1029/2002JD002474]. © 2008 Elsevier B.V. and NIPR.

DOI： 10.1016/j.polar.2007.12.002

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Fluctuation of intensity and rotational temperature of OH airglow caused by acoustic gravity waves 査読有り

Suzuki, H, K. Shiokawa, M. Tsutsumi, T. Nakamura, M. Taguchi

Polar Sci. 2 巻頁： 1 - 8 2008年1月

Development of an automatic procedure to estimate the reflection height of tweek atmospherics 査読有り

Ohya Hiroyo, Shiokawa Kazuo, Miyoshi Yoshizumi

EARTH PLANETS AND SPACE 60 巻 ( 8 ) 頁： 837 - 843 2008年

Rankin Inlet PolarDARN radar observations of duskward moving Sun-aligned optical forms 査読有り

Koustov A., Hosokawa K., Nishitani N., Ogawa T., Shiokawa K.

ANNALES GEOPHYSICAE 26 巻 ( 9 ) 頁： 2711-2723 2008年

Optical and Radio Observations and AMIE/TIEGCM Modeling of Nighttime Traveling Ionospheric Disturbances at Midlatitudes During Geomagnetic Storms

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

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 Monograph Series

© 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

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Simultaneous observations of nighttime medium-scale traveling ionospheric disturbances and <i>E</i> region field-aligned irregularities at midlatitude 査読有り Open Access

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 112 巻 ( A6 ) 2007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

We report on simultaneous observations of very high frequency (VHF) radar backscatter from field-aligned irregularities (FAI) in the E region and medium-scale traveling ionospheric disturbances (MSTID) in 630-nm airglow images. On the night of 6 August 2002, the powerful 46.5-MHz middle and upper atmosphere (MU) radar with five beam directions at Shigaraki, Japan, observed typical quasiperiodic (QP) echoes from FAI in the E region. During this QP echo event, an all-sky charge-coupled device imager at the MU radar site detected MSTID in 630-nm airglow images. The MSTID also propagated southwestward at 80 m/s with fluctuation amplitudes of 50% from the background intensity and a wavelength of 380 km. Period of the MSTID was almost same as that of the Doppler velocity in the QP echoes. The airglow enhancement (depletion) caused by the MSTID coincided with southeastward (northwestward) velocity in the QP echo. These results indicate that the electric fields associated with the F region MSTID could be closely coupled to those associated with QP echoes in the E region. Copyright 2007 by the American Geophysical Union.

DOI： 10.1029/2005JA011548

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Particle and field characteristics of broadband electrons observed by the FAST satellite during a geomagnetic storm 査読有り

Nakajima, A; Shiokawa, K; Seki, K; Strangeway, RJ; McFadden, JP; Carlson, CW

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 112 巻 ( A6 ) 2007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

Broadband electrons (BBEs) are remarkable flux enhancements (>10 13 eV cm-2 s-1) of precipitating electrons over a broad energy range (0.03-30 keV) near the equatorward edge of the auroral oval during geomagnetic storms. We show characteristics of particles (energy spectra and pitch angle distribution) and fields (electric field, magnetic field, and wave spectra) during a BBE event observed by the Fast Auroral SnapshoT (FAST) satellite. The BBEs were observed at an altitude of ∼2000 km at 59°-61° invariant latitudes (ILATs) and 21 h magnetic local time (MLT). The event was observed at ∼7 min after the onset of a substorm during the main phase of the Bastille Day geomagnetic storm (minimum Dst = -301 nT) on 15 July 2000. The precipitation region of the BBEs corresponded to a localized intensification of auroral emission, lasting ∼14 min, observed by the Polar UVI images at 50°-60° geomagnetic latitudes (MLATs) and 20-21 MLTs. These results suggest that rapid particle acceleration was occurring in the inner magnetosphere associated with a storm-time substorm. The pitch angle distribution of BBEs was isotropic except for a loss cone feature around the field-aligned upward direction at a higher energy range above ∼1 keV, while field-aligned electron fluxes were larger than the perpendicular fluxes below ∼1 keV. These results imply that a higher energy part of the BBEs originated from higher altitudes in the inner magnetosphere and that a lower energy part was accelerated parallel to the local magnetic field at lower altitudes near the satellite. Intense fluctuations of electric and magnetic fields were observed during this BBE event. From these results, we discuss possible acceleration of the lower energy part of BBEs through wave-particle interaction. Copyright 2007 by the American Geophysical Union.

DOI： 10.1029/2006JA012184

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Signatures of ultra fast Kelvin waves in the equatorial middle atmosphere and ionosphere 査読有り

Takahashi H., Wrasse C. M., Fechine J., Pancheva D., Abdu M. A., Batista I. S., Lima L. M., Batista P. P., Clemesha B. R., Schuch N. J., Shiokawa K., Gobbi D., Mlynczak M. G., Russell J. M.

GEOPHYSICAL RESEARCH LETTERS 34 巻 ( 11 ) 2007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：Geophysical Research Letters

In the equatorial atmosphere, oscillations with periods of 3 to 4 days have been observed in the meteor radar zonal wind at Cariri (7.4°S, 36.5°W), in the ionospheric minimum virtual height h'F and the maximum critical frequency foF2 at Fortaleza (3.9°S, 38.4°W), and in the TIMED/SABER satellite temperature data in the stratosphere-mesosphere. Wavelet analyses of these time series reveal that the 3-4-day oscillation was observed for all of these data during the period from March 1 to 11, 2005. From the characteristics of the downward phase propagation (wavelength of ∼40 km), longitudinal and latitudinal extension, we conclude that this oscillation must be a 3.5-day Ultra Fast Kelvin (UFK) wave. This is the first report of clear evidence of propagation of a UFK wave from the stratosphere to the ionosphere. The UFK wave could have an important role in the day-to-day variability of the equatorial ionosphere evening uplift. Copyright 2007 by the American Geophysical Union.

DOI： 10.1029/2007GL029612

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Ground observation and AMIE-TIEGCM modeling of a storm-time traveling ionospheric disturbance 査読有り Open Access

Shiokawa, K; Lu, G; Otsuka, Y; Ogawa, T; Yamamoto, M; Nishitani, N; Sato, N

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 112 巻 ( A5 ) 2007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：Journal of Geophysical Research: Space Physics

This paper reports the first comparison between comprehensive observations of equatorward moving traveling ionospheric disturbance at midlatitudes and thermospheric general circulation model with high-latitude energy input based on data assimilation. A prominent traveling ionospheric disturbance (TID) was observed during the major magnetic storm of 31 March 2001. The TID propagated from north to south over Japan with phase speeds of 370-640 m/s. The assimilative mapping of ionospheric electrodynamics (AMIE) technique was used as input to the thermosphere-ionosphere-electrodynamics general circulation model (TIEGCM) to investigate generation and propagation of the observed TID. In the model, two Joule heating enhancements in the high-latitude dayside sector produced two distinct traveling atmospheric waves (TADs), which propagated to Japan in the midnight sector as enhancements in thermospheric temperature and southward wind speed. The phase speed of the TADs was much faster (∼1100 m/s) in the model, probably due to the overestimation of Joule heating in the model. The second TAD corresponds to the observed prominent TID, while signatures of the first TAD were also seen in the observed ionosonde data. The observed TID was characterized by a decrease in southward wind speed, causing a significant F-layer height decrease and a temporal enhancement of F-layer peak density. These characteristics were reproduced by the model as a rarefaction of the second TAD. The temporal enhancement of F-layer peak density was because of the vertical shear of meridional wind. The absolute value of F-layer electron density in the model was several factors smaller than that observed, probably because of the underestimation of the supply of O+ ions from the plasmasphere. Copyright 2007 by the American Geophysical Union.

DOI： 10.1029/2006JA011772

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An intense gravity wave near the mesopause region observed by a Fabry-Perot interferometer and an airglow imager 査読有り Open Access

Shiokawa K., Suzuki S., Otsuka Y., Ogawa T., Nakamura T., Horinouchi T.

Journal of Geophysical Research Atmospheres 112 巻 ( 7 ) 2007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：Journal of Geophysical Research Atmospheres

We report an intense gravity wave event observed at Shigaraki, Japan, at 1500-2000 UT (0000-0500 LT) on 22 December 2001 using a Fabry-Perot interferometer, which measures the Doppler shift of nocturnal airglow emission at a wavelength of 557.7 nm (emission altitude: 90-100 km). The wave had a period of 1.5 hours and a peak-to-peak amplitude of 68 m/s in the horizontal wind velocity. The hodograph of the east-west and north-south wind oscillations showed a polarization direction of the wave of ENE-WSW. An all-sky airglow imager at Shigaraki also recorded a similar southwestward moving wave with a period of ∼1.5 hours and a velocity of 146 m/s in the 557.7-nm airglow images. The horizontal wavelength was estimated to be 790 km from the images. These facts indicate that the wave was generated in the northeast of Japan, where a well-developed low-pressure cell (968 hPa) and a distortion of the jet stream were observed in the troposphere. However, the large horizontal wavelength, the fast phase velocity, and the possible source location apart from the exit of the jet streak are different from those predicted from previous numerical simulations. Copyright 2007 by the American Geophysical Union.

DOI： 10.1029/2006JD007385

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Simultaneous ground and satellite observations of an isolated proton arc at subauroral latitudes 査読有り Open Access

Sakaguchi, K; Shiokawa, K; Ieda, A; Miyoshi, Y; Otsuka, Y; Ogawa, T; Connors, M; Donovan, EF; Rich, FJ

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 112 巻 ( A4 ) 2007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：Journal of Geophysical Research: Space Physics

We observed an isolated proton arc at the Athabasca station (MLAT: 62°N) in Canada on 5 September 2005, using a ground-based all-sky imager at wavelengths of 557.7 nm, 630.0 nm, and 486.1 nm (Hβ). This arc is similar to the detached proton arc recently observed by the IMAGE satellite [Immel et al., 2002]. The arc appeared at 0500-0640 UT (2100-2240 MLT), coincident with strong Pc 1 geomagnetic pulsations in the frequency range of the electromagnetic ion cyclotron (EMIC) wave. The isolated arc did not change its structure and intensity during the late growth and expansive phases of a small substorm that occurred at 0550 UT. From particle data obtained by the NOAA 17 satellite, we found that the isolated arc was associated with the localized enhancement of ion precipitation fluxes at an energy range of 30-80 keV at L ~ 4. Trapped ion flux enhancements (ring current ions) were also observed at two latitudinally separated regions. The localized ion precipitation was located at the outer boundary of the inner ring current ions. The DMSP F13 satellite observed signatures of an ionospheric plasma trough near the conjugate point of the arc in the Southern Hemisphere. The trough is considered to be connected to the plasmapause. These results indicate that the source region of the isolated arc was located near the plasmapause and in the ring current. We conclude that the observed isolated proton arc at subauroral latitudes was caused by the EMIC waves, which were generated near the plasmapause and resonantly scattered the ring current protons into the loss cone. Copyright 2007 by the American Geophysical Union.

DOI： 10.1029/2006JA012135

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